102 BULLETIN 131, UNITED STATES NATIONAL MUSEUM 



Wells. A specimen from the Montana mine showed gold, selenium, 

 lead, a little bismuth, and a trace of copper. A specimen from the 

 dump of the Lucky Boy mine showed gold, selenium, lead, some 

 copper, and a trace of bismuth. Tellurium was absent from both 

 samples. The definite amount of selenium in both of these ores, 

 the only ones analyzed for it, suggests the presence of some selenide; 

 and this is most probably naumannite. The gangue of these veins 

 is line grained quartz with some opal and chalcedony and, occasionally 

 calcite. Some of the calcite is lamellar and much of the quartz has 

 a lamellar pseudomorphous structure, while adularia occurs in 

 microscopic grains. The ore minerals are arranged in blue-black 

 bands parallel to the crustification of the vein. 71 



LEMHI COUNTY 



In the Gravel Range district rich ores containing gold and silver 

 are characterized by microscopic grains of a blue black mineral in a 

 fine grained quartz gangue containing adularia. A specimen of 

 rich ore of this type from the Monument mine, tested by Doctor 

 Schaller, gave a strong reaction for selenium, which suggests that 

 the dark mineral is naumannite. 



The Parker Mountain district contains ores of very similar appear- 

 ance and of the same age and character, so that the occurrence of 

 selenides in them is to be expected, although no tests have been 

 made. 72 



OWYHEE COUNTY 



A specimen of naumannite from the De Lamar mine has been 

 described in detail, this being the first authentic occurrence of this 

 rare silver mineral in the United States. 73 The specimen (Cat. No. 

 76052, U.S.N. M.) was collected by George H. Eldridge in 1893 

 from the silver stopes of the De Lamar mine, at De Lamar in the 

 Silver City district. This mine was noted for its large bodies of rich 

 ore which in part occurred as a white to gray or bluish clay filling 

 fissures, and which contained large amounts of a silver mineral in 

 grains, shot or larger masses. This silver mineral, which was malle- 

 able and sectile, was commonly supposed to be argentite. The 

 specimen which was found to be naumannite was collected as a 

 typical " nodule of argentite" occurring in the clay, and it is quite 

 possible that the silver in a large part of such ore was in the form of 

 the selenide rather than the sulphide. 



« J. B. Umpleby. Some ore deposits of northwestern Custer County, Idaho. U. S. Qeol. Survey Bull. 

 539, pp. 45-47, 1913. 



» J. B. Umpleby. Geology and ore deposits of Lemhi County, Idaho. U. S. Geol. Survey Bull. 528. 

 pp. 79 and 175. 1913. 



n Earl V. Shannon. Naumannite from Idaho. Proc. U. S. National Museum, vol. 58, pp. 604-607, 

 1920. An occurrence of naumannite in Idaho. Amer. Journ. Sci., vol. 50, pp. 390-391, 1920. 



