| Реферат: | eng: We carried out experiments on crystallization of Fe-containing melts FeS 2Ag 0.1-0.1xAu 0.1x (x = 0.05, 0.2, 0.4, and 0.8) with Ag/Au weight ratios from 10 to 0.1. Mixtures prepared from elements in corresponding proportions were heated in evacuated quartz ampoules to 1050 oC and kept at this temperature for 12 h; then they were cooled to 150 oC, annealed for 30 days, and cooled to room temperature. The solid-phase products were studied by optical and electron microscopy and X-ray spectroscopy. The crystallization products were mainly from iron sulfides: monoclinic pyrrhotite (Fe 0.47S 0.53 or Fe 7S 8) and pyrite (Fe 0.99S 2.01). Gold-silver sulfides (low-temperature modifications) are present in all synthesized samples. Depending on Ag/Au, the following sulfides are produced: acanthite (Ag/Au = 10), solid solutions Ag 2-xAu xS (Ag/Au = 10, 2), uytenbogaardtite (Ag/Au = 2, 0.75), and petrovskaite (Ag/Au = 0.75, 0.12). They contain iron impurities (up to 3.3 wt.%). Xenomorphic micro- (<1-5 μm) and macrograins (5-50 μm) of Au-Ag sulfides are localized in pyrite or between the grains of pyrite and pyrrhotite. High-fineness gold was detected in the samples with initial ratio Ag/Au ≤ 2. It is present as fine and large rounded microinclusions or as intergrowths with Au-Ag sulfides in pyrite or, more seldom, at the boundary of pyrite and pyrrhotite grains. This gold contains up to 5.7 wt.% Fe. Based on the sample textures and phase relations, a sequence of their crystallization was determined. At ~1050 oC, there are probably iron sulfide melt L 1 (Fe,S ≫ Ag,Au), gold-silver sulfide melt L 2 (Au,Ag,S ≫ Fe), and liquid sulfur L S. On cooling, melt L 1 produces pyrrhotite; further cooling leads to the crystallization of high-fineness gold (macrograins from L 1 and micrograins from L 2) and Au-Ag sulfides (micrograins from L 1 and macrograins from L 2). Pyrite crystallizes after gold-silver sulfides by the peritectic reaction FeS + L S = FeS 2 at ~743 oC. Elemental sulfur is the last to crystallize. Gold-silver sulfides are stable and dominate over native gold and silver, especially in pyrite-containing ores with high Ag/Au ratios. © 2012.
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