Ore formation at the Kupol epithermal gold-silver deposit in northeastern Russia deduced from fluid inclusion study

The Kupol epithermal gold-silver deposit-the largest of this type of mineralization in northeastern Russia-is situated in the outer zone of the Okhotsk-Chukotka volcanic belt. The results of thermobarogeochemical study of fluid inclusions in quartz from ore veins at the Kupol deposit are compared with the data on the Dvoinoi and Arykvaam deposits. The study of aqueous extracts from fluid inclusions revealed that the chemical compositions of ore-forming fluids at the Dvoinoi and Kupol deposits are similar in most elements. The only substantial difference is that fluids from the Kupol deposit are considerably enriched in sulfate, as is characteristic of the alunite-subtype of epithermal high-sulfidation mineralization. The salinity of aqueous solutions filling inclusions in amethyst and quartz from ore veins at the Kupol and Dvoinoi deposits is two-three times higher than the salinity of fluid inclusions from the barren veins at the Arykvaam occurrence. The data obtained support the hypothesis put forward earlier that fumaroles and solfataras played a part in ore deposition at the Kupol deposit.