1120 A TREATISE ON METAMORPHISM. 



Since the tellurides are very generally associated with gold ores and 

 the free gold deposited by the deep circulation is almost universally 

 associated with pyrite and other sulphides, it .follows that the tellurides 

 deposited by the deep circulation are usually associated with sulphides. 

 This is not only true of those localities in which the tellurides are unim- 

 portant as ores, but is equally true of the great telluride camps. Of 

 Cripple Creek Penrose says: "The close association of tellurides with 

 sulphides, especially iron pyrites, which themselves often carry gold, is 

 also a point worthy of note. Not only are auriferous tellurium and sulphur 

 compounds often thus mechanically associated in different minerals, but 

 sometimes they replace each other in the same minerals, such as tetrady- 

 mite, nagyagite, and tellur-sulphur." a 



The tellurides are also very generally associated with fluorite, and 

 Penrose notes that where the gold is mainly in sulphides fluorite has not 

 often been observed. 



It seems to me certain that the widespread association of the tellurides 

 with gold and silver ores, especially with gold oi'es, has a genetic signifi- 

 cance probably less important only than that of the base sulphides, especi- 

 ally iron sulphide. As to the source of the tellurium, nothing is positively 

 known. In all of the above-mentioned districts in which tellurium is 

 especially abundant, with the possible exception of the Kalgoorlie district, 

 which has not yet been thoroughly studied and in which the age of the 

 mineralizing dikes has not been established, are found comparatively recent 

 igneous rocks, in which doubtless the tellurium largely had its origin. At 

 first thought one might conclude that the gold, silver, and tellurium were 

 transported as tellurides and deposited as such without chemical change, 

 but the recent Avork of Lenher and HalP is decidedly against this view. 

 They have found no solvent whatever for tellurides of gold without 

 breaking up these compounds and producing salts of tellurium, the gold 

 usually being left in the metallic form. Moreover, as has already been 

 noted, they have shown that metallic tellurium and seven of the more 

 common mineral tellurides of gold and silver rapidly reduce g-old from 



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

 Rept. U. S. Geol. Survey, pt. 2, 1895, p. 157. 



''Lenher, Victor, Naturally occurring telluride of gold: Jour. Am. Chem. Soc, vol. 24, 1902, pp. 

 355-360. 



Hall, R. D., and Lenher, Victor, Action of tellurium and selenium on gold and silver salts: Ibid., 

 pp. 918-927. 



