246 



BULLETIN 131, UNITED STATES NATIONAL MUSEUM 



Another crystal, one of the type tabular to (010) gave the following- 

 measurements: 



Measurements of tabular cerusite crystal, Ramshorn mine, Custer County, normal 



-position 



In the Copper Basin district cerusite is the principal valuable 

 mineral of the ore of the Starr-Hope mine. A specimen of the best 

 ore of this mine consists of platy waxy gray cerusite surrounding 

 cores of galena. 



FREMONT COUNTY 



Cerusite is mined as oxidized lead ore in the Dome district, par- 

 ticularly in the Wilbert mine, where the galena of the disseminated 

 ore in quartzite has oxidized to anglesite and cerusite. In the 

 Skull Canyon district, cerusite, principally in the form of sand 

 carbonate, is the most abundant mineral of the ore, particularly in 

 the Kaufman and Weaver mine. Specimens of ore from this mine 

 consist of massive cerusite in yellow ocher, of dull gray or iron 

 stained masses, or of friable dull gray-brown sandy material mixed 

 with a soft pulverulent lemon-yellow to greenish yellow mineral. 

 The cerusite incloses anglesite and galena. In specimens from the 

 Weimer copper mine cerusite occurs massive and as small white 

 crystals twinned on m(110) associated with anglesite and some 

 wulfenite surrounding kidneys of fine granular galena in a gangue 

 of platy barite. 



LEMHI COUNTY 



In Lemhi County the carbonate is by far the most important of the 

 lead minerals mined and forms the principal ore mineral in the Nich- 

 olia, Spring Mountain, and Texas districts. 65 The principal mine in 

 the Nicholia district is the old Viola property which, in the years of 

 greatest activity, 1886 and 1887, yielded lead bullion to the value of 

 SI, 000,000. This ore was lead carbonate with much iron and manga- 

 nese oxides intermixed and ran from 30 to 60 per cent lead and 4 to 

 14 ounces of silver a ton. 68 A specimen from the Lena Delta mine, 



65 J. B. Umpleby. U. S. Qeol. Survey, Bull. 528, p. 76, 1913. 



66 Idem, p. 84 



