Abstract
In this study, we assess the link between morphologies and composition of gold grains and supergene processes of Au migration and redeposition by aqueous solutions in the aggressive environment of cyanidation tailings. High concentrations of both dissolved (10 μg/L) and solid (0.97 ppm) native gold in the upper horizons of the Komsomolsk tailings profile formed as the result of the long-term oxidation of the cyanidation waste. These horizons stand out due to contrasting changes in pH, Eh and the concentration of the elements in solutions (from 0.8 × 10−4 to 72 g/L iron, from 1.5 × 10−5 to 30 g/L arsenic and from 0 to 37 g/L aluminum). One of the main findings of this study is that the Au and Ag contained in tailings as impurities in the residual sulfide minerals are almost completely redeposited in the top few centimeters of the cross-section. Gold dissolves into pore solution in thiosulfate complexes in the reducing environment of the lower part of tailings and mainly in hydroxide complexes in the acidic environment of the upper horizons. Native gold is found only in the upper few centimeters and presents as irregular grains and crystals of an Au–Ag alloy and as microcrystalline and flat growths of pure Au. The surface morphologies of gold grains are the result of its supergene dissolution, redeposition and crystallization in tailings.
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