Литосфера (Jun 2018)
Bismuth sulfosalts from Berezovsk ore region: Chemical composition and mineral associations
Abstract
The paper presents the results of a study of the chemical composition of the sulfosalts of bismuth from the gold-quartz-sulphide ore Berezovsky Deposit and the eponymous ore district of the Middle Urals. Samples of minerals were obtained from quartz veins located in different parts of the ore area. In the South of the district the veins occur among the granites of the Shartash massif and accompanied by the metasomatic gumbeit formation. Veins in its Central part are located into the dikes of granite porphyry, volcanic-sedimentary rocks, hyperbasites. In the North, the veins are localized in gabbro, hyperbasites, volcanic rocks. Here, as in the Central part, they are accompanied by metasomatic changes of the berezite-listwanite formation. The minerals of bismuth form small isometric, prismatic or needle-shaped secretions, as well as large elongated crystals reaching a length of several centimeters. Their diagnosis and study of the composition was performed by X-ray structural and chemical microanalysis. It is shown widespread among minerals of bismuth sulfosalts of the bismuthinite-aikinite series, consisting of 9 members: bismuthine, pecoite, gladite, stroking, salzburger, krupkaite, lindströmite, khammarite, fridrikhite and dramatically prevalent among sulfosalts that number aikinite. In mineral composition pavonite series revealed cuprapawonite, Cu-benjaminite, benjaminite. Other sulphosalts of bismuth are presented kosalite, nafildite, hodrushite, matildite. The relationship of minerals with each other and the peculiarities of the chemical composition allowed to distinguish several paragenetic associations conform with different stages of mineral formation. With high-temperature stage (360-285°C) connects the deposition of disordered solid solutions bismuthine-aikinte and pavonite series, subsequently undergone to disintegration with the formation of ordered phases of bismuthine, gladite, krupkaite, lindströmite, khammarite, benjaminite. For medium and low temperature stage (285-150°C) was formed aikinite, fridrikhite, krupkaite, salzburgite, nuffieldite cozalite, matildite, together with the Ag-Bi-Galena, tetradymite, hessite and gold. The low-temperature stage is associated with the formation of aikinite together with Galena and gold. Established on the example of the sulfosalts of bismuth sequence of mineral formation reflects not only the consistent evolution of mineral-forming fluids, but the pulsed nature of the hydrothermal activity at individual deposits and at ore field in general.
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