Research subject. The structure of the pre-Paleozoic deposits and different-age Precambrian basement of the East European platform based on geological and geophysical data.

Aim. To trace the evolution of the area under study and to study the geodynamics of processes in order to reconstruct the paleostructure of the Baltica continent.

Materials and methods. The current state of the consolidated crust was studied using a geological interpretation of seismic profiling data (transects: “EB-1”, “Tatseys”, “Magnit”) and materials of gravity and geomagnetic surveys. The material composition of the basement rock complexes was studied based on drilling data.

Results. The Baltica continent forms the basement of the modern East European Platform. After the Sveconorwegian folding about 1000 Ma, Baltica had become part of the Rodinia supercontinent and merged with the North American platform. A passive continental margin with the Riphean-Vendian sedimentary cover was formed on the eastern Baltica edge. The Petrozavodsk-Khopersky orogen, which arose in the place of the Karelian (Early Proterozoic) Petrozavodsk-Khopersky paleoocean, was reconstructed. The submeridional suture was a result of this paleoocean closure. The orogen structure, as well as that of the paleocontinent Baltica, was disturbed and partially destroyed by subsequent tectonic processes, which continue at the present time with modern rifting.

Conclusions. The closure of the Petrozavodsko-Khopersky paleoocean led to the formation of the Baltica continent, which included three microcontinents – Sarmatia, Fennoscandia and Volga- Uralia. Baltica became part of the Rodinia supercontinent during the Sveconorwegian orogeny. Volga-Uralia was located on the border with the PaleoPacific and had a Late Riphean sedimentary cover of the Rodinia supercontinent. This margin underwent destruction during a collision with the Timanides. The scale and extent of the reconstructed Petrozavodsk-Khopersky orogen is comparable to Paleozoic orogenic belts, such as Cadomides, Caledonides, Variscides, or Timanides.

Research subject. Lower Pennsylvanian deposits exposed by mine excavations in the watershed part of South Timan.

Materials and methods. The research material included data obtained by a field description of sections and an optical microscopy analysis of rock samples (26 specimens). For micropaleontological analysis, oriented thin-sections (97 specimens) were additionally prepared. Trace fossil taxa were determined based on both field photographs and collected specimens. Four oriented rock samples were used to determine the phase composition of the clay fractions from diffraction patterns.

Results. The rocks of the Askynbashian (2.7 m), Tashastian (1.4 m), and Akavasian (2.5 m) Regional Stages of the Bashkirian Stage are exposed in the Ikhnitovyi quarry, and the Upper Vereiskian deposits of the Moscovian Stage (1.9 m) are exposed in the Vyemka section. The Ikhnitovyi quarry section exhibits a distinctly cyclic pattern. The cycle bases are distinguished by the appearance of coral and algae limestones, above which thin bedded fine-grained bioclastic and peloidal limestones occur. Greenish illite and chlorite clays indicate shallow sedimentation environments. The carbonate sediments experienced two cementation stages separated by the phase of compaction. The trace fossil assemblage recognized in the Ikhnitovyi quarry characterizes Cruziana ichnofacies. The Vyemka section is of particular interest due to the find of Eofusulina and the presence of typical carbonate tempestites.

Conclusions. The Bashkirian deposits were accumulated under quiet shallow-water conditions (coral and algae limestones), on low-gradient tidal flats (fine-grained grainstones), and under a low hydrodynamic activity (probably low-amplitude tides). The illite and chlorite clays identify the accumulation of aeolian material (clay paticles) in ponds.

Research subject. Ostracods and Givetian-Frasnian boundary deposits of the Timan-North Urals Region.

Materials and methods. The work was based on the results of studying ostracods from the stratotype sections of the Southern Timan, which are considered referential for regional and global correlations. The analysis of the distribution intervals of the most significant taxa was based on the results of previous studies, both published and archival materials on the Timan-Urals Region. Ostracods were considered in association with conodonts, which is an important criterion for applying a reasonable biostratigraphic subdivision. The use of different-scale regional cyclicity of sedimentation and individual “marking” levels of manifestation of global events were shown.

