Vol 25, No 3 (2025)
Articles
Petrographic features and provenance reconstruction of the Lower Riphean sandstones of the Mukun Group of the south-eastern Anabar shield
Abstract
Research subject. Lower Riphean terrigenous rocks of the Mukun Group of the East Anabar basin.Aim. Reconstruction of provenance, identification of petrographic features, and restoration of sedimentation environments of these terrigenousrocks.Materials and methods. The upper part of the Mukun Group section located in the lower reaches of the Bolshaya Kuonamka River (southeast of the Anabar Shield) was studied, as well as a set of Lower Riphean sandstone samples of the same level. Reconstruction of provenance and formation environments of terrigenous rocks was based on U-Pb dating of detrital zircons, as well as field observations and study of the mineral composition of these rocks using petrographic, X-ray phase and X-ray spectral analyses.Results. The studied sandstones are characterized by a bimodal granulometric composition (sand-siltstone), dominated by angular grains of potassium feldspar with intense secondary alterations, as well as medium and well-rounded grains of quartz and zircon. The U-Pb dating of detrital zircon (69 grains) showed the presence of several different-aged provenances, represented by igneous and metamorphic rocks, the age of which corresponds to the main peaks of the dating distribution spectrum: 1965±5, 2095 ± 14, 2750 ± 7, and 2891 ± 9 Ma (weighted average).Conclusions. The deposition of Lower Riphean terrigenous rocks of the Mukun Group of the East Anabar Basin occurred in a shallow, calm environment during the erosion of a stable continental block of local origin. The most representative (more than 50%) is the age cluster of detrital zircon ~1965 Ma, which reflects the widespread occurrence of Proterozoic regional granulite metamorphism rocks on the Anabar Shield. In addition to metamorphosed Archean-Proterozoic rocks, the following igneous complexes might have been the source of zircon: Archean Anabar enderbite-charnockite-migmatite and Proterozoic Magan alaskite-leucogranite-migmatite together with Billyakh granodiorite-granitegranosyenite. The absence of detrital zircon younger than 1890 Ma in the studied sandstone indicates different provinces for the West and East Anabar sedimentation basins.
Lithosphere (Russia). 2025;25(3):373-397
373-397
Distribution features of carbon isotopes in carbonates on the example of the Sartiu Formation (Lower Carboniferous, Vorkuta Uplift)
Abstract
Research subject. The carbon and oxygen isotope composition of rock carbonates and brachiopod shells in the section of the upper part of the Sartiu Formation (Mississippian, Vorkuta uplift).Aim. Comparative evaluation of isotopic signal preservation in brachiopod shells and host rock on the example of strongly secondary altered sediments.Methods. Data on foraminifera, conodonts, and brachiopods formed the stratigraphic framework. Carbon and oxygen isotope analyses of carbonates of brachiopod shells and host rock, accompanied by screening tests, were determined for 76 samples from 35 levels within the upper part of the Serpukhovian Stage. Data on carbonate recrystallisation, organic carbon content, carbon-oxygen isotope ratio, cathodoluminescence, and taxonomic affiliation of brachiopods were used for screening.Results. The data on carbon isotope composition showed significant differences in isotopic signals in brachiopod shells and in the host rock. The lower part of the section (approximately 4.3 m) is characterized by a heavying of the carbon isotopic composition of the shell material from 2.0 to 4.1‰. Higher up the section (next 2.5 m), a sharp increase in δ13C up to 7.3‰ is observed (sample with Davidsonina carbonaria) followed by a decrease to 3.4‰ and then a scatter of values from 1.2 to 6‰ in the uppermost part. At the same time, the carbon isotope composition of limestones shows rather stable values along the entire section (from –0.2 to 2.6‰, mean value 1.0‰), showing a slight negative trend towards the upper part. According to the screening tests, all limestone samples show a highly altered signal by secondary processes; however, brachiopod shell carbonate is assumed to have a near-primary isotopic composition. At the same time, the isotopic composition of brachiopod shells strongly depends on taxonomic affiliation. In representatives of the Davidsonina genus, a significant (by 4–6‰) heavying of the carbon isotopic composition was noted. The average δ18O values of limestones are 21.3‰ SMOW (corresponding to –9.3‰ PDB) and brachiopod shells 22.2‰ (corresponding to –8.4‰ PDB), which rules out the primary nature of oxygen isotopic composition.Conclusions. The studied material showed good preservation of the isotopic signal in brachiopod shells even in the case of significant recrystallisation of the host carbonates. The significant vital effect characteristic of representatives of the Davidsonina genus makes it difficult to use isotopic data obtained from these brachiopod shells for the purposes of isotopic stratigraphy. For correct isotopestratigraphic interpretation of variations in carbon isotope composition in sections, taxonomically homogeneous samples within at least one genus should be studied.
