Mineralogy of ores of the Vosneenskoe gold deposit (Southern Ural)

Abstract

The mineralogical features of the ores of the Voznesenskoye gold deposit located in the zone of the Main Ural Fault at the northern end of the Magnitogorsk megazone of the Southern Urals have been studied. The chemical composition of minerals was determined using a Tescan Vega Compact scanning electron microscope with an Oxford Instruments Xplorer 15 energy dispersive analyzer. Two stages of ore formation have been identified and characterized. On the early of them, arsenic pyrite (0.38–0.84% As), which is the main mineral of ores, was first formed, and later sulfurous arsenopyrite (S/As = 1.12–1.19), molybdenite enriched in Fe (7.25–8.07%), and chalcopyrite. Using an arsenopyrite geothermometer, it was found that the formation of sulfides at an early stage occurred approximately in the temperature range of 318–380°C. At a late stage, an association was formed that united pyrite containing Sb (0.28–0.31%), Zn-Fe-tetrahedrite (Cu9.1–9.4 (Fe1.2–1.3 Zn1.1–1.4)2.4–2.6 (As0.2–0.4 Sb3.7–4.1)4.2–4.3 S12.9–13.2) and native high-grade gold (952–997‰) with impurities Ag and Cu. Minerals of this association, which have an insignificant distribution, are found in crushing zones developed in arsenic pyrite. In terms of chemical composition, the studied tetrahedrite is close to the fahlores of the subepithermal mineralization of the Mikheevka porphyry Cu deposit. Based on the results of the studies performed, a preliminary conclusion was made that the Voznesenskoye deposit belongs to the subepithermal type of gold mineralization.