Mineralogy and formation conditions of ore from the Biksizak silver-base-metal occurrence in the South Ural, Russia

Abstract

The Biksizak silver-base metal occurrence is situated in the Birgil'da-Tomino ore cluster of the East Ural Zone. The mineralization is hosted in the Silurian marble (Eastern site) and limestone interbeds in andesitic dacite (Western site). Four mineral assemblages have been established: the earliest hematite-mag netite, the subsequent pyrite-arsenopyrite and chalcopyrite-sphalerite occurring only in the Eastern site, and fahlore-chalcopyrite known only from the Western site. The closest positive correlation links Cu-ZnAg, Zn-Pb, Cu-Ag, and Zn-Au. The correlation between chemical elements varies depending on the local ization of the ore. Correlation pairs Au-Ag, Au-Cu, Pb-Ag, and Pb-Cu are characteristic of ore from the Eastern site and are not established in the Western site. In the Eastern site Cu/(Zn + Pb) in ore is < 1, whereas in the Western site this ratio is markedly higher than unity. As follows from fluid inclusion study and mineral geothermometry, ore minerals at the Bilsizak occurrence were formed at a temperature of 300 to 150°C from low and moderate saline chloride fluids with 1-9 wt % NaCl equiv. The data obtained show that the Bik sizak occurrence was localized at the margin of a porphyry system characterized by hydrothermal and skarn processes.