UC-NRLF 
 
 I 
 
 B 3 in 7bS 
 
 E SAMPLING 
 
 AND 
 
 ESTIMATION 
 
 OF 
 
 ORE IN A MINE 
 
 T.A.RICKARD 
 
 THE ENGINEERING AND MINING JOURNAL 
 
TAKING A SAMPLE:. 
 
THE 
 
 SAMPLING AND ESTIMATION 
 
 OF 
 
 ORE IN A MINE 
 
 BY 
 
 T. A. RICKARD 
 
 Editor of The Engineering and Mining Journal, Member of the American 
 
 Institute of Mining Engineers, Member of the Institution of Mining 
 
 and Metallurgy, Honorary Fellow of the Geological Society 
 
 of Australasia, State Geologist, Colorado, 1895-1901, 
 
 Author of " The Stamp-Milling of Gold Ores" 
 
 FIRST EDITION. FIRST THOUSAND 
 
 NEW YORK AND LONDON 
 
 THE ENGINEERING AND MINING JOURNAL 
 1904 
 
COPYRIGHT, 1903, 
 
 BY 
 
 THE ENGINEERING AND MINING JOURNAL. 
 
PREFACE. 
 
 The republication of the papers and consequent discus- 
 sion upon the sampling of ore in mines and the estima- 
 tion of the tonnage available needs no apology; it is a 
 subject of the utmost practical importance. It is safe to 
 say that the reputation of mining engineers has suffered 
 more from the neglect of this branch of practice than 
 from any other cause. On the other hand, those engi- 
 neers who have won a deserved reputation for excellence 
 of judgment are the men who, as a rule, have learned 
 early in their career how to take samples which are a 
 trustworthy index to the value of large bodies of ore. In- 
 ferences from the results thus obtained are, of course, as 
 important as the sampling itself, but he who is careless in 
 the performance of one duty is hardly likely to be cir- 
 cumspect in the other. There are not many data bearing 
 upon the present and future productiveness of a mine 
 which an engineer can secure at first-hand; all the more 
 reason for the exercise of vigilance in collecting those 
 which are available. Such statements indeed are truisms 
 to the experienced, but they are overlooked with a fatal 
 frequency. 
 
 Allied to this subject is the question of the terms to be 
 employed in describing the variously conclusive evidence 
 regarding ore in a mine. The different terms suggested in 
 the course of the discussion, which is herewith repro- 
 
 390304 
 
duced, can be contrasted with the definition brought for- 
 ward by the council of the Institution of Mining and Met- 
 allurgy, London, in a recent circular. It is not likely that 
 the majority of mining engineers will ever agree to con- 
 fine themselves to the use of exactly the same words, nor 
 would we advocate such a step, because the imposition of 
 cast-iron terms based upon a suppositions uniformity of 
 conditions is calculated to cripple the effort to prepare 
 accurate descriptions of unlike occurrences of ore. No tech- 
 nical word or set phrase will cover the varying degree of 
 evidence obtainable concerning the tonnage of ore in ex- 
 istence in a mine, or in the various portions of it. Neverthe- 
 less, while it is unlikely that every one will agree to use 
 exactly the same terms, it is becoming evident, as the light 
 of intelligence is thrown upon the phrase, "ore in sight," 
 that it not only fails to be descriptive, but it is misleading, 
 especially to the average investor in mines who is apt to 
 take it in its literal and most obvious sense. In its ulti- 
 mate significance only ore in the bins is "in sight" that 
 is, your ore is in sight when you have actually taken it out 
 of the mine. The discussion, however, brings out very 
 clearly the need for precision of language in mine reports, 
 and whether an engineer uses one term or another he 
 should always be at pains to explain just what he does 
 mean. After all, the primary purpose of a report as made 
 by a mining engineer is to state facts as lucidly as possible 
 and in terms which cannot be misunderstood by the person 
 at whose request and expense it has been prepared. It 
 is better to go into details of explanation than to mislead, 
 unconsciously, by the use of terms which are capable of 
 several shades of meaning. 
 
 The discussion of these practical matters will, we trust, 
 serve to emphasize the fact that the estimation of the ore- 
 reserves and the exercise- of judgment concerning the fu- 
 ture prospects of a mine require most of the qualities 
 which make for engineering sense, and that the work of 
 sampling, plus the inferences from it, epitomizes those 
 characteristics which, taken together, constitute the dif- 
 ference between a good and a bad mining engineer. If 
 
we can assist those who are beginning their professional 
 career, we shall be amply recompensed. 
 
 These discussions may point out pitfalls to be avoided 
 by the young engineer. If he profits by the experience of 
 others, he will be exhibiting a noble thrift; if he disre- 
 gards it, he will be guilty of a prodigal squandering, for 
 there is no improvidence so pitiful as the waste of ex- 
 perience. 
 
 T. A. RICKARD, 
 
 Editor of The Engineering and Mining Journal. 
 NEW YORK, July IQ, 1903. 
 
CONTENTS. 
 
 PAGE. 
 
 PREFACE T. A. Richard i 
 
 THE SAMPLING AND ESTIMATION OF ORE IN A MINE 
 
 T. A. Rickard 9 
 
 Introduction 9 
 
 Determination of Costs II 
 
 Determination of the Average Value of Ore 14 
 
 Work of Sampling 17 
 
 Size of Sample 19 
 
 Reduction of Samples 23 
 
 Precautions in Sampling 26 
 
 Wrong Methods of Sampling 31 
 
 Calculations After Sampling 34 
 
 The Question of High Assays 39 
 
 Possible Discrepancies Between Sampling and Mining... 44 
 
 Estimation of Ore- Reserves 51 
 
 Inferences from Sampling 55 
 
 Future Prospects of a Mine 60 
 
 Collateral Evidence 71 
 
 Conclusion , 74 
 
 ORE DEVELOPED A DEFINITION Philip Argall 76 
 
 COST PER TON AS A BASIS OF MINE VALUATION 
 
 R. Oilman Brown 82 
 
 MINE VALUATION /. Parke Channing 88 
 
 ORE DEVELOPED > George E. Collins 93 
 
 DISCUSSION C. W. Purington 96 
 
 DISCUSSION Philip Argall 102 
 
 Size of Sample 103 
 
 Marking Position of Samples 103 
 
 Examining the Places to be Sampled. 104 
 
 Taking the Sample 105 
 
 Checking the Sampling 105 
 
 Sacking the Samples f 107 
 
 Cutting Down Samples 107 
 
 Erratic Samples ill 
 
 DISCUSSION George E. Collins 1 13 
 
 DISCUSSION G. M. Gouyard 1 15 
 
 DISCUSSION John C. Treadwell 115 
 
 DISCUSSION Benjamin B. Lawrence 1 16 
 
 5 
 
PAGE. 
 
 DISCUSSION Philip Argall 117 
 
 UNSYSTEMATIC SAMPLING George Bancroft 118 
 
 ON SAMPLING THE FLOOR OF A WET LEVEL. Ernest Levy 124 
 
 DISCUSSION Chester F. Lee 128 
 
 DISCUSSION W. M. Courtis 129 
 
 DISCUSSION Albion S. Howe 130 
 
 MINE VALUATION T. Lane Carter 131 
 
 SOME ASPECTS OF MINE VALUATION J. H. Curie 138 
 
 DISCUSSION Walter Harvey Weed 145 
 
 DISCUSSION R. Oilman Brown 148 
 
 DISCUSSION. Richard A. Parker 150 
 
 DISCUSSION W.L.Austin 151 
 
 DISCUSSION G. M. Gouyard 152 
 
 DISCUSSION Richard A. Parker 154 
 
 DISCUSSION Blarney Stevens 155 
 
 DISCUSSION Auguste Mathez 161 
 
 DISCUSSION G. A. Denny 163 
 
 Cost of Mine Examination 170 
 
 Sampling Interval 172 
 
 Sketching Samples 172 
 
 Recording Samples 172 
 
 Assay Plans 172 
 
 DISCUSSION F. H. Minard 175 
 
 DISCUSSION George A. Packard 181 
 
 DISCUSSION R. C. Gemmell 184 
 
 DISCUSSION J. Parke Channing 192 
 
 DISCUSSION Forbes Rick ard 195 
 
 REVIEW OF DISCUSSION T. A. Rickard 199 
 
 INDEX 219 
 
THE SAMPLING AND ESTIMATION 
 
 OF ORE IN A MINE. 
 
 BY T. A. RICKARD. 
 
 INTRODUCTORY. 
 
 It is held by some that to publish the details of personal 
 practice is unprofessional. Others are of the opinion that 
 while it may be well for professional men to discuss with 
 freedom, but among themselves, the methods they employ 
 in their work, it is poor policy to take the public into their 
 confidence. As regards the first, no defence should be 
 necessary in the face of the recent growth of technical as- 
 sociations which are founded for the avowed purpose of 
 disseminating the knowledge acquired by their members ; 
 while, as to the second objection, it suffices to say that the 
 mining engineer suffers from the ignorance of the public 
 no less than the public itself, and, therefore, every step 
 which will promote a better understanding between them 
 is bound to be to the interest of both. 
 
 Other considerations, equally strong, prompt the will- 
 ing distribution of the little knowledge which any indi- 
 vidual among us may happen to possess. To give is to 
 receive. No man realizes the limitations of his knowl- 
 edge until he begins to crystallize it into writing, and 
 if he be moved by a fraternal spirit to give a few hints to 
 those who are his juniors he will find that the effort will 
 teach him more, perhaps, than those he has set out to 
 help. It was well said by a man of wide learning that the 
 best way to find out all about a subject was to write a 
 book upon it. 
 
 There was a time when the examination of a mine im- 
 plied merely a perfunctory visit to the underground work- 
 ings, the copying of maps and the tabulation of the output. 
 
; > - * 
 
 On this flimsy foundation it was considered proper to 
 base an estimation of values. Other times, other methods. 
 During later years the common sense of every-day busi- 
 ness has been introduced into the industry of mining and 
 it has become the practice to investigate with a thor- 
 oughness quite unknown twenty years ago. That we owe 
 this betterment to the Rand is likely, for, while those of 
 us who have found an adequate field of activity else- 
 where have improved our own methods without conscious 
 suggestions from the outside, it is probable that the very 
 atmosphere of thought breathed by the earnest men of 
 the profession has been influenced by the great develop- 
 ments in the Transvaal and the consequent introduction 
 of a degree of system previously rare in metal mining, 
 so that there has been exerted an influence not less val- 
 uable because it may not be directly measurable. 
 
 The purpose of examining a mine is, usually, to enable 
 the engineer to pass judgment upon the value of it, both 
 present and prospective. Whatever data he uses as the 
 basis of his opinion must be verified as far as possible. 
 There are many items of information which, on account 
 of the relations of time and place, he may not be able to 
 test at first hand, all the more reason therefore that espe- 
 cial care be taken to get alongside of facts in those mat- 
 ters which are verifiable. Among these the three most 
 important are the determination of the amount of ore 
 in the mine, the average value of it, and the cost of 
 turning it into money. 
 
 In practice these three determinations are undertaken 
 in the reverse order, it being obvious that the results of 
 sampling will be meaningless unless you know how valu- 
 able the ore must be in order to yield a profit, and it is 
 likewise apparent that no estimate of reserves can be 
 made without the safe basis of one's own sampling of the 
 mine. 
 
 "Ore" may be defined as metal-bearing rock which 
 
 can be exploited at a profit, and it should be unnecessary 
 
 .to distinguish a profit-yielding material as "pay-ore"; 
 
 however, it is a common habit to include all vein-matter 
 
containing any value under the term "ore," it being left 
 to sampling and assaying to differentiate. In the present 
 discussion, whenever the word "ore" is employed, it will 
 mean such material only as at the time of the examina- 
 tiomcan be profitably exploited ; and if there be other lode- 
 stuff which will yield a profit in the event of a further 
 probable reduction of the expenses of mining and mill- 
 ing, then such material will be designated as "low-grade 
 ore" ; any other vein-matter, of less value, will be included 
 under the general term "waste." 
 
 DETERMINATION OF COSTS. 
 
 In arriving at the average costs incurred in the busi- 
 ness of a mine, the engineer will encounter conditions 
 which may vary between the extremes of a going con- 
 cern, having detailed accounts covering a period suffi- 
 ciently long to afford thoroughly reliable data, and that 
 of an undeveloped mine in an entirely new region where 
 no such data are available. 
 
 The first renders it possible to obtain the fullest infor- 
 mation, and in such instances, if true figures are not 
 secured, it is often due to mere carelessness. Sometimes 
 the costs are not segregated on the account books, and it 
 will require tactful insistence to get at the actual facts. 
 The investigator may find that there is a tendency to 
 eliminate outlays on improvements for the reason that they 
 are to be regarded as extraordinary items of expenditure, 
 and it is not infrequently found that, in the case of a new 
 equipment, the heavy item of wear and tear is overlooked. 
 Errors may arise from the adoption of figures which 
 cover exceptional periods; for instance, at high altitudes 
 the costs during the summer months are less than in 
 winter on account of cheaper transport, better water sup- 
 ply, and other causes connected with the difference of sea- 
 sons ; similarly, incorrect data as to mining costs may be 
 accepted through overlooking the fact that during the 
 period in question the amount of dead work (exploratory) 
 has been unusually small in comparison to that which 
 is required to keep step with the stoping operations ; fur- 
 
thermore, in milling it is not uncommonly found that 
 the power used during a part of the year is derived from 
 water, which is either free of cost or relatively cheap, and 
 that during the remainder of the year coal or wood has 
 to be consumed, to generate steam, at a much greater ex- 
 pense. These are some of the errors against which one 
 has to be on guard. Speaking broadly, the safest way 
 to avoid them is to quote costs covering a long period, 
 long enough to include the vicissitudes of seasons and 
 markets. 
 
 Mines are rarely in a stationary state of development ; 
 like man himself, they are either growing or declining. 
 When an engineer examines a mine he obtains data which 
 are representative of conditions liable to change on ac- 
 count of the probable expansion or contraction of the en- 
 tire enterprise; therefore, the figures he gets are apt to 
 represent a passing phase in the development of the par- 
 ticular undertaking, and he cannot arrive at the average 
 costs for the future by simply dividing the expenditure 
 for a given period by the tonnage mined during that 
 period. If the property is a steady-going concern, which 
 has been operated for many years under conditions which 
 are likely to continue unchanged, then indeed he has an 
 easy task, and, given correct figures, he has only to per- 
 form a plain sum in simple division. Such cases are rare. 
 Mines are usually bought by capitalists because they think 
 they can enlarge the scheme of operations so as to make 
 the business more profitable than has been the case under 
 the previous ownership. This often entails a sweeping 
 change in the manner of carrying on the enterprise ; the 
 entire business is conducted on broader lines, and it 
 is assumed that a larger scale of operation will result 
 finally in a considerable diminution in the average cost 
 per ton. Apart from the fundamental supposition of ore- 
 reserves big enough to warrant the expansion, there arises 
 the question whether the money to be spent in extra equip- 
 ment, a better trained staff, more vigorous and extensive 
 development of the mine, .etc., will result in a reduction in 
 costs to the extent estimated. Experience has shown that 
 
sanguine expectations in this regard are not always ful- 
 filled, and that a single mine owner or a small local syndi- 
 cate can often, in spite of imperfections of administration 
 and equipment, work a mine at a cost per ton which will 
 compare favorably with that of a big company having the 
 large permanent expenditures inseparable from the very 
 nature of its organization. In judging of this, experience 
 is the only guide; no rules can be laid down; each case 
 must be considered apart and on its own merits. 
 
 In the case of an undeveloped mine, in a new district, 
 reliable data concerning costs are not available. Under 
 such circumstances it is well to supplement one's judg- 
 ment by visiting the nearest mines which are being oper- 
 ated under like conditions. To those devoid of experi- 
 ence the situation is honeycombed with pitfalls. West 
 Australia afforded many lamentable examples of this dur- 
 ing the years between 1895 and 1898. The majority of 
 reports made at that time omitted to include any estimate 
 of costs, all the available space being taken up by flam- 
 boyant statements of results obtained from rough sam- 
 pling, together with wild prophecies concerning enrich- 
 ment in depth based upon the presence of sulphides, tel- 
 lurides, etc. It is a fact that many reports, which con- 
 fessed to an average of 8 or 10 dwts. of gold per ton of 
 ore, advocated the purchase of mines situated in localities 
 where, at that time, the costs could not possibly be less 
 than 20 dwts. per ton. Again and again one found, in 
 examining a mine which had proved a failure or was 
 about to collapse, that the earlier reports contained the 
 results of assays upon what obviously must have been 
 mere specimens of ore. Such reports had served as the 
 foundation for financiering on a napoleonic scale, and 
 prospects had been highly commended on the basis of an 
 average tenor low even under exceptionally favorable 
 conditions, but quite unattainable in an uninhabited desert 
 several hundred miles from any manufacturing center. 
 
 It may seem that the follies of a boom are hardly worth 
 castigation, but they may recur, and if, haply, they do not, 
 then we may at least learn one lesson from them, namely, 
 
 13 
 
that it is quite as important to ascertain the average costs 
 as it is to determine the average value of the ore in a 
 mine. To ask a man who has had no experience in the 
 business and management of mines to appraise the value 
 of a prospect situated in a new region is to court disaster. 
 He may be a chemist, -geologist, mineralogist, mechanical 
 engineer ; however accomplished he may be, unless he has 
 served an apprenticeship as a mining engineer he will be 
 more helpless than helpful. In sizing up the situation it 
 is necessary that a man should know what are likely to 
 be the costs of stoping, timbering, road-making, erection 
 of machinery, equipment, etc., and these things he can only 
 know through actual underground experience and per- 
 sonal participation in the administration of mines. In a 
 new district all the data obtainable will be those furnished 
 by prospectors, diggers and local promoters, very few of 
 whom have accurate knowledge on these points, and when 
 they have it they do not feel called upon to donate it to the 
 novice who happens along. This disregard of the inevit- 
 able high costs attendant upon the opening up of a new 
 mining region under unfavorable conditions has been at 
 the bottom of the blunders which have retarded the early 
 development of many districts. 
 
 THE DETERMINATION OF THE AVERAGE VALUE OF THE ORE. 
 
 The average value of the ore in the past can be ascer- 
 tained from the records of a mine, but to find out the prob- 
 able average value of the production in the future there is 
 no method save that of testing the ore exposed in the 
 workings. This is done by taking representative frag- 
 ments and then subjecting them to assay. The method is 
 termed "sampling." There are many ways of carrying 
 out the operation; the best are the outcome of experi- 
 ence. 
 
 Sampling is expensive. It cost $7,000 to sample one 
 well-known mine, and it cost $12,000 to do the same work 
 in a neighboring property. This did not include the fee 
 of the engineer in either instance. Therefore, an engineer 
 will not commence an elaborate sampling of a large mine 
 
 14 
 
unless he has reason to believe that the circumstances 
 warrant it. The cost mounts up into big figures, because 
 of the large number of assistants necessary, the work- 
 men employed in rigging up such timbering as is required 
 to enable the sampling gang to get at the stope faces, the 
 cost of assays, and other expanses. When a mine has very 
 extensive workings the cost is much increased on account 
 of the necessity for putting up special timbering upon 
 which to rig up a temporary platform, or such other ar- 
 rangement as will permit of convenient access to the faces 
 of ore in the stopes. The figures already quoted indicate 
 very plainly that a thorough sampling must not be lightly 
 undertaken. It should always be preceded by a prelim- 
 inary investigation. In going through the mine for the 
 first time the engineer will observe that either the present 
 value of it or, perhaps, its future prospects, hinges upon 
 certain facts ; it may be a question whether the lower work- 
 ings exhibit a falling off in value ; it may be important to 
 ascertain whether particular ends of levels or partic- 
 ular stopes are really as good as represented. A few 
 samples will throw light on these points, and, if these are 
 satisfactory, then it will be well to test certain portions of 
 the mine more thoroughly, and in this way finally get 
 data which will determine whether a complete sampling 
 of all th'e workings is justified. 
 
 In organizing the sampling gang it is necessary to adopt 
 a system in order to avoid confusion. If it is a small mine, 
 or if the conditions render it advisable to keep quite clear 
 of any assistance from the management, then the engineer 
 will employ only his personal assistants, and, whatever 
 their number, he will divide them into sets, one of whom 
 will break the sample while the other holds the box to re- 
 ceive it as broken. The accompanying photograph illus- 
 trates such a couple at work. If, on the other hand, the 
 examination is being made for the owner of the mine, or 
 the conditions otherwise warrant the engineer in accepting 
 the good offices of the management, so that he can utilize 
 the services of workmen on the property, then the task is 
 easier and he can put each of his assistants to work with a 
 
miner, the latter doing the muscular work of breaking 
 the ore while the assistant watches to see that the sample 
 is fairly taken, and collects it as it falls into the box or 
 other suitable receptacle made for this purpose. 
 
 Next, it is necessary to determine what interval to allow 
 between samples. If the ore is fairly regular in width and 
 value, an interval of 10 ft. will usually suffice ; if it is very 
 spotty in value and subject to sudden changes in width, a 
 lesser interval will be required. I have been compelled to 
 sample every 3 ft. in the case of a vein, the ore of which 
 varied between one inch and one foot, with assay-contents 
 ranging between 10 ounces of silver and 1,000 ounces. In 
 such a case extreme care to sample accurately at very 
 short intervals is absolutely imperative in order to get at 
 any kind of idea regarding the average of the ore. When a 
 lode is built up of the common sulphides, such as pyrite or 
 galena, the variations in value are apt to be small, and un- 
 der such conditions 20 ft. may not be unsafe. Even though 
 you may decide to take samples at much shorter intervals, 
 it is best to start off with a large interval, say of 20 ft., 
 and when the assay-returns are received you can cut 
 this down by taking intermediate samples, if the circum- 
 stances warrant it. This will prevent useless labor over 
 stretches of poor ground, and at the same time suggest 
 the proper interval required wherever the workings are 
 in good ore. Having settled this point, the next step is to 
 take the first assistant and measure as regularly as possible 
 along the workings, marking each successive place with 
 colored chalk so that there can be no mistake as to the 
 point where the sample is to be taken. Then, one of the 
 assistants or the engineer himself, at all events a man 
 who has had some training as a mine surveyor, is told off 
 to make sketches of the workings as the sampling pro- 
 ceeds, noting the variations in the vein, the number of 
 each sample and its position, and gathering other infor- 
 mation, often extremely important, such as develops in 
 the course of the work done by the sampling gang. An- 
 other man sees to the correct labeling of the samples, 
 the sacking and sealing, and the removal of them to 
 
 16 
 
a safe place. All the data thus obtained should be set 
 down upon a longitudinal section of the mine, so that 
 they can be generalized by the engineer later on. 
 
 THE WORK OF SAMPLING. 
 
 The best sampling tool is a moil when struck by a four- 
 pound hammer. Beware of the prospecting pick or the 
 geologist's hammer, or even the larger type of each which 
 the working miner uses; the former insensibly, but in- 
 evitably, seeks out the soft places and crevices in the vein, 
 and does not, therefore, yield a true sample, while, as to 
 the hammer, that does the reverse and tends to break off 
 the projecting points, which usually represent the harder 
 portions of the ore. As a rule, the richest parts of the vein 
 are not in the hard quartz, but, particularly near the sur- 
 face, in the decomposed lode-stuff, so that the pick gives 
 too high an average and the hammer one which is too low. 
 By the right use of the moil and hammer the error of ex- 
 tremes can be avoided. Of course, the excellence of a 
 tool depends upon the right use of it, and it is very easy to 
 get misleading results with the moil as with the other im- 
 plements already criticized; nevertheless, experience de- 
 monstrates that the former is more likely to give an ap- 
 proach to a perfect sample. The ideal method of sampling 
 is the testing of a cheese by a cheese-tester, which removes 
 a core of uniform size. In a mine the intention is to 
 imitate this method as nearly as a material of very vari- 
 able hardness and texture will allow, an effort being made 
 to cut out a channeling or groove of uniform breadth and 
 depth across the full width of the ore. 
 
 Either a moil or a gad is obviously best adapted for this 
 purpose. If the ore is too hard for a moil and a single- 
 hand hammer, get another striker and a double-hand ham- 
 mer. 1 Do not let the hardness of the ore lead you into the 
 mistake of using dynamite, in the form of "pop shots," in 
 order to loosen the ground. No ground that can be mined 
 in the ordinary way, that is, by drilling holes and charging 
 
 *A single-hand hammer, that is, one requiring the use of only one hand, 
 ordinarily weighs 4 Ibs. A double-hand hammer weighs from 8 to 10 Ibs. 
 
 17 
 
Ha.no. RocK-breA.Ke.r- 
 
 FIG. I. 
 18 
 
them with an explosive, is too tough for a moil struck by a 
 double-hand hammer, when swung by a good man. The 
 use of an explosive introduces an element of danger from 
 "salting," as it is easy to charge the cartridges with 
 powdery gold, which the dynamite will distribute very 
 prettily amid the ore. Of course, one can avoid such 
 tricks by using one's own dynamite, but engineers, as a 
 rule, do not find it convenient to travel about with high- 
 grade explosives. Apart from this, there is a commoner 
 danger. Dynamite tends to break a conical cavity, with 
 the drill-hole as the axis of a cone which tapers inward. 
 The product of the drill-hole would not be a fair sample 
 even if it could all be secured without loss or interference. 
 Usually the explosion of the hole breaks a mass of rock, 
 the cross-section of which tapers from the width of several 
 feet to almost a point, so that as a sample the material 
 obtained is misleading. To pick a sample out of a mass 
 of ore thus broken, or to take it all, is a procedure likely 
 to lead to serious errors. 
 
 An accurate sample represents a true cross-section of 
 the ore ; it depends, therefore, upon the uniformity of size 
 of the groove or furrow ; that is to say, an equal amount of 
 ore must be broken across every part of the entire width 
 of the lode. That is what makes sampling difficult, espe- 
 cially in gold-veins, the predominant matrix of which is 
 quartz, in some form, varied by softer, more friable min- 
 erals, which cause marked contrasts in the ease of frac- 
 ture. In one case, which came under rny notice, it took six 
 men (three of whom moiled while the other three held the 
 boxes to receive the samples) the whole of one shift to 
 take three samples across a vein 12 ft. in cross-section, 
 and in accomplishing this they dulled 35 moils. That was 
 good, honest sampling. 
 
 THE SIZE OF THE SAMPLE. 
 
 This question is an important one. It is a matter to 
 be decided by convenience, scientific principle and experi- 
 ence. We will consider the least important first. Large 
 samples are more difficult to handle than small ones and 
 
require more assistance. In mountainous regions or in 
 desert places, where facilities for crushing the ore are 
 lacking, it will be found inconvenient to break samples so 
 big that their reduction by hand consumes much time. 
 Occasionally greater inconvenience than this will arise 
 through the want of facilities for removing the ore from 
 the mine without entrusting it to unsafe hands. The 
 factor of time has been mentioned ; that of cost must not be 
 forgotten, for time and money are valuable alike to the 
 engineer and- to his client, so that the former will find it 
 advisable "to cut the coat according to the cloth." Every 
 engineer runs up against obstacles such as have been re- 
 ferred to, and these vary so much with each individual 
 case that it is needless to attempt to specify them in greater 
 detail. 
 
 The size of the sample will also depend upon the facility 
 with which the ore can be broken, because the scientific 
 principle underlying the act of sampling is the obtaining 
 of a true cross-section of the lode. In the case of an ore 
 having the consistency of cheese, which is by no means an 
 impossible occurrence and is approached by certain lodes 
 which are built up of crushed material, a perfect sample 
 can be obtained by running a "scraper" over it so as to 
 make a narrow furrow across the full width of it. This 
 will result in a sample of minimum size. On the other 
 hand, in order to obtain a true sample of a large lode made 
 up of streaks of varying hardness and uneven fracture it 
 will be found necessary to break a hundred pounds at the 
 very least. In such a case it is impracticable to secure a 
 sample of the hardest portions except in large irregular 
 pieces, and this necessitates the breaking of a propor- 
 tionate amount of material from those places where the ore 
 is much softer or of easier fracture. In hard quartz-veins 
 it will be found that a channeling from 4 to 6 ins. in width 
 and from J^ to I in. deep will be adapted to the securing 
 of a true sample ; in those instances where the ore has a 
 fairly even grain, as with replacement deposits in igneous 
 rocks of granular texture, it will be found that a groove 3 
 ins. wide and from % to $4 m - deep will give a true sam- 
 
pie. The minimum size of groove which will yield a cor- 
 rect result should be chosen because any unnecessarily 
 large groove simply increases all the work of subsequent 
 reduction and handling of the samples without a commen- 
 surate increase of accuracy in the final results. Further- 
 more, one has always to remember that two samples of 
 50 Ibs. each at 5 ft. apart are better than one sample of 
 loo Ibs. at an interval of 10 ft. The whole idea under- 
 lying the operation is that of securing an average, and it is 
 obvious that the larger the number of data the more likely 
 one is to approximate the truth. 
 
 The next factor is more important than the two already 
 considered. I refer to that invaluable guide, Experience, 
 without whom all work of this kind is as dangerous as is 
 mountaineering in the Alps to a thoughtless tenderfoot. 
 To one who has done his own sampling and assaying there 
 has often arisen the inevitable contrast between the di- 
 mensions of the sample and those of the gold button which 
 represents its contents. Whatever the size of the original 
 sample, the outcome is merely one button of minute size. 
 Gold, as at present known to exist in workable lodes, 
 occurs in a metallic form and is usually disseminated 
 through the ore in an extremely irregular and sporadic 
 manner. As a consequence, the final pulp taken for assay, 
 and weighing, as a rule, about an ounce, if not less, is apt 
 to contain a coarse speck of gold, the accidental presence 
 of which vitiates the result. Whatever the weight of the 
 original sample, whether 5 Ibs. or 500 Ibs., the particular 
 particle of gold included within the final pulp will have 
 the same effect of exaggeration, save in one respect, viz., 
 that, given the fact of its occurrence in the original sam- 
 ple, it is more likely to find its way into the assay pulp of 
 a small sample, the latter being to the former in the pro- 
 portion of I oz. to 5 Ibs., or, say, I to 80, than in a large 
 sample the final pulp of which represents, say, one part in 
 8,000 parts of the original. When, however, the gold is 
 not present in the usual condition, but occurs in that pul- 
 verulent state known as "mustard gold," characteristic 
 of the metal when it is the product of decomposed tellu- 
 
rides, then the more even dissemination of the gold causes 
 it to be spread throughout the sample so as to make the 
 size of the latter a factor of safety. Of course, usually, the 
 particles of gold become flattened out during the process 
 of crushing (on the buck-board) previous to the assay, so 
 as to appear on the screen in the form of scales, termed 
 "metallics," and the practice is to pick them up, weigh 
 them, cupel them, and then determine their weight in re- 
 lation to the weight of the sample ; but this does not over- 
 come the interference with accuracy because, although 
 this determines the proportions in which such particles oc- 
 curred in the particular sample, it does not give any clue 
 as to the relative importance of such particles in the 
 enrichment of the entire lode. Naturally, in small sam- 
 ples the interference is relatively greater and therefore 
 more clearly recognizable. On the whole, therefore, one 
 comes back to the conclusion that the best rule to follow 
 is the taking of the smallest sample consistent with se- 
 curing a true average of the lode at each cross-section. 
 The larger the sample, the more difficulty in handling it, 
 the more persons required to help and the greater the 
 chances of poor work. Let me mention an exam- 
 ple. Two engineers examine a mine, and, in carry- 
 ing out their investigations, one gets large samples, re- 
 sulting from a wide groove, while the other takes small 
 samples, the product of a smaller groove. Although both 
 samples are equally good, in so far as they represent an 
 approach to the true cross-section of the lode at each place 
 sampled, nevertheless the former, on account of the 
 greater size of the samples, is, theoretically, the better of 
 the two. However, the second engineer employed fewer 
 assistants, and all those whom he employed in this capac- 
 ity were men whose antecedents he knew and whose re- 
 liability he had previously tested, while the first engineer 
 engaged his gang of samplers at the mine, most of them 
 being vouched for by the management or by a fellow- 
 engineer; yet the chances of error were increased by the 
 number of men employed, the real ability of each to take 
 true samples being merely assumed on the statement of 
 some one else. 
 
THE REDUCTION OF THE SAMPLES. 
 
 When the samples are broken they are put into sacks 
 which are not marked upon the outside, but are, prefer- 
 ably, labeled by inserting a tag with the number upon it. 
 This tag is often merely a piece of paper, detached from a 
 notebook, but in this form it is apt to get torn or the 
 number upon it obscured, especially when the ore is moist, 
 therefore it is best to use a metal or wooden tag especially 
 prepared for this purpose. The latter will be found con- 
 venient. Get a lot of small pieces of soft wood (*/s in. 
 thick, i in. wide and 1^2 ins. long), and mark the num- 
 bers of the samples upon them by the use of a hard pencil ; 
 this will remain as a visible indentation even after the 
 pencil trace has been rubbed off. 
 
 The samples are then removed to a safe place, either 
 temporarily in the mine itself or to a building where they 
 can be locked up. Then conies the work of reducing 
 them in bulk by crushing and subdivision. If an assay 
 office is conveniently at the engineer's disposal, he will 
 probably find a rock-breaker which he can use, otherwise 
 a portable rock-breaker, worked by hand, will be found a 
 useful machine to take with him when a large sampling 
 job is to be done. In the absence of these conveniences the 
 ore is broken by hand with a cobbing hammer, to the size 
 of walnuts, and then subdivided. This is followed by fur- 
 ther reduction in size and subsequent subdivision by 
 quartering. 
 
 It is usual to place the crushed ore upon a square sheet 
 of canvas, which is rolled backward and forward in op- 
 posite directions in such a manner as to mix the ore lying 
 upon it, until finally a conical pile is left standing in the 
 center. This is flattened to a frustum previous to quarter- 
 ing, the two opposite quarters being taken and again 
 mixed previous to a further mixing and quartering, until 
 the bulk of the sample has been reduced to the size con- 
 sidered suitable for shipment to the assay office. 
 
 The foregoing method is open to criticism. In the first 
 place, the rolling canvas is not nearly so good a way of 
 
mixing as it looks, the fines are apt to slide over the sur- 
 face of the canvas instead of becoming thoroughly min- 
 gled with the coarser particles ; moreover, the cone which 
 is finally formed is deceptive in that the fines are likely to 
 be collected not at the center of the base of the cone, as 
 is supposed, but to one side, so that, in quartering, any 
 particular division may include an undue proportion of the 
 fines, which usually form the richest part of the sample. 
 Further, in flattening the cone into a frustum, for con- 
 venience in quartering, it is difficult to distribute the ore 
 evenly, and though great care be taken to draw the ore in 
 a straight line outward, toward the circumference, the 
 distribution is liable to be faulty, and this part of the 
 work may be so imperfectly done as to become a squrce of 
 error. 
 
 An alternative, and better, method can be suggested. 
 Get a few short boards, or cause some to be sawed to the 
 required length, of about 6 ft., and put them together so 
 that they will make a platform which can be kept firmly in 
 place by being spread upon a couple of sills and wedged in 
 with stones. Then, if the joints are not tight, put your 
 sheet of canvas upon it, not to roll the samples within it, 
 but merely to prevent any leakage of fines through the 
 cracks between the boards. When the sample is crushed, 
 gatfiei it up with a scoop or other handy implement to the 
 center, lifting the broken ore, shovelful by shovelful, and 
 pouring it as nearly as possible at the same central point 
 so as to aid the mixing of it. In doing this it will be found 
 convenient to use the "cone," in vogue at many smelters, 
 which consists of a sharp central cone, made of iron, 
 with four thin radiating partitions which cause the ore, as 
 it falls upon the center, to become quartered. 
 
 In order to do accurate work at this stage, it is neces- 
 sary that the particles of ore should not vary too much in 
 size. The fines are apt to obscure the fact that there are a 
 good many large lumps, and the unaided eye is likely to 
 mislead in this respect. For this reason it is well, if con- 
 venient, to use a wire screen, say, >2 or 24-inch mesh, or 
 perhaps two, one of 4 an d the other of %-inch mesh, 
 
to be employed at successive stages of the operation, so 
 that the maximum size of the particles can be kept within 
 defined limits. It is an easy matter to take a piece of wire 
 cloth, say I foot square, and have a frame put around it 
 when you reach the mine. 
 
 If it is necessary to send the samples to a distant assay 
 office or to take them with you on your departure from the 
 mine, then it becomes convenient to reduce them until they 
 weigh only three or four ounces each. In doing this the 
 engineer will anticipate the work of further reduction, 
 which is usually carried out by the assayer. The samples 
 will be crushed smaller and passed through, say, a lo-mesh 
 screen, and, instead of quartering, it will be well at this 
 stage to use a gridiron sampling device, which consists of 
 a series of metallic scoops separated by vacant spaces of 
 equal width, so that one-half of the ore falls through while 
 the remainder is arrested. When this method has reduced 
 the bulk of the samples to the desired dimensions, they are 
 put into small paper or canvas sacks, the latter preferably, 
 especially if it is intended to ship them a long distance. 
 
 If genius be, as has been authoritatively stated, "an 
 infinite capacity for taking pains," then it is safe to say 
 that genius is exactly the mental quality needed for the 
 humdrum work of sampling, for to do it conscientiously 
 and well requires patience, strength and an amount of un- 
 wearied watchfulness sufficient to elevate this common 
 task to the level of a fine achievement. It requires an 
 obstinate persistence to get a true average across a hard 
 and tough quartz- vein; any relaxation of care or muscle 
 will at once result in the spoiling of the sample and the 
 consequent introduction of an error into the calculations of 
 the engineer. It needs judgment to know how to treat a 
 cavity (or vug) or an unusual inclusion of waste rock; 
 it needs a nice sense of proportion to avoid cross-sections 
 which are exceptional, to break an equal weight of ore 
 along a line 10 or 12 feet in length, and to get the true 
 width of an irregular cutting. For these reasons it is best, 
 when carrying out an arduous scheme of sampling, to 
 
 25 
 
divide the muscular from the mental work, allowing a 
 miner to do the actual breaking under the direction of an 
 intelligent trained assistant, who holds the receptacle for 
 the ore as it falls, and at the same time watches the move- 
 ments of the miner. Further, it is well to make the hours 
 of labor short, so as to avoid an excessive strain on the 
 faculties, such as will cause relaxation of the intent watch- 
 fulness and care necessary to good sampling. In order to 
 escape the risk of inferior work, it is good practice to vary 
 it, as, for instance, by putting the assistants to surveying 
 or mapping for a day or so, at intervals. Otherwise your 
 men are apt to get "stale" through weariness. How tire- 
 some such work is those can testify who have done much 
 of it ; the dirt, the wet, the strained positions, the splinters 
 that hit the face and hands, the obstinacy of rock and cir- 
 cumstance, the weary iteration of it these require some- 
 thing better than mere mule-like persistence to overcome 
 them, and the man who can do a difficult piece of sampling 
 honestly and well can be entrusted to do work for which 
 much greater credit is usually given by those in authority. 
 
 PRECAUTIONS IN SAMPLING. 
 
 Although the greater thoroughness with which mines 
 are investigated nowadays has made trickery scarce, in- 
 stances of the latter do occur occasionally. They are 
 rarely exposed because of the lack of evidence, and there- 
 fore the occurrence of them is obscured amid those fail- 
 ures and disappointments in mining which arise from 
 other causes. The tampering with samples, called 'salt- 
 ing/ and the blocking up of workings which might give 
 unfavorable testimony regarding the condition of a mine 
 are two possibilities against which one must be continually 
 on guard. To prevent 'salting' it is imperative that the 
 work be done by trustworthy assistants ; and in the case of 
 a large mine, where it becomes necessary to employ work- 
 men whose antecedents are unknown, it is well to arrange 
 that the work be done in pairs, the miner breaking the 
 samples under the direction of an assistant, who holds the 
 
 26 
 
box to catch the sample as it is broken. When the 
 sampling is done it is well for the chief himself to take a 
 certain number of samples, aided by his first assistant, 
 these samples being taken, not at haphazard, but in such 
 a way as to check the previous work. One of the best 
 guards against any successful tampering with one's 
 samples is to take an occasional sample of waste. If the 
 samples are all salted, the assay of the waste will disclose 
 the fact. Occasionally it may be well to fill one or two 
 sacks with material the exact assay contents of which 
 have been previously determined. In any event, it is bet- 
 ter not to use- sacks which are numbered or otherwise 
 marked on the outside, because, should trickery be pur- 
 posed, such marks make it easy to note from what parts 
 of the mine the various samples come and to 'salt' them 
 accordingly. It is well to assay the samples on the spot, 
 if a suitable assay office is available, particularly when the 
 engineer, or one of his assistants, is a good assayer, as is 
 frequently the case. Of course, in using a strange assay 
 plant it is necessary to guard against fraud, and to this 
 end it is well to test the fluxes used by assaying a charge 
 without ore every time a batch of samples is put through 
 the furnace. 
 
 During the interval which elapses between the time 
 when the sample is first broken in the mine and its final 
 assay, it is necessary that the sack containing it should be 
 sealed. It is a good thing to use uncommon wax and an 
 uncommon seal, so as to render trickery more difficult. 
 It is well even to use a peculiar kind of string for tying up 
 the sacks. "He is most free from danger who, even when 
 safe, is on his guard." Any extra precaution should never 
 be considered a nuisance; on the contrary, it ought to 
 become a habit. Cases of 'salting' have been known where 
 the ore has been artificially enriched without breaking the 
 seal and without puncturing the sack, and I know of an 
 instance in which samples of copper ore, put into a carpet 
 bag, were withdrawn and substituted with others by re- 
 moving the bottom of the bag and sewing it up again while 
 
 27 
 
the engineer was asleep. "Dead things will crawl." 
 "Eternal vigilance is the price of safety." 
 
 Unfortunate consequences have sometimes ensued from 
 the failure of an engineer to see all the workings of a 
 mine. This may be due either to carelessness or over- 
 sight, but it may also be due to the rascality of the mine 
 owner. Cross-cuts are sometimes blocked up with old 
 timbers, drifts may be allowed to cave, shafts may be 
 under water; in each of these cases the engineer must 
 realize that he is under a responsibility if he passes judg- 
 ment on the mine without seeing for himself what these 
 inaccessible workings have to tell. Their testimony may 
 be unfavorable; it usually is in such cases; but, on the 
 other hand, there may be circumstances which influence 
 the owners in desiring to temporarily depreciate their 
 property. 
 
 An opportunity for splendid business was lost in the 
 case of the great Broken Hill mine through an error of 
 this kind. An engineer, and a good one, too, was engaged 
 by a Melbourne financier to make an examination of the 
 new discovery at Broken Hill, with a view to the purchase 
 of an interest. He duly reached the mine, and found a 
 gang of miners engaged in sinking a prospect shaft, which 
 at that time, in 1885, was about 70 feet deep. Much to 
 his annoyance, he was refused permission to go under- 
 ground, except by written order from the manager, who 
 had left the day previous for Adelaide. Disappointed, but 
 not without hope of getting information, he chatted with 
 the men, more especially the foreman, and endeavored to 
 pump the real facts out of them. Their talk indicated that 
 no rich ore had been found, and that the prospects were 
 poor. He examined the dump, took samples of it, and 
 finally returned to Melbourne via Adelaide. The samples 
 from the dump gave 16 ounces of silver at the best. He 
 advised his client to keep out. A few days afterwards it 
 became known that a rich mine had been found at Broken 
 Hill. He had been fooled, the discovery having been 
 made just previous to his visit and covered up for a 
 
 28 
 
particular purpose. That mine has since produced over 
 100,000,000 ounces of silver. 
 
 This is one side of the question. It is rarely that a 
 bonanza is kept out of sight. As a rule, the exclusion of 
 an engineer from certain parts of a mine is intended to 
 cover unfavorable testimony. It is therefore of the great- 
 est importance, more especially in a small mine, the char- 
 acter of which has not been truly established, that an 
 effort be made to personally investigate all the workings. 
 Intentional deception is, I am glad to believe, rare ; never- 
 theless, in passing upon the purchase of property, the 
 engineer should write across his notebook, "Caveat emp- 
 tor." One instance will suffice. Let the accompanying 
 section, Fig. 2, represent the workings of a small mine, 
 where the level A D is 200 ft. from surface and F M is 
 100 ft. deeper. Above A D there has been a line of stopes 
 from B to C, a distance of 200 ft., all the ground being 
 worked out, with results testified to by certified returns 
 from mine and smelter. When the mine is sampled, it is 
 found that there is good ore in the floor of level A D, and 
 along the back of the lower one F M, as indicated in the 
 section. Moreover, the raise at H is going up in good ore, 
 and the drift (at M) is proceeding in ore of an average 
 tenor; in short, the evidence proves that the ore-body is 
 persisting downward with a pitch to the east, similar to 
 its behavior in the upper workings. No winze has been 
 sunk below AD. At E there is a hole about 5 ft. deep, 
 which, according to the statement of the superintendent, 
 is being used as a sump to catch the drippings from the 
 stopes and thus prevent the water running down the shaft. 
 A small pump at A sends this water to surface. 
 
 All looks serene and straightforward, but the facts are 
 as shown in Fig. 3. At E there is a vertical winze which 
 is deeper than 5 ft., and has been carefully filled up. From 
 the bottom of this (at P) an incline has been run down to 
 N; at N there is a drive R O, and all the ground above 
 has been stoped out bodily, leaving a mere shell under 
 the level between B and C. The raise H is situated so as 
 
 29 
 

 \ Ore l ' Ore Ore Ore Ore \ 
 
 \ V- 
 
 i 
 
 \ \ 
 
 d 
 
 Yfe \ 
 
 g 
 
 % ; 
 
 L^X 
 
 
 2 
 
 
 
 
 
 \ Ore 
 
 0) 
 
 CO 
 
 Ore 
 
 
 \ 
 
 ptf 
 
 
 
 \ Ore Ore Ore 
 
 77 
 
 Ore 
 
 \ 
 FIG. 2 
 
 Sloped 
 
 Hidden Slopes 
 
 30 
 
to miss these secret workings. The heart of the ore-body 
 has been taken out, and a clever piece of trickery has been 
 attempted. 
 
