Research subject. This article is devoted to the formation features of the Ural-Timan-Paleo-Asian segment of Eurasia. Materials and methods. The research was based on the authors’ data and those obtained following a review of available publications on the geology of segmentation. The Timan region was investigated using the geological information obtained by V.G. Olovyanishnikov.

Results. A geodynamic map of the Ural-Timan-Paleo-Asian segment with a scale of 1 : 2 500 000 was compiled, which allowed further research into the structure and formation of the north-western part of the Eurasian area. This part was found to be mostly composed of geodynamic associations of orogens, orogenic systems and orogenic belts of the Upper Proterozoic (Riphean) and Paleozoic time intervals, as well as by elements of the Mesozoic-Cenozoic neoplate. These processes were supplemented by the formation of tectonic systems of superimposed depressions and protoplate protrusions. The formation of orogens, orogenic systems and orogenic belts is associated with the development and subsequent transformation of paleooceanic basins under the conditions of accretion and collision. The terranes of the ancient continental crust also participated in the formation of the segment’s geodynamic elements, for which a typification scheme was proposed. The articles present new data on the formation conditions of the segment’s orogenic elements and the relationship of the orogeny with global reconstructions, including the problem of closing the surrounding oceanic space.

Research subject. The article sets out to investigate the change of the geodynamic regime from the island-arc type to the accretionary-collisional type in the Late Devonian–Early Carboniferous, which occurred as a result of 1) a collision between the Western part of the Magnitogorsk island arc and the Eastern margin of the East European continent and 2) its later coupling with the heterogeneous composite East Uralian terrain.

Materials and methods. The content of petrogenic elements and microelements in the rocks of the Late Paleozoic island-arc complexes of the Magnitogorsk island arc were determined using XRF and ICP MS methods at the Laboratory of Physicochemical Research Methods of the Institute of Geology and Geochemistry, Ural Branch of the Russian Academy of Sciences. In addition, available publications on the composition and formation conditions of these complexes were reviewed.

Results. It was found that, in the Late Devonian–Early Carboniferous period, the process of island-arc magmatism of the Magnitogorsk paleoarc was substituted with the formation of intraplate volcano-intrusive complexes. The island-arc magmageneration and its manifestations were controlled by a latitudinal linear zoning and different depths of formation of magmatic cameras, reflecting the self-consistency and spatial isolation of these events.

Conclusion. Due to the intensifying collision, melts from different mantle sources were mixing, thus contaminating the island-arc rocks by intraplate (plume-dependent) magmas. According to the composition and concentrations of high-field strength and fluid-mobile chemical elements, suprasubductional fluids played an important role in the evolution of late-island arc magmatic series.

Research subject. This paper presents original findings about textural-structural, mineralogical, petrological, and geochemical features of the garnet-amphibole miaskites (firstes) of the Ilmenogorsky miaskite massif.

Materials and methods. The microprobe analysis of mineral composition was performed using Tescan Vega3 sbu and REMMA202M scanning microscopes equipped with microanalyzers. The content of major, trace and rareearth elements (REE) in rock samples was determined by the methods of AAS and ICP-MS.

Results. The garnet-amphibole miaskites under study are characterized by a rare mineral paragenesis, i.e. garnet-amphibole-pyroxene-nepheline-plagioclase. The mafic minerals exhibit a high ferruginosity (f = 70–99), while the accessory minerals have high Al, F and low REE contents. The garnetamphibole miaskites contains high concentrations of Al, Fe³⁺, Ca, Na, Be, Rb, Mo, Tl and low concentrations of LILE, HFSE, REE and transit elements.

Conclusions. According to the garnet composition and its ferruginosity (f = 95– 99), high contents of Al and F in accessory minerals, the prevalence of Fe³⁺, as well as negative Eu/Eu* and positive Ce/ Ce* anomalies, the garnet-amphibole miaskites under study are assumed to be the product of acid-alkaline metasomatism occurring under the oxidizing conditions of petrogenesis. The low ratios of Cr/V and Ni/Co indicate the immobility of transit elements during metasomatism, and their clarke of concentration corresponds to the content in metaterrigenous and metacarbonate rocks, which suggests crustal substratum for garnet–amphibole miaskites. Garnet-amphibole miaskites are the markers of the interaction of crustal material with deep fluids, which occurred during the stage of shear tectonics development (270–240 Ma) due to the broad permeability of the rocks composing the Ilmenogorsky miaskite massif.

Research subject. This article focuses on the geological structure of the northern part of the Pai-Khoi carbonate parautochthone.

