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ORE-DEPOSITS. 
 
 A SEQUEL TO THE SECOND EDITION. OF " THE GENESIS OF 
 
 ORE-DEPOSITS," BY FRANZ POSEPNY AND OTHERS; BEING 
 
 A COMPILATION OF CONTRIBUTIONS TO THIS SCIENCE 
 
 FROM THE TRANSACTIONS OF THE AMERICAN 
 
 INSTITUTE OF MINING ENGINEERS, WITH 
 
 A CRITICAL INTRODUCTION AND SYNOPSIS. 
 
 BY 
 
 SAMUEL FKANKLIN EMMONS, 
 
 Economic Geologist of the U. S. Geological Survey. 
 
 CONTAINING ALSO A BIOGRAPHICAL NOTICE OF MB. EMMONS BY DR. GEORGE 
 F. BKCKER ; A BIBLIOGRAPHY OF THE SUBJECT BY PROF. JOHN D. 
 IRVING, H. D. SMITH, AND H. G. FERGUSON ; AND A 
 PREFACE BY DR. ROSSITER W. RAYMOND, SEC- 
 RETARY EMERITUS OF THE INSTITUTE. 
 
 NEW YORK, N. Y. : 
 
 PUBLISHED BY THE DESTITUTE 
 
 AT THE OFFICE OF THE SECRETARY. 
 
 1913. 
 
>**>* * *::, : >>, 
 
CONTENTS. 
 
 PAGE 
 
 Preface, v 
 
 Introduction. By SAMUEL FRANKLIN EMMONS, . . ... vii 
 Biographical Notice of Samuel Franklin Emmons. By GEORGE F. BECKER, xxix 
 
 The Genesis of Certain Ore-Deposits. By S. F. EMMONS, . ... I 
 Structural Eelations of Ore-Deposits. By 8. F. EMMONS, 2d 
 
 Geological Distribution of the Useful Metals in the United States. By S. F. 
 EMMONS. Discussion, by JOHN A. CHURCH, ARTHUR WINSLOW, S. F. 
 
 EMMONS, and WILLIAM HAMILTON MERRITT, 65 
 
 The Torsional Theory of Joints. By GEORGE F. BECKER. Discussion, by 
 
 H. M. HOWE, R. W. EAYMOND, C. K. BOYD, and GEORGE F. BECKER, 92 
 
 The Allotropism of Gold. By HENRY Louis, 105 
 
 The Superficial Alteration of Ore-Deposits. By K. A. F. PENROSE, JR., . 110 
 Some Mines of Rosita and Silver Cliff, Colorado. By S. F. EMMONS, . 139 
 The Genesis of Certain Auriferous Lodes. By JOHN K. DON. Discussion, 
 by JOSEPH LE CONTE, S. F. EMMONS, GEORGE F. BECKER, ARTHUR WIN- 
 SLOW, W. P. BLAKE, and J. R. DON, 162 
 
 Influence of Country-Rock on Mineral Veins. By WALTER HARVEY WEED, 216 
 Igneous Rocks and Circulating Waters as Factors in Ore-Deposition. By 
 
 J. F. KEMP, 235 
 
 A Consideration of Igneous Rocks and Their Segregation or Differentiation 
 as Related to the Occurrence of Ores. By J. E. SPURR. Discussion, 
 
 by ALEXANDER N. WINCHELL, 251 
 
 The Chemistry of Ore-Deposition. By WALTER P. JENNEY. Discussion, by 
 
 JOHN A. CHURCH, 305 
 
 Ore-Deposits near Igneous Contacts. By WALTER HARVEY WEED. Dis- 
 cussion, by W. L. AUSTIN, 364 
 
 Ore-Deposition and Vein-Enrichment by Ascending Hot Waters By WALTER 
 
 HARVEY WEED, . 403 
 
 Basaltic Zones as Guides to Ore-Deposits in the Cripple Creek District, 
 
 Colorado. By E. A. STEVENS, 411 
 
 The Geological Features of the Gold- Production of North America. By 
 WALDEMAR LINDGREN. Discussion, by WILLET G. MILLER, and W. 
 
 L. AUSTIN, . 424 
 
 Osmosis as a Factor in Ore- Formation. By HAL BERT POWERS GILLETTE, 450 
 The Ore-Deposits of Sudbury, Ontario. By CHARLES W. DICKSON, . . 455 
 The Genesis of the Copper- Deposits of Clifton- Morenci, Arizona. By 
 
 WALDEMAR LINDGREN, 517 
 
 The Copper-Deposits at San Jose, Tamaulipas, Mexico. By J. F. KEMP, 557 
 The Magmatic Origin of Vein-Forming Waters in Southeastern Alaska. By 
 
 ARTHUR C. SPENCER, 582 
 
 Genetic Relations of the Western Nevada Ores. ByJ.E. SPURR, . . 590 
 Are the Quartz- Veins of Silver Peak, Nevada, the Result of Magmatic Seg- 
 regation ? By JOHN B. HASTINGS, 621 
 
 The Occurrence of Stibnite at Steamboat Springs, Nevada. By WALDEMAR 
 
 LINDGREN, .... . . . ... . . . . 629 
 
 (hi) 
 
IV CONTENTS. 
 
 PAGE 
 
 A Summary of Lake Superior Geology with Special Reference to Recent 
 
 Studies of the Iron- Bearing Series. By C. K. LEITH, . ' . . . 633 
 
 The Geological Relations of the Scandinavian Iron-Ores. By HJALMAR 
 
 SJOGREN, . . . 657 
 
 The Formation and Enrichment of Ore-Bearing Veins. ( With Supplementary 
 
 Paper. ) By GEORGE J. BANCROFT, 696 
 
 The Distribution of the Elements in Igneous Rocks. By HENRY S. WASH- 
 INGTON, 729 
 
 The Agency of Manganese in the Superficial Alteration and Secondary En- 
 richment of Gold-Deposits in the United States. By WILLIAM H. 
 EMMONS, . . . 759 
 
 Cognate Papers, . 829 
 
 Bibliography of the Science of Ore-Deposits. By JOHN D. IRVING, H. D. 
 
 SMITH, and H. G. FERGUSON, . .... ... . . 837 
 
 Index, . . 929 
 
 ERRATUM. 
 
 Page 761, footnote s : for 1904, read 1894. 
 
PREFACE. 
 
 AT the Chicago meeting of the Institute in 1893, a remarka- 
 bly suggestive and comprehensive paper on the Genesis of 
 Ore-Deposits, by Prof. Franz Posepny, an Honorary Member of 
 the Institute, was presented and discussed. This paper com- 
 prised the substance of the author's teaching on the subject at 
 the Mining Academy of Pribram. It was translated by me 
 from the German manuscript, and that translation, printed by 
 the Institute, was the first publication in any language of this 
 important treatise. I returned the original to Germany, where 
 it was subsequently published. 
 
 Posepny's paper and its discussion, as contained in Vols. 
 XXIII. and XXIV. of our Transactions , aroused wide-spread 
 attention; and, in 1895, were reprinted in a separate volume. 
 The first edition of this volume having become exhausted, a 
 second and revised edition, comprising a large number of addi- 
 tional papers and discussions, was issued in 1902. As an 
 indexed compilation of material scattered through our Trans- 
 actions, the " second Posepny book " proved so convenient to 
 instructors, students, and practicing experts that another, of 
 similar character, is now called for. 
 
 The great recent progress of the science of ore-deposits has 
 been largely due to the labors of the members of the U. S. 
 Geological Survey and to their cordial co-operation in the 
 work of the Institute, through contributions to its Transactions. 
 
 It was in this spirit of co-operation that S. F. Emmons, the 
 distinguished economic geologist of that Survey, who had been 
 since 1877 a member, and thrice during that period a Vice- 
 President, of the Institute, consented to edit the present vol- 
 ume. This generous service I accepted with enthusiastic 
 gratitude, both personal and official ; for it relieved me from a 
 task for which I could scarcely find the necessary surplus time 
 and strength, and it secured the performance of that task by 
 more competent hands and with far greater technical authority. 
 
 Mr. Emmons made the selection and arrangement of the 
 
 (v) 
 
VI PREFACE. 
 
 papers to be, in whole or in part, republished in the volume, 
 and wrote the introductory and the supplementary chapter, thus 
 finishing all the work which he had undertaken, except that 
 final revision of the proof-sheets, which every author or editor 
 claims as a right and needs in self-protection. But it was ar- 
 ranged between us that I should relieve him of the details of 
 proof-reading, beyond his approval of the text of his own con- 
 tributions; and this text had been so thoroughly discussed 
 between us as to make any further change. of it by him highly 
 improbable. He had also approved the Preface which I pro- 
 posed and which, alas ! is no longer appropriate. 
 
 The sudden death of Mr. Emmons has necessitated two 
 changes in this book the sorrowful preparation of a new 
 Preface, and the introduction at the beginning of a Biograph- 
 ical Notice by Mr. George F. Becker, his life-long friend and 
 colleague, commemorating the work of our lost leader and 
 brother. In all other respects the volume is, as it would have 
 been had he been spared to enjoy its completion and publica- 
 tion, the work of Mr. Emmons ; and I cannot but feel that it 
 will constitute a fitting memorial of him, wrought by his own 
 hand. Only too often, death interrupts the sculptor at his 
 work ; but in this exceptional instance, the Messenger waited, 
 and the message was no peremptory summons, but the gentler 
 call, " Finish what thou art doing : then come and rest ! " 
 
 It should be added that, not wishing to alter the work of my 
 friend, I have left the limit of selection where he left it ; and 
 therefore this " Emmons volume " contains no reference to In- 
 stitute papers published later than the Bulletin of December, 
 1910. 
 
 Thanks are also due to Prof. John D. Irving, of the Sheffield 
 Scientific School of Yale University, for the preparation, at Mr. 
 Emmons's request, of the Bibliography which adds to the value 
 of the book as a guide to further study. 
 
 ROSSITER W. RAYMOND, 
 
 Secretary Emeritus. 
 
INTRODUCTION. 
 
 BY SAMUEL FRANKLIN EMMONS. 
 
 THE great demand for the " second Posepny book " on The 
 Genesis of Ore-Deposits, published by the Institute in 1902, has 
 abundantly demonstrated that such volumes fill a real want 
 on the part of members of the Institute and others ; and it has 
 been judged advisable to prepare another, including additional 
 important papers on this subject, which have been published 
 in the Transactions of the Institute. 
 
 That this volume should not have an unwieldy bulk, it has 
 been necessary to omit from it, either entirely or in part, papers 
 which are more descriptive than genetic, and to select only 
 those, the subject matter of which in great part contributes to 
 the elucidation of general questions of genesis. A list of con- 
 tributions that might have been included, except for this 
 restriction, with a brief abstract of each, will be found at the 
 end of the volume, in a supplementary chapter, followed by a 
 general bibliography of the publications on the subject. 
 
 The arrangement of the papers is in general chronological ; 
 but such an arrangement is necessarily imperfect, because those 
 in the* previous volume were contributed in a middle period 
 (1893 to 1901), and some of the papers now published were 
 written before, but the greater part after, those dates. 
 
 The plan followed in the selection of contributions was to 
 make them represent, as far as they can, the progress of inves- 
 tigation and thought on the subject of ore-genesis in the 40 
 years that have elapsed since the organization of the Institute 
 in 1871. The papers themselves were not, however, written 
 for any such purpose, but are merely a set of facts and deduc- 
 tions which the respective authors thought worthy, at the time 
 they were written, of the consideration of their fellow-members ; 
 and since, as already stated, they were written in part before, 
 but for the most part after, those in the previous volume, they 
 do not present a consecutive or connected whole, but rather a 
 disconnected series, which needs some kind of running commen- 
 tary to bind them together. It is, therefore, the province of 
 
 (vii) 
 
Vlll INTRODUCTION. 
 
 this introductory chapter to indicate in a general way the pro- 
 gress of opinion in the period under consideration, and to show 
 the place occupied and the part played in this progress by the 
 different papers in this book and its predecessor. 
 
 At the time of the organization of the Institute in 1871 
 and indeed for many years after that time so little was defi- 
 nitely known as to the processes entering into the formation 
 of metalliferous deposits that purely geological criteria were 
 rarely used in determining the value of an ore-deposit, or the 
 best method of working it. In reading the reports of the min- 
 ing engineers of those periods, one feels that such criteria were 
 either entirely neglected or mentioned in a merely perfunctory 
 way. The quantity and value of ore available or actually 
 opened were determined; but for the estimation of its prob- 
 able extent in unexplored ground, such estimates as were made 
 at all were ordinarily based on an effort to prove the deposit to 
 be a " true fissure-vein," in which it was then assumed that ore, 
 must extend to an indefinite depth, with possibilities of becom- 
 ing richer. Among professional geologists there was no well- 
 defined consensus of opinion with regard to the genesis of 
 ore-deposits. It was the commencement of what I have else- 
 where l called the period of verification, when the abundant 
 and varied speculations and hypotheses of the pioneers in this 
 department of study were about to be brought to the test of 
 practical application in a wide field of newly-developed, ore- 
 deposits. Their minds were hence in the waiting or tentative 
 stage. 
 
 Neither Whitney, who was the greatest American authority 
 of his time, nor his European contemporary, Gotta, who, 
 through Prime's translation of his well-known Treatise on Ore- 
 Deposits, was for many years the recognized authority in 
 American law-courts, had very decided opinions on the subject 
 of ore-genesis. In their publications they presented with con- 
 siderable impartiality the various views proposed by earlier 
 students, leaving it to their readers to select that which might 
 seem most worthy of belief. 
 
 It is difficult for the geologist of the present day to realize 
 the condition of geological belief at that time, since a very 
 
 1 Theories of Ore-Deposition Historically Considered, Bulletin of the Geological 
 Society of America, vol. xv., p. 18 (1903). 
 
INTRODUCTION. IX 
 
 great part of his fundamental data in geology is the result of 
 much later investigations. It was the discovery, in the sixties, 
 that the auriferous slates of California were of Jurassic age, 
 which finally negatived Murchison's dictum that gold could be 
 found only in Palaeozoic rocks. It was not until well in the 
 eighties that microscopical petrography had come to play any 
 essential part in American geological investigations. Before 
 that, it was only personal observation underground, supple- 
 mented occasionally by a few laboratory or blow-pipe tests, that 
 furnished information as to the processes going on in the earth 
 during ore-deposition;, and, as all ores were thought to be 
 necessarily the filling of pre-existing open spaces, evidence of 
 replacement was seldom looked for. 
 
 Richthofen's report on the Comstock lode, in 1865, may 
 probably be regarded, in view of his previous career, as repre- 
 senting the most advanced and best-founded views of his time. 
 After professional study of the metallic deposits of Hungary, 
 the geological relations of which most nearly approach those 
 of our Cordilleran system, he had accompanied, as geologist, 
 the scientific expedition of the Austrian government in its 
 voyage around the world, and had remained in California to 
 take part in Whitney's survey of the Sierra Nevada. His 
 Natural Classification of Eruptive Rocks had been a great step 
 in the scientific study of igneous action, and was generally ac- 
 cepted by petrologists, until it was finally superseded, some 20 
 years later, through new light thrown upon the subject by the 
 modern science of microscopic petrography. Richthofen re- 
 garded the Comstock lode as a true fissure-vein that is, as a 
 result of dynamic action, cutting through different varieties of 
 rock, and extending to indefinite depth. Its mineral contents 
 he believed to have been deposited from solution, the silica 
 having been precipitated in a first stage, and the metallic min- 
 erals introduced in a second stage, after the fissure had been 
 re-opened. The extensive decomposition of the adjoining 
 country-rock could not, in his opinion, be explained by ther- 
 mal action alone; .and he therefore assumed that a process 
 had taken place, similar to that observed in the solfataras of 
 active volcanoes, which he therefore called " solfataric action." 
 As the source of the water which, acting as a solvent, had 
 brought in the chlorine, fluorine, and other vein-materials, he 
 
X INTRODUCTION. 
 
 found the ocean too far away, and therefore resorted to the 
 waters of the Great Basin, which have a composition similar 
 to that of the ocean. These he assumed to have descended to 
 the heated region, where their chlorine and fluorine had be- 
 come as active as they are supposed to be in actual solfataras. 
 For the source of the mineral substances he says : " We have 
 to look to the action of these elements on the surrounding 
 rocks," which is an application of the lateral-secretion theory. 
 It is noteworthy that, in spite of his characterization of the 
 action as solfataric, he considers the waters to have been of 
 meteoric origin. This was the most definite scientific opinion 
 that could be given at that time by the leading economic geolo- 
 'gist of the day. What the average mining engineer would 
 say is illustrated by the statement of A. Sutro in the same 
 report, which was evidently a paraphrase of Bichthofen's 
 opinion, put in terms more comprehensible to the average 
 layman. Sutro says : " The Comstock lode is a true fissure- 
 vein .... through which open fissure ascended steam 
 and vapors, gases, acids, sulphur, chlorine, and fluorine, carry- 
 ing with them silica and metallic particles in a volatile form, 
 which in course of untold ages gradually filled up the fissure, 
 and, after undergoing many chemical changes, formed what is 
 now known as the Comstock lode." 
 
 In the later, more detailed and exact, study of the Comstock 
 by King and Hague, published in 1870, the former declines to 
 go into abstruse speculation as to the genesis of the metals, it 
 being his opinion that, in the existing state of knowledge with 
 regard to ore-deposits, such speculations were more or less futile, 
 inasmuch as they could not be supported by facts. It was in 
 pursuance of this idea that, on assuming the Directorship of 
 the newly established U. S. Geological Survey in 1880, Mr. 
 King founded the Division of Mining Geology, to which about 
 half of the entire appropriation granted by Congress was al- 
 lotted. To Mr. Becker and myself, whom he placed in charge 
 of this division, he pointed out, in the following terms, the ulti- 
 mate results at which he aimed : 
 
 " You will make accurate, detailed, and exhaustive studies of the Comstock, 
 Eureka, and Leadville districts ; and, when these are completed, your principal 
 assistants will be competent to undertake similar studies of other important mining- 
 districts for which the necessary money will be furnished, thus successively dupli- 
 
INTRODUCTION. XI 
 
 eating the field of work, so that at the expiration of, say, ten years, the varied 
 types of deposits in all important mining-districts will have been studied ; and the 
 many phenomena bearing upon the genesis of ore-deposits thus accurately deter- 
 mined should be sufficient for a new theory of ore-deposits, based upon facts accu- 
 rately determined in the light of modern geology rather than, as is that of the 
 present day, upon theoretical speculations." 
 
 While the course of events has not been exactly that which 
 Mr. King planned, and results have been slower in coming, 
 and less definite and decisive, than his sanguine temperament 
 anticipated, they have been, nevertheless, such as to demon- 
 strate the wisdom of his plan. An important factor has been 
 the hearty concurrence and aid in this work afforded by indi- 
 viduals among the body of mining engineers, as soon as the 
 first results of the work planned by Mr. King had demonstrated 
 the immediate and practical aid to mining which might be 
 afforded by a knowledge of the geological relations of an ore- 
 body. It is this factor, emphasized by Dr. Raymond in his 
 Preface, which is especially brought out in the present volume. 
 
 The monographic reports of mining-districts by the U. S. 
 Geological Survey presented all the facts discernible with regard 
 to the geological relations of the deposits in each district, with 
 the conclusions that might be drawn for that special district ; 
 but it was many years before a sufficient number of districts 
 had been studied to permit any generalization applicable to all 
 deposits. These were naturally first formulated by the geolo- 
 gists actually occupied in that work, and were mainly published 
 in the Transactions of this Institute, because they would thus 
 reach a wide audience of working mining engineers, and lead 
 them to contribute facts and discuss results. Thus, the first 
 two papers in this volume present conclusions drawn by me 
 from the early years of my work on mining-geology, mainly in 
 Colorado. 
 
 No. 1. The Genesis of Certain Ore-Deposits. By S. F. Ernmons. 
 This paper was written to correct certain misapprehensions by 
 critics of my views as given in the Leadville report. The theo- 
 retical conclusions therein expressed were of a preliminary 
 rather than final nature. The more important of these con- 
 clusions were : 
 
 a. As to the manner of deposition : that ore-deposition by 
 replacement or metasomatism is not confined to easily-soluble 
 
Xll INTRODUCTION. 
 
 rocks like limestone, but is quite common in vein-deposits, 
 even in siliceous crystalline rocks. 
 
 b. As to genesis : that most ore-deposits are genetically con- 
 nected with eruptive or igneous rocks ; and, 
 
 c. As to the source of the metals : that for ore-deposition 
 from percolating waters (assuming, as was then universal among 
 geologists, that practically all waters circulating within the 
 earth's crust are of meteoric origin), it is more reasonable to 
 suppose that these waters derive their metallic contents from 
 bodies of igneous rocks at moderate distances from the de- 
 posits than from the unknown depth or barysphere. The 
 main reason for this assumption is, that the hypothetical bary- 
 sphere (or region where the rocks are distinctly heavier, hence 
 richer in heavy metals, than those that come under observation) 
 must be at such great depths within the crust that it would 
 have been beyond the reach of meteoric water. Furthermore, 
 the suggestions of Bischof and Sandberger had pointed out a 
 means of verification of this theory, of which the derivation 
 from unknown depths is not susceptible. A modification of 
 the lateral-secretion theory much broader than the restricted 
 one put forth by Sandberger was therefore adopted as affording 
 the most fruitful field for further investigation and verification. 
 
 No. 2. On the Structural Relations of Ore-Deposits. By S. F. 
 Emmons. This presents my generalizations on the geological 
 character of the channels through which ore-bearing solutions 
 may have reached the loci of various ore-deposits, the conclu- 
 sions being that such channels have mostly been produced by 
 dynamic action and are in the nature of actual rock-fractures 
 or fault-fissures, even where no displacement is discernible. 
 
 No. 3. The Geological Distribution of the Useful Metals in the 
 United States. By S. F. Emmons. As here presented, this is 
 a series of extracts from a paper presented by me at the Chi- 
 cago meeting of the Institute (1893), containing the views then 
 entertained as to the genesis of the respective metals. These 
 views were still tentative, and their presentation was very much 
 in the nature of a report of progress ; since the special studies 
 of mining-districts made by the U. S. Geological Survey had 
 not proceeded with the rapidity originally contemplated, and 
 the material for a new theory of vein-formation was still far 
 from complete. 
 
INTRODUCTION. Xlll 
 
 No. 4. The Torsional Theory of Joints. By George F. Becker. 
 This is a scientific demonstration, from the point of view of 
 terrestrial physics, of the laws governing rock-fractures, which 
 he groups under the term of "joints," giving the criteria by 
 which the effects of the agencies of pressure, tension, or torsion 
 maybe recognized. While the term "joints " is applied by 
 him to those partings in rocks on which the throw is not appa- 
 rent without close observation, the laws governing them are 
 applicable to the larger fractures on which mineral veins have 
 formed. 
 
 Meanwhile, an important contribution to genetic investiga- 
 tion had been made by the Norwegian geologist, Vogt, in 
 demonstrating by microscopical study that certain titaniferous 
 iron-deposits of Sweden were in the nature of concentrations 
 taking place before consolidation in the fused magma of an 
 eruptive rock, on the principle of magmatic differentiation 
 recently announced by leading petrographers to account for 
 the varying composition of eruptive rocks in a given region. 
 Such magmatic concentration, I maintained, would furnish a 
 means of accounting for the localization of great mineral de- 
 posits in limited areas or mining-districts, and their absence 
 in other areas where eruptive rocks are equally abundant, by 
 the assumption that, in the fused magmas from which the 
 eruptive rocks of the mining-districts had been formed, there 
 had been a concentration of metallic minerals previous to con- 
 solidation. In so far, then, a fact of observation had been con- 
 tributed to the hypothesis that the metals of ore-deposits might 
 more probably have been derived from bodies of igneous rocks 
 which had consolidated near enough to the surface to be within 
 the reach of meteoric waters, rather than directly from the 
 unknown depths of the barysphere. 
 
 Posepny's well-known paper on The Genesis of Ore-Deposits, 
 read at the Chicago meeting, and forming the leading article 
 in the first and second " Posepny volumes," published by the In- 
 stitute, stated the strongest argument yet presented in favor of 
 the ascension theory, as distinguished from Sandberger's nar- 
 row conception of the lateral-secretion theory ; and had a great 
 influence in bringing about a revolution in the mind of the 
 professional public against lateral secretion in general. In his 
 advocacy of the direct derivation of the metals from the bary- 
 
XIV INTRODUCTION. 
 
 sphere, Posepny did not, however, remove the objections 
 present in the minds of those who favored the broader, or 
 American, conception of the lateral-secretion theory namely, 
 that it seems physically impossible for meteoric waters to have 
 penetrated the crust to the depths at which what is under- 
 stood by the term " barysphere " can be supposed to exist. He 
 tacitly assumes that all waters circulating within the earth's 
 crust have a meteoric origin, and makes a most important dis- 
 tinction between those above and those below what he called 
 the ground-water level, which is assumed to correspond to the 
 lower limit of oxidation. The former, called vadose waters, 
 directly descending from the surface, exert an oxidizing or 
 decomposing action on already-existing deposits. The waters 
 below the ground-water level, or the deep-seated waters, are, 
 according to him, ascending, and were the vehicle through 
 whose agency the metals were brought up from the barysphere 
 and originally deposited. He did not, however, enter into any 
 explanation of the method by which he conceived these waters 
 to have gathered up their metallic contents ; thus leaving this 
 part of the subject as indefinite as it had been at the beginning 
 of the period now under consideration ; for Posepny apparently 
 did not attach much importance to Vogt's idea of magmatic 
 concentration. 
 
 In a general way, therefore, it may be said that the actual 
 progress in verification made in the decade prior to 1893 had 
 been mainly in the line of getting a more accurate knowledge 
 of the structural character of the openings in which ore-deposits 
 are formed, of the channels through which the mineral-bearing 
 solutions reach these openings, and of the processes involved 
 in their deposition. Some important published results of 
 generalization on these lines had, however, not appeared in 
 the Transactions of the Institute such, for instance, as Becker's 
 laboratory experiments on the natural solvents of the pre- 
 cious metals, and his studies on the processes of vein-forma- 
 tion in actual progress at Clear Lake, California, and Steam- 
 boat Springs, Nevada. 
 
 These phenomena, as more or less susceptible of direct ex- 
 perimental investigation and verification, and also as having a 
 direct practical bearing upon the actual exploitation of ore- 
 deposits, were naturally those which first occupied the attention 
 
INTRODUCTION. XV 
 
 of investigators. Speculations with regard to the ultimate 
 source from which the metals have been derived, dealing largely 
 with deep-seated phenomena beyond the reach of actual obser- 
 vation, are less subject to direct experimental investigation, and 
 must, therefore, be verified by indirect or inductive reasoning. 
 The determination of facts on which such reasoning could be 
 based constitutes an increasingly important factor in the pro- 
 gress of scientific inquiry; and it has often been made by 
 geologists, chemists, or physicists, without special reference to 
 the applicability of such facts to the science of ore-deposition. 
 But economic geologists and mining engineers, while directing 
 their attention primarily to problems subject to direct proof, 
 and having practical bearing upon the mining industry, have 
 not neglected the more speculative aspects of these problems. 
 The succeeding papers of the series contained in this volume 
 illustrate this proposition, bearing as they do, in their treat- 
 ment of widely various subjects, now upon one and now upon 
 another branch of the general inquiry. 
 
 No. 5. The Allotropism of Gold. By Henry Louis. This 
 paper, aside from its practical application to the separation of 
 this metal from its ores, records facts which it may be impor- 
 tant to bear in mind in studying the various forms of the oc- 
 currence of gold in nature. 
 
 No. 6. The Superficial Alteration of Ore-Deposits. By R. A. 
 F. Penrose, Jr. This paper, though originally written for the 
 Transactions, was, for reasons not necessary to record here, 
 actually published elsewhere. It is the first complete treatise 
 on the action of vadose waters on ore-deposits. It has been 
 deemed desirable to put it on record here, because it was 
 the only publication extant treating of that subject at the 
 time of the announcement of the important doctrine of 
 secondary sulphide enrichment, at the opening of the next 
 decade. Although the author, like Posepny, does not ex- 
 plicitly make the ground-water level the lowest limit of the 
 alteration he describes, it is evident from the context that, in 
 common with other economic geologists of the time, he regarded 
 this level as more or less identical with that at which oxida- 
 tion ceases, and that he did not admit the feasibility of the 
 actual transference of oxidized material, during such alteration, 
 below that limit. 
 
XVI INTRODUCTION. 
 
 No. 7. Some Mines of Rosita and Silver Cliff, Colorado. By S. 
 F. Emmons. This paper gives the record of actual observa- 
 tion of the occurrence of vadose and deep-seated waters in 
 one and the same mine (the Geyser), separated by a zone, over 
 500 ft. thick, of perfectly dry rock, where observation, as well 
 as analysis, gave an entirely independent source for each of 
 the respective kinds of water. While the conclusions drawn 
 in this paper are based on the then-prevailing belief that all 
 the waters circulating within the earth's crust are primarily of 
 meteoric origin, the facts recorded have an .equally important 
 bearing upon the recently-adopted theory of the magmatic 
 origin of most deep-seated waters. 
 
 No. 8. The Genesis of Certain Auriferous Lodes. By John R. 
 Don. This is an abstract from a record of exhaustive chemical 
 research, carried on for seven years by Dr. John R. Don, of 
 New Zealand, into the possible source of gold, which has con- 
 tributed most important chemical data to the general subject 
 of genesis. Dr. Don's analyses confirm the statements of pre- 
 vious investigators as to the presence of gold in extremely 
 dilute solution in the waters of the ocean ; and his experiments 
 render it highly improbable that gold can have been precipi- 
 tated so as to form a part of sedimentary rocks ; thus confirm- 
 ing the assumption that its source is to be looked for in igneous 
 material. In igneous rocks, however, he determines that it is 
 not contained in the bisilicates, but is necessarily associated 
 with pyrite ; and, as he assumes that the pyrite is a later intro- 
 duction since the consolidation of the rock, he concludes that 
 the gold could not have been derived from the rocks examined 
 by him, but must have been precipitated from solutions ascend- 
 ing from rocks deeper than any now exposed at the surface, 
 without, however, concerning himself " with the question 
 whether this source is the vague bary sphere with its somewhat 
 apocryphal contents of heavy metals." As will be seen from 
 the discussions 2 of this paper, Dr. Don's critics, while not ques- 
 tioning the accuracy of his determinations, do not agree on all 
 points with the conclusions that he saw fit to draw from them, 
 and do not admit that the impossibility of derivation from 
 igneous rocks is conclusively proved. 
 
 2 This volume, pp. 202 to 215. 
 
INTRODUCTION. XV11 
 
 Chronologically, the next steps in the development of the 
 theories of genesis were taken at the Institute meetings of 1900 
 and 1901, at Washington and Richmond, respectively. The 
 papers presented at these meetings were of the greatest and 
 most critical importance in the development of the various 
 stages of the history of ore-genesis, and have been included in 
 the already-published volume, together with the treatise of 
 Posepny, which they so seriously modify and in some respects 
 even negative. Space will not permit a characterization of 
 them at all commensurate with their importance ; and they will 
 only be referred to briefly, in such a way as to give each of 
 them what appears to be its proper place in the historical de- 
 velopment of opinion. 
 
 In his Principles Controlling Ore-Deposition, Van Hise pre- 
 sented a philosophical treatment of the entire question of un- 
 derground circulation as applied to ore-deposits, based on 
 experimental data with regard to underground circulation 
 furnished by the Water Supply Department of the U. .S. Geo- 
 logical Survey. In this he explained, more definitely and in 
 greater detail than had hitherto been done, the manner in 
 which surface-waters, in their downward course, spread over 
 wide areas within the crust, and, as they turn upward, unite in 
 the larger trunk-channels through which they ascend to reach 
 the surface again at some outlet or point of run-off. The ele- 
 ment of lateral movement in underground circulation was 
 shown to be, therefore, much larger than had previously been 
 conceived. Van Hise believed that the descending and later- 
 ally-moving waters had been the main agents in taking up 
 metallic minerals from the rocks through which they passed, 
 and that from these waters, ascending through trunk-channels, 
 the greater part of ore-deposition had taken place. He believed 
 in a ground-water level, but held that downward-moving and 
 oxidizing waters might penetrate some distance below this 
 level, and that when such mineral-charged solutions met other 
 similarly-charged solutions, ascending along trunk-channels, 
 extraordinarily rich deposits would be formed ; whereas below, 
 in the trunk-channels, the ores would be mainly low-grade 
 pyritous ores. 
 
 The following paper in the second Posepny volume contains 
 my announcement of the important doctrine of " Sulphide 
 
XV111 INTRODUCTION. 
 
 Secondary Enrichment," which I had really discovered through 
 my studies, in 1896, of the veins of Butte, Mont., although I 
 had withheld its formal announcement, that I might test the 
 general applicability of the theory by the study of other de- 
 posits, especially those of copper, in which the results are more 
 easily observable than in those of other metals; and, further, 
 in order to investigate the chemistry of the processes involved; 
 for, according to the generally-accepted theory of a universal 
 underground water-level, descending oxidized solutions would 
 become diluted and neutralized on reaching this underground 
 sea, so as to lose their distinctive characters. As explained in 
 this paper, I do not believe in any such universal level, but 
 hold that the level to which water will rise in a given mine or 
 district is dependent on the structural relations in that particu- 
 lar mine or district, which thus constitutes a separate and 
 independent hydrostatic basin, so that the water-level, at 
 points no great distance apart, may be respectively much 
 higher or lower. 
 
 The next paper in the second Posepny book, by W. H. 
 Weed, on The Enrichment of Gold and Silver Veins, is of simi- 
 lar import. In the original survey of the Butte district, in 
 1896, Mr. Weed had acted as petrologist in charge of surface- 
 geology. Having listened to my discussion of the importance 
 of this new doctrine of enrichment by descending waters below 
 the ground-water level, Mr. Weed had appreciated its signifi- 
 cance, and, unknown to me, had studied its working in gold- 
 and silver-mines, principally in Montana of which study this 
 paper was the result. He announced, for the winter meeting 
 of the Geological Society of America, an article on this gen- 
 eral subject, which- was not, however, actually read at the meet- 
 ing of the Geological Society in December, 1899, but was writ- 
 ten for that meeting at the same time that I was preparing, 
 for the Institute meeting of February, 1900, my paper on The 
 Secondary Enrichment of Ore-Deposits. 
 
 In the second Posepny volume, these contributions on sec- 
 ondary enrichment are followed by a very important paper of 
 Waldemar Lindgren, read at the same meeting, and entitled 
 Metasomatic Processes in Fissure- Veins. This is a most exact 
 and philosophic discussion of the part which metasomasis has 
 played during ore-deposition in various classes of deposits, and 
 
INTRODUCTION. XIX 
 
 the changes thereby brought about in the wall-rocks, as well 
 as in the veins themselves. Mr. Lindg'ren shows this process 
 to have an even wider field of application in ore-deposition 
 than had been assumed by me in the early eighties, although 
 at that time my assumption was regarded as extra-hazardous ; 
 but he deprecates the exaggerated importance assigned to it by 
 some over-zealous supporters of the metasomatic theory. 
 
 Able discussions of all these papers by prominent economic 
 geologists, European as well as American, were read at the 
 succeeding meeting of the Institute in February, 1901, at Rich- 
 mond, Va., and are incorporated in the latter part of the second 
 Posepny volume, together with two papers, which pursued a 
 new line of reasoning, destined to have a most important 
 influence on the whole question of genesis, and to set it, so to 
 speak, on a new basis. These were the paper of Prof. J. F. 
 Kemp, on The Role of the Igneous Rocks in the Formation of 
 Veins, and that of Waldemar Lindgren, on The Character and 
 Genesis of Certain Contact-Deposits. Both authors protest 
 against what they regard as the too great importance assigned 
 by Van Hise and others to the agency of meteoric waters in 
 vein-formation Kemp attacking the question on theoretical 
 grounds, and Lindgren bringing practical proofs from a large 
 and increasingly-important class of deposits that could not 
 have been formed by meteoric waters. 
 
 Kemp enters at once into the broad question of the adequacy 
 of meteoric waters to do what had been claimed for them, in 
 bringing vein-material up from the barysphere, and makes a 
 strong argument against this adequacy and in favor of the prob- 
 . ability that not only the vein-materials themselves, but the 
 waters that carried them, were derived from igneous rocks. 
 A significant indication of the inadequacy of meteoric waters 
 was furnished by the recently-observed fact that the rocks at 
 the bottom of very deep mines (1,000 m.) are nearly or abso- 
 lutely dry. The evidence that water in quantity could have 
 been furnished by igneous magmas is necessarily indirect, 
 but was strengthened, a short time after the publication of 
 these papers, by the conclusions reached by Suess, from the 
 prolonged studies that had been made of well-known Euro- 
 pean thermals, namely, that the waters of many thermal springs 
 .are entirely derived from cooling igneous magmas, squeezed 
 
XX INTRODUCTION. 
 
 out, as it were, during the process of crystallization. Such 
 waters having never before appeared at the surface, Suess 
 calls them "juvenile" waters; but in America they are per- 
 haps more frequently called magmatic waters. Suess admits, 
 however, that the waters of some springs are entirely of mete- 
 oric origin, and that .others probably have a mixed meteoric- 
 magmatic origin, while a portion only are exclusively mag- 
 matic. 
 
 Lindgren's paper on contact-metamorphism was also a protest 
 against the extreme views of Van Hise and others, through its 
 demonstration that deposits of this class must have been formed 
 by direct emanations from cooling igneous magmas at a tem- 
 perature above the critical point of water, and hence in gaseous 
 or pneumatolytic state. He expressed the belief (which he 
 confirmed later by actual observation in nature) that, contrary 
 to the statement of European petrographers, this metamor- 
 phism involves also an actual transfer of material from the 
 intruding magma to the invaded rock. When he wrote this 
 paper, there were, it is true, few deposits of economic impor- 
 tance to which a contact-metamorphic origin could, with cer- 
 tainty, be ascribed; but since then, as their characteristics have 
 become better known, the number of such deposits discovered 
 has been so greatly increased that they constitute in reality the 
 strongest argument in favor of the theory of the magmatic ori- 
 gin of vein-forming waters. 
 
 After the appearance of these two papers, there was a marked 
 revival of discussion on the ultimate source of the metals 
 the question, as it came to be called, of " meteoric versus mag- 
 matic waters." The advocates of the latter origin often went 
 further than either Kemp or Lindgren would have been willing 
 to go, in assuming it as proved that the great majority of ore- 
 deposits have been deposited from highly-heated waters of 
 magmatic origin that is, waters occluded in igneous magmas, 
 and expelled or squeezed out of them during the process of 
 crystallization. This theory has the great merit of furnishing 
 a ready explanation for many facts connected with ore-deposi- 
 tion for which it has hitherto been difficult to account. If, for 
 instance, it be admitted that the mineral-bearing waters are 
 furnished by the cooling magmas, it is no longer necessary to 
 assume that surface-waters circulate to impossible depths; since 
 
INTRODUCTION. XXI 
 
 the magmas themselves, which have unlimited powers of pene- 
 tration, may have risen to within the region of possible circu- 
 lation before the commencement of the process of consolidation 
 which would have squeezed out the mineral-bearing waters. 
 Some conservative minds still require more definite proof that 
 magmas contain water in sufficient quantity to fulfill the re- 
 quirements of this hypothesis; for, while petrographers in 
 general admit the possibility that during the consolidation of 
 magmas mineral salts may have been pneumatolytically forced 
 into the adjoining rocks, many of them doubt lhat such consoli- 
 dating magmas are of themselves capable of furnishing the 
 long-continued supply of water, carried through long distances, 
 which seems to be required for the formation of certain classes 
 of deposits. Direct proof of what has taken place at such great 
 depths cannot, it is evident, be obtained. It is, therefore, all the 
 more important to find well-determined facts of observation or 
 experiment that may indirectly contribute to this end. In the 
 later portion of the present volume will be found many papers, 
 the bearing of which upon questions of genesis may seem 
 rather remote, but which have been selected because they con- 
 tain scientific data which may be found later to have inductive 
 value in testing some of the current theories. 
 
 Returning from this discussion of previous contributions, 
 required for the continuous history of the literature of the 
 subject, as embodied in our Transactions, I resume the con- 
 sideration of the papers contained in the present volume. 
 
 No. 9. The Influence of Country-Rock on Mineral Veins. By 
 W. H. Weed. This is a compilation of facts bearing on the 
 change of the mineral contents of vein-deposits as such deposits 
 pass from one rock into another. 
 
 No. 10. Igneous Rocks and Circulating Waters as Factors in Ore- 
 Deposition. By J. F. Kemp. This paper continues the discus- 
 sion of the connection of vein-forming waters with igneous 
 magmas, giving the author's reasons for thinking that Van 
 Rise's final arguments, as presented in the discussion of pre- 
 vious papers, failed to afford an adequate explanation of vein- 
 phenomena through the agency of meteoric waters alone. As 
 will be observed, he inclines to the view that ore-deposits are 
 likely to occur where some intrusive rock charged with me- 
 tallic material has entered the earth's crust and imparted its 
 
XX11 INTRODUCTION. 
 
 material to up-rising mineral waters, and that deposition in 
 such cases has ceased, not, as maintained by Van Hise, because 
 of cementation, but because the stimulating cause the heat of 
 the intruded body became exhausted. He also differs with 
 Van Hise with regard to the abundance of veins, and the uni- 
 versal and uniform occurrence of ground-water within the 
 earth's crust. 
 
 No. 11. A Consideration of Igneous Hocks and Their Segrega- 
 tion or Differentiation as Related to the Occurrence of Ores. By J. 
 E. Spurr. This *is a recapitulation and analysis of arguments 
 recently brought forward in favor of what may be called a 
 magmatic theory of ore-genesis and of the facts that support it, 
 together with certain views peculiar to the author, especially 
 with reference to the magmatic origin of certain gold-bearing 
 quartz veins. His final conclusion is " that the origin of 
 metal-producing districts as contrasted with barren districts is, 
 in most cases, due primarily to magmatic segregation, and that 
 an important class of ore-deposits is due directly to this." 
 Most workable deposits, however, he admits to be due to sub- 
 sequent concentrations, often several times repeated, through 
 the agency of water acting either chemically or mechanically. 
 Like some others, Mr. Spurr has in this paper misconceived 
 the meaning of the word " occlude," assuming it to be equiva- 
 lent to " squeeze out," whereas it really means to " shut in " or 
 " absorb." 
 
 No. 12. The Chemistry of Ore-Deposition. By W. P. Jenney. 
 This is an elaborate compilation of data with regard to the 
 influence which the various forms of carbon found in the rocks 
 may have had in the precipitation of the metals in ore-deposits 
 from their solutions, supplemented with actual observations by 
 the author, mainly in the lead-zinc deposits of Missouri and of 
 Tintic, Utah. 
 
 The reducing power of organic matter of any kind has been 
 recognized from the earliest conceptions of the genesis of ore- 
 deposits; and Dr. Jenney has rendered a valuable service in 
 showing the great extent to which, under one form or other, it 
 is found in nature in connection with them. There will proba- 
 bly be geologists who will question whether, in all instances 
 quoted by him, this has been 'the only, or even the main, agent 
 in the formation of the sulphide-deposits mentioned. Its action 
 
INTRODUCTION. XX111 
 
 is unquestionably reducing; but that a substance has been re- 
 duced implies that it was primarily in an oxidized condition. 
 That this was the case for the secondarily-enriched material is 
 undoubtedly true; but for primary mineral deposits the as- 
 sumption seems hardly authorized. 
 
 No. 13. Ore-Deposits Near Igneous Contacts. By W. H. Weed. 
 This is an attempt to make a genetic classification of ore-de- 
 posits, the majority of which the author believes to be, pri- 
 marily, direct emanations from igneous bodies. Such attempts, 
 when conscientiously and thoroughly made, serve a useful 
 purpose in bringing together for discussion the evidence in 
 favor of the views advocated ; but it is questionable whether 
 this classification of metamorphic contact-deposits, made before 
 there has been time for accurate and extended studies of any 
 great number of such deposits, has really advanced our knowl- 
 edge of them to any considerable extent; for it means the es- 
 tablishing of a standard which nature is expected to follow, 
 whereas, the reverse method is the only one which can yield 
 sound and permanent results. 
 
 No. 14. Ore-Deposition and Vein- Enrichment by Ascending 
 Hot Waters. By W. H. Weed. This paper treats of a phase 
 of secondary enrichment which, though normally included in 
 the original statement of this theory, had thus far received but 
 little attention namely, enrichment by ascending waters, or 
 differential deposition. It is a phase which is less susceptible 
 of actual observation or demonstration than that by descending 
 waters ; hence the data bearing on this subject which Mr. 
 Weed has here gathered are of great importance, and deserve 
 to be put on record. 
 
 No. 15. Basaltic Zones as Guides to Ore-Deposits in the Cripple 
 Creek District, Colorado. By E. A. Stevens. This paper pre- 
 sents the conclusions of the author, who had been profession- 
 ally connected with various Cripple Creek mines, with regard 
 to the effects of recent dikes upon ore-concentrations in that 
 district. They differ in some respects from the theories pre- 
 viously maintained, and may not be confirmed by future 
 studies ; but they are suggestive and worthy of consideration. 
 
 No. 16. The Geological Features of the Gold- Production of 
 North America. By W. Lindgren. The portion of the paper 
 included in this volume presents the practical application of 
 
XXIV INTRODUCTION. 
 
 the knowledge with regard to ore-deposition thus far ob- 
 tained on this continent, and a classification of deposits of 
 gold, primarily by relative age and also to a certain extent by 
 method of genesis, and gives the practical conclusions as to 
 future production that may be drawn therefrom. Coming 
 from one so well qualified for the task, bqth by ability and 
 by the advantages of official position, as Mr. Lindgren, these 
 conclusions may be considered as most important and authori- 
 tative. 
 
 No. 17. Osmosis as a Factor in Ore- Formation. By H. B. Gil- 
 lette. This paper discusses a force, the possible importance of 
 which in the process of ore-deposition has not received the at- 
 tention from economic geologists in general which it seems to 
 deserve. Already, in 1892, Dr. George F. Becker 3 had called 
 attention to the possibility that osmosis might explain the dif- 
 fering action of the same mineral-bearing solutions on the inte- 
 rior of a vein and the adjoining wall-rock, only the solutions 
 of the gangue-materials being able to penetrate the latter. 
 Later, experimental tests were made by Dr. E. A. Schneider * 
 on colloidal sulphides of gold, carrying out the idea in a modi- 
 fied form. Lindgren has practically applied it in his discus- 
 sion of the vein-deposits of Nevada City and Grass Valley, 
 Cal., 6 and of Cripple Creek, Colo. 6 
 
 Mr. Gillette does not refer to these earlier investigations, but 
 makes the suggestion that metasomatic replacement for in- 
 stance, of limestone by kaolin is a physical rather than a 
 chemical process, and that for every particle deposited by 
 crystallization a particle of country-rock may be dissolved. 
 
 No. 18. The Ore-Deposits of Sudbury, Ontario. By C. W. 
 Dickson. The genesis of these important nickel-bearing pyr- 
 rhotite-deposits has been the subject of repeated discussion 
 ever since their discovery. The most contradictory conclu- 
 sions have been reached by different geologists, whose acknowl- 
 edged ability entitled them to equal scientific credence. The 
 view expressed, in this paper differs essentially from those of 
 the majority of writers on the subject, especially the Canadians; 
 
 3 Mineral Resources of the United States, p. 156(1892). 
 
 * Bulletin No. 90, U. S. Geological Survey (1892). 
 
 5 Seventeenth Annual Report, U. S. Geological Survey, Pt. II., p. 183 (1896). 
 
 6 Professional Paper No. 54, U. S. Geological Survey, p. 229 (1906). 
 
INTRODUCTION. XXV 
 
 but it presents the result of most careful microscopic study; 
 and the paper contains so full, and apparently methodical, a 
 statement of previous investigations, not only of these, but of 
 cognate deposits, that it has been thought best to give it in 
 full, since the facts are important and worthy of credence, 
 whatever may be the reader's opinion of the conclusions 
 reached by the author. Even if, as claimed by some of those 
 who hold the opposite view, the phenomena here presented 
 are found in 'only a small portion of the area exploited, that 
 fact does not justify their being disregarded. A preliminary 
 magmatic concentration does not preclude a subsequent con- 
 centration by some form of metamorphic action. It may never 
 be possible, where both these processes have been active, to 
 determine the exact proportion of the resulting deposit which 
 may be due to either, that is, which played the greater part in 
 its formation ; but it would hardly seem proper to characterize 
 a deposit as a magmatic concentration if, it has been brought 
 to its present condition of an economically-workable deposit 
 through the agency of subsequent aqueous concentration. 
 
 No. 19. The Genesis of the Copper-Deposits of Clifton-Morenci, 
 Arizona. By W. Lindgren. This is an admirable supplement 
 to his earlier paper on contact-metamorphism in the previous 
 volume. It contains the genetic conclusions derived from an 
 actual and detailed study of a most typical group of contact- 
 metamorphic deposits, in which he has been able to verify in 
 nature many of his previous theoretical conclusions notably 
 that of the actual contribution of material by intruding igneous 
 magmas to the intruded rocks, as well as many new and valu- 
 able data as to the phenomena of contact-metamorphic copper- 
 deposits. 
 
 No. 20. The Copper-Deposits of San Jose, Tamaulipas, Mexico. 
 By J. F. Kemp. This is a description of contact-metamorphic 
 deposits of copper in limestone in the periphery of an intrusion 
 of diorite-porphyry. It contains a discussion of the chemical 
 processes by which the lime silicates, mainly garnets, are 
 formed, and of the origin of the material which enters into 
 their composition whether it can all be accounted for as 
 originally contained in the limestone, or whether some portion 
 must have been added during the intrusion of the igneous 
 magma. This paper thus forms a supplement to that of Mr. 
 
XXVI INTRODUCTION. 
 
 Lindgren on Clifton-Morenci, and, though descriptive, consti- 
 tutes an addition to our knowledge of the general process of 
 contact-metamorphism. 
 
 'No. 21. Magmatic Origin of Vein-Forming Waters in South- 
 eastern Alaska. By A. C. Spencer. This is an argument in 
 favor of the magmatic origin of vein-forming waters in that 
 region, following the suggestion of Lindgren that the gold- 
 quartz veins of Victoria, Australia, and of California, have been 
 deposited chiefly by water originally contained in a granitic 
 magma, possibly aided to a certain extent by atmospheric 
 waters. 
 
 No. 22. Genetic Relations of the Western Nevada Ores. By J. 
 E. Spurr. This paper ascribes a magmatic origin to the ore- 
 bearing waters which have produced the gold- and silver-de- 
 posits of western Nevada, arid, in the Silver Peak district, even 
 suggests that the gold-bearing quartz veins are siliceous phases 
 of the cooling alaskite. 
 
 No. 23. Are the Quartz Veins of Silver Peak, Nevada, the 
 Result of Magmatic Segregation ? By J. B. Hastings. This is a 
 criticism of Mr. Spurr's views, as applied to the Silver Peak 
 quartz veins in the foregoing paper. 
 
 No. 24. The Occurrence of Stibnite at Steamboat Springs, Nevada. 
 By W. Lindgren. This is a record of recent additional experi- 
 mental observations by the author on the processes going on 
 at Steamboat Springs, Nevada, where Becker had in 1885 
 proved that metallic sulphides were actually being deposited 
 by hot thermal waters. It is interesting as noting the changes 
 that have apparently taken place in the deposits within 16 
 years. 
 
 No. 25. A Summary of Lake Superior Geology with Special 
 Reference to Recent Studies of the Iron-Bearing Series. By C. K. 
 Leith. 
 
 No. 26. The Geological Relations of the Scandinavian Iron- 
 Ores. By Hjalmar Sjogren. 
 
 These papers, Nos. 25 and 26, contain respectively summa- 
 ries, by men especially well equipped for the purpose, of the 
 geology of the two great iron-ore regions of the world, the 
 Lake Superior region of North America and the Scandinavian 
 peninsula in Europe. While not primarily genetic, they pre- 
 
INTRODUCTION. XXV11 
 
 sent summaries of the geological relations of the respective 
 deposits which involve a discussion of their genesis. 
 
 It is interesting to contrast the broader outlines of genesis of 
 these two greatest known concentrations of metallic ores in the 
 world. They both occur in the very oldest rock-series that have 
 yet come under observation and study, and are themselves, in the 
 main, of pre-Cambrian age, though they may have suffered some 
 further concentration in more recent times. They are consid- 
 ered to be essentially concentrations by oxide-laden surface- 
 waters of iron-material, originally disseminated in the form of 
 carbonate, silicate, or even oxide, in the beds of the sedimentary 
 series in which they occur, and are thus what the European geolo- 
 gists would classify as sedimentary in origin. It is true that these 
 primary constituents are considered by Van Hise to have been 
 derived in a last analysis from decomposing igneous rocks, out 
 of which they were dissolved or abraded by sea-waters, while 
 the actual process that has made them of economic value has 
 been later than sedimentation, and entirely independent of it. 
 
 The sedimentary origin formerly maintained for a large 
 proportion of the Scandinavian ores is now considered to be 
 impossible, since metasomatism, the importance of which has 
 been more readily recognized by the Swedish than by any other 
 European geologists, is shown to be the process by which they 
 have been formed, through the agency, however, of deep-seated 
 rather than surface-waters. Although the Scandinavian iron- 
 deposits are here divided into several distinct types, they are 
 all more or less distinctly connected with igneous eruptives. 
 Some are considered to be magmatic segregations ; the greater 
 part are some form of pneumatolytic formation, of which the 
 extreme type is the contact-metamorphic deposit in limestone. 
 One or more of the lime silicates, garnet, amphibole, etc., are 
 very common associates of all the ores. Secondary alteration 
 and concentration by surface-water is considered to have played 
 but a very subordinate part, if any, in producing the present 
 deposits. 
 
 No. 27. The Formation and Enrichment of Ore-Bearing Veins. 
 By George J. Bancroft. This is a discussion, by an experienced 
 mining engineer, from the point of view of his own personal 
 observations in Western mining-districts, of various points in 
 the theories of genesis from aqueous solutions presented in 
 
XXV111 INTRODUCTION. 
 
 the previous papers. The main conclusions peculiar to his 
 point of view, are that veins are formed in relatively short 
 periods, and from rich or concentrated solutions. 
 
 No. 28. The Distribution of the Elements in Igneous Rocks. By 
 H. S. Washington. This is a discussion of the relative amount 
 of the elements, as shown by the improved modern methods of 
 rock-analysis, that go to make up the ore-deposits found in dif- 
 ferent varieties of igneous magmas. From the point of view 
 of the petrographer and chemist, this is an important inquiry; 
 and though at present it yields but few results of actual eco- 
 nomic bearing, it is significant of what may be expected from 
 further research along these lines. It is noteworthy that while 
 the average water-content of crystalline rocks is not over 2 per 
 cent., this percentage may be carried up to 12 in fresh glassy 
 lavas, from which the water was unable to escape, owing to the 
 rapidity of solidification. 
 
 No. 29. The Agency of Manganese in the Superficial Alteration 
 and Secondary Enrichment of Gold-Deposits of the United States. 
 By Prof. "W. H. Emmons, Copperhill, Tenn. This paper forms 
 a fitting close to the series. It is a thorough examination and 
 discussion of the doctrine of secondary enrichment, as applied 
 to the single metal, gold. It had already been noticed that 
 there are gold-deposits which have evidently been, and others 
 that apparently have not been, enriched by surface oxidizing 
 waters. The author and his assistants, by a series of chemical 
 experiments, have discovered the cause of this difference, and 
 thus contributed an important scientific addition to the doctrine 
 of secondary enrichment, which, in practice, should enable the 
 mining engineer to determine whether a given gold-deposit is 
 secondarily enriched ; whether it is capable of producing valu- 
 able placers by disintegration ; or whether neither condition 
 can be expected. It also accounts for transfers of gold from a 
 higher to a lower horizon in certain classes of deposits. This 
 is the type of investigation to which we may look hereafter for 
 the most valuable results in furtherance of the science of ore- 
 genesis. 
 
BIOGRAPHICAL NOTICE OF SAMUEL FRANKLIN" 
 
 EMMONS. 
 
 BY GEORGE F. BECKER, WASHINGTON, D. C. 
 
 (San Francisco Meeting, October, 1911. Trans., xlii., 643.) 
 
 A MERE record of Emmons's professional career would very 
 inadequately represent the man. That he was eminent we 
 know, and our successors will realize in due time ; but they 
 must depend upon us for knowledge of a singularly wholesome, 
 modest, unselfish personality, and of a character that did honor 
 to a profession in which trustworthiness is indispensable. 
 Those members of the Institute who met Emmons are his 
 friends, and I never knew one of these who was not the better 
 for that friendship. 
 
 Emmons was born in Boston, Mar. 29, 1841, the son of 
 Nathaniel H. and Elizabeth (Wales) Emmons, and was named 
 Samuel Franklin after an ancestor who was of the same family 
 as Benjamin Franklin. He took the degree of Bachelor of 
 Arts at Harvard in 1861, and soon afterwards went abroad to 
 complete his education. From 1862 to 1864 he attended the 
 courses at the ficole Imperiale des Mines at Paris, Elie de 
 Beaumont and Daubree being among his professors. The 
 year 1864-1865 he spent at Freiberg under Cotta and other 
 famous teachers ; after which he spent another year in travel- 
 ing through Europe. Like many other renowned geologists, 
 he approached his ultimate profession from its economic side, 
 and was thus from the first imbued with a sense of high re- 
 sponsibility in the promulgation of scientific opinions or con- 
 clusions. With hypotheses which were interesting merely 
 because they were ingenious or even plausible, he would have 
 nothing to do. 
 
 In 1867 he joined the Geological Exploration of the Fortieth 
 Parallel at its organization under Clarence King, serving at 
 first as a volunteer, but soon receiving a regular appointment. 
 This expedition was the first one of purely geological char- 
 acter sent out by the United States government. As Emmons 
 has shown in his admirable presidential address on " The 
 Geology of Government Explorations," its work was founded 
 
 ( xxix ) 
 
XXX BIOGRAPHICAL NOTICE OF SAMUEL FRANKLIN EMMONS. 
 
 on a complete and comprehensive plan, adopted before taking 
 the field, and systematically followed in all essential features 
 during the ten years of its existence. This plan aimed at the 
 highest efficiency compatible with prompt completion. It was 
 important from every point of view that the broad outlines of 
 the geology and mineral resources of the belt of country to be 
 opened up by the completion of the transcontinental railway 
 should be made known as soon as practicable. To execute a 
 final, detailed survey under such conditions was impossible ; 
 and for this reason the work was called an exploration, but as 
 a first approximation to the truth the intention was to make it 
 irreproachable in methods and in symmetry. The best experts 
 to be had were secured ; contour-mapping as a basis for geo- 
 logical work was introduced for the first time in this country ; l 
 and, when lithological collections had accumulated, a well- 
 known European petrographer was engaged to discuss them 
 by the new microscopic methods, then wholly unfamiliar to 
 American geologists. Emmons's associates as assistant geolo- 
 gists were our late eminent colleague James D. Hague, and his 
 brother, Mr. Arnold Hague. The expedition started in 1867 
 from Sacramento : and it will help our younger brethren to 
 grasp the changes which have taken place in the civilization 
 of the West to be reminded that an escort of 30 regular 
 soldiers was needed in that year to protect the civilians from 
 hostile Indians. 
 
 To realize how hard the men worked, it is only needful to 
 glance at the Fortieth Parallel memoirs and maps, but shoot- 
 ing was an available recreation, and afforded a legitimate 
 means of varying a monotonous diet. There was one particu- 
 larly good bear-story which Dr. Eaymond has recorded in his 
 notice of King in Emmons's own words. 2 Of this Dr. Raymond 
 writes me : 
 
 11 King, who always reaped the glory which his splendid audacity deserved, 
 killed the bear ; but the story shows that Eramons was posted at the other end of 
 the passage where the wounded bear would have come out, if King's shot in the 
 dark had not been fatal ! " 
 
 One of the rules of the Fortieth Parallel Survey was, that its 
 
 1 Capt. John Mullan's Keport on the Construction of a Military Road, 1863, 
 contained contour sketch-maps surveyed and drawn by Theodore Kolecki. 
 
 2 Trans., xxxiii., 633 (1902). 
 
BIOGRAPHICAL NOTICE OF SAMUEL FRANKLIN EMMONS. XXXI 
 
 members should be as civilized as practicable, especially at 
 meals. The men believed in a good and varied diet, well- 
 cooked and served; and, when the accounting-officers of the 
 War Department demurred at passing a bill for currant-jelly, 
 they were met with a threat to charge up at the rate of beef 
 the venison furnished by members of the mess. By such 
 means the geologists preserved both their digestion and their 
 adaptability to social life at centers of civilization, in which 
 every one of them took a prominent part in later years. 
 
 Two episodes in the history of the Exploration of the For- 
 tieth Parallel deserve mention. In 1870, the appropriation- 
 bills passed too late for a regular season of field-work, and 
 King decided on an examination of the extinct volcanoes of the 
 Cascade range. He and Emmons ascended Mt. Shasta, and 
 there found the first glaciers recognized within the limits of 
 the United States. Later, in the same autumn, Emmons made 
 the ascent of Mt. Rainier, where he found much more extensive 
 glaciers, which he has very graphically described. Emmons 
 made no claim to the first ascent of this great peak, recogniz- 
 ing that it had been scaled two months earlier by Gen. Hazard 
 Stevens; but our colleague, who was accompanied by Mr. A. 
 D. Wilson, was the first to bring from this dormant volcano 
 valuable information on its topography, geology, and glaciol- 
 ogy. During the same season Mr. Arnold Hague ascended 
 Mt. Hood, where he too discovered typical glaciers. 
 
 In 1872 Emmons took part in the exposure of the famous 
 diamond swindle. Though strong efforts were made to keep 
 secret the locality of the alleged diamond " discovery," King 
 made out that it must be in a region which Emmons had sur- 
 veyed. They set out together to investigate, and Emmons was 
 able to lead the little party to the scene of the crime in Ver- 
 million Creek Basin, Wyoming. This had been selected by the 
 swindlers because it was- in a nearly waterless region, from 
 which almost any expert would retreat *at the first possible 
 moment. A great financial disaster was averted by the detec- 
 tion of this fraud, and it is doubtful whether King could have 
 achieved the disclosure without Emmons's knowledge of the 
 country. 
 
 In King's Exploration, Mr. Arnold Hague and Emmons had 
 charge of the descriptive geology. In 1870 Emmons had con- 
 
XXX11 BIOGRAPHICAL NOTICE OF SAMUEL FRANKLIN EMMONS. 
 
 tributed a chapter on the Toyabe range and some minor notes 
 to Vol. III. (Mining Geology). With these exceptions, and 
 that of his description of Mt. Rainier, all his work on that sur- 
 vey is contained in Vol. II. (Descriptive Geology), printed 
 in 1877, and containing nearly 900 pages. In the letter of 
 transmittal by the authors the limitations of the work are thus 
 emphasized : ^ 
 
 "It will be readily understood by the reader, from the very title of the work, 
 that this does not claim to be a systematic survey like those of Europe, based on 
 accurate maps, but is rather a geological reconnaissance in an unknown and often 
 unexplored region, where geology and topography had to go hand in hand, and 
 that therefore, while details were often, from the necessities of the case, somewhat 
 neglected, it was the general bearing of the leading geological facts that was most 
 constantly in our minds." 
 
 Now-a-days, I suppose, no one would think of reading this 
 volume through, though it remains an important book of refer- 
 ence. In 1877, however, it was full of news, and Gerhard vom 
 Rath, to whom geology (directly and indirectly) owes so much, 
 told me in 1888 that it was the interest the Descriptive Geology 
 aroused in him which led him to visit the United States. It 
 was, I remember, the first work I ever reviewed ; and I greatly 
 enjoyed the task. 
 
 In accordance with the plan of the Exploration of the 
 Fortieth Parallel all the men had constantly to guard against 
 two temptations, one being to follow out their problems by de- 
 tailed studies at an undue expenditure of time, and the other 
 to gain time by slighting important matters in which they 
 might happen to feel relatively slight personal interest. There 
 can be no doubt that they displayed great self-control ; and in 
 my opinion the result was an unrivaled model of a preliminary 
 survey in an unknown region. 
 
 It should not be forgotten that the topographic and the 
 geologic reconnaissances were executed at substantially the 
 same time, so that tfce geologists rarely had maps in the field 
 on which to record their work. This involved keeping in 
 mind and in note-books a vast number of detailed observations 
 systematically co-ordinated and of a prescribed standard in re- 
 spect to generality. Ten years of this sort of thing gave 
 Emmons an unusual command of details, and power to marshal 
 them mentally without extraneous aid. In short, it was the 
 
BIOGRAPHICAL NOTICE OF SAMUEL FRANKLIN EMMONS. XXX111 
 
 training in descriptive geology, as he practiced it, which en- 
 abled him subsequently to deal with the complexities of Lead- 
 ville. 
 
 With the completion of the Descriptive Geology in 1877, the 
 connection of its authors with the Fortieth Parallel ceased. 
 For the next two years, Emmons devoted himself to a cattle- 
 ranch near Cheyenne. The country was still unfenced, and 
 great profits were possible in this business, while the active, 
 out-door life suited Emmons's temperament and habits. Even 
 after his return to scientific life, he retained his interest in this 
 ranch for some years, and kept there a pack of Scotch deer- 
 hounds with which he hunted. 
 
 In March, 1879, the government organizations which had 
 been carrying on geological reconnaissances were merged in 
 the present United States Geological Survey, and King was 
 appointed Director, taking his oath of office on May 24. As a 
 matter of course, a position was offered to Emmons, and he 
 qualified on August 24. 
 
 In the autumn of that year King summoned Emmons and 
 me to Washington, in order to prepare schedules for the ex- 
 amination of the precious metals industries under the Tenth 
 Census, a task undertaken by the Survey as a matter of cour- 
 tesy to the Census Bureau and as germane to its own office. 
 As soon as Emmons arrived, I called upon him ; and when, an 
 hour later, King entered the room to introduce us, we were 
 already friends. Such we always remained without a single 
 misunderstanding. 
 
 It was for each of us a busy and interesting period, and in 
 later years a favorite subject for reminiscence. Emmons, 
 though of course strong on general geology and lithology, 
 was rusty in technical mining and metallurgy, which I had 
 been teaching; and while I had a considerable familiarity with 
 ore-deposits, my knowledge of general geology and lithology 
 was elementary. Indeed, on joining the Survey, I had stipu- 
 lated with the Director that he should call upon me only for 
 mining and metallurgical reports. Thus the preparation of 
 schedules led to many instructive discussions, carried on with 
 the utmost freedom and good-will. We worked hard and 
 long. Wo were in almost daily consultation with King, who 
 was well informed on the whole subject, but I do not remember 
 
XXXIV BIOGRAPHICAL NOTICE OF SAMUEL FRANKLIN EMMONS. 
 
 that he ever made any material change in our plans ; and we 
 also had prolonged sessions with Gen. Francis A. Walker, 
 Superintendent of the Census, who was thoroughly agreeable 
 and agreeably thorough. 
 
 Life was not all work, however. John Hay, then Assistant 
 Secretary of State, and King had at Wormley's a private dining- 
 room, which they invited Emmons and me to share with them. 
 I doubt whether there ever was table-talk more brilliant than 
 that to which we listened in that room. Neither Emmons 
 nor I said much, but we egged on the other two, and laid little 
 plots to get them started on matters we desired to hear dis- 
 cussed. King and Hay were intimate friends, and particularly 
 well-fitted by differences in temperament and experience to 
 complement one another in conversation. Though Hay rarely 
 indulged in humor and was not a man of buoyant spirits, he 
 was never commonplace or ponderous. He was gifted with 
 true wit, whose gleams showed even familiar relations in new 
 aspects and revealed relationships among less familiar things. 
 He offered, but never obtruded, suggestive reflections grace- 
 fully epitomized, and in this intimate companionship disclosed 
 the grasp of affairs and breadth of view which were to make 
 him a great Secretary of State. As for King, hear Hay ! 
 
 " He was inimitable in many ways : in his inexhaustible fund of wise and witty 
 speech ; in his learning, about which his marvellous humor played like summer 
 lightning over far horizons ; in his quick and intelligent sympathy, which saw 
 the good and amusing in the most unpromising subjects ; in the ease and airy 
 lightness with which he scattered his jewelled phrases ; but above all in his aston- 
 ishing power of diffusing happiness wherever he went." 3 
 
 Had these wonderful dinners not been so entertaining they 
 might have been considered as equivalent to a post-graduate 
 course in liberal education. They exerted a lasting influence 
 on Emmons and me, expanding our views and adding symme- 
 try to our standards of thought and achievement. 
 
 It was while we were engaged on the Census schedules that 
 King completed his plans for the investigation of ore-deposits, 
 and placed the work in our charge by the orders quoted in 
 Emmons's introductory chapter to this volume. I was reluct- 
 ant to accept the responsibility, and I should have persisted in 
 
 3 Clarence King Memoirs, p. 131 (1904). 
 
BIOGRAPHICAL NOTICE OF SAMUEL FRANKLIN EMMONS. XXXV 
 
 refusing it, had not Ernmons urged me to make the attempf y 
 assuring me in the kindest manner of his co-operation and 
 assistance, so far as circumstances might permit. He began to 
 cram me immediately; and, during the field-work in Leadville 
 and on the Com stock, we were in constant correspondence on 
 every phase of both problems. 
 
 Early in 1880, each of us had to select and instruct a staff of 
 young mining engineers who were to collect the statistics and 
 technological data under the Census, while at the same time 
 we organized and commenced our ' geological field-work; in 
 fact Emmons began on the geology of Leadville just before the 
 New Year. 
 
 What little is to be said of the Census work may be said 
 here, although it was not completed until Emmons's abstract of 
 his Leadville report had been printed. The purpose of the 
 Statistics and Technology of the Precious Metals was to furnish 
 mining-men with accurate data of production and a record of 
 technical practice in the year 1880, together with such an out- 
 line of the geology of the mining-districts as could be prepared 
 from material already published, supplemented by the informa- 
 tion derived from the reports and collections sent in by the 
 experts in the field. It was a harassing piece of work ; and it 
 is needless to say that some districts were more competently 
 reported than others ; but under the circumstances, and on the 
 whole, the authors were fairly satisfied with the result. Its 
 value would have been enhanced by prompt publication. By 
 working at night and on holidays the manuscript and maps 
 were completed and transmitted on Feb. 8, 1883 ; but more 
 than a year elapsed before the first galley-proofs reached us ; 
 and in the meantime the maps had disappeared from the 
 Census Office. I remember exactly how we felt ! 
 
 After King retired from government work, I was placed in 
 charge of the Statistics and Technology of the Precious Metals, 
 so that for a time I had the honor of counting Emmons nomi- 
 nally as my assistant; but of course we worked together as 
 before, and no question of subordination was allowed to arise. 
 When it came to deciding the order of our names on the title- 
 page, however, he said I was in charge and should come first, 
 while I maintained that he, as the senior and more experienced, 
 should take precedence. As neither would be convinced, I 
 
XXXVI BIOGRAPHICAL NOTICE OF SAMUEL FRANKLIN EMMONS. 
 
 proposed deciding the matter by the turn of a coin. Thus we 
 settled it, standing by the statue of Jackson, in the city of 
 Washington. He won the toss and I my way. - > 
 
 In spite of the labor involved in gathering statistics under 
 the Census, Emmons pushed the examination of the geology of 
 Leadville so energetically that he was able to close his office 
 at the camp on Apr. 1, 1881, and to transmit his Abstract of 
 a Report on the Geology and Mining Industry of Leadville 
 on October 20 of that year. This abstract, which appeared in 
 the Second Annual Report of the Director of the United States 
 Geological Survey, is a memoir of 87 pages and contains the 
 principal results of the investigation. The publication of the 
 Monograph was delayed by various causes till 1886; but his 
 main conclusions were not changed in the intervening time. 4 
 In the field-work he was assisted by Ernest Jacob, Whitman 
 Cross, and W. H. Leffingwell as geologists, and by W. F. 
 Hillebrand and Antony Guyard as chemists. 
 
 Emmons's views of the Leadville ore-deposits, up to the time 
 of the publication of his Monograph, may be condensed into 
 the following statement: Prior to oxidation, the ores consisted 
 of sulphides of lead and silver, zinc and iron, which were de- 
 posited by substitution for country-rock, this being as a rule 
 limestone or dolomite, but in some instances siliceous in char- 
 acter. The ore reached the deposits as hot aqueous solutions 
 at high pressures, and came from above. The temperature 
 was due to the depth (about 10,000 ft.), and the magmatic beat 
 of the intrusive porphyries. The water was of meteoric origin 
 and derived its metallic content, perhaps wholly but demon- 
 strably in part, from masses of porphyry which were not neces- 
 sarily in juxtaposition with the ore. The principal deposition 
 took place at the upper .surf ace of the blue Carboniferous lime- 
 stone. 5 
 
 Twenty-one years later he returned to the subject with Mr. 
 J. D. Irving in a paper on the Downtown District ; 6 and the 
 
 4 In the Abstract Emmons regarded the ores as derived from the porphyries, 
 while in the Monograph he considered them as "mainly " derived from this source. 
 
 5 See Abstract, Second Annual Report, U. S. Geological Survey, p. 234 (1882). 
 Geology and Mining Industry of Leadville, p. 584 (1886). Also, Trans., xv., 
 138 (1886-87). 
 
 6 Bulletin No. 320, U. S. Geological Survey (1907). 
 
BIOGRAPHICAL NOTICE OF SAMUEL FRANKLIN EMMONS. XXXVll 
 
 only important change he was obliged to make was an addition 
 rather than a correction. Developments in the intervening 
 decades had shown that many, instead of few, ore-bodies 
 existed within the mass of the Carboniferous limestone (not 
 merely near its upper surface), and also in the Silurian lime- 
 stone. Meanwhile, however, the subject of juvenile or mag- 
 matic waters, first investigated by Charles Sainte-Claire Deville 
 and other French savants, had been actively studied and dis- 
 cussed, so that in 1907 questions arose as to the possible par- 
 ticipation of such waters in the genesis of the Leadville 
 deposits. How far the original sulphides at Leadville were 
 deposited from juvenile waters, and whether instances of depo- 
 sition as a feature of contact-metamorphism were to be found 
 there, were still unknown. 
 
 This paper by Emmons and Irving was, in fact, a partial ab- 
 stract in advance of a monograph by the same authors, in 
 which the entire Leadville work was to be revised. Fortu- 
 nately the volume was so nearly completed before the senior 
 author's death that Mr. Irving is in a position to finish it 
 within a few months. How far it will answer the questions 
 which were still open in 1907, I do not know. 
 
 Leadville presents the most intricate problem of mining- 
 geology ever attempted ; for the structure is as complex as the 
 chemical history of the deposits. Emmons brought to the 
 study of this district a mind trained to carry a vast number of 
 observations in due relation to one another; and this enabled 
 him to execute a truly monumental work. His Monograph 
 has been of enormous importance to miners, for experience 
 has shown that its predictions were substantially correct; it 
 has been of material advantage to the Geological Survey as an 
 evidence of what geology can do for industry ; and it has set 
 an example to younger geologists of the mode of treatment 
 proper to such a problem. The revision of this great work 
 after the lapse of 30 years worthily closed his career. 
 
 Having concluded that the Leadville ores were deposited by 
 substitution, mainly for limestone, Emmons was led to study 
 instances of the replacement by ore of other rocks. Indeed, 
 even in his Leadville Abstract of 1882, he had recognized 
 limited occurrences of ores substituted for siliceous rocks. 
 Cases of this kind had been described in Europe by G-roddeck 
 
XXXV111 BIOGRAPHICAL NOTICE OF SAMUEL FRANKLIN EMMONS. 
 
 I 
 
 and others; but in this country only the native copper of 
 Lake Superior had been recognized as pseudomorphic by Mr. 
 Pumpelly. Emmons soon found abundant evidence capable 
 of interpretation as indicating replacement or metasomatism in 
 a wide sense; that is to say, he found much ore in situations 
 from which even siliceous rocks or minerals had been re- 
 moved. To cover them all, he denned metasomatism as an 
 interchange of substances, but not necessarily molecule by 
 molecule. 
 
 This breadth (perhaps I aught to say looseness) of defini- 
 tion was unavoidable unless he had been willing to postpone 
 for years the announcement of his results ; for convincing de- 
 tailed proof of the various processes active in the alteration 
 and impregnation of wall-rocks requires prolonged and difficult 
 chemical and microscopical investigation. Among engineers 
 the idea, new to many of them, immediately became popular, 
 too popular, in fact; and at one period there was danger that 
 all deposits would be set down without due proof as cases of 
 replacement. Some, however, were left to protest; and, after 
 a few years, the matter was reduced to proper proportions by 
 Mr. Lindgren, 7 who, adopting as his criterion the principle 
 that the theory of substitution of ore for rock is to be accepted 
 only when there is definite evidence of pseudomorphic, mo- 
 lecular replacement, worked out his results with great labor 
 and discrimination. There can be little doubt that as geolog- 
 ical chemistry is elaborated the importance of deposition by 
 substitution will be still further recognized, and that studies 
 devoted to this subject will shed unexpected light on geo- 
 chemical processes. 8 
 
 Secondary enrichment of sulphide ores attracted attention 
 
 i Trans., xxx., 596 (1900). 
 
 8 Among the very first observations which I made on the Comstock lode was, 
 that much of the pyrite in the wall-rock was pseudomorphic after ferromagnesian 
 bisilicates. (Geology of the Comstock Lode, p. 210, 1882.) Emmons's studies on 
 replacement led me to examine the quicksilver-mines very closely for pseudo- 
 morphic deposition of cinnabar. In spite of profound alteration of wall-rock, 
 attended by other replacements, I found no instance of deposition of cinnabar by 
 substitution for carbonates or silicates. These facts led me to suggest the dia- 
 lytic or osmotic separation of ore-bearing solutions, a hypothesis which is thus 
 indirectly due to Emmons. Geology of the Quicksilver Deposits of the Pacific Slope, 
 p. 396 (1888), and Mineral Resources of the U. S. for 1892, U. S. Geological Survey, 
 p. 156 (1893). 
 
BIOGRAPHICAL NOTICE OF SAMUEL FRANKLIN EMMONS. XXXIX 
 
 in Europe earlier than in this country. The relative affinity of 
 the metals for sulphur was investigated as long ago as 1837, 
 by E. F. Anthon, 9 but the first application to ore-deposits with 
 which I have met is contained in Mr. Joaquin Gonzalo's admi- 
 rable monograph on Huelva, issued in 1888. The secondary 
 deposits of chalcopyrite (occasionally accompanied by other 
 copper-compounds), and galena, as they are found at Rio 
 Tinto, are described by the Spanish geologist as occurring 
 along lithoclastic fractures in the mass of the pyrite. They 
 are attributed to a process of segregation within the mass and 
 to the reduction of sulphates percolating downward from the 
 zone of oxidation. 10 Mr. J. H. L. Vogt, after personal exami- 
 nation, entirely assented to Mr. Gonzalo's views, and pointed 
 out subsequently that secondary enrichment is the true mean- 
 ing of that familiar old proverb: Es thut kein 'Gang so gut, 
 Er hat einen eisernen Hut. 11 
 
 Emmons's own studies on secondary enrichment were begun 
 at Butte in 1896; and he freely discussed his results in private, 
 though they were first published in our Transactions in 1900. 
 In this paper he quotes from that of Vogt, issued the year 
 before, but also sets in order a long series of observations of 
 his own, which form an. extremely important contribution to 
 the subject. This is cognate to his other studies on replace- 
 ment; for his idea of secondary enrichment might be para- 
 phrased as the replacement of pyrite by the sulphides of other 
 metals, especially copper. 
 
 The idea of secondary enrichment was in the air at the close 
 of the last century, and had been very distinctly suggested in 
 this country (for instance by Dr. James Douglas), though with- 
 out sufficient substantiation. Almost simultaneously with Em- 
 mons's memoir appeared important papers by Messrs. Weed, 
 Van Hise, and Lindgren. 
 
 It is not needful here to pass in review all of Emmons's 
 work. A full list of his papers will be found at the end of this 
 notice. All of them are as conscientiously elaborated as those 
 
 9 Journal filr praktische Chemie, vol. x. , p. 333 (1837). See also E. Schurmann, 
 in Leibig's Annalen, vol. ccxlix., p. 326 (1888). 
 
 10 Mem. de la Comm. del Mapa Geol6gica de Espana. Descripcion fisica, 
 geologica y minera de la provincia de Huelva, por Joaquin Gonzalo y Tarin, 
 pp. 217 to 220 et passim (1888). 
 
 11 Zeitschrift fur praktische Geologic, pp. 241 10 254 (July, 1899). 
 
xl BIOGRAPHICAL NOTICE OF SAMUEL FRANKLIN EMMONS. 
 
 which I have selected for mention on account of their peculiar 
 importance. On the other hand, a few remarks seem appro- 
 priate on the tendency and the development of the science 
 which he so admirably represented. 
 
 When Clarence King planned the researches of the U. S. 
 Geological Survey into the origin and nature of ore-deposits, 
 and placed Emmons and me in charge of them, no one of us 
 was in a position to appreciate the multifariousness and intri- 
 cacy of the facts which these investigations would disclose ; but 
 before King's untimely death, the vastness of the task was 
 manifest, as well as the necessity for improved methods of in- 
 vestigation and for experimental researches of the most funda- 
 mental character. 
 
 More than half of the great amount of information now 
 available to mining-geologists is due to the use of the micro- 
 scope, armed with which, the eyes of the generation now pass- 
 ing away have been a hundred times as sharp as those of their 
 predecessors. But the microscope is not merely a powerful 
 magnifying-glass ; it is an instrument of moderate precision, 
 whose use has familiarized us with quantitative measurement 
 and stimulated us to demand exact methods of geological in- 
 vestigation. 
 
 It is not enough to know the facts, for these alone lead only 
 to delusive " rules of thumb." We can and must attain a com- 
 prehension of the mechanical, chemical, and thermal processes 
 which underlie the formation and distribution of ores, as re- 
 vealed not only by the microscope, but also by every other 
 available method of research. Many of the problems presented 
 are of extraordinary difficulty, far exceeding in this respect 
 most of those undertaken by professional physicists and chem- 
 ists ; but they are not insoluble ; and the limits of our knowledge 
 are extended year by year. 
 
 None of us have been more impressed with the necessity for 
 such researches than was King, or even Emmons, who regretted 
 all his life that he had not a better command of the exacter 
 sciences. Let me pass the word on from them that the future 
 of the science of ore-deposits depends on investigations of the 
 utmost precision into the fundamental principles of geophysics. 
 Physics and physical chemistry will be as indispensable to the 
 mining-geologist of the future as mineralogy to the petro- 
 
BIOGRAPHICAL NOTICE OF SAMUEL FRANKLIN EMMONS. xli 
 
 grapher or zoology to the palaeontologist. It is a duty which 
 the Institute owes to its founders, its members, and the world, 
 to promote and foster research of this description; to advance 
 as rapidly as possible the day when mining-geologists, no 
 longer groping, will comprehend why ore-deposits are what we 
 find them to be. 
 
 And now as to the man himself. There is not a geological 
 society or even a mining-camp from Arctic Finland to the 
 Transvaal, or from Alaska to Australia, where Emmons's name 
 is not honored and his authority recognized ; nor is there a 
 society of which he was nominally an active member in which 
 he was not really active and efficient. Thoroughness and good 
 judgment characterized all he did. He had a very high sense 
 of responsibility and rarely made his hypotheses public ; yet 
 his originality has enriched the science to which his life was 
 devoted. In private life, he was modest to the point of diffi- 
 dence, and many of his old acquaintances scarcely knew of his 
 distinction; but none could long enjoy his acquaintance with- 
 out becoming conscious of the kindness of his heart and the 
 elevation of his character. He would not have known how to 
 undertake an unworthy action, or how to do a selfish thing. 
 His published investigations will live on as sources of knowl- 
 edge and models of method ; and in a similar circle his per- 
 sonal example will continue potent for good. 
 
 Emmons died painlessly and unexpectedly in his sleep on 
 Mar. 28, 1911, the eve of his seventieth birthday. Thus fitly 
 ended a career of useful labor faithfully performed. 
 
 Among the societies to which Emmons belonged, none ap- 
 pealed to him more than the American Institute of Mining 
 Engineers. He joined us in 1877, was three times Vice-Presi- 
 dent, contributed many papers to the Transactions, and was 
 always ready to assist in organizing our meetings. He was 
 also a member of the National Academy of Sciences, the 
 American Philosophical Society, the American Academy of 
 Arts and Sciences, the Washington Academy of Sciences, the 
 Geological Society of London, the Geological Society of Amer- 
 ica, the International Congress of Geologists, and the Colorado 
 Scientific Society. He was elected an honorary member of the 
 
xlii BIOGRAPHICAL NOTICE OF SAMUEL FRANKLIN EMMONS. 
 
 Societe Helvetique des Sciences Naturelles, and received the 
 degree of Doctor of Sciences from Harvard and Columbia. 
 
 LIST OF SCIENTIFIC PUBLICATIONS OF SAMUEL F. EMMONS. 
 
 1870. Geology of Toyabe Range. 
 
 U. S. Geol. Exploration of 40th Parallel. Vol. III. Mining In- 
 dustry. Chap. VI, sect. II, pp. 340-348, with colored geological 
 map. 
 
 Geology of Philadelphia or Silver Bend region. 
 
 Ibid., chap. VI, sect. II, pp. 393-396. 
 
 Geology of Egan Canon District. 
 
 Ibid., chap. VI, sect. VI, pp 445-449. 
 
 1871. Glaciers of Mt. Rainier. 
 
 Amer. Jour. Sci., 3d ser. Vol. I, pp. 161-165. 
 
 1877. The Volcanoes of the U. S. Pacific Coast. 
 
 Address delivered at Chickering Hall, N. Y., Feb. 6, 1877. Jour. 
 Amer. Geogr. Soc. Vol. IX, 1876-'7, pp. 44-65. 
 
 1877. Descriptive Geology of the 40th Parallel. 
 
 U. S. Geol. Exploration o 40th Parallel. Vol. Ill (with Arnold 
 Hague). 4to, pp. 850, with 26 plates and atlas of 11 maps and 2 
 section sheets, colored geologically. 
 
 1882. Abstract of Report on Geology and Mining Industry of 
 Leadville, Colo. 
 
 U. S. Geol. Survey. Second Ann. Report. Pp. 203-290, with geo- 
 logical colored map and sections. 
 
 1882. The Mining Work of the U. S. Geological Survey. 
 
 Trans. Am. Inst. Mg. Eng'rs. Vol. X, pp. 412-425. 
 
 1883. Geological Sketch of Buffalo Peaks. 
 
 U. S. Geol. Survey, Bulletin No. 1, pp. 11-17. 
 
 1883-4. Opportunities for Scientific Research in Colorado. 
 Presidential addresses. 
 
 Proc. Colo. Sci. Soc. Vol. I, pp. 1-12 and 57-61. 
 
 1883. Ore-Deposition by Replacement. 
 
 Proc. Phil. Soc. Wash'n. Vol. VI, p. 32. 
 
 1884. What Is a Glacier ? 
 
 Proc. Phil. Soc. Wash'n. Vol. VIE, p. 37. 
 
 1885. Statistics and Technology of the Precious Metals. 
 
 Tenth Census Reports. Vol. XIII (with G. F. Becker) ; Gov't 4to, 
 541 pages. (Submitted in 1883.) 
 
 1886. Geology and Mining Industry of Leadville, Colo. 
 
 U. S. Geol. Survey, Monograph XII, 779 pages and 45 plates, with atlas 
 of 35 sheets of maps and sections colored. (Submitted in 1885.) 
 
BIOGRAPHICAL NOTICE OF SAMUEL FRANKLIN EMMONS. 
 
 1886. Genesis of Certain Ore-Deposits. 
 
 Trans. Am. Inst. Mg. Eng'rs. Vol. XV, pp. 125-147. 
 
 1886. Notes on Some Colorado Ore-Deposits. 
 
 Proc. Colo. Sci. Soc. Vol. II, pp. 85-105. 
 
 1887. On the Origin of Fissure Veins. 
 
 Ibid., Vol. II, pp. 187-202. 
 1887. On Glaciers in the Rocky Mountains. 
 
 Ibid., Vol. II, pp. 211-227. 
 1887. Preliminary Notes on Aspen, Colo. 
 
 Ibid., Vol. II, pp. 251-277. 
 
 1887. Submerged Trees of the Columbia River. 
 
 Science. Vol. XX, pp. 156-157. 
 
 1887. Notes on the Geology of Butte, Mont. 
 
 Trans. Am. Inst. Mg. Eng'rs. Vol. XVI, pp. 49-62. 
 
 1888. Structural Relations of Ore-Deposits. 
 
 Ibid., Vol. XVI, pp. 804-839.* 
 Same translated into French by R. A. Bergier. 
 
 Re>ue Universelle des Mines. Tome X, 3me ser ., 34me a nn., p. 130. 
 Liege et Paris, 1890. 
 
 1888. On Geological Nomenclature. 
 
 Rep. ,of Am. ComHe Intern. Congress of Geologists, pp. 58-61. 
 
 1889. On Orographic Movements in the Rocky Mountains. 
 
 Bull. Geol. Soc. Am. Vol. I, pp. 245-286. 
 
 1890. Age of Beds in the Boise River Basin, Idaho. 
 
 Proc. Bost. Soc. Nat. Hist. Vol. XXIV, pp. 429-434. 
 1890. Notes on Gold-Deposits of Montgomery County, Md. 
 
 Trans. Am. Inst. Mg. Eng'rs. Vol. XVIII, pp. 391-411. 
 
 1892. Fluorspar-Deposits of Southern Illinois. 
 Ibid., Vol. XXI, pp. 31-53. 
 
 1892. Faulting in Veins. 
 
 Eng'r'g and Min'g Journal. Vol. LIII, pp. 548-549. 
 
 1893. Compte Rendu de la 5 me Session du Congres Geologique 
 
 Internationale (Editor). 
 
 Gov't Printing Office. 529 pages, 21 plates, 39 figures. 
 
 1893. Geological Distribution of the Useful Metals in the 
 United States. 
 
 Trans. Am. Inst. Mg. Eng'rs. Vol. XXII, pp. 53-95. 
 
 1893. Genesis of Ore-Deposits (discussion). 
 
 Trans. Am. Inst. Mg. Eng'rs. Vol. XXIII, pp. 597-602. 
 
 1893. Progress of the Precious Metal Industry in the U. S. 
 
 U. S. Geol. Survey. Mineral Resources for 1902, pp. 46-94 ; also in 
 Report of the Director of the Mint for 1893, pp. 117-141. 
 
xllV BIOGRAPHICAL NOTICE OF SAMUEL FRANKLIN EMMONS. 
 
 1894. Geological Guide Book to the Rocky Mountains. 
 
 John Wiley & Sons, New York. 
 
 1894. Geology of Lower California (with G. P. Merrill). 
 
 Bull. Geol. Soc. Am. Vol. V, pp. 489-514. 
 
 1894. Geology and Mineral Resources of the Elk Mountains, 
 
 Colo. 
 
 U. S. Geol. Survey. Folio 9. Explanatory text. 
 
 1895. Geology of the Mercur Mining District, Utah. 
 
 U. S. Geol. Survey. 16th Ann. Keport, pp. 349-369. 
 
 1896. Geological Literature of the South African Republic. 
 
 Journal of Geology. Vol. 4. pp. 1-22. 
 
 1896. Some Mines of Rosita and Silver Cliff, Colo. 
 
 Trans. Am. Inst. Mg. Eng'rs. Vol. XXVI, pp. 773-823. 
 
 1896. The Mines of Custer County, Colo. 
 
 U. S. Geol. Survey. 17th Ann. Report, par* II, pp. 411-472. 
 
 1896. Geology of the Denver Basin in Colorado (with W. 
 
 Cross and G. E. Eldridge). 
 
 U. S. Geol. Survey, Monograph XXVII, 4to, 526 pages, with 31 
 plates, 1 02 figures. 
 
 1897. The Geology of Government Explorations (Presidential 
 
 address before the Geological Society of Wash- 
 ington, December, 1896). 
 
 Science, n. s. Vol. V, pp. 1-15 and 42-51. 
 
 1897. Economic Geology of the Butte District, Mont. 
 
 U. S. Geol. Survey. Folio No. 38. Explanatory text. 
 
 1897. Physiography of the West Coast of Peru, S. A. 
 
 Science, n. s. Vol. V, p. 889. 
 
 1897. The Origin of Green River. 
 
 Science, n. s. Vol. VI, pp. 19-21. 
 
 1898. Geology of the Ten-mile District, Colorado. 
 
 U. S. Geol. Survey. Geol. Atlas of the U. S., Folio No. 48. Ex- 
 planatory text. 
 
 1898. Map of Alaska : Its Geography and Geology. 
 
 U. S. Geol. Survey. 44 pages and geol. maps. Special report to the 
 Fifty-fifth Congress, 2d session. 
 
 1898. Geology of the Aspen Mining District, Colorado. 
 
 U. S. Geol. Survey, Monograph XXX f, pp. xvn-xxxu. Introduc- 
 tion. 
 
 1898. Dr. Don's Paper on the Genesis of Certain Auriferous 
 Lodes (discussion). 
 
 Trans. Am. Inst. Mg. Eng'rs. Vol. XXVIF, p. 993. 
 
BIOGRAPHICAL NOTICE OF SAMUEL FRANKLIN EMMONS. xlv 
 
 1898. A Century of Geography in the United States. 
 
 Science, n. s. Vol. VII, p. 677. 
 
 1898. Geological Excursion Through Southern Russia. 
 
 Trans. Am. Inst. Mg. Eng'rs. Vol. XXVIII, pp. 3-23. 
 
 1899. Plutonic Plugs and Subtuberant Mountains. 
 
 Geol. Soc. Wash'n, and abstract in Science, n. s. Vol. X, pp. 24-25. 
 
 1900. Secondary Enrichment of Ore-Deposits. 
 
 Trans. Am. Inst. Mg. Eng'rs. Vol. XXX, pp. 177-217. Ibid., 
 Genesis of Ore-Deposits (1902), pp. 199-204, 433-473, 756-762. 
 
 1900. Review of Kemp's Ore Deposits of the United States. 
 
 Science, n. s. Vol. XI, pp. 503-505. 
 
 1901. The Delamar and Horn-Silver Mines : Two types of 
 
 ore-deposits in the deserts of Nevada and Utah. 
 
 Trans. Am. Inst. Mg. Eng'rs. Vol. XXXI, pp. 658-683. 
 
 1901. The Sierra Mojada and its Ore-Deposits (discussion). 
 
 Trans. Am. Inst. Mg. Eng'rs. Vol. XXXI, pp. 953-959. Mexican 
 volume XXXII, pp. 566-567. 
 
 1901. Clarence King A Memorial. 
 
 Eng. and Mg. Jour. Vot 73, pp. 3-5. Dec. 28, 1901. 
 
 1902. Biography of Clarence King. 
 
 Amer. Jour. Sci., 4th ser. Vol. 13, pp. 224-237. 
 
 1902. The U. S. Geol. Survey in its Relation to the Practical 
 Miner. 
 
 Eng. and Mg. Jour. Vol. 74, p. 43. 
 
 1902. Sulphidische Lagerstatten vom Cap Garonne. 
 
 Zeitsch. f. Prak Geol. Vol. X, p. 126. 
 
 1902. On the Secondary Enrichment of Ore-Deposits (dis- 
 cussion). 
 
 Trans. Am. Inst. Mg. Eng'rs. Vol. XXXIII, p. 1058. 
 
 1902. On the Hydrostatic Level Attained by the Ore-De- 
 
 positing Solutions in Certain Mining Districts of 
 the Great Salt Lake Basin (discussion). 
 
 Trans. Am. Inst. Mg. Eng'rs. Vol. XXXIII, p. 1062. 
 
 1903. Reminiscences of Clarence King. 
 
 Trans. Am. Inst. Mg. Eng'rs. Vol. XXXIII, pp. 633-634, 636-638, 
 643. 
 
 1903. Drainage of the Valley of Mexico. % 
 
 Geol. Soc. Wash'n, and Science, n. s. Vol. 17, p. 09. 
 
 1903. Little Cottonwood Granite Body of the Wasatch Moun- 
 tains. 
 
 Am. Jour. Sci., 4th ser. Vol. XVI, pp. 139-147. 
 
BIOGRAPHICAL NOTICE OF SAMUEL FRANKLIN EMMONS. 
 
 1903. Contributions to Economic Geology, 1902 (introduc- 
 
 tion). 
 
 U. S. Geol. Survey, Bull. No. 213, pp. 15-30 ; also 94-98. 
 
 1904. Theories of Ore Deposition, Historically Considered. 
 
 Bull. Geol. Soc. Am. (Presidential address). Vol. 15, pp. 1-28 ; also 
 Eng. and Mg. Jour. Vol. 77, pp. 117, 157, 199, 237 ; also Smith- 
 sonian Report for 1904. 
 
 1904. Contributions to Economic Geology, 1903. Metal- 
 liferous Ores. 
 U. S. Geol. Survey, Bull. No. 225, pp. 18-24. 
 
 1904. Economic Resources of the Northern Black Hills, by 
 J. D. Irving, with contributions by S. F. Emmons 
 and T. A. Jaggar, Jr. 
 
 U. S. Geological Survey, Prof. Paper No. 26. 222 pp. 
 
 1904. Clarence King, geologist. 
 
 [In the Century Association, New York. King Memorial Committee. 
 Clarence King Memoirs. The Helmet of Mambrino. N. Y. and 
 London. ] 
 
 1904. Occurrence of Copper Ores in Carboniferous Limestone 
 in the Region of the Grand Canon of the Colorado. 
 
 Abstract : Science, n. s. Vol. XX, pp. 760-761. 
 
 1904. The Virginius Mine. 
 
 Eng. and Mg. Jour. Vol. LXXVII, p. 311. 
 
 1905. Investigation of Metalliferous Ores. 
 
 U. S. Geol. Survey, Bull. No. 260, pp. 19-27. 
 
 1905. Copper in the Red Beds of the Colorado Plateau 
 Region . 
 
 U. S. Geol. Survey, Bull. No. 260, pp. 221-232. 
 
 1905. The Cactus Copper Mine, Utah. 
 
 U. S. Geol. Survey, Bull. No. 260, pp. 242-248. 
 
 1905. Contributions to Economic Geology, 1904. 
 
 In U. S. Geol. Survey, Bull. No. 260. 
 
 1905. Economic Geology of the Bingham Mining District, 
 
 Utah, by J. M. Boutwell ; with a section on areal 
 geology by Arthur Keith, and an introduction on 
 general geology by S. F. Emmons. 
 
 IT. S. Geological Survey, Prof. Paper No. 38. 413 pp. 
 
 1906. What is a Fissure Vein ? 
 
 Econ. Geol. Vol. I, No. 4, pp. 385-387. 
 
 1906. A Map and a Cross Section of the Downtown District 
 of Leadville, Colo. 
 
 Abstract : Science, n. s. Vol. XXIII, pp. 816-817. 
 
BIOGRAPHICAL NOTICE OF SAMUEL FRANKLIN EMMONS. 
 
 1906. Useful Definitions. 
 
 Min. and Sci. Press. Vol. XCIII, pp. 355-356 ; proper use of 
 mining terms. Min. World. Vol. XXV, No. 24, p. 715. 
 
 1906. Los Pilares Mine, Xacozari, Mexico. 
 
 Econ. Geol. Vol. I., No. 7, pp. 629-643 ; Abstract : Eng. and Min. 
 Jour. Vol. LXXXII, pp. 1066-1067. 
 
 1906. Contributions to Economic Geology, 1905 ; Investiga- 
 
 tion of Metalliferous Ores. 
 
 U. S. Geol. Survey, Bull. No. 285, pp. 14-19. 
 
 1907. Biographical Notice of George H. Eldridge. 
 
 Trans. Am. Inst. Min. Eng'rs. Vol. XXXVII, pp. 339-340. 
 
 1907. Uinta Mountains. 
 
 Geol. Soc. Amer.,Bull. Vol. XVIII, pp. 287-302. 
 
 1907. The Downtown District of Leadville, Colo., by S. F. 
 
 Emmons and J. D. Irving. 
 U. S. Geol. Survey, Bull. No. 320. 75 pp. 
 1907. Geological Structure of the Uinta Mountains. 
 
 Abstract : Science, n. e. Vol. XXV, pp. 767-768. 
 
 1907. Investigations of Metalliferous Ores. 
 U. S. Geol. Survey, Bull. No. 315, pp. 14-19. 
 1907. Suggestions for Field Observations of Ore Deposits. 
 
 Min. and Sci. Press. Vol. XCV, pp. 18-20. 
 
 1907. Biographical Memoir of Clarence King, 1842-1901. 
 
 Head before the Nat. Acad. Sci., Apr. 23, 1903. Nat, A cad. Sci., 
 Biog. Mem. Vol. VI, pp. 25-55. 
 
 1909. Development of Modern Theories of Ore Deposition. 
 
 Min. and Sci. Press. Vol. XCIX, pp. 400-403. 
 
 1910. Economic Geology in the United States. 
 
 Mining World. Vol. XXX, pp. 1209-1211. June 26, 1909 Cana- 
 dian Min. Inst. Jour. Vol. XII, pp. 89-101. 
 
 1910. Cananea Mining District of Sonora, Mexico. 
 
 Econ. Geology. Vol. V, No. 4, pp. 312-366. Abstract : Eng. and 
 Min. Jour. Vol. XC, pp. 402-404. 
 
 1910. The Cobalt Mining District of Ontario. 
 
 Abstract : Science, n. s. Vol. XXXI, p. 517. 
 
 1910. Criteria of Downward Sulphide Enrichment (discus- 
 sion). 
 Econ. Geology. Vol. V, No. 5, pp. 477-479. 
 
No. 1. 
 
 The Genesis of Certain Ore-Deposits. 
 
 BY S. F. EMMONS,* WASHINGTON, D. C. . 
 
 (Bethlehem Meeting, May, 1886. Tram., xv., 125.) 
 
 IN a report upon the geology of Leadville and vicinity, 
 which is still in the hands of the Public Printer, I have given, 
 at some length, my conclusions as to the genesis of the remark- 
 able silver-lead deposits of that region, and the data, gathered 
 during a long and careful consideration, upon which my views 
 were founded. In the brief abstract of this report, published 
 in 1881, the bare conclusions are given, with but few of the 
 facts upon which they were founded. Since that time, these 
 conclusions have been variously criticised, and it has even been 
 assumed that the views I expressed with regard to these de- 
 posits were intended as a theory of ore-deposits in general. 
 
 Had my final report been printed, no such misconception 
 could have occurred; for, in that I explicitly disclaim any in- 
 tention of general application of the theories there presented. 
 Even in the abstract I am unable to find any statements which 
 would justify such a conclusion. 
 
 Since my Leadville work, however, I have had further op- 
 portunities of examining ore-deposits, and have given the gen- 
 eral subject much. thought and study, and, as a result, I have 
 made .in my own mind certain generalizations, which, I am 
 conscious, need the test of a far greater number of practical 
 applications than I have yet been able to make, but which, I 
 think, it may be well to present to the members of the Insti- 
 tute as suggestive, that their own observations may further 
 prove or disprove them. I shall use my Leadville observations 
 and the criticisms which have been made upon them as a sort 
 of text for my remarks. 
 
 The salient facts, which I thought to have determined with 
 regard to the Leadville deposits, which, as is well known, are 
 silver-lead deposits in a dolomitic limestone, overlain and in 
 
 * U. S. Geological Survey. 
 1 
 
2 THE GENESIS OF CERTAIN ORE-DEPOSITS. 
 
 part also traversed by various bodies of porphyry, are the fol- 
 lowing : 
 
 1. That they were deposited from aqueous solutions. 
 
 2. That they were originally deposited as sulphides, at a 
 great depth below the rock-surface (probably 10,000 ft); that, 
 by subsequent dynamic movements and by erosion, they have 
 been brought to their present position near the surface, and that, 
 through secondary alteration by surface-waters, they have been 
 changed to oxides, carbonates, and chlorides. 
 
 3. That the process of deposition was a metasomatic inter- 
 change between the minerals brought in in solution and the 
 limestone that is, that they were not deposited in already 
 existing open cavities, but gradually replaced the limestone, 
 from the channels through which they reached it outward. 
 
 4. That the solutions or ore-currents reached the present 
 locus of the deposits directly from above and not from below. 
 
 5. That, whatever may have been the ultimate source from 
 which the mineral components of the deposits came, the ob- 
 served facts point to the neighboring eruptive rocks as the 
 immediate source from which they were derived by the ore- 
 bearing solutions which deposited them in their present locus. 
 
 I will take up these propositions in the above order, and, 
 after discussing the criticisms which have been made upon 
 them, see how far they may be applicable to other deposits 
 than those of Leadville. 
 
 1. That the vast majority of ore-deposits have been deposited 
 from solutions, seems to be now so generally admitted as to 
 require no further discussion here. This view is held by most 
 all American, English and German geologists, while the 
 French may be considered to be those who still cling to the 
 sublimation theory in the modified form which is based on the 
 remarkable synthetic experiments of Senarmont, Daubree, and 
 others. But, as one of their number admits, 1 this is practically 
 only a variety of the solution theory, which assumes that pres- 
 sure and heat, sufficient to vaporize water, are necessary to 
 bring about a solution of the metallic minerals. That many 
 deposits have been formed under conditions of great heat and 
 pressure is most probable ; that heat and pressure greatly 
 
 A. De Lapparent, Traite de Geologic, p. 1170 (1883). 
 
THE GENESIS OF CERTAIN ORE-DEPOSITS. 3 
 
 increase the solvent power of percolating waters is evident; 
 but that heat and pressure are an absolutely essential condition 
 of mineral solution cannot be maintained, since we see in 
 nature many instances of mineral solution and deposition 
 under ordinary pressure and by comparatively cold waters. 
 
 2. That the Leadville ores were originally deposited in the 
 form of sulphides, and that, therefore, they would be found in 
 that condition, when explorations should have been pushed in 
 depth beyond the oxidizing action of surface-waters, was as- 
 sumed by indirect reasoning at the time my abstract was 
 written, since at that time no sulphide deposits had been found 
 on the so-called " contact " in the region. Explorations made 
 since that time have abundantly proved the correctness of the 
 assumption. An interesting description of some of the more 
 important sulphide bodies, and of a previously undiscovered 
 fault, was read at the Chattanooga meeting by F. T. Freeland. 2 
 
 That metallic deposits, with the single exception of tin-ores, 
 pass into sulphides or some allied combination in depth has 
 been so generally observed, that it has almost come to be an 
 axiom in vein-geology that original deposition must have been 
 in this form. Some supposed exceptions have been observed; 
 but the distinction between an original and a secondary de- 
 posit is often so delicate that it requires a most thorough and 
 searching examination to determine the point satisfactorily. 
 The determination beyond the shadow of a doubt of an origi- 
 nal deposit of these metals in an oxidized form would be of 
 the utmost interest to science. 
 
 3. That the process of ore-deposition at Leadville was a 
 metasomatic 3 interchange between the material of the country- 
 rock and the minerals brought in in solution by the ore-cur- 
 rents, is a point upon which I particularly desired to insist, 
 because it is either tacitly or explicitly assumed by most text 
 books that all ore-deposits in limestones are the filling of pre- 
 existing cavities. This assumption, like the one that fissure- 
 veins were once open cavities reaching to an indefinite depth, 
 is, it seems to me, the result of generalizations upon too few 
 
 2 Trans., xiv., 181 (1885-86). 
 
 3 By metasomatic interchange, I understand an interchange of substances, but 
 not necessarily molecule by molecule in such a manner as to preserve the original 
 structure, form, or volume of the substance replaced. 
 
4 THE GENESIS OF CERTAIN ORE-DEPOSITS. 
 
 facts. The facts that support it (the arrangement of the ore 
 in layers parallel -to the walls of the body, etc.) are so striking 
 in the few cases where they have been observed, that they 
 have received universal mention, while the far more numerous 
 cases, where no such evidence of pre-existing cavity is found, 
 have remained in most instances without comment, as regards 
 this question. 
 
 Professor Le Conte* quotes me as saying that the ore at 
 Leadville was " accumulated in hollowed-out channels in the 
 limestone," evidently assuming this as so much of a foregone 
 conclusion that he had not thought it necessary to read my 
 statement of the diametrically opposite conclusion at which I 
 had arrived. Now, I not only distinctly stated that I believed 
 the ore was not deposited in already hollowed-out channels or 
 pre-existing cavities, but I mentioned that the caves, which 
 are so characteristic of limestone formations, were at Leadville 
 formed after the deposition of the ore. I laid stress upon the 
 relation of these caves to those bodies, not because it was the 
 only or even the main proof of the statement I made, but be- 
 cause I thought it would appeal to those who consider all lime- 
 stone deposits as filling cavities hollowed out by surface-waters. 
 The most convincing proof of the statement to my own mind 
 is, that, in a prolonged study of the various deposits, I found 
 no single fact to furnish any evidence that the ore was depos- 
 ited in an open cavity ; and I hold that, in such a case, the 
 burden of proof lies on the side of those who uphold the open- 
 cavity theory. There is, however, a consideration which can 
 be briefly stated and which affords conclusive evidence, if no 
 other were present; namely, that the deposits were originally 
 iormed at a depth of about 10,000 ft. below the surface and 
 before the strata were disturbed, and that, therefore, surface- 
 waters could not have reached their locus to hollow out such 
 cavities. 
 
 I find it difficult to understand Professor dewberry's criti- 
 cisms of my views on this point. In the first place, he makes 
 what seems to me a totally unwarranted assumption, that I 
 consider that the Leadville deposits were formed by surface- 
 waters. Then, in presenting his own views on the formation 
 
 4 American Journal of Science, Third Series, vol. xxvi., No. 151, p. 18 (July, 
 
 1883). 
 
THE GENESIS OF CERTAIN ORE-DEPOSITS. 5 
 
 of the Leadville deposits, he says, " they were deposited by 
 substitution/' 5 and afterwards remarks that the fact that caves 
 in the limestone cut across the ore-bodies " has no bearing on 
 the question." 
 
 In a former article, The Origin and Classification of Ore- 
 Deposits, 6 his meaning is less ambiguous, and I shall take 
 this opportunity of criticising him in turn. One of the divi- 
 sions of ore-deposits there given by him is " chambers or 
 pockets in limestone," 7 of which he says: "From a study of 
 them I have been led to add them to the catalogue of forms of 
 ore-deposit as a distinct and important addition to those given 
 by other writers." As examples, he quotes the Eureka, Rich- 
 mond, Emma, Flagstaff, Kessler, and Cave mines, and (with 
 the modification of their contact-character) the Leadville ore- 
 bodies, of which he says they were " undoubtedly accumu- 
 lated in vacant spaces formed by the solution of the limestone." 
 The formation of the chambers in which he considers these 
 deposits were formed, he compares to that ot the Mammoth 
 Cave, saying, " We must conclude that the chambers were 
 formed, like modern caves, by surface-water." He then makes 
 the following deductions as to the probable extent of such 
 deposits : " They will not be found to extend to so great depth 
 as the ore-bodies of fissure-veins, since the excavation of the 
 limestone, if produced by atmospheric water, must be confined 
 to the zone traversed by surface-drainage." He does not ex- 
 plicitly state what he considers to be the distinctive character 
 of his important addition to the classification of ore-deposits, 
 the want of information in regard to the true nature of which, 
 he says, " has led to much litigation and heavy losses in mining." 
 He surely cannot mean the irregular form of deposits in lime- 
 stone, for this has been recognized from the very earliest days 
 of mining, and has formed an important element in the classi- 
 fication of most writers on ore-deposits. 8 It would seem, there- 
 
 5 The Deposition of Ores. School of Mines Quarterly, vol. v., No. 4, p. 341, et seg. 
 (May, 1884). 
 
 6 School of Mines Quarterly, vol. i., No. 3, pp. 87 to 104 (Mar., 1880). 
 
 7 This division lias been literally adopted by J. Arthur Phillips, in his Treatise 
 on Ore-Deposits (1884). 
 
 8 A criticism of this claim of novelty may be found in the Engineering and Mining 
 Journal, vol. xxx. , No. 1, p. 1 (July 3, 1880). 
 
6 THE GENESIS OF CERTAIN ORE-DEPOSITS. 
 
 fore, that this distinctive character must consist in their having 
 been hollowed out originally by surface-waters. 
 
 Surface-waters, as I understand the common use of the term, 
 means those waters which have so recently left the surface as 
 to still retain constituents common to waters now found at or 
 near the surface (free carbonic and organic acids, chlorides, 
 etc.), and which exert an oxidizing action ; and from the above 
 quotations this would seem to be his interpretation of the term 
 also. Moreover, to dissolve out caves like the modern caves 
 there should be a comparatively free flow of water and ready 
 drainage to carry off the dissolved-out material, which could 
 only be found at comparatively shallow depths. The waters 
 which percolate through rocks, even at the greatest known 
 depths, may in one sense be considered surface-waters; but 
 at a certain depth below the surface these waters will have lost 
 their free carbonic and organic acids and have become, so to 
 speak, saturated and only able to dissolve out by actual inter- 
 change of their constituents with those of the rock through 
 which they pass ; in other words, no longer capable of leaving 
 open caves. What this depth is, I am not yet prepared to say. 
 It would differ greatly under varying local conditions. It would 
 probably correspond with what is known as the " water-level " 
 in Western mines, which is not generally below a thousand 
 feet. 
 
 Now Professor dewberry's theory, or the one he here adopts, 
 for it can hardly be considered original with him, involves a 
 sort of see-saw movement for the rocks inclosing each deposit, 
 which, though not impossible, seems from a geological stand- 
 point highly improbable. He admits, with other geologists, 
 that the original deposits were in the form of sulphides, and 
 that the oxidized condition, in which the ores he speaks of are 
 now found, is due to the action of surface-waters ; hence, as 
 originally deposited, they must have been below the reach ot 
 surface-waters. But the cavities in which they were deposited 
 were formed by surface-waters ; hence, the rocks inclosing the 
 ore-deposits must have been once so near the surface as to have 
 been hollowed out by these waters ; then have been depressed 
 beyond their reach, so that the ore-bearing solutions which 
 deposited their contents in the caves were protected from 
 oxidizing action, and then again raised to their present position, 
 
THE GENESIS OF CERTAIN ORE-DEPOSITS. 7 
 
 where the surface-waters have changed their sulphides to 
 oxides, and hollowed out a new set of caves. When I say 
 raised and depressed, I mean not necessarily actual but only 
 relative movement, as referred to the surface of the earth ; this 
 surface might itself have been raised by the accumulation of 
 deposits over the rocks, and these accumulations again re- 
 moved by erosion, so that the result would be accomplished 
 without actual movement of the inclosing rock. 
 
 In such an assumption, I hold, one is not justified, unless he 
 can find some evidence of it in the geology of the region in- 
 volved. In Leadville there is none. The rocks inclosing the 
 ore-deposits were never so near the surface as they are now, 
 and dynamic action and erosion have gradually raised them 
 from the depth of about 10,000 ft., at which the original sul- 
 phide deposits were formed. The same is true in a general 
 way of the other examples quoted by Professor Newberry the 
 original deposits were deep seated, and, though the geology of 
 the districts has not yet, in all cases, been studied in sufficient 
 detail to afford as good estimates as to the depth of the original 
 deposition as at Leadville, there is no evidence of any such 
 relative oscillations as his theory would involve. 
 
 The practical application made by Dr. Newberry, though a 
 logical deduction from his theory, viz., that deposits in lime- 
 stone must be limited in depth to the zone traversed by surface- 
 drainage, and therefore of less value than fissure- veins, illustrates 
 the danger of a priori reasoning in geology, since it not only 
 leads to geological improbabilities, but gives the influence of 
 his name to a dangerous popular fallacy already too current 
 among miners. I have shown in my Leadville work not only 
 that the geological conditions there are such as to preclude the 
 possibility of the formation of caves by surface-waters prior to 
 the original ore-deposition, but that, in extent and in the quan- 
 tity of ore contained in it, the Blue limestone, which may in 
 one sense be regarded as a sort of horizontal vein, exceeds any 
 known fissure-vein, not even excepting the famous Comstock 
 lode. At Eureka, which is Professor Newberry's typical ex- 
 ample, the exhaustive studies of J. S. Curtis, who came to the 
 work with a priori views similar to those entertained by Pro- 
 fessor Newberry, have shown not only that the ores were not 
 originally deposited in open caves, but that caves formed by 
 
8 THE GENESIS OF CERTAIN ORE-DEPOSITS. 
 
 surface- waters become less frequent in depth, and have nearly 
 disappeared at 1,000 ft. from the surface. As the workings in 
 this district are being rapidly deepened, a practical illustration 
 of the depth at which cave-formation by surface-waters is still 
 possible will soon be furnished. It will also be seen whether 
 ore-deposition in this region stops at the limits of cave-forma- 
 tion. Even should it be found to do so, however, it would 
 merely show a local coincidence, and not a logical conse- 
 quence. 
 
 The possible application of the theory of the formation of 
 ore-deposits by replacement or substitution is almost unlimited, 
 and the limits of its actually demonstrated application are 
 being every day extended, not only by studies of new districts, 
 but by more careful arid unbiased studies of old districts in 
 which a different method of formation had previously been 
 determined upon. 
 
 The process is most readily conceivable in the case of easily- 
 soluble rocks, like limestone and dolomite ; and, in point of 
 fact, it is found that these rocks are the favorite receptacle of 
 metallic deposits in mining-regions where the ores occur in 
 the later stratified rocks, among which calcareous beds are 
 abundant. It is also possible that in the older and more crys- 
 talline rocks, where the calcareous beds are of limited extent, 
 metallic deposits occurring in large masses, like those of iron, 
 may have so completely replaced the calcareous material that 
 little or no trace of it remains. The old theory that iron-ores 
 in the crystalline rocks are of eruptive origin is generally 
 abandoned at the present day. The few geologists who still 
 maintain this origin for individual deposits are doubtless in- 
 fluenced in their opinion by respect for views formerly 
 advanced ; while among those who come to the study with a 
 mind free from preconceived ideas, and who push their exami- 
 nations with sufficient thoroughness and detail, I have known 
 of none of late years who have adopted the eruptive theory. 
 The most striking instance that has come to my notice is that 
 of the famous specular iron-ores of the island of Elba, which, 
 when I was a student, were held as the most typical example 
 of eruptive or sublimation deposits. These deposits were 
 visited by the most prominent geologists of Europe; but, 
 among them, Vom Rath, in 1870, was the first to doubt the 
 
THE GENESIS OF CERTAIN ORE-DEPOSITS. 9 
 
 eruptive origin of the ores, which he showed in certain por- 
 tions was impossible. The island has been systematically 
 studied and mapped by the Geological Survey of Italy ; and B. 
 Lotti, the geologist in charge of this work, after a careful 
 study of all the evidence and of the views held by those who 
 have gone before him, but whose observations were necessarily 
 less complete and exact than his own, decides that they must 
 have been formed by replacement. The following is a literal 
 translation of his conclusions : 
 
 " We may therefore reasonably conclude that the iron- 
 deposits of Elba and their analogues, both of iron and of other 
 metals, on the neighboring continent (excepting those con- 
 nected with the serpentines) are formed by aqueous solutions 
 of the metals, which found an easier passage for their subterra- 
 nean circulation, and perhaps also for reaching the surface, 
 between rock-masses of different nature, and deposited the 
 metallic minerals which they held in solution when they met 
 favorable conditions ; that is, either in proximity to the surface 
 or in contact with calcareous rocks with which an interchange 
 of materials took place, and this in conformity with the law 
 that the more easily soluble minerals are replaced by those 
 that are less soluble. If the waters contained, besides the 
 bicarbonate of iron, sulphydric acid also, there resulted a pre- 
 cipitate of sulphide of iron." 9 
 
 As a reaction against the eruptive theory, it has been re- 
 cently held 10 that all deposits of iron of whatever age have 
 been formed, like the bog ores now forming, by surface-pre- 
 cipitation, and that they were therefore actual sedimentary 
 beds originally, but in many cases have been altered by later 
 metamorphism. This going to the other extreme is, it seems 
 to me, as dangerous as the former a priori reasoning; and, as 
 I read the descriptions of many of our iron-deposits, such a 
 contemporaneous sedimentary origin for them would be im- 
 possible. 
 
 The theory of the formation of ore-deposits by replacement, 
 as opposed to that by the filling of pre-existing cavities, may, 
 however, be applied to deposits in rocks which are not so 
 
 9 Descrizione Geologica deW /so/a d' Elba, p. 232 (1886). 
 
 10 J. S. Newberry, The Genesis of Our Iron-Ores, School of Mines Quarterly, vol. 
 ii., No. 1, pp. 1 to 17 (Nov., 1880). 
 
10 THE GENESIS OF CERTAIN ORE-DEPOSITS. 
 
 readily soluble as limestone, in which cases the percolating 
 solutions would have first attacked the relatively more soluble 
 among their constituents. Very many so-called fissure-veins 
 in crystalline rocks are formed by percolating waters, circulat- 
 ing along joints, shrinkage-cracks, fault-planes, or zones of 
 crushed rock, which have filled the interstitial spaces and re- 
 placed the materials of the adjoining country-rocks to a greater 
 or less extent by the materials they held in solution, but are 
 not the filling of any considerable open cavities. 
 
 The comb-structure of veins, on which the early geologists 
 founded their theory that a vein was necessarily the filling of 
 a pre-existing open cavity, is of comparatively rare occurrence. 
 As early as 1869 Richard Pearce observed in the classic veins 
 of Cornwall that the gangue-material, instead of being a foreign 
 material brought from a distance, was the more or less com- 
 pletely altered country-rock, and his views have been con- 
 firmed and further illustrated by the investigations of C. Le 
 Neve Foster, his successor in that district. The evidence 
 obtained by my own observations, together with the data 
 gathered during the investigation of the precious-metal de- 
 posits of the Rocky mountains under the Tenth Census, led 
 me to conclude that the majority of the deposits there are such 
 replacement-deposits ; and I have not yet seen satisfactory evi- 
 dence of a deposit which consists essentially of the filling of 
 any considerable pre-existing cavity by foreign material. 
 Cracks or fissures must undoubtedly have existed, which de- 
 termined the concentration of mineral solution along their 
 course; but whether such cracks were to any great extent 
 fault-planes, whose movement might have left large open 
 spaces between the irregularities of their walls, seems ques- 
 tionable. The Comstock vein occupies a fault-plane, and its 
 ore fills the interstitial spaces in the crushed material between 
 the walls, but there was no filling of a pre-existing open cavity, 
 as I understand it. In Leadville one of the most noticeable 
 facts is that the fault-planes, which may be supposed to reach 
 to great depths, have been found barren of ore except by sec- 
 ondary infiltration from surface-waters, or as attrition-material 
 from pre-existing deposits, when the fault-line cut across such 
 deposits. 
 
 In this connection I would remark that it seems to me that 
 
THE GENESIS OF CERTAIN ORE-DEPOSITS. 11 
 
 the idea that a fissure-vein necessarily extends to an indefinite 
 depth is another popular error, and not founded on good geo- 
 logical reasoning. Whatever the nature of the fissure along 
 which the deposit has taken place, whether fault-plane, joint, 
 or shrinkage-crack, there must be- some mutual relation be- 
 tween its horizontal and its vertical dimensions. In other 
 words, the study of structural geology shows that the length of 
 such a fissure or crack must bear some proportional relation 
 to its extent in depth, and the probability is that the latter 
 must be less than the former. Now veins can generally be 
 traced continuously for an extremely limited distance; the 
 Comstock, which is probably one of the longest known, is 
 traced only about 20,000 ft., and those which exceed 1,000 or 
 2,000 ft. are comparatively rare. As yet there are not suffi- 
 cient data for establishing any numerical ratio between the 
 depth and the length of mineral veins ; I would suggest to my 
 fellow-engineers that they make notes on this relation, when- 
 ever opportunities present themselves. It may be said that 
 this is not likely to have much practical value, since the depth 
 from which the ore may be profitably extracted is likely to be 
 much less than the deduced depth of the fissure. The question 
 has a bearing, however, upon that of the source from which 
 the ore was derived ; and any fact that contributes to a more 
 accurate knowledge of the origin and manner of formation of 
 ore-deposits has practical value, since it enables the mining 
 engineer to make a more accurate forecast of the probable 
 form and extent of any individual deposit beyond the limits ot 
 exploration. 
 
 4. In regard to the direction from which the ore-bearing so- 
 lutions reach the locus of the deposits, the brief statement made 
 in my abstract that " they came from above," should perhaps 
 have been accompanied by some qualifying explanation. In 
 making the statement, I had in mind the common explanation 
 offered in regard to ore-deposits, that "they came from below," 
 a statement which is more readily made by those who have not 
 examined the deposits of which they speak or write, than by 
 those who have, since they are not under the necessity of ex- 
 plaining observed facts in accordance with this hypothesis. 
 The prevalence of this theoretical method of explaining the 
 formation of any ore-deposit is due probably to the great plau- 
 
12 THE GENESIS OF CERTAIN ORE-DEPOSITS. 
 
 sibility of the theory generally advanced for the formation of 
 fissure-veins namely, that the metallic contents of the solu- 
 tions were taken up by waters under conditions of great heat 
 and pressure (therefore, probably at great depths), and that as 
 these solutions approached the surface, with consequent de- 
 crease of heat and pressure, the solvent power of the water 
 decreased also, and their metallic contents were gradually de- 
 posited all along the walls of the channel through which they 
 were ascending. ~No exception can be taken to this theory, as 
 a theory; but before accepting it as of universal application, it 
 is important to see whether it accords with observed facts; 
 and, as Leadville presented a case where it unquestionably did 
 not so accord, I made the statement as concise and as strong as 
 possible, to counteract the effect of the " coming-from-below " 
 explanation which would undoubtedly be offered. 
 
 Such a one is that made by J. Alden Smith, 11 which has also 
 been quoted by J. Arthur Phillips in his Treatise on Ore-Deposits, 
 " that the ore-deposits of this district came from below through 
 fissures originating in the granitic rocks, and extending up- 
 wards penetrated the limestones and quartzites to the contact 
 with the overlying porphyry ; that these fissures lead to many 
 bedded veins in the limestone and quartzite, and to contact- 
 veins of more or less value between the formations last men- 
 tioned, and between those and the granitic formation ; and that 
 these fissures and deposits will be extensively and profitably 
 worked for centuries after the contact-deposits now operated 
 are exhausted." 
 
 A statement like the above, coming from one whose views 
 would be accepted as of scientific value, might cause much use- 
 less expenditure of money in prospecting before it was dis- 
 covered that the essential facts, upon which it would appear to 
 be founded, existed only in the imagination of the writer. In 
 Leadville, no ore-bearing fissures extending downward from 
 the deposits have yet been found. The facts observed during 
 my examination, and by those who have studied the region 
 since, show that the solutions must have penetrated the lime- 
 stone from its contact with the porphyry, which is generally its 
 upper surface, and, therefore, downward. An apparent excep- 
 
 11 Report on the Resources of Colorado, p. 64 (1883). 
 
THE GENESIS OF CERTAIN ORE-DEPOSITS. 13 
 
 tion to this state of things is found, as pointed out by Charles 
 M. Rolker, 12 on Fryer hill, where, according to him, unreplaced 
 dolomite sand forms the roof of the deposit over large areas, 
 and is not found under it. I am ready to admit, for the sake 
 of argument, the truth of this statement for the upper part of 
 the Blue limestone or ore-horizon, which is included in, or both 
 overlain and underlain by, porphyry. The lower sheet of Blue 
 limestone, however, which has porphyry on its upper surface 
 alone, is, as far as observed, replaced only on that upper sur- 
 face. The exception is, however, in this case only apparent, 
 and does not militate against my supposition. According to 
 this, the intrusion of the porphyry bodies opened channels 
 along, and in some cases across, the sedimentary beds ; more- 
 over, observation shows that these porphyry bodies admit the 
 percolation of water freely in every direction through their 
 mass, whereas the limestones are comparatively impermeable 
 except along joint- or fracture-planes. Thus, the contact be- 
 tween porphyry and limestone would, everywhere, be a prin- 
 cipal water- channel; and this, in the greater part of the region, 
 is at the lower surface of the former and the upper surface of 
 the latter; but where, as on Fryer hill, the limestone is in- 
 closed in porphyry, it might be attacked from either surface. 
 I can offer no direct reason for the irregular way in which com- 
 paratively unaltered remnants of dolomite are left on Fryer 
 hill ; but it seems no more abnormal than the irregular distri- 
 bution of the rich ore within the mass of vein-material, or the 
 fact that, in some places, there is no ore at all at the contact. 
 I cannot quite agree, however, with Mr. Rolker's opinion as to 
 the persistence of the dolomite sand in the roof of the ore-body. 
 His observations in the Chrysolite ground would naturally have 
 been more thorough than mine ; but, if my memory does not 
 deceive me, unreplaced dolomite occurs there under, as well as 
 over, the ore-body, as it certainly does in the Little Chief, 
 Virginius, and other claims. It is to be remarked further that, 
 as the rich ore-bodies are found mostly in the upper part of the 
 ore-horizon, the upper surface has been far more thoroughly 
 explored than the lower, and much unreplaced limestone may 
 exist at this lower surface which has not yet been found. 
 
 12 Notes on the Lead ville Ore-Deposits, Trans., xv., 273 (1886-87). 
 
14 THE GENESIS OF CERTAIN ORE-DEPOSITS. 
 
 It is hardly possible to establish a priori any general direction 
 for the flow of underground waters at considerable depths below 
 the earth's surface. In the distinctly stratified rocks, which 
 form the immediate surface, and in which they may flow with 
 comparative freedom, they obey, within certain limits, the laws 
 of hydrostatic pressure ; but, at the great depths at which the 
 Leadville deposits were formed, their flow must have been very 
 slow, a percolation or mere capillary circulation, for the most 
 part. It may be assumed, in general, that cold waters would 
 have a general downward tendency under the influence of 
 gravity, while superheated waters would under certain condi- 
 tions be forced upward; but the movement would not neces- 
 sarily be vertical in either direction at any given point. In the 
 present state of geological science, it is not possible to predi- 
 cate for any given point within the earth's crust that the flow 
 of underground waters must be either upward, downward, or 
 sideways. There is an a priori possibility of either direction ; 
 and the most probable one in any particular region must be 
 determined by an actual study of the geological conditions at 
 that point. For this reason, it seems to me, the student of 
 ore-deposits should divest himself as soon as possible of any 
 preconceived bias in favor of the old schools of ascensionists, 
 descensionists, or lateral secretionists, as the true theory, when 
 arrived at by actual investigation, will probably not correspond 
 exactly to the theoretical views of either school, and the time 
 given to arguments in favor of the exclusive correctness of one 
 over the other is more or less wasted. 
 
 In his admirably written paper on The Genesis of Metallifer- 
 ous Veins, 13 Prof. Joseph LeConte, after combating the lateral- 
 secretion views of Dr. F. Sandberger, says that the latter's idea 
 of the ascensionists' theory is a misconception, adding ; " Now, 
 I am sure that no one, in this country at least, holds to any 
 such view. All speculators on this subject, I think, now hold 
 that the mineral contents of veins are wholly derived by leach- 
 ing from the rocks forming the fissure-walls. The ascension 
 theory (if we use that name at all) as properly understood, i.e., 
 the theory which connects vein-formation with solfataric action, 
 is wholly a levigation theory. According to this theory, as I 
 
 13 American Journal of Science, Third Series, vol. xxvi., No. 151, pp. 1 to 19 
 (July, 1883). 
 
THE GENESIS OF CERTAIN ORE-DEPOSITS. 15 
 
 understand it, the vein-matters, including the metallic ores, are 
 not derived from an unknown mysterious region of volcanic 
 fires, but are gathered by leaching from the whole wall-rock 
 from top to bottom of the fissure, but mainly from the deeper 
 parts; because these are under heavy pressure and superheated. 
 Subterranean waters, gathering soluble matter from wide areas 
 and great thicknesses of rock, find their way into fissures, and 
 these then become the natural channel back to the surface from 
 which they came." With these views of Dr. Le Conte, as with 
 the rest of his article, I agree in most respects, while differing 
 with him as to their application, and as to some of his geological 
 facts and reasonings, as will be seen later. 
 
 The direction taken by the ore-currents in any given case in 
 bringing the material of ore-deposits to their present position 
 could be readily determined, if the source were known from 
 which these materials were derived. Perhaps even less than 
 the direction of the currents is this source susceptible of direct 
 and positive proof; but its probable location may be established 
 by inductive reasoning, and indirect or even negative evidence 
 may be furnished by actual demonstration, which may in time 
 raise this probability very nearly to practical certainty. 
 
 5. I stated in the abstract of my report on Leadville that the 
 contents of the ore-deposits were derived from the neighboring 
 eruptive rocks. By " neighboring eruptive rocks," I do not 
 mean that they must necessarily be in actual contact with the 
 ore-bodies; they may be at some distance from the bodies, 
 provided there is no impassable barrier to prevent the passage 
 of solutions from one to the other. From a theoretical point 
 of view, it is evident that the absolute distance is not essential, 
 since all theories of derivation of the contents of ore-deposits 
 involve a greater relative distance of the source, than that which 
 would derive them from the bodies of rock in the vicinity, even 
 if not at absolute contact. Le Conte's ascension theory, quoted 
 above, supposes vein-materials to have been derived from the 
 rocks adjoining the fissure at some indefinite depth, where 
 pressure and heat were abundant. These were present here: 
 the pressure, that of 10,000 ft. of superincumbent strata; the 
 heat, that of immense bodies of slowly-cooling eruptive rock; 
 only the fissure, which his theory conceives, was wanting. 
 
 Something analogous to this fissure might be conceived, if 
 
16 THE GENESIS OF CERTAIN ORE-DEPOSITS. 
 
 the Blue limestone, which is, in one sense, the matrix of the 
 principal ore-bodies, had occupied a vertical instead of the 
 more nearly horizontal position that it does. At the time the 
 Leadville deposits were originally formed, it was a practically 
 unbroken horizontal bed, more or less replaced by deposits of 
 ore along its upper surface and extending through joint-cracks 
 at varying distances into its mass and in some few cases reach- 
 ing to its base. If the dynamic action by which the Mosquito 
 range was uplifted, instead of compressing the sedimentary 
 strata and their included eruptive sheets into a series of folds, 
 and fracturing and displacing them by faults, had simply 
 uptilted the whole into a vertical position, we should then have 
 had, in the place of the fissure, a great vertical limestone zone 
 with ore evidently brought in by solutions acting from one side 
 or wall only. It would then seem most natural, in searching 
 for a source from which the metallic contents had been derived, 
 to investigate the rocks on that side. The advantage of the 
 present over such a condition of things is, that the search, 
 instead of being necessarily confined to rocks adjoining a very 
 limited upper portion of the supposed fissure, can be carried 
 on, not only among the various rocks adjoining the whole area 
 of ore-deposition, but for a considerable distance beyond that 
 area. 
 
 Search for the source of the vein-materials of the Leadville 
 deposits was carried on by subjecting the various country-rocks 
 to delicate chemical tests, in order to ascertain the presence or 
 absence in them of the most characteristic components of the 
 vein-materials, gold, silver, lead, and baryta. In selecting spe- 
 cimens for testing, those were chosen which came from points 
 so far removed from any known deposit that there could be no 
 suspicion that the materials found might be infiltrations from 
 such deposits. Among the specimens of eruptive rocks, the 
 freshest and least altered were naturally selected, since decom- 
 position might be expected to have acted on such basic con- 
 stituents first. None of the above substances were found in 
 the specimens of sedimentary rock tested; and the tests of 
 eruptive rock were, therefore, multiplied, as much as the time 
 which could be allotted to their special investigation would 
 permit. The greatest number of tests were those made in the 
 dry way for minute traces of gold and silver, for the reason 
 
THE GENESIS OF CERTAIN ORE-DEPOSITS. 17 
 
 that these could be made with far greater rapidity, and con- 
 sequently in greater number in a given time, than in the wet 
 way. After considerable experiment with methods and mate- 
 rials, it was found possible to determine in this way with accu- 
 racy 0.005 oz. per ton, or 0.000017 per cent,, of silver, an 
 amount which it w r ould have required an enormous amount of 
 concentration to detect in the wet way. 
 
 The results may be briefly stated as follows : Baryta was 
 found in all four specimens of eruptive rock tested for this 
 substance; lead in 14 out of 17 specimens tested; and silver 
 in 32 out of 42 specimens tested. It is to be remarked that 
 the negative results do not necessarily mean an absence of the 
 substance in question, but only that the amount is less than the 
 process employed could detect; so that where lead is found in 
 a rock it is probable that it contains silver also, but in rela- 
 tively small amount. As the medium percentage of lead oxide 
 in the above tests is 0.0032, if this lead oxide contained 40 oz. 
 of silver per ton, the percentage of the latter in the rock would be 
 within the limit of accuracy given above for our determination 
 of silver, and could not have been detected by the methods 
 employed. Several hundred assays for silver were made, the 
 results of which correspond in general to those given above, 
 but possible sources of error were found in some, and the 42 
 represent the residue, which had been confirmed as accurate 
 by repeated tests, after all containing any possible source of 
 error had been eliminated. 
 
 It may be said that these results do not necessarily prove 
 that the materials of the Leadville deposits were derived from 
 these eruptive rocks, and not from some unknown bodies of 
 rock still richer in these materials at unknown depths. Abso- 
 lute proof, as I have already said, could not be expected, espe- 
 cially as against an unknown quantity whose resources, being 
 unknown, are in one sense unlimited, but this evidence shows 
 a possibility which, combined with all the other facts that bear 
 on this question in this particular district, amounts to a very 
 strong probability. The quantities of vein-constituents found, 
 though minute, are quite sufficient when one realizes what 
 vast bodies of eruptive rock still exist there, and reflects, more- 
 over, that probably a very much larger amount was present 
 when the deposits were formed, but has since been removed 
 
18 THE GENESIS OF CERTAIN ORE-DEPOSITS. 
 
 by erosion. As against the probability that the materials were 
 derived from eruptive rocks below, there is the evidence af- 
 forded by the geological structure of the region that the 
 greater mass of eruptive bodies coming under observation are 
 above the Blue limestone, which is only 400 ft. above the 
 Archaean, and that these eruptive rocks came up through the 
 Archaean in extremely narrow channels or dikes, and only spread 
 out in large bodies after reaching the sedimentary strata above ; 
 therefore, that in all probability there are no large bodies of 
 eruptive rock beneath, until the far-distant sources of these 
 rocks are reached ; further, that the Archaean rocks, as far as 
 tested, were not found to contain these substances. 
 
 The criticisms that have been made upon this part of my con- 
 clusions are mostly general rather than special. Mr. Rolker 
 maintains that the overlying White porphyry (felsite) should be 
 stained by basic sulphate of iron, if the vein-materials had 
 been derived from it, and says, " against Mr. Emmons's analy- 
 sis of the felsite stand other analyses which did not find any 
 lead or silver in it (L. D. Ricketts)." To this I answer, the ex- 
 traction of such minute traces of metallic minerals by percolat- 
 ing waters would not necessarily leave any staining visible to the 
 naked eye, since the minerals themselves are rarely visible, even 
 under the microscope. Moreover, I do not maintain that they 
 came from the White porphyry alone there are other bodies 
 of porphyry from which they could have been derived ; and 
 this porphyry is so universally decomposed, as shown by mi- 
 croscopic examination, that it is difficult to see what all of its 
 original constituents were. Out of 11 specimens of it, included 
 in the above-quoted tests, only three yielded silver, a far 
 smaller proportion than that of the other varieties of eruptive 
 rock, which were, as a rule, less decomposed. Still, as Mr. 
 Rolker himself suggests, this may merely prove that its me- 
 tallic contents had been leached out. As for the counterproof 
 of other analyses, Mr. Ricketts himself says explicitly, 14 that 
 he made no study of the question of the source of the mate- 
 rial, and the fact that his single analysis of White porphyry 
 gives no lead or silver may simply prove that he did not make 
 the special test for these materials on the large amount of rock 
 
 The Ores of Leadville, p. 46 (1883). 
 
THE GENESIS OF CERTAIN ORE-DEPOSITS. 19 
 
 which is necessary in order to detect them. He adds that his 
 analysis " showed scarcely a trace of sulphur, though the rock 
 at one time certainly contained much iron pyrites." 
 
 Dr. dewberry's criticisms on my conclusions are entirely 
 vitiated by his complete misapprehension of my views. He 
 assumes that I would derive the ores from superficial igneous 
 rocks, through the agency of surface-waters ; but since I my- 
 self do not believe that they could have been formed either by 
 surface-waters or from recent or superficial igneous rocks, it 
 would seem unnecessary to refer to his objections to that view 
 in the special case of Leadville. I will merely say that the 
 theory which he proposes as a substitute for mine, " that the 
 plane of contact between the limestone and porphyry has been 
 the conduit through which heated mineral solutions coming 
 from deep-seated and remote sources have flowed, removing 
 something from both the overlying and underlying strata," 
 etc., 15 is one which he himself would probably reject, if he had 
 had as good an opportunity of examining the geological struc- 
 ture of the region and the relation of the ore-bodies to the sur- 
 rounding rocks as I have had. 
 
 It may not be amiss to call attention to the fact that Pro- 
 fessor Newberry has similarly misapprehended Mr. Becker's 
 views as to the genesis of the ores of the Comstock lode. To 
 him Professor Newberry attributes the hypothesis that the Com- 
 stock ores were leached from the hanging-wall by cold sur- 
 face-waters. Becker's memoir contains no such statement. 
 On the contrary, he maintains at length that the ore was ex- 
 tracted from the hanging-wall by rising waters of very high 
 temperature, and charged with solvents, acting at considerable 
 pressures. 
 
 As regards the general derivation of the vein-materials from 
 eruptive rocks, it will perhaps be wise to state explicitly what 
 I do think at the present time, reserving the right to modify 
 my views if I see fit, as I gain a wider and more exact knowl- 
 edge of the ore-deposits of the world. I consider that at the 
 present time neither I nor any one else is in possession of 
 accurate geological knowledge of a sufficiently large number 
 of ore-deposits to justify the formulation of that knowledge 
 
 15 School of Mines Quarterly, vol. v., No. 4, p. 341 (May, 1884). 
 
20 THE GENESIS OF CERTAIN ORE-DEPOSITS. 
 
 into a universally applicable theory of the formation of ore- 
 deposits. Ore-deposits occur in nature under such varied con- 
 ditions, moreover, that it seems doubtful if any one theory of 
 their formation will be found applicable to all of them, and 
 probably the final theory will be an alternative one. As one 
 of these alternatives, the derivation from bodies of eruptive 
 rock in the vicinity of the deposits seems to have in its favor 
 more evidence, both direct and indirect, than any other now 
 offered. 
 
 As indirect evidence, European geologists have long re- 
 marked that regions rich in ore-deposits have, in the majority 
 of cases, been regions of long-continued eruptive activity. This 
 association, or coincidence, if such it may be considered, is still 
 more striking in this country ; but it is to be remarked that it 
 is w T ith the older and generally intrusive rocks of eruptive 
 origin that valuable ore-deposits are most frequently associated, 
 while they are rare when these rocks only form surface-flows 
 or are outpourings of actual volcanic vents. 16 dewberry 17 
 brings forward the latter fact as argument against the deriva- 
 tion of vein-materials from superficial igneous rocks, and as such 
 it is certainly valid ; but the greater part of our ore-deposits 
 are evidently of deep-seated and not of superficial formation. 
 I have no evidence to prove whether recent lavas are poorer in 
 vein-materials than the older intrusive rocks or not; nor is 
 that an essential point, since it is evident that they have been 
 subjected to the leaching process for but a comparatively short 
 time ; that the surface-waters which reach them have neither 
 the heat, pressure, nor chemical solvents that render the action 
 of deep-seated waters more energetic, and therefore that con- 
 centrations of vein-materials in ore-deposits from them could 
 not be expected to be as frequent or as considerable as those in 
 the older and deep-seated rocks. 
 
 Professor ISTewberry is inclined to doubt the frequency of the 
 association of eruptive rocks and ore-deposits, and says in re- 
 gard to the mineral belt of the Far West, " the great majority 
 of veins are not in immediate contact with trap rocks, and they 
 could not therefore have furnished the ores." As to the im- 
 
 6 Tenth Census, vol. xiii., p. 63 (1880). 
 17 The Deposition of Ores, School of Mines Quarterly, vol. v., No. 4 (May, 1884). 
 
THE GENESIS OF CERTAIN ORE-DEPOSITS. 21 
 
 mediate contact of trap rock with these veins, I do not feel that 
 I have sufficient data to contradict his statement, although I 
 am equally confident that it is not justified by accurate statis- 
 tical knowledge on his part. But the statement is liable to 
 mislead, in that the reader might be led to infer that, in the 
 instances he gives, eruptive rocks do not occur in the vicinity 
 of the deposits, whereas I am qualified, from my own observa- 
 tion and from knowledge gained during my investigations 
 under the Tenth Census, to state that this inference would be 
 diametrically opposed to the facts. Not only are there, in each 
 of the 11 districts he mentions, known developments of erup- 
 tive rock in the vicinity of the deposits, but in seven of these 
 districts there are important mines some of which he has 
 quoted by name in his list in which eruptive rocks form one 
 or both walls of the deposits. 
 
 Professor Le Conte, on the other hand, not only admits the 
 frequency of the association of great eruptive activity with ore- 
 deposition, but also the possible derivation of the vein-materials 
 from eruptive rocks. His view on this subject, which resem- 
 ble's the Scotch verdict " not proven," is, " not that igneous 
 rocks alone supply the materials, but rather that igneous action 
 supplies the heat necessary for solution." He afterwards ad- 
 mits that heat is not in all cases necessary for solution. As 
 Professor Le Conte's views may be taken as a fair representa- 
 tion of the best speculative theories on the subject of ore-depo- 
 .sition at the present day, it may be assumed that there are no 
 good a priori grounds against the derivation of vein-materials 
 from eruptive rocks ; and it remains to consider what direct 
 evidence there is in its favor. Before doing this, I wish to 
 advert to a geological question, as regards which I do not agree 
 with Le Conte's implied ideas. He says : " We never see any 
 stratified rock that has not been igneous rock nor, I believe, 
 any igneous rock that has not become so by refusion of strati- 
 fied rocks." This statement might be admitted as applied to 
 the earlier stages of the earth's history when its first crust was 
 forming, and yet doubted in such a practical application to the 
 sedimentary rocks now found on the surface, as is made by 
 Professor dewberry when he says : 1S " All the knowledge we 
 
 18 Deposition of Ores, p. 337. 
 
22 THE GENESIS OF CERTAIN ORE-DEPOSITS. 
 
 have of the subject justifies the inference that most of the igne- 
 ous rocks which have been poured out in our Western Terri- 
 tories are but fused conditions of sediments which form the 
 substructure of that country, . . . and it is possible and even 
 probable that the rocks composing the volcanic ridges are 
 but phases of the same materials that form the sedimentary 
 chains." 
 
 The estimated aggregate thickness of sediments above the 
 Archaean varies, roughly stated, from 60,000 to 100,000 ft., but, 
 owing to frequent elevations and subsidences, the series is 
 probably never found complete at any one point, and it may rea- 
 sonably be doubted if the thickness of sediments accumulated 
 at one time and place over the Archaean ever reached even the 
 lowest of the above figures. But, by the agencies of dynamic 
 action and erosion, geologists have been enabled to study not 
 only these great thicknesses of overlying sediments, but great, 
 though unknown, thicknesses of the Archaean formations be- 
 neath ; yet, nowhere in the vast portions of the earth's crust 
 that have already been examined has any evidence of the fusion 
 of sedimentary rocks into an igneous magma been found. For 
 this reason it seems to me, and I believe I express the senti- 
 ments of the majority of geologists who have made a study of 
 eruptive phenomena, that Professor dewberry's inference is 
 not justified by the knowledge we at present possess, and that 
 the region of fusion whence igneous, rocks' may be supposed to 
 be derived, must be relegated to greater depths, and beyond- 
 the reach of the actual sediments which we can now observe on 
 the surface. 
 
 The theory that vein-materials have been derived from ad- 
 joining rocks is by no means a new one. Both Breithaupt and 
 Cotta admitted the probability of such derivation, provided 
 only the existence of the vein-materials could be proved, while 
 Bischof not only strongly upheld the theory, but by chemical 
 investigation actually detected the earthy or gangue-material 
 of veins in the neighboring country-rocks. Acting on Bischof 's 
 suggestion, and employing methods which enabled him to 
 detect minute traces of material in the separate constituents of 
 rocks, Sandberger has been investigating for many years past 
 the country-rocks of European mining-districts. He finds that 
 the basic silicates of the crystalline country-rocks (metamor- 
 
THE GENESIS OF CERTAIN ORE-DEPOSITS. 23 
 
 phic or eruptive) contain ,the same metals as are found in the 
 neighboring deposits, and hence concludes that the materials 
 of the latter were derived from the former. 19 The investiga- 
 tions of country-rocks, carried on by Mr. Becker and myself at 
 "Washoe and Leadville respectively, were in the same line of 
 research, although when they were undertaken we had not the 
 advantage of Sandberger's experience, and our methods differed 
 somewhat from his, owing to the peculiar circumstances under 
 which each inquiry was conducted. Our results in either case 
 showed at least a possibility of the derivation of the materials 
 from the eruptive country-rocks, which the geological condi- 
 tions heightened to a probability. Since that time, I have 
 carried on similar investigations, with some improvements in 
 methods suggested by experience, on the country-rocks of other 
 districts, notably those of Ten-Mile and Silver Cliff, Colo., which 
 have been in the main confirmatory of those obtained at Lead- 
 ville. Although the work thus far done in this line covers but 
 a small portion of the field of investigation, it affords valuable 
 indications from which one necessarily draws conclusions, and 
 which certainly point a way for further research that promises 
 to be fruitful in results. The conclusions that I have reached 
 thus far are, that the vein-materials are probably derived from 
 country-rocks in the neighborhood of the deposits, though they 
 are not necessarily in absolute contact, and it may even happen 
 that they cannot be seen at the surface. And the chemical 
 tests thus far made show that the eruptive rocks rather than 
 the sedimentary are the more likely to carry the materials from 
 which the vein-materials have been derived. I am by no 
 means prepared to say that eruptive rocks will everywhere be 
 found to be the source of the vein-materials; indeed, it would 
 seem that there are many deposits where this would be impos- 
 sible ; and yet it often happens that the published descriptions 
 of such deposits are not sufficiently complete or exact to enable 
 us to form a decided opinion one way or the other. 
 
 Professor dewberry considers 20 that an unanswerable argu- 
 ment against the theory of lateral secretion is furnished by the 
 great diversity of character exhibited by different sets of fis- 
 
 19 Untersmhungen uber Erzgcinye (1882). 
 
 20 School of Mines Quarterly, vol. v., No. 4, p. 334 (May, 1884). 
 
24 THE GENESIS OF CERTAIN ORE-DEPOSITS. 
 
 sure-veins which cut the same country-rock. It seems to me 
 that a certain amount of diversity might be allowed in different 
 sets of veins in the same belt of rock, without disproving the 
 theory as I understand it; first, because the derivation is not 
 confined to the immediate wall-rock; secondly, because obser- 
 vation shows that such accessory or accidental constituents as- 
 these vein-materials may vary very greatly in the same body of 
 rock; and thirdly, because the determining cause of precipi- 
 tation or deposition might differ in the different sets of fissures, 
 so as to produce a difference in the character of deposition from 
 one and the same solution. Dr. dewberry does not state 
 directly how great a diversity he considers necessary to prove 
 his argument; but the only instance in which he actually cites 
 the character of the ores has been unfortunately chosen for this 
 purpose. It is that of the Humboldt, the Bassick, and the 
 Bull-Domingo mines, near Rosita and Silver Cliff, which, he 
 says, " are veins contained in the same sheet of eruptive rock, 
 but the ores are as different as possible." In point of fact, the 
 Bull-Domingo deposit occurs in Archaean gneiss, while the Bas- 
 sick and Humboldt bodies are in separate and distinct bodies 
 of andesite, evidently belonging to different outflows. 
 
 To summarize the above somewhat discursive remarks : The 
 present tendency of the results reached by careful and well- 
 authenticated determinations of the origin and manner of for- 
 mation of ore-deposits is in favor of a continually increasing 
 applicability of the following conditions : 
 
 That they are deposited from solutions made by percolating 
 waters. 
 
 That the deposition takes place very rarely in actually open 
 cavities, but most frequently by a metasomatic interchange, or 
 by replacement of the more soluble or more accessible portions 
 of a rock or members of a rock-series. 
 
 That these solutions do not necessarily come directly upward, 
 but simply follow the easiest channels of approach. 
 
 That these materials are not immediately derived from sources 
 at some unknown depth, but from neighboring bodies of rock 
 within limited and conceivable distances. 
 
 That where, as is so often the case, ore-deposits are associated 
 with, or in the vicinity of, bodies of eruptive rock, especially 
 
THE GENESIS OF CERTAIN ORE-DEPOSITS. 25 
 
 the older intrusive rocks, there is a reasonable probability that 
 their materials have been derived from these rocks. 
 
 In order to accumulate facts upon which to form any well- 
 grounded, broad generalization upon these very important sub- 
 jects, we need, on the part of mining engineers, an almost in- 
 definite multiplication of such papers as those of Messrs. 
 liicketts, Freeland, and Rolker on the Leadville mines, giving 
 facts in the minute detail which can only be arrived at by long 
 personal observation and study. Such papers should, as far as 
 possible, be based upon authoritative determinations of geo- 
 logical structure of the region where the mines occur, and such 
 determinations it seems to be the proper province of a govern- 
 mental geological survey to furnish, as private individuals can- 
 not be expected to have the extended field-experience, or to be 
 able to carry out the costly investigations which they necessa- 
 rily involve. 
 
26 STRUCTURAL RELATIONS OF ORE-DEPOSITS. 
 
 No. 2. 
 Structural Relations of Ore-Deposits. 
 
 BY S. F. EMMONS, WASHINGTON, D. C. 
 
 (Boston Meeting, February, 1888. Trans., xvi., 804.) 
 
 4 
 
 ' ' The obscurity which still veils from us the true nature of veins will become 
 more and more cleared up when they can be considered in connection with the 
 geological structure of the regions in which they occur." 1 
 
 THESE words, according to Lossen, the biographer of the 
 late Dr. A. vori Groddeck, of Clausthal, were the last received 
 by him from that eminent man, perhaps the most far-sighted 
 and carefully progressive of recent writers on ore-deposits. 
 They seem to me to form a fitting 'text for what I am about to 
 say ; since I find that many of the conclusions at which I have 
 arrived by my own study of the structural relations of ore- 
 deposits, or, in other words, of the structural and dynamic 
 geology of the regions in which they occur in this country, 
 Jiave been similarly determined by him within recent years in 
 Europe, and especially in his home field of work, the Harz. 
 
 I shall not enter upon a detailed account of how far other 
 workers may have arrived at similar conclusions with myself, 
 since these questions of priority are of little interest, except to 
 those immediately concerned; but will briefly present the 
 methods by which, in my work in this country, I have arrived 
 at certain generalizations, and will point out the practical 
 bearing which they may have upon the work of mining 
 engineers. 
 
 In my first thorough and systematic examination of an im- 
 portant group of ore-deposits, viz., that of Leadville, Colo., I 
 was enabled, through the generous facilities afforded me by 
 the then Director of the Geological Survey, Clarence King, to 
 
 1 "Das Dunkel, welches uns die wahre Natur der Giinge noch immer verhiillt, 
 wird sich mehr und liiehr lichten wenn sie im Zusammenhang mit dem geognos- 
 tischen Ban der Gegenden, in denen sie auftreten, betrachtet werden konnen." 
 
STRUCTURAL RELATIONS OF ORE-DEPOSITS. 27 
 
 make a most elaborate and detailed study of the geology, not 
 only of the immediate vicinity of the mines, but of the adjacent 
 mountain regions, based upon accurate topographical and un- 
 derground maps, and thereby to determine the structural rela- 
 tions of these ore-bodies with an exceptional degree of detail 
 and accuracy. The inductions based upon these structural 
 relations have now borne the test of seven years of active ex- 
 ploration by a most energetic and enterprising mining commu- 
 nity, and their substantial accuracy has been so abundantly 
 proved as to afford an excellent practical illustration of the 
 importance, in this class of deposits, of the structural study. 
 
 In entering upon this work, I was, I must admit, far from 
 familiar with all that had been written upon the theory of ore- 
 deposits, and I purposely refrained from reading up upon the 
 subject until my field-work was completed, in order to avoid 
 the danger of any unconscious bias which might influence my 
 interpretation of the facts of nature. It was commonly said 
 at that time of the Leadville deposits "that they went contrary 
 to all the theories of geologists." Such statements are in 
 general, I find, liable to originate in a misapprehension, either 
 of the true conditions which prevail at the locality in question, 
 or of what are the best geological theories. In this case 
 I found, in two respects at least, that the process of ore-deposi- 
 tion at Leadville was not in accordance with the most widely 
 accepted theories upon the subject. First, they were not the 
 filling of pre-existing open cavities or caves in the limestone, 
 but had been formed by a gradual replacement of the rock- 
 material by the substances brought in by the ore-bearing solu- 
 tions. Secondly, these solutions did not come directly from 
 below, as seemed to be considered a necessary condition for 
 the deposition of ores, but in this case could be proved to have 
 reached the immediate locus of deposit from above. 
 
 As I pointed out in a paper read before the Institute two 
 years since, 2 in stating the results I had arrived at in regard to 
 the genesis of the Leadville deposits, I made no claim of pre- 
 senting any complete general theory or classification of ore- 
 deposits at that time, nor have my observations been suffi- 
 ciently wide to enable me to do so now. I did, however, con- 
 
 2 This volume, pp. 1 to 25 ; Trans., xv., 125 (1886-87). 
 
28 STRUCTURAL RELATIONS OF ORE-DEPOSITS. 
 
 elude, as a result of my investigations, that existing theories 
 and classifications were inadequate to account for the various 
 forms under which ores are found in nature, and that this in- 
 adequacy arose probably from the want of some common un- 
 derlying genetic basis. Far too few of the descriptions of 
 ore-deposits in various parts of the world, upon which the 
 existing theories have been founded, are based upon accurate 
 determinations of their structural relations. I have, therefore, 
 been emboldened to assume that, by giving more attention to 
 these structural relations than has hitherto been done, many 
 existing uncertainties might be cleared up, and perhaps, in 
 time, a rational or natural classification of ore-deposits might 
 be formed. In the paper above mentioned I stated the conclu- 
 sions I had been enabled to form from my Leadville and later 
 studies in regard to the genesis of certain ore-deposits, mainly 
 those in limestone, and touched lightly on their probable appli- 
 cation to what are known as fissure-veins, of which I had, up 
 to that time, had but limited opportunities of personal observa- 
 tion. Since then, however, especially during the past summer, 
 I have visited many so-called fissure-deposits of great variety 
 of type, and during these visits I have been so struck with the 
 uniform occurrence of certain elementary structural conditions 
 that I have ventured to make some preliminary generalizations 
 based upon them, that seem likely to find a very wide practical 
 application, and to furnish a basis, with modifications that may 
 be afterwards introduced as a result of wider observation, for 
 a general classification of ore-deposits. Whether this prove to 
 be the case or not, it seems that this method of regarding ore- 
 deposits, while I can hardly claim for it much that is absolutely 
 new, has the merit of being a simple, rational method, which 
 obviates many of the uncertainties and misapprehensions, 
 especially in practical application, that constantly arise from 
 the more complicated existing systems. 
 
 Preliminary Statements. The ore-deposits which I propose to 
 consider are original or primary deposits that have been formed 
 later than the inclosing rock. They exclude, therefore, second- 
 ary deposits, whether of mechanical or detrital origin, like 
 placers, or of chemical origin, like bog iron-ores, which result 
 from the superficial leaching of other deposits. They also ex- 
 clude deposits, such as beds of coal, gypsum, and the like, 
 
STRUCTURAL RELATIONS OF ORE-DEPOSITS. 29 
 
 which have been deposited, so to speak, contemporaneously 
 with the inclosing rock. 
 
 Even with these exclusions they include practically all the 
 workable primary deposits of useful metals; for I have yet to 
 see such deposits which can be proved to have been formed 
 contemporaneously with the inclosing rocks. It is possible 
 that in some cases, as Irving holds with regard to the Lake 
 Superior iron-deposits, there was an original nucleus of ore con- 
 temporaneously precipitated with the sediments which formed 
 the rocks, but which has been added to to such an extent by 
 percolating solutions replacing the adjoining portions of the 
 inclosing rocks, that the present ore-body is practically a later- 
 formed deposit. 
 
 I believe, with Pumpelly, Posepny, and others, that all our 
 workable deposits of the useful metals are the result of a pro- 
 cess or series of processes of concentration or aggregation of 
 material previously disseminated in a minute form through the 
 mass of the rocky crust of the earth. 
 
 With regard to these deposits there are certain elementary 
 postulates, which at the risk of apparent unnecessary repetition 
 from former papers I think it best to briefly enumerate. 
 
 1. That these deposits were formed from aqueous solutions. 
 In other words, they have been gathered up by waters contain- 
 ing varying substances in solution, and percolating through the 
 earth's crust, and again deposited in their present concentrated 
 form under a change of conditions which favored precipitation 
 rather than solution. 
 
 It seems hardly necessary at the present day to bring for- 
 ward any arguments in favor of the aqueous deposition of ores 
 as opposed to the notion of an eruptive origin, which at the 
 best has been a theoretical view not founded upon carefully 
 and critically determined facts; but if there exist any linger- 
 ing doubts in any mind as to the capability of solutions to take 
 up and redeposit the various- minerals found in our ore-deposits 
 I would recommend a perusal of Daubree's recent voluminous 
 work upon subterranean waters. 3 
 
 2. That, under given conditions of heat and pressure, all sub- 
 stances are more or less permeable to water. Hence we are 
 
 *Les eaux souterraines ct V epoque actuelle et aux epoques anciennes (1887). 
 
30 STRUCTURAL RELATIONS OF ORE-DEPOSITS. 
 
 justified in assuming that, at sufficient depths within the earth's 
 crust, waters circulate through or permeate all rocks, even 
 those apparently impermeable, and thus may dissolve out 
 minute quantities of the more readily attackable materials 
 within their mass, and remove them to some other place. It 
 is evident, however, that these waters will constantly tend to 
 concentrate in such portions of the rocky mass as offer a more 
 ready passage or flow, and that during such passage or flow 
 they will seek relief from heat or pressure, and hence come 
 into differing conditions which may favor precipitation, deposi- 
 tion, or chemical interchange of the materials they carry in 
 solution. 
 
 Among the determining causes of solution and of precipita- 
 tion or deposition, the chemical forces undoubtedly play an im- 
 portant part. The capacities of various alkaline solutions to 
 take up metallic minerals, especially when hot, and the condi- 
 tions of diminished heat and pressure, or of dilution, which 
 would favor precipitation of these minerals, present an extremely 
 interesting and important subject of discussion; but it is one 
 that would take too much time to treat within the limits of 
 this paper. I shall, therefore, confine myself as far as possible 
 to the mechanical or structural conditions which would favor 
 ore-deposition ; in other words, consider what are the natural 
 water-channels within the earth's crust, and what forms of ore- 
 deposits such water-channels will give rise to, when the chemical 
 and other conditions are such as to favor a deposition of valu- 
 able minerals in workable quantity by them. 
 
 3. A further postulate, which I insist on the more strenu- 
 ously for the reason that in former times the opposite view has 
 been so almost universally held among writers on ore-deposits- 
 is that a large pre-existing open cavity is not a necessary con, 
 dition for ore-deposition. In other words, that ore-deposits 
 are to a large extent the actual replacement of the country- 
 rock by vein-materials, and that the filling-up by these materials 
 is rather that of interstitial spaces than of what might properly 
 be considered open cavities. I by no' means deny that a cer- 
 tain limited amount of unoccupied space may have existed in 
 the water-channel previous to the ore-deposition, but I wish to 
 remove the tendency to misapprehension caused by the previ- 
 ously-conceived view, under which, for instance, one might 
 
STRUCTURAL RELATIONS OF ORE-DEPOSITS. 31 
 
 regard the whole width of an 8-ft. vein as material brought in 
 from a foreign source, when in point of fact more than 7 ft. of 
 it might be more or less completely altered or replaced coun- 
 try-rock, and less than a foot (and this not in one body) rep- 
 resent spaces actually filled in. I can even conceive of cases 
 of veins showing what is supposed to be the comb-structure, 
 from which the idea of the pre-existing open space was origin- 
 ally derived, where this structure is produced by sheeting of 
 the country-rock, the different sheets being replaced by differ- 
 ent mineral combinations, as will be explained later on. 
 
 Let us consider, then, what would be the natural and most 
 readily available channels which w T ould tend to collect the 
 waters circulating within the earth's crust, and constitute their 
 primary water-courses. 
 
 It is evident that the nearest analogy to the flow of under- 
 ground waters which can actually come under our observation 
 will be found in the flow of springs, especially thermal springs. 
 A study of the phenomena connected with spring-action and 
 deposition, such as has been made by Daubree in his valuable 
 work above cited, materially aids our conceptions of what may 
 have taken place in the deeper-seated channels which have 
 been in former geological periods the scene of ore-deposition. 
 
 One must beware of following'this analogy blindly, however, 
 and bear in mind that most ore-deposits must have been formed 
 at considerable depths below the surface, and brought to the 
 comparatively short distance from that surface which they now 
 occupy by upheaval and erosion. 
 
 An instance of the errors into which one may be otherwise 
 led is afforded by a paper read before the Institute two years 
 since by Prof. T. B. Comstock, 4 ori The Geology and Vein- 
 Structure of Southwestern Colorado. 
 
 Owing to the vagueness of Mr. Comstock's statements, and 
 his many misconceptions of geological facts, we cannot always 
 be sure of his meaning; but from a careful consideration of 
 this paper I infer that he considers the head of Red Mountain 
 creek in that region, which he calls a crater-like depression, to 
 be an extinct geyser-basin, and that the ore-deposits opened 
 by the mines now worked there have been formed by geysers. 
 
 Trans., xv., 218 to 265 (1886-87). 
 
32 STRUCTURAL RELATIONS OF ORE-DEPOSITS. 
 
 Now a geyser, as its name implies, is a spring which violently 
 ejects its waters into the atmosphere, and hence, even more 
 than other springs, is essentially a surface-phenomenon. 
 
 As, since the ore-deposits of Red Mountain basin were formed, 
 something like 2,000 ft. in thickness of rock-material has been 
 eroded away to form the basin, it is evident that they could 
 not have been formed by a geyser, nor can it be determined at 
 the present day whether geysers ever existed there or not. 
 Apparently Professor Oomstock has thought to find a resem- 
 blance between certain rounded ridges of light-colored rock 
 near these mines and the mounds formed by deposits from the 
 springs in the Yellowstone Park. Instead, however, of being 
 surface-deposits, they are simply portions of the andesitic coun- 
 try-rock from which acid waters have removed the basic con- 
 stituents, perhaps depositing a certain amount of silica in their 
 place; the resulting quartzose masses, offering greater re- 
 sistance to the disintegrating effect of atmospheric agents and 
 to erosion than the surrounding rocks, have been left as inound- 
 like ridges protruding above the general surface, more or less 
 independent of the natural drainage-channels. 
 
 There are abundant mounds formed by deposits from springs 
 in the vicinity of Red mountain, but they consist mainly of 
 bog iron, and are formed by oxidizing surface-waters passing 
 through and decomposing bodies of sulphides of the metals, 
 whose action is quite distinct from, and in some sense the re- 
 verse of, those which originally formed these bodies. It would 
 seem almost unnecessary to insist on this distinction, but I 
 recall the description given me of similar deposits in the Red- 
 well basin in the Gunnison region by J. K. Hallowell, who 
 claimed as exact a knowledge of the geology of that district as 
 Professor Comstock does of the San Juan region. According 
 to him, galena and pyrite can be found in actual process of 
 formation there at the present day. On personal examination, 
 I found that a bog iron-deposit had been formed throughout 
 the debris filling the bottom of this ancient glacier-basin, and 
 in one place rested directly on the outcrop of a vein carrying 
 pyrite, galena and other sulphurets. Owing to the extremely 
 decomposed condition of the country-rock of this vein where 
 the bog iron rested on it, Mr. Hallowell had evidently con- 
 cluded that it formed part of the spring-deposit, failing to 
 
STRUCTURAL RELATIONS OF ORE-DEPOSITS. 33 
 
 recognize the dividing-line between recent deposit and original, 
 though decomposed, rock-formation. 
 
 Although, in studying a given deposit, it is not safe to assume 
 that there has been a spring at that particular spot, from 
 whose waters it was deposited, it is evident that the under- 
 ground flow of waters which formed ore-deposits would have 
 followed similar laws to those which regulate the flow of water 
 now appearing at the surface as springs. 
 
 Natural Water- Channels. From the study of the flow of 
 spring-water, three principal structural conditions may be con- 
 ceived which would produce natural water-passages in the rocks 
 which form the earth's crust : 
 
 1. Sedimentation or bedding. 
 
 2. Intrusion of eruptive masses. 
 
 3. Dynamic movements producing fractures across rock- 
 
 masses of differing origin or composition. 
 
 1. From the first of the above causes, by the deposition of 
 alternating strata of varying degrees of permeability, or by 
 successive flows of igneous rocks, natural channels will be af- 
 forded parallel to the stratification or bedding-planes, and more 
 or less coincident with them according to the nature of the ma- 
 terial of which the bounding beds are formed. This is proved 
 by the fact that where such strata or beds are inclined or pli- 
 cated, and afterwards eroded so that their edges outcrop, 
 springs will be found along such outcrops where they are at a 
 lower level than the general mass of the strata, or artificial 
 springs may be produced by artesian borings which fulfill the 
 necessary hydrostatic conditions. It is hardly necessary to 
 quote instances of flow of spring-waters under the simple con- 
 ditions of alternating strata of permeable and impermeable 
 sedimentary rocks. The evidences of water-passage between 
 flows of eruptive rock are well shown in Idaho and eastern 
 Oregon, where whole rivers disappear beneath the great lava- 
 flows that cover such immense areas of surface, and reappear 
 .at some lower level at the bounding-plane between the succes- 
 sive flows, evidently having sunk through some natural frac- 
 ture and followed a more permeable bed of mud or breccia, 
 such as is generally found alternating with the beds of solid 
 Java. 
 
 These primary water-channels along bedding-planes may 
 
 3 
 
34 STRUCTURAL RELATIONS OF ORE-DEPOSITS. 
 
 be interrupted by either of the two other causes mentioned 
 above. 
 
 2. Eruptive dikes or cross-cutting intrusive bodies of any 
 form may interpose relatively impermeable masses across their 
 course, or intrusive bodies, running parallel with the bedding, 
 may render the plane of contact a more ready water-passage 
 than it otherwise would have been. Thus in regions of erup- 
 tive activity, springs, especially thermal springs, are generally 
 found along the outcrop of the contact of the later eruptives 
 with the rocks through which they have passed. 
 
 3. The interruptions to these primary water-channels result- 
 ing from the varied forms of rock-fracture caused by dynamic 
 movements are so manifold and numerous that it is not always 
 possible to trace back to cause from effect. Frequently springs 
 issue from the outcrops of fault-planes; and, when crossed 
 underground, the latter are generally found to be water-bear- 
 ing. It is easy to conceive that where a series of beds, includ- 
 ing certain permeable or water-bearing strata, are broken or 
 displaced by fault-movements, the current along the permeable 
 strata may be interrupted. On the other hand, the passage of 
 water along this new water-channel may not be continuous to 
 the surface, but may only follow it until it meets another per- 
 meable stratum and turn off again along that in a manner similar 
 to the well-known occurrence in artesian wells, where, if the 
 bore-hole be not protected by a water-tight casing, the water 
 rising from some deeper bed may gradually be dissipated in 
 other permeable beds passed through by the drill, between the 
 water-bearing bed and the surface, and the surface-flow be 
 finally lost altogether. 
 
 It is evident that the greater number of underground water- 
 channels, though perhaps not those carrying the largest 
 volumes of water, will be afforded by the multitudinous 
 fractures in the crystalline or eruptive rocks and in the older 
 and more metamorphosed sedimentary strata. In one sense 
 these might be made to include the contact-channels along 
 dikes and intrusive bodies of eruptive rock also ; for it is prob- 
 able that such bodies, when forced up from below, have fol- 
 lowed some previously- determined fracture or natural division- 
 plane. 
 
 Before proceeding to consider how far the origin of various 
 
STRUCTURAL RELATIONS OF ORE-DEPOSITS. 35 
 
 types of ore-deposits may be ascribed to the passage of mineral- 
 bearing waters along one or more of the above natural water- 
 channels, I will mention another possible class of division- 
 planes in rocks which have been considered by some as the 
 origin of mineral-bearing fissures, but to which, so far as I 
 know, that of springs has never been ascribed. These are con- 
 traction-planes or joints. The most evident examples of them 
 are naturally found in eruptive rocks, notably the prismatic 
 joints of more recent eruptives. It is possible that the divi- 
 sion-planes which tend to separate most eruptive rocks into 
 parallelopipedic fragments may have been originally determined 
 by contraction of the mass, but it is probable that the actual 
 fracturing along these planes was produced by dynamic move- 
 ments. Whether sedimentary rocks contract after deposition 
 from the expulsion of the water they must have contained when 
 forming the sea-bottom, may be considered an open question. 
 One thing is evident : that contraction-planes must be confined 
 to one rock-mass or bed, and cannot cross several of them, as 
 do most mineral-bearing fissures. It is also evident that, as 
 contraction-planes alone, there would have been no movement 
 or pressure along them. Hence planes where evidences of 
 movement or pressure are found cannot result from contraction 
 alone. For these reasons, and the further one that I have 
 never yet found ore-bodies deposited on planes which I could 
 feel assured were the result of contraction alone, I think it safe 
 to leave contraction-planes out of consideration for the present, 
 at least. 
 
 Ore-Deposits Along Bedding-Planes. The greater part of our 
 ore-deposits are found in mountainous regions where eruptive 
 and dynamic action has been most energetic; consequently, 
 deposits resulting from the flow of water along bedding-planes 
 alone, unconnected with the other classes of water-channels, 
 form but a small proportion of the whole. There are, more- 
 over, other conditions than the simple readiness of flow of 
 water that come into play. It is apparent that deposition will 
 take place more readily from a comparatively sluggish than 
 from a rapid flow ; hence conditions that tend to retard the flow 
 or cause a partial stagnation at a given point will favor pre- 
 cipitation at that point. Such would be the actual contact of 
 an impervious stratum, e.g., a bed of clayey material, with a 
 
36 STRUCTURAL RELATIONS OF ORE-DEPOSITS. 
 
 readily pervious one like a loose sandstone. Again, in pli- 
 cated strata, points where by sharp folding the beds are more 
 closely compressed together as on the side of the fold than 
 at other points, are often found to carry larger bodies of ore. 
 The chemical composition of the different beds is also a most 
 important factor ; so much so that in regions like the Ten-Mile 
 district, where thin beds of limestone are found scattered 
 through considerable thicknesses of sandstone and shales, the 
 ore of the so-called bedded deposit is almost exclusively con- 
 fined to the more readily attackable limestone. The term 
 " bedded vein " or " deposit," as derived from von Cotta's 
 Lagergang (literally, bed-vein), might be objected to as seeming 
 to imply that the ore was deposited contemporaneously with 
 the inclosing beds, and for this reason the less concise term, 
 " deposit along bedding-planes," would be preferable. Where 
 the deposit occurs at the junction of two beds of very dissimi- 
 lar composition, like limestone and quartzite or slate, it is often 
 called a contact-deposit, but it seems that this term should be 
 confined to those of the next class, contact-deposits with rocks 
 not of contemporaneous formation. 
 
 Instances of deposits of this class that occur to me are those 
 of the Ten-Mile region, the Eed Cliff region, and others in 
 Colorado, which are mostly along the bedding-planes between 
 limestones and argillaceous beds, though at Red Cliff some are 
 found in quartzites. The iron-ore beds in the Silurian rocks 
 of the Appalachians are probably of this class, for Prime re- 
 ports that he finds evidence that they are the replacement of 
 the limestone rock, hence cannot have been formed, like bog 
 iron-deposits, contemporaneously with the inclosing rocks, as 
 dewberry maintains. They are not necessarily confined to the 
 immediate bedding-plane, but in a porous rock may spread 
 through the mass, like those of Silver Reef, where precipita- 
 tion has been probably induced by the presence of some re- 
 ducing-agent of organic origin. The copper-deposits of Mans- 
 feld in the Harz, and the lead-deposits of Commern in the 
 Eifel, may be found to belong to the same class, though they 
 have generally been considered to be of contemporaneous origin 
 with the inclosing Triassic beds. 
 
 It will be evident a priori that mineral currents following 
 stratification-planes cannot be considered as necessarily coming 
 
STRUCTURAL RELATIONS OF ORE-DEPOSITS. 37 
 
 from below, as has' been assumed by many to be the universal 
 direction of such currents. As I have shown in a former 
 paper, 5 the direction of flow of underground waters cannot be 
 determined beforehand for a given point; as this flow is a 
 circulation, its direction may vary according to the local con- 
 ditions which would govern it. As far as my observations go, 
 in deposits from currents following stratification-planes the 
 waters have sunk into the bed from its upper surface as if 
 under the influence of gravity. 
 
 Deposits Along Contact- Planes. Mineral-bearing solutions 
 gathering in or flowing along the planes of contact of eruptive 
 bodies with rocks through which they have been forced would 
 have a tendency to deposit their contents along such planes, 
 whatever the direction of their flow. If they were ascending 
 currents, it may be conceived that they were coming from a 
 hotter region, or from the vicinity of a larger and not so thor- 
 oughly cooled mass of igneous rock, where their solvent power 
 was greater, to a cooler region, in which this solvent power 
 would be relatively less. If lateral or descending flows, gather- 
 ing from the mass of one of the walls of the fissure, precipitation 
 might be induced from the solutions thus brought in by a 
 retardation or temporary stagnation of the flow, by dilution 
 through mixing with other waters already circulating in the 
 fissure, or by some chemical interchange resulting from contact 
 with the other wall, if a rock of different chemical composition 
 from that through which the solutions had been passing. For 
 these reasons it seems advisable to distinguish such deposits 
 from those along stratification-planes on the one hand, or along 
 rock-fractures on the other, even in those cases where the con- 
 tact-plane may be in part, or wholly, coincident with a stratifi- 
 cation- or fracture-plane. 
 
 It is quite a common practice among miners to designate as 
 " contact-deposits " ore-bodies occurring along the dividing- 
 plane between two bodies or beds of different rocks, even when 
 such plane is simply a stratification-plane. Such practice 
 should in my opinion be avoided, and the term confined to the 
 planes defined above, which are distinctly of later formation 
 than stratification-planes, and in which the conditions of depo- 
 sition would have certain distinctive characters. 
 
 5 This volume, p. 14; Trans., xv., 137 (1886-87). 
 
38 STRUCTURAL RELATIONS OF ORE-DEPOSITS. 
 
 Contact-planes as defined above will more frequently be 
 found to coincide or connect with planes of rock- fracture, since 
 one can hardly conceive of sheets of eruptive rock being forced 
 through existing rock-masses in the form in which we now 
 find them, unless they had followed some already-determined 
 line of fracture, or at least of readiness to be forced open, and 
 it is well known that eruptions of lava at the present day are 
 generally preceded by earthquake-shocks, which probably in- 
 volve a very considerable shattering and fissuring of the earth's 
 crust in the vicinity of the eruption. 
 
 Ore-deposits along contact-planes are very common, and 
 mining engineers can doubtless recall frequent instances which 
 have come under their own observation. The famous Lead- 
 ville deposits are in great part instances of the less common 
 type of deposits, in contact with intrusive bodies which have 
 generally followed stratification-planes. Among them, how- 
 ever, are deposits along the contact of cross-cutting eruptive 
 sheets, the so-called second contacts, and in some instances the 
 ore-currents have followed rock-fractures, and hence belong to 
 the third class. As in all deposits in limestone, owing to the 
 readily attackable character of the rock, the actual form of the 
 various deposits at Leadville is extremely irregular ; more so 
 than it would be in a more siliceous rock ; but I have as yet 
 been unable to conceive of any classification, founded on the 
 form alone, that would essentially aid in the description of 
 such bodies, or help the miner in exploiting them. 
 
 Of deposits along the contacts of dikes or cross-cutting 
 bodies of eruptive rock, hence generally occupying a more 
 nearly vertical position, abundant examples are found through- 
 out the Archaean areas of the Rocky Mountain region, most of 
 which are commonly classed by the miner as fissure-veins, be- 
 cause of the prevailing prejudice in favor of the supposed 
 greater value of that type of deposit. It may be that the whole 
 mass of a narrow dike is impregnated with mineral, and thus 
 constitutes the ore-body; but in the structural sense it is none 
 the less a contact-deposit, since the deposit has been made by 
 waters acting from the contact-planes outward. Instances of 
 such deposits are frequent in Boulder, Gilpin, and Clear Creek 
 counties, in Colorado. 
 
 On the other hand, when the deposit occurs along a plane of 
 
STRUCTURAL RELATIONS OF ORE-DEPOSITS. 39 
 
 contact of two dissimilar bodies of rock brought into juxtaposi- 
 tion by faulting, like the Comstock lode, it would more prop- 
 erly belong to the third class. 
 
 Deposits Along Planes of Rock-Fracture or Fissures Produced 
 by Dynamic Movements. Many somewhat divergent views have 
 been entertained at various times by geologists as to the origin, 
 manner of formation, and even the proper designation of the 
 many kinds of fissures, cracks, and joints that traverse the rock- 
 masses forming the earth's crust. Those that I propose to 
 briefly present here are the ones which a long field-experience 
 has shown to accord best with the facts of nature, and which, 
 as far as my reading has extended, are in essential harmony 
 with those entertained at the present time by the best structural 
 geologists both of this country and of Europe. 
 
 The most prominent and readily remarked of these rock- 
 fractures are the great faults which have played so important 
 a part in determining the orographic relief of our globe, a part 
 second in importance only to that of the flexures or plications 
 of the strata, to which, as I shall show, they are closely allied 
 both in origin and manner of formation. The greatest of these 
 faults often extend for miles in length, and the displacement 
 of the opposed rock-masses on either side of the fault may 
 amount to several thousand feet. Minor faults or displace- 
 ments, which are found in infinite variety, especially in regions 
 of great dynamic disturbance, may not produce any readily 
 apparent effect upon the surface-features, and yet may be rec- 
 ognizable as determining the flow of springs, or be detected 
 by the underground workings of mines. They have been most 
 thoroughly studied in the workings of coal-mines, where the 
 importance of careful underground mapping is most generally 
 appreciated, since the determination of the direction and amount 
 of throw of such faults has an actual money-value. Much has 
 been written about methods of making such determinations, 
 but more attention seems to have been given to reducing them 
 to mathematical formulae than to tracing their origin or con- 
 nection with other earth-movements. In all these rock-frac- 
 tures the evidence of a movement of displacement, as disclosed 
 by the discrepancy or want of correspondence in the adjoining 
 walls, is usually very prominent. 
 
 There are other and much more numerous rock-fractures, in 
 
40 STRUCTURAL RELATIONS OF ORE-DEPOSITS. 
 
 which there is either no movement of displacement, or it is so 
 slight as to be with difficulty detected. Among them certain 
 classes are characterized by their frequency and their general 
 parallelism in two or more co-ordinated directions, and at 
 angles often approaching a right angle with each other. To 
 these, owing to their apparent uniformity of character, the 
 name of joints, or cross-joints (inasmuch as they are apt to cut 
 across the strata), has generally been given by English-speak- 
 ing geologists. 
 
 As regards the designation of these various forms of fissure 
 or rock-fracture, from the very fact that there has been so little 
 agreement as to their genetic relations, there has necessarily 
 been a great want of uniformity in nomenclature. In different 
 countries, and even in different districts in the same country, 
 local terms have been used to describe phenomena supposed to 
 be peculiar to the locality, which have been perpetuated by 
 geologists and have thus introduced into geological literature 
 a greater diversity and variety of terms than is justified from a 
 strictly genetic point of view. 
 
 Daubree, in his comprehensive view of the phenomena at- 
 tending the flow of underground waters, recognizing the hope- 
 lessness of assimilating all these local terms, proposes the gen- 
 eral name of Lithoclases (rock-fractures) for all rock-fractures 
 of whatever nature, and, as principal subdivisions, uses Para- 
 clases, to designate those in which the movement of displace- 
 ment is readily apparent (in other words, what are generally 
 called faults), and Diaclases to designate those that are gener- 
 ally known as joints and in which there is no perceptible 
 movement of displacement, but which are characterized by 
 a parallelism and uniformity of distribution, and traverse dif- 
 ferent rock-masses. To both of these he attributes a mechani- 
 cal origin ; in other words, considers that they are the result of 
 dynamic movements of the earth's crust. He further desig- 
 nates all the rock-fractures of feeble dimensions, which are 
 confined to a given rock-mass and render it liable to break up 
 into small fragments under various influences, as Leptodases 
 (small fractures), subdividing these further into Syndases (con- 
 traction-fractures), or those which, like prismatic joints, are 
 produced by the contraction of the rock-mass, and Piesodases 
 (compression-fractures), those small fractures, without any ap- 
 
STRUCTURAL RELATIONS OF ORE-DEPOSITS. 41 
 
 parent regularity, whose frequent striated surfaces show them 
 to result from a movement of compression like the diadases. 
 
 On the other hand, Heim, who is the best representative of 
 the German ideas on structural geology, in his classic work on 
 the mechanism of mountain-building, 6 simply divides the larger 
 rock-fractures into two classes : fold-faults (Faltenverwerfunyeri) 
 and fissure-faults (Spaltenverwerfunyeri), both of which are pro- 
 duced by tangential or .lateral compression of the upper por- 
 tions of the earth's crust. In the former, this pressure has 
 resulted in a general plication of the beds involved, which has 
 progressed to such a point that the limit of their plasticity 
 or capability of bending has been passed, and the tension re- 
 lieved by actual fracture and displacement. In the latter, the 
 fracture has taken place without any perceptible bending of 
 the rock-masses adjoining the fault, the tension being relieved 
 by sudden shatterings in the nature of earthquake-shocks, or be- 
 cause the lines of fracture were already determined, and the 
 cohesion sufficient to admit of the preliminary plication of the 
 beds no longer existed. He afterwards traces the effects of 
 the same forces upon the internal structure of individual rock- 
 masses, and shows that cleavage- and foliation-planes are, so 
 to speak, diminutive faults, and that the effects of these move- 
 ments are appreciable even in the microscopic structure of the 
 rocks. 
 
 While DaubreVs nomenclature, as such, is the most com- 
 plete and comprehensive thus far presented, the attempt to in- 
 troduce into so practical a science as mining geology so many 
 new and strange terms would seem to be of very doubtful ad- 
 visability. For the present purposes, therefore, it seems suffi- 
 cient to use the terms " fold-faults," " fissure-faults," and 
 " compression-joints " to designate the most marked types of 
 the various rock-fractures, bearing in mind that, as they are 
 supposed to be the result of the same general force of compres- 
 sion, it may not always be possible to draw a definite line of 
 distinction between the types. 
 
 Causes of Fracture. It seems hardly necessary to state at the 
 present day that the force which produces the folding, fault- 
 ings, and rock-fractures in short, the mountain-building force, 
 
 6 Untersuchungen iiber den Mechanismus der Gebirgsbildung, vol-. ii., p. 44 (1878). 
 
42 STRUCTURAL RELATIONS OF ORE-DEPOSITS. 
 
 is to be considered as a result of the secular contraction of the 
 earth's crust. Of late years, however, some theoretical argu- 
 ments have been presented by physicists tending to throw 
 doubt upon the adequacy of the force which might be produced 
 by secular contraction to account for what they assume to be 
 observed facts. Further, certain American geologists have 
 thought to find conditions which, according to their reading of 
 the facts, contraction could not account for, and for some of 
 which it has even been thought necessary to revive the old and 
 long ago abandoned hypothesis of a vertical upthrust. 
 
 As regards the theoretical objections, it may be said that 
 mathematical demonstrations are of questionable value in a 
 science like the geology of the present day, in which the ex- 
 actly determined facts are as yet too few to afford premises of 
 mathematical exactitude upon which to base them, and that 
 those who are arguing against the contraction theory have 
 presented no adequate hypothesis to take its place. 
 
 On the other hand, among practical observers in geology 
 the personal equation forms so large a factor that it may be 
 fairly questioned whether the readiness of the gentlemen re- 
 ferred to above to find facts that could not be accounted for 
 by the contraction theory was not enhanced by a previously- 
 formed opinion of its inadequacy and a desire to see it dis- 
 proved. In my own pretty large experience in the same 
 general field in which they have worked, I have found that 
 this theory not only accounts for, but is the only one that will 
 account for, all the observed facts ; and where my observations 
 extended over regions actually mentioned by them, I have 
 found their explanations not to be in accordance with the facts 
 of nature, as I read them. 
 
 Under the contraction hypothesis, the forces exerted may be 
 concisely described as resulting from the attempt of an already 
 consolidated crust to fit itself more closely to a shrinking 
 nucleus. Their effect is felt probably only upon a compara- 
 tively thin outer portion of the earth's crust : at any rate, it is 
 a very thin portion of this crust which comes under our obser- 
 vation. This crust may be conceived, therefore, as having 
 been since its first formation in a condition of tension, a gradu- 
 ally increasing force which from time to time found its relief 
 in earth-movements producing corrugations on its surface, and 
 
STRUCTURAL RELATIONS OF ORE-DEPOSITS. 43 
 
 hence relative elevations along certain orographic lines, which 
 from some reason or other were lines of least resistance or of 
 weakness. Such lines, once determined, have been the scene 
 of most marked expression of these constantly-recurring move- 
 ments of relief from tension. Closely connected with such 
 movements have been the eruptions of igneous material, forced 
 up from below, either frorn a region of permanent fusion of the 
 material of the earth's crust, as was formerly most generally 
 maintained, or, according to later views, from local reservoirs 
 brought into a fused condition as a more or less direct result 
 of these movements, by the disturbance of equilibrium between 
 the various forces involved in the general condition of tension. 
 Whatever their source, the eruptions of igneous rocks have 
 unquestionably had a very close connection with orographic 
 disturbances, and further, have indirectly played an important 
 part in the formation of most ore-deposits. 
 
 Observation teaches us that these successive periods of 
 dynamic disturbance, or of mountain-building, must have been 
 followed by periods of relative quiescence, during which the 
 regions elevated into land-masses were worn down by atmos- 
 pheric abrasion, and their comminuted debris carried into the 
 adjoining oceans to form a new series of sedimentary beds. 
 Each successive series of dynamic movements would involve 
 not only this newer series, but also the older and already 
 plicated and fractured series of rocks ; and thus the structural 
 conditions are found to be the more complicated and more 
 difficult to decipher, the older the rocks in which we have 
 occasion to study them. 
 
 The rock-masses of which the earth's crust is formed possess 
 to a certain degree both rigidity and plasticity: the relative 
 degrees of these qualities may vary not only with the composi- 
 tion, association, and molecular structure of the different 
 masses, but, in the same mass, with differing conditions of heat 
 and pressure under which it exists at a given moment. Hence 
 it is impossible to determine a priori whether a given amount 
 of compression will produce plication and fracture combined, 
 or fracture alone. 
 
 In a general way we know that certain rocks are more plastic 
 than others : for instance, argillaceous rocks more than sili- 
 ceous rocks; amorphous rocks more than crystalline rocks. 
 
44 STRUCTURAL RELATIONS OF ORE-DEPOSITS. 
 
 Further, it is evident that under moderate temperatures dis- 
 tinctly stratified rocks will be more readily plicated than 
 massive or crystalline rocks ; in other words, under given con- 
 ditions the latter would be more fractured than the former. 
 
 The fracturing of rocks, moreover, takes place the more 
 readily the lighter the load upon them ; in other words, plas- 
 ticity increases with pressure. Thus, at sufficient depths below 
 the surface, or under the weight of a sufficient mass of super- 
 incumbent rocks, fracturing of the rock-mass would no longer 
 be possible, and compression would only result in some plastic 
 deformation. Heim places at 15,000 ft. the depth at which all 
 fissures sufficiently open to admit the passage of waters must 
 necessarily cease. 
 
 Heim further shows that the plasticity of a given rock-mass 
 will be greater under a slow-working pressure than under a 
 sudden shock, or under the effects of a force of rapidly-devel- 
 oped energy. Now it is a fact of observation that the elevation 
 of mountains, which is in the main the result of plication, is an 
 immensely slow movement, lasting at times through entire 
 geological periods. We can readily conceive, therefore, that 
 while, as observation shows us, under this slow-moving force 
 great thicknesses of beds have been folded together like so many 
 sheets of paper, when the limit of plasticity was reached and 
 fracture took place, that this would be a relatively rapid action 9 
 more in the nature of a sudden shock; indeed, that under such 
 enormous pressure as must necessarily exist, the movement 
 past each other of the lips of the fracture, involving hundreds 
 or even thousands of feet of rock-masses, may have produced a 
 series of violent shocks, which propagated themselves through 
 the adjoning rock-masses, and produced in them a series of 
 fractures such as we see in so-called cross-joints. According 
 to the theory that earthquakes are the relief of tension in the 
 earth's crust, this propagation of movement would resemble 
 the vibratory movement observed in modern earthquakes. 
 Such an origin for cross-joints has already been suggested by 
 W. 0. Crosby. 7 
 
 It has been objected, however, that while the propagation of 
 such vibratory movements would produce the main parallel 
 
 7 Proceedings of the Boston Society of Natural History, vol. xxii., pp. 72 to 85 
 
 (1882-83). 
 
STRUCTURAL RELATIONS OF ORE-DEPOSITS. 45 
 
 joints at right angles to the direction of movement of the wave, 
 it is not so easy to account for the correlated joints which cross 
 the primary joints, generally at a large angle. 
 
 If, however, we assume that all the rocks thus fractured were 
 under a tension which, acting more slowly, would have pro- 
 duced folds, and if this tension was not simple, but complex, or 
 acting in more than one direction at the same time, so that 
 not one, but two or more systems of folds would finally be pro- 
 duced ; then, by the crossing of these systems of folds, there 
 would result not only a plication along parallel axes, but at the 
 same time a torsion of the beds or rock-masses involved. The 
 assumption of a torsional strain, combined with that tending 
 to produce plication, admits of an almost infinite complexity of 
 rock-fractures as a product of these forces under the various 
 conceivable conditions attending dynamic movements. 
 
 The foregoing theoretical consideration of the forces which 
 may have produced .the various rock-fractures under consider- 
 ation has been purposely made very brief, and is hence possibly 
 somewhat incomplete, for the reason that in so practical a 
 science as mining geology, the outward manifestations of geo- 
 logical phenomena the effects are, in my opinion, of more 
 importance than the causes, which always remain to a certain 
 extent in the region of hypothetical conjecture, and that if one 
 becomes too much wedded to a certain theory he is in danger 
 of adjusting his facts to that theory. 
 
 I shall, therefore, insist more particularly upon the physical 
 phenomena which characterize these rock-fractures, as deter- 
 mined by actual observation, and for which, while the above- 
 mentioned hypotheses seem at present to account for them, I 
 shall be quite ready in the future to adopt any other explana- 
 tion 'that, by my own studies or by those of others, may be 
 presented as more reasonable and adequate. 
 
 Common Characteristics of Compression-Fractures There are 
 three phases of structural evidence of rock-fractures and dis- 
 placement resulting from compression, one or more of which 
 I have found to characterize the various types of fissures carry- 
 ing ore-deposits, which have come under my observation. 
 These are : 
 
 1. Striations and " slickenside "-surfaces. 
 
 2. Breccia or fragmentary material in the fissure itself, or 
 
46 STRUCTURAL RELATIONS OF ORE-DEPOSITS. 
 
 zones of crushed or broken rock-material included between 
 intersecting systems of fissures. 
 
 3. A sheeting of the country-rock parallel with the main 
 fracture ; in other words, the occurrence of a system of minor 
 fractures which divide the country-rock up into a system of 
 approximately parallel plates or sheets. The distance between 
 these parallel fractures, or the thickness of the sheets, may be 
 reckoned by inches, by feet, or by hundreds of feet, according 
 to the varying texture of the rock-masses involved, or the dif- 
 ferent dynamic conditions which have produced the fracture. 
 
 It will at once suggest itself that these are all phenomena 
 characteristic of faults. But they are also found, at times, 
 where there may be no recognizable evidence of actual dis- 
 placement of the rock-masses on either side of the fissure or 
 fracture. On the other hand, it will be equally evident that 
 fissures characterized by these phenomena can hardly be the 
 result of contraction, or shrinkage-cracks. 
 
 Striations are not confined to well-defined fissures, but are 
 found on smaller planes within rock-masses ; but in any case 
 they necessarily seem to give evidence of movement under 
 pressure, be the amount of that movement ever so small. 
 
 Fragments of country-rock are often rounded, and writers 
 upon ore-deposits are accustomed to speak of them as having 
 fallen into the fissures from the walls, and, when rounded, as 
 having become so by attrition either against the walls or 
 against each other. As regards the falling in, which seems to 
 imply a fall in a free or open space of considerable dimensions, 
 my observations have led me to consider it of rare occurrence, 
 and to infer that the fragments generally found have been pro- 
 duced rather by the rubbing or dragging of one wall against 
 the other. The greater or lesser size of the fragments would, 
 in a measure, prove a greater or less distance between 'the 
 walls, but it seems that under the enormous pressure that must 
 have accompanied these rock-fractures, the space between the 
 walls must have been more or less completely filled with attri- 
 tion-material, only part of which would be actual rock-frag- 
 ments, and the rest finely-comminuted material, which, under 
 the dissolving agency of percolating waters, would finally result 
 in more or less impure clays. The rounding of the fragments, 
 on the other hand, is readily accounted for as the action of 
 
STRUCTURAL RELATIONS OF ORE-DEPOSITS. 47 
 
 these same percolating waters, it being a well-recognized fact 
 that the decomposing action of moisture in any form acts more 
 rapidly on the corners or angles of a rock-mass than on its flat 
 surfaces, and the sharper the corner the more rapidly is it 
 eaten away. 
 
 Crushed zones are merely larger phases of the same actions 
 as produce the breccia-material, and are subject to the same 
 general laws, only differing in their greater dimensions and 
 the more irregular shape of the inclosing walls. 
 
 The sheeting of the country-rock in faulted or fractured re- 
 gions where ore-deposits abound, is a phenomenon to which 
 hitherto too little attention has been paid. Its importance as 
 a feature of fissure-veins is, however, great both from a geo- 
 logical and from a practical point of view. That it has hith- 
 erto escaped due recognition, is probably due to the prevalence 
 of the old idea that vein-deposits are necessarily the filling of 
 open fissures, and to the failure to appreciate to how great an 
 extent they are .actually the replacement of rock-material ren- 
 dered more readily accessible and attackable by the dynamic 
 movements which produced the fissure. This feature will be 
 more fully illustrated in the practical examples given later. 
 
 Before proceeding to the consideration of how far these 
 features appear in actual ore-deposits, it will be well to exam- 
 ine the typical manifestations of the above-enumerated rock- 
 fractures where their relations are best shown, independently 
 of whether they may have been mineralized or not. 
 
 Typical Rock-Fractures. The typical form of the fold-fault, 
 as observed by Heim in his studies in the Alps, and as shown 
 experimentally by Daubree in his Geologic JZxperimentale, may 
 be produced in the following way : If a given series of strata 
 are compressed into a sharp anticlinal fold by longitudinal 
 pressure, the individual strata will tend to expand or swell 
 along the axis, or in the crest of the anticline and in the bottom 
 of the adjoining syncline, while in the intermediate portions 
 the sides, or as the Germans express it, the shanks (Schenkelri) 
 of the fold they will be contracted and attenuated or drawn 
 out, as it were. When, therefore, the beds in folding have 
 reached their limits of plasticity, the fracturing will take place 
 by preference along the contracted portion; that is, on the 
 sides of the fold rather than along its axis. Such a fault, it is 
 
48 STRUCTURAL RELATIONS OF ORE-DEPOSITS. 
 
 evident, will be necessarily accompanied by marked plication 
 of the strata on either side. Faults exist in nature, however, 
 in which there is no marked plication of the strata on either 
 side, but which are quite evidently the result of folding, since 
 at one or both ends they pass into an unfractured fold. It is 
 evident, therefore, that the latter type may be undistinguishable 
 from the fissure-fault, in cases where the structure of the ad- 
 joining region is so obscured that it is not possible to determine 
 whether the fault actually passes into a fold or not. 
 
 Characteristic examples of the above faults occur in the 
 Mosquito range near Leadville, Colo., and will be found illus- 
 trated in the maps and sections of the Atlas accompanying 
 Monograph XII. of the U. S. Geological Survey. There the 
 Mosquito fault, which splits into two at its southern end, each 
 branch terminating in a fold, and to the north has been traced 
 for a distance of about 25 miles and may extend as much 
 farther, is a typical illustration of Heim's definition of the 
 fault-fold. Where the adjoining strata are exposed and have 
 not been eroded away, they are seen to be sharply folded and 
 to have once formed part of an S-fold, which has been fractured 
 along one side of the anticlinal axis or on the shank of the 
 fold. The Iron and Carbonate faults, on the other hand, 
 which, though of less extent, it has been possible to study more 
 thoroughly, owing to the many mine-openings along their 
 course, show no evidence of folding in the bending of the 
 strata immediately adjoining them on either side, which are 
 cut across by the fracture nearly at right angles to the bed- 
 ding-planes throughout the greater part of their extent. They 
 form, however, a definite part of a system of gentle anticlinal 
 and synclinal folds, and pass into an unfractured fold at either 
 end, being, therefore, properly speaking, fold-faults. 
 
 In other prominent faults in the district, such as the Ball 
 Mountain, Mike, and Pilot faults, it is not possible to trace 
 their direct connection with folds, and yet it is evident that they 
 were produced by the same general dynamic movements as the 
 others, and form part of the same tendency towards plication, 
 which, in their case, has evidently been counteracted by the 
 greater rigidity of the rock-rnasses as a whole, resulting from 
 the large proportion of igneous masses entering into their 
 composition. 
 
STRUCTURAL RELATIONS OF ORE-DEPOSITS. 49 
 
 The phenomena of striation, brecciation, and sheeting of 
 the country-rock are well seen in the Iron and Carbonate 
 faults, which are the only ones that have been explored un- 
 derground. As I have shown elsewhere, 8 these fault-planes 
 are not mineral-bearing, since the principal mineral deposition 
 in the region was accomplished before the faulting took place. 
 But in cases where the faults cut through ore-bodies, consid- 
 erable broken and ground-up vein-material has been dragged 
 into the fault-fissure, in quantity sufficient to give rich returns 
 for extraction. The brecciated character of this material is, 
 however, less readily recognized than when the fragments 
 have been cemented together by metallic minerals, as is the 
 case in many fissure-veins. The sheeting of the country-rock 
 in these two faults has apparently been confined to the side 
 of the fault opposite to that from which the pressure came, 
 and has produced what are sometimes called step-faults, the 
 movement of displacement having been partly distributed on 
 several minor planes, a hundred feet or more apart, and par- 
 allel to the main fault-plane. 
 
 The best region for studying the typical fissure-fault that has 
 come under my observation is the southwestern portion of the 
 Elk mountains, in Gunnison county, Colo. This has been a re- 
 gion of intense and repeated dynamic disturbance, accompanied 
 by enormous eruptions of a great quantity of igneous rocks in all 
 the varied forms in which they occur. Elevated glacial am- 
 phitheaters or basins, at altitudes of about 11,000 ft., whose 
 walls consist of thinly-stratified and nearly horizontal beds of 
 variegated colors, afford unusually favorable opportunities for 
 tracing the many faults, which form a complicated network 
 over a large area, and for determining the amount of displace- 
 ment produced by them, which is generally slight and meas- 
 ured by tens or hundreds of feet. Although, as seen on a 
 cliff-face, these faults seem to consist of a single plane of frac- 
 ture, it is found, when they are examined in underground 
 workings, that what might be called the fissure-plane consists of 
 a series of thin sheets of more or less altered and intensely 
 compressed and striated country-rock, generally only an inch 
 
 8 Notes on Some Colorado Ore-Deposits, Proceedings of the Colorado Scientific 
 Society, vol. ii., part ii., p. 85 (Oct., 1886). 
 
50 STRUCTURAL RELATIONS OF ORE-DEPOSITS. 
 
 or two thick. Where, as is frequently the case, these fissures 
 have been mineralized and constitute important ore-deposits, 
 the original character of the sheets is not readily apparent ; 
 but the amount of breccia, consisting ordinarily of small angu- 
 lar fragments of country-rock, cemented by vein-material, suffi- 
 ciently proves that the fissure is a fault-fissure; and, when explo- 
 rations on the strike have extended beyond the zone of miner- 
 alization, the sheets of country-rock are found to retain enough 
 of the original structure to prove their origin. Further, when 
 cross-cut drifts have been run into the country on either side, 
 a series of more or less parallel cracks or fissures are found, 
 gradually disappearing as the distance from the central fissure 
 increases. As only the ore-bearing portions of such fissures 
 are, as a rule, explored, it is evident that the fracturing and 
 the directions and extent of the fissures can be determined but 
 incompletely. Still, owing to the frequent surface-exposures, 
 a certain regularity of direction is easily detected, showing 
 that the fractures have been determined by definite series of 
 dynamic movements. Although in this particular region the 
 faults are unaccompanied by any considerable plication, yet at 
 no great distance, and nearer a center of disturbance, there 
 has been intense plication, accompanied by fold -faulting. 
 
 Similar fissure-faults, with the same phenomena of thin 
 sheeting of the country-rock, and with breccia cemented by 
 vein-material, are found in the San Juan region. Here, also, 
 the directions of the various faults follow certain systems, which 
 a thorough orographic study of the region would, doubtless, 
 enable one to connect with the dynamic movements which 
 produced them. 
 
 From these individual fissure-faults there is a gradual transi- 
 tion into the co-ordinated fractures, as a rule greater in number 
 in a given area but of less individual extent, which form a sort 
 of fractured zone with two or more prominent directions of 
 fracture, apparently of nearly contemporaneous formation, 
 which I have called compression-joints, because where I have 
 studied them in mining-districts, either by personal observa- 
 tion or from the description of others, I find one or more of 
 the evidences of compression present, viz., striation, brecciation 
 or crushed material, and sheeting of the country-rock. Such 
 complicated systems of fracture would appear to involve, as I 
 
STRUCTURAL RELATIONS OF ORE-DEPOSITS. 51 
 
 have already suggested, the action of more than one system of 
 dynamic movement; that is, of forces of compression acting at 
 the same time in several directions, and hence combining with 
 the direct plicational strain more or less strain of torsion. 
 
 The effects of such torsional strain can be best understood 
 by considering the effect of torsion alone. This is well shown 
 in Daubree's experiment upon a sheet of glass held firmly at 
 either end, and subjected to a torsional strain up to the point 
 of rupture. The following diagram, Fig. 1, showing the cracks 
 thus produced in the glass, is copied from that in his Geologie 
 Experimentale. 
 
 It is to be remarked in regard to the cracks or fissures thus 
 produced : 
 
 1. That they follow two general directions, crossing each 
 other at a nearly uniform angle. 
 
 2. That certain cracks are more prominent and fully devel- 
 oped than the others, and often consist of groups of nearly 
 parallel cracks. 
 
 FIG. 1. SHEET OF GLASS CRACKED BY TORSIONAL STRAIN (FROM DAUBREE). 
 
 3. That, among the subordinate cracks, some extend only 
 from one of these greater cracks to the other, and do not con- 
 tinue on in the same line, but at a little distance dn the one 
 side or the other, so that they might appear to have been 
 faulted or displaced by the larger crack, if one did not know 
 that all had been formed contemporaneously and by the same 
 strain. 
 
 In nature no such regularity or uniformity could be expected ; 
 and yet, when one considers the cross-joints of sedimentary 
 rocks, it is surprising to observe how much they recall the 
 lines in this diagram. In the larger joints or fractures ob- 
 served in mining-districts, the effects of direct compression 
 have been more marked, and the effects of the torsional strain 
 are probably more seen in the minor fractures, or stringers 
 and leaders, as the miners call them. Still, if one calls to 
 
52 STRUCTURAL RELATIONS OF ORE-DEPOSITS. 
 
 mind the map of a mining-district characterized by a multitude 
 of small veins, it will be found that the more detailed the map 
 arid the more thoroughly the veins have been explored and 
 represented thereon, the more regularity and uniformity in 
 their directions are shown. It must be borne in mind, however, 
 that such a map never represents the totality of the fissures in 
 the district, but only such parts of them as have been found 
 sufficiently rich to exploit for ore. 
 
 The following diagram, Fig. 2, represents the veins of a por- 
 tion of the region around Freiberg, Saxony, as given on the 
 official maps. Here two general directions are prominent, and 
 combined with them are certain directions which would appear 
 to be resultant of these two. Even more striking is the uni- 
 formity of system in the mining-districts of Cornwall, which 
 have been worked for so many years that the various fractures 
 are exceptionally well explored. 
 
 FIG. 2. VEINS IN THE ERZGEBIRGE, NEAR FREIBERG, SAXONY. 
 
 The predominance of certain directions in the lines of frac- 
 ture in these, as in almost all well-studied mining-districts, has 
 been the subject of remark, and has given rise to considerable 
 speculation ; but generally this speculation has been based upon 
 the idea that the veins were the filling of considerable open 
 fissures by mineral currents coming from some unknown source 
 below, and has been rather mineralogical than structural; that 
 is, more attention has been given to the character of the filling 
 than to the structural origin of the fissure. If all those who 
 have described mines and ore-deposits had devoted as much 
 and as intelligent study to the structural features of the regions 
 
STRUCTURAL RELATIONS OF ORE-DEPOSITS. 53 
 
 where they occur as the late von Groddeck did in the Harz, 
 we should probably be much nearer a satisfactory theory of the 
 origin and manner of formation of the ore-deposits than we are 
 at the present day. 
 
 It is evident that by a succession of dynamic movements, 
 especially when accompanied by torsional strains, an almost 
 infinite variety of fissures and passages for mineral-bearing 
 waters may be produced, and that it would therefore not be 
 possible beforehand to describe all the various structural con- 
 ditions under which ore-deposits may occur. It is only by an 
 intelligent description of such fissure-deposits as are observed 
 in nature in all parts of the world that we can get a compre- 
 hensive view of the various possibilities. Still there are cer- 
 tain conditions that suggest themselves as a result of the struc- 
 tural method of considering them that would seem to have a 
 general application. 
 
 Structural Generalizations. Extent, of Fissures. Since the 
 dynamic movements are confined to the crust of the earth, it 
 is evident that the fissures produced by them cannot literally 
 have an indefinite extent in depth, though in certain cases it is 
 very possible that this extent may be practically indefinite, as 
 it may go beyond the limits at which mining is practicable. 
 It is fair to assume that those fissures which have the greatest 
 horizontal extent will have the greatest extent in depth ; in 
 other words, that their vertical and horizontal dimensions bear 
 some sort of proportion to each other. If, therefore, as some 
 have maintained, the vein-filling has in all cases been brought 
 from some source at great depths in the earth, the 'greatest 
 fault-fissures would be expected to be the greatest and most 
 frequent ore-producers, since they would reach nearer to this 
 unknown source. 
 
 In my own experience, however, I have found rather the re- 
 verse to be the case, which, as far as it goes, furnishes an argu- 
 ment in favor of the view that the vein-material has been 
 derived from the surrounding, though not of necessity abso- 
 lutely contiguous, rocks. On the great fold-faults I have found 
 no considerable deposits of ore, and it is comparatively rare 
 that continuous deposits are found along a single well-defined 
 fault-fissure. The majority of deposits seem to occur where 
 there are a series of fissures, more or less regularly co-ordinated, 
 
54 STRUCTURAL RELATIONS OF ORE-DEPOSITS. 
 
 in which several of the series are prominently accentuated. In 
 such systems there seems to be a tendency for the rich ore- 
 bodies or bonanzas to extend in a direction which lies at an 
 angle with that of the main fissure, or to continue for a certain 
 distance along one fissure and then to pass into another fissure, 
 set off at a little distance from the first. It would seem prob- 
 able that there must be some structural reason for the concen- 
 tration of ore in this way, and that sufficiently wide and detailed 
 studies might discover this reason and thus throw some light 
 on this, at present, so obscure subject. 
 
 The practical lesson to be learned from the above phenomena 
 is that the miner should not confine his explorations to the 
 single fissure in which his ore occurs ; but when he runs out 
 of bonanza in that, he should seek a continuance of it in some 
 adjoining fissure or plane, in a direction to be determined by 
 the study of the system of the fracturing of the region and of 
 the general direction of the bonanzas. 
 
 Vein- Walls. The second generalization is in regard to the 
 walls, which have generally been considered an important and 
 almost indispensable characteristic of a true fissure-vein. The 
 typical wall which the miner considers an evidence of a strong 
 and well-defined fissure-vein is a comparatively smooth, gener- 
 ally striated, rock-plane, and frequently coated with a clay 
 selvage a band of decomposed argillaceous material which 
 itself generally shows evidence of pressure and movement. 
 From the above structural point of view of the origin of vein- 
 fissures it is evident that the character of the wall and selvage 
 is dependent on the composition of the rock and the amount 
 of displacement and pressure. The grinding of one face of 
 rock against another will undoubtedly tend to plane oft both 
 and to produce a certain amount of fine attrition-material ; but 
 this attrition-material will not necessarily be reduced to clay 
 unless it has further been subjected to the decomposing action 
 of water, which has carried off certain portions and left an 
 argillaceous residue. The extreme instance of such decompo- 
 sition is found in the muddy accumulations at the bottom of 
 caves in limestone, which are simply the less soluble residues, 
 mostly silica and alumina, resulting from the dissolution of 
 large quantities of more or less impure limestone. 
 
 These walls and selvages are a frequent accompaniment, but 
 
STRUCTURAL RELATIONS OF. ORE-DEPOSITS. 55 
 
 by no means an essential characteristic, of an ore-bearing fis- 
 sure. It is quite conceivable that one or both may be wanting ; 
 and such occurrences are not uncommon in nature. Take, for 
 instance, the veins of Butte, of which I gave a brief description 
 at a former meeting. 9 These are a series of co-ordinated frac- 
 tures or compression-fissures in a remarkably homogeneous 
 mass of granite. Apparently there has been little or no dis- 
 placement in the walls of these fissures relatively to each other ; 
 hence, but little attrition-material has been produced; and 
 for this reason and probably, also, on account of the char- 
 acter of the rock and because it was not much decomposed 
 along the fissure-planes before the advent of the ore-bearing 
 solutions no clay selvages have been formed, and the ore- 
 bearing solutions have eaten into the wall-rock to varying 
 distances, replacing it more or less completely by vein-material, 
 and leaving no definite boundaries or walls to the deposits. 
 There is no reason, however, for considering them any the less 
 true fissure-veins or less valuable ore-deposits on this account. 
 
 On the other hand, under certain conditions, instead of an 
 absence of well-defined walls, there may be so many as to mis- 
 lead the miner who depends too implicitly upon them as a 
 boundary of his ore-body. In the Gunnison region above men- 
 tioned, for instance, where, owing to the plasticity of the 
 country-rock, it has been divided along the main fracture- 
 planes into a series of very thin parallel sheets, the space 
 between these sheets has frequently been filled by quartz, 
 which thus forms a thin sheet, often so completely reproducing 
 the form of the fissure as to present a cast of the striation-sur- 
 faces. Such a sheet of quartz, when the adjoining bands of 
 country-rock have been replaced by vein-material, forms a hard, 
 well-defined wall to the ore-body, which delights the eye of the 
 honest miner and enhances in his mind the value of his 
 property. 
 
 Ore may be found as well on one side as on the other of such 
 a wall, and not infrequently is apparently confined to one side 
 for a considerable extent along the length of the vein, and then 
 is found almost as exclusively on the other side. Thus, in one 
 prominent mine in this district I found a drift run for several 
 
 9 Notes on the Geology of Butte, Mont., Trans., xvi., 49 (1887-88). 
 
56 STRUCTURAL RELATIONS OF ORE-DEPOSITS. 
 
 hundred feet in barren country, but following what was appa- 
 rently the direct continuation of the vein which had been 
 yielding a large amount of rich ore. After a change of admin- 
 istration in the mine, it was found by cross-cutting that there 
 was a continuous ore-body only from 4 to 6 ft. to one side of 
 this drift and parallel with it. In another mine in the same 
 district, which had produced a great deal of very rich ore, I 
 found that though there were frequent cross-cuts into the 
 country on the hanging-wall side, disclosing the usual systems 
 of parallel fissures, none had been made on the foot-wall side. 
 The reason given was that this foot-wall was so uniform and 
 well defined throughout the mine that it was considered useless 
 to explore beyond, since it must necessarily be the limit of ore 
 in that direction. An examination showed that there was no 
 geological reason for this assumption in the character of the 
 rock, and that it was simply one of a number of quartz-fillings 
 between two sheets of country-rock. On visiting the mine a 
 few weeks later, I was told that in the southern portion of the 
 mine, where the vein had seemed to be running out at the time 
 of my first visit, a new body of rich ore had been struck by 
 cross-cutting into the foot-wall country. 
 
 The moral is that judicious cross-cutting forms a very im- 
 portant part of vein-mining, but should be conducted with due 
 regard to the fracture-system of the adjoining country, and to 
 the evidence to be obtained as to the course followed by the 
 ore-bearing currents, or it may involve an unnecessary amount 
 of dead work. 
 
 Banded Structure. In most of the deposits of the Gunnison 
 region, referred to above, there is a noteworthy appearance of 
 banded structure parallel with the walls of the fissures. The 
 evidence of faulting and of the thin sheeting of the country-rock 
 is there so clear that the explanation at once presents itself that 
 this appearance arises from the fact that the deposits are partly 
 a filling-in of interstitial spaces, and partly a replacement of 
 thin sheets of country-rock, the differing composition of the 
 bands resulting rather from the necessary variation in the pro- 
 cess of deposition than from essential differences in the ore- 
 bearing solutions. Were one to examine there only a large 
 body of rich ore, and neglect to examine the adjoining poorer 
 deposits and to study the structural conditions of the region, 
 
STRUCTURAL RELATIONS OF ORE-DEPOSITS. 57 
 
 one might be led to adopt some of the complicated explanations 
 set forth in books on ore-deposits, such as successive reopenings 
 of the vein, to account for the conditions found, instead of the 
 simple one given above. Reasoning inversely, I am led to 
 think that much of the banded structure described in books on 
 ore-deposits might be accounted for in this way, if the deposits 
 could be re-examined with a view to determining the structural 
 evidence in favor of it. For instance, in the excellent work of 
 J. Arthur Phillips 10 there is given a diagrammatic section of a 
 vein at Cam Marth, in Cornwall, consisting of six successive 
 bands composed of quartz, with metallic minerals in some of 
 them, separated from each other and from the adjoining 
 country-rock by clay partings or selvages. The explanation 
 there given to account for this condition of things is, that it is 
 " a fissure that has been several times reopened ; " and the 
 author says, " It will be observed that each reopening has been 
 attended by an amount of grinding action between the walls 
 sufficient to produce a clay parting of considerable thickness." 
 This explanation involves so much that is geologically improb- 
 able that I feel convinced that it is not the true one, and that 
 some condition of things analogous to that described above 
 might be found on examination of the mine itself. The clay 
 parting might prove to be a more or less completely decom- 
 posed band of country-rock ; for it is difficult to conceive that 
 clay could be produced by the grinding of quartz on quartz. 
 In reading such descriptions one has to bear in mind that in 
 making a diagrammatic section one is liable, consciously or 
 unconsciously, to bring out strongly points that are in favor of 
 the explanation one has in mind, and to neglect those that are 
 opposed to it. That there may be repeated or continued move- 
 ments along the same fracture-plane cannot be denied, but, as 
 will be argued later, one should not resort to such explanations 
 for phenomena that can be accounted for otherwise. 
 
 Crushed Zones. Thus far we have been considering mainly 
 the sheet-like bodies deposited along fissures having a generally 
 parallel direction. But cases must also occur where the sys- 
 tems of rock-fracture intersect each other, and under suitable 
 conditions considerable portions of the country-rock included 
 
 10 A Treatise on Ore-Deposits, p. 48 (1884). 
 
58 STRUCTURAL RELATIONS OF ORE-DEPOSITS. 
 
 between such intersecting fractures may be broken up or 
 crushed to such an extent as to admit a relatively free passage 
 of percolating waters. Where such waters are mineral-bear- 
 ing, the interstices between the fragments will offer spaces for 
 the precipitation of their contents, or where the rock is readily 
 soluble the fragments themselves may be replaced by vein- 
 material. The forms of ore-bodies thus deposited may evi- 
 dently present much greater variety and irregularity than those 
 deposited along single or parallel fissure-planes. J. S. Curtis, 
 in his memoir on the Eureka district, 11 gives a detailed de- 
 scription of the extremely complicated and irregular zones of 
 crushed limestone to which the ore-deposits there are practi- 
 cally confined. 
 
 Where three or more nearly vertical fracture-planes inter- 
 sect each other near the same point, the prismatic body of rock 
 included between these intersections may be so crushed and 
 broken as, in a district rich in mineral-bearing solutions, to 
 give rise to what are generally known as chimney-deposits. 
 Where the fracture-planes are merely joints along which there 
 has been but little movement, and consequently no clay sel- 
 vages have been formed, the ore-solutions will eat out into the 
 rock in such a way that the ore-chimney may appear to have 
 a rounded instead of an angular horizontal section, and the 
 fracture-planes themselves may have become, by the decompo- 
 sition of the adjoining country-rock, so obscured as to be with 
 difficulty traced in the immediate vicinity of the ore-body. 
 Instances of deposits to which this origin may be ascribed are 
 the Bull-Domingo and Bassick mines in the Silver Cliff dis- 
 trict, and the Yankee Girl mine in the San Juan region of 
 Colorado. 
 
 The first-named deposit occurs in Archaean rocks, traversed 
 by a dike of compact syenite which in places forms one bound- 
 ary of the ore-body. The ore is mainly galena, which consti- 
 tutes the cementing-material of fragments of the country-rock 
 resulting from the movement of displacement. These frag- 
 ments are mostly of gneiss, and as this rock is readily decom- 
 posed by aqueous solutions, the fragments are generally 
 rounded ; the few fragments of the less readily attackable sy- 
 
 11 Monograph VII., U. S. Geological Survey (1884). 
 
STRUCTURAL RELATIONS OF ORE-DEPOSITS. 59 
 
 enite, however, retain in great degree their original angular 
 form. 
 
 The deposit of the Bassick mine is a nearly vertical chimney 
 of somewhat square or lozenge-shaped outline, which has been 
 explored to a depth of about 1,100 ft. from the surface. It 
 occurs in an andesitic breccia, composed of angular fragments 
 of various sizes and forms cemented together by material of 
 essentially the same composition as the fragments. This ce- 
 menting-material, probably by reason of its later consolidation, 
 has been more readily attackable than the fragments, for the 
 ore has replaced it, forming concentric layers around the frag- 
 ments, whose angles have become rounded during the process 
 of deposition. Here the fragments were original and not 
 necessarily produced by the dynamic movements, which prob- 
 ably resulted in a simple fracturing of the rock without much 
 displacement. 
 
 In the Yankee Girl there are several chimneys in which the 
 ore occurs. They are of elliptical outline, the longer axis cor- 
 responding in direction with a main system of fractures run- 
 ning through the region. Although the striated surfaces of 
 these planes show that there has been movement along them, 
 there is but little evidence left of actual brecciation of the 
 country-rock, the ore-solutions having completely replaced the 
 andesitic country-rock between the fracture-planes which ad- 
 mitted them. In places a siliceous skeleton is left, the basic 
 constituents being replaced by vein-materials; in other places 
 a solid body of metallic minerals is found, while the country- 
 rock adjoining the body of pay-ore is impregnated to a consid- 
 erable distance with low-grade sulphurets. 
 
 Repeated Movements along Fissure-Planes. It is a well-recog- 
 nized fact of structural geology that in successive dynamic 
 movements in the same region there will be a tendency for 
 fractures to follow already T determined planes of fracture. Fur- 
 thermore, it appears that the faulting of a rock-mass is not 
 necessarily a geologically instantaneous movement, but that 
 the displacement may continue for some time after the first 
 fracture has been determined, probably dying out very gradu- 
 ally. Some such continued movement seems necessary to give 
 time for the reduction by the action of water of the attrition- 
 material to the clayey condition in which it is often found. 
 
60 STRUCTURAL RELATIONS OF ORE-DEPOSITS. 
 
 We may expect, therefore, to find evidence in large fissures of 
 repeated movements. In the Comstock lode, for instance, 
 which G. F. Becker 12 has so well demonstrated to be a great 
 fault-fissure, accompanied by sheeting of the country-rock on a 
 grand scale, the crushed and sugary condition of the quartz,, 
 which in the fissure has replaced the included masses of coun- 
 try-rock, can hardly be explained, except by movement along 
 the fault-plane subsequent to this replacement, though per- 
 haps prior to the final completion of the ore-deposition. 
 
 On the other hand, it is easy to conceive that the healing of 
 a fissure, as we might regard the filling-in of its interstices by 
 vein-material, might make it better able to resist fracture than 
 it was before, and a second fracture in such a case would not 
 necessarily follow the already-determined plane. Moreover, if 
 we recall the diagram given on p. 51, showing the fractures 
 produced by torsion in a sheet of glass, it will be seen that 
 cross-fractures, and even apparent displacement of one fracture 
 by another, may be produced by one and the same strain. 
 Hence, in studying a system of fissures, one must not too 
 hastily conclude that each direction of fracture means a distinct 
 movement, or even that displacement of one fissure by another 
 necessarily proves that the latter was produced by a distinct 
 and later movement; to be sure of this, some of the other 
 evidences of movement must be found. 
 
 The famous Ontario mine in Utah affords an excellent in- 
 stance of a strong fault-fissure deposit in a region which has 
 been subjected to repeated dynamic movements, associated 
 with successive intrusions of eruptive rock, and illustrates the 
 above-mentioned points. I had intended to submit detailed 
 plans of the underground workings of this mine, drawn to 
 scale, with the geological data indicated thereon, but find that 
 the notes gathered somewhat hastily during my visit of last 
 summer are not sufficiently complete for this purpose. I shall 
 therefore describe, as clearly as I can in words, the character- 
 istic structural features of the deposit. 
 
 It occurs in distinctly-bedded quartzites of middle Carbon- 
 iferous age, which dip about 20 to the northward and strike 
 here nearly east and west. These rocks are traversed by nu- 
 
 12 Geology of the Comstock Lode, Monograph TIL, U. S. Geological Survey (1882). 
 
STRUCTURAL RELATIONS OF ORE-DEPOSITS. 61 
 
 merous bodies of eruptive porphyry, some in the form of dikes, 
 others of irregular shapes. But few appear at the surface in 
 the immediate neighborhood of the mines; they are mostly 
 disclosed by the underground workings, many of the dikes 
 having a direction parallel with the vein-fissure and sometimes 
 forming one of its walls for considerable distances. An older 
 dike is faulted by the vein-fissure. 
 
 The vein-fissure has a somewhat curving direction, running 
 about east and west, or parallel with the strike of the forma- 
 tion, in the eastern part of its course, and bending towards the 
 southwest in the west half. Its dip, however, is much steeper 
 than that of the quartzites, being from 45 to 50 north, in- 
 stead of 20, so that it cuts these at an angle of from 25 to 
 30. In the western part of the mine it is a double fissure, or, 
 as the miners express it, there are two veins, a north and a 
 south one. These are connected by what the miners call 
 " cross-courses," which are smaller, co-ordinated, and nearly 
 parallel fractures, forming an acute angle about 30 with 
 the main fissures. These are regarded there, in accordance 
 with generally-received ideas, as a distinct system of fractures 
 formed at a different time from the main fissure. I find no 
 geological evidence of this, however, either in the structural 
 conditions or in the composition of the vein-material. 
 
 The fissures show plentiful evidence of movement in stria- 
 tions and crushed country-rock, the ore being a filling-in of the 
 interstices between the quartzite fragments, and perhaps a 
 partial replacement of the same. The principal fissure con- 
 sists in places of a zone of broken quartzite, sometimes over 
 100 ft. wide, the ore being distributed in seams along the 
 boundaries of this zone and crossing it along a somewhat 
 irregular series of planes, but in which a certain co-ordination 
 of system can be traced. 
 
 Three distinct series of dynamic movements can be traced in 
 the structural condition of this mine. The first is proved by 
 the existence of a narrow dike of older porphyry, crossing at 
 right angles the western part of the vein-fissures, where the 
 two members are about 600 ft. apart. This is locally called 
 the trap dike, from its somewhat darker color than the other 
 porphyry bodies. By the second series of movements the 
 vein-fissures themselves were produced and this trap dike was 
 
62 STRUCTURAL RELATIONS OF ORE-DEPOSITS. 
 
 faulted and displaced. On the 600-ft. or drain-level of the 
 mine this displacement can be observed in each of the principal 
 fractures. The lateral or horizontal movement is about 40 ft., 
 and, as the striation-surfaces across the face of the dike are 
 inclined at an angle of about 45 with the horizon, it may be 
 assumed that the vertical movement was of the same amount. 
 The third dynamic movement is shown by what is locally called 
 the " dislocating fissure," which runs in the same general 
 direction with the western part of the vein, and on the drain- 
 level is intermediate between the two veins, cutting and dis- 
 placing the cross-fissures. 
 
 There are also large faults in the country-rock at both ends 
 of the workings, which now have a linear extent along the 
 vein-fissure of about 6,000 ft. I had not time to determine de- 
 finitely to which period of movement these last faults belong. 
 
 A careful and accurate study of the structural relations of 
 this most important mine, of which the above is only a hasty 
 glimpse, gathered during a couple of visits to a part only of 
 the underground workings, would form a most valuable con- 
 tribution to our knowledge of vein-structure. 
 
 Another mine recently visited by me, whose structural condi- 
 tions seem peculiarly instructive, is the Queen of the West 
 mine, near Kokomo, in the Ten-Mile district of Colorado. ' It 
 is situated on the steep southeast face of a shoulder of Jacque 
 mountain, and the vein-fissure runs nearly parallel with this 
 slope, or in a northeasterly direction, and has been explored to 
 a length of about 2,000 ft. It stands nearly vertical, thus 
 crossing about at right angles the sedimentary beds in which 
 it occurs, and which have a slight dip eastward, or down the 
 slope of the hill. These beds consist of sandstone, rather rich 
 in feldspar, some shaly beds, and intrusive sheets of porphyry 
 generally conformable with the stratification of the sedimentary 
 beds. 
 
 The faulting of these rocks has taken place not along a 
 single plane, but along a series of parallel and closely con- 
 tiguous planes. In other words, by the dynamic movement 
 the country-rocks have been divided into thin sheets, each of 
 which has moved past the other a certain distance, and in the 
 central part of the fissured zone the interstices between the 
 sheets have been filled with vein-material and the sheets them- 
 
STRUCTURAL RELATIONS OF ORE-DEPOSITS. 68 
 
 selves decomposed, impregnated, and to a greater or less extent 
 replaced by it. There results a condition of things which is 
 extremely puzzling for the miner who expects to find his ore 
 between well-defined walls. Walls there are in abundance, 
 and of excellent definition at times ; but no one wall can be 
 followed continuously for any great distance. Experience has, 
 therefore, taught those who are managing the mine, while they 
 follow in their main drifts or levels as nearly as possible the 
 center of the mineralized zone or vein, to run frequent and ex- 
 tended cross-cuts on both sides of this central drift, which have 
 disclosed ore-bodies running parallel with it, now on one side, 
 now on the other, and often from 15 to 25 ft. distant from it. 
 The longer cross-cut drifts, which have been run 30, 50, or 
 even 100 ft. into the adjoining country-rock, disclose a series 
 of parallel fissures, in general farther apart as the distance 
 from the central drift increases. Although mostly barren of 
 pay-ore, they always give evidence of a certain amount of 
 mineralization : sometimes they are filled by a vein of massive 
 crystalline calc spar from a few inches to a foot in thickness. 
 In the portion above the water-level, owing to the secondary 
 decomposition of both ore and country-rock, and to the diffu- 
 sion of metallic oxides which have stained the whole, it is often 
 difficult to recognize whether partly-replaced portions of the 
 vein-material were originally sandstone or porphyry. The out- 
 crops of no less than four sheets of the latter rock have been 
 traced on the surface ; but, owing to the complicated move- 
 ments along the fissured zone, there would appear at first 
 glance to be many more there; for not only do the walls 
 change from sandstone to porphyry and vice versa, in alternate 
 levels, but on one and the same level one finds these rocks 
 alternating with each other in an apparently unaccountable 
 manner in either wall. One can conceive of such a thing as 
 resulting from the movements described above, combined with 
 the gentle inclination of the beds ; but to represent it accu- 
 rately on paper would require most full and accurate surveys 
 and detailed studies along every drift, map in hand. 
 
 A second and apparently quite recent dynamic movement is 
 evidenced by a faulting of the vein-fissures in the upper part of 
 the mine. The displacement is slight in amount, and, what is 
 rather unusual, it is along a nearly-horizontal plane. As this 
 
64 STRUCTURAL RELATIONS OF ORE-DEPOSITS. 
 
 plane dips gently east, it is probable that it is a movement 
 along a bed of decomposed shale, rendered slippery by the 
 percolating of surface-waters. 
 
 Similar horizontal faults along stratification-planes were ob- 
 served by me in some of the gold-veins of the north slopes of 
 Mt. Guyot, east of Breckenridge, Colo. By these the veins are 
 faulted in a series of gently-inclined steps, only a few feet wide, 
 the movement following the. stratification-planes. The veins 
 themselves are narrow cracks in a dense blue-black argillaceous 
 shale of Cretaceous age. Owing to the insoluble character of 
 the country-rock, there has been comparatively little replace- 
 ment of it by the mineral-bearing solutions. Sulphurets of 
 iron and gold have been deposited in narrow fissures, seldom 
 over an inch thick, and by secondary decomposition the iron is 
 oxidized and the gold left in the form of leaf- or wire-gold. 
 Sometimes a mat of interwoven wires of gold, an inch thick and 
 larger than the palm of the hand, is found. Small quantities 
 of gold have been deposited along the minute natural joints of 
 the shales also, so that extraordinarily rich placers have re- 
 sulted from their disintegration and abrasion by atmospheric 
 agents. 
 
 Many more instances of different structural conditions might 
 be presented did space and time allow ; but I think the above 
 are sufficient to illustrate the main proposition which I wish to 
 lay down, namely : that careful structural study of the district 
 in which a mine occurs and of the manner in which the water- 
 passages were formed, which originally gave access to the 
 mineral-bearing solutions, is of the greatest importance to the 
 mining engineer in his determination of the probable extent 
 and value of a deposit and of the best method of exploiting it. 
 Hence, that he must be something of a structural geologist, as 
 well as a technical mining engineer. 
 
GEOLOGICAL DISTRIBUTION OF THE USEFUL METALS. 65 
 
 No. 3. 
 
 Geological Distribution of the Useful Metals in the 
 United States. 
 
 BY S. F. EMMONS, WASHINGTON, D. C. 
 
 {Chicago Meeting, being part of the International Engineering Congress, August, 1893. 
 Trans., xxii., 53. Here reprinted in extract only.) 
 
 THE first paper which appears in the published Transactions 
 of our Institute is that read by our respected Secretary at its 
 first meeting in Wilkes-Barre, in May, 1871. It is entitled 
 The Geological Distribution of Mining Districts in the United 
 States, and presents a brief but masterly review of what was 
 known of the distribution of our deposits of useful minerals, 
 particularly the metals, not only from a geographical but from 
 a geological stand-point. 
 
 At the request of Dr. Raymond, I agreed, somewhat hastily, 
 perhaps, to write for this occasion a brief sketch of the geo- 
 logical distribution of the deposits of the useful metals in this 
 country, in the light of the increased knowledge of the present 
 day. In the time given no personal investigation was possible, 
 and as it was therefore out of the question to attempt to make 
 anything that could be considered an original contribution to 
 the history of our ore-deposits, I have been obliged to limit 
 myself to an examination of such published data within my 
 reach as bore upon this subject, and could be consulted in the 
 brief time I have been able to give to it. Had the geological 
 investigations undertaken by the Tenth Census been continued 
 systematically by the United States Geological Survey or by 
 the Eleventh Census, it might have been possible to make a 
 fairly-complete review of the subject. As it is, the principal 
 result of my examination * has been to show how very unequal 
 
 1 It would occupy too much space to give a complete list of the various papers 
 and authors consulted in this examination, and it must suffice to say that they 
 have been found for the most part in the publications of the following organiza- 
 tions : Tenth and Eleventh Census, Director of the Mint, various United States 
 and State Geological Surveys, American Institute of Mining Engineers, Colorado 
 Scientific Society ; and in the American Journal of Science, American Geologist, 
 Engineering and Mining Journal, Zeitschrift fur praktische Geologic, etc. 
 
 5 
 
66 GEOLOGICAL DISTRIBUTION OF THE USEFUL METALS. 
 
 and in many directions extremely meager are the data of any 
 kind that are available, and to demonstrate the great need 
 that exists for a systematic investigation of this important sub- 
 ject by some scientific organization, for its field is too vast to 
 be covered by any single individual, and such an investigation 
 will be of little permanent value unless carried out on some 
 uniform plan by which the relative accuracy of its results may 
 be assured. 
 
 The utmost that I can hope, therefore, for the very imper- 
 fect, and from a statistical stand-point possibly somewhat inac- 
 curate, review here presented, is that it may offer to other 
 workers in the field a suggestion of lines of investigation that 
 may be profitably pursued in the future. 
 
 In the 22 years that have elapsed since Dr. Raymond's paper 
 was written, many important contributions have been made to 
 our knowledge of the geological structure of the continent, but 
 a great part of these contributions, especially in late years, 
 have been. rather in the line of modifications and reversals of 
 preconceived theories, than in the firm establishment of new 
 ones. We seem now to have removed most of the unstable 
 stones from the foundation of our geological knowledge, and 
 to be nearly ready to build up a permanent structure in the 
 immensely enlarged field that progress in various lines has 
 opened to us. In like manner the special study of -ore-deposits 
 and of their relations to geological structure, which had hitherto 
 been rather neglected by field-geologists, has in the last decade 
 received more attention, though perhaps not as much as it de- 
 serves ; many false conceptions have been cleared away, and 
 important progress has been made towards a more rational 
 method of correlating their phenomena. 
 
 In the realm of eruptive or igneous rocks, the great change 
 that has come about has been the gradual abandonment of the 
 theory that the mineralogical or structural character of the rock 
 is a criterion of its age. It is no longer a necessary conclu- 
 sion, for example, that because a rock is a trachyte, rhyolite, 
 or basalt, it is of Tertiary or later age. Well-defined rocks of 
 types formerly classed as Tertiary have been found to be as old 
 as Cambrian, and the petrographical character of a rock is now 
 admitted to be dependent on other causes besides geological 
 age. It still holds good that most of the so-called volcanic 
 
GEOLOGICAL DISTRIBUTION OF THE USEFUL METALS. 67 
 
 rocks are of Tertiary or recent eruption, but many crystalline 
 rocks, actually granitoid in structure, are also of Tertiary age, 
 and it is now necessary for the geologist -to determine the age 
 of the various eruptives of each district by their relations to 
 sedimentary rocks of known age. 
 
 From the internal structure of the eruptive rock, whether 
 more or less completely crystalline, one can judge whether it 
 has consolidated at considerable depths and under the pressure 
 of great weight of superincumbent rock-masses, hence very 
 slowly, or at or near the surface and with comparative rapidity. 
 In many cases this furnishes a further aid in the determination 
 of the relative age of different varieties of eruptive rock occur- 
 ring in a given region. 
 
 As regards the origin of eruptive rocks and the determina- 
 tion of the natural order of succession of the many types dis- 
 tinguished by their different chemical and mineralogical com- 
 position, most of the theories hitherto held are gradually being 
 discarded or merged into what may be called the theory of 
 differentiation of igneous magmas, which is now being worked 
 out by the more advanced petrologists in this country and in 
 Europe, and which promises to throw important light upon 
 the origin of ore-deposits also. It proceeds from what is 
 known as Soret's principle, that in a cooling solution of a salt, 
 the salt will concentrate in the parts of the solution which cool 
 first, and reasons that in a molten rock-magma a similar sepa- 
 ration or differentiation of substances may take place. For in- 
 stance, it has long been observed that in eruptive dikes of 
 moderate dimensions, those portions of the dike adjoining the 
 walls, which, when the matter forming the dike was injected, 
 may be supposed to have been relatively cold, have a finer- 
 grained texture than the interior of the dike, and in certain 
 cases there is a'concentration of the more basic minerals com- 
 posing the general mass in the outer zone or in different parts 
 of the rock-mass. It is assumed that on a larger scale the 
 different varieties of eruptive rock which belong to one general 
 period of eruption in a given district and are, so to speak, con- 
 sanguineous, proceed from one general molten magma in the 
 depths of the earth ; and that in this magma a chemical and 
 mineralogical differentiation takes place by virtue of which 
 each successive eruption of igneous rocks differs in character 
 
68 GEOLOGICAL DISTRIBUTION OF THE USEFUL METALS. 
 
 from the one which has preceded it, according to laws not yet 
 fully made out, but which, according to the preponderance of 
 chemically acid or basic material, under varying conditions, 
 produce in the erupted rock a corresponding preponderance of 
 acid or basic minerals. 
 
 On the other hand, considerable advance has been made in 
 the classification of the crystalline rocks, which were formerly 
 all grouped indefinitely as Archsean. More detailed and 
 systematic field-studies in the areas occupied by typical series 
 of crystalline rocks have shown that there are several series 
 that can be distinguished as originally sediments made up of 
 debris of older series, with a greater or less proportion of erup- 
 tive material, in which there is evidence of the former existence 
 of organic life, and which are older than the oldest known 
 Cambrian beds, and younger than Archaean, the latter term 
 being limited to non-clastic rocks, in which there is no evidence 
 of life. Petrological investigation, in the light of the most ad- 
 vanced studies in this branch of geology, has shown the enor- 
 mous capabilities of metamorphism, in that a crystalline and 
 more or less schistose product may result from the alteration 
 of either sedimentary or eruptive rocks, the original form of 
 which may be entirely undeterminable if such rock cannot be 
 traced continuously in the field to some less altered condition 
 in which sufficient traces of its original character can be found 
 to admit of its satisfactory determination. As a result of these 
 investigations, so much discredit has been thrown upon the 
 classification and subdivisions of Eastern crystalline rocks by 
 Hunt and his school, which were based on petrological distinc- 
 tions now shown to be unessential and local in their character, 
 that, until the areas covered by them have been systematically 
 and carefully studied, the relative age of different parts of the 
 series must remain a matter of doubt. In a few cases, fossil 
 evidence has been found in the Appalachian areas to show that 
 certain crystalline beds are altered sediments of Cambrian or 
 later age. In others, remains of organic life have been found 
 which are older than any known Cambrian forms. In most 
 cases, however, it can only be determined on stratigraphical 
 grounds or lithological evidence that the rocks in question are 
 older than any known Cambrian, and younger than the funda- 
 mental complex of non-clastic crystallines for which the term 
 
GEOLOGICAL DISTRIBUTION OF THE USEFUL METALS. 69 
 
 " Archaean" is still retained. To these rock-series the general 
 designation "Algonkian" has been given. 
 
 The Algonkian, as thus defined, necessarily includes a great 
 many rock-series in different parts of the continent, which, in 
 the absence of palseontological evidence, cannot be correlated 
 in age, and whose relative succession must be determined in 
 each geological province separately and by itself. They have 
 been thus far systematically studied only in the Lake Superior 
 region, where the new classification was first proposed by Irving 
 and Van Hise. Here they consist of an aggregate thickness of 
 over 60,000 ft. of rocks, in which three general subdivisions, 
 separated by great unconformities or time-breaks, have thus 
 far been recognized, the Keweenawan or copper-bearing series, 
 which consists of sandstones, conglomerates, lavas, and tuffs, 
 being the upper, and resting unconformably upon the two great 
 iron-bearing series, the Upper and Lower Huronian, which in- 
 clude all the at present economically important iron-deposits of 
 the region. Two, and possibly three, series of Algonkian rocks, 
 each of great thickness, and some showing a large development 
 of eruptive rocks, have been recognized in the Eocky moun- 
 tains, but for the Appalachians, where geological study is 
 rendered more difficult by the intense complications of struc- 
 ture, great metamorphism, and deep covering of weathered 
 material and soil, it can only be said as yet that certain rocks 
 hitherto called Archaean are certainly either altered^Palseozoic 
 or Algonkian, while of the greater part it remains for further 
 study to determine whether they belong to either of these 
 systems or may properly be classed as Archaean. 
 
 Genesis of Iron-Deposits. 
 
 It has always been a matter of wonder to the geologist, as 
 well as to the layman, how such enormous concentrations of 
 metallic minerals as occur in the great iron-mines could be 
 brought about, and whence their materials could have been 
 derived. In the light of the more exact studies of modern 
 times, the easy reference of such knotty questions to the " un- 
 known source in depth " is no longer available, especially since, 
 in the case of the Lake Superior deposits, the last stronghold 
 of the little band of geologists who still maintained the erup- 
 
70 GEOLOGICAL DISTRIBUTION OF THE USEFUL METALS. 
 
 tive origin of iron-ores, the careful and systematic researches 
 of Irving and Van Hise have demonstrated that the supposed 
 eruptive bodies of iron oxide have been deposited from aque- 
 ous solutions as replacements of carbonates, and that the 
 eruptive contact-phenomena result from the fact that the in- 
 closing rocks, instead of the iron-ores themselves, are of 
 igneous origin. 
 
 That iron-minerals, such as pyrite, magnetite, and ilmenite, 
 are frequent and almost universal constituents of eruptive 
 rocks, is well known, but they occur as original constituents 
 of the rock, that have formed within its mass more or less con- 
 temporaneously with the other mineral constituents, and not as 
 later injections into an already consolidated rock-mass ; whereas, 
 critical studies of existing ore-deposits have so universally 
 proved them to be of distinctly later origin than the inclosing 
 rocks, that the burden of proof lies upon those who would main- 
 tain a contemporaneous origin for any particular deposit. The 
 truly scientific method in the study of such questions, at the 
 present day, is the reverse of that which was followed in the 
 early days of geology, when, after the observation of a few 
 isolated facts, some great geological mind was led to a general 
 theory, and humbler followers were only too apt to do mild 
 violence to nature in order to make her facts conform to it. It 
 accumulates, year after year, a multitude of facts of patient ob- 
 servation, gupported by studies with the microscope and in the 
 laboratory, avoiding general theories, an^. only making such 
 deductions in regard to local conditions as are supported by the 
 overwhelming evidence of facts. 
 
 Although we are yet far from having a sufficient accumula- 
 tion of facts bearing upon the origin of iron-ores to justify the 
 putting forth of any general theory, it may be allowable in the 
 present case to indicate the lines of research to which the facts 
 that have lately been accumulated seem to point as promising 
 the most remunerative results. 
 
 A great deal of light has been thrown upon the manner of 
 formation of iron-ore deposits by the researches of Irving and 
 Van Hise in the Lake Superior region, and by the discussion 
 of replacement of limestones by iron-ores in general by J. P. 
 Kimball. By both, the process of formation of workable iron- 
 ore deposits is regarded as a concentration by the agency of 
 
GEOLOGICAL DISTRIBUTION OF THE USEFUL METALS. 71 
 
 percolating waters, such concentration being influenced by 
 physical or structural conditions, and localized, it may be, by a 
 pre-existing nucleus of iron-bearing minerals as original con- 
 stituents of the rock. The deposition is considered to be in 
 very large degree a metasomatic replacement of the rock-mate- 
 rial, and only to a very limited extent a deposition in pre-exist- 
 ing open cavities. 
 
 For the Marquette region, it is found that though the Lower 
 Huronian carried iron originally, the concentration into work- 
 able deposits, of both this and the Upper Huronian series, was 
 brought about subsequent to folding and erosion, and that 
 hence the age of the deposits as such is Upper Huronian or 
 later. Evidence is also found that the deposition was a second- 
 ary concentration from waters percolating downward along 
 the paths of great water-channels until stopped by some im- 
 pervious base. The original condition of the ore is regarded 
 as probably iron carbonate, though it is admitted that this may 
 have been a replacement of calcium carbonate. 
 
 In the Palaeozoic limestones and shales of the Appalachians, 
 the iron-bearing solutions appear in most cases to have been 
 also downward-going currents, or water sinking from the sur- 
 face under the influence of gravity, rather than hot ascending 
 solutions. The original mineral was the carbonate or the sul- 
 phide of iron (pyrrhotite or pyrite), and instances are adduced 
 where the limestones carry in their mass over 2 per cent, of 
 iron carbonate, and in other cases pyrite is known to occur in 
 about the same proportion. Whether these minerals were 
 chemically or mechanically deposited with the limestones or 
 were introduced subsequently remains to be determined, but it 
 appears improbable that deposits (of sufficient size to consti- 
 tute workable deposits) were formed simultaneously with the 
 inclosing rocks by chemical precipitation from sea- waters. 
 
 If it be admitted, then, that our workable deposits of iron- 
 ore are mainly concentrations of iron-minerals already dissemi- 
 nated in sedimentary beds, and that these concentrations have 
 occurred in different forms and places according to varying 
 local structural Or chemical conditions, it still remains to be 
 determined what was the original source of the iron in different 
 regions, and why the concentrations are so much greater in one 
 place than in another. 
 
72 GEOLOGICAL DISTRIBUTION OF THE USEFUL METALS. 
 
 A line of investigation that seems to promise interesting 
 results is suggested by recent researches by Swedish geologists 
 on the formation of concentrations of titaniferous ore by the 
 so-called differentiation process in basic eruptive magmas. In 
 Sweden and Norway, according to them, actually workable 
 deposits of titaniferous iron have been formed by differentia- 
 tion within the eruptive magmas of labradorite, hypersthene, or 
 olivine rocks. Van Hise had already suggested for the titanif- 
 erous magnetites of the eruptive gabbro of Lake Superior that 
 in the crystallization of these rocks, before the magma had 
 solidified, magnetite, which is one of the early minerals to 
 separate, had slowly settled to the base of the mass by virtue 
 of its superior specific gravity. But it is still questionable 
 whether in this differentiation process gravity is a controlling 
 influence, since in most observed cases it is evident that some 
 other force must have influenced the concentration. Metallic 
 concentrations in eruptive rocks have been observed before, 
 the most remarkable of which is the body of metallic iron at 
 Ovifak in Greenland. Although in these cases the ores may 
 properly be said to be of eruptive origin, it may still be doubted 
 whether their concentration as workable deposits is not due, 
 in a measure at least, to secondary action, as has been observed 
 in the case of the Lake Superior gabbros. 
 
 While, therefore, one may not necessarily expect to find 
 economically-valuable deposits in such rocks, the question 
 naturally suggests itself whether the occurrence of large areas 
 of older basic eruptives, which in some parts contain a rela- 
 tively large proportion of iron-bearing minerals, may not fairly 
 be considered to be an indication that neighboring sedimentary 
 beds may contain large concentrations of iron-ores, which have 
 been derived from them. Where such basic eruptives are older 
 than the beds, this derivation would be mainly mechanical, the 
 ores being sediments resulting from the abrasion of the erup- 
 tives, more or less concentrated according to varying condi- 
 tions of sedimentation. Where the eruptives are younger and 
 have broken through or overflowed the sedimentary beds, the 
 derivation would be mainly chemical, through leaching-out 
 and redeposition by the agency of percolating waters. 
 
 While there seems to be some genetic connection between 
 the greatest concentrations of iron-ore and considerable devel- 
 
GEOLOGICAL DISTRIBUTION OF THE USEFUL METALS. 73 
 
 opments of ancient basic eruptives, important deposits also 
 occur where no such relation can be traced. The frequent 
 association of iron-deposits in the West with large bodies of 
 eruptive diorite, suggests that though the very basic rocks 
 would naturally afford the greatest amount of iron, even a rela- 
 tively acid rock, like diorite, may contain concentrations by 
 differentiation, which have yielded to the action of percolating 
 waters and thus allowed their basic constituents to be trans- 
 ferred to easily-soluble rocks like limestone. 
 
 Since water is the principal agent in the final concentration 
 of ore-deposits, it is important in searching for them to study 
 the physical conditions which will favor its ready action both 
 in taking up and in throwing down. In the Northwest, Van 
 Hise has found an impervious basement a general favoring 
 condition. This assumes downward percolation, but within 
 the crust of the earth the circulation of waters may be in any 
 direction, according to local conditions. It may possibly be 
 safe to assume that iron-ores which occur mainly as oxides- 
 would have been deposited from oxidizing waters or those 
 which come recently from the surface, and that pyritous ores 
 would be more likely to bespeak a derivation from subterra- 
 nean waters. Types of the former are furnished by the Lower 
 Silurian ores which pass in depth into ferriferous limestone, 
 and are apparently a concentration due to leaching by surface- 
 waters, in which other minerals have been removed in greater 
 proportion than the iron oxide. The so-called gossan-ores oc- 
 curring in the eastern or metamorphic belt of the Appalachians, 
 and which pass into pyritous ores in depth, would appear to be 
 good types of the latter class. 
 
 Much remains yet to be done in the study of the structural 
 relations of iron-ore deposits. One of the interesting problems 
 is furnished by the line of magnetic deposits occurring, in 
 Pennsylvania and southward, in limestones at the contact 
 of Mesozoic sandstones, and frequently associated with trap 
 dikes. If this prove to be a line of displacement, as there 
 seems to be reason to assume, it would afford a natural water- 
 channel for the collection of iron-bearing waters from various 
 series of iron-bearing rocks, which would preferably collect in 
 limestones, and more readily from their broken edges. "Whether 
 the function of the trap has been to furnish heat for magneti- 
 
74 GEOLOGICAL DISTRIBUTION OF THE USEFUL METALS. 
 
 zation of the iron oxides, as has been frequently assumed, or 
 to interrupt the ore-bearing currents and thereby induce pre- 
 cipitation, may well be the subject of further investigation. 
 
 There is reason to assume that the concentration of iron- 
 ores in the more southern parts of the Appalachians, especially 
 in the extremely complicated regions of the Carolinas, Ten- 
 nessee, Alabama, and Georgia, will be found to have more or 
 less intimate structural relations with the many fault-zones 
 that abound there. 
 
 A careful study of the magnetite-deposits in Colorado is 
 likely to throw some light upon the true genetic connection, 
 if any exists, between the occurrence of this oxide and the vi- 
 cinity of eruptive bodies. In the light of present knowledge 
 it would appear that the iron-ores occur as magnetite in the 
 vicinity of large bodies of eruptive diorite and as limonite 
 elsewhere at the same horizon. It has been asserted, more- 
 over, that there is no evidence of an intermediate hematite or 
 limonite stage in the alteration from pyrite to magnetite. As 
 against the theory that in these cases the formation of the 
 magnetic oxide is due to the heat of the eruptive body, it is 
 probable, in the opinion of the writer, that these ores have 
 
 been concentrated since the eruption of the diorite. 
 
 ********** 
 
 Genesis of Manganese-Deposits. 
 
 The same lines of genesis suggest themselves for manganese 
 as for iron, but owing to its much smaller percentage as a con- 
 stituent of original rocks, it will be less easy to detect the 
 probable localities favorable for secondary concentration in 
 workable bodies. 
 
 In this secondary concentration the study of structural con- 
 ditions which would produce natural water-channels is equally 
 important. It has already been observed that the manganese- 
 ores of the southern Appalachians occur along a great faulted 
 zone, and the frequent mention of breccia conditions in other 
 deposits suggests that further study may show that the concen- 
 trations of this mineral, as well as of iron,Jiave been along such 
 lines of displacement more frequently than has been hitherto 
 realized. 
 
 In the relative chemical behavior of the salts of manganese 
 
GEOLOGICAL DISTRIBUTION OF THE USEFUL METALS. 75 
 
 and iron in terrestrial economy there are certain unexplained 
 contrasts which would appear to offer remunerative results to 
 those who would occupy themselves with its study. 
 
 Genesis of Nickel-Deposits. 
 
 The frequent connection in nature of nickel and magnetic 
 pyrites, and of nickel with native iron and magnesia, in meteor- 
 ites and at Ovifak in Greenland, is suggestive of an intimate 
 connection between the two metals in fused magmas. The 
 frequent occurrence of its silicate ores in connection with ser- 
 pentine and associated with chrome and magnetic iron has 
 often been remarked by geologists and chemists as pointing to 
 a genetic connection between these minerals and magnesian 
 silicate rocks. It is to be noted, however, that both the silicate 
 of nickel and serpentine are secondary products. Serpentine 
 is known to result from the metamorphism of many rocks, both 
 eruptive and sedimentary, most commonly from basic magne- 
 sian silicate rocks in the first case, and from calcareous sedi- 
 mentary rocks. The silicates of nickel may well be assumed to 
 have resulted from the secondary alteration of sulphides, if the 
 assumption is correct, that in those cases where it so occurs in 
 association with magnetic pyrites the neighboring basic erup- 
 tives have not yet reached the extreme of serpentinous alteration. 
 As with iron, therefore, certain portions of basic eruptive 
 magmas may be supposed to have been relatively rich in nickel- 
 bearing minerals, and by secondary concentration these may 
 have been transferred to the water-channels of adjoining rocks. 
 The greater this alteration of the rock the greater concentration 
 
 of nickel-ore, as a general rule, would one expect to find. 
 
 ********** 
 
 Genesis of Copper-Deposits. 
 
 The observed facts with regard to copper-deposits seem to 
 point to eruptive rocks as the original source of the metal, and 
 to indicate that its original form in deep-seated concentrations 
 or deposits was that of sulphide. There seems to be less 
 ground for supposing it to have been generally disseminated in 
 marine sediments than in the case of some of the other metals, 
 though very strong arguments have been advanced by geolo- 
 
76 GEOLOGICAL DISTRIBUTION OF THE USEFUL METALS. 
 
 gists of great ability in favor of the theory of its chemical pre- 
 cipitation from the waters of the Triassic ocean by the agency 
 of decaying organic remains. Its concentration, either in sedi- 
 ments generally or in ore-deposits, seems to have been by 
 chemical rather than by mechanical processes. The assump- 
 tion that certain portions of eruptive magmas are exceptionally 
 rich in this and associated metals furnishes a good working 
 basis for explaining its concentration in most well-known ore- 
 deposits. Its chemical behavior, especially in deposition, pre- 
 sents some peculiarities not always easy to explain. In its 
 ready assumption of the metallic state, as in certain other 
 actions, it resembles gold and silver. Pumpelly explains the 
 absence of the baser metals in the Lake Superior deposits on 
 the assumption that the copper has been reduced from its salts 
 by protoxide of iron, which would not have acted on the salts 
 of the baser metals, which would have been carried farther on ; 
 and that once reduced to a metallic state, the copper was in a 
 condition of greatest permanence in presence of the usual rea- 
 gents. To account for the unusual amount of metal in this 
 region, there is an extraordinary amount of eruptive material 
 to draw from, and unusually intense and long-continued action 
 of metamorphic or alterative processes to produce the concen- 
 tration. On Keweenaw Point, traces of sulphur are found in 
 the melaphyre ; and in two mines, copper occurs as sulphide 
 associated with other metals. Other . exposures of this same 
 series of rocks, in Wisconsin and Minnesota, where no ore- 
 deposits have yet been found, are said to carry small quantities 
 of metallic copper, associated with sulphides of iron and 
 copper. 
 
 It is worthy of remark that the native silver which occurs 
 with the copper in this region is never alloyed, but separates 
 from it by polling. 
 
 The unusual richness in copper of the ores along the limits 
 of the zone of oxidation in veins at Butte and in the Appa- 
 lachians is readily explainable by the leaching- clown of this 
 metal and the removal of the less permanent salts of the baser 
 metals. It is more difficult to account for the frequent sudden 
 appearance and disappearance of copper at different parts of an 
 unaltered deposit of mixed ores, as at Leadville and other 
 places. There does seem to be a more frequent association of 
 
GEOLOGICAL DISTRIBUTION OF THE USEFUL METALS. 77 
 
 deposits of gold and copper with relatively acid rocks, as of 
 iron, chrome, and nickel with basic magnesian rocks, but ex- 
 ceptions are so frequent and data so incomplete, that it is 
 questionable whether this association can properly be assumed 
 to have a genetic cause. The pebbles in the copper-bearing 
 conglomerate of Lake Superior, for instance, are said to be 
 mostly of acid eruptives ; but this may result from the supe- 
 rior hardness of these rocks over the altered basic rocks. In 
 Leadville, the ores carrying copper in the most important de- 
 posits are in a more siliceous limestone than are those which 
 contain no copper, but other copper-deposits in the same region 
 are in the more pure magnesian limestone, and both here and 
 in Arizona more copper is found in the relatively basic lime- 
 stones than in the adjoining acid eruptives. 
 
 The presence of copper in nature is so easily detected on 
 account of the bright colors of its surface alteration-products, 
 that it may be assumed to have been so thoroughly prospected 
 that no important sources of the ore remain undiscovered. It 
 seems probable, however, that the belt of pyritous ores with 
 limonite caps which stretches through the crystalline zone of 
 the Appalachians, and contains generally small percentages of 
 copper, may yet prove a source of this metal of commercial 
 importance in connection with other products of these great 
 deposits. 
 
 Genesis of Lead- and Zinc-Deposits. 
 
 For the original source of lead and zinc there seems no valid 
 reason why we should not look to the massive eruptive rocks, 
 as in the case of other metals. It is true, that their mineral 
 combinations do not form prominently-visible constituents of 
 these rocks, as do the iron-bearing minerals, nor have concen- 
 trations of them yet been discovered which could be considered 
 to be the result of differentiation in an eruptive magma. As 
 their deposits are found in nature, they are essentially precipi- 
 tations from aqueous solutions, and their favorite habitat ap- 
 pears to be sedimentary limestones. Moreover, for the very 
 extensive and important deposits of the Mississippi valley there 
 .are no known eruptive rocks within reach from which their 
 metals could have been derived, and the opinion of most of the 
 
78 GEOLOGICAL DISTRIBUTION OF THE USEFUL METALS. 
 
 geologists who have made careful study of these deposits is 
 that the metals in them were originally deposited with the 
 limestones in a disseminated form, and that the present de- 
 posits are merely concentrations of these finely-disseminated 
 minerals by downward-percolating waters. On the other hand, 
 chemical analysis has detected their presence in appreciable 
 amounts in some eruptive rocks not directly connected with 
 ore-deposits, which is sufficient proof that portions of eruptive 
 magmas may contain them as original constituents. If it is ad- 
 mitted that they were deposited with the Mississippi Valley 
 limestones, whether chemically or mechanically, they must 
 have been derived from some earlier rock-masses, and may 
 well have resulted, either in first or second instance or even 
 further back, from the disintegration or decomposition of older 
 eruptive masses. The latest student of the Mississippi Valley 
 deposits (W. P. Jenney), whose most detailed studies were 
 made in the southeastern Missouri region, finds the fissures in 
 the limestones to be fault-fissures, and argues that they are 
 probably deep-seated, and that the minerals have probably 
 been brought up through these fissures from some deep-seated 
 source in crystalline or eruptive rocks below. The fact that, 
 in the upper Mississippi region, blende, which is at the lowest 
 horizon, is generally of earlier deposition than galena, might 
 be considered an argument in favor of this hypothesis, though 
 it is explainable otherwise. On the other hand, their general 
 association with barite in Silurian limestones, and the fact that 
 fluorspar is found with lead only in Sub-Carboniferous lime- 
 stone, is in so far an argument of derivation from the lime- 
 stones themselves. 
 
 In the West, the frequent association of the deposits with 
 eruptive rocks is most striking, and it seems likely that more 
 systematic studies in the Appalachians may discover a probable 
 association of areas of concentration of their minerals with 
 eruptives, from which they might indirectly have been derived. 
 A most fruitful field of investigation lies open here, and one 
 that is comparatively untouched, for no general truths can be 
 derived from the study of a single deposit or group of deposits, 
 and, as yet, the work either of individuals or organizations, in 
 this country, has scarcely gone beyond this stage. It would 
 also be interesting to determine how far the segregation of the 
 
GEOLOGICAL DISTRIBUTION OF THE USEFUL METALS. 79 
 
 minerals of the two metals was due to differentiation in the 
 original magma, and how far to a process of gradual selection in 
 successive concentrations. In composite sulphide deposits of 
 great extent, like those of Leadville, which may be assumed to 
 be the first concentration after that in the original magma, 
 there appears to have been a certain amount of selective segre- 
 gation by which certain portions contain a larger proportion 
 of one or of the other metal, comparable to the imperfect sepa- 
 ration of the first part of an ore-dressing process. In the min- 
 eral economy of nature there is a generally-observed tendency 
 for like to seek like, as far as freedom of movement admits. 
 It suggests itself, therefore, that those deposits which contain 
 one metal, to the practical exclusion of the other, may be the 
 result of a succession of such selective concentrations, and 
 hence more removed from the original source than the more 
 mixed deposits. 
 
 ********** 
 
 Genesis of Quicksilver-Deposits. 
 
 The original source of the quicksilver and the associated 
 metals is believed to have been in or below the deep-seated 
 granites. The deposits are regarded as having been precipi- 
 tated from heated solutions containing sodium sulphide, rising 
 through fissure-systems, by relief of pressure and contact with 
 surface-waters. The quicksilver-minerals have been deposited 
 in interstices between rock fragments and in masses of porous 
 texture, particularly sandstones, but nothing like actual mo- 
 lecular substitutions or pseudomorphosis has been observed 
 either in California or in Spain. 2 In the Bavarian palatinate, 
 however, cinnabar has been found to play the part of a fossil- 
 izing mineral and has therefore replaced organic matter. 
 
 The only recent important development of quicksilver-ores 
 in California is at the Mirabel mine, formerly known as the 
 Bradford, in the Mayacmas belt, Lake county. This mine 
 yielded in 1892, 3,245 flasks. The production at the older 
 mines, and particularly at the New Almaden, has fallen to a 
 very low point. 
 
 2 Data with regard to this metal are from G. F. Becker's monograph on the 
 subject, 1888, and from private information communicated by him. He draws 
 a distinction between molecular substitution and the deposition of ores in porosities 
 which are due to precedent chemical action. 
 
80 GEOLOGICAL DISTRIBUTION OF THE USEFUL METALS. 
 
 Genesis of Gold- and Silver-Deposits. 
 
 The frequent association of deposits of gold and silver with 
 eruptive .rocks, the world over, has long been remarked. 
 Chemical investigation of many eruptive rocks has detected 
 their presence under such conditions as leave little doubt that 
 they were original constituents of these rocks. Kecently a 
 German geologist has reported the discovery of gold in a late 
 eruptive rock in Chile, which could be actually seen, by the 
 aid of the microscope, to be an original constituent of the rock. 
 There seems very good reason to assume, therefore, at any rate 
 as a working hypothesis, that the original or ultimate source of 
 these metals has been the eruptive rocks. 
 
 With regard to their subsequent dissemination in sedimen- 
 tary beds, whether by mechanical or chemical agencies, there 
 appears to be less satisfactory evidence, as there are few known 
 concentrations which can with much probability be assumed to 
 have derived their material exclusively from sedimentary rocks. 
 The concentration of the metals in workable ore-deposits has 
 evidently been by the agency of aqueous solutions; detrital 
 deposits are only the mechanical rearrangement of such con- 
 centrations, though some maintain that these have been en- 
 riched by precipitation from solutions. 
 
 Aside, then, from the study of the structural relations which 
 would afford favorable conditions for the concentration of metal- 
 bearing solutions and the precipitation of their contained salts 
 in workable ore-bodies, which is of common interest and im- 
 portance with regard to deposits of all the metals, a most 
 fruitful field of research, and one which promises results of 
 economic as well as scientific importance, is afforded by the 
 study of the chemical and mineralogical affinities of these two 
 metals, and their probable behavior under the conditions which 
 may have existed where deep-seated deposits were formed. 
 Much obscurity still exists as to the actual chemical condition 
 of silver in galena and of gold in pyrite. The suggestion has 
 recently been made that combinations of these metals, as alloys 
 or otherwise, with small amounts of tellurium, bismuth, etc., 
 are much more common in nature than has hitherto, been sus- 
 pected, and may be the reason of the unexplainable difficulties 
 found in amalgamating certain ores, and further investigation 
 on this line may produce important results. There are some 
 
GEOLOGICAL DISTRIBUTION OF THE USEFUL METALS. 81 
 
 features, also, with regard to the behavior of these metals 
 under the action of atmospheric waters, and their consequent 
 concentration along the zone of alteration of sulphide deposits, 
 which are not entirely clear, and demand more systematic and 
 careful investigation. 
 
 Conclusion. 
 
 What is at present known about the distribution of ore- 
 deposits west of the 100th meridian does not seem to call for 
 any serious modification of the statement as to their general 
 distribution made by Clarence King in 1870. It is probable 
 that if the subject were carefully worked up in detail it would 
 be found that the meridional zones laid out by Mr. King con- 
 tain, as Kaymond has suggested, a greater variety of minerals 
 than he was at that time aware of. 
 
 In the eastern half of the continent it is evident, from the 
 facts given above, that certain geographical areas are peculiar 
 in containing great concentrations of certain varieties of 
 minerals, but it seems hardly necessary to recapitulate the 
 peculiarities of these areas, since it is the geological rather than 
 the geographical distribution that is of practical importance. 
 The former must have a genetic bearing ; the latter can only 
 have such bearing through geological causes. Unfortunately, 
 our knowledge of the geological relations of the ore-deposits of 
 our country is as yet too incomplete to afford material for any 
 exhaustive generalizations on the geological relations of the 
 useful metals as a whole, or the underlying genetic causes of 
 such relations. The fissure-systems, or the natural water- 
 channels which have admitted of the concentration of the 
 metals into workable deposits, have, as pointed out by King, 
 Becker, and others, certain definite relations with the great 
 orographic movements, and these relations admit of our form- 
 ing an idea of the relative age of the deposits. They do not, 
 however, afford any reason why certain minerals are more 
 prevalent in one district and certain others in another ; nor do 
 they necessarily afford any clue to the original source of the 
 metals. A certain amount of systematic geological work has 
 already been done by our Geological Surveys towards the solu- 
 tion of these important problems, which are of practical, as 
 well as scientific, importance, but a vast amount remains yet 
 
82 GEOLOGICAL DISTRIBUTION OF THE USEFUL METALS. 
 
 to be done, and many, large fields are still practically un- 
 touched. 
 
 The suggestion afforded above as a working hypothesis seems 
 to be one worthy of consideration by the workers in this field. 
 'If the metallic minerals do concentrate in eruptive magmas* 
 within the crust of the earth in accordance with some law not 
 yet clearly known, but which results in what is called differen- 
 tiation, by virtue of which certain areas of igneous rocks, 
 formed by successive extrusions of material of differing chemi- 
 cal composition which have cooled at or near the surface, are 
 found to be unusually rich in minerals containing a given metal 
 or class of metals, a basis is afforded to account for the un- 
 usual abundance of deposits of these metals in a given area. 
 In the case of the older eruptive rocks, the accumulation of 
 mineral combinations of the metals into workable deposits 
 may be the result of many processes of concentration, both 
 mechanical and chemical. The concentration of material de- 
 rived from younger eruptive rocks, on the other hand, would 
 be more direct, and mainly chemical, by the sole action of per- 
 colating waters. In either case, did investigation prove that 
 certain areas of eruptive rock were unusually rich in mineral 
 combinations containing a given metal, it would afford reason- 
 able ground for looking for valuable deposits of that metal in 
 the vicinity, especially if the geological conditions of rock- 
 alteration or metamorphism and dynamic movements are such 
 as to favor concentration. 
 
 If sedimentary beds carry disseminated minerals, or concen- 
 trations of such disseminated minerals into ore-deposits, they 
 might have been derived ultimately from the abrasion of bodies 
 of igneous rocks rich in their minerals by differentiation. How 
 close a proximity would constitute a vicinity would vary widely 
 under varying geological conditions. It is quite uncertain 
 how far percolating waters carrying minute amounts of metallic 
 minerals in solution might travel through underground water- 
 passages without depositing their load, but the possible dis- 
 tance is evidently very considerable ; and the argument some- 
 times advanced against the lateral-secretion theory, that proof 
 can be found in certain cases that the mineral of a vein could 
 not have been derived from the immediate wall-rock, is no 
 valid argument against this theory in its broader acceptation,. 
 
GEOLOGICAL DISTRIBUTION OF THE USEFUL METALS. 83 
 
 which admits the secretion from neighboring bodies of rock 
 not necessarily in immediate proximity, but possibly at con- 
 siderable distance and not visible at the surface. 
 
 For the derivation of sediments, the possible distance of the 
 source of materials has still wider limits ; but analogy from the 
 conditions under which sediments are deposited in present 
 oceans would bring it within 100 miles as a probable limit. 
 Here, also, it may readily happen that the eruptive body from 
 which the metallic minerals were derived is not visible on the 
 surface. 
 
 DISCUSSION. 
 
 (Trans., xxii., 732.) 
 
 JOHN A. CHURCH, New York, K Y. : It requires some cour- 
 age to appear as a critic of a theory which is not only the 
 fashion among American geologists, but is usually presented 
 by them in terms which imply that any other views are an 
 exhibition of ignorance. Still, I am obliged to say that the 
 theory of lateral secretion as it is stated in this and other 
 writings of Mr. Emmons and other geologists has not added 
 much to our real knowledge or clearness of view. In the ear- 
 lier and less developed stages of the theory, when it was used 
 as Sandberger used it, to show that certain veins were proba- 
 bly 'derived from the rocks in which they lie, or which are 
 adjacent, it was valuable in pointing us to an immediate source 
 of ore-deposition. When we are driven to assume the exist- 
 ence of undiscoverable rocks at an unknown but certainly a 
 considerable distance, and in an unknown direction from the 
 vein, I do not see that we have improved upon the despised 
 " unknown source in . depth " jvith which our ignorance has 
 been covered so long. The new theory may suffer from ado- 
 lescence, and these points may be cleared up by further study, 
 but I speak of it as it is. 
 
 Differentiation in a magma, by which a metal is concen- 
 trated in one member of a series of outflows, may explain why 
 certain ores have favored a given locality with their presence ; 
 but it is not a necessary precedent to ore-formation. Concen- 
 tration in the source of supply cannot be a requirement, for 
 the forces that have been able to take up four or five tons of 
 gold from an extensive body of rock must be able to collect 
 
84 GEOLOGICAL DISTRIBUTION OF THE USEFUL METALS. 
 
 four or five thousand tons of lead, copper, or nickel from a 
 proportionately more extended body of rock. That is to say, 
 concentration is no more essential for these metals than it is 
 for gold. 
 
 In fact, differ entiatron, as it is now explained, is not an ad- 
 vance upon old ideas, but a retreat from them. It was noticed 
 long ago that violent eruptive phenomena, however long con- 
 tinued, died away in solfataras ; and when a vein came to be 
 looked upon as an extinct solfatara the inference was ready 
 that veins are eruptive in the sense that the solfataric waters 
 collected the metals from the unerupted residue of the magma 
 and carried them to the veins. The early views carried differ- 
 entiation further than the modern school. 
 
 It is the fashion of the new school, to which I believe all 
 professional geologists in this country adhere, while all profes- 
 sional mining engineers keep themselves aloof from it, to speak 
 of these old ideas as if they were very ignorant, and were 
 necessarily brushed aside by the advance of experimental 
 knowledge. It seems singular to me that the new school 
 should recognize no other origin for ores than the leaching of 
 rocks by comparatively shallow water-currents and yet recog- 
 nize no other origin for the fissures that carry the ores than 
 cataclysmic action ! If it had been found that bed-planes were 
 commonly the channels by which the ore-solutions entered, 
 we might accept the fact as evidence of lateral secretion ; but 
 when I find the adherents of this theory declaring, as does 
 Mr. Emmons (and as do all the others), that every ore-deposit 
 lies in a plane of faulting, or has been filled from a fault, it 
 seems to me hardly logical to carry one branch of the volcanic 
 theory to such an extreme, and totally reject the other branch, 
 with which this view is undoubtedly in sympathy. 
 
 The older geologists looked upon a vein as a channel estab- 
 lished between the surface and the interior of the earth. Into 
 its lower termination poured solutions, the character of which 
 was determined by the pressure and heat normal to the depth 
 at which they may have been formed. The almost uniformly 
 siliceous filling of veins shows that this depth was uniform in 
 its conditions of solution. It may have been the whole bary- 
 sphere or only that upper portion within which we may imag- 
 
GEOLOGICAL DISTRIBUTION OF THE USEFUL METALS. 85 
 
 ine a comparatively lively circulation. At least it was lower 
 than the vein. 
 
 The crevice was supposed to be an open chamber, or series 
 of chambers, with occasional points of support. Through this 
 chamber the waters rose to the surface, where they were dis- 
 charged. As they rose, they necessarily passed through zones 
 of continually-decreasing pressure and temperature, and " relief 
 of pressure " and " lowering of temperature " were the potent 
 agents which were supposed to effect precipitation of the dis- 
 solved solids, discharge of gas being another. The idea that 
 the rocks inclosing the crevice could act as precipitants re- 
 ceived early attention, and has led directly to some of our most 
 widely accepted modern ideas. 
 
 Undoubtedly, these are plausible views; and the agencies 
 invoked are real agencies of precipitation, as we know from 
 the action of hot telluric waters discharging upon the surface. 
 One of our most noted veins the Comstock was studied and 
 explained in the light of this older theory by Eichthofen, in 
 1865 ; and these ideas have not been entirely abandoned there. 
 
 Mr. Becker, within the last ten years, has gone into an elabo- 
 rate argument to prove that there has been almost no erosion 
 of the Comstock rocks. If this argument is sound, the outcrop 
 now is within 25 or 50 ft. of where the original outcrop was 
 formed. It is true, his views contradict each other; and, if 
 the dynamical conduct of the rocks had been what he describes, 
 there would never have been an outcrop where the Comstock 
 was found. Still, I believe all writers upon that noted vein, 
 except myself, have represented it as a solfatara, in the sense 
 that it was formed by hot waters from a deep unknown source 
 discharging into the atmosphere. The attempts to connect 
 lateral secretion with the lode have been failures; and the 
 Comstock still represents the old theories in their advanced 
 form. It seems to me, that the solfataric origin of ores is a 
 more reasonable explanation of the observable facts, in some 
 cases, than the theory of lateral secretion. That minute quan- 
 tities of the metals are found in all or many rocks, is true ; but 
 the crucial question of their origin has never been determined. 
 Do they form an original source, or a secondary deposition like 
 the vein? is a question that has not been conclusively an- 
 
86 GEOLOGICAL DISTRIBUTION OF THE USEFUL METALS. 
 
 swered ; but I agree, and I think most mining engineers agree, 
 with Posepny, in believing them to be the latter. 
 
 We owe to the distinguished author of this paper one of the 
 most striking and valuable contributions to the discussion of 
 the lateral-secretion theory. From his description we may say 
 that, in his view, the ores at Leadville were not exotic, since 
 the rocks in which they lie, the rocks from which they were 
 leached, and the water-currents that formed them, were all at 
 substantially the same depth. These features are essential to 
 lateral secretion ; for, if we allow that the circulating waters 
 sink deep enough to reach the unerupted residue of the magma 
 before they take up their metallic contents, we have the old 
 solfataric theory of origin. 
 
 Sandberger's original idea, that veins are filled by leaching 
 from the rocks that contain them, has been so expanded by the 
 discussion of ore-bodies formed under a cover of three or four 
 miles of rock, that it is brought, riot into conflict, but into close 
 sympathy with the solfataric theory. The question whether 
 the origin was in erupted or in non-erupted magma is interest- 
 ing ; but it is not controlling when the action is acknowledged 
 to have taken place at very great depth, far within the " bary- 
 sphere " in either case. 
 
 Having reached that amount of agreement, it seems to me 
 that the next task of the structural geologists is to determine 
 critically whether any vein has really been formed in a crevice 
 discharging directly into the atmosphere. The conditions 
 found at Steamboat Springs and elsewhere seem to me to point 
 to vein-action (if vein-action there is) at some other point. The 
 discharging waters may be regarded as the nitrate derived from 
 metasomatic precipitation lower down, or as a mixture of 
 waters from the upper and lower regions. As yet, I doubt if 
 we have any proof that ore carried by the deep circulation has 
 been retained long enough to be deposited at the surface. Mr. 
 Becker entertained that view, but I believe his conclusions 
 upon the geology of the Comstock to be radically wrong. 
 
 ARTHUR WINSLOW, Jefferson City, Mo. : I think that others 
 will join me in expressing thanks to Mr, Emmons for his ad- 
 mirable resume of our ore-deposits, and for the many valuable 
 suggestions embodied in it. The ground is so well covered 
 
GEOLOGICAL DISTRIBUTION OF THE USEFUL METALS. 87 
 
 that there remains little -room for additions, jet I should like 
 to make a few remarks concerning some subjects touched on 
 of which I have personal knowledge. 
 
 Mr. Emmons refers to the specular ores of southeastern Mis- 
 souri collectively, as probably of Algonkian age. There is, how- 
 ever, a distinction to be made. Those of Iron Mountain occur in 
 Archaean porphyry, in tongue-like masses or veins which taper 
 out with depth. The ore of Pilot Knob, on the contrary, 
 occurs as a bed interstratified with Algonkian elastics com- 
 posed of debris of the pre-existing Archaean porphyries. These 
 ores have recently been made the subject of renewed study by 
 the Geological Survey of the State, through Mr. Nason. He 
 thinks that the facts at Iron Mountain are such as to favor 
 the theory that the ores there are derived from the decay of 
 great thicknesses of porphyry, accompanied by a leaching-out 
 of the abundant iron-content and its deposition elsewhere in 
 crevices and openings of the same rock, at times possibly re- 
 placing the decomposed porphyry adjacent to these crevices. 
 These deposits would thus be examples of chemical concentra- 
 tion from older basic eruptives. In the case of Pilot Knob, 
 Mr. Nason concludes that the iron-ore body is probably the 
 result of replacement of certain members of the Algonkian 
 series of strata. This would again be an example of chemical 
 concentration from an older basic eruptive, though if we allow 
 that the Archaean specular ores were formed prior to the deposi- 
 tion of the Algonkian series here, it is possible that this Pilot 
 Knob bed is of direct mechanical origin from the abrasion of 
 these earlier ore-masses. 
 
 In the iron-deposits of central Missouri, which consist of a 
 mixture of blue specular and red hematite ores, Mr. Nason 
 concludes that we have instances of accumulation in cavities 
 and depressions produced by subterranean erosion of lime- 
 stone. The disturbed condition of the adjacent strata, their 
 converging dips and other facts corroborate this. That there 
 was some replacement of limestone by the iron-solutions is also 
 undoubted. This is well illustrated by the recent discovery of 
 crinoid remains in the body of the ores, replaced entirely by 
 blue ore. An interesting fact about these fossil remains, and 
 one which adds support to the theory that the ore accumulated 
 in depressions or cavities, is that they are not fossils found in 
 
88 GEOLOGICAL DISTRIBUTION OF THE USEFUL METALS. 
 
 the Cambrian country-rocks, but belong probably to a Lower 
 Carboniferous fauna. All over the Cambrian area of the 
 Ozark uplift patches and fragments of such later rocks are 
 found, indicating that a thin covering once existed there, of 
 which portions are preserved in depressions and pockets in the 
 older dolomites. 
 
 Remote as these ore-bodies are from eruptive rocks, we are 
 obliged to seek for their source in the surrounding sedimenta. 
 ries. Mr. Nason has fixed upon the sandstones of this area as 
 the probable contributors. These are often highly ferruginous, 
 and are readily leached by percolating waters. It is probable 
 that the decaying dolomites also contributed a share. 
 
 In referring to the zinc- and lead-ores of Missouri, Mr. 
 Emmons has brought forward for discussion a series of most 
 interesting and at the same time most perplexing deposits, so 
 far as a satisfactory theory of their origin is concerned. Those 
 of the southwestern portion of the State occur essentially in 
 the Mississippian or Lower Carboniferous limestones. The 
 statement that they extend into the Coal Measures should be 
 made with limitations. They are found in shales of that age 
 in Jasper county, but those shales are in isolated patches, 
 which occupy depressions in the older ore-bearing Mississip- 
 pian rocks. Hence, the metallic contents of the shales may be 
 derived, by some secondary process of transfer, from adjacent 
 ore-bodies. In any case, the Coal Measures in the State, as a 
 whole, are practically destitute of these ores, which, therefore? 
 can hardly be declared to belong to that formation, whether 
 their general absence from it be due to their prior formation, 
 or to limitations in their distribution determined by physical 
 causes. 
 
 Cross-fissures or fault-fissures in these Mississippian rocks, 
 to which Mr. Emmons alludes, if they exist, are not very appa- 
 rent. The strata are, undoubtedly, very much shattered in 
 certain limited areas, have been subjected to extensive subter- 
 ranean erosion and corrasion and great silicification. Of a 
 system of extensive or considerable faults, recent stratigraphic 
 work in this region has, however, revealed nothing. 
 
 In the Cambrian limestones of the eastern part of the State, 
 the conditions are somewhat different. Crevices and fissures 
 are there plainly developed, and evidence of considerable fault- 
 
GEOLOGICAL DISTRIBUTION OF THE USEFUL METALS. 89 
 
 ing is indubitable. In Franklin county, such vertical crevices 
 have supplied large quantities of ore. In that portion of the 
 Southeast to which Mr. Emmons especially refers, however, 
 and which has produced by far the greater part of the lead, 
 the crevices are of insignificant dimensions, and the experience 
 has been that they contain, themselves, little or no ore. On 
 the contrary, the great ore-masses consist of galena dissemi- 
 nated through a thickness of the country-rock often of 50 ft. 
 and more. At Bonne Terre, a tract 1,300 ft. long by 800 ft 
 wide has been mined out of such diffused ore. 
 
 The crevices which traverse this ore-body are frequently 
 almost blind, and can only be detected by the drip of roof- 
 water. These are such as traverse almost any massive rock. 
 They have possibly had their influence upon the ore-deposi- 
 tion ; but to picture them as veins and channels of direct ore- 
 supply seems hardly justifiable, even under the existing differ- 
 ences of opinion among geologists as to just what a vein is. 
 The questions of the source and mode of accumulation of these 
 ores are very broad, and involve considerations of the ore- 
 deposits, and of the geological history of the whole Mississippi 
 valley. Only through studious, detailed analytic methods can* 
 a satisfactory solution be reached. I hope, at a later date, to 
 have something further to contribute to the Institute on this 
 subject. 
 
 Concerning the distribution of barite, to which Mr. Emmons 
 refers on page 78, I would add, that it is not confined to the 
 older Cambrian rocks of Missouri, but is found in Cooper and 
 adjacent counties, at a number of localities, in Lower Carbon- 
 iferous limestones, sometimes associated with lead-ores. In a 
 previous paper, presented to the Institute, 3 Mr. Emmons has 
 suggested the use of the apparent fact of the limited distribu- 
 tion of barite in determining the origin of the ores. This oc- 
 currence in the Lower Carboniferous lessens the value of the 
 suggestion, though it remains still locally serviceable. 
 
 MR. EMMONS : I am very glad to have the details which Mr. 
 Winslow has given us with regard to the ore-deposits of Mis- 
 souri ; and as my knowledge of the greater part of them is 
 
 3 Trans., xxi., 41 (1892-93). 
 
90 GEOLOGICAL DISTRIBUTION OF THE USEFUL METALS. 
 
 derived, not from personal observation, but from the descrip- 
 tions of others, I am quite willing to accept his corrections of 
 my facts, since his information is of later date than that to 
 which I had access. I was aware that barite occurs at times 
 in the Lower Carboniferous limestones of the Mississippi val- 
 ley; indeed, small amounts have been found in the fluorspar- 
 deposits of Rosiclare, HI., since I wrote my previous paper to 
 which he refers ; but I think it still remains true that fluorspar 
 is characteristic of the one horizon and barite of the other. 
 
 (Trans., xxiv., 755.) 
 
 WILLIAM HAMILTON MERRITT,. Toronto, Ont. : With refer- 
 ence to Mr. Emmons's remarks on the nickel-deposits of Sud- 
 bury in the district of Algoma, Province of Ontario, Canada, 
 and his general argument in connection with igneous rocks as 
 the source of supply of ores, I would draw attention to two 
 series of facts personally observed in connection with the Sud- 
 bury deposits. 
 
 1. The Diorite as a Source of Supply. The diorite, as a rule, 
 is speckled with pyrrhotite, and to a less extent with chalcocite. 
 In the diorite I have seen a speck of free gold quite visible to 
 the naked eye. The same diorite, decomposed, has been run 
 through a prospector's stamp-mill in an earthy and gossany 
 state, and free gold and the new platinum mineral, sperrylite 
 (PtAs 2 ), perfectly crystalline, have been collected from it, 
 Near by, a quartz vein, cutting the same diorite formation, has 
 yielded rich samples of free gold, which occurs also in the 
 diorite walls beside the vein, the wall-rock being, in some places, 
 thickly interlaced with threads of gold. 
 
 2. Secondary Action in Concentration Has Produced Some of the 
 Ore-Bodies. As has been noted by Mr. Emmons, the theory of 
 differentiation, or the concentration of the ore-bodies in the 
 fused magma, is offered to explain the source of the Sudbury 
 nickeliferous pyrrhotite masses in the intrusive diorite. This 
 would not appear unreasonable. Yet I am satisfied that a sec- 
 ondary concentration must have taken place to explain the 
 presence of some of the ore-bodies ; at all events, where the 
 contents of copper run comparatively high. The presence of 
 the horses of country-rock cemented by the ore (alluded to by 
 
GEOLOGICAL DISTRIBUTION OF THE USEFUL METALS. 91 
 
 Mr. Emmons), and which I have observed sharply brecciated, 
 seems to strengthen this belief; for if they had been floating 
 in a fused magma, surely all abrupt demarcation would be 
 obliterated. 
 
 Moreover, I have seen such signs of secondary action as thin 
 films of native copper in connection with the ore-body; also a 
 band of " fluccan " cutting across it, which may indicate a por- 
 tion of the chief channel which may have filled the cavities 
 caused by movement. Native copper grains are also seen in 
 the crystalline hornblende rock associated with the deposit. I 
 have not observed serpentine, which might be expected to 
 occur. In another portion of the same ore- body there is free 
 gold visible in chalcopyrite ; and where a very small crack or 
 vug had occurred in the ore, wire-gold has been developed. 
 The ore-body is distinctly more quartzose than the diorite in 
 which it occurs. 
 
92 THE TORSIONAL THEORY OF JOINTS. 
 
 No. 4. 
 The Torsional Theory of Joints. 
 
 BY GEORGE F. BECKER, WASHINGTON, D. C. 
 
 (Virginia Beach Meeting, February, 1894. Trans, xxiv., 130.) 
 
 Complexity of Rock-Fractures. The strains to which rocks 
 have been subjected are manifestly very complex, and it is en- 
 tirely safe to presume that every possible mode of deformation 
 and rupture is exemplified. The most superficial inspection of 
 any ordinary mountain region is sufficient to assure the ob- 
 server that the rocks have been pressed, stretched, bent, 
 buckled, twisted, and shorn. The study of torsional rupture 
 cannot fail, therefore, to throw light on geological phenomena. 
 The question is, how areas which have been broken in this 
 manner are to be distinguished from those which have yielded 
 to other systems of forces. 
 
 Phenomena of Joints. It is well known that a large part of 
 the more homogeneous rocks and some very heterogeneous 
 rocks are intersected by partings, often called joints. These 
 partings are frequently flat surfaces, even when seen in very 
 large exposures, but are sometimes surfaces of moderate single 
 or double curvature. Joints usually occur in groups, in each 
 of which the several partings are parallel to one another, and 
 several such groups often intersect the same rock-mass. In such 
 cases the different systems make large angles with one another. 
 Nearly all students of the subject of jointing have reached the 
 conclusion that joints are faulted surfaces, the dislocations 
 usually being of small amplitude ; and this conclusion receives 
 abundant support from the study of thin sections under the 
 microscope. It has thus been shown that much even of what 
 would be regarded in hand-specimens as mere slaty cleavage 
 consists, in reality, of innumerable microscopic faults. For 
 this reason, Mr. Daubree rejects the term "joint," as failing to 
 imply the existence of relative motion, and has introduced the 
 terms "diaclase" and "paraclase" as substitutes. 1 
 
 1 Bulletin de la Societe Oeologique de France, Third Series, vol. vii., p. 108 (1879). 
 
THE TORSIONAL THEORY OF JOINTS. 93 
 
 Although the word "joint" does not imply relative motion, 
 it does not necessarily preclude such movement, and, as it is 
 universally intelligible, I prefer it. In nearly all cases where 
 joints are suitably exposed they show slicken siding. In many 
 hundreds of joints I have found polished surfaces, although the 
 throw of the faults was so small as scarcely to be determinable. 
 Slickensiding is a very important genetic characteristic of 
 joints, for wherever it prevails over any considerable portion 
 of the parting, it is good evidence that the joint-walls have not 
 only undergone relative motion, but have remained in contact 
 during the dislocation. 
 
 It does not follow that gaping joints should be infrequent, 
 for a rock-mass once affected by joints will present but small 
 resistance to any disturbing force, and such a force may readily 
 spread the joint walls. 2 Indeed, it is somewhat surprising that 
 joints are so often found closed. When a bar of metal is cut 
 by shears, the two parts are in contact immediately after the 
 continuity is destroyed and they slickenside one another, but 
 under ordinary conditions they then fall apart. The compara- 
 tive rarity of gaping joints is explicable in part by the presence 
 of water. The surface-tension of thin films of water leads to 
 adhesions which seem to me of much importance. Thus, if 
 two surfaces of rock are distant 0.01 in. from one another, and 
 if the space is filled with water, the rock-surfaces are drawn 
 together, in consequence of the surface-tension of the liquid, 
 with a force equal to 18.5 Ib. per sq. ft. ; and if the opening is 
 only 0.001 in. wide, the pressure will be 135 Ib. per sq. ft. 3 
 There can be no doubt that many jointed rock-masses, which 
 project above the local water-level, are prevented from dis- 
 organization by this means. 
 
 Explanatory Hypotheses. Jointing is now regarded by all in- 
 vestigators as of mechanical origin. It has been referred by 
 
 2 Prof. William King, Transactions of the Royal Irish Academy, vol. xxv. (1875), 
 has collected much evidence to show that joints were originally close. Mr. 
 Daubr^e also draws from observations by himself and others the conclusion (I.e.) : 
 "A cutting or shearing force, then, was operative during the formation of joints." 
 This is equivalent to asserting that contact existed during and immediately after 
 rupture. 
 
 3 The pressure is equivalent to that of a column of water, the height of which is 
 c centimeters when the distance of the surfaces from each other is d centimeters, 
 and c d 162/981.4. Compare Tait's Properties of Matter, p. 258 (1890). 
 
94 THE TORSIONAL THEORY OF JOINTS. 
 
 eminent authorities to simple tensile stresses, but observers 
 have long protested against this explanation, because such 
 joints would gape from the start and would not be slickensided. 
 Even if a tensile stress leading to rupture were associated with 
 slipping, slickensides would be produced only on a few small 
 portions of the surfaces involved. These surfaces can never be 
 true mathematical planes, and a rupture like that just sug- 
 gested might bring into contact protuberances, however small, 
 but in such cases slickensides would be confined to small por- 
 tions of the surface. In heterogeneous masses, particularly in 
 conglomerates, tensile stresses leading to rupture would pro- 
 duce rough and irregular partings. Even in masses so homo- 
 geneous as steel, tensile rupture takes place on very uneven 
 surfaces. 
 
 For these reasons, jointing has been explained most satisfac- 
 torily by reference to pressure, though it does not follow that 
 all jointing is thus brought about. Mr. Daubree has shown by 
 direct experiments with simple pressure that all the more usual 
 phenomena of joints can be artificially produced, the line of 
 pressure making an angle of about 45 with the joint-planes. In 
 this case the immediate cause of the jointing is shearing stress, 
 and the walls of the joints are not only in juxtaposition, but 
 are pressed together during the rupture and dislocation. The 
 dynamic theory of this case is not difficult even when the 
 strains are finite and the angle between the joint- surfaces is 
 greater than 45 . 4 
 
 Some geologists hesitate to accept the explanation of joint- 
 ing by pressure in a given direction, on the ground that an 
 accompanying lateral pressure of sufficient intensity would pre- 
 clude rupture. It is a very important truth that, under proper 
 conditions, rupture cannot, and flow must, take place. A mass 
 may be subjected to such confining forces that rupture is im- 
 possible by any deformation or change of volume ; but this is 
 true of tension, torsion, or shearing as well as of simple pres- 
 sure. Since rock-fractures are abundant, it is certain that con- 
 ditions permitting of rupture, as well as those compelling flow, 
 have frequently prevailed. 
 
 While Mr. Daubree and others refer many joint-systems to 
 
 4 Bulletin of the Geological Society of America, vol. iv., p. 57 (1892). 
 
THE TORSIOXAL THEORY OF JOINTS. 95 
 
 the action of pressure, the famous author of the Etudes Synthe- 
 tique has also made beautiful experiments on the torsion of 
 glass plates, which produces systems of fractures highly resem- 
 bling joints in their distribution. He has consequently ex- 
 pressed the opinion that torsion, as well as pressure, has led to 
 joint-systems. 5 
 
 Character of Torsion- Fractures. Mr. Daubree has minutely 
 described the phenomena of the rupture by torsion of glass 
 plates, these being mounted on paper to avoid the scattering of 
 the fragments. Torsion, as he describes it, produces two main 
 sets of fractures, approximately at right angles to one another, 
 and usually at nearly 45 to the axis of torsion. The fissures 
 cut the broad surfaces in lines which are nearly straight, and 
 the surfaces of fracture are approximately warped surfaces, the 
 inclination to the vertical in some cases reaching 50 on each 
 side. Some few fissures reach from edge to edge of the plate,, 
 while many do not entirely cross it, and sometimes single fis- 
 sures neither reach the edge nor any other crack, and are thus 
 isolated in the mass. The fissures which reach the edge of the 
 plate cut the narrow face at angles with the line measuring the 
 thickness, which varies greatly from 20 or less up to 50 or 
 thereabout. Besides the more regular systems of parallel 
 fissures, fan-shaped groups are not uncommon. In the neigh- 
 borhood of the finer groups of fissures the glass loses its optical 
 and thermal isotropy. 
 
 By the kindness of Prof. T. C. Mendenhall I have been ena- 
 bled to make experiments similar to those of Mr. Daubree in 
 an apparatus which permits of gradually straining the plates 
 and of measuring the angle of torsion. Besides common 
 window-glass, I employed glass ground on one side, for the 
 purpose of making sure that surface-tension played no part in 
 the result. Well-polished plate-glass was also used, sometimes 
 in simple strips and sometimes cut in the shape of a cross-sec- 
 tion of an I-beam, in order to confine the initial rupture to 
 points remote from the jaws. In a large number of the experi- 
 ments the cut edges were ground with emery, so that imper- 
 fections of the edges might not influence the result. Many 
 
 5 W. O. Crosby also adopts the torsional hypothesis, with the modification that 
 he supposes the final rupture to be determined by shock. American Geologist, vol. 
 xii., No. 6, p. 368 (Dec., 1893). 
 
96 THE TORSIONAL THEORY OF JOINTS. 
 
 different dimensions were selected, and the plates varied from 
 nearly square rods to sheets wider than they were long. It 
 was found best to substitute a thin fabric, known as " cheese- 
 cloth," for the paper on which Mr. Daubree mounted his plates. 
 The paper, in drying, exerts a considerable tension, and the 
 specimens mounted on cloth, besides being more easily handled 
 after fracture, show smaller tendency to fan-fracture. 
 
 All of Mr. Daubree's descriptions are illustrated by my speci- 
 mens, 6 and I have but few observations to add. It scarcely 
 requires mention that the curvature of the surfaces of rupture 
 is ordinarily such as to permit of the free torsion of the broken 
 plate. Sometimes, however, short cracks extending from the 
 main fissure to the edges of the plate are so warped as to ob- 
 struct torsion. Hence, when the axis of torsion is not in the 
 vertical, all the principal faults produced in the experiments 
 are reversed, the hanging-wall rising relatively to the foot. 
 
 When the breadth of a glass plate is large relatively to its 
 thickness, the surfaces of rupture are, as Mr. Daubree remarks, 
 nearly coincident with warped surfaces ; but when the breadth 
 is only a few times the thickness, the departure of the surface 
 from a warped surface is well marked. In such eases it is in- 
 teresting to note that one cropping of the fissure is usually 
 wonderfully straight, while that on the opposite side is an 
 inflected curve. From the point of view of pure dynamics the 
 exact shape of these surfaces would be interesting, but I have 
 reason to believe that the geometrical character depends essen- 
 tially upon that of the cross-section of the twisted bar; and 
 since it will seldom or never be' practicable to determine the 
 shape of a twisted rock-mass, there seems no geological interest 
 in ascertaining the precise form of the surface of rupture. It 
 is probable that the forms are all closely related to the warped 
 surface. 
 
 Among the excessively fine cracks in the glass which are 
 mentioned by Mr. Daubree, there are some which are super- 
 ficial. These are usually near the middle of the plate; they 
 are very straight, and invariably parallel to the straighter edges 
 of the ruptures on the same surface, and do not seem to pene- 
 
 6 I have not tested the anisotropy in the neighborhood of the terminations of 
 cracks not crossing the plates. As the mass at such points is in a permanent state 
 of strain, anisotropy is to be expected. 
 
THE TORSIONAL THEORY OF JOINTS. 
 
 97 
 
 trate quite to the center of the plate. They are clearly in- 
 cipient fractures, and the observations indicate that rupture 
 begins on one of the broad faces in a very straight line, the 
 surface twisting as it spreads through the plate in such a man- 
 ner as best to relieve the torsional stress. Even on rather thin 
 plates it is visible that one cropping of each well-formed crack 
 is straighter than the cropping on the opposite face, and that 
 the straight cropping has a definite relation to the direction of 
 twist. When torsion is so applied as to tend to twist the bar 
 into a righ1>handed screw, the straight lines are inclined like 
 the thread of a left-handed screw, and vice versa. Thus the 
 straight croppings on one surface of a plate are at right angles 
 to the straight lines on the other side of the plate. 
 
 The angles at which the cracks cross the narrow edge-sur- 
 faces of the plate vary considerably, as Mr. Daubree has 
 observed. I cannot find that the inclination of these lines 
 varies in any regular manner with the width of the plate. The 
 average angle which the cracks on these narrow surfaces make 
 with the long edges seems to be about 63 J, or the angle 
 whose tangent is 2. These croppings are in fact curved lines 
 in almost all cases, and the curvature is such that the acute- 
 angled fragments bounded by the edge of the plate and the 
 ruptures are somewhat grooved. 
 
 The following diagram shows two warped surfaces intersect- 
 ing a bar supposed four times as wide as it is thick, and a 
 sketch of two of the more complex surfaces, referred to above, 
 generalized from a considerable number of cases. 7 
 
 FIG. 1. DIAGRAM ILLUSTRATING INTERSECTION OF SURFACES OF RUPTURE 
 
 WITH A BAR. 
 
 7 If the axis of the bar is the x axis, y the distance from this axis parallel to the 
 broad surface, z the distance parallel to the narrow surface, b the breadth, c the 
 thickness, then the following equation represents both the warped surfaces. 
 
98 THE TORSIONAL THEORY OF JOINTS. 
 
 Rupture by Shear. In a pure (or irrotational) shear the re- 
 sultant load on any section passing through the center of the 
 strain ellipsoid is the same. On the sections perpendicular 
 respectively to the greatest and least axes the load is wholly 
 normal. On the sections of unchanged area (which stand at 
 45 to the greatest and least axes when the strain is very 
 small) the load is purely tangential. 8 In a homogeneous mas& 
 thus strained, rupture may conceivably occur by the tension 
 along the greatest axis, or by pressure along the smallest axis r 
 or by tangential motion at 45 to the axes. A mass ruptured 
 by tension sometimes breaks perpendicularly to the direction 
 of tension with a smooth surface, and sometimes, as in the case 
 of mild steel, with a rough or " cupped" surface, the facets of 
 which are in the direction of the planes of unchanged area. A 
 mass broken by uniformly-distributed pressure breaks in the 
 direction of the planes of unchanged area. A mass ruptured 
 by tangential stress also breaks on these planes. Thus a homo- 
 geneous mass subjected to a shear can break in only two ways r 
 viz. : perpendicular to the greatest axis or at 45 to this axis. 
 In the present state of knowledge concerning the constitution 
 of matter, experiment only can determine which rupture will 
 occur. The experiments on glass plates in connection with the 
 theory of torsion, due to the genius of Barre de Saint- Venant y 
 render a decision very easy for this substance. 
 
 Points From the Theory of Torsion. When a rectangular bar 
 of an elastic, homogeneous solid is twisted through a small 
 angle the following conditions are fulfilled : The lateral sur- 
 faces of the bar become warped; the length of every edge 
 remaining substantially unchanged, while diagonal lines are 
 elongated or contracted, but the volume of the mass is neither 
 increased nor diminished by a sensible amount. At the sur- 
 faces of the bar the resultant strains lie in these surfaces. The 
 directions of maximum extension and compression are at 45 
 to the axis of torsion, and at right angles to each other. If the 
 rotation of the torsion-couple is positive (opposite to that of the 
 hands of a watch) the directions of greatest extension on all the 
 sides are inclined in the same sense as the thread of a right- 
 handed screw. The strain at any point in the mass is a pure or 
 
 8 American Journal of Science, Third Series, vol. xlvi., No. 275, p. 339 (Nov.,, 
 1893). 
 
THE TORSIONAL THEORY OF JOINTS. 99 
 
 irrotational shear. The points of maximum strain are on the 
 surface and nearest the axis; in other words, the danger-line is 
 the median line of the broad surface ; and on the narrow surface 
 of the prism the strain is also greater half way between its long 
 edges than elsewhere. 
 
 Most of these conclusions can be exemplified in a very easy 
 and striking manner with a rectangular bar of rubber, such as 
 is in common use for erasing pencil-marks. The surface of 
 such a mass, cross-hatched with lines parallel to the edges, 
 shows, when the bar is twisted, that deformation is greatest 
 nearest the axis and insignificant near the edges of the prism. 
 Lines at 45 to the edges are greatly extended or shortened by 
 twist, and a very small circle is converted into an ellipse with 
 axes at 45 to the edges. 
 
 It evidently follows that rupture should begin at the middle 
 of the broad surface. If rupture takes place by slipping on the 
 planes of no distortion of the shear ellipsoid, the cracks of 
 the broken mass will be parallel to or perpendicular to the axis 
 of torsion. If the mass yields to the tensile component of the 
 shearing stress the cracks will coincide in direction with the 
 lines of greatest linear compression and stand at 45 to the 
 axis of torsion. This is precisely what occurs in the experi- 
 ment on glass. On the other hand, the theory shows that the 
 resultant stresses within the body of the plate are not in general 
 parallel to the surfaces, and it is therefore to be expected that 
 curved surfaces of rupture should ensue. 
 
 Character of Torsional Rupture. It now appears certain that 
 the experiments on the torsion of glass are equivalent to the 
 application of a system of tensions peculiarly distributed, and 
 that the fissures produced by torsion in any mass physically 
 resembling glass, will exhibit the peculiarities of tensional 
 fractures, together with some marked characteristics of their 
 own. The fissures will gape from the start, excepting at cer- 
 tain points, which alone will be slickensided. The surfaces 
 will be rough, excepting when the mass is uncommonly homo- 
 geneous. The surfaces will also show double curvature, which 
 will be very strongly marked unless the mass of rock affected 
 by torsion is immense. If the axis of torsion is vertical the 
 particles originally in contact will separate along horizontal 
 lines, and there will be no faults as these are usually estimated. 
 
100 THE TORSIONAL THEORY OF JOINTS. 
 
 In all other cases every surface will be faulted, and every master 
 fault will be reversed. The network of fissures will show 
 marked regularity, provided that the exposure is an approxi- 
 mately flat surface nearly parallel to the axis of torsion, but any 
 section forming an angle with the axis of torsion, will expose a 
 very complex arrangement of curved partings. If rocks break 
 under torsion at all as glass does, a pronounced characteristic 
 will be the frequency of fissures completely " cut oif" by 
 others, these being much more numerous than " master "joints. 
 Conclusion as to Jointing. It appears from the foregoing that 
 though torsional rupture may be of frequent occurrence in 
 disturbed regions, the systems of dislocations familiar under 
 the designation of joints cannot aptly be ascribed to pure tor- 
 sion, while direct pressure will produce the phenomena called 
 jointing. But the forces acting upon a rock-mass are in general 
 very far from simple ; indeed, it may be assumed that every 
 variety of stress exists in a strained rock-mass. Nevertheless a 
 general idea of the nature of rupture even under such condi- 
 tions may readily be reached. The strain ellipsoid at any 
 point must either be torn apart by tension or cut across by 
 shearing, and in all ordinary cases it is easy to distinguish 
 these modes of rupture. In a mass subjected to a complex 
 stress the orientation of the strain ellipsoid will vary from 
 point to point, and so will the direction of the rupture; but 
 smooth, slickensided surfaces, though curved, will still be due 
 to pressures acting at approximately 45 to the local direction 
 of the surfaces when the material is a hard and homogeneous 
 one ; and tension-cracks will form at right angles to the local 
 direction of the effective tension. Thus in typically jointed 
 areas, curvature of the joint-planes indicates that the direction 
 of the effective pressure has varied from point to point, as it 
 does, for example, in the compressed portion of a flexed bar. 
 The existence of curved joint-planes is consequently by no 
 means inconsistent with the ascription of jointing to pressure, 
 while it does indicate that the entire system of forces, operative 
 and inoperative, which has been brought to bear on the mass 
 is complex. The action of pressure on heterogeneous materials 
 is much more regular than the action of tension ; and it might 
 be possible in some cases from the study of curved joint-sur- 
 faces to infer the nature of the complete stress- system. 
 
THE TORSIONAL THEORY OF 'JOINTS.' ' 
 DISCUSSION. 
 
 (Trans., xxiv., 863.) 
 
 H. M. HOWE, New York, N. Y. : It is, of course, not easy to 
 discuss offhand the paper which Mr. Becker has presented 
 with so much lucidity. I will make only one remark, which 
 is outside of the line of his argument, and concerns merely a 
 passing allusion in his paper. Mr. Becker speaks of the fact 
 that glass breaks with a flat or conchoidal fracture, and that 
 steel shows a rough or " cupped " surface of fracture. This 
 difference we would naturally ascribe to the great difference 
 in the other physical properties of the two substances. Yet I 
 have seen copper-steel which did break in a perfectly flat frac- 
 ture, or apparently so. It seemed to be accurately perpen- 
 dicular; a smooth, mirror-like fracture, such as mineralogists 
 called " splendent." Yet the physical properties of this steel 
 did not differ from those of common steel, or resemble those 
 of glass in the way which this fracture suggests. 
 
 R. W. RAYMOND, New York, N. Y. : The general conclusions 
 reached by Mr. Becker seem to me to be fairly demonstrated. 
 His paper does not contain any precise definition of what we 
 call joints; and possibly such a definition ought to be offered 
 as the basis of any complete theory of the subject. Without 
 venturing to supply such a definition here, I infer from Mr. 
 Becker's paper, and in accordance with our general usage of 
 the term, that joints are to be distinguished, on the one hand, 
 from cleavage- planes, which we may, perhaps, consider as 
 potential rather than actual partings, and, on the other hand, 
 from fissures on a larger scale, such as become the receptacles 
 of mineral veins. And I understand his view to be, that joint- 
 ing is neither produced by tensile stress nor by pure torsion, 
 while direct, more or less oblique, pressure will account for 
 the observed phenomena. At the same time, he recognizes 
 the inevitable complexity of the stresses involved. 
 
 This conclusion may have an important bearing on the sub- 
 ject of larger rock-faults. At the "Washington meeting of 
 February, 1882, I presented a paper on Hoefer's Method of 
 Determining Faults in Mineral Veins, 9 based upon the author's 
 
 9 Trans., x., 456 (1881-82). 
 
102 THE TORSIONAL THEORY OF JOINTS. 
 
 essay, which appeared in volume xxix. of the Austrian Zeit- 
 schrift. The peculiarity of Professor Hoefer's method is, that 
 it provides for the case of a relative movement of the two walls 
 of a fault which is not rectilinear, but to some extent rotatory ; 
 that is, in which a partial revolution of the mass on one side of 
 the fault has taken place around an axis normal to the plane 
 of the fault-fissure. The evidence of such a motion is found 
 in changes of dip and strike, produced by the fault, in the 
 fissure faulted. I wrote to Professor Hoefer at that time, 
 telling him that this phenomenon had not been recognized in 
 our mining-districts to any great extent, and asking whether 
 such movements, distinct from rectilinear ones, had been fre- 
 quently observed by him. His reply was : 
 
 ''Circular movements, combined with movements in straight lines, are very fre- 
 quent in our faults ; in fact, I do not doubt at all that a continued careful study 
 will show them to be the rule. Whether simple revolutions often occur, is very 
 difficult to decide from the observations thus far available." w 
 
 It is my present belief that the circular movements have 
 been, as a rule, not only accompanied by straight-line move- 
 ments, but that the latter have been predominant; and it seems 
 to me most reasonable to suppose that rotation has been caused, 
 not by the direction of the forces which caused rupture, but by 
 the resistance encountered in the course of a rectilinear slide. 
 It is, indeed, almost inevitable that such a movement would 
 not be wholly rectilinear, but that the mass would be turned 
 more or less around points of greater friction. In other words, 
 the seeming effects of torsion might be produced after the 
 occurrence of a rupture in which torsion had taken no part. 
 
 In this view the causes of rupture on the large scale would 
 be entirely analogous to those observed on the small scale in 
 joints. This is a familiar principle to those who have worked 
 upon rocks with the microscope, or have studied in hand- 
 specimens the features exhibited in rock-masses. We find in 
 all sizes the phenomena of faults, contortions, cavities, segrega- 
 tions, etc. ; and we are almost irresistibly led to the conclusion 
 that the microscopic is but the image of the macroscopic, and 
 vice versa. But, in accordance with this principle, it may be 
 (indeed, it ought to be) true that the small ruptures are some- 
 
 10 For a single and uncertain instance of possibly simple circular movement, 
 adduced by Professor Hoefer, see my paper above cited, p. 463. 
 
THE TORSIONAL THEORY OF JOINTS. 103 
 
 times produced, as are larger faults, by tensile stress. In fact, 
 I think such minute tension- ruptures are frequently to be 
 observed, but they do not generally, if, indeed, they ever do, 
 exhibit the smoothness and regularity of joints. 
 
 MR. BECKER : I may remark that faults supposed to be pro- 
 duced by torsion are said to be so common in certain French 
 mining-districts that the miners have a special name for them. 
 They call them hinge-faults, which is, I think, a very good 
 name. 
 
 The term "joint" I regard as used simply for convenience 
 to designate those partings in rocks on which the throw is not 
 apparent without close observation. Excepting in the amount 
 of throw, they are not distinguishable from the paraclastic rup- 
 tures on which mineral veins form. Even on joints ores some- 
 times occur, e.g., the " paints " of the quicksilver-mines. Joints 
 also pass over into cleavage. This structure sometimes con- 
 sists of closely-grouped joints of microscopic throw, and some- 
 times of mere deformation not carried quite far enough to 
 induce rupture. Cleavage and faulting are equally orogenic 
 disturbances. 
 
 C. R. BOYD, Wytheville, Va. : In examining a silver-mining 
 property at Conrad Hill, 6 miles southeast of Lexington, 
 Davidson county, K C., several years ago, I found two series 
 of fissures crossing each other, one set being mainly filled with 
 carbonate of iron and magnesia, the other with iron and copper 
 pyrites, carrying gold and silver. The individual fissures of 
 each series were not more than 15 or 20 ft. apart. The car- 
 bonate veins had a north-and-south strike, and a dip of 30 
 west. The pyrites veins ran east of north and west of south, 
 dipping 40 west of north. The angle between the two series 
 was about the same as that which the mountain ranges of that 
 section make with the true meridian. That both series- could 
 have resulted from simple tangential strains or thrusts would 
 be difficult to prove, and that they could both be fissures of 
 contraction I hardly believe. Possibly torsion may have caused 
 them ; but it is more probable, in my judgment, that they re- 
 sulted from disturbances proceeding from separate foci, and 
 not necessarily simultaneous. 
 
104 THE TORSIONAL THEORY OF JOINTS. 
 
 MR. BECKER : The angle depends on the amount of distor- 
 tion which has preceded rupture. If a substance is brittle, like 
 glass or cast-iron, and yields to rupture before it has been 
 deformed to any considerable extent, the fissures will cross at 
 right angles. If, on the other hand, the character of the mass 
 or its confined position (as is often the case with rocks) pre- 
 vents rupture from occurring until deformation has reached an 
 extreme limit, the angle between the direction of the force and 
 that of fracture may be even 50 or 60, and large angles seem 
 always to mean great preliminary deformation. 
 
 The most usual conditions of rock-fracture involve the simul- 
 taneous formation of two sets of fissures ; but when the resist- 
 ances in all directions perpendicular to the line of force are 
 substantially uniform, four sets of ruptures may form, each 
 being at 45 or more to the line of force, and all four sets will 
 be slickensided. A single system of parallel faults involves the 
 action of a " rotational " stress (which is, of course, utterly dif- 
 ferent from a torsional stress) ; and a solitary fault arises as an 
 extreme, and in my experience rare, case of a rotational stress. 
 I am inclined to believe that when two or three or four sys- 
 tems of joints or fissures intersect a rock-mass they were, as a 
 rule, formed simultaneously. When a rock is once shattered 
 a fresh force meets, in general, with very unequal resistance in 
 different directions, and will cause disturbance on the old fis- 
 sures or brecciate the whole mass rather than induce a new, 
 regular system of intersecting partings. 
 
THE ALLOTROPISM OF GOLD. 105 
 
 No. 5. 
 The Allotropism of Gold. 
 
 BY HENRY LOUIS, LONDON, ENGLAND. 
 
 (Virginia Beach Meeting, February, 1894. Trans., xxiv., 182.) 
 
 IT can scarcely be considered a matter of doubt, in the 
 present state of our knowledge, that the existence of, at any 
 rate, two well-marked allotropic modifications of gold can be 
 recognized, namely (a), the ordinary, yellow variety, and (6) 
 the red, brown or purple, non-lustrous, amorphous variety. 
 
 There are, indeed, not wanting indications that still other 
 allotropic forms may be capable of existing. It is, for instance, 
 possible that the green colors of gold obtained under cer- 
 tain conditions, or the black powder produced when the alloy 
 of gold with potassium is decomposed by water, may represent 
 further allotropic modifications, although this proposition is 
 open to doubt. . It can scarcely be pretended that the two first- 
 named varieties have been absolutely isolated, yet it is, perhaps, 
 quite permissible to speak of the ordinary and the amorphous 
 modifications as having a proved existence. 
 
 Ordinary gold is sometimes found crystallized in nature, 
 although never in a state of purity. When gold is melted and 
 cooled slowly, its surface shows crystalline markings, and the 
 fact that it is capable of crystallizing in the cubic system may 
 be looked upon as established. When gold is produced by 
 precipitation, the form which it assumes is dependent on the 
 conditions of precipitation. G. Rose l says that gold precipitated 
 by ferrous sulphate from very dilute solutions is so finely 
 divided that no regular form can be recognized, but in more 
 concentrated solutions the precipitate consists of minute cubes. 
 When oxalic acid is used as a precipitant, the gold is coarser 
 and forms octahedral crystals. J. Thomsen 2 has obtained 
 similar results. Working with dilute and with highly-dilute 
 
 1 Poggendorff's Annalender Physik und Chemie, vol. Ixxiii., p. 8 (1848). 
 a Journal fur praktische Chemie, vol. xiii., p. 348. 
 
106 THE ALLOTROPISM OF GOLD. 
 
 solutions, I have myself been quite unable to recognize any 
 crystalline structure, even under the highest powers of the 
 microscope ; nor did there seem to be even any tendency of 
 the particles to group themselves into arborescent forms, such 
 as might indicate incipient crystallization. Precipitates from 
 solutions containing between 0.0001 and 10 per cent, of gold 
 gave no indications of crystallization, even when magnified 800 
 diameters. 
 
 Thomsen (loc. cit.) has also pointed out that the physical 
 characters of precipitated gold differ according as it has been 
 precipitated from solutions of its chloride or its bromide. He 
 also found that these different forms possessed different degrees 
 of thermic energy, and hence deduced a strong argument in 
 favor of their being allotropic varieties. 
 
 The specific gravities of various forms of gold differ con- 
 siderably. G. Rose (loc. cit.) found that fused gold had a 
 density of 19.3336 after it had been compressed in a coining- 
 press, it being a little lower before this mechanical treatment. 
 The density of precipitated gold thrown down by ferrous sul- 
 phate he found to vary from 19.5419 to 20.6882, the highest 
 figures being obtained from extremely-dilute solutions, the 
 precipitate from which showed no trace of crystalline form ; 
 when precipitated by oxalic acid its specific gravity was 
 19.4791. When such amorphous gold was struck in the coin- 
 ing-press, its density became reduced to 18.0194. I have found 
 that the density of gold left on dissolving out various metals 
 alloyed with it, when the gold remains behind in a brown, 
 amorphous, lusterless condition, varies between 20.3 and 19. 5. 3 
 
 It is only fair to notice that Rose did not ascribe the differ- 
 ences in the densities of the different forms of gold to allot- 
 ropism, but has suggested another explanation, which is 
 hardly, to my mind, a sufficient one. It is probably safe to 
 assume that there are two modifications of gold one a light 
 one, of density 19.3 or thereabouts, and the other a heavy one, 
 the density of which approaches 20.7 while various combina- 
 tions of these extreme forms are capable of occurring. 
 
 In this connection the curious divergencies in the densities 
 of specimens of native gold, from different localities but of 
 
 3 See note by the writer, Trans., xxii., 117 (1893). 
 
THE ALLOTROPISM OF GOLD. 107 
 
 about the same composition, may also be referred to ; allotro- 
 pism may, at any rate, be suggested as a possible explanation 
 of them. There are thus sufficiently well marked differences 
 in physical characteristics to support the hypothesis of allot- 
 ropism. 
 
 As regards chemical properties, Thomsen has also pointed 
 out that when amorphous, pulverulent gold is acted on by 
 chlorine or bromine, aurylic compounds (Au 2 Cl 4 or Au 2 Br 4 ) are 
 produced ; whereas, these same substances produce auric com- 
 pounds (AuCl 3 or AuBr 3 ) with ordinary gold. 
 
 I have found another point of difference, of far greater 
 practical importance, in the behavior of these modifications 
 towards mercury. Ordinary gold, of course, amalgamates 
 readily, as is well known. I have found that gold precipitated 
 from highly-dilute solutions by ferrous sulphate is not attacked 
 at all by mercury when freshly precipitated, and only slightly 
 after drying on an air-bath. Near the boiling-point of mer- 
 cury, partial amalgamation took place, but it was by no means 
 complete. Mercury containing a large amount of sodium 
 amalgam was equally without effect on the dry gold, although 
 it readily and completely amalgamated it when moist. In 
 these observations I seem to have been partly anticipated by 
 Ludwig Knaffl, 4 who, however, appeared to attach little im- 
 portance to his observations. In a brief note on the prepara- 
 tion of certain amalgams of gold, he says : 
 
 "Gold precipitated by green vitriol or mercurous nitrate is not suitable for 
 amalgamation, as it is too finely divided and always floats on the surface of the 
 mercury 6 as a black powder, whether heated mercury be poured upon heated gold 
 or vice versa. I examined this floating black powder, and found it to contain gold 
 and mercury. . . . Gold precipitated either by means of arsenious acid or by 
 boiling a solution of the chloride in amylic alcohol, when it separates out in small, 
 lustrous octahedra, is best suited for amalgamation." 
 
 It may also be added that the purple of Cassius, which prob- 
 ably contains an allotropic modification of gold, is not attacked 
 by mercury. The black pulverulent form of gold resulting 
 from the decomposition of the potassium-gold alloy likewise 
 resists amalgamation. On the other hand, the coherent gold 
 
 * Dingkr's Polytechnisches Journal, vol. clxviii., p. 282 (1863). 
 5 The italics are mine. H. L. 
 
108 THE ALLOTROPISM OF GOLD. 
 
 sponge left on dissolving out the alloying metal from a gold- 
 alloy amalgamates fairly readily, as does also the coherent pale- 
 brown powder produced by precipitating with sulphurous acid 
 a strong solution of auric chloride. 
 
 All forms of gold are converted into the ordinary yellow, 
 lustrous variety by the action of heat. A very high tempera- 
 ture is not required, but the exact point has not yet been 
 determined; it is certainly well above 200 C., but probably 
 under 600 C. 6 Powerful mechanical action, such as percus- 
 sion, friction, or compression, has the same effect. 
 
 I do not pretend that the above data form anything like a 
 complete chain of evidence proving irrefragibly the allotropism 
 of gold, or that our knowledge of this subject is precise or 
 definite ; yet I venture to think that the facts do warrant us in 
 looking upon the following deductions as probably correct: 
 
 1. Gold is capable of existing in allotropic modifications. 
 
 2. One of these modifications is capable of amalgamation 
 only with great difficulty, if at all. 
 
 3. This modification is capable of being produced and of 
 subsisting under conditions that may reasonably be supposed 
 to exist in nature when gold is deposited in reefs. 
 
