Aggregation and Differentiation of Gold and Silver during the Formation of the Gold-Bearing Weathering Crusts (on the Example of Kazakhstan Deposits)

Abstract

The supergene Au in weathering crusts of both the Suzdal and Raygorodok deposits is characterized by enhanced fineness, grain size, crystallinity, and the appearance of botryoidal aggregates of crystals. In the weathering crust of the Suzdal deposit, the exogenous Au is associated primarily with scorodite and carbonates; for Raygorodok, with chalcocite, bornite, hydrocarbonates and Cu hydrosulfates. The difference in the mineral associations of supergene Au at the deposits is determined by the occurrence of various mineral concentrators of Au in the primary endogenous substrate: arsenopyrite and pyrite at the Suzdal deposit and chalcopyrite with pyrite at the Raygorodok deposit. Due to the much greater mobility of Ag in the supergene zone, the weathering crusts are likely to contain submicron microinclusions of Ag minerals beyond the zones of Au concentration.