Lithosphere (Russia). 2025;25(3):398-418
398-418
Composition, structure, formation environment of the Yaptikshor deposits of the Shezhim facies complex (Upper Katian, Ilych River, Northern Urals)
Abstract
Research subject. The section of the Upper Katian deposits of the Shezhim facies complex, exposed on the Bol’shaya Kos’yu River (a right tributary of the Ilych River, Northern Urals), exhibits a total thickness of 42.3 metres. The factual material is represented by a collection of more than 60 rock samples, 100 thin sections, and 10 slabs.Aim. Reconstruction of the sedimentation conditions of the Upper Katian deposits of the Shezhym facies complex.Methods. Standard lithological and paleontological methods of studying the section were used to dissect the section. Sampling was carried out after no more than 1 m. The sections were studied by the classical optical microscopic method.Results. The Upper Katian deposits are characterized by numerous remnants of conodont and shell fauna, including the zonal brachiopod species Proconchidium cf. muensteri (St. Joseph), exhibiting a highly heterogeneous lithological composition. At the base, there lies a pack of bioclastic algal-crinoid limestones, which are replaced with tectonic contact by limestone mixed-grained sandstones and limestone block breccias upward the section. Above, they overlap with layered bioclastic limestones with numerous fauna typical of this age range and widespread within the Timan-North Ural region.Conclusions. According to the stratigraphic position and faunal characteristics, the Upper Katian deposits are reliably correlated with the stratotype of the Yaptikshor formation of the Subpolar Urals. Established on the basis of studying a variety of sections of the Northern, Subpolar, Polar Urals, and Chernyshev Ridge, the transformation of the outer margin of the Pechora Plate from rimmed platform in the Middle Katian to an open platform and to a ramp in the Late Katian (Yaptikshor Time) can also be traced in the section on the Bol’shaya Kos’yu River. The deposits characterize the shift of sedimentation conditions from shallow to deeper ones, which corresponds to the transgressive stage of the sedimentary basin development. The section on the Kosyu River differs from the stratotype of the Yaptikshor Formation by the significant presence of lithoclastic limestone differences, which were most likely formed as a result of the manifestation of tectonic activity of the Pechora Plate. This fact reflects the regional features of the North Ural margin of the carbonate platform, due to its block structure and different intensity of tectonic processes.
Lithosphere (Russia). 2025;25(3):419-437
419-437
First data on the carbon isotope composition of conodont elements from the Middle Permian (Kazanian Stage) of the Tchimbulat section (Vyatka Dislocations, Volga-Ural Anteclise)
Abstract
Research subject. Carbon isotope composition of conodont elements of Middle Permian age from the section of the Nemda Formation in the Chimbulat quarry.Aim. Paleoecological interpretation of data on the carbon isotope composition of conodont elements from Early Kazanian deposits of the Volga-Vyatska region.Materials and Methods. Carbon isotope composition was studied in 11 conodont elements of the Stepanovites, Sweetina, and Kamagnathus genera from 9 samples. The samples characterize the Kamagnathus khalimbadzhae regional conodont zone.Results. The average carbon isotopic composition of conodont elements in the studied samples was –27.3‰, which is lower than the average value for the Devonian-Carboniferous interval of the palaeotropical realm (–26.7‰) and similar to the isotopic composition of conodonts from biohermal and near-biohermal facies of the Middle Carboniferous of Pai-Khoi. Judging by the relatively light carbon isotopic composition, the Middle Permian Stepanovites–Sweetina group probably occupied the trophic position of primary consumers. The relation of the isotopic composition of conodonts and host carbonates allow us to reconstruct the low to moderate pelagic primary bioproductivity of the Early Kazanian basin in the Volga-Vyatka region. According to the obtained data, a negative trend in the change of carbon isotope composition of conodont elements in the Late DevonianMiddle Permian interval was noted. This trend coincides with the decrease in carbon dioxide content in the atmosphere. The δ13C of conodonts could be related to the atmospheric carbon dioxide content through the intensity of carbon isotope fractionation by phytoplankton.Conclusions. The relatively low pelagic primary bioproductivity of the Early Kazanian marine basin in the Volga-Vyatka region was reconstructed. Conodonts of the Stepanovites–Sweetina group in the pelagic trophic network of the Kazanian basin occupied the position of primary consumers feeding on phytoplankton with a light carbon isotope composition. This light carbon isotope composition may have been caused by a relatively low phytoplankton growth rate and, indirectly, with a low atmospheric carbon dioxide content in the Early Kazanian time. The assumed dependence of δ13C of Prioniodinida conodonts on the atmospheric carbon dioxide content can be used for approximate estimation of carbon dioxide content variations for some stratigraphic intervals.
