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FOR OLD AND SILVE IN NORTH AMERICA. ^ *^'%^!«vv.«vif ;fi-is«KXiftf,i; BV -j4'-5 ARTHUR LAKES. :4»5isTAirr Editor " The Colliery Engineer and Mbtal Late Professor op Geology at the State School OP Mines, Gk>LDEN City, Colorado. •I Au/kor of ^* Geology of Colorado and Western Ore tVtir Deposits* *' Geology of Colorado Coal Deposits,'' Etc. ^^^H^f~ ^^^^Mp»'.'' SECOND EDITION. ^^^^^^K^-'' • *■ K^. SCRANTON, PA. '^ THE COLLIERY ENGINEER CO. 1896. mm^ - .j,^ \ „, r- tij^v y% "'fa. ^ 'I. ^ jij-X" ^'-Vfi * - - . -^.^-1 ), mmmm^mm^ i^P^refP'^v^ "•"PW^PPIPPW^ ^m^^^^mmmmmm^ ^^■ppMppippniimpn 261219 Entered according to the Act of Congress in the Year 1896 By Thk CoLLiEKV Encinekk Co., Id the Office of the Librarian of Congress, at Washingtoa. ! I PREFACE TO FIRST EDITION. In preparing thi^ little work the author has felt the diffi- culty which arises in a theoretical dissertation on so emi- nently practical a subject as prospecting. It seems like giving rules and prescriptions for hunting or fishing or any other natural or practical pursuit. Though theory and practice are not at variance when happily combined, yet either without the other proves very unsatisfactory. Thus, the reader of this book, should he start out armed only with its theory, will find himself for some time pretty much " at sea" when he comes to actual practice in the field. As. however, he gradually obtains some piactical experi- ence, he may find this little work of use to him. So, also, the seasoned prospector, who has hitherto trusted to luck, keenness of observation, intuition, and experience, may find himself in the future much better equipped by acquiring a little of the theory. Whilst we have endeavored to give the prospector all assistance in our power, as to the best means of educating himself, describing his outfit, etc., we have devoted special attention to the description of such geological and other phenomena as he is likely to meet with in connection with his work, so that he may have an intelligent idea of them when he encounters them. We have selected just as much material as we think would be most interesting and useful to him, saving him the time and trouble of wading through heavy tomes and laboriously picking out from a vast amount of, for his purpose, super- fluous matter that which he will most require. The work is intended to be a popular one, addressed to the average student, prospector, and miner, and to the general public. ARTHUR LAKES. January i, 1895. m^^^^m^i^^^mii^mmmmmmmmm ■P»"i»iP^ w^wwwwwwPi»»"»—w sssm PREFACE TO SECOND EDITION. y The kind reception given to " Prospecting for Gold and Silver" by the mining and prospecting fraternity, as well as the general public, has made necessary a second edi- tion. In this we have added to the text sketches of some of the principal prospecting regions of North America, which, besides illustrating the principles presented in the work, will, with their maps and illustrations, prove useful guides to prospectors who may venture into those districts. Having extended the scope of the work, we have accord- ingly g^ven it a more general title, namely : " Prospecting for Gold and Silver in North America." Respectfully, ARTHUR LAKES. Boston Building, Denver. Col.. October i, i8g6. CONTENTS. CHAPTER PAOB I.— On Prospecting— Preparation and Outfit for Work, 7 II.— The Prospector's Geology 25 III.— The Prospector's Paleontology or Study op Fossils 39 IV. — The Prospector's Lithology or Study of Rocks, 50 V. — The Prospector's Mineralogy 63 VI. — Ore Deposits 7a VII. — Various Forms of Ore Deposits. . • . 88 VIII. — Relation of Veins to Eruptive Forces, . . 99 IX. — Gold Placers, iii X.— "Deep Leads," 119 XI. — Mining Regions, Showing Examples of Ore De- posits 125 XII. — Ore Deposits in Sedimentary Rocks, . . .162 XIII. — Examining and Sampling Mining Properties, Pros- pects or Mines. 1&7 XIV. — Prospecting in Various Regions 198 XV. — Geology and Mineralogy of Alaska, . . . 210 XVI. — British America 213 XVII.— California, 223 XVIII. — Montana. Dakotah. Arizona, and New Mexico, 232 XIX. — The Gold of the Ortiz Mountains and Gams- teo and Rio Grande Placers. N. M., . 249 XX. — The Gold and Silver Ore Deposits of the Mbr- CUR District, Utah 255 XXI. — Salting Mines, 264 XXII. — Prospector's Tools, and How to Sharpen and Temper Them, 272 XXIII. — Some Elements of Mining Law Relating to Pros- pecting . . 280 PROSPECTING FOR COLD AND SILVER IN NORTH AMERICA. CHAPTER I. ON PROSPECTING— PREPARATION AND OUTFIT FOR WORK. The regular prospector, as a rule, has at some time of his chequered career had some actual experience in the mines themselves, from which he has learned by obtervap tion the appearance of different ores, their different values, how the veins api)ear on the surface, how to open a vein, and the uses of pick, shovel, and blasting powder. In a word he is a miner who has become too restless to stick to steady work, and so follows the more uncertain and precarious livelihood of seeking for new and undiscovered veins, many of which even in an old mining district may yet be discovered covered up by brush or debris, whilst a new district offers a most enticing field. These mineral veins or ledges may make him in a moment a compara- tively rich man, and if he finds them, they will cost him nothmg, only a simple compliance with the inexpensive regulations of the law. So the life of a prospector offers many attractions to one who is restless and loves to roam and loves to find something new and is nof afraid of consider- able hardship. To save a vast amount of time and labor, he should acquire knowledge. Thus, for instance, if he were prospecting for coal he would be wasting his time in hunt- mg for it in granite, or if he wf s hunting for the precious metals, he would lose time in looking for them among the tanaltered sedimentary strata of the prairie. This is merely for example, but an infinite variety of knowledge is neces- sary for him in his vocation, besides even that of the simpler elements of geology, such as the knowledge of different kinds of minerals, and their value, the kind of places and peculiar rocks they are associated with, their appearance on the surface, etc., etc., together with some knowledge of assaying or blowpiping or panning. In i newly discovered camp, men will rush In for a few weeks, work a little in the different mines, sufficient to give them an idea of the kind of ores and rocks and other cir- cumstances in the locality, and then will strike out on their own account aid prospect around the camp for new veins or extensions of those already discovered. An extension, by the way, of a very rich discovered lode is not always to be relied on. Nature seems often to concentrate her riches at one point, and leave the extension barren, as in the case of the Comstock of Nevada. But little wealth has been found outside of the great lode and mine itself. The best education is in the mines themselves, so a novice on arriving at a mining region had better spend as much time as possible in practical work, in. and around the various mines, before he launches out prospecting. A prospector can rarely carry about much assaying or other apparatus with him for determining the character or value of ores he may find, and hence it is well for him to accus- tom himself to these ores in the mines themselves. Also he should acquaint himself with the peculiar ores of each particular district, before he attempts to prospect in its vicinity, for an ore such as coarse-grained galena in one district may be generally rich, whilst in another it is remarkably poor in silver. The best previous education for a prospector would be a course at a school of mines, where ne will learn the ele- ments of geology, mineralogy, assaying, etc., and next to that, practical work in the mines themselves, and lastly the prospecting field. A little knowledge of blowpiping may also help him, which he may acquire at his school. Having left his school, he should learn the practical use of the pick, drill, and blasting powder. By working around l, Concentrator he will learn the difference between ore and gangue rock ; and " picking" or " sorting" ores will teach him at sight the values of ores. The prospector should know how to open his vein or ledge, when he finds it, with pick, shovel, and blasting apparatus. A little car- pentry will teach him how to make a handwinch, and a fev; lessons in blacksmithing will teach him how to sharpen and temper his tools, for there will probably be no blacksmith's shop, or carpenter's either, within miles of where he may go. Other prospectors will teach him how to use his pun or iron spoon for testing ores, and various other dodges and makeshifts. An important point is to learn how to average approximately the quantity of ore in, and value of, a ledge when he has found one. Valuable ore on a ledge lies in pockets, strings, btmches, irregularly distributed through the quartz or other material of the vein ; he should learn to tell at sight the relative proportion of ore and gangue. He would do well to study the result of working ores in a mill or furnace, such as trying to esti- mate the yield of bullion of the ores which are mined, tak- ing them m weekly or monthly lots. With some such pre- liminary knowledge he is ready for the field. HIS OUTFIT. The following list of necessaries by Mr. A. Balch in his " Treatise on Mining" is as full as can be given by any one, and is more than the average prospector generally needs. " First. Two pairs of heavy blankets weighing about 8 pounds each. " Second. A buffalo robe or a blanket-lined poncho. " TAirJ. Su.t of strong gray woolen clothes, pair of brown jean trousers, a change of woolen underclothing, woolen socks, pair of heavy boots, soft felt hat, three or four large colored handkerchiefs, a pair of buckskin gauntlets, toilet articles, etc. All should go into a strong canvas bag. *' Fourth. A breech-loading rifle or shot-gun and a revolver. Around his waist a strong sash to jarry his holster and knife, in a sheath. His ammunition, if his revolver is large bore, may conveniently fit both his rifle and revolver. Pipe and tobacco. "Fifth. A sure-footed native or mountain pony. A Mexican saddle with its saddle-horn, straps, etc., to tie on various things, such as his pack, bags, water-canteen, etc. / 10 The left stirrup may be fitted with a leather tube, in which the rifle-barrel may be placed. A strap around the saddle horn will secure the gun-stock. The long lariat or stake rope for tethering his horse should be coiled up and tied by a strap to the saddle-horn. " Stxth. For prospecting, a 'poll' pick and prospecting- pan made of iron or a horn spoon should be carried. The pan is also useful besides for washing out sand, as a dish or bathing-vessel. A large iron spoon for melting certain metals is likewise to be carried, and in some cases a small portable Battersea assaying furnace. A PROSPECTOR AND HIS OUTFIT. " Seiienth, A frying-pan 8 inches diameter, of wrought iron, a coffee pot, tin cup, spoon and fork, and matches in tin box, pocket compass, a spy-glass, or pair of field- glasses. ''Eighth. Provisions, bacon, flour, beans, coffee or tea, pepper, salt, and box of yeast-powder, all packed in strong bags, to go into a canvas sack. A few lessons in the kitchen on cooking will be advantageous before starting. It " Ninth. Packing the bronco. Place a folded blanket on the horse's back ; on this lay the saddle. The saddle-bags contain small things. The bags with provisions are placed behind the cantle of the saddle ; on top of this the bag of clothing. The pick goes on top tied by a thong. Coffee- pot and frying-pan are lashed on the bags." A PROSPECTOR S TOOLS. I, 2. Picks. 3. Lone handled Shovel. 4, 5. Drills. 6. Heavy Hammer. 7. Blasting Powder. 8. Pan. 9. Horn Spoon. 10. Iron Spoon. 11. Fuse. Sometimes a prospector takes a horse to ride on and another as a pack animal, or a donkey only. For grass and water for his horse he must trust to the country. He will fix his temporary camp in some suitable location, where these are to be found, and thence, as from headquarters, prospect daily the adjacent country, returning nightly, it may be, to his camp. BRIEF SKETCH OF PROSPECTING. We may divide the ;:rospecting for the precious metals into two general classes : hunting for gold in gold placers ; hunting for gold and silver bearing ledges or veins or deposits. " Placers" are places where gold, having been torn from fi the ledges and rocks by denudation, by water and ice, is swept down by these agencies till it finally finds a resting- place. Gold, being heavier than quartz or country rock. PANNING GOLD AT CRIPPLE CREEK, COLORADO. sinks to the bottom first. If the stream is violent, it will carry the gold on, if fine, till it comes to an eddy or pool, where the waters are more quiet, and there it will sink. The water carries the clay and lighter stones still further 13 on. In this way millions of tons of rocks containing more or less gold disseminated through them may have been reduced and the gold set free, or the gold may have been derived from a few individual gold-bearing ledges or veins. The prospector takes his pick, shovel and pan, and his horn spoon, and finds perhaps an old dry river-bed where the water has ages ago receded. At some point the sides of this old river-course widen out suddenly, forming a basin. " Here," says the prospector, " there must have been FINDING THE FLOAT. an eddy," and he prospects it accordingly; at another point he finds a place where the water must have run over a rock and made a waterfall ; at the bottom he digs again. He loosens the soil with his pick, and shovels it out ; at a certain depth, which may be from 5 to 20 feet or more, he strikes "bed-rock," which may be granite, shale, sand- stone, or some other rock. Here he looks for nuggets, and with his knife digs into all the little crevices of the rock to hunt for them and for scales and wires of gold. Also whilst sinking his shaft, he pans the gravel care- fully at various depths, especially where there are streaks M of clay or "black sand." The latter are grains or little pebbles of magnetic iron-ore, a common accompaniment of gold, altered relics of the iron pyrites in which the gold was originally contained. He fills his pan half full of water, throws into it a shovel- ful of dirt, first picking out the pebbles, stirs the mass with his fingers till the water is fully charged with the clay, and gradually winnows out all the clay. Filling the pan again with water, he gives it a peculiar circular motion and each little wave of sand passes off till the whole is winnowed off, and at last he sees specks of gold shining free in the bottom of the pan. Then it is not difficult to estimate approxi- mately the amount of gold to the bushel or cubic foot of earth of the placer, and thus to estimate the approximate value of the placer. He then locates or stakes out his placer claim according to the regulations of the U. S. Government, which by a single individual cannot exceed twenty acres. The second class of prospectors are those who try to dis- cover ore deposits, ledges, or veins, "in place," that is, in the hard rocks of the hills. The prospector's first effort is to find " float." A vein outcropping on the surface becomes oxidized and crumbles by action of the atmosphere, rain, etc. ; pieces break off and fall down-hill. Smie of this float is barren quartz or country rock, others may be mineralized. Commonly " float" is a rusty, spongy mass of rock, showing besides iron often some copper stains, and in it there may be grains of galena, pyrite, or some other ore. He tries to trace this " float" to its home in the ledge whence it came. Of one thing he is certain, the " float" must have rolled douni and not /// hill. If the " float" is fairly scattered over the lower zone of the hill, and no " float" is found above that zone, on the top of that zone he will hunt for his ledge. If the " float" is all over the hill he assumes the ledge is on the top. If he finds his " float" at the mouth of a canyon or water- course, he walks up that water-course, noticing not only the " float," and its diminishing or increase, but also any peculiar rocky pebbles, such as a peculiar porphyry, per- haps, which he may by chance recognize again further up in place, and give him a hint ias to whence the stream ^i »5 derived most of its material of pebbles. He notices if the " float" fragments increase as he proceeds, and whether they suddenly cease at a certain point: at that point he hunts for the ledge on either side of the canyon, and breaks off any pieces that may look likely. Having found the ledge and traced its croppings, he tries to find out its approximate value. This he does by break- ing off at intervals along it likely looking fragments of the rock, grinding them up to about the size of peas. He mixes these well, and takes a half of them, reducing this to fine powder and again halving it, till of the whole ledge he can carry away an averaged sample of a few ounces. He may wash this in his pan to see if there is any free gold in it ; other ores he will recognize at sight. These samples he will have assayed and the returns will show the approx- imate value. He measures the length and thickness of the vein, and examines the wall enclosing it. He then proceeds to locate or stake it out by measuring off a parallelogram 1,500 by 600 feet. At the comers of this he places piles of stones, and in one or more of them places a stake of wood on which he writes his name, a description of his claim, and the date. At the nearest recorder's office he files a copy of this document. He must do a certain amount of improvement work on this annually, such as digging a ten- foot hole or putting up a cabin or some work equivalent to the value of $100, so as to hold it. He may also claim a mill-site on non-mineral land adjacent not exceeding five acres. Now the property is his to do as he likes with it. THE GEOLOGICAL TRAINMNG OF A PROSPECTOR. One of the first things for a prospector for gold and silver to acquaint himself with is the elements of geology. He can read this up theoretically in many excellent treatises and manuals, such as LeConte, Dana, and Shaler's Manuals, and Geikie's Hand-Book of Field Geology, etc., and become learned in the names of eras and epochs, and the jargon of scientific names of fossils and minerals, and varieties of rocks ; but let him not imagine at the end of this process that he " knows geology."' Geology can no more be learned by means of a book, i6 without field-work and the actual personal contact with nature and rocks, than chemistry or assaying^ can be acquired without ever using a test-tube or a cupel. Tue student may, perhaps, be unfavorably situatea for this practical field-work. There may be no mountains or upheavals of strata, or deep natural ravines within avail- able distance to study. He is located, perhaps, on the great, monotonous, flat prairie. Very well, then, let him study what lies nearest him. This same flat, monotonous prairie has an interesting and wonderful history. Let him read up what he can find about this in his books, then go out and examine what he can of the few feet of horizontal strata exposed in some shallow water-course or dry ravine ; examine minutely, both with eyes and microscope, the minerals composing these strata. Let him classify and collect and note the different kinds of pebbles scattered over the surface, or in the bed of a brook. Let him specu- late as to the cause of the undulations of the surface, the deposition and peculiar character of the clays forming the soil. Let him study thoroughly the geology of his native village, his immediate surroundings, first. The knowledge and practical habit of observation so acquired will lead later to more extensive studies in wider fields. A student may be shut up in a big city ; let him study the paving- stones of the streets and visit the stone-yards of the masons. It will pay him better to take a trip to some distant moun- tain region than to buy another expensive book on geology after he has mastered the first bare elements. Nothing like field-work, eye practice, and hammer practice. The student should endeavor, whenever he possibly can, to verify by actual vision and personal expeiience whatever he reads in his books. When traveling, let him always carry a geological hammer with him, and at any station the train may stop for a few moments step out and try to get a specimen of the country rock; at the same time let him study all he can of the geology of the country he is passing through from the windows of the train, aided perhaps by a geological map. The genuine prospector is always looking about him, is everlastingly cracking stones, has always his eye wide open for " something kind o* curious." If he is near some mountain region, where, as in Colo- rado, the whole strata of the earth's crust is upheaved and «7 Cmctaocous t o o OnKorn Omoup N Jun^aaio J Tf^MSSIO III VI iCahboniferous H Silurian Cambrian "^ Colo- Id and Plate I. A Vertical Section of the Earth's Crust in Colorado. i8 / exposed, along the mountain flanks, in the depths of the canyons, or on the summits of the peaks, after studying his manual, let the student get, if he can, some published geo- logical report on such a country, such as those of the U. 8. Geological Survey, abounding in illustrations and geologi- cal sections. Let him take this book in hand and go to the very place described and pictured as a geological section, and with his hammer study each member of the section closely. This will make him familiar with the different geological periods, formations, rocks, minerals, and fossils, as they actually appear in nature rather than as his imagina- tion has supposed them to be from his study of the text books : book geology and field geology are not always in perfect harmony. Having studied and learned one local section well, such as that cut by a stream along the foothills of a mountain range, let him repeat the course at the other and more dis- tant points. He vill find at each locality, though the main features are the same, there is always an interesting variety, such as new fossils, peculiar minerals, changes of dip, faults, or other structural peculiarities. Along the flanks of a mountain range, a prospective pros- pector cannot study too many of these geological sections. Having become familiar with these foothill sections, he is prepared to plunge into the heart of the range itself. At first, and for long distances perhaps, he will encounter only granitic rocks forming the axis and core of the range. These are well worthy of study and full of variety. Later the canyon may open into some mountain valley or park, where the strata he studied on the foothills or prairie border are again repeated and he finds himself again at home. Seizing upon some well-defined and familiar repre- sentative of a geological horizon, from this as a standpoint he soon reads off the succession of the rest. Here, how- ever, the appearance and texture of the rocks will probably be different to what they were in the foothills. Heat has so changed or metamorphosed the sandstones and shales that they are scarcely recognizable as the same rocks as those of the foothills. Yet even here a highly silicified fossil shell, or a leaf impression on shales, or sandstones changed into slates or quartzite, will give the prospector his clue and his desired and definite geological horizon, and «9 he will have little difficulty in again arranging and group- ing correctly the rocky series. But a prospector has a " practical end" in view. He is " after the precious metal," gold and silver, not after " pure science' or " fossils or sich " ; what practical use is there, he may ask, in this same careful study of geological sections, where probably there is not a speck of ^old or silver? Simply that minerals and metals of^economic value, such as gold and silver, are more frequently found in the rocks of certain geological periods than in others. Locally this is especially true. For instance, nearly all the silver-lead deposits of Colorado are found in j certain bed of limestone not over two hundred feet thick, to be found only in one geological period out of many others, viz. : the lower division of the Carboni- ferous. It would naturally then be advisable for a Colorado prospector to be able surely to identify this limestone, as well as the geological horizon in which it occurs, among the various other limestones of various other periods and ages in the mountains. Again, gold is mainly confined to crystalline rocks of Archaean age or to porphyries associated with these. A prospector should be familiar with these rocks and their varieties. Gold is also found in the placers derived largely from the breaking up of these rocks ; the ability to distin- guish the different pebbles may lead to the source whence the gold was derived. Familiarity with rocks of all kinds is a necessary prospector's education in itself. GEOLOGICAL SECTIONS OF COLORADO. In illustration of what we have said, let us take the two engraved generalized sections showing all we know of the crust of the earth as exposed in Colorado. Plates I and II. Plate I is a vertical section of an ideal cliff, showing all the members of the various periods in a stupendous cliff resting on fundamental Archaean granite at the bottom of a canyon. Plate II represents the same rocks and succes- sion of strata displayed in upturned " hog backs" along the flanks of the mountains and foothills on the border of mountain and prairie. Both of these are ideal sections " generalized" or " made up" of actual partial typical sec- tions found in different localities in Colorado, the vertical 80 one in detached and sometimes widely separated districts in the heart of the mountains; the other at similarly dis- tinct and different localities along the banks of the various rivers issuing from these canyons in the mountains, cutting their way through the upturned strata of the flanking foot- hills and debouching on the prairie. It is very rare to find at one locality anywhere in the world a complete section of the earth's crust exposed. The nearest approach to this in Colorado is the remark- able section between Colorado Springs and Manitou, which shows along the wagon road the succession of strata from Archsean to Quaternary. One of the most remarkable vertical sections in the world is in the grand canyon of the Colorado River, where the stupendous cliffs show in one face, a thickness of some 6,000 to 7,000 feet of strata, representing several geological periods, but by no means a complete section of all that is known of the earth's crust. To show how dilBcult and rare it is to get a complete section of all the periods in the earth's crust, we may state that sometimes the rocks of a single geological period are from 10,000 to 20,000 feet thick. A canyon might thus be cut to a depth of 5,000 feet, and yet be in only part of a single earth-period. By far the most extensive and available sections are, like those represented in the engraving, along the courses of streams on the flanks of a mountain range. It would be a formidable task to scale a clifl 5,000 feet high and examine minutely, in ascending, each of its geological divisions; whilst, on the other hand, in the foothill regions, a pros- pector may walk over and mark and study as much as 10,000 to 40,000 feet of strata along the banks of a river in a single afternoon. In the Weber Canyon in Utah, as much as 40,000 feet of strata, composing the flanks of the Wahsatch Range, can be seen by the traveler from the windows as he glides through in the railway car, and the inquiring pros- pector or geologist can examine and study this vast section leisurely on his mule or on foot, without doing any climb- ing and on a good road. Smaller partial sections can be similarly studied along many of the streams issuing from the Rocky Mountains among the foothills of Colorado. Such, for example, as at Boulder Creek, Clear Creek, Bear I Plate II. Generalised Seotioa of Rocky MonnUina in Colorado. Showing Economic Proi Foothilh and //og^acA ^toup fMf ^K. Tdble Lands i^V. Plains — ~V"" Plate II. Iiowing Economic ProducU in Different Geolofrical Horisons and Strata. > e Plate IX. — Silurian Fossils. 1, 2, Orthis ; 3, 4, Spirifer ; 5, Pleurotomaria ; 6, Murchisonia ; 7a, 7^, Trilobite (Calyinene) ; 8, Coral Fenestella ; 9, Coral Chofitites ; 10, Graptolite ; II, Orthoceratite. the Cambrian is so highly metamorphosed and altered into hard crystalline quartzites, that evidences of past fossil life are as scarce and indistinct as in the Archaean, and prob- ably for the same reason The forms he may find are a little Crustacea called a I'rilobite, something like a " sand crab," also a few little shells and some marks of worms. Plate VIII. 44 SILURIAN. In the next series, the Silurian, he may be more fortu- nate. He may find remains of sea-weeds, corals and shells, and fragments of a sort of sea-worm called a Crinoid, or sea-lily. The little discs with a hole in the centre form- ing a little ring about the size of a pea, constituting the discs or rings of which the stems of the sea-lily are com- Plate X. — Devonian Fossils. X, Spirlfer; 2, Comocardiuin ; 3, Orthis; 4, Goniatites ; 5, 6, 7, Corals ; 8,9, 10, Fish Teeth ; ii, 12, Fish Scales. posed, are sometimes very common in Silurian and Paleo- zoic rocks, though it is rare to find a complete Crinoid, and especially the beautiful comb-like flower or head of the sea-lily. He is likely to find also a more advanced type of the Trilobite and various Spirifers and other shells as pic- tured. Plate IX. 45 nEVr)NIAN. In the Devonian he may find the teeth or bones of fisheA, and a lew remains of peculiar land plants, neither of which are known in the Silurian below, also many corals. CARBONIKEROUS. In the Lower Carboniferous " blue limestone," corals and shells appear, especially Spirifers and Productus. together Plate XI. — Carboniferous Fossils. \a, i/>, ic, Productus ; 2, 2, Spirifers; 3, 3, 3, Rliynconella ; 4, Buumphalus ; 5, 5, Crinoids ; 6, Pleurotomaria ; 7, Belleroplion ; 8, Athyris Subtilita ; Q, Astartella; 10, Ooniatites ; 11, 12, Corals; 13, 14, 15, 16, Plants ; 17, Spine of Echinus. with Crinoids and a very simple curled shell like a snake coiled up, a " Gon.atite," one of the earliest of the Ammo- nite class. At Aspen, associated with the ore-deposits we found in the blue limestone most of these, together with a \ 4« kind of snail-sholl called IMcnrotoTnaria. At I.eadville in the same formation Spirifcrsand Productus arc occasionally found. A very curious coral is one shaped like a screw, called Archimedes, after the author of the screw. Cup- corals are common. In the Middle Carboniferous, associated with the coal- seams, many curious remains of reeds, ferns, and other aquatic plants of that a^c are found, but these are scarce in Colorado and the West. The prospector will observe Plate XII. — Jura-tkias Fo.ssils. I, Dinosaur Lizard ; 2, <, Foot and Slioulder Bone ; 4, 4, Vertebra of Sea Sau- rian, Ichthyosaurus ; 5, 6, 6, Teeth of Sauriansj^, Belemnite ; 8, Echinus ; 9, 9, Ammonites; 10, Exogyra; 11, Trigonia Shell. that there is a general family likeness between the fossils of each division of the Paleozoic and in the Paleozoic as a whole, and it may not always be easy for him to determine whether a shell is Silurian, Devonian, or Carboniferous, but of one thing he will be certain, that it is Paleozoic. 47 TRIASSIC. In the Trias thr()iiKh«>ut the West, he is not likely to find tnany fossils; the rocks are generally too coarse; btit in the Eastern States, though he may not find any true remains, he may observe the tracks left by jjreat Saurians as they walked on their hind feet, or on all fours, on the red sands of the beaches of those dreary salt Triassic seas, leaving " footprints on the sands of time" full of interest. JURASSIC. In the Jurassic shales and limestones in Colorad«). he may be equally unsuccessful, though in the upper Jurassic just below the Dakotah sandstone, he may light on the bones of gigantic Dinosaurs, or great land lizards, such as the author found in Colorado and Wyoming, monsters sixty to eighty feet in length and proportionally tall, standing from twenty to twenty-five feet m height. In the lower Jurassic in Wyoming, he will find great numbers of sea- shells and Ammonites, and a round shell like a cigar called a " Beleninite," or spear-head, the internal shell of an an- cient cuttle-fish. Plate XII. CRETACEOUS. In the Cretaceous, beginning with the lowest group, the Dakotah group, net-veined leaves of deciduous trees, such as the willow, oak, maple, etc., the earliest known leaves of those kinds of trees, may be expected in the sandstone and clays. In the Colorado group of the Cretaceous, above the Da- kotah, abundance of oyster-shells and large clam-shells (Inoceramus) are sure to be found in the limestones and marine shales. In the Montana group of the Cretaceous above this, consisting mainly of drab shales and some sand- stones, great quantities of sea-shells are found, among them various peculiar forms of the Ammonite allied to the mod- ern nautilus, and called Scaphites, resembling snakes or 48 worms u.^-^ oiling, together with shark's teeth and bones of sea Saurian s. In the sandstones of the Laramie Cretaceous, remains of sea- weeds are found ; in the sandstones immediately below Plate XIII.— Cretaceous Fossils. I, I, Inocer^mus; 2, Cardiuir ; 3, Corbula; 4, Mactra ; 5, Margarita ; 6, Fascio- laria ; 7, Anehura ; 8, Pyrifusus ; 0, 10, Scaphites ; 11, Crioceras ; i;<, »>aculites ; 13, Shark's Tooth. the coal-beds, and in those associated with or above the coal, are found great varieties of semi-tropical leaves, such as those of the palmetto, fig, beech, elm, magnolia, sassa- fras, etc. The presence of these leaves is a pretty sure in- dication of coal. V H 49 TKRTIARY. In the Tertiary Ircsh-water beds, siinilar leaves and thm beds of poor li^niite coal are found, together with fossil in- sects and remains of mammals. In the Marine Tertiary are sea-shells. 1 Plate XIV.— Tertiary Fossils. ,* I'alnietlo ; ., Cinnamon Leaf ; 3. Cardium ; 4. Insect ; 5, Numiuulite '''• ' Shell ; 6, 7, Fresh- Water Shells. QUATERNARY FOSSILS. 8. Mammoth lilephaufs Tooth ; q, Mastodon's Tooth ; 10. Flint Implement ; II, Stone Grooved by Olacjer. QUATERNARY. In the Quaternary drift, among the pebbles, sands, and " wash" characteristic of gold-placer beds, an occasiona tooth, tusk, or bone of the great hairy Mammoth elephant or the Mastodon elephant may be discovered, together with the stone implements or bones of prehistonc man and peb- bles grooved by glaciers. :.W so CHAPTER IV. THE PROSPECTORS LITHOLOGY OR STUDY OF ROCKS. A prospector wants to know a gredt deal about rocks. be a They are his constant companions in the field. o a hj a (d tx. 4.1 ol U X 85 H 'o ^ OQ f/j V t^ M u o ^ 1. u. r*' S O >.2 u to r ) t. 4-1 55 ^§ •< < 4i 10 . Scf a* £c) -•^ .« u "5 "3 |5 tn hH <«} P< r>i &« t3 3 ^ < h u u o fltf > X X c w 4) H E :1 •5 Ol Ah cc > < O r n > n > H w > o H > (/I fr u % ./. ■• en >. u "0 4) ft, to BI O 3 C « o c c« O . a ' Si structure, he judges to be Cambrian quartzite, the thin-bed- ded strata above Silurian limestones, and the heavy massive beds above these, Lower Carboniferous blue limestone, whilst 53 a dark greenish-gray rock, running in and out irrejfularly among the strata, sometimes between the stratification planes, at others cutting across them, he judges to oe an intrusive sheet of porphyry, and looks again for " contact deposits." A rock running up like a low wall from the bottom of the canyon to the top may be either a quartz fissure-vein or a porphyry dyke, and well worth examin- ing. There are many ways of studying rocks, one by hand specimens, finding out all the minerals composing them, and then naming the rocks from which they came ; another by observing the appearance of large masses of rocks in the field, and noting their mode of occurrence ; and lastly, if wc wi.;h to be very accurate, making thin microscopic sections and a chemical analysis, but for the average prospector these last will be rarely necessary. If a prospector bought a manual to study rocks, for prac- tical purposes, he would find himself amongst a sea of names of varieties of rocks, nine-tenths of which it is safe to say he Avould never meet with in his field experience. To save him the trouble of wading through such books, we select just about as much as a prospector is liable to meet with in the field or find practically useful, saying little also about such common rocks as are familiar to every one. Those that need most definition and are of most impor- tance in the mining-field, are the crystalline rocks belong- ing to the class called metamorphic and igneous; the last especially needs careful determination. Nearly all sedimentary rocks (limestone excepted) are derived from fragments of igneous and metamorphic rocks. Probably nine-tenths of the sedimentary rocks are derived from granite alone, the remainder from the igneous rocks, such as porphyry, basalt, etc. By describing the parent rock, the derivative one is more easily made out. ROCK-NJAKING MINERALS. ^ Crystalline rocks are made up of certain distinct min- erals, most of them of quartz, feldspar, and mica, with some- times also hornblende and augite. Other minerals may locally occur as occasional elements. yiJART/ scarcely needs description, being kg well known. 54 The hexagonal prism of this crystal is too hard to be scratched with a knife and will scratch glass. This distin- guishes it from calcspar and barite, for which it might be mistaken in the field; moreover it will not effervesce with acids. The Feldspars are nearly as hard as quartz. Their col- ors are white, grayish, and flesh-color. They are rarely as transparent as quartz, being generally opaque. Their form of crystallization is different from quartz, and in a vein they show one smooth face of their crystal, whilst the quartz is more like crushed loaf-sugar. In a porphyry the feldspar crystals are very distinct, and give a characteristic spotted appearance to the rock. Two varieties of feldspar are characteristic of the crystalline rocks, one called orthoclase or common feldspar, a potash-feldspar, the other called oligoclase, a soda-lime-feldspar. The former is very char- acteristic of granitic rocks as well as of igneous porphyries; the latter is rather more characteristic of more recently erupted igneous rocks, such as diorite, basalt, andesite, etc. Orthoclase is generally in large crystals, oligoclase in small. When the crystals are very small, it may take a microscopic examination to determine to which variety of feldspars they may belong. The oligoclase and plagioclase crystals in igneous rocks are commonly but little white dots. To determine accurately, microscopic slides and chemi- cal tests must be made, but this is scarcely within the scope of the prospector who wants to guess roughly at sight as to the name and character of a rock. Mica, both black and white, needs no description. Hornblende differs from mica in being of a duller lustre and of a different form of crystallization, as shown in the plate. The color is a greenish-black; the greenish tint is distinct when the crystal is struck by a hammer. AuGiTE or Pyroxene is scarcely distinguishable from hornblende. In Colorado, augite is mainly confined to two kinds of rock, basalt or dolerite and andesite, both of com- paratively recent volcanic origin. Hornblende and mica are common to nearly all the metamorphic and igneous rocks. Talc amongst miners means almost any soft, sticky, or ! ' ss slippery, decomposed rock, but strictly, talc is a pale green soft mineral like mica and is a silicate of magnesia. Stea- tite or soapstone is massive talc. Miners often wrongly call any soft clay or rock, soapstone also. Chlorite is another magnesian mineral, of a green and soft character. Chlorite is again a name given to almost any greenish rock of a schistose and soft decomposed char- acter. Calcite is carbonate of lime crystal, the element of lime- stone, and is distinguished by softness and effervescing in acids. Dolomite or carbonate of lime and magnesia is very like calcite and is the element of dolomitic or magnesian lime- stone. Dolomite effervesces with much greater difficulty than true limestone. To effervesce, the dolomite should be powdered and the acid heated. GvPSUM or sulphate of lime can be distinguished by its extreme softnes ., being scratched by the finger-nail ; it does not effervesce like lime. Barite or " heavy spar" occurs in some veins, but not as a constituent of rocks. It looks like calcspar, but is heavier and will not effervesce with acids. Fluor-spar occasionally occurs in veins, in cubes or massive. It is easily scratched with a knife ; its colors are green, purple, yellow, blue or white. Garnets, Green Epidote. Black. Tourmaline, and other minerals or gems may occur, but not as important constituents of the rocks. crystalline metamorphic rocks. Granite. — Beginning with the granitic series of the Ar- chaean age, granite proper is massive, shapeless, or amor- phous, and shows no bedding-planes or other signs of for- mer stratification. It is thoroughly crystalline, like lump- sugar. By some it is considered a true igneous rock, one that has been thoroughly fused by heat, as much as the lavas or molten iron ; by others its crystalline amorphous condition is supposed to be the result of extreme metamor- phism of originally sedimentary bedded rocks, such as gneiss or schist, the two latter being sometimes traced down through a gradual change into granite. The compo- 50 sitfon of j^ranite is mica, quartz, and feldspar with some- I lines a little hornblende. The micas may be white mica (muscovite) or black mica (biotite). Both orthoclase and oligoclase feldspar may be present, but more commonly the former, which is often a pinkish flesh color. Granite. in its crystalline texture, differs both in character and appear- ance from porphyries and other igneous rocks, in the fact that its crystals are all jumbled up and crushed together like loaf-sugar, and none of the crystals are set like plvms in a pudding, distinctly in a back- ing or paste of very small crys- tals of amorphous or glassy ma- terial, as in the porphyries or igneous rocks. Granite is prob- ably the oldest and deepest rock known. It is often trav- ersed by sparry veins, both great and small, which con- sist of quartz or feldspar or both, in a more sparry condi- tion than when diffused through the parent rock. These so-called " quartz- veins" are often called " granu- lite" or " pegmatite" or " graphic granite." The quartz and feldspar are often arranged in parallel plates, giving on cross-section curious marks like Hebrew characters ; hence the word graphic. The bulk of our so-called quartz fissure veins in the granite mountains may be called pegmatitic veins. The colors of granite vary from reddish to gray, or nearly white to black, according to the preponderance and colors of the micas and feldspars in them. Syenite is little more than granite in which hornblende supplies the place of mica. Gneiss may be called "bedded granite," showing a Plate XVIII. t, Triclinic GligoclaseFcldsp.ir. 7, MDiioclinic Orthoclase Fekl- spar. 3,Carlsbad Twins Feldspar. 4, Au^ite or Pyroxene. 5 and (<, Hornblende. 57 bedded appearance. Gneiss is often cnriotislv and pret- tily banded r. streaked by seams of mica dovetailing into each other. If mica preponderates, it is called "mica- gneiss," if hornblende " hornblendic gneiss." Schist may be called laminated gneiss or granite, being finally divided into lamina or leaves. This foliated struc- Gkanitc Platk XIX. I'l.ATK XX. SvcMtrc Pf.ATK XXI. ture is due to the arrangement of the flat-lyin^^ crystals of mica or hornblende largely composing- it. It may be a mica-schist or a hornblende-schist. Slatk is shale altered by heat into a hard crystalline structure. QUARTZITE was Originally a sandstone composed of quartz-grains, which by heat have been partially fused to- .,»w*»>5H!>»: &NtlSS Plate XXII. C0WT0flTCflM»C/(5cHiST Plate XXIII. Plate X\I\. gather at the edges, resembling granules of tapioca in a tapioca pudding. Quartzite differs from quartz in being a rock made out of pieces of quartz, and not the original mineral itself. Quartzite may be white like sugar, gray, brown, or rusty. It shows a true stratified structure. Marisle is limestone similarly changed to a more crystal- line condition. 