THE MINERALS OF IDAHO 101 



WASHINGTON COUNTY 



la the Heath district galena, partly oxidized, occurs in a number 

 of properties which have been worked to some extent for lead and 

 silver. Ore from the Keystone mine contains galena, both as coarse 

 granular masses coated with earthy anglesite, cerusite, and limonite 

 (Cat. No. 30198, U.S.N. M.) and as very fine grained steel galena 

 bordered by ashy anglesite (Cat. No. 60940, U.S.N.M.) . One shipment 

 of galena ore was made from the Galena Silver mine in 1917. 



Galena occurs in silver ores from the Mineral district associated 

 with tetrahedrite, chalcopyrite, pyrite, and sphalerite in a calcite 

 gangue. The Silver Bell, Maria, Black Hawk, and Eagan are the 

 principal mines. In the Maria the galena, which is not very abund- 

 ant, is intimately intergrown with the sphalerite in concentric 

 rings. 69 



In the Seven Devils district galena is present as a rarity in all of 

 the contact-metamorphic copper deposits and also sparingly in the 

 low grade disseminated "porphyrj'" copper ore of the Red Ledge 

 mine. 70 



NAUMANNITE (48) 

 Silver selenide, Ag 2 Se. Isometric. 



Naumannite, a comparatively rare silver mineral, is known to 

 occur in Owyhee County; and a selenide, most probably naumannite, 

 is of rather frequent occurrence in gold-silver ores of late Tertiary 

 age in Custer and Lemhi Counties. The mineral differs from ar- 

 gentite or silver glance only in containing selenium instead of sulphur 

 and in its general physical properties it is very similar to argentite 

 so that other occurrences of " silver glance" in the State may prove 

 to be naumannite. The tests for selenium are distinctive and easily 

 applied. When heated in the flame the mineral gives a characteristic 

 odor, described in the textbooks as like that of "decaying horse- 

 radish" and colors the flame blue. Heated in the closed tube it gives 

 a characteristic red and black sublimate of selenium. Selenium 

 seems to be confined to, and characteristic of, late Tertiary veins in 

 volcanic rocks. 



CUSTER COUNTY 



In the Yankee Fork district in all of the silver-gold ores the richest 

 ore is characterized by blue-black submetallic bands and blotches 

 in which pyrite and tetrahedrite and rarely chalcopyrite may be 

 recognized with the aid of the microscope but the predominant 

 mineral shows as olue-black specks too small to be identified. Partial 

 analyses of two specimens of this material have been made by R. C. 



6e Waldcmar Lindgren. U. S. Geo]. Survey, 22d Ann. Rept., p. 755, pt. 2, 1901. 

 "> D C. Livingston and F. B. Laney. Idaho Bur. Mines and Geol. Buil. 1, 1920. 



