The Bolshoy Kanimansur Epithermal Ag–Pb–Zn–Cu–Bi Deposit, Tajikistan: Thermodynamic Modeling of Deposition Conditions of the Early-Stage Mineral Assemblages

Thermodynamic modeling of the evolution of low-salt hydrothermal fluid separated during crystallization of acidic magma was performed. The evolution includes interaction of the fluid with meteoric water in a convective cell, cooling, boiling, and mixing. The calculations were performed using the Hch software, the UNITHERM (Shvarov and Bastrakov, 1999) and SUPCRT 92 (Johnson et. al., 1992) databases, as well as thermodynamic data on stability of sulfide, hydroxo- and chloride copper complexes in aqueous solution (Akinfiev and Zotov, 2001). The modeling of the interaction between host rocks and the predominantly magmatic-hydrothermal fluids in the latter predominance regime led to the formation of associations characteristic of the “high-sulphidation”-type epithermal deposits. An increase in the rock volume during this process contributed to the formation of mineral associations similar to metasomatic alteration associations described in the deposit. Base and precious metal sulfides dissolve and metals enrich the fluid reacting with the host rocks. Subsequent precipitation of metals leads to their separation according to the depth of deposition.