58 Serpentine is a gn'een magnesian rock, sometimes found with marble and igneous rocks, and is formed by alteration of certain minerals in the latter. CRYSTALLINE I(;NE()1:S OR ERUPTIVE ROCKS. • These are rocks which are supposed to have been thor- oughly fused or melted in the bowels of the earth. Some reach the surface by fissures or volcanic vents, others have never attained to the surface or overflown it, but have in- truded themselves between the weak places in the underly- ing strata, or have collected and cooled deep down below the surface in great molten reservoirs called " laccolites" or lakes of stone. When these have been subsequently un- covered by erosion, they may present the forms of consid- erable mountain masses like the Elk Mountains, and Henry Mountains and Spanish Peaks. Geologists distinguish those rocks which have poured out on the surface from craters and volcanic vents as volcanic rocks, while those cooling below are called Plutonic. INTRUSIVE PLUTONIC ROCKS. The component minerals of these intrusive Plutonic rocks, such as are commonly called porphyries, are prin- cipally quartz and feldspar, with mica or hornblende. In color these rocks are some shade of gray, green, or maroon, or even white, but their most striking characteristic is a general spotted appearance. This arises from more or less large, distinct, perfectly formed crystals of feldspar or quartz, set in a finer-grained crystalline paste or back- ground, standing out distinctly from it. This base or back- ground may be comparatively coarsely crystalline, finely crystalline, or so finely crystalline that the crystals can be discovered only by a microscope, while the larger crystals seem set in the paste, like plums in a pudding. In the depths of a mine the porphyry is commonly much decom- posed by water action or mineral solutions, and even passes into a clay or gouge. The characteristic spotty appear- ance, from the presence of individual crystals of feldspar, may even then identify the rock, or by chemical analysis the very aluminous character of the decomposed rock may 59 determine its character. When feldspar is the main con- stituent, it is called a felsite porphyry, when a certain amount of quartz is present a quartz porphyry. DiORiTE, whose crystals are sometimes porphyritic in character, hence called porphyritic diorite or porphyrite, belongs also to this intrusive or Plutonian class, differing only from the others in the fact that its feldspar is of the triclinic plagioclase kind rather than orthoclase. Horn- blende is a prominent constituent of this rock, and gives it, more or less, its dark olive-green tint. In appearance it resembles a dark syenite, but its occurrence as an eruptive, intrusive rock distinguishes it. as syenite is generally a metamorphic rock. The peaks of the Elk Mountains are. many of them, of diorite. Diorite or porphyrite is the so-called porphyry of Aspen, above the ore deposits. PeiVHYmTicniomTs Plate XXV. gUART/ HORPHVRIES. These are the commonest, and may be said to be the pre- vailing eruptive rocks associated with our ore deposits in Colorado, as for instance at Leadville, felsite porphyries as well as quartz porphyries occur in the granite rocks in the Central and Georgetown mining districts. All these rocks are common through the West, and quartz porphyries are the most common eruptive rocks the prospector is likely to meet with in his search for ore deposits. We will describe in detail one or two typical species, though it must be ob- served that these porphyries are of endless varieties and shades of appearance. Quartz porphyry. — A quartz porphyry is a porphyry that contains quartz crystals large or small, in addition usually to large orthoclase feldspar crystals, generally of a vitreous glassy variety called " sanidin," together with small crystals of hornblende or mica. As a typical example we take that which forms the dyke composing the peak of Mt. Lincoln. Colorado, called Mt. Lincoln quartz porphyry. This porphyry riLSITtPOHfMYRY Plate XXVL Plate XXVII. and varieties of it are comtnon in the western mining; sections of Colorado. In appearance it is a Rray rock spotted with large and small crystals of ortho- clase sanidin feldspar, which sometimes show an oblong face two inches long, by an inch wide ; at other times a shape like the gable-end of a house, according to whichever part of the crystal happens to be exposed. Sometimes two crystals are seen locked together, forming what are called Carlsbad twins. When the rock is decomposed, these crystals not unfrequently drop out and lie as pebl)les on the ground. With these may be also seen rounded ends of bluish crystals like broken glass. These are portions of perfect quartz cry.stals, which when extracted show a six-sided pyramid at either end. These larger crystals are set in a crystalline ground mass of much smaller crystals of the same kind, together with many little black cubes of shining mica, or duller lustred, longer, rectangular, oblong crys- tals of hornblende. This porphyry is eruptive and intrusive, occurring in dykes, intrusive sheets and laccolites. Lkadvillk White Porphyry. —At Leadville there is a quartz porphyry known as the Leadville white porphyry or " block porphyry" by the miners, which needs description, as it is the one that more especially is asso( iated with the rich ore deposits. It is a white, compact, homogeneous looking rock, not unlike a shaly white sandstone or quartzite. It consists of feldspar, quartz and a little mica. Its porphyritic or spotted character is so indistinct that one would be inclined to call it a felsite at sight rather than a true porphyry, but the microscope reveals perfect double pyramids of quartz and individual crystals of feldspar set in a paste of the same minerals. It is often stainiul by concentric rings of iron oxide I'l.A'.'E XXVIII. HoHMBitNotAuureJ^iO^s MMNCTITC&ARNtr. Plate XXIX. 6i nnd marked with \vondcrfiil imitation^ of tree?*. The latter have earned for it the title of " photo^jrapliit- roek" or "dendritic porphyry." These tnarkitigs are only the crystallization forms of oxide of irtm or man- ganese, something like fern-frost on a window-pane. The porphyry is very shaly, and breaks up in thin slabs; hence called also " block porphyry." It is common at Lead- villc and is also found elsewhere. In the same rejjion there are many other varieties of quartz porphyry such as the "gray porphyry." the Sacramento, and the pyritiferous porpyhry. The latter is often gold bearing. V<)rN<;KK KKKIJSIVK VOft ANIC ROCKS. These intrusive plutonic porphyries and diorites arc gen- erally older than the other class, which reached the stirfai e and poured over it and which may be called for distinction " effusive" volcanic rocks. Typical of these we may cite the dark basalts and doler- ites that often cap the table lands of the prairie region and overlie our coal beds. A pinkish or dove-colored rhyolile also caps some of the mesas and in certain districts an andesite lava. DoLERiTE AND Basalt. — The la^ 2r being scarcely more than a fine-grained variety of the former, are very dark rocks, consisting of dark, heavy minerals, such as augite, magnetite, and a plagioclase feldspar called labradorite. Such minerals are said to be basic, and the rock composing them also basic. Andesite is very like dolerite, though generally a lighter gray or pink. Both augite and hornblende may occur in it, more especially hornblende, sometimes mica also. The feldspar is called andesite feldspar from the Andes Mountains. Rhvolite, under the microscope, shows a peculiar flow- ing structure, hence its name from " rheo' to flow. The lighter rocks in Colorado and the West are generally rhyo- lites rather than true trachytes. Their colors are pale gray, white, pink, or sometimes dark. Rhyolite consists of a fluent, vitreous, ground mass or Plate XXX. 63 paste, usually containing crystals of sanidin feldspar, or even of quartz. When these crystals are conspicuous so as to give the rock a porphyritic appearance it is called "liparite." In some cases it may have even a granite-like ap^^ear- anre, the crystals of quartz, mica and feldspi^r being more or less intermixed; then it is called Nevadite. It is an acidic rock consisting of acid minerals mainly. Trachyte, from * trachus" rough, is alight colored rock, with a peculiar characteristic rough feel, due to micro- scopic vesicularity. It consists of a ground mass ' sani- din feldspar and augite, containing crystals of the '.atter. In ninety-nine cases out of a hundred, in Colorado at lea^i, also in the West, rocks which are popularly called " tra- chytes" are rhyolites or porphyries. Awv»OAtO/OAL Scon/A I'LATE XXXI. AnocsiticBkcddi^ Plate XXXII. Basalts and some of the other extrusive volcanic rocks assume a columnar form on cooling. Also, on the surface of the flow, the lava becomes minutely honey-combed like sponge, from escape of steam. This is called scoria, and wiien these holes are filled with almond-shaped white crys- tals, amygdaloid. At other times the rock is a volcanic breccia; that is, angular blocks of lava, great or small, are cemented together by lava. This probably was caused when the lava was pouring out of the fissure s^lowly, some portions congealed and were broken up by the onward flow, and again involved in the molten mass vvi+hout being remelted. Enormous masses of volcanic breccia cover the San Juan region. Sometimes, by steam, the lava is blown into dust and descending with water, is worked up into a volcanic sandstone known as volcanic " tafa" or ' tuff." Obsidian is vitrified lava or volcanic glass. 6;> CHAPTER V. THE PROSPECTOR'S MINERALOGY. There are two classes of minerals in which the prospector is interested, one may be called the " earthy" minerals, such as quartz, calcspar, etc., associated with the precious ores; the other, the metallic minerals, constituting the ores them- selves. Both of these he wants to know at sight, or to determine with the simplest appliances. (Generally speaking, his eyesight, his pocket-knife, his ore-glass and a little acid will be all he needs, nor need he concern himself about a great number of minerals, if he only knows the commoner ones well. The earthy minerals form the gangue or vein- stone of the vein in which the precious ores are distributed. c e d e d g e n a EARTHY OANGUE MINERALS. These are principally quartz, calcite, or limespar, dolo- mite, fluorspar and baryta, all of which we have already described among rock-forming minerals. These crystals are nearly always to be found in the adjacent rock as ele- ments of that rock, and their more sparry condition in the gangue of the vein is derived by solution from the enclos- ing country rock. Thus, a vein running through granite will contain mainly quartz, though calcite and fluorspar may be associated with it in small quantities. A vein passing through limestone naturally carries calcite or lime- spar. Sometimes baryta is associated with the calcite, es- pecially if near the limestone ore deposit there are porphy- ries. Baryta has been detected as an element of some porphy- ries which are probably ore-bearing, and when prospecting, we have found baryta to be generally an indication of ore near by, while calcspar, or quartz, alone, may or may not be barren. The float, or loose surface indications of ore deposits at Aspen is commonly made up of calcspar and baryta. Fluorspar in Colorado is generally confined to veins in .•■ ■•-tjt-nuMtia.ar iSi liMMW-^ an the granitic rocks and in some of the eruptive rocks. Its presence is a good sign of ore. (.>xiDKS()h Iron and Manganf.sk. — These, often mixed to- gether, form a large element in the gangue matter of a vein or ore deposit. Manganese can be recognized by its dark black color. A beautiful rose-colored carbonate of manganese called Rhodocrositf, is occasionally met with, associ- ated with quartz and metal in some veins. Carbona TK (ti C(>Pi»KR IS often associated with this gangue matter. It is readily distin- guished by its bright green or azure blue color. " Float" is commonly rusty with iron oxide streaked vith stains of copper carbonate. Spathic Iron or Iron Car- honate or Siderite occurs here and there in the gangue of fissure veins. It is very like brown feldspar, but heavier. These few common min- erals cover nearly all that are generally met with as indi- cations of, or in important connection with, ore deposits. As a rule, most of these minerals occur in a massive state rather than as individual crystals in a vein. I'l.ATE XXX ill. Spathic Iron, METALLIFEROUS MINERALS. Through these gaflgues of vafiotis ctiaraicteis, t1>*» pre- cious metals are distributed in long, narrow patches or strings, or in large crystalline massjes, or in scattered crys- tals, or in decomposed masses. The gangue matt«:-r is gen- erally in the majority in a vein, ar^d the ore thinly, spar- ingly, and irregularly distributed in it. When a vein is said to be ten or more feet wide, it is not to be supposed that ten feet of solid ore is meant, but that mis is the width of the gangue between walls. The ore bod^' nnsay be only a few inches wide. The streak or marn body of - to kt f > near one wall or the other, or at times to cross from wali ,o wall. EEifl <55 HIGH AND LOW (.KAr^F. ORES. Plate XXXIV. Ruby Silver. In gold veins, flakes or wires of " free" or " native" gold occur in the decomposed gangue. and sometimes in the pure, undecomposed quartz : " native" silver is found in much the same way, but more as specimens than as continuous bodies. Isolated patches of rare or valu- able minerals, such as Ruby silver, Horn silver. Silver glance, etc., occur locally in parts of the vein, sometimes coating stalactites or crystals of a " vugh" or cavity lined with qaartz or other crystals. An assay from such picked specimens would give a very unfair average of a mine or prospect. The bulk of the profits of a mine come from the com- moner minerals, such as galena, pyrite, or lead-carbonate, and from the average grade of the mine. In California gold mines, the average yield of gold per ton is $i6. In Dakota, $6. In the silver-lead mines of Leadville, $40 per ton is the average, and the ores are mostly low grade. A few miles of extraordinary high grade may yield from $75 to $100 per fon, but these are exceptional. Quantity of ore, facility tor milling, co^t of freight, the size of the vein, and iti: facility for working and nearness to market give the offset. DECOMPOSFD MINERALS. ir 1- r- is d :h y d )r Sometimes the gangue matter contains a variety of de- composed ore in rich secondary combination intimately mixed through its mass and rarely discernible by the eye. Thus, yellow mud from a mine may assay high, from the presence of invisible chlorides or sulphurets of silver. No accurate estimate of the value of a mine, or even of a piece of, ore, can be found without an assay or mill -run. The reason for such richness in decomposed surface products is, that nature has been for ages leaching out, concentrat- ing, and combining in richer forms the essence, so to speak, of the vein. Gray Copper (Tetrahedrite).— Besides the ordinary galena and pyrites common in most mines, we sometimes S 66 find considerable bodies of gray copper in mines, or inter- mingled with other ores. This is genr»-ally a rich silver- bearing ore, running from sixty ounces to some thousands per ton. It generally occurs massive, rarely showing its pyramidal " tetrahedrite" crystals. In appearance it is not unlike a freshly broken piece of bronze. It is more common in fissure veins in granite and eruptive rocks than in limestone. In Halls Valley, Color- ado, it is associated with baryta in a vein in the gneiss. It occurs in the Georgetown veins in granite. In the San Juan district it occurs also associated with baryta in the Bonanza ,^ . ^ , ,, ^ mine ; and an ore not identical with Gray Copper (Tetrahedrite.) .. . -j.- * ^ ^•■^ 'j. • ' *^' It in composition, but very like it in appearance, called bismuthinite, consisting of bismuth, an- timony, copper and silver, is characteristic of that region and is rich in silver. Bismuthinite has a more shiny, tin- like appearance than gray copper, and the red color which bismuth gives to charcoal under the blowpipe readily dis- tinguishes it from gray copper. Plate XXXV. LOCAL VARIATIONS IN VALUE OF ORES. There are locally in different mining districts consider- able differences in the value of certain minerals and ores. In one district g^ray copper may rarely exceed sixty ounces of silver; in another it is invariably over one hundred ounces. A coarse galena is generally poor in silver, while fine grained " steel galena" is generally rich in silver, but the reverse may also be the case. In some of the mines at Aspen, fine-grained galena, especially near the surface, is quite poor in silver, while in other mines in the same dis- trict it is exceedingly rich. Localities occur also where coarse-grained galena runs well in silver and is richer than fine-grained galena. This is the case at the Colonel Sel- lers mine at Leadville. So one mining district or even one mine is not a rule for another. Pyrites. — Iron pyrites and copper pyrites, common in 67 most of our quartz veins in granite and in the eruptive rocks, may yield both gold and silver, but usually the for- mer. There are certain districts more characterized by pyrites than others, such as the Central City district. The.se are generally gold-producing districts Some of the mines at Breckenridge and South Park have strong pyri- tiferous veins in eruptive dykes, such as the Jumbo mine. These have of late produced a great deal of gold. The same district, however, produces large argentiferous lead- veins. Pyrites generally favors the granite, eruptive and crystallized rocks. The quartzites of the Lower Silurian of South Park and Red Cliff are often pyritiferous and gen- erally gold-bearing. In limestone the pyrites is rare or absent, its place being filled by some form of iron oxide. In the deeper mines of Leadville, however, this iron oxide is beginning to pass down into the iron sulphide or pyrite from which it was derived. Iron pyrites can generally be distinguished from copper pyrites by its paler, more brassy color, by its superior hardness, and by its crystallizing in cubes. Copper pyrites is much yellower and softer, and crystallizes in a more pyramidal form. A vein may glit- ter with showy pyrites and yet be quite valueless. It usu- ally yields more gold in its decomposed, oxidized condition than in its unaltered state. In the one case the gold is free-milling, and in the other it must be smelted at much greater expense. SuLPHURETS. — This tei-m among miners is loosely used, and often means some decomposed ore whose ingredients cannot be determined at sight, but which somehow assays high in silver. True sulphuret or sulphide of .^ilver is a name embracing a large family of rich silver ores, among which are stephanite or brittle silver, argentite or silver-glance, sylvanite or graphic tellurium, and polybasite. All these rich ores are compounds of sulphur and silver and other ingredients in varying proportions. They are somewhat alike in appearance and not always so easy to distinguish. Argentite, silver glance, or sulphuret of silver, is of a blackish, lead-gray color, easily cut with a knife, and con- sists of an aggregate of minute crystals. Its composition in loo parts is sulphur 12.9, silver '7.1. Under the blow- 68 pipe it gives of¥ an odor of sulphur and yields a globule of silver. Stephanite, or " brittle" or " black" silver, is closely allied to argentite. Its composition is sulphur, antimony, and silver, silver being 68.5 per cent. The crystals are small. Under the blow-pipe it gives oft garlic fumes of antimony and yields a dark globule from which, by adding soda, we get pure silver. PoLYBASiTE, commou at Georgetown and in some of the Aspen mines, such as the Regent or J. C. Johnson, on Smuggler Hill, is like the others, but of a more flaky, scaly and graphitic appearance. It is not unlike very fine-grained galena, yielding 150 to 400 ounces of silver per ton. These sulphurets sometimes line little cavities in lime- stones with a dark sooty substance, which under the micro- scope proves to be crystals of one of the sulphurets of silver. Sometimes also a rock is stained all through a blackish gray by these sulphurets. Iron or manganese may produce much the same effect, but an assay will soon reveal the difference. Associated with such a rock we may see flakes or wires of native silver, that have emerged from the sulphide state. Plate XXXVI. Stephunite. ^ 1 CHLORIDES. Chloride of Silver (" Horn silver," or Cerargyrite). — This is another result of secondary decomposition from a sulphide state (slver sulphide). It is a greenish or yellow- ish mineral, like wax, and easily cut with a knife. It is a very rich ore, running 75.3 per cent, silver, the remainder being chlorine. As a secondary product of decomposition it is generally found near the surface or in cavities, some- times deposited on calcite or other crystals. In the mines at Leadville it is commonly associated with other decom- posed ores, such as carbonates. In the Chrysolite mine, a mass weighing several hundred pounds was found. Chlo- ride, bromide, and iodide of silver are closely related, being compounds of chlorine, bromine, iodine and silver. It is 69 noticeable that these salts are the elements of sea water, and that these ores are often found in marine limestones. According to Mr. Emmons, the change at Leadville from sulphide to chloride was produced by surface waters; these waters are found to contain chlorine, which they probably derived from passing through the dolomitic limestones which contain chlorine in their crystals, and these lime- stones perhaps originally derived it from the sea water in which they were deposited. Chloride of silver is found at Aspen and abundantly in the outcrop of mines in New and Old Mexico. SULPHARSFNITKS. Ruby Silver (Pyrargyrite and Proustite). — Composed of sulphur 17.7, antimony 22.5, silver 5q.8=ioo. Crystallizes in rhombohedrons, is seen in spots or crystals on a mass of ore of a deep red or blackish tint. When scratched with a knife it shows a bright or deep red color. In some mines this very rich ore occurs only as specimens, but in others it is present in sufficent quantity to largely influence the value of the ore in bulk. In parts of the Granite Mountain Mine in Montana, it constitutes the principal ore, associ- ated, however, with other minerals. It there occurs in large masses and accounts for the extraordinary richness of that celebrated mine. Proustite is much the same, only lighter red, and consists of sulphur 19.4, arsenic 15.1, silver 65.5 = 100. CARBONATES. This term also embraces a large family, the commonest being carbonate of lead (cerussite) and carbonate of cop- per (malachite and azurite). Copper Carbonate can never be mistaken, owing to its brilliant green and azure blue color. Copper stains are among the common surface signs of a " lead." It is gener- ally associated also with rusty stains. Both are the surface products from copper and iron pyrites forming a vein below ground which may or may not be profitable. Copper stains are common enough in many rocks, but do not always lead to bodies of ore. In South Park the red Triassic sandstones 70 are so stained, but yield no ore. Along our foothills there is quite a stained belt from Golden to Morrison and through Bergen Park. But few promising deposits of copper or other ores have been found, although handsome specimens of native copper have been discovered near Golden. At the Malachite Mine on Bear Creek, near Morrison, a prospect was at one time opened showing a good deal of silicate of copper (chrysocolla) and malachite, but for some reason it has not been worked since. CoiM'ER in its native or uncombined state is rare in Col- orado, and so far we have &s yet no true profitable mine. A great deal of copper is found associated with other ores, and is extracted by some of the smelters. Carbonate of copper is commonest in the limestone districts, as might be expected from the carbonating influence of limestone upon minerals in it, or mineral solutions passing through it. Carbonate of iron (spathic iron, or siderite) constitutes part of the gangue matter in some of our veins, and may also be found associated with coal seams generally, in the latter case in an oxidized condition. Cerussite (Carbonate of lead). — This is mostly found in the limestone districts, such as Leadville. It is there known in two forms, one called "hard carbonates," the other "soft" or "sand carbonates." The crystals of this ore are small prisms, sometimes combined into a cross shape, of a pale grayish white, and might be taken for some form of carbonate of lime or gypsum ; their weight, however, soon shows the difference. They are a secondary product of decomposition, consisting of carbon dioxide and lead oxide ; as a carbonate they effervesce in nitric acid, and yield lead when heated. Cerussite is exceedingly rich in lead, carry- ing seventy-five per cent. The white lead of commerce has the same composition. In Leadville and elsewhere in Colorado it is silver-bearing also, and, though low in silver, the facility of its treatment at the smelter makes it a very desirable ore. As a rule it contains less silver than the un- altered galena, but is more easily treated than the latter. The process of change or derivation from a sulphide state {i.e., from galena) to a carbonate, is well shown sometimes in a piece of Leadville ore. A central cube of galena is surrounded by a grayish green ring of sulphide of lead or anglesite. and outside this may again occur crystals of lead 11^ 7» carbonate. Thus the process is from a sulphide to a sul- phate, then to a carbonate. The so-called " hard carbo- nates" is a brown mass consisting of a hard flinty combina- tion of iron oxide and silica, impregnated with crystals of lead carbonate, with which are often silver chlorides, also. The " sand carbonates" result from the decomposition and Plate XXXVII. Simple and Compound Crystals of Carbonate ot Lead (Cerussite). breaking up of the hard carbonates, or from a mass of pure crystals of carbonate of lead, which are, by nature, loose and incoherent. The Leadville mines are getting below these products of decomposition and entering upon the original sulphides of galena and iron. The yield, how- ever, is said to be equally good. ZiNC-BLENDE (SPHALERITE) "BLACK JACK"). — Common in most mines mixed with other ores. As it is a very refrac- tory mineral in smelting, much of it is not desirable in a mine. It is easily recognized by its brown resinous look, or when very black by its pearly lustre. At Georgetown, near the surface, brown "rosin-zinc- blende" carries silver, and is associated with rich ores, such as polybasite and gray copper. With depth the zinc- blende becomes more abundant and blacker, and loses much of its silver properties. Zinc-blende may run from nothing to twenty dollars silver, and rarely as high as $ioo per ton. In some mines in the San Juan it occurs abundantly near the surface and fades out with depth. We have no true zinc mines in Colorado, the zinc being mixed with other ores. In some mines in Pitkin County the zinc predomi- Plate XXXVIII. Zinc Sulphide (Zinc Blende). 72 nates over all other ores, and though it runs high in silver the smelters do not care to take it, on account of its refrac- tory character. In the Eastern States where zinc smelting is a specialty, such ore might be separated and both silver and zinc saved. In Missouri zinc and lead are found to- gether. In Colorado there are no mines of one mineral alone, as in some other parts of the world. We have no true lead, zinc or cr,p^)er mines; these baser metals are either argen- tiferous or auriferous, and their baser qualities are sacri- ficed for their richer ones. CHAPTER VI. ORE DEPOSITS. i THEORIES REGARDINO IHK ORIGIN OF ORE-DEPOSITS. A prospector will find both a practical as well as scien- tific interest in considering the origin of ore deposits. Where do the precious metals come from? What is their origin? How are mineral veins formed and how do pre- cious metals get into them? The remote origin of metals is a matter of speculation. They may have formed part of that gaseous mist from which, according to the nebular theory, our planetary sys- tem was evolved. As this passed into molten condition the metallic vapors may have separated into various com- binations, and consolidated and been arranged in the gen- eral make-up of the world according to their specific gravity. Some have thought that the interior of the earth may be more metalliferous than the surface crust, since the earth grows heavier toward the centre. Volcanic rocks coming up from depths unknown contain a large per cent, of the heavier metals, particularly iron. But we turn from these speculations to theories of more practical interest to the prospector. A prevalent theory among miners and prospectors is what may be called " the igneous theory" or the fiery origin of veins and metals. They are apt to attribute the fissures themselves to some violent volcanic outburst, and consider 7J the quartz g:anf!nic or veinstone, together with the metalH. as molten volcanic emanations, filling at one tin)e a wide, gapin>f fissure. Others demand an intense heat, considering that the met- als in the veins were reduced in the bowels of the earth by intense heat to a vaporous condition, which, ascending through the fissures, condensed and consolidated in a crys- talline form in the upper and cooler portions of the fissures, as certain sublimed mineral vapors from a smelting furnace sometimes collect and recrystallize in the flues. By many prospectors every indication or surface appear- ance of a vein, or even a likely-looking rock, is called " a blow out," a term suggestive, at least, of some sort of vol- canic explosion at that point. With them, the " fire and brimstone" origin of ore deposits is as deep seat- ed as the veins in the rocks. These ideas contain a measure of truth, and were naturally suggest- ed by observing that our ore deposits are so gen- erally associated with volcanic rocks and evi- dences of past heat ; and it cannot be denied but that the presence of these volcanic rocks had more or less to do with the ore deposits. The modern study of ore deposits inclines to the belief that we need not draw directly upon the unknown profound supposed ignited regio.is of the earth's interior for the direct source of metals found in the veins, nor entirely from violent explosive volcanic agencies, nor from very intense heat, but racher that we may look nearer home for the im- mediate source of both metals and veinstone, namely, in the elements of the common country rock adjacent to the ore deposits; and for the medium of distribution and con- • * ♦ • ♦ \* * ♦ Plate XXXIX. *♦ *♦* Fold Passing into Fault Showing: Broken Character of Fault Fissure and Adjacent Rocks Producinff Later a Brecciated Vein and " Horses." 14 centration of ore nnd veinstone from nothing more violent or volcanic than wattT, more or less heated and alkaline. Nor is it so absolutely necessary to suppose that the filling of a vein fissure with quartz or metal must needs come up from profound depths, and from a foreign source ; but quite as likely from the adjacent sides of the fissure, or even from above the position later occupied by ore. Veins of whatever kind are not vents for molten volcanic matter, but simply courses for water, more or less heated Plate XL. A Tight Fault Crevice Ueingr At- tacked by Solutions ProducitiK Finally a Narrow Fissure Vein- Small Dots = Ore Solutions. Plate XLI. GnHh Vein FiHsures in Jointed Rrup* tive Sheet. and alkaline, in fact, channels of mineral hot springs carry- ing earthy minerals and metals in the same solution, and depositing them, partly by cooling and sometimes by chem- ical precipitation and mainly by relief of pressure in such openings or weak places as may be found convenient. The origin of these openings and weak places in the earth's crust is various. The class of great fissures hold- ing " fissure veins," cleaving our mountains from top to bottom to an unknown great depth, were caused by the fracturing and faulting of rocks, in the gradual process of folding upward, and elevation of the mountain system, a process so slow and gradual that it may be even progress- ing now without one noticing it. The relief of extreme tension from folding results finally in faulting ; though the fault fissure may extend to very great depths, it was prob- ably not violent but gradual. From tmie to time, the 75 Hhock produced by the g:rindinjf tojfctitLT of the walls of a tissurc, in a slip or jerk of only a few inches, may have given rise to severe earthquakes on the surface. A great fault fissure, too, was likely to be accompanied by minor adjacent faults, and also by small incipient fis- sures or loose fractures of the rocks, producing parallel fissures and zones of fissure veins. Other openings, occu- -*-^s*^-^^ :\ h ^f Plate XLIl. Joints and Bedding Planes. >''^ ^ Plate XLIII. Jointed Granite. pied now by fissure veins, may be compared to those joints common to all rocks, the result of contraction and shrink- ''ge of the granitic or volcanic rocks from a soft, semi- plastic condition to one more solid and compact. But in no case, we think, were the fissures now occupied by veins 50 to 100 feet wide originally wide open chasms like that which swallowed up Korah, Dathan and Abiram in Bible history, but rather cracks fitting very tightly together by enormous lateral pressure, such as we see in fault cracks of the present day, not yet occupied by vein- stone or gangue or metal matter. These narrow cracks were worked up- on by alkaline and acid solutions and enlarged 'jy the process, the rock gradually eaten into being replaced by gangue and metal matter, a process often fur- ther assisted by the shattered character of the rock comm >n- ly found adjacent to a great fault : this shattered cavity was sooner or later eaten out, so to speak, and replaced by min« Plate XLIV. Jointed Slate. eral matter. Some of the broken rock, being not consumed in this way, was left, forming fragments in the vein, which when small are called " breccia'" and when large "horses." The gfreat " gash" fissures, such as we find occuped by so- called fissure veins in volcanic sheets such as those of the San Juan region, Colorado, appear to be due hot so much to great earth movements, like the last, as to openings formed by cooling and contraction of the lava, somewhat as may be obset-ved on the cooling of iron in a slag fur- nace. Ore deposits of lead and other ir.'nerals forming / / ManltttSi Plate XLV. Joints in Columnar Basalt. Plate XLVI. Contact Ore Deposits Between Porphyry and Limestone. beUvied deposits in limestones find their way in solution through the vertical joints common to all water-formed rocks, resulting from contraction in consolidating from a soft, muddy condition. Such fissures are short, but they act as channels to a more important line of weakness occu- pied by the main body of the blanket ore deposits, viz., the dividing line between one stratum and another. An- other line of weakness for the attack of mineral solutions is at the juncture of a porphyry sheet or dyke with some other rock. The interval between them is often occupied by a " contact vein." The heat of the volcanic matter to- gether with steam may have influenced the solutions, even if the porphyry did not actually supply the metallic ele- ment in t'le vein. KOI i>iN« ANH kai:i,tin«;. In the many and xreat -ipheavals of the earth's crust, re- siiltinjif in conlinents risinj:^ above tlie sea, and on those continents still greater and sh»r]>er upheavals forming mountain ranges, rocks hav»* l>een nuch broKcn and frac- tured, from great fractures, i--^ lang fissures miles in length and depth, down to little crack-s of but a few inches. Much of this fracturing has been caused by the folding and crumpling upward of strata into mour.tains. accompanied by great crushing and mashing togeth 'r of the rocks. When this lateral tangential folding and compression of the rucks reaches its maxfmum int*;nsity, the rocks break, and a fault or slip is the result, with its attendant fault-fissure. This relieves the strain for a wV' . but the shock, doubt- less at the time accompanied by arth quakes on the sur- face, resulted in a general breaking up of the adjacent country into many parallel and smaller faults and cross faults, besides a gene-al shattering of the ground inter- mediate to the faults. A region thus faulted and shattered is Justin the desired condition for forming a future mineral belt or mining region, when the cracks and scars thus made have been healed and filled up by mineral matter, brought in through the agency of watery solutions more or less al- kaline or heated. A INTRUSIVE KiNKOUS ROCKS. When these fault-fissures descend to a very great depth, taey may tap the molten rock reservoir supposed to lie be- neath great mountain ranges, and the molten lava or por- phyry rushes upward through the weak line of the fissure, fills it with its matter, which on cooling becomes a dyke instead of a mineral vein. These eruptive rocks may or may not reach quite to the surface and overflow it in a lava sheet. Tf they do not, they find relief by intn^ding them- selves laterally between the layers of stratified vocks, whose leaves or bedding planes may have been partially opened, like the leaves of a crumpled book by previous action of folding. In such cases the porphyry dyke or intrusive sheet may, if it be mineralized, answer all intents and pur- pose of a mineral vein, or the ore may be found on one or both sides of such a sheet, in the line of separation and 78 weakness between it and the adjacent strata, or it may permeate and mineralize by a " substitution" process an ad- jacent porous or soluble rock, such as limestone. Thus both in the dyke or intrusive sheet itself, as well as at its contact with other rocks, the prospector should look for signs of precious metal. If the dyke or sheet should be decomposed, clayey, and rusty, it may contain free gold disseminated through i'., which, at a depth which may or may not be ever reached by mining, passes into the auriferous iron-pyrites from which the free gold originally came. In this case the ore will be no longer " free" or " free-milling," but of a charac- ter that must be subjected to the more expensive treatment of roasting or smelting. Little stringers or veinlets of quartz, if observed in such an eruptive rock, should he care- fully examined as the most likely source of the richest gold ore. Some of our most noted gold mines in the West are in these " rotten" mineralized dyk.s or eruptive intrusive sheets. " Likely signs" in such would be rusty " gossan" stains of green carbonate of copper and gouge or clay mat- ter. It is worth obsf.'rving that the dyk j may be only valu- able as a mine as far down as the decomposition lasts and as long as the ore continues in a free state. With depth, the pyrites of the undecomposed lower portion of the dyke may be found too poor in gold to pay for smelting even. As this desirable state of decomposition is the result mainly of the action of surface waters, a prospector may consider sometimes, where, on the outcrop of such a dyke, the rock is most likely to be deepest aJected by surface ac- tion ; for example, more probably below the old stream bed than on the top of a mountain, but this is not always the case. Most dykes and intrusive sheets when mineralized are mineralized by pyrites rather than by galena; hence they are generally more gold-bearing than silver-bearing. The contact deposits adjacent to a volcanic rock may have been aided in their deposition by steam issuing from the molten mass, or by heated waters or steam ascending with it, or generally by the heat of the dyke, as heat together with moisture is a great solvent of rocks and promoter of chemical action. In granitic rocks, if a " contact" deposit occurs adjacent to a porphyry dyke, it is usually a quartz vein, or a vein com- 79 posed of quartz and feldspar, commonly called " pegmatite." Such contact fissure veins may be on one or both sides of a dykie. The telluride veins of Boulder and the gold and silver veins of Idaho Springs. Central and (leorgetown in Colorado are often so situated. CONTACT DEPOSITS. When a porphyry sheet intrudes itself into limestone as at Leadville, the ore may be looked for on either side of ContaetOrit CoiOactOTe OreBea Contact Ore'i Gnei4s ^ Gneiss Plate XLVII. •' Contact Blanket " Ore Deposits and "Contact Fissure Veins." this sheet; but more commonly below it. At first the ore seems to permeate the limestone immediately at the line ^m^mmmmmmmm of contact, but from this somewhat horizontal line it is apt to run down through joint cracks in the limestone, en- larging the cracks by solution, and substituting or replac- ing the dissolved rock with silver-lead ore, by a process called " metasomatic substitution." " Metasomatic" means literally "an interchange between one body and another." In this case it is an interchange between metal and limestone, by which the limestone is gradually replaced, molecule by molecule, with metallic matter. Thus we may suppose, that as the mineral solu- tions were working on the limestone, rotting and soaking and dissolving it, as each molecule of lime was dissolved it was replaced or substituted by a molecule of metallic matter, until a large body of the rock was replaced by ore. This appears to be the true way in which most of our ore bodies were formed in limestone and other soluble rock, rather than that they were " washed in" and " deposited" in " pre-existing large cavities" as some have supposed. BI,ANKET DEPOSITS ON BEDDING PLANES. The solutions, having worked their way down through these vertical joints, may reach a second line of weakness, viz., the bedding plane or line of stratification between one bed or stratum of rock and another, and deposit along it as on a floor. This may be between one heavy bed of lime'- stone and anothei. If it is between two dissimila?- rocks, such as between limestone and quartzite, or even between limestone and magnesian limestone called dolomite, it comes under the name of a " contact" deposit. Thus it is noticeable that besides great fissures, lines of weakness or " bedding planes" are favorite places for ore deposits, to which the natural vertical joints often act as feeders, as well as themselves containing large " pockets" or " cham- bers" of ore. When the deposits are confined to these " pockets" and there appears to be no " blanket" deposit, the mine is said to be " pockety, " and after a " pocket" is exhausted an immense amount of money and work and blind " gophering" often follows in hunting for another pocket. There is in this case little rule to guide the pros- pector. Locally, by experience in the mine, he may notice that some fine line of gypsum, calcspar, or iron stain is apt to lead to a pocket and follow it. In the mines of Aspen, ftl where the mineral zone lies irregularl)' but generally near about the line where the limestone becomes dolomized. a miner, when his ore " plays out," follows as closely as he can this line, which he is able to do by the different hard- ness of the limestone and dolomite, the latter causing his f)ick to "ring." In every mine there is generally some ocal sign to assist the miner in following up his lost ore. SURKACK SIC;NS. The prospector in hunting on the surface oiitcrop for signs of such contact or blanket or pocket deposits must look out for signs of decomposition along the line of con- OreZon0 Ore Plate XLVIII. Prospecting with Diamond Drills. tact, such as lead carbonates, carbonate of copper, oxide of iron, together with crystalline matter, such as calcspar, Q;ypsum, or baryta. He may also observe, in the vertical 8a joints leadinj? down from the surface into the body of the limestone, rusty clay fillings and iron stains, in these "blanket" bedded deposits, prospects on a large scale may sometimes advantageously be made by drilling with diamond drills from the surface down through as many of the strata as are suspected of being ore bearing ; the " cores" brought up will show if an ore body has been penetrated, together with its approximate thickness at a certain point, and if this process is continued over a certain area, the approximate areal lin-'it of the ore'body may be as- certained. This work may fol- low upon a clo^ e examination first of mineral signs along the outcrop, it is sometimes done after an area has been exploited foi some time by Plate XLIX. Brecciated Lode with Quartz Geodes. Plate L. Bzecciated Vein. actual mining with a view of discovering new bodies or cojr.tinuations of the ore. TRUE FISSURE VEINS. Whilst profound fault cracks may be filled by lava, those not descendhig to such great depths doubtless lay open, till they were gradually filled by solutions carrying in earthy vein-stone and metallic matter ; in a word they were 83 the channels of mineral or hot springs. It must not be supposed that these fault cracks were ever " open chasms" commensurate in width with the wide dykes and veins now found in them, but rather in some cases very close-fitting cracks, mere lines of weakness, the walls appressed closely together by prodigious lateral pressure. In other cases the fissure would be rather a shattered zone passing down through the strata, than one definite line of fissure. Doubt- less when the molten lava ascended through these fissures it greatly widened them to admit of its volume. In the case of true fissure veins, the fissure or shattered zone was enlarged by the corroding, substituting power of acid min- eral solutions till we have to-day a fissure vein twenty to fifty or more feet in width. In the shattered zone, this substituting process would go on easily and rapidly, until nearly all the shattered fragments were replaced by min- eral matter except a few " indigestible" pieces, which, if small, would cause what is called a brecciated vein, and if large, " horses" in a vein. These fragments are not so much pieces that have fallen from above into an open fis- sure gradually filling up with solutions of quartz and vein m.atter in which they became entangled, but rather undi- gested, unsubstituted fragments of the wall rock, imme- diately adjacent to the fragments, for at times some line in the fragment corresponds to a line in the adjacent wall- rock without evidence of any serious displacement. Again, the shadowy outlines of fragments can be observed par- tially but not entirely replaced by quartz or vein matter. Sometimes the " breccias" are surrounded by rings of quartz or metal, and called " cockade ores." HORSES. In the San Juan region in Colorado, where we have won- derful opportunities of observing extensive sections of great fissure veins descending the faces of cliffs on either side of a canyon for two or three thousand feet, such broad veins at intervals split up into two or three arms enclosing large fragments or " horses ' of the lava country rock, and again unite to form the main vein. These veins occupy a once shattered fissure, the walls of which were originally neither straight nor regular, but shattered and cracked. «4 The vein matter insinuated itself between the shattered portions, sometimes forming a " breccia" of small frag- ments, at others " >• rses" of Targe ones. The appearance of these great San Juan veins from a little distance is that of broad yellow stains of oxide of iron contrasted with the sombre gray of the 1 a va rocks. In some places in this region the quartz, by rea- son of its superior hardness, stands up above the softer lava like a low, rusty, or white wall. Again, at other localities instead of being a bold outcrops the vein is represented by a sharp, shal- low depression forming a nar- row little ravine or trench, the path of a rivulet and zone of abundant vegetation. In this case the vein was full of decom- posable minerals, such as pyrite, whose oxidation decomposition products were washed out leav- mg a depression in the rocks. So, amongst some of the indications of a fissure vein to the prospector we may note : I St. Brown or green stains on rocks. 2d. A bold quartz vein like a wall above the country. 3d. A narrow ravine or gulch. 