Materials and methods. The study was based on the data obtained on the key sections of the North-Western Pai-Khoi. Research methods included lithological and facies analysis, subsidence curves, reconstruction of the thermal maturity of deposits based on conodont alteration indexes, X-ray microtomography for determining porosity values.

Results. The Upper Devonian–Carboniferous succession (ca. 900 m thick) is composed of the terrigenous and carbonate Pyrkov Fm. (Frasnian), carbonate Lymbadyakha Fm. (Famennian-Tournaisian), Bolvanskii Fm. (Visean-Bashkirian), and Hoiponganase Fm. and Reef Chaika (Moskovian-Kasimovian). The early Frasnian part of the succession was deposited in a shallow-water environment. In the Middle–Late Frasnian, the Korotaikha paleodepression and an isolated carbonate platform was formed on the shelf edge. Filling of the paleodepression was completed at the end of the Early Visean. In the Late Visean–Late Carboniferous, a carbonate platform (ramp) formed. A Middle Paleozoic paleogeothermal gradient reconstructed on the basis of conodont alteration indexes is much higher in the Pai-Khoi carbonate parautochthone than in the most of Pechora Plate regions. This is likely to have been caused by the tectonic activity of the plate border in the Late Carboniferous–Mesozoic. A downward decrease in open porosity (from 6% to 0.1%) is likely to have been associated with increased compaction and recrystallization of the carbonates.

Conclusions. Famennian-Tournaisian carbonate formations of the Pai-Khoi carbonate parautochthone were deposited under the conditions of isolated platform environment; however, the Visean–Late Carboniferous deposits were formed in the outer ramp environment. The Late Devonian–Middle Carboniferous carbonate deposits of the Pai-Khoi parautochthone demonstrate an extremely low open porosity and a high thermal maturity. These properties, along with the pronounced faulting and folding of the rocks, significantly decrease petroleum-bearing prospects of these deposits.

Research subject. The Karabash ore district is a unique structural zone in the Ural folded system, formed at the joint of the Magnitogorsk and Tagil depressions. The uniqueness of this zone is associated with its specific formation conditions: a Paleozoic copper pyrite belt with a width of about 8 km was squeezed between two blocks of ancient metamorphic rocks. This zone features a classic copper-pyrite deposit represented by steeply dipping ore bodies, which were initially characterized by a gentle dip. Elucidation of the primary geological structure and tectonic evolution of the district presents a relevant research task.

Materials and methods. A geological cross section of the Karabash district was studied. Particular attention was paid to interactions between Paleozoic volcanic and sedimentary rocks and ultramafic bodies, whose age was determined by the method of zircon U–Pb dating.

Results. The age of ultramafic bodies in the Karabash district was found to be 430–440 million years. Serpentinite blend (mélange) zones having a width of 60m were discovered in the sites of contact between ultramafites and host rocks. Regularities in the location of these zones in the eastern and western parts of the district make them suitable horizon markers for constructing a geological cross section of the Karabash ore district.

Conclusions. It is established that the Karabash district is represented by a monocline synclinal fold formed by contraction of primary horizontal layers in the direction from east to west. The formation of the Zolotaya Gora golden deposit located in the eastern limb of the synclinal fold was associated with tectonic contraction processes.

Research subject. This article presents data on the age, material composition, petrogenetical and geochemical properties of morion-containing granites in the Etytei and Khamnigadai massifs of Central Transbaikalia.

Materials and methods. The composition of rock samples was investigated using the methods of chemical analysis, XRD and ICP-MS; the age was determined by the zircon U–Pb method using SHRIMP and LA-ICP-MS; the mineral composition was studied using an LEO-1430 electron microscope.

Results. The massifs composed of morion-containing granites belong to Early Jurassic (190–185 Ma) and form the peripheral area of the Early Mesozoic Khentei-Dauria magmatic region.

Conclusion. According to their petrochemical and mineralogical characteristics, the morion-containing granites under study differ from typical intra-plate granitoids and correspond to the “oxidized” A-type granites. The black smoky colour of quartz contained in granite samples is associated with a relatively high radioactivity of rocks caused by the presence of accessory thorium and uranium-containing minerals.

Research subject. The paper presents data on the mineralogical, geochemical and fluid inclusion features of the Southern Ak-Dag gold-sulphide-quartz ore occurrence in Western Tuva.

