PRECIPITATION OF GOLD. 1097 



from Kalgoorlie)," krennerite (AuAgTe 2 ; Au 35.5, Ag 19.4, Te 45.1, uncer- 

 tain), sylvanite (AuAgTe,; Au 24.5, Ag 13.4, Te 62.1), hessite (Ag 2 Te), 

 kalgoorlite (HgAu 2 Ag 6 Tei), nagyagite (Au 2 Pb u Sb 3 Te 7 S 17 ), and coloradoite 

 (HgTe). It thus appears that whether these minerals are largely tellurides 

 of gold, as calaverite; of gold and silver, as krennerite, sylvanite, etc.; of 

 silver, as hessite, or of mercury, as coloradoite, when brought into contact 

 with chloride of gold solutions metallic gold is precipitated. This experi- 

 mental work of Lenher and Hall is of very great importance, probably 

 largely explaining the intimate association of free gold with the tellurides 

 at various places. 



It will be explained (pp. 1170-1171) that in many places the associa- 

 tion of free gold with tellurides is partly due to the reconcentrating action 

 of descending water, the tellurides being the precipitating agent, Doubtless 

 in many cases this process of reconcentration is also combined with that of 

 direct oxidation of the tellurium of the tellurides, leaving gold behind. The 

 spongy gold pseudomorphous after telluride, such as that which occurs at 

 Cripple Creek, is almost certain evidence of one or both of the above 

 processes. But in many cases the free gold associated with tellurides 

 may be due to a first precipitation from ascending waters, the precipi- 

 tating agent being the telluride. This possibility is illustrated by the 

 Kalgoorlie district of Australia, described by Bancroft, who says: "The ore 

 is very slightly altered country rock containing iron pyrites and tellurides 

 of gold. . . . One of the interesting phenomena of the ore is the occurrence, 

 once in a while, of small particles of crystalline gold surrounded by crystals 

 of tellurides low in gold.'"' 



The conclusion that the Kalgoorlie gold may be precipitated ,by the 

 tellurides is confirmed by observations made by Rickard. He states that 

 "free gold at Cripple Creek has invariably that appearance which charac- 

 terizes the metal when it has originated from the disintegration of tellurides; 

 but at (Kalgoorlie ordinary gold, in a bright and crystalline condition, also 

 occurs." ° 



« Rickard, T. A., The telluride ores of Cripple Creek and Kalgoorlie: Trans. Am. Inst. Min. Eng., 

 vol. 30, 1901, p. 711. 



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

 Eng., vol. 28, 1899, pp. 93-94. 



c Rickard, T. A., Telluride ores of Cripple Creek and Kalgoorlie: Trans. Am. Inst. Min. Eng., 

 vol. 30, 1901, p. 714. 