4th. The path of a rivulet and exuberant growth of vege- tation. SIGNS OF FAULTING. As these fissure veins are generally the filling of fault cracks, and the fissures are mainly due to faultio.g, a pros- pector should be able to recognize the surface and other signs of faulting. Faulting, as we have said, is generally the result of ex- treme folding. So, in entering a mountain region by way perhaps of a canyon cutting right through it on the exposed face of the cliffs, he may observe some of these folds or arches, low and gentle at first, but gradually, as the range Plate LI. Horse or Rider. n is penetrated further, increasing in sharpness, steepness, and closeness; with this increase we may CA^ect faults. The presence of the fault may be indicated by a little " sag" or depression in the outline of the hill, or by a line of rubbish and broken rock descending the face of the cliff, or by a zone of exuberant vegetation, or by the pathway of a little rivulet. He will observe a general fractured ten- dency of the rocks as they approach the fault line. By closer search he may notice pieces of rock polished or slickensided by the movement of the walls of the fault slipping and grinding upon one another. Slickenside is a sure proof of motion having taken place in the rocks, and is often observed on the walls of fissure veins. A much faulted region is often marked by a step-like outline, each step representing the fallen or risen side of a fault block. These fault-lines should be carefully examined for mineral indications, especially if the fault line is occupied by a porphyry dyke or a vein of quartz or calcspar. Some- times these fault lines arc totally barren, both of quartz, veinstone, or metal- liferous matter. Tho> may be filled up with clay, rub- bish, and broken roi.k, or the two walls may be ac- tually welded tojfether by pressure accompanied by a cer- tain amount of heat, producing local metamorphio action. Faultiiit, tuo in some regions may have occurred com- paratively recently, or at least after the period u.ost marked by deposit of mineral solutions and ore deposits, in which case the fissures may be barren or at present oc- cupied by hot or mineral spimgs making veins for the future. A stupendous, cofnparattvely modern fault runs along the west base of the Wahsatch Mountains in Utah; its line is marked by a series < I hot springs. Along the face of a canyon wall the piospector may no- tice some peculiar stratum tiear the top of the cliff and its counterpart out of pliMse ne»r the bottom, showing that a fault has occurred, whose aJMount of slip he can easily esti- mate or measure; but when a fault of many thousands of if=^^^^ Plate LI I. Vein a Faulted by Cross-Vein B. ^^•> (. nnnj ttnouf k wnpuof I W 86 feet occurs, a knowledge of the different geological peri- ods involved in the slip is nec- essary to estimate the amount of fall. Thus, if a prospector by his geological knowledge should recognize a Cretaceous rock, brought up in close jux- taposition to a Silurian rock, he would know that a stupend- o ous fault had occurred at that ^ place, involving the entire ^ thickness of the rocks compos- ^ ing the periods intervening j2 between the Silurian and the o Cretaceous. ■5 That a faulted region is one f in which great folding due to S lateral tangential pressure has o taken place, the folds eventu- u ally breaking dov/n in faults, t is well seen in the structure E of the Mosquito Range in ^ South Park, Colorado, which 2 embraces the Leadville min- ■5 ing district. fa The comparatively horizon- 's tal strata of the Park as they * approach the Mosquito Range .§ begin to fold gently, the o folds gradually increasing in steepness and closeness as they approach the axis of the range. As we pass up Four Mile Canyon, which shows a complete cross section of the range, we find the axis to be formed by a magnificent and very steep arch, well shown on the face of Sheep Mountain, which, having arrived at its ut- most tension, breaks down in *% i* 8? i> what is called the London mine fault, traversing? and split- tin>c the ran^c for twenty miles. The line of the fault is shown by a depression between Sheep and Lamb Moun- tains. In nearly every canyon along the flank of this range, the line of the fault is easily traced by similar arches and " sags," and by a peculiar wavy look of the turfed strata as they bend down toward the fault. As we penetrate further across the range, we pass a series of such faults, each one formerly represented by a steep fold that preceded the faulting. Hence it is that we descend from the top of this range down into Leadville and the Arkansas Valley by a series of gigantic steps or benches, each bench represent- ing a fallen faulted block. Faults have their points of maximum depth and disturbance, from which they are apt to die out at either end in folds or rounded hills. Great faults are accompanied by minor parallel and cross faults. The ultimate cause of this folding and faulting is attrib- uted by some geologists to the interior of the earth grow- ing colder and contracting, causing the surface crust to shrink and fold in adapting itself to the shrinking interior. Prof. J. F. Kemp says: "The strains induced by cooling and contraction of the earth are the most important cause of fracture. The contraction develops a tangential strain, which is resisted by the arch-like disposition of the crust. Where there is insufficient support, gravity causes a sag- ging of the material into troughs or synclinal folds which leave corresponding arches or anticlinal folds between them. Where the tangential strain is greater than the ability of the rocks to resist, they are upset and crumpled i *o folds from the thrust. Both kinds of folds are fruitful cv.w.»esof fissuring cracks and general shattering, and every slip from yielding sends its oscillations abroad, which cause breaks along all lines of weakness." JOINTS. Joints, common to all rocks, appear to be due not so much to faulting and motion, as to shrinkage of the rocks in passing from a soft matter or muddy condition to one of consolidation. A good many so-called fissure veins, even in the granite series, appear to occupy extensive joint cracks, rather than fault planes. These may be due to the ^ IMAGE EVALUATION TEST TARGET (MT-S) ■^ Uii 12.2 1.1 l.-^KS IL25 nill 1.4 1.6 <.1l. %^ A .* r Hiotographic _Sciences CorporatJon 23 WRST MASN STREET WEBSTER, N.Y. I45S0 (716) S72-4903 '^ iV s> ^ ■if*. '^"°^\' ^ v^^ v\ '^ 1 6^ 88 general shrinkage of the whole mountain mass in consoli- dating from a semi-plastic or aqueo-i^eous state of soften- ing to one more consolidated and rigid. The joints in lava sheets forming curious columns, like those of the Palisades of the Hudson, are due to the same shrinkage from a molten state. Such joints may sometimes be mineralized for a short depth, forming what are called "gash" veins, rather than true fissure veins. The joints in sedimentary rocks are due to consolidation from a soft, muddy, incoherent condition ; such joints may similarly be occupied by gash veins, or may lead to pockets or wide blanket deposits. The line of weakness between one stratum or one set of strata and another, often a favorite line for blanket de- posits, is due to one stratum being first laid down and par- tially consolidated before the next was laid later on top of it. IMPREGNATIONS. Rocks made up of loose material, such as porous sand- stones and conglomerates, are sometimes permeated by ore solutions, as, for example, the " Silver-reef sandstone of Utah. Sandstones are frequently impregnated with iron and copper stains. In fact, if we consider that ore bodies were deposited from aqueous solutions, we have only to consider the various opportunities the rocks afford by their texture, structure, etc., for this process. Veins, in a word, are filled waterways of many and various kinds. CHAPTER VII. VARIOUS FORMS OF ORE DEPOSITS. ORE BEDS. " Ore beds are metalliferous deposits interstratified be- tween sedimentary rocks of all geological ages. They lie parallel to the planes of stratification and follow all the contortions of the enclosing strata : hence they are thrown into folds, troughs, arches, saddles, or basins. The upper h ! \': i I 89 F Plate LIV. Faulted Ore-Beds in Anticlinal and Synclinal Polda. portions of the arches may often have been removed by erosion, or the strata may be faulted." The ore deposits or beds at Aspen occupy a faulted synclinal fold or basin. The enclosing rock is limestone, in part dolo- mitic. At Leadville the deposits occupy part of a series of fp^ulted anticlinal arches and synclinal troughs, of which the Mosquito range is the main axis. The beds lie between dolomitic lime- stone and sheets of por- phyry. The ore beds partake of all the folding, faulting and other contortions which the enclosing rocks have suf- fered in the upheaval of the mountains. The thickness of such deposits varies much and may gradually thin out and disappear, but may also continue long enough for all mining purposes. Often there are no sharp limits between an ore bed and the enclosing rocks, or between the ore bed and the walls, if walls exist at all. The ore appears to impregnate the surrounding rock by a chemical interchange between the elements of the rock and the ore. Such a " metasomatic' interchange, " substitution," or " replacement" appears to have taken place in the argentiferous lead deposits of Leadville and Aspen between the ore and the limestones. According to Phillips, " a true ore bed never produces a 'combed' or 'ribbon' structure made up of symmetrical layers, such as is common in so-called 'true fissure veins,' and is usually without the crystalline texture observable in veinstones." K UNSTRATIFIED DEPOSITS, FISSURE VEINS, ETC. Mineral veins are changeable in character, and their ap- pearances of a perplexing and complicated nature. There IS a gradual passage from one form to another, so that it is difficult to classify them. There is often no such sharp dis- tinction between one form of ore deposit and another, as 90 legal disputes would sometimes demand, and a witness should hardly be called upon to assert on oath that such a vein is a " true fissure," or another a " bedded vein," or a third a " segregated vein." " Nature abhors straight lines" and sharp distinctions, and delights in blending one form imperceptibly with another. Phillips divides veins into two classes, " regular and ir- regular veins." " Regular unstratified deposits include true veins, segregated veins and gash veins. Irregular deposits i n cl u d e impregnations, fahl- bands, contact and chamber de- posits." Veins are collections of miner- al matter, often closely related to, but differing more or less in character from, the enclosing country rock, usually in fissures formed in those rocks after the rocks had more or less consoli- dated. All veins do not carry metals; some are merely barren quartz, feldspar, or calcspar, like the barren veins we so often see traversing granite or limestone rocks. Veins may divide, " split up" or thin out, and are irreg- ular in shape and structure, owing to the irregular widUi of the fissures and to other causes. Plate LV. A Split Vein. DEFINITION OF MINING TERMS. The rock in which a vein is found is called the " country rock," e.g., limestone, granite, porphyry. The portions of country rock in direct contact with the vein are called respectively the "hanging wall," or roof, and the " foot wall" or floor. This is only in inclined or flat veins, as a vertical fissure vein can have neither roof nor floor, but only two walls, east and west, or north and south, according to the compass. The inclination of a vein to the horizon is its " dip." The horizontal direction of a vein at right angles to its dip is its "strike." The latter may commonly be observed along the surface outcrop, the former either in the workings of the mine or where the vein is exposed on the side of a canyon. \ 9» Both dip and strike of a vein often vary much, the for- mer with depth, the latter with extension across the coun- try. A vein or ore deposit will not unfrequently begin with a gentle dip. and increase rapidly in steepness with depth. The ore deposits on Aspen Mountain commonly begin with a dip of 25°, and at a depth of less than a thou- sand feet reach 60° or more. As fissure veins commonly occupy fault fissures, their irregularities in dip and strike correspond to those we have already spoken about, under faults The angle of Jip is usually taken from its variation from a horizontal, not a perpendicular line. Thus, a dip of 75° means one that is very steep, while one of 10° is a gentle inclination. A layer cr sheet of clay called " gouge." or selvage, often lines one or both walls of a vein between the country rock and the gangue or vein proper. It is derived from the ele- ments of the adjacent country rock, decomposed by water, and sometimes by the friction of the walls of the fissure against one another, or against the vein matter, in the process of slipping and faulting, which is often shown by Its being smoothed, " slickensided," polished, or grooved. Gouge often contains some rich decomposed mineral in it, such as sulphurets of silver. It sometimes occurs in the heart of a vein, especially if that vein has been re-opened anew by movements of the strata. The " Chinese tallow" gouge of Leadville results from the decomposition of the feldspars in the adjacent white porphyry, and is a hydrous silicate of alumina. In the granite veins in Clear Creek County the gouge is derived from the feldspars of the granite. Gouge is some- times useful in defining the limit of the vein between walls, thus preventing unprofitable exploration into the " country." It is also a guide for following down a vein when mineral and gangue may be wanting or obscure. Both walls are not always clearly defined by slickensided surfaces, by gouge or other mark, and so at times the vein is lost. False walls, caused by movements in the adjacent strata, by joints, etc., also mislead. It is not uncommon for a fissure vein to have but one clearly defined wall, the other, if it exists, being obscured 99 or changed by mineral solutions. Sometimes two cracks or fissures occur parallel to each other and the intervening country rock has been altered and mineralized into a vein. It is probably in this way that many wide veins were formed. Mr. Emmons has found that fissures are formed by great movements of the earth's crust or by local contraction of the rocks, and that a fissure is not necessarily one with well-defined walls at considerable distances apart, filled after the formation oi the fissure, but that the ordinary cracks or joints in gran- ite quarries, extending regularly to great lengths or depths, illustrate the original fissures which have been changed by percolating waters carrying mineral solu- tions into veins and deposits of ore. In all crystalline and sedimentary rocks, these cracks or joints run parallel to each other at various distances apart, of- ten plentiful and close together. In cases where percolating waters were charged with the proper metals and veinstone matter and the necessary chemical and physical conditions existed, the rocks ly- mg between those cracks or joints were altered into ore. As one element was dissolved another took its place; so, according to this authority, it would seem that even a fis- sure vein may be only a sort of " metasomatic replacement" of rock by mineral. Hence, what is commonly accepted as a " wall" of a vein is not necessarily one, and cross-cut- ting, in order to determine the lateral boundaries of the ore, is safer than to rely on supposed walls. A so-called " slip" has often been followed by a miner as a supposed wall, until by accident he broke through and found good ore on the other side. If veins are formed according to Mr. Emmons' theory, the occasional loss of one or both walls is easily accounted for. Cross veins of a more recent age sometimes cut or fault an older vein. The point of intersection is generally rich in mineral. Cross veins must not be confounded with " leaders," which are the filling of minor cracks extending Plate LVI. ImpreKnation of Rock by Vein. off from the vein, and are sometimes sufficiently profitable to work. While they sometimes lead a prospector to the main vein, they may also lead a miner underground astray from the true vein. The splitting of a vein by a " horse," or large fragment of the country lying in the vein, may be mistaken for a true cross vein, or the original fracture of the fissure may have been in the form of a star or like the spokes of a wheel radiating from the hub. In such cases there are no true cross veins. Hut when, as in the San Juan district, we have two well-defined sets of veins, one striking northeast by southwest, and the other northwest by southeast, they cut each other diagonally, the cut vein being the older. These opposite sets of veins have been formed at different times. Many contain a charac- teristically different class or variety of minerals. Thus, in Cornwall, England, one set carries'tin and the other lead. SIGNS OF A TRUE FISSURE VEIN. True fissure veins show signs of motion or slipping on the sides of the fissure, such as slickensides, gouge, crushed walls, " horses," or " breccia," the latter being small portions of the country rock surround- ed and cemented by vein mat- ter. In the Comstock, the quartz is ground to powder. The vein itself, though occu- pying a healed fault fissure, may be itself faulted by later movements in the mountain after the vein was formed. Some of the fissure veins on Engineer Mountain, San Juan, are so dislocated. The vein-filled fissures be- ing a line of weakness, may be reopened by mountain move- ments, and other or different combinations of ore introduced into the heart of the vein. Such a reopening would be Plate LVII. Combed, Banded or Ribbon Struct- ure with Quartz Geode. -'* S'« 94 marked by a succession of " combs" or banded ribbon-like deposits of ore, and by gouge matter. OUTCROP OF VEINS. The outcrop of a vein is that which appears at the sur- face and usually attracts prospectors to the spot. Some- times it may be, as in the San Juan district, a bold vein of hard white or rusty quartz, standing up in relief, by its superior hardness, above the surrounding country, like a low wall. Or again, in the same district, from being com- posed of softer or more soluble substances than the pre- vailing eruptive lava sheets, instead of a wall, it causes a depression or trough on the side of a hill, forming the pathway for a rivulet and marked by luxuriant vegetation. Commonly the outcrop consists of a decomposed mass of rock, stained with oxide of iron and streaked here and there with green or blue carbonate of copper, and is called " float" or " blossom" by the miners. This float is the chemically changed or oxidized portion of the true and un- changed vein lying deeper below the soil. On Aspen Mountain the float is generally a rough crystalline mass of calcspar and baryta stained with iron and copper. In this "blossom rock" free gold is not unfrequently found, but unaltered sulphides, such as galena or iron py- rites, are rarely met with on the outcrop. In the San Juan district, on Mineral Point, we have, however, found galena at the grass roots, and broken off large chunks of it from a quartz vein outcropping on the surface. In gold-bearing veins such an oxidized condition is de- sirable if it continues down to any depth, for, so far as it continues, the gold is free, and the ore is a free milling one, easily treated, and often exceedingly rich in gold, as in the celebrated Bowen mine of Del Norte ; but as soon as the hard white quartz and the unoxidized pyrites of the true vein is reached, the ore is no longer free milling, but must be smelted. The gold may still be found free, per- haps, in the hard quartz, but if the pyrites should not prove rich in gold, the palmy days of the mine may be considered as past. Many such rich deposits on the surface, abound- ing with specimens of free gold, have proved great disap- pointments with depth. 95 winni OF VF.iNS. Veins mp.y vary in width or thickness from a half inch to a hundred feet. They also pinch or widen at intervals in Plate LVIII. Metalliferous Veins Exposed to View near Howardsville, San Juan, Colo- rado, Showing Two Systems of Fissure Veins Crossing One Another. their downward course. The widest "mother" veins are not always the must productive, though they are very per- mm 96 sistent in length, and we may suppose m depth also. In the San Juan district the " mammoth" veins of quartz, often a hundred feet wide, are not the favorites for develop- ment, the ore being found too much scattered in them, and the development less easy than in those 10, 30 or 30 feet wide, where the metal is more concentrated. These mammoth veins in the San Juan are easily traceable for miles over the surface of the country and down the sides of the deep canyons. Th'eir limiting depth has never been reached, and probably never will be by mining. DRFINITION OF TRUE FISSURE VEINS. True fissure veins are popularly defined as filling fissures of indefinite length and depth, commonly occurring in parallel systems, traversing the surroundinp^ rocks inde- pendently of their structure or stratification, and commonly, though not necessarily, at an angle different from that of the stratification — in other words, cutting across the planes of stratification. These veins orig- inated in fissures, not neces- sarily wide open ones, but on the contrary rather narrow cracks, descending, however, to great depth, such as those produced by faulting, or the general cleavage lines of the mountain. The latter may be frequently observed in every canyon, and also in the sedimentary rocks of the foot-hills and' even along the flat surfaces of the plains. They are very conspicuous in the plains around Trinidad, and are there not unfrequently occupied by a series of narrow par- allel dykes of basalt instead of by mineral veins. Cleavage lines or joints are familiar to every stone-quarry man. These cracks are caused by extensive movements of the earth's crust in the process of mountain uplift, and also on a smaller scale by contraction of the rocks in cooling from a heated or molten condition, or even in consolidating from a soft or muddy condition. Plate LIX. Fissure Vein Conforming in Part to the Bedding Planes of Strati- fication, in Part Crossing them. 97 The two waIIs enclosinp: a vein do not jjenerally concide. ns might be expected, if the vein occupies a line of fault. A true fissure vein may in some part of its course coincide with the dip of the surrounding strata. As the plane of stratification or line of division between one stratum and another is a natural line of weakness, a crack once started would be liable to follow it for some distance. And when uplift occurs such places are liable to slip one upon the other, and a true parting fiisure ensues conformable to the prevailing dip. Such a vein might appear at first to belong to the class of so-called " bedded veins," but if with depth it should be discovered to be cutting across the strata it would be pro- nounced a " true fissure vein." The ap- pearance of slickensides or other signs of motion on the walls of the apparent- ly " bedded portion" would then prove it to belong to the " true fissure' class, and that actual fissuring had taken place prior to the vein-filling. Plate CAUSE OF I'OCKETS IN FISSURE VEINS. As a fault fissure in its downward course usually pursues a zigzag rather than a straight course with smooth sur- faces on either side of the crack, the in- equalities of one face of the crack are brought into opposition to the inequali- ties on the other face, as one or the other side of the fault slips up or down, and thus are produced pinches and wide cavi- ties, which give rise to the " pinches" and " bonanza pockets" so common in fissure veins. A so-called true fissure vein may sometimes have advantages over some other forms of vein occurrence, from its persistency and comparative regu- larity to gn*eat depths. It must not, however, be expected that it will continue equally rich or equally poor through- out its course. There may be comparatively barren spots and rich spots, pinches and widenings, local c >i ibinations 7 Pocket and Pinches resulting from Slip- pingf of Uneven Walls of Fissure. of richer or poorer varieticH of mineral. rule is not liicely to entirely give out. nut thu vein its h RICHNESS WITH DKPTH. There is no scientific reason why a vein should " grow in richness and size with depth." This is a popular fallacy, originating from the now less accepted theory that veins were formed by thf» precipitation of precious metals, by heated rising waters or vapors, and hence that the greater concentration would take place at greater depths. The " lateral secretion" theory, now by some accepted, ascribes the deposition of ore to solvent waters reaching the vein from ground quite near to it, and coming naturally from above and the sides quite as often as it is ejected ttpward by pressure from below. In Idaho Territory, says Mr. A. Williams, " the rule is rather that veins grow less rich and strong with depth, though strong veins may continue metalliferous to a greater depth than mining can ever reach. The thickness of the earth's crust which we are able to explore is very limited. Increase of heat, as in the deep Comstock mine, and other natural difficulties, limit us to a few thousand feet — 3,000 at most. These deep mines have not, as a rule, proved richer with depth, but to the contrary. Some veins have been worked through alternate zones of richness and barrenness. The Comstock, which has been opened for four miles in length and to a depth of 3,000 feet, snows the ore bodies to be scattered irregularly and the barrenest ground is at the bottom. On the other hand, some of the most celebrated mines derived their wealth from rich ores encountered near the surface and have proved most disappointing with depth." Atmospheric action for a long period has often reduced the ore to its richest compound, and when the hard mate- rial is reached leanness sets in. This, as we have observed, is commonly the case with gold veins. The richness of the Leadville mines is derived from their decom- posed compounds. Again, as the surface crust can be so little explored by mining, it is to be remembered that the erosion by glaciers and waters has already removed thou- sands of feet of the vein, so that we are able to examine 99 only a small fraction of it, while an unknown ({uantity lies in thi" depths below. If these veins, then, continue to the supposed great depths below, we are very far from their starting point, and erosion having rem»)ved their upper portions, we cannot find their surface finishing point; in other words, it is not n fresh "ready made" vein we find, but portions of an old vein already extensively mined by the processes of nature. So far as our experience goes in Colorado, after a moder- ate depth is reached below surface action, or belt>w the " water level," a fissure vein may grow richer or poorer, wider or narrower with depth, without any law except local experience in a district. • VKiNs IN c.wours. Fissure-veins occur in clusters and nearly parallel groups, forming a mining district, and again in that district certain ?ecuHar veins may be grouped together, ftirming a " belt ' 'hus, Boulder district occupies a certain isolated area, out- side of which few mineral deposits occur for a long dis- tance. We have also in that district several distinct belts carrying different characteristic ores, such as the telluride belt, marked by rare telluride deposits, the pyritiferous gold-bearing belt, and the argentiferous galena belt. The Central City region is characterized by auriferous pyrites belts, Georgetown district, not far distant, by argentifcr- t)us belts, and Idaho Springs, lying between the two, by both gold and silver belts. CHAPTKR VIII. RELATION OF VEINS TO ERUPTIVE FORCES. The ultimate cause of the richness in veins of a district or locality is, that local dynamic and eruptive forces were more energetic there than elsewhere, causing great disturb- ance of the rocks, accompanied by fissures and eruptions of porphyry. Thus at Leadville, the Mosquito range is violently folded .^nd fractured, eruptive rucks have issued abundantly, and >li lOO associated with such phenomena we find great lead and silver deposits. Further south the great San Juan district is split up in an extraordinary manner with great fissure veins. The region is an eruptive one, consisting of prodigious flows of eruptive rocks, traversed, not unfrequently, by newer erup- tive dykes. In the Gunnison district the strata have been overturned, disturbed, folded, and faulted in an extraordinary manner by the intrusion of great masses of eruptive rock forming the peaks of the Elk Mountains. The strata everywhere are riddled by dykes or intrusive sheets, and the evidence of heat is apparent in the general metamorphism of the entire region. Mineral veins abound. The same phenom- ena are repeated more or less in the neighboring region around Aspen, and at Pitkin and Tincup. At Boulder, Central, and Georgetown there is a concen- tration of eruptive dykes locally in each district, and a few dykes or eruptive rocks outside of those districts. On the other hand, we have no ore deposits in the undii.turbed rocks of the plains or the flat basins of our parks, and no- tably our mining districts are for the most part well into the core of the mountains, where, in the nature of things, folding, crumpling, faulting, eruptions, and metamorphic heat were more energetic than along the flanks and foot- hills of the range which have usually proved unproductive. The older eruptive rocks, such as the quartz, porphyries, and diorites of the Leadville, South Park, and Gunnison dis- tricts, are more favorable to the production of ore deposits, as a rule, than the more modernly erupted lavas, such as basalt or dolerite, which we commonly find occurring in dykes and surface overflows, traversing cr capping our Cretaceous and Tertiary coal fields along the foothills as at the Table Mountains at Golden and Trinidad. Some of the lighter colored and somewhat recent lavas like the tufaceous rhyolite, which caps so many of the Tertiary mesas on the Divide between Denver and Colo- rado Springs, have also hitherto proved barren. Yet the volcanic rhyolites, andesites and phonolites of Silver Cliflf, Cripple Creek and Creede are productive of both gold and silver. A large portion of the eruptive rocks of the San Juan region, productive of gold and silver-bearing fissure I^I veins, are in andesitic breccias of comparatively modem date. The older eruptive rocks, as we have stated, are nearly all of an intrusive character, never having reached the surface, while the newer ones bear evidence of having flowed over the country like modem lava-streams, as is shown by spongy scoria on their surface, and may be called "effusive." In Colorado the ore body is not usually found in the heart of an eruptive sheet or dyke of porphyry, so much as at the line of its contact with some other rock, such as limestone, granite or gneiss. CONTACT DEPOSITS. The " contact" ore deposits of Leadville occur at the con- tact of quartz, porphyry and dolomitic blue limestone. Some of the veins at Boulder, Central and Georgetown are at the contact of porphyry and granite or gneiss. Exceptions occur, however, where mineral is found either in the heart of a dyke, or the whole dyke may be so impreg- nated ^s to constitute in a sense a vein. These excep- tions are generally confined to pyritiferous gold deposits, and telluride goM deposits as at Cripple Creek. GOLD-BEARING DYKES. Suppose a dyke or mass of eruptive rock to be thoroughly impregnated with gold-bearing pyrites. Near the surface and often for a considerable depth the rock is decomposed and the pyrites oxidized into rusty iron ore, liberating the Hold which is entangled in the " gossan" in wires, flakes or even small nuggets. As long as this decomposed or oxi- dized state continues, the ore is free milling, but with depth the dyke is found in its primitive hardness, studded with iron pyrites, which may or may not prove rich enough for the more expensive treatment of smelting. Such gold- bearing dykes are found at Breckenridge, South Park, also in Idaho Territory, Cripple Creek, Colorado, and in old Mexico, and many other gold-bearing regions. The Printer Boy gold mine at Leadville is a vertical de- posit in a jointing or fracture plane in a dyke of quartz- l)orphyry, rusty and much decomposed near the surface, where it yielded free gold ; with depth this passes into cop- 1 01 9ut090nt per and iron pyrites. The vein is from an inch to four feet in width; stringers carrying ore extend into the porphyry, which is highly charged with pyrites, which doubtless supplied the vein with mineral through the agency of surface waters. In Ari- zona, near Prescott, at the Lion mine we find a green dyke ». f erup- tive diorite penetrating granite. This dyke is traversed by nu- merous small veins of white quartz which near the decomposed and rusty surface are rich in free gold. At slight depth the quartz veins become charged with unoxidized iron pyrites sufficiently rich in Ske';Xw,>,Jox1di"ld'"in§ gold to merit treatment by smelt- Unoxidized Portions. ing. The surface ore is treated by a simple " arrastra," and is, of course, free milling. The gold seems to be mostly con- fined to the quartz veins. Plate LXI <»old Vein or Gold Bearin FISSURE VEINS IN IGNEOUS AND GRANITIC ROCKS. The San Juan district is an exceptional case where im- mense numbers of fissure veins penetrate igneous eruptive sheets. The fissure veins consist of hard gray jaspery quartz traversing lava sheets whose united thickness is from 2,000 to 3,000 feet. The veins produce lead, bis- muthinite, gray copper and other silver-bearing ores. In Colorado true fissure veins are most characteristic of the Archaean granitic series. In fact, all the veins in that series are fissure veins. Locally they occur as in the San Juan, cutting through eruptive rocks. Outside of these formations few true fissure veins occur. An exception may be made of the Gunnison and Elk Mountain region where the fissures traverse all the forma- tions from Archaean granite to the top of the Cretaceous coal beds. Nearly all other mineral occurrences, such as those in the limestone regions, come under the class of bedded-veins or blanket-veins, pipe- veins or " poc ets," and show none of the characteristics of slipping motion or fissure 103 action. Under this latter class the Leadville and Aspen deposits may be grouped. Ore deposits commonly occur at the junction or contact of two dissimilar rocks, as between quartzite and limestone or limestone and dolomite. Lodes occur also between the stratification planes of the same class of rock, sandwiched in between two layers of limestone, and sometimes impregnating the layers on either side for some distance from the dividing line between the two strata, which is commonly the line of principal con- centration of ore, and often descend from this concen- tration line, through the medium of cross joints, to form large pockets in the mass of the limestone. The Aspen and Leadville deposits are of this character. Also when ore bodies occupy a true fissure, /. e., one cutting across the stratification planes, they may locally, for a short dis- tance, impregnate the adjacent walls or country rock more or less. Our fissure veins in granite and gjneiss often im- prep:nate the walls to a small extent. >■ neral deposits favor as a rule the older rocks, such as the .irchaean and Paleozoic series, propably because heat and metamorphic action are commoner in these older rocks, which have felt all the throes of the earth from past to present times, than in the more recent ones, and such cir- cumstances, as we have stated, are peculiarly favorable to vein formation and mineral deposition. The bulk of our precious minerals in Colorado comes from the older Archaean and Paleozoic series of rocks, the exception being the Gunnison region around Crested Butte, Irwin and Ruby, where ore comes from fissure veins in the Mesozoic Cretaceous rocks. The exception is accounted for by the local metamorphism, heat and eruptive phenom- ena of that region. The veins in the San Juan have also been ascribed by some to the Tertiary Period, owing to their occurrence in certain supposed Tertiary lavas covering that district. Besides heat, metamorphism, dynamical disturbances and eruptive agencies, other minor circumstances may favor ore deposition. Certain rocks, such as limestones, may offer, by their tendency to solubility and chemical reac- tions, more favorable conditions than others for mineral solutions to deposit by " metasomatic" interchange between II 0-' li .>^ ro4 mineral and limestone, until the limestone is gp-adually replaced by ore, much in the same way as the elements of a water-logged trunk of a tree are replaced by silica in the process of fossilization. 1 1 It CHANGE OK MINERALS WITH DEPTH. Lodes often change in the character of their minerals with depth, not only after they have left the zone of second- ary decomposition and surface action, but also far below it. Thus, in the San Juan, some of the mines abound in zinc- blende near the surface, which with depth almost disap- pears, gfiving place to gray copper and other superior ores. In Cornwall, England, the shallow workings yield copper, and with depth, tin ; and locally many such changes may characterize a particular district, but cannot be formulated as a rule for other localities. INFLUENCE OK COUNTRY ROCK. In most mining regions, to which Colorado is no excep- tion, a relation has been observed between varieties of " country rock" and ore deposits. Veins in passing from one country rock to another are liable to change in the size or variety of the ore, widening in connection with some rocks, and pinching or growing narrower in connection with others. Certain rocks are notorious ore-bearers, whilst others are notoriously barren over large regions, or in special localities. The presence of certain rocks adjacent to other diflferent rocks has an enriching tendency on the ore bodies. As regards rocks that are good ore-carriers or receptacles of particular classes of ore in Colorado, we may say : That quartzites and silicious rocks generally carry more pyrites, and are gold-bearing. That veins in granitic rocks carry a greater variety of minerals than others, and may be both gold and silver bearing. That certain limestones carry much argentiferous galena. That sandstones and other unaltered rocks carry little ore of any kind. '05 The influence of country rock on veins may be from sev- eral different causes, for instance : Certain rocks are by their structure better adapted than others for forming regular fissures. Thus, massive lime- stone is better fissured than slate or shale, leaving wider open spaces for the ore to collect in. Other rocks may be more porous, and admit mineral solu- tions through their pores. Of such a kind are some of our porphyries, andesites and phonolites. Others, like limestone, are easily acted upon by solutions dissolving out the rock and replacing it with mineral by substitution. Some are better conductors of heat, and therefore would assist chemical action and mineral solution. And lastly, if modern theories of " lateral secretion" be true, viz. : That most ore comes from the adjacent country rock and is precipitated, substituted, or collected in the vein fissure, and further, that the metals themselves are derived from certain metallic elements in the ordinary con- stituent minerals of the country rock, such as mica, horn- blende, or augfite, it is clear that a rock composed largely of such minerals would be liable to influence the vein as an ore generator. Granite, porphyries and andesites are largely composed of these minerals. The frequent presence of eruptive porphyry rocks near veins and ore deposits in Colorado shows that they have an important influence on those deposits, which may be of various kinds. First, that in their component minerals and mass they actually contain the elements of the precious metals sub- sequently deposited in another form in the fissure vein or in the soluble limestone in contact with it. Second, by the heat which they retain for a long time after they have congeakd and hardened, they would assist in the reactions of any chemical or' mineral solutions that might be on hand. Lava, at the time of its eruption, is always highly charged with steam and other gases. By reason, also, of the chemical composition of porphyry, waters passing through it would be alkaline and assist in dissolving silica and other gangue or veinstone matter, and when the porphyry has thoroughly cooled it is exceed- ingly porous, and being much jointed and cross-fractured. ^ 106 becomes like a great sponge for the absorption of all sur- face waters. This may be noticed at Aspen, where all the mines that are at present penetrating through the " porphyry cap" are much troubled with water, far more so than in the underlying limestone. Surface waters, then, becoming alkaline by passing through this rock, and also more or less charged with carbonic acid, chlorine, and other solvents, would be ready to dissolve both gangue and vein ingredients out of the porphyry and redeposit them in the vein fissure, or, by metasomatic substitution, in the limestone usually beneath it. Water circulating in fissures, changes or dissolves the ingredients of the surrounding rock. The rocks enclosing lodes are always so altered, and this decomposition and alteration is not always merely local or confined to the close proximity of the ore body, but we often find a whole mining district, such as Leadville, Aspen and San Juan, pervaded by this feature. So much is this the case that it is often difficult to get a fresh, unaltered specimen of por- phyry or some other country rock within the district. The brilliant red, yellow and maroon tints that color so much of the mining district of San Juan result from the oxidation of pyrites and other iron-bearing minerals per- vading the eruptive rocks, and it is noticeable that this color, resulting from alteration and decomposition, is most prominent in those parts where lodes have been discovered, as, for example, the gorgeous tints of the Red Mountain area around the celebrated " National Belle," " Yankee Girl," and Iron ton mines, between Silverton and Ouray. The rocks in Geneva Gulch, Hall's Valley, Buckskin Can- yon, and in other mining centers, display the same beauti- ful tints of oxidation in the vicinity of the mines. " In lodes a mutual exchange takes place through the reaction of the ingredients of the rock and the materials of the vein. Thus, when water containing carbonates comes in contact with rocks or minerals containing alkalies, a chemical reaction takes place. When these last are com- bined with silicic acid, these silicates are decomposed by the carbonic acid and the bicarbonates. This explains both the crystallizing out of the carbonates and the so fre- quent decomposition of rocks containing lodes, especially those which, like our veins in granite, are feldspathic." I07 The same principle applies to other ores and minerals in lodes. Thus the precious metals, in the mines of Lead- ville in their original condition, have been proved by depth to have been in a sulphide state, such as iron pyrites (sul- phide of iron), or galena (sulphide of lead,) etc. Surface waters charged with carbonic and other acids, passing through the overlying porous alkaline porphyry and enter- ing the underlying limestones, have, as we have previously observed, changed the sulphides into sulphates, oxides, and carbonates. The presence of a dyke near to or cutting a vein has been found often to enrich the latter at the point of contact. In the " Colorado Central" mine at Georgetown a narrow dyke of brown obsidian traverses a large dyke of ore-bear- ing porphyry. The valuable ore is found close to the obsidian dyke. This might be the result of greater heat at that point. The " black dyke" in the Comstock mine is a somewhat similar case. PREJUDICE IN FAVOR OF AND AGAINST CERTAIN ROCKS. There is often a prejudice amongst miners in favor of certain rocks and formations, and against others. Miners who have worked perhaps in the g^eat Comstock mine of Nevada or the Leadville mines of Colorado, or the fissure veins in granite of the Old World, are apt to look out for and favor certain rocks and formations they find like those they have been accustomed to. Thus, as Mr. Williams says : " The peculiar ' porphyry' of the Comstock was hunted up in other districts, but did not prove metalliferous. Solid granite was looked upon by others as unfavorable, gen- erally, because locally some granite above the gold belt of California had proved barren. Yet some of our best veins are in granite. " Limestone was at one time a very unpopular rock and supposed only locally to produce lead, till the discoveries of Leadville, and Eureka, Nevada, overturned the scale in its favor." In the Leadville " excitement" not only was the particu- lar Carboniferous limestone of Leadville hunted for and prospected, but every other limestone in the South Park region, no matter what its geological age or position, was ^v io8 extensively prospected without results, miners not recog- nizing the fact that it was not limestone generally that pro- duces rich ores, but a particular limestone of a particular geological period (the Lower Carboniferous) not over 200 feet thick, that happened locally to be rich near Leadville, and the reason of its being locally rich at that point was owing to the concentration of eruptive energy at that point and the intrusion of an unusual amount of porphyries, which in point of fact are far more responsible for the ore than the limestone, which happens to be merely the receptacle. It was also quite common after the Leadville xcitement to find shafts in all sorts of improbable and hopeless locali- ties, whose owners would tell you : " At Leadville it didn't matter where a man 'went down.' It was all luck whether you 'struck it* or not, and so they might as well 'go down' where they were as elsewhere." It was often said " that Leadville had exploded all so-called scientific theories about ore being in oiic formation or locality more than another. It was all a case of luck." The excuse for this is to be found in the fact that in the immediate vicinity of Leadville it did scarcely matter " where you went down," seeing that that area was prac- tically underlaid by bedded sheets of mineral, but that