HYDRODYNAMIC AND GEOCHEMICAL CONDITIONS OF THE FORMATION OF STRATIFORM ZN-PB ORE MINERALIZATION BY CHLORIDE SOLUTIONS

Abstract

Ore mineralization is formed by postsedimentary (concentrated by evaporation to stage SW2) chloride brines metamorphosed in hydrogeochemical systems that are closed with respect to CO2, evolve according to "calcic" trend, and have high 2mCa2+ > m HCO-3 + 2mCO2-3 ratios. In these situations at high R/W ratios (10-100) and temperatures (100-200°C), these brines concentrate ore elements (Zn, Pb, Fe, and Mn) that are geochemical analogues of Ca. The sulfide precipitation of these elements occurs under the effect of carbonate rocks at the abiogenic sulfate reduction of S(VI) of the original brines at low Eh values, which are created in carbonate rocks at higher (> 100°C) temperatures. This origin of sulfide mineralization is intensified at decreasing R/W ratios during the dilution of the original brines by elision waters and an increase in the temperature. The hydrodynamics of these ore-forming brines is controlled by the elision hydrogeological regime, which is defined in hydrogeological structures by the geostatic pressure. The brines migrate into the zones of geochemical barriers during the relaxation of hydrogeological structures toward their equilibrium hydrostatic state. Hydrogeological structures, optimal for the precipitation of ore mineralization, are hydrodynamically active and able to maintain a steady (during 105-106 years) inflow of ore-forming brines into the zones of geochemical barriers and the maximum number of water-exchange cycles at these barriers. Modern analogues of these structures are miogeosyncline foredeeps with Cl-Na-Ca chloride brines with high concentrations of ore elements and overall flow rates ranging from 0.n to n m3/year. Stagnate hydrogeological platform structures in hydrostatic equilibrium cannot ensure water exchange needed for ore formation, and, hence, the brines of these structures are not able to deposit the ore elements contained in them, in spite of the high concentrations of these elements. © Pleiades Publishing, Inc. 2006.