GOLD MINING and MILLING in the UNITED STATES and CANADA Current Practices and Costs
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U. S. DEPARTMENT OF COMMERCE R. P. LAMONT, Secretary BUREAU OF MINES SCOTT TURNER. Director Bulletin 363 GOLD MINING AND MILLING IN THE UNITED STATES AND CANADA Current Practices and Costs BY CHARLES F. JACKSON and JOHN B. KNAEBEL UNITED STATES GOVERNMENT PRINTING OFFICE WASHINGTON: 1932 For sale by the Superintendent ()f Documents, Washington, D. C. ------ Price 15 cents FOREWORD This bulletin deals with the prospecting, development, mining, and milling of lode-gold ores, and contains a brief discussion of placer mining. It is the first of a series of summary bulletins, which will deal particularly with production methods, as well as costs per ton of the different metallic ores mined, and per unit of metal re covered. During periods of reduced demand and lowered prices for base metals, interest in gold mining invariably revives. This paper is therefore of timely interest. Some of the details here summarized have already been published by the bureau during the past three years, in various information circulars which dealt with practices and costs at each of a large number of properties. Generally, those circulars were writtenbymen in charge of operations, acting as special consultants to the bureau. To details thus accumulated have been added facts secured by field engineers of the bureau at these and other properties, supplemented by data from the bureau files, company reports, and the technical press. A bulletin devoted to each metal will be published, in which will be consolidated the pertinent facts regarding exploitation and operation, and discussion of production trends, ore occurrence, and costs. From comparative insignificance as a gold producer until 1848, the United States came to the forefront with the discovery of gold in California in that year and continued in first or second place among gold-producing countries until 1930, when, if the Philippine pro duction is omitted, Canada took second place and increased its lead over the United States in 1931. The United States production reached its peak in 1915, when 4,823,672 fine ounces of gold ($99,703,300) were produced exclusive of Philippine production. Since 1915, production steadily declined until 1931, when a small increase was recorded. In 1931, our most productive gold mine had a record of slightly less than $9,000,000. Canada first assumed real importance as a gold-mining country during the Yukon rush in 1898, and since that date has become an increasingly important producer. In 1931, each of two Canadian lode mines produced gold in excess of $10,000,000. Some lode deposits have been remarkably persistent in size and grade to great depths and have been profitably operated over a long period of years. Others have been of the bonanza type, and for a few years have yielded large quantities of gold from comparatively shallow depths. The cost of producing an ounce of gold at different American mines varies between wide limits and depends upon a number of factors. Among these factors the grade of the are mined is of importance, as well as size of operations, and physical conditions, such as type of deposit, continuity of are, distribution of gold, and mineral association. One American mine, operating under con- m IV FOREWORD ditions snited to wholesale methods, is now producing gold profitably from an ore which, over a period of years, has yielded less than $1 per ton in gold. Most of the larger producers are mining ore yielding $6 to $12 per ton, but only a few are mining ore yielding over $12 per ton. At a number of properties operating costs per ounce of gold range from about $6.50 to $18.50, the average cost being roughly $10 to $12. If deprectiation, taxes, overhead, and marketing are added, these costs range from about $8.30 to $19.50 and average roughly $12 to $14. These are current costs at profitable mines, and it is obvious that if losses at nonprofitable operations and the cost of unsuccessful ex ploration for gold could be known and were added, the total cost of producing gold in the United States and Canada would be found to be much higher. It is hoped that this bulletin will be found useful to mining men generally. Helpful suggestions would be welcomed by the bureau, and new or improved data might be incorporated in a later revised edition of this gold bulletin. SCOTr TURNER, Director. CONTENTS Foreword _ Page Page III Part·I-Continued. Introduction _ I Occurrence of productive and Object and scope of paper _ I nonproductive horizons__ 32 Acknowledgments _ 2 Teck-Hughesrio mine, Onta-_ Production of gold in United 