 Whatever may have been the nature of the solution by 
 means of which gold has been introduced into the deposits in 
 which we find it, whether as a soluble haloid salt, as is generally 
 supposed, or as an alkaline aurate, as I venture to suggest, 7 it 
 must have been precipitated from such solution in various 
 ways and under varying conditions. We have but few indica- 
 tions of the cause of this precipitation, but it is reasonable to 
 conjecture that such reagents as ferrous sulphate or sulphurous 
 acid, both resulting, perhaps, from the slow oxidation of iron 
 pyrites, may have found their way, in solution, into the fissures 
 within which the gold-solution was circulating, and may thus 
 have caused the deposition of gold within the reefs. Now, if 
 the gold, thus deposited from highly-dilute solutions, happened 
 never to be exposed to a particularly high temperature, or to 
 violent mechanical action, the conditions would be favorable 
 
 6 I am at present engaged in investigating this point, and hope to publish 
 shortly the result of my research. H. L. 
 
 7 On the Mode of Occurrence of Gold, Mineralogical Magazine, vol. x., No. 47, 
 p. 241. 
 
THE ALLOTROPISM OF GOLD. 109 
 
 to the production of that allotropic modification of gold which 
 is indifferent to the action of mercury. In other words, under 
 the above conditions, an auriferous deposit will have been pro- 
 duced in which a greater or smaller part, or perhaps even the 
 whole, of the gold is what gold-miners term " rusty." I have 
 little doubt that the " rustiness " of gold is in different cases 
 due to widely-different causes that, in fact, there is more than 
 one kind of " rustiness ; " but I venture to think, also, that 
 there is sufficient evidence to warrant us in classing allotropism 
 among such causes of " rustiness." If this is correct, I need 
 hardly point out either the great practical value or the applica- 
 tion of this deduction. The gold which is thus allotropically 
 indifferent to mercury is in a condition in which it is readily 
 attacked by such reagents as chlorine and potassic cyanide. I 
 have pointed out long ago that the gold of the Witwatersrand 
 deposits of the Transvaal was probably deposited in situ under 
 some such conditions as I have sketched above, and it is now 
 notorious that a large proportion of the gold in them is not 
 attacked by mercury, but readily by potassic cyanide solution. 
 Again, in some cases it may be economically feasible to con- 
 vert the non-amalgamable modification of gold into the common 
 amalgamable variety by heating the ore to a moderate tem- 
 perature, or the same end may be attained by mechanical 
 means. In any case, the only really sound method of prevent- 
 ing losses of gold in the process of gold-extraction is that of 
 ascertaining, in the first place, the ultimate causes of such loss; 
 and I venture to hope that it will be found that among such 
 causes, the one here treated of namely, allotropism of gold 
 will be found worthy of more consideration than it has hitherto 
 received from scientific gold-miners. 
 
110 THE SUPERFICIAL ALTERATION OF ORE-DEPOSITS. 
 
 No. 6. 
 The Superficial Alteration of Ore-Deposits. 
 
 BY R. A. F. PENROSE, JR., U. S. GEOLOGICAL SURVEY. 
 
 (Reprinted from The Journal of Geology, vol. ii., No. 3, Apr.-May, 1894.) 
 
 I. INTRODUCTION. 
 
 THE superficial alteration of ore-deposits is a recognized 
 principle of geology, in the same way as is the superficial altera- 
 tion of any of the common rocks. Its importance in some 
 classes of ore-deposits is also well understood, as in many 
 precious-metal deposits; while in other classes, its importance 
 has been proved in individual cases, as in the Lake Superior 
 iron-deposits. The causes and effects of superficial alteration 
 in many classes of deposits, however, are not so generally under- 
 stood; and it is the object of the present paper to show that 
 such changes almost invariably give rise to exceedingly im- 
 portant chemical and physical phenomena, while in many 
 deposits, the question as to whether they can or cannot be 
 profitably worked depends largely on the extent and character 
 of this alteration. 
 
 The various treatises on ore-deposits published in the United 
 States and Europe make frequent mention of superficial altera- 
 tion, but have not treated the subject fully. As early as 1854, 
 however, before which time but little accurate information was 
 had on the geologic nature of ore-deposits, Prof. J. D. Whit- 
 ney in his classic volume, The Metallic Wealth of the United 
 States, describes the alteration-products, or gossans, in certain 
 deposits and mentions others. On the more purely chemical 
 side of the question, the work of Bischof, Daubree, Roth, Rose,. 
 Hunt, Breithaupt, Blum, Julien, Deville, Debray, Volger, Mois- 
 san, Fremy, Levy, Fouque, and others has afforded much valu- 
 able information and many useful suggestions. The chemical 
 principles brought out by these various authors have been ap- 
 plied, to a certain extent, to the solution of the phenomena of 
 
THE SUPERFICIAL ALTERATION OF ORE-DEPOSITS. Ill 
 
 the origin of ore-deposits, but have not as yet been applied 
 to anything like their possible extent to the solution of the 
 phenomena of the alteration of ore-deposits. 
 
 II. GENERAL FEATURES. 
 
 Scope of the Subject. 
 
 The modern idea of ore-deposits teaches that formations of 
 this kind represent a process of concentration of mineral matter, 
 either by chemical or physical means; in other words, that 
 they are unusual localizations of certain minerals which are 
 often found disseminated in smaller quantities in many common 
 rocks, and that they differ from the same minerals situated in 
 other conditions, only in their degree of concentration. These 
 concentrations may take place at different times in the history 
 of the rocks in which the deposits occur. If they occur in 
 sedimentary rocks, they may sometimes be formed during the 
 deposition of the rocks with which they are associated, as in 
 the cases of placer-gold, stream-tin, and sometimes of other 
 ores; while if they occur in igneous rocks, they may some- 
 times be the result of concentration by differentiation from 
 fused magmas. 1 More usually, however, ore-deposits are a 
 result of a concentration after the formation of the inclosing 
 rock, whether the latter be of sedimentary or of igneous origin. 
 The mineral matter represented in this concentration may be 
 derived from the inclosing rocks or closely-adjacent rocks, as 
 in the case of many, if not most, iron-ore deposits ; or it may 
 be derived from more distant sources, often from greater or less 
 depths, as in some of the precious-metal deposits. Occasion- 
 ally, both these sources may be drawn on for mineral matter 
 in one deposit. In this subject of the original source of an ore, 
 we enter a field concerning which there has been much dispute 
 of late years between the advocates of the lateral-secretion 
 theory and those who favor the idea of a deep-seated source for 
 many ore-deposits. It is not, however, the purpose of the 
 present paper to enter into this discussion, and the following 
 
 1 This has been shown by J. H. L. Vogt (Zeitschrift filr praktische Geologic, Jan., 
 1893) to be true of certain titaniferous iron-ores and other deposits in the eruptive 
 rocks of Norway. It may also be true of certain titaniferous iron-ores in the 
 United States. 
 
112 THE SUPERFICIAL ALTERATION OF ORE-DEPOSITS. 
 
 remarks are confined to what happens in the superficial parts 
 of ore-deposits, and to a less extent of allied formations, after 
 the materials forming them have been brought into their 
 present, or approximately their present, positions. 
 
 Relation of Alteration in Ore-Deposits and in Country -Hocks. 
 
 Ore-deposits are generally more or less changed in their 
 upper parts by atmospheric influences, so that very rarely do 
 the same mineralogical and physical features that are found in 
 these parts continue to very great depths. In considering this 
 superficial alteration, we discuss a subject analogous to the 
 secular decay of rocks. The latter, however, involves usually 
 but a limited number of common rock-forming minerals, while 
 the secular decay of ore-deposits involves a great variety of 
 minerals, not only the oxides, carbonates, and silicates common 
 in most rocks, but also sulphides, arsenides, tellurides, sele- 
 nides, antimonides, chlorides, bromides, iodides, fluorides, sul- 
 phates, phosphates, tungstates, molybdates, and numerous other 
 classes of minerals, many of which, under surface-influences, 
 give rise to intricate chemical changes. In discussing the sub- 
 ject of the superficial alteration of ore-deposits, therefore, we 
 treat a similar, but much less understood, subject than the 
 superficial alteration of rocks. 
 
 Technical Names of Alteration- Products. 
 
 The altered surface-outcrop of ore-deposits is known by 
 various names in different regions. Among the Cornish 
 miners of England it is known as gossan, a name which has 
 also been adopted into American mining nomenclature, though 
 other special names are given in special classes of deposits. In 
 France it is known &a-chapeau de fer; in Germany as eisener 
 Hut ; among the Spanish Americans as pacos or colorados. As 
 almost all deposits contain more or less iron-minerals, the out- 
 crops are usually stained brown from their oxidation, and 
 hence the reference to iron in the French and German names. 
 Sometimes, however, the outcrops are stained black by the 
 oxidation of manganese carbonate or silicate, or green by cop- 
 per-minerals, or other colors by the formation of other com- 
 pounds. 
 
THE SUPERFICIAL ALTERATION OF ORE-DEPOSITS. 113 
 
 Agents of Alteration. 
 
 The superficial alteration of ore-deposits, as of any rock, 
 results from a combination of mechanical and chemical disinte- 
 gration, brought about by the combined action of the atmos- 
 phere, surface-waters, changes in temperature, and the various 
 organic and inorganic materials contained in the air and water. 
 In nature, we never deal with perfectly pure water, but dif- 
 ferent waters contain different ingredients derived from the air 
 and from the different materials with which they come in con- 
 tact. Among the most important of these ingredients are 
 oxygen, numerous organic acids like carbonic, oxalic, malic, 
 citric, formic, propionic, butyric, acetic acids, etc., certain inor- 
 ganic acids, such as sulphuric, nitric, hydrochloric, hydrobro- 
 mic, etc. Some of the acids mentioned occasionally occur 
 in the free state, but most of them are generally combined 
 with some of the bases present, such as the alkalies, lime, mag- 
 nesia, iron, alumina, etc. These various ingredients, of course, 
 are not all contained in the same waters, but are found in 
 various associations in different waters. The organic acids 
 mentioned represent various stages of oxidation of materials 
 from organic matter, but they all eventually, if allowed to be- 
 come completely oxidized, pass into carbonic acid; while if 
 they are in combination with different bases, these salts are 
 eventually converted to carbonates. 
 
 Method and Chemical Effects of Alteration. 
 Surface-waters thus charged with various chemical ingre- 
 dients percolate down into ore-deposits, and there meet various 
 materials which are even less stable under their influence than 
 most of the common rocks. The alteration, therefore, is com- 
 paratively rapid, and, though only superficial, generally extends 
 to much greater depths than in the surrounding country-rock. 
 From a chemical stand-point, the first effect of this superficial 
 influence is usually the oxidation, or hydration, or both, of cer- 
 tain ingredients, followed generally by the formation of other 
 chemical combinations and by the leaching of certain materials. 
 In the formation of these other chemical combinations, how- 
 ever, the base usually remains the same, and the alteration 
 consists generally in a change of the materials associated with 
 the base, that is, in the acidic portion of the mineral or the 
 
114 THE SUPERFICIAL ALTERATION OF ORE-DEPOSITS. 
 
 part that represents the acidic portion. Thus, iron sulphides 
 are oxidized to iron sulphate, and then this is. converted by 
 further oxidation and by hydration to the hydrous sesquioxide. 
 Copper sulphides may be oxidized to copper sulphate; and 
 from the sulphate, by the agency of materials in surface-waters, 
 may be formed copper carbonates, haloid compounds, silicates, 
 oxides, and even metallic copper; while from some of these, 
 still other compounds may be produced. Similar reactions 
 occur in many lead-, zinc-, silver-, gold-, and other deposits. 
 
 Occasionally, chemical changes may occur without previous 
 oxidation, and sometimes, though rarely, surface-influences 
 under peculiar conditions may have a reducing effect, as in the 
 formation of iron pyrites and copper pyrites from the sulphates 
 of iron and copper, or in the formation of native copper by the 
 action of a ferrous salt on certain copper salts, or in the forma- 
 tion of native silver in surface-outcrops. In many of such 
 cases, however, the chemical action is primarily one of partial 
 oxidation, and the reducing action follows as the effect of one 
 of the partly-oxidized compounds on the other, as in the case 
 of copper just mentioned. In deposits such as gypsum, a 
 reduction, due sometimes to superficial influences, is seen in 
 the occasional formation of sulphur from gypsum. 
 
 An important chemical effect of surface-influences is the re- 
 moval in solution of certain ingredients of the ore-deposit 
 which are soluble in surface-waters ; as the removal of the cal- 
 cite gangue of many silver- and other deposits; the oxidation 
 and removal of the sulphur in various silver-, lead-, zinc-, cop- 
 per-, and other deposits; the oxidation and removal of both 
 the iron and sulphur of iron pyrites in auriferous quartz veins; 
 the removal of silica from certain iron-deposits, such as those 
 in the Lake Superior region, etc. Probably many phosphate- 
 deposits are formed by the superficial leaching of carbonate of 
 lime from calcareous beds, and the corresponding concentra- 
 tion of phosphate of lime once finely disseminated in the same 
 beds. 
 
 Another chemical effect of superficial alteration is seen in 
 the occasional formation of mineral deposits of importance by 
 certain materials carried from outside sources and deposited 
 in a rock of otherwise no commercial value. Thus certain 
 phosphate-deposits of the South Pacific ocean, the West Indies,. 
 
THE SUPERFICIAL ALTERATION OF ORE-DEPOSITS. 115 
 
 and possibly of Florida, are formed by the leaching of soluble 
 phosphates from guano, their transportation down into under- 
 lying limestone or coral reefs, and the precipitation of the 
 phosphoric acid as tribasic phosphate of lime, which, being 
 almost insoluble, arrests further escape of the phosphatic 
 materials. 
 
 Again, another chemical effect is seen in the incrustations, 
 and even extensive beds, of saline materials, like borax, niter, 
 and the various alkaline salts of the Western arid regions, 
 formed by precipitation from water rising by capillary action 
 through the soil, becoming evaporated on the surface and de- 
 positing the saline materials which it has dissolved from below. 
 Many saline deposits are formed by the simple evaporation of 
 surface-waters, such as lakes, seas, etc., but certain deposits 
 undergo only an initial concentration in this way, and are laid 
 down with clay, sand, and gravel, while further concentration 
 is due to this capillary action. In the case of niter, indeed,, 
 the saline material is very often, if not generally, formed in 
 soils or guano-beds and undergoes its first concentration by 
 this capillary action. 
 
 In the various chemical changes mentioned above, the class 
 of salts that remains, whether oxides, carbonates, haloid com- 
 pounds, etc., varies with the nature of the bases affected. 
 Thus, iron sulphides and copper sulphides are both oxidized 
 and form sulphates. But here the similarity of their behavior 
 ends, for the iron sulphate probably passes then into a basic 
 sulphate and then into a hydrous sesquioxide, while the copper 
 sulphate takes up carbonic dioxide and water and forms basic 
 carbonates. The iron sulphate might, under certain condi- 
 tions, form a carbonate in a similar manner, but this compound 
 would be very unstable under the conditions existing in the 
 alteration of sulphide deposits and would quickly go into the 
 form of the hydrous sesquioxide, while the carbonate of copper 
 is stable under existing conditions and remains. 
 
 In the same way, if silver sulphide and iron sulphide are 
 both oxidized and then affected by waters carrying common 
 salt or other chlorides in solution, the silver is converted to 
 chloride, which is insoluble and remains ; while the chlorides 
 of iron are much less liable to be formed, as they are soluble, 
 and some of them unstable, compounds, and even if they were 
 
116 THE SUPERFICIAL ALTERATION OF ORE-DEPOSITS. 
 
 formed, they would be leached out or oxidized. Hence, though 
 chloride of silver is a common product of alteration, in silver- 
 deposits, chloride of iron is never found, at least to any extent, 
 as a product of alteration of iron-deposits. 
 
 Again, it is frequently found that unaltered auriferous iron 
 pyrites contains a certain amount of silver, while the altered 
 part often carries almost none. In such cases, the gold has 
 remained stable during the alteration, while the silver, in the 
 absence of a chloride or other reagents to convert it to an in- 
 soluble compound, has been dissolved and carried away in 
 solution by the acid materials generated during alteration. 
 
 Hence, the materials in surface-waters affect different bases 
 differently, and, therefore, there is a great difference in the 
 classes of salts formed by the same surface-waters on the ores 
 of different metals. In the same deposit there may be formed 
 an oxide of one metal, a carbonate of another, a chloride of 
 another, etc. In fact, in some of the silver-deposits of southern 
 New Mexico, there can be found hydrous sesquioxide of iron 
 formed from iron sulphide, carbonates of copper formed from 
 copper sulphides, and chloride of silver formed probably from 
 silver sulphides, and yet in all probability the same surface- 
 waters produced all these changes practically simultaneously. 
 
 As a result of these various changes, certain materials are 
 sometimes leached from the upper parts of ore-deposits, which 
 have become porous by alteration, and carried down to the less 
 pervious unaltered parts. Here they are precipitated by meet- 
 ing other solutions or in other ways, and hence the richest 
 bodies of ore in a deposit often occur between the overlying 
 altered part and the underlying unaltered part. This is not 
 always the case, but it is true of some copper-, silver-, iron-, 
 .and other deposits. 
 
 Physical Effects of Alteration. 
 
 From a physical stand-point, the effect of superficial altera- 
 tion is generally to make the deposit more open and porous, to 
 cause it to shrink, and, in some cases, to convert it to a loose 
 material of the consistency of sand and clay. In some cases, 
 however, especially where considerable hydration goes on, an 
 expansion may be caused. This is well seen in the formation 
 of gypsum by the hydration of anhydrite, often causing an ex- 
 
THE SUPERFICIAL ALTERATION OF ORE-DEPOSITS. 117 
 
 pansion sufficient to brecciate and fold the associated rocks, 2 
 and amounting to about 33 per cent, of the original material. 3 
 In the conversion of carbonate of iron to the hydrous sesqui- 
 oxide of iron, or limonite, it has been found* that there is 
 a contraction of 19.5 per cent., giving the deposit the loose 
 porous structure characteristic of limonite and forming the 
 familiar limonite geodes. 5 In this case carbon dioxide has been 
 removed from the iron, but oxygen and water have been 
 added. A porosity is also produced by the removal of certain 
 ingredients in an ore-deposit without the addition of others, as 
 in the oxidation and leaching of iron pyrites in veins of aurif- 
 erous quartz, leaving a loose, porous, spongy quartz mass. 
 
 Surface-decomposition has also, in many places, not only 
 affected the ore-deposit itself, but also the country-rock in the 
 immediate vicinity, and has converted it into a loose material 
 of a sandy or clayey consistency, as at Iron Mountain, Mo., in 
 the Batesville manganese-region of Arkansas and in other 
 localities described beyond. In the iron- and manganese- 
 deposits of the Cambrian and Lower Silurian rocks in the 
 Appalachian region, the limestones and shales, which once in- 
 closed the ore-bodies, have often been converted to clay in the 
 same way as in the Batesville region ; and, in fact, the com- 
 mon mode of occurrence of these deposits is as residual clays 
 carrying irregular bodies and nodules of ore. 
 
 This decay of the country-rock in immediate association with 
 ore-deposits, is generally more extensive than in similar rocks 
 not associated with such deposits, and, therefore, requires fur- 
 ther explanation than the simple action of ordinary surface- 
 waters. The explanation is, doubtless, in many cases, that the 
 rock has decayed under the influence of the same waters that 
 originally concentrated the ore ; and as these waters differed 
 from most waters in character and in the materials they held 
 in solution, they often had an abnormal effect. Moreover, 
 when subsequently the ore-body is affected by surface-influ- 
 
 2 Elie de Beaumont, Explic. Carte geologique de France, vol. ii., p. 89. E. A. F. 
 Penrose, Jr., Arkansas Geological Survey, vol. i., pp. 535 to 538 (1890). 
 
 3 A. Geikie, Text Book of Geology, 3d ed., p. 345 (1893). 
 
 4 T. Sterry Hunt, Mineral Physiology and Physiography, p. 262 (1889). 
 
 5 K. A. F. Penrose, Jr., The Tertiary Iron Ores of Arkansas and Texas, Bulletin 
 of the Geological Society of America, vol. iii., pp. 44 to 50 (1891). 
 
118 THE SUPERFICIAL ALTERATION OF ORE-DEPOSITS. 
 
 ences, sulphuric acid is liberated from sulphides and carbonic 
 acid from carbonates, as well as other acids from other min- 
 erals, and all these materials have an active effect on most 
 rocks. Moreover, the porous nature of many ore-deposits, 
 after they have been altered on the surface, allows a freer per- 
 colation of surface-waters than elsewhere in the same country- 
 rock, and, hence, a correspondingly greater decay. 
 
 Another physical effect of surface-influences on ore-deposits 
 is seen in certain forms of brecciation due to physical or chemi- 
 cal causes, such as expansion by hydration, etc. Such breccia- 
 tion, however, has usually occurred in the country-rock before 
 the concentration of the ore-deposit; in fact, its existence, by 
 offering favorable conditions for deposition, has often been the 
 cause of the formation of the ore-deposit in a given place. 
 Though brecciation, therefore, is very important as a factor in 
 the concentration of ore-deposits, it does not belong, to any 
 large extent, in a discussion of the. surface-alteration of ore- 
 deposits after their formation, and, therefore, it will not be 
 treated further in this paper. 
 
 Depth of Alteration. 
 
 Having thus discussed briefly the means by which superficial 
 alteration in ore-deposits is produced, and the results of this 
 alteration, the next feature to be taken up is the depth to which 
 it extends. As already shown, the alteration is primarily one 
 of oxidation and generally of hydration; and, though either 
 may occur without the other, they both very often occ^r 
 together. When surface-waters percolate into the rock, thefi* 
 influence is more active near the surface, because they carry 
 large quantities of oxygen, and because the oxygen of the air 
 itself also has some influence. As they sink deeper, the effect 
 of the oxygen of the air becomes less active, and the oxygen 
 dissolved in the water is consumed in oxidizing various ma- 
 terials which it meets on the way, until finally most of the 
 oxygen is lost and active oxidation ceases. Theoretically, this 
 oxidizing action may extend down as far as, and sometimes be- 
 low, the level of the drainage of the surrounding country, which 
 is called also the zone of permanent saturation. Above that 
 level, there is a constant circulation of water from the surface 
 downward, thus affording means of active oxidation ; but when 
 
THE SUPERFICIAL ALTERATION OF ORE-DEPOSITS. 119 
 
 the water reaches that level, not only has most of the oxygen 
 contained in solution generally been used up, but also the cir- 
 culation of the water is much more sluggish, so that oxidation 
 is less active. 6 
 
 The process of hydration, when the materials affected do not 
 require oxidation before they can become hydrated, may ex- 
 tend down indefinitely below the limit of oxidation ; but when 
 oxidation is necessary before hydration is possible, the latter 
 process of course can extend no deeper than oxidation. Thus 
 the silicate of aluminum in feldspar may become hydrated and 
 form kaolin without the intervention of oxygen. This is 
 brought about by the action of carbonic acid and water, which 
 react on the feldspar and form alkaline carbonates, kaolin, and 
 free or hydrous silica. Theoretically, therefore, kaolinization 
 ought to go on to any depth that can be reached by water and its 
 almost universal accompaniment, carbonic acid. In this case, 
 however, the base in question is already in its peroxide condi- 
 tion (A1 2 3 ) ; but when a base is not in this condition, it 
 frequently requires oxidation previous to hydration. Thus 
 sulphide of iron does not become hydrated until it is peroxi- 
 dized, and this mineral, therefore, requires oxidation previous 
 to hydration. 7 
 
 The various materials other than oxygen in surface-waters 
 have a very important effect on the mineral matter with which 
 they come in contact, and their action sometimes takes place 
 before that of oxidation, though it often requires at least a par- 
 tial previous oxidation. The effect is both to form new chemical 
 compounds with the materials involved, and to dissolve and 
 bodily remove certain materials. As with oxygen, however, so 
 with these other agents of alteration, they are more active 
 above the drainage-level of the country than below it, and an 
 additional reason for this is that many of the materials affected 
 require a primary oxidation before they enter into other 
 chemical combinations. Thus sulphide of lead is oxidized to 
 
 6 It is possible that the oxidation near the surface is due largely to free oxygen 
 in the waters, while, when this becomes exhausted at a depth, the oxidation may 
 be due to the abstraction by mineral matter of the oxygen in combination with 
 materials in solution. 
 
 7 For a full discussion of this subject see H. Kose, Ueber den Einfluss des 
 Wassers bei chemischen Zersetzungen, Poggendor/'s Annaltn der Physik und Chemie, 
 vol. Ixxxii. (1851) et seq. 
 
120 THE SUPERFICIAL ALTERATION OF ORE-DEPOSITS. 
 
 sulphate of lead before it can take up carbonic acid and form 
 carbonate of lead ; while on the other hand, carbonate of lime 
 can be converted to sulphate of lime (gypsum) by the action 
 of sulphuric acid or certain sulphates without any change in 
 the degree of oxidation of the lime, 
 
 It will thus be seen that in going from the surface downward, 
 we pass from a zone of active oxidation into a zone in which 
 oxidation practically ceases. Below the level of permanent 
 saturation, the waters may sometimes gradually sink to very 
 great depths, even deep enough to become intensely heated 
 and possibly dissociated. Such waters may have a very im- 
 portant effect in the formation of ore-bodies, though in a man- 
 ner quite different from their action on the surface. The 
 present discussion, however, relates not to this, but to only 
 superficial influences. 
 
 Though theoretically, therefore, alteration of one kind or 
 another may extend down to, and in some cases much below, 
 the level of permanent saturation, and if given sufficient time 
 would actually go to such depths ; yet in many, if not most, 
 cases it has not yet reached that level. The actual depth to 
 which alteration does extend varies with the topographic con- 
 ditions of the region, the chemical nature and the porosity of 
 the deposits affected, the character of the climate, and other 
 minor conditions. 
 
 The topography of a region affects the depth of alteration 
 because it is one of the principal features in determining the 
 depth of permanent saturation. The chemical nature of the 
 deposit affects the depth of alteration because on this depends 
 the degree of resistance it will offer to the chemical effects of 
 percolating waters. The porosity of the deposit affects the depth 
 of alteration because, in deposits of similar kind but of different 
 porosity, the more porous will be more accessible to surface- 
 influences, and will, therefore, be more affected, in a given 
 time, than the less porous deposit. 
 
 The climatic conditions, such as the amount and manner of 
 occurrence of rain-fall and other forms of atmospheric moisture, 
 and the rate and degree of variation in temperature, have a large 
 influence on superficial alteration. On the amount of rain-fall 
 and other forms of atmospheric moisture depends the amount 
 of moisture available as an agent of alteration ; while on their 
 
THE SUPERFICIAL ALTERATION OF ORE-DEPOSITS. 121 
 
 mode of precipitation depends, other things being equal, the 
 amount of water which would sink into the deposit, thus effect- 
 ing alteration, and the amount that would immediately run off 
 the surface or be evaporated and thus have but little altering 
 effect. The rate and degree of variation in temperature affect 
 the amount of breaking in the rock by expansion and contrac- 
 tion, and, therefore, the accessibility of the rock to surface- 
 influences. The character of the climate also influences, to a 
 certain extent, the nature and amount of vegetation, and from 
 the vegetation are obtained many organic acids which assist 
 the action of surface-waters. In other ways, also, such as in 
 the generation of nitric acid in the atmosphere, the character 
 of the climate influences the agents of alteration. 
 
 As a result of all these influences, surface-alteration is found 
 to extend in different ore-deposits to depths varying from only 
 a few inches, or in fact only a fraction of an inch, to several 
 hundred and even a thousand or more feet. In glaciated re- 
 gions the products of decay have often been swept away by 
 glacial action, and the time which has elapsed since then has 
 not been sufficient for alteration to have extended to any great 
 depths ; while in regions of moist climates, the erosion some- 
 times, though not always, keeps pace with the alteration, so 
 that the depth of the change is shallow. In those regions, 
 however, which have not been recently glaciated and which 
 have dry or only moderately moist climates, so that erosion is 
 slight; or in places which have moist climates, but which, on 
 account of their topography, are not subjected to very active 
 erosion, the products of alteration collect, and the changes are 
 traceable downward often to great depths. 
 
 In the copper-regions of Michigan, the deposits have been 
 exposed to glaciation, and are still exposed to the active effects 
 of erosion in a moist climate, so that here, though the native 
 copper of the region is a material very easily affected by surface- 
 alteration, yet the only change observable is a slight stain of 
 copper carbonate or oxide on the surface of some of the native 
 copper, and even this is not always present. On the other 
 hand, in the arid region of the West, most of which has not 
 been recently glaciated and which has an exceedingly dry 
 climate, the residual products of alteration have accumulated 
 to great thicknesses. This region, however, had once a much 
 
122 THE SUPERFICIAL ALTERATION OF ORE-DEPOSITS. 
 
 more moist climate than now, and some of the alteration may 
 have occurred then. Many of the Arizona copper-deposits in 
 this region originally contained their copper in the form of 
 copper pyrites, which, under similar conditions, is probably 
 more resistant to surface-alteration than the native copper of 
 Michigan, and yet it has been changed to various other copper- 
 minerals for depths often reaching from 100 to over 700 ft. 
 In Chile some of the copper sulphide deposits are said to have 
 been altered to a depth of 1,500 ft., but it is very rare that 
 much alteration extends in any ore-deposits to greater depths 
 than this. In the more moist climate of Tasmania, the results 
 of alteration are also very marked. 
 
 The depth of alteration of ore-deposits in unglaciated regions 
 in the United States varies from a few feet to over 1,000 ft. In 
 the Appalachian region, many of the deposits of auriferous 
 quartz, iron pyrites, copper pyrites, etc.,. are altered to depths 
 varying from less than 1 to 100 ft. or more. Many of the 
 Clinton iron-ore deposits are altered to still greater depths. 
 The depth of alteration in these Appalachian deposits is usu- 
 ally much greater, other things being equal, south of the limit 
 of glaciation than north of it. In the silver-, lead-, gold-, and 
 copper-deposits of the Rocky mountains and the Western arid 
 region, such as at Butte City, Leadville, Central City, Cripple 
 Creek, Silver City, Lake Valley, Eureka, Virginia City, Park 
 City, the Coeur d'Alene district, and elsewhere, the alteration 
 has reached depths ranging from 50 to 600 or 700 ft., and in 
 some rare cases still more. At Granite Mountain, in Montana, 
 signs of alteration are seen in the argentiferous quartz-deposits 
 of that region, even at depths of 900 ft., though of course at 
 such depths the alteration is slight as compared with that 
 nearer the surface. 
 
 Complete alteration rarely extends to these greater depths, 
 and usually parts of a deposit which have as yet escaped altera- 
 tion appear comparatively near the surface. These are at first 
 very few and may be entirely inclosed by altered products, but 
 with increased depth they become more numerous and continu- 
 ous, until they predominate over the altered products, and 
 finally, when the limit of alteration is reached, they, entirely 
 replace them. The planes of contact between an ore-deposit 
 and the country- rock, that is, the walls, afford, when well 
 
THE SUPERFICIAL ALTERATION OF ORE-DEPOSITS. 123 
 
 defined, easy passages for the downward percolation of surface- 
 waters, and therefore alteration frequently continues down 
 along these lines for considerable distances after the limit of 
 alteration in the main part of a deposit has been reached. Any 
 other possible channels, such as the planes of contact of dif- 
 ferent minerals in banded deposits or the series of drusy cavi- 
 ties often found in the central parts of ore-deposits, may act in 
 the same way as passages for water. Hence the not infrequent 
 abundance of alteration-products, such as hydrous sesquioxide 
 of iron, and native copper and silver, along the walls and else- 
 where in certain deposits. 
 
 Classification of the Products of Alteration. 
 
 The products of superficial alteration may be divided into 
 two general classes : (1) Those which occupy the same position 
 as the materials from which they were derived, or are only 
 slightly removed, and possess the same general environment. 
 Thus the altered outcrops of auriferous quartz and iron pyrites, 
 of argentiferous galena, of sulphides of copper and many other 
 similar deposits, represent alteration-products occupying the 
 same general position as the original sulphide ores ; while the 
 iron-ore bodies of the Lake Superior region represent alteration- 
 products changed somewhat in position from that occupied 
 originally, but yet in the same series of rocks and sometimes 
 with somewhat similar environment. (2) In the second class 
 are included those deposits which have been entirely removed 
 from their original position and redeposited under totally dif- 
 ferent environments. Thus, placer gold-deposits, stream-tin, 
 most of the deposits carrying platinum and the allied metals, 
 magnetic and chromite sand, the gravels and sands carrying 
 precious stones, and many other similar deposits, represent this 
 class. They have been derived by the decay and erosion of 
 veins, dikes, or country-rocks carrying the materials now con- 
 centrated in these fragmental deposits. The materials in their 
 original environment may or may not have been sufficiently 
 concentrated to serve as commercial sources of supply, but the 
 fragmental deposits mentioned almost always represent a fur- 
 ther concentration. This class of deposits is of great importance, 
 but the present discussion relates more especially to the super- 
 ficial alteration of deposits that remain in situ, and therefore 
 
124 THE SUPERFICIAL ALTERATION OF ORE-DEPOSITS. 
 
 these will be treated more in detail than the other class (No. 
 2), though the latter will be mentioned as occasion requires. 
 
 III. SUPERFICIAL ALTERATION IN DIFFERENT DEPOSITS. 
 
 Alteration in Iron-Deposits. 
 
 It was once generally believed that most iron-deposits were 
 the result of direct precipitation from aqueous solution, or in 
 rarer cases, were igneous masses. It has long since been 
 shown, however, that most workable iron-deposits are the 
 result of a concentration subsequent to their deposition, while 
 very few are due to a direct precipitation during the formation 
 of sedimentary rocks, though some may be due to a process 
 of differentiation in the cooling of eruptive magmas. 8 The 
 original presence of the iron in sedimentary rocks was doubt, 
 less due to a direct precipitation during the formation of the 
 inclosing rock, but it was then in a finely-disseminated condi- 
 tion, and it was only by being subsequently taken into solution 
 again by percolating waters and concentrated, that it was con- 
 'verted into bodies of greater or less purity. Generally, though 
 possibly not always, this process is superficial, and though it 
 may extend to a depth of several hundred or even a thousand 
 feet or more, it can be traced directly to surface-influences, and 
 its effects are seen to decrease gradually with depth. Shaler, 9 
 in 1877, showed that some of the limonites of Kentucky, Ohio 
 and elsewhere were concentrations of iron derived in solution 
 from shales and other rocks and reprecipitated in underlying 
 limestone. 
 
 Van Hise, 10 in 1889, showed that the iron-deposits of the 
 Lake Superior region are concentrations of iron formerly dis- 
 seminated in a siliceous rock containing carbonate of iron and 
 other carbonates, and called by him cherty iron carbonate. 
 This disseminated iron was taken into solution by surface- 
 
 8 See foot-note *, p. 111. 
 
 9 N. S. Shaler, Kentucky Geological Survey, Report of Progress, vol. iii., New- 
 Series, p. 164 (1877). 
 
 10 C. K. Van Hise, The Iron Ores of the Penokee-Gogebic Series of Michigan 
 and Wisconsin, American Journal of Science, Third Series, vol. xxxvii., No. 217, 
 pp. 32 to 47 (Jan., 1889) ; The Iron Ores of the Lake Superior Region, Transac- 
 tions of the Wisconsin Academy of Science, vol. viii. (1891). For a fuller discussion 
 by Van Hise on this subject see Tenth Annual Report, U. S. Geological Survey, Pt. 
 I., pp. 409 to 422 (1888-89) ; Monograph XIX, U. S. Geological Survey (1892). 
 
THE SUPERFICIAL ALTERATION OF ORE-DEPOSITS. 125 
 
 waters, carried down until its passage was obstructed or im- 
 peded by less pervious rocks, often dikes, and there precipitated 
 by meeting with other solutions of a different nature. These 
 other solutions contained oxygen, while the iron-bearing solu- 
 tions had been largely robbed of their oxygen and had been 
 freed from silica by the large amount of carbonic acid they 
 contained. When, therefore, the two solutions met, the iron 
 in solution was oxidized and precipitated; while the silica, in 
 the spot where this precipitation occurred, was, on account of 
 the dilution of the carbonated waters with the other waters, 
 and through the agency of alkaline carbonates, dissolved and 
 carried off, thus gradually increasing the amount of iron and 
 removing the silica. By this theory, the iron is largely a re- 
 placement of the silica of the cherty iron carbonates, and has 
 been derived from the parts of the strata exposed to superficial 
 influences. The deposits are, therefore, of only superficial ex- 
 tent, though they may reach over 1,000 ft. below the surface, 
 yet when they pass below the action of surface-influences the 
 iron has not been concentrated, and they are of too low grade 
 to be mined for iron-ore. The methods of local concentration 
 proposed by Professor Van Hise for these Lake Superior iron- 
 deposits are equally applicable to certain other iron- deposits, 
 and are a most valuable addition to our knowledge of chemical 
 geology. They also bring out in a most prominent manner, 
 the fact that even rocks composed of materials like silica, 
 which are very resistant to surface-influences, may, under 
 proper conditions, be replaced on a large scale. 
 
 The iron-deposits of the Mesabi range, in Minnesota, which 
 have lately been described by H. Y. Winchell, 11 are supposed to 
 have had a somewhat similar origin to that given for the 
 Michigan and Wisconsin ores by Van Hise. Winchell believes 
 that they are due to the concentration by surface-agencies of 
 iron disseminated as oxides in a highly-siliceous rock, and that 
 in this concentration the silica has been replaced by iron. 
 
 The red hematites of the Clinton horizon of the Upper Silu- 
 rian in the Appalachian region have been at least partly formed 
 by superficial concentration which extends to only limited 
 depths. 
 
 11 Twentieth Annual Report, Minnesota Geological Survey, pp. 136 to 148 (1891). 
 
126 THE SUPERFICIAL ALTERATION OF ORE-DEPOSITS. 
 
 The iron-deposits in other geologic horizons of the Appala- 
 chian valley, especially in the Cambrian, Lower Silurian, and 
 Carboniferous rocks, are also often much changed by the 
 action of surface-influences. Many of the deposits in the 
 Cambrian and Lower Silurian can be clearly shown to be due 
 to a superficial replacement of limestone, or even of more sili- 
 ceous rocks like shales, by iron dissolved from ferruginous 
 rocks in the neighborhood. In such cases, the iron in the 
 original rock has been dissolved and carried off in carbonated 
 surface-water, and re-precipitated in the other rocks, all these 
 stages being directly due to surface-influences. Many of the 
 carbonate iron-ores of the Carboniferous rocks are rendered 
 not only of higher grade, but also more easy to treat, by the 
 oxidation of the carbonate to the sesquioxide and the removal 
 of the carbonic acid. Moreover, these carbonate ores often 
 occur as nodules, " kidney ores," in shale, and, on the surface, 
 this shale has been softened by atmospheric conditions, thus 
 facilitating mining; while away from the surface, the shale 
 becomes harder and makes mining more expensive. 
 
 Surface-influences on carbonate of iron have been made use 
 of artificially in Styria, where a very hard spathic iron-ore has 
 been mined and spread out on a hill-side for from 20 to 25 
 years. By this process the ore was oxidized and made more 
 porous, and thus became very much more cheaply treated. 12 
 
 At the celebrated Iron Mountain, in Missouri, a large part 
 of the ore came from conglomerates composed largely of frag- 
 ments of iron-ore, which had been weathered out of the pre- 
 Cambrian rocks that had originally contained them. These 
 conglomerates lie at the base of the Cambrian strata which 
 overlie the pre-Cambrian rocks, and even in the latter rocks, 
 where exposed, the original ore has been made much more 
 easy to work by the decay of the inclosing material and its 
 conversion to clay. 
 
 In the iron-region of eastern Texas, the limonite ores are 
 often a result of the solution of iron from the superficial oxi- 
 dation of iron pyrites, iron carbonate, and glauconite. Some- 
 times the sequel of this process is the downward passage of the 
 solution to an underlying laminated clay, and the gradual re- 
 
 12 Letter from Charles E. Smith, Philadelphia, Pa. 
 
THE SUPERFICIAL ALTERATION OF ORE-DEPOSITS. 127 
 
 placement of this bed, forming a hard limonite, 13 which still 
 preserves the laminated structure of the clay. 
 
 In Mexico certain hematite-deposits described by E. T. 
 Hill 14 as occurring in Lower Cretaceous limestone at or near 
 the contact with intrusive masses of diorite, and sometimes 
 even in the diorite itself, may, as Hill suggests, be the result 
 of superficial concentration from the limestone. 
 
 Very large deposits of hematite also occur in Grant county, 
 N". M., at the contact of limestone and an eruptive. The 
 origin of this ore is as yet somewhat obscure, but is probably 
 due to a concentration after the original deposition of the 
 iron. 
 
 The iron-deposits in the lakes of Sweden and Norway are 
 most striking instances of a concentration of iron-ore due to 
 surface-influences and going on at the present time. The iron 
 is derived from the oxidation of the neighboring rocks, car- 
 ried by carbonated surface-waters to the lakes, and there, by 
 further oxidation and hydration, precipitated as hydrous ses- 
 quioxide (limonite). The iron-ore is dredged up and used, but 
 the processes of nature gradually replace it, and, in the course 
 of years, the lakes again accumulate a considerable thickness 
 of ore. 
 
 Many other similar cases of superficial enrichment in iron- 
 deposits might be mentioned, but the above are enough to illus- 
 trate the point in question, and it will be seen that, of the 
 regions which are the active producers of iron-ore in this 
 country, almost all, if not all, owe the existence, or at least the 
 availability, of their large bodies of ore, to superficial concen- 
 tration. 
 
 Alteration in Manganese-Deposits. 
 
 Manganese-deposits are affected by superficial influences in 
 much the same way as iron-deposits. Many of the manganese- 
 deposits in the Cambrian -and Lower Silurian rocks of the 
 Appalachian valley were concentrated in a manner somewhat 
 
 18 R. A. F. Penrose, Jr., First Annual Report, Geological Survey of Texas, pp. 
 72 to 76, 79 to 81 (1890) ; also Bulletin of the Geological Society of America, vol. iii., 
 pp. 47 to 50 (1891). 
 
 14 American Journal of Science, Third Series, vol. xlv., No. 266, pp. Ill to 120 
 (Feb., 1893). 
 
128 THE SUPERFICIAL ALTERATION OP ORE-DEPOSITS. 
 
 similar, though not always so, to the iron-deposits in the same 
 regions. 15 
 
 In the Bates ville manganese-region of Arkansas, the ore 
 originally occurred in irregular masses in Silurian limestone, 
 but surface-decay has leached the carbonate of lime out of the 
 limestone, leaving a red siliceous clay, which represents the 
 less soluble part of the original rock. This clay now lies in 
 hollows on the surface of the limestone and contains the masses 
 of ore once disseminated through that rock. The removal of 
 the carbonate of lime has concentrated the ore-masses in the 
 clay, and has also rendered them more easily mined ; in fact, 
 the only manganese-ore that can now be profitably mined in 
 this region is that in the residual clay. 16 
 
 The frequent occurrence of deposits of bog manganese-ore 
 in the areas of crystalline rocks, generally represents a concen- 
 tration of manganese resulting from the oxidation of dissemi- 
 nated carbonate and silicate of manganese in the country-rock. 
 This oxidation-product is taken into solution in surface-waters, 
 and transported until subjected to such conditions that it is 
 oxidized and precipitated as a hydrous oxide. 
 
 Alteration in Copper-Deposits. 
 
 In many copper-deposits superficial alteration has produced 
 very remarkable chemical and economic results, and this is 
 especially well seen in the copper sulphide deposits of Arizona, 
 Chile and elsewhere. In Arizona the upper parts of the 
 deposits are composed of brown or black ferruginous masses, 
 with brilliantly colored oxidized copper-minerals, as cuprite, 
 malachite, azurite, chrysocolla, etc. ; while below, at depths 
 varying from a few feet to several hundred feet, the deposits 
 usually pass into a mixture of copper pyrites and iron pyrites, 
 the latter usually being far in excess. Sometimes other copper 
 sulphides occur, either mixed with copper pyrites or free from 
 it, and they may or may not have been derived from it. Here 
 the carbonates and some of the other alteration-minerals con- 
 tain not only more copper than the unaltered copper pyrites, 
 but they are also in a much more concentrated condition than 
 
 15 K. A. F. Penrose, Jr., Journal of Geology, vol. i., No. 4, pp. 356 to 370 (1893). 
 
 16 R. A. F. Penrose, Jr., Manganese: Its Uses, Ores, and Deposits, Arkansas 
 Geological Survey, vol. i., pp. 166 to 209 (1890). 
 
THE SUPERFICIAL ALTERATION OF ORE-DEPOSITS. 129 
 
 the sulphide which is disseminated through iron pyrites. The 
 total amount of copper has not been increased, in fact it may 
 be decreased by leaching, but it is in a more concentrated 
 form, and therefore the ore obtained from these concentrations 
 averages from 8 to 30 per cent, or more in copper, while the 
 mixture of unoxidized copper pyrites and iron pyrites below 
 averages only about 5 per cent, in copper. Moreover, the 
 altered ores are much more cheaply treated than the unaltered 
 ones, and are therefore still more desirable. It will thus be 
 seen that the economic value of the deposits as a whole has 
 been greatly increased. 
 
 In the surface-alteration of these deposits, the copper sul- 
 phides have first been converted to copper sulphate and then, 
 by the action of surface-waters and the materials contained in 
 solution in them, they pass into the forms of copper carbonates, 
 oxides, silicates, and occasionally to the chlorides and bromides, 
 and sometimes to native copper. The iron sulphide is first 
 converted to sulphate and then this, through other stages, is 
 converted into the hydrous sesquioxide (limonite), though the 
 iron sometimes now occurs in the form of the anhydrous 
 sesquioxide (hematite). This may have been derived from 
 the limonite by dehydration, or, under certain conditions, may 
 have been formed directly by the oxidation of iron pyrites. 
 The oxidized copper-minerals in the upper part of the ore- 
 deposit have been concentrated partly by segregation during 
 alteration, and partly by the leaching of the associated materials. 
 As a result of this, these minerals occur as seams, pockets, or 
 irregular bodies, often a hundred feet or more in diameter, 
 generally inclosed by, and often intimately associated with, 
 the oxidized iron-materials which represent the gangue. 
 
 In the case of the Arizona deposits, alteration has progressed 
 just far enough to increase greatly the value of the deposits 
 without to any extent injuring it. Such products of alteration, 
 however, are more or less soluble in surface-waters containing 
 various organic and inorganic compounds, so that in a moist 
 climate there is a constant tendency to leach them out and 
 leave only the less soluble parts of the gangue. In Arizona, 
 this stage has not yet progressed to a noticeable degree, and 
 one reason for this may be the extreme dryness of the climate, 
 
 9 
 
130 THE SUPERFICIAL ALTERATION OF ORE-DEPOSITS. 
 
 which affords opportunity for only comparatively slight per- 
 colation of surface-waters. 
 
 In the copper-deposits of Montana and the Appalachian 
 region, however, a further stage of alteration is often observ- 
 able. The copper-deposits of Butte City, Mont, are composed 
 .largely of chalcocite, with copper pyrites, bornite, enargite, 
 iron pyrites, and other minerals, in a siliceous gangue. On 
 the surface the copper in these deposits has been almost en- 
 tirely oxidized and leached out, and the ore consists of a 
 porous, rusty, siliceous mass, which was once mined for the 
 small percentage of silver it contained. As depths were 
 reached, the oxidized copper-minerals began to appear, and 
 eventually the sulphides formed the mass of the veins. *In 
 this case, a further stage of alteration is seen than that in 
 Arizona. 
 
 At Ducktown, in eastern Tennessee, 17 deposits of mixed iron 
 and copper pyrites occur and have been altered in a somewhat 
 similar manner on the surface. The copper-minerals have 
 been leached out of the ferruginous gangue in the upper parts 
 of the deposits, and for a depth of from 20 to 80 ft. or more, 
 the deposits are composed simply of a porous mass of more or 
 less hydrous sesquioxide of iron. Below this a part of the 
 copper, which has been leached from above, has been carried 
 down and deposited as a dark material, probably composed 
 largely of oxides and sulphides of copper, and averaging some- 
 times from 20 to 25 per cent, or more in metallic copper. This 
 material immediately overlies the unoxidized mixture of cop- 
 per and iron pyrites, which averages only from 2 per cent, to 
 4 or 5 per cent, in copper. The commercial copper mined in 
 this region came from the part of the deposit below the iron 
 capping and above the unoxidized sulphides. When this was 
 exhausted the mines had to be closed, for the unaltered sul- 
 phides were too poor to be utilized. 
 
 In Chile, Peru, and elsewhere in South America, changes 
 in copper-deposits, somewhat similar to those described in the 
 United States, frequently occur. In fact, the great reputation 
 which Chile once had as a copper-producer was largely due to 
 this surface-alteration, for the oxidized ore once supplied a rich 
 
 17 J. D. Whitney, The Metallic Wealth of the United States, pp. 322 to 324. 
 
THE SUPERFICIAL ALTERATION OF ORE-DEPOSITS. 131 
 
 and easily-treated source of copper; but when the mines reached 
 the unoxidized sulphides, the ores became poor in copper and 
 more difficult to treat, so that the copper industry of Chile 
 began to decline. In that region, however, the oxidation has 
 in some places extended down as far as 1,500 feet. 
 
 ^ Alteration in Lead-Deposits. 
 
 In the case of lead-deposits, the mineral galena, which is the 
 commonest ore, is frequently more or less altered on its sur- 
 face-outcrops and converted to the sulphate (anglesite) and the 
 carbonate (cerussite). The first product of oxidation is angle- 
 site, but this is a soluble compound and readily unites with car- 
 bonic acid or soluble carbonates in surface-waters, forming the 
 carbonate of lead, or cerussite. In rarer cases, other lead-min- 
 erals, like phosphates, may also be formed. 
 
 Alteration in Silver-Deposits. 
 
 Galena-deposits often contain silver, possibly sometimes in 
 the same condition of sulphide as the galena, and this material 
 is altered at the same time as the lead, with the formation of 
 native silver, chloride of silver (cerargyrite), bromide of silver 
 (bromyrite), iodide of silver (iodyrite), and various other min- 
 erals. The native silver is formed, probably, only after a pre- 
 ceding oxidation of the sulphide. Deposits carrying other 
 unaltered silver-bearing minerals, such as the various silver 
 sulphides, arsenides, antimonides, tellurides, etc., are, when 
 exposed to surface-influences, affected in much the same way 
 as the silver in argentiferous galena. 
 
 Alteration in Zinc- Deposits. 
 
 In the case of zinc, the most common ore is the sulphide 
 known as blende. This mineral, like galena, is generally oxi- 
 dized on the surface, and forms by other chemical changes the 
 carbonate (smithsonite), the basic carbonate (hydrozincite), and 
 the basic silicate (calamine), in a manner similar to that 
 described in copper- and lead-ores. 
 
 In the cases of both lead and zinc, oxidized ores are very 
 desirable for metallurgical purposes, and are much sought 
 after. To be sure, the carbonates, sulphates, etc., of lead and 
 zinc contain less of these metals than the pure sulphides, but 
 
132 THE SUPERFICIAL ALTERATION OF ORE-DEPOSITS. 
 
 they occur in a more concentrated form than the sulphides, 
 and, therefore, the ores containing them frequently carry as 
 much or more of the metals than the ores containing the sul- 
 phides. Moreover, the oxidized ores are much more easy to 
 treat and, therefore, have an additional value over the sulphide 
 ores. 
 
 Alteration in Gold-Deposits. 
 
 In the case of gold-deposits, surface-alteration has a most 
 marked effect, and probably in no class of deposits is the 
 change of more geologic and economic importance. The typi- 
 cal unaltered condition of gold in nature is in association with 
 iron pyrites in quartz, the gold being sometimes in such asso- 
 ciation with the pyrites that it cannot be separated by mechani- 
 cal means, while in rarer cases it can be so separated. The 
 effect of surface-oxidation on such a deposit, is first to convert 
 the iron pyrites into a hydrated sesquioxide of iron, which per- 
 meates the white quartz, with which the pyrites is usually as- 
 sociated, and turns it into a rusty brown mass. The next stage 
 is the gradual leaching-out of the hydrous sesquioxide by the 
 action of surface-waters. The iron is, in this way, finally re- 
 moved altogether, and the remaining product is a pure-white 
 quartz, containing the gold which was originally in the iron 
 pyrites, and which has remained stable during the oxidation 
 and leaching of that mineral. Such quartz is usually porous 
 and spongy, and is filled with cavities which represent the 
 shapes of the original crystals of iron pyrites, and which, 
 during an intermediate stage, have been partly filled with hy- 
 drous sesquioxide. This leaching, however, is rarely complete, 
 and the quartz is usually stained brown on the surface. 
 
 In gold-deposits of this kind, other minerals, such as copper 
 pyrites, galena, blende, etc., frequently occur, and when the 
 deposit is affected by surface-influences, these minerals act in 
 the manner already described under copper, lead, and zinc. It 
 is not uncommon to see gold-bearing quartz stained green by 
 -oxidized copper-minerals, or black by manganese-minerals. 
 Sometimes, especially in the Rocky Mountain region, gold 
 occurs in the form of a telluride instead of in iron sulphide, 
 and in such cases, the telluride is oxidized and the gold set free 
 from its combined state. The gold, in being freed from pyrites 
 
THE SUPERFICIAL ALTERATION OF ORE-DEPOSITS. 133 
 
 or other minerals, is not only concentrated by the removal of 
 certain ingredients of the deposits, but it is brought into a con- 
 dition in which it is much easier to treat than the unaltered 
 part of the deposit, and, therefore, the upper parts of most 
 gold-bearing veins are greatly enhanced in value. The ore 
 from these parts is known as " free-milling " ore, because it 
 can generally be ground and the gold extracted by direct 
 amalgamation with mercury ; while the ore in the unaltered 
 parts of the deposit cannot usually be thus easily extracted, 
 but must be smelted or treated by chlorination or some other 
 more or less expensive process. 
 
 When such deposits as those described are eroded, the parti- 
 cles of gold separate from the quartz and are concentrated in 
 the streams as placer-gold. These detrital deposits are the 
 source of a large part of the gold of commerce, and, in fact, 
 were once the source of most of it. Now, however, many of 
 the richest placer-deposits known have been exhausted; and 
 besides, the methods of treating the ores in the original de- 
 posits are better understood, so that the latter are supplying 
 yearly a larger and larger percentage of the gold-production 
 of the world. Hence, it will be seen that, in gold-deposits, 
 surface-alteration not only plays an important part in freeing 
 the gold from the iron pyrites, but also in forming placer-de- 
 posits. Detrital deposits similar to gold-placers and carrying 
 various other materials are not at all uncommon, as in the 
 cases of the platinum group of metals, cassiterite, diamonds 
 and many other gems, chromite and magnetite sands, and, in 
 fact, even with some of the more common ores, as with the 
 iron-conglomerate at Iron Mountain, Mo. 
 
 Alteration in Tin-Deposits. 
 
 In tin-deposits, the typical mode of occurrence of the metal 
 is in veins, dikes, or country-rocks, in the form of the oxide 
 known as cassiterite. Cassiterite is not easily affected chemi- 
 cally by surface-influences, so that it is not much changed by 
 superficial alteration, but, for this very reason, its concentration 
 is most markedly affected by surface-alteration, for in the ero- 
 sion of tin-bearing deposits the masses of cassiterite are broken 
 up and carried off mechanically by surface-waters, to be de- 
 posited somewhere else in the form of gravel-beds, instead of 
 
134 THE SUPERFICIAL ALTERATION OF ORE-DEPOSITS. 
 
 being dissolved and possibly disseminated. In this transition, 
 the fragments of cassiterite are largely separated from the 
 accompanying materials by reason of their greater specific 
 gravity, and hence, gravel-deposits rich in cassiterite frequently 
 occur. These represent the stream-tin of the miner, and have 
 been formed in much the same manner as have the placer gold- 
 deposits. Some chemical action, however, has gone on in the 
 tin-ore itself, but this seems to have been simply a process of 
 solution and redeposition, as is seen in the pseudomorphs of 
 cassiterite after other minerals and in the impregnations of 
 animal remains in Cornwall, such as antlers, with oxide of tin. 18 
 
 Alteration in Antimony-Deposits. 
 
 In many antimony-deposits, alteration similar to that de- 
 scribed in some of the deposits already mentioned frequently 
 occurs. The metal occurs most commonly as the sulphide 
 known as stibnite. By alteration, however, this passes into 
 the oxides valentinite, senarmontite, cervantite, stibiconite, etc., 
 or into the combined sulphide and oxide known as kermesite. 
 Yalentinite and senarmontite have the same chemical composi- 
 tion but differ in their crystalline forms. Native antimony 
 sometimes occurs, and this also, by alteration, gives rise to the 
 oxides. 
 
 Alteration in Bismuth-Deposits. 
 
 The allied metal bismuth occurs most commonly as native 
 bismuth, though the sulphide (bismuthinite), the selenide 
 (guanajuatite), the telluride (tetradymite), etc., also occur. 
 Native bismuth, by alteration, forms the carbonate (bismutite) 
 and probably also the oxide (bismite) and the silicate (eulytite). 
 
 Alteration in Mercury- Deposits. 
 
 In the case of mercury the metal commonly occurs as the 
 sulphide (cinnabar), though other mercury-minerals also occur. 
 By the alteration of cinnabar and some of the other mercury- 
 minerals, metallic mercury is set free and occurs as globules 
 or filling cavities in the ore. 
 
 18 J. H. Collins, Mineralogical Magazine, vol. iy., p. 115 (1882). 
 
THE SUPERFICIAL ALTERATION OF ORE-DEPOSITS. 135 
 
 Alteration in Molybdenum-Deposits. 
 
 Another case of surface-alteration in metalliferous deposits is 
 that seen in molybdenite. This mineral is the sulphide of the 
 metal molybdenum, and often occurs in quartz or calcite veins 
 in the crystalline rocks of parts of Canada, and in many ore- 
 deposits of the Rocky mountains and elsewhere. By surface- 
 oxidation, molybdenite passes into a brilliant yellow oxide of 
 molybdenum, commonly known as molybdite or molybdic ocher, 
 which, in the Canadian region, occurs as a powdery coating on 
 the cleavage-planes of the molybdenite. 
 
 Alteration in Other Deposits. 
 
 Superficial alteration like that already described in various 
 deposits occurs also in many others not yet mentioned, as in 
 aluminum-, nickel-, cobalt-, chromium-, tungsten-, and many 
 rarer deposits, but the changes already described show the 
 general features of the subject. It may be said, however, that 
 one of the important ores of aluminum, known as bauxite, is 
 probably derived from the alteration of feldspar under certain 
 conditions; and its source, therefore, is not altogether unlike 
 that of the hydrous sesquioxide of iron derived from the altera- 
 tion of certain silicates. The conditions during formation, how- 
 ever, were probably quite different. 
 
 IV. THE FORMATION OF HALOID COMPOUNDS IN ORE-DEPOSITS 
 IN ARID EEGIONS. 
 
 The formation of chlorides and other haloid compounds has 
 already been mentioned as one of the phenomena of superficial 
 alteration in ore-deposits. As soluble chlorides and some- 
 times other haloid compounds are common in surface-waters, 
 chlorides and the allied compounds are not at all uncommon 
 as alteration-products, especially in such cases as that of silver, 
 where the chloride, bromide, and iodide are insoluble com- 
 pounds, and are not leached out. For this reason, chloride 
 ores of silver are found to a greater or less extent in almost all 
 silver-districts in America, Europe, and elsewhere, but the 
 occurrence of such compounds in very large quantities in 
 certain parts of North and South America deserves special 
 explanation. 
 
 Over a large part of the arid region of the "West, lying be- 
 
136 THE SUPERFICIAL ALTERATION OF ORE-DEPOSITS. 
 
 tween the Rocky mountains and the Sierra Nevada, ores con- 
 taining chloride of silver (cerargyrite) are abundant, and some- 
 times the bromides and iodides also occur; in fact, parts of 
 this region are characterized by chloride ores. They are 
 especially well developed in parts of New Mexico, Arizona, 
 Utah, Nevada and other States and Territories, and it seems 
 probable that their abundance can be traced to the effect of 
 the peculiar climatic conditions which have prevailed in that 
 region in late geologic times. Most of this arid country was 
 once covered with numerous bodies of water, some of them of 
 great size. In late geologic times, however, these began to 
 dry up, until their waters no longer rose high enough to have 
 outlets, and then, as a natural result, they became highly im- 
 pregnated with salt and other saline matter. Finally, they 
 became desiccated, leaving deposits of various earthy and saline 
 materials in their old basins, and among the most common of 
 these was common salt. It seems probable that the abundance 
 of chloride ores is due to the action of this salt on the pre- 
 existing ore-deposits of the region, in the basins of the lakes, 
 and that the smaller quantities of bromides and iodides were 
 formed by a similar action of the soluble bromides and iodides 
 in association with the salt. Such ores, in some of the mines 
 that have gone to sufficient depths, have passed into various 
 other silver-compounds, such as the sulphide (argentite), argen- 
 tiferous galena, etc., which represent the original condition of 
 the ores. This transition proves the chlorides and other haloid 
 compounds to be of only superficial extent. 
 
 This transition to haloid compounds is not confined to silver- 
 ores, for the basic chloride of copper (atacamite) occurs at 
 Jerome, in Arizona, and both chlorides and bromides of copper 
 occur in the Bloody Tanks district west of Globe, in Arizona, 
 though here, as elsewhere in Arizona, the other copper-minerals 
 already mentioned, such as carbonates, sulphides, etc., form 
 the bulk of the copper-deposits. 
 
 In parts of Mexico, Chile, and Peru, where saline materials 
 have collected in a manner somewhat similar to that in the 
 arid regions of the United States, the chloride of silver is one 
 of the important ores mined, and it sometimes occurs intimately 
 mixed with chloride of sodium, or common salt, forming the 
 mineral huantajayite, or the lechedor of the miners. The 
 
THE SUPERFICIAL ALTERATION OF ORE-DEPOSITS. 137 
 
 bromides of silver are also abundant in Chile, and, in fact, at 
 the mines of Chanarcillo, a common ore is the double chloride 
 and bromide known as embolite. Again, the atacamite, or 
 basic chloride of copper, from the Desert of Atacama is well 
 known. 
 
 It seems probable that this transformation of the silver- and 
 copper-minerals did not necessarily occur exclusively while the 
 deposits were covered by saline lakes, but may have occurred 
 even more actively afterwards, when the surface-waters were 
 highly impregnated with chlorides from the residue left by the 
 lakes, and when oxidation in the ore-deposits was much more 
 active than when they were covered by water. This seems all 
 the more likely w ? hen we consider that the original silver- and 
 copper-minerals probably had to be oxidized before they were 
 converted to chlorides, etc. Of course the oxidation may have 
 partly occurred before, or during, the existence of the lakes, 
 but in many cases it probably also occurred after they were 
 desiccated. 19 
 
 V. SUMMARY. 
 
 It will be seen from the above discussion that : 
 
 (1) After the deposition of ore-deposits and their subsequent 
 exposure'to surface-influences, such as air, water and the mate- 
 rials contained in it, changes of temperature, etc., chemical 
 and physical alterations occur which cause a total change in 
 the mineralogical condition, and generally in the economic 
 value, of the ore-deposit. 
 
 (2) The process of this alteration is primarily one of oxida- 
 tion and generally of hydration, and both of these actions may 
 go on alone, but generally both have their effect on the same 
 material. The other materials in solution in surface-waters 
 also react on the substances in the ore-deposit, either before or 
 after the oxidation of the latter, though generally after at least 
 partial oxidation, and form various compounds different from 
 those originally in the deposit. The difference, however, with 
 few exceptions, is not in the metal or other base which forms 
 the important feature of the deposit, but in the acidic portion 
 
 19 Chlorides of other materials than silver and copper may also have been 
 formed by a similar process, but the solubility of many metallic chlorides would 
 prevent their being accumulated in any but very dry regions. 
 
138 THE SUPERFICIAL ALTERATION OF ORE-DEPOSITS. 
 
 or material representing this portion of the mineral. Thus, 
 sulphide of copper may be altered to carbonate of copper, but 
 the base remains the same. The action of surface-influences is 
 in rare cases one of reduction, which, however, often follows a 
 previous oxidation. The process of alteration also frequently 
 causes a leaching of certain ingredients of the ore-deposit, 
 either with or without previous oxidation, as in the removal of 
 iron pyrites, calcite, etc. It also sometimes renders a hitherto- 
 worthless material valuable by the introduction of a valuable 
 constituent, as in the replacement of carbonate of lime by 
 phosphate of lime. -It also causes the concentration, by capil- 
 lary action in soils, of certain deposits like niter, etc. The 
 compounds formed with different ore-deposits vary with the 
 ores affected and the stability of the compounds formed by the 
 action of the materials in the surface-waters on the constituents 
 of the ores. 
 
 (3) The physical effect of superficial alteration is generally 
 to make the deposit more open and porous, to cause it to 
 shrink, and, in some cases, to convert it into a loose material 
 of the consistency of sand and clay. In some cases, however, 
 especially where hydration is active, expansion may be caused. 
 
 (4) Superficial alteration extends downward as far as sur- 
 face-influences are able to act, though generally alteration is 
 not complete down to the possible limit. The depth of altera- 
 tion depends on the topography of the region, the nature of 
 the rocks, and on the climate. ' In glaciated regions, the glacial 
 action has swept away the products of alteration, and sufficient 
 time has not elapsed since then for alteration to have gone on 
 to any great extent, but in many other regions the products of 
 alteration have accumulated to considerable depths. The 
 depth of alteration, under different conditions, varies from a 
 fraction of a foot to 1,500 ft. or possibly more. 
 
 (5) Superficial alteration is well illustrated in iron-, man- 
 ganese-, copper-, lead-, zinc-, silver-, gold-, tin-, and many 
 other deposits. For special descriptions see text. 
 
 (6) The accumulation of soluble saline materials, like salt, 
 on the surface has a very important effect in converting certain 
 materials in underlying ore- deposits to chlorides, etc. 
 
SOME MINES OF ROSITA AND SILVEK CLIFF, COLORADO. 139 
 
 No. 7. 
 
 Some Mines of Rosita and Silver Cliff, Colorado. 
 
 BY S. F. EMMONS, WASHINGTON, D. C. 
 
 (Colorado Meeting, September, 1896. Trans., xxvi., 773. Published by permission of the 
 Director of the U. S. Geological Survey, and here reprinted in part only). 
 
 MINES IN RHYOLITE NEAR SILVER CLIFF. 
 
 Geological Sketch. The rhyolite area near Silver Cliff includes 
 what may be called the Silver Cliff plateau, with Round moun- 
 tain and the intervening valley. The plateau is about 2 miles 
 long and 1 mile wide. From its northern part rise the 
 White hills, which have no special topographic importance, as 
 their highest point is only 400 ft. above the northern edge of 
 the rhyolite mass. Round mountain, on the other hand, is a 
 quite sharply pointed conical hill, so steep-sided as to consti- 
 tute an important topographic feature, although its elevation 
 above the plains around it is barely 700 ft. The summit of 
 Round mountain is dense banded rhyolite, with steep, irregular 
 dip; the southern end is breccia containing fragments of the 
 banded rock. There are slight exposures of glassy forms of 
 rhyolite on the lower slopes. On the east, the Archaean rocks 
 extend half-way up the side of the mountain, and the contact 
 between them and the rhyolite is vertical, or dips steeply to 
 the west. This mountain is supposed to be at the vent from 
 which the rhyolite of the plateau was poured out. 
 
 The Silver Cliff plateau occupies the site of a former basin, 
 in which at one time there was probably a lake. At the time 
 of the rhyolitic outburst of the Rosita hills there was a local 
 eruption of the same character in this region, commencing with 
 showers of volcanic ash and of rock-fragments, which filled the 
 lake and built up about it hills which' have since been removed 
 in great measure by erosion. At present the southern half of 
 the plateau is capped by solid lava to 'a depth in places of 150 
 ft. The cliff of blackened rhyolite on the southern edge, where 
 the main discovery of ore was made, is from 30 to 50 ft. 
 
140 SOME MINES OF ROSITA AND SILVER CLIFF, COLORADO. 
 
 high. In many places, as in the Yanderbilt mine, the rock is 
 plainly fragmental and stratified, and has a well-defined dip. 
 The contact of Archsean and rhyolite along the western border 
 is a gently-undulating surface, and in most of the prospect-holes 
 the Archaean is much broken and resembles a breccia. The 
 northern half of the area is breccia and tuff, except a few dikes 
 of massive rock. At the Songbird and Mountain View mines, 
 and along the western border generally, the gneiss under the 
 rhyolite has been much altered and is locally ore-bearing, car- 
 rying magnetite, pyrite, and some galena, as in the Immortal 
 and Keystone mines. Near the Sunrise, and along the eastern 
 border as far south as the Vanderbilt, the rock is a finely- 
 bedded tuff', dipping south and west. The thickness of frag- 
 mental material below the highest point of the hills is more 
 than 550 ft. These beds terminate abruptly to the south along 
 an east-and-west line running near the Yanderbilt, which Mr. 
 Cross thinks may be a fault-line. 
 
 The massive rock is everywhere characterized by a banded 
 or fluidal structure, and in it topaz and garnet have been found. 
 Under the massive lava on the southern portion of the plateau 
 is pitchstone or glassy rhyolite, about 50 ft. thick, with about 
 as much more below, containing spherulites, which, when de- 
 composed, form a boulder-zone. These glassy rocks outcrop 
 around the cliff to the south and east, and are found in cellars 
 in the town of Silver Cliff. 
 
 Surface-Deposits. The original outcrop of the ore-bearing 
 rhyolite on the Silver Cliff and Racine Boy claims was appar- 
 ently nothing more than the ordinary banded rhyolite, stained 
 and blackened by oxides of manganese, extensively cracked 
 and fissured, and carrying little flakes of chloride of silver in 
 the cracks. As far as known, no other metallic minerals were 
 detected, nor was there any definite boundary or regularity of 
 form to the part that constituted the ore. An area several 
 hundred feet in diameter and from 30 to 50 ft. thick was thus 
 found to be ore-bearing. When examined by us in the quarry, 
 the principal set of joints or rock-fractures were observed to 
 r,un nearly northwest and southeast, and it was on these that 
 the most silver was found. On some of these cracks was a 
 considerable coating of clear black manganese oxide ; in others, 
 where there was more iron oxide, the coating had a metallic 
 
SOME MINES OF ROSITA AND SILVER CLIFF, COLORADO. 141 
 
 luster; and it was on the latter, according to the observations 
 of the miners who were sorting the ore, that the principal 
 values were found. A set of secondary joints or fractures, 
 crossing the main joints nearly at right angles and reaching to 
 the surface, could be observed along the benches of the quarry. 
 These also were heavily coated with manganese oxide, and 
 carried ore. It was but rarely, at that time, that the flakes of 
 horn-silver could be detected by the naked eye. Our observa- 
 tions indicated that the horn-silver was more frequently de- 
 posited on small cracks, adjoining those filled by iron and 
 .manganese oxides, and apparently of later formation. The 
 light-colored mass of the rock had a faint pink tinge, and a 
 specimen analyzed contained 0.06 per cent, of manganese oxide. 
 It was the experience of the miners that the silver-values did 
 not occur outside of the stained zone. 
 
 When the ore-body was first worked, it is said to have con- 
 tained from 35 to 50 oz. of silver per ton, but it gradually 
 decreased in value as it was taken at a greater distance from 
 the surface. It is said that, while the mills were running, the 
 rock was not sorted, but sent in bulk to the crusher. The last 
 mill-runs are said to have assayed only about 7 oz. to the ton, 
 and the greater part of this went off' in the tailings. 
 
 The ore taken from the quarry was sorted, so as to average 
 from 50 to 60 oz. per ton, at one time ; but this fell off later, and 
 it was apparently so low finally as not to pay for working. 
 
 It has been a cause of much fruitless speculation that the 
 amalgamating-mills were so unsuccessful in treating this ore. 
 It is generally conceded that much the larger portion of the 
 silver was carried away in the tailings, which were afterwards 
 profitably concentrated by hand-jigs. A sample of these tail- 
 ings, carefully quartered down, yielded in the laboratory of the 
 Survey 0.13 per cent, of sulphur, which is sufficient to combine 
 with the silver contained and form sulphides. It is also said 
 that a small amount of antimony has been found in the ore by 
 those who smelted it. 
 
 If the silver is generally in the form of sulphide, it would 
 naturally be difficult of amalgamation, and the presence of 
 antimony would heighten that difficulty. 
 
 . Small amounts of ore were also found near the surface at 
 many other points on the plateau, which, though not compara- 
 
142 SOME MINES OF ROSITA AND SILVER CLIFF, COLORADO. 
 
 ble in amount to the Silver Cliff body, were sufficient to en- 
 courage prospecting to such an extent that over 400 prospect- 
 holes were counted there at the time of our examination. For 
 the most part they had been already abandoned, and there was 
 nothing to show how the ore, if any there was, occurred. 
 Among the more prominent ones, which actually produced 
 considerable values, may be named the Boulder, Vanderbilt r 
 King of the Valley and Silver Bar (formerly the Kate). 
 
 DEEP DEPOSITS OF THE GEYSER MINE. 
 
 The only mine-workings that have extended to any consid- 
 erable depth on the plateau, say over 100 ft., are those of the 
 Security-Geyser mine. As far as is known, the ore of all the 
 plateau-deposits had given out, really or apparently, within 
 considerably less than 100 ft. of the surface. The ore was 
 always chloride of silver where its character could be distin- 
 guished. That from the Kate (Silver Bar) claim, worked in 
 early days, is said to have contained some gold also ; but this 
 is the only case reported and the statement has not been veri- 
 fied. It does not seem likely that silver would be accompanied 
 by gold in one place and free from it in all the others. A& 
 will be seen later, of the two shipments to smelters of ore 
 from the bottom of the Geyser shaft, one contained only 0.1 
 oz. of gold per ton, the other but a trace. 
 
 It is only through the underground workings of the Geyser 
 shaft, therefore, that it has been possible to obtain any informa- 
 tion with regard to the conditions of ore-deposition in depth. 
 The data which it has been possible to obtain with regard to 
 them in occasional visits during past years will therefore be 
 given in considerable detail. 
 
 The Geyser shaft, as it is now called, is located 350 ft. north, 
 a little west, of the mouth of the adit leading from the floor of 
 the Silver Cliff quarry, and its collar is 104 ft. above that level. 
 It was originally intended to sink the shaft only 500 ft., it being 
 supposed, from the position of the various observable contacts 
 of the rhyolite with the underlying Archaean, that the former 
 was a rather shallow body, and that the underlying granite and 
 gneiss would be reached within the depth- named. It was, 
 later, decided to prepare for greater depths, and the hoisting- 
 machinery was given greater capacity. The limit of this ca- 
 
u. OF c. 
 
 SOME MINES OF ROSITA AND SILVER CLIFF, 
 
 pacity was reached in the summer of 1894, when a depth of 
 2,100 ft. was attained. Entirely new and heavier machinery, 
 with a capacity of 4,500 ft., was then ordered, which is now 
 (May, 1896) in working-order, and sinking has been resumed. 
 
 Mine-Levels. The first exploring-levels or drifts were started 
 at a depth of 500 ft. These were run 500 ft. west and 700 ft. 
 east ; likewise some distance in a southerly direction. At 750 ft. r 
 levels were run to the east and south, and one branch passed 
 directly under the quarry. Below this, levels were run at 
 1,450, 1,850, 2,000, and 2,100 ft. from the surface, respectively. 
 The general direction of exploration in these levels appears to- 
 have been to the west and northwest, but the 1,450-ft. level 
 had a drift running southward. Accurate maps of the respec- 
 tive levels could not be obtained, but, in a general way, it is 
 estimated that the main exploring-drifts have a linear extent of 
 about 1.5 miles at the different levels, and that about 600,000 
 sq. ft. of area was more or less thoroughly explored. Fig. 1 
 (Fig. 7 of original paper) gives a somewhat diagrammatic repre- 
 sentation of the ground explored. 
 
 Country-Rocks. For the first 150 ft. the shaft passed through 
 banded rhyolite. In the tunnel leading to the shaft, a narrow 
 zone or band of this rock was found to be changed into a 
 plastic white clay, which was almost pure kaolin. 
 
 Below the solid rhyolite was about 50 ft. of pitchstone, then 
 about 'the same thickness of the boulder or spherulitic zone. 
 Veins and crystals of calcite were found in the rhyolite under 
 the pitchstone. From 250 ft. down to about 1,900 ft. the shaft 
 passed through white rhyolitic tuff" and breccia, the former often 
 distinctly stratified and generally looking like white sandstone,. 
 much kaolinized. The breccia varies from fine to coarse, and 
 contains fragments of all the varieties of Archaean rocks found 
 in the region ; but no eruptive, other than rhyolite, was observed 
 among the fragments. Some of the Archaean fragments are 
 kaolinized and disintegrated ; others are quite fresh. The green 
 decomposition-product of hornblende and mica was in one place 
 thought to be a copper-stain. 
 
 Here and there through the tuff", as far as the 2,000-ft. level, 
 fragments of charcoal or carbonized wood were observed (the 
 special localities are marked by a cross on the section in Fig. 
 1). At 335 ft, pieces 2 ft. long are said to have been found in 
 the shaft. 
 
144 SOME MINES OP ROSITA AND SILVER CLIFF, COLORADO. 
 
 The bedding of the tuff was found to be, for the most part, 
 nearly horizontal. In the shaft a slight dip to the west was noted 
 at times for considerable vertical distances. In the drifts, 
 
 PITCH 
 
 Surface Water 
 
 STRATIFIED TUFF AND BRECCIA 
 500 ft. Level 
 
 750 ft.Level 
 
 RHYOLITIC TUFF 
 
 1450 ft.Level 
 
 ._..,_'' GRANITE 
 -^2000 ft.Level 
 
 2100 ft.Level 
 
 Scale. 
 100 100 
 
 FIG. 1. SECTION THROUGH GEYSER SHAFT. 
 
 the dip to the west or northwest is more marked, in a general 
 way, to the southeast of the shaft, and in one place, for a short 
 distance, this dip was 75. In the shaft there appears to have 
 
SOME MINES OF ROSITA AND SILVER CLIFF, COLORADO. 145 
 
 been a somewhat irregular alternation of white tuff and breccia. 
 For instance, the former was found continuously from 775 to 905 
 ft., and from there to 1,000 ft. the rock was mostly breccia, at 
 times with so many large fragments of Archaean, up to 2.5 ft. 
 in diameter, that it was thought the solid formation would soon 
 be reached. 
 
 The shaft actually entered the granite and gneiss of the 
 Archaean near the 1,850-ft. level. Where cut in the drifts 
 below, the contact of rhyolitic tuff or breccia and Archaean ap- 
 pears to be on fault-planes. The Archaean consists of mica- and 
 hornblende-schists cut by red granite. These rocks are frac- 
 tured and sheeted in a direction parallel to the ore-bearing veins 
 in the rhyolite ; but the actual contact apparently does not, as 
 might be assumed from the section in Fig. 1, conform in every 
 respect to these planes. The intersections of the contact by 
 drifts are too few to permit the tracing of the shape of the 
 Archaean wall that incloses the rhyolite. It was noted, however, 
 that the drifts pass out of the Archaean into rhyolitic breccia as 
 they go north-northwest or west from the shaft. 
 
 In the 2,100-ft. level, drifts run only north and west, and 
 the contact, as contrasted with that in the level above, has an 
 inclination to the northeast. The contact on this level is. not 
 sharp and well defined, but rather a broken zone, first of very 
 coarse fragments of granite and gneiss, then of normal rhyo- 
 litic breccia with small fragments of granite and gneiss. The 
 three lower levels have been run from 300 to 500 ft. north and 
 west in this material, which is sometimes hard and jaspery and 
 of dark-red color, but bleaches on exposure to the air. It is 
 traversed by planes of movement, sometimes irregular and curv- 
 ing, but all having a general northwest strike. Beyond one of 
 these planes is a dark bluish rock, supposed by the miners to 
 be limestone because it effervesces freely with acid, but, on mi- 
 croscopic examination, found to be a decomposed basic eruptive, 
 containing considerable calcite. 
 
 Ore-Bodies. No defined ore-body was found until the 1,850- 
 ft. level was reached. Thin films or stains of metallic sul- 
 phides, said to assay high in silver, occurred occasionally in the 
 shaft and in some of the drifts; lining delicate cracks in the 
 tuff, and sometimes also in the Archaean fragments. On the 
 1,450-ft. level, about 450 ft. south of the shaft, it is said that 
 
 10 
 
146 SOME MINES OF ROSITA AND SILVER CLIFF, COLORADO. 
 
 there was found in the white tuff a 0.25-in. seam of ruby-silver 
 and argentite, with crystalline calcite, which had a general 
 course north-northwest, and was traced about 50 ft, when it 
 disappeared. 
 
 The main ore-vein was first found in the 1,850-ft. level, about 
 200 ft. northwest of the shaft, as a narrow seam, a fraction of 
 an inch wide, with barite and calcite gangue, which widened, 
 as it was followed, to 4 or 5 in., mostly of galena, and narrowed 
 again to a mere knife-edge seam in about 150 ft. A few 
 nearly-parallel seams, containing only calcite and barite, were 
 observed near it. This vein was traced by a winze downward, 
 and was cut afterwards in the 2,000-ft. and 2,100-ft. levels, 
 gaining width and richness as it went down. In the 2,000-ft. 
 level, it is quite thin in the middle, and splits into several thin 
 seams at the northwest, which gradually wedge out. On the 
 2,100-ft. level a smaller vein is found about 40 ft. northeast of 
 and parallel to the main vein ; this also splits at the northwest 
 end. The general strike of the vein is K 37 to 40 W., and 
 it stands nearly vertical, its average dip from the 1,850-ft. to 
 the 2,100-ft. level being 70 to the northeast, 
 
 Vein- Materials. Although very thin, in no case attaining as 
 much as a foot in width, this vein has been remarkably produc- 
 tive, owing to the richness of the ore and the relatively small 
 proportion of gangue. The principal metallic minerals are 
 galena, zinc-blende, chalcopyrite, cupriferous argentite, tetra- 
 hedrite, ruby-silver, and possibly stromeyerite or polybasite. 
 Hessite and leaf-gold are said to occur, but their presence could 
 not be verified. The galena occurs in fine scaly form, rather 
 than in the usual massive crystals. The zinc-blende is generally 
 of the ferriferous variety known as " black jack " by the miners, 
 and is rather porous. It occurs at times in cup-shaped forms, 
 which are lined with fine crystals. It sometimes forms cross- 
 courses, or distinct shoots in* the vein, which carry from 300 
 to 400 oz. of silver to the ton, and always a good deal of 
 galena. The chalcopyrite occurs mostly amorphous and easily 
 disintegrate, in rounded patches, distinct from the other min- 
 erals, and prominent by its dull brass-yellow color. Where the 
 ore occurs in botryoidal form, one can distinguish the following 
 succession from the center outward : (1) barite in tabular crys- 
 tals ; (2) galena (and argentite) ; (3) copper sulpKide ; (4) gray 
 
SOME MINES OF ROSITA AND SILVER CLIFF, COLORADO. 147 
 
 copper in crystals ; (5) small crystals of chalcopyrite. In cer- 
 tain parts of the vein which consist exclusively of metallic min- 
 erals, they have a peculiarly fresh look, as if quite recently 
 deposited and not yet completely consolidated. The average 
 composition of the ore from the Geyser mine is best shown by 
 the following analyses of two car-load lots kindly furnished by 
 the Arkansas Valley Smelting Co., of Leadville, to whom they 
 had been sold : 
 
 Lot No. 1. 
 
 Lot No. 2. 
 
 . Per Cent. 
 Gold Trace 
 
 Per Cent. 
 n 
 
 Silver . b 1 05 
 
 c 1 27 
 
 Lead 23 80 
 
 17 60 
 
 Zinc . 14 00 
 
 11.10 
 
 Copper (wet assay ) 1.50 
 
 2 30 
 
 Iron 2 30 
 
 2 00 
 
 Manganese ... . 1 20 
 
 0.80 
 
 Lime . . . 1 70 
 
 
 Sulphur 12 60 
 
 9.50 
 
 Silica 3360 
 
 46.90 
 
 
 
 Total . 91.75 
 
 91.47 
 
 
 
 a 0.10 oz. per ton. 6 2 ',0.42 oz. c 300.28 oz. 
 
 In addition to the above metals, there was probably anti- 
 mony, w T hich had been proved qualitatively, in the mineral that 
 was supposed at the mine to be hessite, but is probably either 
 tetrahedrite or polybasite. Barium and alumina probably make 
 up a part of the balance. 
 
 Of earthy minerals, the most common are barite, calcite, 
 and quartz, the latter generally in the chalcedonic form. Frag- 
 ments of country-rock are found in the vein, more or less 
 rounded, and changed on the outer part into hornstone-like 
 material, which, in turn, is coated with galena, barite, etc. 
 Rounded cavities in the vein-material are often filled with a 
 white powder, apparently an infiltrated decomposition-product 
 of the rhyolitic tuff. 
 
 Water- Courses. This mine has proved unusually dry for the 
 region. In the upper part of the shaft the first considerable 
 flows of water came in at 340, 390, and especially at 420 ft. 
 This water, collected at the 500-ft. level, amounted to 250 gal. 
 per minute, and was undoubtedly vadose or surface-water, and 
 probably seeped in from the surrounding country. At 945 ft. 
 
148 SOME MINES OF ROSITA AND SILVER CLIFF, COLORADO. 
 
 it had decreased to 65 gal. per minute, and below 1,000 ft. had 
 practically ceased, the little water that was found being prob- 
 ably due to leakage along the shaft. 
 
 In the 1,450-ft. level what may be considered subterranean 
 or deep waters were first struck. They were not very abund- 
 ant, and were only slightly charged with gas. At one point 
 on the south drift there was a slight deposit of tufa. A con- 
 siderable flow was obtained from a vertical drill-hole sunk 300 
 ft. downward from this level. 
 
 In the 1,850-, 2,000-, and 2,100-ft. levels there are many 
 small water-courses, from which proceeds a constant flow of 
 water, not very great in aggregate amount, but highly charged 
 with carbonic acid gas, so that there is a constant hissing, sput- 
 tering, and rumbling, and the water is ejected with such force as 
 to go entirely across the drift at some points. These waters 
 apparently ascend along fissures having a general parallelism 
 with the ore-bearing fissure ; but no water proceeds from the 
 vein itself. They often come into the drifts through small 
 cracks or cross-fissures at an angle with the direction of the 
 main system. As they emerge into the air of the drift they 
 deposit freely a calcareous tufa or sinter on the wall around 
 the crack or orifice out of which they flow. This sinter is 
 sometimes white, sometimes highly iron-stained ; it has the 
 texture and the peculiar wavy or ripple-marked surface char- 
 acteristic of the sinters of the Yellowstone Park. In some 
 places it takes a pisolitic form. Again its surface has a shiny 
 glaze. It deposits very rapidly in some places. At one point 
 on the 2,000-ft. level, which had been opened only four months, 
 the water issuing from a minute vertical crack on the side of 
 the drift had built out a little ridge of sinter over the crack, 
 1.5 in. from its base and less than 0.5 in. thick. 
 
 The water-courses are most active and abundant near the 
 vein or on the line of its extension. On the 2,000-ft. level, 
 where the vein splits to the northwest, the water comes in on 
 all sides ; and when the shaft was first opened, the escape of 
 carbonic acid gas was so abundant at this point that it filled the 
 lower 5 ft. of all the drifts on this level and the shaft below the 
 level so that no light would burn, and the miners were obliged 
 to abandon work until a blower could be put in operation to 
 drive the gas out. Even now, a light is soon extinguished 
 
SOME MINES OF ROSITA AND SILVER CLIFF, COLORADO. 149 
 
 if put at the bottom of the drift. The water-bearing fissures 
 are mostly in the rhyolitic tuff, but a few are found in the 
 Archaean, which shows evidence of faulting within itself, in 
 slickensided clay seams and zones of brecciation. The water- 
 bearing fissures decrease in number and in strength of flow as 
 the distance from the line of the ore-bearing fissure increases. 
 The abundant escape of gas is the most striking feature of 
 these water-courses. Even where no water comes into the 
 drift, one can often hear the bubbling and sputtering of the 
 escaping gas in an adjoining fissure. 
 
 The temperature could not be accurately determined, but is 
 about the same as that of the air in the drift at the 2,000-ft. 
 level, viz., 80 F. 
 
 Analyses of Sinters. Three typical specimens of sinter from 
 the 2,000-ft. level were selected for analysis: one of the per- 
 fectly white, with very slight iron-stain ; one white and brown 
 (both showing the ripple-marked structure well); a third of 
 the pisolitic sinter, strongly iron-stained. They were analyzed 
 by W. F. Hillebrand, with the following results : 
 
 Analyses of Sinters from the 2,000-JFV. Level, Geyser Mine. 
 
 
 White. 
 
 White and 
 Brown. 
 
 Pisolitic 
 Brown. 
 
 Silica and insoluble 
 
 Per Cent. 
 0.08 
 
 Per Cent. 
 10 
 
 Per Cent. 
 0.17 
 
 CaO 
 
 53.11 
 
 52.60 
 
 52.59 
 
 CO. 
 
 42 98 
 
 42 57 
 
 42.03 
 
 FeA 
 
 0.20 
 
 1.08 
 
 1.82 
 
 Mn 2 O 3 (Mn 3 O 4 ?)..... 
 
 a 0.026 
 
 a 0.03 
 
 Undet. 
 
 SrO 
 
 0.17 
 
 0.26 
 
 0.22 
 
 MgO 
 
 1.50 
 
 1.39 
 
 1.01 
 
 K 2 O 
 
 0.03 
 
 0.03 
 
 0.04 
 
 Na 2 O 
 
 0.17 
 
 0.16 
 
 0.09 
 
 Li 2 O 
 
 Trace. 
 
 Trace. 
 
 Trace. 
 
 H 2 O below 110 C 
 
 0.33 
 
 0.51 
 
 0.53 
 
 H 2 O above 110 C 
 
 0.88 
 
 0.72 
 
 0.87 
 
 SO 3 
 
 0.29 
 
 0.50 
 
 0.58 
 
 P 2 O S 
 
 Trace. 
 
 Trace. 
 
 Trace. 
 
 cL? ::::.:: 
 
 Faint trace. 
 
 Faint trace. 
 
 Faint trace. 
 
 
 
 
 
 Total 
 
 99.766 
 
 99.95 
 
 99.95 
 
 
 
 
 
 a Manganese was estimated on 34 g. The same samples showed also minute 
 traces of lead, copper, nickel, cobalt, zinc, alumina, and a double trace of antimony. 
 
 On comparing these analyses with those of the waters which 
 follow, it appears that, under the influence of free access of air, 
 
150 SOME MINES OF ROSITA AND SILVER CLIFF, COLORADO. 
 
 with presumably reduced pressure and temperature, the pre- 
 cipitation has been mainly of carbonates of lime, iron, and man- 
 ganese ; of the alkalies, magnesia, and of other metals a rela- 
 tively small proportion seemed to have been precipitated. 
 
 Analyses of Waters. Carboys of water from the 500-ft. level, 
 i.e., surface or vadose waters, and of waters from the 2,000-ft. 
 level were collected with great care by the foreman of the mine 
 under the direction of C. H. Johnson and sent to Washington 
 for analysis. Upon their arrival, there was found to be con- 
 siderable sediment in each of the carboys, which had presum- 
 ably been precipitated during the journey, since they had been 
 filtered through cotton cloth when gathered. Mr. Hillebrand 
 found evidence, however, that the filtering had not been com- 
 plete, as some splinters of wood were found in the sediment, 
 which casts some doubt on the analysis of the sediment. 
 
 In the 42.6 1. of vadose water of which the analysis is given 
 below, there was a deep blackish-brown sediment, containing, 
 however, no organic matter, which, after drying at 110 C., 
 weighed 0.5592 g., and gave : 
 
 Gram. 
 
 Ignition, . . ... 4 . ,... 0.0642 
 HC1 extract, . / . ., . ... . 0.1588 
 Insoluble silica and silicates, . . . . . . 0.3362 
 
 Total, . ,.' . . . . . . . "(X5592 
 
 It was assumed that the silica and silicates must have been 
 mechanically introduced, through want of sufficient precautions 
 in filtering at the mine; and this portion of the sediment was 
 not analyzed. Of the sediment in the carboy of deep water, 
 however, the insoluble portion was analyzed, with the result 
 given in the following tables. The total sediment in the carboy 
 of deep water was 10.6602 g., of which 5.0134 g. was insoluble 
 in dilute HC1 (at 110 C.). The filtered vadose water had a 
 slightly alkaline reaction and contained no organic matter. 
 The results of analysis are given in the following tables [pp. 
 
 151 and 152] : 
 
 These tables present a remarkably complete series of actual 
 analyses, representing : 
 
 1. The average contents of a vein-deposit of metallic miner- 
 als, rich in silver, lead, copper, and zinc, which was first found 
 at over 1,800 ft. below the present surface. 
 
SOME MINES OF ROSITA AND SILVER CLIFF, COLORADO. 151 
 
 Vadose Water from the Geyser Mine, 500-Ft. Level. 
 
 (W. F. Hillebrand, Analyst.) 
 
 In Sediment. Soluble in HC1. In Filtered Water. 
 
 Assumed 
 Composi- 
 tion Before 
 Sediment 
 was i e- 
 posited. 
 
 
 Amounts 
 Found. 
 
 Referred 
 to Parts 
 in 1,000,000 
 of Water. 
 
 
 Parts in 
 1,000,000. 
 
 SiO 9 ... 
 
 Gram. 
 0.0012 
 0.0010 
 0.0008 
 0.0456 
 
 0.0365 
 
 0.0498 
 0.0104 
 0.0096 
 0.0039 
 
 (c) 
 
 SiO 2 
 
 Trace. 
 Trace. 
 Trace. 
 0.7 
 
 0.8 
 
 0.8 
 0.2 
 0.1 
 0.05 
 2.2 
 
 Cl 
 
 7.9 
 43.2 
 108.3 
 10.6 
 36.4 
 Trace. 
 37.3 
 12.2 
 
 7.9 
 43.2 
 110.5 
 10.6 
 36.4 
 Trace. 
 37.4 
 12.25 
 Trace. 
 Trace. 
 0.8 
 0.2 
 0.7 
 
 0.8 
 25.9 
 
 PbO 
 
 Cu 
 
 SO 
 
 CuO 
 
 CO a 
 
 FeA-. 
 
 Fe 
 
 
 Al A 1 
 
 PA f 
 znd. .!..'.".'! 
 
 CaO 
 
 A1A \ 
 
 Na... 
 
 
 Li 
 
 Ca 
 
 Zn 
 
 Me- 
 
 Ca 
 
 Pb 
 
 MgO 
 
 Mg 
 
 CO 3 d 
 
 Cu 
 Mn 
 
 
 
 CO,... 
 
 
 
 
 
 0.1588 
 
 4.85 
 
 Fe 
 
 
 A1A \ 
 
 
 PA / 
 
 Si"() 2 
 
 
 Free and 
 semi -com- 
 bined CO 2 , 
 
 Total C0 2 , 
 
 
 281.8 
 38.8 
 
 286.65 
 37.2 
 
 320.6 
 118.2 
 
 323.85 
 
 a Calculated. 6 Assumed condition. 
 
 c Any traces of CO 2 present have been neglected. 
 
 d Calculated for the metals, as carbonates before deposition. 
 
 NOTE. No tests for other possible constituents were made. 
 
 2. The contents of subterranean mine-waters taken at 2,000 
 ft. below the surface, and evidently coming from still greater 
 depths, very highly charged with carbonic acid, and carrying 
 small amounts of most of the metals that occur in the deposit; 
 also the sinter deposited by these waters as they issue from the 
 rock into the mine-drifts that is, under ordinary atmospheric 
 pressure. 
 
 3. The contents of atmospheric waters coming from the sur- 
 face, which, in their downward course, had traversed rocks 
 similar to those in which the first-named deposit is inclosed, 
 and through which it may be assumed that metallic minerals 
 similar to those in the deposit may be sparingly disseminated. 
 
152 SOME MINES OF ROSITA AND SILVER CLIFF, COLORADO. 
 
 Deep Water from the Geyser Mine, 2,000-^. Level. 
 
 Specific Gravity 27 C. =1.0036. (W. F. Hillebrand, Analyst.) 
 
 Composition of Sediment. 
 (From 43.76 kg. of Water.) 
 
 Composition of 
 Filtered Water. 
 
 Assumed 
 Composi- 
 tion Be- 
 fore Sedi- 
 ment 
 was De- 
 posited. 
 
 Insoluble in Dilute HC1. 
 
 HC1 Extract. 
 
 
 Parts in 
 1,000,000. 
 
 Chiefly Clayey and 
 Feldspathic Matter., 
 Weight Dried at 110 C. 
 5.0134 g. 
 
 Amounts 
 Found. 
 
 Referred to Parts in 
 1,000,000. 
 
 Cl 
 
 186.40 
 Traces. 
 161.70 
 Trace. 
 /1. 60 
 Trace. 
 1,437.26 
 None. 
 19MIO 
 719.45 
 2.85 
 108.84 
 1.10 
 176.60 
 0.05 
 Trace. 
 0.19 
 0.17 
 0.14 
 None. 
 22.90 
 Not est. 
 
 186.40 
 Trace. 
 161.70 
 Trace. 
 1.60 
 Trace. 
 1,513.44 
 h Trace. 
 198.00 
 719.45 
 2.85 
 146.41 
 1.95 
 177.67 
 1.35 
 0.02 
 0.57 
 0.34 
 3.50 
 i 1.06 
 24.42 
 Not est. 
 
 Br and I 
 
 SO 4 
 
 P0 4 
 NO, 
 
 BA 
 
 S?" 
 
 SiO 2 . 
 
 Per Cent. 
 54.07 
 
 29.70 
 
 A little 
 (as 
 CaFl 2 ?) 
 None. 
 4.40) 
 0.37 [ 
 
 Grams. 
 0.0667 
 
 a 0.0461 
 0.2100 
 
 2.7921 
 
 0.0778. 
 Not 
 tested 
 for. 
 2.3153 
 0.0440 
 None. 
 
 SiO 2 
 
 ALA 
 Fe 
 
 1.52 
 
 1.06 
 3.36 
 
 45.57 
 1.07 
 
 A1A ) 
 
 afi 
 
 CaO 
 
 Ca 
 
 K 
 
 Na 
 
 MgO.... 
 
 Mg.... 
 
 Si 
 
 Ca 
 
 K 2 O 
 
 
 Sr 
 
 Na 2 6 
 
 
 
 MET 
 
 SO 3 
 
 
 
 Pb . 
 
 CO 2 6 
 
 
 CO 3 
 
 c 76.18 
 0.85 
 None. 
 
 Cu 
 
 SrO 
 
 
 Sr 
 
 Mn 
 
 BaO 
 
 
 Ba 
 
 Zn 
 
 Fl 
 
 A little. 
 
 
 Fe 
 
 PbO 
 
 0.0610 
 0.0011 
 0.0232 
 0.0095 
 
 (e) 
 
 Pb 
 
 1.30 
 
 AIA 
 SiO 2 
 Org. mat. 
 
 Total CO 2 
 
 CuO 
 
 
 Cu 
 
 0.02 
 0.38 
 0.17 
 
 (e) 
 
 Mn A d 
 
 
 Mn 
 
 7nO 
 
 
 Zn 
 
 Ignition 
 
 9.47 
 
 3,009.25 
 2,472.60 
 
 3,140.73 
 2,528.43 
 
 98.01 
 
 5.6468 
 
 131.48 
 
 a Perhaps derived from the mechanically-included minerals of the sediment. 
 Contains a little P 2 O 5 . 
 
 6 The sediment was largely incrusted on the glass of the carboy and could only 
 be removed by acid ; hence the CO 2 was caculated for PbO, ZnO, SrO, CaO, MgO, 
 as normal carbonates. 
 
 c This value includes the CO 3 needed by Fe, Mn and Cu, as well as the metals 
 named in the preceding notes. 
 
 d Assumed condition ; perhaps partly as MnCO 3 . 
 
 e Organic matter not estimated. 
 
 / Approximation, not a maximum. 
 
 g Calculated for normal carbonates. 
 
 h The fluorine of the insoluble part of the sediment is probably to be credited 
 to the water. 
 
 i Possibly from the insoluble sediment. 
 
 From th'ese analyses it is possible to apply a practical test to 
 some of the assumed theories of ore-deposition. 
 
 Source of Solid Constituents in the Waters. In the first place, 
 in comparing the contents of the vadose and deep waters, it is 
 seen that though the latter contain about 20 times as much 
 
SOME MINES OF ROSITA AND SILVER CLIFF, COLORADO. 153 
 
 dissolved matter as the former, the relative proportions of the 
 principal constituents are sufficiently alike to permit the assump- 
 tion that they have been derived from a similar source; and 
 this source, in the case of the surface-waters, which should have 
 been practically pure when they entered the rocks, must have 
 been the material of the various rocks through which they 
 have passed in reaching a depth of 500 ft. below the surface. 
 In making this comparison, one must bear in mind that the 
 deep waters had already deposited the greater part of their lime 
 as sinter before they were analyzed ; hence, while the vadose 
 waters contain three times as much lime as magnesia, in the 
 analysis of the deep waters lime is to magnesia in the propor- 
 tion of only 4 to 5. 
 
 The alkalies appear in the same relative proportions in each 
 case, though the aggregate amount of the two constituents is 
 proportionately less in the vadose than in deep waters. 
 
 Iron and manganese are in nearly equal amounts in the vadose 
 waters, the latter slightly predominating, whereas in the deep 
 waters iron is in a hundred-fold greater relative amount. This 
 might be explained by the relatively larger amount of man- 
 ganese oxides present in the surface-rocks. It has often been 
 noted by the writer that manganese oxides are generally pres- 
 ent in much larger proportion in the oxidized portions of ore- 
 bodies than below the zone of oxidation, which may be due to 
 their forming, in contact with atmospheric agents, less soluble 
 salts than do the iron oxides. 
 
 The other metals are in such small proportions in either case 
 that one cannot reason from their relative amounts ; and it is 
 not surprising that most of them could not be detected in the 
 vadose waters. 
 
 Such constituents as fluorine, boric and nitric acids, stron- 
 tium, and barium are characteristic of deep sources, but they 
 also might have been present in the vadose waters without 
 being detected in the small amount of solid constituents avail- 
 able for analysis. 
 
 The greatest apparent discrepancy is the ten-fold greater 
 proportion of silica in vadose than in deep waters ; but this is 
 likely to have arisen from excess of C0 2 in deep waters which 
 would throw down silica in solution, or from the uncertainty in 
 determining what part of the solid material in the waters was 
 due to mechanical admixture, and hence might be neglected. 
 
154 SOME 'MINES OF ROSITA AND SILVER CLIFF, COLORADO. 
 
 In the deep waters chlorine and sulphuric acid are present 
 in about equal proportions, and carbonic acid is greatly in ex- 
 cess of both combined. In the vadose waters, while carbonic 
 acid is still in excess, sulphuric acid appears in relatively 
 greater, and chlorine in relatively smaller, proportion than in 
 the deep waters. In what manner they would combine with 
 the several bases in either case it is of course impossible to say 
 definitely. 
 
 The deductions which the writer draws from these considera- 
 tions are : 
 
 1. That inasmuch as the surface-waters must evidently have 
 derived the substances they contain in solution from the rocks 
 through which they have passed in seeping downward, it is fair 
 to assume that, in like manner, the deep waters have obtained 
 their constituents (in great part, at any rate) from surrounding 
 rocks, and not necessarily at very great distances from where 
 they now issue, since through higher temperature and greater 
 acid contents they would probably have been more active solv- 
 ents than the surface-waters. 
 
 2. On the other hand, the great excess of carbonic acid in 
 the deep waters, combined with the presence of fluorine, boric 
 acid, and chlorine in considerable amount, points to a source 
 where chemical decomposition is actively going on, which 
 might readily be supposed to be a body of still uncooled igne- 
 ous rocks, which surface-waters had reached, and from which 
 they were sent back towards the surface again along the present 
 lines of fissuring. Although the deep waters contain most of 
 the metals found in the vein-deposit of the Geyser mine, it is 
 not easy to conceive how the metallic sulphides of that deposit 
 could have been derived from waters of such chemical composi- 
 tion as these ; and it seems more reasonable to assume that the 
 vein-minerals were deposited by earlier waters of somewhat dif- 
 ferent composition, carrying more barium and silica, and char- 
 acterized by sulphuretted hydrogen rather than by carbonic acid. 
 
 3. The conditions here indicated seem to negative the preva- 
 lent belief that a decrease of temperature and pressure is the 
 principal determining cause of the precipitation of vein-minerals 
 from ascending solutions. In the earlier deposits abundant 
 precipitation ceased before the marked decrease of temperature 
 and pressure that accompanies an approach to the actual rock- 
 
SOME MINES OF ROSITA AND SILVER CLIFF, COLORADO. 155 
 
 surface was reached ; and in the modern mine-openings, where 
 present ascending waters have been artificially cooled and re- 
 lieved from pressure, the abundant deposit has been, like that 
 of thermal springs at the surface, mainly of carbonate of lime 
 and oxide of iron, and contains only faint traces of the other 
 vein-materials that make up the bulk of the neighboring vein- 
 deposits. 
 
 4. It might be assumed that the surface-deposits of chloride 
 of silver and oxides of manganese and iron which are thinly 
 and irregularly disseminated through the rhyolite near the 
 actual surface, were precipitated from the carbonated waters 
 at a time when they reached the present surface, the oxides hav- 
 ing been originally carbonates, and the silver chloride having 
 been deposited as such, and that these deposits are therefore 
 a later phase of ore-deposition than the vein-minerals. A cer- 
 tain color of probability is lent to this hypothesis by the fact 
 noted by Mr. Johnson, superintendent of the Geyser mine, tha't 
 there is evidence of an escape of warm air or gas through holes 
 at the surface, which in cold weather is visible as steam, along 
 a zone about 100 ft. wide, running east and west through the 
 Geyser shaft-house. Moreover, fluorite and barite are said to 
 have occurred, associated as gangue-minerals with chloride of 
 silver, in the Silver Bar (formerly Kate) mine. 
 
 On the other hand, all our evidence goes to show that the 
 chlorides and oxides pass into sulphides at short distances be- 
 low the surface, and that here, as in other deposits, the chloride 
 of silver is a secondary alteration by atmospheric agents of an 
 original sulphide. It appears more probable, therefore, that 
 all the metallic minerals of the plateau were formed under the 
 same conditions and during the same general phase of ore-de- 
 position. That they are so irregularly disseminated is prob- 
 ably due to physical rather than to chemical causes. The 
 rhyolitic tuff which forms the main country-rock is so poorly 
 consolidated, and of so plastic a nature, that fracture-planes 
 are less continuous and less open in it than in harder and more 
 rigid rocks. Moreover, the natural planes of division, the bed- 
 ding-planes, are horizontal rather than vertical. Hence there 
 have been no well-defined and continuous water-channels trav- 
 ersing the whole thickness of the mass, but the ascending solu- 
 tions, after leaving the vicinity of the bounding-walls of the 
 
156 SOME MINES OF ROSITA AND SILVER CLIFF, COLORADO. 
 
 harder Archaean rocks, have been obliged to follow devious 
 courses along minute cracks and fissures that were not continu- 
 ous. Thus, comparatively small amounts of these solutions 
 have reached the upper lavas, and their load has been deposited 
 as thin films in the joints or minute cracks of the rocks. The 
 fact that, at the present time, the descending surface-waters 
 penetrate the mass to so moderate a depth is an argument in 
 favor of this view. 
 
 It is probable that the present vein-fissure will soon reach 
 and pass into the Archaean wall-rock, in which it may widen 
 out. It is very uncertain whether, in this case, the ore will 
 continue to be as rich as it has been ; for a change in wall-rock 
 is generally accompanied by a change in the character of the 
 ore. These points will soon be settled, however, by actual - 
 development, as the workings of the Geyser mine follow the 
 present vein in depth. 
 
 GENERAL CONCLUSIONS. 
 
 Forms of the Ore-Bodies. The preceding pages have been 
 mainly devoted to the description of the Geyser mine in the 
 immediate vicinity of Silver Cliff. Other important deposits 
 within this area, and in the surrounding region, have not been 
 mentioned, because, owing to the irregular and disconnected 
 manner in which they have been worked, it has been impossi- 
 ble to obtain any detailed information with regard to them. 
 With but few exceptions, these deposits belong to the type of 
 the Humboldt-Pocahontas vein ; that is, they are vein-deposits 
 on fault-planes in some of the many varieties of igneous rocks 
 that outcrop in the region. They are, in general, rather nar- 
 row fissures, which do not bear evidence of having at any time 
 constituted large open spaces, but in which the ore-bearing so- 
 lutions have deposited their contents by first filling the inter- 
 stices between the sheets of sheared and banded country-rock 
 and afterwards partly replacing these sheets or bands by vein- 
 materials. The ore in these Ceases is generally confined to the 
 fault-fissure, and the deposits may be characterized as well- 
 defined vein-deposits or true fissure-veins. 
 
 The mines of the Silver Cliff plateau show a different type 
 of deposit, but, in the opinion of the writer, the essential dif- 
 ferences lie rather in the form of the ore-channels than in the 
 
SOME MINES OP ROSITA AND SILVER CLIFF, COLORADO. 157 
 
 character of the ore-bearing solutions. From Mr. Cross's de- 
 scription of the Democrat and Ben Eaton mines, in the cen- 
 tral rhyolitic area, these deposits seem to constitute an inter- 
 mediate stage between the two types. These mines occur on 
 the south point of Democratic ridge, known as Indian Castle. 
 This is a rounded eruptive channel of rhyolite, in which the 
 rock is massive, brecciated, or spherulitic, as the case may be. 
 There are indications that there have been several eruptions. 
 It has since been much altered, and the alteration-products 
 vary from hard quartzite-like material to softer material, re- 
 sulting from the kaolinization of inter-spherulitic glass. Tra- 
 chyte dikes run both north and south and east and west 
 through the mountain, and their decomposition-product is 
 usually soft. The ore-bearing fissures run north and south, 
 with a steep eastern dip, through both rhyolite and trachyte. 
 The ore- solutions followed these fissures primarily, but found 
 the softened spherulitic glass and certain brecciated zones also 
 very good channels. The ore is now found in these seams or 
 fissures, but all soft kaolinized parts are likely to be impreg- 
 nated. The main ore-body was an oval chimney, of varying 
 size, in soft matter, which is connected with a fissure at tunnel- 
 level. From one part, on stoping upward, a soft yellow mud 
 flowed out, which was found to carry 40 oz. of silver and $14 
 in gold to the ton. For the most part, the solid masses of ore 
 are less than 1 in. thick. 
 
 It has already been suggested, in the case of the deposits on 
 the Silver Cliff plateau, that the fact that the surface-deposits 
 are not in the form of fissure- veins, as they are found at the 
 bottom of the Geyser shaft, is due to physical causes which have 
 not permitted the formation of long continuous water-channels 
 along fissures. In this case similar irregularities have been 
 produced by chemical causes; but it has been the physical 
 effect the production of channels of freer flow, through the 
 decomposition of the rock that has led the ore-depositing cur- 
 rents to leave the regular fissures. 
 
 The deposits in the Archaean rocks on the borders of the erup- 
 tive region are likewise unusually irregular in form ; and, in 
 most of the observed cases, this irregularity may be ascribed 
 to a combination of chemical decomposition with dynamic frac- 
 turing of the rocks; that is, while the ore-channels have been 
 
158 SOME MINES OF RQSITA AND SILVER CLIFF, COLORADO. 
 
 primarily determined by the dynamic movements that produce 
 the ordinary rock-fractures, vein-fissures, and brecciated zones, 
 on which ore-bodies are generally deposited, their course has 
 been varied, or they have received unusual forms as the result 
 of the energetic dissolving or decomposing action of heated 
 solutions that traversed them during the closing phases of vol- 
 canic action in the region. This supposes a prolonged altera- 
 tion and decomposition of the rocks along the water-channels 
 before the actual deposition of metallic minerals. In some of 
 the observed cases, there are fairly well defined fissure-veins in 
 the Archaean rocks ; but more commonly, in this region, the 
 ore-deposition appears to have taken place along a zone of de- 
 composed rock, which zone was undoubtedly determined in 
 the beginning by dynamic action. The ore-deposition along 
 such zones, as might be expected, has been more irregularly 
 spaced and less concentrated than would have been the case in 
 a fissure which had not been thus enlarged by chemical decom- 
 position. The Bull-Domingo ore-body is apparently an extreme 
 type of such a form. 
 
 Whether it be or be not admitted that the boulder-filled 
 channel of the Bull-Domingo represents the neck of an ancient 
 crater of explosion, the Bassick ore-body is unique in the evi- 
 dence it affords of a direct connection with volcanic agencies ; 
 and in the determination of its form dynamic agencies have 
 apparently played a very subordinate part. 
 
 Cripple Creek Deposits Compared. It is interesting to contrast 
 the deposits of this region with those of the now famous Crip- 
 ple Creek district, which lies in a closely analogous geological 
 position, 40 miles to the northward, and which presents in its 
 geological structure so many points of resemblance. There, as 
 here, the main ore-deposition has taken place in and around a 
 central volcanic focus, where a series of comparatively recent 
 igneous rocks have broken through an older series of pre-Cam- 
 brian crystalline rocks. There* as here, the principal depo- 
 sition has taken place along a system of fracture-planes, trav- 
 ersing both the eruptives and the underlying crystalline 
 complex, and, while not strictly confined to the eruptives, it has 
 been, so far as present developments show, more abundant in 
 the former than in the latter. 
 
 In the Cripple Creek region there is one principal and pre- 
 
SOME MINES OF ROSITA AND SILVER CLIFF, COLORADO. 159 
 
 dominant system of mineralized fractures, running about north 
 and south. In this district a system running north and south 
 or a little west of north is apparently the more frequent, but 
 there are also abundant fractures running east and west, and 
 others quartering between the two. The geological history of 
 this region has been more complicated ; there have been a 
 greater number of successive eruptions ; and it is probably in 
 consequence of this fact that the fracture-systems are more varied 
 and complicated. 
 
 Mineralogically the contrast is greater. In Cripple Creek the 
 important metal is gold, deposited mainly in the form of tellu- 
 ride, and the characteristic earthy mineral associated with it is 
 fluorite. Here, gold as telluride occurs in certain parts of the 
 district, and fluorite is sparingly found ; but the greater part of 
 the valuable minerals are silver-minerals, in their usual asso- 
 ciation with sulphides of lead, zinc, and iron, and with barite 
 as the leading gangue-mineral. They differ from the ordinary 
 deposits of this class mainly in their greater average richness. 
 
 Source of the Metallic Minerals. While it is possible, by care- 
 ful study of the geological and mineralogical conditions of a 
 series of ore-deposits, to find valid reasons why the ore-bearing 
 solutions deposited their load in certain forms and certain locali- 
 ties, and while reasonable deductions may be made as to the 
 probable direction from which these solutions came, the ques- 
 tion as to the source from which the solvents derived the mate- 
 rials which they have thus deposited in the form of ore-bodies is 
 one that trenches somewhat upon the domain of pure specula- 
 tion. Yet, even here, there are many facts of geological observa- 
 tion that have a distinct bearing, one way or the other, upon the 
 various speculative views that have been put forth by geologists. 
 
 The general views of the writer upon this question, as already 
 expressed in earlier publications, are : that the heavy metals 
 have probably been brought up from the interior of the earth 
 within the magmas of igneous rocks, and that by some process 
 of differentiation not yet completely understood, either previous 
 to or during the process of cooling and consolidation, they have 
 been concentrated within certain bodies or parts of bodies of 
 eruptive rocks; and, further, that ore-bodies, as found at the 
 present day, are the result of a concentration (perhaps many 
 times repeated) of the materials thus brought up, which are in 
 
160 SOME MINES OF ROSITA AND SILVER CLIFF, COLORADO. 
 
 all probability very finely disseminated through the present 
 rock-masses or combined in minute amounts in the more com- 
 mon basic minerals. This seems a more rational hypothesis, 
 and one more in accordance with modern scientific practice, 
 than to content oneself with assuming simply that the ascending 
 waters came charged with metallic minerals from the bathy- 
 sphere, meaning thereby a region in the interior of the earth 
 which is richer in heavy metals than any part of the earth's 
 crust that comes under our observation; for this simple assump- 
 tion affords no explanation why metallic minerals are concen- 
 trated in one part of the earth's crust and not in another, and it 
 supposes a free flow of waters at greater depths than in our 
 present state of knowledge of terrestrial physics it is considered 
 possible that channels which would admit of a flow of water 
 through them could remain open. 
 
 Furthermore, the writer's hypothesis admits of a practical 
 test, which is impossible in the other case. If the vein-materials 
 are found to form a constituent part, even in minute traces, of 
 comparatively fresh and unaltered country-rocks in a given ore- 
 bearing region, and at such distances from any water-channels 
 as to render it improbable that these materials could have been 
 brought in through these channels, it is reasonable to assume 
 that these or similar rocks have been permeated by the waters 
 from which the known ore-deposits were precipitated, and that 
 from them they derived their contained vein-materials. For 
 this reason ,a series of careful tests of selected country-rock for 
 possible contents in the precious metals was carried on under 
 the direction of the writer at the laboratory of the TJ. S. Geo- 
 logical Survey in Denver. Since the office at Denver was 
 broken up, it has not been possible to continue these tests, 
 owing to want of proper facilities in the Washington laboratory. 
 
 Such tests of the rocks from this district as were completed 
 (unfortunately very few in number) are given below. 
 
 The five assays for silver were made upon 4 assay-tons of 
 each sample, and blank assays of a like amount of the lead-flux 
 were simultaneously made, the silver-content of the flux being 
 deducted from that found by the rock-assay. 
 
 In the case of the black granite from the Blue mountains, 
 another portion of the rock was pulverized and the constituent 
 minerals were separated by the Sonstadt solution. The bi- 
 
SOME MINES OF ROSITA AND SILVER CLIFF, COLORADO. 161 
 
 silicates in this case were found, as shown below, to contain 
 both silver and lead ; but no silver was found in either quartz 
 or feldspar. The assays of Ouster county country-rock for 
 silver, by L. G. Eakins, analyst, were : 
 
 Rock. 
 
 Locality. 
 
 Silver 
 per Ton. 
 
 Trachyte 
 
 ('00 ft southwest of Humboldt shaft 
 
 Ounce. 
 007 
 
 Trachvte 
 
 Summit of Game ridge 
 
 None 
 
 Rosita breccia 
 
 South of Game ridge 
 
 None 
 
 Rosita breccia 
 
 South of Game ridge 
 
 None 
 
 Fairview diorite 
 
 Mount Fairview 
 
 01 
 
 Tvndall andesite 
 
 Northeast spur of Mount Tjndall. 
 
 None. 
 
 Rhyolite 
 
 Top of Round mountain 
 
 0.402 
 
 Red granite . . 
 
 Near Haskell's ranch 
 
 0.005 
 
 Black granite . . 
 
 Blue mountains 
 
 0.025 
 
 Bisilicates of black granite (0.045 
 
 
 0.04 
 
 
 
 
 It thus appears that five out of nine of the rocks tested con- 
 tain appreciable amounts of silver; and that in one of these 
 rocks both silver and lead were found to be present in combi- 
 nation with other bases in the bisilicates. It seems, therefore, 
 probable that not only the recent eruptives, but the older gran- 
 ites through which the ascending solutions must have passed, 
 contain enough of the precious metals, and, it may be assumed 
 also, of the other vein-materials, to furnish, in the long time 
 that is accorded to the accomplishment of most geological phe- 
 nomena, sufficient material for the formation of existing ore- 
 bodies. The analysis of the vadose waters in the Geyser mine 
 has demonstrated the capability possessed by even cold surface- 
 waters of taking up such materials in their passage through the 
 rocks. The subterranean waters that were circulating here at 
 the time of the formation of the ore-deposits must have been 
 much more energetic solvents, being heated by contact with the 
 cooling masses of igneous rocks, and probably deriving a cer- 
 tain amount of active and energetic mineralizing-agents, such 
 as fluorine-, chlorine, etc., from these igneous masses at the time 
 of contact. Hence it is fair to assume that the vein-materials 
 in this region were originally derived from both recent and 
 ancient eruptive rocks a conclusion similar to that arrived at 
 by Mr. Penrose, from his more exhaustive study, for the ore- 
 deposits of Cripple Creek. 
 
 11 
 
162 THE GENESIS OF CERTAIN AURIFEROUS LODES. 
 
 No. 8. 
 The Genesis of Certain Auriferous Lodes. 
 
 BY JOHN R. DON, OTAGO, NEW ZEALAND. 
 
 (Chicago Meeting, February, 1897. Trans., xxvii., 564. Here reprinted in part only.) 
 
 CHAPTER V. THE EXAMINATION OF VARIOUS CONSTITUENTS OF 
 CRYSTALLINE AND ERUPTIVE ROCKS FOR GOLD AND SILVER. 
 In the South Island of New Zealand an unusually favorable 
 opportunity is offered for the analysis of the older crystalline 
 rocks, underlying the sedimentary rocks which form the 
 " country" of the gold-deposits. The Manipori formation of 
 this island, comprising the greater part of the mountainous 
 district west of lakes Manipori and Te Anau, in Otago, con- 
 sists of an enormous thickness (estimated by Professor Hutton l 
 at 160,000 ft.) of crystalline schists, gneiss, syenite, and syenitic 
 gneiss, with associated masses of granite ; the whole forming 
 the most picturesque part of New Zealand. The famous 
 West Coast sounds occur in this formation. No paying 
 auriferous lodes have been discovered in it ; and for this reason 
 an examination of the rocks is specially interesting here. Stelz- 
 ner, Posepny, and others, who have criticised the conclusions 
 of Sandberger, have laid great stress on the fact that all the 
 silicates analyzed by him were taken from the vicinity of ore- 
 bodies containing those heavy metals which he notes as oc- 
 curring in the silicates of the country-rock; their contention 
 being that these metals, supposed to occur as silicates in gneiss 
 and other crystalline rocks, were really contained as sulphides, 
 and were therefore impregnations from the neighboring ore- 
 bodies. The same objection, whatever be its weight, might be 
 urged with equal justice against Mr. Becker's derivation of the 
 mercury and gold of the lodes of the Pacific Coast from the 
 granite underlying their country-rock. In the case of the 
 
 1 Geology of Otago, by Hutton and Ulrich, p. 28. 
 
THE GENESIS OF CERTAIN AURIFEROUS LODES. 163 
 
 Manipori formation, just mentioned, such criticism could hardly 
 be made, as no auriferous lodes have been found within many 
 miles of the district from which samples were taken for the 
 present investigation. 
 
 In the South Island also, samples were taken from the gran- 
 ite abutting on the Carboniferous strata near Reefton, which 
 latter are the chief carriers of auriferous lodes in the western 
 part of the island. 
 
 Other samples of granite were collected from various parts 
 of Westland and Nelson, as far north as the granite-quarries of 
 Cape Foulwind. 
 
 Selwyn has pointed out 2 that the auriferous Silurian rocks of 
 Victoria probably rest everywhere on granite ; and this conclu- 
 sion has been supported by the later observations of Murray 3 
 and others. This underlying granite has not been reached in 
 any of the mines working in the stratified rocks about it; but 
 it is exposed at the surface in many parts of the colony, both 
 near to gold-bearing areas and distant from them. Numerous 
 samples of it were taken for this investigation. 4 
 
 The study of the country-rock from Gympie and Charters 
 Towers, Queensland, gave a good opportunity for the analysis 
 of silicates from crystalline igneous rocks. In the case of 
 Charters Towers, the whole country-rock (locally termed gran- 
 ite) is quartz-diorite, with a little accessory mica; while at 
 Gympie a thick sheet of diorite-aphanite (locally termed green- 
 stone), containing a large percentage of carbonate of lime, is 
 interbedded with the shales which bound the auriferous reefs, 
 these kindly shales occurring both above and below it. Messrs. 
 Alfred Lord and R. Steele, of Gympie, have furnished samples 
 of the " greenstone." 
 
 Sandberger's results having been criticised on the ground 
 that all the rocks he analyzed contained sulphides, and Po- 
 sepny 5 having urged the same objection to Becker's conclusions 
 
 2 Geology and Physical Geography of Victoria, by A. K. C. Selwyn and G. F. H. 
 Ulrich. 
 
 3 Geology and Physical Geography of Victoria, by A. K. F. Murray (1887). 
 
 4 In New South Wales, granite forms the country-rock of a number cf aurifer- 
 ous lodes; and it is much to be desired that some investigator on the spot would 
 take up this inquiry. The present paper contains no analyses of New South 
 Wales granite. 
 
 5 The Genesis of Ore-Deposits, Trans., xxiii., 282 (1893). 
 
164 THE GENESIS OF CERTAIN AURIFEROUS LODES. 
 
 in the case of the Comstock lode, this point was carefully 
 guarded. In every instance (even though an examination of a 
 hand-specimen showed no sulphides), an analysis of the rock 
 was first made, to determine whether sulphides were present; 
 and whenever such was the case, the sulphides were isolated 
 by panning, and separately assayed for gold and silver; but 
 when sulphides were thus found, no separation of the other crystalline 
 constituents of the rock was made. 
 
 It was deemed necessary to isolate and examine the follow- 
 ing minerals : (1) mica and (2) hornblende, because to these 
 Sandberger traces the silver and gold of many European lodes ; 
 (3) the pyroxenes of the later eruptives, because Becker traces 
 the gold and silver of the Comstock to the augite of the dia- 
 base, and both Hutton and Park (already cited) are inclined to 
 refer the gold and silver of the Thames district, IN". Z., to the 
 pyroxenes of the andesite ; 6 and (4) magnetite, because of Pro- 
 fessor Huttou's remark : 7 
 
 " I would suggest that, as part, at least, of the pyrites has been formed from 
 magnetite, the gold may have been originally in the magnetite, and have been 
 released during the formation of the pyrites. I do not think that this has been 
 the case, but it is a point worthy of investigation by the chemist. The pyrites is, no 
 doubt, a secondary mineral, formed in the rock after consolidation ; and if it 
 should turn out to be generally auriferous, we must suppose either that the gold 
 came from below with the sulphur, or that its source is the titaniferous magnetite 
 which is one of the original constituents of the rocks." 
 
 Isolation of Minerals. 
 
 The crystalline rocks examined comprised : (1) those in 
 which certain minerals were distributed in large crystals or ar- 
 ranged in folia, so that clean samples could be picked out by 
 hand ; and (2) those from which the various minerals had to 
 be separated by means of a liquid of high specific gravity. 
 
 The first class included many samples from the gneiss, syen- 
 ite, and granite of the Manipori formation, N. Z., from which 
 the separation of mica and hornblende was specially easy. In 
 various parts of this formation mica veins are abundant. It 
 
 6 Professor Hutton says on this point (op. tit., p. 272) : " If, therefore, we assume 
 that the pyroxenes of our volcanic rocks contain gold and silver, that the condi- 
 tions necessary for dissolving them rarely obtain, but that one of the exceptions 
 has been in the Hauraki [Thames] gold-fields, we have a hypothesis which will, I 
 think, explain most of the facts." 
 
 7 Op. tit., p. 271. 
 
THE GENESIS OF CERTAIN AURIFEROUS LODES. 165 
 
 was sometimes possible to pick in a few minutes 2 or 3 Ib. of 
 clean mica in plates up to 2 or 3 in. square. The syenite and 
 syenitic gneiss often contain bands of almost pure hornblende, 
 quite an inch thick, permitting a similarly easy isolation. 
 Finally, magnetite can, of course, be easily separated from any 
 rock in which it occurs. 
 
 The treatment of the second class, comprising many of the 
 rocks examined, may require some explanation. 
 
 The separation of minerals from rocks by means of heavy 
 solutions is extremely tedious, and it is therefore desirable to 
 reduce the quantity of the rock to be operated upon if this can 
 be done without material loss of the mineral to be isolated. 
 As all crystalline rocks contain a large percentage of material 
 below 3 in specific gravity, which can be effectively removed 
 by panning, each sample was concentrated first by panning to 
 get rid of quartz, feldspar, and other specifically light ma- 
 terials. This procedure would, of course, be inadmissible if the 
 object had been to determine accurately the gold and silver per 
 ton of the rock examined ; but the purpose in each case being 
 simply to get as large a quantity as possible of a given mineral, 
 and to get that sample approximately pure, this preliminary 
 crude concentration seemed to be unobjectionable. 
 
 As an illustration, the following record of the process, as ap- 
 plied in one instance (Sample 7, Table I. [Table XVIII. of 
 original paper] ), is here given. With suitable modifications, 
 this method was followed in all similar cases : 
 
 Sample of Syenite. 
 
 1. The sample was roughly broken and examined with a good lens, but no sul- 
 phides were discovered. A chemical analysis of 10 g. of the sample also showed 
 that sulphides were absent. 
 
 2. A portion of 500 g., pulverized so as to pass a No. 30 sieve, was reduced by 
 careful panning to 217 g., of which 58 g. was removed by a weak magnet. The 
 portion thus removed proved, under the microscope, not to be pure magnetite, but 
 to contain a good proportion of hornblende and feldspar (chiefly orthoclase) grains, 
 probably drawn to the magnet by small adhering particles of magnetite. 
 
 3. The 159 g. not attracted by the magnet consisted chiefly of hornblende and 
 feldspar, with a little mica (biotite) and quartz. This powder was introduced into 
 an apparatus modeled on Thoulet's, but made much larger, to save time. The 
 heavy liquid used was Sonstadt's : mercuric iodide, dissolved in excess of potassic 
 iodide, and having 3.175 sp. gr. 
 
 On exhausting the air from the apparatus, 77.5 g. of practically-pure horn- 
 blende fell to the bottom of the liquid. A dilution of this liquid to 2.95 sp. gr. 
 was followed by the precipitation of 35.5 g. more also nearly-pure hornblende. 
 
166 THE GENESIS OF CERTAIN AURIFEROUS LODES. 
 
 The total of 113 g., reckoned as hornblende, was finely powdered and assayed with 
 pure litharge. No trace of gold or silver was obtained. 
 
 4. The 58 g. removed by the magnet was similarly powdered and assayed, with 
 the same result. 
 
 Sonstadt's solution is cheap and easily prepared, but has the 
 great disadvantage of being extremely corrosive. Even with 
 the greatest care, it was found almost impossible for the op- 
 erator to avoid burning his fingers. Hence, in a number of 
 instances Klein's solution of boro-tungstate of cadmium was 
 employed. This has another advantage over Sonstadt's solu- 
 tion, namely, that when a partial separation of hornblende from 
 augite is desired, the greater part of the hornblende can be 
 kept from sinking in the liquid by using the latter in the con- 
 centrated state. 8 
 
 The results of the analysis of minerals separated from 47 
 samples of rock are given in Table I. On this table the fol- 
 lowing additional notes are presented : 
 
 1. Sample 17 represents a rock of peculiar occurrence, occu- 
 pying a narrow strip in an area of Tertiary trachyte at Porto- 
 bello, on the east coast of the Otago peninsula. Samples taken 
 short distances apart vary much in character ; but, on the 
 whole, the rock may be classed as a diorite. Gold was said to 
 have been found in the rock, up to 0.5 oz. to the ton. If this 
 were the case, such an occurrence of gold would have been, so 
 far as the writer knows, unique. 
 
 Of the three samples chosen, one (No. 17) contained pyrite, 
 and this pyrite was but the rock itself was not auriferous. 
 The occurrence of auriferous pyrite in such an area (of recent 
 volcanic rocks) is most unusual, and Professor Ulrich, Director 
 of the Otago School of Mines, 9 who has examined the locality 
 and studied rock-sections from it, thinks that this diorite rock 
 probably underlies the basic volcanics which form the rest of 
 
 8 It was found impossible to separate augite from hornblende completely by the 
 use of heavy liquids ; but since no gold or silver was found in either, this fact did 
 not affect the practical results of this investigation. The same remark applies 
 more or less to all the minerals thus isolated for analysis. The writer knows of 
 no method which will perfectly isolate considerable quantities of one mineral from 
 other minerals not widely removed in specific gravity. In Table L, therefore, 
 the terms " hornblende," "augite," etc., simply designate the greatest part of the 
 mineral samples to which they are applied. 
 
 9 I desire at this point to express my grateful thanks to our respected chief, 
 Professor Ulrich, for much kipd encouragement and practical assistance. 
 
THE GENESIS OF CERTAIN AURIFEROUS LODES. 
 
 167 
 
 TABLE I. (Table XVIII. of original paper). Analyses of Various 
 Minerals Isolated from the Older Crystalline and Newer Erup- 
 tive Rocks of New Zealand, Victoria, and Queensland. 
 
 A. KOCKS OF NEW ZEALAND. 
 
 D 
 
 "3. 
 
 Locality. 
 
 is 
 
 n 
 
 'g'S 
 
 II 
 
 SJ 
 
 Ill 
 lil 
 
 Method of 
 Separation. 
 
 Sulphides. 
 
 Results. 
 
 1... 
 
 2 
 
 From the "Staircase," 
 on the Sutherland 
 Falls road, Mil ford 
 sound, W. coast of 
 Otago. 
 Do 
 
 Gm. 
 
 200 
 
 150 
 
 Mica. 
 Mica 
 
 Gm. 
 200 
 
 150 
 
 Picked 
 by hand. 
 
 Do 
 
 None. 
 None 
 
 No gold or 
 silver. 
 
 Do 
 
 3... 
 4... 
 5... 
 
 6 
 
 Clinton gorge, N. W. of 
 Lake Te Anau, on 
 Milford sound road. 
 Roaring creek, Arthur 
 River valley, near 
 Milford sound. 
 On the track between 
 Milford sound and 
 Lake Ada, W. coast of 
 Otago. 
 Duskv sound W coast 
 
 150 
 
 100 
 100 
 
 Mica. 
 Mica. 
 Mica. 
 
 Hornblende. 
 
 150 
 
 100 
 100 
 
 Do. 
 Do. 
 Do. 
 
 Do 
 
 None. 
 None. 
 None. 
 
 See note 
 
 Do. 
 Do. 
 Do. 
 
 7 
 
 of Otago. 
 Do 
 
 500 
 
 Hornblende. 
 
 113 
 
 Somtadt s 
 
 below. 
 
 below. 
 
 8... 
 9... 
 10... 
 11 
 
 Milford sound, W. coast 
 of Otago. 
 Preservation inlet, W. 
 coast of Otago. 
 West Jacket Arm, W. 
 coast of Otago. 
 George sound W coast 
 
 100 
 100 
 140 
 500 
 
 Hornblende. 
 Hornblende. 
 Hornblende. 
 
 100 
 100 
 140 
 
 solution. 
 Picked 
 by hand. 
 Do. 
 
 DO. 
 
 None. 
 None. 
 None. 
 
 silver. 
 Do. 
 
 Do. 
 Do. 
 
 12 
 
 of Otago. 
 Do 
 
 200 
 
 Hornblende. 
 
 200 
 
 Picked 
 
 below. 
 
 below. 
 
 13 
 
 Do 
 
 1,000 
 
 Hornblende. 
 
 
 by hand. 
 Do 
 
 
 silver. 
 
 14... 
 15. 
 
 Skipper's creek, central 
 Otago. 
 Shotover river, central 
 
 
 Magnetite. 
 Magnetite. 
 
 250 
 150 
 
 Magnet. 
 Magnet 
 
 below. 
 None. 
 
 None 
 
 below. 
 No gold or 
 silver. 
 Do 
 
 16 . 
 
 Otago. 
 Do 
 
 
 Magnetite. 
 
 180 
 
 Magnet 
 
 None 
 
 Do 
 
 17 
 
 Portobello Otago Pen- 
 
 
 
 
 
 
 
 18 
 
 insula, near Dunedin. 
 Do 
 
 500 
 
 
 Horn- 
 
 Sonstadt's 
 
 below. 
 
 below. 
 
 19 
 
 Do 
 
 500 
 
 
 blende, 57 
 Mica. 43 
 Biotite 38 
 
 solution. 
 Sonstadt's 
 
 
 silver. 
 
 Dn 
 
 20 
 
 Near Dunedin 
 
 
 Magnetite 
 
 Horn- 
 blende, 26 
 60 
 
 solution. 
 Magnet 
 
 
 Do 
 
 21... 
 
 22... 
 23... 
 
 24... 
 25... 
 
 26... 
 
 Water of Leith, near 
 Dunedin 
 
 Near Oamaru, Otago. 
 Cape Foulwind, W. 
 coast of Nelson. 
 Inangahua river, Reef- 
 ton. 
 Cape Foulwind quar- 
 ries, W. coast of Nel- 
 son, N. Z. 
 Rangitoto, Westland 
 
 500 
 500 
 
 Hornblende, 
 2.8 to 3 
 Augite, 
 3 to 3. 2 
 Magnetite. 
 Mica. 
 
 Mica. 
 Mica. 
 
 16 
 25 
 
 80 
 200 
 
 84 
 43 
 
 Klein's' 
 solution. 
 
 Magnet. 
 Picked 
 by hand. 
 Klein's 
 solution. 
 Sonstadt's 
 solution. 
 
 Klein's 
 
 None. 
 
 None. 
 None . 
 
 None. 
 None. 
 
 Do. 
 
 Do. 
 Do. 
 
 Do. 
 Do. 
 
 See note 
 
 27... 
 28... 
 29... 
 
 30 
 
 N. Z. 
 
 Bed of Hokitika river, 
 Westland, N. Z. 
 Bligh sound, W. coast 
 Otago. 
 Moanataiari tunnel, 
 Thames district 
 
 Do 
 
 500 
 500 
 1,000 
 
 1 000 
 
 Mica. 
 Mica. 
 
 Pyroxenes of 
 sp.gr. 2.9 to 
 3.2 
 
 48 
 61 
 73 
 
 56 
 
 solution. 
 Do. 
 
 Do. 
 Do. 
 
 Do 
 
 below. 
 None. 
 
 None. 
 None. 
 
 below. 
 No gold or 
 silver. 
 Do. 
 
 Do. 
 
 F)n 
 
 
 
 
 and chlo- 
 rite between 
 sp. gr. 2.8 
 and 3.1. 
 
 
 
 
 
168 
 
 THE GENESIS OF CERTAIN AURIFEROUS LODES. 
 
 TABLE I. A. Hocks of New Zealand. Continued. 
 
 1 
 
 Locality. 
 
 ,C fi 
 
 11 
 
 '^'S'O 
 
 Sis 
 
 *< 
 
 11 
 
 t 
 g 
 
 % 
 
 2 
 
 I 
 
 A 
 
 
 H 
 
 ij 
 
 gSS 
 
 "SH. 
 * 
 
 1 
 
 Qi 
 
 H 
 
 
 
 Gm. 
 
 
 Gm. 
 
 
 
 
 31... 
 
 Waitekauri creek 
 
 1,000 
 
 Hornbl e n d e 
 
 65 
 
 Klein's 
 
 None. 
 
 No gold or 
 
 
 Thames district. 
 
 
 and chlo- 
 
 
 solution. 
 
 
 silver. 
 
 
 
 
 rite between 
 
 
 
 
 
 
 
 
 sp. gr. 2.8 
 
 
 
 
 
 
 
 
 and 3.1. 
 
 
 
 
 
 32... 
 
 Moanataiari tunnel, 
 
 1,000 
 
 Pyroxen's be- 
 
 43 
 
 Do. 
 
 None. 
 
 Do. 
 
 
 Thames district. 
 
 
 tween sp. gr. 
 
 
 
 
 
 
 
 
 2. 9 and 3. 2. 
 
 
 
 
 
 33... 
 
 Fame and Fortune G. 
 
 1,000 
 
 Do. 
 
 84 
 
 Do. 
 
 None. 
 
 Do. 
 
 
 M. Co., Thames. 
 
 
 
 
 
 
 
 34... 
 
 Do 
 
 500 
 
 Do. 
 
 27 
 
 Do. 
 
 None. 
 
 Do. 
 
 33... 
 34... 
 
 Fame and Fortune G. 
 M. Co., Thames. 
 Do 
 
 1,000 
 500 
 
 Do. 
 Do. 
 
 84 
 27 
 
 Do. 
 Do. 
 
 None. 
 None. 
 
 Do. 
 Do. 
 
 
 B. ROCKS OF VICTORIA. 
 
 35... 
 36... 
 
 37 
 
 900-ft. level, Long Tun- 
 nel G. M. Co. 
 Thomson river, near 
 Walhalla, Gippsland, 
 Viet. 
 Do 
 
 1,000 
 1,000 
 
 1,000 
 
 Hornblende. 
 
 73 
 
 Klein's 
 solution. 
 
 None. 
 
 See note 
 below. 
 
 None. 
 
 See note 
 below. 
 None. 
 
 None. 
 None. 
 
 None. 
 None. 
 
 No gold or 
 silver. 
 See note 
 below. 
 
 No gold or 
 silver. 
 See note 
 below. 
 No gold or 
 silver. 
 Do. 
 Do. 
 
 Do. 
 Do. 
 
 Hornblende. 
 Hornblende. 
 Mica. 
 
 Mica. 
 Hornblende. 
 
 Magnetite. 
 Magnetite. 
 
 38 
 
 Klein's 
 solution. 
 
 38... 
 39... 
 40 
 
 Big hill, Bendigo, near 
 the Silurian boundary. 
 Do 
 
 500 
 
 500 
 1,000 
 
 53 
 
 84 
 96 
 
 50 
 40 
 
 Klein's 
 solution. 
 Do. 
 Do. 
 
 Magnet. 
 Magnet. 
 
 Do 
 
 41... 
 
 42... 
 43... 
 
 From Gabo Island, S. E. 
 of Viet., used as a 
 building stone in Mel- 
 bourne. 
 Ballarat East, Victoria. 
 Sunbury, near Mel- 
 bourne, Victoria. 
 
 C. ROCKS OF QUEENSLAND. 
 
 44... 
 45... 
 46 
 
 The 1.070-ft. level, Bril- 
 liant and St. George 
 G. M. Co., Charters 
 Towers, Queensland. 
 Do 
 
 The 950-ft level of the 
 
 500 
 500 
 1 000 
 
 Sp. gr. 2.75 to 
 3 (biotite). 
 Sp. gr. 3 to 3.2 
 (hornblende) 
 Sp.gr. 2. 75 to 
 3 (biotite). 
 Sp. gr. 3 to 3.2 
 (hornblende) 
 
 21 
 
 % 
 
 40 
 36 
 
 Klein's 
 solution. 
 
 Klein's 
 solution. 
 
 None. 
 None. 
 See note 
 
 No gold or 
 
 silver. 
 
 Do. 
 See note 
 
 47 
 
 No. 5 North Phoenix 
 G. M. Co., Gympie. 
 Do 
 
 1 000 
 
 
 25 
 
 
 below. 
 Do 
 
 below. 
 Do 
 
 
 
 
 
 
 
 
 
 1, 2. Gneiss, containing veins of mica, about 0.5 in. wide, mixed with quartz. Several pounds' 
 weight of mica were easily obtained. 
 
 3. Granite, with muscovite in large plates, easily picked out of sample. 
 
 4, 5. Gneiss ; contained veins of muscovite, from which pieces 2 in. square were easily picked 
 
 out. 
 
 6. Syenitic gneiss, consisting of quartz, feldspar, and hornblende, with a little biotite, the 
 
 hornblende in a seam about 2 in. wide. Pyrrhotite and chalcopyrite, with minute specks 
 of native copper, associated with the hornblende ; 500 g. of the rock gave 53 g. of sul- 
 phides, mostly pyrrhotite, which contained 0.0053 of silver. 
 
 7. Syenite. 
 
 8. Syenitic gneiss. A vein of hornblende about 2 in. wide occupied the greater part of the 
 
 sample analyzed. 
 
 9, 10. Syenite-porphyry, showing large patches and crystals of hornblende. 
 11. Syenitic gneiss, consisting of quartz, feldspar, and biotite, with patches of hornblende. 
 
 Sample showed pyrrhotite and pyrite ; 500 g. gave 18.56 g. of these minerals chiefly, but 
 
 no gold or silver was found. 
 
THE GENESIS OF CERTAIN AURIFEROUS LODES. 169* 
 
 12. " Granite," a rock containing pink feldspar, quartz, muscovite, and bands of hornblende.. 
 
 13. "Granite," a rock containing orthoclase, quartz, muscovite, and hornblende in veins; 
 1,000 g. gave 12.18 g. pyrrhotite and arsenopyrite, which yielded no gold or silver. 
 
 14. Chlorite-schist, containing numerous octahedral crystals of magnetite. 
 
 15. Hornblende-schist, containing numerous octahedral crystals of magnetite. 
 
 16. Heavy "black sand," result of erosion of mica-schist. 
 
 17. "Diorite," consisting of triclinic feldspar, hornblende, biotite, magnetite, and a little 
 quartz ; 1,000 g. gave 4.934 g. of pyrite, containing 0.037 grain of gold and 0.0041 grain of 
 silver. 
 
 18, 19. Diorite, like No. 17. 
 
 20. Phonolite. 
 
 21. Basalt, very much decomposed, with large, undecomposed crystals of augite and horn- 
 blende. 
 
 22. Hard, solid basalt, from a quarry. 
 
 23. Gneiss-granite, with large folia of mica, easily picked out of sample. 
 
 24. 25. Fine-grained granite. 
 
 26. Granite, with a pyritous vein ; 1,000 g. gave 28.92 g. of arsenopyrite and pyrrhotite, with a 
 little galena, and this yielded 0.0032 grain of gold and 0.0019 grain of silver. 
 
 27. Granite. 
 
 28. Gneiss. 
 
 29. Nepheline-andesite, hard, very little decomposed. 
 oO. Hard blue hornblende-andesite. 
 
 31. Hornblende-andesite, slightly altered. 
 
 32. Augite-andesite, with much chlorite. 
 
 33. 34. Hard blue unaltered augite-andesite. 
 
 35. "Diorite" dike, near auriferous reef, Walhalla, Gippsland, Victoria. 
 
 36. " Diorite, associated with copper-lode. Showed chalcopyrite, of which there were ob- 
 tained from 1,000 g. of the rock 16.48 g. (with a small quantity of bournonite), yielding 
 0.407 grain of silver and no gold. 
 
 37. " Diorite," fike No. 36. 
 
 38. Syenitic granite (quartz, orthoclase, and muscovite, with large crystals of hornblende) ; 
 1,000 g. gave 16.03 g. of pyrite, yielding neither gold nor silver. 
 
 39. Syenitic granite, like No. 38. 
 
 40. Granite. 
 
 41. Syenite. 
 
 42. Very dense basalt, overlying auriferous slates. 
 
 43. Vesicular basalt. 
 
 44. 45. Quartz-mica diorite (tonalite: the "granite " of Charters Towers). 
 
 46. Diorite-aphanite, with much carbonate of lime (calc-aphanite) ; a very much altered rock ; 
 effervesces strongly with acid (the "greenstone " of the Gympie field) ; it contains pyrite 
 and sphalerite in small quantities ; 1,000 g. gave 8.42 g. of pyrite, yielding no gold or silver. 
 
 47. Diorite-aphanite, like No. 46; 1,000 g. gave 42.7 g. of pyrite and galena, which yielded 
 0.0016 grain of gold and 0.0037 grain of silver. 
 
 the peninsula. In that case, it would be allied rather to the 
 dikes of the Upper Silurian in Victoria than to the newer vol- 
 canic rocks of its immediate neighborhood. 
 
 A prepared thin section of this rock was microscopically 
 examined by a German mineralogist, who says of it: 
 
 " This rock is, without doubt, one of the older volcanic rocks. It consists of 
 feldspar, mica, and hornblende, with a little quartz and magnetite. Mica is to a 
 great extent absorbed, and magnetite has taken its place. The rock is difficult 
 to classify, but would be best described as an elseolite-syenitic rock." 
 
 2. Samples 29 to 34 are from the Thames district. It was 
 found difficult to get samples of the Thames andesites in which 
 
170 THE GENESIS OF CERTAIN AURIFEROUS LODES. 
 
 the analysis of 5 g. would show no trace of sulphides this 
 being, as already explained, a requisite condition for the par- 
 ticular investigation in hand. A large number of samples had 
 to be rejected on this account; but in Kos. 29 to 34 no trace of 
 sulphides was found. . . . 
 
 3. Nine samples in Table I. : namely, NOB. 6, 11, 13, 17, 
 26, 36, 38, 46, and 47 contained sulphides. The results of 
 further examination were as follows : 
 
 No. 6. Sample of 500 g. gave 53 g. of sulphides,jnostly pyr- 
 rhotite arid chalcopyrite, which contained 0.0053 grain of silver. 
 
 No. 11. Sample of 500 g. gave 18.56 g., chiefly pyrrhotite. 
 No gold or silver. 
 
 No. 13. Sample of 1,000 g. gave 12.18 g. of pyrrhotite and 
 arsenopyrite. No gold or silver. 
 
 No. 17. Sample of 1,000 g. gave 4.934 g. of pyrite, contain- 
 ing 0.037 grain of gold and 0.0041 grain of silver. 
 
 No. 26. Sample of 1,000 g. gave 28.92 g. of arsenopyrite 
 and pyrrhotite, with a little galena, containing 0.0032 grain of 
 gold and 6.0019 grain of silver. 
 
 No. 36. Sample of 1,000 g. gave 16.48 g. of chalcopyrite, 
 with a small quantity of bournonite, carrying 0.407 grain of 
 silver and no gold. 
 
 No. 38. Sample of 1,000 g. gave 16.03 g. of pyrite. No 
 gold or silver. 
 
 No. 46. Sample of 1,000 g. gave 8.42 g. of pyrite. No gold 
 or silver. 
 
 No. 47. Sample of 500 g. of pyrite and sphalerite, contain- 
 ing 0.0016 grain of gold and 0.0037 grain of silver. 
 
 Conclusions. The results summarized in Table I. were 
 greatly surprising to the writer. In view of the usually tedi- 
 ous character of the operation of isolating the various con- 
 stituents of a rock, he would not have examined so large a 
 number of samples had he not expected, at each new analysis, 
 that he might succeed in discovering gold in some mineral 
 other than a sulphide. 
 
 It is, perhaps, comparatively easy to conceive why, in a 
 stratified area, gold may occur only in connection with sul- 
 phides ; but that in such a rock as gneiss, granite, syenite, or 
 diorite, it should form no part of the crystalline constituents, 
 but, on the contrary, should occur only in the sulphides found 
 in these rocks, seems more remarkable and significant. 
 
THE GENESIS OF CERTAIN AURIFEROUS LODES. 171 
 
 CHAPTER VI. THE VADOSE REGION. 
 
 Professor Posepny 10 advances the sweeping proposition that 
 the formation of ore-deposits could have taken place by descen- 
 sion and lateral secretion in the vadose region of circulation 
 only, and must have been, in the deep region, the product of 
 ascending currents. This distinction is, perhaps, too sharply 
 drawn by him. It seems to the writer that the lateral-secre- 
 tion theory can scarcely be put out of court by assuming a 
 lateral secretion to be impossible below the ground-water level. 
 Yet the marked difference everywhere observed in the con- 
 tents of auriferous lodes above and below that leVel required 
 that the rocks of the two zones should be distinguished, and 
 separately analyzed in this investigation. 
 
 From an economic stand-point, this difference is expressed by 
 the almost universal experience in the Australasian gold-fields, 
 that the average yield of gold is much smaller below the water- 
 level than near the surface. This statement, which will doubt- 
 less be controverted in some quarters, is based on the concur- 
 rent testimony of a large number of mine-managers and others, 
 having long experience in the auriferous deposits of Australia 
 and New Zealand. The almost unanimous evidence is in 
 favor of the greater richness of vadose deposits. Several men 
 of great experience have even given the opinion that, for ounces 
 per ton above the ground-water level, only pennyweights per 
 ton have been found below it. 
 
 This important economic question is naturally discussed in 
 treatises on ore-deposits. Phillips, 11 for example, gives a num- 
 ber of reasons why the results in the vadose region may seem 
 to be, while they are not really, higher than those of deep levels. 
 Even after taking these considerations into account, however, 
 the evidence of greater richness in the vadose region in Aus- 
 tralia seems overwhelming. 
 
 In this connection, reference may be made to the exhaustive 
 work of K. Brough Smyth, 12 and to a very interesting little 
 work, 13 dealing with the yield of the auriferous deposits of Yic- 
 
 10 Trans., xxiii., 262 (1893). 
 
 11 A Treatise on Ore-Deposits, pp. 60 to 62 (1884). 
 
 1 2 G old-Fields of Victoria, pp. 233 to 281 (1889). 
 
 13 The Gold-Fields of Victoria in 1862, by a Special Keporter of the Argus, Mel- 
 bourne (1863). 
 
172 THE GENESIS OF CERTAIN AURIFEROUS LODES. 
 
 toria from 1851 to 1862. The reader of the latter book may 
 suspect the anonymous author of overstating the facts ; but a 
 comparison of the average yields noted in it with those of mines 
 now working in the same reefs, with the aid of the latest gold- 
 saving appliances, can hardly fail to carry conviction, even to 
 those who, permitting " the wish " to be " father to the thought," 
 deny the impoverishment of auriferous lodes in depth. 14 
 
 This greater richness of the vadose region might be explained 
 in either of two ways. 
 
 1. If the auriferous contents of the lodes are derived from 
 some deeper source, and have been deposited from warm as- 
 cending waters, the decrease of pressure on approaching what 
 was, at the time of the lode-formation, the surface, might 
 account for the precipitation of the precious metals in greater 
 quantities near that surface. 
 
 2. If the reefs and their auriferous contents are due to the 
 leaching action of solutions traversing the country-rock on each 
 side of the fissures, such leaching action would naturally be far 
 more intense near the surface, because the oxidizing action of 
 the surface-water would naturally be much greater in the vadose 
 region. 
 
 Either of these hypotheses might account for the greater 
 richness of the vadose region. In the first case we might have 
 in the present deposits of that region an example of the re- 
 solution and precipitation of gold which had been previously 
 brought up from greater depths ; while in the second case we 
 might expect to trace a leaching action similar to that occurring 
 in depth, only augmented by the effect of the oxidizing vadose 
 waters. 
 
 The question is naturally suggested, whether natural re- 
 agents capable of dissolving gold 15 are to be found in the vi- 
 cinity of auriferous lodes. And this inquiry suggests the 
 further questions : Does gold exist in solution in mine-waters 
 of either the vadose or the deep circulation ? Does the gold 
 of the vadose circulation, in any particular mine, contain a 
 
 14 The gold-field of Bendigo is often cited as an instance to the contrary, good 
 yields having been there obtained in some eases from great depths (2,000 to 2,800 
 ft. ) ; but the reason for this is indicated in the remarks of E. J. Dunn, in his report 
 on the Bendigo Gold-Fields, pp. 6 and 9. 
 
 15 Gold is so easily precipitated from solution that an investigation as to possible 
 precipitating-agents is scarcely necessary. 
 
THE GENESIS OF CERTAIN AURIFEROUS LODES. 173 
 
 smaller percentage of silver than that of the deep circulation ? 
 Is any evidence of re-solution and re-precipitation to be obtained 
 by analyzing samples of country-rock from the vadose region, 
 corresponding in position with samples from the deep region 
 of the same district? 
 
 Natural Solvents of Gold. 
 
 The chief solvents of gold at all likely to occur in the neigh- 
 borhood of lodes are bromine, iodine, ferric chloride, ferric sul- 
 phate, and chlorine. 
 
 Bromine and Iodine. The action of iodine as a solvent for 
 gold in nature has been emphasized by some writers ; 16 but, 
 whatever may have taken place in the past, the present inves- 
 tigation seems to show that iodine is* not at all abundant in au- 
 riferous rocks. The partial or complete analysis of 53 samples 
 of mine-water from both the vadose and the deep circulation 
 has detected no bromine, and only in one instance any trace of 
 a soluble iodide. If, however, bromides and iodides do exist 
 in the vadose region, the agents which liberate chlorine (con- 
 sidered below) would also liberate bromine and iodine. 
 
 Ferric Chloride and Ferric Sulphate. Henry Wurtz 17 remarks 
 that as early as 1859 he called attention to the solubility of gold 
 in these salts ; but he does not state the strength of the solvent 
 solutions employed. The same is true of many other assertions 
 of this reaction, encountered in technical literature. 18 It was 
 therefore deemed necessary in the present investigation to test 
 the solubility of gold in solutions of the above salts of various 
 strengths, not greatly exceeding, however, the degree of con- 
 centration actually found in the most highly mineralized waters 
 analyzed. Solutions of ferric chloride and ferric sulphate, con- 
 taining from 1 to 20 g. per liter, were prepared, and finely 
 divided (1) metallic gold and (2) auriferous sulphides were 
 treated in these solutions, being freely exposed to the air at 
 ordinary temperature for several months ; but no gold was dis- 
 
 16 For example, T. A. Rickard, On the Origin of the Gold- Bearing Quartz of 
 the Bendigo Keefs, 1 Vans., xxii., 309 (1893). 
 
 ir Gold Genesis, Scientific American Supplement, vol. xxxviii., No. 979, p. 15,644 
 (Oct. 6, 1894). 
 
 18 It is highly desirable that in all such statements of solubility, the precise 
 strength of the reagents should be given. Most of the accounts of the solution of 
 gold, for instance, employ, at best, only the vague terms "strong," "dilute," etc. 
 
174 THE GENESIS OF CERTAIN AURIFEROUS LODES. 
 
 solved, even by the strongest solutions. As the highest strength 
 above named considerably exceeded that of the most highly 
 mineralized mine-waters analyzed, no experiments were made 
 with still stronger solutions of the ferric salts. 
 
 The negative result of these experiments is, of course, not 
 conclusive proof that gold may not have been dissolved by these 
 reagents in the vadose circulation in a longer time and under 
 other conditions than those supplied. 
 
 Chlorine. Possibly many reactions in nature, not easily re- 
 produced in the laboratory, may liberate chlorine, even at ordi- 
 nary temperatures. We know, however, that it is produced by 
 the action of hydrochloric acid on the higher oxides of manga- 
 nese, or by the action of sulphuric acid on the same oxides in 
 the presence of chlorides. 
 
 The question whether agents for the re-solution of gold exist 
 in the vadose region is thus practically narrowed to a search, in 
 the waters and rocks of that region, for (1) free hydrochloric 
 acid ; (2) free sulphuric acid ; (3) the higher oxides of manga- 
 nese ; and (4) ferric chloride and ferric sulphate. 
 
 It was desirable, at the outset, to determine the most dilute 
 solution of hydrochloric acid which will, in the presence of the 
 higher oxides of manganese, liberate sufficient chlorine to be 
 detected by ordinary tests. Experiment showed that 1 part of 
 hydrochloric acid of 1.16 sp. gr. in 2,500 of water would give 
 a distinct chlorine reaction, while 1 part of the same acid in 
 1,250 of water produced chlorine enough to dissolve an amount 
 of gold appreciable by delicate tests. As the proportion of 
 pure HOI to water is in the first case only about 1 to 8,000, 
 and in the second case 1 to 4,000, it is evident that extremely 
 dilute acid will, in the presence of manganese oxides, dissolve 
 gold. 
 
 Cause of Acidity in Mine- Waters. The chief cause of acidity 
 in mine-waters (see examples below) is without doubt the oxi- 
 dation of pyrite, which yields ferric sulphate and sulphuric 
 acid. The latter, acting on the chlorides, which are always 
 present to greater or less extent in mine-waters, frees hydro- 
 chloric acid. The writer has never found a water containing 
 free acid in which there was not also a large percentage of fer- 
 ric salts. 
 
 The Occurrence of Oxides of Manganese in Mining-Districts. 
 
THE GENESIS OF CERTAIN AURIFEROUS LODES. 175 
 
 In some mining-districts (notably in Karangahake, in the 
 Thames gold-field) the oxides of manganese often form a great 
 part of the lode-filling. While this, however, is exceptional in 
 Australia and New Zealand, the presence of the higher oxides 
 of manganese in the ferric oxides of the vadose circulation is 
 surprisingly general. Twenty analyses of such material from 
 various localities showed in 17 cases manganese, representing 
 from 0.012 to 43.59 per cent, (reckoned as Mn 3 4 ). To one 
 sample, containing only 0.38 per cent, of Mn 3 4 , dilute hydro- 
 chloric acid and precipitated gold were added, and gold was 
 found to be dissolved. 
 
 If, therefore, the vadose mine-waters are found to contain 
 free hydrochloric acid, it is evident that agents for the re-solu- 
 tion of gold in that zone are not lacking. 
 
 The Acidity of Vadose Mine- Waters. An acid reaction with 
 test-paper does not prove the presence of free acid. Every 
 water examined which contained an appreciable quantity of 
 ferric salts gave a distinct acid reaction, though in a number 
 of cases examination proved the absence of free acid. 
 
 Seventeen samples of vadose waters were examined for free 
 acid ; care being taken to collect the water as it ran from the 
 rock or vein, before any considerable exposure to oxidizing 
 agencies other than the oxygen held in solution by the water 
 itself. 
 
 In calculating the results from those samples which carried 
 much free acid, if both sulphates and chlorides were present, 
 and the amount of free acid exceeded the amount represented 
 by the chlorine radical in the water, the whole of the chlorine 
 radical was taken as combined with H to form free hydro- 
 chloric acid, and the remainder of the free acid found was 
 reckoned as sulphuric acid. The results are shown in Table II. 
 The amount of ferric chloride and sulphate can be approxi- 
 mately calculated from the proportion of iron present as ferric 
 salts. Even after complete oxidation by exposure to the air, 
 the total weight of ferric salts could never exceed 12 g. per 
 liter. For this reason, in the experiments previously described 
 (see p. 173), I did not use solutions of ferric salts containing 
 more than 20 g. per liter. 
 
 Table II. shows the considerable increase in acidity caused 
 by exposure to the air. It is noteworthy that all the samples 
 
176 
 
 THE GENESIS OF CERTAIN AURIFEROUS LODES. 
 
 marked *, when taken from the mine, precipitated gold from 
 solution, but that the same waters, after thorough oxidation, 
 dissolved metallic gold when the higher oxides of manganese 
 were added to them. 
 
 TABLE II. Examination of Mine-Waters of the Vadose Region 
 for Free Acid and Ferric Salts. 
 
 
 
 1 
 
 
 , 
 
 og 
 
 3- 
 
 a* 
 
 ,2 
 
 
 J 
 
 Free Acid in 
 
 Free Acid in 
 
 "be* S 
 
 Bra 
 
 els 
 
 '*P 
 
 Country-Rock. 
 
 Reaction t 
 Pape: 
 
 Grams per 
 Liter before Ex- 
 posure to Air. 
 
 Grams per 
 Liter after Ex- 
 posure to Air. 
 
 ||| 
 
 Iron Pres< 
 Ferric S 
 
 i 
 
 || 
 
 a*... 
 
 Propylite, highly 
 pyritous. 
 
 Strongly 
 acid. 
 
 HC1. 
 0.446 
 
 H 2 SO 4 . 
 7.901 
 
 HC1. 
 0.446 
 
 H 2 S0 4 . 
 
 8.650 
 
 3.198 
 
 2.431 
 
 0.767 
 
 b*... 
 
 Do. 
 
 Do. 
 
 0.287 
 
 Nil. 
 
 0.592 
 
 1.3842 
 
 2.471 
 
 0.946 
 
 1.525 
 
 c*... 
 
 Do 
 
 Acid. 
 
 0.065 
 
 Nil. 
 
 0.208 
 
 Nil. 
 
 1.086 
 
 0.731 
 
 0.355 
 
 d*... 
 
 Do 
 
 Strongly 
 
 0.506 
 
 6.078 
 
 0.506 
 
 8.921 
 
 2.017 
 
 0.896 
 
 1.111 
 
 
 
 acid. 
 
 
 
 
 
 
 
 
 * 
 
 Do 
 
 Acid. 
 
 0.079 
 
 Nil 
 
 0.361 
 
 Nil. 
 
 0.968 
 
 0.834 
 
 0.134 
 
 /*... 
 
 Propylite and rhyo- 
 
 Acid. 
 
 0.216 
 
 Nil. 
 
 0.465 
 
 0.380 
 
 0.758 
 
 0.210 
 
 0.548 
 
 
 lite. 
 
 
 
 
 
 
 
 
 
 0*... 
 
 Propylite, pyritous. 
 Mica-schist. 
 
 Acid. 
 Neutral. 
 
 0.409 
 Nil. 
 
 1.063 
 
 Nil. 
 
 0.605 
 Nil. 
 
 1.582 
 Nil. 
 
 1.903 
 0.095 
 
 1.127 
 
 0.027 
 
 0.776 
 0.068 
 
 j 
 
 Mica-schist. 
 
 Neutral. 
 
 Nil. 
 
 Nil. 
 
 Nil. 
 
 Nil. 
 
 0.872 
 
 0.305 
 
 0.567 
 
 i 
 
 Slate and sandstone. 
 
 Highly 
 
 Nil. 
 
 Nil. 
 
 Nil. 
 
 Nil. 
 
 0.569 
 
 0.481 
 
 0.088 
 
 
 
 acid. 
 
 
 
 
 
 
 
 
 A; 
 
 Mica-schist. 
 
 Do. 
 
 0.087 
 
 Nil. 
 
 0.105 
 
 Nil. 
 
 1.007 
 
 0.783 
 
 0.224 
 
 1 
 
 Mica-schist. 
 
 Strongly 
 acid. 
 
 0.658 
 
 Nil. 
 
 0.816 
 
 Nil. 
 
 1.569 
 
 1.406 
 
 0.163 
 
 m.... 
 
 Mica-schist. 
 
 Slightly 
 
 0.064 
 
 Nil. 
 
 Nil. 
 
 Nil. 
 
 0.987 
 
 0.639 
 
 0.348 
 
 
 
 acid. 
 
 
 
 
 
 
 
 
 n 
 
 Mica-schist. 
 
 Neutral. 
 
 Nil. 
 
 Nil. 
 
 Nil. 
 
 Nil. 
 
 0.640 
 
 0.379 
 
 0.261 
 
 
 
 Mica-schist. 
 
 Acid. 
 
 Nil. 
 
 Nil. 
 
 0.406 
 
 Nil. 
 
 1.206 
 
 0.217 
 
 0.989 
 
 P 
 
 Slate and sandstone. 
 
 Neutral. 
 
 Nil. 
 
 Nil. 
 
 Nil. 
 
 Nil. 
 
 0.489 
 
 0.426 
 
 0.063 
 
 * 
 
 Do 
 
 Neutral. 
 
 Nil. 
 
 Nil. 
 
 Nil. 
 
 Nil. 
 
 0.602 
 
 0.578 
 
 0.024 
 
 <i. From the Whau mine, Thames, N. Z. Contained a large quantity of iron in solution. 
 Color, wine-red. Sp. gr., 1.021. 
 
 *. From Maria reef, Karangahake, Thames, N. Z. Deposited a large quantity of ferric hy- 
 droxide on standing. 
 
 c. From Woodstock reef, Thames, N. Z. Behaved on standing like sample 6. 
 
 d. From the Alburnia mine, Thames, N. Z. In appearance like sample a. Sp. gr., 1.019. 
 
 . From the Grace Darling mine, Thames, N. Z. ' Nearly clear ; slight deposit of ferric hy- 
 droxide on standing. 
 
 /. From the Martha mine, Waihi, Thames, N. Z. Appearance and behavior on standing like 
 sample e. 
 
 g. From the Crown mine, Karangahake, Thames, N. Z. Like samples e and/. 
 
 h. From the Tipperary mine, Macetown, Otago. Clear. 
 
 i. From the Premier mine, Macetown, Otago. Clear. 
 
 j. From the Long Tunnel, Walhalla, Victoria. Clear. 
 
 k. From the Bonanza mine, Nenthorn, Otago. Clear. 
 
 I. From a quartz reef near Roxburgh, Otago. Reddish ; deposited a good quantity of .ferric 
 hydroxide on standing. 
 
 m. From the Bella reef, Waipori, Otago. Clear. 
 
 n. From the Gabriel's Gully reef, Lawrence, Otago, Clear. 
 
 o. From the Game Hen reef, Hindon, Otago. Clear. 
 
 p. From the reef on Sovereign hill, Ballarat, Victoria. Clear. 
 
 q. From the reef on Big hill, Bendigo, Victoria. Clear. 
 
THE GEKES1S OF CERTAIN AURIFEROUS LODES. 177 
 
 The results shown in Table II. point to the following con- 
 clusions : 
 
 1. In districts like the Thames, N. Z., where the country- 
 rock is highly charged with sulphides, the vadose water may 
 often contain free hydrochloric acid sufficient (when the higher 
 oxides of manganese are present) to re-dissolve gold. Though 
 the Thames samples were incapable of holding ordinary salts 
 of gold in solution, they acted as solvents of gold when they 
 were thoroughly oxidized and manganese oxides were present. 
 
 2. The great majority of the mine-waters analyzed contained 
 no free acid which could liberate chlorine by acting on the 
 oxides of manganese that are abundant near quartz reefs. 
 
 3. The higher salts of iron are not present in any samples of 
 water analyzed by me, in sufficient quantity to dissolve gold at 
 ordinary temperatures. (Stronger solutions of these salts failed 
 to dissolve gold.) It may be added, that in every case in which 
 much iron was present, free acids were also found ; so that in 
 any solution of gold that might be effected, the more powerful 
 solvent, chlorine, might also be acting. 
 
 Notwithstanding these conclusions, I must point out that the 
 re-solution of gold has probably gone on, and is still going on, 
 in the vadose region, even where the vadose waters contain 
 neither free hydrochloric acid nor notable quantities of ferric 
 salts. The analyses of samples from the vadose regions of 
 Walhalla and Ballarat (see Tables III. and IV., and Figs. 1 
 and 2 [Tables XX. and XXL and Diagrams 8 and 9 of original 
 paper] ), the vadose waters of which contained no free acid and 
 were very poor in dissolved minerals, show that such re-solu- 
 tion has probably been considerable, though we find no agen- 
 cies now existing which would account for it. 
 
 Does Gold Exist in Mine- Waters of Either or Both Circulations ? 
 Prof. A. Liversidge 19 has pointed out that the search for gold 
 in meteoric and mine-waters has not proved its presence in so- 
 lution. It has been detected, but it may have been in mechani- 
 cal suspension. So far as I know, Messrs. Norman T.aylor and 
 Cosmo Newbery, of the Victorian Geological Survey, are the 
 only persons who have experimentally investigated this subject 
 
 19 On the Origin of Gold Nuggets, Proceedings of the Royal Society of New South 
 .Wales, vol. xxvii., p. 303 (1893). 
 
 12 
 
178 THE GENESIS OF CERTAIN AURIFEROUS LODES. 
 
 in these colonies. Mr. Newbery, who made the most experi- 
 ments, said before the Victorian Royal Commission on Gold- 
 Mining 20 that whenever he got gold, he got also angular frag- 
 ments of quartz, which could find its way wherever gold could 
 find its way, and both might have been conveyed mechanically. 
 
 The evidence for the existence of gold in mine-waters rests, 
 so far as I am aware, on the discovery of gold : (1) in boiler- 
 scale from boilers fed with mine-water ; and (2) in wood taken 
 from old mine-workings, where it has been covered for some 
 time with mine-water the. latter being assumed to have car- 
 ried dissolved gold into the timber, to be precipitated by the 
 organic matter of the wood. But the finding of gold under 
 such circumstances does not prove that it was in solution in 
 mine-waters at deep levels. In the first case, the gold may 
 have been carried into the boiler in suspension, along with the 
 silt which all mine-waters contain. In the second case, even 
 though gold may have been dissolved in the water surrounding 
 the old timbers, it may have been brought into such solution 
 by the action of air in the mine-workings, oxidizing sulphides 
 of the rock to sulphates and setting free sulphuric acid, which, 
 in turn, acting on the chlorides always present in mine-waters, 
 would liberate hydrochloric acid. This acid, acting on oxides 
 of manganese, would free chlorine, which would dissolve gold. 
 This statement applies particularly to all mines the waters of 
 which contain considerable iron. Every sample of chalybeate 
 mine-water analyzed by me acted as a precipitant of gold when 
 taken fresh from the workings, but as a solvent of gold at ordi- 
 nary temperatures, in the presence of the oxides of manganese, 
 when it had been exposed to the air for a week or two. 
 
 Mr. Newbery, however, distinctly said, in his testimony 
 already cited, that he found angular quartz which had been 
 soaked up into the timber examined, and that the gold might 
 have been mechanically introduced in the same way. 
 
 With regard to the suspension of gold in mine-waters, the 
 following evidence, obtained by me last year, may be of interest. 
 
 In the Long Tunnel G. M. Co.'s mine at Walhalla, Gipps- 
 land, Victoria, one of the most productive mines in Australia, 2l 
 
 20 Report of the Commission, p, 68 (1893). 
 
 21 Ramsay Thompson, the general manager, to whom I am indebted for much 
 kind assistance, informed me that up to December, 1894, this mine had produced 
 over 22 tons of gold, and had paid 1,200,000 in dividends. 
 
THE GENESIS OF CERTAIN AURIFEROUS LODES. 179 
 
 the water pumped from various depths, down to about 2,300 
 ft. below the surface, is run into two large settling-tanks, be- 
 fore using. At the time of my visit one of these tanks con- 
 tained a large quantity of fine silt, which had been suspended 
 in the mine-water. I analyzed three samples of about 2 Ib. 
 each, first panning off the lighter part, and then assaying the 
 residue. The first sample gave 0.0063 grain of gold; the sec- 
 ond, no trace ; and the third, 0.0175 grain. 
 
 These results show that assays of boiler-scale do not neces- 
 sarily prove that gold was dissolved in the water depositing it ; 
 and, also, that in all analyses even of samples from the vadose 
 circulation, to test the presence of dissolved gold, care must be 
 taken to free the water beforehand from every trace of sus- 
 pended matter. 
 
 I have tested many old mine-timbers for gold. In every case 
 the outside wood was chipped off to the depth of about 0.5 in.; 
 and, when cracks appeared in the timber, about 0.5 in. on each 
 side of the crack was also chipped off. These parts were 
 burned, and analyzed separately from the inner portions. The 
 results of several such analyses are shown in the table on p. 180. 
 
 Search for Gold in Mine- Waters. It was soon found useless 
 to examine mine-waters which contained much iron, and in 
 which the ferrous salts had not been oxidized to ferric salts by 
 exposure to the atmosphere. The analyses were consequently 
 restricted, for the vadose region, to waters containing a very 
 small percentage of iron-salts, and chalybeate waters which 
 had been thoroughly oxidized (the latter being apparently ex- 
 ceptional, even in that region), and, for the deep circulation, to 
 waters containing so little iron that they do not act as precipi- 
 tants of gold. 
 
 This chapter treats of mine-waters under the conditions of 
 temperature and pressure now -encountered. What might be 
 effected by these waters under other conditions does not concern 
 us at this stage. 
 
 If gold be present in mine-waters at all, it is likely to be in 
 very minute proportions. Hence large quantities of water 
 must be operated upon. The method of evaporation for the 
 assay of the residue was too tedious, especially in view of the 
 limited time at my disposal in each locality. I therefore 
 availed myself of the well-known action of sulphides and or- 
 ganic matter in precipitating gold from solution. 
 
180 THE GENESIS OF CERTAIN AURIFEROUS LODES. 
 
 Analyses of Old Mine-Timbers. 
 
 Sample. 
 
 Description and Locality. 
 
 Part Analyzed. 
 
 Gold Found. 
 
 I. 
 
 Prop from the Tipperary Gold Mining 
 Co., Macetown. Otago, much decom- 
 posed. The part analyzed had been 
 under water for many years 
 
 Outside of the 
 prop. 
 
 None. 
 
 II. 
 
 Do. 
 
 Inside of prop. 
 
 None. 
 
 III. 
 
 Prop from an old tunnel in an alluvial 
 terrace, near Skipper's Point, Otago. 
 The part analyzed had been under 
 water for probably 20 years. 
 
 Outside of prop. 
 
 None. 
 
 IV. 
 
 Do. 
 
 Inside of prop. 
 
 None. 
 
 V. 
 
 A prop from the Premier mine, Mace- 
 town, Otago. Water had been run- 
 ning over it for 2 years at least. 
 
 Outside of prop. 
 
 0.0038 grain. 
 
 VI. 
 
 Eotten wood from the lower part of a 
 rejected prop from the Long Tunnel 
 Gold Mining Co., Walhalla. From a 
 part of the mine where a richly auri- 
 ferous reef had been worked. 
 
 Outside of prop. 
 
 0009 7 grain. 
 
 VII. 
 
 Do. 
 
 Inside of prop. 
 
 None. 
 
 VIII. 
 
 Decayed portion of lath brought up from 
 the deep workings of the Northern 
 Star Gold Mining Co., Ballarat. Had 
 evidently been saturated with water 
 for many years. 
 
 No portion was 
 sound ; all 
 was burned 
 and analyzed. 
 
 None. 
 
 IX. 
 
 Portion of sleeper used in a tramway, 
 Northern Star Gold Mining Co., much 
 decayed. A large quantity of water 
 had been running over it for at least 
 
 Do. 
 
 0.0129 grain. 
 
 
 a year. 
 
 
 
 A filter was constructed, consisting of a tinned-iron cylinder, 
 about 3 in. in diameter and 6 in. long, terminating below in a 
 funnel, inside of which was placed a filter of glass-wool, and 
 above this the reduciug-agents (animal charcoal, artificial iron 
 and lead sulphides, roughly powdered). The upper part was 
 connected by a rubber tube with the tap supplying the water 
 to be tested. 
 
 The following preliminary test proved the efficiency of this 
 filter : A solution in 400 gal. of water (from the Dunedin water- 
 mains) of 28 Ib. of common salt, 8 oz. of magnesium sulphate, 
 8 oz. of ferric chloride, and 0.1 grain of gold in the form of auric 
 chloride, was allowed to trickle slowly through the filter, the 
 operation taking about 48 hr. The mixture of sulphides and 
 
THE GENESIS OF CERTAIN AURIFEROUS LODES. 181 
 
 charcoal was then removed, roasted, and assayed, when 0.0926 
 grain of gold was recovered, showing that practically all the 
 gold had been precipitated. 
 
 In examining mine-waters, the water was first collected in 
 an iron tank, and powdered alum was added to it, completely 
 precipitating all suspended matter. After standing some hours, 
 it was tapped from 2 or 3 in. above the bottom of the tank, and 
 filtered as described. 
 
 Four samples were thus treated; but in no case was gold 
 found. 
 
 The first sample (about 500 gal.) was water from the high- 
 level tunnel of the Tipperary G. M. Co., which had percolated 
 down from the surface through the lode-fissure for from 200 
 to 500 ft., and flowed in a large stream from the tunnel-mouth. 
 This practically represented the vadose circulation only. 
 
 The second sample (about 500 gal.) was from the pump-dis- 
 charge of the New Chum Railway Co., Bendigo, Victoria, and 
 represented the whole drainage of the mine from the surface to 
 a depth of 2,850 feet. 
 
 The third sample (about 700 gal.) was from the Long Tunnel 
 G. M. Co.'s mine, Walhalla, Victoria, near a very rich lode, and 
 represented the whole drainage between the adit (700 ft. below 
 the summit of the hill) and a level about 2,300 ft. below the 
 surface, or over 1,500 ft. below the adit. 
 
 The fourth sample (about 500 gal.), from a deep tunnel of 
 the Premier mine, Advance Peak, Otago, driven on a lode 
 which had proved richly auriferous in places, represented the 
 whole drainage from the surface to probably 2,000 ft. below it. 
 
 The negative results of these tests are the more surprising 
 to me, since other examinations, hereinafter described, afforded 
 strong evidence that solution and re-precipitation of gold have 
 taken place in the vadose region. 
 
 It is, of course, possible that gold may have existed in these 
 samples in some form from which it was not precipitated by 
 the reagents used. This is suggested, indeed, by my experi- 
 ence (see Chapter VII.) in attempting to precipitate gold from 
 sea-water. The question can only be decided by the evapora- 
 tion of samples (first freed from suspended matter) in larger 
 amount and number than mine, and the assay of the residues. 
 I venture to recommend such an inquiry to those who live in 
 the vicinity of rich mines and have time for the work. 
 
182 THE GENESIS OF CERTAIN AURIFEROUS LODES. 
 
 Does the Gold of the Vadose Region Contain Generally Less 
 Silver than That of the Deep Circulation in the Same District ? 
 
 Several investigations have seemed to prove that, on the aver- 
 age, the gold of the alluvial deposits in Australia and elsewhere 
 is appreciably finer in quality than the vein-gold. The matter 
 has been discussed chiefly in connection with the origin of 
 nuggets; 22 . but, so far as I know, no comparison as to fineness 
 has been made between the vadose and the deep vein-gold. 
 
 The observed difference between placer- and vein-gold may 
 be held to show, either that the oxidized mineral-bearing waters 
 running in the ancient drift-deposits dissolved out part of the 
 silver with which the gold was alloyed, or else that these 
 waters dissolved both gold and silver, the gold being again 
 precipitated, alloyed with less silver than before. Similar rea- 
 soning might be applied to an observed difference between the 
 vadose and the deep zone, in the quality of vein-gold. I have 
 therefore made comparative assays of this character in a num- 
 ber of cases. 
 
 The fineness of the gold may vary considerably even in the 
 same level, and within a few feet. This is true even in such 
 districts as Bendigo, Ballarat, and Otago, where the percent- 
 age of silver is comparatively low, while in districts like the 
 Thames, N". Z., the variation observed is sometimes extraordi- 
 nary. On the whole, however, the average quality of the gold 
 won in districts of the former class varies little. 
 
 Five localities were chosen (chiefly by reason of facilities for 
 obtaining specimens from near the surface), namely, (1) the 
 Nenthorn gold-field, in mica-schist, in eastern Otago; (2) the 
 Tipperary and Premier mines, in mica-schist, Macetown, cen- 
 tral Otago; (3) the Dart river, in northern Gippsland, repre- 
 senting the Upper Silurian of Victoria; (4) the Bendigo field, 23 
 representing the Lower Silurian ; and (5) the Thames district 
 of the North Island, in altered Lower Tertiary andesite. 
 
 In a few instances the analyses were made of gold picked 
 out of the reef; but the majority were assays of vein-stone. 
 
 22 Professor Liversidge, in the paper already cited, gives a convenient summary 
 of the literature of this subject. 
 
 23 Surface-samples are hard to get in Bendigo. Nearly all the companies are 
 mining in the deep region, and have long ago exhausted the pay-quartz above. 
 I took many samples from outcrops of reefs, but found in the majority little or no 
 gold. The results given below are those in which a prill of appreciable size was 
 obtained by assaying 1,000 grains of vein-stone. 
 
THE GENESIS OF CERTAIN AURIFEROUS LODES. 183 
 
 The percentage of silver was in each case obtained by differ- 
 ence, and represents the loss per cent of the prill after quarta- 
 tion. The results were as shown in the table on p. 184. 
 
 These analyses of 76 samples go, on the whole, to prove that 
 the average fineness of the gold in the vadose region is appre 
 ciably greater than in the deep circulation in the same district, 
 and also that the vadose gold is considerably more regular in 
 quality. 
 
 It seems to be indicated that considerable solvent action 
 must have been exercised by water percolating through the 
 rocks of the vadose region, as the denudation of the surface 
 has gradually lowered the water-level, converting the deep cir- 
 culation of former times into the vadose of to-day. 
 
 Analyses of Vadose Country-Rock, etc., at Different Distances from 
 
 Auriferous Lodes. 
 
 At the beginning of this chapter I have pointed out the im- 
 portance of separate rock-assays in the vadose region. It was 
 relatively difficult to obtain good samples (other than surface- 
 samples) of this class, because most of the mines are now deep, 
 and the former long cross-cuts run on upper levels into the 
 country-rock are abandoned and closed. The samples there- 
 fore comprise chiefly oxidized rock from pretty near the lodes, 
 and 10 to 100 ft. below the surface, and surface-samples taken 
 at all distances from the lodes. Particular interest attaches to 
 samples of (1) oxide of iron and manganese deposited along 
 bedding-planes or fractures ; (2) solid rock as little altered as 
 possible by the action of percolating water; and (3) secondary 24 
 sulphides, abundant in the vadose region of many mines. 
 
 The remarks covering the methods of concentration and as- 
 say pursued with samples from the deep levels, apply here also. 
 
 24 In calling these vadose sulphides " secondary," I mean that they have prob- 
 ably been formed through the oxidization of the sulphides of the deep circulation 
 by surface-water, followed by a reduction of the sulphates and re-precipitation of 
 the sulphides by orgmic matter. I do not mean to say positively that the sul- 
 phides of the deep zone are not, as many observers believe, also secondary in this 
 sense, that is, due to the reducing action of carbonaceous matter upon soluble sul- 
 phates. This is Sandberger's view (Untersuchung, etc., vol. i., p. 21). Yet so 
 far as my experience of the deep sulphides goes, it certainly favors the theory of 
 their formation by the action on the silicates of metals of hydrogen sulphide, dis- 
 solved in ascending water. 
 
184 THE GENESIS OF CERTAIN AURIFEROUS LODES. 
 
 Relative Fineness of Vadose and Deep Vein- Gold. 
 
 A. Surface-Samples from Nenthorn Gold- 
 Field, Otago, N. Z. 
 
 B. From Deeper Levels of Nenthorn Dis- 
 trict (the Bulk of the Gold was Held 
 by Pyrite). 
 
 No. 
 
 Percentage 
 of Gold. 
 
 Percentage 
 of Silver. 
 
 No. 
 
 Percentage 
 of Gold. 
 
 Percentage 
 of Silver. 
 
 1 
 
 91.85 
 89.27 
 90.43 
 89.19 
 92.01 
 89.38 
 91.46 
 90.79 
 90.07 
 92.00 
 
 7.15 
 10.73 
 9.67 
 10.81 
 7.99 
 10.62 
 8.54 
 9.21 
 8.53 
 8.00 
 
 1 
 
 89.86 
 91.43 
 87.17 
 90.45 
 89.07 
 92 01 
 
 10.14 
 8.57 
 12.83 
 9.55 
 10.93 
 7.99 
 9.83 
 11.25 
 8.97 
 9.70 
 
 2 
 
 2 
 
 3 
 
 3 
 
 4 
 
 4 
 
 5 
 
 5 
 
 c 
 
 6 
 
 
 
 90.17 
 88.75 
 91.03 
 90.30 
 
 g 
 
 8 
 
 9 
 
 9 
 
 10 
 
 10 
 
 
 
 Average fineness of 10 samples, 90.645 per 
 cent. Range of fineness, 89.19 to 92.01 = 
 2.827 per cent. 
 
 Average fineness of 10 samples, 90.024 per 
 cent. Range of fineness, 87.17 to 92.01 = 
 4. 84 per cent. 
 
 C, Surface-Samples from Tipperary Pre- 
 mier, and Sunrise Gold Mining Companies. 
 All near Macetown, Central Otago, N. Z. 
 
 D From Deep Levels (1,000 to 1,500 Ft. 
 
 Below Surface) in Tipperary and Premier 
 
 Mines, Macetown. 
 
 No. 
 
 Percentage 
 of Gold. 
 
 Percentage 
 of Silver. 
 
 No. 
 
 Percentage 
 of Gold. 
 
 Percentage 
 of Silver. 
 
 1 
 
 96.12 
 U3.37 
 94.19 
 92.87 
 95.00 
 94.58 
 93.23 
 95.84 
 95.93 
 94.89 
 
 3.88 
 6.63 
 5.81 
 7.53 
 5.00 
 5.42 
 6.77 
 4.16 
 4.07 
 5.11 
 
 1 
 2 
 
 95.39 
 94.48 
 91.87 
 96.29 
 93.06 
 94.31 
 93.80 
 94.73 
 93.90 
 94.10 
 
 4.61 
 5.52 
 8.13 
 3.71 
 6.94 
 5.69 
 6.20 
 4.27 
 6.10 
 5.90 
 
 2 
 
 3 
 
 3 
 
 4 
 
 4 
 
 5 
 
 5 
 
 6 
 
 g 
 
 7 
 
 
 8 
 
 
 9 
 
 10 ... 
 
 10 
 
 
 
 Average fineness of 10 samples, 94.602 per 
 cent. Range of fineness, 92.87 to 96.12 = 
 3. 25 per cent. 
 
 j 
 
 .Average fineness of 10 samples, 94.293 per 
 cent. Range of fineness, 91.87 to 96.29 = 
 4.42 per cent. 
 NOTE. A sample taken from a bar of 194 oz. 
 from deep levels of Premier Gold Mining 
 Co. contained 94.45 per cent. 
 
 E. Surface-Specimens from Richly Aurif- 
 erous Lode in the Vicinity of the Dart 
 River, North Gippsland, Victoria. 
 
 F. Unoxidized Specimens from the Same 
 Reef, Dart River, North Gippsland, 
 Victoria. 
 
 No. 
 
 Percentage 
 of Gold. 
 
 Percentage ; 
 of Silver. 
 
 No. 
 
 Percentage 
 of Gold. 
 
 Percentage 
 of Silver. 
 
 1 
 
 91.87 
 94.96 
 93.08 
 92.00 
 92.63 
 94.73 
 93.45 
 95.01 
 94.91 
 92.84 
 
 8.13 
 5.04 
 6.92 
 8.00 
 7.37 
 5.27 
 6.55 
 4.99 
 5.09 
 7.18 
 
 1 
 
 91.50 
 90.43 
 87.69 
 96.28 
 91.17 
 84.64 
 88.93 
 95.03 
 90.37 
 90.80 
 
 8.50 
 9.57 
 12.31 
 3.72 
 8.83 
 15.36 
 11.07 
 4.97 
 9.63 . 
 9.20 
 
 2 
 
 2 
 
 3 
 
 3 
 
 4 
 
 4 
 
 5 
 
 5 
 
 g 
 
 6 & 
 
 7 
 
 7 
 
 8 
 
 8 
 
 9 
 
 9 
 
 10 
 
 10 
 
 
 Average fineness of 10 samples, 93.548 per 
 cent. Range of fineness, 91.87 to 95.01 = 
 4. 14 per cent. 
 
 Average fineness of 10 samples, 90.984 per 
 cent. Range of fineness, 84.64 to 96.28 = 
 12.36 percent. 
 a Sample assayed consisted of arsenopyrite 
 and pyrite. 
 6 Sample assayed composed chiefly of galena. 
 
THE GENESIS OF CERTAIN AURIFEROUS LODES. 
 
 Relative Fineness of Vadose and Deep Vein-Gold. Continued. 
 
 G. Surface-Samples from Bendigo Gold- 
 Field, Victoria. 
 
 H. 
 
 Samples from Deep Levels (1,200 to 
 3,000 Ft.) of Bendigo Gold-Field. 
 
 No. 
 
 Percentage 
 of Gold. 
 
 Percentage 
 of Silver. 
 
 Te. Percentage 
 of Gold 
 
 Percentage 
 of Silver. 
 
 ] 
 
 94.76 
 95.03 
 94.05 
 94.27 
 94.10 
 95.00 
 
 5.24 
 4.97 
 5.95 
 5.73 
 5.90 
 5.00 
 
 1 
 
 93 08 
 
 6.92 
 4.96 
 6.00 
 8.73 
 5.70 
 5.81 
 6.04 
 7.05 
 7.63 
 5.30 
 
 9 
 
 2... 
 3 
 
 9o.04 
 
 3 
 
 94 00 
 
 4 
 
 4... 
 
 91.27 
 
 5 
 
 91 30 
 
 6 
 
 6... 
 
 94.19 
 
 
 7 
 
 93 % 
 
 g 
 
 Q2 95 
 
 9... 
 
 .. . 92 37 
 
 10... 
 
 91.70 
 
 
 
 
 
 Average fineness of 6 samples, 94.535 per cent. ; Average fineness of 10 samples, 93.586 per 
 
 Range of fineness, 94.05 to 95.03 
 cent. 
 
 0.98 per 
 
 cent. Range of fineness, 92.37 to 95.04 = 
 2.64 per cent. 
 
 I. Samples from Vadose Region of Various 
 Parts of Thames District, N. Island, N. Z. 
 
 K. Samples from Deep Circulation of the 
 Thames District. 
 
 No. 
 
 Percentage 
 of Gold. 
 
 Percentage 
 of Silver. 
 
 No. 
 
 Percentage 
 of Gold. 
 
 Percentage 
 of Silver. 
 
 1 
 
 63 72 
 
 36 28 
 
 \ 
 
 63 76 
 
 56 4 
 
 2 
 
 79 34 
 
 20 66 
 
 2 
 
 71 14 
 
 28 86 
 
 3 
 
 52.90 
 
 47.10 
 
 I 3 
 
 59 93 
 
 40 07 
 
 4 
 
 57.39 
 
 42 61 
 
 4 
 
 53 01 
 
 46 99 
 
 5 .. . 
 
 67 01 
 
 39 99 
 
 5 
 
 64 25 
 
 35 75 
 
 6 
 
 59 98 
 
 40 02 
 
 6 
 
 43 17 
 
 56 83 
 
 7 
 
 65.55 
 
 34.45 
 
 7... 
 
 66 98 
 
 33 02 
 
 8 
 
 73 07 
 
 36 93 
 
 1 g 
 
 51 30 
 
 48 70 
 
 9 . . 
 
 60 08 
 
 39 9'> 
 
 1 9 
 
 69 04 
 
 30 % 
 
 10 
 
 51 19 
 
 48 81 
 
 ! jo 
 
 48 75 
 
 51 25 
 
 
 
 
 
 
 
 Average fineness of 10 samples, 60.023 pen! Average fineness of 10 samples, 59.133 per 
 cent. Range of fineness, 51.19 to 79.34= \\ cent. Range of fineness, 43.17 to 71.14 = 
 28.15 per cent. 27.97 per cent. 
 
 [In the majority of cases the samples taken weighed 7 or 8 lb.; the samples 
 tested, 4.48 lb. ; and the assays were made from concentrates of the latter, but some- 
 times 4.48 lb. was the actual sample for assay ; in which case the total quantity 
 was pulverized to pass a No. 60 sieve, and divided into 12 parts of about 2,500 
 grains each, and to each part 3,000 grains of purified litharge, 2,000 grains of car- 
 bonate of soda, and 1,000 to 1,500 grains of borax were added for the assay, with 
 sufficient argol to reduce about 400 grains of lead.] 
 
 But concentration of an oxidized rock is much more diffi- 
 cult, because oxidation destroys the heavy sulphides, and also 
 liberates very finely divided gold, which there is danger of 
 losing. Hence my results with vadose country-rock are not 
 quantitatively correct. To minimize the probable error, the 
 samples were not concentrated nearly as far as those from deep 
 levels had been. 
 
186 
 
 THE GENESIS OF CERTAIN AURIFEROUS LODES. 
 
 TABLE III. Analyses of Country-Hock from the Vadose Region 
 of Walhalla Gold-Field, G-ippsland, Victoria. 
 
 
 .2 - o 
 
 i 
 
 
 
 
 ! 
 
 
 ^ *t* ^V-** 
 
 
 
 
 s 
 
 2 
 
 & ;- 
 
 
 
 Q) VH T% 
 
 'g 
 
 
 f. 
 
 3 
 
 t^ 
 
 2 
 
 "3 3 a; ^ 
 
 3 
 
 
 3 
 
 
 
 J t - 
 
 1 
 
 1*8* 
 
 X 
 
 H 
 
 Weight of Concentrates Obtained. 
 
 c p. 
 
 1 
 
 o~5 
 
 
 flP 
 
 1 
 
 
 I 1 
 
 I 
 
 U 
 
 
 Feet. 
 
 Pounds. 
 
 Grains. 
 
 
 Grains. 
 
 Grains. 
 
 o 
 
 3 West. 
 
 4.48 
 
 1,904 Chiefly oxide of iron, showing a 
 
 Trace. 
 
 Nil. 
 
 Nil. 
 
 
 
 
 little mica. 
 
 
 
 
 6 
 
 10 West. 
 
 4.48 
 
 1 650 . . 
 
 Trace. 
 
 Nil. 
 
 Nil. 
 
 c 
 
 16 West. 
 
 2.24 
 
 1 824 
 
 Nil. 
 
 0.027 
 
 27. 
 
 d*... 
 
 100 West. 
 
 2.24 
 
 All assayed . . ... 
 
 Nil. 
 
 Nil. 
 
 Nil. 
 
 
 240 West. 
 
 2 24 
 
 1 463 
 
 Nil. 
 
 0.0183 
 
 18.3 
 
 * 
 
 360 West. 
 
 1 000 g 
 
 All assayed 
 
 Nil 
 
 Nil. 
 
 Nil. 
 
 9 
 
 540 West. 
 
 4.48 
 
 1,280 Chiefly quartz, ferric oxide, with 
 
 Nil. 
 
 0.0027 
 
 1.35 
 
 
 
 
 a little mica. 
 
 
 
 
 h. ... 
 
 1,200 West. 
 
 2 24 
 
 1 640 
 
 Nil. 
 
 0.0076 
 
 7 6 
 
 i.'. .. 
 
 6 East.' 
 
 2.24 
 
 1,356 Mostly ferric oxide, with a little 
 
 Nil. 
 
 0.029 
 
 29. 
 
 
 
 
 magnetite. 
 
 
 
 
 i* . 
 
 75 East. 
 
 2.24 
 
 All assaved 
 
 Trace. 
 
 0.0017 
 
 1.7 
 
 i.:." 
 
 360 East. 
 
 2.24 
 
 1 748 Chiefly ferric oxide 
 
 Nil. 
 
 Nil. 
 
 Nil. 
 
 
 
 
 
 
 
 
 a. Very hard, coarse-grained, solid sandstone, much stained with oxide of iron. 
 
 b. Fine-grained, hard, solid slate, very little altered in any respect. 
 
 c. Oxide of iron from a cavity between sandstone and slate. The country much broken 
 
 near where sample was taken. 
 
 d. Slate, fine-grained, very little altered, very soljd and hard. 
 
 . Broken sandstone, slate, and oxide of iron, from a small fault in the rock, exposed to the 
 
 surface. 
 
 /. White quartz, slightly iron-stained, from small reef-formation about 4 in. wide. 
 g. Hard, fairly coarse-grained sandstone, with seams of ferric oxide along the bedding-planes. 
 h. Slate, sandstone, and ferric oxide from broken country, filling a slight fault. 
 i. Ferric oxide, coating slate and sandstone. 
 j. Hard, solid, fine grained slate, little altered. 
 k. Hard sandstone, much stained with ferric oxide. 
 In the case of samples marked * the whole of the sample left after concentration was assayed 
 
 after the concentrates had been examined. 
 
 Walhalla. A good cross-section of the gold-bearing rocks of 
 Walhalla is extended along both sides of the Walhalla creek, 
 where the cliffs rise steeply from 300 to 600 ft. Analyses of 
 specimens are given in Table III. 
 
 Ballarat. A deep cutting, about 0.25 mile long, running 
 east, across the strike of the rocks, from the summit of Sov- 
 ereign hill, in this district, presented a good cross-section of 
 the country-rock near the surface. Table IV. gives the result 
 of analyses. 
 
 Otago. Examinations of country-rock from the deep region 
 in Otago were confined to one district, Macetown ; but quartz 
 reefs have been worked at various depths in different parts of 
 the province; and vadose samples were taken from three other 
 Otago districts besides Macetown, namely, Waipori, ISTenthorn 
 and Saddle Hill. In every case the country-rock is either phyl- 
 lite or mica-schist. Table Y. gives the analyses of 13 samples. 
 
THE GENESIS OF CERTAIN AURIFEROUS LODES. 
 
 187 
 
 TABLE IV. Analyses of Country- Rock from the Vadose Region of 
 the Ballarat Gold-Field, Victoria. 
 
 
 &* 
 
 c 
 
 
 
 
 *-t i 
 
 2 > 
 
 
 5 
 
 c 
 
 
 o 
 
 jg 
 
 
 .2 
 & 
 
 ^ V 
 
 ss 
 
 6 
 
 1 
 
 Weight of Concentrates Obtained. 
 
 | 
 
 -2J3 
 G O, 
 
 o 
 O 
 
 <tH 
 
 O 
 
 T3 C 
 
 ?P 
 
 I 
 
 o>2 
 2<2 
 
 2 
 
 
 g3 
 COO 
 
 2 
 
 
 
 <=^ 
 
 'O 
 
 
 s -= 
 
 ' 
 
 
 
 
 ?-l 
 
 <u o 
 H 
 
 
 Feet. 
 
 Pounds. 
 
 Grains. 
 
 
 Grains. 
 
 Grains. 
 
 <i 
 b 
 
 8 East. 
 60 East 
 
 1.12 
 2 24 
 
 684 Mostly ferric oxide and quartz 
 1 050 
 
 Nil. 
 
 Nil 
 
 0.037 
 017 
 
 74 
 17 
 
 c 
 
 140 East 
 
 4 48 
 
 
 Nil 
 
 0063 
 
 3 15 
 
 d 
 
 186 East 
 
 4.48 
 
 1 4S5 . 
 
 Nil 
 
 0023 
 
 1 15 
 
 
 
 240 East 
 
 4 48 
 
 2 116 
 
 Nil 
 
 0016 
 
 8 
 
 f 
 
 360 East 
 
 2 24 
 
 1,642 
 
 Nil' 
 
 0058 
 
 2 9 
 
 g 
 
 500 East 
 
 1 12 
 
 856 
 
 Nil 
 
 Nil 
 
 Nil 
 
 
 
 
 
 
 
 
 a. Oxide of iron, with a little quartz and loose sand, formed by the disintegration of sand- 
 
 stone. 
 
 b. Oxide of iron, from a joint separating two adjacent strata of sandstone. 
 
 c. Soft sandstone, pure white. 
 
 d. White pipe-clay, with yellow streaks. A product of the decomposition of slate. 
 
 e. Soft, fine-grained pipe-clay, colored from red to purple by oxide of iron. 
 /. Oxide of iron, mixed with soft sandstone and clay from broken country. 
 g. Oxide of iron, forming clay parting between two beds of pipe-clay. 
 
 Otago. Samples from Districts Remote from Auriferous Lodes. 
 Vadose samples were also taken in Otago, far from any au- 
 riferous lodes. Previous assays having shown that the mate- 
 rials most likely to contain gold were the broken rock, iron 
 oxide, etc., filling fault-fissures, the samples were taken of such 
 materials only. If all the mica-schists of the Otago gold-field 
 contained gold, some of it would be carried by percolating 
 water into such crevices, and lodge there with the ferric oxide. 
 The analysis of samples at a long distance from any auriferous 
 reef is specially interesting, since, as will be seen in the last three 
 tables, deposits of ferric oxide in the vadose region, even at a 
 considerable distance from a reef, were nearly always auriferous. 
 
 A good section of the favorable rock (the middle division of 
 the foliated schists already mentioned), in which, however, for 
 several miles, no gold-bearing reef has yet been discovered, is 
 exposed by the " Skipper's " road from Queenstown to Skip- 
 per's creek. This road is cut around almost vertical cliffs for 
 several miles, on the north side of the Skipper's range. Nine 
 samples of broken rock and ferric oxide from joints, cracks, and 
 faulted country in these cuttings were analyzed, with the results 
 shown in Table VI. 
 
 Lake Wakatipu. Fourteen vadose samples of little-altered 
 Upper Devonian and Carboniferous rocks were taken from the 
 western shore of Lake Wakatipu. No gold was found in them. 
 The examination is reported later on, under the head of " Gold 
 in Marine Sediments." 
 
188 
 
 THE GENESIS OF CERTAIN AURIFEROUS LODES. 
 
 TABLE Y. Analyses of Rocks from the Vadose Region of Otago y 
 
 New Zealand. 
 
 ,2 
 
 la 
 
 Distance from Au- 
 riferous Reef. 
 
 II 
 ^ 
 
 P 
 ^ 
 
 Locality. 
 
 Weight Taken. 
 
 Weight of 
 Concentrates. 
 
 Percentage of 
 Sulphur. 
 
 Yield of Gold. 
 
 Yield of Gold per 
 Ton of Country- 
 Rock. 
 
 a 
 ft , 
 
 Feet. 
 4 
 
 20 
 
 Feet. 
 40 
 
 40 
 
 From a tunnel driven 
 along the Bella reef, 
 Waipori, Otago. 
 
 Do.... 
 
 Pounds. 
 
 4.48 
 
 4.48 
 
 Grains. 
 643 Mostly 
 mica and 
 oxideof 
 iron. 
 1,246 
 
 Nil. 
 Nil. 
 
 Grains. 
 0.0016 
 
 0.0107 
 
 Grains. 
 
 0.8 
 
 5.35 
 
 r 
 d 
 
 g 
 
 3 
 
 60 
 
 35 
 
 50 
 30 
 
 60 
 
 Do 
 Near the mouth of the 
 low-level tunnel, Tip- 
 perary G. M. Co.. Mace- 
 town,' Otago. 
 
 4.48 
 4.48 
 
 2 24 
 
 1,675 
 1,217 
 
 1 176 
 
 Nil. 
 Nil. 
 
 Trace 
 
 0.065 
 Nil. 
 
 0179 
 
 32.55 
 
 Nil. 
 
 17 9 
 
 f 
 
 20 
 
 70 
 
 but 25 ft. nearer the reef. 
 
 2 24 
 
 1 030 
 
 Trace 
 
 0086 
 
 8 6 
 
 n 
 
 1GO 
 
 35 
 
 ft. nearer the reef. 
 From near the mouth of 
 
 1 12 
 
 774 ' 
 
 Nil 
 
 0018 
 
 8.6 
 
 h 
 
 90 
 
 85 
 
 the low-level tunnel, 
 Premier G. M. Co., Mace- 
 town, Otago. 
 From the same tunnel 
 
 2 24 
 
 617 
 
 Trace 
 
 Nil. 
 
 Nil. 
 
 i 
 
 65 
 
 95 
 
 but nearer the reef and 
 at a greater depth. 
 
 2 24 
 
 612 
 
 Nil 
 
 0013 
 
 2.6 
 
 3 
 It 
 
 6 
 3 
 
 40 
 40 
 
 but 15 ft. nearer the reef. 
 From the Bonanza reef, 
 Nenthorn, Otago, with- 
 in 6 ft. of a rich auri- 
 ferous reef. 
 
 From the same mine at 
 
 2.24 
 2.24 
 
 1,738 Princi- 
 pally 
 mica and 
 ferric 
 oxide. 
 1 217 
 
 0.027 
 Nil. 
 
 0.0016 
 0.0073 
 
 n.e 
 
 7.3 
 
 I . 
 
 600 
 
 20 
 
 the same depth, but 
 nearer the reef. 
 From a cliffwest of Saddle 
 
 1 V> 
 
 726 
 
 008 
 
 Nil. 
 
 Nil. 
 
 m 
 
 200 
 
 20 
 
 Hill reef, near Duned in. 
 From the same locality 
 
 224 
 
 1 078 
 
 Nil. 
 
 0.0005 
 
 0.5 
 
 
 
 
 but nearer reef. 
 
 
 
 
 
 
 a, b, c. Mica-schist, yellowish color, soft, very much decomposed. 
 
 d. Hard mica-schist, with quartz bands 0.5 in. wide, Specimen much stained with oxide of 
 
 iron. 
 
 e. Ferric oxide from a slight fault in mica-schist, showing a little quartz in veins. 
 /. Quartz and ferric oxide from broken country. 
 
 g. Solid mica-schist, much stained by ferric oxide. 
 
 h. Ferric oxide and broken mica-schist, from a small fault. 
 
 i. Solid mica-schist, much discolored by ferric oxide. 
 j, Jc. Much decomposed, very soft mica-schist, stained brown with ferric oxide. 
 
 I. Ferric oxide filling the space in joint-planes of phyllite, which forms the country-rock of 
 
 this reef. 
 m. Decomposed phyllite, much stained with ferric oxide. 
 
 Ohinemuri District, Thames. The samples collected for me 
 from the vadose region in the Ohinemuri district, in the south- 
 ern part of the Thames gold-field, differ somewhat from the 
 oxidized samples of other gold-fields. All those analyzed are 
 highly-altered andesites ; and, in many cases, even when most 
 oxidized, they contain much pyrite. This sometimes doubtless 
 represents the pyrite found in the propylites of the deep region 
 
THE GENESIS OF CERTAIN AURIFEROUS LODES. 
 
 189 
 
 TABLE VI. Analyses of Samples from Skipper's Road, near 
 Lake Wakatipu, Otago. 
 
 oJ 
 
 "p. 
 
 Distance from Au- 
 riferous Reef. 
 
 || 
 
 Locality. 
 
 Weight Taken. 
 
 Weight of 
 Concentrates. 
 
 Percentage of 
 Sulphur. 
 
 Yield of Gold. 
 
 Ig 
 
 1 
 
 i 
 
 At least 2 or 3 
 miles. 
 
 About 25 
 
 Feet. 
 50 
 
 80 
 
 All these 
 samples were 
 taken from a 
 deep cutting 
 on the Skip- 
 pers' road. 
 
 Pounds. 
 2.24 
 
 2.24 
 
 Grains. 
 1,127 Chiefly 
 ferric oxide 
 and mica. 
 
 1,416 With a little 
 
 Nil. 
 Nil. 
 
 Grains. 
 Nil. 
 
 Nil. 
 
 Grains. 
 Nil. 
 
 Nil. 
 
 i" 
 
 mile from a. 
 At least 1 mile. 
 About 1 000 
 
 so 
 
 
 2.24 
 ) 04 
 
 pyrite. 
 1.723..!.. 
 1 096 With a good 
 
 Nil. 
 1 384 
 
 Nil. 
 Nil 
 
 Nil. 
 
 Nil 
 
 e .... 
 
 yd. from c. 
 From near 
 
 40 
 
 
 2.24 
 
 percentage 
 of sulph'd's. 
 834 Showed no 
 
 Nil. 
 
 Nil. 
 
 Nil. 
 
 f 
 
 sample d. 
 About 3 miles 
 
 20 
 
 
 224 
 
 pyrite. 
 
 1 568 . 
 
 Nil 
 
 Nil 
 
 Nil 
 
 
 
 40 
 
 
 24 
 
 817 
 
 Trace 
 
 Nil 
 
 Nil 
 
 
 sample/. 
 
 10 
 
 
 1 12 
 
 716 
 
 Nil 
 
 Nil 
 
 Nil 
 
 i* 
 
 
 15 
 
 
 
 618 
 
 Nil 
 
 Nil 
 
 Nil 
 
 
 
 
 
 
 
 
 
 
 a. Ferric oxide from joint-planes. 
 
 6. Broken rock; quartz and mica, with much contorted mica-schist, filling a fissure 18 in. 
 wide. 
 
 c. Broken rock ; quartz and mica. 
 
 d. Broken rock, but the sample contained a few large crystals of pyrite, somewhat decom- 
 
 posed to ferric oxide. 
 
 e. Broken rock, but showed no pyrite. 
 
 f. Quartz and broken mica-schist and ferric oxide, from a fault-fissure or lode-formation, 
 
 about 1 ft. wide, in mica-schist. 
 
 g. Quartz and broken mica-schist. 
 
 h. Ferric oxide, filling joint-planes in broken mica-schist. 
 
 i. Quartz-interlaminations, about 2 in. wide, in mica-schist, much stained with ferric oxide. 
 In the case of sample marked * the whole of the sample left after concentration was assayed 
 after the concentrates had been examined. 
 
 in this district ; but, from the mode of its occurrence, I am in- 
 clined to think the greater part of it is due to the oxidation of 
 the older pyrite to ferrous and ferric sulphate, and the subse- 
 quent reduction of such sulphates by organic matter. I have 
 therefore called it " secondary" pyrite. (The bullion associated 
 with it does not carry the abnormally high percentage of silver 
 which was noticed in the bullion from the sulphides of the 
 deep region a fact which should repay further investigation, 
 and might throw important light upon the solution and re-pre- 
 cipitation of gold and silver by natural agents.) Table VII. 
 gives the results of the analyses of these samples. 
 
190 
 
 THE GENESIS OF CERTAIN AURIFEROUS LODES. 
 
 TABLE VII. Analyses of Samples from the Vadose Region of the 
 Ohinemuri District, Thames, New Zealand. 
 
 
 
 g 
 
 i 
 
 1 I 
 
 . 
 
 
 fe 
 
 fl 
 
 
 Q 
 
 
 *o 
 
 'O 
 
 > 
 
 a> 
 
 d 
 
 A 
 
 s 
 
 ^o . 
 
 J= J; 
 
 ~ t4_; 
 
 Locality. 
 
 1 
 
 Weight of 
 Concentrates. 
 
 i 
 
 Id 
 If 
 
 02 
 
 
 1 
 
 S* 
 
 el 
 
 
 2 
 
 
 2 
 
 2 | 
 
 0) 
 
 2 
 
 2 . 
 
 
 Q 
 
 6T 
 
 
 to 
 '5 
 
 
 H 
 
 S 
 
 > 
 
 
 
 ^ 
 
 
 
 
 
 
 
 FeetT 
 
 Feet. 
 
 Pounds. 
 
 Grains. Grains. 
 
 Grains. 
 
 Grains. 1 Grains. 
 
 a.... 
 
 10 
 
 30 
 
 From a cliff on; 4.48 
 
 1,634 
 
 0.0014 
 
 0.7 
 
 0.0018 
 
 (1 Q 
 
 
 
 
 the tramway be-| 
 tween the Crown 
 
 
 
 
 
 
 
 
 mine and Karan- 
 
 
 
 
 
 
 
 
 
 gahake, Thames. 
 
 
 
 
 
 
 6 
 
 20 
 
 180 
 
 From a fault. 
 
 1.12 
 
 All assayed. 
 
 0.009 
 
 18 
 
 0.0036 i 7.2 
 
 c 
 
 20 
 
 350 
 
 From a fault. 
 
 4.48 
 
 1,065 With a 
 
 0.0062 
 
 3.18 
 
 0.0054 
 
 2.7 
 
 
 
 
 
 
 good per- 
 
 
 
 
 
 
 
 
 
 
 cent age 
 of pyrite. 
 
 
 
 
 
 d.... 
 
 30 
 
 120 
 
 East of the Ma- 
 ria reef, Karanga- 
 
 4.48 
 
 873 With a Nil. 
 good pro- i 
 
 Nil. 
 
 Nil. 
 
 Nil. 
 
 
 
 hake, Thames. 
 
 portion! 
 
 
 
 
 
 
 
 
 
 of pyrite.( 
 
 
 
 
 e 
 
 80 
 
 3 Great Woodstock 
 
 1.12 
 
 All assayed. 
 
 0.0095 
 
 19 
 
 0.0034 
 
 6.8 
 
 
 
 tunnel, Karanga- 
 hake, Thames. 
 
 
 
 
 
 /..... 
 
 10 
 
 60 ! From a cliff on the 2.24 
 
 All assayed. 0.0013 
 
 1.3 
 
 0.0042 ! 4.2 
 
 
 
 Waitawheta river, 
 
 
 ' 
 
 
 
 
 
 
 
 
 near the Crown 
 
 
 
 
 
 
 
 
 
 
 mine, Thames. 
 
 
 
 
 
 fir 
 
 60 
 
 24 
 
 Near the Grace 4.48 
 
 1,372 0.0063 | 3.15 
 
 0.0048 
 
 2.4 
 
 
 
 
 Darling reef, Wai- 
 
 
 
 
 
 
 
 
 tekauri, Thames. 
 
 
 
 
 
 
 h 
 
 60 
 
 30 
 
 Foot-wall side of 
 
 4.48 
 
 846 With a Nil. 
 
 Nil. 
 
 Nil. 
 
 Nil. 
 
 
 
 
 Crown reef. 
 
 
 large pei-! 
 
 
 
 
 
 
 
 
 
 centage of 
 
 
 
 
 
 
 
 
 
 sulphides. 1 
 
 
 
 
 i 
 
 25 
 
 600 
 
 200 yd. off hang- 
 
 2.24 
 
 617 Nearly 0.0093 
 
 9.3 
 
 0.0126 
 
 12.6 
 
 
 
 
 ing-wall side of the 
 
 
 all pyrite. 
 
 
 
 
 
 
 
 Crown reef, 10 ft. 
 
 
 
 
 
 
 
 
 
 
 above the Waita- 
 
 
 
 
 
 
 
 
 
 
 wheta river. 
 
 
 
 
 
 
 3 
 
 10 
 
 660 
 
 From a fault ex- 1.12 
 posed on the tram- 
 
 All assayed. 
 
 0.0071 
 
 14.2 
 
 0.0014 2.8 
 
 
 
 way between the 
 Crown mine and 
 
 
 
 
 
 
 
 
 
 
 Karan gah ake , 
 
 
 
 
 
 
 
 
 
 Thames. 
 
 
 
 
 a. Nearly white propylite ; showed a good percentage of pyrite. 
 
 5. Ferric oxide and higher oxides of manganese, with a little quartz. 
 
 c. Solid, hard andesite, oxidized to brown color on outside. Showed a good deal of pyrite. 
 
 d. Hard, greenish hypersthene-andesite. Showed a good deal of pyrite. 
 
 e. Ferric oxide and higher oxides of manganese, from a vein near the foot-wall of the Great 
 
 Woodstock reef. 
 
 /. Andesite ; brown, much decomposed. No pyrite visible. 
 g. Decomposed andesite and ferric oxide, from a fault. 
 h. Grayish-white andesite, much oxidized on the outside, but showing pyrite freely when 
 
 broken. 
 
 i. Nearly white, very siliceous rhyolite. Showing pyrite freely. 
 j. Ferric oxide and higher oxides of manganese. 
 
 Remarks. These examinations show a striking difference in 
 gold-contents between the vadose and the deep region of the 
 same district. Figs. 1 and 2 show this difference graphically, 
 in curves plotted for the vadose samples and for samples from 
 the deep region (900-ft, and 1,422-ft. levels) of the Walhalla 
 Long Tunnel mine. 
 
THE GENESIS OF CERTAIN AURIFEROUS LODES. 191 
 
 In the deep region, as has been shown, gold was obtained 
 only when pyrite was present in the rock ; and when such py- 
 rite occurred at a considerable distance from the reef, it was 
 seldom gold-bearing. In the vadose region, on the contrary, 
 the country-rock was found to be impregnated with gold to a 
 much greater distance from the reef, and to a much greater 
 degree. 
 
 It is, of course, possible that some of the gold found in the 
 vadose country-rock was carried into it mechanically by per- 
 colating surface-water, and its presence may therefore be no 
 proof of the solution and re-precipitation of gold. But in view 
 of the positions from which most of the samples were taken, I 
 think the results indicate that such solution and re-precipitation 
 have gone on to a considerable extent in the vadose region 
 the gold being in all probability derived from higher parts of 
 the lode, which have long since disappeared through surface- 
 detrition. 
 
 CHAPTER VII. THE ORIGIN OF GOLD IN STRATIFIED DEPOSITS. 
 
 The country-rocks of nearly all the chief Australian gold- 
 fields are more or less altered sedimentaries, originally depos- 
 ited in marine basins. Hence, writers on the origin of the gold 
 in the reefs have laid much stress on the presence of minute 
 quantities of gold and silver in sea-water. The argument is 
 briefly : 
 
 Gold exists in sea-water. Palaeozoic marine sediments there- 
 fore contained gold, either mechanically entangled in them, or 
 precipitated with them by organic matter, which undoubtedly 
 existed in the ancient eeas. These horizontal deposits being 
 subsequently tilted and fractured, their gold and silver were 
 re-dissolved by percolating waters and re-precipitated in the 
 lode-fissures where they are now found. 
 
 This has been the thesis of not a few ingenious speculations, 
 backed sometimes by chemical equations, but not by chemical 
 analyses. 
 
 In 1851, Malaguti and Durocher announced the discovery 
 of silver in sea-water, and made a quantitative estimation of it, 
 namely, 1 mg. in 100 1. (or 0.155 grain per ton). But they did 
 not report any gold. , 
 
192 
 
 THE GENESIS OF CERTAIN AURIFEROUS LODES. 
 
 In 1872, E. Sonstadt 25 discovered gold ill sea-water from 
 Ramsey bay, on the coast of the Isle of Man. He did not de- 
 termine the quantity, but said it was certainly less than 1 grain 
 per ton. Strange to say, many writers who have used this dis- 
 covery as a basis for theoretical speculation have represented 
 Sonstadt as having found 1 grain per ton. 26 
 
 30 
 
 10 
 
 1200 
 West 
 
 1000 
 
 800 
 
 600 
 
 400 
 
 200 
 
 200 
 
 Feet 400 
 East 
 
 FIG. 1. YIELD OF GOLD PER TON OF COUNTRY-ROCK IN VADOSE KEGION. 
 
 (From Diagram 8 of Original Paper, Comparison of Yield of Vadose Region of 
 
 Walhalla, Victoria, with Deep Circulation. See Tables III. and IV. ) 
 
 So far as I am aware, no attempt has been made to verify 
 Sonstadt's discovery, and to determine accurately the amount 
 of gold in sea-water, or to test his statement that this gold is 
 
 25 On the Presence of Gold in Sea- Water, Chemical News, vol. xxvi., No. 671, 
 p. 159 (Oct. 4, 1872). 
 
 26 Thus James Park in his report on the Thames Gold-Field [New Zealand 
 Mining Report for 1893, Appendix] says (p. 65) : "Sonstadt was the first to show 
 that every ton of sea-water contains a grain of gold." A later writer, noting, 
 perhaps, that Sonstadt found "less than a grain," is very scrupulous, and fixes the 
 amount at 0.9 grain ! 
 
THE GENESIS OF CERTAIN AURIFEROUS LODES. 
 
 193 
 
 not precipitated by ordinary reducing-agents, by reason of the 
 presence in sea-water of iodate of calcium. 27 
 
 Methods of Detecting Gold in Sea- Water. 
 
 Sonstadt's Methods. Sonstadt gave three methods for the de- 
 tection of gold in sea-water, two of which he recommended as 
 easily applicable. In the first of these, 150 to 200 cc. of sea- 
 
 d 
 
 150 
 
 100 
 
 50 
 
 *? 
 
 Feet 
 
 FIG. 2. YIELD OF GOLD PER TON OF COUNTRY-ROCK AT 900-FT. LEVEL 
 
 AND 1,422-FT. LEVEL. 
 
 (From Diagram 9 of Original Paper, Comparison of Yield of Vadose Region of 
 Walhalla, Victoria, with Deep Circulation. See Tables III. and IV.) 
 
 water is acidulated with hydrochloric acid, ferrous sulphate is 
 added, and the water is concentrated by boiling. The film of 
 ferric oxide found in the bottom of the dish is treated with 
 
 i7 Since my experiments were made, I have learned from Mr. Eickard's paper 
 On the Origin of the Gold-Bearing Quartz of the Bendigo Reefs (Trans., xxii., 
 308) that Miinster has found gold in the sea-water of Christiania fiord, and has 
 estimated the amount. I find also that Prof. A. Liversidge has estimated that the 
 sea- water off the coast of N. S. Wales contains 0.5 grain of gold to the ton. (See 
 his paper, read before the N. S. W. Royal Society, Oct. 2, 1895, On the Amount 
 of Gold and Silver in Sea- Water. ) 
 
 13 
 
194 THE GENESIS OF CERTAIN AURIFEROUS LODES. 
 
 chlorine-water, and the solution obtained is tested for gold with 
 tin chloride. In the second method, a small quantity of baric 
 chloride is added to the sea-water, and both gold and silver are 
 found to be precipitated. 
 
 The first method I tried upon water from the Pacific, at St. 
 Clair head, near Dunedin, and obtained with tin chloride a dis- 
 tinct coloration, doubtless due to gold. 28 But I found it im- 
 possible to obtain beads of gold by fusing with borax and pure 
 lead, as Sonstadt directs. (This is not surprising, since my 
 subsequent determinations would give, as the quantity of gold 
 in 200 cc. of this sea-water, less than 0.000012 grain.) The 
 necessity of boiling makes this method unsuitable for the treat- 
 ment of samples large enough to yield a weighable bead of gold. 
 
 I therefore tried the precipitation with baric chloride. Son- 
 stadt makes the remarkable assertion that in order to precipi- 
 tate the gold, the baric chloride does not need to be added in 
 sufficient quantity to precipitate as baric sulphate all the solu- 
 ble sulphates in the sea-water, but, on the contrary, that the 
 amount added to a liter of sea-water need not exceed that re- 
 quired to form about 1 grain of precipitate. Baric sulphate 
 being one of the least soluble of salts, this statement seems in- 
 explicable ; nevertheless, I have been convinced, whatever be 
 the explanation, that Sonstadt's method is as effective as if the 
 whole of the soluble sulphates were precipitated as baric sulphate. 
 
 He explains the precipitation by baric chloride by supposing 
 the gold to be present as an aurate. To test this question,, 
 artificial sea-water was prepared, and the aurate of potassium 
 was added to it. Subsequent treatment with baric chloride 
 precipitated no gold. The experiment was repeated, with the 
 same result. 
 
 It seems unlikely, therefore, that the gold exists in sea-water 
 as an aurate. I confess that I can form no conception of its 
 state of combination. The subject would repay a more thor- 
 ough investigation. 
 
 The Author's Method. Having been led, by evidence which 
 I will not here repeat, to doubt whether the precipitation with 
 baric chloride was complete, I tried a different one, which, if 
 
 28 The experiment is more successful with the modification of the tin chloride 
 test prepared by T. K. Rose, Chemical News, vol. Ixvi., No. 1723, p. 271 (Dec. 2, 
 
 1892). 
 
THE GENESIS OF CERTAIN AURIFEROUS LODES. 
 
 195 
 
 successful at all, would certainly precipitate all the gold present. 
 All ordinary salts of gold are reduced to the metallic state by 
 moderate heating. Applying this principle first to an artificial 
 solution, I added to 112 Ib. of artificial sea- water 29 ten times 
 as much calcic iodate as Sonstadt found, and a solution of 
 auric chloride in sodium chloride, containing 0.005 grain of 
 gold, so that the water would contain 0.1 grain of gold per ton. 
 This solution was allowed to stand in a dark place for a week, 
 that the gold might have time to form possible new combina- 
 tions. The whole was then evaporated ; the mixed salts (over 
 4 Ib.) were heated dull red and lixiviated with water ; the in- 
 soluble residue (123 grains) was fused with borax and pure 
 litharge, and 0.0043 grain of gold was obtained. The experi- 
 ment was repeated, the gold being added as an iodate, dis- 
 solved in excess of potassic iodate; and in this case 0.0052 
 grain of gold was recovered. (The slight excess may have 
 been due to a small particle of the cupel remaining in the but- 
 ton. It was not due to silver in the litharge.) 
 
 The method was then applied to actual sea-water; only the 
 sample was doubled in weight, to allow for the smaller propor- 
 tion of gold. The mixed salts (about 8 Ib.) resulting from the 
 evaporation of 0.1 ton of sea-water were heated dull red and 
 lixiviated, and the residue (principally sand, with a little oxide 
 of iron) was fused and cupelled as before. The weight of pure 
 gold obtained from 0.1 ton of sea- water was, in the first ex- 
 periment 0.0065, and in the second 0.9071 grain. In both 
 cases, the prill contained absolutely no silver. 
 
 The following table summarizes the experiments above de- 
 scribed : 
 
 Determinations of Gold in Sea- Water. 
 
 Method. 
 
 Sea- 
 Water. 
 
 Gold Ob- 
 tained. 
 
 Gold per 
 Ton . 
 
 1. Sonstadt's (baric chloride) : 
 a. All sulphates precipitated .. \ 
 
 Pounds. 
 224 
 
 Grain. 
 0.0061 
 
 f\ AAOQ 
 
 Grain. 
 0.061 
 
 Or\na 
 
 b. Small proportion of sulphates precipitated -< 
 
 224 
 224 
 
 0.0074 
 0.0078 
 
 0.074 
 0.078 
 
 2. Evaporation and reduction of gold in residue f 
 by heating \ 
 
 224 
 224 
 
 0.0065 
 0071 
 
 0.065 
 071 
 
 Average per ton.... 
 
 
 
 0.071 
 
 ' 9 Prepared according to the analysis by Roscoe and Schorlemmer. 
 
196 THE GENESIS OF CERTAIN AURIFEROUS LODES. 
 
 I have said nothing concerning the silver in sea-water. Pre- 
 cipitation by baric chloride certainly saves some silver, but 
 only about one-fourth as much as was reported by Malaguti 
 and Durocher. Probably the precipitation is not complete. 
 
 The Precipitation of Gold in Marine Sediments. 
 
 Since gold exists in sea-water, it seems reasonable to believe 
 that it is precipitated at the present time by natural reducing- 
 agents. Those writers who trace the metallic contents of lodes 
 to metals dissolved in sea-water assume, indeed, that such a 
 precipitation is constantly going on ; but experimental proof of 
 this assumption is lacking. I have attempted to investigate 
 the question in two ways : 
 
 1. By the examination of coast-sediments, now being depos- 
 ited under conditions favorable to the reduction of gold from 
 the sea-water. 
 
 2. By the introduction into sea-water of reducing-agents such 
 as naturally occur along the coasts at the present time, and a 
 subsequent examination for precipitated gold. 
 
 Examination of Coast-Sediments. To secure trustworthy re- 
 sults, the whole of the drainage-basin to the erosion of which 
 the sediments are due should consist of non-auriferous rocks, so 
 that we may be sure that any gold detected did not come from 
 the land. Otago harbor, on the upper part of which Dunedin 
 is located, satisfies tjiis requirement. The Leith and other 
 small streams entering the harbor flow wholly through basic 
 Tertiary volcanic rocks which contain no gold. At the same 
 time the shores are more or less covered with timber, so that 
 organic matter is abundant in the sediments of the streams. 
 The volcanic rocks contain much iron. Beds of hematite and 
 limonite abound along the shores. The conditions for the re- 
 duction of gold from sea-water are therefore very favorable. 
 Besides organic matter, there is sulphide of iron, produced by 
 the action of the sulphates in sea-wa*ter upon iron-salts, forming 
 sulphate of iron, reducible to sulphide by organic matter. (As 
 will be seen, some such action does in fact take place. In every 
 case the concentrates contained insoluble sulphides.) 
 
 Analyses were made of mud and silt from different parts of 
 Otago harbor, where the circumstances seemed most favorable. 
 
THE GENESIS OF CERTAIN AURIFEROUS LODES. 
 
 197 
 
 In each case, from 1 to 2 cwt. of the silt was carefully panned 
 off, till a residue of about 1,000 grains was left. This residue 
 consisted chiefly of magnetite, augite, and hornblende, derived 
 from the volcanic rocks of the coast. The percentage of sul- 
 phur (insoluble sulphides) in the concentrate was determined 
 upon a small portion, and the remainder was roasted (giving in 
 every case a strong reaction of sulphur dioxide). 30 The roasted 
 material was then assayed. The details of four assays are given 
 in the following table : 
 
 Examination of Marine Sediments. 
 
 Sample. 
 
 Concentrates. 
 
 Sulphur 
 in Non- 
 Magnetic 
 Concen- 
 trates. 
 
 Gold 
 Obtained. 
 
 Total. 
 
 Extracted 
 by Mag- 
 net. 
 
 a 
 
 Grains. 
 438 
 1,678 
 
 875 
 586 
 
 Grains. 
 365 
 916 
 418 
 307 
 
 Per Cent. 
 12.38 
 7.03 
 16.19 
 4.61 
 
 Nil. 
 Nil. 
 Nil. 
 Nil. 
 
 b : 
 
 c 
 
 d 
 
 
 a. Over 1 cwt. of black mud, containing much organic matter, from Upper 
 Otago harbor, taken at low tide near Logan's Point. 
 
 b. About 2 cwt. of black mud, containing much putrefying organic matter, from 
 the upper harbor, near the outlet of a main sewer. 
 
 c. Over 1 cwt. of silt from Pelichet bay, where a small stream of highly-ferru- 
 ginous water runs into the bay from a bed of hematite. 
 
 d. About 1 cwt. of silt from the upper end of the harbor, near the' outlet of a 
 main sewer from South Dunedin. It contained much decomposing organic 
 matter. 
 
 Examination of Wood That Had Been Lying Under Sea- 
 Water for a Long Time. Several samples of wood, which had 
 been buried many years under sea-water and mud in Otago 
 harbor and elsewhere on the New Zealand coast, were analyzed 
 for gold. In each case from '10 to 30 Ib. of the wood was 
 burned, and the ashes were fused with pure litharge. 
 
 The results are given in the following table : 
 
 When the magnetite was removed by means of a magnet, the remainder did 
 not show, under the microscope, recognizable crystals of pyrite ; but the presence 
 of pyrite was certainly proved by roasting, and by the sulphur-determination. 
 
198 
 
 THE GENESIS OF CERTAIN AURIFEROUS LODES. 
 
 Analyses of Wood for Gold. 
 
 Sample. 
 
 Description. 
 
 Weight 
 Burned. 
 
 Results. 
 
 a. 
 
 Kauri plank, which had lain in Dunedin harbor at 
 
 Pounds. 
 12 
 
 Nil. 
 
 
 least 15 years. Other parts much decomposed. 
 
 
 
 6. 
 
 Pine plank from Catlin's estuary, east coast of Otago. 
 
 20 
 
 Nil. 
 
 c. 
 
 Part of a ship wrecked 20 years ago. 
 Remnant of manuka pile from Otago harbor. Under 
 
 12 
 
 Nil. , 
 
 
 water 20 years. 
 
 
 
 d. 
 
 Do., the decayed part. 
 
 10 
 
 Nil. 
 
 e. 
 
 Part of a pile from the Vauxhall baths, Anderson's 
 
 18 
 
 Nil. 
 
 
 bay, Otago ; in the water 30 years. 
 
 
 
 f. 
 
 Driftwood imbedded in the mud at Madagascar beach, 
 
 16 
 
 Nil. 
 
 
 west coast of Otago. 
 
 
 
 Attempts to Precipitate Gold from Sea- Water. 
 
 These experiments were confined to such natural reducing- 
 agents as might naturally occur along the coast at the present 
 day, namely, sulphides of iron (chiefly formed by the reduction 
 of the sulphates of sea-water), and carbonaceous matter of 
 various kinds. 
 
 To make a suitable filter, an earthenware pipe 4 in. in diam- 
 eter and 1 ft. long was closed at the ends with strong cloth. 
 Next the cloth was placed a loose plug of asbestos, about 
 2 in. in thickness, wrapped in linen, and the middle part of the 
 pipe was filled with coarsely-broken earthenware, with which the 
 reducing-agent was mixed. The reducing-agents used were 
 animal charcoal, wood-charcoal, soot, and sulphides of iron, 
 copper, and lead the latter being prepared by precipitating 
 sulphates of iron and copper and the nitrate of lead, in order 
 to make sure that they should contain no gold. 
 
 Pelichet bay is separated from the upper reaches of Otago 
 harbor by an embankment, in which an opening about 20 ft. 
 wide has been left. Through this passage the sea runs with 
 considerable force at most states of the tide. The apparatus 
 above described was fixed beneath the bridge which spans this 
 opening, so that both the ebbing and the flowing current might 
 pass through it. The filter was kept thus immersed for periods 
 varying from one to two months. The reducing-agents were 
 then taken out, roasted, and assayed. 
 
 The results are given in the following table : 
 
THE GENESIS OF CERTAIN AURIFEROUS LODES. 
 
 199 
 
 Experiments in Reducing Gold from Sea- Water. 
 
 Experi- 
 ment. 
 
 Reducing-Agent. 
 
 Animal charcoal, in fine pow- 
 der. 
 
 Mixture of pounded charcoal 
 and soot. 
 
 Animal charcoal in lumps. 
 Sulphide of iron. 
 
 Remarks. 
 
 The greater part of the animal 
 charcoal had been washed 
 through the filter, a The re- 
 mainder was assayed. 
 
 The smaller particles washed 
 away. Charcoal remained. 
 
 The sulphide was much oxi- 
 dized ; the whole apparatus 
 being coated with ferric 
 oxide. 
 
 Very little altered. 
 
 Carbonate of copper found in 
 the asbestos filter and other 
 parts of the apparatus. 
 
 Mixture of animal charcoal, j Very little oxidation, even of 
 soot, sulphide of lead, sul- i the artificial sulphide of 
 phide of copper, and sul- iron, was noticed, 
 phide of iron. 
 
 Sulphide of lead in lumps. 
 Sulphide of copper in lumps. 
 
 Gold 
 Found. 
 
 Nil. 
 
 Nil. 
 
 Nil. 
 Nil. 
 
 Nil 
 Nil. 
 
 Nil. 
 
 After the first two attempts the reducing-agents were put in, not as powder, 
 but in lumps from 0.25 to 0.5 in. in diameter, it having been found that the 
 strong current carried the finer stuff through the asbestos filter. 
 
 A very large quantity of sea-water must have passed through 
 the apparatus in each of the above cases, but there was no way 
 of estimating it with precision. In view of the negative results 
 of all the experiments, an attempt was made to precipitate gold 
 and silver from a measured quantity of sea-water. Ten thou- 
 sand grains of artificial sulphides of iron, copper, and lead, with 
 animal charcoal and wood-charcoal all in fine powder were 
 mixed in a barrel with 60 gal. of sea-water taken from the 
 Pacific ocean at Tomahawk Head, near Dunedin. The reduc- 
 ing-agents were stirred in the water for half an hour, and the 
 sediment was allowed to settle for some hours. The clear 
 water above was then decanted off, and the barrel was again 
 filled. This operation was repeated 14 times in the same bar- 
 rel, or until over 4 tons of sea-water had been treated., The 
 sediment was then collected and roasted at a dull red heat, to 
 incinerate the charcoal and get rid of the sulphur. On assay- 
 ing the residue, no gold was obtained ; but the result was a 
 
200 THE GENESIS OF CERTAIN AURIFEROUS LODES. 
 
 bead of pure silver weighing 0.0014 grain. I cannot say cer- 
 tainly whether this silver (which contained no gold) came from 
 the sea-water or from the litharge used. I do not think the 
 latter. If it came from the sea-water, however, it is note- 
 worthy that the amount from 4 tons represents only 0.00035 
 grain per ton, or one five-hundredth part of the quantity found 
 in sea-water by Malaguti and Durocher in 1851. 
 
 All my experiments have thus signally failed to show any 
 precipitation of gold (and have practically failed as to silver) 
 from sea-water by natural reagents. So far ' as they go, they 
 lend no support to the theory that the deposition of gold and 
 silver by such reagents in marine sediments is now going on. 
 
 If such deposition had been the rule in former periods, and 
 if this be the origin of the gold in stratified formations, why 
 should only a comparatively small proportion of such formations 
 be traversed by auriferous veins ? This point has not escaped 
 the attention of Posepny. 31 It seems to me that important evi- 
 dence may be drawn from the examination of stratified rocks 
 known to be consolidated marine sediments, but the lodes in 
 which have not proved auriferous. Table VI. gives an exam- 
 ination of nine samples from Skipper's road, east of Lake 
 Wakatipu, Otago, an area in which the rocks are known to 
 belong to the middle division of the foliated mica-schists (the 
 favorable country-rock for gold in Otago), but in which no au- 
 riferous reefs had hitherto been discovered. Only those parts 
 (e. g., fillings of veins and seams, etc.) particularly favorable to 
 the deposition of gold were examined, but no gold was found 
 in any of the samples. 
 
 A second series of examinations was made on samples from 
 the west shore of Lake Wakatipu, which is largely occupied 
 by rocks of the Maitai (Carboniferous) and the Te Anau (Upper 
 Devonian) series. These rocks (mostly sandstones and slates) 
 are undoubted marine sediments, but no gold has been found 
 in this area. 
 
 If the gold of the lodes in the foliated mica-schists east of 
 this lake was originally deposited from sea-water and has since 
 been collected by lateral segregation, it is difficult to under- 
 stand why gold should not have been deposited in the marine 
 sediments west of the lake also. 
 
 31 Genesis of Ore-Deposits, Trans., xxiii., 307 (1893). 
 
THE GENESIS OF CERTAIN AURIFEROUS LODES. 201 
 
 I therefore examined 16 samples of quartz, ferric oxide, etc., 
 from the two series above named, where they are exposed north 
 and south of the Greenstone river. There were 4 samples of 
 fine-grained blue slate; 6 of ferric oxide from joints and fis- 
 sures; 4 of small quartz veins, none of which contained sul- 
 phides ; 2 of slate containing large crystals of pyrite, amount- 
 ing in weight to 254 grains for the two samples. 
 
 No trace of gold or silver was found in any of these samples. 
 
 CHAPTER VIII. SUMMARY OF RESULTS. 
 [The recapitulation of the various results recorded in the 
 preceding chapters is here omitted, to save space.] 
 
 Bearing of these Results on the Origin of Auriferous Lodes. 
 
 When I began this work, seven years ago, I was strongly 
 inclined to believe that the lateral-secretion theory afforded 
 the most reasonable explanation of the origin of auriferous 
 deposits in these colonies ; but, as the result of each series of 
 examinations appeared, I was forced to the following conclu- 
 sions : 
 
 If any reliance can be placed on the examinations detailed 
 in the foregoing chapters, they seem to indicate that the gold 
 of many lodes of the chief mining-districts of New Zealand, 
 Victoria, and Queensiland is due, not to lateral segregation from 
 the adjacent country-rock, but to solutions ascending from some 
 rock deeper than any now exposed at the surface in any part of 
 these colonies. 
 
 I am not concerned with the question whether this source is 
 the vague " barysphere," with its somewhat apocryphal con- 
 tents of heavy metals. I have simply to note that a series of 
 laborious and careful examinations has failed to find it in the 
 rocks of the " lithosphere." 
 
 What may be the value of these investigations in the study 
 of the general question of the origin of ore-deposits I leave the 
 reader to judge, being myself content to quote the opinion of 
 Professor Stelzner, of Freiberg, no mean investigator of that 
 larger question, that 
 
 "Each increase of our positive knowledge of the nature and mode of origin of 
 ore-deposits, each explanation of any question connected with such deposits or 
 with their associated country-rocks, is a distinct gain, not only to science, but also 
 to mining practice." 32 
 
 32 Concluding sentence of Die Lateraisecretionstheorie (1889). 
 
202 THE GENESIS OF CERTAIN AURIFEROUS LODES. 
 
 DISCUSSION. 
 
 (Trans., xxvii., 993.) 
 
 JOSEPH LE CONTE, Berkeley, Cal. : I have read with some 
 care and with extreme interest the work of Dr. Don, and have 
 no hesitancy in expressing my high estimate of its value. We 
 have here an example of laborious work undertaken in the true 
 scientific spirit and by right methods. Loose statements and 
 rash conjectures are here brought to the test of chemical an- 
 alyses. By such work only may we hope to reach reliable con- 
 clusions and finally to solve our complex problems presented 
 by the concurrence of ore-deposits. 
 
 Such work as this is not only scientific but is in the highest 
 degree practical; for while a crude and imperfect science, by 
 interfering with the results of approved empirical methods, 
 may be positively hurtful, a more perfect science must eventu- 
 ally become the only sure guide to practice. Such a more per- 
 fect science can only be reached by such work as Dr. Don's. 
 
 I am sure every member of the Institute will unite with me 
 in the hope that Dr. Don will continue his work, and that his 
 example will incite others to similar work. 
 
 S. F. EMMONS, Washington, D. C. : I desire to bear my hum- 
 ble testimony to the great value of Dr. Don's paper to the sci- 
 ence of ore-deposits, the thoroughness and accuracy of his 
 work, and the immense amount of care-taking and tedious 
 labor which it represents. The only regret with regard to it 
 is that it could not have been published in full. No more 
 important paper in its line has ever appeared in the Transac- 
 tions. Indeed, this is a line in which far too little has been 
 done anywhere. Geologists are not often sufficiently trained 
 chemists to carry on such work, if they had the time ; and for 
 mining-geologists in our country the press of work in other 
 directions is so great that they could not give the necessary 
 time involved in this class of work, if they were so inclined. 
 The chemist, on the other hand, is rarely enough of a geolo- 
 gis", or so placed, as to get sufficient field-experience to keep 
 thoroughly in touch with the processes of nature as shown in 
 mine-workings. By an organization like the U. S. Geological 
 Survey, where the chemist and the geologist might work in 
 harmony for a common purpose, it would seem that investiga- 
 
THE GENESIS OF CERTAIN AURIFEROUS LODES. 203 
 
 tions into terrestrial chemistry might best be carried on ; and 
 15 years ago, in connection wich Mr. Hillebrand, one of the 
 most thorough inorganic chemists of the day, I had planned 
 such a line of experimental work, which I hoped might be con- 
 tinued as part of the regular chemical work of the Survey. 
 But the powers that were willed it otherwise. My colleague, 
 Mr. Becker, has made some important researches in this line, 
 especially with regard to the natural solvents of gold, which 
 do not appear to have come under Mr. Don's notice. Such 
 work is necessarily very slow, and Mr. Don's paper, as he tells 
 us, covers the results of seven years' labor. 
 
 I do not propose to discuss Mr. Don's paper from a chemical 
 point of view, but only to consider the deductions that may be 
 made from it from the geological side ; and I do this with some 
 hesitation, because, not being able to read his statements in 
 detail, I may not infer correctly what his actual conclusions 
 were. I must say, however, that he seems to be most broad- 
 minded in this respect, and his work presents a pleasing con- 
 trast to parts of the great paper of the lamented Posepny, 
 where the effects of the latter's recent contest with Sandberger 
 seemed to make him look at Nature through ascensionistically 
 colored glasses. 
 
 Dr. Don's first and most important conclusion from his tests 
 is that gold does not occur in the rocks of the regions investi- 
 gated by him as an original constituent of the bisilicates, and 
 that where it is found in these rocks it is associated with sul- 
 phides, mainly of iron. His inference seems to be that it can- 
 not be original in the rock, because pyrite is necessarily a sec- 
 ondary constituent, that is, one introduced after the rock 
 consolidated. Now, my work for the past ten years has been 
 bringing me more and more to doubt the adequacy of the 
 bisilicates of eruptive rocks as a source of the metals for our 
 ore-deposits, and, especially in the case of gold, to look to the 
 pyrite, if not as a source, as the visible accompaniment. Where 
 there is no pyrite in the neighboring eruptive rocks, I have 
 not found that the veins are usually rich. But I have not, 
 therefore, abandoned my belief that eruptive rocks, similar to 
 those we see at the surface, are the source of supply from which 
 the great majority of our ore-deposits have been concentrated. 
 Pyrite is not necessarily a secondary constituent in such rocks, 
 
204 THE GENESIS OF CERTAIN AURIFEROUS LODES. 
 
 as seems to be tacitly assumed by many. On the contrary, 
 most petrographers admit the existence of primary pyrite,. 
 though they do not generally appreciate its importance in the 
 study of ore-deposits. .Lindgren has lately discussed primary 
 pyrites as a product of magmatic consolidation in the gold- 
 bearing rocks 33 of California. I cannot even feel absolutely 
 sure, in spite of the apparent conclusiveness of Mr. Don's in- 
 vestigations for his regions, that the bi silicates of our Rocky 
 Mountain eruptives may not contain some of the metals, but 
 must wait until similarly exhaustive tests have been carried on 
 here. Lead and cobalt have been found by Mr. Hillebrand in 
 the bisilicates of some of the eruptive rocks of the Ten-Mile 
 district, and lead and silver similarly by Mr. Eakins in the bi- 
 silicates of granite at Silver Clifi', Colo. 
 
 It seems important to note that the lateral-secretion theory 
 which Mr. Don's tests seem to disprove is not the one that has 
 been generally advocated in the United States ; for I fancy few 
 American geologists believe in the narrower view advocated by 
 Sandberger, that the metals are derived necessarily from the 
 immediately adjacent country- or wall-rock. Dr. Don says that 
 he believes the gold of New Zealand is derived from rocks 
 deeper than any now exposed at the surface there, but adds 
 that he "is not concerned with the question whether this 
 source is the vague barysphere, with its somewhat apocryphal 
 contents of heavy metals." While, therefore, no longer a be- 
 liever in Sandberger, he is apparently not willing to subscribe 
 to the extreme views of Posepny. It has been the fashion for 
 some time to decry Sandberger ; but I think his work has been 
 of the utmost value to the study of ore-deposits, even if hi& 
 ultimate conclusions are not admitted ; for he aroused us from 
 the unthinking belief that the metals necessarily came from 
 unknown depths, which it was fruitless to speculate about or to 
 try to investigate. He started in movement the pendulum of 
 thought, which had so long been stationary at that point ; for 
 a while it swung on his side, then back again to the ascen- 
 sionist side. Now, with some geologists, it has taken a very 
 strong impetus in the direction of the long-ago abandoned sub- 
 limation theory, or something very like it. The Swedish geolo- 
 
 33 Gold Quartz Veins of Nevada City and Grass Valley, by W. Lindgren., 
 Seventeenth Annual Report, U. S. Geological Survey, Part II., p. 94 (1895-96). 
 
THE GENESIS OF CERTAIN AURIFEROUS LODES. 205 
 
 gists represented by Vogt, a disciple of the great petrographer 
 Brb'gger, consider certain workable masses of iron and other 
 ores as segregations from the still molten mass, or direct prod- 
 ucts of magmatic differentiation. Other minerals occurring 
 in pegmatite veins, and some metallic oxides, like tin, for in- 
 stance, they consider to have been deposited in the last stages 
 of consolidation of a molten magma by a mixed process, which 
 they call pneumatolysis, and which brings in the agency of 
 water expelled during cooling from the igneous magma. This 
 comes back to the old French theory of aqueo-igneous fusion 
 in the presence of certain substances, such as fluorine, boron, 
 chlorine, etc., which were called agents mineralisateurs ; but it 
 is less purely theoretical, in that it is founded on certain facts 
 of observation in nature. 
 
 Vogt is at present preparing a new book on ore-deposits, in 
 which he will doubtless extend very widely the scope of his 
 pueumatolytic processes. But the applicability of either the 
 French or the Swedish theory must be limited by a very sinlple 
 geological condition, which is whether the fissures in which 
 ore-deposition has taken place could have been formed during 
 the final consolidation of the eruptive magma. In most of the 
 important ore-deposits which I have had opportunities of study- 
 ing, the fissures or fractures which have served as ore-channels 
 were the result of earth-movements that took place long after 
 the entire consolidation of the eruptive magmas. In' some 
 cases, even, there is evidence of several such movements before 
 the ore-deposition. My belief, as I have had occasion to state 
 already, is that, by reason of some process which, for want of a 
 better name, we may call magmatic differentiation, certain por- 
 tions of an eruptive mass are richer in metals than the average ; 
 and that from such portions circulating solutions have ab- 
 stracted these diffused metals and deposited them in a more 
 concentrated form in favorable situations in rocks in the vicin- 
 ity. The original bringing up of the metals from the bathy- 
 sphere was, however, accomplished by the eruptive magma be- 
 fore consolidation. Present ore-deposits are in this sense the 
 result of a secondary concentration at only moderate depths. 
 
 Dr. Don's investigation of the processes going on, or that may 
 go on, in the vadose region affords interesting and useful data. 
 He first assumes that deposits are generally richer in the pre- 
 
206 THE GENESIS OF CERTAIN AURIFEROUS LODES. 
 
 cious metals above than below the water-line a perfectly justi- 
 fiable assumption, in my opinion and then presents alterna- 
 tive explanations, one based on the ascension, the other on the 
 lateral-secretion, theory; but he does not mention the most 
 obvious explanation of this fact, namely, that the baser metals, 
 which are usually in far greater amount than the precious 
 metals, form by oxidation more readily soluble compounds, and 
 are therefore to a much larger extent removed in the vadose or 
 oxidizing region, while the precious metals are for the most 
 part either not dissolved or are re-precipitated. Hence, the 
 specific gravity of the whole mass of vein-material is decreased 
 in the vadose region; and a given bulk, though it may have 
 absolutely no more of the precious metal in it than before oxi- 
 dation, contains a relatively higher percentage, by weight, of 
 the precious rnetals. There may also be in places an actual 
 enrichment, due to the ready precipitability of the precious 
 metals. I have myself seen cases where, in a zone immediately 
 above the water-line, the ore-body was not only very much 
 richer than in the unoxidized portion below, but also richer 
 than the average of the oxidized ore above, showing that the 
 precious metal had been in a measure leached down and re- 
 precipitated. Dr. Don himself shows various ways in which 
 gold might be dissolved in the vadose region and re-precipi- 
 tated lower down ; he also thinks it may have been carried 
 down mechanically; the result of his investigations of mine- 
 waters being that, where they are found to contain gold, it is 
 usually in mechanical suspension rather than in solution. 
 
 One of the most interesting parts of Dr. Don's investigations 
 is that relating to the gold-content of sea-water, in which he 
 has not contented himself with the vague statement that the 
 metal does occur, but has made a quantitative estimate of its 
 amount, which must be translated into the metric system in 
 order to become intelligible to any but English chemists. The 
 average content as determined by him is 0.0071 grain to the 
 ton, which means, if I have calculated correctly, something like 
 twelve million dollars' worth to the cubic mile a large sum, if 
 it could be gotten out. But Dr. Don has shown by a pretty 
 exhaustive series of experiments that there is no probability 
 that any natural precipitant would throw down any measurable 
 portion of it. 
 
THE GENESIS OF CERTAIN AURIFEROUS LODES. 207 
 
 GEORGE F. BECKER, Washington, D. C. : Dr. Don's paper is 
 an extremely important contribution to mining-geology, and 
 worth the vast amount of labor which it has manifestly cost. 
 I trust that the paper in the Transactions will prove to be only 
 a preliminary abstract, and that the entire memoir will soon 
 appear. 
 
 The greater part of the conclusions which Dr. Don reaches 
 are quite in line with those to which Mr. Lindgren and I have 
 been led by studies of the gold-deposits in this country. 34 I 
 have been greatly impressed of late years with the character of 
 the auriferous wall-rocks of gold-quartz veins. It seems to be 
 true in most cases, for deep mines, that the gold in the walls is 
 contained in the sulphurets ; that it is of smaller fineness than 
 the vein-gold; that the sulphurets are pyrites; and that gold 
 and sulphurets diminish rapidly in quantity as the distance 
 from the vein increases. Sometimes the wall-rock pyrite is 
 almost barren. There appear to me to be two sorts of wall- 
 pyrite. One seems to be the result of the action, on ferro-mag- 
 nesian silicates, of the sulphides of hydrogen or of the alkalies, 
 as I pointed out in treating of the Comstock lode. This variety 
 is sometimes, and I suspect usually, almost worthless. There are 
 other impregnations of pyrite which seem to me to have per- 
 meated from the vein-fissures, in solution, as double sulphides 
 of the alkalies and iron. I have studied such solutions in a 
 memoir on quicksilver-deposits, and shown that solutions of 
 alkaline carbonates, partly charged with hydrogen sulphide, 
 will take up notable quantities of many sulphurets, and also of 
 gold. Dr. Don has, I think, overlooked this investigation. 
 Mr. Dolter has since succeeded, where I failed, in dissolving 
 lead and silver sulphides in a similar menstruum. 
 
 Wall-rocks appear to be much more permeable by solutions 
 of some substances than by those of others. Native gold, 
 quartz, and all the sulphurets excepting pyrite, are for the 
 most part retained in the veins, while carbonates seem to pene- 
 trate freely into the wall-rock. This indicates an osmotic sep- 
 aration of the metal-bearing solution, as I pointed out years 
 ago. 
 
 34 Parts of these studies have been printed in the Fourteenth to Eighteenth Annual 
 Reports, U. S. Geological Survey (1892-96). 
 
208 THE GENESIS OF CERTAIN AURIFEROUS LODES. 
 
 That some undecomposed rocks (granite, andesite) contain 
 free gold in clearly-visible particles appears to be quite certain. 
 There is also strong evidence for the strange hypothesis that 
 some sulphurets in massive rocks are original constituents. I 
 entertain no doubt that some eruptive rocks associated with 
 veins are truly metalliferous. Nevertheless, the possibility 
 presents itself that in such cases vein and rock each derived 
 its metallic contents from a common source, miles beneath the 
 surface. Such a hypothesis is not without difficulties of its 
 own, but accords better with the osmotic phenomena than the 
 theory of derivation from wall-rock. 
 
 Dr. Don's remarks on secondary re-crystallization are inter- 
 esting. That sulphurets are regenerated is certain. The ques- 
 tion of the re-crystallization of gold needs more research. 
 
 ARTHUR WINSLOW, Kansas City, Mo. : Dr. Don's work, even 
 as presented in the abridged form of his Institute paper, is a 
 notable example of painstaking, conscientious research, for 
 which the author deserves great credit. The field and literary 
 work alone must have been very great ; but, in addition, the 
 investigation involved many special experiments on a large 
 scale, and the testing and assaying of over 400 bulky samples, 
 with more than 100 other assays and analyses, which, to any one 
 familiar with such tasks, seems a stupendous labor. The re- 
 suits are especially of quantitative value, furnishing many exact 
 facts and definite data which will control speculation, and upon 
 which theories can be built up. Therefore, in whatever esti- 
 mation one may hold Dr. Don's methods and results, or how- 
 ever one may diiFer in the conclusions to be drawn, all, I think, 
 will agree in admiring the courage and entire disregard for 
 labor which prompted and sustained his inquiries. 
 
 The investigation is, first and principally, one to determine 
 whether the ores of certain auriferous lodes of New Zealand, 
 Victoria, and Queensland were formed by lateral secretion or 
 by ascension. Secondarily and incidentally, it is a valuable 
 -contribution to the general subject of the genesis of ore-deposits. 
 
 The work is of special interest when considered in connec- 
 tion with the hypothesis advanced by T. A. Rickard 35 for the 
 origin of the ores of the Bendigo reefs of Australia. Indeed, 
 
 35 Trans., xxii., 289 (1893). 
 
THE GENESIS OF CERTAIN AURIFEROUS LODES. 209 
 
 it would appear as if Mr. Don must have had this hypothesis 
 immediately in mind in planning his work, so directly does he 
 meet the questions which arise in reading Mr. Rickard's 
 paper. Passing by his experiments and conclusions as to the 
 precipitation of gold in marine sediments, and also allied in- 
 quiries of somewhat negative value, the results of most posi- 
 tive and emphasized importance are his analyses of the country- 
 rocks for the detection of gold. These are principally inter- 
 esting in the uniformity with which they show that the metal 
 was not detected, or was found to be present only in very 
 minute quantities in the normal country-rock; also that, where 
 its presence was detected, it was associated with sulphides, and 
 that both the quantity of the sulphides and the richness in gold 
 increased as the lode or other form of deposit was approached. 
 The question which arises, and which to me seems of great 
 significance, is as to the sufficiency of the evidence. Dr. Don's 
 assay-results marked " Nil " as to gold-content must be con- 
 sidered as relative. They mean simply that no gold was de- 
 tected by the method he used. It is probable that gold and 
 other metals are generally diffused through the rocks of the 
 earth's crust, and are represented normally by amounts pro- 
 portional to their abundance and the solubilities of their natu- 
 rally-formed compounds. The researches of Forschhammer, 
 Dieulafait, Bischof, Sandberger, Malaguti, and others, referred 
 to in my report on the lead- and zinc-deposits of Missouri, M 
 show the frequent diffusion of copper, lead, and zinc in rocks, 
 minerals, and waters. Mr. Robertson's analyses of crystalline 
 -and clastic rocks of Missouri, in connection with the same re- 
 port, 87 sustain this belief. Proof that such diffusion is general 
 would seem purely a question of the amount of rock used and 
 of the refinement of method. The refinement of Dr. Don's 
 methods may be inferred from the fact that 0.1 grain per ton 
 is the lowest result given in figures. There is nothing between 
 this and the " Nil " results. Gold to the amount of more than 
 0.1 grain he shows to be frequently present in the country- 
 rock, remote from lodes, and even amounts of over 1 grain 
 were found. On the assumption that the gold has been de- 
 rived from these rocks, such gold now found to be present must 
 
 36 Reports Missouri Geological- Survey, vol. vi., p. 30 et seq. (1894). 
 
 37 Reports Missouri Geological Survey, vol. vii., p. 479 et seq. (1894.) 
 
 14 
 
210 THE GENESIS OF CERTAIN AURIFEROUS LODES. 
 
 be a residuum after the process of leaching. The question 
 arises, what gold-content is required in a country-rock that it may 
 be regarded as a source of the ores in the veins traversing it. 
 Assuming 0.1 grain to the ton, it would take just 4,800 tons of 
 rock to supply the gold for 1 ton of 1-oz. ore, if all the gold 
 were removed from the country-rock into the veins. On this 
 basis 1 cu. mile of rock would supply 2,300,000 tons of such 
 ore. Mr. Rickard's hypothesis, which ascribes the gold to 
 sea-water retained in the sediments, would hardly call for a 
 greater original concentration, seeing that he allows only -jig- 
 grain per ton to the sea-water of the present day. 
 
 The conception of lateral secretion as a process whereby the 
 contents of the ore-body simple trickle in from the sides or 
 walls can, of course, not be sustained, even though the name 
 may seem to justify it. To harmonize with the ideas now 
 more generally held, the flow and transmission of solutions 
 must have been in devious directions, according to hydrostatic 
 and thermal conditions, and according to the structure of the 
 rocks. The solutions would naturally follow fissures, and flow 
 into open spaces, either in ascending or descending currents. 
 They would at the same time penetrate the wall-rocks of such 
 openings, and when they contained gold these wall-rocks would 
 be enriched. Thus, an increase of the mineralization, or of 
 the gold-content, as the vein is approached, is not incompatible 
 with the large conception of lateral secretion. 
 
 It is true that such an expansion of the original idea of lat- 
 eral secretion appears to rob it of its distinctive features, so 
 that it seeing in fact to embrace the rival process of ascension, 
 and to leave no room for the separate existence of the latter. 
 This is not, however, the case. The essential idea of the as- 
 cension theory is that metals and other constituents of lodes 
 are derived from a deep-seated source of supply a sort of 
 treasure-house of nature whence they were transported for the 
 use of man by the agency of ascending solutions or vapors 
 which followed the paths of profound fissures. The opposed 
 idea of lateral secretion, as developed, if not precisely so ex- 
 pressed in recent writings, is that these constituents of lodes 
 are distributed and diffused in greater or less quantities 
 throughout the rocks of the earth's crust in such rocks as 
 are or have been exposed at the surface that they have been 
 
THE GENESIS OF CERTAIN AURIFEROUS LODES. 211 
 
 gathered from these rocks and concentrated in ore-deposits by 
 the action of percolating waters of various compositions, as- 
 sisted by chemical, l^drostatic, thermal, and structural condi- 
 tions, such as are brought about by sedimentation, by earth- 
 movements, by injection of volcanic rocks, etc. In cases of 
 the more abundant metals, such as iron and manganese, this 
 process is plainly recognized, and the requisite conditions are 
 commonly presented. In the case of less common metals, such 
 as copper, lead, and zinc, the process is not so simple or so gen- 
 erally to be observed. In the case of the precious metals, 
 which are rare and difficult of solution and transportation, 
 more powerful factors and special or stronger reagents, such as 
 highly-heated solutions, seem necessary to produce the result. 
 Thus, according to the lateral-secretion theory, our own home 
 country-rocks are our treasure-houses, and we are not depen- 
 dent upon the foreign depths of the earth for our metals. 
 Such may be in some cases the source of supply, but the ag- 
 gressive secretionist is disposed to throw the burden of the 
 proof upon the ascensionist, and to maintain that his rule is 
 the more satisfactorily proved by the removal of successive 
 supposed exceptions. 
 
 W. P. BLAKE, Tucson, Arizona : As appropriate to the dis- 
 cussion on the origin of quartz-lodes and the deposition of gold, 
 I desire to direct attention to the very general association in 
 California, especially in the Jura-Trias and Carboniferous 
 slates, of gold with slates containing a large amount of carbo- 
 naceous matter. This association is particularly noticeable in 
 the Princeton mine, on the Mariposas estate ; in the Keystone 
 mine, Amador county; in the Plumas mine, and in many 
 other mines in the main gold-belt of the State. It has been 
 noted also by Ross E. Browne, who, in a recent article, gives 
 three cross-sections showing the mother-lode traversing soft 
 black slate. He describes the lode as a " continuous series of 
 parallel quartz veins, following more or less persistently a nar- 
 row belt of soft black slate." M 
 
 At the Arizona School of Mines a sample of coal has been 
 received from Wyoming, which is said to contain gold. Pre- 
 liminary assays, made with great care, show an appreciable 
 
 38 Mining and Scientific Press, vol. Ixxvi., No. 5, p. 105 (Jan. 29, 1898). 
 
212 THE GENESIS OF CERTAIN AURIFEROUS LODES. 
 
 amount of the metal ; but further investigation of the source 
 of the coal and assays upon other samples are desirable before 
 attaching special value to this form of association of gold and 
 
 carbon. 
 
 (Trans., xxviii., 799.) 
 
 DR. DON : I have to express my grateful thanks to Messrs. 
 Le Conte, Emmons, Becker, and Winslow, for their very kiad 
 remarks, presented at the Atlantic City meeting, on my paper. 
 An investigator works practically alone and under many dis- 
 couragements, at this end of the world; and nothing has 
 encouraged me so much in my research as to find my work 
 appreciated by men whose wide knowledge of the subject and 
 whose eminent services to science entitle their opinions to my 
 deepest respect. 
 
 Professor Le Conte's last sentence gives me an opportunity 
 to express the hope that chemical analysis may in future be 
 more generally used as an aid to observation. If any degree 
 of finality is ever to be reached with regard to this most puz- 
 zling question, such finality will only be attained by the com- 
 bination of the experimental work of the chemist with the 
 skilled observation of the mining-geologist. 
 
 Mr. Emmons, in his highly-valued criticism, says : 
 
 "Dr. Don's first and most important conclusion from his tests is that gold does 
 not occur in the rocks of the regions investigated by him as an original constitu- 
 ent of the bisilicates, and that where it is found in these rocks it is associated with 
 sulphides, mainly of iron. His inference seems to be that it cannot be original in 
 the rock, because pyrite is necessarily a secondary constituent, that is, one intro- 
 duced after the rock consolidated. ' 
 
 I confess that I had not in my mind as clearly as I could 
 wish the fact that in the case of crystalline eruptive and plu- 
 tonic rocks the pyrite and other sulphides may be as much a 
 primary constituent of the rocks as the bisilicates. 
 
 This distinction between primary and secondary sulphides 
 need not, however, be observed in the great majority of the 
 country-rocks examined by me. These country-rocks may be 
 roughly divided into four classes : 
 
 a. Those that are unmistakable sediments, more or less 
 altered. These form the great majority of the samples ana- 
 lyzed; and in these cases, all sulphides must be "secondary." 
 
 b. Dike-rocks from the Upper and Lower Silurian of Vic- 
 
THE GENESIS OF CERTAIN AURIFEROUS LODES. 213 
 
 toria. NOUQ of these rocks could be obtained in the unaltered 
 state ; but those that were least altered contained no sulphides. 
 
 c. The remarks under b apply also to the andesites of the 
 Thames gold-field, and the tonalite of the Charters Towers 
 field of Queensland. 
 
 d. In the case of the gneissoid rocks of the Manipori forma- 
 tion of New Zealand, and the granite that probably underlies 
 the sedimentaries of Victoria, the sulphides found in some 
 samples may have been primary. 
 
 Mr. Emmons says : 
 
 . "It seems important to note that the lateral-secretion theory which Dr. Don's 
 tests seem to disprove is not the one that has been generally advocated in the 
 United States ; for I fancy few American geologists believe in the narrower view 
 advocated by Sandberger, that the metals are derived necessarily from the imme~ 
 diately adjacent country- or wall-rock." 
 
 The introduction to Chapter Y. (omitted in the condensed 
 form of my paper) included a discussion of this point, and 
 showed that the analysis of underlying granites and other crys- 
 talline rocks had been undertaken with a view to testing this 
 later extension of the lateral-secretion theory. By reference to 
 my paper [p. 162, this volume], it will be seen that the crystal- 
 line rocks were chosen because they afforded an opportunity 
 for testing, not the actual country-rock bounding the lodes, but 
 the crystalline rock-mass that probably underlies many of the 
 rocks in which our lodes occur. 
 
 The majority of the results noted in Table I., J., J5, and C 
 (Table XVIII. of original paper), come under this heading. 
 Owing to the great labor involved in isolating some of the 
 crystalline constituents of such rocks, the number of these 
 analyses is comparatively small ; but so far as these results are 
 conclusive, they point to a source for the gold below even the 
 crystalline rocks that may be assumed to underlie our gold- 
 bearing sedimentaries. 
 
 I have to thank Mr. Emmons for his criticism pointing out 
 a weakness in my statement of the two alternatives on p. 172 of 
 my paper. The second alternative should certainly have been 
 extended in the direction suggested by him. On page 182, 
 however, the action of the oxidizing vadose waters, in enrich- 
 ing vein-gold by dissolving out part of the silver, is taken into 
 account. 
 
214 THE GENESIS OF CERTAIN AURIFEROUS LODES. 
 
 Mr. Becker draws a clear distinction between the two kinds 
 of pyrite associated with country-rock. This distinction seems 
 to me to be of very great interest, and of the first importance. 
 
 Granted this distinction, and the selective osmotic action 
 exercised by the wall-rock, a new light is thrown on many of 
 the results obtained in my analyses. The apparently abnormal 
 results obtained in some cases more particularly in the Thames 
 andesites and the country bounding the Reefton lodes become 
 much clearer in the light of Mr. Becker's remarks. 
 
 Mr. Becker refers also to the presence of visible particles of 
 gold in undecomposed crystalline and eruptive rocks. Such 
 instances are by no means rare; but is it not possible that 
 the samples in which these occurrences are noticed may have 
 been taken from the vicinity of lodes, so that the gold found 
 may have been an impregnation from the lode itself? An in- 
 teresting example of such an occurrence lately came under my 
 notice. In a sample of syenitic rock taken from the vicinity of 
 a copper-lode in Dusky sound, on the west coast of Otago, 
 minute specks of metallic copper were observed, apparently . 
 forming a constituent of the hornblende of the rock. In this 
 instance there seemed to be no doubt that the copper was 
 derived from the lode. I should be much interested if any 
 members of the Institute could give authentic instances of the 
 occurrence of visible particles of gold actually forming part of 
 crystalline or eruptive rocks at long distances from lodes. 
 
 Mr. Winslow's criticism raises the whole question as to the 
 possibility of obtaining any experimental evidence, other than 
 that founded on observation alone, with regard to the genesis 
 of auriferous deposits, where the amount of metal to be looked 
 for is extremely minute. This is a difficulty that must have 
 presented itself to any honest worker who has made a study of 
 the subject. The question is not so much whether the methods 
 used by any particular investigator have been sufficiently re- 
 fined, as whether any possible test may be delicate enough to 
 give reliable results. 
 
 Now, while it is quite true that the results obtained by me 
 do not show any difference between -fa grain to the ton of coun- 
 try-rock (or one part in 156,800,000) and ml, and while, in my 
 opinion, it is not possible to carry the refinement much further 
 with safety, one must not, I think, lose sight of the fact that if 
 
THE GENESIS OF CERTAIN AURIFEROUS LODES. 215 
 
 the gold of any lode had been derived by segregation from the 
 country-rock or from associated and subjacent rocks (it will be 
 observed that lateral secretion is here indicated in its wider 
 sense), such segregation must have been accompanied by local 
 deposition at many points, as the auriferous solutions made 
 their way to the lode-fissure. It is a matter of common obser- 
 vation that the country, even at considerable distances from 
 lodes, is in many cases a network of miniature lodes, where de- 
 position might reasonably be expected to take place. In col- 
 lecting samples for analysis, care was taken to include many 
 such places of possible deposition ; yet the evidence obtained 
 by me would almost justify the general statement that in solid 
 country, where the possibility of impregnation from a lode or 
 dike was reduced to a minimum, no trace of gold was present, 
 even in the sulphides found. Numerous illustrations in sup- 
 port of this generalization are to be found in most of the tables. 
 
216 INFLUENCE OF COUNTRY-HOCK ON MINERAL VEINS. 
 
 No. 9. 
 Influence of Country-Rock on Mineral Veins. 
 
 BY WALTER HARVEY WEED,* WASHINGTON, D. C. 
 
 (Mexican Meeting, November, 1901. Trans., xxxi., 634.) 
 
 AMONG the many causes of that perplexing feature of mine- 
 exploitation, the unequal distribution of the ore, the influence 
 of the country-rock upon the vein-contents has long been ac- 
 cepted as an important factor in certain districts, but the gen- 
 eral application of the theory has not been proved. It is now 
 possible to obtain trustworthy data with which to test the 
 theory, and either to confirm or to overthrow this time-honored 
 tradition. By the searching methods of modern petrography 
 and chemistry, rock-determinations are now scientifically made, 
 while the examination of thin sections of ores supplements 
 field- and laboratory-study, and affords conclusive evidence of 
 the paragenesis of the ore-minerals. 
 
 In the great mass of data regarding mineral deposits accu- 
 mulated during the past century, there are some facts which 
 stand the test as to reliability ; but the greater part are not 
 available for use in this discussion. Within the last 20 years, 
 however, many able workers have contributed careful and 
 accurate accounts of various ore-deposits; and it is by the 
 facts given in such papers, and by personal experience, that I 
 have become convinced that there is in some districts a true 
 relation between the country-rock and the mineral contents of 
 the veins. 
 
 My own interest in the subject arose from the observation of 
 a number of striking instances of the variation of vein-con- 
 tents with the nature of the inclosing rock. Having already 
 recorded certain observations of this kind, I venture ( to present 
 in this paper further notes, together with a few facts from the 
 literature of the subject, which seem to prove the correctness 
 of my view. It is apparent that if the relation holds true, 
 though in limited districts only, it will be of great practical in- 
 
 * U. S. Geological Survey. 
 
INFLUENCE OF COUNTRY-ROCK ON MINERAL VEINS. 217 
 
 terest to the miner, and will confer upon the geological survey 
 of a mining-district a new value, rendering it, in fact, an almost 
 indispensable preliminary to the extensive working of large 
 properties. 
 
 The influence of the inclosing rocks upon mineral veins evi- 
 dently affects both the vein-structure and the vein-filling. The 
 first effect is physical ; the second is mineralogical or, primarily, 
 chemical. The first has been but lightly touched upon, if no- 
 ticed at all, by writers on mining-geology. The second has 
 long been recognized as a fact in a few well-known examples ; 
 but, although many attempts have been made to show a rela- 
 tionship between certain ores and definite rock-types, the corre- 
 lations have been of local value only. 
 
 I. INFLUENCE OF ROCKS ON VEIN-STRUCTURE. 
 
 It is self-evident that in most mineral deposits the rocks must 
 have been either porous or so fractured as to permit the circula- 
 tion of underground waters as a preliminary to vein-formation* 
 It is also evident that according to the varying hardness, tough- 
 ness, etc., of the rocks, the fissures found in them will vary in 
 character, and the physical aspect of any resultant ore-deposit 
 will be governed by the nature of the rock. 
 
 Fissure-veins, and, indeed, all forms of ore-deposits, are af- 
 fected in size and shape, and probably to some extent in rich- 
 ness, by the character of the fissure or fracture in which the 
 vein was formed. Experience shows that a vein often varies 
 greatly in structural characters, such as width, uniformity r 
 presence of splits and horses, etc., in passing, whether horizon- 
 tally or vertically, from one rock into another. Thus the vein 
 may pinch out in a very tough rock, expand in a more easily 
 shattered material, become dissipated into a stockwork in 
 brittle, shattered rock, or become lost entirely in a shale. In 
 easily-soluble rocks, like limestones and dolomites, the original 
 character of the fissure may be modified by solution, and thus 
 the original effects of its force may be masked. This case stands 
 in such intimate connection with the mineralogical effects due to 
 the nature of the rock that it is best considered in the .second 
 part of this paper. The irregular deposits formed in limestones 
 show the influence of the inclosing rock on the form of the 
 deposit to an even more marked degree than fissure-veins. 
 
218 
 
 INFLUENCE OF COUNTRY-ROCK ON MINERAL VEINS. 
 
 The fissures which, in traversing a tough rock, are clean cut, 
 may, in passing into a more easily fractured rock, or one netted 
 by fine jointing, produce a mass of shattered material in which 
 the mineral is so disseminated in minute and numerous fissures 
 that the entire mass must be extracted. Often the vein, solid 
 and continuous in one rock, splits up, forming horses or drop- 
 pers, or, if very extensive, becomes a zone traversed by many 
 small parallel threads and stringers, too small to be worked. 
 This is discussed by Professor Beck, in his recent book, 1 from 
 which Fig. 1 is taken. 
 
 In the Guadalupe mine, Chihuahua, Mexico, a vein, carrying 
 a solid ore from 10 to 40 ft. wide, changes eastward into many 
 small branches, too small to be worked, though the richness of 
 the ore in them may be unchanged. 
 
 FIG. 1. SCATTERING OF THE GOTTLOB VEIN IN QUARTZ-PORPHYRY, IN THE 
 DAVID SHAFT, NEAR FREIBERG, SAXONY, g, GRAY GNEISS ; p, QUARTZ- 
 PORPHYRY ; m, VEIN. 
 
 Where veins traverse foliated rocks, such as gneisses and 
 schists, the original fissures may have been due to a very slight 
 movement along the plane of schistosity, and the result may be 
 linked veins, composed of numerous connected lenses, such as 
 are commonly found in the Piedmont area of the Carolinas. If 
 the movement is distributed over several folia the vein is not a 
 simple one, but consists of a series of lenticular masses over- 
 lapping each other, and these may occur in a zone ; so that the 
 " vein " may be several hundred feet wide. 
 
 It is evident that, since different rocks break in different ways, 
 the character of the fissures formed in them will depend on 
 the country-rock. Excellent examples of the various effects 
 
 1 Lehre von cten Erzlagerstatten, p. 135 (1901). 
 
INFLUENCE OF COUNTRY- ROCK ON MINERAL VEINS. 
 
 219 
 
 due to the texture, cleavage, hardness, and other properties of 
 the rocks, are to be seen in the silver-lead mines of Neihart, 
 Mont., where steeply-dipping metamorphic rocks are cut by a 
 large and very irregular intrusion of diorite, and both are cut 
 by later intrusions of rhyolite-porphyry. Well-defined fissure- 
 veins cross all these rocks. The metamorphic rocks consist of 
 alternating bands of feldspathic gneiss with softer, more schist- 
 ose micaceous rocks, and, more rarely, tough amphibolites. 
 The veins cross these rocks at nearly right angles to the 
 schistosity. The underground workings show the veins to 
 vary somewhat in width and in the relative abundance of in- 
 cluded rock-fragments, when they pass from one belt of feld- 
 spathic gneiss to another, and more markedly when they pass 
 into the more schistose rocks ; but the change is so abrupt 
 
 Roof of level 
 
 1 clay selvage 
 \ no trace of ore 
 
 FIG. 2. SECTION OF LEVEL, SHOWING THE FLORENCE VEIN, NEIHART, MONT., 
 CROSSING AN AMPHIBOLITE DIKE IN METAMORPHIC SCHISTS. 
 
 where the amphibolites are encountered that the miners say 
 the vein is faulted. In fact, the tough nature of this rock has 
 sometimes deflected the vein, and has always, in the instances 
 observed, narrowed it from 7 to 8 ft. in width of good ore to a 
 foot or more of barren gangue. Fig. 2 2 is an example from 
 Neihart, where the veins, passing from schist into Pinto dio- 
 rite, a peculiar igneous rock of coarse grain and texture, are 
 invariably narrowed, but well defined. In the rhyolite-por- 
 phyry the same fissures lose their compact character, ramifying 
 into a network with shattered rock between, which dissipates 
 the ore ; so that, while the surface- workings are commonly 
 rich, the ore-body does not pay in depth, owing to the large 
 amount of waste. 
 
 2 From the Twentieth Annual Report, U. S. Geological Survey, Part III., p. 421 
 (1900). 
 
220 INFLUENCE OF COUNTRY-ROCK ON MINERAL VEINS. 
 
 The same phenomenon is described by De la Beche. 3 The 
 vein shown in Fig. 3 encounters an elvan dike, 6, in passing 
 from d to e, and passes up the wall of the dike, scarcely show- 
 ing as a vein alongside of the dike until it crosses the dike at c, 
 and continues on through the slates. 
 
 At Butte, Mont., the veins occur in a coarse-grained gran- 
 itic rock (a quartz-monzonite) with intrusions of aplite-granite, 
 and dikes of porphyry. Where the veins cross the porphyry 
 they are narrower to a marked degree ; and the same is true 
 of the aplite. In part this is due to a more intense metaso- 
 matic replacement of the granite than of the other rocks, a 
 fact which will be discussed in describing the influence of the 
 wall-rocks on the tilling. It is quite evident that rock char- 
 acter has influenced the fissure. 
 
 The copper-veins at Yirgilina, Ya., which occur in meta- 
 morphic schists formed from old igneous rocks, show a struc- 
 tural feature common in the veins of the Southern States where 
 
 6 
 FIG. 3. FISSURE DEFLECTED BY DIKE (DE LA BECHE). 
 
 the fissure crosses the rocks at less than 90 to the schistosity. 
 In such cases the veins show many spurs running off for short 
 distances from the vein along the planes of the schist. The 
 Blue Wing mine, at the locality mentioned, shows a diabase 
 dike cutting the schists ; and where the vein crosses this rock 
 it is narrowed and becomes a mere zone of plated rock. The 
 spurs seen in some veins in granite are evidently the result of 
 cross-fissures or joints, and not to be considered as a function 
 of the rock itself. 
 
 Where the veins pass from schists into quartzite, as may be 
 seen at Neihart, there is a marked change in their character. 
 This is well seen at the Big Seven mine, where a well-defined 
 vein changes to many small fissures with shattered rock be- 
 tween. At French town, a small settlement east of Deer Lodge, 
 Mont., the veins in andesite-porphyry are strong and well-de- 
 
 3 Geological Observer, p. 657 (1851 ed. ). 
 
INFLUENCE OF COUNTRY-ROCK ON MINERAL VEINS. 221 
 
 iined fissures, but do not cut any other rock; hence direct 
 comparison cannot be made. At the Porphyry Dike mine, 
 south of Rimini, Mont., the veins are small and tight in the 
 granite, and open out in the rhyolite into wide fissures, ill-de- 
 fined, and really more like bands of shattered rock. 
 
 This variation of fissures in different rocks is especially well 
 shown at Cripple Creek, Colo., as described by Penrose, 4 and 
 alluded to by Van Hise. 5 In hard rock the fissures are sharp 
 and clean-cut breaks, but in the soft rock they are ordinarily 
 mere series of very small cracks, constituting what Van Hise 
 calls " distributive " faults. 
 
 In slates the vein is commonly well defined, as at Copper- 
 opolis in Montana, and Parral, Mexico. In the Cceur d'Alene, 
 in Idaho, the veins cross slates and quartzites, and present only 
 those minor peculiarities which might be expected in passing 
 through such rocks in fact, there is less change than one 
 would naturally look for. 
 
 Throughout the Appalachians the veins show a clustering of 
 quartz lenses whose ends overlap. These have been called 
 "linked veins" by Becker, and "compression-veins" by Stretch. 
 That they are the result of the foliation of the schists is gener- 
 ally accepted. Where the lenses are parallel to the foliation 
 there is reason to believe that they are a result of the spreading 
 apart of the folia by movement. When the quartz lenticules lie 
 across the vein, as they often do in the Carolinian veins, present- 
 ing the structure figured by Rickard 6 for the Victorian veins, it 
 seems that the quartz-filled spaces result from a rending of the 
 rock between two parallel fissures. Many of the minor pecu- 
 liarities of vein-walls are due to the character of the rocks, but 
 these are not intended to be treated here. Rickard has already 
 described many features of vein-walls due to varying rocks. 
 
 The study of a large number of mines all over the country 
 shows that, although no rule can be laid down for all localities, 
 each district will present certain peculiarities. In Montana, 
 the rhyolites are not favorable for well-defined constant veins, 
 as the rock is too easily shattered. The granular rocks vary in 
 
 * Mining Geology of Cripple Creek District, Sixteenth Annual Report, U. S. 
 Geological Survey, Part I., p. 144 (1894-95). 
 
 5 "Some Principles," etc., Trans., xxx., 35 (1900). 
 
 6 Trans., xxi., 686-713 (1892-93). 
 
222 INFLUENCE OF COUNTRY-ROCK ON MINERAL VEINS. 
 
 effect; and the more basic forms, carrying augite or horn- 
 blende, are favorable for well-defined fissures. 
 
 As it is not my intention to do more than call attention to 
 the differences in fissuring in varying rocks, no further men- 
 tion of such peculiarities will be presented here. It is evident, 
 however, that where a single mass of rock varies in texture, as, 
 for example, the granite core of Castle Mountain, 7 Mont., in 
 which continuous exposures show the rock passing from gran- 
 ite through intermediate gradations into rhyolite-porphyry, the 
 vein-fissures will vary with the physical characters of the rock. 
 
 II. INFLUENCE OF COUNTRY-ROCK ON VEIN-FILLING. 
 
 Where a vein, passing through two different rocks, carries 
 one set of ore- and gangue-minerals in one rock, and another 
 set in the other, there is a strong presumption that the varia- 
 tion in the inclosing rock has caused the variation in the vein- 
 materials. Similarly, if in given districts one set of vein-min- 
 erals always occurs with a certain kind of country-rock, and 
 another set with another kind, it is probable that such associa- 
 tion is genetic, and not accidental. 
 
 For many years there has been a widespread belief among 
 mining-geologists and engineers that igneous rocks are an al- 
 most invariable accompaniment of productive ore-deposits of 
 the precious metals. Whether the igneous rocks be regarded 
 as the actual source of the metal, or as the cause of fissuring 
 and ore-deposition by reason of dynamic disturbance, the re- 
 sult is genetically due to the volcanic forces. Professor Yogt 
 has recently given us, in his able and instructive paper, 8 a 
 resume of his studies, and Professor Kemp has shown 9 both the 
 competency of the igneous rocks themselves as a source of 
 supply and of the intrusives as a source of energy. It is not 
 this phase of the subject that I propose to discuss, but the time- 
 honored question of the influence of wall-rock upon the mineral 
 contents of the vein. Many students of ore-deposits, familiar 
 with the common occurrence of galena-ores in limestone, and 
 the changes in mineral character of the Cornish veins with 
 
 7 Weed and Pirsson, Geology of the Castle Mountain Mining District, Bulletin 
 No. 139, U. S. Geological Survey (1896). 
 
 8 Problems in the Geology of Ore-Deposits, Trans., xxxi., 125 (1901). 
 
 9 K61e of the Igneous Rocks, etc., Trans., xxxi., 159 (1901). 
 
INFLUENCE OF COUNTRY-ROCK ON MINERAL VEINS. 223 
 
 change of rock, have sought to establish a relation between 
 certain rocks and certain ores. While such a relation seems to 
 prevail in a few districts, no general law has been established 
 by these attempts. 
 
 Conditions Governing the Relation of Country-Rock to Vein- 
 Contents. 
 
 In considering the relations between country-rock and vein- 
 contents, the following premises are assumed : 
 
 1. Vein-filling may be the result (a) of the filling of open 
 fissures, (b) of replacement, or (c) of both filling and replace- 
 ment. 
 
 2. The ore- and gangue-minerals of all these types vary. 
 Lindgren has divided veins filled by metasomatic replacement 
 into 11 classes, and shows that the chemical processes in- 
 volved were very different in each case. It is made certain by 
 the study of altered wall-rocks and of mine-waters that the 
 mineral-forming solutions have varied greatly in character. 
 Moreover, some veins have been opened after formation, and 
 new minerals have been introduced by later solutions. 
 
 In veins the material of which is well crustified, or is known 
 to be the result of the filling of open fissures, a marked influ- 
 ence of the wall-rock on the contents of the vein would not be 
 expected. In the majority of veins, however, there is evidence 
 of more or less metasomatic replacement; and it is evident 
 that the nature of the wall-rock will be an important factor in 
 the chemical reactions of the processes of replacement. It should 
 be remembered, however, that the evidence of many districts 
 shows that veins of different kinds and ages may form in the 
 same rock, and hence it is not to be expected that any general 
 conclusions, applicable to all veins, can ever be reached. 
 
 Examples. 
 
 Butte, Mont. In the typical silver-veins of this district the 
 filling consists of quartz, showing well-marked " comb "-struc- 
 ture, with rhodonite, rhodochrosite, pyrite, zinc-blende, and sil- 
 ver sulphides. The structure is clearly that of the filling of 
 open fissures. These veins occur in the normal Butte granite, 
 a quartz-monzonite, and in the Bluebird granite, which is an 
 aplite. There is, however, no perceptible difference in either 
 
-224 INFLUENCE OF COUNTRY-ROCK ON MINERAL VEINS. 
 
 the character or the tenor of the ore between the veins in 
 the aplite and those in the normal granite, or in the parts of 
 the same vein where it cuts the two rocks. In the copper- 
 veins, on the other hand, there is a marked difference. These 
 -are of undoubted metasomatic origin, and were formed by the 
 replacement of the rock along fracture-planes. In the copper- 
 area, the veins cut both the two rocks previously mentioned 
 and also a quartz-porphyry, which I have named the Modoc 
 porphyry. In the Butte granite, the veins are commonly rich 
 in copper; in the Bluebird granite, they are almost equally 
 wide and strong, but are lean, and composed chiefly of quartz, 
 with comparatively little pyrite and copper. In the porphyry, 
 the veins are narrow and lean. There are so many instances 
 in which the same veins can be seen cutting all three rocks 
 that there can be no doubt as to the correctness of these con- 
 clusions. The vein-filling consists of quartz which shows no 
 comb-structure, with pyrite and various copper-minerals, of 
 which chalcocite, enargite, and bornite are the most common. 
 The walls on each side are much altered, and the less altered 
 rocks at some distance from the veins show the ferro-magnesian 
 silicates altered to pyrite. The relative richness of the veins 
 in the Butte granite is believed to be due to the basic character 
 of the rock, and its greater content of the easily-replaceable iron 
 silicates. The rock is a quartz-monzonite, the composition of 
 which has been carefully calculated from chemical analyses of 
 the rock, and of the biotite and hornblende isolated from" it, 
 and from microscopic analysis of the rock as well. 10 These 
 show it to contain 15.26 per cent, of hornblende and 4.22 of 
 biotite. There is a little augite also. The aplite contains over 
 10 per cent, more silica than the rock just noted, no hornblende, 
 and very little biotite. The Modoc porphyry also has, when 
 fresh, a very little mica, and is as high in silica as the aplite. 
 H. Y. Winchell has called my attention to the condition shown 
 in the diagram, Fig. 4. In the case here given as a general 
 type, the vein is workable only in the Butte granite. 
 
 A study of thin sections of the rock adjacent to the ore shows 
 that the hornblende is the first mineral to be altered into ore, 
 -and that the bunches of this mineral form the nucleus for a 
 
 10 Granite Kocks of Butte, Mont. W. H. Weed, Journal of Geology, vol. vii., 
 JNo. 8, p. 737 (Nov. -Dec., 1899). 
 
INFLUENCE OF COUNTRY-ROCK ON MINERAL VEINS. 
 
 225 
 
 more or less complete replacement of the entire rock. The 
 general principles of this metasomatic replacement are those 
 given by Lindgren. 11 It is probable that the alteration now 
 seen in the wall-rock, with its nests of pyrite replacing the 
 biotite and the hornblende, may present the earlier stages of 
 the metasomatic process, and that the pyrite thus formed was 
 not only the nucleus for a further deposition of pyrite, but that 
 the pyrite itself was the ' precipitating-agent for the copper- 
 minerals, as has been shown to be the case in the secondary 
 enriched ores. In the aplite there is more quartz and less 
 pyrite, and the latter mineral is noticeably poor in copper. The 
 same general statement also holds true for the porphyry. 
 
 Granite 
 
 K**v/~;l Aplite 
 
 FIG. 4. IDEAL PLAN OF CONDITIONS IN A COPPER- VEIN AT BUTTE, MONT., 
 
 PASSING FROM BASIC GRANITE INTO APLITE MASSES. 
 The solid black represents high-grade copper-ore, when the vein is in basic granite. 
 
 The Dolcoath mine of Cornwall is perhaps the best-known 
 example of a vein, the mineral contents of which vary with the 
 nature of the inclosing rocks. As described by many writers, 
 the veins carry copper-ores in slate and tin-ores in granite. 
 Stretch 12 gives a further example of argentiferous galena with 
 its usual associated blende and pyrite in a decomposed plagio- 
 clase porphyry, changing to auriferous arsenopyrite in the 
 underlying granite. 
 
 Cornwall. Fissures crossing the contact of granite or other 
 intrusive rock with sedimentary rocks are not uncommonly 
 productive, when the district is metalliferous. This is very 
 marked in the Cornwall mines, where bunches of ore occur at 
 
 11 Metasomatic Processes in Fissure- Veins, Trans., xxx., 578 (1900). 
 
 12 Prospecting, Locating, and Valuing Mines, p. 135 (1899). 
 
 15 
 
226 
 
 INFLUENCE OF COUNTRY-ROCK ON MINERAL VEINS. 
 
 the junction of granite and schist. De la Beche 13 mentions 
 fissures traversing schists and passing through a dike of por- 
 phyry (elvan) some 300 ft. thick. The vein above the dike 
 carried little ore ; in the elvan, ore was abundant and rich, but 
 became poor again in the slates beneath (Fig. 5). This occur- 
 rence of ore-bunches where fissure-veins cross such dikes has 
 always been known to the Cornish miners. When the lodes 
 pass into the dikes, they are often branched and split, as shown 
 in Figs. 3 and 6 (after De la Beche); and in such cases, though 
 the total amount and richness of ore be the same, the vein may 
 not pay to work, on account of the large amount of waste. 
 
 Pontgibaud, France. Here the silver-lead veins occur along 
 fractures within granulite dikes, and on the line of contact 
 with the gneiss country. 
 
 FIG. 5. SECTION ACROSS WHEAL 
 ALFRED GWINEAR, CORNWALL. 
 RICH ORE OCCURS IN THE DlKE 
 ONLY. (FROM DE LA BECHE. ) 
 
 FIG. 6. VEIN SPLIT IN TRAVERSING 
 JOINTED " ELVAN " DIKE (Ds LA 
 BECHE). 
 
 " When the dike diminishes in size the vein decreases in width ; when the 
 vein penetrates the gneiss the ore disappears. The best ore is associated with the 
 kaolinization of the feldspar of the granulite ; when the latter becomes hard, un- 
 altered in depth, the ore pinches out." u 
 
 Rico, Colo. Bickard also mentions the veins of rich gold- 
 and silver-ores at Newman hill, Rico, Colo., as " noticeably 
 affected by the character of their rock-walls." There is a 
 marked change in passing from limestone into sandstone ; and 
 generally the veins are richest in the darker-colored sedi- 
 mentary rocks. The interdependence between country-rock 
 and ore is briefly discussed by Bickard, who adopts Cotta's ex- 
 planation that the physical texture and chemical composition 
 
 13 Geological Observer, p. 678 (1851 ed. ). 
 
 14 T. A. Rickard, Vein Walls, Trams., xxvi., 200 (1897). 
 
INFLUENCE OF COUNTRY-ROCK ON MINERAL VEINS. 
 
 227 
 
 of the country-rock affect the deposition of ore, and declares 
 that it was undoubtedly the carbonaceous matter of the rock 
 at Rico which acted as a precipitant. This example differs, 
 therefore, from that of Pontgibaud, where feldspar has been 
 replaced by silver-bearing galena. 
 
 Neihari, Mont. At this locality the veins show a remark- 
 able variation in richness, corresponding to differences in the 
 wall-rock. Robert H. Raymond, the former manager of the 
 Diamond R. properties, found that the veins were barren in 
 the dark-colored gneisses, and held ore-bodies in the pink or 
 white feldspathic gneiss. My own observations enabled me to 
 confirm this in a general way, and also showed that in amphib- 
 olite the vein was barren as well as narrow, and that no work- 
 
 Pinto diorite; no ore. 
 
 Gray gneiss: pay ore. 
 
 Black gneiss; no ore. 
 
 3d gneiss; good ore. 
 
 Dark-gray schist; no or^, 
 
 FIG. 7. DIAGRAM (PLAN) SHOWING KOCKS TRAVERSED BY THE NEIHART 
 VEINS, AND RELATION OF PAY-OKE TO COUNTRY-ROCK. (The veins are 
 indicated by simple parallel lines. ) 
 
 able ore-bodies had been found in the diorite. In quartzite 
 and in the intrusive rhyolite-porphyry the veins have proved 
 rich near the surface, but the values have gone down but a few 
 yards. It is believed, however, that this is because of struc- 
 tural conditions, with secondary enrichment of a shattered 
 zone, rather than because of a mineralogical condition due to 
 the nature of the inclosing rock. These conditions are indi- 
 cated in Fig. 7, reproduced from the report on the district. 15 
 
 Furstenburg. A similar example is quoted from Fournet by 
 De la Beche. 16 The Wenzal vein at Furstenburg is nearly 
 
 15 Geology of the Little Belt Mountains, Montana, Twentieth Annual Report, U. 
 S. Geological Survey, Part III., p. 419 (1900). 
 
 16 Geological Observer, p. 680 (1851 ed.). 
 
228 INFLUENCE OF COUNTRY-ROCK ON MINERAL VEINS. 
 
 vertical and cuts down through many beds of gneiss, about 60 
 ft. thick, that dip east. In the micaceous gneiss the vein is a 
 nearly-imperceptible string of clay. In argillaceous slates it 
 suddenly becomes from 12 to 18 in. thick, consisting of baryta, 
 ruby-silver, large masses of antimonial silver, and argentiferous 
 gray copper. In the hornblende-gneiss it continues, but the 
 silver-ores are wanting and galena is the only ore. In the 
 fourth series, of slightly micaceous beds of gneiss, the silver- 
 ores are as abundant as in the argillaceous slates ; but they 
 gradually disappear in depth, being replaced by selenite and 
 galena. 
 
 It will be noted that the Neihart veins present several con- 
 tradictions to the rule observed in the Butte district. The ores 
 occur in the feldspathic rocks, carrying little ferro-magnesian 
 minerals. The basic amphibolite and the diorite are both bar- 
 ren. It should be noticed also, in this connection, that the ore- 
 depositing solutions were markedly different in the two cases. 
 In the Neihart veins the gangue is mainly a mixture of carbon- 
 ates of lime, iron, and manganese. The ores are also markedly 
 different, as they consist primarily of galena with sphalerite 
 and pyrite, which is secondarily enriched in the upper parts of 
 some veins. The solutions have been of such a character as to 
 react with the feldspars rather than with the ferro-magnesian 
 silicates. 
 
 Other Montana Localities. In the silver-lead camp of Barker 
 in the Little Belt mountains, near Neihart, as at the mines at 
 Castle, Mont., and a score of other places where the ores occur 
 in limestone, it is evident that different action has taken place. 
 Here, as is so very commonly the case, the ore-bodies occur in 
 limestone near the contact with igneous intrusions. The heat 
 of the latter and the vapors of the cooling magma have altered 
 these limestones to more or less coarse-grained marbles, if the 
 limestones were pure, or to mixtures of garnet, epidote, and 
 other silicates, if the limestones were impure. The latter is 
 the case at the Trout mine and other contact ore-bodies near 
 Philipsburg, Mont., where the Granite Mountain vein (of ^quite 
 different and drier ore, without lead) occurs in the granite. 
 In this case the gangue is largely silica; and it is probable that 
 similar solutions circulating as a result of the heat supplied by 
 the igneous intrusion, and, in part, at least, in fissures formed 
 
INFLUENCE OF COUNTRY-ROCK ON MINERAL VEINS. 229 
 
 in rocks by the intrusion, formed one set of ores in the lime- 
 stone and another in the granite. 
 
 Another instance of the difference of mineral contents in 
 the same ore-deposit in different rocks is shown by the Elk- 
 horn mine at the town of that name, Jefferson county, Mont. 
 This deposit is peculiar in its structural relations, being similar 
 to the well-known saddle-reefs of Australia in that it occurs in 
 a saddle-shaped mass along the axis of a steeply-pitching anti- 
 clinal fold. The rocks are sedimentary, of probable Cambrian 
 age, and dip at steep angles towards the contact of a great mass 
 of granite and other intrusive igneous rocks. The ore occurs 
 at the contact between an altered shale and a massive crystal- 
 line limestone, and both rocks have been changed by contact- 
 metamorphism. The bedding-plane is ore-bearing only where 
 the general dip of the rocks is disturbed by flexures. In addi- 
 tion to the ore found along the contact, a number of very large 
 ore-bodies have been found at some little distance in the dolo- 
 mite, though always in the same structural position. The ore 
 found along the altered shale-dolomite contact is essentially a 
 "dry" quartzose milling-ore; that of the dolomite, mainly 
 galena, with accessory sphalerite and pyrite. Both ores are 
 connected by " pipes " and stringers, and both the field- and 
 the microscopic evidence shows that they were formed by the 
 same solutions and at the same time. There is no escape from 
 the conclusion that the difference in the mineralogical char- 
 acter of the ores is the result of the different nature of the in- 
 closing rock. 
 
 It would be tedious to enumerate all the familiar deposits in 
 limestone. Those of Leadville, Colo., and Eureka, Nev., have 
 been thoroughly studied 'and described. Tombstone, Ariz., 
 presents quartzose veins filling fault-fissures, cutting slightly- 
 tilted sedimentary rocks, with the workable ore-bodies formed 
 by replacement of limestone along bedding-planes, and pre- 
 sumably by the same solutions that filled the fissures. 
 
 Derbyshire. The Derbyshire lead-mines of England are also 
 well-known examples of veins carrying galena in limestone, and 
 barren when in the intercalated intrusive trap-rocks (toadstone). 
 Fig. 8, from De la Beche, illustrates the occurrence of galena 
 in the limestones above and below an intrusive sheet in one of 
 the Derbyshire mines. The leader or fissure traverses the 
 
230 INFLUENCE OF COUNTRY-ROCK ON MINERAL VEINS. 
 
 " toadstone " as well as the lime-rock, but it is only in the 
 limestone that galena occurs in the altered area. The channels 
 or rakes (g i, a k, c m,) were fissures, through which solutions 
 reached the pipes or ore-bunches, p p, the bedding-plane de- 
 posits,//, and the joint-deposits, h h. 
 
 Contact-Deposits. 
 
 As Lindgren has remarked in discussing the formation of 
 contact-deposits, a chemical reaction seems to take place be- 
 tween the substances leaving the magma and the carbonate of 
 lime, causing the deposition of new minerals and the liberation 
 of carbon dioxide. In the cases mentioned in this paper, the 
 evidence shows that the veins were probably formed, not by 
 true pneumatolytic action, but by hot circulating waters which 
 were as truly a result of the igneous intrusion as the vapors 
 and gases of pneumatolytic action. The escaping vapors and 
 gases from the magma were, it is believed, taken up by circu- 
 
 FIG. 8. LIMESTONE BEDS OF DERBYSHIRE, WITH INTERCALATED BEDS OF 
 IGNEOUS ROCK (TOADSTONE) TRAVERSED BY VEINS. (Ds LA BECHE.) 
 
 lating waters of either deep-seated or meteoric origin, so that 
 the " mineralizing-agents " which had taken up and formed 
 the volatile compound of various metals, as supposed by Lind- 
 gren, passed into solution. Concerning the occurrence of this 
 class of deposits in limestone, Mr. Emmons's description of the 
 Greenwood ores is quite significant. He says: " The ore- 
 bodies are cut by eruptive dikes that do not apparently disturb 
 or exert any metamorphic influence on the ore, and yet are not at 
 all mineralized themselves;" At a number of localities seen 
 by the writer, the veins, if traced into the granite or diorite, 
 would be found to be barren of galena, and generally without 
 value. On the other hand, at Marysville, Mont, the veins 
 show no appreciable change in character in passing through 
 the altered shales or hornstones into the granite. It should 
 be noted, however, that the ores at this place are .not kad- 
 
INFLUENCE OF COUNTRY-ROCK ON MINERAL VEINS. 231 
 
 bearing. Moreover, I am told by G. H. Robinson, the former 
 manager of the mine, that in the earlier workings the veins 
 showed a marked tendency to be richer in approaching the 
 granite (or rather diorite) contact, and were poor when they 
 passed into the granite. 
 
 Thunder Bay Silver- Veins. H. V. Winch ell tells me that 
 the Thunder Bay district of Canada affords excellent examples 
 of vein-variation in different rocks. The basaltic caps and sills 
 of that region overlie Animikie slates and argillites, resting in 
 turn upon taconites and several hundred feet of cherts. These 
 rocks rest upon the basal quartzite overlying the Archaean com- 
 plex. The silver-veins are often from 8 to 10 ft. wide in the 
 slates, and carry native silver and argentite with small amounts 
 of blende, galena, and pyrite, in a gangue of quartz, barite, 
 calcite, fluorite, etc. They are wide and productive in the 
 slates, but split up into narrow and barren seams in the over- 
 lying trap-rock, and are barren in the underlying cherts and 
 Archaean rocks. The Rabbit, Silver Mountain, Beaver, and 
 other mines have been noted producers. 
 
 Kemp 17 describes the Silver Islet mine as a fissure-vein car- 
 rying native silver, argentite, tetrahedrite, galena, blende, and 
 nickel and cobalt compounds in a calcite gangue. The vein is 
 in flags and shales of the Animikie series (Algonkian) and cuts 
 a large trap dike (gabbro), within which alone the vein is pro- 
 ductive. 
 
 Influence of Carbonaceous Matter on the Formation of Ore. 
 
 The well-known reducing action of carbon has long been an 
 accepted explanation of the occurrence of ore-bodies in car- 
 bonaceous shales. The silver-veins of the Animikie slate are 
 often cited as examples. The Australian veins, which carry 
 rich gold-ores only where they cross " indicators," are a 
 well-known instance, and the Fahlbands of Norway another. 
 Rickard ascribes the Australian ore-bodies to the reducing 
 action of the carbonaceous shales. All the descriptions show, 
 however, that although these indicator-reefs are strata of car- 
 bonaceous shale, they are remarkable for the amount of pyrite 
 they contain, while other shale-beds crossed by the veins are 
 also carbonaceous, but not pyritic. In previously-published 
 
 17 Ore-Deposits, 3ded., p. 283 (1900). 
 
232 INFLUENCE OF COUNTRY-ROCK ON MINERAL VEINS. 
 
 papers I have called attention to the reducing action of pyrite 
 on solutions carrying copper-salts ; and believe that this min- 
 eral is the real precipitating-agent in both the Australian and 
 Norwegian ores cited. This view, based upon field-observa- 
 tions and laboratory-experiments, in connection with the work 
 of the U. S. Geological Survey, is strengthened by the experi- 
 ments made under the direction of my friend, H. V. Winchell, 
 geologist of the Anaconda Copper Co., who finds that the 
 mine-waters of that company's properties, though strongly 
 charged with cupric sulphate and ferric sulphate, also contain 
 large amounts of carbonaceous matter from the old mine-tim- 
 bers. It is evident that if the carbon were an active reducing- 
 agent, it would reduce the ferric iron to the ferrous condi- 
 tion. On the other hand, experiments show that pyrite from 
 the Butte veins left for several weeks in the natural mine- 
 waters became coated with copper-glance (Cu 2 S). 
 
 Dependence of Vein-Minerals on the Character of Wall-Rock, Due 
 to Metasomatic Chemical Reactions. 
 
 The examples given show that a variation of mineral contents 
 coincides with the change of country-rock in many places and 
 in many kinds of veins. A study of the vein- and gangue- 
 minerals and of the rock contiguous to the ore-bearing fissures 
 is therefore essential to a complete understanding of the origin 
 of ore-deposits. The rocks forming the vein-walls are com- 
 monly altered. Where no such alteration is observable, it will 
 usually be found that the veins are the result of the filling of 
 cavities, and are thus excluded from the category discussed in 
 this paper. Nevertheless, some metasomatic alteration of the 
 rock adjacent to the fissure is usually present; and it must be 
 admitted that many veins show evidence both of the filling of 
 open cavities and of deposition by replacement. 
 
 As already indicated, the coincident variation of mineral 
 contents and wall-rock is due to metasomatic action, whereby 
 there is a chemical interchange between the rock and the vein- 
 producing solutions. The metasomatic process varies greatly 
 because the solutions vary. Lindgren 18 has treated the subject 
 fully, and has indicated the chemistry of the process, so that a 
 detailed account of the reactions involved is unnecessary here. 
 
 18 Metasomatic Processes in Fissure- Veins, Trans., xxx., 578 (1900). 
 
INFLUENCE OF COUNTRY-ROCK ON MINERAL VEINS. 233- 
 
 According to his clear demonstration, the alteration of the same 
 kind of wall-rock shows that the vein-forming solutions have 
 varied greatly in their chemical effect upon vein-contents, even 
 where the veins are of metasomatic origin. 
 
 The most frequent process seems to be, in granitic rocks, a 
 reaction between the ferro-magnesian minerals, such as augite r 
 hornblende, biotite, etc., and the vein-forming solutions, with 
 the formation of pyrites and other sulphides. If later recon- 
 centration occurs, bonanzas are formed by reaction of the 
 pyrites on later solutions. This process I have treated quite 
 fully in a monograph now in preparation on the Butte ore- 
 deposits. 
 
 In other cases, the feldspars are attacked, and the iron-min- 
 erals of the rock are not replaced. Such a case is described by 
 R. C. Hills ; 19 and Rickard ascribes the silver-lead ores of 
 Pontgibaud, France, to the replacement of the feldspars of 
 granulite, as already quoted. 
 
 The attempt to tabulate the relation between vein-contents 
 and country-rock has been made by various writers, and lately 
 by Stretch. The latter author, in his very interesting essay, 20 
 has given 139 occurrences, and attempted to eliminate the per- 
 sonal equation of the observer. It is evident, however, that 
 existing literature is not adequate for such work. Too often 
 the rocks are wrongly named, or receive generic terms only. 
 The words "granite" and " porphyry" have long been used 
 in a textural sense by mining engineers, and by many geolo- 
 gists unfamiliar with petrographic distinctions ; and, as is well 
 known, shales, limestones, and sandstones grade into one an- 
 other. For the careful study of metasomatic replacement, 
 which must be made to establish scientifically a relation be- 
 tween country-rock and vein-filling, finer distinctions must be 
 made. The granitic rocks of some writers include gabbros, 
 diorites, granite, and aplite, with a wide range of mineral and 
 chemical compositions. The most that can be attempted at 
 present is to present the known facts of occurrence in deposits 
 about which there can be no doubt, or which have been care- 
 fully studied. The facts here set forth show the advantages of 
 geological examination of the district about a mine, especially 
 
 19 Proceedings of the Colorado Scientific Society, vol. i., p. 20. 
 
 20 Pocket-Book for Prospecting, Locating, and Valuing Mines (1900). 
 
234 INFLUENCE OF COUNTRY-BOCK ON MINERAL VEINS. 
 
 of the area containing the vein. It is evident that it is im- 
 portant to ascertain the extent laterally and the probable extent 
 vertically of the rock in which the ore occurs ; and, if other 
 rocks occur, what they are and what effect, if any, they will 
 have on the vein-fissure and vein-filling. Such associations 
 have long been recognized in a rough way by the miners, who 
 say "that mineral will not live long in such a rock." The in- 
 stances noted in the literature of ore-deposits are few, compared 
 to those actually encountered in mining-operations, where the 
 character of the vein has changed in depth. Such change is, 
 it is true, very often due to secondary alteration, with or with- 
 out reconcentration and enrichment of material, but in many 
 cases it is probably due to change of rock. 
 
 CONCLUSIONS. 
 
 From the evidence presented the following conclusions are 
 drawn : 
 
 1. The structural characters of vein-fissures, such as course, 
 width, etc., vary with the nature of the country-rock. 
 
 2. The mineral contents of veins formed wholly by the fill- 
 ing of open fissures are not affected by the nature of the vein- 
 walls. 
 
 3. The mineral contents of ore-deposits formed by metaso- 
 matic replacement vary with the nature of the inclosing rock. 
 
 4. As metasomatic processes vary in character with the na- 
 ture of the solutions, no invariable general relation can be 
 established between certain rock-types and rich ore-deposits. 
 
IGNEOUS ROCKS AND CIRCULATING WATERS. 235 
 
 No. 10. 
 
 Igneous Rocks and Circulating 'Waters as Factors in Ore- 
 Deposition. 
 
 BY J. F. KEMP, NEW YORK, N. Y. 
 (New Haven Meeting, October, 1902. Trans., xxxiii., 699.) 
 
 IN submitting an additional contribution to the discussion on 
 ore-deposits in the recent volumes of the Transactions, it is my 
 desire to adhere closely to matters of material importance as 
 affecting the actual processes. Judging from the discussion by 
 Professor Van Hise, and from one or two reviews or other arti- 
 cles by associates of his in geological work, the impression 
 seems to prevail that, in so far as my paper* referred to his 
 masterly essay, f I was guilty of misconceptions regarding both 
 the part attributed by him in it to the igneous rocks and the 
 ubiquitous presence of the ground-water. I should regret ex- 
 tremely to be wanting in these particulars or to have misun- 
 derstood one for whose great services in this and other branches 
 of geology no one has a higher esteem than myself. I have, 
 however, in the most careful way, and with these points in 
 mind, read his essay again, and, taking it as a whole, I can- 
 not gain any different impression of relative magnitudes than 
 the one first received. The importance of the igneous phe- 
 nomena and the restrictive influence of the processes described 
 by " cementation " in their effect upon the ground-water, as set 
 forth in Professor Van Hise's " Discussion " ( Trans., xxxi., 292), 
 impress me as being in very marked contrast with the same 
 things in his first essay. If the point seems to anyone of suffi- 
 cient importance, it can easily be decided by reading the origi- 
 nals. My paper was the result of some years of observation, 
 reading and reflection, and was meant to be an independent 
 contribution, controversial only in some subordinate particu- 
 lars. In depicting the drama of the deposition of ores, I can- 
 not but feel that Professor Van Hise assigned to the chorus and 
 the scene-shifters some characters which, it seems to me, should 
 
 * "The Role of the Igneous Rocks in the Formation of Veins," by J. F. 
 Kemp, Trans., xxxi., 169, and Genesis of Ore-Deposits, p. 681. 
 
 f "Some Principles Controlling the Deposition of Ores," by C. R. Van Hise, 
 Trans., xxx., 27, and Genesis of Ore-Deposits, p. 282. 
 
236 IGNEOUS ROCKS AND CIRCULATING WATERS. 
 
 have been among the leading parts. This is not to imply that 
 the chorus or the supernumeraries are unimportant or unessen- 
 tial members of the cast. On the contrary, no presentation could 
 be given without them ; and the earnest student of the text of 
 dramas will quite invariably find them mentioned in the incon- 
 spicuous way appropriate to their modest station. 
 
 Still, psychology on the surface of the earth does not ma- 
 terially affect the production of veins in the depths ; and, with 
 this preliminary clearing of the ground, points of more conse- 
 quence may be taken up. All veins and replacements, and the 
 greater number of contact-deposits, must have been produced 
 through the agency of underground water aided by auxiliary 
 reagents and heat. No sensible man can doubt this. Unques- 
 tionably, moreover, where there is a continuous column of 
 water possessing " head " and operating through sufficiently 
 open channels, circulation will ensue. The underground water 
 and related solvents must be derived either (A) from the 
 emissions of eruptive rocks or (B) from meteoric sources, pos- 
 sibly during sedimentation. When the latter, the heat which 
 is essential to promote circulation must come (IB) from the 
 crushing and frictional rubbing of particles or similar dynamic 
 causes in rocks, or from chemical reactions ; (2B) from the 
 normal increase of temperature with depth ; or (3B) from igne- 
 ous intrusions. (Compare "Principles, etc.," Trans., xxx., 49. 
 Much the same appears in the writer's " Ore-Deposits of the 
 U. S. and Canada," 3d ed., pp. 26 and 27, 1901.) The discus- 
 sion of these several topics will, I believe, cover the debatable 
 points. 
 
 A. Emissions of eruptive rocks. This point has been dis- 
 cussed briefly in the first part of my former paper, and I am 
 led to believe that it deserves all the importance which is there 
 given it. A citation from the Zeitschrift fur praktische Geologic 
 for October, 1901, p. 383, bears on this point. The original in 
 the " Echo " is inaccessible to me. 
 
 "The gases which are emitted by the plutonic rocks, when the latter are 
 strongly heated, present a subject of notable interest in so far as it is necessary to 
 believe that a part of them were enclosed in the rocks at great pressure at the 
 time of consolidation. According to the ' Echo,' Armand Gautier has submitted 
 to strong ignition a number of rocks which had crystallized at high temperatures 
 and pressures. From each 100 volumes of the following varieties he obtained at 
 
IGNEOUS ROCKS AND CIRCULATING WATERS. 237 
 
 a red heat the stated volumes of gases : granite, 670 ; ophite, 760 ; porphyry, 
 740. 8ince we must believe that these rocks, while beneath the surface, were 
 often heated to similar temperatures, which are below those prevailing at their 
 time of consolidation, it is clear that the results possess an important bearing 
 upon the question of the production of the volcanic gases and of those dissolved 
 in hot-springs. If we give due weight to the expansive power which these rock- 
 gases must develop whenever the pressure upon the heated rock in the interior of 
 the earth permits, we see that the old theory of the production of volcanic out- 
 breaks by the introduction of water is no longer necessary. By a stall stronger 
 ignition the volume of the emitted gases appreciably increases. At 1000 degrees 
 (centigrade) granite affords, according to the calculation, 20 times its own volume 
 of various gases, besides 89 times its volume of steam ; that is, more than 100 
 times its own volume of gases and vapors. When one realizes the explosive power 
 which this implies, one may dismiss the introduction of surface waters into the 
 glowing reservoirs of rock from the theories of volcanic action." 
 
 I will, however, bring these matters in as important factors in 
 the production and circulation of underground waters and the 
 formation of ores ; and, so long as their original presence in the 
 igneous rocks is admitted, it is a matter of small moment, in 
 this connection, whether the magmas are brought up into the 
 zone of circulating waters by gravity, according to the views 
 of Dutton, Gilbert and Van Hise, or by the exhaustive force of 
 the once occluded vapors themselves, as other authorities of 
 equal weight maintain. 
 
 The general conception also gains much support from what 
 we know of the contact-deposits which are found on the bor- 
 ders of eruptive rocks and limestones. Mr. Lindgren's paper* 
 bears on this subject. I have recently had the opportunity to 
 study one of the largest of the Mexican cases, and it seems to 
 corroborate the derivation of ores directly from a magma. In 
 the course of the intrusion of a series of eruptives at San 
 Jose, Tamaulipas (which will be soon described in detail by 
 my assistant, Mr. George I. Finlay), about midway in time, 
 there came a laccolithic mass of andesitic rock which embraced 
 in itself huge masses of Cretaceous limestone. It has produced 
 contact-zones of garnet-rock, with magnetite, a little specular 
 hematite, and great quantities of pyrite and chalcopyrite. All 
 these must be considered to be the products of contact-meta- 
 morphism, and, except in the matter of certain minor re- 
 arrangements, there is no reason to think that meteoric waters 
 
 * " The Character and Genesis of Certain Contact-Deposits," by W. Lindgren, 
 Trans., xxxi., 226, and Genesis of Ore-Deposits, p. 716. 
 
238 IGNEOUS ROCKS AND CIRCULATING WATERS. 
 
 have had any share in their production. The limestone, which 
 is quite pure, yielding over 50 per cent, of CaO, as I under- 
 stand from the smelter-records, has been changed to garnet 
 with something like 15 per cent, of CaO. There must have, 
 therefore, been an enormous emission of SiO 2 and other sub- 
 stances from the magma. Certainly a million tons would be a 
 small estimate of the garnet-rock actually in sight within an 
 area of 2 or 3 square miles. Let us suppose, now, that a 
 magma charged with these materials were intruded in some 
 other rock than limestone, such as sandstone or granite, or 
 some intractable material. The same emission of silica, of 
 sulphur and of metallic bases would certainly take place ; but 
 not being able to react on the walls, and not being held by them 
 next to the eruptive, they must migrate upward through fissures. 
 It is, moreover, inconceivable that they should be emitted 
 otherwise than in association with much more steam or poten- 
 tial water than their own mass, and one must believe that they 
 would be yielded under such pressure and with such a vis a 
 tergo that they would not need any other motive power to drive 
 them upward. In higher levels, metallic veins with prevailing 
 quartz-filling and all the common varieties of ore-deposits 
 w T ould result. They might mingle with meteoric waters to a 
 certain degree, and beyond question would; but the latter 
 would play no necessary or essential part in the process. 
 The original deposits might be later rearranged by the circula- 
 tions of meteoric waters, and I realize perfectly, from the 
 recent observations of Messrs. Emmons, Weed, Van Hise, 
 De Launay and others, that there is every reason to believe that 
 they would be ; but it is not necessary to assume such arrange- 
 ments in order to yield an ore-body. 
 
 Mr. Lindgren's paper on contact-deposits refers to a number 
 of others similar to this Mexican one, w r hich, in fact, he also 
 cites, quoting a very brief reference to it by Ordonez ; but there 
 are many more. There is a very large one, for example, at 
 San Pedro, N. M., a detailed description of which has been 
 given by two members of the Institute, Messrs. Yung and 
 McCaffery.* I have had the privilege of going over the 
 ground with them the past summer. Notes upon still ad- 
 
 * "The Ore-Deposits of the San Pedro District, New Mexico," Trans., xxxiii., 
 350. ; 
 
IGNEOUS ROCKS AND CIRCULATING WATERS. 239 
 
 ditional cases have been received from other old students and 
 friends. The very valuable contributions, moreover, of Messrs. 
 Weed and Barrell* upon the Elkhorn district, Montana, have 
 served to show the important preparatory work of contact- 
 metamorphism in producing porous rock wherein ores may 
 later be deposited. Mr. Weed has shown that the Cananea 
 mines, Sonora, Mexico, are of this type; and informally, from Dr. 
 W. L. Austin, the writer has learned of many additional cases. 
 
 The recent exhibitions of vulcanism in the West Indies must 
 bring the force of these statements home to any one who re- 
 flects upon them. That the sea or any form of meteoric water 
 could have contributed more than a small portion, which was 
 caught up as the explosive vapors progressed toward the sur- 
 face, seems to me contrary to sound principles in physics. In 
 fact, I cannot resist the conviction that in the study of vul- 
 canism and its effects lies the promising field of investigation 
 which will throw additional light upon the production at least 
 of the first deposits, f which may afterwards experience en- 
 richment in their upper portions from the action of meteoric 
 waters. 
 
 The pegmatites and at least their limiting quartz-veins were 
 certainly produced in very much the way just outlined. They 
 are very widespread. Mr. Lindgren mentions the general ex- 
 perience that they are barren of ores,! and I have likewise re- 
 marked this feature ; but Dr. 0. A. Derby has recently con- 
 tributed to the Institute some notes on Brazilian gold-veins in 
 which he describes a very extensive series of rather richly pro- 
 ductive veins of this character. || 
 
 If, now, we add to the above considerations the further one 
 of the almost constant association of eruptive rocks with veins, 
 
 * "Geology and Ore-Deposits of the Elkhorn Mining District, Jefferson Co., 
 Mont.," by W. H. Weed ; " Petrography, " by Joseph Barrell, 22d Ann. Rept. 
 U. S. G$ol Survey, Part II., p. 399. "Physical Effects of Contact-Meta- 
 morphism," by Joseph Barrell, Am. Jour. Sci., April, 1902, p. 279. 
 
 f A very suggestive essay bearing on this point is that of L. De Launay, 
 "Contribution a 1' Etude des Gites Me*tallif eres, " Annales des Mines, August, 
 1897, p. 119. 
 
 J "Character and Genesis of Certain Contact-Deposits," Trans., xxxi., 243, and 
 Geneis of Ore-Deposits, p. 732. 
 
 % "Hole of the Igneous Rocks, etc.," Trans., xxxi., 133", and Genesis of Ore- 
 Deposits, p. 694. 
 
 II "Notes on Brazilian Gold-Ores," Trans., xxxiii., 282. 
 
240 IGNEOUS ROCKS AND CIRCULATING WATERS. 
 
 and the usually very restricted occurrence of the latter, it 
 seems to me that, areally considered, we have adequate reason 
 to attribute to the former, and especially when there is no posi- 
 tive contradictory evidence, very great importance in vein-pro- 
 duction. It is reasonable, efficient, demonstrated in important 
 cases, and in no respect more speculative than the inferred 
 deep circulations of descending meteoric water. I do not state 
 this controversially, but as a claim for its recognition. 
 
 When ore-formation is referred to pneumatolytic or fumarolic 
 action, I understand that practically these processes are meant. 
 Under these names, or with a general statement similar to the 
 one given above, the processes have been often appealed to.* 
 Nevertheless, such unquestioning faith has generally been felt 
 in meteoric waters that the possibilities of this general cause 
 have received comparatively little attention. 
 
 B. Regarding the general question of the descent of mete- 
 oric waters into the earth, there developed in our two papers 
 considerable difference of opinion between Professor Van Hise 
 and myself. I am entirely frank to admit that I gained from 
 his " Principles " the idea that he believed the meteoric waters 
 to be everywhere descending, migrating laterally through the 
 smaller waterways, and, although guided by relatively impervi- 
 ous beds, pitching anticlines, etc., to be then returning to the 
 surface by the trunk-channels. This is certainly the concep- 
 tion of the ground-water hitherto held by the lateral-secretion- 
 ists. I have again and repeatedly read the parts of the essay 
 bearing on this subject, and I cannot blame myself for reaching 
 this conclusion. I therefore laid stress, and with entire justifi- 
 cation, upon the dryness of deep mines, in order to delimit or 
 disprove it. Professor Van Hise's rejoinderf to my arguments 
 strikes me as a great restriction upon what I believed to be his 
 conception, and, were it not for his statement to the contrary, 
 I should conclude that his attitude had been much modified. 
 The latter expression makes it less difficult for us to attain 
 
 * For instance, by von Richthofen for the Comstock lode ; by J. S. Curtis for 
 Eureka, Nev., Monograph VII., U. S. Geol. Survey, p. 89 ; and by Arnold Hague, 
 Monograph XX., 294; by J. E. Spurr for Mercur, Utah, IQth Annual Report, 
 U. S. Geol. Survey, Part II., p. 402 ; and by the last named, again, in the 18th An- 
 nual Report, Part III., pp. 297 to 316. 
 
 f Trans., xxxi., 300 and 301. 
 
