Sulfide mineralization, native gold and its geochemical connections in the Riphean deposits of the Avzyan ore-bearing region (the Southern Urals)
In the Avzyan ore-bearing region the sulfides from the low-sulfide gold-quartz deposits (Ulyuk-Bar, Kurgashly) are characterized by higher concentrations of As, Co, Ni, Cu, Pb in comparison with sulfides from sediments outside of ore-bearing zones. The gold is associated with As and sometimes - with S and Co. Gold-bearing sulfides are situated mostly in sandstones, where they were formed as a result of replacement of early formed ore-free pyrites by arsenopyrite and its association with arsenic pyrite during fluid movement ( Т = 250-450°С, Р = 26-360 bar) through fault zones. This process is fixed in the zonal distribution of arsenic pyrite and in varying behavior of total As in rocks. The proportion of p-type conduction pyrite increases with the depth, and zones of its development and high content of As in rocks are controlled by faults. The strong positive correlation of Au with S, Cu, Co, Pb, Ni, Zn is marked at the gold-sulfide (Bogryashka) and gold-sulfide-quartz (Gorny Priisk) occurrences. The connection of Au with As is not clear. At the Bogryashka occurrence pyrites are characterized by high concentrations of Sb, at the Vostochno-Aktashskoe occurrence - by Co and V. The gold in the Gorny Priisk ore deposit and in the Bogryashka occurrence is characterized by high ratio Au/Ag (>21) and impurity of Bi (0.4-1.2 wt %). The ratio Au/Ag is 5-8 in the gold from the Ulyuk-Bar and the Vostochno-Aktashskoe occurrences. Native gold in the Ulyuk-Bar and the Bogryashka occurences is associated with uranium-thorium minerals.