pdf № 272, August

DOI: 10.19110/2221-1381-2017-8-3-11

We have studied the gold-sulfide mineralization of Karavannoe ore occurrence located in Kozhim district of the Subpolar Urals. The sulphides were mainly represented by sphalerite, galena, and pyrite. The gold is closely associated with the sulphides. The size of the gold particles varies from 0.1 to 0.6 mm and in the most cases does not exceed 0.2 mm. The particles with a thickened, isometric, complex shape predominate. The impurity element in the gold is silver, which content varies from 2 to 9.8 wt. %. The temperature of homogenization of fluid inclusions in vein quartz from ore zones ranges from 240 to 400 °C. Water, chlorides of calcium, magnesium, potassium, and sodium, carbon dioxide, nitrogen, and methane are present in the inclusions. Sulphides are characterized mainly by weighted isotope composition of sulfur, d34S varies from 3.7 to 15.6 ‰.The formation of the gold-sulphide mineralization was likely conditioned by the Late Paleozoic hydrothermal-metamorphogenic processes with the predominant mobilization of water, sulphur and other components from enclosing rocks with a relatively low participation of abyssal fluids. The zones of impregnated and vein-impregnated sulphide mineralization in the Riphean shales of Karavannoe occurrence and beyond are very favorable for the development of gold-bearing weathering crusts, which may represent industrial interest.

Keywords: gold-sulphide mineralization, Karavannoe ore occurrence, Subpolar Urals, sulfur isotopy, fluid inclusions, ore formation.

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DOI: 10.19110/2221-1381-2017-8-12-16

Previously not carried out investigation is performed for finite-amplitude 2D small-scale mantle convection in the mantle wedge above the slab subducting at extremely small angle, which appears to be the case at Paleozoic in the course of closing of the former Urals ocean and subduction of the Russian plate under the Timan-Pechora one.

Topography depressions and uplifts at the Timan-Pechora lithospheric plate alternate quasi periodically and are nearly parallel to the South-Western border of the plate. This probably is indicative of the convective origin of topography spatial undulations, the convection at the mantle wedge being due to shear heating in the mantle slab-induced flow.

Numerical modeling of the thermal mantle convection accounting for the effects of phase transitions at 410 km and 660 km depths and temperature- and pressure dependence of viscosity for «wet» olivine shows the subduction velocity ~ 6 cm·y^-1 to correspond to convective cell (Karig rolls) dimension of the same scale as the wavelength of the relief variations, horizontal extent of convection region being equal to horizontal extent of Timan-Pechora oil- and gas bearing province.

Keywords: mantle wedge convection, subduction angle and velocity, mantle rheology, phase transitions.

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DOI: 10.19110/2221-1381-2017-8-17-22

The results of studying barium feldspars from different metasomatic rocks of the complex are summarized in the article. Studies of minerals were performed using a scanning electron microscope РЭММА-202М with a microanalyzer. Forms of barium feldspars, features of composition and conditions of formation are considered. Barium-potassium feldspar is characterized by heterogeneity of composition, an increase in the amount of Ba to the grain edge, and a high content of Ab minal (12—17 %). The composition of celsian, developed in the basic plagioclase, shows significant variations in the CaO content of 0.4—3.6 wt. %. The temperature of formation of barium-potassium feldspar is 610—660 °C, celsian 560—610 °C. In a barite vein, celsian with a high Ba content was formed at T » 450 °C. The formation of barium minerals is associated with postmagmatic processes that occurred after the formation of the alkaline-carbonatite rocks of the complex. Rocks with barium-containing minerals are usually confined to zones of faults, along which barium was introduced.

Keywords: barium-potassium feldspar, celsian, metasomatites, ilmeny-vishnevogorsky complex.

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 DOI: 10.19110/2221-1381-2017-8-23-35

The results of complex mineralogical-geochemical and isotope-geochemical studies of a collection of concrements typical for the Rostov-on-Don region are presented. The anatomical structure, microstructure, thermal properties, chemical and phase composition, assortment and content of microelements are analyzed. According to the data of X-ray diffraction analysis and normative-mineral calculation, uricite, sodium urate, hydroxylcarbonatapatite, oxalates, and sulfates of Fe, K, Ca are found in the calculi. For the first time, an organic substance was isolated from urinary and kidney stones and the isotopic composition of carbon and nitrogen were determined in it. The genetic issues of calculus formation are discussed taking into account the data on the chemical and microelement composition of drinking water.

Keywords: concrements, urolithiasis disease, mineralogical and geochemical studies, uriquite, sodium urate, carbonatopatite, organic matter.

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 DOI: 10.19110/2221-1381-2017-8-36-43

Garnet in ultramafic rocks is a sign of high or ultrahigh pressure (HP-UHP). Garnet peridotites contain unique information about crust-mantle processes in collision environment. We determine four type of garnet in peridotites of Marun-Keu Complex which correspond to progressive (Grt-1), peak (Grt-2) and two regressive metamorphic stage (Grt-3 and Grt-4). Scarce occurrence of Grt-1 and Grt-2 as relic cores in the largest garnet porphiroblasts, wide occurrence of regressive type of garnet (Grt-3 and Grt‑4) and late pargasitic amphibole are evidence of wide post-peak mineral transformations in Marun-Keu peridotites.

Keywords: Marun-Keu Complex, Polar Urals, garnet, peridotites, UHP metamorphism.

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