IGNEOUS ROCKS AND CIRCULATING WATERS. 241 
 
 approximate agreement. I am quite free to admit that it is 
 possible that the advance of " cementation " may plug up cav- 
 ities so as seriously to impede circulation. This would be es- 
 pecially effective in the larger channels where the main ore- 
 bodies such as we mine are precipitated. If, then, a mine 
 went down on a filled and plugged vein, water might reason- 
 ably diminish and disappear with depth. It is less easy to 
 believe that the same results would take place in the smaller 
 and tributary conduits which feed downward and into the 
 larger up-takes, because they must be kept open in order to 
 bring in material wherewith to plug the latter. If, then, 
 deep shafts in a district of heavy rainfall like the copper 
 region of Keweenaw Point, before reaching the ore-body, cut 
 nearly a mile of strongly inclined lava sheets, a hundred or 
 more in number, and many of them amygdaloidal, without find- 
 ing water below a comparatively shallow depth, it proves that 
 rocks are ordinarily much more impervious than has been sup- 
 posed in most discussions in the past regarding the descent of 
 meteoric waters. I learn from friends who have been in the 
 Transvaal gold regions that the deep shafts there, which, as we 
 .all know, are sunk through one flank of a syncline of sedimen- 
 tary strata, likewise find dry ground at a depth of about 250 
 ft. Aside from any bearing upon Professor Van Hise's essay, I 
 think it is important to emphasize these points. I am frank 
 to admit that I did not fully appreciate the force of this obser- 
 vation myself until I came to prepare the paper on the " Role 
 of the Igneous Rocks;"* and yet, despite the force of Professor 
 Van Hise's reply, I cannot say that I believe that the damaging 
 effects of experience in deep .and dry mines upon our older 
 conceptions of the descent of the meteoric waters (conceptions 
 which I have held in common with geologists in general) have 
 been satisfactorily met by Professor Van Hise in advancing the 
 idea of the zone of cementation. The dryness of deep mines 
 destroys for a large part of the earth the very foundations of 
 Professor Van Hise's main contention ; and in meeting this ob- 
 jection with the conception of the zone of cementation he may 
 well be, as it seems to me, merely opposing a damaging ma- 
 
 Trans., xxxi., 169, and Genesis of Ore- Deposits, p. 681. 
 16 
 
242 IGNEOUS ROCKS AND CIRCULATING WATERS. 
 
 terial fact with a largely subjective conception. I am led rather 
 to have the more confidence in the intrusive rocks and their 
 emissions. In this connection it may be of interest to remark 
 that in a paper in vol. vi. of the Transactions, pp. 544 and 
 545, 1877, Dr. Raymond has outlined briefly both sides of this 
 discussion. 
 
 Let us, however, admit that, after periods of upheaval and 
 special fracturing, the meteoric waters descend with all the 
 facility and in all the abundance required by the conception 
 formulated by Professor Van Hise. According to this, as I 
 understand it, the cause of their return to the surface from the 
 depths, which, as the extreme, are about 10,000 meters, is the 
 " head," or the amount by which the pressure at the base of 
 the descending columns exceeds that at the base of the corre- 
 sponding ascending columns. The head is chiefly due to the 
 greater length of the former column, because it is fed from 
 entrance-points which are above the points of emergence of the 
 returning waters ; but the head is reinforced by the expansion 
 produced in the ascending and hotter column because of in- 
 crements of heat absorbed at a greater or less depth within the 
 earth. The motive power is, however, the head in all cases; 
 that is, it is gravity. I do not for a moment question the force 
 or attractiveness of this conception, nor the able way in which 
 it has been presented by Professor Van Hise, even though I 
 have not the same faith in its efficiency which he evidently 
 feels. 
 
 It is clear that if " head " is at all active, there must be a 
 continuous and unbroken column of water from the surface, or 
 from very near the surface, to the ultimate depths reached by 
 the meteoric waters, and back again to their point of emer- 
 gence. This pressure or head must be transmitted through all 
 the cavities, small and large, capillary, subcapillary and supra- 
 capillary, which the waters traverse. It seems to me to de- 
 mand, where it operates, practical saturation of the crust of the 
 earth with water, a condition which experience in deep mines 
 proves to exist, so far as I know, in no mining-region to-day r 
 except, perhaps, in one or two of obvious expiring vulcanism. 
 Despite the conception of the zone of cementation, earlier re* 
 ferred to, I am influenced by this experience. 
 
IGNEOUS ROCKS AND CIRCULATING WATERS. 243 
 
 In discussing the transmission of pressure through cavities 
 of capillary size by the descending waters, I regret that I did 
 do Professor Van Hise an unintentional injustice, as he re- 
 marks in his closing discussion, in that I confused the passage of 
 the descending waters under pressure, through capillary tubes, 
 with capillarity or capillary attraction. The interposition of the 
 latter would destroy " head," but the interposition of the former 
 would only greatly reduce it because of friction, a point em- 
 phasized by Professor Van Hise. 
 
 There is no question that, if meteoric waters enter a frac- 
 tured and open-textured portion of the earth, descend, migrate 
 laterally in unbroken course, and meet uprising fissures which 
 reach the surface at lower points than the place of entry, they 
 must emerge and establish a circulation. The points open to 
 argument are, first, the extent and relative amounts by which 
 the different sources of internal heat may aid them or substi- 
 tute a source of energy even greater than " head " or gravity ; 
 second, whether they are, on the whole, as efficient causes of 
 vein-formation as intruded rocks and their emissions; and, 
 third, whether the general geological relations of veins support 
 one view or the other, and to what extent. In taking up the 
 first point, I revert to the blocking out of the sources of inter- 
 nal heat mentioned above as IB, 2B and 3B, which are essen- 
 tially the same as those mentioned by Professor Van Hise in 
 his "Principles" (Trans., xxx., 49). The second and third 
 points I have already discussed in my previous contribution. 
 
 IB. Doubtless the crushing of rocks under dynamic stress 
 and chemical reactions develops heat, but to what extent I do 
 not know, nor does this source seem to me to be capable of 
 more than this general expression. The development of in- 
 terior heat by chemical reactions shares the same indefinite- 
 ness. 
 
 2B. As to the part which the normal increase of temperature 
 plays in aiding terrestrial circulations, it is possible to reach a 
 more accurate quantitative expression. The heat which will 
 raise the temperature of a column of water from 4 C. to 
 100 C. will produce an expansion of about 4 per cent, and a 
 consequent diminution of density. This calculation is used, 
 with subsequent general modification to meet terrestrial condi- 
 
244 IGNEOUS ROCKS AND CIRCULATING WATERS. 
 
 tions, by Professor Van Hise.* I brought against it the objec- 
 tion that this expansion would be neutralized by the pressure 
 of the accumulating column of water, which, to a height of 
 about 10,000 ft., would rest upon that portion which would 
 attain a depth in the earth where the temperature would be 
 100 C. While I did not have at hand the data for an exact 
 expression, I had submitted the proposition to a friend who 
 could give an authoritative opinion and had been assured that 
 the modification was well grounded. I stated, therefore, that 
 it would practically prevent effective expansion and loss of 
 density. This statement is too sweeping, and Professor Van 
 Hise's objection in the Discussionf is well taken. Professor 
 William Hallock has kindly given me the following references,^ 
 in which it is stated that the cubical compression of water 
 at 4 C. is 0.0000469 per atmosphere. Assuming that this 
 holds good for all temperatures up to 100 C., it means, in 
 a column of 10,000 ft. in height, which would create a pres- 
 sure of about 5000 Ibs. to the square inch, a compression of 
 about 1.6 per cent, at the base, leaving 2.4 per cent, of the 
 original 4 there effective. If, again, the data given by Dr. 
 Carl Barus, and cited by Professor Van Hise, are taken, the 
 results are not greatly modified. Dr. Barus determined the 
 compression of a capillary column of water, 17.4 c.m. in 
 length and at a temperature of 23 C., to be, for 83 atmospheres, 
 .0037; for 160 atm., .0075; for 226 atm., .0108. If we con- 
 tinue it at the same rate for 340 atm. (or 10,000 ft), it is .0165 
 or. 1.65 per cent. At 100 C., on a capillary column 18.1 c.m. 
 long, Dr. Barus determined it to be, for 83 atm., .0046 ; for 
 180 atm., .0098 ; for 244 atm., .0133. Continuing at the same 
 rate, it would be, for 340 atm., 1.84 per cent, at the base. 
 
 Since we assume that the increment of* temperature and the 
 increment of pressure are each uniform in descent, we may say 
 that for an increment of 96 C. we have an expansion of 4 pr 
 cent, or -fa of 1 per cent, for 1. At the same time we have 
 
 * Trans., xxx., 49, and Genesis of Ore-Deposits, p. 304. 
 f Trans., xxxi., 296. 
 
 J W. Watson, Textbook of Physics, p. 182. Wiillner, Lehrbuch der Physik, vol. i., 
 p. 275. Johann Miiller, Lehrbuch der Physik, vol. i., p. 139. 
 I Trans., xxxi., 296. 
 
IGNEOUS ROCES AND CIRCULATING WATERS. 
 
 245 
 
 a compression of 1.6 per cent., or, expressed in the rate per' 
 degree of increased temperature, -fa of 1 per cent. The net 
 expansion per degree expressed in per cents is therefore -^ 
 
 mnus 
 
 or 
 
 
 It is now not difficult to reach a quantitative expression of 
 the actual efficiency of the normal increase in temperature in 
 promoting hot-springs. We may assume a mean annual tem- 
 perature at the surface of the earth of 10 C. For comparison, 
 at New York it is 10.6. If a descending column starts at 10 
 and ends at 100, its mean temperature will be 55. Mr. G. 
 K. Gilbert has found, as quoted by Professor Van Hise, that the 
 waters of the hot-springs in the Cordilleran region range from 
 37 C. to 100 C., and that those of the much more abundant 
 warm springs range from 18 to 37. There is little doubt 
 that many of these, and probably all the hotter ones, are con- 
 nected with expiring vulcanism and have no bearing upon this 
 immediate discussion. If, therefore, we assume springs emerg- 
 ing at 20, 30, 40, and so on to 100, we shall cover the essen- 
 tial cases in Nature. In the calculation we must use the mean 
 temperatures of ascending columns which start at 100 C. and 
 reach the surface at the above temperatures, and we may ex- 
 press the whole matter in a small table, recalling that, for each 
 increase of 1 in the mean temperature of the uprising column, 
 as compared with that of the descending one, there results an 
 expansion of -^ of 1 per cent., which, expressed in feet for a 
 10,000-ft. column, is 2.5 ft. 
 
 TABLE I. Mean Temperature of Descending Column, 55 C. 
 
 Temp, of 
 Emergence. 
 Centigrade 
 Degrees. 
 
 Mean Temp, of 
 Ascending 
 Column. 
 Cent. Deg. 
 
 Excess 
 of 
 Temp. 
 Cent. JDeg. 
 
 Increase of Head. 
 
 Per Cent. 
 Expansion. 
 
 Feet. 
 
 20 
 
 60 
 
 5 
 
 i 
 
 12.5 
 
 30 
 
 65 
 
 10 
 
 
 25. 
 
 40 
 
 70 
 
 15 
 
 
 37.5 
 
 50 
 
 75 
 
 20 
 
 
 50. 
 
 60 
 
 80 
 
 25 
 
 
 62.5 
 
 70 
 
 85 
 
 30 
 
 
 75. 
 
 80 
 
 90 
 
 35 
 
 
 87.5 
 
 90 
 
 95 
 
 40 
 
 1 
 
 100. 
 
 100 
 
 100 
 
 45 
 
 It 
 
 112.5 
 
246 IGNEOUS ROCKS AND CIRCULATING WATERS. 
 
 When we consider how slight an increase this amounts to in 
 a 10,000-ft. column, which is fed by all sorts of small tributa- 
 ries with high friction ; and when we compare the results with 
 the vastly greater head resulting from inequalities of the ground 
 which would almost pass unnoticed ; when, again, we recall the 
 rarity of hot-springs having even the moderately elevated tem- 
 peratures and not obviously in volcanic or eruptive regions ; 
 and when we realize that any ascending column would inevit- 
 ably draw to itself by induced currents much colder water in 
 the rocks toward the surface, I think we are justified in prac- 
 tically dismissing the normal increase of temperature in the 
 earth as of any essential importance in helping to force de- 
 scending meteoric waters through the devious underground 
 passages. We must have a head contributed by a higher 
 source at the point of entry, and therefore a continuous column 
 of water, or we must have local supplies of heat from recently 
 intruded igneous rocks. 
 
 Again, if we have a region where the rate of increase of the 
 interior temperature is less than the basis of the above calcula- 
 tion, viz., 1 C. for each 30 meters (1 F. for each 55 ft.), as, 
 for instance, Keweenaw Point, where the rate is very nearly 1 
 C. for 60 meters (1 F. for each 100-110 ft), or the Transvaal, 
 where, as I learn from Mr. Pope Yeatman, preliminary experi- 
 ments have shown an even slower rate, then the force of my 
 argument is doubled. And if the mean annual temperature is 
 higher than 10 C., the argument is thereby correspondingly 
 strengthened. Naturally, also, a colder mean annual tempera- 
 ture weakens the argument, but not proportionately, since water 
 is densest at 4 C., leaving a range of but 6 for mean annual 
 temperature as between this and the 10 assumed above, before 
 the limit is reached. 
 
 I realize that the expulsive action of the normally heated in- 
 terior was only a minor point in Professor Van Hise's argu- 
 ment, and it is not with reference to his paper that these con- 
 clusions are specially urged, but because it is probable that 
 generally, among geologists, much greater efficiency is attributed 
 to this agent than it would seem to deserve. All these consid- 
 erations make us fall back with the greater reliance on igneous 
 rocks as sources of heat and energy for promoting circulations 
 
IGNEOUS ROCKS AND CIRCULATING WATERS. 247 
 
 which reach the surface. The influence of the increase of tem- 
 perature in the normal ratio must be mainly one of magnifying 
 chemical efficiency in those meteoric waters which come within 
 its influence. 
 
 In this connection I cannot refrain from referring with the 
 greatest admiration to Mr. Weed's recent paper on " Mineral 
 Vein-Formation at Boulder Hot Springs, Montana."* It is of 
 the highest significance, both in reference to the topic here dis- 
 cussed and to the one next to be taken up. 
 
 3B. If we imagine a mass of molten igneous rock injected 
 from below into the upper regions where the meteoric ground- 
 waters exist, a new factor is introduced of enormous efficiency. 
 The molten rock may be considered as having a temperature of 
 about 1200 C. (about 2200 F.). Its influence in expanding 
 to the full limit of the liquid condition any meteoric waters 
 within the sphere of its influence would be relatively abrupt, 
 .and its effect in increasing normal head would be pronounced. 
 If it sufficed to change to vapor any of these waters, their 
 density would be enormously lowered and the head would be 
 still more effective. But even apart from the head of the de- 
 scending column, and even without assuming its existence with 
 reference to waters at the place in question, for meteoric waters 
 may be present even if not under a continuous column to the 
 surface, the expansive force of the steam, or even of the disso- 
 ciated gases, reinforced by the copious emissions of the erup- 
 tive, would start circulations toward the surface, and, as it seems 
 to me, would be a most efficient agent. This is what I have 
 referred to in my paper and elsewhere as contributions of 
 energy, and the process has been indicated by describing in- 
 trusive rocks as stimulators of circulation. 
 
 Gradually the intrusive rock cools and becomes a less and 
 less efficient cause, and in the end it assumes the normal tern- 
 perature for that portion of the earth in which it is situated. 
 Possibly circulating waters continue their migrations, urged on 
 by head, and are effective in depositing ores. Possibly, also, 
 they practically cease, and the period of ore-deposition corre- 
 sponds to the period of efficiency of the eruptive. I am 
 
 '* Twenty-First Annual Report U. S. Geol. Survey, II., 227. 
 
248 IGNEOUS ROCKS AND CIRCULATING WATERS, 
 
 strongly inclined to believe the latter view is correct, and that 
 when the fires under the boiler are quenched, the engine ceases 
 to run. 
 
 Do we, then, find mineral veins provided with ores in those 
 places where, once in a million times, the combination of pre- 
 cipitating agent and metalliferous solution meet under favor- 
 able conditions in the circulation of the meteoric ground- 
 waters ? or do we find them where, down under the surface, 
 some intrusive rock has entered charged richly enough with a 
 metallic burden to impart it to uprising heated waters and 
 yield a series of ore-bodies ? From the experience gained in 
 western mining-districts the latter appeals to me the more 
 forcibly, and I am inclined to believe that original ore-deposi- 
 tion ceased, not so much because cementation plugged the con- 
 duits as because the energy of the stimulating cause became 
 exhausted. But even in making this guarded statement, I 
 trust that I do not fail to appreciate the extent to which the 
 whole matter is speculative and inferential, a phase of the sub- 
 ject adequately emphasized, and I think alone adequately em- 
 phasized, in my previous paper. 
 
 There remain but one or two other points which seem to me 
 to deserve attention beyond the treatment given them in the 
 "Role of the Igneous Rocks, etc." There is some difference 
 of opinion between Professor Van Hise and myself regarding 
 the abundance of veins. While I have the greatest respect for 
 his very wide experience and observation, I nevertheless am 
 strongly of the opinion that, if we leave out pegmatites and 
 their related quartz-veins, which are so extensively developed 
 in metamorphic districts, veins of any sort, commensurate in 
 size with those which we mine, are quite rare phenomena, and, 
 though locally abundant, are yet, on the whole, but seldom 
 seen. This is not alone my own opinion, but that of friends in 
 the practice of mining engineering, and of greater experience 
 in these matters than either Professor Van Hise or myself. 
 Unless some very restricted cause has occasioned them, they 
 ought to be far more abundant than they are. 
 
 As to the presence of the ground-water in all mining-regions, 
 an additional word may be of interest. There certainly are 
 localities in the arid region of the West where, at considerable 
 
IGNEOUS ROCKS AND CIRCULATING WATERS. 249 
 
 depths, it has not yet been met in notable amount, and where 
 its distribution is very irregular. At Tintic, Utah, for in- 
 stance, as I am informed by Dr. W. P. Jenney, the Mammoth- 
 Tintic workings are 2000 ft. deep in the limestone. They 
 have never used a pump nor have had more than a little drip of 
 water in a few places. The ores are oxidized and the bottom 
 levels are perfectly dry. The ground-water may be encountered 
 in time, but it is certainly very deep. One or two miles away, 
 in the monzonite, water is met within 100 or 200 ft. of the 
 surface not in great quantity, indeed, but sufficient to have 
 prevented the oxidation of the ore. Over the divide from the 
 Mammoth, and beginning 550 ft. below it, are the Bullion-Beck 
 and Gemini mines. Their shafts are down 1660 ft, and from 
 very large and extended workings, and of course with no at- 
 tempt to impound the water near the surface, they gather about 
 10 gallons a minute, no more than can be readily removed by 
 a bailer once in a while through the day. The ores are all oxi- 
 dized. 
 
 The Horn-Silver mine at Frisco is down 1600 ft. and is prac- 
 tically dry ; the ore is oxidized. Water for the camp is, of ne- 
 cessity, brought in from a distance. I realize that Mr. Em- 
 mons has stated in his paper* that some water is met, but the 
 quantity is so small that the present management is sinking a 
 bore-hole from the bottom of the mine in the hope of tapping 
 enough, at least, to furnish a supply for the boilers. 
 
 My friend, Mr. John N. Judson, has given me some interest- 
 ing notes on the Mapimi mines in Mexico. The mines were 
 dry to a depth of over 760 meters, or about 2400 ft. Some 
 dampness was first observed in the wall-rock, and later some 
 water appeared in the veins, which are chimneys in lime- 
 stone. Whether the workings will pass through this wet 
 ground (it is not very wet) and again reach dry rock will be 
 one of the interesting things for the future to determine. 
 
 In a review of the separate volume on " The Genesis of Ore- 
 Deposits," recently issued by the Institute, Mr. H. F. Bain, in 
 the Journal of Geology, May-June, 1902, p. 434, emphasizes- 
 
 * "The Delamar and the Horn-Silver Mines," by S. F. Emmons, Trans. r 
 xxxi., 658. 
 
250 IGNEOUS ROCKS AND CIRCULATING WATERS. 
 
 the importance of considering, in this connection, only vertical 
 depths, and not the relatively flat inclines, which, while long 
 and perhaps dry, may not attain great depth nor be significant. 
 I believe all the cases cited by me have been of vertical shafts. 
 Mr. Bain also mentions experience in the Newhouse tunnel, in 
 cutting wet veins, as indicating the presence of water at great 
 depths. To this, however, it may be replied that a tunnel into 
 a mountain merely produces an artificial spring; that springs 
 exist along almost all valleys, and their water at times certainly 
 comes from considerable depths ; but my contention is that, so 
 far as actual experience goes, in very deep mining, water is 
 scarce or almost unknown unless there is expiring vulcanism. 
 From this it follows that the igneous rocks are probably the 
 important factors in deep circulations. 
 
 Regarding points like these, it is most desirable that mem- 
 bers of the Institute should place observations on record. 
 
 In closing, I may add that, although I apparently differ with 
 Professor Van Hise regarding the relative importance of cer- 
 tain factors in the problem, there is no one who has a higher 
 admiration for his essay than myself, a feeling which, as a 
 matter of fact, I had elsewhere expressed before the Rich- 
 mond meeting. At the same time, a somewhat extended cor- 
 respondence has shown that not a few mining-geologists in 
 America and elsewhere are in sympathy with the points em- 
 phasized in my paper, and with the relative importance there 
 attached to the several factors. 
 
IGNEOUS ROCKS AS RELATED TO OCCURRENCE OF ORES. 251 
 
 No. 11. 
 
 A Consideration of Igneous Rocks and their Segregation 
 or Differentiation as Related to the Occurrence of Ores.* 
 
 BY J. E. SPURR, CONSTANTINOPLE, TURKEY, f 
 
 (New York and Philadelphia Meeting, February and May, 1902. Trans., xxxiii., 288.) 
 
 CONTENTS. 
 
 PAGE 
 
 INTRODUCTION, 252 
 
 I. THE RELATION OF ORE-DEPOSITS TO IGNEOUS ROCKS IN GENERAL, 253 
 
 II. THE DISTRIBUTION OF METALS IN SEDIMENTARY ROCKS, . . 254 
 
 III. THE SEGREGATION OR DIFFERENTIATION OF IGNEOUS ROCKS, . 259 
 
 IV. THE ORDER OF CRYSTALLIZATION OF MINERALS IN IGNEOUS ROCKS, 263 
 V. THE FORMATION OF MINERAL SEGREGATIONS IN MOLTEN MASSES, . 264 
 
 VI. THE UNKNOWN FINER LAWS OF ROCK-SEGREGATION, . . . 265 
 VII. THE PRESENCE OF METALS IN THE IGNEOUS ROCKS, . . . 266 
 "VIII. THE CONCENTRATION OF COMMERCIALLY- VALUABLE MINERALS BY 
 SEGREGATION WITHIN MOLTEN MASSES, PREVIOUS TO THEIR CON- 
 SOLIDATION, . . . . . . . . L ... 267 
 
 1. Iron, ...'... 267 
 
 2. Chromium, . . . . . . . . . . 267 
 
 3. Nickel, ". ./, . .268 
 
 4. Cobalt, . 'J69 
 
 5. Platinum, % . 269 
 
 6. Copper, 270 
 
 7. Gold,. . 271 
 
 IX. THE ORIGIN OF CERTAIN GOLD-QUARTZ VEINS, .... 271 
 
 1. Evidence as to the Origin of Quartz- Veins .-> Magmatic Segreyations, . 275 
 
 2. The Genetic Connection of Gold-Quartz Veins with Siliceous Igneous Rocks, 279 
 
 3. The Subordinate Connection of Gold- Quartz Veins with Basic Igneous Rocks, 284 
 X. RESUME OF THE EVIDENCE CONCERNING THE PREFERENCE OF CER- 
 TAIN METALS TO ACCUMULATE, BY MAGMATIC SEGREGATION, IN 
 CERTAIN ROCK-TYPES OF THE ESTABLISHED CLASSIFICATION; . . 284 
 
 1. Basic Rocks, 285 
 
 2. Siliceous Rocks, . . . . . . ' . . . . . 285 
 
 XI. THE RELATION BETWEEN ORE-DEPOSITS DUE TO MAGMATIC SEG- 
 REGATION AND OTHER ORE-DEPOSITS, ...... 236 
 
 XII. THE SEQUENCE OF VOLCANIC ERUPTIONS, CONSIDERED IN CONNEC- 
 TION WITH THE SEQUENCE OF METALLIFEROUS VEINS, . . 288 
 
 XIII. THE PERSISTENCE OF PETROGRAPHIC PROVINCES, CONSIDERED IN 
 
 CONNECTION WITH THE PERSISTENCE OF METALLIFEROUS PROV- 
 INCES . 291 
 
 XIV. CONCLUSION, 299 
 
 POSTSCRIPT, . 301 
 
 * Published by permission of the Director of the U. S. Geological Survey, 
 t Since returned to the United States, and now again in the service of the 
 IU. S. Geological Survey. R. W. R. 
 
252 IGNEOUS ROCKS AS RELATED TO OCCURRENCE OF ORES. 
 
 INTRODUCTION. 
 
 IN a new field like that of the study of ore-deposits, it is 
 hard to keep all sides of the question in sight at once ; to real- 
 ize that the laws worked out for certain types of ore-deposits 
 in one region do not apply to deposits of apparently similar 
 ores the world over. Thus have arisen our most hotly-con- 
 tested controversies, over such questions, for instance, as : 
 Whether bedded ores are mechanical sediments formed at the 
 same time with the enclosing rock, or were introduced later by 
 solution; Whether metals have been deposited by ascending 
 or by descending waters ; Whether they are derived from the 
 immediate wall-rock, from the rocks of the whole district in 
 which they occur, or from the " barysphere " ; Whether they 
 are deposited in pre-existing cavities or are replacements ; and 
 so on. 
 
 The researches of the past score of years or so have rather 
 dampened the heat of these discussions. Investigators have 
 been led to recognize in nature a complexity which permits 
 most of the advocated theories to find their place as factors 
 mutually co-operating to constitute the intricate system which 
 determines the occurrence of ores as we now find them. I 
 think most of us agree with Prof. Van Hise,* that " for many 
 ore-deposits a complete theory must be a descending, lateral-se- 
 creting, ascending, descending, lateral-secreting theory." In- 
 deed, all this and more ! 
 
 Van Hise's discussion of the work of underground water in 
 forming ore-deposits seems to me the best general contribution 
 of recent years, not excepting the famous treatise of Posepny. 
 A masterly discussion like this fills, for the moment, the whole 
 mind of the reader, and he might thus fail to consider the im- 
 portance of principles which the author has purposely omitted. 
 Kemp, Lindgren and Vogt, in their discussions of Van Hise's 
 paper, have called attention to certain of these principles, espe- 
 cially those involving the connection of igneous rocks with ore- 
 deposition, or ore-segregation, as I would like to call it. 
 
 It is concerning this part of the field that I wish to present 
 some considerations, limited in extent and detail by my lack of 
 
 * "Some Principles Controlling the Deposition of Ores," Trans., xxx.,p. 173.. 
 Genesis of Ore-Deposils, p. 428. 
 
IGNEOUS ROCKS AS RELATED TO OCCURRENCE OF ORES. 253 
 
 access to a wide range of literature, and by the difficulty of the 
 subject itself. With most of Van Hise's conclusions, I may 
 remark, I fully agree. 
 
 For the ideas herein set forth I can claim, of course, only a 
 certain amount of originality. It will be seen that my views 
 (which I have previously announced, although not in such com- 
 pact form as this*) resemble, more or less, those of Lindgrenf 
 and KempJ in this country, and De Launay, Beck and Yogt 
 in Europe, but especially the last named. 
 
 I. THE RELATION "OF ORE-DEPOSITS TO IGNEOUS ROCKS IN 
 
 GENERAL. 
 
 Two important points have come to be agreed upon by most 
 of the best writers on ore-deposits, namely : (1) That ores in 
 general were originally derived from igneous rocks; and (2) 
 that present ore-deposits are closely associated with actually-ex- 
 posed eruptives. 
 
 Probably at least nineteen out of twenty important ore-de- 
 posits (excepting those of iron) are acknowledged to have a 
 genetic connection with associated rocks of igneous origin. 
 Especially well-marked is the connection of ore-regions or zones 
 with areas or belts of igneous activity. || The interdependence 
 of eruptive rocks, hot springs and many ore-deposits has at 
 last attained the dignity of a general law. 
 
 The hot springs often owe their heat, and hence their up- 
 ward propulsion, to igneous masses, while the ore-deposits are 
 the direct work of both the other two, the material being 
 largely derived from the rocks and the concentration being 
 effected by the waters. Moreover, the lines of weakness (of 
 
 * J. E. Spurr, "Economic Geology, Mercur Mining District, Utah," IGth An- 
 nual Rpt. U. S. Geol Surv., Part II., pp. 395, 449 (1895); " Geology of the Yukon 
 Gold-District," ISth Annual Rpt. U. S. GeoL Surv., Part III., p. 297(1898); 
 " Quartz-Muscovite Kock, from Belmont, Nevada," Am. Jour, of ScL, 4th series, 
 vol. x., Nov., 1900, p. 355. 
 
 f Waldernar Lindgren, " Character and Genesis of Certain Contact- Deposits," 
 Trans,, xxxi., p. 226, and Genesis of Ore-Deposits, p. 716. 
 
 I J. F. Kemp, "The Role of the Igneous Rocks in the Formation of Veins," 
 Trans., xxxi., p. 169, and Genesis of Ore- Deposits, p. 681. 
 
 g J. H. L. Vogt, "Problems in the Geology of Ore-Deposits," Trans, xxxi., 
 p. 125, and Genesis of Ore- Deposits, p. 636. 
 
 || J. F. Kemp, "The R61e of the Igneous Rocks in the Formation of Veins," 
 Trans., xxxi., 196, 197, and The Genesis of Ore-Deposits, pp. 707-709. 
 
254 IGNEOUS ROCKS AS RELATED TO OCCURRENCE OF ORES. 
 
 faulting, etc.) determined by, or at least coextensive with, the 
 intrusion of the molten masses, frequently form the channels 
 of the springs, and thus operate to restrict the ore-deposits to 
 the eruptive zones. 
 
 The broad explanation of this association is plainly contained 
 in the proof which we now possess, that the eruptive rocks con- 
 tain in varying amounts the rarer elements (among them, most 
 of the metals), in addition to the common ones. 
 
 In the stratified rocks, on the other hand, the metals, though 
 present, seem to be in general less abundant.* 
 
 II. THE DISTRIBUTION OF METALS IN SEDIMENTARY EOCKS. 
 
 All sediments were probably derived in the beginning from 
 the destruction of igneous rocks, but the elements thus de- 
 rived attain through mechanical and chemical surface agencies 
 a degree of concentration hardly equalled in the igneous rocks 
 themselves. Thus calcium becomes concentrated into lime- 
 stones, and silicon into great volumes of sandstone or quartzite. 
 Among the commercially valuable minerals, salt, gypsum, 
 phosphate of lime, borax and others have thus become con- 
 centrated. These facts indicate that metals also must be sim- 
 ilarly dissolved out and dispersed. In the case of some of the 
 metals, we know that they are re-deposited in concentrated 
 form. By chemical and mechanical action, iron is concen- 
 trated in bogs, in greensands, and in ferruginous shales and 
 sandstones, there to yield, after some further concentration, 
 such notable deposits as the iron-ores of the Lake Superior 
 region. By chemical action, manganese is concentrated, not- 
 only in bogs, but on a large scale in marine sediments, such 
 as shales and limestones, so that most of the commercially im- 
 portant deposits are derived, through the medium of further 
 concentration, from these sources. By mechanical and chemi- 
 cal action such rarer metals and minerals as gold, platinum, 
 diamond, tin-ore, monazite, garnet, etc., are very highly con- 
 centrated in river channels and in marine shore-deposits. Ex- 
 amples of the enormous efficiency of surface concentration in 
 producing valuable deposits of the rare metals are furnished 
 
 * J. F. Kemp, " The Kole of the Igneous Kocks in the Formation of Veins," 
 Trans., xxxi., p. 175, and The Genesis of Ore-Deposits, p. 686. 
 
IGNEOUS ROCKS AS RELATED TO OCCURRENCE OP ORES. 255 
 
 by the world's gold-placers, the Cape Nome beach-sands, and 
 (according to some authorities) the South African auriferous 
 beds. As regards platinum, nearly all the known concentra- 
 tions, so complete as to be commercially valuable, have been 
 effected by surface-agencies. 
 
 But, on the one hand, iron and manganese are common ele- 
 ments; and, on the other hand, gold, platinum, tin-stone, etc. ? 
 are relatively insoluble ; and thus their concentration may be 
 explained. Concerning the metals (such as silver, copper, lead y 
 zinc, arsenic, antimony, etc.), which are at the same time rela- 
 tively rare and relatively soluble, no such satisfactory conclu- 
 sion has been reached. That, upon disintegration of the 
 igneous rocks, these metals largely go into solution in sur- 
 face-waters, there is no doubt. These waters (apart from those 
 which pass underground, where we know that the metals are 
 frequently precipitated in concentrated form*) find their way 
 into lakes, and especially into the oceans. What becomes of 
 the metals which they hold in solution ? 
 
 Are they precipitated either in concentrated or in evenly dis- 
 seminated form, or do they remain in solution ? If it be true, 
 as I think it is, that a sedimentary rock, as a rule, contains 
 much smaller proportions of the metals than an igneous rock,f 
 we must conclude that these metals are not evenly precipitated. 
 Yet I find it impossible to believe that all of these metals con- 
 tained in the igneous rocks which have been, ever since the 
 solid world began, going to pieces to form the enormous bulk 
 of known sediments, can have been stored in the sea-water and 
 are there 'still. 
 
 Most of the elements especially silver, copper, iron, man- 
 ganese, and gold have been chemically detected in sea-water; 
 but they are present only in minute traces; whereas the 
 total amount of metals which has passed into the sea in 
 solution during the ages of erosion and deposition must be 
 
 * C. R. Van Hise, " Principles Controlling Deposition of Ores," Trans., xxx., 
 p. 138 et seq., and The Genesis of Ore- Deposits, p. 393. 
 
 t J. F. Kemp, "The Role of the Igneous Rocks in the Formation of Veins," 
 Trans., xxxi., 174, says it appears, from analyses of both the sedimentary and the 
 igneous rocks of Missouri for lead and zinc, that the igneous rocks are, as a rule, 
 richer by one place of decimals than the former. F. Posepny, in The Genesis of 
 Ore-Deposits, p. 122, says that innumerable analyses of marine sediments and 
 precipitates, especially of limestones, have failed to show traces of metals. 
 
256 IGNEOUS ROCKS AS RELATED TO OCCURRENCE OF ORES. 
 
 many times in excess of the solvent power of the water at 
 any one time, and vastly in excess of the dissolved amount 
 now contained therein. We must, therefore, confess that, be- 
 sides the metals mechanically laid down in slates and conglom- 
 erates, derived directly from the abrasion of igneous rocks, the 
 same metals have been chemically precipitated somewhere from 
 marine and other surface-waters. Indeed, the researches of 
 Malaguti, Bibra and Forchhammer* long ago established the 
 fact of such precipitation by finding traces of metals in the 
 ashes of marine plants, and in the hard parts of marine ani- 
 mals, such as corals. Among the metals mentioned above as 
 having the question of their concentration at the surface still 
 undecided, lead, zinc, cobalt and nickel have been thus de- 
 tected. 
 
 Since, therefore, the metals in question (notably lead, zinc, 
 silver and copper), which are both relatively soluble and rela- 
 tively rare, after being extracted from the igneous rocks during 
 the process of weathering, transportation and sedimentation, 
 have neither been uniformly deposited in the sediments nor 
 accumulated in solution, I am forced to believe that, like the 
 commoner elements (among them the commoner metals) already 
 mentioned, they have been (probably by chemical precipita- 
 tion) deposited in certain places as concentrations, which are, as 
 a rule, relatively richer than the igneous rocks in which the 
 said substances were originally disseminated. 
 
 The hypothesis that bedded ores have sometimes been de- 
 posited contemporaneously with the enclosing sediments has 
 been, of late, distinctly out of fashion, and justly so, in the 
 exclusive sense in which it has sometimes been held. Bischof, 
 reasoning from the traces of metals in sea-w r ater, believed that 
 their precipitation as sulphides was possible, and thus ex- 
 plained the occurrences of copper and silver sulphides in the 
 Permian Kapferschiefer, and of lead sulphide in the Buntsand- 
 stein. 
 
 Groddeck advocated the same idea, and advanced the theory 
 that certain horizons are especially ore-bearing. f Hoefer has 
 .applied this explanation to the lead- and zinc-deposits of Upper 
 
 * Chem. u. Phys. Geologic, vol. i., Bonn, 1863, pp. 445-7. C. G. Bischof. 
 f Posepny, Genesis of Ore-Deposits, first edition, p. 112, etc. ; second edition, 
 p. 122. 
 
IGNEOUS ROCKS AS RELATED TO OCCURRENCE OF ORES. 257 
 
 Silesia and other districts, which occur in Triassic marine 
 limestone. In Bohemia and the Urals, as in the German 
 Kupferschiefer district, the Permian rocks contain copper in 
 many places ; in Utah and New Mexico (in the Silver Reef 
 and Nacimiento districts, etc.) the Triassic sandstones con- 
 tain copper and sometimes silver; in the Permian of Texas 
 there are three copper-bearing zones, extending over three 
 counties.* 
 
 These are examples of numerous deposits which have been 
 described by some able investigators as due to deposition con- 
 temporaneous with the enclosing beds, while, in every case, 
 this conclusion has been repeatedly and vigorously contested. 
 The fact is that in every one of these instances the ore-deposits 
 have an evident genetic connection with fissures, joints, dikes, 
 etc., of later age than the rock; and hence it is argued that the 
 ores (including those disseminated in the rock) have been in- 
 troduced through these fissures. 
 
 I. need hardly point out that this conclusion is not logically 
 valid. I confess that, after visiting the Mansfeld deposits, I was 
 so impressed by the evident connection of the faults with the 
 ore-bodies, and by the frequent proofs of the formation of min- 
 erals more recent than the country-rock, that I came away quite 
 satisfied that the idea of contemporaneous deposition was old- 
 fashioned and untenable. Yet neither there nor elsewhere does 
 this opinion certainly follow from the observed facts. The 
 present ore-bodies in most of these districts perhaps in all 
 are largely secondary concentrations, due to percolating waters, 
 and are hence found along water-channels, as held by Posepny 
 and others ; but this does not affect the question whether these 
 waters brought up the metals with them " from below " or con- 
 centrated them from disseminations contemporaneous in depo- 
 sition with the strata. In view of what I have stated above, I 
 am now inclined to hold the latter view. 
 
 Among the detrital rocks, slates are known to contain 
 marked quantities of the metals in question. Frick, Forch- 
 hammer and Sandberger found copper, zinc, lead, arsenic, anti- 
 mony, tin and cobalt in clay-slates. These are, very likely to 
 a large extent, mechanical concentrates from the rocks by the 
 
 * Kemp, Ore-Deposits of the United Stales, third edition, p. 224, etc. 
 
 17 
 
258 IGNEOUS ROCKS AS RELATED TO OCCURRENCE OF ORES. 
 
 destruction of which the slates originated ; yet they are prob- 
 ably also, in some degree, chemical precipitates. 
 
 The Mediterranean has been found to contain copper in solu- 
 tion in the proportion of at least 0.01 gramme to the cubic 
 meter. Philips* says that " the black and usually very sul- 
 phurous matter deposited in basins where sea-water has been 
 left to itself constantly contains copper, and the same is gen- 
 erally true with regard to the dark-colored gypseous muds of 
 all ages." 
 
 Most chemically precipitated rocksf certainly seem to be much 
 poorer in original metallic contents than the fragmental ones. 
 The limestones of the Mississippi valley have been shown 
 to contain lead and zinc, disseminated in small quantity ; and 
 it is the conclusion of Whitney, Chamberlin, Winslow and 
 others that the ore-deposits have been concentrated from these 
 disseminations. But these limestones appear to contain the 
 metals in smaller quantity than do the older igneous rocks of 
 the region, so that the dissemination in the limestones can 
 hardly be regarded as a concentration. (See footnote, p. 255.) 
 
 With these and other facts in mind, we cannot safely give up 
 the idea that metals have been concentrated by surface agencies 
 in favorable places and times, and, consequently, that certain 
 strata (possibly also, and restrictedly, certain geologic periods) 
 are, by reason of their original metallic contents, more favor- 
 able than others to the occurrence of ore-deposits. I would 
 even hesitate equally to deny or to affirm that there is a con- 
 nection between the Triassic and Permian red sandstones and 
 certain copper-deposits. Yet we must be careful not to rush 
 into any such hasty generalization as that of Sir Roderick 
 Murchison, who believed that most auriferous rocks are of Si- 
 lurian age,J an obsolete idea which I have nevertheless found 
 in one of our latest works on the metallurgy of gold. 
 
 The concentration of metals by surface agencies, though a 
 fascinating study, is out of place in the special inquiry to which 
 this paper is devoted that of concentration by segregation 
 within molten rocks. 
 
 * Phillips and Louis, Treatise on Ore-Deposits, 1896, p. 132. 
 f This phrase is meant to include limestones of organic origin. 
 J See Kickard's "Keview," Eng. Min. Jour., Oct. 19, 1901, p. 491. 
 $ Eissler, Metallurgy of Gold, 1900, p. 31. 
 
IGNEOUS ROCKS AS RELATED TO OCCURRENCE OF ORES. 259 
 
 III. THE SEGREGATION OR DIFFERENTIATION OF IGNEOUS 
 
 ROCKS. 
 
 Having pointed out the generally-admitted fact that the larger 
 number of ore-deposits have direct genetic connection with ig- 
 neous rocks, I wish to describe one of the chief processes by 
 which the different kinds of igneous rocks originate, which 
 I believe has an important bearing upon the segregation of 
 ores. 
 
 While it is known that igneous rocks may be formed directly 
 from the fusion of sediments (in which case their composition 
 is determined by the selective action of surface agencies), yet 
 it is now widely accepted that many, perhaps most, of them 
 owe their peculiarities of composition to a process of segrega- 
 tion which goes on within the molten masses of the earth's in- 
 terior. The evidence for this process, and some of the details 
 of it, have been pretty fully stated by the writer elsewhere,* and 
 only a few points will be mentioned here. The line of argu- 
 ment is best seen if we proceed from examples on a small scale 
 to successively larger ones. Thus, in the laboratory, materials 
 intimately mingled in solution may separate into distinct crys- 
 tals, or into segregated bunches of like crystals ; and in veins 
 the different minerals are often found bunched in the same way. 
 Nearly every igneous rock shows irregularities of composition 
 due to a similar clustering together of like minerals. These 
 aggregations increase from microscopic size to the size of 
 a man's head; and from these relatively small patches there 
 is a gradation to larger rock-masses, which have marked differ- 
 ences in structure and composition from the rest of the igneous 
 body, of which they, nevertheless, form integral portions. For 
 example, the borders of dikes are frequently less siliceous, and 
 contain more iron (and associated elements) than the interior 
 of the same bodies. In still larger igneous masses, it is found 
 that different portions have slightly different chemical, miner- 
 alogical and structural characters, while they all grade into one 
 another. Again, it has been observed that in a given district 
 different igneous rocks (such as volcanic rocks erupted at differ- 
 ent times) are often closely related, and pass into one another. 
 
 * "Geology of the Yukon Gold-District," 18th Ann. Rep. U. S. Geol. Surv., 
 Part III., p. SCO. 
 
260 IGNEOUS ROCKS AS RELATED TO OCCURRENCE OF ORES. 
 
 Finally, modern petrographic research and comparison have 
 shown that the rocks of a large region, taken collectively, often 
 present constant differences from those of neighboring regions. 
 
 All these phenomena may be explained by the observed fact 
 that in the molten masses, as well as in solutions, there is a force 
 inducing like elements to group themselves together. 
 
 Concerning the exact process by which the materials of the 
 molten rocks are enabled to make such important migrations 
 in order to cluster together, there is no certainty; and, indeed, 
 for the purposes of this paper, it is hardly necessary to inquire. 
 Until recently, it was common to appeal to Soret's principle of 
 molecular flow T , namely, that molecular concentration maybe 
 caused by differences of temperature. Mr. G. F. Becker,* 
 however, has argued against the applicability of this law, on 
 account of the slowness with which it operates. Mr. Beckerf 
 and the writer,J independently and at about the same time, 
 called attention to the probable importance of convection cur- 
 rents in producing segregation. By these currents the miner- 
 als which first crystallize (namely, the heavier minerals, such 
 as magnetite, olivine, hornblende, pyroxene, etc.) would be, to 
 a greater or less extent, concentrated in the outer portions of 
 igneous rock-masses, where they are actually often found. 
 
 The small segregations in igneous rock are usually either 
 more siliceous or less siliceous (more " acid " or more " basic ") 
 than the enclosing rock ; and extremely acid and extremely 
 basic segregations are often found in close association This ten- 
 dency of the molten mass to segregate its highly siliceous con- 
 stituents from the rest has also been studied on a large scale, 
 chiefly from the order of succession of lavas erupted at suc- 
 cessive periods in the same district, or of dikes successively 
 introduced. Brogger and Geikie, from extensive studies of 
 eruptive rocks in Norway and in Scotland, respectively, both 
 concluded that the rocks progressed from the more basic to the 
 more acid varieties. 
 
 i 
 
 r "Some Queries On Rock Differentiation," Am. Jour. ScL, Jan., 1897, 
 4th series, vol. iii., p. 21. 
 
 f "Fractional Crystallization of Bocks," Am. Jour. Sci., Oct., 1897, p. 257. 
 
 t "Geology of the Yukon Gold-District," 18th Ann. Rep. U. S. Geol. Surv., 
 Part III. , p. 306. 
 
 I J. P. Iddings: "The Origin of Igneous Kocks," Bull. Phil. Soc. Wash., 
 vol. xii.,pp. 122, 145, 146. 
 
IGNEOUS ROCKS AS RELATED TO OCCURRENCE OF ORES. 261 
 
 Iddings's* work goes to show the normal law to be, that a 
 rock of intermediate composition is followed by rocks progres- 
 sively higher and, at the same time, by others progressively 
 lower in silica (the more basic and the more acid varieties 
 being associated and contemporaneous), so that the series 
 begins with a mean and ends with extremes. This has been 
 considered by the writer to hold good for the dike-rocks of 
 the Forty-Mile district, Alaska, f and (a problem on a much 
 larger scale) for the petrographic province of which the great 
 basin of Nevada forms a portion. J In the case of the Forty- 
 Mile dikes, the most siliceous varieties were found to be later 
 than the most basic ones. 
 
 The laws thus deduced agree in this : That a molten rock, 
 mass, under favorable conditions, tends to separate (segregate) 
 into a more acid and a more basic portion ; while the fact that 
 the acid (siliceous) rocks characteristically follow, rather than 
 precede, the basic (less siliceous) at any one period, joined with 
 the other known principles of segregation, indicates that the 
 change is effected at each stage by the separation and crystalli- 
 zation of the more basic constituents, leaving the more sili- 
 ceous residue unconsolidated. 
 
 That the basic minerals in general crystallize first in a cool- 
 ing rock has been proved by microscopic study. If the segre- 
 gation is limited in time, and is broken into by such an occur- 
 rence as eruption and consolidation, the differences attained 
 may be comparatively slight; but under favorable circum- 
 stances extremes may be reached. Thus, rocks consisting 
 almost entirely of olivine, pyroxene, or hornblende, together 
 with iron oxides and sulphides, may originate. On the 
 other hand, rocks made up essentially of quartz and alkali 
 feldspars (alaskites) may be formed, and these may pass by 
 gradual transitions into quartz-veins, as will be dwelt upon 
 later. An illustration of these different results is found in the 
 
 * Opcit. 
 
 f " Geology of the Yukon Gold-District," 18th Ann. Rep. U. S. Geol. Surv., 
 Part III., p. 234. 
 
 J " Succession and Relation of Lavas in the Great Basin Region," Journal 
 of Geology, vol. viii. , p. 621. 
 
 % J. E. Spurr: "Classification of Igneous Rocks," Am. Geologist, Apr., 1900, 
 vol. xxv., p. 229. 
 
262 IGNEOUS ROCKS AS RELATED TO OCCURRENCE OF ORES. 
 
 dikes of the Forty-Mile region,* which consist of rocks closely 
 related, being made up chiefly of hornblende, quartz and feld- 
 spar. Yet by gradual changes in the proportions of these 
 minerals, rocks of all degrees of basicity and acidity are pro- 
 duced, terminating, on the one hand, in hornblendites (com- 
 posed almost entirely of hornblende) and pyroxenites, contain- 
 ing pyrite, pyrrhotite, ilmenite and other metallic minerals; 
 and, on the other hand, in alaskites, growing gradually more 
 siliceous until they pass, with no break, into quartz-veins. 
 
 In the progress of segregation, we have seen that in the 
 acid-gaining portion there is a continuous increase of silica, 
 due to the constant precipitation ^nd removal of the basic por- 
 tions. There is also an attendant increase in the amount of 
 water. 
 
 As is shown by microscopic and chemical study, all rocks 
 contain water, but the molten material contains much more 
 than the resulting rock. Most of this water is expelled at 
 the moment of solidification, together with certain gases and 
 a great variety of other materials held in solution, f When 
 rocks cool at the surface, this escaping water forms the clouds 
 of steam, highly charged with gases and minerals, which issue 
 from fissures and other vents ; but when they solidify below the 
 surface the waters and gases are forced into the enclosing rock, 
 producing the recrystallization and rearrangement of its con- 
 stituents, called contact-metamorphism. This is chiefly confined 
 to the contacts of siliceous igneous rocks, being especially re- 
 markable around intrusive masses of granite, where it occupies 
 a zone which, in extreme cases, may be several miles in width. 
 
 It seems, therefore, that the molten material from which 
 siliceous rocks solidify contains more water than the basic ma- 
 terial. Therefore, we may believe that by the progressive sep- 
 arating out of the more basic constituents the residual portion 
 of a molten mass becomes more aqueous and more siliceous. 
 Thus the peculiar form (often in lenses, not visibly communi- 
 cating with large bodies of igneous rocks) and coarse crystalli- 
 zation of pegmatites are explained; for these rocks are near 
 the end-product of the siliceous series; and the pegmatic 
 
 * "Geology of the Yukon Gold -District," 18th Ann. Eep. U. S. Geol Surv., 
 Part III., p. 233. 
 
 f Daubre'e, Geologic Experim&ntale, Paris, 1879, p. 152. 
 
IGNEOUS ROCKS AS RELATED TO OCCURRENCE OF ORES. 263 
 
 rocks, by the disappearance of feldspar and mica, grade into 
 pure quartz-veins, which show by their structure that they have 
 been deposited from solutions so attenuated that they may best 
 be described as waters highly heated and charged with mineral 
 matter in solution. 
 
 By this process of rock-differentiation, concentration is con- 
 tinually effected through the segregation of like materials. 
 Most of these materials are not commercially valuable. Thus 
 the frequent segregation of masses of nearly pure hornblende, 
 pyroxene or quartz has no lively interest for the miner. But 
 when (as often happens) such segregations are feldspar or mica, 
 they may acquire economic importance. And if the commonest 
 of rock-constituents may be thus concentrated, other substances 
 may be, also. In the basic Forty-Mile dikes, mentioned above, 
 there was so large a proportion of ilmenite, magnetite, pyrrho- 
 tite and other metallic minerals that small pieces of the rock 
 were drawn by the magnet. A slight further concentration 
 would give commercially valuable masses ; and there is good 
 evidence that, in other districts, many such masses have origi- 
 nated in this way. 
 
 IV. THE ORDER OF CRYSTALLIZATION OF MINERALS IN 
 
 IGNEOUS ROCKS. 
 
 The process of segregation, which we have considered on a 
 large scale, with the progressive precipitation of basic ingre- 
 dients and the leaving behind of the siliceous ores, is recorded 
 on a small scale in the internal structures of igneous rocks, as 
 studied under the microscope. 
 
 Under this head I cannot do better than quote Prof. J. F. 
 Kemp,* who says : 
 
 " Microscopic study of the igneous rocks has shown that, with few exceptions, 
 the rock -making minerals separate from a fused magma on cooling and crystal- 
 lizing in a quite definite order, f Thus the first to form are certain oxides, mag- 
 netite, specular hematite, ilmenite, rarely chromite and picotite, a few silicates, 
 unimportant in this connection (zircon, titanite), and the sulphides, pyrite and 
 pyrrhotite. Next after these metallic oxides, etc. , the heavy, dark-colored basic sil- 
 icates, olivine, biotite, augite, and hornblende, are formed. All these minerals are 
 characterized by high percentages of iron, magnesium, calcium and aluminum. 
 
 * Ore-Deposits of the United States and Canada, 4th ed., p. 33. 
 
 f H. Rosenbusch, "Ueberdas Wesen der kornigen und porphyrischen Structur bed- 
 Massengesteinen," Neues Jahrbuch, 1882, ii., 1. 
 
264 IGNEOUS ROCKS AS RELATED TO OCCURRENCE OF ORES. 
 
 They are very generally provided with inclusions of the first set. Following the 
 bisilicates in the order of crystallization come the feldspars, and after these the 
 residual silica, which remains uncombined, separates as quartz." 
 
 V. THE FORMATION OF MINERAL SEGREGATIONS IN MOLTEN 
 
 MASSES. 
 
 It has been shown that in the process of segregation in 
 molten masses there is a recognized tendency to split up into 
 more siliceous and less siliceous portions. The basic materials 
 thus concentrated may be the almost exclusive constituents of 
 the resulting rocks. Thus there are not uncommonly rocks 
 made up essentially of the dark, heavy, basic, ferro-magne- 
 sian minerals, biotite, olivine, pyroxene and amphibole, with 
 metallic minerals, such as magnetite, ilmenite, etc., in smaller 
 amounts. The acid materials likewise may form rocks without 
 important admixture of the basic ones, as in quartz alkali- 
 feldspar rocks (alaskite), or in rocks made up almost entirely 
 of alkali-feldspar (sanadinite, albitite, etc.). Further, as al- 
 ready pointed out, the constituent minerals may separate out 
 from the mixture and the like crystals may group themselves 
 together. Thus, there are rocks consisting almost entirely of 
 olivine alone (dunite), of hornblende alone (hornblendite), of 
 pyroxene alone (pyroxenite), of orthoclase feldspar (sanadinite), 
 of soda-feldspar (anorthosite), and of lime-feldspar (anorthite 
 rock). This completes the roll of the commonest rock con- 
 stituents, save the micas and quartz. Although mica forms 
 small segregations in igneous rocks, the writer is not aware 
 that it occurs as the only essential mineral in any considerable 
 mass of such rock. Quartz also appears at first sight to be an 
 exception ; but the writer will try to show later that this is not 
 so, and that many considerable masses and veins of quartz are 
 the result of segregation from the same molten material that 
 produces other igneous rocks. 
 
 Besides these commonest original or primary minerals, there 
 are others which are commonly present in marked quantity in 
 almost every fragment of igneous rock. Perhaps the most 
 important of these is magnetite, which is found in nearly all 
 rocks. Besides this, there are other common metallic min- 
 erals, such as pyrite, ilmenite and pyrrhotite all iron minerals. 
 Chromite is rarer. Among the non-metallic accessory min~ 
 
IGNEOUS ROCKS AS RELATED TO OCCURRENCE OF ORES. 265 
 
 erals, zircon, titanite and apatite are perhaps the most impor- 
 tant. All of these less common minerals (as well as others 
 not mentioned) are known to segregate, to a certain extent at 
 least, so that they are many times more abundant in some rocks 
 than in others. 
 
 This being the case, it is natural that the still rarer minerals 
 and elements also should segregate, and should be found in 
 certain rocks in far larger quantity than in others ; and, indeed, 
 this is known to be the fact. 
 
 VI. THE UNKNOWN FINER LAWS OP EOCK-SEGREGATION. 
 
 If there were invariable associations between certain rocks 
 and certain valuable minerals, prospectors and miners would 
 probably have detected it long ago, especially as regards the 
 metals. But in the majority of cases the exceptions, to any 
 rule we may be tempted to construct, are so numerous that we 
 abandon the attempt. That this fact, however, does not contra- 
 dict the conclusions above reached in regard to the preferential 
 segregation of these minerals into certain rocks will appear when 
 we consider how we name and distinguish the rocks themselves. 
 The existing classifications of rocks are all based upon the rel- 
 ative content of the common constituents, the rarer ones being 
 necessarily disregarded. The divisions, granite, syenite, dunite, 
 diabase, basalt, phonolite, and the whole legion of others, are 
 (apart from considerations of structure, age, mode of occur- 
 rence, etc., which have for the moment no bearing on this dis- 
 cussion) founded upon the presence and relative proportions of 
 the ordinary minerals quartz, the various feldspars and felds- 
 pathoids, olivine, mica, amphibole and pyroxene. Even in 
 classifications based upon the chemical composition of the 
 whole rock, the component minerals being lumped together for 
 analysis, only certain ordinary elements are taken into account, 
 and the rock is assigned to its place upon the basis of the rela- 
 tive proportions of silicon, aluminum, iron, calcium, magne- 
 sium, sodium and potassium. Rock-divisions based on these 
 elements do not necessarily connote the presence or absence of 
 any others. For example, a petrographer finding a, certain 
 igneous rock knows at once that this rock is unusually rich 
 in calcium, sodium, aluminum or silicon ; but he does not know 
 if it contains more or less than the average quantity of lead, 
 
266 IGNEOUS ROCKS AS RELATED TO OCCURRENCE OF ORES. 
 
 silver or mercury. Each element follows its own independent 
 law of segregation, and disregards the established rock classifi- 
 cation. Even with the commoner minerals and elements upon 
 which this classification is roughly based, the variations are so 
 wide as to lead the petrographer into grave difficulties. Thus, 
 among the rocks which have been called gabbro we may find 
 some consisting almost entirely of feldspar, and others made 
 up chiefly of pyroxene. One of the commonest chemical divi- 
 sions of the rocks is into acid, basic and intermediate kinds, 
 essentially according to the proportion of silica present; but 
 rocks of different mineralogical composition may have the same 
 acidity. The basic rocks are rich in ferro-magnesian silicates, 
 and so should be exceptionally strong in magnesia; but occa- 
 sionally cases may be found where gabbro shows less magnesia 
 than granite. 
 
 We can hardly expect, therefore, that the identification- of 
 a rock-species, under the accepted classification, will be of 
 much help in guiding us to a knowledge of the relative con- 
 tent of the rarer elements. To arrive at such a knowledge, we 
 should have a classification based principally upon the content 
 of these rarer elements, and recognizable in practice by easy 
 physical and chemical marks. But this is clearly impracticable. 
 
 In this difficulty, we may be helped to some extent by the prin- 
 ciple which underlies the laws of chemical affinity and the asso- 
 ciation of minerals. Elements and minerals have tendencies to 
 cluster in groups marked by some common characteristics ; each 
 element or mineral prefers to associate with certain elements or 
 minerals rather than with others. This law of selective asso- 
 ciation has long been recognized by the geologist and the 
 chemist. So it seems reasonable that among the rare elements 
 and minerals not considered in rock-classification, some may 
 have such strong preferential association with certain of the 
 commoner rock-constituents on which this classification is 
 based that WQ may be able to see some connection, even if a 
 rude one, between these rarer constituents and the established 
 rock-types. 
 
 VII. THE PRESENCE OF METALS IN THE IGNEOUS ROCKS. 
 
 Iron is present often in high percentage in nearly every 
 igneous rock. It occurs not only in the dark ferro-magnesian 
 
IGNEOUS HOCKS AS RELATED TO OCCURRENCE OF ORES. 267 
 
 silicates, but also as oxides and sulphides, as hematite, magne- 
 tite, ilmenite, pyrite and pyrrhotite. 
 
 Chromium, in the form of chromite and picotite, chrome- 
 diopside, etc., occurs in marked quantities as an original con- 
 stituent of many basic igneous rocks. Manganese is present 
 in nearly every igneous rock, as a not unimportant constituent' 
 of the ferro-magnesian silicates. The rarer metals, lead, cop- 
 per, zinc, tin, antimony, arsenic, nickel, cobalt, silver, gold, and 
 the still rarer ones, have all been repeatedly found in fresh 
 igneous rocks, particularly in the dark bisilicates. 
 
 VIII. THE CONCENTRATION OF COMMERCIALLY- VALUABLE MIN- 
 ERALS BY SEGREGATION WITHIN MOLTEN BASSES, PREVIOUS 
 TO THEIR CONSOLIDATION. 
 
 1. Iron. 
 
 The fact that iron is unequally distributed in igneous rocks 
 is well known. Many highly siliceous rocks (acid granites, 
 alaskites, etc.) have only a trifling quantity (often 1 per cent, 
 or less), while the basic rocks may contain 10, 15, and even 20 
 per cent, of iron oxide. Of this iron, a part is generally in 
 the form of magnetite, a mineral shown by the microscope to 
 be thickly disseminated in many basic rocks. It is generally 
 titaniferous, and grades into ilmenite. From the highly mag- 
 netiferous phases of ordinary basic rocks to a phase where the 
 magnetite becomes the principal constituent is an easy step. 
 Such are the occurrences at Cumberland, Rhode Island, at 
 Taberg, in Sweden, and in many other places. At some of 
 these localities the iron mineral may gradually increase so as 
 almost to exclude the other constituents, as at Taberg; or it 
 may quite do so, as in the anorthosites of Minnesota and else- 
 where, forming masses of iron-ore. As to the origin of these 
 ores by segregation within the molten masses previous to cool- 
 ing, there is a practical unanimity of opinion. 
 
 2. Chromium. 
 
 Like iron, chromium has a very manifest uneven distribution 
 in igneous rocks, being rare in the siliceous ones, while in many 
 of the basic ones it forms a not insignificant constituent, espe- 
 cially in rocks containing olivine.* In these rocks its relations 
 
 * Zirkel, Lehrbuch der Petrographie, 2d ed., vol. i., p. 426. 
 
268 IGNEOUS HOCKS AS RELATED TO OCCURRENCE OF ORES. 
 
 to other minerals show that, like magnetite, it is one of the earli- 
 est to crystallize during consolidation. That the chromite may, 
 in some portions of these rocks, become so abundant as to form 
 the principal constituent, the rock being nevertheless in nearly 
 the state in which it cooled from fusion, is an occurrence which 
 we might expect from our knowledge of the selective segregation 
 of other constituents, and one which has been repeatedly ob- 
 served. Yogt* has described a fresh peridotite from Norway 
 which was almost or quite rich enough in chromite to be worthy 
 of exploitation. The most important occurrences of chrome- 
 ore occur in serpentines, which can generally be shown to be 
 the product of decomposition of basic igneous rocks, chiefly 
 peridotites (olive rocks); and these deposits are considered 
 by Yogt to be the result of segregation while the mass was 
 molten (magmatic segregation), although they had been ex- 
 plained by others as due to after-actions which took place dur- 
 ing the alteration of the fresh rock to serpentine, or even to 
 pneumatolytic (vaporous) action at the time of the rock's con- 
 solidation. J. H. Pratt, after studying the chrome-ores of 
 North Carolina, arrived at the same conclusion as Yogt for 
 other regions, namely, that the ores were actually magmatic 
 segregations. Kempf favors the same origin for other chromite- 
 deposits in the United States. The writer, after examining the 
 chromite-deposits near Saloniki, Turkey (Macedonia), and also 
 in Asia Minor, inclines to the belief that most of these deposits 
 have originated as magmatic segregations from the enclosing 
 peridotitic rock. 
 
 3. Nickel. 
 
 Nickel occurs as an original constituent of some olivinesj in 
 basic igneous rocks. It is also found in more considerable 
 amount in pyrrhotite, an iron sulphide which is frequently a 
 primary mineral in igneous rocks and one of the first to crys- 
 tallize on consolidation. Nickel occurs also as an alloy with 
 native iron, in meteorites and in basalt. 
 
 In certain igneous rocks as, for example, in the peridotites 
 of Douglas county, Oregon, and of Webster, North Carolina 
 nickel is much more abundant than in others of the same petro- 
 
 * Quoted by J. F. Kemp, Ore- Deposits of the U.S. and Canada, 4th ed., p. 413. 
 f Op. tit., p. 415. J Dana, System of Mineralogy, 6th ed., p. 453. 
 
IGNEOUS ROCKS AS RELATED TO OCCURRENCE OF ORES. 269 
 
 graphical character. In the instances named, the nickel, upon 
 the weathering of the rock, separated out as nickel silicate, and 
 became concentrated sufficiently to be of possible economic im- 
 portance. 
 
 Although these ore-deposits are immediately due to circulat- 
 ing surface-waters, which have accomplished a second concen- 
 tration, the first and most important concentration was that 
 which brought together unusual quantities of nickel in these 
 particular rocks, and this was plainly done by magmatic segre- 
 gation. 
 
 It has already been noted that pyrrhotite, like the other 
 early crystallizing metallic minerals, may become abundant as 
 a primary constituent of igneous rocks as, for example, in the 
 case of the Forty-Mile creek dike, already mentioned.* Cases 
 where niccoliferous pyrrhotite in basic igneous rocks, evidently 
 a primary constituent, gradually increases so as to form com- 
 pact masses and to become a valuable ore, have been described 
 on the best authority. 
 
 Of such origin (partly, at least) seem to be the niccoliferous 
 pyrrhotites of Sudbury, Ontario, and those of the Gap mine, 
 Lancaster, Pennsylvania. f 
 
 4. Cobalt. 
 
 This metal has the closest associations with nickel, and the 
 general conclusions arrived at for the one are probably to a 
 considerable degree good for the other. Like nickel, cobalt is 
 present in perceptible quantity in certain basic igneous rocks, 
 where it has been identified as occurring in olivine,J and, al- 
 loyed with native iron, nickel and copper, in Greenland basalt. 
 
 As yet, however, we have not sufficient reliable data to de- 
 termine whether any important cobalt-ores are formed princi- 
 pally by magmatic segregation. 
 
 5. Platinum. 
 
 Platinum, in perhaps the majority of cases, is found closely 
 associated with chromite or nickel, or both. Like these min- 
 erals, it is almost invariably genetically connected with basic 
 
 * See p. 263. 
 
 f J. F. Kemp, Ore-Deposits of the United States and Canada, 4th ed., p. 431. 
 
 | Dana, System of Mineralogy, 6th ed., p. 453. 
 
270 IGNEOUS ROCKS AS RELATED TO OCCURRENCE OF ORES. 
 
 olivine rocks, or with the serpentine-rocks arising from the 
 alteration of these. As an original constituent in basic igne- 
 ous rocks, it is said to have been found both by Daubree and 
 Engelhardt. More recently, native platinum has been discov- 
 ered in igneous rocks in the Urals, in the Nizhni-Tagil district, 
 and the Goroblagodat district. These are extremely basic peri- 
 dotitic rocks, containing large amounts of magnetite and chro- 
 mite, besides platinum. According to Inostranzeff, the plati- 
 num occurs as grains and leaves in the chromite. In the 
 Goroblagodat district, while the peridotites contain by far the 
 larger amount of platinum, Saytzeff found the metal as an 
 original constituent in other igneous rocks also, such as porphy- 
 rite, gabbro-diorite, and syenite-gneiss. Mr. C. W. Purington 
 also obtained, on crushing and panning the peridotite of this 
 district, many fine colors of platinum.* The writer has also 
 had the privilege of visiting the district, and of collecting 
 some of the platinum-bearing peridotite. 
 
 The Ural occurrence, both by reason of the presence of the 
 platinum disseminated in basic igneous rocks and its connec- 
 tion with chromite and magnetite of acknowledged igneous 
 origin, must be admitted to be a product of magmatic segrega- 
 tion; and how powerful this segregation has been we learn 
 from the fact that assays of the ferrous blebs (the most basic 
 segregations) in the Nizhni-Tagil rocks gave a figure corre- 
 sponding to $50 per ton.f 
 
 That in this region the platinum has been remarkably con- 
 centrated, as compared with similar rocks in other places, is 
 shown by the observation of Saytzeff that even rocks elsewhere 
 not known to be platiniferous " porphyrite, gabbro-diorite and 
 syenite-gneiss " contain it. J 
 
 6. Copper. .. 
 
 Copper, as an original constituent, is known to enter into 
 the composition of the dark ferro-magnesiaii silicates of the 
 igneous rocks. It occurs also in meteorites, and, alloyed with 
 
 * C. W. Purington, "Platinum Deposits of the Tura River-System," Trans., 
 xxix , p. 8. t Purington, op. tit., p. 8. 
 
 J A note in the Eng. and Min. Jour., November 16, 1901, p. 632, says that 
 samples of rock from the State of Washington contain, according to Prof. J. F. 
 Kemp, from 0.375 to 0. 5 oz. of platinum per ton. The nature of the rock is not 
 stated. 
 
IGNEOUS ROCKS AS RELATED TO OCCURRENCE OF ORES. 271 
 
 native iron, in the Ovifak (Greenland) basalt. The segrega- 
 tions of pyrrhotite before noted in connection with nickel, and 
 believed to have formed in the distinctly ante-consolidation, 
 period, are frequently cupriferous, and even contain copper 
 pyrites, as at Sudbury, Ontario. The magmatic segregation of 
 the pyrrhotite being granted, the copper also has probably been 
 chiefly concentrated in the same way.* 
 
 According to some observers, even high-grade copper-ores 
 in various districts have had this origin, f 
 
 7. Gold. 
 
 Pyrrhotite frequently, and chalcopyrite generally, contains 
 gold. Some masses of auriferous pyrrhotite and chalcopyrite 
 have been thought to have originated like the niccoliferous 
 pyrrhotite above mentioned. Such is the case at Rossland, 
 B. C., where the ores have been considered by many writers to be 
 magmatic segregations, while other observers, equally reliable, 
 believe them to be secondary replacement deposits or fissure- 
 veins. The hypothesis of a first concentration by magmatic 
 segregation and a second by circulating waters may possibly 
 be the key to the problem. 
 
 Native gold, probably as an original constituent, has been 
 found in granite, J in eurite (alaskite), in quartz-trachyte, || 
 and in gabbro.^f 
 
 IX. THE ORIGIN OF CERTAIN GOLD-QUARTZ VEINS. 
 
 As remarked in the preceding paragraph, native gold has 
 been found in both basic and acid rocks. It has also been de- 
 tected in the dark ferro-magnesian silicates of rocks of all de- 
 grees of acidity. The commercially-valuable concentrations 
 of gold are generally connected, now with basalt or gabbro, 
 now with diorite, now with phonolite, rhyolite, or granite. 
 They occur also, in many different forms, as replacement-de- 
 
 * J. F. Kemp, Ore-Deposits of the U. S. and Canada, 4th ed., pp. 436-7. 
 f Vogt " Problems in the Geology of Ore-Deposits," Trans., xxxi., p. 131. Gen- 
 esis of Ore-Deposits, p. 642. 
 
 J G. P. Merrill, Am. Jour. ScL, April, 1896, 4th series, vol. i., p. 309. 
 
 I G. W. Card, Records Oeol. Surveys of N. S. W., 1895, p. 154. 
 
 || W. Moricke, Tscherwak, Mih.Mitth., xii., p. 195. 
 
 fl Cited by J. F. Kemp, Ore- Deposits of the United States and Canada, 4th ed., p. 36, 
 
272 IGNEOUS ROCKS AS RELATED TO OCCURRENCE OF ORES. 
 
 posits in limestone; as disseminations in igneous and sedi- 
 mentary rocks ; as contact-deposits near intrusive masses ; and 
 in fissure-veins. Most of the known processes by which ore- 
 deposits are formed have probably been active in producing gold- 
 ores. A possible case of origin by segregation in a basic magma 
 has just been noted (at Rossland). But the writer believes that 
 most frequently the metal is concentrated in siliceous magmas. 
 
 After studying the Yukon gold-quartz veins in 1896-7, the 
 writer announced a theory of their formation as the end- 
 product of rock-segregation in the region where they occur.* 
 In this connection a brief outline of the theory will be given, 
 with a few additional observations, since made, which tend to 
 strengthen it. 
 
 Under a previous heading, in considering the segregation 
 (differentiation) of igneous rocks, the conclusion has been 
 reached that many magmas segregate by a repeated concentra- 
 tion and consolidation of the basic constituents, leaving a more 
 siliceous residue. 
 
 Just as this process may result in rocks of extreme basicity, 
 such as olivine, hornblende and augite rocks, and even in seg- 
 regated masses of the metallic minerals which ordinarily are 
 accessory constituents, so, at the other end of the series, very 
 siliceous rocks arise. From the siliceous granites the transi- 
 tion is gradual (and may often be observed in a single rock- 
 mass) to more siliceous rocks, consisting almost entirely of 
 quartz and alkali-feldspar without important admixture of the 
 dark ferro-magnesian minerals. 
 
 These rocks are regarded by the writer as far more wide- 
 spread and important than has generally been recognized, and 
 to the group he has applied the general term " alaskite."f 
 These alaskites may pass gradually into quartz-veins. 
 
 In the multitudinous and varied dike-rocks of Forty-Mile 
 creek, Alaska, where most of the observations were made 
 which led up to the theory in question, every stage in the in- 
 creasing acidity was observed. J The rocks which here occur 
 
 * J. E. Spurr, "Geology of the Yukon Gold-District," ISth Ann. Kept. U. S. 
 Geol. Surv., Part TIL, p. 312. 
 
 f J. E. Spurr, "Classification of Igneous Rocks," Am. Geologist, April, 1900, 
 p. 229. 
 
 J J. E. Spurr, "Geology of the Yukon Gold-f)istrict," 18th Ann. Rept. U. S. 
 Geol. Surv., PartllL, p. 232. 
 
IGNEOUS ROCKS AS RELATED TO OCCURRENCE OF ORES. 273 
 
 in greatest bulk are hornblende granites and hornblende dio- 
 rites, both of medium acidity. From these rocks the change 
 is very gradual to the extremely basic rocks before mentioned. 
 We -will, however, not dwell on this phase of the segregation, 
 but turn to the development of the siliceous rocks, which is 
 equally well displayed. 
 
 The basic hornblende granite, which forms the greatest rock 
 masses, contains subordinate quantities of biotite. By a very 
 gradual transition the hornblende diminishes in amount as the 
 proportion of biotite increases, so that the rock becomes a 
 biotite-granite ; and in many dikes the amount of biotite be- 
 comes less and less, giving rise to an extremely siliceous 
 granite, in which the biotite is an insignificant constituent as 
 compared with the quartz and feldspar. With further diminu- 
 tion of the biotite the granites change into essentially quartz- 
 alkali feldspar-rocks alaskites. These rocks are sometimes 
 fine-grained, or may be coarse, like granites, but have a nearly 
 uniform structure and composition. In the alaskite series the 
 change is continued by a relative increase in amount of quartz 
 and decrease of feldspar. One remarkable phase studied is a 
 porphyritic dike-rock whose ground-mass consists almost en- 
 tirely of quartz in small interlocking grains, giving, both in 
 the hand-specimen and under the microscope, the exact appear- 
 ance of a quartzite. Yet this rock contains scattered, but regu- 
 larly distributed, porphyritic crystals of feldspar. It is thus 
 not only related by the closest ties to similar slightly less sili- 
 ceous alaskites of the same district, but it is only removed by 
 its scattered porphyritic crystals from being a typical quartz- 
 vein. Moreover, the superabundant quartz in these very sili- 
 ceous dikes tends to segregate into bunches, which may become 
 large, and which have all the characteristics of ordinary vein- 
 quartz. With the progressive increase in silicification the 
 quartz begins to occupy an important portion, and finally the 
 larger portion, of the dike. The feldspar becomes restricted 
 to certain places, sometimes occurring irregularly, sometimes 
 collecting near the walls, while the quartz lies in the center.* 
 
 * This distribution is in accordance with the theory of segregation by the aid 
 of convection-currents ("Yukon Gold-District," 18th Ann. Repi. U.S. Geol.Surv., 
 Part III., p. 306), by which the least siliceous and first-precipitated minerals are 
 concentrated near the cooler dike-walls. 
 
 18 
 
274 IGNEOUS ROCKS AS RELATED TO OCCURRENCE OF ORES. 
 
 Finally, by the disappearance of the feldspar, the dike becomes, 
 an ordinary quartz-vein. 
 
 In one and the same dike the change from a coarse alaskite 
 to a typical quartz-vein may be seen in all its stages. 
 
 The quartz-veins generally contain pyrites, as do all the 
 other dikes of the region ; they contain occasional biotite, and 
 some segregated calcite, as do also the coarse alaskites. It may 
 be remarked, in connection with the calcite, that epidote, the 
 silicate of lime, aluminum and iron, is a constant and impor- 
 tant mineral in all the rocks of the Forty-Mile region, from the 
 hornblendites and pyroxenites to the most siliceous alaskites. 
 
 These veins contain pyrite, argentiferous galena and free gold. 
 From them a portion of the Yukon placer-gold is probably 
 derived, much of the remainder coming from older quartz- 
 veins which, by reason of the shearing and metamorphosis they 
 have undergone, do not offer plain evidence as to their origin. 
 
 Therefore it has been concluded that certain quartz-veins in 
 the Yukon district (part, at least, of which are auriferous) 
 have originated by a process of magmatic segregation, which 
 has separated them from other materials while in a state of 
 aqueo-igneous fusion (the condition of molten rock in general), 
 and that they represent the siliceous extreme of that process. 
 From this standpoint, they are a variety of the igneous rocks. 
 But it has been shown that as magmas become more siliceous 
 they also contain more water ; so, when the stage of quartz- 
 . veins is reached, the magma is believed to be so attenuated 
 that it may best be described as water highly heated and 
 heavily charged with mineral matter in solution. There would 
 thus be no great difference (save in their associations, and very 
 likely in the selection of the mineral matters which they con- 
 tain) between these solutions and others where the water may 
 have had, say, an atmospheric origin ; and a quartz- vein origi- 
 nating by magmatic segregation might often not be distinguish- 
 able from one formed in the many other ways which are possi- 
 ble. The main point of interest, so far as this discussion is 
 concerned, is, as the writer believes, that veins originating by 
 magmatic segregation are especially apt to contain gold (with- 
 out the admixture of so great proportions of the commoner 
 metals as is usual in ore-deposits), and that thus an important 
 class of typical gold-quartz veins has been formed. 
 
IGNEOUS ROCKS AS RELATED TO OCCURRENCE OF ORES. 275 
 
 Having briefly stated the evidence and formulated the theory 
 for the Yukon district, let us recite some of the evidence bear- 
 ing on it elsewhere. 
 
 1. Evidence as to the Origin of Quartz- Veins as Magmatic 
 Segregations. 
 
 Pegmatites are coarsely crystalline rocks which show close 
 relationships with ordinary igneous rocks, such as granites, on 
 the one hand, and with veins, such as are known to be due to 
 precipitation from aqueous solution, on the other. Hence 
 there has been much perplexity and contention, some referring 
 them to the " igneous " rocks and calling them dikes, others in- 
 sisting that they were " aqueous " and true veins. But the 
 latest and best essays on the subject* agree that pegmatites are 
 formed under conditions intermediate between those which 
 govern the formation of siliceous " igneous " rocks like granite, 
 and those under which quartz-veins are formed. There is, in 
 short, no line of demarcation in nature, corresponding to our 
 artificial and arbitrary one, between igneous rocks and certain 
 aqueous veins between granites and certain large masses of 
 quartz. 
 
 Transitions of pegmatite- to quartz-veins, showing absolute 
 and uniform gradation from one to the other, have been noted 
 by Crosby and Fuller, Williamsf and Van Hise,| and transitions 
 or evident close and constant relations between pegmatites 
 and granites have been noted by Crosby, Brogger, Van Hise 
 and Williams. 
 
 Professor C. "W. Hall has furnished notes on eastern and 
 central Minnesota, where, in connection with intrusions of 
 hornblende-biotite granite, are shown " granitic veins." These 
 are " locally pegmatitic, with coarse and well-developed feld- 
 spar individuals imbedded in a matrix of hornblende and bio- 
 tite, while elsewhere they are finely textured, possess a reddish 
 
 * "Origin of Pegmatite," by W. O. Crosby and M. L. Fuller, Amer. Geologist, 
 vol. xix. (1897), p. 147; "Die Mineralien der Syenit-pegmatitgdnge der sudnorive- 
 gischen Augit- und Nephelin-syenite, " by W. C. Brogger, Zeitsch.filr Kryst.,vol. xvi., 
 1890, pp. 215-235. " Origin of the Maryland Pegmatites," by G. H. Williams, 
 15th Ann. Report U. S. Geol Sur. , 1895, p. 675. f Op. tit., p. 679. 
 
 J 16th Ann. Report U. S. Geol. Sur., Part L, 1896, p. 688. 
 
 g Keewatin Area of Eastern and Central Minnesota, Bull. Geol. Soc. Amer., voL 
 xii., pp. 367-8-9 (1901). 
 
276 IGNEOUS ROCKS AS RELATED TO OCCURRENCE OF ORES. 
 
 color, and are highly siliceous in composition." Associated 
 with these are veins of quartz. In the St. Louis river-district 
 the veins, when wide, become pegmatitic. The veins some- 
 times carry segregated sulphides and siderite. One, on Kettle 
 river, has been explored for gold. 
 
 Professor J. F. Kemp* observes that on the north shore of 
 Long Island Sound " pegmatites are abundantly developed in 
 connection with granites, and all grades are shown up to prac- 
 tically pure quartz." One of the largest quartz-veins, which 
 Professor Kemp thinks belongs to the pegmatitic series, car- 
 ries, in portions, ferruginous minerals and traces of gold. 
 
 Dr. E. Hussakf has described an auriferous quartz-vein in 
 Brazil which he regards as an ultra-acid granitic dike. Mr. 
 "Waldemar Lindgren, however, dissents from this conclusion. J 
 
 According to Phillips and Louis, at Timbarra, in Kew South 
 Wales, " gold is found in granite ; these gold-fields consist of a 
 granitic tableland, traversed by dikes of eurite|| and pegma- 
 tite, also occasionally showing veins of auriferous quartz, which 
 'may possibly be segregation deposits." 
 
 At Silver Peak, Nevada, the writer noticed transitions from 
 the granitic rock (which is there intrusive in Cambrian lime- 
 stones) into quartz-veins. Mr. H. "W. Turner, who studied this 
 region more in detail, made the same observation independ- 
 ently, and communicated it subsequently to the writer. Accord- 
 ing to him, these segregated veins seem to be connected in 
 some way with the Silver Peak ore-deposits, which are gold- 
 quartz veins. 
 
 On the Mojave river, in Southern California, the writer ob- 
 served one of the most rapid and complete transitions from 
 quartz-veins into granite which he has ever seen. Here Pale- 
 ozoic limestones and quartzites (considerably metamorphosed) 
 are cut by intrusive granite, whose dikes grade into pegmatite, 
 and these to quartz-veins. In a single dike he observed, within 
 the length of not many yards, a complete transition from a 
 
 * " The Hole of the Igneous Rocks in the Formation of Veins," Trans., xxxi., 
 p. 182. Genesis of Ore-Deposits, p. 693. 
 
 t Zeitschriftfiir prakt. Geologic, 1898, p. 345. 
 
 J " Metasomatic Processes in Fissure- Veins," Trans., xxx., 642, and Genesis 
 of Ore-Deposits, p. 562. 
 
 \ Ore-Deposits, second edition, p. 649. || Alaskite. J. E. S. 
 
IGNEOUS ROCKS AS BELATED TO OCCURRENCE OF ORES. 277 
 
 fine-grained pegmatite to a typical quartz-vein. Gold is found 
 in this locality (Oro Grande), but, unfortunately, he did not 
 remain long enough to find whether it is in these quartz- 
 veins. 
 
 The writer has also studied the transition of granite and 
 alaskite through pegmatitic stages to quartz-veins, in the 
 "Walker river range, in northwestern Nevada, near the Indian 
 reservation ; and again in the Mojave desert, southeast of Ran- 
 deburg, California. 
 
 At Belmont, in Nevada, the writer has made a brief study of 
 an interesting dike-rock and its associated phenomena.* The 
 dike is one of the outlying offshoots from a large body of sili- 
 ceous granite ; it is nearly half a mile wide, and cuts Silurian 
 slates and limestones. Near the contact the slates and lime- 
 stones have been transformed into jasperoidf by the introduc- 
 tion of silica; in part they have also been altered to micaceous 
 schists, often containing disseminated small bundles of yellow 
 and red metallic oxides. In this rock occur quartz-veins which 
 carry rich antimonial silver-ores. 
 
 The dike-rock varies greatly in texture and composition. 
 One specimen collected, classed as a siliceous muscovite-biotite 
 granite, is remarkable for the irregular arrangement of its con- 
 stituent minerals, the quartz often segregating into bunches a 
 quarter of an inch in diameter, with all the characteristics of 
 vein-quartz. A coarser-grained biotite granite at some little 
 distance has the same peculiarity, and in this place the blotches 
 of quartz, mosaics of intergrown grains, are from one-third of 
 an inch to one-half an inch in diameter. But the rock of chief 
 interest is one which looks like a micaceous quartzite, and, 
 indeed, consists essentially of muscovite and quartz. Micro- 
 scopic study reveals it in the presence of the feldspar albite, 
 and proves that the muscovite has largely been derived from 
 the alteration of orthoclase. Yet the rock is fresh and hard, 
 and the change has not been affected by surface weathering. 
 
 "The process must be regarded as one of endomorphism, and as connected and 
 probably contemporaneous with the exomorphism indicated by the alteration of 
 the siliceous limestone of the wall rocks to jasperoid and mica schist. 
 
 * J. E. Spurr, Am. J. Sci., 4th series, vol. x., p. 351 (1900) : "Quartz-Mus- 
 covite Rock from Belmont, Nev., the Equivalent of the Russian Beresite. " 
 t J. E. Spurr, "Geology of Aspen District," Mon. xxxi., U. S. G.S., p. 219. 
 
278 IGNEOUS ROCKS AS RELATED TO OCCURRENCE OF ORES. 
 
 " In both the intrusive and the intruded rock the result of the metamorphism 
 has been the same, producing quartz and muscovite at the expense of the ortho- 
 clase on the one hand, and of the calcite and subordinate minerals on the other. 
 In the case of the wall-rock the metamorphism, being apparently, from its dis- 
 tribution, dependent upon the intrusion, evidently took place after this intrusion, 
 and was brought about by the solutions which accompanied the igneous rock, or 
 were residual from its solidification. Within the dike the similar alteration was 
 probably contemporaneous with that in the country-rock."* 
 
 White quartz-veins, often several feet in width, occur in the 
 immediate vicinity of this intrusive mass. For these the con- 
 clusion is reached that : 
 
 "These quartz- veins are probably contemporaneous with those already de- 
 scribed as occurring in irregular form within the dike-rock itself, and as evi- 
 dently representing the final product of the residual solution of the general 
 magma. In these quartz-veinsf the metallic minerals [chiefly stetefeldtite, an 
 argentiferous ore of antimony, with some lead, copper and iron] are scattered in 
 branches or disseminated particles, rarely in banded form. . . . 
 
 " The metallic minerals being, from their habit, plainly contemporaneous with 
 the quartz-veins which enclose them, it is evident that the deposition of these 
 minerals, the formation of the quartz- veins, the metamorphism of the country- 
 rock to jasperoid and muscovite schist, and the endomorphism of the muscovite- 
 granite to quartz-muscovite rock were contemporaneous occurrences, all brought 
 about by the same agencies, which were the solutions representing the end- 
 product of the differentiation of the granitic intrusive rock." 
 
 This Belmont quartz-muscovite rock acquires additional in- 
 terest as the equivalent of the so-called beresite of the Urals, 
 which the writer has had the privilege of studying in the field. 
 After considerable investigation and discussion, the Ural beres- 
 ite (composed of quartz and muscovite) has been shown by 
 Arzruni to be an alteration from a muscovite-granite in the 
 same way as the Belmont rock. The analogy between the Bel- 
 mont phenomena and those of Berezovsk is still more striking 
 when we consider the close connection of the beresite with 
 gold-quartz veins. This rock forms intrusive dikes from 2 to 
 40 meters wide, cutting schists. Previous to all scientific in- 
 vestigation, these dikes were recognized by the miners as the 
 surest guides to gold. The auriferous veins are found in the 
 dikes, and only rarely extend into the country-rock. They gen- 
 erally stretch across the dikes at right-angles to the walls, and 
 have been considered as filling " fissures of contraction " by 
 
 * Op. cit., p. 355. 
 
 t According to S. F. Emmons, " Geol. Expl. of 4(M Parallel," vol. iii. 
 (Mining Industry), p. 398. 
 
IGNEOUS ROCKS AS RELATED TO OCCURRENCE OF ORES. 279 
 
 Posepny.* This is probably correct, for the veins follow the 
 same lines as the " columnar jointing " of dikes, which are due 
 to contraction. 
 
 At Belmont the important point in determining the age of 
 the quartz- veins is their contemporaneity with the contact- 
 metamorphosis of the wall-rocks, which fixes their period of 
 formation as during the final stage of the consolidation of the 
 granite. We have not sufficient data to announce this same 
 criterion for Berezovsk, and in the study of ore-deposits one 
 must ever beware of reasoning too closely from analogy; but 
 the fact that the " beresite " has, like the Belmont quartz-mus- 
 covite rock, originated not by surface alterations, but through 
 deeper-seated solutions, f that this alteration seems a part of 
 that which produced the gold-quartz veins,J and that the latter 
 are confined to the dikes or their immediate vicinity, all these 
 are in favor of the hypothesis of the origin of the veins as the 
 last and most siliceous and most fluid segregation product of 
 the granitic magma. 
 
 2. The Genetic Connection of Gold- Quartz Veins with Siliceous 
 Igneous Rocks. 
 
 We have reviewed a number of cases of the actually ob- 
 served transition from siliceous igneous rocks to quartz-veins, 
 with or without a pegmatic stage, and in most of these the 
 veins contain disseminated metals, notably gold. When mining 
 engineers and geologists begin to look more carefully for such 
 transitions, it is probable that numerous others will be found. 
 Meantime, the number of instances in which gold-quartz veins 
 are intimately associated with siliceous intrusive rocks is really 
 remarkable. 
 
 On the Pelly river, in British Columbia (a part of the Yukon 
 gold-belt), Dr. G. M. Dawson found evidence to show that the 
 development of quartz-veins had occurred contemporaneously 
 with the upheaval of the granites, and probably by some action 
 superinduced by the granite masses themselves while still in a 
 formative condition. 
 
 * Genesis of Ore-Deposits, first edition, p. 70 ; second edition, p. 76. 
 t The beresite is deeply decomposed by surface agencies, but this is inde- 
 pendent of the agency by which the first rock originated. 
 
 J The beresite itself contains gold in small quantity (50 drachms to the ton). 
 I Ann. Rep. Geol. Nat. Hist. Survey, Canada, vol. iii., Part L, p. 35 B. 
 
280 IGNEOUS ROCKS AS RELATED TO OCCURRENCE OF ORES. 
 
 In the Cook Inlet region, Alaska, gold is found in aplite* 
 dikes, according to Mr. W. C. Mendenhall. In the Nome re- 
 gion, Messrs. Schrader and Brooksf report veins containing 
 sulphides, quartz and calcite, cutting metamorphic marble and 
 schists. A large area of granite is also reported. 
 
 In the Slocan District, British Columbia, according to W. A. 
 Carlyle,J the typical gold-quartz veins, as well as quartz-veins 
 carrying argentite. native silver and gold, appear to be con- 
 fined to granite, while veins containing argentiferous galena, 
 blende, siderite, tetrahedrite, etc., are found both in stratified 
 rocks and granites. In California, "Whitney noted that, While 
 the granite itself is not metalliferous, its appearance seems to 
 be closely associated with the metamorphisrn of the adjacent 
 sedimentary rocks, while this latter condition is, as a general 
 rule, the concomitant of the occurrence of minerals or metal- 
 liferous veins. Prof. J. F. KempH remarks: "The enormous 
 introduction of silica is one of the most extraordinary features 
 of the geology of the Sierras, and indicates a remarkable ac- 
 tivity of circulating waters. The igneous intrusions doubtless 
 promoted, if they did not cause, the circulations." In the 
 Lake of the Woods district, schists, early granite, and gneiss 
 are cut by later granite. The veins are found in the schists, 
 but favor the portions near the contact with the granite or 
 gneiss.^ 
 
 In the gold-bearing region of Nova Scotia, metamorphosed 
 sedimentary rocks containing quartz-veins are cut by many 
 great intrusions of granite.** 
 
 In Madison county, Montana, gold-quartz veins occur in 
 granite; in Beaverhead county, at the contact between lime- 
 stone and granite; in Lewis and Clarke county, in granite 
 and slates, etc. ft 
 
 In Rhode Island, quartz-veins are frequent around the great 
 inclusions of granite. Traces of gold have been met.Jt 
 
 * "Alaskite." J. E. S. t Trans., xxx., p. 238. 
 
 t Quoted by J. F. Kemp, Ore-Deposits of the United States and Canada, 4th ed., 
 p. 395. 
 
 % The Auriferous Gravels of the Sierra Nevada, p. 353. 
 
 || Ore-Deposits of the United States and Canada, 4th ed., p. 370. 
 
 Tf Kemp, op cit.j p. 385. ** Kemp, op cit., p. 397. 
 
 ft Kemp, op cit., p. 320. JJ Kemp, op dt., p. 383. 
 
IGNEOUS ROCKS AS RELATED TO OCCURRENCE OF ORES. 281 
 
 In the Appalachian gold-quartz region are numerous intru- 
 sions of granitic rocks, arid pegmatite is abundant.* 
 
 In British Guiana, gold-quartz veins " occur mostly in meta- 
 morphic schists and gneiss; and nearly all the streams and 
 rivers that traverse regions occupied by the above rocks, or by 
 granite, are gold-bearing, "f 
 
 In the Sutherland gold-fields in Scotland, the rocks are gran- 
 ites, gneiss, mica-schist, and quartzite, and, in a few localities 
 only, quartz-veins. On the stream called the Kildonan, " the 
 miners preferred working either in the vicinity of masses of 
 granite, or in the neighborhood of a partially decomposed 
 greenish schist." 
 
 No gold has been found in situ in this district, but the drift 
 is entirely composed of fragments of purely local rocks, while 
 quartz pebbles are almost entirely wanting. 
 
 Influenced by these and similar considerations, Messrs. Joass 
 and Cameron are disposed to ascribe a granitic origin to the 
 gold of this area.J 
 
 On the island of Bommel, in Norway, the chief country- 
 rock is " gabbro," in which large dikes of " quartz-porphyry," 
 passing into granite, and of altered diorite, occur ; on the south 
 of the district is a large tract of slate, in which are non-aurif- 
 erous quartz-veins. The "quartz-porphyry" dikes, and those 
 of diorite, contain strong gold-quartz veins, whose general con- 
 temporaneity with the period of igneous intrusion is shown by 
 their being older than some dikes and younger than others. 
 
 In the Kotchkar district, in the Urals, the gold-quartz veins, 
 as seen by the writer on the occasion of a brief visit, are imme- 
 diately the results of circulating waters subsequent to the con- 
 solidation of the country-rock ; but they occur in, and are prob- 
 ably primarily dependent upon, the granite. There are analo- 
 gies in many ways between this district and that of Monte 
 Cristo, "Washington State, U. S. A., where, according to the 
 writer's study, the ore-deposits (chiefly replacements of igneous 
 rocks by auriferous sulphides), while immediately the work of 
 ordinary circulating waters, yet are closely dependent upon 
 
 * Phillips and Louis, Ore- Deposits, 2d ed., pp. 786-7. 
 f Phillips and Louis, op cit., pp. 887, 888. 
 J Phillips and Louis, op cit. , p. 320. 
 $ Phillips and Louis, op cit., p. 519. 
 
282 IGNEOUS ROCKS AS RELATED TO OCCURRENCE OF ORES. 
 
 great intrusive bodies of tonalite in which the first concentration 
 has probably been effected by magmatic segregation. 
 
 In India, it has been stated by Mr. King that the so-called 
 quartz-reefs of the Travancore State " are not really veins, but 
 merely the outcrops of beds of quartzite, associated with feld- 
 spar, which run with the foliations of the gneiss. Although 
 minute traces of gold may sometimes be detected in these 
 rocks by assay, the amount present is far too small to render 
 them of any commercial value as a source of that metal." 
 The phrase " beds of quartzite, associated with feldspar," 
 strongly suggests fine-grained siliceous alaskite dikes. In the 
 Wynaad district, " the gold-bearing area consists of granite, 
 gneiss, and various metamorphic rocks, traversed by veins of 
 quartz, which, with their branches, are auriferous." * 
 
 In China, the reported gold-quartz veins occur almost en- 
 tirely in granite, as at Ninghai, the Chao-Yuen district, and 
 Yeshui in Mongolia. f 
 
 In Siberia, the connection of the gold with granite and gran- 
 ititej has been observed in more than one place. 
 
 Turning to Australia, we find a relation of the gold to sili- 
 ceous igneous rocks quite as striking as in California and 
 Alaska. In Victoria, 
 
 "Gold is not only found in veins traversing granite, felsite and diorite, but is 
 also sometimes disseminated throughout the rocks themselves." || 
 
 I quote from Phillips and Louis : ^f 
 
 II In a paper read before the Geological Society of London in April, 1872, Mr. 
 Richard Daintree drew attention to the fact that the auriferous Devonian districts 
 of Queensland are entirely confined to such as are penetrated by certain eruptive 
 rocks, principally pyritous diorites. In these diorites, and near the point of their 
 intersection with the Devonian strata, veins of quartz, calc-spar and iron-pyrites 
 had been examined and found rich in gold, while the extensions of such veins at 
 any considerable distance from the intrusive rocks were found to be barren. In- 
 stances were also adduced to show that the pyrites sporadically distributed 
 through the diorites was occasionally distinctly auriferous, and had, by its decom- 
 position and disintegration, produced drifts containing gold in paying quantities. 
 
 " In a subsequent communication, Mr. Daintree states that since the date of 
 
 * Phillips and Louis, Ore-Deposits, pp. 562-3. 
 
 f Phillips and Louis, op. cit., p. 618. J " Alaskite." J. E. S. 
 
 % Quoted by DeLaunay, "Contribution a F Etudes des Gites Metalliferes, " An- 
 nales d. Mines, August, 1897, 9th series, vol. xii., p. 224. 
 
 || Phillips and Louis, Ore-Deposits, p. 620. fl Op. cit., p. 641-2. 
 
IGNEOUS ROCKS AS RELATED TO OCCURRENCE OF ORES. 283 
 
 his first paper he had learned from Mr. C. Wilkinson, then Government Geolo- 
 gist of New South Wales, that the same facts hold good for the New South Wales 
 gold-fields lying in Upper Silurian or Devonian areas ; and Mr. G. H. F. Ulrich, 
 the Curator of the Technological Museum in Melbourne, in his catalogue of the 
 rocks in that institution, gives details which go to show that the Upper Silurian 
 rocks of Victoria owe their auriferous character to the same cause. 
 
 " He describes the diorites of Victoria as occurring mostly as dikes, varying in 
 thickness from a few feet to several hundred, traversing Upper Silurian strata, and 
 presenting nearly all the ordinary varieties of structure and composition of that 
 rock. They are nearly always impregnated with auriferous pyrites, and are 
 either traversed by or associated with quartz-veins. According to Mr. Ulrich, 
 by far the greater proportion of the quartz-gold furnished by the gold-fields occu- 
 pied by Upper Silurian rocks is derived from dikes of diorite. . . . 
 
 "The question as to when the auriferous pyrites was deposited in these diorites 
 is of much interest, and one that it will be somewhat difficult to solve. It is, 
 however, probable that in the majority of cases the pyrites was contemporaneous 
 with the consolidation of the rock in which it occurs, although it is also possible 
 that it may have occasionally owed its origin to the subsequent passage through 
 the rock of metalliferous solutions. . . . 
 
 " Below the water- level, which usually very nearly coincides with the zone of 
 decomposition, veins of a class which, on the whole, have proved very misleading 
 to the miner, although often rich in gold, usually disappear. These follow the lines 
 of jointing of the rock, and are probably due to the decomposition of auriferous 
 pyrites and the re-deposition, from solution, of a portion of its material in local 
 fissures. . . . Besides the veins above referred to, there are, associated with the 
 intrusive auriferous rocks, others which Mr. Daintree considers as being of far 
 greater practical importance, from being generally of greater width and more 
 likely to be persistent in depth. These he regards as the result of hydrothermal agen- 
 cies which preceded and accompanied the protrusion,* and which in some cases con- 
 tinued long after the intrusive rock had cooled down." 
 
 Again, I quote the following :f 
 
 "Daintree, Racket, Wilkinson and others have shown that a large portion of 
 the gold in Victoria and Queensland is due to the agency of intrusive dikes of 
 felstone, el van and diorite, so that reefs of quartz in Silurian rocks are not, as was 
 at one time supposed, the exclusive source of Australian gold. 
 
 " At Timbarra, gold is found in granite ; these gold-fields consist of a granitic 
 tableland, traversed by dikes of euritej and pegmatite, also occasionally showing 
 veins of auriferous quartz, w hich may possibly be segregation deposits. $ The weath- 
 ered granite is sluiced, and very fine gold, to the extent at times of 5 dwt. to the 
 ton, is obtained. Gold has been found to occur here in unaltered granite, and in eurite,\\ 
 as well as in the decomposed granite." 
 
 In the Transvaal, in the Lydenburg district, a quartz-vein in 
 a diorite dike was worked at Waterfall creek,T and at Ophir 
 Hill is a silicified bed of dolomite, which has been 
 
 * The italics are mine. J. E. S. f Op. cit., p. 649. 
 
 J "Alaskite." J. E. S. g The italics are mine. J. E. S. 
 
 |j The italics are mine. J. E. S. \ Phillips and Louis, op. cit., pp. 734-5, 
 
284 IGNEOUS ROCKS AS RELATED TO OCCURRENCE OF ORES. 
 
 "mineralized by gold-bearing solutions, which are in some way connected geneti- 
 cally with the numerous dioritic dikes that traverse the district." In the De 
 Kaap district the rocks, "both stratified and granitic, are traversed by dikes of 
 diorite and pegmatite. ... In the neighborhood of the granite, these rocks occa- 
 sionally carry small ferruginous intercalated deposits, which are generally aurif- 
 
 3. The Subordinate Connection of Gold- Quartz Veins with Basic 
 
 Igneous Rocks. 
 
 To avoid misunderstanding, I wish to say here that I recog- 
 nize the fact that gold-quartz veins may occur in or near basic 
 intrusives, and may, indeed, be genetically dependent on them. 
 In the Kolar gold-field in India, for example, the auriferous 
 veins invariably occur in a band of "greenstone trap."* In 
 Western Australia the veins are reported to occur chiefly in 
 diorite and biabase.f But certainly an overwhelming majority 
 of gold-quartz veins occur in connection with rocks of the 
 dioritic and granitic families, that is to say, with the two 
 most siliceous families of the three which make up most igne- 
 ous rocks ; and of these granite-diorite rocks, the veins show a 
 decided preference for the more siliceous groups, such as 
 quartz-diorite (tonalite), granite and alaskite. On the other 
 hand, the intimate genetic connection of these typical gold- 
 quartz veins with distinctly basic rocks, such as those of the 
 diabasic family, may be safely called exceptional. 
 
 Therefore, the statement may be formulated that although 
 gold is present in all igneous rocks, and may be unequally distributed 
 in any of them, yet the conditions for concentration by magmatic 
 segregation become more favorable in proportion as the rock becomes 
 more siliceous, and become most favorable in what has been shown to 
 be the extreme siliceous product of rock-differentiation in quartz- 
 veins and dikes. 
 
 The explanation of this is a problem for future study. 
 
 X. RESUME OF THE EVIDENCE CONCERNING THE PREFERENCE 
 OF CERTAIN METALS TO ACCUMULATE, BY MAGMATIC SEG- 
 REGATION, IN CERTAIN ROCK-TYPES OF THE ESTABLISHED 
 CLASSIFICATION. 
 
 I have already pointed out that if the rarer elements, which 
 have been disregarded in establishing the classification of igne- 
 
 * Phillips and Louis, op cit., p. 568. f Phillips and Louis, op. cit., p. 700. 
 
IGNEOUS ROCKS AS RELATED TO OCCURRENCE OF ORES. 285 
 
 ous rocks, find themselves, as a result of magmatic segregation, 
 more closely associated with certain of these rock-types than 
 with others, it is not due to any merit in the classification, but 
 because of the association of these elements with the commoner 
 ones on which the classification is based. In proportion as 
 this association is strong, the preference of a metal for a cer- 
 tain rock becomes more marked. These, then, are some of these 
 preferences : 
 
 1. Basic Rocks. 
 
 Iron, as is well known, is most abundant in basic rocks, and 
 iron-ore deposits formed directly by magmatic segregation are 
 mostly confined to such rocks. 
 
 Chromium ore-deposits, due to magmatic segregation, are 
 chiefly confined to the most basic rocks (peridotites) and their 
 alteration products (chiefly serpentine). 
 
 Platinum also is characteristic of the most basic rocks (peri- 
 dotites and serpentine). 
 
 Nickel is frequently closely associated, as the product of mag- 
 matic segregation, with iron, chromium and platinum, and is 
 especially found in the most basic rocks. 
 
 Vanadium is chiefly found in basic rocks.* 
 
 Copper, on account of its easy mobility, occurs in many dif-. 
 ferent rocks, and as the result of many varied processes. Yet 
 it seems to be especially connected with, and at home in, 
 basic rocks. De Launay saysrf " Copper is geologically close 
 to nickel, with which it is frequently met, notably in the peri- 
 dotites of Canada, for, like nickel, it is, above all, a metal of 
 the basic rocks. . . ." 
 
 2. Siliceous Rocks. 
 
 Molybdenum is chiefly found in connection with the siliceous 
 igneous rocks. 
 
 Tin is seldom met with except in connection with granite. 
 
 Tungsten has practically the same associations as tin. 
 
 The rarer elements in general seldom occur in notable 
 amount, except in pegmatites and granitic rocks. J 
 
 * Resume by J. F. Kemp, Ore-Deposits of the United States and Canada, 3d edi- 
 tion, p. 36. 
 
 f ''Contribution a 1' Etude des Gites Me'tallife'res," Annales des Mines, August, 
 1897, 9th series, vol. xii., p. 191. 
 
 J Kemp, Ore- Deposits of the United States and Canada, 3d edition, p. 36, 
 
286 IGNEOUS ROCKS AS BELATED TO OCCURRENCE OF ORES. 
 
 Gold, as has just been argued, while a mobile metal and 
 widely distributed, seems to show a preference for the siliceous 
 igneous rocks. 
 
 XL THE RELATION BETWEEN ORE-DEPOSITS DUE TO MAGMATIC 
 SEGREGATION AND OTHER ORE-DEPOSITS. . 
 
 In nature there are no hard and fast lines. So we find that 
 ore-deposits originating, as argued, by magmatic segregation, 
 pass by transition stages into others whose characteristics de- 
 mand a different interpretation. 
 
 Especially close is the connection between certain magmatic 
 segregations, certain contact-deposits, and certain deposits of 
 gaseous-aqueous (pneumato-hydatogenic) origin. 
 
 Magmatic segregations take place while the rock, as a whole, 
 is yet liquid; they are due to the mobility of elements or crys- 
 tallizing minerals in this liquid, and may be conveniently con- 
 ceived as taking place through the action of convection-cur- 
 rents. 
 
 Upon the cooling of an igneous intrusive rock, however, 
 what might be called a forced segregation takes place. As the 
 rock becomes solid, those materials which are " left-over " are 
 expelled, and find their way into the neighboring rock, or along 
 the fissures of the igneous rock itself. These "left-over" ma- 
 terials consist chiefly of water, which is usually highly sili- 
 ceous, and contains a great variety of other mineral matters in 
 solution, and also, very commonly, an unusual quantity of 
 gases. In these excretions the proportion of gaseous to liquid 
 constituents appears to vary as widely as possible dependent, 
 probably, partly on the nature of the cooling-rock, partly on 
 the conditions or rate of cooling, etc. According as the gase- 
 ous or the liquid elements preponderate, there result ore-de- 
 posits (for these expelled solutions often contain metals), which, 
 from the internal evidence they offer as to their mode of for- 
 mation, may be classed as pneumatogenic (pneumatolytic) 
 pneumato-hydatogenic (gaseo-aqueous), or hydatogenic. To 
 the first class belong the ores deposited by volcanic fumaroles, 
 and the writer has referred the gold-ores of Mercur, Utah, to 
 the same general division.* The second and third classes are 
 
 * J. E. Spurr, " Economic Geology of the Mercur Mining District," 16^ Ann. 
 Kept. U. S. Geol. Survey, Part II., p. 452. 
 
IGNEOUS ROCKS AS RELATED TO OCCURRENCE OF ORES. 287 
 
 of great importance. To the second belong the tin-veins, and 
 to the third the u contact-deposits " proper.* 
 
 The gold-quartz veins, such as have been considered to be 
 formed by magmatic segregation, the veins of the tin-group,, 
 and the contact-deposits proper, are perfectly distinct in char- 
 acteristics and origin; yet between the first and the second^ 
 and the second and the third, there are all transitions, indicat- 
 ing transitions in the conditions which produced them. In all 
 three cases the mineralizing agents may be described as highly- 
 heated water heavily charged with silica, and containing metals 
 and other mineral matters, all being directly derived from an 
 igneous rock in its last stages of consolidation from a molten 
 condition. All are characteristic of the more siliceous intru- 
 sives. Tin-veins seem to be confined to granitic rocks ; gold- 
 quartz veins prefer granite, and after that diorite ; while con- 
 tact-deposits, like contact-metamorphism in general, are chiefly 
 characteristic of the more siliceous rocks, granite or diorite. 
 Yet the first may be conceived of as quietly segregating under 
 pressure in a mobile though probably slowly congealing magma, 
 the second as escaping from a cooling-rock into fissures or other 
 channels, with relief of pressure and the consequent assump- 
 tion of different form and proportion, and the third as also 
 escaping from a cooling-rock, but under pressure and penetrat- 
 ing largely by capillary or osmotic action into the rock in con- 
 tact with the igneous body. Each of these processes involves 
 a different selection of elements by the solutions hence tin- 
 veins and gold-quartz veins are generally quite distinct. 
 
 Many pegmatites are closely related to tin-veins. They not 
 infrequently contain cassiterite, and are characterized by fluorine 
 and boron compounds, indicating gaseo-aqueous origin. Such 
 pegmatites, like the true tin-veins, are not likely to contain 
 gold, and cannot be taken as an indication of probable gold- 
 quartz veins. On the other hand, pegmatites containing slight 
 evidence of pneumatoiytic origin may be closely related to and 
 associated with gold-quartz veins. In some pegmatites gold 
 has been found. But the quartz-veins that pass into relatively 
 
 * J. H. L. Vogt, "Problems in the Geology of Ore- Deposits," Trans., xxxi., 
 pp. 139,140. Genesis of Ore-Deposits, pp. 650, 651. Waldemar Lindgren, "Char- 
 acter and Genesis of Certain Con tact- Deposits," Trans., xxxi., p. 226. Genesis of 
 Orc-Dcpotils, p. 716. 
 
.288 IGNEOUS ROCKS AS RELATED TO OCCURRENCE OF ORES. 
 
 fine-grained, highly siliceous igneous rocks, with slight display 
 of coarse-grained pegmatite, have probably been formed under 
 the most favorable conditions for the segregation of gold in 
 them,z'.e., comparative freedom from the pneumatolytic actions 
 which are so unusually important in forming the cassiterite 
 veins. Yet the occasional presence of tin and its close asso- 
 ciate, tungsten, as well as tourmaline, fluorite, etc., in gold- 
 quartz veins shows that one set of conditions may pass gradu- 
 ally into the other. The occasional presence of tourmaline, 
 fluorite, wolframite, tin, etc., in zones of contact-metamor- 
 phosis and in contact ore-deposits, contrary to the usual occur- 
 rence, is an illustration of the same principle.* 
 
 THE SEQUENCE OF VOLCANIC ERUPTIONS CONSIDERED IN 
 CONNECTION WITH THE SEQUENCE OF METALLIFEROUS VEINS. 
 
 It has already been described how, in a certain volcanic field, 
 the rocks erupted or intruded at different periods are of quite 
 different character, and how dissimilar rocks may be most 
 closely associated. Extremely acid and extremely basic rocks 
 are often almost or quite contemporaneously intruded or 
 erupted in the same locality. From this, and from the ob- 
 served sequences, rough laws of succession have been de- 
 duced. These differ somewhat, according to the district in 
 which observations were made in each case ; but they practi- 
 cally agree in indicating that magmas tend to segregate into 
 more basic and more acid (more and less siliceous) portions. 
 The writer, following Professor J. P. Iddings, believes that an 
 initial rock of intermediate composition ordinarily passes, by 
 magmatic segregation, into rocks which are progressively more 
 acid and more basic, till extremely siliceous and extremely 
 basic varieties are obtained. According to this, if the rocks 
 were regularly intruded or erupted at stated intervals, we 
 might expect to find the law of segregation fully illustrated in 
 the succession of rocks. -Sometimes, indeed, this is the case; 
 but very often the eruptions have taken place irregularly, so 
 that the normal succession is hardly recognizable. 
 
 Prof. J. F. Kemp has called attention to cases of successive 
 
 * Compare J. H. L. Vogt, " Problems in the Geology of Ore-Deposits," Trans., 
 xxxi., p. 139. Genesis of Ore-Deposits, p. 650. 
 
IGNEOUS ROCKS AS RELATED TO OCCURRENCE OF ORES. 289 
 
 vein-formations of quite different characteristics in a single 
 district, and has supported the idea that new intrusions of igne- 
 ous rock, of a character different from the preceding intrusions 
 (rather than new fractures, as has often been assumed), are 
 responsible for the differences, the metals extracted from one 
 igneous rock being different from those derived from another.* 
 With this idea the writer is in general accord, and would add 
 the suggestion that also the difference in the veins at different 
 periods may often depend upon the progress of rock-segrega- 
 tion (differentiation) in a still unconsolidated magma, from 
 which the metals, directly or indirectly, are derived. By apply- 
 ing the idea of the change of segregated metals with the prog- 
 ress of general rock-segregation, some light on mineral asso- 
 ciation and succession may possibly be obtained. For example, 
 in many districts of the world gold and platinum are closely 
 associated in placers. In these districts it is usual to find ex- 
 tremely acid and extremely basic rocks (complementary varie- 
 ties) intimately associated, representing apparently an extreme 
 stage of rock-segregation ; and frequently, as in the Urals, the 
 platinum is found to be derived from the basic rocks (perido- 
 tites), and the gold chiefly from gold-quartz veins in the sili- 
 ceous ones (granite). This is one of the simplest cases. In an 
 earlier stage of the rock-segregation, when the extreme rock- 
 types had not originated, we would not find any platinum- 
 segregations, and the occurrence of gold-quartz veins would 
 be less probable. A similar example of mineral association, 
 probably dependent upon rock-segregation, is the occurrence 
 in the gold-quartz district of Forty-Mile creek, Alaska, of an 
 ore containing nickel, iron, chromium and magnesia, and no 
 gold.f Just as the gold-quartz veins here are intimately asso- 
 ciated with the ultra-siliceous dikes, so this ore is probably con- 
 nected with the ultra-basic ones ; and, as the two sets of dikes 
 have been considered complementary and due to a single pro- 
 cess of segregation, the contrasted ore-formations must be con- 
 sidered in the same light. 
 
 In many districts it has been noted that the veins of different 
 
 * " Igneous Kocks in the Formation of Veins," Trans., xxxi., p. 180. Genesis 
 of Ore-Deposits, p. 691. 
 
 f J. E. Spurr, " Geology of the Yukon Gold-District," 18th Ann. Rep. U. S. 
 G. S., Part III., p. 295. 
 
 19 
 
290 IGNEOUS ROCKS AS RELATED TO OCCURRENCE OF ORES. 
 
 periods have different contents.. Professor Kemp* has called 
 attention to the San Juan region in Colorado, where the differ- 
 ent veins have been classified by T. B. Comstock as follows : 
 1. The northwest system with tetrahedrite. 2. The east and 
 west with bismuth, and less often nickel arid molybdenum. 3. 
 The northeast with tellurides and antimony, and sulphur-com- 
 pounds of the precious metals. 
 
 The same writer cites, in this connection, the Telluride dis- 
 trict in Colorado, where a heavy vein is cut out and faulted by 
 a later one of different metalliferous character. He also re- 
 calls an occurrence near Freiberg, Saxony, where seven sets 
 of veins have been recognized, distinct from one another min- 
 eralogically, and probably introduced at different periods. At 
 Butte, Montana, there are two distinct sets of veins, one con- 
 taining silver and no copper, and the other containing copper, 
 silver and gold. 
 
 At Mercur, Utah, the writer has described two ore-bearing 
 zones which are parallel and lie about 100 to 150 ft. from 
 one another, f They are of different ages : The oldest, the 
 " Silver Ledge," contains silver with only traces of gold, while 
 the younger, the " Gold Ledge," contains gold to the exclusion 
 of silver, together with cinnabar and realgar, minerals not 
 found in the Silver Ledge. 
 
 This list might be amplified, but will serve to show the main 
 features of the problem. 
 
 It is not safe or reasonable to refer such differences in veins 
 to any one universal cause. In the Mercur case, the writer has 
 reasoned that the Gold Ledge is essentially a pneumatogenic 
 deposit, due to gases ascending along fissures; and that the 
 Silver Ledge is a contact-deposit, due to waters occluded in cool- 
 ing from the intrusive sheet of rhyolite porphyry at whose 
 contact it occurs. In such cases the different nature of the min- 
 eralizing solutions is sufficient to produce entirely different com- 
 binations of vein-minerals derived from a single magma, al- 
 though a change in this magma itself by segregation, or the 
 
 * "Igneous Kocks in the Formation of Veins," Trans., xxxi., p. 179. Also, 
 Ore-Deposits of United States and Canada, fourth edition, p. 288. Genesis of Ore- 
 Deposits, p. 691. 
 
 f J. E. Spurr, " Economic Geology of the Mercur Mining District, Utah," 16th 
 Ann. Rep. U. S. Geol. Survey, Part II., p. 403. 
 
IGNEOUS ROCKS AS RELATED TO OCCURRENCE OF ORES. 291 
 
 intrusion of a rock of a new kind is, of course, not improbable. 
 In other cases the different character of rocks traversed by the 
 same mineralizing solutions might operate to cause the precipi- 
 tation in one rock of a different combination of minerals from 
 that precipitated by another. Where, however, the different 
 veins are in the same rock, and belong in the same category of 
 ore-deposits (from the standpoint of the process of formation), 
 the assumption of a change in the character of the igneous 
 rock below, whether by new intrusions (mechanical change) 
 or by segregation (chemical change), will probably be often 
 justified. The fact that the different veins often occupy frac- 
 tures of different trend and age is far from opposing this 
 theory, for it is only by the aid of mechanical accidents like 
 fracturing that new solutions can rise, and by their effects bear 
 witness to the change that would otherwise not be known. 
 
 XIII. THE PERSISTENCE OF PETROGRAPHIC PROVINCES, CONSID- 
 ERED IN CONNECTION WITH THE PERSISTENCE OF METAL- 
 LIFEROUS PROVINCES. 
 
 While an igneous rock of a certain kind is not necessarily 
 limited to a certain part of the earth's surface, yet the rocks of 
 a given district generally show marked and persistent differ- 
 ences, taken as a whole, from the rocks of other, even adjoin- 
 ing, regions. To these districts, showing within themselves, 
 no matter how varied the rocks they contain, a certain " kin- 
 ship " or " consanguinity" between the different rocks, the term 
 petrograpliic provinces has been assigned. 
 
 For example, many of the rocks of northern Minnesota, es- 
 pecially the granites, show a constant excess of soda over pot- 
 ash, producing the variety soda-granite, which appears to be 
 characteristic of this region.* Other regions have a large de- 
 velopment of rocks especially high in the alkalies, phonolites, 
 nepheline-syenites, etc., rocks which in most regions are want- 
 ing. Rocks characterized by an especially great proportion of 
 magnesia, such as peridotites, occur in certain regions and are 
 wanting in others. 
 
 The differences which give rise to these petrographical prov- 
 ings are evidently due to the unequal distribution of the com- 
 
 * 21st Ann. Rep. Minn. Geol. and Nat. Hist. Survey, pp. 41, 42. 
 
292 IGNEOUS ROCKS AS RELATED TO OCCURRENCE OF ORES. 
 
 moner rock-forming elements, upon which rock-classification 
 is based, in different portions of the earth's crust. In one 
 region sodium is especially abundant, in another both sodium 
 and potassium, in another magnesium, in another aluminum, 
 etc. Some petrographic provinces show mineralogical differ- 
 ences which are wonderfully slight, considering their persist- 
 ence in one the granites may be chiefly hornblende granites, 
 for example, and in another almost entirely biotite granites, 
 owing to constant, slight differences in the proportions of alu- 
 minum, magnesium, calcium, potassium, etc., present in each. 
 The existence of these petrographic provinces, characterized 
 by different proportions of the commoner rock-forming ele- 
 ments, has been explained by extending the theory of rock- 
 segregation or differentiation so as to make it applicable on a 
 large scale, and by supposing that in great internal reservoirs 
 (presumably connecting, or at least once connected) certain ele- 
 ments, by reason of their affinity, become more or less concen- 
 trated in certain portions. We are quite in the dark as to what 
 might be a possible cause for this (as yet) hypothetical process, 
 for certainly the theory of concentration by convection-cur- 
 rents on cooling has slight application here ; but in science the 
 apprehension of the fact very commonly runs ahead of the 
 explanation, and this idea is at least a good working hypothe- 
 sis, which has much to recommend it. By this theory all igne- 
 ous rocks (in so far as they are not formed by fusion 'of sedi- 
 mentary rocks or by mixing of already different magmas) have 
 originated chiefly by segregation from an original universal 
 magma.* 
 
 If one accepts as a working hypothesis (as the writer has done) 
 this theory that the unequal distribution or the relative concentration 
 of the commoner rock-forming elements in certain parts of the earth's 
 crust (giving rise to distinct petrographic provinces and rock-types) 
 has been effected by magmatic segregation, one cannot avoid accepting 
 the same theory for the less common rock-forming elements. 
 
 If one accepts this for the distribution of sodium, potassium, 
 aluminum, magnesium, titanium and phosphorus, he must ac- 
 cept it for manganese, barium, chromium, nickel, strontium, 
 lithium, chlorine and fluorine ; and if he applies it to these 
 
 * J. P. Iddings, "The Origin of Igneous Kocks," Bull. Philosoph. Soc. Wash., 
 vol. xii., p. 185. 
 
IGNEOUS ROCKS AS RELATED TO OCCURRENCE OF ORES. 293 
 
 latter, he must extend it to tin, bromine and cobalt; to lead, 
 zinc, copper, arsenic, antimony, wolfram ; to mercury, silver, 
 bismuth, vanadium, tellurium and thorium; to gold and plati- 
 num, and even to iridium, ytterbium and germanium.* 
 
 Following this idea, and observing that some regions are 
 especially rich in sodium, some in magnesium, and some in 
 titanium (petrographic provinces), we should expect to find 
 some especially rich in chromium, some in nickel, some in tin, 
 some in lead, some in copper, some in mercury, some in gold, 
 some in platinum, etc. This is well known to be the case, and 
 these regions, characterized by special combinations or amounts 
 of the rarer, especially the commercially- valuable, metals, I de- 
 sire to call metalliferous provinces. 
 
 A metalliferous province does not necessarily coincide with 
 a petrographic province, for the reason that I have already 
 pointed out namely, that the petrographic province and its 
 contained rocks is classified solely on the basis of the com- 
 moner rock-forming elements ; while the rarer ones, upon the 
 distribution of certain of which metalliferous provinces may be 
 distinguished, follow independent laws of segregation, which, 
 nevertheless, may sometimes partly coincide with the laws of 
 segregation of some of the commoner elements, by virtue of 
 an affinity or preferential association between a rare element 
 and a common one. 
 
 The helpfulness (to the investigator) and yet the final unre- 
 liability of these affinities will be at once seen upon considera- 
 tion. Platinum, for example, is undeniably most abundant in 
 basic rocks peridotites ; that is to say, it prefers the company 
 of elements like magnesium, calcium or iron, and objects to 
 that of silicon; yet all peridotites do not contain platinum, at 
 least in equal amount. It is only in certain metalliferous prov- 
 inces that platinum is sufficiently abundant in peridotites to be- 
 come commercially interesting. The same remarks apply to 
 chromium, nickel, etc. On the other hand, tin seems to prefer 
 the society of silicon, and is always found in close connection 
 with siliceous igneous rocks, chiefly granites ; yet not all 
 granites contain tin in notable quantities. The variation is 
 
 * For the relative proportion of the elements in the earth's crust, see F. W. 
 Clarke, Bull. U. S. G. S. Nos. 78 and 148 ; also J. H. L. Vogt, * ' Ueber die rela- 
 tive Verbreitung der Elemente," Zcitsch. fur praktische GeoL, 1898, p. 225. 
 
294 IGNEOUS ROCKS AS RELATED TO OCCURRENCE OF ORES. 
 
 enormous. So a study of the distribution of granite gives only 
 a slight clue to the distribution of tin, and a knowledge of the 
 occurrences of peridotite is only the first step toward a knowl- 
 edge of the occurrences of chrome or nickel-deposits. This 
 principle is of wide application. Igneous rocks have long 
 been recognized as the ultimate sources of many, if not most, 
 ore-deposits. Yet not all igneous rocks are connected with 
 ore-deposits. One mass of diorite, for example, may be con- 
 nected with rich ore-bodies (formed, it is needless to say, in 
 most cases, finally through the concentrating action of circulat- 
 ing waters), while an exactly similar diorite in another region 
 may have no ores at all associated with it. One may explain 
 this by assuming that in the first-mentioned case there have 
 been abundant circulating waters, especially heated ones, and 
 plentiful faults, fractures and zones of weakness permitting the 
 passage of these mineralizing agents ; and that in the second 
 case these conditions for concentrating the disseminated metals 
 have not been so favorable. The writer recognizes these con- 
 siderations as of vast and universal importance ; and yet a com- 
 parison of regions equally favored with igneous intrusives, with 
 abundant circulating waters, with the necessary channels for 
 circulation and permeation, and with rocks favorable for the 
 precipitation of the metals held in solution in the circulating 
 waters (such as limestones, carbonaceous shales and porous 
 sandstones), may show an utter difference in the amount and 
 nature of the minerals concentrated. Moreover, the same type 
 of rock a diorite, for example may be associated with chiefly 
 silver-ores in one region, with copper in a second, and with 
 gold in a third. 
 
 Detailed investigations concerning the less abundant metals 
 in igneous rocks, although they have rendered the science of 
 ore-deposits the inestimable service of proving the presence of 
 these rarer elements, afford little ground for more extended 
 conclusions, on account of their being so few and (necessarily, 
 from the minute quantities dealt with) so inaccurate. 
 
 Yet it seems that they also corroborate the conclusion that 
 the metals are very unevenly distributed. 
 
 Professor J. F. Kemp remarks:* 
 
 * il The Role of the Igneous Rocks in the Formation of Veins," Trans., xxxi., 
 p. 172; also, Genesis of Ore-Deposits, p. 684. 
 
IGNEOUS ROCKS AS RELATED TO OCCURRENCE OF ORES. 295 
 
 " Nevertheless, it is a fact of the greatest importance that the presence of the 
 metals* in the igneous rocks has been established. Not all igneous rocks have 
 yielded such results on assay. The general experience has been that when sam- 
 ples of several varieties have been collected in a given district, some have proved 
 barren ; and it must be .admitted that some negative results have been obtained. 
 As a rule, however, they are decidedly fewer than the positive results. It is 
 likewise true that not all igneous districts contain veins of ore." 
 
 To this quotation the writer adds the suggestion that most 
 of the assays made have been of igneous rocks in metalliferous 
 districts, where we should a priori (according to the ideas pre- 
 viously set forth) expect a greater proportion of the metals; 
 and that, if assays of rocks in non-metalliferous districts were 
 made, the proportion of negative results might be decidedly in 
 excess although then, as now, the term " negative results " 
 would probably only mean that the metals sought for were in 
 quantities too small to be detected by chemical methods. 
 
 The chemical determinations of the presence of the more 
 abundant of the relatively rare metals give results fully con- 
 firming the conclusions reached as to their unequal distribu- 
 tion in similar rocks. Nickel, for example, is recognized as 
 especially at home in the most basic rocks peridotites and 
 pyroxenites ; but Vogtf gives a table of nickel determinations 
 in 32 rocks of this kind, which vary all the way from a trace 
 to 0.6 per cent. 
 
 Petrographic provinces may be relatively small in extent, or 
 they may be enormous. The writer has made a study of the 
 volcanic region of the Great Basin,! where an area whose 
 limits are not determined, but which extends as far east as 
 Salt Lake, west into the Sierra Nevada, north into Idaho and 
 Oregon, and south into California, shows the same types and 
 the same general succession of Tertiary lavas. From later 
 studies by the writer in the Monte Cristo mining district, 
 Washington, it appears that the Tertiary eruptions here also 
 correspond in types, age and general succession to thos'e of 
 Nevada ; similar rocks, age and succession have been ob- 
 
 * Referring, of course, to the least abundant metals. J. E. S. 
 
 f "Relative Verbreitung der Elemente," Zeitsch. fur prakt. GeoL, July, 1898, 
 p. 236. 
 
 J Journal of GeoL, vol. viii., p. 621. 
 
 $ See article by author on "The Ore-Deposits of Monte Cristo, Washington," 
 22d Ann. Rept. U. S. GeoL Survey, Part II., pp. 711-865. 
 
296 IGNEOUS ROCKS AS RELATED TO OCCURRENCE OF ORES. 
 
 served on the Southern California coast;* and as far away as 
 Mexico the studies of Ordonezf have established the fact that 
 the principal rocks, their succession and age, remain the same. 
 Without being in danger of carrying this correlation to excess, 
 I may point out that the Pliocene olivine-basalts of the Sierra 
 Nevada;); are abundantly present in .Oregon and Washington ; 
 that the British Columbia basalts are approximately, at least, 
 of the same period ; and that throughout the whole of Alaska 
 and into the Behring Sea occur olivine-basalts of Pliocene age.|| 
 
 Again, the abundance of basic andesites (typically augitic, 
 often hypersthene-bearing, and verging towards basalts), all 
 belonging to one epoch (very late Pliocene-Pleistocene), in a 
 continuous belt in Alaska, running the whole length of the 
 Aleutian Islands and peninsula, turning the same angle as the 
 chief orographic and topographic features, and running down 
 the coast past Sitka;T the occurrence of the same rocks, be- 
 longing to the same age, in Washington and Oregon (Mt. 
 Rainier, etc.); the extension of the belt through the Sierra 
 Nevada and along the western part of the Great Basin ; finally 
 its extension into Mexico,** this is all striking, and deserves 
 recognition. Moreover, this belt of late Pliocene-Pleistocene 
 augite (hypersthene) andesites extends through Central and 
 South America, in the Andes. ft I n Alaska and in the Andes 
 some of the cones of this epoch are still active ; but the ma- 
 jority have become extinct. 
 
 It appears, then, that the whole extreme western part of the 
 western hemisphere (the Pacific coast of the Americ*as) is a 
 zone occupied by what (at some periods, at least) is and has 
 been a single petrographic province. 
 
 It remains to be seen whether this province is not continued 
 
 * I regret I have not at hand the paper of Mr. Smith in a recent U. S. GeoL 
 Survey Ann. Report, in order to give an exact reference. (Santa Catalina Island.) 
 
 f "'Las Rhyolitas de Mexico," Boletin del Institute Geologico de Mexico, No. 14. 
 
 J J. E. Spurr, Jour. Geol., vol. viii., No. 7, chart, p. 643. 
 
 $ G. M. Dawson, Ann. Hep. Geol. Nat. Hist. Surv. Canada, vol. iii., Part I., p. 
 37 B. ; also, Trans. Royal Soc. Canada, vol. viii. , Sec. 4, p. 15. 
 
 || J. E. Spurr, "Geology of the Yukon Gold-District," 18th Ann. Rep. U. S. 
 Geol. Surv., Part III., p. 250. 
 
 ^[ J. E. Spurr, ''Reconnaissance in Southwestern Alaska," 20th Ann. Rep. IT. 
 S. GeoL Surv., Part VII., Map 13. 
 
 ** Ezequiel Ordonez, op. ciL, p. 66. 
 
 ft Zirkel, Lehrbuch der Petrographie, 2d edition, vol. ii., pp. 831-2. 
 
IGNEOUS KOCKS AS RELATED TO OCCURRENCE OF ORES. 297 
 
 into Asia with the change of orogenic trends in Alaska from 
 northwest to southwest. The line of late Tertiary-Pleistocene 
 volcanoes, which extends along the Aleutian Islands to Kam- 
 chatka, is represented by 15 or 20 cones in this peninsula; this 
 line, following the general orogenic trend, runs southwest 
 through the Kuril e Islands, the Islands of Japan, and the Phil- 
 ippines, into the East Indies. Andesites largely pyroxene 
 andesites, and frequently hypersthene andesites are character- 
 istic of this chain also, as far as the famous volcano of Kraka- 
 tua. This investigation might profitably be carried still fur- 
 ther, but this is hardly the place for it. 
 
 Turning from these examples of petrographic provinces on 
 enormous scales, we find that metalliferous provinces may also 
 be of light extent, or may be exceedingly large. Taken 
 broadly, they often coincide more or less roughly with petro- 
 graphic provinces, just as these are apt to show some corre- 
 spondence in their position and trends with zones of folding 
 and fracture in the crust, with mountain ranges and the bor- 
 ders of continents. A metalliferous province which I have been 
 studying somewhat lately is the rich chrome-bearing province 
 of Turkey, which, with its center at the western coast of Asia 
 Minor, extends across the ^Egean Sea and includes Macedonia 
 and eastern Greece, and in the other direction stretches over 
 the western and southern portions of Asia Minor. This metal- 
 liferous province is connected with a petrographic province 
 marked by ultra-basic igneous rocks and serpentines, with 
 which the ore is associated ; yet similar rocks are found in 
 other regions, without the corresponding abundance of 
 chrome. 
 
 Taking a larger example, compare, in North America, the 
 Appalachian with the Cordilleran region. That there is a cer- 
 tain kinship among the ores of the Appalachian chain and 
 its allied ranges has long been recognized by mining men. It 
 is recognized that the metals, though present, are constantly far less 
 abundant than in the Cordilleran region. Every now and then 
 one hears of veins found in this region which give rich results 
 on assay ; but the discovery, though heralded in the news- 
 papers, makes no disturbance in the mining world, for the 
 mining man knows, from long experience with such discoveries, 
 that the vein will directly " peter out." Gold-bearing veins 
 
298 IGNEOUS ROCKS AS RELATED TO OCCURRENCE OF ORES. 
 
 are pretty thoroughly scattered along this zone from Nova 
 Scotia to Georgia; but the uncertainty and the relative poverty 
 of these gold-deposits is proverbial. 
 
 Taking the western Cordilleras, on the other hand, we may 
 remember that the California miners followed new finds north- 
 westward, along the trends of the mountain ranges, into the 
 Frazer river country, the Caribou district, the Omenica, the 
 Cassiar, the Pelly, and the Yukon, until the slow progress has 
 brought them to the neighborhood of the Behring Straits (the 
 Nome district). It seems exceedingly probable, also, that this 
 true " mineral zone " extends into Siberia. For I do not hesi- 
 tate to call it a mineral zone, although the gold-quartz veins of 
 the Yukon are far different in age from those of California. 
 In fact, the existence of rich gold-ores along this zone, in 
 deposits of various ages, and made under various conditions 
 and in various rocks, only serves to emphasize the conclusion 
 that this zone is essentially a metalliferous province, marked 
 by a greater proportion of gold (considering the question of 
 the gold alone) than the earth's crust in general. 
 
 Concerning metalliferous sub-provinces within the Cordil- 
 leras, I quote the following from Phillips and Louis,* not 
 having access to the original authorities : 
 
 "Mr. R. W. Raymond,! in a paper on the mining districts of the United 
 States, recalls the fact that W. P. Blake, in a note to his Catalogue of California 
 Minerals, first pointed out that the mining districts of the Pacific slope are 
 arranged in parallel zones, following the prevailing direction of the mountain 
 ranges. More recently, Clarence King has summarized these phenomena nearly 
 as follows : The Pacific coast ranges carry, on the west, quicksilver, tin and 
 chrome iron-ores. The next belt is that of the Sierra Nevada and of the Cas- 
 cade mountains of Oregon, which, upon their western slope, carry two distinct 
 zones, a foot-hill chain of copper-mines, and a middle line of gold-deposits, 
 which extend into Alaska. Lying to the east of this zone, along the eastern base 
 of the Sierras, and stretching southward into Mexico, is a chain of silver mines 
 which are frequently included in volcanic rocks. Through Central Mexico, Ari- 
 zona, Central Nevada and Middle Idaho there is another line of silver-mines 
 which more often occur in the older rocks. Through New Mexico, Utah and 
 Western Montana lies another zone of argentiferous galena lodes ; and again, to 
 the east, the New Mexico, Colorado, Wyoming and Montana gold-belt forms a 
 well-defined and continuous chain of deposits. Raymond agrees that this paral- 
 lelism exists, though in a somewhat irregular way, and that it is chiefly referable, 
 as Blake and King have shown, to the structural features of the country." 
 
 This quotation the writer makes without deciding his belief 
 
 * Ore-Deposits, 2d ed., p. 740. f Trans., i., p. 33 (1873). 
 
IGNEOUS ROCKS AS RELATED TO OCCURRENCE OF ORES. 299 
 
 for or against the divisions as claimed. Undoubtedly the later 
 discoveries within this region have been so varied as to make 
 some of the distinctions doubtful ; yet a careful consideration 
 of the Cordilleran ore-deposits of western North America 
 would probably result in the determination of definite metal- 
 liferous sub-provinces, which might or might not coincide with 
 those specified. That Nevada, in general, is part of such a 
 sub-province, characterized especially by the abundance of sil- 
 ver, with other minerals subordinate, is strikingly illustrated 
 by the fact that the vigorous mining industry of this State, so 
 exceedingly rich in ore-deposits, was permanently prostrated 
 by the decline in the price of silver, while other regions, differ- 
 ing from this in the nature of their metallic wealth, have pros- 
 pered. 
 
 XIV. CONCLUSION. 
 
 Our inquiries lead us to the hypothesis that by magmatic seg- 
 regation the metals of commercial value, as well as the other rock- 
 forming elements, are irregularly and to a certain extent independently 
 concentrated in certain portions of the earth's crust. Such portions, 
 characterized by the relative abundance of certain metals, may be 
 called metalliferous provinces. It is in these provinces that ore- 
 bodies will generally occur. The provinces may or may not be 
 closely identified with petrographic provinces (divisions based 
 on the relative abundance of the commoner metals and other 
 elements), although, by reason of the chemical affinity which 
 exists between certain of the rarer metals and certain of the 
 commoner elements, they probably generally do so, to a certain 
 extent at least. Moreover, within these metalliferous provinces (as 
 is the case within the petrographic provinces) magmatic segregation 
 produces sub-provinces, secondary, perhaps, in theoretical importance 
 to the grander divisions, but of more practical interest to miners. 
 To limit, again, the scope of our views, by magmatic segregation 
 the rarer metals (like the commoner elements, again) are in many 
 cases preferentially concentrated into certain rocks in. a given sub- 
 province. Finally, within these rocks the metals may be segregated 
 chiefly into certain portions, even producing, in the case of the com- 
 moner metals (iron, chromium, nickel, etc.), workable ore-deposits with- 
 out further concentration ; and, in the case of the less common ones, 
 either directly producing workable deposits (certain gold-quartz veins, 
 certain tin-veins, possibly certain platinum segregations Urals ) 
 
300 IGNEOUS ROCKS AS RELATED TO OCCURRENCE OF ORES. 
 
 or producing rocks relatively so rich that it requires only the concen- 
 trating action of other agents (chiefly circulating waters) to create 
 " ore-bodies" It is the writer's belief that the origin of metal- 
 producing districts, as contrasted with barren districts, is in most cases 
 due primarily to magmatic segregation, and that an important class 
 of ore-deposits is due directly to this. 
 
 Added to this initial process, there are the varied effects pro- 
 duced by gases and liquids occluded by cooling igneous rocks, 
 and the enormous work of waters, surface and underground, 
 which, by continued solution and deposition as well as by me- 
 chanical concentration, may, under favorable conditions, operate 
 to bring the disseminated metals within smaller and smaller 
 compass. Underground, these waters may be hot or cold ; they 
 may be ascending, descending, or moving laterally ; they may 
 transport their metallic load only a fraction of an inch, a few 
 rods, or miles. Their final effect is to create directly what is r 
 perhaps, the most important type of ore-deposits. The study 
 of ore-deposits is a study in concentration the concentration 
 of some of the finely-disseminated rarer rock-forming elements 
 into more or less compact masses. This concentration is ef- 
 fected chiefly by these processes : (1) magmatic concentration , 
 (2) concentration by occluded gases and liquids from consoli- 
 dating magmas ; (3) concentration by the action of hot-spring 
 waters (generally ascending) ; (4) concentration by the action 
 of cold surface-waters penetrating underground (generally de- 
 scending); and (5) concentration by the effects (chiefly me- 
 chanical, though largely chemical) of surface-waters at the 
 surface. 
 
 Any one of these processes may be chiefly responsible for a 
 given ore-body, but in many cases two, three or more of them 
 may be important. Moreover, the history of an ore-deposit 
 may comprise cycles, or repetitions of the same processes at 
 different intervals, before the final concentration is sufficiently 
 complete. Take, for example, the Nome beach-sands, where 
 the gold is concentrated from the concentrates of older beach- 
 sands, now transformed into land by a crustal uplift.* 
 
 On Napoleon creek, a branch of Forty-Mile creek, Alaska, 
 there was found a strip of rich stream gold-placer ground in 
 
 * Schrader and Brooks, Trans., xxx., p. 242. 
 
IGNEOUS ROCKS AS RELATED TO OCCURRENCE OF ORES. 301 
 
 a district where working was not otherwise profitable. The 
 gold was apparently derived from a conglomerate of probable 
 Cretaceous asre which formed a belt crossing the stream at this 
 
 o o 
 
 point. The composition of the conglomerate showed that it 
 was derived from the rocks and quartz-veins of the ancient 
 (Algonkian ?) gold-bearing series. In this ancient series, as al- 
 ready explained, the gold is believed to have been concentrated 
 by magmatic segregation. Here, therefore, we have three dis- 
 tinct processes of concentration : (1) magmatic segregation 
 (Algonkian ?) ; (2) mechanical concentration by surface-waters 
 (beach-sands Cretaceous?); (3) mechanical concentration by 
 surface-waters (stream-placers Pleistocene). And it was only 
 after the third process that the metal was sufficiently concen- 
 trated to become workable with profit to become an ore-de- 
 posit, properly speaking. 
 
 POSTSCRIPT. 
 
 Since the above was written, the writer has received the in- 
 teresting paper of Mr. Luther Wagoner on " The Detection and 
 Estimation of Small Quantities of Gold and Silver/'* Mr. 
 Wagoner gives a series of delicate assays of California rocks, 
 remote from mineral deposits, for gold and silver. 
 
 Four specimens of granite gave respectively the following 
 weights in milligrams per ton: Gold, 104, 137, 115, 1,130; 
 silver, 7,660, 1,220, 940, 5,590. One specimen of syenite showed 
 gold, 720; silver, 15,430. A sample of diabase contained gold, 
 76 ; silver, 7,440 ; and one of basalt, gold, 26 ; silver, 547. The 
 sedimentary rocks tested were three specimens of sandstone 
 from different localities, and two of marble (one of the latter 
 from Italy). The sandstones gave respectively, in gold, 39, 24 
 and 21; in silver, 540, 450 and 320. The California marble 
 showed gold, 5; silver, 212; the Italian sample, gold, 8.63; 
 silver, 201. Several assays of San Francisco bay-mud (contain- 
 ing some organic material) gave gold from 45 to 125. Two 
 assays of sea-water gave a mean of gold, 11.1; silver, 169.5. 
 
 These results are suggestive ; and, although too few to base 
 final conclusions on, the writer would like to call attention to 
 some striking facts. On reckoning up the means of the re- 
 sults, we find that the granite averaged 371.5 gold and 3,852.5 
 
 * Trans., xxxi., p. 798. 
 
302 IGNEOUS ROCKS AS RELATED TO OCCURRENCE OF ORES. 
 
 silver; the sandstone, 28 gold and 436.66 silver; the marble, 
 6.8 gold and 206.5 silver; and the bay-mud, 85 gold. 
 
 The relative proportion or the precious metals in the sedi- 
 mentary and in the igneous rocks first claims attention. The 
 mean of all the igneous rocks assayed in gold 329f , and silver 
 5,546^ ; of the sedimentary rocks (sandstones and marbles, not 
 the bay-mud), 17.5 gold and 344.4 silver. That is to say, the 
 mean of the igneous rocks assayed shows about 19 times as 
 much gold and 16 times as much silver as the mean of the 
 sedimentary' rocks. 
 
 The relative proportion of the metals in the different sedi- 
 mentary rocks is another point. The sandstones average four 
 times as much gold and over twice as much silver as the mar- 
 bles; while bay-mud (which on hardening would become shale) 
 contains nearly 13 times as much gold as the marbles. 
 
 Take, next, the relative proportion of the metals in the differ- 
 ent igneous rocks. We have in the list^ siliceous or acid rocks 
 (granite and syenite) and basic rocks (diabase and basalt). 
 
 Diabase and basalt are, generally speaking, chemical and 
 mineralogical equivalents, differing in their texture and struc- 
 ture. If we compare the average of the granites with that of 
 the diabase-basalt, we find that the former is 371.5 gold and 
 3,852 J silver, while the latter is gold 51 and silver 4,008J ; that 
 is, the granites contain nearly 7.5 times as much gold as the 
 diabase-basalt, but only about the same quantity of silver. If 
 we add the syenite assay (probably unusually high) to those of 
 the granites, and again compare the result with the diabase- 
 basalt contents, we find that the acid rocks contain 9 times as 
 much gold and 1.5 times as much silver as the basic ones. 
 
 In spite of the small quantity of data, these results are 
 in accordance with the theoretical conclusions arrived at in 
 this paper. One of these conclusions was concerning the 
 higher content of precious metals in the igneous rocks as com- 
 pared with the sedimentaries. A second conclusion was in 
 regard to the relative concentration of the metals in the dif- 
 ferent sedimentaries least in the limestones, which are calcium 
 concentrations effected largely chemically from the sea-water 
 through organic agencies; more abundant in the sandstones, 
 which are silica concentrations, but effected mechanically and 
 containing much debris from all sorts of rocks ; and most 
 
IGNEOUS ROCKS AS RELATED TO OCCURRENCE OF ORES. 303 
 
 abundant in the bay-mud, which is a fine ground-up mixture 
 of all rocks, and contains, besides, organic matter which is 
 known to be a precipitant of metals from solution. A con- 
 tinuance of these experiments is highly desirable, to fix the 
 point as to whether the order of richness in gold and silver of 
 the sedimentary rocks is really 1, shales; 2, sandstones; 3 y 
 limestones. 
 
 Thirdly, as regards the igneous rocks, the uniformly superior 
 gold content of the siliceous or acid rocks, as compared with 
 the basic rocks, is noticeable. One must remark, also, that the 
 same does not hold good for silver; for, although the basalt con- 
 tains the least and the syenite the most, yet the diabase has a 
 large amount. This, as far as it goes, is in accordance with 
 the theory above advocated, that during the process of mag- 
 matic segregation the gold (not the silver) seeks the siliceous 
 rocks by preference. 
 
 DISCUSSION. 
 
 (Trans., xxxiii., 1063.) 
 
 ALEXANDER N. WINCHELL, Butte, Mont. : Mr. Spurr calls 
 attention to the fact that an ore-deposit may be due to a succes- 
 sion of concentrations at different geological epochs. He cites 
 an example of such a condition on Napoleon creek, a branch 
 of Forty-Mile creek, Alaska. 
 
 It will perhaps be of interest to call attention to another ex- 
 ample of the same general character, not so remotely situated. 
 The example referred to is located on Pole creek, a tributary 
 of Cherry creek, in the extreme northeastern part of Madison 
 county, Montana. An excellent geological map of this region 
 is to be found in the Three Forks folio (No. 24) of the United 
 States Geological Survey. According to this map, Pole creek, 
 in its upper course, occupies the contact between the " Flat- 
 head " formation, which Peale correlates with the Middle and 
 Lower Cambrian, and an area of gneisses and schists supposed 
 to represent the Archean. A visit to the region last summer 
 enabled the writer to determine the presence of a thick con- 
 glomerate formation between the Flathead and the Archean. 
 The conglomerate in question has an outcrop along the south- 
 west side of Pole creek varying from one-half to one 
 
.304 IGNEOUS ROCKS AS RELATED TO OCCURRENCE OF ORES. 
 
 width; its maximum thickness in this region is at least 500 
 feet; lying conformably above it are 300 or 400 feet of schists, 
 fine sands, etc. It may probably be correlated with the " Belt " 
 formation of Peale, as it lies unconformably upon the schists 
 and gneisses of the Archean, and is overlain (above the fine 
 sands), apparently unconformably, by the Flathead formation. 
 It seems to be auriferous throughout its extent, and somewhat 
 richer at the immediate surface. 
 
 Let us outline, now, the successive concentrations of gold in 
 this district. The igneous rocks of Madison county certainly 
 belong to a " metalliferous province " rich in gold ; but to con- 
 sider that the province is due to segregation from an originally 
 homogeneous magma seems to the writer to be straining the 
 theory of differentiation considerably beyond the breaking- 
 point. As pointed out by Fouque,* we have no evidence that 
 such a primitively homogeneous magma ever existed ; on the 
 contrary, the marked heterogeneity of meteorites argues that 
 cosmic materials are far from homogeneous. 
 
 Omitting, then, from the series, Spurr's concentration by 
 magmatic segregation, which in this case one would probably 
 have to refer to Archean time, we have : (1) mechanical con- 
 centration by surface-waters (ocean conglomerates and gravels 
 : probably pre-Cambrian) ; (2) residual concentration by sur- 
 face-waters due to disintegration and erosion ; and (3) mechan- 
 ical concentration by surface-waters producing stream placer- 
 deposits. 
 
 It seems just possible that the same conglomerate caps the 
 so-called " Gravel Range " about the head-waters of Alder 
 creek (about thirty miles distant as the crow flies), in which 
 case it probably aided in the formation of the famous Alder 
 Gulch placer-deposits. 
 
 * Bull Soc. Fr. 'Mineral., 1902, xxv., p. 349. 
 
THE CHEMISTRY OF ORE-DEPOSITION. 305 
 
 No. 12. 
 The Chemistry of Ore-Deposition. 
 
 BY WALTER P. JENNET, E.M., PH.D., SALT LAKE CITY, UTAH. 
 (New Haven Meeting, October, 1902. Trans., xxxiii., 445.) 
 
 CONTENTS. 
 
 I. The Reducing Action of Carbon and of Hydrocarbons, . . . 305 
 
 II. Protective Action of Carbon and of Hydrocarbons, .... 311 
 
 TIL Contributory Action of Carbonic Acid Gas, . . . * . 312 
 
 IV. The Stability of Carbonic Acid and of Water, 313 
 
 V. Occurrence of Carbon and the Carbon-Compounds, .... 315 
 
 VI. The Occurrence of Carbon, Alone, . . . . . * . 315 
 
 VII. The Occurrence of Carbon Combined with Hydrogen, -4 ' . . 320 
 
 VIII. The Relative Reducing Power of Minerals, . . . -. .347 
 
 I. THE REDUCING ACTION OF CARBON AND OF HYDROCARBONS. 
 
 Carbon has long been recognized as one of the most power- 
 ful reducing agents in the deposition of ores. Investigations, 
 made by myself, of the zinc- and lead-deposits in Southwest 
 Missouri, in the region centering about Joplin, where the 
 formation of the metallic sulphides has been due to the action 
 of bitumen, carbonaceous shales and bituminous coal, have af- 
 forded abundant evidence that the solid oxygenated hydrocar- 
 bons, particularly when in fine powder and in suspension in 
 the waters circulating through the ore-bodies, are the most 
 energetic and powerful reducing agents known. 
 
 Bitumen, liberated by the decomposition of the ore-bearing 
 limestone, is found in the Joplin mines in all degrees of fluid- 
 ity and hardness, dependent on the amount of oxidation it has 
 undergone. From semi-fluid maltha it grades into partly oxi- 
 dized mineral-pitch, which, by further oxidation, changes to 
 hard asphalt, finally breaking up, from continued absorption of 
 oxygen, into a fine powder resembling in appearance powdered 
 coal. In this condition oxidized bitumen, from its light grav- 
 ity, is transported readily in suspension in the underground 
 circulating-waters. 
 
 Bituminous coal and black carbonaceous clays and shales 
 occur as surface formations, often in intimate association with 
 
 20 
 
306 THE CHEMISTRY OF ORE-DEPOSITION. 
 
 the ore-deposits, and when broken up, crushed, and faulted by 
 crustal movements, furnish organic matter in a state of fine 
 division. This is borne by the surface-waters and redeposited, 
 often in large masses, in the channels and spaces in the ore- 
 bodies. 
 
 Apparently the only pure form of carbon occurring in the 
 ore-deposits of the Joplin region is the charcoal, which is found 
 in inconsiderable quantity in the bituminous coal ; all other 
 carbon is combined with hydrogen, oxygen and nitrogen. 
 
 All these hydrocarbons readily absorb oxygen from the air 
 contained in the subaerial waters, and undergo at ordinary 
 temperatures, even below ground-water level, a slow combus- 
 tion, the ultimate product being carbonic acid and water. They 
 deoxidize the circulating waters by consuming all the free oxy- 
 gen ; and they reduce to sulphides any sulphates that may be 
 in solution. Even ferrous and ferric sulphates, on coming in 
 contact, in solution, with any of the solid hydrocarbons, are at 
 once re-formed as pyrite or marcasite, minerals that reduce 
 all other metallic sulphates, first, by being oxidized to ferrous 
 sulphate, and then, by further absorption of oxygen, to ferric 
 sulphate and limonite. 
 
 Bain, writing of these mines, says, " The widespread presence 
 of bitumen has been already emphasized. The ground-water 
 is one great reducing solution."* Nearly every observer in 
 this field has recorded the association of bitumen with the 
 zinc- and lead-ores. 
 
 In my paper on " The Lead- and Zinc-Deposits of the Missis- 
 sippi Valley "f I called attention to the reducing action of 
 bitumen and bituminous shales in the formation of the ore- 
 deposits of the Joplin District, and noted the influence of or- 
 ganic matter in the rocks upon the selective deposition of the 
 ores in certain beds in the Cambrian and Silurian of Central 
 and Southeastern Missouri, and also of the Upper Mississippi 
 lead-region. 
 
 In limestones containing organic matter, especially if the 
 rock be easily dissolved by waters carrying carbonic acid, the 
 efficiency of even so minute a quantity as a fraction of one per 
 
 * The Lead- and Zinc-Deposits of the Ozark Region, by H. F. Bain, p. 159. 
 f Trans., xxii., 171-225. 
 
THE CHEMISTRY OF ORE-DEPOSITION. 307 
 
 cent, of bituminous substances, in inducing the precipitation 
 and crystallization of the ores, is very great. Small as the 
 proportion of the carbonaceous matter may be, it is liberated 
 by the rapid subterraneous erosion of the lime-strata, in quan- 
 tity more than is required to consume the free oxygen in the 
 ore-forming solutions, and to reduce all sulphates to sulphides. 
 In limestones highly soluble in carbonated waters, two-tenths 
 of one per cent, of any strongly deoxidizing material, as bitu- 
 minous coal or bitumen, disseminated in the rock, appears to 
 be ample to effect the reduction of the metals, and to induce 
 the deposition of the ores in the special geological formation. 
 
 Compared with carbon, hydrogen has far greater reducing 
 power, measured by the amount of oxygen consumed, for hy- 
 drogen, in the production of water, combines with three times 
 the weight of oxygen that unites with carbon in forming car- 
 bonic acid. In fact, hydrogen stands first in reducing power, 
 accomplishing nearly nine times the work of pyrite, the most 
 efficient metallic sulphide in the redeposition of ores. Sulphur, 
 oxidizing to sulphuric acid (S0 3 ), requires less than one-fifth the 
 oxygen that combines with an equal weight of hydrogen in 
 forming water. 
 
 For illustration, the relative reducing power of hydrogen, 
 carbon and sulphur may be compared with the heat generated 
 by their combustion, although their calorific values do not run 
 parallel with their respective powers in the deoxidation of min- 
 eral solutions. 
 
 A calory being the quantity of heat necessary to raise 1 Ib. 
 avoirdupois of water 1 C., the heat generated by the combus- 
 tion of 1 Ib. of the following substances is : 
 
 Calories. 
 
 Hydrogen, ..'. 34,462 
 
 Carbon, . 8,140 
 
 Bituminous coal, 8,750 to 7,800 
 
 Lignite, 7,300 to 4,600 
 
 Sulphur, 2,250 
 
 On account of the calorific value of the contained hydrogen, 
 the heating-power of the highest grade of bituminous coals is 
 greater than that of pure carbon. 
 
 It is not improbable that the bituminous coals occurring in 
 association with the ore-deposits of the Southwest, on account 
 of their purity and high percentage of hydrogen, have a some- 
 
308 THE CHEMISTRY OF ORE-DEPOSITION. 
 
 what greater reducing power than pure carbon, and are ex- 
 ceeded in power and intensity of action only by bitumen. The 
 lignitic or finely divided coaly matter, disseminated in the 
 black clays and shales, may be regarded for the purpose of this 
 discussion as a form of highly impure bituminous coal. An- 
 thracite may be classed with the bituminous coals, as it con- 
 tains from 1 to 3 per cent, of hydrogen and 1 to 3.5 per cent, 
 of oxygen. 
 
 The hydrocarbons may be divided into the petroleums, or 
 fluid non-oxygenated compounds of carbon and hydrogen ; the 
 bitumens and asphalts, solid oxidized hydrocarbons, soluble in 
 chloroform or other solvents of the resins ; and the pyro-bitu- 
 mens, which also contain oxygen and nitrogen, including an- 
 thracite, bituminous coal, lignite, etc. 
 
 The Oxygenation of Petroleum. 
 
 Experiments made by the author on the oxidation of petro- 
 leum show that the heavy hydrocarbon oils unite very slowly 
 with oxygen, when first exposed to its action, even at tempera- 
 tures as high as 150 C. ; but after the action is once started, 
 by the combination of even a little oxygen with the hydrocar- 
 bon, the further oxidation then proceeds with constantly in- 
 creasing energy. By aspirating a current of air for ten days 
 through heavy petroleum oil, at 140 to 155 C., there were 
 formed solid hydrocarbons, resembling certain natural asphalts. 
 Very little water was formed ; the oil " cracking " and the hy- 
 drogen being removed in the form of light naphthas and non- 
 condensable gases, containing a greater percentage of hydrogen 
 than the original oil, and leaving oxidized hydrocarbons, with 
 less hydrogen and a greater proportion of carbon.* The 
 asphalts made in the above experiments absorbed oxygen from 
 the air at ordinary temperatures ; the rapidity of the absorption 
 being increased if the asphalt was in a fine powder. Dana 
 refers to these results as the manufacture of grahamite from 
 petroleum, f 
 
 The oxides of lead, zinc and manganese, and certain salts of 
 
 * "On the Formation of Solid Oxidized Hydrocarbons Eesembling Natural 
 Asphalts by the Action of Air on Refined Petroleum," by W. P. Jenney, American 
 Chemist, vol. v. (April, 1875), pp. 359-362. 
 
 f System of Mineralogy, edition of 1898, p. 1020. 
 
THE CHEMISTRY OF ORE-DEPOSITION. 309 
 
 the metals, notably manganese-borate, are. powerful driers of 
 the vegetable oils, such as linseed oil. Even in solution, many 
 salts of the metals have a drying action if agitated with the oil. 
 In the case of the vegetable oils, these metallic oxides and salts 
 appear to exert a catalytic action in accelerating the combina- 
 tion of oxygen with the hydrocarbon.* 
 
 Experiments by the writer indicate that oxides of lead and 
 manganese have a similar action in promoting the union of 
 oxygen with petroleum ; and that the asphalts produced retain 2 
 per cent, or more of lead-oxide, even after treatment with boiling 
 acetic acid and purification by solution in chloroform or ether.f 
 
 From this point of view, it is probable that the oxidation of 
 bitumen, in effecting the re-formation of the sulphides, is accel- 
 erated, and the intensity of the reducing action increased, by 
 the catalytic influence of ferrous and ferric sulphates and by 
 the various sulphates, carbonates, chlorides and oxides of lead, 
 zinc, copper and manganese, which are always present in 
 greater or less amount in the ore-deposits. With petroleum 
 having a paraffin base, the union with oxygen would be ex- 
 tremely slow, were not the chemical activity stimulated in some 
 way. Petro.leum with an asphalt base, owing to the heavy hy- 
 drocarbons in the oil being combined with oxygen, and ap- 
 proaching fluid bitumen or maltha in composition, would prob- 
 ably absorb oxygen more rapidly. 
 
 That the natural asphalts and bitumens, when wet, are more 
 subject to the action of oxygen than when dry, has been ob- 
 served in the wear of asphalt pavements, which rapidly disinte- 
 grate in spots where surface-water accumulates. 
 
 The Chemical Reactions that Take Place. 
 
 In the reduction of metallic sulphates to sulphides, by car- 
 bon, the action in each case is deoxidation, with formation of 
 carbonic acid, according to the following reactions : 
 
 ZnS0 4 + 2H,0 + 20 = ZnS + 2H 2 C0 3 . 
 PbS0 4 + 2H 2 + 2C = PbS + 2H 2 C0 3 . 
 
 * Catalytic action is understood to be the action of a substance which, by its 
 presence, accelerates or retards the chemical activity, and may induce a chemical 
 reaction that would otherwise not occur, or would take place only with extreme 
 slowness. t Op. tit., pp. 359-362. 
 
310 THE CHEMISTRY OF ORE-DEPOSITION. 
 
 The complete reduction of ferrous sulphate to pyrite or to 
 marcasite requires that free sulphuric acid be present : 
 
 2FeS0 4 + 2H 2 S0 4 -f 5H 2 O + 7C = 2FeS 2 + 7H 2 C0 3 . 
 
 The carbonates of lead, zinc and iron, in the presence of alka- 
 line sulphates, are reduced by carbon to the corresponding sul- 
 phides, galena, blende and pyrite : 
 
 PbC0 3 + Na 2 S0 4 + 2H 2 + 20 = PbS -f Na 2 CO 3 + 2H 2 C0 3 . 
 
 ZnCO 3 4- CaSO 4 + 2H 2 + 20 = ZnS + CaCO 3 -f 2H 2 C0 3 . 
 
 2FeC0 8 + 4CaS0 4 -f 5H 2 -f 70 = 2FeS 2 + 4CaCO 3 + 5H 2 C0 3 . 
 
 Chalcopyrite, CuFeS 2 , is formed by the double reduction of 
 cupric sulphate and ferrous sulphate : 
 
 CuS0 4 + FeS0 4 + 4H 2 + 40 = CuFeS 2 + 4H 2 C0 3 . 
 
 The reactions which take place where the hydrocarbons form 
 the reducing agents are more complex. The hydrocarbons at 
 first lose hydrogen and gain oxygen, until disintegration occurs ; 
 then they rapidly oxidize to carbonic acid and water. With 
 bitumen and coal, it is probable that practically all the carbon 
 is finally converted into carbonic acid, and the hydrogen into 
 water. In the oxidation of petroleum some " cracking " may 
 occur, and a portion of the hydrogen and carbon may escape 
 in the form of light hydrocarbon gases, as did take place in the 
 experiments described above.* 
 
 Oxygen seems to be needed to complete the reaction in the 
 reduction by petroleum of the paraffin series : 
 
 12ZnS0 4 -f C 16 H 34 + = 12ZnS -f 16H 2 C0 3 + H 2 0. 
 
 Where the petroleum is partly oxidized, ferric sulphate forms 
 pyrite in the presence of an excess of free sulphuric acid. The 
 reaction may be written as follows : 
 
 3Fe 2 (S0 4 ) 3 4- 3H 2 S0 4 -f C 16 H 30 2 = 6FeS 2 -f 16H 2 C0 3 
 To illustrate the partial reduction of ferric sulphate to pyrite, 
 
 * See p. 308. 
 
THE CHEMISTRY OF ORE-DEPOSITION. 3H 
 
 with formation of ferrous sulphate, the formula of an oxidized 
 hydrocarbon nearly corresponding to humus acid is assumed, 
 as in the following equation: 
 
 4Fe 2 (S0 4 ) 3 + 8H 2 + C 16 H 16 8 = 4FeS 2 + 4FeS0 4 + 16H 2 CO S . 
 
 The complete reduction of ferrous sulphate to pyrite or to 
 marcasite by an oxygenated hydrocarbon, such as gilsonite, 
 O 13 H 20 0, also requires the presence of free sulphuric acid : 
 
 5FeSO 4 + C 13 H 20 + 5H 2 S0 4 + 3H 2 = 5FeS 2 + 13H 2 CO S 
 
 + 5H 2 0. 
 
 II. PROTECTIVE ACTION OF CARBON AND OF HYDROCARBONS. 
 
 Hydrogen and carbon have affinities for oxygen stronger 
 than those of any other chemical elements, under conditions 
 normally occurring in ore-bodies. By consuming the free oxy- 
 gen in the circulating-waters, they act to preserve and shield 
 from decomposition all metallic sulphides. Otherwise stated, 
 all forms of carbon, and of the fluid and the solid hydrocar- 
 bons, when present in excess, owing to their superior affinity 
 for oxygen, prevent the oxidation of the ores ; although many 
 of the minerals in the ore-bodies under other conditions, where 
 carbon and its compounds are absent, or present only in a sub- 
 ordinate degree, are powerful deoxidizing agents. 
 
 In the mines at Joplin, Mo., the metallic sulphide-ores, 
 blende and galena, and the associated minerals, chalcopyrite, 
 pyrite, and even marcasite, are protected from decomposition 
 below ground-water level by the bitumen and the bituminous 
 shale contained in the wall-rock and present in the ore-bodies. 
 ISTear water-level, on the boundary between the zones of oxida- 
 tion and reduction, these hydrocarbons are consumed in places; 
 although, a few feet distant in the same ore-body, they may 
 occur in great excess. In such places the metallic sulphides 
 undergo 1 oxidation, only to be re-formed anew on coming in 
 contact with the hydrocarbon. 
 
 This protective action has long been understood with respect 
 to the rocks which contain organic matter. In the black-band 
 iron-ores, and in many bituminous shales, the iron occurs as the 
 proto-carbonate (siderite), and is preserved from oxidation by 
 
312 THE CHEMISTRY OF .ORE-DEPOSITION. 
 
 the hydrocarbon. In the outcrop, such rocks are bleached by 
 weathering, and the iron is oxidized to limonite or hematite. 
 That organic matter preserves the strata from oxidation is a 
 fact familiar to persons engaged in collecting fossils, particu- 
 larly fossil-plants. The beds of black and gray shales, where 
 the iron occurs as carbonate or sulphide, are carefully searched, 
 while bright-colored strata, in which the iron is peroxidized, 
 are given only a slight examination. 
 
 III. CONTRIBUTORY ACTION OF CARBONIC ACID GAS. 
 
 In the formation of ore-deposits, carbonic acid gas may, un- 
 der special conditions, displace and expel the air from the cav- 
 ities, channels and interspaces in the rocks, and in this way, 
 by mechanically excluding the air, materially aid the reduction 
 and precipitation of the ores by the ordinary deoxidizing agents. 
 Conditions also occur in the oxidation and re-formation of an 
 ore-body, particularly at those points where the zones of oxi- 
 dation and reduction merge one into the other, under which 
 carbon dioxide would be an efficient auxiliary in the process of 
 reduction. 
 
 The specific gravity of carbonic acid gas, compared with air 
 as the standard, is 1.524. Its action in displacing air is not 
 unlike that of water ; a rise in the ground-water from any 
 cause, as is often observed, drives out the air from all the 
 openings in the ore-bodies and checks the oxidation of the 
 minerals. 
 
 In the Parker mine, Wood River, Idaho, the country-rock is 
 a lime shale, heavily charged with graphite. Above the per- 
 manent water-level all the seams and joints in the rock are 
 filled with carbonic acid gas, produced by the oxidation of the 
 carbon. Carbon dioxide is found in a zone reaching from 
 ground- water level to within 100 ft. of the surface ; in this 
 zone it fills all .the rock-openings as perfectly as water fills 
 similar openings below.* 
 
 Sulphuretted hydrogen gas, which has a specific gravity of 
 1.19, may act in much the same manner in excluding the air, 
 although in itself it is a strong precipitating and reducing 
 agent. 
 
 * See pages 319 and 320. 
 
THE CHEMISTRY OF ORE-DEPOSITION. 313 
 
 Natural gas, notwithstanding its low specific gravity (0.558) r 
 may be held under pressure in the strata in much the same 
 way as it occurs sealed in the interspaces of the Trenton lime- 
 stone of the Ohio and Indiana gas-field. 
 
 At the Silver-Islet mine, Lake Superior, pockets filled with 
 hydrocarbon gas were struck in drifting on the vein on the 8th 
 (440 ft, vertical depth) and 10th levels (610 ft. depth). The 
 gas was held confined in the seams of the slate and in the 
 openings in the vein under a water-pressure of from 440 to 600 
 ft., equal to a pressure of from 190 to 265 Ibs. per square inch.* 
 
 Observations at many gas-wells show that the pressure 
 greatly exceeds that which would be due to a water-column 
 equal in height to the depth of the gas-producing strata- 
 There is no record of any measurement of the gas-pressure at 
 Silver-Islet. 
 
 IV. THE STABILITY OF CARBONIC ACID AND OF WATER. 
 
 Carbonic acid when combined with a base is a weak acid r 
 readily displaced by a stronger, as sulphuric, hydrochloric or 
 phosphoric acid, and also by sulphur and by many of the 
 organic acids. But the molecule of carbonic acid is never 
 broken up, is never separated into its component elements 
 under conditions ordinarily subsisting in the earth's crust, at 
 least not at the depths reached in the underground circulation 
 of meteoric water. 
 
 Volcanic action alone, or an earth-temperature far above 
 normal, furnishes the physical conditions in which carbon 
 dioxide is dissociated, or the conditions that admit of its being 
 reduced to the monoxide by carbon, or by other deoxidizing 
 agents. 
 
 Carbonic acid is a permanent refuge of oxygen ; once locked 
 up in combination with carbon, oxygen remains inert for all 
 time, in a condition of stable equilibrium, inactive, and chemi- 
 cally indifferent to all the complex changes taking place in the 
 depths of the earth. f Even in ore-deposits undergoing oxida- 
 
 * " The Silver-Islet Mine and Its Present Development," by Francis A. Lowe, 
 Eng. and Min. Jour., vol. xxxiv., pp. 320-323. See, also, p. 346, this paper. "Sil- 
 ver-Islet Mine, Lake Superior " (author unknown, with Supplement No. 1, by W. 
 M. Courtis), Eng. and Min. Jour., vol. xxvi., p. 438. 
 
 f Carbonic acid gas contains : Carbon, 27.27 per cent. ; oxygen, 72.73 per cent. 
 
314 THE CHEMISTRY OF ORE-DEPOSITION. 
 
 tion and re-formation, carbonic acid, once formed, is itself in- 
 susceptible to chemical change. Neither hydrogen, carbon, 
 sulphur, or the most powerful deoxidizing metallic sulphides, 
 can decompose it at ordinary temperatures. This immutability, 
 however, is maintained only under the conditions subsisting in 
 the depths of the strata, where life does not exist ; the carbonic 
 acid in the soil and in the atmosphere readily gives up its oxy- 
 gen and carbon to plant-life. 
 
 Water almost equals carbonic acid in stability. It is true 
 that water is decomposed by electrolysis and in many chemical 
 reactions in the laboratory; yet, at temperatures approaching 
 the normal, water is probably not dissociated, except in a very 
 limited way, in any of the processes incidental to ore-for- 
 mation. 
 
 In the complex chemical changes that take place in the oxi- 
 dation and re-formation of ores, it is possible that water may 
 be decomposed; but, quantitatively, such dissociation must be 
 insignificant. Practically, w r ater may be regarded as chemi- 
 cally stable under ordinary conditions and temperatures. The 
 fact that, in the presence of the deep-circulating underground 
 waters that contain no free oxygen, the complex sulphides 
 forming the ore-bodies have been preserved unaltered for ages, 
 is evidence that water is chemically inert to all the elements 
 present in the depths of the strata. 
 
 Among minerals, many oxygen compounds, as, for example, 
 quartz, corundum, cassiterite, rutile and zircon, resist decompo- 
 sition, as do also the silica, the alumina and the other acid rad- 
 icals in silicates, aluminates, borates, phosphates, titanates, tan- 
 talates, tungstates and chromates. Minerals containing oxides 
 of the alkalies and the alkaline earths, while usually perma- 
 nent, may have their oxygen displaced by sulphur and by the 
 halogens, chlorine, bromine, iodine and fluorine. In the 
 greater number of the refractory minerals and permanent 
 oxygen-compounds, the chemical union of the elements with 
 oxygen may probably date back to the primal origin of the 
 earth. 
 
 Carbon and hydrogen alone, of all the elements, unite with 
 oxygen under conditions now subsisting in ore-deposits, to form 
 fixed compounds, that, sealed in the rocks, can endure to the 
 end of time. 
 
THE CHEMISTRY OF ORE-DEPOSITION. 315 
 
 Y. OCCURRENCE OF CARBON AND THE CARBON-COMPOUNDS. 
 
 Carbon occurs as graphite in the metamorphic rocks and in 
 the gangue of certain mineral-veins. It is also found, practi- 
 cally free from hydrogen, as graphitic anthracite, and, in small 
 quantities, as native charcoal. In all cases carbon is the re- 
 sidual element in the decomposition of the organic matter de- 
 posited in the original sediments ; the hydrogen, oxygen, nitro- 
 gen and sulphur with which it may have been combined have 
 been eliminated. 
 
 Far more commonly, carbon, when in association with min- 
 eral-deposits, is combined with hydrogen and oxygen, usually 
 in the form of bituminous coal or bitumen in the wall-rocks, 
 or filling the ore-bearing fissures; in some instances, as in the 
 Joplin, Mo., mines, it is distributed generally throughout the 
 ore-bodies. In most carbonaceous shales, in the mining re- 
 gions, the organic matter is mainly in the form of finely dis- 
 seminated bituminous coal.* 
 
 It is somewhat remarkable, considering the almost universal 
 distribution of petroleum, that the non-oxygenated hydrocarbon 
 oils are found so seldom, either in the ore-deposits or in the 
 ore-bearing formations. In a few instances, marsh-gas and 
 other similar hydrocarbons which are gases at ordinary tem- 
 peratures and pressures have been found in association with 
 mineral-deposits. 
 
 VI. THE OCCURRENCE OF CARBON, ALONE. 
 
 Graphite. 
 
 In the metamorphic area of the Black Hills of South Dakota 
 many large, irregular deposits of pyrrhotite occur, associated 
 with belts of graphitic shales. Masses of crystalline pyrrhotite 
 are encased in soft, black, shaly gangue-rock, carrying a large 
 percentage of graphite. As observed by the author, these 
 graphitic shales appear to form a specially favorable gangue for 
 pyrrhotite, associated with ores of nickel and copper, and also 
 for pyrite and arsenopyrite. 
 
 * An analysis of the Hudson-Kiver slates (Lower Silurian) gave 5 per cent, of 
 fixed carbon and 3 per cent, of volatile combustible matter, or nearly in the pro- 
 portion of carbon, 62.5 percent. ; volatile, 37.5 per cent. ; corresponding to the 
 composition of the best gas-coals. "Classification of Coals," by Persifor Frazer, 
 Jr., Trans., vl, 448. 
 
316 THE CHEMISTRY OF ORE-DEPOSITION. 
 
 Pyrrhotite is mined in the vicinity of Deadwood, S. D., for 
 flux in pyritic smelting. The mineral shows on assay an aver- 
 age value of $1.00 to $2.00 per ton in gold, with usually less 
 than 0.25 per cent, of copper. Many of the deposits of pyrrho- 
 tite in the region lying easterly and northeasterly from Har- 
 ney's Peak carry a small percentage of nickel and copper. 
 Dr. Carpenter says that assays of the nickeliferous pyrrhotite 
 from this region, made at the Dakota School of Mines, show 
 an average of 1.5 per cent, nickel, though samples carrying 8 
 per cent, have been found.* 
 
 F. M. F. Cazin describes the occurrence, in the Vermont 
 copper-mine, of deposits of the sulphides of iron and copper in 
 intimate association with graphite. f 
 
 Prof. J. F. Kemp notes that graphite, or some closely re- 
 lated carbon mineral, is not uncommon in the ore of the Mary 
 mine, at Ducktown, Tenn. He says, " It must have been in- 
 troduced as some gaseous or very mobile liquid hydrocarbon, 
 which has penetrated into minute cavities and filled larger 
 cracks, and has been subsequently changed to graphite."J 
 
 Yon Cotta, in his " Treatise on Ore-Deposits," cites many in- 
 stances of the influence of carbon on the localization of ore-de- 
 posits. A single quotation is selected: "Near Freiberg the 
 veins . . . are enclosed in mica schist which contains an irregu- 
 lar layer of black graphitic schist. . . . The veins have only 
 been found productive in the black schist. In the common 
 mica schist they are very poor." 
 
 Silver Islet. In the Silver-Islet mine, Lake Superior, graphite 
 was found associated with native silver, silver-glance, tetrahe- 
 drite, argentiferous galena and a number of rare silver miner- 
 als, in a gangue of quartz, calcite and rhodochrosite. The geo- 
 logical formation is gray slate, nearly horizontal in bedding, 
 traversed by steeply dipping, parallel dikes of diorite and other 
 igneous rocks. The vein cuts vertically across the dikes and 
 
 * " Ore-Deposits of the Black Hills of Dakota," by Franklin K. Carpenter, 
 Trans., xvii., 582. 
 
 f Genesis of Ore-Deposits, pp. 207-209 \ Trans., xxiii., 605, 606. See, also, on ^ 
 this subject, "The Origin of the Gold-Bearing Quartz of the Bendigo Eeefs, Aus- 
 tralia," by T. A. Kickard, Trans., xxii., 314, 315. 
 
 J "The Deposits of Copper-Ores at Ducktown, Tenn," by J. F. Kemp, 
 xxxi., 261. 
 
 \ Treatise on Ore-Deposits, Prime' s Translation, pp. 46, 47. 
 
THE CHEMISTRY OF ORE-DEPOSITION. 317 
 
 the belts of slate included between them, but was ore-bearing 
 only where it faulted the main dike of diorite. This dike, 
 about 200 ft. in width, was in certain places strongly impreg- 
 nated with graphite.* Intersecting fissures appear also to have 
 had an influence on the localization of the ore. Two bonanzas 
 were discovered : (1) The main ore-shoot (that produced over 
 |2,000,000) extending from the surface to a depth of 330 ft., 
 nearly to the 7th level, and formed at the intersection of a 
 cross-vein with the main lode ; (2) the rich body of native sil- 
 ver on the 3d and 4th levels, south (that yielded 800,000 oz. of 
 silver), occurring near the junction of the two branches of the 
 vein. Graphite was not found in the slates, or in any dike of 
 the igneous belt intersected by the vein-fissure, with the excep- 
 tion of this particular dike, which in its limited outcrop above 
 the surface of the lake, at the point where the lode cut through 
 it, formed Silver Islet. The vein in no place carried workable 
 ore-deposits, either in the slates or in the normal diorite. Be- 
 fore the mine was closed down, a small body of ore (that pro- 
 duced about $30,000) was struck on the 13th level, south. 
 Like the larger ore-bodies in the upper-levels, the ore was 
 found to occur in association with graphite. McDermott, writ- 
 ing of this mine, says : " The fact most striking, to one who ex- 
 amines the parts of the vein from which the most valuable ore 
 has been extracted, is the evident connection of the deposit of 
 the silver with the region of graphite impregnation of the wall- 
 
 rock."f 
 
 Graphitic Anthracite. 
 
 An extensive deposit of graphitic anthracite, associated with 
 antimonial silver-lead ores, was found in the Parker mine, in 
 
 * " The trap-dike has usually been called diorite, but is determined to be norite 
 by Wadsworth, Bull. No. 2, Minn. Geol. Sur. , p. 92, and gabbro by Irving, Mono- 
 graph V., V. S. Geol. Sur., pp. 378, 379." Ore-Deposits of the U. S. and Canada, 
 by J. F. Kemp, p. 283. 
 
 t "The Silver- Islet Vein, Lake Superior," by Walter McDermott, Eng. and 
 Min. Jour., vol. xxiii., pp. 54, 55 and 70, 71. 
 
 "The Silver-Islet Mine and Its Present Development," by Francis A. Lowe, 
 Eng. and Min. Jour., vol. xxxiv., pp. 320-323. 
 
 "Silver Islet," by Thomas Macfarlane, Trans., viii., 226-253. 
 
 " The North Shore of Lake Superior as a Mineral-Bearing District," by W. M. 
 Courtis, Trans., v., 473-487. 
 
 " Silver- Islet Mine, Lake Superior " (author unknown, with longitudinal sec- 
 tion of the mine, Supplement No. 1, by W. M. Courtis), Eng. and Min. Jour., 
 vol. xxvi., p. 438. 
 
318 THE CHEMISTRY OF ORE-DEPOSITION. 
 
 Idaho. The vein occurred in a belt of graphitic lime-shales, 
 about 600 ft. in width, included between two intrusive sheets of 
 andesite; the whole formation the vein and the igneous sheets 
 bounding the shales above and below dipping into the moun- 
 tain at an angle of 40 degrees. The ores were galena and 
 polybasite, averaging (in car-lots) from 75 per cent, of lead and 
 125 ounces of silver to 45 per cent, of lead and 680 ounces of 
 silver per ton. The gangue was an intimate mixture of white 
 crystalline calcite and quartz. An intersecting vein, coming in 
 from the foot-wall, carried crystallized pyrite and blende, with 
 only traces of silver. The mine produced $365,000. At a 
 vertical depth of 300 ft. from the surface a flat fissure was en- 
 countered, filled with graphitic anthracite with a little white 
 quartz intermixed. It formed a flat sheet, 2 to 6 ft. in thick- 
 ness, and was explored over an area 200 ft. square. The coal 
 was heavily slickensided, crushed and compacted into a hard, 
 granular mass. It was mined with difficulty with a pick, and 
 often required blasting, owing to the stringers of quartz dis- 
 tributed through it. Analysis gave, excluding ash, 90 percent, 
 of fixed carbon and 10 per cent, of volatile matter, mostly 
 water from the clay contained in the ash. Owing to admixture 
 of quartz and earthy material from the walls, the ash varied 
 from 10 per cent, to 50 per cent. This coal had evidently 
 been formed by the destructive distillation of asphalt or petro- 
 leum, filling the fissure. The intrusion of the sheets of vol- 
 canic rock enclosed the shale stratum as if in a retort. There 
 is evidence, in the large amount of graphite in these shales, 
 that they were originally highly charged with bituminous 
 matter. The hydrocarbons, first distilled by the heat accom- 
 panying the intrusion, were condensed and accumulated in the 
 fissure as heavy petroleum or asphalt, and, by further action of 
 heat, carbon was deposited, hydrocarbon oils being driven oft' 
 in the same way as in the distillation of petroleum-tar in the 
 manufacture of lubricating oils. Subsequently the deposit was 
 crushed by faulting movements of the beds, and at a still later 
 date the ore-deposits were formed in the intersecting vein-fissure. 
 In places the ore lies against and extends into the coal. Natu- 
 ral gas was not encountered, though conditions were favorable 
 for its formation, probably because the workings were near the 
 surface. Heavy flows of carbonic acid gas were, however, fre- 
 
THE CHEMISTRY OF ORE-DEPOSITION. 319 
 
 quently encountered in the mine ; and during occasional periods 
 of low atmospheric pressure the outflow of gas from the seams 
 and fissures in the country-rock was so much increased that the 
 miners were often driven from parts of the mine that were not 
 well ventilated.* 
 
 J. B. Farish notes that the seams in the limestones at New- 
 man Hill, near Rico, Col., were filled with carbonic acid gas.f 
 
 Charcoal. 
 
 Native charcoal, or mineral-charcoal, as it is termed, is prob- 
 ably never pure carbon, yet the amount of hydrogen contained 
 is so small that in the discussion of its reducing power it may 
 be classed with graphite. Observation shows that charcoal, 
 from its soft, porous structure, and from the great surface it 
 exposes to chemical action, is one of the most energetic deoxi- 
 dizing agents in the formation of ore-deposits. 
 
 Small pockets filled with charcoal were found at a depth of 
 800 ft. in the ore-chimney of the Bassick mine, near Silver 
 Cliff, Colorado. This remarkable occurrence of charcoal in. 
 an eruptive formation is set forth in detail in the paper by Iu 
 E. Grabill.J 
 
 In the discussion of this paper, the occurrence of charcoal 
 in anthracite was described by C. A. Ashburner ; and of char- 
 coal in Oregon, formed by the carbonization of the leaves and 
 twigs of plants in the layers of mud between successive over- 
 flows of lava, by Dr. R. "W. Raymond. 
 
 President Rothwell remarked : " Charcoal has also been 
 found in the silver-bearing sandstones of Southern Utah. These 
 sandstones are a simple sedimentary formation, and contain 
 trunks of trees, some finely silicified. ... I have also found 
 there pieces of lignite, with the structure of the wood still 
 quite evident. . . . Other portions of the carbonaceous matter 
 have almost the character of charcoal; the carbon has not 
 become hard, nor taken on the form of lignite. The woody 
 
 * "Graphitic Anthracite in the Parker Mine. Wood Kiver, Idaho," by W. P. 
 Jenney, School of Mines Quarterly (1888-89), vol. x., pp. 313-315. 
 
 f " On the Ore-Deposits of Newman Hill, near Rico, Colorado," Proceedings of 
 the Colorado Scientific Society, vol. iv. , p. 153. 
 
 I "On the Peculiar Features of the Bassick Mine," by L. E. Grabill, Trans. , 
 xi., 110-120. 
 
 g Ibid., p. 119. 
 
320 THE CHEMISTRY OF ORE-DEPOSITION. 
 
 fiber of ordinary charcoal can be traced in it very clearly. . . . 
 In the silver-bearing portions of the beds, the charcoal, the 
 lignite, or the silicified wood, as the case may be, is impreg- 
 nated with chlorides or sulphides of silver, and is in many 
 cases quite rich."* 
 
 The deposits of silver-ore in sandstone at Silver Reef, Utah, 
 are mainly due to the reducing action of wood and plant 
 remains, more or less perfectly altered to lignite, and are 
 treated in more detail under that head.f 
 
 VIE. THE OCCURRENCE OF CARBON COMBINED WITH HYDROGEN. 
 
 Bituminous Coal. 
 
 Blende and galena have been deposited in coal in the outly- 
 ing basins of the Coal Measures, scattered along the broad, 
 northern marginal belt of the Ozark Uplift. 
 
 Near the reservoir at Sedalia, Mo., a basin in the Second 
 Magnesian Limestone carries a little coal of fair quality, in 
 which dark brown crystalline blende occurs in small irregular 
 bunches and in sheets filling both the vertical and horizontal 
 seams and joints. The greater part of the blende is in 
 sheets, J to 1J in. thick, made up of agglomerated imperfect 
 crystals, compressed or flattened between the layers of the coal. 
 Some specimens show blende in thin parallel seams, not thicker 
 than a sheet of paper and -fa to -fa in. apart, distributed regu- 
 larly through the coal. About 2 tons of blende were mined at 
 this locality. 
 
 In Morgan and Moniteau counties, Mo., in a number of 
 places, blende and galena are found in similar deposits of coal. 
 At Martin's coal -bank, near Versailles, Mo., the coal has evi- 
 dently been disturbed since its deposition, and vertical seams in 
 the coal, J in. to 1 in. in width, are filled with sheets of crystal- 
 line blende and galena in a gangue of calcite and white tallow- 
 clay. The strike of the lines of disturbance of the coal, pro- 
 longed 500 to 1000 feet southerly, crosses an extensive tract of 
 old surface-workings in the Second Magnesian Limestone. 
 The ground is thickly covered by shallow pits, dug in search 
 of lead-ore. These deposits of lead were apparently formed 
 
 * Ibid., pp. 117, 118. f See pp. 322-327. 
 
THE CHEMISTRY OF ORE-DEPOSITION. 321 
 
 through the agency of the same system of fissures that intro- 
 duced the ore in the coal. 
 
 Blende and galena were formerly mined at Simpson's coal- 
 bank, in Moniteau county. The coal is a hard cannel, filling a 
 basin in the Second Magnesian Limestone ; the ores occur in 
 seams, seldom more than an inch in thickness, in the joints of 
 the coal. The ore incidentally obtained in mining the coal 
 afforded an occasional shipment to the smelters. 
 
 Vanadium is found in a lignite coal in the province of Men- 
 doza, Argentine Republic. The ashes of this coal carry van- 
 adic acid, V 2 5 . It also occurs in anthracite mined near Yauli, 
 Peru.* 
 
 Gold has been repeatedly reported in the ash of the Creta- 
 ceous coals of the West. H. M. Chance records that the coal 
 of the Cambria Coal Co. near Newcastle, Wyoming, is said, 
 by the chemist of the company, to carry gold.f Mr. H. Rives 
 Ellis, of Salt Lake City, informs the writer that he obtained an 
 average of 60 to 80 cents gold per ton of ash from the Pleasant 
 Valley, Utah, and Kemmerer, Wyoming, coals. In this con- 
 nection, the paper by G. A. Koenig and M. StockderJ is of 
 interest, although the coal described appears to be more nearly 
 an infusible hydrocarbon, such as might result from the par- 
 tial oxygenation of albertite. 
 
 Mr. Henry Sewell describes the occurrence of antimonial 
 silver-ores, in association with strata carrying beds of bitu- 
 minous coal, in the mineral caves of Huallanca, Peru, located 
 at an elevation of 14,700 ft. above the sea. These silver-mines 
 are situated in a coal-formation, upturned on edge by an out- 
 burst of porphyry, the upheaval forming immense backbones, 
 with the stratification standing almost perpendicular. A bed 
 of coal is mined for blacksmithing purposes within a distance 
 of 150 yards of the ore-bearing beds. The ore is tetrahedrite, 
 with about 800 ounces of silver per ton, and occurs lining cav- 
 
 * 2lst Annual Report of U. S. Geol. Sur., 1899-1900, Part VI. ; Mineral Re- 
 sources of the U. S., p. 315. 
 
 f "The Discovery of New Gold Districts," by H. M. Chance, Trans., xxix., 
 227. 
 
 J "On the Occurrence of Lustrous Coal with Native Silver in a Vein in Por- 
 phyry, in Ouray County, Colo.," Trans., ix., 650. See, also, "Modes of Oc- 
 currence of Pyrite in Bituminous Coal," by Amos T. Brown, Trans., xvi., 
 539-546. 
 
 21 
 
322 THE CHEMISTRY OF ORE-DEPOSITION. 
 
 erns, in beds of sandstone. Some of these caverns are 25 to 30 
 ft. long and of nearly equal height, their inner surfaces covered 
 with a coating 2 to 3 in. thick of crystallized silver-ores, mostly 
 tetrahedrite. Silver-ores also occur in the shale beds adjacent 
 to the sandstone.* 
 
 Lignite. 
 
 At Silver Reef, Utah, silver has been deposited in lignitic- 
 sandstones, determined by dewberry to be of Triassic age.f 
 The mines since 1885 have only been worked by leasers in a 
 small way. During the height of production in 1877-79, the 
 total output was 2,122,471 ounces of silver.J The ore-bearing 
 beds were 30 to 40 ft. in thickness, of which usually only 16 
 ft. was pay-ore. The ore occurred in flat shoots that were, in 
 some places, 300 ft. wide, and extended 400 to 500 ft. deep on 
 the dip of the formation. The ore was richest near the out- 
 crop, and, as it was followed in depth, gradually got poor. Near 
 the surface the silver was in the form of chloride, associated in 
 places with the blue and green carbonates of copper in very 
 small quantity. As the ore was followed in depth, the chloride 
 gave place to silver-sulphide, and scales of native silver came 
 in, especially in the branches of trees and distributed in the 
 plant-shales. No other ores were found, and the gangue-min- 
 erals usually occurring in ore-deposits, as quartz, calcite, barite, 
 etc., were absent. When, following the inclination of the 
 strata, the workings attained a vertical depth of 400 to 500 ft., 
 the ore changed, becoming low-grade and difficult to amal- 
 gamate in pans ; the ore-shoots at the same time contracted, 
 becoming narrow, and only 2 or 3 ft. in height. Exploration 
 was continued for several years, but finally all search in depth 
 for pay-ore was abandoned. 
 
 * " The Silver Caves of Peru," by Henry Sewell, Eng. and Min. Jour., vol. 
 xxiv. , p. 292. Abstract taken from the London Mining Journal. 
 
 t "Report on the Properties of the Stormont Silver-Mining Company at Silver 
 Reef, Utah," by J. S. Newberry, Eng. and Min. Jour., vol. xxx., p. 269. See, 
 also, "The Silver Eeef Sandstones," by J. S. Newberry, Eng. and Min. Jour., 
 vol. xxxi., p. 4. 
 
 J Eng. and Min. Jour., vol. xxix., p. 26. 
 
 $ "Silver Reef District, Southern Utah" (author unknown), Eng. and Min. 
 Jour., vol. xxix., pp. 25-26, 45-46, 59-60, 79-80, and 96. 
 
 "The Silver Sandstone District of Utah," by C. M. Rolker, Trans., ix., 21. 
 
 "The Peculiar Features of the Bassick Mine;" Discussion by R. P. Roth well, 
 Trans., xi., 117-119. Genesis of Ore-Deposits, pp. 130, 131. 
 
THE CHEMISTRY OF ORE-DEPOSITION. 323 
 
 Many writers report that traces of silver and copper occur in 
 the extension of these same sandstone reefs, which can be 
 traced by their outcrop for a distance of 10 to 20 miles to the 
 southwest. An unknown author, in the early development of 
 the district (May, 1877), thus describes the peculiar occurrence 
 of the ore : " The formation is a beautifully stratified red and 
 white sandstone, but greatly broken up and eroded. Where 
 the strata have been undisturbed they rise to a height of per- 
 haps a thousand feet above the adjacent valley, in table-moun- 
 tains, alternately banded in red and white, and plainly showing 
 the former height of the whole country. The numerous ex- 
 tinct volcanoes and the vast quantities of volcanic rock found 
 throughout southern Utah, and particularly this section, point 
 to at least one agent, and, no doubt, a powerful one, which 
 served to produce the numerous foldings and contortions of 
 the strata, while the great sandy deserts, covered with sage and 
 cactus, bear abundant evidence to the erosion. On the north- 
 ern side of what was once a vast basin, lying between several 
 ranges of high mountains of old rock, where the erosion of an 
 anticlinal has left ridges of reefs cropping out at various an- 
 gles, are situated the mines. . . . The sandstone consists of 
 red and white deposits, carrying some lime as a cementing ma- 
 terial, with occasional layers of clayey or shaly rock, and con- 
 siderable carbon scattered throughout. This carbon, which is 
 evidently from the decomposition of drift material, of which 
 the impression in the rock and even the plant itself is yet dis- 
 tinct, occurs in important layers in places. . . . Petrifactions, 
 even of the size of large trees, are not uncommon, some of 
 which form a valuable ore. The white sandstone, which ap- 
 pears to be of a somewhat finer texture than the red, seems, 
 so far, to have carried the ore. . . . These veins, as they 
 are there called, are entirely conformable with the strata, and 
 in no case do they cut across the adjacent layers of rock. 
 They appear to be richest where there is the most carbon, 
 which evidently has acted as a reagent to precipitate the silver 
 from solution and to deposit it, sometimes as flakes of metallic 
 silver, in its midst. In some cases the form of the plant, of 
 apparently a reedy nature, is yet distinct, in which the cells are 
 yet visible, but to a great extent filled with valuable ore. Other 
 beds carry considerable copper in the form of blue or green 
 
324 THE CHEMISTRY OF ORE-DEPOSITION. 
 
 carbonate, and also iron in nodules which run very high in sil- 
 ver. ... A light sandstone, containing streaks or fine layers 
 of a dark material, which elsewhere would not attract atten- 
 tion, is there found, sometimes, to run from $50 to $100 a ton ; 
 while the darker rock, containing considerable carbon, copper, 
 or iron-nodules, will at times run into the hundreds, or even 
 thousands."* 
 
 Mr. Watson M. Nesbit, who was connected with mining oper- 
 ations at Silver Reef from 1878 to 1888, gives the author the fol- 
 lowing statement of the manner of occurrence of the ore : In the 
 Barbee and Walker mine, water was struck at a depth of about 
 500 ft. vertically. Near that point the ore changed in appear- 
 ance and character, and gave great trouble in amalgamation, 
 the extraction being very low. The ore was treated hot, in 
 pans; a thick scum rose on the pans, like heavy petroleum oil, 
 and had to be removed from time to time during the amalgama- 
 tion. From a charge of 1| tons of ore, as much as a gallon of 
 this oily material would be obtained. The ore at water-level, 
 if carefully stoped, averaged 12 to 16 oz. of silver per ton ; 
 but only a part of the silver could be saved in pans. A very 
 little pyrite appeared at water-level the first seen in the mines. 
 About 100 to 200 ft. above water-level, on the slope of the beds, 
 the ore was in places very rich ; and small bunches of lignite 
 coal, 4 to 10 in. across, were found imbedded in the soft sand- 
 stone, with native silver deposited in thin scales on the joints 
 of the coal. Most of the ore at this depth was silver-sulphide. 
 At one place a tree-trunk, 18 in. in diameter, was found ; the 
 heart-wood was silicified and very hard, and carried 8 to 10 oz. 
 of silver per ton. The sap-wood and bark, 3 to 6 in. in thick- 
 ness, were altered to soft, crumbling lignite, full of silver-sul- 
 phide ; it assayed 5000 oz. of silver per ton. The ores from 
 the Silver Reef mines never showed any gold by assay ; but in 
 leaching the ore by the Russell process, the silver-sulphides 
 produced contained a trace of gold. 
 
 Review of the Phenomena at Silver Reef. Light is thrown on 
 the change in the mineral character of the ore at water-level, 
 and on the difficulty experienced in amalgamation, by the dis- 
 
 * "The Silver Sandstones of Utah," by C. F. A., Salt Lake City, Eng. and 
 Min. Jour., vol. xxiii., p. 317. 
 
THE CHEMISTRY OF ORE-DEPOSITION. 325 
 
 covery announced by dewberry* that the ores carried selenium, 
 the average of four analyses giving selenium, 0.23 per cent., 
 and silver, 0.26 per cent. The selenium in one specimen 
 amounted to 90 ounces per ton. 
 
 Whether the silver was deposited at the same time the sedi- 
 ments were laid down, or was introduced by solutions upflow- 
 ing through faul ting-fissures in a later geological age, has been 
 a much debated question. Without dwelling upon this point, 
 for, in either event, the primary deposition of the ore was 
 due to the hydrogen and carbon of the plant-remains enclosed 
 in the sandstones, certain peculiar features of the occurrence 
 deserve notice. The structure at Silver Reef may be stated as 
 a broad anticlinal arch, broken up by faults coursing northerly 
 and southerly, rudely parallel to the axis of the fold. A basin, 
 nearly 3 miles across, occupied by the valley of the Virgin river, 
 was eroded through the crest of the arch, leaving the two cliffs 
 facing one another, the strata dipping away from the basin on 
 the two sides. The total area of the several ore-producing 
 belts of sandstone-outcrop, left by erosion, covered less than 
 500 acres. 
 
 Silver Reef conforms to the general law of areal distribution 
 of mining-districts, namely, that " Ore-deposits have been formed 
 only in local areas of disturbance. Between and surrounding such 
 areas of mineralization extend broad, barren tracts of undisturbed 
 strata"-\ and also conforms to the law of mineral occurrence, 
 namely, that " All workable deposits of ore occur in direct associa- 
 tion with faulting-fissures traversing the strata, and with zones or beds 
 of crushed and brecciated rock, produced by movements of disturbance. 
 The undisturbed rocks are everywhere barren of ore."{ The de- 
 scriptions apply to a mineral area which, prior to the recent 
 erosion of the basin, may have possibly covered four or five 
 square miles, with pay-ore found in no place outside this special 
 area. 
 
 A writer notes that only the fractured, jointed and perme- 
 able portions of the bed are rich ; where undisturbed and 
 massive, the sandstone is barren. Also that vertical fault- 
 
 * "The Silver Eeef Sandstones," by J. S. Newberry, Eng. and Min. Jour., vol. 
 xxxi., p. 5. 
 
 f "Lead- and Zinc-Deposits of the Mississippi Valley," by W. P. Jenney, 
 Trans., xxii., 192. J Ibid., p. 184. 
 
326 THE CHEMISTRY OF ORE-DEPOSITION. 
 
 planes frequently bound the ore.* These are conditions that are 
 found in impregnated beds of zinc- and lead-ores in Southwest 
 Missouri and Northern Arkansas, and also in the flat deposits 
 of gold, associated with tellurium, in the Cambrian sandstone 
 near Deadwood, South Dakota. 
 
 Selenium usually occurs with minerals believed to have been 
 formed by highly-heated vapors and solutions and in direct 
 association with igneous disturbances. Its presence at Silver 
 Reef seems to favor the theory of the deposition of the silver 
 through the fissures. It appears that secondary enrichment 
 has taken place on an extensive scale, and that the silver was 
 deposited originally in the sandstone in combination with sele- 
 nium and probably with sulphur by the reducing action of the 
 lignitic matter. Afterwards, these primary ore-bodies were en- 
 riched by the secondary precipitation of silver-sulphides, by the 
 agency of descending surface-waters, aided greatly by the pro- 
 gressive erosion of the basin. In this migration of the ore 
 the outcrop of the sandstone gradually disintegrating and wear- 
 ing away from exposure to weather to the deposits of silver- 
 sulphides, re-formed at deeper levels on the dip of the same 
 beds, the reducing agent has been the organic material distrib- 
 uted through the ore-horizon. Later, these reinforced ores 
 were, near the outcrop, altered to silver-chloride, cerargyrite, 
 the trace of copper occurring with the silver forming the car- 
 bonates, azurite and malachite. When the mine-workings 
 passed below this zone of enrichment there were found only 
 small bodies of ore, that had remained unaltered since the first 
 deposition of silver in the beds. 
 
 Similar occurrences have been described of copper-ores re- 
 placing the wood of trunks and branches of trees, and encrust- 
 ing the leaves and stems of fossil-plants, in the Triassic sand- 
 stones of New Mexico, f and in the Permian sandstones of 
 Russia. J 
 
 E. J. Schmitz writes of the occurrence of copper-ores as 
 
 * " Silver Keef District, Southern Utah," by K. P. Kothwell or Thomas 
 Couch (?), Eng. and Min. Jour., vol. xxix., pp. 25-26. 
 
 f "The Origin of Copper- and Silver-Ores in Triassic Sand-Kock," by F. M. F. 
 Cazin, Eng. and Min. Jour., vol. xxx., p. 381. "The Silver Keef Sandstones," 
 by J. S. Newberry, Eng. and Min. Jour., vol. xxxi., pp. 4-5. 
 
 J Trans., ix., p. 33. 
 
THE CHEMISTRY OF ORE-DEPOSITION. 327 
 
 pseudomorphic replacement of wood and branches of trees in 
 bituminous clay-slate in the Permian of Texas.* In the dis- 
 cussion of this paper, Mr. Henry Louis describes deposits 
 somewhat analogous in the Permian of Nova Scotia, at New 
 Annan, where the ore occurs in nodules of chalcopyrite, chalco- 
 cite, and iron-py rites, f associated with plant-remains converted 
 into anthracite. 
 
 Posepny also describes remarkable specimens of tree-trunks 
 altered to galena from the Vesuvius mine, Freihung, Bavaria. J 
 
 Bituminous Shales. 
 
 Rich deposits of blende, formed in great part by the second- 
 ary enrichment of smaller, or less mineralized, primary ore- 
 bodies, are found near the surface in the Joplin, Mo., district, 
 in the vicinity of Carthage, Lehigh, Central City and Reding's 
 Mill. At these localities the ore occurs in two ways : in the 
 beds of soft, decomposed carbonaceous shales in the Coal Meas- 
 ures, occupying shallow basins in the Subcarboniferous lime- 
 stone of the region ; or, more commonly, in horizontal chan- 
 nels eroded in the underlying limestone and filled with soft, 
 dark mud, intermixed with bituminous matter, derived from 
 these same shales, crushed by faulting movements and washed 
 into the openings by surface-waters. Without regard to the 
 character of the enclosing formation, these forms of ore-deposit 
 are known to the miners as " mud-runs." These occurrences 
 are seldom far from the surface ; the deepest " run " of this 
 character observed, near Reding's Mill, was at a depth of 90 ft. 
 At Lehigh, similar deposits were found in the bottom-lands 
 along the stream, within a few feet of the surface, where the 
 permanent water-level came near to the top of the ground. 
 
 The ore occurs in minute crystals, thickly disseminated 
 through the soft, shaly gangue, or enveloped in semi-fluid 
 black mud. In some of the deposits the crystals of blende are 
 agglomerated, forming irregular masses and sheets of pure ore. 
 The crystals are of uniform size, usually from y 1 ^ to J- of an in. 
 
 * "Copper-Ores in the Permian of Texas," by E. J. Schinitz, Trans., xxvi., 
 101. 
 
 t " Copper-Ores in the Permian of Texas ;" Discussion by Henry Louis, Trans., 
 xxvi., 1051, 1052. 
 
 J Genesis of Ore-Deposits, pp. 129, 130. 
 
328 THE CHEMISTRY OF ORE-DEPOSITION. 
 
 in diameter, transparent, resin-yellow in color, with a sh,ade of 
 red, resembling in appearance the small garnets found in some 
 placer gold-bearing gravels. The small size of the crystals is 
 probably due to the concentration of the solutions from which 
 they were deposited, and to their rapid formation. In some 
 instances blende forms crystals in these shaly beds from J in. 
 to more than an inch in diameter, presumably from a slower 
 and more prolonged growth. In all the deposits of this type, 
 the reducing agent has been bituminous matter acting upon 
 surface-waters, which carried in solution the sulphatesof the 
 metals leached from ore-bodies at higher levels, that were un- 
 dergoing oxidation. The following equation shows the char- 
 acter of the change : 
 
 ZnS0 4 + 2CH + H 2 + = ZnS + 2H 2 C0 3 . 
 
 It has been observed that these shallow mud-runs usually 
 occupy synclinal basins or troughs, and that surface-erosion has 
 often removed a considerable depth of the ore-bearing forma- 
 tions from the immediate vicinity; the deposits being located 
 where they have received the drainage from surrounding min- 
 eral-areas. 
 
 At the Britton mine, Central City, the ore occurs at a depth 
 40 to 50 ft. from the surface, in a broad, flat, compound-run, 
 75 to 150 ft. wide and 6 to 12 ft. high, developed on its course 
 for a length of 550 ft, northerly and southerly.* The ore is 
 granular, crystallized blende in a stratum of soft, black mud 
 and broken chert. The particles of blende are less than ^ in. 
 in diameter, deep garnet-red in ' color, and, although thickly 
 distributed in the mud, are not agglomerated. A number of 
 similar deposits are developed in the vicinity. 
 
 Ore-deposits of this character are easily mined with pick 
 and shovel ; powder is only used to break up an occasional 
 boulder in the ore-body. The ore requires very little crushing 
 and readily concentrates, yielding from 12 to 20 per cent, of 
 clean blende. The product is very pure, assaying from 62 to 
 64 per cent, of metallic zinc. 
 
 Reding's mine, about 4 miles southeast of Joplin, is situated 
 
 * For a definition of these forms of ore-deposits, see " The Lead- and Zinc- 
 Deposits of the Mississippi Valley," by W. P. Jenney, Trans., xxii., 189, 190. 
 
THE CHEMISTRY OF ORE-DEPOSITION. 329 
 
 in a shallow basin in a low range of hills, bordering the north 
 side of the valley of Shoal creek. At the time of the exami- 
 nation, this mud-run was opened 75 ft. in length, north and 
 south, with a width of 36 ft, and a height of 12 to 18 ft. The 
 ore occurs in dark-brown mud, in finely disseminated crystals, 
 and in crystallized masses and sheets of galena and blende. 
 Beautiful specimens of galena are found in very perfect cubical 
 crystals, 1 to 2 in. on a side. The upper part of the run is 
 mostly crystallized galena, while the lower part is blende, with 
 a smaller proportion of galena. Boulders of flint and black 
 clay-shales are found in the ore, together with much coarsely 
 crystalline rotten dolomite. 
 
 This ore-deposit is remarkable for its extreme richness. To 
 the date of my examination, the yield of the mine, estimated 
 upon all material extracted, had been 15 to 20 per cent, of clean 
 ore. When first formed, it was evidently a small run of blende 
 and galena in dolomite ; subsequently, surface-waters eroded a 
 cavern-like channel following the course of the run. Material 
 washed from the surface formations of broken and crushed 
 bituminous shale filled this channel and enveloped the ore-body. 
 Finally, the ore primarily deposited was greatly reinforced by 
 secondary deposition, both galena and blende being crystallized 
 in the fluid mud by the reducing action of the hydrocarbon. 
 
 A small basin of coal-shales, near Belleville, Jasper county, 
 Mo., carried beautifully preserved fossil-plants. The outer 
 surface of the mass of shales, for a depth of about a foot, con- 
 tained scattered crystals of blende, from J to f in. in diameter, 
 mingled with a few crystals of galena and pyrite. The central 
 portion did not carry any mineral, the mass having been min- 
 eralized from the outside, toward the interior, as far only as 
 the mineral-bearing waters could penetrate the dense plastic 
 clay. The crystals, in their growth, have distorted otherwise 
 perfect fossil-plants, crowding parts of the fern-fronds to one 
 side ; giving evidence that the deposition of the minerals was 
 of later date than the preservation of the plant-remains. These 
 plants were determined by David White to belong to a hori- 
 zon near the middle, or the upper part, of the Lower Coal- 
 Measures.* 
 
 * " Flora of the Outlying Carboniferous Basins of Southwestern Missouri," 
 Bulletin of U. S. Geol. Sur., No. 98. 
 
330 THE CHEMISTRY OF ORE-DEPOSITION. 
 
 On the Mine La Motte grant, in Southeast Missouri, deposits 
 of disseminated galena in black shale of Cambrian age outcrop 
 at the surface, and were worked for lead during the early 
 period of mining in that region. The galena occurs in crystal- 
 line nodules, from J to J in. in diameter, thickly distributed in 
 bands through the shale. This shale-bed appears to be a local 
 formation. The ore-deposits closely resemble in mode of occur- 
 rence those of disseminated lead in the Cambrian limestone in 
 the belt extending from Mine La Motte, through the Flat River 
 district, to Bonne Terre. 
 
 The secondary formation of metallic sulphides is now taking 
 place in the Missouri mines ; blende and galena, oxidizing to 
 sulphates in the ore-deposits near the surface, are carried in 
 solution by the subaerial waters to the deeper horizons, and 
 there regenerated by the deoxidizing action of bituminous 
 matter. The subject is too extensive to admit of discussion 
 here, and must be left for a future paper. 
 
 A single instance, however, may be cited of the reproduction 
 of blende from mine-waters. An old tunnel, driven through 
 bituminous shale on the Banker's Tract, near Joplin, became 
 filled with water draining from adjoining mines on which 
 work had been suspended. The tunnel remained closed and 
 submerged for ten or twelve years, until the mines were un- 
 watered in 1898. When reopened, the surface of the shales, 
 011 the roof and sides of the tunnel, was found to be thickly 
 encrusted with minute crystals of blende, one- or two-hun- 
 dredths of an inch in diameter. In places, the blende was de- 
 posited on the pick-marks made when the tunnel was run. 
 
 The paper of T. A. Rickard, on " The Enterprise Mine, Rico, 
 Colorado,"* shows the existence of a strongly-marked resem- 
 blance between the occurrence of the flat ore-deposits at Rico, 
 carrying silver and gold, and the ore-formation of Southwest 
 Missouri, where galena and blende occur in simple runs, and 
 also in compound runs, formed in like manner, in the favorable 
 beds, by mineral-depositing solutions introduced through ver- 
 tical fissures from an unknown source in depth, and where 
 bituminous matter, contained in the ore-bearing strata, has 
 likewise been the precipitating agent in the deposition of 
 the ore. 
 
 * Trans., xxvi., 906-980. 
 
THE CHEMISTRY OF ORE-DEPOSITION. 331 
 
 Experiments made in the laboratory, to determine the re- 
 ducing action of the black shale associated with the ore-bodies, 
 are described by Rickard, as follows : 
 
 " A piece of the Rico shale was put into a weak solution of 
 sulphate of silver (Ag 2 S0 4 ) containing some free acid intended 
 to neutralize the lime (CaC0 3 ) in the shale. The precipitation 
 of metallic silver became visible in three days. The parallel 
 experiment with gold was more interesting. A piece of ore 
 (assaying 1147 oz. of gold per ton) obtained from . . . . 
 Cripple Creek, was taken, and its gold was extracted by a solu- 
 tion containing ferric sulphate (Fe 2 O 3 ,3S0 3 ), common salt (NaCl) 
 and a little free acid (H 2 S0 4 ). This Cripple Creek ore car- 
 ried the black oxide of manganese (Mn0 2 ) in visible quan- 
 tity, and thus the chlorine used to form the gold-solution was 
 liberated in a manner simulating natural conditions. Of the 
 gold, . . . . 99.91 per cent, was extracted and subse- 
 quently precipitated on the Rico shale by inserting the latter 
 in the solution thus formed. The gilding of the black shale 
 by the deposit of gold became visible within four hours."* 
 
 W. Nicholas has made a series of similar experiments in the 
 precipitation of gold by black carbonaceous shales from the 
 Victorian quartz-reefs, f 
 
 The peculiar vein-formation known as the " Indicator " is an 
 example of the localization of rich deposits of free gold, due to 
 the reducing action of carbonaceous shales. Rickard defines 
 the Indicator as " a very thin thread of black slate, which is 
 remarkable on account of its extraordinary persistence, and 
 also because the quartz seams which cross it are notably en- 
 riched at the point of intersection."! It is also referred to by 
 Dr. Don. The Indicator is the most important member of a 
 series of thin seams of black shale, more or less impregnated 
 with pyrite and arsenopyrite, traversing the slate and sandstone 
 formation of the district. 
 
 Different views have been expressed as to whether the car- 
 
 * Ibid., pp. 978, 979. 
 
 t "The Origin of the Gold-Bearing Quartz of the Bendigo Keefs," by T. A. 
 Rickard ; Discussion, Trans. , xxii. , 762-763. 
 
 " The Origin of Gold in Certain Victorian Quartz-Keefs," by William Nicholas, 
 Eng. and Min. Jour., vol. xxxvi., pp. 367, 368. 
 
 J "The Indicator Vein, Ballarat, Australia," Trans., xxx., 1010. 
 
 $ " The Genesis of Certain Auriferous Lodes," This volume, p. 162. 
 
332 THE CHEMISTRY OF ORE-DEPOSITION. 
 
 bon or the pyrite in the Indicator seam was the reducing agent 
 in the formation of the rich bunches of gold-ore. But pyrite 
 was deposited in the black shale by the reducing action of the 
 organic matter ; so that, in any event, it was the presence of 
 carbon compounds which, directly or indirectly, caused the 
 local accumulation of the gold. 
 
 Owing to the far more powerful action of the hydrocarbons, 
 reduction by pyrite contained in carbonaceous shales must al- 
 ways be subordinate, even where local conditions, such as the 
 presence of free oxygen and oxidized metallic salts, admit of 
 the pyrite being decomposed. Any ferrous sulphate produced, 
 at once re-forms pyrite, giving up its oxygen to the carbon. In 
 the depths of the strata, below water-level, wherever any form 
 of carbon is in excess, it absolutely protects the pyrite by con- 
 suming all the free oxygen.* 
 
 Many instances might be cited to illustrate the influence of 
 the organic matter contained in bituminous shales upon the 
 formation of ore-deposits. 
 
 A stratum of black shale in the Mono silver-mine, Dry 
 Canon, Utah, formed the hanging-wall of the rich ore-shoot, 
 from which large masses of horn-silver and high-grade sulphide- 
 ores were mined, carrying from 500 to 3000 oz. of silver per 
 ton. It is reported that a carload of ore from this mine yielded 
 over $55,000. 
 
 Emmons says : " Most famous, in view of the enormous 
 values taken from them, are the rich silver-bodies of the Mollie 
 Gibson and Smuggler mines of Aspen, Colo. ; but, in their case, 
 there is sufficient organic matter present to explain the reduc- 
 tion of the oxidized solutions to sulphides. They occur along 
 a vertical fault, formed since the original mineralization of the 
 district, and consist of great masses of polybasite and pink 
 barite, which, in places, have been further reduced to native- 
 silver. On one wall of the ore-body is the limestone, of which 
 it is a replacement, and on the other a black bituminous 
 
 shale."t 
 
 Bickard, discussing this subject, writes : " The idea of the 
 
 * This subject is discussed in more detail, under the sub-head, Protective Ac- 
 tion of Carbon and of Hydrocarbons, Ante, p. 311. 
 
 f "The Secondary Enrichment of Ore-Deposits," Trans., xxx., 195. See, also, 
 Genesis of Ore-Deposits, pp. 450, 451, 
 
THE CHEMISTRY OF ORE-DEPOSITION. 333 
 
 precipitation of the ore through the agency of carbonaceous 
 matter has been advanced in connection with ore-deposits in 
 other regions. I may quote, as instances, the black Silurian 
 slates of Bendigo, Victoria; the Devonian slates of Gympie, 
 Queensland ; the Jurassic slates of the c Mother Lode ' region 
 in Calaveras and Amador counties, California; the black shale 
 enclosing the gold-specimen ores of Farncomb Hill, Brecken- 
 ridge, Summit county, Colorado ; . . . and the celebrated Indi- 
 cator series of Ballarat, Victoria."* 
 
 In this connection, reference is made to the well-known oc- 
 currence of copper-ores at Mansfeld, Prussia, in beds of bitu- 
 minous slate and bituminous limestone. Certain of the lower 
 limestone beds are fetid. These copper-bearing formations 
 extend over a large district, f The ore contains so much bitu- 
 minous matter that only a little brushwood is required in 
 roasting the ores in piles. 
 
 Limestones Containing Organic Matter. 
 
 In mining-regions where the ores occur in limestone, it is 
 observed that in most instances the largest and most produc- 
 tive mines are in belts or zones of crystalline limestones which 
 are either exceptionally pure lime-carbonates or, more fre- 
 quently, dolomites with only a small amount of insoluble mat- 
 ter. Such formations, peculiarly favorable for ore, are rocks 
 easily crushed by movements of disturbance, readily permeated 
 by circulating-waters, and, from their -chemical composition, 
 rapidly attacked by solutions carrying carbonic acid. Where 
 situated at the surface, they are cavern-forming limestones. 
 Further, it is noted that both the magnesian limestones and the 
 pure lime-carbonates usually contain some form of organic 
 matter which, though small in amount, appears to have 
 strongly influenced the deposition of the minerals in the strata. 
 
 Otherwise stated, ore-deposits in limestone, irrespective of 
 the nature of the minerals constituting the ores, conform to 
 the general law of selective deposition, namely, that " Some 
 geological formations appear to be everywhere barren of ore ; others 
 occasionally carry small deposits, workable where the conditions are 
 
 * "The Enterprise Mine, Kico, Colorado," Trans., xxvi., 978. 
 t Von Cotta, Treatise on Ore-Deposits, Prime's Translation, p. 164. 
 
334 THE CHEMISTRY OF ORE-DEPOSITION. 
 
 exceptionally favorable ; but in each mining region certain strata are 
 ore-bearing in a degree exceeding all other formations combined."* 
 
 Among the causes that have induced the concentration and 
 deposition of the ores in special formations, prominence may 
 rightly be given to the deoxidizing action of the bitumen, bi- 
 tuminous coal, lignite, or other form of carbonaceous matter 
 disseminated in the rock. 
 
 In Southeastern Missouri, the lead-ore now mined is mostly 
 from deposits of disseminated galena in the dark-colored mag- 
 nesian limestone, rich in bituminous matter, of the Cambrian 
 formation at Bonne Terre and the Flat Eiver mines. Prac- 
 tically all the zinc-ore, and the greater proportion of the lead, 
 produced in the Joplin region, in the southwest part of the 
 State, is yielded by the Cherokee limestone, the upper division 
 of the Subcarboniferous.f The Cherokee is a soft, crystalline, 
 pure lime-carbonate, carrying bitumen. Its average composi- 
 tion, from a number of analyses, is as follows : 
 
 Lime, 55.00 
 
 Magnesia, . . . . 0.23 
 
 Alumina, .... ...... 0.10 
 
 Protoxide of Iron, ....... . 0.05 
 
 Protoxide of Manganese, 0.02 
 
 Bitumen and insoluble, . . . . . . . 1.00 
 
 Carbonic acid, 43.60 
 
 100.00 
 
 In the Upper Mississippi lead-region the productive forma- 
 tion has been the Galena limestone, the upper member of the 
 Trenton. It is a soft, crystalline dolomite ; bituminous matter 
 is present in relatively small amount, yet apparently more than 
 sufficient to effect the precipitation of the metals and preserve 
 the ores from oxidation below water-level. The deposits of 
 blende in the mines near Mineral Point and Shullsburg, Wis- 
 consin, occur in the underlying " Blue " limestone of the Tren- 
 ton, and the ores are concentrated about the intersection of the 
 mineral-bearing fissures with thin strata of brown shale, sat- 
 urated with petroleum, the " Oil-rock" of the miners.! 
 
 * " The Lead- and Zinc-Deposits of the Mississippi Valley," by W. P. Jenney, 
 'Tram., xxii., 187-188. 
 
 t " The Lead- and Zinc-Deposits of the Mississippi Valley," by W. P. Jenney, 
 Trans. t xxii., 188. 
 
 % William P. Blake, Discussion of "The Lead- and Zinc-Deposits of the Mis- 
 sissippi Valley," Trans., xxii., 631. 
 
THE CHEMISTRY OF ORE-DEPOSITION. 335 
 
 A summary review of the occurrence of zinc- and lead-ores 
 in the Mississippi valley shows that the formation of the de- 
 posits has been due to solutions of normal temperature ; and 
 that the chief agent in the primary deposition, and in the sec- 
 ondary enrichment of the ores, has been the bituminous sub- 
 stances contained in the strata in which the deposits are found. 
 The larger part of the minerals constituting the ores has been 
 deposited either by crystallization or by crystalline growth in 
 the lime-rock or dolomite of the walls, or has impregnated the 
 beds of specially favored geological formations. 
 
 In the limestone-area at Tintic district, Utah, the productive 
 mines occur in two distinct belts in the Carboniferous forma- 
 tion ; one, extending through the central part of the district, 
 of dark-colored, magnesian limestones ; the other, traversing 
 Godiva mountain, on the eastern border of the lime-area, formed 
 by beds of gray limestone with only a trace of magnesia. 
 
 On the central belt are situated the Gemini, Bullion-Beck, 
 Eureka Hill and Centennial Eureka mines; and farther south, 
 also in magnesian limestones, are located the Grand Central 
 and the Mammoth. A number of these mines have been 
 worked continuously since the early development of the district 
 in 1870-71. All have reached a depth of 1000 to 1750 ft.; 
 the Mammoth is now 2100 ft. deep. 
 
 It is not necessary to discuss the occurrence of the ore, be- 
 yond its relation to the magnesian limestones in which the de- 
 posits are found. Locally, these limestones vary somewhat in 
 character ; they are hard, crystalline, bluish-gray to bluish-black 
 dolomites, the color being due to organic matter. In certain 
 places the beds are filled with nodules and thin bands of hard, 
 black chert. The average composition, from 7 analyses, of the 
 limestones in the vicinity of the Bullion-Beck mine is (the 
 organic matter and loss being estimated by difference) : 
 
 Calcium carbonate, . . . . . . . 48.76 
 
 Magnesium carbonate, 35.43 
 
 Ferrous carbonate, ........ 2.61 
 
 Silica, 9.67 
 
 Alumina, 3.00 
 
 Organic matter and loss, . . . . . . .0.53 
 
 100.00 
 
 In a number of analyses the silica varied from 6.75 per cent. 
 
336 THE CHEMISTRY OF ORE-DEPOSITION. 
 
 to 13 per cent., and the total insoluble matter from 16 per cent, 
 to 18 per cent. 
 
 The amount of silica and insoluble matter is remarkable, 
 for there is every evidence in the mines that these dolomitic 
 limestones are rapidly decomposed and eroded by carbonated 
 waters. The explanation of this marked solubility of the 
 dolomite, notwithstanding the large proportion of impurities, 
 is probably to be sought in the structure of the rock. In 
 the upper levels of the Bullion-Beck and the Eureka Hill 
 mines, where the subterraneous erosion by surface-waters has 
 been greatest, large masses of residual dolomite sand, which 
 have resulted from the disintegration of the fissured and shat- 
 tered beds, occur, filling cavern-spaces or chambers in the lime- 
 stone. Beneath the heavy wash of boulders filling the gulch, 
 the limestone beds, for a depth of near 100 ft., without change 
 in the stratification, are decomposed and altered in situ into soft, 
 sandy dolomite, stained with iron and manganese oxides. 
 Analyses showed that this decomposed rock had substantially 
 the same composition as the loose deposits of sand; being 
 dolomite, with the residual silica, clay, oxidized iron and man- 
 ganese contained in the original formation. Surface-waters, 
 carrying carbonic acid, appear first to attack the calcareous 
 cement between the crystalline grains of dolomite, at the same 
 time oxidizing the carbonates of manganese and iron present, 
 and in this way rapidly disintegrate the rock. 
 
 Many caverns, mostly of small size and usually more recent 
 in formation than the ore-bodies, occur in the limestone. It is 
 noted that they are generally located along the course of the 
 vertical faulting-fissures, which have been the channels fol- 
 lowed by the solutions depositing the ore, the shattering and 
 brecciation of the beds, due to the faulting movement, in- 
 creasing the action of surface-waters in the erosion of the 
 rock. 
 
 In a few instances the ore actually fills pre-existing caverns. 
 The largest of these caverns in the Bullion-Beck mine, formed 
 before the minerals were introduced in the primary deposition, 
 was filled with argentiferous galena, in great part deposited by 
 crystallization. The rock-floor of the cavern was covered by a 
 horizontal stratum of chert nodules, overlain by sand-beds, 10 
 to 15 ft. in thickness, with disseminated pyrite and galena, the 
 
THE CHEMISTRY OF ORE-DEPOSITION. 337 
 
 massive crystalline lead-ore resting on the sedimentary beds. 
 The flat-beds covering the clay floor were unquestionably formed 
 from the residual sand and chert contained in the rock, dis- 
 solved away by the circulating-waters in making the cavern. 
 Such f occurrences of ore deposited by crystallization are rare 
 in these mines ; practically all the quartz, and nearly all the 
 lead- and copper-ores, are formed by replacement. 
 
 The limestones are much purer in the Grand Central and 
 Mammoth mines. An average of 6 analyses gave (ferrous car- 
 bonate, alumina and organic matter not determined) : 
 
 Calcium carbonate, 55.38 
 
 Magnesium carbonate, . . . . . . . .42.84 
 
 Silica, 0.65 
 
 Undetermined and loss, .1.13 
 
 100.00 
 
 This is a bluish-gray, brown, or bluish-black, crystalline dolo- 
 mite, free from chert. The weathered outcrop of certain beds 
 shows the rock to be made up of the broken and water-worn 
 joints of minute crinoid stems, one- to three-hundredths of an 
 inch in diameter, with fragments of shells and an occasional 
 small coral. The stratification is generally preserved ; in some 
 places the rock is cross-sheeted by movements of disturbance, 
 and locally the beds have been brecciated and recemented by 
 their own attrition material into a massive rock, with but traces 
 of bedded structure. 
 
 This limestone, even where not mineralized, is easily distin- 
 guished by the appearance and fracture of the rock, being 
 dark-colored and crystalline, with spots and small vugs of cal- 
 cite and stains of iron and manganese oxides on the joints. It 
 is often sonorous, giving a clear metallic ring when struck with 
 a pick. It crumbles under a blow into small, ragged, rough 
 fragments, having the fracture of loaf sugar. 
 
 The beds are thin, brittle, easily shattered and crushed by fault- 
 ing-movements. On account of the absence of clay in the rock, 
 the breccias and attrition-material produced are permeable to 
 circulating-waters; even small fissures and fractures in the lime 
 keep open. Caves of considerable size are not infrequently 
 encountered in the formation, but appear to have been formed 
 subsequent to the ore. It is noteworthy that deposits of loose 
 
 22 
 
338 THE CHEMISTRY OF ORE-DEPOSITION. 
 
 dolomite-sands are seldom formed in this pure dolomite; neither 
 is the rock usually altered in place to iron-stained rotten dolo- 
 mite. The action of surface-waters is to dissolve the rock com- 
 pletely, and not to disintegrate the rock by attacking the calca- 
 reous cement between the grains. 
 
 The ore-bodies afford evidence that this limestone, especially 
 where fissured and fractured, is easily replaced by silica and by 
 the other gangue-minerals, ankerite, siderite, barite and calcite. 
 Not only has the limestone been metasomatically replaced by 
 primary sulphide-ores, carrying lead, copper, iron, arsenic, 
 silver and gold, but the complex products of their oxidation 
 and redeposition have, also, more or less perfectly replaced the 
 rock. It is observed that the darker and coarsely crystalline 
 lime-beds are highly favorable for ore, beds made up of com- 
 minuted fossil-remains, crinoid stems, broken corals and shells. 
 
 Eliminating the highly impure sediments, which seldom 
 carry workable deposits, the structure of the rock appears to 
 be far more important than the chemical composition in de- 
 termining whether certain strata are ore-bearing or barren. 
 Analyses of the magnesian limestones over a broad belt show 
 that they vary but little in composition. The beds which have 
 been found to be unfavorable for ore are usually dense, finely 
 crystalline and impermeable ; the rock generally breaking 
 under a blow of a hammer with a " dead " sound, and a smooth, 
 splintery fracture, like the fracture of quartzite. Organic mat- 
 ter is not at all prominent in this limestone, although it gives 
 the color to the rock. 
 
 The principal ore-bearing formation in Godiva mountain is a 
 stratum, 200 to 400 ft. in thickness, of massive, gray, very 
 coarsely crystalline limestone. It is a pure lime-carbonate, 
 carrying some undetermined form of bituminous material, 
 which gives to the rock, when broken, a sulphurous, fetid 
 odor. On dissolving the limestone in acid, the bitumen sepa- 
 rates in clots. An analysis of this limestone gave (the organic 
 matter and loss being estimated by difference) : 
 
 Calcium carbonate, . . . . . ..... 98.75 
 
 Alumina and iron-oxides, . . . . . . .0.40 
 
 Silica, . -. " 0.20 
 
 Magnesia, ........ trace. 
 
 Organic matter and loss, 0. 65 
 
 100.00 
 
THE CHEMISTRY OF ORE-DEPOSITION. 339 
 
 The weathered outcrop of the gray limestone is, in many 
 places, bluish-black from the concentration of the bitumen in 
 the surface of the rock. The beds are formed of water-worn 
 grains and broken fragments of small shells. A coral (zaphren- 
 tis), 1 to 2J in. long, is its characteristic fossil. It exceeds in 
 chemical solubility all other ore-bearing limestones in this sec- 
 tion of the district. The perfect manner in which great masses 
 of the rock are replaced by the ore is evidence of this. 
 
 The gray-limestone formation extends northerly and south- 
 erly through the whole length of Godiva mountain, bounded 
 on either side by limestones more or less magnesian in charac- 
 ter. Many of these magnesian limestones, interbedded in the 
 series, are highly impure sediments, with 25 to 35 per cent, of 
 silica, 5 to 10 per cent, of iron and alumina, 6 to 12 per cent, 
 of magnesia, and 20 to 30 per cent, of lime. These formations 
 have been found unfavorable for ore. 
 
 On this gray-lime belt are located the Uncle Sam, May-Day 
 and Yankee Consolidated mines, properties developed since 
 1897. The deepest workings have attained a depth of 800 ft. 
 The Uncle Sam mine has been noted for its large output of 
 high-grade lead-ore, carrying silver, in a gangue mainly, com- 
 posed of lime-carbonate. 
 
 Quartz-ores prevail in the other mines of the belt, with lead, 
 silver, and usually a small amount of gold. 
 
 The ores have been introduced in the strata through belts of 
 nearly vertical faulting-fissures. Along the course of these 
 fissures the ore-bodies have formed in the limestone. In some 
 places the ore-deposits take on the form of fissure-veins, the 
 ore being confined within the walls of the fissure and deposited 
 in a more or less tabular sheet, pitching like the ore-shoots in 
 quartz-veins in the metamorphic rocks. More commonly the 
 faulting movements forming the fissures have so fractured the 
 beds that the mineral deposits are not limited by the fissure- 
 walls and extend irregularly into the limestone. The largest 
 ore-bodies have formed in spaces of multiple fissuring, where 
 the belt of master-fissures cuts through lime-beds, broken and 
 rifted in different directions by the complex intersection of 
 sheeted belts, due to cross-fissures and to diagonal fissures. 
 
 The ores of primary formation are mostly deposited by re- 
 placement of the limestone. Quartz occurs in many varied 
 
340 THE CHEMISTRY OF ORE-DEPOSITION. 
 
 forms, from massive limestone, more or less completely altered 
 to quartz, with little change in structure, to the white, crystal- 
 line mineral, grading insensibly into soft, crumbling, pulveru- 
 lent quartz, in appearance resembling granulated sugar. 
 
 In certain places in these mines the limestone appears to 
 have been sheeted and broken into large, thin and sharp frag- 
 ments before it was replaced by the ore ; the sharp edges of 
 the pieces of limestone were not rounded in the conversion ; 
 there has not been any solution of the rock without the per- 
 fect pseudomorphic replacement of its structure by the min- 
 erals. 
 
 This has occurred not only in the replacement of the lime- 
 stone by quartz, but also in its replacement by massive argentif- 
 erous galena, as fine-grained in its crystalline structure as 
 steel. The galena reproduces the shape of the original lime- 
 stone fragments, so that they are fossilized by lead-sulphide, as 
 wood is petrified by the infiltration of silica, only less per- 
 fectly. 
 
 The largest body of galena of this character occurred in the 
 Uncle Sam mine. The ore-body, 50 ft. long, 13 to 20 ft. wide, 
 and 50 to 60 ft. high, was formed entirely of pure lead-sulphide, 
 with no other minerals except calcite and the lime wall-rock. 
 The ore averaged 75 per cent, of lead and 50 oz. of silver per 
 ton. In this ore-body the massive limestone, prior to its min- 
 eralization, had been fractured vertically in large, sheeted frag- 
 ments, some of which would measure 10 to 15 ft. long and 10 
 to 25 ft. high, but only 6 to 15 in. thick. Even the largest 
 masses of rock were altered throughout to steel-galena. Nu- 
 merous vertical open seams and fractures, from the thickness 
 of a knife-blade to 2 in. in width, separated these irregular 
 sheets of ore one from another. A vertical fracture, 12 to 18 
 in. wide, passed through the ore-body ; it was more recent in 
 formation than the primary ore and was filled w r ith coarsely 
 crystalline galena, with cleavage faces 2 to 3 inches across, de- 
 posited by crystallization. 
 
 In general, in the mines on Godiva mountain, fine-grained 
 galena, replacing the limestone, is of primary origin, while 
 coarsely crystalline galena is usually secondary ; although some 
 of the lead-ore deposited by crystallization (or crustification) 
 appears to be primary. 
 
THE CHEMISTRY OF ORE-DEPOSITION. 341 
 
 Review of the Phenomena of the Deposition of Ores in Limestone* 
 A study should be made of the structure of the ore-bearing 
 limestones, with the special object of determining the causes 
 that have made certain strata favorable for ore, while other 
 beds in the same geological formation, having an almost iden- 
 tical chemical composition, and so situated that they are tra- 
 versed by the same fissures, through which the mineral-depos- 
 iting waters have been introduced, have remained barren. In 
 many instances the productive and the barren strata are inter- 
 bedded and so situated that the ore-bearing fissures cut through 
 all the beds alike, without any change in this selective deposi- 
 tion of the ores. 
 
 Analyses of these ore-producing limestones are needed to 
 determine the amount and character of the carbonaceous sub- 
 stances present, and also the minute traces of other elements, 
 some of which may be found to have had an influence on the 
 formation of the deposits. That such an influence may have 
 been exerted seems probable, when we consider the enormous 
 masses of the highly soluble limestones that have been dis- 
 solved or replaced in the creation of the ore-bodies. It has 
 been shown, for example, that the small percentage of bitu- 
 men or other hydrocarbon contained in the rock, and set free 
 by its dissolution, has strongly aided in the deposition of the 
 ore. , 
 
 Prof. Church, discussing the deposition of ores in limestone, 
 says: " The operation of solutions whose composition we do 
 not know can be judged only by their effects. When metaso- 
 matic replacement takes place in limestone, it is generally as- 
 sumed that lime-carbonate goes into solution, while its place is 
 taken by the ore-substances, that is to say, that the action is 
 molecular substitution, and not atomic; but it is conceivable 
 that the change should begin by an interchange of acidic ele- 
 ments that Si0 2 should drive out CO 2 . Subsequent changes 
 might remove the lime-silicate by another process of substitu- 
 tion, since it is more soluble than silica;* but the point is that 
 C0 2 would be liberated, and, though the original ore-solution 
 were free from C0 2 , it would immediately become charged 
 
 * In the Tintic mines, lime-silicate does not appear to have been formed ; the 
 silica directly replacing the lime-carbonate, or the carbonate of lime and magne- 
 sia, as the case may be. 
 
342 THE CHEMISTRY OF ORE-DEPOSITION. 
 
 with that agent and exert the well-known dissolving power of 
 carbonic acid solutions. In this way a solution which would 
 have but feeble power in other rocks may in limestone set up 
 a chain of reactions that would intensify its effects. . . . Lime- 
 stone contains the elements for self-destruction, since the 
 breaking-up of one lime-carbonate molecule may cause the 
 solution of another; and as this cannot be said of any other 
 rock, we reach a possible explanation of the comparative fre- 
 quency of ore-bodies in limestone. The dolomites would, of 
 course, present similar reactions." Prof. Church continues, 
 respecting " The selection of a favored stratum for ore-deposi- 
 tion. In some situations the* solutions, before reaching the 
 stratum of actual ore-deposition, must have passed several 
 strata suitable for their action, if they had possessed from the 
 beginning the power of solution which they showed ultimately. 
 . . . Ore-solutions exhibit a selective power which is extraordi- 
 nary in a water fully supplied with dissolving qualities, but 
 quite explicable in a solution which lacks this power."* 
 
 Many contributory causes have in all probability co-operated 
 in the deposition of the ore, such as decrease of pressure and 
 reduction in the temperature of the solutions, the mingling of 
 mineral-bearing waters of different chemical composition enter- 
 ing the limestone formation through distinct fissured belts, etc.; 
 but the important factor appears to have been the great solu- 
 bility of these limestones and dolomites in the waters which 
 brought in the minerals, joined with the chemical activity of 
 the contained hydrocarbons released in the dissolution of the 
 rock. 
 
 In the solution of the limestone, the incidental liberation of 
 large volumes of carbonic acid, ever dissolving more and more 
 of the rock, set free a constantly renewed supply of car- 
 bonaceous matter, whose function was to remove all free oxy- 
 gen and reduce the sulphates in the waters to sulphides. At 
 the same time, the calcium- and magnesium-carbonates, when 
 dissolved, neutralized the acids and destroyed the chemical 
 equilibrium, so that the mineral-saturated waters could no 
 longer hold the metals in solution, after the addition of the 
 elements derived from the limestone. The combined action of 
 
 * Genesis of Ore-Deposits, pp. 196, 197. Trans., vol. xxiii., 595, 596. 
 
THE CHEMISTRY OF ORE-DEPOSITION. 343 
 
 the carbon, hydrogen, lime and magnesia contained in the 
 rock was to deoxidize the solutions and bring them to the 
 " critical-point," when deposition of the ores rapidly took 
 place. - 
 
 In conclusion : The ores of primary formation in the Tintic 
 mines have been, in most of the occurrences, deposited from 
 highly heated solutions by the metasomatic replacement of 
 the limestone; only in relatively subordinate amount have 
 the metallic sulphides been formed by crystalline growth in 
 the rock, or by crystallization in the interspaces of the ore- 
 bodies. 
 
 In the instance cited, in the Uncle Sam mine,* in the large 
 body of steel-galena, without quartz, replacing the fractured 
 lime strata, the deposition seems to have been from solutions 
 either free from silica, or more probably of so low a tempera- 
 ture that the chemical reaction in the substitution of quartz for 
 the lime-carbonate could not take place. 
 
 In Tintic, the limestones, when unaltered, retain the included 
 carbonaceous matter deposited with the sediments. In the ore- 
 bodies, all forms of the hydrocarbons have been destroyed, 
 either in the primary formation of the minerals or in the sub- 
 sequent oxidation; the deepest mines in the district (1700 
 and 2100 ft., vertical depth) not having reached ground-water 
 level. 
 
 Whatever may have been the role of the volatile hydrocar- 
 bons in the original creation of the deposits, no evidence has 
 been found of their ever having been present. Tintic district 
 has been a center of intense volcanic activity, and it seems 
 almost inevitable that, with the presence of notable quantities 
 of bituminous matter in the rocks, volatile hydrocarbons would 
 have been formed. 
 
 Many examples might be given of limestones, especially of 
 magnesian limestones, which carry more or less organic matter 
 and constitute the favored geological formations in the selective 
 deposition of the ore. The zinc- and lead-deposits of Missouri 
 and the lead- and copper-ores of Tintic District, Utah, carrying 
 silver and gold, were chosen, owing to the author's more de- 
 tailed acquaintance with the ore-deposits of those regions. 
 
 * See ante, p. 340. 
 
344 THE CHEMISTRY OF ORE-DEPOSITION. 
 
 Petroleum. 
 
 The occurrence of petroleum in the Redington quicksilver- 
 mine, New Idria, California, is reported by Luther Wagoner.* 
 He says : " Mineral-oil occurs in considerable quantity, a barrel 
 of forty gallons being collected in one drift. It was used for 
 lubrication of the machinery." 
 
 Prof. Egleston, writing of the quicksilver-mines in northern 
 California, says : " At the Rattlesnake mine, near Pine Flat, 
 where large quantities of metallic mercury are found, the rock 
 contains so much petroleum that it has been necessary to make 
 special arrangements to burn the carbides of hydrogen, since 
 the distillation of the petroleum causes an extra quantity of 
 poor soot to be formed in the condensation-chambers."f 
 
 At the zinc- and lead-mines near Shullsburg, Wisconsin, thin 
 partings or beds of brown shale, highly charged with petro- 
 leum, are found in the Trenton limestone. Prof. Blake, dis- 
 cussing the peculiar occurrence of this shale, known as the " oil- 
 rock," says : " We find that this petroleum-shale, this horizon 
 of hydrocarbons, is to-day the chief lower horizon of deposi- 
 tion of the lead- and zinc-ores. Certainly, if this shale did not 
 influence or determine the original primary accumulation of 
 the ores, it appears to have exerted a very important influence 
 upon the secondary or later deposition, from solutions perco- 
 lating downwards." J 
 
 In the mines at Silver Reef, Utah, an oily substance, sup- 
 posed to be petroleum, is reported to have occurred in the re- 
 fractory ores at water-level. 
 
 Rudolf Keck notes the association of organic matter with 
 ore-deposits. He says : " Organic matter occurs in the state of 
 asphaltum in the cinnabar mines in the Bavarian Palatinate ; 
 in that of petroleum, in the mines of California, Nevada and 
 Hungary ; in that of anthracite and graphite, in mines in Tran- 
 sylvania, Portugal, Derbyshire, Calcutta, Saxony, Baden, etc."|| 
 
 * "The Geology of the Quicksilver- Mines of California," by Luther Wagoner, 
 Eng. and Min. Jour. , vol. xxxiv. , p. 334. 
 
 f " Notes on the Treatment of Mercury in North California," by T. Egleston, 
 Trans., in., 273. 
 
 J William P. Blake, Discussion of the "Lead- and Zinc-Deposits of the Missis- 
 sippi Valley," Trans., xxii., 631. % See ante, pp. 322-327. 
 
 || " The Genesis of Ore-Deposits," by Kudolf Keck, Eng. and Min. Jour., vol. 
 xxxv., p. 3. 
 
THE CHEMISTRY OF ORE-DEPOSITION. . 345 
 
 Bitumen. 
 
 The occurrence of bitumen, and its influence in the forma- 
 tion of the zinc- and lead-deposits in the Cherokee limestone, 
 in Southwest Missouri, has already been discussed.* 
 
 Becker notes the existence of bitumen in the Manhattan, 
 Knoxville, Phoenix, Oathill, Manzanita, Great Western and 
 Great Eastern quicksilver-mines, and also at Sulphur Bank, 
 California. At the Phoenix mine, a peculiar non-oxygenated 
 hydrocarbon (napalite), with 90 per cent, of carbon and 10 per 
 cent, of hydrogen, occurs quite abundantly. f 
 
 Luther Wagoner, in an article on the geology of the quick- 
 silver-mines of California, says : " Oil (petroleum), more or less 
 oxidized, is observed in all mines of quicksilver on this coast, 
 and in general is found as bitumen or a thick tar."J 
 
 Prof. Christy thus describes the occurrence of bitumen at 
 New Almaden, Cal. : " The ore at New Almaden is cinnabar. 
 Native quicksilver occurs also; but, as a rule, in small quanti- 
 ties only. Pyrite occasionally accompanies the ore. Bitumen 
 is quite common, sometimes as a fragile, black, lustrous solid, 
 resembling soft bituminous coal, but melting easily, like tar ; at 
 other times it occurs in the vugs of the gangue, in a liquid 
 state, like coal-tar. I have found lumps of apparently pure 
 cinnabar from the New Almaden to give a voluminous residue 
 of pulverulent charcoal, when subjected to sublimation out of 
 contact with the air. This would seem to show that the bi- 
 tuminous substance is intimately associated with the cinna- 
 bar.'^ 
 
 Marsh-Gas (CH 4 ). 
 
 In the quicksilver-mines of California marsh-gas was discov- 
 ered by Becker. In the Phoenix mine, on the 150- and 300-ft. 
 levels, inflammable gas, mainly composed of marsh-gas, issues 
 from cracks in the rock.|| At Sulphur Bank, California, 79 
 
 * See ante, pp. 305, 306. 
 
 t " Geology of the Quicksilver-Deposits of the Pacific Slope," by Geo. F, 
 Becker, U. S. Geol. Surv., Monograph xiii., pp. 371, 372. 
 
 J "The Geology of the Quicksilver-Mines of California," by Luther Wagoner, 
 Eng. and Min. Jour., vol. xxxiv., p. 334. 
 
 $ " Quicksilver- Reduction at New Almaden," by Samuel B. Christy, Trans., 
 xiii., 547-548. 
 
 || ''Geology of the Quicksilver- Deposits of the Pacific Slope," by George F. 
 Becker, p. 373. 
 
346 THE CHEMISTRY OF ORE-DEPOSITION. 
 
 parts of marsh-gas were found in 1000 parts of the gases es- 
 caping with the ore-depositing waters.* 
 
 Flows of gas under heavy pressure were struck in the deeper 
 levels of the Silver-Islet mine, Lake Superior. Subsequently, 
 in extending the levels, vugs and cavities in the vein were 
 found, lined with crystals of galena and calcite, in which the 
 gas had probably been stored. In sinking the shaft, gas was 
 also encountered in the slate, and it appears to have per- 
 vaded the country-rock below the 8th level (440 ft., vertical 
 depth). The gas was associated with small flows of strong, 
 acrid mineral-water, carrying much calcium chloride. It 
 burned with a purple, blue, or yellowish flame, and was sup- 
 posed to be light carburetted hydrogen, but it was never 
 analyzed, f 
 
 Small quantities of hydrocarbon-gas are stated by Mr. B. 
 Tibbey to have been struck in following the vein on the 300-ft. 
 level of the Illinois mine, Walkerville, Butte City, Montana. 
 The gas burned with a bright-yellow flame, like ordinary il- 
 luminating gas. This occurrence is remarkable, as the vein 
 occurs in granite. 
 
 Review of the Action of Volatile Hydrocarbons. In the Joplin, 
 Mo., mines, the greater part of the bitumen set free by the ex- 
 tensive subterraneous erosion of the lime strata is still pre- 
 served in the ore-bodies below water-level, owing to the primary 
 deposition having been effected by mineral-solutions of normal 
 temperature. The same is also true of the petroleum occurring 
 with the zinc-ore in the oil-rock in the Trenton limestone in 
 Wisconsin, to which reference has been made. But in many 
 ore-deposits in other mining-regions the heat accompanying 
 the deposition has been so great, and the chemical activities so 
 intense, that every trace of volatile hydrocarbons has been de- 
 stroyed. 
 
 Petroleum contained in the strata may be decomposed by 
 (1) destructive distillation, due to the earth-temperatures or to 
 the heat of the ascending mineral-solutions; (2) by oxidation, 
 the carbon and hydrogen forming carbon-dioxide and water; 
 and (3) by the action of sulphur, which dehydrogenizes the oil. 
 
 * Ibid., p. 258. 
 
 f " The Silver-Islet Mine and Its Present Development," by Francis A. Lowe, 
 Eng. and Min. Jour., vol. xxxiv., pp. 320-323. See also ante, p. 313. 
 
THE CHEMISTRY OF ORE-DEPOSITION. 347 
 
 Petroleum and similar hydrocarbons, when heated and sub- 
 jected to the action of sulphur at temperatures (in the case of 
 the heavier oils) far below that at which distillation occurs, are 
 rapidly decomposed, with formation of sulphuretted hydrogen 
 and of oils with a greater proportion of carbon than the original 
 oil ; or, if the sulphur be in excess, carbon is in some instances 
 deposited. 
 
 The role of the volatile hydrocarbons in the primary forma- 
 tion of mineral-deposits, especially where the deposition is due 
 to igneous disturbances, has not received the attention it de- 
 serves. Investigation is needed of the action that marsh-gas 
 and other hydrocarbon-gases exert in the deposition of ores; 
 particularly in the formation of deposits of cinnabar, which are 
 frequently associated with bituminous shale, bitumen and vola- 
 tile hydrocarbons. 
 
 Marsh-gas has a theoretic reducing power one-half that of 
 hydrogen and fifty per cent, greater than that of pure carbon. 
 In the formation of ore-deposits, directly induced by igneous 
 action, temperatures must inevitably occur in the depths of the 
 strata, such that gaseous hydrocarbons would act with great 
 energy in the deoxidation and precipitation of the metals. 
 Under like conditions, petroleum, and the volatile carbon com- 
 pounds with high boiling-points, would exert a reducing power 
 but little inferior, and, from the high specific gravity of their 
 vapor, would displace steam and all other gases of less relative 
 weight. 
 
 VIII. THE RELATIVE REDUCING POWER OF MINERALS. 
 
 Calculation of the Theoretic Reducing Powers of Various Organic and 
 Inorganic Mineral Substances usually Occurring in Association 
 with Ore-Deposits, Based upon the Weight of Oxygen Consumed. 
 
 The quantitative value, or amount of work accomplished in 
 the formation of ore-deposits by the various reducing sub- 
 stances, is measured by the weight of oxygen with which they 
 unite. This work of deoxidation may be termed the "duty" 
 of the reducing agent. 
 
 In calculating this duty for the more common organic and 
 inorganic minerals which occur in ore-bodies or in strata 
 in which ores were formed, or into which they were intro- 
 
348 THE CHEMISTRY OF ORE-DEPOSITION. 
 
 duced by the waters, either in the original deposition or in the 
 secondary enrichment of the deposits, it has been found more 
 convenient to make the values relative, assuming hydrogen, the 
 most powerful deoxidizing agent, to have a value of 100. 
 Let R represent the relative reducing power, or duty, of any 
 
 mineral substance. 
 Q be the weight of oxygen consumed by one part of the 
 
 mineral. 
 S be the weight of the mineral required to unite with one 
 
 part of oxygen. 
 P be the weight of hydrogen which combines with 100 
 
 parts of oxygen. 
 
 The value of Q may be determined in each case from the 
 chemical reactions which take place. 
 Thus, for hydrogen, 
 
 2H + = H 2 0, 
 2 + 16=18, 
 
 whence, by proportion, the weight of oxygen consumed by I 
 part of hydrogen is determined. 
 
 2 : 16 :: 1 : Q= 8.00. 
 
 R has been assumed for hydrogen as 100. 
 In the case of carbon, the reaction is 
 
 12 -t- 32 = 44, 
 
 whence, 12 : 32 : : 1 : Q = 2.6666. 
 
 The relative power, or duty, of carbon compared with hydro- 
 gen is 
 
 8 : 2.6666 : : 100 : .=33.33. 
 
 For oxygen the value of P is determined from the weight of 
 hydrogen that unites with one atom of oxygen : 
 
 0-f 2H = H 2 0, 
 16 : 2 :: 100 : P= 12.5. 
 
 P is a constant and always a minus quantity; the oxygen 
 combined with a mineral substance diminishing its reducing, 
 power. 
 
THE CHEMISTRY OF ORE-DEPOSITION. 349 
 
 , Q and S are determinable by the following formulas : 
 
 _, = -, -. 
 
 8 100' ' 
 
 whence, by substitution, 
 
 - "l 1 _12.5 1 r>_12.5 
 
 = ~~ -- r= 
 
 100 
 
 From the above it is seen that in assuming, for convenience, 
 the value of R for hydrogen as 100, it was equivalent to multi- 
 plying the corresponding value of Q (= 8) by 12.5. Conse- 
 quently the several values of R, being calculated for equal 
 weights of the mineral substances, are in each instance the 
 weight of oxygen which is consumed by 12.5 parts of the 
 reducing agent. Thus, 12.5 parts of carbon consume 33.33 
 parts of oxygen, etc. 
 
 The " duty " of any compound substance is the sum of the 
 reducing powers of the elements of which it is composed. 
 Thus, for the hydrocarbons : 
 
 Let a = the percentage of carbon, 
 b = " " " hydrogen, 
 
 c = " " " oxygen. 
 
 Then R = (33.33 a + 100 b) 12.5 c. 
 
 By a formula of this kind R can be calculated directly from 
 the percentage-composition of any substance. Even in the com- 
 plex metallic sulphides, arsenides, etc., R may be calculated 
 from the composition by substituting in the formula the value 
 of R for sulphur, arsenic, etc. 
 
 For carbon-monoxide the value of R may be calculated from 
 the percentage-composition: carbon, 42.86; oxygen, 57.14. 
 
 0.4286 X 33.33 = 14.28 
 Less 0.5714 x 12.5 = 7.14 
 
 7.14 = JR. 
 Or from the equations and proportions : 
 
 CO + O = CO,, 
 
 28+16 = 44. 
 
 28 : 16 :: 1 : =0.5714, 
 
 8 : 0.5714 ::100 : ^ = 7.14. 
 
350 THE CHEMISTRY OF ORE-DEPOSITION. 
 
 Marsh- Gas, CH 4 . Marsh-gas (methane) belongs to the paraffin 
 series of volatile hydrocarbons ; its composition is 
 
 Carbon, . . .. . . . . . '. . . 75.00 
 
 Hydrogen, . . . . . . . . . . 25.00 
 
 100.00 
 
 By oxidation, marsh-gas forms carbonic acid and water, thus: 
 
 16 : 64 :: 1 : Q= 4.00. 
 8 : 4:: 100 : R= 50.00. 
 Or, calculated from the composition, 
 
 33.33 X 0.75 = 25.00. 
 100.00 X 0.25 = 25.00. 
 
 Petroleum. American petroleum is in great part a mixture 
 of hydrocarbon oils of the paraffin series, represented by the 
 formula C n H 2n4 . 2 . The heavier oils average, approximately, 
 carbon, 85 per cent.; hydrogen, 15 per cent; corresponding 
 very nearly to the formula, C ]6 H 34 . Assuming that the carbon 
 is completely oxidized to carbonic acid, and the excess of hydro- 
 gen to water : 
 
 from which R = 43.36. 
 
 Ititumen. With bitumen is included mineral-tar, maltha, and 
 the solid oxygenated hydrocarbons, such as grahamite. Their 
 composition, while variable, usually falls within the limits of the 
 analyses No. 1 and No. 2 : 
 
 No. 1. No. 2. No. 3. 
 
 Carbon, . , ..- . . . 80.00 . 89.00 81.00 
 
 Hydrogen,. .... 14.00 11.00 10.00 
 
 Oxygen, . . . . ., 6.00 0.00 9.00 
 
 100.00 100.00 100.00 
 
 The value of R for analysis No. 1 = 39.92, and for analysis 
 No. 2 40.67. Analysis No. 3, of grahamite (gilsonite), with 
 but 10 per cent, of hydrogen, gives a value for R of 35.88. In 
 the above analyses it is probable that some nitrogen and sul- 
 phur are included with the oxygen, so that the deduction made 
 for oxygen is slightly too great. 
 
THE CHEMISTRY OF ORE-DEPOSITION. 351 
 
 Bituminous Coal. The average composition of bituminous 
 coal may be stated as falling within the limits of the analyses 
 1 and 2: 
 
 No. 1. No. 2. 
 
 Carbon, 81.00 88.00 
 
 Hydrogen, 4.00 7.00 
 
 Oxygen, 15.00 5.00 
 
 100.00 100.00 
 
 The duty calculated from the composition in the above anal- 
 yses is. for coal No. 1, jR = 29.13; and for coal No. 2, R = 
 35.71. 
 
 Lignite. The composition of lignite is extremely variable and 
 is much affected by the amount of decomposition it has under- 
 gone. Assuming that the analyses given below represent the 
 ordinary limits of composition, the value of H for lignite "No. 1 
 is 19.50, and for No. 2, 28.83. 
 
 No. 1. No. 2. 
 
 Carbon, . . . * . . .60.00 73.00 
 
 Hydrogen, ... . . 4.00 7.00 
 
 Oxygen, * . . . . . f . 36.00 20.00 
 
 100.00 100.00 
 
 Native Humus Acid. Dana gives the composition of humus 
 acid from Bohemian brown-coal as C^H^O^, which corresponds- 
 
 to: 
 
 Carbon,. . . . ,. . . . . . . 55.31 
 
 Hydrogen, . . - . . . .. . . . 4.61 
 
 Oxygen, . . ........ 40.08 
 
 loo.oa 
 
 998 : 1440 : : 1 : Q = 1.4428. 
 8 : 1.4428 : : 100 : It = 18.04. 
 
 Or, calculated from the composition, 
 
 0.5531 X 33.33 = 18.44 
 
 0.0461x100.00= 4.61 
 
 23J05 
 
 Less 0.4008 X 12.5 = 5.01 
 
 Sulphur. Sulphur in ore-deposits may oxidize under cer- 
 tain conditions to sulphurous acid, but usually sulphuric acid 
 is formed. 
 
352 THE CHEMISTRY OF ORE-DEPOSITION. 
 
 S -f 2 = S0 2 ; whence, R = 12.50 
 
 ,R = 18.75 
 
 S -f- 3 = S0 3 ; whence J Q = 1.50 
 
 Is = 0.667. 
 
 Combined sulphur may, for convenience in calculating the 
 duty of sulphides, be regarded as oxidizing to S0 4 ; as if all the 
 oxygen combined with the sulphur and none with the base, 
 giving the values E = 25.00 ; Q = 2.00 ; = 0.50. 
 
 Sulphuretted Hydrogen. The complete oxidation of sulphu- 
 retted hydrogen forms sulphuric acid, H 2 S -(- O 4 = H 2 S0 4 , from 
 which H == 23.53. When oxygen is deficient, water is formed, 
 with separation of sulphur. The reaction then is : 
 
 H 2 S '+0 = 84- H 2 ; whence, R = 5.88. 
 
 Pyrite and Marcasite. Three distinct reactions may occur in 
 the oxidation of pyrite and marcasite (FeS 2 ) : 
 
 (1) With liberation of sulphur, and formation of ferrous-sul- 
 phate 
 
 FeS 2 -f 4 = S -f FeS0 4 ; whence, R = 6.67 ; Q = 0.533 ; 
 
 S = 1.876. 
 
 (2) With formation of ferrous sulphate and free sulphuric 
 acid, one atom of sulphur may be -regarded as oxidizing to 
 S0 3 , the other to S0 4 
 
 FeS 2 -|- 7 -f H 2 = FeS0 4 -f H 2 S0 4 ; whence, JR = 11.67; 
 = 0.933; =1.072. 
 
 (3) When the oxidation of pyrite takes place with excess of 
 air, ferrous sulphate is first formed, and by a complicated series 
 of reactions, with further absorption of oxygen, the final result 
 is the formation of limonite and sulphuric acid. The equation 
 may be written : 
 
 4FeS 2 + 30 -f 11H 2 == 2Fe 2 3 ,3H 2 + 8H 2 S0 4 , 
 
 Giving R = 12.50 ; Q = 1.00 ; S = 1.00. 
 
 In the substitution of blende and galena for pyrite in secondary 
 deposition, the reactions corresponding to equation (1) may be 
 expressed : 
 
THE CHEMISTRY OF ORE-DEPOSITION. 353 
 
 FeS 2 + ZnSO 4 = ZnS -f- FeS0 4 -f- S. 
 FeS 2 -f PbS0 4 = PbS + FeS0 4 + S. 
 
 Pyrite also deoxidizes sulphuric acid, with the formation of 
 sulphuretted hydrogen and sulphur : 
 
 FeS 2 -f H 2 S0 4 = H 2 S + S + FeS0 4 . 
 
 The reduction of zinc- and lead-sulphate and lead-carbonate 
 by pyrite is shown by the following equations, corresponding to 
 equation (2) : 
 
 FeS 2 -f ZnS0 4 + H 2 + 0, = ZnS + FeS0 4 + H,S0 4 . 
 FeS 2 -f PbS0 4 + H 2 + 0, = PbS -f FeS0 4 + H 2 S0 4 . 
 FeS 2 + PbC0 3 + H 2 + 3 = PbS -f FeS0 4 -f H 2 CO 3 . 
 
 In the presence of an excess of air, reactions, corresponding 
 to equation (3), take place in the reduction of these soluble 
 salts of zinc and lead, as follows : 
 
 4FeS 2 + ZnS0 4 + 11H 2 + 26 = ZnS + 2Fe 2 3 ,3H 2 + 8H 2 S0 4 . 
 4FeS 2 + PbS0 4 + 11H 2 + O 26 = PbS -f 2Fe 2 3 ,3H 2 + 8H 2 S0 4 . 
 4FeS 2 -f PbCO, + 11H 2 -f 26 =PbS + 2Fe 2 3 ,3H 2 O + H 2 C0 3 
 
 -f 7H 2 S0 4 . 
 
 Arsenic and Antimony. The values of R for arsenic and anti- 
 mony are obtained from the following equations : 
 
 2 As + O 6 = As 2 5 ; whence, R = 6.67. 
 
 2Sb -f O 3 = Sb 2 3 ; whence, R = 2.50. 
 
 Arsenopyrite. The composition of arsenopyrite, FeAsS, is as 
 follows : 
 
 Iron, . . . . . . .... . . 34.30 
 
 Arsenic, . '.. . . 46.00 
 
 Sulphur, . . . ... .... . 19.70 
 
 100.00 
 
 The value of R may be calculated either from the reaction, 
 the arsenic oxidizing to As 2 O B , or from the composition, as 
 follows : 
 
 2FeAsS + 13 = As 2 5 + 2FeS0 4 . 
 
 23 
 
354 THE CHEMISTRY OF ORE-DEPOSITION. 
 
 326 : 208 :: 1 : Q = 
 8 : 0.638 : : 100 : E = 7.98. 
 
 0.197X25 =4.92 
 0.46 X 6.67=3.06 
 
 Enargite. For enargite, Cu s AsS 4 , or 3Cu 2 S, As 2 S 5 , the com- 
 position and the computations are as follows : 
 
 Copper, . . . . . . . 48.3 
 
 Arsenic, . . . . . . . . . .19.1 
 
 Sulphur, . . . . . . i" . . . . . 32.6 
 
 100.0 
 
 3Cu 2 S, As 2 S 5 + 2H 2 O + 35 = As 2 O 5 + 6CuSO 4 + 2H 2 S0 4 . 
 
 One-fourth of the sulphur, or 8.15 per cent., is oxidized to 
 S0 3 , and the remainder (24.45 per cent.) to S0 4 . 
 
 786.4: 560 :: 1 : Q = 0.7121. 
 8 : 0.7121 :: 100 : .ft =8.90. 
 
 0.0815 X 18.75 = 1.53 
 0.2445 X 25.00 =6.11 
 0.191 X 6.67 = 1.27 
 
 8^91= . 
 
 Stibnite. For stibnite, Sb 2 S 3 , the composition and the compu- 
 tations are as follows : 
 
 Antimony, . . . . . ; V . . . .71.4 
 Sulphur, . . . . .. ., . , . . . 28.6 
 
 100.0 
 
 Dana gives the product of the oxidation of stibnite as valen- 
 tinite, Sb 2 3 . 
 
 Sb 2 S 3 + 12 + 3H 2 =^Sb 8 O s + 3H 2 S0 4 . 
 336 : 192 :: 1 : Q= 0.5714. 
 
 8 : 0.5714:: 100 : ^ = 7.15. 
 Or, calculated from the composition, 
 
 0.286 X 18.75=5.36 
 0.714 x 2.50= 1.78 
 
THE CHEMISTRY OF ORE-DEPOSITION. 355 
 
 Pyrrhotite. Similarly for pyrrhotite, Fe n S 12 : 
 
 Fe n S 12 + 47 +H 2 = llFeS0 4 + H 2 S0 4 , 
 
 Giving R = 9.40 ; =0.752. 
 
 Ferrous Sulphate. The reactions in the case of ferrous sul- 
 phate, FeS0 4 , are as follows : 
 
 In the oxidation of pyrite and marcasite, a mixture of ferrous 
 sulphate and free sulphuric acid is first formed. Weed* gives 
 the products of the further absorption of oxygen as 
 
 H 2 S0 4 ,Fe(OH) 3 and Fe 2 (S0 4 ) 3 . 
 The reaction that takes place may be written : 
 
 6FeS0 4 + 2H 2 S0 4 + 4H 2 + 3 = 2(H 2 S0 4 , Fe(OH) 3 ) + 
 2(Fe 2 (S0 4 ) 3 ) + H 2 0. 
 
 Six parts of ferrous sulphate absorb 3 parts of oxygen ; or, 
 by reduction, 2 parts of ferrous sulphate absorb 1 part of 
 oxygen. 
 
 304 : 16 :: 1 : =0.05263. 
 
 8 : 0.05263 :: 100: E= 0.66. 
 =19.1. 
 
 Summary. 
 
 The following table of comparative reducing powers gives 
 the quantitative value, or gross amount, of the work done by 
 each of the deoxidizing agents. It is necessary, however, to 
 supplement these theoretic results by observations in the field, 
 especially of ore-deposits undergoing decomposition and re- 
 formation ; and also by experimental research in the labora- 
 tory, in order to estimate accurately in each particular instance 
 the chemical energy, or velocity with which the action takes 
 place. 
 
 Fortunately, with respect to the greater number of the more 
 important reducing substances commonly occurring in ore- 
 deposits, the gravimetric power, or duty, and the chemical 
 
 * "The Enrichment of Gold- and Silver- Veins," by Walter H. Weed, Genesis 
 of Ore-Deposits, p. 478 ; Trans., xxx., 429, 430. 
 
356 THE CHEMISTRY OF ORE-DEPOSITION. 
 
 energy run nearly parallel ; so that one may be taken as the 
 measure of the other. 
 
 The results of these calculations confirm the observations 
 made in the zinc- and lead-mines of the Joplin, Mo., region, in 
 the investigation of the secondary formation of the ores, of 
 the relative order of the reducing powers of the principal de- 
 oxidizing agents, viz. : 1, bitumen ; 2, bituminous coal and car- 
 bonaceous shales ; 3, marcasite and pyrite ; 4, blende ; 5, ga- 
 lena. 
 
 Ferrous sulphate appears to be exceptional ; notwithstanding 
 the extreme low duty (0.66), and notwithstanding that, inform- 
 ing ferric sulphate, 19.1 parts of the salt combine with only 
 one part of oxygen, yet in the zone of oxidation, where the 
 chemical activities have full play in the breaking-up of an ore- 
 body, it fulfils a special mission, at once oxidizing and reduc- 
 ing. Its chemical energy is such that it reduces cuprous oxide 
 to the metallic state ; a change which none of the other deoxi- 
 dizing agents usually found in ore-bodies are able to accom- 
 plish.* Further, its field of operation is the zone of oxidation 
 and that border-land where the zone of oxidation merges into 
 the zone of reduction. 
 
 This low quantitative-value is in many instances more than 
 offset by the large amount of ferrous and ferric sulphates con- 
 tinuously supplied by the progressive oxidation of the pyrite 
 in the ore-deposits. The mine-waters lixiviating the decom- 
 posing ore, although the volume of the flow may be consider- 
 able, are frequently strongly acid from the free sulphuric acid 
 and iron sulphates held in solution. 
 
 In conclusion, the hydrocarbons, combining the highest 
 quantitative deoxidizing power with an intense chemical activ- 
 ity, are the most powerful of all reducing agents. The action 
 of the solid oxygenated hydrocarbons, bitumen, bituminous 
 coal, and the lignitic matter finely disseminated in shales, is 
 greatly accelerated by the facility with which these carbon- 
 compounds, when in powder, are carried by the circulating 
 waters into every part of the ore-bodies. 
 
 * " Enrichment of Gold- and Silver- Veins," by Walter H. Weed, Trans., xxx., 
 431 ; Genesis of Ore-Deposits, p. 480. 
 
THE CHEMISTRY OF ORE-DEPOSITION. 357 
 
 TABLE. 
 
 THE RELATIVE REDUCING POWER, It, OR DUTY, OF EQUAL 
 WEIGHTS OF THE ORGANIC AND INORGANIC MINERAL SUB- 
 STANCES USUALLY OCCURRING IN THE ORE-BODIES, OR IN 
 THE WALL-ROCK, OR INTRODUCED WITH THE CIRCULATING 
 WATERS; HYDROGEN BEING ASSUMED AS 100. 
 
 Hydrogen (occurs combined with carbon), oxi- It. 
 
 dized to H,O, . 100.00 
 
 Marsh-gas, CH 4 (carbon 75 per cent., hydrogen 25 
 
 per cent), oxidized to H 2 CO 3 +H 2 0, . . 50.00 
 Petroleum, C n H 2n+2 (carbon 85 per cent, hydro- 
 gen 15 per cent), . . . . . . 43.36 
 
 Bitumen (carbon 89 per cent., hydrogen 11 per 
 
 cent, oxygen per cent), . * 40.67 
 Bitumen (carbon 80 per cent, hydrogen 14 per 
 
 cent., oxygen 6 per cent), ... . 39.92 
 
 Bitumen (grahamite) (carbon 81 per cent., hydro- 
 gen 10 per cent, oxygen 9 per cent), * . 35.88 
 Bituminous Coal (carbon 88 per cent, hydrogen 
 
 7 per cent, oxygen 5 per cent.), . . . 35.71 
 Bituminous Coal (carbon 81 per cent, hydrogen 
 
 4 per cent., oxygen 15 per cent), . . . 29.13 
 Carbon (graphite, etc.), oxidized to C0 2 , , . 33.33 
 Carbon, oxidized to CO, . . , . . . 16.67 
 Lignite (carbon 73 per cent, hydrogen 7 per cent., 
 
 oxygen 20 per cent), 28.83 
 
 Lignite (carbon 60 per cent., hydrogen 4 per 
 
 cent, oxygen 36 per cent), ... . . ,. 19.50 
 
 Native Humus Acid, C 46 H 46 O 25 (carbon 55 per 
 cent, hydrogen 5 per cent, oxygen 40 per 
 cent), . . , ...... . . . 18.04 
 
 Sulphur (combined), oxidized to S0 4 , . . . 25.00 
 Sulphur, oxidized to S0 3 , . . . . . . 18.75 
 
 Sulphur, oxidized to S0 2 , . . '.-- . . 12.50 
 Sulphuretted Hydrogen, H 2 S, oxidized to H 2 S0 4> . 23.53 
 Sulphuretted Hydrogen, H 2 S, oxidized to H 2 0-f S, . 5.88 
 
 (oxidation of Fe to\ 
 2Fe 2 3 ,3H 2 0; andS 12.50 
 to SO, / 
 
358 THE CHEMISTRY OF ORE-DEPOSITION. 
 
 Pyrite and Marcasite, oxidation to FeS0 4 , . . 11.67 
 
 Pi/rite and Marcasite, oxidation to FeS0 4 and S, . 6.67 
 
 Pyrrhotite, Fe n S w , oxidized to FeS0 4 and H 2 S0 4 , 9.40 
 Enargite, Cu 3 AsS 4 , oxidized to As 2 0_, CuS0 4 and 
 
 HJ30 4 , . . . . . . . 8.90 
 Chalcopyrite) CuFeS 2 , oxidized to CuS0 4 and 
 
 FeS0 4 , ! 8.72 
 
 Covellite, CuS, oxidized to CuS0 4 , . .- . 8.39 
 
 Blende, ZnS, oxidized to ZnS0 4 , . . . 8.25 
 Arsenopyrite, FeAsS, oxidized to As 2 5 and 
 
 FeS0 4 , . 7.98 
 
 Calcium Disulphide, CaS 2 , oxidized to CaS0 4 and S, 7.69 
 
 Stibnite, Sb 2 S 3 , oxidized to Sb 2 3 and H 2 S0 4 , . 7.15 
 
 Carbon Monoxide, CO, oxidized to C0 2 , . . 7.14 
 Bvrnite, Cu 3 FeS 3 , oxidized to Cu 2 S0 4 , CuS0 4 and 
 
 FeS0 4 , ....... ; 7.01 
 
 Arsenic, oxidized to As 2 5 , . -. . . . . 6.67 
 Tetrahedrite, 4Cu 2 S.Sb 2 S 3 , oxidized to Cu 2 S0 4 , 
 
 CuS0 4 and Sb 2 3 , . '. . . . 6.39 
 
 Iron, oxidized to Fe 2 3 , .-> < . . 5.36 
 
 Iron, oxidized to Fe 3 4 , '\ . . ,. . 4.76 
 
 Iron, oxidized to FeO, . . . . . 3.58 
 
 Chakocite, Cu 2 S, oxidized to Cu 2 S0 4 , . .... 5.04 
 
 Galena, PbS, oxidized to TbS0 4 , . . . v 3.35 
 
 Tellurium, oxidized to Te0 2 , ' . . . . .; . 3.20 
 
 Copper, oxidized to CuO, . . . . , 3.15 
 
 Copper, oxidized to Cu 2 0, . . . . . 1.58 
 
 Antimony, oxidized to Sb 2 3 , . . .- . 2.50 
 
 Rhodochrosite, MnC0 3 , oxidized to Mn0 2 , -. . 1.75 
 
 Siderite, FeC0 3 , oxidized to Fe 2 3 , . . . 0.86 
 
 Ferrous Sulphate, FeS0 4 , oxidized to Fe 2 (S0 4 ) 3 , . 0.66 
 Magnetite, Fe 3 4 , oxidized to Fe 2 3 , . . . . 0.46 
 
THE CHEMISTRY OF ORE-DEPOSITION. 359 
 
 DISCUSSION. 
 
 ( Trans., xxxiii., 1065.) 
 
 JOHN A. CHURCH, New York, N. Y. : Professor Jenney has 
 performed a notable service in presenting this summary of the 
 steadily increasing body of observation on the presence of carbon 
 in rocks of all kinds and its probable influence upon ore-deposi- 
 tion, and in formulating a mode of comparing directly the relative 
 resistance of minerals to oxidation, as well as their reducing- 
 power, and the protective action which minerals having higher 
 reducing-powers exert in preventing the oxidation of associated 
 minerals which possess relatively lower affinities for oxygen. 
 
 I have had an opportunity of observing a vein which falls 
 within the scope of his interesting discussion. The vein at Ku 
 Shau Tzu, Mongolia, lies directly across a contact of limestone 
 and overlying bituminous shales. Probably it occupies a com- 
 pression-fissure. The shale has been reduced to such a condi- 
 tion of non-coherence that much of it can be crushed in the 
 hand, producing a handful of angular fragments resembling 
 beech-nuts in shape and size. 
 
 In the limestone the metals are principally in argentiferous 
 galena with some pyrite and blende; but the latter two are 
 very subordinate in quantity to the galena. In short, it is an 
 every-day lead-vein in limestone, with siliceous limestone 
 gangue. It is one of those veins in which the ore is not con- 
 tinuous, but consists of a band in the country-rock in which 
 seams of lead sulphide begin at one wall and cross in a bent 
 form, increasing in thickness, to the other wall, where they 
 thin out and end. This may indicate torsional stress, but the 
 shape of the lenses points to some other action. They often 
 ran nearly parallel to the hanging-wall for a considerable dis- 
 tance and crossed the vein on a moderate angle, but turned 
 sharply along the vein on approaching the foot-wall. The inter- 
 mediate rock contains nodules, bunches and specks of ore, and 
 the lenses vary exceedingly in size, shape and position in the 
 vein. 
 
 In the bituminous shale the deposition of ore is not at all 
 like that in the limestone. The minerals in the shale are tetra- 
 hedrite and native silver, the latter occurring in fine scales and 
 sheets of pure metal, weighing from 50 to possibly 100 oz. 
 I cannot speak of these larger sheets from much acquaintance, 
 
360 THE CHEMISTRY OF ORE-DEPOSITION. 
 
 for all but one of them were stolen by the miners, but the 
 metallic silver in scales and sheets was an important part of 
 the ore. 
 
 It is necessary to exclude the notion of secondary deposition 
 at Ku Shau Tzu, because the influence of the shale with its 
 superabundant store of powerful reducing-agent should have 
 gathered to itself every metal taken into solution by descending 
 surface-waters. Whether that was the case immediately at the 
 surface I do not know, as the mine was an old one when I first 
 saw it. The absence of galena, blende and pyrite from the 
 shale, at depths of 300 and 400 ft, indicates that secondary de- 
 position, if present at any time, did not reach so far; and this 
 was to be expected from the reducing-power of the shale at the 
 surface. 
 
 I considered that the conditions indicated deposition from a 
 solution rising through the limestone first and afterward 
 through the shale which once covered the lime-rock, though 
 now it is tilted and partially eroded. The limestone precipi- 
 tated what it could, and the abundant store of carbon in the 
 shale perhaps took the last traces of metal. But this explana- 
 tion is not without its difficulties when applied to the lime- 
 stone, however confident we may be of the reducing-powers 
 of the shale. 
 
 The feeble reducing-power to which galena yields only 
 3.35 per cent, of II, according to Prof. Jenney explains its 
 presence in the limestone well enough, but why should this 
 rock precipitate also blende (8.25 per cent.) and pyrite (11.67 
 per cent.), while it left tetrahedrite (6.39 per cent.) to the 
 shale ? The reduction of metallic silver in the shale is, of 
 course, not surprising. 
 
 There must have been some other selective agency than mere 
 position or the chemical energy of carbon at work to produce 
 these effects. The same considerations lead us to doubt that 
 there was an interchange of elements between different parts of 
 the ascending column of mineral solution, by which the com- 
 plete precipitation of any mineral in one rock, the shale, for 
 instance, would so dilute the mother-liquor there that this min- 
 eral would pass by diffusion from the solution going through 
 the limestone to that in the shale. Such action is familiar in 
 chemical work. When a drop of reagent causes partial precip- 
 
THE CHEMISTRY OF ORE-DEPOSITION. 361 
 
 itation, the remainder of the dissolved substance is diffused im- 
 mediately through the whole body of liquid. This could not 
 have taken place at Ku Shau Tzu without producing more 
 abundant deposition in one of the rocks than in the other, ac- 
 cording to its precipitating energy, and the phenomenon there 
 is not quantitative, but selective, concentration. The quantity 
 of mineral was greatest in the limestone. 
 
 It is conceivable that the deposition of ore in the shale would 
 liberate carbon, which, going into solution, might reach the 
 limestone and there act upon the advancing ore-solution, thus 
 giving the shale a large radius of action, and making it con- 
 tribute to deposition in the neighboring rock. 
 
 This question of interchange of elements between solutions, 
 or diffusion, is of great interest and importance, and though it 
 is riot germane to the subject of Prof. Jenney's paper, I may 
 be permitted to point out that some observations indicate that 
 there is no horizontal diffusion or exchange of dissolved sub- 
 stances between the two halves or ends of the moving column 
 of solution, which we may consider conveniently to have the 
 same length as the vein. There is evidence that the solution 
 from which an ore of general average composition is deposited 
 may produce ore-bodies that vary in their different parts in a 
 manner important to the miner if not to Nature. 
 
 In the well-known case of the Crown Point-Belcher bonanza, 
 one-half of the ore-body contained more gold in proportion to 
 silver than the other half, and the difference was not fortuitous, 
 but persisted through the whole extent of the bonanza. The 
 country-rock was eruptive, the mass of the deposit was silica, 
 the total length was only 500 ft., and it is difficult to see how 
 there could have been selective deposition from a uniform solu- 
 tion. Granting that the difference began at the point where 
 the solution was formed, this difference in the two halves of the 
 current must have been preserved throughout its wander- 
 ings, a proof that there were no exchanges between the two 
 halves. 
 
 Of course, if lateral secretion in its first and most restricted 
 sense were true, and the ore were derived from the immediate 
 walls of the vein, an explanation might be found. This ex- 
 tremely limited conception is, I believe, entirely abandoned; 
 and the persistent difference of the Crown Point-Belcher solu- 
 
362 THE CHEMISTRY OF ORE-DEPOSITION. 
 
 tion along adjacent vertical and, perhaps, horizontal lines of 
 travel, possibly to great distances, is an unexplained phenom- 
 enon. Other cases are known in which the facts indicate that 
 there was no exchange of elements between the parts of the 
 common solution from which the respective ends of the ore- 
 body were formed. 
 
 It is not probable that the north and south ends of the Crown 
 Point-Belcher ore-body differ in date, for the mass was decidedly 
 lenticular, very thick in the middle and thinning out in all 
 directions. The natural conclusion is that the action, being a 
 replacement of country-rock, began in the central portion of the 
 mass, and the greater thickness there is the effect of longer 
 action. This is equivalent to saying that the action was contin- 
 uous over the whole of the steadily increasing vein-area, and 
 that ore was forming in the center while it was forming at 
 both ends. 
 
 Occurrences of this kind have an obvious bearing upon the 
 views which Prof. Van Hise has expressed upon the movement 
 of waters in the rocks. A natural explanation of the Crown 
 Point-Belcher case is that the thin-leaved porphyry of the Corn- 
 stock offered a means of ready flow which operated as a chan- 
 nel, to which waters from widely different sources of origin 
 were directed ; but this only emphasizes the fact that the two 
 currents maintained their individuality through long wander- 
 ings, and even when joined in a channel of limited section. It 
 also implies that gold and silver can be picked up anywhere in 
 the middle of the earth, a conclusion which cannot be admitted; 
 for it is probable that the solution of metals is as selective and 
 phenomenal as is their deposition. 
 
 Differential deposition, as in this case, necessarily brings up 
 the question of electro-chemical action ; but which way would 
 it work, for or against differentiation ? My impression is that 
 it would act for uniformity, and there is no evidence that elec- 
 trical action in the rocks is strong enough to move a metal or 
 salt through 500 ft. of minute channels. 
 
 Prof. Jenney's description of the ore-deposition in the Tintic 
 limestones may be accepted as accurate for the galena of the 
 celebrated " Emma " mine, in Little Cottonwood Canyon, Utah. 
 I well remember a large mass of galena there, almost pure in 
 the center, and surrounded by a thick mass consisting of de- 
 
THE CHEMISTRY OF ORE-DEPOSITION. 363 
 
 composed limestone fragments in galena, graduating to enclo- 
 sures of galena in limestone as the distance from the center 
 increased, and ending with scattered, small impregnations of 
 galena in the nearly unaltered limestone walls. The angular 
 shape of the inclusions mentioned by Prof. Jenney was note- 
 worthy there also. 
 
 Every mining engineer will recall from his own experience 
 occurrences which sustain the general position which Prof. 
 Jenney takes in reference to the presence of carbon in the 
 rocks of mining districts. One of the problems at Tombstone 
 which the new owners are attacking with such faith is the 
 future of the Contention vein, where it passes through the 
 Lucky Cuss limestone, w T hich is strongly fetid for 100 or 200 ft. 
 in thickness. It may be years before it is reached, but it pre- 
 sents the elements for active chemical exchanges. When I 
 was a superintendent in Tombstone, two of my men, who were 
 mining manganese in the higher strata of this limestone, nearly 
 lost their lives by an effusion of C0 2 into a shallow, open pit 
 where they were working. The gas accumulated during the 
 night and surprised them in the morning. These facts may 
 indicate the influence of carbon in that mining district. 
 
 At the New Almaden quicksilver-mine there is an enormous 
 discharge of carbon dioxide, which bubbles and hisses through 
 the water in the bottom, and twice, at least, has so filled the 
 large chambers of the old mine as to drive the whole mining- 
 force from its work. 
 
 The Mining and Scientific Press, San Francisco, of May 2, 
 1903, has the following interesting note upon the occurrence of 
 carbon dioxide : 
 
 " Metal mines, as well as coal mines, produce carbonic acid gas, though more 
 rarely the inflammable ' fire damp.' In some instances the carbonic acid gas 
 has been so abundant that the mining work has had to be abandoned. This was 
 the case in a long drift from a deep shaft at the New Almaden, Cal., quicksilver- 
 mine. Subsequently, an air-tight bulkhead was built in the drift, and pipes placed 
 connecting an air-compressor at the surface with the bulkheaded drift. The in- 
 take of the compressor was attached to the pipe leading into the mine, the carbon 
 dioxide was drawn from the mine and by means of special machinery compressed 
 into steel cylinders under a pressure of 1,200 Ib. per sq. in., in which form it 
 was sold for the carbonating liquids. The Abbott quicksih 7 er-mine in Lake 
 county, Cal., makes a large amount of ' firegis' similar to the 'fire damp' of 
 coal mines. The occurrence of fire damp in metal mines is unusual. In the 
 case of the Abbott mine its presence is supposed to be due to the bituminous 
 matter in the surrounding rocks." 
 
364 ORE-DEPOSITS NEAR IGNEOUS CONTACTS. 
 
 No. 13. 
 Ore-Deposits Near Igneous Contacts. 
 
 BY WALTER HARVEY WEED, WASHINGTON, D. C. 
 
 (New Haven Meeting, October, 1902. Trans., xxxiii., 715.) 
 
 CONTENTS. 
 
 PAGE 
 
 INTRODUCTION, 364 
 
 WHY ORE-DEPOSITS ARE COMMON ABOUT IGNEOUS CONTACTS, . . . 365 
 OUTLINE OF A GENETIC CLASSIFICATION OF ORE-DEPOSITS, . . . 366 
 
 Ores of Igneous Origin, 366 
 
 Igneous-Emanation Deposits, 368- 
 
 Fumarolic Deposits, . 368 
 
 Gas-Aqueous Deposits, 368 
 
 Deposited by Meteoric Waters, 369 
 
 CONTACT METAMORPHIC DEPOSITS, 369 
 
 Classes of Deposits, 370 
 
 Contact Zones, 371 
 
 Character of Gangue, . . . . 371 
 
 Character of Ore-Deposit, 372 
 
 Literature, 373 
 
 Geographic Distribution, 373 
 
 Copper- Deposits Cananea Type, 374 
 
 British Columbia Boundary District, 374 
 
 Mexico, 376 
 
 Germany, 378 
 
 Gold-Deposits, 380 
 
 Bannack Type, 381 
 
 Elkhorn, 382 
 
 Similkameen, . . . . 383 
 
 CHANGES IN ROCKS DUE TO CONTACT METAMORPHISM, . . . . . 384 
 Changes in Mass, Volume, and Mineral Composition, .... 385 
 
 GENESIS OF CONTACT METAMORPHIC DEPOSITS, 387 
 
 Cause of Contact Metamorphism, 387 
 
 PERMANENCE IN DEPTH, . . . . 393. 
 
 MINERAL VEINS NEAR IGNEOUS CONTACTS, 394 
 
 CONCLUSIONS, . . *-.' ...._; ; v 395- 
 
 INTRODUCTION. 
 
 THIS paper deals with certain ore-deposits whose structural 
 features or mineral contents (or both) result, directly or indi- 
 rectly, from igneous intrusions and their after-effects. It is 
 largely a discussion of contact metamorphic ore-deposits based 
 upon the physical changes in rocks due to contact action. It 
 involves a classification of ore-deposits only so far as is abso- 
 
ORE-DEPOSITS NEAR IGNEOUS CONTACTS. 365 
 
 lutely necessary for brevity of discussion. A genetic classifica- 
 tion of ore-deposits is admitted to be the rational and only cor- 
 rect classification from a scientific point of view. To the 
 practical miner, such a classification may be of utility if the 
 correct discrimination of the nature and genesis of a deposit 
 enables him to more nearly determine the probable extent and 
 value of the deposit, and to exploit it intelligently. It is be- 
 lieved that the facts set forth in this paper and the explanation 
 of them admit of such a practical use. 
 
 WHY ORE-DEPOSITS ARE COMMON ABOUT IGNEOUS CONTACTS. 
 
 As is well known, the granitic rocks which adjoin contact 
 areas are parts of great masses of igneous magma which did 
 not reach the surface, but cooled slowly underground and con- 
 solidated into coarse-grained rocks. Subsequent uplift and 
 denudation have exposed both the great bodies of igneous rock, 
 and the sediments baked and altered by them, in consequence 
 of the heat and vapors given off by the cooling magma. 
 
 Igneous contacts are ore-bearing because, (a) differentiation 
 of the cooling magma tends to segregate the highly basic and 
 metal-bearing portion at the border of the cooling mass ; (b) 
 pneumatolytic processes are most active about the borders of 
 igneous masses ; (c) the force of the intrusion may have shat- 
 tered the adjacent rocks, forming cracks and fissures that be- 
 come channels for circulating waters; (d) the shrinkage of the 
 intrusive magma due to progressive cooling after solidification, 
 and the shrinkage of the metamorphic zone itself, would result 
 in the formation of fissures ; and (e) as will be shown later, the 
 porosity induced in certain sedimentary rocks by contact meta- 
 morphism (which maybe compared to the burning of clay into 
 brick) has furnished channels for circulating waters and gases, 
 so that ore-deposition has resulted. The origin and character 
 of the latter class of deposits is the only strictly novel feature 
 of the paper. The deposits formed near igneous contacts by 
 the operation of these causes have widely different characters. 
 To discuss them a systematic arrangement is necessary, and 
 the following provisional genetic classification has been pro- 
 posed.* 
 
 * Compare Eng. Min. Jour., vol. Ixxv., No. 7, p. 256, Feb. 14, 1903. 
 
366 ORE-DEPOSITS NEAR IGNEOUS CONTACTS. 
 
 OUTLINE OF A GENETIC CLASSIFICATION OF ORE-DEPOSITS. 
 
 I. Igneous (magmatic segregations). 
 
 A. Siliceous. 
 
 B. Basic. 
 
 II. Igneous-emanation deposits (deposited by highly heated 
 vapors and gases in part above the critical 
 point, e.g., 365 and 200 atm. for H 2 O). 
 
 A. Contact-metamorphic deposits. 
 
 B. Veins (closely allied to magmatic veins and to 
 
 division IV.). 
 
 III. Fumarolic deposits (metallic oxides, etc., in clefts in lavas ; 
 
 of no commercial importance). 
 
 IV. Gas-aqueous (pneumato-hydato-genetic) deposits. Igne- 
 
 ous, gaseous and aqueous emanations, alone or 
 mingled with ground-waters. 
 
 A. Filling-deposits. 
 
 B. Replacement-deposits. 
 V. Deposited by meteoric waters. 
 
 A. Underground. 
 
 B. Surficial. 
 
 In this classification I have attempted to group the geological 
 processes forming ore-deposits in such a way as to show genetic 
 relations, it being understood that opinions will differ as to the 
 class to which a particular deposit is to be assigned. 
 
 Major subdivisions are based upon magmatic segregations at 
 one end and cold aqueous deposits at the other, with interme- 
 diate groups due to the emanations from igneous rock, the 
 eruptive after-actions of Vogt, to which the term pneuma- 
 tolytic has commonly been given ; fumarolic, when these ema- 
 nations issue at low temperature and pressure; gas-aqueous, in 
 which the emanations from igneous rocks-, with their burden of 
 metals, mingle with ground-water ; aqueous, in which meteoric 
 waters alone are active, both chemically and mechanically. 
 
 Ores of Igneous Origin. 
 
 The igneous deposits are divided into basic and siliceous, the 
 former including the deposits of iron, copper, etc., found at 
 igneous borders and as dikes, the latter the ore-bearing peg- 
 matites, with quartz-veins as extreme examples. 
 
ORE-DEPOSITS NEAR IGNEOUS CONTACTS. 367 
 
 The existence of certain ore-deposits of an igneous origin 
 seems to be fully proven and generally accepted. It is well 
 known that the igneous magmas differentiate into siliceous and 
 basic portions,* the resulting rocks being the siliceous aplites 
 (alaskites) and highly basic rocks of various kinds. Where ex- 
 treme differentiation has taken place, the basic residual por- 
 tion contains so much iron or copper solidified as to form 
 workable ore-deposits, constituting the subdivision B of the 
 table. The same extreme segregation would produce the sili- 
 ceous magma commonly seen as acid granites or aplites, which 
 frequently pass into pegmatites, and the latter, in turn, into 
 quartz-veins. These facts are well known, f 
 
 Some of these observers, however, believe that pegmatites 
 and allied quartz- veins are due to igneous emanations of watery 
 vapor, and are not direct segregations. Whatever may be the 
 result of further study concerning the origin of these interest- 
 ing veins, there is no doubt that in part, at least, they are of 
 pneumatolytic origin. There is, however, abundant evidence 
 to show that acid rocks are commonly associated with gold- 
 deposits. Richard Beck, in his book on ore-deposits, describes 
 the occurrence of intrusive bodies of granite near Lake Schart- 
 ash which carry gold ; and various observers have described 
 dikes of similar acidic granite at Berezovsk containing quartz 
 filling contraction-cracks, and consequently a normal constit- 
 uent of the rock, which are mined for their gold values. In a 
 treatise entitled " Criaderos Minerales de Mexico," Aguilera 
 has given very many examples of the association of ores with 
 extremely siliceous rocks. J 
 
 In a general way, the laws of segregation outlined by Pirs- 
 son indicate that we should expect the siliceous segregation in 
 the center of the igneous mass and the basic ones at the bor- 
 ders, while the basic dikes would traverse the igneous contacts, 
 cutting both the igneous rock and the adjacent altered sedi- 
 mentary rocks. 
 
 * Weed and Pirsson, "Shonkin Sag Laccolith," Amer. Jour. Sci., July, 1901. 
 
 f Kemp, "Role of the Igneous Rocks in the Formation of Veins," Trans., 
 xxxi., p. 182; also, Genesis of Ore-Deposits, p. 693. Van Hise, Trans., xxxi., p. 
 287. Lindgren, " Character and Genesis of Certain Contact-Deposits," Trans., 
 xxxi., p. 243; also, Genesis of Ore-Deposits, p. 733. A. W. Howitt, Roy. Soc. Vic., 
 Oct. 14, 1886. 
 
 | " Distribucion Geografica y Geologico de los Criaderos Minerales de Mexico,"' 
 Jose* G. Aguilera, Acad. Sci. Off. Secretario Fomento, Mexico, 1901. 
 
368 ORB-DEPOSITS NEAR IGNEOUS CONTACTS. 
 
 Igneous- Emanation Deposits. 
 
 Under this title I have grouped contact-metamorphic depos- 
 its and pneumatolytic veins. The contact-metamorphic de- 
 posits have been shown by Vogt, Lindgren, Beck and others 
 to be formed under conditions which preclude either the pres- 
 ence of ordinary ground-water or steam at low temperature and 
 pressure. 
 
 Pneumatolytic veins, of which the Cornwall tin-veins are 
 classic examples, are admitted by most competent observers 
 to be formed by igneous emanations proceeding from the still 
 hot granite rocks.* The group includes part of those em- 
 braced in Vogt's " Ore-Deposits Formed by Eruptive After- 
 Actions." 
 
 The contact-metamorphic deposits are treated at consider- 
 able length in the succeeding pages. 
 
 Fumarolie Deposits. 
 
 Under this group I have classed deposits of ferric chloride, 
 cuprous oxide, and other metallic minerals formed in clefts of 
 volcanic craters. Deposits of this kind have been observed 
 by G-eikie and many other geologists, and the evidence concern- 
 ing them is summarized in discussing the origin of contact- 
 metamorphic deposits. They are assigned to a separate class 
 because they are formed at the surface of the earth under con- 
 ditions which do not and cannot prevail in depth. 
 
 Gas- Aqueous Deposits. 
 
 This group is formed to include those ore-deposits formed by 
 hot waters containing metallic salts and other substances de- 
 rived wholly or in part from igneous emanations. This class of 
 deposits corresponds closely to Vogt's igneo-aqueous or eruptive- 
 after-action group, f but it is as well to emphasize the distinction 
 to be made between hot waters carrying only the substances 
 dissolved out of the rocks traversed by them and those charged 
 with substances undoubtedly derived from igneous emanations. 
 The evidence concerning these deposits has been very ably 
 summed up by Suess in his recent paper. J Professor Suess 
 
 * Zeitschf. Kryst. u Min., vol. xvi., 1890. | Trans., xxxi., p. 125 et seq. 
 
 1 " Ueber Heisse Quellen," Gesd. Deutsch. Naturforscher und Arzte, 1902. 
 
ORE-DEPOSITS NEAR IGNEOUS CONTACTS. 369 
 
 expresses his belief in the inability of ordinary circulating 
 waters to derive the unusual substances, such as boron, fluo- 
 rine, chlorine, etc., from ordinary igneous and sedimentary 
 rocks. In fact, Professor Suess goes further, and says, the 
 water of the famous hot springs of the Carlsbad region is 
 original or primitive water derived from the underlying igne- 
 ous hearths and containing little, if any, meteoric water. On 
 the other hand, there seems to be no question but that in many 
 instances circulating meteoric waters intercept the uprising 
 primitive waters, and the solutions thus formed deposit ores. 
 In such cases the meteoric waters are the vehicle and not the 
 agent. This has been concisely stated by Lindgren as fol- 
 lows : 
 
 " Where fissures traverse the cooling magmas, and the rocks surrounding 
 them, it is natural that these mineralizing agents [emanations] carrying their 
 load of heavy metals should ascend, at first under pneumatolytic conditions, 
 above the critical temperature. Beaching the zone of circulating atmospheric 
 waters, it is natural that they should mix with these, which probably greatly 
 predominated in quantity. To this combination of agencies, found in the ascend- 
 ing waters of such regions of igneous intrusion, the formation of most metallif- 
 erous veins is probably due."* 
 
 Deposited by Meteoric Waters. 
 
 Under " Underground Deposits " I have grouped the de- 
 posits formed by circulating ground-waters in one class; those 
 of residual origin, being leached veins, in an entirely separate 
 class; as surficial deposits I would include chemical deposits 
 of various kinds, and mechanical deposits, such as sedimentary 
 rocks, placers, etc. 
 
 Believing, with Professor Kemp, that the greatest number of 
 copper and precious-metal deposits of the world are near igne- 
 ous rocks with which they are genetically connected, I hold, 
 with Vogt, that normal terrestrial water-circulation has had a 
 minor part in the primary origin of the deposits in question, 
 though it may have produced later concentration from contact 
 portions of the magmas rich in metals or from low-grade de- 
 posits of direct contact-metamorphic origin. 
 
 CONTACT METAMORPHIC DEPOSITS. 
 
 Under the title of contact metamorphic deposits I include 
 all ore-deposits which result from the metamorphic action of 
 
 * Genesis of Ore-Deposits, p. 612 ; also, Trans., xxx., p. 692. 
 24 
 
370 ORE-DEPOSITS NEAR IGNEOUS CONTACTS. 
 
 intrusive igneous rocks upon the sedimentary rocks which they 
 penetrate. Such deposits occur only in the zones of altered 
 sediments about igneous intrusions; they are genetically con- 
 nected with such intrusions, and are, therefore, fittingly desig- 
 nated as ore-deposits of contact metamorphic origin. The 
 following subdivisions are proposed : 
 
 Deposited by Igneous Emanations. 
 (All classes omitted save the one under discussion.) 
 Contact Metamorphic Deposits. 
 
 Characterized by gangue consisting essentially of gar- 
 net, epidote, actinolite, calcite, and other lime-alumina 
 silicates. 
 
 (a) Deposits confined to contact : 
 
 1. Magnetite deposits. 
 
 2. Chalcopyrite deposits, Kristiania type. 
 
 3. Gold-ores, Bannack type. 
 
 (b) Deposits impregnating and replacing beds of contact 
 
 zone : 
 
 1. Chalcopyrite deposits (a) Pyrrhotite ores, (b) mag- 
 
 netite ores, Cananea type. 
 
 2. Gold tellurium ores, Elkhorn type. 
 
 3. Arsenopyrite ores, Similkameen type. 
 
 In the present paper I shall particularly describe certain ore- 
 deposits occurring in sedimentary rocks altered by contact met- 
 amorphism, and endeavor to show that thermal metamorphism 
 effects certain physical changes in the sedimentary rocks of 
 the contact-zone favorable to ore-deposition, either because the 
 vapors and gases of the cooling magma penetrate the altered 
 rocks and deposit metallic sulphides or by reason of a later 
 impregnation, by circulating waters, of particular strata, made 
 porous by thermal metamorphism. They, therefore, embrace both 
 the " contact "-deposits of the Kristiania type and the types 
 herein described, and which have been called bed-impregna- 
 tions by Dalmer* and " Strikes " by Beck.f These embrace the 
 Cananea type and the types of gold-deposits, heretofore un- 
 known, which structurally and genetically resemble the first 
 types mentioned, but differ in mineral contents. 
 
 * "Problems in the Geology of Ore-Deposits," Genesis of Ore-Deposits, p. 650; 
 also, Trans., xxxi., p. 139. 
 
 f Kichard Beck, Lehre von den Erzlagerstatlen, 1901, p. 485. 
 
- ORE-DEPOSITS NEAR IGNEOUS CONTACTS. 371 
 
 As the admirable treatise of Lindgren* presents a discussion 
 of contact metamorphism in describing the genesis of depos- 
 its of the Kristiania type, much concerning this subject may 
 be profitably omitted from the present paper, though it is 
 necessary for a clear understanding of the subject to give an 
 outline of the principal facts. 
 
 Contact Zones. 
 
 In many mining districts there occur great masses of gran- 
 itic rocks, surrounded by sedimentary strata which, near the 
 contact, exhibit marked alteration, the intensity of which dimin- 
 ishes as the distance from the igneous rock increases until the 
 alteration fades out and the rocks are of normal character. 
 Such areas are known as contact metamorphic zones, which 
 often form a halo about igneous centers; for example, about 
 the " stocks " of granitic rocks of the Crazy Mountains, Mon- 
 tana, or the batholitic masses of the Black Hills, Dakota. In 
 other cases great areas of granitic rock, such, for example, as 
 the great mass of granite called the Butte batholith, of Mon- 
 tana, which is 60 miles long and 40 miles broad, are bordered 
 by a zone of rocks altered by contact metamorphism which 
 may be a mile or more wide, as, for instance, near Helena, 
 Montana. Such contact zones are often the seat of mineral 
 deposits of great economic value, as is illustrated by the Drum- 
 lummon and other mines at Marysville, Montana ; several mines 
 at Granite and Philipsburg, Montana; the Whitlatch-Union 
 and other mines, once productive, at Helena ; the copper-mines 
 at Clifton and Morenci, Arizona; those at Cananea, Sonora, 
 and many other localities in Mexico. I exclude the common 
 contact-deposits of the text-books, in which it appears probable 
 that the igneous rock has, by its presence, localized and de- 
 flected circulating waters and thus determined the site of ore- 
 deposition. 
 
 Character of Gangue. 
 
 Contact metamorphic deposits of whatever type are distin- 
 guished by a gangue consisting essentially of garnet, calcite, 
 epidote, actinolite, with or without accessory wollastonite, vesu- 
 
 * "Metasomatic Processes in Fissure- Veins," Genesis of Ore-Deposits, p. 498; 
 also, Trans., xxx., 578. 
 
372 ORE-DEPOSITS NEAR IGNEOUS CONTACTS. 
 
 vianite, flue-rite, etc., and other minerals characteristic of con- 
 tact metamorphic zones. As will be shown later, the gangue 
 is normally a rock formed by the alteration of an impure lime- 
 stone. Other rocks characteristic of contact action, such as 
 hornrels, marble, quartzite, adinole, etc., are often present, but 
 the ore-deposit is practically confined to the rocks resulting 
 from the alteration of impure limestones, for reasons explained 
 later. 
 
 Character of Ore-Deposit. 
 
 The Kristiania type of contact-deposit has already been de- 
 scribed by Lindgren.* Specular iron and -magnetite are com- 
 mon in true " contact "-deposits, but they occur only rarely in 
 the deposits separated from the contact. The ore-minerals pre- 
 sent considerable variety, and according to their metallic con- 
 tents may be grouped as copper-ores and as gold-ores. A more 
 complete classification would be, however, 
 
 (1) Chalcopyrite deposits : (a) pyrrhotitic type, (b) magnetic. 
 
 (2) Telluride deposits. 
 
 (3) Arsenopyrite deposits. 
 
 The first class includes the chalcopyrite ore-bodies carrying 
 accessory galena at Cananea, Mexico. The subtypes are dis- 
 tinguished at Boundary, British Columbia. In the pyrrhotite 
 type that mineral predominates, but the copper values are in 
 chalcopyrite and accessory pyrite, while in the magnetite type 
 this mineral replaces pyrrhotite. The second class is charac- 
 terized by the presence of telluride of gold. In the Elkhorn 
 example the ore-mineral is an auriferous tetradymite with as- 
 sociated bismuthinite. At Bannack, Mont., there is free gold, 
 with much more abundant sylvanite. In the third class arsen- 
 opyrite occurs, carrying very high values in gold, together with 
 free gold. The only known example of this class is the Nickel 
 Plate mine, near Lake Okanagan, British Columbia. 
 
 The characteristic feature is the gangue of earthy silicate 
 minerals in which the ore-minerals are disseminated. In most 
 cases the ore-minerals and the sulphides are of simultaneous 
 origin (or nearly so). The deposits are the direct result of the 
 deposition of ore by the vapors and gases of the cooling magma 
 
 * " Character and Genesis of Certain Contact- Deposits," Genesis of Ore-Deposits, 
 p. 716; also, Trans., xxxi., 226. 
 
ORE-DEPOSITS NEAR IGNEOUS CONTACTS. 373 
 
 (possibly, in part, the gases given off by the alteration of the 
 
 sediments). 
 
 Literature. 
 
 Geologists have long recognized the peculiar characters of 
 ore-deposits in the contact metamorphic zone about igneous 
 intrusions, nor would it be possible for a careful observer to 
 fail to note the successful mines and the multitude of unsuc- 
 cessful prospect-pits which commonly mark such areas. It is 
 unnecessary to go into detail on this subject, as it has been cov- 
 ered by Lindgren in the paper cited.* It is evident that Kemp,f 
 although grouping contact metamorphic deposits as contact-de- 
 posits, recognized their individual character, as shown by the 
 examples given under that head in his classification, though he 
 gives no details of occurrence nor shows their difference from 
 those of the Kristiania type. 
 
 Despite this very general recognition of such deposits, no dis- 
 crimination was attempted until Yon Groddeck defined contact- 
 deposits of the Kristiania type, showing that they formed a 
 distinct and separate class of ore-deposits, differing in occur- 
 rence and genesis from all other types. The contact meta- 
 morphic deposits discussed herein resemble those of this class, 
 though excluded from it by definition, J as they are not contact- 
 deposits, though quite as truly a result of contact meta- 
 morphism. There is a marked correspondence between the two 
 types as regards mineral association and genesis ; but the struc- 
 tural differences are so important, and have so marked a bear- 
 ing, not alone on the theory of their genesis but, also, in the 
 working of the deposits and a determination of their value as 
 mines, that they merit a full discussion. 
 
 Geographic Distribution. 
 
 Ore-deposits in the zone of contact metamorphism are quite 
 common, though in the past the more noted mines have been 
 fissure-veins whose contents may or may not have been derived 
 from contact metamorphic deposits. As great, massive, igne- 
 
 * " Character and Genesis of Certain Contact-Deposits," Genesis of Ore-Deposits, 
 p. 716; also, Trans., xxxi., 226. 
 
 f Ore-Deposits of the United States, 3d ed., 1902, p. 58. 
 
 J Lindgren, Genesis of Ore-Deposits, p. 717, under heading Position ; also, 
 Trans., xxxi., 227. 
 
374 ORE-DEPOSITS NEAR IGNEOUS CONTACTS. 
 
 cms intrusions are most commonly found in regions where pe- 
 riods of great volcanic activity have been followed by uplift 
 and profound erosion, it is in mountainous districts that most 
 contact metamorphic deposits occur. 
 
 No attempt will be made to discuss or describe contact-de- 
 posits of the Kristiania type. The Jimenez copper-mine, Chi- 
 huahua, Mexico,* is a typical example of this class, and the 
 Indian Queen mine at Birch Creek, in Beaverhead county, 
 Montana, is another example, in which later fracturing and en- 
 richment have taken place. 
 
 Examples of the Cananea type of contact metamorphic de- 
 posits are less common, though the two noted herein are now 
 rated among the most productive mines. 
 
 Copper-Deposits Cananea Type. 
 
 British Columbia. The ore-deposits of the Boundary district 
 of British Columbia have been described by Mr. S. F. Emmons 
 as also of contact metamorphic origin. The deposits are on 
 Boundary Creek, near Greenwood, and comprise the workable 
 ore-bodies of several producing mines. The ores carry 2 to 5 
 per cent, copper and a few dwts. of gold per ton ; but as they 
 occur in very large bodies and are metallurgically docile, they 
 are profitably exploited. The ore-bodies occur in belts of met- 
 amorphosed limestones, 2 miles or more wide, that are ad- 
 jacent to a mass of light-gray, coarsely crystalline, granitic 
 diorite. 
 
 The ores consist of sulphides of iron and copper, associated 
 with considerable magnetic oxide of iron, of contempora- 
 neous formation. These minerals occur in a gangue of al- 
 tered limestone consisting of amphibole, garnet, vesuvianite, 
 zoisite, etc. Microscopic study shows that these are the re- 
 sult of metasomatic replacement, during which a granular lime- 
 stone has been converted into an amphibolitic rock with the 
 simultaneous development of sulphides and magnetite. From 
 Barrell's studiesf I regard it as probable that the action has 
 been the alteration of an impure limestone by normal contact 
 
 * Weed, Trans., xxxii., 396, "Notes on Certain Mines in the States of Chihua- 
 hua, Sinaloa and Sonora, Mexico." 
 
 f Am. Journ. Sci., vol. xiii., April, 1902, p. 279 et seq. 
 
ORE-DEPOSITS NEAR IGNEOUS CONTACTS. 
 
 375 
 
 metamorphism. This is also the view held by Dr. A. R. 
 Ledoux.* 
 
 According to Emmons,f the ore-bodies are irregular in oc- 
 currence, and graduate insensibly in every direction, inward as 
 well as outward, from ore into low-grade rock, the fracture- 
 planes or walls failing to definitely enclose the ore-shoots or 
 define their direction. In this respect they resemble the south- 
 ernmost ore-bodies at Cananea, but differ from the Cananea 
 type, in which relatively thin beds of impure limestone alter- 
 nate with less congenial varieties of this rock, so that the ore- 
 strata are fairly sharply defined. The Greenwood deposits are 
 cut by dikes, which may be regarded as the final result of igne- 
 ous action. As I stated in discussing the genesis of this class of 
 ore-bodies, the process of metamorphism is complete before the 
 magma solidifies ; and if the sulphides were introduced during 
 metamorphism they would be cut by the aplite and lamprophyric 
 dikes that represent the final fissuring of the outer mass of 
 chilled magma and filling of fissures from the molten interior. 
 
 A later and more detailed account of the ore-deposits of this 
 district by BrockJ gives further details, and, in part, confirms 
 these observations of Emmons, though presenting very im- 
 portant additions. The ore-deposits are notable for their great 
 size, the Mother lode ore-body being 140 feet thick and devel- 
 .oped for 1180 feet in length and 500 feet in depth; the Knob- 
 Ironsides lode is much larger, being 800 feet wide, proven for 
 800 feet in depth, and several thousand feet in outcrop. Brock 
 distinguishes two types, a pyritic, characterized by pyrrhotite, 
 with chalcopyrite and iron pyrites, and a magnetitic type, with 
 magnetite and copper pyrites. Though segregated in places, 
 the chalcopyrite is remarkably evenly distributed through the de- 
 posits. " Rarely do magnetite and pyrrhotite occur in the same 
 deposit." Specular iron is found sparingly in a half-dozen 
 properties. Occasionally marcasite, and sometimes arseno- 
 pyrite, galena, zinc-blende and molybdenite, are present. Te- 
 trahedrite occurs in one mine and bismuthinite in another. 
 
 * " Production of Copper in the Boundary District," Canadian Min. InsL, vol. 
 v., p. 172. 
 
 f Genesis of Ore- Deposits, p. 757. 
 
 J Canadian Mining Institute, vol. v., p. 365, March, 1902. 
 
 $ Brock, Canadian Min. InsL, vol. v., p. 368. 
 
376 
 
 ORE-DEPOSITS NEAR IGNEOUS CONTACTS. 
 
 The description of the gangue shows red and green garnet 
 and epidote to be abundant in and near the veins, " and the 
 progress of their formation may be observed in many points 
 in all stages, not only when limestone but also when greenstone 
 and granite form the country- rock,"* thus apparently contra- 
 dicting the hypothesis that such contact minerals result only 
 from the metamorphism of impure limestones. At the Mother 
 lode the marmorized limestones contain the above-mentioned 
 minerals, but the mass of the rock consists of felty actinolite. 
 The gold values are commonly in the chalcopyrite. Magnetite 
 and pyrrhotite, when occurring alone, are commonly almost 
 barren, the Winnipeg pyrrhotite being an exception. There 
 is a lack of veins and stringers enriching the main ore-body, 
 but there appears to be an enrichment of the ore where dikes 
 cross it. The ores are very low-grade, a representative ore 
 carrying copper 1.95 per cent, iron 14 per cent, lime 17 per 
 cent, silica 39 per cent, with 0.119 ozs. gold per ton and 0.44 
 ozs. silver. 
 
 Brock considers the ore-bodies to be composite veins " formed 
 by mineralizing solution traversing the country-rock, princi- 
 pally along fissures or zones of fissures in which they deposit 
 the economic minerals and from which they replace with their 
 mineral contents, particle by particle, sometimes completely, 
 the original material of the country-rock." In the same paper 
 he says, however, that " there seems to be strong reason for 
 supposing the deposits to be connected with eruptive after- 
 actions." 
 
 Mexico. The Cananea copper-deposits, which, during the 
 last year (1901), have been so vigorously exploited that they 
 have produced 140,000,000 Ibs. of copper, are situated in the 
 Cananea mountains, 50 miles southwest of Bisbee, Arizona, 
 and 30 miles south of the international boundary-line. This 
 mountain range is from 6 to 12 miles wide and 25 miles long. 
 It rises abruptly from flat or gently-inclined prairies to a height 
 of 8000 feet above sea-level, or 4500 feet above the plain. The 
 range extends in a northwest and southeast direction, and it is 
 bisected, by the low Puertecitos Pass, into two nearly equal 
 parts. The ore-deposits occur in the southern portion of the 
 range. 
 
 * Brock, loc cit. This author examined no thin sections, however. 
 
ORE-DEPOSITS NEAR IGNEOUS CONTACTS. 377 
 
 The mountains consist of the dissected and denuded remains 
 of an old volcano, probably of late Tertiary age. At Puerteci- 
 tos Pass there is a central core of normal granite surrounded 
 by massive andesite and baked and altered sedimentary rocks. 
 The main crest of the mountains southward is formed of mar- 
 ble, hornstone, quartzite and garnet-epidote rocks, resulting 
 from the intense alteration of impure limestone by the heat of 
 igneous intrusions. These rocks are cut by large intrusions of 
 quartz-porphyry and small diabase dikes. The entire range is 
 flanked by foothills and mesas formed of well-bedded andesitic 
 tuffs dipping away from the range at angles of from 10 to 30, 
 and representing the fragmental products of the old volcano, 
 which once formed its cone. 
 
 The ores consist of chalcopyrite, together with copper glance, 
 pyrite, zinc-blende, and a little galena. They occur in deposits 
 which are, in part, beds of altered limestone tilted at steep 
 angles and richly impregnated with metallic sulphides, and, in 
 part, deposits formed in fractures along and across the quartz- 
 porphyry and quartzite without any very definite relation to 
 the igneous contact. 
 
 Near the Ronquillo smelter of the Greene Consolidated 
 Copper Company the ore-bodies of the group of mines em- 
 bracing the Capote, Yeta Grande, Cobre Grande and Oversight 
 properties occur mainly along these fractures. . The outcrops 
 are great ridges of iron gossan, traceable for Ions: distances, 
 and the ore-bodies are very large, one in the Capote being 165 
 feet by 125 feet, and oval in cross-section. These " veins " con- 
 form, however, in dip and strike, to the ore-bodies that consist 
 of beds of altered limestone. 
 
 The ore-deposits continue for a distance of about 8 miles 
 along the central portion of the range, and north of the Ron- 
 quillo group of mines, just mentioned, they pass into metamor- 
 phosed limestones impregnated with copper. In the exposures 
 near the northerri part of this area the ore is seen to be con- 
 fined almost entirely to the garnet-epidote-diopside rocks, 
 which occur interbedded with hornstones, marble, etc. ; and, as 
 will be shown later, this accords with the views of their genesis 
 presented herein. In addition to the ore-bodies in course of 
 exploitation, there are many beds that contain much galena and 
 zinc-blende. 
 
378 ORE-DEPOSITS NEAR IGNEOUS CONTACTS. 
 
 These copper-ores are usually very low in gold- and silver- 
 content ; but there are certain exceptions to this, notably the 
 Alfreina mine, the ores of which carry high values in gold. 
 
 The development work at most of the northerly properties has 
 not yet reached the sulphide ores. At the Puertecitos mine the 
 working-tunnel passes through a bed 30 feet wide that carries 
 a large amount of chalcopyrite, with a little zinc and galena, 
 the ore averaging about 15 per cent, copper. This bed is 
 capped by a white marble, which, as shown elsewhere, is a rela- 
 tively impervious rock. The ore consists, approximately, of:* 
 
 Per cent. 
 
 Chalcopyrite, 25 
 
 Galena, ........... 5 
 
 Calcite, . . .... . .35 
 
 Actinolite, 20 
 
 Quartz, ........... 15 
 
 The chalcopyrite and galena show an evident association with 
 the dull green, finely fibrous actinolite. The sulphides occur 
 in grains up to three-fourths of an inch across ; they are not 
 crystalline, but of irregular form and of compound structure 
 (i.e.j not of uniform crystalline orientation). The actinolite 
 and calcite occur in patches, but the quartz is idiomorphic, and 
 the crystals penetrate both the minerals just mentioned. The 
 ore, how r ever, appears to cover and enclose the quartz. 
 
 Germany. Richard Beck has described very fully a deposit of 
 this structural type in his recent book, and I therefore insert a 
 translation of his description in full :f 
 
 " 1. The ore-deposits of the contact area of the granite of Berggiesshiibel, 
 in Saxony. 
 
 "The ore-deposits of Berggiesshiibel, in the so-called Elbe Valley moun- 
 tains of southeastern Saxony, represent a specially well-studied and typical 
 example of contact metamorphic ore-occurrences, and for this reason will be here 
 first described, and in some detail, although they have long since lost their eco- 
 nomic importance. 
 
 "At Berggiesshiibel, in the moderately uptilted schist rocks, several granite 
 stocks appear, among which the one of Markersbach occupies the foremost place 
 by its size and by the extent of its contact phenomena. Close to its western bor- 
 der lies the mine district of the old mining town of Berggiesshiibel. 
 
 "The outcrops of the various beds of the Phyllite formation and the lower 
 Silurian formation are there distinctly seen terminating at the border of the 
 
 * These figures are based upon estimates made by measurement of specimens 
 and thin sections of the ore. 
 
 f Lehre von den Erzlagerstatten, Leipzig, 1901, p. 609. 
 
ORE-DEPOSITS NEAR IGNEOUS CONTACTS. 379 
 
 granite, and various exposures and other evidences prove that the surface of the 
 eruptive stock dips at a low angle under the schists thus traversed. The sedi- 
 mentary rocks thus adjoining and, in part, overlying the granite have been sub- 
 jected to strong contact metamorphosis. 
 
 "Turning specially to the Silurian formation, we find that the clay slates 
 were changed into hornstone, horn schists and knot-schist, while the diabase 
 tuffs, the so-called Schalsteine, were changed into various kinds of hornblende 
 schists, especially actinolite schist, also banded salite-hornblende schist. The 
 limestone layers, however, intercalated in the clay schists and especially in the 
 tuffs, were turned into marble beds, or, in part, into salite-garnet rock, or, finally, 
 into magnetic iron beds. 
 
 "These limestone strata may be followed from NW. to SE. in their strike, for 
 long distances, in many good exposures, deep limestone quarries and natural 
 outcrops, from Maxen across the villages of Biensdorf and Gersdorf, to the point 
 where they enter into the contact-area of the granite. Over this whole distance, 
 however, these limestones are devoid of ore, except a few quite insignificant beds 
 of red and brown hematite, which occur in quite limited patches, for example, at 
 Nenntmannsdorf , at the boundary between limestones and schists. 
 
 "In the contact-area, however, the calcium carbonate has been partly or en- 
 tirely displaced from these beds, and replaced by secretions from immigrant sili- 
 cate and ore-solutions, such a$ salite and garnet, as well as magnetite and various 
 sulphide ores. The distribution of the marble, calcium silicates and ores within 
 the beds is very remarkable and diverse, and throws a bright light on the manner 
 of this replacement metamorphosis. 
 
 "First let us note that the marble still shows clearly the stratification of the 
 originally dense Silurian limestone out of which it was formed. Even the altera- 
 tion between thin limestone beds and diabase tuffs, which occurs not infrequently 
 in the Silurian at that place, may repeatedly be observed in the contact-area 
 between marble and hornblende schist, except that the limestone, wherever it 
 formed thin streaks and layers, has for the most part been changed throughout 
 into a light-green pyroxene rock. 
 
 ' ' In the larger limestone layers in the contact-area one notices not infrequently 
 a structure consisting of separate marble bands, separated by layers of salite- 
 garnet rock, and also a thin-stratified alteration between garnet-rock and mag- 
 netic iron-ore. More usually, however, quite irregular nests and lumps of 
 magnetic iron-ore lie in the midst of the marble, cutting across its stratifica- 
 tion. In such cases they frequently penetrate into the marble with jagged or 
 stringer-like projections. At some places, as, for example, in the limestone 
 workings near the Hermann shaft, even irregularly vein-shaped masses of mag- 
 netic iron-ore were observed in the midst of the limestone. On the whole, the 
 ore clings especially to the lower boundary of the marble bed, frequently swell- 
 ing up from there, cutting with its upper boundary across the strata of the 
 marble and entirely replacing it for long distances, in some places for a width of 
 5 m. Finally, the ore-bodies are at times traversed by ramified stringers of the 
 garnet- rock, forming a network among themselves. It thus appears that the 
 ore-mass was broken, but that the infiltration of the solutions furnishing the 
 garnet continued after this mechanical disturbance. That phenomena of disrup- 
 tion took place during the contact metamorphosis, at the time of the transition 
 of the dense limestone into marble, is furthermore indicated by the frequent 
 stringers of coarsely foliated calcspar, which traverse the blackish marble as 
 white bands. They seem to have been formed during the process itself, as 
 primary stringers. Occasionally they carry some garnet. 
 
380 
 
 ORE-DEPOSITS NEAR IGNEOUS CONTACTS. 
 
 " Other ores besides magnetic iron take part in the composition of the ore- 
 beds of the locality, especially copper minerals, such as chalcopyrite, erubescite, 
 copper glance, rarely gray copper-ore. From these have resulted a number of 
 secondary copper-ores, malachite, etc. Less frequent admixtures are iron pyrites, 
 arsenical pyrites,"galena and zinc-blende. 
 
