PRECIOUS METALS 97 



grains. The district is cut through by two Pliocene faults, and 

 the ores are associated with Tertiary eruptives. The ores are of 

 hydatogenetic origin. 



In the Freiberg district the lodes occur in metamorphic acidic 

 intrusives. The ores are native silver, argentite and proustite. 

 The silver ores of Japan belong to the acidic type associated with 

 Tertiary eruptives. 



Ontario, Canada. In the Province of Ontario there are three 

 important silver districts. In the order of their discovery they 

 are Cobalt, South Lorrain and Gowganda. The rocks are essen- 

 tially alike in the three fields. The sedimentaries consist of 

 conglomerates, slates and schists of pre-Canbrian age. The 

 intrusives are diabases, gabbros and granites. The silver lodes 

 traverse the irruptives and often the veins penetrate the sedimen- 

 taries. The veins vary in width from a fraction of an inch to two 

 feet or more. The ores are of hydrothermal origin. The silver 

 minerals are native silver, argentite, pyrargyrite, and breithaup- 

 tite, associated with smaltite, niccolite, pyrite, chalcopyrite, 

 erythrite and annabergite. The principal gangue mineral is 

 calcite. Quartz is sometimes present in subordinate quantity. 

 There seems to have been a distinct order of deposition of miner- 

 als in the Cobalt district. According to Prof. Wm. Campell 

 of Columbia University, smaltite was first introduced into fissures 

 in the diabase, etc. This introduction was followed by niccolite 

 and small quantities of other ores. Then there came a period 

 of disturbance in which the vein materials were brecciated. 

 The infiltration of calcite and the deposition of native silver 

 in plates and threads and grains followed later. Finally bis- 

 muth ores were introduced into a few veins. The author has 

 worked out the same order for several mines in the. Gowganda 

 district. 



Geographical Distribution of the Ore. Silver occurs in all 

 countries. It is most abundant in Mexico, United States, Canada, 

 Australia and Germany, arranged in order of importance: In 

 the United States the distribution of silver is in five distinct 

 belts: (1) The Appalachian; (2) the Lake Superior district; 

 (3) the Cordilleran; (4) the Pacific Coast belt; and (5) Alaska. 

 However, 90 per cent, of all the silver produced in the United 

 States comes from Montana, Colorado, Idaho, Utah and Nevada. 

 Therefore, the area of greatest importance is the Cordilleran 

 section. 



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