Lithosphere (Russia). 2025;25(3):438-450
438-450
Bacterial hydrocarbon seepage structures with a cone-in-cone texture in the rocks of the Taurian series of the Mountain Crimea (South Coast of Crimea)
Abstract
Research subject. Paleogeographic conditions for the formation of structures with cone-to-cone textures by living organisms.Methods. The morphology of polished sections was studied using an Olympus BX 5 microscope equipped with an Olympus DP 12 camera. Geochemical analysis was performed using an ICP ELAN 9000 (Perkin Elmer). Carbon isotope composition was determined by mass spectrometry on a Deltaplus Advantage device.Results. The structures were formed on solid ground. They had several growth phases. The tree-like skeleton of the cone-to-cone structures has a modular structure. Micron-thick laminae extended from its walls. They formed rolls of cones, fused petals with a corrugated surface. The upper surface of the structures is covered with lamina petals and calcite spherulites. Their mineral composition is represented by columnar anthraconite with the presence of rhodochrosite, quartz, and pyrite framboids. The isotopic composition of carbon in carbonate structures varied from –19.14 to –13.59‰, and that of its biogenic material δ13С = –36.64‰. The relationship between carbonate formation and chemosynthesis of archaea and prokaryotes is indicated by the results of carbon isotope composition, δ13C isotope difference between carbonate and biogenic matter, presence of carbonate spherulites, pyrite framboids, biomarkers, light and heavy oil. High contents of lithophile, chalcophile, rare earth elements in the material of the structures, as well as the isotope composition of sulfur (+11.28; +1.72‰), carbon (from –19.14 to –13.59‰) and oxygen (from –14.52 to –13.45‰) confirm the use of deep volcanic fluids by living organisms.Conclusions. Structures with cone-to-cone textures were created by protozoa in symbiosis with prokaryotes and archaea, which processed hydrocarbon volcanic fluids into organic matter and carbonate. The presence of large fauna near the biocenosis structures and other features allow us to attribute the cone-to-cone formations to ancient hydrocarbon seepage carbonates or Triassic methane-liths. Postmagmatic hydrocarbon fluids, which have fed the microorganisms, have a deep genesis.
Lithosphere (Russia). 2025;25(3):451-470
451-470
As-P-REE-bearing zircon in granitic pegmatites of the axial zone of the Polar Urals
Abstract
Research subject. Zircon with high contents of P, Y, REE, and As from altered granitic pegmatites forming veins cutting through the amphibolites of the Kharbey metamorphic complex (Polar Urals). Aim. To study the morphological features, internal structure, and chemical composition of zircon, as well as to establish the mechanism of its formation.Methods. The study of zircon was carried out under binoculars, electron microscopes, and a Raman spectrometer. The internal structure of the mineral was analyzed using images obtained in the BSE and CL modes.Results. In granite pegmatites, i.e., biotite-quartz-oligoclase and biotite-microcline-quartz-oligoclase rocks with a high content of Na2O (about 6 wt %), two morphological types of zircon were identified – prismatic pink and long prismatic brown. Prismatic pink varieties have an internal structure and composition characteristic of “classical zircon”, having crystallized from a magmatic melt at temperatures of 700–750°C. In individual cases, such crystals are overgrown with a thin rim of zircon, which has a dark color in CL images with an increased content of Ca, Al, Fe, Na, P, Y, REE, and As. Brown zircons are characterized by growth areas and those with uneven blocky, mosaic, and porous structures that appear dark in CL images. The darkest areas of the mineral (in images in CL and BSE modes) show increased concentrations of P2O5 (up to 6 wt %), Y2O3 (up to 9 wt %), UO2 (up to 4 wt %), ThO2 (up to 3 wt %), REE, FeO (up to 3 wt %), Al2O3 (up to 3 wt %), CaO (up to 3 wt %), and Na2O (up to 1 wt %), with the degree of disorder of the mineral structure (metamictity) increasing. The above elements, as well as, apparently, the hydroxyl group, are included in the structure of zircon according to complex substitution patterns. Crystallization of this type of zircon and the mineral that forms rims around zircon of the first type occurred at the post-magmatic stage of transformation of granites from hydrothermal fluid of high alkalinity at temperatures of 550–600°C. Zircon was subjected to repeated changes under the influence of solutions according to the principle of dissolution–redeposition, which occurred under a decrease in temperatures down to 240–330°C. As a result, zircon acquired a spongy structure, in the pores of which hydrothermal minerals were formed – arsenic pyrite, quartz, monazite, xenotime, chernovite, ankerite, albite, etc.Conclusions. In the granitic pegmatites that form synmetamorphic veins in the amphibolites of the central area of the Kharbei metamorphic complex, three types of zircon are observed: magmatic (zircon of the first type), hydrothermal, and hydrothermally altered (zircon of the second type), differing in morphological features, internal structure, and composition. Judging by the chemical composition of hydrothermal minerals in the rocks, post-magmatic solutions were enriched in Na, P, As, and REE.