32 . States, its Territorial pos- Mother lode, California _ 32 sessions, and Canada _ 2 Sierra County, CaliL _ 33 History _ 2 Portland mine, Colorado _ 33 Location and status of pro- Part 2. Exploration, develop- ducing regions _ 3 ment, and mining _ 34 Location of mines _ 10 Methods of prospecting, ex Part 1. Geology _ 12 ploration, and sampling__ 34 Types of gold deposits _ 12 Prospecting _ 34 Placer deposits _ 12 Gold placers _ 34 Classification _ 12 Lode deposits _ 36 Lode deposits _ 13 In hilly country _ 36 Geologic age of lode-gold In flat country _ 37 deposits _ 16 ExploratioD _ 38 Mineralogy of lode-gold Shallow work _ 39 deposits _ 17 ])eeper work _ 40 Nonmetallic gangue Adit leveL _ 40 minerals _ 18 Shafts v. crosscuts _ 40 Gossan minerals _ 18 ])rill exploration _ 43 Metallic minerals _ 18 ])rifting _ 44 Changes in gold deposits with Sampling _ 44 depth _ 22 Channel sampling _ 45 Changes near surface _ 22 Pick sampling _ 46 Changes below zone of oxi- ])rill sampling _ 46 dation _ 25 Grab samples _ 47 Homestake mine, South Bulk samples _ 48 ])akota _ 26 References _ 48 Kirkland Lake district, Treatment of samples _ 48 Ontario, and Mother ])evelopmentmines of lode-gold_ lode, California _ 26 48 Alaska-Juneau mine, Exploratory workings _ 49 Alaska, and Grass Val Shafts _ 50 ley district, California_ 26 Costs of shaft sinking _ 50 Bodie district, Californis_ 26 Shaft equipment _ 53 Goldfield district, Ne- ])rifts and crosscuts _ 54 vads _ 27 Level interval _ 54 Tonopah district, Neva- Size of drifts and cross- da _ 27 cuts _ 56 Round Mountain district, Costs of drifting and Nevada, and Brecken crosscutting _ 59 radoridge district, Colo-_ Plan of levels ~ __ 59 27 Raises and subdrifts _ 62 Oatman district, Ari- Exploration during develop- zona _ 27 ment _ 63 Tertiary veins in generaL 28 Costs of development _ 64 Relation of outcrops to ore Tons per foot of develop- shoots _ 29 ment _ 65 Emmons's theory _ 29 Current mine-develop- Oatman, Ariz _ 30 ment costs _ 66 ])epth of fissures _ 31 Pilot milling plant- _ 67 Cripple Creek, Colo _ 31 Stoping methods _ 68 Appalachian regioll _ 31 Classification _ 69 v VI CONTENTS Part 2-Continued. Paae Part 3-Continued. Page Stoping methods-Contd. Milling methods _ 104 Shrinkage stoping _ 70 Outline of chief processes__ 104 Cut-and-fill stoping _ 71 Hand sorting _ 104 Square-set stoping _ 76 Amalgamation _ 105 Open stopes _ 78 Plate amalgamation _ 105 Caving methods _ 81 Barrel amalgamation _ 108 Stoping costs _ 81 Pan amalgamation _ 108 Cost of mining lode-gold ores_ 83 Arrastres _ 108 Management policy _ 83 Concentration " _ 108 Effect of economic condi- Gravity concentration _ 109 tions _ 84 Stt>.tionary tables _ 109 Other considerations _ 85 Shaking tables _ 109 Operating factofs _ 85 Vanners ~ 110 Development costs _ 85 Classification _ 111 Stoping costs _ 86 Treatment of concen-. Rate of productioD _ 86 trates _ 111 Cost dats _ 87 F'lotation _ 111 Part 3. Gold milling _ 89 Cyanidation _ 112 Types of ores _ 89 Chewistry _ 112 Brief outline of history and Applicability and limita- principles of gold milling _ 90 tions _ 113 Factors affecting choice and Methods of treatment- __ 114 operationrnethods of milling_ Examplesofcurrentpractice_ 117 91 Porcupine United Gold Character of ore _ 91 Mines (Ltd.) _ 118 Grade ~ _ 91 Original Sixteen to One Uniformity of tenoL _ 92 Mine (Inc.) _ 118 Size of particles _ 92 Argonaut milL _ 119 Mineral associations _ 93 Central Eureka milL _ 120 Pyrite _ 93 Homestake Mining Co-_ 120 Other sulphides _ 94 Alaska-Juneau concentra- Arsenic and antimony_ 95 tor .. _ 123 Bismuth _ 95 Mountain Copper Co _ 125 Tellurides ~ _ 95 Coniaurum Mines (Ltd.)_ 126 Oxidized minerals ~ 95 Kirkland Lake Gold Carbonaceous matter _ 96 Mines (Ltd.) _ 127 Grease and talc _ 96 Teck-Hughes milL _ 128 Strongalkalies oracids_ 96 Howey milL ~ _ 130 Influence of tonnage to be Spring Hill concentrator_ 132 handled ~ 96 Discussion of milling meth- Amount of money avail- ods _ 133 able _ 98 Application of methods__ 133 Water supply ~_ 98 Hand sorting _ 133 Commercial affiliations _ 98 Amalgamation~ _ 133 Royalties _ 99 Gravity concentration_ 133 Location ~ _ 99 Flotation _ 134 Altitude and climate _ 99 Cyanidation _ 134 Transportation _ 100 Comparison of methods Cost of supplies~ _ 100 and recent trends _ 134 Power and fueL _ 101 Costs of milling _ 136 Tailings dispo'SaI _ 101 Part 4. Costs of producing gold_ 139 Lahor supply _ 102 Lack of complete data ~ 139 Government regulations_ 102 . Factors affecting costs _ 139 Cost of construction _ 102 Cost statistics of earlier years_ 139 General economic condi- Current costs _ 141 uons__ ._~ ••__ Index _ 103 145 ILLUSTRATIONS FIg.