 " While the subsequent introduction of all these ores into the limestone beds of 
 that locality is beyond question, doubts may still be entertained concerning the 
 origin of the metalliferous solutions. Two theories may be advanced in regard 
 to this point. One theory is, that the metallic compounds in question were origi- 
 nally finely distributed through the adjoining rock, especially in the diabase 
 tuffs, and were only later concentrated through the contact metamorphosis, through 
 redeposition in the limestone by means of mineralizing agents derived from the 
 granite, after expulsion of the carbonic acid of the calcium carbonate. The 
 other theory is that these metallic compounds were directly brought up with the 
 granite from great depths, and were infiltrated into the adjoining rock in solution 
 in the over-heated water accompanying the eruption. The latter theory has the 
 greater probability, since all the hornblende schists and hornstones are rich in 
 iron at the contact also, much richer, in fact, than elsewhere, aside from the 
 contact. 
 
 FIG. 1. 
 
 'ese/er Stolln 
 
 Section through the contact zone of Rerggiesshiibel, Saxony. 
 G = Markersbach granite ; ag = andalusite-mica rock ; h = hornblende and 
 pyroxene-schists ; kn = spotted schists ; e = ore-bodies ; k = crystalline lime- 
 stone ; p = quartz-porphyry ; t = Sub-Turonian and Cenomanian. R. Beck, 
 Erzlogerstatten, p. 611. 
 
 "This is rendered still more probable by the fact that in the same district ore- 
 lodes also exist in the granite, which are characterized by copper-ores, and, in 
 part, traverse the ore-beds. They seem to represent the main channels of supply 
 for the metallic solutions emanating from the granite. 
 
 11 Finally, besides these copper-lodes, tin-bearing stringers are also known to 
 occur in the metamorphic limestone-beds of that locality. These stringers consist 
 of orthoclase, fluorspar, quartz and lithia-mica distributed in zones. Near them 
 A. "VV. Stelzneralso discovered tinstone, together with chalcopyrite and pyrite, as 
 impregnations of certain strata of the beds, consisting mainly of chlorite. 
 
 "The Markersbach granite is thus seen to be surrounded by an aureole. of 
 highly diverse metallic compounds. 
 
 " The iron-mining industry of Berggiesshiibel, formerly of some importance, is 
 now practically extinct." 
 
 Gold-Deposits. 
 
 The recognition of telluride ores in contact-deposits is, I be- 
 lieve, new. It is expressly stated by Lindgren, as a result of 
 his review of the literature on the subject and his own experi- 
 
ORE-DEPOSITS NEAR IGNEOUS CONTACTS. 381 
 
 ence, that no tellurides occur in contact-deposits.* I have 
 found several examples of this interesting type of deposit, 
 which is clearly entitled to rank as a special class in meta- 
 morphic deposits. This at once brings up the question of per- 
 manence in depth of such deposits, discussed elsewhere in this 
 paper. 
 
 Western Montana is a mountainous region in which there 
 are several great areas of granitic rocks breaking up through 
 sedimentary strata and earlier igneous rocks. Along the lime- 
 stone contacts of these granitic intrusions (batholiths) ore-de- 
 posits are often encountered, though they are rarely of any 
 great economic importance. Most commonly they are of the 
 Kristiania type, examples of which may be found at George- 
 town, Cable, and other localities west of Anaconda; in the 
 Highland Range south of Butte ; in the Indian Queen mine, on 
 Birch Creek, in Beaverhead county ; at Elkhorn, and at very 
 many localities about the granitic borders mentioned. There 
 are, however, examples of contact metamorphic deposits of the 
 Cananea type at Elkhorn and Philipsburg. 
 
 Bannack Type. The placers of Grasshopper Creek, at Ban- 
 nack, were the first great gold-placers discovered in Montana. 
 Attention was soon attracted by the ledges on the slopes above 
 the basin, in which the richest gravels occurred, and a " lode " 
 excitement, almost as fierce as that of the placer-days, followed. 
 Enormously rich ores were taken out, several mills were 
 erected, and the ground was burrowed to a shallow depth 
 wherever the pockets and streaks of rich ore occurred. Yet, 
 despite the attractive prospects and good returns, the ore-depos- 
 its have never been explored in depth, the deepest shaft being 
 about 300 feet deep. 
 
 The ore-deposits are. typical contact metamorphic deposits. 
 A central boss of diorite, about three-fourths of a mile in di- 
 ameter, is surrounded by a series of upturned Paleozoic lime- 
 stones and associated shaly rocks, dipping away from the 
 granite on all sides at angles of 10 to 45. This dome or an- 
 ticline has been eroded, and the granite now forms the surface 
 of the low central portion of a basin, whose surrounding 
 heights are formed of limestones flanked by heavily-bedded 
 
 * "Character and Genesis of Certain Contact-Deposits," Genesis of Ore-Deposits, 
 p. 717, under heading ''Constituent Minerals;" also, Trans., xxxi., 227. 
 
382 ORE-DEPOSITS NEAR IGNEOUS CONTACTS. 
 
 quartzites of Carboniferous age. The diorite intrusion, though 
 laccolithic in its general character, has a very uneven contact, 
 breaking irregularly through the limestones, and holding in- 
 cluded blocks of the latter within its mass, while tongues of 
 the igneous rock project out and penetrate the adjacent sedi- 
 mentary rock. 
 
 The limestones are highly altered about the contact; but, 
 owing to the fact that the diorite comes in contact with lime- 
 stones of varying composition, the resulting rocks differ greatly 
 in mineral constituents. In the main, these contact rocks are 
 either impure marbles or are composed of brown garnet, epi- 
 dote, calcite, and other common contact metamorphic minerals. 
 The ore-deposits, in part, follow the actual contact between di- 
 orite and contact rocks. Where limestones prevailed, the ore- 
 bodies were irregular ; tongues and chambers of ore extend out 
 into the limestone, and the ore (now oxidized) consists of 
 porous iron-stained quartz the cavities of which show the crys- 
 talline form and striations of coarsely crystalline gold-bearing 
 pyrite. Where the garnet rocks prevail the ores do not follow 
 the contact, except in a general way, but occur in the more 
 garnetiferous bands which alternate with epidotic rocks and 
 marbles and mark the alteration of beds of limestone of differ- 
 ing composition. The ore-minerals consist of telluride of 
 gold, together with some free gold, disseminated and rather 
 abundant specular iron, some pyrite and less chalcopyrite. As 
 usual, the telluride ores are spotty, occurring in rich bunches, 
 but there is also a general dissemination through the rock, and 
 all the garnet-specular-iron rock contains a few dollars per ton 
 in gold, as shown by a large number of assays. 
 
 Elkhorn. The Elkhorn district is situated in central Mon- 
 tana, about half-way between Helena and Butte. The ore- 
 deposits occur at the eastern border of the great granite 
 area that covers the greater part of Jefferson county. At 
 Elkhorn this granite cuts abruptly across the ends of tilted 
 sedimentary beds embracing a great variety of rock types 
 of different geologic ages. The granite is of Tertiary age, 
 and later than the fragmental andesitic rocks which form 
 the neighboring peaks and which rest upon the sediments. 
 The principal ore-deposit, that of the Elkhorn mine, is not a 
 contact metamorphic deposit, but a " saddle " deposit formed in 
 
ORE-DEPOSITS NEAR IGNEOUS CONTACTS. 383 
 
 the axis of a steeply dipping fold, between an altered shale 
 (hornstone) hanging-wall and a crystalline dolomite crushed 
 along the fold. The sedimentary rocks near the igneous con- 
 tacts are highly altered, and are good examples of contact 
 metamorphic rocks. Iron ore-deposits on Elkhorn Peak are 
 contact-deposits of the Kristiania type, and there are several 
 true contact-deposits of pyrite of too low-grade to work. 
 
 A half mile northwest of the Elkhorn mine, on the western 
 slope of a steep and wooded ridge composed of altered sedi- 
 mentary rocks, lies the Dolcoath mine, a property as yet in the 
 prospect stage. Shipments of sorted ore have been made, and 
 the oxidized ore shows native gold flecking the rock. The 
 ore is a bed of garnet-diopside rock (altered limestone) 15 to 
 18 inches thick, dipping at 55 to the east and carrying gold in 
 bismuth sulphide (bismuthinite) and bismuth telluride (tetra- 
 dymite). This ore stratum is conformable with the adjacent 
 beds, but differs from them in composition. The rocks have 
 been studied by Dr Barrell,* who determines their approxi- 
 mate composition to be as follows : . 
 
 Ore Stratum. 
 
 
 Footwall. 
 
 
 Hanging-Wall, 
 
 
 
 . 45 
 
 Diopside 
 
 ... 30 
 
 Augite 
 
 5 
 
 
 . 40 
 
 Garnet 
 
 ... 10 
 
 Biotite 
 
 25 
 
 Calcite 
 
 12 
 
 Basic feldspar 
 
 60 
 
 
 66 
 
 Sulphides, with gold 
 
 . 3 
 
 
 
 Sulphides, no gold 
 
 .. 4 
 
 
 100 
 
 
 100 
 
 
 100 
 
 Samples from the sacked ore of the upper levels yielded 
 $156.00 per ton in gold, but average samples from the bottom 
 level, made during an expert examination of the property by a 
 Butte mining engineer, yielded but $4.50 per ton in gold. 
 
 Similkameen Type (British Columbia). The Nickel Plate mine, 
 which promises to be a great gold-producer, is situated near 
 the Similkameen river, Osoyoos mining division, west of Pen- 
 ticton.f The ore consists of a gar net-calcite-epi dote rock, 
 whose mineralogical comppsition and geological occurrence 
 both show that it is an altered impure limestone. The ore- 
 mineral is arsenical pyrites, disseminated through this gangue 
 
 * Op. cit., Am. Jour. Sri., April, 1902, p. 295. 
 
 f Report of the Minister of Mines of B. C. for 1900, p. 883. 
 
384 ORE-DEPOSITS NEAR IGNEOUS CONTACTS. 
 
 rock and concentrated in the high-grade ores, which occur in 
 extraordinarily rich bands. Mr. H. V. Winchell informs me 
 that the ore-body is of contact metamorphic type. The speci- 
 mens which he collected show the arsenopyrite to be confined, 
 almost exclusively, to the garnetiferous portion of the ore, the 
 green (epidotic ?) portion being very low-grade. 
 
 So far as known, arsenopyrite has never before been founa 
 in contact-deposits. It has, however, been observed in certain 
 pegmatitic veins which are believed by some observers to be of 
 pneumatolytic origin.* 
 
 CHANGES IN ROCKS DUE TO CONTACT METAMORPHISM. 
 
 General Effect. 
 
 It is a well-known fact that certain intruded igneous rocks 
 have exercised a profound influence upon the wall-rocks con- 
 fining and adjoining them, while other types of igneous mag- 
 mas have produced only a slight effect. To a large degree 
 this alteration, or contact metamorphism, is due, as has been 
 shown by Id dings, f to the length of time the adjacent rocks 
 have been heated. If the conduit of a volcano is broken 
 through sedimentary rocks, and this conduit serves as a vent 
 for a prolonged period of time, and is finally filled by magma 
 that cools as a coarse-grained rock, it is evident that* these con- 
 ditions favor extreme metamorphism of the adjacent material. 
 If a small sheet or dike breaks through sedimentary strata, and 
 is promptly chilled, the magma exercises but little apparent 
 influence upon the wall-rock. It is, therefore, largely a ques- 
 tion of physics. The great intrusion takes a long time to cool ; 
 the magma crystallizes as a granular rock, and the adjacent 
 rocks are heated for a long period. It is partly, therefore, a 
 question of the mass of the magma cooling. Professor Kemp { 
 has succinctly stated the known facts upon this subject in his 
 recent paper upon the " Role of Igneous Rocks." On the other 
 hand, although the result of such long-continued heating of 
 
 * O. A. Derby, "Notes on Brazilian Gold-Ores," Trans., xxxiii., 282. 
 f " Electric Peak and Sepulchre Mountain," 12th Ann. Rept. U. S. Geol. Survey, 
 Pt. I., pp. 569-664. 
 
 J Genesis of Ore-Deposits, p. 692 ; also, Trans., xxxi., 180. 
 
ORE-DEPOSITS NEAR IGNEOUS CONTACTS. 385 
 
 wall-rocks has been recognized by geologists for many years, 
 the fact that different rocks show varying effects has been com- 
 monly imputed to the nature of the rock, and until recently 
 there has been no lucid discussion of the effect of contact met- 
 amorphism upon sedimentary rocks. Quite recently there ap- 
 peared a paper by Prof. Joseph Barrell, entitled " The Physi- 
 cal Effects of Contact Metamorphism."* In this paper it was 
 shown that the metamorphism of sedimentary rocks by the 
 heat of igneous masses is accompanied by the liberation of 
 enormous volumes of gases, with attendant shrinkage of vol- 
 ume and the formation of vein-fissures and impregnation de- 
 posits. Several writers, particularly Vogt, Kemp, and Lindgren, 
 have recently drawn attention to the metasomatic and impreg- 
 nation effects of the mineralizing vapors coming from the cool- 
 ing igneous magma and carrying dissolved metallic minerals 
 along favorable channels in the contact zone. In addition to 
 this eruptive after-action of Vogt, there is a more or less com- 
 plete expulsion of carbon dioxide and combined water from the 
 sedimentary rocks, accompanied by the formation of new min- 
 erals and the induration of the rocks. As is well known, the 
 alteration of pure sedimentary rocks by contact metamorphism 
 is as follows : Sandstone to quartzite ; clay-stone, or shale, to 
 hornstone ; limestone to marble; but as, in nature, these pure 
 rocks seldom exist, and it is the impure limestones, sandstones 
 and shales which are most common, the alteration of such rocks 
 produces a more or less striking metamorphism the material 
 recrystallizing as garnet, wollastonite, epidote, etc. 
 
 Changes in Mass, Volume, and Mineral Composition. 
 
 As the chemical elements remain the same in the altered as 
 in the unaltered rocks, save for the greater or less expul- 
 sion of water and carbon dioxide, it is possible to tabulate 
 the mineralogic changes. This has been done by Professor 
 Barrell, and from his table it is possible to work out not only 
 the original composition of the unaltered sediment, but the 
 changes in mass and volume which have taken place in the 
 process of metamorphism. 
 
 The greatest changes in volume are due to escaping gases 
 
 * Am. 'Jour. Sci., vol. xiii., April, 1902, p. 279. 
 25 
 
386 ORE-DEPOSITS NEAR IGNEOUS CONTACTS. 
 
 and vapors. His conclusion that metasomatic additions dur- 
 ing this metamorphism are prevented by the internal pressure 
 of the escaping gases is not regarded as correct for all cases, 
 though it is based upon the belief that by the time the pres- 
 sure is relieved sufficiently to permit the ingress of heated 
 waters or mineralizing vapors from the adjacent magma the 
 rock is recrystallized ; also, as a result of the hydrostatic pres- 
 sure of the still liquid magma, it is usually dense. While it 
 may be true, as stated by Barrell, that metasomatic infiltration 
 of the metamorphic strata does not usually take place, yet in- 
 stances have come within the observation of the writer where 
 such action is very pronounced. Differential shrinkage has 
 given the strata the porosity of a burned brick, and, as aptly 
 noted by Barrel], the analogy is the more appropriate since in 
 these cases the action is one of thermal metamorphism, without 
 sufficient pressure to result in a close texture. Two instances 
 are given by Barrell, both in the Elkhorn region of Mon- 
 tana, one already quoted. The conditions in the region are 
 particularly favorable for a study of the varying effects of the 
 thermal metamorphism caused by the intrusion of a large 
 igneous mass into sediments of widely varying composition. 
 The granite mass cuts across tilted strata whose inclination 
 favors alteration, and whose wide variety of composition results 
 in striking differences in the porosity of the altered rock. In- 
 asmuch as the altered sediments are on top of the granite, 
 they have not been subjected to the same pressure that would 
 have changed them if they had been part of the rock enclos- 
 ing the intrusion. Moreover, the pressure would be trans- 
 mitted by the denser layers, and would not be transverse to 
 the borders. 
 
 A consideration of the physical conditions involved shows 
 that in many instances the porosity induced by thermal meta- 
 morphism of rocks forming the side-walls of igneous intru- 
 sions is probably counteracted by the hydrostatic pressure of 
 the magmas. It has been found that metamorphism of the 
 sedimentary rocks would be practically completed before solid- 
 ification of the magma begins,* and completed while the mag- 
 ma was able to act hydrostatically and transmit lateral pressure. 
 
 * Barrell, op. cit., p. 294. 
 
ORE-DEPOSITS NEAR IGNEOUS CONTACTS. 387 
 
 Under these conditions the shrinkage of the vertical walls 
 would be largely lateral, and result in a corresponding lateral 
 expansion and a vertical subsidence of the magma. Where, 
 however, as is so commonly the case, great masses of granite 
 are capped by relatively thin layers of altered sediments, as, 
 for example, in the region about Helena, Montana, the sedi- 
 ments above the magma, though subjected to pressure, would 
 transmit this pressure along the heavier and more competent 
 beds ; while the intervening, weaker members would retain the 
 porosity due to recrystallization and escape of gases, except, of 
 course, at the immediate contact with the magma. It is evi- 
 dent that in such cases the porosity of the strata near the 
 igneous inclusion favors the escape of pneumatolytic gases 
 along and through the porous strata. 
 
 GENESIS OF CONTACT METAMORPHIC DEPOSITS. 
 Cause of Contact Metamorphism. 
 
 That contact metamorphism is due to intrusive masses of 
 molten magma is now generally accepted. The usual theory 
 advanced is that the heat of the magma, together with the 
 watery vapors given oft by it, have caused the metamorphism. 
 This is the explanation advanced by both Lindgren and Yogt. 
 The latter has quoted the Swedish physicist, Arrhenius, as 
 showing that the physical and chemical action of watery vapors 
 upon a magma proves such vapors to be competent to extract 
 the heavy metals from the magma. Barrell, however, has 
 shown that the intrusion of magma heats the adjacent sedi- 
 mentary rocks to very high temperatures, generating enormous 
 volumes of gas and watery vapor by changes caused in the 
 nature of the sedimentary rocks, and, moreover, that the pro- 
 cess of recrystallization is complete before the magma cools. 
 This latter conclusion, reached from a study of the physico- 
 chemical actions involved, is confirmed by the field-evidence at 
 Elkhorn, Mont., where tongues and dikes of the igneous rock 
 penetrate the contact rocks, and accounts for similar dikes which 
 at Boundary Creek, B. C., cut the contact ore-bodies. It is, 
 therefore, not necessary to assume that watery vapor from the 
 cooling igneous mass has played the only part in the metamor- 
 phism. 
 
 Whether we do or do not accept this statement as completely 
 
388 ORE-DEPOSITS NEAR IGNEOUS CONTACTS. 
 
 proven, it must be admitted that the effect of the igneous 
 magma upon its confining walls is not limited to this first met- 
 amorphism of the sedimentary rock. The molten magma gives 
 off vapors, pneumatolytic vapors they have been called, and 
 that these escape into the adjacent rocks we have abundant 
 evidence. As some geologists appear to question our knowl- 
 edge concerning this action, it may be well to summarize the 
 known facts concerning the gaseous emanations of igneous 
 rocks. At present our knowledge of these is derived from (1) 
 analyses of the gaseous emanations of volcanoes and lava- 
 flows; (2) analyses of the gases occluded in cold rocks; (3) 
 analyses of the sublimation-products formed by fumaroles ; and 
 (4) evidence of contact metamorphism of included masses of 
 sediments entirely surrounded by the igneous rock. 
 
 Concerning the first of these proofs, there is considerable 
 direct positive evidence furnished by competent observers and 
 chemists. This has been summarized by Geikie,* who states 
 that hydrochloric acid is evolved in abundance from the clefts at 
 Vesuvius ; also vast quantities of free hydrogen or combustible 
 compounds of this gas are given off from Vesuvius, and were 
 distinctly recognized by Fouque in the eruptions of Santorin.f 
 These gases, when studied spectroscopically, were found to 
 contain traces of chlorine, soda and copper. Analyses, by 
 Fouque, of the gaseous emanations were found to contain 
 abundant free oxygen, as well as hydrogen, and one analysis 
 
 gave the results in column I. : 
 
 i. ii. 
 
 Carbon dioxide, . .V. . . . 0.22 15.38 
 
 Oxygen, , :. .. - . .... 21.11 13.67 
 
 Nitrogen, . .... . . . 21.90 54.94 
 
 Hydrogen, 56.70 8.12 
 
 Marsh gas (methane), . . . . . .07 5.46 
 
 Argon, . . . . . . . . 0.71 
 
 In column II. is given the analysis by Moissan of the gas 
 collected by Lacroix from a fumarole on the Riviere Blanche, 
 Martinique, whose temperature was high enough to melt lead 
 rapidly, but not zinc (i.e., about 400 C.). An abundance of 
 sulphur and ammonium chloride was deposited about it.J 
 
 Fouque infers that the water vapor of volcanic vents may 
 
 * Manual of Geology, p. 188. f Santorin et ses Eruptions, p. 225. 
 
 Comptes Rendus, cxxxv. 1085, 1902. \ Santorin et ses Eruptions, p. 225. 
 
ORE-DEPOSITS NEAR IGNEOUS CONTACTS. 389 
 
 exist in a state of disassociation from the molten magma when 
 lavas rise. Fluorine and iodine have likewise been observed. 
 
 In a recent lecture, Prof. Eduard Suess* has directed atten- 
 tion to the gaseous emanations of volcanoes, and indicated 
 their part in the formation of mineral veins. After describing 
 his own observations at Vesuvius, he says : 
 
 " Turning now to the gases accompanying the eruptions. 
 After steam, chlorine and gases containing sulphur are the 
 most important, and carbonic acid gas comes next. Their oc- 
 currence follows a definite law. So far as it has been possible 
 to approach them, all fumaroles actually within vents contain 
 steam; but the hottest fumaroles (over 500 C.) on the surface 
 of cooling lava-streams, where approach is easier, are dry. In 
 the emanations from these high-temperature fumaroles are 
 found chlorine compounds, and along with them fluorine, 
 boron and phosphorus, substances which are the first to disap- 
 pear as the temperature of the fumarole sinks. Sulphur per- 
 sists longer, often combined with arsenic. Carbonic acid is 
 given off freely till a much later stage, sometimes till the fuma- 
 role is comparatively cool, notwithstanding that it is observed 
 in the hottest dry fumaroles. Fumaroles in different < phases 
 of emanation ' may occur quite near one another. The steam 
 of the volcano cannot be derived from vadous infiltration ; for, 
 if it is, whence the carbonic acid ? Both must come from the 
 deeper regions of the earth ; they are the outward sign of the 
 process of giving off gases which began when the earth first 
 solidified, and which to-day, although restricted to certain 
 points and lines, has not yet come to a final end. It is in this 
 manner that the oceans and the whole vadous hydrosphere 
 have been separated from the solid crust. Volcanoes are not 
 fed by infiltration of the sea, but the waters of the sea are in- 
 creased by every eruption." 
 
 Concerning the analyses of the gases occluded in the cold 
 rocks, the evidence is not so satisfactory. From the study of 
 microscopic slides it is well known that gaseous and watery 
 inclusions occur in crystalline rocks, and various attempts have 
 been made by chemists to estimate the quantity of included 
 vapor so held. Recently, Dr. M. "W. Travers, in a paper on 
 the " Origin of Gases Evolved on Heating Mineral Substances, 
 Meteorites, etc.," has shown " that in the majority of cases 
 
 * Geographical Journal, London, vol. xx. , p. 520, November, 1902. 
 
390 ORE-DEPOSITS NEAR IGNEOUS CONTACTS. 
 
 where a mineral substance evolves gas under the influence of 
 heat, the gas is the product of the decomposition or interaction of 
 its non-gaseous constituents at the moment of the experiment."* 
 
 Notwithstanding this fact, however, we have abundant evi- 
 dence, in the analyses of obsidian and pitchstone, of the pres- 
 ence of a considerable proportion of water ; and it is well 
 known that these rocks change into pumice on heating. Also 
 the presence of fluorite in the dense and almost glassy phono- 
 lites of Montana is to be remarked here. The Hawaiian 
 Island lavas, though highly vesicular, contain practically no 
 water, and Whitman Crossf has noted the absence of steam 
 from the lava cauldron of Kilauea, although there was an abun- 
 dance of sulphurous vapors and brown vapors of an unknown 
 composition given off from clefts immediately adjacent to the 
 lava lake. 
 
 Attention might also be directed to the recent work of Ar- 
 mand Gautier,J in which he shows that granite and other 
 crystalline rocks evolve large quantities of vapors when heated. 
 
 Third, the analyses of the sublimation products found about 
 fumaroles show conclusively that metallic salts, as well as non- 
 metallic, are given off by the igneous emanations, or result 
 from reactions between the escaping vapors and the solids 
 with which they come in contact. Besides sulphur, chlorides 
 of sodium, potassium, iron, copper and lead also occur, and 
 specular iron, oxide of copper and iron chloride have been ob- 
 served by Geikie and Fouque. 
 
 Fourth, the evidence of contact metamorphism, as studied in 
 included masses, affords direct proof of the action of pneuma- 
 tolytic vapors when the original composition of the included 
 mass can be known with any certainty. Under such conditions 
 one can exclude the reactions indicated in the case of the con- 
 fining walls of the magma, and there is no doubt that in many 
 cases there is a direct migration of material, particularly sili- 
 cates, also fluorine and chlorine, together with copper sulphide 
 and iron oxide, into the included masses. Such masses have 
 been studied by Lindgren|| at the Seven Devils district of 
 
 * Proc. Royal Soc., vol. Ixiv., p. 142. (Read Nov. 24, 1898.) 
 f Verbal communication. 
 
 j Zeit. Prak. Geol, vol. ix., p. 383, 1901. | Geikie, Manual of Geology, p. 188. 
 || ' ' Character and Genesis of Certain Contact-Deposits," Genesis of Ore-Deposits, 
 p. 722; also, Trans., xxxi., 232. 
 
ORE-DEPOSITS NEAR IGNEOUS CONTACTS. 391 
 
 Idaho, and by Kemp in the San Jose district, and Tamaulipas, 
 Mexico. 
 
 Inasmuch as included fragments of pure limestone are 
 changed to garnet-rock and impregnated with metallic sul- 
 phides, vesuvianite, axinite, etc., whose constituents are not 
 normal to any of the original rocks surrounding the intrusion, 
 the evidence is satisfactory that there was a migration of mate- 
 rial in the form of vapor from the igneous magma into the ad- 
 jacent rocks. 
 
 From this evidence we are justified in assuming that there is 
 a series of " eruptive after-effects," as Yogt has called them, 
 which start at the moment of the intrusion and continue until 
 the rocks have completely cooled, and which grade one into 
 the other. 
 
 On the other hand, if the resulting metamorphic rocks are 
 porous, as in certain cases we know them to be, the vapors 
 from the cooling magma will be " blown in " (to use Yogt's 
 term), and ore-deposits may be formed in this way. 
 
 Professor Suess, in the lecture already quoted, has called 
 renewed attention to the fact that mineral veins are to be re- 
 garded as the result of waning phases of volcanic (igneous) 
 phenomena. " Hot springs may be taken as the latest phase of 
 a whole series which led up to the present deposits of ore." His 
 whole paper is an argument against the theory that either the ma- 
 jority of ore-deposits or of hot springs are of meteoric derivation. 
 
 That gaseous emanations rising through fissures toward the 
 earth's surface can mingle with ordinary meteoric ground-water 
 must be admitted, and it is believed that much of the discus- 
 sion between those who advocate the deposition of ores by cir- 
 culating ground-waters, deriving their metallic contents from 
 the generally cold rocks traversed in their course from the 
 earth's surface downward and back again to the surface, has 
 arisen because of the failure to recognize that in this mingling 
 of igneous emanations and ground-waters we have the true 
 explanation. The ground-waters alone, either cold or heated, 
 would not ordinarily take up enough material from the rocks 
 traversed by them to enable the waters to deposit ores in veins. 
 On the contrary, it is the gaseous emanations carried by the 
 ground-waters into trunk-channels that deposit ores by reaction 
 with other currents, wall-rock, etc. 
 
392 ORE-DEPOSITS NEAR IGNEOUS CONTACTS. 
 
 Contact metamorphic deposits, properly so-called, occur as a 
 result of the metamorphism of sedimentary rocks by igneous 
 intrusions. The definition thus excludes all deposits formed 
 along ordinary contacts, due solely to circulating waters, even 
 where such waters contain substances derived from igneous em- 
 anations dissolved in the waters, as, for example, the Mercur, 
 Utah, and Judith Mountain, Montana, deposits, and other ore- 
 bodies of similar character. When the ore-minerals are inter- 
 grown with the garnet-epidote and other gangue minerals, the 
 deposits are clearly pneumatolytic.* Another class is the result 
 of later impregnation by igneous emanations penetrating a 
 porous stratum, the stratum itself made porous as a result of 
 metamorphism. A third class are the result of the precipita- 
 tion of copper or other sulphides from ascending alkaline solu- 
 tions, supposedly hot waters, by the lean sulphides formed by 
 pneumatolytic action (deposits of the second class). In the 
 first class the ores are of simultaneous origin with the gangue 
 minerals which are admittedly due to contact metamorphism. 
 In the second class, ores were introduced subsequent to the met- 
 amorphism of the rock (Elkhorn type). The third is probably 
 difficult to distinguish from the first, but is believed to exist at 
 Cananea, Mexico, though not the kind designated by that name. 
 
 Barrell has calculated the changes taking place in two ex- 
 amples at Elkhorn. The first is a thin band of hornstone oc- 
 curring in marble and consisting of 50 per cent, of diopside, 
 with 46 per cent, of feldspar and 2 per cent, each of quartz and 
 fluorite. It is evident that the crystallization of diopside and 
 feldspar left the stratum very porous, and that the pores were 
 filled by quartz and fluorite from pneumatolytic vapors. 
 
 The second instance given by him is the ore-stratum of the 
 Dolcoath mine, already described. This is a typical instance 
 of a porous layer. 
 
 lt It is seen that even if all the calcite of the ore-bearing stratum be regarded as 
 a primary mineral, the shrinkage in the ore-stratum has been somewhat greater 
 than in either the foot- or hanging-wall, since the feldspars and biotite are min- 
 erals which, as shown by the alkalies present, were formed from sediments not 
 fully hydrated or carbonated. Moreover, a microscopic examination of the ore- 
 stratum shows parallel sinuous cracks due to tension, and not to shear, and now 
 filled with calcite. Elsewhere in the section the calcite exists as a sponge, hold- 
 ing garnet, dicpside, and ore-grains within it, and its secondary nature is not so 
 
 * I.e., formed by the action of gases or vapors at high temperatures and pres- 
 sures reacting upon solid materials. 
 
ORE-DEPOSITS NEAR IGNEOUS CONTACTS. 393 
 
 clear. The ore is associated with the calcite, and also with a certain coarser crys- 
 tallization of the diopside."* 
 
 Professor Barrell calculates the shrinkage of the ore-stratum 
 at 40 per cent., of the hanging-wall at 15 per cent., and the 
 footwall at 25 per cent., so that it is evident that we have here 
 a steeply inclined pervious stratum capped by a relatively dense 
 impervious bed, and offering a favorable channel for uprising 
 vapors, given off by the cooling magma beneath, or for circu- 
 lating waters. 
 
 The source of the metallic mineral deposited in these contact- 
 rocks, if not positively known, is commonly assigned to the sol- 
 fataric vapor given off by the cooling igneous magmas. There 
 has always been more or less skepticism concerning the source 
 of the oxide of iron, magnetite and specularite, which are such 
 common and characteristic features of true contact-deposits. 
 Inasmuch as the disassociation of the interstitial water of the 
 sedimentary rocks by the intrusion of highly-heated magma 
 would provide a sufficient supply of oxygen, the occurrence of 
 such ores, produced by reaction with the iron-compounds pres- 
 ent, would be explained, while the fact that such deposits are 
 almost entirely confined to the immediate vicinity of the igne- 
 ous contact can be readily understood. 
 
 PERMANENCE IN DEPTH OF ORE-DEPOSITS OF THIS CLASS. 
 
 So far as development and experience show, the deposits 
 of the Kristiania type occurring at actual contacts are very 
 bunchy, and cease in depth; a notable example being the Seven 
 Devils, Idaho, deposits. In the Cananea, Mexico, example, 
 and the Boundary, British Columbia, deposits, the copper-ore 
 is more uniformly distributed, and there seems no theoretical 
 reason why the primary sulphide-ore should not continue of 
 unchanged tenor in depth down to the igneous contact. In 
 the case of the gold-ores, both tellurides and arsenopyrite, so 
 little is known that no prognosis. can be made. The deepest 
 workings at Bannack are but 300 feet below the surface. At 
 Cripple Creek, where the deposits are not of contact-metamor- 
 phic origin, though they are considered to result from volcanic 
 emanations, the values decreased with depth. However, recent 
 discoveries indicate workable bodies of auriferous gray copper 
 at greater depths. The Cornwall tin- and copper-veins are 
 
 * Op. tit., pp. 295, 296. 
 
394 ORE-DEPOSITS NEAR IGNEOUS CONTACTS. 
 
 now practically worked out. At the Dolcoath the ore is low- 
 grade at 150 feet. If the theory of genesis be true, there is no 
 reason now known for the impoverishment of contact meta- 
 m orphic deposits in depth. 
 
 MINERAL VEINS NEAR IGNEOUS CONTACTS. 
 In addition to the pneumatolytic deposits on igneous con- 
 tacts and those in altered strata near the contacts, there are 
 many productive mines working true veins cutting the igneous 
 rock and the contact-rocks above them. Such vein-fissures are 
 caused both by the contraction due to the crystallization and 
 cooling of the igneous rock and by the shrinkage of the meta- 
 morphic zone above the igneous rock. Examples of this type 
 have already been mentioned. As shown by Pirsson,* the 
 radial fissures which form so remarkable a feature of certain 
 igneous centers are not due to the initial expanding force of 
 the intruded magma, but to the contraction-cracks. The vast 
 amount of heat given off by the cooling magma effects a con- 
 siderable expansion of the surrounding rocks. As the magma 
 and its surrounding shell of heated sediments cools down it 
 must contract, and this contraction will result in a cracking 
 both of the igneous rock and the contact-zone ; and, if the 
 rocks of the contact-zone are homogeneous, the cracks will as- 
 sume a more or less radial position. If these cracks extend to a 
 depth sufficient to reach still molten magma, they will be filled, 
 and dikes will be formed ; if not, the cracks become channels 
 for pneumatolytic vapors and later circulating waters, and thus 
 pegmatite veins and true mineral veins may be formed, and may 
 merge into one another. It is possible that the (now brecciated) 
 Granite Mountain vein at Philipsburg, and the very pro- 
 ductive veins at Marysville, Montana, may have originated in 
 this manner. But, in addition to radial cracks, the shrinkage 
 would also tend to produce cracks parallel to the borders of 
 the intrusion, f a phenomenon observed in casting, and also in 
 the cooling of lava-sheets, as, for example, those of Obsidian 
 Cliff, in the Yellowstone Park region, a discussion of which 
 has been given by Iddings.J As circulating solutions travers- 
 
 * "Complementary Hocks and Kadial Dikes," Amer. Jour. Sci., vol. 1., 1895, 
 p. 116. 
 
 f For ore-deposits of this type, see Beck, op. cit., p. 182, Fig. 119. 
 J 7th Ann. Rept., U. S. Geol. Surv., for 1885-6, pp. 249-295. 
 
ORE-DEPOSITS NEAR IGNEOUS CONTACTS. 395 
 
 ing contact-zones would course through the more basic differ- 
 entiated part of the magma, which is well known to be richer 
 in metals than the normal magma, there has been a combina- 
 tion of conditions favoring ore-formation, and it is easy to see 
 why such ore-deposits occur in or near the contacts of great 
 igneous masses. 
 
 I hold that the metallic contents of such veins are not gath- 
 ered by ordinary meteoric water, as maintained by Van Hise. 
 The water-content of the sedimentary rocks (ground-water) 
 present at the time of eruption was expelled by contact meta- 
 morphism. The ore-forming solutions were in part of direct 
 igneous origin;* these primitive hot vapors and waters rise and 
 penetrate the zone of circulating meteoric waters, heating the 
 latter and charging them with both metallic salts and with fluo- 
 rine, chlorine, boron and other active mineralizers. The result- 
 ing mixture of plutonic and meteoric waters is a much more 
 energetic solvent than normal ground-water, and is capable of 
 adding metallic salts extracted from the rocks traversed by the 
 waters to the original material derived from the igneous emana- 
 tions. 
 
 CONCLUSIONS. 
 
 Contact metamorphic ore-deposits occur about the margin of 
 intrusive masses of granular igneous rock, either at the actual 
 contact or in the zone of metamorphosed sedimentaries. The 
 deposits of economic value occur only where strata or blocks of 
 impure limestone have been crystallized as garnetiferous or 
 actinolite-calcite rocks, with consequent porosity. The ore- 
 minerals are intimately associated with these aluminous sili- 
 cates, and may be either intergrown, or metasomatic replace- 
 ments, or the result of interstitial filling with partial replace- 
 ment. The conversion to garnet-epidote-calcite, etc., rock was 
 complete before the consolidation of the igneous rock. The 
 ore-minerals were introduced in gases and vapors solfataric 
 emanations from the eruptive masses of which they constitute 
 pneumatolytic after-actions, or by hot circulating primitive 
 waters given off by the cooling igneous mass. This theory of 
 the genesis being true, the deposits should extend downward in 
 depth to the granular rock. 
 
 * I.e., primitive or igneogenous. The geyser waters of Iceland, New Zealand 
 and the Yellowstone regions are probably mainly of this character, as maintained 
 by Suess. 
 
396 ORE-DEPOSITS NEAR IGNEOUS CONTACTS. 
 
 DISCUSSION. 
 
 (Traits., xxxiii., 1070.) 
 
 W. L. AUSTIN, New York, N. Y. : In Mr. Weed's interest- 
 ing paper, frequent reference is made to the Cananea copper- 
 deposits, which are said to have been so vigorously exploited 
 that they produced 14,000,000 Ib. of copper in 1901. 
 
 The ore-bodies which yielded this large quantity of metal are 
 described as a product of contact-metamorphism, and in Mr. 
 Weed's genetic classification of such deposits, they receive a 
 place under the sub-heading, "Deposits impregnating and re- 
 placing beds of contact-zone." They are considered by Mr. 
 Weed to represent a special type under this head, and are fur- 
 ther classified as : " 1. Chalcopyrite deposits : (a) Pyrrhotite 
 ores ; (b) Magnetite ores, Cananea type." 
 
 In condensing much information into a comparatively small 
 space, the presentation of a subject may be so abbreviated as to 
 detract from its clearness. The situation at La Cananea, con- 
 sidering its importance from an economic as well as scientific 
 standpoint, may be worthy of more detailed description. As 
 Mr. Weed rightly remarks, " structural differences are so im- 
 portant, and have so marked a bearing, not alone on the theory 
 of their genesis, but, also, in the working of the deposits and 
 a determination of their value as mines, that they merit a full 
 discussion." 
 
 It is my present purpose : (1) to show that it is doubtful 
 whether the copper of La Cananea is mined, except to a limited 
 extent, from contact-metamorphic deposits; (2) to emphasize 
 the importance of the mineral-bearing porphyry in connection 
 with the genesis of the Cananea deposits ; and (3) to question 
 the correctness of Mr. Weed's opinion that, in this locality, 
 " the deposits should extend downward in depth to the granu- 
 lar rock." 
 
 Contact-metamorphic ore-deposits are very common in the 
 West and Southwest. Among the better known of those in 
 which copper is the principal economic mineral are those of the 
 Seven Devils district, Idaho; Saline Valley, California; the 
 Planet mine on Bill Williams Fork, Marble mountain, in the 
 Santa Catalina mountains, and Clifton, Arizona; La Cananea, 
 and the Santo Emo deposits on the Yaqui river, Sonora; Teras- 
 sas Station, Chihuahua ; and La Jibosa mine, Velardena copper- 
 
ORE-DEPOSITS NEAR IGNEOUS CONTACTS. 397 
 
 mine, and Sacrificio mountain, Durango. There are many others 
 which I have not personally visited, but concerning which I 
 have received private communications, or have found described 
 in current technical literature. 
 
 These may all be classed together as ore-deposits occurring 
 at or near the contact of igneous rocks with limestone beds, and 
 owing their existence to the presence of the eruptives. 
 
 This general type of deposit is recognizable at first sight; 
 but it is not always with a simple contact that the observer has 
 to deal. Associated with the actual contact ore-bodies are 
 mineralized eruptives, fissure-veins and replacements in the 
 limestone. Mr. Weed, recognizing the variations displayed 
 by deposits of this description, has proposed a tentative classifi- 
 cation, which might be further discussed to advantage. 
 
 By reason of the very nature of the genesis of these de- 
 posits, there must be much diversity among them. In fact, 
 hardly any two of them are exactly alike. They all have a 
 certain mutual resemblance, and differ radically from any 
 other class; but, unless a broad significance is given to the 
 term contact-metamorphism, it will scarcely cover them all, 
 and, in any event, there will be almost as many " types " as de- 
 posits. 
 
 The selection of the Cananea deposits as typical of contact- 
 metamorphism, and the ascription to this type of the large pro- 
 duction of copper quoted above, seems to me to be ill-advised ; 
 and the statement that in this instance the primary sulphide- 
 ore should continue of unchanged tenor in depth down to a 
 hypothetical contact with granular rock, certainly calls for fur- 
 ther elucidation. 
 
 There are numerous contacts between the limestone and the 
 igneous rocks of the Cananea district; in fact, all the lime- 
 stone patches are almost surrounded by porphyritic rocks of 
 one kind or another; but neither at any one of the important 
 mines, nor at any other points so far as I know, has a contact 
 between the limestone and a granular igneous rock been ob- 
 served. 
 
 The ore-deposits of La Sierra de la Cananea, as hitherto de- 
 veloped, are scattered through the mountains along a N". W.-S.E. 
 belt for about 8 miles. Puertocito is at the extreme northern 
 end of the belt ; the Elisa mine at about the middle ; Capote 
 
398 ORE-DEPOSITS NEAR IGNEOUS CONTACTS. 
 
 basin (with the Capote, Oversight, Yeta Grande and Chivatera 
 mines) are south of the Elisa ; and at the southern end is the 
 Cobre Grande mine. The Elenita deposits are really a part or 
 Puertocito. At various points between these main ore-bodies 
 are smaller ones. 
 
 At Puertocito and Elenita there are masses of garnetiferous 
 minerals with associated copper carbonates and silicates, pyrite, 
 chalcopyrite and bornite ; at the Elisa there are irregular bodies 
 of chalcopyrite along a fault-fissure in the metamorphosed 
 limestone ; at the Oversight and Capote mines there are much 
 larger masses of feldspathic porphyry carrying chalcocite, which 
 have yielded much the greater part of the copper produced in 
 the district. The deposits of Elenita and Puertocito had no 
 part in the large copper-production mentioned in Mr. Weed's 
 paper; not until late in April, 1903, was any ore shipped from 
 this part of the belt. 
 
 At the present time (April, 1903) the Oversight mine occu- 
 pies the place of honor among the developed properties, having 
 temporarily exceeded the production of the Capote, which was 
 the first large bonanza found in the district. The first-class ore 
 of the Oversight is a soft, white feldspathic porphyry, heavily 
 mineralized with chalcocite. At the southern end of the mine, 
 the surface-indications of underlying ore-bodies are so slight 
 that one not very familiar with the characteristics of deposits 
 of this class would hardly have ventured to predict the dis- 
 coveries which have been made a few feet below. The por- 
 phyry shows at the top no mineralization ; no gossan ; no " cop- 
 per stains." The solutions which effected the decomposition 
 of the original pyrite, carried the iron with them and deposited 
 it elsewhere, a process which can be seen in operation to-day 
 in other parts of the district. In such cases, silica and silicates 
 are usually substituted for the minerals removed. 
 
 Underneath there is an ore-body of irregular shape, already 
 developed for several hundred feet in depth, and in places sev- 
 eral hundred feet wide. It is in reality a southerly continua- 
 tion of the Capote ore-zone a second great concentration of 
 chalcocite in the porphyry. Its limits as here stated are merely 
 those of the ore rich enough to be shipped ; in fact, the chalco- . 
 cite-bearing rock merges into cupriferous pyrite bodies of very 
 much larger dimensions, but of lower grade. This much is 
 
ORE-DEPOSITS NEAR IGNEOUS CONTACTS. 399 
 
 known : but what is the extent of these ore-bodies, or how many 
 more of them there may be, has not yet been ascertained. Only 
 the first-class, and the higher grades of the second-class ore, are 
 at present taken out; lower-grade material is left standing. 
 
 It is not my present intention to discuss the extent and value 
 of the Cananea ore-bodies. That matter has been briefly 
 touched upon, only in order to bring out the fact, that by far 
 the greater part of the copper produced by the mines of La 
 Cananea has come from masses of mineralized porphyry, and 
 not from " chalcopyrite ore-bodies carrying accessory galena, . . . 
 practically confined to the rocks resulting from the alteration of 
 impure limestones." A statement of this kind, coming from 
 such an authority as Mr. Weed, might possibly cause others to 
 feel warranted in making large expenditures upon deposits of 
 the class indicated, basing their hopes on the supposition that 
 the bonanzas of La Cananea were found in contact-metamorphic 
 deposits, with a probability of their extending " downward in 
 depth to the granular rock." 
 
 Porphyry is by far the predominating rock along the Cananea 
 ore-belt. I use the term " porphyry " in its general sense, for 
 there are several varieties. Possibly all varieties have had 
 their origin in the same eruptive magma, the sub-species being 
 due to magmatic differentiation, or to the incorporation of por- 
 tions of other rocks with which the eruptives came into con- 
 tact. In places is found typical quartz-porphyry ; but where 
 the ore-bodies occur, the quartz is not so much in evidence. 
 There are in the district other varieties of igneous rocks, such 
 as granite, diorite, diabase and andesite ; but these are mostly 
 at some distance from the ore-belt, and as far as I know are 
 not mineralized to any noticeable degree. The porphyry, how- 
 ever, wherever it has been artificially exposed within the entire 
 length of 8 miles here in question, is more or less pyritic, and 
 in places the sulphides are massed so as to form ore-bodies. 
 The mineral belt has been extensively prospected, and tunnels 
 many hundreds of feet in length cross its trend in a number of 
 places. In these tunnels, many of which are considerable dis- 
 tances away from the producing mines, this mineralized por- 
 phyry is exposed; and at such points its character can be 
 studied to advantage. It extends from the mines on the ex- 
 treme north to those on the extreme south, and is essentially 
 
400 ORE-DEPOSITS NEAR IGNEOUS CONTACTS. 
 
 the mineral-bearer of the district. The limestone occurs only 
 in spots. Where the heavily mineralized porphyry has come 
 into contact with this limestone, there are the usual contact- 
 metamorphic phenomena; hut these ore-bodies are of subor- 
 dinate commercial importance ; in fact, but for the mineralized 
 porphyry the history of La Cananea would have been a totally 
 different one. 
 
 The quartzites do not contain mineral deposits, except where 
 cupriferous solutions from the decomposing porphyry have 
 found cracks and fissures in which to deposit their burdens ; 
 and these are practically a negligible quantity. 
 
 Where the limestone has been metamorphosed by contact 
 with the porphyries, it has become one of the most, if not the 
 most, resistant of the rocks of the district. Proof of this state- 
 ment is furnished by the garnetiferous bluffs which constitute 
 such prominent landmarks at the Puertocito end of the belt. 
 Not in this district only, but everywhere, such resistance to 
 weathering is characteristic of rocks thus metamorphosed; for 
 the process itself is largely one of silicification. 
 
 The ore-bodies which have made La Cananea famous are 
 soft porphyritic masses, partly of mineralized porphyry, partly 
 of dark-colored plastic clay less heavily charged with copper- 
 ore. The one merges insensibly into the other, and much of 
 the material is of a nondescript character, depending on the 
 degree of decomposition which the rock has undergone. It 
 bears no resemblance to metamorphosed limestone, although 
 fragments of that rock are found in it, as are also masses of 
 quartzite. 
 
 It is common, where porphyritic flows have broken through 
 limestone beds, to find included masses of the latter caught in, 
 and surrounded by, the porphyry ; and the Cananea deposits are 
 no exception. 
 
 The ore is so soft that no amount of timbering can hold the 
 workings open ; the stopes have to be filled as soon as the ore 
 is removed. The ground swells to such an extent that on the 
 third level of the deep Capote workings the shaft can only be 
 kept open by maintaining a passage-way around it. In the 
 bottom of the mine the tops, sides and bottoms of the drifts are 
 squeezed together, like those of a tunnel run into a bank of 
 plastic clay. One peculiarity of the low-grade ore-bodies is, that 
 
ORE-DEPOSITS NEAR IGNEOUS CONTACTS. 401 
 
 although the rock may have lost its pristine character and may 
 be as soft as stiff putty, the pyrite distributed through it is un- 
 oxidized and bright, even on its surface. 
 
 The ore from the Capote and Oversight mines comes to the 
 concentrator and smelter mostly as whitish-gray clayey " fines/'* 
 In the concentrator the Oversight ore in particular gives trouble, 
 because it " thickens " the water, thereby preventing the min- 
 eral from separating out. On the concentrating-tables, garnets 
 and similar minerals, characteristic of contact-metamorphism, 
 are noticeably inconspicuous. At Puertocito the mineralized 
 porphyry taken from one of the shafts " slacks " in the air to a 
 powder. 
 
 That white feldspathic porphyry, similar to, if not identical 
 with, that of La Sierra de la Cananea, may be itself a highly 
 cupriferous mineral-bearer, is evidenced by the deposits at Ajo 
 in southern Arizona, not far northwest of La Cananea. Here 
 masses of mineralized porphyry form hills within a basin of 
 other eruptive matter. The rock is pyritic throughout, and in 
 places the ore is identical with that of the Capote basin. I 
 noticed no sedimentary rocks at Ajo. The ore-bodies are por- 
 phyry, carrying pyrite, with chalcocite, and other cupriferous 
 minerals. 
 
 At Clifton, also, notably on Metcalf hill, the mineralized por- 
 phyry, constituting the ore-bodies of the Arizona Copper Co., 
 is of similar nature, if not the same, as that of Ajo and La 
 Cananea. And the same may be said of the rock in which lies 
 the large pyritic body of Iron mountain, in California. 
 
 For the reasons above given, and without wishing to dispar- 
 age the statements of such an eminent and accomplished geolo- 
 gist as Mr. Weed, I question the propriety of describing the 
 large copper-producing ore-bodies of La Cananea as a type of 
 contact-metamorphic deposits. The porphyries have certainly 
 taken a more important part in the genesis of these cupriferous 
 deposits than that w r hich he has assigned to them. At Puerto- 
 cito, as well as in the Capote basin, it would seem to be more 
 in accord with the facts to assume that the pyritic minerals 
 brought up by the porphyry became, through magmatic differ- 
 entiation, more concentrated in certain localities than in others, 
 and that these heavily mineralized portions were very suscep- 
 tible to attack from atmospheric waters. In the Capote basin, 
 
 26 
 
402 ORE-DEPOSITS NEAR IGNEOUS CONTACTS. 
 
 where the mineralization was the greatest, the porphyry yielded 
 readily to decay, the result being the formation of ferric masses 
 (gossan), which were left on or near the surface, and the con- 
 
 \O / " 
 
 centration of the copper below in the form of chalcocite. The 
 gossan found on the top of the ground is a fairly good flux, and 
 is used as such ; but it becomes more and more siliceous with 
 depth, until it rests on the ore. It presents an irregular bottom- 
 limit, penetrating the ore in places. Immediately under the 
 gossan comes the chalcocite-bearing porphyry. At the junction 
 of the two, native silver is sometimes found. The workings in 
 this portion of the Capote mine were very hot ; and the more 
 it was attempted to ventilate them, the hotter they became. 
 Quartz-sand also (used for building-purposes) was found in this 
 zone. 
 
 The subject of the formation of chalcocite ore-bodies by the 
 oxidation of pyritic minerals and subsequent precipitation of 
 the copper sulphide on deeper-lying, unaltered ore, has been 
 handled in such a masterly manner by Mr. H. Y. Winchell, of 
 Butte,* that it would be superfluous to go further into the 
 matter here. 
 
 There are contact-metamorphic deposits at La Cananea ; but 
 they were of comparatively subordinate importance in con- 
 nection with the output of copper in 1901, and they are still 
 subordinate. The main ore-deposits are concentrations in the 
 porphyry of chalcocite derived from cupriferous pyrite, which 
 came up as an accessory component of the original rock. 
 
 A correct diagnosis of the genesis of an ore-deposit is of 
 more than scientific interest; it is of great economic impor- 
 tance. A better appreciation of this truism by those in respon- 
 sible charge of mining operations would result in the saving of 
 vast sums of money which are uselessly expended at the pres- 
 ent time. 
 
 In regard to the occurrence of arsenopyrite in, or close to, 
 contact-metamorphic deposits, the case of Sacrificio mountain, 
 in Durango, might be cited in addition to those mentioned by 
 Mr. Weed. These deposits, which are typically contact-meta- 
 morphic in the sense given the term by Mr. Weed " zones of 
 altered sediments about igneous intrusions " are associated 
 with veins of arsenopyrite. 
 
 * Engineering and Mining Journal, vol. Ixxv., p. 782. 
 
ORE-DEPOSITION AND VEIN-ENRICHMENT. 40S 
 
 No. 14. 
 
 Ore-Deposition and Vein-Enrichment by Ascending Hot 
 
 Waters. 
 
 BY WALTER HARVEY WEED, WASHINGTON, D. C. 
 
 (New Haven Meeting, October, 1902. Trans., xxxiii., 747.) 
 
 THE enrichment of mineral-veins as a result of the migra- 
 tion of material from an upper oxidized or disintegrated part 
 of a vein to a lower level, where it is redeposited, is now, I 
 believe, quite generally accepted as one explanation of the 
 occurrence of bonanzas in gold- and silver-veins, as well as that 
 of bodies of high-grade ores in cupriferous deposits.* Yogt has 
 called attentionf to the fact that there are numerous examples 
 of such rich shoots which are " of exclusively primary char- 
 acter, and dependent upon the laws which governed the origi- 
 nal ore-deposition." To this I would add that there are also 
 other examples which are neither of primary origin nor due to 
 descending waters, but result from a reopening of the veins 
 and their penetration by ascending heated waters whose metal- 
 lic contents are deposited by reaction with the primary pyrite 
 (and possibly other minerals), forming " secondary " enrich- 
 ments. 
 
 My studies of the copper-veins of Butte, Montana, show: 
 That the veins there are of several ages and systems ; that the 
 older primary quartz-pyrite veins were reopened by later move- 
 ments, correlated with a period of volcanic activity ; and that 
 they were penetrated by hot alkaline waters carrying copper 
 and arsenic in solution, which were deposited presumably by 
 reaction with the pyrite of the original vein. 
 
 The enormous development of the Butte deposits, attendant 
 upon the extraction of nearly 10,000 tons of ore a day, has re- 
 vealed many facts concerning the nature and distribution of the 
 ores. Enargite, the copper sulpharsenate, formerly a relatively 
 rare mineral, is now found to be the chief ore of some veins, 
 
 * Weed, " Enrichment of Mineral- Veins by Later Metallic Sulphides," Geol. 
 Soc. Am. Buil., vol. xi., pp. 179-206. 
 
 f " Problems in the Geology of Ore-Deposits," Genesis of Ore-Deposits, p. 679 ; 
 also, Trans., xxxi., p. 168. 
 
404 ORE-DEPOSITION AND VEIN-ENRICHMENT. 
 
 and to constitute a large part of the high-grade ore of the east- 
 ern properties. Its distribution is peculiar, and its significance 
 can only be understood as a result of detailed study, but sev- 
 eral facts stand out prominently, viz. : It occurs in immense ore- 
 bodies, connected with faults, extending from the oxidation zone 
 to unknown depths in some veins. But, in most cases, it first 
 appears in deep-level workings. This ore was recently found 
 in the 2000-ft. and 2200-ft, level of several mines ; it is clearly 
 younger than the pyritic ores, but older than the great glance 
 ore-bodies, and is formed in small quantity in later fault-veins. 
 
 In the discussion of the genesis of the Butte deposits with 
 the late Clarence King, he at first combated the principle of 
 secondary enrichment, and adduced the presence of enargite as 
 a conclusive argument against it. The later discovery of 
 masses of brecciated enargite cemented by glance proves the 
 enargite to be of earlier formation ; and though the pyrite is 
 the only possible source of the copper and arsenic in the origi- 
 nal vein, numerous assays showed almost total absence of arse- 
 nic from these ores. In brief, all the evidence showed that 
 enargite, though not a " primary " vein-mineral of the original 
 vein, did not come from descending solutions, but must have 
 come from below. 
 
 The bonanza-ore of Neihart, Montana, has been described by 
 me as an example of secondary enrichment by descending waters. 
 In the light of a riper experience and the experimental work of 
 Dr. Stokes, it appears possible that the pearceite (arsenical poly- 
 basite) ores result from uprising alkaline solutions, though 
 later descending solutions, carrying material derived from the 
 oxidation of the ores, have to some extent complicated the 
 situation. At any rate, it is difficult to account for the large 
 amounts of arsenic necessary for the formation of these ores by 
 the oxidation of very large amounts of primary pyrite almost 
 devoid of this element ; and it is known that arsenic occurs 
 elsewhere in hot-spring waters, as at La Bourboule, France,* 
 and in the Yellowstone Park.f 
 
 * Hague, ' ' Notes on the Deposition of Scorodite, ' ' Am. Jour. Sci. , xxxiv. , 3d 
 ser., Sept., 1887, p. 171. 
 
 f Weed and Pirsson, " Sulphur, Orpiment and Kealgar in the Yellowstone 
 Park," Am. Jour. Sci., xlii., p. 401, 1895. 
 
 Gooch and Whitfield, " Waters of the Yellowstone," Bull. 47, U. S. Geol. Surv. f 
 p. teetseq., 1888. 
 
ORE-DEPOSITION AND VEIN-ENRICHMENT. 405 
 
 Recent experiments made in the U. S. Geological Survey 
 Laboratory, by Dr. H. IN". Stokes, show that metallic sulphides 
 are reduced and precipitated from alkaline solutions of the 
 general character of hot-spring waters by pyrite. The metallic 
 substances may be assumed to be present as oxides of zinc, 
 copper, lead, etc. The reaction with the alkaline waters alone 
 is represented by the equation : 
 
 8 FeS 2 + 15 Na 2 C0 3 = 4 Fe 2 O 8 + 14 Na 2 S + ]STa 2 S 2 O 3 +15 C0 2 . 
 
 In the presence of a metallic oxide reacting with Na 2 S, e.g., 
 ZnO, PbO, etc., the equilibrium will not be reached short of 
 total decomposition of FeS 2 , and we get 
 
 8 FeS, + 14 ZnC0 3 + Ha 2 CO, = 14 ZnS + 4 Fe 2 3 
 
 3 +15 C0 2 . 
 
 These are the only products present, and the reaction is com- 
 plete with excess of ZnC0 3 . The formation of Fe 2 3 by action 
 of a metallic salt on FeS 2 and the formation of thiosulphate 
 have not been previously known. The latter was proved beyond 
 question by qualitative and quantitative methods, and there is 
 no evidence of the formation of sulphites. Pyrite and mar- 
 casite, with CuO in bicarbonate solution, react as follows : 
 
 2 FeS 2 + 6 CuC0 3 + 2 KHC0 3 = 3 Cu 2 S + Fe 2 O 3 + 
 K 2 S0 4 + 8 C0 2 + H 2 0. 
 
 Experiments with both pyrite and marcasite at 200 C. show 
 that the theoretical amount of sulphuric acid is actually formed. 
 
 That such waters actually occur in nature is not absolutely 
 known. The Yellowstone Park waters are, however, nearly 
 of this character, and several springs at the Norris Geyser 
 Basin are actually depositing the red and yellow sulphide of 
 arsenic, and one case auriferous pyrite.* The Boulder hot 
 springs, where mineral-veins are now in process of formation, 
 in which small amounts of copper, gold and silver are de- 
 posited, are dilute solutions of alkaline waters. f 
 
 From my study of the waters and veins of the last-named 
 
 * Weed and Pirsson, Am. Jour. Sci., xlii., p. 401, 1895. 
 
 t Weed, " Mineral -Vein Formation at Boulder Hot Springs, Montana," 21st 
 Ann. Sept., U. S. Geol. Surv., Part II., p. 233, 1900. 
 
406 ORE-DEPOSITION AND VEIN-ENRICHMENT. 
 
 locality, I am led to the following theory of primary ore-depo- 
 sition : 
 
 Theory of Ore-Deposition by Thermal Springs. 
 
 Recent researches have demonstrated that openings cannot 
 exist in the rocks which compose the outer crust of the earth 
 at depths of 30,000 feet or more, and that, indeed, under cer- 
 tain conditions, they cannot exist at depths very much less than 
 that. Observations made upon deeply buried rocks, brought to 
 the surface by uplift and erosion, are in perfect accord with 
 these deductions, and prove that the " unknown depths " from 
 which ore-deposits in waters are derived cannot exceed these 
 figures. Assuming this to be true, it will probably be admitted 
 (since heat and pressure facilitate solution), that hot waters cir- 
 culating at considerable depths will dissolve and take into solu- 
 tion the various materials with which they come in contact. 
 The capacity of hot water to contain such substances in solu- 
 tion will depend upon heat and pressure. The water will take 
 up the less readily soluble salts only while the conditions 
 are favorable. With less heat and pressure the solution may 
 become saturated for any one substance, and, though still hold- 
 ing it in solution, be incapable of taking up any more of that 
 substance. In this unstable condition a slightly lessened pres- 
 sure and heat would bring about precipitation. 
 
 For this discussion it does not matter whether the hot waters 
 are of igneous, or of original meteoric origin, since they are 
 admittedly hot and traverse the deep-seated rock. 
 
 In an ideal hot spring, the circulating waters slowly traversing 
 heated, but solid, igneous rocks, out of which they dissolve vari- 
 ous substances, flow toward the point of easiest escape, which 
 is the hot-spring fissure. For convenience, we will assume this 
 fissure to be straight, one thousand or two thousand feet deep, 
 and the waters to move upward very slowly. In its lower part, 
 as in the pores of the adjacent rocks, heat and pressure are 
 very great and the waters are not saturated, even for the most 
 insoluble substances, and no minerals are deposited. Nearer 
 the surface diminished heat and pressure make the water in- 
 capable of taking more of the less soluble materials in solution, 
 forming what may be conveniently called the zone of satura- 
 tion. Some salts, like alkaline sulphates, etc., are extremely 
 soluble, and the point of saturation is scarcely ever reached in 
 
ORE-DEPOSITION AND VEIN-ENRICHMENT. 407 
 
 nature, even at the earth's surface. Others, like silica, may be 
 present in such amount as to saturate the water, but the solu- 
 tion is clear until cooling and relief of pressure cause super- 
 saturation, and precipitation occurs; an example of this was 
 seen at the Opal and the Coral Springs of the Norris Geyser 
 Basin, in the Yellowstone Park. Still higher in the hypotheti- 
 cal hot-spring pipe, diminished heat and pressure cause the 
 separation of the less soluble constituents, and for such mate- 
 rials this part of the tube is the zone of precipitation. It is 
 well known that the metallic sulphides are soluble in alka- 
 line solutions under heat and pressure, but examples show- 
 ing their deposition by living hot springs are extremely rare. 
 The more soluble substances will be carried farther upward be- 
 fore precipitation, and one might even suppose, if the solubili- 
 ties of the substances were sufficiently unlike, that zones would 
 be formed, each one of which consisted mainly of the particu- 
 lar substance thrown out by the change of pressure. This 
 would produce an orderly distribution of the ores in a vertical 
 direction. This, indeed, has been observed frequently. Cham- 
 berlin records it for the lead- and zinc-deposits of Wisconsin, 
 and Rickard* for those of Colorado and elsewhere. In the 
 writer's own experience the order appears to be galena on 
 top, passing into highly zinciferous ores below, and this into 
 low-grade pyrite.f It is a common experience to find this asso- 
 ciation in silver-lead deposits in limestone. This would account, 
 also, for impoverishment in depth and the passing into the 
 ever-present and readily deposited silica. 
 
 The conditions in a hot-spring tube are admittedly those 
 postulated, i.e., lessening heat and pressure as the surface is 
 approached; the assumptions made are natural ones. This, 
 then, would explain why hot springs do not deposit metallic 
 sulphides at the earth's surface. Owing to their relative in- 
 solubility these are deposited (if present in the water) at depths 
 below the surface. The Sulphur Bank quicksilver mines of 
 California are examples. At the surface they showed only 
 
 * T. A. Rickard, Trans. Inst. Min. and Metal, London, vol. vi., 1S?9, p. 196. 
 
 f Weed and Pirsson, "Castle Mountain Mining District, Montana," Bull. 
 139,- U. S. Geol. Surv., 1896. Also abstract in Jour. GeoL, vol. v., p. 210, 1897. 
 
 Weed, "Geology of the Little Belt Mountains, Montana," 2Qth Ann. Rept., 
 U. S. GeoL Surv., Pt. III., pp. 271-461, 1901. 
 
408 ORE-DEPOSITION AND VEIN-ENRICHMENT. 
 
 sulphur and no quicksilver. In depth, quicksilver-ores ap- 
 peared. Were these springs to die out and degradation to 
 remove the upper 200 feet of the ground, quicksilver-veins 
 would be exposed. It is probable that somewhat analogous 
 conditions may exist at many hot-spring localities, and that if 
 we could expose the lower part of the conduit we should find 
 ore-deposits. This is the theory which the writer at present 
 holds as to the genesis of the silver-gold-veins of Lump Gulch 
 and other mining districts of Jefferson county, Montana, and 
 which he believes is a rational ascension theory. All second- 
 ary alterations are here excluded, these remarks applying only 
 to the primary vein-filling. It is lateral secretion only in the 
 very special and limited application of that term to the leach- 
 ing of relatively deep-seated rocks, and the gathering of such 
 waters in a hot-spring conduit. 
 
 The close resemblance in nature and occurrence of these 
 Boulder hot-spring veins to the jasper reefs of Clancy, Lump 
 Gulch and many other mining districts in the granite area of 
 Jefferson county, Montana, has already been stated. It may 
 be accepted as certain that they also owe their origin to hot 
 springs, and that the ore-deposits of such veins were formed 
 
 by hot waters. 
 
 Theory of Enrichment. 
 
 Applying these conclusions to the question of vein-enrich- 
 ments, it is first necessary to recall that bonanzas and rich 
 ore-shoots are very frequently associated with brecciation and 
 recementation of the vein-filling. Where the evidence pre- 
 cludes " secondary " enrichment from above, the possibility of 
 enrichment by a new or renewed supply of hot water coming 
 up the newly-formed fracture must be considered. The suc- 
 cessive reopening of veins was formerly an accepted explana^ 
 tion of an orderly sequence of mineral crusts, implying a re- 
 peated uniform reopening. Such exceptional cases may occur, 
 but it is certain that many veins occupy fissures that are lines 
 of weakness in successive periods of earth movement. Even 
 in the deposits still forming at Boulder Hot Springs, Montana, 
 the veins have been fractured and the fragments cemented by 
 newly deposited silica. At Butte and Neihart the veins have 
 been broken by post-mineral fractures with later deposition of 
 rich ores. The evidence at Butte (furnished by rock-walls, de- 
 
ORE-DEPOSITION AND VEIN-ENRICHMENT. 409 
 
 posited ore and structural conditions) shows that the primary 
 quartz-pyrite veins were broken by fissures that became the 
 conduit for ascending hot alkaline waters. Such waters would 
 tend to deposit any burden of metallic salts in zones as already 
 outlined ; they would also be influenced by the existence of the 
 crushed pyrite of earlier deposition, which is an energetic re- 
 ducing-agent.* 
 
 Dr. H. N". Stokes has continued his painstaking experi- 
 mental work on the action of pyrite and marcasite, and the 
 bearings of his results upon the chemistry of ore-deposition are 
 of very great importance. It is well known that almost all 
 hot-spring waters contain alkaline carbonates in solution. In 
 an unpublished abstract of his report, which I have his per- 
 mission to quote, he says : 
 
 " Behavior of Pyrite with Carbonate or Bicarbonate Solution. 
 
 " The reaction is as follows in case of either pyrite or marcasite and Na^CC^ or 
 KHCO 3 , at 100 or 190 : 
 
 " 8 FeS 2 + 15 Na 2 C0 3 = 4 Fe 2 O 3 + 14 Na,S -f Na^A + 15 CO 2 . 
 
 "The reaction is reversible, as far as the sulphide is concerned, and is more 
 complicated than represented, because some alkaline polysulphide is formed. 
 Being reversible, it is not possible to prove satisfactorily the presence of Fe 2 O 3 
 in the solid residue, but the solution was shown to contain Na 2 S, Na 2 S x and 
 Na 2 S 2 3 . 
 
 "If, however, the sulphide be removed as fast as formed, the reaction pro- 
 ceeds to an end, giving, finally, only Fe 2 O 3 , while the thiosulphate accumulates in 
 the solution. This can be accomplished in several ways : 
 
 11 (a) A circulating alkaline solution, carrying away the sulphur as sulphide 
 and thiosulphate, would leave the pyrite or marcasite ultimately as Fe 2 O 3 or its 
 hydrate. This can hardly be effected in the laboratory on account of experi- 
 mental difficulties. 
 
 " (b) The addition of a metallic salt capable of precipitating the sulphide as 
 fast as formed allows the reaction to proceed to an end. This is what occurs in 
 the above reaction with lead and zinc : 
 
 " 8 FeS 2 -f- 14 PbCO 3 + Na^COs = 14 PbS + 4 Fe 2 O 3 + Na 2 S 2 O 3 + 15 CO 2 , 
 
 and also with copper and silver (modified by the further conversion of thiosul- 
 phate into sulphide and sulphate) : 
 
 " 8 FeS 2 + 14 Ag 2 CO 3 -f Na-jCOg = 14 Ag 2 S + 4Fe 2 O 3 + Na, 2 SO 4 + 15 CO 2 . 
 
 " (c) Since CO 2 partially decomposes soluble sulphides, we actually have a por- 
 tion of free H 2 S, which may be volatilized, thus enabling the reaction tp proceed 
 to an end. By heating FeS 2 with KHCO 3 -solution in a sealed vessel filled with 
 CO 2 , and so arranged that the volatilized H 2 S is continually taken up by an ab- 
 
 * H. N. Stokes, "Pyrite and Marcasite," Bull 186, U. S. Geol. Surv. 
 
410 ORE-DEPOSITION AND VEIN-ENRICHMENT. 
 
 sorbent, it was found possible to convert FeS 2 completely into hematite, without 
 direct contact with metallic salts and in absence of oxygen. The same experi- 
 ment was made with artificial amorphous Fe 2 S 3 , which can be converted into 
 Fe 2 O 3 by long boiling with water, H 2 S escaping. 
 
 " It would seem from the above : 
 
 "1. That the conversion of FeS 2 into Fe 2 O 3 is not a necessary proof of the 
 action of oxidizing (descending) waters, but may be due to any alkaline solution 
 free from oxygen. 
 
 "2. The circulating solutions which have acted on FeS 2 may carry away 
 alkaline sulphide, and cause the deposition of other sulphides, as of copper, zinc, 
 lead, silver, at another place. ' ' 
 
 These reactions apply to enrichment produced by ascending 
 alkaline waters, such as those characteristic of the Yellowstone 
 Park, Boulder Hot Springs, and many of the hot springs of the 
 Rocky Mountain region. 
 
 If the hot ascending waters were acid, a different set of re- 
 actions, determined by Dr. Stokes' work, explain the solution 
 of gold, silver and copper from minerals of the original vein- 
 filling, and their deposition at a higher level on cooling.* The 
 reaction is possible with a neutral solution, but not an alka- 
 line one. 
 
 Conclusions. 
 
 1. Ascending hot-spring waters, if metalliferous, may deposit 
 different ores with an orderly vertical distribution. Existing 
 veins now mined often show this arrangement of metallic 
 sulphide. 
 
 2. Ascending hot alkaline waters coming up through crushed 
 and reopened veins containing pyrite (or marcasite) react with 
 this sulphide, and zinc, lead, copper or silver, if present, is 
 thrown down as sulphide. 
 
 3. Ascending hot acid waters may leach the lower levels of 
 reopened veins and deposit gold, silver and copper upon cool- 
 ing at higher levels. 
 
 * The full results of this very important experimental work of Dr. Stokes 
 will soon be published. See, also, by him, "Pyrite and Marcasite," Bull 186, 
 U. S. Geol. Surv. 
 
BASALTIC ZONES AS GUIDES' TO ORE-DEPOSITS. 411 
 
 No. 15. 
 
 Basaltic Zones as Guides to Ore-Deposits in the Cripple 
 Creek District, Colorado. 
 
 BY E. A. STEVENS,* VICTOR, COLO. 
 (New York and Philadelphia Meeting, February and May, 1902, Trans., xxxiii., 686.) 
 
 IT has been ascertained in recent years that certain rock- 
 types, geological formations and structural conditions may be 
 used as fairly reliable guides, when prospecting in recognized 
 mineral belts or mining districts, with a reasonable certainty 
 of discovering "pay-ore;" and that such is considered as a 
 practically established conclusion may be inferred from a peru- 
 sal of the recent reports of the IT. S. Geological Survey and the 
 literature of the several scientific societies discussing mining, 
 geology, and kindred subjects. 
 
 Cripple Creek is no exception to this conclusion, and the 
 rock-type or association, rather than the structural condition, is 
 the most infallible guide. f 
 
 These guides consist of four, possibly five, dike-rocks, three 
 of which are extremely basic, while the fourth is an acid rock 
 of an entirely dissimilar character. The basic rocks are neph- 
 eline-basalt, limburgite, feldspar-basalt and tephrite. There are 
 grounds, however, for believing that the two latter are subdi- 
 visions of one type, and therefore will be described under one 
 head. The acid rock is quartz-porphyry. 
 
 Nepheline-basalt is a rock encountered in but few localities 
 elsewhere on this continent, and occurs in narrow dikes cut- 
 ting various formations. When typical, J it is composed of 
 
 * Died January 31, 1902. The manuscript of this paper was received only a 
 few days before his untimely death. 
 
 f The writer will not deny that in a very few instances there is apparently a 
 relation existing between a late, extremely basic andesite and ore-deposition, but 
 is very confident that sufficient development will demonstrate, as in similar cases 
 heretofore, that these deposits are more closely allied to basaltic dikes or zones. 
 
 J The nepheline-basalt of this district is not a typical rock ; for instance, the 
 dike extending northward from Battle mountain, along the east side of Arequa 
 gulch, contains glass, much megascopic biotite and plagioclase, and is remarkably 
 poor in nepheline. This condition confirms the opinion of the writer, expressed 
 in a previous paper (Trans., xxx., 763), that much of the so-called nepheline- 
 basalt is limburgite. 
 
412 BASALTIC ZONES AS GUIDES TO ORE-DEPOSITS. 
 
 nepheline, augite and olivine, with hornblende, mica, and, 
 rarely, plagioclase, as accessories. In this district, however, it 
 may contain all of the above, with the addition of magnetite. 
 
 Limburgite, which was positively identified in this district 
 quite recently, is a rock closely allied to nepheline-basalt, both 
 structurally and chemically. It is composed of a glassy 
 ground-mass, containing large and small augites, magnetite, 
 abundant megascopic olivines, and some mica, shading locally 
 into a variety, verite. It also here contains the rare accesso- 
 ries, plagioclase and, occasionally, nepheline. 
 
 The last of the basic rocks, usually referred to as feldspar- 
 basalt, is probably tephrite,* as nepheline, which is present 
 microscopically, is too abundant locally to be considered as 
 other than an essential constituent. This rock is composed of 
 plagioclase, augite, and some nepheline. The accessories here 
 are biotite, magnetite, apatite, titanite, an undetermined min- 
 eral which is probably sanidine, and, rarely, olivine. 
 
 The one dike of quartz-porphyry, with its few branches, is 
 unique in its occurrence. It was casually referred to by Dr. 
 Cross in Part II., Sixteenth Annual Report, U. S. Geological 
 Survey, and has otherwise escaped observation. (See Fig. 4.) 
 It has a very compact, bluish-black ground-mass, composed of 
 orthoclase, much plagioclase, quartz, and some augite or other 
 dark silicate. The structure is distinctly tabular-jointed. Scat- 
 tered through the ground-mass are a few double-terminated, 
 greasy quartz-crystals, and an occasional phenocryst of ortho- 
 clase or sanidine. Physiographically, it, like the tephrite, re- 
 sembles the nepheline-basalt and limburgite. These rocks, as 
 dikes, comprise the later intrusions ; nepheline-basalt and lim- 
 burgite were contemporaneous, and probably the last extruded. 
 
 These dikes cut all the earlier formations of the district. 
 The latter, with the exception of granite, schist and diabase, 
 are generally classed, by the miners, as " porphyry;" they 
 really consist of andesitic and phonolitic tuff and breccia, mas- 
 sive and dike andesite, phonolite, trachytic-phonolite, nepheline- 
 syenite, and, in two instances, trachyte. Owing to the early 
 
 * No nepheline is present in the dike of the Seavey shaft on Block 7 of State 
 land ; but in the same dike, where exposed by the 40-f t. shaft of the ' ' Little 
 Daisy" mine, the higher power of the microscope reveals many crystals in 
 each slide. 
 
BASALTIC ZONES AS GUIDES TO ORE-DEPOSITS. 413 
 
 decomposition of the basalt and limburgite upon exposure to 
 the atmosphere, these dikes, with one exception of limburgite, 
 form no outcrops ; nor have they, except on very rare occasions, 
 been found in a sufficiently fresh condition for determination. 
 The same is also true of the tephrite. The two former, when 
 fresh, are very compact, of a greenish-black color, showing only 
 phenocrysts of olivine, except the verite, which contains many 
 crystals of biotite an inch or more in diameter. The tephrite 
 exhibits a compact ground-mass, containing megascopic pheno- 
 crysts of augite and plagioclase. 
 
 The structure of each basaltic rock, when fresh, is jointed, 
 and the fracture, when broken transversely between joints, is 
 conchoidal. The first stage of decomposition is a zeolitization 
 along the joint-planes, which is soon followed by devitrification, 
 and, subsequently, a breaking down of the entire mass, finally 
 resulting in serpentine. 
 
 The practical importance of the presence of these rocks can- 
 not be overestimated. It is not intended to convey the idea 
 that at every point at which one of these dike-rocks may be 
 exposed, ore is, or will be, found in paying quantities. It is a 
 well-established fact that the ore occurs at varying intervals 
 along the veins in the form of " shoots " or " chimneys," often 
 separated by thousands of feet of barren vein-matter. The 
 assertion is sometimes made that there is not a profitable mine 
 in the district that does not show either the presence of one or 
 more of these dike-rocks or a certain direct relation existing 
 between them and the ore. This relation may be explained 
 thus : The fissures to which the dikes belong are approximately 
 parallel and occur in systems, and one or more of the fissures 
 may contain the dike or dikes, which are very erratic ; and it 
 has frequently been observed that the dike-bearing fissures 
 may be devoid of filling for hundreds of feet in depth and 
 thousands of feet in length. These fissured zones often, al- 
 though not always, extend entirely across the district,* and are 
 
 * The Beacon hill mines are on a direct line with some of the limburgite dikes 
 that cut Gold hill in a northerly and southerly direction, and are unquestiona- 
 bly on the same zones. The writer has traced one fissure, which contains the 
 western branch of the basaltic mass at the Dolly Varden mine, southward 
 through Raven, Guyot and Beacon hills, and has observed ore along it at no 
 less than ten different points. A like condition prevails regarding the position 
 of the mines on the north slope of Bull and the east slope of Ironclad hills, with 
 reference to the basaltic zones to the southward. 
 
FIG. 1. 
 
 Showing the Structure of the Ore-Zone, 
 a, Fissured zone. 6, Basalt, c, Ore-shoots, c/, Cross-fissures. 
 
BASALTIC ZONES AS GUIDES TO ORE-DEPOSITS. 415 
 
 from 100 to 1200 ft. wide. The zone comprises hundreds of 
 fissures (many of which are often detected only by the aid of a 
 powerful microscope), separated at times by microscopic bands, 
 and at others by many feet, of country-rock. The veins and 
 their ore-deposits may occur either in the dike-bearing fissure, 
 including the dike, or any other fissure or fissures of the zone. 
 (See Fig. 1.) 
 
 It may be inferred from an examination of this figure that 
 the ore-deposits should be more properly assigned to the cross- 
 veins, as the greater number of the " shoots " or " chimneys " 
 occur at the points where these intersect the main veins. 
 This condition will be briefly explained for the benefit of those 
 who are not familiar with the local characteristics of ore-depos- 
 its. It will be readily understood that at these points of inter- 
 section the channels for water would be more open, and the 
 solutions containing the minerals w r ould meet with much less 
 obstruction to circulation than if there was but one system of 
 fissures or fractures, and would, consequently, spread over 
 areas and follow lines of least resistance. Comparatively 
 speaking, our studies and observations are but superficial, and 
 we may not judge of the conditions farther down in the earth 
 (where is presumed to be the ultimate source or turning-point 
 of the mineral-bearing solutions) ; we can observe them only as 
 they approach the surface. There are instances where veins 
 crossing the main fractures at a high angle contain the only 
 known shoots, which reach the surface hundreds of feet away 
 from the points of intersection. But in sinking upon or devel- 
 oping these " shoots " in depth, it is found that they gradually, 
 though persistently, approach the point of crossing with the 
 main system in their downward course ; and in many instances 
 they have been found to pass through the intersection, return 
 to it, and then follow the main system to as great a depth as de- 
 veloped. (See Fig. 2.) 
 
 These are the zones, therefore, that must be discovered be- 
 fore permanent mines can be opened up ; but, as usual, the 
 difficulty lies in distinguishing those which are likely to prove 
 productive. 
 
 Dikes of considerable thickness maintain their individuality 
 through the various stages of decomposition and alteration, in- 
 dependent of their environment, while the very thin dikes pass 
 
416 
 
 BASALTIC ZONES AS GUIDES TO ORE-DEPOSITS. 
 
 into the hydrous silicates of magnesium or aluminum, forming 
 the ordinary so-called " talc " of our veins, under which con- 
 dition, from a practical standpoint, identification becomes im- 
 possible. Another obstacle to the determination is the extreme 
 
 FIG. 2. 
 
 W 
 
 Section on line A-A, Fig. 1. 
 a, Fissured zone. 6, Basalt, c, Ore -shoots, d, Cross-fissures. 
 
 secondary silicification to which not only the dikes themselves, 
 but the entire area of eruptive rocks have been subjected.* 
 
 * It has recently been stated that the proximity of the veins, while conducting 
 exploration-work in this district, may be recognized by an increased silicification, 
 which reaches its maximum at and through the veins. A very casual examina- 
 tion of the surface of this region will suggest the untenability of this position. 
 The veins of this district have eroded away proportionately to the enclosing 
 breccia and granite ; no more nor no less. If they were silicified to an extreme 
 or even an unusual degree, comparatively, they would form sharply-defined ridges 
 against the breccia or granite background ; while, if silicified to a less degree, 
 gulches, hollows or depressions would mark their apices. 
 
BASALTIC ZONES AS GUIDES TO ORE-DEPOSITS. 417 
 
 Moreover, it is not always possible, with limited development, 
 to determine to what extent the intrusions may he apophyses, 
 which many of the so-called dikes of these basaltic rocks have 
 proven to be. Under such conditions the accompanying ore- 
 deposits, if any, correspond in amount to the dike-matter, as 
 will be instanced later on. This district has been subjected to 
 many disturbances, both orogenic and volcanic, as is indicated 
 by the many faults, fractures and displacements in and sur- 
 rounding the locality, and the variety of ejectamenta thrown 
 out by the volcano. The disturbances may have been confined 
 to one period, but that period must have been divided by long 
 intervals of time. 
 
 Each movement had its own system of fissures, often inter- 
 secting the preceding system at a low angle, and its distinct 
 type of lava to fill those fissures. 
 
 It is proper at this time to state that the pre-Tertiary fissures, 
 most noticeable in the southern portion of the district, have no 
 observable connection with the Cripple Creek volcano, and, 
 when filled with dike-rock, the filling is of diabase. 
 
 For reasons which have already been given, it is known that 
 the rocks referred to as guides represent the latest lava ex- 
 truded by the volcano. 
 
 It is also positively known that ore-deposition occurred sub- 
 sequent to the latest eruption or intrusions, as mineralization 
 has occurred through and along the latest dikes where they are 
 intersected, crossed or followed by the fissures which form the 
 veins. And it is a significant fact that these later fissures, 
 while occurring almost independently of the dikes, seem to be- 
 long to the same general fissured zones, and doubtless repre- 
 sent shrinkage-cracks, probably along lines of weakness re- 
 sulting from the contraction of the mass upon cooling, imme- 
 diately following the intrusion of the dikes. These cracks were 
 further enlarged, individualized and intensified by faulting- 
 movements, which unquestionably are responsible for transpor- 
 tation, localization, and probably, to some extent, deposition of 
 the ore. 
 
 It has been argued by some that the later dikes cut the 
 veins, and that at the points of intersection for the full width of 
 the dikes no ore could be found. This opinion, it is believed, 
 is formed from a lack of careful investigation and study, and 
 
 27 
 
418 BASALTIC ZONES AS GUIDES TO ORE-DEPOSITS. 
 
 an improper appreciation of circumstances and surroundings. 
 Existing conditions do not warrant such a belief or confirm 
 such an opinion. 
 
 The most prominent instance upon which this argument is 
 based has been thoroughly investigated by the writer, physio- 
 graphically, chemically and microscopically. It was thereby 
 positively determined that the rock in question is not a Terti- 
 ary basalt, but an ancient diabase. Several years ago (owing 
 to its extreme decomposition and alteration and the position 
 which it occupies, being near the contact between the breccia 
 and granite) it was mistaken for andesite. It is also inferred, 
 from such investigation, that the rock was so highly altered 
 long prior to the circulation of the ore-bearing solutions that 
 none of the necessary reagents for precipitation had been re- 
 tained; nor could it, in its condition, maintain the temperature 
 presumed to be necessarily attendant upon ore-deposition. 
 
 It is not to be expected that the fissures would maintain 
 their individuality through a decomposed, crumbling forma- 
 tion, although considerable silicification might characterize the 
 mass locally. 
 
 It has further been urged, in support of this theory, that the 
 deposits, admitting that such occur, through and along dikes, 
 are " secondary enrichments " from decomposition and leach- 
 ing of the ores from the lateral points where the veins have 
 been cut off by, and adjoin, the dikes; but no explanation is 
 offered by its exponents as to why the fissures extend uninter- 
 ruptedly through the dikes,- where in a sufficiently preserved 
 condition to support them. 
 
 The latter argument is not logical, as the deposits occurring 
 in the dikes are composed of sulphides and tellurides, corre- 
 sponding in every particular with the veins before entering or 
 crossing them. And even if these fissures and veins, contain- 
 ing ores consisting of the original minerals, did not extend 
 through the dikes, the explanation would be that the dikes 
 were still in a plastic state when the fissures were formed, all 
 evidence of which would then become obliterated when the 
 lava solidified. There are instances, to be sure, where the 
 original gold-bearing minerals to be seen in the dikes have be- 
 come much more oxidized than in the enclosing country-rock; 
 but this condition should be expected in all basic rocks, owing 
 
to their many easily-destructible 
 constituents. In the quartz-por- 
 phyry, however, the sulphides and 
 tellurides show the effects of oxida- 
 tion much less than in the enclosing 
 breccia and phonolite, although this 
 dike is characterized by both augite 
 or pyroxene and plagioclase. 
 
 The following mines, with which 
 the writer is familiar, having been 
 connected with them professionally 
 or otherwise, will be cited as ex- 
 amples in support of the arguments 
 advanced in this paper : 
 
 1. In various " workings " of the 
 Portland, Independence, Strong, 
 Dillon, Monument and Granite 
 mines, upon Battle mountain, there 
 is a zone containing several distinct 
 nepheline-basalt dikes, all having a 
 general northerly and southerly 
 course, and many short, lenticular* 
 masses or " plugs " of the same ba- 
 salt, often wholly altered or heavily 
 mineralized, forming locally good 
 ore. This zone is about 1200 ft. 
 wide. 
 
 2. The May Belle Tunnel, Gold 
 Coin, Ajax, Dead Pine, Triumph, 
 Coriolanus and Carbonate Queen 
 mines, upon the same mountain, 
 are penetrated or crossed by dikes 
 of limburgite, or the fissured zone 
 to which the dikes belong. This 
 zone is about 600 ft. wide, and a 
 broken, erratic dike of limburgite 
 extends along it, having a N. and 
 S. course. Near the southern ex- 
 tremity of the zone one of the fis- 
 sures is filled with verite for a dis- 
 
 * Inclination with dip of veins, in all cases 
 herein cited. 
 
 3. 
 
 a 
 Showing the .Relation between 
 
 Limburgite and the Ore-Zone. 
 
 a, Fissured zone. 6, Limburgite. 
 
 c, Ore- shoots. 
 
.420 BASALTIC ZONES AS GUIDES TO ORE-DEPOSITS. 
 
 tance of several hundred feet. Near the center of the zone, 
 transversely, occurs a small vent or crater, filled with limbur- 
 gite. (See Fig. 3.) The dike splits near the Ajax mine, the 
 branches separating, and the principal one veers slightly to 
 the northwestward, passing through Eclipse ground near Arequa 
 gulch, and into the Moose mine on Raven hill. 
 
 3. The Thompson, Elkton, Raven and Tornado mines, located 
 upon Raven hill, have their workings in and along nepheline- 
 basalt dikes, the entire thickness of which, at times, comprises 
 the ore-bodies. 
 
 4. The Pointer, Midget, National and Moon- Anchor mines, 
 all upon Gold Hill, save the National, are situated upon a nar- 
 row-fissured zone, having a NNE. course. One strong 'dike of 
 limburgite which enters them is traceable for a half-mile 
 through the granite to the southward. Near the contact (be- 
 tween the granite and breccia) the dike is scattered by a quartz- 
 porphyry dike, which it then follows. A few hundred feet to 
 the northeast of this point it again becomes well-defined and 
 passes to the northward. In the northern portion of this zone 
 occur several parallel dikes of limburgite. 
 
 It has very recently been discovered by the writer that the 
 ore-deposit worked through the National mine is associated 
 with one of the late igneous eruptives. This mine is located 
 on a narrow easterly and westerly fissure-system in the granite, 
 some 500 feet west of the westernmost fissure of the north-south 
 zone. The condition of the few lens-shaped masses of basaltic 
 rock (which is limburgite), conforming to the fissure-cavities, 
 stamps this occurrence as an apophysis. This supposition is 
 also borne out by the fact that the ore-body was very limited. 
 
 5. The Red Spruce, Accident, Mint, Union Belle, Hillside, 
 Moonlight and Anchoria-Leland mines, on Gold Hill, are pene- 
 trated by, or have their ore-bodies composed of, or associated 
 with, quartz-porphyry and limburgite.* The quartz-porphyry 
 
 * The dike of limburgite following the NE.-SW. fissured zone, represented as 
 coming in at the southwest corner of Fig. 4, reaches across, diagonally, from 
 another N.-S. fissured zone to the west. It does not cross the westernmost zone, 
 however, but turns southward and follows it for some distance before "pinch- 
 ing." This N.-S. zone passes through the Gold Bond property, the El Keno 
 mine, famous for having produced the first calaverite-bearing ore of the district, 
 and its influence is next observed in the Dead Shot and Mary Nevin properties 
 to the southward. 
 
BASALTIC ZONES AS GUIDES TO ORE-DEPOSITS. 
 
 421 
 
 dike occupies one or more fissures of a zone having a course 
 approximately northeast. This dike is much brecciated, and 
 not as well defined as the basaltic dikes. It was contempora- 
 neous with a movement of the country which had not entirely 
 
 FIG. 4. 
 
 Gr 
 
 Limburgite Dike in El Reno Mine. 
 6r, Breccia. Gr, Granite. Qp, Quartz-porphyry. 6, Ore-shoots. Ib, Limburgite. 
 
 subsided until the dike had cooled; therefore, its continuity is 
 broken in many places between the contact, where it has its 
 westerly termination, and the point where it is intersected by 
 the limburgite, described in case 4. A portion of the limbur- 
 gite deviates from its regular course at this point, and subordi- 
 
422 BASALTIC ZONES AS GUIDES TO ORE-DEPOSITS. 
 
 nate amounts are observed at various intervals accompanying 
 the quartz-porphyry as far as explored. This is the narrowest 
 zone of the several described, not exceeding 100 feet in width 
 at any point. 
 
 The Red Spruce and Accident mines, in this connection, de- 
 serve especial mention, as they differ considerably from any 
 other mines in the district. They are both situated on the 
 true contact* between the breccia and granite. There are 
 small, detached bodies of phonolite, trachyte, limburgite and 
 quartz-porphyry present in their workings, The first two are. 
 of limited, the third of general, and the last of special, eco- 
 nomic importance. The limburgite which appears in the Acci- 
 dent shaft at a depth of 240 feet crosses the contact at an 
 approximately right angle, piercing the granite to the west- 
 ward. This is an apophysis, and its individual influence is not 
 remarkable. The quartz-porphyry follows the contact, at 
 times, then deviates to the westward, into the breccia, fol- 
 lowing fissures parallel to the contact for 50 or more feet, and 
 then again breaks across the formation to the contact.- A 
 branch of this dike extends northward under conditions as 
 described, while the main dike passes to the northeast into the 
 Mint, Union Belle and Hillside mines. The chief ore-bodies 
 of the Accident and Red Spruce mines contain lead, silver 
 and gray copperf (all characteristic of quartz-porphyry), some 
 gold-bearing pyrite, also calaverite and sylvanite. 
 
 6. The Zenobia, Pharmacist, Burns, Orphan Belle, Isabella, 
 Block 8 of State land, Free Coinage, Lucky Guss, Deadwood, 
 Delmonico, Vindicator, Christmas and Golden Cycle mines, 
 situated upon Bull Hill, are crossed by or associated with 
 tephrite or feldspar-basalt. 
 
 * A line drawn from the northeast shoulder of the contact, near the center of 
 Fig. 4, northwestward, along the easterly side of the detached granite mass, 
 would represent the position of the contact as described in all literature and 
 shown on all maps of the district so far published. This is for the reason that 
 all of the maps are copies, with a few omissions or additions, of the " Special 
 Cripple Creek Sheet" issued by the U. S. Geological Survey. Dr. Cross, who 
 was in charge of the field-work of the Survey, attempted to represent approxi- 
 mately, only, the position of the contact at this and other points. 
 
 f The superintendent of the Accident mine informs me that he found a "kid- 
 ney" of gray copper-ore in a "split" in the dike (quartz-porphyry), containing 
 about 1000 pounds, which sampled 5000 ounces silver and 50 ounces gold per 
 ton. 
 
BASALTIC ZONES AS GUIDES TO ORE-DEPOSITS. 423 
 
 7. An examination of the Victor mine disclosed lenticular 
 masses of a basaltic rock accompanying the vein, too highly 
 mineralized for accurate classification. 
 
 8. The same condition was observed in the Doctor-Jack Pot 
 workings on Raven Hill ; and much of the breccia, heretofore 
 lassed as " andesitic," contains fragments of basalt or limbur- 
 gite. 
 
 It will be observed, therefore, that the mines which have 
 produced 90 per cent, of the gold of this district, which has 
 amounted to more than $115,000,000 during the past ten years, 
 are penetrated or crossed by, or closely associated with, the 
 various basaltic rocks and the dike of quartz-porphyry ; and for 
 these very important reasons I infer, and it appears to be both 
 logical and proper to state, that the rock-types and association 
 above described are the true and only guides to point out the 
 probable course to pursue in order to open a " pay mine " in 
 the Cripple Creek district. 
 
424 THE GOLD-PRODUCTION OF NORTH AMERICA. 
 
 No. 16. 
 
 The Geological Features of the Gold-Production of North 
 
 America.* 
 
 BY WALDEMAR LINDGREN, WASHINGTON, D. C. 
 
 (New Haven Meeting, October, 1902. Trans., xxxiii., 790. Part III. omitted in this 
 republication.) 
 
 CONTENTS. 
 
 PAGE 
 
 I. INTRODUCTION, . . . . . . ' . . . . . 424 
 
 II. GEOLOGICAL FEATURES : . . . ... . 427 
 
 The Gold- Bearing Fissure- Veins, ....... .427 
 
 .Contact-Metamorphic Deposits, . ... . . . 432 
 
 Classification According to Age, . . . . . . 433 
 
 Introduction, .- ... , . 433 
 
 Pre-Cambrian Deposits, . . ... . . . 434 
 
 Cretaceous Veins of the Pacific Coast, . . . . . 435 
 
 Late Cretaceous or Early Tertiary Deposits (Central Belt;, . 436 
 
 Tertiary Deposits, . 438 
 
 Conclusions, . . ...... . . . . 442 
 
 I. INTRODUCTION. 
 
 THE precious metals, gold and silver, are the basis of the 
 monetary systems of the world. It is, therefore, natural and in- 
 evitable that widespread interest should be manifested in their 
 production and in the various classes of deposits in which they 
 are contained. 
 
 At times a great scarcity of the precious metals has pre- 
 vailed; at other times the production has seemed so abnor- 
 mally large that fears have been entertained regarding their 
 ultimate retention as standards of value. Since most nations 
 have adopted the gold standard, and the remaining ones appear 
 likely to do the same in the near future, the question of avail- 
 able supply of gold for the present and future very naturally 
 arises. This necessarily involves a consideration of the char- 
 acteristics of the gold-deposits. 
 
 After the absorption of the gold treasures of the New World 
 by the conquistador es, the gold-placers of Brazil and Russia 
 
 * Published with the permission of the Director of the U. S. Geological Survey. 
 
THE GOLD-PRODUCTION OF NORTH AMERICA. 425 
 
 next filled the world's need ; later, when these sources of the 
 precious metal began to be exhausted, came the great discov- 
 eries of California and Australia, which for a time caused 
 doubts to arise as to the wisdom of maintaining this metal as 
 a standard of value; but from the maximum of output ob- 
 tained during the early years a steady decline began. The un- 
 certainties as to the amount of gold available for the future 
 were emphatically expressed by eminent geologists and mining 
 engineers. 
 
 After an admirable discussion of the gold-resources of the 
 world, Prof. Edward Suess, of Vienna, in his book, The Future 
 of Gold, 1 came to the conclusion that there was scarcely any 
 hope of further considerable discoveries, and that the output 
 would gradually decrease, so that the metal would no longer be 
 able to maintain its present economic position. 
 
 About the same time, in 1880, Alexander Del Mar published 
 his History of the Precious Metals, and arrived, in the main, at 
 similar conclusions. He believed that not only physical devas- 
 tation, but moral and political decay, follows as the result of 
 gold-mining, and that the total supply of both metals, and par- 
 ticularly of gold, will continue to diminish both in the mines 
 of the Pacific coast and in those of other countries. It seemed 
 to him " but too evident that the future supply of these metals 
 will not only fail to keep pace with the growth of population 
 and commerce, but they will absolutely diminish." 
 
 There seemed, indeed, to be good reason for such conclu- 
 sions, for the gold-supply of the world was steadily diminish- 
 ing and no new sources seemed in sight. But these years 
 proved to be the turning-point, and the production again began 
 to increase, at first, however, very slowly. In 1892, S. F. 
 Emmons, in a most valuable review of the gold- and silver-pro- 
 duction, came to the conclusion that a further advance in the 
 output of gold was probable ; that the annual production of the 
 United States would soon " increase to $40,000,000, and per- 
 haps beyond;" and that the gold-production of the world would 
 "increase to $150,000,000 within a few years, and perhaps to 
 $200,000,000 before the close of the decade." 2 These predic- 
 tions have been greatly exceeded by the results of the work of 
 
 1 Die Zukunft des Gotdes (1877). 
 
 2 Mineral Resources of the United States for 1892, pp. 90 to 93 (1893). 
 
426 THE GOLD-PRODUCTION OF NORTH AMERICA. 
 
 the last few years. The treasures of South Africa and West 
 Australia were found; in Alaska and British Columbia new 
 deposits of wonderful extent were opened; and even in such 
 presumably well-prospected regions as Colorado, California, 
 Arizona, Montana, and Mexico, new finds were constantly 
 reported, and the production rose steadily and rapidly. 
 
 About 1880 the world's annual production of gold was ap- 
 proximately $100,000,000; that of the United States about 
 $33,000,000. In 1900 the gold-production of the world had 
 increased to nearly $300,000,000, and that of the United States 
 to $79,000,000. While it is true that it is easier to criticise 
 than to predict, it may be pointed out that two principal errors 
 vitiated the conclusions of Professor Suess and Mr. Del Mar : 
 In the first place, the lands of the world were deemed to be so 
 well prospected that no further discoveries were probable ; the 
 second error lies in the failure to anticipate the possibility of 
 new processes for gold-extraction and the utilization of vast 
 reserves of low-grade ore-bodies. 
 
 The figures of the gold-production during the last decade 
 may indeed cause hesitation in further predictions as to the 
 available amount of gold. As to ultimate results, it would 
 seem as if we should be justified in concluding, with Professor 
 Suess, that the gold-supply of the world will gradually decrease 
 if no further important improvements are made in the pro- 
 cesses for the extraction of this metal ; but regarding events 
 so far distant no predictions may safely be made. Regarding 
 the immediate future, it seems likely that the present produc- 
 tion of the world will be sustained, and possibly increased. 
 
 The purpose of this paper is briefly to consider the product 
 of each State in North America, emphasizing especially the 
 derivation of the gold from its various classes of deposits, so 
 as to arrive, if possible, at an approximate conclusion as to the 
 relative importance of the different kinds of deposits, and 
 finally to indicate the probable outlook in each State for the 
 immediate future. These calculations have been made possible 
 by the aid of the reports of the United States Mint on the 
 production of the precious metals, the character of which has 
 steadily improved, and which afford a vast amount of important 
 data for the student ; and, further, by the reports of the official 
 geological surveys in regard to the economic geology of the 
 
THE GOLD-PRODUCTION OF NORTH AMERICA. 427 
 
 States. Much is still lacking, more especially in the knowledge 
 of the age of many deposits, and this paper must, therefore, be 
 considered only as an imperfect first attempt to collect data 
 which are at the disposition of many, but the arrangement of 
 which has not yet, for some reason, been undertaken. 
 
 II. GEOLOGICAL FEATURES. 
 The Gold-Bearing Fissure- Veins. 
 
 Practically all the gold-output of North America is derived 
 from fissure-veins or from deposits which possess close relation- 
 ship to fissure- veins. Gold-bearing fissure-veins are in most 
 cases accompanied by placers, which are only the result of 
 nature's crushing, concentrating, and refining; and these 
 placers may be of different ages according to the date of forma- 
 tion of the vein. Most of them are naturally of Pleistocene 
 (recent) or Tertiary age. For the present purpose the placers 
 will not be considered separately, but as belonging to the fissure- 
 veins from which they were derived. 
 
 The deposits in fissure-veins are believed to have been formed 
 chiefly by ascending hot waters. The general trend of the tes- 
 timony indicates that the gold is brought up from lower levels 
 rather than derived from rocks near the surface. 
 
 Gold-bearing fissure-veins or- equivalent deposits occur in 
 practically all kinds of rocks known on the continent ; it is 
 apparently not possible to establish wide-reaching genetic con- 
 clusions on the basis of the petrographical character of the 
 wall-rock. 3 
 
 The influence of locality is much stronger. Gold-bearing 
 veins cluster in certain localities. A critical examination will 
 reveal the fact that many vein-systems are massed about the 
 contacts of intrusive masses, which consolidated far below the 
 original surface of the earth at the time of the igneous activity, 
 and which have been exposed by subsequent erosion. Most 
 commonly, perhaps, these intrusive rocks are diorite, monzonite, 
 quatftz-monzonite, granodiorite, or their porphyries, more rarely 
 typical granites. Under favorable conditions it can often be 
 proved, and in other cases established with probability, that 
 
 3 This point has recently been emphasized by W. H. Weed in his paper, The 
 Influence of Country-Rock on Mineral Veins, Trans. t xxxi., 634 (1901) ; p. 216, 
 this volume. 
 
428 THE GOLD-PRODUCTION OF NORTH AMERICA. 
 
 the upper part ot the vein has been removed by the same ero- 
 sion which laid bare the intruded rock-masses. In other words, 
 the top of the vein has been removed, the root remains. It 
 seems plausible that in these cases the igneous intrusion was 
 one, perhaps the principal, of the genetic causes. Dynamic 
 action producing fissures in and about the intrusives is another 
 genetic cause. The age of these veins must in general be con- 
 siderable, for the great erosion involved has usually required a 
 long time-interval. 
 
 Another large class of vein-systems cut the recent or com- 
 paratively recent lavas, which cover the surface of the older, 
 eroded rocks in the form of successive volcanic flows. Fre- 
 quently the age of these lavas may be established with accuracy. 
 From available data we may be enabled to determine the ap- 
 proximate level of the surface of the earth at the time the 
 last flow was erupted; and, in the case of veins cutting this 
 series, we are enabled to say with certainty that a given part of 
 the vein was near the original surface of the earth existing at 
 the time of vein-deposition. This given part may, then, be 
 said to be the top or the true apex of the vein. 
 
 It is true that there are very many cases in which we cannot 
 determine with certainty, or even with probability, at what 
 vertical distance from the part of the. vein under discussion the 
 original surface of the earth, at the time of vein-formation, was 
 located. But this does not diminish the force of the argument 
 in the two principal divisions discussed. There are certainly 
 few gold-bearing districts on the continent which do not occur 
 either near or in intrusive masses, or in or near volcanic flows. 
 In districts of igneous activity the effusion of surface-lavas is 
 generally accompanied by the intrusion of bodies of magma far 
 below the surface, which, owing to physical conditions, consoli- 
 dated as granular or coarsely-porphyritic rocks. This has actu- 
 ally been shown in many volcanic districts which have been 
 deeply and rapidly dissected by erosion. In rare cases we may 
 even trace the vein from the top in the effusive lavas down to 
 the root in intrusive rocks. It may, therefore, be concluded 
 as most probable that the two classes of veins described above 
 are really of the same kind : that the roots reached up through 
 once overlying, now eroded, lavas, and that the tops generally 
 may be traced through the lavas to the vicinity of the intruded 
 masses. 
 
THE GOLD-PRODUCTION OF NORTH AMERICA. 429 
 
 The question whether any difference exists in mineral com- 
 position and metasomatic alteration between the tops and the 
 roots of veins is a most important one, but it cannot be defi- 
 nitely answered in the present state of our knowledge. There 
 are arguments pro and con. Professor De Launay answers the 
 query in the affirmative, and many of his arguments have great 
 force. This much is certain : that in many cases of gold-quartz 
 veins differences of up to 4,000 ft. in elevation have little in- 
 fluence on the minerals and vein-matter, while in some cases, 
 and chiefly with smelting-ores rich in silver, distinct changes in 
 mineral composition appear in depth, which would seem to be 
 independent of secondary alteration or enrichment. 
 
 Fissure-veins carrying gold have certainly been formed at 
 various times in the geological history of the continent. Cam- 
 brian conglomerates bear witness to pre-Cambrian gold-veins, 
 and very recent thermal deposits at Steamboat Springs, Nev. 
 (according to Becker), and at Boulder,' Mont, (according to 
 Weed), prove that gold is deposited by thermal waters to-day. 
 But the process has evidently not been a continuous one. 
 Cambrian, Silurian, Devonian, and Carboniferous gold-deposits 
 are not definitely known to exist in North America. Continu- 
 ous sedimentation, absence of dynamic movements, and rela- 
 tively slight igneous activity characterized these periods. 4 
 
 The great eruptions of the Cordilleran belt of North Amer- 
 ica began during the Triassic period of the Mesozoic age, and 
 igneous activity has continued almost without interruption 
 from that date to recent time. Each eruption has probably 
 been accompanied by more or less extensive deposition of gold 
 in fractures near the igneous focus. On the Pacific coast the 
 eruptions began at an earlier date than in the region of the 
 Rocky mountains; and, likewise, many of the gold-deposits of 
 the Pacific coast antedate those of the Rocky mountains. In 
 the latter province the igneous rocks began to break out at the 
 close of the Cretaceous period, and have continued at least up 
 to the beginning of the Pleistocene. Certain periods of depo- 
 sition, however, stand out prominently, and we may with good 
 reason separate the distinctly Cretaceous or late Mesozoic gold- 
 
 4 Igneous rocks of Palaeozoic age are found at various places along the Sierra 
 Nevada, British Columbia, and Alaska. If Palaeozoic gold-deposits are found on 
 this continent, it will probably be along this line. 
 
430 THE GOLD-PRODUCTION OF NORTH AMERICA. 
 
 belt of the Sierra Nevada and the Pacific coast in general from 
 the Tertiary, mostly post-Miocene, veins so extensively devel- 
 oped in Mexico, Nevada, and Colorado. The former are gen- 
 etically connected with great intrusions of granitic and dioritic 
 rocks, the latter with big flows of surface-lavas which erosion 
 has not, as yet, removed. But both in the Great Basin and in 
 the Rocky mountains there are also many deposits of late Ore. 
 taceous or early Tertiary age genetically connected with intru- 
 sions of granitic rocks and, very commonly, porphyries. In 
 very many cases the age of these deposits is doubtful. If ero- 
 sion has been exceptionally active in the particular district in 
 which they occur, they may well, though occurring in connec- 
 tion with deep-seated intrusions, be of Tertiary age. To this 
 class of doubtful age belong, for instance, many of the gold- 
 veins of Montana. Miocene and later igneous rocks are often 
 lacking in this region, so that an accurate determination of 
 age becomes very difficult. 
 
 Still another complication to be borne in mind consists in 
 possible, though probably rarely occurring, re-opening of veins 
 and superimposition of deposits of two or several epochs. All 
 this being admitted, there still exists, in my opinion, sufficient 
 reason for attempting a division of the deposits according to 
 age. It is readily acknowledged that this first attempt is im- 
 perfect, and that future researches will probably bring many 
 changes in the divisions here tentatively set forth. 
 
 The next question is, whether there is any notable difference, 
 in mineral constituents and metasomatic alteration, between 
 deposits of various periods. The mineral vein is the result of 
 two variable factors : the composition of the mineral waters 
 and the conditions at the time of deposition. Is there any 
 definite gradual change in both or either of those factors by 
 which the older deposits can be distinguished from the younger ? 
 
 The question of depth below the original surface has already 
 been touched upon, and in considering the present problem it 
 is necessary to deal with those parts of deposits of various ages 
 which were formed at the same distance from the original sur- 
 face. A definite answer is difficult because the older deposits 
 are usually more deeply eroded than the recent ones. A priori,. 
 however, there seems no reason why a difference should exist 
 for mineral waters of as many different kinds of composition 
 
THE GOLD-PRODUCTION OF NORTH AMERICA. 431 
 
 as are seen to-day have probably always reached the surface, 
 and the conditions of deposition at corresponding levels and 
 under corresponding circumstances have probably always been 
 about the same. 
 
 Looking over the field, it is undeniable that within many 
 belts of gold-deposits of contemporaneous origin the veins are 
 very similar in mineral composition and metasomatic develop- 
 ment. The Appalachian belt of gold-quartz veins contains 
 deposits of striking similarity from one end to the other. The 
 Mesozoic gold-quartz veins of the Pacific coast are practically 
 identical in character from Lower California to Alaska, and, 
 moreover, closely related in character to the far older Appala- 
 chian belt. Where the wall-rocks were easily altered, they 
 contain abundant calcite and other carbonates, besides much 
 sericite. This points, without doubt, to a remarkable constancy 
 throughout the whole province in the composition of the min- 
 eral waters which formed the veins. They were manifestly 
 distinguished by an abundance of alkaline carbonates. On the 
 other hand, scarcely one of the veins, which in so many part& 
 of the Cordilleran region cut volcanic flows of Tertiary age, 
 can be classed as identical with the Pacific coast type of gold- 
 quartz veins. While it is perhaps not permissible to say that 
 they represent one type, yet most of them have certain com- 
 mon, peculiar features, constituting a relationship. They fre- 
 quently contain both gold and silver; the gold is finely divided, 
 and rarely accumulates below the veins in such rich placers as 
 are found associated with the Pacific coast type of gold-quartz 
 veins ; the metasomatic alteration is generally propylitic ; that 
 is, accompanied by the formation of chlorite, epidote, and, near 
 the veins, of sericite and kaolin, while the extensive carbonatiza- 
 tion found near the California gold-quartz veins is usually 
 absent. The mineral waters accompanying the Tertiary erup- 
 tion certainly differed on the whole, and notably from those of 
 other eruptive periods, and were apparently lacking in alkaline 
 carbonates. Professor Suess recognized this type long ago, 
 basing his conclusions largely on von Richthofen's work. Pro- 
 fessor Vogt has more recently insisted on its importance. 
 There are several types of these Tertiary veins, and it is per- 
 haps not advisable, as I have done in a preliminary note on 
 this subject, to retain the name propylitic for the whole group,, 
 as some of them do not show this alteration in typical form. 
 
432 THE GOLD-PRODUCTION OF NORTH AMERICA. 
 
 In conclusion, it may be said that gold-veins of the same 
 age and province usually have the same characteristics. Belts 
 of different age may differ greatly in general features. This is 
 probably due to varying composition of the mineral waters fol- 
 lowing different periods of eruption. 
 
 Possibly, as suggested above (p. 430), the depth below the orig- 
 inal surface may have something to do with this question, as 
 the older veins are usually deeply truncated by erosion, and a 
 gradual change in the character of the thermal waters may have 
 taken place during the upward passage of the solutions. More 
 likely, however, the principal cause is a radical difference in the 
 composition of the waters throughout the province. 
 
 In comparing different veins with a view to the elucidation 
 of this problem only those having country-rock of similar gen- 
 eral character should be selected, for it is well known that the 
 composition of the wall-rock may have great influence on the 
 metasomatic processes, and hence on the composition of the 
 vein. 
 
 Contact- Metamorphic Deposits. 
 
 The preceding remarks apply exclusively to fissure-veins and 
 the closely-related irregular deposits in which the gold was 
 deposited by heated waters, which, as a rule, probably came up 
 from below. 
 
 There is another source of gold in the so-called contact-met- 
 amorphic deposits formed at or near the contacts of intrusive 
 granitic or porphyritic rocks. The characteristic mineral asso- 
 ciations (ordinarily garnet, epidote, vesuvianite, ilvaite, magne- 
 tite, specular hematite, and sulphides) of these deposits are 
 such that they are probably best explained as the products of 
 the action of water above the critical temperature. This water 
 is believed to have been given off from the hot magma, and to 
 have been accompanied by metallic compounds, sulphur, etc., 
 also probably above their critical temperatures. Under these 
 conditions that is, a temperature of not less than -f- 365 G., 
 and a pressure of not less than 200 atmospheres water can 
 only exist as a perfect gas. Minerals formed under such con- 
 ditions are known as of pneumatolytic origin. 
 
 When the temperature sinks below this limit the water, if 
 under sufficient pressure, remains an ordinary fluid, and the 
 
THE GOLD-PRODUCTION OF NORTH AMERICA. 433 
 
 deposits formed by it appear to undergo a change. To such 
 conditions the deposits of ordinary fissure-veins should proba- 
 bly be attributed. 
 
 .Finally, under conditions of high temperature and slight 
 pressure very near the surface, water, as well as other com- 
 pounds, may be converted into a vapor, and such deposits as 
 may be formed by this action are said to be due to sublimation. 
 Escaping gases from heated rocks near the surface in volcanic 
 districts are called fumaroles. The name of fumaroles or fu- 
 marolic action is sometimes applied to contact-metamorphic 
 deposits, but this usage appears to me to be incorrect. 
 
 Contact-metamorphic deposits occur in the United States, as 
 well as in British Columbia and Mexico. Ordinarily, copper 
 sulphides and magnetite are the principal ore-minerals, but they 
 may carry a small quantity of gold. A certain small amount 
 of gold has been derived from these deposits in the United 
 States and British Columbia; just how much is very difficult 
 to decide. In Mexico contact-metamorphic deposits are more 
 common, and sometimes contain much gold. It is probable that 
 more than $1,000,000 has been obtained from this source in 
 Mexico; but here, again, exact figures are unobtainable. 
 
 Classification According to Age. 
 
 Introduction. In stating the production of gold in the various 
 States, it is necessary to adopt some unit for its measurement. 
 The one selected is $1,000,000 ; this unit will be indicated by 
 M 2 $. 5 In this manner the results will be much more clearly 
 presented than by long series of figures. The most scientific 
 way to express the product is doubtless in kilograms ; but for 
 the present purposes the adopted unit seems much more tangi- 
 ble and more easily understood. 
 
 From the Atlantic to the Pacific ocean, the mountains of 
 North America contain gold, although the largest treasures 
 are stored in the great ranges of the Cordilleran region. From 
 the time of discovery up to 1900 the United States has pro- 
 duced about M 2 $2,529, Mexico at least M 2 $200, and possibly 
 twice as much, and British North America M 2 $140, making a 
 grand total of M 2 $2,869. This great product is divided among 
 
 6 For example, M 2 $1.0 = $1,000,000. M 2 $2.25 = $2,250,000. M 2 $0.5 = 
 $500,000, etc. 
 
 28 
 
434 THE GOLD-PRODUCTION OF NORTH AMERICA. 
 
 primary veins of pre-Cambrian, Mesozoic, and Tertiary age. 
 To separate the last two groups is in many cases a difficult 
 matter. 
 
 Pre-Cambrian Deposits. Gold was discovered in veins of the 
 older rocks of the Appalachian Mountain region about 100 
 years ago, in Georgia, the Carolinas, Tennessee, Maryland,. 
 Virginia, and even farther north. Poorer deposits of the same 
 kind have been found up to the Canadian line, and north of 
 this richer gold-veins occur again in Quebec, Ontario, and 
 Nova Scotia. Again, farther westward in the United States,. 
 in Michigan, probably pre-Cambrian gold-quartz veins occur 
 on a smaller scale. Still farther west they are developed in 
 the Black hills of South Dakota, and also in Wyoming. The 
 last two are the only localities in the Cordilleran region in 
 which pre-Cambrian deposits have been recognized. 
 
 The primary deposits in the above-mentioned districts are 
 chiefly gold-quartz veins with free gold and auriferous sul- 
 phides. The veins were probably to a large extent formed 
 before the Cambrian period, and are thus the most ancient 
 deposits of the continent. Among the evidence pointing di- 
 rectly or indirectly to this conclusion, the following have es- 
 pecial weight : The Triassic sandstones of the Atlantic coast 
 contain placer-gold; no important gold-deposits are found in the 
 Palaeozoic rocks of the Appalachian region ; Carboniferous con- 
 glomerates in Nova Scotia are said to contain water- worn gold 
 of older veins ; in the Black hills the Cambrian conglomerates 
 yield placers of the precious metal. During the 19th century 
 the Southern States produced M 2 $47.0, Nova Scotia and adja- 
 cent provinces M 2 $l 7.0; during the last ten years the South- 
 ern States have yielded M 2 $0.3 and the eastern Canadian prov- 
 inces from M 2 $0.5 to M 2 f 1.0 per annum. The deposits are not 
 rich according to our standards for the Cordilleran region, 
 but the yield is steady, and can probably be relied upon for 
 many years to come. 
 
 Economically, the most important pre-Cambrian deposits are 
 found in the Black hills. The old pre-Cambrian schists here 
 contain fissure-veins and seam-belts of free-milling gold-ores 
 covered by Cambrian sandstones containing placer-gold. These 
 deposits are worked on a large scale ; they have yielded, since 
 discovery in 1876, about M 2 f 74.0, and produce annually M 2 $ B 
 or M*f 4. 
 
THE GOLD-PRODUCTION OF NORTH AMERICA. 435 
 
 Altogether, then, the pre-Cambrian deposits have given us, 
 since discovery, M 2 f 138.0. In most cases extensive erosion has 
 taken place since these veins were formed, and the surface of 
 the land at the time of their formation must in some cases, at 
 least, have been thousands of feet above the level at which they 
 are worked at present. They are the " roots " rather than the 
 " tops " of veins. 
 
 Cretaceous Veins of the Pacific Coast. The most important 
 gold-belt in North America extends along the Pacific coast. 
 It is throughout characterized by quartzose ores with free 
 gold and auriferous sulphides. A great erosion has taken 
 place since the veins were formed; and here, too, as in the 
 pre-Cambrian deposits, we have to deal with the lower parts of 
 veins, the upper parts having generally been removed, in many 
 places to the extent of thousands of feet. 
 
 Beginning in Lower California, Mexico, 100 miles or more 
 south of the boundary-line, this great belt continues through 
 San Diego, Los Angeles, and Kern counties ; through the cen- 
 tral part of California, where it is developed in great strength ; 
 then on to northern California, southwestern and northeastern 
 Oregon, and Idaho. In the latter States it is modified by the 
 appearance of many silver-gold deposits and veins carrying 
 auriferous sulphides without free gold. Covered for a distance 
 by the lava-flows of the Cascades, it again appears in southern 
 British Columbia on Vancouver Island, among other places. 
 Strong development is again attained in the Cariboo district, in 
 central British Columbia, and it continues through the Omi- 
 neca, Cassiar, and Atlin districts to the Klondike region. 
 Thence, bending westward, it follows the Yukon to the western 
 end of the continent at Nome, on the Seward Peninsula. 
 
 The Cretaceous age of this belt is clearly established in Cal- 
 ifornia. In Oregon and Idaho, a late Mesozoic age is extremely 
 probable. In British Columbia and Alaska, the evidence is not 
 so positive, and the deposits may possibly, in part, be older. 
 
 /Throughout this immense stretch of country the veins are 
 accompanied by a great development of placers. Placers are, 
 indeed, characteristic of this class of gold-veins, and by far the 
 larger part of the yellow metal has been obtained from them. 
 At many places in California, as well as in Oregon and Alaska, 
 the veins from which these placers were derived have been very 
 
436 THE GOLD-PRODUCTION OF NORTH AMERICA. 
 
 disappointing, the fact being that the primary deposits are often 
 scattered in many little seams rather than concentrated in great 
 veins. 
 
 California alone has yielded M 2 $l,380.0 from this belt; Ore- 
 gon M 2 $54.0; British Columbia and Northwest Territory 
 M 2 $123.0; Alaska M 2 $30.0. The total is over M 2 $l,700.0. 
 During 1900 the belt probably yielded M 2 $54.0, of which one- 
 half came from British Columbia and the Yukon. This repre- 
 sents a great increase compared with the figures of ten years 
 ago, and it is doubtful whether this increase will be maintained. 
 At least M 2 $27.0 was obtained from the placers on the Yukon 
 and in Alaska. If no further great discoveries are made in 
 this region, our knowledge of placers forces us to the belief 
 that this last figure will gradually decrease. Quartz-mining 
 will to some degree compensate for this; but the quartz-mines 
 have usually, in the older districts, yielded less than the cor- 
 responding placers. California's output will doubtless be main- 
 tained at about the present figure for many years. 
 
 Late Cretaceous or Early Tertiary Deposits (Central Belt}. Be- 
 sides the Pacific gold-belt, there is a broad zone in the central 
 and eastern part of the Cordilleran region which contains an 
 abundance of gold-deposits of varying character. Many of 
 these seem to have been formed a little later than the Califor- 
 nia gold-quartz veins, perhaps largely at the very close of the 
 Cretaceous, or possibly at the very beginning of the Tertiary 
 period. 
 
 This broad zone begins in Mexico, where the Pacific States 
 of Sonora and Sinaloa contain many gold-veins in pre-Creta- 
 ceous sediments, granites, and crystalline schists. According 
 to Professor Durable, many of the Sonoran deposits occur in 
 Triassic rocks, and are considered by him to be of the same 
 age as the California veins. Similar veins in old rocks con- 
 tinue through the southwestern part of Arizona, but their 
 age is not definitely known. Many of them are important 
 producers. 
 
 Although undoubted Tertiary deposits prevail in Nevada, 
 those of an older period are probably not absent. A few of 
 them are free-milling gold-quartz veins, but in the majority the 
 ores consist chiefly of sulphides alone, and the value of the 
 silver exceeds that of the gold. 
 
THE GOLD-PRODUCTION OF NORTH AMERICA. 437 
 
 In Utah the principal gold-mines are those of the Mercur 
 district, in which ores suited to the cyanide process occur in 
 limestone close to intrusive sheets of porphyry. These yielded 
 over M 2 $2.0 in 1900. Most of the remaining amount credited 
 to Utah is derived from gold-bearing silver-ores of the smelting 
 class, which are found in veins and irregular deposits in sedi- 
 mentary rocks close to bodies of intrusive (Cretaceous?) por- 
 phyries. The future of the gold-production is here very closely 
 connected with the vicissitudes of the silver- and copper- 
 markets. 
 
 In Colorado the most important Cretaceous gold-deposits are 
 those of Leadville. Here, again, the ores occur in Palaeozoic 
 sediments and porphyry; and the gold-production, small until 
 a few years ago, reached M 2 f 2.7 in 1900. 
 
 In Idaho and Montana late Mesozoic and early Tertiary veins 
 are developed on a large scale. We note here the interesting 
 fact of a junction with the Pacific belt, through northeastern 
 Oregon and central Idaho, into Montana. Going eastward, the 
 free-milling and quartzose character is partly maintained, but 
 silver becomes more prominent in the ores, and auriferous 
 sulphide ores often replace the native gold. Central Idaho 
 formerly contained many rich placer-camps, which have yielded 
 their millions. As in Oregon and in Montana, the first years 
 of mining were largely devoted to working this form of deposit. 
 Bannack, Alder Gulch, Helena, and Confederate Gulch are 
 well-known names of celebrated placer-camps in Montana. The 
 great producing quartz-mines are not, however, those from 
 which the placers have been derived. They contain much 
 silver, and pan-amalgamation is the most common process. 
 
 After the exhaustion of the placers, silver-ores of the smelt- 
 ing class, containing galena and other sulphides, together with 
 a little gold, were also extensively mined. This industry has 
 declined during recent years; but, as a partial compensation, at 
 least M 2 $1.0 per annum is obtained as a by-product from the 
 smelting of the copper-ores of Butte. 
 
 The majority of gold-bearing veins in Idaho and Montana 
 are genetically connected with the intrusion of very large 
 bodies of granitic rocks during the Cretaceous period. This 
 explains the fact of relationship with the Pacific gold-belt, for 
 there, too, the veins stand in undoubted causal connection with 
 the great Mesozoic granitic " batholiths," as the large intrusive 
 
438 THE GOLD-PRODUCTION OF NORTH AMERICA. 
 
 bodies are called. As far as we know, these batholiths are 
 either absent or only developed on a small scale in Nevada, 
 Utah, and Arizona. 
 
 In the southern part of British Columbia are a number of 
 veins which contain copper-gold ores, and to less extent milling- 
 ores, and which are believed to belong to the late Mesozoic 
 period. They are chiefly found in diorites and allied intrusive 
 rocks. 
 
 Looking at this central Mesozoic gold-belt as a whole, it is 
 believed that, north of Mexico, it has produced at least 
 M 2 $286.0 since discovery, and during 1900 its tribute to the 
 total of North America was about M 2 f 14.0. 
 
 In this chain of deposits the gold-production is closely asso- 
 ciated with the silver and copper industry, for sulphide ores 
 prevail over those containing native gold. No wonderful in- 
 crease of production may be expected, but rather a steady 
 maintenance, and possibly a gradual growth if there is no seri- 
 ous decline in the values of copper and silver. Placer-mining, 
 with its dwindling tendency, is still represented in Montana and 
 Idaho ; in the other States of this belt it plays a comparatively 
 insignificant part. 
 
 Tertiary Deposits. A fourth and last class of gold-produc- 
 ing veins are of Tertiary, mostly post-Miocene, age. They are 
 usually found in regions of intense volcanic activity cutting 
 across heavy andesite-flows, more rarely rhyolite and basalt. 
 In many cases these veins may be seen to continue down into 
 the underlying floor, upon which the volcanic flows were 
 poured out, and which may be of igneous or sedimentary char- 
 acter. -Sometimes, indeed, an active erosion has removed 
 much of the volcanic flows, and the veins crop directly in 
 older rocks. 
 
 The majority of these veins in Tertiary lavas have certain 
 common and persistent characteristics and form a fairly well- 
 defined class, usually called propylitic veins, alluding to the 
 peculiar alteration of adjoining rocks which seems to charac- 
 terize them. The ores are nearly always quartzose, and some- 
 times contain silver alone ; more rarely gold alone ; but most 
 commonly both gold and silver in about equal quantities by 
 value. 
 
 They are often characterized by great richness, the word 
 " bonanza " being employed to represent their big ore-shoots. 
 
THE GOLD-PRODUCTION OF NORTH AMERICA. 439 
 
 While some of these veins yield steady and reliable products? 
 many of them burst out in sudden blazes of glory like shooting- 
 stars, only to be extinguished with equal suddenness. The 
 gold is nearly always in such peculiarly fine distribution that 
 extensive and rich placers are rarely formed from them ; con- 
 trasting, in this respect, with conditions in the Pacific gold- 
 belt. Many of them, in districts of great erosion, show that 
 the values continue in depth ; but the ore is perhaps less rich 
 than in those parts formed nearer to the original surface. In 
 this class we evidently have to do with the part of the vein 
 which was not far from the original surface at the time of ore- 
 deposition. In some cases the ores can be proved to have been 
 formed but a few hundred feet from this surface. Instead of 
 roots of veins, as in the Pacific and Appalachian belts, the pro- 
 pylitic veins ordinarily represent the uppermost part of the 
 area of deposition along the fissure. Not all of the distinctly 
 Tertiary veins possess, however, the character of typical propy- 
 litic veins. Many deviate considerably, but few, if any, show 
 the typical development of gold-quartz veins of the Pacific 
 coast. 
 
 This belt of Tertiary veins is most extensively developed in 
 Mexico. The central plateau contains the great silver-veins of 
 this class, which always contain a small amount of gold, and 
 from which the greater part of Mexico's gold-output has been 
 derived. But along the western slope of the Sierra Madre in 
 Chihuahua, Zacatecas, and Sinaloa, heavy andesite-flows contain 
 gold-silver veins of great importance, and are, together with the 
 veins of the older belt in Sonora, largely responsible for the 
 greatly-increased gold- production of Mexico. 
 
 Entering the United States, Tertiary veins are found in Ari- 
 zona and New Mexico. In Arizona, probably both Cretaceous 
 and Tertiary veins occur, and in the present state of our knowl 
 edge their separation is sometimes difficult. The Common- 
 wealth mine, in Cochise county, is a prominent representative of 
 the younger veins ; it breaks through rhyolite, and is at present 
 one of the largest producers of the Territory. One-third of the 
 value is in gold, and the rest in silver. 
 
 In New Mexico are several districts containing these veins 
 chiefly, it is said, in andesitic rock ; but the output of this Ter- 
 ritory has not as yet reached the million-dollar mark. 
 
 The development of Tertiary veins continues northward into 
 
440 THE GOLD-PRODUCTION OF NORTH AMERICA. 
 
 Nevada and California. San Bernardino county, in California, 
 contains silver-deposits in rhyolite, and probably also Tertiary 
 gold-veins. Veins of similar kind Continue along the eastern 
 foot of the Sierra Nevada as far north as Alpine county, and 
 become most productive in Mono county ; the mines at Bodie, 
 in andesite, produced in nine years M 2 $12.0 in gold, besides 
 much silver. 
 
 Northward from this point few Tertiary veins are found, 
 though intense volcanic activity prevailed in the northern 
 Sierra Nevada and the Cascades during the Tertiary. At one 
 or two places in Oregon, chiefly in the Bohemia district in the 
 Cascade mountains, the volcanic rocks contain gold-veins, but 
 they have not as yet yielded much. Continuing northward into 
 Washington, the Monte Cristo veins, in andesite and diorite, 
 represent this type, but are not credited with extraordinary 
 production. 
 
 No. veins of this class are thus far known in British Co- 
 lumbia or the Northwest Territory, but on the southern coast 
 of Alaska we meet sporadic cases again. The Apollo mine, 
 on Unga Island, breaks through andesite, and has produced 
 gold for the last few years to a maximum annual amount 
 of about $400,000. The Alaskan peninsula also shows evi- 
 dence of more recent Tertiary mineralization. 
 
 Returning southward to Nevada, this class of gold-deposits 
 is abundantly represented. The Comstock vein, Tuscarora, 
 Eureka, Tonopah, the De Lamar veins, are known or believed 
 to be of propylitic character, and, with the exception of the 
 latter, occur in volcanic rocks. The Comstock easily leads, 
 with an estimated production of over M 2 f 148.0 in gold, and the 
 other districts have contributed heavily to the total output, al- 
 though all also contain much silver in their ores. The produc- 
 tion of Nevada has fluctuated greatly, and after long decline 
 is again increasing. 
 
 A line of Tertiary veins continues northward from Nevada 
 into Idaho. In the southern part of that State they are repre- 
 sented by the Owyhee gold-silver mines, which since their dis- 
 covery have yielded M 2 fl2.0 in gold; and farther north by the 
 bonanzas of Rocky Bar, Atlanta, and Custer, which, probably, 
 should be referred to this type. Still farther north is the 
 Thunder Mountain district, which, if reports are reliable, con- 
 
THE GOLD-PRODUCTION OF NORTH AMERICA. 441 
 
 tains gold in rhyolite. No Tertiary primary gold-deposits have 
 been reported north of this point. 
 
 Veins of this class occur in Utah for instance, at the Horn- 
 Silver mine and atTintic; but these deposits carry very little gold. 
 
 Returning now to New Mexico, a belt of these veins continues 
 northward into Colorado and reaches a development not known 
 elsewhere, except in Mexico. The total output of Colorado is 
 probably about M 2 $250.0. In 1900 the output was M 2 $28.8. 
 Excepting the Leadville deposits, the principal gold-producing 
 districts are of Tertiary age. Oldest among them as to discovery 
 are the veins of Gilpin, Boulder, and Clear Creek counties, which 
 crop in Archaean rocks and are accompanied by andesite dikes. 
 These districts have been remarkably steady producers since 
 1859, and contribute annually about M 2 f 3.0. They promise to 
 continue their production for a long time. Another important 
 locality is the San Juan district, in southwestern Colorado, 
 where strong quartz veins cut heavy andesitic flows. The yield 
 has increased greatly since 1890, and in 1900 reached M 2 $4. 
 It promises well for the future ; and some of the mines, like the 
 Camp Bird, have proved veritable bonanzas. The output will 
 probably continue to increase for some years. An interesting 
 feature of the San Juan region is that in some districts which 
 have suffered great erosion the veins are found to continue into 
 bodies of intrusive diorites and porphyries of later age than 
 the andesites, thus offering a comparison of conditions near the 
 original surface and at a considerable distance below it. 
 
 Finally, there is the great Cripple Creek district, which has 
 yielded M 2 $77.3 during the period 1892 to 1900 inclusive, and 
 in 1900 produced M 2 $18. A network of veins occur in ande- 
 site, phonolite, and underlying granite, and have thus far 
 chiefly carried telluride ores. What may be expected of this 
 district in the future is a most important question, and one not 
 easy to answer. 
 
 North of Colorado the propylitic deposits are almost absent, 
 though they appear in sporadic form in Montana. 
 
 Roughly calculated, about M 2 $564.0 has been contributed by 
 the propylitic veins to the total gold-output of the United 
 States, to which should probably be added at least M 2 f 160.0 
 from Mexico. For 1900 we may estimate M 2 $36.0 as the out- 
 put of these veins in the United States, and perhaps M 2 f 7.0 
 in Mexico. 
 
442 THE GOLD-PRODUCTION OF NORTH AMERICA. 
 
 Conclusions. 
 
 Summing up the data obtained, we should estimate as fol- 
 lows : 
 
 Source of Production of Gold in North America. 
 
 Total MS. 1900 M2$. 
 
 Pre-Cambrian, . . . . . , .139.0 5.0 
 
 Cretaceous (Pacific), 1,719.0 54.0 
 
 Cretaceous and early Tertiary (Central), . . 287.0 14.0 
 
 Tertiary (largely propylitic), . . . . 724.0 43.0 
 
 2,869.0 116.0 
 
 The great increase in the gold-production of the continent 
 during the last ten years has been due,/rsf, to important dis- 
 coveries of new districts in almost every producing State ; 
 second, to the increased activity in many old gold-districts and 
 mines ; third, to the late great development of copper-smelting, 
 by which much gold has been obtained as a by-product -, fourth, 
 to the introduction of the cyanide process, rendering many 
 classes of low-grade ores and tailings available; and, fifth, to 
 the introduction of hydraulic elevators and dredgers, giving a 
 new lease of life to many old and decaying placer-camps. 
 
 Many considerations suggest that the increase will probably 
 not continue in the same ratio for the next few years, providing 
 that no great discoveries are made of new placers in the far 
 north or of vein-systems like that of Cripple Creek. The 
 greater part of the increase has been derived from the Northern 
 placers and from Cripple Creek; in 1900 the gold derived 
 from these sources amounted to M 2 $46.0. Subtract this from 
 a total for North America of M*$116.0, and only M 2 $70.0 re- 
 mains. The placer-fields now known in Alaska and Northwest 
 Territory will in all probability gradually decrease their out- 
 put during the next few years. Many reserves of old mill- 
 tailings and dredging-grounds to which new processes have 
 been applied are being rapidly exhausted. Some districts pro- 
 ducing gold from copper-ores and others working bonanzas of 
 the Tertiary veins will not improbably lessen their output. 
 Against this stand always the possibility of new discoveries and 
 the introduction of improved processes. Tentatively striking 
 a balance, a small decrease of the gold-production of North 
 America would seem more likely, for the next few years, than 
 an increase. 
 
THE GOLD-PRODUCTION OF NORTH AMERICA. 
 
 443 
 
 TABLE I. Gold-Production of North America. 
 
 Unit: M 2 $= $1,000,000. 
 
 Divisions. 
 
 Total from 
 Discovery 
 
 1877-1900, incl. 
 
 
 MS$. 
 
 
 United States. 
 
 to 1900, incl. 
 MS$. 
 
 3H$. 
 
 1900. 
 
 1901. 
 
 1902. 
 
 Alaska 
 
 30.7 
 
 30.7 
 
 8.2 
 
 6.9 
 
 7.8 
 
 Arizona 
 
 42.1 
 
 33.6 
 
 4.2 
 
 4.1 
 
 4.2 
 
 California 
 
 1,380.0(?) 
 
 351.1 
 
 15.8 
 
 16.9 
 
 17.1 
 
 Colorado . 
 
 251. 1(?) 
 
 204.3 
 
 28.8 
 
 27.7 
 
 27.5 
 
 Idaho 
 
 112.8 
 
 42.8 
 
 1.7 
 
 1.9 
 
 2.1 
 
 Montana 
 
 203. 5(?) 
 
 83.6 
 
 4.7 
 
 4.7 
 
 4.1 
 
 Nevada . ... 
 
 250.0(?) 
 
 99.7 
 
 2.0 
 
 3.0 
 
 3.5 
 
 New Mexico 
 
 17.6 
 
 13.3 
 
 0.8 
 
 0.7 
 
 0.7 
 
 Oregon 
 
 54.5 
 
 29.7 
 
 1.7 
 
 1.8 
 
 1.9 
 
 South Dakota 
 
 90.0 
 
 89.4 
 
 6.2 
 
 6.5 
 
 7.4 
 
 Utah 
 
 27.0 
 
 24.1 
 
 4.0 
 
 3.7 
 
 3.7 
 
 Washington 
 
 21.4(?) 
 
 8.9 
 
 0.7 
 
 0.6 
 
 0.4 
 
 Wyoming 
 
 1.0(7) 
 
 1.0 
 
 0.1 
 
 
 
 Appalachian States 
 
 47.0 
 
 8.0 
 
 0.3 
 
 0.2 
 
 0.3 
 
 (Mainly Georgia and 
 the Carolines. ) 
 
 
 
 
 
 
 
 2,528.7 
 
 1,020.2 
 
 79.2 
 
 78.7 
 
 80.7 
 
 British North America. 
 
 
 
 
 
 
 Nova Scotia 
 
 13.7 
 
 9.7 
 
 0.6 
 
 0.5 
 
 
 Quebec 
 
 2.0(?) 
 
 0.2 
 
 
 
 
 Ontario 
 
 1.2(?) 
 
 1.1 
 
 0.3 
 
 0.2 
 
 
 British Columbia 
 
 70.7 
 
 21.1 
 
 4.7 
 
 5.3 
 
 
 N. W. Territory 
 
 52.6 
 
 52.6 
 
 22.3 
 
 18.0 
 
 14.6 
 
 
 
 
 
 
 
 
 140.2 
 
 84.7 
 
 27.9 
 
 24.0 
 
 
 Mexico 
 
 200. 0(?) 
 
 66.5 
 
 9.0 
 
 10.3 
 
 
 
 
 
 
 
 
 Total 
 
 2 868.9 
 
 1 171 4 
 
 116.1 
 
 113.0 
 
 
 
 
 
 
 
 
 a Preliminary estimate by the Director of the Mint. 
 
 NOTE TO TABLE I. This table has been compiled chiefly from the Mint Reports 
 of the United States. Regarding the United States, accurate statistics date from 
 1877 ; the first column, showing the total production of each State, is to a great 
 extent based on estimates of the output of early placer-mining, by J. Ross Browne, 
 R. W. Raymond, and the Mint Bureau. The figures given for California, Ne- 
 vada, Montana, Washington, Oregon, and Colorado are especially uncertain. The 
 total (M 2 $2,528.7) exceeds the estimate of the Mint Bureau by nearly M 2 $150.0, 
 though the two calculations are probably based on the same evidence. If the 
 results of the Mint Bureau are accepted as correct, the figures given jn the first 
 column are too high ; but how and where the correction should be applied is very 
 difficult to say. In most States, however, the figures in the first column will be 
 considered too low, locally-current estimates being much higher. 
 
 The figures for British North America are probably fairly correct, but those 
 from Mexico are admittedly only estimates by the Mint Bureau or by other 
 statisticians. 
 
444 
 
 THE GOLD-PRODUCTION OF NORTH AMERICA. 
 
 TABLE II. Tentative Distribution of Gold-Production of North 
 America According to Age of Primary Deposits. 
 
 Unit: M 2 f = $1,000, 000. 
 
 Divisions. 
 United States. 
 
 Distribution of Total Production. 
 From Discovery to 1900, inclusive. 
 
 MS$. 
 
 Distribution of Produc- 
 tion of 1900. 
 M*, 
 
 i* 
 
 
 
 Mesozoic (Paci- 
 fic Coast Belt). 
 
 IS $ 
 
 3I 
 
 fill 
 
 Tertiary (Most- 
 ly Post -Mio- 
 cene). 
 
 Pre-Cambrian. 
 
 Mesozoic (Paci- 
 fic Coast Belt). 
 
 i ^i 
 
 o'S o> 
 
 3Sa~ 
 sl 
 
 Jill 
 
 Tertiary (Most- 
 ly Post - Mio- 
 cene). 
 
 Alaska 
 
 
 29.7 
 22.1 
 1,350.0 
 
 
 1.0 
 
 
 7 8 
 
 
 0.4 
 2.2 
 1.0 
 26J 
 1.0 
 
 2.0 
 0.4 
 
 2.4 
 ? 
 
 6.5 
 
 Arizona 
 
 
 
 20.0 
 
 
 
 2.0 
 2.7 
 
 4.7 
 
 ? 
 
 0.4 
 
 California 
 
 
 34.6 
 
 30.0 
 217.1 
 22.8 
 3.5? 
 230.0 
 10.0? 
 
 ...... 
 
 14.8 
 
 
 
 Idaho 
 
 
 90.0 
 
 
 
 0.7 
 
 Montana 
 
 
 200.0 ? 
 20.0 
 7.6? 
 
 Nevada . 
 
 
 
 
 
 New Mexico 
 
 
 
 
 
 Oregon . . 
 
 
 54.0 
 
 
 0.5? 
 
 
 1.7 
 
 South Dakota 
 Utah 
 
 74.0 
 
 ""25.6"' 
 
 16.0 
 2.0? 
 11.4 
 
 3.8 
 
 
 4.0 
 
 Washington . . 
 
 
 10.0 
 
 b.i 
 
 0.3 
 
 0.2 
 
 Wyoming. . 
 
 1.0 
 
 Appalachian States 
 (Mainly Georgia 
 and the Carolinas. ) 
 
 47.0 
 
 
 
 
 
 
 
 
 122.0 
 
 1,555.8 
 
 286.6 
 
 564.3 
 
 4.2 
 
 25.2 
 
 13.8 
 
 36.0 
 
 British N. America 
 
 
 
 
 
 
 
 
 
 Nova Scotia 
 
 13 7 
 
 
 
 
 0.6 
 0.3 
 
 4.7 
 22.3 
 
 
 
 Quebec 
 
 2.0? 
 1.2? 
 
 
 
 
 Ontario 
 
 British Columbia 
 
 
 70.7 
 52.6 
 
 
 
 N. W. Territory 
 
 
 
 
 
 
 
 
 
 
 
 16.9 
 
 123.3 
 
 
 
 0.9 
 
 27.0 
 
 
 
 
 Mexico. 
 
 
 40.0? 
 
 
 
 160.0? 
 
 
 
 2.0? 
 
 
 7.0? 
 
 
 
 
 Total 
 
 138.9 
 
 1,719.1 
 
 286.6 
 
 724.3 
 
 5.1 
 
 54.2 
 
 13.8 
 
 43.0 
 
 
 NOTE TO TABLE II. It should be expressly stated that this table is only a first 
 tentative estimate, as in very many cases the data for exact subdivision are not 
 available. The distribution for 1900 is, of course, probably more nearly correct 
 than the segregation of the total product attempted in the first part of the table. 
 
THE GOLD-PRODUCTION OF NORTH AMERICA. 445 
 
 DISCUSSION. 
 
 (Trans., xxxiii., 1077.) 
 
 WILLET G. MILLER, Toronto, Canada: With regard to Mr. 
 Lindgren's impression that the gold-supply of the world will 
 gradually decrease if no further important improvements are 
 made in the processes of gold-extraction, it seems to me that 
 no very important improvements are needed to keep up the 
 present production for many years to come. In many regions 
 there are large deposits of auriferous material which can be 
 worked if present conditions are slightly changed. In the ter- 
 ritory occupied by the Archaean protaxis of the Province of 
 Ontario, for instance, there are gold-deposits of large size which 
 apparently could be worked at a profit if the cost of production 
 were slightly decreased. Many of these deposits average ap- 
 proximately from $1 to $1.50 per ton, and consist of quartz 
 veins, shattered, impregnated masses of granite and other rocks, 
 and placer-deposits. 
 
 In the Rainy River district, in Western Ontario, gold occurs 
 in a mass of rock which is thus described in the government 
 reports of the Province : " It consists of a mixture of altered 
 granite, quartz, and chlorite, with streaks of green schist. It 
 has been traced 3 or 4 miles, and has a general direction of 
 northeast and southwest. The boundaries are rather indefinite, 
 but as near as can be ascertained it is 462 ft. wide at the 
 widest known place. On the location we are dealing with it 
 varies in width from 100 to 200 ft. One hundred feet is its 
 width at the narrowest place, as far as known." 6 Judging from 
 careful tests which have been made, much of this rock-matter 
 contains $1.50 value per ton in free-milling gold. It has not 
 been found possible, however, to work it at a profit. 
 
 Gold has been found in the Vermilion River placers, north 
 of Sudbury, in a territory covering many square miles. 7 The 
 metal occurs free, usually in a state of very fine division, and 
 inclosed in pebbles of quartz. Fire-assays show that the sand 
 and gravel frequently carry a value of more than $2 per ton. 
 Much of the material, while lower in value, averages from 12 
 to 15 cents per cubic yard. While the existence of these placers 
 
 6 Seventh Report of the Ontario Bureau of Mines, pp. 65, 130 and 131 (1897). 
 
 7 Idem, pp. 256 to 259 ; Tenth Report, pp. 151 to 159 (1901). 
 
446 THE GOLD-PRODUCTION OF NORTH AMERICA. 
 
 has been known for some years, success has not been achieved 
 in treating them. It would seem, however, that a compara- 
 tively slight improvement in the present methods of treatment 
 should bring about the profitable working of them. 
 
 A year or two ago similar placers were discovered on Savant 
 lake, which is about 150 miles northwest of Port Arthur and 
 500 miles from the last-mentioned area. In panning these 
 sands and gravel I obtained a very few colors. Fire-assays, 
 however, show that much of the material, which consists of 
 coarse sand, gravel, and boulders, averages about $1 per ton in 
 gold. 8 Some of the metal contained in the fragments of rock 
 probably could not be extracted by free-milling processes. 
 Similar deposits, which have not been examined as to their gold- 
 content, cover a large territory in this little-explored region, 
 and it would appear that the metal is present in most of this 
 gravel. 9 In the vicinity of Savant lake the thickness of the 
 sand- and gravel-deposits is at some points over 100 ft. The 
 deposits are of glacial origin, and the average of the gold- 
 content of the gravel from the tops of the higher hills is similar 
 to that found at lower levels. 
 
 The rocks over a great part of the Archaean area of Canada 
 are similar in character, and there is reason to believe that gold- 
 deposits carrying values like those mentioned occur widely ex- 
 tended over this vast, imperfectly-explored region. It may be 
 many years, probably not till the production of the richer de- 
 posits of other parts of the world begins to decline, before these 
 deposits are worked. Since the gold-values which they carry,, 
 however, are so close to those of deposits which even now are 
 being profitably worked, it is within the range of probability 
 that the Canadian protaxis will, in the years to come, be the 
 scene of a great gold industry. Low-grade deposits in other 
 parts of the world also will then add their quota, and the day 
 of a great decline in gold-production, a time of " not only 
 physical devastation, but moral and political decay," thus seems 
 far distant. 
 
 8 Twelfth Report of the Ontario Bureau of Mines pp. 89, 90 (1903). 
 
 9 Summary Report of the Geological Survey of Canada, pp. 92 to 93 (1901). 
 
THE GOLD-PRODUCTION OF NORTH AMERICA. 447 
 
 "W*. L. AUSTIN, New York, N. Y. : In Mr. Lindgren's instruc- 
 tive paper the statement is made in the reference to the pre- 
 Cambrian gold-quartz veins of South Dakota and Wyoming,, 
 that these two " are the only localities in the Cordilleran 
 region in which pre-Cambrian deposits have been recognized." 
 Further along in the paper [Part III., not reprinted here] it is 
 stated that " gold-deposits of Archaean age are not known in 
 Colorado. As far as the age has been determined, the deposits 
 are divided into a smaller Mesozoic and a much greater Ter- 
 tiary and probably chiefly post-Miocene group." 
 
 Mr. Lindgren has apparently overlooked an extensive aurif- 
 erous deposit described by Messrs. E. C. and P. H. van Diest 
 in a paper read before the Colorado Scientific Society in 1894. 
 As the article referred to is not readily accessible, and as the 
 said deposit is of considerable extent the beds cropping out 
 3 miles in one direction, and 1 mile in another a few extracts 
 from the van Diest paper may be considered pertinent in dis- 
 cussing " The Geological Features of the Gold-Production of 
 North America." Furthermore, this matter has commercial 
 importance, for these beds may become at an early day a not- 
 inconsiderable source of the precious metal. 
 
 The van Diests refer tp this deposit as Cambrian; but it is 
 thought that no serious attempt has been yet made to fix the 
 age other than approximately. It is apparently lower than the 
 Silurian, and in some respects resembles the pre-Cambrian 
 deposits of the Black hills. 
 
 Quoting from the van Diest paper : " The district examined 
 is on the Blto Seco. This little stream unites with the Rio de 
 la Culebra near San Luis the county seat of Costilla county 
 a region nearly in the center of the lower neck of the Pliocene 
 lakes, named by Endlich the Coronados lakes. Leaving San 
 Luis, the Rlto flows for about 6 miles in a northerly direction 
 through scattered debris, when the lake beds forming the foot 
 hills are reached. Here the road takes an easterly direction, 
 winding its way for afrout 3 miles through a wide and shallow 
 canyon which has been eroded from the lake beds. According 
 to Hayden the lake beds at this point should lie against the 
 Upper Carboniferous. No dark-red sandstones, such as were 
 observed in coming over Veta Pass, could be seen anywhere, 
 but we found instead, on the north side of the Rito for a dis- 
 
448 THE GOLD-PRODUCTION OF NORTH AMERICA. 
 
 tance of a quarter of a mile, some quartzite beds forming 
 steep cliffs, while further along the stream flows over light- 
 colored limestones and finally over granite. 
 
 " Directly north of the creek a thin bed of conglomerate ap- 
 pears. It is composed of light-bluish and greenish quartz pebbles 
 cemented by oxides of iron and manganese. Resting on this 
 bed follow layers of quartzites whose total thickness is estimated 
 at 160 ft. These quartzites are saccharoidal in appearance, of 
 pure white color when freshly broken, but stained by a film of 
 iron oxide where they have been exposed to the influence of 
 the weather. The quartzites are succeeded by a thin bed of 
 argillaceous shale, and the whole section is topped by layers of 
 light-grey siliceous limestones for about 200 ft., where a quartzy 
 parting separates them from others of somewhat darker color. 
 . . . Although no fossils have been found as yet in the de- 
 scribed beds, it is clear from a stratigraphic point of view that 
 the limestones are of Silurian and the quartzites of Cambrian 
 age. 10 An igneous dike about 30 ft. in width runs through the 
 limestone beds in a northerly and southerly direction. It is 
 of a dark purplish-brown color, very compact and fine grained. 
 In appearance it resembles more the older basalt occurring 
 between the lake beds, and is distinctly different from the 
 younger basaltic overflow which caps the beds south and west 
 of the Bito Seco. The dike had had no disturbing influence 
 whatever on the limestone beds, as is shown by the cuts run 
 into the limestone on either side of the dike. Northerly and 
 higher up on the mountain a light-colored porphyry was ob- 
 served, but owing to lack of time there was no opportunity 
 afforded to determine what the extent of this eruptive mass 
 might be, and what connection, if any, it might have with the 
 dike, nor could w r e determine if, in an easterly direction, other 
 quartzites and limestones rest on the granite. . . : 
 
 " Close inspection of the rusty faces of the quartzite cliff' 
 has lately revealed that three distinct layers of auriferous iron 
 pyrite occur between the quartzite beds,*the low r er one measur- 
 ing about 12 ft. in thickness, the next about 14 ft., and the 
 upper one 8 ft. At the time of our visit a drift had been run 
 
 10 As Cambrian conglomerates bear witness to prc-Cambrian gold-veins, then 
 these deposits must be pre-Cambrian in the same sense as those of the Black hills. 
 
THE GOLD-PRODUCTION OF NORTH AMERICA. 449 
 
 in the middle seam for a distance of 40 ft. The breast and 
 sides of this drift stood in almost solid pyrite. This pyritic 
 ore as broken down assays from $5 to $15 in gold per ton. 
 So far no copper-, zinc-, or other sulphides have been ob- 
 served with the deposit. The field, although but little em- 
 ployed, seems to be of promise, and it is to be hoped that 
 development work will be uninterruptedly prosecuted." u 
 
 Since the above was written these quartzite-beds have been 
 exploited somewhat further; and it is now thought that the 
 beds are more nearly an arkose than quartzite. This deposit 
 is so little known that it is not surprising it should have 
 escaped Mr. Lindgren's. notice. 
 
 11 Proceedings of the Colorado Scientific Society, vol. v., pp. 76 to 80. 
 
 29 
 
450 OSMOSIS AS A FACTOR IN ORE-FORMATION. 
 
 No. 17. 
 
 Osmosis as a Factor in Ore-Formation. 
 
 BY HALBERT POWERS GILLETTE, NEW YORK, N. Y. 
 (New York Meeting, October, 1903. Trans., xxxiv., 710.) 
 
 FROM the known laws of physical chemistry I believe it can 
 be shown that progressive mass movement of water solutions 
 in channels has seldom been the means of ore-concentration in 
 veins. It is my purpose in this paper to show that the force 
 known as "osmosis " has been the principal factor in ore-forma- 
 tion. Convection-currents have doubtless supplemented osmo- 
 sis, and the two working together have been the agencies that 
 have gathered the scattered particles of rare minerals into the 
 larger masses which are called ore. 
 
 Osmosis is commonly thought of as a vague, feeble force 
 that causes slow diffusion of dissolving matter through the 
 solvent. That it is a measurable force, often of great intensity,, 
 few know, except those who are familiar with the laws of mod- 
 ern physical chemistry. Therefore, I may be pardoned for go- 
 ing briefly into the elementary mathematics of osmotic pressure 
 and of convection-currents. 
 
 The velocity of water moving through any channel is given 
 by the Chezy formula : 
 
 (1) v = c i/rs, in which r is the hydraulic mean radius ; s r 
 the slope of the channel in which gravity is the sole propulsive 
 force ; and c, the coefficient of roughness of the sides of the 
 channel. 
 
 From this formula it is evident that the smaller the channel, 
 the smaller the velocity of water under a constant head. In 
 rock-crevices, therefore, where the head is constant, water 
 moves much more slowly than in large fissures, and in moving 
 through sand or porous rock it is to an even greater degree re- 
 tarded. Hence, if a mass of water-saturated sand be heated, 
 the finer the sand-grains, the more slowly will the temperature 
 rise at parts remote from the source of heat. Conversely, cool- 
 ing is retarded the smaller the interstices or channels through 
 which the convection-currents move. The importance of this 
 
OSMOSIS AS A FACTOR IN ORE-FORMATION. 451 
 
 fact \vill appear later. Osmosis is the force which drives a so- 
 lute through a solution. When a substance dissolves it behaves 
 in many respects exactly as if it were vaporized. In fact, it has 
 been proved by Van't Hoff that " The osmotic pressure of a 
 substance in solution is the same pressure which that substance 
 would exert were it in gaseous form at the same temperature 
 and occupying the same volume." l 
 Expressed mathematically the law is : 
 
 in which, p = osmotic pressure in pounds per square inch. 
 R the gas constant = 1,206 Ib. per sq. in. 
 T = absolute temperature = t (Centigrade) 4- 273. 
 V= volume of the solvent containing one molecu- 
 
 lar weight of the solute. 
 
 in which, M = sum of the atomic weights of the atoms in a 
 
 molecule of the substance. 
 r = the rate per cent, of the solution. 
 Hence : 
 
 _ 1,206 r (t + 273) 12 r (t + 273) 
 
 100 M ~M~ 
 
 I have deduced equation (4) for convenience in ascertaining 
 and comparing osmotic pressures. Thus, sugar is C u H 22 O n . 
 Hence for sugar, M = (12 X H) + (1 X 22) + (16 X 11) = 342. 
 For a 2-per-cent. sugar solution, r = 2. Therefore at 15 C. we 
 have the osmotic pressure according to equation (4) as follows : 
 
 p = 12 X 2 (15 + 273) = 20>2 lb _ per gq _ . n 
 342 
 
 By actual experiment p was found to be 20 Ib. per sq. in. under 
 these conditions ; and Van't Hoff 's law of osmotic pressure has 
 been repeatedly proved by similar tests. From the above state- 
 ment it is clear that osmosis is far from being a vague or feeble 
 force. 
 
 When due to a rise in temperature, or for other reasons, 
 ground-water at any given point begins to dissolve a mineral, 
 
 1 Elements of Physical Chemistry, by J. Livingston R. Morgan, New York, John 
 Wiley & Son, p. 96. 
 
452 OSMOSIS AS A FACTOR IN ORE-FORMATION. 
 
 that mineral is immediately forced by osmotic pressure out to 
 the extreme confines of the vessel holding the water. Let us 
 suppose, therefore, that a dike-intrusion has so heated the sur- 
 rounding waters that they have taken up a burden of PbS ; evi- 
 dently, then, osmosis will force this PbS throughout the mass 
 of water into every cranny, crevice, fissure, or cavity. It re- 
 quires no convection-currents to accomplish this distribution, 
 although convection will hasten the process. Having taken up 
 its full burden of PbS there comes a period of inactivity, until 
 the temperature begins to fall. This fall of temperature will 
 be most rapid near the surface of the earth and it will be most 
 rapid in the larger water channels, for the reason that circula- 
 tion there is least retarded. 
 
 In the case of dike-intrusion, I believe that the shrinking of 
 the dike-matter will open the largest crevices and channels 
 along the dike itself, and I conceive that surface-waters flowing 
 into these shrinkage-cracks will accelerate the cooling near the 
 dike. Hence, in such cases, contact ore-deposits will be found 
 on one side of a dike, and that side will be the side which orig- 
 inally faced uphill. The down-flowing surface- or ground- 
 water will enter the first crevices it meets and hasten the cool- 
 ing there, and it is quite evident that where cooling is fastest, 
 crystallization of dissolved mineral will first begin. Let the 
 smallest speck of galena be crystallized out, and immediately 
 osmosis will force more dissolved galena to that point, and thus 
 feed the crystal-mass. Heretofore, the deposition of ore nearest 
 the once-molten dikes has been inexplicable, but in no other 
 place could it have started, and, once started, the tendency 
 toward crystal growth must be due entirely to osmotic pressure 
 
 Let us consider for a moment certain other conditions that 
 accelerate cooling, since it is now evident that much depends 
 upon the first cooling of the solution. At the intersection of 
 two fissures the cooling should be most rapid, for at that point 
 two channels supply convection-currents. Hence the deposition 
 of the most insoluble minerals should occur first at vein-inter- 
 sections, a circumstance which is often verified in known ore- 
 deposits. Again, in fissure walls that have been striated by 
 slipping past one another, the grooves form channels in which 
 convection-currents move most rapidly, and, as should be ex 
 pected, the most insoluble minerals are found in the grooves. 
 
OSMOSIS AS A FACTOR IN ORE-FORMATION. 453 
 
 This, I believe, explains " Clayton's law." 2 Since the richest min- 
 erals are ordinarily the most insoluble, I offer this general propo- 
 sition : " Bonanzas should be sought at points where circulation 
 has been freest, namely, in the widest and most open channels." 
 Since the relative solubility of minerals has evidently played 
 so important a role in ore-formation, a few suggestions may 
 not be out of place. Hot waters carrying metallic sulphides 
 in solution must carry also a great burden of alkaline salts. 
 In fact, the solubility of the metallic sulphides is due to the 
 presence of these alkaline salts which form new ions with the 
 sulphides, just as potassium cyanide dissolves gold salts by 
 forming new ions with the gold. One well-known geologist 
 has erred in assuming that the " solubility product " of every 
 mineral is increased by the presence of other minerals in solu- 
 tion. This, in passing, I would say is not so ; for it is only 
 when new ions are formed with the added elements, that solu- 
 bility is effected, and there are many minerals which do not 
 combine to produce these new ions. The metallic sulphides 
 and the ions formed by them have a very low " solubility pro- 
 duct " at best, and when a lowering of temperature causes the 
 sulphides to crystallize out, the " solubility products " of the 
 substances in solution are often so increased that more country- 
 rock is dissolved. In this manner for every particle of sulphide 
 deposited by crystallization, a particle of country-rock may be 
 dissolved. - This, I take it, is the true explanation of the so- 
 called " metasopnatic replacement " which has been regarded 
 as a true chemical reaction, or precipitation. I have never 
 been able to believe that galena and other natural metallic sul- 
 phides are chemical precipitates, and one of my strongest 
 reasons for this disbelief has been the fact that chemical pre- 
 cipitates of lead and similar sulphides are flocculent and never 
 crystalline. How cubical galena could be precipitated chemi- 
 cally from solution, by any reducing agent in nature, has ever 
 been a most serious stumbling block. I am convinced now 
 that practically all of the hypothetical equations written by 
 geologists to account for ore-deposition by chemical reaction 
 are erroneous. Many of these equations can be demonstrated 
 to be false from the laws of thermal chemistry, and few of 
 
 Ore- Deposits of the United States and Canada > J. F. Kemp, p. 49. 
 
454 OSMOSIS AS A FACTOR IN ORE-FORMATION. 
 
 them appear even plausible when viewed from a thermo-chem- 
 ical standpoint. It is not now my purpose to tear down, but 
 to build up. I am wholly in accord with Professor Kemp and 
 other geologists who voice the movement against the chemical 
 theories of ore-deposition which have so long occupied the 
 arena. It cannot be denied, however, that very many ore- 
 deposits have come from minerals carried in solution to the 
 chambers where they are now found. 
 
 It has been urged in the past that the formation of ore-depos- 
 its from hot-water solutions could not have occurred, for two 
 reasons : (1) Because the same heat that would cause the solu- 
 tion of the precious minerals would also cause the solution of 
 the rocks in which those minerals are scattered, and con- 
 versely, cooling would precipitate them both together, and, 
 (2) Because hot springs are not now depositing metallic sul- 
 phides except in very small amounts and then only in the midst 
 of a mass of gangue. 
 
 I trust that I have indicated how osmosis effects the distri- 
 bution and final concentration of minerals, without any appeal 
 to hot-water-spring theories or to chemical precipitation from 
 cold-water theories, for I am convinced that we must look to the 
 laws of physical chemistry for an explanation of ore-formation, 
 and not to the laws of physics or of chemistry alone. 
 
THE ORE-DEPOSITS OF SUDBURY, ONTARIO. 455 
 
 No. 18. 
 
 The Ore-Deposits of Sudbury, Ontario.* 
 
 BY CHARLES W. DICKSON, COLUMBIA UNIVERSITY, NEW YORK, N. Y. 
 
 (Albany Meeting, February, 1903. Trans., xxxiv., 3.) 
 
 CONTENTS. PAGE 
 
 PART!. THE RELATION OF NICKEL TO PYRRHOTITE, , . . . 455 
 
 Introduction, . . . . . . '.,..-. . . 455 
 
 Minerals of the Sudbury Nickel-Region, . . . . . 456 
 
 Pyrrhotites in General, . . . * . . . . . . 458 
 
 The Origin of Pyrrhotite, . ... ... , ... . .460 
 
 Nickel and Cobalt in Pyrrhotite, . . ... . . . 461 
 
 The Sudbury Pyrrhotites, . . . . . . ... 463 
 
 The Magnetic Separation of Nickeliferous Pyrrhotite, . . . ." 466 
 
 The Nickel-Bearing Mineral, . . . . . . . .470 
 
 The Non-Magnetic Residue, . . . . . I , .. . . 472 
 
 The Formula of the Pyrrhotite, . . . . . . . . 475 
 
 Summary, . . ... . . . . . . . 476 
 
 PART II. GENESIS OF THE SUDBURY ORES, . . . . . . 477 
 
 General Considerations, *'*' . . . . . , 477 
 
 Classification of Pyrrhotites, ... . . . . . .477 
 
 Value of the Classification, . . . . . . . . 478 
 
 The Sudbury Pyrrhotite- Deposits, . . . . . . . . 479 
 
 The Nickel-Belts, . . . . . . . . . .480 
 
 Various Theories of the Origin of Nickeliferous Pyrrhotite, . . . 481 
 
 The Rossland Pyrrhotite-Deposits, . i ... . . . 486 
 
 Microscopical Evidence of the Origin of the Ores; . . . . 497 
 
 Sudbury District, .497 
 
 Wallace Mine, . ... ... . . .... 508 
 
 Rossland, B. C., , ? ..'.-. 509 
 
 Ducktown, Tenn., . . . . . . . . . 510 
 
 Summary, . . . . . ...... . 510 
 
 Relation of Chalcopyrite to Pyrrhotite, . . . . . .513 
 
 Source of the Metals, . . . . .. ,.''-. . . . 514 
 
 Acknowledgments, . . . . ... . . 516 
 
 I. THE RELATION OF NICKEL TO PYRRHOTITE. 
 Introduction. 
 
 The Sudbury district is to-day one of the two great sources 
 of nickel in the world. The peculiar geological relations of 
 
 * This paper was presented by the author as a dissertation for the degree of 
 Ph.D. at Columbia University, New York City. 
 
456 THE ORE-DEPOSITS OF SUDBURY, ONTARIO. 
 
 the ores have long attracted attention, and widespread interest 
 has been aroused by the difference of opinion regarding their 
 origin, whether as igneous segregations or as precipitates from 
 solution. The writer has endeavored to attack this problem 
 with the aid of microscopical and petrographical methods. 
 The field-work of these investigations was carried on during 
 the summers of 1901 and 1902, and the material collected was 
 worked up at Columbia University, New York, during the ses- 
 sions of 1901-02 and 1902-03. 
 
 As a necessary preliminary, it was thought advisable to in- 
 vestigate carefully the chemical composition and geological 
 relations of pyrrhotite, as well as the mineralogical associations 
 of the Sudbury ores. 
 
 Minerals of the Sudbury Nickel- Region. 
 
 Pyrrhotite and chalcopyrite, associated with fragments of 
 the inclosing rock, are the predominant minerals of the Sud- 
 bury deposits. The nickel-mineral pentlandite, which is the 
 principal source of this metal, is distributed through all the ore- 
 bodies in greater or less amount. Its matrix is almost univer- 
 sally pyrrhotite, though a number of exceptions occur, notably 
 at the Copper Cliff mine. 
 
 This mine, which has furnished a number of interesting 
 minerals, contains in the lower levels some massive ore, com- 
 posed very largely of chalcopyrite intimately associated with 
 pentlandite. Other samples from the same place consist of 
 pyrite and marcasite, also with an intimate mixture of pent- 
 landite. 
 
 Millerite is encountered, though rarely. In a sample from 
 the Copper Cliff mine, the writer found small bunches of hair- 
 like crystals of this mineral in the cavities of some radiating 
 pyrite mixed with calcite. It has also been reported in a num- 
 ber of other cases. The millerite is undoubtedly secondary, 
 and was probably derived from pre-existing pentlandite. 
 
 Polydymite (Ni 4 S 5 , with one part of nickel replaced by iron) 
 containing platinum was described by Clarke and Catlett. 1 
 
 Kiccolite, gersdorffite, danaite, and arsenopyrite (containing 
 cobalt) occur in several localities in Denison township, though 
 
 1 American Journal of Science, Third Series, vol. xxxvii., No. 221, p. 372 (May, 
 1889). 
 
THE ORE-DEPOSITS OF SUDBURY, ONTARIO. 457 
 
 the association is not exactly similar to that of the typical 
 deposits. 
 
 Pyrite is by no means uncommon, and Walker has described 
 a nickeliferous variety (over 4 per cent, of nickel) from the 
 Murray mine. A number of samples of this mineral from the 
 Copper Cliff mine were associated with secondary quartz, cal- 
 cite, and millerite. On analysis, they yielded from a trace to 
 over 3 per cent, of M, which, however, may be due to an inti- 
 mate mixture of pentlandite or millerite. 
 
 Samples of a compact, whitish or steel-gray mineral, contain- 
 ing a considerable amount of pentlandite, were submitted by 
 the writer to Professor Penfield, who considers it to be massive 
 marcasite. The analyses conform to the formula FeS 2 , and 
 show the presence of from 2 to 4 per cent, of !N"i, probably as 
 pentlandite. 
 
 Sperrylite (PtAs 2 ) was originally found in the gossan at the 
 Vermilion mine. The writer has also isolated it from the un- 
 altered chalcopyrite of the Victoria mine (see p. 463). 
 
 Galena occurs rarely in streaks through the pyrrhotite, e. g., 
 at the Mount Nickel mine, Blezard township. 2 
 
 Native copper is reported in a few instances in leaves in the 
 associated rocks. Secondary copper-minerals are rare; but 
 bornite is occasionally seen. 
 
 Small masses of titaniferous magnetite (with as much as 18 
 per cent, of TiO 2 ) are at times found. 
 
 This list is probably not complete, but represents the most 
 important minerals found by the writer or recorded by others. 
 
 S. H. Emmens 3 describes what he calls several new species 
 of nickel-minerals from Sudbury. But the doubtful purity of 
 his material and the analytical methods employed do not war- 
 rant the recognition of these new species. 4 
 
 As a preliminary to the discussion of the relation of the 
 nickel to the pyrrhotite and its associates, a brief review of our 
 knowledge of pyrrhotites will be given ; since the uncertainty 
 
 2 Specimen kindly furnished by Prof. W. G. Miller, Provincial Geologist of 
 Ontario. 
 
 3 Journal of the American Chemical Society, vol. xiv., p. 205 (1892). 
 
 . 4 S. L. Penfield, On Pentlandite from Sudbury, Ont. , Can., with Remarks 
 upon Three Supposed New Species from the Same Region, American Journal of 
 Science, Third Series, vol. xlv., No. 270, p. 493 (June, 1893). 
 
458 
 
 which prevails regarding the exact chemical composition of 
 pyrrhotites is probably not generally appreciated by students 
 of ore-deposits . 
 
 Pyrrhotites in General. 
 
 For many years the composition of pyrrhotite has presented 
 to chemists and mineralogists a most difficult and interesting 
 problem, to a large extent still unsolved. 
 
 Various writers have applied to this mineral formulas which 
 range from Fe 3 S 4 to Fe 16 S l7 . In general terms it is usually ex- 
 pressed as Fe n S n+1 . By some it is regarded simply as FeS 
 with impurities. 5 Others consider it a^ varying molecular mix- 
 tures of different sulphides, as nFeS + Fe 2 S 3 or nFeS + FeS 2 . 
 Bodewig's 6 and- Doelter's 7 formula was Fe n S 12 . 
 
 In other words, " pyrrhotite " is regarded, not as a mineral 
 in the true sense of the term, but as a series of minerals, dif- 
 fering slightly from each other in the relative proportions of 
 their constituents. If this is the correct view, the case is 
 unique. Homologous chemical series are by no means uncom- 
 mon, but in these there is always a gradual change in the prop- 
 erties of the different members ; the extremes being so entirely 
 unlike as hardly to be recognizable components of the same 
 group. There seems, however, to be little, if any, difference 
 between pyrrhotites represented by Fe 3 S 4 and Fe 16 S ir It should 
 thus be possible to grade imperceptibly from the monosulphide, 
 FeS, to the disulphide, FeS 2 , when a pyrrhotite with the com- 
 position of pyrite would result. But such a view does not seem 
 reasonable, and is opposed to some of the fundamental laws of 
 chemistry. It seems more reasonable to consider many of the 
 so-called " pyrrhotites " as mixtures of other sulphides with this 
 mineral, and to regard the latter as of a definite composition. 
 
 A fact which may have an important bearing on this ques- 
 tion is that of the magnetic permeability of different pyrrho- 
 tites. In the preparation of various samples, as noted later in 
 this paper, some were observed to be much more magnetic than 
 
 5 Weinschenk, Groth's Zeitschrift fur Krystallographie und Mineralogie, vol. xvii., 
 p. 499 ; Lorenz, Ber. d. chem. Ges., p. 1501 (1891). 
 
 6 Groth's Zeitschrift, vol. vii., p. 180. 
 
 7 Tschermak's Mineralogische und petrographische Mittheilungen, N. F., vol. vii., p. 
 544. A synopsis of the results obtained by different writers will be found in the 
 Handbuch der Mineralogie, Hiutze, vol. i., p 621 ct xeq. (1901). 
 
THE ORE-DEPOSITS OF SUDBURY, ONTARIO. 459 
 
 others, the strength of attraction by a small magnet being, in a 
 general way, proportional to the percentage of iron. Further 
 investigation along this line may lead to important results. 
 
 It should be borne in mind, however, that lack of care in 
 the preparation of samples for analysis may account for many 
 discrepancies, especially as few pyrrhotites are entirely free 
 from other sulphides in more or less intimate mixture. 
 
 The inaccurate methods of analysis, and difficulties of manip- 
 ulation, will also cause many errors. That the reliability of 
 many analytical methods is open to question is shown by the 
 animated controversies of experts in recent years. 8 Errors 
 amounting to 0.75 per cent, in the estimation of sulphur are 
 not uncommon, and in many cases they are possibly larger. 
 The iron-results are also apt to be unreliable. 
 
 In a number of determinations on the same sample Haber- 
 mehl 9 obtained results in which the sulphur varied from 
 39.10 to 39.71 a difference of 0.61, and iron from 60.28 to 
 60.79 a difference of 0.51 per cent. When we consider the 
 theoretical compositions represented by the compounds varying 
 from FeS to FeS 2 it is seen that a comparatively small error 
 would change the formula calculated from the analysis. The 
 calculated composition for different formulas would be as 
 follows : 
 
 Formula. 
 
 Iron. 
 Per Cent. 
 
 Sulphur. 
 Per Cent. 
 
 Formula. 
 
 Iron. 
 Per Cent. 
 
 Sulphur, 
 Per Cent. 
 
 FeS . 
 
 Fe 15 S 16 . 
 Fe n S 12 . 
 
 . 63.61 
 . 62.06 
 . 61.60 
 
 36.39 
 37.94 
 38.40 
 
 Fe 8 S 9 
 
 Fe 7 S 8 
 FeS 9 
 
 60.80. 
 60.40' 
 46.60 
 
 39.20 
 39.60 
 53.40 
 
 A few analyses made by prominent workers (see Table I.) 
 will show the wide variation, both in the analytical results and 
 in the recorded specific gravity of the mineral. The latter varies 
 very widely (3.98 to 4.80) and probably indicates the doubtful 
 purity of the sample. Where the total (as in analysis ~No. 1) 
 is over 101 per cent., any calculations based on the result will 
 be wholly misleading, and it is safe to say that many others 
 recorded, while not indicating such an excess, are equally un- 
 reliable for this purpose. 
 
 8 Gladding and Lunge, Journal of the American Chemical Society, vols. xvi., xvii., 
 and xviii. (1894 to 1896). 
 
 9 Obcrhessische Gesellschaft fur Natur- und Heilkunde, vol. xviii., p. 97 (1879). 
 
460 THE ORE-DEPOSITS OF SUDBURY, ONTARIO. 
 
 TABLE I. Analyses of Pyrrhotite. 
 
 
 1. 
 
 2. 
 
 3. 
 
 4. 
 
 5. 
 
 6. 
 
 7. 
 
 8. 
 
 9. 
 
 Fe 
 
 63 82 
 
 63 15 
 
 63 35 
 
 62 62 
 
 63 41 
 
 62 04 
 
 61 17 
 
 60 83 
 
 58 00 
 
 S 
 
 37.36 
 
 36 35 
 
 35.91 
 
 37 38 
 
 36.29 
 
 38.08 
 
 38 83 
 
 39 17 
 
 42 00 
 
 Total 
 Sp. gr 
 Formula. . 
 
 101.18 
 3.98 
 Nearly 
 FeS. 
 
 99.50 
 4.62 
 Nearly 
 FeS. 
 
 99.26 
 4.787 
 Nearly 
 FeS. 
 (Fe in 
 excess.) 
 
 100.00 
 4.80 
 Nearly 
 FeS. 
 
 99.70 
 ""FeS."" 
 
 100.12 
 4.497 
 Fe 13 S 14 . 
 
 100.00 
 4.546 
 
 Fe 9 S 10 . 
 
 100.00 
 4.580 
 Fe 8 S 9 . 
 
 100.00 
 Fe 4 S . 
 
 No. 1. Nenntmansdorf, Geinitz, N. Jahr., 1876, 609. 
 
 No. 2. Tavetsch, Gutknecht, cited by Kenngott, N. Jahr., 1880, 1, 164. 
 
 No. 3. Seelasgen, Rammelsberg, Poyy. Ann., 1864, cxxi., 368. 
 
 No. 4. Brazil, Berthier, Ann. Mines, 1835, vii., 531. 
 
 No. 5. Jeliza, Servia, Losanitsch, Ber. d. Chem., 1892, xxv., 880. 
 
 No. 6. BoreV, Palfy, Groth's ZeiL, xxx., 184, and xxvii., 101. 
 
 No. 7. Bodemais, Graf Schaffgotsch, Pogg. Ann., 1840, 1., 533. 
 
 No. 8. Hartzburg, Kammelsberg, Pogg. Ann., 1864, cxxi., 356. 
 
 No. 9. Chile, Mennier, Cosmos, 1869, 3d series, v., 581. 
 
 The above results are taken from C. Hintze's Hdb. der Min., 
 vol. i., pp. 653 and 654 (1901). 
 
 Altogether apart, however, from the considerations outlined 
 above, pyrrhotite, as we know it, is not constant in composi- 
 tion ; and an adequate explanation of the variations in its com- 
 position is one of the problems of the future. 
 
 The Origin of Pyrrhotite. 
 
 Little is known of the conditions under which pyrrhotite is 
 formed in nature, except that a strongly-reducing atmosphere 
 is necessary. Those synthetic reproductions of the mineral, 
 which have not been made under conditions analogous to those 
 of nature, do not aid materially in explaining its origin. 
 
 Doelter, 10 however, by heating ferrous chloride to 250 C. 
 in an atmosphere of carbonic acid and hydrogen sulphide gas, 
 produced pyrrhotite much like the natural mineral and having 
 a composition represented by Fe n S 12 . He also produced it by 
 the action of H 2 S gas on solutions of ferrous sulphate, carbon- 
 ate, chloride, and silicate. Other methods of "preparation do 
 not appear to have any direct bearing on the natural formation 
 of the mineral. 
 
 10 Tschermak's Mittheilungen, vol. vii., pp, 85, 86. 
 
THE ORE-DEPOSITS OF SUDBURY, ONTARIO. 
 
 461 
 
 Nickel and Cobalt in Pyrrhotite. 
 
 Nickel is universally recognized as an associate of pyrrho- 
 tite, and in few cases has it proved, when looked for, to be en- 
 tirely lacking. Whether the nickel is an essential constituent 
 of the pyrrhotite, replacing part of the iron, or whether it is 
 present as a separate compound, is still a disputed question. It 
 is hoped, however, that the results here presented will help to 
 clear this matter up to a great extent. 
 
 The percentage of nickel varies widely in different pyrrho- 
 tites. Those occurring in metamorphosed sedimentary and 
 acidic schistose rocks are notably low in nickel, while in those 
 associated with basic igneous rocks, especially of the gabbro 
 family, it may range from a trace to a proportion economi- 
 cally valuable. Cobalt nearly always accompanies the nickel, 
 though usually in very subordinate amount. 
 
 Tables II. , III., and IV. give the nickel-contents of representa- 
 tive pyrrhotites of these two classes. Those of the first class 
 rarely carry more than 0.5 per cent, of nickel, while those 
 from basic eruptives usually exceed this limit, some of the 
 Rossland examples being notable exceptions. 
 
 TABLE II. Percentages of Nickel and Cobalt in Pyrrhotites 
 
 Generally. 
 
 
 Ni. 
 
 Co. 
 
 
 Ni. 
 
 Co. 
 
 ONTARIO. 
 1. Dalhousie twp. Lanark co.. 
 
 0.23 
 
 trace 
 
 BRITISH COLUMBIA. 
 1. West Kootenay 
 
 0.16 
 
 o 
 
 2 Dalhousie twp ' Lanark co 
 
 11 
 
 trace 
 
 *> Kennedy Lake VI 
 
 16 
 
 
 
 16 
 
 trace 
 
 j 3 Deer Creek V I 
 
 1 70 
 
 
 4 Galway twp Peterboro' co 
 
 16 
 
 trace 
 
 ' 4 West Kootenay 
 
 14 
 
 trace 
 
 5 Galway twp Peterboro 1 co 
 
 10 
 
 trace 
 
 5 Crawford Bay 
 
 05 
 
 
 6. Galway twp Peterboro' co.. 
 
 05 
 
 trace 
 
 1 6 Jarvis Island - . 
 
 28 
 
 trace 
 
 7 Victoria co 
 
 15 
 
 trace 
 
 i 7 Rossland 
 
 3 
 
 
 8 Rainy River District 
 
 0.13 
 
 trace 
 
 1 8. Rossland 
 
 13 
 
 trace 
 
 9 District of Nipissing 
 
 3 30 
 
 trace 
 
 9 Kootenay Lake 
 
 68 
 
 
 10. District of Nipissing 
 
 2.10 
 
 trace 
 
 ! SWEDEN, ETC. 
 
 
 
 QUEBEC 
 
 
 
 1 Klefva 
 
 1 08 
 
 07 
 
 1 Ottawa co 
 
 13 
 
 o 
 
 i 2 Klefva 
 
 1 50 
 
 08 
 
 2 Ottawa co 
 
 1 68 
 
 
 3 Klefva 
 
 2 03 
 
 10 
 
 3 Calumet Island 
 
 1 48 
 
 
 4 Sagmyrna 
 
 50- 
 
 
 4 Calumet Island 
 
 4.06 
 
 33 
 
 
 80 
 
 
 5 Pontiac co 
 
 1 50 
 
 trace 
 
 5 Krageroe 
 
 1 75 
 
 
 NOVA SCOTIA. 
 
 
 
 6. Varallo 
 
 1 20- 
 
 
 1 Cape Breton co 
 
 10 
 
 trace 
 
 
 1 44 
 
 
 NEW BRUNSWICK. 
 1 St. Stephen 
 
 1 82 
 
 17 
 
 UNITED STATES. 
 il Gap Mine Pa 
 
 1 75 
 
 10 
 
 2 St Stephen 
 
 trace 
 
 
 2 Gap Mine Pa 
 
 1 00- 
 
 
 
 to 
 4.00 
 
 
 3. Anthonv's Nose, N. Y 
 
 3.00 
 0.30 
 
 
 
 
 
 
 
 
 NOTE. The nickel-mineral gersdorffite occurred in association with some of 
 these pyrrhotites, so that in part the nickel found may mean an admixture of this 
 mineral. 
 
462 THE ORE-DEPOSITS OF SUDBURY, ONTARIO. 
 
 Ontario. 1. Pyrrhotite with pyrite in white translucent quartz and hornblende; 
 2. Pyrrhotite with pyrite in quartz-rnica-diorite (Nos. 1 and 2 occur in dark-gray 
 diorite, which cuts gneiss) ; 3. Pyrrhotite in dark-gray gneissoid rock ; 4. Mas- 
 sive pyrrhotite ; 5. Massive pyrrhotite with pyrite, chalcopyrite, and quartz ; 6. 
 Massive pyrrhotite with chalcopyrite, quartz, and feldspar (other samples from Gal- 
 way gave from a trace to 0.15 per cent, of nickel. The pyrrhotite is associated 
 with bands of gneiss, mica-schist, and quartzite ; i. e., the deposits are fahlbands, 
 like those of Norway, which are likewise poor in nickel) ; 7. Massive pyrrhotite; 
 8. Massive pyrrhotite with a small amount of quartz from the Huronian schists of 
 English river ; 9 and 10. Pyrrhotites with small amounts of chalcopyrite in a 
 gangue of grayish-green diorite. (Pyrrhotites occurring in light- and dark-gray 
 gneissoid rocks from Frontenac county, Ont., Schreiber (Thunder bay), Darlington 
 bay (Lake of the Woods), and numerous other localities all contained nickel, but 
 only in traces. ) 
 
 Quebec. 1. Massive pyrrhotite from Eardley township ; 2. Pyrrhotite in part 
 massive, in part disseminated through a gangue of quartz, feldspar, and horn- 
 blende ; 3. Small quantity of pyrrhotite, etc., in a quartz-amphibolite ; 4. Massive 
 pyrrhotite with a little quartz gangue (the associated rocks of 3 and 4 are diorites,. 
 which cut a series of gneisses and limestones) ; 5. Massive pyrrhotite. 
 
 Nova Scotia. Pyrrhotite in a siliceous gangue from Leitche's creek. 
 
 New Brunswick. Pyrrhotite with a little chalcopyrite and a small amount of 
 quartz gangue, or diorite and quartz. (The association is much like that of Sud- 
 bury. Various samples from the same locality yield from a trace to 4 per cent, of 
 nickel. ) 
 
 British Columbia. 1. Pyrrhotite in quartz, feldspar, and hornblende ; 2. Mas- 
 sive pyrrhotite in a gangue of quartz, garnet, calcite, and hornblende ; 3. Massive 
 pyrrhotite with chalcopyrite in a quartzose gangue (from the Two Sisters and 
 Crow claim) ; 4. Pyrrhotite and chalcopyrite in a dark-green rock ; 5. Pyrrhotite 
 in association with a small amount of chalcopyrite, graphite, quartz, mica, and 
 feldspar ; 6. Pyrrhotite with chalcopyrite in a gangue of quartz-green diorite ; 7 
 and 8. Massive pyrrhotite with chalcopyrite in massive eruptive rocks, the ore- 
 bodies lying between gabbros and surrounding porphyries and diabases ; 9. Pyr- 
 rhotite with pyrite and chalcopyrite in garnet and quartz. 
 
 The above Canadian examples are taken from vols. vi. to xi. of the Reports of 
 the Canadian Geological Survey. 
 
 Sweden, etc. Pyrrhotites in dark eruptive rocks, principally gabbros (authority, 
 Schnabel's Handbook of Metallurgy. ) 
 
 Gap Mine, Pa. Pyrrhotite with chalcoyrite, pyrite, etc., in the outer portions 
 of basic igneous rock-masses, which may be metamorphorsed to amphibolites. 
 
 Mine at Anthony's Nose, N. Y. Pyrrhotite in association with feldspar, pyrox- 
 ene, hornblende, and quartz ; the walls being acidic gneisses. (Authority for 
 this and the preceding examples, The Nickel-Mine at Lancaster Gap, by J. F. 
 Kemp, Trans., xxiv., 620, 883, 1894.) 
 
 The relation of the nickel-content to the mode of origin of 
 the pyrrhotites and the inclosing rock will be considered sub- 
 sequently. 
 
 One of the purposes of this investigation has been to test 
 the validity of the view generally held, that in the Sudbury 
 pyrrhotites the nickel and cobalt replace the iron isomor- 
 
THE OhE-DEPOSITS OF SUDBUKY, ONTARIO. 468 
 
 phously. Another purpose has been to try to find a definite 
 formula for the sulphide of this district, with the idea of com- 
 paring it with similar minerals from other localities. 
 
 The Sudbury Pyrrhotites. 
 
 The Sudbury nickel-region, as treated in this paper, will be 
 considered, for convenience, as including the deposits of simi- 
 lar nature in the adjoining Algoma district, as well as those 
 in the immediate vicinity of the town of Sudbury. 
 
 The ore mined in this region consists chiefly of a mixture of 
 pyrrhotite and chalcopyrite, intimately associated with more 
 or less country-rock. The pyrrhotite carries the nickel, while 
 the chalcopyrite appears to be quite free from that element. 11 
 Table III. gives the nickel and copper in typical samples of the 
 ore of some of the leading Sudbury mines, as taken from the 
 catalogue of the Ontario mineral exhibit at the Buffalo Pan- 
 American Exposition of 1901, and similar data regarding a 
 number of nearly-pure pyrrhotites from claims in various parta 
 of Algoma, taken from the reports of the Canadian Survey. 
 These Algoma deposits have the same geological relations i. e. r 
 they are closely associated with an altered gabbro or norite. 
 
 The average contents of nickel, copper, and cobalt in the 
 ore smelted since 1892 are given in Table IV. The state- 
 ments of Messrs. Turner and Walker, Table V., show that 
 gold, silver, and the metals of the platinum group are constant 
 constituents of the ore, though present only in small quanti- 
 ties. 
 
 Sperrylite, the arsenide of platinum (PtAs 2 ), was first recog- 
 nized in the decomposed products of chalcopyrite and pyrrho- 
 tite at the Vermilion mine. The platinum in the unaltered 
 ore occurs as sperrylite, as proved by the writer. 12 T. L. 
 Walker 13 has shown that the sperrylite is associated with the 
 chalcopyrite, rather than the pyrrhotite. Recent investiga- 
 tions seem to confirm this view, as sperrylite has been found 
 associated with copper-minerals in several other places. 
 
 11 Thus, Nos. 3 and 5 in Table III., which are largely chalcopyrite, contain but 
 little nickel. 
 
 12 American Journal of Science, Fourth Series, vol. xv., No. 86, p. 137 (Feb.,. 
 1903). 
 
 13 Idem, vol. i., No. 2, p. 110 (Feb., 1896). 
 
464 
 
 THE ORE-DEPOSITS OF SUDBURY, ONTARIO. 
 
 Mr. Turner's estimate, given in columns A and B, Table IV., 
 probably presents fair averages of the general run of the ore. 
 The figures under A may give a good idea of the ore of the 
 Creighton mine, while that from Copper Cliff may run up to 
 7 per cent, of copper and 3 per cent, of nickel, according to the 
 particular level from which the ore was taken (copper predomi- 
 nating in the upper, and nickel in the lower levels). Column B 
 is based on the composition of the matte produced, as shown 
 in Table V., column I. 
 
 TABLE III. Nickel and Cobalt in Sudbury and Algoma Pyrrhotites. 
 
 
 Ni. 
 
 Cu. 
 
 
 Ni. 
 
 Cu. 
 
 SUDBURY. 
 
 1 Victoria mine 
 
 Per 
 Cent. 
 3 50 
 
 Per 
 
 Cent. 
 4 50 
 
 ALGOMA. 
 1. Lome township 
 
 Per 
 Cent. 
 
 1 95 
 
 Per 
 Cent. 
 
 
 2 Copper Cliff mine 
 
 9.25 
 
 0.51 
 
 2. Lome township 
 
 2 80 
 
 
 
 3 Copper Cliff mine . . 
 
 1 25 
 
 23 78 
 
 3 Nairn township 
 
 1 95 
 
 trace 
 
 4 Stobie mine 
 
 2.99 
 
 0.37 
 
 4. Drury township 
 
 2.01 
 
 trace 
 
 5 Stobie mine . 
 
 64 
 
 24 23 
 
 5 Denison township 
 
 1 80 
 
 
 
 6 No 2 mine 
 
 4 70 
 
 38 
 
 6 Levack township 
 
 4 13 
 
 
 7 No. 2 mine 
 
 1.87 
 
 13.76 
 
 7. Levack township 
 
 3 00 
 
 trace 
 
 8 No 3 mine Frood 
 
 4 85 
 
 42 
 
 8 Levack township 
 
 1 96 
 
 trace 
 
 9 No. 4 mine 
 
 4.33 
 
 1.39 
 
 9. Morgan township 
 
 3 30 
 
 
 10 No 4 mine 
 
 4 15 
 
 2 49 
 
 
 
 
 11 Creighton mine 
 
 7.03 
 
 1.81 
 
 
 
 
 12 No 2 extension 
 
 4 32 
 
 35 
 
 
 
 
 13 Worthington mine 
 
 3.00 
 
 3.00 
 
 
 
 
 
 
 
 
 
 
 NOTE. The Sudbury figures are from the catalogue of the mineral exhibit of On- 
 tario at the Pan-American Exposition of 1901, except those of the Worthington 
 mine, which are the result of a number of analyses of average samples, obtained 
 through the kindness of R. E. Booraem, New York City. 
 
 The Algoma figures are taken from reports of the Geological Survey of Canada. 
 Most of the samples were massive pyrrhotite, with a small amount of chalcopy- 
 rite. The copper per cent, was not reported. 
 
 TABLE IV. Averages of Smelters' Assays of Sudbury Ores, 
 from 1892 to 1900. 
 
 1892. 1893. 1894. 1895. 1896. 1897. 1898. 1899. 1900. A. B. 
 
 Per Ct. Per Ct. Per Ct. Per Ct. Per Ct. Per Ct. Per Ct. Per Ct. Per Ct. Per Ct. Per Ct. 
 
 Cu, . . 3.19 2.38 3.14 2.73 2.54 2.86 3.43 1.59 1.50 2.00 
 
 Ni, . . 3.36 2.21 2.92 2.67 2.67 2.08 2.28 1.67 3.50 2.50 
 
 Co, . . 0.10 0.08 0.07 
 
 NOTE. The figures for the several years aret^ en from the Sixth Report of the 
 Ontario Bureau of Mines (1896) and Mineral Industry, vol. ix. (1900). The returns 
 for 1900 seem too low. Columns A and B, furnished by President A. P. Turner, 
 of the Canadian Copper Co., contain (A) an estimate of certain ores of that com- 
 pany, and (B) a general average based on the composition of the matte produced 
 from a mixture of all its ores. 
 
THE ORE-DEPOSITS OF SUDBURY, ONTARIO. 465 
 
 TABLE V. Composition of Sudbury Mattes. 
 
 i. n. 
 
 Per Cent. 
 
 Copper, .... 14 percent. 25.92 
 
 Nickel, .... 17 per cent. ") ^ ^ 
 
 Cobalt, . . . . 0.5 to 0.6 per cent. / 
 
 Gold, .... trace 0.000075 
 
 Silver, . . . . 0.5 to 1 oz. per ton. 0.001775 
 
 Platinum, . . . 0.25 to 0.5 oz. per ton. 0.000430 
 
 Palladium, . . . 0.25 to 0.5 oz. per ton. present 
 
 Iridinm, . . . 0.000056 
 
 Osmium, . . . 0.000057 
 
 Rhodium, . . . present 
 
 Iron, . . . 2.94 
 
 Sulphur, . . . 22.50 
 
 I. Average furnished by President A. T. Turner for mattes of the Canadian 
 Copper Co. 
 
 II. Analysis of the matte from the Murray mine, given by T. L. Walker, 
 American Journal of Science, Fourth Series, vol. i., No. 2, p. 112 (Feb., 1896). 
 
 To ascertain as accurately as possible the average nickel- and 
 cobalt-contents of the general run of the pyrrhotite from the 
 whole region, a number of analyses of carefully-selected mate- 
 rial were made by the writer. 
 
 The pyrrhotite was coarsely crushed and the mineral picked 
 out as pure as possible, under a lens when necessary. From 
 the massive varieties good samples were easily obtained ; but in 
 other cases the pyrrhotite was so intimately mixed with chalco- 
 pyrite and rock that it was very difficult to obtain satisfactory 
 samples, some rock always adhering to the sulphide. The re- 
 sults, given in Table VI., show that the percentage of nickel 
 and cobalt in the pyrrhotite, calculated to the pure mineral, is 
 fairly constant over a wide area, embracing all the principal 
 mines and prospects. The pyrrhotites include both coarse- and 
 fine-grained massive varieties, and those mixed with more or 
 less rock and chalcopyrite. The object was to determine, as 
 far as practicable, only the nickel existing as a component of 
 the pyrrhotite, if it occurred as such. In the case of the 
 coarse-grained varieties, where the nickel-mineral pentlandite 
 is often to be recognized, this was carefully rejected, as far as 
 possible. But the difficulty of this separation accounts for the 
 fact that some of these varieties show less nickel than the fine- 
 grained ones, although the former are usually considerably 
 richer. Had the coarse-grained samples been treated in their 
 
 30 
 
466 
 
 THE ORE-DEPOSITS 
 
 original condition, the results would have been more uniform. 
 Subsequent work proves that a large part, at least, of the nickel 
 is not a constituent of the pyrrhotite. The results of these 
 tests, therefore, represent the nickel which is most intimately 
 associated with pyrrhotite and does not appear in visible par- 
 ticles of pentlandite. 
 
 Cobalt is always very subordinate in amount, bearing a ratio 
 between 1 : 40 and 1 : 50 to the nickel. 
 
 TABLE VI. Nickel, Cobalt, etc., in Sudbury Pyrrhotites. 
 
 Location. 
 
 Insol. 
 
 Cu. 
 
 Ni. 
 
 Co. 
 
 Niin 
 Pure Pyr- 
 rhotite. 
 
 1 Elsie (a) 
 
 Per Cent. 
 2.00 
 
 Per Cent, 
 trace 
 
 Per Cent. 
 2 40 
 
 Per Cent. 
 06 
 
 Per Cent. 
 2 46 
 
 2 Elsie (b) 
 
 3.45 
 
 trace 
 
 2 35 
 
 0.05 
 
 2 44 
 
 3 Stobie (a) 
 
 1.50 
 
 trace 
 
 3 00 
 
 08 
 
 3 05 
 
 4. Stobie (b) 
 
 4.00 - 
 
 trace 
 
 2 05 
 
 05 
 
 2 15 
 
 5. Frood, No. 3 mine (a) 
 
 0.40 
 
 trace 
 
 2.35 
 
 0.05 
 
 2 40 
 
 6. Frood, No. 3 mine (b) 
 
 5.00 
 
 trace. 
 
 2.34 
 
 0.06 
 
 2.48 
 
 7 Mount Nickel 
 
 2 20 
 
 
 3 00 
 
 07 
 
 3 06 
 
 8. Copper Cliff, No. 4 mine (a)... 
 9. Copper Cliff, No. 2 mine (b)... 
 10. Copper Cliff, No. 5 mine (c)... 
 11 Creighton (a) 
 
 1.10 
 5.00 
 0.50 
 3 25 
 
 trace, 
 trace, 
 trace, 
 trace 
 
 3.24 
 3.70 
 3.47 
 3 84 
 
 0.06 
 0.08 
 0.08 
 10 
 
 3.30 
 4.00 
 3.50 
 4 00 
 
 12 Creighton (b) 
 
 50 
 
 trace 
 
 2 26 
 
 06 
 
 2 32 
 
 13. Gertrude (a) . . 
 
 5 00 
 
 trace 
 
 3 83 
 
 0.11 
 
 4 05 
 
 14 Gertrude (b) 
 
 6 00 
 
 trace 
 
 3 61 
 
 09 
 
 4 00 
 
 15. Victoria (a) 
 
 50 
 
 trace. 
 
 3.3H 
 
 07 
 
 3.40 
 
 16. Victoria (b) 
 
 0.40 
 
 trace. 
 
 3.14 
 
 08 
 
 3.20 
 
 17. Levar-k 
 
 3.20 
 
 trace. 
 
 2.80 
 
 
 288 
 
 18. North Range 
 
 4.10 
 
 trace. 
 
 2.22 
 
 
 232 
 
 
 
 
 
 
 
 NOTE. These analyses, and others by the writer, were made in duplicate or 
 triplicate to insure the greatest possible accuracy. 
 
 1. Coarse pyrrhotite with a small amount of chalcopyrite and rock ; 2. Compact 
 fine-grained pyrrhotite, with a small amount of rock ; 3. Massive fine-grained 
 pyrrhotite ; 4. Pyrrhotite and chalcopyrite in diorite , 5. Pure, coarse pyrrhotite ; 
 6. Fine-grained pyrrhotite ; 7. Massive pyrrhotite ; 8. Coarse pyrrhotite. 9, 10, 
 11. Massive fine-grained pyrrhotite ; 12. Coarse pyrrhotite ; 13, 14. Massive pyr- 
 rhotite ; 15. Massive fine-grained pyrrhotite; 16. Coarser than No. 15, but with 
 more chalcopyrite ; 17. Massive pyrrhotite (Tuff & Stobie' s property) ; 18. Coarse^ 
 massive pyrrhotite from Wisner township. 
 
 The Magnetic Separation of Nickeliferous Pyrrhotite. 
 
 Many experiments have been performed in recent years to 
 effect a commercial magnetic separation of the nickel in pyr- 
 rhotite ores; or, for scientific purposes, to determine the con- 
 
THE ORE-DEPOSITS OF SUDBURY, ONTARIO. 467 
 
 dition of the nickel in this mineral. The commercial elimina- 
 tion of the nickel is probably an impossibility, and the scientific 
 problem is only now approaching a solution. 
 
 S. H. Emmens 14 refers to the work of Habermehl (1879), who 
 effected a separation of European nickeliferous pyrrhotite into 
 magnetic and non-magnetic portions. 
 
 T. J. McTighe, in 1890, applied magnetic separation in the 
 treatment of Canadian ores; and in 1892 T. A. Edison, in ap- 
 plying for a U. S. Patent, said : 
 
 " I have discovered that where magnetic pyrites, called pyrrhotite, is nickel- 
 iferous, as it usually is to a more or less extent, the nickel is not distributed gen- 
 erally throughout the whole body of the pyrrhotite, but certain crystals are pure 
 pyrrhotite or magnetic pyrites, while other crystals have some of the iron replaced 
 by nickel and sometimes by cobalt, and that the crystals containing the nickel and 
 cobalt are considerably less magnetic than the pure pyrrhotite." 
 
 Emmens himself made some crude experiments on material 
 from the Gap mine, Pa., and from Sudbury, and obtained two 
 products, the non-magnetic being considerably richer in nickel 
 than the original ore. 
 
 Shortly after, David H. Browne 15 contributed a very valua- 
 ble article on the same subject. He shows the existence of a 
 rich nickel-mineral in the ores from the Copper Cliff, Evans, 
 and Stobie mines, in the Sudbury district, and also that it can 
 be separated by rough-crushing and hand-picking, after first 
 removing the magnetic part. His analyses 16 show that the non- 
 magnetic residue bears a close resemblance to the pentlandite 
 described by Penfield. 
 
 Probably the most extensive series of experiments for a com- 
 mercial separation were those made by J. ST. Judson, of the 
 Wetherill Separating Co., in 1900. The results have never 
 been published ; but Mr. Judson has very kindly placed them 
 in the hands of the writer, and a partial abstract is here pre- 
 sented. 
 
 The material operated on was nearly pure pyrrhotite from 
 Copper Cliff, containing, by analysis, Ni, 3.14 ; Cu, 0.42 ; and 
 Fe, 49.78 per cent. The magnetic-separation products, with 
 
 14 Second Report, Ontario Bureau of Mines, p. 163 (1892). Journal of the Ameri- 
 can Chemical Society, vol. xiv., No. 10, p. 369 (1892). 
 
 15 Engineering and Mining Journal, vol. Ivi , No. 23, p. 565 (Dec. 2, 1893). 
 
 16 Nos. 5 to 8 in Table XL of this paper. 
 
468 
 
 THE ORE-DEPOSITS OF SUDBURY, ONTARIO. 
 
 different current-strengths, and the analysis of each, are given 
 in Table VII. 
 
 TABLE VII. Magnetic Separation of Pyrrhotite by the Wetherill 
 Separator. First Experiment Material Crushed to No. 30 Mesh. 
 
 Product 
 
 No. 
 
 52 
 11 
 
 5 
 la 
 2-5 
 
 Amperes. 
 
 Magnetic 
 Product. 
 
 Analyses. 
 
 Magnetic Portion. 
 
 Total Percentage of Metal in 
 Magnetic Portion. 
 
 Ni. 
 
 Cu. 
 
 Fe. 
 
 Ni. 
 
 Cu. 
 
 Fe. 
 
 1 
 15 
 15 
 28 
 tails 
 1 
 
 Per Cent. 
 90.11 
 7.65 
 0.78 
 0.92 
 0.54 
 90.11 
 9.89 
 
 Per Cent. 
 2.46 
 10.83 
 9.68 
 1.76 
 0.70 
 2.46 
 9.33 
 
 Percent. 
 
 0.22 
 0.78 
 2.55 
 13.58 
 2.64 
 0.22 
 2.21 
 
 Percent. 
 53.60 
 14.80 
 13.25 
 20.10 
 11.25 
 53.60 
 14.97 
 
 Per Cent. 
 
 70.58 
 26.38 
 2.42 
 5.87 
 0.13 
 70.58 
 29.42 
 
 Percent. 
 
 47.48 
 14.37 
 4.79 
 29.99 
 3.35 
 47.48 
 52.52 
 
 Per Cent. 
 97.02 
 2.27 
 0.21 
 0.37 
 0.12 
 97.02 
 2.98 
 
 a Making only two products i. e., magnetic and non-magnetic at 1 ampere. 
 
 The results show that with a current-strength of 1 ampere 
 90.11 per cent, of the total sample was magnetic, and this con- 
 tained 2.46 per cent, of Ni, or the equivalent of 70.58 per cent, 
 of the total metal in the original pyrrhotite ; that is, only 29.42 
 per cent, of the total nickel was concentrated in the non-mag- 
 netic portion (making only two products). The second and 
 third products (15 amperes) were highly nickelif erous ; but as 
 they contained less than a third of the total nickel in the ore, 
 the loss in the magnetic portion was very heavy. 
 
 In the next experiment, the first magnetic product, at 1 am- 
 pere (amounting to 90.11 per cent, of the total), containing M, 
 2.46; Cu, 0.22; and Fe, 50.62 per cent, was again treated, 
 using a weaker current. The results are shown in Table VIII. 
 
 TABLE VIII. Magnetic-Separation Product No. 1 of Table VII. 
 Second Experiment (No. 30 Mesh). 
 
 
 
 1. 
 Magnetic 
 
 2. 
 
 
 Analyses. 
 
 
 Product 
 No. 
 
 Amperes. 
 
 Portion 
 of Part 
 Treated. 
 
 Portion 
 of Total. 
 
 Ni. 
 
 Cu. 
 
 Fe. 
 
 1 
 2 
 3 
 4 
 5 
 6 
 
 t 
 
 f 
 
 tails 
 
 Per Cent. 
 33.61 
 54.15 
 4.64 
 1.79 
 2.35 
 3.47 
 
 Per Cent. 
 30.28 
 48.79 
 4.18 
 1.61 
 2.12 
 3.13 
 
 Per Cent. 
 1.93 
 2.08 
 3.46 
 3.70 
 3.95 
 10.60 
 
 Per Cent. 
 0.08 
 0.13 
 0.18 
 0.51 
 0.90 
 2.44 
 
 Per Cent. 
 56.65 
 55.60 
 53.00 
 41.25 
 23.80 
 20.20 
 
THE ORE-DEPOSITS OF SUDBURY, ONTARIO. 
 
 469 
 
 Column 1 gives the percentage of the part treated which 
 was magnetic with the different current-strengths indicated; 
 column 2, the percentage of the total sample which was mag- 
 netic under the same conditions (e. g., 90.11 X 33.61 = 30.28). 
 The portion magnetic at -f% ampere (about one-third of the 
 total) still contained nearly 2 per cent, of Ni ; so the loss was 
 still very great, while the non-magnetic concentrate was not 
 very greatly enriched. 
 
 All the products of these two experiments were then mixed, 
 crushed to pass through 60-mesh and treated as shown in 
 Table IX. 
 
 TABLE IX. Magnetic Separation of Mixed Sample Crushed to 
 Pass No. 60 Mesh. Third Experiment. 
 
 Product 
 No. 
 
 Amperes. 
 
 Magnetic 
 Portion. 
 
 Analyses. 
 
 Ni. Cu. 
 
 Fe. 
 
 
 
 
 Per Cent, of 
 
 Per Cent. Per Cent. Per Cent. 
 
 
 
 
 Total. 
 
 
 1 
 
 
 
 44.26 
 
 1.69 0.13 55.50 
 
 2 
 
 
 
 41.96 
 
 2.16 0.18 
 
 54.80 
 
 3 
 
 i 
 
 
 0.37 
 
 2.16 0.26 
 
 50.30 
 
 4 
 
 
 
 0.37 
 
 4.19 0.70 | 32.50 
 
 5 
 
 
 
 
 0.49 
 
 5.29 0.93 
 
 24.55 
 
 6 
 
 2 
 
 1.13 
 
 8.96 0.97 
 
 20.85 
 
 7 
 
 3 
 
 1.38 
 
 13.55 0.76 
 
 21.55 
 
 8 
 
 4 
 
 3.95 
 
 10.29 0.46 
 
 22.35 
 
 9 
 
 5 
 
 4.19 
 
 12.71 0.60 
 
 19.60 
 
 10 
 
 C 
 
 
 
 0.89 
 
 4.17 3.18 
 
 12.65 
 
 11 
 
 28 
 
 0.77 
 
 1.53 14.36 
 
 19.65 
 
 12 
 
 tails 
 
 0.52 
 
 0.38 1.64 
 
 i 
 
 8.25 
 
 At J ampere, 44.26 per cent, of the sample was magnetic, and 
 the product contained l.(19 per cent, of Ni. At J ampere, 
 86.22 per cent, was magnetic, and the product contained 1.92 
 per cent, of Ni. If the remainder, 13.78 per cent., were consid- 
 ered as the non-magnetic concentrate, we would have a com- 
 paratively rich nickel-ore, but the losses in the magnetic portion 
 are so great that a commercial separation by this method is out 
 of the question. All the other experiments led to the same 
 conclusion. Intermediate products, rich in nickel, were easily 
 obtained ; but in no case was the nickel in the magnetic por- 
 tion reduced to such an extent that it could be economically 
 rejected. 
 
 D. P. Shuler, Sudbury, Ont., has recently (1902) taken out 
 patents for a process whereby he proposes to eliminate the 
 
470 THE ORE-DEPOSITS OF SUDBURY, ONTARIO. 
 
 copper from the nickel-iron portion by magnetic concentration, 
 and subsequently to convert the latter, after roasting, into a 
 nickeliferous pig-iron. The copper-nickel concentrate will, of 
 course, be treated separately for its metallic content. This 
 seems to be the most fruitful field for investigation now open 
 in this connection, and about the only method of treatment 
 which promises to yield results capable of industrial application. 
 The Nickel-Bearing Mineral. 17 Prof. S. L. Pentield 18 first 
 definitely proved the existence of pentlandite in the ores from 
 the Sudbury nickel-copper mines. Later, David H. Browne 19 
 showed that pentlandite was the principal nickel-bearing min- 
 eral. On the assumption that the ores were the result of a 
 magmatic segregation from an original fused magma, he tried 
 to show that the coarser the grain of the pyrrhotite, and the 
 deeper it lies below the surface, the more nickel exists as pent- 
 landite. On the other hand, the finer-grained the ore, and the 
 more rapidly it has cooled from the fused state (i. e., the nearer 
 it is to the surface), the more nickel exists as an element replac- 
 ing the iron in the pyrrhotite. As will appear later in this 
 paper, however, this relation does not hold good. 
 
 In order to determine as nearly as possible how much of the 
 nickel occurs as a separate mineral, and how much, if any, re- 
 places iron, and also to ascertain the composition of the nickel- 
 mineral, several series of experiments were made by the writer. 
 
 First Series of Experiments. A number of representative 
 samples of pyrrhotite were ground to pass through 100-mesh 
 and the non-magnetic portion was removed as completely as 
 possible by repeated treatment with a small horse-shoe magnet. 
 The nickel-contents of the original samples are given in column 
 I., and those of the magnetic concentrate in column II., Table X. 
 The nickel is seen to have been materially reduced, and the 
 results seemed to indicate a pretty constant quantity remaining 
 with the magnetic part. Further experiments, however, showed 
 that this was purely an accidental relation. 
 
 Second Series of Experiments. The original samples were 
 coarsely crushed and the magnetic portion was sized between 
 
 17 A preliminary note on this subject was published in the Engineering and Min- 
 ing Journal, vol. Ixxiii., No. 19, p. 660 (May 10, 1902), by the writer. 
 
 18 .American Journal of Science, Third Series, vol. xlv., No. 270, p. 493 (June, 
 1893). 
 
 19 Engineering and Mining Journal, vol. Ivi., No. 23, p. 565 (Dec. 2, 1893), and 
 School of Mines Quarterly, vol. xvi., No. 4, p. 297 (July, 1895). 
 
THE ORE-DEPOSITS OF SUDBURY, ONTARIO. 
 
 471 
 
 40- and 60-mesh, then freed as well as possible from non-mag- 
 netic material, crushed between 60- and 80-mesh and again 
 concentrated. By successive treatments the mineral was finally 
 reduced to a fine powder. The ultimate product was then as- 
 sayed for nickel. As shown in column III., Table X., the nickel 
 was much reduced, but not entirely eliminated. 
 
 Third Series of Experiments. To see if it were possible to still 
 further reduce the nickel-content, a number of samples were 
 very carefully prepared. They were coarsely crushed and the 
 purest mineral selected. This was crushed to pass through 10- 
 on 20-mesh, and the finer material was rejected. All the non- 
 magnetic portion was eliminated and the concentrate was then 
 crushed to 20- on 40-mesh, the finer part being again rejected. 
 The operations were repeated until the ore was finally ground 
 in an agate mortar, the non-magnetic part being very carefully 
 removed each time. The nickel in the final concentrate is 
 given in column IV., Table X. 
 
 TABLE X. Experiments in the Magnetic Concentration of Nickel- 
 iferous Pyrrhotite. 
 
 Location. ^ J a 
 
 II. 
 
 Ni. 
 
 III. 
 
 Ni. 
 
 ~Pe7 
 Cent. 
 0.98 
 0.68 
 1.05 
 0.75 
 0.70 
 0.83 
 1.20 
 
 Tib" 
 
 0.80 
 
 IV. 
 
 Ni. 
 
 
 Per 
 Gent. 
 1. Elsie mine 2.44 
 
 Per 
 Cent. 
 2.22 
 2.14 
 2.07 
 2.14 
 2.00 
 2.32 
 2.25 
 
 '2.30' 
 2.46 
 
 Per 
 
 Cent. 
 
 Fine-grained pyrrhotite. 
 Fine-grained pyrrhotite. 
 Coarse-grained pyrrhotite. 
 Medium-grained pyrrhotite. 
 Coarse-grained pyrrhotite. 
 Coarse-grained pyrrhotite. 
 Coarse-grained pyrrhotite. 
 Fine-grained pyrrhotite. 
 Massive pyrrhotite. 
 Fine-grained pyrrhotite. 
 
 2 Stobie mine 3 05 
 
 
 3. Frood mine 2.40 
 
 0.65 
 0.70 
 
 4. Mount Nickel mine 3.06 
 5. Copper Cliff, No. 2 mine. 4.00 
 .6. Copper Cliff, No. 4 mine. 3.30 
 7. Creighton mine (a) 2.32 
 Creighton mine (b) 4.15 
 8 Gertrude mine 4 00 
 
 
 0.70 
 0.45 
 
 9. Victoria mine 3.40 
 
 
 
 
 a Nickel with a trace of cobalt. 
 
 The results show conclusively that the nickel present is not 
 replacing part of the iron in the pyrrhotite, but exists as a sep- 
 arate mineral. The fact that all the nickel could not be elim- 
 inated by the methods used does not indicate that even the 
 amount that remained was an essential part of the pyrrhotite, 
 as several factors enter which render its complete removal 
 practically impossible. In the first place, the nickel-mineral 
 is very intimately associated with the magnetic pyrites; and 
 even a minute adhering fragment of the latter will cause it to 
 
472 
 
 THE ORE-DEPOSITS OF SUDBURY, ONTARIO. 
 
 be carried over with the magnetic portion. It is also to be 
 noted that the nickel-mineral itself is slightly magnetic, and in 
 the" form of a powder is attracted by even a small magnet. 
 
 As a result of these experiments I feel justified in saying 
 that all the nickel, in the Sudbury ores at least, occurs as a 
 separate mineral, and that in this district there does not exist 
 a true nickeliferous pyrrhotite, in the sense that the nickel iso- 
 morphously replaces part of the iron in that mineral. 
 
 Experiments on Swedish and Norwegian ores of a similar 
 nature show that a large part of the nickel can be eliminated 
 by magnetic concentration ; and taking these results, in con- 
 nection with the foregoing, it is pertinent to ask, " Is there 
 such a thing as a true nickeliferous pyrrhotite ? " 
 
 The results show that even with the most careful treatment, 
 a commercial separation of the nickel by magnetic concentra- 
 tion is prohibited by the considerable loss of nickel involved. 
 
 The Non-Magnetic Residue. Analyses of the non-magnetic 
 residues, roughly freed from impurities, were made to get an 
 idea of their compositions. 
 
 The small amount of copper was estimated as chalcopyrite, 
 and the necessary amounts of iron and sulphur deducted. The 
 ratios of Fe : Ni : S (taken as 1) were then calculated, and the 
 results are given in Table XL 
 
 TABLE XI. Analyses of the Non-Magnetic Residue from 
 Pyrrhotites.a 
 
 Location. 
 
 Cu. 
 
 Total 
 Fe. 
 
 Total 
 
 S. 
 
 Ni. 
 
 Per 
 Cent. 
 31.65 
 32.25 
 33. 
 29.71 
 35. 
 35. 
 34. 
 34. 
 
 Co 
 
 ~PeT 
 Cent. 
 
 0.65 
 0.84 
 30 
 |0.60 
 35 
 30 
 30 
 70 
 
 Fe.6 
 
 S.6 
 
 Ratios. (S = 1.00.) 
 
 S. 
 
 Ni +Co. 
 
 Fe. 
 
 1. Victoria mine 
 2. Frood mine 
 
 Per 
 Cent. 
 0-95 
 0.84 
 1.20 
 0.80 
 
 
 
 
 
 Per 
 Cent. 
 28.50 
 29.36 
 29.50 
 27.11 
 
 Per 
 
 Cent. 
 31.92 
 32.85 
 34.25 
 30.30 
 
 Per 
 Cent. 
 27.66 
 28.65 
 28.45 
 26.40 
 29.80 
 30.30 
 29.60 
 29.90 
 
 Per 
 
 Cent. 
 30.96 
 3-2.04 
 32.80 
 29.46 
 34.35 
 33.50 
 33.35 
 33.90 
 
 1.00 
 1.00 
 1.00 
 1.00 
 1.00 
 1.00 
 1.00 
 1.00 
 
 0.570 
 0.565 
 0.550 
 0.565 
 0.56 
 0.571 
 0.571 
 0.56 
 
 0.514 
 0.512 
 0.50 
 0.515 
 0.50 
 0.52 
 0.51 
 0.505 
 
 3. Creighton mine 
 4. General sample 
 5. Copper Cliff minec... 
 6. Copper Cliff mine c .. 
 7. Evans mine 
 8. Stobie mine 
 
 
 
 
 
 
 
 For the sake of uniformity the following revised atomic weights are used 
 throughout : Ni, 58.69 ; Co, 58.99 ; Fe, 56.02 ; 8, 32.07. 
 
 6 After deducting the necessary amounts to form chalcopyrite with the copper 
 present. 
 
 c Analyses by D. H. Browne ; Nos. 5 and 8 contained some pyrrhotite ; Nos. 6 
 and 7 were purer. Engineering and Mining Journal, vol. Ivi. , No. 23, p. 565 (Dec- 
 2, 1893). 
 
 20 The residue is spoken of for convenience as being non-magnetic, although in 
 reality slightly so. 
 
THE ORE-DEPOSITS OF SUDBURY, ONTARIO. 
 
 473 
 
 The striking uniformity of the ratios obtained at once indi- 
 cated the similarity of the mineral in all these cases ; and 
 further work on carefully-purified material confirms this view. 
 
 The pyrrhotite from the Creighton, Worthington, and Frood 
 mines shows considerable amounts of the non-magnetic material, 
 in pieces up to 0.75 in. in diameter, fairly pure, and specimens 
 from these localities were chosen as affording the best material 
 to work on. 
 
 The ore was first roughly crushed and the pyrrhotite re- 
 moved by a magnet. The larger non-magnetic fragments were 
 taken and picked over under a lens, carefully discarding any 
 that was even suspected of containing pyrrhotite. 
 
 The samples were then crushed successively to pass through 
 No. 20, No. 40, No. 60, No. 80, and No. 100 mesh, each time 
 discarding the fines and going over them with a magnet, exam- 
 ining under a lens, and removing all foreign material till they 
 were too fine to treat in this way. They were finally ground 
 in an agate mortar and again gone over with a weak magnet, 
 which attracted the mineral but little and served to remove 
 any tracer of pyrrhotite that might remain. In this way the 
 samples were obtained as pure as it is practically possible 
 to get them, and they were ready for analysis ; the results are 
 shown in Table XII. 
 
 TABLE XII. Analyses of Nickel- Bearing Mineral." 
 
 Location. 
 
 Cu. 
 
 Per Cent. 
 
 
 
 
 
 Ni. 
 
 Co. 
 
 Fe. 
 
 s. 
 
 Ratios. (S =1.00.) 
 
 S. 
 
 1.00 
 1.00 
 1.00 
 1.00 
 
 Ni + Co. 
 
 Fe. 
 
 1. Creighton 
 2. Worthington... 
 3. Frood 
 
 PerCent. 
 34.82 
 33.70 
 34.98 
 34.23 
 
 Per Cent. 
 0.84 
 
 0.78 
 0.85 
 0.85 
 
 Percent. 
 30.00 
 29.17 
 30.04 
 30.25 
 
 Per Cent. 
 32.90 
 32.30 
 33.30 
 33.42 
 
 0.589 
 0.583 
 0.58S 
 0.573 
 
 0.518 
 0.517 
 0.513 
 0.518 
 
 4. Copper Cliff 6 . 
 
 a The small amount of residue consisted of siliceous gangue. These analyses 
 were made in the laboratory of the School of Mining, Kingston, Ont., which was 
 kindly placed at the writer's disposal. 
 
 6 Penfield, American Journal of Science, Third Series, vol. xlv., No. 270, p. 
 493 (June, 1893). 
 
 The composition of the non-magnetic residue at once sug- 
 gests pentlandite, and as such Penfield describes the sample 
 he examined (No. 4 in Table XII.). 
 
474 THE ORE-DEPOSITS OF SUDBURY, ONTARIO. 
 
 The pentlandite from Lillehammer, Norway, corresponds 
 very closely to it in physical properties, but carries a lower per- 
 centage of nickel (20 to 22 per cent.) 
 
 The Sudbury mineral occurs, in part, finely disseminated 
 through the pyrrhotite, so that it cannot be detected, even with 
 the aid of a lens, and partly in larger grains and segregations, 
 at times an inch in diameter. Usually it possesses the charac- 
 teristic platy structure and octahedral parting, though this is 
 at times obscured. On fresh fracture, the mineral has a light 
 steel-gray or silver-white color, which soon changes on ex- 
 posure to the peculiar and characteristic light bronze-yellow. 
 When fresh and massive it is with difficulty to be distinguished 
 from the fresh pyrrhotite, but on a slight superficial oxidation 
 the difference becomes quite pronounced. 
 
 The Lillehammer pentlandite has a ratio of FeS : NiS of 
 about 2 : 1, and its formula is given as 2FeS -f NiS. Penfield 2I 
 gives the ratio of the Sudbury mineral as (Fe -f Ni) : S = 1:1, 
 or (Fe -f Ni) S. 22 By a reference to Table XII. it will be seen 
 that the ratio (Fe + M) : S is (1) 11.07 : 10; (2) 11 : 10 ; (3) 
 11.03 : 10 ; and (4) 10.91 : 10 ; that is, there is an excess of the 
 metallic constituents over the amount required by the formula 
 (Fe -f Ni)S. The same excess is indicated in the analyses of 
 less pure material given in Table XI. This relation is con- 
 stant and cannot be regarded as accidental, especially since the 
 analyses of the purest samples from different localities show 
 the ratio to be constant at 11 : 10. Just what this peculiarity 
 signifies it is difficult to say ; but it seems to indicate that the 
 structure of the pentlandite molecule is more complicated than 
 that represented by (Fe + Ni)S, even though it is advantageous 
 to represent minerals by the simplest possible formulas. 
 
 An excess of sulphur over the metal is by no means uncom- 
 mon in minerals (e.g., in pyrrhotite, poly dy mite, beyrichite, 
 etc.) ; but an excess of metallic contents seem unique. 
 
 21 Loc. cit. The analysis given by Professor Penfield, in this paper, agrees 
 almost exactly with those made by the writer, but by a slight error in calculation, 
 his analysis worked out exactly to the formula (Fe + Ni)S, instead of showing an 
 excess of metallic constituents, as is actually the case ; that is, the ratio of (Fe + Ni) : 
 S in the material examined by Professor Penfield is almost 11 : 10, instead of 1 : 1 
 as given. 
 
 22 Nickel and cobalt being taken together. 
 
THE ORE-DEPOSITS OF SUDBURY, ONTARIO. 475 
 
 Such a formula as (Fe -f- Ni) u S 10 is not convenient; but it 
 appears to be the only means of expressing the results of 
 analysis. 
 
 Another interesting feature is the ratio of nickel to iron, 
 which is quite constantly also nearly 11 : 10, while that of 
 nickel to cobalt is about 42 : 1. 
 
 An intimate mixture of some sub-sulphide with what might 
 be regarded as normal pentlandite [(N"i -f Fe)S] is, of course, 
 a possibility ; but if this is the case it must be in a definite and 
 constant ratio, as the mineral shows the same phenomenon 
 throughout the whole district. 
 
 But this is a mere speculation. There is no direct evidence 
 on which to base the assumption, and at present it seems most 
 reasonable to imagine a peculiar molecular arrangement of the 
 atoms of the mineral itself. As the matter now stands, how- 
 ever, the relations are unexplained, and must be the subject of 
 further investigation before a satisfactory conclusion is reached. 
 
 The Formula of the Pyrrhotite. 
 
 A large number of the magnetically-separated samples were 
 analyzed, in an attempt to determine the formula of the pyr- 
 rhotite, and with a fair amount of success. A number of fac- 
 tors had to be taken into consideration, and tended to render 
 the results in some cases rather unsatisfactory, so that absolute 
 uniformity was not attained. 
 
 The nickel present was calculated to pentlandite on the basis 
 of the ratios given above, and the necessary amounts of iron 
 and sulphur were deducted. As there was a persistent, though 
 varying, amount of magnetite in all the samples, it was neces- 
 sary to determine this. The estimation of the oxide (Fe 3 4 ) in 
 the presence of the magnetic sulphide presented considerable 
 difficulty, and this is probably the main cause of the discrep- 
 ancies. 
 
 After a number of experiments, it was found that by treating 
 the sample with a dilute (10 per cent.) solution of nitric acid, 
 the pyrrhotite could be largely removed, while the magnetite 
 was but little affected. The separated sulphur was removed 
 by means of bromine and carbon bisulphide ; and after several 
 treatments the residue of magnetite was obtained pure, and the 
 iron was estimated by titration. The nature of the various 
 
476 THE ORE-DEPOSITS OF SUDBURY, ONTARIO. 
 
 operations involves the possibility of some loss, especially as the 
 amount of magnetite is comparatively small; but, on the 
 whole, the method answered very well. The great majority 
 of the analyses indicated that the pyrrhotite could be repre- 
 sented by the formula Fe 8 S 9 , while two or three worked out to 
 Fe 7 S 8 and Fe 9 S 10 ; so that the former can be regarded as the 
 most probable for the pyrrhotite from the Sudbury district. 
 
 For purposes of comparison, a number of pyrrhotites, as pure 
 as it was possible to obtain them, from various localities, were 
 further purified by magnetic concentration and analyzed. One 
 from Rossland, B. C., conformed to Fe 8 S 9 , one from Anthony's 
 Nose, N. Y., to Fe 7 S 8 , as did also a sample from Enter- 
 prise, Ont. 23 
 
 As absolute uniformity, even in the material from a limited 
 district, was not obtained, it would not be wise to draw general 
 conclusions, or attempt to make any general applications, with- 
 out an exhaustive study of more representative material. 
 
 It seems, however, a justifiable conclusion from the work so 
 far that the pyrrhotite from the nickel-region of Sudbury is of 
 fairly-uniform composition, and is best represented by the for- 
 mula Fe 8 S 9 . 
 
 Summary. 
 
 In recapitulation, the main facts may be summed up briefly 
 as follows : 
 
 1. Our present conception of the constitution of pyrrhotite 
 is very unsatisfactory. The nature and associations of the min- 
 eral are such that analyses are often misleading, and a great 
 deal of careful, systematic work is necessary as a basis for gen- 
 eralisations of any value. 
 
 2. The conditions under which pyrrhotite is formed in nature 
 are still very little understood. 
 
 3. Nickel is universally associated with pyrrhotite in greater 
 or less amount, though in but few instances is it present in quan- 
 tities of economic importance. 
 
 4. The Sudbury pyrrhotites are very uniform over large 
 areas, as to metallic contents and associated minerals. 
 
 5. Aside from the copper- and nickel-minerals, the others 
 
 23 This pyrrhotite is associated with a remarkable deposit of molybdenite, which 
 has recently been exploited. 
 
THE ORE-DEPOSITS OF SUDBURY, ONTARIO. 477 
 
 are of small economic importance, except, perhaps, sperrylite, 
 which is furnishing an increasing amount of the world's supply 
 of platinum. 
 
 6. The magnetic separation of the nickel from pyrrhotite is 
 out of the question commercially. 
 
 7. The nickel occurs in the pyrrhotite as the so-called pent- 
 landite, and not as an essential constituent of this mineral. 
 
 8. Nearly all the pentlandite can be separated from the pyr- 
 rhotite by magnetic methods ; but peculiar physical conditions 
 seem to render its absolute elimination an impossibility. 
 
 9. The pentlandite does not conform to the generally-ac- 
 cepted formula (Fe -f- Ni)S. The metallic constituents are 
 always in excess of the sulphur by a constant ratio of 11 : 10. 
 But, as yet, no satisfactory explanation of this phenomenon can 
 
 be advanced. 
 
 
 
 10. The pyrrhotite from Sudbury can best be represented by 
 the formula Fe 8 S 9 . 
 
 11. Pyrrhotite and magnetite can be separated by a 10-per 
 cent, solution of nitric acid with fairly-satisfactory results. 
 
 II. GENESIS OF THE SUDBURY ORES. 
 
 General Considerations. 
 
 For convenience, pyrrhotites may be divided into two main 
 classes, according to their geological relations. 
 
 1. Those of the first class occur, often with more or less py- 
 rite and chalcopyrite, as lenses in acidic gneisses and schists. 
 These lenticular masses generally conform to the foliation of 
 the schists, and are often repeated and connected by leaner 
 zones, like fahlbands. Such deposits are of world-wide distri- 
 bution ; and, wherever found, generally carry pyrrhotite low in 
 nickel, seldom containing more than 0.5 and usually less than 
 0.25 per cent. 
 
 2. The second class also is widely distributed. The deposits 
 are likewise lenticular in shape, but they are associated with 
 basic igneous rocks, usually of the gabbro type, or their meta- 
 morphic equivalents. Another characteristic feature is, that 
 while they lie well within the limits of the eruptive rock, they 
 generally occur at or near its contact with other rocks, such as 
 granite, mica-schist, porphyry, or diabase. The pyrrhotite is 
 
478 THE ORE-DEPOSITS OF SUDBURY, ONTARIO. 
 
 always associated with more or less chalcopyrite and pyrite, and 
 at times with the rarer minerals, pentlandite, sperrylite, and 
 gersdorffite. The characteristic minerals of the basic rock are 
 also intimately mixed through the prevailing sulphides. Nickel 
 is almost invariably present, at times reaching the amount of 
 10 per cent. Generally, however, from 2 to 4 per cent., as at 
 Sudbury, would be a fair average. In Norway and Sweden the 
 average is lower. 
 
 It should be added that the above general statements as to 
 the nickel-contents of the two classes of pyrrhotite-deposits i& 
 subject to some important exceptions. 
 
 3. Outside of these two classes, pyrrhotite is found at times 
 in considerable quantity in true fissure-veins; but this occur- 
 rence is relatively unimportant. 
 
 Types of the first class, as represented by the Phillips mine,, 
 at Anthony's Nose, N. Y., the Ducktown, Tenn., deposits, and 
 numerous fahlbands in various parts of Ontario, Norway, and 
 Sweden, are believed to be replacement-deposits along crushed 
 zones. 
 
 To the second class of deposits an igneous origin has been 
 attributed in recent years by some of the ablest workers in this 
 field of geology. The sulphides are regarded as original rock- 
 constituents, and it is thought that, being among the first min- 
 erals to crystallize in a cooling rock-magma, they became con- 
 centrated in their present position before the rock solidified. 
 
 It is well established that rock-magmas especially the more 
 basic tend to divide into fractional parts of varying acidity. 
 What forces produce this " magmatic differentiation " is not 
 clearly understood. 
 
 There seems to be excellent evidence to prove that many de- 
 posits of magnetite (always titaniferous), chromite, and cor- 
 undum have originated in this way. That is, they are simply 
 excessively basic developments of magma, in which the mineral 
 in question is a normal, or common, accessory constituent. 
 
 These deposits, however, consist of oxidized compounds; 
 and their segregation presents fewer theoretical difficulties than 
 does that of the sulphides. 
 
 Value of the Classification. Quite apart, however, from 
 theories of origin, the distinction above made as to geological 
 relations is of the utmost importance from an economic stand- 
 point. 
 
THE ORE-DEPOSITS OF SUDBURY, ONTARIO. 47& 
 
 This view of the relative value, of the pyrrhotites in acid 
 and basic rocks, as nickel-ores, is strongly urged by Professors 
 Adams and Kemp in valuable papers which appeared about 
 the same time. 24 
 
 The Sudbury Pyrrhotite-Deposits. 
 
 In studying the origin of pyrrhotite of the second class, par- 
 ticular attention has been paid to the Sudbury deposits. Ref- 
 erence will, however, be made to similar deposits elsewhere 
 when necessary. 
 
 Before proceeding with the consideration of the origin of the 
 ores, it will be necessary to give a brief account of the geology 
 of the deposits, especially as the ideas formerly held have been 
 recently much modified. The Canadian Geological Survey ha& 
 lately paid particular attention to the district, and it is now 
 recognized that its relations are much more complex than wa& 
 at first thought. In his preliminary report on the district, Dr. 
 A. E. Barlow, 25 who has had charge of the work, gave some 
 general ideas of the nature of the rocks and the extent of the 
 ore-bodies. But the field-work was not completed at the time, 
 and many new facts have been collected during the past season; 
 hence, his final views on the subject will not be presented until 
 the full report is issued. Meanwhile, the question must be 
 considered with the understanding that some of the previously- 
 presented conceptions are subject to revision. 
 
 The deposits are prevailingly lenticular, pinching out in both 
 directions and conforming to the general strike of the inclos- 
 ing Huronian strata. The ore always occurs in, and contains 
 fragments of, a basic and altered eruptive of the gabbro type. 
 
 The ore-bodies may occur either well within this eruptive or 
 at its contact with the other prevailing rocks of the district, 
 namely, granite or granite-gneiss, quartzite, or the metamor- 
 phosed representative of a series of basic sedimentaries, now 
 termed " greenstones " by the Survey. 
 
 Dr. Barlow says his investigations prove that the normal 
 
 24 F. D. Adams, Preliminary Eeport on the Geology of a Portion of Central 
 Ontario, Annual Report of the Geological Survey of Canada, vol. vi., Report J 
 (1892-93). On the Igneous Origin of Certain Ore-Deposits, Journal of the Gen- 
 eral Mining Association of the Province of Quebec, vol. ii., pp. 35 to 53 (1894-95). 
 J. F. Kemp, The Nickel-Mine at Lancaster Gap, Trans., xxiv., 620 (1894). 
 
 25 Summary Report of the Geological Survey Department of Canada (1901). 
 
480 THE ORE-DEPOSITS OF SUDBURY, ONTARIO. 
 
 or type-rock associated with the deposits is a member of the 
 gabbro family of rather exceptional character. It nearly always 
 has traces of a broad, ophitic structure, 26 and the presence of 
 hypersthene or enstatite justifies its classification as a norite. 
 Considerable original quartz is, at times, present. In general, 
 the rock consists of a basic plagioclase, hypersthene, or ensta- 
 tite, augite, biotite, hornblende, and quartz, with smaller quan- 
 tities of accessories. Associated with the nickel-bearing norite 
 and grading into it, is a rock which is called " micro-pegma- 
 tite." Microscopically studied, the change consists in the grad- 
 ual assumption of a reddish color and an increase in quartz and 
 feldspar. The hornblende is replaced by biotite and the pla- 
 gioclase by orthoclase. 
 
 The Nickel-Belts. Three main belts of these norites and 
 associated micro-pegmatites are now recognized, designated as 
 the northern, middle, and southern belts, respectively. They 
 are, at present, mapped as separate, but genetically and miner- 
 alogically they are essentially identical. The northern belt 
 runs from the old Ross mine (Foy township) ESE. to Bowell, 
 where it branches. The limits of the smaller branch have not 
 been ascertained, but the larger trends to the north and con- 
 nects with the large area of basic rocks to the west of Lake 
 Wahnipitae. The middle band begins in Levack township to 
 the southwest of the northern, and runs in a southwesterly 
 direction across Windy lake to Trill. 
 
 The southern and most important belt begins in scattered 
 patches in Drury township (south of Trill), which unite and 
 extend unbrokenly NE. for over 32 miles into Denison town- 
 ship, where a maximum width of over 4 miles is attained. 
 Here it is divided into two by an intrusion of coarse " augen " 
 granite-gneiss. The northern, or more important, branch pur- 
 sues a northeasterly direction through Garson township (south 
 of Lake Wahnipitae). The southern branch crosses the Ver- 
 milion river and passes through Copper Cliff, where it rejoins 
 the other. 
 
 It will thus be seen that the norite belt forms a sort of rough 
 and somewhat disconnected ellipse, the center of which is occu- 
 pied by the basin of later silicified volcanic tuffs, and sur- 
 rounded by the so-called Laurentian acidic gneisses. 
 
 26 This was found by the writer, also, to hold true as a general rule. 
 
THE ORE-DEPOSITS OF SUDBURY, ONTARIO. 481 
 
 The unraveling of the complex, which was formerly included 
 under the general name of " greenstone," has proved a very 
 difficult problem. The results seem to show that it can be 
 broken up into several series, comprising eruptives, metamor- 
 phosed sediments, and some as to whose true nature it is diffi- 
 cult to decide. 
 
 The relation of the granite intrusions also presents a difficult 
 problem. These granites in many places, undoubtedly, cut 
 some of the basic rocks in close proximity to the ore-bodies, but 
 in other places they seem to be earlier than these. 
 
 The geologists of the Canadian Survey are now of the opin- 
 ion that these granite rocks are intruded into rocks, largely of 
 sedimentary origin, and classed as greenstones, but that these 
 intrusions are earlier than the ore-bearing norite. The problem 
 is complicated by the close similarity in mineralogical and 
 chemical composition of the so-called altered sediments and the 
 basic eruptives, and by the excessive metamorphism which all 
 have undergone. 
 
 The points at issue are probably not yet finally settled, and a 
 great deal of careful work will, no doubt, be necessary before 
 the last word is spoken. In the absence of the full Survey re- 
 port, 'the matter is in a very unsatisfactory state, but we may 
 confidently expect, in Dr. Barlow's final utterance, a contribu- 
 tion of great scientific and practical value, shedding much light 
 on the question. 
 
 Various Theories of the Origin of Nickeliferous Pyrrhotite. 
 
 A brief statement of the views held hitherto by prominent 
 workers in this field is appropriate here. 
 Dr. Bell 27 brings out the following points : 
 
 1. That this area was the seat of volcanic activity, with ex- 
 plosive violence on a large scale. 
 
 2. The greenstones along certain lines hold an abundance of 
 angular fragments of other rocks, especially quartzite, and this 
 brecciated condition appears to be favorable to the accumula- 
 tion of ore. (Blezard, Stobie, Copper Cliff, etc.) In fact, the 
 ore-masses always consist of a breccia, of sulphides and country- 
 rock in angular and rounded fragments of all sizes. 
 
 27 Annual Report of the Geological Survey of Canada, vol. v., Report F (1890-91). 
 
 31 
 
482 THE ORE-DEPOSITS OF SUDBURY, ONTARIO. 
 
 3. The ore-bodies are lenticular and parallel to the strike of 
 the inclosing rocks. 
 
 4. The. chalcopy rite in large masses is generally nearly pure, 
 but the pyrrhotite is always mixed with a certain amount of 
 stony matter. This may indicate that the former has segre- 
 gated from the original mixture by some secondary process. 
 
 5. The chalcopyrite is often in the form of branching strings 
 and partly surrounds stony inclusions. In some of the 
 brecciated ore-deposits in Levack township, the spiaces be- 
 tween the greenstone fragments are filled, partly with sul- 
 phides and partly with light-colored crystalline granite vein- 
 matter. 
 
 6. The intimate association with the greenstone appears to 
 indicate that they have originated first from a state of fusion, 
 but have been more or less modified by other agencies. The 
 presence of crystals of feldspar, quartz, apatite, etc., together 
 with laminated iron pyrites and galena, indicates the action of 
 solutions. 
 
 7. Both elastics and eruptives have suffered extensive meta- 
 morphism. 
 
 Yon Foullon 28 also calls attention to the metamorphosed 
 and brecciated condition of the diorite (more properly' nor- 
 ite, or altered gabbro ; Bell's greenstone) and to the fact that 
 this appears to v be the most favorable place for ore-deposits. 
 Along a line of fracture which can be traced from the Domin- 
 ion (Blezard) mine to the Vermilion, very similar deposits pre- 
 vail, so it must be considered that the fracture caused them. 
 There is also a fracture-line from the Copper Cliff to the 
 McConnell mine in Denison township, along which ore out- 
 crops, accompanied by diorite and a breccia of gneiss and 
 quartz-syenite. He then adds that the ores are not deposited 
 from solution, but are of igneous origin, because they occur in 
 an eruptive rock. 
 
 Dr. F. D. Adams, 29 speaking of The Igneous Origin of Cer- 
 tain Ore-Deposits, claims such an origin for both the Sudbury 
 and Norwegian pyrrhotites in gabbro. He thinks the ores se- 
 gregated according to Soret's principle, and the formation of 
 the minerals was determined according to Fournet's series. 
 
 28 Jdhrbueh der kaiserlich-koniglichen geologischen Reichsanstalt, vol. xlii. (1892). 
 
 29 Canadian Mining Review, vol. xiii., No. 1, p. 3 (Jan., 1894). 
 
THE ORE-DEPOSITS OF SUDBURY, ONTARIO. 483 
 
 Philip Argall 30 also points out the faulted nature of the dis- 
 trict. He considers that a leaching-out of the nickel and cop- 
 per from the greenstones in which they were originally formed, 
 and a concentration and precipitation along favorable zones, is 
 a more reasonable explanation than that of magmatic differen- 
 tiation. 
 
 E. Renshaw Bush 3l says, the schists in Denison and Graham 
 townships in the vicinity of the nickel-bearing greenstones 
 carry pyrrhotite in grains and aggregates between the layers. 
 He suggests the aqueous origin of the ores for the following 
 reasons : 
 
 1. Because of the tendency of the sulphides to occur along 
 planes of contact and fracture, and the impregnation of the 
 rock near such planes. 
 
 2. Because the ore-bodies occur at the contact between 
 structurally-different rocks. 
 
 3. Because of the impregnation of the schistose areas near 
 the greenstones. 
 
 Merritt 32 thinks that a secondary concentration is necessary 
 to explain certain features of the ore-bodies, viz.: the presence 
 of native copper; the "horses" of barren country-rock, ce- 
 mented by ore ; the " fluccan " observed across certain de- 
 posits; and the sharply-brecciated nature of some of the 
 " horses." 
 
 D. H. Browne, 33 in an article on Segregation in Ores and 
 Mattes, seeks to draw an analogy between a pot of matte, in 
 which he found that the nickel and copper sulphides tended to 
 separate somewhat, and the Sudbury ore-bodies, where it is 
 seen that pyrrhotite and chalcopyrite, to a certain extent, form 
 separate masses. 
 
 Prof. J. F. Kemp 34 appeals to the laws of thermo-chemistry 
 to explain the Sudbury deposits. As is well known, in a fused 
 mass or solution the order of formation of compounds is de- 
 termined by the amount of energy (heat) which they develop 
 
 30 Proceedings of the Colorado Scientific Society, vol. iv., p. 395 (1891-93). 
 
 31 The Sudbury Nickel Region, Engineering and Mining Journal, vol. lyii., No. 
 11, p. 245 (Mar. 17, 1894). 
 
 32 Trans., vols. xvii., 293 (1888-89), and xxiv., 755 (1894). 
 
 38 School of Mines Quarterly, vol. xvi., No. 4, p. 297 (July, 1895). 
 34 An Outline of the Views Held To-day on the Origin of Ores, Mineral Industry, 
 vol. iv., p. 755 (1895). 
 
484 THE ORE-DEPOSITS OF SUDBURY, ONTARIO. 
 
 on crystallizing. If, now, the gabbro magma is considered as 
 an intrusion in which the bases have been concentrated near 
 the walls by Soret's or some other principle, and a stream of 
 sulphuretted hydrogen and sulphurous anhydride gases finds 
 a way of escape along the contact, the sulphides would form in 
 the order indicated above. This should give, in order, the 
 sulphides of iron, copper, and nickel. Professor Kemp, how- 
 ever, recognizes that in this case nickel should be associated 
 with the copper, not the iron sulphide. 
 
 Professor Vogt's views on this subject are well known. 35 He 
 considers that on account of the close chemical and mineral- 
 ogical relations of these deposits the world over, they can be 
 explained only by a common general chemical process. He 
 also emphasizes the fact that there is a regular transition from 
 the pure ore, on the one hand, to normal rock, on the other, by 
 a gradual decrease of sulphides. He claims further support 
 for his theory in the facts that titaniferous magnetite is often 
 present in the ore; that the platinum-metals, which are re- 
 garded as essentially of igneous origin, are found in Sudbury; 
 and that eruptive magmas can dissolve considerable quantities 
 of sulphides. The last seems to be shown by the fact that basic 
 blast-furnace slags often contain from 3 to 5 per cent, of CaS 
 and MnS ; from 4 to 6 per cent, of FeS ; and from 6 to 8 per 
 cent, of ZnS, etc. His conclusion is that the sulphides are un- 
 doubtedly derived from original eruptive magmas by a process 
 of differentiation according to Soret's principle, influenced by 
 other factors, of which gravity may be important. 
 
 T. L. Walker 36 says that near the nickel-deposits the basic 
 eruptives are more or less completely altered by metamorphism, 
 while farther away the change is less, till practically unaltered 
 rock is found. He also brings out the very important fact that 
 some at least of the granites, in contact with the nickel-bearing 
 greenstones, formerly held to be of Lauren tian age, are really 
 younger than the greenstones. This is well seen at the Murray 
 mine, where the " younger granite " sends apophyses into the 
 surrounding greenstones. 
 
 35 Sulphidische Ausscheidungen von Nickelsulphiderzen. Zeitschrift fur prak- 
 tische Geology, vol. i., No. 4, p. 125 (Apr., 1893). 
 
 56 Geological and Petrographical Studies of the Sudbury Nickel District. Quar- 
 terly Journal of the Geological Society, vol. liii., No. 209, p. 40 (Feb., 1897). 
 
THE ORE-DEPOSITS OF SUDBURY, ONTARIO. 485 
 
 Breccias are also formed in places by the inclusion of angu- 
 lar fragments of greenstone in the granite. Similar examples 
 are seen in the granites south of the Blezard mine and the 
 coarse-grained gneiss north of the Copper Cliff, which is essen- 
 tially the same rock. 
 
 In direct opposition to the views of Professor Vogt, another 
 eminent European geologist, Prof. R. Beck 37 (Freiberg), may 
 be quoted. Professor Beck in his admirable work on ore- 
 deposits (Fig. 18) pictures a polished section of mixed ore and 
 rock from the Murray mine, near Sudbury, showing its brec- 
 ciated nature. Such an association, he claims, could not result 
 from a direct magmatic segregation, but must have been due 
 to a separation of the ore, during or after the metamorphism. 
 
 Speaking of the Norwegian nickel-deposits, Professor Beck 
 says there are weighty considerations opposed to the theory of 
 a direct igneous origin of the ores. 
 
 1. On physical grounds it is very difficult to understand how 
 the molten sulphides penetrated so far into the cool, surround- 
 ing rocks (schists) as Yogt figures it. 
 
 2. On the basis of a microscopical examination of the ore, 
 he considers that the corrosion of the residue of the rock- 
 minerals in the ore is due to solution by water, especially as 
 most of the ore occurs in very strongly metamorphosed parts 
 of the gabbro, and that here the ore-separation appears later 
 than the metamorphism. In Figs. 16 and 17 38 the relations are 
 shown. The gabbro and norite, associated with the ore, is 
 nearly always changed to amphibolite, or- garnet-amphibolite, 
 and the ore seems to have followed the metamorphic changes, 
 or in some cases to have been contemporaneous with them. 
 The conclusion is that the important concentration of the ore 
 took place daring the regional metamorphism, and later by the 
 aqueous method. 
 
 Posepny, 39 referring to the Sudbury ore-bodies, claims that an 
 igneous origin is a " chemical impossibility." But the conten- 
 tion is not borne out, when we consider that pyrrhotite is one 
 of the commonest of the early crystallizations from the gabbro 
 magma. 
 
 37 Lehre von den Erzlagerstdtten (1901). 
 
 38 Op. tit, pp. 41 and 42. 
 
 39 The Genesis of Ore-Deposits, p. 146 (1902). 
 
486 
 
 S. F. Emmons 40 is of the opinion that the ore has been con- 
 centrated by percolating waters along lines of faulting and 
 brecciation. 
 
 The Rossland Pyrrhotite-Deposits. 
 
 By way of comparison, a word about the Rossland, B. C., 
 pyrrhotites may not be out of place. The writer has to thank 
 R. "W. Brock, of the Geological Survey of Canada, who has 
 been one of the chief workers in this province, for the latest 
 data. 
 
 The ore-bodies here, while not carrying nickel in any quan- 
 tity, have the same general associations as at Sudbury; and it 
 is now fully established that they are of- secondary aqueous 
 origin. 
 
 During the trial of the suit of the Iron Mask Mining Co. 
 against the Centre Star Co., in 1899, evidence was submitted 
 by Messrs. Clarence King, Waldemar Lindgren, and R. "W. 
 Raymond as to the nature of these deposits. 41 
 
 Stated briefly, the Rossland district forms part of a huge sys- 
 tem, reaching from Cape Horn to the Arctic, and has been 
 involved in the enormous dynamic and volcanic effects which 
 this region has undergone from early geological times. Follow- 
 ing the folding of the dynamic periods, the deposition of min- 
 eral matter in the fissures and along lines of weakness took 
 place. In connection with most of the ore-bodies three types 
 of rocks are represented. 
 
 1. A monzonite, often carrying pyrrhotite, and with the 
 original structure more or less obliterated. 
 
 2. A darker, coarser-grained rock of the gabbro family, con- 
 sisting of augite and triclinic feldspar, with little or no ortho- 
 clase. 
 
 3. The third is composed largely of hornblende and orthoclase. 
 These types are doubtless local variations of the same magma, 
 
 but of successive flows. 
 
 The veins are considered as distinctly of the fissure-type, and 
 many of them are of the "shear-zone" variety i. e., consist- 
 ing of a number of more or less parallel seams, with little dis- 
 placement and no open fissures. The depth of the fissuring 
 
 40 Geological Distribution of the Useful Metals in the United States, p. 65, this 
 volume. 
 
 41 Records of the Supreme Court of British Columbia, 1899. 
 
THE ORE-DEPOSITS OF SUDBURY, ONTARIO. 
 
 487 
 
 FIG. 1. MOUNT NICKEL MINE. 
 Photograph of polished section of ore. 
 The light is chalcopyrite and pyrrhotite ; 
 the dark is gangue and rock. . Slightly 
 enlarged. 
 
 FIG. 2. MOUNT NICKEL, MINE. 
 Photograph of polished section of ore and 
 rock, showing brecciated character. Slightly 
 enlarged. 
 
 FIG. 3. MOUNT NICKEL MINE. 
 Polished section of massive ore with 
 unreplaced rock (dark). Pyrrhotite and 
 chalcopyrite indistinguishable in the pho- 
 tograph. Slightly enlarged. 
 
 FIG. 4. STOBIE MINE. 
 
 Photograph of polished section of ore (light), 
 with angular and rounded rock-fragments (dark). 
 Slightly enlarged. 
 
488 
 
 THE ORE-DEPOSITS OF SUDBURY, ONTARIO. 
 
 FIG. 5. MOUNT NICKEL MINE. 
 Photomicrograph of rock containing ore, 
 showing the ore in parallel veinlets 
 through the rock-minerals. The white is 
 feldspar containing ore (dark), and granu- 
 lar and fibrous hornblende and hyper- 
 sthene (shaded). Field, 2.5 mm. 
 
 FIG. 6. STOBIE MINE. 
 Photomicrograph of ore-rock. The dark 
 is ore in veinlets, etc. The white is feld- 
 spar, and the shaded is hypersthene, often 
 with ore in the cleavages. Field, 2.5 mm* 
 
 FIG. 7/ MOUNT NICKEL MINE. 
 Drawn from blue-print of photomicro- 
 graph, showing the ore in veinlets through 
 the rock-minerals. The dark is mostly 
 pyrrhotite, the white is feldspar, and the 
 shaded is hypersthene. Field, 2.5 mm. 
 
 FIG. 8. STOBIE MINE. 
 Drawn from blue-print of photomicro- 
 graph, showing the ore (dark) sharply 
 outlined against the fresh hypersthene- 
 (shaded) and feldspar (white), and enter- 
 ing the cleavages. Field, 2.5 mm. 
 
THE ORE-DEPOSITS OF SUDBURY, ONTARIO. 
 
 489 
 
 FIG. 9. ELSIE MINE. 
 Photograph of polished section of 
 ore (light), showing the irregular, vein- 
 like replacement of the rock (dark). 
 Slightly enlarged. 
 
 FIG. 10. COPPER CLIFF MINE. 
 Photograph of polished section of 
 ore, showing the vein-like character 
 of the sulphides. The pyrrhotite has 
 been touched out with Chinese white 
 to form a contrast with the chalcopy- 
 rite (dark). Slightly enlarged. 
 
 FIG. 11. COPPER CLIFF, No. 2, MINE. 
 
 Photograph of polished section of ore and rock, showing the brecciated 
 character, and the vein-like nature of the ore (light), and the centers of un- 
 replaced rock (dark). The sulphides are brought out by touching up with 
 Chinese white. Slightly enlarged. 
 
490 
 
 THE ORE-DEPOSITS OF SUDBURY, ONTARIO. 
 
 FIG. 12. ELSIE MINE. 
 Photomicrograph of ore-rock, showing 
 altered feldspar (white) with parallel vein- 
 lets of ore (dark) and irregular patches of 
 pale-green hornblende (shaded). Field, 
 2.5 mm. 
 
 FIG. 13. COPPER CLIFF, No. 2, MINE. 
 
 Photomicrograph of ore-rock, showing 
 ore (dark) replacing fibrous and granular 
 hornblende (shaded), and entering cracks 
 and cleavages. The white is feldspar and 
 quartz. Field, 2.5 mm. 
 
 FIG. 14. CREIGHTON MINE. 
 Drawn from blue-print of photomicro- 
 graph, showing the ore in veinlets, through 
 altered hornblende, chlorite, and biotite 
 (shaded). The white is feldspar and quartz. 
 Field, 2.5 mm. 
 
 FIG. 15. VICTORIA MINE. 
 Drawn from blue-print of photomicro- 
 graph, showing sulphides (dark) between 
 and surrounding fibers of hornblende and 
 biotite (shaded), and entering cleavages. 
 The white is quartz and feldspar. Calcite 
 is also present. Field, 2.5 mm. 
 
THE ORE-DEPOSITS OF SUDBURY, ONTARIO. 
 
 491 
 
 FIG. 16. GERTRUDE MINE. 
 Drawn from blue-print of photomicro- 
 graph, showing the sulphides (dark) parallel 
 to the fibers of the hornblende (shaded). 
 The white is feldspar. Field, 2.5 mm. 
 
 FIG. 17. GERTRUDE MINE. 
 Drawn from blue-print of photomicro- 
 graph, showing sulphides (dark) parallel 
 to the cleavages of the fibrous hornblende 
 (shaded), and following the changes of di- 
 rection. Field, 2. 5 mm. 
 
 FIG. 18. CREIGHTON MINE. 
 Photomicrograph of ore with small resi- 
 dues of hornblende, feldspar, and quartz, 
 partly replaced. Field, -2.5 mm. 
 
 FIG. 19. GERTRUDE MINE. 
 Photomicrograph of ore-rock, with ore 
 (dark) replacing the hornblende and bio- 
 tite (shaded) along cracks and cleavages. 
 The white is feldspar and quartz. Field, 
 2.5 mm. 
 
492 
 
 THE ORE-DEPOSITS OF SUDBURY, ONTARIO. 
 
 FIG. 20. GERTRUDE MINE. 
 
 Photograph of polished section of ore, showing unreplaced rock (dark). 
 The light is pyrrhotite and the shaded is chalcopyrite. Slightly en- 
 larged. 
 
 FIG. 21* CREIGHTON MINE. 
 
 Photograph of polished section of ore, showing the vein-like nature 
 of the sulphides. The light is pyrrhotite and the dark is chalcopyrite. 
 Slightly enlarged. 
 
THE ORE-DEPOSITS OF SUDBURY, ONTARIO. 
 
 493 
 
 FlG. 22. WORTHINGTON MlNE. 
 
 Photograph of polished section of ore, showing irragular patches of 
 unreplaced schistose rock. Slightly enlarged. 
 
 FIG. 23. WORTHINGTON MINE. 
 
 Photograph of polished section of ore, showing round and angular 
 fragments of unreplaced rock. Slightly enlarged. 
 
494 
 
 THE ORE-DEPOSITS OF SUDBURY, ONTARIO. 
 
 FIG. 24. COPPER CLIFF MINE. 
 
 Drawn from blue-print of photomicrographs, showing ore (dark) 
 between the grains and fibers of the rock-minerals. Field, 2.5 mm. 
 
 FIG. 25. PHOTOMICROGRAPH OF ORE FROM 
 
 THE EAST TENNESSEE MINE. 
 The white mineral is calcite. The dark min- 
 eral is chalcopyrite, which has entered cracks 
 and fissures in the calcite. Magnified 40 diame- 
 ters. 
 
 FIG. 26. PHOTOMICROGRAPH OF ORE FROM 
 
 THE EAST TENNESSEE MINE. 
 The white mineral is actinolite. The dark 
 mineral is chalcopyrite, which has filled even 
 minute cracks in the shattered actinolite and 
 has replaced it when crushed and altered. 
 Magnified 17.3 diameters. 
 
THE ORE-DEPOSITS OF SUDBURY, ONTARIO. 495 
 
 permitted a circulation of deep-seated thermal waters and a 
 deposition of the chemicals carried in solution along the lines 
 of weakness by a decomposition and replacement of the rock- 
 minerals. The final result is either: (1) a deposition of the 
 ore on one plane or fissure of the " shear-zone," or (2) a re- 
 placement of the rock between two planes, or (3) the replace- 
 ment of a whole zone, and so on with endless variations. The 
 replacement of the rock-minerals by ore (largely chalcopyrite 
 and pyrrhotite) took place molecule by molecule, producing 
 what is really a pseudomorph. The replacement is well seen 
 near the Iron Horse mine, where large diallages or augites have 
 changed to ore, while the surrounding country-rock was only 
 partly transformed. 
 
 The replacement has, at times, been so intense that an almost 
 solid body of sulphides (with quartz and calcites) results. In 
 other places the original rock, more or less modified and silici- 
 fied, has been only partly replaced and impregnated with ore. 
 
 Messrs. King, Lindgren, and Raymond were practically unan- 
 imous in their interpretation of the phenomena of the district, 
 which agrees very closely with that of the Canadian Geological 
 Survey, though the more recent work shows that slight modi- 
 fications of the rock relations are necessary. 
 
 Briefly, the geology and relative ages of the rocks of the 
 mining-district are as follows : 42 
 
 1. The oldest series represented is classed as the Kootenay 
 volcanic group, consisting of augite-porphyrites, tuffs, ash-beds, 
 etc., of Palaeozoic age. 
 
 2. Next comes a granite or grano-diorite (Nelson granite), 
 probably Jurassic. 
 
 3. The Rossland monzonite, probably post-Jurassic. 
 
 4. Conglomerate, probably Tertiary. 
 
 5. Alkali (Rossland) granite and syenite. 
 
 The ores may occur in any of the rocks older than the alkali 
 granite. This granite, whose main development is outside the 
 limit of the Trail Creek sheet, is probably a Tertiary eruptive, 
 and its dikes have penetrated all through the Rossland district. 
 
 As it happens, the principal mineralization is in the augite- 
 porphyrites and monzonite, probably on account of the fractur- 
 
 42 See Trail Creek map (1897), and Summary Reports ( 1896-1900) of the Geological 
 Survey of Canada. 
 
496 THE ORE-DEPOSITS OF SUDBURY, ONTARIO. 
 
 ing and cutting of these rocks by dikes, together with their 
 relative solubility. The chief factor controlling the location of 
 the mineralization seems to have been the alkali-granite contact 
 and its system of dikes, the eruption of which immediately pre- 
 ceded the formation of the ore-bodies. The deposits are found 
 where the dikes are particularly abundant. 
 
 The monzonite is the chief center of mineralization, but it 
 is not to be considered as a volcanic neck, with the augite por- 
 phyrites and tuffs as part of the cone. These latter are much 
 older and are cut by the Nelson granite. The occurrence of 
 the ore has no relationship to the contact of the monzonite, 
 being found both outside and inside its boundaries and in the 
 younger rocks. 
 
 While magmatic differentiation has gone on to some extent, 
 the sulphides are not the result of it, as is proved definitely by the 
 work of the Survey. 
 
 A peculiarity of the rocks in which the ore occurs is that, 
 while sheared and fractured, they are not brecciated, the dy- 
 namic movement having doubtless taken place under an im- 
 mense load. 
 
 With reference to the ore-bodies themselves, some interest- 
 ing points are brought out. The ore replaces the country-rock, 
 partly or completely, starting from some fissure or line of fis- 
 sures and often fading out gradually, the only " wall " being a 
 commercial (economic) boundary. It may end abruptly at a 
 fissure, in some cases due to a slip, which brought an unminer- 
 alized face against the ore. 
 
 Deposits very similar to those in the eruptives are found in 
 the conglomerate (No. 4), which cannot be regarded in any 
 other way than as of secondary origin. 
 
 The marked similarity of the geological relations in Rossland 
 and Sudbury helps to make clear some of the more obscure 
 points in the latter district. As the conditions of metamor- 
 phism, however, were not identical, the dynamic movements 
 have manifested themselves in different ways, and it is not sur- 
 prising that there should be striking dissimilarities. This dif- 
 ference is seen in the characteristic structures of the ore-bodies 
 in the two districts. In Rossland, the fissure or shear-zone type 
 of vein is predominant, with little or no sign of brecciation. 
 In Sudbury, on the other hand, where the dynamical move- 
 
THE ORE-DEPOSITS OF SUDBURY, ONTARIO. 497 
 
 ments probably took place under a very small load, a breccia- 
 tion from faulting on a large scale, and probably with consid- 
 erable movement, is characteristic. This will be brought out 
 more clearly in speaking of the individual deposits. 
 
 This brief review indicates the wide differences of existing 
 opinion as to the origin of pyrrhotite and the various interpre- 
 tations which have been put upon the same phenomena. 
 
 Microscopical Evidence of the Origin of the Ores. 
 
 The evidence on which the secondary nature of these ores is 
 here advocated is mostly altogether different in character from 
 that already presented. It consists in the relations between 
 the ores and the rock-minerals, brought out by microscopical 
 examination. As no investigation of this kind has been pre- 
 viously made, the results will be given in some detail. Mate- 
 rial from all the principal mining-locations has been studied, 
 in order to avoid laying too much stress on local phenomena 
 and to emphasize the genetic similarity of all the deposits of 
 the district. The character of the ore-bodies in a large way 
 will also be briefly noted as throwing much light on the gen- 
 eral nature of the deposits. 
 
 Sudbury District. The following separate localities in this 
 district will represent its character : 
 
 1. Mount Nickel Mine, Blezard Township. The ore con- 
 sists of pyrrhotite (both coarse- and fine-grained) and a smaller 
 amount of chalcopyrite, through which occur masses of almost 
 barren rock, varying in size from minute particles to large 
 " boulders," or " horses." Near what is considered as the foot- 
 wall, the chalcopyrite increases in amount and the proportion 
 of barren rock is greater. 
 
 The deposit is a good example of what is best described as 
 a " breccia ore-body." Rounded and angular rock-fragments of 
 all sizes, with sulphides as a cementing material, are every- 
 where a striking characteristic. Besides the brecciation as a 
 whole, the rock is often broken and fractured, and little seams 
 and veinlets of ore occur all through it in a very typical 
 manner. 
 
 In some of the open-cuts the ore is seen to run in particular 
 streaks or bands, and may end very abruptly against barren 
 rock. 
 
498 THE ORE-DEPOSITS OF SUDBURY, ONTARIO. 
 
 The brecciated character, as it is seen in a large way, is also 
 faithfully reproduced in hand-specimens. Figs. 1, 2, and 3, 
 from photographs of polished sections, show these features 
 very well. 
 
 While brecciation is one of the most striking characteristics 
 of the deposit, evidences of faulting and shearing are not want- 
 ing in the slickensided and schistose nature of some of the 
 rocks. There are a number of clayey seams, and some of the 
 samples are decidedly fibrous. Along certain of the lines of 
 crushing the rock is partly brecciated and partly slickensided, 
 and here the ore occurs in veinlets and as a cement for the 
 rock-fragments. 
 
 Under'the microscope, the rock associated with the ore is 
 black and dense, and belongs to the gabbro family. Hyper- 
 sthene in fresh idiomorphic grains is very abundant, while 
 augite and diallage are in subordinate amount. The pyroxenes 
 have, in part, been altered to green fibrous hornblende. The 
 feldspar forms an irregular mosaic, among the grains of which 
 are fragments of hypersthene. 43 Biotite and quartz are spar- 
 ingly present. 
 
 The relations of the sulphides to the rock-minerals are well 
 shown. Where the pyroxene is somewhat altered it becomes 
 fibrous ; and here the sulphides are best developed. 
 
 Chalcopyrite and pyrrhotite form numerous veinlets between 
 the fibers and cleavages of the rock-minerals. In places, where 
 not too massive, the sulphides reproduce very faithfully the 
 fibrous structure of the hornblende, though little of this min- 
 eral may remain, so that really a pseudomorph results. In one 
 place or another all stages of replacement can be seen, from a 
 few dust-like particles of sulphides in the hornblende to com- 
 plete replacement. Where the pyroxene is fresh, the sulphides 
 are outlined sharply against its margin, and only enter cleav- 
 ages. In this way grains of pyroxene are more or less com- 
 pletely isolated. Figs. 5 and 7 show veinlets of sulphides 
 through the fibrous minerals. 
 
 The relations seem to indicate a crushed zone, in which the 
 feldspar has yielded and formed a mosaic, and along which the 
 solutions carrying the sulphides have acted ; the greater the 
 
 43 The rocks from all the localities examined show a more or less pronounced 
 migration of the dark silicates, especially secondary hornblende, into the feldspar. 
 
THE ORE-DEPOSITS OF SUDBURY, ONTARIO. 499 
 
 alteration of the rock, the more complete being its replace- 
 ment. 
 
 2. Blezard (Dominion) Mine, Blezard Township. The char- 
 acter of the deposit is very similar to that of the Mount Nickel, 
 showing the same brecciation and shearing. Under the micro- 
 scope, however, the rock shows a more advanced stage of alter- 
 ation than that of Mount Nickel. The pyroxene has changed 
 to greenish fibrous hornblende and chlorite, which, in some 
 cases, makes up nearly the whole rock. The feldspar is largely 
 labradorite, and often contains irregular fibers of hornblende. 
 The pyrrhotite forms reticulating networks among the horn- 
 blende fibers, the veinlets of ore lying parallel to the fibers. 
 
 3. Stobie Mine, Blezard Township. The brecciated char- 
 acter is here very pronounced, and the ore contains a large pro- 
 portion of barren rock-masses of all sizes, as usual filled around 
 with sulphides. Fig. 4 shows the prevailing nature of the more 
 massive ore, with its residual angular and rounded rock-frag- 
 ments. 
 
 Under the microscope, sections of rock, with a small pro- 
 portion of ore, are made up largely of a fine-grained mixture 
 of plagioclase (labradorite and anorthite) and hypersthene, with 
 small amounts of augite, diallage, and biotite ; and magnetite, 
 apatite, and zircon as accessories. Quartz, in varying amount, 
 is also characteristic. The hypersthene is quite abundant, and 
 forms idiomorphic and rounded grains and irregular aggre- 
 gates; it shows the usual microscopical characters of this min- 
 eral. The pyroxenes are, as a rule, quite fresh, but form a mo- 
 saic with the feldspar, probably due to crushing. Along certain 
 lines, however, the pyroxenes have altered to a pale-green 
 uralitic hornblende or chlorite. 
 
 The relations of the sulphides to the rock-minerals are strik- 
 ing. Following the direction of the altered zones, the sulphides 
 are most prominently developed. A veinlet of chalcopyrite 
 an be traced across one of the sections, following the cleavages, 
 and between the fibers of hornblende and around the fresher 
 grains of the other minerals (Fig. 6). In other cases the partly- 
 altered pyroxene has been more or less replaced by ore, the par- 
 ticles of which are elongated in the direction of the cleavages, 
 and follow these even when they change their direction ab- 
 ruptly. When found in connection with the fresher grains, the 
 
500 THE ORE-DEPOSITS OF SUDBURY, ONTARIO. 
 
 sulphides simply inclose them, following their irregularities and 
 larger cleavages (Fig. 8). 
 
 An increasing proportion of ore is accompanied by a corre- 
 sponding change in the character of the rock. The pyroxenes 
 decrease notably in quantity and finally disappear, giving place 
 to secondary green hornblende, chlorite, and biotite. Both 
 hornblende and biotite are fibrous, and often show deformation, 
 due to strain. The hornblende and other secondary products, 
 in their turn, disappear as the ore increases, and various stages 
 of their replacement can be traced from an almost pure silicate, 
 containing a few specks of ore, to pure sulphide. In interme- 
 diate cases the sulphides may preserve very perfectly the 
 fibrous structure of the hornblende or biotite, with little shreds 
 of the mineral marking its original form. In purer ore, still, 
 the dark silicates disappear almost entirely, and the feldspar is 
 filled with inclusions of ore and changed to a confused aggre- 
 gate of secondary products. 
 
 In the latter cases the amount of quartz has increased nota- 
 bly and remains as clear irregular patches through the ore. 
 
 4. Frood, or No. 3 Mine, McKim Township. The ore con- 
 sists of coarse- and fine-grained pyrrhotite and chalcopyrite. 
 The latter at times occurs in almost pure masses, and is most 
 abundant towards the walls. Barren rock-fragments occur all 
 through the ore-body, presenting the usual breccia, cemented 
 by sulphides. 
 
 Microscopic sections show that the rock has undergone con- 
 siderable alteration. No traces of original pyroxene could be 
 found. The secondary hornblende is bleached and ragged, 
 and is intimately associated with the sulphides, as is the biotite, 
 which is also plentiful. Feldspar in many cases is subordinate, 
 while there is a notable amount of clear quartz, which is ap- 
 parently secondary. Calcite also appears in small quantities. 
 The sulphides are always found in connection with the dark 
 silicates, and replace them to a greater or less extent. 
 
 5. Elsie Mine, Snider Township, and Murray Mine, McKim 
 Township. The ore-body (Elsie) is situated well within the 
 basic rocks, the granite contact being some distance off. The 
 ore is largely pyrrhotite, with a varying amount of chalco- 
 pyrite, which increases towards the foot-wall. The ore is in 
 places largely mixed with rock and may become subordinate 
 
THE ORE-DEPOSITS OF SUDBURY, ONTARIO. 501 
 
 in amount, even in the midst of the deposit. Nearly every 
 piece of ore shows a characteristic breccia of rock in a matrix 
 of sulphides, the rock being either practically barren or having 
 veinlets of mineral irregularly through it (Fig. 9). There are 
 many evidences of movement, as shown by the numerous clay 
 seams impregnated with sulphides and in the schistose and 
 slaty character of the gabbro, which is often polished and 
 slickensided. There are also examples of what appear to be 
 fault-planes and fissures, filled with a mixture of tremolite, 
 quartz, calcite, and ore, the latter very evidently having been 
 introduced subsequent to the movement. The structure at the 
 Murray mine is very similar to that at the Elsie, except that 
 the granite contact is close to the ore-body. The granite pierces 
 the associated " greenstones " (altered sediments ?) and is un- 
 doubtedly younger. 
 
 Microscopic sections of rock with a large amount of ore show 
 that most of the pyroxenes have changed to green fibrous horn- 
 blende, though original hypersthene more or less altered is still 
 recognizable. The feldspar is much crushed, and is in an ad- 
 vanced stage of alteration, and often contains hornblende fibers, 
 and parallel veinlets of pyrrhotite along the cleavages (Fig. 12). 
 
 The relation of the sulphides to the rock-minerals is of the 
 usual type, i.e. 9 the replacement proceeds along and between the 
 hornblende fibers and lines of weakness and cleavage in other 
 minerals. 
 
 6. Mines Around Copper Cliff in Snider and McKim Town- 
 ships. This group includes the following mines of the Cana- 
 dian Copper Co. : Copper Cliff", No. 1, No. 2, No. 4, and No. 5, 
 in different stages of development. Some of the deposits are 
 entirely surrounded by " greenstones," while others have the 
 granite-gneiss as one of the so-called " walls." Dr. Barlow, of 
 the Geological Survey of Canada, is of the opinion that the 
 ore-bearing norite often occurs in more or less completely iso- 
 lated passages in the " greenstones," and may consist almost 
 entirely of ore. 
 
 No. 2 mine (and extension) affords a typical example of the 
 " breccia ore-body." The contact is right at the granite, and 
 the ore-bearing rock has numerous small dikes of the latter 
 through it, and in this case, at least, it seems to be indisputa 
 ble that the granite is the younger. Near the contact the 
 
502 THE ORE-DEPOSITS OF SUDBURY, ONTARIO. 
 
 granite contains a small amount of ore, and samples at times 
 consist of both acid and basic rock impregnated with sulphides. 
 The brecciated structure is very pronounced, and veinlets of 
 ore occur everywhere through the rock (Fig. 11). There is 
 also evidence of shearing, and secondary quartz-stringers are 
 common. 
 
 The Copper Cliff mine belongs to the same brecciated type 
 and has yielded a large number of minerals of secondary origin. 
 (See Part I.) 
 
 No. 1 mine in places exhibits a very abrupt transition from 
 rich ore to barren rock. A short distance from the ore-body 
 the rock is slightly mineralized, but on a close examination it 
 is seen that the ore always occurs in small crevices or parting- 
 planes, or other lines of weakness. 
 
 Under the microscope, thin sections show that the rock 
 varies from an almost pure hornblende variety, with other 
 minerals in subordinate amount, to more acid varieties, but in 
 all, the dark silicates are in excess. Nearly all the pyroxene 
 has been altered to fibrous green hornblende, though in some 
 sections traces still remain. Quartz is often quite abundant, 
 and the usual accessories are present. The granular nature of 
 the feldspar, and the bent and twisted hornblende and biotite, 
 indicate severe crushing. The sulphides abut sharply against 
 the fresher minerals, but when they are fibrous and broken, 
 they tend to occur between the fibers and grains, more or less 
 complete replacement resulting. (Fig. 13). 
 
 As the amount of ore increases, the dark silicates disappear 
 largely, leaving areas of clear quartz and feldspar, with the 
 ore sharply defined against their boundaries (Fig. 24). Where 
 the effects of crushing are most pronounced, the sulphides are 
 best developed, and then the replacement extends from these 
 centers along the cleavages and between the hornblende fibers,, 
 resulting in a more or less complete substitution of ore. 
 
 7. Creighton Mine, Near the Boundary Between Snider and 
 Creighton Townships. This mine, which has recently been 
 developed by the Canadian Copper Co., is perhaps one of the 
 most remarkable nickel-deposits in the world. The ore-body 
 is very large, and the ore is above the average in richness and 
 purity. Mining is carried on in a huge open-cut, 200 ft. or 
 more across and about 100 ft. deep, in solid ore, with a shaft 
 from the bottom of the pit. 
 
THE ORE-DEPOSITS OF SUDBURY, ONTARIO. 503 
 
 The ore, which is largely pyrrhotite with more or less chal- 
 copy rite, however, contains many masses of barren diorite 
 (norite) all through it, presenting a very characteristic breccia. 
 The rock-fragments vary in size from minute particles to large 
 " boulders," and are both rounded and angular. Where the 
 ore is not too massive to obscure the relations, it presents much 
 the appearance of a conglomerate cemented by sulphides, with 
 numerous ramifying veinlets along the fracture-planes of the 
 rock. Through the ore-body are a number of intrusions of a 
 coarse granitic rock, which often includes fragments of the 
 diorite (norite) breccia. This rock is itself not heavily miner- 
 alized, but where it has included fragments of the basic rock 
 these are more or less replaced by ore, and the replacement 
 may extend to the acid rock itself to a lesser extent. 
 
 From the evidence collected it would appear that this gran- 
 itic rock had been intruded into and had included fragments 
 of the diorite at the time of, or after, its brecciation. These 
 fragments have then been partly replaced by ore, the minerali- 
 zation extending slightly to the acid rock. 
 
 There are also two dense fine-grained diabase dikes cutting 
 sharply through the ore-body and having well-defined contacts. 
 These are considered as among the youngest rocks of the dis- 
 trict. While they are usually considered to have cut through 
 the ore after its formation, there is a possibility, if the theory 
 of igneous origin is left out of the question, of their being pre- 
 vious to the formation of the deposits. 
 
 They do not include fragments of the ore, and their only 
 mineralization is along fissures and joint-planes, the introduc- 
 tion of the sulphides being very evidently later than the intru- 
 sion. There has also been a movement in the dikes themselves 
 since their formation, as they are composed of numerous verti- 
 cal and parallel divisions with smooth polished faces, along 
 which sulphides at times occur. If the dikes were in place 
 previous to the formation of the ore, their compact fine-grained 
 texture would be unfavorable to the action of the ore-bearing 
 solutions, except along parting-planes, while the more coarsely 
 crystalline and crushed diorite would offer an easy passage for 
 the circulating waters. 
 
 No conclusive evidence of faulting or shearing could be 
 found in the main pit, but in several of the test-pits sunk in 
 
504 THE ORE-DEPOSITS OF SUDBURY, ONTARIO. 
 
 the vicinity, to determine the extent of the ore-body, abundant 
 proof was available. In these, the rock associated with the 
 ore has been severely crushed and squeezed, so that it presents 
 a schistose and slickensided appearance, and is often much like 
 an amphibolite-schist, with seams of ore on the parting-planes. 
 
 If these pits are in a continuation of the main body of ore, 
 as seems probable, we have two different structures resulting 
 from an unequal distribution of the dynamic force which 
 caused them, and probably also due to local differences in the 
 rocks themselves. 
 
 In the neighborhood of the Creighton mine, and towards 
 Copper Cliff, the granite frequently cuts the basic rocks and 
 sends dikes through them. What the relation of these rocks 
 is to the ore-bearing variety could not be accurately deter- 
 mined. 
 
 Under the microscope, the diorite, or altered norite, presents 
 a somewhat gneissoid appearance, with a large part of the 
 pyroxenes altered to fibrous green hornblende and chlorite. 
 Quartz is present in variable amount. 
 
 The sulphides (Fig. 14) are best developed where the effects 
 of crushing are most apparent. Some of the dark silicates 
 have altered to indefinite aggregates of secondary products, 
 which are spotted all through with ore and may even be en- 
 tirely replaced. The veinlets of sulphides typically follow 
 along the cleavages of hornblende and feldspar, which shows in 
 some cases an advanced stage of alteration. Fig. 18 shows mas- 
 sive ore, with only small residues of unreplaced rock-minerals. 
 
 The coarse granitic dikes contain abundant quartz and feld- 
 spar, and where they include fragments of the basic rock these 
 show partial replacement, which also extends to the minerals 
 of the acid rock. 
 
 8. Gertrude Mine, Creighton Township. Besides the usual 
 breccia, which is very pronounced, there is abundant evidence 
 of shearing in the different deposits under development (Fig. 
 20). In No. 1 pit the ore ends very abruptly against a wall of 
 sheared diorite, which is only slightly mineralized along the 
 shear-planes. 
 
 Along this contact, and penetrating the rock breccia, a num- 
 ber of small granite dikes have been intruded, which are 
 slightly mineralized. Sheared diorite, together with actinolite 
 
THE ORE-DEPOSITS OF SUDBURY, ONTARIO. 505 
 
 and other secondary minerals, impregnated with ore, is notice- 
 able in all the pits which have been opened up. As these pits 
 are in line, it is probable that the faulting movement embraced 
 them all, but from lack of exposures between, the fault-line 
 could not be traced. 
 
 The brecciation and shearing, as well as the intrusion of the 
 granite, evidently took place previous to the introduction of 
 the ore, as all are more or less impregnated \vith mineral, 
 either as veinlets or between parting-planes. 
 
 Under the microscope, the ore- rock is seen to consist very 
 largely of actinolitic and chloritic hornblende, with other min- 
 erals of lesser amount. 
 
 The relation of the sulphides to the rock-minerals is quite 
 typical (Figs. 16, 17, and 19). Where the hornblende is of the 
 fibrous variety, it is usually associated with ore, and all stages 
 of progressive replacement can be seen. In samples with a 
 large proportion of the ore, the more compact grains of horn- 
 blende, as well as the feldspar and quartz, are left as isolated 
 patches in a ground-mass of sulphides, while the fibrous 
 variety has nearly all disappeared. 
 
 9. Victoria Mine, Denison Township. The ore consists of 
 pyrrhotite, with chalcopyrite, which increases in quantity to-- 
 wards the foot-wall in a typical rock-breccia. There is a fault 
 passing through the deposit, and in the secondary minerals 
 formed (actinolite, mica, etc.) the ore occurs in veinlets clearly 
 later than the movement. There is also a considerable devel- 
 opment of quartz and calcite intimately mixed through the 
 ore, which cannot be considered as original igneous products. 
 
 The microscope shows the ore-rock to be the usual altered 
 norite with the minerals of a diorite. Green fibrous and gran- 
 ular hornblende is predominant. One of the most noticeable 
 features is the large amount of quartz and calcite which re- 
 mains spotted through the ore when the other minerals have 
 largely disappeared. The replacement of the hornblende and 
 biotite by sulphides is well shown (Fig. 15). The pyrrhotite 
 has many hornblende fibers through it and enters the cleavages 
 of the other minerals in a typical manner. 
 
 10. Worthington and Mitchener Mines, Drury Township. 
 The ore-rock at the Worthington is bounded on the south by a 
 band of dark schistose rock of sedimentary origin, and to the 
 
 32 
 
506 THE ORE-DEPOSITS OF SUDBURY, ONTARIO. 
 
 south of this there is quartzite. The Mitchener mine, about 
 0.5 mile west of the Worthington, is surrounded by the quartz- 
 ite. Two varieties of rock are met with in the ore-bodies, 
 namely, coarse- and line-grained. The coarse-grained variety 
 is sheared and slickensided, and, as a rule, contains little ore, 
 but when it does, it is in the form of veinlets and along the 
 parting-planes. The fine-grained rock has been brecciated, 
 instead of sheared, and numerous rock-fragments of different 
 sizes, surrounded and cemented by sulphides, remain in the 
 ore-bodies (Figs. 22 and 23). Through the ore-body there are 
 also numbers of small lenticular masses of schistose diorite, 
 giving the ore somewhat the appearance of an " augen " gneiss. 
 These are evidently residual portions of the rock which have 
 escaped replacement, and clearly show that the introduction of 
 the ore was subsequent to the movement which caused the 
 shearing and brecciation. 
 
 The ore at the Worthington is often very rich, and the nickel- 
 mineral pentlandite occurs quite abundantly. 
 
 The fault which occurs at the Victoria seems to be continued 
 through Denison township, embracing the deposits containing 
 niccolite and gersdorffite, through the Worthington, and gradu- 
 ally dying out towards the Mitchener. 
 
 Under the microscope, it is seen that the original structure 
 of the rock has been almost entirely obliterated, and green- 
 fibrous hornblende and chlorite are the most abundant minerals, 
 and often show the effects of severe crushing. As the quan- 
 tity of ore increases, the amount of secondary products (epi- 
 dote, etc.) increases also, and the feldspar is more or less altered 
 and peppered with sulphide grains. Quartz is often present in 
 large amount. Progressive replacement can be traced in both 
 the irregular aggregates and the fibrous masses of hornblende 
 and biotite. In many cases, the introduction of the sulphides 
 appears to start along cleavages, gradually spreading and uniting 
 till only isolated patches of rock-minerals remain, or the whole 
 may be replaced, leaving no trace of the original structure. In 
 this way, reticulating networks of sulphide veinlets form all 
 through the rock, oftentimes ramifying through the areas of 
 quartz and separating the individual grains. Samples of the 
 coarse diorite containing ore present much the same features 
 i. e.j a branching network of sulphide veinlets between the 
 
THE ORE-DEPOSITS OF SUDBURY, ONTARIO. 507 
 
 fibers and along cleavages of hornblende, etc., and separating 
 the different rock-minerals. 
 
 11. Levack Township Deposits. On the northwest are the 
 large deposits in Levack township on the western side of the 
 nickel-belt. These deposits have been thoroughly prospected 
 and opened up to show their extent, and promise to be large 
 contributors of ore in the future. 
 
 To the north and west the contact is on the large granite- 
 area, formerly mapped as Laurentian, but which may prove 
 to be much later. At the contact the ore-bearing diorite and 
 granite are mixed up, and the acid rock is impregnated with 
 ore for a short distance, though not to the same extent as the 
 basic rock. 
 
 The brecciated nature of the ore-body is very pronounced, 
 and is emphasized on the weathered exposures, where pebbles 
 and boulders of rock stand out from the oxidized sulphides of 
 the gossan. 
 
 The vein-like nature of the sulphides is everywhere seen, 
 and is especially well shown in the diamond-drill cores. 
 
 As seen under the miscroscope, the rock consists, as usual, 
 largely of secondary fibrous green hornblende, and shows many 
 evidences of severe crushing in the bent and twisted horn- 
 blende fibers and the granular aggregates of hornblende and 
 feldspar. The minerals, also, have a marked undulatory ex- 
 tinction. The feldspar is, at times, in idiomorphic individuals, 
 giving the rock a somewhat diabasic aspect. 
 
 Good examples of the relation of ore to rock-minerals are 
 presented in some of the sections. One shows a large frag- 
 ment of fibrous hornblende which has been bent and twisted, 
 with pyrrhotite between the fibers, following all the curves and 
 leaving the comparatively fresh fibers intact. In other places 
 the pyrrhotite has replaced the uralitic hornblende to a greater 
 or less extent, in some cases with such delicacy as to preserve 
 the original fibrous structure perfectly. Where the feldspar 
 and hornblende form granular aggregates, the sulphides form 
 a mass of radiating veinlets around and between the grains, 
 leaving the nucleus unreplaced. 
 
 12. North Eange. Location, W. D. 16, Wisner Township. 
 On the northern extension of the nickel-belt a number of 
 promising deposits have been opened up, but so far have not 
 passed the "prospect" stage. 
 
508 THE ORB-DEPOSITS OF SUDBURY, ONTARIO. 
 
 Deposits with good showing have been exploited in lot 6, 
 concession 3, Norman township (Whistle mine); in Bowell 
 township, W. D. 35, 150, 151, and 155, but lack of transporta- 
 tion-facilities has been a serious drawback to more active work. 
 The ore-rock is a fine-grained altered norite, shading to a 
 coarser and more granitic variety to the south, and bounded 
 on the north by the so-called Laurentian granite. 
 
 As far as could be determined from the limited exposures, 
 the ore-bodies are very similar to those farther south. That 
 is, they consist of a breccia of almost barren rock cemented by 
 sulphides and with irregular veinlets of ore running through 
 them. Besides the prevailing brecciation, there has been shear- 
 ing, and numbers of samples of schistose rock are found seamed 
 with ore, especially on the parting-planes. 
 
 Microscopically, the rock is seen to be composed largely of 
 secondary hornblende and chlorite, both fibrous and granular. 
 Feldspar is often in idiomorphic crystals, giving the rock a 
 decided ophitic structure. The structure of the sulphides is 
 decidedly vein-like, some of the veinlets continuing across the 
 sections and having numerous accessory ramifications. The 
 ore is most closely associated with the hornblende, and follows 
 between the fibers and grains, conforming to all the irregulari- 
 ties and replacing it partly or wholly, often preserving the 
 fibrous structure very well. As the amount of ore increases, 
 the alteration of the rock-minerals becomes more pronounced, 
 and the sulphides spread all through the section, forming a 
 very characteristic secondary network of reticulating veinlets. 
 
 The Wallace Mine, Near ike Mouth of the White-fish River, Lake 
 Huron. This deposit lies outside what is commonly under- 
 stood as the "nickel-belt." While essentially the same in some 
 respects, so that it must be considered as genetically similar, it 
 presents certain peculiar features of its own. 
 
 The mine is of historic interest, and was opened up as early 
 as 1847 for copper. A year later it was discovered that the 
 ore carried nickel, and a sample containing about two-fifths 
 rock, analyzed by Dr. T. Sterry Hunt, yielded more than 8 per 
 cent, of this metal. After a series of disasters, and the loss of 
 trial-shipments on Lake Huron, the mine was abandoned in 
 1867, and work has not since been resumed. The deposit 
 occurs at the junction of two small dikes of so-called diorite, in- 
 
THE ORE-DEPOSITS OF SUDBURY, ONTARIO. 509 
 
 truded in the country quartzite. The quartzite at the contact 
 is very black and dense, and has been sheared and slickensided. 
 
 Some large masses of heavily-mineralized ore-rock on the 
 dump, which have resisted oxidation, show a decidedly brecci- 
 ated structure, with sulphides (pyrrhotite, pyrite, and chalco- 
 pyrite) cementing the fragments. 
 
 The junction of the dikes seems to have been the center of 
 dynamic disturbances, which caused the brecciation and shear- 
 ing, and formed a favorable place for the circulation and con- 
 centration of ore-bearing solutions on a small scale. 
 
 There seems little doubt that the ore was precipitated from 
 solution, and the relations are very suggestive when compared 
 with those of the Sudbury deposits. 
 
 The microscope shows that the rock has been severely 
 crushed and presents a typical mosaic in places. The horn- 
 blende is both granular and fibrous, and gives the rock a schis- 
 tose appearance. The rock is also much more acidic than the 
 Sudbury types, and contains a good deal of orthoclase and 
 quartz, often in the form of a micropegmatite, differing in this 
 respect also from the others. The ore is mainly in veinlets, 
 surrounding and penetrating the remaining rock-fragments, 
 and replacing the dark silicates (hornblende and biotite) to a 
 greater or less extent. As the amount of ore increases, the dark 
 silicates largely disappear, and the feldspar is broken up into 
 grains, inclosed by ore, and this, together with quartz, is left to 
 a large extent unreplaced, while the remaining fragments of 
 hornblende contain sulphides along the cleavages and between 
 fibers. 
 
 The Rossland, B. (7., District. The Josie Mine. 44 The micro- 
 structure of the Rossland ore is so strikingly similar to that 
 from Sudbury that a brief reference will be made to it. 
 
 The rock usually associated with the ore is a monzonite, more 
 or less altered. The specimens examined were samples of vein- 
 matter from the Josie (Le Roi No. 2) mine, and presented a 
 decidedly altered and schistose appearance, and contained 
 pyrrhotite and chalcopyrite. Thin sections show that the rock 
 is more or less silicified, and consists largely of secondary 
 fibrous hornblende and biotite, and a smaller amount of feld- 
 spar with many fragments of the dark silicate through it. 
 
 44 Material kindly furnished by George H. Dickson, Rossland, B. C. 
 
510 THE ORE-DEPOSITS OF SUDBURY, ONTARIO. 
 
 The relation of the sulphides and rock-minerals is also very 
 similar to that of the Sudbury examples. 
 
 They are intimately associated with the dark silicates and 
 form veinlets between the hornblende and biotite fibers, and 
 extend from these in the form of reticulating networks, which 
 in places wholly replace the minerals involved. Where asso- 
 ciated with the more granular silicates and quartz, the sulphides 
 form veinlets along the cleavages and around the grains and 
 present the same features as the Sudbury ore, and can only be 
 explained as due to a secondary introduction by means of cir- 
 culating, ore-bearing solutions. 
 
 The Ducktown, Tenn., Deposits. Figs. 25 and 26 45 show the 
 relations of the ore- and rock-minerals in the Ducktown copper- 
 deposits. 
 
 An inspection will show that these are very similar to some 
 of the Sudbury examples. Professor Kemp considers that ore- 
 bearing solutions entered along zones of crushing or faulting, 
 where the material was of a more or less open texture, and 
 replaced silicates and other minerals; the sulphides often in- 
 sinuating themselves into the broken silicates and abutting 
 sharply against the fresher specimens. In this connection he 
 says : " It therefore seems probable that the replaced material 
 consisted of the crushed and greatly comminuted country-rock, 
 which in this condition would prove an easier prey to the ore- 
 bearing solutions. Where the crushing was most severe, the 
 large ore-bodies are found. Unless some factor of this sort 
 exercised an influence, it seems strange that the process of re- 
 placement should cease so sharply against perfectly fresh and 
 unchanged representatives of the presumably replaced min- 
 erals." 
 
 Summary. 
 
 The above results are given in some detail, even at the risk 
 of repetition. But in a problem of this kind it is all-import- 
 ant that the facts should be clearly presented, so as to obtain 
 a grasp of the entire situation and avoid a narrow interpreta- 
 tion based on one or two occurrences, which might not be 
 typical of the whole. 
 
 The investigations covering the whole field of the nickel- 
 
 45 From Professor Kemp's paper, The Deposits of Copper-Ores at Ducktown, 
 Term., Trans., xxxi., 255, 256 (1901). 
 
THE ORE-DEPOSITS OF SUDBURY, ONTARIO. 511 
 
 range show that all tne deposits have certain prominent fea- 
 tures in common. 
 
 1. Brecciation, with accompanying faulting, and shearing are 
 everywhere characteristic. This 'is shown not only on a large 
 scale, but is also corroborated by the microscopical relations. 
 
 2. The main brecciation and shearing took place previous to 
 the formation of the ore-bodies proper. 
 
 3. The abrupt change from massive sulphides to barren 
 rock, so often noticed, seems irreconcilable with the theory of 
 magmatic segregation, and it is also difficult to imagine how 
 the included rock-fragments could retain their angular form if 
 they were once part of, or floated in, a molten magma. 
 
 4. The ore prevailingly occurs as a cement for the brec- 
 ciated rock-fragments and along shear-planes. 
 
 5. The rocks associated with the ore are all members of the 
 gabbro family and can generally be referred to norite. 
 
 6. The rocks are more or less altered and now resem- 
 ble diorite, the original pyroxene having in nearly all cases 
 changed to a fibrous green hornblende and chlorite. Where 
 original pyroxene remains (e. g., at the Stobie and Mount Nickel 
 mines), the structure is markedly brecciated. 
 
 7. The effects of metamorphism and the development of 
 secondary hornblende are most marked near the ore-bodies, 
 and diminish away from them. 46 
 
 8. In general, the more complete the alteration of the rock, 
 the more complete has been its replacement by sulphides. 
 
 9. The relation of the ore to the rock-minerals is practically 
 identical throughout the whole district. In all cases the ten- 
 dency of the sulphides is to occur along planes of weakness 
 and in connection with the fibrous minerals. 
 
 Occasionally the relations of the pyrrhotite to the silicates 
 suggest that it is an original constituent of the rock and one 
 of the first minerals to crystallize from the magma. This is 
 seen at times in the less altered specimens some distance from 
 the ore-bodies. 
 
 The amount of this apparently original pyrrhotite is, how- 
 ever, always very subordinate, and is probably no more than 
 might reasonably be expected in a gabbro. 
 
 46 Compare Walker, Quarterly Journal of the Geological Society, vol. liii., No. 209, 
 p. 47 etseg. (Feb., 1897). 
 
512 THE ORE-DEPOSITS OF SUDBURY, ONTARIO. 
 
 So that while a small percentage of the pyrrhotite may be 
 original, the main contention still holds, namely, that the sul- 
 phides are essentially and predominantly secondary. 
 
 10. Secondary quartz and ealcite are often present in the 
 ore in appreciable amount, while they are insignificant or lack- 
 ing at a little distance. 47 
 
 11. Sulphides are practically lacking in the rock a short 
 distance from the ore. The rock-fragments included in the 
 deposit are also comparatively free from ore, except in veinlets. 
 
 12. The relation of the magnetite to the rock-minerals is in 
 marked contrast to that of the sulphides, the former being 
 always in more or less rounded grains in the dark silicates and 
 generally primary. 
 
 13. With regard to the relations of the sulphides to the rock- 
 minerals themselves, several different types might be differen- 
 tiated. These types are, however, all alike in kind, and several 
 may occur in a single specimen. 
 
 (a) Replacement starting between and extending along the 
 fibers of hornblende, often resulting in a pseudomorph of ore 
 after this mineral. 
 
 (6) Replacement along cleavages of the more compact and 
 less altered minerals, breaking them up into grains and, at 
 times, forming complete pseudomorphs. 
 
 (c) Replacement between crystals and fragments of the same 
 or different minerals, often extending into the mineral sub- 
 stance, when it could be classed under (a) or (b). 
 
 (d) Replacement along planes or zones of parting and shear- 
 ing, the veinlets being in general parallel and ramifying through 
 the neighboring minerals as indicated in (a), (6) and (c). 
 
 (e) In the more crushed and granular examples, where the 
 rock-minerals are much altered, the sulphides are peppered all 
 through them and form an intricate and ramifying network of 
 veinlets in the rock, at times completely replacing the minerals 
 around certain centers. 
 
 (/) The dark silicates fall the easiest prey to the ore-bearing 
 solutions, but many instances are noted in which the feldspar 
 suffers. This is generally the case where the crushing and 
 shearing have been most severe and the mineral is partly or 
 wholly changed to secondary products. As a rule, though not 
 
 47 Walker, Joe. cit. 
 
THE ORE-DEPOSITS OF SUDBURY, ONTARIO. 513 
 
 invariably, this change is especially noticeable where the min- 
 eralization of the rock is most pronounced. 
 
 14. A comparison of the Sudbury deposits with those of 
 Rossland, B. C., and Ducktown, Tenn., shows many remarkable 
 and essential points of similarity. These deposits are now 
 proved beyond all reasonable doubt to be of secondary aqueous 
 origin, and this, aside from direct evidence, points strongly to 
 a similar origin for the Sudbury occurrences. 
 
 Relation of Chalcopyrite to Pyrrhotite. From the massive na- 
 ture of the sulphides, very little can be accurately determined 
 as to the paragenesis of the minerals. There are, however, 
 certain relations existing between the chalcopyrite and the pyr- 
 rhotite which may help to explain it. 
 
 1. In a number of cases where copper is predominant, the 
 ore consists of numerous small parallel veinlets of pyrrhotite 
 and chalcopyrite very intimately associated. This is well illus- 
 trated by examples from the Copper Cliff and Creighton mines 
 (Figs. 10 and 21). The same relation is a prominent feature of 
 the Rossland ore, and hand-specimens from the two localities 
 are almost indistinguishable. 
 
 2. The chalcopyrite is usually most strongly concentrated 
 near the outside of the deposits, especially towards the so-called 
 foot-wall. As a rule, the proportion of chalcopyrite in the 
 main ore-body is rather small, and it tends to form fairly-pure 
 masses without much pyrrhotite. Taking these facts into con- 
 sideration, it seems likely that the pyrrhotite at first constituted 
 the largest part of the ore-body. Later, due to some dynamic 
 movement, opening up passages through the ore-bodies, espe- 
 cially towards the outer limits, copper-bearing solutions entered 
 and deposited their mineral contents among the rock-masses 
 and partly replaced pyrrhotite along certain lines. In some 
 deposits, as at the Copper Cliff, where copper-minerals pre- 
 dominate, the fracturing may have been greater and the solu- 
 tions more active or concentrated. 
 
 It is also possible that the copper disseminated in the upper 
 part of the ore-bodies, now eroded, has been secondarily de- 
 posited by downward-moving currents, but this does not seem 
 to have been the case to any great extent. In the first place, 
 there is very little in the way of an oxidized gossan, and the 
 ground-water level is comparatively near the surface. Secondly, 
 
514 THE ORE-DEPOSITS OF SUDBURY, ONTARIO. 
 
 there is little, if any, indication of this secondary change in the 
 way of enriched sulphides which accompany the process. . 
 
 Pyrrhotite is quite generally admitted to be a product of 
 primary concentration by upward-moving solutions in a strongly 
 reducing atmosphere, and if any considerable concentration by 
 downward-moving waters had taken place, we would expect to 
 find the pyrrhotite largely oxidized or removed entirely. It is, 
 however, a notable fact that when the thin surface-covering is 
 removed, the pyrrhotite appears perfectly fresh and with no 
 appreciable admixture of secondary minerals, such as are 
 formed in the process of secondary enrichment. 
 . Source of the Metals. What the exact sequence of events 
 leading up to the formation of the ore-bodies and the immedi- 
 ate source of the metallic contents was, is not yet satisfactorily 
 settled. The question involves many intricate problems, both 
 of a local and a general nature, and with the evidence at hand 
 an authoritative discussion would be premature. 
 
 The metamorphic processes appear to have been very com- 
 plicated, and are still more obscured by the later alteration due 
 to the mineralizing solutions. 
 
 Pyrrhotite is a product of many metamorphic processes and 
 may be formed in any of the classes designated by Lindgren 
 dynamo, hydro-thermal, solfataric, or contact. 48 
 
 Under which head the metamorphism of the Sudbury dis- 
 trict could be accurately classified, it is difficult to say. Indeed, 
 it might be considered as a combination dynamo, hydro-thermal, 
 and solfataric. From a study of the history of the district, 
 however, it is quite evident that it was a region of vulcanism 
 and metamorphic processes on a large scale, and the immense 
 stores of heat and energy involved could be readily available as 
 stimulators of the circulation and chemical activity of the min- 
 eral solutions, so that the theory of an aqueous origin presents 
 nothing at all unreasonable. 
 
 Hvdrogen sulphide is so common a constituent of mineral 
 and thermal springs that its presence in the mineral solutions 
 can be assumed. From the nature of the deposits, the ore- 
 bearing solutions were probably highly charged with alka- 
 
 48 W. Lindgren, Nevada City and Grass Valley Districts, Seventeenth Annual 
 Report, U. S. Geological Survey, Pt. II., p. 90 (1895-96). 
 
THE ORE-DEPOSITS OF SUDBURY, ONTARIO. 515 
 
 line carbonates and hydrogen sulphide, but with subordinate 
 amounts of carbon dioxide. 
 
 The microscopical investigations show that the dark silicates 
 are often bleached and robbed of iron, or else " resorbed," 
 forming aggregates of magnetite grains. It is thus possible 
 that a certain amount of the iron was derived from the altera- 
 tion of the minerals of the replaced zone as well as from extra- 
 neous sources. The source of the nickel may, to some extent, 
 have been the associated rocks, which contain small amounts, 
 but it seems more probable that the larger part was derived 
 from greater depths traversed by the circulating waters. 
 
 Many of those who are familiar with the district, and who 
 have discarded the theory of a direct " magmatic segregation," 
 still consider that there was a preliminary concentration of 
 metals with the intrusion of the norite, and that the ore-bodies 
 assumed their present position and dimensions by subsequent 
 processes. 
 
 This may, to a certain extent, be true, and the presence of 
 small quantities of what appears to be original pyrrhotite in 
 the ore-rock is cited in support of this view. Moreover, this 
 theory does not involve many of the difficulties of the first. 
 Still, a consideration of the whole subject and the relations in- 
 volved seems to indicate that this " preliminary concentration " 
 was comparatively slight, and appeal must be made to a more 
 distant source of the metals, probably minutely disseminated in 
 the rocks through which the depositing solutions passed. 
 
 In conclusion, it might be safely stated that at present the 
 whole weight of the evidence points to the secondary forma- 
 tion of the Sudbury ore-bodies as replacements along crushed 
 and faulted zones, with only minor indications of open cavities. 
 
 Previous observers have naturally been impressed by the 
 massive character of the sulphides, in which are found the min- 
 erals of the inclosing rock, and this seems to fall in readily 
 with the idea of an igneous origin. 
 
 The clue to the interpretation of the matter, however, ap- 
 pears to be furnished by the leaner material, where the relations 
 have not been obscured or obliterated by the excessive develop- 
 ment of the sulphides. 
 
 The universal association of these ores with essentially simi- 
 lar rocks is also striking. That the norite (or gabbro) has an 
 
516 THE ORE-DEPOSITS OF SUDBURY, ONTARIO. 
 
 intimate connection with the development of the ores cannot be 
 doubted, but in just what way they are related is not clear. 
 
 After a review of the ideas held of these and similar deposits 
 elsewhere, it will be seen that the evidence adduced in support 
 of the igneous hypothesis can be equally well, if not better, in- 
 terpreted on the basis of replacement, while many of the 
 observed phenomena cannot be satisfactorily explained on the 
 assumptions of the old hypothesis. 
 
 With the additional light thrown on the subject by these in- 
 vestigations, there seems to be no reasonable doubt left as to 
 the true nature of the deposits, and it may be confidently ex- 
 pected that future work will give additional weight to the views 
 here advanced. 
 
 Finally, with regard to my personal connection with the 
 matter, it may be well to say that, in taking up the work, I 
 went into the field with an open mind and for the sole purpose 
 of interpreting the phenomena as they were presented by the 
 facts, without being hampered by any preconceived theories. I 
 had always been taught to regard the deposits as essentially of 
 igneous origin, and this theory was, of course, uppermost in my 
 mind. But as instance after instance of the relations in the 
 field was presented in the different deposits, the " igneous J> 
 theory was not sufficient to explain the facts. Then, on calmly 
 studying the material collected in the laboratory, the convic- 
 tion became a certainty, and I present my views only for the 
 purpose of throwing as much light as possible on these compli- 
 cated problems. 
 
 Aside from the main contention that the deposits are replace- 
 ments, any arguments advanced as to the actual source, manner 
 of concentration, and paragenesis of the ore may be regarded 
 as largely tentative and as inviting discussion, by which we may 
 hope to arrive at more definite conclusions as to the actual pro- 
 cesses and sequence of events, culminating in these remarkable 
 bodies of ore as we find them to-day. 
 
 Acknowledgments. The writer wishes especially to acknowl- 
 edge his indebtedness to Professor Kemp, of Columbia Univer- 
 sity ; Dr. Goodwin, Director of the School of Mining, Kingston, 
 Ontario; Prof. W. G. Miller, Provincial Geologist of Ontario; 
 and J. "Walter Wells, late Chemist to the Ontario Bureau of 
 Mines, for assistance and kindly interest in the work. 
 
GENESIS OF THE COPPER-DEPOSITS OF CLIFTON-MORENCI. 517 
 
 No. 19. 
 
 The Genesis of the Copper-Deposits of Clifton- Morenci, 
 
 Arizona.* 
 
 BY WALDEMAR LINDGREN, WASHINGTON, D. C. 
 
 (Lake Superior Meeting, September, 1904. Trans., xxxv., 511.) 
 CONTENTS. 
 
 PAGE 
 
 Topography and Geology, . . .... . , . . 518 
 
 Occurrence and General Features of Ore-Deposits, . 520 
 
 Metamorphic Processes, . . . ... . . . . 522 
 
 Contact-Metaraorphism, . . . . . . . . . 522 
 
 Hydrothermal Metamorphism, . . . . . , . . 529 
 
 Kelation of Contact- and Hydrothermal Metamorphism, . . . 530 
 
 Processes Due to Oxidation and Hydration in the Oxidized Zone, . 531 
 
 Sulphate Waters, .' . . . . i ' . . .532 
 
 Processes in Fissure- Veins, . . . > ,. \ . . . 532 
 
 Oxidation of Chalcocite, ....... 534 
 
 Oxidizing- Processes in Limestone, 535 
 
 Oxidizing-Processes in Shale, . . . . . . . 536 
 
 Paragenesis, . ..-,.. ... . . . . 536 
 
 Characteristics of Deposits, . . . . .... . . . . 537 
 
 Deposits of Carbonates and Oxides in Limestone and Shale, . . 537 
 
 Fissure-Veins and Related Deposits of Morenci Type, .... 539 
 
 The Coronado Type of Veins, . ' . ;' . . . . . 543 
 
 Gold-Bearing Veins, . . . . 544 
 
 Conditions of Ground-Water, . . . . . . . . . 544 
 
 Depth of Oxidized Zone, . . . . . . . . . . 545 
 
 Fluid-Inclusions, . . . . . . . . . . . . 545 
 
 In Granite, . ..... . . . . . . . 546 
 
 In Metamorphic Limestones, . . . . . . , . . 545 
 
 In Porphyry, . . . . , . . ... . . , 545 
 
 In Vein-Quartz, . . ' . . . . . . . . . 549 
 
 Summary of Genesis, . ^ ' * .'. . , .... . . 55^ 
 
 Genetic Classification, . .. ... .* . .. .... . . 555 
 
 THE following pages are a resume of some of the conclusions 
 reached during a study of the copper-deposits near Clifton. 
 The field-work was finished in 1902 and a complete report is 
 now in the press. A preliminary description of the district 
 was published in 1903, in Bulletin U. S. Geological, Survey, No. 
 213, pp. 133-140. 
 
 * Published by the permission of the Director of the U. S. Geological Survey. 
 
518 GENESIS OF THE COPPER-DEPOSITS OF CLIFTON-MORENCI. 
 
 The Clifton mines, always important, are at present the 
 largest in the territory, the output in 1902 having reached 
 50,000,000 Ib. of copper, chiefly divided between the two prin- 
 cipal producers, the Arizona and the Detroit copper companies. 
 The Shannon Copper Co. also contributed to this figure, and its 
 output has greatly increased since then. The total output of 
 the district to the end of the year 1903 is estimated at a value 
 of about $49,000,000. 
 
 TOPOGRAPHY AND GEOLOGY. 
 
 Clifton is situated on the San Francisco river, a few miles 
 above its confluence with the Gila river, in the southeastern part 
 of the territory, and not many miles from the New Mexican 
 boundary. An irregular mountain region, without well-defined 
 ranges, lies here north of the broad, detritus-filled valley of the 
 Gila river, which has an elevation of about 3,000 feet. The 
 highest elevations in the mountains scarcely attain 8,000 feet. 
 
 Between the San Francisco river and Eagle creek, both trib- 
 utaries to the Gila river from the north, a core of older rocks of 
 about 70 sq. miles is exposed, consisting of pre-Cambrian gran- 
 ites, Cambrian quartzites, Paleozoic limestones, and a capping- 
 formation of Cretaceous beds all intruded by post-Cretaceous 
 granitic porphyries. This older core, which seems to represent 
 the broken-down edge of the great plateau-province, is com- 
 pletely surrounded and largely covered by volcanic flows of 
 Tertiary age, including basalts, andesites and rhyolites, which 
 have been extensively eroded ; hence the lack of regularity so- 
 plainly apparent in the mountain complex. 
 
 The copper-deposits are all contained in the older rocks and 
 distinctly antedate the Tertiary lavas. 
 
 The sedimentary rocks rest on a basement of red, coarse 
 granite, forming two great buttresses, the Coronado and the 
 Copper King mountains, both rising more than 3,000 ft. above 
 the San Francisco river. 
 
 The Paleozoic series consists of the following-named forma- 
 tions : 
 
GENESIS OF THE COPPER-DEPOSITS OF CLIFTON-MORENCI. 519 
 
 Modoc limestone. Up to 200 ft. thick, heavy-bedded, gray limestones of 
 (Lower Carboniferous.) great purity, with some equally pure dolomites at the 
 
 base. 
 Morenci shale. 100 ft. of clay-shales, sometimes underlain by 75 ft. of 
 
 (Devonian ?) argillaceous limestone. 
 
 Longfellow limestone. Up to 400 ft. of limestones, partly cherty and, near 
 ( Ordovician. ) the base, containing sandy beds. Some of these strata 
 
 are dolomitic. 
 
 Coronado quartzite. 200 ft. of reddish, quartzitic sandstones resting on 
 
 (Cambrian?) granite. Lowest member is a quartzitic conglom- 
 
 erate. 
 
 The three upper divisions contain characteristic fossils, while 
 only a few small Lingula shells have been found in the Coronado- 
 quartzite. 
 
 The Cretaceous series rests unconformably on the Modoc 
 limestone and consists of a succession of clay-shales and dark 
 sandstones at least 200 ft. thick. Scant fossils indicate that it 
 belongs to the Fort Benton horizon. 
 
 Gentle dips, rarely above 20 and generally directed west- 
 ward, characterize the sedimentary rocks. 
 
 All of the above-mentioned rocks are intruded by a great 
 stock of porphyry which extends in a northeasterly direction 
 between the foothills near Eagle creek across to the great Cop- 
 per King granite ridge overlooking San Francisco river. The 
 main stock, which is about 8 miles long and up to a mile and 
 a half wide, breaks up, at the southwest end, into a network 
 of irregular dikes and sheets, and, at the northeast, into a sys- 
 tem of northeasterly-trending dikes cutting through the granite. 
 Laccolithic masses of porphyry occur in the Cretaceous shales 
 and sandstones. The rock of the main stock ranges from a 
 granite-porphyry to a quartz-monzonite porphyry. The sills 
 and laccoliths are usually composed of diorite-porphyry, but the 
 different types of rock are clearly facies of the same magma, 
 connected by transitions and forming a single geological unit. 
 Dikes of diabase occur in a few places. 
 
 The intrusion of the poryhyry took place during the latest 
 Cretaceous or the earlier Tertiary, and was accompanied by 
 great disturbances in the immediately adjoining rocks, particu- 
 larly well noticeable in the Paleozoic sediments ; but these dis- 
 turbances of the strata did not extend far from the contacts. 
 
 The intrusion of the porphyry was followed by important 
 
520 GENESIS OF THE COPPER-DEPOSITS OF CLIFTON-MORENCI. 
 
 structural movements. The surface of the granite, together 
 with the whole covering sedimentary series, was buckled into 
 dome-shaped folds and then extensively fractured, the blocks 
 sinking successively deeper towards the valley and settling un- 
 equally around the two great buttresses, or " horsts," the Coro- 
 nado and Copper King mountains, the maximum throw of the 
 normal faults being 3,000 feet. 
 
 An epoch of erosion followed, but floods of Tertiary lavas 
 soon surrounded and largely covered the old rocks which have 
 only lately emerged by the energetic action of a second epoch 
 of erosion. The effects of the large faulting-movements, which 
 preceded the lavas, are still visible in the greater topographic 
 features of the region, especially in the bold escarpment of the 
 Copper King ridge. 
 
 OCCURRENCE AND GENERAL FEATURES OF THE ORE-DEPOSITS. 
 
 The geographical distribution of the copper-deposits is prac- 
 tically coextensive with the great porphyry stock and its dike- 
 systems. The deposits occur either in the porphyry or close to 
 its contacts, or along dikes of porphyry in some other rock. 
 Areas in which no intrusions have taken place are practically 
 barren. This intimate connection with the porphyry is certainly 
 a most important fact. There is only one small division of de- 
 posits which deviates from this rule namely, that connected 
 with the diabase-dikes. 
 
 Practically all types of deposits contain copper as the most 
 valuable metal. Gold and silver occur, as a rule, only in minute 
 quantities, except in some of the outlying districts where they 
 become of more importance. The two most important mining- 
 centers, Morenci and Metcalf, which are 3 miles apart, are 
 both situated at the main contact of the porphyry stock and 
 the series of Paleozoic limestones. Elsewhere the intrusive 
 rock generally adjoins granite or Cretaceous sediments. 
 
 The ores consist of chalcocite, chalcopyrite, malachite, azu- 
 rite, chrysocolla, brochantite, cuprite, and native copper. Covel- 
 lite and bornite are practically absent. Brochantite, a basic 
 copper sulphate, is very commonly present, especially in the 
 oxidized veins in porphyry ; and, in fact, constitutes in places an 
 important ore. On account of its similarity to, and intimate 
 intergrowth with, malachite it has usually been overlooked. 
 
GENESIS OF THE COPPER-DEPOSITS OF CLIFTON-MORENCI. 521 
 
 The following-named minerals have been found : Native 
 copper, native gold, quartz, chalcedony, rutile, magnetite, 
 hematite, limonite, pyrolusite, coronadite (a new mineral, 
 chiefly PbO and Mn0 2 ), cuprite, pyrite, chalcopyrite, zinc- 
 blende, galena, molybdenite, chalcocite, diopside, tremolite, 
 garnet, epidote, muscovite, chlorite, serpentine, asbestos, kao- 
 lin, willemite, calamine, dioptase, chrysocolla, copper pitch ore, 
 morencite (a new mineral, chiefly a ferric silicate), calcite, dolo- 
 mite, zinc carbonate, malachite, azurite, libethenite (copper 
 phosphate, not previously found in the United States), brochan- 
 tite, al unite, gypsum, spangolite (basic chloro-sulphate of cop- 
 per and aluminum), chalchanthite, goslarite, epsomite and ger- 
 hardtite (a basic copper nitrate forming green crusts on weath- 
 ered surfaces of porphyry, and associated in these with a cop- 
 per chloride, possibly atacamite). 
 
 The deposits with payable copper-ore take many widely dif- 
 fering forms, as follows : 
 
 Deposits in limestone and ghale, not connected with fissure-veins. 
 
 Irregular bodies near contacts of main stock or dikes. 
 
 Tabular bodies near contacts of main stock or dikes following stratification. 
 
 Tabular bodies, following contacts of porphyry dike (all of these carry oxi- 
 dized ores, almost exclusively ; rarely chalcocite). 
 Fissure-veins. 
 
 Normal veins in porphyry or in any of the other rocks near porphyry-con- 
 tacts. Include central veins and surrounding partly- replaced porphyry 
 forming together a lode. Carry chalcocite as the important ore ; in upper 
 levels also sometimes oxidized ores. 
 
 Normal veins, following porphyry dikes in granite. Chalcocite and oxidized 
 copper-ores. 
 
 Normal veins following diabase-dikes. Chalcocite and oxidized copper-ores. 
 Stock-werks. Irregular disseminations in porphyry, quartzite and other rocks. 
 
 Contain chalcocite and oxidized copper-ores. 
 
 The above classification is based on occurrence and form, and 
 a more general genetic system, given below, shows a somewhat 
 different arrangement. 
 
 Native copper, all of the oxy-salts of copper, and chalcocite 
 are wholly secondary minerals produced by direct or indirect 
 oxidation from primary pyritic ores. In all of the divisions 
 given above, this primary ore consists of pyrite and chalco- 
 pyrite, with some zinc-blende and molybdenite. The scant 
 gangue of the veins consists of quartz, while the deposits in 
 
 33 
 
522 GENESIS OF THE COPPER-DEPOSITS OF CLIFTON-MORENCI. 
 
 the first division are usually accompanied by garnet, epidote> 
 magnetite, diopside, tremolite, or their products of oxidation. 
 
 METAMORPHIC PROCESSES. 
 
 The region described in this paper is practically unaffected 
 by regional or dynamic metamorphism, and even the ordinary 
 hydro-metamorphism has altered the rocks but little, produc- 
 ing some slight changes in granite and porphyry and introduc- 
 ing cherts into the limestones. Epidote, chlorite, and a little 
 pyrite are apt to develop in the hornblendic phases of the 
 porphyry. 
 
 Contact- Metamorphism. 
 
 Contacts of porphyry with sedimentary rocks often show typi- 
 cal instances of this metamorphism. The granite-porphyry and 
 the quartz-monzonite porphyry show themselves most effective 
 in this direction, while there is usually but little metamorphic 
 action at the contacts of the diorite-porphyry. The effect 
 seems in direct proportion to the amount of quartz contained 
 in the porphyry. Granite and quartzite are unaltered; the 
 shales and sandstones of the Cretaceous series are hardened 
 and baked. The shales change, as a rule, only at the imme- 
 diate contact, to dense, greenish hornfels. 
 
 The Paleozoic limestone-series comes in contact with the- 
 main stock in two places at Morenci and at Metcalf. In both 
 places extensive copper-deposits are encountered. Dikes also 
 occur at both places and along some of these radiating out 
 into the unaltered areas the metamorphic processes may be 
 examined to best advantage. 
 
 In studying the phenomena along dikes, it is found that the 
 metamorphism varies greatly in the different strata, and even 
 in apparently similar limestone layers there may be great dif- 
 ference in the degree of alteration. A well-defined dike 50 ft. 
 wide on Modoc mountain was studied with special care as it 
 cut through all of the formations present. Where contained 
 in the Longfellow limestone the metamorphism extends at most 
 20 ft. outward into the limestone, and generally only a few feet. 
 Garnet, epidote, diopside, specularite, and magnetite are the 
 minerals which form abundantly by metasomatic replacement 
 along the contacts, and intergrown with them are chalcopyrite, 
 pyrite, and zinc-blende, unquestionably of contemporaneous 
 
GENESIS OF THE COPPER-DEPOSITS OF CLIFTON-MORENCI. 523 
 
 formation. The contact metamorphic limestone has certainly 
 a very different composition from the unaltered rock, and it is 
 apparent that much silica, iron, copper and zinc, at least, have 
 been added. Epidote often forms in considerable quantities 
 close to the contacts, while a little farther away garnet prevails. 
 The Morenci shales overlying the Longfellow limestone are 
 hardened and baked, but not materially altered in compo- 
 sition. Finally, when the dike enters the pure limestone of the 
 Modoc formation, garnet forms in enormous quantities from 
 the latter ; the metamorphism exerted by the dike here merges 
 into that affecting the whole block of limestone, due to the con- 
 tact of the main stock of porphyry. 
 
 The principal metamorphic area at Morenci is about 2 miles 
 long; its width is from 1,000 to 1,500 feet. The Modoc forma- 
 tion, however, has been affected to an extraordinary degree, 
 and extends as a stratum of garnet and magnetite 2,000 ft. 
 distant from the contact between almost unaltered Devonian 
 and Cretaceous sediments. 
 
 The Longfellow limestone, though somewhat irregularly 
 altered, is, next to the contact, generally transformed into a 
 coarsely granular rock of garnet, epidote, diopside, magnetite, 
 pyrite, zinc-blende, and chalcopyrite, and there is a most de- 
 cided change of composition, chiefly consisting in additions of 
 silica and iron. Other parts are less altered, but contain much 
 magnetite, together with the sulphides mentioned, disseminated 
 through a medium-grained crystalline mass of the carbonates 
 of lime and magnesia. The development of magnetite, metaso- 
 matically, is a most pronounced feature of the process. Look- 
 ing at the formation as a whole; sulphur, iron, copper and zinc 
 have certainly been added, and probably also silica and mag- 
 nesia. Large masses of magnetite, locally used as a flux, have 
 been mined at this horizon. 
 