Lithosphere (Russia). 2025;25(3):471-484
471-484
High-pressure metamorphism in the area of the Main Ural fault in the Severnaya Sosva River basin (Northern Urals)
Abstract
Research subject. Metamorphic rocks of the Khomasya formation of the Lower-Middle Ordovician in the Northern Urals (the basin of the Severnaya Sosva River) in the area of the Main Ural fault (GUR) were studied.Aim. Reconstruction of the formation environment of methamorphic rocks.Materials and Methods. Geochemical and petrological-mineralogical studies were performed, along with geothermobarometry coupled with mineral formation modeling.Results. The geochemical features of the basalts of the Khomasya formation rocks indicate an enriched mantle source. The spatial association of metabasalts with arkose, quartz sandstones, and siltstones suggests that the accumulation of strata occurred during the transition from continental rifting to oceanic spreading, and that the structure under study is a fragment of an Early Paleozoic passive volcanic continental margin. Against the background of widespread metamorphism of the facies of green shales, zones of glaucophane-containing rocks are mapped near the GUR, and garnet-containing chlorite-epidote-amphibole-muscovite-quartz-albite shales are observed in tectonic lenses. Amphiboles in the GUR area are represented by actinolites, vinchites, barroisites, glaucophanes, and magnesian hornblende; garnets demonstrate a progressive (direct) zonality. White micas are represented by phengites, and sometimes there are relics of paragonite in the inner zones of garnet crystals. Garnet-containing rocks were formed at pressures not lower than 7–8 kbar and at temperatures up to ~ 600°C.Conclusions. It is assumed that the mineral composition of rocks and the thermodynamic regime of their formation correspond to the geodynamic regime of subduction (granite-free glaucophane shales) followed by a transition to the collision regime (paragenesis with garnet, actinolite, and hornblende), which agrees with the results of isotope dating of rocks and the revealed P-T parameters of their metamorphism.
Lithosphere (Russia). 2025;25(3):485-505
485-505
First results of U-Pb dating of detrital zircon from terrigenous rocks of the Obeiz Formation of the Subpolar Urals: isotope age and possible provenance sources
Abstract
Research subject. Lower Paleozoic terrigenous deposits of the northern part of the Lyapin anticlinorium in the Subpolar Urals.Materials and methods. From the quartzite sandstones of the Obeiz Formation, which lies in the lower part of the Paleozoic section of the area under consideration, a monofraction of detrital zircon grains was isolated and their optical and isotope-geochronological U-Pb (LA-SF-ICP-MS) studies were carried out.Results. The analysis of the distribution of age values of zircon grains, taking into account their morphological features, revealed the internal structure and geochemical characteristics, the presence of four age populations of this mineral. Probable sources of the removal of terrigenous material were shown, and the age of formation of the Obeiz Formation was clarified.Conclusions. According to the available paleontological (for the overlying sediments) and newly obtained isotope-geochronological data, the Obeiz Formation is of Early Ordovician (Tremadocian-Floian). Clastic material entered the sedimentation area mainly from local sources of sediment, i.e., nearby massifs of granites and granodiorites. The source of redeposited clastic material was mainly the underlying terrigenous sediments of the Moroi Formation (RF3) and Alkesvozh Formation (Є3-O1).
