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Research subject. In this work, we investigated the crystals of pyrite, one of the key gold-bearing minerals, from the Berezovskoe (the Middle Urals) deposit using modern research approaches.Materials and methods. Samples for the analysis were collected from the ladder sulphide-quartz veins and related berezites in the Ilinskaya, Pervopavlovsk and Vtoropavlovsk dykes of the Berezovskoe deposit. The ores were studied using the methods of optical microscopy, X-ray microanalysis (PCMA), scanning electron microscopy (SEM) and LA-ICP-MS. The latter method was largely used to examine pyrite. Along with pyrite, the materials under study included faded ore, galena, and such rare occurring minerals as aikinite, cosalite, tetradymite and tsumoite. Results. According to the point and profile analysis, as well as grain mapping, the main impurity elements in the stu died samples are found to be Co, Ni and As. The distribution of these elements has shown a zonal character: the amounts of Co and Ni tend to increase and that of As tends to decrease towards the grain centre. In the pyrite samples, Cu, Zn and Pb occur either in the form of their sulphide micro-inclusions or as evenly distributed admixtures. The pyritic ore of later genera tions in the Pervopavlovsk dyke is established to contain gold in amounts of up to 22 g/t, with Au being zonally distributed. The goldbearing variety of pyrite is characterized by abnormally low contents of Co and Ni, as well as by an increased content of As (up to 8000 g/t). Conclusion. A common character of the distribution of main impurity elements in the pyritic ores in the studied dikes indicates similar conditions of their crystallization. The presence of late-generation pyrite with fine gold in the Pervopavlovsk dike evidences to a heterogeneous distribution of gold mineralization therein, likely due to the multistage character of the latter. This may also be an indicator of the concentration of ore columns, which fact requires further elucidation.

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.

Embreyite from the Berezovskoe, Urals, Russia, was studied by the means of powder X-ray diffraction (XRD), single-crystal XRD, infrared spectroscopy and microprobe analysis. The empirical formula of embreyite obtained on the basis of microprobe analysis is Pb1.29Cu0.07Cr0.52P0.43O4 (without taking into account the presence of H2O). An examination of single-crystal XRD frames of the tested crystals cut from embreyite intergrowths revealed split reflection spots of weak intensities, even after a long exposure time. The crystal structure of embreyite (monoclinic, C 2/ m , a = 9.802(16), b = 5.603(9), c = 7.649(12) Å, β = 114.85(3)o and V = 381.2(11) Å3) has been solved by direct methods and refined to R 1 = 0.050 for 318 unique observed reflections. The powder XRD patterns of the holotype embreyite and the fresh material studied are close in both d values and the intensities match the pattern calculated from the structural single-crystal XRD data. The unit-cell parameters were re-calculated for the holotype sample using a new cell setting and corresponding hkl indices. The crystal structure of embreyite is based on layers formed by corner-sharing mixed chromate-phosphate tetrahedra and PbO6 distorted octahedra. The interlayer space is filled by disordered Pb2+ and Cu2+ cations. Generally, the crystal structure of embreyite can be referred to the structural type of palmierite. {Pb[(Cr,P)O4]2]} layers in embreyite are similar in topology to those in yavapaiite-type compounds. The general formula of embreyite can be represented as (Pb x $M_y^{2 +} $ □1 –x– y )2{Pb[(Cr,P)O4]2}(H2O) n , where M 2+ = Cu and Zn and 0.5 ≤ x + y ≤ 1, or, in the simplified form: (Pb,Cu,□)2{Pb[(Cr,P)O4]2}(H2O) n . The simplified formula of embreyite is similar in stoichiometry to vauquelinite and may explain the existence of the solid-solution series. The determination of the crystal structure of embreyite may also help to resolve the crystal chemical nature of cassedanneite. The XRD pattern of cassedanneite contains a distinct reflection with d = 13.9 Å, forbidden for the embreyite unit cell. This feature may indicate the doubling of the c unit-cell parameter of cassedanneite in comparison with embreyite. We assume that cassedanneite has structural similarity to embreyite with, presumably, a disordered distribution of Cr and V. [ABSTRACT FROM AUTHOR]

A novel complex continuous system of solid solutions involving vauquelinite Pb2Cu(CrO4)(PO4)(OH), bushmakinite Pb2Al(VO4)(PO4)(OH), ferribushmakinite Pb2Fe3+(VO4)(PO4)(OH), and a phase with the endmember formula Pb2Cu(VO4)(PO4)(H2O) or Pb2Cu(VO4)(PO3OH)(OH) is studied based on samples from the oxidation zone of the Berezovskoe, Trebiat, and Pervomaisko-Zverevsky deposits in the Urals, Russia. This is the first natural system in which chromate and vanadate anions show a wide range of substitutions and the most extensive solid solution system involving (CrO4)2- found in nature. The major couple substitution is Cr6+ + Cu2+ ↔ V5+ + M3+, where M = Fe, Al. The correlation coefficients calculated from 125 point analyses are: 0.96 between V and (Fe + Al), 0.96 between Cr and (Cu + Zn), -0.96 between V and (Cu + Zn), -0.97 between Cr and (Fe + Al), and -0.97 between (Fe + Al) and (Cu + Zn). The substitutions V5+ Cr6+ (correlation coefficient -0.98) and to a lesser extent P5+ ↔ As5+ (correlation coefficient -0.86) occur at two types of tetrahedral sites, whereas the metal-nonmetal/metalloid substitutions, i.e., V or Cr for P or As, are minor. The substitution Fe3+ ↔ Al3+ is also negligible in this solid solution system. [ABSTRACT FROM AUTHOR]