 As a possible check against the perpetration of such 
 practical jokes, it is not out of place to ask the manager 
 in charge of the mine to sign a statement which sets forth 
 that he has informed the engineer of all the existing work- 
 ings, and to this can be attached a map or a brief descrip- 
 tion of such workings as are inaccessible through caving 
 or other causes. Such a paper will serve as a record to 
 make clear the position of the engineer and fix the respon- 
 sibility on the management of the mine should false state- 
 ments have been made with the intent to deceive. 
 
 WRONG METHODS OF SAMPLING. 
 
 In the early days of Western Australia, and, indeed, one 
 may say in the early days of most gold-fields almost any- 
 where, it was a common practice for the gentlemen, 
 vaguely known to the press as "experts," to sample an 
 incline shaft, on a vein, by having a few shots put into the 
 ore, and then collecting the material thus thrown down 
 to the bottom of the shaft and having it hoisted to sur- 
 face, where it formed one of those "large" samples, the 
 tonnage of which was referred to with pride in the re- 
 ports as evincing an accurate testing of the value of the 
 ore in the mine. Such work is the travesty of sampling. 
 A bunch of specimen ore, a few inches in extent, was 
 enough to vitiate the whole result. Such spots of free 
 gold were commonly characteristic of the Westralian reefs 
 near the surface, and, if this unintentional "salting" was 
 not enough, the subsequent performance at surface and 
 the handling of the ore by a large number of men of un- 
 known character gave sufficient opportunity for further 
 tampering with this suppositious sample. There is a lot 
 of this sort of thing perpetrated during the windy days of 
 mining booms, not in Western Australia alone. 
 
 In the case of wide lodes that is, such as exceed the 
 average stoping width it is advisable to take sectional 
 
samples, dividing the lode into successive divisions, each of 
 which is, say, 4 ft. across. The results thus obtained will 
 be useful in indicating the distribution of values. Occa- 
 sionally it will be discovered that a vein is being worked 
 for a bigger width than circumstances justify, while, quite 
 as commonly, it may be found advisable to change the 
 practice radically, and in the opposite way ; that is, it may 
 be proved by sectional sampling that, while a mine cannot 
 be profitably operated if only a narrow width of rich ore 
 is mined, it will become remunerative if it is worked on a 
 larger scale by adopting a bigger stoping width, so as to 
 include parallel streaks, feeders and branch veins, which 
 will yield a much bigger tonnage of low-grade ore, unsuit- 
 
 Level 
 
 Level 
 
 Stoped 
 
 FIG. 4 
 
 able, it may be, for shipment, but profitable in a mill, to be 
 erected at the mine or near it. 
 
 In the sectional sampling of wide lodes particular care 
 must be taken to get the true width. Measurements must 
 be taken at right angles to the walls of the vein. In 
 sampling, however, a horizontal line may be followed, if it 
 ,is convenient; it will give a larger quantity of ore than a 
 right-angle section, but if each sample is taken along a 
 parallel line, the proportion will be maintained and a true 
 sample will be secured. 
 
The importance of an accurate recognition of the slope 
 of a vein and the pitch of an ore-shoot, when making esti- 
 mates, cannot be emphasized too much. An example 
 will be of service. Thus, in Fig. 4, A B and D F repre- 
 sent an ore-shoot traversed by the two levels, which are 
 100 ft. apart. The ore has been stoped out above the 
 upper level, and a portion had been removed between 
 the levels. The stopes inaccessible above B C and 
 the stoping begun at the bottom of the left-hand raise 
 are calculated to obscure the real condition of affairs. 
 The engineer samples the raise E B and the back of the 
 level between E and F, with results which cause him 
 to assume a block of ore A E F C. He has failed to 
 recognize the pitch of the ore-shoot because the stoping 
 above B C has obscured it. It will be said that if he 
 had sampled the bottom of the level this mistake might 
 not have occurred, but the sampling of bottoms is not 
 always practicable, and is usually very unsatisfactory 
 on account of water and other factors. It is not realized 
 often enough that ground which has been stoped was not 
 necessarily profitable. Stopes are frequently started with 
 the hope of an improvement or with the purpose of test- 
 ing a run of ground. For this reason the workings of a 
 mine, both underground and on the map, are apt to sug- 
 gest unwarranted deductions as to the distribution of ore, 
 and many misleading inferences have been caused thereby. 
 Thorough sampling will usually make the truth clear to an 
 experienced man. 
 
 Among the things to be avoided one must mention the 
 so-called "grab" sample. This is the last resort of inca- 
 pacity. A grab or haphazard handful of ore is taken in- 
 discriminately from all over a pile of ore at the face of a 
 level or in the stopes, and this is put into a small sack for 
 subsequent assay. The idea of the grab sample is to shut 
 your eyes and be "absolutely impartial," but the brutal 
 fact is that one usually gets a deceptive proportion of the 
 fines and quite disregards the large pieces of waste or poor 
 rock scattered through the heap. It is still the practice in 
 
 33 
 
many mines for the foreman to take samples in this man- 
 ner while making his daily round of the workings. As a 
 consequence, the record of the assay office is often an 
 iridescent dream, which may mislead the management 
 and become the cause of a serious error in the estimates 
 of ore. It takes more time to use a moil and a hammer, 
 thereby obtaining a true average sample, than it does to 
 pick up a "grab" and stick it into one's pocket or into a 
 sack; for this reason the former procedure is objected to 
 by many foremen. The fact is, the daily sampling of the 
 faces of ore should be a task allotted to men who have the 
 time and the training for such work ; it should be no part 
 of the duty of a foreman or a shift-boss, both of whom 
 are usually men of a type which confounds system with 
 "red tape," but it should be placed in the surveyor's de- 
 partment, so that the record of results can be incorporated 
 with the maps of the mine. "Chacun a son metier et les 
 vaches seront bien gardees" It is a good saying. Let the 
 important work of sampling be put into proper hands, 
 separate from the particular supervision of the operations 
 of the mine, the control of the men and other departments 
 with which it has no kind of connection. The ordinary 
 multifarious official has no time for a job which essentially 
 requires time to do it properly. And before everything 
 else, begin by prohibiting "grab samples" in any form ! 
 
 CALCULATIONS AFTER SAMPLING. 
 
 The calculations consequent upon sampling are based 
 on the theory of averages. An arithmetical mean is the 
 sum of all the numbers forming the series of figures under 
 consideration divided by their number without reference 
 to their weight or relative importance among themselves* 
 This method has been applied to the results of sampling, 
 with most unhappy consequences. Thus, let the following 
 series of figures represent the data obtained from sampling 
 a length of 100 ft. of gold-bearing ore at intervals of 
 10 ft. : 
 
Width. 
 4.4 feet 
 6.2 " 
 7.6 ' 
 4.0 
 2-5 
 3-6 
 2.5 
 
 .8 
 
 1.2 
 2.2 
 
 Assay. 
 
 2.35 oz. per ton 
 .45 oz. 
 .62 oz. 
 .85 oz. 
 
 1.02 OZ. 
 
 2.40 oz. 
 4-25 oz. 
 
 5.20 oz. 
 4.65 oz. 
 
 3.21 oz. 
 
 35.0 25.00 
 
 The arithmetic mean yields 3^ ft. of ore averaging 2,^/2. 
 Oz. of gold per ton. This is woefully wrong. It disre- 
 gards the fact, for instance, that the third sample yielded 
 7^ ft. of ore containing only 0.6 oz. of gold, while the 
 richest ore, at the eighth sample, was less than I ft. wide. 
 
 The geometrical mean is the sum of such figures di- 
 vided by their number, with due allowance made for their 
 weight. This is done in practice by what many call the 
 "foot-ounce" method, which, applied to the foregoing 
 example, works out thus : 
 
 Width. 
 
 4.4 feet 
 6.2 " 
 7-6 
 4-0 " 
 
 2.5 " 
 
 3.6 " 
 
 2. 
 
 2.2 
 
 35-0 
 
 Assay. 
 
 2.35 oz. per ton 
 
 45 oz. " 
 
 .62 oz. " " 
 
 .85 oz. " " 
 
 I. O2 OZ. ' 
 
 2.40 oz. " " 
 
 4-25 oz. " 
 
 5.20 oz. " " 
 
 4.6502. " " 
 
 3.21 oz. " " 
 
 25.00 
 
 Foot-ounces. 
 
 10.34 
 2.79 
 
 47i 
 3-40 
 
 8. 
 
 10.62 
 4.l6 
 5-58 
 7.06 
 
 59.85 
 
 The assay per foot of width is 1.71 oz. per ton, instead 
 of 2*/2 oz. In matters of this kind mathematical reasoning 
 confirms the conclusions of rough common sense. The 
 method just described is based upon the higher mathe- 
 matics, as the following integrations, kindly suggested by 
 Mr. Ross Hoffman, will demonstrate : 
 
 Problem i. To determine the average value of the sec- 
 tion of vein A between the samples whose widths are w x 
 and w 2 , and values v, and v 2 , respectively, under the as- 
 sumption that the values vary gradually over the area 
 
 35 
 
from YJ to v 2 in the direction d, then at any distance x from 
 Wj the value 
 
 W 1 
 
 w * 
 
 also 
 
 d x 
 
 y-w 2 
 
 v=- (v 2 Vl 
 d 
 
 x(w 2 wj 
 
 d 
 
 = (w l + w 2 ) d 
 
 (1) 
 (2) 
 
 (3) 
 
 x = o 
 
 f v y dx -j- A = average value for the section A. 
 
 From 1 and 2 v y = (w l v l + w 2 v 2 ) 
 d 2 
 
 x x z 
 
 d d 2 
 
 2 
 
 /' 
 
 i 
 
 T ) Wi Vj 
 
 Q ' 
 
 Wi V x -}- W 2 V 2 
 
 W 2 V 2 ^ (wj W 2 ) (v 2 YJ- 
 
 The last term = O when Wj = w 2 or v l = v 2 
 
 Under normal conditions, where ordinary sampling" 
 can be depended on to give fairly approximate averages, 
 this last term will be small enough to neglect. (See by 
 substitutions.) Hence 
 
 W r Vj + W a V 2 
 
 - j can be taken as the average value 
 
 for section A. 
 
Problem 2. To find the average value from a number 
 of samples taken as above, where w equals width of 
 
 sample, v equals value, d equals distance between samples 
 and A the area of various sections of vein between 
 samples : 
 
 A Wn V Q + Wj V r 
 
 )0 
 - average value for A = 
 
 A = ( w -f- w I " " " A 
 
 A 2 = (w 2 + w 3 ") " " " A 2 
 
 3 = (w 
 
 A 3 
 
 WjVj + W 2 V 2 
 
 w 2 v 2 + w 3 v 3 
 
 W 2 + W 3 
 
 (See Prob. i.) 
 
 S (AX average value for A) = ayerage yalue oyer ^ 
 
 whole area sampled = 
 
 (d ) 
 
 x v x -f- w 2 v a ) -- + (w 2 v 2 + w 3 v 3 ) -j- + (w 3 v 3 + w 4 v 4 ) ~ 
 
 W 21 2 w 3 
 
 
 w 4 (d,) 
 
 Cw (d )^ (w^do + d, 
 
 -- J+v, - 
 
 ( 2 ) _ ( 2 
 
 (w c (d )) ( Wi_(dojfdJ ) | w 2 (d, + d a ) } 
 
 I 2 ) I 2 ) ( 2 f 
 
 j 
 4 1 
 
 ( 
 
 w 4 (d 3 ) 
 
 } 
 
 
 37 
 
The bracketed terms represent areas and may be con- 
 sidered the importance or weight factors with which the 
 various sample values taken separately enter into the gen- 
 eral average value for the whole area. It is equivalent to 
 giving each sample value an importance (or weight) pro- 
 portional to its sample width multiplied by half the sum 
 of the distances to the two adjacent samples. 
 
 Averaging in this manner assumes, as in problem I, 
 that the values between various adjacent samples change 
 gradually. 
 
 If the samples are taken equidistantly, the above aver- 
 age becomes 
 
 V W + V W 
 
 W W 4 
 
 + Wi + w 2 + w 3 - 
 
 which, with the exception of the two end samples, is 
 simply giving each value an importance in the general 
 average proportional to the width of its sample. The two 
 end-sample values are shown to have half this importance, 
 though in practice, with many samples under considera- 
 tion, it is customary to give the two end samples the full 
 importance proportional to their respective widths. 
 
 In the calculations for tonnage the cubic feet of ore 
 are converted into tons on the basis of a certain specific 
 gravity; thus, quartz is usually taken at 15 cub. ft. per 
 ton, while ores containing sulphides are rated at 8 to 12 
 cub. ft. It is not unusual to guess at this proportion, be- 
 cause experience does enable an engineer to approximate 
 the correct figure fairly well. But it is a dangerous prac- 
 tice. Approximat.ons should never suffice where greater 
 accuracy is possible. It is well to weigh a series of meas- 
 ured pieces of ore or to determine actually the specific 
 gravity of a few pieces of average vein-stuff. Surface 
 quartz, on account of its cellular structure, may require 
 20 cub. ft. to weigh a ton. Pyritic ores will vary to an 
 extent hardly appreciable even to the experienced eye. 
 Grievous errors in tonnage estimates have been caused 
 by the assumption of an incorrect basis of calculation. 
 
 38 
 
A minor source of error is sometimes created by the 
 occurrence in the vein of numerous cavities, or Vugs,' 
 as the miners call them. In some cases they form a very 
 appreciable proportion of the space occupied by the lode, 
 so that they are apt to lessen the tonnage obtainable from 
 a block of stoping ground. 
 
 THE QUESTION OF "HIGH ASSAYS." 
 
 In these calculations, whether they be mathematical or 
 rough-and-ready, it is assumed that where two adjoining 
 samples vary there is a gradation from one to the other. 
 Generally the assumption is warrantable, but occasionally 
 the difference between any two such adjoining samples is 
 so marked as to require further consideration. In the 
 sampling of gold mines, especially where the metal occurs 
 in a native condition and visible to the eye, there will be a 
 few very high results which affect the average of a run of 
 samples to an extent quite out of proportion to the im- 
 portance of a single sample. 
 
 This question of "high assays" demands careful dis- 
 cussion. It can be viewed from two standpoints : the seller 
 of a mine is apt to argue that if you are going to base an 
 estimate of the ore-reserves upon the results of sampling 
 and assay you ought to take all the data without favor, just 
 as they come, and that to eliminate high assays is no more 
 fair than it would be to omit poor ones ; to this the engi- 
 neer, representing the interests of a possible purchaser, 
 will reply that the occasional very high assays are largely 
 accidental, that they affect the estimates to a degree out of 
 proportion to their weight, and to an extent by no means 
 comparable to the omission of an equal number of poor 
 results; finally, he will murmur under his breath some- 
 thing about a factor of safety being necessary. 
 
 In the first place, it is incumbent upon the engineer to 
 find out whether these occasional high results do, or do 
 not, represent the average of the ore, not at the particular 
 place sampled only, but over the whole space or interval 
 which that sample is supposed to represent. Each sample 
 
 39 
 
in the final calculation speaks not for a spot, but for a 
 section of the vein, the length of which is the interval be- 
 tween samples and the height is the distance separating it 
 from the next working overhead or underfoot ; thus, when 
 the distance between samples is 10 ft. and the next series 
 of samples is on a level 100 ft. distant, above or below, 
 then the section represented by a single sample contains 
 10 by loo ft., or 1,000 sq ft., which, if the vein be, for 
 example, 3 ft. wide, may contain over 200 tons of ore. 
 In practice the responsibility of one series of such samples 
 is shared by that of a corresponding series taken on the 
 level above or below; nevertheless, it is obvious that a 
 single sample represents something very different to the 
 mere spot or place in a particular working. In order to 
 answer the question whether an individual high assay 
 is accidental or representative, the only thing to do is to re- 
 sample at the same place ; if the result is confirmatory, then 
 evidently that spot is as rich as the first sampling indicated. 
 But this does not determine whether the high values gra- 
 date on either side toward the adjoining samples. Thus, if 
 A, B and C in the diagram represent three points, 10 ft. 
 apart, which have been sampled with the results shown, 
 then, if B assayed 10.40 oz. and was re-sampled with 8.22 
 oz. as the assay return, the next question arising is 
 
 0.86 oz. 
 
 whether the ore midway between B and A, or B and C, is 
 correspondingly intermediate in value ; for this is what the 
 calculations assume. For this reason it is best to check 
 the high assays by taking further samples at these inter- 
 mediate places, thereby finally settling the query whether 
 the high results are trustworthy factors in estimating the 
 average value of the ore-bodies. 
 
 The treatment of "high assays" has caused much dis- 
 cussion among engineers, especially when they are en- 
 countered in the course of a sampling, the results of which 
 
 40 
 
are to decide the price of a mine. The seller, or his repre- 
 sentative, is apt to suggest that a re-sample of poor spots 
 is also in keeping with the theory of the whole business, 
 and to this I would say that where a barren or nearly 
 barren result is obtained amid a series of samples indi- 
 cating good ore it is correct to re-sample such a place or 
 places. The occasional barren and the occasional high 
 assay return, however, are not comparable in their effect 
 upon the estimates. In the first place, the "nil" or "trace" 
 indicates the entire absence of the metal and has not the 
 accidental feature arising from the presence of a stray 
 speck of gold, which may cause the abnormally high assay ; 
 further, one very high assay affects the calculations more 
 than a number of poor ones, supposing both to be devia- 
 tions from fact, as can be easily shown, thus : Take the 
 following series of samples and assay returns : 
 
 Width. Assay. Foot-ounces. 
 
 7 feet 1.22 oz. gold 8.54 
 4 .54 oz. 2.16 
 
 12 i. 20 oz. 14.40 
 
 8 2.20 OZ. 17.60 
 
 5.3 " 27.40 oz. 144.22 
 
 7 1.60 oz. 11.20 
 
 3-5 " -95 oz. " 3.32 
 
 6 " .39 oz. 2.34 
 
 6 " trace " 
 
 7.2 " trace " ... 
 
 66.0 35.50 203.78 
 
 The average of the ore, using these data, is slightly 
 over 3 oz. per ton. If, however, the fifth sample, which is 
 very high, is eliminated, the average drops to less than I 
 oz. per ton, while, on the other hand, if the high sample is 
 retained and the last two poor places are omitted, the re- 
 sult is affected to a much less degree, the average then 
 being about 3^4 o z - per ton. 
 
 In re-sampling these apparently very rich spots, it 
 will be found that three contingencies may occur; the 
 result may be corroborated or it may be proved to be 
 accidental, while, should every high assay be found in- 
 correct, then there is a third possibility to be considered, 
 namely, whether the samples have been tampered with, 
 
 41 
 
If out of a considerable number of high results not one is 
 confirmed, then it is time to look around. If some are 
 confirmed by re-sampling, while others are not, then, 
 obviously, the values in the ore are erratic, and a correc- 
 tion must be made for each case ; if most of the high re- 
 sults are approximately repeated by the second sam- 
 ple, then it is evident that the first sampling was correct, 
 2Oid that the ore is very rich in spots ; intermediate sam- 
 ples must be taken, and when this is done the data for 
 calculations will be complete. It is wise to take intermedi- 
 ate samples, both when the high assays are wholly, and 
 when they are only partially, confirmed. 
 
 It has been argued by certain engineers that the mill 
 or smelter always fails to confirm the very high assays 
 occasionally obtained in sampling and that, therefore, 
 they should be omitted as a factor of safety. This is not 
 a fact. Exceptions occur. In the case of the Argentine 
 lode of the Tomboy Mining Company, at Telluride, Colo., 
 a careful sampling of a block of ground, at intervals of 
 IO ft., yielded an average of $7 per ton, all rich spots 
 carrying visible gold being avoided. This work was 
 done by an inspecting engineer of recognized capacity; 
 nevertheless, the actual mill returns were $28 per ton. 
 Nor is this inexplicable when the nature of the ore is 
 considered. The writer saw a piece weighing 25 lb., 
 yellow with finely disseminated gold, so that it contained 
 $100 worth of the native metal, which came from the 
 treast of a level on a certain day and the very next 
 day the foreman's sample from the face of the same drift, 
 which had been advanced two or three feet during the in- 
 terval, yielded only two-hundredths of an ounce of gold 
 per ton. The Pandora vein, in the neighboring Smuggler- 
 Union mine, affords another exceptional case; the mill 
 results are usually higher than the assays, and this is 
 explained as being due partly to the greater hardness of 
 the rich ore, but chiefly because the gold occurs almost 
 entirely in coarse particles which, being readily visible, 
 are apt to be carefully shunned by the conscientious sam- 
 pler. These instances are corroborated by the thor- 
 
oughly experienced managers of the properties quoted. 
 It remains to add that while it is true of the veins specific- 
 ally mentioned, that the assays are usually lower than 
 the mill returns, such is not the case with the Tomboy 
 lode, which is near the Argentine, nor is it true of the 
 Smuggler lode, which is intersected by the Pandora in 
 the Smuggler-Union mine. The above are, however, 
 well-authenticated exceptions, which serve effectually to 
 undermine a generalization which is the last resort of a 
 timid engineer. Not that the factor of safety is to be 
 discarded, quite the contrary; in all engineering such a 
 precautionary measure is imperative, but do not intro- 
 duce it disguised ; face the facts, state them, and then in- 
 troduce your factor of safety without any circumlocu- 
 tion. 
 
 Why do sampling results differ from the mill returns? 
 In the unusual instances, just mentioned, the difference 
 was traceable 'to conditions which are relatively rare, but 
 are always within the range of possibility. There is no 
 doubt in my mind that the usual experience of finding 
 the mill-extraction below the estimates, based upon sam- 
 pling and assay, is due to the fact that rich ore is 
 ordinarily in the softer, more crumbly parts of a lode, 01- 
 it is associated with sulphides which are not only easier 
 to break than quartz, but they also make a shining mark 
 which invites the blow of the moil and hammer. This 
 aspect of the inquiry emphasizes the weak factor in sam- 
 pling, it is not absolutely mechanical, a man and not a 
 machine does the work, and the results partake of that 
 liability to error which is essentially human. 
 
 It may be asked, in conclusion, what course should 
 be adopted with high assays when it is not possible to re- 
 sample? Frequently, the samples are not assayed near 
 the mine, but are taken, or sent, by the engineer to a re- 
 liable assayer living in a distant locality. Time, an ele- 
 ment in all business matters, may prevent the engineer 
 from returning to the mine to take further samples. 
 This is a dilemma not infrequent in current practice. 
 Judgment and experience must decide. The relative 
 
 43 
 
frequency of high assays, the degree to which they affect 
 the final estimates, the character of the ore, the results 
 of sampling as compared to the actual recorded average 
 of the mine, the character of the work done by the engi- 
 neer and his assistants; these and similar factors will 
 determine the decision. One cannot lay down rules 
 to direct any man's judgment. 
 
 It may be permitted to say that if you are uncertain 
 of your results, don't use them. Do not let yourself be 
 hurried, either by your client or, as is more probable, by 
 the vendor, to committing yourself to a decision based 
 upon data the accuracy of which, in your own mind, is 
 in any doubt. It is better to be sure than sorry. 
 
 THE POSSIBLE DISCREPANCIES BETWEEN SAMPLING AND 
 MINING. 
 
 In sampling the workings it is necessary that the en- 
 gineer should have an eye to the manner in which the 
 mine is being worked. It is useless, for instance, to sam- 
 ple two feet of vein-matter without any regard to the 
 fact that in stoping it is the practice to remove a width of 
 four feet. Unless judgment is exercised, the samples 
 are apt to represent cleaner ore than the output of the 
 mine, so that the estimates based upon them will be mis- 
 leading. The material sent for treatment to mill or smel- 
 ter may differ from the ore composing the lode as seen 
 in the mine, in several respects. Thus ; 
 
 A. The lode may be smaller than the minimum width 
 removed in stoping, so as to necessitate the mining 
 of a certain portion of barren rock. 
 
 B. The lode may be as wide as th'e convenient size 
 for stoping, but it may have a casing of soft rock, 
 which breaks down with the ore and becomes min- 
 gled with it so as to increase the tonnage and di- 
 minish the average yield per ton. 
 
 C. The lode may be built of one or more streaks of 
 rich ore irregularly distributed through it, so 
 
 44 
 
that in stoping it is necessary to break down a large 
 
 and variable width. 
 
 In the preliminary trip through the mine the engineer 
 will be able to find out by observation, together with the 
 information obtainable from either the foreman or the 
 manager, how the ground is being worked, and how the 
 ore is being handled. If he does not secure these data at 
 the preliminary examination he will light upon them in 
 the course of his investigations into costs, for without 
 them the relative expenditures at mine and mill will be 
 contradictory, if not unintelligible. 
 
 Concerning the conditions first mentioned, under the 
 heading A, it is obvious that the width broken in stoping 
 has a minimum, which in ordinary practice varies accord- 
 ing to the method employed; that is, with hand labor a 
 width of two to three feet will ordinarily suffice; while 
 at least three to four feet is necessary when machine 
 drills are used. 1 In both cases this minimum width will 
 be exceeded if the rock is very hard or if it breaks along 
 easy lines of fracture, which cause more rock to be taken 
 down in blasting than is absolutely required for mere 
 convenience in working. If the streak of ore is less than 
 the width of the stope there will be, inevitably, an ad- 
 mixture of waste, except in the rare cases where it is 
 practicable to strip the pay-streaks, that is, stope the 
 country without removing the vein, which is subsequent- 
 ly taken down separately. This method, which is cov- 
 ered by the Cornish term "resue," is excellent when the 
 vein of ore is narrow, but it depends for success upon 
 the ore being closely attached or "frozen" to one of the 
 vein walls, so that it will not be shaken down when the ad- 
 joining waste is shot away. In many mines in Colorado, 
 Montana and Idaho, especially in the case of narrow 
 streaks of very rich silver ore, it is not unusual to spread 
 canvas or sacking along the floor of the stope and then 
 break down the ore upon it, which in this way is kept 
 free from admixture with waste, and can be sacked with- 
 
 *A small (2 Y\ -in. cylinder) drill usually requires a stope of 3^ to 4 ft 
 In width, the large air drills (with 3^-in. cylinder) take from 4% to 5 ft. 
 
 45 
 
out any sorting. The canvas is covered for protection 
 with 6 by 3 by 12-in. timbers. In such a mine as this the 
 sampling of the vein itself would give data which closely 
 approximate the actual returns from ore sent away to the 
 smelter. 
 
 When it is not possible to mine the ore separately from 
 the waste it is usual to pass it over the sorting tables, 
 where the waste is picked out by hand. In the deter- 
 mination of the percentage thus eliminated lies th'e diffi- 
 culty of getting the proper relation between the assays of 
 the ore as sampled and the value of the material as sent 
 to the reduction works. Unless this is determined, and 
 the sampling is corrected in accordance, the figures of 
 the engineer will not harmonize with th'e results of future 
 operations. The most practical way to find out the per- 
 centage sorted out is to measure the ground stoped dur- 
 ing a given period, and, knowing the tonnage extracted 
 from such a particular block of ground, to determine the 
 average width of clean ore actually obtained from that 
 block. If the average width of the vein is fairly consist- 
 ent, one can, from these data, deduce the amount of waste 
 which gets mingled with the pay-streak and then cor- 
 rect the assay returns, from sampling, accordingly. 
 
 However, gold-veins are rarely uniform in width, and, 
 moreover, any given mine may contain several lodes, 
 the output of which is not kept separate. In such local- 
 ities as Kalgoorlie and Cripple Creek, where the veins 
 are rich, erratic, and so diffuse in their mineralization as 
 to make it compulsory to break down a great deal of 
 waste in extracting a small width of clean ore; where, 
 also, the large mines include within their boundaries two 
 or three distinct lodes of variable width and richness, it 
 becomes an extremely difficult task for an engineer to 
 determine, within the short period of his inspection, to 
 what degree the vein-stuff is mixed up with waste. An 
 example will emphasize the matter under discussion. 
 Take a lode or series of lodes having an average width 
 of one foot of four-ounce ore. Assume, as is usually the 
 case, that a width of at least four feet of rock is actually 
 
 4 6 
 
removed in mining, so that one foot of ore is shot down 
 with three feet of waste. If you sample the vein alone 
 you get an average of four ounces of gold per ton ; if 
 you sample the four feet of sloping width you get an 
 average of one ounce per ton, unless there happen to be 
 one or more stringers of ore outside the main pay- 
 streak, not rich enough to be worked on their own ac- 
 count, but near enough to the vein proper to be included 
 within the ground which is removed. In this case the 
 average may become slightly higher than the figure 
 which is based on the supposition that the extra three 
 feet is barren material. That is a detail. The point to 
 be emphasized is that the product of the mine will be 
 more than the tonnage based on one foot of ore and 
 considerably less than the tonnage based upon the stoping 
 width; more is broken than one foot, because mining 
 does not copy sampling methods, and less is shipped 
 than four feet, by reason of the sorting which intervenes 
 between stope and smelter. Similarly, as to the average, 
 value, the production of the mine will average less than 
 . the four ounces in the clean ore, but more than the 
 one ounce which is the assay value of the stoping width. 
 
 At Cripple Creek, and in other districts where the costs 
 of transport and treatment are high, this four feet, 
 or more, of ore is sent to the ore-house and is sorted by 
 hand. It may have been first culled underground, the 
 large pieces of waste being retained on the stulls. This 
 is the practice in most mines. In any event, a certain pro- 
 portion of waste is thrown out, and it is only the 
 remainder that is milled or marketed. What is that pro- 
 portion which is taken out? 
 
 Here lies the difficulty which has been at the bottom of 
 many an erroneous estimate. If the engineer is pressed 
 for time, by reason of agreements made between the 
 buyer and seller of the mine, he will not have the oppor- 
 tunity to conduct such tests as would give him the 
 requisite data. The management is apt to have loose 
 ideas on the subject; the ratio of waste eliminated to 
 clean ore actually shipped will vary from week to week, 
 
 47 
 
just as the different stopes underground will change from 
 time to time, so that it is rarely possible within the period 
 of a brief examination to get, save at second-hand, at the 
 percentage which so seriously affects all calculations. 
 Under these conditions the only thing to do is to state the 
 results just as they are obtained, explaining how they are 
 obtained, and then make the correction which judgment 
 dictates. If the vein has been sampled by itself, then an 
 addition for the unavoidable admixture with waste must 
 be estimated, the amount being based upon the observa- 
 tion both above and underground. If the sampling has 
 included the full stoping width, then a similar correction 
 must be made for the amount of material subsequently 
 removed by sorting, otherwise the statement of sampling 
 returns may prove unintelligible, it being not uncommon 
 for the average value of the ore as stoped, before sort- 
 ing, to be less than the total working costs. 
 
 However, except in the unpleasant circumstance of 
 limited time due to the unavoidable exigencies of busi- 
 ness, which unfortunately do often hamper, hinder and 
 obstruct the engineer in his professional work, it is pos- 
 sible to arrive at the ratio of ore and waste, and, there- 
 fore, to formulate accurate estimates. It requires time 
 and it needs money, but in the examination of large 
 mines nowadays it is appreciated by financiers and syndi- 
 cates employing first-class engineers that they must 
 make provision for plenty of time and money in order 
 to get good men to do good work. This may seem a 
 digression, but it vitally affects the consideration of this 
 branch of the subject under discussion. 
 
 When, therefore, conditions do permit of every precau- 
 tion, the engineer will cause the ore, as it comes to the 
 surface, to be weighed, he will get the weight of the clean 
 ore after sorting, and he will check this with the weight 
 of the material which goes over the dump. He will 
 also take samples of the dump to correct his estimate of 
 the average values. The weighing and sampling will, of 
 course, be done by his own men. He will also take 
 careful note of any waste which is retained underground, 
 
 - 4 8- 
 
as is usually the case in a well-managed mine. If this is 
 done during the space of a month or so, which is the 
 minimum period permissible for an important examina- 
 tion, he will have data enough to enable him to correct 
 the results secured from the sampling of the mine. In 
 the suppositious case quoted above, the one foot of 
 four-ounce ore would be mined (and sampled) with three 
 times as much waste, one-half of the material thus broken 
 would be sorted out at surface, and with it would go some 
 of the fines, so that the net result might be about two feet 
 of ore assaying 1.75 oz. and two feet of waste assaying 
 about 0.25 oz. per ton. 
 
 These final estimates should be borne out by the future 
 record of the mine. As a safeguard, however, the engi- 
 neer ought to state in detail, in his report, how he 
 arrived at his figures, lest, later on, an ignorant direc- 
 torate or an unscrupulous manager should either work 
 more than a proper width, in order to get an increase in 
 tonnage, or mine only the richest portion of the lode 
 with a view to a brief period of inflated returns. Such 
 things have happened, and honest men have been drawn 
 into the blame which followed. 
 
 Coming to the consideration of the second point, 
 specified under B, it is evident that here also there is 
 room for error. In most lodes of gold-bearing quartz, 
 where sorting is out of the question on account of 
 the low grade of the ore and the uncertain dissemina- 
 tion of the gold, it is not possible to break the ore in 
 the stopes as clean as it is broken in the course of 
 sampling. Should the lode be free from an admixture 
 Of country it is, nevertheless, rarely practicable to stope 
 it without bringing down some of the encasing rock. 
 This is slight in some instances of very well-defined 
 quartz veins, large enough to admit of a full-sized stope 
 and so separated by selvages from the wall-rock as to 
 come clear away. In most instances, however, the stop- 
 ing will include a large proportion of waste, and when it 
 happens, as is not infrequent, especially with big, generous 
 ore-deposits, that the lode throws out branch-veins or is 
 
enriched by feeders, then it will be found that there is a 
 very considerable admixture of comparatively barren rock. 
 
 Circumstances such as these, overlooked or under- 
 estimated, have been at the root of the differences be- 
 tween rthe estimates of capable engineers and the subse- 
 quent record of the mines they have reported upon. 
 Managers, as a rule, like to emphasize the clean-cut char- 
 acter of their operations, and are apt to accentuate the 
 fact that the ore "breaks easy" and free from wall-rock. 
 Moreover, in all mining, there is an element of the unex- 
 pected, which in this case takes the form of the breaking 
 away of "slabs" of wall-rock, the admixture of large 
 pieces of "casing," the occasional "horse" or intru- 
 sion of barren rock amid a width of ore, and other 
 contingencies, all of which tend inevitably to an in- 
 crease of tonnage and a diminution in the average 
 value of the output. One must look for these features 
 in a mine and obtain data sufficient to warrant an esti- 
 mate of their perturbing influence upon the accuracy of 
 those calculations which are at first based solely on 
 the results of sampling. 
 
 The third subdivision, C, includes a large proportion 
 of the big low-grade lodes from which so much of the 
 metallic wealth of the world is derived. An examina- 
 tion of a mine is usually confined to those workings 
 which are confessedly profitable or likely to become so. 
 The non-payable workings are neglected. In actual min- 
 ing, however, a level or a raise is apt to be carried 
 forward through poor ground in the hope of encounter- 
 ing better ore, and it is not uncommon to remove blocks 
 of unprofitable ground lying between good stopes be- 
 cause of practical convenience in working. In this way 
 there is a tendency to vitiate the results of sampling, if 
 not corrected in accordance with a recognition of such 
 indubitable facts. Moreover, in the working of large de- 
 posits of low-grade ore, where the width to be removed 
 is not determined by well-defined boundaries, but is left 
 to the arbitrament of the assay, as a consequence of a 
 diffused impregnation of ore, there is a tendency to in- 
 
 50 
 
crease the stoping width. The result of a steady diminution 
 in working costs, due to better management, improved 
 equipment and more favorable economic conditions, is to 
 permit of the exploitation of poorer ores. This leads to 
 the utilization of neglected stopes, previously considered 
 unprofitable, and the enlargement of the stoping width so 
 as to include more and more of the outer poorer edges of 
 the lode. An increase in the capacity of the mill is usually 
 followed by a drop in the average value of the output. 
 On the Rand this tendency has become very marked; 
 thus, for example, most of the original estimates of the 
 life of particulajr mines were based on ore-reserves cal- 
 culated upon the basis of a certain width of 'banket/ 
 but since the substitution of rock-drills for hand labor 
 it has been found advisable, consequent upon observa- 
 tion and experience, to increase the stoping width by as 
 much as 50 per cent. This increase has necessitated the 
 Breaking of a larger amount of barren rock, but a com- 
 pensating factor has been found in the introduction of 
 revolving circular tables, which facilitate the picking out 
 of the waste by natives. 
 
 These are considerations which the engineer must 
 keep in mind. He is not expected to write next year's 
 almanac, but if he is to be justified by the actual record 
 of the mine, his report must be aided by some of that 
 farsightedness and shrewdness which is necessary to a 
 successful meteorological forecast. 
 
 ESTIMATION OF ORE-RESERVES. 
 
 It has been well said that "if you want to arrive at in- 
 telligible issues not to say conclusions in any discus- 
 sion, begin by settling the meaning of the terms you are 
 going to use." 1 This is particularly necessary in dis- 
 cussing a subject which suffers from the want of defini- 
 tion. "Ore in sight" has become one of those nebulous 
 phrases which are only noise and smoke. It is impera- 
 tive that we have a clear conception of the fact signified 
 
 1 Dr. Thompson, late master of Trinity College, Cambridge. 
 Si 
 
by the technical terms we employ; when we find that 
 they are robbed of sense as soon as we dissect them, it 
 devolves upon us to discard them and seek for better 
 ones. "Ore in sight," as used to describe the ore- 
 reserves of a mine, is, if taken literally, a contraction in 
 terms, and, if taken otherwise, it has an elasticity which 
 has caused many to stretch it until it has become so 
 indefinite as to include the ore which is beyond even the 
 most imaginative vision. 
 
 In order to express the results of careful sampling 
 and estimation by a phrase which will at once convey 
 its meaning, even to the untechnical, I would suggest 
 "ore in reserve and ready to be broken," or "ore ready 
 for stoping." 1 This would cover those parts of a mine 
 which have been so.cut up by systematic workings as to 
 permit of very close calculations. Next would come the 
 blocks of ground incompletely developed, but known. 
 to carry ore, which, in character and persistence, are 
 similar to the main portion of the mine. These could be 
 covered by the term "probable ore-reserves." Beyond 
 this point a careful engineer will not go, avoiding "pos- 
 sible ore-reserves," or any similar phrase, as a snare of 
 the devil, because of the great likelihood that his client, 
 or the shareholders who may follow, will disregard the 
 qualifying adjective and commit him to a meaning" 
 which he did not intend to convey. When it comes to 
 the chances of development, itself a most important part 
 of the engineer's exercise of judgment, it will be best 
 to include the consideration of this aspect of the inquiry 
 under the paragraphs which deal with "the future pros* 
 pects of the mine." 
 
 That is reserved which is stored for future use, there- 
 fore that which is to be used forthwith is not in reserve, 
 from which it follows that by "ore-reserves" is meant 
 such bodies of ore as are kept back for the present with 
 
 discussion of terras was written some time ago, before Mr. Argall 
 brought forward the sensible suggestions which appeared in THE ENGINEER- 
 ING AND MINING JOURNAL of February 14, 1903. They will be found on 
 page 76 of this book. 
 
a view to future use, when those are exhausted which 
 are now being sloped. A mine which is being stoped 
 at a rate so rapid in ratio to its development that it has, 
 at any given time, only enough ore to keep the mill 
 going for a few palpitating moments cannot be said to 
 have any "ore-reserves." The idea of the latter includes 
 a reservoir of supply not to be exhausted at short no- 
 tice. As a consequence of these considerations it is 
 obvious that the amount of ore which warrants being 
 entitled "reserves" will depend upon the relative size 
 of the reduction plant which is attached to the mine. 
 
 At the outset it is permissible to quote the famous 
 dictum of President Cleveland, in referring to the tariff: 
 "It is a condition which confronts us, not a theory." 1 
 Any attempt to establish uniformity of procedure in the 
 estimation of ore-reserves is bound to break down be- 
 cause it disregards the inevitable diversity of the condi- 
 tions which obtain in mining. Mines differ, as men do. 
 A safe presumption in one case is a hazardous guess in 
 another. During a recent discussion of this subject it 
 was suggested that it was desirable for mining engi- 
 neers to agree upon certain general rules as to the al- 
 lowance to be made in estimating ore. You might as 
 well sign an agreement upon the percentage of trust to 
 be placed in human nature. There are mines, the ore- 
 bodies of which are of such a character that it is safe 
 to predict their persistence for several hundred feet; 
 there are others where the lode is so erratic that ten feet 
 is a dangerous assumption. 
 
 Examples will serve to emphasize the range of varia- 
 tion. On the Rand a bedded vein of gold-bearing con- 
 glomerate extends for a great distance, and over portions 
 of its known length it maintains an average tenor so 
 fairly constant that "the values of unworked portions 
 may be closely calculated from the results achieved in 
 adjoining developed mines." 2 In any given mine 
 to narrow the assumption it is quite safe to calculate 
 
 l Messages of the Presidents, Richardson. Vol. viii, p. 590. 
 2 G. A. Denny. The Deep-Level Mines of the Rand, p. 119. 
 
 53 
 
the average value of the ore in a block of ground, say, 
 300 ft. long and 150 ft. high, that is, after this block, 
 I 5 by 3 ft., has been sampled at intervals of, say, 10 
 ft., on every one of the four sides of the rectangle. This 
 would be the ideal "ore in reserve," a thoroughly sam- 
 pled block, not too big to vitiate the assumption of a 
 certain uniformity in value per ton. In contrast to this 
 I would quote such mines as, for example, the Seven- 
 Thirty at Silver Plume, Colorado, or the Yellow Pine, 
 near Boulder, in the same State, both of them mines 
 which have been at some time richly productive, but 
 with a distribution of value, in silver chiefly, so varying, 
 so spotty and uncertain, that careful sampling, at regu- 
 lar intervals of even less than 5 ft., around the four 
 sides of a block only 50 ft. square, would afford the 
 basis for an estimate which at its best would be only a 
 reasonable guess. Each mine must be judged on its 
 merits, in each instance the conditions vary, and while 
 there may be a general similarity of method in getting 
 at the various facts, there never can be any cast-iron 
 uniformity in the nature of the inferences deducible 
 from the facts. Experience, silvered with age, is the pre- 
 siding judge, and will decide whether this or that piece 
 of evidence is relevant or not. Nor is there any room 
 for pessimism or for optimism ; one is as much out of 
 place as the other ; indeed, it is not too much to say that 
 while a sanguine temperament will lead sometimes to 
 exaggerated expectations, it is equally true that an over- 
 cautious hesitancy is to be condemned. Occasionally, 
 an engineer in his effort to avoid risking his own reputa- 
 tion is apt to lean toward a timid conservatism which 
 sacrifices the interest of his client. He is engaged to 
 determine the facts, in the first place, and then to apply 
 his best judgment to them. If the facts are insufficient, 
 let him say so; if they are sufficient to warrant a de- 
 cided opinion, let him enunciate it clearly, to the end that 
 his client may get the maximum benefit of his investi- 
 gations. 
 
 "The proof of the pudding is in the eating." The 
 
 54 
 
exact profit to be won from a certain block of ore- 
 bearing ground is best known when it has been mined 
 and milled; even the most uniform ore has its spots of 
 greater and lesser richness ; the best estimate is there- 
 fore only a close approximation based upon the doctrine 
 of averages. Nevertheless, if such estimates are occasion- 
 ally wide of the mark it is not merely because of la malice 
 des c hoses, that essential contrariness of things which will 
 baulk even the best of engineers, but more frequently 
 it arises from the disregard of the A, B, C of proper pro- 
 cedure and a judgment vitiated by financial participation 
 in the undertaking itself. I am not of those who believe 
 that the sampling of a mine is the one decisive factor in 
 the diagnosis of it, on the contrary, I hold that as evi- 
 dence it is crucial or merely collateral, according to the 
 circumstances of the case, which may depend upon the 
 past record of the mine, its future possibilities, the geo- 
 logical environment, economic conditions and other fac- 
 tors of primary importance. 
 
 INFERENCES FROM SAMPLING. 
 
 When the sampling has been thoroughly done, the en- 
 gineer is in possession of many important facts. If he 
 is a novice he will have learned the assay-value of the 
 ore at each of the spots he has sampled and he will have 
 learned little else. 
 
 Nothing illustrates so well the proverb that "a little 
 knowledge is a dangerous thing" as the direct infer- 
 ences from the results of sampling. To emphasize this 
 statement, I will take an instance which is founded on 
 fact. In Fig. 5 you have a longitudinal section of a 
 small mine, which has been apparently well opened up. 
 The shaft is vertical, and does not follow the vein, which 
 inclines to the west. The levels to the north have found 
 nothing, those to the south (A B and C D) have cut 
 through ore which is also explored by a raise (K L), and 
 two winzes (E F and G H). At the lower levels, stopes 
 have been started and the 'backs' make an excellent show- 
 ing, as the figures indicate. The latter are not expressed 
 
 55 
 
JKain.Shafc 
 
 SECTION OF WORKINGS EXHIBITING THE RESULTS OF SAMPLING, 
 
 FIG. 5. 
 
 Ore estimated 
 
 Main Shaft 
 
 r-i \r^^-~ttr~- ~~r^+^-^L 
 
 Granite 
 
 SECTION OF WORKINGS SHOWING T,HE GEOLOGICAL FEATURES. 
 
 FIG. 6. 
 
 5 10 feet. 
 
 + + t Granite [:'. '::':': : . : .\ Porphyry 
 
 Ore Bodies 
 
in any particular unit, but it is to be supposed that zero 
 means barren, 2^2 means pay-ore and so on, up to 8, 
 which marks rich ore. The results are indicated on the 
 section. The inference, as to the amount of ore in the 
 mine, is exhibited by the cross-hatching. 
 