Lithosphere (Russia). 2025;25(3):506-520
506-520
Typomorphic features of platinum group minerals from alluvium of the Kytlym platinum-bearing cluster (North Ural), Russia
Abstract
Research subject. The article presents the results of an integrated study of platinum group minerals from platinum-bearing alluvial placers of the river Kosva, draining the Kytlym concentrically zonal ultramafic massif (Northern Urals) and its southern tributary stream Bogaty Log.Materials and methods. Materials were sampled during the fieldwork of 1990–1991. The chemical composition and structural and textural features of platinum group minerals were determined using ore (AxioScope.A1) and scanning electron (MIRA 3 LMU with an INCA Energy 450 XMax 80 microanalysis system) microscopy.Results. Platinum group minerals in placers of the river Kosva and stream Bogaty Log are represented by Pt-Fe(±Cu) alloys, which correspond to isoferroplatinum and ferroan platinum with inclusions of Os-Ir-(Ru) intermetallic compounds, laurite, and irarsite. Most grains of platinum group minerals were subject to postmagmatic alteration, which manifested itself in the formation of replacement rims of a tetraferroplatinum–thulaminite composition. Among the secondary platinum group minerals, the authors encountered a mineral phase – unnamed intermetallic compound of rhodium, copper, palladium, and tin (Rh,Cu,Pd,Pt)3Sn that has not been previously described in nature.Conclusions. The main sources of platinum-bearing placers are ultramafic complexes of the Kytlym concentrically zonal ultramafic massif, primarily chromitites from eroded serpentinized dunites. The grains of platinum group minerals do not bear traces of hypergene chemical alteration and completely inherit the composition of platinum mineralization from the primary sources that feed the placers. The influence of intermediate pre-Quaternary reservoirs on the formation of the studied platinum placers is minimal.
Lithosphere (Russia). 2025;25(3):521-545
521-545
Material composition and formation conditions of the Yubryshka titanium-magnetite ore deposit
Abstract
Research subject. The Yubryshka intrusion with titanomagnetite mineralization.Materials and methods. Research materials included rock and ore samples from the Yubryshka intrusion. The concentration of major oxides was determined by X-ray fluorescence at the Institute of Geology, UFIC RAS (Ufa), on a VRA-30 spectrometer (Carl Zeiss, Germany) using an X-ray tube with a W-anode (30 kV, 40 mA). The mineralogy study was carried out using a Tescan Vega Compact scanning electron microscope equipped with an Xplorer Oxford Instruments energy-dispersive analyzer (IG UFITs RAS, Ufa).Results and conclusions. The petrochemical analysis indicated the isochemical nature of metamorphism in the rocks of the Yubryshka intrusion. In comparison with the rocks of the Kusa-Kopan complex, the Yubryshka analogues are characterized by a lower degree of differentiation, consisting in the absence of varieties of extreme basicity. Clinopyroxene, amphibole, epidote, fluorapatite, titanite, micas, chlorite, barite, zircon, ore minerals (sulfides, oxides) are described with a varying degree of detail. The genetic conditions for the formation of amphibole from the Yubryshka deposit were found to characterize the metamorphic history of rock transformation, being directed from igneous amphibole (T ≈ 800°C, P ≈ 3.2 kbar) to metamorphogenic amphibole (T ≥ 550°C, P ≈ 7 kbar) with temperature stabilization when pressures decrease to > 3 kbar. The calculations established that the decomposition temperature of ilmenite–titanomagnetite aggregates ranges within 559–375°С. In this case, elements of zoning are observed when re-equilibration of the system in the edge parts of the crystals occurs at lower temperatures. The simulation of the crystallization process using the COMAGMAT software found that changes in the chemical composition of the melt are implemented through the filter-pressing mechanism. The formation of the ore horizon was caused by a mass crystallization of magnetite together with clinopyroxene and plagioclase at a temperature of 1097°С. This model satisfactorily describes the observed structure of the ore horizon, namely, its location in the upper part of the intrusive body and the disseminated nature of the ores.
