74 BULLETIN 131, UNITED STATES NATIONAL MUSEUM 



CUSTER COUNTY 



In the Alder Creek district thin films of copper occur along fractures 

 on the 300-foot level of the Empire mine and also as small specks in 

 nodules of cuprite. 22 



LATAH COUNTY 



Native copper occurs in the oxidized ore of the Mizpah mine, 

 Hoodoo district, along with malachite, copper pitch ore, and cuprite. 



LEMHI COUNTY 



Copper appeared occasionally in thin films along fractures in ores 

 of the Indian Creek district and also in the Beaver Creek district. 23 



SHOSHONE COUNTY 



Copper occurred rarely and in small amount in ores of the Snow- 

 storm mine at Larsen. Fine crystallized specimens have been 

 obtained from the Iron Mask mine. In the Caledonia mine copper 

 is rather common in the oxidized ore in dendritic moss-like forms 

 entirely like those characteristic of the native silver. These occur 

 implanted upon cerusite or embedded in spongy limonite. In the 

 Boyle stope small nugget-like masses of native copper were intimately 

 mixed with similar masses of native silver. 24 Crystalline wires of 

 native copper occurring on the 700-foot level of this mine bore a thin 

 outer plate of native silver. Native copper formerly occurred in 

 similar wire-like forms at the Tyler mine. 25 



AMALGAM (17) 



Silver amalgam sometimes with gold (Ag, Au, Hg). Isometric. 



CUSTER COUNTY 



Native amalgam has been reported from the gold-bearing gravels 

 worked by the Willis dredge across the divide from Joe's Gulch in 

 the Stanley Basin district. The amalgam is associated with cinnabar, 

 the latter mineral becoming more abundant as the dredge is moved 

 upstream. 26 A sample of pan concentrate received from H. C. Willis, 

 manager of the dredge, consists largely of brannerite or a similar 

 radioactive black mineral associated with which is considerable 

 cinnabar and a few grains of amalgam. The largest grain of the 

 latter, when selected from the concentrate and heated in a closed tube, 

 gave a sublimate of mercury. The remaining metallic mass was 

 malleable and after being flattened with a hammer was heated with 

 nitric acid. The residue was yellow gold and the nitric acid gave a 



« J. B. Umpleby. U. S. Geol. Survey, Prof. Paper 97, p. 52, 1917. 

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



84 Earl V. Shannon, Econ. Geol., vol. 8, p. 565, 1913. 



85 W. Howard McBride. Oral communication. 



" J. B. Umpleby and D. C. Livingston. Idaho State Bur. Mines and Geol., Bull. 3, p. 16, 1920. 