Results. The ostracod distribution in the Givetian-Frasnian boundary interval of the Timan-Northern Urals region was analyzed. The following most significant taxa were identified: Cavellina devoniana, Cavellina uchtensis, Cavellina batalinae, Cavellina chvorostanensis, Nodella faceta, Nodella ex gr. hamata. The correlation of established assemblages with ostracods from the Franco-Belgian basin was shown. The difference consists in the absence of a polyzygid assemblage with Polyzygia beckmanni beckmanni, which was established at the base of the Nismes Formation of Belgium near the historical boundary between the Givetian and Frasnian stages. The determined relationship of biostratigraphic data in combination with the transgressive-regressive sequence of sedimentation shows a more reasonable solution to the problem of the position of the lower boundary of the Frasnian stage of the Upper Devonian in the Timan-Northern Urals Region.

Conclusions. An updated version of the scheme of zonal subdivision of the Givetian-Franian boundary interval in the Timan- Northern Urals region has been developed, taking into account the ostracod distribution of the Cavellinidae and Nodellidae families, as well as the discrepancies in the levels of the first appearance of index species and the boundaries of zones in the regional stratigraphic scheme. The correlation of ostracod zones relative to the conodont scale is shown.

Research subject. Saussurite-amphibole rocks (metagabbroids) of the Bazhenov gabbro-hyperbasite massif (eastern sector of the Middle Urals).

Materials and methods. The material composition of metagabbroids and their mineralogy were studied in the analytical laboratories of the Institute of Geological Geology, Ural Branch, Russian Academy of Sciences (Ekaterinburg), Urals State Mining University (Ekaterinburg), Institute of Mineralogy, Ural Branch, Russian Academy of Sciences (Miass), Institute of Geology of Ore Deposits, Petrography, Mineralogy and Geochemistry, Russian Academy of Sciences (Moscow), and Moscow State University (Moscow). Isotope analyzes of zircon were performed on a SHRIMP-II ion microanalyzer at the Center for Isotope Research of VSEGEI (St.Petersburg).

Results. The metagabbroids under study feature the following mineral composition: clinozoisite (zoisite, epidote), magnesian hornblende (pargasite, tremolite), albite, clinochlore, and dolomite. According to petro-geochemistry data, saussurite-amphibole rocks were formed after gabbronorites and olivine gabbro-norites, belonging to the alpine-type formation of gabbro-hyperbasite complexes. U-Pb dating showed the ancient age of zircons from metagabbroids, most of the analyzes are grouped below the concordia line, forming a discordia line, the upper intersection of which with the concordia corresponds to the age of 1992 Ma. Two points on the diagram located below the concordia line, although not falling on the continuation of the discordia line, apparently reflect the influence of intermediate stages of metamorphism, and two points with concordant ages of 256 and 251 Ma record the time of the last tectono-thermal episode.

Conclusions. The formation of saussurite-amphibole rocks took place under the conditions of greenschist facies. In local areas of the massif, metamorphism reached the zeolite facies with signs of hydrothermal reworking. The primary gabbroids of the Bazhenov massif were most likely formed under the conditions of a suprasubduction basin. The age of zircons of about 2 Ga obtained by the U-Pb method indicates that the crystallization of the studied zircons occurred in the mantle rocks. It is not yet possible to unambiguously explain the presence of grains of these zircons in the metagabbroids of the Bazhenov massif; several possible explanations have been proposed. Zircons with the youngest age (256 and 251 Ma) were most likely formed as a result of metamorphic transformations under thermal influence from the nearby Aduy granite-leucogranite complex.

Research subject. Andesitic complexes of the Tondono caldera and Lokon-Empung volcano locate din the northeastern part of the Sulawesi Island (Indonesia).

Aim. To determine the petrogenesis conditions of andesites in the northeast Sulawesi Island based on detailed studies of volcanic rocks of the Tondono caldera and Lokon-Empung volcano.