Lithosphere (Russia). 2025;25(3):546-571
546-571
Bakayskoe gold occurrence (Southern Urals): Ore mineralogy and formation conditions
Abstract
Research subject. In morphological terms, the Bakayskoe gold occurrence comprises an area of fracture and crushing of sublatitudinal strike in the granitoids of the Turgoyak massif (C1-2), which contains quartz veins with sulfide mineralization. The vein zone is about 1.5 km in length. The Turgoyak massif is located on the border of the Magnitogorsk and Central Ural areas, being a satellite of the Syrostan massif.Materials and methods. Samples collected in old workings and ore stockpiles were studied by optical and SEM microscopy. Fluid inclusions in vein quartz were studied by thermoscryometry.Results. The predominant ore minerals were found to be pyrite and galena; rarely, the ores contain chalcopyrite, tetrahedrite, sphalerite, sulfosalts, and bismuth sulfotellurides. In the studied samples, gold is present as both native gold (primary and supergene), and tellurides and sulfides. Ores are partly oxidized. The average and median values of the homogenization temperature (Tg) of primary and primary-secondary inclusions from ore quartz are about 242– 247°C. The average and median Tg of quartz from shale is slightly lower (222 and 215°C, respectively), with a significant scatter of values. The concentration of salts in NaCl equivalent, determined by the melting point of the last ice crystal, varies from 1.4 to 13.0 wt % in FI from the host shales and 0.2–5.6 wt % in ore quartz. Such wide variations in salinity in all the studied cases may indicate changes in FI by secondary processes.
Lithosphere (Russia). 2025;25(3):572-594
572-594
Spheroidal formations of ore and non-metallic matter in nature and experiment
Abstract
Research subject. Spheroidal formations from technogenic placers, paleoplacers, and granitoids of the Nizhneselemdzhinsky gold-bearing node; from the placer of the Urkimi gold-bearing node; spheroidal nano-sized gold of the Oktyabrsky gold-bearing node; gold balls resulted from experiments on the concentration and consolidation of precious metals; as well as metallosilicate spheroids from the gastrointestinal tract of the flat sea urchin.Methods. Spheroids were studied by raster electron microscopy; their composition was determined using atomic absorption spectrometry.Results. The mor phology and chemical composition of spheroids were studied. The following types were established: metal spheroids – gold, lead, iron, spheroids consisting of Fe-based alloys; metal-alloyed (Sb); metal oxides (Fe, O) and (Cu, O); silicates (Si, O) and metalolylic (Ag and others, Si, О). Depending on the environment in which the studied spheroids were formed, different factors determined the formation of round forms of mineral matter, including the following. (1) Gas metamorphism – natural hydrothermal-metallurgical process leading to the formation of spherical forms of minerals. (2) Cluster formation of aggregated (polycrystalline) balls under conditions of an unbalanced process of self-organization of particles of matter. (3) Geochemical barriers that became the centers of origin of spheroid nanoparticles. (4) Secondary processes affecting the surface layer of the spheroid particles after the formation of their main composition: (a) hypergenesis leading to the destruction of some and formation of other minerals and (b) mechanical processing of hard materials in the splits. (5) Non-equilibrium biogenesis (for bio-organisms).
Lithosphere (Russia). 2025;25(3):595-618
595-618
Bulan gold-sulfide-quartz ore deposit of the Makarovsky ore cluster (Western Sayan, Russia): Mineralogical and geochemical features, formation conditions, and fluid sources
Abstract
Research subject. Mineralogical and geochemical features and formation conditions of the Bulan gold-sulfide-quartz ore occurrence of the Makarov ore cluster in the Western Sayan.Methods. A Linkam TMS-600 thermostage and Olympus BX 51 optical microscope were used to determine temperatures, compositions, and fluid salinities in inclusions of mineral- forming fluid in quartz of gold-sulfide-quartz veins (SUSU, Miass, analyst Natalia N. Ankusheva). The chemical composition of gold was determined by SEM Hitachi TM-1000 (TuvIENR SB RAS, Kyzyl, analyst Renat V. Kuzhuget).Results. The conducted mineralogical and geochemical studies determined that gold formation at the Bulan ore field was single-stage in the form of gold-sulfide-quartz veins and veins with pyrite, chalcopyrite, arsenopyrite, pyrrhotite, as well as rare isolations of galena, fahlore, gold, and electrum. The results of fluid inclusion study from gold-sulfide-quartz veins showed that they were formed in the temperature range 170–230°C due to a weakly to moderately saline (3.5–6.8 wt % NaCl eq.) magmatic fluid of the K-Na-Mg±Fe-chloride composition. The stable range of fluid salinity and the narrow range of δ18O indicate a single magmatic source and insignificant influence of host rocks and meteoric waters. Conclusions. According to mineralogical and geochemical features and PT parameters, the Bulan ore occurrence is similar to low-sulfide deposits of gold-sulfide-quartz berezite-listvenite formation.
