88 GEOLOGY OF TONOPAH MINING DISTRICT, NEVADA. 



Carbonates. A carbonate is sometimes found microscopically mingled with 

 the quartz as a gangue material, and has also been noted macroscopically. Doctor 

 Hillebrand has determined that this is composed of the carbonates of lime, iron, 

 magnesia, and manganese, in the proportions stated later on. 



Silver sulphides. The principal metallic mineral of the ores is a black sulphide, 

 usually dense, fine grained, and intimately intermingled with quartz. As seen 

 under the microscope, this black sulphide has a typical blue-black color, and 

 often shows cleavage, but almost always lacks crystal outlines. In tiny cavities, 

 however, crystals form. These are usually the six-sided, tabular, striated crystals 

 characteristic of polybasite and stephanite. Partial analysis by W. T. Schaller 

 of such crystals from the Montana Tonopah crystals which may possibly be 

 secondary (see p. 95) showed appreciable amounts of antimony and copper, the 

 latter ingredients indicating that the mineral is polybasite rather than stephanite. 

 In such cavities argentite crystals also occur. 



Silver chloride. What is apparently silver chloride (cerargyrite) is found in 

 some of the primary ores, interwoven with the primary sulphides in such a way 

 as to seem to denote contemporaneous crystallization. In thin sections of such 

 ores the chloride is apt to be more or less bunched, as is the sulphide, but the 

 two are occasionally intergrown, with clear-cut lines of demarcation, seeming to 

 denote independent and contemporaneous origin. 



Chalcopyrite. Chalcopyrite in occasional small grains is often noted in the 

 primaiy ores, and is frequently so intergrown with the primary silver sulphide 

 and with the gangue minerals as to indicate its primary character. In quantity, 

 however, it is relatively unimportant. 



Pyrite. Pyrite in the veins is comparatively scanty, much more so than in 

 the wall rock. In many thin sections of the ores it is not found at all; in others 

 it occurs in considerable amount. In the primary ores it is frequently intergrown 

 with the silver sulphide, with which it is evidently contemporaneous, though 

 usually less in quantity. 



Galena. Galena has been noted in the high-grade sulphide ores of the 

 Montana Tonopah, where it is associated with silver sulphides, chalcopyrite, and 

 pyrite. A picked specimen from the 460-foot level which contained galena was 

 analyzed for the Survey by R. H. Officer & Co., of Salt Lake City, and showed 

 8.9 per cent lead, 5.08 per cent silver (1,481.8 ounces per ton), and 38.26 

 ounces gold. 



Blende. What is probably zinc blende has been detected microscopically by 

 the writer in the primary ore of the Midway shaft. Zinc sulphide has been 

 detected chemically in the Montana Tonopah primary ores. 