Materials and methods. We studied volcanic rock samples collected by I.Yu. Safonova. To determine the petrogenesis conditions of andesites, conventional petrochemical, geochemical and mineralogical methods were used. Melt inclusions were also studied using a MIRA 3 LMU scanning microscope equipped with Aztec Energy XMax 80 system of microanalysis, and a Horiba LabRam HR800 Raman spectroscope. The PT-parameters of crystallization were estimated from the data on the composition of melt inclusions using approaches reported by K.D. Putirka, F. Yavuz and D.K. Yıldırım.

Results. The Sulawesi andesites represent tholeiitic and calc-alkaline island-arc magmas. Pyroxenes phenocrysts crystallized from melts that evolved with accumulation of alkalis and silica. Plagioclase phenocrysts crystallized from the felsic magmas, which are characterized by a decreasing role of alkalis. The composition of volcanic glass of the mesostasis suggests participation of felsic melts with a very high content of alkalis. The compositions of minerals and glasses in inclusions and in the mesostasis allowed us to estimate PT-parameters of the petrogenesis of the andesites. The phenocrysts of pyroxene crystallized in two intermediate magma chambers at depths of 27.6–14.6 and 11.3–7.2 km and temperatures ranging from 1150 to 970ºС. The phenocrysts of plagioclase crystallized at 930–910 and 900–890ºС. The microcrystals (laths) of plagioclase in the mesostasis crystallized at lower temperatures of 875–865 and 840–810ºС.

Conclusions. The andesites of the Sulawesi Island were derived from tholeiitic to calc-alkaline melts compositionally similar boninites. The compositions of the glasses in melt inclusions and mesostasis showed three types of compositionally different parental magmas, which produced the Sulawesi andesites. The phenocrysts of pyroxenes crystallized from these melts in two magma chambers at depths of 27.6 to 7.2 km and at temperatures of 1150 to 970ºС. The phenocrysts and laths of plagioclase crystallized at lower temperatures of 930 to 810ºС.

Research subject. The Lake Sabakty sediments core, as a source of data on the Holocene and Lateglacial environments in the Southern Urals.

Aim. To obtain a multiple regression model for quantitative reconstructions of the electrical conductivity of water based on the geochemistry of lake sediments and to reconstruct the Late Glacial and Holocene environments based on the study of the Lake Sabakty geochemical record.

Materials and methods. After determination of correlations between the content of chemical elements in lake sediments and hydrochemical parameters of 107 Ural lakes, multiple regression models were obtained. Reconstructions were performed based on the results obtained by accelerator mass spectrometry (AMS 14C), 210Pb activity determination, and an analysis of chemical elements and organic matter contents in the sediment core.

Results. Three multiple regression models using the concentrations of Na, Ca, Li, and Sr were obtained for electrical conductivity of water reconstruction. In the cold and dry Lateglacial (>12.0 ka cal BP), Lake Sabakty was a slightly brackish reservoir. During the transition from the Lateglacial to the Holocene (12–11.6 ka cal BP), the Lake Sabakty became more productive. In the Early (11.6–8.2 ka cal BP) and Middle (8.2–4.2 ka cal BP) Holocene, the electrical conductivity of water varied under the action of fluctuations in effective moisture. In the Late Holocene (4.2 ka cal BP – present), the Lake Sabakty became less saline due to an increase in effective moisture.

Conclusions. The proposed multiple regression models enable rapid quantitative reconstructions of the electrical conductivity of water, which are particularly relevant for Lateglacial–Early Holocene sediments with a low number of microfossils. The Lake Sabakty geochemical record reflects global and regional climatic fluctuations, being more informative compared to the geochemical records of forest lakes in the Southern Urals. The decrease in the electrical conductivity of water of Lake Sabakty of approximately 7.9 and 4.2 ka cal BP coincides with similar data for several other lakes in the Urals.