Lithosphere (Russia). 2025;25(3):619-632
619-632
Capabilities of geophysical methods in identification of potential gold-bearing structural karst zones in the Urals
Abstract
Research object. The results of geophysical works in the periphery of the Krasnoturyinsk ore cluster to assess the prospects of discovering gold-bearing placers in structural weathering crusts and karst formations. The structural-erosional-karst placers of the Mesozoic age in the Urals are characterized. Basic information about the geology and minerals of the Turinsko-Auerbakhovsky ore region is provided.Research methods. A set of geophysical methods was used, including gravimetry, magnetometry, electroprofiling by radio interferometry, and audiomagnetotelluric sounding. The methodological foundations of field observations and the principles of office processing and interpretation of the obtained data are described.Results. For the area under study, maps of absolute elevations of the day surface, gravitational and magnetic fields, as well as a map of apparent resistivity are presented. Transformed sections of the electrophysical parameters of the medium are constructed based on the results of processing the audiomagnetotelluric sounding data. The obtained sections are compared with the graphs of potential fields for the studied profiles. Characteristic features of geophysical fields and parameters for identifying the structural elements associated with predicted mineralization are discussed.Conclusion. The main geophysical criterion for the detection of a contact-karst weathering crust, promising in terms of gold content, is assumed to be a synchronous decrease in the values of gravitational field and electrical resistance. A stepwise shift of the magnetic field level may serve as an additional sign. Areal geophysical surveys are not sufficient for identification of deep karst traps. Due to the complex shape of karst cavities, the correct location of exploration wells can only be determined based on the results of electromagnetic soundings.
Lithosphere (Russia). 2025;25(3):633-643
633-643
Application of geoacoustic emission and electromagnetic radiation in combination with standard geophysical research methods to identify geodynamic activity areas in ore boreholes
Abstract
Research subject. Borehole 1 of the Severo-Taratashsky site (Middle Urals) and borehole 2 of the Vostochno-Tarutinsky deposit (Southern Urals). The lithological section of borehole 1 is composed mainly of gneisses with thin interlayers of dolerites, quartzites, gabbro, and magnetite quartzites. The lithological section of borehole 2 is represented by diorite porphyrite, skarn, propylite, and metasomatites. Sulfide and magnetite mineralization with different contents of ore components is observed throughout the section.Aim. Identification of geodynamic activity areas in rocks by measuring geo-acoustic emission signals and electromagnetic radiation in combination with standard methods of geophysical borehole surveying.Methods. Calculation and analysis of Pearson correlation coefficients for parameters of geoacoustic emission, electromagnetic radiation, and parameters of a standard set of geophysical studies. Comparison of diagrams of measured parameters taking into account significant correlation coefficients and the lithological structure of the studied wells. Results. The correlation coefficients between the parameters of electromagnetic radiation and geoacoustic emission, apparent electrical resistance, self-polarization potentials, magnetic susceptibility, caliper measurements, and natural radioactivity of rocks were calculated. In boreholes 1 and 2, geodynamic activity areas were identified in mineralization intervals and along ore-host rock contacts. A qualitative assessment of the geodynamic activity of the boreholes was givenConclusions. Geodynamic activity areas of rocks are manifested in the fields of geoacoustic emission and electromagnetic radiation in a wide range of frequencies. The use of logging of geoacoustic emission and electromagnetic radiation in combination with standard methods of geophysical borehole surveying allows not only lithological dissection of the borehole section, but also identification of areas of rock disturbance and fracturing.
Lithosphere (Russia). 2025;25(3):644-655
644-655
Features of the seismic process prior to a catastrophic earthquake in the area of the East Anatolian fault (February 6, 2023, MW = 7.8)
Abstract
Research subject. The seismic process in the area of the East Anatolian Fault (EAF), where two catastrophic earthquakes (doublet) occurred in February 2023.Aim. Identification of specific features of the seismic process, which might indicate a connection (or a lack thereof) between the two earthquakes from the doublet, as well as the presence of any predictive signs before seismic events (medium- or short-term).Materials and methods. An analysis of seismic activity graphs constructed by summing periods between earthquakes based on a local seismic catalog.Results. Activity graphs were plotted for six regions at the epicenter of the first earthquake. Characteristic periods with a constant velocity of the seismic process and transition points were established. Local activations were detected in 2012 and 2022, which are confined to the epicenters of the doublet and are dominant for the EAF as a whole (for at least 300 km). All activations were timed to the same area slightly east of the epicenter of the February earthquake. It is shown that these activations do not correspond to the standard scheme of operation of a seismic center, i.e., they do not have an unambiguously determined main event and a characteristic aftershock process.Conclusions. According to the distribution of earthquake epicenters, the local activation of 2012 was probably the initial stage in the development of the process, which was continued in 2022. The abrupt process of activity in 2022 ended 40 days prior to the earthquake doublet, and can be considered as a short-term predictive sign. The main characteristics of such a short-term anomaly in seismic activity are a reduction in the duration of each subsequent activation and a decrease in the time between them.
