FORMATION OF GOLD AND SILVER SULFIDES IN THE SYSTEM Au-Ag-S
G.A. Pal'yanovaa, K.A. Kokha, and Yu.V. Seryotkina,b
a V.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences, pr. Akademika Koptyuga 3, Novosibirsk, 630090, Russia
bNovosibirsk State University, ul. Pirogova 2, Novosibirsk, 630090, Russia
Keywords: Au-Ag-S melt, uytenbogaardtite, petrovskaite, solid solutions Ag2- x AuxS
Pages: 443-449
Abstract
Gold and silver sulfides were synthesized from melts Ag2- x AuxS ( x = 0.1, 0.4, 0.8, 1.6) in the system Au-Ag-S with Au/Ag = 0.1-7.4. Optical microscopy, X-raying, electron probe microanalysis, and scanning electron microscopy were used to identify and analyze the solid products. It has been established that aсanthite, solid solutions Ag2- x Au x S ( x < 0.5), and electrum are produced in the Ag-rich binary system Ag2S-Au2S. Petrovskaite, high-fineness gold, and sulfur are produced in the systems with low Ag contents ( x > 1). The systems with an intermediate composition produce petrovskaite, uytenbogaardtite, and solid solutions Ag2- x Au x S (0.5 < x < 1). The results of experimental studies together with data on the compositions of natural gold and silver sulfides suggest that the wide variations in Au and Ag contents in uytenbogaardtite and petrovskaite from different deposits are, most likely, due to the inhomogeneous structure of mineral grains and the presence of solid solutions Ag2- x Au x S. It is assumed that gold and silver sulfides crystallizing from Au-Ag-containing sulfide melts might be of magmatic genesis. Poorly extractable gold in sulfide ores might be present as microinclusions of Au-Ag sulfides.
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