Methods. Mineral formation temperatures, salt composition and fluid salinity were examined using a Linkam TMS-600 cryostage and an Olympus BX 51 microscope. The chemical composition of samples was identified using a MIRA 3 LMU (Tescan Orsay Holding) scanning electron microscope equipped with INCA Energy 450+XMax 80 and INCA Wave 500 microanalysis systems; BSE photos were taken by Tescan Vega 3 and Hitachi ТМ-1000 SEM instruments.

Results. The ores under study were found to contain both high-grade and medium-grade gold with an Ag content of up to 17.05 wt %. The average gold fineness comprised 904 ‰, ranging from 830 to 928 ‰. According to fluid inclusion data, gold-sulphide-quartz veins were formed at temperatures of 280–240 °C and pressures of 0.8–1.2 kbar from aqueous fluids having a salinity of 8.6–6.4 wt % NaCl eq. The narrow range of fluid salinity at decreasing temperatures and the prevalence of high-grade gold in sulphide-quartz veins indicate a relatively high rate of mineral formation in a narrow permeable zone without any significant interaction with host rocks or mixing with meteoric waters.

Conclusions. Gold mineralization in the Southern Ak-Dag ore occurrence, which was formed within one ore substage, corresponds to the type of gold-galena-chalcopyrite with barite. The established similarity of native gold in the Southern Ak-Dag occurrence and other deposits in the Aldan-Maadyr ore cluster in terms of P-T parameters of ore formation and mineralogical and geochemical features, as well as association of the ore mineralization with beresites, indicate the possibility of discovering industrial ore deposits in the region and confirm its paragenetic relation with Devonian magmatic activity.

Research subject. In this paper, we investigate the possibility of recycling wastes from copper smelting facilities in brown mountain forest soils. The research object was “technical sand” obtained at the Sredneuralsky copper smelter as a byproduct. This finely dispersed material rich in copper, zinc and other chalcophilic elements undergo mechanical activation during crushing of the cast slag.

Materials and methods. Experiments were carried out in the southern taiga district of the Trans-Ural hilly-foothill province (Middle Urals) in autumn before snow cover. Two types of forest areas identified according to the genetic forest typology were investigated: cowberry shrub pine forest and berry pine forest with linden, both under trees and in clear-cutting areas. The experiments involved scattering 1kg of waste across 1m2 of experimental soil, packing such a sand in 100 g packages made of non-woven material and burying these packages in 3 experimental plots a depth of 7–10 cm. Following 2 years, the packages were retrieved and weighed. The microelement analysis of soil samples was carried out by the method of inductively coupled plasma mass-spectrometry using an Elan-9000 ICP mass-spectrometer at the Geoanalitik center of the Institute of Geology and Geochemistry, Ural Branch of RAS.

Results. It was found that, after 2 years of residing in the soil, copper smelting waste slag loses 11% of its mass. The majority of chalcophilic elements are involved in the biogeochemical cycle. The content of zinc, arsenic, cadmium and selenium varies most signfificantly. A difference in the degree of element migration from the “technical sand” to the brown mountain forest soil was observed for 2 forest types and clear-cutting areas. A single surface application of mineral waste (1 kg/m2 ) in autumn did not affect the qualitative composition of the grassy layer of all forest types and clear-cutting areas in the following spring–summer period.

Conclusion. The findings can be of interest for specialists developing new methods for recycling mineral wastes from copper smelters. Future research should analyse the distribution of components migrating from the “technical sand” along the soil profile of forest soils, as well as their involvement in biogeochemical cycles.

Research subject. The geological structure and evolution of the Earth’s continents.

Methods. This article is based on a long-term study and review of geological, geophysical and bathymetric published data, as well as on an analysis of the major geological discoveries of the 20th century.

Results and conclusions. It is established that all the continents on the Earth, except for Antarctica, constitute a single Northen megamaterik, which was being formed during a prolonged period of time (4.4 billion years) in a deep three-beam cavity on the surface of the peridotite mantle. The ancient Hadean– Archean basement of the megacontinent was being formed during the period of 3 billion years, which comprises about 70% of the Earth’s geological history. In the Late Proterozoic and Phanerozoic, periodically formed local depressions were flooded with sedimentary material leading to the formation of sedimentary basins and folded rock structures. As a result, the thickness of the megacontinent’s crust steadily increased reaching a large size of 15–40 or 60–70 km. During this period, the primary oceanic (peridotite) crust with a thickness of 3–5 km remained unchanged until the Mesozoic–Cenozoic, when it was covered with a layer of younger basalts and loose rock sediments with a thickness of 1–2 km.