 In arriving at this estimate the novice is guided bv 
 his sampling alone ; he has failed to take note of the geo- 
 logical features. It may happen that the .superintendent 
 of the mine, an old, practical miner, we will suppose, has 
 told him that the ore is fairly uniform within the limits of 
 the shoot, and that while the rock does indeed vary a 
 little in places, this variation does not seem to affect 
 the general distribution of values. Or, again, it may be, 
 as happens often, that the man in charge of the mine is 
 .honest, but not honorable, and, instead of committing 
 himself to such statements as the foregoing, he keeps 
 discreetly silent, or, under cover of appearing to refrain 
 from influencing our young engineer, 1 he absents himself 
 while the sampling is in progress, and leaves his shift- 
 boss or some other underling to do the talking. Per- 
 haps, indeed, those in charge of the mine really do not 
 appreciate the true condition of affairs, and the engineer 
 is deceived by an oversight which will appear almost ex- 
 cusable. However, the mischief is done, the mine is 
 taken over by a financial syndicate or a mining company. 
 Before the business is actually consummated, another 
 engineer, representing another financial interest, is sent 
 out to make an examination. We will suppose that this 
 man is of greater experience than the last; he is, more- 
 over, familiar with the geological structure of this par- 
 ticular district or of another similar to it. He proceeds 
 to sample. The accuracy of the previous sampling is 
 confirmed, but in the course of his investigation he has 
 noticed that the country is not uniform, and that there 
 
 U have supposed the blunder to be due to youthful inexperience, for this 
 is the least blamable but as a matter of fact, blunders of this kind are due 
 to ignorance and are frequently made by older men of the kind described 
 as "thoroughly practical," where the particular emphasis on "practical" is 
 indicative of utter lack of training or such technical education as an engi- 
 neer requires. 
 
 57 
 
are two different rocks exposed by the workings. One 
 is obviously granite, the other he cannot label accurately 
 without a microscopic section, but it is evidently an erup- 
 tive which has intruded into the granite ; so, on account 
 of its speckled appearance, he applies the term 'por- 
 phyry' to it, and when the sampling is finished he spends 
 a few days in carefully examining the workings with a 
 view to getting an idea of the structural relations be- 
 tween these two rocks. The results are set down graph- 
 ically, and he obtains the information illustrated in Fig. 
 o. By examining this section, side by side with Fig. 5, 
 it will be seen that his inferences are warranted. The 
 consequences are surprising. He discovers that there 
 is no continuous ore-shoot from the surface downward, 
 but that there are two comparatively small lenticular 
 ore-bodies which occur where the vein cuts through the 
 porphyry sheets, and only in those portions of the por- 
 phyr) where certain cross-veins have exercised an en- 
 riching effect. When the vein gets into granite it be- 
 comes poor, and, moreover, it pinches, a fact which the 
 sampling did not sufficiently emphasize. The ore-reserves 
 are cut down to a fraction of the previous estimate, 
 and the future prospects of the mine are considered 
 most uncertain, because the ore already found is due 
 to local structural conditions which are unlikely to recur. 
 Another kind of error may be instanced. It is more 
 frequent in placer mining than in the estimation of ore 
 in lodes. Fig. 7 represents the cross-section of a deposit 
 of tin gravel in an old river channel now capped with 
 basalt. The deposit was sampled through shafts which 
 cut right down to the 'gutter/ 180 ft. deep, below the 
 basalt. In this sampling the gravel was taken all the way 
 down the shafts and mined together, so that each shaft 
 yielded one large sample. From the weight of this and 
 that of the resulting grains of tin, after panning down, 
 the percentage was calculated. The estimate of quantity 
 was based upon the length of channel, within the bound- 
 aries of the property, multiplied into an inverted tri- 
 angle, ABC, the base of which was the top width of the 
 
 -58- 
 
deposit and the apex the 'gutter.' The cubic yards 
 thus obtained gave an approximately correct result as 
 to quantity of material, but the estimated average con- 
 tent was all wrong, because the method of calculation 
 disregarded the fact that the richest stuff was concen- 
 trated at the lowest end of the triangle, and actually 
 formed a very small proportion, in weight, of the whole. 
 Subsequently, the ground was re-sampled. The total 
 depth of 1 80 ft. was, in the case of each shaft, subdivided 
 into sections of 30 ft., except the last 30, which was fur- 
 ther divided into two portions, one of 20 ft., and a lowest 
 
 I'f^'vm.l 
 
 EE Basalt' 
 
 Gravel 
 
 m 
 
 Granite 
 
 of all, only 10 ft. thick. The first 30 ft. was found to be 
 almost barren, the next 30 ft. assayed 0.2 per cent, of tin, 
 the next 30 ft. 0.28 per cent., and so on, increasing grad- 
 ually until the last 10 ft. was reached. This was very 
 rich, 1.5 per cent., on account of concentration in the 
 'gutter' or bed of the channel. Each layer was calcu- 
 lated separately as to quantity and average contents, giv- 
 ing results which proved the bottom to be very profit-, 
 able, but difficult to work on account of want of gradient 
 for hydraulicking operations ; while the uppermost por- 
 tions of the deposit were found to be too poor for profit, 
 but yet requiring handling in order to get at the lower- 
 lying part of the gravel. 
 
 59 
 
The method first described would have given a very 
 much exaggerated idea of the cubic yardage and a false 
 notion of a uniformity of value, besides ignoring the 
 working difficulties to be encountered in the extraction 
 of the tin from the successively deeper layers of the 
 gravel. This is very much like the sampling of a vein in 
 a prospect shaft where the samples are taken every 10 ft. 
 and are allowed to fall to the bottom where they mingle 
 confusedly and eventually form a "large sample," the 
 weight of which is mistakenly supposed to give assurance 
 of the accuracy of the average deduced from the subse- 
 quent assay. 
 
 It is not necessary to cite other instances of this kind. 
 Happily, they are rare. The real work of good judgment 
 usually commences in the estimation of future prospects. 
 Mines are very rarely bought merely for the ore proved 
 up by complete evidence; the attractive feature is, as a 
 rule, a speculative enhancement of value likely to arise 
 from further discovery. This is where the trouble begins. 
 
 THE FUTURE PROSPECTS OF A MINE. 
 
 There is room for the exercise of a wonderful lot of 
 common sense in the judgment of a mine. Science, after 
 all, is, as Huxley himself said, "organized common 
 sense." If you have been walking along a road which 
 has been straight and level for five miles you are un- 
 likely to go wrong in supposing that it will continue 
 straight and level for another half mile, even though the 
 foliage prevents you from seeing more than a hundred 
 yards ahead, but if you have proceeded along a road 
 for a half mile or so only, it would be deemed foolish to 
 predict that the road will maintain the same gradient and 
 direction for five miles further. Thus, in estimating the 
 persistence of an ore-body you may be justified in count- 
 ing upon its continuity for another hundred feet if the 
 ore has already persisted with some degree of uniformity 
 for five or six hundred feet downward, and so, on the 
 contrary, you will be playing with Providence if you as- 
 
sume a continuation for several hundred feet on the 
 part of an ore-shoot which has as yet been traced for 
 only 50 ft. from the surface. In this respect the mines 
 of the Rand afford a striking contrast to most precious 
 metal mines. The 'banket/ in comparison with the ordi- 
 nary type of gold-vein, has the persistence and uniform- 
 ity of a coal-seam, and explorations on a large scale all 
 over a very extensive region will warrant an engineer in 
 making assumptions which would be ludicrous in Cali- 
 fornia or Colorado. Yet, even under these exceptional 
 conditions, such general evidence of continuity, when 
 applied to an individual mine, must be amenable to the 
 particular testimony obtainable in that particular mine 
 or in the workings of its immediate neighbors. In most 
 gold-mining districts there is such an absence of uni- 
 formity in the structure and behavior of gold-bearing 
 lodes that it becomes imperative to rely upon the par- 
 ticular testimony afforded by each mine. Such testi- 
 mony, however, must be read in the broad light of ex- 
 perience. For this reason the estimates of ore likely 
 to be opened up by further development will be more 
 nearly correct on the Rand than similar calculations made 
 by the same engineer elsewhere. Another distinction ob- 
 tains ; a precious metal mine in Colorado or California, by 
 reason of mining laws which give the owner of the outcrop 
 the right to follow the vein indefinitely in depth, has a 
 future which is not confined to the narrow limits of mere 
 acreage, such as is imposed in the Transvaal, in Australia, 
 Mexico, etc. This renders the future of the American mine 
 more speculative, while at the same time it lays upon the 
 engineer the responsibility of appraising possibilities 
 which are quite beyond the limits of ascertainable fact. 
 It is no solution of the problem to say that such possi- 
 bilities have no assessable value, for to adopt this attitude 
 is to disregard the entire history of precious metal min- 
 ing in the Great West, and the engineer who rests con- 
 tent with 1 the evidence which is before his nose will prove 
 but a disappointing, and often misleading, adviser to an 
 enterprising client. 
 
 61 
 
In arriving at general conclusions concerning the per- 
 sistence of an ore-body in a mine, the engineer may have 
 several guides, namely, the internal evidence afforded by 
 the behavior of th'e ore-body in the ground which he has 
 examined, the collateral suggestions afforded by the be- 
 havior of other ore-bodies in the same mine, the general 
 evidence obtainable in other mines within the same 
 region. 
 
 When the value of a mine centers upon one large ore- 
 body, rather than several, there is no opportunity for 
 inferences founded on similarities of behavior. The 
 engineer is compelled to seek for internal evidence. If 
 the sampling has been properly conducted and the re- 
 sults have been set down on the longitudinal section of 
 the workings, it will be found that the ore exhibits local 
 variations from which certain deductions are possible. 
 The relatively richer parts of the ore-body may be so dis- 
 tributed as to indicate mere absence of uniformity, and 
 nothing more, but, as a rule, the indications will go fur- 
 ther and suggest either that the ore-body is becoming 
 richer with increasing depth or poorer in the same direc- 
 tion, or that there are successive zones of richer or 
 poorer. Again, the lode may be as rich as heretofore, 
 but a change may be apparent either by way of a short- 
 ening of the ore-shoot or of a narrowing of the pay- 
 streak. For all these possibilities one has to search amid 
 the tangled mass of evidence. 
 
 One or two instances will serve to illustrate such pos- 
 sibilities. In the San Juan region of Colorado the pre- 
 vailing geological formation is a volcanic breccia, of 
 Tertiary age, built up of fragments of andesite, which are 
 arranged in neatly horizontal layers. The veins cut 
 through this rock without, commonly, causing any very 
 big dislocation. In these gold-bearing quartz veins 
 there occur ore-shoots having a pitch which is usually 
 not far from the vertical, and while such ore-shoots may 
 be worked out in their entirety so as to exhibit an un- 
 broken continuity in the stoping, nevertheless, to those 
 who are observant of the variations in the grade of the 
 
 62 
 
ore, as recorded by daily assays or weekly mill returns, 
 it is very clear that such variations coincide with the 
 changes in the country ; that is to say, the ore-body will 
 be characterized by nearly horizontal bars of enrichment 
 which are traceable to the effect produced upon the vein 
 by the particular layer of breccia through which it is 
 passing at a particular horizon. My observations lead 
 me to suppose that th'e composition of certain layers of 
 the fragmental volcanic rock is responsible for the effects 
 noticed, and that the layers which have the finest texture 
 are those which are the most beneficial, for reasons out- 
 side of the present discussion. One example will suf- 
 fice. In Fig. 8 it is seen that a series of adits penetrate 
 a steep mountain which is entirely composed of andesite 
 breccia. The lowermost adit goes through an average 
 of 2^/2 ft. of 6 dwts. of gold, which is, in the district 
 where the mine is situated, rather low-grade. The first 
 portion of the level and the end of it pass through barren 
 ground, so that there is some evidence of the exist- 
 ence of an ore-shoot of this low-grade stuff. In the 
 stopes there is no change to record until the next level 
 overhead, No. 2, is approached. A raise connecting with 
 this level passes through 8 dwt. ore. No. 2 adit makes 
 a much better showing, and averages, fairly uniformly, 
 ii dwts. for an average width of 4 ft. Here also the 
 level passes out of ore at a point nearly vertically over 
 the corresponding impoverishment at No. I. The stopes 
 above No. 2 give, at first, results as good as the drift, 
 but in going upward they show a marked falling off, 
 so as to average one-half the results given by the No. 2 
 level. At No. 3 the average of the level is only 3^ ft. 
 of 4-dwt. ore; this is doubtless the reason why the drift 
 was not extended to the limit of the sh'oot. A raise put 
 up from this level is in poor ground until within 50 ft. 
 of No. 4; then marked improvement sets in. This is 
 confirmed by the results from the No. 4 adit, which gives 
 an average of 3 ft. of lo-dwt. ore. This good mill-stuff, 
 however, does not extend much above the level, as is 
 proved by a raise, which gets into poor ground. 
 
 -63- 
 
No.r 
 
 FIG. 8. 
 SHOWING KESULTS OF SAMPLING. 
 
 No.2. 
 
 FJG. 9 
 SHOWING BOCK STRUCTURE 
 
 ^Ore QoodOre 
 
 No. l 
 
These data are perplexing and indicate an alternation 
 of values which renders any estimate very hazardous. 
 When, however, the geological structure is investigated, 
 there is found to be a relation, between values and struc- 
 ture, which illuminates the entire problem. In Fig. II 
 there is given a section, on the plane of the vein, which 
 exhibits the position of the series of layers through 
 which the vein cuts. This helps to explain the results 
 shown in Fig. 9. The zones of enrichment penetrated 
 by adits No. I and No. 4 coincide with two layers of 
 close-textured tuff, or fine-grained breccia, laid down 
 during the intermittent violence of volcanic eruption. 
 The intermediate, overlying, and underlying beds of 
 breccia are coarse, and, for some reason which does not 
 concern the present inquiry, they are less favorable to 
 ore-deposition than the occasional layers of tuff. 
 
 In this instance the evidence was very clear ; in other 
 mines situated in the same region it is not practicable, 
 on account of the decomposition of the enclosing country, 
 to establish the relationship so clearly, but it is a matter 
 of experience that notable variation in both the width 
 and value of the lodes does occur in a similar nearly 
 horizontal direction. The understanding of it is, there- 
 fore, a clue to many apparent vagaries in the distribution 
 of rich ore. 
 
 In the case of a mine which contains several ore- 
 bodies there are many useful suggestions to be obtained 
 from a comparison of their characteristics. Careful 
 investigation will lead sometimes to the detection of 
 peculiarities applicable to the general occurrence of ore 
 in that particular mine. The longitudinal section of the 
 stopes warrants the close study given by a general to the 
 map of the region which is to be the scene of his cam- 
 paign. Stope-maps are not always correct; sometimes 
 they are incorrect to a very misleading degree. A few 
 measurements, at least, should be made to test this 
 point, and occasionally, when the general accuracy of 
 the surveys warrants a doubt, it is a good precaution to 
 make one's own map of the mine, either personally, or 
 
 65 
 
by engaging the services of a reliable surveyor. The 
 conditions are so diverse that it is impossible to give a 
 typical illustration, but, by way of suggestion, I will 
 append an example of inferences derived from a study of 
 the old workings of a mine. It is a small mine ; for, 
 after all, the most perplexing of problems is a 'pros- 
 pect/ and it is found in practice that the greatest mis- 
 takes and the exercise of the keenest judgment are alike 
 exhibited in the appraising of the uncertainties of an 
 undeveloped mine; therefore, the size of the property 
 chosen as an illustration scarcely requires apology. 
 
 Prospect 
 
 ShaftX" 
 
 SECTION OP A MINE 
 SHOWING ORE 
 IN CHIMNEYS 
 
 Stoped 
 
 5| Rich Ore 
 
 FIG. 10 
 
 Fig. 10 represents a section of the workings. These 
 consist of two adits, on the vein, together with a dis- 
 covery shaft, which joins the upper level (G H), and a 
 raise connecting the latter with the lower level (K M). 
 The problem is to determine what weight should be 
 given to the occurrence of a good width (say, 4 ft.) of 
 very rich ore (say, 5 oz. of gold per ton) in the ends 
 (H, M) of the two levels. In such a case it is most im- 
 portant to investigate, with 1 thoroughness, the mode of 
 occurrence of the ore-bodies previously encountered in 
 
 66 
 
the mine. This is not always easy; old workings have 
 been allowed to cave or the ground is heavy, and they 
 are carefully timbered so as to impede examination. 
 Sometimes this is intentional. In the case cited the 
 upper level appears to carry one continuous body of 
 ore from P to the breast at H, with a small compara- 
 tively barren interval S. T. The timbering obscures the 
 fact that the first half of the stope P S is only a cutting- 
 out stope, which was worked for the purpose of testing 
 a low-grade portion of the vein; the same applies to 
 more than two-thirds of the stope V W, at the lower 
 level. Similarly, while the timbering between T and Z 
 indicates a good length of stope, as a matter of fact the 
 innermost half of this is little more than a 'cutting-out 
 stope' in comparatively poor ground. The truth is, 
 the ore-body A B did not go to surface, having been first 
 cut by 'the discovery shaft at 70 ft. down ; it is a very 
 short body of ore, almost a chimney, and it diminishes 
 in approaching the lower level; further, the ore-body C 
 D is still less persistent ; it is a narrow, short lens which 
 does not hold out to the lower level, nor does it go up 
 more than half-way to surface, but it makes a sort of 
 spurious connection, by means of the raise, with another 
 patch of ore E, on the second level. In practice, such 
 workings as these are largely inaccessible and usually 
 dangerous ; as a consequence, the statements of an in- 
 accurate superintendent, who desires to serve his em- 
 ployer by putting things in the most favorable light,, are 
 apt to carry more weight than they should, so that, with 
 the usual desire for quick decision on the part of both 
 th'e vendor and the vendee, the engineer may be pushed 
 to a conclusion which the actual facts do not warrant. It 
 may seem to one who has missed the essential character 
 of these ore-bodies, through the failure to examine the 
 old workings, that th'e good width of rich ore at H and 
 at M indicates the beginnings of a big body of ore 
 which persists, at least, from one level to the other; but 
 to another man, who has carefully studied the old work- 
 ings, it is evident that the probabilities point merely to 
 
 67 
 
A Crosscut B 
 
 PLAN 
 SHOWING SAMPLING 
 
 Supposed Ore 
 
 FIG. 11 
 
 PLAN 
 SHOWING LODE STRUCTURE 
 
 lii^lil Ore Lenses 
 
 FIG. 12 
 
another narrow lens of uncertain extent. The moral is, 
 don't allow yourself to be hurried into an opinion by 
 either party to the transaction, and beware of workings 
 which are stated to be inaccessible, because such inac- 
 cessibility may have a purpose. 
 
 Another illustration will emphasize the warning con- 
 veyed in the last sentence. In Fig. n is represented the 
 single level of a California mine which is reached by 
 the western cross-cut shown to the left of the drawing. 
 The level is 450 ft. long ; owing to the fact that the coun- 
 try is a soft black slate the ground is very heavy, and 
 the level is closely timbered throughout, permitting 
 only occasional glimpses of ore, at the points where short 
 cross-cuts have been run out eastward. At these places, 
 D E, F G, B C and H K, the lode is plainly visible, and 
 exhibits from 6 to 8 ft. of fairly uniform quartz carry- 
 ing an average of from 6 to 7 dwt. of gold, in a district 
 where working costs are about $3 per ton. After sam- 
 pling these cross-cuts, examining the little there was to 
 be seen, and finding that the ground really seemed heavy 
 enough to justify the close timbering over the level, the 
 engineer came to the conclusion that he was dealing 
 with one of those persistent ore-bodies not uncommon 
 in that part of California, and he estimated the ore to 
 have the continuity exhibited by the cross-hatching in 
 the drawing. However, he had wholly misunderstood 
 the real character of the ore-occurrence, as Fig. 12 will 
 indicate. The close timbering was not necessary in 
 order to sustain the ground alone ; it was an excuse for 
 obscuring certain facts. The quartz exposed by the sev- 
 eral cross-cuts belonged to a number of small lenses. 
 These abutted against the "fissure," or main line of 
 fracture, which constituted the supposed lode ; the lenses 
 were short-lived and lay with their longer axis parallel 
 to the cleavage of the slate ; the body at D E only lasted 
 as far as two sets of timber ; that of F G died out at 60 
 ft., and that at B C ''petered out" at 40 ft. above the 
 level, while the last one, H K, went up as a narrow body 
 for a distance of 160 ft. Compare Fig. n with Fig. 12 
 
and quote Hamlet's comment on his own portrayal of 
 his mother's successive husbands. This incident did not 
 befall a tyro, but an old campaigner who was caught 
 by his own carelessness under circumstances from which 
 only the greatest wariness could have saved him. 
 
 Misconceptions concerning the conditions contribu- 
 tory to the localization of ore-shoots and the conse- 
 quent mistaken ideas as to the future possibilities of a 
 mine have often arisen from a misunderstanding of vein 
 intersections. In the case of a well-known mine in south- 
 western Colorado a length of 2,700 ft. of ore had been 
 opened tip by an upper level, and stopes, which had 
 
 I Winze 58 Ft. Deep , 
 
 Winze 143 Ft. Deep 
 
 HI Stoped 
 
 Feet 
 160 2<!>0 
 
 LONGITUDINAL SECTION 
 
 FIG. 13 
 
 worked out most of the ore except at one end, and had 
 proved that it persisted to the surface, an average dis- 
 tance of 150 ft. above this upper level. In the mean- 
 time two winzes had demonstrated the apparent down- 
 ward continuance of the ore-body. A longitudinal sec- 
 tion of these workings is shown in Fig. 13. In the ex- 
 amination of the mine by several distinguished mining 
 engineers, it was assumed that the winzes, one of which 
 was 58 ft. and the other 143 ft. deep, proved the con- 
 tinuity of the ore-body to an extent sufficient to warrant 
 a price for the property which was a good deal in ex- 
 cess of th ; e net profits to be won from the ground as 
 measured to the bottom of the winzes. In the sequel 
 it was found, after the mine had been purchased, and 
 when deeper workings had explored the lower horizon, 
 that the ore-body owed its existence, and certainly its 
 shape and position, to th'e intersection with another lode. 
 This made a "scissors crossing," the hinge of which was 
 
 70 
 
a line, dipping west at an angle of 7 30'. The ore-body 
 reached from this line to the surface, while downward it 
 extended about a hundred feet or so. Other scattered 
 smaller bodies of ore were, it is true, encountered, but 
 the main ore-body of the mine, upon which its value 
 was based, extended only about a hundred feet below 
 the broken line shown across the longitudinal section in 
 Fig. 13. Such an instance as this proves the need for 
 deciphering the conditions which have affected the dis- 
 tribution of ore. The crossing referred to was visible 
 in the stopes at the east end, but only to an inquiring 
 observer who suspected some eccentricity of lode struc- 
 ture. 
 
 COLLATERAL EVIDENCE. 
 
 Of all the collateral evidence likely to aid the engineer 
 in a correct diagnosis of the condition of the mine he is 
 examining, none is so useful as that derived from a study 
 of the surrounding district. Mines situated in the same 
 district are apt, on account of an identical geological en- 
 vironment, to exhibit similar symptoms and to suggest 
 like possibilities. The general study of a region, there- 
 fore, is a useful preliminary to the investigation of a 
 particular mine. Moreover, there is, I am glad to say, 
 a certain spirit of camaraderie among professional men 
 of the right sort which will enable a stranger to obtain 
 many useful hints from resident engineers, if he is prop- 
 erly made known to them. 
 
 The characteristics of ore-deposits within limited areas 
 are often well marked; in one case persistence, without 
 probabilities of either bonanzas or borrascas, is the rule, as 
 on the Rand ; in another case an irregular distribution of 
 values is to be expected, as in most silver-lead deposits in 
 limestone, and also in many rich telluride veins where sec- 
 ondary enrichment has been at work ; again, certain lines 
 of faulting and well-defined contacts between sedimentary 
 and eruptive rocks may be recognizable as factors in deter- 
 mining the place of rich bodies of ore, as is illustrated by 
 the Aspen and Rico districts in Colorado. 
 
 71 
 
Another very important factor, in influencing the rela- 
 tive richness of a lode in depth, is the position of the 
 ground-water level. No engineer can afford to disre- 
 gard it. Two opposite cases may be cited. In certain 
 arid regions of the southwestern part of North America, 
 which it would be invidious to specify further, the per- 
 sistence of rich ores coincides roughly with the zone of 
 oxidation. I recall a well-known mine which, .at the time 
 it was examined by several reputable engineers, exposed 
 an ore-body nearly 1,800 ft. in length. This was the 
 length of the ore traversed by the longest level, which 
 was also the deepest. (See Fig. 14.) Both ends of this 
 level were, however, still in ore. Three winzes proved 
 
 Sulphides U beginning to [] appear 
 
 FIG. 14 
 
 the ore for a further depth of about 30 ft. The upper 
 workings contained carbonates of lead and iron-stained 
 quartz rich in the precious metals. At the third level 
 there was evidence of the edge of the oxidized zone, for 
 sulphides predominated. All of the winzes left off in sul- 
 phides, of average tenor as regards gold and silver, but 
 exhibiting a noteworthy admixture of zinc-blende amid 
 the galena. One engineer who examined the mine allowed 
 50 ft. below the lowest level as ore to be considered 
 in appraising the value of the property, but he allowed 
 nothing beyond the ends of the level. This was adversely 
 criticized. However, among the reasons prompting 
 a conservative attitude was the recognition of the fact 
 that many gold and silver veins in that region turned 
 into poor zinc-bearing lodes at a short distance below 
 the limit of visible oxidation. In the sequel he was 
 proved to be right. When, later on, the mine underwent 
 
 72 
 
extensive development, it was found that at 45 ft. below 
 the lowest level the ore became poor in gold and silver, 
 but heavily charged with zinc-blende, while at the same 
 time the lowest level ran out of the ore-body within a 
 few feet at both ends. In this regard it is a curious fact 
 how often good miners, especially if they are selling a 
 mine, stop their explorations at the proper psychologi- 
 cal moment. 
 
 The great copper region around Butte, in Montana, 
 exemplifies another aspect of the inquiry. Very exten- 
 sive exploration, prompted by the extreme richness of 
 the lodes, has permitted of the accumulation of evidence 
 which proves conclusively that the big ore-bodies are 
 thte result of a secondary enrichment brought about by 
 the leaching of copper by the ground-water and its pre- 
 cipitation upon the sulphides of the deeper zone. The 
 original vein stone consisted of iron pyrite, copper 
 pyrite and, probably, enargite, while the bonanzas con- 
 sist of the higher sulphides, bornite, covellite and chal- 
 cocite. Experiments have been made 1 in the laboratory 
 which illustrate the formation of chalcocite (copper 
 glance) on pyrite by precipitation from a solution con- 
 taining copper sulphate, such as would be the product 
 of oxidation through the agency of the ground-water. 
 As a result of such reactions the outcrops are poor in 
 copper and silver, because these have been leached out; 
 the silver appears at a comparatively shallow depth 
 (three or four hundred feet below the surface) so as to 
 form a zone of maximum enrichment in that metal, while 
 the copper has been deposited deeper still, so as to form 
 the magnificent masses of high-percentage ores which 
 have made Butte so productive. Below these come the 
 first-formed ores, chiefly pyrite with a little copper 
 pyrite, without the higher copper sulphides which have 
 enriched the overlying zone. While, therefore, the lower 
 limit of the horizon of secondary enrichment has been 
 passed through in some of the mines, it must be added 
 
 ^'The Synthesis of Chalcocite," by H. V. Winchell. ENGINEERING AND 
 MINING JOURNAL, May 23, 1903. 
 
that in others the rich sulphides extend to a depth of 
 over 2,000 ft. from the surface, so that the effects of the 
 ground-water circulation continue to a profundity quite 
 exceptional in the experience of mining. This may be 
 due to the intensity of the fracturing which followed the 
 deposition of the earlier sulphides, and it may be partly 
 a result from the open character of th'e lode channels 
 which has permitted of the far-reaching penetration of 
 the ground-water, but, whatever the cause, it renders the 
 problem of ore-occurrence at Butte quite exceptional, 
 particularly when compared to cases such as the one 
 quoted in the preceding instance, in Fig. 14. A novice 
 who has sampled the shallow workings of a young mine 
 in a region such as Butte would be likely to be misled 
 by the low percentage of copper, and therefore enunciate 
 an unfavorable opinion, whereas one who recognized 
 the effects of ground-water leaching and was guided pos- 
 sibly by a knowledge of the changes encountered at 
 greater depth, in a neighboring mine, would make quite 
 a different inference. Under other circumstances in an- 
 other region the occurrence of the higher sulphides, 
 such as covellite and chalcocite, would suggest second- 
 ary enrichment and warn the engineer against counting 
 upon a persistence of conditions which are frequently 
 quite local. 
 
 Considerations sucW as these suggest very forcibly 
 that keen observation and wide experience are required 
 for the appraisement of the potentialities of a prospect. 
 
 CONCLUSION. 
 
 This discussion of the subject has emphasized one 
 great factor in work of this kind, and that is the per- 
 sonal equation. No two men set to work in exactly the 
 same way, and no two men make exactly the same deduc- 
 tions from a complicated series of data. My views on 
 the subject are those based upon my own experience 
 hence the inevitable limitations of my presentation of it. 
 For this reason, also, I have omitted to refer to the litera- 
 
 74 
 
ture which deals with sampling and estimates of ore, be- 
 cause it would have extended this contribution to un- 
 comfortable length, had I taken up the other aspects of 
 the inquiry as discussed by other men. Herein lies my 
 excuse and apology to the Institution of Mining arid 
 Metallurgy, to Messrs. J. D. Kendall, E. B. Kirby, A. G. 
 Charleton, W. Wybergh, G. A. Denny, S. J. Truscott, 
 D. W. Brunton, W. McDermott and other authoritative 
 writers on the same subject. 
 
 The conclusion of the whole matter is sufficiently 
 obvious so obvious as to need but little further in- 
 sistence. If the discussion of the methods to be applied 
 in the sampling and estimation of ore has served to ac- 
 centuate the difficulties to be encountered in the diag- 
 nosis of a mine, then it will have fulfilled one of the 
 purposes of this contribution. "Chi va piano, va sano." 
 Extreme care is necessary at every stage of the work 
 care and experience, the experience born of wide knowl- 
 edge and practical work, without which a man in a mine 
 is no better than the proverbial bull in a china shop, 
 with a strong suggestion of a coming smash ! 
 
 The old hands the engineers who have sampled 
 mines from China to Peru do not need my maxims to 
 guide them. They have lost the cheerful confidence of 
 their apprentice days and are saturated with the experi- 
 ence of difficulty and doubt which have been frankly 
 faced on a hundred occasions. To the youngster, who 
 still has to receive his first fall and to realize that few 
 data are absolutely certain, also that data carelessly ob- 
 tained are inevitably uncertain to him this analysis of 
 methods of work will, it is earnestly hoped, serve as a 
 red flag of warning. To the general reader who is usual- 
 ly more in sympathy with 1 the pains of the unfortunate 
 investor in mines than he is with the causes which may 
 vitiate good advice from the expert, to him these obiter 
 dicta will, I trust, suggest forcibly that good advice is 
 hard to get and expensive yet cheap indeed compared 
 to tWe costly experience of entrusting onerous profes- 
 sional duties to the inefficient. 
 
 75 
 
"ORE DEVELOPED," A DEFINITION.* 
 
 BY PHILIP ARGALL. 
 
 The phrase "Ore in Sight," so commonly used as an 
 alleged measure of value in mine reports, is, in my opin- 
 ion, a very poor expression. Taken literally, as the non- 
 professional man is most likely to understand it, one 
 cannot defend its use except as a misleading, if not de- 
 ceptive, euphony. 
 
 The only "ore in sight" in or about a mining property 
 is that broken and displayed at surface in the ore-bins, or 
 in dumps. Perhaps I should also include ore broken or 
 visible in the underground workings ; but this is not what 
 is usually meant by "ore in sight" in mine reports. 
 
 I believe the majority of mining engineers call vein- 
 matter blocked out and accessible for measuring and 
 sampling on all four sides, or at the very least on three 
 sides, as "ore in sight," while strictly speaking it is only 
 the four planes bounding the block that are visible to the 
 physical eye. The "mind's eye" should have no place 
 in such an estimate. 
 
 I take it that the whole purpose of sinking shafts and 
 winzes, running cross-cuts, levels and raises, is, first, to 
 open up and develop ore ; and, secondly, to provide ready 
 means to extract and market this ore when developed. 
 Once a given piece of vein-matter is blocked out by, say, 
 two drifts, 150 ft. apart, and two winzes, 200 ft. apart, it 
 has reached its highest state of development, that is, it is 
 ready for removal by sloping; and it is also in the best 
 form for sampling and measurement, in order to obtain 
 a close estimate of its commercial value. I would sub- 
 mit, then, that such a block had best be called "ore de- 
 
 * From THK ENGINEERING AND MINING JOURNAL of February 14, 1903. 
 76 
 
veloped" and not "ore in sight." The former phrase 
 would correctly describe what it is, while the latter just 
 as clearly shows what it is not. 
 
 "Ore developed" should in every case be accessible 
 for measurement, sampling and full examination on all 
 
 sides. 1 Block A, on the diagram attached, showing four 
 exposed sides, is perhaps the more usual form met with 
 in a developed mine. Block B, however, with three ex- 
 posed sides, also comes under our classification of "ore 
 
 planes called foot and hanging walls are not considered as sides. 
 77 
 
developed," as would also any irregularly shaped ore- 
 body visible and fully accessible, on and along all por- 
 tions of its perimeter. 
 
 Inasmuch as "ore developed" forms the subject of the 
 highest possible, or most accurate, estimate engineers can 
 make of ore in place, it should be hedged in with the in- 
 variable and unalterable requirement, exposed on all 
 sides up to the full thickness of the ore. Under this con- 
 dition the estimates of independent examining engineers 
 shbuld agree within the limits of experimental error. As 
 a general rule, one is safe in stating that the smaller the 
 blocks of "developed ore" the more accurately can their 
 contents be estimated. These blocks, then, should be 
 of moderate dimensions. In ordinary vein mining the 
 levels are usually placed at intervals of 100 to 150 ft. 
 apart, as measured along the dip of the vein. I would 
 suggest as a safe rule, within these limits, that the length 
 of such blocks of "ore developed" should not exceed 
 twice their depth. 
 
 It may be suggested that it is not always imperative to 
 completely block out ore-ground before stoping. Quite 
 true. The parties, however, who are developing their 
 mines for the purpose of selling them, would be well ad- 
 vised to do so. Otherwise the ore partially blocked out, 
 and in various minor stages of development, must receive 
 separate and lower classifications. 
 
 For blocks of partially developed vein-material, hid- 
 den on one or more sides, I would suggest the phrase 
 "ore being developed," or, for shortness, "ore develop- 
 ing." Two levels, say, 150 ft. apart, simultaneously pene- 
 trating an ore-shoot, are, as they advance, daily increas- 
 ing the amount of "ore being developed," which, on fur- 
 ther opening up by winzes or raises connecting these 
 levels and cutting the ground into blocks, becomes "ore 
 developed." 
 
 "Ore being developed" naturally falls into three 
 classes: First, where one side only is Mdden; second, 
 where two sides are hidden; third, where three sides 
 are hidden. 
 
 78 
 
As an example of the first class, we will take block C, 
 which on a casual glance might appear just as safe an 
 estimate as block B. On closer examination, however, 
 it will be noticed that on the hidden side we can neither 
 determine the assay value of the ore, its thickness, nor its 
 actual termination. For example, if the shoot follows the 
 heavy line, as one naturally assumes it would, we have 
 data for a certain tonnage, while if it follows the dotted 
 line, we have an increased tonnage. Similar remarks ap- 
 ply to block D, showing h'ow the assumed tonnage might 
 be decreased. 
 
 It is therefore abundantly clear that a given block of 
 ground having one hidden side cannot be estimated as 
 closely as one having all sides exposed, inasmuch as in 
 the former about 25 per cent of the necessary data is un- 
 obtainable. We are therefore fully justified in excluding 
 the block having one side hidden from an estimate of 
 "ore developed," or, if you please, "ore in sight." 
 
 Again referring to the diagram, block E, w r ith two sides 
 hidden, cannot in the very nature of things be estimated 
 as closely as blocks C and D, hence we class it "ore de- 
 veloping," second class, while block F, with three sides 
 hidden, very naturally falls into the third class estimate 
 of "ore being developed." 
 
 We next come to the future value of the ore-shoot. In 
 other words, to what depth will the pay-ore extend ? We 
 assume the ore-shoot is of fairly uniform dimensions and 
 value ; that it continued so to the lowest point of explora- 
 tion, the 45O-ft. level on our diagram. The experience in 
 the district went to show that the horizon of pay-ore 
 extended to 1,000 ft. In this case the ore is not even 
 in a stage of "ore developing" ; it may be entirely in- 
 visible, yet one has reasonable assurance from the appear- 
 ance of the vein and ore-shoot, from the experience ob- 
 tained in adjoining properties,, and from other physical 
 phenomena, that pay-ore exists in this shoot to a depth 
 of at least 900 ft. ; consequently the engineer, after mak- 
 ing such allowances as he deems safe, looks forward with 
 confidence and reasonable assurance that the shoot of 
 
pay-ore will extend to some considerable depth, perhaps 
 to 1,000 ft. This I class as "ore expectant." It deals 
 rather with 1 the future than with the present, and more in 
 the region of the imagination than of fact, but is, never- 
 theless, an important factor in every mine valuation, deal- 
 ing as it does with the probable life of the property as a 
 producing mine. 
 
 "Ore expectant" is perhaps the most difficult estimate, 
 if estimate it can be called, that engineers are compelled 
 to make, because of the few facts available; hence it is 
 only to be supposed that opinions and estimates of dif- 
 ferent engineers must widely vary. While, therefore, 
 with "ore developed" the highest and most accurate esti- 
 mate of ore in place can be made, "ore expectant," in the 
 same sense, forms the lowest and least accurate. Very 
 few, if any, mine owners would sell a property for the net 
 value of the "developed" and "developing ore," unless 
 they had good reason to believe the mine to be practically 
 bottomed ; hence the necessity of having a phrase to 
 cover such estimates, as well as uniform and thoroughly 
 recognized rules to govern their compilation. 
 
 These three phrases, "ore developed," "ore being de- 
 veloped" and "ore expectant" should cover, in metal- 
 liferous mines, all estimates a mining engineer is called 
 upon to make. I now put them forward for the consid- 
 eration of the profession, not as the best possible names 
 and classifications, but as sound, useful and definite 
 phrases to govern ordinary estimates of mine valuation. 
 Th"ey will cover any condition I have met with in a prac- 
 tice extending over 25 years in this and other countries ; 
 and they have not only proved useful in my work, but are 
 also the best phrases I can evolve to correctly designate 
 clear and concise estimates. 
 
 Every report on a mining property should give the cost 
 of stores, the mining and milling cost, and the gross and 
 net values of the ores ; therefore it should not be a neces- 
 sary requirement to have "ore developed" always pay- 
 ore. TWe gross and net values at the time the examina- 
 tion is made will fully govern the then value, while at 
 
later dates the improvements in mining and milling can 
 usually be depended on to increase the net value, often 
 to the extent of showing good profits, in the course of a 
 few years, on formerly practically valueless ores. The 
 gross value is, when reported in ounces and percent- 
 ages of metals, always a fixed point of departure, from 
 which the net value can at all future times be deduced 
 when the price of the metals and cost of treatment are 
 taken into consideration. 
 
 It may be the ambiguous phrase "ore in sight" is so 
 deeply rooted in the minds of mining operators, pro- 
 moters and investors, that it cannot well be replaced 
 by a better one. I hope this is not so; nevertheless, 
 should these notes provoke a sound discussion of the 
 whole subject, preparing the way for definite classifica- 
 tions of ore estimates, with clear and concise rules gov- 
 erning each class, I shall feel that my efforts have been 
 to some purpose. 
 
 In conclusion, permit me to state that the various 
 methods of mine sampling, and the possible errors in 
 estimating tonnage and value, are excluded from the 
 scope of this letter. I simply desire to present for the 
 consideration of mining engineers the classifications 
 above outlined, and which 1 I summarize as : 
 
 Ore Developed. Absolutely and without variation, 
 ore exposed on all sides. 
 
 Ore Being Developed. First class, blocks with one 
 side hidden ; second class, blocks with two sides hidden ; 
 third class, blocks with three sides hidden. 
 
 Ore Expectant. The prospective value of a mine be- 
 yond or below the last visible ore, based on the fullest 
 possible data (clearly set forth) from the mine being 
 examined, and from the characteristics of the mining 
 district. 
 
 8 1 
 
COST PER TON AS A BASIS OF MINE 
 VALUATION.* 
 
 BY R. OILMAN BROWN. 
 
 Hardly second in importance to the determination of 
 value per ton, by careful and systematic sampling, is the 
 determination of cost per ton from the mine accounts. 
 The object of sampling has been attained when the gross 
 valuable contents of the ore exposed in the mine have 
 been determined. This, for the sake of convenience in 
 subsequent calculation, is usually reduced to value per 
 ton. From this gross value per ton must be deducted the 
 total cost per ton and the loss per ton in treatment, the re- 
 mainder being the net value per ton. Obviously an error 
 in cost per ton is just as important as an error in gross 
 value per ton, so that it is necessary to examine with as 
 careful scrutiny the method of obtaining the one as of 
 the other. Several pitfalls have been pointed out recently 
 in the columns of this JOURNAL which will be ignored in 
 this present article; or, rather, will be assumed to have 
 been satisfactorily avoided, the desire being not to obscure 
 another factor in valuation which has been touched upon 
 but lightly, if at all. 
 
 It is not intended in the present article to go into the 
 details of mine accounting, but it will be assumed that in 
 some way or other the engineer has obtained certain segre- 
 gated totals representing the expenditure during a definite 
 period in the various operations connected with mining 
 and beneficiating the ore, and that the sum total of these 
 segregated accounts represents the total cost of operations 
 for the period in question. 
 
 It is usual to divide these segregated totals by the tons 
 
 *From THE ENGINEERING AND MINING JOURNAL of August 29, 1903. 
 82 
 
of ore treated during the same period, and to call the 
 quotients the cost per ton for the various departments. 
 In a certain sense the sum of these is a cost per ton, though 
 not properly to be considered the cost per ton, as the 
 result is rather a hazy approximation representing, per- 
 haps, average work for the mine, but not sufficiently defi- 
 nite to be used with confidence in the delicate work of 
 valuing ore reserves. 
 
 Let us assume certain natural divisions of the accounts 
 into stoping, development, reduction and general expenses. 
 All the segregations can be easily grouped under these 
 headings ; and this would naturally be done in the process 
 of arriving at the cost, in the manner to be described. In 
 the inexact method commonly employed, these totals 
 would all be divided by the same tonnage probably by 
 the tonnage reported from the mill or reduction works, 
 whereas, this would only give true results for the last 
 two items, namely, reduction and general expense. For 
 stoping, the result might be approximate except in the 
 case of a mine carrying a considerable amount of ore in the 
 stopes. For development, it could only give the true value 
 when the same amount of ore was stoped as was developed 
 during the period. If development fell behind, the result 
 per ton would be too little; if it exceeded the output, it 
 would be too much. 
 
 This is the general statement of the matter, but it can 
 be made clearer by considering a concrete case. It is 
 proper to say that this, though based on practice, has been 
 elaborated, with the assumption of certain values, to suit 
 more general conditions. 
 
 The period is 12 months. 
 
 Tons treated, 50,000. 
 
 Total return per ton, $5.26. 
 
 Total loss per ton, 64c. 
 
 Total gross value per ton in ore, $5.90. 
 
 Below is given in tabulated form the costs of the va- 
 rious departments and the costs per ton, as commonly 
 calculated : 
 
 -8 3 
 
Per ton 
 
 on basis 
 
 of tons 
 
 Total. treated. 
 
 Stoping $58,000 $1.16 
 
 Development S * 000 J- 00 
 
 Reduction 92,000 1.84 
 
 General expenses 22,000 .44 
 
 Total $222,000 $4.44 
 
 The following tonnages are also given : 
 
 Tons. 
 
 Ore broken in the stopes > 10,000 
 
 Ore standing, blocked out, ready for breaking 100,000 
 
 Ore reasonably expected, but partly, if at all, developed. .. 50,000 
 
 Total 160,000 
 
 These are the quantities assumed to be found by the 
 engineer on his investigation of the property, and the re- 
 coverable value per ton will be taken at the average of the 
 past year, which we will assume to have been determined 
 to be the fact by careful sampling. The most natural way 
 of calculating the value of these reserves would be as 
 fellows : 
 
 Total recoverable value of 160,000 tons, at $5.26 $841,600 
 
 Costs on 160,000 tons, at $4.44 710,400 
 
 Apparent profit in reserves $131,200 
 
 This is manifestly incorrect. Stoping and develop- 
 ment should not be charged against ore already broken, 
 nor should development be charged to that standing 
 blocked out and ready for stoping. The estimate should 
 read as follows, assuming the figures for cost per ton 
 to be correct: 
 
 10,000 tons broken in stopes, at $2.28 per ton for milling 
 and general expense $22,800 
 
 100,000 tons developed, ready for stoping, at $3-44 ($2.28 
 + $1.16) 344,ooo 
 
 50,000 tons, reasonably expected, but not developed, at 
 $4,44 222,000 
 
 Total costs $588,800 
 
 160,000 tons, recoverable value as above 841,600 
 
 Net profits 252,800 
 
 The cause of the great difference is obvious. It should 
 be noted that in the accounts, transportation and handling 
 
 84 
 
costs are assumed to belong in general expenses. The 
 above figures must be taken as thrown in, apart from the 
 fundamental matter with which this article opened and 
 they contain errors, as was indicated in our opening lines. 
 
 Reduction costs and general expense are properly re- 
 duced to the per ton basis by dividing by 50,000 tons, but 
 stoping and development cannot properly be so reduced 
 until we know whether 50,000 properly represents the tons 
 stoped and the tons developed. In what follows we are 
 using some quantities that an engineer examining the 
 property can scarcely have come at directly, and indeed 
 he will be fortunate if he has them at all ; but, recognizing 
 their importance, by inquiry and estimate, he must arrive 
 at some sort of a probable value for them. 
 
 We have, as a general proposition, that the actual 
 amount of ore broken during the year is equal to the ore 
 on hand broken at the end of the year, plus the ore treated 
 during the year, and minus the ore on hand broken at the 
 beginning of the year. In the same way the ore devel- 
 oped during the year is equal to the ore blocked out at the 
 end of the year, plus the tons of ore broken during the 
 year, and minus the ore standing blocked out at the be- 
 ginning of the year. Applying this to our concrete case, 
 we will assume the following values for tonnage at the 
 beginning of the year : 
 
 Tons. 
 
