Hydrochemistry and mobilization of gold in the hypergenesis zone (KuznetskAlatau, Russia)

Based on the results of the geochemical study of groundwater from the Centr al ore held (Kuznetsk Alatau) and of the distribution of gold in the latter , the mechanism of mobilization, migration, and concentration of this eleme nt under conditions of the mountainous-forest landscape is outlined. Physic ochemical modeling and thermodynamic calculations indicate that the water-r ock system is of the equilibrium-disequilibrium type, which provides contin uous incongruent dissolution of major minerals accompanied by the formation of kaolinite and, less commonly, of montmorillonite and hydromicas. As a r esult, most elements transferred into dissolution (70.6%) form the secondar y mineral phase, while their minor part (29.4%) is concentrated in the solu tion. Because of the disequilibrium system, the amount of elements in the s olution grows as the Lime of water-rock interaction increases. A similar be havior is also characteristic of gold, 63.0% of which is fixed by forming s econdary compounds and 37.0% is concentrated in the aqueous solution. The o btained results elucidate the mechanism of dissolution, migration, and conc entration of gold in the solution, which indicates that gold mobilization o ccurs in the process of incongruent aluminosilicate dissolution, pyrite oxi dation, and partial dissolution of gold grains. Cold that was entrapped by the aqueous solution is concentrated in the latter and forms, reaching an e quilibrium, a native phase in certain geochemical environments or at geoche mical barriers. II is shown that gold mobilization is only one part of a mo re general ore-generating process that is peculiar to the water-rock system as a whole.