Surface structure of Amur region high grade native gold

Abstract

The purpose of the research is to study the surface structure of high grade gold. The subject of research is gold ore fields in the Amur region. The object of the study is samples of native high grade gold grains from these fields. The study uses the methods of thermodynamics and X-ray electron microscopy. The study results in revealing a multilayer structure of the surface of high grade minerals of the Amur region native gold with the following levels: a boundary layer with zero oxidation degree Au0 in the form of yellow metallic gold; an oxide layer with the oxidation degree Au+1 in the form of purple Au2O; an oxide layer with the oxidation degree Au+3 in the form of a yellow-brown Au2O3; a hydrated oxide layer with the oxidation degree Au+3 in the form of a red-yellow-brown Au(OH)3. The methods of electron microscopy have allowed to identify external surface structures – dense oxide layers of the form of Au2O3 and loose hydrated layers of the form of Au(OH)3, whereas the inner layers of metallic and monovalent gold are not visible. Important thermodynamic characteristics of the presented levels are the values of standard oxidation-reduction potentials (E°), which determine their physicochemical properties: for metallic gold E° = +1.68 V; for the oxide layer with the oxidation degree Au+1 in the form of Au2O – E° = +0.32 V; for the oxide layer with the oxidation degree Au+3 in the form of Au2O3 – E° = +1.36 V; for the hydrated oxide layer with the oxidation degree Au+3 in the form of Au(OH)3 – E° = +0.7 V. The results of the conducted studies indicate that the surface structure has several layers that lower the oxidation-reduction potential, which explains the generation and formation of migratory forms of gold in humid hypergene conditions of natural environment.