Deformational and metasomatic transformations of detrital gold in the course of placer formation

Abstract

The richest gold placers periodically mined since 1838 are known in the north of the Republic of Tyva, within the basin of the Amyl and Sistig-Khem rivers. Ag-Au gold is the most common, and cuprous and mercuric varieties are presented in small quantities. Lode gold occurrences are confined to quartz veins and have no economic value. Detrital gold in the placer deposits has the typical typomorphic features of placer gold: roundness, compositional heterogeneity, the presence of rims and intergranular veinlets of high-fineness gold, and particle deformation structures. We have considered the transformation mechanisms of detrital gold within the mentioned placers due to the deforming interaction of transported particles in the sedimentogenic environment at the stage of motogenesis, as well as crystallophysical effects at the stage of syngenesis – early diagenesis during heterogeneous metasomatic recrystallization of endogenous gold under conditions of differential mobility of the main mineral-forming elements of gold, Au, Ag, Cu, and Hg. As a result, compositionally polyphase structures formed in the particle, they are high-fineness rims along the periphery of the particles, intergranular veins of high-fineness gold, deformation structures, and increased fineness in the particle kernels.