Peculiarities of fluid composition in the mineralized and barren zones of the Sovetskoe quartz-gold deposit, Yenisei Mountain Range based on fluid inclusion study

New data are presented on fluid inclusions in quartz, gold, and host schist s studied by Raman spectroscopy, gas chromatography, thermometric and cryom etric methods. Stable sulfur isotope characteristics were determined in sul fides from mineralized and barren quartz vein zones of the Sovetskoe quartz -gold deposit (Yenisei Range). A conclusion was reached that the barren qua rtz veins were formed largely during the greenschist metamorphic process wi th the participation of aqueous fluids derived mainly from the host rocks. CO2 concentrations in the fluids varied from 2.7 to 7.5 mol %, while the to tal salinity usually did not exceed 8.0 wt % NaCl equivalent. The barren zo nes were formed at temperatures of 100-350 degreesC and a pressure of up to 1.5 kbar. The higher gold contents found locally in these zones are most p robably related to the later superimposed hydrothermal mineralization, whic h is indicated by the presence of essentially aqueous inclusions with homog enization temperatures of 390-410 degreesC, as well as by the presence of e ssentially carbon dioxide inclusions in quartz from these zones. The carbon dioxide contents in the fluids from the most auriferous sites rise to 12.5 mol %, while the salinity increases to 10-15 wt % NaCl equivalent. Subsequ ent superimposed hydrothermal processes played an important part in the for mation of the mineralized quartz vein zones of the deposit. At that time, f luids arriving into the mineral-forming system along zones of deep faults w ere the most active. The mineralized zones were formed at temperatures rang ing from 100 to 630 degreesC and a pressure up to 2.0 kbar. The salt concen tration in the solution was considerable and attained values of 20-25 wt % NaCl equivalent. On parity with water, CO2, N-2, and CH4 played an importan t role in mineral formation in the mineralized zones. Their total concentra tion reached 70.0 mol %, and carbon dioxide making up to 62 mol % was a mai n component. The delta S-34 values in sulfides disseminated in the host roc ks and concentrated in the quartz vein zones of the deposit are close to ea ch other. The delta S-34 values fall within the range of + 13.3 to + 17.9 p arts per thousand in pyrite, + 12.9 to + 19.97 parts per thousand in pyrrho tite, and + 14.8 to + 16.5 parts per thousand in arsenopyrite. This warrant s the assumption that there was a single source of sulfur.