 Broken in the stopes 20,000 
 
 Standing blocked out 120,000 
 
 Reasonably expected 60,000 
 
 Ten thousand tons plus 50,000 minus 20,000, equals 
 40,000 ; which turns out to be the actual ore stoped during 
 the year, so that the true cost of stoping per ton is 58,000 
 divided by 40,000, equals $1.45 per ton. In the same way 
 100,000 plus 40,000 minus 120,000, equals 20,000 tons, the 
 actual ore developed during the year; and $50,000, the 
 total spent on development, divided by 20,000 tons, equals 
 $2.50 per ton, the true cost of developing a ton of ore. 
 Inasmuch as no costs are credited in this discussion to the 
 ore reasonably expected, we need not carry this further, 
 
 85 
 
though the same reasoning would hold in regard to it. 
 Collecting our true cost per ton we have : 
 
 Stoping $1.45 
 
 Development 2.50 
 
 Reduction 1.84 
 
 General expenses 44 
 
 Giving the true total cost per ton at $6.23 
 
 This shows that the ore at this mine will not actually 
 pay expenses for handling unless greater economies can 
 be practiced; whereas, our first calculation gave a profit 
 per ton of about 80 cents. To a certain extent, then, the 
 matter concerns the mine manager as well as the exam- 
 ining engineer, though it is in the interest of the latter in 
 particular that this article was prepared. 
 
 Proceeding next with the valuation of ore reserves, we 
 reproduce our earlier figures with the corrected costs 
 introduced : 
 
 10,000 tons, broken, at $2.28 per ton $22,800 
 
 100,000 tons, developed, ready for breaking, at $373 ($2.28 
 
 + $1.45) per ton. : 373,ooo 
 
 50,000 tons ore, reasonably expected, at $6.23 3i I ,5oo 
 
 Total $707,300 
 
 Recoverable value, as above 841,600 
 
 Net value on the reserves I34>30O 
 
 In order to lay the whole matter more clearly open and 
 even at the risk of being tedious, it is worth our while to 
 make another assumption regarding tonnages at the be- 
 ginning of the period, as below : 
 
 Tons. 
 
 Broken in the stopes None. 
 
 Standing ready for breaking 80,000 
 
 The tonnage and cost per ton follow in summary : 
 
 Tonnage Cost 
 
 for year. per ton. 
 
 Stoping 60,000 97c. 
 
 Development 80,000 fee. 
 
 Reduction and general expense, as be fore. 50,000 $2.28 
 
 Total .$3.87 
 
 On this basis, the value of the ore reserves is : 
 
io,ooo tons, broken in slopes, as before $22,800 
 
 100,000 tons, ready for sloping, at $3.25 ($2.28 + 070.) 
 
 per ton 325,000 
 
 50,000 tons ore, reasonably to be expected, at $3.87 193,500 
 
 Total charges $541,300 
 
 The gross recoverable value, as before 841,600 
 
 Profit in reserves 300,300 
 
 The differences shown clinch the statement with which 
 this paper opened. 
 
 As a summary of the above there are two general prin- 
 ciples to be enunciated: 
 
 (A). Cost per ton is the quotient of total cost divided 
 by the actual tonnage resulting from that expenditure. 
 
 (B). Net value per ton is the gross recoverable value 
 per ton, less cost per ton for those natural divisions of the 
 work still to be performed upon the different classes of 
 ore. 
 
 Although the above principles are fundamental, like all 
 general statements, they may easily be pressed to ex- 
 tremes, and it is for the engineer, after analysis of the 
 situation, to decide the particular extent of their applica- 
 tion ; a failure to recognize them at all, on the other hand, 
 may invalidate the conclusions drawn from otherwise re- 
 liable work. 
 
MINE VALUATION.* 
 
 BY J. PARKE CHANNING. 
 
 May it not be possible to have a mine with too much 
 "ore in sight"? I ask this question because the gen- 
 eral tenor of the discussion on mine valuation has made 
 "ore in sight" the crucial test of the value of a property. 
 
 If based on this test, many of our good iron mines 
 would make a sorry showing; and yet their capacity for 
 production is well known, and year after year they come 
 up to expectation. If one has a fairly regular deposit, is 
 anything to be gained by rushing the openings so that 10 
 or 20 years' supply of ore is opened up ? Will not the in- 
 terest charges on the cost of this development, the expense 
 of re-timbering the openings and the pumping charges be 
 a heavy drain on the income ? 
 
 In Butte, to-day, litigation has forced development to 
 such excess that it is estimated that certain drifts will have 
 to be re-timbered four times before the ore is stoped. 
 Several of the prominent Lake Superior copper mines 
 have ground opened up many years in advance with but 
 questionable benefit, as the drifts driven every 100 ft. do 
 not show the full width of the lode and the rock from 
 these openings has not been stamped by itself, so as to 
 show its yield. Cutting out stopes every 300 ft. would at 
 least have been cheaper and have given more idea of the 
 yield to be expected. 
 
 The president of a prominent western railway boasted 
 that he had just added to the company's coal-land hold- 
 ings a 90 years' supply. A little figuring showed him 
 that the interest on his investment would make his coal 
 90 years hence pretty expensive. 
 
 A few years ago Prof. Robert Peele, Dr. John H. Banks 
 and myself were required to place a valuation on four 
 
 'From THE ENGINEERING AND MINING JOURNAL of September 12, 1903. 
 88 
 
pyrite mines for a proposed consolidation. They were in 
 various stages of development, and one of them had more 
 ore in sight than the combined tonnage of the other three. 
 This large tonnage left in the mine consisted of ore which 
 in the earlier days would have produced fines then of little 
 value. At the time of the examination the development 
 of mechanical roasting furnaces had placed fines on a par 
 with lump, and this ore was now available for extraction. 
 The question arose, What value was to be given to this 
 ore in sight ? I quote from our report : 
 
 "We have taken the ground that in mines of this char- 
 acter the deposits are so regular that the better test of 
 their relative values is to be found in their capacity for 
 production per 100 ft. of depth, rather than in the number 
 of tons of ore available for immediate shipment; that is, 
 'in sight.' Taking, as we do, this view, we desire to mini- 
 mize the effect produced on the value of each mine by the 
 varying amounts of ore in sight, believing, for example, 
 that by sinking B mine and C mine each about 200 ft., and 
 running the necessary drifts, we would have in each of 
 these mines an amount of ore in sight equal to that at A 
 mine. This result would be accomplished by the expen- 
 diture of a comparatively small amount of money in each 
 case, which would be charged to development." 
 
 Following this line of reasoning, and attempting per- 
 haps the rather difficult task of "giving mathematical ex- 
 actness to phenomena governed by the complex laws of 
 nature," we evolved the following formula : 
 V = 5 ax + by + c, in which 
 V = Value of the mine. 
 a = Net profit per ton of ore mined. 
 x = Annual estimated output in tons. 
 b =. Cost of development per ton of ore opened up. 
 37 = Tonnage of ore in sight above the bottom level. 
 c = Value of the equipment and stocks on hand. 
 
 In the above formula it will be seen that the practical 
 valuation of the mine was assumed at five times the an- 
 nual profit. The figures substituted in the above formula 
 for the four mines were as follows : 
 
x y 
 
 a Tons. b Tons. c V 
 
 A $0.84 96,500 $0.062 293,000 $97,100 $520,566 
 
 B 0.94 120,500 0.058 88,800 115,400 686,900 
 
 C 1.15 79,5oo o.ioo 117,200 67,650 536,495 
 
 D 0.91 15,000 0.150 63,000 35,ioo 112,800 
 
 Some three years later I had almost the same problem 
 in a group of copper-silver-gold properties in a western 
 State which it was proposed to consolidate, as the various 
 ores, with the addition of a little limestone, would make a 
 most economical smelting mixture. In this problem the 
 copper mines E and H were well opened up, while the two 
 silicious gold and silver mines F and G had not the open- 
 ings and development that proper mining would demand. 
 The bottoms looked fairly well and the past records were 
 good, but no such assurance of "future performance" was 
 to be counted on as in the regular gyrite mines previously 
 described. 
 
 From the data available the following figures were 
 
 compiled : Owner's 
 
 ay -f c ax price. 
 
 E $800,000 $284,375 $6,000,000 
 
 F 128,000 112,000 , 250,000 
 
 G 866,000 630,000 3,200,000 
 
 H 600,000 175,000 750,000 
 
 $2,394,000 $1,201,375 $10,200,000 
 
 In the above ay + c represented the profit in sight, the 
 tonnage in sight y being multiplied by the estimated profit 
 per ton a, instead of by b, as in the pyrite mines. 
 
 The figures ax were only tentative in this case, and 
 would have to be used as a guide only. 
 
 The scheme of consolidation was never carried out on 
 account of the high valuation placed upon their properties 
 by the owners of E and G. The owners of E wanted 60 
 per cent of the consolidated stock, while they had but 33 
 per cent of the total value in sight and were capable of 
 contributing only 25 per cent of the earnings. The own- 
 ers of G were not unreasonable in their demands, were it 
 not for the fact that their future was doubtful and with 
 only a little over one year's ore in sight they were demand- 
 ing a five years' purchase. 
 
 Had the decision been in my hands I would have con- 
 
solidated on the following basis : E, $2,000,000 ; F, $250,- 
 ooo ; G, $2,000,000 ; H, $750,000 ; total, $5,000,000. 
 
 I give these two cases, the first showing the extreme 
 limit in which "profit in sight" is almost negligible. The 
 other limit in which "profit in sight" is a sine qua non has 
 been gone into most thoroughly by your previous con- 
 tributors. My second case is a mean between the two; 
 and in estimating the value of a property either as an 
 arbiter or for a purchaser the engineer must integrate his 
 equation between the two limits. Buying a mine on the 
 basis of "profit in sight" is much like dealing in pork or 
 dry goods, and needs not the services of a trained engineer 
 as much as it does careful, plodding samplers and as- 
 sayers. 
 
 What I wish to bring home to the engineer examining 
 properties for an investor is the point that his client's 
 greater profits are not to be made from the purchase of 
 those properties where the "profit in sight"' is so great, but 
 from those which the engineer's judgment tells him will 
 improve with development. As the late Marcus Daly said 
 to one of his men who had spent two years in fruitless 
 search for a mine, "Why the devil don't you get reckless 
 once in a while and spend forty or fifty thousand dollars ?" 
 
DISCUSSION. 
 
 ORE DEVELOPED. 
 
 The Editor: 
 
 Sir. It is with some diffidence that I venture to ques- 
 tion the advantage of Mr. Philip Argall's proposed 
 classification of ore-tonnage estimates as used in mine 
 reports. I am, of course, ready to agree that "ore in 
 sight" is always an unwise and, frequently, a misleading 
 expression, as applied to ore-ground in place ; the phrase 
 is sufficiently discredited by this time for its use to be 
 discontinued by general consent. 
 
 But may not any other definition prove misleading to 
 a less extent? Take, for instance, Mr. Argall's "ore de- 
 veloped" meaning, in all cases, "ore exposed on all 
 sides." Most of us have known, many of us have ex- 
 perienced, cases where blocks of ore so exposed on four 
 sides have been found to enclose a large barren patch 
 in the center. However rigid a rule we may adopt, we 
 cannot arrive at certainty. 
 
 The amount of weight to be attached to exposure on 
 four sides, on three, on two, or one one only, varies with 
 the conditions of each particular case. Fig. I, for in- 
 stance, shows a section of vein-workings from which, 
 with other data, estimates were made by my brother, 
 the late Arthur L. Collins, under the three headings of 
 "positive ore," "probable ore," and "possible ore." 
 Who, after examining the section, and bearing in mind 
 the phenomenal lateral extension of the ore-body shown, 
 can doubt that far more reliance can be placed on blocks 
 marked in the section as "positive ore," even though 
 some of them are exposed on three sides only, than 
 on many blocks opened up on four sides in veins where 
 the ore-bodies are of the bunchy and erratic type which 
 we must recognize to be, after all, by far the most fre- 
 
 93 
 
quently encountered? Even the "possible ore" of Fig. 
 i ground where the ore is proved to exist on one side 
 only can be depended on to a far greater extent than 
 usual. 
 
 My contention is that the amount of evidence to be re- 
 quired when making estimates of ore-tonnage, and the 
 number and nature of classes into which estimates 
 should be divided, must depend on our general conclu- 
 sions as to the nature and permanence of the ore- 
 bodies in the mines under consideration, the distance 
 between the workings, etc. I do not think that any 
 rules can be made which will lessen the necessity for de- 
 pendence on the examining engineer's individual judg- 
 ment ; and I distrust all cast-iron classifications, which 
 do not allow for the infinite complexity of natural con- 
 ditions. The only useful general rule is that no estimate 
 of tonnage should be made unless accompanied by 
 sketches indicating the basis on which it rests. 
 
 I understand Mr. Argall to suggest that, as it is fre- 
 quently not advisable in the ordinary course of mining 
 to block out ore so as to come under his definition of 
 "ore developed," parties desirous of selling should go to 
 the additional expense of doing so. While, however, 
 I admit that the valuation of mines for sale-purchase is a 
 very important duty of the mining engineer, I cannot see 
 that methods of mining should be modified to suit it. A 
 mine primarily exists for the purpose of being worked to 
 the greatest economical advantage, and an engineer must 
 expect to make his estimates conform to the particular 
 case. There are many instances where the additional 
 openings which would become necessary to bring proved 
 ore-ground within the limits of Mr. Argall's definition of 
 'ore developed" would increase the cost of exploitation 
 to such a figure that the profit-margin would be seriously 
 curtailed. 
 
 Take, for instance, the ore-body shown in Fig. 2 a 
 case which is typical of perhaps the largest number of 
 ore-bodies in fissure-veins. Such ore-bodies are usually 
 most economically developed by a single raise through 
 
 94 
 
the ore, as shown. According to Mr. Argall's classifica- 
 tion there is no "ore developed." Yet, certainly the ore 
 is there, more or less ; it is certainly developed, so far 
 as it is economically required to be. I have indicated 
 by shading the basis which I should have taken for the 
 purpose of making an estimate of ore developed. Such 
 ore is by no means certain, nor is any other ; but I should 
 use such words in referring to it as would clearly signify 
 with what degree of confidence I regarded it. Actual 
 
 Limits of pay ore as 
 ultimately worked out. 
 
 FIG 2. 
 ORE DEVELOPED, AS ESTIMATED FROM WORKINGS SHOWN. 
 
 certainties as to ore are reached only after it has been 
 crushed and sampled ; and I might almost add, paid for. 
 
 It would be a mistake to sacrifice the two essentials, 
 clearness and accuracy, for the sake of getting concise 
 and well-sounding phrases; and equally so to attempt 
 to classify all possible estimates of ore under prejudged 
 headings. Nature does not always plan ore-occurrences 
 to suit our systems of classification. 
 
 While it hardly comes within the limits of the same 
 
 95 
 
discussion, I would say a word in favor of the prospect- 
 ing pick for purposes of mine sampling, notwithstand- 
 ing the authority of Mr. T. A. Rickard. I have found 
 that by the alternate use of the pick and hammer ends, 
 very fair samples can be taken in all but exceptionally 
 tight ground, where the single jack and moil become 
 necessary. It has the additional advantage that an en- 
 gineer can take his samples personally, and that the time 
 and labor of sampling are greatly lessened; points of 
 which Mr. Rickard would be the first to admit the sig- 
 nificance. It certainly, however, requires more indi- 
 vidual judgment on the part of the sampler. 
 
 I remember a case where I took a large number of 
 samples alone, some time after sampling by a very 
 prominent firm, the evidence afforded by their grooves 
 still standing to show that the work was properly done. 
 In this case the subsequent working of the mine proved 
 that my average was more reliable ; by no means because 
 it was done in a more honest or painstaking manner. 
 
 GEORGE E. COLLINS. 
 Denver, Colo., Feb. 24, 1903. 
 
 The Editor: 
 
 Sir. The letter of Mr. George E. Collins, in the issue 
 of the JOURNAL for March 14, 1903, continuing the dis- 
 cussion in regard to sampling and estimates of ore, in- 
 duces me to offer a few suggestions along the same line 
 of criticism. Mr. Collins says : "The amount of weight 
 to be attached to exposure on four sides, on three, on 
 two, or on one only, varies with the conditions of each 
 particular case." And further on, "And I distrust all 
 cast-iron classifications, which do not allow for the 
 infinite complexity of natural conditions." 
 
 However much ability the man to whom the examina- 
 tion of a mine is entrusted may have to sample the avail- 
 able ore geometrically blocked out, he is unworthy the 
 confidence reposed in him if he is unfamiliar with, or 
 neglects to take cognizance of, the principles which 
 
 96 
 
govern the deposition of ores. A knowledge of these 
 geological principles implies not only mineralogical 
 training, and a knowledge of the broad general rules by 
 which ore-deposits, through the accumulation of ex- 
 perience, have been classified, but it includes a consid- 
 eration of the nature of the enclosing and adjacent rocks, 
 and, what is more important, a recognition of the phe- 
 nomena of ore-shoots. 
 
 The much-abused term, ore-shoot, or shoot of ore, as 
 applied to mineral veins, may be defined as that portion 
 of a metalliferous deposit within whose boundaries the 
 mineral mass is commercially valuable. This definition 
 purposely omits specifying the shape of an ore-shoot, 
 and any reference to the reasons for its existence. It is 
 evident that the form and size of the ore-shoots in a 
 given mine must depend, not on any scientific law, but, 
 for the most part, upon the actual working expenses. 
 In a mine which has been worked for a period of years, 
 th'e worked-out portions of the vein usually afford, by 
 their form and dimensions, a fairly reliable index of the 
 size and shape of the ore-shoots for that mine, but for 
 that mine alone. 
 
 The mining engineer who examines and reports on a 
 mine in which the ore-shoots have thus been defined by 
 local experience may commit an act of injustice to the 
 intending purchasers, to the vendors and to himself, 
 if he neglects to moderate his calculations, based upon 
 the actual sampling of ore blocked out, by a proper 
 consideration of the system of ore-shoots as developed 
 by previous workings. 
 
 In a mine whose workings are on a fissure-vein, ex- 
 perience has shown that the ore-shoots lying in the 
 plane of the vein have frequently a considerable amount 
 of regularity, as regards size and distribution. This is 
 especially the case in veins whose principal gangue is 
 quartz, and whose values consist of any or all of the 
 minerals, gold, silver, lead and copper. The engineer 
 should consider it a part of his duty to ascertain if 
 the characteristics of the ore-shoots in the vein he is 
 
 97 
 
examining are peculiar to that particular mine, or are 
 duplicated in other mines of the same district. The 
 gathering of such data is frequently rendered impossible 
 by local jealousy or other motives. The data are usually 
 obtainable, however, and sometimes detailed published 
 maps of the district in question exist. In most large 
 mining districts of the world, both surface and under- 
 ground data have been published and are available for 
 those who care to use them. If the vein under examina- 
 tion is one of a series, upon which operations in different 
 mines have been conducted for a long period, and which 
 have been shown to present a uniformity or similarity of 
 conditions, the engineer has a largely increased supply 
 of material at hand from which he may draw conclu- 
 sions. 
 
 To take another example of ore-deposits, if the mine 
 in question is operated on a silver-lead bedded lime- 
 stone deposit, of the kind sometimes referred to as a 
 "contact," the form of one ore-shoot may afford no clue 
 as to the form of the next one to be encountered. From 
 the very origin of such 1 a deposit, it may generally be 
 assumed that the occurrence of the ore will be subject to 
 less definite laws than is the case in fissure-veins. It 
 is occasionally found, however, that a definite local dis- 
 position of the ore in shoots in a bedded silver-lead 
 or zinc deposit occurs. The engineer, in examining a 
 mine in which such an occurrence has been proved by 
 the work already done, will naturally be at fault if he 
 takes no account of the history of the property and its 
 previous underground development. He will, however, 
 be likely to exercise unusual caution in estimating the 
 three classes of "positive," "probable" and "possible" 
 ore, when dealing with a class of deposits which 1 are 
 genetically connected with the chemically induced re- 
 placement of limestone by metallic sulphides. 
 
 In the accompanying diagram (plan) the ore-body rep- 
 resented is an occurrence in a limestone bed, say, 7 ft. 
 thick. The bed, itself lying flat, is heavily mineralized. 
 The carbonate of lime has been replaced by metallic sul- 
 
 -98 
 
phides carrying values. The enclosing beds, namely, 
 those lying above and below, are barren, and the min- 
 eralized bed itself contains barren patches, sporadically 
 distributed. Assume that the ore-body thus defined, a 
 portion of which is here represented, had dimensions as 
 follows : Seven feet thick, that is the thickness of the 
 limestone stratum, 150 ft. long and 90 ft. wide. The 
 
 PLAN OF A PART OF THE WORKINGS OF A SILVER-LEAD 
 MINE IN HORIZONTALLY BEDDED LIMESTONE. 
 
 four tunnels represented are all run in this ore-body, 
 and by their intersections enclose a portion of it, A B 
 C D. In other words, a block of ore is exposed on four 
 sides, 7 ft. thick, 45 ft. wide, and 70 ft. long. If one 
 should apply an arbitrary rule of sampling in the ex- 
 amination of the mine in which this case occurs, the ore 
 in question must be classed under the head of "positive." 
 While not questioning the correctness of his classifica- 
 tion, I have endeavored to show, by the diagram, the 
 error to which' the examiner would be liable, should he 
 estimate the block represented by A B C D as ore. On 
 the other Hand, if the examiner takes into consideration 
 
 99 
 
the geological principles on which the class of limestone 
 silver-lead deposits depends, he will probably allow in 
 his calculations for the possibility of the presence of the 
 patch or horse of barren limestone L. At any rate, 
 he will be most assiduous in his efforts to find out if 
 patches of normal limestone, unaffected by the ore-bear- 
 ing solutions, have been encountered in previous work- 
 ings of the mine, or in the surrounding mines of similar 
 character. 
 
 The term ore-sh'oot may be said to be a development 
 of the experience of that invaluable member of the min- 
 ing profession, the mine foreman. His every-day con- 
 tact with the ore, and with the profit and loss conditions 
 of handling it, makes him keen to recognize its slightest 
 variations, so far as can be judged from its appearance. 
 The very fact, however, that the term "shoot of ore" 
 has primarily a commercial and not a scientific defini- 
 tion, has resulted in an exceedingly loose application of 
 it. 'Would it not be an advisable point for discussion 
 as to whether the word "shoot" should not be more 
 closely limited in its uses ? 
 
 A fissure may be primarily of varying width, especially 
 when the enclosing walls are slates or metamorphic 
 schists, and the vein is conformable in strike with their 
 schistosity. The vein-filling, or ore, with which the 
 fissure has been filled, may, when drifted on, present at 
 one station a width of 6 ins., and at another, perhaps 100 
 ft. farther along, of 6 ft. Assume that the ore carries 0.5 
 oz. in gold. There may be a recurrence of the wide and 
 narrow portions of the fissure, giving a succession of 
 lenses of ore. Naturally the drift must be carried wide 
 enough for the operations as long as the vein is followed. 
 The vein will be stoped only in those portions where the 
 vein-filling widens to such' an extent as to warrant its 
 being extracted and milled, or, in other words, where it 
 may be defined as pay-ore. In those parts of the vein 
 where the vein material occupies only 6 ins., or possibly 
 even a narrower space, no more ground will be broken 
 than necessary, and the foreman will define the inter- 
 
V 
 
 vening narrow space along the drift, between any two 
 lenses of ore, as barren ground. His "shoot" will be 
 limited in its length along the drift by th'e imaginary 
 planes between which the two walls of the lenticular 
 opening in the vein contain sufficient ore to be profit- 
 ably extracted. All inside the wide part of the vein will 
 be the "shoot," and all outside will be reckoned, for the 
 time being at least, as "barren ground." 
 
 On the other hand, take the example of a fissure-vein, 
 with straight parallel walls, and with a width of 3 ft. 
 The filling is quartz-gangue containing sulphides, and 
 the width does not vary for long distances. In certain 
 portions the operations have shown that high values 
 in gold and silver occur in the vein-matter, while other 
 portions, indistinguishable by their physical character- 
 istics from the ore, are practically waste-rock. I need 
 not recall to miners, and to those familiar with mines 
 generally, how frequently such alternations of rich and 
 barren vein-matter occur. 
 
 The last case cited is, according to the present system 
 of nomenclature, as much an occurrence of ore in shoots 
 as is the instance of the vein of varying width in slate 
 country, where the distribution of the shoots depended 
 on the form of the original fissure. In the one instance 
 the shoot resulted from physical causes; in the other 
 the distribution of the shoots was due to chemical dif- 
 ferentiation in the solutions from which it was deposited. 
 Explanations of the selective activity exhibited by these 
 solutions, resulting in the formation of shoots of ore, 
 are, up to the present, largely speculative. In addition 
 to the above two classes of ore-shoots must be consid- 
 ered those occurring in connection with fissure-veins 
 in bedded deposits. In these the chemical action result- 
 ing in their formation has been in some cases controlled 
 by physical causes. A consideration of them is hardly 
 pertinent to the point I have raised regarding shoots 
 in fissure-veins. 
 
 I can hardly allow to pass one point made by Mr. Col- 
 lins in his valuable letter. In Fig. 2, of the illustra- 
 
tions accompanying his article, he shows "a case which 
 is typical of perhaps the largest number of ore-bodies 
 in fissure-veins/' The shape of the ore-body figured by 
 Mr. Collins, I am inclined to think, is of a rather excep- 
 tional kind. From the context it is to be inferred that 
 Fig. 2, of Mr. Collins, represents a shoot of ore in a 
 vein. Shoots of ore in fissure-veins, as they have been 
 defined above, my experience has induced me to believe, 
 have in the majority of cases a lenticular form, whatever 
 their origin. A definite pitch in the plane of the vein is 
 generally characteristic of them. The pitch may make 
 any angle with a horizontal line representing the strike 
 of the vein. The longest axis of the shoot may form a 
 right angle with this horizontal line, or again the longest 
 axis of the shoot may coincide with the horizontal, con- 
 stituting the "course" of the Cornish miner. The main 
 point I wish to make is that, in the majority of cases 
 hitherto noted, it has been found that the longest axis 
 of an ore-shoot is a straight, or nearly straight, line, and 
 not a curved line in the sense figured by Mr. Collins. 
 
 My contention is not that ore-shoots of very irregular 
 form do not occur, and the above criticisms and remarks 
 are offered mainly in the hbpe that those who have ob- 
 served the phenomena extensively will record the results 
 of experience. The literature of ore-shoots is not ample, 
 and no one will deny that the subject possesses much 
 practical interest and importance in its relation to the 
 mining industry. 
 
 C. W. PURINGTON. 
 
 Denver, Colo., March 24, 1903. 
 
 The Editor: 
 
 Sir. This excellent series of articles is without ques- 
 tion the best presentation of the difficult and important 
 subject of mine sampling that has yet appeared; neverthe- 
 less, there are, I believe, a few points that have not been 
 treated as fully as their importance demands, and some 
 
others where there is at least room for discussion as to 
 the better practice. As Mr. Rickard says, "No two men 
 set to work in exactly the same way." Each person nat- 
 urally believes his own system the best or he would 
 not follow it. Consequently, I propose briefly describing 
 the methods that have in my experience given the best re- 
 sults in such cases. 
 
 Size of Sample. The engineer having decided the 
 proper distance between the points of sampling, it next 
 becomes necessary to determine the safe weight of the 
 original sample, taking fully into account the nature of 
 the ground and its breaking qualities. The sample is then 
 estimated at so many pounds per foot in width of the vein. 
 In gold and silver mines from 2 to 10 Ib. should cover the 
 limits in ordinary cases, and an average of, say, 5 Ib. per 
 foot will usually be found quite safe. Thus a vein 10 ft. 
 wide would give a 5<>lb. sample. This factor determined 
 for the particular vein under consideration, the samplers 
 should be instructed as to the width and depths of the 
 sample cuts required, and, as a check on the accuracy 
 of their work, the samples should be weighed, and those 
 exceeding 10 per cent, variation from the adopted stan- 
 dard rejected. The irregular weight of samples is a 
 fruitful source of error in mine examination because the 
 excess weight invariably comes . from the softer and 
 usually richer portion of the vein, or else it comes from 
 loose or shattered rock containing, in its fissures, con- 
 centrated vein material not rightly belonging to a true 
 sample. Large samples are usually a mistake in the sys- 
 tematic sampling of a gold or silver mine, and so we rely 
 on "The smallest sample consistent with securing a true 
 average of the lode at each place sampled." 
 
 Marking the Position of the Samples Where arbitrary 
 distances are chosen for the points of sampling, the posi- 
 tion of each cut should be marked off in advance and tied 
 to cross-cuts, survey stations, and other prominent marks, 
 so as to check up with the general plan of the mine. The 
 position of each cut is best marked with a number, pre- 
 ferably the sample number, painted or chalked on the rock 
 
 103 
 
at one side of the workings; this facilitates re-sampling, 
 or the examination of the cut, as one can walk directly to 
 the point. It is a great advantage to the engineer to be 
 able to examine the sample cuts while they are yet fresh, 
 and, having with him the assay value of the ore, he will 
 then quickly see from the nature of the mineral exposure 
 those places that appear abnormally high or low and order 
 the re-sampling accordingly. 
 
 Examining the Places to be Sampled. After the posi- 
 tion of the proposed sample cuts is established as above 
 explained, the vein at the places marked is carefully ex- 
 amined, brushed, or washed clear from accumulated dust, 
 
 mud or dope, and irregular projections knocked off, so 
 that the cut will be practically at right angles to the dip 
 of the vein, or, at least, a straight line across the ore to be 
 sampled. 
 
 In Fig. i the hard portions A, B should be removed 
 before sampling. 
 
 Fig. 2 shows at once one of the most difficult samples 
 to take, as well as the most fruitful source of error in mine 
 sampling. I have usually seen in such cases the ordinary 
 sampler make a cut around the back of the drift from A 
 to B, say, 8 ft., whereas the vein would not be over 6 ft. 
 wide, and so reported. To accurately sample such a sec- 
 tion is well-nigh impossible, and so it is often advisable 
 
to shoot off the wings on the walls, preparatory to 
 sampling. 
 
 Taking the Sample. A moil and hammer are the best 
 all-round tools for the sampler, though a heavy pick in 
 medium ground will usually give a thoroughly even cut 
 and hence a correct average. A box to catch the cuttings 
 is perhaps as good and convenient as anything ; it should 
 not, however, be much, if any, wider than the cut, par- 
 ticularly in vuggy or porous ground, as the pounding may 
 shake loose (and into a larger box) more or less fine and 
 possibly rich material, from outside the sample cut, and so 
 salt the sample. Where this sort of thing is suspected, it 
 is best to use one's hand to remove or catch the chips or 
 rocks as they are loosened by the moil. 
 
 Where two sets of samplers are employed, I invariably 
 work them together, giving one the odd and the other the 
 even numbers ; this helps to eliminate the personal ele- 
 ment, and tends towards uniformity of practice. It is 
 also safer. 
 
 Checking the Sampling. It is always expedient to re- 
 sample a certain portion of the cuts, say, from 5 to 10 per 
 cent, varying on the importance of the work. Where the 
 examining engineer is depending on assistants to do the 
 regular sampling, these check samples should be his 
 especial care. When samples cannot be assayed at the 
 mine or in the immediate vicinity, the engineer is at a 
 considerable disadvantage. In such cases he must, as a 
 safeguard, take a large number of check samples, par- 
 ticularly of the more important cuts, say, not less than 20 
 per cent ; otherwise he may have to pay a second visit to 
 the property for the purpose of checking up some of the 
 sampling, which, from the look of the charts, may not 
 conform to other work and may, or may not, be correct. 
 In most important mine examinations an assayer forms 
 one of the party, and the samples are assayed on the 
 ground. In such cases check samples should be taken im- 
 mediately the work is started. These thoroughly test the 
 whole process of sampling in the mine, the cutting down 
 of the samples, and also the assaying. It is only such work 
 
 105 
 
as this, checking the original assay, that gives one confi- 
 dence in the methods employed, and at the same time 
 serves as a perfect safeguard against salting. 
 
 When all possible precautions are taken, two samples 
 from the same cut across the vein will seldom check with 
 that exactness expected from original and duplicate 
 samples taken by sampling machines from a lot of crushed 
 ore. In a recent examination I decided to re-sample in the 
 original cuts two strips of poor ground occurring in shoots 
 of pay ore. Here are the results : 
 
 Orig. sample. 
 
 Re-sample. 
 
 Orig. sample. 
 
 Re-sample. 
 
 $2.54 
 
 $3-54 
 
 $1.17 
 
 $1-39 
 
 2.30 
 
 1.50 
 
 1-57 
 
 1.39 
 
 2.71 
 
 2.57 
 
 1.24 
 
 1.84 
 
 2.18 
 
 3-35 
 
 1.68 
 
 1.50 
 
 1.98 
 
 I- 35 
 
 
 
 
 
 1.76 
 
 0.88 
 
 Average, $14! 
 
 $1-53 
 
 1.27 
 
 1-25 
 
 
 
 1.26 
 
 1.87 
 
 
 
 2.32 
 
 2.60 
 
 
 
 Average, $2.035 $2.10 
 
 It will be noticed that while some of the assays run 
 higher on re-sampling, others are lower, yet the averages 
 of the nine originals and duplicates check to within 3 per 
 cent. Thus it can be seen that averages cut quite a figure 
 in mine sampling, hence many small samples are prefer- 
 able to a few large ones. In another case, where the 
 average values were running in the neighborhood of $240, 
 one sample over 3 ft. wide assayed $1,258; a re-sample 
 gave $1,208, and yet another $1,296, the average being 
 $1,254, and the variations about 4 per cent from the 
 original sample. I have another recent case in mind which 
 will serve to illustrate more than one point: A line of 
 check samples along a practically barren portion of the 
 vein gave, as was expected, a series of very low assays. 
 One, however, ran $25.41, and a re-sample was called for. 
 The same man took both samples, but with the re-sample 
 he sent this note: "Sample probably salted; cut a small 
 vug and fine ore ran out into the sample box." It was 
 salted. The assay of the re-sample ran $102.74. I then 
 
 1 06 
 
sampled the cut myself, and, noticing a small seam of 
 quartz containing some rich silver ore, I sampled that first, 
 and the vein matter on either side afterwards, the result 
 being as follows : 8 ins. of $151.60 ore ; I ft. 3 ins. of $0.89 
 ore ; 3 ft. 4 ins. of $4.47 ore ; average, 5 ft. 3 ins. of $22.30 
 ore, practically confirming the original assay and showing 
 that in certain cases the box as a means of catching the 
 samples chipped off by the moil is, to say the least, 
 misleading. 
 
 Sacking the Samples. I prefer having the sample sacks 
 plainly marked on the outside with a letter to designate 
 the series, and a number, but not necessarily the number 
 of the sample. One can then see at a glance and without 
 opening the sacks just what sample it is, and can give 
 them to the assayer in any order one may choose, prefer- 
 ably, however, in serial numbers. The check samples, 
 taken as the work proceeds, also receive a serial number, 
 having, however, no relation to that of the original sample. 
 The small samples are at once tied up in their sacks, placed 
 in a large sack and taken along by the samplers as the 
 work proceeds. 
 
 Cutting Down Samples. Where nothing better is at 
 hand, a board platform, covered with a sheet of canvas, 
 as described by Mr. Rickard, answers admirably. A small 
 rock-breaker is, however, much preferable, and with it at 
 least two sets of riffles and pans should be provided, to 
 the end that the samples can be riffled down from the first 
 in a rapid, accurate and cleanly manner, and all coning, 
 quartering and brushing up from sheets or plates abol- 
 ished, and with them many sources of error. For this 
 class of work I prefer a form of riffle known in the trade 
 as the Jones sampler, the safest, neatest and most expedi- 
 tious apparatus for cutting down samples that I know of, 
 and one that I have used for several years with perfect 
 satisfaction. The sampler consists of a series of riffles, 
 say, y 2 in. wide, but instead of being U-shaped, as the 
 ordinary riffle, the bottom slopes downwards at an angle 
 of 65 (Fig. 3). The sampler is made up of a series of 12 
 or more riffles of uniform width (Fig. 4), soldered firmly 
 
 107 
 
together so that the spouts are alternately right and left ; 
 thus ore that enters the first riffle would be deflected, say, 
 to the right, that which passes the second, to the left, and 
 so on. It is supported on a stand (B) and the metal pans 
 (C) placed under the discharge from the riffles on either 
 side (Fig. 3) ; a small shovel with turned-up sides (Fig. 
 5) is provided of the exact width of the riffles. If the 
 sample to be cut down is crushed in a laboratory breaker, 
 
 THE JONES SAMPLER. 
 
 the sampler shovel can be placed to receive the ore as it 
 drops out of the jaws of the machine ; this crushed ore is 
 then leveled off to a uniform thickness on the shovel and 
 gently emptied across the central axis of the riffles. Should 
 the latter consist of six pairs, then one-half the sample 
 
 108 
 
will fall in six streams into the right-hand pan, and the 
 remainder in six streams into the pan at the left. The 
 sample is thus divided into two equal parts, the result of 
 12 cuts in one single operation. The contents of one pan 
 is taken for the sample, it matters not which ; the other is 
 rejected. The sample is then crushed finer and the op- 
 
 J L 
 
 FIG. 5. 
 
 eration repeated after the sampler is brushed out and 
 clean pans placed in position below the riffle spouts. The 
 operation of crushing finer and passing through the rif- 
 fles is repeated until the sample is reduced to the weight 
 and mesh required. It will be noticed that no sheet or 
 cloth of any kind is required nor is it necessary to spread 
 
 109 
 
the ore on the floor or on plates, that the ore comes in 
 contact with metallic surfaces only, to which precious 
 metals cannot stick or become entangled, as they so often 
 do in canvas, in brushes and in brooms ; while the errors, 
 the labor, and the superstition of ' 'coning and quarter- 
 ing" are eliminated. 
 
 All samples should be put up in duplicate, and in 
 such manner that reliable assayers can determine 
 their value to within I per cent. In order to ac- 
 complish this desirable end, the samples should be 
 reduced to pass at least a loo-mesh sieve, and this 
 work, be it remembered, rightly falls to the sam- 
 pler and not to the assayer. The latter cannot be held 
 responsible unless reliable samples are furnished him. 
 Furthermore, no careful engineer could afford to trust 
 the ordinary assayer's helper to cut down and reduce his 
 samples. It is only when the samples are reduced to 100- 
 mesh and put up in duplicate that the engineer is through 
 with his part of the business. It is folly to divide samples 
 of coarse ore and send them to rival assayers and expect 
 the work to check ; like as not, both will be wrong. Where 
 there are no facilities for bucking samples at the mine, and 
 the engineer has not brought the necessary apparatus with 
 him, samples can be reduced to, say, 20 or 3O-mesh, the 
 finer the better; they should be put up in stout paper 
 sacks for shipment from the mine, and then ground and 
 cut down in the office of the assayer in the presence of 
 the engineer or his representative. Sampling is expen- 
 sive. It must be done well to be of value, and in no stage 
 of the proceedings is as much care necessary as in the 
 final one of cutting down the samples. This work is 
 often relegated to the assayer's assistant, who, while 
 competent for ordinary routine work, preparing speci- 
 men assays, etc., yet rarely has the training or ability to 
 prepare samples for assay in the manner that smelters 
 and sampling works find necessary and mining engineers 
 should demand. The samples taken each day should, 
 where possible, be reduced to the smallest limit before 
 evening, put up in paper sacks, and placed under lock. 
 
Erratic Samples. The proper treatment of erratic 
 samples is always a difficult matter. Mr. Rickard has 
 given both sides of the subject very careful handling, and 
 little more can be said. Where re-sampling confirms the 
 original high result, the inference is that the values are 
 there, and it remains to make the proper disposition of 
 the'm. When examining for an intending purchaser, I 
 usually first reject the erratic, high samples, if under 10 
 per cent, and determine the average value of the remainder. 
 Next, I insert the average value so found as the assumed 
 value of the higher assays, and estimate the block of ground 
 on that basis. Where erratic samples are numerous, their 
 relative importance to the whole number of the samples 
 must be taken into account, as well as the amount of 
 ground that they strictly represent, remembering that any 
 given block of ground is not likely to maintain as high an 
 average stoping value as that shown by sampling. When 
 erratic samples run low and re-sampling confirms the re- 
 sult, they must stand. The whole object of sampling be- 
 ing to establish the average value of the ore, it is well to 
 remember that it is not an exact science ; consequently, in 
 computing results, each man will, to some extent, be gov- 
 erned by his experience in determining the factors to be 
 used, so that his final estimates will conform to the actual 
 production of any given block when stoped out. This is 
 what we mostly strive for, and the engineer who is 25 
 per cent below the actual value in his estimates of "ore 
 developed" is as culpable as he who is 25 per cent above. 
 
 In a former issue of this JOURNAL, I attempted to de- 
 scribe a classification for ore reserves in different stages 
 of development, and also for ore to be developed in the 
 ordinary course of mining. These definitions have been 
 discussed together with the articles on mine sampling, 
 so I ask the same liberty of reply. "Ore in sight," I am 
 pleased to note, has no defenders. Mr. George E. Collins 
 appears to take exception to any method of classifying ore 
 reserves, but gives an example of estimates made by his 
 brother where the classification I suggested is very nearly 
 followed. I further note that the distinguished engineer 
 
 117 
 
for whom Mr. Collins made this classified estimate, bring- 
 ing to bear a wide and varied experience in such matters, 
 unqualifiedly indorses my classification, using, however, 
 the phrases "positive ore," "probable ore" and "possible 
 ore" for those suggested by me. 
 
 Mr. Collins objects to my definition, "ore developed" 
 exposed on four sides because, forsooth, some such blocks 
 have been found, in certain cases, "to enclose a large bar- 
 ren patch in the center," though why it should be in the 
 center instead of any other part of the block, is not stated. 
 Others have found a rich patch in the interior of a block, 
 and can with equal propriety object on that account. These 
 matters have nothing whatever to do with the proposed 
 classification; they are taken care of in the factors the 
 engineer employs in making his estimates of net values. 
 It appears to me that Mr. Collins does not quite under- 
 stand the significance of my classification. The real point 
 is not seen in the comparison of one vein with another, 
 but in the various stages of development in one and the 
 same vein. Where ore exposed on four sides can be more 
 safely estimated than ore hidden, say, on two or more 
 sides, the former, being a safer estimate, is properly placed 
 in a separate class. 
 
 The geological and other conditions necessary to be 
 taken into account in estimating the production of a given 
 block of ore, and applying the factors of correction, are 
 so fully treated by Mr. Rickard and also by Mr. Puring- 
 ton, that it would be absurd for me to attempt to add 
 another word. 
 
 Mr. Collins next calls attention to the expense of open- 
 ing out a mine in blocks of 150 ft. by 300 ft. His ideas 
 are apparently connected with low-grade veins, and not 
 over good mining. Taking the other extreme of values, 
 by way of contrast, I have seen winzes sunk that produced 
 over $1,000 worth of ore per foot (in one case $1,500), 
 and they were placed at less than 50 ft. apart. Between 
 these extremes the blocks that I suggested, with winzes or 
 raises at intervals of 300 ft. or of 200 ft., will, I believe, 
 fairly conform to the best modern practice. The ore-body 
 
shown in Fig. 2 by Mr. Collins is not typical of anything 
 I have ever seen, and such is the opinion of others. That 
 an ore-deposit of that shape may occur is admitted, but 
 that it is "typical of perhaps the largest number of ore- 
 bodies in fissure veins" is denied. 
 
 A final word on my suggested system for the classifica- 
 tion of ore reserves. We will assume the various blocks 
 in a vein have been measured, sampled and carefully ex- 
 amined regarding their geological environment, and that 
 the engineer finally decides that a factor of 10 per cent 
 should be applied as a deduction from the values shown 
 in the blocks exposed on four sides ; then, everything being 
 equal, this factor of safety should be something like 15 
 per cent for blocks with one concealed side, 20 per cent 
 where two sides are concealed, and something like 33 per 
 cent where only one face of the ore is exposed. While on 
 development these partially exposed ore blocks may equal, 
 or even exceed, the averages found in the fully developed 
 blocks, still the chances are that they will not, and a 
 careful engineer will limit his risks in a manner some- 
 thing similar to the above factors, if, indeed, he will be 
 willing to concede any estimate for ore exposed only on 
 one face. 
 
 PHILIP ARGALL. 
 Denver, Colo., May 28, 1903. 
 
 The Editor: 
 
 Sir. It would seem from Mr. Philip Argall's refer- 
 ences, in your issue of June 13, to my criticisms of his 
 former article, that we are arguing somewhat at cross- 
 purposes. I certainly did not object to the classification 
 of ore estimates. What I do deprecate is the adoption 
 of cast-iron definitions for such classes, which will not 
 admit of variation with varying conditions. To illustrate : 
 I object to using the same expressions to denote estimates 
 of ore in a pockety fissure-vein and a comparatively regu- 
 
 113 
 
lar impregnated bed, merely because both are exposed on 
 one, two or more sides, as the case may be. 
 
 I did not suggest that my brother was the originator 
 of the division of ore-reserves into the three classes of 
 "positive," "probable" and "possible" ore. I believe he 
 adopted the idea from Mr. Arthur Winslow, who has 
 made use of three similar classes in his Liberty Bell an- 
 nual reports for years past. Mr. Winslow, however, 
 using his own discretion and relying on his personal judg- 
 ment as to the mine he is dealing with, is far less exacting 
 in his requirements as to number of sides exposed than 
 Mr. Argall, Mr. Lawrence, or the late Mr. Arthur L. Col- 
 lins. He carries out, in fact, the principle that "the 
 amount of evidence to be required when making estimates 
 of ore-tonnage, and the number and nature of classes into 
 which estimates should be divided, must depend on our 
 general conclusions as to the nature and permanence of 
 the ore-bodies in the mines under consideration, the dis- 
 tance between the workings, etc." 
 
 In figuring the ore-body No. 2 in my letter I did not 
 mean to imply that that particular shape was typical, but 
 that similarly irregular ore-bodies are "typical of perhaps 
 the largest number of ore-bodies in fissure-veins." The 
 regular ore-shoots of the text-books, in fact, are not very 
 common in the field. 
 
 I think Mr. Argall may fairly be asked to explain what 
 he means when he speaks of my ideas being apparently 
 connected with "not over-good mining." It will be re- 
 membered that I was discussing the mining of irregularly- 
 occurring ore-bodies in fissure-veins, ars to which I will 
 venture to state two propositions : 
 
 1. It is not, necessarily or usually, good mining to open 
 up such a vein in blocks of 150 ft. by 300 ft. Each case 
 must be decided on its own merits. 
 
