THE MINERALS OF IDAHO 105 



posit of the Red Ledge mine the best ore has been enriched by the 

 replacement of chalcopyrite and especially galena by chalcocite. 75 

 Specimens of ore from the Fidelity Group show rather abundant 

 chalcocite partly altered to chrysocolla and malachite. 



CUSTER COUNTY 



In the Mackay district chalcocite is very rare in the copper ores. 

 It occurs only in small amounts as thin films along fracture planes 

 and as minute specks imbedded in chrysocolla in the oxidized ores. 76 

 In northwestern Custer County copper glance is found locally as 

 films along cracks in the upper level of the Lost Packer mine and is 

 probably also present in the upper levels of the silver-copper deposits. 77 



BANNOCK COUNTY 



Judging from specimens in the National Museum, the best and 

 most typical chalcocite from any locality in the State is from the 

 Moonlight mine of the Pocatello Gold and Copper Co., on Rabbit 

 Creek, 9 miles east of Pocatello in the Fort Hall district. The speci- 

 mens (Cat. No. 75521, U.S.N.M.) show clean gray lustrous masses 

 of chalcocite in an indeterminate chalky white rock. The chalcocite 

 is in considerable part altered to brochantite. As described by 

 Weeks and Heikes 78 the chalcocite occurs with bornite in small 

 kidney-shaped masses and seams along fractures and fissures in 

 conglomerate. 



LEMHI COUNTY 



In Lemhi County chalcocite, though nowhere abundant, can gen- 

 erally be found a short distance below the surface in the copper bear- 

 ing deposits. 79 



SHOSHONE COUNTY 



In Shoshone County chalcocite occurs in the Snowstorm, National, 

 Park, Reindeer, Carney Copper, and probably other copper mines 

 and prospects in the vicinity of Mullan. At the Snowstorm mine it 

 occurred with bornite disseminated through quartzite and occasion- 

 ally concentrated in bunches in small quartz veins which cut the 

 disseminated deposits. At the Park mine, 4 miles south of Mullan, 

 the chalcocite, which has apparently been formed by the action of 

 descending sulphate waters on pyrite and chalcopyrite, occupied a 

 vein near the bottom of the zone of oxidation. 80 



75 D. C. Livingston and F. B. Laney. The copper deposits of the Seven Devils and adjacent districts 

 Idaho Bur. Mines and Geol. Bull. 1, 1920. 



™ J. B. Umpleby. U. S. Oeol. Survey, Prof. Paper 97, p. 50, 1917. 



» J. B. Umpleby. U. S. Geol. Survey Bull. 539, p. 52, 1913. 



78 F. B. Weeks and V. C. Heikes. Notes on the Fort nail Mining district, Idaho. U. S. Geol. Survey 

 Bull. 340, p. 180, 1908. 



" J. B. Umpleby. U. S. Geol. Survey Bull. 528, p. 76, 1913. 



'• F. L. Ransome. U. S. Geol. Survey, Prof. Paper 62, p. 91, 1908. 