such would be the case elsewhere and everywhere or "nywhere, experience unfortunately has shown to be untrue. It is not a particular rock or formation, but a combination of favorable circumstances, that alone can make a rich mining district. As experience advances, geologists and miners have proved that ore deposits have a mtch wider range than was once supposed. F'ormerly only the Archaean g^ranite series was supposed capable of bearing ore deposits, because in the Old World, tin, copper and lead came prin- cipally from fissure veins in those rocks. Then deposits were found in the Paleozoic series and supposed to ascend no higher. But in the present day, and even in Colorado, they are traceable even to the Tertiary. It is not the rock, nor the age, but a combination of cir- cumstances, principally heat and metamorphism, that may make any rock of any period an ore-bearing one. And in prospecting in new regions it is these combinations rather than any particular rock that should be looked for. 109 STRIKE ANU DIP OF VEINS. The dip of veins approaches more nearly the vertical than the horizontal, usually from 75° to verticality. Nearly all our ore deposits, in Colorado, even those of the bedded class, dip more or less steeply from 25° to 75°. For a few feet from the surface, on the steep slope of a mountain, it is common to find an ore deposit dipping quite gently or even folded over and dipping in a contrary direc- tion to that which it assumes with depth. This appears to arise from the weight of the strata above it tending to bend it over downward in tl direction of the slope of the hill. Th re is generally a prevailing dip and strike amongst a number of parallel fissure veins of a district. In the San Juan, the bulk of the fissure veins have a prevailing north- easterly strike and dip to the southeast. The angle of dip is generally between 60° and verticality. CROSS-CUTTING UNCERTAIN. The dip, as we have said, not unfrequently changes con- siderably with depth, usually becoming more and more vertical. From the degree of uncertainty as lo the con- tinuity of the dip, it is not always safe, on the discov- ery of an outcrop, to endea- vor to cut it at a much low- er point, so as to get the coveted depth, and better opportunities for stoping. drainage and other devel- opments of the mine. Ow- ing to a change of dip or fault, perhaps, the miner may liave to make a much longer cross-cut tunnel than he had calculated upon be- fore striking the vein. Sometimes, too, he may miss the vein altogether, cutting it perhaps at some point where it is exceedingly thin or poor, so poor in fact that he passes through it without noticing it or believing Plate LXIl. Showing How Cross-cut Tunnels and Shafts May Miss Veins by Change of Dip or Faulting. no it to be the same vein whose outcrop looked so promising on the surface. Cross tunnels through " dead rock" should hardly be undertaken until the vein has been proved to be a strong one for a considerable depth. As we have already shown, great depths may not after all be so desirable in even a fissure vein, as there is no certainty whatever about veins becoming richer or poorer with depth. Extensive cross-cut tunnels have seldom proved paying concerns. The greatest in the United States, the Sutro tunnel, six miles in length, which tapped the Comstock fissure at a depth of 2,000 feet, did not prove a financial success, and had it tapped the fissure still lower, at 3,000 feet, it would have found the vein in the impoverished condition it is today. It is not uncommon for a miner to strike a rich outcrop on the top of some mountain, and on the strength of its richness in- duce a company to run a long cross-cut tunnel in " dead rock" half through the moun- tain to cut this vein, and the company's resources are nearly exhausted in so do- ing, while the vein itself gives no returns, owing to its being left idle. Finally, perhaps, the vein is missed, or if struck, proves far poorer than was anticipated. Of course there are exceptions where cross-cut tunnels in " dead rock" may be advisable. If a fissure vein, as in the San Juan, should outcrop near the top of a mountain and be exposed on its dip all the way to the bottom, there may be some reason for opening a tunnel in it near the base, thereby facilitating drainage, development and exportation. In that case the miner is on the vein, with no fear of losing it ; but even here, there is no guarantee that it will prove rich all the way to its out- crop a thousand feet above. " Follow your ore. and be careful how you leave it for any experimental theories," is a common and wise saying among experienced miners. We remember a tunnel in the Gunnison region which was Plate LXHI. Fissure Vein Exposed from Outcrop to Dip. 1 1 1 run several hundred led at a cost of tnany thottsands of dollars, all through "dead rock," in the hopes of cross-cut- ting a certain ore body that had proved rich near the sur- face. At last it was given up, and subsequently a short cross-cut was made from it, and the original vein was found only a few feet from the tunnel, which had been running parallel with it all the time. The cause of the mistake was an unforeseen fault in the vein that had shifted its dip much further on one side than had been calculated upon. CHAPTER IX. GOLD I'l.AChRS. PROSPECTINC FOk I'LACKR C.OU^ AND C.Ol.Vt VF.INS. Having given in preceding chapters a sketch of veins and ore deposits in the rocks, it follows in order to speak of gold placers, because these arc derived from the former by the agencies of water, either in the form of glaciers of old, or of ancient or modern streams. ti Plate LXIV. Open Placer Grounds in Canyon. The glaciers in olden times heavily mined the rocks and the veins, by cutting broad gashes through them, thus originating the canyons. In this way millions of tons of rock were mined, together with the gold-bearing veins in 111 I 12 them, and also the precious metals minutely diffused and scattered throughout their masses. After the glaciers, the rivers took up the work, deepened the canyons, broke up the boulders and sorted them, setting free the gold and other metals they contained, and again sifted and sorted them and deposited them along their banks and in their beds. Of the various metals thus handled by nature's jigging process, many were dissolved and destroyed by various acids in the waters, and by acids of vegetation and iron salts percolating through the placer dumps after they had been laid down. So with the exception of a few very hard minerals, such as magnetite, diamonds, garnets, rubies, Plate LXV. Section in Gold Placer. etc.. little remained in the placer but the imperishable gold, and even that appears to have been refined of its alloy of silver which it contained in the original vein, for placer gold is generally much purer and more valuable than that in the original vein. In some cases, too, the fine gold disseminated through the placer appears to have been acted upon by certain salts, such as the persalts of iron, and concentrated and amalgamated into large nuggets. Some contend, however, that these nuggets are only waterworn pebbles of gold, brought direct from the vein, the result perhaps of con- centration there of the contents of large masses of gold- bearing pyrites; it is to be noted, however, that whilst gold-bearing nuggets of various sizes are to be found, not »«3 lUK «iinin»)nly in ifold placers, ihcy arc very rarely lounU in j;olci veins. With the gold in placers is commonly found what is called " black sand," which is composed of grains or peb- bles of magnetic iron ore. relics of the old gold-bearing pyrites chemically changed. Being near in gravity to gold, and originally associated with it, the two are gener- ally found together in a placer, and a prospector in sur- veying a bank of placer-material made up of sand, pebbles and boulders, generally looks for a streak ot " black sand" as a likely place for gold. Also by reason oi the gravity of gold he is inclined to look for it more down on bed- rock than in the upper loojier strata. Ancient river beefs as well as those of" modern rivers may be found gold-bearing, rivers that have long ceased to flow, by reason perhaps of change in the configuration of the country. In California and Australia many of these ancient gold-bearing river-beds have, at a period not long distant, been deluged and covered by lava, and the gold is extracted by tunnelling beneath the lava-sheet or by shaft- ing down through it to the gravel below. These are called deep leads, whilst the ordinal y uncovered gravels are called "shallow placers." Almost anywhere along ancient or modern water courses not far from mountains, a prospector by panning can get colors of gold even on the pebbly " wash" covering the sur- faces of large portions of our plains, or even on the tops of table lands that once were plains, over which broad rivers and glaciers and large bodies of water distributed their debris, but as a rule it will only pay to work where the " wash" or " drift" or " alluvial" matter is plentiful and thick, and more than this, only where water is accessible to the work. PROSPECTING. A prospector hunting for a gold placer follows up the water channels in which he finds specimens of all the rocks in the neighborhood. In Australia, the prospector looks amongst these to find samples of granitic, porphyritic and quartzose rocks or clay-slate as likely signs, ana also pieces of quartz honey-combed and rusty, which we have de- 8 114 I ; scribed before as " float or blossom. " Plenty of broken up quartz he considers a good sign, but very pure, hard, dull white quartz is generally considered as " hungry" or " bar- ren;" the size of the fragments denotes his nearness or otherwise to the reef, i.e., the vein. A prospector examines closely the fine sandy matter of the stream bed, especially where eddies and backwater have Deen formed. A likely deposit should be scraped up, even down into every crevice and depression in the bed rock or solid rock bottom over which the river, modern or ancient, has worn its channel. This material should be panned. Gold, too, is often found on points and slopes of the bed rock as well as in the deepest portion. Nuggets \> t0 Plate LXVl. Shallow Placer— Gold Sand in Potholes A, A and Beluw a Hard " Hat I?. found on high reefs above the level of the stream, imply that their weight enabled them to remain in their position, during the deeper erosion of the neighboring streams, and that the original vein from which they came is not far off. As a rule, large nuggets and coarse gold are found much nearer to the source whence they came, than fine or " flour" gold, which is often carried to unlimited distances away out on the plains. The character of quartz veins and of their enclosing rocks in the immediate viciniiy, decides the character, too, of gravels derived from them, hence sometimes a peculiar pebble may be traced up to the peculiar rock whence it came, and the gold vein be found near it in place. It has been observed that " Xesidis" following the course "5 or lines of a gold-bearing reef, maintain a more continuous yield than those crossin^t^ a number of gold reefs at intervals. Gold occurs in pockets and " shoots" at intervals, with barren portions between, which accounts for what we have stated above. In a country where the gold quartz veins are small, though rich at wide intervals, the gravels will also be small. In very deep ground where the " wash" is very heavy a series of borings or even shafts are made to test the quality of the bank. The following points have been observed as worthy of note in prospecting for gold placers. r. Streams crossing the lamina or stratification planes (»f gold reefs at right angles are likely to be richest. 2. Gold is rarely found plentiful where there are indica- tions that the current was strong, but rather in the lee under projecting points of rock, where beaches are usually formed and the water was slack. 3. Gold in streams is deposited in crevices of the " bed rock," which should be laid as dry as possible and picked up to such depths as the sand descends between the laminations. 4. Terraces are shelf-like excavations and deposits upon hill slopes above valleys, and are the remains of old glacier or river beds. The prospector should discover the inlet and outlet of the terrace and examine the gravel. The " wash" sometimes contains gold in layers one above the other. 5. Whilst working up stream a<:tention should be paid to the banks on each side where sections are exposed so that no outcropping vein be overlooked. 6. Alluvial gold should if possible be traced to its source whence the " float" came. When the gold is large and plentiful and the boulders large and angular the reef is likely not far distant. 7. Sometimes there is a distinct peculiar feature in all the veins of a district, such as a peculiar band of a definite color. 8. Coarse alluvial gold is not always incompatible with fine reef gold as a source, because the reef gold may be so fine in general as to lend itself to very wide distribution when once it is liberated, while the rarer coarse grains would not be transported far. ii6 9. Alluvial placers are richest where the current of the stream is interrupted by diminution in fall, by sudden change of direction, or by entrance of a tributary, also by reefs, bars, eddies, etc. Absolute richness depends upon local circumstances and the size and weight of floated masses. i ii Plate LXVII. Sliallow Placer— Gold Sand Behind Bar on One Side of Creek. 10. Creases, holes and fissures of bed-rock over which the stream passed are favorite places. 1 1. The lowest layers of each separate period of deposi- tion are the richest. Sometimes several different periods of deposition have succeeded each other. 1 2. The courses of present streams and of ancient chan- nels are placers. " Loaming" is a form of prospecting. It is preliminary to such prospecting as cutting experimental trenches, or sinking trial shafts or boring. It consists in washing sur- face prospects from the bases and slopes of the ranges, until specks of gold, or specimens are found to be obtain- able with tolerable frequency, within certain limits. The prospector then proceeds to trace the gold up hill to its source, narrowing the limits of his work as by patient search he approaches the vein, whence the gold has been derived. When he can obtain surface prospects of gold up to a certain point, or line, but no farther, he then pro- ceeds by means of trenching to search for the gold vein. The prospector has often to work along a steep scrubby mountain side, selecting his prospects, numbering them, i f 117 and placing samples in .lis " loam bapf." If he discovers prospects of gold, he finds his way back to the spots the samples were taken from, so as to continue his up-hill search, and trace the gold to its source or vein. Some- times there is no indication of a vein, soil and bush<;s and debris covering its out-crop, but by loaming, the prospector ascertains its position, so as to expose it by a trench not many feet, in length. We remember an ingenious way in which a valuable and long sought for vein was at last discovered. Prospectors liad long found very rich " float" at the base of a hill whose surface was so deeply covered with loose debris that no trace of the vein could be found. A prospector found a small lake on top of this hill, and conceived the idea of cutting a trench from this body of water to the edge of the hill, and by damming up the trench, and then suddenly letting out the water to full force, it cut a deep trench through the loose debris down to bed rock and the vein was discovered. This process is called " booming." The cleava[^e of quartz is said to be freer, sharper and better defined, in gold-bearing quartz than in that which is barren. Pyrite is a good indication. A soft, fatty clay or gouge often flanks the vein in its gold-bearing portions. The mountain spurs should first receive attention for veins; if the quartz is hard, it stands up, if soft, as it more commonly is, it will leave a streak-like depression. On finding such, the prospector should first wash out some of the decaying rock. If only a trace of gold is found in the quartz, there is probably a gold vein in the neighborhood, and trenches should be dug and exploration systematically followed up. Gold is generally near one wall of a vein, seldom all through the stone. Quartz gold occurs in " shoots" with barren spaces. Before setting a valuation on a discovery, the facilities for working the mine, such as we have alluded to, should be considered. Placer mines as well as other mines are often supposed to be " worked out." These are sometimes well worth investigating and examining by cross-cuts or other means. Sometimes it happens that more gold is ob- tained from " leader" veins that had been overlooked, than from the main worked vein. Quite commonly, especially in the lower part of a placer, ii8 I the pebbles and sand are firmly cemented together into a coarse conglomerate by inliltration of iron oxide and clay. This may consolidate into a false-bottom and not be true " bed rock." Generally two or three such false-bottoms, with intervening strata of greater richness, alternate with barren ones. So, many old diggings, thus supposed to have been exhausted, ni.;y be worked again, the true bot- tom not having been reached. These conglomerate bot- toms may lie just upon bed-rock, with a white clay rich in gold beneath them. Gold occurs also in the conglomerate and must be stamped out. Modern rivers frequently cross in their course old river courses, and redistribute their golden sands. Placers are richer in their richer parts, tha.i the veins from which their gold was derived. When shallow placers are due to the wearing down of quartz veins, no placer will be found above these veins, or above the point where the vein crosses the placer. In the Sierra Nevada there is but little alluvium, the gold comes from veins near by. Gold placers may sometimes occur below silver mines. Thus the Comstock vein was discovered by following up placer gold to its source. This vein has produced a gold- bearing silver-ore, the silver rapidly disappearing and leaving the geld behind. EXAMPLE OF A PLACER. In Ballarat, Australia, the '* wash-dirt" runs in a series of " leads" of varying width, starting from the same point, and trending in different directions towards the " deep leads.' The " reef wash" is about loo feet deep, the " pay dirt" 5 feet. The barren drift wash overlying the " pay dirt" is of black clay. The reef itself is of green slate, the bed- rock is sandstone. Gold lies sometimes on thin layers of sand or " pipe clay" on the surface of the " bed-rock," more often in crevices of the bed-rock itself, which is more or ".ess rotten. This bed-rock is broken up for some 12 to 20 inches and the gold is found in "pot-holes" in it 15 to 18 inches in diameter and 6 to 10. inches deep, cut out of the solid rock. The alluvial gold is found chiefly in bed-rock of slate, dipping 90 degrees. Some of these slates are soft and rotten, tithers are indurated. On the soft rock only is 119 the gold found. Nuggets are found in the soft clay lying on "bed-rock." Slate forms natural " riffles" for catching the gold. Deep pools under waterfalls in gold-bearing streams rarely carry much gold. So in rivers, gold is found in " bars" or points rather than in deep pools or bends. CHAPTER X. DEEP LEADS. A " deep lead" lies deep below the surface, often covered by beds of lava, especially in California. These lava beds may be many in number, and hundreds of feet in thickness. The " deep lead" is an ancient river bed. In the Sierra Nevada the gold is derived from metamor- phic crystalline rocks of the range, partly from quartz veins in the slates, and partly from gold distributed in minute quantities all through the metamorphic rocks. The quartz veins lie between the planes of stratification of the slates, also in irregular bunches and lenticular masses of limited extent. In many localities, the rocks are penetrated in every direction by little irregular quartz veinlets, which often carry gold, and in spots are extremely rich, even where the quartz vein is only an inch thick. In some Cali- fornia districts, wherever a basalt capping exists, the drift beneath it is auriferous. In California the modes of occurrence of auriferous gravel deposits are various. " Sometimes they exist in well-defined ancient river-beds under a capping of basalt which has filled the channels of the rivers in past ages. Again, they appear in isolated mounds or hillocks, evidently the remains of such channels, which, being unprotected by a covering of lava, have been broken up by the action of the elements, also in basins or flats whch have received the wash of these disintegrating rivers, also in low, rolling hills neai the base of the Sier- ras, and beyond the reach of the lava-flows." One of the most remarkable and important gold leads is that beneath Table Mountain in Tuolumne County. " The waters per- colating through these lava-flows and reaching the gravels 120 beneath, are charged with alkali from the lava. These alkaline waters are charged with silica in solution from the same source. Hence the fossil drift-wood of these ancient rivers has all been silicified by these silicious waters. The gravels are also cemented by the same ma- terial. These percolating waters also contained iron, for iron pyrites is found in contact with the silicified wooc's. In this iron-cement, gold is found in rounded grains and m minute crystals, and threads deposited by a solution of sulphate of iron at the moment of the reduction of the latter to a sulphide," BABnr Plaik LXVIII. Deep Placer, Table Mountain, Cul.— A A, Ancient River Channel, with Gold-bearing Gravel ; B B, Sandstones and Shales with PoFsil Bones and Silicified Wood. The dead rivers of California are on the west slopes of the Sierra Nevada, from 500 to 7,000 feet above sea-level. The largest and richest lead is the " Big Blue Lead," traced 65 miles and even 1 10 miles. It is parallel with the main divide of the Sierra Nevada. The live modern rivers run at right angles to it, cutting canyons 1,500 to 3,000 feet deep. The " Blue Lead" runs across these ridges from 200 to 1,000 feet below their summit. The lead was discovered by following up surface washings. Miners found that the modern streams were richly gold-bearing up to a certain point, increasing as this point was neared but ceasing when It was passed. These parts were in the line of the different streams, and by following up indications, the lead was eventually struck on several sections and tunnelled on. The deposit is 300 feet deep, composed of gravel, boulders, clay, and sand, on strata distinguished by degrees of fine- T3I nes5>, by the character of the rocks, and the amount of {fold, also by colors, the prevailing color being a bhiegray. (iold is coarser near the bottom, and contains a greater alloy of silver. The silver in the gold in the upper strata has been eaten out by sulphurous acid resulting from de- composition of iron pyrites. The whole deposit is like that in existing rivers, showing banks, bars, eddies, falls, rapids and riffles. There is much gold in the eddies, and but little in the rapids. The space between the boulders is filled with sand and contains gold, the bed-rock is slate. Where dead-rivers meet, the " wash" is generally rich. Where a lead becomes very narrow, dips fast, and is in- closed between steep walls, the gold will be very sparingly distributed in holes and behind ridges and will be coarse in size. Very large and abundant boulders in gold-bearing stream beds are often a serious obstacle in getting out the gold, from the difficulty of handling them. More than one placer has been abandoned from this cause alone. HYDRAULICS. Placer banks are worked on a large scale by " Giant noz- zles" or Hydraulics. Before commencing such work the total depth of the placer deposit should be examined and ascertained, and the richness of the strata throughout tested. Shafts should be sunk here and there to bed-rock for this purpose, and topograhical surveys made to ascer- tain what fall and head of water can be obtained, and what outlet also for the tailings, as the latter would soon choke up the work ; the ground sometimes may be too flat to dis- l)ose of the tailings by stream-power. The choking of out- lets is a fertile source of abandoning placers. Beach Mining. — " The beach sands of the Pacific and else- where contain minute scales of gold and sometimes plati- num, together with a great deal of magnetic iron ore. Winds, tides, and surf act as natural concentrators or sepa- rators in parting the light and useless material from the heavier. Wind drives heavy swells on the beach at high tide together with sandy matter. At ebb of tide, the surf lashes the beach and carries back light portions of the mass with the undertow, leaving some iron sand, gold and plati- I y i: 3 ; num, whose weight enables them to hold their place. At low water, miners go down on the beach, scrape up the iron sand, which is generally left in thin layers, stacking it back from reach of the surf, and subsequently washing out the gold." In some beaches much of this sand contains titanif- erous iron ore, and if attempts are made to use certain pro- cesses to save the finer gold the character of the iron may be a formidable obstacle. EXAMPLE OF COLORADO PLACER GOLD MINES. California gulch, the site of the present Leadville, fur- nished a great amount of gold in the early days till the dis- covery of the lead-silver deposits in place. This discov- ery, also, was due to placer mining. Whilst examining the gravel in the gulch, Mr. Wood, an intelligent prospec- tor, was struck by the appearance of what the miners called "heavy rock," some of which he assayed. His specimens yielded 27 per cent, lead and 1 5 ounces silver to the ton. He put prospectors to work to find the croppings of the ore deposits, and in June, 1874, the first "carbonates in place" were found on Dome Hill. This was practically the be- ginning of Leadville. It is said that upwards of 2,000,000 dollars worth of gold was taken out of this gulch in one summer before the mines in place were discovered or opened up. It is noticeable that California gulch alone furnished almost all this placer gold, whilst Iowa and Evans gulches adjoining it on either side and carved out of the same se- ries of rocks, yielded little or nothing. Why should the smaller gulch contain exceptionally rich gravels and its neighbors be barren? The richest portions of California gulch were found at bends in the course of the gulch. In one place near Oro in the narrow bed of the gulch, a gold-bearing cement was found containing hydrated oxide of iron, below the gravel, yielding an ounce of gold to the ton. The gulch-gold was worth $19 per ounce whilst that from the mines in place only $15. The Printer Boy porphyry containing actual gold veins in place may have been the source of some of the gold in the gravels, together with the oxide of iron resulting from the decomposition of pyrites in the pyritif- erous porphyry as a cementing material. Also the " Weber- »«3 grit" sandstones at the head of the jn^lch have been found to carry small gold veins, and from their abrasion also gold-bearing gravels would have been carried down the gulch. Also of late the rich gold deposits of Breece Hill at the Ibex and Little Johnnie mines have been found. " It is doubtful," says Mr. Emmons, " whether in general, all or even the greater part of the gold contained in placer gravels is derived from the abrasion of actual gold veins. Traces of gold may be found in a very large proportion of the massive rocks which form the earth's crust. Gold veins are concentrations of this mineral in sufficient quantity to attract attention and yield a profit. But doubtless there are a vast amount of smaller concentrations which may escape notice. As the rock disintegrates and is worn away Ijy atmospheric agencies, the gold from these smaller de- posits as well as from the larger is set free from its inclos- ing rock and subjected to the concentrating action of moun- tain streams. " Placer deposits are the results of nature's vast sluicing processes. To bring them into the condition in which they may be made available by man, requires not only the gold- bearing rock, which her agencies may grind up into sand and gravel, but the sifting power of rapid streams, which may carry down the lighter and coarser material, and a suitable channel in which the heavier particles may lodge, as in the riffles of a sluice box. All mountain gravels, all sands of rivers coming from the mountains, contain a cer- tain amount of gold, but it is only under peculiarly favor- able conditions that the gold is so concentrated as to render the gravel remunerative. " Among the most favorable of these conditions is a com- paratively narrow channel having a hard and compact bed- rock, and ridges or bends in its course, which by causing a partial arrest in the rapidity of the current shall allow the heavier particles of gold to settle to the bottom, and hold them there when once they have settled. " From this point of view there is a very evident reason why California gulch should have furnished rich placers, and why the gold which may exist in Iowa and Evans gulches should not yet have been extracted even though the detrital material which has been carried down the gulch should originally have been equally rich in gold. M.. i i ^' 194 " California gulch is a valley of erosion, formed entirely by the action of running water, and since the glacial period. It has therefore a bottom or bed of hard rock. Its trans- verse section is V shaped and therefore favorable for the concentration of heavy particles at its bottom. When com- paratively full of water, its numerous bends formed eddies in the down-flowing currents, and allowed a longer time at these points for the settling of the surface particles, and as it cuts across many different formations m its course, its bed must have transverse ridges, which have caught some of the gold and prevented it from being carried farther down the stream. " Evans and Iowa gulches on the other hand are glacier- carved valleys. Their courses are straight, their bottoms broad and comparatively smooth. The glacial moraine material with which they are largely filled has not been subjected to the sifting or jigging process to which gravel is subjected in the bed of a stream. The lower part of their present beds is cut, not out of rock, but out of the loose gravelly formation of the 'Lake beds.' This later bed, along which the material brought down by post-glacial erosion has been carried, has not a sufficiently hard and permanent bed-rock to allow of the concentration of gold on its surface." A A AND FAIRPLAV PLACERS, SOUTH PARK. Along the banks of the Platte river are enormous masses of glacial morainal matter consisting of boulders and sand brought down partly and principally from Mount Lincoln and receiving contributions from side glaciers of the Mos- quito range. This material forms undulating banks on either side of the river. This placer " wash," from 50 to 100 feet thick, is worked for gold principally at Alma and Fairplay. At Alma the heavy bank of " wash" is mined by the giant nozzle. The banks are also cut back into blocks of ground, by water from a flume, which is let out at intervals along the bank above ; at each place it cuts a narrow ravine in the loose debris and at the same time makes the banks easier to be attacked by the water of the giant nozzles, which rapidly undermine them. The water and sand from 12< these streams run down into the shiices. whose ht)ttoms are paved with discs of wood, forming " riffles'" to catch the gold, whilst the lighter sand is carried onward by t"^e stream. In their " clean up" in the stream bed. they not only wash down to bed-rock, but after hunting with their knives in every crack and crevice of the latter, they dig it up for a foot or two, and further examine it. The rock is a jointed sandstone. Quicksilver is thrown into the sluices, to collect the finer gold which is afterwards retorted. Whilst gold is found all through this bank of " wash" from " grass roots" down to bed-rock, the greatest quantity of gold and largest nuggets are found at " bed-rock" or in its interstices. The .source of some of this gold may be a series of large, but not very productive quartz veins iu granite, near Mount Lincoln, whence the main glacier originated. It is also probable that a good deal of the gold came, as said before, from the breaking up of the various rocks in which it was disseminated, more especially the porphyries and crystalline rocks. In the winter, owing to freezing of the water supply, the work has to be discontinued till the following spring. CHAPTER XI. MINING REGIONS SHOWING EXAMPLES OF ORE DEPOSITS. FISSURE VEINS IN GRANITIC ROCKS. Having described in previous chapters the nature of veins, ore deposits, etc., and how to prospect them, it will be of interest as well as profit to the prospector, to learn something of the mines and mining regions them- selves. For this purpose we propose giving a sketch of some of the leading mining regions of Colorado and the West, as instructive illustrations and examples of what we have written in previous chapters. As we said in our advice as to the education of a prospector, the best educa- tion for him is to go to, and spend as much time as he can in, the mines and mining regions themselves. 126 Wc will take first the regions iharactcrized by Jissure veins. These veins are in the granitic and igr^euiis districts of Colorado. In the granitic ranges, the mining districts of HouUkr county, Gilpin and Clear Creek, are the most noted, the jirincipal mining towns being Boulder, Jimtown, Georgetown, and Central and Idaho Sjirings. ROUI.DF.R MINFS. The geological features of Boulder consist in a series of ridges or hogbacks rising up from the prairie and flanking the granite mountains. These represent Mesozoic strata consisting of sandstones, limestones and shales, containing beds of coal and other economic products, but no precious metal. Volcanic action has occurred in their vicinity as shown by a large dyke of basalt at Valmont. These hog- backs, so universally present, flanking the granite moun- tains, are, in Colorado, destitute of precious ores. Inside of and west of these is the Archaean granitic front range, consisting of heavily bedded granite-gneiss, profusely traversed by veins of *' pegmatite" or very coarse sparry granite, consisting of white feldspar and quartz, with very little mica, and from a few inches to 40 or 50 feet in width; with these also occur some dykes of eruptive rock, some of it a dark black rock like basalt, called "diabase"; others are lighter colored quartz porphyries and diorites. In the telluride belt, whilst pegmatite veins are abundant, erup- tive rocks are scarce, but west of the telluride belt, which is more or less confined to a special area underlying the Magnolia, Sugar Loaf, Gold Hill and Central districts, enormous masses of eruptive rock are foun^. but no tellu- rides. In the non-telluride districts, such as Caribou, Weird and Jimtown, rich silver ores are found associated with galena, gray copper, etc., and gold ores associated with copper and iron pyrites. Thus there are two or three distinct belts in the region, a telluride gold belt, and a silver belt, and a gold pyrites belt. It is noticed that the entire region has been locally disturbed by volcanic forces, and volcanic rocks abound ; outside of this disturbed region there are no mines for a long distance. The Boulder mines are celebrated for the occurrence of telluride minerals, some of the richest and rarest ores oc- '»7 I currit)}; in nature. These ores are confined to a belt oc- cupyiiij^ the eastern part of tlie district, and nearer to the lin;^baek region of the phiins than any other important ore deposits in Colorado. West of this belt in the Caribou district the ores are argentiferous galena, with brittle silver. In the Ward dis- trict pyrites abound, and where it is decomposed the gold is free. The pyrites though gold-bearing are dirficult of reduction. The pegmatite veins containing the ore stand at a high angle and are often very wide, but the rich ores, especially the tellurides, are concentrated in thin streaks and not very continuous bodies. The gangue or vein material is simply an alteration of the adjacent granite, or gneis- sic country rock, into a more sparry, larger crystalline form, consisting of (luartz feldspar and some mica. This is impregnated with rich mineral whose source is probably not far to find, the metal elements being microscopically or chemically diffused through the mineral elements com- posing the adjacent country rock, which is sometimes por- phyry, and at others gneiss. This impregnation has taken place either along the contact of an eruptive rock with the country rock granite, or else in a pre-existing vein of peg- matite, or along some fault or jointing plane in the coun- try rock itself which has been favorable to the concentra- tion and precipitation of metallic minerals from their solutions. The direction of the veins is generally between northeast and northwest, or east and west; their dips are steep or vertical. The quartz of the pegmatite gangue, when impregnated with telluride ore, has a pale, bluish-gray and rather greasy appearance, streaked here and there with a dull blackish, greasy stain, upon which sometimes the true telluride min- erals, such as sylvanite, can be seen, generally in long thin crystals of a bright tin-like appearance. It is sometimes called graphic tellurium, because the crystals crossing one another assume the form of Hebrew characters. Sylvanite is a telluride of silver and gold. There are many varieties of tellurides, some rich in silver and others in gold, and some with both combined. When a piece of gangue con- taining tellurium is roasted, the gold comes out in good sized globules on the surface. 1 ^ 128 Two g, eat tnotliLT-veins. called the Maxwell and Hoobier veins, traverse the telluride district for several miles, easily traceable by their rusty color. One carries pyrites and tel- lurides, the other silver ore and gray copper. Gold Hill district, in the telluride belt, is traversed by the Hoosier .uangue. Several veins cross the Hoosier gangue and arc richer in its vicinity; in some, the ore is a telluride at the surface, but with depth passes down into gold-bearing py- rites. The Ward district outside the telluride belt carries copper andiron pyrites bearing gold. Caribou is silver-bearing; its ores are galena, copper pyrites and zinc-blende occur- ring in gneiss near a dyke of eruptive diabase. The No- Name vein crosses and faults the Caribou vein. Its ores carry both silver and gold; the ores are silver glance, brit- tle silver, gray copper, galena, copper pyrites, with native and ruby silver. The copper pyrites carries more gold than silver. The granitic rocks near Boulder are thrown into a series of parallel folds, one series cut diagonally by another: The telluride veins run along the slopes of these folds. The veins are in cracks and fissures coinciding with this folding, some of the main fissures being filled at once by porphyry dykes, the others more gradually by vein material. The veins occur along, on, and near these dykes, along lines at the junction of the more massive granite with the bedded gneiss, along and between stratification planes of schist, and along the joint planes of granite. The veins are due to percolating alkaline waters dissolving metalliferous material and veinstone from the surrounding rocks. It is noteworthy that alkaline springs still exist in the neighbor- hood, as they do also at the mining district of Idaho Springs. The veins occur where the foldings are abrupt, and the direction of the veins is parallel to the strike of the stratification. As a rule the veins are not of great ex- tent. A single vein can rarely be traced on the surface or beneath it for more than 600 feet. Before that distance is reached, the vein spurs off again into another Where veins cross at a small angle or where a spur branches oflE from the main vein, accumulation and enrich- ment of ore takes place. There are two courses of veins, one east and west, the other northeast by southwest ; the 129 former system appears to be the older, as the latter faults it. The ore occurs in chimneys or pockets, with a good deal of barren ground between. Small veins run parallel with each other for some dis- tance, the interval filled with granite or pegmatite. Some- times a vein pinches out entirely (contrary to the general habit of true large fissure veins occupying great fault fis- sures). The ore streak is from i to 20 inches wide contain- ing more of this blue, greasy, fine-grained " horn quartz" than the country rock. Some of the veins interlace like arteries in a human body. Minute particles of pyrites (marcasite) often produce the dark stains we have noted on the telluride quartz. By moistening the stone, the tel- luride minerals and pyrite appear distinctly. A TYPICAL BOULDER COUNTY MINE. A good typical and very instructive example of a contact fissure, gold-bearing vein is that of the Golden Age at Jim- town, north of Boulder. " At Jimtown a quartz-diorite dyke occurs, of light color containing much hornblende and titanic iron, running nearly through the street of the village. The cliffs at Jimtown, over 500 feet high, are of quartz porphyry, of white color, consisting mainly of large crystals of quartz and feldspar, set in a fine grained crystalline ground mass or paste." GOLDEN AGE AND SENTINEL VEINS. From the town, the road winds up a steep mountain composed of coarse gray granite, with occasional belts of gneiss. Here are located the Golden Age and Sentinel mines. The Golden Age covers the outcrop of a quartz-porphyry dyke cutting through the granite. This dyke varies in width, from a few feet to about fifty. The outcrop of the m «n ore chute of the Golden Age extends along the " con- tact" on the lower side of the porphyry dyke. At a depth of 100 feet the main shaft discloses a split in the vein. The hanging wall of the vein continues into the dyke, but with porphyry hanging and footwalls, until a depth of 330 feet, where it enters the upper contact between the porphyry and '30 1 1 i! h! I granite. The dyke has been much acted upon and decom- posed by vein-forming agencies in the upper workings, but in the lower it is less decomposed and shows considerable pyrites. The Golden Age veins are well defined, present- ing a banded or ribbon structure. They are inclosed in dis- tinct walls with gouge or selvages, which at times show slickensides. The seams and feeders that have enriched both veins come in from the porphyry dyke. The ore from the Golden Age contains rich and magnifi- cent specimens of free gold. It is a free milling ore. When rich, the gangue is a hard, flinty, vitreous white quartz. The gold is seldom accompanied by pyrites. It is gener- ally imbedded in the white quartz as bright, yellow gold, in size, from coarse grains to nuggets several ounces in weight; after it reaches the lower contact between the por- phyry and granite and enters the granite, there is an in- crease in the baser metals, such as zinc-blende, galena and pyrites, but the ore still retains its value in free gold. Returning to the surface, the Sentinel location covers the apex of a vein, which there appears enclosed in a belt of schistose or gneissic rock. This vein dips south at an angle of 70° and passes through the Golden Age vein on its course. The Sentinel vein ore is entirely distinct from that of the Golden Age. It is the characteristic bluish horn quartz of the tellurium veins of Boulder County, with characteristic chalcedony quartz crystals and finely disseminated pyrites. The value is in metallic gold and such tellurium ores as petzite and sylvanite. Whilst most of the gold was de- posited as native gold, a portion has evidently been rendered free by partial decomposition of the tellurides. This ore is very rich. The richest ore usually occurs in two narrow seams or streaks from a foot to ten feet apart, the interven- ing space being more or less mineralized country rock. It is richest when in the schistose rock, and poorest when it passes through the porphyry dyke. The crossing of the Sentinel vein through that of the Golden Age is very clearly marked ; it very slightly faults the Golden Age vein. The gold mines of Boulder Count" belong to two dis- tinct periods of vein formation; to one belong the non- telluride ores, and to the other those producing tellurium. The tellurium veins appear to be the later of the two. 131 1 The ores of the Sentinel tellurium vein are lower grade where the vein passes through the porphyry dyke. This is due to the Golden Age vein being formed first, and drain- ing the dyke of its disseminated mineral values. The Sen- tinel received its mineral from the schistose or gneissic rocks, and is consequently richer where enclosed in those rocks than when in the dyke. Prospectors look for richer or larger bodies of ore when veins unite or cross each other. In the Golden Age the two veins unite about loo feet below the surface. There are similar veins of the same age, and large and rich ore bodies are found at their junction. On the other hand, the Sentinel vein of later age, passing through the earlier S »» 1^ 'fin Plate LXIX. Section of Golden Age Vein, Jimtown, Boulder Co., Colo. Golden Age vein, produced no enrichment of the ore Dodies. Tc form such ore bodies, the veins should be of contemporaneous origin. The ore deposits of Gilpin and Clear Creek counties are very similar to those of Boulder, only they do not produce tellurium ores. The country rock is the same granite- gneiss, penetrated here and there by porphyry dykes. The pegmatitic veins are either in the gneiss or between the dykes and the granite. In some cases the porphyry dyke constitutes a vein in itself, such as the Minnie, which 132 is a felsite porphyry, and the Cyclops, a quartz porphyry. In Gilpin County, around Central City, the ores are a mix- ture of copper pyrite and iron pyrite with a very little galena and zinc-blende. All are gold-bearing. The richer ore occurs in streaks not over a foot wide, in a compact, fine-grained mass of pyrite. Copper pyrite is richer than iron pyrite. The rest of the vein, often many feet wide, carries pyrite irregularly disseminated through decomposed