Thermodynamic Models of Redeposition of the Substance of Pb–Zn Ore Veins at a Carbonate Barrier upon Reactivation of Hydrothermal Processes

The methods of equilibrium–dynamic modeling have been applied to evaluate the probability of redeposition of previously formed Pb–Zn vein ore substances at a carbonate barrier upon reactivation of a hydrothermal system. The natural prototype is the Ursdon ore occurrence (Dzhimidon ore field, North Ossetia, Russia) in Oxfordian limestone (J3); the formation of polymetallic vein deposits of the region occurred in the pre-Callovian time of the Middle Jurassic. Calculations have been performed using the HCh software package, which includes the Unitherm thermodynamic database (the H–O–K–Na–Ca–Mg–Al–Si–Fe–C–Cl–S–Zn–Pb–Cu system described by 54 minerals and 78 particles of an aqueous solution). It has been established that late low-temperature hydrothermal solutions may provide pyritization, silicification, and the formation of Pb–Zn mineralization in carbonate rocks. The deposition of quartz and sulfides occurs along fractures and at the dissolution front of carbonate rocks.