The Role of Hydrocarbons in the Formation of Epithermal Gold–Silver Deposits in Kamchatka, Russia

Data on the mineralogical and geochemical features of three epithermal gold deposits in Kamchatka, as well as on the compositions and physicochemical parameters of ore-forming fluids, based on scanning electron microscopy, microthermometry, Raman spectroscopy, and gas chromatography–mass spectrometry, are reported. All deposits are comparable in terms of temperature, salinity, and the predominance of CO 2 in ore-forming fluids. The high-sulfidation Maletoivayam deposit differs from the other two low-sulfidation ones (Baran’yevskoe and Rodnikovoe) in the substantial enrichment in Se and much higher concentrations of organic compounds (OCs) (20 rel. %) in fluid inclusions. It has been concluded that OСs played an important role in the concentration and transportation of Au and Se, while the oxidation environment contributed to the formation of numerous selenides, including AuSe. The hydrocarbon composition in inclusions records both biogenic and abiogenic origins, while the relative content of OCs in solutions controls the degree of sulfidation of the deposit.