Abstract:
Fahlore (formerly, gray copper ore) in ores of Shaumyan and Harvana gold-polymetallic-massive sulfide deposits forms xenomorphous segregations inside aggregates of the earlier minerals: pyrite, sphalerite, chalcopyri-te, and idiomorphous tetrahedral crystals within aggregates of manganese calcite and quartz. All studied fahlores are stoichiometric by their composition; there are typically Zn-tctrahedrite and Zn-tennantite with admixtures of Hg (up to 3 wt %), Ag (up to 1.7 wt %), Te (up to 1.4 wt %). These mineral species are Bi-poor with stable low contents of Cd, Mn, Sn, Se. Concentration of each one chemical element in fahlore varies irregularly. Its crystals are usually sharply zoned, and outer zones contain more Sb and Ag, than internal ones. The low contents of Ag and Те are probably connected with predominant fractionation of these elements into tellurides: sylvanite and hessite, which occur in these deposits. Cuprousity (Cu2+/ΣMe2+,%) of investigated fahlores is moderately low (0-27 %), and that means the low oxidation potential during formation of these deposits. Tetrahedrite from Harvana deposit contains more Cu2+ and Te than tennantite-tetrahedrite of Shaumyan deposit. Insignificant contents of selenium in the fahlore composition may indicate deep erosion of the ore fields. In the whole, chemical composition of studied fahlores corresponds to fahlores from epithermal subvolcanic gold deposits, but the main their individual feature is the above mentioned sharp zoning of crystals.