PRECIOUS METM.S 91 



tat i>n of silver in a metallic state. Pyrite, chalcopyrite, and 

 many other sulphides, reduce silver solutions readily to the 

 metallic state. According to Dr. F. W. Clarke, the metal will he- 

 precipitated by any reaction in which nascent hydrogen is 

 brought in contact with a silver solution. The nature of silver 

 solutions in metalifferous veins is not positively known. Silver 

 sulphate is readily formed by the oxidation of the sulphide, 

 and that will be transformed into the chloride by percolating 

 chlorine-bearing waters. The antimonides, arsenides, and selen- 

 ides of silver are rarer minerals, and are of only small impor- 

 tance in the production of the metal. These by subsequent 

 enrichment might become of commercial importance. 



Character of Ore Bodies. At Butte, Montana, the ore occurs 

 as native silver, with galenite in veins of quartz-bearing manganese. 

 These are true fissure veins cutting irruptive granite. At Granite 

 Mountain, 20 miles from Butte, the ore is ruby silver associated 

 with gold in a true fissure vein cutting a gray granite. At Neihart, 

 the ore occurs in veins in gneiss and other igneous rocks, mostly 

 as replacement deposits which have been subsequently fractured 

 and secondarily enriched. Argentiferous galenite is common in 

 Montana as contact deposits between porphyritic igneous rocks 

 and Carboniferous limestone. 



In the production of silver, Colorado ranks high, the chief sil- 

 ver-producing region of the state being Leadville. This district 

 is situated in the Mosquito Range near the headwaters of the 

 Arkansas river. It began its history in 1860 as a gold camp, 

 but upon exhaustion of the gold resources the camp lost its 

 significance as such. It then became a silver-producing camp 

 which position it lost nearly a decade ago when Leadville became 

 a lead and zinc camp. Eight or ten different metals are produced 

 within the camp at the present time. 



The Geology of Leadville. The base of the mountain consists of 

 a series of Archean granites, gneisses, schists and amphibolites. 

 These are overlain by a series of Cambrian quartzities and shales 

 which in turn are covered by Silurian limestones and quartzites. 

 Above these there appear limestones, shales and grits of Carbon- 

 iferous age. Associated with this vast series of sedimentaries 

 there appears also many late Mesozoic and Tertiary irruptives 

 (Fig. 66.) 



The uplift of the Mosquito Range, of which the Leadville dis- 

 trict forms the western slope, resulted in a series of anticlinal and 



