Vol 276 Iss. 2

A comprehensive study of the Carnian diamonds of the Bulkur anticline in the northeastern Siberian craton has been conducted. Two most common diamond types in the Bulkur area have been identified: scarred dodecahedroids and crystals of varieties V-VII according to the Yu.L.Orlov classification. These groups are characterized by a lighter carbon δ13C isotope composition from –19.6 to –24.7 ‰, differing in morphology, concentration and forms of nitrogen aggregation, and composition of melt inclusions. Submicroscopic inclusions in diamonds of these groups have been studied for the first time. Such inclusions in dodecahedroids are of less ferruginosity (12 and 31 wt.% FeO on average) and more enriched in potassium (5.5 and 1.7 wt.% K2O on average) compared to diamonds of varieties V-VII. It is concluded that the studied dodecahedroids with scars from the Carnian deposits of the Bulkur anticline represent a separate type of diamonds characteristic to the northeast of the Siberian platform. It is assumed that the primary sources are Precambrian in age and that the diamonds entered the Triassic and younger placers as a result of the erosion of Proterozoic coastal-marine deposits within the Precambrian protrusions, in particular on the Olenek uplift.

Polymodality of statistical sand grain size distribution is due to the changes in kinematic energy of aquatic environment during the process of sediment deposition in open system-facies. Improving relevance of information about deposition paleoenvironment is of high significance in interpretation of granulometric analysis results. The paper investigates the results of granulometric analysis of sandy-aleuritic deposits confined to different formations in the wells located in the oil fields on the Yamal Peninsula. Based on the kinematic theory of open system transformation, the equation that describes the dependence of grain size on grain kinematic parameters – time period and transport distance – was developed. Therefore, it is possible to calculate these parameters within the studied facies on the basis of available grain sizes and percentage of fraction with diameter range from 0.001 to 1 mm. The aim of this study is to present a new approach to facies identification based on the calculations of kinematic parameters of sand grain flow and fine grains using the equations of open system transformation intensity within the universal kinematic theory. The parameter which was proved the most informative is sediment transport distance during deposition, which is controlled by the size of the settling grains. This parameter is influenced by bed slope angle, grain size, and deposition depth. Comparing the value of this parameter with fraction diameter, it is possible to identify the facies of the studied area.

Drilling of horizontal wells with multi-stage hydraulic fracturing (MFHW) is one of the most common solutions in the development of low-permeable oil and gas reservoirs. At the same time, the estimation of the well and reservoir parameters by well test analysis is complicated due to long time response to the radial flow regime. It is possible to eliminate uncertainty dealt with the absence of radial flow response by using data from the early radial regime that occurs at early times of pressure buildup. However, its appearance is only possible if the distance between the parallel fractures is much larger than the fracture half-lengths, which is not usual in practice. At the same time, MFHW demonstrate a complex buildup behavior due to fracture interference. By analytical and numerical simulations it is shown that the early time buildup behavior depends on duration of well production before shut-in. This behavior is similar to the buildup of a vertical well near the sealed boundary. For short production times, a radial-like regime may appear at early buildup times caused by elliptical flow around the fractures. The consistency of this regime and the relation of the pressure derivative plateau level to the parameters of the elliptical flow are justified. An empirical formula of sufficient accuracy has been obtained for reservoir transmissibility (flow capacity). This formula is applicable for the most common range of parameter values of the MFHW. These results open up new opportunities for reliable assessment of the well and reservoir parameters from well tests in MFHW in low-permeability reservoirs, including new wells or wells restarted after a long inactive period.

