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.