Fluid regimes during the formation of the principal types of gold deposits

The fluid regimes of ore formation in the main types of gold deposits of the gold-carbonaceous and gold-silver ore associations are discussed. A generalization of data on the geochemistry of sulfur, carbon, and oxygen isotopes and the results of gas chromatography and thermobarometry provided new evidence that makes it possible to evaluate the water sources in the fluid systems and to recognize sedimentary-biogenic, hydrothermal-sedimentary, and hydrothermal (the principal commercial) ore types of gold mineralization. It was proved that the primary redox potential of fluid systems responsible for hydrothermal-sedimentary ore formation was reducing with a CO2/CH4 ratio less than or equal to 15. Data from the Murun Tau and Koch Bulak deep holes show that the CO2/CH4 potential within the 2-4 km depth interval suggests an originally reducing character of the fluid systems responsible for hydrothermal ore formation. The genetic types of the waters and the origin of economic gold mineralization in the zones of their discharge are discussed.