GOLD MINING AND MILLING IN THE UNITED dggs. · PDF fileShrinkage stoping _ 33. Stoping method...
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U. S. DEPARTMENT OF COMMERCER. P. LAMONT, Secretary
BUREAU OF MINESSCOTT TURNER. Director
GOLD MINING AND MILLING IN THEUNITED STATES AND CANADA
Current Practices and Costs
CHARLES F. JACKSON and JOHN B. KNAEBEL
GOVERNMENT PRINTING OFFICE
For sale by the Superintendent ()f Documents, Washington, D. C. - - - - - - Price 15 cents
This bulletin deals with the prospecting, development, mining,and milling of lode-gold ores, and contains a brief discussion ofplacer mining. It is the first of a series of summary bulletins, whichwill deal particularly with production methods, as well as costs perton of the different metallic ores mined, and per unit of metal re-covered. During periods of reduced demand and lowered prices forbase metals, interest in gold mining invariably revives. This paperis therefore of timely interest.
Some of the details here summarized have already been publishedby the bureau during the past three years, in various informationcirculars which dealt with practices and costs at each of a largenumber of properties. Generally, those circulars were written by menin charge of operations, acting as special consultants to the bureau.To details thus accumulated have been added facts secured by fieldengineers of the bureau at these and other properties, supplementedby data from the bureau files, company reports, and the technicalpress. A bulletin devoted to each metal will be published, in whichwill be consolidated the pertinent facts regarding exploitation andoperation, and discussion of production trends, ore occurrence, andcosts.
From comparative insignificance as a gold producer until 1848, theUnited States came to the forefront with the discovery of gold inCalifornia in that year and continued in first or second place amonggold-producing countries until 1930, when, if the Philippine pro-duction is omitted, Canada took second place and increased its leadover the United States in 1931.
The United States production reached its peak in 1915, when4,823,672 fine ounces of gold ($99,703,300) were produced exclusiveof Philippine production. Since 1915, production steadily declineduntil 1931, when a small increase was recorded. In 1931, our mostproductive gold mine had a record of slightly less than $9,000,000.
Canada first assumed real importance as a gold-mining countryduring the Yukon rush in 1898, and since that date has become anincreasingly important producer. In 1931, each of two Canadianlode mines produced gold in excess of $10,000,000.
Some lode deposits have been remarkably persistent in size andgrade to great depths and have been profitably operated over a longperiod of years. Others have been of the bonanza type, and for afew years have yielded large quantities of gold from comparativelyshallow depths.
The cost of producing an ounce of gold at different Americanmines varies between wide limits and depends upon a number offactors. Among these factors the grade of the are mined is ofimportance, as well as size of operations, and physical conditions,such as type of deposit, continuity of are, distribution of gold, andmineral association. One American mine, operating under con-
SCOTr TURNER, Director.
ditions snited to wholesale methods, is now producing gold profitablyfrom an ore which, over a period of years, has yielded less than $1per ton in gold.
Most of the larger producers are mining ore yielding $6 to $12per ton, but only a few are mining ore yielding over $12 per ton. Ata number of properties operating costs per ounce of gold range fromabout $6.50 to $18.50, the average cost being roughly $10 to $12. Ifdeprectiation, taxes, overhead, and marketing are added, these costsrange from about $8.30 to $19.50 and average roughly $12 to $14.
These are current costs at profitable mines, and it is obvious thatif losses at nonprofitable operations and the cost of unsuccessful ex-ploration for gold could be known and were added, the total cost ofproducing gold in the United States and Canada would be found tobe much higher.
It is hoped that this bulletin will be found useful to mining mengenerally. Helpful suggestions would be welcomed by the bureau,and new or improved data might be incorporated in a later revisededition of this gold bulletin.