Research subject. Mineral associations, their chemical composition, and formation conditions of metasomatic rocks of the Voznesenskoye gold deposit located in the area of the Main Ural Fault in the Southern Urals.

Methods. The chemical composition of minerals was studied using a Tescan Vega Compact scanning electron microscope equipped with an Oxford Instruments Xplorer 15 energy-dispersive analyzer. The formation P-T parameters were estimated using a chlorite geothermometer and a dolomite-calcite geothermobarometer.

Results and conclusions. Two types of metasomatic rocks were identified: 1) propylites, which make up the outer zones of the metasomatic aureole, and 2) beresite-listvenites, common in its inner parts and hosting gold mineralization. The main propylite minerals were amphibole, orthoclase, albite, and ripidolite. Amphibole is represented by two generations, with the early generation comprising magnesian and actinolite hornblende and the late generation comprising actinolite. The crystallization temperature of ripidolite (307–313°С) corresponds to the temperature range of formation of propylites of the albite-actinolite facies. Beresite-listvenites (association: quartz, albite, chlorite, white mica, and carbonate) were formed at a temperature of 255–338°C and a pressure of 0.48–0.72 kbar. Gold ore mineralization was concentrated in the highest temperature zones of the halo of beresite-listvenite alterations. Such temperature conditions existed in dikes and their exocontact zones disturbed by ruptures. Light mica in beresite-listvenites is represented by sericite and phengite, and carbonate is a paragenesis of calcite and dolomite-ankerite. According to the composition and formation period, chlorite is differentiated into early ferruginous ripidolite and late pycnochlorite, depleted in Fe and enriched in Si, which is probably associated with a decrease in temperature during mineral formation and an increase in the activity of sulfide sulfur in the fluid. Along with an increase in the distance from the ore bodies, pycnochlorite exhibits greater contents of Si and lower contents of AlIV. The observed changes in the pycnochlorite composition are related to a decrease in temperature. The research results indicate the formation of the Voznesenskoye deposit under mesothermal conditions.

Research subject. Аndalusite- and kyanite-bearing (13–19 wt % Al2SiO5) rocks of the Teya metamorphic complex (Mayakon and Panimba areas), Yenisei Ridge.

Aim. To study the composition and mineral content of high-alumina rocks from the Panimba and Mayakon areas.

Materials and methods. Laboratory mineral processing was employed to estimate the mineral content of metamorphic rocks of the Teya complex using a magnetic and gravity separation at the Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences (Novosibirsk). The concentrates were obtained from typical samples of andalusite, kyanite, and andalusite-kyanite metapilites. After crushing and grinding, the rock samples were separated into size fractions <0.06, 0.06 ≤ x < 0.1 and 0.1 ≤ x < 0.25 mm. The concentrates were recovered from size fractions ≥0.06 mm. Phase, bulk rock, and trace element composition of the rock samples, mineral concentrates, and other fractions were analyzed using XRD, XRF, ICP-MS, and SEM.

Results. The magnetic product obtained at the first stage of mineral processing using magnetic separation accumalated staurolite, biotite, chlorite, ilmenite, pyrrhotite, and pyrite. At the second stage, light products containing quartz, feldspars, and muscovite were separated from non-magnetic products with CHBr3 using a centrifugal concentrator. At the last stage, using a double-knife separator, the heavy product from the previous beneficiation stage was separated into a “magnetic” raw concentrate (52–92 wt % Al2SiO5) and a “non-magnetic” final (70–97 wt % Al2SiO5) concentrate. The andalusite-kyanite concentrates (up to 97 wt % Al2SiO5) were obtained by the combination of cheapest and simplest methods of magnetic and gravity separation. The concentrates containing andalusite and kyanite with low recovery (0.7–6%) are comparable to the grade of kyanite-bearing ores of Karelia, the Kola Peninsula, and Gansu Province, China.

Conclusions. The study shows that high-quality andalusite and/or kyanite concentrates can be recovered from high-alumina metapelites of the Teya metamorphic complex.