Surface Typochemistry of Native Gold

Abstract

Using the methods of electron spectroscopy of the surface and SEM–EDS, it is shown that native gold of the deposit related to the epithermal Au–Ag ore formation contains oxidized gold with an oxidation degree of Au (I) or higher on the surface. A thin layer (~15 nm) with high concentrations of Ag and S and an underlying SiO₂-bearing layer with a thickness of ~30–60 nm play a protective role providing preservation of Ag and Au sulfides in the surface parts of the Au–Ag grains under the oxidizing conditions. S-rich marginal parts of native gold particles may be represented by solid solutions Ag_2–xAu_xS or (with a lack of S) by agglomerates of Ag_nAu_mS clusters. The formation of surface zoning in the nanoscale on the surface of native Au is abundant in nature and may be applied in prospecting.