Plate tectonic model of the South Urals development

The Uralian Fold Belt originated due to the East European-Kazakhstan continental collision in the Late Paleozoic-Early Triassic. The Uralian paleo-ocean existed from the Ordovician to Early Carboniferous. It evolved along the Western Pacific pattern with island arcs and subduction zones moving oceanwards from the East European margin and leaving newly opened back-arc basins behind from the Silurian to the Middle Devonian. A fossil spreading pattern similar to present one can be reconstructed for the Mugodjarian back-arc basin with the spreading rate of 5 cm/yr and depth of basaltic eruption of 3000 m. Since the Devonian, the closure of the Uralian paleo-ocean has begun. A subduction zone flipped over under the Kazakhstan continent, and remnants of an oceanic floor were completely consumed before the Late Carboniferous. After that the continental collision began which lasted nearly 90 Ma. As a result, the distinct linear shape and nappe structure of the Urals were formed.     

Mineralogy of metamorphosed manganese deposits of the South Urals

A mineralogical investigation of metamorphosed manganese rocks was carried out at ore deposits related to the Devonian volcanic complexes of the Magnitogorsk paleovolcanic belt of the South Urals. The mineralogical appearance of these rocks is determined by three consecutively formed groups of mineral assemblages: (1) assemblages occupying the main volume of orebodies and formed during low-grade regional metamorphism (T = 200−250°C, P = 2–3 kbar); (2) assemblages of segregated and metasomatic veinlets that fill the systems of late tectonic fractures; and (3) assemblages of near-surface supergene minerals. Sixty-one minerals have been identified in orebodies and crosscutting hydrothermal veinlets. The major minerals are quartz, hematite, hausmannite, braunite, tephroite, andradite, epidote, rhodonite, caryopilite, calcite, and rhodochrosite. The mineral assemblages of metamorphosed manganese rocks (metamanganolites) are characterized. Chemical compositions of braunite, epidote-group minerals, piemontite, pyroxenes, rhodonite, pyroxmangite, and winchite are considered. The bibliography on geology and mineralogy of the South Ural manganese deposits is given.     

Porphyry Deposits of the South Urals: Rhenium Distribution

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Zirconology of miaskites from the Ilmeny Mountains,South Urals

It is shown that the replacement and long evolution of miaskitic zircons led to the formation of two main age groups: 420–380 Ma (I) and 260–240 Ma (II). The age of miaskites is estimated at 440–445 Ma. Zircons I bear traces of fragmentation, dissolution, and replacement; they have “flat” REE patterns typical of metasomatic (hydrothermal) types, which is caused by allochthonous nature of the studied miaskites. Zircons II with differentiated REE patterns are similar to magmatic varieties, but have metamorphic origin. Mineralogical–geochemical and age characteristics of zircons in combination with structural–compositional features of miaskites define their metasomatic nature. The origin of the early zircon generations was related to the Ordovician rifting, while late generations were formed during shear deformations at the final stage of the evolution of the Uralian orogen.     

Origin of vitriol Lake Gay,South Urals

This paper can be considered a case history in which geology, geophysics, and more particularly geohydrology and geochemistry, when applied to the problem of origin of a vitriol lake, led to discovery of a copper prospect. After a review of various postulated origins for the vitriol lake and previous interpretation of the local structure, new evidence based on borehole and geophysical data demonstrated that the structure consists of two anticlines and two fault systems. Study of the geohydrologic conditions as related to the fault systems and the geochemistry of their water indicate the lake is the result of mineralized water whose circulation is controlled by the fault zone. Source of the copper in these waters may be some hidden copper deposit in a direction away from the known ore bodies. -- J. Lemish.     

Belogubite,a New Mineral of the Chalcanthite Group from the Gaiskoe Deposit,South Urals,Russia

Geology of Ore Deposits - Belogubite CuZn(SO4)2 ⋅ 10H2O, a new mineral of the chalcanthite group, is found in the Gai (Gaiskoe) massive sulfide deposit, South Urals, Russia. This mineral...     

Berdyaush pluton of rapakivi granites,South Urals: New data on the geological structure and geodynamic evolution

The new version of the geological structure of the Berdyaush pluton (a single intrusion of rapakivi granites in the Urals) presented in this paper is significantly distinct from the previous structural schemes. Rapakivi granites compose no more than 10–20% of the area of the pluton and they are widespread only in its northeastern and southwestern flanks. The contacts between gabbro (I phase), hybrid syenodiorites (II phase), and rapakivi granites (III phase) are transitional, metasomatic. The hybrid syenodiorites and rapakivi granites are formed after gabbroic rocks as a result of their intense thermal and metasomatic transformation by the deep fluids. The driving force of this process could be the unilateral compression of the Berdyaush pluton resulting from formation of the eastward continental rift in the beginning of the Middle Riphean.     