A potential method for modifying saponite (intercalation) ensuring its high sorption capacity for gold was theoretically and experimentally substantiated. Saponite isolated from recycled water of processing plant tailings dam is modified by mixing a suspension of the mineral and acetone with the surfactant hexadecyltrimethylammonium bromide (CTAB) followed by four washings with ethanol and distilled water, and drying. The intercalation mechanism of saponite-containing product involves the introduction of positively charged cations of organic compounds into the interlayer space through cation exchange or adsorption, which leads to expansion of mineral layers and an abrupt shift in zeta potential toward the positive side. The appearance of bands in the IR spectral ranges of 1460-1490 and 2850-2920 cm^–1 related to the deformation and stretching vibrations of the CH₂ group, respectively, confirms the successful incorporation of CTAB molecules into the mineral structure. Studies of the maximum sorption capacity of modified saponite revealed that at initial gold concentration 22.6 mg/l, complete extraction is achieved after 7.5 min. The maximum static exchange capacity of modified saponite was achieved after contact with the third portion of fresh gold-bearing solution and amounted to 100.5 mg/g. Gold sorption isotherms correspond to the Langmuir model which presumes that a monomolecular sorption layer forms on the surface of the modified saponite, and all active sites have equal energy and enthalpy of sorption. The kinetic dependences of sorption are best described by a pseudo-second order model, which presumes that the chemical exchange reaction limits the sorption process. It was found that saponite intercalation with hexadecyltrimethylammonium bromide ensures a more efficient sorption of negatively charged gold complex ions ([AuCl₄]^–). The calculated equilibrium static exchange capacity of modified saponite was 92-119 mg/g, while the experimentally determined value was 102 mg/g.

Subsurface use waste accounts for the overwhelming majority of waste generated and accumulated in Russia. The increase in the volume of processing of minerals by the mining and processing industries leads to an aggravation of environmental problems – the negative impact of overburden dumps, tailings of enrichment and processing of mineral raw materials on the environment is increasing. Using the example of three types of rocks, the possibility of using carbonate subsurface use waste as raw materials in the formation of photocatalytic composite materials (PCM) in the production of building materials and products, and simultaneously solving environmental problems of territories through large-scale utilization of man-made waste, is considered. A complex of physical (porosity, specific surface area, dispersion, surface morphology) and chemical (chemical composition, acid-base centers, zeta potential, hydrogen index) studies of the properties of carbonate materials of various genetic types have been carried out to determine the possibility of their use as a substrate in the production of PCM. The photocatalytic material obtained by depositing sol-gel synthesized titanium compounds onto a mineral carrier is intended for incorporation into cement building composites and for giving them self-cleaning properties during operation. The mineral powders of limestone from the Tyushevskoye (T) and Porechenskoye (P) deposits and marble from the Polotskoye deposit were ranked according to certain requirements – dispersion, porosity, and adsorption activity. The establishment of numerical indicators for each type of raw material made it possible to determine the degree of suitability of mineral powders of carbonate rocks for the production of composite materials introduced into the composition of building materials. A ranking of mineral powders was carried out to increase the potential efficiency of use in the composition of PCM in the following sequence: limestone T → limestone P → marble. PCM based on carbonate carriers exhibit high rates of organic pollutant degradation (more than 90 %) and are applicable as photocatalytic agents.

The lithological features of the Middle Cambrian sublittoral-littoral deposits of the Lower Evenki Member (Baykit Anteclise) have been refined. Four types of dolomites are identified: with stromatolitic texture, clotted-peloidal, replacement crystalline without preservation of the protolith primary structures, and replacement variably-crystalline with relict silt-pelitic structure. Post-sedimentary alterations of the rocks are associated with multi-stage dolomitization processes – early, syngenetic (in dolomite with stromatolitic texture and/or bacterial structures) and later (in replacement dolomites and silt-sandstones with dolomitic cement). The isotopic composition of carbon and oxygen in carbonates is analyzed. The elemental composition of carbonate, terrigenous-carbonate, carbonate-terrigenous, and terrigenous rocks is studied. A heat map with clustering was used to visualize the general pattern of enrichment by various elements. Carbonate lithology types are significantly enriched in Co, Cr, Sc, Rb and depleted in Cu, Zn, Li, Ba, Pb, and Sr in comparison with carbonate Clarke values. The nature of the positive Eu anomaly is investigated; its origin is attributed to Eu-bearing minerals in the terrigenous component of the rocks, rather than to hydrothermal solutions. No direct correlation is observed between the Rare Earth Element (REE) content and the amount of terrigenous admixture, thus the influence of reducing conditions or the composition of the dolomitizing fluid on the REE distribution cannot be ruled out. Terrigenous varieties are depleted in Cu, Zn, Pb, Ba, Th, U relative to the Clarke values for clays and clay shales. When normalized to PAAS, dolomitic argillites, dolomitic siltstones, sandstones, and silt-sandstones generally show enrichment in HREE relative to LREE. The source of the terrigenous clastic material was the Precambrian terranes of the Yenisei Ridge, formed by island-arc complexes, and recycled sedimentary material.