country rock. The bulk of these ores are diffi- cult to treat, and are milled, the loss being 40 per cent, higher in the unoxidized ores than in the oxidized. The veins follow the cleavage planes of the gneiss, cutting the stratification planes at right angles with a vertical dip. The porphyry dykes are older than the veins, as the cleav- age planes intersect both the porphyry and gneiss alike. For an interval of 20 miles between these mining districts and the plains, there are no ore deposits of any importance known. In Clear Creek County the ores are mainly silver-bearing ; the silver is derived mainly from galena and gray copper. Dykes of obsidian occur in one of tho mines parallel with the vein, which is itself a porphyry dyke. The richest mineral is close to the obsidian dyke. \\ i i FISSURE VEINS IN TRUE IGNEOUS ROCKS. Whilst most of our fissure veins and ore deposits gener- ally are more or less associated with the presence of igneous rocks, there are some which are essentially in igneous erup- tive rocks alone. The most remarkable of these are the fissure veins of the San Juan region in southwestern Colorado. This region consists of an enormous plateau of lavas of great thickness resting upon and originally overflowing a low mountain range or plateau of granitic and upturned sedimentary rocks, the latter representing most of the geologic periods from Cambrian to Tertiary. The thick- ness of these great lava flows, which were erupted about the Eocene period of the Tertiary, is upwards of 1,500 feet; this lava mass has been cut up by glacial and river action by profound canyons, into a rugged mountain range, the summits of some of the castellated moimtains reaching a 'J.J height of 14,000 feet above the sea. The lava sheets are also traversed to a depth of 1,500 feet, more or less, by an extraordinary number of great quartz-fissure veins. These veins appear to fill shrink- age cracks resulting from the con- traction on cooling of the lava sheets; strictly speaking they are rather "gash veins" on a larger scale than " true fissure veins," for they are mostly limited to the thick- ness of the lava avcrflinvs and cease when they reach the underlying granite. There appear to have been two principal eruptions ; the first, dur- ing the early part of the Tertiary, covered the higher region of the San Juan mountains to a depth of 1,500 feet with an overflow of brecciated andesitic lava, which on cooling developed fissures of contraction traversing the lava mass in all directions ; these were subsequently and slowly filled with a hard bluish quartz contain- ing more or less ore. Following the first grand over- flow were others of less magni- tude, consisting of non-brecciated andesitesandrhyolites. This sec- ond dynamic movement produced locally, fissures extending below the horizon of breccia into the stratified rocks. These, however, are seldom productive below the eruptive zone. There are also metal deposits in connection with still older eruptions of andesite and diorite, such as Mineral Farm, Calliope, etc. ^ H i t- 01 ^ B ^ ft S C3 2. > § ^ t P ft en > H W > O H > s; C/3 /.JA \ii^^- M •7/ \r i» 134 RED MOUNTAIN, In the Red Mountain district the ore deposits form a peculiar group. They occupy a seres of more or less con- nected irregular chambers, trending downward, probably channels of ancient hot mineral springs. The mineralizing '35 water completely silicified the surrounding eruptive rock for some distance away from the ore chambers. So the ore bodies are distributed through a huge irregular column of quartz extending to an undetermined depth. Large masses of brilliantly colored material are con- spicous in this region. They have been acted upon by mineral waters circulating through their crannies and fis- sures. Ore bodies are occasionally found in these, and such mines are locally known as cave mines. The ores of the San Juan are mostly argentiferous gray copper, copper pyrites and galena associated with zinc- blende and iron pyrites in usually hard horn-quartz matrix. Some of the ore locally contains a high percentage of bis- muth: others produce pyrargyrite and polybasite, rich silver minerals; others carry considerable gold, such as the recently discovered gold belt at Ouray. This belt oc- curs in Dakotah Cretaceous sandstone, which has been altered into a quartzite by the intrusion of dykes and sheets of eruptive diorite. One of these sheets spreads out in the quartzite. The ore occurs at the top of the quartzite, at its junction with a bed of shale. The gold, which is free and enclosed in brown oxide of iron, doubtless originated from the porphyry, and entered the joints and bedding planes of the quartzite, where they wcre opened by faulting. Above the shale the ore does not penetrate, the shale acting as an impervious resistance to uprising solutions. Ore bodies also occur in the Jurassic limestones below the quartzite, especially where they are penetrated by eruptive rocks. In the eastern portion of the San Juan region some im- portant gold deposits occur near Del Norte in the Little Annie or Bowen Mine, which appear to be a decomposed dyke of eruptive rock, containing free gold in brown iron, in the upper portion, and with depth iron pyrites also gold- bearing. CREEDE. At the newly discovered camp of Creede, not very far from Del Norte, the fissure veins are very similar in char- acter to those elsewhere in San Juan ; they are quartz fis- sure veins traversing andesitic breccia and other volcanic rocks. The gangue matter in these veins is exceedingly rich in silver-bearing ore, so much so that the amethystine -V: 1 36 quartz composing the gangue or veinstone is quite in a minority to the ore, and the vein may be said to be nearly a mass of ore from wall to wall. The thick lavas of Creede rest doubtless with depth upon Carboniferous limestone or else on bare granite ; the former is found outcropping at some distance from Creede, from beneath the lava over- flow, and being penetrated by intrusive eruptive rocks shows signs here and there of productive ore deposits simi- lar probably to those at Leadville. Creede is an encour- aging example to a prospector, that all productive veins in Colorado have not been discovered yet, even in districts that have been pretty well tramped over. Creede had doubtless often been more or less walked over by prospec- tors for years before the great discovery was made, and in a year's time we may hear of several more similar discov- eries in the great San Juan. ROSITA AND SILVER CLIKK. The next important and peculiar igneous district carry- ing fissure veins is that of Rosita and Silver Cliff in the Wet Mountain Valley near the edge of the prairie country in southeastern Colorado. Here a local eruption of con- siderable power and magnitude and of comparatively recent date has occurred. These eruptions, consisting of andesi- tic, rhyolitic and trachytic material have built up cones and rounded hills largely of fragmental material such as consolidated tuffs, ashes, and breccia, all of which, as at Cripple Creek, rest on granitic basement rock. From the fragmentary character of the rocks it is evident that most of the eruptions were explosive, alternating, however, with quieter flows ; in some cases the dykes can be seen, where some of the lava came, at others the " necks "or throats of the volcanoes themselves filled up with volcanic boulders; of such is the celebrated Bassick Mine. The mine is in the throat of an old crater cf andesite, filled with boulders of granite and andesite bedded in gravel and sand. The ore of the Bassick appears as concentric zones or shells around these boulders, as a replacement of the gravelly matrix. The entire mass has been permeated by heated waters which have decomposed the rocky fragments, depositing opaline quartz and kaolin in abundance. '37 The concentric shells around the boulders carry alter- nately several minerals, such as galena, antimony, zinc- blende, copper and iron pyrites, all more or less gold- bearing. The ore deposition in this region seems t'.o have taken place at the close of the eruptive period, when the eruptions were dying out into hot springs, fumaroles, etc., and producing great decomposition of the lava rocks. The district was not thought much of, until Mr. Bassick made his discovery in the unpromising-looking throat of the old volcano, containing a formation quite anomalous, and which the regular prospector, accustomed to true, orthodox fissure veins, would have passed by as very unlikely. So it may happen to future prospectors, that some very un- likely formations may turn out great riches; hence it is well to keep a sharp lookout for everything examinable. A STUDY OF MODERN LIVING VOLCANOES TO UNDERSTAND THE CRIPPLE CREEK VOLCANO. By far the most typical, instructive and important gold camp in Colorado and the West is that of Cripple Creek. ■'iSS^UIWiimi^' Plate LXXIl. Stromboli Volcano, To understand the geology of the Cripple Creek region and gold-bearing volcanic regions and rocks and their relations to the ore-deposits, a knowledge of the phenomena attend- ing modern volcanic eruptions is necessary. Let us take that of the living volcano of StromI oli, described by Pro- fessor Judd, as throwing some light on the phenomena that >3« may have occurred many thousands of years ago in the now extinct volcano of the Cripple Creek district. From a point on the sides of the mountain of Stromboli. masses of vapor issue and unite to form a cloud over the mountain. This cloud is made up of globular masses, each of which is the product of a distinct outburst of the volcanic forces. At night a glow of red light appears on the cloud, increasing gradually in intensity, and as gradu- ally fading away. After an interval this is repeated and continues till the light of dawn causes it to be no longer visible. When we land on the island we find it built up of the " ejecta" from the volcano like a gigantic iron furnace with its heaps of cinders and masses of slag. The irregular shape and surface of the land is due to erosion removing the loose materials at some points, and leaving the hard slaggy masses standing u p promi- nently as dykes and hard portions of lava flows, as Pisgah, Rhy- olite Mt. and others at Cripple Creek do, above the eroded and more fragmentary tuffs and breccias. This great heap of cin- ders and slags rises 6,000 feet above the sea bottom with a base four miles in diameter; 2,000 feet above sea level is a circular depression, tiie crater of the active volcano. Looking down into the crater an outburst takes places. Before the outburst, many light curling wreaths of vapor ascend from fissures on the sides and bottom of the crater. Possibly this is the origin of some of the dyke-filled fissures of Cripple Creek. Suddenly a sound is heard like a locomo- tive blowing off its steam. A great volume of watery vapor is thrown up into the atmosphere, and with it a number of dark fragments are hurled 500 feet above the crater, some Plate LXXIII. Map of Island of Stromboli. '39 falling on the '.nountain, others baik itiio the rratcr with a loud rattling noif.e. Those rolling down the mountain are Plate LXXIV. Stroinboli Crater. Still hot and semi-molten. This is a clue to the origin of the fragmentary materials composing the tuflFs and breccias at Cripple Creek. The black slaggy bottom of the crater is. as we have said, traversed by many fissures emit- ting jets of vapor. Some of these are quite large and vary in size and number and position at differ- ent periods. From some, only steam is emitted in loud snorting puffs. In others molten mate- rial is seen welling up and flowing outside the crater. Such fis- sures when all erup- tion has ceased would be found, as at Crip- ple Creek, sealed up with solid lava with a lava flow on their tops. From this liquid mass, steam escapes in considerable quantities. Within the walls of the fissures, a viscid semi-liquid lava heaves up and Plate LXXV. Dykes Cutting Beds of Scoria and Tuflf in the Wall of a Crater. I40 clown and churns around till at last a gigantic bubble or blister is formed, which bursts violently and a great rush of steam takes place carrying fragments of the scum-like surface of the liquid high into the air. At night the fissures glow with ruddy light. The liquid matter is white hot and the scum on it a dull red. Every time a bubble bursts a fresh glowing surface is e::posed. It is the reflection of this upon the clouds of steam above the mountain that causes the fitful glows of light we mentioned. The phenomena show there arc cracks communicating with the earth's interior highly heated matter beneath the surface, together with great quantities of imprisoned water, which escaping as steam gi /e rise to all the active pheno- mena. What is popularly supposed to be flame in an eruption is the reflection on the cloud of steam and dust, from glowing masses in the mouth of the crater. Sulphur is not, as com- monly supposed, erupted from a volcano, but is formed by the union of sulphurous acid and sulphureted hydrogen issuing from volcanic vents. A volcano is a steam vent, like a geyser, which may be called a water volcano, |i ORICWN OF FISSURES. Some light is thrown on the possible origin of some of the Cripple Creek dykes and fissures by the eruption of Vesuvius in 1872. The bottom of the crater was entirely broken up and the sides of the mountain rent by fissures in all directions. So numerous were these fissures that liquid matter appeared to be oozing from every part of its surface and the mountain to be " sweating fire." One fissure was enormous, extending from the summit to far beyond the base of the cone. This, filled with a dyke of lava, is visible to-day. From both crater and fissures enormous volumes of steam rushed out with a prodigious roar. This roaring was from explosion of bubbles one after another, and the vapor cloud above Vesuvius, as at Stromboli, was made up of globular masses of steam ejected at successive explosions. Each explosion carried upward quantities of fragments which fell back on the mountain. All along the course of the stream of lava, volumes of steam were thrown off. i ' I' f)Rir;iV UK TJTFS. The dischar^'e (.f such laryjfo quantities nf steam eaunes le atmosphere to be saturated with watcrv vai)..r. which". condenstiiK. falls in excessive rain storms, nroducinir mu th producing mud PlCLYL Plate LXXVI. Plan and Cross-Section of the Roots of a Crater. Black = D..kes Filling Fissures. * ?/tfio'^«!r"'5'^^V^^" ^^^^"^ sweeping along the loose vol- ?r?in1. Tri'^v^/f "'-^ }"" '^."^^ '^"^^^ ^^y- doubtless, the Cripple Creek tuffs and breccias were formed. GASES AND MATERIALS EJECTED FROM VOLCAXOES. The most abundant of the substances ejected from vol- canoes IS steam, and with it many volatile materials, such 142 as hydrochloric acid ind carbonic acid, also hydrogen nitrogen and ammonia, and at Cripple Creek fluorine gas! Microacopic Structure of Glassy Lava Showing Microlites and Crystallites. ,0, Microscopic Structure of Some Crystals Showing Microlites and Crystallites Plate LXXVII. These different gases at Cripple Creek had much to do with the formation of ore deposits. Volatile metals, such 143 as arsenic, antimony and cinnabar are erupted ; these sub- stances, issuing from volcanic vents at high temperature, react upon one another forming new compounds, such as sulphur. Hydrochloric acid unites with the iron in the rocks to form yellow ferric chloride, common at Cripple Creek, and looking like a greenish yellow sulphur. Acid gases change lime, alkaline and iron elements into sulphates, chlorides, carbonates and borates, which, when removed by rain, leave a white substance like chalk, composed of pure silica. Beds of such material occur not far from Cripple Creek and powdered silica in some of the mines. The lips of fissures from which steam and gases issue are coated with yellow and red incrustations of sulphide and oxide of iron, such as are common in many prospect holes at Cripple Creek. Solid materials are ejected in vast quantities ; fragments of the rock masses through which the fissure is rent are carried upwards by the steam blast, together with other matter far beneath the surface in a semi-fluid condition. Hence it is that at Cripple Creek we occasionally find frag- ments of red granite imbedded in the volcanic breccia torn from the throat of the volcano in its passage through the underlying granite of the region. MINERAL AND CHEMICAL ELEMENTS OF LAVAS. Eight chemical elements make up the mass of lavas, oxygen, silicon, aluminum, magnesium, calcium, iron, sodium and potassium. Oxygen makes up the larger pro- portion, so that lavas are mostly oxides. Next is silicon and aluminum, giving the quartz and feldspar and silicate element. Lavas are of two kinds, acidic and basic. Acid lavas contain eighty per cent, silica, basic forty-five per cent. The former are rich in potash and soda, the latter in lime and iron; the former are commonly light in color and weight, the latter dark and heavy. Rhyolite is an example of an acidic lava, basalt of a basic one. The andesites and phonolites of Cripple Creek are intermediate. The minerals composing these lavas are principally quartz and feldspar, together w^ith the dark minerals, mica, augite, hornblende, olivine and magnetite. 144 CRYSTALS AND MICROSCOPY OF I,AVA. Many lavas are of a glassy nature, others contain many crystals, some of large size. Microscopic sections of lavas show them to be made up of a ground mass of a glassy character, with distinct crystals set in it like plums in a pudding. In others, the crystals are so thick that the glassy base can scarcely be seen. Through the midst of the glass, cloudy matter is observed ; a higher power shows this " nebula" to be composed of min- ute particles called crystallites, the embryonic forms of crystals. Sometimes we can see an attempt of these par- Plate LXXVIIl. Minute Cavities Containitig Liquids in the Crystals of Kouk. tides to aggregate into a geometrical form, sketching out the outline of the large crystal they intended to foim, but weie prevented from finishing, by the cooling of the glassy magma. These crystallites assume forms like ferns, hairs, spiders, etc. In subterranean regions the conditions were particularly favorable for the development of crystals. The lavas cooled with extreme slowness, under enormous pressure, allowmg plenty of time for the crystals to form. Those lavas containing most soda and potash (acid lavas) assume a glassy condition, and these have often cooled near the surface rapidly, the more crystalline varieties MS slowly at great depth. Obsidian and rhyolites are glassy types, granite and some porphyries with large crystals are of the latter class, whilst andesite and phorolite may be intermediate. The latter, however, at Cripple Creek, may have cooled quickly near the surface, and the crystals are for the most part small. Besides the natural imprisoned water, crystals in lavas are found microscopically to contain globules, sometimes filled .vith gas, salt, and water, which may add to the ma- terials for the production of steam. KRUI'TIONS OK DUST. steam escapes from lava so violently that the froth or scum, called scoria, is broken up and scattered in all direc- tions. This scoria like pumice is full of little holes like a sponge, due to escape of the steam in it. Such spongy scoria is found scattered over the hills of Cripple Creek. During violent eruptions a continuous upward discharge of these fragments is maintained; the cindery masses hurt- ling one another in the air, fall back into the vent, or are scattered over the mountain. Being often shot up again and again from the vent, they are reduced to the finest im- palpable dust. They fill the atmosphere to such an extent as to bring on an " Egyptian darkness." This dust, mingling with descending rain, forms destructive mud flows, and sets or consolidates into the tufas or tuffs so abundant at Cripple Creek. When larger angular fragments are caught up and consolidated with these, the rock so formed is a breccia, as already illustrated. Volcanic craters, after having been formed, are liable to be disturbed by later eruptions. Thus the crater of Vesu- vius was reduced 400 feet by a later eruption, the old crater blown up and a much vaster crater opened. Cripple Creek also witnessed its second disturbance, after the andesitic eruption had ceased, by one of phonolite lava. FLUIDITY AND OTHER PROPERTIES OF 1,AVAS. Some lavas, such as basalt, are reduced to such a state of fluidity that their streams run like water to great distances. Others are of a more viscid, mortar-like consistence, espe- 10 IB 146 cially the acid lavas, such as those of Cripple Creek. These are apt to flow but a short distance from their source, and to build up big domes and thick masses; of such a nature seems the structure of Nipple Mountain, south of Cripple Creek. The peculiar columnar structure often observed in basal- tic lava sheets, and in a rough way developed in the phono- lite of the cliff above Victor mine, is due to cooling and contraction somewhat in the same way as mud cracks are formed in a drying up pond. A block of lava isolated by these cracks assumes a polygonal form like the basaltic columns of the Giants' Causeway. During the cooling down of lava and the escape of steam and gases, deposits of sulphur, specular iron and (at Cripple Creek) fluorspar, are deposited. Specular or micaceous iron is not uncommon at Cripple Creek. Rock masses are completely disguised by these incrustations. STRATIFICATION OF TUFFS. Tuffs and breccias are often found stratified. The frag- mentary materials in falling through the air are sorted, the finer particles being carried farther from the vent than the larger ones. Craters built up of tuffs and breccias fallen in the condition of a muddy paste, show very fine stratifica- tion. Large cones are built up of uniformly spread layers of more or less finely divided material disposed in parallel succession. At Cripple Creek the bedding is indistinct, and often difficult to trace, the dip of stratification being still more compressed by the cross fracturing of the rocks ; hence it is hard to tell whether the lines represent cross fracture cleavage, or bedding planes. In most volcanoes the stratified tuffs are cut and crossed, as at Cripple Creek, by numerous dykes running in various directions, cracks filled by lava from below. Movements, too, have taken place subsequent to the accu- mulation and consolidation of the whole material as shown in Plate LXXIX, whereby the masses are faulted and fresh fissures opened in them. Faults are found in some of the mines at Cripple Creek, faulting not only the lavas, but the veins also. Cliff sections of volcanoes show alternate M7 beds of solid lava, scoria and tuff, representing different eruptions or flows. There seems an order and succession in the eruption of the different varieties of lava. During the earlier periods rhyolites, andesites and phonolites are erupted, and later basalts. This appears to be the case in the volcanic region west of Cripple Creek around Mt. Maclntyre, Thirty-Nine Mile Mt., and Black Mt. The prevalence of basalt capping the other lavas in that region, together with the greater 'MJ/iimMi Plate LXXIX. Cliff Section, Composed of Alternate Beds of Lava and Suuria, Cut by Lava Dykes, and Faulted. freshness of the rocks, imply that its eruptions were some- what later than those of Cripple Creek, where basalt is not found, and where the rocks are much decomposed. Volcanic eruptions shift their centers from time to time, making new cones along a line of fissure (for volcanoes are built upon lines of fissure). See Plate LXXX. Extinct craters are frequently filled by beautiful deep lakes. Cones rise within cones, and within great crater rings. At each successive great eruption, the old cone is blown away, and a new one formed. Hot springs contain large quantities of silica or quartz in solution. The solution of silica is effected at the moment of its separation from combination with the alkali during the decomposition of volcanic rocks, and is favored by the presence of alkaline carbonates in the water, high tempera- , - 148 ture, and the pressure under which it exists in subterranean regions. When the water reaches the surface and is re- lieved from pressure and begins to cool, silica is deposited. So are the basins of geysers formed, and so the opal and hydrated quartz we find in many of the Cripple Creek veins, and in resilicated rocks. Hot and cold springs rising in volcanic regions are charged with carbonic acid, and passing through calcareous rocks dissolve large quantities of carbonate of lime, and rede- posit it in a crystalline form known as " travertine." Near the base of Mt. Maclntyre, west of Cripple Creek, a pros- pect is opened on a fissure filled with this substance. Nearly all eruptions take place along lines of fissures (See Plate LXXX). Probably all volcanoes are located upon fissures of some kind, and even the general distribution of Plate LXXX. Showing Craters Found Along a Line of Fissure in the Eruption of Ktna. volcanoes over the earth's surface has been attributed to lines of fissures, as if the earth had been cracked like a glass globe. We have plenty of opportunities of seeing ancient fissures filled with lava in the numerous dykes at Cripple Creek, and in the greater volcanic region west of it; but so far no distinct volcanic craters have been found. Nevertheless it is probable that craters existed along these fissures, long since removed by erosion, or buried deep under flows and surface matter. We not unfrequently find at Cripple Creek that fissures did not all succeed in break- ing through to the surface, for at some depths in the mines the apices of buried dykes are found and fissures filled by vein matter, whose outcrops do not appear at the surface. A single vein is followed from the surface, and with depth '49 two or more veins are often encountered, together with various small fissures. Earthquakes doubtless accompanied the eruptions, and developed many smaller fissures, and further shattered the rocks. Added to this at Cripple Creek, there was the sec- ond eruption of phonolite, after the andesite had ceased. This second eruption doubtless added new fissures in the efforts of imprisoned vapors to rcrce for themselves chan- nels to the surface. r.ASF'' AND SOLFATARIC ACTION. The several stages in the decline of each volcanic out- burst are marked by the appearance at the vent of certain acid gases. As the temperature at the vent declines, the nature of the volatile substances emitted undergoes a regu- lar series of changes. In fumaroles, sulphurous acid and hydrochloric acid abound, with sulphureted hydrogen and carbonic acid in much smaller proportions. Around these fumaroles, de- posits of sulphide of arsenic, chloride of iron and of am- monia, boracic acid, and sulphur take place. Arsenical pyrites are a common associate for the ores near the sur- face at Cripple Creek, and many rocks are permeated with iron pyrites. Where a volcanic vent sinks into extinction, hydrochloric and sulphurous acids are first evolved, and later sulphureted hydrogen and carbonic acid springs. Such springs are common in the volcanic districts of Colorado to-day, but we have long passed the stage of the stronger acids, which could only be expected in the pit of an active modern vol- cano like Kilauea. We may, however, expect to find traces left of these gases, in the rocks of Cripple Creek, such as a bleaching and decoloration of the rocks, leaching and precipitation of iron, forming those varied patterns of oxi- dation so common at every prospect hole ; also deposits of various sulphates and chlorides, rocks deprived of iron and alkalies reduced to powdery siliceous masses. One action of subterranean springs is the transportation of material in a state of solution and redepositing of it else- where, especially in lines of relief of pressure, such as 558 !B 150 fissures, shattered rocks, ami decomposed rocks and zones in the rocks. At Steamboat Springs, Nevada, metallic gold, cinnabar and other minerals have been found coating the sides of fissures from which living hot springs issue at the surface. In great volcanic foci the transfer of various sulphides, oxides and salts, which fill veins, has been effected either by solution or sublimation, or the action of powerful cur- rents. This applies to the veins and ore deposits in ques- tion. As the igneous activity of a district declines, the temper- ature of the issuing gases and waters diminishes, till at last the volcanic forces appear to have wholly abandoned the region and been transferred to another. This may have been the case with Cripple Creek and the volcanic region west of it, of apparently later date. The history of a volcanic disturbance is as follows : First. The area is troubled by subterranean shocks and earthquakes. Second. The origination of fissures is indicated by the appearance on the surface of hot and carbonic acid springs and other gases. Third. "With increased subterranean activity the tem- perature of the springs and gases increases. Fourth. A visible rent is formed at the surface. Fifth. From this fissure gas and imprisoned vapor es- capes so violently as to disperse the lava in clouds of scoria or dust, or to cause it to well out in flows. Sixth. Volcanic action concentrates at one or several points, and the ejected material accumulates from volcanic cones. Sometimes the volcanic activity dies out entirely, leav- ing cones thrown up along the line of fissure. At others, some such center becomes for a long time the habitual vent for the volcanic forces of the district, and a large cone is built up. When the height and thickness of the cone have grown great, the succeeding eruption rends the sides of the cone, producing fissures, quickly filled by lava, forming radiating dykes and surmounted by parasitic cones. The dykes of Cripple Creek may in cases represent such occurrences. When volcanic energies can no longer raise material to 151 the summit of the crater, nor rend the sides, they find relief by making new fissures and small cones in the country out- side the main volcan; crater. The numerous phonolitic dykes in the granitic region outside of the main center at Cripple Creek may have so originated. At last volcanic energy diminishes, eruptions of lava cease, fissures are sealed up with solid lava, volcanic cones crumble away. But still the existence of heated mater at no great depth is indicated by outbursts of gases and vapor, formation of geysers, mud volcanoes and hot springs. As the under- lying rocks cool down, the issuing jets of gas and vapor lose their high temperature, diminish in quantity, geysers and mud volcanoes become extinct, hot springs disappear, and all is quiet. It was in the latter or hot spring stage, that the ores were at Cripple Creek leached from the volcanic rocks, probably from great depths as well possibly as from the sides, and concentrated and deposited in the fissures, shat- tered zones, and decomposed rocks. The last stage is as we find things to-day. GENF.RAf, SUMMARY OF PROBABLE VOLCANIC EVENTS THAT OCCURRED AT CRIPPLE CREEK. At Cripple Creek there was a volcanic eruption in Tertiary times due probably to some mountain elevation going on in the region of Pike's Peak or generally in the mountains. We may assume that preluding the eruption the area was troubled by earthquakes. Various kinds of acid and hot springs appeared above the surface, indicating the fissuring of the ground that followed. At the bottom of these fractures, which may have been numerous, molten rock appeared, giving off imprisoned vapor from bursting blisters of lava. These shoots of steam formed into a cloud overshadowing the area, and carried upwards quantities of scoria and fragments which fell back around the orifice, forming a crater cone, or cra- ters. These fragments being repeatedly shot up, and fall- ing back into the crater, were comminuted into fine dust, and fell, together with larger angular fragments, over the surface. The atmosphere charged with condensing steam gave '52 rise to heavy rainfalls. The water descending the ravines caup;ht up the volcanic dust and fragments, forming mud- flows, the material rapidly setting into the rocks we call tuffs and breccias. As the first eruption at Cripple Creek was of andesite. these are called andesitic tuffs and breccias, and constitute the principal mineralized rock of the mining area. These tuffs are sometimes stratified by the materials being sorted in the air by the water. After this first eruption ceased, there may have been a rest for a time, the lavas may have cooled and consolidated, and the region been covered by various acid and hot springs issuing from fissures caused by the late eruption. Then the district was a second time disturbed, this time by an eruption of phonolite, ascending through numerous rents and fissures, not only in the overlying andesite, but also in the granitic region outside of the first volcanic "focus," probably finding the old seat of action too much choked by eruptive matter. This second eruption added many new fissures to the already shattered rocks, and gave many opportunities for the deposition of metallic and vein material deposited through the medium of gaseous and hot spring and solfa- taric action which followed upon the cessation of the phonolite eruption. After the eruptions at Cripple Creek ceased, the volcanic forces seem to have transferred their field of action to the area west of Cripple Creek in the Four-mile district. The rest is the history of to-day. CRIPPLE CREKK AS A PROSPECTING FIELD. A visitor standing on top of one of the hills like Mt. Pisgah, overlooking Cripple Creek, and glancing at the various mines and multitudinous prospect holes speckling the hills, is struck with the compactness of the mining dis- trict within the limited area of i8 square miles. In this small area all the principal mines are located, and one can ride ..round the entire camp in an hour or two. Outside of this area, there are as yet no mines of importance, though prospect holes may be found for a circuit of many miles. ^ «5.? ANDKSnK \Nf» t.RANITK AKKAS. He will observe that the principal mines are located on the round smooth hills, on their tops, slopes, and on the gulches, where the vegetation is mostly grass and quaking aspen. These too are within a sort of natural rampart of more rugged hills wooded with pine. In these outlying hills, only a few scattered prospects are visible. The rea- son for this is to be found in the geology of the region, and the differences between the areas occupied by andesitic breccia and granite. The rounded grassy aspen-covered hills representing the andesitic breccia carry most of the ore bodies, and the principal mines are restricted to them. The more rugged hills covered with fir trees, represent the granite area, and in them for the most part are few mines of imp6rtance, though many likely prospects are opened upon dykes of phonolite, which, so far as known, does not as a rule seem to be so productive a rock as the andesite. There are intermediate areas, such as that of Battle Mt., characterized by the presence of both andesitic breccia, phonolite dykes, and granite, in which are some of the richest mines of the district, such as the Independence, Portland, Annie Lee, and others. It will appear how important and useful a geological sur- vey is of such a region, a fact not always recognized by practical miners. If the ore bodies are mainly associated with the particular rock called andesitic breccia, it is well for them to be able to recognize that rock, and ascertain the limits of its area. SIGNS THAT LEAD TO PROSPECTING. The next thing that strikes the observer is the prodigious amount of prospecting holes and prospecting trenches, the latter being particularly common. He may ask what was there in the general appearance and character of this dis- trict that led the " eagle-eyed" prospector to suspect the existence of ore bodies in it, or that it was " a kind'er likely looking place"? Again, how is it that it was so long over- looked by the " eagle-eyed," especially when so easily ac- cessible? '54 On general principles, in past yearn, miners in Color/ulo, after the Leadville and Aspen excitement, were more on the lookout for silver than gold ; they looked therefore for rocks like those of Leadville, with contacts between por- phyry and limestone, and every limestone ledge in the country was ransacked. Silver was rarely found in vol- canic lava rocks, except perhaps in the great San Juan region, and miners thought as little about prospecting un- promising looking hills of lava, as they would the basaltic caps of the table mountains on the plains. Again, gold leads do not show their ore on the surface like some silver- lead veins. There is nothing perhaps but a little seam of rust that might occur almost anywhere, and in any kind of rock. Hence lava districts of somewhat recent origin were overlooked, rather than looked over. The discovery of the gold-bearing properties of the Cripple Creek lavas, together with the increased thirst for gold, turned the tables, and now throughout Colorado every lava formation is being prospected with as much zeal and indiscriminate- ness as were the limestones in the Leadville days, ^he prospector now needs to know volcanic lavas at s'^^ht, to distinguish varieties, and to know all he possibly can about their origin, varieties and mode of occurrence. Hence the importance we gave to the subject in the preceding re- marks on volcar oes. A prospector mm' would at a glance consider the area about Cripple Creek as worth looking over; and the geologist would consider it a very likely place, not merely from the presence of the lavas, but mainly from the great decomposition of the rocks, and the evidence of the presence of past solfataric action. DIFFICULTIES IN PROSPECTING. But the " eagle-eyed" one did not entirely overlook this district in the past, for some years ago he was sufficiently prepossessed with the appearance of things to drive a couple of short tunnels in Arequa gulch, and narrowly escaped becoming a millionaire. What troubled the prospector was, that though he found the hills covered with an extra- ordinary amount of " float," he could not trace this float to any ledge or rocks " in place." For the most part the hills were grassed over, or covered with vegetation ; and through T •55 tlu' turf were very few outcroppings of a likely kind, so far as he could see. There were no pronunent quartz veins, or zones deeply iniprej^nated with irt)n. hence he ^^ve up the region, mentally wondering; where on earth all this rich float could have come from, perhaps solacinjf his mind by one of his igneous, brimstony theories that it had been scat- tered over the country from a distant volcano, or washed there by flood or glaciers from some unknown distant region. The former theory after all was not far from the truth but the absence of all rounding and smoothing of the fragments of float precludes the latter hypothesis. Evi- dences of former glaciation are remarkably absent from the vicinity. THE RKr.lON IMPREONATF.D WITH ORE. To those who have studied Cripple Creek of to-day, the source of this " float" is no mystery. Little, if any of it, has been broken off from orthodox quartz fissure veins, or even extracted from well-defined ore zones. The fact is, that the whole andesitic area is more or less impregnated with the precious metals, and the float on the surface is little more than the surface debris of the general underly- ing rock. There is scarcely a stone that you may kick with your foot over the entire area, but ..hat will show some trace of gold. On one hill an experienced mining superintendent told me that, for an experiment, he went around with a wagon and picked up the " float" almost at hap-hazard, and it averaged 23 dollars in gold. That such a " floaty" region should receive attention some day is not to be wondered at, and we believe Colorado Springs men were amongst the first to give it serious attention by open- ing holes and prospecting trenches almost at random, re- sulting in important discoveries. As a rule even after this, the best mines were discovered by mere chance and guess work, or by plodding but blind prospecting, something like the Leadville prospector who in early days had all Lead- ville before him to prospect, but did not know where to begin, till sitting down under a tree eating his lunch he saw a squirrel scratching in the ground ; he accepted the happy omen and "went down," so the story goes, and of course ! f? if >56 " struck it rich ;" so we understand the Pharmacist and many other now noted mines were discovered at Cripple Creek. MODE OK I'ROSl'ECTINt;. This absence of surface outcrops or visible leads, when thQ " rush ' came, led to indiscriminate and abundant pros- pecting which has been kept up till the present time, hence the extraordinary frecklinji: of the hills with prospect holes and trenches. Sometimes they would select any piece of land they thought, for some reason or other or without any reason at all, likely, and go to work to punch holes and dig trenches all over it to find something. In this way they frequently came across enough signs to warrant putting down a pros- pect hole, and holding the claim, and then went on " to pastures new." CHARACTER OF FLOAT AND OTHER SURP^ACE SIGNS. As we have said, the whole region is covered with float. This float is usually a somewhat porous piece of lava, or andesitic breccia, or tuff, stained with yellow, brown, or red oxide of iron, sometimes in patterns or concentric rings. It is often found to be honeycomoed when broken with a hammer. There is no visible ore, but an assay will most likely show traces of more or less gold. Again, a species of red porphyritic granite has been desilicated and robbed of many of its crystal constituents, and left as a porous skeleton of a rock by the action of gases and springs. The pores in this are often occupied by oxide of iron, or even by crystals of fluorspar. This is a likely kind of float. Honeycombed rusty rock with quartz crystals is a likely float, both of these representing the action of mineral hot springs. At rare intervals we may see a little of this oxi- dized rusty rock in place protruding from under the grass, and if so, there is sure to be a prospect hole alongside of it. Bold outcrops of lava rock are comparatively scarce, and when they do appear, as in the cliff above Victor mine, M t. Pisgah, Bahr, and Rliyolite peaks, the rock is apt to be so hard as to preclude the probability of much ore deposit'* in it. »57 ^ Pieces of rock or float stained a violet purple color bv fluorine are considered a good sign of an ore body not far ott this fluorspar being found characteristic of some of the richest veins in the camp; and fluorine gas was doubtless sr ■o a o r* O ►1 c ft r a rs « X o' s n n "1 ■5' ■a n It I i connected with the deposits of ore matter, especially of the tellurium, the present matrix of the gold in *he deeper parts of the mines. 158 Pyrites is not usually found on the surface till the rock is broken open, and tellurium in little silver scales and spots, not till considerable depth is attained. But free gold may be found in surface float, and from the grass roots down, and in the early development of a mine, in the oxi- dized upper portions, associated v/ith iron oxide and black manganese or " psilomelane." Mi' ceous or specular iron, is seen in some prospect holts; and localities marked by evidences of past hot spring action, such as the appearance of botryoidal chalced- ony or opal, should be prospected. A common and curi- ous marking in some of the bleached volcanic lavas is that of an imitation of trees, ferns and mosses, popularly called " photographic rock," scientifically " dendrite" or tree rock. This remarkable imitation of nature is due to crystalliza- tion of solutions of manganese, a.^'^ .nay be compared to fern-like appearances on a frosty window-pane in winter, which are certainly not of organic origin, or in anyway connected with the processes of photograpliv. These dendritic markings may or may not be considered as signs of ore. Similiar markings are very common in the por- phyries of Leadville overlying the silver deposits. i SURFACE PROSPECTING OF A MINE. In some of the surface discoveries of mines, when a con- siderable area, covered by a blow-out of iron oxid« as- sociated or not with purple fluorspar, has been found to run well in free gold, the ground is prospected and de- veloped to the depth of a few feet, and over a certain area, with plows and scrapers, the material so obtained being sent wholesale to the stamp-mill and often giving rich returns. The object of this work is not merely to get all the values out of this rich float, but in hopes of uncovering the vein or veins of which it is the oxidized cap or blossom. This was the way in which the Deerhorn mine was opened up, and its veins discovered on Summit Hill. The ground on the top of the hill is observed to have been " gophered'' in all directions like the catacombs to a depth of about ao feet, and over an area of a square acre or so. This w;*« done partly to gather up and collect the rich floa^ which »59 was found scattered over the hill nnd partly to discover the leads in place. This rich float was stained with purple fluo-iue. and up- wards of 25,000 dollars* worth of gold was obtained from this, the material being dug up by plows and scrapers, before the subsequently discovered veins were found or worked. In the case of the Anaconda mine on Gold Hill, the out- crop of a dyke of andesite was discovered on the hillside covered with an oxidized crust carrying gold. The owners developed this by an open quarry, about a hundred feet in length and 40 to 50 feet deep, from which they extracted the bonanza which made this mine at its outset so cele- brated, and later proceeded to uncover the dyke on the sur- face, to a depth of about 20 feet along the entire length of their claims, but nothing comparable with the bonanzas of the first quarry has been found since in extension or depth. RICHNESS WITH DEPTH, ETC. Many of the mines shipped their best ore from the grass roots and upper oridized portions of the veins, which con- tained free gold and were free milling. With depth some of these mines have not. done nearly as well, especially when they reached the unoxidized zone, ..way from surface influences, and the ore was found v/rapped up in tellurium or iron pyrites. The palmiest days of many a gold camp are its earliest days. SUGGESTIONS TO PROSPECTORS. In the more productive area the prospector will do well to keep to the andesitic breccia, and follow the signs we have mentioned. Outside of this area his course may be a little different, as then he is in the granite district, and looks out for the appearance of dykes of phonolite, rarely more than a few feet, though sometimes many yards, in width, and easily distinguished from the red granite by their light gray or white color. These dvkes do not often appear out- cropping in the granite clifl^s, but are more commonly to be found buried beneath the debris and grass of the slopes. i6o On these he may find no indication and trust to hap-hazard trenching; or a few stray pieces may lead him to the spot. The more rusty, oxidized and decomposed the phonolite, the more likely it is to carry gold; at times he mav find ore and free gold in the dyke itself, but more often at its con- tact, on one or both sides, with the granite. There he is likely to find a crevice filled with clay or iron-oxide, car- rying seams and cavities lined with quartz crystals or stains of purple fluorspar. Sometimes he may find the coarse granite, as in the case Plate LXXXII. A Section Moose Mine Vein, Raven Hill. i. Country Rock Breccia, z. Yel- low Jasper, with Cavities of Quartz Crystals. 