The behavior of Ag in the oxidation zone of the Kyzyk-Chadr gold–sulfide–quartz deposit (Tuva Republic, Russia) is investigated. The primary focus is on the mechanisms of Ag differentiation under supergene conditions, including the formation of secondary minerals and silver incorporation as an isomorphic impurity into other phases. It was established that Ag in the oxidation zone forms chalcogenides (acanthite, petrovskaite, uytenbogaardtite, and jalpaite) and halides (iodargyrite, bromargyrite, and mayersite), which are associated with malachite, chrysocolla, brochantite, quartz, and iron hydroxides. Electron probe microanalysis reveals Ag concentrations in secondary copper sulfides (covellite, chalcocite, yarrowite, etc.) of ≤0.7 wt.%. Optimization of the microanalysis parameters to enhance resolution lowers the detection limit, enabling the determination of low Ag contents in chalcopyrite (≤0.05 wt.%) and bornite (≤0.09 wt.%). The sources of Ag are primary Ag tellurides and selenides, as well as primary and secondary Cu sulfides that decompose during the oxidation. Computer thermodynamic modeling is used to describe the behavior of Fe, Cu, and Ag during the progressive oxidation of primary assemblages (bornite, chalcopyrite, and acanthite). The Eh-pH conditions controlling mineral migration and reprecipitation are calculated, and the element concentrations required for the formation of secondary phases were estimated.
Shavekina et al. (Tue,) studied this question.