Simulation of physicochemical processes of dissolution, transport, and deposition of gold in epithermal Au-Ag deposits in northeastern Russia

Water-bearing fluids are suggested to result from thermodynamically equilib rium interaction andesite-water in the zone of accumulation of hydrothermal solutions from peripheral magma chambers. Thus, intermediate magma chamber s, which are derivates of the primary andesite magma, are assumed to exist. As a result of the interaction, Au and Ag, which are found in andesites an d rhyolites in clarke concentrations, are mobilized into a fluid phase with Au enriched by a factor of 200-500 and with Ag enriched by a factor of 100 -200. In addition, meteoric waters, infiltrating to the root zone of the hy drothermal block through andesites and coming to the surface through fissur e chammels, cannot be a potential source of Au epithermal deposits. However ,,,empty" Au hydrotherms of meteoric origin can participate in redistributi on and remobilization of gold, early deposited, with its removal to the sur face at the final stage of evolution of a hydrothermal system. At the final stage, the now of deep fluids begins to run out. The main dissolved Au mod e of occurrence is hydrosulfide AH(HS)(2)(-). Chloride complexes of Au are subordinate no matter which rock (andesite or rhyolite) is in equilibrium. Silver occurs both as chlorides and as hydrosulfides. However, chlorides ar e predominant in the rhyolite fluid.