THE TELLURIDE ORES. 1119 



TELLl'KIDES. 



The only important telluride ores are those of gold and silver. These 

 compounds, until comparatively recently, were regarded as somewhat 

 exceptional, and for the most part rather as mineralogical rarities than as 

 ores. The earliest gold and silver tellurium ores to be mined were those of 

 Nagyag, in Transylvania." Gold mining in Colorado has added other and 

 much more important localities where the tellurides are produced in impor- 

 tant amounts. About 1872 the tellurides of Boulder County became of 

 consequence. But of more importance than all of the previously known 

 tellurides are those of Cripple Creek, Colorado, which began to be exploited 

 in 1S91. 6 Here the various tellurides are found, but the greater part of the 

 gold is believed to occur in calaverite. 



Close mineralogical studies of ore deposits in recent years have shown 

 that subordinate and usually unimportant amounts of tellurides, from an 

 economic point of view, occur very generally associated with gold. Indeed, 

 it appears that the presence of the tellurides with the gold ores of the first 

 concentration is scarcely less prevalent than the association of pyrite with 

 gold ores. The widespread occurrence of tellurides in connection with gold 

 ores is illustrated by the Kalgoorlie district of West Australia, described 

 by Bancroft ; d by the Sierra Nevada gold deposits, described by Lindgren; 6 

 by the Judith Mountains and Little Rocky Mountains, Montana, described 

 by Weed and Pirsson/ by the Potsdam gold ores of the Black Hills, 

 described by Smith and Irving;' 7 by the mines of Custer County, Colo., 

 and by the Appalachian gold deposits, described by S. F. Emmons.' 



a Kemp, J. F., Geological occurrence and associates of the telluride gold ores: Mineral Industry, 

 vol. 6, 1898, p. 295. 



& Penrose, R. A. F., jr., Mining geology of the Cripple Creek district: Sixteenth Ann. Rept. 

 U. S. Geol. Suvey, pt. 2, p. 118. 



c Penrose, cit., p. 121. 



d Bancroft, Geo. J., Kalgoorlie, Western Australia, and its surroundings: Trans. Am. Inst. Min. 

 Eng., vol. 28, 1899, pp. 88-100. 



«Lindgren, Waldemar, The gold-quartz veins of Nevada City and Grass Valley, California: Seven- 

 teenth Ann. Rept. U. S. Geol. Survey, pt. 2, 1896, p. 117. 



/Weed,"W. H., and Pirsson, L. V., Geology and mineral resources of the Judith Mountains, Mon- 

 tana: Eighteenth Ann. Rept. U. S. Geol. Survey, pt. 3, 1898, pp. 589-592. Weed, W. H., and Pirsson, 

 L. V., Geology of the Little Rocky Mountains, Montana: Jour. Geol., vol. 4, 1896, pp. 426-428. 



g Smith, F. C, The Potsdam gold ores of the Black Hills of South Dakota: Trans. Am. Inst. Min. 

 Eng., vol. 27, 1898, pp. 414-420. Irving, J. D., A contribution to the geology of the northern Black 

 Hills: Annals New York Acad. Sci., vol. 11, 1899, pp. 297-311. 



''Emmons, S. F., The mines of Custer County, Colorado: Seventeenth Ann. Rept. U. S. Geol. 

 Survey, pt. 2, 1896, p. 433. Emmons, S. F., Notes on the gold deposits of Montgomery County, Mary- 

 land: Trans. Am. Inst. Min. Eng., vol. 18, 1890, p. 407. 



