LEADVILLE DEPOSITS. 377 



Antimony, probably as sulphide. 



Molybdenum, in the form of molybdate of lead or wulfenite. 



Copper, as carbonate or silicate. 



Bismuth, as sulphide and its secondary product, a sulpho-carbonate. 



Vanadium, as dechenite or the vanadate of lead and zinc. 



Tin, indium, and cadmium have been detected in furnace products. 



Iron occurs as an ore, though in the Leadville deposits in general it con- 

 stitutes an essential part of the gangue or matrix in which the valuable ore 

 is found. In the former case it occurs in considerable bodies as pyrite or 

 sulphide and as anhydrous oxide or red hematite, with a little magnetite. 



Gangue. The other components of the ore deposits, which may be con- 

 sidered as gangue, although this term is perhaps more strictly applicable to 

 non-metallic minerals, are: 



Silica, either as chert or as a granular cavernous quartz, and chemic- 

 ally or mechanically combined with hydrous oxides of iron and manganese. 



A great variety of clays or hydrous silicates of alumina, generally 

 very impure and charged with oxide of iron and manganese, the~extreme 

 of purity being white normal kaolin, containing at times sulphuric acid in 

 appreciable amount. 



Sulphate of baryta or heavy spar. 



Carbonate of iron, pyrite, and sulphate of lime are comparatively rare 

 in the deposits of Leadville itself. 



The miner's term, Chinese talc, has been retained for a substance 

 which is found with singular persistence along the main ore channel, or at 

 the dividing plane between White Porphyry and underlying limestone or 

 vein material, and also at times within the body of the deposit. It is com- 

 posed of silicate and a varying amount of sulphate of alumina, to which 

 no definite composition can be assigned. It is compact, semi-translucent, 

 generally white, and so soft as to be easily cut by the finger-nail. It is 

 very hygroscopic; hardens and becomes opaque on exposure to the air. 



Distribution. With regard to the distribxttion of the above ores the prin- 

 cipal generalizations to be made are: 



I. That the main mass of argentiferous lead ores is found incalcareo-magnesianbeds. 

 II. That ores containing gold and copper are more frequently found in silicious beds, 

 in porphyries, or in crystalline rocks. 



