pdf № 291, March

DOI: 10.19110/2221-1381-2019-3-3-8

The first data on the composition and physical properties of magnesioferrite from carbonatites of the Shishimskaya pit in the South Urals are presented. The chemical composition and features of the distribution of mineral inclusions in it were investigated using a microanalyzer and Raman spectroscopy, its diagnosis was confirmed by a diffractogram. The mineral was found in the eluvial grus at the outcrop of one of the carbonatite dikes, a cutting rock of the exocontact gabbro zone.

Magnesioferrite differs from magnetite in the presence of significant amounts of MgO (up to 14.1 wt. %) and MnO (up to 7.6 wt. %). It composes highly magnetic octahedral crystals 0.3—3.0 mm in size and very small inclusions in spinels and perovskite. Magnesioferrite contains microinclusions of perovskite, hematite, spinel, chlorite, and calcite. For diagnostic purposes, the Raman spectra of magnesioferrite are the most informative. The ideal form of its crystals is similar to metacrystals. The morphological features of the crystals, the absence of possible «shadows» of protominerals in the magnesioferrite, the compromise boundaries of the crystals of magnesioferrite and calcite are all evidence of the simultaneous formation of these minerals, without traces of replacing them with each other. The predominantly calcite composition of the rock, its occurrence in the form of dikes and veins in a diverse substrate, suggest that its minerals were formed during the crystallization of the carbonate melt.

Keywords: carbonatites, magnesioferrite, Shishimskaya pit, South Urals.

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DOI: 10.19110/2221-1381-2019-3-9-13

The article presented the results of isotopic-geochronological studies of zircons from the garnet-biotite plagiogneiss of the Vishnevogorsky series of Ilmeny-Vishnevogorsky complex (southeastern shore of the Sungul Lake, Southern Urals). Isotopic analyzes (U/Pb zircon, SHRIMP II) were performed using the ion microprobe at IRC VSEGEI by standard methods. Analytical studies were preceded by mineralogical investigations. We selected sites in heterogeneous grains corresponding to an important stage in their development. The maximum age of the substrate of plagiogneiss was Neoarchean (2700 Ma). The nature of zircons corresponded to the concepts of their polygenicity and polychronicity. Rounded fragments zircon crystaled reflect sedimentary rocks involved in substrate of plagiogneiss and the structure of some of the zircons indicated their primary magmatic formation. In the time interval of 2200—1060 Ma, Paleoproterozoic (≥ 1740 Ma) granulite metamorphism and two (1500 and 1090 Ma) transformation stages were recorded. Late generations of zircons (Th/U = 0.004—0.08; 460, 350—380, and 270—300 Ma) reflected the final processes of metamorphism — metasomatism. The age of plagiogneisses of the Vishnevogorsky series was older than the gneiss of the Selyankinsky block (2080 Ma).

Keywords: zircon, age, garnet-biotite gneiss, Vishnevogorsky series.

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DOI: 10.19110/2221-1381-2019-3-14-23

Unique location of numerous early Protognathodus Ziegler in the Devonian-Carboniferous boundary interval of Izyayol River section (South of the Chernyshev Swell) is considered in the article. Early representatives of Protognathodus in the north of the Urals are common for deep-water sediments of the outer slope of the carbonate platform or the inner side of the depressions on the shelf similarly to other known localities. The highest concentrations of elements are noted in calciturbites, where conodonts are hydrodynamically concentrated. Small number (except for hydrodynamically enriched intervals in calciturbites) and narrow facies range exclude the possibility of using of Protognatnus kockeli as a North Ural regional D/C boundary biostratigraphical marker. Well recognized in the sections of the region Hangenberg event transgression (priority) or regression can be used as a regional interfacial abiotic boundary marker.

Keywords: Famennian, Tournaisian, conodonts, Protognathodus.

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DOI: 10.19110/2221-1381-2019-3-24-30

The paper analyzes paleoecological and paleobiogeographic regularities of tabulation evolution in the Late Ordovician and Early Silurian in the north of the Urals. By now there are no works completely describing the taxonomic composition, stratigraphic and geographical distribution and evolutionary development of Ordovician and Silurian tabulates of the north of the Urals. It is important to study the temporal and spatial distribution of tabulates, which is necessary for a more complete use of this group of benthos for practical purposes.

Keywords: tabulates, Ordovician, Silurian, paleobiogeography, paleoecology.

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DOI: 10.19110/2221-1381-2019-3-31-40

Ferromanganese crusts of the Sea of Japan are characterized by a high content of manganese (up to 63 %) and barium (up to 3 %). A detailed analysis of 64 FMC samples taken on 19 submarine volcanic elevations showed that barium was found in them both as barite, and was a part of the manganese matrix, enriching it in some areas up to 6.5 %. Barite in the form of fine grains was present in the manganese matrix of almost all studied samples, sometimes filling cracks in it completely or partially. There were dendritic crystals of barite, forming spotted precipitates on iron-siliceous or in manganese-iron-siliceous matrices. Features of the allocation of barite suggest that the process of barite formation is superimposed and occurs in the last stage of the formation of FMC.

Keywords: ferromanganese crusts, barite, barium, submarine volcanic Seamount, Sea of Japan.

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DOI: 10.19110/2221-1381-2019-3-41-50

The results of mineralogical investigation of glauconite from the Karinskoe deposit are presented. Grains were studied using complex of chemical and physical methods: X-ray diffraction, Mцssbauer spectroscopy ⁵⁷Fe, scanning electron microscopy and microprobe analyses, Fourier-transform infrared spectroscopy.

Special attention is given to the crystal-chemical features of mineral and processes of glauconite formation.

Glauconite from the Karinskoe deposit is characterized by a relatively high content of K, Fe, Mg. Content of total iron and potassium display a direct correlation. According to Mцssbauer and IR spectroscopy data Fe²⁺ occupies not more than 10 % of the total iron content in glauconite. Crystal-chemical composition of mineral corresponds to «mature» glauconite, which was formed during the slow «maturing» of glauconite grains with increasing of the mica layers in its structure. Glauconite contains a small (10—15 %) amount of swelling layers. It can be proposed that smectite was a «precursor» for glauconite formation.

Keywords: glauconite, crystal-chemical features, glauсonite maturity, Mцssbauer and FTIR-spectroscopy, X-ray diffraction.

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DOI: 10.19110/2221-1381-2019-3-51-55

Full members of Chita branch, RMS, presented their research results. They studied copper sandstones and slates, cladding stones, carbonaceous materials, zeolites, gold, plumbum, zinc, etc. They established basic patterns of their distribution and conditions of formation of the developed classification schemes that allowed prospecting assessment and recommendations on their development. Attention was paid to geotechnogenic deposits, which contained significant reserves of many useful components. The geological and technological studies of natural and technogenic mineral raw materials of the Eastern Transbaikalia resulted in new methods for discovery of dispersed (nanoscale) forms of noble metals and methods for their extraction, which significantly expanded prospects for the development of not only large deposits, but also medium and small — scale objects, as well as mining and technological waste.

Keywords: East-Transbaikal deposits of natural and technogenic raw materials, geological and technological research, regularities of placement, conditions of formation, practical use.

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