А.Sh. Khusainova О.L. Gaskova Yu.А. Kalinin S.B. Bortnikova

: Russian Geology and Geophysics

Gold-bearing dumps of processed pyrite-polymetallic ores of the Ursk ore field (Novo-Urskoe and Beloklyuchevskoe deposits, Salair Ridge) have been studied. Physicochemical modeling of the gold behavior in wastes allowed us to describe quantitatively the gold precipitation process in different horizons of the dumps. In the upper part of the sulfide-rich section, sulfide minerals undergo intens oxidation accompanied by the dissolution of structural and surface-bound gold. Gold redeposition on the pyrite surface (sorption reduction barrier) as a result of electrochemical processes is accompanied by the formation of heavy-metal sulfates and barite. Under the sorption barrier, there is a loose leaching horizon with high humidity, where gold is present in pore solutions as thiosulfate, hydrosulfide, and hydroxo complexes; its content reaches 68 mg/L. In the middle part of the section, composed of compact siliceous sandstones (hardpan), high-grade (up to 973 ‰) gold forms through the disintegration of thiosulfate complexes, but its content decreases to 10-6 mg/L (lithologic reduction barrier). No visible gold was found in the lower part of the section (soil bed), but its high contents (up to 0.35-0.42 g/L) might be due to the sorption by organic high-molecular compounds, such as humic acids. The morphology and chemical composition of native gold from the gold-containing dumps of processed pyrite-polymetallic ores have been first studied. It is shown that the gold surface has traces of supergene trans- formations, e.g., gold nano- and microparticles as sponge overgrowth on the gold or barite particle surface or as newly formed gold phases in Fe, Mn, and Al hydroxide films.