 2. Any expenditure in the working of such deposits 
 beyond the minimum necessary to discover and extract 
 them may assist good experting. It is not part of good 
 mining. 
 
 I did not, however, object to the expense of opening up 
 114 
 
a mine "in blocks of 150 ft. by 300 ft.," but to expense in 
 raises, etc., for the sole purpose of blocking out irregular 
 ore-bodies, and not necessary for their economical ex- 
 ploitation; working mines, in fact, for the best showing 
 rather than for the greatest profit. 
 
 Are we not all apt to forget, at times, that mining engi- 
 neers exist only for the sake of the mines, and not vice 
 versa? 
 
 GEORGE E. COLLINS. 
 
 Denver, Colo., June 22, 19/53. 
 
 The Editor : 
 
 Sir. The article by Mr. Argall, in your issue of Feb- 
 ruary 14, on the merits or demerits of the old-fashioned 
 expression of "ore in sight" is of great interest to the 
 profession, and the result of the different views which it 
 will bring forward should induce a change in terms 
 such as, it appears, is very much needed. 
 
 Taking advantage of the opportunity of discussing 
 this subject, I would suggest the following terms : 
 
 Ore Blocked. Such bodies as are accessible on all 
 sides, that can be accurately measured and thoroughly 
 sampled, and the values of which can be reliably de- 
 termined. 
 
 Ore Partly Blocked. Those bodies that are only par- 
 tially developed, and the values of which can only be 
 approximately determined. 
 
 Ore Faces. Would designate those bodies that are 
 exposed on one side or sh'ow only one face, and whose 
 values can only be determined in a prospective manner 
 as deduced from the general condition of the mine or 
 prospect. 
 
 G. M. GOUYARD. 
 
 Denver, Colo., Feb. 20, 1903. 
 
 The Editor: 
 
 Sir. Referring to the discussion regarding "Ore De- 
 veloped," kindly allow space for this bit of experience 
 from actual practice. 
 
 us 
 
There had been blocked out on three sides a piece of 
 ground as shown in sketch. The result of sampling 
 showed the block to be payable ore, though with but a 
 small margin of profit remaining above mining and mill- 
 ing expenses. Upon stoping th'e ground, there was en- 
 countered a pocket of ore within 6 ft. of the upraise No. 
 2, which carried a value three times that of the result of 
 sampling the block, and which amounted to about one- 
 third of that of the whole piece of ground. 
 
 This is a reverse, though more desirable case than 
 the ones referred to in Mr. Collins' article of February 
 24, in which the ground might have been poorer instead 
 of richer. It, however, illustrates the same principle of 
 uncertainty with which we have to deal. 
 
 JOHN C. TREAD WELL. 
 
 Sahuayacan, Mexico, April 6, 1903. 
 
 The Editor : 
 
 Sir. I was very much interested in an article by Mr. 
 Philip Argall, in your issue of February 14, in regard 
 to the use of the term "ore in sight." What Mr. Argall 
 has to say is very much to the point, and quite agrees 
 with my views upon this subject. 
 
 I would use the following terms to qualify and more 
 fully explain the purely general expression of "ore in 
 sight": 
 
 116 
 
1. Positive Ore. Ore exposed on all sides. 
 
 2. Probable Ore. Ore exposed on two or three sides. 
 
 3. Possible Ore. Ore below the lowest level, or, as 
 Mr. Argall expresses it, "below the last visible ore/' 
 
 The use of these three simple words is recommended 
 
 to engineers. 
 
 BENJ. B. LAWRENCE. 
 
 New York, Feb. 21, 1903. 
 
 The Editor : 
 
 Sir. Mr. Collins now defines his position as objecting 
 to "the same expressions to denote estimates of ore in a 
 pockety fissure-vein and a comparatively regular impreg- 
 nated bed, merely because both are exposed on one, two or 
 more sides." Here we differ radically, assuming, for the 
 sake of argument, such an unusual phenomenon as a "com- 
 paratively regular impregnated bed" ; the engineer would 
 use a lower factor of correction in dealing with the latter 
 than in the case of a pockety fissure-vein, to the end that 
 in either case his estimates may be as near correct as he 
 can get them. : So long as mines are developed by levels 
 and winzes, or the counterpart of the latter raises the 
 present method of estimating ore reserves in blocks will 
 in all probability prevail and a block with all sides exposed 
 will also receive a higher estimate than those with one or 
 more concealed sides. In my definition "ore developed," 
 I stated that as a general rule "the smaller the blocks of 
 developed ore the more accurately can their contents be 
 estimated" ; suggesting a? a safe rule in such matters that 
 the length of a block should not exceed twice its depth. 
 Within the limits I gave, there is nothing very rigid about 
 this. Then it must not be forgotten that other classifica- 
 tions are provided to cover cases of incomplete develop- 
 ment ; consequently I cannot see where the so-called "cast- 
 iron" definition comes in, unless it is the requirement that 
 first-class reserves should have no concealed sides. 
 
 It is good business, and good mining also, to know, 
 within the limits of commercial accuracy, what materials 
 
or ore one can safely depend on; taking stock does not 
 directly increase the profits in any business, yet it is 
 usually considered imperative at certain intervals. Turn- 
 ing now to the hypothetical ore-body (Fig. 2 of Mr. Col- 
 lins) to which I am again referred, I desire to state that 
 there is no evidence in the sketch to justify one in assum- 
 ing that the outer lines drawn by Mr. Collins to represent 
 the boundary of the ore-body have any foundation in fact. 
 Considering the peculiarity of the assumed form of the 
 ore-body and the development given, I would construct the 
 outline of pay-ore as shown by the hatching, and, while 
 this would give about 60 per cent less than Mr. Collins 
 finds, I believe it is as much as a careful engineer dare 
 allow on the development outlined. 
 
 PHILIP ARGALL. 
 Denver, Colo., July n, 1903. 
 
 UNSYSTEMATIC SAMPLING. 
 
 The Editor: 
 
 Sir. I have been much interested in your articles on 
 the systematic sampling of mines. May I contribute 
 a few remarks upon the un-systematic sampling of mines 
 in order to point out that, like all other good methods, 
 systematic sampling has its limitations? 
 
 That these limitations are not generally recognized 
 is indicated by the fact that certain large mine invest- 
 ment companies are reputed to go so far as to formulate 
 rules by which their scouting engineers are bound. 
 Two such rules I have encountered more than once 
 and they are substantially as follows : 
 
 1. No ore shall be considered as "in sight" unless it 
 can be sampled at regular intervals on at least three 
 sides. 
 
 2. A purchase is not to be recommended unless there 
 is a fixed percentage of the purchase price in sight. 
 
 Now, I think, the making of any such rules as these 
 is open to criticism from a business standpoint. They 
 are not conducive to the acquiring of good mining in- 
 
vestments. I can, in fact, recall an instance where a 
 good opportunity for a profitable purchase was lost in 
 this way, and I have no doubt many of my readers can 
 recall others. 
 
 The scheme of systematic sampling is based on the 
 idea that mineral deposits occur in definite and measur- 
 able shapes, as, for instance, a fissure vein or a mineral- 
 ized stratum, but we know from experience that a very 
 large percentage of all mineral deposits are most irregu- 
 lar in shape and size, and in such deposits it seems to me 
 that systematic sampling is apt occasionally to be actu- 
 ally misleading. By systematic sampling I mean the 
 taking of samples across the lode at regular intervals on 
 all the. accessible drifts and entries with a view to figur- 
 ing out the ore in sight from the measurements and as- 
 says thus obtained. 
 
 Th'at there are limitations to this system can be shown 
 by recalling a few irregular ore-bodies. Take, for in- 
 stance, the Richmond mine at Eureka, Nevada; the 
 Copper Queen mine at Bisbee, Arizona, or the Cortez 
 mine at Cortez, Nevada, all of them mines which are 
 identified with bodies of great value and magnitude, but 
 of such erratic form that I cannot see how the ordinary 
 methods of sampling could be applied at all; or consider 
 the countless silver-lead deposits which occur as con- 
 nected, or partially connected, chambers in limestone. 
 How, may I ask, is one to figure the ore in sight, accord- 
 ing to rule, in such cases ? 
 
 Adopting Mr. Philip Argall's very valuable sugges- 
 tions as outlined in your paper of February 14, and ap- 
 plying them literally, one could figure no "ore devel- 
 oped" in this class of deposits. Even blocks developed 
 on four sides are like as not to be solid country rock in 
 the center, and yet, in mines of this class there are fre- 
 quently hundreds of feet of development with ore on 
 from one to four sides of the passages. It is obviously 
 most unjust to say this is all ore "being developed" or 
 ore "expectant," and it should not be forgotten that 
 these pockety and irregular deposits have contributed 
 
 119 
 
very largely to the world's supply of metals, and have 
 produced some phenomenal dividend payers. It seems 
 to me that, in cases of this kind, rules must be in a large 
 measure disregarded, and the value of the engineer's 
 report will depend entirely on the man and not on the 
 system. 
 
 Take again the matter of outcrops; gold outcrops 
 often assay more, and the outcrops of silver, lead or cop- 
 per veins often assay less than the average of the shoots 
 beneath. The outcrops of the famous Nacozari cop- 
 per mine was a large mass of iron gossan, showing only 
 a little copper carbonate here and there. The big cop- 
 per mines at Cananea presented a similar appearance on 
 the surface. Obviously, in cases of this kind the judg- 
 ment must be guided much less by sampling than by 
 mineralogical and geological indications. 
 
 What alternative is there to take the place of syste- 
 matic sampling? The question is hard to answer, except 
 in a general way that the method of sampling must be 
 fitted to the individual case. Mines are such unsystematic 
 things at best that no two will stand exactly the 
 same treatment, and as I said at the outset, this contri- 
 bution is intended to accentuate the limitations of sys- 
 tematic sampling, and it is obviously impossible to pre- 
 scribe any system for a procedure which is essentially 
 un-systematic, but I will give two examples which I hope 
 will illustrate my point, and I can show that even in 
 those cases where systematic sampling fails us there are 
 still avenues of procedure, which, if they fail to give the 
 concise data which are desirable, do at any rate provide 
 a way by which a fair estimate can be made of a mine. 
 In both cases the examinations were made by mining 
 engineers who take the highest rank in the profession. 
 
 The first case was that of sampling a large gold mine 
 in Mexico. Th'e engineer spent two days poking around 
 the mine with a sampling pick, studying the vein and 
 the ore-occurrence. He put in the evenings studying 
 the shipments and acquiring general information con- 
 cerning the conditions of the locality. Now, in studying 
 
the vein he found that there were three or four distinct 
 kinds of ore exposed in the workings and his wide ex- 
 perience in such matters enabled him to make a close 
 mental estimate of the respective amounts of such ore 
 in sight, so it only required a few samples of each kind 
 of quartz to give him, at one stroke, data from which he 
 could form a very fair estimate of the mine. These sam- 
 ples were taken and assayed under his directions, and 
 I know that the returns from them led him to a correct 
 opinion of the mine ; for, although he at once proceeded 
 to sample the mine in a systematic manner, the vein 
 being one which yielded itself readily to such an opera- 
 tion, and although he and I kept in touch with the mine 
 until its decline, he never had occasion to change his 
 opinion. 
 
 The above example shows how a man gifted with 
 good judgment can get at the facts without systematic 
 sampling, but it is also an example of the fact that no 
 thorough engineer will ever neglect so valuable an aid 
 as systematic sampling wherever such a method is at all 
 applicable. By treating the various mineral constituents 
 of a lode we find a way, hardly a system, by which much 
 valuable information may be gained. Every mine shows 
 different kinds of ore, and very often th ! ey are of such a 
 nature that having once educated the eye, by assaying 
 the various kinds, it is entirely possible to distinguish 
 the different grades on sight. In deposits of very erratic 
 shape the information to be gained in this way may be 
 very considerable, and may lead to a comprehension of 
 the deposit which will facilitate systematic sampling 
 afterwards. 
 
 The second case was that of a large copper-silver de- 
 posit which I sampled with the other of the two engi- 
 neers previously alluded to. Here the ore-bodies left 
 standing were so shapeless that the ordinary methods 
 of sampling and measurement were utterly useless. He 
 went at once to the pith of the matter by taking a few 
 general samples, examining them carefully and separat- 
 ing them by concentration into their constituent parts, 
 
namely, clean concentrates, middlings, slimes and tail- 
 ings. These various parts were each carefully inspected, 
 accurately weighed and assayed, and with the knowledge 
 gained thereby he was able to go through the mine and 
 decide correctly, not only as to what was ore and what 
 was waste, but he could pass upon the concentrating 
 qualities of the material. This method of sampling 
 showed the instincts of the metallurgist. The location 
 of the mine was such that concentration was the only 
 practicable treatment. Like the last example, this was 
 a case of educating the eye, but it differed in that the 
 eye was educated to read in values and percentages of 
 concentrates as well as in values of crude ore. To this 
 experienced metallurgist it was a useful "short cut" to 
 results, but, like all short cuts, I imagine it might be 
 dangerous to a beginner. The question of structural 
 geology was also interesting in this case. The owners 
 considered the deposit a large chimney, and worked it 
 with the idea that the ore went down, found it did not 
 go below a certain level, let the mine partly fill with 
 water and put it on the market with the usual tale of 
 inadequate pumping machinery. The deposit proved 
 to be a large anticlinal fold with the axis dipping slightly 
 to the east. There was more ore and more water in the 
 eastern part of the mine than anywhere else, and the 
 chance that the ore might continue along the axis seemed 
 tempting enough to justify a little work. This interest- 
 ing question, however, has not been completely solved 
 as yet. 
 
 Another case will serve to illustrate my theme. I 
 lately investigated a large low-grade deposit in Colorado. 
 The lode is a brecciated band, in a schist country, about 
 200 ft. wide and two or three times as long. In this case 
 also the structural geology is far more interesting and 
 vital a question than the sampling, but as this is an arti- 
 cle on unsystematic sampling, I will speak only of the 
 conditions which affected that part of the work. The 
 brecciation was complete and coarse; by this I mean 
 that large open spaces had been formed as would occur 
 
in a pile of rocks. Some of these spaces were filled 
 nearly solid with chalcopyrite which carried $35 in gold 
 per ton and many others had only a little chalcopyrite, 
 the remainder of the filling being a loose sinter, and 
 both it and the schist contained very little of value. In 
 fact, 50 per cent, of the values lay in these nodules of 
 copper pyrite. As the mine had been worked by lessees 
 it was only natural that the surfaces exposed under- 
 ground were destitute of copper nodules. Here was a 
 case where systematic sampling with a moil and ham- 
 mer would result in error, but where the method of talc- 
 ing samples by car-load lot and shipping the same to 
 the smelter would give useful information. 
 
 I cannot resist the temptation to say a few words in 
 regard to the method of sampling "by car-load lot." 
 One cannot but feel a little cheap and inefficient with a 
 sackful of carefully reduced little samples all carefully 
 tied up and sealed, when confronted by the man who 
 believes in "sending a car-load to the smelter and get- 
 ting your money for it." Somehow this "sending a car- 
 load to the smelter and getting your money for it" has 
 such a grand and practical sound to it, that it impresses 
 people. But let us follow the car-load to the smelter 
 and see what is done with it. Do they take a nice, clean 
 furnace and smelt that car-load separately and weigh 
 up the values from the results? Oh, no; they just put 
 it through a sampler, which often is none too clean or 
 too carefully handled, and reduce the car-load to one 
 little assay sample. It is a noticeable thing also that 
 the man who believes in taking his samples by the car- 
 load is generally the same man that believes in hand- 
 sampling at the smelter in preference to machine sam- 
 pling. So that the man who does his sampling by car- 
 load lots does his buying on one assay sample, while 
 the other man does his buying on the results of many 
 dozen assay samples, and, I believe, that each one of 
 the many may be made as truly representative as the 
 machine-sampled car-load. 
 
 I have just shown an instance where car-load sam- 
 
 123 
 
pling was needed, but in the majority of cases, I think, 
 the sampling by hammer and moil is preferable, because 
 it can be made to yield, not only the average value of 
 the ore in a given block of ground, but the quantities and 
 qualities of the various grades as well. 
 
 I hope that I have succeeded in calling attention to 
 the fact that systematic sampling is only one of many 
 tools at the engineer's command. Just as the skilled 
 mechanic uses now one tool and now another, when 
 the work before him changes, so the engineer may find 
 it advantageous to vary his methods. 
 
 GEORGE J. BANCROFT. 
 Denver, Feb. 17, 1903. 
 
 ON SAMPLING THE FLOOR OF A WET LEVEL. 
 
 The Editor: 
 
 Sir. I have read the articles by Mr. T. A. Rickard on 
 sampling of ore with great interest, and it gives me 
 pleasure to contribute some data upon one branch of 
 the subject which has lately come within my experience. 
 I refer to the sampling of the bottom of a wet level. 
 
 This is by no means a pleasant or easy branch of sam- 
 pling; neither can the sample procured be expected to 
 be as accurate as one taken in a back or wall, since the 
 ore broken along the groove made by the moil remains 
 more or less in place until collected by hand and, in 
 doing this one allows many of the smaller pieces to 
 escape. The tendency, therefore, is rather to obtain 
 under-average values, because the richest ore is usually 
 the most brittle. On the other hand, however, the 
 cracks in the floor of a level form a good receptacle for, 
 and in general, become filled with, the rich fines, and 
 this would ordinarily tend to give over-average values; 
 but, in the case to be described, water was always at 
 hand, and by washing each sample carefully this source 
 of error was eliminated. 
 
 All samples were taken in the usual way, by chipping 
 a straight groove across the vein with the aid of a ham- 
 
 124 
 
mer and moil. In places we tried shooting, but found 
 it unsatisfactory. The flow of water was about 300 gals, 
 per minute, nearly all of which, in most cases, we suc- 
 cessfully dammed back and carried in a flume over that 
 stretch of level being sampled. The grade of the level 
 was usually enough to keep the head of the flume higher 
 than the discharge, but in places where the floor was 
 flat or where it sagged, the difficulty was overcome by 
 making the dam one plank or more higher; in all such 
 cases the dam should be kept as low as possible, other- 
 wise the unnecessary pressure behind it will accelerate 
 leakage. The dam consisted of a 2-in. plank, 12 ins. 
 wide and 4 ft. 6 ins. long, the level being timbered with 
 sets, 4 ft. 6 ins. between the timbers, at 5 ft. intervals. 
 The mud and loose rock were removed from the sill, and 
 the dam spiked on it, all passages for water being- 
 stopped up with clay procured in neighboring workings 
 of the mine, or with thick mud when the supply of clay 
 gave out. Nailing the dam to the side of the sill was 
 tried, but this failed to keep out the water as effectually. 
 The flume was 12 by 10 ins. inside cross-section, and 
 was made by nailing together three 12 by 2-in. planks in 
 sections of 16 and 9 ft., the longer ones being used for 
 the straight parts of the level and the shorter ones for 
 the curves. The inlet section was made wedge-shaped, 
 being i ft. wide at its lower end and 2 ft. 3 ins. at the 
 dam end; the latter end fitted into a recess sawn in the 
 dam. On the lower end of each section, overlapping it 
 by 4 ins., was nailed a collar, made of two 14 by 8 by 2-in. 
 planks at the side and one 12 by 8 by 2 ins. at the bot- 
 tom, and in putting up the flume the head end of each 
 section was laid in the protruding half of the collar on 
 the section above and made water-tight with clay. At first 
 we had the collars made of i-in. plank, but these proved 
 unserviceable, because they were apt to be broken by 
 the rough handling, accompanying the shifting of the 
 flume. To give the flume a fairly even grade, it was 
 blocked up underneath with timbers. With three sam- 
 plers, taking samples at lo-ft. intervals, it was found that 
 
 125 
 
126 
 
a stretch of 200 ft. usually required a full day's work ; 
 the time, of course, varied with the local conditions ; in 
 this particular case the veins did not exceed an average 
 width of 2 ft. 
 
 The way the work was conducted was as follows : On 
 the previous shift a gang of men took up the rails, re- 
 moved the loose dirt, which was one to two feet deep, 
 and relaid the rails so that the flume could be brought in 
 upon timber trucks. The rails were originally spiked to 
 sleepers above the sills., but were relaid on the sills so 
 that the track was lowered 6 to 12 ins. The flume was 
 then laid on that side of the level opposite to that occu- 
 pied by the vein. The places to be sampled were then 
 marked off, and men were set to work to shovel the re- 
 maining dirt to one side and pick down trenches as far 
 as the ore in place and bail out the water which oozed 
 through. For bailing they used tomato cans. This 
 was slow and tedious work; often it became necessary 
 to build a small clay dam on that side of the trench from 
 which the water came, or even all round it, or else to dig 
 another trench just above the place where the sample was 
 to be taken and bail from it. 
 
 If the vein be of such a nature that it breaks in slabs 
 parallel to its strike, an accurate sample can be taken 
 from under water ; if not, it becomes necessary to make 
 the trench dry because the muddy water prevents one 
 from seeing what is being done. 
 
 Should the vein jump from one side to the other, it is 
 advisable to take all samples on the one side first, then 
 move the flume and take those on the other side. In re- 
 gard to starting the samples at the lower end of the 
 stretch 1 first and working upwards, or vice versa, the 
 local conditions of each stretch have to be taken into 
 consideration. As regards working up or down the 
 level, owing to the removal of dirt and lowering of the 
 track, work must of necessity commence at the lower 
 end. 
 
 The first day we used a I5~in. galvanized iron pipe in 
 place of the flume, but found it unsatisfactory for many 
 
 127 
 
reasons. It takes too much time to put the sections to- 
 gether, also the pipe cannot be made to follow the bends 
 of the level as easily as a flume can. It cannot be sawn 
 or cut to any desired length as easily. By being open 
 along its whole length a flume possesses another great 
 advantage over a pipe. In the case of a cross-cut con- 
 ducting extra water into that stretch of level being sam- 
 pled, a clay dam with a 4-in. pipe leading into the flume 
 was found sufficient to rid that part of the level of the 
 extra inflow. The water bailed from the trenches could 
 be poured straight into the flume, whereas with the use 
 of a pipe much inconvenience and loss of time was occa- 
 sioned by the water bailed from the trench above running 
 down and filling the lower ones. The cost of the pipe 
 was 95c. per foot, and that of the flume I7c. (timber at 
 the mine in question costing $20 per 1,000 ft.). Except 
 in the matter of weight, which, on account of the 
 small amount of moving necessary, is of no moment, 
 it is obvious that the flume possesses all the advantages. 
 
 The accompanying sketch shows the plan, side eleva- 
 tion and end elevation of the flume. 
 
 ERNEST LEVY. 
 Denver, Colo., Feb. 25, 1903. 
 
 The Editor : 
 
 Sir. Referring to Mr. T. A. Rickard's excellent article 
 in the JOURNAL of February 14 on mine sampling, permit 
 me to offer suggestions on a few points. A gad made 
 with an eye and fitted with a handle will be found con- 
 venient for taking samples in place' of the moil Mr. 
 Rickard uses. It is easier held in a variety of positions 
 than the moil and more rapid work can be done with it. 
 For the hardest rock the moil is better. For spreading 
 the broken up sample, when coned on the canvas, a 
 piece of thin sheet iron or tin, about 4 by 8 ins., will be 
 found convenient ; with it the same sort of even distribu- 
 tion can be made, by going round and round, that is ob- 
 tained with the square-pointed shovel on the sampling 
 
 128 
 
works floor with larger samples. As a tag for the 
 sacked samples, half of an ordinary manila express tag 
 is excellent. The number is put on in duplicate with 
 pencil, and the tag folded twice and put into the sack. 
 This will resist any amount of hard usage that the sacks 
 will stand. Wooden tags sometimes become illegible 
 when samples are sent a long distance by express. In 
 rich or otherwise important bodies of ore a good safety 
 device is to divide the sample at the mine in triplicate, 
 give each portion a separate number, send two sets to the 
 assayer and reserve the third for control. This makes a 
 check both on the assaying and the sampling. Only 
 those control or triplicate samples are assayed in which 
 discrepancies between the original and duplicate appear. 
 This device is specially applicable in cases where the 
 mine is remote and difficult of access and the sacked ore 
 is taken away by the sampler. The use of it has saved 
 the writer the necessity of a long and costly return trip 
 and a re-sample. A discussion from Mr. Rickard of the 
 advisability of combining several cuts across the vein at 
 short intervals into one sample, or of taking separate 
 samples at greater intervals, and in what cases each of 
 these methods is preferable, would be interesting. This 
 is a matter that requires judgment, and a decision on it 
 has much to do with 1 the time and expense required to 
 make a given examination, as well as often determining 
 the thoroughness of the work. 
 
 CHESTER F. LEE. 
 Seattle, Wash., Feb. 25, 1903. 
 
 The Editor: 
 
 Sir. I have read your article on sampling with much 
 interest. Personally, however, I believe in what you call 
 ''grab samples." Experience in buying ore has given me 
 a fair judgment as to the average appearance of any 
 special lot. In veins I like to know what each band of 
 particular appearance runs, and especially I want the 
 owner of the m:ne to show me the richest part of the 
 
 129 
 
lode, so that I may know its proportionate value with 
 the rest of the vein matter, from which I take grab sam- 
 ples. These samples act as checks on the larger average 
 samples taken. Now these, when put away in my 
 pocket, have twice saved me from being "salted." 
 
 I think a man with experience can tell pretty well in 
 most cases what is a representative piece of ore, and use 
 it as a check on the average samples which are so easily 
 tampered with. 
 
 For taking samples, I believe in a locked mail bag of 
 leather, which will easily show punctures, and also blank 
 samples already prepared to put in with the samples 
 taken from the mine. This bag when taken under- 
 ground is as safe a guard as anything can be against the 
 samples being tampered with'. 
 
 Large samples weighing a ton or more are, of course, 
 best, but at mines unprovided with crushers, help is 
 needed to crush them down, which increases the risk. 
 
 One man, whom I know, prepared little balls of clay 
 containing gold washed out of the ore, which could be 
 thrown from quite a distance into the pile without it 
 being likely that they would be observed. A grab sam- 
 ple in this case would be all that would save one from a 
 false estimate. 
 
 For young men your advice could not be improved 
 upon, but each man as he gains experience has to be a 
 
 law unto himself. 
 
 W. M. COURTIS. 
 New York, March 7, 1903. 
 
 The Editor : 
 
 Sir. I have read with much interest the articles and 
 discussions on mine sampling appearing in your Journal. 
 I agree with Mr. Courtis that specimen or grab samples, 
 representing the different classes of ore in a mine, are use- 
 ful in sizing up the situation underground, and some, 
 times serve as a check on the other samples. 
 
 In sampling a vein where most of the values are in 
 
 130 
 
or two streaks of friable ore and the remainder hard 
 quartz, I have obtained good results by measuring and 
 sampling the rich streak separately and figuring the 
 average grade from the assays. This usually saves time 
 in sampling, but requires another assay. 
 
 The information obtained is worth the cost of the extra 
 assay, and to the mine operator it may save the cost of 
 breaking down quartz too poor to pay, although the aver- 
 age across the vein, thanks to the pay streak, may indicate 
 that all should be mined. 
 
 In a large vein there may be a streak next to a wall 
 that will pay to mine, while the rest of the vein may be 
 practically barren. A sample across such a vein would be 
 wrong, and might indicate that the vein was too low 
 grade to work. 
 
 In figuring averages, values, etc., the engineer's slide 
 rule is very useful. 
 
 ALBION S. HOWE. 
 
 San Francisco, April 3, 1903. 
 
 MINE VALUATION. 
 
 The Editor : 
 
 Sir. In reading the papers on "Sampling and Estima- 
 tion of Ore in a Mine," it has occurred to me that a few 
 remarks on South African practice may prove of interest 
 to your readers, and in submitting them I am encouraged 
 by Mr. Rickard's reference to the influence of the Rand 
 on gold mining practice to believe that American engi- 
 neers are keenly appreciative of methods used in the 
 Transvaal. 
 
 No two gold-fields are exactly the same. To a certain 
 extent each is a law unto itself. General rules must be 
 supplemented by a thorough knowledge of local condi- 
 tions. The importance of sampling varies considerably in 
 different localities. For instance, suppose there is a huge 
 deposit of low-grade material which must be quarried 
 from a mountain. In such a case there may be little op- 
 portunity for selection. On the other hand, if you have 
 
 131 
 
to deal with gold-bearing deposits, such as those of the 
 Witwatersrand beds, then sampling becomes of vital im- 
 portance. In some districts sampling may be considered a 
 desirable luxury ; here it is an absolute necessity. 
 
 It has always been recognized on the Rand that sam- 
 pling was of the utmost importance, but the mistake was 
 made at first of imagining that anyone could sample 
 efficiently. An applicant who professed ignorance of all 
 mining matters was looked upon as a proper man for a 
 sampler. All this is changed now. Whereas, one ineffi- 
 cient man was once considered sufficient for sampling, 
 many of the big properties now employ at least two good 
 men, who give their entire time to the sampling of the 
 underground workings and the keeping of the records. 
 Experience has shown that this pays well. 
 
 As is well known, before milling commences on a Trans- 
 vaal gold mine, big ore reserves are blocked out, as much 
 as 350,000 tons being usually developed by the time the 
 stamps commence to drop. For a short period after the 
 shafts first cut the reefs, the samples are generally as- 
 sayed on an adjoining mine, or in the town. When the 
 samples become numerous, the mine opens its own assay 
 office. Sometimes, in the development stage of a mine, 
 one man is employed to do the assaying and sampling, 
 but it is considered better to keep the assay and the samp- 
 ling departments separate. More often a man is engaged 
 to do the sampling and surveying. As the mine opens out, 
 more men are required, and when in full swing a prop- 
 erty of 200 stamps employs a surveyor and assistant, 
 an assayer and assistant, and a sampler and assistant. 
 These six men are responsible for the mine valuation. 
 
 Before the war a fashionable way of developing a mine 
 was to run what are known as intermediate drifts parallel 
 with the main levels. In Fig. I a sketch of an intermediate 
 drift is given. These drifts are started off east and west 
 from the raise ; and at intervals of 35 ft. or so, as at A A, 
 box holes are blown through to the main levels. Not only 
 was the main level carefully sampled, but the intermedi- 
 ate drift as well. The height of the intermediate drift was 
 
 132 
 
made one-half that of the level. Individual samples vary 
 considerably, but over a long distance, as from I to 2, 
 the average value comes out about the same. I am glad to 
 say that the practice of running these intermediate drifts 
 is dying out, for they are needlessly expensive. 
 
 During the development stage of a mine a frequent 
 method of procedure is to sample the faces of the drifts 
 after each blasting operation. This means an interval of 
 about 5 ft., which is considered a fair distance between 
 samples. The advantage of sampling the mine in this 
 
 PKL 1 
 
 manner is that the assay will show whether the miner is 
 keeping on the rich seam, or "leader." The disadvantages 
 are that, as a rule, the drift at the face is nearly choked up 
 with broken ore, so that only one section can be obtained, 
 and that the sampler is necessarily hurried by the miner, 
 who objects to the delay caused by him. The same 
 method is pursued in winzes and raises, samples being 
 taken after every "round." 
 
 Mr. Rickard gives an instance of three samples being 
 taken across a vein 12 ft. wide. On the Rand a sample 
 over such a big width would not be taken, but the 12 ft. 
 would be divided off into sections of 2 ft., and each sec- 
 tion sampled separately. Look at Fig. 2, and you will 
 understand why samples of sections are taken. In this 
 example four distinct samples would be taken, one from 
 each of the stringers, as it is of the utmost importance to 
 find where the gold lies. Suppose stringer No. I persis- 
 tently assayed 2 to 3 dwts., or much below the limit of 
 
 133 
 
pay-ore ; then it would probably be decided to leave this 
 stringer in the hanging wall and narrow up the stope. 
 No matter if the stringers are thick or very thin, they 
 are invariably sampled separately. On some mines, the 
 waste rock found between the stringers is also sampled 
 and assayed, but it is really only necessary to take occa- 
 sional samples of this waste, as it seldom contains gold in 
 payable quantity. 
 
 Let us suppose that there is an unbroken mass of aurif- 
 
 ~o>- - ~"~ S> ' 
 
 ${vj&Mf& : &*- 
 
 - o o f o ,. ^;_ 5 o 2^- -*^ 
 
 FIG. 2 
 
 erous material from A to B, 12 ft. wide, and that even 
 below B there is still reef. Even in this case, according to 
 Rand practice, the face would be divided into sections of 
 18 to 24 ins., and each would be sampled and assayed 
 separately. For an ordinary drift showing imparted reef, 
 the face is divided into three sections, namely, "hanging 
 wall," "middle" tand "foot-wall," and each section is 
 sampled separately. 
 
 Thousands of tons of material on the main reef, which 
 is the bulky producer of the banket series, are being left 
 in the mines. As a rule, this material is too poor to be 
 worked under present industrial conditions, but there are 
 payable patches in it, and in the future more attention 
 will be paid to the sampling of this material. An ideal 
 way to test it is to use a diamond drill and get cores at 
 regular intervals from the stuff which is left below the 
 foot wall. In fact, it is likely that the diamond drill will 
 become an important auxiliary in mine sampling. 
 
 134 
 
In sampling drifts, winzes and raises it is found of con- 
 siderable advantage for the sampler to make use of the 
 surveyor's mine stations, for by so doing the exact posi- 
 tion of each sample in the mine is determined. 
 
 On some parts of the Rand, where the reef is only an 
 inch thick, it is a common practice to measure off equal 
 distances on both top and bottom of the reef and take the 
 sample over this width. If proper care is taken to get the 
 right proportion of country rock in the sample, this 
 method is a good one for small rich leaders. Of course, 
 the calculation is made for a width embracing the waste 
 rock sampled, together with the reef. 
 
 Some years ago panning was very popular on the Rand, 
 but it has gone out of vogue of late. On account of the 
 pyritic character of the matrix and the fact that much of 
 the gold is "bound," panning can never be relied on for 
 accurate determination on these fields, but as a rough 
 test it is excellent. Panning serves three purposes: First, 
 in a large mine that is being developed, where hundreds 
 of samples are assayed each month, it is a check on the 
 assayer's work. Then, panning gives a close approxima- 
 tion of the amount of pyrite in the sample, so that the 
 assayer can decide whether there is need for a preliminary 
 treatment for sulphur, such as roasting, etc. Lastly, in an 
 office where hundreds of samples are being assayed in the 
 course of mine valuations, I believe it would save money 
 if the samples were divided according to the results from 
 panning into rich and poor. The samples high in gold 
 could be assayed by the scorification method, while the 
 crucible would be used for the poor ones. I know some 
 peoply decry the scorification assay and demand a "pot 
 assay" for every sample, but with proper care I find the 
 scorification assay satisfactory for rich ore. 
 
 The grouping together of all the assay values is en- 
 trusted to the surveyor, who, of course, is also responsible 
 for the determination of the ore reserves. The assay plan 
 contains the values of the samples taken in the mine, and 
 it is this plan that the surveyor uses in estimating the 
 reserves. Assay plans are made on one of three different 
 
 135 
 
planes, namely, the horizontal, the vertical, and the plane 
 of the reef ; the one which is best adapted for the purpose 
 will depend upon the dip of the reef. 
 
 It is when the mill starts crushing and gold returns are 
 reported that the mine valuation is finally tested. I must 
 admit that it is somewhat discouraging to review the past 
 history of the Rand and notice the difference between 
 what was promised before the mill started and what was 
 actually obtained when the battery commenced to work. 
 If there was a constant in the discrepancy, it would be a 
 simple matter to apply it to future determinations, but the 
 results are too contradictory. 
 
 On one mine it was found that the returns from the 
 reduction works were 70 per cent, of what the assay plan 
 called for. On a neighboring mine this factor was subse- 
 quently employed. When the mill commenced crushing, 
 however, much to the delight of every one it was found 
 that a pennyweight more gold per ton was extracted than 
 was promised by the estimates. 
 
 This goes to prove that the value obtained after sam- 
 pling is not a mathematically correct figure, and that an 
 engineer cannot always guarantee that the mine will give 
 what the sampling calls for. In spite of such occasional 
 discouraging results, sampling on the Rand is looked upon 
 with more favor than ever, and with extended local experi- 
 ence the work of estimation is certain to be better done. 
 
 From what has been said, it must not be thought that 
 the work of the sampler is over, or lessened, when the 
 mill commences crushing. At all stages the sampler is 
 necessary. After mining begins he watches the stopes 
 most carefully to see that no payable material is left in 
 the workings. From the stope samples, taken throughout 
 the month, the value per ton of what the mill should re- 
 turn for that month is worked out. Every day a "lip 
 sample" is also sent up from the mill. As inside amalga- 
 mation is now almost entirely omitted, only a spoonful of 
 mercury being fed into the boxes every hour, with proper 
 care a very accurate sample of the ore being crushed is 
 given by the "lip sample." 
 
 136 
 
I am glad to see that Mr. Rickard condemns the "grab" 
 sample so emphatically. Better not sample at all than 
 adopt this haphazard method. The only place where the 
 "grab" sample is employed is in testing the waste rock 
 leaving the sorting house. 
 
 Space will not allow me to enter into the discussion of 
 ore reserves. The expression, "ore in sight," which ap- 
 pears to be causing so much discussion among American 
 engineers, is seldom used out here at all. "Tons of ore 
 developed" is employed, and care is taken to give the 
 number of tons developed on each separate reef. As Mr. 
 Philip Argall, in his suggestive contribution, has pointed 
 out, the engineer should go into detail and give a precise 
 statement as to the condition of the "ore in reserve." Al- 
 most invariably on the Rand the number of tons of ore in 
 reserve are underestimated, due to too small a stoping 
 width being assumed in the calculation. The question of 
 stoping width is a very important one, for, if it is wrongly 
 assumed, not only is the tonnage too small, but the assay 
 value over the stoping width is made too high. At one 
 time the stoping width was arrived at in the office, but 
 
 now the custom is to examine every block of ground and 
 work out carefully what the actual stoping width will be. 
 On those mines which have the misfortune to be cut up 
 
 137 
 
by dikes the management is at considerable disadvantage 
 as regards ore development. Fig. 3 will illustrate a case. 
 The dike cuts in two the block of ground developed by the 
 fourth and fifth levels. Ordinarily, the calculation for re- 
 serves would be made for backs from A to D. The general 
 Rand practice is to only consider the backs from A to B in 
 working out reserves. From C to D is not considered 
 developing ground at all. 
 
 On most mines the amount of ground developed each 
 month is usually at least as much as the tonnage mined 
 during that month. Unfortunately just now, on account 
 of the scarcity of labor, it is found difficult to maintain a 
 
 parity. 
 
 T. LANE CARTER. 
 Johannesburg, April 4, 1903. 
 
 SOME ASPECTS OF MINE VALUATION. 
 
 The Editor : 
 
 Sir. As there are no gold mines in Scotland, I, a 
 would-be valuer of mines, had to seek my ideals elsewhere. 
 I found them in American methods. The American engi- 
 neer goes at once to the vital point. He says : "/ want to 
 know the net profit in sight in this mine. On that one fact 
 we will base everything. Don't bother me with details; 
 just let us set to work to get the sampling through." At 
 least, if he doesn't say that he ought to, because it is the 
 one thing in mining that matters. Frankly, I have got 
 "profit in sight" on the brain. 
 
 There is no marked cleavage between the American and 
 the English schools as regards mine valuation ; but an 
 Englishman, as a rule, has got a less clearly defined idea 
 of the net value of any given mine than an American. 
 As a mine manager he is perhaps the better man of the 
 two, but on the question of valuation he is not so clear. 
 There is a certain haziness and slovenliness about English 
 gold mining. Some of the mines use a ton of 2,000 Ibs. ; 
 others, one of 2,240 Ibs. We calculate our yields and our 
 assays in the wearisome Troy weight, instead of in that 
 
 138 
 
Sterling with which nature has supplied us. We put our 
 best properties under the control of titled incompetents, 
 and we write reports on mines so lacking in a grasp of the 
 vital points that the compilers ought to be led out at sun- 
 rise and shot. 
 
 This slovenliness in the English system shows itself, 
 naturally, in the all-important branch of mine valuation. 
 We do not, it seems to me, rush in and grasp the one great 
 fact the profit in sight as do Americans. We play 
 round the edges of it, and our reports, which should be 
 merely a statement of this fact in its several bearings, are 
 made bulky with useless details and side issues. I believe 
 that often, too, having got the fact, we don't quite know 
 how to use it. We cannot crystallize it sufficiently into 
 thought. If our fact, as is so often the case, shows the 
 mine to be on the borderland of good and bad, in the re- 
 gion of doubt, we are afraid to say to our principal, 
 definitely, either "y es " or "no." We try to shift the re- 
 sponsibility of the decision to someone else, and write a 
 report which has no backbone or individuality about it. I 
 think it takes a strong man to be a good mine valuer a 
 man to whom the taking on of responsibility comes natu- 
 rally. You must know how to handle your fact to be suc- 
 cessful. An able engineer told me that he judged his 
 subordinates by the way they could condense a report into 
 the limits of a cable ; and the shortest cable meant the best 
 man. I think he was not far wrong. He was an 
 American. 
 
 English engineers often fall short of doing good work 
 because they are unable to view the problem from their 
 employer's point of view. They get their fact all right 
 that is to say, the net value of the mine but they don't 
 know how that fact ought to be set before the capitalist. 
 To be a good mine valuer, a man must have the instincts 
 of a financier. He must put himself in that particular 
 financier's place. He would then realize how needful it is 
 that his report should be a clear-cut statement, saying yes 
 or no to each question and taking full responsibility. As 
 it is, four out of five reports I read are written by men who 
 
 139 
 
hedge, who are weak on the financial aspect, and who 
 leave an impression of vagueness that is exasperating. 
 These same reports will be voluminous, and deal at length 
 with side issues, but they don't satisfy one on the vital 
 points. The system is wrong. 
 
 The environment of the English engineer is against him. 
 In America the capitalist who sends a man to value a mine 
 probably intends to buy that mine himself and work it; 
 and as likely as not he knows nearly as much about mining 
 as the engineer does. His first question to the mine valuer 
 on his return is, "Well, what's the net profit in sight ?" He 
 takes the report and turns it inside out, and if in his sev- 
 eral capacities as mining man, financier and student of 
 men it fails to satisfy him, its compiler may understand 
 that he has been "turned down." But the London capital- 
 ist is a man who does not buy mines to work himself. He 
 is essentially a middleman. His life's work consists in 
 educating a large public to come forward and buy the 
 wares good or bad which he may from time to time 
 offer them. He would hardly appreciate the significance 
 of being told that he had got hold of a valuable mine. To 
 him the great question would be, "Can I get the shares 
 well introduced on the market ?" On your returning from 
 the mine, his first question would be, not "What is the net 
 value of the ore?" but, "Can you lunch here to-morrow? 
 I want you to explain your report to Lord So-and-So, who 
 is to be our chairman." 
 
 The English school of mining is seen at its worst in 
 Australia; that is to say, in Australian mines controlled 
 and managed locally. Some of these mines for instance, 
 those at Gympie, Queensland are pockety, and would be 
 difficult to sample correctly, but four out of any five mines 
 in Australia might be sampled with some exactness. The 
 Australian, however, flatly refuses to sample any of his 
 mines; he just goes along from one ore-shoot to another, 
 picking the eyes out of each, and so far as this great min- 
 ing continent is concerned with the exception of West 
 Australia, whose mines are owned in England mine 
 sampling, or valuation, is almost an unknown art. In the 
 
 140 
 
Melbourne Argus on a Monday morning there will be the 
 weekly reports of perhaps 300 local gold mines. In these 
 the managers will describe development work as "exposed 
 gold," "good gold," "pyrites," "colors," "pay dirt," etc., 
 etc., but from beginning to end there will be no word of 
 either systematic sampling, assay results, or estimates of 
 ore reserves. 
 
 Now, mark the force of evil example. The gold mining 
 industry in the Malay Peninsula was started by Australian 
 prospectors, and they were succeeded by Australian mine 
 managers trained to these methods. The principal mine 
 there was the Raub. Some years ago I was asked to re- 
 port on it, because of its failing to keep up to previous 
 yields. The mine had been working for eleven years, and 
 at that time had a ob-stamp mill. The manager had just 
 written a report stating that there were 300,000 tons of 
 rich ore in sight (value, about $20), and that the lowest 
 workings showed no falling off in results. 
 
 Then I made the following discoveries : First, that the 
 mine had never been sampled; second, that there were only 
 41,000 tons of pay-ore reserves (value, $9) ; lastly, that 
 the lowest workings in the mine showed no pay-ore. This 
 property at the time was valued at $6,000,000. 
 
 That was an extreme case even under the Australian 
 system but it is a warning that careless mine managers 
 might take to heart. 
 
 I started to write this article under the idea that I was 
 about to make some profound remarks on the minutiae 
 of mine valuation about sampling methods, irregular 
 values, ore reserves, and so forth. But after reading Mr. 
 Rickard on "Mine Sampling," Mr. Argall on "Ore Re- 
 serves," and other authorities who have lately spoken in 
 this paper, my assurance is not what it was. They have 
 left little loophole for any one coming after. 
 
 I have never allowed a sample to be broken down, ex- 
 cept in my presence. However much I trusted an assist- 
 ant, I could only accept the assurance of my eyes that the 
 section in question was fairly represented by the 10, 20 or 
 50 pounds of ore going into the bag. Soft streaks in 
 
 141 
 
the ore generally mean richness hard streaks, poverty. 
 The adjustment of the two is a problem which only one's 
 own conscience can satisfy. 
 
 I have my assays done in duplicate, especially so when 
 there is a plant on the mine and I can take my own assayer. 
 If the beads vary only slightly in weight, you cannot but 
 feel the more satisfied with the eventual result. At the 
 Chuquitambo mine, in Peru, a conglomerate ore assaying 
 $5, in four samples out of five, my duplicate beads used 
 almost to balance. For instance, a series would read: 
 4.01, 4.026.83, 6.852.31, 2.31 4.98, 5.00. When 
 there is a big difference it is as well to re-assay the sample 
 not to take the mean of the two beads. I expect to be 
 sampling a mine in Hungary shortly, where the ore carries 
 tellurides ; there I shall have the assays done in triplicate. 
 
