114 BULLETIN 131, UNITED STATES NATIONAL MUSEUM 



CUSTER COUNTY 



Cinnabar is found in some quantity in the gravels worked by the 

 Willis dredge in Stanley Basin, where it is associated with gold and 

 native amalgam. The cinnabar is becoming more abundant as 

 the dredge is moved upstream. 84 A sample of pan concentrate 

 from this placer sent to the National Museum by H. C. Willis consists 

 in the main of a heavy radioactive mineral, possibly brannerite, 

 with small grains of clear red crystalline cinnabar and occasional 

 grains of monazite, zircon, and amalgam. 



VALLEV COUNTY 



Economically the most promising cinnabar deposits yet opened 

 in Idaho are those of the Yellow Pine district in Valley County. 

 These appear to have been formed by replacement of marble and to 

 be mostly near the contacts of marble with quartzite and schists. 

 There is little evidence of continuous veins but the deposits are 

 rather in the form of irregular or lenticular bodies such as are com- 

 mon in replacement deposits in the limestone. In some places the 

 silica forms a network of anastomosing veinlets in the marble, in 

 others it completely replaces the marble. Cinnabar is the only sul- 

 phide in most of the ore, although considerable pyrite, more or less 

 altered, is present in some parts of the deposits, and stibnite is 

 associated with cinnabar on the ridge just north of the Fern mine. 

 The cinnabar is rather coarsely crystalline and most of it is in the 

 cherty silica, but some is in a friable sandy marble near the silica 

 zones and a little is disseminated in the hard white marble. 



A considerable part of the ore treated at the Fern mine came from 

 material partly filling a cave in the marble and was made up of 

 blocks of hard ore embedded in a silica-rich sand. The antimony 

 deposits in the granodiorite just south of the cinnabar deposits 

 carry a little cinnabar and the two are probably related in origin. 

 The principal mercury claims are the Fern, Yellow Pine, Idaho, 

 Abstein, and Monumental groups. The production of the Fern 

 Co. up to August, 1918, was largely derived from float and from 

 the cave deposit. 85 



COVELLITE (67) 

 Cupric sulphide, CuS. Hexagonal. 



BOISE COUNTY 



Coarse sphalerite from sulphidic gold ores of several mines in 

 the Summit Flat and Centerville districts is characterized by a 

 peculiar deep indigo blue color of all fractures, although yielding 



81 J. B. Umpleby and D. C. Livingston. Idaho State Bur. Mines & Geology, Bull. 3, p. 16, 1920. 

 85 E. S. Larsen and D. C. Livingston. Geology of the Yellow Pine quicksilver mining district, Idaho 

 U. S. Geol. Survey Bull. 715, pp. 73-83, 1920. 