 The Morenci shales have suffered a change to dense, green- 
 ish hornfels with a development of amphibole and, in places, 
 also muscovite. Pyrite and magnetite are also present, but on 
 the whole, the change in composition is probably slight. 
 
 The Modoc limestone, containing about 96 per cent, of car- 
 bonate of lime, has proved extremely susceptible, and over large 
 areas at Morenci, as well as at Metcalf, it is converted to a 
 massive sheet of lime-iron garnet ; magnetite is usually present; 
 
524 GENESIS OF THE COPPER-DEPOSITS OF CLIFTON-MORENCI. 
 
 epidote and oxidized copper-ores are also of frequent occur- 
 rence. This transformation, involving large additions of silica 
 and ferric iron is very noteworthy, as the evidence is entirely 
 micontrovertible. Analyses of the garnet and of the unaltered 
 limestone are given in my report, now in press. 
 
 The contacts of the sedimentary series and the porphyry are 
 sharp and show no evidence of assimilation. All of the con- 
 tact metamorphic rocks, when unaffected by oxidation, are very 
 compact and hard, atmospheric waters finding great difficulty 
 in attacking them. Considering that great amounts of carbon 
 dioxide have been expelled during the metamorphism, it is 
 clear that a great shrinkage of volume should have taken place 
 if no additions of material had been received. Such a reduc- 
 tion of volume has evidently not taken place, and I believe that 
 any loss has been fully balanced by gains from material con- 
 tained in magmatic solutions. 
 
 The question whether contact metamorphic rocks simply rep- 
 resent a recrystallization, or whether they have received addi- 
 tional substance from the cooling magma, is a most important 
 one. Prof. Rosenbusch believes that little or no additional 
 substance has been received and considers that it is possible to 
 determine the original character of metamorphic rocks from 
 their present composition. 1 This idea has recently been fol- 
 lowed out by Dr. J. Barrell in his study of certain contact meta- 
 morphic rocks of Montana. In this paper 2 he advances the fol- 
 lowing generalization that " carbonic acid is only expelled 
 where the siliceous impurities of the limestone are sufficient to 
 combine with the lime set free." Based on this he obtains the 
 further result that a great loss of volume has taken place and 
 that it is possible to calculate original constituents (kaolin, 
 silica, magnesite, and calcite) from any given rock more or less 
 altered to wollastonite, garnet, epidote, etc. If these statements 
 are really meant as generalizations, as would appear from the 
 paper, they are not supported by convincing proofs. Magmatic 
 additions, though mentioned, are not considered important. 
 
 1 Man kann es also als ein Gesetz aussprechen dass bei der Kontakt-meta- 
 morphose urn Tiefengesteine das Eruptivgestein nur physikalisch und im allge- 
 meinen nicht durch Stoffabgabe cliemisch wirkte. Mikroskopische Physiographic, 
 3ded., p. 85. 
 
 3 The Physical Effects of Contact-Metamorphism, American Journal of Science, 
 vol. xiii., pp. 279 to 296 (April, 1902). 
 
GENESIS OF THE COPPER-DEPOSITS OF CLIFTON-MORENGI. 525 
 
 Prof. Zirkel says 3 that in nearly all cases the contact-meta- 
 m orphic rocks simply represent a recrystallization of original 
 constituents. He believes that the contact-metamorphism sim- 
 ply took place by reason of the pressure and heat exerted by 
 the molten rock, and speaks rather slightingly of the view that 
 substance from the magma can be transferred to the surround- 
 ing strata, although admitting that in one or two cases it seems 
 to have happened. Hawes, as is well known, proved in the 
 case of the Albany contact-zone an increase of silica towards 
 the contact and also a certain amount of boron which appeared 
 to have been given off by the granite. Prof. Brogger, to whom 
 we owe a most careful description of the Kristiania contact- 
 zone, says, that on the whole, the alteration seems to involve 
 chiefly a recrystallization, although certain of the phenomena 
 strongly suggest local accession of material, though rather from 
 adjacent strata than from the intrusive body. 
 
 This seems a rather crushing array of authoritative testimony 
 from the petrographic side and it has even been intimated by 
 Prof. Klockmann, 4 in a recent paper combatting the theory of 
 transfer of material from magmas to sediments, that it ought 
 to be sufficient to settle the question. While I do not doubt 
 in the least the correctness of the conclusions drawn in indi- 
 vidual cases by such eminent authors as Professors Rosenbusch 
 and Zirkel, it is certain that contact-metamorphism manifests 
 itself in many various ways, and that the particular phases con- 
 nected with mineral deposits have been rather conspicuously 
 neglected by many petrographers, whose data and statements 
 in regard to the occurrence of ores, even in ordinary rocks, 
 have always seemed to me to suffer somewhat from lack of 
 detail and precision. 
 
 On the other hand, many French authors, among these Prof. 
 Michel-Levy, and, lately, Prof. J. H. L. Yogt, 5 of Kristiania, to- 
 gether with a growing number of younger scientific men, have 
 strongly contended that many substances are given off by the 
 cooling magma and enter the adjoining strata. This view is 
 
 3 Lehrbbch der Petrographie, 2d ed., vol. i., p. 587, 588. 
 
 4 Zeitschrift/iir Praktische Geologic, vol. xii., p. 78 (March, 1904). 
 
 5 See Trans., xxxi., 637 to 640 and The Genesis of Ore-Deposits, p. 648, 2d ed. 
 (1902). 
 
526 GENESIS OF THE COPPER-DEPOSITS OF CLIFTON-MORENCI. 
 
 shared by myself and expressed in a recent paper on contact- 
 metamorphic deposits. 6 
 
 The truth seems to be that in many cases no perceptible ac- 
 cession of substance from the magma has taken place, while 
 perhaps, equally often, important additions have been received. 
 How far the heat and the gases from the intruded magma will 
 penetrate, and what effects they will produce, depend on many 
 factors. As shown above, the composition of the magma is 
 sometimes a factor of importance. In case of the Morenci con- 
 tact-zone, the quantity of substance available seems to stand in 
 direct relation to the quantity of quartz in the porphyry. In 
 many intrusive magmas there may be a very small quantity of 
 water present ; the access of material may then be slight and the 
 contact-phenomena mostly due to the heat of the rock. The dif- 
 ference in susceptibility of the various beds is also strongly 
 marked ; all investigators agree on this point. In this district 
 impure and very compact limestones resist alteration much 
 more than coarse-grained pure rocks of the same kind; and 
 the change in composition in the case ot clay-shales is extremely 
 slight. 
 
 Study of the Morenci contact-zone, as a whole, proves conclu- 
 sively that most important accessions of substance have been 
 received. The rocks inside of the altered zone contain an 
 enormous quantity of sulphur, iron, copper, and zinc. Iron is, 
 of course, contained in the unaltered rocks to some slight ex- 
 tent, but in nothing like the quantities accumulated in the 
 contact-zone ; sulphur, copper and zinc in noticeable amounts 
 are absent from the unaltered rocks. Were they present, to 
 the extent of a small fraction of the percentage contained in the 
 contact-zone, they could be detected, either directly or through 
 the products of their surface-oxidation. The minerals in which 
 these substances are contained were certainly formed contempo- 
 raneously with the ordinary contact-minerals of the district, 
 like garnet, diopside and epidote. 
 
 The metasomatic development of magnetite in pure lime- 
 stones which has recently been questioned by Prof. Klockmann 
 may be observed in almost countless localities at Morenci and 
 Metcalf, both in the field and under the microscope. It is 
 
 6 Trans., xxxi., 226-244 (1901) and The Genesis of Ore-Deposits, p. 716, 2d ed. 
 (1902). 
 
GENESIS OF THE COPPER-DEPOSITS OF CLIFTON-MORENCI. 527 
 
 known that iron was not contained to this extent in the original 
 rock, but to demonstrate its actual derivation in each case is, 
 of course, difficult. The question becomes clear only when we 
 compare the contact-zone as a whole with the original unal- 
 tered rocks. 7 
 
 It seems very strange that any one can doubt the possibility 
 "of such additions, and overlook what must happen when a 
 magma in aqueous fusion is suddenly brought up to higher 
 levels and strongly ionized water-gas above the critical temper- 
 ature is largely released from its bonds. It must of necessity 
 contain dissolved substances. Even at comparatively low tem- 
 peratures water is one of the most powerful solvents known, 
 and its action, when a perfect gas, is probably far in excess of 
 that at 100 or 200 C. It is well known that some rapidly 
 congealed rocks, like the " pitch stone " from Saxony, contain 
 up to 8 per cent, of water, indicating an amount of water- 
 gas which, per cubic meter of magma, would at -f 4 C. cor- 
 respond to from 250 to 300 liters. 8 All magmas may, of course, 
 not have contained this amount. The water-gas seems to have 
 penetrated the limestones like a sponge, inducing extreme 
 molecular mobility. Even should we deny any additions of 
 substance, a most remarkable transferring of substance has 
 certainly taken place in the rock, as shown, for instance, by 
 large crystals of garnet developing in limestones of uniform 
 
 7 Professor Kloekmann's article, which is really intended to prove that no im- 
 portant deposits of magnetite can have a contact-metamorphic origin and that no 
 important material can be transferred from cooling-magmas to adjoining sedi- 
 ments, was published in Zeitschrift fur Praktinche Geologie, vol. xii., p. 78 (1904). 
 Among the arguments used is one referring to the content of alumina in epidote, 
 and to the improbability of transfer of that metal from magma to limestone. At 
 Morenci the massive epidote is usually confined to the immediate vicinity of the 
 contacts, and I fully believe that some transfer of alumina has actually occurred. 
 Regarding the occurrence of that mineral within the contact-metamorphic zone, 
 but at some distance from the actual contact, it is not likely that the alumina repre- 
 sents an addition from the magma, but it is certain that under the peculiar condi- 
 tions obtaining during the metamorphism the alumina to no small degree shared 
 in that wonderful molecular mobility which characterized the whole process. 
 
 When, however, Prof. Klockmann refers to garnet as an essentially aluminous 
 mineral, a typographical error must surely have occurred. All garnets do not 
 contain alumina, and the contact-metamorphic garnets at Morenci and Metcalf 
 are throughout andradites or lime-iron garnets. 
 
 8 E. Weinschenk, Vergleichende Studien ueber den Kontakt-Metamorphismus, 
 Zeitschrift der deutschen Geologuschen Gesellschaft, vol. liv., p. 443 (1902\ 
 
528 GENESIS OF THE COPPER-DEPOSITS OF CLIFTON-MORENCI. 
 
 composition containing far less iron and silica than the amounts 
 required by the newly-formed mineral. In a chapter on inclu- 
 sions cogent proof will be brought that the magma actually 
 was accompanied by water that contained a large amount of 
 substances in solution. 
 
 A misapprehension of the character of contact-deposits seems 
 to exist in many quarters, as shown, for instance, by Prof. 
 Klockmann, 9 in considering the presence of minerals contain- 
 ing boron, fluorine, etc., as necessary to prove the contact- 
 metamorphic character of these deposits. To such arguments 
 I would reply that the character of magmatic waters evidently 
 varies greatly in different magmas. Some may carry large 
 quantities of the substances mentioned, as shown by the presence 
 of tourmaline, cassiterite and other minerals in the contact-met- 
 amorphic rocks, while others may be almost wholly deficient 
 in them, and, instead, carry sulphur, copper, iron, and other 
 metals. In the Clifton group of deposits, I would be inclined 
 to consider molybdenum a characteristic constituent, taking 
 the place of tungsten in the tin-deposits. Any attempt to re- 
 duce the wonderful variety in the contact-metamorphic deposits 
 to a single pattern is doomed to failure. 
 
 In a short paper dealing with contact-metamorphic deposits 
 in North America, 10 1 emphasized the irregular form of most 
 ore-deposits of this kind and declared that they only occur 
 close to the contact or, at most, a hundred feet away. As a re- 
 sult of wider observations I would modify this statement; as 
 far as we know at present, they may occur several hundred or 
 even 2,000 ft. away from the contact. In fact, disseminated 
 sulphides and magnetite occur at Morenci as far as 2,000 ft. 
 from the main contact. 
 
 A tabular form of deposits often noted is usually due to the 
 strongly marked difference in susceptibility of the various beds. 
 Wherever the deposits have been enriched by oxidation the 
 form may be more or less dependent upon these changes. 
 
 Mr. W. H. Weed has noted the tabular shape in contact- 
 deposits at Cananea, Mexico, and makes the form a basis of 
 classification. 11 I do not believe, however, that distance from 
 
 9 Zeitschrift/iir Praktische Geologic, vol. xii., p. 75. 
 
 10 Trans., xxxi., 226 (1901). 
 
 11 Ore-Deposits near Igneous Contacts, p. 364, this volume. 
 
GENESIS OF THE COPPER-DEPOSITS OF CLIFTON-MORENCI. 529 
 
 contact (within limits given above) and shape are at all essen- 
 tial, and can find no mineralogical difference between deposits 
 varying in these respects. 
 
 Hydrothermal Metamorphism. 
 
 Both the porphyry- and the contact-zone are traversed by fis- 
 sure-veins which carry pyrite with a small quantity of chalcopy- 
 rite, zinc-blende and molybdenite, whenever oxidation has 
 not changed these minerals. These pyritic veins are of low 
 generally unpayable tenor ; they consist of prevailingly gran- 
 ular or massive, very rarely crustified, minerals with a little 
 quartz-gangue, and are believed to have been formed by pyri- 
 tic replacement along well-defined fissure-planes. In the por- 
 phyry these veins are surrounded by very wide zones in which 
 the rock is greatly altered by the introduction of sericite and 
 pyrite, and this applies to Metcalf as well as to Morenci. At 
 the latter place almost the whole of Copper mountain, contain- 
 ing the most important lodes, is thus altered. The process 
 which, in my complete report, is elucidated by many analyses, 
 produces bleached rocks of varying hardness in which all of 
 the feldspar has been replaced by sericite and some pyrite. 
 The biotite and hornblende are transformed into chlorite and 
 serpentine, while the silica of the rock remains almost constant. 
 All of the lime and soda is eliminated, while potash is greatly 
 increased. No carbonates are formed during this process. 
 
 Little alteration is noted where fissure-veins cut through 
 contact-metamorphic shale, nor when highly altered garnet- 
 magnetite rock forms the walls, but in unaltered or slightly 
 metamorphosed limestone a change is observed, For a short 
 distance from the vein a few inches or a few feet the rock 
 is bleached and proves to have been converted into tremolite, 
 more rarely diopside, with disseminated pyrite, chalcopyrite, 
 and zinc-blende, all more or less intimately intergrown with 
 magnetite. This alteration involves a loss of carbon dioxide 
 and some lime, as well as addition of silica, iron, magnesia, 
 and the sulphides mentioned above. More rarely argilla- 
 ceous limestones are altered to sericitic minerals with magne- 
 tite and sulphides. Magnetite has not been observed in the 
 massive pyritic veins, although it occurs in the altered country- 
 rock. 
 
530 GENESIS OF THE COPPER-DEPOSITS OF CLIFTON-MORENCI. 
 
 Relation of Contact and Hydrothermal Metamorphism. 
 
 The alteration of limestone along fissure-veins to tremolite 
 (or diopside) with magnetite and sulphide is, so far as I know, a 
 novel one. Ordinarily, limestone alters next to fissure.-veins to 
 dolomite or quartz or jasperoids. 12 The addition of silica and 
 iron and the mineralogical trend of the hydrothermal process 
 at Morenci undoubtedly connects it in some way with contact- 
 metamorphism, making it probable that the alteration took 
 place at high temperature comparatively soon after the solidi- 
 fication of the porphyry. 
 
 At first glance, it might seem plausible to assign all the 
 changes which have taken place in the metamorphic zone to 
 the same hydrothermal alteration which has affected the por- 
 phyry along the fissure-veins. This view, however tempting, 
 is surely incorrect. Instead of one set of phenomena, there are 
 two related and, in part, superimposed processes. Among the 
 proofs of this are the absence of sericitization in the porphyry 
 of many dikes which have exerted strong contact-metamor- 
 phism. Further, the entire independence which the masses of 
 extremely altered garnet-magnetite rock show in regard to the 
 fissure-veins, and their distinct dependence on contact of dikes 
 and main stock. The vein-alteration produces dull, earthy 
 rocks from the limestone, while contact-metamorphism results 
 in hard, compact and granular rocks. On the other hand, 
 there is undoubtedly a certain relation between the two pro- 
 cesses for amphibole (and pyroxene) occurs in the true contact- 
 metamorphic rocks, and the intergrowth of magnetite and 
 pyrite is characteristic of both. I should, therefore, conclude 
 that after the completion of the contact-metamorphism, prop- 
 erly speaking, and after the consolidation of the porphyry, an 
 extensive fissuring took place and solutions derived from the 
 cooling porphyry, probably ascending and laterally extending 
 from this rock, flowed through these fissures. Everything in- 
 dicates that these solutions were closely related to those which 
 emanated from the magma at the moment of intrusion and, in 
 fact, similar in general composition. 
 
 As to the quantitative relation of contact-metamorphism and 
 hydrothermal metamorphism, it is difficult to speak with ab- 
 
 12 W. Lindgren, Metasomatic Processes in Fissure- Veins, Trans., xxx., 578 to 692. 
 
GENESIS OF THE COPPER-DEPOSITS OF CLIFTON-MORENCI. 531 
 
 solute certainty. In some parts of the contact-metamorphic 
 rocks small seams with sulphides and magnetite are very abund- 
 ant (for instance, in the Yuvapai mine) and it is not easy to say 
 how much of this should be credited to each form of alteration, 
 for the sedimentary rocks were evidently solid during the in- 
 trusion, and seams filled with sulphides may well have formed 
 in them. Generally speaking, they would be, and, in fact, are 
 at present much less permeable to solutions than the porphyry, 
 as shown by the slight depth which oxidation has attained in 
 them, and it is believed that the hydrothermal solutions were 
 chiefly confined to cracks and fissures in contradistinction to 
 the much more searching action of gaseous water. The facts 
 above given show indeed how slight is the lateral spread of 
 alteration from the veins in limestone. That the solutions 
 producing the contact-metamorphism effected such intense re- 
 sults is probably due to the existence of a far greater degree 
 of heat and gas-pressure. 
 
 Processes Due to Oxidation and Hydration in the Altered Zone. 
 
 Under influence of surface-waters (but protected from direct 
 oxidation), chlorite and serpentine form from the tremolite and 
 diopside of the contact-zones, while garnet is little altered. 
 Under direct oxidizing-action, garnet changes to limonite and 
 quartz, while lime is probably carried away as carbonate. 
 Tremolite and related minerals are similarly affected. Magne- 
 tite oxidizes to hematite and limonite, many large bodies of 
 which are mined for fluxing-purposes. Pyrite changes by 
 direct oxidation into ferrous sulphate and free sulphuric acid ; 
 the ferrous sulphate upon further oxidation yields ferric sul- 
 phate and the latter is easily decomposed into basic sulphates, 
 ferric hydrates and free acid; ferric sulphate is also ready to 
 attack pyrite and other sulphides, changing them to sulphates 
 and being itself reduced to ferrous sulphate. 
 
 This cycle of reactions will finally transform all of the sul- 
 phides present into various, more or less soluble, oxy-salts. A 
 large part of the pyrite will be changed to limonite. Such 
 " iron caps " are seen at the outcrops of many veins in regions 
 where oxidation proceeds undisturbed by erosion, but in this 
 region they are generally absent. 
 
 The veins are marked by siliceous outcrops, either entirely 
 
532 GENESIS OF THE COPPER-DEPOSITS OF CLIFTON-MORENCI. 
 
 barren or containing small amounts of oxidized copper-ores. 
 N"o basic ferric sulphates have been seen either in the mines 
 or on the surface. The waters percolating downwards must 
 soon have lost their oxygen and, for the alteration at greater 
 depths, ferrous sulphate and dilated sulphuric acid are prob- 
 ably the only reagents of importance resulting from the py- 
 rite. It is clear that the upper part of the veins have not 
 been formed by simple oxidation of pyrite and accumulation 
 of limonite. 
 
 Direct oxidation of chalcopyrite yields cupric and ferrous 
 sulphates, while the zinc-blende produces zinc sulphate; both 
 of these processes are in evidence wherever the disseminated 
 sulphides in the metamorphic rocks are exposed to oxidation. 
 The general order of attack of oxygen is usually stated as 
 follows : Arsenopyrite (most easily attacked), pyrite, chalco- 
 pyrite, blende, galena and, finally, chalcocite (most difficultly 
 attacked). This rule is probably true only for one set of con- 
 ditions as to mass, aggregate and character of solutions. Very 
 marked exceptions from it occur at Morenci. 
 
 Sulphate Waters. Descending-waters from a lode of decom- 
 posing pyrite, chalcopyrite and zinc-blende should contain 
 chiefly ferrous, cupric and zinc sulphates, together with free 
 sulphuric acid. The first two salts are easily soluble, but far 
 more so is the zinc sulphate. 
 
 Cuprous sulphate is stable only under certain conditions and 
 is not believed to be an important reagent, though it may form 
 during subsidiary or intermediate reactions. Its presence in 
 any mine-waters has not been satisfactorily proved. 
 
 In this district, some moisture percolates the upper workings, 
 as shown by efflorescences and stalactites of sulphates, but the 
 mines are practically dry. In the porous porphyry the mois- 
 ture spreads easily, while the hard metamorphic rocks offer con- 
 siderable resistance. 
 
 Processes in Fissure- Veins. Below the region of oxidizing- 
 influences the veins consist of pyrite, chalcopyrite and zinc- 
 blende, while the upper few hundred feet contain chalcocite 
 and oxidized copper-ores. The most important action of the 
 descending sulphate solutions has been a development of chal- 
 cocite by the action of cupric sulphate on primary py rite-ore ; 
 this process began at the time the veins were first touched by 
 
GENESIS OF THE COPPER-DEPOSITS OF CLIFTON,MORENCI. 533 
 
 oxidizing waters, and continues to some extent to the present 
 time. 
 
 If secondary deposition of sulphides has taken place accord- 
 ing to Schuermann's reactions, they should be arranged in the 
 upper zones of the deposit in the following order: (Top), 
 galena, zinc-blende, chalcocite, bornite, chalcopyrite and pyrite. 
 (Bottom.) 
 
 In Morenci, practically only chalcocite thus forms. The first 
 of the primary minerals attacked is the zinc-blende which ap- 
 pears to be rapidly transformed, first into covellite and then 
 into chalcocite, as follows : 
 
 ZnS + CuS0 4 = ZnS0 4 + CuS. 
 
 Chalcopyrite, present only in small quantities, is probably 
 attacked at the same time. The zinc sulphate is carried away 
 and no zinc minerals appear in the upper, oxidized part of the 
 veins. 
 
 Contrary to the list just given above, blende is thus attacked 
 before the pyrite. The conversion of pyrite to chalcocite may 
 be studied in all stages of the process; it is a molecular re- 
 placement attacking the pyrite from cracks and fissures, and 
 gradually eliminating it entirely. However, even in the best 
 chalcocite-ores residual pyritic cores ordinarily remain. Dr. 
 Stokes has shown that the reaction at + 100 C. and -f 200 C. 
 proceeds as follows : 
 
 5 FeS 2 + 14 CuS0 4 -f 12 H 2 = 7 Cu. 2 S + 5 FeS0 4 -f- 9 H 2 S0 4 
 -f- 3 H 2 S0 4 , the last H 2 S0 4 being formed by oxidation of the 
 sulphur of FeS 2 . It is probable that the reaction likewise goes 
 on, though more slowly, between -f 100 C. and -|- 20 C., the 
 range probably existing in the deposit during the period of oxi- 
 dation. Mr. H. V. Winchell's reaction 13 necessitates sulphur- 
 ous acid as a reagent, the presence of which seems unlikely. 
 The equations given by Prof. Van Hise u for the formation of 
 secondary copper sulphides seem improbable, as they require 
 
 13 Synthesis of Chalcocite and Its Genesis at Butte, Montana, Bulletin of the 
 Geological Society of America, vol. xiv., pp. 269-276. 
 
 14 Some Principles Controlling the Deposition of Ores, Trans., xxx., 101, 111, 
 112. 
 
534 GENESIS OF THE COPPER-DEPOSITS OF CLIFTON-MORENCI. 
 
 the presence of free oxygen, and as they are generally based 
 on cuprous sulphate. 
 
 By this process of alteration the massive pyritic veins have 
 been transformed into almost solid, dull, sooty chalcocite; and 
 the zones of dissemination surrounding them in the porphyry 
 have changed into low-grade chalcocite-ores. The process is ac- 
 companied by the formation of some kaolin, quartz, chalcedony, 
 and probably also opal. No sericite forms. The kaolin develops 
 metasomatically at the expense of the sericite, and sulphuric 
 acid was evidently the reagent. Alunite is in places formed in 
 the same manner. Extremely large amounts of ferrous sulphate 
 must have been carried away during 'this process. 
 
 Oxidation of Chalcocite. After a large part of the chalcocite 
 in the lode had been formed, there came a time when erosion 
 and degradation, working faster than oxidation, began to expose 
 the upper part of the chalcocite-zone to active and direct attack 
 by oxygen. Practically all of the veins are in this stage. The 
 present zones of active oxidation are therefore due, not to direct 
 oxidation of the primary lode, but to the destruction of the upper 
 horizon of the chalcocite-zone. As reagents, there are here fer- 
 rous sulphate, sulphuric acid, cupric sulphate and free oxygen. 
 Any ferric sulphate present would soon be reduced to ferrous 
 salt by the abundant pyrite. Chalcocite changes to cuprite and 
 cupric sulphate, sometimes with an intermediate stage of cov- 
 ellite. 
 
 2 Cu 2 S + = 2 CuS + Cu,0 and CuS + 40 = CuS0 4 . 
 
 Cuprite partly reduced to metallic copper is, in fact, abundantly 
 present in the upper limit of the chalcocite-zone. 
 
 Cu 2 + H 2 S0 4 = Cu + CuS0 4 + H 2 0. 
 
 By some process not quite elucidated, chalcocite may, in places,, 
 change directly into native copper. The zone of cuprite and 
 metallic copper has rarely great vertical extension, for the 
 reason that both minerals are rapidly converted into cupric sul- 
 phate, brochantite, malachite, azurite and chrysocolla; but these 
 products are soon dissolved by free sulphuric acid from pyrite, 
 a mineral which tenaciously remains until the last, and descend 
 
GENESIS OF THE COPPER-DEPOSITS OF CLIFTON-MORENCI. 535 
 
 as soluble sulphates to enrich the upper part of the chalcocite 
 zone. 
 
 In the Copper Mountain veins, contained in porphyry, oxi- 
 dized copper-minerals are almost entirely absent, probably be- 
 cause of the great amount of free sulphuric acid present. The 
 chalcocite disappears at from 100 or 200 ft. below the surface, 
 and the lode consists of a rusty mass of sericitized porphyry, 
 with considerable amounts of remaining pyrite and efflores- 
 cences of cupric sulphate. The last particles of pyrite only 
 disappear close to the surface. 
 
 In places, chalcocite may change directly into brochantite 
 or malachite. Cupric oxide (melaconite or tenorite) has not 
 been found. 
 
 Oxidizing Processes in Limestone. The processes which have 
 resulted in the oxidized deposits now forming irregular or tab- 
 ular masses in limestone or shale, and not connected with fis- 
 sures, are materially different from those occurring in the lodes. 
 In most cases the original material consisted of disseminated 
 lean pyritic ores, containing pyrite, chalcopyrite, zinc-blende, 
 and magnetite, locally more or less* concentrated in irregular 
 masses, or following certain strata- or dike-contacts. Free oxy- 
 gen and sulphuric acid, ferrous and cupric sulphates, with an 
 abundance of calcium carbonate, formed the reagents. Though 
 oxygen and carbon dioxide may in part have produced limonite 
 and malachite directly from pyrite and chalcopyrite, the most 
 important reactions doubtless were those between calcium car- 
 bonate and sulphate solutions, partly derived from nearer the 
 surface. 
 
 2 CuSQ 4 -t- 2 CaC0 3 -f H 2 O = (CuOH) 2 , C0 3 , + 2 CaS0 4 + 
 
 C0 2 + H 2 S0 4 . 
 3 CuS0 4 -f- 3 CaC0 3 + H 2 = (CuOH) 2 , Cu (C0 3 ) 2 -f 3 CaS0 4 
 
 + C0 2 . 
 
 In the first case malachite, in the second azurite forms, to- 
 gether with gypsum. The latter mineral, though largely car- 
 ried away in solutions, is not uncommon in these deposits at 
 Morenci. Ferric hydrate will be produced from ferrous sul- 
 phate and calcium carbonate. Thus, in general, is explained 
 the constant occurrence in these deposits of malachite, azurite 
 
536 GENESIS OP THE COPPER-DEPOSITS OF CLIFTON-MORENCI. 
 
 and limonite. Crusts of replacing-malachite and azurite fre- 
 quently surround residual, rounded masses of limestone. The 
 gangue of garnet and magnetite alters to ferric hydrate and 
 quartz. Chrysocolla forms when silica is plentiful ; zinc-min- 
 erals are not uncommon in these deposits, and efflorescences of 
 the zinc and magnesia sulphates sometimes cover the tunnel- 
 walls. During the process outlined above, lime is almost 
 wholly eliminated, while alumina forms residual concentra- 
 tions. 
 
 Oxidizing Processes in Shale. Disseminated cuprite in beds 
 of Morenci shale is a common occurrence, and some of the 
 large ore-bodies of the Manganese Blue mine were of this 
 character. It occurs as flakes on the bedding-planes, or in 
 small replacement-veins, sometimes accompanied by distinctly- 
 later malachite and by limonite. These occurrences seemed 
 difficult to explain, but light is thrown on them by recent ex- 
 periments by Dr. E. Kohler, 15 who shows that solutions of cupric 
 sulphate, filtered through kaolin, become hydrolyzed by adsorp- 
 tion. The copper is precipitated as oxide, and sulphuric acid 
 is set free. (Experiments'are now in progress which seem to 
 indicate that the Morenci shale possesses remarkable power of 
 adsorbing copper from aqueous solutions.) 
 
 Azurite also occurs frequently in shale, as shown by the 
 second ore-body in the Detroit mine. Large crystals of that 
 mineral develop here, metasomatically, in a metamorphic shale 
 composed of sericite and amphibole. Cases have been observed 
 where azurite envelops masses of un decomposed pyrite accom- 
 panied by a little limonite. During the oxidizing process the 
 alumina possesses considerable mobility. It is dissolved by sul- 
 phuric acid from clay-shale and forms certain aluminous min- 
 erals, notably sericite. The aluminium sulphate formed is ex- 
 tremely soluble in water, and thus easily transported. At many 
 places in the mines of Morenci, pure kaoli-n forms, together 
 with azurite and malachite. 
 
 Paragenesis. 
 The minerals formed during successive stages are as follows : 
 
 15 Adsorptionsprozesse als Faktoren der Lagerstattenbildung und Lithogenesis, 
 Zeitschriftfur praktische Geohgie, vol. xi., p. 49 (1903). 
 
GENESIS OF THE COPPER-DEPOSITS OF CLIFTON-MORENCI. 537 
 
 VEINS. 
 
 Primary Processes. Pyrite, chalcopyrite, zinc-blende, molybde- 
 
 nite (rarely magnetite), sericite, quartz, rarely 
 tremolite, diopside and epidote. 
 
 Introduction of iron, sulphur, zinc, copper, 
 .molybdenum, potassium and silica. Elimi- 
 nation of calcium and sodium. 
 Processes of Oxidation. ( Chalcocite (rarely covellite, chalcopyrite, 
 
 , I and bornite), quartz, chalcedony, kaolin, alu- 
 Action of sulphate solu- I . 
 
 tions without oxygen. J m ' . 
 
 Introduction of copper. Elimination of 
 
 L zinc, some iron and sulphur. 
 f Cuprite, native copper, brochantite, mala j 
 I chite, chrysocolla (rarely azurite), chalchan- 
 Action of directly oxi-J thite, limonite, quartz. 
 
 dizing solutions. Introduction of carbon dioxide. Elimina- 
 
 >tion of sulphur, together with some iron and 
 copper. 
 CONTACT-DEPOSITS. 
 
 Primary Processes. Pyrite, magnetite, chalcopyrite, zinc-blende, 
 
 molybdenite, specularite, garnet, epidote, di- 
 opside, tremolite, quartz. 
 
 Introduction of much iron and silica, to- 
 gether with copper, zinc, molybdenum, sul- 
 phur, possibly magnesia. Elimination of 
 carbon dioxide and probably some lime. 
 
 Processes of Oxidation. Limonite, malachite, azurite, cuprite, rarely 
 
 native copper and chalcocite, copper-pitch ore, 
 chrysocolla, goslarite, zinc carbonate, wille- 
 mite, calamine, pyrolusite, quartz, calcite, 
 chlorite, serpentine. 
 
 Introduction of carbon dioxide and addi- 
 tional copper. Elimination of calcium, sul- 
 phur, some zinc and iron. 
 
 CHARACTERISTICS OF DEPOSITS. 
 
 Deposits of Carbonates and Oxides in Limestone and Shale. 
 
 The important occurrences of these ore-bodies are found in 
 the Longfellow, Manganese Blue, Detroit, Copper Mountain, 
 Montezuma, and Shannon mines. 
 
 They contain practically all of the oxy-salts of copper known 
 from the district; but chiefly malachite, azurite and cuprite, 
 with very subordinate amounts of native copper and chalco- 
 cite. The accompanying minerals consist of limonite, manga- 
 nese peroxide, kaolin, and soft, yellowish material which, in a 
 large proportion of deposits, generally proves to be decompos- 
 
 34 
 
538 GENESIS OF THE COPPER-DEPOSITS OF CLIFTON-MORENCI. 
 
 ing and hydrated forms of tremolite, diopside, garnet, or epi- 
 dote. Some deposits of chrysocolla and limonite occur, how- 
 ever, in unaltered limestone, and the cuprite-bearing shales are 
 not accompanied by any gangue except a little limonite. The 
 copper-minerals are sometimes formed by crustification, but 
 replacements in shale or lime are almost equally common. 
 
 The form is sometimes wholly irregular, but there is a 
 marked tendency towards a tabular form following certain 
 strata evidently favorable for deposition. The horizontal ex- 
 tent varies greatly, but rarely exceeds 300 or 400 ft., and the 
 two dimensions are apt to be approximately equal. The thick- 
 ness ranges from 1 to 30 ft. and is sometimes more. Regular 
 boundaries rarely occur, and the pay-ore easily shades off into 
 the country-rock. In the Manganese Blue and the Detroit 
 mines several superimposed ore-bearing horizons are found 
 within 300 ft. of the surface. The Longfellow deposit has the 
 form of an inverted pyramid. 
 
 Acidic porphyry is found in the immediate vicinity of all de- 
 posits. Some of them immediately adjoin the contact of the 
 main stock, but others show decided dependence upon dikes 
 of porphyry ; one class of deposits forms tabular masses along 
 the contacts of dikes ; others, such as the Detroit, the Manga- 
 nese Blue, and the Longfellow, lie between two or three por- 
 phyry dikes, the latter being largely barren, except for some 
 disseminated chalcocite. Fissures antedating the oxidation, 
 but subsequent to the contact-metamorphism, have sometimes 
 influenced the form by guiding the descending waters. 
 
 The deposits may be found in any of the Paleozoic horizons 
 between the Coronado quartzite and the Cretaceous beds. 
 They frequently crop at the surface, azurite appearing to resist 
 decomposition quite obstinately. 
 
 Driving laterally, or sinking deeper from these ore-bodies, is 
 apt to develop hard limestone with typical contact-metamor- 
 phic minerals and scattered pyritic ores. The very confident 
 conclusion has been drawn that the majority of these deposits 
 have been formed by the oxidation of irregular or tabular 
 masses of low-grade pyritic ores, such as the lower mine-work- 
 ings have disclosed in such abundance, for instance, in the 
 Yavapai mine. 
 
 An enrichment accompanied the oxidation, both on account 
 
GENESIS OF THE COPPER-DEPOSITS OF CLIFTON-MORENCT. 539 
 
 of reduction in volume and introduction of additional copper 
 as sulphate. The oxidation does not reach the water-level 
 which is far below the present workings, but acts most irregu- 
 larly, sometimes leaving fresh metamorphic limestone near the 
 surface and again penetrating along fissures to a depth of 400 
 feet. 
 
 The above explanation does not fit all of these deposits, for 
 some are unaccompanied by evidence of contact-metamorphism 
 and have probably primarily been formed by the action of 
 thermal, vein-forming waters, and others are entirely of sec- 
 ondary origin, being deposited in shales and in the clays along 
 important faults by migrating sulphate solutions. The oxida- 
 tion of the present ore-bodies followed the faulting movement 
 and probably began at a rather early epoch of Tertiary times. 
 
 Fissure- Veins and Related Deposits of Morenci Type. 
 
 Fissure-veins with a northeasterly or northerly trend, but of 
 no great individual length, follow the entire length of the por- 
 phyry stock, but are especially developed between Morenci and 
 Metcalf and on Copper King mountain. The most prominent 
 lode system at Morenci extends for about 2 miles, and consists 
 of a number of shorter-linked and branching fissures, forming 
 two belts slightly curved towards the southeast. One of them 
 lies in porphyry within a few hundred feet of the contact and 
 comprises the principal mines of the district the West Yan- 
 kee, the Humboldt, and the Copper Mountain. The other and 
 parallel system traverses the metamorphic rocks a few hundred 
 feet southeast of the contact. 
 
 The dip is steep to the NW. or SE. and the system is thus 
 a conjugated one, bearing every evidence of origin by com- 
 pressive stress. 
 
 Outcrops are very poor, frequently wholly unrecognizable, 
 and it is most difficult to trace the veins on the surface. Low- 
 grade malachite, chrysocolla, and brochantite-ores are con- 
 tained in the outcrops of some veins. Large masses of limo- 
 nite while common enough in the oxidized contact-metamor- 
 phic deposits do not usually occur in the vein-croppings. 
 
 Underground exposures always show one or more well-de- 
 fined walls frequently polished and striated. The faulting- 
 movement on these fissures is slight. 
 
540 GENESIS OF THE COPPER-DEPOSITS OF CLIFTON-MORENCI. 
 
 In the majority of these deposits there is a central vein which 
 ordinarily is 4 ft. wide or less, but may sometimes expand to 50 
 ft. ; it is composed of nearly massive sulphides, arid closely fol- 
 lows the fissure. In the porphyry, this is surrounded by a 
 much wider zone of altered rock which may constitute ore; 
 the central vein and the altered zone together are characterized 
 as a " lode." In almost all of the veins the following vertical 
 distribution of ores is noted : 
 
 SURFACE ZONE. { From 50 to 20 ft deep from the cr PP in g s - Contains oxi- 
 
 l dized copper-minerals or is barren. 
 p 7 / From 100 to 400 ft. in vertical extent ; possibly more in 
 
 l places. Contains clialcocite and pyrite. 
 
 PYEITIC ZONE I Begins ^ rom 2 ^ to 600 ft. below the surface. Contains pyrite, 
 I chalcopyrite and zinc-blende. 
 
 It has been shown that the minerals of the two upper zones 
 have been derived from those of the pyritic zone by processes 
 of direct and indirect oxidation ; that the chalcocite is wholly 
 formed by replacement of pyrite effected by solutions of cupric 
 sulphate ; that secondary covellite, chalcopyrite and bornite only 
 occur in very small amounts. Also, that the surface-zone is 
 derived from the chalcocite-zone by its direct oxidation. It 
 has further been emphasized that the pyritic zone is generally 
 very poor ; that the chalcocite-zone produces the richest ore, 
 and that the surface-zone is always poor and sometimes barren. 
 
 The pyritic part of the veins is, with good reason, believed 
 to represent the primary deposition of sulphides along the fis- 
 sures. It contains a small amount of quartz-gangue with inti- 
 mately intergrown pyrite, zinc-blende and chalcopyrite; the 
 two last-named minerals are present only in small quantities; 
 molybdenite also occurs. A well-defined foot-wall is usually 
 present, while the hanging-wall may be more or less indistinct 
 or represented by several subordinate fissures. The deposition 
 seems to have been chiefly effected by metasomatic replace- 
 ment of crushed and sheeted porphyry, or metamorphic rock. 
 The zone of altered rock surrounding the vein consists of seri- 
 citized and pyritic porphyry when the vein is in this rock, and 
 may then be very wide. In the hard, metamorphic limestone 
 and shale, this zone is narrow and shows either an amphibo- 
 litic or a sericitic alteration and contains besides pyrite, chal- 
 
GENESIS OF THE COPPER-DEPOSITS OF CLIFTON-MORENCI. 541 
 
 copyrite and zinc-blende intergrown with magnetite, a mineral 
 absent from the vein proper. In the chalcocite-zone, commer- 
 cially the most important, magnetite has largely, but rarely 
 wholly, replaced the pyrite, both in the massive veins and in 
 the zones of pyritization and sericitization surrounding them 
 at a certain depth. It is generally sharply separated from the 
 pyritic zone, the transition taking place within a surprisingly 
 short distance. Below this limit, evidence of chalcocitization 
 can only be found along fissure-planes. The uppermost part of 
 the chalcocite-zone is invariably the richest. The massive py- 
 rite veins form pure, dull black chalcocite, or a mixture of 
 pyrite and chalcocite. This* constitutes high-grade ore with 
 more than 5 per cent, of copper ranging up to 70 per cent. 
 while the pyritized porphyry turns into low-grade ores with 
 from 2 to 5 per cent, of copper. 
 
 To these large bodies of low-grade ore the recent great de- 
 velopment of the district is due. In some mines, which are 
 generally on the lower slopes, or in the bottoms of canyons, the 
 chalcocite begins almost at the surface. At Morenci, situated 
 high up on the hills, the depth from the surface is rarely less 
 than 200 ft. The depth on the vein attained by the chalcocite- 
 zone, from the level where direct oxidation begins to the upper 
 limit of the pyrite-zone, varies greatly ; it is sometimes less 
 than 100 ft., while under Copper mountain the average would 
 somewhat exceed 200 ft. Directly below the summit it is 300 
 ft., and its lower limit in some cases has not yet been reached. 
 In general, the upper limit would be represented by a curved 
 line somewhat less convex than the contours of the mountain. 
 The lower limit seems to be flatter, but great irregularities 
 exist, due no doubt to exceptional conditions of circulation of 
 surface-waters. 
 
 The great bodies of low-grade ore are almost wholly con- 
 fined to the lodes in porphyry; and the pay-zone generally 
 contracts greatly when contact-metamorphic shales or lime- 
 stones are entered. Stopes of low-grade ore range from a few 
 feet to 100 ft. or more in width ; many are 200 ft. long and 
 have been stoped for the same vertical distance. The great 
 body of concentrating ore between the two Humboldt walls, 
 which dip against each other, is about 300 ft. long, up to 200 
 ft. wide, and has been stoped 200 ft. high. Values gradually 
 
542 GENESIS OF THE COPPER-DEPOSITS OF CLIFTON-MORENCI. 
 
 decrease on both sides unless, as sometimes happens, cut off 
 by fissures on one or both sides. The limit is thus usually 
 simply determined by the lowest grade of ore workable. Seri- 
 citization and chalcocitization has spread considerably farther, 
 laterally, than is indicated by the 2.5 or 3 per cent, of copper 
 contained in the lowest grade of ore mined. 
 
 The ore-shoots of Copper mountain are thus materially dif- 
 ferent from those usually found in gold- and silver-veins. Their 
 greatest extent is horizontal rather than vertical, and their size 
 depends more upon conditions of circulation of surface-waters 
 than upon the primary distribution of copper in the vein. 
 Prospecting for reserves must proceed laterally rather than 
 towards extreme depth. 
 
 The surface-zone is always richest near the lowest limit of 
 oxidation where cuprite and native copper form from chalco- 
 cite. The upper part contains poorer ores of malachite, bro- 
 chantite, etc., and may be entirely barren. 
 
 In the Copper Mountain veins the chalcocite apparently 
 changes directly to cupric sulphate ; and other copper oxy-salts 
 are practically absent. The pyrite remains, in part, rusty and 
 accompanied by limonite, until near the surface, where it finally 
 disappears. The surface-zone is thus directly derived from the 
 chalcocite-zone by gradual erosion and oxidation, indicating 
 that the latter is not a very recent development. 
 
 Two of the principal faults of the district cut across the Mo- 
 renci veins and dislocate them. Some of the ore-bodies are 
 clearly faulted, so that rich chalcocite-ore is brought opposite 
 leached and barren surface-rock. Brecciated zones, accompany- 
 ing this faulting, contain fragments of chalcocite-ore. In all> 
 the evidence is pretty clear that, at least a part of the chalco- 
 cite-zone had already been formed when the faulting took 
 place, and that, consequently, the beginning of chalcocitization 
 and oxidation must be placed in the earlier or middle part of 
 Tertiary times. 
 
 Descriptions of chalcocite-ores from other districts show that 
 the secondary sulphides develop at a point just below the 
 water-level. In none of the important mines in this district 
 has the water-level been reached; it is probably far below the 
 present workings. Chalcocite may now form in the upper 
 part of the zone, in places away from fissures and faults, where 
 
GENESIS OF THE COPPER-DEPOSITS OF CLIFTON-MORENCI. 543 
 
 sulphate solutions are slowly descending and free oxygen scarce, 
 but I doubt very much whether it is now forming in the lower 
 part of that zone. I regard the chalcocite-zone as formed 
 about an ancient, gradually-receding water-level. During the 
 early Quaternary, that level was evidently several hundred feet 
 higher than at present, but the occurrences of the chalcocite 
 appear to require a still higher stand, such as existed during 
 the probably moist climate of the middle Tertiary. 
 
 The payable deposits, as a rule, lie at high elevations, and no 
 large deposits have been opened on the lower slopes of Chase 
 Creek canyon, or along its bottom. The lower down on the 
 slope a deposit is located, the nearer to the surface will the 
 chalcocite-zone be found. Chalcocite-ores do occur, in fact, in 
 veins along the bottom of Chase Creek canyon, but the mineral 
 shows only as a slight coating on pyrite. This topographical 
 distribution is the more remarkable when it is recalled that 
 Chase Creek canyon antedates the early Quaternary conglom- 
 erates (Gila formation) and that, therefore, oxidation would 
 apparently have had a long time in which to act. It confirms 
 the conclusions as to the great age of the chalcocite-zone and 
 emphasizes the very slow rate at which oxidation works. 
 
 Chalcocite-ores and oxidized ores forming a " stock- werk " 
 of seams in porphyry (at Metcalf mines), or in quartzite (at 
 the East Yankee mine), or occurring as disseminations in por- 
 phyry dikes (West Yankee lode and Shannon mine), in general 
 correspond to the descriptions of the altered zones surrounding 
 the veins. They pre-suppose an earlier sericitization and py- 
 ritization effected by the primary vein-forming solutions. 
 
 The fault-planes of the principal epoch of dislocations are 
 later than the Morenci veins and generally barren, but may 
 locally contain " drag " or cuprite-ores deposited from migrating 
 sulphate solutions by processes of adsorption. 
 
 The Coronado Type of Veins. 
 
 Almost the only representative of the Coronado type of 
 veins is the Coronado lode, which outcrops on the summit of 
 Coronado ridge about 2,000 ft. above Metcalf. It presents the 
 feature unusual for a fissure-vein of following one of the prin- 
 cipal faults of the district with a throw ranging from 1,000 to 
 2,000 ft., and it is traceable for nearly 2 miles, finally disap- 
 
544 GENESIS OF THE COPPER-DEPOSITS OF CLIFTON-MORENCI. 
 
 pearing towards the west under the basaltic foothills of Eagle 
 creek. The fault-zone, which is from 50 to 200 ft. wide, is 
 followed by a diabase dike which has been crushed and partly 
 deformed. Oxidized ores, malachite, azurite and chrysocolla, 
 of medium to poor grade, occupy irregular shoots in the sur- 
 face-zone, but are replaced at a depth of from 200 to 300 ft. by 
 chalcocite-ores. At some points the latter, however, reach 
 the surface. Explorations during the last two years are re- 
 ported to have developed large bodies of these, even at a depth 
 of 500 ft. below the surface. The evidence as far as it goes 
 here, too, points to secondary origin of chalcocite and its de- 
 rivation from pyritic ores, but here, as well as at Morenci, the 
 maximum depth attained by the secondary chalcocite has not 
 been fully demonstrated. 
 
 The Coronado lode was formed later than the Morenci type 
 of veins and subsequent to the intrusion of diabase, which is 
 younger than the porphyries of Morenci and Metcalf. Regard- 
 ing the relative age of the diabase and the fault-fissure, the evi- 
 dence is hardly conclusive. It seems as if the dike had been 
 intruded during the epoch of faulting, and the solutions de- 
 positing the copper certainly followed the intrusion of the dike. 
 
 Gold-Searing Veins. 
 
 Gold, silver and lead are practically absent from the prin- 
 cipal deposits, but it is an interesting fact that they begin to 
 appear in many of the outlying- veins somewhat distant from 
 the central mass of porphyry. These veins, in which copper is 
 apt to play a less important part, have not as yet attained much 
 importance from an economic standpoint. 
 
 CONDITIONS OF GROUND- WATER. 
 
 Permanent water has not thus far been encountered in any 
 of the mines in the whole district with which this paper deals. 
 Morenci is situated on the hills from 800 to 1,500 ft. above the 
 principal streams, Chase creek and Eagle creek ; and the deepest 
 workings in no place reach farther than 600 ft. below the surface. 
 A little seepage from the surface takes place in case of heavy 
 rains, or from the local water-supply ; and some drifts and cross- 
 cuts underneath the town are somewhat damp, especially in the 
 Manganese Blue and Arizona Central mines. The mines at 
 
GENESIS OF THE COPPER-DEPOSITS OF CLIFTON-MORENCI. 545 
 
 Metcalf are situated on Shannon mountain from 500 to 1,200 ft. 
 above Chase creek, and here, too, the workings are dry, ex- 
 cepting one place in the Shirley tunnel where a winze struck 
 some standing water. The few shafts and prospects, sunk in 
 the bottom of Chase creek, are the only places containing per- 
 manent water. The Copper King mine, situated a few hun- 
 dred feet below the summit of the mountain of the same name, 
 has a shaft 600 ft. deep; some crevices containing water have 
 been found in it, but they soon drained out and no more has 
 since come in. 
 
 The present stand of the water-level, -except along the creeks, 
 is practically unknown. It probably rises as a slightly curved 
 surface from the creek-levels towards the high hills. The 
 total amount of water stored below this water-level is probably 
 small. 
 
 DEPTH OF OXIDIZED ZONE. 
 
 The presence of products of direct or indirect oxidation 
 shows the depth to which the oxidizing-waters or the sulphate 
 solutions have penetrated; but the porphyry and the metamor- 
 phosed limestones should be separated, because they act very 
 differently. In that part of Copper mountain which has been ex- 
 plored, the average depth of the lower limit of the chalcocite- 
 zone is 400 ft., but it increases in places to 500 or even 600 ft. 
 To this depth from the surface, the sulphate solutions descended, 
 and along important fissures they may have gone somewhat 
 farther. The solutions not only followed fissures, but pene- 
 trated the porous, sericitized porphyry with considerable ease. 
 On the other hand, the altered limestones and shales are very 
 compact, non-porous and impervious. Where circulation was 
 facilitated by fissures, as in the Manganese Blue and the Joy 
 mines, the rocks may be partly oxidized to a depth of 400 ft., 
 but this is generally a maximum. There is no well-defined 
 plane expressing the depth of oxidation, which, on the contrary, 
 proceeds very capriciously, fresh sulphides being frequently 
 found very close to the surface. 
 
 FLUID-INCLUSIONS. 
 
 Fluid-inclusions have been observed in the quartz-grains of 
 granite, quartzite, porphyry and vein-quartz occurring in this 
 district. There is nothing uncommon in this; it is, indeed, the 
 
546 GENESIS OF THE COPPER-DEPOSITS OF CLIFTON-MORENCI. 
 
 ordinary condition of affairs. As these fluid-inclusions, beyond 
 doubt, contain aqueous solutions, it may be regarded as certain 
 that such fluids were present when the quartz-grains in ques- 
 tion were formed. It is the purpose of the following para- 
 graphs to call attention to certain phenomena in these inclu- 
 sions which have not been described previously. 
 
 In Granite. Inclusions, filled with a fluid and a bubble of 
 gas, occur abundantly in the quartz-grains of all of the granites 
 examined. They are of rare occurrence, though not unknown 
 in the feldspars. The form is round or elliptical, or may be 
 that of a negative quartz-crystal with prism and pyramid. The 
 size averages perhaps 0.02 mm. The relation of volume be- 
 tween the fluid and the bubble varies considerably among 
 inclusions in the same grain. In the smaller inclusions the 
 bubble frequently is in active motion. Heated to 40 or 50 
 C. there is no perceptible change in volume of fluid or bubble, 
 and consequently it may be considered certain, that the fluid is 
 not liquid carbon dioxide, which has sometimes been observed 
 in the granites, but chiefly water. In some, but by no means 
 all, of the inclusions there is also a solid body contained in the 
 fluid ; in some cases this is a transparent cube, in others, and 
 more commonly, an irregular grain or a rod of the solid mate- 
 rial. This also has occasionally been observed and described 
 in granites from other districts. 
 
 In Metamorphic Limestones. The metamorphism of the lime- 
 stone to garnet, epidote, diopside, quartz and other minerals 
 took place under conditions of high temperature and pres- 
 sure, and almost certainly in the presence of aqueous solutions 
 in fluid or gaseous form. It is a curious fact that these min- 
 erals only very exceptionally contain fluid-inclusions. The 
 quartz-grains formed seem entirely homogeneous and free from 
 these interpositions. Only one or two very small inclusions 
 with moving bubble were noted. The same applies to the gar- 
 net and other heavy minerals. The calcite would hardly be 
 expected to preserve any such inclusions on account of its per- 
 fect cleavage. 
 
 In Porphyry. The inclusions in the porphyry are again prac- 
 tically confined to the quartz. They occur chiefly in the pheno- 
 crysts, but also in the quartz of the ground-mass, although they 
 are here usually very small. Naturally, the diorite-porphyries 
 
GENESIS OF THE COPPER-DEPOSITS OF CLIFTON-MORENCT. 547 
 
 are poor in inclusions, but they appear abundantly in the gran- 
 ite-porphyries and the quartz-monzonite porphyries with which 
 the ore-deposits are chiefly connected. They are found through- 
 out the Metcalf granite-porphyry, which is characterized by 
 large bi-pyramidal quartz-phenocrysts, and they are almost 
 equally common in the smaller quartz-crystals of the Copper 
 mountain porphyry of Morenci. The sericitization of the por- 
 phyry affects them but little, for the quartz-grains of the por- 
 phyries are very rarely altered by this process. In specimens 
 taken from the oxidized zone near the surface, many of the in- 
 clusions are empty, probably due to the cracking of the grains, 
 and the attending expulsion of the highly-compressed. fluid. 
 
 The peculiar feature of these fluid-inclusions is that, as a 
 rule, they contain, besides the gas-bubble, an extremely sharply- 
 defined cube of transparent material, and a smaller opaque 
 particle. The invariable recurrence of this association is a 
 proof that these bodies are not accidental inclusions, but were 
 present, dissolved in the fluid, at the time the quartz crystal- 
 lized and imprisoned the drop of solution. 
 
 The inclusions are elliptical, irregularly rounded, or show 
 the form of their host, that is, a hexagonal pyramid with short 
 prism. Their size ranges from those barely visible up to 0.02 
 mm. in diameter; the latter being about the maximum. A 
 frequently recurring size is 0.012 mm. Their distribution in 
 the phenocrysts is irregular ; they are not ranged along any 
 given plane or surface. Moving bubbles are often noted in the 
 smaller inclusions. 'Heating to 40 and up to 80 C. does not 
 noticeably affect the relation of fluid cube and gas ; they do not 
 therefore consist of carbon dioxide, but of some aqueous solu- 
 tion. The proportion of volume between bubble and inclusion 
 is not constant ; many of them contain large gas-bubbles, while 
 in others they may be quite small. To some extent this may 
 be explained by leaking, but comparing a great number in very 
 fresh rocks there certainly appears to be considerable variation 
 in this proportion. The fluid is colorless. ' 
 
 As to the cube of transparent salt, it is very sharply defined 
 and well developed. In polarized light the cube appears iso- 
 tropic. Its size varies, but is usually of about the same volume 
 as the bubble, and occupies from 4 to 15 per cent, of the vol- 
 ume of the inclusion. Such cubes have been sometimes ob- 
 
548 GENESIS OF THE COPPER-DEPOSITS OF CLIFTON-MORENCI. 
 
 served before, especially in inclusions contained in quartz crys- 
 tals; and in some cases they have been proved to consist of 
 sodium chloride. They have also been noted in quartz pheno- 
 crysts of certain Cornish granite-porphyries. In the present 
 case the small size of the inclusions, and especially the degree 
 of alteration and oxidation to which most of the specimens 
 have been subjected, renders experimental determination of the 
 salt impracticable, at least with the material in hand at present. 
 It may be said, however, that in all probability the substance 
 is sodium chloride. Several inclusions were measured to de- 
 termine the degree of saturation when the substance was dis- 
 solved in the fluid, assuming that it is Nad, and that the liquid 
 is a saturated Solution of the same salt at ordinary temperature. 
 Results indicate that this was ordinarily from 5 to 20 per cent, 
 above the maximum amount soluble in water under ordinary 
 conditions. In one case it was found that the water must have 
 contained 45 per cent, of salt. Most of the inclusions also con- 
 tain a small opaque particle, generally measuring only a frac- 
 tion of the volume of the bubble or the cube. It has no dis- 
 tinct form ; occasionally, rod-shaped outlines may be observed, 
 but ordinarily it is so small that it only appears as a black 
 speck. Examined in reflected light, one unusually large parti- 
 cle seemed decidedly black, while another inclusion, contained 
 also in a Copper Mountain porphyry, seemed distinctly reddish 
 in transmitted light. 
 
 These inclusions are certainly a characteristic feature of the 
 granite-porphyries of Morenci and Metcalf. They prove, I 
 think, conclusively, that the acid porphyry-magma was accom- 
 panied by notable quantities of aqueous solutions containing a 
 large quantity of a salt, which probably was E"aCl; and also a 
 smaller amount of some compound containing one or several of 
 the heavy metals. From what follows, it is extremely probable 
 that this compound is largely ferric oxide. It may well also 
 contain copper, although a direct evidence of this cannot be 
 furnished. 
 
 These observations gain in interest when it is considered that 
 the porphyry has caused a strong metamorphism of adjoining 
 limestone, the principal feature of which is an acquisition of 
 silica and iron, which in all probability were given off by the 
 porphyry. It is now shown that the magma contained heavy 
 
GENESIS OF THE COPPER-DEPOSITS OF CLIFTON-MORENCI. 549 
 
 metals in aqueous solution. Very likely these solutions also 
 contained much silica, but it should be remembered that this 
 material would most likely have been deposited, upon the cool- 
 ing of the rock, on the walls of the inclusion, and in such a case 
 it would naturally have the crystallographic orientation of the 
 host from which the new substance could not readily be distin- 
 guished. 
 
 It is perhaps a significant fact that these inclusions are ab- 
 sent in the diorite-porphyries, which, as a rule, have no con- 
 nection with the copper-deposits. 
 
 As to the quantitative importance of the inclusions, it may be 
 estimated that in some specimens they make up a very percep- 
 tible percentage of the rock volume. 
 
 In Vein-Quartz. The results of the examinations of the por- 
 phyries encouraged a search in the vein-quartz. In a greatly 
 altered pyritic porphyry from the Butler and London tunnel at 
 Morenci, the ground-mass is silicified and contains irregular 
 replacement-veinlets of quartz, which were found to contain in- 
 clusions entirely similar to those in the porphyritic quartz with 
 cubic and opaque body. In some cases three small opaque 
 masses were found in one inclusion. 
 
 At Metcalf the granite close to the porphyry is greatly shat- 
 tered and cemented by veinlets of quartz with scattered and 
 minute foils of specularite and occasionally some pyrite. The 
 quartz of the granite has the usual fluid-inclusions mentioned 
 above. The cementing-veinlets of granular quartz are full of 
 remarkably beautiful and fairly large (up to 0.02 mm.) inclu- 
 sions of the usual rounded or pyramidal-prismatic form. Most 
 of these contain bubble, cube and opaque body. The bubble 
 varies as usual in its relative size ; the cube is sharply defined 
 and of the size described under the inclusions in porphyry. In 
 a few of the inclusions the dark bodies are unusually large and 
 have a rounded flat form ; they are here translucent with red- 
 dish color, and there can be little hesitation in identifying them 
 as ferric oxide or specularite. In some inclusions small grains 
 or crystals, beside the cube, and occasionally transparent matter 
 adhering to the wall, are also found. All this shows that 
 the same or very similar solutions, which formed a part of the 
 magma, deposited quartz in the immediately surrounding rock 
 or in the solidified porphyry itself. It is clear that these solu- 
 
550 GENESIS OF THE COPPER-DEPOSITS OF CLIFTON-MORENCI. 
 
 tions must have been very hot and probably also under great 
 pressure, since they held dissolved not only much larger quan- 
 tities of salt than can be taken up by water at ordinary tem- 
 perature, but also a substance, which probably is ferric oxide, 
 entirely insoluble under ordinary conditions. This directly 
 connects the solutions contained in the magma with those 
 which deposited quartz shortly after the intrusion and shows 
 that the general quartz-cementation which occurred, closely 
 following the consolidation of the magma, is probably not due 
 to atmospheric waters, but to eruptive after-effects. 
 
 In the next place, the strong pyritic, primary fissure-veins 
 were examined, which cut across both porphyry and metamor- 
 phosed limestcme at Morenci. They are associated with a little 
 normal, coarsely crystalline, vein-quartz. Specimens from the 
 Montezuma vein from different places showed typical vein- 
 quartz full of fluid-inclusions, either irregularly arranged or in 
 places following certain planes in the grains. The quartz- 
 grains often show cry stall ographic outlines, are occasionally 
 speared by smaller quartz-prisms and are associated with a few 
 large irregular grains of pyrite. Though some of the inclu- 
 sions are irregular, the majority have rounded outlines, more 
 seldom bi-pyramidal. The size ranges up to 0.012 mm. The 
 relation of bubble and cavity is not constant; many inclusions 
 are empty, no doubt due to leaking, for the quartz is consider- 
 ably crushed. No change is apparent upon heating the slide 
 to 40 and even to 80 C. Almost always the inclusion con- 
 tains solid bodies. Cubes, so abundant in the porphyries, are 
 of rare occurrence and seldom well-developed. Most frequent 
 are transparent adhesions to the wall, rod-like masses, pyra- 
 midal crystals, or irregular grains. None seem to act on 
 polarized light, possibly on account of the minute size. In 
 most cases the inclusions also contain one or two minute opaque 
 bodies, which cannot be further determined. In a few inclu- 
 sions the solid material is so abundant as to cause the bubble 
 to assume an elongated form. 
 
 Entirely similar inclusions are found in the quartz of the 
 Humboldt vein, occurring as branching-veinlets in porphyry. 
 
 The granite along Chase creek, half a mile above the foot of 
 the Longfellow incline, contains many quartz-veins with pyrite r 
 chalcocite and molybdenite. The quartz contains fluid-inclu- 
 
GENESIS OF THE COPPER-DEPOSITS OF CLIFTON-MORENCI. 551 
 
 sions, though many of the cavities are empty. Most of the in- 
 clusions contain some solid material ; a few of these are imper- 
 fect cubes ; most common are transparent adhesions to the 
 walls, while many also contain opaque bodies. 
 
 These observations indicate that the quartz in the fissure- 
 veins was formed in the presence of aqueous solutions of prob- 
 ably several salts. The cubes, so prominent in the porphyry 
 and in some probably earlier veinlets of quartz, seem to be 
 less uniformly present in those of the regular veins. It also 
 follows that the solutions were very hot, for they contained a 
 much larger proportion of salts than can be dissolved at ordi- 
 nary temperature or even at -j- 100 C. The opaque bodies 
 indicate that some combination of the heavy metals was also 
 present in the waters. 
 
 The quartz-veinlets, connected with the processes of forma- 
 tion of chalcocite and of copper carbonates, contain only few 
 and small inclusions, in which, thus far, nothing but the fluid 
 and the bubble have been observed. 
 
 SUMMARY OF GENESIS. 
 
 It has been shown that the intrusions of stocks and dikes of 
 granite-porphyry and quartz-monzonite porphyry, which took 
 place in late Cretaceous, or early Tertiary times, produced an 
 important contact-metamorphism in shales and limestones of 
 Paleozoic age, which happened to adjoin them. This meta- 
 morphism resulted in metasomatic development of garnet, epi- 
 dote, diopside, and other silicates, accompanied by pyrite, mag- 
 netite, chalcopyrite, and zinc-blende. The sulphides are not 
 later introductions, but contemporaneous with the other contact 
 minerals. 
 
 The contact-zone received' very substantial additions of 
 iron oxides, silica, sulphur, copper, and zinc, enough to form 
 good-sized deposits of pure magnetite and low-grade deposits 
 of chalcopyrite and zinc-blende, all of which are entirely un- 
 known in the sedimentary series away from the porphyry. 
 
 In view of the evidence, I consider it impossible that circu- 
 lating atmospheric waters have effected these changes. The 
 occurrences of metamorphosed rocks are manifold and found 
 under many varying conditions; there is only one common fac- 
 tor and that is the presence of the porphyry. It is shown that 
 
552 GENESIS OF THE COPPER-DEPOSITS OF CLIFTON-MORENCI. 
 
 the porphyry magma contained much water which held dis- 
 solved various salts, among them some of the heavy metals. 
 Sodic chloride and ferric oxide prohably predominated. I be- 
 lieve that it contained all of the substances mentioned above, 
 and that large quantities of this gaseous solution (for the criti- 
 cal temperature must have been exceeded) dissolved in the 
 magma were suddenly released by diminution of pressure as 
 the magma reached higher levels, and forced through the ad- 
 joining sedimentary beds ; the purest and most granular lime- 
 stones suffering the most far-reaching alteration and receiving 
 the greatest additions of substance. It is thus held that a di- 
 rect transfer of material from cooling magma to adjacent sedi- 
 ments took place. The formation of garnet indicates large 
 gains of ferric oxide and silica. If the magmatic waters car- 
 ried iron only as ferric oxide some of it must have been reduced 
 to magnetite during the metamorphism, for the latter mineral 
 is much more common than the specularite. These contact 
 metamorphic deposits often occur at the immediate contact 
 of the main porphyry stock and the limestones. But more 
 commonly they seem to be connected with dikes of the same 
 porphyry close to the principal mass, these dikes being proba- 
 bly more highly charged with magmatic waters. 
 
 It is shown that fissures and extensive shattering developed 
 both in porphyry and altered sediments after the congealing of 
 the magma, and that these fissures and seams were cemented 
 by quartz, pyrite, chalcopyrite, and zinc-blende ; forming nor- 
 mal veins largely of the type of replacement-veins. The amount 
 of copper contained in these is usually small, though in places 
 possibly large enough to form pay-ore. The bulk of the veins 
 consists of pyrite. Two classes of veins may be distinguished. 
 The usual type is practically always connected with granite- 
 porphyry or quartz-monzonite porphyry ; it occurs in this rock 
 or along dikes of the same. The smaller division consists of 
 those connected in their occurrence with diabase dikes. The 
 genesis of the former type will first be discussed. 
 
 As far as the metallic minerals are concerned there is a 
 striking similarity between the veins connected with porphyry 
 and the contact-metamorphic deposits, the only difference being 
 in the magnetite, which does not occur in the veins proper and 
 only subordinately in certain of the altered wall-rocks. A rela- 
 
GENESIS OP THE COPPER-DEPOSITS OF CLIFTON-MORENCI. 553 
 
 tionship is also clearly seen in the remarkable action of the 
 vein-solutions on the adjoining wall-rock wherever this is lime- 
 stone, tremolite and diopside being formed in it by replace- 
 ment. On the whole, iron and silica are the main substances 
 added, during contact-metamorphism, as well as during the 
 vein-formation. 
 
 A study of the fluid-inclusions in the vein-quartz proves con- 
 clusively that the veins were formed by aqueous solutions and 
 that these solutions were at a high temperature, for they con- 
 tained various salts, in part, those of heavy metals, probably 
 iron, which have separated out during the cooling of the crys- 
 tallized quartz. This entirely eliminates the possibility of de- 
 position by cold surface-waters and points to two or three even- 
 tualities. Deposition by atmospheric waters heated by contact 
 with the cooling porphyry, or deposition by ascending mag- 
 matic waters, or, finally, by a mixture of both. In any case the 
 metals must be derived from the porphyry, or from deep-seated 
 sources below the porphyry, for, as stated above, the presence 
 of porphyry is the only common factor in all occurrences. It 
 is clear that a positive solution of these problems must be most 
 difficult, but, here again, the fluid-inclusions offer the only di- 
 rect evidence. In the quartz-seams penetrating the granite 
 near the porphyry-contact at Metcalf, inclusions were found 
 which are indistinguishable from those characteristic of the 
 quartz-phenocrysts in the porphyry, and it must be concluded 
 that the same highly heated and highly charged solutions 
 were -active in both cases. This directly connects some of 
 the probably earlier quartz-veins with magmatic water and 
 is evidence of considerable importance. The vein-quartz of 
 Morenci contains inclusions which, in some cases, are identical 
 with those in the porphyry, and in other cases slightly different 
 from them, but always indicate highly heated solutions. The 
 metasomatic action of the waters proves them to have been rich 
 in silica and various salts, among them some of the heavy 
 metals, but entirely deficient in carbon dioxide. Considering 
 this evidence, together with the similarity of the products of 
 these processes with those of contact-metamorphism,! think it 
 certain that parts of the mineral solutions were directly derived 
 from and formed part of the porphyry magma, and I believe it 
 is probable that they were entirely derived from this source. 
 
 35 
 
554 GENESIS OF THE COPPER-DEPOSITS OF CLIFTON-MORENCI. 
 
 It seems likely, that the fissuring, which took place after the 
 cooling, opened vents of escape for magmatic waters under 
 heavy pressure at lower levels, and that they ascended on these 
 fissures depositing the heavy metals and the silica and acquir- 
 ing at the same time carbon dioxide from the sediments which 
 they traversed. 
 
 As to the depth at which deposition took place, no positive 
 evidence is available on account of lack of data concerning the 
 extent of erosion. But from stratigraphic consideration, it is 
 not likely that the depth from surface was more than two or 
 three thousand feet. The cause of the deposition was no doubt 
 a decrease in temperature, just as the deposits are formed in 
 the cooled fluid-inclusions. I think it likely that, in most 
 cases, the solutions were present as liquids, for, assuming that 
 the waters communicated with the surface, neither pressure nor 
 temperature could have been high enough to reach the critical 
 point. Probably this does not matter very much, for the proper- 
 ties of water appear to be very similar for some distance each 
 side of this point. Copper, iron and zinc are practically the only 
 important metals present in the main deposits close to the main 
 porphyry stock ; but it is interesting and suggestive to note 
 that gold begins to appear in veins which are located some dis- 
 tance away from the central porphyry. 
 
 The veins connected with diabase dikes are few in number, 
 and the opportunity for their study has been limited. It seems 
 risky, therefore, to express a definite opinion on their genesis, 
 except that the copper and iron sulphides in all probability were 
 derived from the diabase itself, either by means of magmatic or 
 heated atmospheric waters. 
 
 The deposits thus far described are, in general, of low-grade, 
 only rarely containing enough copper to be classed as econom- 
 ically important. Those in shale or limestone consist of dis- 
 seminated sulphides, in places irregularly concentrated, or accu- 
 mulated along certain strata, according to the well-defined tend- 
 ency of contact-metamorphism. Those in porphyry consist of 
 heavy veins of pyrite and a small amount of other sulphides, 
 surrounded by zones of dissemination of the same sulphides. 
 
 It remained for the surface-waters, as erosion gradually ex- 
 posed the deposits, to alter and enrich them in manifold forms. 
 
 From the evidence presented above, it must be concluded 
 
GENESIS OF THE COPPER-DEPOSITS OF CLIFTON-MORENCT. 555 
 
 that some of the deposits, especially the fissure-veins, were laid 
 bare by erosion, and attacked by surface-waters at an early 
 date, probably before the principal faulting-movement, and 
 certainly before the eruption of the Tertiary basalts and rhyo- 
 lites. Oxidation has thus acted on them for a very long period. 
 
 The irregular and tabular deposits of oxidized ore in lime- 
 stone and shale have been formed, partly by direct oxidation 
 of sulphides and partly by the influence of sulphate solutions 
 derived from widely disseminated chalcopyrite due to contact- 
 metamorphism ; a great enrichment has taken place, due to 
 decrease of volume and addition of copper from the circulating 
 sulphate solutions. Some of the oxidized deposits in shale, how- 
 ever, may be wholly due to adsorption, exerted by the kaolin in 
 the shale on these sulphate solutions. 
 
 In the veins, and especially in those which traverse the por- 
 phyry stock, or follow porphyry dikes, the history is more 
 complicated. It has been shown that oxidation dates back 
 to Tertiary times, and that the water-level then was con- 
 siderably higher than it is at the present time. By action 
 of descending sulphate solutions on pyrite, chalcocite was 
 deposited very extensively, and very likely the great ver- 
 tical extent of the chalcocite-zone, ordinarily from 200 to 
 500 ft., is due to slow and gradual changes in the water- 
 Jevel. Disintegration and erosion removed the iron-cap (the 
 products of direct oxidation of the primary vein) and began to 
 oxidize the exposed chalcocite-zone. In practically all of the 
 veins, the surface-zone of poor ore is due to the direct oxi- 
 dation of chalcocite. The solutions from this part descend and 
 add richness to the upper part of the remaining chalcocite- 
 zone. But at the present low stand of the water-level, and the 
 exceedingly dry climate, the lower limit of the chalcocite-zone 
 is probably almost stationary. 
 
 The copper-deposits of Clifton and Morenci are thus believed 
 to have been formed primarily by mineral-laden magmatic 
 waters, partly acting as gas and partly as liquids, and in 
 both cases derived from a magma of granite-porphyry. These 
 solutions were evidently directly released from the magma 
 without a preliminary concentration in pegmatitic or aplitic 
 dikes, which, indeed, do not occur in this district in association 
 with the porphyry. It is perhaps superfluous to emphasize 
 
556 GENESIS OF THE COPPER-DEPOSITS OF CLIFTON-MORENCI. 
 
 that these conclusions are not generalizations, and that this mode 
 of origin is not necessarily that of all other metalliferous veins. 
 The earlier processes of magmatic origin produced low-grade 
 deposits of pyritic ores, and the final concentration to payable 
 ore-bodies has chiefly been effected by descending and oxidiz- 
 ing surface-waters of atmospheric origin. 
 
 GENETIC CLASSIFICATION. 
 
 The following scheme of genetic classification of the deposits 
 is presented : 
 
 I. FIRST EPOCH. Formed during the consolidation of porphyry 
 
 by laterally moving water-gas. 
 
 a. Contact metamorphic deposits. Irregular or tabular dis- 
 seminations in shale or limestone, sometimes fol- 
 lowing stratification planes or dike contacts. Ores 
 consist of pyrite, chalcopyrite, zinc-blende and mag- 
 netite. Generally unpayable. 
 
 II. SECOND EPOCH. Formed shortly after the consolidation of 
 
 the porphyry by ascending hot, magmatic waters. 
 Continued on porphyry, granite or more or less 
 altered sedimentary rocks. 
 
 a. Fissure-veins. Lode-systems or single veins. Cen- 
 
 tral seams of pyrite, chalcopyrite and zinc-blende 
 accompanied by wide zones of sericitization and 
 pyritization of the porphyry. Generally unpayable. 
 
 b. Stock-werks and irregular disseminations. Same charac- 
 
 ter of mineralization. Unpayable. 
 
 III. THIRD EPOCH. Fissure-veins formed by ascending-waters 
 
 shortly after the intrusion of diabase. 
 
 IV. FOURTH EPOCH. Deposits formed by descending atmos- 
 
 pheric waters acting on Classes I., II. and III. 
 
 a. Concentrations by direct oxidation and secondary chalco- 
 
 cite-dcposition in type I. Payable. 
 
 b. Concentrations by direct oxidation and secondary chalco- 
 
 cite-deposition in type Ila. Payable. 
 
 c. Concentrations by direct oxidation and secondary chalco- 
 
 cite-deposition in type lib. Payable. 
 
 d. Deposits caused by sulphate-waters along otherwise barren 
 
 fault-planes. Occasionally payable. 
 
 e. Deposits caused by sulphate-waters along shale beds. 
 
 Partly payable. 
 
COPPER-DEPOSITS AT SAN JOSE, TAMAULIPAS, MEXICO. 557 
 
 No. 20. 
 The Copper-Deposits at San Jose, Tamaulipas, Mexico. 
 
 BY J. F. KEMP, NEW YORK, N. Y. 
 
 (Washington Meeting, May, 1905. Trans., xxxvi., 178). 
 CONTENTS. 
 
 PAGE 
 
 I. Introduction, .... ....... 557 
 
 1. Situation, . . .557 
 
 2. Geology, . ... .559 
 
 IL Eruptive Rocks, v. . . . . . 561 
 
 1. Deep-Seated Eruptives, . . ... . . . 562 
 
 (a) Nephelite-Syenite, . . . . . . .562 
 
 (b) Gabbro, . ..."..". . . . .563 
 
 2. Laccolith, . . ' .~ . . . ' . .' . . . .563 
 
 3. Dikes, . , .. . ' . . , . . j. . .565 
 
 (a) Tinguaite, . . . . . . '. . . 565 
 
 (b) Camptonite, . .. . . . ..... 566 
 
 (c) Vogesite, . . .' . ' . . . ^, '* .567 
 
 (d) Olivine-Basalt, . - . . . ". . . .. .567 
 
 4. Surface-Flow, '., . k . . ... . . '. .567 
 
 (a) Basalt, . . . ...'.. . .567 
 
 III. Contact- Effects, . . .... . . . .567 
 
 IV. Genetic Conclusions, . ' . . . . . . . . . 574 
 
 1. Recrystallization Process, . . / . ... . .. 575 
 
 2. Absorption Process, * . . . . . . .579 
 
 3. Process by Contributions from the Eruptive, . . . , . 579 
 
 4. Oxidized Ores, . . . '. . . ' .. . . 581 
 
 I. INTRODUCTION.* 
 
 1. Situation. From Monterey in the State of Nuevo Leon, 
 the Sierra Madre mountains stretch away to the southeast and 
 present a steep front to the northeast. The Monterey and Mexi- 
 can Gulf railway, which connects Monterey with Tampico, fol- 
 lows their general line with its road-bed a few miles out from the 
 foothills. At a distance of 100 miles from Monterey it passes 
 through the town of Linares, and from Linares one can see far 
 away to the southeast the peaks of another group of mountains 
 
 * For much assistance and cordial interest in the preparation of this paper, I de- 
 sire to express my acknowledgments to E. D. Self, General Manager of the mines 
 at San Jose, and to W. H. Nichols, Jr., President of the San Carlos Copper Co. 
 
558 COPPER-DEPOSITS AT SAN JOSE, TAMAULIPAS, MEXICO. 
 
 rising from the general plateau and forming a more eastern 
 uplift distinct from the main mountain system. The outlying 
 group is the San Carlos range, and is one of extreme geoldgical 
 interest because of its nephelite-syenites and rare types of 
 associated eruptives. These have been recently described by 
 George I. Finlay, 1 who was my companion during the trip 
 upon which the observations for the present paper were made. 
 The San Carlos mountains extend east and west, and are about 
 15 miles long. Their highest point, Pic de Diablo, which is 
 just south of San Jose, has been determined by aneroid to be 
 
 FIG. 1. MAP OF NORTHEASTERN PART OF MEXICO, THE CIRCLE SHOWING THE 
 LOCATION OF THE SAN JOSE DEPOSITS. 
 
 6,000 ft. above sea-level. The peaks are rugged, and have pre- 
 cipitous escarpments, surrounding inner amphitheaters. They 
 are clothed with a noble growth of pines in the upper portions 
 and receive enough precipitation to support a number of 
 brooks, which, however, except in the wet season or imme- 
 diately after heavy storms, are lost in the gravel of the arroyos 
 below. The range soon dies out to the east of San Jose. Its 
 main mass lies to the south. 
 
 1 The Geology of the San Jose District, Tamaulipas, Mexico,. J.wia/s of the New 
 York Academy of Sciences, vol. xiv., pp. 247 to 318 (1901-03). 
 
COPPER-DEPOSITS AT SAN JOSE, TAMAULIPAS, MEXICO. &59 
 
 San Jose, the little town where the copper-mines are located, 
 is situated in a valley on the northern side of the mountains. 
 Its arroyo leads out to the northeast, and the pass to the south 
 goes around the eastern extremity of the nephelite-syenite, over 
 a divide, and south to the town of San Carlos. San Jose is 
 about 40 miles from Linares, with which it is connected by a 
 good road across a plain covered with the familiar growths 
 of cactus and mesquit, so characteristic of northern Mexico. 
 The construction of a railway between San Jose and Linares is 
 nearly finished. 
 
 2. Geology. From Linares to San Jose the country-rocks are 
 generally concealed by the soil, but at the ford over the creek 
 near Pretil shales are to be seen, in which a brief search failed 
 to reveal fossils. As one nears the mountains, however, heavy 
 strata of limestone rise gradually until the road follows the 
 arroyo in a quite narrow canyon with cliffs on either side. 
 Finally, having crossed the strata of outwardly-dipping lime- 
 stone, the town of San Jose is met, resting upon the carved and 
 eroded remains of a great exposure of eruptive rock. 
 
 Detailed study shows, however, that the eruptive area is 
 surrounded on all sides, except the south, by the limestones, 
 which rest upon the porphyry and dip away outwardly. There 
 is no doubt, therefore, that we have to do with an eroded lac- 
 colith of eruptive rock, which has heaved up the limestones 
 into their present positions and which has been cut off on the 
 south by the nephelite-syenite, probably along a fault. These 
 features are shown on the geological map, Fig. 2, reproduced 
 with a few modifications from Dr. Finlay's paper, in which it 
 forms Plate VIII. 
 
 The altitude of the village of San Jose is approximately 
 2,250 ft. above sea-level. The hills of porphyry within the 
 laccolithic valley rise from 500 to 600 ft. higher, are steep, and 
 obviously present what the physiographers call a young topog- 
 raphy. A bore-hole sunk since my visit shows the laccolith to 
 be over 1,000 ft. thick at the Santo Domingo mine. The sur- 
 rounding ridge of limestone and on the south the syenite reach 
 the elevations marked on the map at the several stations. The 
 limestone rim thus rises at its lowest summit 750 ft. above the 
 valley, and at its maximum 1,550, while the nephelite-syenites 
 attain heights of from 2,500 to 3,000 ft., and at the Pic de 
 Diablo (not shown on the map) 3,750 ft. above it. 
 
560 COPPER-DEPOSITS AT SAN JOSE, TAMAULIPAS, MEXICO. 
 
 GKEOLOGICA.L IMAiP 
 OF THE 
 
 SAN JOSE DISTRICT 
 
 TAMAULIPAS, MEXICO 
 
 FIG. 2. GEOLOGICAL, MAP OF THE SAN JOSE DISTRICT. 
 
COPPER-DEPOSITS AT SAN JOSE, TAMAULIPAS, MEXICO. 561 
 
 The limestone is a rather fine-grained bluish variety, where 
 it has not been exposed to contact-metamorphism. It is be- 
 lieved to be Cretaceous and to belong to the very thick forma- 
 tion which is such a prominent feature of northeastern Mexico. 
 It is almost entirely devoid of fossils. I only succeeded in 
 finding one poorly-preserved belemnite and one larger form 
 resembling an Exogyra, the latter in a rock altered to a white 
 marble by the neighboring eruptive. R. T. Hill has reported 
 that a formation probably the same with this limestone, but 
 .in the valley of the Miquehuana, which is west of Victoria and 
 southwest from San Jose, though still in the State of Tamauli- 
 pas, is 20,000 ft. thick. 2 As many earlier observers have re- 
 marked, the limestone most closely resembles in its appearance 
 the Palaeozoic limestones of the eastern United States and es- 
 pecially the Siluro-Cambrian ones of the Great Valley, which, 
 like the Mexican occurrence, are singularly lacking in fossils. 
 Near San Jose we have neither the top nor the bottom of the 
 series, but there are certainly from 1,000 to 2,000 ft. exposed. 
 The limestone is well bedded and it at times contains streaks of 
 black flint or chert. From the central eruptive area it dips 
 radially outward and is therefore in the form of the great eroded 
 dome, so characteristic of laccolithic intrusions. On the south, 
 however, where the mountains of nephelite-syenite cut off the 
 limestone, this structure does not hold, and it is believed that 
 the nephelite-syenite was elevated by faulting before the intru- 
 sion of the laccolith. 
 
 II. ERUPTIVE ROCKS. 
 
 The eruptive rocks are of exceptional scientific interest be- 
 cause of the rare types represented. They will be briefly de- 
 scribed in their order of age from the oldest to the latest, so 
 far as the succession can be made out. The following varieties 
 are present : Irregular masses of nephelite-syenite and gabbro ; 
 the laccolith of diorite-porphyry ; about 50 dikes in all -of tin- 
 guaite, diabase, camptonite, and vogesite ; finally a surface-flow 
 of basalt. While some of these names are not generally famil- 
 iar, a few explanatory sentences under each, as taken up below, 
 will serve to tie them up to varieties which have long been 
 well established. 
 
 2 K. T. Hill. The Cretaceous Formations of Mexico, etc. , American Journal of 
 Science, Third Series, vol. xlv., No. 268, p. 309 (April, 1893). 
 
562 COPPER-DEPOSITS AT SAN JOSE, TAMAULIPAS, MEXICO. 
 
 1. Deep-Seated Eruptives. 
 
 (a) Nephelite-Syenite. The oldest of the eruptives is the nephe- 
 lite-syenite which constitutes the high peaks to the south. It 
 is a rather coarsely crystalline rock, which for all practical pur- 
 poses may be likened to a granite. It is a peculiar variety of 
 syenite in that it contains the mineral nephelite. The rock is 
 sometimes nearly pure feldspar and nephelite, and is light in 
 color. Again, it has, with these two, more and more black 
 hornblende and pyroxene, until it becomes dark gray. Almost 
 always honey-yellow titanites are visible to the eye. The sev- 
 eral varieties have been fully described by Dr. Finlay. 
 
 The following chemical analysis, made by Dr. Henry S. 
 Washington, illustrates the composition of one of the varieties : 
 Si0 2 , 58.40; A1 2 O 3 , 20.25; Fe 2 s , 1.78; FeO, 2.41 ; MgO, 0.49; 
 CaO, 3.11; Na 2 0, 7.01; K 2 0, 5.39; H 2 (110), 0.27; H 2 
 (ign.), 0.57; Ti0 2 , 0.25; P 2 6 5 , 0.20; S0 3 , 0.06; C1 2 , 0.2; total, 
 100.21 per cent. This shows a typical nephelite-syenite rich in 
 feldspar. Dr. Finlay estimated the percentage-composition of 
 the several minerals by measuring areas in thin sections, and, 
 for three varieties of the rock, his results, showing the in- 
 creasing amounts of the dark silicates, are as follows : 
 
 Percentage Percentage Percentage 
 
 of Areas. of Areas. of Areas. 
 
 Orthoclase 60.0 12.0 5.6 
 
 Plagioclase 5.0 
 
 Nephelite 25.0 18.0 13.2 
 
 Augite 1.0 23.0 13.9 
 
 Hornblende 40.0 60.5 
 
 Biotite 2.2 
 
 Magnetite 8.0 2.7 0.4 
 
 Titanite 0.7 2.0 2.8 
 
 Apatite 1.2 1.4 
 
 Total 99.7 98.9 100.0 
 
 Average size of grain 0.36mm. 0.2mm. 0.16 mm. 
 
 The coarsely crystalline texture of the syenite proves it to 
 be a rock which has consolidated far below the surface, slowly 
 and under pressure. Its present elevated position is believed 
 to be due to faulting, as earlier stated. It is older than the 
 porphyry, but whether it is older than the limestones was not 
 determined, because in no place could the two be found in con- 
 
COPPER-DEPOSITS AT SAN JOSE, TAMAULIPAS, MEXICO. 563 
 
 tact. Whether, therefore, the syenite formed an old land-area 
 and shore along which the limestones were laid down on the 
 sea-bottom, or whether it was intruded into them and later 
 faulted into its present position, we do not know. It is possi- 
 ble, however, that the question could be solved at the western 
 end of the range. 
 
 (b) Gabbro. This rock was found in three places, two near 
 each other and mapped as one along the road from San Jose to 
 the Yegonia mine, and one in a gulch northwest of the village. 
 Recent work has shown the former to be somewhat more ex- 
 tensive than is given on the map. The exposures are deeply 
 weathered and rusty brown. The fresh specimens are grani- 
 toid in texture, medium grained and dark gray. The constitu- 
 ent minerals are plagioclase, biotite, augite, titanite, magnetite, 
 apatite, pyrite, and zircon. This rock was called a diorite by 
 Dr. Finlay on account of its moderately acidic feldspar, but in 
 order to be clear to readers more especially familiar with rock- 
 names employed in mining-districts, and on account of the pre- 
 ponderating augite, it is here called gabbro. The analyses 
 of slightly differing varieties, made by Dr. Finlay, are : Si0 2 , 
 45.75 (48.49); A1 2 3 , 18.51 (18.99); Fe 2 3 , 6.55 (9.59); FeO, 
 6.02 (1.00); MgO, 5.06 (5.05); CaO, 11.85 (10.78); JSTa 2 O, 3.41 
 (3.47); K 2 0, 2.35 (1.42); ^a 2 0, trace (nil); H 2 (100), 0.06 
 (0.10); H 2 O (ign.), 0.20 (0.55); total, 99.76 (99.44) per cent. 
 
 These analyses show the rock to be a rather basic variety, 
 but one which does not differ in any extraordinary degree from 
 those of many gabbros. The syenite and gabbro are two char- 
 acteristically deep-seated rocks. 
 
 2. The Laccolith. 
 
 The next in order of formation is the rock constituting the 
 laccolith, which is here described under the general name 
 diorite-porphyry. This eruptive combines the features of a 
 deep-seated rock with those of a dike or sheet. It is visibly 
 porphyritic, but the ground-mass, as often happens in lacco- 
 lithic types, is subordinate and it may almost, if not quite, dis- 
 appear. The rock therefore shades texturally into a very feld- 
 spathic diorite, and in the diamond-drill cores and some of the 
 deeper exposures it can with difficulty be separated, by the eye 
 alone, from the whiter varieties of syenite. The rock is named 
 
564 COPPER-DEPOSITS AT SAN JOSE, TAMAULIPAS, MEXICO. 
 
 in accordance with the underlying conception that igneous 
 varieties belonging to the andesite-diorite series vary from glassy 
 and felsitic surface-flows of true typical andesites; through 
 porphyritic varieties with increasingly abundant phenocrysts, 
 the andesite-porphyries of the dikes and sheets, on through 
 those with less and less ground-mass, the diorite-porphyries, 
 in laccoliths and stocks, to the granitoid diorites in the batho- 
 liths and deep-seated masses. As the phenocrysts are very 
 abundant and the ground-mass almost disappears in most of the 
 exposures of the laccolith, diorite-porphyry best describes the 
 rock. The name andesite was used by Dr. Finlay, and while I 
 regard with misgivings any change in a nomenclature already, 
 although unavoidably, confusing, the term " diorite-porphyry " 
 is coincident with the usage of Whitman .Cross in the folios and 
 papers on the San Juan region of Colorado, where analogous 
 laccoliths occur in many mining-districts. It is hoped that it 
 will therefore be most significant to readers interested in min- 
 ing-geology. 
 
 The diorite-porphyries are light yellow to bluish gray in color 
 and vary by insensible gradations from more basic to more 
 acidic facies. They contain plagioclase, orthoclase, augite, bio- 
 tite, magnetite, titanite, zircon, and at times quartz in consid- 
 erable quantity. The ground-mass is fully crystallized and the 
 contrasts are much less between it and the phenocrysts than 
 are usually seen in surface-flows. But this relation always 
 holds in the laccoliths and intruded sheets, as all observers are 
 well aware. 
 
 An analysis, made by Dr. Finlay, gave the following results r 
 Si0 2 , 62.31; A1 2 3 , 18.63; Fe 2 3 , .2.38; FeO,1.33; MgO, 0.60; 
 CaO, 5.91 ; ^a 2 0, 4.97 ; K 2 0, 3.52 ; P 2 5 , 0.07 ; H 2 0(110), 0.16 ; 
 H 2 (ign.), 0.07; total, 99.98 per cent. 
 
 This analysis indicates a rather acidic variety. Column I. of 
 the analyses on the following page gives the percentage-com- 
 position of the several minerals obtained by recasting the anal- 
 ysis. Column II. gives the percentage-composition of a still 
 more acidic variety, a dacite-porphry, obtained by measuring 
 the diameters of the minerals in thin sections. 
 
 No biotite is tabulated under column I., because, although 
 present in very small quantities, its complicated composition 
 prevents its calculation. 
 
COPPER-DEPOSITS AT SAN JOSE, TAMAULIPAS, MEXICO. 565 
 
 Percentage- Composition of a Dacite-Porphyry. 
 
 i. n. 
 
 Per Cent. Per Cent. 
 
 Plagioclase 60.0 32.0 
 
 Orthoclase 20.6 25.0 
 
 Pyroxene 6.6 16.0 
 
 Magnetite 3.5 6.7 
 
 Quartz 8.9 17.0 
 
 Biotite 2.4 
 
 Accessories 0.9 
 
 Total 99.6 100.0 
 
 The diorite-porphyry is the most important rock connected 
 with the ore-formation, since it has produced the garnet-zones 
 and has apparently occasioned the introduction of the ore, as 
 will be later described. Messrs. Aguilera and Ordonez, who 
 have published a short note about the rock and its contact-zones, 
 speak of it as an andesitic diorite. 3 
 
 Where exposed near the contact-zones, the diorite-porphyry 
 is at times supplied with pyrite which appears throughout the 
 rock and which follows the innumerable tiny fissures ramifying 
 through it in every direction. 
 
 The diorite-porphyry is found in the great laccolithic mass 
 and also as innumerable dikes, penetrating the gabbro and es- 
 pecially the limestone, where the latter has been opened up in 
 the mines. It constitutes the greater part of the San Jose 
 valley, its unbroken extent being chiefly prevented by the in- 
 clusions of limestone, which resemble islands in the midst of 
 the eruptive mass. 
 
 It may be that there is more than one intrusion of the dioritic 
 rock. Considerable range in mineralogy is exhibited; and 
 while no positive field-evidence could be secured, and while the 
 amount of the varieties must be small as compared with the 
 main mass, yet the possibility may be considered. 
 
 The diorite-porphyry is later in age than the gabbro, since it 
 cuts the latter in dikes. It is also later than the syenite, since 
 along the contacts it shows the effects of chilling and becomes 
 denser. 
 
 3. Dikes. 
 
 (a) Tinguaite. Dikes of this interesting rock cut the diorite- 
 porphyry in every direction and one in particular runs clear 
 
 3 Bosquejo geologico de Mexico, Boktin del Institute geologico de Mexico, Nos. 4, 
 5,6, p. 222 (1897). 
 
566 COPPER-DEPOSITS AT SAN JOSE, TAMAULIPAS, MEXICO. 
 
 across the valley from limestone-wall to limestone-wall. Tin- 
 guaites are dense, dark-green rocks closely allied to phonolites, 
 but containing the soda-pyroxene segirite in great abundance, 
 together with nephelite and orthoclase. A little plagioclase, 
 titanite, magnetite, and in some varieties a great deal of analcite, 
 complete the list of the minerals. Fine phenocrysts of ortho- 
 clase are sometimes abundant, but again the rock appears as a 
 dense, green, felsitic one, and then has analcite as a rule. 
 
 Two analyses of the analcite-tinguaites, one made by H. 8. 
 Washington, the second by Gr. I. Finlay, are as follows : SiO, 
 52.83(49.42); Ti0 2 , 0.16 (not det.) ; A1 2 3 , 20.70 (22.99); Fe 2 O 3 , 
 2.84 (2.70); FeO, 1.19 (1.89); MgO, 0.41 (0.45); CaO, 1.00 
 (2.59); Is T a 2 0, 9.94 (9.63); K 2 0, 4.97 (4.21); H 2 (110), 0.37 
 (not det.) ; H 2 (ign.), 5.28 (5.73) ; P 2 5 , 0.03 (not det.) ; 01, 0.06 
 (not det); total, 99.62 (99.99) per cent. 
 
 The tinguaite dikes have been intruded after the formation 
 of the ore and the garnet-zones. They cut the latter and are 
 met in several places in the mines. They also appear as far as 
 20 miles away from the syenite, both towards San Carlos and 
 towards Linares. Mr. Self concludes that these dikes become 
 more abundant as one leaves San Jose in each of these direc- 
 tions. In other parts of the world tinguaites have proved to 
 be characteristic associates of nephelite-syenites and it is quite 
 natural that they should occur near San Jose. So far as we 
 know, they do not cut the syenite, but are limited to the sur- 
 rounding rocks. 
 
 (b) Camptonite. In great contrast with the green dikes of tin- 
 guaite are a number, of dark basaltic habit, which display long, 
 black, slender prisms of hornblende on fresh fractures. They 
 proved on microscopic examination to be the basaltic rock 
 whose chief dark silicate and predominant mineral is chestnut- 
 brown hornblende, and which contains also a little augite, pla- 
 gioclose, magnetite, and apatite. An analysis by Dr. Finlay 
 yielded: Si0 2 , 42.49; A1 2 3 , 17.68; Fe 2 3 , 5.12; FeO, 5.90; 
 MgO, 5.28; CaO, 15.81; Na 2 0, 4.29; K 2 0, 2.97; H 2 0, 0.38; 
 total, 99.92 per cent. 
 
 The camptonite is thus a very basic rock. Elsewhere it is a 
 rather characteristic associate of nephelite-syenite and its occur- 
 rence at San Jose is quite in accord with the general rule. 
 
 The camptonites cut the nephelite-syenite, the diorite-por- 
 
COPPER-DEPOSITS AT SAN JOSE, TAMAULIPAS, MEXICO. 567 
 
 phyry, and the limestone. They are also later than the ore. 
 No intersections have' been found which would establish their 
 relative ages as compared with the other dikes. 
 
 (c) Vogesite. A 4.5-ft. dike of this interesting rock has been 
 found, which consists chiefly of orthoclase, hornblende, and 
 augite, but there are also small quantities of magnetite, plagio- 
 clase, titanite, and biotite. It is practically a very basic syenite, 
 of which hornblende makes up the major part of the rock. 
 
 (d) Olivine- Basalt. One other dike of olivine-bearing basalt 
 was found by Dr. Finlay in the syenite area 5 miles south of 
 San Jose. It has, however, no connection with the ores. 
 
 4. Surface-Flow. 
 
 Basalt. There is also a remarkable surface-flow of basalt 
 which comes out of the eastern side of the San Carlos moun- 
 tains, in the syenite area, and extends for 4 or 5 miles down 
 the Arroyo Grande. It is scoriaceous and still not greatly re- 
 duced by erosion. No cone is associated with it and it seems 
 to be a fissure-eruption. It is the last outbreak in the region. 
 The rock is porphyritic and consists chiefly of plagioclase, 
 augite, and magnetite, with smaller amounts of biotite, titanite, 
 and glass. The habit is basaltic. An analysis by Gr. I. Finlay 
 yielded: Si0 2 , 48.03; A1 2 3 , 20.98; Fe 2 O 3 , 7.06; FeO, 4.51; 
 MgO, 4.43; CaO, 9.54; Ta 2 0, 3.28; K 2 0, 1.99; H 2 (110), 
 0.21 ; H 2 (ign.), 0.40 ; total, 100.00 per cent. 
 
 This analysis indicates a quite normal olivine-free basalt. 
 The outbreak had nothing to do with the ores and is 5 or 6 
 miles distant from the nearest mine. 
 
 III. CONTACT-EFFECTS. 
 
 The contact-effects are limited to the borders of the diorite- 
 porphyry and the limestone and they are variable in their in- 
 tensity. The starting-point in their study is the composition 
 of the unchanged limestone, because from this one may infer 
 whether silica and the bases have been added in the meta- 
 morphism or whether we are dealing with the rearrangement 
 and crystallization of materials already in the limestone itself. 
 Samples have been very kindly furnished me by E. D. Self, 
 one from an exposure near the Yegonia claim and the other 
 from a quarry operated for flux at the north side of the lacco- 
 
568 COPPER-DEPOSITS AT SAN JOSE, TAMAULIPAS, MEXICO, 
 
 lithic valley and in the surrounding rim. Both were unaltered 
 blue limestone, resembling very much the usual Cambro-Silu- 
 rian variety so abundant in the Great Valley of the eastern 
 United States. A third sample was taken of a white marble, 
 from the east side of the valley on Armadillos hill. It came 
 from a large mass of limestone, which had been included in 
 the laccolith, and changed to a beautiful, saccharoidal marble. 
 
 Vegonia. Furnace Quarry. Marble. 
 Per Cent. Per Cent. Per Cent. 
 
 Insoluble 5.04 4.31 9.55 
 
 Fe 2 O 3 . A1 2 O 3 0.35 0.95 1.28 
 
 CaCO 3 94.55 93.83 88.92 
 
 MgCO 3 0.58 1.29 0.91 
 
 Total 100.52 100.38 100.66 
 
 These analyses indicate a limestone fairly pure, so far as in- 
 soluble silica or silicates go, and one low in magnesia. It may 
 be queried whether the analyses are representative of the gen- 
 eral rock of the section, where uninfluenced by the eruptives. 
 Broadly speaking, it seems to me that this is probably not far 
 from the truth. There are some beds with chert observed in 
 the field which would run higher in silica, but these are very 
 minor factors in the total. There may be more argillaceous 
 beds, yet any which are markedly shaly failed to impress them- 
 selves upon us, the section presenting a rather strikingly uni- 
 form series of limestones. The analysis of marble shows a 
 higher percentage and it is possible that all of it was indigenous 
 in the original unaltered limestone. This sample came from 
 the specimen holding the still recognizable lam.ellibranch fossil, 
 a type of shell favoring muddy bottoms. We may therefore 
 be prepared to admit in some parts of the limestone section 
 even as much as 10 per cent, of insolubles. Still, as the sam- 
 ple showed recrystallization to marble, and as it gave gelatinous 
 silica, and probably therefore contained wollastonite, it may also 
 be true that some silica had been introduced. At this point, 
 however, it is the purpose to state facts rather than draw con- 
 clusions, and further discussion is postponed to a later page. 
 
 The simplest contact-effect which has been noted is the de- 
 velopment of little bundles of tremolite in a limestone which 
 has scarcely lost its blue color. The specimen was found on 
 the southwestern edge of the laccolith near the Santa Rita 
 
COPPER-DEPOSITS AT SAN JOSE, TAMAULIPAS, MEXICO. 569 
 
 trail. For the production of the tremolite it would not seem 
 necessary to assume the introduction of silica from outside, but 
 rather the recrystallization of what was probably already in 
 the limestone, under the influence of heat, or hot waters from 
 the eruptive. 
 
 The next effect is to change the blue limestone into white 
 marble. This change is the rule, both with and without the 
 further production of garnet or other minerals. Sometimes 
 the change to marble appears to be the only result brought 
 about by the eruptive. The marble is of the usual variety. It 
 has no associated minerals prominently developed and has been 
 produced by the recrystallization of fairly-pure calcium carbo- 
 nate with slight admixture of magnesium carbonate. In one 
 interesting case observed on the eastern side of the valley, and 
 already referred to, a fairly well preserved Exogyra was still 
 recognizable in the marble. 
 
 The most important and extensive contact-effect is the alter- 
 ation of the limestone to garnet and other lime silicates. Many 
 of the hand- specimens which appear to the eye to be only brown 
 garnet are found to be more complex under the microscope. 
 The production of the lime silicates has taken place on a very 
 large scale. Fig. 2 exhibits 65 different exposures. The focus 
 of change is on the hill called Remedies, the summit of which 
 is the mass of magnetite called the Piedra Iman, or loadstone. 
 The contact-zones are also extensive in Reina hill, and in a 
 general course from the Santo Domingo claim through the 
 Bretana and the San Mauricio towards and to the Yegonia. 
 Around the rim, however, although not absolutely lacking, 
 they are much less common. 
 
 The extent of the change varies from scattered nodules of 
 garnet in limestone up to belts and masses many feet across. 
 In most cases they lie along the borders of the limestone and 
 porphyry, but there are occurrences with no visible limestone 
 near, and then the masses of silicates seem to have resulted 
 from the complete alteration of included blocks, torn off by 
 the eruptive. 
 
 The garnet and its associated silicates are occasionally in 
 banded or streaked formation, but more commonly they are 
 quite massive. Small vugs or cavities with crystals exhibiting 
 the rhombic dodecahedron are not uncommon. In larger cavi- 
 
 36 
 
570 COPPER-DEPOSITS AT SAN JOSE, TAMAULIPAS, MEXICO. 
 
 ties well-developed octahedral crystals of pyrite also appear, 
 and all through the cavities and along cracks in the garnet, as 
 well as included in its substance, chalcopyrite and pyrite mani- 
 fest themselves. Some calcite is also occasionally visible in the 
 garnet-zones and, as will be later noted, in two or three places 
 considerable bodies of magnetite have been met, seamed in 
 every direction with chalcopyrite and pyrite. After this gen- 
 eral statement the more detailed discussion of the chemistry 
 and mineralogy may be taken up in connection with the indi- 
 vidual minerals. 
 
 The simplest change in the alteration of the limestone to 
 silicates is the production of wollastonite, CaO,Si0 2 (CaO, 48.3 ; 
 Si0 2 , 51. 7), by the replacement of the C0 2 of the limestone with 
 Si0 2 . This mineral has only been noted in the microscopic 
 way. It shows an aggregate of brightly-polarizing grains, 
 many of which have a well-marked cleavage with parallel ex- 
 tinctions. In many cases the mineral lacks the elongated, 
 fibrous or prismatic character of the usual wollastonite, but the 
 optical and physical properties indicate its identity. 
 
 The next change, which involves the fewest chemical rear- 
 rangements, is the production of diopside, the double bisilicate 
 of lime and magnesia, CaO,Si0 2 , MgO,SiO 2 (CaO, 25.9; MgO, 
 18.5 ; Si0 2 , 55.6), which differs chemically from the wollastonite 
 only in the fact that some magnesia is present with the lime. 
 The replacement of C0 2 with Si0 2 is the only change involved. 
 The reaction is the same as in the case of the tremolite, which 
 has essentially the same chemical composition, but the latter 
 was found in the blue limestone, while the diopside has only 
 been observed in the zones of silicates. One slide revealed it 
 in association with garnet, and calcite. It formed irregular, 
 brightly-polarizing, almost colorless grains, with its character- 
 istic optical properties. The low percentage of magnesia, both 
 in the limestone and in the eruptive, has militated against its 
 extensive production, garnet, which requires no magnesia, tak- 
 ing natural precedence. 
 
 The most widespread and characteristic mineral of the con- 
 tact-zones from limestone is garnet. Garnet is, however, rather 
 a name for a group than for a single species. The group con- 
 sists of orthosilicates involving three molecules of H 4 Si0 4 and 
 having twelve bonds of affinity which are satisfied by three pro- 
 
COPPER-DEPOSITS AT SAN JOSE, TAMAULIPAS, MEXICO. 571 
 
 toxides, such as CaO and FeO ; and by one sesquioxide, such as 
 A1 2 3 or Fe 2 O 3 . By combinations of these, several distinct gar- 
 nets can be made. Thus, 3CaO, Al,0 3 , 3Si0 2 is grossularite,. 
 
 Grossularite. Andradite. 
 
 SiO 4 = Ca. >Si0 4 = Ca. 
 
 e 
 
 \\Si0 4 =Ca. 
 
 the one which has been usually considered to be present in the 
 zones. The fact that the garnets are light brown or pale green 
 has given rise to this impression in the absence of chemical 
 analysis, and upon the basis of the grossularite molecule the 
 inferences about the constitution of the original limestone and 
 development of the zones have usually been reached. Some 
 doubt, however, arose in my mind regarding the correctness of 
 this view and a massive variety was selected for analysis. It 
 was a pale reddish brown in color. The results obtained, in- 
 cluding the molecular ratios, are as follows : 
 
 Per Cent. Molecular Ratios. 
 
 SiO 2 ...................................................... 37.15 619 
 
 A1 2 3 .................................................... 6.98 69 
 
 Fe 2 O 3 ................................................... 19.40 120 
 
 CaO. ...................................................... 32.44 576 
 
 CaCO 3 ................................................... 4.20 
 
 Soluble A 1 2 O 3 , Fe 2 O 3 ................................ 0.43 
 
 Total .............................................. 100.60 
 
 It was found on trial that the sample contained some calcite. 
 It was therefore treated with very dilute hydrochloric acid and 
 from the solution enough lime was obtained to make 4.20 
 CaC0 3 . The solution also yielded 0.43 A1 2 3 , Fe 2 3 , with per- 
 haps a little Si0 2 ; the total was so small that no attempt to 
 separate the constituents was made. No visible magnesia could 
 be precipitated. It is possible that a little manganese was also 
 present in the sample. It was not specially sought. 
 
 If we recast the above analysis so as to determine the rela- 
 tive amounts of the grossularite and andradite molecules, the 
 results are as follows, using respectively the molecular ratios of 
 the alumina and ferric iron as the basis. 
 
572 COPPER-DEPOSITS AT SAN JOSE, TAMAULIPAS, MEXICO. 
 
 Grossularite. 
 3CaO 207 
 
 11.60 
 6.98 
 12.42 
 
 31.00 | 
 
 3CaO 
 
 Andradite. 
 360 
 
 20.10 
 19.40 
 21.60 
 
 61.10 
 
 ALA-. 
 
 69 
 
 Fe.Oo 
 
 120 
 
 3SiO 2 
 
 207 
 
 * ^2^3 
 
 3SiO 2 . 
 
 360 
 
 
 
 
 
 There are not sufficient molecules of the alumina and ferric 
 iron to care for all the silica and lime. The excess of the 
 former is 619 (207 + 360) = 52, corresponding to 3.12 per 
 cent. This would lead one to infer the presence of a little 
 quartz in the sample, or else that in the garnet th'ere was some 
 diopside or wollastonite, both of which contain more silica than 
 does garnet. Yet in any event the amount does not seriously 
 .affect the result. The lime is as follows, 576 (207 + 360) = 9, 
 corresponding to 0.5 per cent. This may be due to the sup- 
 posed diopside or wollastonite, as just stated, or perhaps to 
 error in the analysis. It also is not a serious factor. The 
 chief result of importance, even admitting slight errors in 
 determinations and assumptions, is to establish the relative 
 amounts of the grossularite and andradite molecules. These 
 are to each other as 31 to 61.1, or in percentages grossularite, 
 33.7 ; andradite, 66.3. 
 
 The lime-iron garnet must therefore be esteemed of very 
 great importance in the chemistry of the production of the 
 zones, and theoretical discussions based on the grossularite 
 molecule are open to objection to this extent. The importance 
 of the whole matter lies in its bearing upon the question of the 
 production of the garnet, whether by recrystallization of an 
 impure limestone or by contributions of silica, alumina, and 
 iron from the eruptive to a fairly-pure limestone. This ques- 
 tion will be taken up later. It may be remarked, however, that 
 Waldemar Lindgren 4 also records the presence of the andradite 
 molecule in large amounts in the zones at Morenci, Ariz., 
 although the analyses have not yet been published. 
 
 In association with the garnet is also found vesuvianite, a still 
 more complicated compound, regarding whose exact formula 
 there has been some difference of opinion. Writing it as it is 
 given by F. "W. Clarke, 5 it is HCa 5 ,MgAl 3 ,Si 5 21 , or if we expand 
 
 * The Genesis of the Copper-Deposits of Clifton-Morenci, Arizona, Trans., 
 xxxv., 511 to 550 (1904) ; p. 517, this volume. 
 
 5 Bulletin No. 125, U. S. Geological Survey, p. 25 (1895). 
 
COPPER-DEPOSITS AT SAN JOSE, TAMAULIPAS, MEXICO. 573 
 
 it into a graphic form, which always helps towards a clear under- 
 standing, the following is obtained : 
 
 H Al = 
 // 
 Al 
 
 Si0 = Ca. 
 
 The vesuvianite, as compared with the other minerals, only 
 involves the addition to the limestone of the same silica, alumina, 
 and ferric oxide, together with hydroxyl or hydrogen ; and both 
 of the last named could easily be supplied by steam, conceiv- 
 ably dissociated under the pressures and temperatures attendant 
 on igneous intrusion. The vesuvianite has been observed in 
 one rare instance extending out as a small vein, 1 in. wide by 4 
 in. long, into the limestone, as if it had been formed on either 
 side of a small crack by the introduction of the elements needed 
 to change over the neighboring limestone. In the general 
 mass of the contact-rock the microscopic examination has not 
 indicated that it is frequent. 
 
 Of the other silicates, epidote, zoisite, biotite, albite, anorthite, 
 etc., which are sometimes met in limestone-contacts, no occur- 
 rences have been noted. 
 
 Magnetite is a contact-mineral locally developed in irregular 
 masses, which are of very considerable size. On the borders 
 there are intermingled garnet and diopside, and throughout 
 the magnetite are abundant veinlets of chalcopyrite and pyrite, 
 but sections of the magnetite exhibit practically no transparent 
 minerals. One prominent outcrop gave the name Piedra Iman, 
 or loadstone, to the summit of Remedies hill. A large mass 
 has been opened in the Santa Elena claim. 
 
 The magnetite must have been introduced in the same way 
 as have the silica and alumina which have developed the sili- 
 cates. The iron oxide has probably replaced the limestone and 
 has thus formed local contact-masses different from the usual 
 type. So far as the available evidence goes, the introduction 
 of the magnetite has followed the garnet and diopside and has 
 
574 COPPER-DEPOSITS AT SAN JOSE, TAMAULIPAS, MEXICO. 
 
 preceded much of the chalcopyrite and pyrite, since all manner 
 of crevices in it are filled with veinlets of the latter. 
 
 In small pockety masses throughout the garnet and other 
 silicates calcite is occasionally seen. It may be either residual 
 limestone not changed over into silicates, or it may be calcite 
 of secondary introduction. 
 
 Molybdenite has also been found by E. D. Self to be quite 
 abundant in some of the workings opened since my visit. Thus 
 in the Santa Elena adit, assays covering a considerable distance 
 yielded from 0.5 to 1 per cent, of MoS 2 . In the Santo Do- 
 mingo shaft Mr. Self has observed it, apparently in a garnet- 
 zone that contained also vesuvianite. The occurrence of molyb- 
 denite at San Jose corresponds with Mr. Lindgren's observations 
 at Morenci. The home of molybdenite is in the pegmatite 
 dikes, and it is interesting and suggestive to find it also in the 
 zones, which must likewise be ascribed to expiring igneous 
 activities. 
 
 The most important copper-mineral is chalcopyrite, quite in- 
 variably in association with pyrite. The two must have come 
 in together. They appear not only as inclusions in the silicates, 
 but also as veinlets and as coatings in cavities. They cover at 
 times the well-developed crystals of garnet so as to mold around 
 them like a paste. The sulphides may themselves form large 
 masses analogous to the magnetite and thus yield the best 
 stopes of ore. 
 
 The usual oxidized compounds malachite, chrysocolla and, 
 less often, cuprite may be seen. The mine-waters from the 
 Santo Domingo shaft yield appreciable amounts of dissolved 
 copper. 
 
 Since my visit, narrow veinlets of sulphide ore rich in gold 
 have been discovered in the porphyry and far from known lime- 
 stone or garnet-zones, as observed by Mr. Self. These occur- 
 rences suggest parallels with Morenci. 
 
 IV. GENETIC CONCLUSIONS. 
 
 Having the comprehensive statement of the minerals and 
 their relations to the contact-zones before us, we may consider 
 the possible, as well as the most reasonable, methods whereby 
 they could have been produced. As incontrovertible we may 
 establish at the outset the following premises : 
 
COPPER-DEPOSITS AT SAN JOSE, TAMAULIPAS, MEXICO. 575 
 
 1. The garnet-zones have been produced by the action of the 
 diorite-porphyry upon the limestone. 
 
 2. The garnet-zones are irrrgular in distribution and in size. 
 They are sometimes very thick, and again white marble is alone 
 developed next the eruptive. 
 
 3. The chemical compositions of the active agent, the dio- 
 rite-porphyry, and of the raw material, the limestone, are as 
 follows. Some, though probably not great, variation is admis- 
 sible for each. To these are added the theoretical analyses 
 of andradite and of grossularite, the most abundant molecules 
 in the zones. 
 
 Diorite-Porphyry. 
 
 Limestone. 
 
 Andradite. 
 
 Per 
 
 fiiO 
 
 Cent. 
 tt9 31 
 
 Per Cent. 
 
 SiO 2 
 
 Per Cent. 
 40.0 
 
 Ai n 
 
 1 Q 
 
 AlA,Fe 2 3 
 0.5 to 1.2 
 CaCO 3 93 to 94 
 MgC0 3 ...0.5tol.2 
 
 A1 2 O 3 
 
 22.7 
 
 AljUj 
 TTo O 
 
 9 '48 
 
 CaO 
 
 37.3 
 
 Stf' 
 
 .... 133 
 
 Total.. .. 
 
 100.0 
 
 \f f\ 
 
 OAfl 
 
 MgU 
 CaO 
 
 ... 5.91 
 
 
 
 Grossularite. 
 
 Na 2 O 
 
 4.97 
 
 K,O 
 
 3 52 
 
 SiO 2 
 
 Per Cent. 
 35.4 
 
 T> f\ 
 
 
 &$ 
 
 .Oi 
 
 Fe.,O, .. 
 
 31.5 
 
 1 2 U 
 
 Total 
 
 ,o 
 
 99 95 
 
 CaO 
 
 33 1 
 
 Total 
 
 100 
 
 
 
 
 
 1. The Recrystallization Process. 
 
 We may first raise the question whether it is conceivable 
 that the garnet has been produced from the limestone alone. 
 That is, are we justified in believing that the limestone was 
 sufficiently siliceous and argillaceous, where we now find the 
 zones, to have yielded the garnet and the other silicates with- 
 out contributions from the eruptive ? The belief that contact- 
 zones are formed in this way is rather widespread and is based 
 partly on general considerations and partly on the following 
 specific cases : 6 
 
 1. In studying the contact-effects produced by the famous 
 Shap granite of Westmoreland, England, upon amygdaloidal 
 and altered basaltic rocks which it crosses, Alfred Harker con- 
 cluded that the contact-minerals produced from the amygda- 
 
 6 For a general review of views upon this question with citations of authorities, 
 see W. Lindgren, The Genesis of the Copper-Deposits of Clif ton-Morenci, Arizona, 
 Trans., xxxv., 519 to 524 (1904) ; p. 517, this volume. 
 
576 COPPER-DEPOSITS AT SAN JOSE, TAMAULIPAS, MEXICO. 
 
 loidal fillings did not involve new contributions from the gran- 
 ite nor the migration of the old materials farther than -^ 
 inch. 7 
 
 2. Great bodies of favorable eruptive rocks, such as granite, 
 sometimes break across thick sections of sedimentary rocks of 
 all sorts, perhaps miles in extent, and yet produce extremely 
 variable effects. Thus Dr. Joseph Barrell has described a case 
 in the Elkhorn district, Montana. A mass of granitic rock has 
 cut a thick sedimentary series. It has produced but slight 
 changes where it penetrated pure limestones, the new minerals 
 scarcely extending 5 ft. from the contact; whereas, where it 
 cut the Starmount limestone, recognized to be siliceous and 
 argillaceous, it has changed the latter to a mass of lime silicates 
 and feldspars for a quarter of a mile from the eruptive. The 
 average composition of the contact-zone is, grossularite, 60 ; 
 diopside, 25; wollastonite, 15; total, 100 per cent. 
 
 When referred back to an original limestone which would 
 yield this mixture Dr. Barrell 8 found by recasting the mineral- 
 ogy that it must have contained quartz, 21.3; kaolinite, 25.0; 
 calcite, 46.6; magnesite, 7.1; total, 100 per cent. 
 
 The magnesite molecule was of course combined with the 
 calcite in dolomite. If we express the above in percentages 
 of oxides they will be, Si0 2 , 32.9; A1 2 3 , 9.9; CaO, 26.1; MgO, 
 3.38: CO 2 , 24.22; H 2 0, 3.5; total, 100 per cent. 
 
 Dr. Barrell does not give any analyses of the Starmount 
 limestone, but from field-observation he apparently esteemed it 
 to be sufficiently siliceous and aluminous to yield the lime sili- 
 cates. On the other hand, on p. 291 of the paper in the Amer- 
 ican Journal of Science, it is stated regarding the contact-zones 
 from this limestone that 
 
 " The rocks are dense and even-grained and without cracklings or infiltrations 
 of quartz or calcite. The thin sedimentary banding is still preserved with the 
 same lenticular, somewhat concretionary structure observed at a distance from 
 the igneous intrusions, and the adjacent layers, where of different mineral com- 
 position, are sharply separated from each other. Certain strata may show a few 
 
 7 Quarterly Journal of the Geological Society, vol. xlix., No. 195, pp. 368 to 369 
 (Aug., 1893). 
 
 8 Physical Effects of Contact-Metamorphism, American Journal of Science, 
 Fourth Series, vol. xiii., No. 76, pp. 291 to 292 (Apr., 1902). See also Weed and 
 Barrell, Twenty-Second Annual Report, U. S. Geological Survey, Ft. II., p. 399 
 (1900-01). 
 
COPPER-DEPOSITS AT SAN JOSE, TAMAULIPAS, MEXICO. 577 
 
 per cent, of calcite, but this is distributed in a manner which indicates that it is 
 not a secondary addition, but on the contrary is due to those beds containing 
 originally more calcium carbonate than could combine under metamorphic ac- 
 tion with the quartz and kaolin present. These features sharply separate the 
 mass of Starmount strata from certain beds, which owing to special conditions do 
 show infiltrations, as indicated by nuclei of quartz with fluorite and ore grains." 
 
 Three paragraphs further on it is stated on p. 292. 
 
 11 In the process of metamorphism this mass of strata [i. e., the Starmount] has 
 lost approximately 28 per cent, of its weight, and 45 per cent, of its volume, from 
 70 to 90 times its volume of water vapor and 320 volumes of carbonic dioxide, the 
 gases being measured at C. and 760 mm.'' 
 
 While it is the purpose at this point to state, with all possi- 
 ble emphasis, the points favorable to the recrystallization of 
 the material in situ, and while the perfect preservation of the 
 old bedding with the introduction of new material may not be 
 without difficulties, yet one cannot but remark in passing that 
 the production of a rock " dense and even-grained and with- 
 out cracklings," while at the same time losing " 28 per cent, of 
 its weight and 45 per cent, of its volume," is also fraught with 
 other, perhaps greater, difficulties. 
 
 3. We sometimes find the zones of silicates, even in the same 
 great stratum of limestone, following certain beds for a long 
 distance away from the eruptive, while the beds on either side 
 are white marble. The zones may even be greatly contorted 
 and yet persistent. Dr. W. L. Austin has called my attention 
 to a very striking illustration of these relations at Sacrificio 
 mountain, Nombre de Dios, Durango, Mexico, of which a pho- 
 tograph is reproduced in Fig. 3, in which the zones are wollas- 
 tonite. It would seem from this as if the siliceous beds yielded 
 wollastonite, and the neighboring calcareous beds, marble. No 
 doubt these cases strongly favor recrystallization in situ. The 
 interesting zones at San Pedro, N. M., described by Messrs. 
 Yung and McCaffery, 9 might also be considered to give addi- 
 tional support when one studies the map and section, showing 
 the occurrence of both shaly and purer limestones, but they 
 also remark (p. 355), " The limestone left in contact with the 
 garnet is always more siliceous than the limestone further re- 
 moved from the ore-body," and as will be brought out for San 
 Jose, it does not seem probable, when the varying occurrences 
 
 9 The Ore-Deposits of the San Pedro District, N. M., Trans., xxxii., 350 (1901). 
 
578 COPPER-DEPOSITS AT SAN JOSE, TAMAULIPAS, MEXICO. 
 
 of the garnet rock are properly considered, that the eruptive, 
 when the garnets were developed, happened always to be next 
 to a specially siliceous portion. 
 
 Before we turn to the considerations positively favoring the 
 contribution of material from the eruptive, it may be remarked 
 that wide experience has demonstrated that the development of 
 contact-effects is, as a rule, irregular, showing great strength at 
 certain places and a well-nigh incomprehensible failure at other, 
 apparently equally favorable, points. We have best accounted 
 
 FIG. 3. ZONES OF WOLLASTONITE IN MARBLE, NOMBRE DE Dios, 
 DURANGO, MEX. 
 
 (From a photograph by W. L. Austin.) 
 
 for these relations by believing that the contact-effects are the 
 results of the emission of gases, vapors, and liquids, especially 
 water in its several physical states, and that these were freely 
 afforded at certain points and failed at others. There is great 
 reason for believing that this is true. Those eruptives, more- 
 over, which fail to produce contact-effects, are probably lack- 
 ing in the dissolved gases, etc., and are cases of relatively dry 
 fusion. 10 . 
 
 Admitting the addition of material from the eruptive, two 
 possible methods are to be considered. A contact-zone may be 
 
 10 This subject is briefly summarized in Kemp's Handbook of Rocks, 3d ed., 
 Chapter IX. 
 
COPPER-DEPOSITS AT SAN JOSE, TAMAULIPAS, MEXICO. 579 
 
 due to the fusion of the wall-rock into the eruptive and its con- 
 sequent absorption, yielding a product of intermediate composi- 
 tion ; or it may be due to the emission of gases, vapors and 
 heated liquids in the process generally described as hydrother- 
 mal. We may consider the first method at the outset. 
 
 2. The Absorption Process. 
 
 The garnet-zones at San Jose are in a general way interme- 
 diate in composition between the eruptive and the limestones ; 
 but, so far as observation goes, they lack feldspar entirely, and 
 this mineral ought not to fail if absorption took place. More- 
 over, the irregularity of distribution ; the sharp contacts ; the 
 obvious effects of chill on the eruptive, as shown by the changes 
 in texture and the occasional presence of scattered garnets in 
 predominating limestone, all militate against its application. 
 Experiments, moreover, in the artificial production of garnets 
 of the grossularite type have shown that when their component 
 materials are fused together, or when they themselves are 
 melted, the resulting product is anorthite, melilite, and pyrox- 
 ene. Therefore, while absorption-phenomena have been with 
 good reason called into play to account for some contact-phe- 
 nomena, as, for instance, the curious rocks at Pigeon Bay, Minn., 
 described by W. S. Bayley ; n yet in the typical garnet-zones 
 they have small claims to confidence. 
 
 3. The Process by Contributions from the Eruptive. 
 
 In the cooling of the eruptive there must have been a stage 
 when the emissions were of necessity gaseous, and a later stage 
 when they were liquids, and still a third stage when meteoric 
 waters, if such could penetrate to the still heated eruptive, must 
 have been set in circulation by it at temperatures below the 
 boiling-point, else it is difficult to conceive of water reaching 
 the heated eruptive against steam-pressure, except perhaps very 
 locally and for a brief season. 
 
 In his study of the Clifton district, Mr. Lindgren has attrib- 
 uted the garnets and. other silicates to the stage of gaseous 
 emissions, particularly of water-gas accompanied by silica and 
 iron. This is quite reasonable, and it may be that at San Jose 
 the garnet-zones, the magnetite, and the copper-ores were formed 
 
 11 Bulletin No. 109, U. S. Geological Survey (1893). 
 
580 COPPER-DEPOSITS AT SAN JOSE, TAMAULIPAS, MEXICO. 
 
 at this time. From the evidence in hand, however, there seems 
 no reason to eliminate heated waters as also possible agents. 
 The chief and most tangible interest centers around the ques- 
 tion of the introduction of silica, iron, and perhaps alumina, 
 from the eruptive. 
 
 That these three must have been added to the limestone in 
 order to produce the zones of silicates, the chemical analyses 
 of the unaltered rock and the field-observations make practi- 
 cally certain. Otherwise we cannot easily understand how 
 limestones ranging from 4 to 5 per cent, of insolubles attain to 
 from 40 to 50 per cent, of silica and alumina. Regarding the 
 silica and the iron there is no special chemical difficulty, but 
 the alumina is perhaps different. In the general weathering 
 of rocks, such as granites, we usually consider the alumina as 
 the stable oxide, and, assuming that it remains comparatively 
 unaffected by the natural agents, we calculate back to original 
 compositions. At the same time, we have as a suggestive com- 
 pound of aluminum the fluoride, cryolite, a mineral easily sol- 
 uble in sulphuric acid, with the evolution of hydrofluoric acid. 
 Its properties would suggest the inference that at the tempera- 
 tures and pressures prevailing during the cooling of a rather 
 deep-seated intrusive rock, it may well happen that aluminum is 
 far from being inert. When we compare its great abundance 
 in the porphyry, from 18 to 19 per cent., with the 1 per cent, 
 and less in the limestone analyzed, the former seems to be much 
 the more probable source. 
 
 Again, if we are still favorably inclined to believe in an 
 original siliceous and argillaceous composition of the limestone 
 and, recognizing the comparative rarity of this variety so far 
 as observation goes, if we try to conceive of just this variety 
 happening to be next the eruptive wherever we find the garnet- 
 zones, widely distributed as they are, both vertically and hori- 
 zontally ; shading off as they occasionally do into pure white 
 marble, without regard to original stratification ; and in neigh- 
 boring places abruptly failing in favor of the marble, we are 
 confronted with grave difficulties much graver ones, in fact, 
 than are presented by the assumption that the eruptive con- 
 tributed the necessary materials. 
 
 Still again, if we recall the fact that the garnet-rock is on the 
 whole a fairly dense and solid variety, which might be pro- 
 
COPPER-DEPOSITS AT SAN JOSE, TAMAULIPAS, MEXICO. 581 
 
 duced from limestone by new contributions of silica, alumina, 
 and iron, able to take the place of the eliminated carbon diox- 
 ide ; whereas, the recrystallization of an impure limestone re- 
 quires the production of cavities, theoretically more than 40 
 per cent, of the original volume ; we shall find for the San Jose 
 case that the addition of new material involves fewer difficulties 
 and is, in fact, the only reasonable explanation. The cavities, 
 which are observable and which are filled in part by the sul- 
 phides, are probably due to the rearrangements brought about 
 by the combination of the 4 or 5 per cent, of insolubles with 
 the lime of the calcite and the attendant loss of carbonic acid 
 involved. 
 
 The bodies of magnetite were doubtless formed by direct re- 
 placement of the limestone with the iron oxides and seem to 
 indicate a local richness in iron for the emissions from the 
 eruptive where they are found. There is slight, if any, reason 
 to regard them as other than purely contact-products. One or 
 two little pockets of specularite were observed, but this mineral 
 does not exhibit the abundance shown elsewhere, as, for instance, 
 in the zones at the Seven Devils, Idaho. 
 
 The introduction of the sulphides seems to have been in 
 largest part one of the later phases of the contact-metamor- 
 phism and to have followed the production of the silicates, at 
 least in part. We infer this from the relations described under 
 the sulphides that, besides forming inclusions in the silicates, 
 they mold around the garnets, and follow crevices in the mag- 
 netite. Where they constitute large masses they doubtless re- 
 placed the limestone, although in the midst of the contact- 
 zones. 
 
 4. Oxidized Ores. 
 
 The production of the oxidized minerals has been favored in 
 at least one or two cases by faults. It is possible to show the 
 existence of the latter by the heaved condition of the tinguaite 
 dikes, and near the natural conduit thus afforded for the de- 
 scending meteoric waters the formation of oxidized minerals 
 has been recognizable. 
 
 As is often the experience with copper-ores in deposits of 
 this type, a small amount of gold is shown by the assays. Other 
 metals are practically lacking and the matte is very clean. 
 
582 MAGMATIC ORIGIN OF VEIN-FORMING WATERS. 
 
 No. 21. 
 
 The Magmatic Origin of Vein-Forming Waters in 
 Southeastern Alaska.* 
 
 BY ARTHUR C. SPENCER, WASHINGTON, D. C. 
 (Washington Meeting, May, 1905. Trans., xxxvi., 364.) 
 
 HAVING suggested magmatic waters as the probable agents 
 of vein- and ore-deposition in southeastern Alaska in a paper en- 
 titled, The Geology of the Treadwell Ore-Deposits, 1 it is with 
 particular interest that I note W. Lindgren's application of the 
 hypothesis of igneous emanations to the gold-quartz veins of 
 Victoria and of California. 2 
 
 Mr. Lindgren says : 
 
 " In the above paragraphs I have repeatedly called attention to remarkable 
 similarities in vein-filling and metasomatic action between the Victorian quartz 
 veins and those of Sierra Nevada. Another striking similarity is that in both of 
 these regions the veins were formed just after the intrusions of vast masses of 
 granite or dioritic magma into crumpled and compressed sediments. I am con- 
 vinced that these similarities are due to closely similar modes of formation. With 
 some confidence, I would formulate the hypothesis that the gold and the quartz in 
 this type of veins have been deposited chiefly by ' eruptive after-effects / in other 
 words, chiefly by hot ascending waters originally contained in the granitic magma 
 and released from it by decreasing pressure, due to its eruption into the upper parts 
 of the lithosphere. It is quite possible that atmospheric waters may have played 
 a certain part by aiding the precipitation and by effecting certain forms of concen- 
 tration in the deposits." 
 
 There are many reasons for extending this hypothesis to 
 southeastern Alaska. This region and the Sierra Nevada belt 
 of California are undoubtedly parts of one geologic province, 
 throughout which the main events of geologic time are evi- 
 denced by identical or closely similar records in the rocks. 
 Our knowledge of the former region is still fragmentary, to be 
 sure, but the origin-dates of the most prominent features of 
 
 * Published by permission of the Director of the U S. Geological Survey. 
 
 1 Trans., xxxv., 473 (1904). 
 
 2 Characteristics of the Gold-Quartz Veins of Victoria, Engineering and Mining 
 Journal, vol. Ixxix., No. 10, p. 460 (Mar. 9, 1905). 
 
MAGMATIC ORIGIN OF VEIN-FORMING WATERS. 583 
 
 geology have been located in the time-scale, and found to cor- 
 respond completely with the red-letter dates in the California 
 record. In both regions, viz. : (1) intense folding and meta- 
 morphism followed the deposition of strata which palaeontolo- 
 gists agree are either uppermost Jurassic or lowest Cretaceous 
 (Mariposa beds of California) ; (2) intrusion of granitic rocks 
 (mainly granodiorite and diorite) accompanied the later stages 
 of folding or closely followed the plication and metamorphism ; 
 (3) after the intruded rocks had solidified both they and the 
 inclosing formations were fractured ; (4) the multitude of 
 wounds were healed by the deposition of vein-fillings, the min- 
 eralogy of which corresponds in almost every respect in the 
 two fields ; and finally, (5) erosion ensued and was followed by 
 the deposition of formations of Tertiary age. 
 
 Reasoning from the above outline alone, is it not to be ex- 
 pected that the origin of the veins in the two regions must be 
 identical, and does it not add strength to the suggested hypo- 
 thesis that it has been developed and applied independently 
 in two regions geologically so similar ? 
 
 Students of ore-deposition will wait with keen anticipation a 
 complete exposition by Mr. Lindgren of the data on which his 
 hypothesis is based. My own suggestions concerning the veins 
 of southeastern Alaska are necessarily founded on a very in- 
 complete knowledge of the facts involved, since all of the ob- 
 servations upon which they rest were made during a single 
 summer. The hypothesis here presented, therefore, undoubt- 
 edly borders too closely on pure speculation to carry much 
 weight by itself. Nevertheless, none of the data at hand seem 
 to be antagonistic to it, and it is hoped that by stimulating 
 the collection of data having a definite bearing pro or con its 
 prematureness may be in a measure compensated. 
 
 The most striking feature of geology in the Alaska Panhan- 
 dle region is the great dioritic core of the Coast range, a com- 
 plex of coarsely-granular intrusive rocks which is known to be 
 continuous from near the northern boundary of Washington 
 State to beyond the head of Lynn canal. Outside of this band, 
 many masses of similar rock occur throughout the Alexander 
 archipelago, and likewise in the region back of the coastal bar- 
 rier in British Columbia. 
 
 The wide occurrence of this invading rock has led to the 
 
584 MAGMATIC ORIGIN OF VEIN-FORMING WATERS. 
 
 conception that it may exiet as an underlying mass throughout 
 a very extensive region, in which the surface-formations are 
 mainly metamorphosed sedimentary rocks comprising repre- 
 sentatives of the different geologic periods from Silurian to 
 Lower Cretaceous. 
 
 Metalliferous quartz veins are found in all parts of the re- 
 gion, though in general they occur less frequently in large 
 intrusions than in small masses of diorite, and are most numer- 
 ous in the metamorphosed formations which inclose the intru- 
 sive rocks. They are quite as numerous away from the bodies 
 of diorite as near them and, in fact, show no distribution rela- 
 tion to the masses of intrusive rock. From the structural fea- 
 tures of the veins there can be little doubt that most of them 
 were formed during a single period of water-circulation which 
 followed not only the invasion of the diorite, but, in fact, the 
 complete solidification of those parts of the intrusive masses 
 now exposed to view. 
 
 Seeking to explain the relations observed and to determine 
 the source of the vein-forming waters, it may be assumed that 
 the deep-seated portion of the magma which furnished the 
 Coast range diorite remained in an unconsolidated condition 
 long after the complete crystallization of the masses observable 
 at the present surface. Under certain conditions the existence 
 of a deep-seated and widely-distributed magma in any region 
 might be favorable to the production of general fracturing in 
 the solid rocks above it, and the magma itself might well be 
 the principal source of the vein-waters. Leaving the origin of 
 the vein-openings for separate consideration, let us turn to the 
 question of the magma as a source of vein-forming solutions. 
 
 If, during and subsequent to the fracturing of the rocks, the 
 abyssal portion of the magma was gradually consolidating, it 
 must have given off large amounts of water, for it is now gen- 
 erally agreed by petrologists that the order of crystallization 
 exhibited by the minerals of the granular rocks can be best 
 explained by admitting the existence of more water in the 
 magma before and during its consolidation than is shown by 
 analysis of the resulting rock. Accepting this, crystallization 
 would be the sine qua non for a continuous and sufficient supply 
 of water, which can be properly conceived of as containing 
 in solution all the elements necessary to form the observed 
 
MAGMATIC ORIGIN OF VEIN-FORMING WATERS. 585 
 
 veins. Deposition from such magmatic or original waters 
 would be controlled by any or all of such circumstances as de- 
 crease of pressure or temperature, metasomatic action on the 
 country-rocks, and mingling with solutions which might bring 
 about chemical reaction. 
 
 The applicability of the hypothesis depends upon (1) the 
 existence of the supposed extensive bed of diorite beneath the 
 area in which the veins occur, (2) the possibility that such a 
 mass could rid itself of water freed during the process of crys- 
 tallization, and (3) the competence of solutions of magmatic 
 origin to produce the results observed. 
 
 The first requirement may be assumed to exist in the region 
 under discussion on the ground of probability, while the second 
 and third, which are inherent in all problems of ore-deposition 
 where the instrumentality of magmatic solutions is suspected, 
 can be reasonably inferred from well-known observations. The 
 manner in which water has escaped from masses of rock dur- 
 ing deep-seated solidification is not readily arrived at, but, that 
 most magmas must have contained more water than is to be 
 found in their crystallized products, that is to say, in the rocks, 
 is reasonably well established, and is accepted by such recent 
 writers as J. H. Vogt, J. F. Kemp, A. C. Lane, and C. R. Van 
 Hise. The fact that water must have escaped is patent from a 
 comparison of the dryness of the rock with the fairly-presumed 
 wetness of the magma. 
 
 As to the ability of magmatic solutions to produce quartz 
 veins carrying gold and metallic sulphides, sometimes, as in 
 Australia, California, and Alaska, with albite and rutile, or 
 with tourmaline, there can be little doubt. During deep-seated 
 solidification, the material dissolved in the magma-water will 
 vary with the progress of fractional crystallization, and as 
 crystallization proceeds the mother liquor, that is to say, the 
 remaining magma, becomes more and more siliceous. For 
 granitic and dioritic magmas, this follows from the fact that 
 the minerals separate essentially in the order of their relative 
 basicity, apatite and magnetite being followed by mica and 
 hornblende, and these by the less siliceous feldspars, and finally 
 by the siliceous feldspars and by quartz, if there be an excess 
 of silica. During the later stages of consolidation, silica and 
 'salts of the alkalies and of lime come to be the main constitu- 
 
 37 
 
586 MAGMATIC ORIGIN OF VEIN-FORMING WATERS. 
 
 ents of the solutions. This may be inferred, so far as silica 
 and the silicates are concerned, from the position of quartz and 
 the siliceous feldspars, orthoclase and oligoclase or albite, in 
 the scheme of crystallization given above. 
 
 In general, the solutions escaping from a mass of crystalliz- 
 ing rock would carry with them the greater part of all the 
 highly-soluble constituents of the original magma, among which 
 chlorides, fluorides, carbonates, and sulphates may have been 
 present in important amounts, and, if present, certain of these 
 salts would increase the dissolving power of the waters in re- 
 spect to silica, the metallic sulphides, and gold, so that the mag- 
 matic solutions could readily have produced the veins referred 
 to them by the hypothesis. The quotation from Arrhenius 
 given by Vogt 3 bears directly upon this point, as does Brogger's 
 statement 4 of the order of formation of the minerals in the 
 pegmatites of southern Norway, where the so-called mineraliz- 
 ing-agents, fluorine, chlorine, and boron, do not enter, to any 
 great extent, into the constitution of the minerals formed dur- 
 ing the first stages of solidification, but are found in consider- 
 able amounts in the minerals formed after the principal mass 
 of the magma has crystallized. 
 
 The list of vein-minerals found in southeastern Alaska in- 
 cludes most of those recorded from the California mines, but 
 the occurrence of tourmaline is frequent rather than rare, and 
 considerable amounts of rutile are present in a certain set of 
 veins near Juneau and in the Treadwell ores. In both in- 
 stances the rutile is associated with albite and carbonates of 
 lime, magnesia, and iron. The bearing which the presence of 
 tourmaline and rutile may have upon the hypothesis of mag- 
 matic waters will be considered in some detail. (For a recent 
 list of localities where ores are accompanied by tourmaline see 
 Zeitschrift fur praktische Geologic, vol. xii., 1904, p. 66). 
 
 When, in 1895, Mr. Lindgren 5 assigned the vein-forming 
 waters of the Nevada City and Grass Valley districts to surface- 
 waters penetrating the dioritic rocks and dissolving from them 
 
 3 Genesis of Ore-Deposits, by Posepny and others, p. 644 (1902). 
 
 * Die Mineralien der Syenitepegmatitegdnge der Sildnorwegischen Augit- und Nephe- 
 linsyenite, pp. 148 to 181 (1890). 
 
 5 Bulletin of the Geological Society of America, vol. vi., pp. 221 to 224 (1894) ; 
 also Seventeenth Annual Report, U. S. Geological Survey, Pt. II., p. 176 (1895-96;. 
 
MAGMATIC ORIGIN OF VEIN-FORMING WATERS. 587 
 
 metallic elements afterwards deposited during the return jour- 
 ney towards the surface, a difficult point to explain was " the 
 absence of fluorine and boron-compounds which so often occur 
 in ore-deposits in granitic rocks." The occurrence, in the Ju- 
 neau region, of tourmaline which contains these elements may 
 be regarded as favoring a source in igneous rocks, and in my 
 belief their presence lends weight to the magmatic hypothesis. 
 
 Titanium oxide and albite occurring as original vein-miner- 
 als may point in the same direction, in the light of Daubree's 
 conclusions concerning the genesis of the titaniferous albite 
 veins of the Alps. This distinguished synthesist produced 
 crystals of titanium oxide by submitting titanium chloride 
 vapor to the action of steam, 6 a procedure which was supposed 
 to imitate natural conditions of deposition, indicated by the 
 paragenesis of the three oxides of titanium rutile, anatase r 
 and brookite in the Alpine veins. Daubree therefore had no 
 hesitation in suggesting " sublimations " as the active agents 
 in forming the veins marked by the peculiar association of the 
 minerals named with titaniferous hematite, quartz, albite, adu- 
 laria, calcite, dolomite and siderite, mica, fluorite, tourmaline, 
 etc. In this connection, he refers to the discussion by filie de 
 Beaumont of the relation between metalliferous veins and vol- 
 canic emanations, showing that in his own mind Daubree re- 
 garded the sublimations as related to igneous activity. 
 
 Both Vog't and Lindgren 7 suggest that chloride or fluoride 
 solutions, or vapors, have been important factors in the forma- 
 tion of topaz-cassiterite, scapolite-apatite, and tourmalinic gold- 
 copper veins, the importance of which in the present connec- 
 tion is, that rutile is a common accessory mineral in the types 
 of veins enumerated. 
 
 Bischof has shown the efficiency of sodium chloride solu- 
 tions in transforming potassium feldspar to albite, 8 a fact which 
 suggests the possibility that the metasomatic change of micro- 
 perthite to albite which has taken place in the Treadwell de- 
 posit 9 may have been produced by the action of waters carry- 
 ing common salt. 
 
 6 Annaks des Mines, Fourth Series, vol. xvi. , p. 130 (1849). 
 
 7 Genesis of Ore-Deposits, Posepny, pp. 540 to 564 and 643 to 648 (1902). 
 
 8 Chemical Geology, vol. ii., p. 410. 
 
 9 Spencer, Trans., xxxv., 505 (1904). 
 
588 MAGMATIC ORIGIN OF VEIN-FORMING WATERS. 
 
 In the Juneau district the formation of albite as a vein-min- 
 eral, and as a metasomatic replacement in the wall-rock, is 
 natural if the depositing waters were of magmatic origin, be- 
 cause the diorites of the region from which such waters would 
 have been derived are essentially soda rocks. Likewise, the 
 presence of rutile in some of the ore-deposits corresponds with 
 unusual amounts of titanite in the intrusive rocks. That chlo- 
 rine and possibly fluorine were also present in the parent 
 magma may be properly assumed from the presence of abun- 
 dant apatite in the diorites. On the magmatic hypothesis, 
 either fluorine or chlorine may, therefore, well have taken part 
 in the formation of the quartz-albite-rutile veins. In conform- 
 ity with the ideas of de Beaumont and Daubree, which have 
 been especially elaborated along original lines by Vogt and 
 Arrhenius, these and several other elements may play an im- 
 portant role in vein-deposition without entering into the con- 
 stitution of any of the vein-minerals, and it is strongly sus- 
 pected that sodium chloride may have been an essential com- 
 ponent in the vein-forming solutions of this region. 
 
 In the veins of the Juneau district which have not yielded 
 rutile or albite, boron and fluorine are present in the mineral 
 tourmaline, and it is possible that chemical tests may reveal 
 chlorides mechanically inclosed in some of the vein-quartz, as 
 in the case of certain California veins investigated by Mr. 
 Lindgren. Unfortunately, proper material for this determina- 
 tion is not at hand, but research along this line will undoubt- 
 edly be undertaken in connection with future studies of ore- 
 genesis in southeastern Alaska. 
 
 The existence near each other of tourmaline-bearing veins, 
 which, so far as observation shows, contain no albite and rutile, 
 and others containing the latter minerals, without the former, 
 is a feature the bearing of which is still unrecognized. "No 
 difference in relative age of the two types can be suggested, all 
 the information at hand going to show the practical contempo- 
 raneity of the fractures in which they occur, so that it seems 
 not at all improbable that the depositing solutions were of prac- 
 tically the same nature, the difference in the mineral aggregates 
 in the two sorts of veins depending upon unlike conditions con- 
 trolling deposition. An indication that this explanation may 
 be true is the fact that the veins containing albite are in general 
 
MAGMATIC ORIGIN OF VEIN-FORMING WATERS. 589 
 
 those inclosed by igneous rocks which have suffered consider- 
 able metasomatic changes, due to the vein-forming waters, 
 while the albite-free veins occur typically in metamorphic sed- 
 iments, or in igneous masses practically unaltered by the de- 
 positing solutions. 
 
 The above considerations seem to me sufficient to show that 
 the magmatic hypothesis is adequate to account for the facts 
 in southeastern Alaska. It remains, however, to show the in- 
 adequacy of the meteoric hypothesis before the suggestion of 
 magmatic waters can be raised to the dignity of a theory. For 
 the great metalliferous region bordering the Pacific coast it 
 seems that the true theory of vein-genesis can be fully developed 
 only by establishing with the greatest possible degree of accu- 
 racy the position which ore-deposition occupies in the geological 
 history of the region. When this has been done I foresee the 
 probability that a point of fatal weakness, in any attempt to 
 explain the ore-deposits by waters derived from the surface of 
 the earth, will be the impossibility of attributing to the action 
 of downward-percolating waters any changes observable in the 
 rocks, though such changes should be recognizable if the as- 
 cending waters by which the veins were undoubtedly deposited 
 had been thus derived. 
 
590 GENETIC RELATIONS OP THE WESTERN NEVADA ORES. 
 
 No. 22. 
 
 Genetic Relations of the Western Nevada Ores.* 
 
 BY J. E. SPURR, WASHINGTON, D. C. 
 
 (British Columbia Meeting, July, 1905, Trans,, xxxvi., 372. 
 
 CONTENTS. 
 
 PAGE 
 
 I. Introduction, . . . ... ... . ... 590 
 
 II. Tonopah, . . . . . / . . . . . . . 591 
 
 1. General Geology, . , . . .-'.'. . . 591 
 
 2. Mineral Veins, . . . .593 
 
 (a) Veins of the Earlier Andesite, ..... . . 593 
 
 (b) Vems of the Tonopah Rhyolite-Dacite Period, . . . 594 
 
 (c) Veins Dependent upon the Oddie Khyolite, . . 594 
 
 (d) Alteration of Wall-Rocks, . . *. . . . .595 
 
 (e) Source of Mineralizing Solutions, . ... . . . 596 
 
 (f) Summary of Genesis of Tonopah Ores, .... 598 
 
 III. .Districts near Tonopah and Similar to It, . . . . . . 599 
 
 1. Gold Mountain, . .... . . . . . .599 
 
 2. Goldfield, . . . ,4 . ... . .. . 599 
 
 3. Bullfrog and Kawich, . . . . . . . .600 
 
 IV. Comparison of the Tertiary Tonopah Ores with those of Other Regions, 601 
 V. Characteristics and Significance of the Vein-Group, .... 602 
 
 VI. Silver Peak Quadrangle, .- . 603 
 
 1. General Geology, . . . . . . . . . .603 
 
 (a) Stratified Rocks, . . . . .. i . . .603 
 
 (b) Granitic and Aplitic Rocks, . . . . . .604 
 
 (c) Dioritic Rocks, . . .606 
 
 (d) Tertiary and Quaternary Lavas, . . . '. . . 606 
 
 2. Mineral Veins, 607 
 
 (a) Genetic Relations of the Ores of Mineral Ridge, . . 607 
 
 (b) Genetic Relations of the Great Gulch Ores, . ".' .612 
 
 (c) Genetic Relations of the Silver-Ores of Mineral Ridge, . 613 
 
 (d) Genetic Relations of the Ores of Lone Mountain, . . 614 
 
 (e) Genesis of the Ores of the Southern Part of the Quadrangle, 615 
 (f ) General Conclusions as to the Origin of the Metalliferous 
 
 Ores, . .616 
 
 VII. Comparison of Silver Peak with Other Ore-Deposits, . . . , .617 
 VIII. Conclusions Concerning the Silver Peak Type of Ores, ..... .619 
 
 IX. Magmatic Origin of Ores of Both Provinces, . . . r , . . 620 
 
 I. INTRODUCTION. 
 
 The region here discussed is that part of western Nevada in 
 which, during the last few years, discoveries of rich gold- anti 
 
 * Published by permission of the Director of the U. Geological Survey. 
 
GENETIC RELATIONS OF THE WESTERN NEVADA ORES. 591 
 
 silver-ores have been made at Tonopah, Goldfield, and other 
 camps. The special studies which have been made of the ore- 
 deposits have chiefly to do with Tonopah and the older camp, 
 Silver Peak, about 25 miles southwest of Tonopah. Other 
 camps in the same region have also been visited. 1 
 
 II. TONOPAH. 
 1. General Geology. 
 
 Only those features of the general geology which are essen- 
 tial to the understanding of the ore-deposition will here be dis- 
 cussed. Tonopah is situated in a region of Tertiary volcanics, 
 and the study of the general geology has chiefly to do with the 
 nature, period, and effects of the different volcanic eruptions. 
 The volcanic rocks comprise andesites, rhyolites, dacites (la- 
 tites), and basalt. There are also present Tertiary lake-beds, 
 mostly stratified tuffs derived from the volcanic outbursts. 
 The structure and succession of these lavas indicate a varied 
 history, comprising many volcanic eruptions, which brought 
 forth showers of ash and pumice, or streams of lava. The vol- 
 canic activity was accompanied by movements in the crust, which 
 produced tilting of the rocks and a very intense and complex 
 faulting. 
 
 There are grounds for believing that beneath the Tertiary 
 volcanics of Tonopah there is an older formation of Palaeozoic 
 limestone and intrusive granite. Such formations outcrop both 
 to the south and to the north at frequent intervals. At Tono- 
 pah fragments of limestone and granite are among the blocks 
 which were hurled out from the volcanoes at the time of some 
 of the dacitic eruptions. 
 
 The oldest of the Tertiary volcanic rocks is an andesite which 
 I have called the earlier andesite, to distinguish it from a sub- 
 sequently erupted rock of similar composition. This earlier 
 andesite, wherever found, is decomposed to a variable extent. 
 From microscopic study it appears that the original fresh rock 
 was a hornblende-biotite-andesite, the feldspar being typically 
 andesine-oligoclase. In the present altered condition, no actual 
 biotite or hornblende has been found, these minerals being 
 represented by their decomposition-products, quartz, sericite, 
 
 1 I have described these camps in Professional Papers of the U. S. Geological 
 Survey, soon to be issued. 
 
592 GENETIC RELATIONS OF THE WESTERN NEVADA ORES. 
 
 pyrite, siderite, and hematite, sometimes chlorite and calcite. 
 The feldspar is usually altered to quartz and sericite or quartz 
 and adularia. As a result of the alteration-processes the whole 
 rock is usually more or less completely altered to an aggregate 
 which is composed of quartz and sericite, with usually some 
 pyrite and siderite, and frequently adularia, kaolin, and iron 
 oxides. Chlorite and calcite are not so common, but may be 
 abundant. They indicate a process of decomposition different 
 from the ordinary. As a rule the rocks may be divided accord- 
 ing to their processes of decomposition into two classes : (1) 
 quartz-sericite-adularia-pyrite-siderite rocks, most abundant 
 and most closely associated with the metalliferous veins; and 
 (2) chlorite-calcite rocks, not associated with the ores. 
 
 The next oldest rock is the later andesite. This is much 
 like the earlier andesite, but is slightly less siliceous. It is 
 often nearly fresh, and is in other places largely decomposed. 
 The general process of decomposition is usually different from 
 that of the earlier andesite. The phenocrysts are larger and 
 more abundant than in the earlier andesite, and consist of bio- 
 tite, augite, hornblende, and feldspar which is predominantly 
 andesine-labradorite. In general the decomposition-products 
 are quartz, chlorite, calcite, pyrite, and siderite. The later an- 
 desite overlies the earlier andesite and covers up the metallifer- 
 ous veins which occur in the latter rock. 
 
 Younger than the andesites are a series of rhyolitic rocks 
 (rhyolite-dacites or latites). These lavas differ slightly in com- 
 position among themselves and were erupted at different times 
 during a single general period of volcanic activity. In the com- 
 plete report upon this district, 2 several of these eruptions have 
 been distinguished and separately mapped, but only three of 
 these need here be mentioned. One of these, which I have 
 called the Tonopah rhyolite-dacite, is a dense, glassy rock, 
 occurring in intrusive masses and thin sheets. This rock con- 
 tains porphyritic crystals of biotite, feldspar, and quartz in a 
 glassy ground-mass. The most common feldspars are orthoclase 
 and andesine-oligoclase. Near its intrusive contacts, this rock 
 is often greatly silicified, the alteration having evidently been 
 accomplished by hot-spring action succeeding the intrusion. 
 
 2 Geology of the Tonopah Mining District, Nevada, Professional Paper No. 42, 
 U. S. Geological Survey (1905). 
 
GENETIC RELATIONS OF THE WESTERN NEVADA ORES. 593 
 
 Secondary quartz, pyrite, and sometimes siderite, are the chief 
 results. 
 
 A dacite of later age and of somewhat different character is 
 the rock which forms the hills around Tonopah. These emi- 
 nences represent the columns of lava which rose from the 
 abysmal regions to the surface. Near the contacts of these 
 necks the intruded rocks are usually hardened and silicified 
 and the cracks are coated with chalcedony. 
 
 A few of the volcanic necks consist of white siliceous rhyo- 
 lite (Oddie rhyolite) of nearly the same age as the dacite necks. 
 This rhyolite has a micro-granular ground-mass of quartz and 
 feldspar, with porphyritic crystals of coarse quartz, orthoclase, 
 and occasional plagioclase and biotite. 
 
 2. Mineral Veins. 
 
 (a) Veins of the Earlier Andesite. The most important veins 
 of the Tonopah district are in the early andesite and do not 
 extend into the overlying rocks. Where the early andesite is 
 not exposed at the surface the later rocks form a capping to 
 the veins. This fact shows plainly that the veins were de- 
 posited before the eruption of the later andesite and imme- 
 diately after that of the earlier andesite ; indeed, there is every 
 evidence that they were formed by ascending hot waters suc- 
 ceeding and connected with the earlier andesite intrusion, and 
 that these waters had become inactive by the time of the later 
 andesite. The openings which afforded channels for these as- 
 cending waters were sheeted zones in the rock. The rock was 
 complexly fractured, apparently soon after cooling, and certain 
 zones of maximum fracturing became the chief circulation- 
 channels. These fractured zones have become veins, largely 
 by a process of replacement of the rock. That the mineraliz- 
 ing agency was water is evident from the character of the vein 
 and the nature of the alteration of the wall-rock ; that its action 
 was probably connected with the earlier andesite eruption is 
 shown by the fact that it followed this, and, at least so far as 
 mineralizing activity was concerned, was of limited duration, 
 for its effects have not been discovered in the succeeding later 
 andesite. It appears probable, therefore, that the mineralizing 
 agents were volcanic waters, such as are usual among the after- 
 effects of volcanic outbursts, and that they were hot and as- 
 cending. 
 
594 GENETIC RELATIONS OF THE WESTERN NEVADA ORES. 
 
 In the primary sulphide ores, lying below the oxidized zone, 
 the principal gangue-minerals are quartz, adularia, and some 
 sericite, with occasional carbonates of lime, magnesia, iron, and 
 manganese. The ore-minerals consist of sulphides of silver, 
 antimony, copper, iron, lead, and zinc, in the form of stephanite, 
 polybasite, argentite, chalcopyrite, pyrite, galena, and blende. 
 A considerable quantity of silver selenide is also present, and 
 gold in a yet-undetermined form. The remarkable thing about 
 the metallic contents is the relative scarcity of the common 
 elements and the abundance of the rarer ones. 
 
 The depth of oxidation in these veins is very irregular, de- 
 pendent upon the relative perviousness of the overlying rocks. 
 In the oxidized zone, horn-silver is abundant, with some bro- 
 mides and iodides. Free gold has been deposited. The pres- 
 ence of limonite and black oxide of manganese is characteristic. 
 
 Pyrargyrite or ruby-silver and argentite frequently occur, 
 coating crevices in primary ore, and in such cases are evidently 
 6f secondary deposition. 
 
 (b) Veins of the Tonopah Ehyolite-Dacite Period. The veins 
 connected with the earlier andesite constitute the principal 
 class at Tonopah, but veins belonging to a later period are fre- 
 quently found. These veins are associated with the Tonopah 
 rhyolite-dacite intrusions and are dependent upon them, in the 
 same way as the earlier andesite veins depend upon the earlier 
 andesite. The veins of the Tonopah rhyolite-dacite period are 
 characterized by irregularity and the lack of persistence, though 
 their size may locally be considerable. The veins are barren or 
 contain small quantities of gold and silver, except locally, where 
 rich bunches of ore may occur. A characteristic of the rhyo- 
 lite-dacite veins, to which there are, however, numerous excep- 
 tions, is the greater ratio of gold and silver in them as com- 
 pared to that in the earlier andesite veins. These rhyolite- 
 dacite veins are also plainly the result of ascending hot waters. 
 The lack of definition and persistence as compared with the 
 veins in the earlier andesite shows that at the time they were 
 formed no definite fracture-zones were available as channels. 
 
 (c) Veins Dependent Upon the Oddie Rhyolite. In one of the 
 rhyolite volcanic necks (Mount Ararat) veins of a different 
 character from those previously described have been formed. 
 Near the contact of the rhyolite plug with the older rocks, the 
 
GENETIC RELATIONS OF THE WESTERN NEVADA ORES. 595 
 
 rhy elite is peculiarly brecciated, showing great blocks jumbled 
 together, with, however, rhyolitic matrix between. The dim 
 outlines of these blocks and the nature of the matrix show that 
 the breccia was formed when the lava was only partly rigid and 
 in the process of cooling. This brecciation is confined to the 
 zone near the contact. Many sharp fractures, chiefly parallel 
 to the contact, are present in the rhyolite. These have been 
 filled with vein-material, consisting of quartz, with ferruginous 
 calcite containing some manganese carbonate. This gangue- 
 material contains a little gold. These fissures and fractures 
 plainly resulted from the continuation of the driving upward 
 of the plug after consolidation was practically complete. The 
 vein-fillings are the result of ascending hot waters which fol- 
 lowed the channels thus opened and cemented them. 
 
 A consideration of these veins and their wall-rocks does not 
 afford evidence of the mineralizing waters having contained 
 anything beyond silica, lime and magnesian carbonates, and a 
 trace of gold. The presence of iron is contrasted with the 
 probable absence of iron in the waters which produced the 
 veins in the earlier andesite. 
 
 (d) Alteration of Wall-Hocks. In the altered' phases of the 
 earlier andesite there are all transitions between the typical 
 quartz-sericite phase, in which calcite and chlorite are not abun- 
 dant, and the typical calcite-chlorite phase, in which quartz and 
 especially sericite are decidedly subordinate. Hence it has been 
 concluded that these different phases are due to the chemical 
 effects of the same mineralizing waters, which differed in na- 
 ture as they penetrated to a greater and greater distance from 
 the circulation-channels. Along these channels, which became 
 veins, the rock was transformed by the deposition of silica, 
 sulphides of silver, antimony, etc., gold, and selenides. The 
 soda and magnesia, and part of the lime and iron, were re- 
 moved. In the wall-rock near the vein, lime, iron, magnesium, 
 and soda have been replaced by silica and potash. In the rocks 
 more remote from the vein-channels, though the alteration has 
 been complete, there has been no very great increase or de- 
 crease in the original elements. 
 
 From a study of these different effects of the mineralizing 
 waters, it has been concluded that they were charged with an 
 excess of silica and potash, together with silver, gold, antimony, 
 
596 GENETIC RELATIONS OF THE WESTERN NEVADA ORES. 
 
 arsenic, copper, lead, zinc, selenium, etc. They were notably 
 deficient in iron, but contained carbonic acid and sulphur, as 
 well as some chlorine and fluorine. The presence of the two 
 last-named gases is shown by some probably original silver 
 chloride and by the presence of muscovite in the gangue, a 
 mineral which is believed to crystallize almost invariably in 
 the presence of fluorine. 3 
 
 The later andesite is not altered as much as the earlier an- 
 desite, but is, however, locally greatly decomposed. From a 
 study of the nature of this alteration, the conclusion has been 
 drawn that the waters which produced it were highly charged 
 with carbonic acid and sulphur, and that they contained mag- 
 nesia and iron, and also probably lime, in considerable quan- 
 tity. They were clearly hot-spring waters, as shown by the 
 excessive carbonation and sulphuration, as well as the for- 
 mation of sericite and talcose materials, uralite, chlorite, ser- 
 pentine, zeolites, etc. Their chemical composition was quite 
 different from that of those waters which altered the earlier 
 andesite. From a study of the localization of the decomposi- 
 tion of the later andesite, it seems likely that it was due to the 
 influence of solutions following the contacts of later intrusive 
 rhyolitic rock. 
 
 (e) Source of Mineralizing Solutions. The waters which pro- 
 duced the veins and the rock-decomposition in the early 
 andesite were rich in silica and potash and poor in the other 
 common rock-forming elements. They seem to have directly 
 followed the earlier andesite eruption. Those that altered the 
 later andesite were rich in magnesia, lime, and iron, and low 
 in silica and the alkalies, and seem to have followed the 
 eruption of rhyolitic rocks, especially the Oddie rhyolite. Both 
 were hot-spring waters, which differed in their composition as 
 much as the rocks which they accompanied. There is an 
 apparent antithesis in each case between the composition of 
 the erupted rock and the accompanying hot solutions. The 
 earlier andesite, a rock of intermediate composition, was fol- 
 lowed by the advent of waters rich in the elements character- 
 istic of extremely acid rocks. The eruption of the Oddie 
 rhyolite, a very siliceous rock, was followed by the advent of 
 
 3 Doelter, Chemische Mineralogie, p. 161 ; and Brauns, Chemische Mineraloyie, p. 
 247 (1896). 
 
GENETIC RELATIONS OF THE WESTERN NEVADA ORES. 597 
 
 waters rich in elements characteristic of basic rocks and poor 
 in the elements represented in the rhyolite. The exact expla- 
 nation of this antithesis is a matter for future study. 
 
 There are two possible explanations of hot springs : one is 
 that they a?e due to atmospheric water which has sunk down 
 from the surface to such a depth that it becomes highly heated 
 and then rises again ; the other is that they are due to water 
 which forms a part of the molten material in the earth's inte- 
 rior and which is concentrated and separated from the magma 
 upon the cooling of a molten mass. Lavas which cool at the 
 surface give off vast quantities of water-vapor, and the phe- 
 nomena of contact-metamorphism, especially that connected 
 with siliceous rocks, show that in depth similar water-vapor is 
 expelled from cooling rock. It seems therefore impossible to 
 escape the conclusion that at least some hot springs, the after- 
 phenomena of volcanic activity, are due to magmatic water. 
 
 In the arid Nevada region there are, as a rule, no flowing 
 surface-waters, the whole supply emerging from the ground as 
 springs. These springs may be either warm or cold. The cold 
 springs usually show two characteristics which indicate that 
 they are of vadose or atmospheric origin : (1) they fluctuate 
 with the season, and (2) they become more numerous in regions 
 of greater precipitation and rarer in the more arid portions. 
 The hot springs, however, so far as the writer knows, do not 
 show these characteristics. They are notably associated with 
 areas of volcanic rocks and they are often very vigorous in the 
 heart of an arid region. 
 
 Volcanic activity has lasted in this province from the begin- 
 ning of the Tertiary to within a few hundred years ago, but 
 many of the hot springs which accompanied or followed the 
 different manifestations of volcanic activity are now extinct. 
 At Tonopah, waters ascending after several of the volcanic 
 eruptions, mineralized and altered the formations through 
 which they passed, and became extinct in a relatively short 
 space of geologic time. It is difficult to explain the totally 
 different composition of the waters of the different periods on 
 the hypothesis that they were of atmospheric origin, and the 
 antithesis pointed out between the contents of waters of differ- 
 ent periods and the composition of lavas which they followed 
 is equally difficult to account for on this hypothesis. A third 
 
598 GENETIC RELATIONS OF THE WESTERN NEVADA ORES. 
 
 consideration is the peculiar combination of materials in the 
 waters which produced the veins of the earlier andesite, espe- 
 cially the presence of unusually large quantities of the rare 
 metals silver and gold, and unusually small ones of the com- 
 moner ones, copper, lead, zinc, and iron. Plainly some process 
 of separation and concentration has furnished the noble ele- 
 ments contained in the mineralizing waters, separating them 
 from the baser metals. A view concerning this same problem 
 at the Comstock, expressed by von Richthofen, 4 appeals to me 
 as an explanation of the Tonopah ores also. Von Richthofen 
 pointed out that the volatile materials, chiefly fluorine, chlorine, 
 and sulphur, given off during solfataric action, would extract 
 from the cooling rock metallic substances of much the same 
 character and proportion as those present in the Comstock lode r 
 while ordinary waters would furnish primarily the more abun- 
 dant metals, such as iron and manganese, and only small 
 amounts of silver and gold. 
 
 (f) Summary of Genesis of Tonopah Ores. The considera- 
 tions pointed out appear to indicate the following conclusions. 
 
 The Tonopah district was during most of Tertiary time a 
 region of active vulcanism, and probably after each eruption,, 
 certainly after some of them, solfataras and fumaroles, suc- 
 ceeded by hot springs, thoroughly altered the rocks in many 
 parts of the district. At the surface,, during these periods, 
 the phenomena of fumarolic, solfataric, and hot-spring action 
 were similar to those witnessed to-day in volcanic regions; 
 but the rocks now exposed were at that time below the sur- 
 face. The veins have cemented the conduits which were 
 formed by the fractures due to the heavings of the surging 
 volcanic forces below, and along which gases, steam, and finally 
 hot waters, growing gradually cooler, were expelled, relieving 
 the explosive energies of the subsiding volcanism. The water 
 and other vapors, largely given off by the congealing lavas be- 
 low, carried with them, separated and concentrated from the 
 magma, metals of such kind and of such quantity as are pres- 
 ent in the veins, together with silica and other materials. The 
 nature of the metallic minerals in the veins is believed to have 
 depended largely upon the particular magma whence the ema- 
 nations proceeded. 
 
 4 Cited in Monograph IIL, U. S. Geological Survey, pp. 19 to 20 (1882). 
 
GENETIC RELATIONS OF THE WESTERN NEVADA ORES. 599 
 
 III. DISTRICTS J^EAR TONOPAH AND SIMILAR TO IT. 
 1. Gold Mountain. 
 
 The mining-district of Gold mountain, 4 miles south of 
 Tonopah, has been prospected for several years, but has not 
 developed into a camp of any importance. The rocks here are 
 rhyolite, rhyolite-breccia, and tuffs, in which fracture- or brec- 
 cia-zones have been formed, and have been transformed into 
 veins by circulating waters. The vein-material is quartz, often 
 chalcedonic, and the metallic mineral chiefly pyrite, which 
 sometimes contains gold and sometimes silver. In some cases 
 the veins contain gold only, while in others considerable silver 
 is also present. Some of the richest ore is oxidized and occurs 
 in pockets near the surface. From such ore, shipments have 
 been made, but most of the veins are of low grade. 
 
 The rocks at Gold mountain are similar to the Tonopah 
 rhyolite-dacite series of lava, breccias, and associated tuifs at 
 Tonopah, and the characteristics of the Gold mountain veins 
 are similar to those of the rhyolite-dacite veins at Tonopah. 
 In both cases the veins, while they are locally strong, have not 
 the regularity or persistence of the earlier andesite veins. 
 
 2. Goldfield. 
 
 I have visited Goldfield, about 24 miles south of Gold moun- 
 tain, but I have not yet studied the geology thoroughly. The 
 rocks, chiefly volcanic, consist of rhyolites, rhyolite tuffs, ande- 
 sites, and basalts, all probably of Tertiary age. One andesite 
 examined microscopically resembles the earlier andesite at To- 
 nopah, and a specimen of basalt resembles the basalt of that 
 district. The rhyolite also resembles the rhyolite of Gold 
 mountain. The ores occur in both rhyolites and andesites, 
 showing that the mineralization occurred subsequent to the 
 eruption of both lavas. It is therefore possible that the Gold- 
 field deposits are identical in origin with the later series of 
 veins at Tonopah, which accompany the Tonopah rhyolite- 
 dacite, although at Goldfield these veins are of vastly greater 
 economic importance. 
 
 There is also a resemblance in the physical characteristics of 
 the later Tonopah veins and the ore-bodies at Goldfield ; in the 
 latter, however, the quartz masses are still more irregular; the 
 
600 GENETIC RELATIONS OF THE WESTERN NEVADA ORES. 
 
 outcrops may be roughly elongated, nearly circular or crescen- 
 tic. The quartz is gray and jaspery and is due to the silicifi- 
 cation of the volcanic rock, which is undoubtedly the work of 
 hot springs. Had the rocks been strongly fractured we should 
 have had more definite veins like those of the earlier andesite 
 at Tonopah. 
 
 The greater part of one of these quartz reefs at Goldfield 
 contains little or no gold, although pyrite is disseminated 
 throughout. Frequently, however, ore-shoots of relatively 
 small size occur, which are difficult to distinguish, except by 
 assaying, from the barren portion. It seems probable that 
 these pay-shoots represent the main channels of circulation, 
 while the siliceous casings are the result of water soaking 
 through the adjacent rock. The values of the ores are chiefly, 
 sometimes entirely, in gold, but in some cases considerable 
 silver has lately been found. 
 
 The sulphide ores lying beneath the oxidized surface-ores 
 contain tetrahedrite which is highly auriferous. Tellurium is 
 present, probably in the form of gold telluride. Bismuth sul- 
 phide is not uncommon. Free gold also occurs in these sul- 
 phide ores. In the gangue, barite is common, but not abundant. 
 
 3. Bullfrog and Kawich. 
 
 Since the opening up of Goldfield, more than a year ago, a 
 number of promising new camps have been discovered in the 
 neighborhood, especially to the south and east. Chief among 
 these are perhaps the Bullfrog and the Kawich districts, the 
 former of which lies 60 miles southeast of G-oldfield ; the latter 
 72 miles east. I have not yet visited these camps, but from 
 personal correspondence I have obtained some idea of their 
 nature. Oscar Rohn has sent photographs, samples and de- 
 scriptions of the Kawich district, which indicate for this camp 
 a close analogy to Goldfield, the ore-bodies occurring in similar 
 rocks and being of the same character. Mr. Rohn reports 
 that one of the principal formations at Bullfrog is rhyolite and 
 rhyolite-breccia, which he regards as equivalent to lavas of the 
 Tonopah district. The veins occur in part at least along fault- 
 or fracture-zones in the volcanic rock. The gangue is chiefly 
 quartz, and the values are gold and silver. 
 
GENETIC RELATIONS OF THE WESTERN NEVADA ORES. 601 
 
 IV. COMPARISON OF THE TERTIARY NEVADA ORES WITH 
 THOSE OF OTHER REGIONS. 
 
 Among the nearest analogies to Tonopah yet described else- 
 where are the contiguous mining-districts of Pachuca and Real 
 del Monte, in Mexico. 5 These districts are similar to Tonopah 
 in character and age of the wall-rocks (Miocene andesites) ; in 
 the nature of the alteration of the rock near the veins (silicifi- 
 cation near the veins, propylitic alteration farther away) ; in 
 the structural character of the veins (splitting and reuniting) ; 
 the general character of the ores (both oxide and sulphide), 
 and of gangue (though adularia as a gangue-material and 
 selenides as ores have not been recognized at Pachuca); and in 
 the occurrence of the rich ores in bonanzas, which seem to be 
 due to the intersection of transverse fractures with the main 
 vein-zone. 
 
 Many other deposits in Mexico which have not been fully 
 described seem, from their recorded characteristics, to be 
 closely similar to Tonopah. 6 
 
 Pachuca is about 2,000 miles southwest of Tonopah, but an 
 analogous deposit lies 150 miles to the northwest, the Corn- 
 stock. The Comstock is similar to Tonopah in respect to the 
 character and age of the rocks in which the lode lies (Tertiary 
 andesite) and their " propylitic " alteration ; in the nature of 
 the gangue and ore ; and in the occurrence of the rich ore in 
 irregular " bonanzas." The chief distinction is that the Com- 
 stock consists of a single very strong lode, while at Tonopah 
 there are a number of small ones. 
 
 Another region having many striking peculiarities in com- 
 mon with Tonopah lies about 400 miles due north of it, the 
 districts of Silver City and Delamar in southwestern Idaho. 7 
 These districts are similar to Tonopah in that the ores occur 
 in Tertiary volcanics and are probably in both cases post-Mio- 
 cene in age ; to a striking degree in the character of the ores 
 and gangue-materials ; in the structural characteristics of the 
 veins, which form a group knit together by branches ; in the 
 
 6 Aguilera and Ordonez, Boletin del Institute Geologico de Mexico, Nos. 7, 8 and 
 9 (1897). 
 
 6 J. G. Aguilera, Trans., xxxii.,.513 (1901). 
 
 7 Lindgren, Waldemar, Twentieth Annual Report, U.S. Geological Survey, Pt.IIL, 
 pp. 107 to 189 (1898-99). 
 
 38 
 
602 GENETIC RELATIONS OF THE WESTERN NEVADA ORES. 
 
 general character of the alteration of the wall-rock ; and in the 
 occurrence of the rich ores in irregular " bonanzas." The 
 chief difference is that, in these Idaho districts, the wall-rocks 
 are mainly rhyolite, and not andesite. 
 
 V. CHARACTERISTICS AND SIGNIFICANCE OF THE VEIN-GROUP. 
 
 The different mineral districts, mentioned above, exhibit a 
 definite group of veins, characterized by the following features : 
 They occur in Tertiary volcanic rocks of similar character 
 in the different localities, being chiefly Miocene andesites or 
 rhyolites. They constitute strong masses or veins which have 
 as gangue essentially quartz with frequently a little calcite, 
 while adularia, barite, rhodochrosite, or rhodonite may also 
 be present in limited quantity. The ore is characteristically a 
 silver-gold one, silver being usually predominant in the values 
 in varying proportions, though the relative value may be re- 
 versed, and in some extreme cases either metal may occur with 
 little admixture of the other. In any case the abundance of 
 silver or gold, or both, in reference to lead, zinc, iron, etc., is 
 characteristic. Silver sulphides, especially argentite, also ste- 
 phanite and polybasite (together with ruby-silver), and gold, 
 probably largely in a free state, are a distinguishing feature in 
 the great majority of cases. Tellurides and selenides may also 
 be present. Pyrite, blende, chalcopyrite, and galena are usu- 
 ally present in varying quantity. Where they become pre- 
 dominant the vein becomes relatively low-grade. Tetrahedrite, 
 stibnite, and bismuthinite are also known to occur. The wall- 
 rocks are much altered to quartz, sericite, chlorite, calcite, epi- 
 dote, pyrite, etc., and sometimes to adularia. Frequently the 
 rocks nearest the veins are chiefly altered to quartz and seri- 
 cite ; those farther away to the softer " propylitic " alteration, 
 consisting of calcite, chlorite, pyrite, epidote, etc. The rich 
 ores occur in irregularly outlined portions of the lode called 
 " bonanzas," which are of limited extent, both horizontally and 
 vertically, and are believed to have arisen as a consequence of 
 the irregular intersection of transverse fractures or fissures with 
 the main vein-channels. 
 
 Unquestionably the close relation between the different min- 
 eral districts mentioned shows a metallographic province, which 
 in this case coincides with a portion of a petrographic prov- 
 
GENETIC RELATIONS OF THE WESTERN NEVADA ORES. 603 
 
 ince. 8 It is probable indeed that the co-extension of the metal- 
 lographic and petrographic provinces is greater than thus es- 
 tablished. At many points along the belt of the petrographic 
 province in the Andes of South America, for example, in Peru 9 
 veins are reported to have, so far as can be made out, a mode 
 of occurrence, age, and composition similar to those of Mexico. 
 In that better-established portion of the metallographic prov- 
 ince which comprises Mexico and Nevada, the ores occur in 
 Miocene andesites in a great majority of cases. In occasionally 
 recurring cases they appear in Miocene-Pliocene rhyolites which 
 succeeded the andesites. The ores are believed to be due to 
 the after-actions of the eruptions, in the shape of fumaroles, 
 solfataras, and hot springs. Moreover, since these manifesta- 
 tions follow all volcanic eruptions, it is probable that the metals 
 deposited by the after-processes owe their nature and amount 
 to an unusual proportion of them in the magma with which, 
 they are genetically connected. 
 
 VI. SILVER PEAK QUADRANGLE. 
 
 Of quite a different class of ore-deposits from that described 
 in the preceding pages are those of the Silver Peak quadrangle, 
 whose northeastern corner is only about 10 miles west of To- 
 nopah. The deposits of this quadrangle have been made the 
 subject of a Professional Paper, to be published by the U. S. 
 Geological Survey. 
 
 1. General Geology. 
 
 (a) Stratified Eocks. Palaeozoic limestones with slates and 
 some quartzites are well represented in the area of the Silver 
 Peak quadrangle. They belong entirely within the Cambrian 
 and Ordovician eras. Most of our knowledge of the Palaeozoic 
 strata is due to the work of Messrs. Turner, Walcott, and Weeks, 
 of the U. S. Geological Survey. The known fossils show the 
 presence of strata belonging to the lower Cambrian, the upper 
 Cambrian, and the Ordovician. The rocks, however, are char- 
 acteristically considerably folded and faulted and frequently 
 metamorphosed, and the series, which is several thousand feet 
 
 8 Spurr, J. E., Trans., xxxiii., 332 to 333 (1902) ; p. 295, this volume. 
 
 9 Fuchs et de Launay, Traite des Gites Mineraux et Metalliftres, vol. ii., p. 829 
 
 (1893). 
 
604 GENETIC RELATIONS OF THE WESTERN NEVADA ORES. 
 
 thick, presents no very striking and constant lithologic differ- 
 ences. The detailed stratigraphy and structure, therefore, are 
 still in some doubt. 
 
 In the district where the principal gold-mines are situated, 
 near Silver Peak village, there is, below the fossiliferous Cam- 
 brian, a series of considerable thickness consisting of limestones 
 and slates, with some dolomitic marble beds. This series has 
 been intruded by numerous alaskitic sheets and by quartz 
 veins. (Alaskite is a granitic rock composed essentially of 
 quartz and alkali feldspar.) It has become largely schistose 
 find gneissic. 
 
 No sedimentary rocks intermediate in age between the Ordo- 
 vician and the probable Eocene have been found within the 
 area of the quadrangle, but there are extensive and thick de- 
 posits belonging to the Tertiary. These Tertiary deposits flank 
 the edges of the mountains and underlie in part at least the 
 Pleistocene veneer of the valleys. They consist of soft shales, 
 sandstones, marls, tuffs, volcanic breccias, etc., with interbedded 
 layers of andesitic and rhyolitic lava. The thickness of the 
 whole accumulation is very likely several thousand feet. 
 
 (b) Granitic and Aplitic Rocks. Granitic rocks, intrusive into 
 the Palaeozoic strata, are well represented in the quadrangle, 
 especially in three chief areas in the northeast corner near 
 Lone mountain, on Mineral ridge near Silver Peak village, and 
 in a long belt running northwesterly across the southern part 
 of the quadrangle. In the first-named region, near Lone 
 mountain, H. W. Turner has found that the granitic rocks 
 are chiefly true granites, composed of alkali feldspar and quartz, 
 with some biotite and muscovite. The feldspar includes ortho- 
 clase, micrpcline, and albite. 
 
 In Mineral ridge, the interbedded slates and thin limestones 
 have been thoroughly injected by siliceous granitic rock, mostly 
 along the stratification, forming chiefly interbedded, more or 
 less lenticular bodies, and often penetrating the intruded rock 
 thoroughly and altering it to a schistose or gneissic condition. 
 The prevalent phase of the intrusive rock is alaskite or quartz 
 alkali-feldspar rock, having a granular texture like that typi- 
 cal of granite, which very frequently becomes coarser or finer 
 (pegmatitic or aplitic). A frequent, but not common, facies of 
 this alaskite is a siliceous biotite-granite like that at Lone 
 mountain. On the other hand, the alaskite passes by gradual 
 
GENETIC RELATIONS OF THE WESTERN NEVADA ORES. 605 
 
 transitions, by a diminution of the feldspar, into pure quartz 
 veins (dikes), which have very much the same chemical and 
 genetic relation to the alaskite that the alaskite has to the 
 granite. The alaskite consists almost wholly of quartz and 
 feldspar, the chief species of the latter having heen determined 
 as orthoclase, microcline, and oligoclase-albite. 
 
 The granite masses studied by Mr. Turner in the southern 
 part of the quadrangle show a variety of different phases. In 
 composition the rock varies from normal granite to alaskite on 
 the one hand, and to quartz-monzonite or granodiorite on the 
 other, the proportions of lime, soda, and potash being variable. 
 
 In connection with the granitic areas near Lone mountain 
 and in the southern part of the quadrangle there are numerous 
 aplitic dikes which clearly represent the later facies of the in- 
 trusions. They are mostly quartz-feldspar rocks or alaskites, 
 more siliceous than the related granites. At Mineral ridge 
 this rock is the predominant type, but in the other regions is 
 subordinate to the granite proper. In many phases of these 
 alaskitic rocks a tendency is seen under the microscope for the 
 feldspar and quartz to segregate in bunches, which are irregu- 
 lar or more frequently elongated. These segregations increase 
 in size until they are conspicuous to the naked eye, and by 
 further enlargements quartz masses (veins), often feldspathic, 
 are formed. Such granitic and magmatic quartz is found in 
 all the granite areas, but in the siliceous alaskitic area of Min- 
 eral ridge occurs in great quantities, in thick veins or lenses. 
 The various closely related phases of the granitic intrusions 
 are regarded as variations from a single general granitic magma. 
 
 It is probable also that the different bodies present represent 
 essentially a single period of intrusion. In the Silver Peak 
 quadrangle the granitic rocks were intruded subsequent to the 
 deposition of the Palaeozoic strata and previous to the Tertiary 
 sediments and lavas. The date of their intrusion is therefore 
 post-Ordovician and pre-Tertiary. A short distance north of 
 the Silver Peak quadrangle granitic rocks similar to those at 
 Silver Peak are probably intrusive into Triassic and Jurassic 
 strata at several points in the Pilot, Excelsior, Ellsworth, and 
 Star Peak ranges. 10 
 
 10 J. E. Spnrr, Bulletin No. 208, U. S. Geological Survey, 2d ed., pp. 102, 103, 109 
 (1903) ; and G. D. Louderback, Bulletin of the Geological Society of America, vol. 
 xv., pp. 317, 336 (1903). 
 
606 GENETIC RELATIONS OF THE WESTERN NEVADA ORES. 
 
 The work of Mr. Turner has shown that the granitic rocks 
 in the southern part of the Silver Peak range cross Fish Lake 
 valley, which lies west of the range, and are represented in the 
 White Mountain range, which is separated from the Sierra 
 Nevada only by Owen's Valley. This adjacent portion of the 
 Sierra Nevada is made up almost wholly of granitic rocks, con- 
 sisting mainly of granodiorite and granite, and the date of 
 their intrusion has been fixed as in the epoch known as post- 
 Jurassic. 
 
 It appears probable, therefore, that the granitic rocks of the 
 Silver Peak quadrangle and of various other ranges of western 
 Nevada are similar in general nature, age, and origin to the 
 granitic rocks of the Sierra Nevada, and are late Jurassic or 
 early Cretaceous in age. 
 
 (c) Dioritic Rocks. Small dikes of diorite are abundant in 
 the Silver Peak region. They are almost always more or less 
 altered, sometimes completely. In their fresh form they con- 
 sisted essentially of feldspar and hornblende in varying propor- 
 tions, but by alteration they have become a mass of secondary 
 products. They are thus conveniently designated by the field- 
 name of greenstones. The alteration-products include chlorite, 
 quartz, calcite, zeolites, epidote, zoisite, kaolin, talc, biotite, etc. 
 
 These dioritic rocks appear, from Mr. Turner's mapping, to 
 be associated with the areas of associated granitic rocks. In 
 point of age the dioritic rocks are always younger than the 
 granitic rocks, which they frequently cut. When they occur 
 associated with the aplitic rocks (alaskites) they are also younger 
 than these, and, as Mr. Turner has found, they are younger 
 than the quartz veins of Mineral ridge, which I have determined 
 to be the siliceous extreme of the alaskitic injection. These 
 greenstone dikes are older than the Tertiary rocks, since they 
 are not found in them. Therefore, the only direct evidence of 
 their age is that they are post-0 r do vician and pre-Tertiary. 
 The apparent association with the granitic areas and the limited 
 quantities of the diorite, whose habit and amount approximate 
 those of the alaskites, suggest, however, that the dioritic rocks 
 may be a later manifestation of the granitic intrusions. 
 
 (d) Tertiary and Quaternary Lavas. In the area under con- 
 sideration, lavas were erupted in large quantity during most of 
 the Tertiary, and the volcanic activity continued into the Qua- 
 
GENETIC RELATIONS OF THE WESTERN NEVADA ORES. 607 
 
 ternary. The knowledge of the Tertiary lavas of the Silver 
 Peak region is entirely the result of the work of Mr. Turner, 
 who has mapped the different rocks separately and has distin- 
 guished and studied rhyolites, andesites, basalts, and some 
 dacites. These lavas seem to have been repeated at different 
 periods. 
 
 2. Mineral Veins. 
 
 (a) Genetic Relations of the Ores of Mineral Ridge. The au- 
 riferous quartz-ores of Mineral ridge are economically the most 
 important in the quadrangle, and some of the mines here have 
 had a considerable production. The Drinkwater mine and 
 some adjacent mines make up the most important group. 
 
 The typical auriferous quartz of Mineral ridge is white and 
 crystalline and is seen under the microscope to be crowded with 
 liquid inclusions. Its appearance is that of the characteristic 
 gold-quartz found in so many districts in the world. Occasion- 
 ally this quartz contains original muscovite and, rarely, original 
 chlorite crystals. Contemporaneous sulphides are sparsely dis- 
 seminated, principally pyrite, more rarely galena. Occasionally 
 copper pyrite has been observed. The quartz throughout con- 
 tains gold and a little silver, the proportion of the latter to the 
 former being about 1 to 100. The gold is finely disseminated 
 in a free state through the quartz and is also contained in the 
 scattered sulphides. It is estimated that about 87 per cent, is 
 in the free disseminated form and the remainder in sulphides. 
 The gold-values are irregularly concentrated into certain groups 
 of quartz lenses and certain lenses within these groups. Thus, 
 in certain portions, it is high-grade, while in others it is low- 
 grade or nearly barren. 
 
 The quartz lenses are intimately associated with alaskite in- 
 trusions, one not occurring without the other. Petrographi- 
 cally, typical quartz and typical alaskite form two ends of a 
 rock series, between which every gradation is abundantly 
 represented. The alaskite becomes quartzose and passes to 
 a state where it contains quartz blotches and veinlets and so 
 gradually passes over into typical vein-quartz. Nearly every 
 quartz lens which has been mined or prospected shows in 
 places considerable feldspar mixed with the quartz. As a 
 rule, the gold-content grows rapidly less with increasing feld- 
 
608 GENETIC RELATIONS OF THE WESTERN NEVADA ORES. 
 
 spar, although occasionally feldspar-bearing rock carries good 
 values. In one place primary free gold has been found in 
 pegmatite. 
 
 It was long ago recognized that granite rocks (which family 
 includes the alaskites) had originated from magmas essentially 
 different in nature from those which form the more basic 
 plutonic rocks and from those which produce surface-lavas. 
 This recognition was due to the discovery of many minerals 
 in granite which cannot be formed from dry melts. Moreover, 
 the relative order of crystallization of the chief granitic min- 
 erals is not the order of their relative fusibility, showing that 
 the different materials were not held in the fluid state by the 
 power of heat alone. All the granitic minerals have been arti- 
 ficially formed in the presence of mineralizers, such as water, 
 fluorides, boron compounds, tungstic acid, etc., at a relatively 
 moderate heat, but most of them cannot be formed by cooling 
 from a dry melted mass. The contact-metamorphism which 
 intrusive granitic rocks exert upon the rocks which they cut 
 is of such a character as to show the presence of mineralizers. 
 Minerals like tourmaline, scapolite, muscovite, etc., frequent in 
 the contact-metamorphic aureoles of granites, testify to the 
 emanation of boron, chlorine, fluorine, acid, water, etc., from the 
 consolidating granitic magma. From these and other consid- 
 erations it is probable that granite has crystallized at a rela- 
 tively low temperature (compared with that of less siliceous 
 igneous rocks), and that it has remained mobile below the 
 fusing-point of most of the granitic constituents on account of 
 the intermixture of water and other mineralizers. It is likely 
 that water was one of the most abundant and efficient factors 
 in these processes. The quantity of water in a magma has 
 never been even approximately determined. Scheerer u esti- 
 mated it as between 1 and 50 per cent., but believed that the 
 actual quantity approached much nearer the minimum than 
 the maximum of these figures. 
 
 Microscopic study of thin sections of the alaskite of Mineral 
 ridge shows that the crystallization of the rock was slow and 
 interrupted. Two distinct periods or generations of crystals 
 are always represented. In different sections the nature and 
 
 11 Bulletin de la Societe Geologique de France, Second Series, vol. iv., p. 490 
 (1846-47). 
 
GENETIC RELATIONS OF THE WESTERN NEVADA ORES. 609 
 
 relative amounts of the minerals belonging to each genera- 
 tion vary greatly, but the following observations apply to all 
 cases : 
 
 1. Quartz' is usually absent from the first generation, or if 
 present is subordinate. In the second generation it is always 
 predominant. In some cases the first generation is made up 
 entirely of feldspar and the second entirely of quartz ; but the 
 separation is usually not so marked, some of the feldspar crys- 
 tallizing with the. second generation together with the predomi- 
 nating quartz. 
 
 2. Microcline is almost always of the second generation. 
 
 3. Albite and oligoclase-albite occur generally in both the 
 first and second generations. 
 
 4. Zircon and pyrite have been noted included in the min- 
 erals of the second generation, but not in those of the first. 
 
 In some cases the rock is almost entirely made up of crystals 
 of the first generation, with the second generation represented 
 in a very subordinate way. Other sections show the first gen- 
 eration only as scattering idiomorphic crystals, with the second 
 generation making up the general area. In most cases, how- 
 ever, the division is fairly equable. 
 
 The chief lesson taught is that the quartz is slightly, but dis- 
 tinctly, younger than the feldspar. It is frequently segregated 
 into irregular chains of grains, which lie between bands of 
 more feldspathic material. 
 
 In nearly every section muscovite is present, generally in 
 fine fibers. This muscovite in many cases is plainly an altera- 
 tion-product which has formed at the expense of feldspar. It 
 is, however, only the feldspars of the first generation which 
 have been thus altered, while those of the second generation 
 are clear. From study of numerous 'sections, three general 
 points in regard to the muscovite are learned: 
 
 1. The microcline is almost always clear and subsequent to 
 the muscovitization. 
 
 2. The quartz is almost always clear and subsequent to the 
 muscovitization, but sometimes incloses fibers and blades of 
 muscovite. , 
 
 3. The orthoclase and striated feldspars (chiefly albite and 
 oligoclase-albite) are in part muscovitized and in part clear, as 
 is natural from their belonging to both generations. 
 
610 GENETIC RELATIONS OF THE WESTERN NEVADA ORES. 
 
 From this it appears that a partial alteration of the feldspar 
 to muscovite took place when the magma was partly con- 
 solidated, and before the deposition of the remainder of the 
 magma, which formed the second generation. 
 
 These observations show that the crystallization process of 
 the alaskite was slow, so that in many cases the magma became 
 filled with contiguous idiom orphic feldspar crystals of the first 
 generation, the interstices between which were filled with resid- 
 ual fluid. The mass composed of the first generation of crys- 
 tals was sometimes rigid enough to be partly cracked and 
 fissured. In these cracks and fissures, as well as in the inter- 
 stitial spaces between the crystals, the residual fluid solidified. 
 Study indicates that many of the fissures were formed by con- 
 traction consequent upon partial consolidation ; others seem to 
 have been due to movements brought about by pressure. Thus 
 the quartz (which makes up always the chief part of the second 
 generation), besides forming as intergranular quartz within the 
 unbroken alaskitic fabric, filled the small fissures, and collect- 
 ing in larger masses formed by itself on a small scale an inde- 
 pendent intrusive in nearly the same sense as the alaskitic 
 magma had done. We may logically conclude that this quartz 
 left, upon consolidation, a residue which was still finer grained 
 and more aqueous. 
 
 The ore-deposits are lenses of such magmatie quartz, which 
 have various dimensions, as seen both on horizontal and verti- 
 cal planes. These lenses are most abundant along certain 
 zones in the intruded formation and overlap on one another. 
 They disappear by wedging or by forking and by splitting into 
 two or more branches. These lenses are original, and not frag- 
 ments of larger dike-like bodies which have attained their form 
 as a consequence of shearing. The wedging-out of the lenses 
 is not attended by evidence of unusual movement; moreover, 
 the phenomena of splitting and uniting forbid the assumption 
 that the form is not primary. 
 
 In the chief mines of the district the formation of ore-min- 
 erals subsequent to the primary consolidation of the quartz 
 lenses has taken place on an unimportant scale. Occasionally, 
 however, some later precipitation has taken place. Along 
 cracks in the quartz, frequently near the contact of the quartz 
 with decomposed greenstone (altered diorite) dikes, subsequent 
 
GENETIC RELATIONS OF THE WESTERN NEVADA ORES. 611 
 
 vein-material has formed, having a gangue of quartz with some 
 calcite and chlorite, and carrying pyrite and galena. The in- 
 ference is that subsequent to the first or primary deposition of 
 minerals, and subsequent to the intrusion of the diorite, min- 
 erals were again deposited along cracks in the original quartz. 
 These minerals are the same as those first deposited, and might 
 be thought to be due to subsequent concentration, the material 
 being derived from the first-formed minerals, and simply con- 
 centrated by subsequent circulating waters. This perhaps has 
 sometimes been the case, but in one mine where the subse- 
 quent ore is economically important (the Mary mine), the 
 amount of the subsequent deposition is so large as to suggest 
 a fresh and independent supply of material. The phenomena 
 in the Mary mine indicate the work of ascending waters, and 
 these new solutions must have had a composition much like 
 that of the solutions from which the primary ore was deposited. 
 
 The close association of the diorite dikes with the quartz- 
 alaskite bodies, and frequently with the subsequent ores, easily 
 leads one to the hypothesis that this subsequent mineralization 
 was dependent on the diorite; but most of the diorite dikes 
 have no later ores in their vicinity, and in the mine where the 
 largest deposit of subsequent ore was noted (the Mary) there 
 is no diorite. 
 
 The general conclusion is that in this district a series of 
 shaly limestones have been intruded by a highly siliceous alka- 
 line magma. From this magma crystallized principally feld- 
 spar and quartz, the consolidation of the feldspar in general 
 preceding that of the quartz. The local phenomena indicate 
 that the crystallization was practically all accomplished subse- 
 quent to the injection. This crystallization, however, was 
 slow, so that the residual quartz was, before its final consolida- 
 tion, in part drawn off into large and small reservoirs, and so 
 could play the role of an independent intrusion. A process of 
 magmatic differentiation by partial crystallization is here 
 proved. 
 
 That the lenses are the fillings of cavities which were present 
 in the schist is out of the question. The parallelism of the 
 schistosity with the curving walls of the lenses shows that the 
 intrusion filled spaces which it itself created. The lentic- 
 ular form of these alaskite and quartz masses (including the 
 
612 GENETIC RELATIONS OF THE WESTERN NEVADA ORES. 
 
 ore-bodies) is like that of the masses of pegmatite and pegma- 
 titic quartz which have been observed in many places in schists 
 near intrusive granitic contacts. I believe that this form is 
 the normal one for attenuated, aqueous, but still viscous, gran- 
 itic material, injected into schists. The fact that the same 
 characterizations apply as a rule to the alaskite lenses and the 
 quartz lenses, indicates that the alaskitic fluid must have been 
 much the same as that of the quartz, both being less viscous 
 than that which has formed the true granite, which neither in 
 this quadrangle nor in similar provinces is accustomed to form 
 lenticular intrusions, but rather bold and well-defined dikes 
 and sheets of which all the ramifications are easily traceable. 
 
 After the last crystallization of the intrusive alaskite and 
 quartz, diorite dikes were injected, and, probably directly after- 
 ward, relatively thin aqueous solutions circulated along cracks 
 and produced a subsequent mineralization, not approaching, 
 however, in commercial importance (in this especial district), 
 the primary mineralization. The brittle quartz of the lenses 
 having been cracked offered the best channels, and here the 
 subsequent mineralization took place, generally under the rela- 
 tively impervious schist hanging-walls, indicating ascending 
 waters. 
 
 For various reasons it is believed that these subsequent min- 
 eralizing solutions represented a residue from the granitic erup- 
 tions, more aqueous than that from which the primary quartz 
 crystallized. 
 
 (b) Genetic Relations of the Great Gulch Ores. One of the 
 gold-mines of Mineral ridge displays, at first examination, a 
 different character from the general type which has just been 
 discussed. At the Great Gulch mine the general geology is, 
 for the most part, like that of most of the typical gold-ores of 
 the district. The country-rock is a thiri-bedded limestone- 
 slate, considerably altered and schistose. Alaskite and quartz, 
 frequently feldspathic, occur in interbedded lenses in the schist. 
 The ore is auriferous arsenopyrite, which occurs in solid 
 streaks of all thicknesses up to 1 or 2 ft. It is distinctly later 
 than the quartz, but the larger streaks are noticeably associated 
 with the alaskite and quartz lenses, especially with the latter. 
 The hanging-wall of quartz lenses is an especially favorable 
 locality. 
 
GENETIC RELATIONS OF THE WESTERN NEVADA ORES. 613 
 
 Here, fracturing has occurred subsequent to the intrusion of 
 the primary alaskite and quartz. Along the channels thus 
 formed ascending waters arose and deposited sulphur, iron, 
 arsenic, and gold. The period of this mineralization is uncer- 
 tain from the local data, but from the resemblance of the phe- 
 nomena here to those of the subsequent mineralization in the 
 Mary mine of the Drinkwater group, it is probable that the ore 
 in the two cases has a similar origin. 
 
 (c) Genetic Relations of the Silver- Ores of Mineral Ridge. On 
 the periphery of the gold-quartz district of Mineral ridge there 
 are at several points ores which contain more silver than gold. 
 The chief of these are at the Pocatello and Vanderbilt mines. 
 The general geology here is like that of the Great Gulch mine. 
 Alaskite and quartz lenses are intrusive into a schist which 
 represents an altered shaly limestone. Greenstone dikes and 
 sheets are present, following especially a zone of quartz lenses. 
 Near the greenstone the quartz is frequently cracked, broken, 
 and mineralized, and in these cracks the silver-bearing ore has 
 been deposited. The most characteristic mineral is a mixed 
 sulphide and oxide containing copper, antimony, silver, and 
 gold. 
 
 Here the schists were first injected by a siliceous magma 
 which crystallized as alaskite and quartz. Basic dikes were 
 subsequently injected, which followed along the zone of quartz 
 and alaskite lenses, because here fracturing was more easy on 
 account of the greater brittleness of the materials. The intru- 
 sion of the diorite produced considerable additional fracturing 
 in the quartz. Along the cracks thus produced mineralizing 
 solutions circulated and deposited the ore. The whole history 
 indicated is analogous to those cases of mines of the typical 
 gold-quartz type which show notable subsequent mineraliza- 
 tion, although the character of the ore is somewhat different in 
 that more silver and copper in proportion to gold are present. 
 
 In other deposits on the periphery of the Mineral ridge aurif- 
 erous quartz district there are ores which have the same type 
 of metallic minerals as in the Pocatello and Vanderbilt group, 
 but which have formed by replacement of a dolomitic marble 
 which overlies the schist formation in which the gold-bearing 
 veins lie. In these cases the inclosing quartz of the vein is 
 contemporaneous with the metallic minerals, instead of being 
 antecedent to them as in the above-described silver-mines. 
 
614 GENETIC RELATIONS OF THE WESTERN NEVADA ORES. 
 
 The mineralization in all these silver-mines seems to differ 
 from the subsequent mineralization described in the case of the 
 gold-mines and prospects, in the presence of more silver and 
 copper; otherwise the facts are not unfavorable for regarding 
 all of this subsequent mineralization as belonging to the same 
 period. I desire to put forth here, as a plain hypothesis, an 
 idea which has been arrived at by considering and reasoning 
 from the distribution and character of ore-deposits throughout 
 the quadrangle, The hypothesis is, that solutions of granitic 
 origin have deposited predominantly gold in the granite or in 
 rocks silicified by the metamorphic effect of the granite, and 
 that in or near calcareous or dolomitic rocks more silver and 
 copper were deposited from the same solutions, the difference 
 being due to the different precipitative influence of the wall- 
 rocks. 
 
 (d) Genetic Relations of the Ores of Lone Mountain. The Lone 
 Mountain group of mines are all situated in Palaeozoic lime- 
 stones, dolomites, and shales which have been more or less meta- 
 morphosed by intrusion of granitic masses. Metamorphism is 
 most intense near the contact, and fades away gradually as the 
 distance increases. The limestones and dolomites are changed 
 into marble, the shales into hornstones and schists, with the 
 development of typical metamorphic minerals. The veins 
 characteristically follow the stratification of the sedimentary 
 rocks. Where they thus occur along bedding-planes these 
 planes have evidently been the sites of differential movement, 
 producing crushing and greater openness. More rarely the 
 veins occur in cross-cutting shear- or fault-zones. In one type 
 of ores, the black mineral containing copper and antimony, de- 
 scribed in the case of the silver-mines of Mineral ridge, occurs, 
 together with galena and pyrite. This mineral is similar to that 
 which has been described under the name stetefeldtite, and will 
 be referred to under this name in the present article. Copper, 
 silver, and gold are present in these ores. The ores of another 
 type are characterized by typical contaci>metamorphic minerals 
 as gangue, chiefly epidote and garnet. In this type the metallic 
 minerals are magnetite, specular iron, pyrite, chalcopyrite, ga- 
 lena, gold, and silver. In another type a quartz gangue con- 
 tains a small amount of stetefeldtite, with galena, free gold, 
 and a little copper. In another type the primary ore is galena, 
 
GENETIC RELATIONS OF THE WESTERN NEVADA ORES. 615 
 
 now largely altered to carbonate. In general there is a strong 
 likeness among the different ores of this district. 
 
 From their location and the nature of their gangue the ore- 
 deposits in the Lone Mountain district are plainly connected 
 with the metamorphism of the sediments produced by the 
 granite. At the time of the granite intrusion siliceous solu- 
 tions emanated from the hardening mass and penetrated the 
 surrounding sediments, which were thus recrystallized and 
 metamorphosed. Such solutions circulated most vigorously 
 along openings which had been formed by the intrusion. 
 These openings were chiefly along bedding-planes, sometimes 
 along cross-cutting shear-zones. Along them circulating gran- 
 itic waters deposited quartz and metallic minerals, forming the 
 veins. 
 
 (e) Genesis of the Ores in the Southern Part of the Quadrangle. 
 In the southern part of the quadrangle the ore-deposits are 
 all prospects, no paying deposit having yet been discovered. 
 One type of deposits consists of quartz veins of granitic origin, 
 similar to the primary quartz of the Mineral Ridge district. 
 These quartz segregations, however, are small in quantity and 
 unimportant economically. As in the Mineral Ridge type, they 
 contain some gold and very little silver. Other quartz veins of 
 a different type follow shear-zones in granite. The quartz con- 
 tains pyrite and gold, and the wall-rocks are altered. The re- 
 semblance of these veins in composition to the magmatic quartz 
 veins of the first type leads to the belief that this second type 
 also is due to siliceous residual solutions derived from the con- 
 solidation of the granite, which have circulated along available 
 channels in portions of the granite which had already consoli- 
 dated. Another type of veins occurs in calcareous and argilla- 
 ceous sediments near the contact of the granite. The gangue 
 is chiefly quartz, the metallic minerals chiefly stetefeldtite, ga- 
 lena, copper, pyrite, etc. The values are chiefly in silver with 
 some gold. The country-rock consists of metamorphosed sedi- 
 ments containing typical contaci>metamorphic minerals. Veins 
 of this type follow fracture-zones, and along such a zone vein- 
 formations may outcrop at intervals for short distances. In one 
 case veins of this type in calcareous strata lie apparently along 
 the same fracture-zone as auriferous quartz veins, of the second 
 type above described, which lie in granite, the fracture-zone 
 
616 GENETIC RELATIONS OF THE WESTERN NEVADA ORES. 
 
 crossing from the granite into the intruded rock. The fact that 
 along what seems to be the same great fracture-zone the ores 
 are of different types in the granite and in the intruded sedi- 
 ments, suggests that they were probably formed by the same 
 solutions, and the different character of the veins is assumed to 
 be due to the different character of the wall-rock. 
 
 (f) General Conclusions as to the Origin of the Metalliferous Ores. 
 
 An intimate inter-relation has been recognized for all- the 
 metalliferous ores of the quadrangle, and all have been traced 
 to the consequences of one event, namely, the intrusion of gran- 
 itic rocks into Palaeozoic sediments in probably pos1>Jurassic 
 time. This district is favorable for such determinations as 
 have been made, since the granitic masses are small and the 
 grouping of the ore-deposits around them is therefore more 
 evident than in a region, like the Sierra Nevada, where the 
 masses of granite are vastly larger. 
 
 The ore-deposits may be divided into the two chief groups : 
 
 1. Bodies of auriferous quartz, probably separated out in 
 gelatinous form from alaskite, during the process of crystalliza- 
 tion, and of the same age and nature as the intergranular 
 quartz of granite and alaskite. In such quartz bodies gold is 
 in places segregated in commercial quantities. 
 
 2. Quartz veins due to replacement or impregnation of 
 crushed material along fracture-zones by siliceous solutions 
 more attenuated than those described above and residual from 
 the crystallization of the magmatic quartz of the first type. 
 These solutions were probably in various degrees of dilution 
 by magmatic water. Such deposits were formed chiefly along 
 movement-zones following bedding-planes in the intruded 
 strata; also in cross-cutting movement-zones in the strata, and 
 to a less degree in the granites. They were formed contempo- 
 raneously with the recrystallization and contact-metamorphism 
 of the sediments under the influence of the granite intrusion. 
 They are more or less typical quartz veins in the pure carbonate 
 rocks and in the granites, but in the argillaceous rocks the 
 quartz is often intermixed in various degrees with metamorphic 
 silicate minerals, such as garnet, epidote, etc. The metallic ele- 
 ments present are principally silver, gold, lead, arsenic, anti- 
 mony, copper, iron, etc., in various combinations. There is 
 
GENETIC RELATIONS OF THE WESTERN NEVADA ORES. 617 
 
 more gold in the granite, more silver and lead in the intruded 
 strata. In the granite the metallic mineral is mostly pyrite, 
 sometimes arsenical. In the sedimentary strata the charac- 
 teristic metallic minerals are the altered sulphide containing 
 silver, copper, and antimony, which we may provisionally call 
 stetefeldtite, and galena. The different character of the metallic 
 minerals is believed to be largely due to the wall-rocks, which 
 have precipitated certain things from solution. Aside from 
 the quartz the nature of the gangue is also believed to be 
 chiefly due to the nature of the walls. 
 
 In all the types of ore-deposits studied, the character of the 
 solutions is believed to have been highly siliceous and alkaline, 
 with mineralizers, such as fluorine, boron, etc., present, but in 
 a limited amount. The presence of gold and silver and other 
 metals is sufficiently explained by the composition of solutions 
 such as described, in which the necessary solvents are present. 
 
 VII. COMPARISON OP SILVER PEAK WITH OTHER ORE-DEPOSITS. 
 
 Fifty miles northeast of the northeast corner of the Silver 
 Peak quadrangle is the Belmont district, at one time produc- 
 tive, but long since abandoned. The ore-deposits consist of 
 quartz veins which occur in the immediate vicinity of an intru- 
 sive mass of granite. From some microscopic work done by 
 me 12 on this granite, it appears that magmatic solutions have 
 been active, producing quartz and muscovite at the expense of 
 the orthoclase in the intrusive rock, and altering the siliceous 
 limestone of the wall-rock to jasperoid and mica-schist. The 
 mineral-bearing quartz veins, it was suggested, were probably 
 contemporaneous with those which were found to occur in 
 irregular form within the intrusive rock, and which were held 
 to represent the final product of the magma. In these quartz 
 veins the metallic minerals are chiefly stetefeldtite and some 
 lead, copper, and iron. 
 
 In the Toyabe range there are numerous ore-deposits, of 
 which the chief ones lie near Austin, about 65 miles north of 
 Belmont. S. F. Emmons has described many of the deposits, 
 which in nearly every case consist of white quartz veins carry- 
 ing metallic sulphides. In the vicinity of Austin the veins are 
 
 12 American Journal of Science, Fourth Series, vol. x., No. 59, p. 355 (Nov., 
 1900). 
 
 39 
 
618 GENETIC RELATIONS OF THE WESTERN NEVADA ORES. 
 
 mainly in granite. In other parts of the district, however, the 
 veins occur in the stratified rocks. In some of the veins the 
 chief silver-bearing mineral is a mixed sulphide of antimony, 
 as is the case in the neighborhood of Belmont. There is prob- 
 ably here an intimate connection between the metalliferous 
 quartz veins and intrusive rocks. 
 
 About 15 miles east of the eastern edge of the Silver Peak 
 quadrangle is the Southern Klondike district, which I have 
 visited and studied briefly. At this camp the main country- 
 rock is Palaeozoic limestone, which is intruded by a long, dike- 
 like mass of siliceous granitic rock, of a composition similar to 
 alaskite. The rock as a whole is closely related to that which 
 I described from Belmont, and also to the alaskite of Mineral 
 ridge at Silver Peak. Occasionally there are in the igneous 
 mass small segregated portions of pure quartz, in which bunches 
 of pyrite and, more rarely, galena occur. The limestone near 
 the contact has been altered to hornstone containing epidote, 
 zoisite and other characteristic products of contact-metamor- 
 phism. Not many yards from the contact, in the altered lime- 
 stone, is a quartz vein which follows parallel to the contact 
 closely for a mile or more, and carries scattered values of silver 
 and gold. The minerals contained are chiefly galena and py- 
 rite, with small bunches of the rich black copper-silver sulphide 
 or stetefeldtite, which has been described as characteristic of 
 those veins in the Silver Peak quadrangle which are near the 
 contact of the intrusive granite, but not in the granite itself. 
 
 All these mineral districts are closely similar. All the ores- 
 have evidently originated as the result of the intrusion of gran- 
 itic bodies into Palaeozoic sediments, and in all cases the ore- 
 deposition was associated with contact-metamorphism. The 
 granitic and alaskitic rocks which make up these intrusive- 
 bodies are similar in those districts which I have examined, 
 namely, Silver Peak, Southern Klondike and Belmont, and, 
 from Mr. Emmons's description, in the Toyabe range. 13 
 
 In the three districts which I have examined there are simi- 
 lar peculiarities of the intrusive rocks, notably the segregation 
 of small contemporaneous quartz masses within the rock, and 
 the alteration of the feldspar to muscovite by magmatic pro- 
 cesses. 
 
 13 Geological Exploration of the Fortieth Parallel, vol. iii., p. 324 (1870). 
 
GENETIC RELATIONS OF THE WESTERN NEVADA ORES. 619 
 
 In the Sierra Nevada, associated with the granitic intrusions, 
 are auriferous quartz veins whose formation immediately suc- 
 ceeded the granitic eruption. The relation between these 
 quartz veins and the granite has long been noted. 14 Recently 
 Mr. Lindgren has adopted the hypothesis that the solutions 
 which deposited the veins were of magmatic origin. These 
 California gold-quartz veins are characterized by the common 
 occurrence of albite as a gangue-mineral. 15 
 
 YIII. CONCLUSIONS CONCERNING THE SILVER PEAK TYPE OF 
 
 ORES. 
 
 The general conclusion is that the Silver Peak deposits are 
 part of a larger province, which is represented more abun- 
 dantly in the Sierra Nevada of California, with only outlying 
 smaller areas in adjacent portions in Nevada. All the ore-de- 
 posits of this province seem to owe their existence to the intru- 
 sion of the post-Jurassic granite. The ores of this province 
 have been concluded to be due to siliceous solutions, which 
 were due to the crystallization of the granitic rocks. These 
 solutions deposited the minerals they contained (silver, gold, 
 etc.) along fractures or shear-zones or other channels, thus 
 forming the typical gold-quartz veins of the region. In Ne- 
 vada these solutions formed, where the wall-rock consisted of 
 the calcareous strata intruded by the granite, a type of noble 
 silver-gold veins (that is, veins often containing a comparatively 
 small proportion of the baser metals) characteristic of this 
 period. 
 
 This metallographic province appears to be most typically 
 developed in California, for which reason we may call it the 
 California province, while the province characterized by the 
 ores in Neocene lavas is best represented east of the Sierra 
 Nevada in the State of Nevada, and may therefore be called 
 the Nevada province. In western Nevada the Nevada province 
 
 14 Whitney, J. D., The Auriferous Gravels of the Sierra Nevada, p. 353 (1880). 
 Kemp, J. F., Ore-Deposits of the United States and Canada, 3d ed., p 370 (1900). 
 Lindgren, W., Gold-Quartz Veins of Nevada City and Grass Valley, Seventeenth 
 Annual Report, U. S. Geological Survey, Pt. II., pp. 175 to 176 (1895-96). 
 
 15 American Journal of Science, Second Series, vol. xxviii., No. 83, p. 249 (Sept., 
 1859) ; and Eansome, F. L., Mother Lode Folio, No. 63, U. S. Geological Survey, 
 p. 8 (1900). 
 
620 GENETIC RELATIONS OF THE WESTERN NEVADA ORES. 
 
 overlaps upon the California province, and along this overlap 
 the ore-deposits belonging to one group are superimposed upon 
 the other. The Nevada province is coextensive with the .ap- 
 pearance of Neocene andesites and rhyolites at the surface, the 
 California province with the appearance at the surface of post- 
 Jurassic granitic rocks. Where, as in western Nevada, these 
 granitic rocks and the strata which they intrude are exposed by 
 erosion in patches lying in the midst of Tertiary volcanics, we 
 may have veins belonging to the different periods very close 
 together. 
 
 IX. MAGMATIC ORIGIN OF ORES OF BOTH PROVINCES. 
 According to the previously expressed conclusions, all the 
 ore-deposits of this rich region of Nevada can be referred to 
 two chief periods of intrusive igneous activity. The various 
 ore-deposits discussed appear to be genetically connected with 
 one or the other of these two great periods. In both cases the 
 mineralization has been ascribed, as the result of close study, 
 to the final processes of rock-solidification subsequent to intru- 
 sion, the residual solutions and gases resulting from consolida- 
 tion having been the agents which produced the mineraliza- 
 tion. The metals also are in all cases considered to have been 
 derived, together with the mineralizing solutions, from the 
 respective magmas. In this whole district, therefore, the effect 
 of the concentrating action of ordinary circulating ground- 
 water does not enter perceptibly into our conclusions, and so 
 far as we yet know it is negligible, except for some minor 
 effects in rearranging the ores of the oxidized zone. 
 
QUARTZrVEINS OF SILVER PEAK, NEVADA. 621 
 
 No. 23. 
 
 Are the Quartz- Veins of Silver Peak, Nevada, the Result 
 of Magmatic Segregation ? 
 
 BY JOHN B. HASTINGS, DENVER,* COLO. 
 (British Columbia Meeting, July, 1995. Trans., xxxvi., 647). 
 
 CHIEF among the varied problems facing the mine-manager 
 is that of vein-structure and origin, which is highly important 
 as a guide to successful discovery and development. If metal- 
 liferous deposits can be traced to the intrusion of waters along 
 definite lines, then is there something tangible for him to study. 
 But when he is told by a geologist that metalliferous deposits 
 are due to some other cause, like magmatic differentiation, 
 while not perhaps discouraged, he is impressed with a vague 
 sense of new worlds to be conquered. 
 
 In 1897, while manager of the War Eagle mine at Rossland, 
 B. C., where, previously, the ore-bodies had not been supposed 
 to occur as veins, I suggested to visiting members of the Cana- 
 dian Geological Survey that, perhaps, the structure of the pyr- 
 rhotite-bodies of that mine, which had been proved to occur 
 along well-defined fractures, might throw some light on the 
 similar deposits of Sudbury, then held to be basic aggregations 
 from the original magma. Later investigation has at least pro- 
 voked discussion of this last deduction, questioning its correct- 
 ness and suggesting that, perhaps, the deposits are actual veins. 
 
 The following extract from a paper by J. E. Spurr l is quoted, 
 because it sets forth Mr. Spurr's theory of the quartz-occurrences 
 of the Silver Peak mines, which will be discussed in this article. 
 It also graphically describes the attendant geological features. 
 
 " The Drinkwater group of mines, which is the most important part of the 
 Blair gold properties, and which has produced practically all of the million 
 dollars' worth of ore, as above stated, may be taken as typical of the gold- veins 
 which, though widespread and numerous, show a wonderful similarity of character. 
 On the surface two adjacent veins outcrop, the Crowning Glory and the Drink - 
 
 1 Ore Deposits of Silver Peak Quadrangle, Bulletin No. 225, U. S. Geological 
 Survey (1904). 
 
622 QUARTZ-VEINS OF SILVER PEAK, NEVADA. 
 
 water, the former the larger, the latter containing the greater quantity of good 
 ore. The quality of the ore still left standing (only the richer portions having 
 been removed for milling) has been more or less carefully determined a number 
 of times 
 
 " Geologically, the veins of the Blair mine are interesting. Properly speaking, 
 they are hardly veins, but flattened lenses of quartz occurring in a definite zone 
 100 ft. or more in thickness. The lenses wedge out and disappear both horizontally 
 and vertically, and their place is taken by overlapping lenses. The wall-rock is a 
 schist, derived chiefly from the metamorphism of an original limy shale or lime- 
 stone. Frequently, also, the wall- rock is a very siliceous granitic rock (alaskite), 
 made up essentially of quartz and feldspar. This alaskite occurs in the schist in 
 lenses similar to the quartz. There is, moreover, every transition between the 
 alaskite and the quartz ; and the schist has been, so to speak, saturated with this 
 siliceous material, which forms seams and thin lenses in it. The auriferous quartz- 
 lenses in the mine in many places run laterally into quartz-feldspar rock (alaskite) . 
 As a rule, the values grow insignificant with the coming-in of the feldspar, but 
 occasionally high values may still be found. 
 
 "The general conclusion is, that here a series of fissile shales and thin-bedded 
 limestones has been invaded by a very siliceous granitic intrusion which has meta- 
 morphosed the sediments to schists. The quartz has plainly the same origin and 
 nature as th& alaskite, both being siliceous phases of a granitic magma [the italics are 
 mine. J. B. H.]. The gold in the quartz is usually free, sometimes associated 
 with scattered galena [and pyrite. J. B. H.]. Greenstone or diorite dikes cut 
 the veins or follow along them, but are of later age. Along the dikes there has 
 been water-circulation, resulting sometimes in impoverishment, sometimes in rela- 
 tive concentration of the original values. 
 
 "This zone of veins outcrops for a mile along the mountain side. At one point, 
 some distance below the vein-zone, free gold in fresh alaskite-pegmatite country- 
 rock was found. 
 
 ' ' In the main, the other gold-mines or prospects of the district have exactly the 
 same geological relations." 
 
 At my first examination of the Blair properties, in December, 
 1900, having, to guide me, the thorough reports of James D. 
 Hague and George "W. Maynard, I spent only one day on the 
 hill; at my second visit, in May, 1905, I was half a day at the 
 Blair mines and three days at the adjoining Valcalde group. 
 
 The mines are on ridges north from the Silver Peak, not on 
 that mountain proper, which rises 1,500 ft. higher (to 9,000 ft.). 
 It is volcanic; the various flows extend for miles easterly, and 
 the successive stages of its growth are marked. It is reported 
 that there is on the top an oblong depression, 2,000 ft. long, 
 filled with water from melting snow. 
 
 Many mining engineers, who have examined veins in schists, 
 will recognize the accuracy of Mr. Spurr's description of the 
 formation in lenses, the disappearance both horizontally and 
 vertically, and the replacement by overlapping ones. They also 
 
QUARTZ-VEINS OF SILVER PEAK, NEVADA. 623 
 
 have sampled veins in granite which have passed gradually from 
 quartz to granite, and have noted the usual disappearance of 
 metallic values with the appearance of the feldspars. 
 
 At my first visit, having no idea of the quartz ever being 
 considered a phase of the granite, and at my last, being busily 
 engaged with the economic features of the Yalcalde group, I 
 did not closely study the occurrence of alas kite within the gran- 
 itic area ; but it was seen in proximity to the great cuts on the 
 Drinkwater mine, especially on the northeasterly or hanging- 
 wall ; and large masses in front of the vein presented a gneis- 
 soid appearance and were extremely silicified. In the south 
 westerly or foot-wall of the veins, the rock appeared to be nor- 
 mal granite, with muscovite and biotite ; occasionally it looked 
 as if the muscovite might be an alteration-product, but usually 
 the rock was in normal condition, except that in all the pieces 
 found the biotites were in the last stages of alteration. Alas- 
 kite was observed in other places among the mines, and away 
 from the veins; and it seemed as if the absence of the micas 
 was due, in part, to their elimination near the veins and other 
 zones of movement, and sometimes to differentiation of the 
 magma. The lenses in the schists are usually alaskite, but as 
 most of these areas have been subjected to solfatarisni, I could 
 not decide whether the absence of the mica was primary or sec- 
 ondary. At the Drinkwater group the outer area bordering 
 the limy shales is alaskite, and at the Yalcalde group the gran- 
 ite adjoins the same rocks. The whole granitic mass of the 
 mines is one magma. There has been fissuring of the normal 
 granite, attended with injection of dikes and formation -of veins, 
 but sometimes without either. The micas adjacent to the move- 
 ment have been more or less destroyed (as in the Boise basin) 
 and aplite has been formed ; and again aplite occurs as a phase 
 of the original magma. 
 
 The whole granitic area is slightly fractured, the cracks 
 cemented with the usual quartz as seen in granite, sometimes 
 auriferous, usually not. These quartz seams are white and solid, 
 glassy, chalcedonic or crystalline, and contain cavities, which 
 are sometimes filled in with chalcedonic quartz. 
 
 Mr. Spurr speaks of finding gold in fresh alaskite-pegmatite 
 country-rock below the veins. I found coarse gold at a point 
 in the gulch below the Frank ~No. 2 mine, possibly on the Co- 
 
624 QUARTZ-VEINS OF SILVER PEAK, NEVADA. 
 
 lumbus, and south of the New York, from 200 to 500 ft. from 
 the veins. The gulch follows a line of movement occupied more 
 or less by a greenstone dike, from 6 to 8 in. wide, dipping flatly 
 to the west. At this particular place the dike is not seen. 
 Along the denuded foot-wall the alaskite is unaltered, except 
 for small deposits of quartz and iron in masses an inch or so in 
 diameter where the gold occurred, and which I take to have 
 been connected with a small quartz vein 6 in. or less wide, 
 intermittently accompanying the dike, which is also the foot, 
 wall. This vein outcrops at the bottom of the gulch, and the 
 quartz is clearly different from the component quartz of the 
 alaskite. Its strike is TE. and dip NW. ; the Blair veins strike 
 NW. and dip NE. ; and the Valcalde veins in this neighbor- 
 hood strike north and dip east. 
 
 The following characteristics of the Blair veins were noted : 
 Beginning at the workings farthest south, a 50-ft. tunnel is run 
 in the foot-wall, and two cross-cuts made to the vein ; the first 
 one is 20 ft. in the solid white vein-quartz, and not through it; 
 the quartz comes in on well-defined fissuring, course N. 30 W., 
 with regular dip 20 NE. The second cross-cut just enters, at 
 the roof, the same white quartz ; there is strong fissuring on the 
 contact; the course is more westerly and the dip is the same as 
 in No. 1. The foot-wall is alaskite, containing a few quartz 
 seams ; the vein, as specified, is hard white quartz, separated 
 from the fooi>wall by uniform and distinct fissuring. The 
 workings on the south side of the gulch expose the vein with 
 the same quartz and the same flat dip, which follows a well- 
 defined fissuring of the alaskite, and a thin greenstone dike, 
 also fissured. A projected cross-section, showing the uniform 
 dip of the Crowning Glory and Drinkwater veins for 1,000 ft. 
 in depth, is given in Fig. 1. 
 
 The main Blair deposits, as Mr. Spurr says, occur in two 
 separate veins ; and it may be added that these are parallel and 
 100 ft. apart. 
 
 This outcrop of sheared country-rock and quartz, from 75 
 to 100 ft. wide, striking about 1ST. 35 W., and dipping from 
 15 to 50 NE., can be traced for 6,000 ft. across a deep gulch, 
 from the Crowning Glory to the New York. Throughout the 
 whole distance, it is attended with fissuring. At the New 
 York there is a belt of the limy shale, with possibly a fissured 
 
QUARTZ-VEINS OF SILVER PEAK, NEVADA. 
 
 625 
 
 dike which the vein follows, being always parallel to the fissur- 
 ing. The quartz outcrop is very prominent for 500 ft. over 
 the New York hill, and extends some distance beyond. The 
 belt of foreign rock (limy shale, etc.), included in the granite, 
 is about 100 ft. wide, but is local; another inclusion joins it on 
 the north, more evidently the limy shale country-rock; here 
 both the shale and granite are sheared, but more nearly north 
 and south than at the vein, and with some silicification. Along- 
 side the vein the granite is not sheared on the NQW York 
 (as it is further south), as if there had been enough of the 
 shale to take up the movement. 
 
 HIGHEST POINT 
 
 STORED ON 
 CROWNING GLORY VEIN 
 
 FIG. 1. PROJECTED CROSS-SECTION OF CROWNING GLORY AND 
 DRINKWATER VEINS. 
 
 There are, perhaps, three ages of greenstone dikes, a diorite 
 quite recent, running ISTW-SE. ; a greenstone later than the 
 veins and sometimes faulting them ; and a greenstone older 
 than the veins, which, to a great extent, the latter have followed. 
 
 Mr. Spurr thinks that all the dikes are later than the veins ; 
 but those followed by the veins sometimes inclose them, and 
 the quartz is not sheared or broken, while the dike, espe- 
 cially that portion occupied by the vein, is sheared to schis- 
 tosity. The quartz, both in the dikes and granite, is usually 
 remarkably clean. Distinct silicifi cation of the dikes is seen, 
 which, however, might be secondary. 
 
626 QUARTZ-VEINS OF SILVER PEAK, NEVADA. 
 
 The Sentinel mine is on the divide between the New York 
 and the Drinkwater, in the limy shale. The only ore-body and 
 occurrence of quartz of consequence is at the open-cut alongside 
 the road. This lens is about 30 ft. long, 20 ft. at the widest, 
 strikes K 20 W., and dips from 20 to 25 E., conformably 
 with the schists. It is near the granite contact. The fissuring 
 differs from that of the Blair mines, and agrees with the regu- 
 lar foliation of the limy shales ; it continues down hill to the 
 north, and is accentuated by lenticular streaks of alaskite in- 
 trusions. There has evidently been solfataric action along it, 
 resulting in alteration on a small scale of the schists, and some- 
 times of the alaskite, and the formation of compact, crystalline 
 and chalcedonic seams of quartz. On the whole, the silicifica- 
 tion seems to have affected the schists more than the alaskite. 
 
 The Valcalde group, adjoining the Blair, exhibits much nar- 
 rower veins. It comprises in one vein-system the Columbus, 
 Lincoln, Frank No. 2, Washington, and Porto, to which might 
 be added the Lucky Sam, owned by other parties. It seems 
 as if all these claims were on one vein. At least, their 
 characteristics are so uniform, and the portions developed 
 occupy such relative positions, that they may be considered 
 'as belonging together. The vein-fissuring and deposition of 
 quartz has followed a pre-existing flat dike, sometimes horizon- 
 tal, and again dipping as much as 15 easterly or westerly; the 
 dike as seen is from a few inches to 5 ft. thick, and the quartz 
 from a few inches to 6 ft. The dike is distinctly sheared, as 
 is also the granite near the contact, and, in some places, for a 
 foot or two away, the quartz is not broken in the least. The 
 quartz, which is sometimes lenticular in the sheared dike, also 
 occurs in continuous streaks several feet wide within the dike, 
 and also on top of it, with the granite for a distinct hanging- 
 wall. In some places the dike is not seen at all, the quartz 
 occurring as a regular streak in the granite, from 4 to 6 ft. 
 wide, with a remarkably smooth and well-defined hanging- 
 wall ; the fooi>wall is not exposed. 
 
 This flat fissure, extending from the New York 2,000 ft. 
 southerly, outcrops along both sides of a north-and-south gulch 
 (the central portion having been eroded away), and terminates, 
 so far as known, in the basin at the head of it. Laterally, it 
 may be 1,500 ft. wide ; this width is only indicated by the Porto 
 
QUARTZ-VEINS OF SILVER PEAK, NEVADA. 627 
 
 mine. It has been disturbed by north-and-south movements, 
 with and without dikes. 
 
 The area is either granite or alaskite, the latter in small 
 patches. The quartz is entirely similar to that of the Blair 
 mines, carrying a little galena and iron sulphides in the 
 best ore. 
 
 The Soda mine lies south of the flat vein above described. 
 The vein strikes north and dips 50 westerly. The hard, white 
 vein-quartz is similar to that of the other mines, the best con- 
 taining galena arid pyrite. At the working farthest south it is 
 found on the hanging-wall of a lenticular mass of an alaskite 
 dike in limy shale. About 30 in. of the alaskite has been 
 silicified. The east or hanging-wall of the quartz is limy shale 
 and -a greenstone dike, the relations of which could not be as- 
 certained. The wall is fissured parallel to the vein. The foot- 
 wall is alaskite ; and the quartz merges into it. The alaskite 
 lens, as developed, is 25 ft. long, 10 ft. wide at the middle, and 
 of unknown extent, the northern half only being exposed. 
 Beyond this northern half no more alaskite is found ; but the 
 vein, composed of quartz stringers and lenses parallel to the 
 foliation of the schists, has been developed, with a width of 
 from 6 to 10 ft., for 300 ft. further. 
 
 The Salisbury mine is in granite, a quarter of a mile from the 
 end of the flat vein. It strikes IS". 18 E. and dips 55 east- 
 erly. The foo1>wall is well defined by 2 ft. of strong fissuring, 
 with a small dike. The vein is 40 in. wide and merges into 
 the granite, having no defined hanging-wall ; but the width 
 of the vein, developed for 55 ft., is uniform. It is cut off on 
 the strike by a !N"W. fault and dike, dipping northeasterly, 
 which carries quartz without values, as the result of a second- 
 ary silicification. The vein-quartz is, like that of the other 
 mines, hard and white, and carrying galena and pyrite. 
 
 The Paris mine has about the same character as the Soda, 
 but without an alaskite dike; the inclosing walls are schists, 
 within a granite area; the veins are lenticular and small, from 
 2 to 4 ft. wide, and contain the same white quartz, with galena 
 and pyrite in the best ore. The course is north and south, and 
 the dip 35 east. 
 
 A few specimens from the Yalcalde group exhibited : (1) 
 wire gold in soft crystalline quartz (called " decomposed " by 
 
628 QUARTZ-VEINS OF SILVER PEAK, NEVADA. 
 
 the miners) ; (2) crystalline gold in a dog-tooth quartz lining 
 of a cavity, which was afterwards filled with chalcedony ; (3) 
 sheets of gold from cracks in chalcedony; and (4) particles of 
 gold in the ordinary vein-quartz, that has been freed by oxida- 
 tion of the sulphides. 
 
 From the above it appears to me : (1) That this district pre- 
 sents bodies of quartz of uniform type, following a well-defined 
 fracture-zone with regular course and dip, each great fissure hav- 
 ing its own direction, varying from IsTW. in the Blair mines to 
 N. 18 E. in the Salisbury mine, and a dip from horizontal to 
 15 westerly and 55 easterly, the easterly dip prevailing. 
 
 (2) That the values are in the quartz, which is confined to 
 narrow lateral limits, being well-defined walls, which may be 
 granite, schist, or, in a subsidiary way, greenstone dikes. The 
 passing of the quartz into the granite occurs in the usual man- 
 ner of veins in a granitoid rock; and the relative amount of 
 accompanying silicified or mineralized granite is not more than 
 usual. 
 
 (3) That, consequently, the veins are not siliceous segrega- 
 tions from the granite, but have been formed in the usual man- 
 ner by ascending waters along lines of fracturing. 
 
OCCURRENCE OF STIBNITE AT STEAMBOAT SPRINGS, NEVADA. 629 
 
 
 
 No. 24. 
 
 The Occurrence of Stibnite at Steamboat Springs, 
 Nevada. 
 
 BY WALDEMAR LINDGREN, WASHINGTON, D. C.* 
 
 (Washington Meeting, May, 1905. Trans., xxxvi., 27.) 
 
 THE important investigations of Dr. G. F. Becker at Steam- 
 boat Springs, Nev., in 1885, aided by the analytical work of 
 W. H. Melville, established the fact that sulphides were being 
 deposited at the surface by hot ascending waters. 1 Steamboat 
 Springs is situated near the eastern base of the escarpment of 
 the Sierra Nevada, six miles distant from the Comstock lode. 
 In a region of former volcanic activity, hot springs with a tem- 
 perature of about 80 C. break forth through a fissure in gran- 
 odiorite, and at the base of a basaltic bluif the waters have 
 deposited a large amount of siliceous and calcareous sinter, 
 some of which is colored red by antimony sulphide. The sin- 
 ter from one of the springs was analyzed by Mr. Melville, 2 and 
 his results, re-calculated to grams per kilogram, showed : 
 
 Grams per Kilogram. 
 
 Ferric oxide, 1.0263 
 
 Antimonious and arsenious sulphides, .... 22.9298 
 
 Mercuric sulphide, ........ 0.0021 
 
 Cupric sulphide, . ....... 0.0124 
 
 Lead, 0.0211 
 
 Gold 0.0010 
 
 Silver, 0.0003 
 
 The relative quantities of antimonious and arsenious sul- 
 phides are not given in the above analysis, but I believe that 
 the former greatly predominated. 
 
 The water of one of the springs was also analyzed by Mel- 
 ville and the re-calculation of this analysis to salts that were 
 possibly present is given in Table I. 
 
 * Published by permission of the Director of the U. S. Geological Survey. 
 
 1 Monograph XIII. , U. S. Geological Survey, pp. 331-353. 
 
 2 Op. cit., p. 344 (Sample II.). 
 
630 OCCURRENCE OF STIBNITE AT STEAMBOAT SPRINGS, NEVADA. 
 
 TABLE I. Possible Composition of the Water of Steamboat 
 Springs, Prior to Oxidation? 
 
 Grams per 1 Liters. 
 
 Ferrous carbonate, FeCO 3 , . . . . . . 0.0029 
 
 Magnesium carbonate, MgCO 3 , 0.0099 
 
 Calcic carbonate, CaCO 3 , 0. 1577 
 
 Calcic phosphate, Ca 3 P 2 O 8 , 0.0137 
 
 Potassic chloride, KC1, 1.9735 
 
 Lithic sulphate, Li 2 SO 4 , . , 0.5650 
 
 Sodic chloride, NaCl, 14.1475 
 
 Sodic sulphydrate, NaHS, 0.0358 
 
 Sodic sulphate, Na 2 SO 4 , .1.1147 
 
 Sodic bicarbonate, NaHCO 3 , 2.9023 
 
 Sodic monocarbonate, Na 2 CO 3 , ...... 0.4314 
 
 Sodic biborate, Na 2 B 4 O 7 , 3.1368 
 
 Sodic tetrasilicate, Na^Si^g, , 8.9090 
 
 Sodic sulphantiraonide, Na^SbSg, 0.0100 
 
 Sodic sulpharsenide, Na 2 AsS 3 , ...... 0.0866 
 
 Alumina, A1 2 O 3 , .. . . *'..- . , 0.0025 
 
 Sodium-mercury sulphide, HgS, wNa 2 S, . . . . trace 
 
 The recalculation given in Table I. is, of course, only of very 
 approximate value, since it is not known with certainty in what 
 condition the different acids and bases are present. Moreover, 
 the salts are partly dissociated. Attention should be called to 
 the fact that the water contains far more arsenic than antimony, 
 but during its nitration a red precipitate formed, consisting of 
 arsenic and antimony sulphides, in what relative amounts the 
 report does not state. 
 
 Having assisted Dr. Becker in his examinations in 1885, I 
 naturally felt a strong interest in this locality; and, in 1901, I 
 revisited the place for a few hours, making a few observations 
 which are here recorded. 
 
 The flow of water from the springs was found to be greatly 
 reduced, probably on account of clogging of the channel. Sev- 
 eral bore-holes had been sunk in order to obtain a better flow, 
 and from these holes fragments of quartz had been brought up 
 which were said to assay high in gold and silver. Of this I 
 know nothing except from hearsay; but, at any rate, these results 
 seern to have stimulated prospecting activity, for a shaft had re- 
 cently been sunk to a depth of 30 ft. near the railway-station, 
 on the sinter-flat a few hundred feet away from, and about 20 
 
 3 Op. cit., p. 347. 
 
OCCURRENCE OF STIBNITE AT STEAMBOAT SPRINGS, NEVADA- 631 
 
 ft. above, Steamboat creek, which is the main drainage-line of 
 the valley. After sinking 25 ft. through sinter, a loose sandy 
 gravel was struck containing well-washed pebbles of granite 
 and andesite, which carried so great an abundance of hot water 
 as to lead to the suspension of mining operations. The gravel 
 was said to contain small quantities of gold and silver, but I 
 am not prepared to discuss this aspect of the case ; moreover, the 
 assays or the material would have no great value regarding the 
 derivation of the gold and silver if found, for they might have 
 been introduced in different ways. A sample of the same or 
 similar material, transmitted to me in the summer of 1904 by 
 Mr. W. H. Weed, was assayed and yielded a trace of gold. 
 
 Upon examining the dump, I found that the gravel through- 
 out contained small shining prisms and particles of metallic 
 luster. A generous sample of the material was collected, but 
 further work was delayed, until 1903, when an examination of 
 the sandy part of the gravel showed it to contain a consider- 
 able quantity of stibnite, in the form of loose slender prisms of 
 the usual type, up to about 1mm. in length, and usually with- 
 out terminal faces. The prisms are sometimes bent and often 
 combined in radiating groups, and may be observed adhering 
 to the surface of nearly every pebble of the gravel, both large 
 and small. Some of the larger granite-cobbles, which usually 
 are soft and decomposed, contain bunches of stibnite crystals 
 in cracks and crevices. With the exception of clastic magne- 
 tite, the only other metallic mineral found in the gravel is 
 pyrite, which forms loose or intergrown crystals of octahedral 
 form, sometimes combined with the cube. In many cases both 
 pyrite and stibnite have crystallized on the surface of pebbles, 
 the former often being tarnished to a black color. Grains of 
 quartz occur with the pyrite, but they are not clearly crystallized 
 and may be clastic. A black opaline material containing about 
 1 per cent, of carbon, according to Dr. E. T. Allen, of the 
 U. S. Geological Survey, sometimes adheres to the andesite 
 pebbles. 
 
 In order to obtain an idea of quantitative relationships, the 
 sandy part of the gravel was further examined by Dr. E. T. 
 Allen, who found that lead, copper, zinc and mercury were 
 absent, and that the material contained antimony, 0.4, arsenic, 
 0.067, and sulphur, 1.88 per cent., which corresponds to stib- 
 
632 OCCURRENCE OF STIBNITE AT STEAMBOAT SPRINGS, NEVADA. 
 
 nite (Sb 2 S 3 ), 0.56; orpiment, (As 2 S 3 ), 0.107; and pyrite (FeS 2 ), 
 3.13 per cent. 
 
 It is not certain in what form the arsenic is present. Stib- 
 nite does not usually contain arsenic, and, on the other hand, 
 no separate arsenical mineral could be recognized. 
 
 That stibnite and pyrite could be of clastic origin is entirely 
 out of the question, and I believe it absolutely certain that they 
 have been deposited by the hot waters which permeate the 
 gravel. Considering that the waters have been shown to con- 
 tain a considerable quantity of antimony, the occurrence seems 
 of great interest. 
 
 No metallic sulphides, corresponding in appearance to the 
 normal minerals, were found by Dr. Becker in the sinters, but 
 cinnabar occurs disseminated in the decomposed granite, some 
 distance away from the present springs. The antimonious sul- 
 phide, which colors parts of the sinter and always appears red 
 and amorphous, was called metastibnite by Dr. Becker. The 
 absence of ordinary minerals of metallic luster indicated, in a 
 way, a missing link in the chain of evidence to prove the dep- 
 osition of ores from hot ascending waters ; and this link is now 
 supplied by the observations recorded above. 
 
 Physical conditions differing very slightly from those at the 
 actual surface will evidently produce crystallized minerals of 
 normal habit and form. Many years ago Senarmont succeeded 
 in forming crystals of stibnite from the amorphous sulphide by 
 heating it to 250 C. in a closed tube with a solution of sodium 
 carbonate. 
 
 During the investigation of the quicksilver-deposits of the 
 Pacific slope, Messrs. Becker and Melville found that stibnite is 
 easily crystallized from solutions similar to the waters of Steam- 
 boat Springs in sealed tubes heated to about 150 C. This 
 renders it probable that a moderate pressure, such as exists at 
 a small distance below the surface, is sufficient to induce the 
 formation of the crystals described in this paper. Very likely, 
 also, the presence of organic matter in the gravel is one of the 
 conditions favoring such deposition. 
 
 Many important deposits of stibnite occur in sedimentary 
 rocks in a manner which renders very probable a genesis some- 
 what similar to that of the occurrence here described. 
 
GEOLOGY OF LAKE SUPERIOR IRON-BEARING SERIES. 633 
 
 No. 25. 
 
 A Summary of Lake Superior Geology with Special Refer- 
 ence to Recent Studies of the Iron-Bearing Series.* 
 
 BY C. K. LEITH, MADISON, WIS. 
 (Lake Superior Meeting, September, 1904. Trans., xxxvi., 101.) 
 
 GENERAL GEOLOGY OF THE LAKE SUPERIOR IRON-BEARING AND 
 COPPER-BEARING SERIES. 
 
 ********** 
 
 The ores of the region are contained in rocks of pre-Cam- 
 brian age, which, for most of the country up to recent years, 
 have usually been referred to as " crystalline schists " or " crys- 
 talline complex;" and regarded principally as a metamorphosed 
 basement-unit upon which the sedimentary rocks, beginning 
 with the Paleozoic, were laid down. In the Lake Superior re- 
 gion this pre-Cambrian complex presents an unusual variety of 
 rocks with determinate relations. It has been possible, with 
 the large expenditures which the magnitude of the iron-mining 
 industry warrants, to work out their stratigraphy to a larger 
 degree than has been possible in almost any other area of pre- 
 Cambrian rocks. 
 
 ********** 
 
 [The portion here omitted contains descriptions of the Archean, Algonkian, and 
 Keweenawan rocks of the several districts, their structure, distribution, correlation, 
 and succession. Table I. and the geological map of the Lake Superior region be- 
 long to this portion, but are here reproduced on account of their value as guides 
 to the readers of the rest of the paper.] 
 
 The simplest and clearest conception of the pre-Cambrian 
 succession for the Lake Superior region may perhaps be ob- 
 tained by thinking of it as primarily divided into six series 
 Keweenawan, Upper Huronian, Middle Huronian, Lower Hu- 
 ronian, Keewatin, and Laurentian all but the last two sepa- 
 rated by unconformities of varying and disputed relative im- 
 
 * Published by permission of the Director of the United States Geological 
 Survey. Reprinted here in part only. 
 
 40 
 
634 GEOLOGY OF LAKE SUPERIOR IRON-BEARING SERIES. 
 
 TABLE I. Correlation of Pre- Cambrian 
 
 
 
 Mesabi District. 
 
 Penokee-Gogebic 
 District. 
 
 Vermilion 
 District. 
 
 Marquette 
 District. 
 
 
 KEWEENAWAN. 
 (Copper -bear- 
 ing.) 
 
 Great basal gab- 
 bro and gran- 
 ite. 
 
 Gabbros, dia- 
 bases, etc. 
 
 Great gabbro. 
 
 
 
 
 
 
 
 Upper Marquette : 
 Michiga m m e 
 
 
 
 
 
 
 formation 
 
 
 
 
 
 
 (slate) (local- 
 
 
 
 
 
 
 ly replaced 
 
 
 
 
 
 
 by Clarks- 
 
 ALGONKIAN. 
 
 UPPER HURON- 
 IAN. 
 (Iron-bearing.) 
 
 Mesabi Series : 
 Virginia for- 
 mation (up- 
 per slate). 
 Biwabik for- 
 mation (iron- 
 bearing and 
 productive). 
 Pok egam a 
 formation 
 (quartzite 
 and quartz- 
 slate). 
 
 Penokee- Gogebic 
 Series: 
 Tyler forma- 
 tion (upper 
 slate). 
 Iron wood for- 
 mation (iron- 
 bearing and 
 productive}. 
 Palms forma- 
 tion (quartz- 
 slate). 
 
 A nimikie Series : 
 Upper slate 
 formation. 
 Gunflint for- 
 mation (iron- 
 bearing, but 
 non - produc- 
 tive). 
 
 burg v o 1- 
 canic forma- 
 tion). Con- 
 tains produc- 
 tive iron-ores 
 near base. 
 Ishpeming for- 
 mation, con- 
 sisting of two 
 memb ers: 
 Bijiki schist 
 (in western 
 part of dis- 
 trict) and the 
 
 
 
 
 
 
 Goo drich 
 
 
 
 
 
 
 quartzite 
 
 
 
 
 
 
 containing 
 
 
 
 
 
 
 productive 
 
 
 
 
 
 
 detrital ores 
 
 
 
 
 
 
 at its base. 
 
 
 
 
 
 
 Middle Marquette: 
 
 
 
 
 
 
 Negaunee for- 
 
 
 MIDDLE HURON- 
 
 
 
 
 mation (iron- 
 bearing and 
 
 
 (Iron-bearing.) 
 
 
 
 
 productive). 
 Siamo slate. 
 
 
 
 
 
 
 Ajibik quartz- 
 
 
 
 
 
 
 ite. 
 
 
 
 
 
 Intrusives. 
 
 
 
 
 Granite intru- 
 
 
 Knife slate. 
 
 
 LOWER HURON- 
 IAN. 
 
 sive in lower 
 formations. 
 Slate- gray- 
 wacke-con- 
 
 Bad River lime- 
 stone forma- 
 tion (cherty 
 limestone) . 
 
 Agawa forma- Lower Marqnette : 
 tion (iron- We we slate, 
 bearing, but j Kona dolomite, 
 non - produc- Mesnard 
 
 
 
 glomerate for- 
 mation. 
 
 Quartzite. 
 
 tive). quartzite. , 
 Ogishke con- 
 
 
 
 
 
 glomerate. 
 
 
 
 LAURENTIAN. 
 (Intrusive into 
 Keewatin.) 
 
 Granites and 
 porphyries. 
 
 Granite and 
 gra nito i d 
 gneiss. 
 
 Intrusive gran- 
 ites, porphy- 
 ries and green- 
 stones. 
 
 Granite, sye- 
 nite. 
 Palmer gneiss. 
 
 
 
 
 
 
 Kit chi schist 
 
 ARCHEAN or 
 BASEMENT 
 COMPLEX. 
 
 KEEWATIN. 
 (Iron-bearing.) 
 
 Greenstones, 
 hornblende- 
 schists and 
 porphyries. 
 
 Green schists 
 and f i n e- 
 grained gneiss. 
 
 Soudan forma- 
 t i o n (i r o n- 
 bearing and 
 productive). 
 Ely greenstone, 
 an ellipsoid- 
 ally-parted 
 basic igneous 
 and largely 
 volcanic rock. 
 
 and M o n a 
 schist, the lat- 
 ter banded, 
 and in a few 
 places con- 
 taining nar- 
 row bands of 
 non - produc- 
 t i v e i r o n- 
 bearing for- 
 mation. 
 
 
 
 
 Peridotite. 
 
GEOLOGY OF LAKE SUPERIOR IRON-BEARING SERIES. 635 
 
 Series of the Lake Superior Region. 
 
 
 
 
 
 Other Parts of 
 
 Crystal Falls 
 District. 
 
 Menominee 
 District. 
 
 Keweenaw 
 Point. 
 
 Michipicoten. 
 
 Ontario North 
 of Lake Supe- 
 rior. 
 
 
 
 Lower, Middle 
 
 
 
 
 
 and Upper 
 Keweenawan. 
 Interbedded 
 lavas and sed- 
 iments grad- 
 ing up into 
 
 
 Interbedded 
 sediments and 
 traps along 
 Lake Superior 
 shore. 
 
 
 
 sandstones. 
 
 
 
 
 Upper Menominee: 
 
 
 
 
 
 Hanbury forma- 
 
 
 
 
 
 tion, mainly 
 
 
 
 
 
 slate, bearing in 
 
 
 
 
 Michigamme 
 formation.con- 
 taining a pro- 
 ductive iron- 
 bearing hori- 
 zon not sepa- 
 rated in map- 
 ping for much 
 of the district. 
 
 lower portions 
 calcareous 
 slates, etc., con- 
 taining siderite 
 and iron oxide. 
 Vulcan formation, 
 consisting of 
 three members : 
 Curry member 
 (iron - bearing), 
 
 
 
 Animikie series 
 of northwest 
 shore compris- 
 ing iron -for- 
 mation over- 
 lain by slate. 
 
 
 Brier slate and 
 
 
 
 
 
 Traders mem- 
 
 
 
 
 
 ber (iron-bear- 
 
 
 
 
 
 ing). 
 
 
 
 
 Hemlock forma- 
 tion (basic vol- 
 canic). 
 Negaunee for- 
 mation (iron- 
 bearing). 
 
 Negaunee forma- 
 tion doubtfully 
 present. 
 
 
 
 1 
 
 Undivided pre- 
 Animikie 
 sediments, 
 
 
 
 
 
 mainly gray- 
 
 
 
 
 
 ^ w a c k e s, 
 r slates and 
 
 
 
 
 
 conglomer- 
 
 Randville dolo- 
 mite. 
 Sturgeon quartz- 
 ite. 
 
 Lower Menominee : 
 Randville dolo- 
 mite. 
 Sturgeon quartz- 
 ite. 
 
 
 Basic eruptives. 
 Acid eruptives. 
 Don* conglom- 
 erate. 
 
 ates, much 
 m e t a m o r- 
 phosed. 
 
 Granite. 
 
 Granites and 
 gneisses. 
 
 
 Granites and 
 gneisses. 
 
 Granites and 
 gneisses. 
 
 
 
 
 Eleanor slates. 
 
 
 
 
 
 Helen forma- 
 
 Greenstone and 
 
 
 
 
 tion (i r o n- 
 
 Iron formation, 
 
 
 Quinnesec schist. (?) 
 
 
 bearing and 
 productive). 
 Wawa tuffs. 
 
 similar 10 that 
 of Vermilion 
 district of 
 
 
 
 
 Gros Cap green- 
 
 Minnesota. 
 
 
 
 
 stones. 
 
 
636 
 
 GEOLOGY OF LAKE SUPERIOR IRON-BEARING SERIES. 
 
 This sketch-map of the geology of the Lake Superior region is generalized and 
 modified from a general geological map of the Lake Superior region, on a scale 
 of ten inches to the mile, compiled by C. E. Van Hise and C. K. Leith for publi- 
 cation in a final general monograph on Lake Superior geology in preparation for 
 the IT, S. Geological Survey. 
 
GEOLOGY OF LAKE SUPERIOR IRON-BEARING SERIES. 637 
 
 portance, and with age-values not yet decided. These series 
 may then be grouped under the two terms, Algonkian and 
 Archean, thereby expressing our opinion that the unconformity 
 at the base of the Huronian, in connection with difference in 
 lithological characters above and below this horizon, should be 
 singled out for special emphasis. If we believe, as Lawson does, 
 that the essential break is at the base of the Upper Huronian 
 series, his " Eparchean interval," then we should express our 
 view, as he has done, by grouping all of the rocks beneath this 
 unconformity under one major heading. 
 
 Since the manuscript of this paper was written, the joint 
 committee of the Canadian and United States Geological Sur- 
 veys, appointed to reach an agreement on disputed points of 
 correlation and nomenclature, has completed its report, and 
 recommends this nomenclature, without expressing opinion as 
 to the desirability of a major grouping of the series under 
 Archean and Algonkian. It is agreed further, in recognition 
 of the difficulties of mapping broad granitic and gneissic areas 
 in Canada, that the term Laurentiaii may sometimes be applied 
 to areas of such rocks which locally may be known to be pre- 
 Huronian, but which for the most part may be of unknown age. 
 
 THE IRON-ORES. 
 Nature, Occurrence, Relations to Adjacent Rocks, Origin. 
 
 A general summary of the work of the U. S. Geological 
 Survey on the iron-ores of the Lake Superior region is given 
 by Van Hise. 11 The present summary covers much of the same 
 ground, but includes also developments subsequent to the pub- 
 lication of his report. 
 
 The iron-ores of the Lake Superior region occur as concen- 
 trations in " iron-formations," ranging from a few hundred to 
 1,000 ft. or more in thickness. These formations, in their pres- 
 ent form, represent the alterations of chemically deposited sedi- 
 ments, for the most part interbedded with normal clastic sedi- 
 ments, such as slate and quartzite. 
 
 Because of the definite stratigraphical position of the iron- 
 ores, in contrast to many vein-deposits, the mapping and inter- 
 pretation of the general geology of the region has been found 
 to be of direct and practical value to the mining-industry, thus 
 
 11 21st Annual Report of the U. S. Geological Survey. 
 
638 GEOLOGY OF LAKE SUPERIOR IRON-BEARING SERIES. 
 
 explaining the large expenditures by mining-interests on geo- 
 logical work. 
 
 In the Vermilion and Michipicoten districts the productive 
 iron-formation is in the Keewatin division of the Archean. In 
 the Mesabi and Gogebic districts the iron-formation is a part of 
 the Upper Huronian series. In the Marquette district two pro- 
 ductive iron-formations are present, one in the Middle Huro- 
 nian and another in the Upper Huronian, the former being the 
 more important. In the Crystal Falls district the iron-forma- 
 tion is in both Upper Huronian and Lower Huronian series, 
 the former being the principal producer. In the Menominee 
 district the formation is of Upper Huronian age. 
 
 The iron-formations of the different districts and ages are 
 surprisingly similar in their general characters. Indeed, it was 
 long assumed, erroneously, that because of their similarity they 
 must be of the same age and origin. A single description will 
 therefore suffice for them all. 
 
 The iron-formation consists mainly of chert or quartz, and 
 ferric oxide, segregated in bands or shots, or mingled irregu- 
 larly. Where in bands, with the quartz bands colored red and 
 the rock highly crystalline, it is called jasper. Where less crys- 
 talline and either in bands or irregularly intermingled, the rock 
 is known as ferruginous chert. In the Mesabi district the local 
 name " taconite " is applied to the ferruginous chert. Other 
 phases of the iron-formation subordinate in quantity are, (1) or- 
 dinary clay slates, showing every possible gradation through 
 ferruginous slate into ferruginous chert; (2) paint-rocks, altered 
 equivalents of the slates; (3) amphibole-magnetite schists; (4) 
 cherty iron carbonate (siderite) and hydrous ferrous silicate 
 (greenalite) ; (5) the iron-ores themselves. 
 
 It may be emphasized that almost the entire bulk of the iron- 
 formation now consists of iron oxide and silica, with carbonates 
 and alumina present in subordinate quantity. The varying 
 combination of part or all of these constituents, mechanically, 
 or chemically, or both, gives all of the rock-types above listed. 
 
 A series of cross-sections, Figs. 1, 2, 3 and 4, summarizes 
 better than a description the structural relations of the ores to 
 the adjacent rocks in the different districts and formations. 
 
 It has been shown that the ferruginous cherts, jaspers, am- 
 phibole-magnetite schists, and iron-ores of the iron-formation 
 
GEOLOGY OF LAKE SUPERIOR IRON-BEARING SERIES. 
 
 639 
 
 result from the alteration either of the cherty iron carbonate or 
 of ferrous silicate (greenalite), or, to a minute extent, from iron 
 sulphide. The small amounts of iron carbonate or ferrous sili- 
 cate now found in the formations represent mere remnants left 
 
 FIG. 1. GENERALIZED VERTICAL SECTION IN MARQUETTE DISTRICT, MICHIGAN, 
 SHOWING KELATION OF DIFFERENT CLASSES OF ORE-DEPOSITS TO ASSO- 
 CIATED FORMATIONS. 
 
 unaltered where so protected by other rocks as not to have been 
 affected by altering agents. The steps of the alteration may be 
 observed, and, in the end-products, the structures and textures 
 
 FIG. 2. GENERALIZED VERTICAL SECTION THROUGH PENOKEE-GOGEBIC ORE- 
 DEPOSIT AND ADJACENT ROCKS ; COLBY MINE, BESSEMER, MICH. 
 
 of the original rocks are often preserved to a remarkable de- 
 gree. The chemistry of the change is summarized in Table II. 
 Let it be emphasized that the ores and ferruginous cherts or 
 jaspers and the amphibole-schists represent alterations from the 
 
640 GEOLOGY OF LAKE SUPERIOR IRON-BEARING SERIES. 
 
 sam e original types. There is a prevailing notion that the orig- 
 nal source of the ores is the jaspers or ferruginous cherts them- 
 
 FIG. 3. GENERALIZED VERTICAL SECTION THROUGH MESABI ORE-DEPOSIT 
 AND ADJACENT ROCKS. 
 
 selves, in their present form. While the leaching out of silica 
 from such rocks does yield ore in many cases, it is believed that 
 
 SHAFT NO. 2 
 
 Jg^/M 
 
 mm 
 
 FIG. 4. VERTICAL SECTION THROUGH ORE-DEPOSIT AND ADJACENT ROCKS 
 OF VERMILION IRON RANGE ; CHANDLER MINE, ELY, MINN. 
 
 ores and jaspers, often of the largest deposits, develop side by 
 side contemporaneously from the alteration of iron carbonates, 
 or iron silicates. 
 
GEOLOGY OF LAKE SUPERIOR IRON-BEARING SERIES. 641 
 
 The agent of the alteration is water, coming more or less 
 directly from the surface, carrying oxygen and carbon dioxide. 
 The concentration of the ores has been found to occur where 
 such waters have been converged. Various factors have de- 
 termined this convergence fracturing and brecciation of the 
 iron-formation, existence of impervious layers in such attitudes 
 as either to converge waters coming from above or to impound 
 the waters and deflect their course between two layers. The 
 presence of an impervious layer, forming a pitching-trough, is 
 perhaps the most conspicuous structural feature determining 
 the convergence of waters concentrating the ores. The imper- 
 vious troughs consist, in the Mesabi district, of slate or paint- 
 rock layers w r ithin the formation itself; in the Vermilion dis- 
 trict, of greenstone with which the iron-formation is infolded 
 or interbedded ; in the Penokee-Gogebic district, of the inter- 
 section of diorite dikes with a foot-wall quartzite; in the Mar- 
 quette district, of a greenstone intrusive into the iron-formation, 
 or of a slate underlying the iron-formation ; in the Menominee 
 district, of dolomite underlying the iron-formation or of slate 
 layers within the formation itself. In all these districts, except 
 the Mesabi, the presence of this impervious basement seems to 
 be clearly the controlling factor in the convergence of waters 
 which have concentrated the ores. 
 
 In the Mesabi district, also, impervious troughs may be im- 
 portant, but they probably are subordinate to, or, at least, not 
 more important than, other factors. The iron-formation and 
 its associated rocks lie in beds on the south slope of the Giant's 
 range, and dip off gently to the south at angles averaging from 
 8 to 10. In addition to the general southward tilting of the 
 beds, they are gently flexed into folds with axes transverse to 
 the trend of the range. Waters falling on the south slope of 
 the Giant's range, and flowing to the south, enter the eroded 
 edges of the iron-formation and continue their way down along 
 its layers, some of which are pervious and some of which are 
 slaty and comparatively impervious to water. The flow thus 
 tends to become concentrated along the axes of the synclines 
 which pitch gently to the southward. Such synclines are not 
 necessarily surface-troughs. They are evidenced by the atti- 
 tude of the layers of the iron-formation, and may not be ap- 
 parent in the unequally-eroded rock-surface or at the surface 
 
642 GEOLOGY OF LAKE SUPERIOR IRON-BEARING SERIES. 
 
 ORIGINAL ROCKS 
 
 TABLE II. Origin and Development of the 
 
 (Prepared for the St. Louis Exposition by C. R. 
 CHEMICAL ALTERATIONS 
 
 /Th 
 
 rThe original rocke from which the Iron orfs have 
 I developed wen deposited ID sedimentary "iron fc 
 / aliens" (in general In rather massive beds, bat In 
 / part slaty), the Iron of which was probably derived 
 / largely from the more ancient ba*lc volcanic rocki 
 j of the Lake Superior region. The iron formation* 
 
 are underlain and overlain by sedimentary formation* 
 I which are relatively Impcrriong to 
 \ qnartzite and slate; also in part by Keweenawan 
 \ gabbro. They are cat by intrusive rocks of varton* 
 \ kinds, and cbaracterUtlcally folded and metamor- 
 
 V 
 
 CO, liberated. 
 
 FeO uniting with 310,, and prodneing- 
 Oranerite (FeO. 3iO,) 
 Fayallte (2FeO. SIO,) 
 
 Fe, Mg, Ca, etc., uniting with SiO,, and producing- 
 Cnmmlngtonite (FeMg)SiO, 
 Chrysolite (MgFe),SiO, 
 
 Hornblende 
 Actinolite (CaMgFe)SiO 
 
 FeO partially oxidized, and producing- 
 
 Magnetite (FeO. Fe,O,) (This occurs exten- 
 sively where Iron formation has been affect- 
 ed by Keweenawan gabbro intrusion). 
 
 Where FeS, (pyrite) is originally present in aband- 
 pyrite is found In resulting rocks. 
 
 CHEKTT IRON CARBONATE. (FeCO,, with CaCO,. and SIO,) 
 
 Locality 
 
 Age 
 
 Vermilion District, Minn. 
 Michiplcoten Ontario 
 Marqnette " Mich. 
 Penokee-Qogebic " Wle. and Mich. 
 Menominee " Mich. 
 Crystal Fall 
 
 Archean 
 
 Algonkian Lower Huron 
 Upper " 
 
 FERROUS SILICATE ROCK. 
 
 (FeSiO,nH,0, with Mg and other impurities. 
 
 ilesabi Diotrict, Ml! 
 
 Ugonsian-Cpper 
 
 PYRITIC CARBONATE ROCK. 
 
 (FeS, disseminated through carbonate Iron formation 
 of very subordinate importance). 
 
 1 Vermilion District, Minn. 
 Mlcbiplcoren District, Ontario 
 
 Archean 
 
 Partial oxidation 
 
 formation of silicates; 
 and removal of / 
 
 carbon dioxide. / 
 
 'Oxidation of ferrons\ 
 iron; separation \ 
 
 t silica; and removal ) 
 of carbon diox 
 
 "/ 
 
 I. CHERTY IRON CARBONATE. 
 
 (1) 3FeOO, 4- SiO, 4- O 4- nH,0 = 
 Fe,0,nH,0 + SiO, + 2CO, 
 
 (8) 2FeCO, 4- SiO, 4- O 4- nH,0 = 
 Fe,0 3 4- SiO, 4- 2CO, -r nH,O 
 SFeOO, 4- SIO, 4- 2O 4- nH.O = 
 Fe,O, 4- Fe,0 4 4- SiO, 4- SCO, + uH,0 
 
 II. FERROUS SILICATE ROCK. 
 
 Fe8iO,nH,0 + CO, + nH,O = 
 FeCO, + H 4 8iO. + nH,O 
 
 2FeC0 3 4- O 4- nH,O = 
 Fe,O,nH,0 4- SCO, 
 
 Also reactions analogous to (8) and (8) 
 
 above. 
 
 III. PYRITIC CARBONATE ROCKS. 
 
 FeCO, 4- FeS, + SiO, 4- 6O 4- H,O = 
 
 Fe,O, . nH,O 4- SiO, 4- 2SO, 4- CO, 
 Also reactions analogous to (2) and (3) 
 above. 
 
GEOLOGY OF LAKE SUPERIOR IRON-BEARING SERIES. 
 
 643 
 
 Iron- Ores of the Lake Superior Region. 
 
 Van Hise, C. K. Leith and W. N. Smith.) 
 
 RESULTING PRODUCTS 
 
 .MPHIBOLITIC - MAGNETITIC BOCKS. 
 YROXENIC - CHRTSOLITIC - MAGNETITIC ROCKS, 
 
 d 
 
 JASPrLITE-" Hard Ore Jasper." 
 
 (Produced by dehydration and rccrystalllzatlon ] 
 of ferruginous cherts and ferruginous elites 
 probably under conditions of deep burial, 
 Igneous Intrusion.) 
 
 / rn?*Ti 
 
 FERRUGINOUS CHERTS. 
 
 (Produced by alteration of more massive 
 bedded phases of iron formation.) 
 
 I From Cherty Iron Carbonate. (" Soft Ore Jasper.") 
 II From Ferrous Silicate Rock. ("Taconlte.") 
 
 FERRUGINOUS SLATES. 
 
 (Produced by alteration of slaty 
 phases of Iron formation.) 
 
 'IRON ORES, HARD. 
 
 Produced by farther metamorphism 
 of the soft on 
 
 cherts by processes which include 
 dehydration, derillclficBtion, and 
 enrichment by lofllitratlon, prob- 
 ably nnder conditions of deep 
 burial, dynamic action, or ig- 
 neous Intrusion, or any combina- 
 tion of them. 
 
 Blue non-bydrated hematite. 
 Red non-hydrated hematite. 
 Micaceous or specnlar non- 
 
 hydrated hematite. 
 Magnetite.. 
 
 
 
 Produced nnder weathering conditions 
 by oxidation of magnetite to hematite. 
 
 f IRON ORES, SOFT. 
 
 Soft Hydrated Hematite or Liraonite. 
 Hard Hydrated HeraaUw. 
 
 DETRITAL IRON ORES. 
 
 (Formed by breaking up through wavt 
 action of pre-existing ores or 
 ferruginous cherts and jaspers. In 
 the latter case often Involving 
 concentration by assorting, by 
 leaching oat of silica, and by 
 subsequent enrichment.) 
 Detrltal ore (conglomerate ore) from 
 
 base of Upper Huronian. Sediment 
 formed from pre-existing ferrug- 
 inous chert or jasper which bas 
 been subsequently deeilicified and 
 enriched. 
 
 Oetrital ore from Menominee district. 
 
 Mich., from base of Upper Huronian. 
 Sediment formed directly from pre- 
 existing ores. 
 
 Detrital ore from Menominee district. 
 
 Mich., from base of Cambrian. 
 Produced by breaking up of pre- 
 
644 GEOLOGY OF LAKE SUPERIOR IRON-BEARING SERIES. 
 
 of the irregular covering of glacial drift. The concentration of 
 the flow along the synclines in the layers of the iron-formation 
 seems so simple and evident that there is a temptation to gen- 
 eralize and say that the underground circulation has prohably 
 concentrated the ores along these broad synclines. When the 
 district was first examined by the U. S. Geological Survey this 
 simple explanation was applied. But further study shows that 
 other factors modify the circulation of water and the localiza- 
 tion of the ore, and that these secondary factors may be locally 
 dominant. 
 
 The most important of these modifying factors is the fractur- 
 ing of the iron-formation, which has furnished numerous trunk- 
 channels for the circulation of underground-waters. The water 
 has been confined to narrow, irregular and most devious trunk- 
 channels formed by the fracturing of the iron-formation, and, 
 while it has probably followed the fracture-openings along syn- 
 clines to a greater extent than along anticlines, it has not filled 
 the entire syncline formed by the folding of the iron-formation. 
 The result is that the ores have developed along limited and 
 irregular areas within the synclines. They may occupy a con- 
 siderable part of the syncline, in which case the synclinal struc- 
 ture of the iron-formation may be observed in the layers of 
 wall-rock adjacent to the ores. In other cases, they occupy 
 so small a proportion of the syncline that the layers of the 
 iron-formation in the adjacent wall-rock give no indication of 
 synclinal dips. Not infrequently, several more or less inde- 
 pendent deposits may have developed in the same general 
 syncline, as, for instance, in the area adjacent to the town of 
 Virginia. To put it briefly, the ores show such position, irreg- 
 ularity, extent, and relations to wall-rocks as to make applica- 
 ble the expression sometimes heard in the district that the ores 
 have developed through the " rotting " of the iron-formation 
 along fractures, usually, but not always, in broad synclinal 
 areas. 
 
 Other factors modifying the general underground-flow ot 
 water in the Mesabi iron-formation are the numerous impervi- 
 ous slaty layers within the iron-formation, and the Virginia 
 slate capping the iron-formation of the south ; all of which have 
 considerable effect. So far as the water is free to flow T south- 
 ward through the iron-formation, the impervious layers serve 
 
GEOLOGY OF LAKE SUPERIOR IROX-BEARING SERIES. 645 
 
 only to limit the flow below. But the continuous south dip 
 of the impervious strata carries the waters down to a point 
 when the ground is saturated and the waters are ponded be- 
 tween impervious layers above and below. That ponding actu- 
 ally occurs is shown by the fact that drill-holes penetrating 
 the slates and entering the iron-formation frequently meet 
 water under pressure, indicating artesian conditions. When 
 ponded, the water seeks the lowest point of escape, which 
 is likely to be found near the north margin of the slate-layers. 
 The movement of the water towards the lowest point of escape 
 causes a considerable lateral movement in the circulation, and 
 this lateral movement has probably, at least in part, controlled 
 the shape of certain deposits on the range, which have their 
 longer dimensions parallel to the strike of the layers of the 
 iron-formation. 
 
 The ponding of the water and consequent overflow has still 
 another effect. Where ponded the flow is governed by the 
 point of lowest escape rather than by the shape of the impervi- 
 ous basement. When water is drawn off at the edge of a basin, 
 the flow is greatest near the point of escape and diminishes in 
 all directions away from that point. This statement is true, 
 whether the bottom of the basin is flat or fluted ; hence, in the 
 Mesabi iron-formation, where the water is ponded, the flow is 
 concentrated near the point of lowest escape regardless of 
 whether this be over a syncline or anticline provided both are 
 below water-level. The lowest point of escape is likely to be 
 over synclines, but the surface erosion, both by glacial' and me- 
 teoric agencies, has been such that this is not always the case. 
 For this reason it is not certain that iron-ore deposits near the 
 edge of the Virginia slate or near the edge of interstratified 
 slate-layers may not have developed along arches as well as in 
 synclines of the iron-formation. 
 
 The above facts are intimately related to the problem of 
 finding ore under the solid black Virginia slate. The ques- 
 tion is frequently asked, is there any reason why ore shall not 
 be found under the black slate? The absence of ore under 
 the slate has not been demonstrated by actual drilling; only a 
 comparatively few holes have penetrated any considerable 
 thickness of the Virginia slate and entered the iron-formation 
 below. Yet such holes as have been put down have revealed 
 
646 GEOLOGY OF LAKE SUPERIOR IRON-BEARING SERIES. 
 
 ore only near the slate-margin and frequently of low-grade. 
 In several cases, the iron-formation beneath the slate has been 
 shown to be of a green, unaltered variety, indicating that the 
 alteration necessary for the development of ore-deposits has not 
 gone far. If the development of the ore is dependent upon a 
 vigorous circulation, and this vigorous circulation is lacking 
 under the Virginia slate because of the ponding, we have here 
 an adequate cause for the non-existence of ore-deposits under 
 the black slate. Yet, further work may show that other factors 
 have entered; and, considering the extent and value of the 
 new iron-bearing territory, which would be thrown open were 
 ore found under the Virginia slate, additional actual drilling 
 seems to be advisable. 
 
 In the Gogebic district, while the impervious basement has 
 been the controlling factor in the concentration of waters, and 
 consequently of the ores, faulting through the dikes has afforded 
 free passages for waters which have been taken advantage of, 
 with the result that the ores follow such faulting-planes and are 
 not uniformly confined to positions on the impervious troughs. 
 
 In Figs. 1, 2, 3 and 4, it will be noted that, for all of the dis- 
 tricts except the Mesabi, the vertical element in the distribution 
 of the ores is an important one. In the Mesabi district the 
 horizontal element is the greatest one in most cases. Here, a 
 single ore-body or a group of ore-deposits may give practically 
 a continuous surface of iron-ore for several miles, with a depth 
 ranging from a few feet to 400 ft. or more. In the other ranges 
 a depth of ore of 1,000 ft. is common and 2,000 ft. has been 
 exceptionally reached. It is not unlikely that in some places, 
 particularly the Gogebic district, the ores will be found to 
 greater depth, although the lower limit is well determined for 
 the most part. Theoretically, the lower limit of the ore-bodies 
 ought to be the lower limit of the active circulation of oxidiz- 
 ing waters from the surface. In the Mesabi district the pro- 
 portion of the area of the ore-bodies appearing at the rock- 
 surface, to that of the iron-formation as a whole, is about 8 per 
 cent, for the productive part of the district, and 5 per cent, for 
 the entire district. For the other districts of the Lake Supe- 
 rior region, the area of the iron-ore deposits is far less than this 
 percentage of the area of the iron-formation as a whole. In bulk, 
 the percentage of ores to the iron-formation is much smaller 
 
GEOLOGY OF LAKE SUPERIOR IRON-BEARING SERIES. 647 
 
 throughout the Lake Superior country, for it will be remem- 
 bered that the ores are essentially surface-alterations and are 
 therefore well represented at the surface. 
 
 The alteration of the iron-formation, resulting in the concen- 
 tration of the iron-ores or in the development of ferruginous 
 cherts and jaspers and amphibole-schists, has taken place in 
 different geological periods under various conditions, with a 
 result that the ores of each of the districts, as well as of differ- 
 ent parts of the same district, show considerable lithological 
 variety. The same ingredients iron oxide and silica appear 
 here mechanically combined as highly crystalline jasper, there 
 in the hydration as a soft ferruginous chert, or both mechani- 
 cally and chemically combined as an amphibole-magnetite 
 schist. The iron-oxide may appear here as a brilliant specular 
 hematite or magnetite, and there as a soft granular hematite or 
 limonite. The ores of the Mesabi district are soft and granu- 
 lar and associated with ferruginous cherts. At the east end 
 they become amphibolitic, magnetitic and non-productive. The 
 ores of the Gogebic district are of a similar nature and become 
 amphibolitic, magnetitic and non-productive at both the east 
 and west ends of the district. The ores of the Vermilion dis- 
 trict are hard, blue and red ores, at Ely, brecciated, associated 
 with jaspers. The ores of the Marquette district comprise 
 hard blue ores and brilliant specular ores associated with jas- 
 pers, called " hard-ore jaspers," soft ores associated with fer- 
 ruginous cherts, or " soft-ore jaspers," and with underlying 
 slates, and at the west end of the district, magnetite and specu- 
 lar hematite ores associated with jaspers and with amphibole- 
 magnetite rocks. 
 
 Without going into the variable conditions in the several 
 districts and the varying geological history of the different ores 
 and rocks, it may be said that, so far as the alteration of the 
 iron-formation has proceeded continuously under the influence 
 of surface-waters without interruption by igneous activity or 
 Orogenic movements, the soft ores and ferruginous cherts have 
 resulted. So far as these have been subsequently under deep- 
 seated conditions of alteration, they have become dehydrated 
 into hard red and blue specular ores and brilliant jaspers. This 
 phase of the alteration did not require the agency of surface oxi- 
 dizing-waters. So far as the alteration of the original iron-forma- 
 
648 GEOLOGY OF LAKE SUPERIOR IRON-BEARING SERIES. 
 
 tion took place within the sphere of influence of great intrusive 
 masses where the waters were heated and oxygen was not abun- 
 dant, or under similar conditions developed by deep burial and 
 orogenic movement, the iron oxide and silica of the formation 
 combined with small amounts of other substances to form fer- 
 rous silicates, and the ferrous iron was oxidized to magnetite, 
 making one of the variety of rocks usually described as amphi- 
 bole-magnetite schists. 
 
 In the discussion of the development of the ores, we have 
 begun with the original rocks of the iron-formation, namely, 
 the iron carbonates and greenalite rocks, containing minute 
 amounts of sulphide, which constituted the formation when it 
 was first deposited. The origin of these rocks themselves is a 
 subject of absorbing interest, but it is a subject in which direct 
 evidence, such as we have been dealing with, is lacking; and 
 a subject, furthermore, of less practical importance and less 
 direct bearing upon the study of the ores themselves. Certain 
 facts are well known. Both the iron carbonates and the green- 
 alites (and their altered equivalents) constitute a conformable 
 part of a continuous sedimentary succession, being interbedded, 
 overlain and underlain by fragmental rocks, such as quartzite 
 and slate. They are themselves bedded. It is impossible to 
 escape the conclusion that they are water-deposited sediments. 
 It is, further, clear that they are not water-deposited sediments 
 of an ordinary nature. They are not fragmental ; their nearest 
 analogues are chemical sediments, such as limestones. 
 
 From here on in our explanation we must depend rather 
 upon analogy with chemical sediments, such as limestone, and 
 with iron compounds now being precipitated in bogs and lakes 
 and elsewhere, than upon direct evidence in the formation 
 itself. On this basis, the history of the development of these 
 rocks, as outlined by Van Hise, 12 is as follows : 
 
 . . . ' ' It is, however, my belief that the iron for the iron-bearing formations 
 was largely derived from the more ancient basic volcanic rocks of the Lake Supe- 
 rior region. When the individual districts are taken up it will be seen that a green- 
 stone, often ellipsoidal, in many places porous and amygdaloidal, in many places 
 
 12 The Iron-Ore Deposits of the Lake Superior Kegion, by C. R. Van Hise, 21st 
 Annual Report, U. S. Geological Survey, Pt. III., pp. 319, 320. 
 See also : 
 Monograph XLIIL, U. S. Geological Survey, by C. K. Leith. 
 
GEOLOGY OF LAKE SUPERIOR IRON-BEARING SERIES. 649 
 
 schistose, and rich in iron, is the most characteristic rock of the Archean, and 
 that similar rocks occur abundantly in the Huronian. Where these igneous 
 rocks were adjacent to the seas they would be leached by the underground water 
 and the iron transported to the adjacent seas. It is probable that to some extent 
 this leaching process also went on below the waters cf the sea. The iron was 
 probably transported to the water mainly as carbonate, but to some extent as 
 sulphate. The carbonate would there be thrown down by oxidation and hydra- 
 tion as limonite, and the sulphate in part as basic ferric sulphate. Much of the 
 sulphate was probably directly precipitated as sulphide by the organic material. 
 The limonite would be mingled with the organic matter which was undoubtedly 
 present, as shown by the associated carbonaceous and graphitic shales and slates. 
 When deeply buried the organic matter would reduce the iron sesquioxide to 
 iron protoxide. By the simultaneous decomposition of the organic matter carbon 
 dioxide would be produced, which would unite with much of the protoxide of 
 iron, producing iron carbonate. The sulphate of the basic ferrous sulphate 
 would be reduced to the sulphide by the organic material, thus producing the 
 pyritic carbonates. Where the iron was brought to the water mainly as sulphate 
 the direct reduction of this salt by organic matter would form iron sulphide with 
 little or no carbonate. Simultaneously with the production of these substances 
 chert was formed, probably through the influence of organisms. 13 
 
 "Some of this silica would unite with a part of the protoxide, producing fer- 
 rous silicate. More or less mechanical sediment would also be laid down. Thus 
 the original rocks the cherty iron carbonates, the ferrous silicate rocks, and the 
 pyritic cherts would be produced. 
 
 " It has chanced that at three different periods in the history of the Lake 
 Superior region, these processes of the development of the original rocks of the 
 iron-bearing formations have occurred extensively. While this might at first be 
 thought remarkable, there is no good reason for thus regarding it. At some time 
 during each of the Archean, Lower Huronian and Upper Huronian periods the 
 quiescent conditions of chemical and organic sedimentation have occurred, and 
 since the iron-bearing volcanic rocks were each time available for the work of 
 underground waters and sea- waters, naturally iron carbonate and the other origi- 
 nal rocks have been produced. In each period the source of the material and 
 the process of its formation were essentially the same." 
 
 Time of Concentration. 
 
 The concentration of the ores of the Lake Superior region 
 was far advanced before Cambrian time, as shown by the ex- 
 istence of ore and other iron-formation boulders, derived from 
 the pre-Cambrian, in Cambrian conglomerates. For each of 
 the districts the particular time of concentration has been more 
 closely calculated, but this is a subject which would require a 
 longer discussion than the scope of this paper warrants, and 
 
 13 The Penokee Iron-Bearing Series of Michigan and Wisconsin, by E. D. 
 Irving and C. R. Van Hise : Monograph, U. S. Geological Survey, vol. xix., 1892, 
 pp. 246-253. 
 
 Fossil Medusae, by C. D. Walcott: Monograph, U. S. Geological Survey, vol. 
 xxx., 1898, pp. 17-21. 
 
 41 
 
650 GEOLOGY OF LAKE SUPERIOR IRON-BEARING SERIES. 
 
 the reader is referred to Van Hise's general paper already 
 cited. 
 
 Topographic Relations of the Ores. 
 
 With very few exceptions, the ore-deposits of the Lake Su- 
 perior region lie either on the slopes or at the foot of conspicu- 
 ous ranges or hills. This has been explained by Van Hise as 
 due to the concentration of ores through the circulation of 
 ground-waters. Topographic elevations have given the waters 
 sufficient head to search the ground on their slopes and per- 
 haps at the base of the slopes. On the slopes the movement of 
 the water is largely downward and more or less direct from the 
 surface, thus carrying an abundance of altering agents, particu- 
 larly oxygen and carbon dioxide ; while in intervening low-lying 
 areas, the waters escape with a lateral and upward movement 
 after a longer underground journey, during which they have 
 lost considerable proportions of the agents which alter the iron- 
 formation to ores. Van Hise holds that, in the latter positions, 
 the ores have not developed so abundantly as on the slopes. 
 The present topography is, in many places, not the same in de- 
 tail as the topography which existed at the time the ores were 
 concentrated ; and accordingly it is not safe, in discussing the 
 relations of the ores to the topography, to consider too small 
 topographic units. Believing that the present major topo- 
 graphic conditions represent, at least in part, the past condi- 
 tions, Van Hise has discussed in some detail the relations of 
 the Lake Superior ores to the particular topographic features 
 of the different districts. In one or two cases, and especially 
 in the Glogebic district, the topographic units selected for dis- 
 cussion may have been too small, and this has resulted in criti- 
 cism of the entire theory. It is believed that his main conclu- 
 sions as to the relations of the ores to the major topographic 
 features have been confirmed, rather than disproved, by recent 
 work. 
 
 Present Studies of the Origin of the Ores. 
 
 The ores of the Lake Superior region have been shown, in 
 certain districts, to have been developed from the alteration of 
 iron carbonate, in other districts from the alteration of iron 
 silicate, and in others, from both. In the Marquette, Gogebic, 
 Vermilion, and Crystal Falls districts, the original rock has 
 
GEOLOGY OF LAKE SUPERIOR IRON-BEARING SERIES. 651 
 
 been described as iron carbonate. In the Mesabi district, tbe 
 original rock bas been described as consisting of ferrous sili- 
 cate or " greenalite " granules principally, but witb subordinate 
 amounts of iron carbonate. In tbe Felch Mountain and Re- 
 public areas, the presence of granules similar to the Mesabi 
 granules has been noted. In the Menominee district, both iron 
 carbonate and silicate granules have been supposed to yield 
 the ore. 
 
 The vast scale on which the alteration of ferrous silicate 
 granules has occurred in the Mesabi district, together with 
 the evidence of the somewhat wide-spread distribution of such 
 granules in unknown but small quantity, has led to a re-exami- 
 nation of the ores and rock of the remaining districts, with the 
 result that evidence of the prior existence of granules has been 
 found also in both the Gogebic and Crystal Falls districts. So- 
 far as the re-examination has gone, however, it tends to confirm 
 the essential correctness of the determination of iron carbonate 
 as the original iron-formation rock for these districts. 
 
 In the new Animikie iron-range, on the northwest coast of 
 Lake Superior, the eastern continuation of the Mesabi range, 
 original and secondary iron carbonate and pseudomorphs after 
 greenalite are found so well exposed and so closely associated 
 that it is hoped that the study of this district now in progress 
 will furnish decisive evidence of the real relations of these two 
 substances. 
 
 In the new Baraboo iron-range of Wisconsin, which is of 
 pre-Cambrian age and similar in many respects to the Lake 
 Superior deposits, Weidman has attempted to show that the 
 ores are original bog-deposits, which have become dehydrated. 
 His conclusion does not necessarily affect the remaining Lake 
 Superior ores, but the similarity in geology is so close that, 
 until the contrary is proved, it is believed that the explanation 
 applied to one region will apply substantially to others. Rea- 
 sons are given on a subsequent page for believing that his ex- 
 planation is not a true one. 
 
 Experimental work in the laboratories of the University of 
 Wisconsin shows the great ease of the alteration of the iron car- 
 bonates through the agency of water. In a few hours this sub- 
 stance becomes coated with hydrous iron oxide when treated 
 with warm water containing only small amounts of oxygen de- 
 
652 GEOLOGY OF LAKE SUPERIOR IRON-BEARING SERIES. 
 
 rived from contact with the air. Iron silicate has been found 
 to be much more refractory, but still has yielded slightly to the 
 action of ordinary water. Quantitative results are looked for 
 at an early date. Analysis of mine-waters from the Lake Supe- 
 rior region as a whole, it is hoped, will yield results indicating 
 the manner in which the ores and rocks of the iron-formation 
 have been altered. 
 
 The form in which the phosphorus occurs is not definitely 
 settled. Some of it is certainly in the form of apatite. But 
 many ores, and especially Mesabi ores containing phosphorus, 
 apparently do not contain apatite. The association of phos- 
 phorus with aluminum, both in ores and in other phases of the 
 iron-formation, suggests the possibility that the phosphorus is 
 chemically combined with aluminum. The solubility of the 
 phosphorus compounds in the ores is still a mooted question. 
 Incidents may be cited of the remarkable change of phospho- 
 rus-content in stock-piles and mines, because of the washing of 
 surface-waters; and in drilling, allowances are frequently made 
 for changes in phosphorus-content in washing. Whether this is 
 mechanical or chemical, its extent and its commercial impor- 
 tance are yet to be decided. ,It is hoped that investigations 
 now in progress will settle these questions. 
 
 Iron-Ranges of Recent Discovery. 
 
 ********** 
 
 [The portion here omitted contains a description of the Baraboo range, of south 
 central Wisconsin, where, associated with pre-Cambrian quartzites, beneath the 
 Paleozoic rocks, slate, dolomite, and iron-ore occur. The district has been described 
 in Bulletin xiii. of the Wis. Geol. and Nat. Hist. Survey (1904), by Dr. Samuel 
 Weidman. The iron-ore is low-grade (below 55 per cent.) Bessemer hematite ? 
 with a little limonite, associated with and grading into "dolomite, cherty 
 ferruginous dolomite, ferruginous chert, ferruginous slate, and ferruginous dolo- 
 mitic slate." It is stratified conformably with the rocks below and above it. For 
 the following reasons, Dr. Weidman thinks the Baraboo ores are bog-deposits, 
 subsequently dehydrated.] 
 
 "1. The iron-ore deposits are bedded and, to all appearances, stratified like 
 other sedimentary deposits. 
 
 " 2. The stratified iron-ore deposits are not set off sharply from the surrounding 
 associated stratified rocks, such as slate, chert and dolomite, but grade into them 
 through all possible gradations. The iron-ore is not especially associated with 
 any particular kind of the various rocks adjacent, and the stratification of these 
 various kinds of rocks is always conformable to that of the iron-ore. Since the 
 slate, dolomite and chert are original sedimentary deposits, and since the iron- 
 ore grades into them and is conformable to them, it is believed that the iron-ore 
 has the same origin as these conformable interstratified deposits of related rock. 
 
GEOLOGY OF LAKE SUPERIOR IRON-BEARING SERIES. 653 
 
 " 3. That the physical conditions in the district at the time the iron-formation 
 was deposited were favorable for the formation of such shallow-water deposits as 
 iron-ore is indicated by the presence of sun-cracks in the rocks of the iron-forma- 
 tion immediately adjacent to the iron-ore and also by the presence of carbona- 
 ceous material, probably decayed vegetable matter in the iron-ore and associated 
 ferruginous rocks. Furthermore, the rapid alternation in the various strata of 
 the iron-formation indicates changing conditions of sedimentation, a common 
 characteristic of shallow-water deposits, and the composition of the iron-bearing 
 formation itself, with its chert, carbonate rock and slate, is identical with the 
 composition of shallow- water deposits being formed to-day. 
 
 " 4. That the iron-ore deposits originated long antecedent to the folding and 
 fracturing of the iron-formation and the deposition of the mineral veins is 
 shown by the fact that the strata of iron-ore are generally folded, crumpled and 
 fractured, and that the mineral veins cut across the stratification and also across 
 the folds of the iron-ore and associated rocks. The folding of the ore-deposits 
 appears to conform in all respects to the folding of the associated rocks, and the 
 ore-deposits appear to have the position and distribution which they should have 
 if formed before the general folding of the pre-Cambrian formations into their 
 present position took place. 
 
 "5. The change in the ore subsequent to its original deposition as limonite, 
 as shown by the microscopic and chemical study of the rocks, is believed to be 
 mainly a change to hematite by dehydration of the limonite under deep-seated 
 conditions of metamorphism. This change is exactly parallel to the dehydration 
 of the original clay-minerals of the gray Seeley slate-formation and of the clay- 
 minerals in the slate-phases of the iron-formation, which now contain very little 
 water of constitution, only 2 or 3 per cent. , but which originally must have con- 
 tained from 10 to 25 per cent. This change of limonite by dehydration is also 
 analogous to the probable dehydration of the original siliceous deposits now con- 
 stituting the chert layers. 
 
 " The geological data which led the writer to believe that the Baraboo iron-ore 
 was very probably deposited as limonite under conditions similar to those under 
 which bog- and lake-ore are formed to-day, and later merely partially dehydrated 
 to form hematite, have just been briefly outlined. The principal evidence be- 
 lieved to be directly opposed to the theory of the secondary development of the 
 iron-ore as replacement- and alteration-deposits by work of the underground water 
 is mainly furnished by the character of the work of the underground water at 
 present, as indicated by its chemical composition, and by the work of the ground- 
 water of the past, as indicated by the character and composition of the mineral 
 veins in the ore and associated rocks. 
 
 "From the study of the composition of the ground-water now circulating 
 through the iron-bearing rock and associated formations in the district, and its 
 comparison with that of ground-water outside the district and with river-waters 
 and with chalybeate mineral waters, it has been concluded that very probably the 
 present work of the ground-water in the iron-formation is not that of depositing 
 iron-ore. It is quite generally accepted that mineral veins are deposited from 
 underground water circulating through fractures in rocks ; and the fact that the 
 mineral veins in the iron-ore and associated rocks are largely quartz and not iron- 
 ore is interpreted as evidence that the work of the ground-water of the past was 
 very probably not that of depositing iron-ore. If the work of circulating ground- 
 water of the past could have or did develop the iron-ore deposits, why should not 
 the work be now in progress, since ground-water is now circulating through the 
 ore-deposits and associated rocks as it has in the past ; and if the iron-ore could 
 have been or was developed by the work or agency of ground-water, why should 
 
654 GEOLOGY OF LAKE SUPERIOR IRON-BEARING SERIES. 
 
 not the mineral veins that ramify through the ore-deposits and associated iron- 
 bearing rocks be composed largely of iron-ore instead of quartz?" 
 
 As the Baraboo district is related geographically and strati- 
 graphically with Lake Superior ore-bearing districts, Weidman's 
 conclusion that the ores are original deposits immediately 
 suggests that the same origin may hold for the ores elsewhere 
 in the Lake Superior region, or, vice versa ; and that explana- 
 tions of the secondary origin of the Lake Superior ores may 
 really apply in the Baraboo district. It is believed that Weid- 
 man has not proved the Baraboo ores lo be an original deposit, 
 for the following reasons : 
 
 His arguments 1, 2 and 3, without change, may be used equally 
 well in support of a theory of secondary concentration from an 
 originally deposited chemical sediment iron carbonate or iron 
 silicate described as laid down in shallow waters. 
 
 ~No evidence is presented in support of argument 4. The 
 secondary alteration of previously folded and contorted iron- 
 formations to iron-ore, with the retention of all the folded and 
 contorted structures, is the common feature for the Lake Supe- 
 rior country. Accompanying and following this change, there 
 has been some additional folding, followed in some cases by an 
 introduction of normal mineral veins, but usually it has been a 
 minor phenomenon. The fact of the folding and contortion of 
 iron-formation layers could not be accepted elsewhere in the 
 Lake Superior country as evidence of the subsequent occur- 
 rence of the major folding. 
 
 The argument that the presence of quartz-veins shows that 
 quartz only, and not iron-ore, has been introduced or concen- 
 trated subsequent to the deformation, it is believed, will not 
 stand analysis. In the Lake Superior region, abundant evi- 
 dence may be presented to show that quartz-veins have devel- 
 oped both before and after the concentration of the iron-ore, 
 and I know of no criteria that will enable one to say that the 
 presence of quartz, rather than iron-ore, in particular fractures or 
 veins, proves or disproves the secondary origin of the ore. In 
 the Vermilion district, minute veins of ore may be seen cross- 
 ing both quartz-veins and an earlier concentration of the ore, 
 and in turn are crossed by later quartz-veins. 
 
 The dehydration of limonite (5) has probably occurred, but it 
 would make little difference whether the limonite were an 
 original deposit or were itself a secondary alteration. 
 
GEOLOGY OF LAKE SUPERIOR IRON-BEARING SERIES. 655 
 
 The argument that the composition of the waters seems to 
 show that ore-concentration is not at present occurring is beside 
 the mark when we remember that for the Lake Superior region 
 as a whole, and hence for the Baraboo district itself until the 
 contrary is proven, the concentration of the ores was largely 
 finished before Cambrian time. The conditions at that time 
 doubtless differed widely from present conditions, but even ad- 
 mitting that they are similar, the fact that waters from the iron- 
 formation, which have been analyzed, contain no ingredients 
 different from the surface-waters of the region, does not show 
 that they may not still be doing work. Van Hise has empha- 
 sized the fact that the ordinary surface-waters are the ones that 
 do the work, and that the development of iron oxides from iron 
 carbonates and iron silicates is the normal work of percolating- 
 waters for the belt of weathering in general. The presence of 
 silica in the Baraboo waters shows that silica is being carried 
 away from this general zone or region, and there is every reason 
 to believe that it may be carried as well from the ore as from 
 the overlying sandstone. Certainly it could not be assumed 
 that the silica contained in the water, notwithstanding the fact 
 that it is no more abundant in mine-waters than elsewhere, 
 might not be coming from the ores themselves, thus enriching 
 them. It is believed, also, that the process of alteration has 
 gone so far in the mines from which the waters were secured, 
 that the waters now circulating there are, for the most part, in 
 contact with oxidized products the end-products of alteration 
 under such conditions and that they could scarcely be expected 
 to contain any considerable amounts of ferrous compounds. It 
 is not at all certain that waters, working through less-altered 
 parts of the formation, either in the past or elsewhere in this 
 district, might not show a different composition. 
 
 Finally, Weidman's theory would require that, after straight- 
 ening out the secondary folds and contortions, the iron-ore 
 should lie in a continuous even bed or layer, having only such 
 irregularities as would result from uneven deposition in shal- 
 low waters. If, in the Lake Superior region as a whole, the 
 iron-formation layers should be straightened out, the resulting 
 bed or layer would have strange shapes indeed, and would here 
 and there end abruptly along the strike or dip, against other 
 phases of the iron-formation or even against a dike or boss 
 of greenstone. (See Fig. 1.) Indeed, Weidman's theory is 
 
656 GEOLOGY OF LAKE SUPERIOR IRON-BEARING SERIES. 
 
 squarely opposed to nearly all conceptions of the structural 
 relations of the ores to the adjacent rocks, worked out inde- 
 pendently for each of the Lake Superior districts, where ex- 
 ploitation has gone far enough to allow of satisfactory study. 
 It is believed that these structural facts, worked out for the re- 
 gion as a whole, will apply in the Baraboo district itself, so far 
 as the facts are known in the present state of exploration. 
 
 The ores thus far found have been along the eroded edges 
 of the iron-formation. Attempts to locate the ore in the center 
 of the great Baraboo valley beneath the dolomite have met 
 with failure. Straightening out the folds in the iron-ore bodies, 
 and reproducing the original attitude and distribution, the iron- 
 ore deposits would appear, so far as is now known, as a series 
 of lenses, limited by dolomite or feathering-out beneath it, 
 down the dip, in the direction of what is now the center of the 
 valley. On Weidman's theory, the ore might be found any- 
 where beneath the dolomite, and its truncation by an erosion- 
 surface would be purely a matter of accident. It must be ad- 
 mitted that drilling has not gone sufficiently far to prove that 
 the iron-ore lenses uniformly reach the pre-Cambrian erosion- 
 surface at some point; but sufficient drilling has been done to 
 lead certain mining engineers of the district and me to conclude 
 that the evidence is strongly in favor of this view and that the 
 normal Lake Superior conditions here prevail. 
 
 While it is believed, for the above reasons, that Weidman's 
 conclusion as to the origin of the Baraboo ores is not supported 
 by the evidence he has presented, the fact that the ore grades 
 into, and is overlain by, dolomite a unique occurrence for the 
 Lake Superior region would make it easy to accept an ex- 
 planation of the origin of the Baraboo ores different from that 
 applied to the remaining Lake Superior ores, if sufficient evi- 
 dence be presented ; and such acceptance would not necessarily 
 imply a revision of views of the secondary origin of the remain- 
 ing Lake Superior ores. 
 
 ****5)*5iC*** 
 
 [The portion here omitted gives brief accounts of the Guyana range in Crow 
 Wing county, Minn, ("containing ore of possible commercial value," and possi- 
 bly of Archean, Middle Huronian or Upper Huronian age) , and the Animikie 
 range, extending NE. from Gunflint lake along the international boundary to the 
 east end of Thunder bay, and regarded as an eastward continuation of the 
 Mesabi. The paper ends with a statement of the work which must still be done, 
 before the complex problems of the general and the economic geology of the 
 Lake Superior region can be regarded as completely solved.] 
 
GEOLOGICAL RELATIONS OF SCANDINAVIAN IRON-ORES. 657 
 
 No. 26. 
 The Geological Relations of the Scandinavian Iron-Ores. 
 
 BY PROF. HJALMAR SJOGREN, PH.D.,* STOCKHOLM, SWEDEN. 
 
 (Toronto Meeting, July, 1907. Trans., xxxviii., 766.) 
 ********** 
 
 AMONG the feldspar-rocks there are certain types which occur 
 constantly in different areas viz., the amphibolitic plagioclase- 
 rocks and the granulitic rocks composed of quartz and alkaline 
 feldspars. Among the latter soda-granulites as well as potash- 
 granulites are met with ; also the corresponding gneisses occur. 
 
 ********** 
 GROUP I. THE ORES OF THE ARCH.EAN CRYSTALLINE SCHISTS. 
 
 ********** 
 
 The Rocks. 
 
 The ore-bearing rocks of the ore-province of central Sweden 
 are chemically and petrographically unlike the more monoto- 
 nous gneiss- and granite-areas which surround them. On the 
 whole, they constitute a quartz-feldspar formation in which 
 purer quartzitic rocks, limestones, " skarn " rocks and ore- 
 bodies are very subordinate members. (Skarn is the Swedish 
 name for rocks of varying composition, mostly consisting of 
 lime, magnesia, iron, and alumina silicates of the pyroxene, 
 amphibole, and garnet groups ; as secondary minerals, epidote, 
 chlorite, biotite, and talc occur. The skarn is scarcely an inde- 
 pendent rock but is connected with the ore-deposits. It is 
 formed through an interchange between the silica of the quartz- 
 feldspar rocks and the basic constituents of the ore-formation.) 
 
 [ABRIDGED SUMMARY. The amphibolites must be considered as stretched and 
 dynamo-metamorphosed dioritic* rocks. The granulites are divided into two 
 groups, one showing predominant plagioclase, the other equal or predominant 
 orthoclase. Evidently, the iron-ore deposits are connected in some way with the 
 
 * Director of the Mineralogical Department of the State Natural History 
 Museum, Stockholm, Sweden. 
 
658 GEOLOGICAL RELATIONS OF SCANDINAVIAN IRON-ORES. 
 
 rocks of granulitic structure. This structure is most probably due, in general, 
 to a recrystallization, under stress and movement, within the anamorphic zone of 
 depth. "Simultaneously with the mechanical deformation of the rock-masses 
 
 there has been also a supply of iron-bearing ma^matic material by solutions, 
 imparting to the ore-deposits their present peculiar epigenetic characters." 
 Numerous pegmatitic dikes, penetrating both ore and rock, are to be considered 
 
GEOLOGICAL RELATIONS OF SCANDINAVIAN IRON-ORES. 659 
 
 as crystallized from aqueo-igneous solutions in contraction-fissures, during the 
 cooling of the rock. Stripes, stratification, contortion, and even brecciation of the 
 country-rock near the ore-body, indicate the metasomatic deposition of the latter 
 in shear-zones, or in portions of the original rock contracted in volume by the 
 chemical changes involved, as well as fractured by movement. There is also a 
 linear or stretched structure, sometimes conformable to the pitch of the ore-bodies. 
 The arnphibolites and a great part of the granulites seem to be igneous rocks of 
 deep-seated origin. 
 
 The ores are of five types : (A) Ores carrying apatite, disseminated or in stripes, 
 with low percentage of silica and feldspar. These were originally magnetite, but 
 have been altered in many places to specular hematite by a process which simul- 
 taneously reduced the proportion of apatite. They are products either of mag- 
 matic differentiation in the granulite or of metasomatic replacement of feldspar- 
 rock by iron-bearing solutions in the anamorphic zone. The constant large amount 
 of apatite favors the former hypothesis. (B) Mixed hematites and magnetites, 
 nearly related to the preceding, and evidently formed through injection of 
 iron-bearing solutions and partial replacement the ore being therefore much 
 younger than the country-rock. (C) Quartz-banded ores, chiefly specular hema- 
 tites. The alternation of ore and gangue is often, but not always, as definite as in 
 the jasper-banded ores of Lake Superior. This structure has been generally re- 
 garded as due to a primary stratification, on which hypothesis the ores must have 
 formed by the alteration of stratified rocks. But it seems more probable that the 
 structure is a secondary feature, produced during the replacement process. (D) 
 The tl skarn 1 ' ores, rich magnetites, accompanied and connected by beds of 
 tl skarn" minerals (see definition of "skarn," on a preceding page). They have 
 often been formed by metasomatic replacement of limestone and dolomite, ore and 
 gangue-minerals being thus younger than the country-rock. (E) Limestone-ores, 
 occurring in or with limestone and dolomite, of which they are metasomatic re- 
 placements. ] 
 
 The Origin rf the Ore-Deposits. 
 
 During the last century the ores of this group were regarded 
 by Swedish geologists as sedimentary deposits, laid down to- 
 gether with the over- and underlying granulite formation. Such 
 opinions were advocated by A. Erdmann, Anton Sjogren, A. 
 E. Tornebohm, B. Santesson, and others ; among the Norwe- 
 gian geologists Yogt has with eagerness developed this theory. 3 
 Only with respect to the Gellivare ores, opinions were much 
 divided, and several geologists e.g., Lundbohm, v. Post and 
 L of strand believed them to be of igneous origin. 
 
 3 See, for instance, J. H. L. Vogt, De lagformigt optraedende jernmalmfore- 
 komster, Geologiska Foreningen Forhandlingar, vol. xvi., p. 275 (1894) ; Dunder- 
 landsdalens jernmalmfelt, Norges Geologiska Under so g else, No. 15, pp. 56 to 63 
 (1894) ; Om de lagrade jernmalmsfyn-digheternas bildningssatt, Werml. Bergsman- 
 nafor Ann. (1896). 
 
 The same opinion has also been expressed by several foreign geologists, for in- 
 stance, De Launay, Annales des Mines, Tenth Series, vol. iv., pp. 49 to 209 (1903), 
 as well as in the German treatises on Ore-Deposits by Beck (1901), and Stelzner- 
 Bergeat (1906). 
 
660 GEOLOGICAL RELATIONS OF SCANDINAVIAN IRON-ORES. 
 
 Since 1890, the present writer has in several papers argued 
 that metasomatic processes undoubtedly played a prominent 
 part in the formation of these ores, and has been able to point 
 out several analogies with the iron-ores of the Lake Superior 
 region. 
 
 In this paper I shall attempt to show that the metasomatic 
 processes must have taken place, not in the surface-zone but in 
 the anamorphic zone, and that the ores bear fully, in their min- 
 eralogical features and association, characters of formations of 
 the deep-seated zone. 
 
 In several cases, it may not be possible to determine whether 
 the original iron-bearing material was the product of primary 
 magmatic differentiation, as in the apatite-ores, or iron-bearing 
 magmatic solutions producing metasomatic deposits, as in the 
 lime- and s&arn-ores, or possibly altered chemical sediments, as 
 in the quartz-banded-ore type. 
 
 The iron-bearing solutions may frequently have been of mag- 
 matic origin, thus carrying iron-bearing material from below; 
 or it may be that the very small amount of water contained in 
 the rocks was sufficient, under the condition of dynamic meta- 
 morphism in the anamorphic zone, to collect and concentrate the 
 iron particles. The occurrence of ore-deposits in connection 
 with surface-rocks, above pointed out, and their absence in the 
 greater granite laccolites seems to prove that the deposits are 
 formed in a depth less than that in which the granite consoli- 
 dated, but still in the anamorphic zone. 
 
 Arguments Against the Sedimentation Theory. That these de- 
 posits are not sedimentary is indicated by the fact that the 
 surrounding rocks are igneous. So long as the granulite of 
 Grangesberg and Gellivare was considered a sedimentary rock, 
 it was possible to ascribe the same nature to the ore-deposits. 
 But this foundation of the sedimentary theory seems more and 
 more to give way. 
 
 Again, the form of these ore-deposits differs as widely as pos- 
 sible from that of stratified bodies. They have been termed 
 lenses, stocks, lineals, etc. In general, they are much more 
 irregular than is consistent with a sedimentary formation. Some- 
 times these ores divide or branch into the surrounding rock (see 
 Fig. 2, showing the central part of Dannemora), a feature which 
 does not agree with any known form of primary sedimentation,. 
 
GEOLOGICAL RELATIONS OF SCANDINAVIAN IRON-ORES. 661 
 
 but must be interpreted as secondary. At other places, the ore 
 incloses portions of the surrounding rock, which sometimes 
 take the form of irregular sinuous bands, cutting obliquely 
 through the ore from the hanging-wall to the foot-wall. (See 
 Fig. 3, showing the central part of Grangesberg.) In such 
 cases it appears that the overlying and the underlying rock, 
 together with the narrow partition-walls between the ore-lenses, 
 form " a continuous whole, pre-existing to the ore." This 
 mode of occurrence also is incompatible with sedimentary de- 
 position. 
 
 Diorite 
 
 Gangue 
 
 FIG. 2. DANNEMORA MINE, CENTRAL PART. 
 
 In a few cases only, a structure resembling primitive stratifi- 
 cation is met with; e.g., in the banded quartziferous ores (type 
 C), which for this reason possess special interest. The ores 
 rich in silica and alumina (type B) sometimes present a schis- 
 tose structure ; but this is without any doubt a foliation caused 
 by pressure. 
 
 Even where the stratified structure is present, we are not 
 justified in concluding that the material is primitive; for in 
 this case also, though retaining the original structure, it may 
 have been subjected to subsequent metasomatic transformation. 
 Thus the banded quartziferous ores may have originally con- 
 sisted of alternating bands of a carbonate and of amorphous 
 silica, since altered or replaced in situ. 
 
662 GEOLOGICAL RELATIONS OF SCANDINAVIAN IRON-ORES. 
 
 lUi'JW.I O 
 
GEOLOGICAL RELATIONS OF SCANDINAVIAN IRON-ORES. 663 
 
 Concentration and Transformation Within the Deep-Seated Ana- 
 morphic Zone. To this zone the rocks were transferred during 
 the period of the plication, by which evidently a part were 
 folded to a considerable depth, being at the same time sub- 
 jected to dynamo-metamorphic alterations, which in many 
 cases determined their present characters. 
 
 During this period the ores and the gangue were formed by 
 thermal iron-bearing solutions acting under high pressure. To 
 what degree these solutions were magmatic, carrying ore-sub- 
 stance from below, or to what degree the small amount of 
 water contained in the rock was active, it is not possible to 
 determine. In either case, the process was different from the 
 action of solutions circulating in open channels. It consisted 
 in a solution of the rock-substance, which was intensified by 
 the stress and friction, according to the principle of Riecke, 
 and also in an accumulation and concentration of the ore, the 
 surface-tension operating to unite particles of the same sub- 
 stance. 
 
 The ore-material, participating in the plication process, with 
 its upheavals, folding and dislocations of the strata, has suf- 
 fered some mechanical changes. One of the effects which, in 
 many cases at least," may be ascribed to the mechanical fold- 
 ing is the peculiar overlapping which many ore-bodies pre- 
 sent. This may be a primitive form of metasomatic deposi- 
 tion, but may also be considered as a result of the mechanical 
 displacement of an ore-layer. Through a number of inclined 
 or even vertical planes of dislocation, the deposit has been cut 
 into pieces, which have then been somewhat displaced in rela- 
 tion to one another. Often these dislocations can be pointed 
 out only with difficulty, or not at all ; they are more obvious 
 when the iron-ore occurs associated with a limestone bed. (See 
 Fig. 4, showing the plan of Stallberget.) The whole limestone 
 horizon, with its accompanying iron-ore, is here fractured into 
 several lenses, oblique to one another. The planes of disloca- 
 tion have been effaced by the recrystallization of the granulite, 
 and the schistose structure thereby developed, with its lamina- 
 tion running obliquely to the different lenses, which gives the 
 appearance of being situated on different levels of the strati- 
 graphical series. 
 
 Another mechanical effect of the rock-plication is the stretch- 
 
664 GEOLOGICAL RELATIONS OF SCANDINAVIAN IRON-ORES. ' 
 
 ing of the surrounding rock, by which it has assumed a linear 
 structure, a system of smaller folds, with the axis of folding 
 parallel to the stretching, having often been formed at the same 
 time. In many cases (e. g., the Lekomberga mine in the parish 
 of Ludvika, and the Smedje and Mossaberg mines in Striberg), 
 a connection between the stretching of the rocks and the pitch 
 of the ore-bodies is observable, the axis of the stretching coin- 
 ciding with the direction of the pitch. Yet it cannot be as- 
 sumed as beyond dispute that this connection is in every case 
 
 -Itroithinaqrufy 
 
 Magnetite. Limestone. Granulite. Diorite. 
 
 FIG. 4. STALLBERG MINES'. 
 
 due to a stretching of the ores themselves ; it may also be ex- 
 plained as produced by the ferriferous solutions, chiefly follow- 
 ing the directions indicated by the folds, formed simultane- 
 ously with the stretching of the rocks. 
 
 The stretching of the rocks has given rise to the character- 
 istic form presented by the Swedish ores of this type, which 
 form is evidently due to a factor acting in a vertical direction. 
 This form is represented in Fig. 5, which is a longitudinal sec- 
 tion of part of the Svartvik mines, according to B. Santesson. 
 Sometimes this form will be developed into such an extreme 
 type as that of the mine of Stora Malmsjoberg, in which the 
 ore mined in 1898 had, according to H. Sundholm, a length of 
 15 m., a breadth of 12 m., and a depth of 150 meters. 
 
 The Chemical Changes. These have been much increased, not 
 only by the high temperature in the anamorphic zone, but also 
 by the stress and mechanical deformation, which tends to in- 
 crease the solubility of the ore-material, as well as of the rocks. 
 
GEOLOGICAL RELATIONS OF SCANDINAVIAN IRON-ORES. 665 
 
 The more easily soluble limestones were especially adapted 
 to take up the ore-deposition ; and generally great changes and 
 transfers of the ores to secondary places of deposition have 
 taken place in them, depending on water-courses, impermeable 
 sub-strata, etc. The concentration has occurred especially along 
 folds, fracture-zones, fissure-systems, and contacts. Thus the 
 ores assume the irregular, secondary forms characteristic of 
 metasomatic deposits, as shown in Fig. 2, representing the cen- 
 tral part of Dannemora. 
 
 . Q METER 
 
 O40 
 
 GranuRte 
 
 FIG. 5. LONGITUDINAL SECTION OF THE SVARTVIK MINES. 
 
 Other instances of concentration by solutions are offered by 
 the fairly numerous cases in which the ore proves to be younger 
 than dikes which traverse it. Such an instance is the Timans- 
 berg, a deposit of type D, which is traversed by minor dioritic 
 dikes. Of these, C. H. Vrang writes that " in their vicinity 
 the ore increases considerably in thickness." 4 In the Kran- 
 grufva, in the Persberg district, the rich and pure ore is chiefly 
 found on one side of a large diorite dike; a dislocation is out 
 of the question, for the ore-bearing layer is also found on the 
 other side of the diorite, but without equally distinct ore-con- 
 centration. H. V. Tiberg has described how, in the Qustavus 
 mine of the Langban district, a deposit consisting of specular 
 iron-ore and magnetite, with gangue, continues from the sur- 
 face to a flat system of diabase apophyses occurring at a depth 
 
 4 Geologiska Foreningen Forhandlingar, Stockholm, vol. ix., p. 244 (1887). 
 
 42 
 
666 GEOLOGICAL RELATIONS OF SCANDINAVIAN IRON-ORES. 
 
 of from 54 to 60 m., on which the ore spreads like a cake, 
 while below the diabase dikes the rock is dolomite only. In 
 such cases the intrusive dikes have evidently preserved the 
 underlying rock from transformation. A similar instance from 
 Dannemora is mentioned by A. E. Fahlcrantz, 5 who says that 
 over a dike of halleflinta (felsite-porphyry) a band of iron-ore 
 a few inches in thickness was met with, accompanying the hal- 
 leflinta. In this case, however, it is probable that the ore is a 
 more recent formation; for the majority of the Dannemora 
 ores are certainly older than the felsite-porphyries. 
 
 Many limestone beds have been largely, or even wholly, trans- 
 formed into ores, especially of type D, the gangues of which, 
 consisting of calcium and magnesium silicates, clearly indicate 
 their origin. 
 
 At Uto it is questionable whether the concentration of the 
 most prominent ore-deposit is not connected with the two trav- 
 ersing pegmatite dikes. The largest and deepest mines, which 
 have followed the deposit down to a vertical depth of more than 
 200 m., are situated between these two pegmatite dikes; more- 
 over, on the outer sides of the pegmatites there is a continuous 
 ore-mass, which has been followed down to a comparatively great 
 depth. At some distance from these dikes the ore has every- 
 where been less thick and less concentrated, and has, therefore, 
 been mined on a small scale only. While the pegmatite dikes 
 evidently originated at a great depth, it follows that the ore-con- 
 centration could not have been accomplished earlier than the 
 submersion in the deep-seated zone. 
 
 The numerous mines of the Grangesberg, Blotberg, Fred- 
 muiidsberg, and Grasberg districts offer good opportunities to 
 observe the relation between the pegmatites and the ores. The 
 former occur here as dikes, partly traversing the ores, and 
 partly parallel to the stratification, but in a manner which indi- 
 cates that they are of later formation than the ores. Coarsely 
 crystalline magnetite is often found in the pegmatite veins, in- 
 dicating that the aqueo-igneous solutions giving rise to the peg- 
 matite originated from the same source as the iron-ore. 
 
 In this connection attention may be called to the not uncom- 
 mon fact that the ores of this type occur along contacts, gener- 
 
 5 Bihang till Handlingar Kongliga Svenska Vetanskaps- Akademie, Stockholm, 4 
 (1876). 
 
GEOLOGICAL RELATIONS OF SCANDINAVIAN IRON-ORES. 667 
 
 ally between limestone and granulite, but also along the contact 
 with intrusive rocks. A marked instance of the former mode 
 of occurrence is seen at Persberg (Fig. 6), where the upper ore- 
 bearing horizon occupies a basin with granulite in the foot- wall 
 and dolomized limestone in the hanging-wall. Similar instances 
 
 SCALE 1 : 10,000 
 
 Limestone 
 
 Pron-ore 
 
 GTamilite 
 
 FIG. 6. PERSBERG. 
 
 are found in several other ore-deposits of type D ; e.g., the 
 grufve mine and the Nordmark mines in Vermland, and Sten- 
 ring and Ramhall in Upland. In such cases the situation of the 
 ores along the contact can hardly be explained by assuming 
 them to be of primary origin ; the only explanation possible is 
 
668 GEOLOGICAL RELATIONS OF SCANDINAVIAN IRON-ORES. 
 
 that the ores have been precipitated along the contact from fer- 
 riferous solutions. 
 
 The same explanation presents itself in such a case as that of 
 the Hogborn district in Orebro, where the most important de- 
 posits occur on a certain level between a diorite mass and the 
 granulite (Fig. 7). If the ores were assumed to have been laid 
 down as a sedimentary deposition on a certain level within the 
 granulite, it would be necessary to explain the fact that the 
 diorite had been injected on this very level and formed a lac- 
 colite there. The assumption that the ores are younger than 
 
 r Juren *,*\ * V % ** *JuSf?***t'** ** V* '* * V * *[***** ' *" 
 
 **^*l^ a ^'ldJSSF^* * * * ^* x x *' * * *** *" * ** "* 
 
 ^J-;/;^:;^L>.':^--- 
 
 Wankagrna 
 
 SCALE 1 : 10,000 
 
 Granulite K*xVV| Diorite j 
 
 FIG. 7. HOGBORN MINES. 
 
 Diabase 
 
 the dioritic laccolite, and that they have been precipitated from 
 ferriferous solutions, removes this difficulty. The most satisfac- 
 tory view, therefore, is that the ores along such contacts are 
 epigenetic formations. 
 
 To this period also belongs the formation of the gangues, 
 which are the result of the silicification that takes place in the 
 deep-seated zone. Whole layers of limestone have, through 
 the interchange of constituents, been transformed into lime- 
 magnesia-iron silicates (sto-ft-deposits). If the limestone has 
 already undergone a dolomitizing process, or if Mg is added 
 
GEOLOGICAL RELATIONS OF SCANDINAVIAN IRON-ORES. 669 
 
 by the solution, the chief alteration-products will be amphi- 
 boles, which are rich in magnesia; if the limestones are com- 
 paratively pure, pyroxenes are formed. Though the garnet of 
 the gangues may often be an alteration-product of pyroxene 
 or amphibole minerals, it may, however, frequently be of pri- 
 mary formation, depending on the chemical composition of the 
 solutions and the transformed material. 
 
 Transformations in the Surface-Zone. When the erosion and 
 removal of the overlying Cambro-Silurian strata exposed the 
 Archaean rocks, the ore-deposits were subjected to the influence 
 of catamorphic agencies. 
 
 Among the transformations of this period we have to note 
 the formation of many skolar of chlorite and talc (soapstone) 
 by the decomposition of the pyroxene and amphibole of the 
 gangues or the granulite of the wall-rock. Many skolar ', too, 
 owe their origin to the decomposition of intrusive greenstone 
 veins. 
 
 Indeed, the wl ole mass of the gangues may, under certain 
 circumstances, be changed, quite new ore-types being the re- 
 sult of the transformation. A common phase of this transfor- 
 mation is the occurrence of epidote, quartz, and calcite in the 
 gangue ; if the alteration proceeds to a certain degree, hydrated 
 minerals of the talc and chlorite groups are formed. As has 
 been shown by H. V. Tiberg, 6 the gangue in the Taberg mines 
 in Vermland, the ore of which is, in its upper part, markedly 
 talcose, has been formed by metasomatic transformation of 
 augite and amphibole. This transformation reaches only as 
 far down as 320 m., at which depth the ore is cut nearly hori- 
 zontally by a fissure which yields plenty of water. The same 
 author adduces, also, the Alabama mine in the Persberg dis- 
 trict as an instance of similar transformation ; in its southern 
 part the ore is talcose, but in the northern part the original 
 gangues, pyroxene and amphibole, are still found. No doubt 
 the ores of Dalkarlsberget, as well as all the ores belonging to 
 the so-called " Rosberg type " of B. Santesson, ought to be in- 
 terpreted in the same way, as being derived from type D 
 through alteration. 
 
 Several other transformations may be viewed as compara- 
 
 6 Werml. Bergsmannafor. Ann. (1908). 
 
670 GEOLOGICAL RELATIONS OF SCANDINAVIAN IRON-ORES. 
 
 lively recent and, consequently, belonging to this period. The 
 ores of the Striberg type are often found to lose their charac- 
 teristic bandedness in the direction of the strike, the quartz 
 being replaced by a somewhat porous magnetite, sometimes 
 also by calcite. Concentrations of richer magnetite often occur 
 among the ores of this type ; they are generally accompanied 
 by quartzose segregations or chloritic skolar. 
 
 Simultaneously with this, a concentration of the iron may 
 take place, Si0 2 being dissolved by means of alkaline car- 
 bonates and the silica replaced by ferric oxides. It is by such 
 concentration, for instance, the rich ore deposits have been 
 formed which are often met with in folds; e. g., in Nordmark 
 and in the Hogborn mines in Vermland. In localities where 
 very thick deposits of ore not enriched, and retaining the prim- 
 itive structure, occur in folds, as at the Stripa mine, the abnor- 
 mal thickness must be ascribed to mechanical deformation. 
 