3, Blue Gray Jasper, with Seams of Quartz and Iron containing Gold. of the Independence mine on Battle Mt., just at the contact with the dyke of lava, to be very rotten, much honey- combed and robbed of many constituent minerals, and these, by replacement with metals, may yield him the richest ore. Again, the dyke between walls may be re- duced to a blue or yellow jaspery clay, with a vertical lami- nation or cleavage, the lines of cleavage filled with quartz and iron oxide (See Plate LXXXII) ; in such lines he is apt to find the richest ore. After opening a prospect, the ore signs, consisting of stains of oxide of iron and manganese, instead of pursuing an even or regular course are apt to scatter amongst the infinite number of crevices shattering the rocks, no one ■i 1: i6i little lead being of sufficient richness to follow with profit, and the whole body bet.veen walls scarcely paying to work. The ore sig^s often follow a very uneven course, now lying upon a fairly defined wall, then running for a dis- tance into one wall or other, or again following the main course of the creviced lava breccia between walls, now in pockets and crevices, again scattered, or again impregnat- ing the porous and decomposed rock. There are very few true, well-defined veins in the camp; the ore rather impreg- nates certain ill-defined, shcittered zones of rocks between certain ill-defined boundaries called walls. At others the ore occupies narrow cleavage planes in the rock, of which there may be two or three in a mine, some of them produc- tive, others very little so. Ore bodies in the harder or more compact rocks, such as the Buena Vista and Victor mines, are apt to have something more like defined veins and defined walls. In some cases surface signs have been poor, and with depth have done well ; the exact opposite has often been the case. Some mines have been good from bottom to top, but we have to be careful here, as in most gold camps, of the old fallacy of " richness with depth." There is little more criterion for this than in other camps, and many a once famous mine is looking vainly with depth for its lost bonanza, though in other respects doing fairly well. As regards the granite itself, we have heard of few ordi- nary quartz fissure veins unaccompanied by lava intrusions proving productive. The fine grained, red, eruptive granite on Barnard Creek, north of Cripple Creek, has shown a promising ore body in a lava dyke in the granite, which, singularly enough, pro- duces a fine grained galena, rich in gold. Galena is quite a rare ore in Cripple Greek. Green carbonate of copper stains appear at times in the schists and gneisses, but none so far productive. The railroad from Canyon City to Cripple Creek did some good prospecting work in the granite area, its cut- tings exposing quite a number of phonolite and other dykes, together with some granitic veins. Outside of Cripple Creek, in the great volcanic area to the north, between Cripple Creek, and South Park, is a fair prospecting field. The rocks are mainly granites, II l62 rhyolites. trachytes, andesites and basalt, the products, as at Cripple Creek, of a series of volcanic eruptions, of which the latest appears to have been basalt, which commonly caps the other and lighter colored lavas. The rocks in this region are for the most part less decom- posed than those at Cripple Creek, which is not so favor- able a sign. Here the prospector should look out for all signs of decomposition, such as we observed at Freshwater district, a not unlikely spot. The very hard, massive rocks are not likely to be productive, such as the hard black basalts. The lighter colored and more decomposable lavas offer a better chance. Centers of eruption, such as relics of old craters and dykes from v/hich these different lavas issued, should be sought for and prospected. Balfour, a small mining camp at the north of this area, is established among granite and eruptive rocks, which have been found to be mineralized by pyrites. The granites here have several fissure veins and dykes in them, showing considerable disturbance to have taken place in that neighborhood. The low hills in which the prospect holes are located are capped with basalt, apparently resting on volcanic tuffs and other lavas. So far, nothing very productive has been found, though here, as elsewhere, much is hoped for with depth. Singularly enough, in one of these veins in lava, \;e noticed a tarry substance or inspissated bitumen in the cavities of the rock, an unusual occurrence in fissure veins or in volcanic rock. CHAPTER XII. ORE DEPOSITS IN SEDIMENTARY ROCKS. BLANKET ORE DEPOSITS, CONTACT DEPOSITS. This great second class of ore deposits, occurring prin- cipally in Paleozoic limestones at contact more or less with intrusive sheets of porphyry, is mainly represented in Colo- rado by the Leadville and South Park mining district, the Kokonio and Red Cliff districts, and the Aspen and Gun- nison districts, though locally here and there, wherever '63 Paleozoic strata accompanied by igneous rock may be ex- posed, silver mines may be fotmd. We will begin with Leadville and South Park as primarily instructive and typical. SOUTH PARK ORE DEPOSITS. The basin plain of South Park is underlaid by sedimen- tary rocks from the Cambrian below, to the Upper Creta- ceous on top. These strata slope up to the crest of the Mosquito range on the west, where they become violently folded and faulted and eroded. SiaeASAal* '/■'M^y ^^^^ l" =?iK^>0 Contact Orm S'/^^U^m^^m9^^^^< ^-^ ^ ' I I I f r Hljiiii 'i|W'l' ' Cimtaet Dtpoatt CA Mtm ^^^^^^^^^li^'^/.'^^^ " Louxr CarboniArou* J^^I^^^^^^^^^^^^ Z^rerd etolomitie Plate LXXXIII. Section of Leadville Cliff. The mineral developments are on the slopes of this range on both sides of it. The order of succession of strata forming the structure and cliffs of the range and resting on the granite, is as follows, beginning with the lowest : Feet thick. Cambrian quartzite '°o Silurian drab limestone (dolomite) 200 Lower Carboniferous blue limestone 200 Middle Carboniferous sandstones and guartzite (Weber grits). .2,000 Upper Carboniferous limestones, reddish sandstones 1,000 Total 3.6oo to 4,000 164 These formations have been traversed by eruptive quartz- porphyry and porphyrite dykes and intrusive sheets. 'The dykes occur principally in the Archaean, but the intrusive sheets are many and are spread out between the quartzites and limestones of the Cambrain, Silurian and Carboniferous. The connection hchvcen the eruptive masses and deposition of ore is very marked. The ore bodies are a concentration of the metallic minerals originally disseminated through the mass of these eruptive porphyries and deposited along their plane of contact with the sedimentary beds, and by metasomatic substitution extending more or less into the mass of the latter. On mountains Lincoln and B'ross, in the principal mines, the ores are mainly argentiferous, yielding galena and its products of decomposition, viz., carbonate of lead (cerussite) and sulphate of lead (anglesite) with chloride of silver. Barite (heavy spar) is a common gangue or vein rock espe- cially in the richest parts of the mine. Iron pyrites decom- posed and passing into a hydrated oxide of iron, together with a black oxide of managnese, give to the ore its rusty and black color. The deposits occur in irregular bodies or pockets often of great size, in the blue limestone, near its upper surface, but not always easy to find or follow. This limestone was originally covered by a sheet of quartz-porphyry which has been locally removed from the ore deposits, but exists in the peak. This porphyry, generally recognized by its large feldspar crystals, is called Mt. Lincoln porphyry and is quite common and characteristic of Western Colorado. In the Dolly Varden mine the ore occurs in the limestone at con- tact with a vertical dyke of white quartz-porphyry. In the Fanny Barrett mine, on Loveland Hill, rich de- posits of galera and anglesite occur in a vertical fissure (probably a gash vein) crossing tiie hill from side to side and traversing the Paleozoic strata at right angles to their dip. but probably not entering into the underlying granite. This mine was discovered by noticing little pieces of iron following a general line across the hill. In Buckskin Gulch the Phillips mine is an immense mass of gold-bearing iron pyrites, deposited, in beds of Cam- brian quartzite near a dyke of quartz-porphyry. This mine was discovered by its rusty outcrop being exposed along •65 the edge of the stream. At first this crust of iron oxide was loose enough to be panned for gold with good success by the old-timers, and afterward milled. But when the hard pyrite set in, the ore was found to be too low grade to pay for roasting and smelting, and for many years lay idle, en The Criterion in the cliff above this consists of large caves in Cambrian quartzite. still partly occupied by oxidized gold- bearmg iron ore. and galena-bearing silver close to a />or. phynte dyke. ^ i66 The London mine in Mosquito ^^ulcli is peculiar and in- structive as bein^ involved in the great London fault. There are two strong veins or deposits of pyrites carrying both gold and silver; the gangue of one is quartz, the other calcite. They occur in the limestone in connection with an int rustic bed of white porphyry. These deposits stand in a vertical position, the beds containing them having been turned up abruptly against the great London fault, by whose movement the Archjean granite rocks forming the eastern half of London Mt. are brought up into juxtaposi- tion with the Silurian and Carboniferous beds at its western point. London HiU i^':- /"^ t^.v§ / Ar^yry \n ^^^ Plate LXXXV. The London Mine Fault. Going south along the Mosquito range the intrusive por- phyries diminish in extent and with them also the mineral deposits. The Sacramento mine is a good example of a " pocket" mine. Rich bodies of galena and rich decomposed ores have been found at uncertain intervals in a series of pockets or cavities. Some of these pockets or cavities are empty, and lined with modern stalactites, others contain loose sand, with pebbles of rich ore, others are quite full of rich ore deposits. These deposits are difficult to follow with : 107 any degree of certainty, unci much of the prohts made in the rich pockets have been used upinblimlly * gophcrinjf " after other pockets. From some of these i hambers open fissures or joint planes ascend to the surface. The lime- stone was originally rapped by a porphyry which has since been eroded off. This porphyry doubtless supplied the ore. LEADVII.I.K IHSTRK r. The western boundary of this district is the Sawatch range of Archiean granite. The slope of the Mosquito range in the east and the hills o\\ the north, forming the watershed between the (»rand and Arkansas rivers, have a basis of Archtean granite and gneiss more or less covered by patches and remnants of the Paleozoic formations, />., Cambrian, Silurian and Carboniferous, which have escaped erosion. Their lower position relative to corresponding beds on the eastern or South Park side of the Mosquito range is due in part to faulting, and in part to folding of the beds. Within these Paleozoic formations, these beds of quartzite and limestone, //urf /s an enormous development of eruptive rocks, principally quartz-porphyries partially occurring as dykes but generally as immense intrusive sheets following the bedding plane of the sedimentary rocks. Glaciers have been at work also in this neighborhood. A huge " mer de glace" occupied the great valley of the Arkansas to whose bulk numerous side glaciers contributed ; these glaciers have carved and sculptured the mountains. In the flood period following the first glacial epoch a lake was formed occupying the head of the Arkansas Valley. The stratified gravel and sand beds which were deposited at the bottom of this lake now form terraces bordering the valley of the Arkansas River. These beds, known as " wash" or placer grounds, yield gold and are open to further development. Leadville is the center of the min- ing district, the ores are argentiferous galena and zinc- blende. They are smelting ores. Their value is increased by their having been oxidized, the lead occurring as car- bonate, th? silver as chloride in a clayey, or else silicious, mass of hydrated oxides of iron and manganese. The ore is principally confined to the horizon of the i68 " blue" or Lower Carboniferous liniestone, covered by an intrusive sheet of " white Leadville quartz-porphyry." The ore bodies occur not only at the immediate contact of these rocks, but extend down in irregular pockets and chambers int(» the mass of the limestone, sometimes to a depth of loo icet. Sometimes the ore completely replaces the lime- tone between two sheets of porphyry, as in the " Col. Sellers mine," Chrysolite, Little Pittsburg, and CUoroflTo ./>«>•« lUtn^ifm MltUnxdt /Jf^'i/'*''-^*'^^"^^'*^*'^' A^7*'*^^'*/** ^"otoieSec, between SMuatckand Front Jfangt t great Mountatn Eievatton at Close of Cretaceous. * ^" Crmteicmo€*s Jit rvtJr'iats -^ ' \ JicthvU »rt» acT^gr* tShtttfi JPoi'^K .Bc**ir%. Ootoi-cictof^crrKt Aen\grm V^HfC t great Post -Cretaceous Uplift and the folding Hp of the Mosquito Range. Wimfmitltlia'vr* StuthPhtrlt Begirt Catorma^^mntAtf^* nge and South Parh as it is To^ay, showing result of Faulting and subsequent Erosion. Plate LXXXVI. ical Development of the Leadville and South Park Region, Colorado. "■•il» fl.'.(Jif Wl !!P_i HtJ.KH"! I ■iimttmmrn^liifmmrmmi^mmimiim'Wiim 'I ..-■ t/ ^' •' if J Ik * S ^ i-^s L :.:.;■ -k ■ ^•*pn"^«aaHmp «7' The deposits were formed by the uction of percolating waters taking up certain ore materials in their passajfe through neighboring rocks, and depositing them in more concentrated form in their present position. This may have taken place while the sedimentary beds were still covered by the waters of the ocean, and the waters there- fore may have been derived from it, or the area of the Mos- quito range may have already emerged from the ocean and the waters have been estuarine. The uplift of the Mosquito range consisted of a series of folds fractured by faults. The crest is formed by the Mosquito fault, another parallel fracture is the London fault. The greatest move- ment is towards the center or Leadville region, dying out at either end north and south; the greatest displacement is 10,000 feet. Whatever cliffs may have originally been formed by this faulting have been planed down by glacial erosion. ORIGIN OF LEADVILLE ORE DEPOSITS. The ores are deposited for the most part in the blue limestone of the Lower Carboniferous. As the ores were deposited by water solutions, the soluble limestone beds would be more easily acted upon by solutions than the sandstones and shales composing the other rocks of the neighborhood, which are less susceptible to percolating water. The Paleozoic frrmations in America are the prin- cipal repositories for lead and silver ores, not by reason of their geological age, so much as by their containing such a quantity of soluble limestone and being physically as well as chemically favorable for the reception of mineral solutions. The physical Ptructural conditions of Leadville are par- ticularly favorable to the concentration of percolating waters in the blue limestone. Great intrusive sheets of porphyry follow the limestone persistently, principally on its upper surface. This porphyry is very porous, and full of cracks and joints, affording ready channels for water from above, and also channels for ascending water from below, along the walls of the fissures, through which it is erupted. Such waters passing through a medium of different composition would be ready for a chemical interchange with the lime- stone. m iff COMPOSITION OF ORES. The ores were deposited originally as sulphides. This is shown by the fact that the oxidized ores near the sur- face pass down with depth into sulphides. In Ten-Mile district these oxidized ores are seen to result from the alteration of a mixture of galena, pyrite, and zinc-blende. There is very little gold in the average Leadville ores; what little there is comes from the Florence mine (native gold), and from others where it is associated with pyrites. It is usually associated with porphyry rocks, and a porphyry commonly called pyritiferous porphyry shows gold to exist diffused through the pyrites disseminated through its mass. Silver occurs as chloride, a secondary condition, its ori- ginal condition probably being sulphide. Lead occurs as carbonate and sulphate and, deep in the mines, as sulphide. Specimens are common of galena nodules surrounded by a thin coat of sulphate, and that again by a coat of carbonate, showing the order of transi- tion from sulphide to sulphate and thence to carbonate. In the iron mine native sulphur occurs as an alteration product of galena. Iron and manganese constitute rather a gangue material than an ore. They are hydrated oxides and protoxides. The iron was originally deposited as sulphide or pyrites, but has been wholly transformed by oxidation. Zinc is not common, but occurs as calamine (zir.c silicate) in needle-like hairs and white crystals in caviiie.s in the mines. Its original form was zinc-blende (zinc sulphide), as shov.T in the Ten-Mile district. The earthy minerals, alumina, lime, silica and magnesia, are in fair proportions, as might be expected from ores which are a replacement of limestone in close connection with poiphyry. The alktrline element among the ores might also be traced to the influence of the latter rock. The agents of alteration were surface waters, which con- tain everywhere carbonic acid, oxygen, organic matter, chloride of sodium (common salii, and phosphoric acid. The rocks through which these waters passed, bucb as por- phyries and limestones, were found to contain phosphoric acid and chlorine, while organic matter exists in the blue »73 limestones; atid in the overlying shales and sandstones arc many carbonaceous beds and even beds of coal. Water passing through these rocks would take up all these ele- ments and be ready for chemical reactions. Galena (lead sulphide) is much richer in silver than its alteration product, carbonate of lead, or cerussite. On Car- bonate Hill the carbonate averages 40 oz. silver, the galena is 145 oz. to the ton. But galena is harder of treatment. Silver is found at times disseminated througli vein matter and country rock, without the presence of lead, proving that during alteration, silver was removed farther from its original condition and more widely disseminated than lead. Outcrop deposits have proved in many cases richer than those at depth. The deposits near the surface have been the refined, concentrated remains of larger bodes gradually removed by erosion, as the alteration by surface waters went on. The baser and more soluble metals have thus been removed in solutions, leaving behind the more valu- able and perhaps less soluble metals in new and richer secondary combinations. " Kaolin' or " Chinese talc," which occurs both along the line of contact and between the porphyry and limestone and also in the heart of the ore deposit, is a decomposition product from porphyry. It consists principally of hydrated silicate of alumina derived from the feldspars of the por- phyries, perhaps at the time when acted upon by sulphurous waters, which brought in the original ore deposits. Calcite occurs incrusting recent jrevices and lining recent cavities. Barite is common, generally associated with chloride of sih'er and manganese, and is locally recognized as a sign of rich ore. MODE OF FORMATION OF LEADVILLE ORE DEPOSITS. The ores were deposited from water solutions by a meta- somatic interchange, i.e., substance exchanged for substance with the limestone ; and lastly or originally as sulphides. Mineral matter is carried from one place to another within the earth's crust by heat and water, or these combined. Metasomatic interchange of metal for limestone and the removal of dolomite could only have been produced by T74 I The ores were not deposited i, a replacement of the country pr(-t\istin,i^' rarities, rock, i.e., dolomitic water, but are limestone. The ores grade off gradually into the material of the limestone, with a definite limit, as would not have been the case if the limestone had been previously caverned. The only limiting outline to the ore bodies is that formed by the contact porphyry. Fragments of unaltered limestone are found entirely en- closed within the ore bodies, and ore bodies often occupy the entire space for long distances between two horizontal sheets of porphyry, which space further on is occupied by the limestone. This is well seen in Colonel Seller's mine. Examination of ores and veinstone shows lime and magne- sia not in the crystalline condition they would have, had they been brought into a pre-existing cavity and deposited, but in the same granular condition in which they exist in the country rock. The deposits in rocks other than limestone consist of me- tallic materials and of altered portions of the country rock, in which the structure of the latter can sometimes be still traced, and are not the regular layers of matter foreign to the country rock, which results from the filling of a pre- existing fissure or cavity by materials brought in from a distance and deposited along the walls. In the Ten-Mile district the arrangement of the particles of the original rock is frequently seen to be preserved in the metallic minerals, which maintain a certain parallelism with the original bedding planes in the lines defined by minute changes in these minerals. The common characteristic of caves which have been dissolved out of limestone is, that their wails are coated with a layer of clay which has been left undissolved by the percolating waters, and these walls have a peculiar surface of little cup-shaped irregularities from which also stalac- tites frequently hang. There is also an accumulation at the bottom of the cave of fragments of limestone, fallen from the sides of the roof. None of these characteristics are found associated with the ore replacements. Also, when mineral matter is deposited in " pre-existing cavities " it takes the form of regular layers parallel with the walls of the cavity, as is beautifully shown in geodes 75 I lined with a succession of zeolites or with layers of chalced- ony, opal and quartz. No such successive arrangement in layers is found in the Leadville ore bodies. Again, could such large, open cavities have existed for long distances without support between the layers of porphyry? Why did not these porphyry sheets close to- gether? And further, how could such extensive cavities have been formed and kept open under a pressure of lo.ooo feet of rock, which the geology of the region shows to have existed above the deposits at the time they were being formed? Such cavities as we do find in the region are all of very recent origin, cutting through both limestone and ore bodies, and have been hollowed out by surface waters more recent even than those which produced the secondary alterations in the ore bodies. The ore deposits of Ten-Mile district about Kokomo, not far north from Leadville, are very similar in character to those of Leadville. They occur, however, in a some- what higher division of the Carboniferous, and the ores as a rule are not so decomposed and oxidized, and the transi- tion from the original sulphide character of the deposits to the oxidized condition is more easily show"*; RED CLIFF OOI-n 1»KP()SITS. At Red Cliff, still further north of Leadville, in the val- ley of the Eagle, the same geolc%ic series are found, pene- trated, as at Leadville ansits occur, but the peculiar and in- structive feature of tiie jamp is the rich deposits of gold in chambers and cavities in the hard and usually unproductive Cambrian quartzites resting on the granite. The gold in these chambeis often occurs as nuggets. The quartzites dip about lo^ N. E., and between their bed- ding planes lies the ore. The so-called contact or bedding plane between one stratum of quartzite and another is clearly defined. At this line there is a filling so to speak of " brecciated," broken up quartzite fragments cemented by iron rust and at times by iron pyrit** Thu thickness of this breccia varies between four and six feet. Ore chim- neys on this breccia occur at mtervali, I i V ill V ' II IKi 176 Their presence is indicated on the outcrop by seams of rusty clay, which lies on top of the ore body and follows it along the roof of the deposit for 100 to 200 feet, then thins out gradually and disappears entirely; at the point of its disappearance, unaltered iron pyrites set in. These ore chimneys are about 4 feet in width, their thick- ness is limited to the space between the floor and roof. The quartzite roof is always smooth, but the lower quartz- ite floor is rough and corrugated and shows chemical action on it attendant on deposition of ore. The floor at times is impregnated with ore, which does not, however, extend any great distance into it. Though the ore chimneys are from 4 to 6 feet wide the pay ore is only a few inches, swelling form floor to roof. The pay ore in the oxidized rusty por- tion yields 7 ounces gold and 50 ounces silver. In mining, the floor is followed as a guide. Individual ore chimneys are connected laterally by ore chutes like a network. These ore chimneys divide and separate, the branches reuniting or again splitting up. The whole rami- fication conies together again at intervals in one main chimney. The rock filling the space where the divergence has taken place is the same as the breccia filling, only more compact and impregnated with pyrite. These fillings are left standing as pillars after the ore is mined. To sum up, the characteristics of these deposits are : First. The outcrop of the ore chimney indicated by what is locally called a " joint-clay." Second. A zone of oxidation for 200 feet, which grad- ually merges, as the natural water level is approached, through a zone of mixed oxides and sulphides to the zone ^f unaffected sulphides. Third. The "joint-clay" gradually disappears as the sulphides are approached. The ore on analysis shows ses- quioAide and sesquisulphate of iron, silica and alumina, and sulphate of barium. In the Ground Hog mine the ore chimneys are 600 feet apart, but are probably connected. They abound in nug- gets ; the latter are sometimes twiated like bent horns ; in other chutes they are lumpy, composed of crystalline gold particles cemented together by sesquisulphate of iron and horn silver. Nuggets are found in troughs in the quartzite floor ini- ^77 bedded in clay associated with rich silver or horn silver ore. With the nuggets are lumps of sesquisulphate of iron carrying much gold. This proves, according to Mr. Ciui- terman, that the secondary deposition of gold in crystals was through the medium of persulphate of iron derived from slow xidation of iron pyrites, and is an admirable confirmation of the theory as stated by Prof. Le Conte in his geology. ASPEN ORE DEPOSITS, The Aspen mining region is geologically related to that of Leadville; each is on the shore line of the old Archwan island of the Sawatch, one on the east, the other on the west, opposite one another, but about 50 miles apart. The ore deposits occur in the same general horizon, viz., the Lower Carboniferous. Both regions show intense disturbance, both by volcanic intrusions of igneous rock, folding, and faulting. The process of ore deposition in both regions has been an ac- tual replacement of the country rock by vein material. At Aspen the ore is not found in actual contact with the overlying eruptive igneous rock, but at some depth down in the limestone, at a zone where the " blue limestone" be- comes dolomized, or, as Aspen miners say, " passes from blue lime into short lime." The mines of Aspen are situated in Paleozoic strata re- clining upon the slope of a narrow ridged mountain, form- ing a granite spur " en echelon" with the Sawatch range. The strip of '^untry in the vicinity of Aspen constitutes the dividing li.. between the two distinct uplifts of the Sawatch range on the east, and the Elk mountains on the west, and has been successively affected by each upheaval. The Sawatch upheaval was a gradual elevation of this mountain mass resulting from a gradual subsidence of the adjoining sea bottoms, which caused the sedimentary beds deposited in those sea bottoms to slope up at varying angles all along the ancient shore line toward the central mass of the Archaean island. The Elk Mountain range, which extends to the west and south of this region, was upheaved later than the Sawatch, with greater violence and eruptive energy, and the up- 13 ^ \r 1^ "> IMAGE EVALUATION TEST TARGET (MT-3) y // // ^ >^ .»* V / %* ^^< ^^ 1.0 1.1 11.25 " I. IMA 1.4 11.6 Photographic .Sciences Corporation 23 WIST MAIN STRHT WIBSTBR.N.Y. I4SI0 (716) •72-4503 ■ of AlMka. f$$ tmutt n m mi ii t»immL* 'n": i ^K" 205 sequent glaciers, many of which are still remaining in the mountain fastnesses, or running down into the fiords that open into the sea. These are still doing the work of their predecessors, viz., wearing down mounta'ns, cutting can- yons, exposing veins, grinding down gold-bearing rocks, and filling up ravines and valleys and river bottoms with placers and gold bars. Consequently the prospector will expect to find this country the paradise of placers. Bui, again, the mountains being a continuation of the Great Cordillera system have the same crystalline granite core, the mother of gold, and this is traversed by many eruptive rocks, porphyries, and old lavas, and even overflown in places by modern lavas from " craters" still in a state of active eruption. Here, then, are elements the readers of this book will have recognized as " good sign" to the pros- pector for finding gold veins and gold and silver deposits, viz., granite, eruptive and volcanic rocks, and much dis- turbance, heat and metamorphic action. Like all pioneers in a new country, the prospector will most likely begin with placer mining, and end up, it may be, by the discov- ery of the lead or vein from which the gold came. Vast areas of gold-bearing territory lie partly in British Columbia and partly in Alaska, known as the Yukon coun- try. In 1887 coarse gold was found on tributaries of the Yukon. At low water these tributary streams yieldeti large profits, from $50 to $100 per day by sluicing. The rich spots on the low bars were worked out and led to dis- coveries on Forty Mile, Glacier, Birch Creek and others. High bars are also rich and untouched, owing to the diffi- culty of getting water on them and the frozen condition of the ground. The largest nugget found was valued at S42. SuHie deposits are covered by twenty-five feet or more of loam before pay gravel is reached. Single clean-ups have been made of 55 pounds of gold and $36,000 in gold dust taken out in a season. On Glacier Creek pans of dirt run from a few cents to $4. On Bircli Creek, remarkable for the number of elephant bones found in its gulches, very rich finds have been made. Prospectors have got as high as $13 to the pan. The gold is described as like pumpkin seed, yielding $3 to $10, and sometimes under a big boulder or a little stone on bed-rock they could pick up from $15 to $20. 2o6 SILVKR HOW HASIN. The first important discovery of gold in Alaska was in Silver Bow Basin in 1880 in gravels of Gold Creek. The discovery and progress of this district is very instructiv to the prospector. The first prospectors came on the de- l)<)sits on the hillside, and soon, as they supposed, cleaned fiut everything in the Basin. But a Mr. Nowell, quietly looking over things, decided to tap the bottom of the basin Plate C. Silvir How Basin Looking Soutlit'ast, Showing Placer and otlivr Mining Operations. with a tunnel to be used as a sluiceway and so work the entire basin on a large and systematic scale. The first prospectors on the hillsides exposed numerous quartz veins, and stringers of quartz under the placers in bed-rock. They located a few holes on these veins, but having noth- ing but an arastra to work with, soon abandoned the vein mining. Several patterns of mills were tried on the flint- like quartz unsuccessfully, till a Webster mill with five stamps and later ten stamps proved a success. The veins !! 207 are called " contact vein fissures," the reef having a black slate hanging-wall and a greenish gneiss foot-wall. Be- tween the walls of contact a space of several hundred feet occurs, filled in with schists, quartz veins, and vein matter. The filling is networked with veins from a knife blade to several feet in thickness, according to the Alaska Record, which also says: " The ore in Silver Row Basin is iron py- rites and galena with zinc blende, antimony, copper pyrite, carrying gold and silver, but richer in gold, in some veins in this basin now silver and now gold predominates. Mill- ing consist in reducing their bulk by concentration without free gold-saving appliances. Where the gold reef leaves the valley and climbs the mountain sides, veins outcrop on the surface. So there was not much difficulty in tracing the reef through Silver Bow Basin to the summit of the divide, where veins were found cropping just beyond the upper break of the glacier. Some of these croppings showed upwards of 48.6 ounces of gold to the ton. The Gold and Curry mine lies north of the reef and is a chim- ney or up-shoot from the main mineral zone. It shows on the surface for several hundred f'set a number of well-de- fined perpendicular veins running high in gold. Great granite dykes cut through the slates east of Takon Inlet, and run for a long distance down the coast from north to south, belonging to the same general zone of mineralized disturbance." Sum Dum Bay, Shuck Bay and Basin Reef have all their noted ore deposits, and along the mainland and numerous islands indications of mineral-bearing bodies exist in veins of quartz with " colors" in the streams, while in the lime- stone of Glacier Bay rich silver ores occur. In Admiralty Island the Willoughby group of veins cut diagonally across a gneissic formation. The veins are from a foot to ten feet wide and entirely gold-bearing. BEACH SANDS. Rub)'' and black sand arc found along the beach at the foot of the Fairweather range for many miles up the coast. They are rich in fine gold, but heavy and bright, amalga- mating readily and by sluicing. The deposits come from grinding glacial action in the ranges back of them, streams 2o8 • \ carry the sand to the sea, and the surf rocks and pans and separates the heavy material, leaving it in alternate layers and windrows along the beach. The black and ruby sand and gold, being the heaviest inaterials, naturally affiliate. 1 COPPER RIVER. The Copper River section is one of romantic interest and speculation. Natives living at the headwaters used copper implements and brought down to the coast chunks of native copper to the Russians, who were thus tempted to explore the source, but ill-treating the natives after their wont, the exploring party were brained when asleep. Prospectors, since, who have tried to ascend, have been intimidated by glaciers, swift currents and rapids, high precipitous banks and other almost insurmountable diffi- culties. So the upper Copper River is still an unsolved problem. At the head of Cook's Inlet Russians placer-mined for years. Rich diggings and much coarse gold were found lately at Turn-again Arm. Both silver and gold are mined in Unja and Unimak Islands, the ore running from $24 to $143 to the ton. A stamp mill here high above the mouth of the Yukon is the most northern mill in the world. DISCOVERY OK THE TREADWELL MINE. The discovery of the Treadwell, the most noted mine in Alaska, as told in the Alaska Mining Record, is another in- structive lesson to the prospector. Like many other instances, the discovery of gold in placers led to the discovery of the renowned Paris or Treadwell mine. On the 27th of January, 1882, prospectors from Juneau crossed Gastineaux Channel to Douglas Island and found pay dirt upon the beach, and the following March they washed on ground called Ready Bullion, and in three days washed and cleaned up 27 ounces of gold-dust. This led to finding another deposit of gold dirt and decomposed quartz, and in washing the gravel from the bedrock, the great Tread- well ledge ivas exposed. Peter Erussard, or " French Pete," located the ledge, calling it the " Paris." Placer miners, however, by right or might, held the surface for two years 209 and washed out amounts estimated at $50,000 to §100,000. Nothing was done by " Pete," as he considered the ore t» ■ •**■■ 217 with iron pyrites in (jtiartz. Those in stratified rocks carry i;alena, blende and pyrite, and are l<>\v jj;rade in silver. Such are the Hendryx and Hot Springs mines. The richer ores at Hot Springs are in green and gray schists and lime- stones. The richness is due to the influence of country rock and proximity to the granite. Stratified rocks con- taining the ore deposits of Toad Mountain are surrounded by granite. Alteration of rocks is due to the heat of the granite. So the country rock consists of altered old vol- canic material derived from the detritus of an eruptive porphyry. Greenish-gray rocks spotted over with coarse porphyritic white crystals of plagioclase feldspar and black augite crystals are characteristic of the ore-bearing zone. The Spokane Mine occurs near a wide belt of quartz and a dyke of eruptive andesite lava. In the " Number One" the rock is limestone with veins cutting across it north and south and veins traceable for miles. Ores range from 20 to 300 ounces in silver. The richest deposits are in lime- stones and black clay slates. The ore is principally silver- bearing galena decomposed in the limestones to carbonates for some depth, together with native silver and gray copper occurring in irregular pockets and impregnating the lime- stone by substitution, as at Leadville, Colorado. The Cassiar mines are worked at great disadvantage in an Arctic climate with the soil permanently frozen, with a short season of floods disastrous to mines. THE PECULIAR GOl.D-BEARINd ROCKS. On Leech River are some persistent gold-bearing rocks found through British Columbia, showing a great area and extent of these peculiar rocks. In the southern part of British Columbia these rocks are black slates and schists traversed by quartz veins. It is from these mainly that the placers derive both their material and gold. In pros- pecting the extent and distribution of these slaty areas is important, though only a portion of the streams flowing over them carry gold in paying quantities. Still, when once the prospector has become familiar with these rocks he keeps to them and avoids other and barren regions. The slates are sometimes calcareous, micaceous and graphitic. Probably a small quantity of organic matter in 2l8 the sediments from which these rocks were made may have aided in precipitating metalliferous matter and accounts in part for their richness. Their fissile character later ren- dered them easily permeable by waters which have con- centrated the minerals of economic value with quartz and other crystalline minerals of secondary origin in the veins. Geologically this set of strata appears to lie between the Carboniferous and Mesozoic rocks and may be meta- morphosed Triassic or Jurassic strata. The group runs all along the west coast from California to Alaska, and a knowledge and recognition of them as the gold-bearing series is of great importance to the prospector. The rapid character of the Eraser River has distributed the finer particles of gold throughout its entire course, though the heaviest, coarsest gold is found in that part of the river occupied by the slates. Where the slates are absent it is derived from the igneous Tertiary rocks, volcanic tuffs, breccias, and lavas, which often yield gold placer matter just as certain volcanic andesites and breccias carry gold in Colorado, and are worthy everywhere of er^amination. Fine gold also was carried far by the ice and currents of the glacial period. On the Tranquille River the gold is scaly, and with it are particles and scales of platinum of the same shape as the gold; the same metal occurs in the beach sands and some of the placers of California, though no platiniim in place has been found on the Pacific Coast, Besides the gravel in the bottom of the stream an older series is exposed loo feet above it interstratified at the top with a white silt deposit. This deposit is a delta formed by the Tranquille when the water of the lake was at a , higher level, in times following the glacial epoch. The gold is derived from eruptive rocks and slates, and the best paying ground is where the creek crosses a belt of soft slates. In some cases the pay is derived from a cement consolidated by calcareous matter resting upon rotten slate. Gold is found in gravels resting on the surface of the older rocks in irregular pockets and uneven hollows, and again it is not till these gravels are found spreading more widely and in thicker masses over the Tertiary beds that the richer gold deposits occur. The rocks underlying the Tertiary formations are decomposed and shattered and pass upward into a clayey breccia followed by clays and shales. 219 The natural history of Cherry Creek is instructive as typical of how placer valleys and deposits are formed. The actual valley of the stream is at the productive part a narrow depression scoring the bottom of a deeply rounded valley. This valley existed and carried a stream like the present in pre- glacial times. When the glacier from the gold range retreated, leaving the valley blocked with morainal matter and boulder clay, the stream again began excavating its bed down the valley. Soft materials were rapidly removed. The stream at first changed its bed frequently, but at last subsided into the deep narrow valley in which it now flows, cutting a new course in the rock of the wide valley and leaving the old channel yet buried with drift on one side of the present valley. The best paying claim is situated on a little bench 30 feet above the stream. Indians o1)tained gold from the veins by lighting fires over them and dashing cold water on the heated rock, thus disintegrating the rock and exposing the metal. Placer grounds extend over 100,000 square miles of Lower Canada. The gravels are generally covered by a layer of vegetable earth or by a bed of clay. They lie on Lower Silurian diorite and scrpctitine gold-hcaring rocks, as in the Ural Mountains of Siberia; hence Russian engi- neers consider that the gold originates from the rusty quartz of the crystalline schists in the vicinity of serpentines and diorites. Diorite in appearance is commonly a greenish- gray rock speckled over with little white crystals of feld- spar and often too with crystals of hornblende or mica. From the alteration of the hornblende it derives its green- ish-gray color, and hence is often called " greenstone," while its speckled character would name it by miners as a porphyry. Diorite is in many countries an accompani- ment of gold, or gold-bearing, particularly in Northwestern America, where it is often associated with serpentine. The latter is commonly a green streaky rock like green marble, and is often the result of alteration of volcanic rocks and others containing magnesian silicate minerals; hence the frequent association of serpentine with eruptive rocks. Both serpentine and diorite are imijinant factors in the gold-bearing zone of the Northwestern and Pacific Coast areas. 230 i Where the Chaiulieve River makes sharp turns, Rold is foxincl in cavities and fissures of the clay slates, which run in parallel ridges and are uncovered at low water, when miners break it up and search the slates to a depth of sev- eral feet. The fissures are filled with a clay gravel which carries the gold. Many hundreds of dollars have been ex- tracted from between the layers of slate. The gold is sometimes tarnished by a black coating of manganese. At Devil's Rapids the gold lies in a bed 200 feet thick of a hard alluvial conglomerate cemented by clay. The Des Plantes River runs over serpentine, diorite, and schist yielding grains of gold mingled with black sand. The gold occurs in the re-entering angles and cracks of the diorite. In some streams in Lower Canada most of the gold is extracted from fissures in the sandstone bed-rock to a depth of five or six feet. In the joints and lamina where gravel has pene- trated and indurated, gold is found in the largest masses in abundance. The worn appearance of the gold implies that its source is remote. When gravel lies on blue clay with boulders in it in this region, it is poor, but becomes richer when resting on bed-rock. In two layers of gravel sep- arated by a stratum of clay the lower only is gold-bearing. These clays are barren but contain cubic pyrites, pebbles, black sand, and garnets. The layers of gold-bearing allu- vion are not continuous, but occur in sheets or belts of variable extent and thickness. The gold, too, occurs in patches, isolated or remote from one another. A week's work at a good spot is often better than months in poor ground. Quartz veins in Lower Canada run in the direction of the stratification, northeast by southwest, often ob- scured by vegetable soil, and require prospecting by trenches as at Cripple Creek, Colorado and many other regions. The veins conta'n pyrite, zinc blende, galena, and native gold. The pyrite and blende carry the gold, which is de- rived from lower Silurian rocks. These veins occur in soft blackish schists and greenish-gray rocks, or in fine-grained felsite trap or indurated volcanic ash with seams and stains of green epidote. The latter is a grass-green mineral often found associated with quartz and mineral veins, and with iron, garnets, and hornblende. It is a secondary mineral derived from iron-bearing minerals such as hornblende. 