 The question of high assays is a difficult one. Even Mr. 
 Rickard handled this question gingerly. As he implied, it 
 is one which varies with nearly every mine ; it cannot be 
 reduced to definite system. In some mines : but I think 
 very few the occasional high assay truly represents the 
 nature of the ore. Mr. Rickard's example of the Tomboy 
 mine, as falling under this heading, is also the one I 
 would suggest. If the fantastic assays at Tomboy were 
 eliminated, the ore would work out at an average recovery 
 of $4 or $5 but it is actually double that. At the adja- 
 cent Camp Bird mine, the assays of which run into hun- 
 dreds of dollars and they occur rather often are judged 
 in their relation to the assays on each side, and, should 
 those be much lower, are reduced considerably. For ex- 
 ample, three following assays going $52 $165 $79 
 would be entered on to the plan, but in a series reading 
 $5 $104 $11, the middle assay would be drastically cut 
 down. In the Camp Bird there are so many very high 
 assays that this method leaves the management with a 
 something "up its sleeve," but, for accuracy, it is nearer 
 the mark than putting every high sample on to the plan at 
 its theoretical value. On the Rand, at least in my day, 
 exceptional assays were rigidly reduced to something like 
 the general average of the mine. I feel sure this was 
 
 142 
 
correct. The collapse of many of the outside Transvaal 
 mines, banket and quartz, may be traced to the fact that 
 their sampling was inefficient, and that their incapable 
 managers had included all high assays at their full value. 
 Mr. Denny has written very well on the subject of sam- 
 pling on the Rand. This year I sampled a certain mine. 
 I took seventy-five samples, of which four gave fantastic 
 results, showing coarse gold. The general average with- 
 out these was unpayable, so I was spared the trouble of 
 even re-sampling at these spots. I included these four 
 samples on the assay plan, giving to each a value four 
 times greater than the general average without them, and 
 thereby raising the general average $i a ton. The result, 
 curiously enough, brought the theoretical value of the ore 
 out at the precise figure which some thousands of tons 
 had already yielded in actual treatment. 
 
 As Mr. Rickard pointed out, you may either re-sample 
 a rich spot or you may sample on each side of it, close up, 
 and take the mean of the two. My own idea is that in a 
 low-grade ore, especially one carrying regular values, a 
 high assay is out of place. Even if I re-sampled such a 
 spot a dozen times, and kept getting higher and higher 
 results, I should still cut it down to the average. In a 
 high-grade ore it would be more natural to find a few big 
 assays, but I would not recommend the purchase of a mine 
 on them the margin would have to be represented with- 
 out their assistance. 
 
 In figuring out ore reserves a mine valuer has got to 
 take certain risks, for not one mine in fifty changes hands 
 on the basis of net profit in sight. If the ore-shoot under 
 valuation is of biggish dimensions and the lode well de- 
 fined, I think the engineer is entitled to allow something 
 for "good-will." In such a case, I should allow 25 or 30 
 ft. beyond the face of a drive in good ore ; below a single 
 winze I would allow 10 ft. and below two winzes not a 
 great distance apart, 25 ft. A similar margin of risk 
 would hold good at other development points. If the ore- 
 shoot was a short one, or a series of short shoots, and the 
 lode of "scraggy" appearance, I do not think I would 
 
 143 
 
make any allowance at all. In either case, one would be 
 guided by the condition of neighboring mines. 
 
 Of course, it were better to be in the position of never 
 taking a risk beyond, let us say, a block of ore exposed on 
 two sides but, as I have said, mines can rarely be bought 
 on such conditions. The mine valuer knows that he is 
 liable to error, and that the ore "assumed to exist" may 
 turn out valueless. But if he is an honorable man, whose 
 experience tells him he is justified in taking such risks, 
 I see nothing wrong with the system. If a man is true to 
 himself, he is not dealing falsely by his employers. 
 
 With the assistance of a good surveyor and draughts- 
 man and of a reliable assayer, there is no reason why a 
 mine valuer who is very careful, who is practical, who is 
 experienced, and who, down in the depth of his heart, has 
 confidence in himself, should not arrive at a fairly cor- 
 rect estimate of the intrinsic value of most ore-bodies. 
 But he must be practical. In mine valuation, practice 
 and theory are apt to clash rudely. I once sampled a gold 
 mine which had previously been reported on by one who 
 wrote after his name "Lecturer on Mining." He had fine 
 credentials. This man, as a theorist, was in the upper 
 ranks of mining, but in practice, as a valuer of mines, I 
 found him, to say the least, eccentric. He satisfied him- 
 self with only thirteen samples altogether, although the 
 workings were quite extensive; and from the results of 
 these assumed the average value of 60,000 tons of ore. 
 One block of 18,000 tons he valued on a single sample. 
 Across this same spot my own sample gave $30 less than 
 his, and the rest of the block, from samples taken every 
 few feet, was still poorer. My valuation for the whole 
 mine, from a big number of assays, worked out at one- 
 third of his, and the tonnage at one-third. I do not infer 
 that my own figures were necessarily correct; but those 
 who style themselves "Lecturers on Mining" should real- 
 ize that mines cannot be summarized in thirteen samples, 
 nor 1 8,000- ton blocks of ore by single assays. This per- 
 son, I believe, meant well by his report, but nature did not 
 fit him with that practical and active nature necessary to a 
 
valuer of mines. As a plumber he might have been a 
 success. 
 
 J. H. CURLE. 
 
 London, April 25, 1903. 
 
 The Editor : 
 
 Sir. The interesting series of articles recently pub- 
 lished in the JOURNAL upon mine sampling suggest com- 
 ments resulting from the writer's own experience. 
 
 In the first place, it seems that the prospect pick should 
 not be so summarily cast aside. In cases where the engi- 
 neer is sampling small prospects, or must get along with- 
 out an assistant other than a local helper whose sympa- 
 thies are with the mine, it is possible with a proper use 
 of the head and the point to get a fair sample. In the 
 taking of check samples and for testing particular ore 
 streaks it is very useful, if its weak features are borne 
 in mind. The use of "pop shots" is admittedly unwise, 
 but the flat cone resulting from their use is no more unfair 
 than the numerous irregularities of face encountered in 
 sampling. The salting of the dynamite is all but impos- 
 sible, if the sticks are taken out of the original package 
 and the miner has not been warned. Another point 
 worthy of attention is the condition of the face to be sam- 
 pled. This is very often dirty with mud, powder smoke, 
 and dust. Aside from the actual danger of salting, always 
 possible with dirty faces, it must be remembered that the 
 rich ore minerals of many deposits are brittle and the fines 
 are very rich. Such material may give false values to a 
 sample taken from a dirty face. If the ore be very hard, 
 the only way to get a clean face may be to use pop shots. 
 
 A word about the use of a box to catch the ore cut in 
 sampling. If the ore be very hard it will fly orr" in chips, 
 a considerable part of which will not go into the box ; if 
 soft streaks occur, all the material goes into the box. The 
 result is an unfair sample. If a strip of canvas 20 ft. 
 long be used and the width is sufficient to reach the sides 
 of the drift, all the chips will be caught. There will be no 
 
 MS 
 
danger of any one salting the sample by flipping in ma- 
 terial, if the engineer follows the commendable practice 
 of excluding every one from the workings but his own 
 men. The use of the canvas is also an advantage if the 
 ore be spotty, since it is easy to cut a number of narrow 
 grooves at close intervals, letting the material all form one 
 sample. 
 
 In quartering down the sample it is not always possible 
 or convenient to use the method described by Mr. Rickard, 
 especially in the examination of small and remote prop- 
 erties. If the usual method of rolling the sample on can- 
 vas be used, the fines will be more uniformly distributed 
 if the canvas be rolled by one person, taking hold of oppo- 
 site corners alternately and rolling with the cloth close 
 against the sample. Too often caution is not used to 
 brush off the dust when the rejected quarters are removed. 
 Personally, I find a piece of white enameled table oil-cloth 
 preferable to canvas in quartering down. It is quite as 
 flexible and the glazed surface prevents the material from 
 sticking, while the cloth can be bought at any country 
 store. 
 
 In marking samples some engineers carry small brass 
 disks with numbers punched on them. If used at hap- 
 hazard, and the number entered in the notebook, identi- 
 fication by other parties is impossible. If numbers are 
 put on the outside of the sacks, do not make them con- 
 secutive. 
 
 In extreme cases, as in long trips in Mexico, where the 
 samples cannot be under observation all the time, it is 
 safer to use tin cans made and taken out for this purpose 
 and sealed after filling. 
 
 When inspecting a mine it is both good sense and 
 economy to make a preliminary examination, and to take 
 samples at long intervals. Personally, I believe it is good 
 practice to take samples of foot and hanging-wall streaks, 
 even where apparently barren, also of separate ore-streaks 
 and lenses. It affords valuable information about the dis- 
 tribution of values and as to the advisability of sorting the 
 ore. In my own experience I have found the waste of 
 
 -146- 
 
altered gneiss, constituting the vein-filling alongside of a 
 vein of galena, to be full of cobweb-like films of rich silver 
 ore (pear cite), constituting better ore than the galena, and 
 yet this had been thrown over the .dump for some time. 
 The discovery of the Camp Bird by Mr. Walsh was, he 
 tells me, due to his recognition of the value of a similar 
 condition but of different character. In another mine I 
 found the hanging was an altered andesite containing 
 pyrite and carrying $60 per ton in gold, while the recog- 
 nized pay-ore carried only $12 per ton. While it is true 
 that the local miner generally knows the ore as well as, or 
 better than, the examining engineer, it is well not to fol- 
 low the miner in his prejudices. 
 
 The valuation of a block of ore being based on assay 
 results, it is well to consider how these results should be 
 used. The common method is to multiply each assay 
 value by the width of ore at the point where the sample 
 was taken, adding up the resulting "foot-dollars" and 
 striking an average, to be used with the tonnage of each 
 block to give the total value. In still more accurate work, 
 two assays are made of each sample, and these are aver- 
 aged. Another way, and one which has given very re- 
 liable results, is to average the values of two adjacent 
 samples and multiply the result by the average of the two 
 widths of the vein ; the product is to be used as the value 
 of that particular part of the ore block ; the result is quite 
 different from that obtained by the first method, as will 
 be seen below : 
 
 Width .... 2 (6) 10 (6.5) 3 (2) i (5-5) 10 
 Value $20 ($11) $2 ($10) $18 ($14) $10 ($20) $30 
 
 The average is $16.31, using the first method, and 
 $13.45, using the last. 
 
 Dressing a mine for examination is easier than salting 
 and more difficult to detect. If the ore occurs in bunches 
 or small shoots it is an easy matter to carry up a stope 
 as long as the ore is low grade, or the material is waste, 
 and to stop work as soon as good ore is reached. In a cer- 
 tain Wood River property the mine was so well dressed 
 that a reliable engineer figured that the ore developed was 
 
 147 
 
worth $450,000, and when it was worked it was found to 
 be but $125,000. In a recent case a million-dollar prop- 
 erty, with, what appeared to be, a safe margin of profit in 
 the great blocks of ore developed, was shown by the work 
 after purchase to have been similarly dressed for examina- 
 tion. The irregular workings of some mines and a lack 
 of rectilinear development are likewise misleading. Where 
 the workings follow irregular ore-streaks an ordinary 
 calculation is apt to give a wholly erroneous estimate of 
 the ore developed. This is particularly true of Mexican 
 mines, where the irregular workings follow the ore in 
 utter disregard of any other consideration, such as econ- 
 omy of extraction or systematic development. 
 
 WALTER HARVEY WEED. 
 Washington, July 7, 1903. 
 
 The Editor : 
 
 Sir. Referring to Mr. Weed's letter of July 7, it seems 
 desirable to call attention to the fact that his second meth- 
 od of obtaining averages is indefensible. Starting at the 
 root of the matter, the true average of any set of samples is 
 obtained by multiplying the value of each by the width of 
 each and dividing the sum of the products by the sum of 
 the widths. The average width, of course, in the case where 
 samples are taken equi-distant is the numerical average of 
 the widths. This has been explained recently in the series 
 of articles in the JOURNAL that prompted this discussion ; 
 a little earlier Mr. A. G. Charleton referred to the matter 
 in Volume IX. of the Transactions of the Institution of 
 Mining and Metallurgy, and once at least in an earlier 
 volume of our own Institute the subject has been dis- 
 cussed. All of these papers have been of admirable clear- 
 ness, and will certainly bear re-reading at intervals by 
 every engineer. In passing on, I would like to call atten- 
 tion to one detail: While the average value of the rock 
 will truly be determined as above, the average stoping 
 value of the rock in cases where the widths run down to a 
 
 148 
 
space smaller than that in which a man can work must, 
 for correctness, be referred to least stoping width. 
 
 However, this is a matter aside. Returning to the 
 question in hand, I append below a list showing the aver- 
 age values of the five samples according to Mr. Weed's 
 two methods, substituting for his results those obtained 
 by using the proper average width divisor, and the aver- 
 ages also worked out (rather as matter of curiosity) for 
 the second method, but using true averages for the sections 
 between each pair of samples. As a further explanation of 
 this last let it be noted that Mr. Weed's parenthetical val- 
 ues in nowise represent the true values for those sections, 
 as they are bare numerical averages, giving the same 
 weight to a two-foot sample and a ten-foot sample. Thus 
 he gives the average for the width between the first two 
 samples as 6 ft., which is correct ; he obtains his average 
 value in the same way : 
 
 * 20 + ^ 2 equals 11.00. The error is erident: 
 
 #20.00 X 2 ft. equals 40 foot-dollars. 
 
 2.00 X 10 " " 20 " " 
 
 12 " " 60 " " 
 
 *- equals, 5, the true average for the first section. 
 
 But there is another error that crops up in this method 
 of sections or panels ; it is that the three middle samples 
 are used twice, the first and last but once ; and as, in this 
 case, the first and last samples are the highest, the re- 
 sulting average is too low. Of course with a large suite 
 of samples, such as would obtain in most practical work, 
 this error would not be large, but it is hard to see any ex- 
 cuse for this method in mine valuation. The comparison 
 is as follows : 
 True averages as given by Mr. Weed's first 
 
 method $16.31 5.2 ft. 
 
 Average by sections, Mr. Weed's second 
 
 method $1345 5o ft. 
 
 The same with true sectional averages $12.69 5- ft- 
 
 This comparison satisfactorily shows the extent of 
 149 
 
error easily obtainable by an incorrect system of averag- 
 ing, which extends to width as well as value. 
 
 All of us, I fancy, have had experience of the matter 
 mentioned in Mr. Weed's last paragraph, of a mine being 
 "dressed for examination." It is the common dodge of 
 the prospector, who runs well into a good "bunch," and 
 leaves it for the engineer to sample and. goes to another 
 part of the property to repeat the "dressing." But there 
 is another point, which calls for the careful investigation 
 of the engineer : It is a common claim among promoters 
 that the actual results from mill-runs furnish a better 
 indication of the value of the ore reserves in a property 
 than any amount of sampling, and this claim can be so 
 plausibly supported that, by the investor at least, it is fre- 
 quently accepted as truth. As a matter of fact the own- 
 ers are apt to be pressed for money, otherwise they might 
 not have wished to sell the mine, and in that case they are 
 sure to have handled the better grade of rock, so that the 
 result of past operations would not in any way represent 
 the value of the ore left. I have a case in mind where the 
 drifts were at times run very high. The high spots turned 
 out to be in particularly good ore; in this case but little 
 stoping had been done and considerable development, and 
 until one had seen the property the claim that the value 
 of the ore extracted represented the value of the ore left 
 seemed a most plausible one. 
 
 R. GILMAN BROWN. 
 
 San Francisco, July 25, 1903. 
 
 The Editor : 
 
 Sir. In common with many of your readers I have en- 
 joyed the discussion that has appeared in your columns 
 over the methods and details of mine sampling, and, in 
 connection therewith, I am tempted to break the silence 
 generally held by me, to mention an interesting incident 
 of sampling that occurred in a mine in California. 
 
 The ore was the usual quartzose schist of the middle 
 counties of the Mother Lode. About 50 Ib. had been 
 
 150 
 
broken from a 12-ft. face of ore, and while wet and a little 
 sticky, it was broken down to about ^-in. pieces; after 
 the usual rolling and quartering upon ordinary cotton 
 duck, it occurred to me that it would be interesting to take 
 the two final quarters, crushed to about 3/8 in., and weigh- 
 ing about 10 lb., as two samples, and have them assayed 
 separately, because it is generally assumed that the final 
 quarterings are of equal assay value. 
 
 Much to my surprise one quarter assayed $14.80, the 
 other, $3.90, in gold per ton. Upon inspecting the sam- 
 ples from other cuts, carefully, I found the gold occurred 
 in small wires, and that these wires were sharp and very 
 easily penetrated the cotton duck, so that a form of con- 
 centration was being effected the more the sample was 
 rolled. To obviate the trouble the large samples were 
 placed in a gunny-sack, brought to the surface and dried, 
 and a canvas having a prepared or soft enameled sur- 
 face was used thereafter in all work involving gold and 
 silver determinations. The enamel of the cloth admits of 
 a thorough admixture of the sample, and at the same time 
 prevents the gold from adhering to the canvas the ac- 
 tion being similar to that of glazed paper in the laboratory. 
 
 I think it a great mistake not to have some means of 
 identifying a sample after it has been closed and sealed, 
 and a serial number, not necessarily the sample number, 
 should always be placed on the bag as soon as the sample 
 is sacked and tied. 
 
 RICHARD A. PARKER. 
 
 Boston, June 20, 1903. 
 
 The Editor: 
 
 Sir. Mr. Richard A. Parker, in your issue of July 4, 
 touches upon a subject of interest to those whose duty it 
 becomes sometimes to sample auriferous deposits. 
 
 Mr. Parker's meaning, in the letter referred to, is not 
 altogether clear. Does he mean that the concentration 
 of the gold in the interstices of the duck took place during 
 
 151 
 
the rolling of the sample, which had been broken up to 
 pieces about ^2 -in. size, or after the final quarterings had 
 been crushed to about ^-in. ? 
 
 If the former was the case, how was the gold trans- 
 ferred from ^-in. pieces of a wet and sticky quartzose 
 schist into the pores of an ordinary sampling cloth ? 
 
 If the concentration took place after the final quarter- 
 ings, how does it come that those quarterings assayed 
 $14.80 and $3.50, respectively? Why was not the concen- 
 tration equal in each of the quarterings ? 
 
 The question of gold being removed from samples and 
 caught in the interstices of a sampling canvas, is an old 
 one. The writer had an experience of a similar nature 
 some years ago. The promoter of a gold mining prop- 
 erty urged, as the cause of extremely low results obtained 
 from a sampling of the various openings, that the writer 
 had broken down the samples onto canvas, and quartered 
 them down on same, rolling them over and over as many 
 as twenty times or more. He enclosed with his letter a 
 piece of the canvas to show how easily the gold could be 
 caught in it. He failed, however, to explain how the gold 
 got out of the quartz, for the samples were large ones, and 
 the material was broken to about the size of hickory nuts. 
 
 W. L. AUSTIN. 
 New York, July 6, 1903. 
 
 The Editor : 
 
 Sir. In your issue of July 4, 1903, Mr. Parker gives 
 an example of the very indifferent results obtained by roll- 
 ing and quartering samples on canvas sheets. 
 
 Every one, of course, admits that quartering samples on 
 a canvas is not the most reliable way of obtaining per- 
 fectly accurate results. Still, away from railroads where 
 one is obliged to pack for days, riffles not being made, as a 
 rule, substantial enough to stand rough handling, nothing 
 is left to the engineer but the use of a canvas sheet which 
 can be replaced anywhere when necessary. 
 
 152 
 
In the case cited by Mr. Parker, and where he found 
 such difference between his two ultimate quarterings as to 
 render the results useless, I hardly think that it was due 
 to concentration on the canvas, but that the cause lay with 
 the nature of the sample itself. Mr. Parker states that 
 the ore was a quartzose schist, "slightly wet and a little 
 sticky." Naturally, if the sample carried fine metallics 
 which were set free by the partial crushing, these particles, 
 as a matter of course, would be picked up by the larger 
 "wet and sticky pieces 1 ' of the samples, which pieces acted, 
 in fact, as clay does in a sluice. Under such conditions a 
 fair sample can hardly be expected. As stated above, we 
 all recognize that canvas quartering is far from being 
 accurate, but still very close checking can be done with it. 
 
 The example given further on, although not at first in- 
 tended to check canvas results, will, however, give an idea 
 of how close results can be obtained by using ordinary 
 precautions. 
 
 The following samples were taken from a quartz vein, 
 ribboned in structure ; the quartz was middling hard and 
 carried small amounts of sulphides of iron, zinc, lead and 
 copper. Three mill-runs of twelve hours each gave re- 
 spectively 80, 83.34 and 87 per cent of the gold values 
 on the plates ; consequently the ore could almost be called 
 free milling, notwithstanding the small amount of sul- 
 phides present. The samples weighed originally 30 to 60 
 or 70 lb., according to width of vein, and after being thor- 
 oughly dried they were crushed by hand to about quarter- 
 inch size, and then thoroughly rolled and quartered down 
 on a large piece of canvas, the owner of the mine securing 
 the two rejected quarters of the sample. 
 
 The samples were assayed in Denver by a well known 
 and reliable assayer and gave the results below, or an 
 average of gold 2.333 foot-ounces, and silver 8.45 foot- 
 ounces. Later I received the results from the mine own- 
 er, as giving an average of gold 2.42 foot-ounces, and 
 silver 10.4 foot-ounces. 
 
 153 
 
Mine Owner's Engineer's 
 
 Samples. Samples. 
 
 No. Ag. oz. Au. oz. Ag. oz. Au. oz. 
 
 i 5.60 0.87 4.13 0.87 
 
 2 13.70 1.16 12.00 i.oo 
 
 3 3-26 0.44 1.33 6.40 
 
 4 17.38 1.31 16.00 1.28 
 
 5 6.12 4.52 3.72 5.08 
 
 6 3.80 1.74 2.00 1.40 
 
 7 5.48 0.64 4.00 0.56 
 
 8 13.12 7.58 12.40 8.00 
 
 9... 16.42 1.07 15.00 0.88 
 
 10 6.61 1.04 2.47 0.93 
 
 ii . , 8.05 5.78 3.42 4.48 
 
 12 4.17 0.35 3-00 0.39 
 
 13 7-52 1.32 4-20 1.20 
 
 14 15.60 1.45 17.00 1.26 
 
 The difference in the gold average of the two sets of 
 samples is 4 per cent, which is close enough for all prac- 
 tical purposes ; but the diff erence in silver of 19 per cent 
 is rather large. However, taking into consideration that 
 the assays from the mine owner were made away from any 
 railroad, in Mexico, where supplies are not always stand- 
 ard, and also taking into consideration that his interest 
 in the matter might have made him perhaps rather partial 
 to the mine, 'the above results show that pretty accurate 
 work can be done on the canvas sheet, when one is obliged 
 by circumstances to use it. Ordinary care should be 
 taken, samples should naturally be well dried and broken 
 to about %-inch size, then carefully rolled so as to obtain 
 a perfect mixture ; if the mass slides instead of rolling on 
 the canvas the ultimate quarters will be spotted, as a con- 
 centration in that case occurs; after each quartering the 
 sheet should be thoroughly brushed with a stiff broom and 
 close checking of the quarter's assays will invariably fol- 
 low. 
 
 G. M. GOUYARD. 
 
 Denver, Colo., July 27, 1903. 
 
 The Editor : 
 
 Sir. In answer to Mr. W. L. Austin's queries in the 
 JOURNAL of July n, I would say that the original sample 
 
 154 
 
was broken to about 5/2 in. before quartering and rolling 
 began ; the final samples were broken to between % and % 
 in. In a more or less clayey mass which had been rolled 
 frequently it is impossible to say when the concentration 
 took place, if indeed it was a concentration ; the more the 
 sample was rolled wet as taken from the face, the greater 
 the tendency of the gold wires to find lodgment in the soft 
 duck, or in the clayey film that readily forms after fre- 
 quent rollings of such samples. 
 
 The differences in assay value were due to the greater 
 number of gold particles in one sample than the other, and 
 the reason these particles were not more uniformly dis- 
 tributed by rolling was due to the sticky nature of the ma- 
 terial sampled. 
 
 Any one at all familiar with the auriferous schists of 
 the Mother Lode of California would readily see the im- 
 portance of the suggestion made: the difference between 
 ordinary gold quartz and the schists named is apparent 
 and readily accounts for the greater ease with which the 
 gold particles leave the sample in the latter case. 
 
 The point I wish developed is the danger of quartering 
 down ores carrying free gold, wet or damp, and doing 
 this upon the ordinary canvas such as is generally used 
 for such purpose ; it is difficult to properly clean the canvas 
 after each sampling owing to the sticky, clayey material 
 that fills the interstices of the duck, and particles of gold 
 left from one sample may be incorporated in the following 
 one, thus rendering one too high and the other too low by 
 the value of the gold misplaced. The samples should be 
 fairly dried and then quartered upon canvas having an 
 enameled surface. 
 
 RICHARD A. PARKER. 
 
 Saranac Lake, N. Y., July 17, 1903. 
 
 The Editor: 
 
 Sir. In experimental physics it is often necessary to 
 know how far the results are accurate after all positive 
 corrections have been applied. The method of least 
 
 155 
 
squares is a mathematical process which accomplishes this 
 by combining the limiting inaccuracies of the instruments 
 and methods employed, and gives a figure representing 
 the mean probable error of the final result. 
 
 In a mine only a very small portion of the ore is ex- 
 posed to the sampler, and as the values are very unevenly 
 distributed the mean probable errors are very large, as 
 compared with those of other methods of measurement 
 which we have to make. In a great many cases, the cost 
 of mining and treatment being deducted, there is only a 
 very small margin of profit left, and it is then important 
 that the engineer should be able to represent to the owners 
 or prospective purchasers how far the mine is a safe in- 
 vestment and how far a speculation. 
 
 If a block of ore is sampled and said to average A, 
 we mean this as the nearest approach to its true average, 
 which can be obtained by taking samples around its 
 boundaries ; the figure A may be somewhat too great or it 
 may be somewhat too small. To be precise, therefore, we 
 should say the average is A . V, where V is the mean 
 probable error. Now suppose we have several blocks 
 constituting a mine and averaging A V , A 2 V 2 , A 3 
 V 3 , etc., and weighing respectively M^ M 2 , M 3 , etc.; 
 then by the method of mean squares the average of the 
 whole mine will be 
 
 M! A! + M 2 A 2 + M, A 3 + etc. 
 
 M l + M 2 + M 3 + etc. 
 
 M 2 3 V 2 3 
 
 M! + M 2 + M 3 + etc. 
 which may be more conveniently written 
 
 Z M A + s M2 V2 
 
 S M S M 
 
 The following is a tabulated example : 
 
 M A+ V 
 
 Tons. Ozs. Per Ton. M A. MV*. 
 
 Block No. i.... 2,100 3.60 +.32 7,560 4Si,S94 
 
 Block No. 2.... 5,800 4.50 +.20 26,100 1,345,600 
 
 Block No. 3.... 1,200 6.20 +.55 7,440 435,600 
 
 Totals ........ 9,100 41,100 2,232,794 
 
 156 
 
Mean 
 
 41,100 
 
 2,232,794 
 
 9.i< _L_ 9,100 
 
 or 4.51 + 0.16 oz. per ton. 
 
 The mean probable error involved in the usual method 
 of sampling cannot be deduced in any very rigorous 
 mathematical manner, but requires certain broad assump- 
 tions. Suppose a square to be divided into eight equal 
 
 li 9 1 
 
 triangular portions so that each presents an equal and 
 similarly situated sampling face as shown in Fig. I, and 
 that two samples assaying a and b, are taken on each 
 such face; then we may assume the average for the tri- 
 angle, as far as can be ascertained from the face, to be 
 m a a -j- 
 
 . 
 
 m a a 
 
 for each triangle, where m a and mb are respectively the 
 thicknesses of the vein at a and b. The term 
 
 m a a 
 
 m a m b 
 
 represents the variation from the simple average to just 
 the same accurac as 
 
 m a a 
 
 m a 
 
 represents that average. 
 
 If we now compound the averages of the triangle by 
 the method of least squares, we get for the whole block : 
 
 157 
 
2(m a a + m b b) , S(m a a m b b) a 
 A V - S(m a + m b ) S(m a +m b ) 
 
 When a block of ore is not square it may be divided 
 in a similar manner, as shown in Fig. 2. Greater accu- 
 racy (or a smaller variation from the average) is obtained 
 by dividing off the ore-shoots separately where their 
 boundaries are reasonably well defined; the results can 
 afterward be compounded with those of other blocks of 
 pay ore. 
 
 If the one below the bottom level is divided off into 
 two 45 right-angled triangles, as in Fig. 2, a large value 
 is obtained for V. This is illustrated by the following 
 table, which also shows the method of deducing the mean 
 variation where more than two samples to the triangle 
 are taken. 
 
 Sample 
 
 No. 
 
 (I 
 
 Width 
 
 Ft. 
 (m) 
 
 26 
 
 Assay 
 oz. per ton 
 (a) 
 2.2O 
 2.05 
 
 1.09 
 
 .05 
 
 .07 
 .18 
 
 Variation from 
 Oi.-Ft. simple mean 
 per ton of ma 
 (ma) (5.720 I.787&C.) 
 
 5.720 3-933 
 3.895 2.I08 
 
 .654 I-I33 
 .065 1.722 
 .084 1.703 
 .306 1.381 
 
 2 
 
 I Q 
 
 3 
 
 :::: o% 
 
 4 
 
 i. * 
 
 5 
 
 . . . . 1.2 
 
 6.:..:::: 
 
 1.7 
 
 i Totals 
 
 
 . . 10.724 
 
 II.980 
 
 1.997 
 
 0.279 
 0-439 
 1.471 
 0.881 
 1.792 
 3.427 
 
 
 
 
 I 787 
 
 !7.. 
 
 . .. . 20 
 
 1.22 
 
 I.OO 
 0.30 
 
 0.80 
 
 041 
 
 5.08 
 
 2.440 
 2.60O 
 .690 
 1.280 
 
 8 
 
 26 
 
 o 
 
 2 ^ 
 
 10 
 
 1.6 
 
 ii. . 
 
 , O.Q 
 
 12 
 
 . .. . II 
 
 2 Totals 
 
 
 . TO 8 
 
 12.967 
 
 2.161 
 
 8.289 
 1.381 
 
 2 Means. . 
 
 Ufc 
 
 From which we deduce 
 and 
 
 10.724 + 12.967 
 
 A --- 153- 
 
The law of least squares only applies strictly where V 
 is small compared with A, but in extreme cases, such as 
 the above, V is none the less useful as indicating the low 
 degree of accuracy of A ; and although a more complex 
 law may be used for these cases, it is obvious that V can- 
 not be expected to be more accurately ascertained with 
 the same data than A. 
 
 No attempt is here made to estimate the probable quan- 
 tities of ore beneath the bottom level ; we are dealing only 
 with the degree of variation of value of given quantities 
 of ore- 
 
 159 
 
If greater certainty is required on a smaller amount of 
 ore below the bottom level the assays may be divided 
 among several smaller triangles, which will be equivalent 
 to a row of rectangles of the same areas and bases. A 
 will then remain the same, but V will be considerably re- 
 duced, and this should be done if the averages are to be 
 combined with those of ore better blocked out. The same 
 remarks may also apply to ore exposed on two sides ; 
 rectangles may be used instead of rectangular triangles, 
 except at corners, but they should not vary much in 
 dimensions from the ratio of 2 to I, except in the cases 
 where ore or barren ground evidently runs in shoots or 
 horizontal zones. 
 
 The averages of all the ore considered payable having 
 been combined in classes according to average value, mean 
 error and other considerations and the method of min- 
 ing and treatment having been decided upon, the value 
 of the mine may be investigated by examining them sev- 
 erally by the following formulae: 
 
 Where $ is the value in money of an ounce or unit of 
 the crude. 
 
 P is the percentage extraction. 
 
 q is the tonnage. 
 
 /* is the sum of costs of mining, machinery, treatment 
 and bank rate of interest compounded on the time the ore 
 is to stay in the ground. 
 
 As regards presentation to the financier, I find the 
 word "risk" is fairly well understood on Wall Street; 5 
 per cent risk is an even chance of making or losing 5 per 
 cent on the investment and 100 per cent risk means an 
 even chance of doubling or losing the investment. There- 
 fore, if R represents the percentage risk, it is given by 
 
 which becomes an appreciable figure even in the best de- 
 veloped mines. 
 
 160 
 
Purely business men in the ordinary competition of 
 trade do not expect to make more than bank interest on 
 their capital and their salary as clerks without running 
 some risk, but they make money in the long run by sound 
 judgment of the comparative chances of profit and loss 
 and by seizing the opportunities for the greatest probable 
 profit at the least risk. The engineer who does not take 
 proper account of the high assays obtained in fair sam- 
 pling is therefore a poor adviser to the financier. 
 
 The use of the compound system of averages does away 
 with the necessity for the use of such indefinite and arti- 
 ficial terms as "ore in sight," "probable ore," etc. ; not only 
 do the number of sides exposed count in determining the 
 average, but the spotty character of the ore, the size of the 
 ore blocks and the extent of the mine development are 
 all properly compounded in the value V and make them- 
 selves known to the capitalist as the value R which he 
 fully appreciates, and which ought also to be a guide to 
 the engineer in recommending that the installment of ma- 
 chinery be immediate or deferred until the mine is further 
 developed. 
 
 Just as much reliance can be placed upon V as a meas- 
 ure of the probability (or degree of "insightedness") of 
 the ore as upon A, for whereas A has its origin in values 
 of single samples which are very variable, so V is built 
 up of differences of values of single samples which are 
 not much more variable quantities. 
 
 I have used these rules, with modifications to suit local 
 conditions, for over two years upon every set of samples 
 I have come in contact with, and now place absolute con- 
 fidence in the reliability of the results. 
 
 BLAMEY STEVENS. 
 
 Valdez, Alaska, July 21, 1903. 
 
 The Editor: 
 
 Sir. In the perusal of the articles on the estimation 
 and sampling of ore-bodies which have appeared in your 
 
 161 
 
paper recently, and which, by the way, have afforded me 
 much interest and pleasure, I have not noticed any men- 
 tion made of the prismoidal formula in its application to 
 the measurement of irregular ore-bodies. Some years 
 since I discussed the value of it in one of a series of papers 
 on mine surveying which I wrote for Mines and Minerals. 
 The application of it is so simple and its results are so 
 accurate in practice that I should think its usefulness 
 would appeal to mining engineers, as it always has to civil 
 engineers. 
 
 Naturally care must be exercised in its use ; to illustrate, 
 take a body acgefhdb, as shown by the accompany- 
 ing diagram, the calculation would need to be made first 
 for the smaller volume, a c d b, then for c g e f h d. 
 
 Re-entering angles must, of course, also be taken into 
 account; but the three sections of a body being given 
 top, middle and bottom their areas can be quickly ascer- 
 tained by dividing the sections into triangles. The vol- 
 
ume of the body, calling the top section a, middle section 
 a', bottom section a" and height h, is : 
 a + 4a' + a" 
 ~6~ ~ h 
 
 I know by frequent use both in the estimation of ore in 
 mines and in piles, that it gives results accurate enough 
 for practical purposes. 
 
 Another point I would like to bring up is the protec- 
 tion of mine samples. The value of accurate measure- 
 ment and sampling of ore-bodies is self-evident, but to my 
 mind the protection of the sample from mine to assay 
 office is at least of equal importance. A device which has 
 given great satisfaction to me, and which I have used for 
 years, is a lead seal like that used by the express com- 
 panies. The seal is of lead jMj in. diameter, % in. thick, 
 with two holes through its circumference large enough 
 for a thin copper wire to pass through. When the sample 
 bag has been tied with the wire passed through the seal 
 the holes in the latter are closed by pressure of a die with 
 a name sunk on one side and some mark or monogram on 
 the other. Any novelty company will make such a die, 
 and usually has the lead seals for sale. Samples, thus 
 sealed, and locked in sole leather bags, also sealed, are 
 safe. 
 
 The advantage of using this method as compared to 
 sealing-wax is also apparent, where sampling is done in 
 open-cuts or draughts. 
 
 AUGUSTE MATHEZ. 
 
 New York, August 12, 1903. 
 
 The Editor: 
 
 Sir. I have followed with great interest your series of 
 articles on "The Sampling and Estimation of Ore in a 
 Mine," and with your permission will make some com- 
 ment thereupon from the standpoint of the practice fol- 
 lowed in the group of mines of which I am the technical 
 head. 
 
 163 
 
The function of sampling is now well recognized on 
 these gold-fields as one of the most important contribu- 
 tions to the commercial success of the mines. The old- 
 time haphazard method of promiscuous sampling, either 
 by taking pieces of ore from trucks or "picking" down odd 
 sections in the mine, has no present adherents, nor is the 
 work of sampling relegated to the inexperienced "new 
 chum,"* who formerly, if not thought intelligent enough 
 for any other class of work, was provided with a sampling 
 job. The enormously valuable part played in the economy 
 of mining by systematic and conscientious sampling is 
 now well recognized. A class of skilled, intelligent, alert 
 men, culled largely from trained engineers, has arisen, and 
 these have raised the status of mine sampler from infe- 
 riority to one of importance. It is gratifying to read that 
 the peculiar and constant calls upon the integrity and 
 will of the sampler have been duly acknowledged in the 
 articles under review, and I believe the mine sampler will 
 be encouraged and assisted to still greater efforts because 
 of them. 
 
 In your introductory article, you dwell upon the fact 
 that methods of mine valuation and examination have 
 undergone very considerable development during the past 
 decade, and you indicate the possibility that the close 
 attention to this part of gold mining business on the Rand 
 has, to some extent, influenced for the better the mining 
 industry at large. Speaking as an Australian, and being 
 also personally acquainted with American and European 
 methods of some ten years since, I can cordially indorse 
 the views which you have expressed as to the present ad- 
 vanced stage reached in the practice of mine sampling and 
 valuation compared with the period I have named. Nor 
 does the advance relate only to other countries ; it is true 
 no less of the Rand. The systems now in vogue repre- 
 sent the outcome of evolutionary growth, and are based 
 upon experience and sound principles ; but the writer well 
 remembers some few years ago having to deal with assay 
 reports and plans which were prepared and averaged in 
 
 *This is the colonial equivalent of our Western "tenderfoot." Editor. 
 164 
 
the most elementary fashion, without any regard to widths 
 of reef or intervals between sections. Now, happily, 
 these instances are rare, and, in fact, so far as the Rand is 
 concerned, things of the past; and the engineer is no 
 longer troubled by enormous discrepancies between assay 
 reports and milling returns, making, of course, the allow- 
 ances which experience dictates as necessary between mere 
 assays and actual recovery. 
 
 The engineer practicing on the Rand recognizes that 
 here is, par excellence, the field which lends itself to the 
 application of method. The banket beds, while fluctuating 
 violently both in width and value in local areas, are unpar- 
 alleled for consistency when considered throughout the 
 Witwatersrand area, and the great range of development 
 made possible by the natural condition of the ore and gold 
 deposition give quite unusual facilities for estimation and 
 the application of the law of averages. That these facili- 
 ties have been recognized and embraced is undoubtedly 
 creditable to the engineers, past and present, on the Rand, 
 but it cannot be gainsaid that the conditions were such as 
 to make the scheme almost self-suggestive. In looking 
 back over one's past experience in other countries, and 
 taking the natural conditions generally present in quartz 
 deposits into account, whether these have been exfiltrated 
 into previously existing fissures or segregations within 
 rock masses, and considering further the small amount of 
 development done upon the "prospect" which one was 
 engaged to examine and value, and at the same moment 
 transporting oneself mentally to the mines of the Rand, 
 the conclusion is forcibly impressed upon one's mind how 
 exceedingly advantageously situated is the man working 
 on these fields, and how, in comparison, the risks of error 
 he runs, given careful work, are minimized to the last 
 degree in comparison with the engineer who is employed 
 on deposits of a different character. 
 
 Mine examination in South Africa is shorn generall}- 
 of many of the dangers present in pursuing similar inves- 
 tigations either in America or Australia. The mine salter, 
 with his many ingenious methods of introducing gold 
 
 165 
 
either in the ore face or into samples, is unknown. The 
 assayer who returns high-grade results from "grindstone" 
 specimens has not flourished. The reason, probably, why 
 there is no room for people of this class is that banket 
 mining is essentially a capitalist's operation. 
 
 In quartz, or in other forms of ore-deposit, the metal 
 worked may occur in rich bunches, which enable a pros- 
 pector of limited means to collect sufficient of it to pay 
 his way. In banket this is not the case, and therefore 
 the banket bearing ground is sold on option to a company 
 financially strong enough to exploit it. In the case of the 
 examination of mines, the personal incentive to defraud 
 for profit is wanting, because the mine is owned generally 
 by a company, and individuals are not interested suffi- 
 ciently to make it worth their while to seek means to create 
 results more favorable than are actual. No claim can 
 therefore be made that persons connected with the gold 
 mining business here are more scrupulous than elsewhere. 
 The simple fact is that opportunity seldom arises for an 
 individual to perpetrate fraud for his personal advantage, 
 owing to the special conditions of the case, and hence, 
 having no temptation to err, all are alike honest. 
 
 I cannot quite agree with you, Mr. Editor, in your state- 
 ment that "average value of the ore in the past can be 
 ascertained from the records of a mine," if by "ore" you 
 intend to convey the larger meaning of the exhausted por- 
 tion of the mine. In my experience, I have found it just 
 as necessary to make an inspection of the exhausted por- 
 tion of the mine as of the current producing section, for 
 the following reasons : Firstly, to prove to my own satis- 
 faction that the mine has been fairly worked in regard to 
 area of reef. It will readily occur to the reader that a 
 mine can be easily manipulated to show high returns over 
 a short period. Take the case of a mine which has two 
 widely separated, narrow, rich shoots of ore. On such a 
 proposition it would be possible to develop for a period of 
 one year, and at the expiration of that time commence 
 milling on high-grade rock. Assume that during the 
 twelve months 100,000 tons of ore have been developed 
 
 166 
 
at a cost of 25,000, but that actually the rich pay ore 
 represents only 25 per cent of the total tonnage. Then 
 the charge for the redemption of the ore would have to 
 appear in the working account as at 4 by 5, or 205. per 
 ton milled, and it is obvious that such a charge would 
 require unusually rich rock to bear it. It would also be 
 doubtful if a mine yielding so low a percentage of pay- 
 rock could be developed fast enough to supply any but a 
 mill of very small capacity. 
 
 The second reason why it is important to examine for- 
 mer workings in a mine under examination is to find out 
 the relation between reef width and stope width. It has 
 occurred in the writer's experience that the grade of a 
 mine showed much lower than its mean average, because 
 of including unpayable bands of reef or waste in the stopes 
 for the purpose of showing low working costs. 
 
 Now, it is indisputable that mines should be operated 
 for profit per ton, and such an objective as low operating 
 costs is quite unjustifiable, excepting after the considera- 
 tion of the main issue stated. I believe it will be agreed 
 therefore that "the average value of the ore in the past" 
 is not a criterion for the engineer to accept unquestion- 
 ingly ; otherwise, in the first instance quoted, he would be 
 liable to have his judgment of the existing development 
 prejudiced too favorably, and in the second instance the 
 past records might lead him, even in the light of present 
 satisfactory development, to put much too low a value on 
 the mine. 
 
 Mines in New Districts. You have plainly indicated 
 some of the precautions to be observed by the engineer in 
 estimating values of undeveloped mines in new districts, 
 all of which are pertinent. It seems to me that one chief 
 difficulty in estimating values in mines so placed is the 
 want of facilities for observation. The engineer is called 
 upon to decide whether a certain "prospect" is valuable or 
 otherwise, and the available data upon which his judg- 
 ment and previous experience are brought to bear are often 
 meager in the extreme. Perhaps the points exposed are 
 widely separated ; he has no opportunity of studying dike 
 
 167 
 
Form No. 99. 
 
 Meyer & Charlton Gold 
 
 v 
 
 Shaft- 
 
 WIDTH of 
 
 DISTANCE FROM. 
 
 Assay, 
 
 of 
 Sections 
 
 alue over 
 Width 
 Sampled 
 
 lili 
 
 
 II 
 
 Assay 
 Inches: 
 
 /& 
 
 /f 
 
 /*'/ 
 
 9- 
 
 Jo 
 
 '*'/ 
 ,*? 
 
 /fa- 
 7*' 
 
 7* 
 
 7 
 
 3-6- 
 
 * 
 
 /-A' 
 
 f? 
 
Mining Company, Limited. 
 
 Drive 
 
 Date- 
 
 f y** < *-* o^-^^^c/- 
 
 160 
 
or fault effects, nor the probable width or trend of the 
 shoot; nor, in fact, any of the vital factors entering into 
 the ultimate consideration of the value of the mine as a 
 commercial undertaking. He is therefore forced to one of 
 two alternatives, either (i) to intuitively sum up the 
 value of the property, or (2) to refuse to commit himself 
 to an opinion until more work is done. The first alterna- 
 tive will always be avoided by the judicious engineer in 
 favor of the second, both in his own interest and in that 
 of his client ; nor is it consistent with sound professional 
 practice. The new district is always fertile in the class 
 of property that is alleged to yield ore of the same grade 
 as that in some adjacent successful district. In this coun- 
 try, for instance, it is usual to find the prospector or claim- 
 holder filled with the conviction that as the working costs 
 on the Witwatersrand approximate to 6 dwts. of fine gold 
 per ton milled, he has only to establish the fact that he 
 has 7 dwts. assay value in his ore to claim payability. He 
 conveniently forgets, or probably does not know that 
 from an assay value of 7 dwts. he can only recover by the 
 ordinary processes 4.2 dwts., which would leave him 1.8 
 dwts. on the wrong side, figuring costs at 6 dwts. per ton. 
 The engineer has therefore to be careful when fixing the 
 value of a proposition to allow, as a margin of safety, that 
 only 60 per cent of the original assay will be recovered. 
 And here I would plead for the general expression of 
 values in terms of currency, as in speaking of gold 
 ounces may be fine ounces, worth 845. nd., or bullion, 
 worth 505. per ounce ; and in all cases the estimated recov- 
 ery values of ore per ton treated should be given and 
 expressed as so much money value per ton. 
 
