Mineral Composition and Formation Conditions of Copper-Sulfide Ores of the Aginskoe Au–Ag Deposit, Kamchatka, Russia

Abstract The article presents the results of mineralogical and geochemical studies of copper-sulfide ores from the Vyun ore occurrence, which is part of the Aginskoe gold-silver-telluride deposit, located in the Central Kamchatka Mining District. The Vyun ores are represented by ribbon-like and lens-shaped vein bodies, the core of which is composed of a quartz vein. The veins are often replaced by veinlets, sometimes without a distinct core. As a result of detailed mineralogical studies, two mineral associations have been established: the bornite-digenite-telluride and the gold-chalcopyrite-bornite. The last one includes gold-silver tellurides. Bornite is characterized by high concentrations of Mo (10.5 ppm) and W (19.7 ppm) and the presence of solid solution decomposition structures, such as bornite-chalcopyrite and bornite-digenite. The native gold has a high purity (870–980). It is hypothesized that the copper-sulfide ores of Vyun were formed in two stages of endogenous mineral formation with significant sulfur fugacity, variable oxygen potential, and low tellurium activity. During the crystallization of high-sulfide minerals, there were fluctuations in composition with a gradual drift towards enrichment in copper. Structures of solid-solution decomposition based on bornite were formed at temperatures below 265°C and are associated with a decrease in the solubility of chalcopyrite and digeneite in the low-temperature modifications of bornite, while the joint crystallization of bornite and chalcopyrite corresponds to high-temperature crystallization.