THE MINERALS OF IDAHO 71 



mately equal parts by weight of gold and silver is given the varietal 

 name electrum. Many of the lode mines of Idaho have produced 

 gold high enough in silver to be properly designated by this name. 

 A few examples may be mentioned. 



ELMORE COUNTY 



Vein gold from the Rocky Bar district contains 70 per cent gold 

 and 30 per cent silver, computed from the assay value recorded. 



IDAHO COUNTY 



Placer gold from the Florence district is only 0.660 to 0.705 fine. 

 Placer gold from the outcrops of the Thunder Mountain deposits 

 contains 55 per cent of gold and 45 per cent of silver. 



OWYHEE COUNTY 



Practically all of the vein gold of the Silver City district is electrum. 

 Placer gold from this district is very pale in color and contains about 

 half gold and half silver. 



MALDONITE 



BISMUTH GOLD 



Gold bismuthide, Au Bi 2 . 



CUSTER COUNTY 



Maldonite, the rare combination of bismuth and gold, has been 

 reported to occur in the Empire claims of the Idaho-Montgomery 

 Mining Co. in Washington Basin. 17 This report has not been authen- 

 ticated. 



GOLD AMALGAM 



Natural alloy of mercury and gold, Au + Hg. 



CUSTER COUNTY 



A natural amalgam containing gold as well as silver occurring iu 

 the auriferous gravels of the Willis dredge property in Stanley Basin 

 is described below under the heading Amalgam. 



SILVER (14) 



Silver, Ag. Isometric 



Although nowhere very abundant, native silver is of rather com- 

 mon occurrence in the oxidized portions of silver-bearing veins in 

 Idaho. The principal occurrences are here listed. 



BLAINE COUNTY 



In Blaine County silver occurred in several mines of the Wood 

 River district, especially the Bullion. A specimen labeled Neptune 

 mine, Blaine County, in the National Museum (Cat. No. 56536, 

 U.S.N.M.) shows thin folia and grains of native silver with mossy 

 grains of argentite disseminated through altered granite. 



» Editorial. Eng. Mining Journ., vol. 83, p. 23, 1907. 