331 etc. ftomctitncs it occurs in distinct crystals, but uioro commonly as a v;tass-}^rcen staininj; t<» the rock. The prospector is likely t)ften to come across this mineral in his searches among the crystalline rocks and veins. It is no particular sign of the presence or not of precious metals, but a common accf)mpaniment of them; it is much lighter, more grassy-green than copper carbonate. e. GOLD IN SI.ATES. In all parts of the slaty belt quartz veins abound. A band of slates is often characterized by small thin streaks of quartz and lenticular bunches through all its layers with- out showing any well-defined large veins. The quartz holds little pyrite. Good pay is obtained by cleaning up the bed of the river itself and by crevicing in potholes, pockets, fissures, or slates, or sides of the valley. In Leech River, the gold was generally diffused in small quartz seams through certain parts of the slaty rocks, of which a great mass was worn down in excavating the valley, leaving the heavy gold by natural process of concentration in a nar- row line on the bottom of the excavation. Copper ores and gold in some localities are associated, especially where diorites, green slates, and dolomites are extensively devel- oped. Gold has been obtained from " gossan," or surface float filling the crevices in a cavernous, rusty dolomite. Dolomite is a magnesian limestone, the carbonate of lime of an ordinary limestone replaced in a great measure by carbonate of magnesia. As magnesian carbonate takes less place or volume than carbonate of lime, the replace- ment often gives by shrinkage a minutely cavernous in- coherent structure to the dolomite limestone. And just such a structure is that of which metal-bearing solutions are liable to take advantage and to deposit in it their metals; as, for instance, the silver-charged dolomites of Leadville and Aspen, Coloudo. A gold copper vein at Palmerston carries much copper pyrites; it is associated with dark greenish hornblende rocks and slates, and the gangue is a translucent quartz divided into layers or rib- bons by strings of iron and copper pyrite and calcspar. The last mineral is sometimes, but not commonly a gangue of metalliferous veins. a J 2 ' Gold veins occur near Lake Ontario in fissures in syenitic granite, tliat is, in granite containinj^a good deal of horn- blende as well as mica, with micaceous and talcose slates forming the walls and horses in the veins. The talcose or soft, greasy, greenish soapstone-like slates result from chemical decomposition of the sy«'nite along the sides of th" fissure, apparently a sort of indurated gouge or selvage to the ([uartz vein containing gold-bearing arsenical pyrites. Tliesj veins are irregular in t'lickness and quality, the fiss.iic opening out wide in some places and pinching in others, and the ore richer in places than in others. Diorite is associated with some of these veins like the "porphyry contacts" of Colorado. All over the glacial drift of the plains from Lake Manitoba to the Rockies gold is more or less present, and appears to have been washed from the shingle terraces along the eastern base of the mountains where it is believed the precious metal is most abundant. On the Saskatchewan small red garnets and black or mag- netite sand form the bulk of the residue of the pannings. The gold is not derived so directly from the mountains themselves as from the drifts of granitoid pebbles spread over the face of the country, derived from the denudation of the great belt of Laurentian rocks extending from the shores of Lake Superior northwest to the Arctic Sea. Li New Brunswick gold is found in the pebbles composing the Carboniferous conglomerates of the coast. Gold veins also occur in diorite; some are short gash veins. NFAVKHNIH.ANI) AND NOW SCOTIA (WJLD. In Newfoundland quartz veins occur in serpentine of the Lower Silurian, and where serpentine is absent there is no ore. It occurs in pockets rather than veins. Small veins intersect one another, forming a knot or bow, at point of in- tersection often rich in gold. The rock is a dark-green chlorite schist. In Nova Scotia the gold-bearing series is in Cambrian greenish-gray grits and sandstones with bands of shale overlaid by black earthy pyritous slates and sandy beds much crumpled and contorted. The lodes are in the most metamorphosed quartzitic rocks and in soapstone with rutile and garnets. These strata are thrown into waves (Plate CIII), the elevated points of which having 1 'jen plani'd off show the Rohl-brnrinj; fpmrt/ \(h\vs in the l-rni of irrogular ellipses, tinld occurs as spots aiul himchos »'P to 6o-()Z. nuj(^;ets, 'I'hc leads confonii with the strati- fication. It is alleged that much ol the ^old dritt of Nova Scotia has been carried into the Atlantic to form the sub- fi$9 OOLusov ammtmmtm ms li«r«v «••«« I'l.ATK cm. Contorted (jold Veitis m Hit- Ciiribcii iJistriil, Novn .SluIih. ( Locke. > marine banks of the coast. Copper Lake is a curious in- stance of ^old occurrence. The lake was drained. A layer of tough clay and }< ^35 veins. Resting unconformably on these is a sedimentary formation composed of debris derived from the schists containing fossils of the Potsdam period. The base of this formation is a conglomerate. Gold in early days was found in the lowest stratum of this conglomerate. It was obtained by horizontal drifts, and many hundred thousands of dollars were taken out in a short time. The mines were called 'cement' mines; the conglomerate needed the stamp mill for reduction. This conglomerate merges upward into sandstone or quartzite. It is a mixture of quartz boulders, pebbles and worn fragments of schist with pebbles of hematite. Gold occurs in tliis both as mechanical and Tm« OOLutRv KMaiummm aho MmrAi. Mimmm, Plate CV. The Homestake Mine, Deadwood, Black Hills. /', Porphyry ; /), Potsdam Conglomerate ; C. Cement Mines ; S, Schist. chemical constituents. The horizontal character of the sed- iments and the fact that their fossils belonged to saltwater types shows they were ocean sediments formed in shallow water where there was strong wave action. These depos- its were later overlaid by the porphyry. Ore mined from this ground milled $50 per ton, and the stratum lying next bed-rock was exceedingly rich. Small channels and depres- sions caused local concentrations, and these channels were followed in mining. The ore was hard and required blast- ing. There were the same variations of quantity as in ordi- nary placer gravels. Local channels showed alternations of rich and poor material due to diflferent conditions of current, and the occurrence of the greater part of the gold at bed-rock about six feet thickness as a rule paid. The 236 jfolcl was like placer f^oUl in shot gold or smooth rounded grains slivjhtly flattened. The cetnenting material was iron oxide, and bed-rock j^old was often attached to the overlying boulders by this medium. The gold was most abundant with larj^e cpiartz boulders or pebbles of hema- tite. The latter nearly always carried gold. Each grain of gold is generally covered with a thin coating of iron oxide which needs a blow to loosen it. The richest ore is tiot always found in the deepest portion of the channel but sometimes upon one slope. Hasins occur in these channels which are rich. They seem to have been formed by whirl- pools." VVHiere the slate was soft cement, gold worked down into the crevices for several feet. The history of these singular deposits appears as follows : " The gold veins were in existence before the Potsdam period. The Potsdam seas washed away. the debris result- ing from the disintegration of the quartz veins and depos- ited it in deeper water according to its specific gravity; at the same time gradual wave action carried the gold to bc'1-rock in the same manner as it settles in a miner's pan. The Homestake vein was a hard reef or low island. In time the sediments became an island gradually cementing into rock, until later eruptions of porphyry caused great local metamorphic action. The gold now became partially dissolved and vvas again precipitated as thin films in the schists below. A period of rest ensued until fresh-water streams cut through the upper strata and disintegrated the matrix of the gold and afforded material for a new concen- trating process. This disenveloping process has continued to the present. Gold from the conglomerate found its way to the bottom of IJeadwood gulch and was joined with sup- plies from the Homestake vein and formed the great Dead- wood placer." The gold belt is a zone of slates and schists with many lenses and shoots of ore. Zones impregnated v/ith pyrite pass into quartzites forming foot and hanging walls. Such deposits have to be worked on a large scale to pay, and con- centration and chlorination are necessary. The " contact" gold deposits carry silver also and vary in thickness from a few inches to 10 feet, averaging $15 to $60 in value. They are in connection with igneous intrusive 111 S! M'i' rocks. In the I'otsdatn placrr conKl<»niornti* \hv ^AK<)TA. E.xperiences in this region with the gravels as related by Jenny are very suggestive to the placer prospector. " Tlie placer gravels result from decomposition and ero- sion of the' rocks, and these included gold deposits in Ter- tiary times. The gravel deposits of French Creek show a local rich concentration of gold on the outer edge of the bed-rock. Though very encouraging at first, on driving an open cut into the bar where the gravel was undisturbed the richness of the pay dirt rapidly decreased and soon bec'iiiit uniform, showing the result .irst obtained was only a super- ficial rim rock 'prospect.' The richest layer was rarely ov bed-rock, but 10 to 20 feet above it in a sort of false bottom of compact clayey gravel which had retained most u£ the Ilii '39 lit lie gold. The gold was in flattened scales free from black sand but associated with little-worn garnet crystals. The gold is derived from quartz ledges in schists rather than from the intruded granites, as shown by the fact that the gulches paved wholly with granite were barren. Pay gravel is of heavy pebbles, clayey sand, and many garnet crystals derived from the schists. It is soft, rarely cemented to a conglomerate, and easily washed in a sluice. There was a general diffusion of gold in the creek beds but little concentration in rich deposits, due to slight denudation of the ledges and want of sufficient grade in the valley to cause a concentration of gold into a paying channel. Down Spring Creek where a large quartz vein crosses the gulch, gold is found in the stream bed, derived from a decomposed stratum of clay slate which retained the gold swept over it from the quartz vein. It is noticeable that enormous quartz ledges carrying gold in place are in the vicinity, and these have made the placers. In another locality the rich- est layer was the lower part of the red garnet gravel resting on the surface of blue plastic clay. Where the bed-rock is soft and decomposed it is liable to be rich, but when hard and smooth, poor. Large placer flats and elevated bars occur at bends of the stream and are rich. The region is just such as would lead the prospector to expect rich placers. The source of supply is great, the side valleys are excavated for miles along the outcrops of gold-bearing veins, slates and quartzites, all contributing to the placer of the main valley. Gold has been partly retained in the gulches and then carried out and scattered far and wide in the drift. In flats and creek beds where a stratum of soft slates is found crossing the gulch below, a high and hard bur with rich deposits may be sought for. Pits were some- times sunk in the flats near the channel of the stream, but failed to reach bed-rock owing to uprising springs of water which could not be controlled. Panning has varied from i cent per pan to lo cents on an average. On Bear Creek one pan yielded $27 and a rocker in 8 days took up $165. On Deadwood Creek gold is derived from igneous rocks and the gravel is of the same material, yielding 12 colors to the pan. Manganese and limonite iron were found asso- ciated with the gold san^l, showing the gold came from a heavy manganese and iron ledge in the cliffs. The :gold 240 i)ein^ cntirel}' free from quartz appears to have been de- rived directly from the igneous rock itself, not from quartz veins. A j^ravel wash from the Black Hills is found all !»ver the surface of the plains, made of every kind of rock found in the hills and doubtless carrying a certain amount of scattered gold. Miners prospecting up a dry gulch of Whisky Creek obtained 25 colors from clirt shaken from the roo of a small bush growing in a crevice in the bare sand- st(.ne bed-rock at the bottom of the ravine; hence the locality is called the Rosebush diggings, which derives its gold from the washing down into ravines, by occasional heavy rains, of gravel deposits capping the hills ; such a sud- den stream would sluice the gravel accumulated in the gulch, the gold being cauirht in the crevices of bed-rock. It yielded 5 cents to 15 cents per pan. The gold was in fine panicles associated with gar.i^vs which cam.e from the schists of Harney's Peak. The ravine is hollowed out 200 feet through red sandstones. Its bottom is paved with Carboniferous sandstone, and the hills on boi' sides are covered with deposits of slate and quartz which furnished the gold. The supply of water was so small in force, though the deposits were rich, that miners v/aited till spring rains filled the water-holes and made it possible to work the pay dirt in rockers in rich spots. Most of the streams sink in their beds among the foothills miles from the ])lacers. In dry ravines cutting through gravel deposits mitiers can make wages by washing the earth from the bottom of the gulches during early spring months when there is water enough." PROSPECTING IN ARIZONA. Arizona is in the northern portion of the great plateau system. We visited Prescott some time ago and the mir> ing region around the Hassyampa Creek. Between the Union Pacific and Prescott the country is very sterile, com- posed mainly of contorted granitic schists and lavas. About Prescott we come into massive granite and syenitie rocks traversed by dark greenish-gray dykes of diorite. These dykes are in places gold-bearing, especially in the oxidized decomposed surface, yielding a good deal of fi,-** gold over a considerable width of the rotten dyke, v^hich at 241 le the lime of our visit was beinj; trealc:! by an arastva iti the creek below. At a little depth, however, we found the free character of the ore changed to rather rich K"lU-bcarin^f pyrites requiring smelting. On examining a cross suction of the dyke, v/hich was upwards of loo feet wide, we found it traversed by numerous little veinlets, which assjiys showed to carry the gold, the diorite matrix being p<.or or barren. The main difficulty in this region is the general lack or uncertainty of water, the creeks being liable to dry tip at certain seasons and to boom at fitful intervals, Arizona is noted also for its rich copper mines. In the southern part of the State near Tombstone you rise from I'ost-i'lioccne gravels to a granite plateau of gray, crystalline eruptive granite, weathering in gigantic rounded blocks lying on one another. Near Tombstone stratified formations overly the granite, consisting of quartzites, limestones, and slates of :it Plate CVI. Arched Fold, Toughnut Mine, Arizona, i, NovacutilH under Liini'Hldnt; ; 2, Limestone bending over the Novaculite ; 3, hhalb., bundlnK uvur the Limestone. Lower Carboniferous and of Paleozoic age, dipping at a low angle toward the east. The Tcughnut mine, dcscribud by W. P. Blake, is an instructive one to the prospector. " Here porphyry dykes cut through the strata following the general faulting lines of the country, the veins also following the same general course. The stratified rocks are shales and quartzites very fine-grained, the latter rock changed to the variety called 'novaculite' or whetstone rock. Abundance of iron pyrites occur in the layers of quartzite. Above the quartzite are dark blue limestones and black shales. The black limestones above the novacu- lite are silver-bearing. These beds are folded into arches. The Toughnut is on the anticlinal of one of these arches. The ore was discovered cropping out in the soil and vein stuff. The rich ore lies in the folds. The folds have also 27 242 broken into faults. The Grand Central Chief mine is located in the outcrop of a dyke of diorile porphyry which carries ore, in, through and alongside it. The prospector found the outcrop obscure, being a confused mixture of porphyry, flints, quartz and porous quartzite. None of the outcrops rise high above the soil. Ho was led, how- ever, to the spot by a considerable stain of iron, and a little digging revealed good ore near the surface. " The dyke varies in thickness from a few feet to 70 feet, dipping west 55 degrees. It cuts through the shales, quaitzites and limestones. The dyke is vertically lami- nated or divided from top to bottom by layers or cleavage planes filled with thin veins of quartz (in this respect as in many others resembling the phonolite dykes of Cripple Creek with their cleavage zones produced by shearing or slight faulting movements and filled with rich ore). Large portions of the dyke are so penetrated by quartz as almost rata oouionr Plate CVll. Cross Section of the Mineralized Dyke, Contention Lode, Arizona. Show- ing %ertical laminated structures with seams and cavities o£ quartz crys- tals and ores. to consist of that mineral. The dyke itself is much im- pregnated with pyrites in cubes, many of which having dropped out leave square cavities and produce a honey- combed structure of the quartz. Though it has been worked 600 feet deep and there are 1 2 miles of workings, undecomposed ores below water level have not been reached. The minerals are oxidized and so red with iron oxide that miners emerge from the mine like red men. " Along the upper 300 feet of the dyke extensive decom- position of porphyry has produced pure white or stained kaolin or china clay. This kaolinization extends to the adjoining shales. The ores are gold and silver, the gold being free, the silver as chlorides with carbonate of lead. Metallic gold and silver chloride are disseminated through the mass of the porphyry, while portions of the porphyry carry quartz veins. The porphyry also passes iiUo soap- stone and serpentine. " Gold occurs in crystalline flakes and scales chiefly in and along thin seams and cracks in the mass of the rock as if infiltrated and deposited from solution. Free gold is found in the quartzite. Both dyke and strata have been moved Plate CVIII. Dyke Matter Penetrated by Veinlets of Mineral-Bearing Quartz. Quartz Veinlets. Light Shaded, Feldspar. Biack, and faulted as shown by breaks in continuity and by brec- ciated cross courses, seams traversing both igneous and stratified formations. This breaking up of the dyke and fracturing and brecciating of the country rock, accompanied by the movement of the dyke upon itself and the formation of heavy clay seams, provided suitable places for the accu- Plate CIX. Faulting of Ore Body or Vein, Contention Mine, Arizona. " I mulation of ore found in the softer, more broken portions of the dyke. Bedded ore deposits are associated with bedded dykes and vertical fissures parallel with the Con- tention lode. One lode is traceable for two miles till it passes into underlying granite. " A line of fissures cuts acrops the arch of the Toughnut 244 m which has been followed in ore and is connected with the side bedded deposits. This lode is marked by heavy out- crops of quartz and by flinty boulders lying above the limestone on the surface. The bedded deposits fill irregu- lar cavernous spaces eroded in the strata by metalliferous Plate CX. Bcdilutl Deposits of Lead I'assinj? from Stratum to Stratum, ll»r<»tiKli Joint Cracks. (Arizona.) solutions without definite boundaries, and are apparently explained by the metasomatic or substitution theory. " There have been shearing movements of the dyke upon itself resulting in heavy clay seams from attrition, also Plate CXI. Section of Moose Mine Vein, Cripple Creek, Colorado, i, Country Rock breccia ; 2, Yellow Jasper with Cavities of Quartz Crystals ; 3, Blue-gray Jasper with Seams of Quartz and Iron containing Gold. iiiit lateral and vertical displacements from west to east and downward, the top of the dyke having been carried off in successive blocks by the sliding of masses of the stratified 245 formations upon the planes of deposition of the beds and partly on steeper planes of fracture. These movements have been accompanied favorably by ore occurring in the softer, most broken portions of the dyke, coincident with great original metallization and subsequent movement at- tended by clay seams. The fragments are not cemented by quartz but loosely by clay, showing mere mechanical force." The vertical lamination of the dyke by shearing and the filling of the interstices so caused with quartz and mineral is like to what we find so often at Cripple Creek, Colorado, in the mineralized dykes of phonolite forming the lode of many of the mines such as the Moose, Elkton, Raven, and others — phenomena to which the prospector's attention is particularly called, as he is likely again and again to meet with it. Mr. Penrose in his description of the veins of Cripple Creek gives a very clear account of these peculiari- ties in ore deposits. According to him, " the nature and mode of occurrence of ore deposits at Cripple Creek depend on the character of the fissures containing them. Fissuring occurred before the formation of the dykes which filled the fissures. Sometimes veins alone occupied these early formed fissures, sometimes dykes. Generally, however, the veins were formed at a late date long after the fissuring and dyke filling, as the veins in- tersect the dykes following the course of pre-existing fissures and intersecting the dykes longitudinally or crossing them diagonally. There are sometimes two systems of parallel fissures. The fissures are very numerous and their course fol- lows that of the veins and dykes, viz., northeast and northwest or generally north and south. Fissures were not open gaps, but closed lines of fracture and veins in them are due to replacement of country rock along these courses. These fissures were at times held open by loose fragments of rock broken from the walls or by protruding parts of the walls brought opposite each other by movements along the fissures. The course of fissures is sometimes a clean-cut break but ■rai mmn>, Plate CXI I. Section of the Zeno- bia Vein, Cripple Creek. Example of a clean cut fissure occupied bv a Brec ciated Vein, a. Vein. I>1 l!H > r46 ii ' 5 »1 : usually with parallel cracks on either side so numerous as to give the rock a banded, sheeted or slaty structure, bome- times not parallel but intersecting, producing 'linked fis- sures.' Outside this fissured zone Assuring becomes less and less and farther apart with receding from the main Plate CXI II. Shearing Parallel Fissures Parallel to a Fault. Creek. C. O. D. Mine, Cripple zone. This parallel fissuring is due to strong compressive stress in which dislocation is spread over a series of par- allel surfaces instead of confined to one fissure. The dis- tribution of these lines of dislocation in a homogeneous mass follows definite mathematical laws. Fissures occu- pied by veins result from movement and faulting as shown by presence of breccia, groovings or striae and slick- ensides. These movements were of the nature of earthquake shocks. The character of fissures depends on the nature of the rocks they intersect. In massive hard rocks the fissures are sharper than in soft plastic ones like breccia. !n one case force causing a ,, ,. . „,, , „ . fissure overcomes cohesion of hard Section of Elkton Vein, , , . , i , • ., Cripple Creek, .Show- rock, makmg a sharp break, m the ing reinion (.f a vein other only to the extent of faint frac- to sheareu Phonolite , -^i . ^^ ■% n ^ Dyke. ^4, Vein ; /?, tures Without any one well-defined Sheared Dyke; c, break. The Ore deposits are bodlesof Country Rock. , . , ^i,. ,, £. secondary mmerals fillmg the fissures, sometimes a single fissure, sometimes a number of thin parallel seams filling a fissured zone. Ore deposition w^as a sequel to dyke action depending on heated rocks for its effect. Dykes may liave cut water channels in country Plate CXIV. ■I ^I't I 247 rock, and water from these channels forced up the sides of the dyke caused ore deposition. Shrinkage cracks also in the dykes at their contacts with country rock may have offered favorable places for ore deposit. Hence the con- nection between veins and dykes." PROSPECTING IN NKW MEXICO. This is a region characterized by great flows of basalt and recent lavas, so recent that they often cover the placer grounds and modern river deposits. Old craters occur here and there, and the foothills and prairie border are studded with lava-capped mesas. To the west the country is a con- tinuation of the Rocky Mountain system, with many rocks and formations similar to those in Colorado and producing much the same ore deposits and in much the same geolog- ical relations. Thus there are contact deposits between porphyry and Carboniferous limestones as at Leadville, and fissure veins in granite as in Clear Creek County, Col., and mineralized dykes as at Boulder. The Rocky Mountain system is lower and more broken up into individual ranges than to the north. Besides the veins of gold and silver in place there are vast areas of gold placer ground ; but the prevailing feature is a lack of water to work them. The great Rio Gran-^.e system, it is true, traverses the region, but the fall of the river is not sufficient in most part to bring its waters out of its bed for mining operations. Lrold occurs in the Jicarilla Mountains but no water, and the gold ores in the veins distribute their wealth in beds of dry gulches furrowing the sides. In Grouse gulch a placer occurs resting on hard red clay from decomposition of red granite bed-rock. At Santa Fe the gold placers lie in the Placer Mountains, for the placers in this region are true " hill deposits" on slopes and ridges of the Rocky Moun- tains carrying coarse gold like those of the high plains of California. Pay gravel lies deep below the surface and is generally very rich. Absence of water leaves many of these untouched. Mexicans sink well-like shafts, according to Locke, through the soil to the gravels and tunnel upon bed-rock, and take the richest gravel to the surface in sacks, cart it two or three miles to water, and pan out the gold in wooden bowls called " bateas." In winter they obtain water by melting snow with hot stones. 34^ ;*! Gold occurs locally in quart/osc sandstones of Carbonifer- ous age and in rusty beds rather than in veins. The sand- stone appears to have been charged with gold-bearing pyrites, by decomposition of which the gold has been lib- erated. In localities there are regular quartz veins bearing gold pyrites which have been worked for twenty years. The erosion or breaking down of a bed of sandstone would supply gold to a stream or deposit without its being accom- panied by beds of quartzose gravel. So rich deposits may exist on the hillsides without indications of their presence by beds of rolled gravel or broken fragments of veins on the surface. Professor Silliman, speaking of the great placer deposits in New Mexico, says: " Here are countless millions of tons of rich gold quartz reduced by the great forces of nature to a condition ready for the hydraulic process, while the entire bed of the Rio Grande for 40 miles is a sluice on the bars of which the gold derived from the wearing away of the gravel banks has been accumulating for coimtless ages, and now lies ready for extraction by the most approved methods of river mining. The thickness of the Rio Grande gravels exceeds often 600 feet, or three times that of the like beds in Cali- fornia, while the average value per cubic yard is believed to be greater than in other accumulations yet discovered." The area, according to him, covered by these gravels is 400 square miles ; only three portions of this area are avail- able or within reach of the Rio Grande waters, and the lava circumscribes much of the river-frontages. Nothing corre- sponding to the " top dirt," ' pipe-clay" or fossil wood of the California gravel beds occurs. The gravel for many miles is unbroken except by valleys of erosion cut down 200 feet deep in them, with yet 400 more before bed-rock is reached. The gravels above the second " malpais" will be of less value than the under bed, and zones of poor gravel may occur. Over limited areas beds of fine yellow sand occur which are poor or barren, but the great mass of these heavy beds are compact gold-bearing gravels and contain boulders of quartzite with blue or gray stains and seams of magnetic iron and rusty quartz stained by decomposing iron pyrites, with but few pebbles of granite, syenite, porphyry or greenstone characteristic of the mountain 249 ranges, and with no volcanic debris or ashes. Quartz and (juartzite pebbles form 80 per cent, of the gravel in these beds; the S(nirceof the material is from con r^pondinj; beds of the San^re de Cristo Mountains north and cast. Prospec- tors claim t!iat the ^ra\ els will average 50 cents to 75 cents to the cubic yard. An artesian well was sunk at the Ranches de Taos 423 feet, and throu)>j;h the entire depth only gravel was met and the material showed the presence of gold for the whole distance. Along the Rio (irande mining operations by ground sluicing have been carried on ever since this locality was first possessed by the Spaniards. Dredging is being carried on in some parts of the Rio Grande on the bed of the stream itself. CHAPTER XIX. THE GOLD OF THE ORTIZ MOUNTAINS AND GALISTEO AND RIO GRANDE PLACERS. N. M. Important mineral deposits and placers lie at the base of the Ortiz Mountains and along the Galistco and Rio Grande rivers. The placers are being worked by dredges by the Santa Fe Placer Mining Company, to the chief en- gineer of which, Mr. F. E. Nettleton, and to Prof. E. Walters (geologist), we are indebted for our information on this region as published in the Southwestern Manufacturer, The Ortiz Mountains are 25 miles from Santa Fe city. The elevation of axis of this mountain is 10,000 feet above sea level, the valley of the Galisteo River at its foot is 5,674, at Los Cerillos railroad station. Along this axis are granite, syenite and porphyry. East and west of the axis, paralleling it, are black trap rock, volcanic dykes extending across the country indefinitely from three to five miles from the axis of the range. Between the axis and the dykes, about three-fourths of the distance, are well-defined lodes parallel to the axis of the range. At right angles to these lodes are secondary lodes reaching from the primary down to the dykes, especially on the east side of the range. The great western primary lode extends south to San Pedro. On the secondary lodes are fine bodies of low grade ore. •^iich as Cuiiniiigham Hill near Dolores. The main western lode is rich in copper, and copper mines, as the San Pedro copper mines. Others, such as the Oipsy (Juccn and " Lincoln-lucky," ari' gold producers. The nain primary lode on the eastern side of the range has been worked at intervals since 1711. soon after the second con- (|uest of New Mexico by the Spaniards. Senor Ortiz located on this lode the celebrated Ortiz gold mines. The vein matter of the Ortiz lode is decomposed quartz carry- ing free gold, with depth changing to sulphides or pyrites. The Spaniards worked out great quantities of this ore by means of old-fashioned slopes and inclined galleries, but owing to their crude methods they could not successfully Plate CXV. The Ortiz Mountains and Galisteo River. work the mines below the depth that yielded the free mill- ing or* s. The axis of the Ortiz Mountain range is in close proxim- ity to the newer formations closely flanking its slopes. This uplift came, as in the Colorado range, after the Creta- ceous period. The axis is raised some 2,000 feet above the sandstones flanking the mountain, which contain both anthracite and soft coal. The green trap-rock dykes were thrust up through the newer formations. These Cretaceous sandstones are soft and easily eroded, and form the country rock that tisually includes the gold-bearing veins, hence a large quantity of gold is freed and carried to lower levels by each rainy season. The slopes of these mountains are so steep and the sandstone so soft, that erosion is extraor- dinarily rapid. 25" On the cast side the ratine are larRc liulds nf riih placers —deconi posed quartz in sand and K''kVil w hi( h Ikivl- inun- dated the entire eastern shtjie. Here are millions of cubic yards of j^old-bearinj; material resting? on soft samlstone. These deposits were made in a past a^c after the mountains uplifted and had atTorded great (luantities of ^old-hearing material freed by the rauid erosion of the coinitry mck. Above the main eastern ayko and paralleling it for several miles is probably the richest "dry placer" in the entire field. The geology of the region is simple : the strata rise from the (ialisteo River at an angle of lo degrees up to the primary main eastern lode. Hetween that and the a.xis of the mountain the incline is much greater. The lode is in a true fissure into which the vein material has been in- jected. The sandstone constituting the general matrix of the country rock is so soft and porous that the vein matter lying near the surface rapidly oxidizes. The oxidized honey- combed quartz remains, with its vast supply of free gold that erosion is gradually freeing and carrynig down the slopes to feed the placers below. The great trough that affords a line of rest for these enormous placer deposits is the bed of the Galisteo River. This river is four to ten miles from the main eastern lode, and close to the dry placers which are from hundreds to thousands of leet higher than the river, though the deposit extends in more or less richness down to the banks of the river. There is considerable uniformity of values through- out the field. Placers of workable richness are found almost anywhere where there are drift deposits on tlie entire eastern slope of the range. Water supply is the most difficult problem. The Cun- ningham mesa, or " old placers," on the eastern slope has been worked for hundreds of years by ancient Aztecs and later Spaniards, yet it is said by experts that if water could be brought to bear the placers could yield a million annu- ally for twenty-three years despite the hundreds of past years they have been worked. These dry placers have only been worked hitherto by the Mexican dry washer and by " batea" and dry panning and hauling the material to the nearest water on the backs of burros. Hundreds of thousands of dollars' worth of gold have l)een extracted, and 3<;2 i 'I Still but a minntc fraction of the deposit has tjeon touched. For live miles frotn I^os Cerillos to Ortiz station he bed of the Galisteo River is a rich placer and will pan well where- ever samples are taken. The sandstone bed-rock is 1 5 to 35 feet below the surface. There is not enough fall and pressure power in the river for hydraulicking the dry placer above. The next nearest is the Rio Grande. The water in the river is mostly " sub-flow" penetrating the deposit from top to bottom, hence all the material is in a /tssuv I 'a /lie] pi-r Ch. Yd. 10 cts.. $2.75.. 3-75- 4.0J.. <,.40 4.94. • %«•—••••• \: :: — •.•.••.••••■-" f). 25 . • . . .River bank, lo feet. .Coarse drift sand, 3 feet. .Adobe clay, 3 feet, .('oarse gravel, i foot. .Adobe clay, i foot. Coarse sand and gra%'el, 4 feet. .Gravel and stones, 2 feet. .Fine sand, 2 feet. .Large gravel and stones, 4 feet. .Coar.se sand, gravel and stones 3 feet. .Gray sandstone, dipping 20° 1". (bed-rock). MHO MmTAL MiMmm. Plate CXVI. Section of Rio Grande Rivtr Med, showing Strata Values. partial state of suspension, so that any particle of gold lodg- ing on the surface finds its way to the bottom, where it remains. Thus the material near the surface shows $2.46 and at bed-rock $6.42 per cubic yard. The Santa Fe Placer Company used the air caisson for maUine tests of the materials, the strong sub-flow prohibit- ing the use of the (irdinary cut and pumps. The stratifica- tion of the matter penetrated is shown in the sketch. 253 MoHK. or WORKINc; IT ACF.R. The process proposed for extractinjj the gold is i)y the Nettleton placer raachine. a powerful steam bucket dredge of a capacity of i cubic yard <^f inatt-rial per iniii- ute, having as an auxiliary a six-inch ^t'ntrifngal pump, whose suction pipe will extend down tip Iredge ladder to within 1 2 inches of the lowest i:>oint reached by the buckets. This pump will not only bring up the neces«»try water for sluicing, but such loose material as mav be left by the buckets and in a great measure clear the bed-'ock of gold. The product of dredge and pump is deposited in a sluice Plate CXVII. The Nettleton Placer Mining Machine for River Work, Yards per Day. Capacity, low box 25 feet above the deck of the barge, from which eleva- tion the work is done by gravity until the material and water is disposed of. Passing down the first sluice of 30 feet a grizzly or grating is reached, removing stones over 3 inches in diaineter, finer material passing through screens which reduce it to one-half inch. So the non-productive ma- terial is removed at once and deposited behind the barge. Having passed through the screens, the material and water fall into a box containing quicksilver and thence flow into table sluices, giving additional length of sluice of 70 feet, by which time even the freest gold has gravitated in the riffles of the sluices and been held there by quick- silver, with which they will be charged. The percentage 254 i of fine flour gold being very large, tbe material is passed over a burlap sluice, the fibers of vvhicli arrest and hold the gold. Tile usual accompanying " black" or magnetic iron ■ sand" carries a great dt;al of goUl, as high, so it is reported at times, as $2,000 per ton, the gold probably in sulphides. To save this, after pissing the burlap, the luatter comes in contact with strong magnets placed in the circumference of a cylinder, the iron adhering to the magnets, from which it is removed b_, a revolving brush, the non-magnetic matter passing on to a revolving screen, where it is reduced to one-sixteenth inch preparatory to being run over amal- gam plates, such as are used in stamp mills, or into a series of boxes filled with quicksilver. By this time all collecta- ble gold will have been saved, and after being run through traps to save any strav amalgam or quicksilver the now unproductive material will pass into a tailings well and be taken up by an 8-inch centrifugal pump and depositf^d far beh'nd the boat. Fine sand settling in the riffles of the c'iuices or burlap will be treated with cyanide. Depressions in bed-rock the dredge cannot reach v/ill be reached by the air caisson and bed-rock thoroughly cleaned. Another plan suggested is to raise the material andw^ter for sluicing with a centrifugal pump to the amalgamating plant placed on the bank. Large stones and gravel from the screens will be deposited in the excavation back of the workings and the fine tailings, sluice and surplus water will be conducted down the river by flume a sufficient dis- tance to prevent its return. This plan will enable the bed- rock depressions and crevices to be cleaned by hand at less expense than by dredge or caissons. The waier flow of the river will not exceed 10,000 gallons per minute during 10 months of the year. So no great capacity of pumps will be needed. The natural conditions have made the Galisteo River a promising placer proposition. The extent of its gold deposits can only be conjectured. '■i U 255 CHAPTER XX. THE GOLD AND SILVER ORE DEPOSITS OF MERCLR DISTRICT. UTAH. THE For our information on this district wu art- indebted to the valuable reports of the United States Oculo^ical Survey by Mr. S. F, Emmons and Mr. E. Spurr. From the base of the Wahsatch Mountains on the east to the Sierra Nevada on the west is an arid region called the (ireut Basin, be- Plate CXVIIX. Mercur Basin, Looking South, Meruur Hill on lliu UIkIiI, cause it has no sxternal drainage to the ocean. This was once occupied by two large fresh-water seas, represented now by only small salt lakes. The Basin consists of broad level valleys 6,000 feet above the sea, intersected Ijy moun- tain ridges called the Basin ranges. The Oquirrh range, in which is the Mercur gold-mining district, is the first of these ranges west of the Wahsatch, about 13 miles from them. The Great Basin is an arid, .sage-brush desert. A few small streams arc in the Oquirrh range but insufficient I i 256 for mininjijpnrpo.-^cs. The raiiKc is jomilcs lonjj, cultninal- iiij; in Lewiston I\'ak, 10,628 feet above the sea. Utah has hitherto been celebrated more for its silver than .i;()ld products. Hence the importance of the gold-mining district of Mcrcur. Hi.igham Canyon, Ophir, Stockton, Camp Floyd and Tintic liave all been noted more for their silver than for i;i)ld. The Oquirrh Mountains are composed of Carbonif- erous limestones and quartzites compressed into a series of complicated folds, accompanied by metamorphism and in- Plate CXIX. Mcrcur Basin, Looking Nortli, Nfarion Hill in Left Foreground. jection of porphyry sheets and dykes with subsequent min- eralization in the more disturbed districts. The Lower Car- boniferous limestone of Lewiston canyon is the ore-bearing horizon of the Mercur district. On the north side of Ophir canyon an arch of Cambrian quartzite has been uplifted by a fault. There are no large exposures of eru])tiv'e rocks such as result from eruptive overflows, but rather narrow dykes and intrusive sheets. In Bingham Ce.nyon the ore occurs only in the vicinity of porphyry bodies that occur there. In the Mercur district the igneous rocks are in thin sheets parallel to the stratification, and beneath these sheets the ore deposits occur. There have been two dis- tinct periods of mineralization. During the first the silver lodge was formed, during the second the minerals of the gold ledge were deposited. In both cases the ore was de- 257 posited alonjjf the lower contact of a ])orpliyry sheet where a porous or brecciated /one has been formed l)y intrusions of igneous rock which the mineralizing solutions reached through fractures or fissures extending downwards from the respective sheets. The principal vein materials of the sliver ledge are silica, barium, antimony, copper and silver brought up by ascending hot solutions as sulphides and sulphates. They were deposited in the contact zone below the lowest porphyry sheet and occasionally above it. The limestone in this zone is replaced by silica. The fissures through which the mineral solutions ascended have since been filled with calcite. There are two kinds of quartz porphyry. The Eagle Hill porphyry is a light white rock, like Leadville white porphyry; the Birdseye is gray and speckled with horn- blende mica quartz and feldspar crystals. Two ore-bearing beds or zones loo feet apart occur near the middle of a great series of limestones. The lower bed is of a dark silicified quartzose limestone, brecciated and porous, carry- ing silver, copper, antimony, but no gold. It is called the Silver ledge. The upper zone, called the Gold ledge, is of decomposed bleached red or yellow limestone and shale containing realgar and cinnabar 'vith low but uniform per- centage of gold. The Silver ledge, owing to the hardness of the rock, causes it to stand out as a distinct ledge and is easily fol- lowed, but the Gold ledge of softer material could only be traced by a slight ochreous appearance in the rock. The gold is invisible. Certain beds supposed to be clay or shale in the mine proved to be altered sheets of white porphyry. Three cl these were traced on the ore-bearing zone and revealed the oft-observed connection of igneous rock and ore deposit. Th^ vein materials of the gold ledge are realgar (sulphide of arsenic), cinnabar, pyrite and gold, with these are barite, calcite and gysum. The deposits occur at thr intersection of zones of fracture with the lower contact of the middle of the three porphyry sheets, reaching a thickness of 20 feet. Some of the fissures are still open, showing no evidence of filling or erosion by circulating waters. (See Plate CXX. ) These fractures cut across the silver ledge and, as a rule, do not extend above the gold ledge. ^i. 25« W The section of the region is as follows 1. Blue gray, Lower Carboniferous limestone occupying the bottom of the canyons, 200 feet thick. 2. Interbedded limestones or calcareous sandstones, 600 feet. 3. Thick blue gray limestone, 5,000 feet thick, cf)ntaining J 'V' . , Plate CXX. Natural Open Fissures in the Face of the LJiift of ihe Silver Cloud Mine, in Silver Ledge, Mercur. thin Strata of water-bearing shale, and in its lower portion it carries the ore horizons. 4. Above this again more lunestoiies and sandstones, 5,000 feet thick. So in Mercur Basin a total thickness of 12,000 feet of strata is exposed. 