Silver Deposits of the Pamir Region,Tajikistan: Metallogeny,Mineralogy, and Genesis |
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| Abstract: | Silver deposits of the South Pamir region of Tajikistan occur as siderite veins with sulfosalts and sulfides, and formed during a late Mesozoic-early Alpine cycle of rifting and orogenesis. Three mineral-geochemical types of ore deposits that occur in several ore districts are recognized: Ag-Sb, Ag-Pb, and Ag-Hg. The Ag vein deposits all occur in terrigenous-carbonate sedimentary rocks and in intrusive granites. The veins are controlled by late Mesozoic faults, and are the products of the last endogenous event in the region. The most significant group of Ag-Sb vein deposits is located in the Bazardara ore district. Three stages of mineralization are recognized in this region: siderite-tetrahedrite, quartz-tetrahedrite, and quartz-galena-freibergite. Most of the veins were deposited during the first stage. Tetrahedrite is the prevailing and most economically important mineral, and contains 0.2 to 15.5% Ag. Associated freibergite contains from 19.5 to 32% Ag. Fluid-inclusion studies indicate that Ag-Sb ore deposits formed over a temperature interval of 280-100°C and pressure of 750-450 bars. Ore deposits were formed from saline solutions (up to 38%) that in late stages were diluted (1.5%). Considerable fluctuations apparently occurred in the associated regional hydrothermal system. Temperature gradients ranged from 8-10°C/100 meters to 14-15°C/100 meters. Temperatures and concentrations of hydrothermal solutions significantly decreased from the main ore-controlling fault toward the north and south flanks of the ore districts. |
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