pdf № 296, August

DOI: 10.19110/2221-1381-2019-8-3-13

Electron microscopic, isotopic, X-ray diffraction and spectroscopic studies to clarify the genesis of crypto- and micro-grained limestones of the Upper Ordovician in the Northern Urals and fine- and micro-grained dolomites of the Wenlockian in the Chernyshev Uplift revealed their bio-chemogenic nature. According to the data of the unit cell parameters, dolomites are of primary sedimentary nature. The revealed phases of different ordering of carbonaceous matter in calcite (chlorite stage of metamorphism) and dolomite (debituminated OM) reflect a different degree of their post-sedimentation transformation as a result of processes of different intensity of tectonic events on rocks. The isotopic data of primary sedimentary dolomites in this case actually reflect the primary isotopic ratios d¹³С (–3.5 ... –2.8 ‰), d¹⁸O (22.4—24.1 ‰), characteristic of the offshore somewhat desalinated back-reef lagoon. The wide distribution of fossilized biofilms (glycocalyx), framboidal pyrites, and the presence of bacteriomorphic structures indicate the active participation of microbial organisms in the genesis of the studied microgranular limestones and dolomites.

Keywords: limestones, dolomites, organic matter, d¹³С, d¹⁸O, fossilized glycocalyx, bacteriomorphs, framboidal pyrite.

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DOI: 10.19110/2221-1381-2019-8-14-19

Three types of microbial structures of the Sedyu Reef Comples, exposed in the Southern Timan, were described: skeletal stromatolites, fine-grained stromatolites, and microbial clotted limestones. Skeletal stromatolites were constructed by oxygenic phototrops, cyanobacteria, and made up a significant part of the Sedyu Reef. Clots were resulted from vital activity of ancient heterotrophic bacteria and widespread in the lagoon facies. Fine-grained stromatolites occupied an intermediate position. The dependence of the distribution of different types of microbial structures on the predominance of different functional groups of bacteria was revealed. The bacteria spread, in turn, were regulated by trophic links. The developed hypothetical scheme of the trophic structure of the Sedyu Reef Complex showed the presence of a large trophic loop between the reef and the lagoon, which, in general terms, repeated the modern one.

Keywords: «reef — lagoon» system, microbial formations, trophic links, Southern Timan, Frasnian.

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DOI: 10.19110/2221-1381-2019-8-20-24

Lower Devonian deposits of the West-Magnitogorsk zone of the Southern Urals in some regions are represented by Mansurovo, Iltibanovo, Uskul’ and Ryskuzhino strata. For a long time these strata were considered as a part of the Irendyk suite due to the macroscopic similarity, insufficiency of biostratigraphic data and complicated tectonic structure of the territory. After the adoption a new Stratigraphic scheme of the Urals in 1993 and the geological survey, carried out in the study area, the age identity with the Lower Devonian Mazovo suite was established. Based on the results of detailed stratigraphic and geological studies of the Devonian sections, V. A. Maslov and O. V. Artyushkova decided to consider the Lower Devonian strata as independent units.

The Uskul’ strata are located in the Uzynkyr subzone of the West-Magnitogorsk zone (Republic of Bashkortostan, the southwestern shore of the Uscul’ Lake and the northwestern slope of the mountain of the same name). They are composed of volcaniclastic, carbonaceous and siliceous rocks, rarely volcanic rocks. The apparent thickness of the section is approximately 700 m. For a long time, the age of the Uskul’ strata was determined by the fauna from the lentiform limestones located in the upper part of the section. The article presents the first finds of macrofauna from a rhythmic packet of tephroturbidites lying in the lower part of the section. The fauna is represented by fossils of brachiopods and crinoids. Brachiopods correspond to the Early Devonian Pragian-Emsian age. The new data allow to speak about close time of sedimentation tephroturbidites and overlying limestones, and in general to determine the age of the Uscul’ strata as Pragian-Early Emsian based on conodonts.

Keywords: Lower Devonian, biostratigraphy, macrofauna, Magnitogorsk megazone, Southern Urals.