259 As the hills around Mercur are not covered by drift it is easy for the prospector to trace the line of contact between the eruptive porphyries and sedimentary rocks. The c EP «Mo UKrsL Mtmmm- BP Plate CXXI. Map and Section of the Oquirrh Mountains. D, Drift ; 7, C\ Lower Cs niferous; (/ C, Upper Carboniferous ; C, Cambrian ; £ J', Bagle Hill phyry ; B /*, Birdseye Porphyry. Carbo- Por- zone can generally be identified by fragments lying on the surface. In the weathered rock limestone chips are of the typical dark-blue color, while those of porphyry are yel- 26o I ■i^ I ' low, browti or jj;rccti. On a bare hillside the line separat- inj^ the two can ha easily traced. The Birdseye porphyry weathers an olive-^rcen colrr and the Ea^le porphyry gen- erally breaks up into small blocks and chips. Most of the rocks in the Mercur Uasin showtracesof gold like at Cripple Creek. Col., suggesting a widespread miner- alization. The porphyries showed the highest traces and the limestones the least. Pure white calcite veins uncon- nected with the main mineralization showed small quan- tities of gold. Certain localities are so greatly mineralized as to furnish profitably worked bodies of gold and silver 'C V ra MP Mar*** li this result, intensely la.iled solutions arise capable of mueh corrosive elTect on the rocks and of aidinj; ore solution. These solutions act most violently at the contact and be- come rapidly cooled on penetiatiujj; the adjoining; rock. The plicUMinena at the silver ledj;e indicate brief intense action, lii>;lily heated waters with ^reat luetamorphosinK and corr linj; power. The mass is full of cavities showing this. Tlie l)ariinn found in the silver ledj^e was derived frotn the porphyry, as probably were the metals, which were deposited as at Steamboat Springs, Nev., by ascending hot solutions. These exuding at every point in the cooling porphyry found in the limestone a zone where the passage of sohitions was easy by opening of Hssutes and formation of breccias. The heated waters under great pressure would move along this broken weak zone, as also occasionally in an upward direction. Where porphyry sheets cut across the strata water would rise rapidly. Where circulation was retarded accumulation and mineralization would be greatest. In the case of the gold ledge the mineralizing agents were probably more in a gaseous than a liquid con- dition. The various metals, antimony, cinnabar, etc., found associated with the gold are such as would easily pass into the state of vapor and be the last deposited. After the eruption of the porphyry a disturbance brought about a set of vertical fissures establishing a communica- tion with a body of uncooled igneous rock at an uncertain depth, affording a vent for moist volcanic vapors, and along the porous zone at contact of porphyry and limestone, and in the brecciated limestone the vapors spread out and be- coming cooled deposited the gold and associate minerals. The gold . dge is a mineralized zone in the lower part of Mercur Basil. It consists of an altered limestone follow- ing the under contact of a thin sheet of altered porphyry. The thickness of the contact zone varies from 20 feet down to nothing. The lines of greatest mineralization coincide in direction with p. Ect of vertical fissures forming shoots or channels. The ores are oxidized or else sulphides. The former are extracted by the cyanide process, the latter by roasting. The zone is soft and pulverulent and full of cherts. The amount of gold in the ores rarely exceeds 3 ounces to the ton. Silver is absent. .^J^ IMAGE EVALUATION TEST TARGET (MT-3) // ^ >\ V 1.0 1.1 U|21 Hi £ i^ 12.0 IL25 i 1.4 1.6 <%i >^ V Photographic .Sciences Corporation 23 WEST MAIN STREET WEBSTER, N.Y. 14SS0 (716) 172-4503 ^ 4 -^^ k s> ^ i\ :-^A '^ o^ ^ 2^4 CHAPTER XXI. SALTING MINES. In these days when, owing to the depression of silver, so much attention is being turned towards gold and gold mines, too much care cannot be taken by those investing or acting as examiners or experts in gold mines, that there are no tricks played upon them by the astute miner ; for " for ways that are dark and tricks that are vain" the Western miner is at times " peculiar." One of these tricks is what is known as " salting" mines or ledges ; that is, by various means and ways introducing into the mine or into the samples taken from it, certain rich minerals which do not rightly belong by nature in the mine or property, in order to raise the value of the mine in the eyes of the in- vestor or expert. When samples are taken from such a tampered-with mine the values and results must be ac- cepted cum grano salts, with a very large grain of salt in- deed. Whether this classical allusion be the origin of the word " salting" we do not know. " Take care you ain't salted" is the advice to the inex- perienced investor or novice expert. So clever are the miners, that cases are on record where even a most experi- enced expert has been taken in, and comparatively or wholly valueless properties sold for large sums, the pur- chase followed later by woful dismay and surprise, when dividends were called for and did not appear. Gold mines, of all others, are the most easy to salt, hence the precaution in these days is timely. Whilst a mining engineer or expert can hardly prevent salting, with care he can and ought to be able to avoid be- ing taken in ; to be forewarned is to be forearmed. On entering a mining camp in the far West, especially in the more remote outlandish districts, an investor or an ex- pert may consider that the whole village, from the hotel bell-boy to the mayor (who, by the way, may be the prin- cipal saloon-keeper), is in league against him. Directly he arrives, everybody in town wants to know his business ; on // 265 this he should keep as mum as possible, and, if he can, throw impertinent inquirers off the scent. The idea is, " Here is a capitalist to fleece and an expert to delude." Every one, too, has a " hole in the ground" of his own to present. Should they get wind of the particular property in view, there are confederates and middlemen anxious to share the spoils. Moreover, it is considered to the general credit of the camp to sell a mine, be it whose it may, good or bad, and if you mention any property, you will invari- ably hear it "xiracked up." The Eastern " tenderfoot" is somewhat of a "sheep among wolves" in such a camp. The expert, too, is at a certain disadvantage on entering into a strange mining camp, not being familiar with the local conditions. Ores, for instance, in one section or re- gion are not always of the same value as similar ores in another, the rocks may look new and strange to him, and there are a hundred local conditions known only to the resident miner. It would be well, when poss'ble, for an expert, before passing a decided opinion on an important property, to stay around in the vicinity for a while till he knows the " hang of things." On his way to the mine there will be plenty to fill his ears with the untold value of the property he is about to examine ; this friendly duty is not unfrequently performed by an officious middleman. To favor and " soften up" the expert's mind and heart and make him " feel good" toward the property, attentions of all kinds are showered on him. He is driven about town like a nabob, and if he shows a weakness for a " wee drappie," champagne and whiskey are at his service ad lib. , as judicious preparation for the com- ing examination. It may be observed here that attempts are made sometimes to "salt" the expert as well as the mine, not merely by befuddling his brain with intoxicants, but by offering bribes, and as an expert is often not too well off, the latter is a great temptation. We will now suppose, after this ordeal, he goes to the mine with the superintendent or miner. All may be, and we may say generally is, honest and square, or it may not. The expert looks over the exterior and surface signs of the property, studies the outcrop of the vein on the surface, its probable surface continuity, the advantages and disadvan- tages of the situation of the mjne, its proximity to rail- 266 roads, smelting works, markets, etc., and then enters the mine in company with the miner. As a rule the latter will naturally point out lo him the richest portions and ignore the poorer ; sometimes he excuses himself from taking him down into the latter because it is dangerous or full of water. If full of water the expert if possible should have it pumped out. He may suggest, here and there, that such and such a spot would be a good one for the expert to take his sam- ples, and so forth. The expert of course assents to all he is told, but with one eye open, and does not stop to take any samples for assaying until he has seen the whole of the mine; then he requests his companion to go out on the dump and smoke his pipe there, as he insists upon having no one with him in the tunnel when he is taking his sam- ples for assay. He will be inclined to rather avoid those particularly favorable spots suggested to him by the miner, as probably giving too rich an average for the general run of the mine, or as not impossibly being " fixed" for him. If he suspects the latter, he will take a sample or two to see if the mine has been tampered with, taking a little of this out on the dump, crushing it, and washing it in an iron spoon. If a very astonishing amount of gold colors show up, his suspicions are aroused. The judicious miner does not generally want to salt too heavily, for fear of the enor- mous results exciting suspicion, but despite his care he nearly always salts a little higher than he intended. In a mine where the rock is hard, a miner may salt by drilling holes and inserting mineral or ore and disguising the hole. In loose ground or one full of cracks, a shot-gun loaded with a moderate charge of gold-dust will do the work. The skill of the miner in this case lies in his choice of a spot where he thinks it probable the expert will take sam- ples, or in coaxing the expert to take samples from such ground. In hard ground the expert may avoid such salt- ing by having the work blasted out in his presence till a purely fresh, virgin face is shown and then taking his sam- ple. These precautions are not necessary under all cir- cumstances, but only in such cases where the expert has a suspicion that there is an attempt to " put up a job" on him. After getting his samples, and as many as possible, he will sack and seal them then and there in the mine, and never lose sight of them until he has expressed them to his \ 367 own home. Sometimes a mine is so timbered up. that sampling is difficult. Now as they go down the shaft, it may be the expert remarks, " I should like to take a sample in this shaft, but it is so timbered up that I don't see how we can do it without ripping out some of these boards." " Why of course, so you oughter," says the miner, " and see here, I think this board is loose." Now beware lest that board was purposely loosened and behind it the ground is salted. By taking a great number of samples at comparatively close intervals, provided afterv,Mrds the samples are not tampered with, the expert is less liable to be deceived by salting, than if he took very few. A mine cannot be salted all over from end to end if it is a large one, only at judi- cious intervals, and it will be hard if the expert does not escape some of t'lose intervals and get some true samples. Besides taking his regular assay samples by cutting all around the walls, roof and floor of the tunnels at intervals of five, ten, or twenty feet, according to circumstances, crushing and quartering the debris, and finally sacking and sealing his sample bags, he should occasionally take a " grab sample," or a bit of rock at random, or a small sack- ful from the great mass of his samples, and put them in his coat-pocket, and keep them on his person, to act as a refer- ence in case of any possible tampering or accident to his samples whilst in the vicinity or in transit. He should also take bulk samples, good-sized chunks of uncrushed rock which should agree with the assay results of his quartered samples. A disadvantage an expert is under in a strange camp, if he cannot take his own assistant with him, is, that he is very much at the mercy of the miner, if any hard work has to be done, such as blasting or hard digging. Whilst en- gaged in such work the miner, if he pleases, has many chances of scattering around a little gold-dust on the rock of the vein or the loose dirt of a placer. Whilst gold-dust is the favorite medium for salting a gold mine, chloride of gold is sometimes used. The lat- ter, however, is rather a dangerous and barefaced trick to try on a competent expert, as its quality can readily be detected by the chemist, it being soluble in water. In a case of this kind that came to our knowledge, an experi- 268 eticed expert had examined a certain mine and condemned it. Later, the owner who was an honorable man. asked him if. as a special favor, he would re-examine it. as in his absence the assay values from the mine had of late shown much better results. The expert reluctantly consented to do this, though contrary to his general rule. In going along the workings he noticed here and there on the walls certain patches and streaks of clay or mud, he had not ob- served on his first visit. Guessing what they were, he casually observed to the miners, " Seems to have been rain- ing in the mine since I was here." However, to the great delight, doubtless, of the miners he took several samples of these, and forwarded them to a reliable chemist. The latter pronounced them chloride of gold. This of course gave the salting schemie away, as chloride of gold does not occur free in nature, much less in a mine. The owner of the mine was exceedingly angry when he learned what the miners had done without his knowledge or connivance. The men themselves being commonly more or less inter- ested in the sale of a mine, are apt to try and salt it with- out any connivance of the owner or superintendent. We heard of a case in the San Juan district where a mine that was fairly good was about to be examined. This mine carried occasionally specimens of the very rich ore called ruby silver. Not satisfied with the fair, natural richness of the mine, the miners must needs import into the hole quantities of ruby collected from other mines in the dis- trict, whose men were of course in sympathy with the scheme and probable sale. This was acting without the knowledge of the owners. , SALTING GOLD PLACERS. Although a gold placer usually covers a very large area of ground, it is possible to salt it. Usually a miner shows up his placer by opening up pits at convenient intervals, so as to cover the property. Nothing is easier than to salt these pits with gold-dust. Consequently whilst an expert will examine these holes and pan the dirt, he should be on his guard, and insist, where possible, on holes being freshly dug in his presence. Even then he is not safe. Generally in a placer, by the cutting of a stream, sections are shown 269 sometimes from grass roots to bed-rock. From such he should take and pan samples at different levels in the ex- posure; this too, privately and without too much super- vision of the interested miner. SALTING ASSAY SAMPLES. This may be done in several ways. If the expert is im- prudent enough to allow a miner to accompany and assist him in breaking down or crushing samples or panning them, then the infusion of a little gold-dust is easy. Again, after the expert has made up, sacked and duly sealed his samples with wax, should he leave them any- where within reach of the miners, they are not wholly safe, for the miner may insert the point of a fine syringe containing gold-dust into the bag, or he may make a bread mould of the wax seal, open the sacks, and either change the ore for richer, or infuse some gold-dust. Changing of samples for others is not an uncommon trick. The expert cannot watch his samples too closely. He should sack and seal them on the ground, sleep with them under his pillow if need be at night, yet even then cases have been known when the wary miner has succeeded in extracting and changing them for bags to all appearance exactly similar. The samples are never safe till boxed up and expressed and on the way to the city address. He should never fail, as we have said, to have partial duplicates of these about his person. If the expert wishes to assay the ore at a friendly assay office near the mine, whilst he is grinding down his sample to dust, an innocent looking miner may loaf in, and whilst watching the operation, accidentally upset the ashes in his pipe over the sample. Probably these ashes contain gold- dust, and we might here observe that a single grain of gold smaller than a pin's head may materially alter the results of an assay. Some years ago an individual who had succeeded in booming a certain placer district and getting up an excite- ment and a rush, constituted himself as a referee, and pro- fessor; and when miners brought samples for his inspec- tion, they were always found to be very rich in gold. But similar samples from the same spot if uninspected were 27© somehow invariably barren. The wizard's mere look seemed to change the sand into gold, until it was found that he concealed in his ringer-nails " which were taper" not wax, but fine particles of gold. Hence. Midas-like, what- ever he touched he turned into gold. Whilst the Salter may lay traps for the expert, the expert may sometimes lay traps for the Salter. An expert, who had reasons to suspect a certain mine he was examining had been tampered with, and guessing there was a likelihood of an attempt on his samples, after securing himself with duplicates, left his samples exposed on the floor of his room at the hotel, then went out and hired a reliable Mexican boy to watch his room and report to him immediately if he saw any one enter it. He had not long to wait. At dinner the boy tapped him on the shoulder, and he went to his room and caught the miner in the act of tampering with his samples. Sometimes miners, if wealthy enough, will go to great expense to salt a property. Some miners took a couple of well-to-do eastern capitalists to a certain placer, panned the gravel before their eyes and showed up wondrous col- ors. The investors having been warned of miners' ways, refused to entirely swallow the bait, but told the boys to go ahead and develop the property, and if at their next visit, it showed up as well as the pans did on this occasion, they would buy it. When the easterners were gone, at a cost of several thousand dollars they built a flume, put in a hydraulic plant, and gathered a pile of loose dirt to wash down the flume, where the gold is gathered upon quick- silver. The " sharks" raised $50,000 for a gold-dust fund. This dust was run evenly over the quicksilver so that, when the capitalists returned, there was everything to show an enormously rich placer-ground. The capitalists insisted upon a clean-up after the first fortnight's run, which added so much more joy to the sharks. This time the bait was swallowed whole, string and all. The capitalists paid down promptly $250,000 for the ground. The sharks left the country. In a few weeks nothing could be found but the amalgam of the sharks. An ingenious trick once baffled some experienced ex- perts and came very near selling a mine. The mine was a well-developed one and had done great things in its day. It was claimed that at the face of the tunnel, or where the 271 workings left off, there was still a fine showing of ore in place to go on with. The experts found it as stated ; on the face or end of the tunnel there was a fine showing of ore, and the probable amount in place and for the future was duly measured up and estimated. It leaked out later that this block of ore was only a thin screen purposely left, all back of. and behind it. having been carefully worked out and the opening for the miners' ingress and egress skil- fully concealed. The mine was re-examined, the cheat discovered, and the reputation of the experts saved as well as many thousands of dollars from the pockets of guileless investors. This brief sketch of some of the ways of some miners, for some regions and properties, would give an unfair idea of some mines and miners as a whole, if it were supposed that all miners are given to salting, and all properties for sale are beset by a network of dishonest devices. On the con- trary, many, very many, miners are as straight as a string and hundreds of properties are to be examined without fear of tampering. But it often happens that a miner, who in every other relation of life is as honest as the day. draws a line, when it comes to the selling of a mine, which he considers " fair game." But, as elsewhere the world through, honesty pure and simple is the right policy, and in the end would be found the best paying one. For the notorious dishonesty con- nected with mines (much more common in the past than in the present) scares away capitalists from investing, whilst if truth and honesty were maintained, money would roll in freely. One lesson at least may be learned from what we have said, and that is, that if in some cases a professional expert is ever taken in, what chances has a capitalist, ignorant of mines, to buy a mine on his own examination? What man ignorant of horseflesh would venture to buy a steed from a professional horse-jockey, without taking with him a friend who is knowing about horses? How much more so in such a difficult and delicate prob- lem as that of purchasing a mine, is it the duty of an investor never to purchase or induce his friends to purchase a mine, until he has employed the services of a competent expert to previously examine it. If the expert's fee should •7« amount to a few hundreds, and after all he should decide on condemning the property, it is far better for the com- pany to entail this expense, and perhaps lose this small sum, than to involve themselves in the loss of thousands of their own as well as other people's money in a bogus, worthless, or wildcat scheme. CHAPTER XXII. PROSPECTORS' TOOLS AND HOW TO SHARPEN AND TEMPER THEM. The principal tools a prospector takes into the field are picks, drills, hammers and shovel. A prospector, especially when climbing mountains, likes to be as light-handed and unencumbered as possible. For his trip as a whole, he may carry several different tools packed on his donkey, but when he has arrived at a locality, the vicinity of which looks likely, he leaves most of his heavier tools in his temporary camp, or near to where he pickets his pack animal. He makes a short ex- cursion up the mountain for a general reconnoitre, armed with nothing more than a light prospecting pick, weighing not more than three or four pounds. This little pick is about ten inches in length, with a handle about fifteen inches long; the longer portion is sharpened into a pick, and the shorter ends in a square-faced hammer. We recom- mend a square sharp-cornered face to the hammer, in pref- erence to the bevelled face, as the sharp edges and corners are better adapted for breaking rock than the rounded or bevelled ends. This prospecting pick or geological pick and hammer, should be all of good steel, with a good sized eye to admit a springy handle of hickory. See Plate CXXV, Figs. 1, I, I. Armed with this little weapon he climbs the hillside, hunting for " float" or for rusty outcrops of ledges. Loose pieces of rock he cracks open with the hammer end, softer rock in place he explores with the pick. "When I am climbing over the hills," said an old weather-beaten pro- spector to me. " I want nothing but my little pick, then if «73 I find anything likely 'in place.' I mark the spot, and go on, and at noon I come down to camp, or to where the 'burro' is feeding, I take up my heavy digging pick and shovel and 'open up'; this will occupy me till evening at least, then if I find tnere is a ledge worth more thorough exploring, I leave my tools by the hole, and next morning bring up the drills, hammers and blasting outfit. But the first thing I would advise a tenderfoot, is to get his eye trained, trained to looking for float and observing mineral signs, trained to the whole business of close observation. Why ! I myself, old hand as I am, after being away for some months about town or looking at other things, can't get my eye in and down to it for two or three days; then it kind of comes natural. "You must have an eye for float and rocks like an artist has an eye for color, and a musician an ear for music. A tenderfoot had better go along with an old hand for a few days to get into training." DESCRIPTION OF TOOLS, PICKS AND DRILLS. Picks and drills are the main tools that need sharpening and tempering. The kind of sharpening and nature or de- gree of tempering depend upon the kind of work or kind of rock to be worked, whether hard or soft, loose grained or flne grained, siliceous or clayey. Drills, for example, would have to be differently sharpened and tempered for hard vitreous quartzite than for soft sandstone or hardened clay. The same remark applies also to picks. Picks may be double pointed or single, or with a hammer head called a poll, if It is to be used for breaking rock. The main points of a pick are, strong cutting tips, stout eye and a tight handle. The little prospecting pick is made of the best steel throughout, but in tne heavier pick, the wearing Plate CXXV. 3U parts ar« the tips, which should be replaceable. An all Htee! pick is liable soon to bo shortened up and useless, whilst the iron pick eye. a 14 inch length of best iron, gives long service by welding on tip ends, whenever de- sired. Professor Ihlseng, in his " Manual of Mining." as also Mr. George Andre, in his book on " Rock Blasting," gives excellent descriptions of tools used as well as the mode of sharpening and tempering them ; to them we are indebted for many of the details ot this article, and to their works we refer the reader for fu' ther information on this sub- ject. " The picks are sharpened to form on an anvil, and commonly drawn to a four-sided pyramidal point, for hard rock, and a slim taper for fissured rock, and a bluff taper to cut crisp ground, and to a chisel ,' nd for chipping the ground. The eye is oval and well surrounded with metal. All the strain of the prying falls on the eye. which must be true and stout." DRILLS. " The dnV is a bar which has one cutter edge and one hammer end. It is of round or octagonal steel. Drills may be of various lengths, from a foot to four or five or even more feet. For prospecting purposes two or three medium short drills from two to four feet are generally enough, as the prospector's business is rather to find than to develop. In beginning to drill, it is common to use a short thick drill, with a stout 'bull edge' rather than a thin, tapering one. especially in hard rock ; smaller sized. i.e., narrower drills may be used for increasing depth. " The rock drill consists of chisel edge, bit. stock and striking face. To allow the tool to free itself readily in the bore hole, and to avoid introducing unnecessary weight onto the stock, the bit is made wider than the latter. In hard rock, the liability of the edge to fracture increases as the difference of width; the edge A the drill may be straight or slightly curved, a straight edge cuts more freely than the curved; a bull bit for hard rock is generally curved, a straight edge is weaker at the comers than the curved. The width of bits varies from i inch to 2 >i inches. Figs. I, 2, la, 2d, Plate CXXVI, show the straight and curved bits and angles of cutting edges for use in rock. The stock is octagonal in section. It is made in lengths //". ...i' »75 varying from 20 inchvs to 42 inches. The shorter the stoik, the more effectively it transmits the forte of the blow. To insure the longer drills working freely in the hole, the width of the bit should be very slightly reduced in cat I. length. Diameter of stock is less than the width of the bit generally by ^ of an inch. "The smith cuts up the 'borer' steel bars into desired lengths to form the bit, the end of the bar is heated and flattened out by hammering to a width a little greater tlian the diameter of the hole to be bored. The cutting edge n Fl9,4. & DrUt tn in roe*. ^—fM, MMta, ab 3r Plate CXXVI. Forms of Drills. is then hammered up with a light hammer to the requisite angle and corners beaten in to give the exact diameter of the bore hole intended. The drills arc made in sets and the the longer stocks will have a bit slightly narrower than the shorter ones for reasons already given. The edge is touched up with a file. Heavy hammering and high heats should be avoided. The steel should be well covered with coal, in making the heat, and protected from the raw air. Over- heated or burned steel is liable to fly, and drills so injured are useless until the burned portion has been cut away. Care is required to form the cutting edge evenly, and of the full form. If the comers get hammered as in Fig. 3a, Plate CXXVI, they are said to be 'nipped' and the tool will not free itself in cutting. When a depression of the 27^ straight or curved line forming the edge occurs, as Fig. ib, " the bit is said to be 'backward' and when one of the cor- ners is too far back, as Fig. y, it is spoken of as 'odd cor- nered.' Either of these defects causes the force of the blow to be thown upon a portion only of the edge, which is thereby overstrained and liable to fracture." SHARPENING TOOLS. , Professor Ihlseng in his " Manual of Mining" says : " The best fuel for blacksmithing may be a slightly caking coal, giving flame and high heat. Coke is hotter but harder to keep fire in. The fuel should be as free from sulphur as possible. White ash coal is better than red ash ; sulphur makes the iron hot short, and tends to produce scales. The coal should be clear of shale or slate, for they fuse and make a pasty cinder that is annoying." A prospector away from civilization may have to use wood; in that case he should use chips, and blow them with a portable bellows. The prospectors who try to get along on as small an out- fit as possible usually take one to three blasting powder cans and cut the heads out of all but the bottom one, and one head of that must be cut out ; these they place one on top of the other to make a furnace. They punch an inch and a half hole in the side of the bottom one at the bottom tor draft, and to put in the points of the tools to heat them. They use charcoal for fuel and then a chunk of steel or railroad iron about 6 inches long serves fo; an anvil. Some take a small bellows and anvil with them. For tem- pering drills they give the drill, when red, a plunge in water. After two or three rubs on wood, to brighten it, they hold it up to the light and watch it until it takes on a straw color. Then they dip it in water again. For picks a blue color is the most satisfactory in general. " Steel is a compound of iron and carbon, and its homo- geneity and presence of carbon impart to it a capability of hardening and tempering to a degree depending on the temperature of the heating and subsequent cooling. As the amount of carbon increases, the melting point of the iron decreases, and this greater fusibility reduces its weld- ing quality. ■ f 277 " A steel is called 'hardened' when it has been suddenly cooled and thereby become as hard as possible. This is owing to the presence of carbon, for pure malleable iron is not affected by the operation, while both steel and cast iron are to a marked degree. " The operation consists in forging the steel to a certain degree of temperature, and then plunging it into some fluid which abstracts the heat from the tool. The quicker it is done, and the greater the difference of temperature, the harder is the tool. Either water or oil is used ; both volatilize at a temperature much below that of the im- mersed tools, so the hardening takes place in a vapor ; oil generally produces the best effects. On the first plunge the metal is chilled and coated with soot, after which a slow process of cooling takes place." t TEMPERING. " Tempering follows hardening, whereby the steel is sub- jected to a subsequent lower heat, which softens it, and re- moves its brittl3ness. When the hardened iron is slowly reheated, its surface gradually assumes phases of color, beginning with a light straw, passing through shades of yellow, brown, purple, blue and red. At a cherry-red heat, the original color before hardening, the effects of the chilling are practically removed. " Tempering consists in carrying the second heat to one of the above mentioned colors, according to the amount of the brittleness to be annealed. This depends upon the use to which the article is to be put. A second stage of the operation finishes the job. The aforementioned reheat goes on a little way beyond the desired color. The tool is carefully plunged part way into the water or oil, till the disappearance of the steam indicates that it is cold, when another portion of the distance is further immersed for a moment. The tool is withdrawn, the scales rubbed off and the heat of the remaining portion draws to the edge, until it has assumed the proper tempering color. It is then thor- oughly cooled. The idea that the steel is cool :;r at a blue, than at a yellow, in final drawing, is erroneous; for more of the heat is conducted from the red portion to the point, than it radiates to the air, and the first heat to the edge 278 only gives a yellow ; with more, it becomes purple, and so on. Hardened drill and pick points are treated in this way, 4" of the end being heated to a yellow ; and, in thirds, the tempering is proceeded with as above. " Care should be taken that the plunged tool, while tem- pering, be not held too long a time at a certain color line, as it has a tendency to break at that point. The tool should be slightly waved in the water. ' Pieces' which are to be tempered throughout must be allowed to soak, i.e., become uniformly hot, before plunging. "The proper color for a given ground is only ascer- tained by experience. Generally speaking, the picks and drills are stopped at a ' straw, ' if intended for hard ground ; at a blue, for mild ground. The toughness of the steel should be preserved as much as possible, therefore select the lowest color compatible with the service to be per- formed. A high carbon steel is given a lighter color than steel of low carbon. " A pick is made of a square iron bar 14" x i%" heated at the middle, and then struck endwise, till r.bout ij4" across. This spot is softened, and at red heat cut open, and swelled by a drift to form the eye. This is then slit at the ends, and softened, while a 6" length of pick steel is being heated. When ready, this steel is tong^ied into the iron, and hammered. A reheating with borax, and a ham- mering complete the weld, after which the picks are sharp- ened and tempered ; no signs of the weld should be visible." " Pick-steel" is a special steel that can be had in bars i%" or lyi" X. }i" OT ^•", and used only for tips. Steel bars for drills come in lengths of about 14 feet ieach and from }i" to 2" diameier. The American "Black Dia- mond" brand is a favorite. The bars are cut into pieces as long u3 can conveniently be used, e.g. , 30" and 36". The bits are wider than the tool, to prevent it sticking to the hole. They are widened according to pattern, so they can "follow" well. The first drill has the widest bit; the fol- lowers narrower ones. In hard rock the flare is smaller than that in soft rock. " The temper is a lighter color for hard than for soft rock. If the edges of the returned drills are cracked or broken the steel is too brittle, and should be made softer or other coal used. If the edges blunt much by wearing ' 279 round they are all right, though a harder temperature may give them longer life. Cast steel borers are never heated above a cherry. They are annealed at the striking end." PRACTICAL SUGGESTIONS AND POINTS BY A BLACKSMITH. A prospector must have something to act as an anvil ; a hard pebble won't do, he can carry a small anvil or a chunk of railroad iron. A small hand bellows or even a portable forge worked with a crank will make his outfit complete. The following practical hints I picked up from a blacksmith whilst watching him at work tempering both picks and drills for some prospectors He said : " You must temper your drill according to the character of the rocks. " For hard rock, use a short thick edged 'bull bit' which will stand a high brittle temper such as 'straw. ' For picks, a light blue color is a good temper, rather than 'straw' which is too brittle. Cherry red is the heat of your bar, not hotter; 1 lying this on the anvil and hammering it well all over giv it toughness. If blisters show on the steel you must hammer it over again. By occasionally dipping your hammer in water and then striking with it, you get the steel down v a fine grain. When you are dipping for tempering, put the point in the water, that cools the point, and the heat runs the color down to the cool point ; when the color reaches the tint you want, then is your time to cool oflf quickly. The color progresses from a white or pale straw to copper color to blue. Copper tint is a good one to stop at for a drill, — blue, for a pick. The right mo- ment to stop and cool is just at the turning point from one color to another." He took a piece of steel, heated it to cherry red, laid it on the anvil and pounded it lightly with his hammer all over, to toughen it by blows, occasionally dipping his ham- mer in the water to " water temper" it ; this further tough- ens it, by partially cooling it. Now the bar was again put in the fire and heated to a cherry red, care being taken not to keep the bar loo long in the fire, as that would tend to take its toughness out, or produce blisters. The bar was plunged about an inch into the water, and then rubbed against a brick, to show the colors plainer. These passed from the point upwards, gradually through the colors we 28o have mentioned, to arrest it by suddenly cooling off at "straw," would make it too brittle for ordinary drills, ex- cept a " bull drill." Now the " straw" turns into a copper hue, a good point to cool off for a drill. Now it passes into a blue, at this point it would be well to cool off for Bipick. The edge of n drill is almost of secondary impor- tance to the sharpness of the projecting corners; when these are gone, the drill is used up, and clogs in the hole. Some rocks like sandstone will, by reason of the quartz in them, wear off the comers very rapidly, others, like lime- stone or granite, less rapidly. Another blacksmith advised me not to dip (as is com- monly done) the point only an inch in water as it is apt in use to break at the water line, but plunge it all over in the water. " Who shall decide when doctors disagree?" A prospector should take with him a regular black- smith's hammer for sharpening, as well as the 4 or 5-lb. hammer he uses for striking drill or the rock. CHAPTER XXIII. SOME ELEMENTS OP MINING LAW RELATING TO PROSPECTING. A prospector would do well to acquaint himself with a few elements of mining law, so we will give a few samples of Colorado mining law for his benefit. Extent of Lode or Claim. — The length of any lode may equal, but not exceed, 1,500 feet along the vein. Dimensions. — The width of lode claims in Gilpin, Clear Creek, Boulder and Summit counties, shall be 75 feet on each s'de of the center of the vein or crevice. Certificate of Location. — The discoverer of a lode shall, within three months from the date of discovery, record his claim in the oflfice of the recorder of the county in which such lode is >situated, by a location certificate, which shall contain : 38l !st. The name of the lode. 2d. The name of the locator. 3d. The date of the location. 4th. The number of feet in length claimed on each side of the center of the discovery shaft. 5th. The general course of the lode as near as may be. Discovery Shaft.— ^eiore filing such location certificate, the discoverer shall locate his claim by first sinking a dis- covery shaft on the lode, to the depth of at least 10 feet, or deeper if necessary, to show a well-defined crevice. Second, by postmg at the point of discovery on the sur- face a plain sign or notice containing the name of the lode, the name of the locator and the date of the discovery. Third, by marking the surface boundary line of the claim. Staking. —SviCh surface boundaries shall be marked by six substantial posts, hewed or marked on the side or sides of which are in toward the claim, and sunk in the ground, to wit, one at each comer, and one at the center of each side line. Where it is impossible on account of bed-rock, or precipitous ground, to sink such posts, they may be placed in a pile of stones. Open Cuts.— Any open cut or cross-cut tunnel, or tunnel which shall cut a lode at the depth of ten feet below the surface, shall hold it, the same as if a discovery shaft were sunk thereon, or an adit of at least ten feet along the lode from the point where the lode may be in any manner dis- •covered, shall be equivalent to a discovery shaft. Time.—T\iQ discoverer shall have 60 days from the time of uncovering or disclosing a lode, to sink a discovery shaft thereon. Construction of Certificate. — The location certificate of any lode claim shall be constructed to include all surface ground within the surface lines thereof, and all lodes and ledges throughout their entire depth, the top or " apex" of which lies inside of such lines extending downward verti- cally, with such parts of all lodes or ledges as continue to dip beyond the side-lines of the plane, but shall not in- 283 elude any portion of such lodes or ledges beyond the end lines of the claim, or at the end-lines continued, whether by dip or otherwise, or beyond the side-lines in any other manner than by the dip of the lode. Cannot be Followed. — If the top or " apex" of a lode in its longitudinal course extends beyond the exterior lines of the claim at any point on the surface, or as extended verti- cally downward, such lode may not be followed in its long- tudinal course beyond the point where it is intersected by the exterior lines. Proof of Dtvclopment. — The amount of work done, or im- provements made during each year shall be that pre- scribed by laws of the United States. Placer Mining Claims. — The discoverer of a placer claim shall, within 30 days from the date of discovery, record his claim in the office of the recorder of the county in which said claim is situated, by a location certificate, which shall contain : I St. The name of the claim, designating it as a placer claim. 2d. The name of the locator. 3d. The date of the location. 4th. The number of feet or acres claimed. 5th. The description of the claim by such reference to natural objects or permanent monuments as shall identify the claim. Before filing such location shall locate his claim : certificate, the discoverer 1st. By posting upon such claim a plain sign or notice containing the name of the claim and of the locator, the date of discovery, and number of acres or feet claimed. 2d. By marking the surface boundaries with substantial posts sunk in the gn*ound, one at each angle of the claim. On each placer claim of 160 acres, not less than 100 dol- lars* worth of labor shall be done by the first of August each year, and upon less or more ground a sum in pro- portion. f' INDEX. < V PACK Alaska 199. 204 Andesite f)i Archaean 21, 27, 42 Argentite <>7 Arizona 240 Aspen 68,177 Augite 54 Barite 55 Basalt 25. 61, 62 Beach Mining 121. 226 Beach Sands 207 Beds 88 Bismuthinite 66 Black Hills 237 Black Sdnd 112 Blanket Veins 79. 80, 162 Blossom 94 Blue Limestone 23 Boise Basin 231 Boulder Mines 126 Breccia 62 Brecciated Veins 82 British America 213 British Columbia 200, 214 Brittle Silver 68 Calcite 55 California 223 California Placers 224 Cambrian 22. 30, 42 Canyons 38 Carbonates 69 Carboniferous 23, 33, 45 Caribou 203 Caves 174 Cerussite 70 Change with Depth 104 Chemistry of Rocks 143 Chlorite 55 I 284 PAGE Coal 24 Colorado Placers 123 Contact Deposits 76 Contacts 79, loi, 162 Copper 70 Country Rock 104 Cretaceous 24. 35, 47 Cripple Creek 137, 151, 245 Cross-cuts 109 Cross-vein 84 Dakota 233 Deep Leads i ig 226 Devonian 3ii 44 Diamond Drill 81 Diorite 5g. 219 Dolomite 55 Dolomitization 182 Dredging 253 Dykes loi Earth's Origin 26 Education of Prospector 8 Effusive Rocks 61 Epidote s 55 Eruptive Forces 99 Examining Mines 187 Faults 74. 84, 86 Feldspar 54 Fissures 140 Fissure Veins 82, 89, 93, 96, 103, 125, 132. 258 Fluor-spar 55. 63 Folds 86 Folding and Faulting 77 Fossils 39, 41, 42 Eraser 203 Free-milling 78 Garnet 55 Generalized Section of Rocky Mountains 21 Geological Section of the Earth's Crust 17 Geological Training 15 Glacial Epoch 37 Gneiss 5^ Gold in Archaean Rocks 29 Gold in Slates 221 Granite 55 Gray Copper 65 Gypsum 55 A' 285 ;i . PAGE Historical Geology 3 j Hornblende 54 Horn Silver ....'..'.'.. 68 '• Horses" 83 Hot Sprines !..... 147 Hydraulicking ! lai Idaho 200 Idaho Mines 230 Igneous Rocks 58^ 103. 132 Impregnations 88. 92 Intrusive Rocks 5g Iron !........... .64 o'nts. 75, 87 urassic 24, 47 ura-Trias 34. 46 Caolin 173 Cootenai 202, 216 -.ake Ontario Veins 222 Laws ! . . 280 Lavas 1^3 Leadville • 70/ 167 Lithology 50 Loaniing 116 Locating Vein 15 Lower Canada 219 Manganese ] 64 Marble 57 Mercur District 255 Metals. Table of 41 Metamorphic Rocks 55 Metasomatic 80 Mica 54 Microscopy of Rocks 142, 144 Mineralogy 63 Minerals 65 Earthy 63 Metalliferous 64 Rock-making , e-i Table of Ji Mining Laws 280 Mining Terms 90 Montana 232 Moraines 38 Newfoundland 222 New Mexico 247 Northwest, The 198 286 PAuB Nova Scotia aaa Obsidian 6a, 107 Ore-t)earing Rocks 107 Oregon aoo Ores 65 Ores, Free-milling 78 Ore Deposits 72, 88, 135, 16a Ortiz \iountains 349 Outcrop 94 Outfit 9 Paleontology 39 Paleozoic. Meaning of 34 Panning Gold la, 14 Pegmatite 57 Phonolite 15a Placers n. iii. 133, 347, 253 Pockets . . . . ^ 80, 97 Polybasite 68 Porphyries' 31, 58 Pre-Cambrian 39 Prospecting, Sketch of 11 Pyrites 66 luartz 53 )uartz- Porphyry 59 martzites 30, 57 quaternary 25, 49 Led Cliff Gold Deposits 175 Reporting on Mines 187 Rhyolite 61 Richness with Depth 98 Rocks 50. 55, 61 Igneous 58 TaV)le of 41 Rosita Mine 136 Ruby Silver 65,69 Salting Mines 264 Sampling Mines 187, 192 San Juan Mines 132 Schist 57 Scoria 62 Sedimentary Rocks 162 Serpentine 38 Sharpening Tools 272 Sheared Dykes 244 Signs 81, 93 Silica 147 «tr l>A(->l. Silurian 33. 30. 43 Silver Bow Basin 306 Silver Reef 88 Slate 57 Slickensides 91 Solfataric Action 149 South Park Mines 163 Splits go Sulphurets 67 Steamboat Springs 150 S'ephanite 68 Strike and Dip of Veins 109 Syenite 56 Talc 54 Tellurium 67 Tempering Tools 377 Tertiary 34. 36. 49 Tin Deposits 237 Tools II Tourmaline 55 Trachyte 62 Treadwell Mine 208 Triassic 24, 47 Tufa or Tuff 62. 141. 146. 15a Unconformity 3* Values of Ores 66 Veins 14. 82. 89, 95 Veins and Eruptive Forces 99 Volcanoes '37 Walls 9a White Porphyry 60 Zinc Blende 7i