The influence of Cl concentration and pH on solubility and species of Zn and Pb in water-chloride fluids at T-P parameters of granitoidic magmas degassing

Abstract

The study of concentrations and species of ore elements in the aqueous fluid phases separating from magmatic melts during their uprising to the surface and crystallization is important for understanding of a role of magmatic fluids in ore-forming systems formation. The purpose of this investigation is determination of solubility and possible species of zinc and lead in water-chloride fluids at Т–Р parameters of granitic magmas degassing. In this report the results of thermodynamic modeling of equilibrium relations of Zn and Pb complexes in water-chloride solutions depending on temperature (600–900С), pressure (0.7–5 kbar), composition and acidity of a fluid (NaCl, KCl, NaCl+HCl), and also initial concentration Zn and Pb in system in the form of ZnO(c), PbO(c) or ZnCl2, PbCl2 are presented. Modeling was conducted by means of program complex HCh [Shvarov, 1999] with use of thermodynamic information received by Shock model [Shock, 1997]. Values of free energy formations of solid phases are borrowed from bank of thermodynamic data of Holland and Powell [Holland, Powell, 1998]. In ZnO-NaCl-H2O system within studied Т–Р range at low chlorine concentrations (CCl 700C Pb(OH)3 is dominant complex within all investigated range of pressure and CCl.