PECULIARITIES OF FLUID COMPOSITION IN THE MINERALIZED AND BARREN ZONES OF THE SOVETSKOE QUARTZ-GOLD DEPOSIT, YENISEI MOUNTAIN RANGE BASED ON FLUID INCLUSION STUDY

Abstract

New data are presented on fluid inclusions in quartz, gold, and host schists studied by Raman spectroscopy, gas chromatography, thermometric and cryometric methods. Stable sulfur isotope characteristics were determined in sulfides from mineralized and barren quartz vein zones of the Sovetskoe quartz-gold deposit (Yenisei Range). A conclusion was reached that the barren quartz veins were formed largely during the greenschist metamorphic process with 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 total salinity usually did not exceed 8.0 wt % NaCl equivalent. The barren zones were formed at temperatures of 100-350°C and a pressure of up to 1.5 kbar. The higher gold contents found locally in these zones are most probably related to the later superimposed hydrothermal mineralization, which is indicated by the presence of essentially aqueous inclusions with homogenization temperatures of 390-410°C, as well as by the presence of essentially 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. Subsequent superimposed hydrothermal processes played an important part in the formation of the mineralized quartz vein zones of the deposit. At that time, fluids arriving into the mineral-forming system along zones of deep faults were the most active. The mineralized zones were formed at temperatures ranging from 100 to 630°C and a pressure up to 2.0 kbar. The salt concentration in the solution was considerable and attained values of 20-25 wt % NaCl equivalent. On parity with water, CO2, N2, and CH4 played an important role in mineral formation in the mineralized zones. Their total concentration reached 70.0 mol %, and carbon dioxide making up to 62 mol % was a main component. The δ34S values in sulfides disseminated in the host rocks and concentrated in the quartz vein zones of the deposit are close to each other. The δ34S values fall within the range of+13.3 to +17.9%o in pyrite, +12.9 to +19.9‰ in pyrrhotite, and +14.8 to +16.5%o in arsenopyrite. This warrants the assumption that there was a single source of sulfur.