THE MINERALS OF IDAHO 119 



BORNITE (78) 



Copper iron sulphide, 2Cu 2 S. CuS. FeS. Isometric. 



Bornite is commonly known as peacock copper and is a relatively 

 high .grade copper ore. It is easily distinguished by its unusual 

 colors. On fresh fracture the mineral is coppery or bronze red but 

 it tarnishes quickly to blue or purple with occasionally shades of red 

 and green. In Idaho chalcopyrite, which often is iridescent on 

 fractures, is frequently erroneously called peacock ore. This is the 

 principal ore mineral in the Seven Devils district and occurs in minor 

 amount in a number of other districts. 



ADAMS COUNTY 

 (Including Washington County in part) 



Bornite in massive form is the principal primary copper mineral 

 in the Seven Devils copper district where it generally occurs in 

 association with epidote and garnet in contact metamorphic deposits 

 in limestone (Cat. Nos. 51871 and 67391, U.S.N.M.). Upon weather- 

 ing it alters to chrysocolla and malachite or sometimes to brochan- 

 tite. 95 The bornite from the contact deposits is argentiferous, 

 carrying 20 ounces of silver a ton. 96 Bornite occurs also as brilliant 

 masses in white quartz veins as in the Great Eastern vein and it 

 forms the principal metallic mineral in a peculiar pegmatitic ortho- 

 clase-quartz vein in the Panama Pacific prospect. 97 



BANNOCK COUNTY 



Bornite occurs with chalcocite in quartz in fissures in conglomerate 

 in ore of the Moonlight mine of the Pocatello Gold and Copper 

 Mining Co. near Pocatello. In the specimens seen the bornite is 

 in considerable part altered to dull purplish black "copper-pitch." 98 



CUSTER COUNTY 



Bornite is rare in the contact metamorphic copper ores of the 

 Mackay district (White Knob), the principal mineral of the un- 

 oxidized copper ores here being chalcopyrite as contrasted with the 

 Seven Devils district. Where it does occur bornite is apparently 

 secondary and often forms narrow veinlets along joints and cracks 

 in chalcopyrite. 99 In specimens from the second east drift, 300 

 level, Empire mine bornite occurs as disseminated grains with 

 chalcopyrite in garnet rock. In another specimen from the ad- 

 joining Tiger claim masses of bornite. now largely altered to chryso- 

 colla and copper pitch and a turquoise blue clayey copper silicate, 

 occur with fluorite in garnet rock. 



'» Charles Palache. Amer. Jour. Sci., vol. 8, pp. 299-302, 1899. 



•« W. H. Melville. U. S. Qeol. Survey Bull. 90, p. 34, 1892. 



« D. C Livingston and F. B. Laney. Idaho Bur. Mines and Qeol., Bull. 1, p. 38, 1920. 



« F. B. Weeks and V. C. Heikes. U. S. Oeol. Survey Bull. 340, p. 180, 1908. 



"J. B. Umpleby. U. 8. Qeol. Survey Prof. Paper 97, p. . r ,0, 1917. 