Lithosphere (Russia). 2025;25(3):656-663
656-663
Combined application of land seismic methods in engineering research
Abstract
Research subject. The upper part of a geological section (low-velocity layer).Aim. To demonstrate the feasibility of combining two seismic methods (active and passive) for determining the depth of bedrock roof and the presence of structural changes in the soil layer.Materials and methods. Geophysical methods in engineering studies are faced, as a rule, with the task of determining the depth and relief of rock occurrence. This task, although not being the sole one, is of particular importance. Among the variety of geophysical methods, seismic methods are the most informative and mobile. In this article, we compare the results of a combined application of the methods of refracted waves and microseismic sounding in different geological conditions. These are two basically different land seismic methods. The former method is active and has a source of elastic vibrations. The latter method is passive and records natural- and artificial-origin surrounding background microtremor. At each of the sites under study, one profile was selected, on which sections were built along P-waves Vp and S-waves Vs. The microtremor was recorded at several points, along with calculation of the spectral power density of the displacement rate and the spectral ratio curve. Given the rate of shear waves in the loose layer, a conversion formula from the frequency domain (Nakamura transfer characteristic) to depth is used. Thus, at the observational points of microseisms, the depth of boundaries contrasting in acoustic rigidity can be calculated and traced.Results. On the example of different soil conditions, the correlation between velocity cross-sections and Nakamura microseism results is shown.Conclusions. The combination of the classical refracted wave method and microseismic sounding provides a more detailed information on the structural features of the upper part of a geological section.
Lithosphere (Russia). 2025;25(3):664-673
664-673
Mineralogy of copper slags of Ekaterinburg Metallurgical Plant
Abstract
Research subject. Copper slags of Ekaterinburg Metallurgical Plant, founded in 1723 and discontinued in 1808.Materials and methods. Copper slags were collected from an archaeological excavation site in the Historical Square of Ekaterinburg. The material composition of the slags was studied in the Laboratory of Physical and Chemical Research Methods of the Institute of Geology and Geochemistry of the Ural Branch of the Russian Academy of Sciences (Ekaterinburg). The chemical composition of minerals and their photographs were taken using a TESCAN MIRA LMS, S6123 scanning electron microscope with an INCA Energy 450 X-Max 80 energy-dispersive attachment from Oxford Instruments. X-ray phase analysis of the slag was performed on an XRD-7000 X-ray diffractometer from Shimadzu.Results. The studies showed that copper slags are represented by different types – pyroxene, fayalite-wustite, and pyroxene-fayalite. The first type is composed of a homogeneous aggregate of augite with the presence of glass, magnesiochromite, copper, and covellite. The second type is represented by fayalite and wustite with the presence of glass, copper, and idaite, as well as cuprite, barite, and atacamite. The third type of slag is composed of hedenbergite and fayalite with the presence of glass, sulfides, as well as silver, gypsum, and secondary copper minerals (cuprite, atacamite, sampleyite, malachite, etc.).Conclusions. Such a variety of slags in a small excavation area confirms the available information about the various sources of copper ores for the Ekaterinburg plant. At the same time, it can be argued that both oxidized and sulfide copper ores were delivered to the plant. The latter came from the Shilovsky copper mine and were smelted at the Ekaterinburg plant in the first years of its operation. From these ores, slags of the third type were obtained, i.e., of fayalite-hedenbergite composition. Oxidized ores most likely originated from the Gumeshevsky mine (fayalite-wustite slag) and some unknown small mine from the area of the future large Pyshminsko-Klyuchevskoye deposit (pyroxene slag). An interesting technological trend at the Ekaterinburg plant was revealed: here, pyrites were first smelted and only then transition to oxide copper ores was made.
Lithosphere (Russia). 2025;25(3):674-687
674-687