BEHAVIOR OF Ag IN THE OXIDATION ZONE OF THE KYZYK-CHADR DEPOSIT (Tuva Republic, Russia)
A.Sh. Shavekina1, V.A. Danilovsky1, O.L. Gaskova1, Yu.A. Kalinin1, R.V. Kuzhuget2
1 V.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences,Novosibirsk, Russia
2 Tuvinian Institute for Exploration of Natural Resources, Siberian Branch of the Russian Academy of Sciences, Kyzyl, Russia
Keywords: Ag, silver, oxidation zone, halides, chalcogenides, supergene processes, Kyzyk-Chadr deposit, thermodynamic modeling.
Abstract
The behavior of silver (Ag) in the oxidation zone of the Kyzyk-Chadr gold-sulfide-quartz deposit (Tuva Republic, Russia) has been studied. The main focus was on the mechanisms of Ag differentiation under supergene conditions, including the formation of its secondary minerals and its incorporation as an isomorphic impurity into other phases. It was found that Ag in the oxidation zone forms chalcogenides (acanthite, petrovskaite, uytenbogaardtite, jalpaite) and halides (iodargyrite, bromargyrite, mayersite), which are associated with malachite, chrysocolla, brochantite, quartz, and iron hydroxides. Electron probe microanalysis (EPMA) revealed that Ag concentrates in secondary copper sulfides (covellite, chalcocite, yarrowite, etc.), with levels as high as 0.7 wt.%. Optimization of EPMA parameters to improve resolution lowered the detection limit, enabling the determination of low Ag contents in chalcopyrite (up to 0.05 wt.%) and bornite (up to 0.09 wt.%). The sources of Ag are primary Ag tellurides and selenides, as well as primary and secondary Cu sulfides that break down during oxidation. Thermodynamic modeling simulated the behavior of Fe, Cu, and Ag during progressive oxidation of the primary assemblages (bornite, chalcopyrite, acanthite). The Eh-pH conditions controlling mineral migration and reprecipitation were calculated, and the element concentrations necessary for the formation of secondary phases were estimated.
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