 Among the Grasberg mines, which are worked on a folded 
 layer in the form of a trough sloping NNW. 9 there occurs in the 
 Bolag mine a highly concentrated magnetite in the fold, the 
 rest of the ore being a poor hematite with quartz bands. 7 That 
 a concentration process has taken place here is beyond doubt, 
 though it is not possible to determine to what period it should 
 be assigned. 
 
 On a still larger scale, a similar transformation has taken 
 place in the Bispberg mine, producing a rich, pure magnetite, 
 mined in the deeper levels of this mine, while in the upper 
 parts the ore was a typical low-grade quartz-banded hematite. 
 
 Such transformation on a large scale of specular hematite 
 into magnetite has long been known from several ore-deposits ; 
 e. g., Korberg, Striberg, Gellivare. In the ends of the ore- 
 bodies and in the sides contiguous to the surrounding rocks 
 the transformation is most advanced, but also the interior por- 
 tions of the ores consist of a mixture of specular hematite and 
 magnetite. The cause of this transformation is not fully un- 
 derstood; but it is evidently a reaction, depending on mass- 
 action, and continuing to a certain limit, where equilibrium 
 ensues. It looks as if the reaction proceeded from the sur- 
 rounding or traversing silicate-rocks; and it has been conjec- 
 
 7 H. Sundholm, Jern-Kontorets Annaler, vol. liii., p. 162 (1898). 
 
GEOLOGICAL RELATIONS OF SCANDINAVIAN IRON-ORES. 671 
 
 tared that the alteration has been produced by organic sub- 
 stances (humic acids) contained in the surface-waters descending 
 along the walls of these rocks. Even though it might be sup- 
 posed that ; these organic substances had the power of reduc- 
 ing specular hematite into magnetite, this explanation is not 
 very satisfactory; for the transformation that has taken place 
 is not a reduction of hematite into magnetite with retention of 
 the structure of the former, but a solution and recrystallization 
 of the iron-ore. One might rather suggest the action of alka- 
 line solutions proceeding from the silicate-rocks, or some other 
 reagent. 
 
 The change from hematite to magnetite is reversible; and 
 in some places we meet with transformations on a large scale 
 of magnetite into hematite. Of the anhydrous iron oxides, 
 magnetite is more stable in the deep-seated zone, hematite in 
 the surface-zone ; and it seems safe to assume that the last- 
 mentioned alteration belongs to the surface-zone. Such a 
 transformation is found in the Grangesberg mines, where the 
 ore close to the foot-wall consists of a scaly hematite low in 
 phosphorus. 
 
 The Grangesberg and Norrbotten Deposits. 
 
 A separate position should be assigned to those ores of the 
 type which are chiefly represented by the large deposits of 
 Grangesberg, in central Sweden, and Gellivare, in Norrbotten. 
 They diverge in some points from the majority of the ores of 
 the Archaean schists; and their characteristic properties seem 
 to be most satisfactorily explained by assuming them to be 
 transformed basic segregations in gneiss - granites (ortho- 
 gneisses). 
 
 Analogous Deposits. 
 
 The ores of this group are well represented within the Ar- 
 chaean series of the United States and Canada ; indeed, all. the 
 different types mentioned above are found there. This feature, 
 that the same ore-types may be recognized in areas so far apart 
 as North America and the Scandinavian peninsula, strongly 
 indicates that these types correspond to certain genetic con- 
 ditions. 
 
672 GEOLOGICAL RELATIONS OF SCANDINAVIAN IRON-ORES. 
 
 [ABRIDGED SUMMARY. Ores of type A are found at Mineville, Lake Cham- 
 plain, N. Y., corresponding to the Swedish ores in appearance, composition, form 
 of ore-bodies, etc. Type B, rich in silica and alumina, represents in part the Ar- 
 chaean deposits of New York and New Jersey. Type C recalls at many points the 
 siliceous banded ores of Lake Superior, especially the Archaean ores of the Ver- 
 milion range, but also, in some respects, the Huronian ores of Marquette and 
 Crystal Falls. Type D (the " Skarn"-ores) has also its representatives among 
 the Archaean deposits of New York, New Jersey, and Pennsylvania, and in the 
 Cranberry range of North Carolina and Tennessee, and some deposits in Eastern 
 Ontario, Can. The Tilly Foster mine, in Putnam county, N. Y., is a striking 
 instance. Type E seems to be comparatively rare in the United States, but the 
 iron-ore of Franklin, N. J. , and some other places in the United States and Onta- 
 rio, occurs in limestone. 
 
 GROUP II. THE ORES OF THE PORPHYRIES (KERATOPHYRES). 
 
 The province of Norrbotten contains many times as much iron 
 as all the rest of Sweden. Some of the deposits in this province 
 may be reckoned among the largest in the world. The export 
 from Kiirunavaara commenced as late as 1902, when the rail- 
 way to Narvik on the fjord of Ofoten was opened ; in the fol- 
 lowing year the exploitation of the less considerable neighbor- 
 ing deposit of Tuollavaara also began. 
 
 Geologically, the iron-ore deposits of Norrbotten are of three 
 kinds : (1) the ores of the crystalline schists, which embrace the 
 deposits of Gellivare and Svappavare, treated in the preceding 
 section ; (2) the ores of the Kiiruna type, connected with sye- 
 nitic porphyries; and (3) ores connected with basic igneous 
 rocks. These ores will be treated in the next section. (See Fig. 8.) 
 
 Topographically, the more important deposits may be divided 
 into four groups : (1) Gellivare, embracing Malmberget and 
 Koskulls Kulle and a few copper ore-deposits north of the Lina- 
 elf; (2) Svappavare, Leveaniemi and Mertainen, situated be- 
 tween the Kalix and the Tornea rivers; (3) a group in the 
 vicinity of Lake Luossajarvi, embracing Kiirunavaara, Luossa- 
 vaara, and Tuollavaara ; (4) Ekstromberg, which belongs to the 
 basin of the Kalix river. Besides these, minor deposits, for the 
 most part only imperfectly known, are scattered all over the 
 wide area. 
 
 Kiirunavaara, Luossavaara, and Tuollavaara. 
 
 The iron-ore deposit of Kiirunavaara is undoubtedly the largest 
 deposit of ore found in Europe. The neighboring deposits of 
 
GEOLOGICAL RELATIONS OF SCANDINAVIAN IRON-ORES. 673 
 
 Luossavaara and Tuollavaara are geologically of the same nature, 
 though smaller. The first two of these deposits have been 
 known for more than two centuries. Luossavaara is mentioned 
 as early as about the year 1690, Kiiruna not before 1736 ; a de- 
 scription of both is given in the Report of the Government Min- 
 ing Inspector for 1751. The first survey was made shortly be- 
 fore 1760. Tuollavaara, being concealed under a thick moraine, 
 was not discovered until 1897. (See Fig. 9.) 
 
 Basic Eruptives, Older Cambrian Pre-Cambrian. Silurian' 
 Silurian or younger. Basic 
 
 Eruptives. 
 
 Gneissic Rocks. 
 
 Granite Granulite Porphyritic 
 
 and and Rocks. 
 
 Syenite. Archaean Schist. 
 
 FIG. 8. ORE-PROVINCE OF NORBOTTEN. 
 
 The ores in question prove to be genetically connected with 
 a group of eruptive rocks of syenitic composition, and charac- 
 terized by their high percentage of soda. These rocks show 
 the structures of deep-seated as well as of vein-rocks. They 
 are intruded in a sedimentary, partly clastic, complex of strata, 
 including conglomerates and semi-crystalline schists. 
 
674 GEOLOGICAL RELATIONS OF SCANDINAVIAN IRON-ORES. 
 
 The porphyritic rocks were, for a long time, regarded by the 
 Swedish geologists, Hummel, Gumselius, Fredholm, and others 
 (in analogy with the case of central Sweden), as a sedimentary 
 halleflinta, and the stratified rock-complex in which they occur 
 was called hdlleflinta-schist. In 1889, however, Tornebohm 
 pointed out the porphyritic nature of the so-called hdtteflinta, 
 and afterwards the hatteflwto-Bchista were found to consist of 
 partly clastic rocks. 
 
 The ores of the three deposits form stratiform masses of con- 
 siderably greater length than breadth the length of the Kiiru- 
 navaara deposits is about 2.8 kilometers. 
 
 FIG. 9. PART OF ORE-DEPOSIT OF KIIRUNAVAARA (LOOKING NORTH). 
 
 The ores are immediately surrounded by intrusive rocks of 
 porphyritic development which, on account of their composi- 
 tion, are to be referred to the soda-syenite-porphyries. They 
 have also been called keratophyres (H. Backstrom) ; however, 
 as this name is applied to effusive rocks, and the effusive nature 
 of the Kiiruna porphyries seems to me at least questionable, I 
 prefer, for the present, the name porphyries. Two kinds of 
 porphyry may be distinguished : one more basic, occurring 
 chiefly in the foot-wall, but partly also in the hanging- wall of 
 the ore, and one more acid, often developed as quartz -porphyry 
 and occurring in the hanging-wall of the ores of Kiirunavaara 
 and Luossavaara, around Tuollavaara, etc. The basic porphyry 
 
GEOLOGICAL RELATIONS OF SCANDINAVIAN IRON-ORES. 675 
 
 is closely connected with the syenitic rock which accompa- 
 nies it. 
 
 The Syenite. This is a soda-syenite, the chief mass of which 
 is a soda-feldspar. Secondary basic minerals are present in 
 abundance. The structure is eugranitic. This soda-syenite 
 shows gradations into the porphyry of the foot-wall, with 
 whidh it is closely allied in composition. 
 
 The Porphyry of the Foot- Wall. This rock presents, micro- 
 scopically as well as macroscopically, a fluidic structure with a 
 trachytoidal arrangement of the feldspar of the ground-mass ; 
 sometimes, also, spherulitic structures are observable. The 
 primary structures are, however, frequently difficult to distin- 
 guish, being in part totally obliterated by the alteration of the 
 rock. The basic constituents are almost wholly altered into 
 amphibole, epidote, and chlorite. Magnetite seems to occur in 
 two generations : one primary, the other of later immigration. 
 As fissure-minerals, indicating a secondary action of pneuma- 
 tolytic nature, occur amphibole, titanite, apatite, and magnetite. 
 In the contact-zone the fissures sometimes form cavities a deci- 
 meter in diameter, filled with the said mineral combination. 
 
 The Porphyry of the Hanging-Wall. This is considerably 
 more acid (containing 10 per cent, more of Si0 ) than the syen- 
 ite and the porphyry of the foot- wall, which circumstance places 
 it among the quartz-porphyries. Quartz occurs in the ground- 
 mass partly as so-called " quartz globulaire" but in larger quan- 
 tities where the ground-mass has undergone a recrystallization. 
 Here, too, a secondary generation of magnetite can be observed. 
 The primary basic mineral constituents are completely altered, 
 having produced amphibole, epidote, and chlorite. The rock 
 shows, even macroscopically, a distinct fluidic structure. 
 
 Segregations of pure magnetite, mostly in rounded pieces, are 
 worthy of notice ; these segregations sometimes show a concen- 
 tric structure and at times inclose grains of the feldspar of the 
 porphyry. When the fragmentary character is more distinct, 
 they are probably portions of segregations, solidified in depth 
 at an earlier date, which have been partly rounded by resorp- 
 tion. These segregations have also been interpreted as fragments 
 of the great ore-body ; and from this it has been concluded that 
 the porphyry of the hanging-wall should be younger than the 
 mass of ore. 
 
676 GEOLOGICAL RELATIONS OF SCANDINAVIAN IRON-ORES. 
 
 The unmistakable " consanguinity " between the soda-syenite 
 and the porphyries is manifested by the high percentage of Na, 
 which varies between 5.5 and 7.5 per cent.; apatite, titanite, 
 and magnetite are, besides, minerals common to the syenite, the 
 porphyries, and the ore-deposits. 
 
 The Ores. (In the following exposition of the Kiirunavaara 
 and Luossavaara ore-deposits, I follow chiefly the official report 
 made by Hj. Lundbohm in 1898.) The iron-ore occurring 
 among the porphyry masses forms, on the whole, pure, nearly 
 homogeneous ore-deposits; other minerals found in it are of 
 comparatively subordinate significance. 
 
 A property characteristic of the ore of Kiiruna-, Luossa-, and 
 Tuollavaara is its general extremely fine-grained texture, which 
 proves that it has been subject to a slight degree only to the 
 action of recrystallizing agents. By this structure, which is 
 also found in a few other ores in Norbotten, this ore-type is dis- 
 tinguished from the rest of the Scandinavian ores. 
 
 The only mineral that occurs in the ore with undoubtedly 
 primary characters is apatite, the distribution of which is ex- 
 ceedingly irregular, so that the percentage of phosphorus in 
 the ore varies greatly. 
 
 In Kiirunavaara, chiefly close to the foot-wall, but also here 
 and there in the interior of the ore, occurs an ore-type with 
 mostly grayish-black and dull, compact fracture (Lundbohm's 
 type 5). When examined with the microscope it proves to be 
 interlarded with apatite individuals idiomorphically developed ; 
 its phosphorus-percentage is from 3 to 6 per cent. This ore 
 frequently presents a stratiform structure. 
 
 The ore-type which quantitatively predominates contains the 
 apatite in nodules and irregular lenses (Lundbohm's type 4). 
 Here, too, the apatite seems to be, at least in part, of primary 
 origin, since it occurs partly as a minute impregnation of the 
 ore, partly in irregular nests and veins, giving rise to a structure 
 which bears some resemblance to a largely developed flow- 
 structure (Fig. 10). 
 
 Primary structural forms which may be referred to flow- 
 structure may also be observed in the relations between different 
 ore-types, when, e.g., one type contains fragments or " schlieren " 
 of another type, or when one ore-type occurs as intruding dikes 
 in another (Fig. 11). Especially on weathered ore-surfaces 
 these structures are easily observable. 
 
GEOLOGICAL RELATIONS OF SCANDINAVIAN IRON-ORES. 677 
 
 It is likely that the highly phosphoric ores, though embracing 
 several types, must in general be regarded as primary, and those 
 poorer in apatite as secondary, leached, and in part recrystal- 
 lized. The latter also contain martite and specular hematite, 
 the occurrence of which is here evidently secondary. 
 
 FIG. 10. IRREGULAR VEINS OF APATITE IN MAGNETITE, KIIRUNAVAARA 
 
 (Lundbohm). 
 
 In the low-phosphorus ores occur also calcite (formed at the 
 expense of the apatite), secondary quartz in fissures, and second- 
 ary silicates as amphibole, talc, and chlorite minerals. The 
 secondary ore-types are sometimes porous, the more soluble 
 minerals having been leached out. 
 
 FIG. 11. FLOW-STRUCTURE IN MAGNETITE, KIIRUNAVAARA (Lundbohm). 
 
 From a practical point of view, the ores in question have 
 been divided into several classes according to their percentage 
 of phosphorus. Those classes which range above 1 per cent, 
 constitute the principal mass of the ores of Kiirunavaara. As 
 a fairly certain result of the examinations of the ores with regard 
 to their percentage of phosphorus, it may be said that ores con- 
 
678 GEOLOGICAL RELATIONS OF SCANDINAVIAN IRON-ORES. 
 
 taining less than 0.05 per cent., and ores with from 0.05 to 0.1 
 per cent., of phosphorus, occur separately in such a mode that 
 they can be utilized, but that both kinds, especially the former, 
 are, as regards quantity, rather subordinate to those richer in 
 phosphorus. 
 
 The Genesis of the Deposits. The genetic connection of these 
 ores with the porphyry-rocks is so manifest, that it has been 
 admitted by all who have expressed their opinion on the sub- 
 ject. Even those geologists (Hummel and Gumselius in 1875, 
 Fredholm in 1891), who regarded the porphyries as sedimen- 
 tary katteflintor, acknowledged this connection, and consequently 
 considered the ores as sedimentary formations. Lofstrand, in 
 1891 and 1892, in describing other basic segregations and vein- 
 like formations of iron-ore in acid igneous rocks, pointed out 
 that the connection of the ores of Kiiruna with the porphyries 
 ought to be interpreted in the same way. The same opinion 
 was expressed more positively in 1898 by Hogbom, 17 who laid 
 special stress on the agreement with the deposits connected 
 with syenitic rocks in the eastern Ural: Wyssokaia Gora, Le- 
 biajaia, and Gora Blagodat. A similar opinion was pronounced 
 at a later time by 0. Stutzer, who holds that the ores have 
 been formed in an epigenetic-magmatic way as " eine nach oben 
 gewanderte magmatische Ausscheidung " i. e., a magmatic 
 vein-formation. 
 
 A pneumatolytic sedimentary mode of formation has been 
 maintained by Backstrom and, later, by De Launay (1903). The 
 latter author, who gives the most detailed exposition of this 
 view, has formed the following conception of the process : The 
 porphyry of the foot-wall is an effusive rock, on which the iron- 
 ore, formed through the decomposition of chloride and sulphide 
 of iron in contact with water, has been deposited. Later on a 
 new eruption of porphyry followed, by which the porphyry of 
 the hanging-wall was formed. 
 
 This interpretation is based on the opinion that the ore is 
 younger than the porphyry of the foot-wall and older than the 
 porphyry of the hanging-wall, which, however, is hardly com- 
 
 1T Geologiska Foreningen Forhandlingar, Stockholm, vol. xx., p. 115 (1898). 
 
GEOLOGICAL RELATIONS OF SCANDINAVIAN IRON-ORES. 679 
 
 patible with the fact that the magnetite is, in places completely 
 surrounded by the basic porphyry. 
 
 The above-mentioned fluidic structures in the magnetite can 
 be accounted for only by assuming that the magnetite, together 
 with the greater part of the apatite, has formed a segregation 
 from an iron-alkali-silicate magma, intruded as a vein between 
 the porphyries. After this intrusion the effects of pneumato- 
 lytic agencies, which are especially well-marked at the contact 
 with the basic porphyry, have arisen. Hogbom has given a 
 theoretical exposition of the formation of ores of this kind. He 
 starts from an iron-alkali-silicate magma composed, approxi- 
 mately, in the proportion of 1 molecule of orthoclase, 1 mole- 
 cule of albite, and 1 molecule of magnetite. Such a magma 
 differs in composition from known and common magma-types 
 only by containing a little more ferric oxide and a somewhat 
 smaller amount of lime and magnesia. As, at the solidification 
 of such a magma, the larger part of the iron must segregate as 
 magnetite, because, owing to the absence of lime and magnesia, 
 it cannot combine with the silica, the differentiation of two rocks, 
 one chiefly consisting of magnetite, the other of feldspar, is easily 
 accounted for. Hogbom, therefore, holds that the alkali-silicate 
 magmas rich in iron, to which petrography has as yet paid but 
 little attention, have a just claim to a place in the system, and 
 that their most typical representatives are magnetite-bearing 
 syenitic rocks of this kind. 
 
 [ABRIDGED SUMMARY. At Mertainen, 30 km. southeast of Kiiruna, the ores 
 are connected with a syenite-porphyry, mainly consisting of a soda-feldspar. At 
 the contact, the rock has undergone pneumatolytic transformation. Its original 
 basic constituents have disappeared and new magnesia silicates appear in their place. 
 The soda-feldspar has, in part, been transformed into scapolite, but biotite and 
 titanite also have been produced. The magnetite occurs partly finely disseminated, 
 partly in small segregations, from the size of an almond to that of an egg. These 
 have been interpreted as cavity-fillings ; but the deposit is properly a magnetite 
 breccia. A fine-grained magnetite fills the corrosion-fissures of the rock, associated 
 sometimes with amphibole, less frequently with apatite. A similar deposit occurs at 
 Painirova, 8 miles to the south. The deposits of Mertainen and Painirova are, 
 like those of Kiiruna, genetically connected with the syenite-porphyries. But at 
 Mertainen the pneumatolytic characters are most marked, and there is nothing like 
 the pure ore-masses of magmatic origin and partly of fluidic structure which form 
 the main deposit at Kiiruna. At Ekstromberg, about 30 km. west of Kiiruna- 
 vaara, the ore is connected with syenitic porphyries ; and many other deposits of 
 this general class are known in Norrbotten.] 
 
680 GEOLOGICAL RELATIONS OF SCANDINAVIAN IRON-ORES. 
 
 Analogous Deposits. 
 
 The ores in Norrbotten of the Kiiruna type belong to a 
 particularly well-defined geological-petrographical type, which 
 is also met with in other parts of the world. 
 
 Hogbom has already, in the above-mentioned paper, pointed 
 out the agreement between the iron-ore deposits in the eastern 
 Ural and the Kiiruna type. In the iron-mountains of the Ural 
 a secondary epidotization of the rocks has taken place on a 
 larger scale than in Norbotten, especially along certain planes 
 of dislocation. On the other hand, the pneumatolytic charac- 
 ters so well marked in the Kiiruna type are not met with in the 
 deposits of the Ural. The secondary transformations, such as 
 the development of martite and specular hematite, the leaching 
 out of pyrite and apatite, the formation of porous ore or ore 
 containing calcite, and the accumulation of the apatite chiefly 
 near the foot-wall, are common to the two districts. 
 
 The ores of the (for the most part exhausted) deposits of 
 Iron Mountain and Pilot Knob in Missouri, which also occur 
 in association with porphyry-rocks, have been compared to and 
 classed with the Kiiruna type by several authors. At Iron 
 Mountain the ore mined occurred as veins and irregular masses 
 of martite and specular iron-ore in a mostly decomposed por- 
 phyry of Archaean age. At Shepherd Mountain similar de- 
 posits in porphyry were worked. The deposits of Pilot Knob, 
 on the contrary, are secondary redepositions of the primary 
 iron of the porphyry ; they seem to bear a strong resemblance 
 to the deposit of specular iron-ore in the Hauki schists east of 
 Luossavaara. 
 
 Also, the Mexican deposits at Durango and Las Truchas 
 agree in some respects with those in Norbotten; but their 
 geological conditions have not, as yet, been sufficiently inves- 
 tigated to make a direct comparison possible. 
 
 GROUP III. IRON-ORES FORMED BY MAGMATIC SEGREGATION IN 
 BASIC ERUPTIVES. 
 
 The ores of this kind form a natural and well-defined class 
 encountered in all parts of the world. That they are geneti- 
 cally connected with eruptive rocks has long been admitted. 
 The nature of their facies of differentiation was not understood 
 
GEOLOGICAL RELATIONS OF SCANDINAVIAN IRON-ORES. 681 
 
 until the differentiation of rock-magmas was clearly conceived. 
 In this regard, their structural characters, which are the same 
 as those of the eruptive rocks, and their frequent presentation 
 of all degrees of transition to the normal rock, are evidential. 
 (Fig. 13.) 
 
 Magmatic differentiations of this kind seem to be connected 
 only with intrusive eruptives, and occur in laccolites as well as 
 in vein-like intrusions. In general, a distinction can he made 
 between such differentiations as have taken place within the 
 mass of the laccolite, in situ, and such as have taken place in 
 the deep-seated magma. In the latter case the product of 
 magmatic segregation has been carried up to the level of the 
 laccolite by a separate act of eruption. 
 
 Taberg in Smdland. 
 
 As far as a hundred years back Hausmann 18 expressed the 
 opinion that " the mass of Taberg is a greenstone bed of toler- 
 ably great thickness, mixed with much iron-ore and lying in 
 gneiss." Through the investigations of A. Sjogren 19 and 
 Tornebohm 20 it was established that the ore-deposit of Taberg 
 ought to be considered as a segregation in a basic eruptive, the 
 chief constituents of which are olivine, plagioclase, a rhombic 
 pyroxene, and magnetite. The structure is that of a deep-seated 
 rock, and the rock, which has been called hyperite by the 
 Swedish geologists, is olivine-norite according to the nomen- 
 clature of Rosenbusch. Taberg was the first iron-ore deposit 
 interpreted as a phase of an eruptive rock. Tornebohm 21 says 
 that the Taberg ore " may be regarded as a variety of hyperite 
 rich in iron." As the ideas of magnetic differentiation were 
 not clearly formulated until later, the nature of the ore could 
 not in 1881 be expressed in plainer terms. The whole of the 
 eruptive constitutes an intrusion (laccolite) in the surrounding 
 gneiss, above which it now rises, by reason of its greater power 
 of resistance to erosion. (Fig. 14.) 
 
 The ore-deposit occupies the central portion of the mountain. 
 The ore-segregation consists of titaniferous magnetite and 
 
 18 R&ise durch Skandinavien, Pt. I., pp. 158 to 167 (1806-07). 
 
 19 Geologiska Foreningen Forhandlingar, vol. iii., p. 42 (1876). 
 
 20 Idem, vol. v., p. 610 (1881). 
 
 21 Loc. cit. 
 
 43 
 
682 GEOLOGICAL RELATIONS OF SCANDINAVIAN IRON-ORES. 
 
 2 6 8 10 II if Itf |ft 10 it, i*t- 16 28 
 
 FIG. 13. DISTRIBUTION OF TITAN i FERGUS IRON-ORES. 
 
GEOLOGICAL RELATIONS OF SCANDINAVIAN IRON-ORES. 683 
 
 J^rofil of Tdbcrg from. 
 
 Scale, 1:10,000 
 
 a ____/ , . ,., L- r-*- :.-.'.- .:::.. 
 
 ^I^^v:^X^?r^v^:^ 
 
 :& . 
 
 The surface of 
 -fhf rividet:. 
 
 I','/,'/! Gneiss and 
 I . . n iilgntMssir granite 
 
 jv:-'::^;v : .v'jj Magnetite 
 ''' '''''''' olivinite- 
 
 . L ., ,. 
 A Amphibohte. 
 
 ''' 
 
 -".' Gabbro - 
 diorite. 
 
 FIG. 14. TABEBQ (Tornebohm). 
 
684 GEOLOGICAL RELATIONS OF SCANDINAVIAN IRON-ORES. 
 
 olivine and has received the petrographical name magnetite- 
 olivinite. Where it approaches the normal rock, it first takes 
 up plagioclase, then pyroxene, so that there is a transition from 
 the ore to the normal rock, which also contains magnetite and 
 olivine. The ore-stock thus forming the kernel of the moun- 
 tain is next surrounded by a shell or mantle of normal gabbro, 
 which, in its turn, towards the inclosing gneiss, passes into the 
 schistose, dynamo-metamorphic border-facies, the gabbro-am- 
 phibolite. 
 
 The ore is poor throughout, carrying generally from 20 to 30 
 per cent, of iron. Vein-like segregations containing up to 60 
 per cent, occur as rare exceptions. Titanic acid varies between 
 4 and 6 per cent. ; the percentage of phosphorus does not exceed 
 0.1 ; to which may be added a constant percentage of vanadine. 
 
 [ABRIDGED SUMMARY. Minor deposits in central and southern Sweden, and 
 several in Norway, belong to this class. And in the small islands along the coast 
 of Angumanland occur similar segregations in a diabase younger than the Dala 
 sandstone, forming, between stratified quartzites, bed-like intrusions which have 
 been exposed by erosion. The darker bands of this rock have acquired, in some 
 places, through a concentration of titano-magnetite, the character of iron-ore. 
 The proportion of titanic acid may amount to 25 per cent. In the island of Alno 
 concentrations of titano-magnetite in a boss of nepheline-syenite have been worked 
 in a small way as iron-mines. At Ekersund and Soggendal, in Norway, deposits 
 of iron-ore occur in a colossal laccolite of highly differentiated basic rocks, sup- 
 posed to be of post-Silurian age. They have been worked at different times, but 
 without commercial profit, since they contain, as an average, only 40 per cent, of 
 iron, and from 40 to 42 per cent, of titanic acid. Deposits of this class are nu- 
 merous along the coast of Norway, in laccolites laid bare by the fjords. One of 
 the largest in Scandinavia is that of Routivare in Norrbotten, which was formed 
 by segregations in an intrusive rock, occurring as a laccolite in the metamorphic 
 Silurian formations.] 
 
 Summary. 
 
 Though the rocks which inclose the deposits of this class 
 differ in composition (as real gabbros, norites, diabases, or neph- 
 eline-syenites), as well as in age (some of them belonging to 
 the oldest Archaean formation, and the youngest dating from 
 post-Silurian time), yet a marked degree of basicity seems to 
 be a necessary condition for the formation of such concentra- 
 tions. Yogt puts the highest acidity at 57 per cent, of Si0 2 . 
 The majority of the deposits occur in rocks with a silica-per- 
 centage of from 48 to 54 per cent. The different facies of 
 gabbro-rocks inclose deposits of different character. The pure 
 
GEOLOGICAL RELATIONS OF SCANDINAVIAN IRON-ORES. 685 
 
 ilmenite-segregations (Ekersund, Soggendal, Lofoten, etc.), 
 seem to be confined to the labradoritic rock. In the same rock- 
 series we also find the ilmenite-norite. In the olivine-gabbro, 
 rich in magnesia, which incloses the deposit of Taberg, the seg- 
 regation has assumed the mineralogical character of magne- 
 tite-olivinite, and in the rocks which are richer in alumina, 
 magnetite-spinellite has been segregated, as at Routivare, Ando- 
 pen, on Stjerno in Finnrnarken, and elsewhere. 
 
 A remarkable feature of the ore-concentrations in question 
 is their occurrence, almost without exception, in the central 
 parts of the eruptive masses. This gives them a character dif- 
 ferent from that of those concentrations of basic constituents 
 in an eruptive rock which are often met with along the mar- 
 gins of rock-veins, and in which the enrichment has not pro- 
 ceeded so far as to form an iron-ore. 
 
 As to the degree of concentration of the iron, the ore-types 
 differ also from one another. The concentrates richest in iron 
 are the magnetite-spinellites, with an iron-percentage exceed- 
 ing 50 per cent. (Routivare, 50 to 54; Solnor, 54; Hellevig, 
 51 ; Andopen, nearly 60). Next to these come the segrega- 
 tions of the nepheline-syenites, of which in Alno some con- 
 tain from 46 to 53 per cent. ; and after these the ilmenite-seg- 
 regations in the labradoritic rock and the norite, with about 
 40 per cent, of iron, and nearly as high a percentage of titanic 
 acid. Poorer still are the ores of the olivine-gabbros of the 
 Taberg type, which contain little more than 30 per cent, of 
 iron. Comparable to them are the ores of the oli vine- diabase 
 (the Ulfo type), with about 34 per cent. At the bottom of the 
 scale stands the ilmenite-norite, the Storgang type, with about 
 21 per cent, of iron. 
 
 Besides the iron, it is chiefly the titanic acid, the magnesia, 
 and the alumina that have been concentrated. The percentage 
 of titanic acid is highest in the ilmenite-segregations of the 
 labradorite and norite, where it amounts to from 39 to 43 per 
 cent.; next come the ilmenite-norites, which contain 18 per 
 cent. ; the magnetite-spinellites (type Routivare) vary between 
 10 and 18 per cent.; the segregations of the nepheline-syenite 
 show about 10 per cent, (the Trygg mine, in Alno, from 9.10 
 to 12.14); in the Taberg type, the magnetite-olivinite, the per- 
 centage of titanium, like that of iron, is the lowest viz., 6.30 
 
686 GEOLOGICAL RELATIONS OF SCANDINAVIAN IRON-ORES. 
 
 in the Taberg ore and 8.50 in the ore of Langhult. The Ulfo 
 type, with about 10 per cent, of Ti0 2 , shows the greatest agree- 
 ment with the Taberg type. 
 
 The concentration of magnesia has taken place not so much 
 in the ore as in the concentration-facies between the normal 
 rock and the segregations richest in iron. It manifests itself 
 in the formation of Mg-Fe silicates of the olivine and pyroxene 
 groups. The rock-facies, which have received the names mag- 
 netite-olivinite, ilmenite-norite, and ilmenite-enstatite, have 
 originated in this way. A certain percentage of Mg is found 
 even in the purest segregations of ilmenite in the labradoritic 
 rock, owing to a mixture with MgTi0 2 . The alumina left in 
 the final concentrates combines particularly with the magnesia, 
 thus forming spinel, the formation of which is favored by the 
 relation-deficiency of silica in the magma. This mineral occurs 
 in the following ore-types : the magnetite-olivinite (Ransberg) ; 
 the ilmenite-norite (Ekersund); and the magnetite-spinellite 
 (Routivare, Hellevig, Lofoten, and Stjerno). Yogt has called 
 attention to the fact that the Mg-percentage increases in the 
 first stage of concentration and then diminishes. While the 
 original magma contains more A1 2 3 than MgO, the case is 
 quite the reverse in the earlier stages of concentration. In the 
 final product, however, the amount of alumina again exceeds 
 that of magnesia. 
 
 Besides the aforesaid substances, chrome and vanadium, 
 which occur in small quantities, have undergone a concentra- 
 tion. The phosphorus, on the other hand, is not in general 
 concentrated to any noteworthy degree. To this, however, 
 there are exceptions, such as the segregations of ilmenite-norite 
 traversing the labradoritic rock in the Soggendal-Ekersund 
 field, which contain a fairly high percentage of phosphorus, 
 while the surrounding rock carries little, and the above-men- 
 tioned concentrations, rich in apatite, in the hypersthene-gab- 
 bro at Krekling, Norway, and also in the nepheline-syenite of 
 Alno. 
 
 That silica, lime, and alkalies occur in smaller quantities in 
 the concentrates than in the rest of the rock-mass is manifested 
 mineralogically by the total absence of feldspar from these con- 
 centrations. 
 
GEOLOGICAL RELATIONS OF SCANDINAVIAN IRON-ORES. 687 
 
 Vogt has pointed out 22 that in several places in Lofoten and 
 Vesteraalen, in the labradoritic rock containing olivine and 
 hypersthene, there are besides segregations of magnetite-dial- 
 agite, also schlieren-\ike segregations of pure olivine rock as 
 well as of hypersthenite. This shows that in the same magma 
 differentiation processes following different lines have taken 
 place nearly contemporaneously. As extreme basic segrega- 
 tions the limestones occurring in the nepheline-syenite may 
 also be explained. 
 
 Many different attempts to suggest the cause of these differ- 
 entiations have been made, but no satisfactory explanation has 
 as yet been proposed. 23 It seems as if, with respect to this 
 kind of segregations, the view according to which the magma 
 is regarded as a mixture of different liquids, partly insoluble 
 in one another, were decidedly preferable to the theory which 
 considers the laws of dilute solutions applicable to the magma. 
 The principle of limited solubility must be considered as the 
 physico-chemical principle governing the differentiation-phe- 
 nomena of silicate-magmas in general. 
 
 Neither " Soret's principle," nor any other form of the theory 
 of diffusion, nor " connection currents," nor the magnetic at- 
 traction of the " liquid molecules," nor the different weight of 
 the segregated solid constituents can afford an explanation of 
 differentiation-phenomena of this kind. The geological condi- 
 tions also seem to harmonize better with the view which con- 
 nects the differentiation with the segregation and solidification 
 of liquids insoluble in the remaining magma. These are sepa- 
 rated out in consequence of the cooling of the magma, by 
 which the conditions of solubility are changed, or of the escape 
 of water or other mineralizers ; the segregation takes place at 
 first in the form of drops throughout the magma, which drops? 
 on account of the surface-tension, have a decided tendency to 
 coalesce and flow together into schlieren and larger concen- 
 trations. Which of the liquids is attracted to the side-walls 
 and solidifies there, and which of them solidifies in the center, 
 will in each case depend on the relative force of the adhesion 
 to the side-walls. 
 
 22 Zeitschrift fur praktische Geologic, vol. xiv., pp. 217 to 233 (1906). 
 
 23 Vogt, Zeitschrift fur praktische Oeologie, vol. ix., pp. 327 to 340 (1901). 
 
688 GEOLOGICAL RELATIONS OF SCANDINAVIAN IRON-ORES. 
 
 Analogous Deposits. 
 
 Titaniferous iron-ore segregations in basic eruptive masses 
 constitute a well-defined class, which has representatives in all 
 parts of the world. Several of the different types found in 
 Scandinavia occur in other countries also. 
 
 In the United States and Canada these ores have long been 
 grouped together as a separate class, and a great many deposits 
 of this kind have been described. 
 
 The magnetite-olivinite or Taberg type is analogous to the 
 deposit at Iron-mine Hill in Cumberland, R. L, described by 
 Wadsworth, though the latter is of smaller dimension. The 
 " gabbro titanic-iron-ores " of the Mesabi range in Minnesota, 
 described by N. H. and H. V. Winchell, also seem to come 
 very near to the type, though the concentration of the iron and 
 the titanium has in these ores proceeded further. Among the 
 segregations occurring in large masses in the various gabbro 
 and labradoritic rocks of the eastern Adirondacks, the Taberg 
 as well as the Ekersund type is represented. 
 
 Perfect analogies to the Ekersund type of ilmenite-segrega- 
 tions in labradoritic rock are offered by the Canadian ilmenite- 
 deposits of Quebec and Ontario, which frequently contain from 
 30 to 40 per cent, of titanic acid and, in consequence thereof, 
 a low percentage of iron. Some of these ores seem to consist 
 of a mixture of ilmenite and titano-magnetite with a diminu- 
 tion of the percentage of titanic acid and an increase of that of 
 iron. The inclosing rocks are labradorite and norite. 
 
 Deposits analogous to the magnetite-spinellites of the Routi- 
 vare type also occur in the United States namely, the chemi- 
 cally closely allied magnetite-spinellite deposits, accompanied 
 by corundum, in the norites of the Cortlandt series, described 
 by G. H. Williams. 24 
 
 To the titanic ores of the nepheline-syenites correspond 
 segregations of quite the same character in the rock-series of 
 Magnet Cove. 25 
 
 24 " The Iron-Ore and Emery in the Cortlandt Norite," in Norites of the " Cort- 
 landt Series," on the Hudson Kiver near Peekskill, N. Y., American Journal of 
 Science, Third Series, vol. xxxiii., No. 195, p. 194 (Mar., 1887). 
 
 25 H. S. Washington. Igneous Complex of Magnet Cove, Arkansas, Bulletin of 
 the Geological Society of America, vol. xi., pp. 389 to 416 (1900). 
 
GEOLOGICAL RELATIONS OF SCANDINAVIAN IRON-ORES. 689 
 
 Utilization. 
 
 From the above it appears that the Scandinavian countries- 
 inclose very large supplies of iron-ores of this kind, and that, 
 in reality, some of these deposits, such as Taberg, Routivare, 
 Ekersund-Soggendal, etc., are among the largest iron-ore de- 
 posits in Sweden and Norway. Numerous attempts at exploit- 
 ing them have been made in different parts of the two countries. 
 Taberg has given rise to a local iron industry on a small scale 
 carried on during two centuries. The ores of Ulfo have been 
 used in several blast-furnaces in Norrland; from Ekersund- 
 Soggendal during a succession of years ore was exported to 
 England and smelted there ; numerous minor mines scattered 
 all over Sweden and Norway bear testimony to the attention 
 which these deposits have attracted. However, all these 
 attempts have been given up because of the unfitness of the 
 ores for metallurgical purposes, which is also the cause why 
 all or nearly all other titaniferous iron-ores all over the world 
 lie unworked. 
 
 GROUP IV. THE IRON-ORE-? OF THE METAMORPHOSED CAMBRO- 
 SILURIAN SCHISTS. 
 
 These ores, which form a very well-defined geological class, 
 are also territorially confined to a certain " ore-province." They 
 occur exclusively within the area of more or less metamorphosed 
 schists which forms the greater part of the mountain-districts 
 of the Scandinavian peninsula north of the 65th degree of lati- 
 tude. Through the abrasion of the Atlantic and the erosion the 
 ore-bearing horizons have in places been laid bare ; these ores 
 are therefore almost exclusively confined to the Norwegian coast 
 and the valleys penetrating into the country from the sea. The 
 fjord-valleys deeply indenting the coast, as well as the nearest 
 islands, are rich in deposits of this kind. 
 
 These ores have long been known, but, in spite of the favor- 
 able situation of several of the larger deposits on or near the 
 Atlantic, they have been exploited, either not at all or to very 
 small extent, by reason of their low percentage of iron. Only 
 since the introduction of magnetic ore-concentration have at- 
 tempts been made to utilize them for export on a larger scale. 
 
 [A discussion of the geological horizon of this group, and descriptions of Dunder- 
 land, Naeverhaugen, Salangen, etc., follow.] 
 
690 GEOLOGICAL RELATIONS OF SCANDINAVIAN IRON-ORES. 
 
 Summary. 
 
 The deposits of this group belong to a ferriferous formation 
 of vast horizontal extent, occupying nearly the same geological 
 horizon in the series as the mica-schist-marble member of this 
 sedimentary series. The ferriferous formation occurs regularly 
 associated with limestones, in most cases, however, in the schists 
 underlying the limestone. The connection with the limestone 
 is so strongly marked that in certain districts nearly every 
 limestone bed is accompanied by iron-ore; some observers 
 have even been inclined to assume a connection between the 
 thickness of the limestone beds and the size of the iron-ore 
 deposits. 
 
 Mineralogically, the ores are characterized as mixtures of 
 magnetite and specular hematites ; and further, by the occur- 
 rence of iron-magnesia-lime silicates of the amphibole, augite, 
 epidote, and garnet groups. Quartz is always present in large 
 quantity. Chemically, these ores are characterized by a high 
 percentage of silicic acid, low percentages of CaO, MgO, and 
 A1 2 O 3 , a medium percentage of phosphorus, and small amounts 
 of sulphur and titanic acid. Whether these ores are primary 
 sedimentary deposits or secondary concentrations of leaner iron- 
 bearing formations is still an open question of the greatest prac- 
 tical importance. 
 
 These ores have, e.g., in Dunderland, an extent of several 
 kilometers in length and, at the same time, a considerable thick- 
 ness. If, taking the syngenetic point of view, we regarded 
 these ores as ordinary stratified formations, altered only by re- 
 gional metamorphism, we would have to assume an extent of 
 several kilometers in the direction of the dip. Such a conclu- 
 sion might be highly misleading w r ith regard to the ore-supply. 
 As to the depth which the ores of this kind reach, there is as 
 yet no practical experience, as neither exploratory work nor even 
 any borings below the present or former ground- water level have 
 been performed. 
 
 A comparison with the Archaean ores of Group I. shows, it 
 is true, some points of agreement. On the whole, the primary 
 characters of chemical sediments are much more evident in this 
 class of ores than in the Archaean ores. Above all, the trans- 
 
GEOLOGICAL RELATIONS OF SCANDINAVIAN IRON-ORES. 691 
 
 formations in the anamorphic zone are less marked; this is 
 shown by the gangues being less developed and the alteration 
 into magnetite less advanced. No analogies to the large mag- 
 netite-stocks among the Archaean ores are found here. Although 
 the nearness to the magnesian limestone has offered plenty of 
 material for the formation of lime-magiiesian silicates of the 
 pyroxene, amphibole, and garnet groups, these silicates never 
 are formed in such abundance as to compare with the skarn 
 gangue of the Archaean ores. The interchange of constituents 
 between the schist, the iron-ore, and the limestone, lying close 
 to one another, has been rather limited. Probably also the sub- 
 mersion in the anamorphic zone did not go so deep as to reach 
 a temperature high enough for the formation of anhydrous sili- 
 cates on a large scale. The depth and the temperature under 
 which the crystallization of these ores occurred seem to have 
 been better adapted to produce the slightly hydrated silicates of 
 the epidote group. 
 
 The transformations in the catamorphic zone also are less 
 marked ; one finds no concentrations of so great richness,' no 
 " s&o/ "-formations, and no accumulations of ores in pitching 
 troughs or on impervious basements. The ores are of more 
 equal leanness, and in general the concentration does not 
 exceed 40 per cent, of iron. 
 
 On the whole, one may consider these deposits as the roots 
 or the deepest, comparatively unconcentrated parts of regional 
 metamorphosed chemical depositions, laid open by the deeply 
 penetrating fjords and valleys of the Norwegian coast; the 
 upper, probably more concentrated and richer parts of the 
 same deposits, having been destroyed by erosion. 
 
 Analogous Deposits. 
 
 The ores of this class are in many respects comparable to 
 those of the lower Silurian formation in the eastern United 
 States, especially to those occurring in a belt from Vermont to 
 Alabama. These ores occur only where the lower Silurian 
 limestone and the Hudson shales meet, as the Norwegian ores 
 always occur at or near limestones, sometimes dolomitized. 
 This is, indeed, one of their most important geological char- 
 acters. The Norwegian rock-strata are, of course, more meta- 
 morphosed, the rocks consisting of crystalline schists and mar- 
 
692 GEOLOGICAL RELATIONS OF SCANDINAVIAN IRON-ORES. 
 
 ble or magnesia-limestone, and the ores being specular hema- 
 tite or magnetite, instead of red and brown hematite. The 
 Clinton ores likewise show, with regard to geological condi- 
 tions, great agreement with the Norwegian Palaeozoic ores. 
 
 GROUP V. CONTACT-DEPOSITS IN THE CHRISTIANIA REGION. 
 
 These ores were considered by Keilhau, Daubree, and Kjerulf 
 as genetically connected with the intrusion of granite in the 
 same region ; and this opinion was afterwards confirmed by 
 Vogt, who executed a minute survey of the deposits. 27 
 
 Classification of the Rocks. 
 
 According to Brogger, the igneous rocks of the Christiania 
 region may be divided into seven groups of different age ; the 
 oldest three are more basic, and consist of (1) gabbro-diabases ; 
 (2) basic augite-, mica- and nepheline-syenites (laurvikite and 
 laurdalite) ; and (3) quartz-bearing augite-syenite (akerite). 
 Of later age is the following syenitic and granitic series, com- 
 prising (4) red quartz-syenites (nordmarkite) ; (5) soda-granites 
 (grorudite) ; and (6) granitite. As the youngest members occur 
 dike-forming diabase and diabase-porphyrite. The eruptives 
 are probably of Devonian, surely of post-Silurian, age. They 
 occupy an area about 250 km. long, and in some places more 
 than 100 km. wide. 
 
 The intrusives are bordered partly by Archaean rocks, partly 
 by the Silurian strata, and by porphyry-outflows. The con- 
 tact-deposits are found in all these different pre-granitic rocks. 
 
 Most of the deposits are connected with the red quartz- 
 syenite (nordmarkite), some of them with the soda-granite 
 (grorudite) and the granitite. 
 
 The Ores. 
 
 The iron-ores are, as a rule, mixed with true contact-min- 
 erals, such as different species of the garnet and vesuvian 
 groups, scapolite, wollastonite and others. This is especially 
 the case with the deposits occurring in the limestone and marly 
 slates. In the clay-slate, chiastolite is found as contact-mineral. 
 The percentage of iron is through the gangue reduced to from 
 
 27 Zeitschrift fur praktische Geologic, vol. ii., pp. 177, 464 (1894), vol. iii., p. 154 
 (1895). 
 
GEOLOGICAL RELATIONS OF SCANDINAVIAN IRON-ORES. 693 
 
 30 to 35, and only exceptionally exceeds 40. The ores are 
 generally strongly pyritic, but low in phosphorus and titanium. 
 Frequently they occur in the immediate vicinity of the intru- 
 sive rock, but they may also be found up to 1 km. from the 
 contact. In a few cases the distance from the visible contact 
 is more than 1 km., but the ores never are found outside of 
 the metamorphic zone of the contact. The majority of the 
 deposits occur in the Silurian strata, partly at the borders of 
 the Silurian rocks, partly in big metamorphosed Silurian rock- 
 fragments, completely surrounded by the igneous rock. The 
 different Silurian horizons are equally impregnated with ores ; 
 and the clay-slates as frequently contain ore-deposits as do the 
 limestones and marly slates. Also, the Archaean gneisses, and 
 sometimes the porphyries, are ore-bearing. 
 
 The ore-deposits show generally a stratiform extension, and 
 may be followed with varying thickness along the same bed 
 for several hundred meters. 
 
 These deposits, though numerous, are quantitatively too in- 
 significant to play any commercial role. In earlier times sev- 
 eral hundred small ore-bodies were worked. The ore is mainly 
 magnetite, but also specular hematite. Also, sulphides of iron 
 and copper occur in so great amount that the ore may obtain 
 the character of a copper-ore. Exceptionally, also, galena and 
 blende have been found in such quantities as to be mined as 
 ores. But all the deposits are small. From the seventeenth 
 up to the latter part of the nineteenth century, they furnished 
 a group of small blast-furnaces with iron-ores ; and an insignifi- 
 cant copper- and lead-production was in early times based on 
 these ores. 
 
 Analogous Deposits. 
 
 The ore-deposits of the Christiania territory are genetically 
 most similar to the Pitkaranda deposit in Finland, and the 
 known deposits of Schmiedeberg in Silesia and Berggiesshiibel 
 in Saxony. 
 
 There are a great number of deposits of this kind in the 
 western United States, chiefly in Colorado and California, 
 where they occur associated with the younger eruptives of the 
 Rocky mountains and the Sierra Nevada. 
 
694 GEOLOGICAL RELATIONS OF SCANDINAVIAN IRON-ORES. 
 
 GROUP VI. LAKE- AND BOG-ORES. 
 
 These ores formed the raw-material for the oldest iron-in- 
 dustry in Scandinavia, long before the blast-furnace process 
 was known. For this reason, Carl Linnaeus called them Tophus 
 Tabalcaini, after Tubal Cain, the first blacksmith (Gen. iv, 22). 
 The lake-ores occur in most provinces of Sweden and in 
 the southern part of Norway. But their abundant occurrence 
 is confined to regions where the ground consists of moraine 
 and glacial gravel and sand, especially the high plateau of 
 Smaland, the northern parts of Vermland, Vestmanland and 
 Dalarne, and the greater portion of Norrland. They occur 
 only sparingly in the regions covered by glacial and post-gla- 
 cial marine-deposits, such as the lower coast-belt of southern 
 Sweden, and the plains surrounding the great lakes of Vanern, 
 Yettern, Hjelmaren and Malaren. In short, the lake- and bog- 
 ores are most frequent above the marine level of the glacial 
 period. A certain connection with the distribution of the 
 peat-mosses is indicated. On the other hand, the bog-ores are 
 by no means more frequent in the districts rich in other iron- 
 ore deposits. In some places, a connection with the greater 
 pyrite-deposits may be suggested. 
 
 The bog-ores are recent formations, produced before our 
 eyes. In lakes, where the ore has once been exploited, it 
 grows and may be utilized again. In some lakes of Smaland 
 mining-operations have been resumed at places exhausted 25 
 years before. 
 
 In the ore-bearing lakes, the iron is precipitated from dilute 
 solutions chiefly along certain zones, parallel to the shores, at 
 a depth of from 2 to 4 m., and the ores are thus distributed in 
 belts on the bottom of the lake, to a thickness of at most 0.5 m. 
 Lakes connected by a water-course frequently all contain bog- 
 ores. In the upper lakes the ore is more tine-grained (" gun- 
 powder-ore," " pearl-ore "), while in the lower lakes the ore 
 has grown to coarser concretions (" money-ore," " cake-ore "). 
 
 The purer lake-ores generally contain from 50 to 60 per cent, 
 of Fe 2 3 and from 10 to 15 per cent, of water. Silicic acid is 
 frequently mechanically intermixed, reducing the iron-percent- 
 age. Sometimes the ores contain a considerable amount of 
 manganese (up to 20 per cent.). The percentage of phosphorus, 
 as well as of sulphur is generally high. 
 
GEOLOGICAL RELATIONS OF SCANDINAVIAN IRON-ORES. 695 
 
 Bog-ores are often formed in lakes as lake-ores, and later, by 
 a natural draining, brought above the water-level. But fre- 
 quently bog-ores occur in a manner indicating their formation 
 in the ground close to the surface ; in such cases they are often 
 formed in connection with peat-mosses. 
 
 The utilization of the lake-ores has in later years much de- 
 creased, and is to-day without importance. From 1860 to 
 1875 the annual production in Sweden was about 10,000 tons. 
 From 1900 to 1905, it was only about 1,000 tons, varying from 
 300 up to 1,500 tons, according to the severity of the winters. 
 The whole product comes from Smaland and is used for the 
 fabrication of cast-iron. 
 
696 FORMATION AND ENRICHMENT OF ORE-BEARING VEINS. 
 
 No. 27. 
 The Formation and Enrichment of Ore-Bearing Veins. 
 
 BY GEORGE J. BANCROFT, DENVER, COLO. 
 
 (New York Meeting, April, 1907. Trans., xxxviii., 245). 
 
 INTRODUCTION. 
 
 IT is unnecessary to repeat here the contents of many valu- 
 able contributions to this subject which have appeared in the 
 Transactions and in the publications of the U. S. Geological 
 Survey. As a basis for the further suggestions of this paper, 
 the following are the most important : 
 
 1. The investigation of J. R. Don, 1 showing the gold of cer- 
 tain Australasian veins to have been deposited by ascending 
 solutions, and not by lateral secretion. 
 
 2. The theory of Prof. Posepny, 2 distinguishing the vadose 
 from the deep circulation, and ascribing the origin of certain 
 classes of ore-deposits to ascending solutions of the latter class. 
 
 3. The theory of Prof. Van Hise, 3 as to the underground 
 circulation and the primary enrichment of veins thereby. 
 
 4. The paper of Prof. J. F. Kemp, 4 showing that ore-de- 
 posits are largely the products of " expiring vulcanism." Many 
 of Prof. Kemp's ideas have been widely adopted by mining 
 men. 
 
 5. The theory of secondary enrichment, so lucidly expounded 
 by Mr. S. F. Emmons. 5 This theory, dealing with the rear- 
 rangement of ore-bodies after primary mineralization, has been 
 generally adopted, and seems to me to have been as completely 
 proved as the nature of the case permits. 
 
 There are two facts which I think should be constantly 
 borne in mind in formulating a theory of the genesis of ore- 
 
 1 The Genesis of Certain Auriferous Lodes, p. 162, this volume. 
 
 2 Genesis of Ore-Deposits, pp. 1 to 187, and Trans., xxiii., 197 to 369 (1893). 
 
 3 Some Principles Controlling the Deposition of Ores, Genesis of Ore- Deposits, 
 pp. 282 to 432 ; also, Trans., xxx., 27' to 177 (1900). 
 
 4 The Hole of the Igneous Kocks in the Formation of Veins, Genesis of Ore- 
 Deposits, pp. 681 to 709 ; also, Trans., xxxi., 169 to 198 (1901). 
 
 6 Genesis of Ore- Deposits, p. 462, and Trans., xxx., 206 (1900). 
 
FORMATION AND ENRICHMENT OF ORE-BEARING VEINS. 697 
 
 bodies. The first is that commercially valuable mines are rela- 
 tively few. Countless veins present all the characteristics of 
 good mines, except the values. I suppose that there are a 
 hundred barren veins for every enriched one, and even the lat- 
 ter are rarely enriched to the extent of more than 20 per cent, 
 of their volume. The stope-map of any old mine, showing the 
 proportion of stopes to barren ground, will very seldom indi- 
 cate that more than 20 per cent, of the vein has been removed. 
 
 The second fact is, that nearly all ore-bodies are found in 
 close association with eruptive rocks. So generally is this fact 
 recognized that an old mining man does not like to spend 
 money on a prospect in a new district where there is no " por- 
 phyry " (" porphyry," in the broad miners' sense, meaning any 
 kind of eruptive rock). 
 
 In view of these two facts, it seems to me that any theory 
 which does not recognize that only exceptional conditions 
 could produce such exceptional results of enrichment, which 
 does not recognize and explain the relationship between 
 " porphyry" and ore, falls short of the mark. 
 
 My own observations as a mining engineer have led me to 
 the following tentative views : (I.) that the majority of mineral- 
 ized veins are the product of expiring vulcanism; (II.) that 
 most of these veins were primarily mineralized by compara- 
 tively rich solutions in comparatively short periods of time ; 
 (III.) that the solutions derived their metal-values from a com- 
 paratively rich source ; (IV.) that there is a barysphere con- 
 taining large amounts of the useful metals ; (Y.) that eruptions 
 spring from various depths and bring various kinds of magma 
 towards the surface ; and (VI.) that only those eruptions which 
 disturb the barysphere, and bring a magma rich in metals suf- 
 ficiently near the surface to be leached by vein-making solu- 
 tions, are productive of valuable ore-deposits, other eruptions 
 producing barren veins. 
 
 Ore-bodies due to magmatic segregation are not included in 
 this general survey. 
 
 These propositions will be successively considered in the 
 present paper. 
 
 44 
 
698 FORMATION AND ENRICHMENT OF ORE-BEARING VEINS. 
 
 I. THE MAJORITY OF MINERALIZED VEINS ARE THE PRODUCTS 
 OF EXPIRING VULCANISM. 
 
 This proposition has been so fully demonstrated by Prof. 
 Kemp in his very valuable article entitled The Role of the Igne- 
 ous Rocks in the Formation of Veins, 6 that I feel it would be 
 superfluous to add much to it. 
 
 There is, however, one small matter in which I differ with * 
 Prof. Kemp namely, I do not think there is good reason to 
 believe, that the surface-water does not sink down into the 
 rocks to very considerable depths. Prof. Kemp notes that 
 many mines are dry to the point of being " dusty," at depths 
 below 1,000 ft. This is true; but in a drift which is being rap- 
 idly driven the freshly-broken breast will always be found to 
 be damp. The reason the lower levels of so many mines are 
 dry and dusty is that the evaporation, slow as it is, is neverthe- 
 less faster than the very torpid movement of the ground-water. 
 This torpidity of the ground-water in depth is caused by the 
 " tightness " of the rocks. It is a familiar experience in min- 
 ing that the ground gets tighter the deeper one goes. Of course, 
 in individual districts there may be other obstacles, such as 
 sills of impervious rocks or clay, preventing the ground-water 
 from sinking into the lithosphere; but, in almost every case 
 known to me, the tightness of the rocks in the lower levels will 
 account for any observed diminution of water-flow. "Where re- 
 cent fissuring has occurred, there is generally no diminution of 
 water-flow with depth. Indeed there may be, as at Cripple 
 Creek, an increase. 
 
 It is often overlooked, in discussing the saturation of the 
 ground, that in many mining districts the yearly evaporation is 
 greater than the yearly rain-fall less the run-off. This question 
 has been very extensively studied by the U. S. Hydrographic 
 Survey. One of its publications, entitled The Relation of 
 Rain-fall to Run-off, sets forth data on this subject gathered 
 in many places. ~No general conclusions are drawn; but I figure 
 that in Colorado the run-off is about one-third the rain-fall. The .* 
 rain-fall varies from 12 to 24 in., or, after deducting the run-off, 
 we have from 8 to 16 in. per year. The capacity for evaporation 
 is more than 3 ft. per year ; so that, except in those channels 
 
 6 Genesis of Ore-Deposits, pp. 681 to ^09, and Trans., xxxi., 189 to 223 (1901). 
 
FORMATION AND ENRICHMENT OF ORE-BEARING VEINS. 699 
 
 where water quickly gathers after a rain, the country must be in 
 a state of continual thirst, and only such water will remain un- 
 der ground as is held there by capillary attraction. As depth 
 is gained and the water-gathering channels become less fre- 
 quent, we find the rocks to be moist but not always wet. Simi- 
 lar conditions prevail in many mining regions. 
 
 Prof. Van Hise has drawn attention to what he calls the zone 
 of flowage, which begins at depths of from 5,000 to 12,000 m. 
 To my mind the zone of flowage is more a matter of time, and 
 less a matter of depth, than he considers it. I think a chan- 
 nel may exist at much greater depth than his limit for a short 
 time, but when a long time is involved, I think the zone of 
 flowage may come very close to the surface. 
 
 It seems to me entirely logical to suppose that a channel may 
 remain open as long as it takes a laccolite to cool and yet grad- 
 ually close till it is tight, except where quartz or other vein- 
 matter has formed in it. A channel that would stay open when 
 the surrounding rocks were quiet would have a strong tendency 
 to close gradually if those rocks were subjected to forces which 
 cause flexure or other movement in the earth's crust. If this 
 supposition be well founded, it will account for those cases 
 where the quartz is in lenticular masses and mere tight cracks 
 in the rocks represent the veins beyond the limit of any lenti- 
 cles. Such cases simply indicate that the channels have closed 
 since the vein was formed. It is noticeable that such veins are 
 often found in schist, or other rocks that show the effect of 
 movement and pressure. The matter of open channels is fur- 
 ther discussed under my third proposition. 
 
 In districts which have been fissured quite recently, like 
 Cripple Creek, we find open fissures and much water as far down 
 (about 1,500 ft.) as the deepest shafts have gone. But even in 
 this camp the deep shafts in the granite are nearly dry at the 
 bottom. Whether this is because the granite was fissured less 
 than the eruptive rocks in the first place, or because the gran- 
 ite is more mobile under pressure and has closed in on its fis- 
 sures, I am not prepared to say. At all events, the shafts in 
 the granite are dry at horizons where shafts in the eruptive 
 rocks are troubled with a great deal of water ; and this water 
 has been conclusively proved to be simply rain-water stored in 
 the vast underground reservoir formed by the countless open 
 
700 FORMATION AND ENRICHMENT OF ORE-BEARING VEINS. 
 
 fissures in the eruptive rocks. There are no volcanic springs 
 active in Cripple Creek to-day. Hence, I think Prof. Kemp 
 gives a wrong impression, and one which he probably did not 
 intend, when he says that many mines are dry to the point of 
 being dusty in depth, which were wet near the surface. I be- 
 lieve that the earth is very generally impregnated with mois- 
 ture; but I quite agree with Prof. Kemp that this " sea of un- 
 derground water " is utterly inadequate to account for ore- 
 bodies. In most formations, there is practically no movement 
 in this water below the 500-ft. level. In many cases it will not 
 run into a mine fast enough to equal the slow evaporation ; 
 and it is beyond conception that such a torpid agent could ac- 
 complish anything in the line of vein-making before a fissure 
 would close up, even at moderate depths. 
 
 All mining men have met with " swelling ground," and most 
 of them have known of swelling ground that could not be ac- 
 counted for by the action of the air admitted by the mine-work- 
 ings. This kind of swelling is, of course, very much slower than 
 that due to the " slacking " of lime or other rocks influenced 
 by the air; but it shows the general tendency of rocks to close 
 up any opening beneath the surface. Yet this tendency is 
 always a function of time, and time is one of the most puzzling 
 factors in any geological discussion. 
 
 It is impossible to state in years how long a geological oper- 
 ation lasted. The most that can be done is to compare the 
 duration of one geological operation with that of another. To 
 my mind, most ore-deposits show that the time consumed in 
 their formation was very short, compared, for instance, with the 
 time necessary to carve out the canyon of the Colorado ; hence, 
 I think that a fissure that would in time close up tight, might 
 nevertheless stay open during the (geologically) brief interval 
 required to cool a mass of eruptive rocks. 
 
 II. MOST OF THESE VEINS WERE PRIMARILY MINERALIZED BY 
 
 COMPARATIVELY RICH SOLUTIONS IN COMPARATIVELY 
 
 SHORT PERIODS. 
 
 That considerable mineralization has been effected where the 
 solutions passed through very small channels, leaving those 
 channels very little altered, is evidenced in many places. The 
 so-called " flats " of the Black Hills are cases in point. In the 
 
FORMATION AND ENRICHMENT OF ORE-BEARING VEINS. 701 
 
 Penobscot mine, for instance, several flat deposits of gold-ore 
 in the sedimentary rocks have been extensively worked. The 
 ore occurs in shoots averaging perhaps 45 ft. wide and 4.5 ft. 
 thick. Each ore-shoot has a vertical fissure coming up through 
 the so-called " quartzite " beneath it; and over these fissures 
 the richest ore is found. These fissures are so small as to be 
 easily overlooked. Those that I saw varied from 0.125 to 0.675 
 in. in thickness. In some places they were open, while in other 
 places, where the width was about the same, they were filled with 
 quartz, a circumstance which indicates that these fissures have 
 not closed up to any great extent. 
 
 That such extensive ore-bodies should be mineralized through 
 such small fissures suggests strongly that the solutions were 
 comparatively rich and that they flowed for a comparatively 
 short time. A long-continued flow, I think, would have either 
 enlarged the little fissures or filled them completely full of 
 quartz. 
 
 The Cortez mine, Nevada, and the Lisbon Valley copper- 
 fields of Utah are also cases in point. At these places mineral- 
 ized solutions came up through hard strata of sedimentary rocks 
 and spread out in soft porous strata, mineralizing considerable 
 areas. In both localities the vertical fissures are small, and 
 show little alteration of the wall-rocks. From specimens I have 
 seen which were brought from Cobalt, Ontario, Can., I would 
 say this is another case in point. The specimens show solid 
 sheets of silver between comparatively unaltered walls. 
 
 That the lavas issuing from volcanoes contain large quantities 
 of steam is well known. During the early stages of the erup- 
 tion of Vesuvius, in 1898, 1 observed a small lava stream on two 
 occasions, about 6 days apart. The stream was about half* a mile 
 long, and was moving very slowly. I presume it had taken 
 three weeks to gain this length, yet it was spitting steam con- 
 tinually from every pore throughout its entire length. I was 
 much impressed with two things : the great amount of steam 
 escaping from a stream 15 ft. wide and 4 ft. deep; and the fact 
 that the lower end continued to advance when it had only a 
 very dull red heat. I wondered whether the escaping steam 
 did not account for its mobility in some way. If all magmas 
 have stored in them as great quantities of water as the Vesuvius 
 lavas and if they tend to discharge it when brought into condi- 
 
702 FORMATION AND ENRICHMENT OF ORE-BEARING VEINS. 
 
 tions of lessened pressure we have here a source of water of no 
 small moment. It is hardly conceivable, however, that this 
 source can alone supply all the water used in vein-making in all 
 cases. For instance, if a magma contained as much as 25 per 
 cent, of water, then a spring running 10 miners' inches would 
 in 200 years exhaust a body of the magma 40 ft. thick and 3,600 
 acres in extent. I think we must agree, therefore, that in some 
 cases the volcanic waters are serviceable principally in starting 
 and maintaining open waterways and establishing a current. 
 In such cases they are probably joined by other waters, and the 
 combined flow accounts for the volume of water which we find 
 issuing from some mineral springs. Thus we find ore-deposits, 
 such as the immense quartz-veins of the San Juan, in Colorado, 
 or the big quartz-lenses of the Homestake, in S. Dakota, and of 
 the Mother Lode, in California, that seem to have been formed 
 by a generous supply of water ; and we find other ore-bodies 
 which indicate that very little water ever circulated through 
 the veins, as, for instance, the ore-shoots of Goldfield, Nev., 
 which occupy single cracks or net-works of cracks, made since 
 the big quartz-reefs were formed, and in which angular cor- 
 ners of the walls frequently stick out into the solid masses of 
 sulphide ore. As the ore-bodies are found in the easily altered 
 country-rocks as well as in the quartz-ledges, such angular cor- 
 ners are the more remarkable. If the mineralized solutions had 
 run a long time, these corners would have been rounded off. 
 At Cripple Creek, likewise, we find areas where the joints 
 and seams of the country-rock are coated with sylvanite, and 
 where there is no other evidence of vein-making agencies. In 
 the veins themselves silicification is very slight. Kalgoorlie, 
 West Australia, where a great deal of enrichment has taken 
 place with very little silicification or other alteration of the 
 country-rock, is another illustration. Such camps are irrecon- 
 cilable, in my mind, with the theory that veins were formed by 
 very lean solutions acting through long periods of time. Even 
 the big low-grade quartz-veins seem to indicate an agent much 
 more active than is generally recognized. To my mind, the 
 evidence suggests that some ore-bodies were formed by the 
 magmatic waters or vapors alone, while others were formed or 
 rearranged by considerable volumes of water. There is some 
 reason to believe that the quartz of an ore-body is not always a 
 
FORMATION AND ENRICHMENT OF ORE-BEARING VEINS. 703 
 
 full-blooded brother to the mineral contents of that body ; but 
 I will not discuss that matter at this time. 
 
 In most genetic processes nature is extremely wasteful. In 
 the formation of a sand-bar in the Mississippi river, hundreds 
 of tons of material pass down the river every day ; but it is only 
 an occasional grain that lodges on the sand-bar. Or in the 
 growth of mounds around mineral springs, the water that flows 
 over them is all charged with mineral matter but it is only an 
 occasional atom that lodges on the mound. In view of this con- 
 sideration, it seems to me that the theory that ore-deposits were 
 formed by leaching the extremely lean, eruptive, or other rocks 
 known to us on the surface, involves one of two rather unten- 
 able suppositions. Either we must conclude that nature has 
 operated with a degree of accuracy which is almost unattain- 
 able in the laboratory ; that she has leached absolutely clean 
 the metal-contents of a rock which had the merest trace 
 to start with, and that she has precipitated every bit of the 
 metal so gathered in an ore-body, leaving the solution abso- 
 lutely barren; or else, in case it is admitted that nature prob- 
 ably operated with her usual prodigality, we must assume that a 
 tremendously large mass has been subjected to leaching action 
 to form a relatively small ore-body. In accounting for a large 
 ore-body, such as those of our leading copper-camps, it is diffi- 
 cult to understand how the leachings from such a great area as 
 this hypothesis necessitates could have been gathered together 
 into one underground channel. We are forced to assume that 
 veins must branch out downwardly like the limbs and twigs of 
 a giant tree inverted. Such conditions are contrary to ordi- 
 nary observation. Veins not infrequently unite as depth is 
 gained, but very seldom branch out with depth. This again 
 leads to the conclusion that the solutions that formed ore-bodies 
 were not the extremely dilute solutions which would result from 
 leaching lean rocks. 
 
 Another reason for believing that ore-bodies were formed 
 from comparatively rich solutions is the well-known difficulty 
 of precipitating the last trace of any metal in solution. Who- 
 ever has had to do with a leaching process, such as cyanidation 
 or chlorination, knows how difficult it is to get into solution the 
 last trace of gold in the ore, and to precipitate the last trace of 
 value from the solution. In fact, this is practically impossible ; 
 
704 FORMATION AND ENRICHMENT OF ORE-BEARING VEINS. 
 
 tailings carrying from 30 to 60 cents per ton are considered in 
 most cases to indicate good work; and foul solution that con- 
 tains no more than 20 or 30 cents of value per ton is considered 
 poor enough to throw away. Yet the surface-rocks, considered by 
 some to be the source of the metals, are much leaner than the 
 poorest tailings; therefore, solutions picking up metals from 
 them must be poorer than the solutions we are forced to dis- 
 card as worthless in fact, not less dilute than the sea-water, 
 which Don found to contain 0.071 grain of gold per ton of 
 2,240 Ib. Don was unable to precipitate directly from this 
 sea-water any gold at all, although he used the best precipitants 
 under the most favorable conditions. He made his determina- 
 tions by slowly evaporating several tons of sea-water and assay- 
 ing the residue. 
 
 As to the time occupied in forming veins, it seems to me that 
 most of the work has been done during the period that Prof. 
 Kemp so fittingly calls that of "expiring vulcanism." This is 
 a relatively short period so short, in fact, that changes in its 
 conditions may be noticed within a human life-time. Hot springs 
 are very generally associated with expiring vulcanism; and 
 nearly all the hot springs that I know of are noticeably drying up. 
 At Steamboat springs, Nevada, at least two borings have had 
 to be made to bring the flow up to its original capacity. Old 
 settlers at Glenwood springs, Colorado, testify that hot water 
 used to issue from a number of minor vents which are now dry,, 
 and that the main streams are slowly decreasing in flow. At 
 Aguacaliente, in Sonora, the water is used for irrigation, and 
 the abandoned fields farthest down the gulch bear mute testi- 
 mony to the gradually decreasing flow. This spring is a fine 
 example of the fact that hot mineral springs have some source 
 other than rain-water. The only range in this dry country that 
 receives any rain-fall to speak of is the Sierra Madre, 100 miles 
 east and across the Yaqui valley. The largest cold springs 
 within a radius of 20 miles are only large enough to supply 
 water for domestic use. 
 
 In discussing mineral springs, it must be borne in mind that 
 some of them are no doubt of secondary origin. Thus, Trimble 
 springs, Colorado, gives every evidence of having received its 
 heat and mineral contents from the oxidization of a large body 
 of iron pyrites. 
 
FORMATION AND ENRICHMENT OF ORE-BEARING VEINS. 705 
 
 inco 
 
 CO O CN rH iO CC 
 1C rH r-( 
 
 grHjOrH 
 
 $$3 
 
 GO rH rH g) I- <N O 
 
 CO "^ l> O* rH CO O 
 
 g d r~ oi c^i 
 
 \ rH T!< <M_ rH !>. CO C 
 
 rH I d rH in rH GO OS O 
 10 rH 
 
 rH ^OOOlNOOOrH 
 
 00 rH 10 C<J O 
 
 0040t^00400O 
 
 o o 04 
 
 O rH rH rH -5 lO O O -C 
 
 |S88 
 
 iodd 
 
 iooo- 
 
 ooi> 
 
 j :8SSSS 
 
 icic 
 
 c '^ 
 
 ! 18 
 
 8 " 
 
 ricOCOOriij>faSo 
 
 ^"HcIfsJ^S"! 
 
 Cllfiftfii 
 
 w <uS."SaQo i^;<u 
 
 !|ill!^l I 
 
706 FORMATION AND ENRICHMENT OF ORE-BEARING VEINS. 
 
 TABLE II. Analyses of Spring- Waters. 
 
 Parts in one thousand. 
 
 No. 
 
 1 
 
 2 
 
 3 
 
 4 
 
 0.3040 
 0.0094 
 0.0121 
 0.0004 
 
 5 
 
 6 
 
 7 
 
 8 9 
 
 10 
 
 11 
 
 12 
 
 0.0020 
 0.0128 
 0.0012 
 
 Na 
 
 0.1042 
 tr. 
 0.5060 
 
 0.7743 
 0.0669 
 0.0305 
 0.0010 
 
 0.3554 
 0.0191 
 0.0367 
 0.0034 
 
 0.6116 
 0.0630 
 0.0589 
 0.0604 
 
 
 
 
 
 0.0310 
 0.0372 
 
 K 
 
 
 
 
 0.1285 
 1.0739 
 0.2352 
 
 Ca 
 
 Me.... 
 
 
 
 
 
 Ba 
 
 
 
 
 
 tr 
 
 
 
 Sr 
 
 
 
 
 
 
 
 
 
 
 
 
 Li 
 
 fr. 
 
 
 
 
 
 
 
 ! 6603 
 
 
 
 Fe 
 
 tr. 
 
 
 
 
 
 
 
 O0'>7 
 
 
 
 Mn 
 
 tr, 
 
 
 
 
 
 
 
 0009 
 
 
 
 Cl 
 Br 
 
 tr. 
 
 0.9697 
 
 0.2396 
 
 6.2070 
 
 0.2272 
 
 0.9524 
 
 
 
 14.2730 
 00 9 5 
 
 0.0480 
 
 
 
 I 
 
 
 
 
 
 
 
 
 tr. 
 
 
 
 Fl 
 
 
 
 
 
 
 
 
 
 
 
 CO 2 
 S0 3 
 HPC>4 
 
 0.0852 
 0.1614 
 tr 
 
 0.3555 
 
 tr. 
 0.3901 
 
 6.3492 
 
 0.5787 
 0.3131 
 
 0.1776 
 0.1039 
 
 0.2624 
 
 1.7513! 0.1792 
 2.0318 
 tr |H rwu 
 
 6.0383 
 
 0.0089 
 0.0040 
 0.0179 
 
 6.0012 
 0.0317 
 
 B,O 7 
 
 
 
 
 
 
 6. 21741.8784 
 0.0003! 
 0,31060.0371 
 
 2.4043; tr. 
 6.0418 "6" 2464 
 
 tr, 
 
 0.0022 
 0.0080 
 0030 
 
 "" 
 
 SK,: : 
 
 SiO 9 .... 
 
 tr. 
 tr. 
 
 0.0010 
 0.2788 
 
 6.1136 
 
 6.1310 
 
 0.0018 
 0.1220 
 
 H 
 
 
 tr 
 
 
 
 
 
 
 0.0050 
 6V6645' 
 
 0076 
 
 
 
 
 O 
 H 2 S 
 KHS and S 
 
 0.0500 
 
 0.0194 
 
 6.0255 
 
 6.0080 
 
 0.0325 
 
 0.0005 
 
 0069 
 
 6/6bo7 ";;;;;!;;; 
 
 
 
 
 
 
 
 AsO 
 
 
 
 
 
 
 0036 
 
 
 
 
 
 SbO* 
 
 
 
 
 
 
 0005 
 
 
 
 
 
 p 9 o<T 
 
 
 
 
 
 
 0006 
 
 
 
 
 
 
 HgS " " 
 
 
 
 
 
 
 tr 
 
 
 
 
 
 
 FeO 
 
 
 
 
 
 
 0.0002 
 
 
 
 
 
 
 MgO 
 
 
 
 
 
 
 0005 
 
 
 
 
 
 
 NaoO 
 
 
 
 
 
 
 9193 
 
 
 
 
 
 
 CaO 
 
 
 
 
 
 
 0005 
 
 
 
 
 
 
 KoO 
 
 
 
 
 
 
 1246 
 
 
 
 
 
 
 FeCO 3 
 
 
 
 
 
 
 
 
 O.ob'lO tr. 
 1.039713.6226 
 0.3809: 4768 
 
 2.0398 
 
 6.0154 
 
 0.0109 
 0.0243 
 
 NaCl 
 Alk Carb 
 
 
 
 
 
 
 
 
 
 
 
 
 1.1027 
 2 0075 
 
 KSC>4 
 
 
 
 
 
 
 
 
 3005 
 
 
 
 
 CaSO 4 
 
 
 
 
 
 
 
 0.0234 
 
 1 1548 
 
 
 
 
 NaSO4 
 
 
 
 
 
 
 
 
 6890 
 
 
 
 
 MffCl ... 
 
 
 
 
 
 
 
 
 1637 
 
 
 
 
 KC1 
 NaBr 
 
 
 
 
 
 
 
 
 
 
 0.0470 
 
 0.0747 
 
 0704 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 0.1149 
 
 Total 0.9068 
 
 2.5171 
 
 1.1834 
 
 1.0211 2.0692 
 
 2.81945.3675 
 
 6.3910 16.0352 
 
 9.9814 
 
 0.1699 
 
 SPRINGS. 
 
 No. 1, Sulphur springs, Los Angeles ; Annual Report U. S. Geological Survey, 
 p. 195, 1876. No. 2, Hot spring at Hot Spring station, C. P. K. K. ; Chamberlin 
 and Salisbury's Geology, pp. 224-225. No. 3, Hot springs at the base of the 
 Granite mountains, Nevada ; Chamberlin and Salisbury's Geology, pp. 224-225. 
 No. 4, Boiling spring at Honey Lake valley, California ; Chamberlin and Salisbury's 
 Geology, pp. 224-225. No. 5, Warm spring, Mono basin, California ; Bulletin No. 
 9, U. 8. Geological Survey, p. 27. No. 6, Steamboat springs, Nevada ; G. F, 
 Becker, Geology of the Quicksilver Deposits of the Pacific Slope; Monograph xiii. 
 U. S. Geological Survey, p. 347. No. 7 and No. 8, two different shafts at Sulphur 
 Bank, California ; G. F. Becker, Geology of the Quicksilver Deposits of the Pacific 
 Slope ; Monograph xiii, U. S. Geological Survey, p. 259. No. 9, Glenwood springs, 
 Colorado ; Glenwood Springs Hotel Pamphlet. No. 10, artesian well at Sheboygan, 
 Wisconsin ; C. F. Chandler, American Chemist, p. 370, 1876. No. 11, the Mississippi 
 river ; W. J. Jones, Report Louisiana State Board of Health, p. 370, 1882. No. 12, 
 the Sacramento river ; W. J. Jones, Report California State Board of Health, 1878. 
 
FORMATION AND ENRICHMENT OF ORE-BEARING VEINS. 707 
 
 Table I. contains analyses of 23 eruptive rocks, and Table II. 
 the analyses of 12 spring-waters, the first nine of the latter be- 
 ing hot springs, the tenth an artesian well, and the eleventh 
 and twelfth river-waters. The rock analyses, which are from 
 representative surface eruptives, show that these rocks must be 
 very lean indeed in the useful metals. Mr. Waldemar Lind- 
 gren 7 mentions the finding of traces of pyrite, chalcopyrite and 
 galena in the gray gneiss of Freiberg. Prof. Kemp mentions the 
 finding of various metals in various eruptive rocks, but does not 
 give any quantitative analyses. 8 
 
 Don was unable to find any gold at all in the rocks he ex- 
 amined except in association with iron pyrites, which latter 
 gave evidence of being the result of vein-making agencies. Of 
 course, it may be said that all the analyses of the eruptive rocks 
 are made after they have been leached out. If it could be 
 shown that the surface eruptive rocks have a tendency to throw 
 off metals, as they do steam and sulphur, during the cooling 
 process this would remove many of my objections to considering 
 them the source of the metals in our ore-bodies. In the lack of 
 such proof, however, we must recognize that they are extremely 
 lean, and therefore a very unlikely source of mineral wealth. 
 
 Of the four rocks from the Telluride quadrangle only one 
 shows manganese ; yet rhodonite and rhodocrosite are very com- 
 mon to the veins of this district. Of the six analyses from the 
 La Plata quadrangle, every one shows manganese ; yet it has 
 been my observation that manganese is a rare constituent of the 
 veins of this quadrangle. In the 13 analyses of rock from the 
 Port Orford quadrangle a wide range of minerals is seen, which 
 often are found in veins, yet the veins of this locality contain 
 little but quartz, pyrite, chalcopyrite and gold. 9 
 
 The table of spring-waters was rather surprising to me in 
 that it shows that an artesian well-water may contain as much 
 mineral matter in solution as the average hot spring. I do not 
 see that a comparison of the minerals found in hot springs with 
 those minerals found in the eruptive rocks is very instructive. 
 Unfortunately, I have no complete analyses of all the rocks im- 
 
 7 Metasomatic Processes in Fissure- Veins, Trans., xxx., 659 et seq. (1900). 
 
 8 The R61e of the Igneous Rocks in the Formation of Veins, Genesis of Ore- 
 Deposits, pp. 681 to 709, and Trans., xxxi., 169 to 198 (1901.^ 
 
 9 Port Orford Folio, U. S. Geological Survey. 
 
708 FORMATION AND ENRICHMENT OP ORE-BEARING VEINS. 
 
 mediately surrounding a hot spring. If such analyses were 
 available they would be very instructive. As it is, the only dis- 
 tinguishing characteristic of hot springs brought out by the 
 analyses is the presence of sulphur and sulphur gases and of 
 chlorine combinations. Fresh lava, we know, gives off fumes 
 of sulphur and chlorine ; hence it is natural to connect hot sul- 
 phur springs with fresh eruptives. 
 
 The analyses given in Table I. show very few of the useful 
 metals in solution, but Posepny in his Genesis of Ore-Deposits 
 mentions that lead occurs in the springs of Rippoldsau (accord- 
 ing to Will, 1.6 to 3.7 mg. per ton), and in the Kissingen spring 
 (13 mg. per ton), and quotes from G. Bischof, as follows, the 
 maxima found in mineral springs up to 1854, in milligrams per 
 ton of water: 10 Arsenious acid, 1.5; antimony oxide, 0.1; zinc 
 oxide (sulphate), 13.3; lead oxide, 0.1; copper oxide, 6.4; tin 
 oxide, 0.1. 
 
 It is not mentioned whether or not any of these may have 
 been enriched in a secondary way. It would not, however, be 
 surprising if no spring among those analyzed had been prima- 
 rily enriched with useful metals. We have only a few analy- 
 ses ; ore-bodies are very rare things, and give evidence of hav- 
 ing been made in comparatively short periods, while veins are 
 very common things ; so that, granted the hot springs are mak- 
 ing veins, the probabilities are that they are nearly all making 
 barren veins or barren parts of veins. Posepny found that the 
 Sulphur Bank spring, whose enrichment is probably primary, 
 carried small quantities of mercurial sulphide in suspension. 
 At least he found this material on his filter-paper after filtering 
 the water, but he found only a trace of mercury in the water. 
 Unless we accept this case, I have not read of any in which a 
 mineral spring has been " caught in the act " of making an 
 ore-body, and this only emphasizes my belief that ore-bodies 
 are formed in relatively short periods of time. Ore-bodies seem 
 to have been formed in every geological age since early Palaeo- 
 zoic times ; and if we grant that each mineralized district was 
 enriched in a relatively short period, it would not be strange if 
 very few ore-bodies, or none at all, were in process of formation 
 at the present moment. 
 
 10 Genesis of Ore-Deposits, p. 47. 
 
FORMATION AND ENRICHMENT OF ORE-BEARING VEINS. 709 
 
 We know that many veins are now in process of formation ; 
 and we find that many springs carry in solution the materials 
 found in veins, showing that nature is prodigal in her methods. 
 Probably a small part only of the vein-making contents of any 
 spring is deposited in the underground channel; the rest " goes 
 down the creek." If we should find a mineral spring in the 
 process of forming an ore-body, we might expect most of the 
 metallic constituents of the solution to have remained in it after 
 it issued from the ground. 
 
 It is true that we analyze spring-waters after they have 
 passed through the zone of precipitation ; and it is conceivable 
 that a water showing at the surface no trace of metal may have 
 carried material quantities of metal before it reached the zone 
 of precipitation. But in that case the water must have been 
 completely robbed of metal-values in the zone of precipitation ; 
 and it is hard to understand how such a clean precipitation 
 could be effected by such precipitating-agents as we attribute 
 to the superficial zone. It is easier to believe that we have 
 not as yet found an ore-body forming or a spring engaged in 
 forming one. 
 
 It has been asserted lately that the curative effect of some 
 mineral springs is largely due to radio-activity. Nearly all the 
 radio-active metals are of high specific gravity ; so that the as- 
 sociation of mineral springs with ore-bodies or with magmas 
 rich in heavy metals is further indicated in this way. 
 
 Glenwood springs, Colorado, and Hot springs, Arkansas, have 
 both been found to be slightly radio-active. But the springs 
 most remarkable in this respect hitherto discovered are the 
 Doughty springs, in Delta county, Colo. Dr. Wm. P. Headden 
 has made some very fine radiographs from the sinter surround- 
 ing these springs. 11 
 
 There are several springs, and the analyses differ somewhat; 
 but the principal radio-active spring (called the Drinking spring) 
 has the following analysis, in parts per 1,000 : ISTa, 0.045863; 
 K, 0.001576; Li, 0.000446; KE 4 , 0.000068; Ca, 0.005272; 
 Ba, 0.000192; Sr, 0.000150; Mg, 0.003230; Fe, 0.000026; 
 Al, 0.000054; Mn, 0.000060 ; Zn, trace; Cl, 0.019762 ; Br, 
 0.000065; I, trace; S0 4 , 0.013022; Si0 2 , 0.000696; B0 2 , 
 0.000174; total, 0.090656. 
 
 11 Proceedings Colorado Scientific Society, vol. viii., pp. 1 to 30 (1905). 
 
710 FORMATION AND ENRICHMENT OF ORE-BEARING VEINS. 
 
 These are not hot springs ; and whether or not they are 
 springs of primary enrichment is not clearly shown. It will be 
 noted from the analysis that ETa, Cl, and S0 4 are the principal 
 substances found in solution; but the distinguishing feature of 
 the spring is the barium sulphate which the water is actively 
 precipitating on the mound around the spring. Dr. Headden 
 says : " The deposition of practically pure baric sulphate by a 
 mineral spring is, so far as I have been able to find, a unique 
 fact." 12 The radium is intimately associated with the barium 
 sulphate. 
 
 III. THE SOLUTIONS DERIVED THEIR METAL-VALUES FROM A 
 COMPARATIVELY RICH SOURCE. 
 
 This follows necessarily, if it be admitted that ore-bodies 
 give unmistakable evidence that they were formed by rich solu- 
 tions. If we believe that the source of the values was the sur- 
 face-rocks, but admit that " expiring vulcanism " set matters in 
 motion for vein-making, we should expect all veins to show a 
 certain amount of concentration of mineral values ; at least all 
 of the veins in the vicinity of eruptive rocks. But the com- 
 plete barrenness of most veins, even in mining districts, is one 
 of the hard facts that are pressed home upon every experienced 
 mining man. There are also, of course, countless absolutely 
 barren veins and dislocations outside the mining districts. 
 
 Some writers suppose that the surface eruptive rocks carry 
 appreciably more mineral than other rocks, and that they are 
 the source of the mineral in the ore-deposits. It is, however, a 
 common observation that the characteristic eruptive rocks of 
 a mining camp are not confined to the mineralized area. As 
 examples, I will mention Cripple Creek, Colo., The Homestake, 
 S. D., Kalgoorlie, W. A., Monte Christo, Wash., Goldfield, 
 Nev., Arizona King, Ariz., and El Trinidad, Sonora. It is also 
 common that these rocks carry either no values at all or a 
 metal that is not characteristic of the camp. In the analyses 
 given in Table I. it will be noticed that the eruptives of the La 
 Plata quadrangle all carry manganese, while only one of those 
 in the Telluride quadrangle carries manganese. Rhodocrosite 
 and rhodonite are very prevalent in the Telluride quadrangle, 
 but only occasionally met with in the La Platas, if my own 
 
 12 Proceedings Colorado Scientific Society, vol. viii., p. 26 (1905). 
 
FORMATION AND ENRICHMENT OF ORE-BEARING VEINS. 711 
 
 limited observations are to be relied upon. I think that all this 
 points to the exceptional and unusual sources for such ore-bodies. 
 The principal objection to a deep-seated and rich source for 
 the mineralization of veins which I have read is that of Van 
 Hise, who, calling attention to the limits of the zone of frac- 
 ture, says : 13 
 
 ** On the assumptions (a) that the strength of the rocks is the same as at the sur- 
 face, (b) that the rocks are all of the same kind, (c) that the temperature is the 
 same as at the surface, (d) that the water present does not make any difference in 
 the character of deformation, (e) that the rocks yield as readily by fracture as by 
 flowage, (f) that the rocks break as readily by fracture when the deformation is 
 slow as when it is rapid, and (g) that the rocks are among the strongest, I have 
 calculated that the maximum depth of the upper part of the zone of flowage under 
 mass-static conditions can not be greater than 12,000 meters." 
 
 He concludes that the practical limit in depth of the zone of 
 fracture is about 5,000 m., and that a fissure would close almost 
 at once at a depth of 12,000 meters. 
 
 The resistance of a large number of rocks to binding and 
 crushing has been determined; but such figures give us no sat- 
 isfactory basis for the calculation here involved. It is necessary 
 to consider also the " arching " of any material, even of crushed 
 material. Loose coke and ore have no strength whatever to re- 
 sist flexure, yet they will " bridge " a blast-furnace, and broken 
 ore will often arch in an ore-chute and choke it up. 
 
 If Prof. Van Hise's conclusion is correct, why does not rock- 
 flowage prevent the continued existence of mountain-peaks 5,000 
 m. high, and of springs at the base of such masses? 14 If a 
 fissure could not exist at a given depth, how can a peak exist to 
 an equal height ? Such a peak may represent the foot-wall of 
 a rather flat fissure, the opposite side of which has been re- 
 moved. Would the absence of the opposite side prevent the 
 action of rock-flowage ? Has the phenomenon of rock-flowage 
 ever been observed, bulging out the solid rock at the base of a 
 peak or precipice ? 
 
 If a spring can flow from under a mass of rock 20,000 ft. high, 
 why could not a fissure exist 20,000 ft. below the surface ? 
 
 13 A Treatise on Metamorphism, Monograph xlvii., U. S. Geological Survey, p. 189 
 (1904). 
 
 14 According to Mr. M. W. Con way's Climbing and Exploration in the Karakoram- 
 Himalayas (vol. i., p. 486, 1894), Peak K2 of that range is 28,000 ft. above sea- 
 level, and many other peaks exceed 20,000 ft. In Bolivia there are mountains 
 rising somewhat abruptly 21,000 or 22,000 ft. from sea-level. Many other in- 
 stances could be cited, from British Columbia and Alaska. 
 
712 FORMATION AND ENRICHMENT OF ORE-BEARING VEINS. 
 
 Again, the effect of rock-flowage, whatever it may be, is ad- 
 mittedly slow, and must be subject to arrest or diversion by the 
 greater force of rock-movements in mass. Such movements, 
 indicated in innumerable instances by their geological effects, 
 are continually presented for our observation in non-volcanic 
 earthquakes, like those at Charleston, San Francisco, Jamaica, 
 etc., and are reported daily by the seismometers of the world. 
 Is it reasonable to believe that a movement felt at a horizontal 
 distance of 10,000 miles has had no effect below the depth of 
 5,000 or 12,000 m. (3 or 7 miles) ? If it has had such effect, 
 it must have counteracted the previous work of rock-flowage, 
 and opened new fissures, upon which that slow agency must 
 commence operations de novo. 
 
 Very recent seismometric observations (preceding by a few 
 weeks the Jamaica earthquake of January, 1907) reported a 
 submarine earthquake in the deepest part of the Pacific, far ex- 
 ceeding in intensity and energy anything hitherto observed on 
 land. Such earthquakes occur under, say, 24,000 ft. of sea- 
 water (the maximum depth off the coast of Asia is greater than 
 that), equivalent in weight to 10,000 ft. of rock; yet they not 
 only break the sea-bottom, but possess surplus energy enough 
 to lift the sea itself, producing enormous tidal waves. May we 
 not safely conclude that they might still occur under a greater 
 superincumbent pressure, and, in particular, that 15,000 or 
 20,000 ft. of rock, the pressure of which, producing rock-flowage, 
 operates much more slowly than an equal pressure producing 
 water-flowage, would not necessarily prevent an earthquake suf- 
 ficient to make and, for a time at least, maintain fissures? 15 
 
 Again, it is not proved that the pressure which would close 
 an open crack by rock-flowage would be sufficient to change 
 the density of the rock itself, and close all pores and capillary 
 passages in it. On the contrary, it is probable that the slow de- 
 formation of rocks under pressure takes place without fracture 
 or change of density. This, at least, is indicated by the early 
 experiments of Sorby and others, and by the actual observed 
 conditions of limestone, etc., which have been thus changed in 
 form, yet show their original structure. It follows, apparently, 
 that the assumed lower limit of rock-flowage is not necessarily 
 the limit of rock permeability, and also that any interruption 
 
 15 This consideration was suggested to me in a private communication by the 
 Secretary of the Institute. 
 
FORMATION AND ENRICHMENT OP ORE-BEARING VEINS. 713 
 
 of the closing of a fissure by rock-flow age might continue for 
 an indefinite period, or until rock-flowage in new directions, or 
 a forced change in the density of the rock, had completed the 
 process thus interrupted. This leaves room for the hypothesis 
 here advanced, which requires, not the endless persistence, but 
 only the existence for a sufficient period, of deep channels of 
 circulation. 
 
 Now, there is here no question of an absolutely open fissure, 
 with walls nowhere in contact. On the contrary, fissures are al- 
 most always formed by movements of one wall relatively to the 
 other, and are almost always " closed " to a certain extent by 
 the " misfit " contact of the walls in their new relative position. 
 This leaves more or less continuous and connected channels for 
 underground waters and gases, the further closing of which by 
 the pressure of the inclosing rocks may be long delayed by the 
 fact that the pressure tending to close the openings must over- 
 come the resistance of the solid masses which are keeping them 
 open and the " arching " of the material around such openings. 
 It must be admitted that the complete " squeezing out " of all 
 such residual and interstitial cavities is likely to be a much 
 slower process than the closing of altogether open and con- 
 tinuous fissures. - 
 
 In view of the foregoing considerations, I can see no reason 
 why small open channels may not exist as far below the surface 
 of the earth as mountain peaks extend above the average grav- 
 ity-level; and, moreover, as these channels would doubtless be 
 filled with water, a practically incompressible liquid, having 
 material weight of its own, I think we may conclude that they 
 would resist closing all the more on that account, and, indeed, 
 could not be completely closed, unless the water were provided 
 with the means of escape in other words, with channels ! 
 
 Prof. Van Hise calls attention to the fact that at a certain 
 depth the critical temperature of water (360 C.) would be 
 reached, and that it could not exist as water below that depth. 
 But it does not follow that the form in which it could exist 
 would not possess equal density and solvent power. 
 
 According to the rate of increase assumed by many writers 
 1 C. for every 30 m. of added depth the critical temperature 
 would be reached at 10,350 m., if 15 C. be taken as the tem- 
 perature of the surface. But we are scarcely warranted in as- 
 
 45 
 
714 FORMATION AND ENRICHMENT OF ORE-BEARING VEINS. 
 
 suming that rate as uniform to great depths. M. Walferdin, 
 by a series of careful observations in two shafts at Creuzot, 
 proved that down to a depth of 1,800 ft. the increase in temper- 
 ature amounted to 1 F. for every 55 ft. of descent; but below 
 the depth named the rate of increase was as great as 1 F. for 
 every 44 ft. On the other hand, in the great boring of Gren- 
 elle, at Paris, the increase in temperature down to 740 ft. was 
 1 F. for every 50 ft. ; but from 740 to 1,600 ft. it diminished 
 to 1 F. for every 75 ft. A similar remarkable fact was shown 
 in the Sperenberg boring, near Berlin, where the rate of in- 
 crease for 1,900 ft. was 1 F. for every 55 ft., and for the next 
 2,000 ft. only 1 F. for every 62 ft. In the deep well at Buda 
 Pesth there was actually found a decline in temperature below 
 the depth of 3,000 ft. 
 
 A list of 164 wells, from 400 to 2,220 ft. deep, bored in the 
 United States, 16 shows irregularities of temperature not to be re- 
 ferred to any general formula. To the rule mentioned above 
 namely, 1 C. for every 30 m. of added depth there are far more 
 exceptions than confirmations. No doubt these variations are 
 due to local physical or chemical causes ; and, in like manner, 
 it must be conceded that under conditions of expiring vulcan- 
 ism very high temperatures may prevail, prob.ably even beyond 
 the critical temperature of water. But it seems unsafe to reckon 
 upon a transcendently hot interior of the mass of the earth. 
 
 Finally, it is not safe to assume that this mass is under such 
 pressure as to be precluded from all movement whatever below 
 a few thousand feet of its 4,000 miles of radius; and a move- 
 ment causing displacement would give opportunity for the rise 
 of a heavy magma to a higher level. 
 
 In view of the above considerations, I find nothing preclud- 
 ing the idea that the solutions which have formed ore-bodies 
 have had comparatively rich sources, and that these sources 
 were very likely laccolites of heavy magmas, brought up from 
 the barysphere into the lower part of the zone of fracture. 
 
 IV. THERE is A BARYSPHERE CONTAINING LARGE AMOUNTS OF' 
 
 THE USEFUL METALS. 
 
 This, I think, has never been seriously questioned. Physi- 
 cists and astronomers have weighed the earth and found it not 
 
 16 Water Supply and Irrigation Paper No. 149, U. S. Geological Survey (1905). 
 
FORMATION AND ENRICHMENT OF ORE-BEARING VEINS. 715 
 
 " wanting," but over-weight. R. von Sternbeck determined the 
 specific gravity of the earth to be 5.6, while the average density 
 of the surface-rock is 2.5. Charaberlin and Salisbury in their 
 treatise on geology give the specific gravity of the earth as 5.57, 
 and that of the lithosphere as 2.7. There is a theory that the 
 greater relative weight of the earth is caused by pressure alone ; 
 that the material is the same throughout, but that the pressure 
 has made the interior rocks more dense. I believe it has been 
 demonstrated that rocks do yield somewhat to such pressure as 
 may be artificially applied; but such evidence comes far short 
 of the proof here required. To satisfy this theory it would be 
 necessary for the rocks to be compressed, near the center of the 
 earth, to one-fourth their volume at the surface. Against this 
 hypothesis, we have the facts that magmas of very different 
 specific gravity issue from the interior of the earth, and that 
 eruptive rocks, as a class, are heavier than surface-rocks. 
 Van Hise remarks : 17 
 
 "It is noticeable in the altered rocks that in proportion as deep-seated meta- 
 morphism is advanced the heavier (of the above) minerals appear." 
 
 Y. ERUPTIONS SPRING FROM VARIOUS DEPTHS AND BRING 
 VARIOUS KINDS OF MAGMA TOWARD THE SURFACE. 
 
 This seems to me to be shown by what is known of eruptions. 
 As vents filled with molten material would not be subject to the 
 causes limiting the depths of water-channels there is no limit to 
 the depths to which we may expect them to extend. I under- 
 stand that the majority of both astronomers and geologists re- 
 gard the earth's interior as solid and rigid as steel. Eruptions 
 are generally considered to be the result of local stress and 
 friction. Just what is the cause of the stress and just how the 
 force is applied are matters of discussion. A very simple ex- 
 planation, but one which does not seem to appeal to most 
 writers, is that the axis of the earth is gradually shifting, and 
 the earth being an oblate spheroid has to keep rearranging its 
 mass to suit the new positions of the axis. 
 
 At Cananea, Sonora, in 1902, I saw an illustration of a vol- 
 cano on a very small scale. A block of heavy iron gossan, con- 
 stituting, roughly, a cube of about 200 ft. on a side, or 8,000,- 
 
 17 A Treatise on Metamorphism, Monograph xlvii., U. S. Geological Survey , p. 
 183(1904). 
 
716 FORMATION AND ENRICHMENT OF ORE-BEARING VEINS. 
 
 000 cu. ft. in volume, had been undermined, and slipped down 
 6 ft., crushing the timbers. The heat produced underground, 
 near the foot-wall, was intense, and on the surface two or three 
 small jets of steam appeared. If a little block of ground like 
 that, slipping 6 ft., could generate sufficient heat to produce 
 such jets of steam, it is easy to understand how the movements 
 of a large region might incidentally produce a volcano or two. 
 Suppose, for example, that an eruption is caused by a force 
 which produces faulting under great pressure. The first ef- 
 fect may be confined to the lithosphere, so that barren magmas 
 are squeezed out. But, as the force gathers intensity, the fault 
 extends into the bary sphere, and some of the latter is forced 
 upward, crowding out the lighter lavas above it. By reason of 
 its greater specific gravity it floats the lighter rocks above it, 
 and forms, within the reach of underground waters, a laccolite, 
 which may subsequently become the source of valuable mineral 
 deposits. 
 
 Chester "Wells Purington, in the Telluride Folio of the U. S. 
 Geological Survey, says, in effect, that the basic parts of eruptive 
 rocks, such as hornblende, augite, biotite, contain more of the 
 useful metals than the other parts, and deems it probable that 
 the mother magma had a basic portion, which might be the 
 source of the metals in the ore-deposits. His idea and mine are 
 not widely at variance. 
 
 VI. ONLY THOSE ERUPTIONS WHICH DISTURB THE BARYSPHERE 
 AND BRING A MAGMA RICH IN METALS SUFFICIENTLY NEAR 
 THE SURFACE TO BE LEACHED BY VEIN-MAKING SOLUTIONS 
 ARE PRODUCTIVE OF VALUABLE ORE-DEPOSITS, OTHER ERUP- 
 TIONS PRODUCING BARREN VEINS. 
 
 In support of this proposition there are many indications not 
 mentioned above. In many mining districts there have been 
 successive eruptions, but the ore-bodies are definitely associated 
 with one eruption and appear to have no relationship with 
 the others. Thus, at Butte, Mont, the ore-bodies are associated 
 with a quartz-porphyry eruption, while the acid granite, basic 
 granite and rhyolite eruptions produced no ore-bodies. At 
 Cripple Creek we have a whole series of eruptions ; but the 
 mineralization of the veins followed on the heels of the nephe- 
 line-basalt eruption. 
 
FORMATION AND ENRICHMENT OF ORE-BEARING VEINS. 717 
 
 We often find in a mining district several series of veins, 
 only one of which, bears mineral values. At Rico, Colo., for 
 instance, there is a series, terminating at the so-called " con- 
 tact," which has been enriched with silver and other metals ; 
 and there is another series of strong quartz-veins not thus 
 enriched. These facts suggest that, among the eruptions, one 
 must have been radically different from the others. Yet analy- 
 ses of the surface-rocks do not reveal any startling differences. 
 It seems evident that the mineralized series of veins must have 
 been formed from a source radically different from that of the 
 barren ones. My explanation is, that in a series of eruptions, 
 one may have been sufficiently deep-seated to disturb the bary- 
 sphere and force some of its material toward the surface. It 
 would never reach the surface, because its specific gravity 
 would cause it to form, sooner or later, a laccolite, floating the 
 surface-rocks. But, in exceptional cases, it might rise far enough 
 to become subject to the agencies which make mineral-bearing 
 veins. 
 
 I presume that the barysphere includes different kinds of 
 unsegregated magmas. It may be built up concentrically, or it 
 may be simply spotted, as the surface is, with different rocks. 
 A laccolite of magma rich in copper might give rise to a sur- 
 face region yielding copper ; one rich in gold might become 
 the origin of a gold-bearing district, etc. 
 
 I do not mean that the constituents of the magma would 
 govern entirely. It is conceivable that conditions of the solu- 
 tion and precipitation of the metals might also be influential. 
 But this general hypothesis suggests an explanation of those 
 cases in which totally different kinds of ore-deposits occur in 
 the same surface-rocks, close together, and under conditions 
 apparently similar, except as to age. Butte, Rico and Leadville 
 are cases in point. At Butte there is a great mass of dark, 
 basic granite, which contains two vein-systems. In the southern 
 part of the camp are the famous veins of copper, containing 
 sulphide ore-bodies with more or less quartz. The northern 
 system produces ores of silver, lead, zinc and iron. Prof. Kemp 
 has called attention to the fact that the northern ores are 
 abundantly associated with manganese minerals, especially rho- 
 donite; that no manganese occurs in the copper belt and no 
 copper in the silver belt; and infers that "such results could 
 originate only in different deep-seated sources." 
 
718 FORMATION AND ENRICHMENT OF ORE-BEARING VEINS. 
 
 This hypothesis offers also an explanation of cases in which 
 there is an extensive surface-area, showing similar eruptive 
 rocks throughout, yet only a small part of which has been min- 
 eralized. Thus, in areas like southern Nevada and the Yaqui 
 River country of Sonora, there are vast quantities of eruptive 
 rocks of much the same kinds, but only in isolated localities 
 have paying veins been found. Sometimes these localities are, 
 and sometimes they are not, characterized by a trifling ex- 
 posure of a peculiar eruptive rock. In the former case, the tri- 
 fling surface manifestation seems utterly inadequate to account 
 for the very exceptional vein-contents of the localities. 
 
 Cripple Creek is another case in point. The whole Arkansas 
 plateau is prolific of all the rocks characteristic of Cripple 
 Creek (unless, it may be, the basalt dikes). The largest masses 
 of phonolite I know of are found, as in Grouse mountain and 
 Little Pisgah peak, outside the productive area, while around 
 Saddle mountain and at Bare hills there are large masses of 
 andesitic breccia, yet no ore-deposits. At Globe, Ariz., there 
 is an extensive area, northwest of the camp, that has the same 
 formation as that surrounding the mines ; but thus far no ore- 
 deposits of value have been found in it, though it is not lacking 
 in veins. 
 
 Of Grass valley, Cal., the U. S. Geological Survey folio says : 
 "The veins occur in almost any one of the many rocks making 
 up the bed-rock series. Excellent mines are located in the 
 grano-diorite, diabase, slate and schists." Evidently the surface- 
 eruptives did not govern in this case. 
 
 In the case of several eruptions, only one of which is associ- 
 ated with ore-bodies, the theory would be that the one associ- 
 ated with the ore-bodies was the deep-seated one, which 
 brought some of the mineralized magma within reach of the 
 vein-making agencies, and that, while the surface-manifestation 
 may have been weak, and not different essentially from other 
 eruptions in the same locality, the eruption in depth was radi- 
 cally different. 
 
 As to the series of veins in a given district, we would say 
 that the barren ones were the products of the shallow erup- 
 tions, while the rich ones were the product of an eruption that 
 brought a rich magma surface-ward. In the case of a large 
 area of eruptive rocks containing a very small mineralized dis- 
 
FORMATION AND ENRICHMENT OF ORE-BEARING VEINS. 719 
 
 * 
 
 trict, it seems to me hard to understand why the mineralization 
 is not much more general, if the surface eruptives are account- 
 able for the metal-values. If, however, these values came from 
 a relatively small buried mass of very richly mineralized erup- 
 tive rock, the restricted mineralized surface-area is at once ex- 
 plained. 
 
 Again, there are occasional mining districts in which no 
 eruptive rocks at all appear on the surface, such as the zinc- 
 lead deposits of southwestern Illinois, and the Otago gold-fields 
 of the South Island of New Zealand. (The latter are described 
 byRickard in his discussion of Posepny's Genesis of Ore- Deposits.) 
 In such cases the influence of a richly mineralized underlying 
 laccolite is highly reasonable. 
 
720 FORMATION AND ENRICHMENT OF ORE-BEARING VEINS. 
 
 
 
 No. 27 A. 
 
 
 
 The Formation and Enrichment of Ore-Bearing Veins. 
 SUPPLEMENTARY PAPER. 
 
 BY GEORGE J. BANCROFT, DENVER, COLO. 
 
 (Spokane Meeting, September, 1909. Trans., xl., 809.) 
 
 AT the New York meeting of the Institute, April, 1907, I 
 presented a paper entitled, The Formation and Enrichment of 
 Ore-Bearing Veins, 1 in which paper I advanced the following 
 propositions : 
 
 (1) That the majority of mineralized veins are the product of 
 expiring vulcanism ; (2) that most of these veins were primarily 
 mineralized by comparatively rich solutions in comparatively 
 short periods of time ; (3) that the solutions gained their metal- 
 values from a comparatively rich source ; (4) that there is a bary- 
 sphere containing large amounts of the useful metals ; (5) that 
 eruptions spring from various depths and bring various kinds 
 of magmas towards the surface; and (6) that only those eruptions 
 which disturb the bary sphere and bring a magma rich in metals 
 sufficiently near the surface to be leached by vein-making solu- 
 tions are productive of valuable ore-deposits, other eruptions 
 producing barren veins. Ore-deposits due to magmatic segre- 
 gation were not included in this general survey. 
 
 As a result of considerable further study I have modified my 
 views in some respects,' while in others I feel more sure than 
 ever of the ground taken at that time. 
 
 That ore-bodies are infrequent occurrences and born of ex- 
 traordinary conditions I think is now generally accepted. The 
 theory that persisted for a time namely, that ore-bodies were 
 formed by the ordinary ground-water, which consists of ex- 
 tremely dilute solutions, derived from leaching extremely lean 
 surface-rocks, and which must occupy enormously long periods 
 of time in concentrating the values so leached, is, I think, now 
 pretty generally regarded as not applicable to the great majority 
 
 1 P. 696, this volume. 
 
FORMATION AND ENRICHMENT OF ORE-BEARING VEINS. 721 
 
 of our mining-districts, although it may account for a few isolated 
 deposits. 
 
 I note that a few recent writers still use this theory as a sort 
 of " point of departure " for their discussions, but the majority 
 seem to realize that the tendency of ordinary ground-water 
 circulation is to diffuse any soluble matter rather than to con- 
 centrate it, and that an unusual precipitant must be present to 
 provoke an important concentration under this hypothesis. 
 
 That the forces of expiring vulcanism are the agencies which 
 account most logically for ore-bodies is an opinion very gen- 
 erally held, not only because of the intimate association of ore- 
 bodies with eruptive rocks, but also because the study of active 
 volcanoes and of the springs rising near them shows that ore- 
 making agencies to a limited extent, at least, are at work there. 
 Thus, A. Lacroix 2 found pyrite, pyrrhotite, and galena, together 
 with sulphates of sodium, potassium, calcium, magnesium, and 
 aluminum, in the sublimates of fumaroles on Vesuvius ; J. "W. 
 Mallet 3 discovered silver in volcanic ash at Cotopaxi and Tun- 
 guragua; 0. Silvestri 4 found copper in the fumes of Etna, while 
 traces of practically all the common metals have been found in 
 eruptive rocks. 
 
 Similarly, it has been recognized that the. period of expiring 
 vulcanism could not have been of very long duration, geologi- 
 cally speaking, although it has been shown that in some dis- 
 tricts the repeated recurrence of eruptive action has had the 
 effect of continuing the mineralizing action through long 
 periods of time. 
 
 My fifth and sixth propositions have not been so well estab- 
 lished. I think it is generally admitted that certain eruptive 
 rocks produce mineralized areas, while others do not; this sug- 
 gests most forcibly that the eruptives themselves differed very 
 decidedly in the matter of mineral content; and it seems rea- 
 sonable to infer that those eruptives which 'do produce mineral 
 richness have been rich themselves and probably originated at 
 great depth. The advance of science has still further substan- 
 
 2 Bulletin de la Societe Francaise de Mineralogie, vol. xxx., p. 219 (1907). 
 
 3 Proceedings of the Royal Society, vol. xlii., p. 1 (1887) ; vol. xlvii., p. 277 
 (1889-90). 
 
 4 / Fenomeni Vulcanici presentati deW Etna, etc. (Catania, 1867), per Bulletin 
 No. 330, U. S. Geological Survey, p. 217 (1908). 
 
722 FORMATION AND ENRICHMENT OF ORE-BEARING VEINS. 
 
 tiated the theory that the earth has a very heavy center, and it 
 is reasonable to suppose that this increased specific gravity is 
 partly due to relatively large metal-content. It is not, how- 
 ever, generally conceded that it is necessary for a mineralizing 
 eruptive to be so rich in metals and so heavy that it would 
 rarely or never reach the surface, but would form laccolites, 
 according to my old hypothesis. Nor do I longer hold this 
 view. At that time I remarked : 
 
 "If it could be shown that the surface eruptive rocks have a tendency to throw 
 off metals, as they do steam and sulphur, during the cooling process this would 
 remove many of my objections to considering them the source of the metals in our 
 ore-bodies. In the lack of such proof, however, we must recognize that they are 
 extremely lean, and therefore a very unlikely source of mineral wealth." 
 
 Now, I think there are very good reasons for believing that 
 this very thing is true namely, that eruptive rocks do have a 
 tendency to throw off their metal-content during the cooling 
 process, or, rather, as soon as they reach a horizon of lessened 
 pressure, which condition is apt to be coincident with cooling. 
 
 The wonderful crystallographic researches of J. E. Spurr, 
 Waldemar Lindgren, and others, have shown that magmas are 
 totally different from dry melts, and the cooling of a magma is 
 accompanied by a remarkable series of differentiations. Mr. 
 Spurr has shown how the metals would be concentrated either 
 in a very base or a very acid magma, and finally, in the case of 
 the acid magma, would be extruded together with pure silica 
 and water, thereby forming veins. I think, however, that those 
 who have made a great deal of the powerful agency of mag- 
 matic differentiation have overlooked a' very active contem- 
 porary agent namely, chlorine. Bromine, iodine, and fluorine 
 may be equally active agencies in volcanic emanations; but as 
 these elements are relatively rare, I shall confine myself here 
 to the very active part which chlorine may play in carrying 
 away from the hot eruptive its metal-content and depositing 
 the -same in ore-bodies. These considerations have been sug- 
 gested to me by studying the dry-chlorination process for the 
 treatment of complex ores, as developed by J. L. Malm, at 
 Corbin, Mont., and -at Denver, Colo. This process depends 
 primarily upon the facts that, in the dry state, chlorine has a 
 greater affinity for the metals than sulphur or oxygen, and that 
 the chlorides of all the metals are soluble together in hot water. 
 
FORMATION AND ENRICHMENT OF ORE-BEARING VEINS. 723 
 
 Thus, cupric chloride, lead chloride, zinc chloride, gold chlor- 
 ide, and iron chloride are soluble in hot water direct, and silver 
 chloride is soluble in hot cupric chloride. 
 
 Now, it is noticeable that chlorine is nearly always present 
 in volcanic emanations. Thus, J. W. Judd says : 5 
 
 "The most abundant of the substances which are ejected from volcanoes is 
 steam or water-gas, which, as we have seen, issues in prodigious quantities during 
 every eruption. But with the steam a great number of other volatile materials 
 frequently make their appearance. The chief among these are the acid gases 
 known as hydrochloric acid, sulphurous acid, sulphuretted hydrogen, carbonic 
 acid, and boracic acid ; and with these acid gases there issue hydrogen, nitrogen, 
 ammonia, the volatile metals arsenic, antimony, and mercury, and some other 
 substances." 
 
 After dwelling upon the large amount of C0 2 present in 
 volcanic gases, Chamberlin and Salisbury have the following 
 to say with reference to emanations : 6 
 
 " Sulphur gases are very common accompaniments of volcanic eruptions. They 
 take the forms of sulphuretted hydrogen and sulphurous acid and perhaps of sub- 
 limated sulphur, all of which are liable to pass by oxidation and hydration into 
 sulphuric acid. Chlorine and hydrochloric gases are also common, particularly 
 at high temperatures. Fluorine and other gases are occasionally present." 
 
 T. Wolf found that near the crater of Cotopaxi the fumes 
 were mostly of hydrochloric acid with- some free chlorine, 
 while at lower levels hydrogen sulphide was found with a 
 trace of sulphur dioxide. 7 
 
 Sainte-Claire Deville found chlorides of iron and copper in a 
 fumarole of Vesuvius. 8 
 
 R. Bunsen found various metallic chlorides in the sublimates 
 around fumaroles of Mt. Hecla in Iceland. 9 
 
 A characteristic of volcanic emanations is, that chlorine is 
 found either free or as the chloride of the metals, or as hydro- 
 chloric acid, while a characteristic of hot mineral springs is 
 that the water contains large quantities of the chlorides of 
 sodium and potassium. Granting that such hot mineral springs 
 
 5 Volcanoes: What They Are and What They Teach, p. 40 (1881). 
 
 6 Geology, 2d ed., vol. i., p. 619 (1906). 
 
 7 Neues Jahrbuchfiir Mineralogie, Geologic und Palaeontologie, p. 163 (1878). 
 
 8 Bulletin de la Societe Geologigue de France, Second Series, vol. xiii., p. 606 
 (1855-56). 
 
 9 Annales de Chimie et de Physique, Third Series, vol. xxxviii., p. 215 (1853). 
 
724 FORMATION AND ENRICHMENT OF ORE-BEARING VEINS. 
 
 are related to eruptions, and that the chlorine in both emana- 
 tions and springs had a common origin, it is evident that the 
 part which has escaped by the medium of spring-water has 
 undergone certain reactions, which the part which escaped as a 
 hot gas, from an open vent, did not undergo. Does not this 
 suggest what may take place in case the chlorides are extruded 
 through crevices or veins where they may encounter gradually 
 lessened temperatures together with water ? 
 
 Now, it is known that the temperature of fluid magmas may 
 range up to 3,000 F. 10 
 
 Let us suppose that, under a temperature of 1,100 C., we 
 had a magma which contained chlorine, water-gas, sulphur, 
 silver, copper, lead, iron, zinc, and gold. Of course, there 
 would also be other elements present, but, as previously stated, 
 I shall not try to cover the whole field. Let us suppose that 
 there is sufficient chlorine to form chlorides with all the metals 
 and an excess besides. Any hydrogen present would be com- 
 bined with the chlorine, the affinity for chlorine being greater 
 than for sulphur. E"ow, let us try to imagine what would happen 
 as this magma approached the surface. 
 
 At the temperature given, the chlorine would attack all the 
 metals, except gold, and the chlorides would all be gases, for it 
 is well known that the metallic chlorides are all volatile at rela- 
 tively low temperatures. 
 
 The chloride of gold under atmospheric conditions decom- 
 poses at about 120 C. Of course, the volcanic gases are under 
 some pressure even when escaping from the magma, and, as 
 pressure raises the temperature of decomposition, it is difficult 
 to say just how cool the magma must become before the gold 
 would accompany the other metals. 
 
 The fact that gold is often found by itself in a state of great 
 purity may be accounted for by its isolation from the other 
 metals as regards chemical reactions. Thus, at Farcum Hill, 
 Breckenridge, are found deposits of most beautiful crystalline 
 gold by itself, while less than a mile away are large deposits of 
 complex ores. The complex ores occur in the eruptive dikes 
 or on the contacts, while the gold is found in carbonaceous 
 shale. It is well known that carbon will precipitate gold from 
 
 10 Geology, Chamberlin and Salisbury, 2d ed., vol. i., p. 615 (1906). 
 
FORMATION AND ENRICHMENT OF ORE-BEARING VEINS. 725 
 
 a chloride solution, as is done in wet-chlorination mills, but it 
 will not precipitate the other chlorides. 
 
 The chlorine would not attack the silicates of the eruptive, 
 as is shown by the experiments of Brun, 11 who heated a Lipari 
 lava and observed the following exhalations : 
 
 From to 825, volatilization of water. 
 
 At 825, first evolution of chloride vapors. 
 
 From 874 to 1,100, temperature of explosions. 
 
 At 1,100, mean temperature of flowing lava. 
 
 Although the dry-chlorination process does not use high tem- 
 peratures, Mr. Malm has experimented with chlorine and the 
 ordinary rock-minerals at high temperatures and has shown 
 that they do not react. 
 
 The sulphur would occur as sulphur gas and partly as sul- 
 phur chloride. There would, of course, be a great deal of 
 water-gas present. As the magma rose to a horizon of less- 
 ened pressure these gases would expand and leave the magma, 
 bursting out through any veins or vents or porous strata that 
 might provide, a means of escape. The great distance to which 
 the metals have penetrated porous strata, as, for instance, at 
 Morenci, Ariz., may be accounted for in this way. 
 
 The farther from the magma the gases traveled the cooler 
 they would become, and as they became cooler they would be- 
 come a liquid. "We would then have the chlorides of the 
 metals in a hot aqueous solution, together with sulphur chlor- 
 ide and elemental sulphur, the latter in an extremely fine 
 state of subdivision (as it is found in many mineral springs). 
 
 Precipitation would not take place till some precipitating- 
 agent was encountered in the rocks. 
 
 The cooling of the solution would throw down the lead and 
 the lead only. Silver chloride is difficultly soluble and easily 
 precipitated. This may account for the exceeding purity of 
 some lead-deposits and the frequent association of silver and 
 lead. 
 
 If CaO in abundance were encountered all the metals would 
 be precipitated together. This may account for the complex 
 nature of many deposits in porphyry-lime contacts, as, for in- 
 stance, at Leadville, Rico, Breckenridge, etc. 
 
 11 Archives des Sciences Physiques et Naturelles, Fourth Series, vol. xix., pp. 439, 
 589 (1905). 
 
726 FORMATION AND ENRICHMENT OF ORE-BEARING VEINS. 
 
 It is fair to assume that the heated eruptive would drive off 
 the CO 2 from any limestone in immediate contact with it. 
 The chloride gases emanating from the same eruptive would 
 find an immediate and abundant precipitant in the form of 
 CaO thus formed, or, in case conditions became cool enough 
 for water to convert the oxide to the hydroxide, the latter 
 would be equally efficient as a precipitant. Thus, 
 
 2 MCl a + xCaO = M 2 X + 2 
 
 2 MCl^ + xCaO + zH 2 = 2 M (OH) X + xCaC! 2 . 
 
 In granitic or eruptive rocks, the methods of precipitation 
 are not quite so simple. I have immersed pieces of Boulder 
 County granite in solutions of the metallic chlorides, sulphur 
 chloride, and a little free acid, and at the end of three days 
 there was no appreciable result. Again, I have boiled pieces 
 of the same granite in strong hydrochloric and sulphuric acid, 
 and in half an hour the reactions were very considerable. The 
 hydrochloric acid was the more active. The piece of granite 
 was eaten away considerably. Examination of the remaining 
 piece with a magnifying-glass showed that the surface was re- 
 duced to a covering of spongy silica and white mica. Whether 
 the mica had been whitened by leaching the iron, or whether 
 only those bits remained intact which had no iron, I am not 
 prepared to say. In addition to the piece remaining undis- 
 solved'(at the end of 30 min.), there was a sediment which, on 
 examination, appeared to be rounded and porous pieces of 
 silica and minute flakes of pure white mica. The test with 
 sulphuric acid rendered the piece darker. Only a very small 
 part went into solution. An examination with a glass has 
 shown the feldspars to be lacking and the surface to be covered 
 with a coating of pearly silica and black mica. In this connec- 
 tion Clarke says : 12 
 
 ' ' Hot waters, charged with sulphuric or hydrochloric acid, attack nearly all 
 eruptive rocks, dissolve nearly all bases, and leave behind, in many cases, mere 
 skeletons of silica." 
 
 On this subject Judd says: 13 
 
 12 Bulletin No. 330, U. S. Geological Survey, p. 408 (1908). 
 
 13 Volcanoes: What They Are and What They Teach, p. 41 (1881). 
 
FORMATION AND ENRICHMENT OF ORE-BEARING VEINS. 727 
 
 "In many volcanoes the constant passage through the rocks of the various acid 
 gases has caused nearly the whole of the iron, lime, and alkaline materials of the 
 rocks to be converted into soluble compounds known as sulphates, chlorides, car- 
 bonates, and bo rates; and, on the removal of these by the rain, there remains a 
 white, powdery substance, resembling chalk in outward appearance, but composed 
 of almost pure silica. There are certain cases in which travelers have visited 
 volcanic islands where chemical action of this kind has gone on to such an extent, 
 that they have been led to describe the islands as composed entirely of chalk." 
 
 F. Henrich shares the same view, claiming that the chlorides 
 of potassium and sodium found in sublimates of aqueous fuma- 
 roles were formed by the action of moisture and hydrochloric 
 acid on the alkaline silicates of the heated lavas. 14 
 
 We know from observation underground that granitic and 
 other rocks are attacked by mineral solutions which produce 
 first a softening of the rocks, and eventually remove all the 
 original constituents except the silica and hydrous alumina 
 silicates. 
 
 It is, of course, difficult to reproduce in the laboratory with a 
 few simple salts the complex reactions that take place far under- 
 ground ; and here at least we must take the evidence as we 
 find it, even if it is difficult to reproduce the reactions. 
 
 We find chlorine or hydrochloric acid or metallic chlorides 
 issuing from volcanoes, and we find sodium, calcium, and po- 
 tassium chlorides issuing from mineral springs; so it seems 
 highly probable that the sodium and potassium silicates break 
 up, and the chlorine, after it has become cooled below the boil- 
 ing-point of water, reacts with the sodium or potassium, drop- 
 ping any metals with which it may have been combined. 
 
 The reactions leading to the formation of calcium chloride 
 have been explained above. The reactions with the silicates 
 would most naturally begin with the free hydrochloric acid, 
 thereby liberating hydrogen, which would combine with the 
 sulphur to form H 2 S, and this in turn would precipitate the 
 metals according to the following reactions : 
 
 MC1 X + X H 2 S = xHCl + MS 
 
 and would convert any metals already precipitated by other 
 agencies to the sulphides, as follows : 
 
 14 Zeitschrift fur angewandte Chemie, vol. xix., No. 30, p. 1326 (July 27, 1906) ;, 
 vol. xx., No. 5, p. 179 (Feb. 1, 1907). 
 
728 FORMATION AND ENRICHMENT OF ORE-BEARING VEINS. 
 
 MO X + :rH 2 S =a> MS, + xll 2 O 
 M -f xH 2 S = MS, -f zH 2 . 
 
 The first reaction would result in more hydrochloric acid, 
 which would be available to repeat the cycle. 
 
 Whether the metals are precipitated by CaO or by reactions 
 with the silicates, they would be almost at once converted to 
 sulphides, according to the above reactions; and that is the 
 condition in which we find them. Gold, which is precipitated 
 by carbon, would not be subject to the action of H 2 S, and hence 
 would likely occur as free gold in carbonaceous formations, 
 which agrees with the facts as we find them. 
 
 As stated above, I have confined myself, for the sake of sim- 
 plicity, to an arbitrarily-chosen condition. It is my purpose to 
 point out the very active part which the halogens may play in 
 divesting an eruptive of its metal-contents, and conveying the 
 same into neighboring veins or openings in the rocks, rather 
 than to prescribe the exact steps that are followed. It is con- 
 ceivable that under certain conditions the above-mentioned 
 reactions may be very important, while in others they may be 
 negligible. It is conceivable that in some cases an eruptive 
 may be totally divested of its useful metals and yet little of it 
 be precipitated short of the atmosphere. This may account for 
 the Snake river placer gold, which is extremely fine, and so 
 often found associated with volcanic ash as to provoke the 
 theory that it had an atmospheric origin. On the other hand, 
 a metalliferous eruptive may be only partly relieved of its 
 metal-content, the residue remaining in a more or less segre- 
 gated form in the body of the eruptive, as at Ely, Nev., where 
 the sedimentaries adjoining the eruptive area contain veins and 
 deposits of copper-ore, while the eruptive itself contains large 
 masses of low-grade ore which appear to be due to magmatic 
 segregation. 
 
 I think these considerations, helping to explain some of the 
 puzzling things about ore-bodies, maybe of service in promoting 
 progress towards the goal of a perfect understanding of the 
 subject. 
 
DISTRIBUTION OF ELEMENTS IN IGNEOUS ROCKS. 729 
 
 No. 28. 
 The Distribution of the Elements in Igneous Rocks. 
 
 BY HENRY S. WASHINGTON, NEW YORK, N. Y. 
 (Chattanooga Meeting, October, 1908. Tram., xxxix., 735.) 
 
 I. INTRODUCTION. 
 
 DURING the last twenty years or so the chemical investigation 
 of rocks has made great advances, and it is now generally rec- 
 ognized that a knowledge of the chemical composition is as 
 essential as that of the texture or mineral composition if not 
 more so for the proper classification of rocks and study of 
 their origin and relationships. Rock-analyses have vastly 
 increased in number and, what is of greater importance, in 
 quality. New and improved methods permit of greater accu- 
 racy than was possible in the early days, and the list of chemi- 
 cal constituents frequently determined has risen from the seven 
 or eight of the greater part of the nineteenth century, to twenty 
 or more. Indeed, rock-analyses with determinations of so 
 many constituents are now commonly made by the chemists of 
 the United States and Australia, while in Germany, Great 
 Britain, France, and Italy the rarer constituents are determined 
 more frequently than formerly. 
 
 As a consequence of this modern, accurate work, it has been 
 discovered that some elements which were formerly supposed 
 to be rare are of wide-spread occurrence and are often present 
 in considerable amount. The fact is further being developed 
 that the elements tend to show certain relations of occurrence 
 or abundance in connection with each other. This is a fact 
 which is applicable to the rarer elements, and which also finds 
 a broad geological and petrological expression in the recog- 
 nition of petrographic provinces. We are beginning to obtain 
 some definite, though as yet rudimentary, knowledge of the 
 distribution of the elements among igneous rocks, 
 
 Some of the results along these lines obtained by study of 
 the vast accumulation of analytical data now available are \vell 
 know r n to petrologists, while others do not seem to be so gener- 
 
 46 
 
730 DISTRIBUTION OF ELEMENTS IN IGNEOUS ROCKS. 
 
 ally understood. To the non-petrologist they are, naturally,, 
 mostly unknown, and, as the general principles involved, and, 
 indeed, some of the specific instances, have a more or less im- 
 portant bearing on the occurrence and characters of certain 
 deposits of metallic ores and other economically important 
 minerals, a discussion of the subject may be of interest to ; 
 mining engineers. 
 
 Indeed, to the observations and operations of mining engi- 
 neers and mining interests generally, the petrologist is indebted 
 and must look for some of his data. This is especially true of 
 those relating to the precious metals and others of commercial 
 importance, the amounts of which usually present in rocks are 
 so small as almost or quite to defy detection by ordinary ana- 
 lytical methods, and whose presence is often revealed only 
 through search for and the exploitation of localities where they 
 have undergone concentration. It must be premised, however, 
 that our knowledge is at present very uneven, allowing fairly 
 safe and detailed generalizations as regards some of the ele- 
 ments, very rudimentary or general ones as regards others, and 
 again allowing almost none at all. 
 
 II. GENERAL CHEMICAL COMPOSITION OF IGNEOUS ROCKS. 
 
 The first and most important fact to be noted of igneous 
 rocks is that, with the exception of some rare ore-bodies due 
 to the differentiation of igneous magmas, they are composed 
 almost wholly of silica and silicates. The vast majority of 
 igneous rocks are silicate rocks, in which silica forms the most 
 prominent and the never-failing constituent. Most of the min- 
 erals which compose them are combinations of silica with 
 various bases, and it is a striking fact that the number of min- 
 erals which go to make up the majority of igneous rocks, and 
 which are most abundant and most often met with, is very 
 small. 
 
 The proportions in which these minerals may be present 
 vary very widely. Some rocks are known which are com- 
 posed wholly, or practically so, of but one mineral. Combina- 
 tions of two are not infrequent, while most rocks contain at 
 least three, and usually many more, minerals and in the most 
 widely diverse proportions. It follows, therefore, that the 
 chemical composition of igneous rocks may vary within very 
 
DISTRIBUTION OF ELEMENTS IN IGNEOUS ROCKS. 731 
 
 wide limits, as regards any or all of the chemical constituents ; 
 and that, furthermore, some rocks may he of very simple 
 chemical composition, while others may be very complex, with 
 many constituents present, since the minerals themselves may 
 be either very simple or highly complex in chemical compo- 
 sition. 
 
 The most important chemical constituents (stated as oxides, 
 in accordance with the usual custom) are as follows : silica, 
 Si0 2 ; alumina, A1 2 3 ; ferric oxide, Fe 2 3 ; ferrous oxide, FeO; 
 magnesia, MgO ; lime, CaO ; soda, Na 2 ; potash, K 2 ; and 
 water, H 2 0. Some or all of these major constituents, as they 
 are termed, are invariably present, so far as known, and col- 
 lectively they constitute about 98 per cent, of all known rocks. 
 The chief oxides, from silica to potash inclusive, enter into the 
 composition of the most important and most commonly occur- 
 ring rock-forming minerals, as well as the glass of imperfectly 
 crystallized rocks. 
 
 The role of water is somewhat different. It would seem to 
 be universally present in the magma, and its presence (along 
 with that of other substances) lowers the freezing-point and 
 increases the tendency to crystallization of the liquid mass. 
 Most of this water is lost if the magma reaches the surface and 
 it appears in the enormous clouds which accompany volcanic 
 eruptions and the steam of volcanic fumaroles ; and much of it 
 also escapes if the magma solidifies beneath the surface, giving 
 rise to subterranean water-supplies, which are held by many to 
 be an important factor in the formation of many ore-deposits. 
 A small proportion of the water originally present may remain 
 in the solidified rock in a combined form, as part of the more 
 complex mineral molecules, those of pyroxenes, amphiboles, 
 and micas, for instance; and some may also remain as inclu- 
 sions of water in the minerals of intrusive rocks. 
 
 There are also almost invariably present in igneous rocks 
 small amounts of titanium, phosphorus, and manganese, though 
 these are often neglected and thus overlooked in the less com- 
 plete analyses. Carbon dioxide is also met with, but' its pres- 
 ence, as reported in analyses of igneous rocks, is almost inva- 
 riably due to decomposition, and it cannot be usually regarded 
 as an essential or original constituent of rocks. 
 
 In addition to these most important constituents, the refine- 
 
732 DISTRIBUTION OF ELEMENTS IN IGNEOUS ROCKS. 
 
 merits and increasing completeness of modern rock-analysis 
 show that many others are frequently present, often in scarcely 
 more than traces, but again in very appreciable quantities. 
 The most important of these minor elements are : zirconium, 
 sulphur (as sulphides and as sulphur trioxide), chlorine, fluor- 
 ine, vanadium, chromium, nickel, barium, strontium, and 
 lithium. Exceptionally, others may be determined : as boron, 
 cobalt, copper, gold, silver, molybdenum, the metals of the 
 cerium and yttrium groups, nitrogen, and others. Indeed, as 
 Dr. Hillebrand 1 says, " a sufficiently careful examination of 
 these rocks would show them to contain all or nearly all the 
 known elements, not necessarily all in a given rock, but many 
 more than anyone has yet found." The researches of Sand- 
 berger, Stelzner, and Dieulafait also point to the same con- 
 clusion. 
 
 Considering the quantitative distribution of the major con- 
 stituents, silica is almost invariably present in igneous rocks, 
 and almost always in greatest amount. In general, the per- 
 centage may vary from nearly 80, as in granites and rhyolites, 
 to a minimum of about 24 per cent. Indeed, it may even form 
 100 per cent., if some dikes consisting wholly of quartz are 
 really of igneous origin, as is believed to be the case; while 
 in some ores derived from igneous magmas the amount of 
 silica may drop almost to zero. Alumina is usually the next 
 most abundant constituent, the percentage varying from a maxi- 
 mum of about 60, as in some corundum-syenites of Siberia 
 and Canada, to a minimum of zero, in certain rocks composed 
 wholly of olivine. The two iron oxides each show maxima of 
 about 15 per cent, except in the rare iron-ores due to magmatic 
 differentiation, where they constitute together almost all the 
 rock. Magnesia attains maxima of from 45 to 50 per cent, in 
 dunites of New Zealand and North Carolina; while lime reaches 
 a maximum of about 20 per cent, in the anorthosites of Canada. 
 Iron, magnesia, and lime may be practically absent in highly 
 siliceous rocks, like granites and rhyolites, and in some syenites. 
 Soda may be present up to 17 per cent, in some rare rocks in 
 which nephelite is abundant; while potash attains a maximum 
 of only about 12 per cent, in some unusual rocks rich in leucite, 
 
 1 Bulletin No. 305, U. S. Geological Survey, p. 20 (1907). 
 
DISTRIBUTION OF ELEMENTS IN IGNEOUS ROCKS. V33 
 
 which are found in Italy and in Wyoming. Both the alkalies 
 may be wholly wanting in rocks composed essentially of 
 pyroxene or olivine. 
 
 The amount of water present in wholly crystalline rocks 
 seldom exceeds -2 per cent., if the rock is unaltered, though 
 weathering very materially increases this quantity, and high 
 figures for water are usually to be attributed to this cause. 
 But some perfectly fresh, glassy lavas may carry up to 12 per 
 cent, of water, which was unable to escape from the magma 
 owing to the rapidity of solidification. 
 
 Titanium dioxide may rarely reach figures of about 6 per 
 cent., as in some basalts of the Western Mediterranean which 
 I am now investigating, but is usually present in much less 
 quantity, though it is seldom or never entirely absent. In some 
 titaniferous iron-ores of igneous origin, as those of the Adiron- 
 dacks and Norway, it may even reach 18 per cent. The 
 amount of phosphoric pentoxide rarely exceeds 3 per cent., and 
 that of manganous oxide is scarcely ever more than 1 per cent., 
 . the higher figures sometimes reported for this latter constituent 
 being almost invariably due to errors of analysis. It is but 
 seldom that either of these three elements is entirely absent. 
 
 The maximum amounts of the other minor constituents may 
 be briefly stated, as attention will thus be called to their rela- 
 tively great rarity, it being understood that the maxima are 
 seldom attained and that very frequently these elements are 
 wholly absent. 
 
 Zirconium is much less common than the chemically related 
 titanium, and seldom exceeds 0.20 per cent., though in some 
 very exceptional cases it may reach 2 per cent. Chromium 
 seldom occurs in amounts above 0.5 per cent., though a few 
 rocks are known in which it is reported to range between 2 and 
 3 per cent. Mckel seldom exceeds 0.20 per cent., and the 
 allied cobalt is scarcely ever present in more than mere traces. 
 The maximum amount of copper found in unaltered igneous 
 rocks may be placed at about 0.2 per cent, of CuO. Barium 
 almost always exceeds strontium in quantity, but only very ex- 
 ceptionally exceeds 0.25 per cent., though some rocks are 
 known in which about 1 per cent, is present; while the amount 
 of strontium is usually much less than 0.1, but may occasion- 
 ally reach 0.3 per cent, in the rocks very high in barium. 
 
734 DISTRIBUTION OF ELEMENTS IN IGNEOUS ROCKS. 
 
 Although figures of 0.1 or 0.2 per cent, have been reported for 
 lithium, these are somewhat doubtful, and it seldom occurs in 
 more than spectroscopic traces. Sulphur and chlorine may 
 both be present up to 2 per cent, or slightly more, but both 
 usually occur only in tenths of a per cent., and the latter 
 amount is the maximum for fluorine. Of the other minor con- 
 stituents the amounts present are so small as usually to be in- 
 significant except as to their actual presence. 
 
 III. THE AVERAGE COMPOSITION. 
 
 The estimation of the average composition of igneous rocks 
 as a whole is not such a simple matter as may be thought at 
 first, because of several complicating factors which should be 
 taken into account, and certain corrections in some of our data 
 which should be made, to obtain fairly satisfactory results. We 
 are not yet in a position to make precise allowance for these, 
 into the discussion of which we cannot enter here, so that the 
 results so far obtained can be regarded as but first approxima- 
 tions, only roughly correct but of some value. 
 
 The most recent and reliable calculations are three made 
 successively by Prof. F. W. Clarke, of the United States Geolog- 
 ical Survey, two of the igneous rocks of the British Isles by 
 Prof. A. Harker, of Cambridge, and one made by myself some 
 years ago. 2 
 
 Clarke's latest estimate is based on more than a thousand 
 analyses of igneous rocks of the United States made by the 
 chemists of the Geological Survey, and mine is based on about 
 1,800 analyses of igneous rocks from all parts of the globe, 
 and made by many analysts of various nationalities. These are 
 shown respectively in columns I. and II. of Table I., only the 
 more important constituents being considered^ and the whole 
 being reduced to 100 per cent. Harker's estimates are omitted, 
 but in general they conform to those here presented. 
 
 It is evident that the two are very closely alike, the only 
 noteworthy divergence being in the amount of silica. The 
 
 2 F. W. Clarke, Bulletin of the U. S. Geological Survey, No. 148, p. 12 (1897) ; 
 No. 168, p. 14 (1900); No. 228, p. 18 (1904) ; A. Harker, Geological Magazine, 
 vol. xxxvi., p. 18 (1899) ; Tert Ign. Kocks of Skye, p. 416 (1904) ; H. S. Wash- 
 ington, Professional Paper No. 14, U. S. Geological Survey, p. 108 (1903). I am 
 at present engaged in new calculations of the average rock, based on more than 
 3,000 analyses, but this is not yet ready for publication. 
 
DISTRIBUTION OF ELEMENTS IN IGNEOUS ROCKS. 
 
 735 
 
 TABLE I. Average Composition of Igneous Hocks. 
 
 
 I. 
 
 
 United 
 
 
 States, 
 
 
 Clarke, 
 
 
 1904. 
 
 SiO 2 . . . 
 
 . 60.48 
 
 A1 2 3 . . . 
 
 . 15.17 
 
 Fe 2 3 . . . 
 
 . 2.61 
 
 FeO ... 
 
 . 3.44 
 
 Mgo . .**; 
 
 . 4.10 
 
 CaO . . . 
 
 . 4.84 
 
 Xa. 2 O . . , 
 
 . 3.43 
 
 K 2 O .... 
 
 2.96 
 
 H 2 0(110+) 
 
 . 1.48 
 
 H 2 O (110) 
 
 . 0.41 
 
 Ti(X . . . 
 
 . 0.72 
 
 PA - - 
 
 . 0.26 
 
 MnO . . . 
 
 . 0.10 
 
 CO 2 .... 
 
 
 S . . 
 
 
 BaO 
 
 
 Cl .... 
 
 
 OoOo 
 
 
 V ^ A 2 VV 3 * 
 
 SrO .... 
 
 
 ZrO 2 . . . 
 
 
 KiO 
 
 
 V 9 (X. 
 
 
 F 
 
 
 LioO . 
 
 
 100.00 
 
 II. 
 
 III. 
 
 
 The 
 
 Complete 
 
 
 World, 
 
 Average, 
 
 
 Washington, 
 
 Clarke, 
 
 
 1903. 
 
 1904. 
 
 
 57.78 
 
 59.87 
 
 O 
 
 15.67 
 
 15.02 
 
 Si 
 
 3.31 
 
 2.58 + 
 
 Al 
 
 3.84 
 
 3.40 + 
 
 Fe 
 
 3.81 
 
 4.06 
 
 Ca 
 
 5.18 
 
 4.79 
 
 Na 
 
 3.88 
 
 3.39 
 
 Mg 
 
 3.13 
 
 2.93 
 
 K 
 
 1.42 
 
 1.46 
 
 Ti 
 
 0.36 
 
 0.40 
 
 H 
 
 1.03 
 
 0.72 
 
 C 
 
 0.37 
 
 0.26 
 
 P 
 
 0.22 
 
 0.10 
 
 S 
 
 
 0.52 
 
 Ba 
 
 
 
 0.11 
 
 Mn 
 
 
 0.11 
 
 Cl 
 
 
 0.07 
 
 Sr 
 
 
 0.05 
 
 Cr 
 
 
 0.04 
 
 Zr 
 
 
 
 0.03 
 
 Ni 
 
 
 
 0.03- 
 
 F 
 
 
 
 0.03 
 
 V 
 
 
 
 0.02 + 
 
 Li 
 
 
 0.01 
 
 
 100.00 
 
 100.00 
 
 
 IV. 
 
 Clarke, 
 1904. 
 
 47.09 
 28.23 
 
 7.99 
 
 4.46 
 
 3.43 
 
 2.53 
 
 2.46 
 
 2.44 
 
 0.43 
 
 0.17 
 
 0.14 
 
 0.11 
 
 0.11 
 
 0.089 
 
 0.084 
 
 0.07 
 
 0.034 
 
 0.034 
 
 0.026 
 
 0.023 
 
 0.02 + 
 
 0.02 
 
 0.01 
 
 100.00 
 
 higher figure in I. may be ascribed in part, as pointed out by 
 Clarke, to the inclusion of many separate silica-determinations, 
 which were undertaken on rocks comparatively high in this con- 
 stituent; in part to the inclusion in the estimate of some analy- 
 ses of siliceous gneisses and schists, rocks which were not 
 regarded in my estimate ; and probably in part to the fact that 
 in Clarke's estimate only rocks from the United States were 
 considered. But notwithstanding the slight discrepancies and 
 the uncertainty introduced by non-allowance for the disturbing 
 factors mentioned above, the results of the two calculations are 
 so concordant that we may feel a high degree of confidence in 
 the belief that the data given here approximate closely to the 
 average composition of the earth's accessible igneous rocks. 
 
 In column III. are given the results of a more complete esti- 
 mate by Clarke, which includes the minor constituents fre- 
 quently present in igneous rocks, but which are only deter- 
 
736 DISTRIBUTION OF ELEMENTS IN IGNEOUS ROCKS. 
 
 mined in the more complete analyses, as those made by the 
 chemists of the II. S. Geological Survey. It will be seen that 
 the data are in agreement with the general composition of the 
 most common rock-forming minerals, their constituents, silica, 
 alumina, ferric and ferrous oxides, magnesia, lime, soda, potash, 
 and .water, making up 97.9 per cent. 
 
 The estimated amount of carbon dioxide is undoubtedly too 
 high, and is due to the number of analyses of altered rocks 
 which were included in the estimates. 
 
 We may examine the matter further and, resolving the oxides 
 into their elementary components, ascertain the average amounts 
 of the elements in the igneous crust of the earth. This problem 
 has been studied by Clarke in the papers already cited, and by 
 Yogt 3 in Norway. The results of Clarke's latest calculations 
 are given in column IV. of Table I., the figures including those 
 for the minor constituents of column III., just noticed. In an 
 earlier computation Clarke introduced estimates of the ele- 
 ments which make up the air, the water of the oceans, and such 
 non-igneous rocks as limestone and coal. But the introduction 
 of these into the calculation does not materially alter the final 
 results from those given here, in which they are omitted, since 
 these bodies are of relatively very slight quantitative import- 
 ance compared with the whole mass of known rocks, however 
 large they may loom to our eyes. Ore-bodies also are quite 
 negligible in this connection. 
 
 These data show that oxygen composes almost one-half, sili- 
 con more than one-quarter, and aluminum about one-twelfth of 
 the earth's crust (the three together amounting to 83.3 per 
 cent.), while iron, calcium, sodium, magnesium, potassium, and 
 titanium follow after in the order named in decreasingly small 
 amounts. Thus, only nine elements together constitute 99 per 
 cent, of the igneous crust. This is certainly a very remarkable 
 fact, and one doubtless of great significance for the proper under- 
 standing of the true constitution of our globe, could we but in- 
 terpret it aright, as some day we may hope to do. 
 
 The relatively high position occupied by titanium, ninth on the 
 list in the order of abundance, is also a striking feature, as this 
 element is commonly supposed to be rare. The establishment 
 
 3 J. H. L. Vogt, Zeitschrift fur praktische Geologic, pp. 225-238, 314-325 (July 
 and September, 1898). 
 
DISTRIBUTION OF ELEMENTS IN IGNEOUS ROCKS. 787 
 
 of this fact is largely due to the accuracy and completeness of 
 the rock-analyses made by the chemists of the U. S. Geological 
 Survey, and its great abundance was unsuspected before they 
 began their long series of excellent analyses, though its wide 
 distribution had been noted. 
 
 It is also noteworthy that, with the exception of iron, alumi- 
 num, manganese, and nickel, none of the metals commonly 
 used as such appear in the list, while others, which are of very 
 limited practical application, are present. While nearly, if not 
 quite, all of the elements are presumably present in igneous 
 rocks, the average amounts of those not given in the list are 
 so extremely small that they may be regarded as minor correc- 
 tions to be applied in the future to certain of those here given, 
 since nearly all of them would be precipitated and weighed in 
 the course of analysis with some of those more abundant. 
 
 In the important paper cited above, Vogt has discussed the 
 probable amounts of these missing elements, and a brief state- 
 ment of those of his results which pertain "to the more im- 
 portant metallurgical elements may be given. The estimates, 
 it must be premised, are but approximations, and only indicate 
 the magnitude of the several amounts as percentages of the 
 earth's crust. But they serve to show the average extremely 
 small quantities of many metals and other elements which are 
 usually regarded as quite common or at least not very rare. 
 
 The percentage amounts of tin, zinc, and lead are expressed 
 by a digit in the third or fourth decimal-place, that of copper 
 in the fourth or fifth, that of silver in the sixth or seventh, that 
 of gold in the seventh or eighth, the amount of platinum being 
 about the. same. Mercury is rather more abundant than silver, 
 and arsenic, antimony, molybdenum, and tungsten less than 
 copper and greater than silver; while bismuth, selenium, and 
 tellurium are less abundant than silver but more so than gold. 
 
 III. PETROGRAPHIC PROVINCES. 
 
 More than 30 years ago, Vogelsang 4 pointed out that the 
 igneous rocks of certain districts called by him geognostische 
 Bezirke showed certain textural or mineral characters in com- 
 mon, which served to distinguish them from the rocks of other 
 
 4 H. Vogelsang, Zeitschrifl der deufschen geologischen Gesellschaft, vol. xxiv., No. 3, 
 p. 525 (May- July, 1872). 
 
738 DISTRIBUTION OF ELEMENTS IN IGNEOUS ROCKS. 
 
 districts. The same idea was expressed later by Judd, 5 who 
 introduced the term Petrographic Province, and was afterward 
 elaborated by Iddings, 6 who likened the districts of similar 
 rocks to families and referred to their relationships as "Consan- 
 guinity." Neither Judd nor Iddings seems to have been aware 
 of Vogelsang's prior publication. The first two statements 
 referred only to geological occurrence and to textural and min- 
 eralogical peculiarities ; while Iddings, writing at a time when 
 the chemistry of rocks had begun to assume its due prominence 
 (largely owing to the earnest labors of the chemists of the IT. 
 S. Geological Survey), showed that the relationship is also in- 
 dicated by the chemical composition of the various rocks, and 
 is fundamentally dependent on this, and he consequently de- 
 votes much space to the chemical evidence of consanguinity. 
 
 The doctrine of consanguinity, as it may be termed, has now 
 received general acceptance, and it is commonly recognized 
 that the igneous areas of the earth's surface are divisible into dis- 
 tricts the rocks of which show certain features in common which 
 serve to distinguish them from those of other districts. It is 
 also assumed that the possession of these common features, 
 especially those dependent on the chemical composition, indi- 
 cates that the rocks of a given district have a common genetic 
 origin, that is, are derived from a common parent body of 
 magma. The processes by which this differentiation and de- 
 rivation from a common magma are brought about are still ob- 
 scure, and form the subject of much modern investigation and 
 discussion, into which we cannot enter here. Such areas of re- 
 lated rocks are usually called petrographic provinces, though the 
 term comagmatic region, which indicates more clearly .their deri- 
 vation from a common magma, has recently been introduced. 7 
 
 Though petrographic provinces represent one of the promi- 
 nent phases of the distribution of the elements in the earth's 
 crust, and though their existence is, in general, undeniable, yet 
 their characters are so complex and made up of so many factors 
 that the characterization in most cases cannot be made very 
 
 5 J. W. Judd, Quarterly Journal of the Geological Society, vol. xlii., pt. ], No. 165, 
 p. 54 (Feb. 1, 1886). 
 
 6 J. P. Iddings, Bulletin of the Philosophical Society of Washington, vol. xii., pp. 
 128-144 (1892). 
 
 7 H. S. Washington, Carnegie Publication No. 57, p. 5 (1906). 
 
DISTRIBUTION OF ELEMENTS IN IGNEOUS BOCKS. 739 
 
 precise or the limits be very sharply drawn. Their study is still 
 almost in its infancy, and the accumulation of many more data, 
 especially from the analytical side, is needed before definitive 
 studies can be undertaken, and the characters of any petro- 
 graphic province be precisely defined. 
 
 The geological evidence of consanguinity is at times clear. 
 Thus, as Iddings 8 says: 
 
 " The constant recurrence of particular series of rocks, often with a certain order 
 of eruption in different localities, and the frequent occurrence of such series at 
 neighboring centers of volcanic activity, would be enough to justify the belief that 
 there was a definite connection between the members of a group." 
 
 On the other hand, cases are known where such geological 
 evidence is lacking or conflicting, or where the relations are so 
 generally observed as to be meaningless in this connection. 
 
 Geologically speaking, a petrographic province may belong 
 to any period of geologic time, or may conceivably extend over 
 more than one period. The region may be small or large, 
 covering hundreds or hundreds of thousands of square miles. 
 It may be of any shape, forming an elongated band or zone, a 
 highly irregular area, or one more or less equidimensional. It 
 may consist of a single, large area of connected intrusive or 
 effusive rocks, or of adjacent but isolated areas. 
 
 The chemical characters which, being common to the rocks 
 of a province, indicate consanguinity are manifold. The rocks 
 may be uniformly high in soda or in potash, or in potash and 
 lime, low in magnesia and high in iron, generally deficient in 
 silica, and so on. Throughout one province the soda may in- 
 crease relatively to potash as silica decreases, while in another 
 the reverse holds good. Or again, there may be some combi- 
 nation of such two kinds of characters, called respectively abso- 
 lute and serial. The subject is complicated by the possibility 
 of local differentiation, so that in a region of unquestionably 
 related rocks, we may meet with some the character of which 
 does not conform to the general law of the region, but the 
 presence of which is to be explained by the extreme differenti- 
 ation of some portion of the general magma. 
 
 Conforming to the chemical features, and in general largely 
 dependent on them, are the common mineral ogical characters. 
 
 8 Loc. cit., p. 43 
 
740 DISTRIBUTION OF ELEMENTS IN IGNEOUS ROCKS. 
 
 These are very important, not so much in themselves, as be- 
 cause they often enable one practically to determine the general 
 relationship without the necessity of a long series of analyses. 
 The mineralogical similarity may be evident in two ways: either 
 by the general presence of certain minerals which are rare or are 
 not usually found in certain kinds of rock, as the rare zirconium 
 minerals, or neph elite, or leucite, the occurrence of hypersthene 
 in the basalts and andesites, or of biotite in peridotites; or by 
 certain peculiarities of color, form, or other characters shown 
 among the more usual mineral groups, and which are dependent 
 on the introduction of certain chemical constituents into the 
 molecule, as bright green, pleochroic augites or blue horn- 
 blendes, due to their containing much soda, purple augites or 
 red-brown hornblendes, due to titanium, and so on. Here 
 again the possibilities of difference are numerous, but the 
 mineralogical evidence of relationship is often so marked as to 
 be unmistakable to the petrographer. 
 
 A good illustration of such petrographic provinces and of 
 their distribution is furnished by the United States, which may 
 be briefly described, though our knowledge is still incomplete. 
 Stretching along and rather close to the Atlantic coast is a zone 
 of small, isolated areas of igneous rocks which are chiefly charac- 
 terized by a high content in soda, resulting in the common 
 presence of nephelite-syenites and other rocks containing nephe- 
 lite, peculiar hornblendes, and other minerals characteristic of 
 such magmas. This zone includes areas in Quebec, New 
 England, New Jersey, Arkansas, Texas,, extends into eastern 
 Mexico and the West Indies, and probably as far south as 
 Brazil and Paraguay. Parallel with this, but usually farther 
 inland, is a second zone of areas of rocks which are low in 
 silica and the alkalies, but high in lime and iron. This starts 
 in the great anorthosite area of eastern Canada and Labrador, 
 appears in New England, the Adirondacks, Delaware, Mary- 
 land, and extends to Georgia and possibly farther south. 
 The rocks of this region are typically gabbros, diabases, and 
 pyroxenites, dunite and other peridotites, with some granites 
 high in lime, and are often accompanied by very basic ores and 
 other products of differentiation which are very rich in iron 
 and titanium. Farther inland and west of the Appalachian 
 range is another belt, less well defined but apparently in 
 
DISTRIBUTION OF ELEMENTS IN IGNEOUS ROCKS. 741 
 
 general parallel to the others, of widely isolated small occur- 
 rences of peculiar peridotites and other rocks, low in silica and 
 very high in magnesia and iron, with little lime or soda but 
 much potash. This last feature gives rise to the common pres- 
 ence of peculiar micas, which distinguish these peridotites 
 mineralogically from those of the preceding region. These 
 areas occur in Quebec, New York, Pennsylvania, Kentucky, 
 Arkansas, and probably still farther south. 
 
 Passing over the broad central part of the continent, where 
 igneous rocks are very sparingly present, we find a province 
 east of the Rocky mountains which is characterized by high 
 alkalies, especially potash, so that the usually rare mineral 
 leucite is here quite common. This region is best known in 
 Montana, Wyoming, and Colorado, and may possibly extend 
 into western Texas. In the region of the Rocky mountains, 
 and the cordilleras generally the occurrences of igneous rocks 
 are so numerous and the relations so complex that it is some- 
 what difficult to unravel the various petrographic provinces. 
 As a whole, however, the igneous rocks of this part of the con- 
 tinent seem to belong to one very extensive province, which is 
 continued into Alaska on the north and along the Andes to the 
 south. In general chemical character the rocks show rather 
 low alkalies, with more soda than potash, rather high lime, and 
 but moderate amounts of iron and magnesia, leading to the 
 abundance of such ordinary rocks as feldspar-basalts, andesites, 
 dacites, and some rhyolites. There is some evidence that the 
 province as a whole may be divisible into several subordinate 
 districts, but it is noteworthy that rocks so high in soda or 
 potash as to contain nephelite or leucite are practically unknown 
 west of the Rocky mountains. There are also indications' ol 
 what may be a distinct region along the coast ranges which is 
 characterized by high soda and generally high silica, but this 
 demands further investigation. 
 
 A number of petrographio provinces outside of the United 
 States may also be briefly indicated. One of the best known is 
 that of southern Norway, which is prominent through the 
 classic researches of Brogger, the rocks of which are charac- 
 terized by high alkalies, especially soda, and the presence of 
 many minerals elsewhere rare. This is possibly connected with 
 the region of the Kola peninsula in northern Finland. The 
 
742 DISTRIBUTION OF ELEMENTS IN IGNEOUS ROCKS. 
 
 British Islands, with, the Faeroes, Iceland, and probably Spitz- 
 bergen, form another well-defined province, the rocks of which 
 resemble on the whole those of our Rocky Mountain region, 
 though they differ in some respects. Leaving aside Germany, 
 Austria, and France, each of which contains several petro- 
 graphic provinces, the relations of which appear to be some- 
 what complex, in the basin of the Mediterranean we find at 
 least three well-defined and quite distinct provinces. In the 
 eastern part, including the Grecian archipelago and parts of 
 Asia Minor, the rocks are rather siliceous, with fairly high lime 
 and rather low alkalies, soda dominating potash, so that dacites, 
 andesites, and feldspar basalts are prominent. Hypersthene is 
 here rather common. The Italian peninsula shows a second, 
 very well-defined province, which embraces seven distinct 
 .volcanic centers along the west coast. The rocks of this are 
 remarkable for their high content in potash, which at times 
 reaches extraordinary figures, and leads to the abundant pres- 
 ence here of the mineral leucite, which is elsewhere decidedly 
 rare. Lime is also rather high, while soda, iron, and magnesia 
 are low. The other provinces of continental Italy have not been 
 thoroughly studied and are less well known. In the western 
 basin of the Mediterranean, including localities in Spain, Sar- 
 dinia, some islands south of Sicily, and probably southern 
 France, there appears to be a third province, which differs 
 from the others in that soda is much higher and the more 
 basic rocks (basalts) contain very large amounts of titanium, 
 and in other ways. This last may be connected with a province 
 in eastern Africa, running down the Great Rift valley and in- 
 cluding parts of Madagascar, in which rocks rich in soda are 
 very common. A somewhat similar province appears to exist 
 in New South Wales and Queensland in Australia. 
 
 The descriptions just given, which are but the barest sketches 
 of only some of those which are known, and with no references 
 to authorities, will serve to give an idea of some of the leading 
 distinguishing features of petrographic provinces, and how 
 multifariously they are scattered over the earth's surface. 
 Their existence and distribution indicate clearly that the un- 
 derlying magma basins, or the sources from which the igneous 
 rocks are immediately derived, are not everywhere uniform 
 and alike, but that there exists a certain heterogeneity in the 
 
DISTRIBUTION OF ELEMENTS IN IGNEOUS ROCKS. 743 
 
 non-sedimentary parts of the earth's crust. It should, how- 
 ever, be noted that two provinces, though widely separated, 
 may be essentially alike in all their features, as is the case 
 with that of the eastern Mediterranean and that which extends 
 from the Andes to Alaska. 
 
 IY. THE CORRELATION OF THE ELEMENTS. 
 
 The existence of petrographic provinces is a broad phase of 
 the distribution of the elements among igneous rocks, the dis- 
 tribution being essentially a spacial one and the evidence rest- 
 ing almost entirely on the relative proportions of the most 
 abundant elements. But apart from this spacial distribution 
 there is evident, also, a correlated variation among the ele- 
 ments ; that is, a tendency for certain ones to increase or de- 
 crease, to be relatively abundant or not, according to the pres- 
 ence or absence of others. The causes of this behavior are 
 obscure and apparently complex. In part they may be prob- 
 ably referred to certain fundamental relations among the ele- 
 ments, as shown by the periodic classification and chemical 
 affinity ; in part to the effect of certain physico-chemical laws 
 leading to the mutual segregation of elements affected simi- 
 larly; and possibly in part to the degradation of some of the 
 elements, as indicated by recent experiments of Ramsay. But 
 any discussion of the causes is outside the province of this 
 paper, in which we can only deal briefly with some of the facts 
 of distribution. 
 
 The study of these mutual relations among the elements in 
 igneous rocks is of recent date, and "has been made possible, 
 especially so far as the rarer elements go, only by the complete- 
 ness and accuracy of modern chemical analyses of rocks. Such 
 analyses supplement the evidence afforded by study of min- 
 erals, mineralogical associations, and ore-deposits, and, dealing 
 as they do with what must be regarded as*the ultimate source 
 of the ores, are of the highest significance and importance. 'In 
 the following brief discussion, therefore, stress will be laid on 
 the evidence afforded by rock-analyses, with some reference to 
 chemical mineralogy, while ore-deposits, as being more techni- 
 cal and better known to the mining engineer, will be alluded 
 to only occasionally. 
 
 Considering first only the most abundant elements, a study 
 
744 DISTRIBUTION OF ELEMENTS IN IGNEOUS ROCKS. 
 
 of the igneous rocks in general shows that silica, alumina, soda, 
 and potash tend to increase or decrease together, though not 
 always at the same rate ; while, on the other hand, the iron 
 oxides, magnesia, and lime tend to vary together and in general 
 inversely as the preceding constituents. The more siliceous 
 rocks almost invariably show relatively high alumina and alka- 
 lies and low iron oxides, magnesia, and lime, leading to the 
 common presence in abundance of the alkali feldspars and the 
 comparative paucity in calcic feldspars and the ferromagnesian 
 minerals, which tend to increase rapidly with diminution in the 
 silica-content. Highly siliceous rocks which contain more iron, 
 magnesia, and lime than alumina, soda, and potash are of very 
 exceptional occurrence. The rule mentioned above is so 
 generally true that it may be regarded as the normal one 
 for igneous rocks in general, and is commonly accepted as 
 such in petrology. 
 
 At the same time, there is considerable evidence that certain 
 subsidiary relations obtain among the constituents other than 
 silica, which, while by no means universal, are at times very 
 pronounced, and occasionally seem to supersede the more gen- 
 eral law. Thus, soda not uncommonly tends to vary with the 
 iron oxides, while potash shows similar relations to magnesia, 
 resulting in the presence of potassium minerals in highly mag- 
 nesian rocks and the abundance of sodium minerals in those 
 high in iron. Again, while neither iron nor magnesia shows 
 any marked affinity towards or tendency to vary with alumina, 
 this constituent and lime are occasionally found to occur 
 together in great abundance and to the general exclusion of 
 the others. These relations are also evident in certain facts of 
 chemical mineralogy, as the usual predominance of magnesium 
 over iron in the potassic biotites and phlogopites, the abundance 
 of soda and absence of potash among the highly ferriferous 
 augites and hornbtendes, and the numerous silico-aluminates 
 containing much calcium, while those with iron or magnesium 
 are comparatively very rare. 
 
 But this tendency to selective and correlated variation among 
 the chemical constituents of igneous rocks is not confined to 
 those which are present in greatest amount. It is equally well, 
 and indeed in some respects more strikingly, shown among the 
 rarer elements, both as compared with those which are most 
 
DISTRIBUTION OF ELEMENTS IN IGNEOUS ROCKS. 745 
 
 abundant and with each other. Furthermore, the distribution 
 of some of these rare elements would seem to have important 
 bearings on some of the problems of economic geology and the 
 distribution of ore-deposits. 
 
 The general facts of this distribution and variation of the 
 rare elements have been summarized in several recent publi- 
 cations, 9 but many of the details are still un-coordinated and 
 widely scattered through the vast mass of petrographic litera- 
 ture, and there are certain aspects and recent developments 
 which are either neglected, or only briefly alluded to, in the 
 publications cited. 
 
 It is now commonly understood that certain elements are 
 prone to occur most often and in largest amounts in rocks 
 which are high in silica, the so-called "acid" rocks; while 
 others are met with similarly in those low in silica the 
 "basic" rocks. This is essentially the only set of relations 
 recognized by Vogt, while De Launay in addition to these two 
 groups proposes two others, the ll mineralizing agents " and 
 the vein-metals. 
 
 Evidence, however, is accumulating that the relations of the 
 rare elements to the igneous rocks cannot be expressed so 
 simply as is done by Yogt and De Launay. Their relative 
 abundance is not dependent on the silica alone, and hence ref- 
 erable only to the " acidity " or " basicity " of the rock. The 
 relations are more complex, and dependent, not so much on the 
 amount of silica, as on the relative amounts of other constit- 
 uents, notably soda, potash, iron, magnesia, or lime. They 
 conform, on the whole, to the general relations of the most 
 abundant constituents, some of the rarer elements being char- 
 acteristically at home in the rock groups which show high 
 alumina and alkalies, and which include those high in silica; 
 while others again are most abundant in the rocks high in iron, 
 magnesia, or lime, and which consequently most often show 
 low silica percentages. Further than this, on the one hand, 
 certain rare elements are not equally at home in the alkalic 
 
 9 J. H. L. Vogt, Zeitschrift fur praktische Geologic, p. 326 (September, 1898) ; 
 J. F. Kemp, Ore Deposits, 3d edition, pp. 34-37 (1900) ; H. S. Washington, 
 Manual of the Chemical Analysis of Rocks, p. 14 (1904) ; L. De Launay, La Science 
 Geologigue, p. 637 (1905) ; W. F. Hillebrand, Bulletin No. 305, U. S. Geological 
 Survey, p. 21 (1907). 
 
 47 
 
' 746 DISTRIBUTION OF ELEMENTS IN IGNEOUS ROCKS. 
 
 rocks in general, but are most abundant either in those high 
 in soda or in those high in potash. On the other hand, some 
 of the elements segregated in the basic rocks seem to be 
 most at home in those which are highly calcic, others in those 
 which are high in iron or in magnesia, though here the evi- 
 dence is not so clear and the distinctions apparently not so 
 well marked as in the preceding case. 
 
 We may consider first those minor constituents of rocks 
 which are determined in the most modern and complete 
 analyses, and next those which exist in rocks in such small 
 amount as almost to defy determination by the usual analytical 
 methods, but whose presence is made known either miner- 
 alogically or by their segregation in ore-deposits. The second 
 group includes almost all of the commercially important 
 metals (except iron and manganese), while the former includes 
 many elements w T hich are assuming an increased practical im- 
 portance as their economic possibilities and uses become better 
 known. In a general way the elements will be taken up in the 
 order of their positions in the periodic classification. No ref- 
 erences will be given, as an attempt to render them complete 
 would unduly lengthen the paper. This course seems the more 
 advisable, in spite of the apparent injustice to those whose in- 
 valuable work and contributions must thus be ignored, since 
 the present paper may be considered as merely a preliminary 
 one to a more exhaustive and monographic treatment which it 
 is hoped to publish later. 
 
 Lithium is very widely distributed among igneous rocks, but 
 always in very small amounts. While it frequently is to be 
 detected by the spectroscope, it seldom occurs in weigh able 
 quantities, and the difficulty of its exact separation from the 
 other alkali metals and its comparative unimportance cause it 
 to be but seldom estimated quantitatively. Although such 
 minute traces are present in both acid and basic rocks, yet 
 it is undoubtedly more closely connected with those which 
 are highly siliceous and alkalic. The minerals in which it 
 forms an essential component, as spodumene, lepidolite, am- 
 blygonite, and some tourmalines, are most often met with in 
 granites and pegmatites derived from granitic magmas. Un- 
 fortunately, the granites and pegmatites which carry lithium 
 minerals most prominently do not appear to have been analyzed, 
 
DISTRIBUTION OF ELEMENTS IN IGNEOUS ROCKS. 747 
 
 but there is reason for the belief that they are sodic rather than 
 potassic in general character. The very common association 
 of lithium with soda rather than with potash in many minerals 
 also points to the same conclusion. 
 
 Beryllium is much like lithium in its associations, beryl and 
 other rarer minerals which contain it occurring for the most 
 part in granites or pegmatites. Few analyses exist of such 
 beryl-bearing rocks, and beryllia has seldom been estimated 
 separately from alumina in rock-analysis, but such data as are 
 available and the common mineralogical association of beryl- 
 lium and sodium point to the conclusion that the element is 
 most at home in sodic magmas. 
 
 Attention may be called to the fact that beryl, in spite of 
 its common occurrence, is not given in the list of descrip- 
 tions of the rock-forming minerals, such as those in the 
 standard works of Zirkel, Rosenbusch, and Iddings, though 
 Levy and Lacroix briefly described it in their work 10 and it is 
 placed on their large colored table of bi-refringences. In its 
 optical properties it closely resembles nephelite and apatite, and 
 being hexagonal in crystallization as well, might readily be 
 mistaken for one of these minerals. I have noted the fact that 
 analyses of nephelite-syenites and other highly sodic rocks fre- 
 quently show a decided excess of alumina which cannot be 
 explained by the apparent mineralogical composition of the 
 rock, and the suggestion is made that this is possibly due to 
 the presence of beryl, the beryllia of which would appear as 
 alumina in the course of analysis, unless special means were 
 taken to separate the two. On the other hand, the excess of 
 alumina may be real and due to the composition of the magma. 
 
 Strontium has been shown by the analyses of the U. S. Geo- 
 logical Survey to be widely distributed in the rocks of this 
 country. I have found it almost invariably when looked for in 
 many European rocks, and it is almost constantly present in 
 those of Australia. But it seldom occurs in more than traces, 
 and the evidence in regard to its distribution is as yet incon- 
 clusive, in spite of the many modern analyses in which it is 
 now determined, chiefly because of the small amounts usually 
 met with. It would appear to be most abundant in rocks some- 
 what high in lime and with moderate to rather low silica, 
 
 10 Les Mineraux des Roches (Paris, 1888). 
 
748 DISTRIBUTION OF ELEMENTS IN IGNEOUS ROCKS. 
 
 though it is worthy of note that the highest figures recorded for 
 it are in some rocks of Wyoming which are low in lime and 
 extraordinarily high in potassium and barium. Being but rarely 
 a constituent of silicate minerals, decisive evidence from this 
 side is wanting, though it occurs with lime in some heulandite 
 and brewsterite. 
 
 Barium is another element which the analyses of the Wash- 
 ington chemists showed to be widely distributed, and almost 
 invariably in decidedly greater amounts than strontium. It is 
 now often determined by analyses of superior quality, and in a 
 recent study, embracing the rocks of Italy, the United States, 
 and New South Wales, I have shown that it is specially prone 
 to occur in potassic rocks, sometimes when the potash is accom- 
 panied by considerable lime, but that it is rarely met with in 
 notable amount in decidedly sodic or calcic rocks. Neither the 
 amount of silica nor the relative proportions of iron and mag- 
 nesia, appears to be a determining factor of much importance. 
 This association of barium and potassium in igneous rocks is 
 in harmony with the mineralogical evidence. Barium is a fre- 
 quent minor constituent in potassium minerals, as orthoclase, 
 muscovite, and biotite, while potassium accompanies barium in 
 hyalophane and harmotome. On the other hand, barium is not 
 reported in analyses of sodium minerals, but occurs in small 
 amounts in the calcium zeolites, brewsterite and phillipsite. 
 Barium also seems to tend to associate with manganese, as 
 shown by its common occurrence in psilomelane, and the occur- 
 rence of minerals of the two metals in certain mines. 
 
 Boron is seldom or never mentioned in rock-analyses, chiefly 
 because of the complexity and difficulty of its exact determina- 
 tion, especially in very small amounts. But it is not infre- 
 quently present in weighable amounts in granites and peg- 
 matites, chiefly as a constituent of tourmaline. The few 
 analytical data that we have of such tourmaline-bearing rocks 
 are not decisive, but boron does not appear to have very decided 
 preferences for either soda or potash. Its associations in min- 
 erals are likewise not strongly marked, but among the silicates 
 calcium is the basic element which most frequently accompanies 
 it, and soda is more commonly met with in boron-bearing min- 
 erals than is potash. Boron is commonly regarded as one of 
 the pneumatolytic elements. 
 
DISTRIBUTION OF ELEMENTS IN IGNEOUS ROCKS. 749 
 
 Cerium, yttrium, and the other metals of the so-called " rare 
 earths," as well as thorium and uranium, are only rarely deter- 
 mined in rock-analysis. Minerals containing them are com- 
 monly associated with acid pegmatites, which, judging from 
 occurrences in Norway, Greenland, and elsewhere, are most 
 apt to be sodic, though the few determinations available of the 
 rare earths are in highly potassic igneous rocks. 
 
 Titanium is, as we have seen, far from being the rare element 
 which it was formerly considered, and it is probably never 
 wholly absent from any rock. It is distinctly much more 
 abundant in basic than in acid rocks, and its affinities in the 
 magma seem to be decidedly rather with iron than with mag- 
 nesium, and still less with lime. While it is not commonly 
 associated with alkalic rocks, yet when these are low in silica 
 it shows a tendency to be present in considerable amount 
 when the rock is sodic, as indicated by recent rock-analyses; 
 and this tendency to association of titanium with sodium appears 
 mineralogically, as in the soda-amphiboles, some of which are 
 highly titaniferous, and in certain rare minerals, as astrophyl- 
 lite and rosenbuschite. Highly potassic and highly calcic 
 rocks seldom show large amounts of titanium, though most of 
 the mineral titanates contain calcium as the base. 
 
 Zirconium., so closely allied to titanium chemically, also shows 
 certain analogies in its magmatic relations. While unlike tita- 
 nium in being rare in the basic rocks, those high in iron, 
 magnesia, and lime, and referred by Vogt to the acid rocks, 
 presumably because of the common occurrence of zircons in 
 granites, it is now commonly recognized by petrographers that 
 zirconium is by far most abundant in the rocks which are high 
 in soda. Indeed, zirconium maybe considered to be a charac- 
 teristic minor chemical constituent of the sodic rocks, whether 
 the silica be so high that quartz is present, or whether it be so 
 low that nephelite is abundant, as in the nephelite-syenites and 
 phonolites. Practically all modern, complete analyses bear out 
 this view, which is confirmed by the common association of 
 sodium and zirconium mineralogically, as in eudialyte, cata- 
 pleiite, w^dhlerite, and the zirconium pyroxenes. 
 
 Phosphorus, as a constituent of apatite, is universally diffused 
 in small amounts through igneous rocks, and is most abundant 
 in the basic ones, though its relations to the constituents 
 
750 DISTRIBUTION OF ELEMENTS IN IGNEOUS ROCKS. 
 
 other than silica are not clear. Study of large collections of 
 analyses indicates that it is usually, but not always, associated 
 with high lime, rather than with high iron or magnesia, and 
 in some distinctly sodic provinces the more basic rocks with 
 high soda and abundant nephelite show high figures for phos- 
 phorus pentoxide. Some of the phosphates are met with in 
 granitic and syenitic pegmatites. 
 
 Vanadium has been shown by the researches of Hillebrand 
 to be quite widely distributed, but always in very small amount 
 and almost wnolly confined to the basic rocks. As it exists as 
 the sesquioxide, V 2 0s> replacing alumina and ferric oxide in 
 ferro-magnesian minerals, it is especially abundant in rocks 
 composed largely of pyroxene, hornblende, or biotite, while it is 
 present only in traces or not at all in rocks very rich in olivine, 
 where the iron is present mostly as ferrous oxide, as in the 
 peridotites. It is associated with iron rather than with mag- 
 nesium, and occurs in most abundance in some iron-ores of 
 magmatic origin, but no definite relations to the alkalies can be 
 made out. Its common occurrence in ashes of coals and its 
 abundance in certain carbonaceous deposits recently described 
 are noteworthy, though outside the present discussion. 
 
 Sulphur is, by far, more abundant in the basic than in the 
 siliceous rocks. It may exist, in the oxidized condition, in the 
 minerals hauynite and noseliie, in which case the rocks con- 
 taining these minerals are almost invariably distinctly sodic; 
 or it may form sulphides, as pyrite, pyrrhotite, and chalcopyrite, 
 these being most common in rocks rather high in iron, magne- 
 sia, and lime. 
 
 Chromium, like vanadium, is a constituent of the basic 
 rocks, but, unlike this, is most abundant when magnesia and 
 not iron is high, and when olivine, rather than pyroxene or 
 hornblende, is abundant, in spite of the fact that it occurs as 
 the sesquioxide, Cr 2 3 . Presumably this is because, instead of 
 replacing alumina and ferric oxide in the ferromagnesian min- 
 erals, it is most commonly met with in the minerals chromite 
 and picotite. It is reported to reach very high figures again 
 in certain effusive rocks which are so high in lime and low in 
 silica that the rare mineral melilite is present. 
 
 Molybdenum is seldom looked for in rock-analysis, and our 
 knowledge of its magmatic relations is based almost wholly on 
 
DISTRIBUTION OF ELEMENTS IN IGNEOUS ROCKS. 751 
 
 an investigation by Hillebrand. He found that it is much less 
 common and is present in smaller quantity than vanadium, and 
 that, unlike the latter, it is present only in the more siliceous 
 rocks, though in quantities too small to permit of further dis- 
 crimination. As molybdenite it occurs most often in quartzose 
 rocks. 
 
 Fluorine is almost universally present in very small amount 
 as a constituent of most apatites, and is usually regarded as a 
 " mineralizing agent," and, as such, is frequently present in 
 pneumatolytic minerals. As stated by Vogt, it seems to be 
 more common in the acid rocks, but there seems to be a 
 marked tendency on its part to favor especially rocks which 
 are high in soda. This is seen in the fact that fluorite is fre- 
 quently present as an original constituent of such highly sodic 
 rocks as nephelite-syenite, phonolite, and tinguaite; the asso- 
 ciation of fluorine and sodium in certain rare minerals, as leu- 
 cophanite, meliphanite, johnstrupite, rinkite, .etc., which are 
 almost always found in sodic rocks ; and by the recent dis- 
 covery by Lacroix of sodium fluoride in nephelite-syenites of 
 West Africa. 
 
 Chlorine resembles fluorine in being a pneumatolytic con- 
 stituent, and is present in igneous rocks chiefly in the minerals 
 sodalite and noselite, which are almost wholly confined to sodic 
 rocks and especially those which are low in silica, in this re- 
 sembling the occurrence of S0 3 . 
 
 Manganese, though as widely distributed as titanium and 
 phosphorus, is usually present in such small amounts as not to 
 allow a clear judgment of its magmatic relations, especially as 
 the high figures often reported for it are apt to be due to ana- 
 lytical error. As a general rule, its amount is greater in the 
 basic rocks, and certain considerations indicate a preference 
 for rocks high in iron rather than in magnesia or lime, but the 
 variations are not very significant. We have already noted 
 above the tendency to association of barium and manganese. 
 
 Nickel is pre-eminently at home in the basic rocks, especi- 
 ally in the peridotites and serpentines, where it replaces iron in 
 the olivine, while it likewise occurs in small amounts in horn- 
 blende, biotite, and in pyrite and pyrrhotite. Certain rather 
 high figures reported for it may be ascribed to analytical con- 
 fusion with platinum derived from the utensils employed; but 
 
752 DISTRIBUTION OF ELEMENTS IN IGNEOUS ROCKS. 
 
 researches now in progress indicate that it may be present in 
 considerable amount (up to about 0.20 per cent), not only in 
 the "basic" but in the more siliceous rocks of certain localities 
 where its presence has not hitherto been suspected. It is 
 reasonable to suppose that it is most apt to be present in rocks 
 which are relatively high in iron rather than in magnesia and 
 lime, and the results of the investigation just mentioned are in 
 harmony with this supposition. 
 
 Cobalt almost always accompanies nickel in igneous rocks, 
 but always in extremely small and scarcely weighable amounts. 
 
 The elements belonging to the next group to be discussed, 
 those which are scarcely detectable in igneous rocks by the 
 usual analytical methods on account of the excessively minute 
 amounts usually present, need not detain us long, even though 
 they are commercially among the most important. Since the 
 analytical data are either very scanty, untrustworthy, or want- 
 ing altogether, and their presence is revealed to us mostly 
 through secondary processes of concentration in veins, placers, 
 and other ore-deposits, we are not yet in a position to generalize 
 with confidence as to the magmatic relations of most of them. 
 
 Furthermore, having but slight affinity for silica, and thus 
 (with few exceptions) seldom forming silicates or entering as 
 minor constituents into the silicate minerals of other elements, 
 we are deprived to a very great extent of this kind of evidence. 
 
 Copper is not infrequently reported in analyses of igneous 
 rocks, but, as pointed out by Hillebrand, its apparent presence 
 may often be attributed to contamination during the course of 
 analysis, or, as may be suggested here, to confusion with 
 platinum likewise due to contamination, as was suggested in 
 the case of nickel. But notwithstanding these sources of error 
 copper seems to be widely distributed among igneous rocks r 
 though in very small amounts. There seems to be little doubt 
 that it is most abundant in the more basic rocks, especially 
 those which carry pyroxene and hornblende rather than olivine, 
 but no evidence seems to exist as to its relations to the chemical 
 constituents other than silica. 
 
 Silver and gold have both been detected analytically in 
 igneous rocks, while metallic gold has also been observed as an 
 apparently primary ingredient of some rhyolites and granites. 
 Both of these metals are " cosmopolitan in their relations," as 
 
DISTRIBUTION OF ELEMENTS IN IGNEOUS ROCKS. 753 
 
 Kemp puts it, and they are known to occur in such highly 
 siliceous rocks as granite, rhyolite, and quartz-porphyry, and, 
 on the other hand, in diabase and gabbro. There is, however, 
 good reason for the belief that gold, and probably silver as 
 well, are most apt to occur in rocks high in silica, but their 
 relations to the other elements are still quite unknown. 
 
 Zinc and cadmium (which latter is found only in connection 
 with the former) are also very uncertain. There is, however, 
 some reason for thinking that, zinc is more apt to be present 
 in acid rocks, as granites, this opinion being based on a few 
 analytical data and the facts of some of its occurrences. The 
 common occurrence of zinc in limestones, due presumably, at 
 least in part, to the precipitating effect of the sedimentary rock, 
 has no apparent bearing on its relations to igneous magmas. 
 
 Mercury is considered by G. F. Becker to be associated with 
 granites, but his evidence is not very convincing. Its usual 
 occurrence in sedimentary rocks tends to obscure its true re- 
 lations, and, to the best of my knowledge, it has never been 
 looked for or reported in an analysis of an igneous rock. 
 
 Tin, as the oxide, cassiterite, almost invariably occurs as the 
 result of pneumatolytic processes in pegmatites, granites, and 
 other rocks high in silica, and the mineral has been found in 
 some rhyolites. Judging from the common association of 
 cassiterite with lithium and beryllium minerals, and the pres- 
 ence of small amounts of tin in certain feldspars, micas, zircons, 
 and in the rare mineral stokesite, it is probable that tin is asso- 
 ciated rather with distinctly sodic than with potassic or calcic 
 magmas, but much more chemical study of the rocks in which 
 it occurs is needed to elucidate its relations. 
 
 Lead can often be found in rocks by using large amounts of 
 material, and is occasionally reported, as in the analyses of 
 rocks from British Guiana by J. B. Harrison and in those of 
 rocks from New South Wales. No generalization in regard to 
 it is possible as yet, but I am inclined to think that, like zinc, 
 it favors the acid rather than the basic rocks, though it has 
 been observed in both. The remarks in regard to the occur- 
 rence of zinc in limestones apply as well to lead. 
 
 Platinum and the other metals of this group are, as is well 
 known, most commonly found in connection with peridotites, 
 rocks low in silica and high in magnesia, though it has been 
 
754 DISTRIBUTION OF ELEMENTS IN IGNEOUS ROCKS. 
 
 observed by Kemp in gabbros, which were presumably con- 
 nected genetically with peridotitic rocks. Recent developments 
 point to a somewhat wider distribution than was formerly 
 thought to be the case, and indicate that platinum not infre- 
 quently is associated with copper-ores. 
 
 The true relations of such elements as arsenic, antimony, bis- 
 muth, selenium and tellurium to igneous magmas are quite un- 
 known. It is possible that arsenic and selenium are most at 
 home in the basic rocks, while antimony, bismuth, and tellu- 
 rium are more apt to occur in siliceous ones. 
 
 We may summarize the observations recorded above as 
 follows: Of the rarer elements whose distribution is better 
 known, lithium, beryllium, cerium and yttrium, zirconium, 
 uranium, thorium, sulphur (as trioxide), fluorine, chlorine, and 
 possibly tin occur most abundantly in sodic magmas; barium 
 in potassic magmas; titanium, vanadium, manganese, nickel, 
 and cobalt in iron-rich magmas; chromium and platinum in 
 magnesian magmas; and phosphorus (?) and chromium (?) in 
 calcic magmas. 
 
 Of the other elements it can only be said that boron and 
 molybdenum are certainly, and zinc, cadmium, lead, antimony, 
 bismuth, and tellurium are possibly, connected with magmas 
 high in silica; sulphur and copper almost certainly, and 
 arsenic and selenium possibly, with those low in silica; while 
 the relations of gold, silver, and mercury are very uncertain, 
 but they are probably most at home in acid rocks. 
 
 This statement, it will be seen, differs from that of Vogt, in 
 that, in the best-established cases, silica plays a less determina- 
 tive role than some of the other major constituents. At the 
 same time, the influence of the general law of the association 
 of the most abundant oxides comes into play, and in a general 
 way the potassic and sodic magmas are most apt to be highly 
 siliceous (though the facts of distribution are shown in them 
 even when silica is low) ; while tljose which are high in iron, 
 magnesia, and lime are most apt to be low in silica. 
 
 Possibly the most striking feature of the distribution as thus 
 shown is the great number of elements which are prone to 
 occur in highly sodic magmas. As is well known, such magmas 
 are those which show most tendency to differentiation and the 
 formation of a great variety of rocks, many of them character- 
 
DISTRIBUTION OF ELEMENTS IN IGNEOUS ROCKS. 755 
 
 ized by the presence of rare or otherwise unusual and interest- 
 ing minerals, and there may probably be some connection be- 
 tween the two features of these magmas. 
 
 It will be noted that some of these elements, as fluorine, 
 chlorine, sulphur (as trioxide), and boron, are among those to 
 which is usually attributed the role of so-called " mineralizing 
 agents," they being supposed to be present as dissolved vapors 
 in the magma and to exert a marked effect on the crystalliza- 
 tion of the mass, the formation of pegmatites, and so forth. It 
 may be argued that such mineralizing and pneumatolytic ele- 
 ments are universally, and presumably quite uniformly, dis- 
 tributed among the rock-magmas, and that their presence in 
 the highly siliceous and sodic rocks is due to the greater vis- 
 cosity of these when molten, which would hinder the escape of 
 gaseous constituents, while the basic magmas are more fluid 
 at low temperatures and would hence allow such gases to escape 
 before or during consolidation. On the other hand, it may be 
 urged that the undeniable distribution, among magmas of dis- 
 tinctly different general chemical characters, of elements to 
 which no such mineralizing or pneumatolytic role can be 
 reasonably assigned, as barium, beryllium, zirconium, titanium, 
 manganese, nickel, chromium, and platinum, would lead to the 
 inference that the apparent distribution of the gaseous and 
 " mineralizing " elements in igneous rocks is real and not 
 dependent on physical causes. The subject is highly complex, 
 and our knowledge of the fundamental facts and of the physico- 
 chemical laws involved is as yet inadequate for solution of the 
 problem, further discussion of which would be outside the scope 
 of this paper. 
 
 V. PRACTICAL CONSIDERATIONS. 
 
 When the facts of the relations of the occurrence of the 
 rarer elements to the chemical characters of igneous magmas 
 are considered, it is evident that their distribution over the 
 earth's surface must be largely determined by that of the petro- 
 graphic provinces. In other words, in any given petrographic 
 province those rarer elements and minerals containing them 
 would be most apt to occur abundantly which show a correla- 
 tive tendency to association with the characteristic major con- 
 stituents of the province. Thus, zirconium-bearing minerals 
 and those of the " rare earths " should be most abundant in 
 
756 DISTRIBUTION OF ELEMENTS IN IGNEOUS ROCKS. 
 
 provinces whose magmas are highly sodic and where such rocks 
 as nephelite-syenite and phonolite are common; while chro- 
 mium, nickel, and platinum would not be expected in these y 
 but would rather be likely to occur in provinces where such 
 rocks as gabbros and peridotites are the prevailing ones. 
 
 This idea has been recognized by Spurr 11 in his proposed/ 
 term of " metallographic provinces," which is based largely on 
 ore-associations, and which he applies more especially to those 
 metals of most economic importance, such as gold, silver, cop- 
 per, lead, and zinc. The probable very close connection between 
 " petrographic " and " metallographic" provinces is pointed out 
 by him, but the two classes seem to be regarded by him as dis- 
 tinct, at least to a certain extent. 
 
 When we deal with such complex bodies as veins and other 
 ore-deposits, the matter is complicated by such factors as geo- 
 logical structure, the existence of faults, the occurrence of the 
 igneous rock as plutonic masses, dikes or effusive flows, climatic 
 conditions, 12 and other disturbing features. These may tend 
 either to favor or to retard the processes of concentration which 
 result in economically-exploitable metalliferous deposits. But 
 these, .though undoubtedly of the highest commercial import- 
 ance, are subsidiary to the more fundamental facts of the dis- 
 tribution of the elements in igneous magmas, and it seems rea- 
 sonable to suppose that a study of these latter features should 
 be susceptible of results of great practical importance. 
 
 It seems that, at present, the knowledge gained by exact 
 chemical analysis that the granites of a certain region contain 
 minute traces of gold or of copper, would be of little use in guid- 
 ing one in the search for the location of a gold- or a copper-mine. 
 The prospector must always remain a valuable, indeed an invalu- 
 able, member of the mining fraternity. We cannot enter here 
 into the vast and vexed subject of the genesis of ore-deposits, 
 but if it were known by future researches that, for instance, 
 gold or copper is normally associated with magmas of a certain 
 general chemical character, a knowledge of this might con- 
 ceivably be of material assistance in a search ; not so much by 
 
 11 Trans., xxxiii., 336 (1902) ; Professional Paper No. 42, U. S. Geological 
 Survey, p. 276 (1905) ; and No. 55, p. 128 (1906). 
 
 12 H. V. Winchell, Popular Science Monthly, vol. Ixxii. , No. 6, pp. 534 to 542 
 (June, 1908). 
 
DISTRIBUTION OF ELEMENTS IN IGNEOUS ROCKS. 757 
 
 indicating the exact position of a favorable location, but, in a 
 more general way, by leading the prospector to confine his 
 attention to a given region of favorable igneous rocks, and to 
 disregard one whose rocks, on theoretical grounds, would prob- 
 ably result in loss of time and effort. Such a knowledge could 
 be gained, not only by the complex and laborious methods of 
 accurate and minutely complete chemical analysis, but more 
 readily, at least in many conceivable cases, by simple petro- 
 graphical examination and field-study of the most abundant 
 and characteristic rock-minerals. 
 
 These considerations, it is true, are scarcely applicable as yet 
 to search for such metals as gold, silver, or copper, concerning 
 the magmatic relations of which our knowledge is of the vaguest 
 description. But, in view of what has been ascertained by 
 petrographical and chemical means of the distribution of other 
 elements, it is not unreasonable to think that we shall eventually 
 obtain well-founded and definite knowledge concerning the dis- 
 tribution of these also. Indeed, the opinion may be expressed 
 that future petrographers will wonder at the fact that, for 
 instance, the presence of such deep-seated and extensive deposits 
 of copper as those at Buite, Mont., and in Shasta county, Cal., 
 was so long unsuspected, and that their discovery came as a 
 surprise. 
 
 At the present time a knowledge of the distribution of the 
 elements is practically applicable, not so much to the metals of 
 greatest human utility, as to certain elements the economic 
 possibilities of which are only recently beginning to be appre- 
 ciated as their chemical and physical properties and the appli- 
 cation of these to commercial and economic purposes are be- 
 coming better known. Some illustrations may be permitted of 
 the practical application of the facts set forth in the preceding 
 pages. 
 
 If, for instance, one were in a new country or were engaged 
 in a search for minerals containing such elements as zirconium, 
 uranium, the rare earths, or beryllium, one would welcome a 
 district of highly sodic igneous rocks, where albitic granites, 
 neph elite-syenites, and phonolites were abundant; in this the 
 chances of success would be most favorable. If the rocks were 
 prevailingly gabbros, diabases, or feldspar-basalts one would 
 reasonably assume that such minerals could not be expected to 
 
758 DISTRIBUTION OP ELEMENTS IN IGNEOUS ROCKS. 
 
 occur, at least in such amount as to repay exploitation, and 
 they would be neglected, or prospected for platinum or chro- 
 mium, let us say. Similarly, if the. platinum metals were found 
 in the sands of a river the water-shed of which covered areas 
 of gabbros, granites, and limestones, one would naturally turn 
 to and explore the first in an attempt to trace the grains to their 
 source, and would, with good reason, leave the others alone. 
 
 Instances of this kind could be multiplied, and, indeed, 
 some present applications of the general principles are now 
 practiced not infrequently, but without any suspicion of the 
 true principles underlying them or realization of their more 
 general applicability. Thus, in certain districts the occurrence 
 of topaz or spodumene may be recognized as generally indi- 
 cating the possible or probable presence of cassiterite, without 
 appreciation of the more general and fundamental fact that the 
 conjunction of tin, fluorine, and lithium is due to the distinctly 
 sodic character of the igneous rocks. 
 
 With increase in our knowledge of the origin of ore-deposits, 
 and a general agreement as to their ultimate source in igneous 
 rocks (whatever be the divergence of views as to the processes 
 of concentration), the probability of the future importance of 
 such observations as have been outlined above, from a practical 
 as well as from a theoretical standpoint, is fairly evident. We 
 cannot as yet predict the probable presence of gold, silver, or 
 copper in economic quantities from the petrographical and 
 chemical study of the country-rock ; but the time may come 
 (and our increasing knowledge of igneous rocks justifies us in 
 a certain degree of confidence that it will come) when such 
 seemingly erudite and impractical studies will be able to guide 
 us in certain regions, as to either the probable absence or pres- 
 ence of ore-bodies of such metals. 
 
 The problem is admittedly very complex, and is one which 
 has not yet been studied enough to do much more than enable 
 us to make a few broad guesses at the truth. But we are 
 beginning to discern some glimmer of light, and the fact 
 that we cannot make out clearly our guiding stars, veiled as 
 they are by the mists of imperfect knowledge, should not 
 cause us to disdain such help as glimpses of them may now 
 afford, or underrate their possible importance when the mists 
 shall have been dispelled. 
 
MANGANESE AND GOLD-ENRICHMENT. 759 
 
 No. 29. 
 
 The Agency of Manganese in the Superficial Alteration and 
 
 Secondary Enrichment of Gold-Deposits in the 
 
 United States.* 
 
 BY WILLIAM H. EMMONS, CHICAGO, ILL. 
 
 (Canal Zone Meeting, November, 1910. Trans., xlii., 3.) 
 CONTENTS. 
 
 PAGE. 
 
 I. INTRODUCTION AND SUMMARY, 760 
 
 II. SALTS CONTAINED IN THE WATERS OP GOLD- AND SILVER-MINES IN 
 
 NON-CALCAREOUS KOCKS, 764 
 
 1, Sulphates; 2, Chlorides; 3, Carbonates and Alkaline Earths; 
 4, Alumina ; 5, Nitrates ; 6, Phosphates ; 7, Silica ; 8, Iron ; 
 
 9, Manganese; 10, Copper. 
 
 III. CHEMICAL EXPERIMENTS IN THE SOLUTION AND DEPOSITION OF GOLD, 771 
 
 IV. DISCUSSION OF EXPERIMENT.*, . . 776 
 
 1, Nitrates ; 2, Manganese Oxides ; 3, Lead Oxides ; 4, Ferric Com- 
 pounds ; 5, Efficiency of Ferric Iron and of Cupric Copper to 
 Supply Nascent Chlorine, Compared with that of Manganitic 
 Manganese ; 6, The Amount of Chlorine Necessary for the So- 
 lution of Gold in the Presence of Manganese Compounds ; 7, 
 The Precipitation of Gold. 
 V. THE TRANSFER OF GOLD IN COLD SOLUTIONS, . . . . . 785 
 
 1, Kestatement of the Processes as Related to Secondary Enrich- 
 ment ; 2, Association of Gold with Manganese Oxides ; 3, The 
 Oscillating, Descending, Undulatory Water-Table ; 4, The 
 Several Successive Zones in Depth ; 5, Criteria for the Recogni- 
 tion of Secondary Enrichment ; 6, Lateral Migration of Man- 
 ganese-Salts from the Country- Rock to the Ore ; 7, Concentra- 
 tion in the Oxidized Zone ; 8, Vertical Relation of Deep-Seated 
 Enrichment of Gold to Chalcocitization ; 9, Vertical Relations 
 of Silver-Gold and Gold-Silver Ore in Deposits Carrying Both 
 Metals. 
 
 VI. REVIEW OF MINING-DISTRICTS, 805 
 
 Gold-Provinces of the United States, .806 
 
 1, Southern Appalachian Districts ; 2, Black Hills, S. D. ; 3, Tread- 
 well Mine, Alaska; 4, Berner's Bay, Alaska; 5, Mother Lode 
 District, Cal. ; 6, Nevada City and Grass Valley, Cal. ; 7, Ophir 
 District, Cal. ; 8, Silver Peak, Nev. ; 9, Philipsburg, Mont. ; 
 
 10, Other Montana Districts; 11, Edgemont, Nev. ; 12, Lead- 
 ville, Colo. ; 13, Georgetown, Colo. , Silver-Lead Deposits ; 14, 
 Auriferous Deposits of the Georgetown Quadrangle, Colo. ; 15, 
 San Juan, Colo. ; 16, Cripple Creek, Colo. ; 17, Summit Dis- 
 trict, Colo. ; 18, Bodie, Cal. ; 19, Exposed Treasure Mine, Cal. ; 
 20, Tonopah, Nev. ; 21, Goldfield, Nev. ; 22, Manhattan, Nev. ; 
 23, Annie Laurie Mine, Utah ; 24, Bullfrog District, Nev. ; 25, 
 Gold Circle, Nev. ; 26, Delamar Mine, Nev. 
 
 * Published_by permission of the Director of the U. S. Geological Survey. 
 
760 MANGANESE AND GOLD-ENRICHMENT. 
 
 I. INTRODUCTION AND SUMMARY. 
 
 FERRIC iron, cupric copper, and manganitic manganese are 
 present in many mineral waters, and under certain conditions 
 any one of them will liberate chlorine from sodium chloride in 
 acid solutions. Nascent chlorine dissolves gold. Each of these 
 compounds will thus release chlorine at high temperatures, and 
 at low temperatures in concentrated solutions. In cold, dilute 
 solutions, ferric iron will not give nascent chlorine in appreci- 
 able quantity in 34 days, and cupric copper is probably even 
 less efficient ; but manganitic compounds (supplied by pyrolu- 
 site, etc.) liberate chlorine very readily. In a cold solution con- 
 taining only 1,418 parts of chlorine per million, considerable 
 gold is dissolved in 14 days when manganese is present. It 
 should be expected, then, that those auriferous deposits, the 
 gangues of which contain manganese, would show the effects of 
 the solution and migration of gold more clearly than non-man- 
 ganiferous ores. 
 
 Gold thus dissolved is precipitated by ferrous sulphate. It is, 
 therefore, natural to suppose that gold in such solutions could 
 not migrate far through rocks containing pyrite, since it would 
 be quickly precipitated by the ferrous sulphate produced through 
 the action of air, oxidizing waters, or the gold-solution itself, 
 upon the pyrite. But the dioxide and higher oxides of manga- 
 nese react immediately upon ferrous sulphate, converting it to 
 ferric sulphate, which is not a precipitant of gold. Conse- 
 quently, manganese is not only favorable to the solution of gold 
 in cold, dilute mineral waters, but it also inhibits the precipitat- 
 ing action of ferrous salts, and thus permits the gold to travel 
 further before final deposition. 
 
 These statements apply to the action of surface-waters de- 
 scending through the upper parts of an auriferous ore-deposit, 
 since such waters are cold, dilute, acid (i.e., oxidizing) solutions. 
 In deeper zones, where they attack other minerals, they lose 
 acidity, until the manganese compounds, stable under oxidiz- 
 ing conditions, are precipitated together with the gold. Thus, 
 manganite, as well as limonite and kaolin, is frequently found 
 in secondary (i.e., dissolved and reprecipitated) gold-ores. More- 
 over, in the precipitation of secondary copper and silver sul- 
 phides, ferrous sulphate is generally formed ; and, consequently, 
 the secondary silver or copper sulphides frequently contain gold. 
 
MANGANESE AND GOLD-ENRICHMENT. 761 
 
 Those deposits in the United States in which a secondary 
 enrichment in gold is believed to have taken place are, almost 
 without exception, manganiferous. Since secondary enrich- 
 ment is produced by the downward migration, instead of the 
 superficial removal and accumulation, of the gold, it should 
 follow that both gold-placers and outcrops rich in gold would 
 be found more extensively in connection with non-manganif- 
 erous deposits ; and this inference is believed to be confirmed 
 by field-observations. 
 
 The problem is not as simple as this preliminary statement 
 of it may seem to indicate. Some of the numerous and com- 
 plex data bearing upon it are collated and discussed in the 
 pages that follow. 
 
 Among the papers which treat the superficial alteration and 
 secondary enrichment of copper-, gold-, and silver-deposits, are 
 those of S. F. Emmons, 1 Weed, 2 Penrose, 3 Winchell, 4 Van Hise, 5 
 Kemp, 6 and Eickard. 7 The processes upon which the changes 
 depend are clearly outlined in these, and subsequent work has, 
 in a large measure, confirmed the premises stated. The chem- 
 ical laws and physical conditions controlling secondary enrich- 
 ment have been reviewed in several reports more recently 
 published and examples illustrating the processes have been 
 multiplied. The papers of Lindgren, Eansome, Spencer, Bout- 
 well, Irving, Graton, McCaskey, Spurr, and Garrey and Ball 
 are particularly valuable. Such work has shown that the sec- 
 ondary enrichment of pyritic copper-deposits is an important 
 and almost universal process; that many silver-deposits are 
 enriched by superficial agencies ; but that many gold-deposits 
 do not show deep-seated secondary enrichment. 
 
 T. A. Eickard 8 has brought out clearly the processes by 
 
 1 The Secondary Enrichment of Ore-Deposits, Trans., xxx., 177 to 217 (1900). 
 
 2 The Enrichment of Gold and Silver Veins, Trans., xxx., 424 to 448 (1900). 
 
 3 The Superficial Alteration of Ore- Deposits, Journal of Geology, vol. ii., No. 3, 
 pp. 288 to 317 (Apr. -May, 1904). 
 
 4 Bulletin of the Geological Society of America, vol. xiv., pp. 269 to 276 (1902). 
 
 5 Some Principles Controlling the Deposition of Ores, Trans., xxx., 27 to 177 
 (1900). 
 
 6 Secondary Enrichment in Ore-Deposits of Copper, Economic Geology, vol. L, 
 No. 1, pp. 11 to 25 (Oct.-Nov., 1905). 
 
 7 The Formation of Bonanzas in the Upper Portions of Gold-Veins, Trans., 
 xxxi., 198 to 220 (1901). 
 
 8 Loc. cit. 
 
 48 
 
762 MANGANESE AND GOLD-ENRICHMENT. 
 
 which gold-deposits may be enriched relatively near the sur- 
 face in the oxidized zone by the removal of valueless minerals 
 which are more readily dissolved than gold. On the problem 
 of deeper-seated precipitation of gold below the zone of oxi- 
 dation there is less evidence. In some mines, however, the 
 transportation and deep-seated precipitation of gold is clearly 
 shown, as was pointed out long ago by Weed. 
 
 While engaged in the investigation of certain auriferous 
 deposits in the Philipsburg quadrangle, Montana, for the U. S. 
 Geological Survey, I was confronted by evidence gained in two 
 important mines, which seemed to be conflicting on this point. 
 In one of them, the Cable mine, there was no evidence that 
 gold had been concentrated by cold solutions below the zone 
 of oxidation, but in the Granite-Bimetallic lode there was 
 enrichment of both gold and silver below the zone of leached 
 oxides. The richer silver-minerals occur in cracks and in 
 small fissures cutting across the banding of the primary 
 deposits and are related very distinctly to the present topog- 
 raphy of the country. The evidence therefore appeared to be 
 conclusive that these minerals were deposited by cold mineral 
 waters and that their metallic contents had been dissolved from 
 portions of the lode higher up. The enriched silver-ore carries 
 considerably more gold than the primary ore in the bottom of 
 the mine, and more than the upper portion of the oxidized 
 zone, including the outcrop. No placers have been formed from 
 this deposit, although it has produced considerable gold. On 
 the other hand, important placers have been developed just 
 below the outcrop at the Cable mine. Clearly there has been 
 a kind of selection in the operation of the processes of solution 
 and precipitation of gold. 
 
 Although the ores of the two deposits differ in other respects, 
 the most striking difference is in the manganese-content. The 
 abundance of manganese in the Granite-Bimetallic manifests 
 itself in the characteristic coloration of the ores pink in the 
 unoxidized, brown or black in the oxidized zone. In the 
 Cable, manganese is practically absent. The difference in 
 manganese-content is so striking as to suggest a causal rela- 
 tionship with the equally-marked difference in the amount of 
 secondary enrichment. 
 
 The use of manganese in the chlorination process to give 
 
MANGANESE AND GOLD-ENRICHMENT. 763 
 
 free chlorine, which dissolves gold, is well known. Le Conte 9 
 said as early as 1879 that free chlorine is the most important 
 natural solvent of gold, and Richard Pearce, in his presiden- 
 tial address before the Colorado Scientific Society, in 1885, 
 recorded experiments in which gold had been dissolved in hot 
 sulphate solutions with common salt and manganese dioxide. 10 
 Don obtained similar results with more dilute solutions. 11 It 
 appeared desirable, therefore, to ascertain whether these reac- 
 tions are carried on appreciably in cold dilute solutions similar 
 to mine-waters ; and Nicholas Sankowsky and Clarence Russell, 
 in a seminar on the Chemistry of Ore-Deposits, which I con- 
 ducted at the University of Chicago, compiled all available 
 analyses of waters from gold- and silver-mines in non-calcareous, 
 rocks. A. D. Brokaw conducted a series of experiments at my 
 request, using cold dilute solutions of compositions suggested 
 by the analyses. He performed other experiments also, show- 
 ing the action of manganese dioxide on ferrous salts, which are 
 applicable to the study of the precipitation of gold. During 
 the progress of this investigation, "W. J. McCaughey, of the 
 Bureau of the Mint, Washington, D. C., published his valua- 
 ble paper on the solvent effect of ferric and cupric salt solutions 
 upon gold, 12 and this in a large measure supplemented the work 
 carried on in the seminars at the University of Chicago, 
 
 The experiments conducted by Brokaw showed that man- 
 ganese in the presence of chlorides and sulphates is very 
 much more efficient in the reactions dissolving gold than 
 are the other salts which are common in mine-waters. To 
 verify these results by field-evidence, the review of the lit- 
 erature was taken up in greater detail, and there also the 
 results indicate a marked difference in the behavior of the 
 cold dilute mineral waters in the presence and in the absence 
 of manganese. Lindgren's classification of the gold-deposits of 
 North America has been of great value in reviewing these 
 deposits; since in the United States manganese is rarely a 
 garigue-mineral in the primary gold-deposits as old as the 
 early Cretaceous California gold-veins, whereas it is frequently 
 
 9 Elements of Geology, p. 285. 
 
 10 Proceedings of the Colorado Scientific Society, vol. ii., p. 3 (1885-87). 
 
 11 Trans., xxvii., 654 (1897) ; p. 176, this volume. 
 
 18 Journal of the American Chemical Society, vol. xxxi., No. 12, pp. 1261 to 1270 
 (Dec., 1909). 
 
764 MANGANESE AND GOLD-ENRICHMENT. 
 
 present in very appreciable quantities in those deposits which 
 were formed nearer the surface and which are related to intru- 
 sives of Tertiary age. Possibly this difference is due to con- 
 ditions of temperature and pressure which prevailed when the 
 deposits were formed. 13 Since there are no data which show 
 the effect of highly-carbonated waters on these reactions, I 
 have as far as possible eliminated examples of gold-deposits in 
 limestone, and the discussion is confined mainly to deposits in 
 non-calcareous rocks. I have not attempted to review exhaust- 
 ively the evidence afforded by deposits outside of the United 
 States with respect to the hypothesis suggested, but some of 
 these deposits appear to supply accurate confirmatory data. 
 
 In a statistical study of outcrops, to ascertain whether gold 
 is more extensively leached in manganiferous lodes than in the 
 outcrops of those which do not carry manganese, and whether 
 placers are more frequently developed in connection with non- 
 man ganiferous lodes, the reports of Dr. R. W. Raymond, 14 
 written soon after the discoveries of many of the deposits, have 
 been of great value. 
 
 I wish to acknowledge my indebtedness to my colleagues of 
 the U. S. Geological Survey, and to many other geologists 
 whose accurate observations I have drawn upon to test the 
 hypothesis. Their conclusions respecting the secondary en- 
 richment of gold appear to support the hypothesis, and, differ- 
 ing as they do with respect to the migration of gold in partic- 
 ular deposits, they become reconciled when inspected from 
 this view-point, and thus they are themselves supported. Dr. 
 R. C. Wells, of the U. S. Geological Survey, has read critically 
 certain portions of this paper, where the principles of physical 
 chemistry are involved. 
 
 II. SALTS CONTAINED IN THE WATERS or GOLD- AND SILVER- 
 MINES IN NON-CALCAREOUS ROCKS. 
 
 The composition of mine-waters depends upon the character 
 of the ore and wall-rock and the position of the deposit with 
 respect to bodies of salt water. There are certain compounds 
 which are generally present, and some which nearly always 
 predominate. Of the few analyses which have been made of 
 
 13 W. Linlgren, The Relation of Ore-Deposition to Physical Conditions, Eco- 
 nomic Geology, vol. ii., No. 2, pp. 105 to 127 (Mar. -Apr., 1907). 
 
 14 Mines and Mining West of the Rocky Mountains (1868-1875). 
 
MANGANESE AND GOLD-ENRICHMENT. 765 
 
 waters from gold-mines, a large proportion are incomplete; 
 and it is not always stated whether compounds not reported 
 were looked for. Sankowsky and Russell, utilizing all data 
 available to them, recalculated the analyses to the ionic form- 
 of statement, and where necessary to parts per million, and 
 made a general average of the results. Where compounds 
 were not reported in the analyses it was assumed that they 
 were not present. Arsenic, antimony, and other elements, 
 small traces of which must be present in some waters, are not 
 reported. Since the averages were obtained by dividing the 
 sums by the total number of analyses (29) and not by the 
 number of analyses showing a particular element, and since 
 some analyses are incomplete, any corrections applied for this 
 source of error would tend to increase the number of parts per 
 million indicated. On the other hand, some of the mine-waters 
 w r ere taken from places protected from the more active vadose 
 circulation, and are clearly more concentrated than the major 
 part of the waters. The average of analyses, although a rude 
 approximation, is useful, since it gives some quantitative value 
 to their factor in the problem, and indicates the general nature 
 of the cold solutions in which the metals are transported. 
 
 TABLE I. Average of 29 Analyses of Waters taken from Gold-, 
 
 Silver-, and Gold-Silver Mines in Non- Calcareous Rocks. 
 
 (Compiled by N. Sankowsky and C. Russell.) 
 
 
 
 Number of 
 
 Absent or 
 
 
 Parts Per Million. 
 
 Determinations. 
 
 Not Determined. 
 
 Cla... 
 
 873.10 
 
 22 
 
 7 
 
 so, 
 
 .... 7,292.29 
 
 13 
 
 16 
 
 C0 3 
 
 77.59 
 
 7 
 
 22 
 
 N0 3 a 
 
 0.06 
 
 1 
 
 28 
 
 P0 4 
 
 0.00 
 
 traces in 2 
 
 27 
 
 SiO, 
 
 34.94 
 
 12 
 
 17 
 
 K 
 
 17.25 
 
 7 
 
 22 
 
 Na 
 
 261.20 
 
 9 
 
 20 
 
 Li 
 
 0.10 
 
 1 
 
 28 
 
 Ca 
 
 295.00 
 
 11 
 
 18 
 
 Sr 
 
 0.06 
 
 1 
 
 28 
 
 Mg 
 
 242.44 
 
 9 
 
 20 
 
 Al 
 
 333.65 
 
 6 
 
 23 
 
 Mn 
 
 30.91 
 
 6 
 
 23 
 
 Ni . 
 
 trace 
 
 traces in 3 
 
 26 
 
 Co 
 
 trace 
 
 traces in 3 
 
 26 
 
 Cu 
 
 5.09 
 
 2 
 
 27 
 
 Zn 
 
 2.70 
 
 5 
 
 24 
 
 Fen 
 
 277.66 
 
 22 
 
 7 
 
 Feiii 
 
 603.07 
 
 25 
 
 4 
 
 H (in acids), 
 
 97.26 
 
 10 
 
 19 
 
 Probably too high (see discussion). 
 
766 MANGANESE AND GOLD-ENRICHMENT. 
 
 1. Sulphates. 
 
 Primary gold-ores generally carry pyrite, which, oxidizing 
 at or near the surface, yields ferrous sulphate, ferric sulphate, 
 and sulphuric acid. The acid is not formed directly from 
 galena, PbS, or from zinc-blende, ZnS, but pyrite, FeS 2 , carries 
 more sulphur than is required to supply S0 4 radical to satisfy 
 the iron, even if ferric sulphate, Fe 2 (S0 4 ) 3 , is formed instead of 
 FeSO 4 . As lately shown by Buehler and Gottschalk, 15 galena 
 and zinc-blende dissolve very much more slowly in the absence 
 of FeS 2 . The reaction probably requires free acid, which the 
 iron sulphide, owing to its excess of sulphur, supplies. The 
 sulphuric acid from pyrite is increased also by the hydroliza- 
 tion of ferric sulphate and the deposition of limonite . 
 
 In Table I. the sulphate radical (7,292 parts per million) is 
 nearly ten times as abundant as all other negative ions and 
 is also in excess of bases, so that on any basis of adjustment to 
 form salts much H 2 S0 4 remains. The table shows also an aver- 
 age of 97.26 parts per million of hydrogen in acid. In view of 
 the low atomic weight of hydrogen, this indicates the strongly 
 acid character of the solutions. 
 
 2. Chlorides. 
 
 Chlorine is present in most mine-waters. In 22 out of the 
 29 analyses it is reported as traces or as determined quantities. 
 The average of 29 analyses shows 873 parts per million, but if 
 the one abnormally-rich sodium-chloride water of Silver Islet, 
 Lake Superior, is excluded, the remaining 28 analyses show 
 but 111 parts per million. This figure is probably a better 
 average. It would be further reduced some 2 or 3 parts by 
 excluding the waters of the Geyser mine, Silver Cliff, Colo., 
 which may have come from a deep source. With these two 
 exceptions, it is noteworthy that the waters from mines remote 
 from salt water contain less chlorine than those near the sea or 
 in undrained areas. The distribution of chlorine is an impor- 
 tant element in the migration of gold, and therefore I shall con- 
 sider the sources of chlorine in some detail. 
 
 The salt in sedimentary rocks may be dissolved by ground- 
 water. From the available analyses it appears that this source 
 is of less importance than would be supposed. The chlorine- 
 
 15 Economic Geology, vol. v., No. 1, p. 30 (Jan., 1910). 
 
MANGANESE AND GOLD-ENRICHMENT. 767 
 
 content of composite samples of 78 shales and of 253 sand- 
 stones was only a trace, while an analysis of a composite of 345 
 limestones showed only 0.02 per cent. 16 A few rock-making 
 minerals, such as chlor-apatite, scapolite, haiiyne, and nosean, 
 contain combined chlorine ; but of these all but apatite occur 
 mainly in very rare types of rocks. In some rocks chlorine is 
 present probably as NaCl in the solid particles contained in 
 fluid inclusions. The work of R. T. Chamberlin, A. Gautier, 
 and others has shown that many granular igneous rocks, when 
 heated to high temperatures, give off gases equal to several 
 times their own volume. While further inquiry of this char- 
 acter is desirable, it is probably true that in general but little 
 chlorine is present in such gases. But gases from certain 
 volcanic rocks, such as obsidian, often contain a high proportion 
 of chlorine and chlorides. Albert Brun 17 has shown that some 
 of the Krakatoa lavas contain gases which equal about one-half 
 the volume of the rock, and that more than half of such gases 
 consists of chlorine, hydrochloric acid, and sulphur mono- 
 chloride. 
 
 Apatite, though widespread in igneous rocks, is a very stable 
 mineral, and consequently cannot be looked upon as an important 
 source of chlorine, although it may contribute small amounts 
 when exposed to favorable conditions of weathering. The aver- 
 age chlorine-content of igneous rocks is, according to F. W. 
 Clarke, 0.07 per cent. 
 
 Chlorine is present in nearly all natural waters. Its chief 
 source is from finely-divided salt or salt water from the sea and 
 from other bodies of salt water. The salt is carried by the wind 
 and precipitated with rain. 18 The amount of chlorine in natu- 
 ral waters varies with remarkable constancy with the distance 
 from the shore ; several determinations very near the seashore 
 show from 10 to 30 parts of chlorine per million; a few miles 
 away it is generally about 6 parts per million ; 50 miles from 
 shore it is generally less than 1 part per million. A surface- 
 
 16 F. W. Clarke, Bulletin No. 330, U. S. Geological Survey, p. 27 (1908). 
 
 17 Quelques Recherches sur le Volcanisme aux Volcans de Java. Cinquime 
 partie. Le Krakatau. Archives des Sciences physiques et naturelles, Geneve, vol. 
 xxviii., No. 7 (Juillet, 1909). 
 
 18 D. D. Jackson, The Normal Distribution of Chlorine in the Natural Waters 
 of New York and New England, Water Supply and Irrigation Paper No. 144, U. S. 
 Geological Survey (1905). 
 
768 MANGANESE AND GOLD-ENRICHMENT. 
 
 water from a reservoir at Leadville contained 1.14 parts of Cl 
 per million. 19 The isochlores parallel the shore-line with great 
 regularity, as indicated in the map, Fig. 1, taken from Jackson's 
 report. The amount of chlorine contributed from this source 
 even near the seashore appears small (from 6 to 10 parts per 
 million) ; but it may be furthur concentrated in the solutions 
 by evaporation or by reaction with silver, lead, etc., forming 
 chlorides, which in the superficial zone may subsequently be 
 changed to other compounds. In arid countries, as suggested 
 by C. B. Keyes, dust containing salt doubtless contributes 
 chlorine to the mine-waters. Penrose, 20 discussing the distri- 
 bution of the chloride ores, pointed out long ago that these 
 minerals form most abundantly in undrained areas. 
 
 3. Carbonates and Alkaline Earths. 
 
 The analyses in Table I. do not include those from mines in 
 limestones. The carbonate reported gives an average of 77 
 parts per million. In the acid waters under consideration, the 
 carbonates of the bases would necessarily be present as bicar- 
 boiiates, although this fact is not indicated in the analyses. 
 
 Even in non-calcareous rocks considerable calcium (295 parts 
 per million) and magnesium (242 parts) are carried by the 
 waters. They are derived in part from reactions between the 
 acid sulphates and the silicates of the wall-rock. 
 
 4. Alumina. 
 
 In some waters aluminum sulphate is abundant (the average 
 of aluminum, 333 parts per million). It forms where sulphate 
 waters attack kaolin, setting free Si0 2 and taking alumina into 
 solution. The above average is probably high on account of 
 one concentrated alum-water in a Comstock mine. 21 
 
 5. Nitrates. 
 
 Nitrates are not abundant in mine-waters. In one analysis 
 only 22 is N0 3 reported (1.60 parts per million), and this in a 
 deep-seated water of questionable genesis. 
 
 19 S. F. Emmons, Geology and Mining Industry of Leadville, Colorado, Mono- 
 graph No. XII. , U. S. Geological Survey, p. 552 (1886). 
 
 20 Journal of Geology, vol. ii., No. 3, p. 314 (April-May, 1894). 
 
 21 Bulletin of the Department of Geology, University of California, vol. iv., No. 10, 
 p. 192 (1904-06). 
 
 22 Geyser Mine, Silver Cliff, Colo. See S. F. Emmons, Seventeenth Annual Re- 
 port, U. S. Geological Survey, Part II., p. 462 (1895-96). 
 
MANGANESE AND GOLD-ENRICHMENT. 
 
 769 
 
770 MANGANESE AND GOLD-ENRICHMENT. 
 
 6. Phosphates. 
 
 Traces only of P0 4 are reported from two mine-waters ; others 
 contained none, if determinations were made. 
 
 7. Silica. 
 
 Silica (35 parts per million) appears high for acid waters. 
 The analyses include a manganiferous sulphate water from the 
 Gomstock, abnormally high in silica. 23 
 
 8. Iron. 
 
 Iron is the most abundant metal in the waters of gold-mines. 
 Ferric iron (603 parts per million) is, according to these analy- 
 ses, more than twice as abundant as ferrous iron (277 parts per 
 million). Probably too little attention has been given to the 
 state of oxidation of iron in unaltered mine-waters. Ferrous 
 salts in solution, when exposed to air, rapidly become ferric ; 
 yet, so far as I know, no mine-water which has clearly not had 
 access to air has been examined with respect to the state of 
 oxidation of the iron. Ferrous iron is much more abundant 
 below than above the water-table. 
 
 9. Manganese. 
 
 If manganiferous minerals are present in the primary ore, 
 they oxidize in the upper portion of the deposit to manganese 
 dioxide or other high oxides of manganese; and these, in turn, 
 oxidize ferrous sulphate, in the presence of sulphuric acid, to 
 ferric sulphate. Consequently, the iron in manganiferous waters 
 is likely to be in the oxidized state. 
 
 10. Copper. 
 
 One analysis shows 147 parts of copper per million. Two 
 other analyses show traces. Small amounts must be present in 
 many other waters, since gold-ores often carry copper. Possibly, 
 small traces of the heavy metals were not looked for in many 
 of the waters analyzed. 
 
 23 Bulletin of the Department of Geology, University of California, vol. iv., No. 10, 
 p. 192 (1904-06). 
 
MANGANESE AND GOLD-ENRICHMENT. 771 
 
 III. CHEMICAL EXPERIMENTS IN THE SOLUTION AND 
 DEPOSITION OF GOLD. 
 
 The superficial alteration of gold-deposits and the migration 
 of gold in the deposits take place at. low temperatures. At the 
 very surface the temperatures range between and 50 C. 
 and pressures do not exceed one atmosphere. At the normal 
 gradient of increase, the temperatures, even several thousand 
 feet below water-level, would not exceed 100 C., and in the 
 main are considerably lower. The general character and, ap- 
 proximately, the concentration of the solutions are known from 
 the analyses of mine-waters. The conditions are fairly constant. 
 From the mass of chemical data relating to the subject, the fol- 
 lowing experiments seem to be particularly suggestive in con- 
 nection with the present problem. 
 
 1. Stokes 24 placed gold leaf in a solution containing 25 g. per 
 liter of ferric sulphate, and, after heating to 200 C., found that 
 not a trace of gold had been deposited in the cold part of the 
 sealed tube in which the experiment was carried on. This ex- 
 periment does not confirm the statement frequently made that 
 ferric sulphate will dissolve gold. 
 
 2. Don 25 exposed to air finely-divided gold and auriferous 
 sulphide ores in solutions containing from 1 to 20 g. of ferric 
 chloride and ferric sulphate per liter of water ; and after several 
 months no gold had been dissolved. Presumably the gold was 
 not mixed with the sulphide in all of the experiments. 
 
 3. "W. J. McCaughey, 26 upon boiling for several hours 50 cc. 
 of HC1 (sp. gr. 1.178) diluted to 125 cc. with 250 mg. of gold, 
 found there was no loss of gold. 
 
 4. In a bent tube Stokes 27 heated gold leaf for 16 hr. at 
 200 C. in a solution composed of 85 g. of cupric chloride and 
 133 cc. of 20 per cent. HC1 in a liter of water. The gold leaf was 
 dissolved and redeposited in the upper portion of the tube. He 
 writes the reaction as follows : 
 
 Au + 3 CuCl 2 ** AuCl 3 + 3 CuCl. 
 
 24 Economic Geology, vol. i., No. 7, p. 650 (July-Aug., 1906). 
 
 25 Trans., xxvii., 598 (1897) ; p. 173, this volume. 
 
 26 Journal of the American Chemical Society, vol. xxxi., No. 12, p. 1263 (Dec., 
 1909). 
 
 27 Op. cit., vol. i., p 649. 
 
772 
 
 MANGANESE AND GOLD-ENRICHMENT. 
 
 5. Stokes 28 heated gold leaf to 200 C. in a closed tube con- 
 taining a solution of 25 g. of ferric sulphate and 0.01 g. of NaCl. 
 Gold was dissolved in 40 hours. 
 
 6. Stokes 29 found that at 200 C. gold leaf was dissolved in a 
 mixture of 2 parts of 20 per cent, solution of ferric chloride and 
 1 part of 20 per cent, solution of HC1. 
 
 7. W. J. McCaughey 30 dissolved gold at from 38 to 43 C., 
 in hydrochloric acid solutions of ferric sulphate. The results 
 are indicated by the curves in Fig. 2. Solution A contained 
 1 g. of iron, introduced as ferric sulphate, and 25 cc. of HC1 (sp. 
 
 80 100 
 
 TIME, HOURS 
 
 1-,'U 
 
 140 
 
 160 
 
 180 
 
 FIG. 2. DIAGRAM SHOWING THE BATE OF SOLUTION OF GOLD IN CONCEN- 
 TRATED SOLUTIONS OF HYDROCHLORIC ACID AND FERRIC SULPHATE. 
 (Illustrating Experiment No. 7, by McCaughey. ) 
 
 gr. 1.178) in a solution diluted to 125 cc. containing 250 mg. of 
 gold rolled to 0.009 in. Solution B contained the same amount 
 of iron sulphate and 50 cc. of HC1. Solution C contained 2 g. 
 of Fe as ferric sulphate and 25 cc. of HC1. Solution D had 
 twice the concentration of A. The diagram shows the amount 
 of gold dissolved after different periods of treatment. 
 
 8. McCaughey 31 found that gold is dissolved at from 38 to 
 43 C. in a strong solution of cupric chloride and HC1. The 
 
 28 Economic Geology, vol. i., No. 7, p. 650 (July- Aug., 1906). 
 
 29 Idem, p. 650. 
 
 30 Journal of the American Chemical Society, vol. xxxi., No. 12, p. 1263 (Dec., 
 1909). 
 
 31 Idem, p. 1264. 
 
MANGANESE AND GOLD-ENRICHMENT. 
 
 773 
 
 amounts dissolved are shown by the curves in Fig. 3. Solution 
 A contained 1 g. of Cu as cupric chloride and 25 cc. of HC1 
 (sp. gr. 1,178) ; solution _B, 1 g. of Cu as CuCl 2 and 50 cc. of 
 HC1; solution (7, 2 g. of Cu as CuCl 2 and 25 cc. of HC1; and 
 solution D, 2 g. of Cu as CuCl 2 and 50 cc. of HC1; the final so- 
 lution being in all cases diluted to the volume of 125 cc. The 
 diagram shows that D, which was twice as concentrated as A, 
 dissolved about 12 times as much gold. 
 
 20 
 
 40 
 
 GO 80 100 
 
 TIME, HOURS 
 
 180 
 
 FIG. 3. DIAGRAM SHOWING THE SOLUBILITY OF GOLD IN CONCENTRATED 
 
 SOLUTIONS OF HYDROCHLORIC ACID AND CUPRIC CHLORIDE. 
 
 (Illustrating Experiment No. 8, by McCaughey.) 
 
 9. Richard Pearce 32 placed native gold in a flask contain- 
 ing hydrated manganese dioxide with 40 g. of salt and 5 or 6 
 drops of H 2 S0 4 . After heating for 12 hr. appreciable gold had 
 been dissolved. 
 
 10. T. A. Rickard 33 extracted 99.9 per cent, of the gold 
 from rich manganiferous ore with a solution of ferric sulphate, 
 common salt, and a little H 2 SO 4 . 
 
 11. Don 34 found that 1 part of HC1 in 1,250 parts of H 2 0, in 
 the presence of Mn0 2 , dissolves appreciable gold. 
 
 A number of experiments on the solubility of gold in cold 
 dilute solutions were made at my request by A. D. Brokaw. 35 
 The nature of these experiments is shown by the following 
 statements, in which (a) and (b) represent duplicate tests : 
 
 32 Trans., xxii., 739 (1893). 
 
 33 Trans., xxvi., 978 (1896). 
 
 34 Trans., xxvii., 599 (1897) ; p. 175, this volume. 
 
 85 Journal of Geology, vol. xviii., No. 4, pp. 321 to 326 (May-June, 1910). 
 
774 MANGANESE AND GOLD-ENRICHMENT. 
 
 12. Fe 2 (S0 4 ) 3 + H 2 S0 4 + Au. 
 
 (a) no weighable loss. (34 days.) 
 (6) no weighable loss. 
 
 13. Fe 2 (SO 4 ) 3 + H 2 S0 4 + Mn0 2 + Au. 
 
 (a) no weighable loss. (34 days.) 
 (6) 0.00017 g. loss. c 
 
 c This duplicate was found to contain a trace of Cl, which probably accounts for 
 the loss. 
 
 14. FeCl 3 + HC1 + Au. 
 
 (a) no weighable loss. (34 days.) 
 (6) no weighable loss. 
 
 15. FeCl 3 + HC1 + Mn0 2 + Au. 
 
 (a) 0.01640 g. loss. Area of plate, 383 sq. mm. 
 
 (34 days.) 
 (6) 0.01502 g. loss. Area of plate, 348 sq. mm. 
 
 In each experiment the volume of the solution was 50 cc. 
 The solution was one-tenth normal with respect to ferric salt 
 and to acid. In experiments 13 and 15, 1 g. of powdered 
 manganese dioxide was also added. The gold, assaying 999 
 fine, was rolled to a thickness of about 0.002 in. ; cut into 
 pieces of about 350 sq. mm. area, and one piece, weighing about 
 0.15 g., was used in each duplicate. 
 
 To approximate natural waters more closely, a solution was 
 made one-tenth normal as to ferric sulphate and sulphuric acid, 
 and one twenty-fifth normal as to sodium chloride. Then 1 g. 
 of powdered manganese dioxide was added to 50 cc. of the 
 solution, and the experiment was repeated. The time was 14 
 days. 
 
 16a. Fe 2 (S0 4 ) 3 + H 2 S0 4 + STaCl + Au. 
 
 ~No weighable loss. 
 166. Fe 2 (S0 4 ) 3 + H 2 S0 4 + STaCl + Mn0 2 + Au. 
 
 Loss of gold, 0.00505 gram. 
 
 The loss is comparable to that found in experiment 15, allow- 
 
 ing for the shorter time and the greater dilution of the chloride. 
 
 To determine whether the free acid or the ferric chloride is 
 
MANGANESE AND GOLD-ENRICHMENT. 
 
 775 
 
 the solvent, experiment 17 was made, in which 50 cc. of one- 
 tenth normal HC1 was used with 1 g. of powdered Mn0 2 . 
 
 17. HC1 + Mn0 2 + Au. 
 
 Loss of Au, 0.01369 g. Time, 14 days. 
 
 In experiment 18, sodium hydroxide was added to 50 cc. of 
 one-tenth normal ferric chloride solution until the precipitate 
 
 0.04 0.08 0.12 0.16 0.20 0.25 
 
 GRAMS FE AS FERROUS SALT IN 125 cc. 
 
 FIG. 4. DIAGRAM ILLUSTRATING THE EFFECT OF FERROUS SULPHATE IN 
 SUPPRESSING THE SOLUBILITY OF GOLD IN FERRIC SULPHATE SOLUTIONS, 
 WHERE GOLD is DISSOLVED AS CHLORIDE. 
 
 (Illustrating Experiment No. 19, by McCaughey. ) 
 
 formed barely re-dissolved on shaking, after which 1 g. of 
 powdered Mn0 2 was added. 
 
 18. FeCl 3 + Mn0 2 + Au. 
 
 Loss of Au, 0.00062 g. Time, 14 days. 
 
776 MANGANESE AND GOLD-ENRICHMENT. 
 
 These results show, that in the presence of manganese 
 dioxide, free hydrochloric acid is more efficient than ferric 
 solutions. 36 
 
 19. McCaughey's experiments show the effect of very small 
 amounts of ferrous sulphate on solutions of gold in ferric sul- 
 phate. To a solution, 125 cc., containing 1 g. of iron as ferric 
 sulphate and 25 cc. of HC1, ferrous sulphate was added in 
 quantities containing from 0.01 to 0.26 g. of ferrous iron. 
 The solutions were immersed in boiling water and subse- 
 quently 250 mg. of gold was added. The dissolved gold was 
 determined at the end of 1 hr. and 3 hr. At the end of 3 hr. 
 the gold dissolved was greater, probably because some ferrous 
 sulphate had changed to ferric sulphate. Even 0.01 g. of the 
 ferrous iron greatly decreases the solubility of gold in the ferric 
 sulphate and HC1 solution, and 0.25 g. of ferrous sulphate 
 drives nearly all the gold out of solution. These experiments 
 are illustrated by Fig. 4, in which the horizontal lines represent 
 ferrous salt put in the mixture and the vertical lines the 
 amount of gold (in milligrams) dissolved by chlorine in the 
 solution. The lower curve represents conditions at the end of 
 1 hr., the upper curve at the end of 3 hr., when some of the 
 ferrous salt had oxidized by contact with the air. 
 
 20. To determine the rate at which ferrous sulphate, in the 
 presence of sulphuric acid and manganese dioxide, would be 
 oxidized to the ferric salt, Brokaw made the following experi- 
 ment : 
 
 100 cc. of 1.6 normal FeS0 4 was acidified with sulphuric 
 acid and shaken vigorously with 5 g. of powdered Mn0 2 . 
 After 5 min., the solution was filtered. No ferrous iron was 
 detected by the ferricyanide test, showing that the iron had 
 been completely oxidized to the ferric state. 
 
 IV. DISCUSSION OF EXPERIMENTS. 
 1. Nitrates. 
 
 Dilute acid nitrate-chloride waters readily dissolve gold, 
 since they are equivalent to weak aqua regia. The chlorine 
 
 36 Brokaw, Journal of Geology, vol. xviii., No. 4, pp. 322 to 323 (May- June, 
 1910). 
 
MANGANESE AND GOLD-ENRICHMENT. 777 
 
 set free by the reaction oxidizing HC1 is more active than a 
 solution of chlorine in water, and converts gold into gold 
 chloride. For present purposes we may consider that the 
 reaction is as follows : 
 
 9 HC1 + 3 HIS T 3 + 2 Au-6 H 2 + 3 NOC1 4- 2 AuCl 3 . 
 
 Nitrosyl chloride, NOC1, which is formed in this reaction, 
 does not react directly with gold, but is thought by some to 
 affect the reaction favorably as a catalytic agent. Whether this 
 is true or not, in each of the reactions by which gold is dis- 
 solved in chloride solution its solvent power may be ascribed to 
 its " nascent " state. In this reaction, as in those which follow, 
 the presence of an element with more than one valence is a 
 necessary condition, and its valence is reduced as gold passes 
 into solution. 
 
 The reaction given above, 3 HC1 -f NH0 3 , may be written 
 as follows : 37 
 
 O 
 
 Cl ;H + H O j N I = O + 2 H I Cl _> 2 H 2 O + C1 2 + Cl N = O. 
 
 The chlorine reacts with gold, forming soluble gold chloride. 
 2 Au + 3 Cl 2 -2 AuCl 3 . 
 
 With regard to the latter reaction, Dr. R. C. Wells, of the 
 U. S. Geological Survey, supplied the following note : 
 
 " The reaction (2 Au -f 3 C1 2 ^2 AuCl 3 ) aims to express the 
 initial and final stages, but says nothing of the mechanism of 
 the reaction or the necessity for the chlorine being in the i nas- 
 cent' state. In accordance with present theories, a * nascent' 
 chlorine atom, while taking a negative charge to form chloride, 
 allows the corresponding positive charge to ionize the gold, 
 
 Au + O = Au '. 
 
 This ionization occurs with greater difficulty in the case of 
 gold than with almost any other metal. The aurous ion passes 
 with great readiness into the auric ion, Au""". Moreover, 
 both ions form complexes with chlorides. The effectiveness of 
 
 37 Alexander Smith, General Inorganic Chemistry, p. 449 (1907). 
 
 49 
 
778 MANGANESE AND GOLD-ENRICHMENT. 
 
 chlorine in dissolving gold in accordance with this theory may 
 be ascribed partly to the production of the complex gold 
 chloride ions, thus removing the gold ions from solution with 
 such effectiveness that more gold ionizes, and thus the process 
 continues until equilibrium is established." 
 
 In the 29 analyses of mine-waters NO 3 is reported from but 
 one (Geyser mine, Silver Cliff, Colo., 1.6 parts per million), 
 and this is a water of questionable genesis. Possibly, nitrates 
 are more abundant than is indicated by the analyses ; and if so, 
 they must increase the solvent power of chloride solutions; 
 but the data at present available do not indicate that they affect 
 the superficial reactions to any important extent. 
 
 2. Manganese Oxides. 
 
 That gold is dissolved in moderately dilute solutions con- 
 taining salt and manganese oxides is shown by experiments 
 11, 15 and 16. The reaction with manganese used to prepare 
 chlorine commercially is illustrated by the following equation : 
 (The reaction is not so simple as stated. It is discussed later.) 
 
 Mn im 2 + 2 aCl 4- 3 H 2 S0 4 -* 2 H 2 + 2 ]STaHS0 4 + 
 Mn u S0 4 + 2 01. 
 
 At the beginning of the reaction the manganese has a valence 
 of four ; at the end a valence of two. With acid the reaction 
 may be as follows : 
 
 Mn0 2 + HC1 - 2 H 2 O + MnCl 2 + C1 2 . 
 
 Besides the presence of a chloride, some other conditions 
 are essential to the solution of gold. There appear to be two. 
 One is that some other substance must also be present which 
 is capable of being reduced so as to liberate chlorine as, for 
 example, a ferric salt which may be reduced to the ferrous, a 
 cupric to the cuprous, the higher manganese salts to the lower, 
 etc. The other is the evolution of " nascent " chlorine. This 
 is particularly illustrated by the action of aqua regia or the pro- 
 duction of chlorine by hydrochloric acid and pyrolusite. In 
 short, any of a number of methods of producing free chlorine 
 would be effective in the solution of gold. Possibly both of the 
 conditions just mentioned may in the last analysis be identical. 
 
MANGANESE AND GOLD-ENRICHMENT. 779 
 
 The essential point is that the atomic chlorine in a state of 
 molecular exchange or evolution is able to combine with the 
 gold. For present purposes the gold may be considered to 
 dissolve as gold chloride, although chemical investigations favor 
 the theory that a complex ion containing gold is formed. The 
 only consideration which becomes important in its geological 
 aspect is the presence of the compounds which not only admit 
 of easy changes of valence, but which act upon hydrochloric 
 acid with the production of free chlorine. 
 In mine-waters chlorine is supplied as Nad. 
 
 166. Fe 2 (S0 4 ) 3 + H 2 S0 4 + STaCl + Mn0 2 + Au 
 
 N/10 N/10 N/25 1 g. - 0.15 g. 
 
 0.00505 g. loss of gold by solution in 14 days (cold). 
 
 Under the same conditions without manganese there was no 
 weighable loss (see experiment 16a). 
 
 As used herein the normal solution contains 1 g.-equiva- 
 lent of the solute in 1 1. of solution. A solution normal with 
 respect to chlorine contains 1 g. of chlorine times 35.45, the 
 molecular weight of chlorine, in 1 1. of solution. 
 
 In this experiment the concentration of Cl (1,418 parts per 
 million) is not so great as has been observed in a few mine- 
 waters, and not more than three times as great as Don deter- 
 mined in waters from a number of Australasian mines. 38 The 
 solutions, however, contain more chlorine than the average of 
 29 analyses of mine-waters (873 parts of Cl per million), con- 
 siderably more than that of 28 analyses (111 parts of Cl per 
 million), and more than most mine-water analyses from Ameri- 
 can gold-mines. 
 
 Manganese is abundant in many gold-bearing deposits ; is 
 sparingly represented in some ; and from a very large number 
 it has not been reported. The chief primary minerals are the 
 carbonates (rhodochrosite and manganiferous calcite), the sili- 
 cate (rhodonite), amethystine quartz, and the less abundant 
 sulphite, alabandite. Some rock-making minerals carry small 
 amounts of manganese. It readily forms sulphates, chlorides,, 
 etc., and is dissolved by acid mine- waters. In the 29 analyses 
 of Table I. it is reported from 6 mines. In some waters it i& 
 
 38 Trans., xxvii., 654 (1897) ; p. 176, this volume. 
 
780 MANGANESE AND GOLD-ENRICHMENT. 
 
 abundant. The average of the 29 shows 30.9 parts per million. 
 Even a little manganese generally stains the gossan black or 
 chocolate-brown, and consequently it is readily recognized in 
 the oxidized ores. Manganese changes its valence more read- 
 ily than other elements common in gold-ores and it is in many 
 respects unique among the elements. The following note is 
 abridged from Alexander Smith, General Inorganic Chemistry, 
 p. 737: 
 
 It stands on the left side of the eighth column of the periodic table ; the 
 right side of that column is occupied by the halogens. It is never univalent as 
 the halogens are ; but the heptoxide, Mn 2 O 7 , and corresponding permanganic acid, 
 HMnO 4 , are in many ways closely related to the heptoxide of chlorine and per- 
 chloric acid, HC1O 3 . Permanganic acid is a very active acid. Contrary to the 
 habit of feebly acidic and feebly basic oxides such as those of zinc, aluminum and 
 tin, the basic oxides of manganese are not at all acidic and the acidic oxides, 
 with the possible exception of Mn 2 O 3 , are not also basic. There are thus five 
 rather well defined sets of compounds showing five different valences of the 
 element. 
 
 These include maiiganosite (MiiO), pyrochroite (MnO.H 2 0), 
 itnanganite (Mn 2 3 .H 2 O), hausmannite (Mri 3 4 ), pyrolusite 
 (Mn0 2 ), psilomelane, etc. 
 
 3. Lead Oxides. 
 
 Lead oxide, like manganese oxide, is said to facilitate the 
 solution of gold 39 when added to solutions of ferric sulphate 
 and sodium chloride. Lead is both bivalent and quadrivalent 
 and forms corresponding oxides and hydroxides. These, how- 
 ever, are generally not abundant in the oxidized zones of lead- 
 bearing ore-deposits, probably because the lead carbonate and 
 the sulphate are relatively insoluble in water and usually are 
 formed instead of the oxides. Lead is reported in but one of 
 the 29 analyses of water from gold- and silver-mines, tabu- 
 lated above, and in this case the water carried but 1.35 parts 
 per million. Many gold-deposits contain but little lead and 
 some contain none. It is believed to be of very subordinate 
 importance in connection with the solution of gold. 
 
 4. Ferric Compounds. 
 
 As shown by experiments, gold is not dissolved by hydro- 
 chloric acid, by ferric sulphate, or by ferric chloride. It is 
 
 39 Victor Lehner, Journal of the American Chemical Society, vol. xxvi., No. 5, p. 
 552 (May, 1904). 
 
MANGANESE AND GOLD-ENRICHMENT. 781 
 
 dissolved at 38 C. in concentrated solution containing both 
 ferric sulphate and hydrochloric acid. 
 
 5. The Efficiency of Ferric Iron and Cupric Copper to Supply 
 
 Nascent Chlorine, Compared with that of Manganitic 
 
 Manganese. 
 
 As shown by experiment 4, a concentrated solution of CuCl 2 
 with HC1 dissolves appreciable gold at 200, and Fig. 3 shows 
 that a solution containing 1 g. of copper as cupric chloride and 
 25 cc. of HC1 (sp. gr., 1.178) in 125 cc. of solution at 38 + , 
 dissolves 0.23 mg. of gold in 163 hr. Since cupric copper and 
 ferric iron are present in many mineral waters, the nature of 
 these reactions should be considered in some detail in order to 
 compare their efficiency with that of manganitic manganese. 
 
 Solutions of ferric sulphate with sulphuric acid and salt dis- 
 solve gold at high temperatures. Concentrated solutions of 
 ferric sulphate and hydrochloric acid dissolve gold at from 38 
 to 43 C. In the cold, the reaction may go on in concentrated 
 solutions, but in those approximating the concentration of mine- 
 waters (and one of them considerably more concentrated than 
 most mine-waters) no weighable loss of gold was obtained. 
 With Mn0 2 under the same conditions there was a very appre- 
 ciable loss in a solution containing only 1.4 g. of 01 in a liter. 
 It appears, therefore, that the action of ferric iron on gold in 
 cold dilute mine-waters with H 2 S0 4 and NaCl is probably neg- 
 ligible ; for the experiments with ferric iron in such solutions, 
 without manganese, extended over a period of 34 days without 
 weighable loss of gold. 
 
 Many auriferous deposits contain copper; and it is desirable 
 to compare the efficiency of cupric with ferric salts and with 
 manganitic salts in similar solutions. Since the reactions which 
 give nascent chlorine are conditioned upon the presence of 
 some element that changes its valence in the reactions, and 
 since the processes underground take place in sulphate solu- 
 tions, it did not appear necessary, after ferric salt had been 
 shown to be incompetent, to conduct experiments with copper; 
 for, as is well known, cuprous salts, though they may be pres- 
 ent, have never been detected in acid sulphate mine-waters, 
 whereas ferric and ferrous sulphate are very common in such 
 waters. 
 
782 MANGANESE AND GOLD-ENRICHMENT. 
 
 Fig. 2 shows that in 163 hr. a solution carrying 2 g. of fer- 
 ric iron as sulphate and 50 cc. of HC1 (sp. gr. 1.178) diluted 
 to 125 cc., with 250 mg. of gold in the solution, dissolves 6 
 mg. of gold. In the same time, as shown by Fig. 3, a solu- 
 tion containing 2 g. of copper as cupric chloride and 50 cc. of 
 HC1 diluted to 125 cc., dissolves but 2.84 mg. of gold, the same 
 amount of gold being exposed. These results indicate that, in 
 concentrated solutions at least, cupric salt is less efficient than 
 ferric sail. Comparing the details of the curves, however, it 
 appears that the reaction with ferric salt is probably near a 
 state of equilibrium ; but the experiment with cupric salt sug- 
 gests that, given a longer time, considerably more gold may 
 be dissolved. It cannot be concluded, therefore, that the sol- 
 vent action of a cupric salt would be less than that of a ferric 
 salt, if a very much longer time were allowed to lapse before 
 the loss of gold in the two experiments was ascertained, al- 
 though the experiments suggest that this is probable. 
 
 The curves of Fig. 3 show that a dilution of the concen- 
 trated solution of cupric chloride and hydrochloric acid greatly 
 decreases the amount of gold dissolved under the same condi- 
 tions. For example, the solution containing 2 g. of copper as 
 cupric chloride and 50 cc. of HC1 (sp. gr. 1.178) dissolved 2.84 
 mg. of gold in 163 hr. Under the same conditions a solution 
 of the same salts, but of one-half the concentration, dissolved 
 only 0.23 mg. of gold in 163 hr. It thus appears that a dilu- 
 tion of the solution to one-half decreases its solvent action (2.84 
 divided by 0.23) to about one-twelfth. If the solvent were 
 diluted to approximately the strength of mine- waters, it should 
 be expected that the efficiency of cupric salt in these reactions 
 would be almost immeasurably decreased. Indeed, the lower 
 curve, A, in Fig. 3, strongly suggests this, and indicates also 
 that the reaction with cupric salt at this concentration is near- 
 ing completion ; for about half as much gold (0.11 mg.) was 
 dissolved by this solution in 66 hr. as was dissolved in 163 hr. 
 (0.23 mg.). It is improbable that the character of this curve 
 would greatly change if the reaction continued over a period 
 twice as long, and, projecting the curve to 14 days, in order 
 that the solvent action of cupric salt may be compared with 
 that of manganitic salt, it appears that in 14 days 0.48 mg. of 
 gold would be dissolved in waters of this concentration, assum- 
 
MANGANESE AND GOLD-ENRICHMENT. 783 
 
 ing that the gold dissolved is in proportion to the time exposed, 
 thus giving the advantage to cupric salt. The experiments 
 with MnO 2 were carried on at about 18 C., and those with 
 cupric salt at from 38 to 45 C. 
 
 The gold dissolved (experiment 166) in the dilute solution 
 with manganese was more than 10 times as much as that dis- 
 solved with the cupric salt (experiment 8). The hydrochloric 
 acid (sp. gr. 1.178) with cupric chloride contained 34.99 per 
 cent, of HC1 and 34 per cent, of 01. Disregarding the 01 in- 
 troduced by cupric chloride, the solution used (25 cc. diluted 
 to 125 cc.) contained 6.8 per cent, of 01. The solution with man- 
 ganese dioxide (one-twenty-fifth normal) contained but 0.14 
 per cent, of 01. The chlorine (in acid) in the experiment with 
 copper was thus 49 times as much as the total chlorine in the 
 experiment with manganese. 
 
 The amount of solution used in experiment 8, with cupric 
 salt, was 2.5 times as much as the amount of solution used in 
 experiment 166, with manganese, but the area of gold exposed 
 was not so great. In experiment 8, the gold was rolled to a 
 thickness of 0.009 in. and cut into 1-mm. squares, whereas that 
 used in experiment 166 was rolled to a thickness of 0.002 in., 
 exposing areas of about 350 sq. mm. In the experiment with 
 copper 250 mg. of gold was introduced, whereas only 150 mg. 
 was introduced in experiment 166. Correcting for areas ex- 
 posed, a cupric solution 50 times as concentrated as the man- 
 ganitic solution with respect to chlorine will dissolve about one- 
 fifth as much gold where equal areas are exposed. In other 
 words, the action with manganese appears to be more than 250 
 times as efficient as with cupric salt, even if it is assumed that 
 further dilution would not decrease the solvent action of cupric 
 salt in a geometrical ratio, as is indicated by the curves in 
 Fig. 3. Comparing the end-points of curves A and Z>, Fig. 3, 
 it is seen that a dilution of the solution to one-half decreases 
 the solvent action with cupric salt to about one-twelfth. If 
 further dilution to one-twenty-fifth normal HOI decreases the 
 solvent action with cupric salt in this ratio, then the efficiency 
 of the solution with cupric salt would be about T 00 ^ -^-^ as 
 great as with Mn0 2 . It is thus shown that the efficiency of 
 cupric salt compared with that of manganitic salt under these 
 conditions is somewhere between 0.004 and 0.000001. 
 
784 MANGANESE AND GOLD-ENRICHMENT. 
 
 6. The Amount of Chlorine Necessary for the Solution of Gold 
 in the Presence of Manganese Compounds. 
 
 In experiment 15 (a), with Mn0 2 , 0.01640 g. of gold was dis- 
 solved in 34 days with solution one-tenth normal with respect 
 to chlorine. A solution with but 40 per cent, as much Cl (ex- 
 periment 166) dissolved 31 per cent, as much gold in 14 days as 
 was dissolved in the more concentrated solution in 34 days. 
 These results show that in 15 (a) conditions are probably ap- 
 proaching equilibrium and also that the solvent power of chlo- 
 rine is approximately proportional to the amount present. That 
 a weighable quantity of gold is dissolved when only a trace of 
 chlorine is present is shown by experiment 13 (6), in which 
 chlorine was introduced without intention. 
 
 7. The Precipitation of Gold. 
 
 Although gold is readily precipitated by organic matter, this 
 reaction is not of great importance in igneous rocks. There 
 ferrous sulphate is the chief precipitating-agent. Ferrous sul- 
 phate is formed by the oxidation of pyrite, but in the presence 
 of oxygen and H 2 S0 4 it becomes ferric sulphate, which does 
 not precipitate gold. Below the water-table, where pyrite is 
 more abundant and free oxygen less abundant, ferrous sulphate 
 may persist in the mine- waters. Ferrous sulphate is so effective 
 as a precipitant of gold that it is used for that purpose in metal- 
 lurgical processes. Experiment 19, by W. J. McCaughey, shows 
 that a minute amount of ferrous sulphate greatly decreases the 
 solubility of gold, although it does not precipitate it completely. 
 With excess of ferrous salt practically all of the gold is pre- 
 cipitated. Don 40 has shown that many of the sulphate mine- 
 waters of New Zealand and Australia contain abundant ferrous 
 iron ; and that such waters will first precipitate gold, but after 
 oxidation will dissolve it. 
 
 Ferrous sulphate is formed in the upper part of a lode above 
 the water-table ; but, owing to the open condition of that part of 
 the lode, air is freely admitted and ferric sulphate forms, at the 
 expense of ferrous sulphate and sulphuric acid. This reaction 
 takes place almost instantaneously if Mn0 2 is present (experi- 
 ment 20), for ferrous sulphate and manganese dioxide are under 
 
 40 Trans., xxvii., 599 (1897) ; p. 175, this volume. 
 
MANGANESE AND GOLD-ENRICHMENT. 785 
 
 these conditions incompatible. Manganese dioxide then not 
 only releases the solvent for gold, but eliminates the salt which 
 precipitates it. It is doubtful whether appreciable amounts of 
 gold are ever carried far below the water-table in mines where 
 the waters carry ferrous sulphate, but, in the presence of MnO 2 , 
 ferrous sulphate may be eliminated below the water-table. 
 
 When manganese dioxide takes part in the reactions by 
 which, under the conditions named, gold is dissolved, trans- 
 ported and precipitated, the manganese salt is itself "changed. 
 At the surface pyrolusite, Mn0 2 , forms, for there an excess of 
 oxygen prevails ; and this mineral is commonly found in the 
 gossan of manganiferous lodes. When solutions containing 
 H 2 S0 4 and Nad react on Mn0 2 there is a tendency to form 
 MnS0 4 , and some manganese goes into solution as sulphate, 
 but salts of manganese with higher valence may also form. In 
 this connection Dr. R. C. Wells has offered the following state- 
 ment : 
 
 " In an acid solution containing some free chlorine, such as has been assumed 
 to be effective in dissolving gold, there would also be a tendency towards the 
 formation of permanganic acid. On the other hand, the production of the chlorine 
 necessarily results in the reduction of the manganese compound. Now a mangan- 
 ous salt is known to react with permanganate to reproduce MnO 2 , and this illus- 
 trates the tendency of manganese to pass with ease from one stage of oxidation to 
 another. The precipitation of manganese will occur more and more as the solu- 
 tion loses its acidity. It is well established that manganous salts in an acid envi- 
 ronment are very stable ; but in neutral or alkaline solutions they oxidize more 
 vigorously, one stage of their oxidation being the manganic salt which hydrolyzes 
 into Mn 2 O 3 .H 2 O (manganite), with even greater ease than ferric salts into limonite. 
 
 "In these ways the migration of an acidic solution would result in the transpor- 
 tation of both gold and manganese. But in a region of basic, alkaline and 
 reducing environment the manganese would be re-precipitated, the free acid neu- 
 tralized, the chlorine absorbed by the bases and removed, and owing to the accu- 
 mulation of the ferrous or other reducing salts, the gold would be re-precipitated. " 
 
 V. THE TRANSFER OF GOLD IN COLD SOLUTIONS. 
 
 1. Restatement of the Processes as Related to Secondary 
 Enrichment. 
 
 Every theory of secondary enrichment of the metals consists 
 essentially of three parts : (a) solution, (6) transportation, (<?) 
 precipitation. 
 
 (a) As already stated, there is in the upper part of the ore- 
 deposit, where oxidation prevails, abundance of ferric sulphate 
 
786 MANGANESE AND GOLD ENRICHMENT. 
 
 and sulphuric acid. A little salt, NaCl, or other chloride, is 
 generally present. The H 2 S0 4 , reacting upon Nad, gives 
 HC1, which,- in the presence of Mn0 2 , gives nascent chlorine, 
 which dissolves gold. Some manganese goes into solution as 
 sulphate, but certain higher manganates are probably formed 
 as well. 
 
 (6) This chemical system will move downward under hydro- 
 static head. If it comes into a zone containing pyrite it will 
 react upon the pyrite, and in the oxidation of the latter more 
 iron sulphates and acid will be formed. If manganese dioxide 
 is present, or if permanganic acid had been formed, no gold 
 will be precipitated, and the system, with gold still in solution, 
 will move to greater depths before ferrous sulphate can be- 
 come effective. 
 
 (c) But as the system moves downward, where no new 
 sources of oxygen are available, the excess of acid is removed. 
 There are many ways by which acidity is reduced along with 
 these reactions, but the principal one is probably the kaoliniza- 
 tion of sericite and feldspar. In these reactions sodium, potas- 
 sium, calcium, magnesium, and other sulphates are formed 
 from acid and silicates; the silica remaining as Si0 2 and 
 kaolin ; the alkalies and alkalic earth sulphates going into solu- 
 tion. As the acidity decreases, iron and manganese compounds 
 tend to hydrolyze and deposit oxides. At this stage of oxida- 
 tion FeS0 4 becomes increasingly prominent, and not only com- 
 pletely inhibits further solution of gold but becomes increas- 
 ingly effective as a precipitant. Thus manganite is probably 
 precipitated with gold. The fractures in the primary pyritic 
 gold-ore below the water-level thus become coated with a 
 manganiferous gold-ore, which may be very rich. The excess 
 of oxygen which the system has carried down is used up in the 
 manner indicated, and in this process limonite is formed, con- 
 sequently the manganiferous gold-ore deposited in the fissures 
 and cracks contains iron and kaolin as well as manganese 
 oxides. 
 
 2. Association of Gold with Manganese Oxides. 
 
 Oxidized manganiferous ore frequently carries silver 41 with- 
 out gold. In the oxidized zone such ore should be common; 
 
 41 Mining and Scientific Press, vol. xciv., No. 25, p. 796 (June 22, 1907). 
 
MANGANESE AND GOLD-ENRICHMENT. 787 
 
 but in the sulphide zone different relations, according to the 
 requirement of the theory, should generally be shown. In 
 this zone the manganese acts not so much as a solvent for gold, 
 but rather as an agent which delays precipitation by converting 
 the ferrous sulphate, which precipitates gold, to ferric sulphate. 
 The gold has presumably been dissolved higher up, but it trav- 
 eled downward in solution in cracks in the primary sulphide 
 ore. It would be expected that the deeper-seated manganif- 
 erous ore, unlike the lean ore in the oxidized zone, would be 
 rich in gold. S. F. Emmons informs me that there is a com- 
 mon feeling among the miners in Colorado that manganese is 
 a very good sign of rich ore. The same feeling exists in the 
 minds of many prospectors elsewhere. F. L. Ransome says ^ 
 that in the Camp Bird and Tomboy mines black oxide of man- 
 ganese occurs in the deeper workings (year 1901), and usually 
 indicates good ore. In these cases, according to Rausome, 
 " The oxide appears to be associated with post-mineral fractur- 
 ing . . . and to have been deposited later than the bulk of the 
 ore." In general, the gold-deposits near Telluride and Ouray 
 show very little secondary enrichment and the primary ore is 
 rich enough to pay handsomely, but the small rich manganese 
 streaks may be rationally explained by the processes indicated. 
 In the deposition of chalcocite ferrous sulphate is formed, and 
 this would readily precipitate the gold if any were held in the 
 solution. . The relation of chalcocitization and deep-seated pre- 
 cipitation of gold is discussed on p. 798. 
 
 In the oxidized zone small bunches of very rich mangan- 
 iferous gold-ore are often found. I have seen such ore above 
 the sulphide zone in certain camps in Nevada. Such bunches 
 of rich ore were probably formed when they were surrounded 
 by sulphides, but were overtaken by the oxidized zone, which 
 moves progressively downward, and the gold in the rich ore 
 has not yet been dissolved. Such ores should in general be 
 more abundant and richer in the lower part of the oxidized 
 zone than near the apex, where they have been exposed for 
 longer periods to the solutions dissolving gold. They may 
 be compared with the rich partly-oxidized chalcocite which 
 appears near the surface in certain copper-mines. Such ore 
 
 42 A Keport on the Economic Geology of the Silverton Quadrangle, Colorado, 
 Bulletin No. 182, U. S. Geological Survey, p. 101 (1901). 
 
788 MANGANESE AND GOLD-ENRICHMENT. 
 
 remains above the water-level because the table has been de- 
 pressed more rapidly than the copper sulphide has been dis- 
 solved. The mutual relation of these processes is discussed by 
 W. Lindgren in his monograph on the copper-deposits of the 
 Clifton-Morenci district, Arizona. 43 
 
 3. The Oscillating, Descending, Undulatory Water-Table. 
 The terms " water-table " and " level of ground-water " are 
 generally used to describe the upper limit of the zone in which 
 the openings in rocks are filled with water. This upper limit 
 of the zone of saturation is not a plane, but a warped surface. 
 It follows in general the topography of the country, but is less 
 accentuated. It is not so deep below a valley as below a hill, 
 but it rises with the country towards the hill-top and in general 
 is higher there than in the valley. Nor is it stationary. In 
 dry years it is deeper than in wet years, and in dry seasons it 
 is deeper than in wet seasons. The difference of elevation be- 
 tween the top of this zone in a wet year and in a dry year is 
 normally greater under the hill-top than on the slopes and in 
 the valleys, "in mines where the ground is open the level of 
 ground-water probably changes with every considerable rain. 
 Consequently, there is a zone above ground-water in dry periods 
 but below it in wet periods, and in hilly countries this may be 
 of considerable vertical extent. Thus the water-table oscillates, 
 though in general moving downward with degradation of the 
 land-surface. It is in this zone of oscillation of the water-table 
 that chemical activity is most varied. Without any change in 
 the character of the drainage or of the more-constant condi- 
 tions controlling the water-circulation, the chemical composi- 
 tion of the solutions affecting this zone may change from season 
 to season. They may at one time be ferric sulphate or oxidiz- 
 ing waters and at another time ferrous sulphate or reducing 
 waters, since, after a wet season, the ferrous sulphate waters 
 from below would tend to rise, after dilution with fresh water 
 added by the rains. Consequently, the minerals of this zone 
 may include, besides the t residual primary and secondary sul- 
 phides, the oxides, native metals, chlorides, sulphides, carbo- 
 nates, etc. Between the top of this zone and the surface or 
 the apex of the deposit chemical activity is probably slow, be- 
 
 4S Professional Paper No. 43, U. S. Geological Survey, p. 232 (1905). 
 
MANGANESE AND GOLD-ENRICHMENT. 789 
 
 cause there is a scarcity of sulphides and other easily-altered 
 minerals to supply the salts upon which the chemical activity 
 of ground-water in a large measure depends. As the country 
 is eroded, this zone also descends ; and if .a mineral or metal 
 persists long enough, the upper limit of the zone of active 
 change passes below it. The mineral is thus " marooned," 
 and, not being exposed to mineral-laden waters, it may ulti- 
 mately be exposed at the outcrop of the deposit. 
 
 4. The Sever o.l Successive Zones in Depth. 
 
 As is clearly set forth by S. F. Emmons, W. H. Weed, and 
 others, many metalliferous lodes, when followed from the sur- 
 face down the dip, show characteristic changes. Below the 
 outcrop, the upper part of the oxidized portion of the lode 
 may be poor. Below this there may be rich oxidized ores ; 
 still farther down, rich sulphide ores; and below the rich 
 sulphides, ore of relatively low grade. Such ore is commonly 
 assumed to be the primary ore, from which the various kinds 
 of ore above have been derived. The several types of ore have 
 a rude zonal arrangement, the so-called "zones" being, like the 
 water-table, highly undulatory. They are related broadly to the 
 present surface and to the hydrostatic level, but are often much 
 more irregular than either; for they depend in large measure on 
 the local fracturing in the lode which controls the circulation of 
 underground waters. Any zone may be thick at one place and 
 thin, or even absent, at another. If these zones are platted on 
 a longitudinal vertical projection, it is seen that the primary 
 sulphide ore may project upward far into the zone of secondary 
 sulphides, or into the zone of enriched oxides, or into the zone 
 of leached oxides, or may even be exposed at the surface. The 
 zone of secondary sulphide enrichment (which is not every- 
 where present) may project upward far into the zone of rich 
 oxidized ore, or into the zone of leached oxides, or may outcrop 
 at the surface. The zone of sulphide enrichment nearly always 
 contains considerable primary ore, and very often the secondary 
 ore is merely the primary ore containing in its fractures small 
 seams of rich 'minerals. The zone of enriched oxides is gen- 
 erally found above the water-table when the latter is at the 
 lowest. The zone often extends to the outcrop. Indeed, it is 
 at such places that most mines are discovered, for in districts 
 
790 MANGANESE AND GOLD-ENRICHMENT. 
 
 not known to contain metalliferous deposits a lean or barren 
 outcrop is generally not extensively explored by prospectors. 
 In regions of rapid erosion, and especially of rugged topogra- 
 phy, the conditions for the exposure of rich oxides, or even 
 rich sulphides or primary ore, are more favorable. In places 
 along the outcrop of a deposit where erosion is rapid the richer 
 oxidized or sulphide ores may be exposed, whereas in other 
 places, protected from erosion, and therefore exposed longer 
 to solution, the same outcrop is frequently leached. It is evi- 
 dent that the amount of metal remaining in the upper part of 
 the oxidized zone and at the outcrop depends upon the ratio 
 between the rate at which the metal is dissolved, and the rate 
 at which the valueless constituents are dissolved and removed. 
 Under certain conditions gold is removed very slowly, and the 
 removal of valueless constituents may effect a concentration at 
 the very apex of the lode ; while under other conditions, favor- 
 able to the solution of gold, it is removed more rapidly than 
 the valueless constituents (such as silica and iron), and, in 
 consequence, the apex and the upper portion of the zone below 
 it are leached. In a country not subject to erosion it would be 
 supposed that the outcrops of manganiferous lodes would be 
 everywhere leached; but rapid erosion may remove the upper 
 part of the lode before it is completely leached, and, under fa- 
 vorable conditions, placers accumulate from the debris of the 
 apex. 
 
 It thus appears that all of these zones except that of the pri- 
 mary ore are, broadly considered, continually descending; so 
 that ore taken from the outcrop may represent what was once 
 primary ore ; afterwards, enriched sulphide ore ; still later, 
 oxidized enriched sulphide ore ; later still, leached oxidized 
 enriched sulphide ore; and finally become the surface-ore. 
 Through more rapid erosion at some particular part of the 
 lode, any one of these zones may be exposed ; and hence an 
 outcrop-ore of any character is possible. Consequently, longi- 
 tudinal assay-plans, showing the changes of value in depth, 
 though highly suggestive, and especially so when gold and 
 silver are shown separately, are supplemented by studies of 
 the paragenesis and by physiographic studies, in order that 
 the approximate rate of erosion of the lode at various places 
 may be known. In the absence of such knowledge, it is gener- 
 
MANGANESE AND GOLD-ENRICHMENT. 791 
 
 ally impossible to tell the genesis of a particular sample of ore 
 from a mine, although this may sometimes be done. When all 
 the data are assembled, however, greater confidence may be 
 placed in the conclusion, since all the factors in the problem 
 are intimately related. 
 
 5. Criteria for the Recognition of Secondary Enrichment. 
 
 I shall not attempt to review all the criteria for the recog- 
 nition of secondary enrichment. They involve practically all 
 available data relating to the geology and physiography of the 
 region, as well as the observed characteristics of its ore-deposits. 
 But each group of deposits may be studied with certain gen- 
 eral criteria in view. Among these are : (1) the vertical dis- 
 tribution of the richer portions of the lode with respect to the 
 present surface and to the level of ground-water; (2) the miner- 
 alogy of the richer and poorer portions of the deposits, and the 
 character and vertical distribution of the component minerals ; 
 (3) the paragenesis, or the structural relations shown by the 
 earlier ore and that which has been introduced subsequently. 
 
 In applying these principles, it should be remembered that 
 circulation is generally controlled by post-mineral fracturing ; 
 that the changes depend upon climate and rapidity of erosion, 
 and are affected by regional changes of climate, etc. Although 
 the mineralogy of the ore is a useful aid, there are many min- 
 erals which are precipitated from cold solutions and also from 
 ascending hot solutions, and there are many others, the genesis 
 of which is uncertain. Of th'e minerals formed in the zone of 
 secondary sulphide enrichment, few, if any, are known posi- 
 tively to form under such conditions only. There are some, 
 however, such as chalcocite and covellite, which nearly every- 
 where are clearly of secondary origin. Ruby silver is fre- 
 quently, but not always, secondary. Other minerals, such as 
 chalcopyrite, bornite, argentine, etc., have no definite indicative 
 value unless their occurrence suggests that they are later than 
 the primary ore. Where minerals, known to have formed 
 elsewhere by processes of secondary sulphide-enrichment, are 
 clearly later than primary ore, there is a strong presumption 
 that they were deposited by cold descending waters. If it can 
 be shown, in addition, that they do not extend to the bottom 
 of the mine, but are related to the present topography of the 
 
792 MANGANESE AND GOLD-ENRICHMENT. 
 
 country, then this presumption may be regarded with consider- 
 able confidence as confirmed. 
 
 Where paragenetic evidence suggests secondary enrichment, 
 it should be determined whether the later minerals are those 
 commonly formed by secondary processes, for, as shown by 
 Weed and others, certain minerals, such as enargite and rho- 
 dochrosite, may be deposited by ascending solutions in open- 
 ings in older ore-bodies. 
 
 With respect to gold, the problem is difficult, because the 
 native metal is the only stable gold-mineral known to be de- 
 posited from cold dilute solutions. Consequently, the appli- 
 cable criteria are limited; and the vertical distribution of 
 the richer ore, though suggestive, is not in itself conclusive. 
 Lindgren and Ransome, in their studies at Cripple Creek, have 
 shown that the richer ore-bodies may have in general a rela- 
 tionship to elevation, where there is little or no evidence of 
 deep*seated secondary enrichment. The maximum deposition 
 by ascending hot waters may be greater at one horizon than 
 at another ; and the rich ore, though showing broadly certain 
 variations with depth, is in no way related to the water-table. 
 If, however, it can be shown that rich seams of ore cross the 
 primary ore and do not extend downward as far as the bottom 
 of the primary ore, but are related to the present topography 
 of the country, and if it is known that the associated minerals 
 which fill such openings are those which may be deposited by 
 cold waters, the evidence of their secondary origin is practi- 
 cally conclusive. As already shown, seams of gold with .limo- 
 nite and manganese oxides occur in such relations. Similar 
 ore frequently contains chalcocite and argentite also. Such 
 occurrences could with great confidence be attributed to de- 
 scending waters ; and since it is known that they are commonly 
 related to the present surface, a fair presumption is that they 
 will disappear in depth. 
 
 In the practical application of such reasoning to gold-bearing 
 deposits it will sometimes be necessary to discriminate between 
 the oxidized manganiferous gold-ore which has "resulted simply 
 from the oxidation of a primary manganiferous ore like one 
 containing rhodochrosite, and that which has been deposited in 
 fractures in the sulphides lower down. In other words, it is 
 desirable to know whether rich manganiferous ore in the upper 
 
MANGANESE AND GOLD-ENRICHMENT. 793 
 
 part of a mine is residual from a primary ore-body, and there- 
 fore will probably prove extensive, or represents the result of 
 concentration under more deeply seated conditions after the 
 manner indicated above. This discrimination may be easy in 
 the sulphide zone, where the fractures with rich manganif- 
 erous ore are clearly shown; but in the oxidized zone one 
 must rely upon the shape and distribution of the rich bunches. 
 If they are related to cracks in the mass of the oxidized ore, 
 the inference is warranted, in the absence of other evidence, 
 that they are residual secondary ore, and, being genetically 
 related to the present topographic surface, are limited. 
 
 The tellurides and selenides of gold are seldom or never de- 
 posited from cold solutions; hence native gold is, as already 
 stated, the only gold-mineral which may be so deposited. But 
 native gold is deposited by primary processes also, and is by 
 far the most abundant gold-mineral so deposited. Conse- 
 quently, in distinguishing between primary gold and gold 
 deposited by cold solutions, one must rely upon associated 
 minerals. When secondary chalcocite or certain secondary 
 silver-minerals are deposited, the attendant reactions precipitate 
 gold. Consequently, the richer bunches of gold-ore in the oxi- 
 dized zone, residual from secondary ore formed under the 
 deeper-seated conditions, may carry also considerably more 
 copper and silver than the primary ore. But copper, and 
 (unless cerargyrite is formed) silver also, are more readily 
 leached than gold, even when manganese is present. Hence, 
 the evidence of this character may have been destroyed. 
 
 With respect to other minerals associated with the secondary 
 gold-ore, we are not warranted, in the present state of our 
 knowledge, in drawing definite conclusions. From the nature 
 of the reactions, I think it may be possible to show that man- 
 ganite, Mn 2 3 .H 2 O, is, under conditions of incomplete oxida- 
 tion, more often associated with the rich gold in such relations 
 than pyrolusite, MnO 2 , ; for, as already observed, the lower 
 oxide is more likely to be precipitated than the higher, when 
 secondary gold is deposited under deep-seated conditions. But 
 under oxidizing influences the manganese oxides change their 
 character so readily that this criterion, if it has any value, is 
 probably not applicable to ores in the upper part of the oxi- 
 dized zone, where they have been exposed to more highly 
 
 50 
 
794 MANGANESE AND GOLD-ENRICHMENT. 
 
 oxygenated waters for a longer time. I make these sugges- 
 tions with respect to the character of the manganese oxides 
 associated with the rich ore, not because I think the reactions 
 which precipitate manganese are well enough understood to 
 give a positive paragenetic value to the oxidized manganese- 
 minerals themselves, but in the hope that others will ascertain 
 and report the character of the manganese oxide associated 
 with gold in the deeper zone and in the residual products from 
 that zone. The streak of manganite is reddish brown, some- 
 times nearly black, whereas the streak of pyrolusite is black or 
 bluish black; but mixtures and pseudomorphs of the minerals 
 occur, and it is sometimes almost impossible to determine 
 which oxide is present. 
 
 In some gold-veins 44 the vein-cavities near and even a con- 
 siderable distance below the oxidized zone are filled with a 
 brown or black mud, which is frequently very rich. It is not 
 safe to assume that the gold in such cavities was carried to its 
 present position in solution and precipitated by ferrous sul- 
 phate. The fine pulverulent ore which collects in the cracks 
 is rich in gold, and may have been carried downward in sus- 
 pension. But such ore will generally show a horizontal strati- 
 fication, which will seldom be shown by the ore deposited from 
 solution. As suggested above, manganite, rather than pyrolu- 
 site, is probably formed when gold is precipitated. Such mud, 
 deposited from suspension, may contain either pyrolusite or 
 manganite or both; but it is rational to assume that the mud 
 formed by precipitation in the deeper zone carries very little 
 pyrolusite, but is mainly manganite. 
 
 6. Lateral Migration of Manganese-Salts from the Country - 
 
 Rock to the Ore. 
 
 Clarke's analyses 45 show that igneous rocks carry an average 
 of 0.1 per cent, of manganese oxide, and many basic rocks 
 carry from 0.2 to 0.9 per cent. Where basic dikes have cut 
 an ore-body, they doubtless contribute manganese to the waters 
 circulating in the deposit. The ore of the Haile mine, in South 
 Carolina, is cut by basic rocks ; and the ore-bodies of the 
 Delamar mine, in Nevada, are crossed by a basic dike. Both 
 
 41 Cripple Creek, Professional Paper No. 54, U. S. Geological Survey, p. 199 
 (1906). 
 45 Bulletin No. 330, U. S. Geological Survey (1908). 
 
MANGANESE AND GOLD-ENRICHMENT. 795 
 
 of these deposits show secondary enrichment of gold ; and in 
 both the better ore is found along .the dikes. In general, how- 
 ever, the manganese from the country-rock cannot safely be 
 assumed to have migrated extensively into the ore-deposit, for 
 many analyses of mine-waters do not show manganese ; but 
 where manganiferous rocks are intimately fractured and filled 
 with seams of ore it would be supposed that the reactions 
 requiring manganese could take place. 
 
 The experiments of Dr. Eugene C. Sullivan, performed at 
 the request of S. F. Emmons, in the investigation of another 
 problem, have an important bearing here and Mr. Emmons 
 has kindly permitted me to publish them in advance of his own 
 paper. In so doing, I have abridged somewhat the statements 
 of Dr. Sullivan. 
 
 A sample of the lower white porphyry from the Thespian mine, Leadville, Colo. r 
 was finely ground and treated with carbonic acid and with sulphuric acid ; the 
 rock contained 0.8 per cent, of iron and 0.033 per cent, of manganese. The ratio 
 is about 24 to 1. 
 
 Carbonic Add. 20 g. of the porphyry was taken in 40 cc. of water, and carbon 
 dioxide was passed into the mixture for some hours. In 20 cc. of the solution 0.03 
 mg. of manganese were found and no iron. The results are probably correct for 
 manganese to 0.01 rag. Less than 0.01 mg. of iron would have been detected, if 
 present. To preclude the possibility that the solution of manganese was facili- 
 tated by its reduction with metallic iron introduced from the hammer in pounding 
 up the sample, another portion was similarly treated after metallic iron and mag- 
 netite had been removed by a hand-magnet. In this case 0.1 mg. of manganese 
 and 0.02 mg. of iron were found in 20 cc. of solution. 
 
 Sulphuric Acid. 20 g. of the powdered porphyry stood over night in contact 
 with 40 cc. of one-tenth normal sulphuric acid (0.196 g. of H 2 SO 4 in 40 cc. ). This 
 has roughly the same molecular concentration as a saturated solution of carbon 
 dioxide. The filtrate, 20 cc., contained 1.05 mg. of iron, all in the ferrous condi- 
 tion, and 1 mg. of manganese. The experiment was repeated under the same con- 
 ditions, e x cept that contact between the rock-powder and the acid was of but a 
 few minutes' duration ; 1.20 mg. of iron, practically all ferrous, and 0.90 mg. of 
 manganese were found in 20 cc. of solution. One-tenth of a milligram is about 
 the limit of accuracy in these cases. 
 
 Potassium Sulphate. Neither iron nor manganese could be detected in the solu- 
 tion after treatment of the rock-powder with potassium sulphate. 
 
 Manganese is therefore more readily extracted from the rock than iron under 
 surface-conditions ; for, although it is present in the ratio of only 1 : 24 as com- 
 pared with iron, yet carbonic acid takes out more than three times as much man- 
 ganese as iron, and sulphuric acid gives a ratio of about 1 : I. 46 
 
 As to the precipitation of the two metals from a mixture of their salts in solu- 
 
 46 Penrose, The Chemical Relation of Iron and Manganese in Sedimentary 
 Rocks, Journal of Geology, vol. i., pp. 356 to 370 (May-June, 1893). Vogt, Bog 
 Manganese-Ores, Zeitsehri/t filr praktische Geologic, vol. xiv., p. 217 (July, 1906). 
 
796 MANGANESE AND GOLD-ENRICHMENT. 
 
 lion, the following experiment shows that ferrous compounds are more readily 
 oxidized and precipitated than manganous compounds. Ferrous sulphate solution 
 and manganous sulphate solution weVe mixed in equi-molecular quantities (50 cc. 
 containing 2 mg.-molecules of each i. e., 0. 112 g. of iron and 0.110 g. of man- 
 ganese), with sufficient powdered calcite (Iceland spar) to react with one of the 
 metals (0.200 g.-molecule of calcite). During four weeks the mixture, in a roomy 
 flask, was occasionally shaken, the stopper at the same time being removed for a 
 moment to allow free access of air. At the end of that time all but 1.5 mg. of the 
 iron had been precipitated, while the manganese was in solution in practically the 
 same quantity as originally. Calcite, however, when in contact with manganous 
 salts alone, in the presence of air, will precipitate the manganese as a higher oxide 
 or hydroxide, especially at elevated temperature. 
 
 It thus appears that some manganese is probably contributed 
 to the ore-deposits from the country-rock. I believe, however, 
 that said additions are small, except where space-relations of 
 ore and country-rock are peculiarly favorable. In the upper 
 parts of a vein the circulation is in general downward, and is 
 controlled very closely by fractures, which are more abundant 
 in the upper zone, 'where the rocks are in general more exten- 
 sively shattered. Gouge-seams on the walls would also limit 
 the circulation, and tend to keep the vein free from waters of 
 the country-rock. Where calcite or other carbonates are present 
 to precipitate the small amount of manganese in the solutions, 
 one would suppose that the opportunities for slight additions 
 would be increased. Manganese carbonate is less soluble than 
 calcite, and the latter could, under favorable conditions, be re- 
 placed by manganese compounds. One part of calcium carbo- 
 nate is soluble in 1,428 parts of water saturated with carbon 
 dioxide, while one part of manganese carbonate is soluble in 
 2,000 parts of water so saturated. 47 
 
 In my own experience I have found only trivial stains of 
 manganese in those lodes where it was not present in the 
 gangue of the primary ore ; and, in view of its wide distribu- 
 tion in igneous rocks, I believe that the lateral migration of 
 manganese into the ore under the conditions which generally 
 prevail is very subordinate. Though the amount so contrib- 
 uted may facilitate the solution of gold, it is probably inade- 
 quate to form sufficient higher manganates or similar salts to 
 suppress effectively the action of ferrous sulphate. Under 
 such conditions the gold could not travel to the reducing-zone 
 below the water-level, but would be precipitated practically at 
 the place where it had been dissolved. 
 
 47 Lassaigne, in Comey's Dictionary of Solubilities (1896). 
 
MANGANESE AND GOLD-ENRICHMENT. 797 
 
 7. Concentration in the Oxidized Zone. 
 
 The concentration of gold in the oxidized zone near the 
 surface, where the waters remove the valueless elements more 
 rapidly than gold, is fully treated hy T. A. Bickard in his 
 paper on the Bonanzas in Gold-Veins. 48 Undoubtedly this is 
 an important process in lodes which do not contain manganese, 
 or in manganiferous lodes in areas where the waters do not 
 contain appreciable chlorine. In the oxidized zone it is some- 
 times difficult to distinguish the ore which has been enriched 
 by this process from ore which has been enriched lower down 
 by the solution and precipitation of gold, and which, as a result 
 of erosion, is now nearer the surface. It cannot be denied 
 that tine gold migrates downward in suspension; but in all 
 probability this process does not operate to an important extent 
 in the deeper part of the oxidized zone. If the enrichment in 
 gold is due simply to the removal of other constituents, it is 
 important to consider the volume- and mass-relations before 
 and after enrichment, and to compare them with the present 
 values. In some cases, it can be shown that the enriched ore 
 occupies in the lode about the same space as was occupied 
 before oxidation. Jjet it be supposed that a pyritic gold -ore 
 has been altered to a limonite gold-ore, and that gold has 
 neither been removed nor added. Limonite (sp. gr. from 3.6 
 to 4), if it is pseudomorphic after pyrite (sp. gr. from 4.95 to 
 5.10) and if not more cellular, weighs about 75 per cent, as 
 much as the pyrite. In those specimens which I have broken, 
 cellular spaces occupy in general about 10 per cent, of the 
 volume of the pseudomorph. With no gold added, the ore 
 should not be more than twice as rich as the primary ore, even 
 if a large factor is introduced to allow for Si0 2 removed and 
 for such cellular spaces. 
 
 Rich bunches of ore are much more common in the oxidized 
 zone than in the primary sulphides of such lodes. They are 
 present in some lodes which carry little or no manganese in the 
 gangue, and which below the water-level show no deposition 
 of gold by descending solutions. Some of them are doubtless 
 residual pockets of rich ore which were richer than the main 
 ore-body when deposited as sulphides, but others are very 
 
 * 8 Trans., xxxi., 198 to 220 (1901). 
 
798 MANGANESE AND GOLD-ENRICHMENT. 
 
 probably ores to which gold has been added in the process of 
 oxidation near the water-table by the solution and precipitation 
 of gold in the presence of the small amount of manganese con- 
 tributed by the country- rock. In view of the relations shown 
 by the chemical experiments it is probable that very little 
 manganese will accomplish the solution of gold, but, as already 
 stated, it requires considerably more manganese to form ap- 
 preciable amounts of the higher manganese-compounds which 
 delay the deposition of gold, suppressing its precipitation by 
 ferrous sulphate. In the absence of larger amounts of the 
 higher manganese-compounds, the gold would probably be 
 precipitated almost as soon as the solutions encountered the 
 zone where any considerable amount of pyrite was exposed in 
 the partly-oxidized ore ; for Buehler and Gottschalk have lately 
 shown that oxygenated solutions attack pyrite and dissolve it 
 in a comparatively short time, and McCaughey has shown that 
 even traces of the ferrous sulphate thus formed precipitate gold 
 almost immediately. From this it follows that deposits show- 
 ing only traces of manganese, presumably supplied from the 
 country-rock, are not enriched far below the zone of oxidation. 
 
 8. Vertical Relation of Deep-Seated Enrichment of Gold to 
 Chalcodtization. 
 
 In several of the great copper-districts of the West (see 
 group 3, p. 806) gold is a by-product of considerable value. In 
 another group of deposits, mainly of Tertiary age (see group 4, 
 p. 807), and younger than the copper-deposits, silver and gold 
 are the principal metals, and copper, when present, is only 
 a by-product. But in some of these precious-metal ores chal- 
 cocite is, nevertheless, the most abundant metallic mineral, 
 often constituting 2 or 3 per cent, of the vein-matter. Fre- 
 quently it forms a coating over pyrite or other minerals. 
 Some of this ore, appearing in general not far below the water- 
 table, is fractured, spongy quartz, coated with pulverized chal- 
 cocite. It frequently contains good values in silver, and more 
 gold than the oxidized ore or the deep-seated sulphide ore. 
 Clearly, the conditions which favor chalcocitization are favor- 
 able also to the precipitation of silver and gold. 
 
 The exact chemical reaction which yields chalcocite is not 
 
MANGANESE AND GOLD-ENRICHMENT. 799 
 
 known. At 100 C., according to Dr. H. K Stokes, 49 the re- 
 action with pyrite is probably about as follows : 
 
 5 FeS 2 + 14 CuS0 4 + 12 H 2 = 7 Cu 2 S + 5 FeS0 4 + 12 H 2 S0 4 . 
 
 In the cold, the reaction may differ in details, but without 
 doubt much ferrous and acid sulphate is set free. Attendant 
 reactions confirm this statement; for, if calcite is present, gyp- 
 sum is formed by the reaction of H 2 S0 4 on lime carbonate ; 
 and, if the wall-rocks are sericitic, kaolin is formed by the acid 
 reacting upon potassium-aluminum silicate, the potash going 
 into solution as sulphate. The abundant ferrous sulphate must 
 quickly drive the gold from solution, and it apparently follows 
 that there may be no appreciable enrichment of gold below the 
 zone where chalcocitization is -the prevailing process. In de- 
 posits such as those of disseminated chalcocite in porphyry, 
 where the chalcocite' occurs in flat-lying zones related to the 
 present surface, and where the ore from which chalcocite was 
 derived carried gold, and suitable solvents were provided, 
 there should be a comparatively even distribution of gold, 
 which should increase and decrease with the chalcocite of the 
 secondary ore. A different ratio of values should be found in 
 the oxidized low-grade capping above the chalcocite, for the 
 solution of gold, even under the most favorable conditions, 
 appears to lag behind the solution of copper, and this should 
 be more marked in these deposits, since in all available analyses 
 the porphyries are low in manganese, and rhodochrosite is not 
 noted in the primary ore. I am informed that a fairly-constant 
 ratio between copper and gold is very noticeable in the dis- 
 seminated deposits at Ely and at Bingham. That whatever 
 gold is present in the rock below chalcocitized pyrite is not a 
 result of deposition from cold solution, is reasonably certain 
 under the conditions named. 
 
 9. Vertical Relations of Silver-Gold and Gold-Silver Ore in 
 Deposits Carrying Both Metals. 
 
 This paper will not discuss in detail the processes of second- 
 ary enrichment of silver-deposits a subject already treated in 
 
 49 Unpublished MSS. quoted by Lindgren in Professional Paper No. 43, U. S. 
 Geological Survey, p. 183 (1905), and in Weed's translation of Beck's text-book. 
 
800 MANGANESE AND GOLD-ENRICHMENT. 
 
 our Transactions by S. F. Emmons, W. H. Weed, and C. R. 
 Van Hise. There are, however, certain deposits mainly asso- 
 ciated with Tertiary rocks, in which both silver- and gold- 
 values are important. Examples are the Comstock lode, Tono- 
 pah, Tuscarora, etc. Where physical conditions are favorable, 
 deposits of this type should show in "general a concentration of 
 gold at certain horizons, and of silver at other horizons, de- 
 pending upon the composition of the mine-waters and other 
 factors. The determination, in such mines, of the principles 
 controlling the mutual relations, especially in the deeper zones 
 of the gold-silver and the silver-gold ore-bodies, would have 
 great practical value. So far as I know, no record of experi- 
 ments with solutions containing both sulphates and chlorides 
 and a mixture of gold and silver is available. The solubilities 
 of silver-salts lately determined by Kohlrausch (quoted by Alex- 
 ander Smith) are suggestive. He found that at 18 C. a sat- 
 urated aqueous solution of AgS0 4 contains 5.5 g. per liter; but 
 at this temperature water holds in solution only 0.0016 g. of 
 silver chloride per liter. That silver is held in solution by 
 mine-waters carrying sulphates and chlorides was shown by 
 J. A. Reid. 50 Such waters in a Comstock mine carried about 
 188 mg. of silver and 4.15 mg. of gold in a ton of solution. 
 
 The effect, on a manganiferous silver-ore, of a solution carry- 
 ing chlorides would be to liberate chlorine, which would react 
 with silver to form " horn-silver." This would be fixed in the 
 manganiferous ore, and such a silver-ore would be compara- 
 tively stable. The oxidized manganiferous silver-ore at Lead- 
 ville, Colo., 51 and at Neihart, Mont., in which silver is generally 
 supposed to be carried largely as chloride, may have originated 
 in this manner. On the other hand, rich ores could hardly be 
 formed where the solutions carried abundant sulphuric acid 
 and little or no chlorine, for the soluble silver sulphate would 
 be formed, and the manganiferous ore leached. To determine 
 the genesis of such manganiferous ore, it is desirable to know 
 the silver-content of the primary rhodochrosite, for, as indi- 
 cated above, two interpretations of the phenomenon are other- 
 wise possible. 
 
 50 Bulletin of the Department of Geology, University of California, vol. iv., No. 10, 
 p. 193 (1904-06). 
 
 51 S. F. Emmons, Monograph No. XII., U. S. Geological Survey, p. 562 (1886). 
 
MANGANESE AND GOLD-ENRICHMENT. 801 
 
 As pointed out by Penrose, 52 silver chlorides are formed 
 extensively in arid countries, at or very near the surface. Fre- 
 quently the workable ore gives out a few feet down. At many 
 places in Nevada, the so-called " chloriders " stripped the sur- 
 face over considerable areas; but where the unoxidized ore 
 was encountered the mines were abandoned. At some of these 
 places the chloride ore carried little, if any, more gold than the 
 unoxidized, unprofitable silver-gold ore below. The primary 
 ore of many of these deposits carries relatively little pyrite ; 
 and the inspection of a number of them gives the impression 
 that the siliceous ores are more favorable than the more highly 
 pyritic ores to the formation of a surface chloride zone. Man- 
 ganese oxides are not necessary for the formation of the chloride 
 zone. In many of them manganese is absent. If it is present 
 in appreciable amount, if the physical conditions for a down- 
 ward circulation in the lode are favorable, and if the primary 
 ore carries gold, it would be reasonable to expect an enrich- 
 ment of gold below the zone of the chloride-enrichment of 
 silver. In the presence of strong acid sulphate waters, silver, 
 like gold, is dissolved from the outcrop ; and in some mines, 
 where both metals are present in important quantities, the 
 outcrop and the oxidized zone for a short distance below are 
 leached of both silver and gold. 
 
 The migration of both metals with selective solution and pre- 
 cipitation is suggested by the relation of silver-gold and gold- 
 silver ore-bodies on the Comstock lode. The Comstock lode, 
 which has produced more than $200,000,000 silver and $150,- 
 000,000 gold, is a broad fault-zone in late Tertiary rocks. The 
 ore-shoots occur here and there in this zone,which is developed 
 more than 4,000 ft. below the surface. 53 Since the deposits 
 were formed there has been extensive fracturing. In the lode 
 there are great bodies of " sugar " quartz which are due, ac- 
 cording to Becker, 54 to this movement. Over considerable 
 spaces one cannot obtain fragments of rock as large as one's fist 
 
 62 Journal of Geology, vol. ii. f No. 3, p. 314 (Apr. -May, 1894). 
 
 53 Clarence King, Geological Exploration of the 40th Parallel, vol. iii., Mining In- 
 dustry (1870); John A. Church, The Comstock' Lode (1879); G. F. Becker, Mono- 
 graph No. 777. , U. S. Geological Survey (1882); J. A. Reid, Bulletin of the Depart- 
 ment of Geology, University of California, vol. iv., No. 10, pp. 177 to 199 (1904-06). 
 
 54 Op. tit, p. 272. 
 
802 MANGANESE AND GOLD-ENRICHMENT. 
 
 which do not show fissures. There were clearly two periods 
 of movement, one before the deposition of the primary ore and 
 one following it. The latter movement, mainly parallel to the 
 lode, gave conditions for an active circulation of water after the 
 primary deposition. According to Dr. Becker, "it is possible 
 that the seams of rich ore in the great bonanza represent a de- 
 position posterior to the final cessation of movement," and " it 
 is also by no means impossible that some of the richer ores have 
 been redeposited, forming at the expense of surrounding bodies 
 of lower grade." 55 As already remarked, analysis of the vadose 
 water of the Comstock shows that it contains both gold and 
 silver. It is noteworthy that this water contains much manga- 
 nese, presumably as sulphate. Some associated placers were 
 developed, but they are of very subordinate value compared 
 with that of the lode. Oxidation extended downward as far 
 as 500 ft. According to Clarence King, 56 " a zone of manga- 
 nese oxide occupies the entire length of the lode from the out- 
 crop 200 ft. down." The upper part of this manganiferous 
 zone was probably not of high grade in general, especially in 
 the uppermost portions. I infer that the outcrop and the ore 
 immediately below were in general not so rich as the ore lower 
 down. The longitudinal projections 57 show that many of the 
 stopes carried from below stop some distance below the surface. 
 Von Richthofen (quoted by Becker) says that " the propor- 
 tion of gold to silver decreased during the early period of 
 working the lode, but is now (1865) on the increase again," 
 Presumably, silver at the very surface was leached more 
 rapidly than gold. The vadose waters, as shown by Reid, 58 
 are rich in ferric sulphate ; and his analyses, as well as others, 
 show the presence of chlorides in appreciable amounts. The 
 conditions appear to have been favorable for the solution of 
 both silver and gold in the upper levels, even in the compara- 
 tively short geological period which has elapsed since the pri- 
 mary ores were deposited. The bonanza ore below consisted 
 largely of stephanite, polybasite, argenite, and other dark, rich 
 
 55 Monograph No. IIL, U. S. Geological Survey, p. 273 (1882). 
 
 56 Geological Exploration of the 4Qth'Parallel, vol. iii., Mining Industry, p. 75 (1870). 
 
 57 Becker, op. cit. 
 
 58 Bulletin of the Department of Geology, University of California, vol. iv., No. 10, 
 pp. 177 to 199 (1904-06). 
 
MANGANESE AND GOLD-ENRICHMENT. 803 
 
 silver-minerals, and in places, according to Dr. Becker, ap- 
 peared to fill fractures which involved the primary ore. It is 
 well known that this rich ore was more abundant in the upper 
 than in the lower levels. When I visited the district in 1907 
 I was informed by the foreman at the Consolidated Virginia 
 that large bodies of the hydrothermally-altered porphyry on 
 the Sutro level and below, which contained considerable pyrite, 
 etc., carried also considerable gold and silver, although below 
 the limit of profitable mining. Very few of the ore-bodies 
 which had been worked at those levels were then accessible. 
 The deposits in the upper levels yielded, according to Rich- 
 thofen, from $70 to $107 a ton, whereas in later years the 
 average value of the ore was not more than $37. 
 
 It thus appears that the evidence of the Comstock lode, from 
 the surface down, is favorable to the hypothesis that extensive 
 solution and deposition of gold and silver has taken place, 
 while it is insufficient to show to what extent the great bonan- 
 zas owed their values to such processes. In ores formed so 
 near the surface, there is always the possibility that ascending 
 hot waters deposited the maximum portion of their gold and 
 silver at the horizon where they encountered cold oxygenated 
 solutions. Sulphate may form, in such mixtures, and ferrous 
 sulphate tends to drive both gold and silver out of solution. 
 The proportion of gold to silver was presumably higher in the 
 upper part and in the lower part of the lode than in the middle 
 portion. When Richthofen made his report, he estimated that 
 the lode had produced, to the close of 1865, $15,250,000 of 
 gold and $32,750,000 of silver (gold equals 47 per cent, of the 
 silver) ; whereas Becker reports the amount recovered from 1865 
 to 1881 as $87,121,988 of gold and $105,548,157 of silver (gold 
 equals 83 per cent, of the silver). If much of the change is 
 due to reworking by descending waters, the greater gold-values 
 in the upper portions of the bonanzas indicate that gold was 
 dissolved less readily than silver, and silver precipitated less 
 readily than gold, in the sulphate-rich water of this mine. 
 
 The relation of " horn-silver " to the surface is different from 
 hat shown in the " chloride mines " mentioned above. Ac- 
 cording to Clarence King, 59 silver chloride is accidental, although 
 
 59 Op. cit., p. 82. 
 
804 MANGANESE AND GOLD-ENRICHMENT. 
 
 rare small crystals were found at the outcrop in the Gold Hill 
 group. It occurred, however, at the 900-ft. level of the Yellow 
 Jacket, where, judging from the descriptions, it was present in 
 considerable amount. 
 
 Ferrous sulphate precipitates both silver and gold in acid 
 solutions. The precipitation of gold is, however, many times 
 more rapid and more effective than that of silver. Where sil- 
 ver chloride is not precipitated, one would suppose that cold 
 solutions would transfer the silver to greater depths than gold. 
 Since silver chlorides are not abundant (King), this, if no other, 
 is an argument for the hypothesis that the lower-grade gold- 
 silver ores ($37 a ton or less, Becker 60 ), which were worked in 
 the levels below the great silver-gold bonanzas, were in the 
 main primary. These ore-bodies were not accessible to me 
 when I visited the Comstock mines, and the speculation is not 
 based on paragenetic evidence. 
 
 The relations of silver-gold to gold-silver ores in the Exposed 
 Treasure mine, near Mojave, differ from those at the Com- 
 stock. In the surface-zone, horn-silver has been formed in 
 considerable amount. The proportion of gold to silver in this 
 zone is 1 : 72 (weight). In the lower friable siliceous ores, the 
 proportion of gold to silver is 1 : 12 ; and in the sulphide ores 
 below the water-table, where the gold-content had increased 
 150 per cent, above the average in the friable siliceous ores, 
 the proportion of gold to silver was as 1 to 2. 61 The Exposed 
 Treasure ores are, like those of the Comstock, manganiferous. 
 
 It thus appears that there are two types of enrichment in 
 deposits of manganiferous gold- and silver-ores. In one of 
 them silver chloride is concentrated in the manganiferous oxi- 
 dized ores of the upper levels, and gold is concentrated below. 
 In the other, silver chloride is subordinate, while both gold and 
 silver are concentrated below the oxidized zone. Possibly the 
 difference could be explained if the amount of chlorine were 
 determined in the waters of deposits of both types. Silver 
 .chloride is soluble in an excess of alkaline chlorides. Those 
 deposits in which horn-silver is not present may have been 
 leached by waters unusually rich in chlorides. 
 
 60 Monograph No. III., U. S. Geological Survey, p. 18 et seq. (1882). 
 
 61 Courtenay DeKalb, Trans., xxxviii., 319 (1907). 
 
MANGANESE AND GOLD-ENRICHMENT. 805 
 
 VI. REVIEW OF MINING-DISTRICTS. 
 
 The purpose of this inquiry is to ascertain whether the ore- 
 deposits of the United States give evidence that gold is more 
 readily transferred in manganiferous deposits than in deposits 
 which do not contain manganese, a hypothesis suggested by 
 the chemistry of the processes of solution and precipitation. 
 
 1. If gold is more readily dissolved in manganiferous de- 
 posits, it would be supposed that placers form less readily from 
 pyritic manganiferous lodes than from lodes containing no 
 manganese. If, in areas where the waters carry appreciable 
 chlorine, placers have formed as extensively from such lodes 
 as from lodes free from manganese, then the hypothesis fails. 
 
 2. The manganiferous lodes, in areas of chloride waters, as 
 in the undrained areas of the Great Basin, should in general 
 show less gold at the outcrop and in the upper portion of the 
 oxidized zone than below. In silver-gold deposits, however, 
 silver, on account of the insolubility of the chloride, may re- 
 main, or be concentrated, in the oxidized manganiferous zone. 
 Bunches of rich gold-ore carrying oxidized manganese in the 
 oxidized zone are not necessarily fatal to the theory; for, as 
 already stated, these are probably residual from the zone of 
 secondary enrichment. An extensive enrichment in gold of 
 the oxidized manganiferous ores at the surface, which are 
 shown not to be residual from the zone of secondary ores, 
 would indicate that the selective processes lack quantitative 
 value, if the waters carry chlorine, and if the primary ores, 
 from which the manganiferous oxidized ores are derived, carry 
 appreciable pyrite to supply sulphate. 
 
 3. If in certain lodes gold migrates below the water-table, it 
 should be precipitated quickly by ferrous sulphate. But Mn0 2 
 converts ferrous sulphate to ferric sulphate, which does not 
 precipitate gold. Hence, MnO 2 favors the solution of gold, and 
 converting the ferrous salt to ferric sulphate removes the pre- 
 cipitant. Consequently, if auriferous lodes show enrichment 
 in the deeper zone but related to the present surface of the 
 country, manganiferous lodes should, the other favorable con- 
 ditions provided, show greater differences in values with respect 
 to gold than lodes free from manganese. 
 
806 MANGANESE AND GOLD-ENRICHMENT. 
 
 Gold-Provinces of the United States. 
 
 As Lindgren 62 pointed out in 1902, the principal gold-de- 
 posits of the United States may be divided into four groups. 
 The deposits of each group belong mainly to one metallogenetic 
 epoch, and certain relationships are clearly shown. This classi- 
 fication, which has thrown much light on the genesis of the 
 deposits, is useful as an instrument for study and for compari- 
 son of the deposits with respect to the problem of the migra- 
 tion of gold in them. 
 
 1. The Appalachian gold-deposits, and those of the Home- 
 stake type in South Dakota, are the most important representa- 
 tives of the oldest group. These deposits generally yield 
 placers, are usually low grade below the water-level and are 
 singularly free from bonanzas. They are, in general, not 
 greatly leached near the surface, and may have been enriched 
 by the removal of other material more rapidly than gold. At 
 only one of them, the Haile mine, in South. Carolina, it is 
 thought probable that gold has been carried below the water- 
 level. The Homestake mines show little evidence of secondary 
 enrichment by transfer of gold, as will appear in the review that 
 follows. Judging from descriptions, practically all of these 
 deposits are free from manganese. 
 
 2. The California gold-veins and related deposits in Nevada 
 (Silver Peak) and in Alaska (Treadwell, etc.) are younger 
 than the Appalachian deposits, and were probably formed in 
 the main in early Cretaceous times. These deposits, where 
 physiographic conditions are favorable, have generally yielded 
 rich placers. At many places, moreover, the ore is worked at 
 the very surface, and, as will appear in the subsequent review, 
 there is very little evidence of the migration of gold to the 
 deeper zones. In the places where detailed work has been 
 done, rhodochrosite is never a gangue-mineral, although man- 
 ganese oxide does occur in traces in the country-rock, and 
 rhodochrosite is found in a few places in veinlets in the min- 
 ing-districts but not associated with the gold-veins. 
 
 3. The deposits of the third group are later than the early 
 Cretaceous, and some of them are probably early Tertiary. 
 
 62 The Gold Production of North America, Trans., xxxiii., 790 to 845 (1902); 
 p. 424, this volume. Metallogenetic Epochs, Economic Geology, vol. iv., No. 5, 
 pp. 409 to 420 (Aug., 1909). 
 
MANGANESE AND GOLD-ENRICHMENT. 807 
 
 They are extensively developed in Montana, Nevada, Utah, and 
 Colorado. Mr. Lindgren calls this, group the Central Belt. 
 Many of its deposits have yielded considerable gold, and in 
 certain other districts very closely related genetically (Butte, 
 Georgetown silver-gold lodes, Cortez Nevada, Tintic, etc.) 
 much gold has been obtained as a by-product to copper- or 
 silver-mining. Some of these deposits have yielded placers 
 and some have not. At Philipsburg and Neihart, Mont, 
 Georgetown, Colo., and elsewhere, the deposits show a second- 
 ary enrichment of silver below the water-table. At Philips- 
 burg, and probably at some other places, an enrichment in 
 gold accompanies this concentration of silver. Some of the 
 lodes of group 3 carry much manganese, and some carry none. 
 Present data are meager for most of these districts. The deter- 
 mination of gold from the surface down in a large number of 
 deposits would serve as a useful check to the conclusions based 
 upon the chemistry of the processes involved in its solution 
 and precipitation. 
 
 4. Group 4 includes the most recent ore-deposits in the 
 United States. All of them are Tertiary, and most of them are 
 Miocene or Pliocene. In general, they were formed relatively 
 near the surface, and in some places it is highly probable that 
 not more than a thousand feet of vein-material has been re- 
 moved by erosion since the ores were deposited. The majority 
 of these deposits carry silver, arid in many of them its value is 
 greater than that of the gold ; but they have supplied, notwith- 
 standing, about 25 per cent, of the gold-production of North 
 America. They are typically developed in Nevada (Corn- 
 stock, Tonopah, Goldfield, Tuscarora, Gold Circle) ; California 
 (Bodie); Idaho (De Lamar); South Dakota (later than Home- 
 stake type) ; Colorado (Cripple Creek, Idaho Springs, Rosita 
 Hills, San Juan, etc.) ; Montana (Little Rockies, Kendall, etc.). 
 Many occurrences in Mexico should probably be placed here, 
 and likewise those of the Aleutian Islands, described by Becker. 
 The deposits of this group have not supplied much placer-gold. 
 They have not been exposed to erosion so long as the older 
 deposits. In general, the gold is finely divided. It may have 
 been scattered or it may have been redissolved and deposited 
 lower down. Many of these deposits are in arid countries, 
 where conditions for working placers are not favorable ; but, 
 
808 MANGANESE AND GOLD-ENRICHMENT. 
 
 even those in well-watered districts supply relatively little 
 placer-gold. Manganese is abundant in some of these deposits 
 (Comstock, Exposed Treasure, Tonopah) ; it is very sparingly 
 present in others (Little Rockies) ; in still others (Goldfield) it 
 is almost entirely absent. 
 
 A few small placers are associated with the manganiferous 
 lodes, although at some places, as at Tuscarora, Nev., they 
 seem to have been derived from veins near-by which are not 
 manganiferous, as is probably the case with some deposits of 
 group 3 (Butte, Philipsburg). Many of the California veins 
 (group 2) carry rich ore at the very surface, but the Tertiary 
 gold-veins are- generally richer in gold a few feet below the 
 surface than at the outcrop. Doubtless, many of them would 
 have been overlooked if it had not been for the concentration 
 of horn-silver and argentiferous pyromorphite at the surface. 
 At many of these deposits, however, good gold-ore is found 
 only a few feet below the surface. 
 
 It thus appears that practically all of the manganiferous 
 gold-deposits of the United States, so far as they have been de- 
 scribed, may be included in groups 3 and 4 ; that nearly all 
 described deposits where relations indicate a migration of gold 
 belong to the same groups ; that placers are much less abun- 
 dantly developed than in groups 1 and 2 ; and that outcrops 
 less frequently supply gold ; that secondary enrichment below 
 the water-table, if carried on at all, proceeds with extreme slow- 
 ness in groups 1 and 2, but may be more pronounced in de- 
 posits of groups 3 and 4. Not all of these deposits carry man- 
 ganese, however, and those which do not carry it should be 
 expected to show relationships more nearly approximating 
 those of groups 1 and 2. 
 
 5. Some deposits formed at hot springs carry gold. As a 
 rule, traces only are found in the sinters, and at many places 
 even traces are not detected. This is readily explained when 
 it is noted that these springs frequently carry both sulphates 
 and iron. If the sulphates are due to contamination with oxy- 
 genated surface-waters, then such waters, before complete oxi- 
 dation, would precipitate gold. Since only a little ferrous sul- 
 phate precipitates practically all of the gold in a solution, it 
 would be supposed that the major deposition would be some 
 distance below the surface, where oxygen-bearing waters first 
 
MANGANESE AND GOLD-ENRICHMENT. 809 
 
 contaminated the hot solutions, and not at the surface. The 
 same argument should apply to silver also, although the action 
 of the ferrous salt on solutions carrying silver is not nearly 
 so rapid as on solutions carrying gold. In the hot solutions, 
 manganese, even if it were present, would probably not hold 
 the gold or silver in solution by oxidizing ferrous salts, for 
 ascending hot waters deposit manganous rather than man- 
 ganitic compounds. 
 
 1. Southern Appalachian Districts. The gold-deposits of the 
 southern Appalachians are among the oldest gold-deposits of 
 the United States, and were probably formed, 63 in the main, 3 
 or 4 miles below the surface at the time of deposition. Many 
 of them are in mica-schist and other crystalline rocks, and 
 some are closely associated with granitic intrusions. Some are 
 cut by diabasic intrusives, presumably later than the ore. The 
 deposits have yielded considerable placer- and lode-gold. The 
 minerals, according to Graton, 64 include quartz, sericite, biotite, 
 fluorite, gold, pyrite, galena, blende, pyrrhotite, chalcopyrite, 
 magnetite, etc. Manganese-minerals are not mentioned. In 
 Becker's tabulation of the minerals of the gold-mines of the 
 southern Appalachians, compiled from all previous descriptions 
 and including mines not described by Graton, pyrolusite is 
 mentioned in only three mines and rhodochrosite in one. 65 
 
 Few of these deposits have been extensively explored in 
 depth, and consequently data respecting the vertical distribu- 
 tion of the gold-values are meager. Many of them are profit- 
 able near the surface, partly by reason of the rotten condition 
 of the rock, which renders it more easily worked, and partly 
 because gold is accumulated or enriched by the removal of 
 valueless material. In general there is, according to Graton, 
 very little evidence for or against the theory of the migration 
 of gold; but such migration, if it has taken place, has been 
 extremely slow, for areas which have probably been exposed 
 since Tertiary time show a marked concentration at and near 
 the surface. Possibly some gold has been transferred to lower 
 
 63 Lindgren, Bulletin No. 293, U. S. Geological Survey, p. 124 (1906). 
 6 * Idem, p. 62. 
 
 65 Sixteenth Annual Report, U. S. Geological Survey, Part III. t Mineral Resources 
 of the U. S., p. 277 (1894-95). 
 
 51 
 
810 MANGANESE AND GOLD-ENRICHMENT. 
 
 levels at the Haile mine, South Carolina, 66 where the limit of 
 profitable mining is in general less than 200 ft. below the limit 
 of complete oxidation. In this zone scales of pyrite and free 
 gold are found in joint-cracks, indicating a comparatively re- 
 cent age. The deposits are cut by basic dikes. Prior to 
 Graton's work, many thought that the primary deposition of 
 gold was genetically related to the dikes, 67 since the workable 
 ore appears to be limited to the area cut by them. If the 
 basic dikes (like most basic rocks) carry manganese, then our 
 hypothesis supports, and is supported by, Graton's opinion that 
 secondary enrichment has probably taken place, and the con- 
 flicting views of Graton and Maclaren respecting the genesis 
 of the ores are thus reconciled. 
 
 Certain ore-deposits of Alabama recently described by H. D, 
 McCaskey 68 comprise fissure-veins in granite and lenticular 
 bodies in schists. The principal minerals are quartz, pyrite,. 
 and gold. Some garnet is found in the vein-quartz at Pine- 
 tuckey. Weathering extends to water-level (from 40 to 80 ft. 
 below the surface). The ores are oxidized above this level 
 and are generally free-milling, but below this level the ore i& 
 not profitably amalgamated so far as explored in depth. The 
 ores are fairly regular in width and values, and no evidences 
 of enrichment below the water-level are recorded. 
 
 2. Black Hills, S. D. The principal gold-deposits of the 
 Black Hills 69 are in pre-Cambrian schists which, like the ore- 
 bodies, are cut by Tertiary intrusives. Since the Cambrian 
 conglomerates contain placer-gold, 70 some of the ores must 
 have been deposited in pre-Cambrian times. The most impor- 
 tant deposits are comprised in the Homestake belt, about 
 miles long and 2,000 ft. wide. The principal minerals are 
 quartz, dolomite, calcite, pyrite, arsenopyrite, and gold, with 
 which are associated the minerals of the schist : quartz, ortho- 
 clase, hornblende, biotite, garnetj tremolite, actinolite, titanite r 
 and graphite. 71 The ores, though uniformly of low grade, are 
 
 66 Graton, Bulletin No. 293, U. S. Geological Survey, p. 67 (1906). 
 
 67 Maclaren, Gold, pp. 57, 592 (1908). 
 
 68 Bulletin No. 340, U. S. Geological Survey, p. 36 (1908). 
 
 69 Irving, Emmons, and Jaggar, Professional Paper No. 26, U. S. Geological Sur- 
 vey (1904). 
 
 70 W. B. Devereux, Trans., x., 469 (1881-82). 
 
 71 J. D. Irving, loc. cit., p. 90. 
 
MANGANESE AND GOLD-ENRICHMENT. 811 
 
 very profitable. Some of the ores at the surface were below 
 the average tenor, while other surface-ores were two or three 
 times as rich as the average. The values extend downward as 
 far as exploration has gone, and are fairly uniform to 1,000 ft. 
 or more below the surface. In general, according to S. F. 
 Emmons, secondary enrichment by surface-leaching has had 
 relatively small importance. 72 
 
 3. Treadwell Mines, Alaska. At the Treadwell mines, Doug- 
 las Island, Alaska, large dikes of albite-diorite intrude green- 
 stones and schist, and the shattered diorite has been extensively 
 replaced by mineralizing solutions, and cemented by low-grade 
 gold-ore. The minerals include quartz, albite, rutile, chlorite, 
 epidote, calcite, siderite, pyrite, pyrrhotite, magnetite, chal- 
 copyrite, and molybdenite. Manganese-minerals are not re- 
 ported. 
 
 The mines have been developed 2,000 ft. down the dip. 
 According to A. C. Spencer, 73 the ore shows no progressive 
 change in appearance or values with increasing depth. In the 
 lowest level it is quite as rich as in the upper workings ; and 
 it is evident that changes on the dip are no greater than along 
 the strike. Nothing in the character of the ore indicates any 
 important concentration of values by oxidizing waters. The 
 fact that extensive placers were not formed is not opposed to 
 the view expressed by Spencer that the gold has not been 
 transferred ; the country has been recently glaciated, and sur- 
 face-accumulations have been scattered. The gold accumulated 
 at the apex since glacial time was, indeed, recovered by sluicing. 
 
 4. Berner's Bay, Alaska. According to Adolph Knopf, the 
 lodes of the Berner's Bay district are fissure-veins in diorite. 
 There is no evidence of secondary enrichment of gold or of 
 leaching near the surface. The deposits contain no manganese. 
 
 5. The Mother Lode District, Cal The Mother Lode dis- 
 trict, as described by F. L. Ransome, 74 is an area of crystalline 
 schists and altered igneous rocks with intruded granodiorite 
 and related rocks. The deposits are fissure-veins, which gen- 
 erally trend northwestward, and, at many places, parallel the 
 schistosity of the country- rock. The ore does not contain 
 
 72 Professional Paper No. 26, U. S. Geological Survey, p. 79 (1904). 
 
 73 Bulletin No. 287, U. S. Geological Survey, pp. 32 and 115 (1906). 
 
 74 Mother Lode District, Folio No. 63, U. S. Geological Survey, p. 3. 
 
812 MANGANESE AND GOLD-ENRICHMENT. 
 
 manganese-minerals. Placers are abundantly developed, and at 
 many places rich ore is found at the very surface. According 
 to Ransome, there is no evidence that the mines grow suddenly 
 richer at any -arbitrary depth, nor is there any recognizable 
 regular change in the value of pay-shoots with depth, below 
 the zone of superficial weathering. Some of these deposits are 
 very regular and uniform in values, and have been developed 
 to very great depth. 
 
 6. Nevada City and Grass Valley, Cal. The area of Nevada 
 City and Grass Valley 75 includes metamorphosed Carboniferous 
 sedimentary rocks, compressed into isoclines, and associated 
 igneous rocks less intensely metamorphosed. Above these 
 are slates with associated diabase and serpentine. These rocks 
 are folded and metamorphosed, but are not so intensely com- 
 pressed as the Carboniferous. Intruded into these rocks are 
 great bodies of granodiorite, probably of early Cretaceous 
 age. The ore-deposits are strong fissure-veins, formed after 
 the granodiorite intrusions. The minerals are quartz, chalce- 
 dony, magnetite, sericite, mariposite, pyrite, pyrrhotite, chalco- 
 pyrite, galena, blende, scheelite, arsenopyrite, tetrahedrite, 
 stephanite, and cinnabar. Some earthy manganese-ore occurs 
 in small fissures in the granodiorite, but not in connection with 
 the quartz veins. 
 
 Near the surface 76 the upper part of a vein is generally 
 decomposed, forming a mass of limonite and quartz. The 
 decomposition seldom extends more than 200 ft. on the incline 
 of a vein dipping 45, or more than 150 ft. below the surface. 
 Fresh ore is sometimes found almost at the surface. The sur- 
 face-ore is generally richer than the fresh ore below, owing to 
 the liberation of gold from the sulphides and the removal of 
 substances other than gold. In this process, silver is also 
 partly removed. In some of the mines, the lodes have been 
 followed down the dip for 2,000 or even 3,000 ft. The unoxi- 
 dized ore shows no gradual diminution of tenor in the pay- 
 shoots below the zone of surface-decomposition. " Within the 
 same shoot there may be many and great variations of the 
 tenor, but there is certainly no gradual decrease of it from the 
 
 75 Waldemar Lindgren, Seventeenth Annual Report, U. S. Geological Survey, Part 
 II. (1895-96). 
 
 76 Loc. cil., p. 128. 
 
MANGANESE AND GOLD-ENRICHMENT. 813 
 
 surface down." 77 Important placer-deposits were formed from 
 these veins. 
 
 7. The Ophir District, Cal. The rocks of the Ophir dis- 
 trict 78 comprise amphibolite-schists and massive amphibolites, 
 with intrusions of granodiorite. These rocks are cut by quartz 
 veins which fill co-ordinate fissures. The minerals are gold, 
 electrum, some iron, copper and arsenical pyrites, with galena, 
 blende, tetrahedrite, and molybdenite. The gangue is mainly 
 quartz with a little calcite. The proportion of gold to silver 
 varies by weight from 1:1 to 1 : 10, the values of gold pre- 
 dominating. Certain small ore-shoots, in veins in the amphi- 
 bolite, carry more than the usual tenor of gold ; and the richest 
 shoots are usually found where veins cross the belts rich in iron. 
 According to Lindgren, such ore-bodies may have been en- 
 riched by leaching. The common statement, that the gold- 
 vein becomes barren as the depth from the surface increases, 
 is not justified, in his opinion, 79 by the evidence afforded in the 
 mines. The extensive development of placers, the value of 
 the ore near the surface, and the occurrence of valuable ore- 
 shoots just below the surface, are opposed to the notion of 
 extensive migration of gold in these deposits. 
 
 8. Silver Peak, Nev. According to J. E. Spurr, 80 the de- 
 posits of Silver Peak, Nev., are lenticular masses and fissure- 
 veins in Palaeozoic sedimentary rocks. Genetically, they are 
 related very closely to granitic rocks, which, as shown by Mr. 
 Spurr, have alaskitic or pegmatitic phases. They are probably 
 post-Jurassic, and should be grouped with the California gold- 
 veins, with which geologically they have much in common. 
 Of the Drinkwater and Crowning Glory deposits, which are 
 the most important examples, Spurr says that no decided en- 
 richment of the ores by oxidation can be established. The 
 ores in the upper tunnel seem to have been locally richer than 
 any found in the lower tunnel; but this difference has no evi- 
 dent relation with the surface, and is probably original. The 
 values are finely disseminated gold and auriferous sulphides, 
 
 77 Op. cit., p. 163. 
 
 78 Waldemar Lindgren, Fourteenth Annual Report, U. S. Geological Survey, Part 
 II., p. 252 (18*2-93'. 
 
 79 Idem, p. 279. 
 
 so- Professional Paper No. 55, U. S. Geological Survey (1906 j. 
 
814 MANGANESE AND GOLD-ENRICHMENT. 
 
 scattered through vitreous quartz. The character of the ore 
 affords no ground for supposing any great concentration by 
 surface-waters, since the minerals are not easily reached by 
 percolating waters. No ore-shoots correspond to the fractures 
 which cross the ore an indication that the waters which cir- 
 culated along such subsequent fractures had little effect in the 
 redistribution of values. 
 
 9. Philipsburg, Mont. The Philipsburg quadrangle is an 
 area of sedimentary rocks, ranging from pre-Cambrian to late 
 Cretaceous, with intrusions of quartz-monzonites and related 
 rocks, probably belonging to the same period of intrusion as 
 that of the Butte granites and other batholiths in Montana. 
 The most important ore-deposits in this quadrangle are those 
 of the Granite-Bimetallic and the Cable mines. 
 
 The Granite-Bimetallic is a strong fissure-vein in quartz - 
 monzonite, which carries chiefly silver, but also an important 
 amount of gold. There is conclusive paragenetic evidence of 
 the secondary enrichment of silver below the water-level, and 
 the rich silver-ore carries also more gold than the low-grade 
 silver-ore in the bottom of the mine. The outcrop of this 
 deposit carried some silver, but very little gold ; and, after the 
 discovery, the location was allowed to lapse, by reason of the 
 small assay-returns from the gossan. Richer ore appeared not 
 far below the surface and extended down to the 10th level. 
 The shoot of high-grade ore, which extended for about a m ile 
 along the strike of the deposit, followed, in a broad way, the 
 present rugged surface. The gangue is rich in manganese. 
 Some migration of gold has undoubtedly taken place. No 
 associated placers have been developed. 
 
 At the Cable mine the deposits are included in a long, thin 
 block of limestone, in contact on either side with quartz-mon- 
 zonite. The principal minerals are calcite, quartz, pyrrhotite, 
 pyrite, magnetite, and chalcopyrite, with chlorite, muscovite, 
 and other silicates. At one or two places small traces of man- 
 ganese dioxide have been noted in the oxidized ore, but it is 
 very much less abundant than in the deposits of the Granite- 
 Bimetallic type. This deposit yielded important placers. Good 
 ore was found at or very near the surface ; and, according to 
 the best obtainable data, the values increased somewhat for a 
 short distance below the surface. Some concentration has 
 
MANGANESE AND GOLD-ENRICHMENT. 815 
 
 taken place by the removal of calcite and other valueless ma- 
 terial more rapidly than gold ; but there is no evidence of 
 secondary enrichment in gold below the water-table. The 
 indications are, that the gold has not been extensively trans- 
 ported since the deposit was formed. 
 
