期刊
RUSSIAN GEOLOGY AND GEOPHYSICS
卷 63, 期 7, 页码 789-801出版社
GEOSCIENCEWORLD
DOI: 10.2113/RGG20214386
关键词
gold; oxidation zone; physicochemical model; Kopto deposit; the Republic of Tuva
资金
- V.S. Sobolev Institute of Geology and Mineralogy (Novosibirsk)
- Tuvinian Institute for Exploration of Natural Resources of the Siberian Branch of the Russian Academy of Sciences (Kyzyl) [0384-2016-0012]
This article examines the morphological features of primary and oxidized ores from the Kopto gold deposit. Through computer thermodynamic modeling, the transformation process and stability conditions of gold are analyzed, providing valuable information on its redistribution and origin.
The Kopto deposit (northeastern Tuva) is assigned to gold ore objects with a combination of the Au-Cu-skarn and superposed quartz-gold-sulfide stockwork types of mineralization. From the surface, the ores underwent intense oxidation, which formed a zone of secondary gold enrichment, containing a supergene paragenesis with gold and silver chalcogenides and newly formed gold. The depth of distribution of oxidized ores from the surface is 80-90 m. The Au content varies from fractions of ppm to 150 ppm (on average, 30.8 ppm). Using computer thermodynamic modeling, it is shown how the ore gold-sulfide-quartz association transformed under oxidizing conditions with a decrease in the pH of solutions. Gold becomes more and more high-grade; acanthite appears and disappears; limonite prevails (pH = 1.65; Eh = 0.69 V). The conditions for the stability of pyrite, iron hydroxides, and gold and silver chalcogenides (petrovskaite (AgAuS) and uytenbogaardtite (Ag3AuS2)) have been estimated. It requires weakly acidic solutions with pH = 5-6 and Eh values close to zero, which ensures the stability of thiosulfate and hydrosulfide complexes of noble metals. The main difference between solutions in equilibrium with petrovskaite and uytenbogaardtite is the Ag/Au ratios, which are maximum in the first case and approximately equal in the second. The paper is concerned with a comparative analysis of the morphologic features of gold from primary and oxidized ores of the Kopto gold deposit. The aim of this work is to identify a set of signs of the supergene nature of gold and to assess the extent of its redistribution.
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