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DOI: 10.19110/2221-1381-2019-8-25-32

The article presents data on determining the crystallization temperature of zircons (78 crystals) from ultramafites of the Ilmeny-Vishnevogorsky complex and the Karabash massif by Ti-in-zircon geothermometer. The content of RE and REE in zircon is determined by Secondary-Ion Mass Spectrometry using the ion microprobe CAMEKA IMS-4F. A variety of heterogeneous polychronous zircons from ultramafic rocks include varieties with certain specific mineralogical-geochemical and age characteristics. The Early Proterozoic magmatic zircons PR1 (1770—1740 Ma) are characterized by the concentration of titanium from 16.7 to 29.9 ppm, low contents SREEср = 482 ppm, LREEср = 25.4 ppm and impurity elements Caav = 33 ppm, Baav = 1.4 ppm and Sr  0.5 ppm. High Ce and minimum Eu are distinctly manifested. Th/Uср = 0.65. The Cambrian magmatic zircons V—Є1 (580—520 Ma) contain 7.9—12.9 ppm titanium, higher concentrations SREEav = 623 ppm, LREEav = 30 ppm and impurity elements Caav = 17 ppm, Th/Uav = 0.86. The Early Silurian magmatic zircons O3—S (450—420 Ma) are characterized by titanium concentration from 7.4 to 19.6 ppm, high SREEav = 1142 ppm, low LREE/HREE = 0.03 and Th/Uav = 0.42. Transition and hydrothermal type of zircons (274—1793 Ma) have wide variations of titanium concentrations from 2.5 to 1160 ppm, that are mainly characterized by high concentrations in zircon LREE, Ca, Ba and Sr. For a real assessment of the crystallization temperature of zircon, and, therefore ultramafites zircons of magmatic type can be used. The crystallization temperature of magmatic zircon types (the formation-transformation of ultramafites) amount to Early Proterozoic PR1 — (822.5 ± 37) °C; Cambrian V—Є1 — (742 ± 17) °C and Early Silurian O3—S — (768 ± 27) °C.

Keywords: Ilmeny-Vishnevogorsky complex, ultramafites, zircon, Ti-in-zircon geothermometry.

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DOI: 10.19110/2221-1381-2019-8-33-41

 The Niyahoy-2 occurrence of the gold-arsenic type belongs to the Niyayusk gold ore node, within the boundaries of which the Niyahoyskoye and Verkhneniyayus gold ore fields are distinguished. The gold occurrence is localized in the volcanogenic-terrigenous flyschoid of the Enganepey Formation of the Upper Vendian — Lower Cambrian. Within the occurrence, gold-bearing quartz-sulfide veins and streaks are developed. Inter-vein intervals in mineralized zones are also gold-bearing. The surface parts of the ore occurrence to a depth of 15—60 m are significantly affected by weathering processes, representing an oxidation zone. The main ore mineral is arsenopyrite, pyrite is present in a subordinate amount. Minor minerals are represented by chalcopyrite, silver-containing tetrahedrite, lead and copper sulfosalts (aikinite), native bismuth, and gold. As microinclusions in arsenopyrite and pyrite, tetrahedrite, sphalerite, galena, lead sulfosalts and copper of variable composition with bismuth are present. Hypergenic minerals — scorodite, covellite, barite, lead hydroxy sulfosalts with bismuth. The mineral composition of ores, including rare minerals, and the features of native gold, the occurrence of Niyahoy-2 and Verkhneniyayus-2 deposit are close, which may indicate their formation in a single hydrothermal system.

Keywords: gold-arsenic mineralization, vein type, sulfides, sulfosalts, faded ore, gold, Niyahoy-2 occurrence, Verkhneniyayus-2 deposit, Manitanyrd ridge.

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DOI: 10.19110/2221-1381-2019-8-42-44

The article is devoted to the discussion of the logical connection of the concepts of symmetry, dissymmetry and antisymmetry in the university course of crystallography. The link between symmetry and dissymmetry is quite obvious, which cannot be said about the link between dissymmetry and antisymmetry. On the example of convex polyhedra, antisymmetry is defined as radical dissymmetry, i. e. translation of all faces of the polyhedron along the normals on the other side of the origin. This methodical technique unites the three concepts and leads to the further development of the theory.

Keywords: symmetry, dissymmetry, antisymmetry.

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