 10. Other Montana Districts. The secondary enrichment of 
 gold- and silver-deposits at Neihart, at Butte, and in other 
 Montana districts, has been described by W. H. Weed, in 
 various papers. These deposits generally contain appreciable 
 manganese. In that respect they differ from the Idaho deposits 
 described by Lindgren, which do not carry rhodochrosite or 
 appreciable manganese dioxide. With some notable exceptions, 
 such as the De Lamar deposits, the Idaho veins are probably 
 older than those of Montana, and, as Lindgren has pointed out, 
 should be grouped with the early Cretaceous California gold- 
 veins- rather than with the late Cretaceous or early Tertiary 
 group, to which most of the Montana deposits belong. The 
 Idaho veins which have been closely studied do not give evi- 
 dence of the downward migration of gold. 
 
 11. Edgemont, Nev. The gold-deposits at Edgemont, Elko 
 county, Nev., which should be classed with group 3, are in an 
 -area of quartzite, with intrusions of granodiorite. The de- 
 posits are fissure-veins, and their gold-values are comparatively 
 uniform. The ore consists of pyrite, galena, and arsenopyrite 
 in a gangue of quartz. Copper carbonates and manganese- 
 minerals are rare or absent. The ore is stoped practically to 
 the surface. There has probably been a slight amount of en- 
 richment by removal of certain substances in the oxidized zone 
 more rapidly than gold; there is no evidence that gold has 
 been transferred below the water-level by descending surface- 
 waters. 81 
 
 12. Leadville, Colo. The deposits of Leadville yield silver, 
 lead, and gold. The country is an area of Palaeozoic limestones 
 and quartzites, with intrusive sills and dikes of porphyries. 82 
 Some of these deposits carry in the upper horizons a large 
 amount of manganese; and this ore is frequently rich in silver, 
 presumably in the form of the native metal or as chloride. 
 
 81 W. H. Emmone, Bulletin No. 408, U. S. Geological Survey (1910). 
 
 82 S. F. Emraons, Geology and Mining Industry of Leadville, Colorado, Mono- 
 graph No. XI L, U. S. Geological Survey (1886) ; and S. F. Emmons and J. D. 
 Irving, BuUetin No. 320, U. S. Geological Survey (1907). 
 
816 MANGANESE AND GOLD-ENRICHMENT. 
 
 Assays of this ore, showing the amount of gold contained in 
 it, are not available to me. According to the requirements of 
 the theory under investigation, it would be expected to be low 
 in gold in this upper zone, where the waters probably carry 
 ferric salts and chloride. Of considerable interest in this con- 
 nection are some small fractures in the quartzite at a lower 
 horizon, which, as Mr. Emmons informs me, often carry small 
 amounts of high-grade manganiferous gold-ore. This ore he 
 regards as a deposit from descending waters. Possibly it is the 
 gold leached out above, where ferric salts predominate, and was 
 carried to greater depth by the manganiferous solutions which 
 delay the action of ferrous sulphate as a precipitant of gold. 
 
 13. Georgetown, Colo., Silver-Lead Deposits. The silver-lead 
 lodes of Georgetown and Silver Plume, Colo., are of early 
 Tertiary age. The veins cut crystalline schists and Tertiary 
 igneous rocks. According to Spurr, Garrey and Ball, 83 several 
 thousand feet of overlying rocks have been eroded since the 
 ores were deposited, and some of the values in the eroded por- 
 tions of the lodes have migrated to the portions still remaining. 
 The principal metallic minerals are argentiferous galena and 
 blende, with pyrite and chalcopyrite ; the ores usually carry 
 about $2 gold per ton. The silver-values are mainly in poly- 
 basite, freibergite, argentite, pyrargyrite, and proustite. The 
 gangue is quartz, chalcedony, barite, with carbonates of lime, 
 iron, manganese, and magnesia. 
 
 The rich silver-minerals were the last to be deposited, and 
 form on the walls of the fractures in the older, baser ore, or cut 
 the older deposits. The zone of complete oxidation extends 
 from 5 to 40 ft. below the surface. The oxidized ore often 
 contains several hundred ounces of silver per ton. Below this 
 ore are friable black sulphides and secondary galena. This 
 secondary ore, according to Spurr and Garrey, is rich in silver 
 and lead and carries more gold than occurs at greater depth. 
 This ore cuts the primary sulphide ; and the latter, which may 
 have contained from 20 to 30 oz. of silver per ton, is enriched 
 to more than 200 oz. per ton. 
 
 Quoting from Spurr and Garrey: 84 
 
 83 Professional Paper No. 63, U. S. Geological Survey, p. 136 (1908). 
 
 84 J. E. Spurr and G. H. Garrey, Professional Paper No. 63, U. S. Geological 
 Survey, p. 144 (1908). 
 
MANGANESE AND GOLD-ENRICHMENT. 817 
 
 " Below the zone where soft secondary sulphides occur and irregularly overlap- 
 ping the lower portion of this zone the rich ores contain polybasite, argentiferous- 
 tetrahedrite, and ruby silver, better crystallized and more massive than the pulve- 
 rulent sulphides, but also subsequent in origin to the massive galena-blende ore. 
 These richer ores diminish in quantity as depth increases, though gradually and 
 irregularly, so that the lower portion of the veins contains relatively less silver and 
 lead. The best ore in most veins has been found in the uppermost 500 feet, 
 although good ore extends locally down to 700 or 800 feet, and in the Colorado- 
 Central, and to a minor extent in other veins, down to a thousand feet or more." 
 
 14. Auriferous Deposits of the Georgetown Quadrangle, Colo- 
 rado. The auriferous deposits of the Georgetown quadrangle 
 are mainly at Idaho Springs and in the Empire district, 
 although some are developed near Georgetown in the area of 
 the silver-lead deposits. As shown by Spurr and Garrey, the 
 gold-lodes are probably of later age than the silver-lead de- 
 posits. They cut the crystalline schists and the Tertiary por- 
 phyries, but are genetically related to alkali-rich intrusive rocks 
 of middle or late Tertiary age. They carry pyrite, chalcopy- 
 rite, chalcocite, quartz, adularia, and gold, with minor amounts 
 of barite, fluorite, telluride, etc. Carbonates of iron, magne- 
 sium, lime, and manganese occur, but are relatively rare. In 
 many of the mines the ore averages from 1 to 2 oz. of gold 
 and from 20 to 40 oz. of silver per ton. The lodes are usually 
 oxidized at the surface and from 15 to 70 ft. downward. They 
 have yielded some moderately-productive placers. In several 
 mines, the oxidized is much richer than the average ore. 
 Below the zone of oxidation, secondary chalcopyrite and chal- 
 cocite prevail for several hundred feet from the surface, but 
 decrease at greater depth. There is an important enrichment 
 of gold and silver, coincident with the occurrence of the cop- 
 per-minerals. As stated by Spurr and Garrey : 
 
 "In the mines mentioned a portion of the copper which has contributed to the 
 enrichment of the original sulphides has been derived from the oxidized zone, but 
 it seems unlikely that this has been the case with the gold and silver, which, like 
 the enriched superficial portions of the argentiferous veins, must have been derived 
 from the overlying portions of the lodes which are now eroded. . . . 
 
 ' ' On the whole, the strongest evidence of the reworking of the ores by surface 
 waters is afforded by markedly cupriferous ores. . . . Apart from this, how- 
 ever, and from the probable partial reconstruction of galena near the surface in 
 some mines, the evidence of rearrangement of the ores by descending waters is in 
 general not nearly so great as in the Georgetown district, and such reworking has- 
 probably taken place to a considerably less extent." 
 
818 MANGANESE AND GOLD-ENRICHMENT. 
 
 15. San Juan, Colo. The gold-deposits of the San Juan re- 
 gion, 85 including those near Telluride, Silverton, and Ouray, 
 are, as shown by Ransome, of varied character. ' They are 
 mainly Tertiary, and should be classed with group 3 or 4 
 above named. The lead-silver deposits and the stocks near 
 Ironton are not here considered. 
 
 In this elevated area the ground is frozen much of the year, 
 and the rapid erosion is due largely to mechanical disintegra- 
 tion. Secular decay or oxidation of the ores, according to 
 Ransome, is not as a rule very extensive, and is at some places 
 negligible. Purington has pointed ' out, however, that the out- 
 crops of the San Juan lodes are, in general, of lower grade 
 than the ore a few feet below the surface, possibly by reason of 
 the migration of gold in suspension. Many of the lodes are 
 tight, and do not appear to offer favorable conditions for down- 
 ward migration of waters. The country is well drained, and 
 chlorine is probably not abundant in the mine-waters. The 
 conditions for deep-seated enrichment are therefore not par- 
 ticularly favorable, although some concentration has taken 
 place locally by the leaching and removal of the less- valuable 
 materials from the ore. The workable ore appears to be 
 mainly of primary origin. 
 
 At some places the gangue includes manganiferous minerals. 
 There is some evidence that gold was transported to a limited 
 extent. As Ransome points out, 86 in the Tomboy and Camp 
 Bird mines, black oxide of manganese occurs in the deepest 
 workings (in 1901) and usually indicates good ore. These 
 little sheets of rich, dark, manganiferous ore, which fill post- 
 mineral fractures, Ransome regards as later than the general 
 mass of the ore. It is reasonable to suppose that they repre- 
 sent the deposition from solutions which dissolved gold in the 
 upper portion of the lode, where ferric salts prevail, and which, 
 in the presence of manganese, were able to transport their load 
 to greater depths, but which, coming into contact with pyrite, 
 
 85 F. L. Ransome, A Keport on the Economic Geology of the Silverton Quad- 
 rangle, Bulletin No. 182, U. S. Geological Survey (1901) ; and C. W. Purington, 
 Preliminary Report on the Mining Industries of the Telluride Quadrangle, Eigh- 
 teenth Annual Report, U. S. Geological Survey, Part III., p. 745 (1896-97) ; Puring- 
 ton, Woods, and Doveton, The Camp Bird Mine, Ouray, Colo., Trans., xxxiii., 499 
 to 550 (1902). 
 
 86 Op. cit., p. 101. 
 
MANGANESE AND GOLD-ENRICHMENT. 819 
 
 were ultimately reduced and forced to give up their gold when, 
 through the oxidation of pyrite, ferrous sulphate had been 
 formed. 
 
 16. Cripple Creek, Colo. The gold-deposits of Cripple 
 Creek, Colo., have yielded some $200,000,000 gold and less 
 than $1,000,000 silver. The lodes are fissure-veins and replace- 
 ment-deposits in volcanic breccia, in Tertiary intrusive rocks, 
 and in granite. The fissures, according to Lindgren and Ran- 
 some, 87 were formed at about the same time as the intrusion of 
 associated basic dikes, and represent a late phase of volcanic 
 activity. The deposits are probably of middle or late Tertiary 
 age, and were formed by hot ascending waters, relatively near 
 the surface. Calaverite is the chief primary constituent; native 
 gold is rarely present in the unoxidized ores. Pyrite is widely 
 distributed; tetrahedrite, stibnite, and molybdenite are spar- 
 ingly present. The gangue is quartz, fluorite, adularia, carbo- 
 nates (including rhodochrosite), some sulphates, etc. Some of 
 the deposits were workable at the surface, but the placers which 
 have formed are relatively unimportant. Although rhodochro- 
 site is subordinate in amount, the highly-fractured country- 
 rock contains appreciable manganese (0.20 per cent.). Ac- 
 cording to Lindgren and Ransome, the processes of oxidation 
 were attended by the formation of kaolin, hydrous silica, and 
 oxides of iron and manganese. Manganese oxides are often 
 present in the oxidized zone, and, according to Penrose, form 
 nodules in the Pharmacist and Summit mines. They result 
 from the alteration of rhodochrosite, manganiferous calcite, 
 or other minerals, and are generally distributed in the oxidized 
 zone as stains filling cracks and fissures. 88 Daring oxidation, 
 manganese is greatly concentrated in the seams of the rock. 
 In general, the lower part of the zone of oxidation is above 
 water-level, and usually less than 200 ft. below the surface. In 
 some places silver has been completely leached from the oxi- 
 dized ores. Horn-silver is not noted. 
 
 Whether a slight enrichment of gold has taken place in the 
 oxidized zone it is not easy to decide. Lindgren and Ran- 
 some are inclined to the belief that the oxidized zone as a whole 
 
 87 Professional Paper No. 54, U. S. Geological Survey (1906). 
 
 88 Idem, p. 123. 
 
820 MANGANESE AND GOLD-ENRICHMENT. 
 
 is somewhat richer than the corresponding telluride zone. 89 If 
 this is true, no extensive downward migration of gold can have 
 taken place. The trivial enrichment in the oxidized zone may 
 have resulted from the removal of some constituents of the pri- 
 mary ore. 
 
 If gold was dissolved in the Cripple Creek deposits, it was 
 precipitated again at practically the same horizon ; for, in these 
 deposits, the zone in which solution takes place is as rich or 
 richer than that in which precipitation usually takes place. The 
 ground is open, providing paths for downward-circulating 
 waters, but it should be remembered that, while the ore-bear- 
 ing complex is very pervious to water, it is surrounded by 
 impervious rocks. After the volcanic rocks had been drained 
 in mining, the flow of water was comparatively small. Lind- 
 gren and Ransome have compared the volcanic complex to a 
 " sponge in a cup." As shown by them, the conditions for a 
 circulation of atmospheric water were most unfavorable a fact 
 which had an important bearing on their conclusion that the 
 ores had been formed by-magmatic waters. In the absence of, 
 a circulation, the gold could not be transported. A check to 
 this reasoning with respect to a downward circulation is the 
 fact that in the porous, brecciated mass, filled with stagnant 
 water, the oxidation extended downward to a depth generally 
 less than 200 ft, and even in this zone residual sulphides are 
 often present. If the solutions did not carry oxygen down- 
 ward, it would be supposed that they could not carry gold ; 
 and if the latter had been dissolved at the higher levels, in 
 the absence of a circulation it could not descend. There is 
 some evidence which may be interpreted as an indication that 
 the gold migrated laterally, or possibly that it has been pre- 
 cipitated essentially in place from cold solution. 'Richard 
 Pearce ^ has recorded analyses of oxidized and unoxidized ore. 
 The material for the analyses was taken from a section drawn 
 clear across the two diiferent portions of the specimen. The 
 analyses show that the oxidized ore carries 14.58 oz. of gold per 
 ton, or 2.34 oz. more gold than the unoxidized ore, and that all 
 the silver has been leached out. In ore so rich such a con- 
 
 89 Professional. Paper No. 54, U. S. Geological Survey, p. 203 (1906). 
 
 90 Further Notes on Cripple Creek District, Proceedings of the Colorado Scientific 
 Society, vol. iv., pp. 11 to 16 (1894-96). 
 
MANGANESE AND GOLD-ENRICHMENT. 821 
 
 centration may result merely from leaching-out of the sub- 
 stances other than gold ; but, on the other hand, the analyses 
 of the altered rock indicate that little leaching of the silicate 
 minerals has taken place, and that the oxidized portion was 
 originally richer than the unoxidized, or else that some gold 
 had been added. Since 0.27 per cent, of Mn0 2 is present in 
 the oxidized ore, while none is reported in the unoxidized ore, 
 it appears that Mn0 2 was added in the process of secondary 
 alteration, and it is possible that the same solutions added gold 
 and iron. 
 
 If the gold was dissolved in the Cripple Creek " sponge," it 
 was precipitated in the stagnant solutions where they were in 
 contact with pyrite. In the absence of a downward circulation 
 of water, such lateral migration would not be unlikely. 
 
 The results of oxidation processes are described as follows : 91 
 
 " Thorough oxidizing decomposition will destroy the original structure of this 
 vein. In sheeted lodes with many small parallel fissures and joints the latter may 
 become effaced and the lode appears as a homogeneous brown, soft mass. In other 
 cases a central seam may be retained and usually appears as a streak of soft, more or 
 less impure kaolin ; in other cases it may be filled by white compact alunite, more 
 rarely by jasperoid or opaline silica. Crusts of comb quartz, if originally present, 
 lie included in the clayey seams, but neither the original fluorite nor the carbonates 
 are ordinarily preserved. Very rich oxidized ore sometimes fills the central cavi- 
 ties of the lode like a thick brown mud of limonite, kaolin, and quartz sand, and 
 easily flows out when the vein is opened. ' ' 
 
 It should not be inferred, however, where channels are large 
 and open that the rich, gold-bearing brown mud is necessarily 
 a deposit from solution. It may have been carried down in 
 suspension ; for similar rich mud, with 2 oz. of gold per ton, 
 was found on the floor of the 12th level of the Gold Coin mine 
 after it had been filled with water and allowed to stand. 
 
 It thus appears that the conditions at Cripple Creek, which 
 at first appear fatal to the hypothesis, may be rationally ex- 
 plained, when it is recalled that downward migration of gold 
 depends not only upon solution and precipitation, but requires 
 a circulation, and that conditions for a circulation here were 
 peculiarly unfavorable. They show also that conditions for a 
 relatively rapid circulation are prerequisite, if the dissolved 
 gold is to be carried below the zone of mixed oxides and sul- 
 phides. 
 
 91 Professional Paper No. 54, U. S. Geological Survey, p. 199 (1906). 
 
822 MANGANESE AND GOLD-ENKICHMENT. 
 
 17. Summit District, Colo. This district is located south- 
 west of Alamosa near the Rio Grande-Conejos county-line. 
 According to R. C. Hills, 92 the metal-bearing horizon is near 
 the middle of the Tertiary eruptive series of south and south- 
 west Colorado. The associated rocks are andesites, trachytes, 
 rhyolites, etc. ; but, unlike the eruptives of most Tertiary dis- 
 tricts in this province, these rocks appear to have been closely 
 compressed, yielding a series which, as shown in Mr. Hills'& 
 sketches, are probably isoclinals. Some features of the ore- 
 deposits are puzzling; but, whatever their genesis, they illus- 
 trate very clearly the theory of secondary enrichment a fact 
 which was fully recognized by Mr. Hills as long ago as 1883. 
 
 The ore-bodies, so far as exposed, are rudely tabular and 
 approximately vertical. The ore is chiefly quartz and pyrite, 
 but contains some enargite, galena, sphalerite, and other min- 
 erals. Placers appear to be of subordinate importance. The 
 mineralized matter may be separated into three divisions : (1) 
 the impoverished zone near the apex; (2) the zone of rich and 
 partly-oxidized ore; and (3) the low-grade sulphides. The 
 zone of impoverishment, with two exceptions, includes the out- 
 crops of all the lodes and extends downward to 50 ft. or more. 
 The zone of incompletely-oxidized ore extends to a depth vary- 
 ing from a few feet to 300 ft. In this zone the quartz is 
 colored dark brown by oxides, and the more-highly auriferous 
 material is characterized by an abundance of brown oxide. 
 The gold in this ore carries only about 0.025 silver. All the 
 bonanzas were, according to Mr. Hills, confined to this zone. 
 In some places gold appears in a disseminated form in innum- 
 erable small grains, so aggregated as to resemble a continuous 
 sheet of metal. Locally, the grains unite and form flat nug- 
 gets, one or more ounces in weight. The occurrence of this 
 richer material is confined, according to Mr. Hills, to the im- 
 mediate vicinity of a central channel which has been filled with 
 earthy matter, fragments of rock and iron oxides. Some of 
 the rich seams of gold powder have been introduced into frac- 
 tures which cut barite. Below the rich and partly-oxidized 
 ore, the primary sulphides appear to have been unworkable 
 under conditions then existing. There is, however, in three 
 mines 93 a concentration of silver at greater depth than that of 
 
 92 Proceedings of the Colorado Scientific Society, vol. i., p. 20 (1883-84). 
 
 93 Op. cit. t p. 35. 
 
MANGANESE AND GOLD-ENRICHMENT. 823 
 
 the gold-bonanzas. Mr. Hills ascribes the two rich outcrop- 
 ping ore-bodies, which are exceptional in this district, to in- 
 tense kaolinization on either side of the ore-bodies, causing 
 the country-rock to be much more readily eroded than the 
 extremely hard quartz outcrop. This consequently remained 
 considerably above the general surface, forming a precipitous 
 ridge, which was, as he explains, protected from solution, 
 which went on more vigorously below, in the places where 
 snow and water accumulated. 
 
 Although Mr. Hills mentions brown oxides at several places, 
 he does not say that they are manganiferous. 
 
 Dr. Raymond 94 says that the oxides include those of pur- 
 plish hue. 
 
 18. Bodie, Cal. The deposits of Bodie, Cal., are east of the 
 Sierras, near the State-line. They are not of the California 
 type, but are associated with andesite and belong to the late 
 Tertiary group so extensively developed in Nevada. R. P. 
 McLauglilin 95 has described the most important mines. The 
 lodes are fissure-veins in andesite. Nearly all strike north- 
 ward and are approximately parallel. The ore carries about 
 equal amounts of gold and silver. The deposits are developed 
 extensively to a depth of 500 ft. below the surface. One shaft 
 is 1,000 ft., another 1,200 ft. deep. Outcrops of encouraging 
 value are rare. Almost without exception the veins have 
 failed to carry pay-ore beyond 500 ft. below the surface ; but 
 above this depth occur large, rich ore-bodies, which, according 
 to McLaughlin, carry ore worth as high as $400 a ton. Fault- 
 ing and displacement are probably of later date than the period 
 of vein-formation. Some of the oxidized ore carries man- 
 ganese dioxide. It is " loose and clayey in texture and carries 
 some silver to the exclusion of gold." 96 
 
 19. Exposed Treasure Mine, Cal. The Exposed Treasure 
 mine, 97 which is near Mojave, has produced considerable gold 
 and silver. It is in an area of granitic rocks cut by quartz- 
 porphyry and capped by rhyolite. The lodes are probably 
 Tertiary (group 4). The Exposed Treasure vein dips about 
 45 E. and is a sheeted brecciated zone. Considerable fissur- 
 ing has taken place since the ore was deposited. 
 
 94 Mines and Mining West of the Rocky Mountains, vol. x., p. 329 (1875). 
 
 95 Mining and Scientific Press, vol. xciv., No. 25, p. 796 (June 22, 1907). 
 
 96 Idem, p. 796. 
 
 97 Courtenay De Kalb, Trans., xxxviii., 310 to 320 (1907). 
 
824 MANGANESE AND GOLD-ENRICHMENT. 
 
 " . . . While the lodes are continuous, and often of great width, sometimes 
 being 40 ft. and more from wall to wall, the pay-streaks, from 4 to 15 ft. in width, 
 lie in well-defined chutes and overlapping sheets or lenses. It is noteworthy that 
 only those chutes or lenses which now reach the surface contained important 
 quantities of calcite and manganese dioxide." 
 
 The oxidized ores contain much Mn0 2 , the concentrates car- 
 rying 12 per cent. In the altered oxidized ore are kernels of 
 ore containing pyrite, chalcopyrite, galena, and sphalerite, and 
 these are richer in the precious metals than the altered friable 
 ore. As observed by De Kalb : 
 
 " . . . The altered ore bore manifest signs of extensive leaching, and where 
 it had become almost completely decolorized by the removal of iron, the precious 
 metal contents had nearly disappeared, and such ore never contained copper except 
 in the form of chrysocolla. 
 
 " The absence of sulphides in all the [oxidized] ores, except in the cherty skele- 
 tons, and in the undecomposed kernels of hard ore, was very complete. The mill- 
 concentrates (150 into 1) had an average composition of SiO 2 , 30 ; FeO, 37 . , . 
 and MnO 2 , 12 per cent. These concentrates never contained more than 1.5 per 
 cent, of sulphur. 
 
 ' ' In the lower friable siliceous ores, the ratio of gold to silver was as 1 to 1 2, 
 while in the upper mangano-calcite ores the ratio was 1 to 72. Assays of gold-scale, 
 and of coarse gold panned out, from all parts of the mine, showed 'a remarkably 
 uniform alloy of 1 part of gold to 0.461 part of silver. The silver in the upper 
 portion of the mine was present almost wholly in the form of silver chloride. 
 
 "On the assumption, from the evidence, that the abundance of chlorides would 
 prevent the leaching-out of the silver and its reconcentration below water-level, 
 and that the ferric and cupric sulphates would have abstracted large quantities of 
 the gold, which would be re-deposited lower down together with the copper in the 
 form of secondary enrichments, it was natural to predict an ore below permanent 
 water rich in these metals, and relatively lean in silver. It would be difficult to 
 conceive a nicer justification of theory than that which was afforded when develop- 
 ment at length extended below water-level. The ore consisted of a hard bluish- 
 gray mass of original chert-cemented breccia, re-cemented by quartz, with partial 
 replacement of the granite and quartz-porphyry by silica, heavily impregnated with 
 sulphides, among which were considerable quantities of chalcopyrite, bornite, and 
 some covellite. The gold-content of the ore had increased 150 per cent, above the 
 a,verage in the friable siliceous ores on the upper levels, and the ratio of the gold to 
 silver was as 1 to 2." 
 
 20. Tonopah, Nev. The deposits at Tonopah, Nev., are 
 silver-gold replacement-veins in andesite. They are of mid- 
 dle or late Tertiary age, but possibly somewhat older than the 
 Comstock lode. Placers are not developed. The primary ore, 
 according to J. E. Spurr, 98 is composed of quartz, adularia, seri- 
 cite, carbonates of lime, magnesia, iron, and manganese, with 
 argentite, stephanite, polybasite, chalcopyrite, pyrite, galena, 
 
 98 Professional Paper No. 42, U. S. Geological Survey, p. 90 (1905). 
 
MANGANESE AND GOLD-ENRICHMENT. 825 
 
 blende, silver selenide, and gold in an undetermined form. 
 The zone of oxidation extends to greater depth in the more 
 highly fractured places ; and for this reason the brittle and 
 more broken lodes are more deeply oxidized than the wall-rock. 
 The Mizpah vein is for the most part oxidized to a depth of 
 700 ft. Standing ground-water is lacking. The oxidized ore 
 contains limonite and manganese dioxide, with plentiful horn- 
 silver and some bromides and iodides of silver. The so-called 
 oxidized ore from the outcrop down is, according to Spurr, a 
 mixture of original sulphides (and selenides), together with 
 secondary sulphides, chlorides, and oxides. At a depth of 500 
 ft. (in the Montana Tonopah mine) good crystals of argentite, 
 polybasite, and chalcopyrite have been formed freely in cracks 
 and druses of the sulphide ore. These minerals are later than 
 the massive ore; but it cannot be shown that they were not 
 deposited upon it by ascending waters. The case of dark ruby- 
 silver (pyrargyrite) is different, however, for this is formed in 
 cracks in the oxidized ore, and some argentite fringes minute 
 particles of horn-silver as if secondary to it. " The evidence 
 therefore favors the view that these secondary sulphides in the 
 oxidized zone originated from descending surface waters, and 
 probably part, but not all, of the sulphides in druses in the 
 sulphide ore have a similar origin." 
 
 The waters which descend through the oxidized zone carry 
 sulphates and chlorides, and "wad" is plentiful; but judging 
 from the fairly-constant proportion of gold to silver (about 1 to 
 100 by weight) there has been little selective migration of gold 
 and silver during oxidation, although the vein has been en- 
 riched to some degree by downward penetration of minerals 
 leached from the outcrop as it was eroded. The rich ore- 
 shoots, though partly oxidized, seem to be in the main original 
 without thorough rearrangement. According to Mr. Spurr, 
 this may be ascribed in part to the relatively scanty supply of 
 water in this arid region. 
 
 21. Goldfidd, Nev. The ledges of Goldfield are in middle 
 or late Tertiary rocks, and, according to F. L. Rarisome, were 
 probably deposited within 1,000 ft. of the surface at the time 
 of deposition. Ransome states convincingly the hypothesis 
 that these deposits were formed by hot ascending solutions 
 which mingled with descending sulphate-water contaminated 
 
 52 
 
826 MANGANESE AND GOLD-ENRICHMENT. 
 
 by the oxygen of the air. Although the deposits are probably 
 the most remarkable bonanzas of native gold-ores carrying little 
 silver which have yet been discovered, it does not appear that 
 they 'have been enriched to any considerable extent since they 
 were deposited, for, as remarked by Ransome, it is difficult to 
 harmonize the extent and intensity of alunitization which ac- 
 companies the gold with the hypothesis of the oxidation and 
 enrichment of lean deposits during erosion. The mine-waters 
 are rich in sulphates; and, judging from the geographical 
 position of the deposits, they probably carry chlorides. Man- 
 ganese dioxide is practically unknown in these ores, which in 
 this respect differ from the ores at Tonopah and from a great 
 many Tertiary deposits of the Great Basin province. No work- 
 able placer-deposits have been discovered ; yet notwithstanding 
 the fact that there may have been several hundred feet of vein- 
 matter removed from these deposits since they were formed, 
 there is little reason to suppose that much gold has migrated 
 into the existing bonanzas from above. The gold is very finely 
 divided, and could easily have been scattered, if it had been 
 eroded with the ledges. As shown by the analyses of deposits 
 elsewhere that were formed close to the surface by ascending 
 hot waters, they seldom carry much gold. The maximum 
 deposition is lower down ; for, as soon as the ascending hot 
 waters are contaminated by ferrous sulphate from the surface, 
 gold must be precipitated. 
 
 The evidence offered at Goldfield is not out of harmony 
 with the conclusion that, in the absence of manganese, gold is 
 not readily transported in mine-waters. 
 
 22. Manhattan, Nev. The gold-deposits at Manhattan, al- 
 though inclosed in schists, are in an area of Tertiary volcanic 
 activity, and should be classed with the deposits formed in Ter- 
 tiary times. Although the schists contain stringers of gold of 
 uncertain genesis, the principal deposits are steeply-dipping 
 lodes of quartz and calcite, stained with iron and manganese 
 oxides. Some placers are developed. Rich ore was found 
 very near the surface, but it was richer a few feet below the 
 outcrop than at the surface. Some fracturing has taken place 
 since the deposits were formed. In many instances the gold 
 of the pockets of rich ore is intimately associated with iron and 
 
MANGANESE AND GOLD-ENRICHMENT. 827 
 
 manganese oxides." In view of the fact that the unaltered 
 sulphides had not been encountered when the mines were 
 visited, the character of the primary ore is unknown to me. 
 
 23. Annie Laurie Mine, Utah. The Annie Laurie mine, 100 
 175 miles south of Salt Lake, is in an area of dacite, rhyolite 
 and rhyolite-tuff, and probably belongs to the later Tertiary 
 group. The vein is poorly exposed at the surface, being largely 
 covered by morainal material. Mr. Lindgren says : 
 
 " The quartz forms an almost continuous sheet along the vein, rarely less than 
 3 feet in thickness and often expanding to a width of 20 feet or more. As a rule 
 the walls are poorly defined and slickensides indicating motion are rare. In 
 places it contains, parallel to the walls, streaks of iron oxides and black, sooty, 
 manganese ores. . . 
 
 "The mine-workings have not penetrated below the zone of oxidation, and 
 neither the quartz nor the country-rock seem to contain any unoxidized sulphides." 
 
 In the absence of extensive post-mineral fracturing, one would 
 suppose that the conditions for migration of gold were not par- 
 ticularly favorable. Since the workings had not penetrated 
 sulphide ore at the date of Lindgren's report, direct evidence 
 was lacking. 
 
 24. The Bullfrog District, Nev.In the Bullfrog district 101 the 
 principal deposits are fissure-veins in rhyolite. The minerals 
 include pyrite, quartz, and manganiferous calcite. Enough 
 manganese is present in the calcite to stain much of the oxi- 
 dized ore chocolate-brown or black. No placers are developed. 
 The outcrops were comparatively poor, but within a few feet 
 of the surface good ore was encountered, and some of the de- 
 posits were worked by open-cut. Some of the ore-deposits 
 decrease in value below the 400-ft. level, where ore carrying 
 less than $5 per ton is encountered. Since the ore above this 
 level carried many times this value, it appears that there has 
 been a secondary concentration by surface-waters, and that the 
 rich ore is related to the present topographic surface. 
 
 25. Gold Circle, Nev.The deposits of Midas, (Sold Circle 102 
 
 99 G. H. Garrey and W. H. Emmons, Bulletin No. 303, U. S. Geological Survey, 
 pp. 84 to 93 (1907). 
 
 100 Waldemar Lindgren, Bulletin No. 285, U. S. Geological Survey, pp. 87 to 90 
 (1906). 
 
 101 Ransome, Emmons, and Garrey, Bulletin No. 407, U. S. Geological Survey 
 (1910). 
 
 102 w. jj Emmons, Bulletin No. 408, U. S. Geological Survey (1910). 
 
828 MANGANESE AND GOLD-ENRICHMENT. 
 
 district, are in an area of late Tertiary rhyolites. The lodes 
 are replacement-veins and sheeted zones and carry consider- 
 ably more gold than silver (value). In the oxidized zone 
 some of the ore is rich, but the sulphides are comparatively 
 regular in value and give no evidence of extensive secondary 
 enrichment. Some oxidized ore-shoots appear to have been 
 increased in value by the removal of substances more soluble 
 than gold. The minerals are chiefly quartz and pyrite. In 
 the oxidized zone are seams of very rich gold-ore, composed 
 of manganese, limonite, kaolin, and soft hydrous silica. 
 
 26. Delamar Mine, Nev. The Delamar mine, in southeast- 
 ern Nevada, is in quartzite cut by porphyry dikes of acid 
 composition. It is presumably a Tertiary deposit, and is pro- 
 visionally classed with group 4. The ore-body described by 
 S. F. Emmons 103 is related to a strong zone of fracturing which 
 strikes with the quartzite, but dips about 75, or nearly at 
 right angles to the dip of the quartzite. The ore is in shoots, 
 or zones of crushed quartzite. The chief ore-body, which is, 
 roughly speaking, a long and comparatively thin, nearly up- 
 right cylinder, is divided into four parts by a dike of quartz- 
 porphyry and a more basic dike, which cross nearly at right 
 angles in the ore-body. The ore follows the line of intersec- 
 tion of the two dikes rather closely. The ore at the bottom of 
 the mine consists of quartz and pyrite, which fill fractures in 
 the altered quartzite. Where the dikes cross in the ore-body 
 the light-colored dike appears to be continuous, but notwith- 
 standing this the line of the dark dike across the light one is 
 generally marked by a slight stain of manganese dioxide, 
 which, as stated by Mr. Emmons, is characteristic of the 
 " black " dike, and perhaps gives it that name. 
 
 Oxidation extends as far down as the tenth level. The ore 
 that has been found below that level is too poor in grade to pay 
 for mining. The gold-ore carries silver and some copper. 
 The tenor in gold increased from the surface downward to 
 about the 7th level, although the values were not evenly dis- 
 tributed. Some lots of ore ran as high as 30 oz. per ton, and 
 the richer parts of the mine averaged from $30 to $70 per ton. 
 At the 10th level they had decreased to $4 or $5 per ton. 
 
 103 Trans., xxxi., 658 to 675 (1901). 
 
COGNATE PAPERS. 829 
 
 COGNATE PAPERS NOT REPUBLISHED IN THIS 
 
 VOLUME. 
 
 Many papers which were considered for printing in this vol- 
 ume were not chosen because, though possessing merit, their 
 material did not seem to constitute essential additions to the 
 science of ore-deposits. A brief statement with regard to each 
 is here given. 
 
 The Detection and Estimation of Small Quantities of Gold and 
 Silver. By Luther Wagoner, San Francisco, Cal. (Mexican 
 Meeting, November, 1901. Trans., xxxi., 798-810.) This 
 paper contains some determinations of small amounts of gold 
 and silver in rocks and in sea-water by Luther Wagoner, which 
 in part confirm and in part differ from those already given by 
 Don. It is for chemists to determine, in the case of such dif- 
 ferences, which of the two is the more trustworthy, primarily 
 by a discussion of methods, but more satisfactorily by a new 
 series of determinations. In such work, the practical impossi- 
 bility of procuring reagents that are absolutely free from silver 
 or gold is a serious handicap. 
 
 The Geology and Copper-Deposits of Bisbee, Arizona. By F. 
 L. Ransome, Washington, D. C. (Albany Meeting, February, 
 1903. Trans., xxxiv., 618-642.) This paper is an abstract of 
 the geological relations of the district, which were so accurately 
 determined by the author that his work has served as the basis 
 of mining since it was published. Genetically, however, the 
 deposits are not typical. Indeed, though some contact-meta- 
 morphic minerals are found associated with the ore, the author 
 is not willing to assign a contact-metamorphic origin to it, but 
 contents himself with saying that it is genetically connected 
 with the intrusion of the porphyry around the periphery near 
 which it is mainly found. The action of sulphide secondary 
 enrichment in the district is very clear and typical. 
 
 Some Practical Suggestions Concerning the Genesis of Ore-De- 
 posits. By Max Boehmer, Denver, Colo. (New York Meet- 
 ing, October, 1903. Trans., xxxiv., 449-453.) The author of 
 
830 COGNATE PAPERS. 
 
 this paper is a practical mining engineer who does not profess 
 to be a geologist. The value of his paper as a contribution to 
 theoretical views on ore-genesis is impaired by the fact that 
 some of his premises are such as would not be admitted by 
 geologists of the present day. 
 
 Yellow Ocher Deposits of Cartersville District, Bartow County, 
 Ga. By Thomas Leonard Watson, Granville, Ohio. (New 
 York Meeting, October, 1903. Trans., xxxiv., 643-666.) 
 This paper is mainly descriptive of the yellow ocher deposits 
 of the Cartersville district of Georgia. At its close it contains 
 the brief statement that the ore is a metamorphic replacement 
 of quartzite by material probably derived from pyrite existing 
 somewhere in the neighborhood. 
 
 The Garnet-Formations of Chillagoe Copper-Field, North Queens- 
 land, Australia. By George Smith, Sydney, N. S. W. (New 
 York Meeting, October, 1903. Trans., xxxiv., 467-478.) 
 This paper is an interesting and apparently accurate descrip- 
 tion of copper- and lead-deposits in Australia, which, from their 
 association, are evidently of contact-metamorphic origin. The 
 author, while suggesting the possibility of this origin, does not 
 commit himself to a belief in it, because certain facts are to him 
 unaccountable on that theory. 
 
 Observations on Mother-Lode Gold-Deposits, California. By 
 W. A. Prichard, Kalgoorlie, Western Australia. (New York 
 Meeting, October, 1903. Trans., xxxiv., 454-466.) This 
 paper is interesting as being the views of an able Australian 
 mining engineer on California gold-deposits along the Mother 
 Lode. It makes, however, no addition to our knowledge either 
 practical or theoretical. 
 
 Geology of the Treadwell Ore-Deposits, Douglas Island, Alaska. 
 By A. C. Spencer, Washington, D. C. (Lake Superior Meeting, 
 October, 1904. J!r<ms.,xxxv., 473-510.) This paper is an elabo- 
 rate and detailed study of the famous Treadwell deposit, made 
 in the light of eight years' exploitation, since the previous 
 examination by D'r. George F. Becker. Except for some minor 
 petrological changes, resulting from later developments, Dr. 
 Spencer's conclusions as to the genesis agree essentially with 
 those adopted by Dr. Becker. 
 
COGNATE PAPERS. 831 
 
 Features of the Occurrence of Ore at Red Mountain, Ouray 
 County, Colo. By T. E. Schwarz, Denver, Colo. (Washington 
 Meeting, May, 1905. Trans., xxxvi., 31-39.) This paper is a 
 criticism of Ransome's description of the Yankee Girl and 
 adjoining mines in the San Juan district, and a contribution of 
 interesting additional facts, by T. E. Schwarz, who was long 
 superintendent of the mines. This mine presents one of the 
 most interesting instances of the action of secondary enrich- 
 ment by downward-circulating waters. 
 
 Genesis of the Ore-Deposits at Bingham, Utah. By J. M. 
 Boutwell, Washington, D. C. (Washington Meeting, May, 
 1905. Trans., xxxvi., 541-580.) In spite of its title, this paper 
 has been judged to be more descriptive than theoretical, inas- 
 much as the discussions apply only to this special group of de- 
 posits, which, like those of Bisbee, are not distinctly typical of 
 any one particular form of genesis, and do not, therefore, con- 
 stitute a definite contribution to generally applicable theories. 
 The paper contains, however, a careful and detailed enumera- 
 tion and discussion of the facts which bear upon the origin of 
 the three classes into which the author divides the Bingham 
 deposits. 
 
 The Origin of Vein- Filled Openings in Southeastern Alaska. 
 By A. C. Spencer, Washington, D. C. (Washington Meeting, 
 May, 1905. Trans., xxxvi., 581-586.) This paper is a discus- 
 sion of the physical strains which may have produced the vein- 
 openings of the regions cited, and is intended by the author to 
 indicate certain conditions under which the deformation of 
 rocks by their own weight might lead to the production of 
 fractures in which vein-deposits could be formed. 
 
 Lead- and Zinc-Deposits of the Virginia- Tennessee Region. By 
 Thomas Leonard Watson, Blacksburg, Va. (British Columbia 
 Meeting, July, 1905. Trans., xxxvi., 681-737.) This paper 
 is a detailed and scientific description of all the features and 
 characteristics of these important, but little known, deposits, 
 together with a chemical and genetic discussion. Only a single 
 deposit mentioned is connected genetically with igneous in- 
 trusions; the others, in the opinion of the author, are concen- 
 trations, along zones of fracture (largely structural anticlines), 
 
832 COGNATE PAPERS. 
 
 of material originally disseminated in the sedimentary rocks. 
 The deposits in limestone have been formed by replacement 
 through the agency of circulating, but not necessarily deep- 
 seated, waters. 
 
 The Secondary Enrichment of Copper -Iron Sulphides. By 
 Thomas T. Read, New York, N. Y. (Bethlehem Meeting, 
 February, 1906. Trans., xxxvii., 297-303.) This paper pre- 
 sents the results of experiments made by the author to illus- 
 trate the reactions that go on in the process of secondary en- 
 richment. Certain errors in the experiments are shown in 
 the discussion by the chemist, E. C. Sullivan, 1 which throw 
 some doubt on the accuracy of the results, but the investiga- 
 tion is along an important line, and is instructive, even if all 
 the conclusions may not be accepted. 
 
 The Mojave Mining-District of California. By Charles E. W. 
 Bateson, New York, N. Y. (Bethlehem Meeting, February, 
 1906. Trans., xxxvii., 160-177.) This paper is descriptive of 
 one of the little-known mining-districts of the western mining- 
 region of southern California, with a discussion of its general 
 geological relations. 
 
 The Geology and Petrography of the Goldfield Mining-District, 
 Nevada. By John B. Hastings, Denver, .Colo., and Charles P. 
 Berkey, New York, 1ST. Y. (Bethlehem Meeting, February, 
 1906. Trans., xxxvii., 140-159.) This paper is the result of 
 a reconnaissance of this important district made in May and 
 June, 1905. It does not contain any genetic conclusions with 
 regard to the ores. Such may be found, however, in subse- 
 quent publications of the U. S. Geological Survey concerning 
 this district. 
 
 The Tin-Deposits of the Kinta Valley, Federated Malay States. 
 By William R. Rumbold, Oruro, Bolivia, So. America. (Lon- 
 don Meeting, July, 1906. Trans., xxxvii., 879-889.) 
 
 The South African Tin-Deposits. By William R. Rumbold, 
 Oruro, Bolivia, So. America. (New York Meeting, April, 1907. 
 Trans., xxxix., 783-789.) These two papers, by the same 
 
 1 Trans., xxxvii., 893 to 895 (1906). 
 
COGNATE PAPERS. 833 
 
 author, are descriptive of tin-deposits in the Kinta valley of the 
 Malay States, and of South Africa, respectively. These descrip- 
 tions are interesting because of the rarity of such deposits ; but 
 the papers contain nothing of genetic importance, though the 
 author is inclined to consider it possible that some of the Kinta 
 valley deposits were formed in limestone. Elsewhere 2 the 
 author has written an important paper on the Bolivian tin- 
 deposits, in which he disproves the hitherto generally-accepted 
 idea that these new economically-important deposits differ 
 genetically from tin-deposits in other parts of the world. 
 
 Geology and Mining of the Tin-Deposits of Cape Prince of Wales, 
 Alaska. By Albert Hill Fay, New York, N. Y. (Toronto 
 Meeting, July, 1907. Trans., xxxviii.,' 664-682.) This paper 
 is a description of the tin-deposits of the Seward Peninsula of 
 Alaska. While the tin, as elsewhere, is genetically associated 
 with granite, some of it is found in limestone. 
 
 The Extraordinary Faulting at the Berlin Mine, Nevada. By 
 Ellsworth Daggett, Salt Lake City, Utah. (New York Meet- 
 ing, April, 1907. Trans., xxxviii., 297-309.) This paper is a 
 complete reconstruction, by descriptive geometry, of a most 
 remarkably faulted fissure-vein. 
 
 The White Knob Copper-Deposits, Mackay, Idaho. By J. F. 
 Kemp, New York, N. Y., and C. G. Gunther, Clifton, Ariz. 
 (New York Meeting, April, 1907. Trans., xxxviii., 269-296.) 
 This paper is the description of a singular occurrence of 
 contact-metam orphic copper-ore, which is found, not in the 
 limestone which has been intruded by granite, but in quartz- 
 porphyry between this limestone and the granite, the limestone 
 itself being singularly free from contact-metamorphic products. 
 
 The Vein-System of the Standard Mine, Bodie, Cal.Bj E. 
 Gilman Brown, London, England. (New York Meeting, April, 
 1907. Trans., xxxviii., 343-357.) This paper is a description 
 of a series of very productive and complicatedly-faulted gold- 
 bearing veins in eruptive rocks. 
 
 The Ore-Deposits of the Joplin Region, Missouri. By F. L. 
 
 2 Economic Geology, vol. iv., p. 329 (1909). 
 
834 COGNATE PAPERS. 
 
 Clerc, Denver, Colo. (New York Meeting, April, 1907. Trans., 
 xxxviii., 320-343.) This paper is an interesting account of 
 this much-described region by one who has long been practi- 
 cally familiar with it, and whose views as to the genesis of the 
 ores differ in some respect from those that have been published 
 by other geologists. 
 
 Geology of the Exposed Treasure Lode, Mojave, California. 
 By Courtenay De Kalb, Los Angeles, Cal. (New York Meet- 
 ing, April, 1907. Trans., xxxviii., 310-319.) This paper is a 
 description and discussion of the geological relations of this, 
 the most important deposit of the Mojave district, from the 
 genetic point of view. 
 
 The Occurrence of Nickel in Virginia*. By Thomas Leonard 
 Watson, Blacksburg, Va. (Toronto Meeting, July, 1907. 
 Trans., xxxviii., 683-697.) This paper is a description of an 
 occurrence of nickel with pyrrhotite in gabbro, which is intru- 
 sive in crystalline schists. The author does not regard the 
 sulphides as magmatic segregations, but as a later introduction, 
 taking place after the whole eruptive body had been meta- 
 morphosed. 
 
 Geology of the Virginia Barite-Deposits. By Thomas Leonard 
 Watson, Blacksburg, Ya. (Toronto Meeting, July, 1907. 
 Trans., xxxviii., 710-733.) This paper is a description of the 
 manner of occurrence of the many and varied barite-deposits 
 of Yirginia. The author regards this mineral as for the most 
 part the result of concentration by circulating waters of mate- 
 rial once disseminated through the limestone. 
 
 The Promontorio Silver-Mine, Durango, Mexico. By Francis 
 Church Lincoln, New York, N. Y. (Toronto Meeting, July, 
 1907. Trans., xxxviii., 734-746.) This deposit is a vein in 
 rhyolite-porphyry carrying primarily sulphides of lead and zinc 
 with less iron and copper. The silver occurs mainly in the 
 native state, as the result of secondary enrichment. 
 
 Ore-Deposits of the Eastern Gold-Belt of North Carolina. By 
 W. 0. Crosby, Boston, Mass. (Toronto Meeting, July, 1907. 
 Trans., xxxviii., 849-856.) This paper, descriptive of certain 
 gold-mines, contains in the introduction a classification of the 
 
COGNATE PAPERS. 835 
 
 gold-veins of this region, based on geological relations and 
 genesis, which may prove of practical use to mining engineers 
 in that district, if its generalizations be confirmed. The gold- 
 deposits in the central and southern parts of the State will be 
 found treated by L. C. Graton. 3 
 
 The Evergreen Copper-Deposits, Colorado. By Etienne A. Rit- 
 ter, Colorado Springs, Colo. (Toronto Meeting, July, 1907. 
 Trans., xxxviii., 751-765.) This paper describes the occurrence 
 of original bornite in a fresh-looking eruptive rock of remark- 
 able composition, which cuts the crystalline schists. Accord- 
 ing to the author, the copper-mineral in this dike is a pneuma- 
 tolytic or sublimation-product, and has not been subjected to 
 secondary enrichment; whereas, the copper-minerals in the 
 adjoining schists, which include also chalcopyrite, have been 
 secondarily enriched to chalcocite and covellite. 
 
 Genesis of the Lake Valley, New Mexico, Silver-Deposits. By 
 Charles R. Keyes, Socorro, IS". M. (New York Meeting, Febru- 
 ary, 1908. Trans., xxxix., 139-169.) This paper is a descrip- 
 tion of the geological relations of these long ago abandoned de- 
 posits with the views of the author as to their genesis views 
 which may not be generally accepted, but which, owing to the 
 condition of the district, are difficult to controvert. 
 
 Borax-Deposits of the United States. By Charles R. Keyes, 
 Des Moines, Iowa. (Spokane Meeting, September, 1909. 
 Trans., xl., 674-710.) This paper is a description by the same 
 author of the various borax-deposits in the western part of the 
 United States, including Death valley, Furnace canyon, and 
 the Mojave desert, with some considerations on the chemis- 
 try of borax-deposits in general. 
 
 8 Bulletin No. 293, U. S. Geological Survey (1906). 
 
ORIGIN OF METALLIFEROUS ORE-DEPOSITS. 837 
 
 A Selected List of the More Important Contributions to 
 the Investigation of the Origin of Metalliferous Ore- 
 Deposits. 
 
 BY J. D. IRVING, H. D. SMITH, AND H. G. FERGUSON. 
 
 CONTENTS. 
 
 PAGE. 
 
 INTRODUCTION, 839 
 
 LIST OF ABBREVIATIONS USED, 841 
 
 LIST OF REFERENCES (Alphabetically Arranged), 847 
 
 GENERAL TREATISES ON MINERAL DEPOSITS, 908 
 
 ASCENSION THEORIES, 908 
 
 CAVITIES IN KOCKS, - . 909 
 
 General, 909 
 
 Pore-Spaces, 909 
 
 Amygdaloidal Cavities, . . 909 
 
 Fissures, . 909 
 
 Joints, 909 
 
 Gash- Veins and Pitches, 910 
 
 Dolomitization-Cavities, 910 
 
 Saddle-Keefs, 910 
 
 Solution-Cavities, 910 
 
 Cavities Due to Fissility, Cleavage, and Metamorphism, 910 
 
 Depth to which Cavities may Extend and Exist. See under Depth. 
 
 CONTACT-METAMORPHIC DEPOSITS, 910 
 
 Character and Genesis of, 910 
 
 Chemical and Physical Changes which Occur during Contact-Meta- 
 
 morphism, 910 
 
 Contact-Deposits of Copper, 910 
 
 Gold and Silver, ."..*....,.. 911 
 
 Cobalt, 911 
 
 Silver and Lead, ....*................. 911 
 
 Iron, i ............;... 911 
 
 Tin, % . . . . . . \ ...... . . . . . 911 
 
 Zinc, ..."........... 911 
 
 Miscellaneous, 911 
 
 CLASSIFICATION OF ORE-DEPOSITS (Chronologically Arranged), . . . . 911 
 
 DEFINITION OF TERM "ORE," - 912 
 
 DEPTH, INFLUENCE OF, ON ORE-DEPOSITION, . 912 
 
 General, -*."....... 912 
 
 Depth to which Cavities Extend, .'.*.'. 912 
 
 Changes in Primary Mineralogy with Depth, 912 
 
 DESCENSION THEORIES, 912 
 
838 ORIGIN OF METALLIFEROUS ORE-DEPOSITS. 
 
 DETRITAL DEPOSITS, 912 
 
 General, 912 
 
 Distribution of Gold in Placers, Origin of Nuggets, etc., 913 
 
 Gold-Placers, * 913 
 
 Stream- Placers, 913 
 
 Fossil-Placers, 913 
 
 Australasia, 913 
 
 Black Hills, 913 
 
 California, 913 
 
 South Africa, 914 
 
 Beach- Placers, 914 
 
 ^Eolian Placers, 914 
 
 Tin-Placers, 914 
 
 Platinum-Placers, 914 
 
 General, 914 
 
 Individual Localities, 914 
 
 Iron-Placers, , . 914 
 
 DISSEMINATED METALS ORIGINAL, IN EOCKS, 914 
 
 General, 914 
 
 In Eruptive Rocks, 914 
 
 In Sedimentary Eocks, 915 
 
 In Metamorphic Eocks, 915 
 
 ELECTRICAL ACTION IN ORE-DEPOSITION, 915 
 
 EMANATIONS FROM IGNEOUS MAGMAS, 915 
 
 General, 915 
 
 Magmatic vs. Meteoric Waters, 916 
 
 Pegmatitic Ore-Deposits, 916 
 
 Pneumatolysis, 916 
 
 Hydrothermal Emanations, 916 
 
 EXPERIMENTAL DATA APPLIED TO ORE-DEPOSITION, 917 
 
 FAULTS AND FAULTING, 917 
 
 FISSURE- VEINS, 917 
 
 General, 917 
 
 Fissures. (See especially also under "Cavities in -Eocks"), .... 917 
 
 Systems of, 917 
 
 Origin of, 918 
 
 Displacements and Irregularities of. Also Eelative Ages, . . . 918 
 
 Classification of Fissure- Veins, 918 
 
 Structure and Arrangement of Mineral Contents of Fissures, . . 918 
 
 The Filling of Mineral Veins, 918 
 
 GEOGRAPHIC DISTRIBUTION OF METALLIFEROUS DEPOSITS, 919 
 
 GEOLOGIC AGE OF ORE-DEPOSITS, 919 
 
 LATERAL SECRETION, 919 
 
 MAGMATIC DIFFERENTIATION, 919 
 
 General Discussion, 919 
 
 Applied Chiefly to Eocks, 919 
 
 Applied to Ore-Deposits, 919 
 
 Of Oxide Deposits, . 919 
 
 Of Sulphides, '...'..' 920 
 
 Comparison with Solidification of Slags, 920 
 
ORIGIN OF METALLIFEROUS ORE-DEPOSITS. 839 
 
 METASOMATISM. See Replacement. 
 
 MINERALOGY OF METALLIFEROUS ORES, 920 
 
 ORE-SHOOTS, 921 
 
 General, 921 
 
 Shoots as Described in Individual Localities, 921 
 
 ORIGIN OF METALLIFEROUS DEPOSITS, 921 
 
 Historical Resume's of Literature of Ore-Deposits, 921 
 
 Summaries of Theories of Origin of Particular Metals, 921 
 
 Origin of Deposits in Particular Districts, 922 
 
 General Papers Dealing with the Origin of Ore-Deposits as a Whole, . 922 
 
 OXIDATION. See under Superficial Alteration. 
 
 ORE-SOLUTIONS, 923 
 
 Nature and Origin of the Agent of Deposition, 923 
 
 Processes of Deposition from Solutions, 923 
 
 Temperatures and Pressures of Solutions and Their Effect on the Re- 
 sulting Ore-Deposits, 924 
 
 PRECIPITATION FROM SOLUTION. See under Ore-Solutions. 
 
 PHYSICAL CONDITIONS OF ORE-DEPOSITION. See under Ore-Solutions. 
 
 PRESSURE AND TEMPERATURE IN ORE-DEPOSITION. See under Ore- 
 Solutions ; also Contact-Metamorphic Deposits. 
 
 REGIONAL METAMORPHISM. Deposits Produced by It and General Effects 
 
 on Previously-formed Deposits, 924 
 
 REPLACEMENT, 924 
 
 General Discussions, 924 
 
 Criteria of, 925 
 
 Replacement Advocated and Discussed for Individual Ore-Deposits, . 925 
 
 SEDIMENTARY PROCESSES AS ORE-BUILDERS, 925 
 
 Ores Supposed to be a Direct Result of Sedimentary Processes, . . . 925 
 Ores Supposed to be Derived by Later Concentration of Sedimentary 
 
 Particles in Rocks, 925 
 
 SUBLIMATION, 926 
 
 SUPERFICIAL ALTERATION, 926 
 
 Ground- Water and Its Movement, 926 
 
 Oxidation, 926 
 
 Secondary Sulphide Enrichment, 927 
 
 UNDERGROUND WATERS, 927 
 
 Bibliography, 927 
 
 Mine-Waters, 927 
 
 General Discussions. ... 927 
 
 WALL-ROCK : EFFECT OF, IN ORE-DEPOSITION, 928 
 
 INTRODUCTION. 
 
 The purpose of this bibliography is to present a list of the 
 
 more important contributions to the problems involved in the 
 origin of ore-deposits. The literature of this subject has be- 
 come so voluminous that it is a matter of great difficulty for 
 any one to glance over all that is published, or even to keep 
 informed of the appearance of new and important papers. 
 
840 ORIGIN OF METALLIFEROUS ORE-DEPOSITS. 
 
 This difficulty is felt keenly by those whose work is exclu- 
 sively concerned with the study of ore-deposits, but to a very 
 much greater degree by mining engineers, who are chiefly 
 occupied with business affairs, and who can spare the time 
 only to read those books which seem immediately pertinent to 
 the work with which they are at the moment occupied. 
 
 Much that is of great practical value has appeared of recent 
 years on this subject; many special problems have been dis- 
 cussed in the literature which vitally affect not only the thought 
 of the geologist and investigator, but the estimates of value and 
 plans for mining development which are the work of the 
 engineer. 
 
 The idea which is kept in view in compiling this bibliogra- 
 phy is that of grouping together all references which refer to 
 any particular problem in ore-deposition. Much of the litera- 
 ture of ore-deposits, and especially the geological reports of Fed- 
 eral and State surveys, is necessarily geographically arranged. 
 While attempts to find information concerning any geographic 
 locality, therefore, offer no difficulty, it is often extremely difficult 
 to find discussions of any particular problem in ore-deposition. 
 The writers have for this reason attempted in this paper to 
 compile an index according to the problem upon which infor- 
 mation is sought. Thus the secondary enrichment of copper- 
 ores, the segregation of the sulphides from molten magmas, 
 the relation of eruptive rocks to deposits of the metallifer- 
 ous ores, etc., are given as headings. 
 
 The paper is arranged in two portions. In the first, is a list 
 of the more important papers bearing either directly or in- 
 directly on the genesis of ore-deposits. The second part is a 
 classification and rearrangement of the list under separate 
 headings representing the departments and elements of the 
 subject. In this way it is possible to follow each special 
 problem through the literature. 
 
 In presenting this list the writers wish particularly to em- 
 phasize that it makes no claim to completeness. A. few only 
 of many possible titles are selected. The original list of papers 
 is, therefore, far from exhaustive. All works on non-metallic 
 deposits have been excluded, as well as all works on general 
 geology, except those which contain especially appropriate dis- 
 cussions of ore-deposits. Descriptive reports on mining-dis- 
 
ORIGIN OF METALLIFEROUS ORE-DEPOSITS. 841 
 
 tricts which offer no conclusions on genesis, and which attempt 
 no solution of problems connected with their description, have 
 also been, for the most part, excluded, as their inclusion 
 would have swelled this paper beyond all due proportion. 
 Many references are given to books not primarily concerned 
 with ore-deposits, as these aid in the comprehension of the 
 problems involved. Except where omission of titles has been 
 inadvertent, the writers assume full responsibility for the 
 exclusion of papers which have seemed to them of minor 
 importance. 
 
 It is hoped, therefore, that this brief theoretical index will 
 be of service. The writers are conscious that it lacks much 
 both in amplitude and in the selection of references, but it will 
 in any event serve to indicate the lines on which a valuable 
 bibliography may be compiled. 
 
 ABBREVIATIONS. 
 
 In order to economize space the following abbreviations have 
 been used in this bibliography : 
 
 Of General Import. 
 
 Hist. Chiefly of historic interest. 
 
 Rec. Strongly recommended as of value in the understanding of ore-genesis. 
 
 E. Elementary. 
 
 D. Of no especial importance. 
 
 Des. Mainly descriptive, and only incidentally concerned with questions of ore- 
 genesis. 
 
 Geol. Dealing with geological problems which, though not directly concerned 
 with ore-deposits, have important applications to the subject. 
 
 Rev. Review or reviewed. 
 
 Abbreviations for Periodical Publications. 
 
 Abb. K. Bayer. Akad. d. Wissc. Abbildung der Kdniglwhe Bayer ische Akademie der 
 Wissenschaften ; Munich, Germany. 
 
 Act. Soc. Espanola d. Hist. Nat. Ada de la Sociedad Espanola de Historia Natural. 
 
 Am. Geol. American Geologist ; Minneapolis, Minn. (Merged with Econ.GeoL, 
 1906.) 
 
 Am. Jour. Sci. American Journal of Science ; New Haven, Conn. 
 
 Ann. d. Mines. Annales des Mines ; Paris, France. 
 
 Ann. d. Min. de Belg. Annales des Mines de. Belgiqm ; Brussels, Belgium. 
 
 Ann. N. Y. Acad. Sci. Annals of the New York Academy of Sciences ; New York, N. Y. 
 
 Ann. Rept. Cal. State Min. Annual Report of the California State Mineralogist ; Sac- 
 ramento, Cal. 
 
 Ann. Rept. Smith. Inst. Annual Report of the Smithsonian Institute ; Washington, 
 D. C. 
 
 53 
 
842 ORIGIN OF METALLIFEROUS ORE-DEPOSITS. 
 
 Ann. Eept. U. S. G. S. Annual Report of the United States Geological Survey ; 
 
 Washington, D. C. 
 
 Ann. Soc. Geol. d. Belg. Annales de la Societe Geologique de Belgique; Liege, Bel- 
 gium. 
 
 Archivf. prak. Geol. Archiv fur praktische Geologie; Vienna, Austria. 
 Ark. Geol. Sur. Geological Survey of Arkansas ; Little Bock, Ark. 
 Aust, Min. Stand. Australian Mining Standard ; Sydney, N. S. W., Australia. 
 Australas. Inst. Min. Eng. Australasian Institute of Mining Engineers ; Melbourne, 
 
 Victoria, Australia. 
 
 Sal. Zeit. Balneologische Zeitung ; Berlin, Germany. 
 Ber. d. K. K. Ak. d. W. Berichte der Kaiserlich Koniglichen Akademie der Wis- 
 
 senschaft. ; Vienna, Austria. 
 
 Berg- u. Hiltt. Rund. Berg-und Huttenmdnnische Rundschau ; Kattowitz, Germany. 
 Berg- u. Hiltt. Zeit. Berg- und Hiittemdnnische Zeitung ; Freiberg, Germany. 
 Bol. Inst. Geol. Mex. Boletin del Institute Geologico de Mexico; Mexico City, 
 
 Mexico. 
 Bol. Soc. Geol. de Mex. Boletin de la Sociedad Geologica de Mexico ; Mexico City, 
 
 Mexico. 
 Bull. A. I. M. E. Bulletin of the American Institute of Mining Engineers ; New 
 
 York, N. Y. 
 Bull. Can. Dept. Mines. Bulletin of the Department of Mines, Mines Branch, Canada; 
 
 Ottawa, Canada. 
 Bull. Com. Geol. Fin. Bulletin de la Commission Geologique de la Finlande ; 
 
 Helsingfors. 
 Bull. Dept. Geol. Univ. Gal. Bulletin of the Department of Geology of the University 
 
 of California; Berkeley, Cal. 
 Bull. Dept. Mines, Tasm. Bulletin of the Department of Mines, Tasmania; Hobart, 
 
 Tasmania. 
 Bull. Geol. Nat. Hist. Sur. Minn. Bulletin of the Geological and Natural History 
 
 Survey of Minnesota ; St. Paul, Minn. 
 
 Bull. Geol. Soc. Am. Bulletin of the Geological Society of America ; Rochester, N.Y. 
 Bull. Geol. Sur. W. Aust. Bulletin of the Geological Survey of Western Australia; 
 
 Perth, Western Australia. 
 
 Bull. N. Y. State Mus. Bulletin of the New York State Museum ; Albany, N. Y. 
 Bull. N. Z. Geol. Sur. Bulletin of New Zealand Geological Survey; Wellington, 
 
 N. Z. 
 Bull. No. Car. Geol. Sur. Bulletin of the North Carolina Geological Survey ; Ealeigh, 
 
 N. C. 
 
 Bull. Soc. Beige de Geol. Bulletin de la Societe Beige de Geologie ; Brussels, Belgium. 
 Bull. Soc. Geol. de France. Bulletin de la Societe Geologique de France; Paris, 
 
 France. 
 Bull. Soc. de VInd. Min. Bulletin de la Societe de V Industrie Minerale ; St. Etienne, 
 
 France. 
 
 Bull U. S. G. S. Bulletin of the United States Geological Survey ; Washington,D. C. 
 Bull. Wis. Geol. Nat. Hist. Sur. Bulletin of the Wisconsin Geological and Natural 
 
 History Survey ; Madison, Wis. 
 
 Cal. St. Min. Bu. California State Mining Bureau ; San Francisco, Cal. 
 Can. Dept. Mines. Canadian Department of Mines; Ottawa, Canada. 
 Can. Geol. Sur., Sum. Rept. Summary Report of the Canadian Geological Survey ; 
 
 Ottawa, Canada. 
 Can. Min. Jour. Canadian Mining Journal; Toronto, Canada. 
 
ORIGIN OF METALLIFEROUS ORE-DEPOSITS. 843 
 
 Can. Min. Rev. Canadian Mining Review ; Toronto, Canada. 
 
 Cent. f. Min. Geol. u. Pal. Centralblatt fur Mineralogie, Geologie and Paleontologie ; 
 
 Stuttgart, Germany. 
 
 Chem. News. Chemical News ; London, England. 
 
 Compt. rend. Acad. Sci. Comptes rendus de 1 J Academic des Sciences ; Paris, France. 
 Compt. rend. Cong. Geol. Int. Comptes rendus du Congres Geologique Internationale. 
 
 Published every three years at the place where the session is held. 
 Compt. rend. Soc. de V Ind. Min. Comptes rendus de la Societe de V Industrie Mine- 
 rale; St. Etienne, France. 
 Denkschr. Akad. Wien. 
 Deut. Naturforsch. u. Aert. Deutsche Naturforscher und Aertze Gesellschaft ; Leipzig, 
 
 Germany. 
 
 E. and M. Jour. Engineering and Mining Journal ; New York, N. Y. 
 Econ. Geol. Economic Geology; Urbana, 111. 
 Ess. Gluck. Essener Gluckauf; Essen, Germany. 
 
 Field Col. Mas. Pub. Field Columbian Museum Publications; Chicago, I1L 
 Geog. Jahresheft. Geognostiche Jahreshefte; Cassel, Germany. 
 Geog. May. Geographical Magazine ; London, England. 
 Geol. Centralb. Geologisches Centralblatt; Leipzig, Germany. 
 Geol. For. i Stock. Fdrhand. Geologiska Foreningens i Stockholm F or handling ar ; 
 
 Stockholm, Sweden. 
 
 Geol. Mag. Geological Magazine ; London, England. 
 Geol. Sur. Ark. Arkansas Geological Survey ; Little Bock, Ark. 
 Geol. Sur. Can. Geological Survey of Canada ; Ottawa, Canada. 
 Geol. Sur. Eng. and Wales. Memoirs of Geological Survey of England and Wales; 
 
 London, England- 
 
 Geol. Sur. Ga. Geological Survey of Georgia; Atlanta, Ga. 
 Geol. Sur. Gt. Brit. Geological Survey of Great Britain; London, England. 
 Geol. Sur. Ky. Bulletin of Kentucky Geological Survey ; Lexington, Ky. 
 Geol. Sur. N. S. W. Memoirs of Geological Survey of New South Wales ; Sydney, 
 
 Australia. 
 Geol. Sur. Queensl. Publications of Geological Survey of Queensland; Brisbane, 
 
 Australia. 
 Geol. Sur. So. Aust. Report of Geological Survey of South Australia; Adelaide, 
 
 Australia. 
 Geol. Sur. W. Aust. Bulletin of the Western Australia Geological Survey; Perth, 
 
 Western Australia. 
 
 Gluckauf. Gluckauf, Essen, Germany. 
 Jahrb. d. K. K. Geol. Reichsanst. Jahrbuch der Kaiserlich Koniglichen Geologische 
 
 Reichsanstalt ; Vienna, Austria. 
 Jahrb. d. Kgl. Pr. Geol. Landesanst. Jahrbuch der Koniglich Preussichen Geolog- 
 
 ischen Landesanstalt und Bergakademie ; Berlin, Germany. 
 Jahrb. d. Naturhist. Landes. in Kdrnten. Jahrbuch der Naturhistorisches Landes- 
 
 museums in Kdrnten; Klagenfurt, Austria-Hungary. 
 Jahrb. f. Berg- und Hiitt. im Konig. Sachs. Jahrbuch fur Berg- und Hiittenwesen 
 
 im Konigreich Sachsen ; Freiberg, Germany. 
 
 Jour. Am. Chem. Soc. Journal of the American Chemical Society; Easton, Pa. 
 Jour, and Proc. Roy. Soc. N. S. W. Journal and Proceedings of the Royal Society of 
 
 New South Wales; Sydney, Australia. 
 
 Jour. Can. Min. Inst. Journal of the Canadian Mining Institute; Montreal, Canada. 
 Jour. Coll. Sci. Imp. Univ. Jap. Journal of the College of Science of the Imperial 
 
 University of Japan ; Tokyo, Japan. 
 
844 ORIGIN OF METALLIFEROUS ORE-DEPOSITS. 
 
 Jour. Geol. Journal of Geology ; University of Chicago, Chicago, 111. 
 
 Jour. Iron and Steel Inst. Journal of the Iron and Steel Institute ; London, England. 
 
 Jour. Roy. Inst. Cornw. Journal of the Royal Institution of Cornwall; Truro, England. 
 
 Jour. Soc. Arts. Journal of the Society of Arts; London, England. 
 
 K. K. Ackerb. Minist. Statistich Jahrbuch der Kaiserlich Kb'niglicher Ackerbaumin- 
 isterium; Vienna, Austria. 
 
 K. K. Ak. d. W. in Wien. Kaiserlich Kb'nigliche Akademie der Wissenschaft in 
 Wien ; Vienna Austria. 
 
 Mem. Geol. Sur. Eng. and Wales. Memoirs of the Geological Survey of England and 
 Wales; London, England. 
 
 Mem. Geol. Smt Ind. Memoirs of the Geological Survey of India ; Calcutta, India. 
 
 Mem. Geol, Suf. Viet. Memoirs of the Geological Survey of Victoria; Melbourne, 
 Australia. 
 
 Mem. Mmes Dept. Transvaal. Memoirs of the Mines Dept. Geological Survey, Trans- 
 vaal, So. Africa; Pretoria, So. Africa. 
 
 Mem Mus. Comp. Zool. Har. Coll. Memoirs of the Museum of Comparative Zoology 
 of Harvard College ; Cambridge, Mass. 
 
 Mem. Soc. Cien. Ant. Alz. Memorias y Revista de la Sociedad Cientiftca "Antonio 
 Alzate" ; Mexico City, Mexico. 
 
 Mem. Soc. Ing Civ. Memoires de la Societe des Ingenieurs Civils de France; Paris, 
 France. 
 
 Min. and Sci. Press. The Mining and Scientific Press ; San Francisco, Cal. 
 
 Min. Ind. The Mineral Industry. Published by the Engineering and Mining Jour- 
 nal, New York, N. Y. 
 
 Min. Jour. The Mining Journal ; London, England. 
 
 Min. Mag. (J). The Mining Magazine. W. J. Johnston, publisher ; New York, 
 N. Y. 
 
 Min. Mag. (R). The Mining Magazine. T. A. Kickard, editor ; London, England. 
 
 Min. Met. Soc. Mining and Metallurgical Society of America ; New York, N. Y. 
 
 Min. Res. Mineral Resources of the United States, U. S. Geological Survey; Wash- 
 ington, D. C. 
 
 Mineralog. Mag. Mineralogical Magazine ; London and Truro, England. 
 
 Mines Dept. Tasm. Mines Department Tasmania; Hobart, Tasmania. 
 
 Mines Dept. Trans. Mines Department Transvaal; Pretoria, South Africa. 
 
 Mitt. d. Naturwiss. Vereinsf. Neuvorkommen u. Rilgen. Mittheilungen der Naturwis- 
 senshaftliches Vereinsf iir Neuvorkommen und Rilgen. 
 
 Mitt. d. Philomat. Gesel. in Els. Lothr. Mittheilungen der Philomatischen Gesellschaft 
 im Elsass- Lb'thringen. 
 
 Mon. U. S. G. S. Monograph of the United States Geological Survey ; Washington, 
 D. C. 
 
 Monatsb. d. D. Geol, Gesel. Monatsberichte der Deutschen Geologischen Gesellschaft; 
 Berlin, Germany. 
 
 N. Z. Inst. Min. Eng. New Zealand Institute of Mining Engineers; Auckland. New 
 Zealand. 
 
 N. Z. Mines Rec. New Zealand Mines Record; Wellington, N. Z. 
 
 Nat. Nature; London, England. 
 
 Naturf. Der Naturforscher ; Berlin and Tubingen, Germany. 
 
 Neues Jahrb. f. Min. Neues Jahrbuch fur Mineralogie, Geognosie, Geologic und Petre- 
 factenkunde; Heidelberg, Germany. 
 
 Norsk Teknisk Tids. Norsk Teknisk Tidsskrift ; Christiania, Norway. 
 
 Ost. Zeit. f. Berg- u. Hutt. Osterreichische Zeitschrift fur Berg- und Huttenwesen ; 
 Vienna, Austria. 
 
ORIGIN OF METALLIFEROUS ORE-DEPOSITS. 
 
 Phil. Mag. Philosophical Magazine; London, England. 
 
 Poyg. Ann. Poggendorff's Annalen der Physik und Chemie; Berlin, Germany. 
 
 Proc. Am. Acad. Arts and Sci. Proceedings of the American Academy of Arts and 
 Sciences ; Boston, Mass. 
 
 Proc. Am. Assoc. Adv. Sci. Proceedings of the American Association for the Advance- 
 ment of Science; Washington, D. C. 
 
 Proc. Am. Phil. Soc. Proceedings of the American Philosophical Society; Philadel- 
 phia, Pa. 
 
 Proc. and Trans. Nov. Scot. Inst. Sci. Proceedings and Transactions of the Nova 
 Scotia Institute of Science ; Halifax, N. S. 
 
 Proc. Colo. Sci. Soc. Proceedings of the Colorado Scientific Society ; Denver, Colo. 
 
 Proc. Gen. Min. Assoc. Que. Proceedings of the General Mining Association of the 
 Province of Quebec ; Ottawa, Canada. 
 
 Proc. Lake Sup. Min. Inst. Proceedings of the Lake Superior Mining Institute; Ish- 
 peming, Mich. 
 
 Proc. Roy. Soc. Proceedings of the Royal Society of London; London, England. 
 
 Proc. Roy. Soc. Viet. Proceedings of the Royal Society of Victoria; Melbourne, Aus- 
 tralia. 
 
 Proc. Wash. Acad. Sci. Proceedings of the Washington Academy of Sciences ; Wash- 
 ington, D. C. 
 
 Prof. Paper U. S. O. S. Professional Paper of the United States Geological Survey ; 
 Washington, D. C. 
 
 Quar. Jour. Geol. Soc. The Quarterly Journal of the Geological Society of London ; 
 London, England. 
 
 Rept. Brit. Assoc. Adv. Sci. Report of the British Association for the Advancement of 
 Science; London, England. 
 
 Rept. Col. St. Bu. Min. Report of the Colorado State Bureau of Mines ; Denver, Colo. 
 
 Rept. Mich. Acad. Sci. Report of the Michigan Academy of Science; Ann Arbor, Mich. 
 
 Rept. Mich. State Geol. Report of the State Geologist of Michigan; Lansing, Mich. 
 
 Rept. Ont. Bu. Mines. Report of the Ontario Bureau of Mines ; Toronto, Canada. 
 
 Rev. Gin. d. Sci. Revue generale des Sciences, pures et appliques ; Paris, France. 
 
 Rev. Univ. d.' Mines. Revue Universelle des Mines et de Metallurgie ; Liege, Belgium. 
 
 Rosenb. Fests. Rosenbusch Festschrift. 
 
 Roy. Soc. Tasm. Royal Society of Tasmania; Hobart, Tasmania. 
 
 Sch. Min. Quar. School of Mines Quarterly Columbia School of Mines ; New York. 
 
 Schles. Ges.f.Vater. Kult. Schlessische GeseUschaftfiir Vaterlandische Kultur; Breslau, 
 Germany. 
 
 Sci. Mon. Scientific Monthly, published by the Colorado State School of Mines ; 
 Golden, Colo. 
 
 Sci. Prog. Science Progress; London, England. 
 
 Science. Science. Weekly Journal, published by the American Association for 
 the Advancement of Science ; New York, N. Y. 
 
 Sitz. d. Wiirz. phys. tried. Gesel. Sitzungsberichte des Wiirzburger physikalisch medi- 
 zinischen Gesellschoft ; Wiirzburg, Germany. 
 
 So. Af. Assoc. Eng. Transactions of the South African Association of Engineers; 
 Johannesburg, So. Africa. 
 
 Stahl u. Eisen. Stahl und Eisen ; Diisseldorf, Germany. 
 
 Tech. Quar. Technology Quarterly. Published by the Massachusetts Institute of 
 Technology ; Boston, Mass. 
 
 Trans. A. I. M. E. Transactions of the American Institute of Mining Engineers ; 
 New York, N. Y. 
 
846 ORIGIN OF METALLIFEROUS ORE-DEPOSITS. 
 
 Trans. Aust. Inst. Min. Eng. Transactions of the Australian Institute of Mining 
 
 Engineers; Melbourne, Australia. 
 Trans. Fed. Inst. Min. Eng. Transactions of the Federated Institution of Mining 
 
 Engineers; London, England. 
 Trans. Geol. Soc. So. Af. Transactions of the Geological Society of South Africa; 
 
 Johannesburg, South Africa. 
 Trans. Inst. Min. and Met. Transactions of the Institute of Mining and Metallurgy ; 
 
 London, England. 
 
 Trans. Int. Min. and Met. Cong. Transactions of the International Mining and Met- 
 allurgical Congress. 
 Trans. Min. and Geol. Inst. Ind. Transactions of the Mining and Geological Institute 
 
 of India; Calcutta, India. 
 Trans. N. Y. Acad. Sci. Transactions of the New York Academy of Sciences; New 
 
 York, N. Y. 
 Trans. N. Z. Inst. Min. Eng. Transactions of the New Zealand Institute of Mining 
 
 Engineers; Auckland, New Zealand. 
 Trans. No. Eng. Inst. Min. and Mech. Eng. Transactions of the North of England 
 
 Institute of Mining and Mechanical Engineers ; Newcastle-upon-Tyne, England. 
 Trans. Roy. Geol. Soc. Cornw. Transactions of the Royal Geological Society of Cornwall ; 
 
 Plymouth, England. 
 
 Trans. So. Af. Assoc. Eng. Transactions of the South African Association of Engi- 
 neers; Johannesburg. South Africa. 
 
 Trans. Wis. Acad. Sci. Transactions of the Wisconsin Academy of Sciences; Madi- 
 son, Wis. 
 Tscher. Min. u. Pet. Mitt. Tschermak's Mineralogische und Petrographische Mittheil- 
 
 ungen; Vienna, Austria. 
 
 U. S. G. S. United States Geological Survey ; Washington, D. C. 
 Univ. Geol. Sur. Kans. University Geological Survey of Kansas ; Topeka, Kan. 
 Verhand. d. Naturhist. V. d. Pr. Rheinlande. Verhandlungen des Nalurhistorischen 
 
 Vereins der Preussischen Rheinlande und Westphalens ; Bonn, Germany. 
 Verhand. d. Wurzburger Phys. Med. Ges. Verhandlungen der Wurzburger Physi- 
 
 kalisch-Medizinischen Gesellschaft ; Wiirzburg, Germany. 
 Verhand. Geol. Reichsanst. Verhandlungen der Kaiserlich-Koniglichen Geologischen 
 
 Reichsanstalt ; Vienna, Austria. 
 Wat. Sup. and Irr. Paper. Water Supply and Irrigation Paper, U. S. Geological 
 
 Survey ; Washington, D. C. 
 Wis. Geol. Nat. Hist. Sur. Wisconsin Geological and Natural History Survey; 
 
 Madison, Wis. 
 
 Zeit. f. Angew. Chem. Zeitschrift fur Angewandte Chemie ; Leipzig, Germany. 
 Zeit. f. Berg- Hutt. u. Salinenw. Zeitschrift fur Berg- Hiitten und Salinenwesen in 
 
 dem Preussichen Staate ; Berlin, Germany. 
 Zeit. d. D. Geol. Gesel. Zeitschrift der Deutschen Geologischen Gesellschaft ; Berlin, 
 
 Germany. 
 
 Zeit. f. Kryst. Zeitschrift fur Krystallographie und Miner alogie; Munich, Germany. 
 Zeit.f.prak. Geol. Zeitschrift fur praktische Geologic; Berlin, Germany. 
 
ALPHABETICAL LIST OF AUTHORS. 847 
 
 ALPHABETICAL LIST OF AUTHORS. 
 
 Numbers serve to distinguish separate papers by the same author. They are 
 used in the next chapter in referring to individual papers. 
 
 ABBOTT, C. E. 
 
 The Iron-Ore Deposits of the Ely Trough, Vermilion Kange, Minn. Proc. 
 
 Lake Sup. Min. Inst., vol. 12, pp. 116-142 (1907). 
 ADAM, J. W. H. 
 
 Versuch einer neuen Behandlungsart der Erzlagerstattenlehre. Zeit. f. prak. 
 
 Geol., vol. 18, pp. 5-10 (1910). 
 ADAMS, F. D. 
 
 1. On the Igneous Origin of Certain Ores. Proc. Gen. Min. Assoc. Que. 
 (Jan. 12. 1894). 
 
 2. An Experimental Investigation into the Action of Differential Pressure on 
 Certain Minerals and Rocks, employing the Process Suggested by Professor 
 Kick. Jour. GeoL, vol. 18, pp. 489-525 (1910). 
 
 3. An Experimental Contribution to the Question of the Depth of the Zone of 
 Flow in the Earth's Crust. Jour. GeoL, vol. 20, pp. 97-118 (1912). 
 
 ADAMS, G. I. 
 
 1. Zinc- and Lead-Deposits of Northern Arkansas. Trans. A. I. M. E , vol. 
 34, pp. 163-174 (1903). 
 
 2. Zinc and Lead Deposits of Northern Arkansas. Prof. P^iper 24, U. S. G. S. 
 (1904). 118 pp. 
 
 ADIASSEURCH, A. I. 
 
 A Journey to Central Asia. Trans. Inst. Min. and Met., vol. 17, pp. 498-527 
 
 (1907-08). 
 AGUILERA, J. G. 
 
 The Geological Distribution of the Mineral Deposits of Mexico. Trans. 
 
 A. I. M. R, vol. 32, pp. 497- 520 (1901). 
 ALLEN, E. T. 
 
 The Mineral Sulphides of Iron. Am. Jour. Sci., 4th ser., vol. 32, pp. 169- 
 
 236(1911). 
 ALLEN, R. C. 
 
 The Occurrence and Origin of the Brown Iron Ores of Spring Valley, Wis- 
 consin .llth Rept. Mich. Acad. Sci., pp. 95-103 (1909). 
 ANDRE, G. C. 
 
 A Practical Treatise on Coal Mining (London, 1879). 
 ANDREWS, A. C. 
 
 Molybdenum. Mineral Resources Series, No. 11, GeoL'Sur. N. S. W. (1906). 
 
 17pp. 
 ARQALL, G. O. 
 
 Recent Developments on Iron Hill, Leadville, Colo. E. and M. Jour., vol. 89, 
 
 No. 5, p. 261 (1910). 
 ARGALL, PHILIP. 
 
 1. Nickel ; Occurrence, Geological Distribution and Genesis of Its Ore De- 
 posits. Proc. Colo. Sci. Soc., vol. 4, pp. 395-421 (1893). 
 
 2. Rock Oxidation at Cripple Creek. Min. and Sci. Press, vol. 96, pp. 883- 
 886 (1908). 
 
 3. Zinc Resources of Canada. Report of the Commission to investigate the 
 Zinc Resources of British Columbia, pp. 147-252 (Ottawa, 1906). 
 
 ARNOLD, RALPH. 
 
 Gold Placers of the Coast of Washington. Bull, 260, U. S. G. S., pp. 154- 
 
 157 (1905). 
 ASHLEY, G. H. 
 
 Geology of the Paleozoic Area of Arkansas South of the Novaculite Region. 
 Proc. Am. Phil. Soc., vol. 36, pp. 217-318 (1897). 
 
848 ALPHABETICAL LIST OF AUTHORS. 
 
 ASTON, J. 
 
 1. The Solidification of Alloys and Magmas. Jour. Geol., vol. 17, pp. 569- 
 585 (1909). 
 
 2. The Genesis of the Gold Deposits of Barkerville (British Columbia). 
 Quar. Jour. Geol. Soc., vol. 60, pp. 389-393 (1904). 
 
 3. Some Further Considerations of the Genesis of the Gold Deposits of Bark- 
 erville, B. C., and the Vicinity. Geol. Mag., vol. 3, pp. 514-516 (1906). 
 
 AUSTIN, W. L. 
 
 The Nickel Deposits near Riddles, Oregon. Proc. Colo. Sci. Soc., vol. 5, pp. 
 173-196 (1894-96). 
 
 BABANEK. 
 
 Die Erzfiihrung der Pribramer Sandsteine und Schiefer, in Ihrem Verhalt- 
 nisse zu Dislokationen. 6st. ZeH. f. Berg- u. Hull, vol. 19, pp. 340-342, 
 347-348. 
 BABB, P. A. 
 
 Dulces Nombres Quicksilver Deposit, Mexico. E. and M. Jour., vol. 88, No. 
 
 14, pp. 684-686 (1909), 
 BAGG, JR., R. M. 
 
 Some Copper Deposits of the Sangre de Christo Range, Colorado. Econ. Geol., 
 
 vol. 3, pp. 739-749 (1908). 
 BAIN, H. F. 
 
 1. Zinc and Lead Deposits of Northwestern Illinois. Bull. 246, U. S. G. S. 
 (1905). 56pp. 
 
 2. Zinc and Lead Deposits of the Upper Mississippi Valley. Bull. 294, U. 
 S. G.S. (1906). 155pp. 
 
 3. Sedi genetic and Igneo-geneticOres. Econ. Geol., vol. 1, pp. 331-339(1906). 
 
 4. Some Relations of Paleogeography to Ore Deposition in the Mississippi 
 Valley. Econ. Geol, vol. 2, pp. 128-144 (1907). 
 
 5. Types of Ore Deposits (Introductory Chapter). 376 pp. (San Francisco, 
 1911). 
 
 BAIN, H. F.,, and ULRICH, E O. 
 
 The Copper Deposits of Missouri. Butt. 267, U. S. G. S. (1905). 52 pp. 
 BAIN, H. F. , and VAN HISE, C. R. 
 
 Preliminary Report on the Lead and Zinc Deposits of the Ozark Region. 
 
 22d Ann. Eept., U. S. G. S., part 2, pp. 23-227 (1901). 
 BALL, S. H. 
 
 1. Geological Reconnaissance in Southwestern Nevada and Eastern Cali- 
 fornia. Bull. 308, U. S. G. S. (1907). 218 pp. 
 
 2. Titaniferous Iron Ore of Iron Mt., Wyoming.^//. 315, U. S. G. S., 
 p. 206 (1907). 
 
 BALL, S. H., and SHALER, M. K. 
 
 Mining-Conditions in the Belgian Congo, Trans. A. I. M. E., vol. 41, pp. 
 
 189-219 (1910). 
 BANCROFT, G. J. 
 
 1. Kalgoorlie, West Australia, and Its Surroundings. Trans. A. I. M. E., 
 vol. 28, pp. 88-100 (1898). 
 
 2. Secondary Enrichment at Cripple Creek. E. and M. Jour., vol. 75, pp. 
 111-112 (Jan.. 17, 1903). 
 
 3. The Yaqui River Country of Sonora, Mexico. E. and M. Jour., vol. 76, 
 pp. 160-162 (1903). 
 
 4. The Formation and Enrichment of Ore-Bearing Veins. Trans. A. I. M. 
 E., vol. 38, pp. 245-268 (1907) ; vol. 40, pp. 809-817 (1909). 
 
 5. Cripple Creek. Secondary Enrichment. E. and M. Jour., vol. 74, pp. 
 752-753 (1902). 
 
 BARLOW, A. E. 
 
 1. Report on the Nickel and Copper Deposits of Sudbury, Ontario. Geol. 
 Sur. Can., vol. 14, part H (1904). 
 
 2. On the Origin and Relations of the Nickel and Copper Deposits of Sud- 
 bury, Ontario, Canada, with bibliography. Econ. Geol, vol. 1, pp. 454- 
 466, 545-553 (1906). 
 
ALPHABETICAL. LIST OF AUTHORS. 849 
 
 BARRELL, JOSEPH. 
 
 1. The Physical Effects of Contact Metamorphism. Am. Jour. Sci., ser. 4, 
 vol. 13, p. 279 (1902). 
 
 2. Geology of the Marys ville Mining District, Montana : a study of igneous 
 intrusion and contact metamorphism. Prof. Paper 57, U. S. G. S. (1907). 
 178 pp. 
 
 BARROW, GEORGE. 
 
 The High-Level Platforms of Bodmin Moor aVid Their Relation to the De- 
 posits of Stream Tin and Wolfram. Quar. Jour. Oeol. Soc., vol. 64, pp. 
 384-400 (1908). 
 
 BARUS, CARL. 
 
 1. The Electrical Activity of Ore-Bodies. 1 Vans. A. I. M. E., vol. 13, pp. 
 417-477 (1884-85). 
 
 2. On the Thermal Effect of the Action of Aqueous Vapor on Feldspathic 
 Rocks. Sch. Min. Quar., vol. 6, pp. 1-23 (1884). 
 
 BASTIN, E. S. 
 
 Chemical Composition as a Criterion in Identifying Metamorphosed Sedi- 
 ments. Jour. GeoL, vol. 17, pp. 445-472 (1909). 
 BATESON, C. E. W. 
 
 The Mojave Mining District of California. Trans. A. I. M. E., vol. 37, pp. 
 
 160-177 (1906). 
 DE BATZ, RENE. 
 
 The Auriferous Deposits of Siberia. Trans. A. I. M. E., vol. 28, pp. 452- 
 
 467 (1898). 
 BAUMG ARTEL, B. 
 
 Beitrag zur Kenntniss der Kieslagerstatten zwischen Klingenthal und Gras- 
 litz im Westlichen Erzgebirge. Zeit. f. prak. Geol., vol. 13, pp. 353-358 
 (1905). 
 BAYLEY, W. S. 
 
 1. The Menominee Iron-Bearing District of Michigan. Mon. 46, U. S. G. S. 
 (1904). 513pp. 
 
 2. Magnetite Ores of the Hibernia Mine. Folio 157, U. S. G. S. (1908). 
 DE BEAUMONT, ELIE. 
 
 1. Bulletin de la Societe Geologique de France, 2d series, vol. 4, p. 1249. Trans- 
 lated by B. von Cotta, in his 4. "Gangstndien," under title, " Ueber die 
 vulkanischen und Metallischen Emanationen oder Ausstromungen," pp. 
 329-436 (Freiberg, 1850). 
 
 2. Dolomitization. Bull. Soc. GeoL de France, vol. 8, pp. 174-177 (1836). 
 DE LA BECHE, HENRY T. 
 
 Report on the Geology of Cornwall, Devon, and West Somerset (London, 1839). 
 BECK, RICHARD. 
 
 1. Die Zinnerzlagerstiitten von Bangka und Billiton. Zeit. f. prak. GeoL, 
 vol. 6, pp. 121-127 (1898). 
 
 2. Ueber die Erzlager der Umgebung von Schwarzenberg im Erzgebirge. 
 Jahrb. f. Berg- u. Hutt. in Konig. Sachs., A 51, 87 (1902) ; A 55-97 (1904). 
 
 3. Die Nickelerzlagerstiitten von Sohland a. d. Spr. und ihre Gesteine. Zeit. 
 d. D. Geol. GeseL, p. 296 (1903). 
 
 4. Uber die Beziehungen zwischen Erzgiingen und Pegmatiten. Zeit. f. prak. 
 Geol, vol. 14, pp. 71-73 (1906). 
 
 5. Einige Bemerkungen iiber afrikanische Erzlagerstatten. Zeit. f. prak. 
 GeoL, vol. 14, pp. 205-209 (1906). 
 
 6. On the Relation between Ore Veins and Pegmatites. Geol. Mag., Decade 
 V, vol. 3, No. 1 (1906). 35pp. 
 
 7. Ore Veins and Pegmatites. Trans. Geol. Soc. So. Af., vol 8, p. 147 (1905). 
 
 8. The Nature of Ore Deposits. Trans, by Weed, W. H. (New York, 1909). 
 685 pp. 1st ed., 2d imp. 
 
 9. Lehre von den Erzlagerstatten. (Berlin, 1909). 2 vols , 1082 pp. 
 
 10. Erlauterungen zu. Sect. Berggiesshiibel der Geologische Specialkarte von 
 Sachsen, pp. 25-60 (Leipzig, 1889). 
 
 BECKER, G. F. 
 
 1. Geology of the Comstock Lode and the Washoe District. Mon. 3, U. S. 
 G. S. (1882). 422pp. 
 
850 ALPHABETICAL LIST OP AUTHORS. 
 
 BECKER, G. F. Continued. 
 
 2. Summary of Geology of Comstock Lode and Washoe District. 2d Ann. 
 Kept., U. S. O. S., pp. 291-330 (1881). 
 
 3. The Relations of the Mineral Belts of the Pacific Slope to the Great Up- 
 heavals. Am. Jour, Sci., Ser. 3, vol. 28, p. 209 (1884). 
 
 4. Geology of the Quicksilver Deposits of the Pacific Slope. Mon. 13, U. S. 
 G. S. (1888). 486 pp. 
 
 5. Summary of Geology of Quicksilver Deposits of the Pacific Slope. 8th 
 Ann. RepL, U. S. G. S., part II, pp. 961-985 (1887). 
 
 6. The Structure of a Portion of the Sierra Nevada of California. Bull. Geol. 
 Soc. Am., vol. 2, p. 49 (1891). 
 
 7. Finite Homogeneous Strain, Flow, and Rupture of Rocks. Bull. Geol. 
 Soc. Am., vol. 4, p. 13 (1893). 
 
 8. The Finite Elastic Stress-Strain Function. Am. Jour. Sci., vol. 46, 3d 
 series, pp. 337-356 (1893). 
 
 9. The Torsional Theory of Joints. Trans. A. 1. M. E.,vol. 24, p. 130 (1894). 
 
 10. Schistosity and Slaty Cleavage. Jour. Geol., vol. 4, p. 429 (1896). 
 
 11. Quicksilver Ore Deposits. M in. Res. for 1892, U. S. G. S., pp. 139-168 
 (1893). 
 
 12. Gold Fields of the Southern Appalachians. IQth Ann. Eept., U.S. G. 
 S., part 3, pp. 251-331 (1895). 
 
 13. The Genesis of Ore-Deposits. Discussion of paper by F. Posepny. 
 Trans. A. I. M. E., vol. 23, pp. 602-604 (1893). 
 
 14. Reconnaissance of the Gold Fields of Southern Alaska. 18^ Ann. RepL, 
 U. S. G. S., part3, pp. 1-86 (1897.) 
 
 15. Some Queries on Rock Differentiation. Am. Jour. Sci., 4th ser., vol. 3, 
 pp. 21-40 (1897). 
 
 16. Fractional Crystallization of Rocks. Am. Jour. Sci., 4th ser., vol. 4, pp. 
 257-261 (1897)'. 
 
 17. The Witwatersrand Banket ISth Ann. RepL, U. S. G. S., part 5, pp. 
 153-184(1897). 
 
 18. Auriferous Conglomerates of the Transvaal. Am. Jour. Sci., 4th ser., vol. 
 5, pp. 193-208 (Mar., 1898). 
 
 19. Experiments on Schistosity and Slaty Cleavage. Bull. 241, U. S. G. S. 
 (1904). 34 pp. 
 
 20. Some Features of the Rand Banket Ebon. Geol., vol. 4, pp. 373-384 
 (1909). 
 
 BECKER, G. F. , and DAY, A. L. 
 
 The Lineir Force of Growing Crystals. Proc. Wash. Acad. Sci., vol. 7, pp. 
 283-288 (1905). 
 
 BELL, J. M. 
 
 Iron Ranges of Michipicoten West. RepL Ont. Bu. Mines, vol. 14, part I, 
 pp. 278-355 (1905). 
 
 BELL, E. 
 
 The Cobalt Mining District. Jour. Can. Min. Inst., vol. 28, No. 10, pp. 246- 
 
 248 (1907). 
 BENOIT, FELIX. 
 
 Gites de nickel de Nouvelle-Caledonie. Bull. Soc. de VInd. Min., vol. 6, pp. 
 753-804 (1892). 
 
 BERG, G. 
 
 1. Die Magneteisenerzlager von Schmiedeberg im Riesengebirge. Jahrb. d. 
 Kgl. Pr. Geol. LandesansL, pp. 200-267 (1892). 
 
 2. Beitriige zur Kenntniss der kontaktmetamorphen Lagerstatte von Balia- 
 maden (Turkey). Zeit. f. prak. Geol., pp. 365-367 (1901). 
 
 BERGEAT, ALFRED. 
 
 1. La Granodiorita de Concepcion del Oro en el Estado de Zacatecas. Bol. 
 27, Inst. Geol. de Mex. (1910). 
 
 2. Beitriige zur Kenntniss der Erzlagerstatten von Campiglia Marittima inbe- 
 sondere des Zinnstein Vorkommens Dortselbst. NeuesJahrh.f. Min., vol. 1, 
 pp. 135-156 (1901). 
 
 3. Die Adischen Inseln. Abb. K. Bayer. Akad. d. Wissc. II., cl. XX., pp. 
 192-194 (1899). With bibliography. 
 
 4. Von den aolischen Inseln. Zeit. f. prak. Geol. p. 43 (1899). With biblio- 
 graphy. 
 
ALPHABETICAL LIST OF AUTHORS. 851 
 
 BERGEAT, ALFRED, and STELZNER. 
 
 Die Erzlagerstatten (Leipzig, 1904-1906). 3 vols., 1330 pp. 
 VON BEUST, J. C. 
 
 Kritische Beleutung der Wernerschen Gangtheorie (Freiberg, 1840). 
 BEYSCHLAG, KRUSCH and VOGT. See Vogt. 
 BIDDLE, H. C. 
 
 The Deposition of Copper by Solutions of Ferrous Salts. Jour. Geol., vol. 9, 
 
 pp. 430-436 (1901). 
 BISCHOF, G. 
 
 1. Lehrbuch der Chemischen und Physikalischen Geologie. Edition 2, 4 
 vols., including Suppl't (Bonn, 1863-1871). 
 
 2. Elements of Chemical and Physical Geology. English Translation of. 
 Translated bv B. H. Paul and J. Drummond, 3 vols. (Cavendish Society, 
 London, 1854-59). 
 
 BLAKE, W. P. 
 
 1. The Ore Deposits of the Eureka District, Eastern Nevada. Trans. A. I. 
 M. E., vol. 6, pp. 554-563 (1877-78). 
 
 2. The Geology and Veins of Tombstone, Arizona Trans. A. I. M. E., vol. 
 10, rp. 334-345 (1881-82). 
 
 3. Tin Ore Veins in the Black Hills of Dakota. Trans. A. L M. E., vol. 
 13, pp. 691-698 (1884-85). 
 
 4. Iron-Ore Deposits of Southern Utah. Trans. A. I. M. E., vol. 14, pp. 
 809-812 (1885-86). 
 
 5. The Rainbow Lode, Butte City, Montana. Trans. A. L M. E. } vol. 16, 
 pp. 65-80. (1887-88). 
 
 6. The Copper- Deposits of Copper Basin, Arizona, and their Origin. Trans. 
 A. L M. E., vol. 17, pp. 479-485 (1888-89). 
 
 7. The Mineral Deposits of Southwest Wisconsin. Trans. A. L M. E., vol. 
 22, pp. 558-568 (1893). 
 
 8. The Zinc-Ore-Deposits of Southwestern New Mexico. Trans. A. I. M. E., 
 vol. 24, pp. 187-195 (1894). 
 
 9. Notes on the Structure of the Franklinite and Zinc-Ore Beds of Sussex 
 County, New Jersey. Trans. A. L M. E., vol. 24, pp. 521-524 (1894). 
 
 10. Cinnabar in Texas. Trans. A. I. M. E., vol. 25, pp. 68-76 (1895). 
 
 11. Gold in Granite and Plutonic Rocks. Trans. A. I. M. E., vol. 26, pp. 
 290-298 (1896). 
 
 12. The Caliche of Southern Arizona: An Example of Deposition by the 
 Vadose Circulation. Trans. A. I. M. E., vol. 31, pp. 220-226 (1901). 
 
 13. Copper-Ore and Garnet in Association. Trans. A. I. M. E., vol. 34, pp. 
 886-890 (1903). 
 
 BLATCHFORD, T. 
 
 The Geology of the Coolgardie Goldfield. Bull. 3, Geol. Sur. West. Aust. 
 
 (1899). 98 pp. 
 BLOW, A. A. 
 
 The Geology and Ore-Deposits of Iron Hill, Leadville, Colorado. Trans. A. 
 L M. E., vol. 18, pp. 145-181 (1889-90). 
 
 BODIFEE. 
 
 tiber die Genesis der Eisen- und Manganerzvorkommen bei Oberrosbach iin 
 Taunus. Zeit. f. prak. GeoL, vol. 15, pp. 309-316 (1907). 
 
 BODLANDER, G. 
 
 Versuche iiber Suspensionen. Neues Jahrb. f. Min., pp. 147-168 (1893). 
 
 BOEHMER, MAX. 
 
 1. Some Practical Suggestions Concerning the Genesis of Ore-Deposits. 
 Trans. A. L M. E., vol. 34, pp. 449-453 (1903). 
 
 2. Secondary Enrichment and Impoverishment. Econ. Geol., vol. 3, pp. 337- 
 340 (1908). 
 
 3. The Genesis of the Leadville Ore-Deposits. Trans. A. L M. E., vol. 41, 
 pp. 162-165 (1910). 
 
 BOKER, B. H. C. 
 
 Mineralausfiillung der Inerwerfungsspalten in Bergrevier Werden und eini- 
 gen Angrenzenden Gebreiten. Berg- u. Hiitt. Zeit., pp. 1065-1083 (1906). 
 
852 ALPHABETICAL LIST OF AUTHORS. 
 
 BORDEAUX, A. 
 
 Les Anciens Chenaux AurifSres de California Ann. d. Mines, vol. 2, 10th 
 
 Ser., pp. 217-258 (1902). 
 Boss, C. M. 
 
 Some Dike Features of the Gogebic Iron-Kange. Tram. A. I. M. E. , vol. 
 
 27, pp. 556-563 (1897). 
 BOURDAKOFF and HENDRIKOFF. 
 
 Description de 1' exploitation de Platine. (Ekaterinburg, 1896). 
 BOUTWELL, J. M. 
 
 1. Vanadium and Uranium Deposits in Southeastern Utah. Bull. 260 U.S. 
 G. S., pp. 200-210 (1905). 
 
 2. The Park City Mining District, Utah. Bull. 213, U. S. G. S., pp. 31-40 ; 
 225, pp. 141-160; 260, pp. 150-153 (1903-05). 
 
 3. Iron Ores of the Uinta Mountains. Bull. 225, U. S. G. S.. pp. 221-228 
 (1904). 
 
 4. Genesis of the Ore-Deposits at Bingham, Utah. Trans. A. I. M. E.. vol. 
 36, pp. 541-580 (1905). 
 
 5. Economic Geology of the Bingham Mining District, Utah. Prof. Paver 38, 
 U.S. .51(1905). 413pp. 
 
 6. Geology and Ore Deposits of the Park City District, Utah. Prof. Paper 
 77, U. X. G. S. (1912). 231pp. 
 
 BOWMAN, AMOS. 
 
 Mining Developments on the Northwestern Pacific Coast, and Their Wider 
 
 Bearing. Trans. A. I. M. E., vol. 15, pp. 707-717 (1886-87). 
 BOWRON, W. M. 
 
 1. The Geology and Mineral Resources of Sequachee Valley, Tennessee. 
 Trans. A. I. M. E., vol. 14, pp. 172-181 (1885-86). 
 
 2. The Origin of Clinton Ked Fossil-Ore in Lookout Mountain, Alabama. 
 Trans. A. I. M. E., vol. 36, pp. 587-604 (1905). 
 
 BRANNER, J. C. 
 
 1. The Zinc and Lead Kegion of North Arkansas. Ark. Geol. Sur.. vol. 5 
 (1892). 395 pp. 
 
 2. The Manganese Deposits of Bahia and Minas, Brazil. Trans. A. I. M. E.. 
 vol. 29, pp. 756-770 (1899). 
 
 3. The Zinc- and Lead-Deposits of North Arkansas. Trans. A. I. M. E.. vol. 
 31, pp. 572-603 (1901). 
 
 BRANNER, J. C., and NEWSOM, J. F. 
 
 1. Syllabus of Economic Geology. Stanford University. 2d ed .(1900). 368pp. 
 BRAUNS, R. 
 
 1. Chemische Mineralogie (1896). 
 BREWER, W. M. 
 
 1. The Gold-Regions of Georgia and Alabama. Trans. A. I. M. E.. vol. 25, 
 pp. 569-587 (1895). 
 
 2. The Copper Deposits of Vancouver Island. Trans. A. 1. M. E., vol. 29, 
 pp. 483-488 (1899). 
 
 3. The Copper Deposits of Vancouver Island. E. and M. Jour., vol. 69, 
 pp, 465, 526 ; vol. 70, p. 34 (1900). 
 
 4. Some Observations Relative to the Occurrence of Deposits of Copper Ore 
 on Vancouver Island and Other Portions of the Pacific Coast. Jour. Can. 
 Min. Inst., vol. 9, pp. 39-48 (1906). 
 
 BROADHEAB, G. C. 
 
 The Southeastern Missouri Lead District. Trans. A. I. M. E., vol. 5, pp. 
 
 100-107 (1876-77). 
 BROCK, R. W. 
 
 1. Original Native Gold in Igneous Rocks. E. and M. Jour., vol. 77, p. 511 
 (1904). 
 
 2. Platinum in British Columbia. E. and. M. Jour., vol. 77, pp. 280-281 
 (1904). 
 
 BROGGER, W. C. 
 
 Die Mineralien der Syenitpegmatitgange der Siidnorwegischen Augit und 
 Nephelinsyenit. Zeit. f. Kryst., vol. 16, p. 64 (1890). 
 
ALPHABETICAL LIST OF AUTHORS. 853 
 
 BROOKS, ALFKED H. 
 
 1. A New Occurrence of Cassiterite in Alaska. Science, New Ser., vol. 13, p. 
 593 (1901). 
 
 2. An Occurrence of Stream Tin in the York Region, Alaska. Min. Res. 
 U. S. for 1900, U. S. G. S., pp. 267-271 (1901). 
 
 3. Placer Gold Mining in Alaska in 1902. Bull. 213, U. S. G. S., pp. 41- 
 48 (1903). 
 
 4. Stream Tin in Alaska in 1902. Bull. 213, U. S. G. S.. pp. 92-93 (1903). 
 
 5. Placer Mining in Alaska in 1903. Bull. 225, U. S. G. S., pp. 43-59 (1904). 
 
 6. The Geography of Alaska, with an Outline of the Geomorphology. Rept. 
 8th Int. Geol. Cong., pp. 204-230 (1905). 
 
 7. Placer Mining in Alaska in 1904. Bull. 259, U. S. G. S., pp. 18-31 
 (1905). 
 
 8. The Geology and Geography of Alaska. A summary of existing knowl- 
 edge. Prof. Paper 45, U. S. G. S. (1906). 327 pp. 
 
 9. The Kougarok Region (Alaska). Bull. 314, U. S. G. S., pp. 164-181 
 (1907). 
 
 10. The Circle Precinct (Alaska).^//. 314, U. S. G. S., pp. 187-204 (1907). 
 BROOKS, A. H., RICHARDSON, G. B., and COLLIER, A. J. 
 
 A Reconnaissance of the Cape Nome and Adjacent Gold Fields of Seward. 
 
 Peninsula, Alaska. U. S. G. S. (1901). 184 pp. 
 BROUGH, B. H. 
 
 The Nature and Yield of Metalliferous Deposits. Jour. Soc. Arts, vol. 48 
 
 (1901). 56pp. 
 BROWN, A. J. 
 
 The Formation of Fissures and the Origin of their Metallic Contents. 
 
 Trans. A. /. M. E., vol. 2, pp. 215-219 (1873-74). 
 BROWN, E. P. 
 
 The Development of an Ore Shoot in Nova Scotia. Can. Min. Jour., vol. 1, 
 pp. 457-458 (1907). 
 
 BROWN, K. G. 
 
 1. The Ore-Deposits of Butte City. Trans. A. /. M. E., vol. 24, pp. 543-558 
 (1*94). 
 
 2. The Vein-System of the Standard Mine, Bodie, California. Trans. A. I. 
 M. E., vol. 38, pp. 343-357(1907). 
 
 BROWNE, D. H. 
 
 1. The Distribution of Phosphorus in the Ludington Mine, Iron Mountain, 
 Michigan : A Study in Isochemic Lines. Trans. A. I. M. E., vol. 17, pp. 
 616-632 (1888-89). 
 
 2. Segregation in Ores and Mattes. Sch. Min. Quar., vol. 16, pp. 297-311 
 (1895). 
 
 3. Notes on the Origin of the Sudbury Ores. Econ. Geol., vol. 1, pp. 467- 
 475 (1906). 
 
 BROWNE, E. Ross. 
 
 The Ancient River Beds of the Forest Hill Divide. 10th Ann. Rept., Gal. St. 
 
 Min., pp. 435-465 (1890). 
 BRUHNS, W. 
 
 Uber Erzlagerstatten. Mitt. d. philomat. Gesel. in Els. Lothr. 
 BRUN, A. 
 
 Re"cherches Sur L'Exhalaison Volcanique (Geneva and Paris, 1911). 
 BRUNLECHNER, A. 
 
 Die Entstehung und Bildungsfolge der Bleiberger Erze und ihre Begleiter. 
 Jahrb. d. Naturhist. Landes. in Karnten, vol. 25 (1899). 36 pp. 
 
 BUCKING. 
 
 Das Grundgebirge des Spessarts. Jahrb. d. Kgl. Geol. Landesanst. (1889). 
 
 BUCKLEY, E. R. 
 
 1. Geology of the Disseminated Lead Deposits of St. Francois and Washing- 
 ton Counties, Missouri. Missouri Bu. of Geol. and Mines, vol. 9 (1909). 
 259 pp. 
 
 2. Building and Ornamental Stones (with many admirable colored plates) . 
 
 ilding am 
 I. 4, Wis. 
 
 Bull. 4, Wis. Geol. Nat. Hist. Sur. (1898). 544 -pp. 
 
854 ALPHABETICAL LIST OF AUTHORS. 
 
 BUCKLEY, E. R., and BUEHLER, H. A. 
 
 Geology of the Granby Area. Missouri Bu. of Oeol. and Mines, vol. 4, 2d 
 
 ser. (1906). 120pp. 
 BUEHLER, H. A., and GOTTSCHALK, V. A. 
 
 Oxidation of Sulphides. Econ. Oeol., vol. 5. pp. 28-35 (1910). 
 BURAT, AMADEE. 
 
 Geologic Appliquee ; Gites Me'talliferes (Paris, 1870). 5th ed., 505 pp. 
 BURGH ARD, E. F. 
 
 The Clinton Iron-Ore Deposits in Alabama. Trans. A. I. M. E., vol. 40, 
 
 pp. 75-133 (1909). 
 BURCHARD, E. F., BUTTS, C., and ECKEL, E. C. 
 
 Iron Ores of the Birmingham District, Alabama. Bull. 400, U. S. Q. S. 
 
 (1910). 204 pp. 
 BUSH, E. E. 
 
 The Sudbury Nickel Kegion. E. and M. Jour., vol. 57, pp. 245-246 (1894). 
 
 BUTTGENBACH, H. 
 
 1. Quelques Faits a propos de la Formation des Pe*pites d'Or. Ann. Soc. 
 Oeol. de Belg., vol. 33, part II, pp. M51-M70 (1905-06). 
 
 2. Les Gisements de cuivre de Katanga. Ann. Soc. Geol. de Belg., vol. 31, 
 (1904). 
 
 CAMERON, W. E. 
 
 The Heberton Tin Field. Queensland Dept. of Mines, No. 192 (1904). 
 
 CAMPBELL, A. C. 
 
 Ore-Deposits. .E. and M. Jour., vol. 30, pp. 39-40 (July 17, 1880). 
 CAMPBELL, JOSEPH. 
 
 The Gold-Fields of the Hauraki Peninsula, New Zealand Trans. Inst. Min. 
 
 Eng., vol. 12, pp. 462-487 (1897). 
 CANAVAL, E. 
 
 1. Natur und Entstehung der Erzlagerstatten am Schneeberg in Tirol. Zeit. 
 f. prak. Geol., vol. 16, pp. 479-483 (1908). 
 
 2. tJber das Vorkommen von Manganerzen bei Wandelitzen nachst Volker- 
 markt in Karnten. Jahrb. d. Naturhist. Landes. in Karnten., vol. 28, pp. 
 357-368 (1909). 
 
 CARLYLE, E. J. 
 
 The Pioneer Iron Mine, Ely, Minn. Jour. Can. Min. Inst., vol. 7, pp. 335- 
 
 367 (1904). 
 CARPENTER, F. E. 
 
 Ore- Deposits of the Black Hills of Dakota. Trans. A. I. M. E., vol. 17, pp. 
 
 570-598 (1888-89). 
 CARTHAUS, EMIL. 
 
 Die Sandberger'sche Erzgangtheorie. Zeit. f. prak. Oeol., vol. 4, pp. 107-112 
 (1896). 
 
 CASE, W. H. 
 
 The Bertha Zinc-Mines at Bertha, Virginia. Trans. A. I. M. E., vol. 22, pp. 
 
 511-536 (1893). 
 CATHARINET, JULES. 
 
 Copper Mountain, British Columbia. E. and M. Jour., vol. 79, pp. 125-127 
 
 (1905). 
 CATLETT, CHARLES. 
 
 Iron-Ores of the Potsdam Formation in the Valley of Virginia. Trans. A. I. 
 
 M. E., vol. 29, pp. 308-317 (1899). 
 CAYEUX, L. 
 
 Le Quartz Secondaire des Mine'rais de Fer Oolithiques du Silurien de France 
 et son Eeplacement en Profondeur par du Fer Carbonate*. Compt. Rend. 
 Acad. Sci., vol. 149, pp. 1095-1097 (1909). 
 CHALMERS, E. 
 
 The Sources and Distribution of the Gold- Bearing Alluvions of Quebec. 
 Ottawa Nat., vol. 15, pp. 33-36 (1901). 
 
ALPHABETICAL LIST OF AUTHORS. 855 
 
 CHALON, P. F. 
 
 1. Note sur la Genese des Gisements Metalliferes et des Roches Eruptives. 
 Trans. Int. Min. and Met. Cong. (1905). 30 pp. 
 
 2. La Genese des Gisements Metalliferes et des Roches Eruptives. (Paris, 
 1906). 236 pp. 
 
 CHAMBERLIN, R. T. 
 
 1. The Gases in Rocks. Jour. GeoL, vol. 17, pp. 534-568 (1909). 
 
 2. The Gases in Rocks. Publication 106, Carnegie Institution of Washington 
 (1908). 
 
 CHAMBERLIN, T. C. 
 
 1. The Requisites and Qualifying Conditions of Artesian Wells. 5th Ann. 
 Rept., U. S. O. S., p. 125 (1885). 
 
 2. The Fault Problem. Econ. GeoL, vol. 2, pp. 585-601, 704-724 (1907). 
 
 3. Geology of Wisconsin, vol. 4 (3882). 
 CHANCE, H. M. 
 
 1. Report on the Mining Methods and Appliances Used in the Anthracite 
 Coal Fields. 2d GeoL Sur. Penna., Rept. A. C., pp. 6-14 (1883). 
 
 2. The Rich Patch Iron Tract, Virginia. Trans. A. I. M. E., vol. 29, pp. 
 210-223 (1899). 
 
 3. The Discovery of New Gold-Districts. Trans. A. I. M. E., vol. 29, pp. 
 224-230 (1899). 
 
 4. The Iron-Mines of Hartville, Wyoming. Trans. A. I. M. E., vol. 30, pp. 
 987-1003 (1900). 
 
 5. Gold-Ores of the Black Hills, South Dakota. Trans. A. I. M. E.,\ol. 
 30, pp. 278-285 (1900). 
 
 6. The Pyritic Origin of Iron-Ore Deposits. E. and M. Jour., vol. 86, pp. 
 408-410 (1908). 
 
 7. The Origin of Bombshell Ore. Can. Min. Jour., vol. 29, pp. 402-403 
 (1908). 
 
 8. Rock Pressure and Metamorphism. Min. and Sci. Press, vol. 97, pp. 299- 
 302 (1908). 
 
 9. A New Theory of the Genesis of Brown Hematite-Ores ; and a New Source 
 of Sulphur Supply. Trans. A. I. M. E., vol. 39, pp. 522-539 (1908). 
 
 CHAFER, M. 
 
 Note sur un Gite cuivreux d' origin volcanique du Caucase meridional. Bull. 
 
 Soe. GeoL de France, vol. 21, pp. 101-109 (1893). 
 CHARPENTIER, H. 
 
 Geologic et Mine"ralogie Appliques (Paris, 1900). 
 CHAUTARD, J., AND LEMOINE, P. 
 
 La laterisation et ses relations avec la genese de quelques mine"rais d' alumin- 
 ium et de fer et de certains gites auriferes. Compt. Rend. Mens. Ind. Min., 
 pp. 119-125 (Apr., 1908 ; Abstract in GeoL CentralbL, vol. 11, No. 11, p. 488 
 (1908). 
 CHIBAS, E. J. 
 
 The Manganese Deposits of the Department of Panama, Colombia. Trans. A. 
 
 I. M. E., vol. 27, pp. 63-76 (1897). 
 CHISM, R. E. 
 
 1. The Vallecillo Mines, Mexico. Trans. A. I. M. E., vol. 13, pp. 351-369 
 (1884-85). 
 
 2. Sierra Mojada, Mexico. Trans. A. I. M. E., vol. 15, pp. 542-588 (1886- 
 87). 
 
 CHRISTY, S. B. 
 
 On the Genesis of Cinnabar Deposits. Am. Jour. Sci., 3d ser. , vol. 17, pp. 
 
 453-463 (1879). 
 CHURCH, J. A. 
 
 1. Faulting in Veins. E. and M. Jour., vol. 53, pp. 469-470, 613-614, 637- 
 638 (1892). 
 
 2. The Cause of Faulting. Trans. A. I. M. E., vol. 21, pp. 782-792 (1892- 
 93). 
 
 3. The Tombstone, Arizona, Mining District. Trans. A. I. M. E., vol. 33, 
 pp. 3-37 (1902). 
 
 4. The Comstock Lode : its formation and history (New York, 1879). 
 
856 ALPHABETICAL LIST OF AUTHORS. 
 
 CIRKEL, FRITZ. 
 
 Report on the Chrome Iron-Ore Deposits in the Eastern Townships of the 
 Province of Quebec (with Bibliography). Bull. 29, Mines Branch, Can. 
 Dept. Mines (1909). 141 pp. 
 CLAPP, C. H., and BALL, W. G. 
 
 The Lead-Silver Deposits of Newburyport, Mass., and their Accompanying 
 
 Contact- Zones. Econ. GeoL, vol. 4, pp. 239-250 (1909). 
 CLARK, ELLIS. 
 
 The Silver-Mines of Lake Vallev, New Mexico. Trans. A. I. M. E., vol. 24, 
 
 pp. 138-167 (1894). 
 CLARKE F "W 
 
 1. Some Nickel Ores from Oregon. Butt. 60, U. S. G. S., pp. 21-26 (1890). 
 
 2. The Data of Geochemistry. B nil. 330, U. S. G. S. (1908). 716 pp. 
 CLAYPOLE, E. W. 
 
 The Tin Islands of the Northwest. Am. GeoL, vol. 9, pp. 228-236 (1892). 
 CLEMENTS, J. M. 
 
 The Vermilion Iron-Bearing District of Minnesota. Mon. 45, U. S. G. S. 
 
 (1903). 463 pp. 
 CLEMENTS, J. M., and SMYTH, H. L. 
 
 1. The Crystal Falls Iron-bearing District of Michigan. 19th Ann. Rept., U. 
 S. G. S., part 3, pp. 1-151 (1898). 
 
 2. The Crystal Falls Iron-bearing District of Michigan. Mon. 33, U. S. G. S. 
 (1899). 512 pp. 
 
 CLERC, F. L. 
 
 The Ore-Deposits of the Joplin Region, Missouri. Trans. A. I. M. E., vol. 
 
 38, pp. 320-343 (1907). 
 COHEN, E. 
 
 Uber die Entstehung des Seifengoldes. Mitt. d. Naturwiss. Vereins f. Neu- 
 
 vorkommen u. Riigen, vol. 19 (1887). 
 COLE, G. A. J. 
 
 Aids in Practical Geology (London, 1906). 431 pp. 
 
 COLEMAN, A. P. 
 
 1. The Vermilion River Placers (Ontario). Rept. Ont. Bu. Min., vol. 10, pp. 
 151-159 (1901). 
 
 2. The Sudbury Nickel Field. Rept. Ont. Bu. Mines, vol. 14, part 3 (1905). 
 
 3. The Helen Iron Mine, Michipicoten. Econ. GeoL, vol. 1, pp. 521-529 
 (1906). 
 
 4. The Sudbury Laccolithic Sheet. Jour. Geol., vol. 15, p. 759-782 (1907). 
 
 5. The Alexo Nickel Deposit. Econ. GeoL, vol. 5, pp. 373-376 (1910). 
 
 COLLIER, A. J. 
 
 1. Reconnaissance of the Northwestern Portion of Seward Peninsula, Alaska. 
 Prof. Paper 2, U. S. G. S. (1902). 70 pp. 
 
 2. The Tin Deposits of the York Region, Alaska. Bull. 229, U. S. G. S. 
 (1904). 61 pp. 
 
 3. Gold-Bearing River Sands of Northeastern Washington. Bull. 315, U. S. 
 G. S., pp. 56-70 (1907). 
 
 COLLIER, A. J., HESS, F. L., SMITH, P. S., and BROOKS, A. H. 
 
 The Gold Placers of parts of Seward Peninsula, Alaska. Bull. 328, U. S.G. 
 & (1988). 343pp. 
 
 COLLINS, G. E. 
 
 The Relative Distribution of Gold and Silver Values in the Ores of Gilpin 
 County, Colorado. Trans. Inst. Min. and Met,, vol. 12, pp. 480-499 (1902- 
 1903). 
 COLLINS, J. H.- 
 
 On the Origin and Development of Ore Deposits in the West of England. 
 Jour. Roy. Inst. Cornw. (1895). 
 
 COLTON, H. E. 
 
 Notes on the Topography and Geology of Western North Carolina. Trans. 
 A. I. M. E., vol. 16, pp. 839-851 (1887-88). 
 
ALPHABETICAL LIST OF AUTHORS. 857 
 
 COMBES, C. F. 
 
 Trait6 de 1' exploitation des mines, vol. 1 (Paris, 1844). 
 COMSTOCK, T. B. 
 
 1. Notes on the Geology and Mineralogy of San Juan County, Colorado. 
 Trans. A. I. M. E., vol. 11, pp. 165-191 (1882-83). 
 
 2. The Geology and Vein-Structure of Southwestern Colorado. Trans. A. I: 
 M. E., vol. 15, pp. 218-265 (1886-87). 
 
 3. The Geology and Vein-Phenomena of Arizona. Trans. A. I. M. E '., vol. 
 30, pp. 1038-1101 (1900). 
 
 CORNU, F. 
 
 1. Uber die Paragenese der Minerale, namentlich die der Zeolithe. 6st. Zeit. 
 f. Berg- u. Hiitt., vol. 56, pp. 89-93 (1908). 
 
 2. Die Bedeutung gelartiger Korper in der Oxydationszone der Erzlagerstat- 
 ten.Zeit. f. pra/c. GeoL, vol. 17, pp. 81-87 (1909). 
 
 CORNU, F., and LAZEREVIC, M. 
 
 Zur Paragenesis der Knpfererze von Bor in Serbien. Zeit. f. prole. GeoL. vol. 
 
 16, pp. 153-155 (1908). 
 VON COTTA, BERNHABD. 
 
 1. Gangstudien, herausgegeben von B. von .Cotta l-III. darin Kollektaneen 
 der Literatur von H. Miiller (1850-1861 ). 
 
 2. A Treatise on Ore-Deposits. Trans, of Die Lehre von den Erzlagerstiitten 
 (Freiberg, 1859-1861), into English by F. Prime (New York, 1870). 575 pp. 
 
 COURTIS, W. M. 
 
 Gold-Quartz. Trans. A. L M. E., vol. 18, pp. 639-644 (1889-90). 
 
 DE LA COUX, H. 
 
 L'or ; (Gites auriferes ; extraction de Tor ; traitement du minerai ; emplois et 
 
 anylyse de 1'or) (Paris, 1896). 328 pp. 
 CRAGOE, SPENCER. 
 
 Notes on the Mines of the Frontino and Bolivia Company, Colombia. Trans. 
 
 A. L M. E., vol. 28, pp. 591-000 (1898). 
 CREDNER, H. 
 
 1. Beschreibungen von Mineralvorkommen in Nord Amerika. Berg- u. Hiitt. 
 Zeit., p. 209 (1866). 
 
 2. Elements der Geologie, 10th ed. (Leipzig, 1906). 
 
 3. Die Genesis des Siichsischen Granulitgebirges. Cent. f. Min. GeoL u. Pal.. 
 pp. 513-525 (1907). 
 
 CROSBY, W. O. 
 
 1. Absence of Joint Structure at Great Depths. GeoL Mag., p. 416 (Sept., 
 1881). 
 
 2. Classification and Origin of Joint Structure. Proc. Bost. Soc. Nat. Hist.. 
 vol. 22, p. 72 (1882). 
 
 3. On the Joint Structure of Rocks. Tech. Quar., vol. 1, pp. 245-250 (1887). 
 
 4. The Origin of Parallel and Intersecting Joints. Tech. Quar., vol. 6, p. 
 230 (1893) ; Am. GeoL, vol. 12, p. 368 (Dec., 1893). 
 
 5. A Classification of Economic Geological Deposits. Am. GeoL, vol. 13, pp. 
 249-268 (1894) ; Tech. Quar., vol. 7, pp. 27-48 (Apr., 1894). 
 
 6. Geological History of the Hematite Iron Ores of the Antwerp and Fowler 
 Belt in New York. Am. GeoL, vol. 29, pp. 233-242 (1902). 
 
 7. The Limestone-Granite Contact- Deposits of Washington Camp, Arizona. 
 Trans. A. L M. E., vol. 36, pp. 626-646 (1905). 
 
 CROSBY, W. O., and FULLER, M. L. 
 
 Origin of Pegmatites. Am. GeoL, vol. 19, pp. 147-180 (1897). 
 CROSS, WHITMAN. 
 
 Geology of Silver Cliff and the Kosita Hills, Colorado. 17th Ann. Rept., U. 
 
 S. G. S., part 2, pp. 263-403 (1896). 
 CROSS, WHITMAN, and PENROSE, E. A. F., JR. 
 
 Geology and Mining Industries of the Cripple Creek District, Colorado. 16^ 
 
 Ann. Rept., U. S. G. S., part 2, pp. 1-209 (1895). 
 CROSS, WHITMAN, and SPENCER, A. C. 
 
 Geology of the Bico Mountains, Colorado. 2lst Ann. Rept, U. S. G. S., part 
 2, pp. 7-165 (1900). 
 
 54 
 
858 ALPHABETICAL LIST OF AUTHORS. 
 
 CUMENGE, M. E. 
 
 Kiinstliche Darstellung von Gold fiihrendem Conglonierat. Reunions de St. 
 Etienne, pp. 57-59 (1896) ; Rev. in Zeit. f. prak. GeoL, vol. 5, p. 26 (1897). 
 CUMENGE, E., and ROBELLAZ, F. 
 
 L'or dans la Nature (Paris, 1898). 112 pp. 
 CURLE, J. H. 
 
 Gold Mines of the World (London, 1905). 324 pp. 
 CURTIS, J. S. 
 
 1. Abstractof Report on Mining Geology of Eureka District, Nevada. 4th 
 Ann. Rept., U. S. O. S., pp. 221-251 (1884). 
 
 2. The Silver- Lead Deposits of Eureka, Nevada. Mon. 7, U. S. G. S. (1884). 
 200 pp. 
 
 GUSHING, H. P. 
 
 The Direction of Movement and Nomenclature of Faults. Econ. GeoL, vol. 
 2, pp. 433-435 (1907). 
 
 CZYSZKOWSKI, S. 
 
 The Deposition of Gold in South Africa. Am. GeoL, vol. 17, pp. 306-323 
 (1896). 
 
 D'ACHIARDI, A. 
 
 I Metalli, Loro Minerali e Miniere (Milan, 1883). 
 DAGGETT, ELLSWORTH. 
 
 The Extraordinary Faulting at the Berlin Mine, Nevada. Trans. A. I. M. E., 
 
 vol. 38, pp. 297-309 (1907). 
 DAHLBLOM, TH. 
 
 IJber Magnetische Erzlagerstatten und deren Untersuchung durch Magne- 
 tische Messungen. Translated into German by T. Uhlich (Freiberg, 1899) . 
 DAHSE. 
 
 Report of the Effuenta Gold Mines, 1879 (cited by Bergeat-Stelzner 1, p. 1268). 
 DAINTREE, R. 
 
 Note on Certain Modes of Occurrence of Gold in Australia. Quar. Jour. GeoL 
 
 Soc,, vol 34, pp. 431-438 (1878). 
 DALMER, K. 
 
 1. Die Erzlager von Swarzenberg im Erzgebirge. Zeit. f. prak. GeoL, vol. 
 5, pp. 265-272 (1897). 
 
 2. Die westerzgebirgische Granitmassivzone. Zeit. f. prak. GeoL, vol. 8, pp. 
 297-312 (19UO). 
 
 3. Der Altenberg-Graupener Zinnerzlagerstattendistrict. Zeit.f. prak. GeoL, 
 vol. 2, p. 313 (1894). 
 
 DALY, HERBERT J. 
 
 The Mount Lyell Copper Deposits, Tasmania. Trans. Inst. Min. and Met., vol. 
 
 9, pp. 80-106 (1900-01). 
 DALY, R. A. 
 
 1. Mechanics of Igneous Intrusion. Am. Jour. Sci., 4th ser., vol. 15, pp. 
 269-298; vol. 16, pp. 107-126; vol. 26, pp. 17-50 (1903-08). 
 
 2. Differentiation of a Secondarv Magma through Gravitative Adjustment. 
 Eosenb. Fests., pp. 203-233 (1906). 
 
 DANA, J. D. 
 
 Manual of Geology, 4th ed. (New York and London, 1895). 1087 pp. 
 
 DANNENBERG, ROBERT. 
 
 Uber Verwerfungen (Freiberg, 1884). 
 DARAPSKY, L. 
 
 Tage oder Tiefenwasser ? (Leipzig, 1903. ) 32pp. 
 DAUBREE, ADOLPHE. 
 
 1. Me"moire sur la relation des sources thermales de Plombieres avec les 
 filons me'talliferes. Ann. d. Mines, 5th ser., vol. 13, pp. 227-256 (Paris, 
 1858). 
 
 2. Etudes Synthetiques de Geologie Experimental^ (1879). 828 pp. 
 
 3. Me'moir sur la gisement, la constitution et 1'origine des amas de minerai 
 d'etain. ^466. K. Bayer Akad. d. Wissc., vol. 20, p. 193 (1899). 
 
ALPHABETICAL LIST OF AUTHORS. 859 
 
 DAUBREE, G. A. 
 
 1. Les Eaux Souterraines aux Epoques Anciennes (Paris, 1887). 
 
 2. Les Eaux Souterrainnes a 1'Epoque Actuelle. 2 vols. (Paris, 1887). 
 
 3. Recherches Experimentales sur le role possible des gas a hautes tempera- 
 tures doues de tres fortes pressions et animes d'un mouvement fort rapide 
 dans divers phenomenesge'ologiques. Bull. Soc. Geol. de France, 3d ser., vol. 
 19, p. 313 et seq. (1891) ; Abstract, Zeit. f. prak. Geol., vol. 1, pp. 284- 
 295 (1893). 
 
 DAVID, T. W. E. 
 
 Geology of the Vegetable Creek Tin-Mining Fields of New England District, 
 New South Wales. Geol. Sur. N. S. W., pp. 4-169 (1887). 
 
 DAVIES, D. C. 
 
 A Treatise on Metalliferous Minerals and Mining. 5th ed. (London, 1892). 
 548pp. 
 DAY, D. T. 
 
 Notes on the Occurrence of Platinum in North America. Trans. A. I. M. E. t 
 
 vol. 30, pp. 702-708 (1900). 
 DAY, D. T., and RICHARDS, E. H. 
 
 Useful Minerals in the Black Sands of the Pacific Slope. (Bibliography.) 
 
 Min. Res. of U. S. for 1905, pp. 1175-1258. 
 DE BEAUMONT See under B. 
 DE BATZ, RENE See under B. 
 VON DECHEN,H. 
 
 Die Nutzbaren Mineralien und Gebirgsarten irn Deutschen Reiche (Berlin, 
 
 1873). 
 DEKALB, C. 
 
 Diffusion as a Factor in Ore Deposition. Min. and Sci. Press, vol. 96, pp. 
 226-227(1908). 
 
 DELAUNAY, L. 
 
 1. Formation des Gites Me'talliferes, 2d ed. (Paris, 1893). 190 pp. 
 
 2. L' Argent ; geologic, metal lurgie, r61e e'conomique (Paris, 1896). 382 pp. 
 
 3. Les Mines d'Or du Transvaal (Paris, 1896). 550 pp. 
 
 4. Contributions a 1'etude des gites mtalliferes (Paris, 1897). 
 
 5. Sur le r61e des phe'nomenes d' alteration superficielle, et de remise en mouve- 
 ment dans la constitution des gites metalliferes Ann. d. Mines, 9th ser., 
 vol. 12, pp. 147-227 (August, 1897). 
 
 6. Contributions a 1' Etude des Giles Metalliferes. Ann. d. Mines, 9th ser., 
 vol. 12, pp. 119-227 (1897). 
 
 7. Recherche, Captage, et Am^nagement des Sources Thermes Mine"rales, p. 
 80 etseq. (Paris, 1899). 
 
 8. Les Variations des Filons Metalliferes en Profondeur. Rev. Gen. d. Sci., 
 vol. 11, pp. 575-588 (Apr., 1900). 
 
 9. Les Richesses minerales de PAfrique (Paris, 1903). 
 
 10. L'Origine et les Caracteres des Gisements de Fer Scandinaves. Ann. 
 d. Miriest, 10th ser., vol. 4, pp. 49-106 ; 109-211 (1903). 
 
 11. La Science Geologique (Paris, 1905). 747 pp. 
 
 12. Application de la Methode Techtonique a la Mdtallogenie de la Region 
 Italie'nne. Rev. Gen. d.Sci., vol. 16, pp. 812-821 (1905). 
 
 13. La Metalloge'nie de 1' Italic. Published by the 10th International Geo- 
 logical Congress, Mexico (1906). 
 
 14. L'Or dans le Monde (Paris, 1907). 265 pp. 
 
 15. The World's Gold. Its Geology, Extraction, and Political Economy 
 (New York, 1908). 
 
 16. Sur la formation des gisements d'or. Compt. rend. Acad. Sci., vol. 
 149, pp. 298-300 (Paris, 1909). 
 
 17. La me'talloge'nie de 1'Asie Russe. Ann. d. Mines, 10th ser., vol. 15, 
 pp. 220-295, 303-427 (1909). 
 
 18. La Geologic et les Richesses Minerales de 1'Asie (Paris, 1911). 
 DELKESKAMP, R. 
 
 1. Die hessichen und nassauischen Manganerzlagerstatten und ihre Ensteh- 
 hung durch Zersetzung des dolomitisirten Stringocephalenkalkes resp. 
 Zechsteindolomits. Zeit. f. prak. Geol, vol. 9, pp. 356-365 (1901). 
 
860 ALPHABETICAL LIST OF AUTHORS. 
 
 DELKESKAMP, E. Continued. 
 
 2. Die weite Verbreitung des Baryums in Gesteinen und Mineralquellen und 
 die sich heraus ergebenden Beweismittel fiir die Anwendbarkeit der Lat- 
 eralsecretions- und Thermal theorie auf die Genesis der Schwerspath- 
 gange. Zeit. f. prak. GeoL, vol. 10, pp. 117-126 (1902). 
 
 3. Die Genesis der Thermalquellen von Ems, Wiesbaden und Kreuznach und 
 ihre Beziehungen zu den Erz-und Mineralgangen des Taunus und der 
 Pfalz. Deut. Naturforsch. u. Aert. (Sept., 1903). 
 
 4. Die Bedeutung der Geologic fiir die Balneologie. Zeit. f. prak. GeoL, vol. 
 12, pp. 202-209 (1904). 
 
 5. Die Bedeutung der Konzentrationsprozesse fiir die Lagerstattenlehre und 
 die Lithogenesis. Zeit. f. prak. GeoL, vol. 12, pp. 289-316 (1904). 
 
 6. Juvenile and Vadose Springs. Bal Zeit., vol. 16, No. 5 (1905). 
 
 7. Vadose und juvenile Kohlensaure. Zeit. f. prak. GeoL. vol. 14, pp. 33- 
 47 (1906). 
 
 8. Fortschritte auf dem Gebiete der Erforschung der Mineralquellen. Zeit. 
 f. prak. GeoL, vol. 16, pp. 401-443 (1908). 
 
 DEMARET, L. 
 
 1. Les Giseraents des Minerals de Cuivre. Rev. Univ. d. Mines, vol. 50, pp. 
 234-275 (1900). 
 
 2. Les Principaux Gisements de Mine'rais de Fer du Monde (Paris, 1903). 61 pp. 
 
 3. Les Principaux Gisements des Minerals de Mercure du Monde. Ann. d. 
 Min. de Belg., vol. 9, pp. 36-112 (1904). 
 
 4. Les Principaux Gisements des Mine'rais de Manganese du Monde. Ann. 
 d. Min. de Belg., vol. 10 (1905). 95 pp. 
 
 5. La Genese des Gisements. Ann. d. Min. de Belg. , vol. 11, pp. 541-624 
 (1906). 
 
 DENCKMANN, A. 
 
 Uber das Nebengestein der Kamsbecker Erzlagerstatten. Jahrb. d. Kgl. Pr. 
 
 GeoL Landesanst., vol. 29, pt. 2, pp. 243-253 (1908). 
 DENNY, G. A. 
 
 The Origin of the Gold of the Eand Gold Fields. Econ. GeoL , vol. 4, pp. 
 
 470-485 (1909). 
 DERBY, O. A. 
 
 1. Notes on Brazilian Gold-Ores. Trans. A. I. M. E., vol. 33, pp. 282-287 
 (1902). 
 
 2. On the Original Type of the Manganese Ore Deposits of the Queley Dis- 
 trict, Minas Geraes, Brazil. Am. Jour. Sci., pp. 213-216 (1908). 
 
 DEVEREUX, W. B. 
 
 The Occurrence of Gold in the Potsdam Formation, Black Hills, Dakota. 
 
 Trans. A. L M. E.,vol. 10, pp. 465-475 (1881-82). 
 DEWEY, F. P. 
 
 Some Canadian Iron Ores. Trans. A. I. M. E.,vo\. 12, pp. 192-204 (1883-84) 
 DICKSON, C. W. 
 
 1. The Ore-Deposits of Sudbury, Ontario. Trans. A. L M. E., vol. 34, pp. 
 3-67 (1903). 
 
 2. Distribution of the Platinum Metals in Other Sources than Placers. Jour. 
 Can. Min. Inst., vol. 8, pp. 192-214 (1905). 
 
 3. Genetic Relations of Nickel-Copper Ores. Jour. Can. Min. Inst., vol. 9, 
 pp. 236-260 (1906). 
 
 DlEULEFAIT. 
 
 1. Existence de la baryte et de la strontiane dans toutes les roches constitu- 
 tives des terrains primordiaux. Compt. Rend. Acad. Sci., vol. 87, pp. 934- 
 936 (1878). 
 
 2. Diffusion du Cuivre dans les roches primordiales et les dep6ts Sedimentaires 
 qui en precedent. Compt. Rend. Acad. Sci., pp. 453-455 (1879). 
 
 3. Existence du Zinc a Fe'tat de diffusion complete dans les terrains dolomi- 
 tiques. Compt. Rend. Acad. Sci., vol. 96, pp. 70-72 (1883). 
 
 4. Le manganese dans les terrains dolomitiques. Compt. Rend. Acad. Sci., 
 vol. 96. pp. 125-126 (1883). 
 
 5. Le manganese dans les eaux des mers actuelles et dans certains de leur 
 depdts.- Compt. Rend. Acad. Sci., vol. 96, pp. 718-721 (1883). 
 
ALPHABETICAL LIST OF AUTHORS. 861 
 
 DIEULEFAIT Continued. 
 
 6. Sur la presence constante du cuivre et du zinc dans les depots du fond des 
 mers. Compt. Rend. Acad. ScL, vol. 101, p. 1297 (1885). 
 
 DlLLER, J. S. 
 
 1. The Bohemia Mining Kegion of Western Oregon. 20th Ann. Rept., U. S. 
 G. S., part3, pp. 1-64 (1899). 
 
 2. Iron Ores of the Kedding Quadrangle, California. Bull. 213, U. S. Q. S.. 
 pp. 219-220 (1903). 
 
 3. Age of the Pre- Volcanic Auriferous Gravels in California. Proc. Wash. 
 Acad. Sci., vol. 8, pp. 405-406 (1907). 
 
 4. Port Orford Folio, Oregon. Folio 89, U. S. G. S. (1903). 
 D'INVILLIERS, E. V. 
 
 The Cornwall Iron-Ore Mines, Lebanon County, Pennsylvania. Trans. A. 1. 
 M. E., vol. 14, pp. 873-904 (1885-86). 
 
 DOELTER, C. 
 
 1. Minerogeneses und Stabilitatsfelder der Mineralien. Tscher. Min. u. Pet. 
 Mitt., vol. 25, pp. 79-112 (1906). 
 
 2. Einige Versuche iiber die Loslichkeit der Mineralien. Tscher. Min. u. Pet. 
 Mitt., vol. 11, pp. 319-330 (1890). 
 
 DON, J. R. 
 
 The Genesis of Certain Auriferous Lodes. Trans. A. I. M. E., vol. 27, pp. 
 564-668 (1897). 
 
 DORFFEL, D. 
 
 The Balmoral Cobalt Lodes. Trans. Geol. Soc.So. Af., vol. 80, part v. (1904). 
 DOUGLAS, JAMES. 
 
 The Copper Queen Mine, Arizona. Trans. A. I. M. E., vol. 29, pp. 511- 
 
 546 (1899). 
 DOYLE, P. 
 
 On Some Tin-Deposits of the Malayan Peninsula. Quar. Jour. Geol. Soe. t 
 
 vol. 35, pp. 229-232 (1879). 
 DRAKE, FRANK. 
 
 The Manganese-Ore Industry of the Caucasus. Trans. A. I. M. E., vol. 28, 
 
 pp. 191-208 (1898). 
 DRAPER, W. M. 
 
 Gold Deposits of Colombia and Ecuador. E. and M. Jour. , vol. 58, p. 532 
 
 (1894). 
 DRESSER, J. A. 
 
 Copper Deposits of the Eastern Townships of Quebec Eton. Geol.. vol. 1. 
 
 pp. 445-453 (1906). 
 DUNN, E. J. 
 
 The Mount Morgan Gold Mine, Queensland. Proc. Roy. Soc. Viet., vol. 17 
 (new ser.), part II, pp. 341-355 (1905). 
 
 DUNNINGTON, F. P. 
 
 On the Formation of the Deposits of Oxides of Manganese. Am. Jour. Sci., 
 3d ser., vol. 36, pp. 175-178. 
 
 DUNSTAN, B. 
 
 Some Croyden Gold Mines. Geol. Sur. Queensl. , No. 202 (1905). 36 pp. 
 
 DUROCHER. 
 
 Production artificielle, par voie s6che, des principally minerals contenus dans 
 les gites metalliferes. Compt. Rend. Acad. ScL, vol. 32, p. 623 (1851); vol. 
 42, p. 850 (1856). 
 
 DUSSERT, M. 
 
 Etude sur les gisements metalliferes de 1' Alge*rie. Ann. d. Mines, vol. 17, pp. 
 
 24-84, 91-203 (1910). 
 DUTTON, C. E. 
 
 The Charleston Earthquake. 9^ Ann. Rept, U. S. G. S., pp. 203-528 
 
 (1887-88). 
 
 ECKEL, E. C., BURCHARD, E. F., and BUTTS, C. 
 
 Iron Ores, Fuels, and Fluxes of the Birmingham District, Alabama. Bull. 
 400, U. S. G. S. (1910). 204 pp. 
 
862 ALPHABETICAL LIST OF AUTHORS. 
 
 EGLESTON, THOMAS. 
 
 The Formation of Gold Nuggets and Placer Deposits. Trans. A. I. M. E., 
 
 vol. 9, pp. 633-646 (1880-81). 
 ELEVENTH INTERNAT. GEOL. CONG., STOCKHOLM, 1910. 
 
 The Iron-Ore Kesources of the World (with Atlas). (1910). 2 vol. 1100 pp. 
 EMMENS, S. H. 
 
 The Chemistry of Gossan. #. and M. Jour., vol. 54, pp. 582-583 (1892). 
 EMMONS, S. F. 
 
 1. Abstract of Eeport on Geology and Mining Industry of Leadville, Colo. 
 2d Ann. Kept., U. S. G. S., pp. 201-290 (1881). 
 
 2. Geology and Mining Industry of Leadville, Colorado. Mon. 12, U. S. G. 
 S. (1886).' 770 pp. 
 
 3. The Genesis of Certain Ore-Deposits. Trans. A. I. M. E., vol. 15, pp. 
 125-147 (1886-87). 
 
 4. Origin of Fissure Veins. Proc. Colo. Sci. Soc., vol. 2, part 3, p. 189 (1887). 
 
 5. Notes on the Geology of Butte, Mont. Trans. A. I. M. E., vol. 16, pp. 
 49-62 (1887-88). 
 
 6. Structural Relations of Ore-Deposits. Trans. A. I. M. E., vol. 16, pp. 
 804-839 (1887-88). 
 
 7. Faulting in Veins. E. and M. Jour., vol. 53, p. 548 (1892). 
 
 8. Fluorspar-Deposits of Southern Illinois. Trans. A. I. M. E., vol. 21, p. 
 31 (1892-93). 
 
 9. Geological Distribution of the Useful Metals in the United States. Trans. 
 A. I. M. K, vol. 22, pp. 53-95 (1893). 
 
 10. The Genesis of Ore-Deposits. Discussion of Paper by F. Posepny. 
 Trans. A. I. M. E., vol. 23, pp. 597-602 (1893). 
 
 11. Some Mines of Rosita and Silver Cliff, Colorado. Trans. A. I. M. E., 
 vol. 26, pp. 773-823 (1896). 
 
 12. The Mines of Custer County, Colo. 17 th Ann. RepL, U. S. G. S., part 
 2, pp. 405-472 (1896). 
 
 13. The Secondary Enrichment of Ore- Deposits. Trans. A. I. M. E , vol. 30, 
 pp. 177-217 (1900). 
 
 14. The Delamar and the Horn-Silver Mines : Two Types of Ore- Deposits in 
 the Deserts of Nevada and Utah. Trans. A. I. M. E., vol. 31, pp. 658-683 
 (1901). 
 
 15. Theories of Ore Deposition Historically Considered. Bull. Geol. Soc. Am., 
 vol. 15, pp. 1-28 (1904) ; E. and M. Jour., vol. 77, pp. 117-119, 157-159, 
 199-200, 237-238 (1904). 
 
 16. Copper in the Red Beds. Butt. 260, U. S. G. S. (1905). 
 
 17. Useful Definitions. Min. and Sci. Press, vel. 93, pp. 355-356 (1906). 
 
 18. Los Pilares Mine, Nacozari, Mexico. Econ. Geol., vol. 1, pp. 629-643 
 (1906). 
 
 19. The Cananea Mining District of Sonora, Mexico. Econ. Geol., vol. 5, pp. 
 312-356 (1910). 
 
 20. Butte Special Folio, Montana. Folio 38, U. S. G. S. (1897). 8 pp. 
 EMMONS, S. F., and IRVING, J. D. 
 
 The Downtown District of Leadville, Colorado. Butt. 320, U. S. G. S. 
 (1907). 75 pp. 
 
 EMMONS, W. H. 
 
 1. The Cashin Mine, Colo. Bull. 285, U. S. G. S., pp. 125-128 (1906). 
 
 2. Gold Deposits of the Little Rocky Mountains, Montana. Bull. 340, U. S. 
 G. S., pp. 96-116 (1908). 
 
 3. A Genetic Classification of Minerals. Econ. Geol., vol. 3, pp. 611-627 (1908). 
 
 4. Some Regionally Metamorphosed Ore Deposits and the So-called Segre- 
 gated Veins. Econ. Geol., vol. 4, pp. 755-781 (1909). 
 
 5. Outcrop of Ore Bodies. Min. and Sci. Press, vol. 99, pp. 751-754 ; 782-787 
 (1909). 
 
 6. A Reconnaissance of Some Mining Camps in Elko, Lander, and Eureka 
 Counties, Nevada. BttM. 408, U. S. G. S. (1910). 130 pp. 
 
 7. The Agency of Manganese in the Superficial Alteration of Gold-Deposits. 
 Trans. A.' I. M. E., vol. 42, pp. 3-73 (1911). 
 
 8. Secondary Enrichment in Granite- Bimetallic Mine, Phillipsburg, Montana, 
 Science, New Series, vol. 27, p. 92). (1908). 
 
ALPHABETICAL LIST OF AUTHORS. 863 
 
 ERHARD. 
 
 Uber Elektrische Strome auf Erzgiingen. Jahrb. f. Berg- u. Hutt in Konig. 
 
 Sachs., pp. 160-174 (1885). 
 ERMTSCH, KARL. 
 
 Die gangformigen Erzlagerstatten der Umgegend von Massa Marittima in 
 Toskana auf Grund der Lottischen Untersuchungen. Zeit. f. prak. Geol., 
 vol. 13, pp. 206-241 (1905). 
 EUSTIS, W. E. C. 
 
 The Nickel Ores of Orford, Quebec, Canada. Trans. A. I. M. E., vol. 6, pp. 
 
 209-214 (1877-78). 
 EVANS, J. W. 
 
 The Direction of Movement and Nomenclature of Faults. Econ. Geol, vol. 
 2, pp, 803-806 (1907). 
 
 FAIRBANKS, H. W. 
 
 1. The Tin Deposits at Temescal, Southern California. Am Jour. Sci., 4th 
 ser., vol. 4, pp. 39-42 ; Min. and Sei. Press, vol. 75, p. 362 (1897). 
 
 2. The Relation between Ore Deposits and Their Inclosing Walls. E. and M. 
 Jour., vol. 55, p. 200 (Mar. 4, 1893). 
 
 FAIRCHILD, H. L. 
 
 The Direction of Movement and Nomenclature of Faults. Discussion of Han- 
 some 8. Econ. Geol., vol. 2, p. 184 (1907). 
 FARIBAULT, E. R. 
 
 1. No va Scotia Gold-Fields. Can. Geol. Sur. Sum. Rept, 1901, pp. 214-221(1902) 
 
 2. Nova Scotia Gold-Fields. Can. Geol. Sur. Sum. Rept., 1902, pp 399-427 
 (1903). 
 
 3. Gold-Fields of Nova Scotia. Can. Geol. Sur. Sum. Rept., 1903, pp. 174- 
 186 (1904). 
 
 4. Gold-Fields of Nova Scotia. Can. Geol. Sur. Sum. Rept., 1904, pp. 319- 
 332(1905). 
 
 5. Gold-Fields of Nova Scotia. Can. Geol. Sur. Sum. Rept., 1905, pp. 122- 
 124 (1906). 
 
 6. Gold-Fields of Nova Scotia. Can. Geol. Sur. Sum. Rept., 1906, pp. 147- 
 152 (1906). 
 
 7. The Gold Measures of Nova Scotia, and Deep Mining. Published by the 
 Mining Society of Nova Scotia. Jour. Can. Min. Inst.,vol. 2, pp. 119-129 
 (1899). 
 
 8. Nova Scotia, Deep Gold Mining. Publication of the Commissioner of Public 
 Works and Mines (1903.) 
 
 FARISH, J. B. 
 
 1. On the Ore-Deposits of Newman Hill. Proc. Colo. Sci. Soc., vol. 4, pp. 
 151-164 (1892). 
 
 2. Interesting Vein-Phenomena in Boulder County, Colorado. Trans. A. L 
 M. E., vol. 19, pp. 547-553 (1890-91). 
 
 FARRELL, J. H. 
 
 Practical Field Geology (New York, 1912). 
 FARRELL, jT. K. 
 
 The Copper and Tin Deposits of Katanga. E. and M. Jour., vol. 85, p. 747- 
 
 753 (1908). 
 FARRINGTON, O. C. 
 
 Observations on the Geology and Geography of Western Mexico, including 
 an account of the Cerro Mercado. Pub. Field Col. Museum, No. 89, Geol. 
 Ser. II, No. 5, pp. 197-228 ; E. and M. Jour., vol. 78, pp. 345-346 (1904). 
 FAWNS, SYDNEY. 
 
 1. Notes on the Mount Bischoff Tin Mine. Trans. Tnst. Min. and Met., vol. 
 14, pp. 221-249 (1904-05). 
 
 2. Some Notes on the Mount Lyell Mine, Tasmania. Trans. Inst. Min. and 
 Met., vol. 4, pp. 279-289 (1895-96). 
 
 3. Tin Deposits of the World. Published by Min. Jour. (London, 1907). 304 pp 
 FAY, ALBERT H. 
 
 Geology and Mining of the Tin-Deposits of Cape Prince of Wales, Alaska. 
 Trans. A. L M. E., vol. 38, pp. 664-682 (1907). 
 
864 ALPHABETICAL LIST OF AUTHORS. 
 
 FERMOR, L. L. 
 
 1. Manganese in India. Trans. Min. and Geol Inst. Ind., vol. 1. pp. 69-131 
 (1907). 
 
 2. The Manganese Ore- Deposits of India. Mem. Geol. Sur. Ind., vol. 37 
 (1909). 1294pp. 
 
 FERNEKES, GUSTAVE. 
 
 Precipitation of Copper from Chloride Solutions by Means of Ferrous Chlo- 
 ride. Econ. Geol, vol. 2, pp. 580-584 (1907). 
 FINCH, J. W. 
 
 The Circulation of Underground Aqueous Solutions and the Deposition of 
 
 Lode Ores. Proc. Colo. Sci. Soc., vol. 7, pp. 193-252 (1904). 
 FINK, W. 
 
 Das Eisenglimmer am Gleissingerfels. Ein Beitrag zur Geologic und Berg- 
 baugeschichte des Fichtelgebirges. Geog. Jahresheft., vol. 19, pp. 153-167 
 (1906). 
 
 FlNLAY, J. R. 
 
 1. Notes on the Gold-Mines of Zaruma, Ecuador. Trans. A. L M. E., vol. 30, 
 pp. 248-260 (1900). 
 
 2. The Mining Industry of the Coeur d' A16nes, Idaho. Trans. A. I. M. E., 
 vol. 33, pp. 235-271 (1902). 
 
 FlNLAYSON, A. M. 
 
 1. Problems of Ore Deposition in the Lead and Zinc Veins of Great Britain. 
 Min. Jour., vol. 88, p. 169 (1910). 
 
 2. The Pyritic Deposits of Huelva, Spain. Econ. Geol., vol, 5, pp. 357-372 ; 
 403-437 (1910). 
 
 3. The Metallogeny of the British Isles. Quar. Jour. Geol. Soc., vol. 56, pp. 
 281-298 (1910). 
 
 4. Secondary Enrichment in the Copper Deposits of Huelva, Spain. Trans. 
 Inst. Min. and Met., vol. 20, pp. 61-72, and 16 pages of admirable discussion 
 by members of the Institute (1910-1911). 
 
 VON FlRCKS, W. 
 
 Die Zinnerzlagerstatten des Mount Bischoff in Tasmanien. Zeit. d. D. Geol. 
 
 GeseL, vol. 51, part 3, pp. 431-464 (1899). 
 FLECK, HERMAN, and HALDANE, W. G. 
 
 A Study of the Uranium and Vanadium Belts of Southern Colorado. Rept. 
 
 Colo. St. Bu. Min., pp. 47-115 (1905-1906). 
 
 FLORES, T. 
 
 Las Criaderos Argentiferos de " Providencia " y " San Juan de la Chica," 
 San Felipe. Bol. Soc. Geol. Mex., vol. 1, pp. 169-173 (1905). 
 
 FOOTE, H. W. 
 
 Criteria of Downward Sulphide Enrichment. Econ. Geol., vol. 5. pp. 485-488 
 (1910). 
 
 FORCHHAMMER. 
 
 Uber den Einfluss des Kochsalzes auf die Bildung der Mineralien. Pogg. 
 Ann., vol. 91, pp. 568-585 (1854), but especially vol. 95, pp. 60-96 (1855). 
 
 FORSTNKR, WM. 
 
 1. The Quicksilver Resources of California. Bull. 27, Cal. St. Min. Bu. 
 (1908). 273pp. 
 
 2. The Genesis of the Copper Ores in Shasta County, west of the Sacramento 
 River. Mm. and Sci. Press, vol. 97, pp. 261-262 (1908). 
 
 FOSTER, C. IE NEVE. 
 
 Ore and Stone Mining, 5th ed (London, 1905). 
 VON FOULLON, H. B. 
 
 Uber Einige Nickelerzvorkommen. Jahrb. d. K. K. Geol. Reichsanst., vol. 
 
 43, pp. 276-302 (1872), 
 FRANCOIS. 
 
 Sur 1'Origine des fers limoneux et des Sables auriferes de 1'Ariege et de la 
 
 Haute-Garonne. Ann. d. Mines, 3d ser., vol. 18, pp. 417-432 (1840). 
 FRASER, COLIN, and ADAMS, J. H. 
 
 Geology of the Coromandel Subdivision, Hauraki, Auckland. Bull. 4, N. 
 Z. Geol. Sur. (1907). 154 pp. 
 
ALPHABETICAL LIST OF AUTHORS. 865 
 
 FRAZEB, PERSIFOR (JR. ) 
 
 1. A Study of the Specular and Magnetic Iron Ores of the New Red Sandstone 
 in York County, Pa. Trans. A. I. M. E., vol. 5, pp. 132-143 (1876-77). 
 
 2. Missing Ores of Iron. Trans. A. I. M. E., vol. 6, pp. 531-542 (1877-78). 
 FRAZER, PERSIFOR. 
 
 1. Some Copper Deposits of Carroll County, Maryland. Trans. A. I. M. E., 
 vol. 9, pp. 33-40 (1880-81). 
 
 2. The Whopper Lode, Gunnison County, Colorado. Trans. A. I. M. E., vol. 
 9, pp. 249-258 (1880-81). 
 
 3. The Iron Ores of the Middle James River. Trans. A. I. M. E., vol. 11, 
 pp. 201-216 (1882-83). 
 
 4. The "Centennial" and "Lotta" Gold Properties, Coahuila, Mexico. 
 Trans. A. I. M. E., vol. 14, pp. 196-205 (1885-86). 
 
 5. Geogenesis and Some of Its Bearings on Economic Geology. Trans. A. I. 
 M. E., vol. 35, pp. 298-308 (1904). 
 
 FRECHEVILLE, K. J. 
 
 Great Main Lode of Dolcoath. Trans. Roy. Geol. Soc. Cornw., vol. 10, pp. 
 
 146-156 (1887). 
 FREELAND, F. T. 
 
 1. The Sulphide Deposit of South Iron Hill, Leadville, Colorado. Trans. 
 A. I. M. E., vol. 14, pp. 181-189 (1885-86). 
 
 2. Fault-Rules. Trans. A. I. M, E., vol. 21, pp. 491-502 (1892-93). 
 FRITSCH. 
 
 tlber die Mitwirkung Elektrischer Strome bei der Bildung einiger Miner- 
 alien (Gottingen, 1862). 
 
 FUCHS, W. 
 
 Beitriige zur Lehre von den Erzlagerstiltten (1846). 
 FUCHS, E., and DELAUNAY, L. 
 
 Trait^ des Gites Mine'raur et Metalliferes (Paris, 1893.) 2 vols., 823-1004 pp. 
 
 FUKTTCHI, U. 
 
 Mineral Parageneses in the Contact Metamorphic Ore Deposits found in 
 
 Japan. Beitr. zur Mineral von Japan, No. 3 (Tokyo, 1907). 
 FULLER, MYRON L. 
 
 1. Bibliographic Review and Index of Papers Relating to Underground 
 Waters. Wat. Sup. and Trr. Paper 120, U. S. G. S. (1905). Covers years 
 1879-1904. 
 
 2. Total Amount of Free Water in the Earth's Crust. Wat. Sup. and Irr. Paper 
 160, U. S. G. S., pp. 59-72 (1906). 
 
 FULTON, JOHN. 
 
 Mode of Deposition of the Iron-Ores of the Menominee Range, Michigan. 
 Tram. A. L M. K, vol. 16, pp. 525-536 (1887-88). 
 
 FURLONGE, W. H. 
 
 Notes on the Geology of the DeKaap Gold-Fields in the Transvaal. Trans. 
 A. I. M. E., vol. 18, pp. 334-348 (1889-90). 
 
 GABERT. C. 
 
 Die Gneise des Ergzebirges und ihre Kontaktwirkungen. Zeit. d. D. Geol. 
 
 Gesel., vol. 59, pp. 308-376 (1907). 
 GAETZSCHMANN, M. F. 
 
 Die Auf- und Untersuchung von Lagerstatten nutzbarer mineralien, 2d ed. 
 
 (1866). 
 GAGE, J. R. 
 
 On the Occurrence of Lead Ores in Missouri. Trans. A. I. M. E., vol. 3, pp. 
 
 116-125 (1874-75). 
 GALE, H. S. 
 
 1. Gold Placer Deposits near Lay, Routt County, Colorado. Bull. 340, U. S. 
 G. S., pp. 84-95 (1908). 
 
 2. Geology of the Copper Deposits near Montpelier, Idaho. Bull. 430, U. S. 
 G. S., pp. 112-121 (1910). 
 
 3. Carnotite in Western Colorado. Bull. 340, U. S. G. fl., pp. 256-262 (1908). 
 
 4. Carnotite in Rio Blanco County, Colorado. Bull. 315, U. S. G. S., pp. 
 110-117 (1907). 
 
866 ALPHABETICAL LIST OF AUTHORS. 
 
 GARNIER, J. 
 
 Mines de nickel, cuivre et platinedu District deSudbury, Canada. Mem. Soc. 
 
 Ing. Civ. (Paris, March, 1891). 
 GARRISON, F. L. 
 
 1. Chemical Characteristics of Limonite Iron Ores. The Genesis of Limonite 
 Ores in the Appalachians. E. andM. Jour., vol.78, pp. 258, 470-471 (1904). 
 
 2. Ores Formed by Magmatic Segregation. Min. and Sci. Press, vol. 98, pp. 
 451-456 (1909). 
 
 GASCUEL, M. L. 
 
 Gisements Stanniferes au Laos Francais. Ann. d. Mines, 10th ser., vol. 8, pp. 
 321-331 (1905). 
 
 GAUTIER, ARMAND. 
 
 1. Ge'ne'se des eaux thermales et ses rapports avec le volcanisme. Ann. d. 
 
 2. Action de 1'hydrogene sulfure sur quelques oxydes me'talliques et Metal- 
 
 Mines, 10th ser., vol. 9, pp. 316-370 (1906). 
 
 ilfi 
 
 loides. Applications aux ph^nomenes volcaniques et aux eaux thermales. 
 Compt. Rend. Acad. Sci., vol. 142, pp. 7-12 (1906). 
 
 3. Action de la vapeurd'eau surles sulfures au rouge. Production de Me"taux 
 Natifs. Applications aux Phenomenes Volcaniques. Compt. Rend. Acad. 
 Sci., vol. 142, pp. 1465-1470 (1906). 
 
 4. The Genesis of Thermal Waters, and their Connection with Volcanism 
 (Trans., by F. L. Eansome). Econ. GeoL, vol. 1, pp. 688-697 (1906). 
 
 5. L' Intervention et le K61e de 1'Ean dans les Phenomenes volcaniques. 
 Ann. d. Mines, vol. 16, 10th ser., pp. 213-230 (1909). 
 
 GAUTIER, F. 
 
 Etudes sur la formation des gisements aurifSres. Compt. Rend. Acad. Sci., pp. 
 
 99-109 (1901). 
 GEBHARDT, R. 
 
 Beitriige zur Kenntniss der Beziehungen zwischen Erzgjingen und faulen 
 
 Euscheln des nordwestlichen Oberharzes (Rostock, 1899). 38 pp. 
 GELKIE, ARCHIBALD. 
 
 Text-Book of Geology, 4th ed., 2 vol. (London, 1882). 
 GEIKIE, J. S. 
 
 The Occurrence of Gold in Upper Sarawak, Borneo. Trans. Inst. Min. and 
 
 Met., vol. 15, pp. 63-79 (1905-06). 
 GEORGE, R. D. 
 
 The Main Tungsten Area of Boulder County, Colorado. (Bibliography). 
 Colo. Geol. Sur., vol. 9, pp. 7-103 (1909). 
 
 GHOSE, A. 
 
 The Mode of Occurrence of Manganite in the Manganese Ore Deposits of the 
 Sandus State, Bellary, Madras, India. Trans. Brit. Inst. Min. Eng., vol.35, 
 partS, pp. 685-691. 
 GILBERT, G. K. 
 
 t. On the Origin of Jointed Structure. Am. Jour. Sci., 3d ser., vol. 24, p. 50 
 
 (July, 1882). 
 
 2. Post-Glacial Joints. Am. Jour. Sci., 3d ser., vol. 23, pp. 25-27 (1882). 
 GILLETTE, H. P. 
 
 Osmosis as a Factor in Ore-Formation Tram. A. I. M. E., vol. 34, pp. 710- 
 TH (1903). 
 
 GILPIN, EDWARD, JR. 
 
 1. The Iron-Ores of Pictou County, Nova Scotia. Trans. A. L M. E., vol. 
 14, pp. 54-63 (1885-86). 
 
 2. The Nova Scotia Gold Mines. Trans. A. I. M. E., vol. 14, pp. 674-689 
 (1885-86). 
 
 3. The Geological Relations of the Principal Nova Scotia Minerals. Trans. 
 A. I. M. E., vol. 18, pp. 198-205 (1889-90). 
 
 GLASSER, M. E. 
 
 Les Richesses Minerales de la Nouvelle Caledonie. (Paris, 1904.) 560. pp. 
 Also Ann. d. Mines, vol. 5, 10th ser., pp. 503-701 (1904). 
 
ALPHABETICAL LIST OF AUTHORS. 867 
 
 GLENN, WILLIAM. 
 
 1. The Form of Fissure-Walls, as Affected by Sub-Fissuring and by the Flow 
 of Kocks. Trans. A. I. M. E., vol. 25, pp. 499-513 (1895). 
 
 2. The Chrome Ores of Turkey. 19<A Ann. Rept., U. S. G. S., pt. 6, pp. 
 261-264 (1897-98). 
 
 3. Chromic Iron. Occurrence, Character, Uses, etc., of. 17th Ann. Rept., U. 
 S. G. S., pt. 3, pp. 261-273 (1895-1896). 
 
 GOLDSCHMIDT,V. M. 
 
 Die Kontaktmetamorphose im Kristianiagebiet (Kristiania, 1911). 483 pp. 
 GOODCHILD, J. G. 
 
 GeoL Mag. (May, 1883). 
 GORDON, H. A. 
 
 Hysteromorphous Auriferous Deposits of the Tertiary and Cretaceous Periods 
 in New Zealand. Trans. A. L M. E., vol. 25, pp. 292-301 (1895). 
 
 DE LA GOUPILLIERE, HATON. 
 
 Cours d' exploitation des mines (Paris, 1883). 
 GRABILL, L. R. 
 
 On the Peculiar Features of the Bassick Mine. Trans. A. I. M. E , vol. 11, 
 
 pp. 110-120 (1882-83). 
 GRANGER, H. G. 
 
 Gold in the Guyanas. Trans. A. L M. E., vol. 25, pp. 516-52-3 (1898). 
 GRANGER, H. G., and TREVILLE, E. B. 
 
 Mining Districts in Colombia. Trans. A. L M. E., vol. 28, pp. 33-87 (1898). 
 GRANT, U. S. 
 
 1. Preliminary Report on the Lead and Zinc Deposits of Southwestern Wis- 
 consin. Bull 9, Wis. GeoL Nat. Hist. Sur. (1903). 103 pp. 
 
 2. Investigations of the Lake Superior Iron Ore Deposits. Min. Mag. (J.), 
 vol. 10, pp. 175-183 (1904). 
 
 3. Structural Relations of the Wisconsin Zinc and Lead Deposits. Econ. 
 GeoL, vol. 1, pp. 233-242 (1905). 
 
 4. Report on Lead and Zinc Deposits of Wisconsin. Bull. 14, Wis. GeoL 
 Nat. Hist. Sur. (1906). 100 pp. 
 
 GRANT, U. S. , and BURCHARD, E. F. 
 
 Lead and Zinc Deposits of Lancaster and Mineral Point Quadrangle. Folio 
 
 145, U. S. G. S. (1907). 
 GRATON, L. C. 
 
 1. Reconnaissance of some Gold and Tin Deposits of the Southern Appala- 
 chians. Bull. 293, U. S. G. S. (1906). 134 pp. 
 
 2. The Occurrence of Copper in Shasta County, California. Bull. 430, U. S. 
 G. S., pp. 71-111 (1910). 
 
 GRESLEY, W. S: 
 
 Faulting in Veins. E. and M. Jour., vol. 53, p. 517 (1892). 
 GREENWELL, G. C. 
 
 A Practical Treatise on Mine Engineering, 3d ed. (London, 1889). 
 GREGORY, J. W. 
 
 1. Variation of Ores in Depth. Aust. Mm. Stand, vol 20, pp. 962-963 (1901). 
 
 2. Factors that Control the Depth of Ore- Deposits. Trans. Austral Inst. 
 Min. Eng., vol. 8, p. 2 (1904). 
 
 3. The Mount Lyell Mining Field, Tasmania. Trans. Austral. Inst. Min. Eng., 
 vol. 10, pp. 26-196 (1905). 
 
 4. The Ancient Auriferous Conglomerates of Southern Rhodesia. Trans. 
 Inst. Min. and Met., vol. 15, pp. 5<i3-586 (l<)05-0t>). 
 
 5. The Mt. Lyell Mining Field. Aust. Min. Stand, vol. 34, p. 34, (1905). 
 
 6. The Mount Lyell Mining Field, Tasmania, with some account of the 
 Geology of Other Pyritic Ore Bodies. Min. Jour. (1906). 
 
 7. Ore Deposits and Their Distribution in Depth. Min. Jour., vol. 79, pp. 
 583-584, 617 (1906) ; N. Z Mines Rec., vol. 9, pp. 489-492, 529-531 ; vol. 10, 
 
 pp. 38-40 (1906). 
 J. Th ~ - - - 
 
 8. The Geological Plans of Some Australian Mining Fields. Sci. Prog., 
 No. 1 (1906). 20 pp. 
 
 9. The Ballarat East Gold Field. Mem. 4, GeoL Sur. Viet. (1907). 52pp. 
 
868 ALPHABETICAL LIST OF AUTHORS. 
 
 GREGORY,*J. W. Continued. 
 
 10. The Origin of the Gold in the Rand Banket. Trans. Inst. Min. and Met., 
 vol. 17, pp 2-85 (1907-08). 
 
 11. Geology of the Inner Earth; Igneous Ore. Ann. Rept. Smith. Inst., pp. 
 311-330 (1908). 
 
 12. The Origin of the Gold of the Band Goldfield. Econ. Geol., vol. 4, pp. 
 118-129 (1909). 
 
 13. The Downward Enrichment of Sulphide Deposits. Disc, of paper by F. 
 L. Eansome. Econ. Geol., vol. 5, pp. 678-681 (1910). 
 
 GRIFFITHS, A. P. 
 
 The Oharawai Quicksilver Deposits. Trans. N. Z. Inst. Min. Ena., vol. 2. 
 
 p. 48 (1910). 
 GRIMM, J. 
 
 Die Lagerstatten der Nutzbaren Mineralien (Prague, 1869). 
 VON GRODDECK, ALBRECHT. 
 
 1. Die Lehre von den Lagerstatten der Erze (Leipzig, 1879). 
 
 2. Bemerkungen zur Classification der Erzlagerstatten. Berg-u. Hiitt. Zeit., 
 pp. 217-220, 229-232 (1885). 
 
 3. Traite des Gites Metalliferes, Traduit par H. Kuss (1884). 
 GUDZENT, DR. 
 
 Die Bestimmung der Radioaktivi tilt von Mineral- und Thermalquellen. Zeit 
 f.prak. Geol., vol. 18, pp. 147-149 (1910). 
 
 GUNTHER, C. G. 
 
 1. The Gold Deposits of Plomo, San Luis Park, Colorado. Econ. Geol., vol. 1, 
 pp. 143-154 (1906). 
 
 2. The Examination of Prospects (New York, 1912). 222 pp. 
 GUNTHER, S. 
 
 Handbuch der Geophysik (Stuttgart, 1897). 
 GURICH, G. 
 
 1. Uber die Eintheilung der Erzlagerstatten. Schles. Gen. f. Vater. Kul. 
 (Breslau, 1899) ; Zeit. f. prak. Geol, vol. 7, pp. 173-176 (1899). 
 
 2. KupfererzlagerstJitte von Wernersdorf bei Radowenz in Bohmen. Zeit. f. 
 prak. Geol, vol. 1, pp. 370-371 (1893). 
 
 GURLT, ADOLF. 
 
 On a Remarkable Deposit of Wolfram-Ore in the United States. Trans. A. L 
 M. E., vol. 22, pp. 236-242 (1893). 
 
 HABER, E. 
 
 Der Blei-und Zinkerzbergbau bei Ramsbeck im Bergrevier Brilon, unter be- 
 sonderer Beriieksichtigung der Ge^gnostischen und Mineralogischen Ver- 
 haltnisse der Erzlagerstatten. Zeit. f. Berg- Hiitt. u. Salinenw., vol. 42, pp. 
 74-112 (1894). 
 
 HAGUE, ARNOLD. 
 
 1. Geology of the Eureka District, Nevad a. Mon. 20, U.S. G. S. (1892). 419 pp. 
 
 2. The Origin of the Thermal Waters in the Yellowstone National Park. 
 Science, New Series, vol. 33, pp. 553-568 (1911). 
 
 HALAVATS and SJOGREN. 
 
 Das Eisenerzgebiet von Dognacska und Moravicza im Banate. Ost. Zeit. f. 
 
 Berg-u. Hiitt., vol. 39, pp. 91-96, 102-106 (1891). 
 HALEY, D. F. 
 
 The Auriferous Antimony Ore of West Gore, Nova Scotia. E. and M. Jour., 
 
 vol. 88, No. 15, pp. 723-724 (1909). 
 HALL, A. L., and HUMPHREYS. W. A. 
 
 1. Geological Notes on the Bush veldt Tin-Fields. Trans. Geol. Soc. So. Af., 
 vol. 8. p. 47(1905). 
 
 2. The Occurrence of Chromite Deposits along the Southern and Eastern 
 Margins of the Buschveldt Plutonic Complex. Trans. Geol Soc. So. Af.. 
 vol. 11, pp. 69-77 (1908). 
 
 HALL, C. E. 
 
 Geological Notes on the Manganese Ore-Deposit of Crimora, Virginia. 
 Trans. A. I. M. E., vol. 20, pp. 46-49 (1891). 
 
ALPHABETICAL LIST OF AUTHORS. 869 
 
 HALLA, OTTO. 
 
 The Beaches of Nome. Min. and ScL Press, vol. 94, p. 688 (1907). 
 HALSE, EDWARD. 
 
 1. The Occurrence of Tin-Ore at Sain Alto, Zacatecas, with reference to simi- 
 lar deposits in San Luis Potosi, and Durango, Mexico. Trans. A. I. M. E., 
 vol. 29, pp. 502-511 (1899). 
 
 2. The Occurrence of Pebbles, Concretions, and Conglomerate in Metallifer- 
 ous Veins. Trans. A. I. M. E., vol. 36, pp. 154-177 (1905). 
 
 HAMMOND, J. H. 
 
 1. The Auriferous Gravels of California.- 9th Ann. Rept., Cal. State Min., 
 
 pp. 105-138 (1890). 
 5. G(f " 
 
 2. Gold Mining in the Transvaal, South Africa. Trans. A. I. M. E., vol. 31, 
 
 p. 817 (1901). 
 HANCOCK, E. T. 
 
 Notes accompanying Lectures on Geology Applied to Mining (Houghton, 
 
 Mich., 1908). 210 pp. 
 
 HANKS, H. G. 
 
 Cassiterite : Notes of Tin Ores from Temescal, Cal. Mh Ann. RepL, Cal. State 
 
 Mm., pp. 115-123 (1884). 
 HARBORT, E. 
 
 Probleme der Erzlagerstattengeologie. Zeit. f. prak. Geol., vol. 15, pp. 372- 
 
 387, 437-441 ; vol. 16, pp. 34-44, 71-83 (1907-08). 
 HARE. 
 
 Die Serpentin Masse von Reichenstein und die darin Vorkommenden Min- 
 
 eralien ; Inaug. Diss. (Breslau, 1879). 
 HARKER, A. 
 
 1. Igneous Rock-Magmas as Solutions. Sri. Prog. (N. S. ), vol. 2, No. 6, 
 pp. 239-254 (1907). 
 
 2. Natural History of the Igneous Rocks (Macmillan Co., New York, 1909). 
 384 pp. 
 
 HARKNESS, R. 
 
 On the Jointings in the Carboniferous and Devonian Rocks in the District 
 around Cork ; and on the Dolomites of the same District. Qaar. Jour. Geol. 
 Soc., vol. 15, pp. 86-104 (1859). 
 HARRISON, J. B., FOWLER, F., and ANDERSON, C. W. 
 
 The Geology of the Goldfields of British Guiana, and an Appendix giving 
 the Laws and Regulations concerning the Mining Industry (Dulau, -Lon- 
 don, 1908). 320pp. 
 HASTINGS, J. B. 
 
 1. Are the Quartz- Veins of Silver Peak, Nevada, the Result of Magmatic 
 Segregation? Trans. A. I. M. E., vol. 36, pp. 647-654 (1905). 
 
 2. Sub-Classification of Zenogenous Ore-Deposits. E. and M. Jour., vol. 59, 
 p. 268 (March 23, 1895). 
 
 3. Primary Gold in a Colorado Granite. Trans. A. I. M. E., vol. 39, pp. 
 97-103 (1908). 
 
 4. Association of Magnetite with Sulphides in Mineral Deposits. Min. and 
 Sri. Press, vol. 97, pp. 333-334 (1908). 
 
 5. Origin of Pegmatite. Trans. A. I. M. E., vol. 39, pp. 104-128 (1908). 
 
 6. Volcanic Waters. Trans. A. I. M. E., vol. 39, pp. 129-138 (1908). 
 HATCH, F. H. 
 
 1. Geology of the Witwatersrand and other Districts in the Southern Trans- 
 vaal. Quar. Jour. Geol. Soc., vol. 54, pp. 73-100 (1898). 
 
 2. Notes on the Witwatersrand Gold Deposits and their Associated Rocks. 
 Trans. So. Af. Assoc. Eng. (1903). 8 pp. Also Geol. Mag., vol. 10, pp. 
 543-547 (1903). 
 
 HATCH, F. H., and CHALMERS, J. A. 
 
 The Gold Mines of the Rand (London, 1895). 306 pp. 
 HATCH, F. H. , and CORSTORPHINE, G. S. 
 
 1. The Petrography of the Witwatersrand Conglomerates, with Special Ref- 
 erence to the Origin of the Gold. Trans. Geol. Soc. So. A/., vol. 7, pt. 3, 
 p. 140 (1904). 
 
 2. The Geology of South Africa (London, 1905). 348 pp. 
 
870 ALPHABETICAL LIST OF AUTHORS. 
 
 HAWORTH, ERASMUS, CRANE, W. R., and KOGERS, A. F. 
 
 Special Report on Lead and Zinc. Univ. Geol. Sur. Kansas, vol. 8 (1904). 
 543 pp. 
 
 HAYES, C. W. 
 
 1. Geological Relations of the Iron-Ores in the Cartersville District, 
 Georgia. Trans. A. I. M. E., vol. 30, pp. 403-419 (1900). 
 
 2. Handbook for Field Geologists (New York, 1909). 159 pp. 
 
 3. The Iron-Ore Supply of the United States. Bull. 28, A. I. M. E., pp. 
 373-379 (Apr., 1909). 
 
 4. Iron Ores of the U. S.Bull. 394, U. S. G. S., pp. 70-113 (1909). 
 HEADDEN, W. P. 
 
 The Doughty Group of Radium Bearing Springs on the North Fork of Gun- 
 
 nison River, Colo. Proc, Colo. Sci. Soc., vol. 8, pp. 1-30 (1905). 
 HEANAGE, E. F., and HOLFORD, W. G. 
 
 Notes on the Occurrence of Gold in Primary Formations. Trans. So. Af. 
 . Assoc. Eng., Johannesburg (1905). 
 
 HEDBTJRG, ERIC. 
 
 The Missouri and Arkansas Zinc-Mines at the Close of 1900. Trans. A. I. 
 M. E., vol. 31, pp. 379-404 (1901). 
 
 HEIM, A. 
 
 Untersuchungen iiber den Mechanismus der Gebirgsbildung (Basel, 1878). 
 
 HELMH ACKER. 
 
 1. Beitrage zur Kenntniss der Sekundaren Goldlagerstatten Berg- u. Hiitt. 
 Zeit., vol. 50 (1891). 
 
 2. Uber das Vorkommen des Goldes in Dioriten und Serpentinen. Ost. Zeit. 
 f.Berg-u. Hutt., vol. 28, pp. 97-99, 110-113, 127-128, 142-144, 155-156 
 (1880). 
 
 HENDERSON, C. H. 
 
 The Copper Deposits of the South Mountain. Trans. A. I. M. E., vol. 12, 
 
 pp. 85-90 (1883-84). 
 HENRICH, CARL. 
 
 1. Notes on the Geology and on some of the Mines of Aspen Mountain, 
 Pitkin County, Colorado. Trans. A. I. M. E., vol. 17, pp. 156-206 
 (1888-89). 
 
 2. Zinc-Blende Mines and Mining near Webb City, Missouri. Trans. A. I. 
 M. E., vol. 21, pp. 3-25 (1892-93). 
 
 3. The Ducktown Ore- Deposits. Trans. A. I. M. E., vol. 25, pp. 173-245 
 (1895). 
 
 HENRICH, F. 
 
 Uber die Einwirkung von kohlensaurehaltigem Wasser auf Gesteine und 
 iiber den Ursprung und den Mechanismus der kohlensaurefiihrenden 
 Thermen. Zeit.f. prak. Geol., vol. 18, pp. 85-94 (1910). 
 
 HENRICKSON, G. 
 
 Die Eisenerzlagerstatten von Sydvaranger und die Sonderung oder Differen- 
 tiation von Eruptivmassen durch Druck. Ost. Zeit. f. Berg- u. Hiitt., vol. 
 54, p. 168 (1906). 
 
 HENWOOD, W. J. 
 
 1. On the Metalliferous Deposits of Cornwall and Devon. Trans. Roy. Geol. 
 Soc. Comw., vol. 5 (1843); vol. 8. 
 
 2. Observations on Metalliferous Deposits. Trans. Roy. Geol. Soe. Cornw., 
 vol. 7 (1871). 
 
 3. On the Detrital Tin-Ore of Cornwall. Jour. Roy. Inst. Cornw., vol. 15 
 (1873); Ann. d. Mines, 7th ser., vol. 6, pp. 114-130 (1874). 
 
 HERMANN, O. 
 
 Steinbruch's Industrie und Steinbruch's Geologic (Berlin, 1899). 
 
 HERSHEY, O. H. 
 
 1. Age and Origin of Certain Gold "Pocket" Deposits in Northern Cali- 
 fornia. Am. 'Geol., vol. 24, pp. 38-43 (1899). 
 
 2. Age and Origin of Certain Gold Deposits on the Isthmus of Panama. 
 Am. Geol, vol. 24, pp. 73-77 (1899). 
 
 3. Primary Chalcocite in California. Min. and Sci. Press, vol. 96, pp. 429- 
 430 (1908). 
 
ALPHABETICAL LIST OF AUTHORS. 871 
 
 HESS, F. L. 
 
 The Arkansas Antimony Deposits. Bull. 340, U. S. G. S., pp. 241-252 (1908). 
 HESS, F. L. , and GRATON, L. C. 
 
 The Occurrence and Distribution of Tin. (With bibliography. ) Bull. 260, 
 
 U. S. G. S., pp. 161-187 (1905). 
 HEUSLER, C. 
 
 tJber die Beziehungen von Erzgangen zu Eruptivgesteinen. Verhand. d. 
 
 NaturhisL V. d. Pr. Eheinlande, vol. 58, pp. 53-65 (1901). 
 HEWETT, D. F. 
 . New Occurrence of Vanadium in Peru. Trans. A. L M. E., vol. 40, pp. 274- 
 
 299 (1909). 
 HILL, K. T. 
 
 1. The Occurrence of Hematite and Marti te Iron Ores in Mexico. Am. Jour. 
 Sc>Vvol.*45, 3dser., pp. 111-119 (1893). 
 
 2. The Upland Placers of La Cienega, Sonora, Mexico. E. and M. Jour.. 
 vol. 73, pp. 132-134 (1902). 
 
 HlLLE, F. 
 
 1. The Atik-Okan Nickeliferous Pyrrhotite Deposits and their Origin. Jour. 
 Can. Min. Inst., vol. 9, pp. 285-301 (1905). 
 
 2. Correction in the Classification of our Gold Formations. Jour. Can. Min. 
 Inst., vol. 8, pp. 183-191 (1905). 
 
 3. Some Iron Ore Deposits in the Districts of Thunder Bay and Kainy Eiver, 
 Ontario. Can. Dept. of Mines (1908). 
 
 HlLLEBRAND, W. F. 
 
 1. Some Principles and Methods of Kock Analysis. Bull. 176, U. S. G. S.. 
 pp. 1-114 (1900). 
 
 2. The Analysis of Silicate and Carbonate Rocks. Bull. 422, U. S. G. S. 
 (1910). 239 pp. 
 
 3. The Vanadium Sulphide Patronite. Jour. Am. Chem. Soc., vol. 29 (1907) ; 
 Am. Jour. Sci. , 4th ser., vol. 24, pp. 141-151 (1907). 
 
 HILLEBRAND, W. F., and RANSOME, F. L. 
 
 Carnotite in Western Colorado. Am. Jour. Sci., 4th ser., vol. 10, pp. 120- 
 
 144 (1900) ; Bull. 262, U. S. G. S., pp. 9-31 (1905). 
 HILLEBRAND, W. F., and SCHALLER, -W. T. 
 
 The Mercury Minerals from Terlingua, Texas. Bull. 405, U. S. G. S. (1909). 
 174 pp. 
 
 HlNTZE. 
 
 Handbuch der Mineralogie (Leipzig, 1889-1891). 2 vols. 
 HIXON, H. W. 
 
 1. Magmatic Waters. Jour. Can. Min. Inst., vol. 10, pp. 300-320 (1907). 
 
 2. A Theory of Volcanic Action and Ore Deposits, their Nature and Cause. 
 Trans. Inst. Min. and Met., vol. 18, pp. 202-219, 230-272 (1908-09). 
 
 HOBBS, W. H. 
 
 1. Old Tungsten Mine at Trumbull, Conn. 22d Ann. Rept., U. S. G. S., 
 part 2, pp. 7-22 (1901). 
 
 2. Iron Ores of the Salisbury District of Connecticut, New York, and Massa- 
 chusetts. Econ. Geol., vol. 2, pp. 153-181 (1907). 
 
 HOCHSTETTER and TELLER. 
 
 Uber einen Neuen Geologischen Aufschl. im Gebiete der Karlsbader Ther- 
 
 men. Devkschr. Akad. Wien (1878). 
 HODGES, A. D., JR. 
 
 Notes on the Topography and Geology of the Cerro de Pasco, Peru. Trans. 
 A. I. M. E., vol. 16, pp. 729-753 (1887-88). 
 
 H5FER, H. 
 
 1. Uber Verwerfungen. Ost. Zeit. f. Berg- u. Hiiit., vol. 34, p. 350 (1886). 
 
 2. Die Ausrichtung der Verwerfungen. Ost. Zeit. f. Berg- u. HutL, vol. 29, 
 pp. 167-171 (1881). 
 
 3. Benennung und Systematik der Lagerstatten nutzbarer Minerale. Zeit.f. 
 prak. Geol., vol. 5, pp. 113-116 (1897). 
 
 4. Zur Bestimmung des Alters der Gange. Oft* Zeit. f. Berg- u. Hiitt., vol. 
 47 (1899). 15 pp. 
 
872 ALPHABETICAL LIST OP AUTHORS. 
 
 HOFER, H. Continued. 
 
 5. Erdol-Studien. K. K. Ak. d. W. in Wien, Math. Phys. Class., vol. 3, 
 No. 1 (July, 1902). 
 
 HOLLTSTER, O. J. 
 
 Gold and Silver Mining in Utah. Trans. A. I. M. E., vol. 16, pp. 3-18 
 
 (1887-88). 
 
 HOOVER, H. C. 
 
 The Superficial Alteration of Western Australian Ore-Deposits. Trans. A. 
 
 I. M. E., vol. 2, pp. 758-765 (1898). 
 
 HOPKINS, T. C. 
 
 Cambro-Silurian Limonite Ores of Pennsylvania. Bull. Geol. Soc. Am. 3 vol. 
 
 II, pp. 475-502 (1900). 
 
 HORE, K. E. 
 
 1. Origin of Cobalt-Silver Ores of Northern Ontario. Jour. Can. Min. InsL, 
 vol. 11, pp. 275-286 (1908). 
 
 2. Origin of the Cobalt-Silver Ores of Northern Ontario. Econ. Geol., vol.3, 
 pp. 599-610 (1908). 
 
 HORNER. 
 
 Vorkommen von Platin und Diamanten auf Borneo. Pogg. Ann., vol. 55, 
 pp. 526-529 (1842). 
 
 HORNUNG, F. 
 
 1. Formen, Alter und Ursprung des Kupferschiefererzes. Zeit. d. D. Geol. 
 Gesel., vol. 56, pt. 2, pp. 207-217 (1904). 
 
 2. Ursprung und Alter des Schwerspates und der Erze im Harze. Zeit d. D. 
 Geol. Gesel., vol. 57, pts. 2 and 3, pp. 291-360 (1905). 
 
 3. Ursprung und Alter des Schwerpates und der Erze im H.a,rze.Zeit. d. D. 
 Geol. Gesel. , vol. 57, No. 2, pp. 291-320. 
 
 HORWOOD, C. B. 
 
 The Red Granite of Balmoral and Its Relation to the Cobalt Lodes. Trans. 
 Geol. Soc. So. Af., vol. 7, part 2, pp. 110-114 (1904). 
 
 HOSKINS, L. M. 
 
 Flow and Fracture of Rocks as Related to Structure. IQth Ann. Rept., U. S., 
 
 G. S., part 1, pp. 845-874 (1896). 
 HOWE, J. L. 
 
 Bibliography of the Metals of the Platinum Group. 1748-1896 (Washington, 
 
 1898). 318 pp. 
 HUNT, T. S. 
 
 1. Chemical and Geological Essays (1874). 
 
 2. The Origin of Metalliferous Deposits. Trans. A. L M. E., vol. 1, pp. 
 413-426 U871-73). 
 
 3. The Ore Knob Copper Mine and some Related Deposits. Trans. A. I. 
 M. E., vol. 2, pp. 123-131 (1873-74). 
 
 4. The Cornwall Iron Mine and some Related Deposits in Pennsylvania. 
 Trans. A. L M. E., vol. 4, pp. 319-325 (1875-76). 
 
 5. Coal and Iron in Alabama. Trans. A. L M. E., vol. 11, pp. 236-248 
 (1882-83). 
 
 6. The Iron-Ores of the United States. Trans. A. L M. E., vol. 19, pp. 
 3-17 (1890-91). 
 
 HUNT. 
 
 British Mining (1884). 
 HUSSAK, E. 
 
 1. Uber das Vorkommen von Palladium und Platin in Brasilien. Zeit. /. 
 prak. Geol., vol. 14, pp. 284-293 (1906). 
 
 2. The Occurrence of Palladium in Brazil. (Abstract). Min. Jour., pp. 130- 
 131 (1908). 
 
 3. Der goldfiihrende, kiesige Quarzlagergang von Passagem in Minas Geraes, 
 Brazilien. Zeit. f. prak. Geol., vol. 6, pp. 345-357. 
 
 HUTCHINS, J. P. 
 
 1. The Essential Data of Placer Investigations. E. and M. Jour., vol. 84, 
 pp. 339-342, 385-387 (1907). 
 
 2. The Nomenclature of Modern Placer Mining. E. and M. Jour., vol. 84, 
 pp. 293-296 (1907). 
 
ALPHABETICAL LIST OF AUTHORS. 873 
 
 IDDINGS, J. P. 
 
 Igneous Rocks. (Discussions of Magmatic Differentiation and Physical Chem- 
 
 istry:) (1909.) 464pp. 
 INGALLS, W. E. 
 
 1. The Tin Deposits of Durango, Mexico. l^ans. A. I. M. E., vol. 25, pp. 
 146-163 (1895). 
 
 2. The Silver-Lead Mines of Eureka, Nevada.!?, and M. Jour., vol.84, pp. 
 1051-1058 (1907). 
 
 VON INKEY, B. 
 
 De la Relation entre I'e'tat propylitique des roches andesitiques et leur filons 
 
 mine'raux. Ccmipt. Rend. 10th Cong. Geol. Int., vol. 1, p. 501 (1907). 
 IRVING, J. D. 
 
 1. A Contribution to the Geology and Ore Deposits of the Northern Black 
 Hills, South Dakota. Ann. N. Y. Acad. Sci., vol. 12, part 2, pp. 187-340 
 (1899). 
 
 2. Some Recently Exploited Deposits of Wolframite in the Black Hills of 
 South Dakota. Trans. A. I. M. E., vol. 31, pp. 683-695 (1901). 
 
 3. Ore Deposits of the Northern Black Hills. Min. and Sci. Press, vol. 87, 
 pp. 166-167, 187-188, 205, 221-222 (1903). 
 
 4. Ore Deposits of the Northern Black Hills. Bull. 225, U. S. G. S., pp. 
 123-140 (1904). 
 
 5. Ore Deposits of the Ouray District, Colorado. Bull. 260, U. S. G. S., 
 pp. 50-77 (1905). 
 
 6. Ore Deposits in the Vicinity of Lake'.City, Colorado. Bull. 260, U.S. G. S., 
 pp. 78-84 (1905). 
 
 7. The Localization of Values in Ore-Bodies and the Occurrence of " Shoots'' 
 in Metalliferous Deposits. Econ. Geol., vol. 3, pp. 143-154 (1908). 
 
 8. Special Problems and Their Study in Economic Geology. (Editorial) 
 Econ. Geol., vol. 5, pp. 670-677 ; Discussion of, pp. 772-790 (1910). 
 
 9. The Formation of Ore-Bodies by Replacement and the Criteria by means 
 of which they may be Recognized. Quart. Bull. Can. Min. Inst., No. 17, 
 pp. 3-79 (Dec., 1911). 
 
 10. Some Features of Replacement Ore-Bodies and the Criteria by which they 
 may be Recognized. Econ. Geol., vol. 6, pp. 527-561 ; 619-669 (1911). 
 
 11. The Sub-structure of Geological Reports. Econ. Geol., vol. 8, No. 1 (1913). 
 IRVING, J. D. , and BANCROFT, H. 
 
 Geology and Ore Deposits near Lake City, Colorado. Bull. 478, U. S. G. 
 
 S. (1911). 128 pp. 
 IRVING, J. D., EMMONS, S. F., and JAGGAR, T. A., JR. 
 
 Economic Resources of the Northern Black Hills Prof. Paper 26, U. S. G. S. 
 (1904). 222 pp. 
 
 IRVING, R. D. 
 
 1. The Copper- Bearing Rocks of Lake Superior. Mon. 5, U. S. G. S., 
 (1883). 464 pp. 
 
 2. Copper-Bearing Rocks of Lake Superior. 3d Ann. Rept., U. S. G. S., pp. 
 89-188 (1883). 
 
 3. On the Origin of "the Ferruginous Schists and Iron Ores of 'the Lake Su- 
 perior Region. Am. Jour. Sci., 3d ser., vol. 32, pp. 255-272 (1886). 
 
 IRVING, R. D., and VAN HISE, C. R. 
 
 1. The Penokee Iron-Bearing Series of Michigan and Wisconsin. IQth Ann. 
 
 Rept., U. S. G. S., part 1, pp. 341-507 (1890). 
 The Penokee Iron-Bearing Series of 
 Mon. 19, U. S. G. S. (1892). 534 pp. 
 
 ., . ., , . 
 
 2. The Penokee Iron-Bearing Series of Northern Wisconsin and Michigan. 
 
 JACKSON, C. F. V. 
 
 Geological Features and Auriferous Deposits of Mount Morgan. Bull. 18, 
 
 Geol. Sur. West. Aust. (1905). 22 pp. 
 JAGGAR, T. A., JR. 
 
 How Should Faults be Named and Classified 1Econ. Geol., vol. 2, pp. 58-62 
 
 (1907). 
 JAQUET, J. B. 
 
 1. Iron Ore Deposits of New South Wales. Mem. 2, Geol. Sur., N. S. W. 
 
 55 
 
874 ALPHABETICAL LIST OF AUTHORS. 
 
 JAQUET, J. B. Continued. 
 
 2. Platinum Deposits of Millga Coerls near Booken Hill. Aust. Min. Stand. , 
 vol. 9, p. 50 (1893) ; vol. 12, pp. 720-721 (lt>96). 
 
 3. The Occurrence of Platinum in New South Wales. Geol. Sur. N. S. W., 
 Records of, p. 33 (1896). 
 
 4. Geology of the Broken Hill Lode and Barrier Eanges Mineral Field, New 
 South Wales. Mem. Geol. Sur. N. S. W., No. 5 (194). 
 
 JAQUET and WILLM. 
 
 Les eaux mine'rales de la France (Paris, 1894). 
 JENNEY, W. P. 
 
 1. The Lead and Zinc-Deposits of the Mississippi Valley. Trans. A. I. M. 
 E., vol. 22, pp. 17l-22o (Ih93). 
 
 2. The Chemistry of Ore-Deposition. Trans. A. I. M. E., vol. 33, pp. 445- 
 498 (1902). 
 
 3. The Mineral Crest, or the Hydrostatic Level Attained by the Ore-Deposit- 
 ing Solutions, in Certain Mining Districts of the Great Salt Lake Basin. 
 Trans. A. I. M. E., vol. 33, pp. 46-50 (1902). 
 
 4. Block-Faulting and Its Relation to Ore Deposition. Min. and Sci. Press, 
 vol. 92, pp. 54-55 (1906). 
 
 JENNINGS, E. P. 
 
 1. The Copper Deposits of the Kaibab Plateau, Arizona. Trans. A. I. M. E., 
 vol. 34, pp. 839-841 (1903). 
 
 2. The Genesis of the Copper Deposits of Yerington, Nevada. Can. 3Jin. 
 Jour., new ser., vol. 1, pp. 365-366 (1907). 
 
 JOHANSSON, H.Geol. For. i Stock. Forhand., vol. 28, pp. .516-538 (1906) ; vol. 
 
 29, pp. 143-186 (1907). 
 JOHNSON, J. E., JR. 
 
 The Origin of the Oriskany Limonites. E. and M. Jour., vol. 76, pp. 231- 
 
 232 (1903). 
 JOHNSON, J. P. 
 
 1. The Ore Deposits of South Africa. Part I Base Metals (190S). 61 pp. 
 
 2. The Auriferous Conglomerates of the Witwatersrand and the Antimony 
 Deposits of the Murchison Kange (London, 1908). 
 
 JONES, F. A. 
 
 The Placers of Santa F6 County, New Mexico. Min. World, vol. 25, p. 425 
 
 (1906). 
 JONES, S. P. 
 
 Gold Deposits of Georgia. (2d rept. )Bull. 19, Geol. Sur. Ga. (1909). 283 pp 
 
 JULIEN, A. A. 
 
 1. On the Part played by Humus Acids in Ore Deposits, Wall Rock, Gossan^ 
 etc. Proc. Am. Assoc. Adv. Sci., pp. 382, 385 (1879). 
 
 2. The Genesis of the Crystalline Iron Ores. E. and M. Jour., vol. 37, pp. 
 81-83 (1884). 
 
 KATTEKFELD. 
 
 tfber die Platina Production Russlands. Bery- u. Hiltt. ZeiL, vol. 45, pp. 
 68-69 (1885). 
 
 KAY, G. F. 
 
 Nickel Deposits of Nickel Mountain, Oregon. Bull. 315, U.S. G. S., pp. 
 
 120-127 (1907). 
 KECK, R. 
 
 Genesis of Ore Deposits.^, and M. Jour., vol. 35, pp. 3-4 ( 1883). 
 KEDZIE, G. E. 
 
 The Bedded Ore- Deposits of Red Mountain Mining District, Ouray County > 
 
 Colorado. Trans A. I. M. E., vol. 16, pp. 570-581 (1887-88). 
 KEELE, JOSEPH. 
 
 The Duncan Creek Mining District. Can. Geol. Sur. Sum. Rept. for 1904, pp. 
 
 18-42 (1905). 
 KEILHACK, K. 
 
 1. Spaltenbildung. Zeit. f. prak. Geol., vol. 3, p. 254 (1895). 
 
 2. Lehrbuch der praktischen Geologic (Stuttgart, 1896). 638 pp. 
 
ALPHABETICAL LIST OF AUTHORS. 875 
 
 
 KELLOGG, L. O. 
 
 Sketch of the Geology and Ore Deposits of the Cochise Mining District, 
 
 Cochise County, Arizona. Econ. GeoL, vol. 1, pp. 651-659 (1906). 
 KEMP, J. F. 
 
 1. The Literature of Ore Deposits. Sch. Min. Quar., vol. 10, pp. 54, 116, 
 326 (1889); vol. 11, p. 359 (1890); vol. 12, p. 218 (1891). 
 
 2. The Precipitation of Metallic Sulphides by Natural Gas E. and M. Jour., 
 vol. 50, p. 689 (1890). 
 
 3. On the Filling of Mineral Veins. Sch. Min. Quar., vol. 13, p. 20 (Oct., 
 1891). 
 
 4. The Classification of Ore Deposits. Sch. Min. Quar., vol. 14, pp. 8-24 
 (1893). 
 
 5. The Ore Deposits at Franklin Furnace and Ogdensburg, New Jersey. 
 Proc. N. Y. Acad. Sci., pp. 76-96 (1894). 
 
 6. The Development of Views on the Origin of Ores. Min. Ind., vol. 2, pp. 
 835-840 (1893). 
 
 7. The Nickel-Mine at Lancaster Gap, Pennsylvania, and the Pyrrhotite 
 Deposits at Anthony's Nose on the Hudson. Trans. A. I. M. E., vol. 24, 
 pp. 620-633 (1894). 
 
 8. An Outline of the Views Held To-day on the Origin of Ores. Min. Ind., 
 vol. 4, pp. 755-766 (1895). 
 
 9. The Geology of the Magnetites near Port Henry, N. Y., and Especially 
 those of Mineville. Trans. A. I. M. E., vol. 27, pp. 146-203 (1897). 
 
 10. Geological Occurrence and Associates of the Telluride Gold Ores. Min. 
 Ind., vol. 6, pp. 295-320 (1898). 
 
 11. The Titaniferous Iron Ores of the Adirondacks. 19th Ann. Eept., U. S. 
 O. S., part 3, pp. 377-422 (1898). 
 
 12. A Brief Keview of the Titaniferous Magnetites. Sch. Min. Quar., vol. 20, 
 pp. 323-356 (July, 1899) ; pp. 56-65 (Nov., 1899). 
 
 13. The Deposits of Copper-Ores at Ducktown, Tennessee. Trans. A. L M. E., 
 vol. 31, pp. 244-265 (1901). 
 
 14. The Kole of Igneous Hocks in the Formation of Veins. Trans. A. L 
 M. E., vol. 31, pp. 169-198 (1901). 
 
 15. The Geological Relations and Distribution of Platinum and Associated 
 Metals. Bull. 193, U. S. G. S. (1902), 95pp.; Min. Ind., vol. 10, p. 540 
 (1902) ; E. and M. Jour., vol. 73, pp. 512-513 (1902). 
 
 16. Igneous Kocks and Circulating Waters as Factors in Ore-Deposition. 
 Trans. A. I. M. E., vol. 33, pp. 699-714 (1902). 
 
 17. Keview of the General Literature on Ore Deposits. Min. Ind., vol. 12, 
 pp. 385-395 (1903). 
 
 18. The Formation of Veins. M in. Mag. (J.), vol. 10, pp. 89-93 (1904). 
 
 19. A Keview of the Literature on Ore Deposits in 1904 and 1905. Min. Ind., 
 vol.13 (1904). 
 
 20. The Copper- Deposits at San Jose, Tamaulipas, Mexico. Trans. A. I. 
 M. E., vol. 36, pp. 178-203 (1905). 
 
 21. The Ore Deposits of the United States and Canada (New York and Lon- 
 don, 1906). 3d ed. ; 481 pp. 
 
 22. Literature on Ore-Deposits in 1906. Min. Ind., vol. 15, pp. 781-789 
 (1906). 
 
 23. Secondary Enrichment in Ore-Deposits of Copper. Econ. GeoL, vol. 1, 
 pp. 11-25 (1906). 
 
 24. The Problem of the Metalliferous Veins. Econ. Geol, vol. 1, pp. 207- 
 232 (1906). 
 
 25. Some New Points in the Geology of Copper Ores. Jour. Can. Min. Inst., 
 new ser., vol. 1, pp. 274-275 (1907) ; E. and M. Jour., vol. 83, pp. 1192- 
 1193 (1907) ; Min. and Sci. Press, vol. 94, pp. 402-403 (1907). 
 
 26. Ore Deposits at the Contacts of Intrusive Kocks and Limestones ; and 
 their Significance as Kegards the General Formation of Veins. Econ. Geol. , 
 vol. 2, pp. 1-13 (1907) ; Compt. Rend. Cong. Geol. Int., 10th sess., pp. 519- 
 531 (Mexico, 1906). 
 
 27. Garnet Zones. Mm. and Sci. Press, vol. 92, pp. 220-221 (Mar. 31, 1906). 
 
 28. Waters, Meteoric and Magmatic. Min. and Sci. Press, vol. 96, pp. 705-708 
 (June 20, 27, 1908). 
 
 29. " What is an Ore?" Jour. Can. Min. Inst.,vol. 12, pp. 356-370 (1909). 
 
 30. "What is an Ore ?" Min. and Sci. Press, vol. 98, pp. 419-423 (Mar. 20, 
 1909). 
 
 31. The Iron Ores of the Iron Springs District, Utah. Econ. Geol, vol. 4, 
 pp. 782-791 (1909). 
 
876 ALPHABETICAL LIST OF AUTHORS. 
 
 
 
 KEMP, J. F. , and GUNTHER, C. G. 
 
 The White Knob Copper-Deposits, Mackay, Idaho. Trans. A. I. M. E., 
 
 vol. 38, pp. 269-296 (1907). 
 KEMPTON, C. W. 
 
 The Tin-Deposits of Durango, Mexico. Trans. A. I. M. E., vol. 25, pp. 997-98 
 
 (1895). 
 KENDALL, J. D. 
 
 The Iron Ores of Great Britain and Ireland (London, 1893). 224 pp. 
 KENNEDY, WILLIAM. 
 
 Iron Ores of East Texas. Trans. A. I. M. E., vol. 24, pp. 258-288 (1894). 
 KERR, W. C. 
 
 The Gold-Gravels of North Carolina. Tram A. I. M. E., vol. 8, pp. 462- 
 
 466 (1879-80). 
 KESSLER, L. 
 
 The Gold Mines of the Hand and the Determination of Their Value (Lon- 
 don, 1904). 135pp. 
 KEYES, C. R. 
 
 1. Origin and Classification of Ore-Deposits. Trans. A.L M. E., vol. 30, pp. 
 323-356 (1900). 
 
 2. Ore Formation on the Hypothesis of Concentration through Surface De- 
 composition. Am. GeoL, vol. 27, pp. 355-362 (1901). 
 
 3. Criteria of Downward Sulphide Enrichment. Econ. GeoL, vol. 5, pp. 558- 
 564 (1910). 
 
 4. Cerargyritic Ores: Their Genesis and Geology. Econ. GeoL, vol. 2, pp. 
 774-780 (1907). 
 
 5. Genesis of the Lake Valley, New Mexico, Silver-Deposits. Trans. A. L 
 M. E., vol. 39, pp. 139-169 (1908). 
 
 6. Porphyry Coppers. -Sail. 25, Min. Met. Soc. Am. (1910). 
 
 7. Garnet Contact- Deposits of Copper and the Depths at which They are 
 Formed. Econ. GeoL, vol. 4, pp. 365-372 (1909). 
 
 KEYES, W. S. 
 
 The Eureka Lode, of Eureka, Eastern Nevada. Trans. A. L M. E., vol. 6, 
 pp. 344-371 (1877-78). 
 
 KlMBALL, J. P. 
 
 1. Genesis of Iron-Ores by Isomorphous and Pseudomorphous Replacement 
 of Limestone. Am. Jour. Ski., 3dser., vol. 42, pp. 231-241 (1891). 
 
 2. The Iron-Ore Range of the Santiago District of Cuba. Trans. A. L M. E., 
 vol. 13, pp. 613-634 (1884-85). 
 
 KING, F. H. 
 
 Principles and Conditions of the Movements of Ground Water. 19^ Ann. 
 EepL, U. S. G. S., part 2, pp. 59-294 (1898). 
 
 KlRBY, E. B. 
 
 The Ore Deposits of Rossland, British Columbia. Jour. Can. Min. List., vol. 
 
 7, pp. 47-69 (1904). 
 KJERULF. 
 
 Udsigt over det sydlige Norges Geologi (Kristiania, 1879). 
 KLEINSCHMIDT, J. L. 
 
 Gedankeniiber Erzvorkommen. Berg- u. Hutt. Zeit., p. 413 (1887). 
 
 KLEMENT, C. 
 
 Expose* de quelques vues ge"nerale sur la formation des gites metalliferes. 
 Bull. Soc. Beige de GeoL, vol. 11, pp. 179-184 ; vol. 12, pp. 95-100, 121-126 
 (1897-98). 
 KLOCKMANN, F. 
 
 1. Lehrbuch der Mineralogie (1892) ; new edition (1900). 
 
 2. Das Erzlager des Rammelsberges. Zeit. d. D. GeoL Gesel.,vol. 45, pp. 281- 
 284 (1893). 
 
 3. Uber kontaktmetamorphe Magnetitlagerstiitten, ihre Bildung und sys- 
 tematische Stellung.--Ze^./. prak. GeoL, vol. 12, pp. 73-85 (1904). 
 
ALPHABETICAL LIST OF AUTHORS. 877 
 
 KLOCKMANN, F. Continued. 
 
 4. tiber den Einfluss der Metamorphose auf die Mineralische Zusammen- 
 setzung der Kieslagerstatten. Zeit. f. prak. GeoL, vol. 12, pp. 153-160 
 (1904). 
 KNETT, J. 
 
 Schwefel und Pyrite als Absatzvon Karlsbader Thermal wasser. Neues Jahrb. 
 
 f. Min., vol. 2, pp. 81-84 (1899). 
 KNIGHT, C. W. 
 
 Notes on Some Deposits in the East Ontario Gold Belt. Jour. Can. Min. Inst., 
 
 vol. 7, pp. 210-244 (1904). 
 KNIGHT, F. C. 
 
 A Suspected New Mineral from Cripple Creek. Proc. Col. Sci. Soc. , vol. 5, 
 
 pp. 66-71 (1894-96). 
 KNOPF, ADOLPH. 
 
 1. Geology of the Seward Peninsula Tin Deposits, Alaska. Bull. 358, U. S. 
 G. S. (1908). 71 pp. 
 
 2. Notes on the Foothill Copper Belt of the Sierra Nevada. Bull. Dept. GeoL 
 Univ. Col., vol. 4, No. 17, pp. 411-423 (1906). 
 
 3. Some Features of the Alaska Tin Deposits. Econ. GeoL, vol. 4, pp. 214- 
 223 (1909). 
 
 KNOX, H. H. 
 
 An Instance of Secondary Impoverishment. Trans. Inst. Min. and Met. , vol. 
 
 18, pp. 273-290 (1908-09). 
 KNOX, N. B. 
 
 Dredging and Valuing Dredging-Ground in Oroville, California. Can. Min. 
 Rev., vol. 22, pp. 211-213 (1903). 
 
 K5BRICH, B. 
 
 Magnetische Erscheinungen an Bauxiten. Zeit. f. prak. GeoL, vol. 13, pp. 
 
 23-36 (1905). 
 KOENIG, G. A., and STOCKDEB, MORITZ. 
 
 On the Occurrence of Lustrous Coal with Native Silver in a Vein in Porphyry, 
 in Ouray County, Colorado. Trans. A. I. M. E., vol. 9, pp. 650-656 
 (1880-81). 
 
 KOHLER, G. 
 
 1. Lehrbuch der Bergbaukunde (Leipzig, 1884). 
 
 2. Die Storungen der Gange, Flotze und Lager (Leipzig, 1886). Transla- 
 tion by W. B. Phillips : Irregularities of Lodes, Veins, and Beds. E. and 
 M. Jour., vol. 43, p. 454 ; vol. 44, p. 4 (1887). 
 
 3. Beitriige zur Kenntniss der Erdbewegungen und Storungen der Lagerstat- 
 ten. Berg- u. Hiltt. Zeit., vol. 56, pp. 217-2^9, 261-263, 341-345 (1897). 
 
 KOHLER, E. 
 
 Adsorptionsprozesse als Factoren der Lagerstiittenbildung und Lithogenesis. 
 Zeit. f. prak. GeoL, vol. 11, pp. 49-59 (1903). 
 
 KOHLER, EUGEN. 
 
 Die neueren Quellen-und Grundwassertheorien (Kondensationstheorien). 
 
 Zeit. f. prak. GeoL, vol. 18, pp. 23-29 (1910). 
 KONIG, F. 
 
 Die Vertheilung des Wassers iiber, auf, und in, der Erde, und die daraus sich 
 
 ergebende Entstehung des Grundwassers und seiner Quellen, mit einer 
 
 Kritik der Bisherigen Quellentheorien (Jena, 1901). 
 
 K5NIGSBERGER, J. 
 
 Die Minerallagerstatten im biotit protogin des Aar Massives. Neues Jahrb. 
 f. Min., vol. 14, pp. 43-49 (1901). 
 
 KOSMANN. 
 
 tiber die Bildung Magnetischer Eisenoxyde und Eisenhydroxyde. Ess- 
 
 Gluck., vol. 4 (1893). 3pp. 
 KOTO, B. 
 
 On the Cause of the Great Earthquake in Central Japan. Jour. Coll. Sci. Imp. 
 
 Univ. Jap., vol. 5, part 4 (Tokyo, 1893). 
 KRAHMANN, MAX. 
 
 1. Fortschritte der Praktischen Geologic (Berlin, 1903). 2 vols., 410 pp. 
 
878 ALPHABETICAL LIST OF AUTHORS. 
 
 KRAHMANN, MAX. Continued. 
 
 2. Lagerstatten-Schatzungen im Anschluss an eine Beurteilung der Xachhaltig- 
 keit des Eisenerzbergbaues an der Lahn. Zeit. f. prak. Geol., vol. 12, 
 pp. 329-348 (1904). 
 
 3. Der deutsche Erzbergbau. Zeit. f. prak. Geol., vol. 13, pp. 265-304 
 (1905). 
 
 KRAUSE, P. R. 
 
 IJber den Einfluss der Eruptivgesteine auf die Erzfiihrungder Witwatersrand- 
 Conglomerate und der im dolomitischen Kalkgebirge von Lydenbnrg auf- 
 tretenden Quartzflotze, nebst einer Kurzen Schilderung der Grubenbezirke 
 von Pilgrimsrest und De Kaap (Transvaal). Zeit. f. prak. Geol., vol. 5, pp. 
 12-25 (1897). 
 
 KRECKE, F. 
 
 Sind die Roteiaensteinlager des nassuaischen Devon primiire oder sekundare 
 Bildungen? Zeit.f. prak. Geol, vol. 12, pp. 348-355 (1904). 
 
 KRUSCH, PAUL. 
 
 1. tiber die Veranderungen der Erzgange in der Tiefe. Zeit. f. prak. Geol., 
 vol. 8, pp. 313-322 (1900). 
 
 2. Bilder von den Blei und Zink Lagerstatten in Kaibl. K. K. Ackerb. 
 Minist. (Wien, 1903). 
 
 3. Uber die Zusammensetzung der Westfalischen Spaltenwiisser. Zeit. f.prak. 
 Geol., vol. 12, pp. 252-254 (1904). 
 
 4. Die Einteilung der Erze mit besonderer Beriicksichtigung der Leiterze 
 sekundarer und primarer Teufen. Zeit. f. prak. Geol., vol. 15, pp. 129-139 
 (19U7). 
 
 5. Die Untersuchung und Bewertung von Erzlagerstatten. (Stuttgart, 1907. ) 
 517 pp. 
 
 6. Uber primare und sekundare Metasomatische Prozesseauf Erzlagerstatten. 
 Zeit. f.prak. Geol., vol. 18, pp. 165-180 (1910). 
 
 KUNTZ, J. 
 
 1. Copper Ore in Southwest Africa. Trans. Geol. Soc. So. Af., vol. 7, pt. 2, 
 pp. 70-76 (1904). 
 
 2. The Hand Conglomerates : How they were formed. Trans. Geol. Soc. So- 
 Africa, vol. 1, pt. 6, pp. 113-122 (1896). 
 
 KYN ASTON, H., and MELLOR, E. T. 
 
 The Geology of the Waterberg Tin-Fields. Mines Dept. Trans., Mem. 4 (1909). 
 124 pp. 
 
 LACHMANN, E. 
 
 Neue ostungarische Bauxitkorper und Bauxitbildung uberhaupt. Zeit. f. 
 prak. Geol., vol. 16, pp. 354-362 (1908). 
 
 LACROIX, A. 
 
 1. Sur un gitede magnetite en relation avec le granite de Querigut (ariege). 
 Compt. rend. Acad. Sci., vol. 12, p. 6 (1890). 
 
 2. Sur 1' Origin e de 1' Or de Madagascar. Compt. rend. Acad. Sci., vol. 132, 
 pp. 180-182 (1901). 
 
 3. Notice sur les Travaux Scientifiques de M. A. Lacroix (Paris, 1908). 
 
 LAKE, J. V. 
 
 The Deposition of Alluvial Gold. Min. Jour., vol. 73, p. 11 (1903). 
 
 LANE, A. C. 
 
 1. The Theory of Copper Deposition. Rept. Mich. St. Geol., vol. 34, pp. 240- 
 250 (1903) ; Am, Geol., vol. 34, pp. 297-309 (1904). 
 
 2. The Influence of Varying Degrees of Superfusion in Magmatic Differentia- 
 tion. Jour. Can. Min. Inst., vol. 9, pp. 210-217 (1906). 
 
 3. The Formation of Lake Superior Copper. Science, new ser., vol. 25, p. 
 589 (1907). 
 
 4. Mine Waters. Proc. Lake Sup. Min. Inst., vol. 13, pp. 63-152 (1908). 
 
 5. Mine Waters and Their Field Assay. Bull. Geol. Soc. Am., vol. 19, pp. 
 501-512 (1908). 
 
 6. Mine Waters. Jour. Can. Min. Inst., vol. 12, pp. 145-146 (1909). 
 
ALPHABETICAL LIST OF AUTHORS.- 879 
 
 LANG, O. 
 
 Titanhaltige Magneteisenerze.--AStaW u. Eisen, vol. 20, pp. 377-382 (1900). 
 LARSSEN, PER. 
 
 The Chapin Iron Mine, Lake Superior. Trans. A. I. M. E., vol. 16, pp. 
 
 119-129(1887-1888). 
 LAUR, M. 
 
 1. Du Giaement et de Texploitation de Tor en Californie. Ann. d. Mines, 
 ser. 6, vol. 3., pp. 347-435 (1863). 
 
 2. Les Bauxites dans le Monde. Compt. rend. Acad. Sci., pp. 94-104,432- 
 461 (1908). 
 
 LAURENT. 
 
 1. Notes sur 1' Industrie de 1'or et du Platine dans 1'Oural. Ann. d. Mines, 
 
 ser. 8, vol. 18, pp. 537-579 (1890). 
 LAWSON, A. C. 
 
 1. The Post-Pleistocene Diastrophism of the Coast of Southern California. 
 Bull Dept. Geol, Univ. CW.,vol. 1, No. 4, pp. 115-160 (1893). 
 
 2. The Copper Deposits of the Robinson Mining District, Nevada. Bull. Dept. 
 Geol, Univ. Col., vol. 4, No. 14, pp. 287-357 (1906). 
 
 LECKIE, R. G. 
 
 On the Nickel Deposits of Norway. Jour. Can. Min. Inst., vol. 7 (1904). 
 
 9pp. 
 LE CONTE, JOSEPH. 
 
 1. Elements of Geology (Edited by H. L. Fairchild, New l r ork,1904). 649pp. 
 
 2. On Mineral Vein Formation in Progress at Steamboat Springs. Am. Jour. 
 Sci., 3d ser., vol. 25, pp. 424-428 (1883). 
 
 3. Genesis of Metalliferous Veins. Am. Jour. Sci., 3d ser., vol. 26, pp. 1-19 
 (1883). 
 
 4. Discussion of Posepny' s Paper, " The Genesis of Ore-Deposits." Trans. 
 A. I. M. E., vol. 24, pp. 942-1006 (1894). 
 
 5. Origin of Jointed Structure in Undisturbed Clay and Marl Deposits. Am. 
 Jour. Sci., ser. 3, vol. 23, pp. 233-234 (1882). 
 
 6. The Old River Beds of California. Am. Jour. Sci.', 3d ser., vol. 19, pp. 
 176-190 (1880). 
 
 LE CONTE, JOSEPH, and RISING, W. B. 
 
 The Phenomena of Metalliferous Vein Formation now in Progress at Sulphur 
 
 Bank, Cal.Am. Jour. Sci., 3d ser., vol. 24, pp. 23-33 (July, 1882) ; vol. 
 
 25, pp. 424-428 (June, 1883). 
 LEITH, C. K. 
 
 1. The Mesabi Iron-Bearing District of Minnesota. Mon. 43, U. S. G. S. 
 (1903). 316 pp. 
 
 2. A Summary of Lake Superior Geology, with Special Reference to Recent 
 Studies of the Iron- Bearing Series. Trans. A. L M. E., vol. 36, pp. 101- 
 154 (1905). 
 
 3. Rock Cleavage. Bull, 239, U. S. G. S., 153pp. (1905). 
 
 4. Genesis of the Lake Superior Iron Ores. Econ. Geol, vol. 1, pp. 47-65 
 (1906). 
 
 5. The Geology of the Cuyuna Iron Range, Minnesota. Econ. Geol, vol. 2, 
 pp. 145-152 (1907). 
 
 6. The Iron Ores of Canada. Can. Min. Jour., vol. 29. pp. 370-374 (1908.) 
 
 7. The Iron Ores of Canada. Econ. Geol, vol. 3, 276-291 (1908). 
 
 8. Iron Ores of Iron Springs, Utah. Answer to Review by J. F. Kemp on 
 contact metamorphism. Econ. Geol, vol. 5, pp. 188-192 (1910). 
 
 LEITH, C. K., and HARDER, E. C. . 
 
 The Iron Ores of the Iron Springs District, Southern Utah. Bull. 338, U. S. 
 
 G. S. 102pp. (1908). 
 LENHER, VICTOR. 
 
 Some Observations on the Tellurides. Econ. Geol, vol. 4, pp. 544-564 (1909)' 
 LEONARD, A. G. 
 
 1. Origin of the Iowa Lead and Zinc Deposits. Am. Geol, vol. 16, pp. 288- 
 294 (1895). 
 
 2. Lead and Zinc Deposits of Iowa. Iowa Geol Sur., vol. 6,*pp. 11-66 (1897). 
 
880 ALPHABETICAL LIST OF AUTHORS. 
 
 LEV AT, DAVID. 
 
 1. L' Industrie Aurif ere (Paris, 1905). 878pp. 
 
 2. L'or en Siberie orientale (Paris, 1904). 2 vols., 670 pp. 
 LEVAT, M. D. 
 
 Bassin cuprifSre du Kovilou-Niari Congo fran9ais. Ann. d. Mines, 10th ser., 
 
 vol. 11, pp. 5-65 (1907). 
 LINCOLN, F. C. 
 
 1. Magmatic Emanations. Econ. GeoL, vol. 2, pp. 258-274 (1907). 
 
 2. Certain Natural Associations of Gold. Econ. GeoL, vol. 6, pp. 247-302 
 (1911.). 
 
 3. Gold Ores of Washington and Oregon. E. and M. Jour., vol. 92, pp. 13- 
 15 (1911). 
 
 4. Some Gold Deposits of the Northwest. E. and M. Jour., vol. 92, pp. 
 408-410 (1911). 
 
 LINDGREN, WALDEMAR. 
 
 1. The Silver Mines of Calico, California. Trans. A. L M. E.. vol. 15, pp. 
 717-734 (1887). 
 
 2. Two Neocene Rivers of California. Bull. GeoL Soc. Am., vol. 4, pp. 257- 
 298 (1893). 
 
 3. Gold-silver Mines of Ophir, California. 14th Ann. Rept., U. S. G. S., 
 Part 2, pp. 243-284 (1894). 
 
 4. The Auriferous Veins of Meadow Lake, California. Am. Jour. Sci., 3d 
 ser., vol. 46, pp. 201-206 (1893). 
 
 5. An Auriferous Conglomerate of Jurassic Age from the Sierra Nevada. 
 Am. Jour. Sci., 3d ser., vol. 48, pp. 275-280 (1894). 
 
 6. Geological Atlas of the U. S. Sacramento Folio (No. 5) (1894). 
 
 7. Characteristic Features of California Gold-Quartz Veins. Bull. GeoL Soc. 
 Am., vol. 6, pp. 221-240 (1895). 
 
 8. The Gold-quartz Veins of Nevada City and Grass Valley Districts, Cali- 
 fornia. llth Ann. Rept., U. S. G. S., Part 2, pp. 1-262 (1896). 
 
 9. The Mining Districts of the Idaho Basin and the Boise Ridge, Idaho. 
 ISth Ann. Rept., U. S. G. S., Part 3, pp. 617-744 (1897). 
 
 10. Orthoclase as Gangue Mineral in a Fissure Vein. Am. Jour. Sci., 4th 
 ser., yol. 5, p. 418 (1898). 
 
 11. The Gold and Silver Veins of Silver City, De Lamar, and other Mining 
 Districts in Idaho. 20th Ann. Rept., U. S. G. S., part 3, pp. 65-256 (1899). 
 
 12. Metasomatic Processes in Fissure Veins. Trans. A. I. M. E., vol. 30, 
 pp. 578-692 (1900). (Also Special Volume, "Genesis of Ore-Deposits," 
 pp. 498-612, 1902). 
 
 13. The Gold Belt of the Blue Mountains of Oregon. 22d Ann. Rept., U. S. 
 G. S., part 2, pp. 551-776 (1901). 
 
 14. The Character and Genesis of Certain Contact-Deposits. Trans. A. L M- 
 E., vol. 31, pp. 226-244 (1901). 
 
 15. Tests for Gold and Silver in Shales from Western Kansas. Bull. 202, U. 
 S. G. S. 21pp. (1902). 
 
 16. The Geological Features of the Gold Production of North America. 
 Trans. A. I. M. E., vol. 33, pp. 790 845 (1902). 
 
 17. Characteristics of the Gold Quartz Veins in Victoria. E. and M. Jour., 
 vol. 79, p. 458 (1905). 
 
 18. Neocene Eivers of the Sierra Nevada. Bull. 213, U. S. G. S., pp. 64-65 
 (1903). 
 
 19. The Genesis of the Copper Deposits of Clifton-Morenci, Arizona. Trans. 
 A. I. M. E., vol. 35, pp. 511-551 (1904). 
 
 20a. The Copper Deposits of the Clifton-Morenci District, Arizona. Prof. 
 Paper 43,' U. S. G. S. (1905). 395 pp. 
 
 20. A Geological Reconnaissance across the Bitterroot Range and the Clear- 
 water Mountains in Montana and Idaho. Prof. Paper 27, U. S. G. S. 
 (1904). 123pp. 
 
 21. The Occurrence of Stibnite at Steamboat Springs, Nevada. Trans. A. L 
 M. E., vol. 36, pp. 27-31 (1905). 
 
 22. Occurrence of Albite in the Bendigo Veins. Econ. GeoL, vol. 1, pp. 163- 
 166 (1906). 
 
 23. Metasomatic Processes in the Gold Deposits of Western Australia. Econ. 
 GeoL, vol. 1. pp. 530-544 (1906). 
 
 24. Ore-Deposition and Deep Mining. Ebon. GeoL, vol. 1, pp. 34-46 (1906). 
 
ALPHABETICAL LIST OF AUTHORS. 881 
 
 LINDGREN, WALDEMAR. Continued. 
 
 25. The Gold Deposits of the Dahlonega (Ga. ) Mines. Bull. 293, U. S. G. 
 S., pp. 119-128 (1906). 
 
 26. The Relation of Ore- Deposition to Physical Conditions. Econ. GeoL, 
 vol. 2, pp. 105-127 (1907). 
 
 27. Present Tendencies in the Study of Ore-Deposits. Econ. GeoL, vol. 2, 
 pp. 743-762 (1907). 
 
 28. Metallogenetic Epochs. Can. Min. Jour., vol. 30, pp. 430-434 (1909). 
 
 29. Metallogenetic Epochs. Econ. GeoL, vol. 4, pp. 409-420 (1909). 
 
 30. The Localization of Values in Ore-Bodies and the Occurrence of Shoots 
 in Metalliferous Deposits. Econ. GeoL, vol. 4, pp. 56-61 (1909). 
 
 31. The Hot Springs at Ojo Caliente and Their Deposits. Econ. GeoL, vol. 
 5, pp. 22-27 (1910.) 
 
 32. Some Modes of Deposition of Copper Ores in Basic Rocks. Econ. GeoL , 
 vol. 6, pp. 687-700 (1911). 
 
 33. The Nature of Replacement. Econ. GeoL, vol. 7, pp. 521-535 (1912). 
 
 34. The Tertiary Gravels of the Sierra Nevada, California. Prof. Paper 73, 
 U. S. G. S. (1911). 
 
 35. Geologic Introduction to the Mining Districts of the Western U. S. BulL 
 507, U. S. G. S., pp. 1-43 (1912). 
 
 36. Chemistry of Copper Deposits.^, and M. Jour., vol. 79, p. 189 (1905). 
 LINDGREN, W., GRATON, L. C., and GORDON, C. H. 
 
 The Ore Deposits of New Mexico. Prof. Paper 68, U. S. G. S. (1910). 
 
 361 pp. 
 LINDGREN, WALDEMAR. and DRAKE, N. F. 
 
 Nampa Folio, Idaho-Oregon. Atlas of the U. S., Folio 103, U. S. G. S. 
 (1904). 
 LINDGREN, WALDEMAR, and KNOWLTON, F. H. 
 
 The Age of Auriferous Gravels of the Sierra Nevada, with a Report of the 
 
 Flora of Independence Hill. Jour. GeoL, vol. 4, pp. 881-906 (1896). 
 LINDGREN, WALDEMAR, and RANSOME, F. L. 
 
 1. The Geological Resurvey of the Cripple Creek District, Colorado. BulL 
 260, U. S. G. S., pp. 85-98 (1905). 
 
 2. The Geology and Gold Deposits of the Cripple Creek District, Colorado. 
 Prof. Paper 54, U. S. G. S. (1906). 516 pp. 
 
 LINDOREN, WALDEMAR, and TURNER, H. W. 
 
 Geological Atlas of the U. S.Placerville Folio (No. 3) (1894). 
 LITSCHAUER, L. 
 
 Die Vertheilung der Erze in den Lagerstatten der metallischen Mineralien. 
 Zeit.f.prak. GeoL, vol. 1, pp. 174-182 (1893). 
 
 LlVERSIDGE, A. 
 
 1. On the Formation of Moss Gold and Large Nuggets. Proc. Roy. Soc.. t 
 N. S. W., vol. 27, p. 287 (1893) ; Rev. in Zeit. f. prak. GeoL, vol. 2, pp. 401- 
 402(1894). 
 
 2. The Origin of Gold Nuggets. Austr. Min. Stand., vol. 13, pp. 2554-2557 
 (1897). 
 
 3. Gold Nuggets from New Guinea Showing a Concentric Structure. Jour, and 
 Proc. of Roy. Soc. N. S. W., vol. 40, p. 161 (1906). 
 
 4. Gold in Sea \Vater. Proc. Roy. Soc. N. S. W., vol. 29, pp. 335-350 (1895). 
 
 5. Distribution of Silver. Jour. Am. Chem. Soc., vol. 71, p. 298 (1897). 
 LOCK, A. G. 
 
 Gold (London, 1882). (Bibliography.) 
 LODIN. 
 
 Origine de certains Gites de Blende et de Calamine. Compt. rend. Soc. de Vind. 
 
 mm., pp. 210-215 (1905). 
 LOEWINSON-LESSING, F. 
 
 1. Uber die Magneteisenerzlagerstatte des Berges Blagodatj in Ural. GeoL 
 Zentralb., vol. 12, p. 170 (1909). 
 
 2. Uber den Fundort des Magneteisensteins im Berge Wvssokaja im Ural. 
 GeoL Zentralb., vol. 12, p. 480 (1909). 
 
 LOR AM, S. H. 
 
 Notes on the Gold District of Canutillo, Chile, S. A. Trans. A. L M. E., vol. 
 35, pp. 696-711 (1904). 
 
882 ALPHABETICAL LIST OF AUTHORS. 
 
 LOSSEN, K. A. 
 
 Uber ein durch Zufall in einer Fensterscheibe enstandenes Torsion^paltenritz. 
 
 Jahrb. d. Kgl. Pr. Geol. Landesanst., p. 336 (1886). 
 LOTTI, B. 
 
 1. La ge"nese des giseraents cupriferes des depots ophiolitiques tertiares de 
 1' Italic. Bull. Soc. Beige de GeoL, vol. 3 (18b9). 
 
 2. I Deposit! dei Minerali Metalliferi (Torino, 1903). 150 pp. 
 
 3. Die Zinnober und Antimon fuhrenden Lagerstatten Toscanas und ihre 
 Beziehungen zu den quartiiren Eruptivgesteinen. Zeit.f. prak. Geol.. vol. 9. 
 pp. 41-46 (1901V 
 
 4. Geologische Verhaltnisse und Genesis der Zinnoberlagerstatte von Corte- 
 vecchia am Monte Amiata. ei<. /. prak. GeoL, vol. 11, pp. 423-427 (1903). 
 
 5. Die geologischen Verhaltnisse der Therraalquellen im toscanischen Erzge- 
 birge (Catena Metallifera). Zeit. f. prak. GeoL, vol. 1, pp. 372-378 (1893). 
 
 LOTTNER, E. H. , and SERLO, A. 
 
 Leitfaden zur Bergbaukunde (Berlin, 1869-1872. Also 1878). 
 Louis, HENRY. 
 
 1. On the Mode of Occurrence of Gold. Mineralog. Mag. (London), vol. 20,- 
 No. 47, p. 241 (1893). 
 
 2. The Allotropism of Gold. Trans. A. I. M. E.,vo\. 24, pp. 182-186 (1894). 
 
 3. Grundsatze der Classification der Minerallagerstatten. Zeit. f. prak. GeoL, 
 vol. 8, pp. 275-278 (1900). 
 
 4. The Occurrence and Treatment of Platinum in Kussia. Min. Ind., vol. 
 6, pp. 539-552 (1898). 
 
 LOVEMAN, H. M. 
 
 Geology of the Miami Copper Mine. Min. and Sci. Press, vol. 105, pp. 146- 
 148 (1912). 
 
 LOVEWELL, J. T. 
 
 Gold in Kansas Shales. Trans. Kans. Acad. Sci., vol. 18, pp. 129-137 (1903). 
 LUNGWITZ, E. E. 
 
 1. Uber die Kegionalen Veranderungen der Golderzlagerstatten. Thesis, 
 Leipzig (1899). 
 
 2. Der geologische Zusammenhang von Vegetation und Goldlagerstatten. 
 Zeit.f. prak. GeoL, vol. 8, pp. 71-74 (1900). 
 
 LYMAN, B. 8. 
 
 Geology of the Low Moor, Virginia, Iron-Ores. Trans. A. I. M. E., vol. 14, 
 pp. 801-809 (1886). 
 
 MABSON, R. E. 
 
 Mines of the Transvaal (London, 1906). 776 pp. 
 MAC A LISTER, D. A. 
 
 1. Vertical Distribution of the Commercially Valuable Ores of Tin in the 
 Camborne Lodes. Geol. Sar. Gt. Brit. (1903). 
 
 2. Geological Aspect of the Lodes of Cornwall. Econ. GeoL, vol. 3, pp. 363- 
 380 (1908). 
 
 MACALISTER, D. A., and HILL, J. B. 
 
 The Geology of Falmouth and Trnro, and of the Mining Districts Camborne 
 and Redruth. GeoL Sur. Eng. and Wales (1906). 335 pp. 
 
 MCCALLTE, S. W. 
 
 1. The Iron Ores of Georgia. Butt. IOA, GeoL Sur. Ga. (1900). 190 pp. 
 
 2. Fossil Iron Ores of Georgia. Bull. 17, GeoL Sar. Ga. (1908). 199 pp. 
 MCCARTY, E. T. 
 
 Mining in the Wollastonite Ore-Deposits of the Santa Fe Mine, Chiapas, 
 Mexico. Trans. Inst. Min. and Met., vol. 4, pp. 169-189 (1895-1896). 
 
 McCONNELL, K. G. 
 
 1. .Report on Gold Values in the Klondike High Level Gravels. Can. GeoL 
 Sur., Bull. 979 (1907). 34 pp. 
 
 2. The White Horse Copper Belt, Yukon Territory. Can. Geol. Sur., Bull 
 1,050 (1909). 63 pp. 
 
 3. Klondike District, Yukon Territory. Can. GeoL Sur., Ann. Rept., vol. 15 
 (1903) ; Summ. Rept., pt. A A, pp. 34-42 (1904). 
 
ALPHABETICAL LIST OF AUTHORS. 883 
 
 MCDONNELL. R. G. Continued. 
 
 4. Report on the Klondike Gold Fields. Can. OeoL Sur., Ann. Rept., vol. 
 
 14, pt. B. 71 pp. (1905). 
 
 5. The Kluana Mining District. Can. Geol. Sur., Ann. Rept., vol. 16 (1904); 
 Summ. Rept., pt. A, pp. 1-18 (1905). 
 
 McCREATH, A. S. 
 
 The Iron Ores of the Valley of Virginia. Tram. A. I. M. E., vol. 12, pp. 
 17-26 (1886). 
 
 MACDONALD, D. F. 
 
 Notes on the Gold Lodes of the Carrville District, Trinity County, Califor- 
 nia. JS^/. 530, U. S. G. S. (1912). 37 pp. 
 
 MACFARLANE, THOMAS. 
 
 Silver Islet. Trans. A. I. M. E., vol. 8, pp. 226-254 (1879). 
 
 MADDREN, A. G. 
 
 The Ruby Placer District, Alaska. Butt. 520, U. S. G. S. (1912). 14 pp. 
 
 McGEE, W. J. 
 
 Note on Jointed Structure. Am. Jour. Sci., 3d ser., vol. 25, pp. 152-153 
 (1883). 
 
 MACKELLAR, PETER. 
 
 The Gold-Bearing Veins of Bag Bay, near Lake of the Woods. Tram. A. I. 
 M. E., vol. 29, pp. 104-115 (1899). 
 
 MACLAREN, J. M. 
 
 1. The Occurrence of Gold in Great Britain and Ireland. Trans. lust. Min. 
 Eng., vol. 25, pp. 4/5-508 (1902-03). 
 
 2. Gold: Its Geological Occurrence and Geographical Distribution. Pub. 
 by The Mining Journal. London, 1908. Reviewed by Ransome in Econ. 
 Geol., vol. 4, pp. 391-396 (1909). 
 
 MADDREN, A. G. 
 
 The Innoko Gold- Placer District, Alaska. Bull. 410, U. S. G. S. (1910). 
 
 87pp. 
 MALCOLMSON, J. W. 
 
 The Sierra Mojada, Coahuila, Mexico and Its Ore- Deposits. Trans. A. I. M. 
 
 E., vol. 32, pp. 100-140 (1901). 
 MALLET, J. W. 
 
 On the Occurrence of Silver in the Volcanic Ashes from the Eruption of Cota- 
 paxi of July 22 and 23. Proc. Roy. Soc., vol. 42; also Chem. News, vol. 
 55, p. 17 (1881). 
 MALLERY, W. 
 
 Native Gold in Igneous Rocks. E. and M. Jour., vol. 77, p. 596 (1904). 
 MAYNARD, G. W. 
 
 The Chromite Deposits on Port au Port Bay, Newfoundland. Trans. A. I. M. 
 
 E., vol. 27, pp. 283-288 (1897). 
 MEAD, W. J. 
 
 The Relation of Densitv, Porosity, and Moisture to the Specific Volume of 
 
 Ores. Econ. Geol., vol. 3, pp. 319-325 (1908). 
 MELL, P. H., JR. 
 
 Auriferous Slate Deposits of the Southern Mining Region. Trans. A. I. M. 
 
 E., vol. 9, pp. 399-402 (1881). 
 MENDENHALL, W. C. 
 
 1. Reconnaissance from Fort Hamlin to Kotzebue Sound, Alaska. Prof. 
 Paper 10, U. S. G. S. (1902). 68pp. 
 
 2. A Reconnaissance in the Norton Bay Region, Alaska, in 1900. Special 
 Publication, U.S. G. S. (1901). 
 
 3. Geology of the Central Copper River Region, Alaska. Prof. Paper 41, 
 U. S. G. S. (1906). 133 pp. 
 
 4. The Chistochina Gold Field, Alaska. Bull. 213, U. S. G. S., pp. 71- 
 75 (1903). 
 
 5. A Phase of Ground Water Problems in the West. Econ. Geol., vol. 4, pp. 
 35-45 (1909). 
 
 MENDENHALL, W. C., and SCHRADER, F. C. 
 
 The Mineral Resources of the Mount Wrangell District, Alaska. Prof. Paper 
 
 15, U. S. G. S. (1903). 71 pp. 
 
884 ALPHABETICAL LIST OF AUTHORS. 
 
 MERENSKY, HANS. 
 
 1. Neue Zinnerzvorkommen in Transvaal. Zeit. f. prak. Geol., vol. 12, pp. 
 409-411 (1904). 
 
 2. Die goldfiihrenden Erzvorkommen der Murchison Range im Nordostlichen 
 Transvaal. Zeit. f. prak. Geol, vol. 13, pp. 258-261 (1905) ; also Trans. 
 GeoL Soc. So. Af., vol. 8, pp. 42-46 (1905). 
 
 3. The Kocks belonging to the Area of the Buschveldt Complex in which 
 Tin may be Expected. Trans. Geol. Soc. So. Af., vol. 11 (1908). 
 
 MERRILL, G. P. 
 
 1. An Occurrence of Free Gold in Granite. Am. Jour. Sci., 4th ser., vol. 1, 
 pp. 309-311 (1896). 
 
 2. The Non- Metallic Minerals, Their Occurrence and Uses. Wiley and Son 
 (1904). 414pp. 
 
 MERRITT, W. H. 
 
 The Occurrence of Gold-Ore in the Rainy River District, Ontario, Canada. 
 Trans. A. I. M. E., vol. 26, pp. 853-863 (1896). 
 
 MlETZSCHKE, W. 
 
 tiber das Verhalten des Guides in Pyriten bei deren Verwitterung. Bery. 
 
 u. Hutt. Zeit., vol. 55, p. 193 (1896). 
 MILLER, A. M. 
 
 The Lead and Zinc-Bearing Rocks of Central Kentucky, with Notes on the 
 
 Mineral Veins. Bull. 2, Geol. Sur. Ky. (1905). 35 pp. 
 MILLER, W. G. 
 
 1. The Cobalt-Nickel Arsenides and Silver Deposits of Temiskaming. Rept. 
 Out. Bu. Mines, vol. 16, Part 11 (1907). 212 pp. 
 
 2. Notes on the Cobalt Area. E. and M. Jour., vol. 92, pp. 645-649 
 (1911). 
 
 MlRON, F. 
 
 Gisements miniers; stratification et composition (Paris, 1903). 192 pp. 
 MITCHELL, D. P. 
 
 The Peculiar Ore-Deposit of the East Murchison United Gold-Mine, Western 
 
 Australia. Trans. A. I. M. E., vol. 29, pp. 556-562 (1899). 
 MOFFIT, F. H. 
 
 1. Fairhaven Gold Placers, Seward Peninsula, Alaska. Bull. 247, U. S. G. 
 S. (1905). 85pp. 
 
 2. The Kotzebue Placer Gold Field of Seward Peninsula, Alaska. Bull. 
 225, U. S. G. S., pp. 74-80 (1904). 
 
 3. The Nome Region, [Alaska]. Bull. 314, U. S. G. S., pp. 126-145 
 (1907). 
 
 4. The lower Copper River Basin, Alaska. Bull. 520, U. S. G. S. (1912). 
 19 pp. 
 
 5. Headwater Regions of Gulkana and Susitna Rivers, Alaska. Bull. 498, 
 U. S. G. S. (1912). 82 pp. 
 
 MOFFIT, F. H., and KNOPF, ADOLPH. 
 
 Mineral Resources of the Nabesna- White River District, Alaska. Bull. 417, 
 
 U. S. G. S. (1910). 64 pp. 
 MOFFIT, F. H., and MADDREN, A. G. 
 
 Mineral Resources of the Kotsina-Chitina Region, Alaska. Bull. 374, U. S. 
 G. S. (1909). 103 pp. 
 
 MOISSENET, L. 
 
 Observations on the Rich Parts of the Lodes of Cornwall ; their Form and 
 their Relations with the Directions of the Stratigraphic Systems (London, 
 
 1877). 
 
 M5NCH. 
 
 tiber die elektrische Leitfahigkeit von Kupfer sulphur, Silber, Blei, und 
 Schwarzen Quecksilbersulphid. Neues Jahrb. f. Min., vol. 20, pp. 365-435 
 (1905). 
 MONTGOMERY, A. 
 
 Some Geological Considerations Affecting Western Australian Ore Deposits. 
 Trans. Aust. Tnst. Min. Eng., vol. 13, pp. 160-193 (1909). 
 
ALPHABETICAL LIST OF AUTHORS. 885 
 
 MOORE, CHARLES, 
 
 Keport on Mineral Veins in Carboniferous Limestone, and their Organic 
 
 Contents. Rept. of Brit. Assoc. Adv. Sci., 1869, p. 360, et seq. 
 MOREAU, GEORGE. 
 
 Etude Industrielle des Gites Metalliferes (Paris, 1894). 453 pp. 
 MORGAN, P. G. 
 
 The Geology of the Greymouth Subdivision, No. Westland. Bull. 13 (New 
 
 Ser.), Geol. Sur. Branch N. Z. Dept. of Mines (1911). 159 pp. 
 DE MORGAN. 
 
 1. Note sur la geologic et sur P Industrie miniere du royaume de Perak et des 
 pays voisins Ann. d. Mines, 8th ser., vol. 9, pp. 368-442 (1886). 
 
 M5RICKE, W. 
 
 1. Betrachtungen und Beobachtungen iiber die Entstehung von Goldlager- 
 statten. Zeit. f. prak. GeoL, vol. 1, pp. 143-148 (1893). 
 
 2. Uber edle Silbererzgiinge in Verbindung mit basischen Eruptivgesteinen. 
 Zeit. f. prak. GeoL, vol. 3, pp. 4-10 (1895). 
 
 MOROZEWICZ, J. 
 
 1. Die Eisenerzlagerstatten des Magnetberges im siidlichen Ural und ihre 
 Genesis. Tscher. Min. u. Pet. Mitt., vol. 23, pp. 113-152 ; 225-262 (1904). 
 
 2. Experimentalle Untersuchungen iiber die Bildung der Minerale im Mag- 
 ma. Tscher. Min. u. Pet. Mitt, vol. 18, pp. 1-90, 105-238 (1899). 
 
 MORRIS, H. C. 
 
 Hydro-Thermal Activity in the Veins of Wedekind, Nevada. E. and M. 
 'Jour., vol. 76, pp. 275-276 (1903). 
 
 MOULAN, PH. 
 
 Origin et Formation des Minerals de Fer (Bruxelles, 1904). 14S pp. 
 
 MULLER, A. 
 
 1. Erzgange (Basel, 1880). 
 
 2. Uber die Erzlagerstatten der umgegend von Berggiesshubel (Leipzig, 1890). 
 
 3. Uber die Beziehung zwischen Mineralquellen und Erzgiingen im Nord- 
 lichen Bohmen und in Sachsen ; von Cotta's Gangstudien, III. (Freiberg, 
 1869). 
 
 MULLER, H. 
 
 1. Beitrage zur Kentniss der Mineralquellen und Stollenwtisser Freiberger 
 Gruben. Jahrb. f. Berg-u. Hutt. in Konig. Sachs. (1885). 
 
 2. Die Erzgange des Freiberges Bergreviers (Leipzig, 1901). 350 pp. 
 
 3. Erzlagerstatten bei Freiberg, Cotta's Gangstudien, 1850, vol. 1, pp. 209-248 
 (1850). 
 
 MUNROE, H. S. 
 
 List of Books on Mining. Sch. Min. Quar., vol. 10, pp. 176-184 (1889). 
 MUNSTER, HERMANN. 
 
 Die Brauneisenerzlagerstiitten des Seen- undOhmtals am Nord rand des Vogels- 
 gebirges. Zeit. f. prak. GeoL, vol. 13, pp. 242-258 (1905). 
 
 MURCHISON, R. I. 
 
 General View of the Conditions under which Gold is Distributed. Quar. Jour. 
 GeoL Soc., vol. 8, pp. 134-136 (1852). 
 
 NASON, F. L. 
 
 1. Iron Ores of Missouri. GeoL Sur. of Missouri, vol. 2, pp. 1-365 (1892). 
 
 2. The Franklinite- Deposits of Mine Hill, Sussex County, New Jersey. 
 Trans. A. I. M. E., vol. 24, pp. 121-130 (1894). 
 
 3. The Geological Structure of the Eingwood Iron Mines, New Jersey. 
 Trans. A. I. M. E., vol. 24, pp. 505-521 (1894). 
 
 4. Some Phenomena of the Folding of Rock Strata. Econ. GeoL, vol. 4, pp. 
 421-437 (1909). 
 
 NAUMANN, C. F. 
 
 Lehrbuch der Geognosie, Bd. III., Lief 3. (Unvollendet) (1872). 
 NAVARRO, L. F. 
 
 Mas sob re la teoria de la sustitucion en Almaden. Act. Soc. EspaHola d. Hist. 
 
 Nat., vol. 3, 2d series (1894). 
 NECKER, A. L. 
 
 On the Sublimation Theory. Proc. GeoL Soc. London, vol. 1, p. 392 (1826-33). 
 
886 ALPHABETICAL LIST OF AUTHORS. 
 
 NEUNIER, S. 
 
 Geologic Experiment ale (Paris, 1904). 321 pp. 
 NEWBERRY, J. S. 
 
 1. Report on the Property of the Stormont Silver Mining Company, No. 30, 
 1880 ; No. 21, 1881. 
 
 2. The Genesis of our Iron Ores. E. and M. Jour., vol. 31, pp. 286-287; 
 298-300 (1881). 
 
 3. Genesis and Distribution of Gold. E. and M. Jour. , vol. 32, pp. 416- 
 417, 433 (1881). 
 
 4. The Origin and Classification of Ore-Deposits. Sch. Min. Quar., vol. 1, 
 pp. 87-104 (1880). Also E. and M. Jour. , vol. 29, pp. 421-422, 437-438 (1880). 
 
 5. The Origin and Classification of Ore- Deposits. Proc. Am. Assoc. Adv. Sci., 
 vol. 32, p. 243 (1883). 
 
 6. The Deposition of Ores. E. and M. Jour., vol. 38, pp. 38-40 (1884). 
 
 NEWBIGIN, H. T. 
 
 1. The Siliceous Iron Ores of Northern Norway. Trans. Inst. Min. Eng., vol. 
 
 15, pp. 154-171 (1897-98). 
 NEWLAND, D. H. 
 
 1. Tin. Min. Ind., vol. 12, pp. 325-339 (1904). 
 
 2. On the Association and Origin of the Nontitaniferous Magnetites in the 
 Adirondack Region. Econ. Geol., vol. 2, pp. 763-773 (1907). 
 
 3. The Clinton Iron Ore Deposits in New York State. Trans. A. I. M. E., 
 vol. 40, pp. 165-184 (1909). 
 
 NEWLAND, D. H., and HARTNAGEL, C. A. 
 
 Iron Ores of the Clinton Formation in New York State. Bull. 123, New 
 
 York State Miiseum (1908). 76 pp. 
 NEWLAND, D. H., and KEMP, J. F. 
 
 Geology of the Adirondack Magnetic Iron Ores. Bull. 119, New York State 
 Museum (1908). 184 pp. 
 
 NICHOLAS, WM. 
 
 The Origin of Gold in Certain Victorian Quartz Reefs. E. and M. Jour. , 
 
 vol. 36, pp. 367-368 (1883). 
 NICHOLS, H. W., and FARRINGTON, O. C. 
 
 The Ores of Colombia. Field Col. Mus. Pub. No. 33, Geol. ser., vol. 1, No. 3 
 
 (1899). 
 NITZE, H. B. C. 
 
 1. Notes on Some of the Magnetites of Southwestern Virginia and the Con- 
 tiguous Territory of North Carolina. Trans. A. I. M. E., vol. 20, pp. 
 174-188 (1891). 
 
 2. The Magnetic Iron-Ores of Ashe County, North Carolina. Trans. A. I. 
 M. E., vol. 21, pp. 260-280 (1892). 
 
 3. Monazite. 16th Ann. Rept., U. S. G. S., part 4, pp. 667-693 (1895). 
 
 4. Iron Ores of North Carolina. Bull 1, No. Car. Geol. Sur. (1893). 239pp. 
 
 5. Monazite and Monazite Deposits in North Carolina. (Bibliography.) 
 Bull. 9, No. Car. Geol. Sur. (1895). 47pp. 
 
 NITZE, H. B. C., and HANNA, G. B. 
 
 Gold Deposits of North Carolina. Bull. 3,No. Car. Geol. Sur. (1896). 200 pp. 
 NITZE, H. B. C., and PURINGTON, C. W. 
 
 The Kotchkar Gold-Mines, Ural Mountains, Russia. Trans. A. I. M. E., vol. 
 
 28, pp. 24-33 (1898). 
 NITZE, H. B. C., and WILKENS, H. A. J. 
 
 The Present Condition of Gold-Mining in the Southern Appalachian States. 
 Trans. A. I. M. E., vol. 25, pp. 661-796 (1895). 
 
 NOVARESE, V. 
 
 Die Erzlagerstatten von Brosso and Traversella in Piemont. Zeit. f. prak. 
 Geol, vol. 10, pp. 179-187 (1902). 
 
 OCHSENITTS, CARL. 
 
 1. tiber unterirdische Wasseransammlungen. Zeit. f. prak. Geol., vol. 1, 
 pp. 36-40 (1893). 
 
 2. Sikin als Bildner von Erzlagerstatten. Zeit. d. D. Geol. GeseL, vol. 57, 
 p. 567 (1905). 
 
ALPHABETICAL LIST OF AUTHORS. 887 
 
 ORDONEZ, E. 
 
 1. Note sur les gisements d'or du Mexique (Mexico, 1898). 
 
 2. Les filons Argentiferes de Pachuca. Bull. Soc. Geol. de France, vol. 26, 
 pp. 244-258 (1898). 
 
 3. The Mining District of Pachuca, Mexico, Trans. A. I. M. E.,vol. 32 
 pp. 224-241 (1901). 
 
 4. A. Brief Review of the Mining Industry of Mexico. Econ. Geol , vol. 3, pp. 
 677-687 (1908). 
 
 ORDONEZ, E., and AGUILERA, J. G. 
 
 Bosquejo geologico de Mexico. Bol. Inst. Geol. Mex., Nos. 4, 5, 6, pp. 
 
 68-222 (1897). 
 ORTON, E. 
 
 The Trenton Limestone as a Source of Petroleum and Natural Gas in Ohio 
 
 and Indiana. 8th Ann. Rept., U. S. G. S., Pt. 2, pp. 483-662 (1889). 
 O' HARRA, 
 
 The Mineral Wealth of the Black Hills. Bull 3, Geol. Sur. S. Dakota (1902). 
 136 pp. 
 
 PACKARD, R. L. 
 
 Genesis of Nickel Ores. Min. Res., U. S. G. S., pp. 170-177 (1893). 
 VON PALFY, M. 
 
 Das Goldvorkommen im Siebenbiirgischen Erzgebirge und sein Verhaltnis 
 zum Nebengestein der Giinge. Zeit. f. prak. Geol., vol. 15, pp. 144-148 
 (1907). 
 PAGE, DAVID. 
 
 Economic Geology (London, 1874). 336 pp. 
 PAIGE, SIDNEY. 
 
 Mineral Resources of the Llano-Burnet Region, Texas, with an account of 
 
 the Pre-Cambrian Geology. Bull. 450, U. S. G. S., p. 103 (1911). 
 PAIGE, S., EMMONS, W. H., and LANEY, F. B. 
 
 Copper. Bull. 470, U. S. G. S. (1911). 47 pp. 
 PALMER, C. 
 
 The Geochemical Interpretation of Water Analyses. Bull. 479, U. S. G. S. 
 (1911). 31pp. 
 
 PARK, JAMES. 
 
 1. The Geology and Veins of the Hauraki Gold Fields, New Zealand. N* 
 Z. Inst. Min. Eng. (1897). 105 pp. 
 
 2. On the Cause of Border Segregation in Some Igneous Magmas. Trans. 
 Inst. Min. and Met, vol. 14, pp. 537-541 (1904-1905). 
 
 3. Ore Deposits in Relation to Thermal Activity. E. and M. Jour., vol. 79, 
 pp. 606-607 (1905). 
 
 4. A Text-Book of Mining Geologv (London, 1906). 219 pp. 
 
 5. Magmatic Segregation in its Relation to the Genesis of Certain Ore-Bodies. 
 Trans. N. Z. Inst. Min. Eng., vol. 38 ; algo N. Z. Mines Rec., vol. 9, pp. 
 414-416 (1906). 
 
 6: Contact Metamorphism in its Relation to the Genesis of Certain Ore-De- 
 
 rits. Trans. N. Z. Inst. Min. Eng., vol. 38 ; also N. Z. Mines Rec., vol. 
 yp. 476-477 (1906). 
 
 7. Thermal Activity in its Relation to the Genesis of Certain Metalliferous 
 Veins. Trans. N. Z. Inst. Min. Eng., vol. 38; also N. Z. Mines Rec., vol. 
 
 . 9, pp. 512-515 ; vol. 10, pp. 59-62 (1906). 
 
 8. Some Principles of Concentration in River-Bed Gravels. Min. Jour., 
 vol. 84, pp. 145-146 (1908). 
 
 PARSONS, H. G. 
 
 A Handbook to Western Australia and its Goldfields (London, 1894). 
 PASLEY, C. S. 
 
 The Tin Mines of Bolivia. Trans. Inst. Min. and Met., vol. 7, pp. 77-90 
 
 (1908). 
 PATERA. 
 
 Zu den Beraerkungen Sandbergers iiber die Resultate der Untersuchungen 
 von Nebengestein der Pribramer Erzgiinge. Verhand. Geol. Reichsanst., pp. 
 86-88 (1888). 
 
888 ALPHABETICAL LIST OF AUTHORS. 
 
 PEARCE, KICHARD. 
 
 1. On Replacement of Walls. Chem. News, vol. ii., pp. 100-101 (1865). 
 
 2. Farther Notes on Cripple Creek Ore. Proc. Col. Sci. Soc.., vol. 5, pp. 11- 
 16 (1894-1896). 
 
 3. The Association of Gold with Other Minerals in the West. Trans. A. L 
 M. E., vol. 18, pp. 447-458 (1890). 
 
 PEARCE. 
 
 Nomenclature of Shoots. Proc. Aust. Inst. Min. Eng. (July, 1909). 
 PENROSE, K. A. F., JR. 
 
 1. Manganese ; Its Uses, Ores, and Deposits. Ark. Geol Sur. Ann. Rept. 
 for 1890, vol. 1. (1892). 642pp. 
 
 2. The Superficial Alteration of Ore Deposits. Jour. Geol, vol. 2. pp. 288- 
 317 (1894). 
 
 3. Tin Deposits of the Malay Peninsula. Jour. Geol, vol. 11, pp. 135-154 
 (1903). 
 
 4. Some Causes of Ore Shoots. Econ. Geol, vol. 5, pp. 97-133 (1910). 
 PENROSE, K., and CROSS, W. 
 
 Geology and Mining Industries of Cripple Creek District, Colo. 17th Ann. 
 
 Rept., U. S. G. S., Pt. 2, pp. 263-403 (1896). 
 PHALEN, W. C. 
 
 1. Origin and Occurrence of Certain Iron Ores of Northeastern Kentucky. 
 Econ. Geol., vol. 1, pp. 660-669 (1906). 
 
 2. Potash Occurrence of Potash Salts in the Bitterns of the Eastern United 
 States. Butt. 530, U. S. G. S. (1911). 19 pp. 
 
 PHILLIPS, J. A. 
 
 1. The Rocks of the Mining Districts of Cornwall and Their Relation to Met- 
 alliferous Deposits. Quar. Jour. Geol. Soc., vol. 31, pp. 319-345 (1875). 
 
 2. A Contribution to the History of Mineral Veins. Quar. Jour. Geol. Soc., 
 vol. 35, pp. 390-396 (1879). 
 
 3. Connection of Certain Phenomena with the Origin of Mineral Veins. 
 Phil. Mag., 4th ser., vol. 42, pp. 401-413 (1871). 
 
 4. Notes on the Chemical Geology of the Gold-Fields of California. Phil. 
 Mag., 4th ser., vol. 36, p. 321 (1868). 
 
 5. A Treatise on Ore Deposits (London, 1884). 
 PHILLIPS, J. A., and Louis, HENRY. 
 
 A Treatise on Ore Deposits, 2nd edition (London, 1896). 943 pp. 
 PILZ, RICHARD. 
 
 Die Bleierzlagerstatten von Mazarron in Spanien. Zeil f. prak. Geol., vol. 13, 
 pp. 385-409 (1905). 
 
 PlRSSON, L. V. 
 
 Rocks and Rock Minerals. Wiley and Son (1908). 414 pp. 
 PITTMAN, E. F. 
 
 1. On the Geological Occurrence of the Broken Hill Ore Deposits. Geol. 
 Sur. N. S. W., vol. 3, Part 2 (1892). 
 
 2. Tin Deposits of New South Wales. Geol. Sur. N. S. W. (1889). 
 PORTER, E. A., and ELLSWORTH, C. E. 
 
 Mining and Water Supply of Fortymile, Seventymile, Circle and Fairbanks 
 
 Districts, Alaska, 1911. Bull. 520, U. S. G. S. (1912). 63 pp. 
 POSEPNY, FRANZ. 
 
 1. The Genesis of Ore Deposits. American Institute of Mining Engineers. 806 
 pages. Special Volume. (Contains other papers also. ) (1902.) 
 
 2. The Genesis of Ore Deposits. Trans. A. L M. E., vol. 23, pp. 197-369 
 (1893). 
 
 3. Reply to the Discussion of No. 2, by Becker, Emmons, et al. Trans. A. I. 
 M. E., vol. 24, pp. 962-980 (1894). 
 
 4. Uber die Entstehung von Blei, und Zinklagerstatten in aufloslichen Ge- 
 steinen. Zeit. f. prak. Geol., vol. 1, pp. 398-401 (1893). 
 
 5. Tiber die Bewegungsrichtung der Untererdischen Zirkullerenden Fliissig- 
 keiten. Compt. rend, de la 3, sess. du Congres Intern. (Berlin, 1885). 
 
 6. Die Golddistrikte von Berezov und Mias am Ural. Archiv f. prak. Geol, 
 vol. 2, pp. 499-598 (1895). 
 
ALPHABETICAL LIST OF AUTHORS. 889 
 
 POSEPNY, FRANZ. Continued. 
 
 7. Zur Genesis der Metalseifen. Ost. Zeit. f. Berg- u. Hutt., vol. 35, p. 325 
 (1887). 
 
 8. Die Goldvorkommen Bohmens und der Nachbarlander. Archiv f. prak. 
 Geol,, vol. 2, pp. 1-499 (1895). 
 
 9. Setzt das Gold in die Tiefe? Ost. Zeit. f. Berg- u. Hutt., vol. 15, p. 169 
 (1867). 
 
 POSEWITZ. 
 
 1. Die Zinninseln im Indischen Ozeane. Mittheilungen der Kaiserlich ungarish 
 
 geologischen Anstalt, vol. 7, pp. 155-182 (1885) ; vol. 8, pp. 59-106 (1886). 
 POWER, F. D. 
 
 The Classification of Valuable Mineral Deposits. Trans. Aust. Inst. Min. 
 
 Eng. (1892). 
 PRATT, J. H. 
 
 1. The Occurrence, Origin and Chemical Composition of Chrormte, with 
 Especial Reference to the North Carolina Deposits. Trans. A. I. M. E., 
 vol. '29, pp. 17-39 (1899). 
 
 2. Separation of Alumina from Molten Magmas, and the Formation of Corun- 
 dum. Am. Jour. Sci., 4th ser., vol. 8, pp. 227-231 (1899). 
 
 3. On the Origin of Corundum associated with the Peridotites in North Caro- 
 lina. Am. Jour. Sci., 4th ser., vol. 6, pp. 49-65 (1898). 
 
 4. Corundum and Its Occurrence and Distribution in the United States. 
 Bull. 269, U. S. G. S. (1906). 
 
 PRATT, J. H., and STERRETT, D. B. 
 
 The Tin Deposits of the Carolinas. Bull. 19, No. Car. Geol. Sur. (1904). 
 
 64pp. 
 PRESCOTT, BASIL. 
 
 The Occurrence and Genesis of the Magnetite Ores of Shasta County, Califor- 
 nia. Econ. Geol, vol. 3, pp. 465-480 (1908). 
 PRESTWICH, JOSEPH. 
 
 Chemical, Physical and Stratigraphical Geology (Oxford, 1886). 
 PRICHARD, W. A. 
 
 Observations on Mother Lode Gold-Deposits, California. Trans. A. I. M. E., 
 
 vol. 34, pp. 454-466 (1903). 
 PRIME, FREDERICK, JR. 
 
 On the Occurrence of the Brown Hematite Deposits of the Great Valley. 
 
 Trans. A. I. M. E. } vol. 3, pp. 410-422 (1875). 
 PRINDLE, L. M. 
 
 1. The Gold Placers of the Fortymile, Birch Creek, and Fairbanks Regions, 
 Alaska. Bull. 251, U. S. G. S. (1905). 89 pp. 
 
 2. The Yukon-Xanana Region, Alaska. Bull. 295, U. S. G. S. (1906). 
 27 pp. 
 
 3. The Fortymile Quadrangle, Yukon-Tanana Region, Alaska. Bull. 375, 
 U. S. G. S. (1909). 52pp. 
 
 PRINDLE, L. M., and HESS, F. L. 
 
 1. The Rampart Gold Placer Region, Alaska. Butt. 280, U. S. G. S. (1906). 
 54 pp. 
 
 2. The Fairbanks and Rampart Quadrangles, Yukon-Tanana Region, Alaska. 
 With a Section on the Rampart Placers. Bull. 337, U. S. G. S. (1908). 
 102 pp. 
 
 PRINDLE, L. M., and KATZ, F. J. 
 
 The Fairbanks Gold Placer Region, Alaska. B M. 379, U. S. G. S., pp. 
 
 181-200 (1903). 
 PRINDLE, L. M., and MERTIE, J. B., JR. 
 
 Gold Placers between Woodchopper and Fourth of July Creeks, Upper Yukon 
 
 Valley, Alaska. Bull. 520, U. S. G. S. (1912). 12 pp. 
 PUMPELLY, RAPHAEL. 
 
 1. Metasomatic Development of the Copper-Bearing Rocks of Lake Superior. 
 Proc. Am. Acad. Arts and Sci. , 1877-1878, vol. 13, pp. 253-310 (1878). 
 
 2. The Paragenesis and Derivation of Copper and its Associates on Lake Supe- 
 rior. Am. Jour. Sci., 3d ser., vol. 2, p. 33 (1891). 
 
 3. Ore Deposits. Johnson's Encyclopaedia. Edition of 1877, vol. 3, pp. 974- 
 981. 
 
 56 
 
890 ALPHABETICAL LIST OF AUTHORS. 
 
 PURINGTON, C. W. 
 
 1. Preliminary Report on the Mining Industries of the Telluride Quadrangle^ 
 Colorado. ISth Ann. Eept., U. S. G. S., part 3, pp. 745-848 (1897). 
 
 2. The Platinum-Deposits of the Tura River-System, Ural Mountains, Rus- 
 sia. Trans'. A. I. M. E., vol. 29, pp. 3-16 (1899). 
 
 3. Observations on Gold Deposits. E. and M. Jour., vol. 75, pp. 854-855; 
 893-894; 929-931 (1903). 
 
 4. The Occurrence of Platinum in the Ural Mts. E. and M. Jour., vol. 77, 
 pp. 720-722 (1904). 
 
 5. Ore Horizons in the Veins of the San Juan Mountains. Econ. GeoL, vol. 
 1, pp. 129-133 (1906). 
 
 6. Methods and Costs of Gravel and Placer Mining in Alaska. Bull. 263, U. 
 S. G. S. (1905). 273 pp. 
 
 7. The Camp Bird and Smuggler Union Fissure (Colorado). E. and M. 
 Jour., vol. 79, pp. 1243-1244 (1905). 
 
 PURINGTON, C. W., WOODS, T. H., and DOVETON. G. D. 
 
 The Camp Bird Mine, Ouray, Colorado, and the Mining and Milling of the 
 Ore. Trans. A. I. M. E., vol. 33, pp. 499-550 (1902). 
 
 QUENEAU, A. L. 
 
 The Gold Sands of Cape Nome [Alaska]. Eng. Mag., vol. 23, pp. 497-510 
 (1902). 
 
 RADFORD, G. K. 
 
 Mining for Gold in the Auriferous Gravels of California, U. S. A. Trans. 
 
 Inst. Min. Eng., vol. 17, pp. 452-481 (1898-99). 
 RAINER. 
 
 Vorkommen und Gewinnung des platins im Ural. Leoben Jahrbuch, L., pp. 
 
 255-298 (1902). 
 RAKLI, GEORGES. 
 
 1. The Lead Mines of Balia, Turkey. E. and M. Jour., vol. 77, p. 274 (1904). 
 RANGEL, VILLARELLO and BOSE. 
 
 Los Criaderos de fierre del cerro Mercado, Durango, Mexico. Bol. 16, Inst. 
 
 GeoL de Mex. (1902). 
 KANSOME, F. L. 
 
 1. A Peculiar Clastic Dike near Ouray, and its Associated Deposit of Silver 
 Ore. Trans. A. L M. E., vol. 30, pp. 227-236 (1900). 
 
 la. Geological Atlas of the U. S. Mother Lode Special Folio, No. 63 (1900). 
 
 2. A Report on the Economic Geology of the Silverton Quadrangle, Colorado. 
 Bull. 182, U. S. G. S. (1901). 265 pp. 
 
 3. The Ore Deposits of the Rico Mountains, Colorado. 22d Ann. Rept., U. 
 S. G. S., part 2, pp. 229-397 (1901). 
 
 4. The Geology and Copper Deposits of Bisbee, Arizona. Trans. A. I M. E., 
 vol. 34, pp. 618-642 (1903). 
 
 5. Geology of the Globe Copper District, Arizona. Prof. Paper 12, 17. S. 
 G. S. (1903). 168 pp. 
 
 6. Geology and Ore Deposits of the Bisbee Quadrangle, Arizona. Prof. 
 Paper 21, U. S. G. S. (1904). 168 pp. 
 
 7. The Geographic Distribution of Metalliferous Ores within the United 
 States. Min. Mag. (J], vol. 10, pp. 7-14 (1904). 
 
 8. The Directions of Movement and the Nomenclature of Faults. Econ. 
 GeoL, vol. 1, pp. 773-783 (1906). 
 
 9. The As'sociation of Alunite with Gold in the Goldfield District, Nevada. 
 Econ. GeoL, vol. 2, pp. 667-692 (1907). 
 
 10. Preliminary Account of Goldfield. Bullfrog, and other Mining Districts 
 in Southern "Nevada. Bull. 303, U. S. G. S., pp. 7-83 (1907). 
 
 11. The Relation between Certain Ore-Bearing Veins and Gangue-Filled Fis- 
 sures. Econ. GeoL, vol. 3, pp. 331-337 (1908). 
 
 12. A Theory of Ore Deposition. Econ. GeoL, vol. 3, pp. 420-425 (1908). 
 
 13. Notes on some Mining Districts in Humboldt County, Nevada. Bull. 414, 
 U. S. G. S. (1909). 75pp. 
 
ALPHABETICAL LIST OF AUTHORS. 891 
 
 RANSOME, F. L. Continued. 
 
 14. The Geology and Ore Deposits of Goldfield, Nevada. Prof. Paper 66, 
 U. S. G. S. (1909). 258 pp. 
 
 15. Criteria of Downward Sulphide Enrichment. Econ. GeoL, vol. 5, pp. 
 205-220 (1910). 
 
 16. Geology and Ore Deposits of the Goldfield District, Nevada. Econ. GeoL, 
 vol. 5, pp. 301-311 ; 438-470 (1910). 
 
 17. The Literature of Ore-deposits in 1910. Econ. GeoL, vol. 6, pp. 325-339 
 (1911). 
 
 18. Geology and Ore Deposits of the Breckenridge District, Colorado. Prof. 
 Paper 75, U. S. G. S. (1911). 187 pp. 
 
 19. The Turquoise Copper Mining District, Arizona. Bull. 530, U. S. G. S. 
 (1912). 12pp. 
 
 RANSOME, F. L. , and CALKINS, F. C. 
 
 The Geology and Ore Deposits of the Coaur d'Al^ne District, Idaho. Prof. 
 
 Paper 62, U. S. G. S. (1908). 203 pp. , 
 RANSOME, F. L., EMMONS, W. H., and GARREY, G. H. 
 
 Geology and Ore Deposits of the Bullfrog District, Nevada. Bulletin 407, 
 
 U. S. G. S. (1910). 130pp. 
 RAYMOND, R. W. 
 
 1. Mining Statistics for 1869. 
 
 2. Mineral Resources West of the Rocky Mts. Report of the Mining Commis- 
 sioner, 1870-1876. 7 volumes. 
 
 3. The Geographical Distribution of Mining Districts in the United States. 
 Trans. A. I. M. E., vol. 1, pp. 33-39 (1871-73). 
 
 4. Hoefer's Method of Determining Faults in Mineral Veins. Trans. A. I. 
 M. E., vol. 10, pp. 456-465 (1882). 
 
 5. A New Classification of Economic Geological Deposits. E. and M. Jour., 
 vol. 58, pp. 412-413 (1894). 
 
 6. Recent Contributions to the Science of Ore-Deposits. (A general review 
 of progress, chiefly of historical value). Min. Ind., vol. 9, pp. 753-762 
 (1900). 
 
 READ, T. T. 
 
 1. The Phase Rule and Conceptions of Igneous Magmas. Their Bearing on 
 Ore Deposition. Econ. GeoL, vol. 1, pp. 101-118 (1906). 
 
 2. The Secondary Enrichment of Copper-Iron Sulphides. Trans. A. L M. 
 E., vol. 37, pp. 297-303 (1906). 
 
 RECKNAGEL, R. 
 
 On the Origin of the South African Tin Deposits.-- Trans. GeoL Soc. So. 
 
 Af., vol. 12, pp. 168-202 (1909). 
 REDLICH, K. A. 
 
 1. Sedimenlaire ou Epigenetique ? Contribution a la connaissance des Gites 
 M6tallifres des Alps orientales. Congres Int. des Mines (1905). 9 pp. 
 
 2. Die Genesis der Pinolit-ma:nesite, Siderite und Ankerite der Ostalpen. 
 Tscher. Min. u. Pet. Mitt., vol. 26. 
 
 REID, J. A. 
 
 1. The Structure and Genesis of the Comstock Lode. Bull. Dept. GeoL, Univ. 
 CaL, vol. 4, pp. 177-199 (1905). 
 
 2. A Sketch of the Geology and Ore Deposits of the Cherry Creek District, 
 Arizona. Econ. GeoL, vol. 1, pp. 417-436 (1906). 
 
 3. The Ore-Deposits of Copperopolis, Calaveras County, California. Econ. 
 GeoL, vol. 2, pp. 380-417 (1907). 
 
 4. Discussion of Ransome 8. Econ. GeoL, vol. 2, pp. 298-308 (1907). 
 REID, H. F. 
 
 Proposed Nomenclature of Faults. Advance Bull. G. S. A. (May, 1912). 
 
 17pp. 
 REYER. E. 
 
 1. Theoretische Geologic (1888). 
 
 2. Zinn (Berlin, 1881). 248 pp. 
 
 3. Zinn in Australien und Tasmanien. Ost. Zeit. f. Berg- u. Hiitt., vol. 28, 
 pp. 47-49, 61-63, 74-76, 85-87 (1880). 
 
 VON RlCHTOFEN, F. 
 
 Studien an den ungarisch-siebenbiirgischen Trachytgebirgen. Jahrb. der 
 K. K. GeoL Reichsanst,, p. 275 (1860). 
 
892 ALPHABETICAL LIST OF AUTHORS. 
 
 EICKARD, EDGAR. 
 
 Tin Deposits of the York Kegion, Alaska. E. and M. Jour., vol. 75, pp. 
 
 30-31 (1903). 
 EICKARD, FORBES. 
 
 1. Notes on the Vein-Formation and Mining of Gil pin County, Colorado. 
 Trans. A. L M. E., vol. 28, pp. 108-126 (1898). 
 
 2. Notes on Nome, and the Outlook for Vein-Mining in the District (Alaska). 
 E.-and M. Jour., vol. 71, pp. 275-276 (1901), 
 
 EICKARD, T. A. 
 
 1. The Mount Morgan Mine, Queensland. Trans. A. I. M. E., vol. 20, pp. 
 133-155 (1891). 
 
 2. The Bendigo Gold-Field. Trans. A. I. M. E., vol. 20, pp. 463-545 (1891). 
 
 3. The Gold Fields of Otago. Tram*. A. L M. E., vol. 21, pp. 411-442 
 (1893). 
 
 4. The Bendigo Gold-Field (Second Paper) ; Ore Deposits other than Sad- 
 dles. Trans. A. L M. E., vol. 21, pp. 686-713 (1893). 
 
 5. The Origin of the Gold-Bearing Quartz of the Bendigo Eeefs, Australia. 
 Trans. A. L M. E. } vol. 22, pp. 289-321 (1893). 
 
 6. The Mines of the Chalanches, France. Trans. A. L M. E., vol. 24, pp. 
 689--705 (1894). 
 
 7. The Genesis of Ore-Deposits (Discussion of Posepny's Paper). Trans. 
 A. L M. E., vol. 24, pp. 942-956 (1894). 
 
 8. Vein- Walls. Trans. A. L M. R, vol. 26, pp. 193-242 (1896). 
 
 9. The Enterprise Mine, Eico, Colorado. Trans. A. L M. E., vol. 26, pp. 
 906-980 (1896. 
 
 10. The Minerals which Accompany Gold and their Bearing upon the Eieh- 
 ness of Ore Deposits. Trans. Inst. Min. and Met., vol. 6, pp. 194-214 
 (1898). 
 
 11. The Alluvial Deposits of Western Australia. Trans. A. L M. E., vol. 28, 
 pp. 490-537 (1898). 
 
 12. The Telluride Ores of Cripple Creek and Kalgoorlie. Trans. A. I. M. E., 
 vol. 30, pp. 708-719 (1900). 
 
 13. The Indicator Vein, Ballarat, Australia. Trans. A. L M. E., vol. 30, 
 pp. 1004-1020 (1900). 
 
 14. The Formation of Bonanzas in the Upper Portions of Gold-Veins. 
 Trans. A. I. M. E., vol. 31, pp. 198-220 (1901). 
 
 15. The Lodes of Cripple Creek. Trans. A. L M. E., vol. 33, pp. 578-618 
 (1902). 
 
 16. The Veins of Boulder and Kalgoorlie. Trans. A. L M. E., vol. 33, pp. 
 567-577 (1902).' 
 
 17. Eecent Progress in the Study of Ore Deposits. E. and M. Jour., vol. 73, 
 pp. 106-107 (1902). 
 
 18. The Copper Mines of Lake Superior (1905). 164 pp. 
 
 19. The Geological Distribution of Gold. Min. andSci. Press, vol. 93, pp. 477- 
 480 (1906); Mines and Minerals, vol. 27, pp. 256-257 (1907); Rept. Proc. 
 Am. Min. Cong., 9th Ann. Sess., pp. 226-283 (1907). 
 
 20. Waters, Meteoric and Magmatic. Min. and Sci. Press., vol. 96, pp. 872- 
 875 (1908). 
 
 21. Geological Distribution of the Precious Metals in Colorado, 1. Min. and 
 Sci, Press., vol. 100, pp. 89-96 (1910). 
 
 EICKARD, T. A., et al. 
 
 1. Ore Deposits: A Discussion. E. and M. Jour. (1903). 90pp. 
 
 2. Water in Veins : A Theory. E. and M. Jour., vol. 75, pp. 402-403, 589- 
 590, 624, 661, 776, 848 ; vol. 76, p. 117 (1903). 
 
 ElCKETTS, L. D. 
 
 Faulting in Veins. E. and M. Jour., vol. 53, pp. 565-566 (1892). 
 EIES, HEINRICH. 
 
 Economic Geology with Special Eeference to the United States. Eevised 
 ed. (New York, 1910). 589 pp. 
 
 ElMANN, E. 
 
 Magmatische Ausscheidung von Zinkblende in Granit. Zeit. f. prak. Geol., 
 vol. 18, pp. 123-124 (1910). 
 
ALPHABETICAL LIST OF AUTHORS. 893 
 
 HITTER, E. A. 
 
 1. The Evergreen Copper-Deposit, Colorado. Trans. A. I. M. E., vol. 38, 
 pp. 751-766 (1907). 
 
 2. Ore Formation in the Wonder District, Nevada. E. and M. Jour., vol. 
 87, pp. 289-292 (1909). 
 
 ROBERTSON, J. D. 
 
 The Missouri Lead and Zinc Deposits. Am. GeoL, vol. 15, pp. 235-248 (1895). 
 
 R5LKER, C. M. 
 
 1. The Alluvial Tin Deposits of Siak, Sumatra. Trans. A. I. M. E., vol. 20, 
 pp. 50-84 (1892). 
 
 2. The vSilver Sandstone District of Utah. Trans. A. I. M. E., vol. 9, pp. 
 21-33 (1880). 
 
 3. Note on an Exhibition of Banded Structure in a Gold- Vein. Trans. A. I. 
 M. E., vol. 14, pp. 265-266 (1885). 
 
 ROLLIER, L. 
 
 liber das Bohnerz und seine Entstehungsweise. Verh. d. Naturf. Geo., Zurich, 
 
 1905, pp. 150-162 ; Abstract Stahl und Eisen, vol. 25, p. 1270 (1905). 
 ROSE. 
 
 Reise nach dem Ural, vol. 1, pp. 325-338 (1837) ; vol. 2, pp. 386-401 (1842). 
 
 ROSENBUSCH, H. 
 
 Uber die chemische Beziehungen der Eruptivgesteine. Tscher. Min. u. Pet. 
 Mitt., vol. 11, pp. 144-178 (1890). 
 
 ROTHWELL, R. P. , 
 
 The Silver Sandstone Formation of Silver Reef. E. and M. Jour., vol. 29, 
 
 pp. 25, 48, 79 (1880). 
 ROTH, J. 
 
 Allgemeine und Chemische Geologic (1879). 
 RUHL, OTTO.. 
 
 Unconformity and Deposits. Min. and Sci. Press, vol. 96, pp. 778-780 
 (1908). 
 
 RUMBOLD, W. R. 
 
 1. The Origin of the Bolivian Tin Deposits. Econ. GeoL, vol. 4, pp. 321- 
 364 (1909). 
 
 2. The Tin Deposits of the Kinta Valley, Federated Malay States. Trans. 
 A. I. M. E., vol. 37, pp. 879-889 (1906). 
 
 RUSSELL, I. C. 
 
 A Geological Reconpaisance in Southern Oregon. kth Ann. Rept., U. S. G. S., 
 1882-83, pp. 431-464 (1884). 
 
 RUTLEDGE, J. J. 
 
 The Clinton Iron Ore Deposits in Stone Valley, Huntingdon County, Penn- 
 sylvania. Trans. A. I. M. E., vol. 40, pp. 134-164 (1909). 
 RUTTMAN, F. S. 
 
 Notes on the Geology of the Tilly Foster Ore- Body, Putnam County, N. Y. 
 
 Trans. A. 1. M. E., vol. 15, pp. 79-92 (1886). 
 RYBA, FRANZ. 
 
 Beitrag zur Genesis der Chromeisenerzlagerstatte bei Kraubat in Obersteier- 
 mark. Zeit. f. prak. GeoL, vol. 8, pp. 337-341 (1900). 
 
 SALES, R. H. 
 
 1. Superficial Alteration of the Butte Veins. Econ. GeoL, vol. 5, pp. 15-21 
 (1910). 
 
 2. Ore shoots at Butte, Montana. Econ. GeoL, vol. 3, pp. 326-331 (1908). 
 SAMUELS, L. A. 
 
 Origin of the Bendigo Saddle Reefs (Bendigo, 1893). 40 pp. 
 SANDBERGER, F. 
 
 1. Zur Theorie der Bildung der Erzgiinge. Berg- u. Hiltt. Zeit., vol. 36, pp. 
 377-381, 389-392 (1877). 
 
 2. Uber die Bildung von Erzgiingen mittelst auslaugung des Nebengesteins. 
 Berg- u. Hiitt. Zeit., vol. 39, pp. 329-331, 337-339, 390-392. 402-405 
 (1880). 
 
 3. Untersuchungen uber Erzgange. 2 vol. (1883-1885). Abstract in E. 
 and M. Jour., vol. 37, pp. 196-198, 218-219, 232-233 (1884). 
 
894 ALPHABETICAL LIST OF AUTHORS. 
 
 SANDBERGER, F. Continued. 
 
 4. Neue Beweise fur die Abstammung der Erze aus dem Xebengestein. Ver- 
 
 hand. der Wiirz. Phys. Med. Gesel., 1883 ; Neu.es Jahrb. f. Min., p. 291 (1878). 
 
 5. Theories of the Formation of Mineral Veins. E. and M. Jour., vol. 37, 
 
 pp. 196-198, 218-219, 232-233 (1884). 
 6. Untersuchungen an den Erzgangen von Pribram in Bohmen. Sitz. d. 
 
 Wiirz. Phys. Med. Gesel. (18-6). 
 SANDEMAN. 
 
 The Mineral Kesources of Tasmania. Trans. Fed. Inst. Min. Enq., vol. 18, 
 
 pp. 24-41 (1899-1900). 
 SASS, C. 
 
 Beobachtungen von Schwankungen des Grundvvassers. Zeit. f. prak. Geol.. 
 
 pp. 297-300 (1901). 
 SAWYER. 
 
 The Tarcquah Goldfield, Gold Coast, West Africa. Trans. Fed. Inst. Min. 
 
 Eng.,voL 22, pp. 402-417 (1901-02). 
 SAYTZEFF, A. 
 
 Die Platinlagerstatten am Ural. Tomsk, 1898. Abstract in Zeit. f. prak. 
 Geol., vol. 6, pp. 395-398 (1898). 
 
 SCHAEFFER, C. A. 
 
 Notes on Tantalite and other Minerals, accompanying the Tin-Ore in the 
 Black Hills. Trans. A. I. M. E., vol. 13, pp. 231-233 (1884). 
 
 SCHARTTZER, E. 
 
 Beitrage zur Kenntniss der chemigchen Kon^stitution und der Genese der 
 naturlichen Eisensulfate. Zeit. f. Krist., vol. 43, pp. 113-129 (1907). 
 
 SCHEERER, TH. 
 
 Die Gneuse des Sachsischen Erzegebirges und verwandte Gesteine, uach 
 ihrer chemischen Konstitution und Geologischen Bedeutung. Zeit. d. D. 
 Geol. Gesel., vol. 14. pp. 23, et seq. (1862). 
 SCHIERL, A. 
 
 Einteilung der Erzlagerstatten und kurze Darstellung der Theorien iiber die 
 Entstehung von Erzgangen. 22 Jahr. d. Landes-Oberrealschule in Mahr. 
 Ostrau, 1904-05, pp. 3-13. 
 SCHMEISSER, KARL. 
 
 The Gold Fields of Australasia (London, 1898). 254 pp. 
 SCHMIDT, ALBRECHT. 
 
 Uber Kupfer und die Entstehung der Kupfererze. Sera- u. Hiltt. JRund., pp. 
 
 85-90 (1910). 
 SCHMIDT, J. C. L. 
 
 Theorie der Verschiebung Alterer Gange (Frankfurt, 1910). 
 SCHMIDT and PREISWERK. 
 
 Les Mines de Fer et de Cuivre de Cala. Rev. Univ. d. Mines, 4th ser., vol. 11, 
 p. 217 (1905). 
 
 SCHMITZ, E. J. 
 
 Copper-Ores in the Permian of Texas. Trans. A. I. M. E., vol. 26, pp. 97- 
 
 108 (1897). 
 SCHOCH, E. R. 
 
 The Genesis of the Tarkwa Banket. E. and M. Jour., vol. 79, pp. 1235-1236 
 
 (1905). 
 
 SCHRADER, F. C. 
 
 1. Notes on the Antelope District, Nevada. Bull. 530, U. S. G. S. (1912). 
 14 pp. 
 
 2. A Reconnaissance of the Jarbidge Contact and Elk Mountain Mining Dis- 
 tricts, Elko County, Nevada. Bw//. 497, U. S. G. S. (1912). 162 pp. 
 
 SCHRADER, F. C., and BROOKS, A. H. 
 
 1. Preliminary Report on the Cape Nome Gold Region, Alaska. U. S. G. S. 
 (1900). 56 pp. 
 
 2. Some Notes of the Nome Gold Region of Alaska. Trans. A. I. M. E., vol. 
 30, pp. 236-248 (1900). 
 
 SCHRADER, F. C., and HAWORTH, ERASMUS. 
 
 Economic Geology of the Independence Quadrangle, Kansas. Bull. 296, 
 U. S G. S. (19U6). 74 pp. 
 
ALPHABETICAL LIST OF AUTHORS. 895 
 
 SCHRADER, F. C., and SPENCER, A. C. 
 
 The Geology and Mineral Resources of a Portion of the Copper River District, 
 Alaska. U. S. G. S., Special Reports on Alaska (1901). 94 pp. 
 
 SCHRAUF, A. 
 
 Uber Metacinnabarit von Idria und dessen Paragenesis. Jahr. d. K, K. Geol. 
 Reichsanst., vol. 41, pp. 349-400 (1891). 
 
 SCHROEDER. 
 
 Uber Zinnerzgange des Eibenstocker Granitgebiets und die Entstehung der~ 
 selben. Sitzungsberichte der naturhistorischen Gesellschofi zu Leipzig (1883). 
 Rev. Neues Jahrb. f. Min., vol. 1, p. 268 (1887). 
 
 SCHURTZ. 
 
 Der Seifenbergbau in Erzgebirge und die Walensagen (1890). ( Cited by Ber- 
 
 geat-Stelzner, p. 1289.) 
 SCHWA RZ, T. E. 
 
 1. The Ore- Deposits of Red Mountain, Ouray County, Colorado. Trans. A. 
 I. M. E., vol. 18, pp. 139-145 (1889). 
 
 2. Features of the Occurrence of Ore at Red Mountain, Ouray, Colorado. 
 Trans. A. I. M. E., vol. 36, pp. 31-39 (1905). 
 
 SCOTT, H. K. 
 
 1. The Manganese Ores of Brazil. Jour. Iron and. Steel Imt., vol. 57, pp. 
 179-218 (1900). 
 
 2. The Gold Field of the State of Minus Geraes, Brazil. TVa MX. A. I. M. E., 
 vol. 33, pp. 406-444 (1902). 
 
 SCRIVENOR, J. H. 
 
 The Origin of Tin Deposits. Min. Jour., vol. 85, pp. 307, 340 (1909). 
 SERLO, ALBERT. 
 
 Leitfaden zur Bergbaukunde. Dritte Aufl., vol. 1 (Berlin, 1878). 
 SHARPLES, S. P. 
 
 Note on Black Band Iron Ore in West Virginia. Trans. A. 7. M. E., vol. 
 
 10, pp. 80-81 (1&82. 
 SHARWOOD, W. J. 
 
 Notes on Tellurium-bearing Gold Ores. Econ. Geol., vol. 6, pp. 22-36 (1911). 
 
 SIMPSON, J. F. 
 
 The Relation of Copper to Pyrite in the Lean Copper Ores of Butte, Mon- 
 tana. Ecvn. Geol., vol. 3, pp. 628-63(3 (1908). 
 
 SlNOEWALD, J. T., JR. 
 
 1. The Erzgebirge Tin Deposits. Econ. Geol, vol. 5, pp. 166-177, 265-272 
 (1910). 
 
 2. The Mount Roudny Gold Deposits. Econ. Geol., vol. 5, pp. 257-264 
 (1910). 
 
 SJOGREN, A. 
 
 Om forekomstren af Tabergs jernmalmsfindighet i Smaland. Geol. Fb'ren. 
 
 Fohr., vol. 3, pp. 42-62 (1876-7). Rev. in Neues Jahrb. f. Min., pp. 434- 
 
 435 (1876). 
 SJOGREN, HJALMAR. 
 
 1. Beitrage zur kentnissder Erzlagerstatten von Moraviczaund Dognaeska ira 
 Banat und Vergleichung derselben mit den Schwedischen Eisenerzlager- 
 stlitten. Jahrb. d. K. K. Geol. Reichsanst., vol. 36, pp. 607-668 (1886). 
 
 2. Uber die Entstehung der schwedischen Eisenerzlager. Geol. For. i 
 Stock. Forhand., vol. 13, p. 373 et seq. (1891) ; Rev. in Zeit. f. prak. Geol., 
 vol. 1, pp. 434-437 (1893). 
 
 3. The Geological Relations of the Scandinavian Iron-Ores Trans. A. I. M. 
 E., vol. 38, pp. 766-835 (1907). Rev. by Leith in Econ. Geol, vol. 3, pp. 
 658-661 (1908). 
 
 4 The Localization of Values in Ore Bodies and the Occurrence of Shoots in 
 
 Metalliferous Deposits. Econ. Geol., vol. 3, pp 637-643 (1908). 
 SKEWES, EDWARD. 
 
 The Ore-Shoots of Cripple Creek. Trans. A. I. M. E., vol. 26, pp. 553-579 
 (1896). 
 
896 ALPHABETICAL LIST OF AUTHORS. 
 
 SLIGHTER, C. S. 
 
 1. Theoretical Investigation of the Motion of Ground- Waters. 19th Ann. 
 Rept., U. S. G. S., Part 2, pp. 295-384 (1899). 
 
 2. The Motions of Underground Waters. Prof. Paper 67, U. S. G. S., Water 
 Supply and Irrigation (1902). 106 pp. 
 
 SMITH, A. M. 
 
 Geology of the Kolar Gold Field. Trans. Inst. Min. and Met, vol. 13, pp. 
 
 151-180 (1903-1904). 
 SMITH, F. C. 
 
 1. The Potsdam Gold-Ores of the Black Hills of South Dakota. Trans. A. L 
 M. E., vol. 27, pp. 404-428 (1897). 
 
 2. Localization of Values in Ore Bodies and Occurrence of "Shoots" in 
 Metalliferous Deposits. Econ. Geol., vol. 3, pp. 224-229 (1908). 
 
 SMITH, GEORGE. 
 
 1. The Ore-Deposits of the Australian Broken Hill Consols Mine, Broken 
 Hill, New South Wales. Trans. A. I. M. E., vol. 26, pp. 69-78 (1896). 
 
 2. The Garnet Formations of the Chillagoe Copper-Field, North Queensland, 
 Australia. Trans. A. I. M. E., vol. 34, pp. 467-478 (1903). 
 
 SMITH, G. O. 
 
 Gold Mining in Central Washington. Bull. 213, U. S. G. S., pp. 76-80 
 
 (1903). 
 SMITH, G. O., and WILLIS, BAILEY. 
 
 The Clealum Iron-Ores, Washington. Trans. A. I. M. E., vol. 30, pp. 356-367 
 
 (1900). 
 SMITH, P. S. 
 
 1. The Gray Iron Ores of Talladega County, Alabama. Bull. 315, U. S. G.S., 
 pp. 161-184 (1908). 
 
 2. The Alatna-Noatak Region, Alaska. Bull. 520, U. S. G. S. (1912). 
 12pp. 
 
 SMITH, P. S., and EAKIN, H. M. 
 
 A Geologic Reconnaissance in Southeastern Seward Peninsula and the Norton 
 
 Bay-Nulato Eegion, Alaska. Bull. 449, U. S. G. S. (1911). 146 pp. 
 SMITH, W. N. 
 
 Loon Lake Iron-Bearing District. Rept. Ont. Bu. Mines, vol. 14, Pt. 1, pp. 
 
 254-260 (1905). 
 SMITH, W. S. T., and SIEBENTHAL, C. E. 
 
 Description of the Joplin District [Missouri-Kansas]. Folio 148, U. S. G. S. 
 (1907). 20 pp. 
 SMOCK, J. C. 
 
 Geologic-Geographical Distribution of the Iron Ores of the Eastern United 
 
 States. r l Vans. A. L M. E., vol. 12, pp. 130-144 (1884). 
 SMYTH, C. H., JR. 
 
 1. On the Clinton Iron Ore Am. Jour. Sci., 3d ser., vol. 43, pp. 487-496 
 (1892). 
 
 2. The Genetic Relations of Certain Minerals of Northern New York. 
 Trans. New York Acad. Sci., vol. 15, pp. 260-271 (1896). 
 
 3. Replacement of Quartz by Pyrite and Corrosion of Quartz Pebbles. Am. 
 Jour. Sci., 4th ser., vol. 19, pp. 277-285 (1905). 
 
 SMYTH, H. L. 
 
 1. The Origin and Classification of Placers. E. and M. Jour., vol. 79, pp. 
 
 1045-1046, 1179-1180, 1228-1230 (1905). 
 2. The Relations Between Gold and Pyrite. Min. and Sci. Press, vol. 93, pp. 
 
 58-59 (1906). 
 SMYTH, H. L., and FINLAY, J. R. 
 
 The Geological Structure of the Western Part of the Vermilion Range, 
 
 Minnesota. Trans. A. I. M. E., vol. 25, pp. 595-645 (1895). 
 SOPER, E. K. 
 
 The Genesis of Ore Deposits. E. and M. Jour., vol. 92, pp. 897-900, 947- 
 
 949 (1911). 
 SORBY, H. C. 
 
 Microscopical Structure of Crystals Indicating the Origin of Minerals and 
 Rocks. Quar. Jour. Geol. Soc., vol. 14, pp. 453-500 (1858). 
 
ALPHABETICAL LIST OF AUTHORS. 897 
 
 SOUDER, HARRISON. 
 
 Mineral Deposits of Santiago, Cuba. Trans. A. I. M. E., vol. 35, pp. 308- 
 
 321 (1904). 
 SPENCER, A. C. 
 
 1. Genesis of the Magnetic Deposits in Sussex County, New Jersey. Min. 
 Mag. (J), vol. 10, pp. 377-381 (1904). 
 
 2. The Copper Deposits of the Encampment District, Wyoming. Prof. Paper 
 25. U. G. S. (1904). 107pp. 
 
 3. The Geology of the Tread well Ore-Deposits, Douglas Island, Alaska. 
 Tram. A. /. M. E., vol. 35, pp. 473-511 (1904). 
 
 4. The Magmatic Origin of Vein-Forming Waters in Southeastern Alaska. 
 Trans. A. I. M. E., vol. 36, pp. 364-372 (1905). 
 
 5. The Origin of Vein-Filled Openings in Southeastern Alaska. Trans. A. 
 I. M. E., vol. 36, pp. 581-586 (1905). 
 
 6. The Juneau Gold Belt, Alaska. Bull. 287, U. S. G. S. (19! 6). 161 pp. 
 
 7. Magnetite and Zinc Ores of Franklin Furnace Quadrangle. Folio 161. 
 U. S. G. S. (1908). 
 
 8. The Mine Hill and Sterling Hill Zinc Deposits of Sussex County, New 
 Jersey. Ann. Rept. of State Geologist for 1908, Geol. Sur. New Jersey, pp. 
 23-52 (1909). 
 
 9. Magnetite Deposits of the Cornwall Type in Pennsylvania. Bull. 359, 
 U. S. G. S. (1908). 102 pp. 
 
 SPIREK, V. 
 
 Das Zinnobererzvorkommen am Monte Amiata. Zeit. f. prak. Geol., vol. 5, 
 
 pp. 369-374 (1897). 
 SPRING, K. 
 
 Einige Beobachtungen in den Platmwaschereien von Nischnji Tagil. Zeit. 
 
 f. prak. Geol., vol. 13, pp. 49-54 (1905). 
 SPURR, J. E. 
 
 1. The Iron Ores of the Mesabi Range (Minnesota). Am. Geol.. vol. 13, pp. 
 335-345 (1894). 
 
 2. The Iron-Bearing Kocks of the Mesabi Range in Minnesota. Butt. 10, 
 Geol. and Nat. Hist. Sur. Minn. (1894). 259 pp. 
 
 3. Economic Geology of the Mercur Mining District, Utah. 16^.4nn. Rept.. 
 U. S. G. S., part 2, pp. 343-455 (1895). 
 
 4. Geology of the Yukon Gold District, Alaska. 18th Ann. Rept., U. S. G. S., 
 part 3, pp. 87-392 (1897). 
 
 5. Geology of the Aspen Mining District, Colorado. Mon. 31, U. S. G. S., 
 (1898). 260 pp 
 
 6. The Ore Deposits of Monte Cristo, Washington. 22d Ann. Rept., U. S. 
 G. S., part 2, pp. 777-865 (1901). 
 
 7. The Original Source of the Lake Superior Iron Ores. Am. Geol., vol. 
 29, pp. 335-349 (1902). 
 
 8. A Consideration of Igneous Rocks and their Segregation or Differentiation 
 as Related to the Occurrence of Ores. Trans. A. I. M. E., vol. 33, pp. 
 288-340 (1902). 
 
 9. Relation of Rock Segregation to Ore Deposition. E. and M. Jour., vol. 
 76, p. 54-55 (1903). 
 
 10. In Discussion of Lindgren on The Geological Features of the Gold Pro- 
 duction of North America. Trans. A. I.M. E., vol. 33, pp. 1081-1083 (1902). 
 
 11. The Ore Deposits of Tonopah, Nevada (preliminary report). Bull. 219, 
 U. S. G. S. (1903). 34 pp. Also Bull. 215, pp. 89-110 (1904). 
 
 12. Genetic Relations of the Western Nevada Ores. Trans. A. I. M. E., vol. 
 36, pp. 372-402 (1905). 
 
 13. Geology of the Tonopah Mining District. Nevada. Prof. Paper 42, U. S. 
 G. S. (1905). 295 pp. 
 
 14. Ore Deposits of the Silver Peak Quadrangle, Nevada. Prof. Paper 55, U. S. 
 G. S. (1906). 174 pp. Also E. and M. Jour., vol. 77, pp. 759-760 (1904). 
 
 15. The Southern Klondike District, Esmeralda County, Nevada. A Study 
 in Metalliferous Quartz Veins of Magmatic Origin. Econ. Geol., vol. 1, 
 pp. 369-382 (1906). 
 
 16. Geology Applied to Mining (New York, 1907). 326 pp. 
 
 17. A Theory of Ore-Deposition. Econ. Geol., vol. 2, pp. 781-795 (1907). 
 
898 ALPHABETICAL LIST OF AUTHORS. 
 
 SPUER, J. E. Continued. 
 
 18. How should Faults be Named and Classified? Econ. GeoL, vol. 2, pp. 
 601-602 (1907). 
 
 19. Ore-Deposition at Aspen, Colorado. Econ. GeoL. vol. 4, pp. 301-320 
 (1909). 
 
 20. Native Gold Original in Metamorphic Gneisses E. and M. Jour., vol. 77, 
 pp. 198-199 (1904). 
 
 SPURR, J. E., and GARREY, G. H. 
 
 1. The Idaho Springs Mining District, Colorado. Bull. 285, U. S. G. S.. 
 pp. H5-40 (1905). 
 
 2. Ore Deposits of the Velardena District, Mexico. Econ. GeoL. vol. 3. pp. 
 688-725 (1908). 
 
 3. Economic Geology of the Georgetown Quadrangle, together with the Em- 
 pi re District, Colorado. Pro/. Paper 63, U. S. G. S. (1908). 422pp. 
 
 4. Gold in the Dioritic Bock from Mashonaland. E. and M. Jour., vol. 76, 
 p. 500 (1903). 
 
 STAPPENBECK, K. 
 
 Ubersicht iiber die nutzbaren Lagerstatten Argentiniens und der Magelhaens- 
 
 lander. Zeit. f. prak. Geol. t \ol. 18. pp. 67-81 (1910). 
 STAPFF, F. M. 
 
 Goldvorkomnisse in Schweden und Tornebohm's geologische Unter-uchung 
 
 von Falnngrube. Rev. in Zeit. f. prak. GeoL, vol. 2, pp. 181-202 (1894). 
 STEIDTMANN, EDWARD. 
 
 A Graphic Comparison of the Alteration of Eocks by Weathering with their 
 
 Alteration by Hot Solutions. Econ. GeoL, vol. 3, pp. 381-409 (1908). 
 STEINMANN, G. 
 
 Die Entstehung der Kupfererzlagerstatte von Caro-Caro und verwandter 
 
 Vorkommnisse in Bolivia. Rosenb. Fests., pp. 335-368 (1906). 
 STELZNER, A. W. 
 
 1. Die Lateral Secretions Theorie und ihre Bedeutung fiir das Pribramer 
 Ganggebiet. Berg- u. Hiltt. der K. K. Bergaka., vol. 37 (1889). 
 
 2. Beitrage zur Entstehung der Freiberger Bleierz und der erzgebirgischen 
 Zinnerz-Gansre. Zeit. f. prak. GeoL, vol. 4, pp. 377-412 (1896). 
 
 3. Die Silver-Zinnerzlagerstatten Bolivias. Ein Beitrag znr Naturgeschichte 
 der Zinnerzes. Zeit. d. D. GeoL GeseL, vol. 49, pp. 51-142 (1897). 
 
 STEVENS, BLAMEY. 
 
 The Laws of Fissures. Trans. A. I. M. E., vol. 40, pp. 475-491 (1909). 
 STEVENS, E. A. 
 
 Basaltic Zones as Guides to Ore-Deposits in the Cripple Creek District. 
 
 Trans. A. I. M. E., vol. 33, pp. 686-698 (1902). 
 STEVENS, H. J. 
 
 The Copper Handbook (annual). Houghton, Michigan. 
 STIRLING, JAMES. 
 
 1. Notes on some Observations of Temperature, etc., in the Deep Mines of 
 Bendigo. GeoL Sur. Victoria (1897). 
 
 2. The Geological Ages of the Gold Deposits of Victoria. Trans. Fed. Inst. 
 Min. Eng., vol. 20, pp. 442-475 (1900-1901). 
 
 STOKES, H. N. 
 
 1. On Pyrite and Marcasite. Bull. 186, U. S. G. S., pp. 1-50 (1901). 
 
 2. Experiments on the Solution, Transportation and Deposition of Copper, 
 Silver and Gold. Econ. GeoL, vol. 1, pp. 644-650 (1906). 
 
 3. Experiments on the Action of Various Solutions on Pyrite and Marcasite. 
 Econ? GeoL, vol. 2, pp. 14-23 (1907). 
 
 STORMS, W. H. 
 
 1. Ancient Gravel Channels of Calaveras County, California. Min. and Sci. 
 Press, vol. 91, pp. 170-171 ; 192-193 (1905). 
 
 2. The Genesis and Character of Ore Deposits. Min. and Sci. Press, vol. 88, 
 pp. 193-194 (1904). 
 
 STRAUSS, L. W. 
 
 Quicksilver at Hnancavelica, Peru. Min. and Sci. Press, vol. 99, pp. 561- 
 566 (1909). 
 
ALPHABETICAL LIST OF AUTHORS. 899 
 
 * 
 
 STREMME, H. 
 
 Zur Kenntniss der wasserhaltigen und wasserfreien Eisenoxydbildungen in 
 
 den Sedimentgesteinen. Zeit f. prak. Geol., vol. 18, pp. 18-23 (1910). 
 STRETCH, R. H. 
 
 Notes on the White Horse Copper Belt, Yukon Territory. E. and M. Jour., 
 
 vol. 70, pp. 277-278 (1900). 
 STRUTT, E. J. 
 
 On the Origin of Gaes Evolved by Mineral Springs. Proc. Roy. Soc., vol. 
 
 79, pp. 436-439 (1907). 
 STDTZER, O. 
 
 1. Die Eisenerzlagerstatten bei Kiruna. Zeit.f. prak. GW., vol. 14, pp. 65-71 
 (1906). 
 
 2. Alte und neue geologische Beobachtungen an den Kieslagerstatten Suli- 
 telma-Roros Norwegen. Ost. Zeit. f. Sera- u. Hiitt.. vol. 54, pp. 567-572 
 (1906). 
 
 3. Turmalin fiihrende Kobalterzgiinge. Zeit. f. prak. OeoL. vol. 14, pp. 294- 
 298 (1906). 
 
 4. Die Eisener/.lagerstatte Gellivare in Nordschweden. Zeit. f. prak. OeoL. 
 vol. 14, pp. 137-140 (1906). 
 
 5. Uber die Enstelmng und Einleitunar der Eisenerzlagerstatten. Zeit. f. 
 Berg- Hiitt. u. Salinenw., vol. 54, pp. 301-304 (1906). 
 
 6. Der Stammbaum der Erzlagerstiitten. 6st. Zeit. f. Berq- u. Hiitt, pp. 317- 
 320 (1907). 
 
 7. Magmatische Ausscheidungen von Bornit. Zeit. f. prak. OeoL, vol. 15, 
 pp 371-372 (1907). 
 
 8. The Geology and Origin of the Lapland Iron Ores. Jour. Iron and Steel 
 Inst., vol. 74, pp. 106-206 (1907). 
 
 9. Versuche uber das Eindringen schmelzflussiger Metal'sulfide in Silikat- 
 gesteine. Zeitf. prak. OeoL, vol. 16, pp. 119-122 1908). 
 
 10. Uber Pegmatite und Erzinjektionen nebst einigen Remerkungen iiber die 
 Kieslagerstatten Sulitelma-Roros. Zeit. f. prak. Geol , vol. 17, pp. 130-135 
 (1909). 
 
 11. Die Kontaktmetaraorphen Kupfererzlagerstatten von White Horse in 
 Yukon (Canada). Zeit.f. prak. GeoL, vol. 17, pp. 116-121 (1909). 
 
 12. Kontakraetamorphe Erzlagerstatten. Zeit. f. prak. Geol., vol. 17, pp. 
 145-155 (1909). 
 
 13. Juvenile Quellen. Int. Kong. Diisseldorf, 1910. Abteil. IV., Vortrag 
 21, pp. 1-8. 
 
 SUE.-S, EDOUARD. 
 
 1. Zukunft des Goldes (1877). 
 
 2. Uber Heisse Quellen. Gesdlschaft Deut. Naturforsch. u. Aert. Verhand' 
 lungen (1902). 
 
 3. Hot Springs. .E, and M. Jour., vol. 76, pp. 52-53 (1902). 
 SULLIVAN, E. C. 
 
 1. The Chemistry of Ore- Deposition Precipitation of Copper by Natural 
 Silicates. Econ. OeoL, vol. 1, pp. 67- 73 (1906). 
 
 2. The Interaction between Minerals and Water Solutions, with special refer- 
 ence to geologic phenomena. B all. 312, U. S. G. S. (1907). 69 pp. 
 
 3. Experiments on the Separation of the Constituents of a Solution by Filtra- 
 tion through a Mineral Filter. Econ. GeoL, vol. 3, pp. 750-756 (1908). 
 
 SUTHERLAND, GEORGE. 
 
 Earth Currents and the Occurrence of Gold. Nature, vol. 42, pp. 464-465 
 (1890). 
 
 TARR, R. S. 
 
 Economic Geology of the United States (New York, 1894). 509 pp. 
 TARR, W. A. 
 
 Copper in the Red Beds of Oklahoma. Econ. GeoL, vol. 5, pp. 221-226 
 
 (1910). 
 THOMAS, H. H., and MACALISTER, D. A. 
 
 The Geology of Ore Deports (London, 1908). 416 pp. 
 
900 ALPHABETICAL LIST OF AUTHORS. 
 
 TOLMAN, C. F., JR. 
 
 1. How Should Faults be Named and Classified tEcon. GeoL, vol. 2, pp. 506- 
 511 (1907). 
 
 2. Secondary Sulphide Enrichment. Min. and Sci. Press, vol. 106, pp. 38- 
 43, 141-145, 178-181 (1913). 
 
 3. The Southern Arizona Copper Fields. Min. and Sci. Press, vol. 99, pp. 
 356-359, 390-393 (1909). 
 
 4. Disseminated Chalcocite Deposits at Kay, Arizona. Min. and Sci. Press, 
 vol. 99, pp. 622-624 (1909). 
 
 5. The Miami-Inspiration Ore Zone. Min. and Sci. Press, vol. 99, pp. 646- 
 648 (1909). 
 
 6. Graphical Solution of Fault Problems. Min. and Sci. Press, vol. 102, pp. 
 810-812 ; vol. 103, pp. 128-130 (1911). 
 
 TOULA, F. 
 
 tiber den nuesten Stand der Goldfrage (Wien, 1899). 60 pp. 
 TOWER, G. W., JR., and SMITH, G. O. 
 
 Geology and Mining Industry of the Tintic District, Utah. 19th Ann. Rept., 
 
 U. S. O. S., Part 3, pp. 601-767 (1898). 
 TRENER, G. B. 
 
 Diffusion fester Metalle in feste Kristallinische Gesteine. Verhand. GeoL 
 
 Reichsanst., pp. 360-370, 372 (1905) 
 TRUCHOT, P. 
 
 Les Pyrites (Paris, 1907). 348 pp. 
 TRUSCOTT, S. J. 
 
 The Witwatersrand Goldfields (London, 1907). 517 pp. 
 TRUSTEDT, O. 
 
 1. tiber die Erzlagerstatten von Pitkaranta. Compt. rend. d. Congres d. nat. 
 et med. du nord, pp. 7-12 VII. 1902. Rev. in Zeit. f. prakt. GeoL, vol, 11, p. 
 317 (1903). 
 
 2. Die Erzlagerstatten von Pitkaranta am Ladagoasee. Bull. 19, Com. GeoL 
 de Finlande (1907). 333 pp. 
 
 TSCHERNE, M. 
 
 Beitrage zur Paragenese der Mineralien (Wien, 1892). 29 pp. 
 TURNER, H. W. 
 
 1. Notes on the Gold Ores of California. Am. Jour. Sci., 3d series, vol. 47, 
 pp. 467-473 (1894). Vol. 49, pp. 374-389 (1895). 
 
 2. Replacement Ore Deposits of the Sierra Nevadas. Jour. GeoL, vol. 7, pp. 
 389^00 (1899). 
 
 3. The Copper-Deposits of the Sierra Oscura, New Mexico. Trans. A. I. M. 
 E,, vol. 33, pp. 678-681 (1902). 
 
 4. Notes on Contact-Metamorphic Deposits in the Sierra Nevada Mountains. 
 Trans. A. I. M. E., vol. 34, pp. 666-668 (1903). 
 
 5. The Cretaceous Auriferous Conglomerate of the Cottonwood Mining Dis- 
 trict, Siskiyou County, California. E. and M. Jour., vol. 76, pp. -653-654 
 (1903). 
 
 6. The Terlingua Quicksilver Deposits. Econ. GeoL, vol. 1, pp. 265-281 
 (1906). 
 
 7. The Ore-Deposits at Mineral, Idaho. Econ. GeoL, vol. 3, pp. 493-502 (1908. 
 TWEL.VETREES, W. H. 
 
 1. The Deep Leads of Infra-Basaltic Stanniferous Gravels of the Ringarrooma 
 Valley near Derby. Mines Dept. Tasm. (1900). 
 
 2. Report on the Anchor Tin Mine and other mines of the Blue Tier District, 
 Tasmania. M ines Dept Tasm. (1902). 
 
 3. The Lisle Goldfield. Bull. 4, Mines Dept. Tasm. (1909). 46 pp. 
 TWELTVETREES, W. H., and PETTERED. 
 
 On the Topaz Quartz Porphyry or Stanniferous Dykes of Mt. Bischoff. Roy. 
 
 Soc. Tasm. (Oct. 11, 1897). 
 TYRRELL, J. B. 
 
 1. Vein Formation at Cobalt, Ontario. Can. Min. Jour., vol. 28, pp. 301-303 
 (1907). 
 
 2. Concentration of Gold in the Klondike. Econ. GeoL, vol. 2, pp. 343-349 
 (1907). 
 
ALPHABETICAL LIST OF AUTHORS. 901 
 
 ULRICH, E. O., and SMITH, W. S. T. 
 
 The Lead, Zinc, and Fluorspar Deposits of Western Kentucky. Prof. Paper 
 
 36, U. S. O. S. (1905). 218 pp. 
 UMPLEBY, J. B., CALKINS, F. C., and JONAS, E. L., JR. 
 
 Gold and Silver in Idaho. Butt. 530, U. S. O. S. (1912). 23 pp. 
 UPSENSKY. 
 
 Die Eisenerzlagerstiitten im Bogoslowskschen Bergrevier. Kev. in NeuesJahrb. 
 f. Min., vol. 2, p. 235 (1903). 
 
 VALE, W. H. 
 
 The Indicators of the Daylesford Gold Mines, Victoria. Trans. Austral. Inst 
 
 Min. Eng., vol. 10, pp. 340-352 (1905). 
 VAN HISE, C. K. 
 
 1. The Iron Ores of the Lake Superior Region. Trans. Wis. Acad. ScL, vol. 8 
 pp. 219-227 (1892). 
 
 2. Principles of North American Pre-Cambrian Geology. 16th Ann. Rept., 
 U. 8. G. S., part 1, pp. 571-874 (1896). 
 
 3. Deformation of Rocks. Jour. Geol., vol. 4, pp. 195-213 (1896). 
 
 4. Some Principles Controlling the Deposition of Ores. Trans. A. I. M. E., 
 vol. 30, pp. 27-177 (1900). Reprinted in Special Volume, Genesis of Ore- 
 Deposits, pp. 282-432 (1902). 
 
 5. The Iron Ore Deposits of the Lake Superior Region. 21st Ann. Rept., U. S. 
 O. #.,part 3, pp. 305-434 (1900). 
 
 6. Some Principles Controlling the Deposition of Ores (Discussion). Tram. 
 A. I. M. K, vol. 31, pp. 284-303 (1901). 
 
 7. Metamorphism of Rocks and Rock Flo wage. Bull. Geol. Soc. Am., vol. 9, 
 p. 269 (1897). 
 
 8. A Treatise on Metamorphism (The Relation of Metamorphism to Ore-De- 
 posits, Chap. 12). Man. 47, U. S. G. S. (1904). 1286 pp. 
 
 VAN HISE, C. R., and BAYLEY, W. S. 
 
 1. Preliminary Report on the Marquette Iron-Bearing District of Michigan. 
 15th Ann. Rept., U. S. G. S., pp. 477-650 (1895). 
 
 2. The Marquette Iron-Bearing District of Michigan, with Atlas. Mon. 28, 
 U.S. G. S. (1897). 608pp. 
 
 VlLLANUEVA, B. F. 
 
 Distrito de Real de Saltepec (Mexico, 1888). 
 
 VlLLARELLO, J. D. 
 
 1. Genesis de los Yacimientos Mercuriales de Palomas y Huitzuco. Mem. 
 Soc. Cien. Ant. Alz., vol. 19, pp. 95-136 (1903). 
 
 2. Distribucion de la Riqueza en los criaderos Metaliferos Primaries Epige- 
 neticos. Bol. Soc. Geol. de Mex., vol. 1, pp. 175-206 (1905). 
 
 VOGT, J. H. L. 
 
 1. Bildung von Erzlagerstatten durch Differentiationsprocesse in basischen 
 Eruptivmagmata. Zeit. f. prak. Geol, vol. 1, pp. 4-11, 125-143, 257-284 
 (1893). 
 
 2. Beitriige zur genetischen Classification (1894). 
 
 3. Uber die Sedimentation der Eisenerzlager und der Eisenglimrnerschiefer. 
 Salten og Ranen, pp. 214-224 (1891), rev. in Zeit. f. prak. Geol., vol. 2, pp. 
 30-34 (1894). 
 
 4. Uber die Kieslagerskatten vom Typus Roros, Vigsiiiis, Sulitelma in Norwegen 
 und Rammelsberg in Deutschland. Zeit. f. prak. Geol., vol. 2, pp. 41-50, 
 117-134, 173-181 (1894). 
 
 5. Beitriige zur genetischen classification der durch magmatische Differentia- 
 tionsprocesse und der durch Pneumatolyse entstandenen Erzvorkommen. 
 Zeit.f. prak. Geol., vol. 2, pp. 381-399; vol. 3, pp. 145-156, 367-370, 444- 
 459, 465-484 (1894-1895). 
 
 6. The Formation of Eruptive Ore Deposits. Min. Ind., vol. 4, pp. 743-754 
 (1895). 
 
 7. Kan norske nikkelverk konkurrere med de canadiske ? Norsk Teknisk Tids. 
 (1897). 6 pp. 
 
 8. Uber die relativ Verbreitung der Elemente besonders der Schwermetalle, 
 und iiber die Concentration des urspriinglich fein vertheilten Metallgehaltes 
 zu Erzlagerstatten. Zeit.f. prak. GeoL, vol. 6, pp. 225-238, 314-327, 377- 
 392, 413-420 (1898) ; vol. 7, pp. 10-16 (1899). 
 
902 ALPHABETICAL LIST OF AUTHORS. 
 
 VOGT, J. H. L. Continued. 
 
 9. Das Huelva-Kiesfeld in Siid-Spanien und dem angrenzenden Theile von 
 Portugal. Zeit. f. prak. Geol., vol. 7, pp. 241-254 (1899). 
 
 10. Problems in the Geology of Ore- Deposits. Trans. A. L M. E., vol. 31, pp. 
 12o-169 (1901). 
 
 11. Weitere Untersuchungen iiber die Ausscheidungen von Titaneisenerzen 
 in basischen Eruptivgesteinen. Zeit. f. prak. Geol., vol. 8, pp. 233-242, 
 370-382 (lyOO) ; vol. 9, pp. 9-19, 180-186, 289-296, 327-340 (1901). 
 
