Abstract
The microthermometric and bulk analysis data on fluid inclusions in vein quartz of 16 orogenic gold deposits located in various parts of the Yana-Kolyma belt are presented. The deposits were found to have formed in the temperature range 350–220°C with weakly mineralized carbon dioxide-aqueous fluids (< 5 wt. % NaCl-eq.) typical for orogenic ore-forming systems. The composition of the salts is dominated by sodium bicarbonate, and trace elements are K, B, As, Sb, Rb, and Cs. The molar fraction of CO2 varies from 0.19 to 0.03 depending on the RTX conditions. The molar fraction of methane in carbon dioxide does not exceed 0.1. Intense degassing of solutions in the range between 320° and 270°C could be one of the reasons for ore deposition. Gold–bearing quartz veins and veinlets were formed at depths of 6–3 km with a decrease in pressure from 1.5–1.0 to 0.9–0.8 kbar while the orogeny dynamic regime evolved. At the final stage, the opening of fractures led to a change of the lithostatic regime to hydrostatic with a pressure drop to 0.5–0.1 kbar. At the final stages of mineral formation, fluid systems are characterized by increased salinity and the gas phase comprising essentially nitrogen and methane, which indicates their supply from another source. Thus, the parameters of fluid inclusions in quartz reflect a long history of evolution of the processes involved in mineral and ore formation that associated with the orogen development.
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