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Bulletin №253, Series E, Chemistry and Physics, 44 USGS, Washington, 1905. - 31 p.
The subject of inquiry is the accuracy of the crucible assay method for telluride gold ores. The question is a very important one in the very important telluride gold fields, and it is satisfactory to be assured that the doubts which have been entertained as to the accuracy of the dry method are not well founded. A critical investigation of this problem seemed to promise results of some value to those engaged in mining and smelting the telluride ores, and the data and conclusions set forth in this bulletin are the outcome of experiments on telluride ores from Cripple Creek, Colo.
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Bulletin No. 253
Series E, Chemistry and Physics, 44
DEPARTMENT OF THE INTERIOR
UNITED STATES GEOLOGICAL SURVEY CHARLES D. WALCOTT, DIRECTOR
COMPARISON
A WET AND CRUCIB1E-FIRE METHODS FOB THM
ASSAY OF GOLD TELLURIDE ORES WITH NOTES ON THE ERRORS OCCURRING IN THE OPERATIONS OF FIRE ASSAY AND PARTING
W. F. HILLEBRAND and E. T. ALLEN
WASHINGTON GOVERNMENT
PRINTING OFFICE
1905
CONTENTS. Pago.
Letter of transmittal. .....................................................
5
Introduction. ___ .__._..._..._.._._...-......-- _.__.-.-.._...._.._._.-_..... Part I. Assay of Cripple Creek telluride ores -...I........................ Nature of the ores assayed ......-.-..-...- ... .........................
7 7 7
Preparation of the samples. ---...-....---...............--...........
9
Combination wet and fire assay ......-.-....--..-..-...-------..--..
9
Fire assay ..............................^...............................
12
Conduct of the assay......-.--....---..:..-..........-........... Charges used in assaying slags and cupels ..............^.,....-... Assays for gold and silver together............................... Discussion of results........-...-.....--........-..-----..... Assays for gold alone .........--.....-.--...-.....--.,..-........
12 12 12 14 15
Comparison of results .......................... ^......................
18
Part II. The errors in gold assaying..---..--.-..--.--.--..-.-.--..-_..... Cupellation losses..--...-.......-..---.-...--.-....................... Absorption and volatilization .-....-......:.........-.-.......... Retention of lead by cupelled beads .............................. Losses of gold in slags ............................................... Errors in parting :................................................... Strength of acid ..................--.......--..-.--..----......... Incomplete extraction of silver...................................
19 19 19 23 24 24 24 25
Impurities in acid ....^................................'..........
25
Action of nitrous acid ............................................ Action of nitric acid -.......-.-_-...-............-.-............. Summary of results.....--.....--...-.......---.--........-........--.... Index -.-..--...._.......................-.-........-....................
26 27 28 31
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3 '
LETTER OF TRANSMITTAL. DEPARTMENT OF THE INTERIOR, UNITED STATES GEOLOGICAL SURVEY, Washington, D. C. , November 1, 1904. SIR: I transmit herewith, for publicatioiras a bulletin, a paper by Messrs. W. F.. Hillebrand and E. T. Alien, in which the subject of inquiry is the accuracy of the crucible assay method for telluride gold ores. The question is a very important one in the very important telluride gold fields, and it is satisfactory to be assured that the doubts which have been entertained as to the accuracy of the dry method are not well founded. x While this main p