244 



BULLETIN 131, UNITED STATES NATIONAL MUSEUM 



BOISE COUNTY 



Cerusite is not rare in the oxidized gold ores of the Boise County 

 gold mining districts. Much of the primary ore of the gold-bearing 

 veins contains galena along with other sulphides, and in some cases 

 the galena is highly auriferous. Where these veins are weathered 

 the galena has been converted to cerusite, which is more or less 

 mixed with limonite, and is frequently rich in spongy gold. It 

 has been especially mentioned from the Wolf Creek area and from 

 the Morning Star vein at Grimes Pass. Specimens from Hall Bros. 



property, Deadwood district, 

 contain small colorless twinned 

 cerusite crystals on limonite- 

 stained rock and small gray to 

 black crystals associated with 

 pyromorphite on rusty quartz. 



CUSTER COUNTY 



The carbonate is the most 

 important ore of lead in Custer 

 County, where it is mostly in 

 earthy masses stained by iron 

 and manganese oxides or in 



Fig. 55.— Cerusite. Simple prismatic crystal elon- \,\\q oranular form known as 



GATED ON THE AXIS. RED BIRD MINE, BATHORSE (( , ,, ™, . 



district, Custer county sand carbonate. 1 lie latter 



forms friable coarse to fine 

 sandy masses and results from the shrinkage due to decrease in 

 volume of the ore during oxidation. The carbonate is especially 

 prominent in the deposits of the Bayhorse district where it forms 

 the ore of the Beardsley, Excelsior, Pacific, River View, Cave, and 

 other mines. 61 This is mainly in the form of the friable incoherent 

 material heavily impregnated with manganese and iron oxides, 

 known as sand carbonate. Specimens which have been examined 

 from the Red Bird mine consist of glassy masses of pure white 

 cerusite embedded in limonite or surrounding residual cores of 

 galena, forming high-grade ore. Some of the ore masses contain 

 vugs which are lined with calcite and cerusite crystals. One simple 

 prismatic crystal from this mine which was measured is shown in 

 the drawing, Figure 55. This gave the following measurements. 



« J. B. Umpleby. U. S. Qeol. Survey, Bull. 539, pp. 66-7G, 1913. 