We examine crystallization conditions for saturated brines of calcium, potassium, and magnesium chlorides from the Angara‑Lena artesian basin, Siberian Platform. The study focuses on temperatures matching actual thermal conditions in wells of the “Lithium” site at the Kovykta gas‑condensate field. This critical type of lithium‑bearing raw material is classified as hard-to-recover reserves. In most wells (depths to 2.2 km), rock temperatures in the upper geological section remain below 20 °C. During well operation, various salts precipitate from saturated magnesium-calcium chloride brines within the production line. This leads to rapid wellbore clogging and eventual production shutdown. Thermodynamic analysis of phase diagrams reveals that crystallization yields antarcticite CaCl₂·6H₂O, tachhydrite Mg₂CaCl₆·12H₂O, minor amounts of carnallite KMgCl₃·6H₂O, bischofite MgCl₂·6H₂O, and several other chlorides, depending on temperature. At temperatures above 55 °C, salt precipitation becomes negligible. Thermohydrodynamic simulations of a single flowing well under hydrogeological conditions similar to those at the Kovykta area (southern Siberian Platform) demonstrate the feasibility of long-term (1 month to 1 year) exploitation of saturated sodium-chloride and calcium-chloride lithium-bearing brines. Such operations can yield lithium production rates of 31.2 to 4.2 t per well.

The goal of this study is to enhance the method for predicting geomechanical processes during mine working construction in an elastoplastic rock mass with dilatancy. We present the results of experimental research into the volumetric strength of rocks and the specifics of volumetric strain development under plastic shear. We demonstrate rock dilatancy and provide diagrams showing how volumetric plastic shear strains change at different levels of accumulated shear strains. We process the rock testing results using A.N.Stavrogin’s plasticity condition. We propose a new analytical solution for predicting the stress-strain state of the rock mass in areas with inelastic strains, based on A.N.Stavrogin’s plasticity condition. This includes equations for modelling the limit state zone of rock around a mine working. We introduce an algorithm for predicting the stress-strain state of the rock mass. We investigate how the size of the limit state zone around a mine working relates to rock dilatancy parameters, lateral stress coefficient, and working depth. We examine how contour displacements develop for a circular mine working under plane strain conditions, considering various plasticity parameters and rock dilatancy indicators. We implement A.N.Stavrogin’s plasticity condition in the Abaqus software package. Our research results help define the scope of the analytical solution. The solution remains physically meaningful only when the limit state zone forms around the entire perimeter of the mine working. The proposed numerical approach removes this limitation. It applies to any geomechanical state of the rock mass and to mine workings with any cross-sectional shape.

Recent research on predicting petrophysical and mechanical properties of carbonate rocks, integrating textural and microstructural observations with geotechnical measurements, has sparked critical discussions. While some studies present robust experimental methods and fresh insights, others rely on less rigorous approaches. In the Mediterranean area, shallow-water calcarenites crop out along both the coastline and internal areas. Typically, these carbonates are soft and exhibit high porosity, open in type, controlled by the depositional fabric and post-depositional processes. Their strength primarily depends on the type and amount of calcite cement, with water presence significantly impacting their stress-strain behavior. Strength and stiffness decrease markedly in the transition from dry to saturated conditions. Well-cemented calcarenites with early and late diagenetic cement exhibit brittle behavior in both dry and saturated states, whereas poorly cemented types with early calcite cementation alone show brittle behavior when dry and pseudo-ductile to ductile behavior when saturated. Dual-porosity systems, combining micro- and macro-pores, dominate the hydraulic properties of calcarenites, playing a key role in decay mechanisms and patterns. This study compares existing literature with laboratory analyses of calcarenite lithofacies from Apulia and Basilicata (Southern Italy), yielding new insights into their mechanical and physical behavior, as well as durability.

