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An epigenetic occurrence of vein type Köstere Deposit is located in Late Cretaceous felsic volcanic rocks. Host rocks around the mine composed of dacite, dacitic tuff, dacitic aglomera and brecciate, and commonly interbedded with red biomicrite layers. The Torul Pluton, covers an area of approximately 40 km2, cuts the Late Cretaceous formations, and shows good agreement with the major tectonic directions (NE-SW, NW-SE). Ore vein in Köstere was formed in felsic volcanic rocks as N 35-45 E strike and 45o NE dip along fault zones by the hydrothermal solution. Galena, sphalerite, chalcopyrite, pyrite and fahlore are the main paragenesis of the deposit.
In addition to the major component of Pb, Zn and Cu, trace amount of As (28-1189 ppm), Sb (17-209 ppm), Cd (37-4761 ppm), Ag (13-212 ppm), Co (0.6-61 ppm), Ni (0.8-9.7 ppm) have been detected in bulk ore analyses. The Fe content of sphalerite is low (0.05-0.82 wt %) whereas Zn varies in the range 64.18-66.81 wt %. Cd is present in all sphalerite grains, in the range of 0.44-0.75 wt %. Pyrite shows a quite homogeneous composition in each grain, containing trace amounts of Cu, As, Ag and Cd up to 2.43, 0.11, 0.1 and 0.06 wt %, respectively. Fahlore is rich in silver and poor in iron, and has the composition (Cu7.99-10.09Ag0.01-1.93)10(Fe0-0.38Zn1.87-2.33)2(As0.23-4.22Sb0-4.07)4S12.68-13.00.
Fahlore and sphalerite are an ideal indicator of intensive parameters of ore forming fluids because they often preserve primary depositional chemistry. The significant Zn contents of the fahlore and sphalerite generally suggest their precipitation from Zn-rich fluids. The Zn/Cd ratios in sphalerite (88-137) and bulk ore analyses (51-125) from the Köstere deposit are close to those hydrothermal deposits. The similarity of Zn/Cd ratios in both mineral chemistry of sphalerite and bulk ore analyses are an indication of Zn-Cd substitution in sphalerite. Highly variable Co/Ni ratios of pyrite separate (7-39) and bulk ore analyses (1-5.65), greater than one, point out an acidic magma source. When bulk ore analyses compiled together with the results of mineral chemistry of sphalerite and pyrite, it is suggested that deposition of ore related with emplacement of the Torul Granitoid nearby.
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