 The Cost of Mine Examination. I observe with satis- 
 faction that you have drawn attention to the cost involved 
 in mine examination. In two recent instances of developed 
 mines sampled under the writer's supervision the number 
 of sections totaled about 5,000 in each case, the cost of 
 assaying alone apart altogether from the labor involved 
 in obtaining the samples amounting to an enormous 
 figure. It frequently happens also that, prior to an ex- 
 
 170 
 
-- - - 
 
 - - 
 
amination, the mine workings have to be cleared of water. 
 This is an operation costly in proportion to the quantity 
 of water to be handled. The writer has had instances of 
 pumping amounting to over 1,000, and a monthly cost 
 while the examination was in progress of 350 for this 
 item alone. 
 
 The Sampling Interval. In all mines under the control 
 of the writer the sampling interval is 5 ft., and no longer 
 spacing is, in his opinion, to be recommended. The pre- 
 liminary examination made by the engineer ought to de- 
 cide whether the mine is worthy of examination or not. 
 If it be, then the 5-ft. interval should be adopted. I have 
 found quite remarkable differences in sampling a length 
 of, say, 500 ft., at lo-ft. intervals, and subsequently sam- 
 pling again at intermediate points, and the difference as 
 shown by the original lo-ft. sampling and the mean of the 
 first and second has often been sufficient to reverse the 
 conclusions arrived at from the lo-ft. intervals. The 
 importance of taking the samples at regular distances 
 cannot be over-estimated. 
 
 Sketching Samples. The system of sketching samples, 
 as employed by the writer, is illustrated herewith, and is 
 based upon a scheme suggested by Mr. F. Burnham, now 
 in the employ of the State Mining Department. This 
 system gives in detail a longitudinal section of the shaft, 
 level, or winze, in a continuous length, and is specially 
 valuable when dealing with reefs having a tendency to 
 split. The loss of any part of the reef is plainly denoted 
 in the continuous section, and if of sufficient value the lost 
 portion can be re-attacked. 
 
 Recording Samples. The recording of the samples is 
 plainly shown in the accompanying sheet, which is a copy 
 of a sampler's usual return on the Meyer & Charlton Mine. 
 It will be observed that waste rock is always separately 
 shown, and in the actual sampling it is never sectioned, 
 but simply measured. 
 
 Assay Plans. Of these, two are kept, one being the 
 ordinary outline development plan, and the other a con- 
 tinuous section plan. Specimen extracts from the actual 
 
 172 
 
173 
 
plan are attached herewith. The scheme of the outline 
 plan is to show both development and stope values, the 
 width sampled appearing on the one side, in the case of 
 levels, etc., and the value as upon the estimated stoping 
 width on the other ; the minimum stoping width for pur- 
 poses of calculation being 36 inches. Referring to the 
 plan, it will be seen that the widths are shown in blue and 
 the values in red. The outlines between the levels show 
 the stope faces for the various months, and the assay 
 values are shown in general monthly averages. 
 
 If the widths of reef fall below 36 ins., the actual width 
 of the reef is shown, but the value is calculated always 
 upon a minimum of 36 ins., and appears as upon that 
 width opposite the actual reef width, the reason being 
 that we never estimate the stoping width as likely to be 
 less than 36 ins. 
 
 The scheme of the continuous section plan is to provide 
 details of each sectioned portion of the reef, and a con- 
 tinuous actual sketch of the reef in the levels. Referring 
 to the extract, it will be seen that the sections sampled are 
 shown separately, referring in each instance to the reef 
 matter and waste in their alternate bands. 
 
 The average recovery value of the reef is shown on 
 continuous section plan by different colors represented as 
 
 under : 
 
 Per ton. 
 
 Black indicates a recovery value of o to 20 shillings 
 
 Blue indicates a recovery value of 20 to 25 
 
 Green indicates a recovery value of 25 to 30 
 
 Mauve indicates a recovery value of 30 to 40 
 
 Yellow indicates a recovery value of 40 to 50 
 
 Violet indicates a recovery value of 50 to 100 
 
 Gray indicates a recovery value of 100 shillings and over 
 
 The recovery value (given in shillings) means the 
 actual estimated gold per ton which, from the different 
 processes, the ore will yield, and is roughly based on 70 
 per cent of the actual mine assay value, postulating a 
 
 sorting basis of 20 per cent. 
 
 G. A. DENNY. 
 
 Johannesburg, Transvaal, May n, 1903. 
 
 (Mr. Denny refers above to the colors used to denote various values 
 on the sampling diagrams in use at the Meyer & Charlton Mine. The lira- 
 
itations of our printing-press have compelled us to substitute in the dia- 
 grams, cross-hatching for colors. The explanation is given on the dia- 
 gram itself, on the page accompanying. 
 
 In reference to the sampling sheet, given under Fig. i, it is well to 
 add that the total of sloping widths, in inches, viz., 394, and the total of 
 assay inches, viz., 1527, is carried forward to the end of a series of sec- 
 tions or lengths of drift or stope, when the latter is divided by the former, 
 which then gives the average value in dwts. of gold per ton. EDITOR.) 
 
 The Editor : 
 
 Sir. The articles and discussions which have appeared 
 in the JOURNAL for the past few months on the sampling 
 and valuation of a mine have been exceedingly instruct- 
 ive; although I have read each week's contribution as it 
 came from the press, yet within the past few days I have 
 read the entire matter as a whole, and find there is more 
 information in such a second reading than one obtains in 
 the first perusal of the weekly editions. 
 
 The sampling of a mine is not an easy or simple task, al- 
 though many self-styled engineers think it so and will 
 often return from a mine with a few sacks of hand-gath- 
 ered samples and then write a voluminous report as to the 
 merits of the property and the value of the ore-reserves 
 therein. Sampling is hard labor under the best conditions, 
 and the actual moiling requires the skill of a good miner, 
 carefully watched, of course ; and I have found that good 
 moiling is often foreign even to miners, not to mention the 
 young and uninitiated who come west to get their first 
 experience in mining by doing sampling work. I well 
 recollect the incident referred to by Mr. Rickard in the is- 
 sue of February 14,* when he says, "It took six men (three 
 of whom moiled while the other three held the boxes to 
 receive the sample) the whole of one shift to take three 
 samples over a vein 12 ft. in cross-section, and in accom- 
 plishing this they dulled 35 moils." This incident was at 
 the Camp Bird mine some three years ago, when it was 
 first examined. The moiling was done by strong, able- 
 bodied miners, and Mr. Rickard put me in charge of the 
 sampling at the time. Many engineers regard the sam- 
 pling of a mine as a perfunctory performance, to be gone 
 through lightly, and they aim to accomplish the task in the 
 shortest time and with the least trouble. 
 
 'Page 19 of this volume. 
 
 175 
 
All these points are well known to the readers of the 
 JOURNAL, but I desire to bring them out again, in order to 
 more fully emphasize the hazard and risk courted when 
 the sampling of a partially developed mine is given into the 
 hands of an inexperienced college graduate often unac- 
 companied by the engineer in charge who has come west 
 to supplement his college training with actual practice in 
 the field. This procedure has been adopted by some engi- 
 neers in the last two or three years, but it ought to be dis- 
 couraged. Unquestionably it is a cheap way, for the 
 young men are very ready to undertake the work and at a 
 reasonable figure, some of them being glad to go for their 
 expenses alone. When an engineer is retained to examine 
 a mine, his clients are entitled to all the knowledge of that 
 property which his years of observation and experience are 
 able to yield him ; in fact, his experience, knowledge and in- 
 tegrity are all that is valuable to his clients, and he should 
 give the products of such qualities to them unremittingly. 
 It is obvious that any engineer can learn more concerning 
 a mine under examination by being on the ground and 
 overseeing the actual sampling, and sometimes taking a 
 few himself, than he can possibly gather by going through 
 the workings a dozen times and looking at the places sam- 
 pled after the work is completed, especially in a wet mine 
 where the fresh cuts soon become smeared. I have known 
 of cases where inexperienced men have been sent out to a 
 property for the purpose of sampling, even before their 
 chief has been on the ground, and after the work was com- 
 pleted the engineer then came and walked through the 
 workings and thought he thoroughly understood the 
 chemical, physical and metallurgical conditions. One en- 
 gineer of my acquaintance, and one who is well-known in 
 this country and abroad, and with whom I was fortunate 
 enough to be associated in my days of little experience, has 
 gained an enviable reputation as a thorough engineer, and 
 I attribute his success, in a great degree, to his thorough- 
 ness in sampling. He never intrusted this work to novices, 
 and even when employing an experienced man he was 
 present invariably and superintended the work ; and to this 
 
 176 
 
day he will be found in his overalls, personally directing 
 the sampling of any mine which he is examining. If one 
 is sick and a surgical operation is necessary, is it satisfac- 
 tory, after calling in the favorite doctor, to have him send 
 a fresh medical graduate, whom he has known but a short 
 time, to perform the operation, and after the wound is 
 dressed have the surgeon arrive and pass an opinion on the 
 case? 
 
 Please understand that I am not in any way criticising 
 the employment of young college men ; not at all ; in fact, 
 I am very much in their favor, for I was one myself ; but 
 I am decidedly against their being sent to sample a mine, 
 without the constant supervision of their chief, long be- 
 fore they have had sufficient sampling experience or are 
 capable of assuming such responsibility, because, as before 
 stated, the sampling of a.mine is not a simple problem, and 
 I know of no other process in mine examination that is 
 more important, or from which the engineer himself can 
 gain more information. It is neither fair to the clients nor 
 to the young men. I am glad to learn from the discussion 
 that in several localities, especially in South Africa, the 
 engineers in charge recognize the importance of mine sam- 
 pling to the degree that the samplers are "culled largely 
 from trained engineers." 
 
 Let me say, to those who take the trouble to transport 
 over the country small hand rock-breakers for reducing 
 samples, that three or four good men with short-handled 
 hammers and old stamp-dies or hard rocks for breaking, 
 with a canvas underneath, will break more rock, and do it 
 quicker and with less fines, than an equal number of rock- 
 breakers. I have tried them. 
 
 When there are two or more distinctly different vein- 
 materials, or when the vein does not equal the stoping 
 width, I have found that much better results are obtained 
 by sampling each class of material separately, as it is im- 
 possible to obtain an average by taking the sample across 
 the entire width with a continuous cut, because the differ- 
 ent materials differ widely in specific gravity. With the 
 separate samples it is an easy matter to calculate the aver- 
 
 177 
 
age across the full width. This is the best way out of the 
 difficulty mentioned by Mr. Argall, in the issue of June 
 13, in his Figs. I and 2.f 
 
 I have read the short articles of Messrs. Richard Parker 
 and W. L. Austin in regard to the discrepancy in the as- 
 says of two quarters of a sample which was rolled on can- 
 vas. Mr. Parker gave it as his opinionj that the gold, 
 which was free, very easily penetrated the duck, conse- 
 quently the ore underwent a form of concentration. I agree 
 with Mr. Austin that the gold does not penetrate the 
 canvas ; at any rate, the use of whisk brooms in quartering 
 would remove it ; and I am surprised that neither of them 
 considered the fact that the sample was wet or sticky, for 
 my experience is that most any kind of an assay can be 
 obtained from wet samples, especially if they contain free 
 gold. Without doubt the free gold was enveloped in the 
 sticky material as the sample was rolled, and it certainly 
 could not be homogeneously mixed through the sticky 
 matrix. 
 
 As to numbering samples, I have used wooden, brass, 
 hard rubber and paper tags, and I have found the latter to 
 be the easiest and best. Use a tough bond paper in sheets 
 about the size of a nickel tablet and use a pigment pencil. 
 Write the number in the center of the sheet and fold it in 
 the center, then begin at the folded end and fold to the size 
 of a lead pencil and crimp it by folding over each end. In 
 this way the number is folded in many thicknesses of 
 paper, and I have found that these withstand rough hand- 
 ling in samples which are extremely wet. After the sample 
 is reduced and sacked, beside the number inside 1 number 
 it by a very small number, made with a lead pencil, inside 
 the neck of the sack just as close to the string as possible. 
 It can be found by the sampler, but it is out of sight an4 
 unknown to anyone else. 
 
 After trying canvas and boxes for catching the samples 
 I find the box, a 5O-lb. powder-box, is unquestionably the 
 
 t On page 104 of this volume. 
 J Vide Supra Page 151. 
 Ante. Page 152. 
 
 -178- 
 
best thing to use. It can be obtained readily, and can be 
 used in wet levels, awkward stopes, and anywhere in the 
 mine. It will catch all the sample if held properly, and the 
 samples are easily sacked from it. Mr. W. H. Weed does 
 not explain how one can use a piece of canvas, 20 ft. long 
 by 6 ft. wide, in wet levels, or at the top of high, narrow 
 stopes.* The box merely requires the watching of an area 
 of not over 4 square feet, while the latter necessitates keep- 
 ing an eye out for dropping material from 120 square feet. 
 
 I would like to call your attention to a method of sam- 
 pling which recently came to my notice. The incident is 
 interesting only from the fact that it shows what a loose 
 procedure may be employed when an engineer is in a 
 hurry, due to the pressure of business expediency. But 
 similar mistaken methods have been employed by others 
 who had no such valid excuse and serious consequences 
 have ensued therefrom. 
 
 The mine in question was a mine of some size, contain- 
 ing three levels and having some 935 ft. of workings. The 
 report of the engineer read as follows : "Cuts were made 
 across the full width of the vein from wall to wall at inter- 
 vals of three feet," which should have made some 310 sam- 
 ples. Notwithstanding this statement, the valuation of the 
 property was based upon the assay value of 29 samples as 
 located on the section cut. Subsequent investigation and 
 examination of the workings showed that the statements 
 regarding the sampling were correct, but the results were 
 arrived at in the following manner : Take, for instance, the 
 triangular block of ground between the surface and levels 
 Nos. 2 and 3. The sampling was begun in Tunnel No. 3 
 and samples were taken every three feet, then (and here is 
 the dumfounding step) these 17 samples were all dumped 
 into one large sack and labeled "Sample No. i." No at- 
 tention was paid to quantity of ore from each three-foot 
 section. As each cut was made the width was taken, and 
 the 17 widths averaged and given as the width for Sample 
 No. i. The same process of mistaken reasoning was fol- 
 
 * On page 145. 
 
lowed in obtaining samples 2, 3, 19, 18 and 7, as well as 
 the remaining 23 samples shown in the cut. The samples, 
 as made up from the 3-foot cuts, also represent different 
 lengths along the drifts. The value of the block was then 
 given as follows : 
 
 No. Value 
 Sample, per ton. feet 
 . . . $10.86 
 7.24 
 
 . . . 10.58 
 . . . 20.80 
 . . . 18.34 
 18.82 
 
 Length 
 
 Total 
 
 ngth, Width, factor, 
 feet. feet. feet. 
 50 3-7 5 
 50 2.1 5 
 40 2.5 4 
 60 2.5 6 
 40 2.5 4 
 
 Width 
 factor. 
 3.7x5=18.5 
 10.5 
 
 IO.O 
 
 15-0 
 
 IO.O 
 
 9.0 
 
 foot 
 value. 
 
 200. QT 
 
 76.02 
 105.80 
 312.00 
 183.40 
 ,169.38 
 
 27 
 
 73.0 $1,047.51 
 
 Average width, 2.704 ft. 
 Average assay per ton, $14.35. 
 
 The above operation reminds one of that old reductio ad 
 absurdum problem in algebra where, in letting a = b, the 
 final result proves the startling fact that 2=1. The fal- 
 
 a b 
 
 lacy was in the assumption that 
 
 = i. Just so, in the 
 
 a b 
 
 above method of sampling, the fallacy was in taking sam- 
 ples every three feet, throwing them into one sack and as- 
 suming the sack to be sample No. i, or the average of the 
 50 ft. of drift from which they were taken. If such a pro- 
 cess of elimination gave the correct averages, it is difficult 
 to understand why it was not carried further and one sam- 
 ple obtained for the entire mine, thereby reducing the assay 
 bill to $2.50. 
 
 Could one have guessed, for it was guesswork, the value 
 of the property after it had been sampled by such a 
 method, whether it was worth $500,000 or $100,000? 
 Fortunately the mine was afterward sampled correctly 
 and carefully at lo-ft. intervals and in accordance with 
 the best methods, such as have been outlined in the articles 
 on this subject in the JOURNAL, resulting in the taking of 
 some 150 samples, and you will readily believe that the 
 difference in the gross value of the ore, as arrived at from 
 the two methods of sampling, in a property of this size, 
 although containing only 935 ft. of workings, amounted to 
 
 180 
 
$95.009.59 ' The description of the two methods affords 
 a sufficient explanation. 
 
 F. H. MlNARD. 
 
 Denver, Colo., August 15, 1903. 
 
 The Editor: 
 
 'Sir. Owing to absence I have but recently had the 
 pleasure of reading the extremely valuable articles on 
 "The Sampling and Estimation of Ore in a Mine." I 
 trust this may serve as an excuse for the following rather 
 belated suggestions: 
 
 In the consideration, on pages 39 to 41, of the much 
 discussed question of ''High Assays," the statement 
 is made that "the occasional barren and the occasional 
 high assay returns are not comparable in their effect upon 
 the estimates." While this statement is true in the ma- 
 jority of cases, especially in the sampling of gold mines, 
 it must be evident that the effect of the abnormally high 
 or low assay would depend entirely upon the ratio which 
 such assay has to the average. Thus, in the series of 
 samples and assay returns, given on page 41, to demon- 
 strate the above statement, if all three abnormal results, 
 one very high and two very low, are omitted, the aver- 
 age becomes slightly less than 1.25 oz. per ton. The 
 abnormally high assay, 27.4 oz., is 26.15 oz. higher, or 
 approximately 2,100 per cent greater than the average, 
 while in the case of the two low assays the total of the 
 variation of both from the average is only 2.5 oz., or 200 
 per cent. Of course the effect of these assays upon the 
 average is increased or decreased when the width covered 
 by the sample is considered, but the above is sufficient 
 to illustrate why such abnormal high assays "affect the 
 estimates . . . to an extent by no means comparable 
 to the omission of an equal number of poor results." 
 That the occasion may arise wherein the elimination of a 
 low assay would affect the result as much, or more, than 
 the omission of a high assay is indicated by the follow- 
 ing series based upon an examination of a silver lead 
 property : 
 
 181 
 
Property : Oz. Silver Foot- 
 Number. Width. per ton. Ounces. 
 
 1 5-3 574 304-22 
 
 2 4.9 39.2 192.08 
 
 3 4-6 53-1 244.26 
 
 4 4-o 59-6 238.40 
 
 5 4-0 101.3 405-20 
 
 6 4-2 54-9 230.58 
 
 7 4-9 42.8 209.72 
 
 8 4-7 i-4 6.58 
 
 9 4-5 38.2 171.90 
 
 Total 41.1 2,002.94 
 
 The average of the ore, using all of these results, is 
 48.7 oz. per ton. If No. 5 is omitted, this falls to 43.0 
 oz. per ton, while if the low assay is omitted, the result 
 becomes 54.8 oz. per ton. None of these assays can be 
 considered abnormal, nor is the effect of the elimination 
 of either very large, with silver at 53c. per oz. In this 
 particular instance, however, the effect was further em- 
 phasized by the fact that the sample containing 101.3 oz. 
 silver per ton also assayed 63.0 per cent lead and '5.5 per 
 cent, zinc, while the sample containing low silver con- 
 tained 3.5 per cent lead and 11.4 zinc, the latter an espe- 
 cially objectionable feature. 
 
 In Mr. Argall's letter in the issue of June 13, Fig. 2, He 
 shows what he truthfully states to be "one of the most 
 difficult samples to take." When the vein assumes a 
 
 182 
 
flatter dip, as in the accompanying figure, it becomes 
 practically impossible to secure a fair sample clear across 
 the vein, and it is better to sample in sections, being care- 
 ful to get a straight line across each section. I find it de- 
 sirable to take samples very largely in sections if there is 
 any difference in the parts of the vein which is clearly 
 observable by the eye. In the examination of properties 
 not equipped with treatment plants, where the metal- 
 lurgical side of the question is necessarily an important 
 one, results so obtained are of especially great assist- 
 ance. Of course this increases costs. 
 
 The term "unequipped property" suggests another 
 point, though perhaps it is beyond the pale of a discus- 
 sion on the sampling of a mine. Mr. Denny remarks 
 that when the engineer is called upon to decide whether 
 a "prospect" is valuable or otherwise, and the available 
 data are meagre, he is "forced to one or two alternatives, 
 either ( i ) to intuitively sum up the value of the property ; 
 or (2) to refuse to commit himself to an opinion until 
 more work is done." Now some of us who have not 
 yet reached the Ultima Thule of being retained entirely 
 by corporations which purchase only "going properties" 
 are unfortunately, not infrequently, called upon by the 
 man who, on the advice of "a friend who has seen it him- 
 self," has put money into a mine until he is tired and 
 wishes to know what he has got. As Mr. Denny states, 
 we are too judicious to adopt the first of the above alter- 
 natives, and Mr. Silkmerchant, who employs us, will not 
 be satisfied with the second. It seems to me there is a 
 third possibility, which perhaps, after all, is a combina- 
 tion of the other two. Why not state to Mr. S. that the 
 present value of the property is only the small amount 
 in cash which some development company would pay, ad- 
 vising from our experience what this might be, and admit- 
 ting that from the information obtainable we can not ex- 
 press an opinion as to probable future value. Tell him 
 it is "a gamble." By all means let us force upon the in- 
 vesting public, if possible, the difference between mining 
 speculations and mining investments. Since, however, 
 
 -183- 
 
we estimate "possible ore" and "probable ore'' may we not 
 state definitely and succinctly, guardedly, the possible fu- 
 ture value that might be expected from the expenditure 
 of a stated sum in a certain definite development, which, 
 so far as possible, is outlined in the report? To be sure, 
 if this sum is expended and the property fails to come up 
 to our guarded expressions of possibilities, we are liable 
 to be blamed, especially by this class of clients ; but, as 
 Mr. Rickard has said "difficulty and doubt" have to be 
 faced, and "judgment and experience must decide." 
 
 GEO. A. PACKARD. 
 Baker City, Ore., July n, 1903. 
 
 The Editor: 
 
 Sir. I have been much interested in the discussion of 
 mine sampling, and hope you will continue to encourage 
 such exchange of views upon practical subjects. 
 
 In some of the letters that you have published it seems 
 that unnecessary refinement and care in doing the work 
 are advocated. For instance, I confess I cannot see the 
 necessity of having a canvas 20 ft. in length, to catch 
 the pieces of ore while sample is being cut. It hardly 
 seems advisable to cut such small samples as to render it 
 necessary to catch every minute particle. With a piece 
 of canvas 6 or 7 ft. long and as wide as the drift, using 
 also, when convenient, a box or large Mexican sombrero, 
 good sampling can be done. Again, it seems to involve 
 unnecessary work and loss of time to seal up each sample 
 as taken. It is assumed that the engineer has with him 
 at least one man whom he can trust. Let him also take 
 underground two sample bags, fitted with locks and keys 
 one bag for the originals and one for the duplicates. The 
 samples can then be safely taken to the surface, there to 
 be securely locked in a box or trunk until shipped or as- 
 sayed. If the engineer is entirely alone, then sealing, as 
 well as all other imaginable precautions, is necessary ; but 
 it is assumed that he will not alone attempt a job of any 
 importance. 
 
 184 
 
It is the custom of some engineers to have the samples 
 (weighing perhaps 25 Ib. each) packed out to the surface, 
 to be "bucked" and quartered down. This is a slow and 
 expensive method, unless the mine is supplied with a 
 small crusher, and even then it is better to do a part of the 
 "bucking" and quartering underground. The engineer 
 should have two or three careful, honest assistants, to 
 watch and quarter samples ; two good, intelligent, reliable 
 miners, to cut the samples ; one man to help in quartering 
 and tying, and three or four to do the bucking down. 
 Such a gang can do good and fast work, and can carry all 
 the tools and appliances necessary for the entire operation 
 of cutting, bucking, and quartering underground. 
 
 I give below a leaf from my sample book, which is self- 
 explanatory. It is well to have exactly 50 of such leaves 
 in each book, bound in pasteboard. These books possess 
 the following advantages : tags can be numbered before 
 going down in the mine, and numbers checked; when 
 duplicates of each sample are kept, tags can easily be torn 
 in two ; complete notes of each sample can quickly be made 
 as sample is cut ; results of assays can be recorded under 
 head of "Remarks," on the back of the leaf ; notes are in 
 convenient shape for future reference. 
 
 Sample Taken 
 
 At point 
 
 From 
 
 Across 
 
 For Feet Inches. 
 
 Measurement: Right Angle to Dip Vertical or 
 Horizontal. 
 
 To 
 
 Dip Strike 
 
 No 
 
 (OVER) 
 
 ( Perforation here) 
 
 No 
 
 No 
 
 SAMPLING CARD. 
 
 -185 
 

 186 
 
I also include a sketch of an iron ring and handle. Sev- 
 eral of such rings add very little to the weight of one's 
 luggage. When used in conjunction with 4-lb. hammers 
 and large flat rocks or old stamp-dies, these rings enable 
 the breaking of the ore (when reducing the bulk of the 
 sample) to be done very quickly and thoroughly, and, at 
 the same time, prevent pieces of ore from flying off the 
 canvas and fingers from being smashed. Sometimes it is 
 convenient to pack along a small hand-power jaw-crush- 
 er, but even then these rings will be found useful for the 
 rough part of the crushing. 
 
 Leather sample-bags, two by two by one-half foot in 
 size, made and looking like mail bags, with leather strap - 
 handle on each end, are very useful. When filled with 
 samples, two such bags make a proper and convenient 
 load for a pack mule. Small pieces of tightly woven cloth 
 are preferable to sample sacks, because suitable cloth may 
 be obtained cheaply almost anywhere, and the sample can 
 be poured onto a cloth more easily than into a small 
 sample sack. It is well to mark the number of the sample 
 on the outside of each cloth with an indelible pencil, at the 
 time the sample is tied up. For quartering, oil-cloth is 
 better than canvas or muslin, because it prevents the fines 
 from sifting through and being lost during the process of 
 rolling the samples. For soft and moderately hard ore, a 
 well-balanced poll-pick, made of good steel, is the best tool 
 for cutting the samples ; for hard ore, moils should be 
 used for very hard ore, more moils. The poll-picks 
 should be made of good drill steel, and should be provided 
 with strong but springy handles. 
 
 It is the belief of the writer that the results of mine 
 sampling should be considered as only close approxima- 
 tions to the average values of the ores exposed, and that 
 it is hardly worth while to take the trouble of making fine- 
 haired calculations, to obtain average values. If proper 
 care is used with regard to abnormal assays, the usual 
 method of "foot-ounces" or "foot-dollars" gives results as 
 close as are practical. 
 
 It is well enough to talk and write about taking a sam- 
 
 -187- 
 
pie that truly represents the value of the ore, but doing 
 it is another matter. If the ore for the full width of the 
 section cut is more or less uniform as to hardness, and is 
 not crumbly, a good sample can be obtained ; but if it is 
 decomposed, porous and crumbly, no amount of care will 
 enable one to cut a true sample. In such cases it is well 
 to take very large samples ; and, in a general way, it may 
 be said that there is greater safety, not only in large 
 samples, but also in large numbers of them. If the ore 
 varies greatly as to hardness, the hard or soft parts occur- 
 ring in spots or bunches scattered promiscuously through- 
 out the vein, it is difficult to do accurate sampling. If the 
 hard or soft ore occurs in streaks, the difficulty may be 
 obviated by sampling the streaks separately. Sometimes 
 the only practical method is to do the sampling as care- 
 fully as possible, realizing that it does not truly represent 
 the ore values, and then, after thorough study of the sub- 
 ject, apply a percentage correction to the average value 
 thus obtained, as in the four following cases: 
 
 Case I. Large bodies of low-grade gold ore, in 
 which it was suspected that the soft ore was better than 
 the hard; ore-bodies thoroughly prospected in the upper 
 levels, and about 700,000 tons developed before milling 
 was begun; ore-bodies carefully determined by samples 
 taken 10 ft. apart and assays accurately platted upon 
 maps ; successful development of ore was continued after 
 the mill was started; as a general rule, ore decreased in 
 value with depth. After 140,000 tons had been milled, a 
 second examination of the mine was made; new ore-re- 
 serves were sampled, and what remained of the old ones 
 were resampled. Resampling of old-bodies gave prac- 
 tically the same results as first sampling. By use of the 
 assay-maps, stope-maps, and records, a close comparison 
 could be made between the mine sampling of the 140,000 
 tons, and the results from milling it, and it was found that 
 the mine samples should have been discounted 14 2-3 per 
 cent. This rate of discount was applied in calculating 
 the average value of the large tonnage yet remaining, and 
 
 188 
 
with good results, as was afterward proved in the milling 
 of it. 
 
 Case II. Enormous body of very low-grade copper 
 ore, occurring in form of small grains of chalco- 
 cite; could be determined easily by the eye that the soft 
 parts of the ore were leaner than the hard; adits were 
 driven into the ore-body, and samples were taken every 5 
 ft., alternating from side to side, so that samples were 10 
 ft. apart on each side; a separate mill-test was made on 
 the ore from each adit; thus it was possible to compare 
 the average of the mine samples with the average value of 
 the ore as milled. Varying results were obtained in the 
 different adits; in those where bunches of soft ore were 
 scattered promiscuously throughout the harder ore, it was 
 found necessary to add as much as 15 per cent to the aver- 
 age values shown by the mine samples, to make them 
 correspond with the mill-tests. 
 
 Case III. The property was represented as being a 
 large body of low-grade, free-milling gold ore, having a 
 width of 500 to 600 ft. The only workings were two open- 
 
 
 cuts and two shallow shafts. The deposit had a width of 
 outcrop of 500 to 600 ft., but a careful examination showed 
 that its actual thickness, while great, was only 50 to 60 
 
 189 
 
ft. The accompanying sketch shows how the mistake in 
 estimating the width occurred. The ore- deposit was in 
 quartzite, containing here and there small, irregular seams 
 of quartz. It was observed that the quartzite itself car- 
 ried values, although values were higher in the quartz 
 veinlets. The gold was finely divided, and only rarely 
 visible to the naked eye. In 'bucking' the samples, for the 
 purpose of quartering down, once in a while a few pieces 
 of rock would be found showing comparatively eoarse 
 gold, and such pieces were rejected as a matter of safety. 
 The ore was sampled in lo-ft. sections across the deposit, 
 269 samples being taken. These samples were 'bucked' 
 and quartered down by hand in the usual manner, except 
 that, before the last quartering, they were put through a 
 small hand-crusher and reduced to pieces that would all 
 pass %-in. mesh. Samples were taken and assayed in 
 duplicate, and the average value was $3 per ton. The 
 price asked was a very large one, and as the deposit did 
 not give much promise of going down, the proposition 
 was rejected. Later it was bought for about one-fifteenth 
 of the price first asked ; a mill was built, and the ore was 
 mined by the open-cut system. The writer was afterward 
 reliably informed by the manager of the mine that the ore 
 as mined averaged about $3.75 per ton. 
 
 Case IV. In this case the ore-bodies were irregular 
 ones in limestone, carrying gold, silver and lead. The 
 mother lode of the district is a contact between diorite and 
 Cretaceous limestone. The ore occurs in a system of three 
 veins, situated at a distance of 1,500 to 1,800 ft. away 
 from the main contact. They are parallel fissure-veins in 
 limestone, usually conformable to the strike and dip of the 
 stratification. The pay-ore is easily detected by the eye, 
 and in mining great care is used to keep it clean. There 
 was not much ore 'in sight' in the mine, but in the lower 
 workings it had been mined in such a way that there was 
 an opportunity to check the hand-sampling of the faces 
 against the smelter returns on product for eight months. 
 This check gave the following results: Lead, as deter- 
 mined by hand-samples, practically the same percentage 
 
 190 
 
as was shown by the smelter returns ; silver values, from 
 hand-samples, 13 per cent greater than from smelter re- 
 turns ; gold-values, from hand-samples, 36 per cent less 
 than from smelter returns. Notwithstanding these differ- 
 ences in the silver and gold values, it was decided to rely 
 upon the results of assays of hand-samples, for the fol- 
 lowing reasons : The sampling, as well as old smelter re- 
 turns, showed that the ore was increasing in silver and 
 decreasing in gold values, with depth ; on the dump were 
 several thousand tons of ore that had been mined during 
 the two years previous to the eight months checked, which 
 had not been shipped on account of lack of cheap trans- 
 port facilities; this old ore carried about the same value 
 in lead, but was lower in silver and higher in gold than 
 the ore mined during the eight months' period. This lat- 
 ter ore had been piled up against the old ore, and in sack- 
 ing it for shipment some of the old ore became mixed 
 with it, so that about one-fourth of the ore sold to the 
 smelters during the eight months was old ore. 
 
 One point that I do not remember having seen empha- 
 sized in this discussion is : The ore should be sampled 
 in the same manner as it is to be mined.* This is espe- 
 cially true in Mexico, where labor is cheap and where 
 Mexican miners are very clever at mining small streaks 
 and assorting ore. The "plodding sampler," fresh from 
 the States, with no experience in Mexico, might go 
 through the workings in an irregular lead deposit in lime- 
 stone, taking his cold-blooded samples at regular meas- 
 ured intervals, and then easily turn the property down as 
 being of no value; while, afterward, by using Mexican 
 methods, modified somewhat, perhaps, by American in- 
 telligence and skill, the mine might be made to pay thou- 
 sands of dollars. 
 
 Another practical point, that might have been covered 
 to advantage by the many engineers of wide experience 
 who have contributed to this discussion, is this : In calcu- 
 lating ore-reserves, what allowances are to be made on 
 
 *This point was considered in the original discussion of the subject; see 
 page 44 of this volume. 
 
 191 
 
account of "horses" included within ore-bodies? Natu- 
 rally, the percentage to be deducted varies widely with 
 different veins or deposits, but results in some cases from 
 actual experience might be of help in others. The fol- 
 lowing is contributed as one case : 
 
 Conditions: Large bodies of low-grade ore in an al- 
 tered limestone, thoroughly developed; samples carefully 
 taken 10 ft. apart ; limits and thicknesses of ore-bodies de- 
 termined by the extensive development and sampling; 
 average specific gravity determined by a number of tests ; 
 stope-maps and records during mining kept in such a 
 manner that comparison could be made between tons cal- 
 culated and tons actually mined ; about 450,000 tons mined 
 by caving system ; estimated loss due to caving system, not 
 over 3 per cent. Result : Many lime "horses" found with- 
 in supposedly solid bodies of ore, and tonnage mined was 
 20 per cent less than tonnage calculated. 
 
 R. C. GEMMELL. 
 Avalos, Zacatecas, Mexico, Sept. 22, 1903. 
 
 The Editor : 
 
 Sir. In reading reports on mining properties, I find a 
 tendency, when it comes to the calculation of the value of 
 the ore and the profits in treatment, to mix up, unneces- 
 sarily, assays as expressed in percentages, ounces, penny- 
 weights or grams, with values and costs, as expressed in 
 dollars, pounds, francs or pesos. 
 
 I recently examined a report on a silver mine in Mex- 
 ico, in which the assay maps purported to give the value 
 of the ore in United States currency. The assays had 
 been made in grams per metric ton of 1,000 kg. ; this had 
 been combined with the value of silver taken at $35, Mexi- 
 can, per kilogram, and then exchange had been taken at 
 237. The mint value of a kilogram of silver is actually 
 $40.914, Mexican currency, and the figure $35 only rep- 
 resented the allowance from a particular smelter on that 
 particular ore, the difference being supposed to cover 
 
 192 
 
metallurgical losses and bullion taxes. Exchange is con- 
 stantly fluctuating and, as nearly all expenses of mining 
 are based on Mexican currency, the profit fluctuated with 
 the rate of exchange. When it came to determining the 
 comparative advantages of lixiviation and smelting, all 
 the values in the maps had to be calculated back to grams 
 per metric ton. Had the maps shown this in the begin- 
 ning, all this trouble would have been saved. Nor should 
 these assays have been reported in ounces troy per ton 
 of 2,000 Ib. avoirdupois. It is always well in a foreign 
 country to figure and, if possible, think in the standards 
 of the country, and not make a conversion till the very 
 last item is reached the net profit per annum, when the 
 amount may be expressed in the currency of the country 
 where the report goes. 
 
 It is a very common error in case of a copper or a lead 
 ore to express the value in dollars by multiplying the 
 value of the metal per pound by the number of pounds of 
 metal shown in the ore by assay; then at some period in 
 the chain of calculation to subtract a certain sum of money 
 to represent metallurgical losses. When the ore has to be 
 both concentrated and smelted, most unintelligible figures 
 result and errors unwittingly creep in, or can be intro- 
 duced by designing individuals. The only safe and logi- 
 cal way is to separate the metallurgical and commercial 
 calculations into two operations. 
 
 As an example, I give a hypothetical sulphide copper 
 ore carrying gold and silver, which is first hand-picked 
 and the balance subjected to water concentration, to re- 
 move an excess of silica. The concentrates are divided 
 into two classes, fines and coarse; the fines a r e roasted 
 and then smelted in reverberatory furnaces, and the 
 coarse concentrates, together with the hand-sorted ore, 
 are smelted in blast-furnaces. The resulting matte is 
 bessemerized and shipped to the Atlantic coast for elec- 
 trolytic refining. This is an extreme case, but shows the 
 method of calculation, which would be simpler in case 
 the operations were fewer. 
 
 We will assume the treatment of 1,000 tons per day 
 
 193 
 
assaying 4 per cent copper, 4 oz. 
 per ton of 2,000 Ib. avoirdupois, 
 follows : 
 
 silver and 0.04 oz. gold 
 The metallurgical table 
 
 Tons, 
 
 I,OOO 
 
 Material. p 
 Crude ore 
 
 Assay, 
 er cent Cu. 
 
 4 
 
 Contents, 
 Ib. copper. 
 
 80,000 
 
 Assay, 
 oz. Ag. 
 
 Contents. 
 oz. silver. 
 
 Assay, < 
 oz .Au. < 
 
 Contents 
 z. gold. 
 
 40 
 
 IOO 
 
 
 
 20,000 
 
 IO 
 
 I,OOO 
 
 O. IOO 
 
 IO 
 
 900 
 
 45 
 
 Concentrating ore .. 
 Tailings (a) 
 
 3.00 
 I 67 
 
 6o,OOO 
 
 3-33 
 i 67 
 
 3,000 
 7^O 
 
 0.033 
 
 30 
 
 
 
 
 
 
 
 
 
 450 
 
 Concentrates 5 
 
 45.000 
 
 2,250 
 
 0.050 
 
 22.5 
 
 200 Coarse concentrates . . 5 
 
 100 Selected ore 10 
 
 300 B. F. charge 
 
 400 B. F. slag 0.40 
 
 33.46 Matte 55 
 
 250 Fine concentrates. . . 5 
 50 Roasting loss (&) 
 
 200 Calcines 6.06 
 
 200 R. F. slag 0.70 
 
 23.83 Matte 45 
 
 57.29 Matte 
 
 Converting loss (f) . . . 
 
 29 Pig copper 98.42 
 
 Toll deductions (rf) . . 
 
 20,000 
 20.OOO 
 
 4O,ooo 
 
 3,200 
 
 36,800 
 
 5 
 
 IO 
 
 0.20 
 54-40 
 
 5 
 
 5.56 
 
 0.30 
 
 48.34 
 
 97,34 
 
 1,000 
 
 1,000 
 2,000 
 
 80 
 
 1,820 
 
 0.050 
 O.IOO 
 
 0.600 
 0.050 
 
 0.063 
 0.524 
 
 1. 121 
 
 10 
 10 
 
 20 
 
 20 
 2O 
 
 25,000 
 750 
 
 1,250 
 
 38 
 
 12.5 
 
 24,250 
 2,800 
 
 1,212 
 60 
 
 12.5 
 12.5 
 
 21,450 
 
 1,152 
 
 12.5 
 
 58,250 
 1,165 
 
 2,972 
 149 
 
 32.5 
 
 '754 
 
 2,823 
 141 
 
 32.5 
 
 Refined copper 
 
 Fine silver 
 Fine gold . 
 
 Total loss . 
 
 56,331 
 
 23,669 
 
 2,682 
 1,318 
 
 32.5 
 7-5 
 
 (a) Concentration by water, 2 into i, with 25 per cent loss in values. 
 (fe) Roasting loss, 20 per cent in .weight, 3 per cent of copper and silver. 
 
 (c) Converting loss, 2 per cent copper, 5 per cent silver. 
 
 (d) Toll deductions for electrolytic refining, 1.3 per cent off electrolytic assay 
 of pig copper and 5 per cent off silver assay. Gold all allowed for at $30 per oz. 
 troy. 
 
 Coming, now, to the commercial side of the problem, 
 we have the following table, showing returns and ex- 
 penditures : 
 
 RETURNS. 
 
 56,331 Ib. copper, at 130. per Ib $7,323.03 
 
 2,682 oz. silver, at 550. per oz 1,475. 
 
 32.5 oz. gold, at $20 per oz 650.00 
 
 Total $9,448.13 
 
 194 
 
EXPENSES. 
 
 Mining 1,000 tons ore, at $1.50 per ton $1,500.00 
 
 Transport 1,000 tons ore, at 250. per ton 250.00 
 
 Administration 1,000 tons ore, at 150. per ton 150.00 
 
 Concentrating 900 tons ore, at 350. per ton 315.00 
 
 Roasting 250 tons concentrates, at 3oc. per ton 75-OO 
 
 B. F. smelting 300 tons ore and cone., at $2 per ton 600.00 
 
 R. F. smelting 200 tons calcines, at $2.50 per ton 500.00 
 
 Converting 57,085 Ib. copper, at .oo6c. per Ib 342.51 
 
 Freight, 29 tons copper, at $12 per ton 348.00 
 
 Refining 29 tons copper, at $16 per ton 464.00 
 
 Comm., etc., 56,331 Ib. copper, at .oosc. per ton 281.66 
 
 Total $4,826.17 
 
 Gross profit $4,621.96 
 
 From the above figures the annual net profit can be 
 deduced after allowing for a fixed annual amount to 
 cover construction, depreciation, etc. 
 
 I must disclaim any intention of giving the above 
 figures of cost as representative, though there are places 
 in the West where the conditions as to cost might obtain. 
 My idea is simply to give a form for calculation where 
 losses and costs are not mixed. 
 
 J. PARKE CHANNING. 
 
 New York, Dec. 14, 1903. 
 
 The Editor : 
 
 Sir. As illustrating that mine sampling, already suffi- 
 ciently tedious and exacting, can be extended until it be- 
 comes a sampling of a sampling, I venture to contribute 
 the following notes, made in the course of practical work 
 and recent mine examination experience; also thinking 
 that the item may be suggestive without having claim to 
 any great originality. 
 
 This note refers to the sampling of the 'quarterings' 
 of a definite number of samples, as convenience dictates, 
 for subsequent comparison of the resulting assay of this 
 special sample with the average assay results of the par- 
 ticular samples included in the former. 
 
 The necessity for such practice as I am about to de- 
 scribe suggested itself to me in an instance where I was 
 
 195 
 
making an examination, and had to limit myself to one 
 assistant, under circumstances which demanded more 
 than usual precaution in the care to be exercised in the 
 sampling, as well as in the safeguarding of the samples 
 taken. 
 
 A pre-requisite to the carrying out of this scheme of 
 sampling check is that the sampling-cut shall be made of 
 a regular width, so that the wider vein shall be repre- 
 sented in its due proportion, as also the narrower (and 
 generally higher grade) streak in its proportion. 
 
 The sampling described herein was more extensive 
 than the sampling numbers indicate, but the part of it 
 published will, I think, sufficiently illustrate the idea 
 which it is wished to convey. The quartering or reduc- 
 ing of the samples was done in the mine as sampling pro- 
 gressed; the calculation of averages is based on the 
 geometric mean or "foot-dollar" method. The detail of 
 the sampling compares with the result of special samples 
 as follows : 
 
 No. 
 ii 
 
 12 
 13 
 14 
 
 Vein 
 width, 
 ft. 
 
 4 
 S5 
 
 2 
 3-5 
 
 5 
 3 
 
 Assay value. 
 $3-60 
 5-00 
 5-00 
 0.60 
 3-6o 
 i. 20 
 
 3 5/6 ft. av. $4.ioJ 
 
 Special sample of quarterings of 
 Samples 11 to 16, inclusive, $2.70. 
 
 20 
 
 21 
 22 
 23 
 
 4-5 
 6-5 
 5-5 
 5-5 
 
 $3-20 
 2.60 
 8.00 
 3-20 
 
 5 1/3 ft. av. 
 
 $4-13^ 
 
 26 
 27 
 28 
 2p 
 30 
 32 
 
 5-5 
 
 6 
 6 
 
 5-5 
 6 
 
 $3-60 
 i. 80 
 3.20 
 1.80 
 4.00 
 *i8.oo 
 
 6 ft. av . 
 
 $2.70 
 
 Special sample of quarterings of 
 *" Samples 20 to 23, inclusive, $3.20. 
 
 Special sample of quarterings of 
 ^Samples 26 to 32, inclusive, $1.50. 
 
 -196- 
 
42 
 
 2-5 
 
 $8.oo\ 
 
 43 
 
 3-5 
 
 6.80 
 
 44 
 
 3 
 
 0.40 
 
 45 
 
 3 
 
 2.40 
 
 46 
 
 3 
 
 2.20 
 
 47 
 
 3-50 
 
 1.60 
 
 48 
 
 3 
 
 O.60 
 
 49 
 
 5 
 
 O.40 
 
 
 3 i/3 ft. av. 
 
 $2.6V 
 
 51 
 
 3 
 
 $4.80 
 
 52 
 
 4 
 
 6.80 
 
 53 
 
 4 
 
 1.40 
 
 54 
 
 3 
 
 1.40 
 
 
 3-5 ft. av. 
 
 $3-67] 
 
 Special sample of quarterings of 
 Samples 42 to 49, inclusive, $1.60. 
 
 ^Special sample of quarterings of 
 Samples 51 to 54, inclusive, $3.10. 
 
 *Eliminated sample No. 22 as "spotty" and substituted average 
 value. 
 
