Physicochemical Conditions of Quartz Formation at the Bazov Gold-Ore Deposit (East Yakutia, Russia)

The evolution of the hydrothermal system forming the Bazov gold-ore deposit is traced by the data on the composition and properties of the fluid inclusions within the veined quartz. The gold-bearing quartz veins were formed under a moderate decrease of temperature from 290 to 230°C and considerable decrease of pressure from 0.75 to 0.25 kbar. The pressure drop was accompanied by the volume crystallization of quartz from SiO 2 -saturated hydrothermal springs with the appearance of a residual fluid phase. In addition, the fluid composition was transformed from hydrocarbonate into hydrocarbonate–methane with the increase in the concentrations of chlorides of alkali and alkaline-earth metals (from 1 to 8 wt % of NaCl-equiv) along with the ore-forming elements (As, Sb, Fe, Zn, etc.). The pressure under which the formation of the gold–quartz veins occurred (about 0.25 kbar) limited the formation depth of the deposit to the range from 1 to 2.5 km (for the lithostatic and hydrostatic gradient, respectively).