Foreword _Introduction _
Object and scope of paper _Acknowledgments _Production of gold in United
. States, its Territorial pos-sessions, and Canada _
History _Location and status of pro-
ducing regions _Location of mines _
Part 1. Geology _Types of gold deposits _
Placer deposits _Classification _
Lode deposits _Geologic age of lode-gold
deposits _Mineralogy of lode-gold
deposits _Nonmetallic gangue
minerals _Gossan minerals _Metallic minerals _
Changes in gold deposits withdepth _Changes near surface _Changes below zone of oxi-
dation _Homestake mine, South
])akota _Kirkland Lake district,
Ontario, and Motherlode, California _
Alaska-Juneau mine,Alaska, and Grass Val-ley district, California_
Bodie district, Californis_Goldfield district, Ne-vads _Tonopah district, Neva-da _
Round Mountain district,Nevada, and Brecken-ridge district, Colo-rado _
Oatman district, Ari-zona _Tertiary veins in generaL
Relation of outcrops to oreshoots _Emmons's theory _Oatman, Ariz _])epth of fissures _Cripple Creek, Colo _Appalachian regioll _
Part I-Continued.Occurrence of productive and
nonproductive horizons __Teck-Hughes mine, Onta-rio _Mother lode, California _Sierra County, CaliL _Portland mine, Colorado _
Part 2. Exploration, develop-ment, and mining _
Methods of prospecting, ex-ploration, and sampling__
Prospecting _Gold placers _Lode deposits _
In hilly country _In flat country _
ExploratioD _Shallow work _])eeper work _
Adit leveL _Shafts v. crosscuts _])rill exploration _])rifting _
Sampling _Channel sampling _Pick sampling _])rill sampling _Grab samples _Bulk samples _References _Treatment of samples _
])evelopment of lode-goldmines _Exploratory workings _Shafts _
Costs of shaft sinking _Shaft equipment _
])rifts and crosscuts _Level interval _Size of drifts and cross-
cuts _Costs of drifting and
crosscutting _Plan of levels ~ __Raises and subdrifts _Exploration during develop-ment _Costs of development _
Tons per foot of develop-ment _Current mine-develop-
ment costs _Pilot milling plant- _
Stoping methods _Classification _
Part 2-Continued.Stoping methods-Contd.
Shrinkage stoping _Cut-and-fill stoping _Square-set stoping _Open stopes _Caving methods _Stoping costs _
Cost of mining lode-gold ores_Management policy _Effect of economic condi-
tions _Other considerations _Operating factofs _
Development costs _Stoping costs _Rate of productioD _
Cost dats _Part 3. Gold milling _
Types of ores _Brief outline of history and
principles of gold milling _Factors affecting choice and
operation of millingrnethods _Character of ore _
Grade ~ _Uniformity of tenoL _Size of particles _Mineral associations _
Pyrite _Other sulphides _Arsenic and antimony_Bismuth _Tellurides ~ _Oxidized minerals ~Carbonaceous matter _Grease and talc _Strong alkalies or acids_
Influence of tonnage to behandled ~
Amount of money avail-able _Water supply ~_Commercial affiliations _Royalties _Location ~ _
Altitude and climate _Transportation _Cost of supplies~ _Power and fueL _Tailings dispo'SaI _Lahor supply _Government regulations_Cost of construction _
General economic condi-uons__ ._~ __
Part 3-Continued.Milling methods _
Outline of chief processes__Hand sorting _Amalgamation _
Plate amalgamation _Barrel amalgamation _Pan amalgamation _Arrastres _
Concentration " _Gravity concentration _
Stt>.tionary tables _Shaking tables _Vanners ~Classification _Treatment of concen-.
trates _F'lotation _
Cyanidation _Chewistry _Applicability and limita-
tions _Methods of treatment- __
Examplesofcurrentpractice_Porcupine United Gold
Mines (Ltd.) _Original Sixteen to One
Mine (Inc.) _Argonaut milL _Central Eureka milL _Homestake Mining Co-_Alaska-Juneau concentra-
tor .. _Mountain Copper Co _Coniaurum Mines (Ltd.)_Kirkland Lake Gold
Mines (Ltd.) _Teck-Hughes milL _Howey milL ~ _Spring Hill concentrator_
Discussion of milling meth-ods _Application of methods __
Hand sorting _Amalgamation~ _Gravity concentration_Flotation _Cyanidation _
Comparison of methodsand recent trends _
Costs of milling _Part 4. Costs of producing gold_
Lack of complete data ~. Factors affecting costs _
Cost statistics of earlier years_Current costs _Index _
1. Map showing location of principal gold-producing districts in theUnited States and Canada, 1930-3L