 12. Beitrage zur Kenntniss der Gesetze der Mineralbildung in Schmelzmassen 
 und in den neovulkanischen Ergussgesteinen (Kristiania, 1902). 
 
 13. Die regional-metamorphosierten Eisenerzlagerstatten im nordlichen Nor- 
 wegen ._ Zeit. f. prak. Geol., vol. 11, pp. 24-28, 59-65 (1903). 
 
 14. Tiber anchi-eutektische und anchi-mono-mineralische Eruptivgesteine. 
 Norsk geol. Tids., vol. 1 (1905). 33 pp. 
 
 15. tiber manganwiesenerz und iiber das Verhaltnis zwischen Eisen und 
 Mangan in den See- und Wiesenerze. Zeit. f. prak. Geol., vol. 14, pp. 217- 
 233 (1906). 
 
 16. Uber magmatische Ausscheidungen von Eisenerz im Granit. Zeit. f. prak. 
 Geol., vol. 15, pp. 86-89 (1907). 
 
 17. tiber die Rodsand-Titaneisenerzlagerstatten in Norwegen. Zeit. f. prak. 
 Geol., vol. 18, pp. 59-67 (1910). 
 
 VOGT, J. H. L., BEYSCHLAG, and KRUSCH. 
 
 Lehre von den Erzlagerstatten. First two volumes issued (1910). 
 VOIT, F. W. 
 
 1. Ursprung des Goldes in den Randconglomeraten. Monatsb. d. D. Geol. 
 GeseL, pp. 107-119 (1908). 
 
 2. A Contribution to the Geology of German Southwest Africa. Trans. Geol. 
 Soc. So. Af., vol. 7, Pt. 2, pp. 77-94 (1904). 
 
 WABNER, K. 
 
 Uber die Eintheilung der Minerallagerstiitten nach ihrer Gestalt, sowie die 
 
 Anwendung und die Bedentung der Worte Lager und Flotz. Berg- u. 
 
 Hiitt. Zeit., vol. 50, pp. 1-3 (1891). 
 WADSWORTH, M. E. 
 
 1. The Theories of Ore Deposits. Proc. Bost. Soc. Nat. Hist., vol. 23, pp. 
 197-208 (1888). 
 
 2. The Lateral Secretion Theory of Ore Deposits. #. and M. Jour., vol. 37, 
 pp. 364-365 (1884). 
 
 3. Classification of ore deposits. Rept, Mich. State Geol., 1891-92, p. 144. 
 
 4. The Origin and Mode of Occurrence of the Lake Superior Copper- De- 
 
 posits. Trans. A. I. M. E., vol. 27, pp. 669-696 (1897). 
 5. On the Origin of the Iron-Ores of the Marquette District', Lake Superior. 
 Proc. Bost. Soc. Nat. Hist., vol. 20, pp. 470-480 (1881). 
 
 WAIT, C. E. 
 
 The Antimony Deposits of Arkansas. Trans. A. L M. E., vol. 8, pp. 42-52 
 
 (1880). 
 VON WALDENSTEIN, J. W. 
 
 Die besonderen Lagerstatten der nutzbarer Fossilien. 2 vol. (Vienna, 1824.) 
 
 WALLACE, J. P. 
 
 Ore Deposits for the Practical Miner (New York, 1908). 347 pp. 
 
 WALKER, E. 
 
 The Copper Sulphate Deposits at Copaquire, Chile. E. and M. Jour., vol. 
 
 75, p. 710 (1903). 
 WALKER, T. L. 
 
 1. Geological and Petrographical Studies of the Sudbury Nickel District 
 [Canada]. Quor. Jour. Geol. Soc., vol. 53, pp. 40-66 (1897). 
 
 2. Eeport on the Tungsten Ores of Canada. (Bibliography.) Bull. 25, Mines 
 Branch, Can. Dept. of Mines (1909). 56 pp. 
 
 WARD, L. K. 
 
 1. The Mount Farrell Mining Field. Butt. 3, Dept. Mines Tasm. (1908). 
 120 pp. 
 
 2. The Tin Fields of North Dimdas. Bull. 6, Dept. Mines Tasm. (1909). 
 166 pp. 
 
ALPHABETICAL LIST OF AUTHORS. 903 
 
 WASHBURNE, CHESTER. 
 
 1. The Distribution of Placer Gold in Oregon. Oregon Univ. Bull., New Ser., 
 vol. 1, No. 4, pp. 18-19 (1904). 
 
 2. Beach Gold and its Source. Oregon Univ. Bull., New Ser., vol. 1, No. 4, 
 pp. 19-21 (1904). 
 
 WASHINGTON, H. S. 
 
 1. Chemical Analyses of Igneous Rocks, Pub. from 1884 to 1900, with a criti- 
 cal discussion of the character and use of analyses. Prof. Paper 14, U. 
 G. S. (1903). ^ 495 pp. 
 
 2. The Distribution of the Elements in Igneous Rocks. Trans. A. I. M. E. 
 vol. 39, pp. 735-764 (1908). 
 
 WATSON, T. L. 
 
 1. Geological Relations of the Manganese Ore-Deposits of Georgia. Trans. 
 A. I. M. E., vol. 34, pp. 207-254 (1903). 
 
 2. The Lead and Zinc Deposits of the Virginia- Tennessee Region. Trans. A. 
 L M. E., vol. 36, pp. 681-737 (1905). 
 
 3. Lead and Zinc Deposits of Virginia. Bull. 1, Geol. Ser., Virginia Geol. 
 Sur. (1905). 156pp. 
 
 4. The Occurrence of Nickel in Virginia. Trans. A. I. M. E.. vol. 38, pp. 
 683-697 (1907). 
 
 5. A Preliminary Report on the Manganese Deposits of Georgia. Bull. 14. 
 Geol. Sur. Ga. (1908). 195 pp. 
 
 6. The Manganese-Ore Deposits of Georgia. Econ. Geol., vol. 4, pp. 46-55 
 (1909). 
 
 WATSON, T. L., and HESS, F. L. 
 
 Zirconiferous Sandstone near Ashland. Virginia. Bull. 530, U. S. G. S* 
 
 (1912). 9pp. 
 WATT, J. A. 
 
 Saddle Reefs at Hargreaves. Rec. Geol. Sur. N. S. W., vol. 5, pt. 4, p. 153 
 
 (1898) ; vol. 6, pt. 2, p. 83 (1899). 
 WATTS, VV. L. 
 
 Across V'atna Jokull, or, Science in Iceland, pp. 101, 109, 119, 153-157 
 
 (London, 1876). 
 WEDDING, H. 
 
 Die Eisenerze der Insel Cuba. Stahl und Eisen, vol. 12, pp. 545-550 (1892). 
 WEED, W. H. 
 
 1. A Gold-Bearing Hot Spring Deposit. Am. Jour. ScL, 3d ser., vol. 42, pp. 
 166-169(1891) 
 
 2. Enrichment of Mineral Veins by Later Metallic Sulphides. Bull. Geol. 
 Soc. Am., vol. 11, pp. 179-206 (1900). 
 
 3. Mineral Vein Formation at Boulder Hot Springs, Montana. 21st Ann. 
 Rent., U. S. G. S., part 2, pp. 227-255 (1900). 
 
 4. Types of Copper Deposits in the Southern United States. Trans. A. I. M. 
 E., vol. 30, pp. 449-i04 (1900). 
 
 5. The Enrichment of Gold and Silver Veins. Trans. A. I. M. E., vol. 30, 
 pp. 424-448 (1900). 
 
 6. Influence of Countrv-Rock on Mineral Veins. Trans. A. L M. E., voL 
 31, pp. 634-653 (1901). 
 
 7. The El Paso Tin Deposits. Bull. 178, U. S. G. S., pp. 1-15 (1901). 
 
 8. The Copper Deposits of the Eastern United States. Bull. 260, U. S. G. &, 
 pp. 217-220 (1905). 
 
 9. Notes on Certain Mines in the States of Chihuahua, Sinaloa, and Sonora, 
 Mexico. Trans. A. I. M. E., vol. 32, pp. 396-443 (1901). 
 
 10. Ore-Deposits near Igneous Contacts. Trans. A. L M. E , vol. 33, pp. 
 715-746 (1902). 
 
 11. Ore-Deposition and Vein-Enrichment by Ascending Hot Waters. Trans. 
 A. L M. E., vol. 33, pp. 747-754 (1902). 
 
 12. Copper Deposits of New Jersey. Ann. R pt. Slate Geologist, 1902, Geol. 
 Survey of New Jersey, pp. 125-139 (1903). 
 
 13. The Genetic Classification of Ore Bodies (Geol. Soc. Am.). E. and M. 
 Jour., vol. 75, pp. 256-257 (1903). (See also Rickard, T. A., et a/., 1.) 
 
 14. Ore Deposits at Butte, Montana. Bull. 213, U. S. G. S., pp. 170-180 
 (1903). 
 
904 ALPHABETICAL LIST OF AUTHORS. 
 
 WEED, W. H. Continued. 
 
 15. Occurrence and Distribution of Copper in the United States. 3 fin. Mag., 
 (J), vol. 10, pp. 185-193 (1904). 
 
 16. Original Native Gold in Igneous Rocks. E. and M. Jour., vol. 77, pp. 
 440-441 (1904). 
 
 16a. The Copper Mines of the United States in 1905. Bull. 285, U. S. G. S., 
 pp. 93-124 (1905). 
 
 17. Adsorption in Ore Deposition. E. and M. Jour., vol. 79, p. 364 (1905). 
 
 18. Mutual Dibplncement by Intersecting Veins. E. and M. Jour., vol. 83, 
 pp. 1145-1146 (1907). 
 
 19. Copper Mines of the World (New York, 1908). 375 pp. 
 
 20. Geology and Ore Deposits of Butte District, Montana. Prof. Paper 74, 
 U. S. Q. S. (1912). 262pp. 
 
 21. Copper Deposits of the Appalachian States. Bull. 455, U. S. G. S. 
 (1911). 466pp. 
 
 WEED, W. H., and BARBELL, JOSEPH. 
 
 Geology and Ore-Deposits of the Elkhorn Mining District, Jefferson County, 
 
 Montana. 22d Ann. Rept., U. S. G. S., part 2, pp. 399-549 (1901). 
 WEED, W. H., and PIRSSON, L. V. 
 
 1. Geology of the Castle Mountain Mining District, Montana. Bull. 139, U. 
 S. G. S. (1896). 164pp. 
 
 2. Geology and Mineral Resources of the Judith Mountains of Montana. 
 18th Ann. Rept., U. S. G. S., part 3, pp. 437-616 (1897). 
 
 3. Geology of the Little Belt Mountains, Montana. 20th Ann. Rept., U. S. 
 G. S., part 3, pp. 257-581 (1899). 
 
 4. Occurrence of Sulphur, Orpiment and Realgar in the Yellowstone Na- 
 tional Park. Am. Jour. Sci., 3d ser., vol. 42, pp. 401-405 (1891). 
 
 WEED, W. H., and W T ATSON, T. L. 
 
 The Virginia Copper Deposits. Econ. GeoL, vol. 1, pp. 309-330 (1906). 
 
 WEEKS, F. B. 
 
 Geology and Mineral Resources of the Osceola Mining District, White Pine 
 
 County, Nevada. Bull. 340, U. S. G. S.,pp. 117-133 (1908). 
 WEIDMAN, SAMUEL. 
 
 The Baraboo Iron-Bearing District of Wisconsin. Bull. 13, Wis. GeoL and 
 Nat. Hist. Sur. (1904). 190 pp. 
 
 WEILL, L. 
 
 L'or ; proprie'te's physiques et chemiques ; gisements ; extraction ; applica- 
 tions ; dosage (Paris, 1896). 420 pp. 
 WEINSCHENK, E. 
 
 Die Nickelmagnetkieslagerstatten imBezirk St. Blasien in siidlichen Schwarz- 
 
 wald. Zeit. f. prak. GeoL, vol. 15, pp. 73-86 (1907). 
 WEISKOPF, A. 
 
 Uber Anreicherung von Eisenerzen. Stahl und Eisen, pp. 471-475, 532-535 
 (1905). 
 
 WELLS, R. C. 
 
 The Fractional Precipitation of Sulphides. Econ. GeoL, vol. 5, p. 1-14 (1910). 
 
 WELTON, W. S. 
 
 Notes on Gold-Bearing Gravels. Trans. Inst. Min. and Met., vol. 8, pp. 
 519-534 (1899). 
 
 WENDEBORN, B. A. 
 
 Beziehung der Mineralabsonderungen aus Gesteinen zu Erzlagerstiitten. 
 
 Berg- u. Hiltt. Zeit., vol. 63, pp. 568-569 (1904). 
 WENDT, A. F. 
 
 1. The Iron Mines of Putnam County, N. Y. Trans. A. L M. E., vol. 13, 
 pp. 478-485 (1885). 
 
 2. The Copper Ores of the Southwest. Trans. A. I. M. E., vol. 15, pp. 25- 
 77 (1887). 
 
 3. The Potosi, Bolivia, Silver-District. Trans. A. I. M. E., vol. 19, pp. 
 74-107 (1891). 
 
 WERNER, A. G. 
 
 Neue Theorie von der Entstehnns: der Giinge, mit Anwendung auf den 
 Bergbau, besonrlers den freibergischen (Freiberg, 1791). 
 
ALPHABETICAL LIST OF AUTHORS. 905 
 
 VAN WERVEKE, L. 
 
 Bemerkungen tiber die Zusammensetzung und die Entstehung der lothring- 
 isch, luxemburgischen oolithischen Eisenerze (Minetten). Zeit. f. prak. 
 GeoL, vol. 9, pp. 396-403 (1901). 
 WHERRY, E. T. 
 
 The Newark Copper Deposits of Southeastern Pennsylvania. Econ. GeoL, 
 
 vol. 3, pp. 726-738 (1908). 
 WHITNEY, J. D. 
 
 1. The Metallic Wealth of the United States (Philadelphia, 1854). 510 pp. 
 
 2. Remarks on the changes which take place in the structure and composition 
 of mineral veins near the surface, with particular reference to the East Ten- 
 nessee Copper Mines. Am. Jour. Sci., 2d ser., vol. 20, p. 53-57 (1855). 
 
 3. The Auriferous Gravels of the Sierra Nevada of California. Mem. Mus. 
 Comp. Zool. Har. Col., vol. 6 (1879-1880). 569 pp. 
 
 WHITTLESEY, C. 
 
 On the Origin of Mineral Veins. Proc. Am. Assoc. Adv. Sci., vol. 25, p. 213 
 
 (1876). 
 WILLIAMS, ALBERT, JR. 
 
 1. Popular Fallacies Regarding Precious Metal Ore Deposits. 4th Ann. 
 Rept., U. S. G. S., pp 257-271 (1884). 
 
 2. Why Dip is more likely to be Regular than Strike with Fissure Veins. 
 E. and M. Jour., vol. 53, p. 398 (1892). 
 
 WILLIAMS, E. G. 
 
 The Manganese Industry of the Department of Panama, Republic of Colom- 
 bia. Trans. A. I. M. E., vol. 33, pp. 197-235 (1902). 
 WILLIAMS, S. G. 
 
 Applied Geology (New York, 1886). 386 pp. 
 WILLIS, BAILEY. 
 
 1. The Mechanics of Appalachian Structure. 13^ Ann. Eept , U.S. G. S., 
 Pt. 2, pp. 211-281 (1892). 
 
 2. Studies in Structural Geology. Trans. A. I. M. E., vol. 21, p. 551 ; E. and 
 M. Jour., vol. 54, pp. 390-391 (1892). 
 
 WlLLMOTT, A,. B. 
 
 The Origin of Deposits of Pyrites. Jour. Can. Min. Inst., vol. 10, pp. 118- 
 
 128 (1907) ; Can. Min. Jour., vol. 28, No. 18, pp. 500-503 (1907). 
 WILTSEE, ERNEST. 
 
 Notes on the Geology of the Half Moon Mine, Pioche, Nevada. Trans. A. 
 L M. E., vol. 21, pp. 867-873 (1893). 
 
 WlNCHELL, A. N. 
 
 1. The Oxidation of Pyrites. Econ. GeoL, vol. 2, pp. 290-294 (1907). 
 
 2. A Consideration of Igneous Rocks and their Segregation or Differentiation 
 as related to the Occurrence of Ores. Discussion of a paper by J. E. Spurr. 
 Trans. A. L M. E., vol. 33, pp. 288-340 (1902). 
 
 WlNCHELL, H. V. 
 
 1. The Mesabi Iron-Range. Trans. A. I. M. E., vol. 21, pp 644-686 (1892). 
 
 2. The Genesis of Ore- Deposits. (Discussion of a paper by Posepny in Trans. 
 A. I. M. E., vol. 23, pp. 197-368); Trans. A. L M. E., vol. 23, pp. 591-597 
 (1893). 
 
 3. The Lake Superior Iron-Ore Region. Trans. Fed. Inst. Min. Eng., vol. 13, 
 pp. 493-562 (1896-97). 
 
 4. Synthesis of Chalcocite and its Genesis at Butte, Montana. Bull. GeoL Soc. 
 Am., vol. 14, pp. 269-276 (1903); also E. and M. Jour., vol. 75, pp. 782- 
 784 (1903). 
 
 5. Genesis of Ores in the Light of Modern Theory. E. and M. Jour., vol. 84, 
 pp. 1067-1070 (1907). 
 
 6. A Theory of Ore-Deposition Min. and Sci. Press, vol. 96, pp. 385-387 
 (1908). 
 
 7. The Localization of Values in Ore Bodies and the Occurrence of Shoots in 
 Metalliferous Deposits. Econ. GeoL, vol. 3, pp. 425-428 (1908). 
 
 8. The Genesis of Ores. Min. and Sci. Press, vol. 95, pp. 55-58 (1907). 
 
 9. Prospecting in the North. Min. Mag. (E), vol. 3, pp. 436-438 (1910). 
 
 57 
 
906 ALPHABETICAL LIST OF AUTHORS. 
 
 WINCHELL, H. V., and GRANT, IT. S. 
 
 Preliminary Report on the Rainy Lake Gold Region [Minnesota]. 23e/ Ann. 
 
 Rept., Geol. and Nat. Hist. Sur. Minn., pp. 36-104 (1894). 
 WINCHELL, H. V., and JONES, J. T. 
 
 The Biwabik Mine. Trans. A. I. M. E., vol. 21, pp. 951-961 (1893). 
 WINCHELL, H.V., and WINCHELL, N. H. 
 
 The Iron Ores of Minnesota Bull. 6, Minn. Geol. and Nat. Hist. Sur., pp. 
 
 1-429 (1892). 
 WINCHELL, N. H. 
 
 1. The Cuyuna Iron Range. Econ. Geol, vol. 2, pp. 565-571 (1907). 
 
 2. Structure of the Mesabi Iron-Ore. Proc. Lake Sup. Min. Insi., vol. 13, pp. 
 189-204 (1908). 
 
 WlNKLER, C. 
 
 1. Die Relative Seltenheit der Elemente mit Bezug auf deren technische Ver- 
 wendung. Zeit. f. Anyew. Chem., pp. 93-98 (1899). 
 
 2. On the Possibility of the Immigration of Metals into Eruptive Rocks 
 through the Agency of Carbon Dioxide. Ber. d. Math. Phys. K. K. Ak. d. 
 W., Leipzig, p. 9 (1900). 
 
 WINSLOW, ARTHUR. 
 
 1. Notes on the Lead and Zinc Deposits of the Mississippi Valley and the 
 Origin of the Ores. Jour. Geol., vol. 1, pp. 612-619 (1893). 
 
 2. Lead and Zinc Deposits of Missouri. Trans. A. I. M. E., vol. 24, pp. 634- 
 689 (1894). 
 
 3. The Disseminated Lead Ores of Southeastern Missouri.^//. 132, U. S. G. S. 
 (1896). 31 pp. 
 
 4. The Liberty Bell Gold-Mine, Telluride, Colorado. Trans. A. I. M. E., 
 vol. 29, pp. 285-307 (1899). 
 
 VON WlSSENBACH. 
 
 Gang verhaltnisse (1836). 
 
 WOAKEB, E. R. 
 
 Modern Gold-Mining in the Darien Notes on the Re-opening of the Espirito 
 Santo Mine at Cana. Trans. A. I. M. EJ,voL 29, pp. 249-280 (1899). 
 
 W8LBLING, H. 
 
 1. Bildung der oxydischen Eisenerzlager. Stahl und Eisen, vol. 29, p. 1248 
 (1909). 
 
 2. Zur Bildung von Eisenglanz. Gluckauf, vol. 45, pp. 1-5 (1909). 
 WOOD, G. C. 
 
 Determination of the Specific Electrical Resistance of Coals, Ores, etc. Trans. 
 
 No. Eng. Inst. Min. and Mech. Eng., vol. 56, pp. 27-37 (1906). 
 WOOD, J. E. T. 
 
 1. The Great Western Tin Deposits, Heberton (1881). 
 
 2. The Tin Deposits of the Northern Territory. Geol. Sur. So. Aust. (1886). 
 WOODMAN, J. E. 
 
 1. Studies in the Gold-Bearing Slates of Nova Scotia. Proc. Boston Soc. NaL 
 Hist., vol. 28, pp 375-407 (1899). 
 
 2. Geology of the Moose River Gold District, Halifax, Nova Scotia. Proc. 
 and Trans. Nov. Scot. Inst. Sci., vol. 11, pp. 18-88 (1905). 
 
 3. Report on the Iron Ore Deposits of Nova Scotia. Bull. 20, Mines Branch^ 
 Can. Dept. Mines (1909). 226 pp. 
 
 WOLFF. 
 
 Das Australische Gold. Zeit. d. D. Geol. Gesel, vol. 29, pp. 156-157 (1877). 
 WRIGHT, F. E., and LARSEN. 
 
 Quartz as a Geologic Thermometer. Am. Jour. Sci., 4th ser., vol. 27, pp. 421- 
 
 447 (1909). 
 WRIGHT, C. W. 
 
 1. The Porcupine Placer District, Alaska. Bull. 236, U. S. G. S. (1904). 
 35pp. 
 
 2. The Lead and Zinc Mines of Monteponi. Min. Mag. ( J), vol. 12, pp. 33- 
 38 (1905). 
 
 3. The Copper Deposits of Kasaan Peninsula, Alaska. Econ. Geol., vol. 3, 
 pp. 410-417 (1908). 
 
ALPHABETICAL LIST OF AUTHORS. 907 
 
 WRIGHT, C. W. and F. E. 
 
 Ketchikan and Wrangell Mining Districts, Alaska. Bull. 347, U. S. G. S. 
 
 (1908). 210pp. 
 WRIGHT, L. T. 
 
 Diffusion as a Factor in Ore Deposition. Min. and Sci. Press, vol. 96, pp. 844- 
 
 845; vol. 97, p. 149 (1898). 
 WUENSCH, A. F. 
 
 The Cause of Ore Shoots Sci. Mon., pp. 74-76 (1893). 
 
 YEATES, W. S., McCALME, S. W., and KING, F. P. 
 
 A Preliminary Keport on a Part of the Gold Deposits of Georgia. Bull. 4 A, 
 Oeol. Sur. Ga. (1898). 542 pp. 
 YEATMAN, POPE. 
 
 The Braden Copper Company [Chile]. E. and M. Jour., vol. 92, pp. 1128- 
 
 1132, 1186-1188 (1911). 
 YUNG, M. B., and MCCAFFERY, K. S. 
 
 Ore-Deposits of the San Pedro District, New Mexico. Trans. A. I. M. E.. vol. 
 
 33, pp. 350-363 (1902). 
 YOUNG, R B. 
 
 Notes on the Auriferous Conglomerates of the Witwatersrand. Trans. Oeol. 
 Soc. So. Af., vol. 10, pp. 17-30 (1907). 
 
 ZERRENER, CARL. 
 
 Manganerz-Bergbaue in Deutschland, Frankreich, und Spanien (Freiberg, 
 1861). 186 pp. 
 
 ZlMMERMANN, C. 
 
 1. Die Wiederausrichtung vervorfener Gange, Lager und Flotse. Dormstadt 
 und Leipsig, pp. 49, 72, 80 (1828). 
 
 2. Uber den Magnetberg Katschkanar am Ural. Zeit. d. D. Geol. GeseL, vol. 
 1, pp. 475-482 (1849). 
 
 ZlRKEL. 
 
 1. Lehrbuch der Petrographie (1893). 
 
 2. Bergaunnische Mittheilungen iiber Cornwall. Zeit. f. Berg-, Hutt. u.Salinenw., 
 vol. 9, pp. 248-261 (1861). 
 
 ZlRKLER. 
 
 Uber die gangverhaltnisse der Grube Bergmannstrost bei Clausthal. Gl'dckauf, 
 vol. 33, p. 84 (1897). 
 
 ZlNCKEN. 
 
 Die Mineralschatze des Europaischen Kusslands. Berg- u. Hutt. Zeit, vol. 39, 
 pp. 340-341 (1880). 
 
SUBJECT INDEX. 
 
 NOTE. Authors' names are alphabetically arranged unless otherwise stated. 
 Numbers after authors' names refer to the number of the paper in the list of papers. 
 When names or numbers are in Italics papers are not written in English. 
 
 ABBREVIATIONS. Hist, chiefly of historic interest; Rec., strongly recommended 
 as of value in the understanding of ore-genesis ; E. , elementary ; D., of no especial 
 importance; Des. , mainly descriptive and only incidentally concerned with questions 
 of ore-genesis ; Geol., dealing with geological problems which, though not directly 
 concerned with ore-deposits, have important applications to the subject; Rev., 
 review or reviewed. The abbreviations "Rec.," "Des.," etc., are attached to 
 only a few of the more general . papers. Where omitted the paper is usually a 
 valuable one in that particular phase of the discussion where it is cited. 
 
 GENERAL TREATISES ON METALLIFEROUS 
 DEPOSITS. 
 
 Beck, 8, Rec., 1909. 
 
 9, Rec.. 1909. 
 
 Bergeat-Stelzner, Spec. Rec., 1906. 
 Branner and Newsom, 1 (Syllabus), Rec., 1910. 
 Bruhns, D., 1870. 
 Burat,!, Hist., 1870. 
 Campbell, A. C., 1, 1880. 
 Cfiarpentier, 1900. 
 Cole, 1906. 
 von Cotta, 1, Rec. Hist., 1861. 
 
 2, Translation in English by F. Prime, Hist., 
 
 Rec., 1870. 
 de la Coux, 1896. 
 
 Oumenge and Robettaz, Gold only, 1, 1898. 
 Curie, 1, Gold only, 1905. 
 d'Achiardi, Rec., 1883. 
 de Launay, 1, Rec., 1893. 
 
 4, Rec., 1897. 
 
 6, Rec., 1897. 
 
 11, Rec., 1905. 
 Fawns, 3, Tin only, 1907. 
 
 Fuchs and de Launay, 1, Encyclopaedic, 2 vols., 
 Rec., 1893. 
 
 2, Second Edition, Rec., 1912. 
 Grimm, Hist,, 1869. 
 
 von Groddeck, 1, Hist., 1879. 
 
 3, French translation of 1, 1884. 
 Giinther, S., Geol., 1897. 
 
 Gilrich, 1, Rec., 1899. 
 
 Hancock, E., 1908. 
 
 Hayes, 2, Suggestions for field observations on 
 
 ore-deposits, pp. 66-70, 109-154, 1909. 
 Kenwood, 2. Hist., 1871. 
 Hunt, T. S..2, 1873. 
 Johnson, J. P., 1, South Africa, 1908. 
 Keck, 1883. 
 
 Keilhack, 2, 1896. 
 
 Kemp, 21, Rec., 1906. 
 
 Kohler, G., 1, Rec., 1884. 
 
 Krahmann, 1, 1903. 
 
 Krusch, Vogt and Beyschlag, see Vogt, Rec. 
 
 1907. 
 
 Lindgren, 36, Rec., 1913. 
 Lotti, 2, 1903. 
 
 Lottner and Serlo, Hist., 1872, also 1878. 
 Mabson, Transvaal only, 1906. 
 Miron, 1903. 
 Moreau, 1894. 
 Mutter, H., 3, 1850. 
 Neunier, Exper. geol., 1904. 
 Page, 1874. 
 Park, 4, 1906. 
 
 Phillips-Louis, Rec., 1896. 
 Posepny, 1 and 2, Spec. Rec. , 1893. 
 Pumpelly, 3, Rec., 1877. 
 Rickard, T. A. (et al.), " a Discussion," Rec., 
 
 1903. 
 
 Rickard, T. A., 7, Rec., 1902. 
 Ries, H., E., Rec., 1910. 
 Sandberger, 1, Hist., Rec., 1885. 
 Spurr, 16, Rec., 1907. 
 Tarr, R. S., D., 1894. 
 Thomas and MacAlister, 1909. 
 Van Hise,4, Rec., 1900. 
 Vogt, Krusch and Beyschlag, 2 vols. published. 
 
 others in press, Rec., 1910. 
 Wadsworth, 1, 1888. 
 Wallace, D., 1908. 
 Werner, Hist., 1791. 
 Whitney, 1, Rec., 1854. 
 Williams, S. G. , 1886. 
 von Wissenbach,~L8'24.. 
 
 ASCENSION THEORIES. 
 
 (Also called Ascension by Infiltration, Thermal Theories, etc. See also under : 
 "Emanations from Igneous Rocks," " Pegmatitic Ore- Deposits," "Ore-Solu- 
 tions," " Pneumatolysis," ' ' Magmatic Differentiation," etc. ). 
 
 Bancroft, 4, pp. 245-268 (vol. 38), 1908. 
 
 4, pp . 809-817 (vol. 40) , 1910. 
 de Beaumont, 1, 1850. 
 Beck, 8, pp. 420-432, 1909. 
 
 9, vol. ii., pp. 51-70, 1909. 
 Becker, 6, pp. 438-450. 
 
 Bergeat-Stelzner, pp. 1202-1239, 1906. 
 Bischof, 1, pp. 904-912, Analyses of metal-bear- 
 ing springs. 1866. 
 Daubree, A., 1, pp. 227-256, Relation of veins to 
 
 springs, 1858. 
 2, pp. 235-246, 1879. 
 
SUBJECT INDEX. 
 
 909 
 
 d e Launay, 7, pp. 85, et seq., 1899. 
 
 Emmons, S. F., 3, Argues against ascension, 
 
 pp. 135-147, 1887. 
 Gautier, A, 1, pp. 316-370, 1906. 
 Hochstetter and Teller, 1878. . 
 Jenney, 3, pp. 445-499, 1902. 
 Kemp, 14, pp. 169-198, 1901. 
 
 16, pp. 699-714, 1902. 
 
 21, pp. 39-44, 1906. 
 Le Conte and Rising, Sulphur Bank, pp. 23- 
 
 33, 1883. 
 
 Le Conte, 3, pp. 942-1006, 1894. 
 Mutter, H., 1, pp. 261-309, 1885. 
 Newberry, 5, 1883. 
 
 Phillips, 5, p. 321, 1868. . 
 Phillips-Louis, p. 136, 1896. 
 Posepuv, 2. pp. 220-244 and 247-254, 1894. 
 
 5. Underground waters, pp. 71 and 38, 1885. 
 : Roth, Analyses of min. springs, pp. 564 et seq., 
 
 118/9. 
 Spurr, 17, 781-795, 1907. 
 Stelzner, 2, pp. 377-412, 1896. 
 Suess, g, 1902. 
 
 Van Hise, 8, pp. 1072 et seq. General discus- 
 sion, 1904. 
 Weed, 3, pp. 227-255, 1900. 
 
 (Other references will be found under the 
 headings mentioned above.) 
 
 CAVITIES IN ROCKS. 
 
 GENERAL. 
 
 Bancroft, 4, Depth of formation of, pp 259- 
 
 263, 1908. 
 
 Beck, 8, pp. 161-175, also 607-610, 1909. 
 Bergeat-Stelzner, pp. 476-521, 1906. 
 Bra'nner and Newsom, pp. 24-30 (Syllabus 
 
 only), 1900 
 Chance, 8, Depth of fracture zone, pp. 299-302, 
 
 1908. 
 
 Fuller, 2, pp. 63-64, 1906. 
 Heim, 1, p. 44, 1878. 
 
 Hoskins, pp. 845-874, Flow and fracture, 1896. 
 Kemp, 21. pp. 13-32, 1906. 
 Louis, 1, 1893. 
 Phillips-Louis, pp. 67-85, also in part, 86-187, 
 
 1896. 
 
 Posepny, 2, pp. 207-210, 1893. 
 Ransome, 2, pp. 43-67, 1901. 
 Ries. pp. 323-325, 329-335, 1910. 
 Spurr, 16, pp. 148-196, 1907. 
 Van Hise, 2, pp. 589-603, Cleavage and fissility, 
 
 pp. 633-668, 1896. 
 
 4, pp. 29-45, Cavities in general, 1900. 
 8, General, pp. 125-146. 155, 618, 1201; Depth 
 
 Of openings, pp. 159-191, 1006-1008, 1904 
 
 PORE-SPACES. 
 
 Buckley, 2, pp. 225 etseq., 1898. 
 
 Fuller. 2, p. 61, 1906. 
 
 Mead, 1908. 
 
 Slichter, pp. 305 et seq., 1899. 
 
 Van Hise, 8, pp. 123-146, 1904. 
 
 AMYGDALOIDAL CAVITIES. 
 
 Van Hise, 8, pp. 127, 134, 1904. 
 
 FISSUKES. 
 
 Bancroft, 4, pp. 2-i9-263, 1909. 
 Beck, 8, pp. 161-175, 1909. 
 Becker, 4, pp. 407-415, Good general discus- 
 sion. 1888. 
 
 7, p. 49, 1891 ; 8, 1893 ; 9, 1893 ; 10, p. 130, 1894. 
 13, pp. 269-272, fissures in schists, 18%. 
 
 Bergeat-Stelzner, pp. 476-478, 1007-1188, 1906. 
 
 Brown, A. J., 1874. 
 
 Burnt, pp. 32-61, 1870. 
 
 Church, 1, pp. 469-613, 637, 1892. 
 
 Daubree, A., 2, pp. 300-374, 1879. 
 
 Daubree, O. A., 1 and 2, Excellent papers on 
 
 fissures, 1879-1887. 
 de Launay, 11, pp. 596-605, 1905. 
 Emmons, S. F.,4, p. 200, 1887. 
 6, 1888. 
 
 8, p. 49, 1892-3. 
 7, p. 548, 1892. 
 
 Fuller, 2, pp. 63-64. 1906. 
 Glenn, 1, pp. 499-514, 1895. 
 Heim, 1, p. 44, 1878. 
 Hofer, 4, 1899. 
 
 Irving, J. D., Emmons, S. F. and Jaggar. T. A., 
 pp. 126-136, Torsion fissures, 1904. 
 
 KeUhack, 1, 1895. 
 
 Kemp, 21, pp, 13-32, 1906. 
 
 Kohler, O., 1, 1884. 
 
 3, 1897. 
 
 Koto, Earthquake fissures, 1893. 
 Lindgren, 8, Grass Valley fissures, pp. 164-171, 
 
 1896. 
 
 9. p. 647 et seq., also pp. 690-693, 1897. 
 11, at Silver City, pp. 101-103, 1899. 
 Lindgren and Ransome, 2, Cripple Creek Has 
 very general bearing on fissure formation 
 in general, pp. 153-168, 1906 
 Lossen, 1, Torsion fissures, p. 336, 1886. 
 MiMer, H., 2, Freiberg fissures, 1901. 
 Penrose and Cross, Cripple Creek, pp. 139-150, 
 
 1896. 
 
 Phillips, 2, Origin of veins, 1871. 
 Phillips-Louis, pp. 60-85, 1896. 
 Posepny. 2, pp. 207-210. 1893. 
 Purihgton, 1, 764-781. 1897. 
 
 7, Camp bird region, 1905. 
 Ransome, 1, Termination of fissures in shales, 
 1900. 
 
 2, pp. 43-67, Excellent discussion of origin 
 of Silverton fissures which has wide appli- 
 cation. 1901. 
 
 3, Rico Mts., 1901., 
 
 Ransome and Calkins, Cceur d'Alene, Ex. 
 
 gen discussion, pp. 114-122, also 134-135, 
 
 1908. 
 
 Ries, pp. 329-335, 1910. 
 Rickard, 9, 1896. 
 Spencer, 5, p. 586, 1905. 
 
 6, Juneau, pp. 27-28, 1906. 
 Spurr, 16, pp. 148-196, 1907. 
 
 6, Monte Cristo, pp. 805-831, 1901. 
 Spurr and Garrey,3, Contains many admirable 
 
 illustrations of different types of fissures 
 
 showing their irregularities but no general 
 
 discussion of fissure formation, 1908. 
 Stevens, B., 1, pp. 475-491, Laws of fissures. 
 
 Chiefly mathematical, D., 1909. 
 Tarr. R. S., 1, Rifting in granite, 1891. 
 Tower and Smith, Tintic fissures, pp. 676-683, 
 
 1898. 
 
 Tyrrell, 1, Cobalt fissures, 1907. 
 Van Hise, 2, pp. 672-678, 1896. 
 Watts, Whittlesey, 1876. 
 Williams, A., Jr., 2, Dip and strike, 1892. 
 Winslow, 2, pp. 670-673, in Mo. limestone, 1894. 
 (Many other references on fissures might be 
 cited, but are omitted as they would occupy 
 undue space. References to them are avail- 
 able in all the general treatises mentioned on 
 page 908.) 
 
 JOINTS. 
 
 Becker, 7, 1893 ; 8, 1893 ; 9, 1894 ; 10, 1896 ; 19, 
 
 1904. 
 
 Crosby, 1, 1881 ; 2. 1882 ; 3, 1887 ; 4, 1893. 
 Gilbert, 1, p. 50, 1882 ; '2, 1882. 
 Herman, p. 112, 1899. 
 Le Conte, 5, p. 233, 1882. 
 
 ., I McGee, pp. 152. 476, 1883. 
 ! Tarr, R. S., 1, 1894. 
 
910 
 
 SUBJECT INDEX. 
 
 GASH-VEENS, PITCHES AND 
 FLATS, ETC. 
 
 Bain, 2, pp. 35-45, 53-66, 1906. 
 Branner, 3, 1901. 
 
 Chamberlin, T. C., 3, pp. 451-488, 1882. 
 Grant, 3, 1905 ; 4, pp. 64-79, 1906. 
 Grant and Burchard, 1907. 
 
 DOLOMIT I Z ATION-C AVITIES. 
 
 Bain and Van Rise, pp. 208-212, 1901. 
 
 de Beaumont, 2, pp. 174-177, 1836. 
 
 Bischof, 2, vol. Ill , pp. 169-170, 1859. 
 
 Dana, 4th ed.. p. 133, 1895. 
 
 Harkness, p. 101, 1859. 
 
 Hunt, 1, p. 92. 
 
 Orton, pp. 582-587, 619-620,- 641-643, also plate 
 
 LX., 1889. 
 
 Pirsson, pp. 307-309, 1908. 
 Prestwich, vol. i., pp. 113-114, 1886. 
 Spurr, 5, pp. 206-216, 1898. 
 Van Hise, 8, pp. 238-239, 798-808, 1904. 
 
 SADDLE-REEFS. 
 
 Faribault, 7 and 8, Nova Scotia, 1899, 1903. 
 
 Jaquet, 4, 1894. 
 
 Phillips-Louis, pp. 155-160, 1896. 
 
 Pittman, 2, p. 45, 1892. 
 
 Rickard, T. A., 2, pp. 463-529, 1891. 
 
 Samuels, Behdigo, 1893. 
 
 Schmeisser, 1898. 
 
 Watt, 1898, p. 153, also 1899, p. 83. 
 
 SOLUTION-CAVITIES. 
 
 (A few references only are given on 
 this topic as the literature is extremely 
 voluminous. ) 
 
 Curtis, 2, pp. 94-96, 1884. 
 
 Dana, 1895. 
 
 Emmons, S. F., 2, pp. 566-569, 1886. 
 
 Leonard, 1. pp. 288-294, 1895. 
 
 2, pp. 30, 43, 61, 1897. 
 Posepny, 2, p. 207, et seq., 1893. 
 Winslow, 2, pp. 670-673, 1894. 
 
 (See also all books on ore-deposits, and all 
 text-books of geology.) 
 
 CVVITIES DUE TO FISSILITY, 
 CLEAVAGE, AND METAMOR- 
 PHISM. 
 
 Becker, 10, pp. 429-448, 1896 ; 19, 1904 ; 12, pp. 
 
 269-272, 1896. 
 
 Le Conte, 1, pp. 189-196, 1904. 
 Leith, 3, 1905. 
 Van Hise, 2, pp. 633-668, 1896. ' 
 
 3, 1896; 7, pp. 294-328, Rock-flowage . 
 
 CONTACT-METAMORPHIC DEPOSITS. 
 
 CHARACTER AND GENESIS. 
 
 Barrell, 1, 1902- 
 
 2. pp. 116-150, 1907. 
 Beck, 8, pp 482-606, 1909. 
 
 9, vol. i., pp. 98-168, 1909. 
 Bergeat, 1, Concepcion del Oro, 1910. 
 Bergeat-Stdzner, pp. 1131-1188 (metaso m a t i c 
 
 type), 1904-1906. 
 
 Credner, 2, Geol., pp. 288-298, 1903. 
 Fakuchi. General for Japanese ore-deposits, 
 
 1907. 
 
 Gabert, Erzgebirge, 1907. 
 von Groddeck, 1, Hist., 1879. 
 Hastings, 4, 1908. 
 Kemp,. 26, 1907. 
 
 27, 1906. 
 
 Kemp and Gunther, 1907. 
 Keyes, 7, 1909. 
 Kjerulf, 1879. 
 Klockmann, 3, 1904. 
 Leith, 6, 1908. 
 
 7, pp. 277-281, 1908. 
 
 Lindgren, 14, Excellent general paper. Espe- 
 cially Rec.. 1901 ; 19, 1904 ; 20 a., 1905. 
 Lindgren, Graton and Gordon, pp. 51-55 (1910). 
 Lindgren and Ransome, 2, pp. 19-20, 123-164, 
 
 176-177, Rec., 1905. 
 Lotti, 2, pp. 51-78, 1903. 
 McCarty, 1896. 
 Park, 6, 1906. 
 
 Spencer, 8, pp. 49-52, 1909. 
 Spurr, 3, pp. 395-398, 399-402, 1895. 
 
 16, pp. 16, 107, 108, 245, 1907. 
 Stulzer, 5, 1906. 
 
 12, 1909. 
 
 Thomas and MacAlister, pp. 349-358, 1909. 
 Vogt. 5, Vol. iii., p. 154, 1895. 
 
 8, Vol. vi.. p. 415^16, 1898. 
 
 10, pp. 137-140, Rec., 1901. 
 Weed, 10, 1902. 
 
 9, pp. 404-406, 428-435, 1902. 
 
 CHEMICAL AND PHYSICAL 
 CHANGES WHICH OCCUR DUR- 
 ING THE FORMATION OF CON- 
 TACT-METAMORPHIC DEPOSITS 
 
 Barrell, 1, pp. 279-296, 1902. 
 
 2, pp. 116-150, 1907. 
 Kemp, 20, 1905. 
 
 26, pp. 190-194, 1907 ; 27, 1906 ; 31, 1909. 
 Leith and Harder, pp 24-37, 75-89, 1908. 
 Lindgren, 19, pp. 511-551, 1904. 
 
 20 a., pp. 19-20, 123-164, 176-177, 1905. 
 
 CONTACT-DEPOSITS OF COPPER. 
 
 Bergeat-Stelzner, pp. 1131-1188, Many individual 
 deposits in detail with references to foreign 
 literature; pp, 1148-49, Maidanpek, Med- 
 norudiansk ; pp. 1175-1176 ; Bogoslowsk, p. 
 1176 ; 1906. 
 
 Blake, 13, 1903. 
 
 Boutwell,4, Bingham, Utah, pp. 511-580, 1905. 
 
 Brewer. 2, Vancouver, 1899. 
 
 3, ditto, vol. 69, pp. 465-466, 526 ; vol. 70, pp. 
 34-35, 1900. 
 
 4, ditto. 1906. 
 Crosby, 7, 1905. 
 Emmons, S. F., 19, 1910. 
 Emmons, W. H., 4, 19Q9. 
 Kemp, San Jose', Mexico, 20, 1905. 
 
 Kemp and Gunther, White Knob, Idaho, 1907. 
 Lindgren, 11, pp. 249-253, Idaho, 1899. 
 Lindgren, Graton and Gordon, pp. 51-55, 172- 
 
 174, 184-185, 205-206, 220, 241-243, 292, 305, 
 
 329-330, New Mexico, 1910. 
 McConnell, 2, Yukon, 1909. 
 Schmidt and Prciswerk, 4, p. 217, Cala, 1905. 
 Smith, George, 2, Australia, 1903. 
 Spurr and Garrey, 2, Velardefia, Mexico, 1908. 
 Stutzer, 11. Alaska. 1909. 
 Trilstedt, 1, Finland, 1903. 
 Weed, 9, Jimenez, Mexico, pp. 404-405, 1901. 
 General, 19, pp. 74-77, 1908. 
 
SUBJECT INDEX. 
 
 911 
 
 CONTACT-DEPOSITS OF GOLD 
 AND SILVER 
 
 Barrell, 2, 1907. 
 
 Bergeat-Stelzner, pp. 1136-7, Reichenstein, 1906. 
 
 Hershey, 1, 1899. 
 
 Spurr, 3, Mercur, Utah, pp. 395-398, 1895. 
 
 OF COBALT. 
 
 Bergeat-Stelzner, Daschkessan, p. 1179 ; Tuna- 
 berg, p. 1168, 1906. 
 
 SILVER AND LEAD. 
 
 Berg, 2, Balia-Maden, Turkey, 1901. 
 Bergeat-Stelzner, Sala, p. 1166 ; Balia-Maden, p. 
 
 1180, R^zbanya, p. 1147, 1906. 
 Clapp and Ball, Eastern U. S., 1909. 
 Lindgren, Graton and Gordon, New Mexico, 
 
 1910. 
 
 Posepny, 2, 286-289, 1893. 
 Ralli, Turkey, 1904. 
 
 IRON. 
 
 Beck, 2, Schwarzenberg, 1902, 1904. 
 8, Banat, p. 587 : Berggieshubel, p. 583 ; Elba, 
 
 p. 596 ; Magnitnaia p. 598 ; Schmiedeberg, 
 
 p. 586 ; Schwarzen Cruz, p, 587 ; Traversella 
 
 and Brosso, p, 595, 1909. 
 Berg, 1, Schmiedeberg, 1892. 
 Bergeat-Stelzner, Banat, p. 1141; Berggieshiibel, 
 
 p. 1139 : Elba, p. 1159 ; Magnitnaia, p. 1177 ; 
 
 Schmiedeberg, p. 1135 ; Schwarzenberg, p. 
 
 1137 ; Traversella and Brosso, p. 1150 ; Gala, 
 
 pp. 1149-50 ; Wyssokaia and Goroblagodat, 
 Ural Mts., pp. 1171-1175; Katschkanar, 
 Siberia, p. 1179; Cerro Mercado, Mexico, 
 
 p. 1186. 
 d'Achiardi, 1883. 
 Dalmer, 1, Schwarzenberg, 1900. 
 Diller, 2, Redding, Cal., 1903. 
 Farrington, Cerro Mercado, Mexico, 1904. 
 Halavdts and Sjogren, Banat, Hungary, 1891. 
 Hill, 1, Mexico, 1893. 
 Kemp, 31, Iron Springs, Utah, 1909. 
 Kimball, 2, Cuba, 1885. 
 Lacroix, 1, Que>igut, 1890. 
 Leith, 8, Iron Springs, Utah, 1910. 
 Leith and Harder. Iron Springs, Utah, 1908. 
 Lotti, 2, Brosso and Traversella, pp. 56-68, 1903. 
 
 Loewinson-Lessing, 1, Goro-blagodat, 1907. 
 
 2, Wyssokaia, 1909. 
 
 Morozewicz, 1, Magnitnaia, Urals, 1904. 
 Mutter, A., 2, Berggieshubel, 1890. 
 Novarese, Brosso and Traversella, 1902. 
 Prescott, California, 1908. 
 Rangel, Villarello and Bdse, 1, Cerro Mercado, 
 
 Mexico, 1902. 
 
 Schmidt and Preiswerk, p. 217, Cala, 1905. 
 Sjogren, 1, Banat, 1886. 
 
 2, Sweden, p. 373, 1891. 
 
 3, Sweden (English), pp. 766-835, 1907. 
 Smith, George, 2, Chillagoe, Australia, 1903. 
 Souder, Cuba, 1904. 
 
 Triistedt, 1, Pitkaranta, Finnland, 1903. 
 Vogt, 5, Christiania, pp. 154-155, 1895. 
 Wedding, Cuba, 1892. 
 
 TIN. 
 
 Claypole, 1892. 
 
 Collier, 1, Seward Peninsula, Alaska, 1902. 
 
 2, York region, 1904. 
 
 Fawns, 3, pp. 159-164, 1st Ed., 1905. 
 Fay, pp. 664-682, 1907. 
 Gabert, Erzgebirge, 1907. 
 Knopf, 1, Alaska, 1908. 
 
 3, ditto, 1909. 
 
 Merensky, 3, Transvaal, 1908. 
 Rickard, Edgar, 1903. 
 
 ZINC. 
 
 Beck, 2, Schwarzenberg, 1902-4. 
 
 Blake, 8, 1894. 
 
 Crosby, 7, 1905. 
 
 Dalmer, 1, Schwarzcberg, 1900. 
 
 Lindgren, Graton and Gordon, pp. 220, 241-243, 
 
 1910. 
 
 Spencer, 7, Franklin Furnace, 1908. 
 Spurr and Garrey, 2, Velardefia, Mexico, 1908. 
 Trustedt, 1, Pitkaranta, Finnland, 1903. 
 
 MISCELLANEOUS CONTACT-ME- 
 TAMOKPHIC OCCURRENCES. 
 
 Oanaval, 1, 1908. 
 
 Gabert, 1907. 
 
 Kjerulf, 1879. 
 
 McCarty, pp. 169-189, Mexico, 1895. 
 
 Ordonez, 1, p. 233, Mexico, 1898. 
 
 Ordonez and Aguilera, 68-222, 1897. 
 
 Upsensky, 1903. 
 
 CLASSIFICATION OF ORE-DEPOSITS. 
 
 (These references are chronologically arranged.) 
 
 von Waldenstein, pp. 4-6, Hist., 1824. 
 
 Fuchs, pp. 81-86, 1846. 
 
 Whitney, 1, pp. 1-68, 1854. 
 
 von Cotta, 2, p. 2, 1859 (also later editions). 
 
 Lottner and Serlo, pp. 3-32, 1869. 
 
 Grimm, pp. 14-15. 1869. 
 
 Burnt, pp. 9-12, 1870. 
 
 von Cotta (Prime's translation), 2, 1870. 
 
 Pumpelly, 3, Vol. 3, pp. 974-981, 1877. 
 
 von Groddeck, 1, p. 84, 1879. 
 
 Newberry, 4, 1880. 
 
 Geikie, A., pp. 807-812, 1882. 
 
 Le Conte, 2, 1883. 
 
 Kdhler, G., 1, 1884. 
 
 Phillips, 6, p. 3, 1884. 
 
 von Groddeck, 2, 1885. 
 
 Emmons, S. F., 2, pp. 367-375, 1886. 
 
 6, pp. 805-808, 1888. 
 
 Munroe, (referred to in Kemp 21, Appendix I.) 
 Wabner, 1891. 
 
 Wadsworth, 3, p. 144, 1891. 
 Power, 1892. 
 Kemp, 4, pp. 3-24, 1893. 
 KLockmann, 1, pp. 400-406, New Edition of 1900, 
 
 pp. 595-602. 1892-1900. 
 Jenney, 1, pp. 190-191, 1893. 
 Posepny, 2, 1893. 
 Crosby, 5, 1894. 
 Raymond, 5, 1894. 
 
 Vogt, J. H. L.,2, 1894. 
 
 Hastings. 2, 1895. 
 
 Phillips-Louis, pp. 3-10, 1896. 
 
 Hofer, 3, pp. 112-116, 1897. 
 4, pp. 173-176, 1899. 
 
 Giirich, 1, 1899. 
 
 Lindgren, 12, by metasomatic minerals, 1900. 
 
 Louis, 3, 1900. 
 
 Van Hise, 4, 1900. 
 
 Keyes, 1, pp. 323-356, 1900. 
 
 Bergeat-Stelzner, pp. 15-19, 1900. 
 
 Lindgren, 13, of veins of the Blue Mts., Oregon, 
 1901. 
 
 Rickard, et al, 1 (Edited by) " A Discussion." 
 Contains many valuable papers on classi- 
 fication and genetic subjects, 1903. 
 
 Lotti, 2, p. 28, 1903. 
 
 Weed, 13, pp. 256-257, 1903. 
 
 Schierl, 1904. 
 
 Van Hise, 8, p. 1005, 1904. 
 
 Hille, 2, of gold deposits, 1905. 
 
 Foster, pp. 3-18, 1905. 
 
 Kemp, 21, pp. 54-79, also pp. 447-462, 1906. 
 
 Weed, 19, of copper deposits, pp. 69-81, 1908. 
 
 16 a, of copper deposits, pp. 
 Beck, 8, pp. 2-4, 1909. 
 
 9, pp. 4-8, 1909. 
 Adam, J. W. H., 1910. 
 Ries, 1910. 
 
 96-97, 1905. 
 
912 
 
 SUBJECT INDEX. 
 
 DEFINITION OF THE TERM "ORE." 
 
 (See general treatises on ore-deposits on p. 908 of this index.) 
 
 Beck, 8, p. 1, 1909. 
 9, pp. 1-2, 1909. 
 Kemp, 29, 1909. 
 
 Kemp, 30, 1909. 
 Ries, p. 305, 1910. 
 Weed, 19, p. 22, 1908. 
 
 DEPTH, INFLUENCE OF, ON ORE-DEPOSITION. 
 
 Changes which affect the continuation and occurrence of ore-deposits in depth 
 maybe due to secondary causes, for which see under "Superficial Alteration," 
 and "Oxidation," or to primary or original causes. These latter are (1) Ex- 
 istence of fissures or cavities. (2) Effects of temperature and pressure on min- 
 erals deposited, i. e., changes in primary mineralogy with depth. ) 
 
 GENERAL. 
 
 de La.unay, 1, 1893. 
 
 8, 1900 ; 16, 1909. 
 Emmons, S. F., 12, pp. 428-429, Ouster Co., 
 
 Colo., 1896. 
 Gregory, J. W., 1, 1901. 
 
 2, 1904; 7,1906. 
 Lindgren, 24, 1906. 
 Posepny, 9, 1867. 
 Van Hise, 8, pp. 1081-1138, 1904. 
 
 DEPTH TO WHICH CAVITIES CAN 
 EXTEND. 
 
 Adams, F. D., 3, 1912, Rec. 
 Bancroft, 4, pp. 259-263, 1907. 
 Beck, 8, pp. 121-125, 1909. 
 Bergeat-Stelzner, pp. 476-479, 1906. 
 Chance, 8, pp. 299-302, 1908. 
 Emmons, S. F., 2, at Leadville, p. 568, 1886. 
 Fuller, 2, pp. 63-64, 1906. 
 Faribault, 7 and 8, Nova Scotia, 1899-1903. 
 Heim, pp. 89 etseq., 107, 1878. 
 Reyer, 1, pp. 454-593, 1888. 
 Van Hise, 2, pp. 589-603, 1896. 
 8, pp. 187-191, 1005-1013, 1904. 
 
 CHANGES IN PRIMARY MINER- 
 ALOGY WITH DEPTH. 
 
 Beck, 8, pp. 361-363, 1909. 
 Bergeat-Stelzner, pp. 992-995, 1906. 
 de Launay, 1, 1893. 
 
 8, 1900. 
 
 16, 1909. 
 Gregory, 1, 1901. 
 
 2, 1904 ; 7, 1906. 
 
 Lindgren, 25, pp. 123-125, Applied to Dah- 
 lonega veins, 26, Excellent general paper 
 on physical conditions, 1907. 24, 1906. 
 Sjogren, 4, Changes with depth in Swedish 
 
 ores, 1908. 
 
 Spencer, 6, Alaska, 1906. 
 Spurr, 16, pp. 295-299, 1907. 
 Spurr and Garrey, 3, Georgetown, pp. 148-149, 
 1908. 
 
 1, Idaho Springs, p. 40, 1905. 
 Van Hise, 8, pp. 1072-1138, 1904. 
 Vogt, 9, Huelva, 1899. 
 
 10, pp. 158-164,1901. 
 Williams, A., Jr., 1, pp. 259-262, 1884. 
 Weed, 3, p. 249-252, 1900. 
 Weed and Barrell, 1901. 
 
 Zirkler, p. 84, Change in mineralogy of Claus- 
 thal veins, 1897. 
 
 DESCENSION THEORIES. 
 
 (See also under " Sedimentary ores " sub-head : " Ores supposed to be derived 
 from disseminated particles deposited in sedimentary rocks during deposition.") 
 
 Beck, 8, pp. 411-413, 1909. 
 
 9, vol. II., pp. 41-43, 1909. 
 Bergeat-Stelzner, pp. 1192-1193, 1906. 
 von Beust, 1840. 
 Bucking, pp. 51-52, 1889. 
 
 Emmons, S. F., 3, pp. 125-147, 1887. 
 2, Leadville, pp. 379, 569-584, 1886. 
 Hornung, 2, 1905. 
 Krusch, 3, 1904. 
 Moore, 1869. 
 Werner, Hist., 1791. 
 
 DETRITAL DEPOSITS. 
 
 GENERAL. 
 
 Beck, 8, pp. 611-660, especially 651-656, 1909. 
 
 9, vol II., pp. 417-491, especially pp. 477-484, 
 
 1909. 
 
 Bergeat-Stelzner, pp. 1258-1297, 1906. 
 Brooks, 8, 1906. 
 Cohen, 1887. 
 de Launay, 14, 1907. 
 
 15, 1908.' 
 Emmons, W. H., 5, Relation of placers to lodes 
 
 1909. 
 
 Helmhacker, 2, Altai, 1891. 
 Hutchins, 2, 1907. 
 
 Lake, p. 11, 1903. 
 
 Maclaren, 2, pp. 80-99, Excellent general sum- 
 mary, 1908. 
 Park, 8, 1908. 
 Phillips-Louis, pp. 20-28, see also pp. 619-633 
 
 and 648-649, 1896. 
 Posepny, 7, General treatise, 1887. 
 
 2, pp. 331-342, Excellent general review. 1893. , 
 
 6, pp. 499-598, 1895. 
 Smyth, H. L., 1, 1905. 
 Spurr, 16, pp. 205-233, 1907. 
 Thomas and MacAlister, pp. 376-409, 1908. 
 Welton, 1899. 
 
SUBJECT INDEX. 
 
 913 
 
 DISTRIBUTION OF GOLD IN PLA- 
 CERS, ORIGIN OF NUGGETS, ETC. 
 
 Beck, 8, pp. 651-656, 1909. 
 9, vol. it, pp. 477-484, 1909. 
 
 Brauns, p. 406, 1896. 
 
 Buttgenbach, 1. 
 
 Chalmers, Quebec, 1901. 
 
 Cohen, Exhaustive discussion on origin of al- 
 luvial gold, 1887. 
 
 Crane, W. R., A Treatise on Gold and Silver, pp. 
 159-171, 1908. 
 
 Devereux, Discusses formation of nuggets, 
 pp. 465-475, 1881. 
 
 Eggleston, Nuggets, 1881. Also, Sch. Min. Quar, 
 vol. 7, p. 101, Good general discussion of 
 placers, 1885. 
 
 Francois, 1840. 
 
 Gordon, 1895. 
 
 Harrison, Fowler, and Anderson, Gold in vege- 
 tation, 1908. 
 
 Knox, N. B., pp. 211-213, 1903. 
 
 Lake, p. 11, 1903. 
 
 Lindgren, 13, pp. 634-637, 1901. 
 
 Liversidge, 1, 1893^. 
 
 2, Nuggets, 1897. 
 
 3, ditto, 1906. 
 
 Lotti, 2, pp. 121-123, 1903. 
 
 Lungwitz, 2, Gold in vegetation, 1900. 
 
 Maclaren, pp. 80-86, Ex. general summary. 
 
 1908. 
 
 Murchison, 1851. 
 Park, 4, pp. 10-19, 1906. 
 
 8, 1908. 
 
 Phillips, 5, 1868. Also, Am. Jour. Sci., 2nd Sen, 
 
 vol. 47, p. 134. 
 Phillips-Louis, p. 631, 1896. 
 Posepny, 7, 1887. 2, pp. 336-339, 1893. 
 Smyth, H. L., 1, 1905. 
 Spurr, 4, pp. 366-379, 1897. 
 Tyrrell, J. B., 2. Concentration in Klondike, 
 
 1907. 
 
 GOLD PLACERS. 
 
 Stream Placers. 
 
 Bancroft, 3, Sonora, Mexico, 1903. 
 de Batz, Siberia, 1898. 
 Becker, 14, Alaska, 1897. 
 
 12, Southern Appalachians, 1895. 
 Bergeat-Stelzner, pp. 1266-1275, Bibliography of 
 literature of foreign deposits, only a few 
 of which are given here, 1906. 
 Blatchford, West Australia, pp. 21-30,1899. 
 Boutwell, 5, Bingham, pp. 331-360, 1905. 
 Branner and Newsom, p. 126, 1900. 
 Brooks, A. H., 3, pp. 41-44, Alaska, 1903. 
 
 5, ditto, pp. 43-59, 1903. 
 
 7, Alaska, pp. 18-31, 1905. 
 
 9, Kougarok, Alaska, 1907. 
 
 10, Circle Precinct, Alaska. 1907. 
 
 Brooks, Richardson and Collier, Alaska, 1901. 
 Browne, E. R , California, 1890. Also E. and 
 
 M. Jour., vol. 58, p. 101, 1895. 
 Chalmers, Quebec, 1901. 
 Coleman, 1, Ontario, 1901. 
 Collier, 3, N. E. Washington, 1907. 
 Collier, Hess and Smith, Seward Peninsula, 
 
 Alaska, 1908. 
 
 Credner, 1, California, 1866. 
 Cumenge and Robellaz, 1898. 
 Devereux, Fossil placers, Black Hills, 1882. 
 Egleston, Sch. Min, Quar., vol. 7, pp. 101-131, 
 
 1885. 
 
 Gale, 1, Routt Co., Colo, 1908. 
 Gordon, New Zealand, 1895. 
 Granger, Guyanas, 1896. 
 Hammond, 1, California, 1881 ; also, Mint Re- 
 
 portfor 1881, p. 616. 
 Hanks, Mint Report, 1882, p. 728. 
 Harrison, Fowler and Anderson, British 
 
 Guiana, 1908. 
 Hill, 2, Sonora. Mexico, 1902. 
 
 Irving, Emmons, and Jaggar, Fossil placers, 
 pp. 98-111, 181-184 ; Recent placers, 179-180, 
 1904. 
 
 Keele, pp. 18-42, Yukon, 1905. 
 
 Kemp, 21, California, especially pp. 353-362. 
 
 Kerr, North Carolina, 1880. 
 Knox, N. B.,1903. 
 Laur, 1, California, 1863. 
 LeConte, 6, California, 1880. 
 Lawson, 1, California, 1893. 
 Levat, D., 2, Siberia, 1904. 
 Lindgren, 9, Idaho Springs, especially pp. 657- 
 680, 718-719, 1897. 
 
 2, California, 1893. 
 
 6, California, 1894. 
 
 18, California, 1903. 
 
 13, especially pp. 634-637, 1901. 
 20, Bitter Root Mis., pp. 
 
 pp. 83-85, 88-S9, 91-96, 
 
 97, 102-103, 108, 1904. 
 34, Excellent general pa,per on California 
 
 gold gravels, 1911. 
 Lindgren and Drake, Nampa, 1904, 
 Lindgren, Graton and Gordon, New Mexico, 
 
 pp. 74-76, 1910. 
 Lock, A. G., 1882. 
 Maclaren, 2, pp. 78-100, 1908. 
 McConnell, Klondike, 1, 3, 4, 5, 1904-1907. 
 McGillivray, Mint Report for 1881, p. 630. 
 Mendenhall, 4, Alaska, 1903. 
 
 1, Kotzebue, Alaska, 1902. 
 
 2, Norton Bay, Alaska, 1901. 
 Moffit, 1, Fairhaven, Alaska, 1905. 
 
 2, Kotzebue dist., 1904. 
 Moffit and Maddren, Alaska, 1909. 
 Newberry, 3, 1881 : also, Sch. Min. Quar., vol. 3. 
 Prindle, 1, Forty-mile, Alaska, 1905. 
 
 2, Yukon-Tanana, 1906. 
 
 3, Forty-mile, Seventy-mile, Alaska, pp.34- 39, 
 1909. 
 
 Prindle and Hess, 1, Rampart region, Alaska, 
 
 1906. 
 
 2, Fairbanks, Alaska, pp. 64-96, 1908, 
 Prindle and Katz, Fairbanks, Alaska, 1903. 
 Purington, 6, Alaska, 1905. 
 Radford, 1, California, 1899. 
 Ransome, la., California, 1900. 
 Rickard, T. A., 3, New Zealand, pp. 428-442, 
 
 1893. 
 
 Smith, G. O., 2, pp. 76-78, 1903. 
 Spencer, 6. Juneau, Alaska, pp. 77-85, 1906. 
 Spurr, 4, pp. 317-379, Yukon. Alaska, 1897. 
 Spurr and Garrey, 1, pp. 36-37, Idaho Springs, 
 
 1905. 
 
 Storms, 1, Ancient Gravels of California, 1905. 
 Turner, 1, California, 1895. 
 Tyrrell. 2, Klondike, 1907. 
 Washburne, I, Oregon, 1904. 
 Whitney, 3, California, 1879-80. 
 Wright, C. W., 1, Porcupine, Alaska, 1904. 
 
 Fossil Placers. 
 
 AUSTRALASIA. 
 
 Daintree, 1878. 
 
 Posepny, 2, General, pp. 342-345, 1894. 
 
 BLACK HILLS. 
 
 Carpenter, pp. 571-573, 1889. 
 
 Devereux, pp. 465-473, 1882. 
 
 Irving, J. D., 4, pp. 131-132, 1904. 
 
 Irving, J. D., Emmons, S. F., and Jaggar, pp. 
 
 98-111, 181-184, 1904. 
 O'Harra, pp. 32-37, 1902. 
 Turner, 5, 1903. 
 
 CALIFORNIA. 
 
 Blake, Mint Rept. for 1884, p. 572. 
 Bordeaux, 1902. 
 
 Browne, E. R., 1890. Also', 12th Rept. Cal. State 
 Min., p. 202, 1894. 
 
914 
 
 SUBJECT INDEX. 
 
 Cre.dner, 1, 1866. 
 
 Diller, 3, 1907. 
 
 Hammond, 1, 1890. 
 
 Kemp, 21, pp. 353-362, 1906. 
 
 Laur, 1, 1863. 
 
 Lavvson, 1, 1893. 
 
 LeConte, 6, 1880. 
 
 Lindgren, 5, 1894. 
 
 2, 1893 ; 6, 1894 ; 18, 1903. 34. Excellent gene- 
 ral paper, 1911. Also, Folio$ 17, 18, 29, 31. 39 
 and 66, U. S. G. S. 
 
 Lindgren and Knowlton, 1896. 
 
 Lindgren and Turner, 1894. 
 
 McGillivray, Mint Report for 1881, p. 630. 
 
 Ransome, Folio 63, U. S. G. S., 1900. 
 
 Silliman, Am. Jour. Sci., 2nd ser., vol. 40, p. 1. 
 
 Storms, 1, 1905. 
 
 Turner, 5, 1903. Also, Am. Geol., vol. 15. pp. 
 371-379, 1905. 
 
 Whitney, 3, 1879-80. 
 
 SOUTH AFRICA. 
 
 Beck, 5, 1906. 
 
 Becker, 17, 18, 20, 1897, 1898, 1909. 
 
 Czyszkowski, 1896. 
 
 de Lannay, 3, 1896. 
 
 Denny, 1909. 
 
 Gregory, J. W., 10, 1907-8. 
 
 12, 1909. 
 
 Hammond, 2, 1901. 
 Hatch, 2, 1903. 
 Kessler, 1904. 
 Krause, 1897. 
 Mabson, 1906. 
 
 Maclaren, pp. 435-447, 1908. 
 Phillips- Louis, Gold Coast, pp. 729-731 ; Trans- 
 vaal, 731-740, 1896. 
 Sawyer, Gold Coast, Africa, 1902. 
 Schoch, ditto, 1905. 
 Truscott, 1907. 
 Vott. 1, 1908. 
 Wolff, Australia, 1877. 
 Young, R. B., 1907. 
 
 Beach Placers. 
 
 Halla, Nome, 1907. 
 
 Mendenhall, 2, 1901. 
 
 Moffit, 3, Nome, 1907. 
 
 Queneau, Nome, 1902. 
 
 Rickard, F., 2, Nome, 1905. 
 
 Schrader and Brooks, 1, Nome, 1900. 
 
 2, Nome, 1900. 
 Washburne, 2, Oregon, 1904. 
 
 JEolian Placers. 
 
 Rickard, T. A., 11, Australia, pp. 490-537, 1898. 
 Spurr, 14, Auriferous Sand Dunes, Nevada, 
 pp. 30-31, 96-97, 1906. 
 
 TIN PLACERS. 
 
 Barrow, 1908. 
 
 Beck, 1, Bangka and Billiton, 1898. 
 
 8, General, pp. 625-635, 1909. 
 
 9, General, vol. ii., pp. 436-450, 1909. 
 Bergeat-Stelzner, pp. 1288-1294, 1906. 
 Brooks, 1, Alaska, 1901. 
 
 2, ditto, pp. 267-271, 1901. 
 4, ditto, pp. 92-93, 1903. 
 
 David, New England Dist., Australia, 1887. 
 
 Doyle, Malay Peninsula, 1879. 
 
 Farrell, Katanga, p. 752, 1908. 
 
 Fawns, 3, 1907. 
 
 von Fircks, Mt. Bischoff, 1899. 
 
 Gascuel, France, 1905. 
 
 Henwood, 3, Cornwall, Eng., 1874. 
 
 Hess and Graton, General paper with excel- 
 lent bibliography, 1905. 
 
 Ingails, 1, Durango, "Mexico, Placers only in- 
 cidentally mentioned, 1895. 
 
 Kynaston and Mellor, Waterberg, Australia, 
 pp. 80, 83, 83, 89, 114-115, 1909. 
 
 MacAlister and Hill, Cornwall, Eng., pp.6, 11, 
 15, 95-98, 1906. 
 
 MacAlister, 2, pp. 379-380, 1908. 
 
 de Morgan, Bangka and Billiton, 1886. 
 
 Penrose, 3, Malay Peninsula, 1903. 
 
 Reyer, ditto, 2, 1881. 
 3, Australia and Tasmania, 1880. 
 
 Rolker, 1, Sumatra, 1892. 
 
 Rum bold, 2, Malay States, 1906. 
 
 Sandeman, Tasmania, 1899-1900. 
 
 Schurtz, Erzgebirge, 1890. 
 
 Twelvetrees, 1, Tasmania, 1900. 
 
 Wood, 1, 2, Australia, 1881, 1886. 
 
 PLATINUM PLACERS. 
 
 General. 
 
 Beck. 8, pp. 656-660, 1909. 
 
 9, vol. ii., pp. 484-490, 1909. 
 Berffeat-Stelzner,pp. 1284-12*8, 1906. 
 Kemp, 15. Complete discussion with full bib- 
 liography, 1902. 
 
 In Individual Localities. 
 
 Bourdakoff and Hendrikoff, Russia, 1896. 
 
 Brock, 2, British Columbia, 1904. 
 
 Day, North Am., 1900. 
 
 Day and Richards, Black Sands, pp. 1226-1227, 
 
 1905. 
 
 Diller, 4, Oregon, 1903. 
 Homer, Borneo, 1842. 
 
 Howe, Bibliography for years 1748-1896, 1898. 
 Hussak, 1, Brazil, 1906. 
 Jaquet, 2, Bookin Hill, Australia, 1893. 
 
 3, New South Wales, 1897. 
 Katterfeld, Russia, 1885. 
 Kemp, 15, General, 1902. 
 Laurent, Urals, 1890. 
 Louis, 4, Russia, 1898. 
 Purington, 2, Urals, 1899. 
 
 4, ditto, 1904. 
 Rainer, 1, 1902. 
 
 Rose, Russia, 1837-1842. 
 Saytzeff, 1, Urals, 1898. 
 Spring, Russia, 1905. 
 Zincken, Russia, 1880. 
 
 IRON PLACERS. 
 
 Beck, 8, pp. 49-60, 82-111, 1909 ; 9, pp. 363-415, 
 
 vol. ii., 1909. 
 
 Bergeat-Stelzner, pp. 85-470, 1906. 
 Hunt, T. S., Prog. Rept. Can. Geol. Sur., 1866- 
 
 69. E, p. 264, F, p. 269, 1869. 
 Kemp, 21, pp. 180-181, 1906. 
 Smith, E. M., E. and M. Jour., vol. 61, p. 566, 
 
 1896. 
 Vogt, 17, Norway, 1910. 
 
 DISSEMINATED METALS ORIGINAL IN ROCKS. 
 
 GENERAL. IN ERUPTIVE ROCKS. 
 
 Forchhammer, 1854-1855. 
 
 Lincoln, 2, Association of gold with rocks, 
 
 pp. 247-302, 1911. 
 Vogi, 8, 1898, 1899. 
 Washington, 2, pp. 735-764, 1908. 
 
 Blake, 11, Gold in granite, 1896. 
 
 Brock, 1, 1904. 
 
 Catharinet, Bornite, 1905. 
 
 Derby, 1, Gold in pegmatite, 1902 
 
 Emmons, S. F., Leadville, 2, pp. 574-584, 1886. 
 
SUBJECT INDEX. 
 
 915 
 
 Harrison, Fowler and Anderson, pp. 52, 78, 96, 
 204-211, see also review in Econ. Geol., vol. 
 4, p. 493, 1908. 
 
 Hdmhacker, 2, 1891. 
 
 Hussak, 3, 1898. 
 
 Lincoln, 2, pp. 247-302, 1911. 
 
 Maclaren, 2, pp. 100-103, 1908. 
 
 Mallery, Oregon, 1904. 
 
 Mallet, In volcanic ash, 1881. 
 
 Merrill, 1, Gold in granite, 1896. 
 
 Hitter, 1, 1908. 
 
 Washington, 2, 1908. 
 
 (See also under " Magmatic differentiation 
 of native metals.") 
 
 IN SEDIMENTARY ROCKS. 
 
 Chance, 3, Gold in coal, pp. 227-228, 1899. 
 Itieulefait, 2, 1879. 
 5, Zinc in dolomite, 1883. 
 
 4, Manganese in dolomite, 1883. 
 
 5, do., 1883. 
 
 6, Copper and Zinc, 1885. 
 Kemp, 21, ditto, p. 397, 1906. 
 Lincoln, 2, pp. 265-270, 1911. 
 Lindgren, 15, Shales in Kansas, 1902. 
 Lovewell, Shales, 1903. 
 
 IN METAMORPHIC ROCKS. 
 
 DieiOefait, 1, 1878. 
 
 2, 1879. 
 
 Lacroix, 3, p. 21, 1903. 
 Sandberger, 1, 2, 3, 4, 5, 6, 1877-1886. 
 Spurr and Garrey, 4 p. 500, 1903. 
 
 Spurr and Garrey, 4, 
 Stelzner, 1, 1889. 
 
 ELECTRICAL ACTION IN ORE-DEPOSITION. 
 
 Barns, 1. 1884. 
 
 Becker, 1, pp. 309-367, 1882. 
 
 Erhard, 1885. 
 
 Fritsch, 1862. 
 
 Kenwood, 1, 1843. 
 
 Hunt, pp. 385-396, 400, 1884. 
 
 Kemp, 21, pp. 52-53, 1906. 
 
 Monch, pp. 365-435, 1905. 
 Phillips-Louis, pp. 12-5-126, 1896. 
 Smith, George, 1, p. 77, 1896. 
 Sutherland, 1890. 
 Whitney, 1, pp. 65-66, 1854. 
 Wood, G. C., 1906. 
 
 EMANATIONS FROM IGNEOUS MAGMAS. 
 
 (Ore-deposits have been conceived as arising from igneous magmas as a source 
 and depositing ores under three different conditions : ( 1 ) As final products of dif- 
 ferentiation or solidification of the rock mass, more or less extensively mingled 
 with molten eruptive rock, and producing pegmatite veins ; (2) As solutions not ap- 
 preciably mingled with molten magma, i. e. t as pneumatolytic vapors, producing 
 deposits under conditions of high temperatures and pressures usually conceived as 
 produced by deep burial. When such vapors act on limestones contact-metamorphic 
 deposits are produced (which see) ; (3) As solutions emanating from the magmas 
 in the same way, but migrating to greater distances from them, and giving rise 
 both to hot mineral springs, and to the usual types of ore-deposits, veins, replace- 
 ments, etc. Commonly called hydrothermal deposits ( Hyd-atogenetic] . These three 
 headings are used in classifying the following references. ) 
 
 EMANATIONS IN GENERAL. 
 
 Bancroft, 4, vol. 38, pp. 245-268, 1909. 
 de Beaumont, 1, Hist., 1850. 
 Beck, 8, pp. 424-132, 1909. 
 
 9, vol. ii., pp. 55-70, 1909. 
 Sergeat-Stelzner, pp. 1213-1230, 1906. 
 Brun, 1911. 
 
 Buckley, Econ. Geol., vol. iv, pp. 178-186, 1909. 
 Chamberlin, R. T., 1, Gases in rocks, 1909; 2, 
 
 1908. 
 
 Church, Trans. A. I. M. E . vol. 23, p. 593. 
 Clarke, F. W., 2, pp. 201-205 ; 248-276, 1908. 
 Daubree, A., 1, p. 236, 1858. 
 de Launay, 1, 1893. 
 Emmons, 19, Cananea, pp. 352-356, 1910. 10, 
 
 1893, 
 
 Finch, 1904. 
 Frazer, 5, 1904. 
 
 Gautier, A., Relation of thermal waters to vul- 
 canism, 1906. 
 
 S, 1906; 3, 1906. 
 
 4, Gases in rocks, 1906. 
 Graton, 1, 1906. 
 
 2, Shasta Co., Cal., pp. 71-111, 1910. 
 Gregory, 11, Geology of the inner earth, 1908. 
 Gudzent, 1910. 
 Heusler, Relations of ores to igneous rocks, 
 
 1901. 
 
 Hochsletter and Teller, 1, 1878. 
 Kemp, 14,1901. 
 
 16, 1902 ; 18, 1904 ; 24, 1906 ; 28, 1908. 
 Lincoln, 1, 1907. 
 
 Lindgren and Ransome, 3, Cripple Creek, pp. 
 252-269 ; gases in rocks, pp. 225-231 ; mag- 
 matic origin of ores advocated, 1906. 
 
 Lotti, 5, pp. 372-378, Tuscany, 1893. 
 
 Newberry, 4, 5, 6, 1880, 1883, 1884. 
 
 Park, 3, Relation of ores and thermal activity, 
 1905 ; 7, 1906. 
 
 Pirsson, pp. 189-190, 1908. 
 
 Posepny, 2, pp. 247-262, 1893. 
 
 Ransome, 2, pp. 132-141, Silverton, Colo, 1901. 
 3, Rico, Colo., pp. 294-304, Argues against 
 emanations, 1901. 
 
 5, pp. 128-132, Against magmatic waters, 
 Globe, 1903. 
 
 6, Bisbee, pp. 146-160, 1904. 
 10, pp. 189-201, Goldfield, 1907 
 14, Goldneld, 1910. 
 
 Ransome and Calkins, Coaur d'Alene, pp. 134- 
 
 140, 1908. 
 Rickard, T. A., 7, pp. 949-956, 1894. 
 
 20, 1908. 
 
 Rickard, et al, 2, 1903. 
 Ries, pp. 311-323, 1910. 
 Spencer, 4, S. E. Alaska, 1905. 
 
 6, Juneau Veins, 1906. 
 Spurr, 3, Mercur, pp. 396-401, 1895. 
 
 8. General, 1902. 
 
 12, 1905. 
 
 13, Tonopah, pp. 253-262. 1905. 
 
 14, Silver Peak, pp. 99-156, 1906. 
 
 15, Southern Klondike, pp. 369-38-2, 1906. 
 17, 1907. 
 
916 
 
 SUBJECT INDEX. 
 
 Spurr and Garrey, 3, Georgetown, pp. 157-158, 
 
 169-171,1908. 
 Stelzner, 2, 1896. 
 Strutt, Gases in rocks, 1907. 
 Van Hise, 6, 1901. 
 Vogt, 1., Sulphides of Norway and Rammels- 
 
 berg, 1894. 
 
 9, Rio Tinto, 1899 ; 5, 1894. 
 
 10, pp. 130-158, 1901. 
 
 Weed and Pirsson, 2, Judith Mts., pp. 594-598, 
 
 1897. 
 
 Winchell, H. V., 2. pp. 591-593, 1907. 
 5, 1908 ; 6, 1908 ; 8, 1907. 
 
 Magmatic vs. Meteoric Waters. 
 
 Clark, 2, pp. 201-205, 1911. 
 Darapsky, 1903. 
 Daubree, 6. A., 1 and 2, 1887. 
 Delkeskamp, 1904, 1905. 
 Hague, 2, 1911. 
 Henrich.F., 1910. 
 Kemp, 14, 1901. 
 
 16, 1902 ; 18, 1904 ; 24, 1906 ; 28, 1908. 
 Rickard, T. A., 20, 1908 ; 5, 1893 ; 7, pp. 949-956. 
 Van Hise, 4, pp. 27-177, 1900. 
 
 6, pp. 284-303, 1901. 
 
 8, pp. 1052-1069, 1904. 
 Vogt, 5, 1894. 
 
 10, 1901. 
 
 PEGMATITIC OKE-DEPOSITS. 
 
 Beck, U, 1906. 
 
 6, 1906 ; 7, 1909. 
 
 Bergeat-Stelzner, pp. 918-964, 1906. 
 Brogger, pp. 215-235, 1890. 
 Catharinet, Bornite in pegmatite, 1905. 
 Crosby and Fuller, Origin of pegmatites, 1897. 
 Derby, 1, Gold in pegmatite, 1902. 
 Hastings, 5, Origin of pegmatite, 1908 ; 1, 1905. 
 Hussak, 3, Gold in pegmatite, 1898. 
 Kemp, 14, pp. 182-183, 1901. 
 Pirsson, General excellent discussion, pp. 174- 
 
 180, 1908. 
 Rickard, et al., 1, "A discussion." Many 
 
 other authors, 1903. 
 Ritter, 1, Sulphides in pegmatite, 1908. 
 Spencer, 1, 1904. 
 
 7, 1908. 
 
 Spurr, 4, pp. 297-316, Esp. 308-316, good gen- 
 eral discussion. Yukon veins, 1897. 
 
 8, General, 1902. 
 
 9, 1903. 
 
 12, W. Nevada ores, 1905. 
 
 14, Excellent general discussion on pegma- 
 titic origin of veins, pp. 99-156, 1906. 
 
 15, 1906 : 16, pp. 1-22, 1907 ; 17, 1907. 
 
 Spurr and Garrey, 3, pp. 157-158, 169-171, 1908. 
 Stutzer, 10, 1909. 
 Vogt, 5, 1894. 
 6, 1895 ; 10, 1901. 
 
 PNEUMATOLYSIS. 
 
 Beck, 8, pp. 421-424, 1909. 
 
 Bergeat-Stelmer, pp. 19, 24, 527, 920, 921, 1186, 
 1213, 1906. 
 
 Clarke, 2, New Edition, pp. 606-610, 1911. 
 
 Dolmer, 5, 1894. 
 
 Phillips-Louis, pp. 127-129, 173, 1896. 
 
 Rickard, etal.,1," Discussion," pp. 19-20 (Em- 
 mons), 25-27 (Weed) ; also excellent dis- 
 cussion by others, 1903. 
 
 Scrivenor, Origin of Tin Ores, 1909. 
 
 Thomas and MacAlister, pp. 5, 72-115, 1908. 
 
 Vogt, 1, 1893 ; 5, 1894. 
 
 10, 1901. 
 Vogt, Beyschlag and Krusch, pp. 165-167, 1910. 
 
 (A few references only are given on pneuma- 
 tolysis, as the process is not generally very 
 sharply distinguished from other processes 
 of magmatic emanation. See also under 
 Sublimation.) 
 
 HYDROTHERMAL EMANATIONS. 
 
 (See also under Mine Waters, p. 927 of this 
 bibliography.) 
 
 Beck, 8, pp. 424-432, 1909. 
 
 9, vol. ii., pp. 55-70, 1909. 
 Bergeat-Stelzner, pp. 1213-1230, 1906. 
 Chalon, 1, 1905. 
 Chamberlin, R. T., 1, 1909. 
 Clarke, F. W., 2, New Edition, pp. 201-205, 283- 
 
 286, 606-610, 1911. 
 Darapsky, 1903. 
 Daubree, A., 1,1858. 
 
 2, pp. 71-102, 1879. 
 
 de Lannay, 7, 1899 ; 1, 1893. 
 
 Delkeskamp, 3, 4, 5, 6, 7, 8, 1903, 1908. 
 
 Finch, 1904. 
 
 Fink, Deposition of specularite by thermal 
 
 waters, 1906. 
 
 Griffiths, Quicksilver, New Zealand, 1910. 
 Gudzent, Radio active thermal springs, 1910. 
 Hague, 2, 1911. 
 Hastings, 6, 1908. 
 Headden, Radium springs, 1905. 
 Henrich, F., 1910. 
 Heusler, 1901. 
 Hixon, 1, 1907; 2, 1908-9. 
 Kemp, 14, 1901 ; 16, 1902: 17, 1903: 18, 1904; 19, 
 
 1904 ; 22, 1906 ; 24, 1906 ; 26, 1907 ; 28, 1908. 
 Kohler, Eugen, 1910. 
 Konig, F., 1901. 
 
 Le Conte, 2, Steamboat Springs, 1883. 
 Le Conte and Rising, Sulphur Bank, Cal., 
 
 1883. 
 
 Lincoln, 1, Excellent general summary, 1907. 
 Lindgren, 11, Gold and silver, in sinter, 1899. 
 21, Steamboat Springs, 1905. 
 31, 1910 ; 14, pp. 240-242, 1901 ; 19, pp. 219-223, 
 
 1904 ; 27, p. 749, 1907. 
 Lindgren, Graton and Gordon, pp. 56, 71, 74, 
 
 New Mexico, 1910. 
 
 Lindgren and Ransome, 3, pp. 225-231, 1906. 
 Lotti, 5, pp. 372-378, Tuscany, 1893. 
 Morris, 1903. 
 Mutter, H., 1, Mineral springs in Freiberg 
 
 mines, 1885. 
 Park. 3, 1905; 7,1906. 
 Phillips-Louis, pp. 115-119, 135-142, 793-795, 
 
 1896. 
 Phillips, 3, 1879. 
 
 4, 1871. 
 
 Rickard, T. A., 7, 1894 ; 20, 1908. 
 Rickard, et al., 1, "A Discussion," pp. 27-29 
 
 (Weed), also excellent discussion by many 
 
 writers, 1903; 2,1903. 
 Spurr, 17, 1907. 
 Strutt, 1907. 
 Stutzer, 18, 1910. 
 Suess, , S, 1902. 
 
 Thomas and MacAlister, pp. 116-236, 1908. 
 Van Hise, 4, pp. 47-51, 1900. 
 6, 1901. 
 
 8, pp. 1052-1069, 1904. 
 Vogt, 5, 1894-5 ; 10, pp. 132-147, 1901. 
 Weed, 1, Gold-bearing hot springs, 1891. 
 
 3, 1900 ; 13, 1903. 
 
 Weed and Pirsson, 4, 1893. 
 
 Winchell, H. V., 5, 1907 ; 6, 1908 ; 8, 1907. 
 
SUBJECT INDEX. 
 
 917 
 
 EXPERIMENTAL DATA APPLIED TO ORE- 
 DEPOSITION. 
 
 Aston, 1, Alloys and magmas, 1909. 
 
 Biddle, Deposition by ferrous salts, 1901. 
 
 Browne, D. H., 2, Magmas and mattes, 1895. 
 3, ditto, 1906. 
 
 Daubree, A., 2, General, Many applications on 
 fissure formation and synthesis of min- 
 erals, 1879. 
 
 Doelter, 1, pp. 79-112, Stability of minerals 
 under certain temperatures and pressures, 
 
 2, Solubility of minerals, 1890. 
 Fernekes, Precipitation of copper, 1907. 
 Gautier, A., 2, Action of H 2 S on certain oxides, 
 1900. 
 
 S, Action of water vapor on sulphides, 1906. 
 Jenney, 2, Reducing agents in nature, 1902. 
 Neunier, General, 1904. 
 
 Stokes, 1, Pyrite and marcasite, 1901. 
 
 2, Solution of copper, silver and gold, 1906. 
 
 3, Solution of pyrite and marcasite, 1907. 
 ullivan, 1, Precipitation of copper bv Sili- 
 
 Sullivan, 
 
 cates, 1906. 
 
 2, Reactions of water solutions and min- 
 erals, 1907. 
 
 3, Mineral filters, 1908. 
 Weed, 17, Adsorption, 1905. 
 
 Wells, Fractional precipitation of sulphides, 
 1910. 
 
 Winchell, A. N.,1, Oxidation of pyrite, 1907. 
 
 Winchell, H. V., 3, Synthesis of chalcocite, 
 1903. 
 
 Wright and Larsen, Quartz as a geologic ther- 
 mometer, 1909. 
 
 FAULTS AND FAULTING. 
 
 Barrell, 2, at Marysville, Montana, pp. 94-104. 
 
 1907. 
 
 de la Beche, General, pp. 283-348, 1839. 
 Beck, 8, pp. 138-163, General, 1909. 
 
 9, vol. ii., pp. 199-225, General, 1909. 
 Becker, 1, pp. 156-187, at Comstock lode, 1882. 
 Bergeat-Stdzner, General, pp. 100, 487, 492, 496, 
 
 501, 507, 1906. 
 
 Burnt, pp. 44-54, General, Hist., 1870. 
 Chamberlin, T. C., 2, General, very theoreti- 
 
 cal, 1907. 
 
 Chance, 1, p. 11, 1883. 
 Church, 2, Causes of, 1893. 
 
 1, In Veins, 1892. 
 von Cotta, 1, 1861. 
 
 2, pp 29-32, 1870. 
 
 Gushing, Discussion of Ransom e, 8, 1907. 
 Daggett, at Berlin Mine, Nevada. 
 Dana, 1, 1907. 
 Dannenberg, General, 1884. 
 Daubree, A., 2, pp. 289-378, 1879. 
 Emmons, S. F., 2, especially pp. 284-292. Of 
 general application, 1886. 
 
 6, General, 815-829, 1888. 
 
 7, In veins, 1892 
 
 Evans, Discussion of Ransome, 8, 1907. 
 
 Fairchild, ditto, 1907. 
 
 Farish, 1, at Rico, Colo., pp. 151-164, 1892. 
 
 Farrell, pp. 94-102, 1912. 
 
 Freeland, 2, Fault- rules, excellent but old 
 
 Bibliography, 1893. 
 Goupilliere, vol. I., pp. 68-86, 1883. 
 von Groddeck, 1, pp. 18-27, 1879. 
 Greenwell, p. 116, 1889. 
 Gunther, 2, pp. 33-42, 1912. 
 Heim, 1, vol. ii., General, 1878. 
 Henwood, 1, 1843. 
 
 2, pp. 17, 31, 1871. 
 Hofer, 1, General, 1886. 
 
 2, Determination of faults, 1881. 
 
 Jaggar, Discussion of Ransome, 8, 1907. 
 
 Jenney, 4, Block-faulting, 1906. 
 
 KoMer, <?., 2, pp. 21-39, 1887. 
 
 Moissenet, pp. 50, 54, 71, 85, 1877. 
 
 Park, 4, Rules for finding faults, pp. 93-104, 
 
 1906. 
 
 Phillips-Louis, pp. 11-21, 74-80, 1896. 
 Prestwich, vol. I., pp. 252-256, 318-321, 1886. 
 Ransome, 6, at Bisbee, pp. 85-104, 1904. 
 8, Direction of movement and nomenclature 
 
 of, 1906. 
 14, at Goldfield, pp. 83-85, 161-162, 196, 201, 
 
 1909, 
 
 5, at Globe, pp. 9^106, 144-148, 1903. 
 Ransome and Calkins, at Coaur d'Algne, pp. 
 
 17, 18, 61-69, 73-76, 84, 107, 117, 120-121, 134. 
 
 139, 142, 1908. 
 Raymond, 4, Hofer's method, discussion of, 
 
 1882. 
 
 Reid, H. F., 1912. 
 Reid, J. A., 1, at Comstock lode, 1905 
 
 4. Discussion of Ransome, 9, 1907. 
 Russell, pp. 442, 450-453, 1884. 
 Schmidt, J. C. L., 1910. 
 Serif), pp. 35-48, 1878. 
 
 Spurr, 5, at Aspen, Colo., much of general ap- 
 plication, pp. 58-72, 84-107, 117, 120-130, 145- 
 
 146, 148-149, 244, 251-256, 1898. 
 16, General, pp. 148-164, 1907. 
 18, Discussion of Ransome, 8, 1907. 
 13, Tonopah, pp. 7, 21-22, 37-38, 47-82, 115- 
 
 116, 141-142, 146, 149, 158-161, 164, 1905. 
 Tolman, 1, Discussion of Ransome, 8, 1907. 
 
 6, Graphical solution of faults. 
 Van Hise, 2, pp. 672-678, 1896. 
 Weed, 18, Mutual displacement of veins, 1907. 
 Whitney, 1, p. 57, 1854. 
 Willis, 1, Appalachians, 1892. 
 Zimmermann, 1, pp. 49-72, 80, 1828. 
 
 FISSURE-VEINS. 
 
 GENERAL. 
 
 Beck, 8, pp. 111-431, 1909 ; 9, pp. 169-540, 1909. 
 
 Bergeat-Stdzner, pp. 471-1006, 1906. 
 
 Brown- A. J., 1874. 
 
 Emmons, S. F., 4, 1887; 6, 1888. 
 
 Kemp, 21, pp. 39-53, 1906. 
 
 Phillips-Louis, pp. 69-150, 1896. 
 
 Rickard, T. A., 8, Vein- walls, 1896, 
 
 Ries, pp. 329-335, 1910. 
 
 Thomas and MacAlister, pp. 116-236, 1908. 
 
 Spurr, 16, pp. 177-193, 1907. 
 
 Vogt, BeyscMag and Krusch, Band II., H. 2, pp. 
 
 1-209, 1912. 
 Wallace, J. P., pp. 174-205, 1908. 
 
 FISSURES. 
 
 (See also under " Cavities in Rocks." ) 
 
 Systems of. 
 (With many illustrations of vein groups.) 
 
 Beck, 8, Map of Freiberg, 1909. 
 
 9, Map of Freiberg veins, 1909. 
 Brown, R. G., 2, at Bowie, Cal., 1907. 
 Bergeat-Stdzner, pp. 618, 625, 654, 659, 766, 854, 
 
 1906. 
 Daubree, A., 2, pp. 289-378, 1879. 
 
918 
 
 SUBJECT INDEX. 
 
 Lindgren, 8, pp. 164-170, Grass Valley, 1896. 
 11, pp. 101-103, of Central Idaho, 1899. 
 13, pp. 600-601, at Blue Mts., Oregon, 1901. 
 Lindgren and Ransome, '6, at Cripple Creek, 
 
 pp. 158-167, ] 906. 
 MacAlister and Hill, p. 206, at Cornwall, Eng- 
 
 land, 1906. 
 
 Muller, H. , 2, at Freiberg, Saxony, 1901. 
 Ransome, 2, at Silverton, pp. 43-67, 1901. 
 
 3, pp. 255-261, 290-293. at Rico, Colo., 1901. ' 
 Ransome and Calkins, pp. 115-116, at Cceur 
 
 d'Algne, Idaho, 1908. 
 Rickard, T. A., 9, Rico, Colo., 1896. 
 Phillips-Louis, pp. 80-85, 1896. 
 Spurr, 11, pp. 18-21, at Tonopah, Nevada, 1903. 
 
 16, pp. 177-193, 1907. 
 Tower and Smith, at Tintic, Utah, pp. 676-683, 
 
 1898. 
 Vogt, Beyschlag and Krusch. 
 
 Origin of Fissures. 
 
 Beck, 8, pp. 163-173 ; 9, pp. 226-235, 1909. 
 Becker, 4, pp. 407-415, At Comstock Lode, 1888. 
 
 7, 1893 ; 8, 1893 ; 9, 1894. 
 Bergeat-Stelzner,. pp. 471-508, 1906. 
 Beutlien, Berg- und Hiitten, Zeitung, p. 165, 1891. 
 Brown, A. J., 1874. 
 Crosby, 2, 1882 ; 3, 1887 ; 4, 1893. 
 Daubree A., Les Eaux Souterraines, III, 1887. 
 Daubree, G. A.,1 and 2, 1887. 
 Emrnons, S. F., 4, pp. 193-208, 1887 ; 6, pp. 810- 
 
 839. 1888. 
 
 Heim, J, p. 44, 1878. 
 Keilhack, 1, Review of longer paper, 1895. 
 
 Kemp, 21, pp. 13-31, Cavities in rocks, 1906. 
 
 , 8, 
 1897. 
 
 , 
 Lindgren, 8, pp. 169-170, Ib96 ; 11, pp. 102-103, 
 
 Lindgren and Ransome, 3, pp. 167-168, Cripple 
 
 Creek veins. 
 Lossen, 1886. 
 Margerie and Htim, " Die Dislocation der Er- 
 
 drinde," Zurich, 1888. 
 Muller, H., 2, of Freiberg fissures, 1901. 
 Nason. E. and M. Jour., vol. 71, pp. 177-179, 
 
 209-210, 1901. 
 
 Phillips-Louis, pp. 80-85, 1896. 
 Posepny, Leoben Jahrbuch, vol. 22, p. 233, 1874. 
 Purington, 1, pp. 771-781, 1897. 
 Ransome, 2, pp. 43-47, Excellent discussion of 
 
 general application, 1901. 
 Ransome and Calkins, pp. 134-135, 1908. 
 Spencer, 5, of S. E. Alaska fissures, pp. 581-586, 
 
 1905 ; 6, of Juneau fissures, pp. 27-28, 1906. 
 Spurr, 6, pp. 806-828, Relation to joints (of 
 
 general import), 1901; 16, pp. 177-184, 1907. 
 Voyt, Beyschlag and Krusch, Band II, H. 1, pp. 
 
 1-11, Excellent general discussion, 1912. 
 Weed, Science, New series, vol. 20, p. 761, Dila- 
 
 tion fissures, 1904. 
 Werner, Hist., 1791. 
 Whittlesey, p. 213. 
 
 Displacements, Irregularities and 
 Relative Ages of Fissures. 
 
 (See also under " Faulting.") 
 Beck, 8, pp. 112-161, 1909. 
 
 9, pp. 172-184, 190-226, 1909. 
 Bergeat-Stelzner , pp. 492-520, 1906. 
 Church, 1, Faulting in veins, 1892 
 Emmons, S. F., 7, p. 548, 1892. 
 Freeland, 2, 1893. 
 Gresly, p. 517, 1892. 
 Hofer, 4, Age of veins, 1899. 
 Klockmann, Zeit. f. prak. Qeol., vol. 1, p. 466, 
 
 1893. 
 
 Kohler, G., 2, 1884. 
 Lindgren, 9, pp. 647-651, 1897. 
 Park, 4, pp. 59-77, 93-104, 1906. 
 Phillips-Louis, pp. 13-19, 60-84, 150-168, 1896. 
 Ricketts, p. 565, 1892. 
 Spurr, 13, pp. 96-206. Tonopah, 1905. 
 
 14, pp. 36-96, Silver Peak. 
 
 16, p. 177-199 etseq., 1907. 
 
 Spurr and Garrey, 1, pp. 39-40. Faulting at 
 Idaho Springs, Colo., 1905. 
 
 3, Rel. age of Georgetown Veins, pp. 99-101, 
 1908. 
 
 Van Hise, 2, pp. 589-603, 633-C68, 669-678, 1896. 
 
 8, p. 1201, 1904. 
 Weed, 18, 1907. 
 
 Williams, Albert, Jr., 2, Dip and strike, 1892. 
 
 Classification of Fissure-Veins. 
 
 Beck. 8, pp. 191-195. 1909, 9, pp. 257-260, 1909. 
 Bergeat-Sttlzner, pp. 566-571, 1904-1906. 
 Breithaupt, "Die Parageuesis der Mineralien," 
 
 Freiberg, 1849. 
 
 von Cotta, 2, pp. 478-500, 1870. 
 von Qroddeck, 1, 1879. 
 Werner, pp. 224-251, 1791. 
 
 Structure and Arrangement of Mineral 
 
 Contents of Fissure-Veins. 
 
 (Paragenesis. ) 
 
 Beck, 8, pp. 173-193, 1909. 
 
 9, pp. 237-256, 1909. 
 Bergeat-Stelzner, pp. 530-541, 1906. 
 Boutwell, 5, pp. 158-160, 161, 1905. 
 Breithaupt, "Paragenesis," Freiberg, 1849. 
 Cornu, F., 1, of Zeolites, 1907. 
 
 Cornu and Lazerovic, in copper-ores of Servia, 
 
 1908. 
 
 Farish, 1, 1892. 
 von Qroddeck, 1, p. 61, 1879. 
 Hqfmann, A., Kurze Ubersicht der montangeolo- 
 
 gischen Verhaltnisse des Pribramer Bergbaues, 
 
 Filhrer /. d. Exkurs. IX. Int. Geol. Kongr., 
 
 Wein, 1903, No. 1. 
 Kemp, 21, pp. 47-53, 1906. 
 Klockmann, Zeit. f. prak. Geol., vol. 1, p. 466. 
 
 1893. 
 
 Kohler, G., 2, 1887. 
 Lindgren, 8, pp. 128-144, Grass Valley ores, 1896. 
 
 13, pp, 601-603. in Blue Mt. veins, 1901. 
 Lindgren and Ransome, 3, pp, 176-182, Cripple 
 
 Creek lodes, 1906. 
 Lindgren, Graton, and Gordon, New Mexico 
 
 ores, pp. 58-59, 1910. 
 Muller, H., Uber eine merkw. Druse auf einem 
 
 Schneeberger Kobaltgange. Zeit. d. D. GeoL 
 
 Gesel., vol. 2, pp. 14-18, 1850. 
 Naumann-Zirkel, Elemente der Mineralogie, 14th 
 
 ed., pp. 166-174, 1901. 
 Neubert, Gang geologische Verhaltnisse bei Him- 
 
 melsfurstFundgr.,Jahr.f.d. Berg. u.Huttenw. 
 
 i. Sachs., p. 663, 1881 ; pp. 126-127, 1890. 
 Posepny, 2, pp. 217-220, 244-247, 254-262, 1894. 
 Pumpelly, 2, 1891. 
 Purington, 1, pp. 796-802. 1897. 
 Ransome, 2, in Silverton lodes, pp. 67-70, 87- 
 
 93, 1901. 
 
 3, pp. 261 to 265, Rico lodes, 1901. 
 Ransome and Calkins, Cceur d'Alene, pp. 107. 
 
 127-129, 1908. 
 Reuss, A. E., Paragenese der auf den Erzgangen 
 
 von Pribram einbrechenden Mineralien ; 
 
 Sitzber. k. k. Akad. d. Wiss., Ivii, pp. 13-76, 
 
 1863. 
 Rickard, 8, pp. 193-241, 1896. 
 
 9, Scattered discussion, pp. 919-980, 1896. 
 Rogers, A. F., Econ. Geol., vol. 7, pp. 638-646, 
 
 1912. 
 
 Rolker, 3, in Honduras vein, 1885. 
 Schraiif, of metacinnabarite, 1891. 
 Simpson, of Butte ores, 1908. 
 Smyth, H. L , 2, gold and pyrite, 1906. 
 Spurr, 6, Monte Cristo ores, pp. 835-840, 1901. 
 Tower and Smith, Tintic. p. 704, 1898. - 
 Tschermak, Lehrbuch der Mineralogie, 1894. 
 Tscherne, General discussion, 1892, 
 Vogt, Beyschlag, and Krusch, pp. 93-114, 1909. 
 von Weissenbach, G. A., " Abbildungen merkw. 
 
 GangverhdUnisse aus dem sdchs. Erzgebirge r 
 
 Leipzig, 1836. 
 
 THE FILLING OF MINERAL 
 VEINS. 
 
 (See under " Sublimation," " Injection," 
 " Ascension Theories," " Descension Theo- 
 ries," " Lateral Secretion '' and subhead " Hy- 
 drothermal Emanations " of " Emanations- 
 from Igneous Magmas." 
 
SUBJECT INDEX. 
 
 919 
 
 GEOGRAPHIC DISTRIBUTION OF METALLIF- 
 EROUS DEPOSITS. 
 
 Bain, 4, Relation of ores to paleogeography, 
 1907. 
 
 Becker, 3, Relation of ores to zones of up- 
 heaval, 1884. 
 
 von Cotta, 2, pp. -509-516, 1870. 
 
 de Launay, 9, Theories of geographic distri- 
 bution applied to Africa, 1903. 
 IS, to Italy, 1906. 
 
 17, to Russia, 1909. 
 
 18, to Asia, 1911. 
 
 Ransome, 7, Distribution in U. S., 1904. 
 
 Raymond, 3, U. S., 1871. 
 
 Smock, of iron in the Eastern U. P., 1884. 
 
 Spurr, 13, Excellent discussion of geographic 
 
 distribution in general, pp. 278-287, 1905. 
 ! Spurr and Garrey, 3, pp. 102-130, General dis- 
 cussion of distribution in Colorado, 1908. 
 
 Weed, 19, Copper deposits of the world, 1908. 
 
 GEOLOGIC AGE OF ORE-DEPOSITS. 
 
 Aguilera, Geologic distribution of ores in 
 
 Mexico, 1901. 
 
 von Cotta, 2, pp. 526-546, 1870. 
 Kemp, 21, pp. 445-447, 1906. 
 Lindgren, 28, Metallogenetic epochs, 1909. 
 29, ditto, 1909. 
 
 16, Geologic features of U. S. gold-produc- 
 tion, 1902. See also, Proc., 5th Int. Min. 
 Congress, pp. 29-36, 1903. 
 
 Lindgren and Knowlton, Age of gold-placers 
 
 California, 1896. 
 Purington, 1, Age of Telluride ores, pp. 824-825, 
 
 Rickard, T. A., 21, of Colorado ores, 1910 ; Gold, 
 
 19, 1906-7, 
 
 Ries, Metallogenetic epochs, pp. 342-345, 1910.. 
 Spurr, 3, Mercur ores, pp. 437-439, 1895. 
 
 10, Discussion, 1903. 
 Stirling, 2, Victoria, Australia, 1900-1901. 
 
 LATERAL SECRETION. 
 
 Beck, 8, pp. 413-420, General, 1909. 
 9, General, vol. I., pp. 43-50, Argued for cop- 
 per in basic rocks, vol. I., pp. 342, 1909. 
 
 Bergeat-Stelzner, pp. 1193-1202, General, 1906. 
 
 Bischoff, 1, 2nd Ed., pp. 1209, 2121-2126, 1863- 
 1871. 
 
 Carthaus, Discussion of Sandberger, 1896. 
 
 Clarke, 2, New Edition, pp. 600-602, 1911. 
 
 Delkeskamp, 2, Significance of barite veins, 
 1902. 
 
 Dieulefait, 1, 2, 3, U, 5, 6, Original metals in 
 rocks, 1878-1885. 
 
 Don, Argument against in New Zealand gold- 
 ores, 1897. 
 
 Emmons, S. F., 2, Applied to Leadville ores, 
 1886. 
 
 Forchhammer , Presence of metals in rocks, 
 1854-1855. 
 
 Kemp, 21, pp. 40-43, 1906. 
 
 Mallet, Silver in volcanic ash, 1881. 
 
 Patera, Applied to Pribram, 1888. 
 Phillips-Louis, pp. 129-136, Excellent general 
 
 discussion, 1896. 
 
 Posepny, 2, pp. 248-254, 1893 ; 5, 1885. 
 Purington, 1, Discussion for Telluride, Colo., 
 
 pp. 819-824, 1897. 
 Robertson, J. D., Missouri Qeol. Sur., vol. 7. pp. 
 
 479-481, 1894. 
 Sandberger, 1, pp. 377-381, 389-392 et seq., 1877. 
 
 2, General, 1880. 
 
 3, voL I., pp. 31-36, vol. II., pp. 159-245, 1883- 
 1885. 
 
 -4, 1883. 
 
 5, Theories of vein-formation, 1884. 
 
 6, Researches at Pribram, Bohemia, 1886. 
 Sehroeder, in connection with tin, 1883. 
 Stelzner, 1, Criticism of Sandberger's theories, 
 
 1889. 
 
 Wadsworth, 2, 1884. 
 Wendeborn, 1904. 
 
 MAGMATIC DIFFERENTIATION. 
 
 GENERAL DISCUSSION. 
 Applied to Rocks. 
 
 Becker, 15, 1897. 
 
 16, 1897. 
 Brogger, 1890. 
 
 Clarke, 2, New Edition, 1911. 
 Daly, 2, 1906. 
 Gregory, 11, 1908. 
 Harker, 1, Rec., 1907. 
 
 2, 1909. 
 
 Iddings, 1, 1909. 
 Lane, 2, 1906. 
 Morozewicz, "2, 1899. 
 
 Pirsson, pp. 164-180, Especially Rec., 1908. 
 Rosenbusch, 1890. 
 Zirkel, 1, pp. 778-794, 1893. 
 
 Applied to Ores. 
 
 General. 
 Beck, 8, pp. 11-49, 1909. 
 
 9, vol. I., pp. 17-97, 1909. 
 
 Bergeat-Stelzner, pp. 19-85, with full bibliogra- 
 phy, 1906. 
 Garrison, 2, 1909. 
 Gregory, 11, 1908. 
 Kemp, 21, pp. 59-67, 72, 1909 ; E. and M. Jour., 
 
 vol. 76, pp. 804-805, 1903. 
 Lotti, 2, pp. 18, 19, 29-50, 1903. 
 
 Park, 2, 1905. 
 
 5, 1906. 
 
 Phillips- Louis, pp. 179-184, 1896. 
 Rickard, et. al., 1, Discussion by many writers^ 
 
 1903. 
 
 Thomas and MacAlister, pp. 21-71, 1908. 
 Trener, 1905. 
 Vogt, 1, General, 1893. 
 
 5, Classification of types. Oxides, pp. 383- 
 384, sulphides, pp. 394-395, native metals, 
 pp. 395-399, 1894. 
 
 6, English, excellent review of subject, 1895. 
 
 10, (English), p. 131, 1901. 
 
 11, Titaniferous ores, 1900. 
 
 12, in Effusive rocks, 1902. 
 U, 1905. 
 
 16, Magnetic iron-ores in granite, 1907. 
 
 17, Rtfdsand iron-ores, 1910. 
 
 Vogt, Beyschlag and Krusch, General. Vol. J. v 
 pp. 162-165, vol. II., pp. 239-344, 1910. 
 
 OXIDIC OKE-DEPOSITS. 
 Chromium. 
 
 Cirkel, pp. 85-87, 1909. 
 Glenn, 2, 1897-8. 
 Hall and Humphreys, 2, 1908. 
 Pratt, 1, 1899. 
 Vogt, 5, pp. 384-393, 1894. 
 
 Vogt, Krusch, and Beyschlag, vol. i, pp. 241-246 
 1910. 
 
920 
 
 SUBJECT INDEX. 
 
 Corundum. 
 
 Pratt, 2, 1899. 
 
 3, 1898 ; 4, 1906. See also vol. i, Nor. Car. 
 Geol. Sur., pp. 331-357, 1905. 
 
 Iron. 
 
 Adams, F. D., 1,1894. 
 Beck, 9, vol. 1, pp. 28-67. 
 de Launay, 10, 1903. 
 Henrickson, 1906. 
 Kemp, 11, pp. 417-419, 1898. 
 
 12,1899. 
 Lowinnson- Leasing, 1, Ural Mts., 1907. 
 
 , ditto, 1909. 
 Newland, 2, 1907. 
 Newland and Kemp, 1908. 
 Sjogren, 1, Taberg, Smaland, 1886. 
 
 2, 1891. 
 
 3, Scandinavian iron-ores, 1907. 
 Stutzer, 1, Kiruna, 1906. 
 
 8, 1907. 
 Vogt, 11, 1901. 
 
 16, Iron-ore in granite, 1907. 
 
 17, Titaniferous ore in Norway, 1910. 
 
 Vogt, Krusch, and Beyschlag, vol. i, pp. 247-274, 
 
 1910. 
 Warren, Cumberland, R. I., Am. Jour. Sci., 4th 
 
 ser., vol. 25, 1908. 
 
 SULPHIDE DEPOSITS. 
 
 Adams, F. D., 1, General discussion of nickel- 
 bearing sulphides. Excellent, 1894. 
 
 Austin, Riddles, Oregon, Nickel, 1896. 
 
 Barlow, 1, Sudbury, 1904. 
 2, ditto, 1906. 
 
 Bastin and Hill, Econ. Geol., vol. vi, pp. 465- 
 472, 1911. 
 
 Beck, 3, Sohland, Nickel, 1903. 
 
 8, pp. 12-48, General, 1909. 
 
 9, vol. I., pp. 67-97, General, 1909. 
 Bergeat-Stelzner, pp. 41-63,il906 (with full refer- 
 ences to literature). 
 
 Browne, D. H., 3, Sudbury nickel, 1906. 
 Catharinet, Bornite, 1905. 
 Chaper, Caucusus Mts. copper, 1893. 
 Coleman, 2, Sudbury nickel, 1905. See also, 
 Butt. Geol. Soc. Am., 1904. 
 
 4, ditto, 1907. 
 
 5, Nickel, 1910. 
 
 Dickson, 1, Sudbury nickel (argument against 
 
 magmatic differentiation), 1903. 
 3, ditto, 1906. 
 
 Gamier, "Mines de Nickel de Sudbury," Paris, 
 1891. 
 
 Hille, 1, Atik-Okan nickel, 1905. 
 
 Kay, nickel, 1907. 
 
 Kemp, 7, Nickel, Penna., 1894. 
 
 Leckie, Norwegian nickel, 1904. 
 
 Packard, Summary of theories of origin of 
 nickel-ores, 1893. 
 
 Eimann, Zinc-blende, 1910. 
 
 Ritter, 1, Bornite and chalcopyrite, 1908. See 
 also recent paper on Econ. Geol., by U. S. 
 G. S. man, on same deposit. 
 
 Stutzer, 7,*Bornit,e, 1907. 
 
 Vogt, 7, Comparison of Norwegian and Cana- 
 dian nickel-ores, 1897. 1, pp. 125-143, 257- 
 268, 1893 ; 4, 1894 ; 5, pp. 381-399, 1895 ; 6 (in 
 English), 1895. 
 
 Vogt, Krusch, and Beyschlag, Band 1, pp. 16-241, 
 275-336, 1910, also Band 1, H. 1, pp. 162-164, 
 1909. 
 
 Walker, 1, Sudbury nickel-ores, 1897. 
 
 Watson, 4, pp. 683-698, 1907. 
 
 Weinschenclc, Nickel, Germany, 1907. 
 
 Comparison with Solidification of 
 
 Slags. 
 Browne, D. H., 2, 1895; 3, 1906. 
 
 Native Metals. 
 
 See under " Disseminated Metals Original 
 in Rocks;" sub-head: "Eruptive Rocks." 
 
 METASOMATISM. 
 
 ("See under l< Replace oient.") 
 
 MINERALOGY OF METALLIFEROUS ORES. 
 
 (A few of these papers containing chapters especially devoted to descriptive 
 mineralogy are indicated here. ) 
 
 Bain, 2, pp. 46-53, Miss. Valley ores, 1906. 
 Bain and Van Hise, Miss. Valley ores, pp. 111- 
 
 124, 1901. 
 
 Barlow. 1,93-107,1904. 
 Becker, 12, Appalachian gold-ores, pp. 272-281, 
 
 1895. 
 
 14, pp. 60-64, Gold-ores of S. Alaska, 1897. 
 Bergeat-Stelzner, pp. 527-530, General, 1906. 
 Boutwell, 5, Bingham ores, pp. 103-122. 1905. 
 Clarke, F. W., 2, General, pp. 541-618, 1908. 
 
 New Edition, pp. 599-680, 1911. 
 Coleman, 2, Sudbury, pp. 159-163, 1905. 
 Courtis, Gold quartz, 1890. 
 Day and Richards, of Blacksands, 1905. 
 Emmons, W. H., 3, General paper 011 genesis 
 
 of minerals, 1908. 
 Ermisch, 1905. 
 Farrell, "Practical Field Geology," Chap. X, 
 
 1912. 
 
 Fermor, 2, Manganese-ores, 1909. 
 Frazer, P., Jr., 2, Iron oxides, 1878. 
 Haber, of Lead and Zinc, 1894. 
 Hastings, 4, Magnetite and sulphides asso- 
 ciated, 1908. 
 
 Hershey, 3, Primary chalcocite, 1908. 
 Hillebrand and Schaller, Mercury minerals, 
 
 1909. 
 
 Irving, J. D., 11, Relations of mineralogy to 
 depth of ore-formation at Lake City, Colo., 
 pp. 33-37, Paragenesis, 46-51, descriptive 
 mineralogy, 51-64, 1911. 
 
 Irving, J. D., Emmons, S. F., and Jaggar, pp. 
 68, 82-88, 138-140, 165, 166, Black Hills ores, 
 1904. 
 
 Jenney, 1, Mississippi Valley, lead and zinc, 
 pp. 198-200, 210-211, 1893. 
 
 Kemp, 10, of Telluride ores, 1898. 
 13, of Ducktown ores, pp. 249-250, 1901. 
 
 21, General, pp. 32-38, 1906. 
 
 Knight, F, C., new mineral from Cripple 
 
 Creek, 1896. 
 Konigsberger, 1901. 
 Lenher, of Telluride ores, 1909. 
 Lincoln, 2, pp. 275-301, Association of gold 
 
 with minerals. 
 
 Lindgren, 10, Orthoclase gangue, 1898. 
 8, pp. 114-144, of Grass Valley ores, 1896. 
 
 22, Albite, Bendigo, 1906. 
 
 Lindgren and Boutwell, pp. 100-122, of Morenci 
 
 ores, 1904. 
 
 i Lindgren and Ransome, 2, Cripple Creek ores, 
 pp. 114-129, 173-175, 185-188, 1905; 26, Rela- 
 tion of mineralogy to physical conditions 
 of ore-deposition, 1907. 
 
SUBJECT INDEX. 
 
 921 
 
 Lindgren, Graton and Gordon, pp. 77-81, 50- 
 53, 57, 63, 69, 77, New Mexico, 1910. 
 
 Mietzschke, Gold in pyrite, 1896. 
 
 Moulan, Iron minerals, 1904. 
 
 Pearce, Richard, 3, Association of gold with 
 minerals, 1890. 
 
 Purington, 1, Telluride dist., pp. 781-799, 1897. 
 
 Ransome, 2, Silverton, pp. 67-93, 1901. 
 3, Rico Mts., pp. 248-254, 1901. 
 
 5, Globe, pp. 110-125, 1903. 
 
 6, Bisbee, pp. 120-135, 1904. 
 9, Alunite, 1907. 
 
 14, Goldfield, pp. 108-134 ; also 165-171, 1910. 
 
 15, Criteria of sulphide enrichment, 1910. 
 Ransome and Calkins, Coaur d'Alene, pp. 90- 
 
 103, 107-113, 1908. 
 Ransome, Emmons and Garrey, Bullfrog, pp. 
 
 92-100, 1910. 
 Rickard, T. A., 10, Minerals accompanying 
 
 gold, 1898. 
 12, Tellurides of Cripple Creek and Kal- 
 
 goorlie, 1900. 
 Schaeffer, Tantalite minerals, Black Hills, 
 
 1884. 
 
 Kcharitzer, Iron sulphates, 1907. 
 : Smith and Siebenthal, Joplin, pp. 12-15, 1907. 
 ' Smyth, C. H., Jr., 2, Genetic relations, 1896. 
 Smyth, H. L., 2, Gold and pyrite, 1906. 
 Spencer, 6, pp. 33-37, Treadwell minerals, 1906. 
 1 Spurr, 3, Mercur, pp. 389-394, 1895. 
 13, Tonopah, pp. 86-92, 1905. 
 16, pp. 299-301, 1907. 
 
 Spurr and Garrey, 1, p. 38, Idaho Springs, 1905. 
 3, Georgetown, pp. 99-101, 136-138, 147-148, 
 
 1908. 
 
 Tower and Smith, Tintic, pp. 683-704, 1898. 
 Van Hise, 8, pp. 192-408, Applies chiefly to 
 
 rock-making minerals, 1904. 
 Vogt, k, of various European sulphide ores, 
 
 1894. 
 I Vogt, Beyschlag, and Krusch, vol. i, pp. 60-93, 
 
 1909. 
 Weed, 19, of Copper-ores in general, pp. 22-35, 
 
 1908. 
 Weed and Pirsson, 2, Judith Mts., pp. 589-592, 
 
 1897. 
 
 Weed and Barrell, Elkhorn, Mont., pp. 459- 
 469, 1901. 
 
 ORE-SHOOTS. 
 
 (See also effects of wall-rock. ) 
 
 GENERAL. 
 
 Beck, 8, pp. 382-395, 1909. 
 9, vol. II., pp. 1-22, 1909. 
 
 Bergeat-Stelzner, pp. 987-1006, General, 1906. 
 
 von Cotta, 2, pp. 522-525, 1870. 
 
 Crawford, Bull. Col. Geol. Sur. No. , 1913. 
 
 Irving, J. D., 7, 1908. 
 
 Lindgren, 30, 1909. 
 
 Lindgren and Ransome, 3, pp. 205-216, excel- 
 lent general discussion, 1905. 
 
 Litschauer, 1893. 
 
 Lotti, 2, pp. 133-135, 1903. 
 
 Pearce, nomenclature, 1909. 
 
 Penrose, 2, 1894 ; 4, 1910. 
 
 Phillips-Louisy pp. 93-97, 1896. 
 
 Purington, 5, 1906. 
 
 Sales, 2, at Butte, Montana, 1908. 
 
 Smith, F. C., 2, 1908. 
 
 Smith, George, 1, 1896. 
 
 Spurr, 16, pp. 195-196, 1907. 
 
 Van Hise, 4. pp. 166-172, 1900 ; 8, pp. 1223-1230, 
 1904. 
 
 Villarello, 2, 1905. 
 
 Weed, E. and M. Jour., vol. 76, p. 193, 1903. 
 
 Winchell, H. V., 7, 1908. 
 
 Wuensch, 1893. 
 
 SHOOTS AS DESCRIBED IN IN- 
 DIVIDUAL LOCALITIES. 
 
 Lindgren, 8, Grass Valley, pp. 158-163, 1896. 
 
 13, Blue Mts., pp. 605-610, 1901. 
 Lindgren, Graton and Gordon, New Mexico. 
 
 p. 70, 1910. 
 
 Moissenet, Cornwall, 1877. 
 von Pdlfy, Erzgebirge, 1907. 
 Ransome, 2, Silverton, Colo., pp. 96-101, 1901. 
 3, Rico, pp. 299-303, 1901. 
 
 14, Goldfleld, Nov., pp. 158-165, 1909. 
 Ransome and Calkins, Coeur d'Alene, pp. 122- 
 
 130, 1908. 
 
 Rickard, T. A., 13, Ballarat, 1900. 
 Kjogren, 4, in Swedish mines, 1908. 
 Skewes, Cripple Creek, 1896. 
 Spurr, 13, Tonopah, pp. 85, 119-122, 276-278, 
 
 1905. 
 
 Spurr and Garrey, 3, pp. 159-161, 1906. 
 Vogt, 9, Rio Tinto. 1899. 
 Weed and Barrell, Elkhorn, Mont., 477-495, 
 
 1901. 
 
 ORIGIN OF METALLIFEROUS DEPOSITS. 
 
 (For the 
 headings, s 
 
 phic Deposits," "Processes of Deposi 
 place are given Historical Resumes of Theories of origin or Summaries of Theories 
 of the origin of particular metals and those portions of a number of reports which 
 deal with the Origin of Deposits in Particular Districts ; also Theoretical Papers 
 Dealing with the Origin of Ore-Deposits as a whole. ) 
 
 HISTORICAL RESUMES OF THEO- 
 
 RIES AND LITERATURE 
 ORE-DEPOSITS. 
 
 Emmons, S. F., 15, 1904. 
 Kemp, 6, 1893. 
 
 8, 1895. 
 
 Klement, 1, 1897-8. 
 Lindgren, 27, 1907. 
 Ransome, 17, 1911. 
 Raymond, 6, 1900. 
 Rickard, T. A., 17, 1902. 
 Rickard el. al.,1, pp. 3-17, 1903. 
 Winchell, H. V., 5,1907. 
 
 OF 
 
 SUMMARIES OF THEORIES OF 
 THE ORIGIN OF PARTICULAR 
 METALS. 
 
 Bateman and Ferguson, Tin, Economic Geology, 
 vol. 7, pp. 209-262. 
 
 de Launay, 16, Gold, 1909. 
 
 Demaret, 1, Copper, 1900; 2, Iron, 1903; 3, Mer- 
 cury, 1904 ; ^ Manganese, 1905. 
 
 Fawns, 3, Tin, 1907. 
 
 Gautier, F., 1901. 
 
 Hess and Graton, Tin, Bibliography and geo- 
 graphic distribution only, 1905. 
 
 Julien, 2, Iron, 1884. 
 
 58 
 
922 
 
 SUBJECT INDEX. 
 
 Kemp, 10, Tellurides, 1898. 
 
 15, Platinum, 1902. 
 Leith, 6, Iron, 1908. 
 
 7, ditto, 1908. 
 Louis, 1, Gold, 1893. 
 Maclaren, pp. 1-117, Gold, 1908. 
 Newberry, 2, Iron, 1881. 
 
 3, Gold, 1881. 
 
 Schmidt, Albrecht, 1, Copper, 1910. 
 Scrivenor, Tin, 1909. 
 Stutzer, 5, Iron, 1906. 
 
 Van Hise, 8, Tellurides, pp. 1120-1125, 1904. 
 Weed, 19, Copper, pp. 53-68, 1908, also Bull. 260, 
 U. S. G. S., pp. 96-97, 1906. 
 
 ORIGIN OF DEPOSITS IN PAR- 
 TICULAR DISTRICTS. 
 
 (Only a few titles, mainly of American 
 localities, are included under this heading. 
 Further references may be easily secured in 
 various published bibliographies.) 
 
 Antimony. 
 
 Haley, Gore, Nova Scotia, 1909. 
 
 Cinnabar. 
 
 Lotti, 4, Cortevecchia, 1903. 
 
 3, Tuscany, 1901. 
 Becker, 4, pp. 394^50, 1888. 
 
 Chromium. 
 
 Eyba, Kraubat, 1900. 
 
 Copper. 
 
 Boutwell, 5, pp. 162-211, 1905. 
 Finlayson, 2, Rio Tinto, 1910. 
 Hershey, 3, California, 1908. 
 Lane, 1, Lake Superior, 1903. 
 
 3, ditto, 1907. 
 
 Lawson, 2, Ely, Nevada, pp. 330-343, 1906. 
 Lindgren, 19, Clifton-Morenci, 1904 ; 32, 1911. 
 Lindgren and Boutwell, pp. 19, 20, 23-25, 96, 
 
 218-223, ditto, 1905. 
 Lindgren, Graton, and Gordon, pp. 51, 56, 67, 
 
 71, 78, New Mexico. 1910. 
 
 Spencer, 2, Encampment, Wyo., pp. 56-60, 1904. 
 Steinmann, Caro-Caro, 1906. 
 Van Hise and Leith, Mon. Lit., U. S. 6. S., pp. 
 
 580-591, 1911. 
 
 Gold and Silver. 
 
 Aston, 3, Barkerville, B. C., 1906. 
 
 Becker, 2, pp. 266-289, Comstock Lode, 1882. 
 
 Boutwell, 6, pp. 128-130, 1912. 
 
 Denny, Rand, S. Africa, 1908. 
 
 Emmons, S. F., 2, pp. 539-584, 1886. 
 
 Harrison, Fowler, and Anderson. British 
 Guiana, pp. 204-211, 1908. 
 
 Hatch, Rand, S. Africa, 1903. 
 
 Hershey, 2, Panama, 1899. 
 
 Irving, Emmons, and Jaggar, Black Hills, pp. 
 78^0, 154-157, 1904. 
 
 Lacroix, 2, Madagascar, 1901. 
 
 Lindgren, 8, pp. 172-184, Grass Valley, Cal. , 
 1896. 
 
 Lindgren and Ransome, 3, Cripple Creek, 1906. 
 
 Lotti, 1, Italy, 1889. 
 
 Purington, 1, Telluride, pp. 819-824, 1897. 
 
 Ransome, 14, Goldfield, pp. 189-199, 1910. 
 Rico, pp. 294-302, 1901 ; 18, Breckenridge, pp. 
 164-174,1911 ; 2, Silverton, pp. 132-143, 1901. 
 
 Ransome, Emmons and Garrey, Bullfrog, Ne- 
 vada, pp. 101-103, 1910. 
 
 Ransome and Calkins, pp. 134-140, 1908. 
 
 Reid, J. A., 1, pp. 177-199, ditto, 1905. 
 
 Rickard, T. A., 5, Bendigo, 1893. 
 
 Spurr, 3, Mercur, pp. 395-402, 1895 ; 4, Yukon 
 
 veins, pp. 297-316, 1897. 
 6, Monte Cristo, pp. 859-865, 1901. 
 
 12, Western Nevada, 1906; 5, Aspen, pp. 224- 
 236, 1898 ; 19, ditto, 1909. 
 
 13, Tonopah, pp. 253-261, 1905. 
 
 14, Silver Peak, Nevada, 1906. 
 
 15, Southern Klondike, pp. 369-382, 1906. 
 Spurr and Garrey, 3, pp. 159-161, 1908. 
 Voit, 1, Rand Conglomerate, 1908. 
 
 Weed and Barrell, Elkhorn, Mont , pp. 496- 
 
 503, 1901. 
 Weed and Pirsson, 2, Judith Mts., Mont., pp. 
 
 594-598, 1897 ; 1, Castle Mountains, 1896 ; 3, 
 
 Little Belt Mts., 1891. 
 
 Iron. 
 
 Eckel, Burchard, and Butts, Clinton ore, pp. 
 
 26-39, 1910. 
 
 Irving, R. D., 3, Lake Superior, 1886. 
 Leith, 1, pp. 237-277, 1903. 
 2, Lake Superior, 1906. 
 
 4, Genesis, Lake Sup. ores, 1906. 
 Phalen, 1, Kentucky, 1906. 
 
 Smyth, C. H., Jr., 1, Clinton ore, 1892. 
 Spurr, 1, Mesabi, 1894. 
 
 2, ditto, 1894 ; 7, Lake Superior, 1902. 
 Stutzer, 5, 1906. 
 Van Hise, 1, Lake Superior, 1892. 
 
 5, ditto, pp. 323-330, 1900. 
 
 Van Hise and Leith, Mon. Lii., U. S. G.S., pp. 
 499-571, 1911. 
 
 Lead and Zinc. 
 
 Bain, 2, Upper Mississippi Valley, pp. 124-142, 
 
 ' 1906. 
 
 1, Northwestern Illinois, pp. 44-50, 1905. 
 Bain and Van Hise, pp. 203-215, Ozark, 1901. 
 Finlayson, 1, Great Britain, 1910. 
 Leonard, 1, Iowa, 1895. 
 Smith, W.S. T., and Siebenthal, Joplin, 1907 
 
 Nickel. 
 
 Adams, F. D., 1, Sudbury, 1894. 
 Austin, Riddles, Oregon, 196. 
 Barlow, 2, Sudbury, 1906. 
 
 1, ditto, pp. 123-132. 1904. 
 Konigsberger, Quartz-adularia-zeolite veins, 
 
 Aar, 1901. 
 
 Tin. 
 
 Bateman and Ferguson, 1, 1912. 
 MacAlister and Hill, Cornwall, 1906. 
 Recknagel, South Africa, 1909. 
 Rumbold, 1, Bolivia, 1909. 
 
 2, Kinta Valley, Malay States, 1906. 
 
 GENERAL PAPERS DEALING 
 WITH THE GENESIS OF ORE- 
 DEPOSITS AS A WHOLE. 
 
 A dam, J. W. H., 1910. 
 
 Beck, 8, 1909. 
 9, 1909. 
 
 Becker, 4, pp. 442-450, 1888 ; 13, Discussion of 
 Posepny, 1893. 
 
 Bergeat-Stelzner, pp. 11S8-1239, Excellent gen- 
 eral discussion, 1906. 
 
 Brough, 1901. 
 
 Carpenter, Proc. Col. Sci. Soc.,vol. 7, pp. 253- 
 266, 1904. 
 
 Chalon, 1, 1905. 
 2, 1906. 
 
 Clarke, 2, pp. 541-618, 1908. Also New Edition, 
 pp. 599-613, 1911. 
 
 von Cotta, 2, pp. 546-552, 1870. 
 
 de Launay, 1, 1893. 
 k, 1897 ; 5, 1897 ; 6, 1897 ; 11, 1905. 
 
 Demaret, 5, 1906. 
 
SUBJECT INDEX. 
 
 923 
 
 Eckel, Bibliography, Jour. GeoL, vol. 11, pp. 
 
 71(5-719, 1903. 
 Emmons, S. F., 3, 1887. 
 
 4, Fissure veins, 1887. 
 
 9, 1893 ; 10, 1893. See also Science, New Series, 
 
 vol. 17, pp. 541-542, 1903. 
 Frazer, 5, 1904. 
 Heusler, 1901. 
 Jenney, 2, 1902 ; 3, 1902. 
 Keck, 1883. 
 Keilhack, 2, 1896. 
 Kemp, 3, 1891. 
 
 4, 1893 ; 6, 1893 ; 8, 1895. 
 
 14, Reply to Van Hise, 1901. 
 
 16, 2d ditto, 1902. 
 
 17, 1903 ; 19, 1904. 
 
 21, pp. 37-46, 1906 ; 24, 1906. 
 26, 1907 ; 27, 1906 ; 28, 1908 ; also, Contributions 
 to Col. Univ. Geol. Dept., vol. 10, No. 86, 
 1902. 
 
 Keyes, 1, 1900. 
 Kleinschmidt, 1887. 
 Klement, 1898. 
 Le Conte, 3, 1883. 
 
 4, Discussion of Posepny, 1894. 
 Lindgren, 14, 1901. 
 
 26, 1907. 
 Lotti, 2, 1903. 
 Maclaren, Min. and Sti. Press, vol. 85, p. 281, 
 
 1903. 
 Newberry, 6, 1884. 
 
 5, 1883. 
 
 Phillips, 2, 1871. 
 
 4, 1871 ; 3, 1879. 
 Phillips-Louis, pp. 121-150, Excellent general 
 
 discussion revised up to 1895, 1896. 
 Posepny, 1, 1902. 
 
 2, 1893. 
 
 Pumpelly, 3, General, 1877. 
 Ransome, 17, 1911. 
 Raymond, 6, 1900. 
 
 Rickard, T. A., et al., 1, " A Discussion." Val- 
 uable collection of papers, 1903. 
 
 2, 1903. 
 Rickard, T. A., 20, 1908. 
 
 7, Discussion of Posepny, 1894 ; 5, 1893. 
 Schierl, 1904. 
 
 Spurr, 16, pp. 9-22, 1907. See also, E. and M. 
 Jour., vol. 76, pp. 54-55, 1902. 
 
 17, 1907. 
 Stutzer, 5. 1906. 
 Van Hise, 4, 1900. 
 
 6, 1901. 
 
 8, pp. 1004-1243, 1904. See also, Scientific Am- 
 erican Suppl., vol. 52, pp. 21, 504,1901. 
 
 Vogt, 10, 1901. 
 
 Vogt, Beyschlag and Krusch, pp. 161-186, Excel- 
 lent general discussion, 1910. 
 Wadsworth, 1, 1888. 
 Werner, Hist, 1791. 
 Whittlesey, 1, 1876. 
 Winchell, H. V., 5, 1907. 
 6, 1908. 
 
 OXIDATION. 
 
 (See under " Superficial Alteration.") 
 
 ORE-SOLUTIONS. 
 
 (For Effect on Wall Kock, see under " Replacement." 
 
 NATURE AND ORIGIN OF THE 
 AGENT OF DEPOSITION. 
 
 Beck, 8, pp. 424-432, 1900. 
 
 9, vol. II., pp. 55-70, 1906. 
 Becker, 4, pp. 444-445, 1888. 
 Bergeat-Stelzner, pp. 1213-1239, 1905. 
 Bischof, 1, 2d ed., vol. III., pp. 904-912, 1866. 
 Clarke, F. W., 2, New Edition, pp. 201-205, 599- 
 
 610, Excellent general discussion, 1911. 
 Darapsky, 1903. 
 
 Daubree, A., 2, p. 180, et seq., 1879. 
 Daubree, G. A., 1, 1887. 
 
 2, 1887. 
 
 de Launay, 7, pp. 85, et seq., 1899. 
 Delkeskamp, 3, 4, 5, 6, 7, 8, 1899-1908. 
 Doelter, 2, Solubility of minerals, 1890. 
 Finch, Origin of water, 1904. 
 Griffiths, Quicksilver in mineral springs of 
 
 New Zealand, 1910. 
 Hague, 2, 1911. 
 
 Headden, Radium Springs, 1905. 
 Kemp, 14, 1901. 
 
 16, 1902 ; 18, 1904 ; 24, 1906. 
 
 21, pp. 39-46, 1906; 27, 1906. 
 Knelt, 1899. 
 Konig, .P., 1901. 
 Krusch, 3, 1904. 
 Lane, 4, 5, 6, 1908-9. 
 Le Conte, 2, 1883. 
 
 4, pp. 996-1006, 1894. 
 
 1, pp. 253-260, 1904. 
 Le Conte arid Rising, 1882. 
 Lindgren, 21, Steamboat Springs, 1905. 
 
 31, 1910. 
 Lindgren, Graton and Gordon, pp. 56, 71-74, 
 
 New Mexico, 1910. 
 Lotti, 5, pp. 372-378, 1893. 
 Mutter, 1, Mineral springs in Freiberg mines, 
 
 1885. 
 
 Phillips-Louis, pp. 115-119, 134-142, 793-795, 
 1896. 
 
 Phillips, 3, 1871. 
 
 4, 1871. 
 
 6, 1884. 
 
 Rickard, et al., "A Discussion," many valu- 
 able discussions are scattered through this 
 volume, 1903. 
 Rickard, T. A., 20, 1908. 
 Roth, vol. I., pp. 564 et seq., 1879. 
 Strutt, 1907. 
 Stutzer, IS, 1910. 
 Suess, 2, and 3, 1902. 
 Van Hise, 4, 1900. 
 
 6, 1901. 
 
 8, pp. 1052-1139, 1904. 
 Van Hise and Leith, Mon. Lii. U. S. G. S., pp. 
 
 580-591, 1911. 
 Vogt, 5, 1894-5. 
 
 8, 1899 ; 10, 1901. 
 
 Vogt, Krusch and Beyschlag, vol. 1, pp. 118-135, 
 Excellent discussion, also pp. 171-179, 1909. 
 Weed, 1, 1891. 
 
 3, 1900 ; 13, 1903. 
 Weed and Pirsson, 4, 1893. 
 
 PKOCESSES OF DEPOSITION FROM 
 SOLUTIONS. 
 
 Bain and Van Hise, pp. 95-110, Excellent dis- 
 cussion, 1901. 
 
 Becker, 4, Deposition of mercury, pp. 331-353. 
 419-450, 1888. 
 
 Biddle, Copper, 1901. 
 
 Bischof, 1, 1863-1871. 
 
 Carthaus, 1896. 
 
 Clarke, 2, pp. 603-609, New Edition, 1911. 
 
 Doelter, 1, 1906 ; g, 1890. 
 
 Fernekes, Copper, 1907. 
 
 Gillette, Osmosis, 1903. 
 
 Jenney, 2, By reducing agents, 1902 ; discus- 
 sion of by Church, Trans. A. I. M. E., vol. 
 33, pp. 1065-1070, 1902. 
 
924 
 
 SUBJECT INDEX. 
 
 Kemp, 18, 1904. 
 
 Kohler, E., adsorption, 1903. 
 
 Konigsberger. 1901. 
 
 Le Conte. 1, pp. 253-256, 1904. 
 
 Lenher, Tellurides, 1909. 
 
 Lindgren, 24, By loss of temperature and pres- 
 sure, 1906. 
 31, 1910. 
 
 Lotti, 4, Cinnabar, 1903. 
 
 Louis, 2, Gold. 1894. 
 
 Newberry, 6, General, 18S4. 
 
 Sharwood, of Tellurides, 1911. 
 
 Smith, G. O., E. and M. Jour., vol. 73, p. 826, 
 1902. 
 
 Sorby, Evidences of temperature and pres- 
 sure of quartz formation. 1858. 
 
 Steidtrnann, Comparative effect of surface- 
 waters and mineralizers, 1908. 
 
 Stokes, 1, of Pyrite and marcasite, 1901. 
 2, General, 1906 ; 3, Pyrite and Marcasite,1907. 
 
 Sullivan, 1, of Copper by silicates, 1906. 
 
 2, Reactions between solutions and min- 
 erals, 1907. 
 
 3, Mineral niters, 1908. 
 
 Van Hise, 4, of Copper in Lake Superior, pp. 
 
 67-71, 84-91, 99-102, 1900. 
 8, By ascending solutions, pp. 1081-1132,1904. 
 
 Van Hise and Leith, Mon. LiL, U. S. G. S., Pre- 
 cipitation of Copper, pp. 589-590, 1911. 
 
 Vogt, Beyschlag, and Krusch, vol. I., pp. 118-135, 
 Excellent general disdussion, 1909. 
 
 PRECIPITATION FROM SOLUTION. 
 
 (See under "Ore-Solutions.) 
 
 PHYSICAL CONDITIONS OF ORE-DEPOSITION. 
 
 (See under *' Ore-Solutions " and " Contact-Metamorphic Deposits.") 
 
 PRESSURE AND TEMPERATURE IN 
 ORE-DEPOSITION. 
 
 (See under " Ore-Solutions " and " Contact-Metamorphic Deposits.) 
 
 REGIONAL METAMORPHISM, DEPOSITS PRO- 
 DUCED DURING, AND EFFECT ON PREVIOUSLY 
 FORMED DEPOSITS. 
 
 (In many of the references cited here the relation of ore-deposition to regional 
 metamorphism is not definitely stated. ) 
 
 Weed, 17, By adsorption, 1905. 
 11, By ascending waters, 1902. 
 
 Wells, Fractional precipitation of sulphides, 
 1910. 
 
 Wright and Larsen, Quartz as an indicator of 
 temperature and pressure of ore-deposi- 
 tion, 1909. 
 
 TEMPERATURES AND PRESSURES 
 OF ORE-SOLUTIONS AND THEIR 
 EFFECT ON THE RESULTING 
 ORE-DEPOSITS. 
 
 de Launay, 8, 1900. 
 
 Doelter, 1, pp. 79-112, 1906. 
 
 Emmoris, W. H., 3, Genetic classification of 
 minerals, 1908. 
 
 Komgscberger, Temperature and pressure of 
 quartz formation, 1901. 
 
 Lindgren, 25, in veins of Dahlonega, pp. 123- 
 
 125, 1906. 
 
 26, Excellent general paper on physical con- 
 ditions of deposition, 1907. 
 24, In deep deposits, 1906. 
 
 Lindgren and Ransome, Evidence on tempera- 
 ture and pressure of solutions, 1905. 
 3, pp. 181, 226, 1906. 
 
 Wright and Larsen, Quartz formation, 1909. 
 
 Abbott, 1907. 
 
 Bastin, Criteria of regional metamorphism, 
 Jour. Geol., pp. 445-472, 1909. 
 
 Beck, 8, Ores in the Crystalline schists (Rela- 
 tions to regional metamorphism some- 
 what indefinite), pp. 433-477, 1909. 
 9, vol. II., pp. 71-131, 1909. 
 
 Becker, 12, Gold, Southern Appalachians, 1895. 
 
 Sergeat-Stelzner, pp. 86-470, occasional types 
 described on these pages have been meta- 
 morphosed, 1906. 
 
 Blake, W. P., 9, Zinc, 1894. 
 
 Dresser, Copper, 1906.. 
 
 Emmons, W. H., 4. 1909. 
 
 Fermor, 2, Manganese, 1909. 
 
 Henrich, C., 3, Copper, 1895. 
 
 Kemp, 5, Zinc and manganese, 1893. 
 
 Thomas and MacAlister, pp. 371-358, 1908. 
 
 REPLACEMENT. 
 
 GENERAL DISCUSSIONS. 
 
 Bams, 2, 1884. 
 
 Beck, 8, pp. 392-407, 1909. 
 9, vol. II., pp. 20-36, 1909. 
 
 Becker, 4, pp. 394-401. Good general discus- 
 sion, 1888. 
 
 13, Discussion of paper by Posepny, pp. 602- 
 604, 1894. 
 
 Bergeat-Stelzner, General, pp. 1007-1188. A very 
 extensive series of bibliographic refer- 
 ences will be found under the descriptions 
 of the several districts, 1906. 
 
 Emmons, S. F., 2, pp. 563-569, 1886. 
 10, Discussion of Posepny, p. 602, 1893. 
 3, pp. 125-135, 1887 ; 6, scattered discussion, 
 1888 ; 9, pp. 64, 85, 86, 1893 ; also Trans. A. I. 
 M.E., vol. x., p. 418, 1882. 
 20, In fissure-veins of Butte, 1897. 
 Irving, J. D., 9, General paper on replacement, 
 
 1911. 
 
 Irving, R. D., and Van Hise.l, pp. 413-422, 1890. 
 Irving, Emmons, and Jaggar, In Black Hills 
 
 ore-bodies, South Dakota, 1904. 
 Kemp, 21, pp. 44-46, 1906. 
 14, Discussion of Van Hise, 1901. 
 
SUBJECT INDEX. 
 
 925 
 
 Kimball, J. P., 1, 1891. 
 
 Krusch, 6, 1910. 
 
 Lindgren, -12, Metasomatic processes in fissure 
 
 veins, 1900. 
 23, 1906. 
 Lindgren and Boutwell, pp. 123-126, Brief but 
 
 excellent general discussion, 1905. 
 Phillips-Louis, pp. 143-150, also pp. 175-179,1896. 
 Posepny, It, General discussion of lead- and 
 
 zinc-deposits in soluble rocks, 1893. 
 
 2, (in English) Excellent general paper, pp. 
 210-212, 283-304, 318-321, 1893. 
 
 3, Reply to discussion of 2, 1894. 
 Pumpelly, 1, 1878. 
 
 Purington, 1, Replacement versus impregna- 
 tion, pp. 802-809, 1897. 
 
 Rickard, T. A., 7, pp. 942-948, Discussion of 
 Posepny, No. 2, 1894. 
 
 Spurr, 16, p. 247, 1907. 
 
 Thomas and MacAlister, pp. 237-300, 1908. 
 
 Vogt, 10, pp. 147-158, 1901. 
 
 Vogt, Bey&chlag and Krusch, vol. i., pp. 4, 13, 40- 
 42, 131, 170-171, 235, 1910. 
 
 Wallace, pp. 220-231, 1908. 
 
 Winchell, H. V., 2, Discussion of paper by 
 Posepny (2), 1893. 
 
 CRITERIA OF REPLACEMENT. 
 
 Becker, 13, pp. 602-604, 1893. 
 Irving, J. D., 9. 10, 1911. 
 Lindgren, 12, pp. 595-597, 1900. 
 
 REPLACEMENT ADVOCATED OR 
 DISCUSSED FOR INDIVIDUAL 
 OCCURRENCES. 
 
 (A few references only are given here ; the 
 literature is extremely voluminous. For com- 
 plete bibliography of metasomatic deposits 
 see Bergeat-Stelzner, pp. 1007-1138.) 
 
 Abbott, Ely, Iron, 1907. 
 
 Barrell, 2, pp. 126-128, 129, 131, 144, 146, 1907. 
 Bayley, 1, Iron, pp. 395-401, 1904. 
 Becker, 4, pp. 394-401. Cinnabar not a replace- 
 ment, 1887. 
 Blake, 1, Lead, silver, 1878. 
 
 2, Gold, silver, 1882. 
 Blow, Leadville, 1889. 
 Boutwell, 4, Bingham, pp. 549-564,566-570. 1905. 
 
 5, ditto, pp. 168-172, 179, 180, 194-201, 1905. 
 Carpenter, Black Hills, pp. 582-583, 1889. 
 Church, 4, Comstock lode, 1879. 
 Curtis, 1, Eureka, pp. 244-250, 1884. 
 
 2, ditto, pp. 93-106, 1884. 
 Douglas, Bisbee, pp. 531-537, 1899. 
 
 Emmons, 2, Leadville, pp. 565-569, 1886. 
 
 5, Butte, pp. 56-58, 1888 ; 20, Butte, 1897. 
 14, pp. 669-672, Gold, 1901. 
 
 Emmons and Irving, Leadville, 1907. 
 Ermisch, Tuscany, 1905. 
 Finlayson, 1, 1910. 
 
 2, Rio Tinto, 1910. 
 
 Irving, Emmons and'Jaggar, Black Hills, pp. 
 
 111-160, 1904. 
 
 Irving and Van Hise, pp. 411-422. 
 Lindgren, 9, pp. 646-647, 1897,. 
 
 13, Blue Mts., Oregon, pp. 604-605, 1901. 
 23, Western Australia, 1906. 
 
 Lindgren and Boutwell, Clifton, Morenci, pp. 
 
 123-191, 1905. 
 Lindgren and Ransome, 3, Cripple Creek, pp. 
 
 184-196, 1906. 
 Lindgren, Graton and Gordon, Pre-Cambrian 
 
 veins, New Mexico, p. 59, In limestone, pp. 
 
 62-67, In veins, p. 71, 1910. 
 Malcolmson, Sierra Mojada, pp. 108-131, 1901. 
 Moffit and Maddren, of Greenstone by copper, 
 
 pp. 48, 80-88, 1909. 
 Navarro, Almade'n, Spain, 1894. 
 Pumpelly, 1, Lake Superior copper, 1877. 
 Ransome, 5, Globe, Ariz., pp. 125-132, 1903. 
 
 6, Bisbee, Ariz., pp. 146-154, 1904. 
 
 14, at Goldfield, Nev., pp. 176-186, 1909. 
 Ransome and Calkins, at Coeur d'Alene, pp. 
 
 112, 138-139, 1908. 
 Raymond, Trans. A. I. M. E., vol. 6, pp. 371- 
 
 393. 1877-1878. 
 
 Rickard, T. A., 1, Mt. Morgan, pp. 145-150, 1891. 
 Rutledge, Clinton iron-ores of Pennsylvania, 
 
 1909. 
 
 Smith, F. C., 1, Black Hills, 1897. 
 Smith, W. S. T., and Siebenthal, p. 14, Joplin 
 
 jasperoid, 1907. 
 Smyth, C. H., Jr., 1, Clinton ores, 1892. 
 
 3, Replacement of quartz by pyrite, 1905. 
 Spencer, 6, Juneau, pp. 24, 62 and 111, 114, 1906. 
 
 9, Cornwall magnetites, p. 13, 1908. 
 Spurr, 5, Dolomitization, pp. 206-216, Silicifi- 
 
 cation and Ferration, pp. 216-223, Of ore, 
 
 pp. 232-236, Aspen, Colorado, 1898. 
 6, of Igneous rocks, Monte Cristo, pp. 831- 
 
 833, 1901. 
 13, of Andesite by vein-matter at Tonopah, 
 
 in Rock-alteration at Tonopah, pp. 207-252, 
 
 1905. 
 Spurr and Garrey, 3, at Georgetown, Colo., pp. 
 
 160-161, 1908. 
 
 Tower and Smith, at Tintic, pp. 705-708, 1898. 
 Turner, 2, in Sierra Nevada, 1899. 
 Watson, 2, Lead and zinc of Virginia, p. 716, 
 
 1905. 
 Weed and Barrell, at Elkhorn, Montana, pp. 
 
 496-501, 1901. 
 Weed and Pirsson, 2, Judith Mts., pp. 592-598 
 
 1897. 
 
 SEDIMENTARY PROCESSES AS ORE-BUILDERS. 
 
 ORES SUPPOSED TO BE A DIRECT 
 RESULT OF SEDIMENTARY 
 PROCESSES. 
 
 Beck, 8, pp. 49-111, General, 1909. 
 
 9, vol. II., pp. 331-416, 1909. 
 Bergeat-Stelzner, General, pp. 85-470, 1906. 
 Bowron, 2, Alabama-Clinton ores, 1905. 
 Burchard, Butts, and Eckel, Clinton, Birm- 
 ingham, pp. 28-39. Argument against, 1910. 
 Hopkins, Iron, Penna., 1900. 
 Hornung, 1, Kupferschiefer, 1904. 
 McCallie, S. W., 1, Iron, Georgia, 1900. 
 
 2, Ditto, 1908. 
 
 Newland, 3, Clinton ores of New York, 1909. 
 Newland and Hartnagel, Clinton, 1908. 
 Phalen, 1, Kentucky, Clinton, 1906. 
 Phillips-Louis, General , pp. 35-66, 1896, 
 Redlich, 1, W. Alps, ores, 1906; S, 1907. 
 Rolker, 2, Silver sandstones, 1880. 
 
 Rutledge, Against sedimentary origin, 1909. 
 Stremme, Iron in sedimentary rocks, 1910. 
 Spurr, 16, General, 1907. 
 Van Hise, 1, 1892. 
 
 8, General, pp. 1037-1043, 1904, 
 Van Werveke, Minettes of Luxembourg, 1901. 
 Vogt, 3, Criteria for recognition of sedimen- 
 tary ores, 1891 and 1894. 
 Wherry, Sedimentary copper, 1908. 
 
 ORES SUPPOSED TO BE DERIVED 
 BY LATER CONCENTRATION OF 
 SEDIMENTARY PARTICLES IN 
 ROCKS. 
 
 Abbott, 1, Vermillion Iron Range, 1907. 
 Adams, G. I., 2, pp. 39-62, 1904. 
 Adiasseurch, Siberian copper-ores in sand-\ 
 stone, 1907. 
 
926 
 
 SUBJECT INDEX. 
 
 Bain, 3, Comparison of sedi-genetic and ig- 
 
 neo-genetic ores, 1906. 
 
 4, Paleogeography and Mississippi Valley 
 ores, 1907. 
 
 Ball, and Shaler, Congo copper, 1910. 
 
 Hergeat-Stelzner, bibliography of Mansfeld cop- 
 per-shales, pp. 391-417, 1906. 
 
 Buckley and Buehler, pp. 9. 13, 14, 15, 25, 26, 
 78-85, 97-110, Lead and 7,inc, 1906. 
 
 Boutwell, 1, p. 200-210, 1905. 
 
 Buttgenbach, 2, Congo, 1904. 
 
 Chamberlin, T. C., 3, Lead-ores, Wisconsin, 
 pp. 377-568, 1882. 
 
 Clarke, 2, p. 611, 1908. New Edition, Discus- 
 sion of Source of the Metals, pp. 600-680, 
 1911. 
 
 Emmons, S. F., 16, pp. 221-232, 1905. 
 
 Emmons, W. H., 1, pp. 125-128, 1906. 
 
 Farrell, Congo, 1908. 
 
 Fleck and 'Haldane, Vanadium, pp. 47-115, 
 
 1905-1906. 
 Gale, 2, Idaho, 1909. 
 
 3, Carnotite. 1908. 
 
 4, pp. 110-117, Carnotite, 1900. 
 Giirich, 2, Copper, Bohemia, 1893. 
 Hewett, 1909. 
 
 Hillebrand, 3, Patronite, p 141, 1907. 
 
 Hillebrand arid Ransome, Carnotite, 1900. 
 
 Jennings, 1, 1903. 
 
 Kemp, 21, p. 333, 1906. 
 
 Lindgren, Graton and Gordon, New Mexico, 
 
 pp, 76-79, 1910. 
 
 Newberry, 1, Silvers. S., 1880-1887. 
 Rolker, 2, Silver in S. S., 1880. 
 Roth well, pp, 25, 48, 79, Silver sandstone, 1880. 
 Schmitz, Copper, Texas, 1897. 
 Spurr, 1. 2, 1894. 
 Steinmann, pp. 335-368, 1906. 
 Tarr, W. A., Oklahoma copper in S. S., 1910. 
 1 Turner, 3, New Mexico, 1902. 
 
 SUBLIMATION. 
 
 (See also under sub-head " Pneumatolysis" of "Emanations from Igneous 
 Magmas.") 
 
 Beck, 8, pp. 421-424, 1909. 
 
 9, vol. 2. pp. 52-55, 1909. 
 Becker. 
 Bergeat, 3, 1899. 
 
 4, ditto, 1899, 
 
 Bergeat-Stelzner, pp, 1208-1213, 1906. 
 Clarke, 2, pp. 248-276, 1908. 
 
 Duroclier, Artificial production of minerals in 
 
 the dry way, 1851-1856. 
 Necker, General, 1833. 
 Phillips-Louis, pp. 127-129, General, 1896. 
 von Richtofen, p. 275, Hungarian propvlites, 
 
 gold, 1860. 
 
 SUPERFICIAL ALTERATION. 
 
 (The superficial alteration of ores is brought about by atmospheric waters which 
 seep downward from the surface. These produce, first, a zone of oxidation, and, 
 second, a zone of secondary sulphide enrichment. References are, therefore, given 
 under the following heads : (1) Ground- water and its Movement, (2) Oxidation. 
 (3) Secondary Sulphide Enrichment.) 
 
 GROUND- WATER AND ITS MOVE- 
 MENT. 
 
 Daubrte, G. A., 1, 1887. 
 
 2, 1887. 
 
 deLaunay, 7, 1899; 5, 1897. 
 Finch, 1904. 
 Finlayson, 4, 1910. 
 Fuller, 2, Excellent general summary, 1906 ; 1, 
 
 General bibliography from 1879-1904. 
 Kemp, 14, pp. 184-195, 1901. 
 
 16, 1902. 
 
 King, Excellent general discussion, 1898. 
 Mendenhall, 5, Relating especially to Los An- 
 geles, 1909. 
 Ochsenius, 1, 1893. 
 Posepny, 2, pp. 212-247, 1893. 
 Ransome, 2, p. 141, 1901. 
 Ries, General, pp. 293-301, 311-316, 1910. 
 Sass, 1, Oscillations of ground-water level, 1901. 
 Slichter, 1, Motion of ground-water (mathe- 
 matical treatment), 1899. 
 
 2, ditto, Excellent discussion, 1902. 
 Spurr, 16, General, pp. 237-242, 1907. 
 UMig, Motion of ground-water, 1893. 
 Van Hise, 4, General discussion, 1900. 
 
 6, 1901. 
 
 8, General, pp. 65-119, circulation and work 
 of, 120-159, 1052-1024, 1904. 
 
 OXIDATION. 
 
 Beck, 8, pp. 363-378, 1909. 
 
 9, vol. II., pp. 308-327, 1909. 
 Biddle, 1901. 
 
 Buehler and Gottschalk, Experimental, 1910. 
 Butler, At Leadville, Econ. GeoL, vol. viii. pp. 
 
 1-18, 1913. 
 
 Chance, 6, Iron sulphides, 1908. 
 9, 1908. 
 
 Chautard and Lemoine, Laterization, 1908. 
 Cornu, 2, 1909. 
 
 Curtis, 1, Eureka, pp. 51, et seq., 1884. 
 deLaunay, 5, 1897. 
 
 8, 1900. 
 
 Dodler, 2, Solubility of minerals, 1890. 
 Eckel, Burchard and Butts, pp. 28-39, 1910. 
 Emmens, 1, 1892. 
 Emmons, S. F., 1, Chemical, 1882. 
 
 13, 1900. 
 Emmons, W. H., 5, 1909. 
 
 7, Manganese in ores and its effect in oxida- 
 tion of gold-veins, 1911. 
 
 Gregory, 1, 1901. 
 
 2, 1904; 7, 1906. 
 
 Hoover, Western Australia, 1898. 
 Julien, 1, 1879. 
 Kemp, 23, Copper. 1906. 
 Keyes, 4, Silver chlorides, 1901. 
 
 5i ditto, 1908. 
 Kruscfi, 4, Criteria, 1907. 
 Lindgren and Graton, pp. 55-56, 59, 70. 
 Litschciuer, 1893. 
 
 Phillips-Louis, pp. 97-99, 106-107, 1896. 
 Penrose, 2, 1894. 
 Rickard, T. A., 14, Bonanzas in gold-veins, 
 
 1901. 
 
 Scharitzer, 1907. 
 
 Spurr and Garrey, 3, pp. 148-149, 1907. 
 Stokes, 2, Chemical, 1906. 
 Thomas and MacAlister, pp. 362-375, 1908. 
 Van Hise, 4, pp. 99-150, 1900. 
 
 8, pp. 461-472, 1904. 
 
 Walker, E., Copper sulphate, 1903. 
 Weed, 5, Chemical, 1907. 
 
 19, pp. 43-52, in copper deposits, 1908. 
 Weifikopf, Iron, 1905. 
 Whitney, 2. 1855. 
 Winchell, A. N., 1, Oxidation of pyrite. 1907. 
 
SUBJECT INDEX. 
 
 927 
 
 SECONDAKY SULPHIDE ENRICH- 
 MENT. 
 
 Bain and Van Hise, Chemical, pp. 103-106, 
 
 Bancroft, 2, 1903. 
 4, General, 1909. 
 
 Bastin, Replacement in sulphide enrichment 
 Econ. GeoL, vol. viii., pp. 51-63, 1913 
 
 Beck, 8, pp. 378-382, Extensive discussion, 
 chemical, 1909 ; 9, vol. 2, pp. 308-220, Ex- 
 cellent general discussion, 1909. 
 
 Bergeat-Stelzner, pp. 541-564, Excellent general 
 discussion, 1906. 
 
 Bout well, 5, pp. 212-217, 218-223, 228-230, 1905. 
 
 Brock, Min. Mag. (R.), vol. 4, pp. 203-204, 1911 ; 
 Effect of climate on secondary enrich- 
 ment, discussion of Winchell, 1911. 
 
 Burgess, E. and'M. Jour., vol. 76, p. 153, 1903. 
 
 Church, E. and M. Jour., vol. 80, p. 695, 1905. 
 
 de Launay, 5, 1897. 
 6, 1900. 
 
 Emmons, S. F., 13, 1900 ; 20, 1897. 
 
 Emmons, W. H., pp. 615-617, 618-627, 7, Man- 
 ganese and gold, 1911; Effect of climate 
 on, Min. Mag. (R). vol. iv, p. 116 ; 8, 1908. 
 
 Farrell, J. H., Chapter XI, 1912. 
 
 Finlayson, 4, 1910-11. 
 
 Foote, 1910. 
 
 Fuchs and de Launay, vol. ii, pp. 230-234, 1893. 
 
 Gautier, 1, 1906 ; 3. 1906 ; 1, 1906 ; 5, 1909. 
 
 Graton and Murdoch. Excellent discussion on 
 copper. Advance Bull. A. I. M. E. at Feb. 
 Meeting, 1913. 
 
 Gregory, J. W., 1, 1901. 
 2, 1904 ; 6, 1906 ; 13, 1910. 
 
 Gunther, 2, Chapter X. 1912. 
 
 Herrick, Min. and Sci. Press, vol. 87, pp 1-97 
 1903. 
 
 Hill, E. and M. Jour., vol. 80, pp. 645-646, 1905 
 
 Kemp, 23, Copper, 1905. 
 25, 1907. 
 21, pp. 49-52, 1906. 
 
 Keyes, 3, 1910. 
 
 Krusch, 4, Criteria, 1907 ; 1, 1900. 
 
 Lazerovic, Zeit.f. prak. Geol. vol. 19. pp. 321-327 ; 
 vol. 20, pp. 337-371, 1911, 1912. 
 
 Lindgren, 19, pp. 511-550, by replacement, 1904 ; 
 
 36. Copper, 1905 ; 20 a, pp. 177-208, 1905 ; 26, 
 
 190/ . 
 
 Lindgren and Graton. pp. 315-317, 1910. 
 Lotti, 2, pp. 133-135, 1903. 
 MacAlister and Hill, Extensive discussion of 
 
 secondary alteration at Cornwall, Eng., 
 
 pp. 187-194, 1906. 
 cla 
 
 Maclaren, of gold, pp. 79-86, 100-105, 111-115, 
 
 1908. 
 
 Moffit and Maddren, pp. 52-54, 1909 
 Penrose, 2, 1894. 
 Purington, E. and M. Jour., vol. 75, pp. 472-473, 
 
 1903. 
 Ransome, 2, pp. 138-141. 1901 ; 5, pp. 128-132, 
 
 1903 ; 6, pp. 132-160, 1904 ; 15, Criteria, 1910 ; 
 
 Discussion of, Econ. GeoL, vol. 5, pp. 81-89 ; 
 
 479-480,488-491; 558-564; 681-682. 
 Read, T. T., 2, 1906. 
 
 Rickard, T. A., 14, Bonanzas in gold-veins, 1901. 
 Ries, pp. 338-340, 1910. 
 Sales, 1, 1910. 
 Simpson, 1908. 
 Spurr, 16, pp. 265-293, 1907; E. and M. Jour., 
 
 vol. 80, pp. 597-598, 1905. 
 Spurr and Garrey, 3, p. 143, 1908. 
 Starbird, E. and M. Jour., vol. 75, pp. 702-703, 
 
 Stokes, 1, Pyrite and marcasite, 1901. 
 
 2, Chemical, 1906 ; 3, 1907. 
 Thomas and MacAlister, pp. 359-375, 1908. 
 Tolman, 2, 1913; 3, 1909; 4, 1909 ; 5, with bib- 
 liography, 1909. 
 Van Hise, 4, pp. 104-138, 1900. 
 
 8, pp. 1139-1193, 1904. 
 
 Weed, 2, Excellent general discussion, orig- 
 inal paper, 1900. 
 
 5, ditto, 1900. 
 
 14, At Butte. Mont. pp. 176-179, 1903 ; also 
 Bull. Geol. Soc. Am., vol. 15, pp. 179-206, 1900. 
 
 19, In copper-ores, pp. 43-52, 1908. 
 Weed and Barrell, p. 503, 1901. 
 Wells, Chemical, 1910. 
 Winchell, H. V., 4, Chemical, copper, 1903. 
 
 8, Effect of climate on, 1910. 
 
 9, ditto, 1911. 
 
 UNDERGROUND WATERS. 
 
 BIBLIOGRAPHY OF. 
 
 Clarke, 2, p. 170, 1908 ; 2nd ed., pp. 204-205, 
 1911. 
 
 Fuller, 1, For years 1879-1904, 1905. 
 
 Slichter, 1, pp. 381-384, Contains many refer- 
 ences which for lack of space are not 
 here repeated, 1899. 
 
 MINE-WATERS. 
 
 Becker, 1, Analyses and temperature of water 
 of Comstock lode, p. 152, 1882 ; 4, pp. 258- 
 261, 346-350. 
 
 Bergeat-Stelzner, pp. 555-560, General discussion, 
 analyses, 1906. 
 
 Buckley, 1, Analyses, pp. 231 ; Analyses of, p. 
 249, 1909. 
 
 Don, Assays for gold in, pp. 601-605, 1897. 
 
 Fernekes, Analyses Lake Sup. copper-mine 
 waters, 1907. 
 
 Kemp, 21, Analyses and brief general dis- 
 cussion, pp. 29-31, 1906. 
 
 Krusch, S, 1904. 
 
 Lane, 3, Lake Superior copper-mine waters, 
 1907. 
 
 4, ditto, 1908. 
 
 5, Field analyses of mine-waters, 1908. 
 
 6, 1909. 
 
 Lindgren, 8, pp. 120-124, 1896. 
 
 Mulle.r, H., 1, 1885. 
 
 Posepny, 2, pp. 220-247, Excellent general dis- 
 cussion, 1893. 
 
 Spurr, 13, pp. 105-108 ; 23. 
 
 Spurr and Garrey, 3, pp. 125-126, Georgetown, 
 1908. 
 
 GENERAL DISCUSSIONS ON UN- 
 DERGROUND WATERS. 
 
 Bain and Van Hise, Excellent general dis- 
 cussion, pp. 95-110, 1901. 
 
 Blake, 12, Deposition by vadose waters in 
 Arizona, 1901, 
 
 Chamberlin, T. C., 1, Artesian water-supply, 
 1885. 
 
 Clarke, F. W., 2, pp. 139-171, Mainly chemi- 
 cal, 1908 ; Juvenile vs. meteoric 'water, 2. 
 pp. 201-205, 2nd edition, 1911. 
 
 Darapsky, Juvenile vs. meteoric waters, 1903. 
 
 Daubree, G. A,, 1, Subterranean waters in an- 
 cient epochs, 1887. 
 
 2, Subterranean waters of the present day, 
 1887. 
 
 de Launay, 7, 1899. 
 
 Delkeskamp, 3, Genesis of thermal waters, 1899. 
 4, 1904. 
 
 6, Juvenile vs. vadose springs, 1905. 
 
 7, Juvenile and vadose carbonic acid, 1906. 
 
 8, Progress in the sciences of mineral 
 springs, 1908. 
 
 Don, Genesis of gold-ores (in relation to min- 
 eral waters), 1897. 
 
 Finch, Excellent discussion oh depth of 
 ground-water, 1904. 
 
 Fuller, 2, Excellent paper, 1906. 
 
 Gautier, A., 1, Excellent general paper on 
 
 magmatic water, 1906. 
 2, General, 1906. 
 
 4, General, 1906. 
 
 5. 1909. 
 
 Griffiths, Quicksilver, New Zealand, 1910. 
 Gudzent, Radio-activity of thermal waters,1910 
 
928 
 
 SUBJECT INDEX. 
 
 Hague, 2, Origin thermal waters, 1911. 
 Henrich, F., 1910. 
 
 Kemp, 14, pp. 184-194, Excellent general dis- 
 cussion, 1901. 
 
 16, Excellent general discussion, 1902. 
 King, F. H., Excellent general discussion, 
 
 1898. 
 
 Krusch, 3, Westphalian vein- waters, 1904. 
 Lindgren, 31, Deposition of sulphides by hot 
 
 springs, 1910. 
 
 21, Steamboat Springs, 1905. 
 Le Conte, 2, Ditto, 1883. 
 
 4, Sulphur Bank, Cal., 1894. 
 Mendenhall, 5, General problems in ground- j 
 
 water near Los Angeles, Cal., 1894. 
 Mutter, H., 1, Mineral springs in Freiberg 
 
 mines, 1885. 
 
 Ochsenius, 1, General, 1893. 
 Posepny, 2, Excellent general discussion, pp. 
 
 212-247, 1893. 
 
 Rickard, et al., 2, water in veins, 1903. 
 Eickard, T. A., 20, Meteoric vs. magmatic 
 
 waters, 1908. 
 
 Hies, General, pp. 293-301, 311-316,1910. 
 
 Sass, 1, Oscillations of ground-water level, 
 1901. 
 
 Slichter, 1, Motion of ground -water, mathe- 
 matical, 1899. See also Water Sup. and 
 Irr. Bull. U. S. O. S., Nos. 67 and 140, 1902-5. 
 
 2, ditto, 1902. 
 
 Spurr, 16, General, pp. 235-242, 1907. 
 Stutzer, 13, Juvenile springs, 1910. 
 Suess, 2, Hot Springs, 1902. 
 
 3, English translation of 2, 1902. 
 Thorkellson, Hot Springs, Iceland, 1910. 
 Ulilig, General discussion on motion of un- 
 derground waters, 1894. 
 
 Van Hise, 4, Excellent general discussion, 
 1900. 
 
 6, Discussion with Kemp regarding under- 
 ground circulation, 1900. 
 
 8, Chemistry and physics of, pp. 65-119: cir- 
 culation and work of. pp. 123-159 ; circula- 
 tion of ore-solutions, pp. 1017-1029 ; mete- 
 oric origin of waters, pp. 1065-1069, 1904. 
 
 WALL ROCK. 
 
 INFLUENCE OF ON ORE- 
 DEPOSITION. 
 
 (For influence of wall-rock on fissure formation see u Fissures," sub-head under 
 Cavities in Rocks." These references apply only to mineral contents.) 
 
 Beck, 8, pp 384-395, 1909. 
 
 9, pp. 16-20, 1909. 
 Bergeat-Stelzner, pp. 608, 718, especially pp. 995- 
 
 1006, 1906. 
 Boutwell, 5, pp. 180-183, 1905. 
 
 6, p. 119, 1912. 
 
 von Cotta, 2, pp. 516-525, 1870. 
 Denckmann, Ramsbecker, 1908. 
 Fairbanks, 2. 1893. 
 Foster, p. 12, 1900. 
 Irving, J. D., 7, 1908. 
 Jenney, 2, Reducing agents, 1902. 
 Kemp, 21, pp. 42-44, 1906. 
 Lindgren, 12, The relations between wall rocks 
 and deposition are discussed in some de- 
 tail, 1900. 
 
 3, p. 279, 1894. 
 
 13, pp. 612-613, 1901. 
 
 Lindgren and Ransome, 3, pp. 159-160, 208-209, 
 1906. 
 
 Mutter, H., 3, Freiberg veins, 1850. 
 
 2, p. 296, 1901. 
 
 Phillips-Louis, pp. 108-112, General, 1896. 
 Purington. 1, Telluride, 1897 ; 5, 1906. 
 Ransome, 14, Goldfield, 1909. 
 18, pp. 165-166, 1911. 
 
 3, pp. 299-302, 1901. 
 
 Ransome and Calkins, pp. 104-107, 139, 1908. 
 Rickard, T. A., 13, 1900. 
 
 8, 9, 1896. 
 
 Scheerer, Erzgebirge, 1 862. 
 Smith, W. S. T., U. S. G. S. Prof. Paper 36, pp. 
 
 148-149, 1905. 
 
 Spurr and Garrey, 1, pp. 160-161, 1905. 
 3, pp. 234-237, 1908 : 6, pp. 828-830, 859, 1901 ; 
 
 12, pp. 396-401, 1905. 
 Van Hise, 4, pp. 88-91, 1900 ; 8, pp. 1086-1088, 
 
 1229,1904. 
 Weed, 6, General, 1901. 
 
INDEX. 
 
 [NOTE. In this Index the names of authors of papers are printed in small capitals, 
 and the titles of papers in italics. Eeferences to papers expressly treating of the sub- 
 ject named are likewise in italics ; and casual notices, giving but little information, 
 are usually indicated by bracketed page numbers.] 
 
 A., C. F. : silver sandstones of Utah, 324. 
 Absorption process in contact-metamorph- 
 
 isin, 579. 
 
 Accident mine, Cripple Creek, Colo., [420]. 
 Acidity in mine-waters: cause, 174. 
 Adams, F. D. : origin of nickel-ores, 482. . 
 Age of igneous rocks : determination, 67. 
 Agency of Manganese in the Superficial Al- 
 teration and Secondary Enrichment of 
 
 Gold- Deposits in the United States (EM- 
 
 MONS), xxviii, 759-828. 
 Aguilera, J. G. : mineral deposits of Mex- 
 ico, [367]. 
 Aguilera and Ordonez ; rocks of San Jose, 
 
 Tamaulipas, Mexico, 565. 
 Ajax mine, Cripple Creek, Colo., [419]. 
 Alaska, Forty-Mile district ; dike-rocks, 
 
 272. 
 igneous rocks, 261, 262, 263. 
 
 gold-production, 436. 
 
 Napoleon creek placers: origin, 300. 
 
 Panhandle region : geology, 583. 
 Alaskite : crystallization process, 609. 
 
 definition, 272, 604. 
 
 occurrence and composition, 273. 
 
 Silver Peak, Nev., 623. 
 Albite : crystallization from magmas, 609. 
 
 in veins of Juneau district, Alaska, 588. 
 Alfreiua mine, Cananea, Mexico, [378]. 
 Algoma district, Ontario, nickel-deposits, 
 
 463. 
 Algonkian ; Lake Superior region, 637. 
 
 rocks included in, 69. 
 Algonkian rocks; classification, 69. 
 
 distribution, 69. 
 Alkaline earths: in mine-waters, 768. 
 
 solutions; solvent capacity, 30. 
 Allen, E. T. : composition of gravel at 
 
 Steamboat Springs, Nevada, 631. 
 Allotropism of Gold (Louis), xv, 105-109. 
 Alteration : agents, 113. 
 
 antimony-deposits, 134. 
 
 bismuth-deposits, 134. 
 
 copper-deposits, 128-131. 
 
 Arizona: climatic effect, 129. 
 process, 129. 
 
 depth of, 118. . 
 factors controlling, 120. 
 
 gold-deposits, 132-133. 
 
 in fissure-veins, 532. 
 
 lead-deposits, 131. 
 
 manganese-deposits, 127. 
 
 mercury-deposits, 134. 
 
 method and chemical effects, 113. 
 
 molybdenum-deposits, 135. 
 
 physical effects, 116. 
 
 Alteration : silver-deposits, 131. 
 
 Silver Cliff, Colo., 155. 
 sulphides to oxides, carbonates, and 
 
 chlorides, 2. 
 
 superficial : ore-deposits, xv. 
 tin-deposits, 133-134. 
 varying depths from surface, 121. 
 wall-rocks, Tonopah, Nev., 595. 
 zinc-deposits, 131-132. 
 Alteration-products: classification, 123. 
 
 technical names, 112. 
 Alumina: in mine- waters, 768. 
 
 quantity in igneous rocks, 732. 
 Amalgamation : gold, 107. 
 Analyses: analcite-tinguaite, 566. 
 basalt, 567. 
 camptonite, 566. 
 deep water from Geyser mine, Silver 
 
 Cliff, Colo, 152. 
 diorite-porphyry, 564. 
 eruptive rocks, 705. 
 gabbro, 563. 
 limestone, 568. 
 mine-timbers, 180. 
 minerals isolated from rocks of New 
 
 Zealand, 167. 
 nephelite-syenite, 562. 
 nickel-bearing mineral, 472, 473. 
 non-magnetic residue from pyrrhotites, 
 
 472. 
 ore from Geyser mine, Silver Cliff, Colo., 
 
 147. 
 
 radioactive water, 709. 
 sinter, 629. 
 sinters from Geyser mine, Silver Cliff, 
 
 Colo , 149. 
 spring waters, 706. 
 
 vadose country-rock ; Ballarat gold- 
 field, Victoria, 187. 
 Lake Wakatipu, N. Z., 189. 
 Ohinemuri district, N. Z., 190. 
 Otago, N. Z., 188. 
 Walhalla gold-field, Victoria, 186. 
 vadose water from Geyser mine, Silver 
 
 Cliff, Colo., 151. 
 volcanic gas, 388. 
 water, 152, 630. 
 wood for gold, 198. 
 Anchoria-Leland mine, Cripple Creek, 
 
 Colo., [420]. 
 
 Andesite : Tonopah, Nev., 591. 
 Andradite : San Jose, Tamaulipas, Mexico. 
 
 572. 
 
 Animikie iron-range : Lake Superior re- 
 gion, 651. 
 Annie Laurie gold-mine, Utah, [827]. 
 
930 
 
 INDEX. 
 
 Anthon, E. F. : affinity of metals for sul- 
 phur, xli. 
 Anthracite, graphitic; association with 
 
 silver-lead ores, 317. 
 
 Auti mony : in silver-ore, Silver Cliff, Colo., 
 141, 147. 
 
 reducing power, 353, 358. 
 
 relations to igneous rocks, 754. 
 Antimony-deposits: alteration, 134. 
 Apatite: in magnetite: Kiirunavaara, 677. 
 Apollo gold-mine, Unga Island : gold- 
 production, 440. 
 
 Apparatus for examining mine-waters,180. 
 Aqueous solutions: ore-deposition, 29. 
 Archean : Lake Superior region, 637. 
 
 rocks included in, 68. 
 
 Silver Cliff, Colo., 139, 145. 
 Areal distribution of mining-districts, 325. 
 Argall, Philip : origin of Sudbury nickel- 
 ores, 483. 
 Arid regions: alteration of ore-deposits, 
 
 136. 
 
 Arizona : Clifton copper-deposits, 401, 517- 
 556. 
 
 gold-production, 440. 
 Arsenic : reducing power, 353, 358. 
 
 relations to igneous rocks, 754. 
 Arsenopyrite : in contact-inetatnorphic de- 
 posits of Sacriflcio mountain, Durango, 
 Mex., 402. 
 
 reducing power, 353, 358. 
 Arseuopyrite type of ore-deposits, 372. 
 Ascending meteoric waters : cause, 242. 
 Ascension-theory of ore-deposition, xiii, 
 12, 14, 15, 201. 
 
 objections to, 160. 
 Ashburner, C. A. : charcoal in anthracite, j 
 
 319. 
 
 Assays: for determination of fineness of i 
 gold, 182. 
 
 for gold in California rocks, 301. 
 
 marine sediments, 197. 
 
 silver, [17]. 
 
 Sudbury, Ontario, ores, 464. 
 
 vadose and deep vein-gold, 184. 
 
 methods, 185. 
 Atacamite: occurrence at Jerome, Ariz., 
 
 136. 
 
 Augite: separation from "hornblende, 166. | 
 Auric compounds : formation, 107. 
 Auriferous lodes: origin, 201. 
 Aurylic compounds: formation, 107. 
 AUSTIN, W. L. : Discussion on Ore-Deposits 
 near Igneous Contacts, 396-402. 
 
 DiNCussion on The Geological Features of i 
 the Gold- Production of North America, I 
 447-449. 
 
 contortion in wollastonite, 577. 
 Austin district, Nevada, ore-deposits, 617. 
 
 Backstrom : genesis of iron-ores of Norr- 
 botten, Sweden, 678. 
 
 Ball, Spurr, and Garrey: silver-lead de- 
 posits, Georgetown and Silver Plume, 
 Colo., [816]. 
 
 Ball Mountain fault, Leadville, Colo., 48. 
 
 Ballarat gold-field, Victoria : vadose coun- 
 try-rock : analyses, 187. 
 
 BANCROFT, G. J. : The Formation and En- 
 richment of Ore-Bearing Veins, xxvii, 696- 
 719; Supplementary Paper, 720-728. 
 
 Banded structure in ore-bearing rock ; ori- 
 gin, 56. 
 
 Banuack, Mont., gold-deposits, 381. 
 Baraboo iron-range, Wisconsin : origin of 
 
 ores, 651, 652. 
 
 Baric chloride: precipitant for gold, 194. 
 Barite; distribution in Missouri, 89. 
 Barite-deposits : Virginia, 834. 
 Barium : distribution in igneous rocks, 748. 
 
 quantity in igneous rocks, 733. 
 Barlow, A. E, ; geology of Sudbury, Onta- 
 rio, nickel-deposits, 479. 
 Barrell, Joseph : contact-effects in Elkhorn 
 
 district, 576. 
 contact-rnetamorphism, 374, 392, 524. 
 
 physical effects, 385. 
 rocks of Elkhorn district : composition, 
 
 383. 
 
 Barus, Carl : compression of water, 244. 
 Barysphere : metals in, 714. 
 Baryta: tests for: in rocks at Leadville, 
 
 Colo., 16-17. 
 
 Basalt: San Jose, Tamaulipas, Mexico, 567. 
 Basaltic rocks : Cripple Creek district, 
 
 Colo., 411. 
 
 Bassick mine, Silver Cliff district,Colo., 158. 
 example of chimney-deposits, 58, 59. 
 locus of ore-bodies, 24. 
 BATESON, C. E. W. : The Mojave Mining- 
 District, California [Trans., xxxvii, 160- 
 177], Notice, 832. 
 Batesville, Ark. : manganese-deposits : 
 
 concentration, 128. 
 Bauxite : origin, 135. 
 Bayley, W. S. : absorption-phenomena at 
 
 Pigeon Bay, Minn., 579. 
 Beck, Richard : gold-bearing granite, 367. 
 nickel-ores, origin, 485. 
 ore-deposits, [218]. 
 genesis, [253]. 
 Berggiesshiibel, 378. 
 
 BECKER, G. F. : Biographical Notice of 
 Samuel Franklin Emmons, xxix-xlvii. 
 The Torsional Theory of Joints, xiii, 92- 
 104: Discussion (HowE), 101; (RAY- 
 MOND), 101-102 ; (BECKER), 103, 104 ; 
 (Bo YD), 103. 
 
 Discussion on The Genesis of Certain Au- 
 riferous Lodes, 207-208. 
 bitumen associated with quicksilver,345. 
 Comstock lode, 60. 
 production, 803. 
 quartz, 801. 
 replacement, xl. 
 source of ore-materials, [164]. 
 Comstock rocks, erosion, 85. 
 convection currents in magmas, 260. 
 deposition of sulphides by hot ascend- 
 ing waters, 629. 
 investigations of country -rocks, Washoe, 
 
 23. 
 
 " linked veins," 221. 
 minerals in Appalachian gold-deposits, 
 
 809. 
 natural solvents of precious metals, xiv, 
 
 [203]. 
 
 osmosis in ore-formation, [xxiv]. 
 quicksilver-deposits, [207]. 
 
 genesis, 79. 
 
 vein-formation at Clear Lake, Cal., and 
 Steamboat Springs, Nev., xiv. 
 
INDEX. 
 
 931 
 
 " Bedded vein ": definition, 36. 
 
 Bedding: agency in producing water- 
 channels, 33. 
 
 Bell, Eobert: origin of nickeliferous pyr- 
 rhotite, 481. 
 
 Bel mont district,Nevada : ore-deposits,617. 
 
 Ben Eaton mine, Silver Cliff region, Colo., 
 157. 
 
 Beudigo gold-field, Victoria : assays, 185. 
 
 Beresite at Belmont, Nevada, 278. 
 
 Berggiesshiibel, Saxony, ore-deposits, 378. 
 
 BERKEY, C. P., and HASTINGS, J. B. : The 
 Geology and Petrography of the Goldfield 
 Mining- District, Nevada [Trans., xxxvii, 
 140-159], Notice, 832. 
 
 Berner's Bay, Alaska : gold-deposits, 811. 
 
 Beryllium: distribution in igneous rocks, 
 746. 
 
 Bibliography: Science of Ore-Deposits, 
 (IRVING, SMITH, FERGUSON), 837-928. 
 Scientific Publications of S. F. Emmons, 
 xlii-xlvii. 
 
 Bibra: metals in ashes of marine plants, 
 [256]. 
 
 Big Seven mine, Neihart, Mont., 220. 
 
 Bischof, G. : derivation of vein-materials, 
 
 22. 
 
 metals in water of springs, [708]. 
 ores in sedimentary rocks, 256. 
 transformation of potassium feldspar to 
 albite, 587. 
 
 Bisilicates : metal-content, 203-204. 
 
 Bismuth : relations to igneous rocks, 754. 
 
 Bismuth-deposits: alteration, 134. 
 
 Bispberg mine, Sweden: origin of iron- 
 ores, 670. 
 
 Bitumen : association with ore-deposits, 
 
 345. 
 reducing power, 305, 350, 357. 
 
 Bituminous coal : reducing power, 351, 357. 
 
 Bituminous shales ; association with ore- 
 deposits, 327. 
 
 Black Hills, S. Dak. : fissures conducting 
 ore-bearing solutions, 700. 
 gold-deposits, 810. 
 
 Blair mines, Silver Peak quadrangle, Ne- 
 vada, 621, 622, 624. 
 
 BLAKE, W. P. : Discussion on The Genesis 
 
 of Certain Auriferous Lodes, 211-212. 
 petroleum associated with zinc- and 
 lead-ores, 344. 
 
 Blende: deposition from mine- waters, 330. 
 mode of occurrence in Missouri, 327. 
 reducing power, 358. 
 
 Blezard (Dominion) mine, Blezard town- 
 ship, Sudbury district, Ontario, 499. 
 
 Block 8 of State laud mine, Cripple Creek, 
 Colo., 42-2. 
 
 Blue limestone, Leadville, Colo. : geologic 
 
 horizon, 18. 
 ore-bodies in, 7, 13. 
 receptacle of ore-materials, 7, 16. 
 
 Bluebird granite, 223, 224. 
 
 Bodie, Cal. : gold-deposits, 823. 
 
 BOEHMER, MAX : Some Practical Sugges- 
 tions Concerning the Genesis of Ore-De- 
 posits [Trans., xxxiv, 449-453], Notice, 
 829-830. 
 
 Bog iron-deposits : Gunnison region, Colo., | 
 
 32. 
 Red mountain, Colo., 32. 
 
 Bog-ore: Scandinavia, 694. 
 
 Boiler-scale: examination for gold, 178- 
 
 179. 
 
 Bonanzas : occurrence, 453. 
 Bo rax -deposits: formation, 115. 
 
 United States (KEYES), 835. 
 Bornite : reducing power, 358. 
 Boron : distribution in igneous rocks, 748. 
 Boundary district, B. C. : copper-deposits, 
 
 374. 
 
 BOUTWELL, J. M. : Genesis of the Ore-De- 
 posits at Bingham, Utah [Trans., xxxvi, 
 
 541-580], Notice, 831. 
 BOYD, C. E. : Discussion on The Torsional 
 
 Theory of Joints, 103. 
 Breccia : in fissures, 45. 
 
 in fissure-veins : origin, 46. 
 
 Silver Cliff, Colo., 143. 
 Brecciation in country-rock : effect on ore- 
 deposits, 118. 
 Breithaupt : derivation of vein-materials, 
 
 22. 
 
 British Columbia : Boundary district : cop- 
 per-deposits, 374. 
 
 gold-production, 436. 
 
 Eossland : pyrrhotite-deposits, 462, 486. 
 British Guiana: gold-quartz veins, 281. 
 Brock, E. W. : copper-deposits of Boun- 
 dary district, 375. 
 
 pyrrhotite-deposits, Eossland, B. C., 486. 
 Brogger, W. C. : contact-metamorphic phe- 
 nomena, 525. 
 
 igneous rocks of Christiania region, 692. 
 
 origin of igneous rocks, [260]. 
 Brokaw, A. D. : experiments on solution 
 
 of gold, 763, 773, 776. 
 Bromine : solvent of gold, 173. 
 BROWN, E. G. : The Vein System of the Stan- 
 dard Mine, Bodie, Cal. [Trans., xxxviii, 
 
 343-357], Notice, 833. 
 
 Browne, D. H. : magnetic separation of 
 nickel-ores, 467. 
 
 nickel-ores of Sudbury, 470, 483. 
 Browne, Eoss E. : association of gold with 
 
 slate in California, 211. 
 Brun, Albert: experiments on lavas, 725. 
 
 gases in lavas, [767]. 
 Buehler and Gottschalk: role of pyrite, 
 
 766. 
 Bull-Domingo mine, Silver Cliff district, 
 
 Colo., 24, 58, 158. 
 
 Bullfrog, Nev. : geology and ore-deposits, 
 600. 
 
 gold-deposits, 827. 
 Bullion-Beck mine, Tintic district, Utah, 
 
 335, 336. 
 
 Buusen, E. : volcanic gases, 723. 
 Burns mine, Cripple Creek, Colo., 422. 
 Bush, E. E. : origin of Sudbury nickel- 
 ores, 483. 
 
 Butte, Mont. : copper-deposits: alteration, 
 130. 
 
 genesis, 76. 
 
 vein-formation, 55, 220. 
 Butte granite, 223, 224. 
 
 Cable mine, Philipsburg quadrangle, 
 Mont., [762], 814. 
 
 character of gold-enrichment, 762. 
 Cadmium : distribution in igneous rocks, 
 
 753. 
 
932 
 
 INDEX. 
 
 Calcium : in mine-waters, 768. 
 
 Calcium disulphide : reducing power, 358. 
 
 California : assays for gold, 301. 
 gold production, 436. 
 
 California metal lographic province, 619. 
 
 California region : geologic history, 583. 
 
 Cambrian: Silver Peak quadrangle, Ne- 
 vada, 604. 
 
 Camp Bird gold-mine, Ouray, Colo., [787], 
 [818]. 
 
 Camptonite : San Jose, Tamaulipas, Mex- 
 ico, 566. 
 
 Cananea, Sonora, Mex. : copper-deposits, 
 
 376, 396. 
 volcanic action, 715. 
 
 Cananea mountains: physiographic fea- 
 tures, 376. 
 
 Carbon : mode of occurrence, 315. 
 protective action, 311. 
 reducing action, 305. 
 reducing power, 307. 
 
 Carbon dioxide: occurrence in New Al- 
 
 maden quicksilver mine, 363. 
 r6le in formation of ore-deposits, 312. 
 
 Carbon monoxide : reducing power, 358. 
 
 Carbonaceous matter : influence on forma- 
 tion of ore, 231. 
 
 Carbonate fault, Leadville, Colo., 48. 
 
 Carbonate Queen mine, Cripple Creek, 
 Colo., 419. 
 
 Carbonates : in mine- waters, 768. 
 
 Carbonic acid gas : in subterranean water : 
 
 Silver Cliff, Colo., 148. 
 role in formation of ore-deposits, 312. 
 stability, 313. 
 
 Carboniferous rocks : relation to Cambrian 
 country-rock in Ozark region, Mo., 88. 
 
 Carlyle, W. A. : gold-quartz veins in Slo- 
 can district, B. C., 280. 
 
 Cam Marth, Cornwall : banded ore-depos- 
 its, 57. 
 
 Catalytic action : definition, 309. 
 
 Caves : formation by solution, 6. 
 
 Leadville, Colo. : formation subsequent 
 to ore-deposits, 4. 
 receptacles for ore-bodies, 7-8. 
 
 Cavities: ore-deposition in, 87. 
 
 Cazin, F. M. F. : origin of copper- and sil- 
 ver-ores in Triassic sand-rock, [326]. 
 
 Cerium : distribution in igneous rocks, 
 749. 
 
 Chalcocite: chemical relations with py- 
 
 rite, 798. 
 in diorite, 90. 
 oxidation, 534. 
 reducing power, 358. 
 
 Chalcocitization : vertical relation to deep- 
 seated enrichment of gold, 798. 
 
 Chalcopyrite : formation, 310. 
 
 in Geyser mine, Silver Cliff, Colo., 146. 
 
 reducing power, 358. 
 
 relation to, pyrrhotite, 513. 
 
 San Jose, Tamaulipas, Mexico, 574. 
 
 Chalcopyrite type of ore-deposits, 372. 
 
 Chamberlin and Salisbury : gases in vol- 
 canic emanations. 723. 
 specific gravity of earth, 715. 
 
 Chamberlin, K. T. : gases in rocks, [767]. 
 
 Chamberlin, T. C. : succession of ores in 
 lead- and zinc-deposits of Wisconsin, 
 [407]. 
 
 ! Chance, H. M. : coal carrying gold, 321. 
 Channels: , conducting ore-bearing solu- 
 tions. 700. 
 for circulating waters in earth's crust, 
 
 30. 
 
 in rock-masses : closing of, 699. 
 Chapeau de fer (gossan) : definition, 112. 
 Character and Genesis of Certain Contact- 
 Deposits [Lindgren], xix. 
 Charcoal in Geyser shaft, Silver Cliff, 
 
 Colo., 143. ' 
 
 native : deoxidizing agency, 319. 
 Charters Towers, Queensland : rocks, 163. 
 Chemical changes (rocks and ore-depos- 
 its) : see Alterations. 
 Chemical composition of beds : factor in 
 
 ore-deposition, 36. 
 
 Chemical forces: role in solution and de- 
 position, 30. 
 
 Chemistry of Ore-Deposition (JENNEY), 
 xxii, 305-363; Discussion (CHURCH), 
 359-363. 
 Cherokee limestone, Missouri : character 
 
 and composition, 334. 
 Chile : copper-deposits, 130. 
 Chimney-deposits: definition, 58. 
 
 examples, 58. 
 
 China: gold-quartz veins, 282. 
 Chloride ores: distribution, [768]. 
 
 occurrence, 136. 
 Chlorides : copper : effect in solution of 
 
 gold, 77H, 781. 
 in mine-waters, 766. 
 Chlorine: agency in transportation of 
 
 metals, 722. 
 
 amount necessary for solution of gold 
 in presence of manganese compounds, 
 784. 
 distribution, 767. 
 
 in igneous rocks, 751. 
 in mine-waters, 766, 779. 
 in natural waters : map, New England 
 
 and New York, 769. 
 in volcanic emanations, 723. 
 nascent : agency in solution of gold, 777. 
 quantity in igneous rocks, 734. 
 solvent of gold, 174. 
 with manganese compounds: solubility 
 
 of gold in, 784. 
 Christiania regi on , Norway: igneous rocks : 
 
 classification, 692. 
 
 Christmas mine, Cripple Creek, Colo., 422. 
 Christy, S. B. : bitumen associated with 
 
 quicksilver, 345. 
 Chromium: distribution in igneous rocks, 
 
 750. 
 
 in basic rocks, 285. 
 in igneous rocks, 267. 
 quantity in igneous rocks, 733. 
 CHURCH, JOHN A. : Discussion on Geolog- 
 ical Distribution of Useful Metals in the 
 United States, 83-86. 
 
 Discussion on The Chemistry of Ore-Depo- 
 sition, 359-363. 
 
 deposition of ores in limestone, 341. 
 Circulation : meteoric waters. 242, 243. 
 ore-bearing solutions: factors control- 
 ling, 791. 
 
 Clarke, F. W. : average composition of ig- 
 neous rocks, [734]. 
 chlorine-content of igneous rocks, [767]. 
 
INDEX. 
 
 933 
 
 Clarke, F. W. : formula of vesuvianite, 
 
 [572]. 
 
 manganese in igneous rocks, [794]. 
 
 reactions produced by hot waters, [726]. 
 
 relative proportion of elements in 
 earth's crust, [293], 
 
 rock-analyses, [767], [794]. 
 Classification : Algonkian rocks, 69. 
 
 genetic : Clifton-Morenci ore-deposits, 
 556. 
 
 ore-deposits, 286, 366. 
 
 products of alteration, 123. 
 
 rock -fractures, 40. 
 Cleavage-planes : cause, 41. 
 
 definition, 101. 
 CLEKC, F. L. : The Ore-Deposits of the Jop- 
 
 lin Region, Missouri [Trans., xxxviii, 
 
 320-343], Notice, 833-834. 
 Clifton-Morenci district, Arizona : depth 
 of oxidized zone, 545. 
 
 distribution of ores, 540. 
 
 fluid inclusions, 545. 
 
 genesis of ores, 551. 
 
 genetic classification of deposits, 556. 
 
 geology, 519. 
 
 groundwater conditions, 544. 
 Climatic conditions : effect on alteration, 
 
 120. 
 
 Coal, bituminous: association with ore- 
 deposits, 320. 
 Coast-sediments : examination for gold, 
 
 196. 
 Cobalt: in igneous rocks, 269, 752. 
 
 in Sudbury pyrrhotites, 466. 
 
 presence in pyrrhotite, 461. 
 
 quantity in igneous rocks, 733. 
 Colorado : Cripple Creek district : ore-de- 
 posits, 411. 
 
 gold-production, 437, 441. 
 
 pre-Mesozoic gold-deposits, 447. 
 
 relation of rain-fall, run off, and evapo- 
 ration, 698. 
 
 Eico : mineral veins, 226. 
 
 San Juan region: vein-system, 290. 
 Colorados (gossan) : definition, 112. 
 Cornagrnatic region : definition, 738. 
 Comb-structure : veins, 10. 
 Compression-fissures : Butte, Mont., 55. 
 Compression-fractures : characteristics, 45. 
 Compression -joints : definition, 41, 50. 
 Comstock, T. B. : genesis of Red Mountain 
 deposits, 31. 
 
 The Geology and Vein-Structure of 
 Southwestern Colorado, [31]. 
 
 vein-system of San Juan region, Colo., 
 
 290. 
 Comstock district : comparison with Tono- 
 
 pah, Nev., 601. 
 
 Comstock lode, Nevada : genesis of ores, 
 ix, x, 19, 85, 803. 
 
 gold -production, 440. 
 
 production of silver and gold, and rela- 
 tion of ores, 801, 802. 
 
 structural features, 60. 
 Comstock vein : extent, 11. 
 
 structure, 10. 
 Concentration : gold : in oxidized zone,797. 
 
 iron-deposits : Lake Superior, 125. . 
 
 natural : minerals, 255. 
 
 ore-metals, 300. 
 Concentration -process : ore-deposits, 29. 
 
 Consanguinity : in rOcks, 738. 
 Contact-deposits : character and genesis, 
 
 xix. 
 
 examples, 38. 
 formation, 230. 
 miners' use of term, 37. 
 Contact-metamorphic deposits, 432. 
 distribution, 396. 
 genesis, 387, 392. 
 geographic distribution, 373. 
 Contact-metamorphic effects : variability, 
 
 578. 
 
 Contact-metamorphic ore-deposits : char- 
 acter, 371. 
 
 Contact-metamorphic zones, 371. 
 Contact-metamorphism : Bannack, Mont., 
 
 382. 
 
 Clifton-Morenci district, Arizona, 522. 
 effects, 385. 
 
 Elkhorn district, Montana, 576. 
 hydrothermal, 529. 
 origin, 262. 
 
 San Jose, Tamaulipas, Mexico, 567. 
 western Nevada, 617. 
 Contact-planes : definition, 37. 
 Contour-mapping : introduction, xxy.ii. 
 Contraction hypothesis, 42. 
 Contraction-planes : origin and extent, 35. 
 
 relation to ore-deposition, 35. 
 Copper : deposition from sea-water, 258. 
 distribution in igneous rocks, 752. 
 in basic rocks, 285. 
 in igneous rocks, 270. 
 in mine-waters, 770, 781. 
 in nature : detection, 77. 
 quantity in igneous rocks, 733. 
 reducing power, 358. 
 Copper chlorides: effect on solubility of 
 
 gold, 773, 781. 
 i Copper Cliff mine, Sudbury, Ontario, 456. 
 
 501. 
 
 photomicrographs of ore, 489, 494. 
 i Copper-deposits: alteration, 114, 128-131. 
 Appalachians : genesis, 76. 
 Arizona : Bisbee, 829. 
 Clifton, 401. 
 Clifton-Morenci (LINDGREN),XXV, 517- 
 
 556. 
 
 classification, 521. 
 climatic effects, 122. 
 Jerome, 136. 
 
 superficial alteration, 128. 
 Australia: Chillagoe district, North 
 
 Queensland, 830. 
 Cananea type, 374. 
 Chile, 130. 
 
 climatic effects,, 122. 
 Colorado : Evergreen, 835. 
 concentration, 76. 
 genesis. 75-77. 
 Idaho : Mackay, 833. 
 kind of rock in which found, 77. 
 Lake Superior district, 76. 
 Mansfeld, Harz mountains, 36. 
 Mexico : Cauauea, 396. 
 Michigan : climatic effects, 121. 
 Montana: Butte City: alteration, 130. 
 
 genesis, 76. 
 San Jose, Tamaulipas, Mexico (KEMP), 
 
 xxv-xxvi, 557-581. 
 source of material, 75. 
 
934 
 
 INDEX. 
 
 Copper-deposits: Tasmania: climatic ef- 
 fects, 122. 
 
 Tennessee : Ducktown : alteration, 130. 
 Copper-iron sulphides : secondary enrich- 
 ment, 832. 
 Copper-veins : Butte, Mont., 224, 225, 403. 
 
 Virgilina, Va., 220. 
 
 Coriolanus mine, Cripple Creek, Colo., 419. 
 Cornwall, England : veins : structure, 10, 
 
 225. 
 
 Coronadite, Clifton-Morenci district, Ari- 
 zona, 519. 
 Coronado lode, Clifton-Moreuci district, 
 
 Arizona, 543. 
 
 Coronado quartzite, Cliftou-Morenci dis- 
 trict, Arizona, 519. 
 Correlation of the elements, 743. 
 Correlation table : pre-Cambrian series of 
 
 the Lake Superior region, 634. 
 Cotta, B. : derivation of vein-materials, 22. 
 
 Treatise on Ore-Deposits, [viii], 316. 
 Country-rock : auriferous lodes : examina- 
 tion, 183. 
 
 Colorado : Custer county : assays for sil- 
 ver, 161. 
 
 Leadville : investigations, 23. 
 Silver Cliff: assays for silver, 161. 
 
 investigations, 23. 
 Ten-Mile : investigations, 23. 
 Influence on Mineral Veins (WEED), 216- 
 
 234. 
 
 influence on vein-filling, 222, 223. 
 Nevada : Washoe : investigations, 23. 
 New Zealand : classes, 212. 
 of ore-deposits : decay, 117. 
 sheeting, 46, 47. 
 vadose region of Walhalla gold-field, 
 
 Victoria, 186. 
 
 Covellite : reducing power, 358. 
 Cracks : in glass : produced by torsioual 
 
 strain, 51. 
 Creighton mine, Sudbury, Ontario, 502. 
 
 photomicrographs of ore, 490-492. 
 Cretaceous gold-deposits, 435-438. 
 Cretaceous rocks, Tamaulipas, Mexico,561. 
 Cripple Creek and Silver Cliff ore-depos- 
 its compared, 158. 
 
 Cripple Creek district, Colorado : gold- 
 production, 441. 
 ore-deposits, 411, 819. 
 rocks, 718. 
 
 underground-water conditions, 699. 
 CROSBY, W. O. : Ore-Deposits of the Eastern 
 Gold-Belt of North Carolina [Trans., 
 xxxviii, 849-856], Notice, 834-835. 
 origin of cross-joints, 44. 
 torsional hypothesis, [95]. 
 Crosby and Fuller : origin of pegmatite, 
 
 275. 
 Cross, Whitman : absence of steam in 
 
 Kilauea, 390. 
 Democrat and Ben Eaton mines, Colo., 
 
 [157]. 
 Cross-joints : definition, 40. 
 
 origin, 44. 
 
 Crown Point- Belcher bonanza, 361. 
 Crowning Glorv gold-mine, Silver Peak, 
 
 Nev., 621, [813]. 
 cross-section, 625. 
 Crushed zones : ore-deposits, 57. 
 Crystalline rocks : see Rocks. 
 
 Crystallization : in igneous rocks : order, 
 
 261, 263. 
 in magmas : order, 585. 
 
 Cupric chlorides : see Chlorides, copper. 
 
 Cupric salts : efficiency in promoting solu- 
 tion of gold, 782. 
 
 Curtis, J. S. : ore-deposits of Eureka dis- 
 trict, Nev., 7, 58. 
 
 Curve : gold in vadose country-rock, Wal- 
 halla, Victoria, 192. 
 
 Custer county : country-rock : assays, 161. 
 
 Dacite : Tonopah, Nev., 593. 
 Dacite-porphyry : percentage composition, 
 
 565. 
 DAGGETT, ELLSWORTH : The Extraordinary 
 
 Faulting at the Berlin mine, Nevada 
 
 [Trans., xxxviii, 297-309], Notice, 833. 
 Daintree, Eichard : auriferous rocks of 
 
 Queensland, 282. 
 
 Daunemora mine, Sweden : diagram, 661. 
 Dart Eiver : auriferous lode, North Gipps- 
 
 land, Victoria : assays, 184. 
 Daubree, A. : classification of rock frac- 
 tures, 40. 
 
 experiments on glass. 51. 
 
 genesis of titaniferous albite veins, 587. 
 
 movement in rocks, 92, 93, 94. 
 
 production of joints, 94. 
 
 subterranean waters, 29. 
 
 synthetic experiments, [2]. 
 
 torsion experiments on glass plates, 95. 
 Dawson, G. M. : quartz-veins associated 
 
 with granite, 279. 
 
 Dead Pine mine, Cripple Creek. Colo., 419. 
 Deadwood mine, Cripple Creek, Colo., 422. 
 Death valley : borax-deposits, [835]. 
 Decomposition of volcanic rocks, 727. 
 Deep mines : dryness, 241. 
 Deformation : modes, 92. 
 DE KALB, COURTENAY : Geology of the 
 Exposed Treasure Lode, Mojave, Cali- 
 fornia [Trans., xxxvii, 310-319], No- 
 tice, 834. 
 
 gold-deposits of Exposed Treasure mine, 
 
 Cal., 824. 
 De la Beche: mineral veins of Corn wall,226. 
 
 mineral veins of Derbyshire, 229. 
 
 vein-formation, 220. 
 Delamar district, Idaho : comparison with 
 
 Tonopah, Nev., 601. 
 
 Delamar gold-mine, Nevada, [794], [828], 
 De Launay, L. : distribution of rare ele- 
 ments, 745. 
 
 genesis of iron-ores, 678. 
 
 genesis of ore-deposits, [253]. 
 Del Mar, Alexander : gold-resources of the 
 
 world, 425. 
 
 Delmonico mine, Cripple Creek, Colo. ,422. 
 Democrat mine, Silver Cliff region, Colo., 
 
 157. 
 Depth of alteration of ore-deposits in un- 
 
 glaciated regions, 122. 
 Derby, O. A. : Brazilian gold- veins, [239]. 
 Derbyshire lead -mines, 229. 
 Descending solutions: agency at Lead- 
 ville, Colo., 12. 
 Descending waters : agency in formation 
 
 of iron-deposits, 69-71. 
 Detection and Estimation of Small Quantities 
 of Gold and Silver (WAGONER), 829. 
 
INDEX. 
 
 935 
 
 Deville, C. St. C.: juvenile waters, [xxxviij. 
 
 volcanic gases, 723. 
 Diaclase : rocks, 92. 
 Diaclases : definition, 40. 
 Diamond swindle : Vermilion Creek Basin, 
 
 Wyoming, [xxxiii]. 
 
 DICKSON, C. W. : The Ore-Deposits of Sud- 
 bury, Ontario, xxiv-xxv, 455-516. 
 Differentiation : igneous magmas, 67. 
 Dikes (see also Intrusions) : Forty-Mile 
 district, Alaska, 272. 
 
 San Jose, Taniaulipas, Mexico, 565. 
 Dillon mine, Cripple Creek, Colo., 419. 
 Diopside : San Jose, Tamaulipas, Mexico, 
 
 570. 
 
 Diorite : source of nickel-ores, 90. 
 Diorite-porphyry : San Jose, Tamaulipas, 
 
 Mexico, 563! 
 Distribution of the Elements in Igneous Rocks 
 
 (WASHINGTON), xxviii, 729-758. 
 "Distributive" faults, 221. 
 Doctor- Jack Pot mine, Cripple Creek, 
 
 Colo., 423. 
 
 Doelter : preparation of pyrrhotite, 460. 
 Dolcoath mine, Cornwall, 225. 
 Dolcoath mine, Montana, [383]. 
 Dolomite : disintegration, 336. 
 
 unaltered : distribution on Fryer hill, 
 
 Leadville, Colo., 13. 
 
 DON, JOHN R. : The Genesis of Certain Au- 
 riferous Lodes, xvi, 162-215 ; Discus- 
 sion (LE CONTE), 202 ; (EMMONS), 202- 
 206; (BECKER), 207-208; (WINSLOW), 
 208-211; (BLAKE), 211-212; (DON), 
 212-215. 
 
 analyses of Australian mine-waters, 
 [779]. 
 
 chlorine as solvent of gold, 763. 
 
 genesis of auriferous lodes, 696. 
 
 method of determining gold in sea- 
 water, 194. 
 
 solution of gold, 763, 771, 773. 
 Douglas, James: secondary enrichment, 
 
 xli. 
 Drinkwater mine, Silver Peak, Nev., 621. 
 
 cross-section, 625. 
 Dryuess of deep mines, 241, 698. 
 Ducktown, Tenn., copper-deposits, 510. 
 
 alteration, 130. 
 
 Dunderland, Norway, iron-ores, 690. 
 Dustiness of mines: explanation, 698. 
 Duty of a reducing ageut : definition, 347. 
 Dynamic disturbance of earth's crust : 
 
 periodicity, 43. 
 
 Dynamic movements: effect on water- 
 channels, 34. 
 
 Eakins, L. G. : assays for silver, 161. 
 Earthquakes: relation to rock-flowage, 
 712. 
 
 theory, 44. 
 Earth's axis : shifting as explanation of 
 
 stress, 715. 
 East Tennessee mine : photomicrographs 
 
 of ore, 494. 
 
 Edgemout, Nev., gold-deposits, 815. 
 Edison, T. A. : magnetic separation of 
 
 nickel-ores, 467. 
 Egleston, T. : petroleum associated with 
 
 quicksilver, 344. 
 Eisener Hut (gossan) : definition, 112. 
 
 Elba Island : iron-ores, 8-9. 
 Elements : correlation, 743. 
 
 distribution in igneous rocks, 754. 
 rare: distribution, 745. 
 Elenita mine, Cananea, Mexico, 398. 
 Elisa mine, Cananea, Mexico, 398. 
 Elk mountains, Gunnisou county, Colo. : 
 
 fissure-faulting, 49. 
 Elkhorn district, Montana : ore-deposits, 
 
 382. 
 
 Elkton mine, Cripple Creek, Colo., 420. 
 Ellis, H. E. : coal carrying gold, 321. 
 Elsie mine, Snider township, Sudbury dis- 
 trict, Ontario, 500. 
 photomicrographs of ore, 489-490. 
 Emma mine, Tintic district, Utah, 362. 
 Emmens, S. H. : nickel-minerals from 
 
 Sudbury, 457. 
 
 EMMONS, SAMUEL FRANKLIN : Biograph- 
 ical Notice (BECKER), xxxi-xlix. 
 List of Scientific Publications, xliv-xlix. 
 Introduction, vii-xxviii. 
 The Genesis of Certain 'Ore-Deposits, xi, 
 
 1-25. 
 
 Geological Distribution of the Useful Met- 
 als in the United States, xii, 65-83 ; 
 Discussion (CHURCH), 83-86: (WIN- 
 SLOW), 86-89; (EMMONS), 89-90; 
 (MERRITT), 90-91. 
 Some Mines of Rosita and Silver Cliff, 
 
 Colorado, xvi, 139-161. 
 Structural Relations of Ore-Deposits 
 
 [Trans., xvi, 804], xii, 26-64. 
 Discussion on The Genesis of Certain Au- 
 riferous Lodes, 202-206. 
 association of gold with manganese, 
 
 [787]. 
 
 chlorine in natural water, 768. 
 copper-deposits of Boundary district, 
 
 British Columbia, 374, 375. 
 Delamar mine, Nev., 828. 
 genesis of certain ore-deposits, [27]. 
 genesis of Leadville ore-deposits, xxxvi. 
 gold-deposits of Black Hills, [Sll]. 
 increase in production of gold, 425. 
 investigations of country-rocks, Lead- 
 ville, 23. 
 
 manganese as indication of rich ore, 787. 
 manganiferous gold-ore, Leadville, 
 
 Colo., 816. 
 manganiferous silver-ore at Leadville, 
 
 Colo., 800. 
 non-mineral-bearing fissures, Leadville, 
 
 Colo., 49. 
 
 origin of Sudbury nickel-ores, 486. 
 secondary enrichment of ore-deposits^ 
 
 [696], [761], [811]. 
 silver-ores of Aspen, Colo., 332. 
 Theories of Ore-Deposition Historically 
 
 Considered, [viii]. 
 veins of Butte, Mont., 55. 
 Emmons, S. F., and Irving, J. D. : Down- 
 town District, xxxviii. 
 Emmons, Irving, and Jaggar : gold-de- 
 posits, Black Hills, S. D., [810]. 
 EMMONS, W. H. : The Agency of Manganese 
 in the Superficial Alteration and Second- 
 ary Enrichment of Gold-Deposits in the 
 United States, xxviii, 759-828. 
 gold-deposits, Edgemont, Nev., [815]. 
 Midas, Gold Circle district, Nev., [827]. 
 
936 
 
 INDEX. 
 
 Emmons, W. H., and Garrey, G. H. : gold- 
 deposits, Manhattan, Nev., [827] . 
 
 Enargite: in Butte,Mout.,ore-deposits,403. 
 reducing power, 354, 358. 
 
 Enrichment of ore-deposits : see Ore-de- 
 posits. 
 
 Enrichment theory, 408. 
 
 Eruptions: ejecting metalliferous mag- 
 mas, 716. 
 
 kinds of magmas ejected, 715. 
 of igneous material ; source, 43. 
 
 Eruptive activity : association with ore- 
 deposition, 21. 
 
 Eruptive rocks : see Eocks. 
 
 Eruptive theory : ore-deposits, 8. 
 
 Erzgebirge, Freiberg, Saxony : vein-sys- 
 tem, 52. 
 
 Eureka district, Nev. : ore-deposits, 58. 
 genesis, 7. 
 
 Evergreen Copper-Deposits, Colorado (EiT- 
 TER), 835. 
 
 Exposed Treasure lode, Mojave, Cal.: geol- 
 ogy, 834. 
 
 gold-deposits, 823. 
 relations of ores, 804. 
 
 Extraordinary Faulting at the Berlin mine, 
 Nevada (DAGGETT), 833. 
 
 Fahlcrantz, A. E. : iron-ores, Sweden, 666. 
 Faltenverwerfungen (fold-faults) : defini- 
 tion, 41. 
 
 Faulting (see also Fissures) : character of 
 movement, 102. 
 
 determined by stresses, 104. 
 
 horizontal : Mt. Guyot, Colo., 64. 
 
 illustrated by torsion experiments, 99. 
 
 in Cambrian rocks of Missouri, 88. 
 
 in Mississippian rocks of Missouri : ab- 
 sence, 88. 
 
 Leadville, Colo., [3] . 
 
 Nevada, Berlin mine, 833. 
 
 Ontario mine, Utah, 62. 
 
 Queen of the West mine, Colo., 62-64. 
 Fault-fissure deposits: Ontario mine, 
 
 Utah, 60. 
 Fault-planes : effect on water-channels, 34. 
 
 Leadville, Colo. : lack of ore-deposits, 10. 
 Faults (see also Fissures and Fold-faults) : 
 extent, 39. 
 
 lack of uniformity in nomenclature, 40. 
 FAY, A. H. : Geology and Mining of the 
 
 Tin-Deposits of Cape Prince of Wales, 
 
 Alaska [Trans., xxxviii, 664-682J, Notice, 
 
 833. 
 Features of the Occurrence of Ore at Red 
 
 Mountain, Our ay County, CWo^ScHWARz), 
 
 831. 
 FERGUSON, H. G., IRVING, J. D., SMITH, 
 
 H. D. : Bibliography of the Science of Ore- 
 Deposits, 837-928. 
 
 Ferric chloride : solvent of gold, 173. 
 Ferric salts : efficiency in solution of gold. 
 
 781. 
 
 Ferric sulphate : solvent of gold, 173. 
 Ferrous sulphate : precipitant of gold, 784. 
 
 reducing power, 355, 356, 358. 
 Filter for sea- water in testing for gold, 198. 
 Finlay, G, I. : analysis of analcite-tingua- 
 ite, 566. 
 
 analysis of basalt, 567. 
 
 analysis of camptonite, 566. 
 
 Finlay, G. I. : analysis of diorite-porphyry, 
 
 564. 
 
 eruptive rocks of San Carlos range, 
 
 Mexico, 558. 
 
 Fiulay, J. E. : analyses of gabbro, 563. 
 Fissure-faults : definition, 41. 
 
 examples : Gunnison county, Colo., 49. 
 
 San Juan region, Colo., 50. 
 Fissure-planes : repeated movements, 59. 
 Fissure-systems : 
 
 Clifton-Morenci district, Arizona, 539. 
 
 Conrad Hill, Davidson county, N. C. : 
 character and origin, 103. 
 
 origin, 60. 
 
 simultaneous production, 104. 
 Fissure-veins: extent in depth, 11. 
 
 gold-bearing, 427. 
 
 relations of length and depth, 11. 
 
 so-called : formation, 10. 
 
 walls, 54. 
 Fissures (see also faults) : 
 
 conducting ore-bearing solutions, 700. 
 
 extent, 53. 
 
 limiting depth, 44. 
 
 relation of walls, 713. 
 
 structural features characterizing, 45. 
 Fissuring : relation to ore-bodies, 339. 
 Flowage-zone : effect on open channels, 
 
 699. 
 Fluid-inclusions : Clifton-Morenci district, 
 
 Arizona, 545. 
 Fluorine : distribution in igneous rocks, 
 
 751. 
 Fold-fault : definition, 41. 
 
 examples, Leadville, Colo., 48. 
 
 typical form : origin, 47. 
 Foliation-planes : cause, 41. 
 Forchharnmer : metals in ashes of marine 
 
 plants, [256]. 
 Formation and Enrichment of Ore-Searing 
 
 Veins (BANCROFT), 696-719 ; Supplemen- 
 tary Paper (BANCROFT), 720-728. 
 Formulae for reducing power of minerals, 
 
 348. 
 
 Fossil remains : replaced by ore, 87. 
 Foster, C. Le Neve: veins of Cornwall, 10. 
 Fouque, F. A. : volcanic gases, 388. 
 Fracture : causes, 41. 
 
 copper-steel : character, 101. 
 Fracture-system : Ontario mine, Utah, 61. 
 Free Coinage mine, Cripple Creek, Colo., 
 
 422. 
 Freelaud, F. T. : sulphide ores, Leadville, 
 
 Colo., 3. 
 
 Freiberg, Saxony : vein-system, 52. 
 Frood mine, McKim township, Sudbury 
 
 district, Ontario, 500. 
 Fryer hill, Leadville, Colo.: ore-deposits, 13. 
 Fumaroles: gases from, 389. 
 
 sublimation products : composition, 390. 
 Fumarolic deposits, 368. 
 Fumarolic origin of ore-deposits, 240. 
 Furnace canyon : borax deposits, [835]. 
 Furstenburg : Wenzal vein : varying with 
 
 country-rock, 227. 
 Fusion, region of: depth, 22. 
 
 Gabbro : Tamaulipas, Mexico. 563. 
 Galena : effect of pyrite on solubility, [766], 
 
 occurrence in shale, Missouri, 330. 
 
 reducing power, 358. 
 
INDEX. 
 
 937 
 
 Garnet : San Jose, Tamaulipas, Mexico, 570. 
 
 Gar net- Formations of Chillagoe Copper Field, 
 North Queensland, Australia (SMITH), 830. 
 
 Garrey, Ball, and Spurr : silver-lead de- 
 posits of Georgetown and Silver Plume, 
 Colo., [816]. 
 
 Garrey, Emmons, and Ransome : gold-de- 
 posits, Bullfrog district, Nev., [827]. 
 
 Garrey. G. H., and Emmous, W. H. : gold- 
 deposits, Manhattan, Nev., [827]. 
 
 Garrey, G. H., and Spurr, J. E. : ore-de- 
 posits of Georgetown, Colo., [816], [817]. 
 
 Gas-content of rocks, 767. 
 
 Gautier, Arrnand: gase&occluded in rocks, 
 [390], [767]. 
 
 Geikie, A. : origin of igneous rocks, [260]. 
 volcanic gases, 388. 
 
 Gellivare iron-deposits, Norrbotten, 
 Sweden, 671. 
 
 Genesis: Auriferous Lodes (DON), xvi, 
 
 162-215. 
 
 copper-deposits, 75-77. 
 gold- and silver-deposits, 80-81. 
 iron-deposits, 69-71. 
 Lake Valley, New Mexico, Silver-Deposits, 
 
 (KEYES), 835. 
 
 lead- and zinc-deposits, 77-79. 
 
 manganese-deposits, 74-75. 
 
 nickel deposits, 75. 
 
 Ore-Deposits ( EMMONS), xi, 1-25. 
 
 Ore-Deposits at Bingham, Utah '( BOUT- 
 WELL). 831. 
 
 quicksilver-deposits, 79. 
 
 Sudbury, Ontario, nickel-ores, 477. 
 
 Touopah ores, 598. 
 Genetic Relations of the Western Nevada 
 
 Ores (SPURR), xxvi, 590-620. 
 Geologic history: California region, 583. 
 Geological Distribution of the Useful Metals in 
 
 the United States ( EMMONS/, xii, 65-83, 
 
 89-90 ; Discussion, 83-91. 
 Geological maps : 
 
 central Sweden, 658. 
 
 Lake Superior region, 636. 
 
 Norrbotten, Sweden, ore-province, 673. 
 
 San Jose district, Tamaulipas, Mexico, 
 
 560. 
 
 Geology and Copper-Deposits of Bisbee. Ari- 
 zona (RANSOME), 829. 
 Geology and Mining of the Tin-Deposits of 
 
 Cape Prince of Wales, Alaska (FAY), 833. 
 Geology and Petrography of the Goldjield 
 
 Mining- District, Nevada (HASTINGS and 
 
 BERKEY), 832. 
 
 Geology: Clifton-Morenci district, Ari- 
 zona, 518. 
 
 Exposed Treasure Lode, Mojave, Cali- 
 fornia (DE KALB), 834. 
 
 Lake Superior iron-bearing and copper- 
 bearing series, 633. 
 
 Rossland, B. C., pyrrhotite-deposits, 48. 
 
 South Island, New Zealand, 162. 
 
 Sudbury, Ontario, nickel-deposits, 479, 
 481. 
 
 Treadwell Ore- Deposits, Douglas Island, 
 Alaska (SPENCER), 830. 
 
 Virginia Barite- Deposits (WATSON), 834. 
 Georgetown, Colo. : silver-lead deposits, 
 
 816. 
 
 Georgetown quadrangle, Colo. : gold-de- 
 posits, 817. 
 
 Gertrude mine, Creighton township, Sud- 
 bury district, Ontario, 504. 
 photomicrographs of ore, 491-492. 
 Geyser: definition, 32. 
 Geyser shaft : Silver Cliff, Colo. : section, 
 
 144. 
 
 Geyser gold-mine, Silver Cliff, Colo., xvi. 
 analyses of ore, 147. 
 analyses of water, 151, 152. 
 country-rocks, 143. 
 deep deposits, 142. 
 exploration-work, 143. 
 nitrate-content of waters, 768, 778. 
 ore-bodies, 145. 
 vein-materials, 146. 
 water-courses, 147. 
 Gilbert, G. K. : temperature of thermal 
 
 waters, 245. 
 GILLETTE, H. P. : Osmosis as a Factor in 
 
 Ore- Formation, xxiv, 450-454. 
 Glaciation : control of depth of alteration, 
 
 121. 
 
 Glaciers in the United States : first dis- 
 covery, xxxi. 
 
 Glass cracked by torsional strain, 51. 
 Glass plates : torsional experiments, 95. 
 God iva mountain ore-bearing beds, 338. 
 Gogebic district : locus of ore-deposits, 
 
 646. 
 Gold : allotropic forms : behavior with 
 
 mercury, 107. 
 conditions produciug,-108. 
 - conversion to ordinary form, 108. 
 Allotropism (Louis), 105-109. 
 amalgamation, 107. 
 association : with carbonaceous slates in 
 
 California, 211. 
 with coal, 321. 
 with manganese oxides, 786. 
 with platinum in Urals, 289. 
 with pyrites, 132. 
 with sulphides, 203. 
 chemical properties, 107. 
 concentration in oxidized zone, 797. 
 contact-metamorphic deposits, 432. 
 criteria for determining secondary 
 
 origin, 792. 
 crystallization, 105. 
 
 deep-seated enrichment : vertical rela- 
 tion to chalcocitization, 798. 
 determination of small amounts in sea- 
 water, 829. 
 
 difference between placer- and vein- 
 gold, 182. 
 
 distribution in igneous rocks, 752. 
 experiments in solution and deposition, 
 
 [763], 771. 
 
 fineness : variation, 182. 
 forms from precipitation, 105. 
 free: in undecomposed rocks, 208, 214. 
 general diffusion, 209. 
 geologic age of deposition, 429. 
 in assays of California rocks, 301. 
 in coal from Wyoming, 211. 
 in country-rock, 210. 
 in country-rock at deep levels, Walhalla, 
 
 Victoria ; curve, 193. 
 in diorite, 90. 
 in igneous rocks, 271. 
 in mine-waters: evidence for, 178. 
 search for, 179. 
 
 59 
 
938 
 
 INDEX. 
 
 Gold : in sea-water, 191, 192. 
 
 determinations, 195. 
 
 methods of detecting, 193. 
 in siliceous igneous rocks, 286. 
 in vadose country-rock, Walhalla, Vic- 
 toria : curve, 192. 
 mode of occurrence, 108, 724. 
 native : deposition by primary processes, 
 
 793. 
 
 natural solvents, 173. 
 occurrence in sulphides, New Zealand, 
 
 170. 
 
 origin in stratified deposits, 191. 
 placer-deposits, 133. 
 precipitation, 784. 
 
 by black shales, 331. 
 
 from sea-water, 194. 
 experiments, 198, 199. 
 
 in marine sediments, 196. 
 
 reagents, 108. 
 
 relative fineness of vadose and deep vein- 
 gold, 184. 
 Crustiness," 109. 
 solution : reactions, 777. 
 
 and re-precipitation, 206. 
 
 in vadose waters, 177. 
 source, 201. 
 
 in pyrite, 203. 
 specific gravities, 106. 
 tests for : in rocks at Leadville, Colo., 16. 
 transfer in cold solutions, 785. 
 varieties, 105. ' 
 Witwatersrand, Transvaal : action with 
 
 reagents, 109. 
 
 Gold Circle, Nev. : gold-deposits, 827. 
 Gold Coin gold-mine, Cripple Creek, Colo., 
 
 419, [821]. 
 
 Gold-concentrations: occurrence, 271. 
 Gold-content of sea-water: amount, 206. 
 Gold-deposits (see also Gold-silver de- 
 posits) : 
 Agency of Manganese in Alteration and 
 
 Enrichment, 759-828. 
 Alabama, [810J. 
 Alaska: Berner's Bay, 811. 
 
 Treadwell mines, 811. 
 alteration, 132-133. 
 Appalachian, 806. 
 
 association with eruptive rocks, 80. 
 Bannack type, 381. 
 California, Bodie, 823. 
 
 Mojave: Exposed Treasure mine, 823. 
 
 -Mother Lode district, 811, 830. 
 
 Nevada City and Grass Valley district, 
 812. 
 
 Ophir district, 813. 
 classification according to age, 433. 
 classification (Lindgreu's), [763], [806]. 
 Colorado : Cripple Creek, 159, 819. 
 
 Georgetown quadrangle, 817. 
 
 Leadville, 815. 
 
 Mt. Guyot, near Breckenridge, 64. 
 
 San Juan, 818. 
 
 Summit district, 822. 
 concentration, 80. 
 
 in oxidized zone, 797. 
 Cretaceous, 435, 806. 
 formation, 172. 
 
 greater richness in vadose region, 171. 
 Homestake type in South Dakota, 806. 
 Idaho, [815]. 
 
 Gold-deposits : Montana, Granite moun- 
 tain, 122. 
 
 other districts, 815. 
 Philipsburg, [762], 814. 
 Nevada : Bullfrog district, 827. 
 Delamar mine, 828. 
 Edgemont, 815. 
 Gold Circle district, 827. 
 Goldfield, 825. 
 Manhattan, 826. 
 Silver Peak, 813. 
 Tonopah, 68. 
 Ontario, 445. 
 Pre-Cambrian, 434. 
 South Carolina: Haile mine, 806. 
 South Dakota: Black Hills, 810. 
 Southern Appalachian districts, 809. 
 Tertiary, 807. 
 
 United States : superficial alteration and 
 secondary enrichment by ageney of 
 manganese, 759. 
 Utah : Annie Laurie mine, 827. 
 Golden Cyele mine, Cripple Creek, Colo. r 
 
 422. 
 Goldfield district, Nevada: geology and 
 
 ore-deposits, 599. 
 geology and petrography, 832. 
 gold-deposits, 825. 
 
 Gold Ledge, Mercur, Utah : origin, 290. 
 Gold-mine waters : salts in, 764. 
 Gold-mines (see also Gold-silver mines) : 
 Alaska : Treadwell, Douglas Island, 811. 
 California : Exposed Treasure, Mojave, 
 
 804, 823. 
 
 Colorado : Camp Bird, Ouray, [787], [818]. 
 Geyser, Silver Cliff, [766]. 
 Gold Coin, Cripple Creek, [821] 
 Pharmacist, Cripple Creek, [819]. 
 Summit, Cripple Creek, [819]. 
 Tomboy, Silverton, [787], [818]. 
 Montana: Cable, Philipsburg, [762], [814]. 
 Granite-Bimetallic, Philipsburg, [762], 
 
 [814]. 
 Nevada : Crowning Glory, Silver Peak, 
 
 [8.13]. 
 
 Delamar, [794], [828]. 
 Drinkwater, Silver Peak, [813]. 
 South Carolina: Haile, [794], [810]. 
 Utah: Annie Laurie, [827], 
 Gold Mountain, Nev. : geology and ore- 
 deposits, 599. 
 
 Gold-ores : in contact-deposits, 380. 
 Gold-production : future status, 442. 445. 
 increase: causes, 442. 
 North America, 442-444. 
 
 The Geological Features: (LiNDGREN),. 
 
 xxiii-xxiv, 424-444. 
 Tertiary deposits, 438. 
 unit of measurement, 433. 
 Victoria, 171. 
 
 Gold-provinces of the United States, 806. 
 Gold-quartz veins: connection with basic 
 
 igneous rocks. 284. 
 
 genetic connection with siliceous ig- 
 neous rocks, 279. 
 Gold-silver and silver-gold ores : vertical 
 
 relations, in deposits, 799. 
 Gold-silver deposits : 
 California : Bodie, 823. 
 Mojave, 823. 
 Ophir district, 813. 
 
INDEX. 
 
 939 
 
 Gold-silver deposits Montana : Philips- 
 burg, [762], [814]. 
 
 Nevada: Gold Hill group, Comstock 
 lode, [804.] 
 
 Gold-silver mines (see also Silver-gold 
 
 mines): 
 Nevada: Gold Hill group, Comstock 
 
 lode, [804]. 
 Yellow Jacket, Comstock lode, [804]. 
 
 Gonzalo, Joaquin : copper - deposits of 
 Huelva, xli. 
 
 Gooch and Whitfield : arsenic in hot- 
 springs waters, [404]. 
 
 Gossan : appearance, 112. 
 definition, 112. 
 
 Gossan-ores: Appalachians, 73. 
 
 Gottlob vein, Freiberg, Saxony, 218. 
 
 Gottschalk and Buehler: effect of pyrite 
 on solubility of galena, [766]. 
 
 Grabill, L. E.: charcoal in the Bassick 
 mine, 319. 
 
 Grand Central mine, Tintic district, Utah, 
 335, 337. 
 
 Grangesberg, Sweden : map, 662. 
 
 Grangesberg iron-deposits, Sweden, 671. 
 
 Granite : New Zealand : samples for anal- 
 ysis, 163. 
 solution by acids, 726. 
 
 Granite-Bimetallic gold-mine : Philips- 
 burg quadrangle, Mont., 814. 
 
 Granite-Bimetallic lode : Philipsburg 
 quadrangle, Mont. : character of gold- 
 enrichment, 762. 
 
 Granite mine, Cripple Creek, Colo., 419. 
 
 Granite Mountain, Montana, gold-depos- 
 its : depth of alteration, 122. 
 
 Granitic rocks : origin, 608. 
 
 Graphite : occurrence. 315. 
 
 Grarberg mines, Sweden : origin of iron- 
 ores, 670. 
 
 Grass Valley, Cal.: gold-deposits, 812. 
 
 Graton, L. C.: enrichment of gold-depos- ! 
 
 its, Haile mine, S. C., [810]. 
 gold-deposits of central and southern 
 
 North Carolina, [835]. 
 minerals in Appalachian gold-deposits, 
 809. 
 
 Gravity : influence in magmatic differen- 
 tiation, 72. 
 
 Great Gulch ores : genetic relations, 612. 
 
 Groddeck, A. von : nature of veins, 26. 
 Kristiania type of contact-deposits, 372. 
 ores in sedimentary rocks, 256. 
 replacement ores, xxxix. 
 
 Grossularite : San Jose, Tamaulipas, Mex- 
 ico, 572. 
 
 Ground-water : in mines, 248. 
 in lithosphere, 698. 
 
 Guadalupe mine, Chihuahua, Mex.: vein- I 
 formation, 218. 
 
 Gunnison region, Colo.: bog-iron deposits, i 
 
 32. 
 walls of fissure-veins, 55. 
 
 GUNTHER, C. G., and KEMP, J. F.: The ; 
 White Knob Copper- Deposits, Mackay, 
 Idaho [Trans., xxxviii, 269-296], Notice, 
 833. 
 
 Gyrnpie, Queensland : rocks, 163. 
 
 Gypsum-deposits : alteration, 114. 
 expansion in formation, 116. 
 formation, 116. 
 
 Habermehl: composition of pvrrhotite, 
 
 459. 
 Hague and King : genesis of Comstock 
 
 lode, x. 
 Haile gold-mine, South Carolina, [794], 
 
 [806], [810]. 
 
 Hall, C. W. : origin of pegmatite, 275. 
 Hallowell, J. K. : ore-deposits in Gunnison 
 
 region, Colo., 32. 
 Halogens : agency in transferring metals, 
 
 728. 
 
 Haloid compounds in ore-deposits : forma- 
 tion in arid regions, 135. 
 Harker, Albert : average composition of 
 igneous rocks, [734]. 
 
 contact-effects in Westmoreland, 575. 
 HASTINGS, J. B. : Are the Quarts- Veins of 
 . Silver Peak, Nevada, the Result of Mag- 
 matic Segregation?, xxvi, 621-628. 
 HASTINGS, J. B., and BEEKEY, C. P. : The 
 
 Geology and Petrography of the Goldfield 
 
 Mining- District, Nevada [Trans., xxxvii, 
 
 140-159], Notice, 832. 
 Hausmann : iron-ores of Taberg, Smaland, 
 
 681. 
 Hawes : contact-metamorphic phenomena, 
 
 525. 
 
 Headden, W. P. : deposition of basic sul- 
 phate, 710. 
 
 Heat : role in ore-deposition, 2. 
 Heim, A. : classification of rock-fractures. 
 41. 
 
 limiting depth of fissures, 44. 
 Hematite : Grant county, N. M. : origin. 
 127. 
 
 transformation to and from magnetite, 
 
 670, 671. 
 i Henrich, F. : decomposition of volcanic 
 
 rocks, 727. 
 
 | Hill, E. T. : Cretaceous rocks of Tamau- 
 lipas, Mexico, 561. 
 
 origin of Mexican iron-deposits, 127. 
 Hillebrand, W. F. : analyses : sinters, 149. 
 water from Geyser mine, 151. 152. 
 
 elements in igneous rocks, 732. 
 Hills, E. C. : formation of ore-deposits, 
 [233]. 
 
 gold-deposits, Summit district, Colo.,822. 
 Hillside mine, Cripple Creek, Colo., 420. 
 Hinge-faults : definition, 103. 
 Hoefer : ores in sedimentary rocks, 256. 
 Hoefer's Method of Determining Faults 
 
 in Mineral Veins, [101]. 
 Hogbom : iron-ores of Norrbotten, Swe- 
 den, 678, 679. 
 
 Hogborn mines, Sweden : plan, 668. 
 Horn-silver : in Exposed Treasure mine, 
 Mojave, Cal., [804]. 
 
 in mines on Comstock lode, Nev., [804]. 
 
 theories of formation, 800. 
 Hornblende : in rocks of New Zealand, 
 Victoria, and Queensland : analyses, 
 167-168. 
 
 separation from augite, 166. 
 
 separation from rocks for examination, 
 165. 
 
 separation from syenite, 165. 
 Hot springs : decrease in flow, 704. 
 
 explanation, 597. 
 HOWE, H. M. : Discussion on The Torsional 
 
 Theory of Joints, 101. 
 
940 
 
 INDEX. 
 
 Huanatajayite : occurrence, 136. 
 Humboldt mine, Eosita, Colo. : locus of 
 
 ore-bodies, 24. 
 
 Humus acid : reducing power, 351, 357. 
 Hunt, T. S. : classification of crystalline 
 
 rocks, 68. 
 
 Huronian rocks : Lake Superior region, 69. 
 Hussak, E. : auriferous quartz-vein in 
 
 Brazil, 276. 
 
 Hutton, F. W. : geology of Otago, New 
 Zealand, [162J. 
 
 source of ore-materials of Thames dis- 
 trict, N. Z., 164. 
 Hydration, depth of, 119. 
 Hydrocarbons : classification, 308. 
 
 protective action, 311. 
 
 reducing action, 305. 
 Hydrogen : reducing power, 307. 
 Hydrothermal metamorphism, 529. 
 
 Idaho : gold-production, 437, 440. 
 Iddings, J. P. : consanguinity of rocks, 738. 
 contact metamorphic effects, 384. 
 formation of veins, [394]. 
 origin of igneous rocks, 261. 
 Igneous activity : periods, 429. 
 Igneous contacts: relation to ore-deposi- 
 tion, 365. 
 
 Igneous rocks (see also Eocks) : 
 Igneous Bocks and Circulating Waters as 
 Factors in Ore- Deposition (KEMP), xxi- 
 xxii, 235-250. 
 
 Segregation or Differentiation as Related to 
 the Occurrence of Ores (SPURR), xxii, 
 251-303 ; Discussion (WiNCHELL), 303- 
 304. 
 
 Ilmenite : in eruptive rocks, 70. 
 Immortal mine, Silver Cliff, Colo., [140]. 
 Independence mine, Cripple Creek, Colo., 
 
 419. 
 
 India : Tfavancore : quartz-reefs, 282. 
 Indian Queen mine, Birch Creek, Beaver- 
 head county, Montana, [374]. 
 Influence of Country Bock on Mineral Veins 
 
 (WEED), xxi. 
 Intrusions : effects on circulating waters, 
 
 247. 
 
 effect on water-channels, 34. 
 Ontario mine, Utah, 60-62. 
 source of ore-materials, 20. 
 Iodine : solvent of gold, 173. 
 Iron : concentration, 255. 
 in basic rocks, 285. 
 in igneous rocks, 266, 267. 
 in mine-waters, 770, 781. 
 reducing power, 358. 
 Iron and manganese: in rocks: chemical 
 
 relations, 795. 
 relative amounts in vadose and deep 
 
 waters, 153. 
 
 Iron-deposits : alteration, 114, 124. 
 Appalachian region : mode of occur- 
 rence, 117. 
 origin, 71. 
 
 surface-action, 125-126. 
 bog : Colorado, 32. 
 conditions favoring formation, 73. 
 contact deposits in Christiania region, 
 
 692. 
 
 contraction in formation, 117. 
 Elba Island, 8-9. 
 
 Iron-deposits : eruptive-origin theory 
 
 abandoned, 8. 
 formed by magmatic segregation in 
 
 basic eruptions, 680. 
 genesis, 9, 69-71, 124. 
 keratophyre type, ,672. 
 lake- and bog-ores, 694. 
 Lake Superior region, 637. 
 
 character, 647. 
 
 mode of concentration, 641. 
 
 origin and development, 29, 69-71, 
 
 124, 642, 654. 
 
 magnetic : Pennsylvania, 73. 
 Marquette region, Mich.: origin, 71. 
 Mesabi range, Minn.: origin, 125. 
 Missouri : genesis, 87. 
 
 Iron Mountain : 87, 126. 
 
 Pilot Knob, 87. 
 of metamorphosed Canibro-Silurian 
 
 schists, 689. 
 Ovifak, Greenland, 72. 
 relations to eruptives, 72-73. 
 Scandinavian: The Geological Relations 
 
 of (SJOGREN), xxvi, 657-695. 
 Styria: surface-action, 126. 
 Sweden : central : types and origin, 659. 
 
 Norrbotten : structure, 676. 
 
 genesis, 677. 
 
 Sweden and Norway : lake region, 127. 
 Texas : origin, 127. 
 
 eastern: surface-alteration, 126. 
 titauiferous : map of distribution in 
 
 Scandinavia, 682. 
 types : derivation, 73. 
 
 examples: 73. 
 
 Iron fault, Leadville, Colo., 48. 
 Iron Mountain, Mo. : ores : occurrence, 87. 
 Irving, J. D. : classification of Algonkian 
 
 rocks, '69. 
 genesis of Lake Superior iron-deposits, 
 
 29. 
 
 iron ores: origin, 70. 
 minerals of gold-deposits, Homestake 
 
 belt, Black Hills, S- D.,810. 
 Irving, J. D., and Emmons, S. F. : Down- 
 town District, xxxviii. 
 Irving, Emmons, and Jaggar : gold-depos- 
 its, Black Hills, S. D. [810]. 
 IRVING, J. D., SMITH, H. D., FERGUSOX, 
 H. G. : Bibliography of the Science of Ore- 
 Deposits, 837-928. 
 Isabella mine, Cripple Creek, Colo., 422. 
 
 Jackson, D, D.: chlorine in waters, 767. 
 Jacque mountain, Ten-mile district, Colo.: 
 
 structural features, 62. 
 Jaggar, Emmons, and Irving : gold-depos- 
 its, Black Hills, S. D., [810]. 
 JENNEY, W. P.: The Chemistry of Ore-De- 
 position, xxii, 305-363. 
 formation of solid oxidized hydro-car- 
 bons, 308. 
 
 genesis of Missouri lead- and zinc-depos- 
 its, 78. 
 lead- and zinc-deposits of the Mississippi 
 
 Valley, 306. 
 
 Jerome, Ariz;: copper-deposits, 136. 
 Jimenez copper-mine, Chihuahua, Mexico, 
 
 [374]. 
 
 Joass and Cameron : Sutherland gold- 
 fields of Scotland, 281. 
 
INDEX. 
 
 941 
 
 Joints : definition, 40. 101, 103. 
 
 ore-bearing: Silver Cliff. Colo., 141. 
 
 origin and extent, 35, 93. 
 
 phenomena, 92. 
 
 relation to ore-deposition, 35. 
 
 Torsional Theory (BECKER), 92-104. 
 Joplin region, Missouri : ore-deposits, 833. 
 Josie mine, Eossland district, B. C., 509. 
 Judd, J. W.: chlorine in volcanic emana- 
 tions. 723. 
 
 disintegration of volcanic rocks, 727. 
 Judson, J. N.: magnetic separation of 
 
 nickel-ores, 467. 
 Juvenile waters : origin, xx. 
 
 Kaolinization, depth of, 119. 
 
 Kawich district, Nevada : geology and 
 
 ore-deposits, 600. 
 Keck, Rudolph : association of organic 
 
 matter with ore-deposits, 344. 
 KEMP, J. F.: Igneous Rocks and Circulating 
 Waters aft Factors in Ore-Deposition, 
 xxi, 235-250. 
 
 The Copper-Deposits at Fan Jose, Ta- 
 maulipas, Mexico, xxv-xxvi, 557-581. 
 Ducktown, Tenn., copper-deposits, 810. 
 genesis of ore-deposits, [253]. 
 igneous rocks a source of vein-materi- 
 als, 222. 
 
 metals in eruptive rocks, [707]. 
 metals in igneous rocks, 295. 
 order of formation of minerals in crys- 
 talline rocks, 263. 
 origin of pegmatites, 276. 
 origin of Sudhury nickel-ores, 483. 
 role of igneous rocks, 384. 
 R6le of the Igneous Rocks in the Formation 
 
 of Veins, xix. 696. 
 
 secondary enrichment in copper-depos- 
 its, [761]. 
 
 silica in the Sierras, 280. 
 Silver-Islet mine, 231. 
 vein-system of San Juan region, Colo., 
 
 290/ 
 
 KEMP, J. F., and . GUNTHER, C. G.: The 
 White Knob Copper- Deposits, Mackay, 
 Idaho [Trans., xxxviii, 269-296], Notice, 
 833. 
 
 Keweenawan rocks, Lake Superior re- 
 gion, 69. 
 
 KEYES, C. E.: Borax- Deposits of the United 
 States [Trans., xl, 674-710]," Notice, 835. 
 Genesis of the Lake Valley, New Mexico, 
 Silver-Deposits [Trans., xxxix, 139- 
 169], Notice, 835. 
 chlorine in arid regions. 768. 
 Keystone mine, Silver Cliff, Colo., [140]. 
 Kiirunavaara iron-ore deposits, Sweden, 
 
 672. 
 Kimball, J. P.: replacement of limestones 
 
 by iron-ores, 70. 
 King, Clarence: genesis of Butte, Mont., 
 
 deposits, 404. 
 horn-silver, 803. 
 
 manganese in Comstock lode, 802. 
 meridional zones of mineral -deposits, 
 
 .[81]. 
 
 views as to genesis of ore-deposits, x. 
 King and Hague : genesis of Comstock 
 
 lode, x. 
 King, William : joints. 93. 
 
 Kinta Valley, Federated Malay States: 
 tin-deposits, 832, 
 
 Klein's solution : ad vantages,- 166. 
 
 Klockmann : contact-metamorphic phe- 
 nomena, 525, 527. 
 
 Knaffl, Ludwig : amalgamation of gold, 
 107. 
 
 Knopf, Adolph : gold-deposits, Berner's 
 Bay district, Alaska, 811. 
 
 Kceuig, G. A., and Stockder, M.: occur- 
 rence of coal with silver, 321. 
 
 Kohler, E.: adsorption process, 536- 
 
 Kohlrausch : solubilities of silver-salts, 
 800. 
 
 Kolecki, Theodore : contour sketch-maps, 
 [xxxii]. 
 
 Kootenay volcanic group, 495. 
 
 Kristiania type of contact ore-deposits, 
 
 372. 
 permanence in depth, 393. 
 
 Laccolith: San Jose, Tamaulipas, Mexico, 
 
 563. 
 
 Lacroix, A.: metals in fumaroles, 721. 
 Lake Superior iron-ores : character, 647. 
 Lake Superior region : Algonkian rocks, 
 
 69. 
 
 development of rocks, 648. 
 geological map, 636. 
 iron-deposits, 69. 
 genesis, 29. 
 
 mode of concentration, 641. 
 origin and development, 642, 650, 
 
 654. 
 
 time of concentration, 649. 
 topographic relations, 650. 
 pre-Cambrian series, 634. 
 Lake Wakatipu, New Zealand : vadose 
 
 country-rock : analyses, 189. 
 Lapparent, A. de : solution-theory of ore- 
 deposition, 2. 
 
 Lassaigne : solubility of manganese, [796]. 
 Lateral migration : manganese salts, 794. 
 Lateral-secretion theory : ore-genesis, xiii, 
 23-24, 82, 83, 160, 171, 201, 204, 210, 213. 
 Lava : experiments on, 725. 
 
 gaseous content, 767. 
 
 Lava streams : Vesuvius : steam from, 701. 
 Law of areal distribution of mining-dis- 
 tricts, 325. 
 
 Law of replacement, 9. 
 Lead : distribution in igneous rocks, 753. 
 tests for : in rocks at Leadville, Colo., 
 
 16-17. 
 Lead-deposits : alteration, 131. 
 
 Australia : Chillagoe district, North 
 
 Queensland, 830. 
 Cornmern, Eifel district, 36. 
 genesis, 77-79. f 
 source of material, 77. 
 Virginia-Tennessee region, 831. 
 Lead- and zinc-deposits : association with 
 
 eruptives, 78. 
 Missouri : occurrence in Carboniferous 
 
 rocks, 88. 
 
 occurrence in Franklin county, 89. 
 Missouri region : genesis, 78. 
 Virginia- Tennessee Region (WATSON), 831- 
 
 832. 
 
 Lead oxides : agency in solution of gold, 
 780. 
 
942 
 
 INDEX. 
 
 Leaders : definition, 51. 
 Leadville, Colo. : investigations of coun- 
 try-rocks, 23. 
 
 ore-deposits : character, 27, 38. 
 genesis, xi, 5. 
 investigation, 26. 
 original depth, 7. 
 sulphide origin, 3. 
 silver-, lead-, and gold-deposits, 815. 
 silver-lead deposits: aqueous origin, 2. 
 LE CONTE, JOSEPH : Discussion on The 
 Genesis of Certain Auriferous Lodes, 202. 
 association of eruptive activity with ore- 
 deposition, 21. 
 
 chlorine as solvent of gold, 763. 
 genesis of metalliferous veins, 14-15. 
 mis-statement of Emmons's views on 
 
 Leadville ores, 4. 
 Ledoux, A. R. : coutact-metamorphism in 
 
 Boundary district, 375. 
 Lehner, Victor: lead oxide: effect on 
 
 solubility of gold, [780]. 
 LEITH, C. K. : A Summary of Lake Superior 
 Geology with Special Reference to Recent 
 Studies of the Iron-Bearing Series, xxvi, 
 633-656. 
 
 Leptoclases : definition, 40. 
 Levack township deposits, Sudbury dis- 
 trict, Ontario, 507. 
 Levigation theory : ore-deposits, 14. 
 Lignite : association with ore-deposits, 322. 
 
 reducing power, 351, 357. 
 Limburgite : Cripple Creek district, Colo., 
 
 412. 
 
 Lime : quantity in igneous rocks, 732. 
 Limestone : analyses, 334, 335, 337, 338. 
 Chlorine-content, 766. 
 oxidation, 535. 
 relation to ore-deposits, 333. 
 Sail Jose, Tamaulipas, Mexico, 568. 
 Limonite : eastern Texas: origin, 126. 
 Limonites : origin, 124 
 LINCOLN, F. C. : The Promontorio Silver- 
 Mine, Durango, Mexico [Trans., xxxviii, j 
 734-746], Notice, 834. 
 
 LINDGREN, WALDEMAR : The Genesis of \ 
 the Copper- Deposits of Clifton-Morenci, j 
 Arizona, xxv, 517-556. 
 The Geological Features of the Gold-Pro- 
 duction of North America, xxiii-xxiv, 
 424-444 
 The Occurrence of Stibnite at Steamboat 
 
 Springs, Nevada, xxvi, 629-632. 
 andradite at Clifton-Morenci, Arizona, 
 
 [572]. 
 
 Annie Laurie gold-mine, Utah, 827. 
 auriferous quartz-vein in Brazil, 276. 
 Character and Genesis of Certain Contact- 
 Deposits, [xixj. 
 
 contact-deposits, 236, 237, [372]. 
 contact-metamorphic deposits, 528. 
 contact metamorphism, 371. 
 copper-deposits, Clifton-Morenci dis- 
 trict, Arizona, [788]. 
 formation of metalliferous veins, 369. 
 garnetization at Clifton-Morenci, Ariz., 
 
 579. 
 
 genesis of ore-deposits, [253]. 
 gold-deposits : classification, [763], 807. 
 Nevada City and Grass Valley, Cal., 
 812. 
 
 LINDGREN, WALDEMAR: 
 
 gold-deposits: Ophir district, Cal., 813. 
 southern Appalachians : associated 
 minerals, [809]. 
 
 hypothesis of igneous emanations, 582. 
 
 magmatic differentiation, 722. 
 
 rnagmatic origin of ore-deposits, 619. 
 
 metallogenetic epochs, 806. 
 
 metals in gneiss, [707]. 
 
 Metasomatic Processes in Fissure- Veins, 
 [xviii]. 
 
 metasomatic replacement, [223], 225, 
 232. 
 
 metasomatism, xl. 
 
 osmosis in ore-formation, [xxiv]. 
 
 primary pyrites, 204. 
 
 relation of ore-deposition to physical 
 conditions, 763. 
 
 telluride ores, 380. 
 
 vein-forming waters, 586. 
 Lindgren, W., and Eansome, F. L. : gold- 
 deposits, Cripple Creek, Colo., 819. 
 List of Scientific Publications of Samuel F. 
 
 Emmons, xlii-xlvii. 
 Lithium: distribution in igneous rocks.746. 
 
 quantity in igneous rocks, 734. 
 Lithoclases: definition, 40. 
 Liversidge, A.: gold in sea-water, 193. 
 
 gold in solution, 177. 
 
 origin of nuggets, [182]. 
 Lodes : metalliferous : suceessive zones in 
 
 depth, 789. 
 
 Lofstrad : iron-ores of Norrbotten, Swe- 
 den, 678. 
 Lone Mountain ores, Nevada: genetic 
 
 relations, 614. 
 Longfellow limestone, Clifton-Morenci 
 
 district, Arizona, 519, 523. 
 Lossen : quotation from Groddeek, 26. 
 Lotti, B.: studies of Elba iron-ores, 9. 
 Louis, HENRY : The Allotropism of Gold, 
 xv., 105-109. 
 
 mode of occurrence of gold, 108. 
 
 ore-deposits in Permian of Nova Scotia, 
 
 [327]. 
 Lucky Guss mine, Cripple Creek, Colo., 
 
 422. 
 Luossavara iron-ore deposits, Sweden, 673. 
 
 McCaskey, H. D.: gold-deposits, Alabama, 
 
 [810]. 
 
 McCaughey, W. J.: experiments on solu- 
 tion of gold, 763, 771, 772, 776, 798. 
 McDerniott, W.: association of graphite 
 
 and silver in Silver-Islet mine, 317. 
 McLaughlin, E. P.: gold-deposits, Bodie, 
 
 Cal., [823]. 
 McTighe, T. J.: magnetic separation of 
 
 nickel-ores, 467. 
 
 Macetown gold-district, N. Z.: assays, 184. 
 Magmas : action during cooling, 725. 
 
 differentiation phenomena, 687. 
 
 kinds ejected in eruptions, 715. 
 
 relations to ore-bodies, 717. 
 
 temperature, 724. 
 
 water in, 702. 
 Magmatic differentiation : ore-deposits, 
 
 67, 84, 205, 274. 
 Magmatic Origin of Vein-Forming Waters in 
 
 Southeastern Alaska (SPENCER), xxvi, 
 
 582-589. 
 
INDEX. 
 
 943 
 
 Magmatic segregation, 288. 
 
 as working hypothesis, 292. 
 
 effect on ore-deposits, 300. 
 Magmatic waters : origin, xx. 
 
 role, 584. 
 
 Magnesia: quantity in igneous rocks, 732. 
 Magnesium : in mine-waters, 768. 
 Magnetic iron-ore deposits, Pennsylvania, 
 
 73. 
 Magnetite: in eruptive rocks, 70. 
 
 in rnagmas, 72. 
 
 in rocks of New Zealand and Victoria: j 
 analyses, 167, 
 
 reducing power, 358. 
 
 San Jose, Tamaulipas, Mexico, 573. 
 
 transformation to and from hematite, 
 
 670, 671. 
 
 Magnetite-deposits : Colorado : genesis, 74. 
 Malaguti : metals in ashes of marine plants, 
 
 [256]. 
 
 Malaguti and Durocher: silver in sea- 
 water, 191. 
 
 Mallet, J. W.: silver in volcanic ash, 721, 
 Malm, J. L.: chlorination treatment of 
 
 ores, 722. 
 Mammoth mine, Tintic district, Utah, 
 
 335, 337. 
 
 Manganese : Agency in Superficial Altera- 
 tion and Secondary Enrichment of Gold- 
 Deposits, 759-828. 
 
 chemical relations with iron in rocks,795. 
 
 chemistry of, 780. 
 
 concentration, 255. 
 
 distribution in igneous rocks, 751. 
 
 effect on solubility of gold, 778. 
 
 experiments on solution, 795. 
 
 in igneous rocks, 267. 
 
 in mine-waters, 770, 781. 
 
 occurrence in gold-deposits, 779. 
 
 quantity in igneous rocks, 733. 
 
 use in chlorination process, 762. 
 Manganese and iron, relative amounts in 
 
 vadose and deep waters, 153. 
 Manganese-deposits : alteration, 127-128. 
 
 Batesville, Ark., 128. 
 Manganese-ore : bog : formation, 128. 
 
 southern Appalachians, 74. 
 Manganese oxides : association with gold- 
 deposits, 786. 
 
 occurrence in mining-districts, 174. 
 
 reactions in dissolving gold, 778. 
 Manganese-salts : lateral migration from 
 
 country-rock, 794. 
 
 Manganite : association with gold, 793. 
 Manhattan, Nev. : gold-deposits, 826. 
 Matiipori formation, South Island, New 
 
 Zealand, 162. 
 Map : New England and New York : 
 
 iiormal chlorine, 769. 
 Marble : San Jose, Tamaulipas, Mexico, 
 
 569. 
 
 Marcasite : reducing power, 352, 357, 358. 
 Marquette region, Michigan: iron-depos- 
 its : origin, 71. 
 
 vertical section, 639. 
 
 Marsh-gas : association with ore-deposits, 
 345. 
 
 reducing power, 350, 357. 
 Martinique: volcanic gas: analysis, 388. 
 May Belle Tunnel mine, Cripple Creek, 
 
 Colo., 419. 
 
 Melville, W. H. : analysis of sinter, 629. 
 Mendenhall, W. C. : gold in aplite dikes, 
 
 Alaska, 280, 
 Mercury (see also Quicksilver) : 
 
 relations to igneous rocks, 753. 
 MERRITT, W. H. : Discussion on Geological 
 
 Distribution of Useful Metals in the United 
 States, 90-91. 
 
 origin of Sudbury nickel-ores, 483. 
 Mesabi ore-deposit : vertical section, 640. 
 Mesozoic gold-belt, 435-438. 
 Metalliferous lodes : successive zones in 
 
 depth, 789. 
 Metalliferous province : definition, 293. 
 
 relation to petrographic province, 293, 
 
 297. 
 
 Metallographic province of California, 619. 
 Metallographic province of Nevada, 619. 
 Metals : distribution in sedimentary 
 rocks, 254. 
 
 in detrital rocks, 257. 
 Metamorphism (see also Contact-meta- 
 morphism) : 
 
 effects, 68. 
 
 hydrothermal, 529. 
 
 Sudbury district, Ontario, 514. 
 Metasomatic interchange : definition, 3. 
 Metasomatic processes, 232. 
 
 in Fissure- Veins (LiNDGREN), xviii. 
 Metasomatic replacement : explanation, 
 453. 
 
 Tintic district, Utah, 342. 
 Metasomatism : definition, xl. 
 
 in Leadville ore-deposits, 2. 
 
 in Scandinavian iron-ores, xxvii. 
 Metastibnite : Steamboat Springs, Nevada, 
 
 632. 
 
 Meteoric hypothesis : inadequacy for ore- 
 deposition on Pacific coast, 589, 
 Meteoric waters : circulation, 240. 
 
 role in formation of ore-deposits, xix. 
 Mexico : gold production, 435, 436, 438, 
 439. 
 
 Cananea copper-deposits, 376. 396. 
 
 Chihuahua: Guadalupe mine, 218. 
 
 San Jose : ore-deposits, 237. 
 Mica : in rocks of New Zealand and Vic- 
 toria : analyses, 167-168. 
 
 separation from rocks for examination, 
 
 164. 
 Michel-Levy, A. : contact-metamorphic 
 
 phenomena, 525. 
 Microcline : crystallization from magmas, 
 
 609. 
 
 Midget mine, Cripple Creek, Colo., 420. 
 Mike fault, Leadville, Colo., 48. 
 MILLER, W. G. : Discussion on The Geolog- 
 ical Features of the Gold- Production of 
 
 North America, 445-446. 
 Millerite : Sudbury, Ontario, 456. 
 Mineral-bearing currents : direction of 
 
 flow, 37. 
 
 Mineral ridge, Tonopah, Nev. : mineral 
 veins. 607. 
 
 rocks, 604. 
 
 silver-ores : genetic relations, 613. 
 Mineral vein : genesis, 430. 
 Mineral veins : Influence of Country-Rock 
 on (WEED), 216-234. 
 
 near igneous contacts, 394. 
 Mineral zone, western America, 298. 
 
944 
 
 INDEX. 
 
 Mineralization : due to rich solutions, 700. 
 
 of veins : rapidity, 700. 
 
 source of ores, 710. 
 Mineralized veins : product of expiring 
 
 vulcanisrn, 698. 
 
 Mineralizing agents: distribution in ig- 
 neous rocks, 755. 
 
 Mineralizing process : Tonopah, Nev., 594. 
 Mineralizing solutions: source: Tonopah, 
 
 Nev., 596. 
 
 Minerals: isolated from rocks of New 
 Zealand : analyses, 167. 
 
 isolation for examination, 164. 
 
 of secondary origin, 791. 
 
 reducing power, 347, 357. 
 
 segregation in magmas, 264. 
 
 separation from rocks by solutions, 165. 
 Mines (see also Gold-mines : Silver-mines, 
 etc.) : 
 
 of Rosita and Silver Cliff, Colorado 
 (EMMONS), 139-161. 
 
 scarcity of commercially valuable, 696. 
 Mine-timbers : examination for gold, 180. 
 Mine-waters : acidity: cause, 174. 
 
 average of analyses, 765. 
 
 composition, 764. 
 
 examination : apparatus and results, 
 180-181. 
 
 vadose : acidity, 175. 
 
 examination for free acid and ferric 
 
 salts, 176, 
 Mining-districts : areal distribution, 325. 
 
 review, 805. 
 
 Mint mine, Cripple Creek, Colo , 420. 
 Mirabel mine, Lake county, Cal.: quick- 
 silver, 79, 
 
 Mississippi valley zinc-and lead-ores, 335. 
 Missouri : lead-and zinc-deposits, 327. 
 
 Sedalia: coal associated with blende, 
 320. 
 
 Versailles: coal associated with blende, 
 
 320. 
 Mitchener mine, Drury township, Sud- 
 
 bury district, Ontario, 505. 
 Mizpah silver-gold mine, Tonopah, Nev., 
 
 [825]. ^ 
 Modoc limestone, Clifton-Morenci district, 
 
 Arizona, 519, 523. 
 Modoc porphyry, 224. 
 
 Moissan, H.: analysis of volcanic gas, 388. 
 Mojave desert : borax-deposits, [835]. 
 Mojave Mining-District, California (BATE- 
 SON), 832. 
 
 Molybdenite : San Jose, Tamaulipas, Mex- 
 ico, 573. 
 
 Molybdenum : distribution in igneous 
 rocks, 750. 
 
 in siliceous rocks, 285. 
 Molybdenum-deposits: alteration, 135. 
 Mongolia : Ku Shau Tzu : ore-deposition, 
 
 359. 
 Montana : Bannack gold-deposits, 381. 
 
 Butte : copper-veins, 224, 225, 403. 
 silver- veins, 223. 
 vein-formation, 220. 
 
 Elkhorn district : ore-deposits, [239], 
 382. 
 
 gold-production, 437. 
 
 gold-quartz veins, 280. 
 
 Jefferson county : Lump Gulch silver- 
 gold-veins : genesis, 408. 
 
 Montana: Madison county : ore-deposits 
 produced by successive concentra- 
 tions, 303-304. 
 mrneral veins, 228-229. 
 Neihart: mineral veins, 227, 228. 
 
 silver-lead mines, 219. 
 Monument mine, Cripple Creek, Colo., 419. 
 Moon-Anchor mine, Cripple Creek, Colo., 
 
 420. 
 
 i Moonlight mine, Cripple Creek, Colo., 420. 
 Morenci shale, Clifton-Morenci district, 
 
 Arizona, 519, 523. 
 
 Morencite, Clifton-Morenci district, Ari- 
 zona. 519. 
 
 Mosquito fault, Leadville, Colo., 48. 
 Mosquito range, Leadville, Colo.: faulting, 
 
 48. 
 
 uplift. 16. 
 Mother Lode district, Cal.: gold-deposits, 
 
 811. 
 
 ; Mounds : deposits from springs, 32. 
 Mount Guyot, near Breckenridge, Colo.: 
 
 horizontal faulting, 64. 
 Mount Hood : ascent by Arnold Hague, 
 
 fxxxil. 
 Mount Nickel mine, Blezard township, 
 
 Sudbury district, Ontario, 497. 
 photomicrographs of ore, 487-488. 
 Mount Eainier : ascent by Emmons, 
 
 [xxxi]. 
 
 Mount Shasta: ascent by King and Em- 
 mons, [xxxi]. 
 
 Mountain-building: periodicity, 43. 
 Mountain View mine, Silver Cliff, Colo., 
 
 [140]. 
 
 'Movements: repeated: along fissure- 
 planes, 59. 
 Mullan, John : Report on the Construction 
 
 of a Militarv Road, 1863, [xxxii]. 
 Miinster : gold in sea- water, [193]. 
 Murchison, R. I. : age of auriferous rocks, 
 
 258. 
 
 horizon of irold, [ix]. 
 1 Murray, A. R. F. : auriferous rocks of 
 
 Victoria, 163. 
 Murray mine, McKim township, Sudbury 
 
 district, Ontario, 500. 
 
 Muscovite : crystallization from magmas, 
 609. 
 
 Nason, F. L. : genesis of iron-deposits, 
 
 Missouri, 87. 
 
 | National mine, Cripple Creek, Colo., 420. 
 | Natural gas : confinement, 313. 
 I Natural water-channels : causes, 33. 
 Neihart, Mont. : silver-lead mines, 219. 
 
 veins, 227, 228. 
 
 I Nelson granite, Rossland, B. C., 495. 
 Nenthorn gold-field, Otago, N. Z. : assays, 
 
 184. 
 Nepheline-basalt : Cripple Creek district, 
 
 Colo., 411. 
 Nephelite-syenite: analysis, 562. 
 
 Tamaulipas, Mexico, 562. 
 Nevada : Belmont : dike-rocks, 277. 
 gold-production, 440. 
 metallographic province, 619. 
 silver-mining industry, 299. 
 Tonopah : geology, 591. 
 
 mineral veins, 593. 
 Nevada City, Cal. : gold-deposits, 812. 
 
INDEX. 
 
 945 
 
 New Brunswick : pyrrhotite, 462. 
 
 New Mexico : San Pedro : ore-deposits, 
 
 [238]. 
 
 New Zealand : South Island : geology. 162. 
 Newberry, Cosmo : source of gold, 178. 
 Newberry, J. S. : age of lignitic sandstone 
 at Silver Reef, Utah, [322]. 
 
 criticism of Emmons's views answered, 
 4, 19. 
 
 genesisof Appalachian iron-deposits, [36] 
 
 selenium in Silver Reef, Utah, sand- 
 stones, 325. 
 
 theory of formation of solution-cham- 
 bers, 6. 
 
 Newberry's theory of ore-genesis: criti- 
 cism, 6, 21, 24. 
 Nickel : associates in rocks, 75. 
 
 distribution in igneous rocks, 751. 
 
 in basic rocks, 285, 295. 
 
 in igneous rocks, 268. 
 
 in Sudbury pyrrhotites, 466. 
 
 occurrence, 316. 
 
 quantity in igneous rocks, 733. 
 
 relation to pyrrhotite, 455, 461. 
 
 Virginia, 834. 
 
 Nickel-deposits : characteristic features. 
 511. 
 
 genesis, 75. 
 
 Sudbury, Ont., 90-91. 
 Nickel-ores : classification, 477. 
 
 concentration -experiments, 470. 
 Nickel Plate mine, British Columbia, 383. 
 Nickeliferous pyrrhotite : magnetic sepa- 
 ration, 466. 
 
 theories of origin, 481. 
 Niter-deposits : formation, 115. 
 Nitrates : in mine- waters, 768. 
 
 reactions in dissolving gold, 776. 
 Norite : Sudbury, Ontario, 480. 
 Norrbotten, Sweden, iron-ores, 672. 
 Norway : island of Bommel : igneous 
 rocks, 281. 
 
 titaniferous iron-ore : concentration in 
 
 magmas, 72. 
 Nova Scotia : pyrrhotite, 462. 
 
 Observations on Mother- Lode Gold- Deposits, 
 California (PRICHARD), H30. 
 
 Occurrence of Nickel in Virginia (WATSON), 
 834. 
 
 Occurrence of Stibnite at Steamboat Springs, 
 Nevada (LlNDGRBN), xxvi, 629-632. 
 
 Ocher-deposits : Cartersville district, Bar- 
 tow county, Ga., 830. 
 
 Oddie rhyolite, Tonopah, Nov., 593. 
 
 Ohinemuri district, N. Z. ; vadose country- 
 rock : analyses, 190. 
 
 Ontario : gold-deposits, 445. 
 pyrrhotite, 462. 
 
 Ontario mine, Utah : structural features 
 of deposit, 60-62. 
 
 Ophir district, Cal. : gold-deposits, 813. 
 
 Ore-bearing solutions : source, 11. 
 
 Ore-bodies : association with eruptive 
 
 rocks, 697. 
 
 limited to certain magmas, 716. 
 mode of formation, 720. 
 mode of occurrence, Lead ville, Colo., 13. 
 Queen of the West mine, Colo., 63. 
 relations to vein-walls: Gunnison region, 
 Colo., 56. 
 
 Ore-currents : descent from above, 2. 
 Ore-deposition : aqueous solution, 29. 
 ascending theory, 12, 14, 15. 
 association with eruptive activity, 21. 
 by Ascending Hot Waters (WEED), xxiii, 
 
 403-410. 
 
 by thermal springs, 406. 
 causes, 37, 342. 
 character of receptacles, 30. 
 Chemistry, 305-363. 
 conditions, 24-25, 35, 37. 
 determining factors, 24. 
 differential, 362. 
 Igneous Rocks and Circulating Waters as 
 
 Factors (KEMP), xxi, 235-250. 
 Ku Shau Tzu, Mongolia, 359. 
 lateral secretion theory, 23-24. 
 process, 342. 
 
 processes : western Nevada, 616. 
 Principles Controlling ( VAN HISE), xvii. 
 selective hypothesis, 614. 
 variation in parts of an ore-body, 361. 
 Ore-deposits (see also names of metals) : 
 Alaska, Tread well, 830. 
 along bedding-planes, 35. 
 along contact-planes, 37. 
 along planes of rock-fracture, 39. 
 alteration in situ, 123. 
 ascending theory, 201. 
 bibliography, 837-928. 
 classification, 286. 
 climatic effects on, 120-121. 
 concentration, 83. 
 Cripple Creek District, Colorado : Basaltic 
 
 Zones as Guides (STEVENS), xxiii, 411- 
 
 423. 
 
 definition, 111. 
 depth of alteration in uuglaciated 
 
 regions, 122. 
 Eastern Gold-Belt of North Carolina 
 
 (CROSBY), 834-835. 
 Enrichment of Gold and Silver Veins 
 
 (WEED), xviii. 
 formation : influence of cai'bonaceous 
 
 matter, 231. 
 
 from meteoric waters, 369. 
 fumarolic origin, 240. 
 Genesis (EMMONS), xi, 1-25, 300. 
 genetic classification. 366. 
 haloid compounds : formation in arid 
 
 regions, 135. 
 in limestone : depth, 7. 
 
 form, 5. 
 
 Joplin Region, Missouri (CLERC), 833-834. 
 Kristiania type : permanence in depth, 
 
 393. 
 
 lateral -secretion theory, 82, 83. 201. 
 Leadville, Colo. : investigation, 26. 
 levigation theory, 14. 
 magmatic differentiation, 83. 
 materials : source and concentration, 
 
 159. 
 Montana : Butte, 55. 
 
 produced by successive concentra- 
 tions, 303-304. 
 Near Igneous Contacts (WEED), xxiii, 
 
 364-402. 
 occurrence, 53. 
 
 of contact-metamorphie origin, 369. 
 of fumarolic origin, 368. 
 of gas-aqueous origin, 368. 
 
946 
 
 INDEX. 
 
 Ore-deposits: of igneous origin, 366. 
 
 of igneous-emanation origin, 368, 370. 
 
 open-cavity theory, 4. 
 
 origin in depth, 84. 
 
 pneuraatolytic origin, 240. 
 
 primary or original, 28. 
 
 receptacles: assumptions regarding, 3. 
 
 Ked Mountain, Colo., 21-32. 
 
 relation to igneous rocks, 253. 
 
 relations to petrographic provinces : 
 practical considerations, 755. 
 
 replacement theory : application, 8. 
 
 rich : factors determining location, 790. 
 
 secondary concentration : Sudbury, 
 Ont., 90. 
 
 secondary enrichment, 761, 791, 810 
 et seq. 
 
 selective concentration, 79. 
 
 Silver Cliff, Colo.: genesis, 155. 
 
 solfataric origin, 85. 
 
 source and concentration (summary), 82. 
 
 source of materials, 15, 111. 
 
 status of investigations, 81. 
 
 Structural Relations (EMMOXS), xii, 26-64. 
 
 Sudbury, Ontario (DiCKSON), xxiv-xxv, 
 455-516. 
 
 Superficial Alteration (PENROSE), 110-138. 
 
 sulphide secondary enrichment, xvii. 
 
 Utah, Bingham, 831. 
 Ore-Formation : Osmosis a Factor in (GiL- 
 
 LETTE), xxiv, 450-454. 
 Ore-genesis: ascension theory, xiii. 
 
 lateral secretion theory, xiii. 
 Ore-materials: migration, 123. 
 Ore-minerals: source in eruptive rocks, 2. 
 Ore-regions : association with ores of ig- 
 neous activity, 253. 
 Ore-segregation: definition, 252. 
 Ore-zone: Cripple Creek, Colo.: structure, 
 
 413, 414. 
 Ores (see also names of metals) : 
 
 deposition contemporaneous with sedi- 
 ments, 256. 
 
 derivation from magmas, 237. 
 Oregon : gold-production, 436. 
 Origin of Vein-filled Openings in Southeast- 
 ern Alaska (SPENCER), 83. 
 Orphan Belle mine, Cripple Creek, Colo.,422 
 Osmosis as a Factor in Or e- Formation ^( GIL- 
 LETTE), xxiv, 450-454. 
 Osmotic pressure : law, 451. 
 Osmotic separation of metal-bearing so- 
 lutions, 207. 
 Otago, New Zealand : vadose country-rock: 
 
 analyses, 188. 
 Otaso harbor : sediments : examination 
 
 for gold, 196. 
 
 Oversight mine, Cananea, Mexico, 398. 
 Ovifak, Greenland : iron -ore deposit, 72. 
 Owyhee mines, Idaho : gold-production, 
 
 440. 
 
 Oxidation : limiting depth, 118. 
 Oxidized ores, 581. 
 
 Pachuca district, Mexico: comparison 
 
 with Tonopah, Nev., 601. 
 Pacos (gossan) : definition, 112. 
 Paraclase : rocks, 92. 
 Paraclases : definition, 40. 
 Paragenesis of minerals : Clifton-Mor- 
 
 euci district, Arizona, 536. 
 
 Paris mine, Silver Peak district, Nevada, 
 
 627. 
 Park, James: gold in sea- water, [192]. 
 
 source of ore-materials of Thames dis- 
 trict, N. Z., 164. 
 
 Pearce, Richard : analyses of gold-ores. 
 [820]. 
 
 experiments in solution of gold, [763]. 
 [773). 
 
 veins of Cornwall, 10. 
 Pearceite ores, Neihart, Montana, genesis, 
 
 404. 
 
 Pegmatite veins. 239. 
 Pegmatites: definition, 275. 
 Penfield, S. L.: pentlandite in Sudbury 
 
 ores, 470. 
 
 Penokee-Gogebic ore-deposit: vertical sec- 
 tion, 639. 
 
 PENROSE, R. A. F., JR.: The Superficial Al- 
 teration of Ore- Deposits, xv. 110-138, 
 [761]. 
 
 chemical relations of iron and man- 
 ganese in rocks, [795]. 
 
 distribution of chloride ores, [768]. 
 
 fissures at Cripple Creek, Colo., 221. 
 
 formation of silver chlorides in arid 
 countries, 801. 
 
 manganese in gold-deposits of Cripple 
 
 Creek, Colo., 819. 
 Pentlandite: formula, 474-475. 
 
 Lillehammer, Norway, 474. 
 
 Sudbury, Ontario, 456, 474. 
 Permeability of rocks under heat and 
 
 pressure, 29. 
 Persberg, Sweden : iron-deposits : map, 
 
 667. 
 Petrographic provinces, 737. 
 
 distribution, 295-299. 
 
 in the United States, 740. 
 
 of foreign countries, 741. 
 
 persistence, 291. 
 Petrographic pi'ovinces and ore-deposits: 
 
 practical considerations, 755. 
 Petroleum: associated with ore-deposits, 
 344. 
 
 oxvgenation, 308. 
 
 reducing power, 350, 357. 
 ; Pharmacist gold-mine, Cripple Creek, 
 
 Colo., 422, [819]. 
 
 Philips: deposition of copper from sea- 
 water, 258. 
 
 Philipsburg, Mont.: gold-deposits, 814. 
 Phillips, J. A.: banded structure in ore- 
 deposits, 57. 
 
 ore-deposits in vadose region, 171. 
 
 Treatise on Ore-Deposits, [5, 12]. 
 Phillips and Lewis: ore-deposits, [282]. 
 
 pegmatite-dikes at Timbarra, New 
 
 South Wales, 276. 
 
 Phosphate-deposits: formation, 114-115. 
 Phosphates: in mine-waters, 770. 
 Phosphorus : distribution in igneous rocks, 
 749. 
 
 in Lake Superior iron-ores, 652. 
 
 quantity in igneous rocks, 733. 
 Piesoclases : definition, 40. 
 Pilot fault, Leadville, Colo., 48. 
 Pilot Knob. Mo., iron-ores : occurrence, 87. 
 Pirsson, L. V.: radial dikes. 394. 
 Placer-deposits (see also Gold-deposits), 
 
 133, 134. 
 
INDEX. 
 
 947 
 
 Placers : distribution in western America, 
 435. 
 
 relation to manganiferous gold-depos- 
 its, 805. 
 
 Plant- remains, Jasper county, Mo., 329. 
 Plasticity of rock -masses, 44. 
 Platinum: association with gold in Urals, 
 289. 
 
 distribution in igneous rocks, 753. 
 
 in basic rocks, 285. 
 
 in igneous rocks, 269. 
 Plication of rock masses, 44. 
 Pneumatolysis : definition, 205. 
 Pneumatolytic origin of ore-deposits, 240. 
 Pneumatolytic vapors : action, 388. 
 Pocatello mine, Mineral ridge, Nev., 613. 
 Pointer mine, Cripple Creek, Colo., 420. 
 Pontgibaud, France: silver-lead veins, 
 
 226. 
 Porphyry : in Norbotten ore-fields, 675. 
 
 percolation by water, 13. 
 
 white : Leadville, Colo.: condition and 
 
 composition, 18. 
 
 Leadville, Colo.: source of ore-materi- 
 als, 18. 
 
 Porphyry Dike mine, Rimini, Mont., 221. 
 Portland mine, Cripple Creek, Colo., 419. 
 Posepny, Franz : Genesis of Ore-Depos- 
 its, v, vii, xiii, 86, 171, 696. 
 
 gold in stratified formations, 200. 
 
 metals in water of springs, [70d]. 
 
 origin of Sudbury nickel-ores, 485. 
 Potash : quantity in igneous rocks, 732. 
 Pre-Cambrian gold-deposits, 434. 
 
 production, 435. 
 
 Pre-Cambriau series of the Lake Supe- 
 rior region, 634. 
 Precious metals : greater abundance in 
 
 vadose region : cause, 206. 
 Precipitation : circumstances favoring, 30. 
 
 of mineral solutions: causes, 37. 
 
 ore-materials : conditions favoring, 35. 
 Pressure : in relation to jointing, 94, 
 
 r61e in ore-deposition, 2. 
 PRICHARD, W. A.: Observations on Mother- 
 Lode Gold-Deposits, California [Trans., 
 
 xxx iv, 454-466], Notice, 830. 
 Prime, F.: on Appalachian iron-ores, 36. 
 Principles Controlling Ore- Deposition (VAN 
 
 HISE), xvii. 
 Promontorio Silver-Mine, Durango, Mexico 
 
 (LINCOLN), 834. 
 Prophylitic veins : definition, 438. 
 
 gold-production, 441. 
 Puerticitos mine, Cananea, Mexico, 378, 
 
 398. 
 
 Pumpelly, R.: copper of Lake Superior 
 region, xxxviii. 
 
 genesis of copper-deposits in Lake Su- 
 perior region, 76. 
 
 Purington, C. W. : ore-deposits of San 
 Juan region, Colo., 818. 
 
 source of useful metals, 716. 
 Pyrite : as primary constituent of rocks, 
 203, 212. 
 
 behavior with carbonate solutions, 409. 
 
 chemical reactions with chalcocite, 
 [799]. 
 
 crystallization from magmas, 609. 
 
 effect on solubility of galena [766]. 
 
 in eruptive rocks, 70. 
 
 Pyrite: precipitating-agency, 232. 
 
 reducing action, 405. 
 
 reducing power, 352, 357, 358. 
 Pyrolusite: association with gold, 793. 
 Pyroxenes : in rocks of New Zealand : 
 
 analyses, 167. 
 Pyrrhotite: analyses, 460. 
 
 composition and formula, 458, 475. 
 
 Deadwood, S. D., 316. 
 
 in diorite, 90. 
 
 origin, 460. 
 
 relation to chalcopyrite, 513. 
 
 reducing power, 355, 358. 
 Pyrrhotite-deposits : Rossland, B. C., 486. 
 Pyrrhotites : associated minerals, 478. 
 
 classification, 477. 
 
 geological relations, 477. 
 
 Quartz: crystallization from magmas, 609. 
 
 Quartz-porphyry : Cripple Creek district, 
 Colo., 412. 
 
 Quartz-veins : origin, 275. 
 
 origin as magmatic segregations, 275. 
 
 Quarts- Veins of Silver-Peak, Nevada (HAST- 
 INGS), xxvi. 621-628. 
 
 Quebec : pyrrhotite, 462. 
 
 Queensland : gold-quartz veins, 282. 
 
 Queen of the West mine, Ten-mile dis- 
 trict, Colo.: structural conditions, 62. 
 
 Quicksilver, associated with petroleum, 
 344. 
 
 Quicksilver-deposits : alteration, 134. 
 genesis, 79. 
 Mirabel mine, Lake county, Cal., 79. 
 
 Racine Boy claim: Silver Cliff, Colo., 
 
 [140], 
 
 Radioactive water: analyses, 709. 
 Rainfall run-off, and evaporation : rela- 
 tion in Colorado, 698. 
 
 Rainy River district, Ontario: gold-de- 
 posits, 445. 
 
 RANSOME, F. L.: The Geology and Copper- 
 Deposits of Bisbee, Arizona [Trans., 
 xxxiv, 618-642]. Notice, 829. 
 association of gold with manganese, 
 
 [781]. 
 
 gold-deposits, Goldfield, Nev., 825. 
 gold-deposits, Mother Lode district, Cal., 
 
 811. 
 
 gold-deposits, San Juan region, Colo., 818. 
 manganese as indication of rich ore, 787. 
 Ransome, F. L., and Lindgren, W.: gold- 
 deposits, Cripple Creek, Colo., 819. 
 Raven mine, Cripple Creek, Colo., 420. 
 RAYMOND, R. W.: Preface, v. 
 
 Discussion on The Torsional Theory of 
 
 Joints, 101-103. 
 
 charcoal between lava flows, 319. 
 Geological Distribution of Mining Dis- 
 tricts in the United States, [65]. 
 gold-deposits, Summit district, Colo., 
 
 [823]. 
 
 King's meridional zones of mineral- 
 deposits, [81], 
 
 origin of ore-deposits, [242]. 
 Reports on Mines and Mining West of 
 
 the Rocky Mountains, [764]. 
 READ, T. T.: 'The Secondary Enrichment of 
 Copper-Iron Sulphides [Trans., xxx vii, 
 297-303], Notice, 832. 
 
948 
 
 INDEX. 
 
 Real del Monte district, Mexico : compari- 
 son with Tonopah, Nev., 601. 
 Receptacles for ore-deposition : charac- 
 ter, 30. 
 Recrystallization process: San Jose, Ta- 
 
 maulipas, Mexico, 575. 
 Red Cliff region, Colo.: ore-deposits, 36. 
 Red Mountain, Ouray county, Colo.: oc- 
 currence of ore, 831. 
 
 ore-deposits, 31-32. 
 Red Spruce mine, Cripple Creek, Colo., 
 
 429. 
 Reducing action of volatile hydrocarbons, 
 
 346. 
 
 Reducing power of minerals, 347, 357. 
 Reid, J. A.: analyses of vadose waters : 
 Com stock lode, 802. 
 
 silver-content of mine-waters, 800. 
 Repeated movements along fissure-planes, 
 
 59. 
 Replacement-deposits : Rocky mountains, 
 
 10. 
 
 Replacement iron-deposits : Appalach- 
 ians, 36. 
 
 Replacement-theory : ore-deposits, 8, 9. 
 Rhodochrosite : reducing power, 358. 
 Rhyolite: near Silver Cliff, Colo., 139, 
 
 143, 157. 
 
 Rhyolite-dacite: Tonopah, Nev., 592. 
 Richthofen, F. von : genesis of Comstock 
 lode, ix, 85. 
 
 mineralization of the Comstock lode, 
 598. 
 
 Natural Classification of Eruptive 
 Rocks, [ix]. 
 
 production of Comstock lode, 803. 
 
 proportion of gold to silver in Com- 
 stock lode, 802. 
 
 Rickard, T. A.: bonanzas in gold-veins, 
 [797]. 
 
 formation of bonanzas, 761. 
 
 mineral veins varying with country- 
 rock, 226 
 
 ore-deposits of Rico, Colo., [3301. 
 
 origin of ores of Bendigo reefs, Aus- 
 tralia, [208]. 
 
 reduction of ore-bodies by black shale, 
 331, 332. 
 
 solution of gold, 773. 
 
 vein-structure, 221. 
 
 vertical distribution of ores, [407]. 
 Rico, Colo., veins, 226. 
 RITTER, E. A.: The Evergreen Copper-De- 
 posits, Color ado [Trans., xxxviii, 751-765], 
 
 Notice, 835. 
 Robertson : analyses of rocks of Missouri, 
 
 [209]. 
 Rock-flowage: locus and conditions, 711. 
 
 relation to earthquakes, 712. 
 Rock-fracture : causes, 41. 
 
 effect on water-channels, 34. 
 Rock -fractures : character and extent, 39. 
 
 classification, 40. 
 
 complexity, 92. 
 
 Rock-intrusions (see Intrusions). 
 Rock -masses : plication and fracture, 44. 
 
 rigidity and plasticity, 43. 
 Rocks: changes due to contact meta- 
 morphism, 384. 
 
 crystalline: classification, 68. 
 determination of age, 68. 
 
 Rocks : eruptive : analyses, 705. 
 emissions, 236. 
 geological age, 66. 
 
 Leadville, Colo.: mode of eruption, 18. 
 source of ore-materials, 15. 
 tests for ore-materials, 16. 
 source of vein-materials, 20-22. 
 Tamaulipas, Mexico, 561. 
 gaseous content, 767. 
 igneous: average composition, 734. 
 central Sweden, 657. 
 
 origin, 659. 
 chlorine-content, 767. 
 crystallization : order in, 261. 
 derivation from refusion of stratified 
 
 rocks, 21. 
 
 determination of age, 67. 
 general chemical composition, 730, 734. 
 geological age, 66. 
 origin, 67, 259. 
 Role in the Formation of Veins (KEMP), 
 
 xix. 
 
 segregation or differentiation, 259. 
 superficial : lack of ore-materials, 20. 
 influence on vein-structure, 217. 
 New Zealand : examination, 167-168. 
 permeability to water, 29. 
 Queensland : examination, 168. 
 salts in waters of non-calcareous, 764. 
 secular decay, 112. 
 sedimentary, at Leadville, Colo.: tests 
 
 for ore-materials, 16-17. 
 distribution of metals, 254. 
 stratified : derivation from igneous 
 
 rocks, 21. 
 
 Victoria ; examination, 168. 
 Rock -segregation : unknown finer laws,265 
 Rohn, Oscar : Bullfrog and Kawich dis- 
 tricts, Neyada, 600. 
 Rolker, Charles M.: ore-deposits at Lead- 
 
 ville, Colo., 13. 18. 
 
 Roscoe and Schorlemmer : analysis of sea- 
 water, [195]. 
 Rose, G.: forms of gold from precipitation, 
 
 105. 
 
 specific gravities of gold, 106. 
 Rosenbusch, H.: contact-metamorphic 
 
 phenomena, 524. 
 
 Rosita. Colo.: Mines (EMMONB), 139-161. 
 Rosslaud monzonite, Rossland, B. C., 495. 
 J Rossland, B. C.: pyrohotite-deposits, 486. 
 Rotation in faulting. 102. 
 Rothwell, R. P.: charcoal in silver-bear- 
 ing sandstones, 319. 
 Silver Reef district, Utah, 326. 
 j Rounding of rock-fragments: origin, 46. 
 RUMBOLD, W. R.: The South African Tin- 
 Deposits [Trans., xxxix, 783-789.], No- 
 tice. 832-833. 
 
 The Tin-Deposits of the Kinta Valley, Fed- 
 erated Malay Nates [Trans., xxxvii, 
 879-889], Notice, 832. 
 Rupture : angle of, 104. 
 by shear, 98. 
 torsion al : character, 99, 
 Rupture-surfaces, experimentally pro- 
 duced, 97. 
 
 Russell, Clarence : compilation of analy- 
 ses, 763, 765. 
 
 Rutile : occurrence in veins of Alaska, 
 586, 587. 
 
INDEX. 
 
 949 
 
 Saline deposits : formation, 115. 
 
 Salisbury mine, Silver Peak district, Ne- 
 vada, 627. 
 
 Salt : in sedimentary rocks, 766. 
 
 Sandberger, F.: derivation of vein-ma- 
 terials, 22. 
 genesis of ore-deposits, 14, 86, 204. 
 
 Sandstone : chlorine-content, 766. 
 
 San Jose district, Tamaulipas, Mexico : 
 
 geology, 559. 
 geological map, 560. 
 ore-deposits, 237. 
 situation, 559. 
 
 San Jose deposits, Tamaulipas, Mexico : 
 map showing location, 558. 
 
 San Juan region, Colo.: fissure-faulting, 50. 
 gold-deposits, 818. 
 
 Sankowsky, Nicholas : compilation of an- 
 alyses, 763, 765. 
 
 San Pedro, N. M. : ore-deposits, [238] . 
 
 Savant lake, Ontario : gold-deposits, 446. 
 
 Saxony : Berggiesshiibel ore-deposits, 378. 
 Freiberg : Gottlob vein, 218. 
 
 Scandinavian Iron-Ores, The Geological 
 Relations o/[Sj6GREN), xxvi, 657-695. 
 
 Scandinavian lake- and bog-ores : distri- 
 bution and origin, 694. 
 
 Scheerer: amount of water in magmas, 
 608. 
 
 Schmitz, E. J.: copper-ores in the Per- 
 mian of Texas, 327. 
 
 Schneider, E. A.: experimental tests on 
 colloidal sulphides of gold, [xxiv]. 
 
 Schrader and Brooks: quartz-veins in 
 Nome region, Alaska, 280. 
 
 SCHWARZ, T. E.: Features of the Occurrence 
 of Ore at Red Mountain, Ouray County, 
 Colo. [Trans., xxxvi, 31-39], Notice, 831. 
 
 Science of Ore-Deposits : Bibliography 
 (IRVING, SMITH, FERGUSON). 837-928. 
 
 Scientific method of study, 70. 
 
 Scotland : Sutherland gold-fields, 281. 
 
 Secondary concentration : ore-deposits, 74. 
 Sudbury, Ont., ore-deposits, 90. 
 
 Secondary enrichment : Copper-Iron Sul- 
 phides (READ), 832. 
 criteria for recognition, 791. 
 gold-deposits, 761. 
 of metals, 785. 
 ore-deposits, 326. 
 sulphide ores, xl. 
 
 Secular contraction of earth's crust, 42. 
 
 Security-Geyser mine : Silver Cliff, Colo., 
 142. 
 
 Sedimentation : agency in producing 
 water-channels, 33. 
 
 Sediments : aggregate thickness, 22. 
 
 Segregation of igneous rocks: laws, 261. 
 
 Segregation of rock materials : cause, 260. 
 
 Selenium : mode of occurrence, 326. 
 occurrence in Silver Reef, Utah, sand- 
 stones, 325. 
 relations to igneous rocks, 754. 
 
 Selwyn, A. R. C.: auriferous rocks of Vic- 
 toria, 163. 
 
 Se'narmont : synthetic experiments. [2]. 
 
 Sentinel mine, Silver Peak district, Ne- 
 vada, 626. 
 
 Serpentine : metamorphic origin, 75. 
 
 Sewell, H.: silver-ore associated with coal, 
 321. 
 
 Shale : oxidation, 536. 
 Shaler, N. S.: origin of limonites, 124. 
 Shales : chlorine-content, 766. 
 Sheeting of country-rock, 46, 47. 
 Shuler, D. P. : magnetic separation of 
 
 nickel-ores, 469. 
 Siderite : reducing power, 358. 
 Silica : in mine-waters, 770. 
 
 quantity in igneous rocks, 732. 
 Silver : association with gold, 182. 
 
 assays, [17], 161. 
 
 determination of small amounts in sea- 
 water, 829. 
 
 distribution in igneous rocks, 752. 
 
 in assays of California rocks, 301. 
 
 in mine-waters, 800. 
 
 in rocks of New Zealand, 170. 
 
 in sea-water, 191. 
 
 native: in Lake Superior district, 76. 
 
 precipitation by black shales, 331. 
 
 removal by solution, 116. 
 
 salts: reactions, 115. 
 
 tests for : in rocks at Leadville, Colo., 
 
 16-17. 
 Silver City district, Iduho: comparison 
 
 with Tonopah, Nov., 601. 
 Silver Cliff, Colo.: country-rock : assays 
 for silver, 161. 
 
 investigations of country-rocks, 23. 
 
 Mines (EMMONS), xvi, 139-161. 
 
 mines in rhyolite : geology, 139. 
 
 ore-deposits : genesis, 155. 
 
 silver-mines : production, 141. 
 
 surface-deposits, 140. 
 
 Silver Cliff and Cripple Creek ore-depos- 
 its compared, 158. 
 Silver-deposits: alteration, 131. 
 
 association with eruptive rocks, 80. 
 
 Colorado: Silver Cliff region, 157. 
 Bassick mine, 158. 
 Ben Eaton mine, 157. 
 Bull-Domingo mine, 158. 
 Democrat mine, 157. 
 genesis, 155. 
 Summit district, [823]. 
 
 concentration, 80. 
 
 New Mexico, Lake Valley : genesis, 835. 
 Silver-gold and gold-silver ores : vertical 
 
 relations in deposits, 799. 
 Silver-gold deposits : associated minerals, 
 825. 
 
 Nevada: Tonopah, 824, 
 Silver-gold mines (see also Gold-silver 
 mines) : 
 
 Mizpah, Tonopah, Nev., [825]. 
 
 Montana-Tonopah, Tonapah, Nev., 
 
 [825]. 
 
 Silver-gold ores : Comstock lode, Nev., 800. 
 Silver-Islet mine, Lake Superior, 231. 
 
 gas-flows, 346. 
 
 Silver-lead deposits : Colorado : George- 
 town and Silver Plume, 816. 
 
 in dolomitic limestone, 1. 
 Silver-lead-gold deposits: Leadville, Colo., 
 
 815. 
 Silver-lead mines, Neihart, Mont., 219, 
 
 220. 
 Silver Ledge, Mercur district, Utah: 
 
 origin, 290. 
 Silver-mine : Mexico, Durango (Promon- 
 
 torio), 834. 
 
950 
 
 INDEX. 
 
 Silver-mine waters : salts in, 764. 
 
 Silver-ore: Leadville, Colo., 800. 
 
 Mineral ridge, Nevada : genetic rela- 
 tions, 613. 
 mode of occurrence, Silver Cliff, Colo., 
 
 140. 
 
 Neibart, Mont., 800. 
 Silver Cliff, Colo.: treatment, 141. 
 
 Silver-ores of West : origin, 136. 
 
 Silver Peak, Nevada : geology and ore- 
 deposits, 622, 
 gold-deposits, 813. 
 ore deposits : origin, 628. 
 Quartz-Veins (HASTINGS), xxvi, 621-628. 
 
 Silver Peak quadrangle, Nevada : geol- 
 ogy, 603. 
 mineral veins, 607. 
 
 Silver Eeef ore-deposits, 36. 
 
 Silver-salts : solubilities, 800. 
 
 Silver-veins, Butte, Mont., 223, 
 
 Silvestri, O.: copper in volcanic fumes, 
 721. 
 
 Similkameen type of ore-deposits, 383. 
 
 Sinter : analyses, 149, 629. 
 
 Sinters: Geyser mine, Silver Cliff, Colo., 
 148. 
 
 Sjogren, A.: iron -ores of Taberg, Sma- 
 land, 681. 
 
 SJOGREN, HJALMAE: The Geological Re- 
 lations of the Scandinavian Iron-Ores, 
 jxxvi, 657-695. 
 
 Skarn : definition, 657. 
 
 Skolar : formation, 669. 
 
 "Slickenside"-surfaces : fissures, 45. 
 
 Slickensiding: in joints, 93. 
 
 Smith, Alexander : chemical reactions in 
 
 solution of gold, [777]. 
 chemistry of manganese, 780. 
 
 SMITH, H. D., IRVING, J. D., FERGUSON, 
 H. G. : Bibliography of the Science of Ore- 
 Deposits, 837-928. 
 
 SMITH, GEORGE: The Garnet Formations 
 of Chillagoe Copper-Field, North Queens- 
 land, Australia [Trans., xxxiv, 467-478], 
 Notice, 830. 
 
 Smith, J. Alden : deposition of ores by 
 ascending solutions, 12. 
 
 Smyth, R. Brough : gold-fields of Vic- 
 toria, 171. 
 
 Soda: quantity in igneous rocks, 732. 
 
 Soda mine, Silver Peak district, Nevada, 
 627. 
 
 Solfataras : source of ores, 84. 
 
 Solution chambers : formation, 5. 
 
 Solutions: role in ore-deposition, 2. 
 
 Some Practical Suggestions Concerning the 
 Genesis of Ore-Deposits (BOEHMER), 829- 
 830. 
 
 Songbird mine; Silver Cliff, Colo., [140]. 
 
 Sonstadt, E.: gold in sea- water, 192. 
 methods of detecting gold in sea-water, 
 193. 
 
 Sonstadt's solution : disadvantages, 166. 
 
 Soret's principle of cooling solution, 67. 
 
 Soret's principle of molecular flow, 260. 
 
 South African Tin-Deposits (EUMBOLD), 
 832-833. 
 
 Southern Klondike district, Nevada, ore- 
 deposits, 618. 
 
 Spaltenverwerfungen (fissure-faults) -.def- 
 inition, 41. 
 
 SPENCER, A. C.: Geology of the Treadwell 
 Ore-Deposits, Treadwell Island, Alaska 
 [Trans., xxxv, 473-510], Notice. 830. 
 The Magmatic Origin of Vein-Forming 
 Waters in Southeastern Alaska, xxvi, 
 582-589. 
 
 The Origin of Vein-Filled Openings in 
 Southeastern Alaska [Trans., xxxvi, 
 581-586], Notice, 831. 
 Treadwell gold-mines, Alaska, [811]. 
 Sperrylite: in diorite, 90. 
 
 Sudbury district, Ontario, 463. 
 Spherulites : Silver Cliff, Colo., 140. 
 Spring waters : analyses, 706. 
 Springs : Nevada region : source, 597. 
 
 production, 33. 
 
 SPURR, J. E.: A Consideration of Igneous 
 Rocks and their Segregation or Differen- 
 tiation as Related to the Occurrence of 
 Ores, xxii, 251-303. 
 Genetic Relations of the Western Nevada 
 
 Ores, xxvi, 590-620. 
 convection currents in magmas, 260. 
 differentiation in igneous rocks, 261. 
 gold-deposits, Silver Peak, Nov., [813]. 
 magmatic differentiation, 722. 
 metallographic provinces, 756. 
 ore-deposits of Silver Peak quadrangle, 
 
 621. 
 
 silver-gold deposits, Tonopah, [824]. 
 Spurr and Garrey : ore-deposits of George- 
 town, Colo., 8i6, 817. 
 
 Spurr, Garrey, and Ball : silver-lead depos- 
 its, Georgetown and Silver Plume, Colo., 
 [816]. 
 
 Stallberg mines, Sweden : plan, 664. 
 Standard mine, Bodie, Cal.: vein-system, 
 
 833. 
 
 Steamboat Springs, Nevada : ore-deposi- 
 tion, 86. 
 stibnite at, 629. 
 
 Stelzner: origin of ore-deposits, [201]. 
 Step-faults, Leadville, Colo., 49. 
 Sternbeck, E. von : specific gravity of 
 
 earth, 715. 
 
 Stetefeldite, Mineral ridge, Nevada, 614. 
 STEVENS, E. A.: Basaltic Zones as Guides 
 to Ore-Deposits in the Cripple Creek Dis- 
 trict, Colorado, xxiii, 411-423. 
 Stevens, Hazard : ascent of Mt. Eainier, 
 
 [xxxiii]. 
 Stibnite : at Steamboat Springs, Nevada, 
 
 629, 631. 
 
 reducing power, 354, 358. 
 Stobie mine, Blezard township, Sudbury 
 
 district, Ontario, 499. 
 photomicrographs of ore, 487-488. 
 Stokes, H. N.: action of pyrite and mar- 
 
 casite, 409. 
 reaction with pyrite in production of 
 
 chalcocite, 799. 
 solution of gold, 771, 772. 
 Stratification : agency in producing water- 
 channels, 33. 
 
 Stretch, E. H. : "compression-veins," 221. 
 mineral-veins varying with country- 
 rock, 225. 
 
 vein-contents and country-rock, 233. 
 Striations : fissures, 45. 
 Stringers: definition, 51. 
 Strong mine, Cripple Creek, Colo., 419. 
 
INDEX. 
 
 951 
 
 Strontium : distribution in igneous rocks, ] 
 747. 
 
 quantity in igneous rocks, 733. 
 Stutzer, O.: genesis of iron-ores of Nor- ! 
 
 botten, Sweden, 678. 
 
 Styria : iron-deposits: surface-action, 126. 
 Sublimation theory of ore-deposition, 2, 
 
 204. 
 
 Substitution theory: ore-deposits, 8. 
 Subterranean water : limiting depth, 44. j 
 Subterranean waters : Geyser mine, Sil- 1 
 
 ver Cliff, Colo., 148. 
 Sudbury district, Ontario : metamorphism, 
 
 514. 
 
 Sudbury, Ontario, nickel-region : miner- 1 
 als, 456. 
 
 nickel-deposits, 90-91. 
 geology, 479, 481. 
 
 nickel-ores : genesis, 477. 
 
 Ore-Deposits (DiCKSON), xxiv-xxv, 455- 
 
 516. 
 
 Sudbury mattes: composition, 465. 
 Sudbury ores: assays, 464. 
 
 origin : microscopical evidence, 497. 
 Suess, Eduard : formation of mineral ! 
 veins by gaseous emanations, 389. 
 
 gold resources of the world, 425. 
 
 hot springs of Carlsbad region, 369. 
 
 ore-deposits derived from igneous ema- 
 nations, [368]. 
 
 origin of ore-deposits, 391. 
 Sullivan, E. C.: chemical relations of iron 
 and manganese in rocks, 795. 
 
 experimentation on copper-iron sul- 
 phides, 832. 
 
 Sulphates : effect on solution of gold, 772, 
 775. 
 
 in mine-waters, 766. 
 
 solution and precipitation of mangan- 
 ese by, 795. 
 
 Sulphide secondary enrichment : ore-de- 
 posits, xvii. 
 Sulphides : alteration, 2. 
 
 deep : formation, 183, 
 
 in rocks, 163. 
 
 secondary: definition, 183. 
 Sulphur: distribution in igneous rocks, 750. 
 
 quantity in igneous rocks, 734. 
 
 reducing power, 307, 351, 357. 
 Sulphuretted hydrogen: reducing power, 
 
 352, 357. 
 Summary of Lake Superior Geology with 
 
 Special Reference to Recent Studies of the 
 
 Iron-Bearing Series (LEITH), xxvi, 633- 
 
 656. 
 
 Summit district, Colo.: gold-deposits, 822. 
 Summit gold-mine, Cripple Greek, Colo., 
 
 [819]. 
 Sunrise gold-mine, Macetown, 1ST. Z.: 
 
 assays, 184. 
 
 Sunrise mine: Silver Cliff, Colo., [140]. 
 Superficial Alteration of Ore-Deposits (PflN- 
 
 KOSE), xv. 
 
 Surface-alteration : varying depths, 121. 
 Surface-waters : definition, 6. 
 
 varying action on ore-deposits, 116. 
 Sutro, A.: genesis of Conistock lode, x. 
 Svartvik mines, Sweden : section, 665. 
 Sweden : map of ore-province, 658. 
 
 titaniferous iron-ore : concentration in 
 magmas, 72. 
 
 Swedish iron-deposits : lake region : con- 
 centration, 127. 
 
 Syenite : in Norbotten ore-fields, 675. 
 treatment for isolation of hornblende, 
 165. 
 
 Synclases : definition, 40. 
 
 Taberg, Sweden, iron-district: map, 683. 
 Taberg mines, Sweden: origin of iron- 
 ores, 668. 
 
 Telluride type of ore-deposits, 372. 
 Tellurium : relations to igneous rocks.. 
 754. 
 
 reducing power, 358. 
 Temperature: increase with depth, 246. 
 
 of descending column of water, 245. 
 
 of fluid magmas, 724. 
 
 rate of increase in earth's crust, 713. 
 Ten-Mile district, Colo.: investigations of 
 country-rocks, 23. 
 
 ore-deposits, 36. 
 Tephrite : Cripple Creek district, Colo.: 
 
 412. 
 
 Tertiary gold-deposits, 438-441. 
 Tertiary volcanic rocks, Tonopah, Nev., 
 
 591. 
 
 Tetrahedrite : reducing power, 358. 
 Thames district, N. Z. : vadose and deep 
 
 vein-gold : assays, 185. 
 Thermal springs : ore-deposition, 406. 
 Thompson mine, Cripple Creek, Colo., 
 
 420. 
 
 Thomsen, J.: chemical properties of gold, 
 107. 
 
 forms of gold from precipitation, 105. 
 Thorium : distribution in igneous rocks, 
 
 749. 
 
 Thunder Bay, Canada, silver- veins, 231. 
 Tibbey, B.: hydrocarbon -gas in Illinois 
 
 mine, Montana, 346. 
 Tiberg, H. V., iron-ores of Sweden, 665, 
 
 669. 
 
 Time in geologic operations, 700. 
 Tin : distribution in igneous rocks, 753. 
 
 in siliceous rocks, 285. 
 Tin chloride test for gold, 194. 
 Tin-deposits : Alaska, Cape Prince of 
 Wales : geology and mining, 833. 
 
 alteration, 133-134. 
 
 Kinta Valley, Federated Malay States 
 
 (EUMBOLD), 832. 
 
 South African, 832. 
 Tin-veins : occurrence, 287. 
 Tiuguaite : San Jose, Tamaulipas, Mexico, 
 
 565. 
 Tipperary Premier gold-mine, Macetown, 
 
 N. Z.: assays, 184. 
 
 Titaniferous iron-ore : concentration in 
 magmas, 72. 
 
 Norway, 72. 
 
 Sweden, 72. 
 Titanium : distribution in igneous rocks, 
 
 749. 
 Titanium dioxide : quantity in igneous 
 
 rocks, 733. 
 
 Tomboy gold-mine, Silverton, Colo., [818]. 
 Tonopah, Nevada: geology, 591. 
 
 mineral veins, 593. 
 
 silver-gold deposits, 824. 
 Topography : effect on depth of altera- 
 tion, 120. 
 
952 
 
 INDEX. 
 
 Tornado mine, Cripple Creek, Colo., 420. 
 Tornebohm : iron-ores of Taberg, Sma- 
 
 land, 681. 
 Torsion : effects, 51. 
 
 experiments on glass plates, 95 
 
 of rock-masses, 45. 
 Torsion-fractures : character, 95. 
 Torsional rupture : character, 99. 
 Torsional Theory of Joints (BECKER), xiii, 
 
 92-104. 
 
 Tourmaline : occurrence in ores, 586. 
 Toyabe range, Nevada: ore-deposits, 617. 
 Travers, M. W.: origin of gas in mineral 
 
 substances, 389. 
 Tread well gold -silver mine, Douglas 
 
 Island, Alaska, 811, 
 Treadwell ore-deposits : Alaska, Douglas 
 
 Island, 830. 
 Tremolite : San Jose, Tamaulipas, Mexico, 
 
 569. 
 
 Triumph mine, Cripple Creek, Colo., 419. 
 Tungsten in siliceous rocks, 285. 
 Tuollavaara iron-ore deposits : Sweden, 
 
 673. 
 
 Turner, A. T. : Sudbury mattes, 465. 
 Turner, H. W.: field-work in Silver Peak 
 region, Nevada, 604. 
 
 quartz-veins at Silver Peak, Nevada, 
 276. 
 
 Ulrich, G. H. F.: auriferous rocks of Vic- 
 toria, 283. 
 
 rocks of Otago peninsula, N. Z., 166. 
 Uncle Sam mine, Tintic district, Utah, 
 
 339, 340, 343. 
 
 Underground water : agency in forma- 
 tion of Lake Superior iron-ores, 644. 
 
 circulation : factors, 237. 
 
 derivation, 236. 
 
 direction of flow, 14. 
 Union Belle mine, Cripple Creek, Colo., 
 
 420. 
 
 United States Geological Survey : found- 
 ing, [xxxiii]. 
 Urals : relations of gold and platinum, 
 
 289. 
 Uranium : distribution in igneous rocks, 
 
 749, 
 Utah, Dry Canon, Mono silver-mine, 332. 
 
 Mercur district: gold-production, 437. 
 vein system, 290. 
 
 Silver Eeef : geologic structure, 325. 
 ore-deposits, 322. 
 silver-ore in sandstone, 320. 
 
 Tintic district ore-deposits, 335-340, 362. 
 
 Vadose country-rock at different distances 
 from auriferous lodes : examination, 183. 
 
 Vadose region : greater richness of gold- 
 deposits, 171. 
 
 Vadose waters, xiv. 
 
 Valcalde mines, Silver Peak district, 
 
 * Nevada, 626. 
 
 Vanadium : association with coal, 321. 
 distribution in igneous rocks, 750. 
 in basic rocks, 285. 
 
 Vanderbilt mine, Mineral Eidge, Nev., 
 613. 
 
 Vanderbilt mine : Silver Cliff, Colo., [140]. 
 
 Van Diest, E. C. and P. H.: Eito Seco 
 gold-deposits, Costilla county, Colo., 447. 
 
 Van Hise, C. E.: classification of Algon- 
 kian rocks, 69. 
 
 critical temperature of water, 713. 
 
 development of rocks of Lake Superior 
 region, 648. 
 
 fissures at Cripple Creek, Colo., 221. 
 
 formation of secondary copper sul- 
 phides, 533. 
 
 genesis of ore-deposits, [252]. 
 
 iron-ores : origin, 70. 
 
 magnetite in magmas, 72. 
 
 meteoric waters, 240. 
 
 origin of iron-ores of Michigan and 
 Wisconsin, 124. 
 
 origin of pegmatite, 275. 
 
 principles of ore-deposition, xvii, [235], 
 696, [761]. 
 
 zone of flowage, 699, 711. 
 
 zone of fracture, 711. 
 Veins: comb-structure, 10. 
 
 dependence on rock-structure, 217. 
 
 derivation of mineral contents, 14. 
 
 frequency, 248. 
 
 productive : explanation, 718. 
 
 relation to trap rocks, 20. 
 
 view of older geologists as to their 
 
 nature, 84. 
 Vein-enrichment : by Ascending Hot 
 
 Waters (WEED), xxiii, 403-410. 
 Vein-fissure : Ontario mine, Utah, 61. 
 Vein-material : source, 53, 161. 
 Vein-materials: derivation from adjoin- 
 ing rocks, 22-24. 
 
 derivation from eruptive rocks, 19-22. 
 
 Leadville, Colo.: source, 16. 
 Vein -structure: influence of rocks. 217. 
 Vein-system : Cornwall, England, [52]. 
 
 Erzgebirge, Freiberg, Saxony, 52. 
 
 Standard Mine, Bodie, Gal. (BROWN), 833. 
 Vein-systems : age and relations, 290. 
 Vein-walls: structural features, 54. 
 
 Butte, Mont., 55. 
 
 Gunnison region, Colo., 55. 
 Vermilion Creek Basin, Wyoming : dia- 
 mond swindle, [xxxiii]. 
 Vermilion iron range: vertical section, 640. 
 Vermilion Eiver, Ontario : gold-deposits, 
 
 445. 
 Vesuvianite : San Jose, Tamaulipas, 
 
 Mexico, 572. 
 
 Victor mine, Cripple Creek, Colo., 423. 
 Victoria : gold-quartz veins, 282. 
 Victoria mine, Deuison Township,Sudbury 
 district, Ontario, 505. 
 
 photomicrographs of ore, 490. 
 Vindicator mine, Cripple Creek, Colo., 422. 
 Virginia : .Virgilina : copper-veins, 220. 
 Vogelsang, H.: petrographic provinces, 
 
 737. 
 Vogesite : San Jose, Tamaulipas, Mexico, 
 
 567. 
 Vogt, J. H. L.: chromite in Norway, [268]. 
 
 contact-metamorphic phenomena, 525. 
 
 distribution of rare elements, 745. 
 
 genesis of ore-deposits, [253], 403. 
 
 genesis of titaniferous iron-deposits of 
 Sweden, xiii. 
 
 geology of ore-deposits, [222]. 
 
 iron-ores of Christiania region, 692. 
 
 nickel in basic rocks, 295. 
 
 origin of nickel-ores, 484. 
 
INDEX. 
 
 953 
 
 Vogt, J. H. L.: rare chemical elements, 737. 
 
 secondary enrichment, xxxix. 
 
 source of iron, 205. 
 
 titauiferous iron-ores of Norway, [111]. 
 Volcanic eruptions : sequence in connec- 
 tion with sequence of metalliferous 
 
 veins, 288. 
 
 Volcanic gas : analysis, 388. 
 Vorn Rath : Elha iron-ores, 8. 
 Von Foullon : Sudbury nickel-ores, 482. 
 Vrang, C. H.: iron-ores of Sweden, 665. 
 Vulcauism : expiring: cause of ore bodies 
 721. 
 
 relation to ore-deposits, 239. 
 
 vein forming by, 704. 
 
 WAGONER. LUTHER: The Detection and 
 Estimation of Small Quantities of Gold 
 and Silver [Trans, xxxi, 798-810], 
 Notice, 829. 
 
 assays of California rocks, 301. 
 petroleum associated with quicksilver, 
 
 344. 
 Walferdin : temperatures in earth's crust, 
 
 714. 
 Walhalla, Victoria, gold-bearing rocks: 
 
 analyses, 186. 
 gold in country-rock : curves showing, 
 
 192, 193. 
 
 vadose country-rock : analyses, 186. 
 Walker, T. L. : sperrylite associated with 
 
 chalcopyrite, 463. 
 Sudbury nickel-ores, 484. 
 Wallace mine, near Whitefish River, ! 
 
 Ontario, 508. 
 
 Wall-pyrite : origin and content, 207, 214. j 
 Wall-rocks: permeability to solutions, 207. 
 Walls (see Vein-walls). 
 WASHINGTON, H. S.: The Distribution of j 
 the Elements in Igneous Rocks, xxviii, 
 726-758. 
 
 analysis of analcite-tinguaite, 566. 
 analysis of nephelite-syenite, 562. 
 Washoe, Nev.: investigations of country- 
 rocks, 23. 
 
 Water (see also Mine- waters) : 
 agency in producing breccia, 47. 
 amount in magmas, 608. 
 analysis, 630. 
 compression, 244. 
 descending : temperature, 245. 
 films : action in joints, 93. 
 Geyser mine, Silver Cliff, Colo.: 
 
 analyses, 150. 
 in igneous rocks, 262. 
 ingredients, 113. 
 movement in porphyry, 13. 
 oxidizing agents lost in descending, 6. 
 quantity in crystalline rocks, 733. 
 role in magmas, 731. 
 stability, 314. 
 underground : direction of flow, 14. 
 
 limiting' depth, 44. 
 velocity moving through a channel, 
 
 450. 
 
 Water-channels: in eruptive rocks, 33. 
 locus at Leadville, Colo., 13. 
 natural : causes, 33. 
 Water-courses : Geyser mine, Silver Cliff, j 
 
 Colo., 147. 
 "Water-level" : locus, 6. 
 
 60 
 
 Waters, ascending, 85. 
 
 circulating in earth's crust : channels 
 
 for, 30. 
 
 deep -seated, xiv. 
 in mines: analyses, 765, [779]. 
 salts in, 764. 
 
 silver- and gold-content, [800]. 
 natural, chlorine-content, 767. 
 vadose, xiv. 
 
 Water-table : definition and characteriza- 
 tion, 788. 
 
 relation to chemical activity, 788. 
 seasonal variation, 788. 
 WATSON, T. L.: Geology of the Virginia 
 Barite- Deposits [Trans., xxxviii, 710- 
 733], Notice, 834. 
 
 Lead- and Zinc-Deposits of the Virginia- 
 Tennessee Region [Trans., xxxvi, 681- 
 737], Notice, 831-832. 
 The Occurrence of Nickel in Virginia 
 [Trans., xxxviii, 683-697], Notice, 834. 
 Yellow Ocher Deposits of Cartersville Dis- 
 trict, Bartow County, Ga. [Trans., 
 xxxiv, 643-666], Notice, 830. 
 Wells: temperatures in, 714. 
 Wells, R. C.: reactions in dissolving gold, 
 
 777. 
 
 reactions of manganese compounds, 785. 
 services rendered by, 764. 
 WEED, W. H.: Influence of Country-Roclc 
 
 on Mineral Veins, xxi, 216-234. 
 Ore- Deposition and Vein- Enrichment by 
 Ascending Hot Waters, xxiii, 403-410. 
 Ore-Deposits Near Igneous Contacts, xxiii, 
 
 364-402. 
 Enrichment of Gold and Silver Veins, 
 
 xviii. 
 
 form of contact-deposits, 528. 
 mineral vein-formation at Boulder 
 
 Hot Springs, Montana, [247]. 
 minerals of secondary origin, [792]. 
 secondary enrichment of gold and 
 
 silver veins, [761], [815]. 
 Weed and Barrell : Elkhorn 
 
 Mont., ore-deposits, [239]. 
 Weidman, S.: origin of Baraboo iron- 
 ores, 651, 652. 
 White, David : plant-remains in Missouri, 
 
 [329]. 
 White Knob Copper Deposits, Mackay, 
 
 Idaho (KEMP and GUNTHER), 833. 
 Whitney, J. D.: locus of metalliferous 
 
 veins, 280. 
 ore-genesis, [viii]. 
 The Metallic Wealth of the United 
 
 States, [110]. 
 
 Williams, G. H. : origin of pegmatite, 275. 
 Wilson, A. D.: ascent of Mt. Rainier, 
 
 [xxxiii]. 
 
 WINCHELL, A. N.: Discussion on A Consid- 
 eration of Igneous Rocks and their Segre- 
 gation or Differentiation as Related to the 
 Occurrence of Ores, 303-304. 
 Winchell, H. V.: genesis of chalcocite at 
 
 Butte, [761]. 
 
 genesis of copper-ores, 402. 
 origin of iron-deposits of Mesabi range, 
 
 Minn., 125. 
 
 pyrite as a precipitant, 232. 
 synthesis of chalcocite, 533. 
 Thunder Bay silver-veins, 231. 
 
 district, 
 
954 
 
 INDEX. 
 
 WINSLOW, ARTHUR : Discussion on Geolo- 
 gical Distribution of Useful Metals in 
 the United States, 86-89. 
 Discussion on The Genesis of Certain 
 
 Auriferous Lodes, 208, 211. 
 lead- and zinc-deposits of Missouri, [209], 
 Wisconsin lead-ores, 334. 
 Wolf, T.: volcanic gases, 723. 
 Wollastouite : contorted zones, Durango, 
 
 Mexico, 578. 
 
 San Jose, Tamaulipas, Mexico, 570. 
 Wood lying under sea- water : examination 
 
 for gold, 197. 
 Worthington mine, Drury township, 
 
 Sudbury district, Ontario, 505. 
 photographs of sections of ore, 493. 
 Wurtz, Henry: solubility of gold in 
 ferric salts, 173. 
 
 Yankee Girl mine, San Juan region, 
 Colo., example of chimney-deposits, 
 58, 59. 
 
 occurrence of ore, 831. 
 Yellow Ocher Deposits of Cartersville 
 District, Bartow County, Ga. (WATSON). 
 830. 
 
 Yttrium : distribution in igneous rocks, 
 749. 
 
 Yukon: gold-quartz veins: formation, 
 
 272. 
 Yung and McCaffery : ore-deposits of San 
 
 Pedro district [577]. 
 
 Zenobia mine, Cripple Creek, Colo., 422. 
 Zinc: distribution in igneous rocks, 753. 
 Zinc-blende: effect of py rite on solubility, 
 [766]. 
 
 in Geyser mine, Silver Cliff, Colo., 146. 
 Zinc-deposits : alteration, 131-132. 
 Zinc: distribution in igneous rocks, 753. 
 
 genesis, 77-79. 
 
 source of material, 77. 
 
 Virginia-Tennessee region, 831. 
 Zircon : crystallization from magmas, 
 
 609. 
 
 Zirconium : distribution in igneous rocks, 
 749. 
 
 quantity in igneous rocks, 733. 
 Zirkel, F.: contact-metamorphic phenom- 
 ena, 525. 
 
 Zone of cementation, 241. 
 Zone of flowage : effect on open channels, 
 
 699. 
 Zones in ore-deposits, 789. 
 
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