The Ulug-Sair Gold Occurrence (Western Tuva, Russia): Mineralogy, Ore Genesis, and S-O Isotope Systematics

Ulug-Sair Au-Bi-Te-Se mineralization is one prospect for native Au in the Western Tuva, and its origin remains debated. Mineralization consists of gold–sulfide–quartz veins host sedimentary rocks (conglomerates, siltstones, shales), quartz–tourmaline, quartz–carbonate–sericite–altered rocks. To determine origin, we examined mineralogical–geochemical features, formation conditions, fluid sources ore. A investigation outlines two substages with Au: an early pyrite, chalcopyrite, galena, gold, electrum; a late gold–telluride–sulfide–quartz, characterized by presence Bi-bearing minerals (AgBiTe, Bi2Te2Se, Cu3BiS3, Bi), tellurides (Au Ag), Se-tellurides (Ag selenides (Au, Ag, Hg). The paragenesis Au–Ag tellurides, inclusion study data (microthermometry, Raman spectroscopy, LA-ICP-MS, crush leach analysis (gas ion chromatography, ICP-MS) quartz showed that quartz–tourmaline-altered were formed aqueous Mg–Na–K-chloride salinity 8–10 wt % NaCl eq. at 325–370 °C, whereas quartz–carbonate–sericite-altered from CO2–H2O containing CH4 N2, 0.18–6.1 200–400 °C. Gold-bearing mineral assemblages P ~ 0.75–1.0 kbar (~2.3–3 km) due to chloride (Na–K ± Fe, Mg) CH4, Na2SO4, Na2B2O5, salinities 1.7–12.5 temperatures decreasing 360 up 115 °C (gold–sulfide–quartz veins—360–130 gold–telluride–sulfide–quartz veins—330–115 °C), variable fO2, fS2, fSe2, fTe2. Results isotope composition S pyrites indicates magmatic (δ18SH2S −0.4 +2.5‰). stable O that, substage, ore involved metamorphic (from +8.2 +11.6‰), and, later multiple hydrothermal fluids +3.1 +10.4‰), including magmatic-derived, metamorphic-derived, meteoric waters. These data, conjunction structurally controlled mineralization, point towards similarities system orogenic gold deposits.