 The care taken in preparing these samples and the ac- 
 curacy of the assaying is indicated by the uniformly close 
 result of the control assay, which was taken to a public 
 assayer of good repute. Thus : 
 
 Special sample, 
 ii to 16 
 20 to 23 
 26 to 32 
 42 to 49 
 5i to 54 
 
 Original, 
 oz. gold 
 per ton. 
 
 0.14 
 
 0.16 
 
 0.08 
 
 0.08 
 
 0.18 
 
 Control assay, 
 oz. gold 
 per ton. 
 
 0.13 
 
 0.16 
 
 0.07 
 
 0.08 
 
 0.13 
 
 While this particular ore happens to be a low-grade 
 ore, it might be interesting to carry out a similar test on 
 ores of higher grade and different character. 
 
 It will be noticed that the special sample of the 26 to 32 
 series catches the irregularity occurring in No. 32 sam- 
 ple, and proves that the nature of this discrepancy was in 
 the assay rather than in the sample itself. 
 
 Another thing, the result of the quarterings sample is, 
 in every case, appreciably lower than that of the average 
 of the equivalent sample series. As these samples were 
 all of them quite dry when quartered down, this latter ob- 
 servation rather indicates that the fines which cling to 
 canvas to some extent (and almost unavoidably) tend to 
 carry higher values than the coarser material. This 
 
 197 
 
property of canvas has been remarked in other papers on 
 the subject of sampling; and it is my observation that the 
 extent to which the fine residuum or dust that clings to 
 canvas, and with it, sometimes, particles of very fine me- 
 tallic gold, can be approximately determined in almost 
 any case. This can be done by the simple resort of tak- 
 ing, and repeatedly taking, about an even bulk (relative 
 to samples) of absolute waste material, and reducing this 
 and quartering it down in the same way as the regular 
 samples of 'die mine. In addition to the special samples, 
 I took precaution to include among my samples a number 
 of waste samples. Such samples constitute not only a 
 check on the sampling, but on the assay er, and bring to 
 light any irregularities that might possibly creep into the 
 most careful sampling. I am inclined to think that there 
 is much more said about the inclusion of waste samples 
 than is actually carried into practice. 
 
 While the extra trouble of sampling the discarded por- 
 tions of regular mine sample may not always be war- 
 ranted, nor oftentimes be deemed necessary, it certainly 
 gives additional data upon which to depend for informa- 
 tion of general values, and under some circumstances it 
 more than compensates for the trouble that it involves. 
 
 FORBES RICKARD. 
 Denver, Colo., Dec. i, 1903. 
 
 198 
 
REVIEW OF DISCUSSION. 
 
 BY T. A. RICKARD. 
 
 In closing the discussion on mine sampling, I desire to 
 thank those who have contributed their comment and ex- 
 perience. Whatever service my treatment of the subject 
 may have done, it has been much increased by the dis- 
 cussion. 
 
 The efforts to give precision to the terms used in de- 
 scribing the ore opened up by mining operations will, I 
 doubt not, leave their influence on the practice of the pro- 
 fession. Already "ore in sight" is tabooed and "ore de- 
 veloped" has appeared in several reports upon mines. Mr. 
 Argall has driven the last nail in the coffin of a phrase 
 which was previously almost in extremis by reason of the 
 action of the Institution of Mining and Metallurgy, whose 
 circular (published in the ENGINEERING AND MINING 
 JOURNAL of October 18, 1902) made a distinct pro- 
 nouncement concerning the careless use of such terms. 
 In endeavoring to supply a definition the council of the 
 Institution did a good service to engineering practice, but 
 ventured upon dangerous ground. No set terms can al- 
 ways cover the relative degree of evidence to be obtained 
 concerning the tonnage of ore available in different mines. 
 Each mine has its own "personal equation," as it were ; 
 in each instance there is a degree of regularity, or irregu- 
 larity as it may be, of ore occurrence, both as regards 
 value and width, so that two sides of a block as exposed 
 in one class of mine possessing persistent ore-shoots af- 
 fords better assurance of a certain amount of ore in re- 
 serve than four sides in other mines where the vein is 
 sporadic and fickle. This point has been brought out by 
 199 
 
Messrs. Geo. E. Collins, Chester W. Purington and John 
 C. Treadwell. 1 
 
 This aspect of the enquiry is also emphasized by the 
 consideration of unsystematic sampling, as outlined by 
 Mr. Geo. J. Bancroft. 2 The writer happens to know the 
 two engineers whose methods are adumbrated by Mr. 
 Bancroft, and he can appreciate that men of such wide ex- 
 perience are able, by the exercise of sagacity, to make one 
 or two, apparently haphazard, tests which will throw more 
 light on the character of a mine than the laborious sam- 
 pling of an inexperienced man. Short cuts are proverbi- 
 ally dangerous to the novice, while they may be safe to a 
 veteran. There is no doubt that clients who have to pay 
 heavily for the detailed sampling of a large mine will ap- 
 preciate the acumen of an engineer who by a few tests, 
 judiciously distributed, can, at a small expense, find out 
 the real inwardness of things. This applies particularly 
 to preliminary examinations. 
 
 The shape of ore-bodies is an important factor, as Mr. 
 Purington makes clear. 3 One cannot sample intelligently, 
 that is, one cannot arrive at the size and average composi- 
 tion of a large mass of any material unless one has some 
 notion of the shape of it. Here geological structure plays 
 an important part, as it has been my endeavor to show in 
 the two or three instances which I have described. The 
 instances have been invariably founded on fact and de- 
 scribed with care, so that many readers must have been 
 able to spot the localities from which they were borrowed. 
 
 That sampling is hard work, as well as an important 
 part of mining practice, is a fact scarcely needing empha- 
 sis to professional men, but I doubt if it is, as yet, proper- 
 ly appreciated by the people in whose interests it is done. 
 Therefore the detailed description of the sampling of the 
 bottom of a wet level by Mr. Ernest Levy will do good 
 service. 4 Moreover, it suggests the extreme care required 
 
 1 See pages 93, 96 and 115. 
 2 Page 1 1 8. 
 3 See page 96. 
 4 See page 124. 
 
to sample underfoot, especially in a wet mine. As a rule, 
 if sufficient data are otherwise procurable, it is best to 
 leave the bottoms of levels alone, because of the great 
 danger of vitiated results due to the washing of fine ore 
 into the channeling made by the moil or pick ; moreover, 
 it is rarely possible to be sure that the proper width of ore 
 is being broken when working in the bottom of a drift. 
 The necessity to tear up the track, stop the tramming and 
 interfere with the operations in any part of the mine 
 causes the management to look with disfavor upon the 
 sampling of bottoms and leads usually to the work being 
 done in a hurry, under great discomfort and under serious 
 disadvantage. These tend to impair the reliability of the 
 results. Therefore, if practicable, sample the backs over 
 the level or the nearest winzes in preference. If these are 
 not available, that is, if the ground above the level is 
 stoped out and the ground underfoot has not been pene- 
 trated by winzes, then sample underfoot and make up 
 your mind not to be rushed, to do it carefully and to have 
 the operation conducted under your immediate super- 
 vision. 
 
 Mr. Chester F. Lee asks 5 whether it is admissible to 
 combine several cuts across the vein at short intervals or 
 to take separate samples at greater intervals? To this I 
 would say that the mixing of samples obscures the in- 
 formation which they can give and spreads the element of 
 error. If one is limited, by time or money, in the number 
 of samples to be taken, I would prefer, for example, one 
 hundred separate cuts at intervals of ten feet to the same 
 number of samples obtained by combining every two cuts 
 taken at intervals of five feet. If a bad sample is taken, 
 either by encountering an accidental rich spot or by break- 
 ing an undue proportion of one part of the cross-section 
 of the vein, then by mixing this with the next cut, the 
 error is only made so much more difficult of detection. 
 Moreover, such sampling by requiring twice the number 
 of cuts, without any increase of precision, unnecessarily 
 
 "See page 129; also Mr. Gemmell's remarks on page 184. 
 20 1 
 
augments the time and labor involved. Each assay re- 
 sult and each width represents a factor in the final calcu- 
 lations for tonnage and value ; the more of these there are 
 the closer the estimate. But by combining two adjacent 
 cuts there is no increase in the number of assay results, 
 although there may be double the number of measure- 
 ments for width. In an erratic ore-streak the latter would 
 prove useful. 
 
 Mr. T. Lane Carter and Mr. G. A. Denny have enriched 
 the discussion by their descriptions of South African 
 practice. 6 Nowhere in the world is sampling so nearly an 
 exact science as in the mines of the Transvaal, simply 
 because these contain ore-deposits of such persistence and 
 uniformity that they afford the basis for careful work. 
 The stuff is there, and it is not so erratic in occurrence or 
 in richness as to upset calculations founded upon the doc- 
 trine of averages. After all, the value of any system 
 must depend upon the comparative regularity of condi- 
 tions assumed to exist by the mere fact of a regularity of 
 method. Stereotyped procedure is stultified by the want 
 of some measure of uniformity. For these reasons, the 
 engineers on the Rand have had a great opportunity to 
 improve sampling methods. This they have abundantly 
 done. One of the best systems is the scheme of a con- 
 tinuous section-plan, proposed by Mr. F. Burnham,* which 
 has been adopted by several mines, and is described by 
 Mr. Denny. By indicating the average assay of separate 
 lengths of reef by means of tints upon the mine map, it is 
 possible to get, at a glance, the relative value of the work- 
 ings ; the unit is a full stoping width, so that the tints 
 mean not the gold contents per ton of any streak or vein, 
 but the value as sloped a very different thing. This 
 continuous section-plan is of great service to the manage- 
 ment of a large mine. When supplemented by the sam- 
 pling record, which contains a continuous sketch of the 
 distribution of the pay-streaks in a wide vein, as shown in 
 
 6 See pages 131 and 163. 
 
 *'Continuous Section System Mine Sampling,' by M. H. Burnham, Trans- 
 actions Institution of Mining and Metallurgy, Vol. X, pp. 204-218. 
 
the section-plan, this system affords, in a compact and 
 logical manner, a great deal of the vital information neces- 
 sary to good management. 
 
 Mr. Denny pleads for a minimum of 5 ft. as the sam- 
 pling interval, and quotes differences observed when a 
 longer interval has been adopted. It is obvious that the 
 shorter the interval the more accurate the averages ob- 
 tained, for every interval represents a column of ore hav- 
 ing the length of the interval, the width of the ore, and 
 the height of the block. The last dimension is shared, 
 usually, with a corresponding sample on the next level. 
 In practice the interval is usually determined by the exi- 
 gencies of time and expense. When a mine is well or- 
 ganized and has men who are told off to attend regularly 
 to the sampling of the workings, it is practicable to reduce 
 the interval and do the work up to the extreme of detail ; 
 when, on the contrary, an engineer is sampling a mine 
 preparatory to submitting a report upon it, he is apt to be 
 limited by time and by the funds placed at his disposal by 
 his client ; as a consequence, he cannot spend all summer 
 on one examination. It depends as much upon the client 
 as the engineer; the better class of the former will not 
 hurry the work and will not stint the expenditure neces- 
 sary to do it well. One can only say that the engineer 
 cannot be too careful, and to that end he will endeavor to 
 find time and money sufficient to take samples at the 
 shortest interval required by the nature of the lode. In 
 one mine, quoted by me, I sampled every three feet, and 
 even then the interval was short enough, seeing that the 
 vein averaged 4 inches of ore carrying 500 oz. of silver 
 per ton; in other cases, of uniform low-grade pyritic 
 lodes, a 2O-ft. interval would give closer results than the 
 3-ft. interval in the case just referred to. 
 
 Mr. Denny pleads for the general expression of values 
 in terms of currency. This is a good point. Ounces of 
 gold mean bullion of uncertain value; ounces of silver, 
 percentages of copper, lead, etc., vary in value with 
 changes in the market. Mining is a matter of money. I 
 remember hearing of the case of an engineer who exam- 
 
 203 
 
ined an Indian mine in the early days of the Wynaad, and 
 instead of using" the assay-ton he employed the old-fash- 
 ioned percentage method, with the result that he mis- 
 placed the decimal point! A colossal blunder followed. 
 If he had used currency instead of percentages as his 
 unit, he would not have made such a fatal slip. Further- 
 more, mining operations nowadays cover regions of such 
 diversity that the bullion contents may range from a 50 
 per cent alloy to gold of 995 fineness. To report in quan- 
 tity of bullion is only to afford one more chance of mis- 
 understanding, and, after all, the purpose of all engineer- 
 ing work is to get at the facts and then to state them be- 
 yond the peradventure of misconception. 
 
 Mr. T. Lane Carter describes 7 current practice on the 
 Rand and the arrangements made by the mine manage- 
 ment for the regular sampling of the workings. It is 
 plain that at Johannesburg the sampler has won a distinct 
 position for himself. Incidentally he accentuates the use- 
 fulness of correct assay-plans as indicating the value of 
 any portion of the reef which is too poor to be worked 
 now, but may be found profitable under more favorable 
 economic conditions. When that time comes, an accurate 
 record of the values as determined by the previous daily 
 sampling of the drifts will be found of great service. The 
 use of surveyor's points to locate the places sampled is a 
 good scheme, since other points of departure may become 
 obscured. Furthermore, it suggests the friendly relations 
 which should exist with the surveyor's department; in 
 fact, it would be well in most mines to put the sampling 
 work, and the records of it, under the charge of the sur- 
 veyor attached to the property. 
 
 Mine sampling on the Rand has been developed to the 
 dignity of a distinct branch of practice; therefore, Mr. 
 Denny's description of the methods in vogue is most op- 
 portune. His criticism 8 in regard to the ascertainment of 
 the "average value of the ore in the past" from "the rec- 
 ords of a mine" is due to a misconception of my meaning. 
 
 7 Pages 131 to 138. 
 8 On page 166. 
 
 204 
 
I meant the value per ton, as treated in the mill or 
 smelter, of the ore produced in the past, and not the aver- 
 age yield of the ground which has been removed by stop- 
 ing. I quite agree with Mr. Denny that it is difficult to 
 arrive at the yield per fathom, or per square foot, of lode 
 in workings which have been abandoned ; and, of course, 
 we are well aware that many a false notion of the grade 
 of lode-contents has arisen from a literal acceptation of 
 the story told by mill and smelter records. On the other 
 hand, if the examination of a mine extends over several 
 months, it is occasionally possible to check sampling re- 
 sults by measuring a block of ground and then getting the 
 actual yield of it in tons of ore and in ounces of bullion. 
 There are also instances where the management of a mine 
 is in honest hands for all sellers of mines are not dishon- 
 est, nor are all buyers immaculate and then it may hap- 
 pen that the stope-maps have been kept in such a way that 
 the yield per fathom, the average width of clean ore as 
 compared to the stoping width, the percentage of sorting, 
 and other data, can be secured and utilized as a check on 
 the estimates based on sampling alone. 
 
 Mr. J. H. Curie taps the milk in the cocoanut in his 
 contribution on mine valuation. 9 It is the net profit that 
 an engineer is asked to determine ; all the rest is noise and 
 smoke; tonnage of ore, assays, machinery, water power, 
 timber rights, dump facilities, scenery all these are mere 
 frills on the outside of the essential problem, How much 
 money will the mine yield? This is being recognized 
 more and more; twenty years ago it was customary to 
 make a perfunctory trip through the underground work- 
 ings, to break off a specimen or two, and then to spend a 
 few days copying the past records of production, getting 
 tracings of the maps and interviewing the oldest inhab- 
 itants. With such data, it is no wonder that mine reports 
 became a thing for derision. It is just such plain talk, 
 straight from the shoulder, as this of Mr. Curie's, which 
 goes to the heart of the problem and brings the thoughtful 
 
 9 See pages 138 to 145. 
 
 205 
 
engineer into touch with the financial side of a great in- 
 dustry ; it means the passing of the professor type and the 
 development of the experienced engineer, who knows 
 human nature and the brutalities of the financial arena no 
 less than the contents of text-books and the talk of the 
 library. 
 
 There is no doubt that Mr. Curie is right in saying that 
 the environment of the English engineer is against him in 
 this respect. In America the engineer deals directly with 
 a capitalist who usually knows a bit about the business of 
 mining, but in London he is apt to run against a wholly 
 impossible type, the middleman, to whom the mine is 
 merely the basis for clever dealing, or the titled incompe- 
 tent who is in the hands of the former and plays a part 
 like that of the Indian whose wooden image stands in 
 front of the cigar store. 
 
 Mr. Curie speaks of a mine valuer taking certain risks 
 in figuring out the ore reserves ; it is not in the estimates 
 of ore blocked out that the chances of error are so great 
 as in appraising the future prospects, the "good-will," as 
 it were, of the property, that the largest margin for differ- 
 ence will occur. Mines are not bought only for the ore 
 actually calculable in the existing workings, but also with 
 the idea of a future enhancement in value due to intelli- 
 gent development. Here it is where a man must be true 
 to himself and to his employers, by facing the facts frank- 
 ly; and if the facts are insufficient to warrant a forecast, 
 let him dig them out by further investigation. If they 
 are not available after thorough examination of all the 
 circumstances, then let the engineer say so frankly, to the 
 end that his client may know just what risk he is taking; 
 in many cases a risk may be warranted, in others the 
 condition of the mine and its past history may render it 
 out of the question. 
 
 Mr. Argall emphasizes 10 the necessity for taking samples 
 of approximately equal weight; this is important. Of 
 course, the samples will vary in bulk with the width of the 
 lode ; the amount broken should be equal per foot of cross- 
 
 10 On page 103. 
 
 206 
 
section. When you leave it to such accidental factors as 
 hardness and accessibility to fix the size of the sample, 
 you simply introduce an unnecessary element of error, 
 because excess of ore broken means usually that it comes 
 from a soft part of the lode, while a meager sample will 
 coincide with extra hardness. In most lodes the differ- 
 ence in ease of fracture is due to some constituent min- 
 eral, the presence of which is likely to coincide with a 
 variation in the value of the ore. 
 
 It is good practice to brush the face clear of dust or re- 
 move any mud which is not in place, because this foreign 
 material frequently contains finely powdered sulphides 
 which may vitiate the sample, especially in a low-grade 
 gold ore. Mr. Argall makes several other good sugges- 
 tions, such as that of allowing two gangs of samplers to 
 take alternate intervals in sampling, thereby checking each 
 other's work. 11 As to the use of a hand rock-breaker, that 
 is almost imperative where a big mine is being investi- 
 gated; it will facilitate the careful quartering down of 
 samples. 
 
 Both Mr. Curie and Mr. Argall discuss that much- 
 mooted question: what to do with erratic high assays. 12 
 This was considered at some length in my own treatment 
 of the subject ; 13 but as a general method, to be departed 
 from only where peculiar conditions arise, as in the cases 
 described by Mr. Curie. and by myself, I do not know of 
 any better advice than that of Mr. Argall, that is, to reject 
 the erratic results and there will not be many of them, 
 otherwise they are not erratic and then insert the aver- 
 age values as given by the other results. In getting at 
 this average it will be well, it seems to me, to omit those 
 results which give nil and insert the figure given by aver- 
 aging only the pay ore. This will lean a little to the idea, 
 which is true, that these erratic assays do indicate unusu- 
 ally rich spots but spots, not masses. 
 
 "See page 105. 
 
 12 See pages in and 142. Also Mr. Packard's remarks on low assays, given 
 on page 181. 
 
 13 On pages 39 to 44. 
 
 207 
 
Thus, take the following list of actual assay returns 
 from the sampling of a gold mine : 
 
 No. of 
 Sample. 
 
 i. 
 
 2. 
 
 3- 
 4- 
 
 6. 
 
 7 s. 
 
 9- 
 10. 
 
 ii. 
 
 12. 
 14. 
 
 16. 
 17- 
 
 19. 
 
 20. 
 21. 
 22. 
 
 23- 
 24. 
 
 26! 
 27. 
 28. 
 29- 
 
 30. 
 
 31. 
 
 Width 
 
 Gold value in dollars 
 
 in feet. 
 
 Original. 
 
 Duplicate. 
 
 Mean. 
 
 7.0 
 
 $24.20 
 
 $48.00 
 
 $36.10 
 
 4.0 
 
 10.80 
 
 8.00 
 
 9.40 
 
 12.0 
 
 24.00 
 
 23.20 
 
 23.60 
 
 8.0 
 
 84.00 
 
 78.00 
 
 81.00 
 
 5.3 
 
 740.00 
 
 496.00 
 
 618.00 
 
 7.0 
 
 32.00 
 
 40.00 
 
 36.00 
 
 3.5 
 
 19.20 
 
 64.00 
 
 41.60 
 
 6.0 
 
 8.00 
 
 8.40 
 
 8.20 
 
 6.0 
 
 24.40 
 
 64.00 
 
 44.20 
 
 7-0 
 
 28.00 
 
 16.00 
 
 22.00 
 
 
 9.60 
 
 40.00 
 
 24.80 
 
 s!o 
 
 230.00 
 
 392.00 
 
 311.00 
 
 3-3 
 
 30.40 
 
 45.6o 
 
 38.00 
 
 9-8 
 
 6.60 
 
 15.20 
 
 10.90 
 
 8.5 
 
 1.20 
 
 6.00 
 
 3.60 
 
 9.2 
 
 1340 
 
 1 1. 20 
 
 12.30 
 
 10.5 
 
 5-00 
 
 II.2O 
 
 8.10 
 
 IO.O 
 
 7.20 
 
 17.60 
 
 12.40 
 
 6.7 
 
 I7.OO 
 
 19.40 
 
 18.20 
 
 11.4 
 
 4.OO 
 
 5.00 
 
 4-50 
 
 4-6 
 
 3.60 
 
 4.40 
 
 4.00 
 
 IO.O 
 
 1540 
 
 9.20 
 
 12.30 
 
 5.o 
 
 2 1. 60 
 
 30.20 
 
 25.90 
 
 10.7 
 
 2O.OO 
 
 17.00 
 
 18.50 
 
 8-4 
 
 16.00 
 
 1 2.80 
 
 14.40 
 
 8.0 
 
 31.20 
 
 20.80 
 
 26.00 
 
 9.0 
 
 13.20 
 
 20.40 
 
 1 6.80 
 
 6.4 
 
 6.80 
 
 7.60 
 
 7.20 
 
 6.2 
 
 13.60 
 
 16.00 
 
 14^80 
 
 8.0 
 
 6.00 
 
 6.40 
 
 6.2O 
 
 9.9 
 
 20.00 
 
 8.60 
 
 14.30 
 
 Foot- 
 dollars. 
 $252.70 
 37.6o 
 283.20 
 648.00 
 3,275.40 
 252.00 
 145.60 
 49.20 
 265.20 
 
 181.04 
 2,488.00 
 
 106.82 
 
 30.60 
 
 113.16 
 
 124.00 
 
 121.94 
 
 5I-30 
 
 18.40 
 
 123.00 
 
 129-50 
 
 Totals 
 Averages 
 
 120.96 
 
 208.00 
 
 151.20 
 
 46.08 
 
 91.76 
 
 49.60 
 
 I4L57 
 
 236.7 $1,486.40 $1,562.20 $1,524.30 $10,068.23 
 7-6 47-95 50.39 49.17 
 
 In the first place, the assays were made on two parts of 
 the original sample, and not on the two halves of the final 
 pulp; therefore the high results given by Nos. 5 and 12 
 indicate that there was this amount of gold present in the 
 sample as a whole and not in a small portion of the pulp 
 alone. The difference in the "original" and "duplicate" 
 are due not to faulty assaying, but to the fact that the 
 two halves of the sample actually differed in their con- 
 tents. It is obvious that the division of the original 
 sample into two, in this way, serves the purpose of test- 
 ing the distribution of the values, and it is also a check on 
 the high assays by indicating whether they are due merely 
 
 208 
 
to an accidental particle of gold in the assay pulp or really 
 to a rich spot in the lode. If done by different assay ers, 
 this method is a check on the assaying itself. The arith- 
 metical mean of the assays of the two halves differs, as 
 will be seen, 4.8 per cent only; which, having regard to 
 the character of the ore, a free gold quartz, is most satis- 
 factory. 
 
 On the figures, as given, the ore averages 7.6 ft. in 
 width and $42.53 ( 10068.23 divided by 236.7) in value per 
 ton, which is about $6.50 less than the arithmetical mean 
 of the assays. If, now, the two high assays are omitted, 
 the average becomes $19.27 (that is, 10068.23 minus 
 5763.40, divided by 236.7 minus 13.3), which, having re- 
 gard to the fact that rich spots are known to contribute an 
 integral part of the output of the mine, is probably too 
 small. If the engineer has the opportunity, he will re- 
 sample the rich spots and also take intermediate samples 
 between Nos. 4 and 5, 5 and 6, n and 12, 12 and 13 
 thereby finding out for certain whether the rich ore does 
 occur to the extent of the 10 ft. in length, which in this 
 case is the interval between the samples. In default of 
 such re-sampling, as, for instance, if he has left the mine 
 by the time he gets his assay returns, then he should sub- 
 stitute for 5 and 12 the average obtained by omitting the 
 two high assays and also the very poor samples, such as 
 Nos. 2, 8, 14, 15, 1 6, 17, 1 8, 20 21 22, 28 and 30. This 
 will give an average of $27.70 for the richer ore as ob- 
 tained by subtracting 5763.40 (3275.40 and 2488) from 
 10068.23, an d also deducting 834.21 (the sum of the foot- 
 dollars representing the 12 lowest assays), and then di- 
 viding by 126 (236.7 less 111.7, the aggregate width of 
 the 14 samples omitted). 
 
 Now, substituting $27.70 in place of the two high as- 
 says and putting in the corresponding foot-dollars for 
 Nos. 5 and 12 in the last column, we get a final average of 
 $19.75 P er ton > tnat is > 4673.24 ( 10068.23 minus 5763.40, 
 but plus 368.41), divided by 236.7. This $19.75 com- 
 pares with $49.17 without any correction and $19.27 
 when the two high assays only are omitted. 
 
 209 
 
In most cases the result obtained in this way will be 
 corroborated by actual mining and milling. In this case 
 the difference made by taking the average of the better 
 grade ore, instead of taking the average of all the other 
 samples save the two "high assays," is comparatively 
 slight, but the example quoted is intended chiefly as illus- 
 trating a method rather than a result. 
 
 Mention has been made, by Mr. Bancroft, for instance, 14 
 of the air of importance given to the supposed greater 
 accuracy of mill-runs as compared to the assay of numer- 
 ous small samples. This is a heritage from an older 
 period. It is obvious that the bulk of a sample weighing 
 several tons requires that it shall be handled by several 
 men, and that this affords plenty of opportunity for tam- 
 pering with the ore. Either the choice of the ore broken 
 can be made so as to favor the desired result, or actual 
 "salting" can be perpetrated with comparative ease. 
 Furthermore, the number of ounces of amalgam scraped 
 off the plates in a mill depends largely on the previous 
 conditions of the plates, that is, the amount of gold amal- 
 gam which they carried when the test began. If rich ore 
 follows poor ore in a mill, the plates get part of it, and 
 the yield is too low, while if the reverse happens and poor 
 stuff is milled after rich ore has passed over the plates, 
 the result will be unduly high. In one case, which came 
 under my notice, several lots of ore were broken in a cer- 
 tain mine and were sent to a custom chlorination works 
 for treatment, with results which ranged between $12 and 
 $17 per ton, but when the mine had been bought, on the 
 evidence of these returns, it was found that the ore yield- 
 ed about $8 per ton. Of course, in breaking the sup- 
 posed "samples," no average was really secured because 
 there was a general desire among all concerned, quite 
 honestly, to get a satisfactory yield. As to the use of 
 stamp-mills for such tests, it is obvious that there is great 
 danger of both willful and innocent deception. From 
 feeding amalgam into the mortar boxes to scraping the 
 plates down to the bare copper, there is every modifica- 
 
 14 On page 123. 
 
tion. It is the old question of one big sample versus 
 many small ones. However big the sample may be, you 
 get one figure and one factor ; with many results from a 
 large number of samples you average the data, minimiz- 
 ing the errors and, often, detect them by the mere process 
 of comparison. 
 
 The discussion has brought out many sides of the prob- 
 lem of mine valuation; what may be called the purely 
 mechanical side, the sampling itself, obtained the first 
 emphasis because it is fundamental to all the mental pro- 
 cesses which result in the estimation of ore in reserve. 
 Mr. F. H. Minard points out 15 that to delegate sampling to 
 inexperienced youths is a dangerous procedure, because 
 the carrying out of the work involves something more 
 than ability and energy ; the measuring of ore and break- 
 ing of samples requires experience, and if the preceding 
 treatment of the subject has not made this abundantly 
 clear, it has failed egregiously. Therefore engineers 
 should not delegate their work indefinitely, nor, if they 
 are wise, will the younger men court disaster by under- 
 taking tasks for which they are unfitted. There is such a 
 thing as learning one's profession; a man must be an 
 apprentice before he becomes a master. And when all 
 the sampling and investigation are done the great prob- 
 lem of valuation is there still, to try the mettle of the en- 
 gineer. It takes a strong man to be a good valuer, says 
 my friend Mr. Curie. It does, indeed the kind of moral 
 courage which faces facts and sends sophistry to the 
 devil. It is the courage which animates science and re- 
 fuses to make two and two anything but four, neither 
 making it three by over-caution nor swelling it to five by 
 an unhealthy optimism. The engineer whose estimate is 
 25 per cent below the fact is, in my opinion, as blame- 
 worthy as the one who makes it 25 per cent too high. It 
 is well enough to say that you safeguard your client, if a 
 buyer, by putting a low valuation on a mine, but there is 
 no honesty in such a line of reasoning, for you are helping 
 another man to get something for less than it is worth 
 
 15 On page 176. 
 
and giving the lie to your professional judgment. To 
 overvalue a property, when caught by the enthusiasm of 
 the seller, is foolish enough, and, as the world goes, it 
 brings a speedy retribution by becoming destructive to 
 reputation. But the two departures from fact are of a 
 piece; there is nothing to choose between them; and to 
 say that they are both equally unprofessional is as much a 
 euphemism as it would be to say that it is unseemly to 
 tell an untruth. 
 
 Every mine is a new and distinct problem; the valua- 
 tion of it requires not only the determination of actual 
 ore measurable, but the appraisal of future possibilities. 
 There was a time when the gambling element was in- 
 volved in the sampling, for it was rendered as haphazard 
 as the throw of the dice; but since the thorough testing 
 of mines has grown to become a recognized procedure, 
 the judgment of prospective value looms up with added 
 significance. Mines will not be bought and sold, in the 
 future, like a cheese that has been tested; they will be 
 taken over for the speculative enhancement to be secured 
 by skillful development. As Mr. J. Parke Channing 
 shows, 16 you can buy pyrites mines on the basis of a for- 
 mula, in which certain determined factors are properly 
 included ; but when it comes to appraising the prospective 
 enhancement of gold, copper and lead mines, for instance, 
 formulas are thrown overboard, and there is need for that 
 instinct, judgment, nous call it what you will which 
 enables one miner to arrive at a safe guess, while the 
 other sees no further than the head of his pick. It is the 
 training of the "tributer" or "leaser" which is needed. 
 
 While the moil is the accepted tool for sampling, the 
 gad is advocated by Mr. Lee and the small pick, but only 
 for special work, by Mr. Walter H. Weed. 17 In certain 
 places underground a gad, fitted with a handle, is 
 more serviceable than a moil, that is, when the 
 ore to be sampled is so situated that one cannot hold 
 a moil in the left hand so as to strike it with the 
 
 "See pages 88 to 90. 
 "See pages 128 and 143. 
 
 212 
 
hammer held in the right. The gad with a handle is 
 one of the oldest implements of the miner, and figures in 
 the insignia of the Schools of Mines at Leoben and Claus- 
 thal. As to the small pick, the geologist's or expert's 
 pick, as it would be termed in the West, it is useful in pre- 
 liminary sampling and in testing various parts of a vein 
 to find out which streaks carry the values, but I am loath 
 to recommend it for systematic sampling, especially in 
 hard ground. It can be used by an experienced man with 
 discretion to good purpose, but I would advise the 
 younger engineers to leave it at home or in the black- 
 smith's shop. Much the same is true of the "grab" sam- 
 ple which I consigned to perdition as being at the root of 
 so many untrustworthy estimates of ore. Mr. W. M. 
 Courtis and Mr. Albion S. Howe say, 18 very properly, that 
 the grab sample is serviceable in finding out which band 
 of ore, in a multiple vein, carries the values, and in this 
 way, by taking one or two grab samples, Mr. Courtis has 
 saved himself, on more than one occasion, from being 
 salted. Here, too, for a specific purpose, this method is 
 well enough, but as a general way of arriving at the ton- 
 nage and value of large bodies of ore, it is hopelessly un- 
 scientific ; in fact, the very notion of a ''grab," that is, to 
 seize blindly at a handful of broken ore, with the idea that 
 by being blind you are impartial, is wholly opposed to the 
 earnest effort to eliminate the element of chance as much 
 as possible, by collecting the maximum number of data, 
 and applying to them the doctrine of averages which is 
 the basis of systematic sampling. 
 
 In regard to the matter of rolling sticky ore on canvas 
 or duck, as discussed by Messrs. Richard A.Parker, W.L. 
 Austin and G. M. Gouyard, 19 any error due to this cause 
 may arise from the fact that rich ore becomes powdered 
 in the course of reduction, especially in the presence of 
 pieces of 'gouge' or clay, such as frequently mark the 
 walls of lodes. A sample of poor ore may become 'salted' 
 
 18 On pages 129 and 130. 
 "See pages 150, 151, 152. 
 
 213 
 
if rolled on the canvas cloth which has been used in 
 quartering a richer material. The discussion of this point 
 serves to accentuate the dangers surrounding the quarter- 
 ing of samples ; but while the use of canvas for this pur- 
 pose is open to objections, it still remains the quickest 
 way to accomplish the desired end of reducing the bulk 
 of the sample in the absence of suitable split-shovels and 
 other apparatus, which are not readily portable to distant 
 mining localities. Wherever convenient, and especially in 
 the case of the examination of important mines, I would 
 advise the employment of a split-shovel and sampler, of 
 the kind used in assay offices. 20 
 
 In regard to the use of a strip of canvas to catch the 
 ore as it is broken instead of using a candlebox, I cannot 
 agree with Mr. Walter Harvey Weed, 21 because, even if 
 intentional 'salting' be prevented by excluding everyone 
 save those engaged in taking the samples, unintentional 
 interference with correct results will arise from the falling 
 of bits of ore outside of the range of the section sampled. 
 In many lodes carrying friable minerals or pulverulent 
 ore, or even sugar quartz, which has been loosened during 
 the course of mining, there will be a tendency for particles 
 to drop onto the canvas from spots not being sampled, 
 owing to the vibration set up by the blows of the hammer 
 on the moil. Rock at a distance will be jarred loose and 
 will get mixed up with the sample being taken. Of 
 course, if the candle-box is not held near the face of ore, 
 the chips broken off by the sampler will fly wide and 
 some of the material broken will escape the box, but this, 
 with a little experience, can be obviated. The man hold- 
 ing the box can put his hand up to the face of ore so as 
 to catch the broken rock and the candle-box can be held 
 so as to arrest the flying chips. In any event, to my 
 mind the use of a canvas is open to the objection men- 
 tioned, and should not be resorted to except in one con- 
 tingency that is, when an engineer is alone, has no 
 assistant with him, and has reason to distrust any help 
 
 also page 25. 
 21 See page 145 and also page 179. 
 
which is offered by those on the mine. Under such cir- 
 cumstances he cannot very well take a large sample, 
 without placing a canvas on the floor of the level or stope 
 so as to catch the ore broken down by him, because it is 
 physically impossible for him to hold a box and break a 
 sample at the same time. 
 
 The remarks of Mr. George A. Packard 22 concerning 
 low assays are much to the point. In ores containing 
 metals in quantities large as compared to the minute pro- 
 portion of gold usually present in lodes, there is a tend- 
 ency for erratic low results to disturb the real average 
 just as much as the "high assay" in gold mines. But, as 
 pointed out already, the high result always differs from 
 the low, especially in the case of the precious metals, be- 
 cause the former may be due to an accidental inclusion of 
 a small particle of specimen ore or a "metallic' in the final 
 pulp, while the latter simply bespeaks an absence of rich 
 ore in the whole of the sample, provided the latter has 
 been reduced so that the assay pulp represents the average 
 contents of the crude ore broken in the process of 
 sampling. 
 
 In regard to talking straight to one's client, telling him 
 whether the facts are sufficient to be the basis of an 
 opinion or not, explaining the element of risk and taking 
 care to distinguish between probabilities and possibilities 
 in all this I agree heartily with the views expressed by 
 Mr. Packard, 23 and, as the reader is aware, I have en- 
 deavored to emphasize the advisability of being outspoken, 
 for business reasons, as well as from finer considera- 
 tions. 
 
 The mathematical demonstrations and methods of cal- 
 culation described by Mr. Blarney Stevens 2 * and by Mr. 
 Auguste Mathez 25 are interesting, not only because they 
 will facilitate the arrival at conclusions, but chiefly from 
 the fact that they illustrate the methematical basis for the 
 methods which men reach more laboriously through ex- 
 
 ^On page 181. 
 
 ^See page 183. 
 
 24 On pages 155 to 161. 
 
 ^On pages 161 to 163. 
 
 215 
 
perience. Empiricism, rule of thumb, practical ways 
 these are all reached by a process of elimination, and, in 
 so far as they are logical and survive the test of usage, 
 they can be expressed in terms of mathematics. 
 
 Mr. Gemmell offers several useful hints. 26 In deprecat- 
 ing "unnecessary refinement" of method he exhibits a 
 natural impatience, for once a man is thoroughly experi- 
 enced he can dispense with certain details of procedure, 
 as a golf player who is in good form may not need to 
 waggle his club before making a drive. But in describing 
 all the possible precautions against error, I did so for the 
 benefit of the novice, who, as he gains experience, will 
 be warranted in dispensing with some of them, while 
 retaining others, according to the circumstances of each 
 case. 
 
 The examples quoted by Mr. Gemmell are full of sug- 
 gestion; it is by contact with such facts that a man ac- 
 quires the judgment which enables him to detect the 
 weak points of any estimate, and so avoid them. No con- 
 tribution to this discussion will be more valuable than 
 these transcripts from experience as given by Mr. Gem- 
 mell, if they emphasize the enormous variety of conditions 
 to be faced in the valuation of mines. 
 
 Impatience with an apparently needless consideration of 
 niceties of method has become apparent in the latter part 
 of this discussion on sampling, and a letter received from 
 a veteran engineer voices this sentiment by suggesting 
 that too much emphasis is being placed upon useless de- 
 tails, which have the effect of obscuring the essential 
 facts. 
 
 Well, there is something to be said for that; an en- 
 gineer should not get so tied up with his paraphernalia 
 and methods as to lose sight of the purpose of it all, for, 
 if he does that, he will resemble the centipede who got 
 along very well on his multitudinous legs until the scorpion 
 asked him which leg he put out first, and thereupon the 
 centipede became so self-conscious that his extremities 
 became all tangled up and he fell by the wayside. There 
 
 page 184. 
 
 216 
 
is a happy medium between discarding a proper pro- 
 cedure and becoming the victim of it, to be so 'practical' 
 as to neglect precautions and to be so 'technical' as to 
 lack sense of proportion. This entire consideration of a 
 difficult part of mining practice illustrates the importance 
 of the personal factor. The mathematical demonstrations 
 and occasional short-cuts, such as have been described 
 by Messrs. Channing, Hoffman, Stevens and Mathez, are 
 all suggestive of the fact that the methods evolved by ex- 
 perience, if good, are logical ; but beyond this there is an 
 insistent element present in all estimates of ore in a mine, 
 that is, the personal equation, which cannot be expressed 
 by any algebraic sign save x. No branch of professional 
 work, not even the management of men, requires more 
 resourcefulness and skill; for this reason it is considered 
 one of the severest tests of an engineer's capacity. If, 
 therefore, the importance of this subject has become 
 recognized increasingly during the last few years, it is 
 good evidence of the emergence of mining from the 
 mists of speculation on to the firm ground of serious busi- 
 ness. 
 
INDEX. 
 
 PAGE. 
 
 Argall, Philip 76, 93, 114, 116, 119, 137, 182 
 
 Contribution to Discussion 102, 1 17 
 
 On Ore Developed 76 
 
 Assay Plans 172 
 
 Austin, W. L 178, 213 
 
 Contribution to Discussion 150 
 
 Bancroft, George J 200, 210 
 
 On Unsystematic Sampling 118 
 
 Banks, John H 88 
 
 Brown, R. Oilman, Contribution to Discussion 148 
 
 On Cost Per Ton as a Basis of Mine Valuation 82 
 
 Brunton, F. W 75 
 
 Burnham, F 202 
 
 Butte Copper Mines 73 
 
 California Gold Mines 150 
 
 Camp Bird Mine 142, 175 
 
 Cananea Mines 120 
 
 Carter, T. Lane 202 
 
 On Mine Valuation 131 
 
 Channing, J. Parke 212, 217 
 
 Contribution to Discussion 192 
 
 On Mine Valuation 88 
 
 Charleton, A. G 75, 148 
 
 Check Samples 105 
 
 Collateral Evidence in Mine Valuation 71 
 
 Collins, Arthur L 93 
 
 Collins, George E 96, 102, 112, 117, 200 
 
 Contribution to Discussion 113 
 
 On Ore Developed 93 
 
 Cost of Mine Examination 14, 170 
 
 Cost Per Ton as a Basis of Mine Valuation 82 
 
 Courtis, W. M 213 
 
 Contribution to Discussion 130 
 
 Cripple Creek Mines 47 
 
 Curie, J. H 205 
 
 On Some Aspects of Mine Valuation 138 
 
 319 
 
PAGE. 
 
 Denny, G. A .75, 183, 202 
 
 Contribution to Discussion 163 
 
 Erratic Samples in 
 
 Explosives, Use of 18, 145 
 
 Future Prospects of a Mine 60 
 
 Gemmell, R. C 216 
 
 Contribution to Discussion 184 
 
 Gouyard, G. M 213 
 
 Contribution to Discussion. . . .' 115, 152 
 
 Grab Samples 34, 130 
 
 High Assays 39, 181, 207 
 
 Treatment of 40 
 
 Hoffmann, Ross 217 
 
 Mathematical Basis of Sampling 35 
 
 Howe, Albion S 213 
 
 Contribution to Discussion 130 
 
 Jones Sampler 108, 109 
 
 Kendall, J. D 75 
 
 Kirby, E. B 75 
 
 Lawrence, Benjamin B'., Contribution to Discussion 116 
 
 Lee, Chester F 201, 212 
 
 Contribution to Discussion 128 
 
 Levy, Ernest 200 
 
 On Sampling the Floor of a Wet Level 124 
 
 Low Assays, Influence of 181, 215 
 
 Mathez, Auguste 217 
 
 Contribution to Discussion 161 
 
 McDermott, W 75 
 
 Method of Least Squares as Applied to Sampling 157 
 
 Meyer & Charlton Gold Mining Co., Ltd., Sampling Record. 168 
 
 Minard, F. H 211 
 
 Contribution to Discussion 175 
 
 Mine Valuation 131, 205 
 
 Mining Costs, Determination of 1 1 
 
 Numbering Samples 178 
 
 Ore, Definition of 10 
 
 Determination of Value 14, 147, 149 
 
 Ore Blocked, Definition 115 
 
 Ore Developed, Definition 93 
 
 Ore Expectant, Definition 80 
 
 Ore Faces, Definition 115 
 
 Ore-Reserves, Estimation of 51, 206 
 
 Organization of a Sampling Gang 15 
 
 Packard, George A 215 
 
 Contribution to Discussion 181 
 
 Panning 135 
 
PAGE. 
 
 Parker, Richard A 151, 152, 178, 213 
 
 Contribution to Discussion 150, 154 
 
 Peele, Robert ' 88 
 
 Prismoidal Formula as Applied to Ore-Bodies 162 
 
 Probable Error in Sampling 157 
 
 Probable Ore, Definition of 117 
 
 Positive Ore, Definition of 117 
 
 Purington, C. W 200 
 
 Contribution to Discussion 96 
 
 Pyrites Mines, Valuation of 89 
 
 Quartering Samples 23, 146 
 
 Rand Mines 51, 61, 131, 164, 202 
 
 Raub Mine 141 
 
 Reduction of Samples 23 
 
 Rickard, Forbes, Contribution to Discussion 195 
 
 Rickard, T. A 103, 137, 175 
 
 Review of Discussion 199 
 
 Sampling and Estimation of Ore in a Mine 9 
 
 Sample Card 185 
 
 Samples, Reduction 23, 107 
 
 Marking Position 103 
 
 Sacking 107 
 
 Screening 24 
 
 Size 206 
 
 Sampling, Bottom of Wet Level 200 
 
 Cost of 170 
 
 Inferences from 55 
 
 Influenced by Pitch of Lode 33 
 
 Interval 16, 172, 201, 203 
 
 Narrow Veins 177 
 
 On the Rand 131, 163, 196 
 
 Precautions in 26 
 
 Quarterings 195 
 
 Record 168, 169 
 
 Rings 186, 187 
 
 Tools 18, 212 
 
 Work of 17, 105 
 
 Wrong Methods . 31 
 
 Sampling and Mining, Discrepancies Between 44, 136 
 
 San Juan ( Colo. ) Mines 62 
 
 Screening Samples 24 
 
 Seven-Thirty Mine 54 
 
 Silver Plume Mine 54 
 
 Sketching Samples 172 
 
 Smuggler-Union Mine 42 
 
PAGE. 
 
 Stevens, Blarney 217 
 
 Contribution to Discussion 155 
 
 Tin Gravels, Sampling of 58 
 
 Tomboy Mine 42, 142 
 
 Treadwell, John C 200 
 
 Contribution to Discussion 115 
 
 Truscott, S. J 75 
 
 Unsystematic Sampling 200 
 
 Valuation of a Prospect 183 
 
 Of Mines 131, 205 
 
 Of Mines in New Districts 167 
 
 Weed, Walter Harvey 179, 212, 214 
 
 Contribution to Discussion 145 
 
 Wet Level, Sampling in 124, 194 
 
 Winslow, Arthur 114 
 
 Wybergh, W 75 
 
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