Stibiomicrolite from granitic pegmatite in the Dzhabyk-Karagai pluton of the South Urals

Stibiomicrolite has been identified in the Lepidolite Vein (53°06.8′N, 60°15.4′E) as metasomatic veinlets with tantite replacing stibiotantalite along fractures. The mineral is light gray-yellow, isotropic, and with reflectance of ～12%. The average chemical composition of two stibiomicrolite samples is as follows, wt %: Sb₂O₃ 23.34, CaO 4.91, Na₂O 0.96, MnO 0.17, Ta₂O₅ 58.97, Nb₂O₅ 6.64, total 94.99; H₂O_calc 3.4. The empirical formula is (Sb_1.02Ca_0.55Na_0.20Mn_0.02)_1.79(Ta_1.68Nb_0.32)_2.0O₆(OH)_1.18. Trilithionite, polylithionite, albite, manganotantalite, beryl (goshenite), elbaite, stibiotantalite, and tantite are associated with stibiomicrolite in the central zone of the Lepidolite Vein.     

Structure of magnetite lodes at the Estyunino iron deposit in the central Urals

The structure of magnetite lodes is determined by iron and sulfur distribution, as well as texture and structure of ore. These features have been revealed by documentation of cores from ore intervals in exploration boreholes penetrating two main lodes 21 and 22 of the Estyunino iron deposit. The documentation of cores was accompanied by sampling for microscopic examination of texture and structure of ore and selection of Fe and S contents in ore. Then these data were summarized as sections of the lodes. It was established that the structure of magnetite lodes is characterized by conformable ore layers distinguished by texture, structure, and Fe and S contents. Banded and spotty ores containing less than 50% magnetite are predominant. Layers of homogeneous massive ore are infrequent. The textural pattern indicates a volcaniclastic nature of host rocks. The spotty texture is characteristic of hyaloclastites with vitreous shards. The banded texture with oriented distribution of fiamme is inherent to volcaniclastic rocks. In both cases, magnetite selectively replaces dark-colored vitreous fragments and is also dispersed in the salic matrix and lava fragments. No indications of crosscutting superposed relationships are observed. The available data can be satisfactorily explained by an impregnation-metasomatic mode of ore deposition.     

A New Dinosaur Fossil from the Southern Urals

Doklady Earth Sciences - A caudal vertebra of a dinosaur (Iguanodontia indet.) is described from Upper Cretaceous (lower Campanian) coastal marine deposits of Izhberda Quarry near Orsk (Orenburg...     

Lithochemical composition of sandstones of the Vendian Asha Group,South Urals

The mineralogical–petrographic and chemical study of sandstones of the Vendian Asha Group in the Bashkir anticlinorium, the western slope of the South Urals, showed that this large stratigraphic unit consists of sedimentary associations formed in different conditions: (1) Pre-Uryuk sediments (Tolparovo, Suirovo, and Bakeevo formations) accumulated during marine regression possibly in the course of significant glacioeustatic sea level fluctuations and formation of the foredeep of Timanides. (2) Sediments of the Uryuk Formation, including alluvial and several related sediments. Analysis of the Qm–F–Lt, Qt–F–L, and ln(Q/L + CE)–ln(Q/F) diagrams showed that they were derived from magmatic/plutonic rocks in the inner parts of the East European Craton. Based on the distribution of data points of psammites in the Qt/(F + R)–Qp/(F + R) diagram, they were accumulated in the semihumid/semiarid conditions. (3) Coastal, shallowmarine, and fluvial/proluvial (?) sediments of the Basa, Kukkarauk, and Zigan formations. They were formed by the erosion of provenances located supposedly east of the present-day Bashkir anticlinorium. The psammites of the Asha Group were analyzed using the sandstone formation model proposed models proposed in (Dickinson et al., 1985; Garzanti et al., 2007). The distribution of data points of psammites from three uppermost formations of the Asha Group in the Qm–F–Lt and Qt–F–L diagrams suggests that they were accumulated by the redeposition of erosion products of the so-called clastic wedges of recycled orogens (clasticwedge provenance) made up of the fluvial and turbidite complexes of the foreland, fore-arc, or residual oceanic basins.     

Geochemistry of Early Devonian rocks of the Sakmara zone,South Urals

This paper reports first isotope–geochemical data on the Early Devonian magmatic rocks of the Chanchar potassic mafic volcanoplutonic complex of the Sakmara zone of the South Urals. The incompatible element distribution and ratios indicate that the rocks of the volcanic, subvolcanic, and intrusive facies are comagmatic and were derived from a common source. The low HFSE concentrations relative to MORB and relatively low ⁸⁷Sr/⁸⁶Sr and high ¹⁴³Nd/¹⁴⁴Nd ratios suggest that primary melts were generated from a moderately depleted mantle. The LILE enrichment of the rocks indicates a flux of mantle fluid in the primary magma during its evolution.     

The Serpukhovian Stage in the Verkhnyaya Kardailovka section,South Urals

The paper describes a Serpukhovian Stage section, exposed along the Ural River near the village of Verkhnyaya Kardailovka (Bashkortostan). The section is uniquely complete and is proposed as a GSSP candidate for the base of the Serpukhovian. The Upper Visean and Serpukhovian beds are represented by relatively deep facies, which contain ammonoids, conodonts, ostracods, foraminifers, and other fossils. The section is described bed-by-bed and subdivided into zones based on four faunal groups. The lower boundary of the Serpukhovian is placed at the base of the Lochriea ziegleri conodont zone. The stratigraphic units are correlated with synchronous beds of the East European Platform, the Donets Basin, Western Europe, Central Asia, and North America.