“INVISIBLE” GOLD ON THE NATIVE SURFACE OF ARSENOPYRITE OF THE NATALKA GOLD DEPOSIT (<i>northeastern Russia</i>): LA-ICP-MS DATA

Using the laser ablation-inductively coupled plasma–mass spectrometry (LA-ICP-MS) complex, with the involvement of X-ray photoelectron spectroscopy (XPS), we obtained new data on the distribution and the degree of concentration of “invisible” gold on the native surface of arsenopyrite crystals from the Natalka gold deposit (northeastern Russia). The study has shown that these parameters are intimately related to the formation conditions of the deposit. The highest contents of Au are detected on the surface of arsenopyrite crystals formed at the hydrothermal stage of ore generation, and the minimum ones are found on the surface of crystals formed at the early metamorphogenic stage. The extreme variability of the gold distribution profile and contents even within the surface of a single crystal is best pronounced in arsenopyrite of vein and veinlet–vein ores, which is due to the instability of the physicochemical parameters of the processes of hydrothermal ore formation at the later stages of the deposit formation. Basically, these are oxidation processes that lead to a change in the composition of the primary (as-grown) nonautonomous phases and to the redistribution of gold in the surface layer of the crystal, containing highly charged arsenic species, As5+ and As3+. The intricate and long-term metamorphic/magmatic genesis of the giant Natalka gold deposit has been confirmed. The high contents of “invisible” gold in the easily destroyed surface layer of sulfides during enrichment are of significant practical interest for the extraction of gold from “refractory” ores, as they increase the quality and value of the mined raw materials.