The Role of Selenium and Hydrocarbons in Au-Ag Ore Formation in the Rodnikovoe Low-Sulfidation (LS) Epithermal Deposit, Kamchatka Peninsula, Russia

• Published in: Minerals
• Main Authors: Nadezhda Tolstykh, Maria Shapovalova, Elena Shaparenko, Daria Bukhanova
• Format: Article in Journal/Newspaper
• Language: English
• Published: MDPI AG 2022
• Subjects: low-sulfidation epithermal deposits; gold-silver ores; selenium; hydrothermal fluids; mineral assemblages; hydrocarbons; Mineralogy; QE351-399.2; Kamchatka Peninsula; Kamchatka
• Online Access: https://doi.org/10.3390/min12111418; https://doaj.org/article/de6f4249e6f04801a3850347cbfd9cab

Gold-silver mineralization in the Rodnikovoe LS epithermal deposit is characterized by selenium speciation. Two main alternating ore assemblages have been identified: silver-aguilarite-acanthite and gold-uytenbogaardtite-acanthite. The former mineral association is intergrown with secondary silver (Ag 0.77–0.91 ), whereas the latter assemblage is closely associated with high-grade gold (Au 0.63–0.67 ). However, both are dominated by Ag 0.49–0.56 Au 0.44–0.51 alloys. The geochemical evolution of the ore-forming system developed in the direction: Fe → Cu; Ag → Au; S → Se; As → Sb. Organic compounds (1 relative %) of both biogenic and thermogenic origin were found in fluid inclusions. These molecules participated in the formation of Ag,Au-complexes and transported noble metals along with selenium. Hydrothermal fluids are characterized by f Se 2 / f S 2 ratios < 1, conditions such that the deposition of selenide minerals is inhibited, except for the naumannite and acanthite series. These conditions allow active entry of selenium into sulfosalts (the selenium substitutes for sulfur).