Bulan gold-sulfide-quartz ore deposit of the Makarovsky ore cluster (Western Sayan, Russia): Mineralogical and geochemical features, formation conditions, and fluid sources

Research subject . Mineralogical and geochemical features and formation conditions of the Bulan gold-sulfide-quartz ore occurrence of the Makarov ore cluster in the Western Sayan. Methods. A Linkam TMS-600 thermostage and Olympus BX 51 optical microscope were used to determine temperatures, compositions, and fluid salinities in inclusions of mineral- forming fluid in quartz of gold-sulfide-quartz veins (SUSU, Miass, analyst Natalia N. Ankusheva). The chemical composition of gold was determined by SEM Hitachi TM-1000 (TuvIENR SB RAS, Kyzyl, analyst Renat V. Kuzhuget). Results. The conducted mineralogical and geochemical studies determined that gold formation at the Bulan ore field was single-stage in the form of gold-sulfide-quartz veins and veins with pyrite, chalcopyrite, arsenopyrite, pyrrhotite, as well as rare isolations of galena, fahlore, gold, and electrum. The results of fluid inclusion study from gold-sulfide-quartz veins showed that they were formed in the temperature range 170–230°C due to a weakly to moderately saline (3.5–6.8 wt % NaCl eq.) magmatic fluid of the K-Na-Mg±Fe-chloride composition. The stable range of fluid salinity and the narrow range of δ18O indicate a single magmatic source and insignificant influence of host rocks and meteoric waters. Conclusions. According to mineralogical and geochemical features and PT parameters, the Bulan ore occurrence is similar to low-sulfide deposits of gold-sulfide-quartz berezite-listvenite formation.