The article presents the results of a comprehensive study of diamondiferous lherzolite from the V.Grib kimberlite pipe. The composition of rock-forming minerals (olivine, orthopyroxene, Cr-diopside, Cr-pyrope) in terms of major elements mainly corresponds to minerals from inclusions in diamonds of the lherzolite association and diamondiferous lherzolites of the world. The elevated modal amount of orthopyroxene (18 vol.%) as well as the concentration of FeO (7.5 wt.%) and the value of MgO/SiO2 ratio (0.89) for lherzolite allow assigning it to orthopyroxene-enriched lherzolites. Specific features of the composition of Cr-diopside and Cr-pyrope in respect of rare elements indicate that at the time of capture by kimberlite, lherzolite retained the signs of a slight impact of mantle metasomatism. Modelling results allowed suggesting magnesiocarbonate and silicate high-density fluids (HDF) as the metasomatic agent. No signs of influence of proto-kimberlite melt were found. The degree of nitrogen aggregation in diamond (%B from 6 to 15) indicates a long stay in mantle conditions, which excludes formation shortly before the emplacement of kimberlite. Extremely light values of carbon isotope composition (δ13C = –18.59 ‰) indicate the involvement of organic carbon of subduction origin in diamond formation. Diamond formation could be associated with an ancient metasomatic event occurring with the leading role of low-Mg silicate-carbonate HDF, the source of which were eclogites and/or subducted sedimentary deposits containing organic carbon. The calculated P-T parameters (3.7 GPa, 814 °C) of the last equilibrium of mineral phases of lherzolite point to its capture from a depth of ~118 km, which corresponds to a section of the lithospheric mantle (approximately 95-120 km), within which rocks also demonstrating features of specific transformations under the influence of subduction-related fluids were earlier discovered.

This paper addresses the necessity of refining standard triaxial testing methods for characterizing the mechanical behaviour of salt rocks. Triaxial testing is a key tool for determining the strength and deformation characteristics of rocks; however, existing standards often fail to account for the unique features of salts, such as their highly plastic behaviour, creep, temperature sensitivity, and defect-healing capability. The work highlights the critical importance of considering large strains and volumetric changes of specimens during testing, as this enables a more accurate representation of the behaviour of salt rocks, as this enables a more accurate representation of the behaviour of salt rocks. It is proposed that current standards be updated by incorporating well-established correction equations for geometry evolution and volumetric strain, as well as by adopting the Hencky strain measure. Experimental results obtained on natural salt rock specimens and salt-based geomaterials demonstrate significant errors in the evaluation of the stress-strain state when traditional data-processing methods are applied without accounting for the specific properties of salts. The analysis underscores the need to revise existing triaxial testing standards in line with the proposed approaches, thereby improving the accuracy and reproducibility of data that underpin geomechanical modelling and engineering design.

In the Severny pluton in Chukotka, an association of rare-metal, tin-bearing topaz-zinnwaldite greisens (zwitters) and tourmaline metasomatites has been identified through geological mapping and mineralogical-petrographic studies. These formations are genetically linked to magmatism producing Li-F granite intrusions. The distribution and composition of zwitters and muscovite-quartz-tourmaline metasomatites forming halos around quartz-tourmaline veins were investigated. A wide spectrum of tourmaline mineral species was established, occurring in pegmatoid pockets of leucogranites (tourmaline I), pre-ore quartz-tourmaline metasomatite veins with fluorite (tourmaline II), early ore quartz-tourmaline metasomatite veins (tourmaline III), and ore tourmaline and quartz veins (tourmaline IV). An evolution of tourmaline from Sc-bearing fluor-schorl in pre-ore metasomatites to oxy-schorl and tin-bearing ferro-bosiite in tin-ore metasomatites was revealed, with a gradual increase in lithium content and variable iron oxidation state. In zwitters, muscovite-quartz-tourmaline metasomatites, and tourmalinite veins, a combination of tin and rare-metal mineralization is noted. The research results can be used to assess the metallogenic potential and develop criteria for forecasting rare-metal (Nb, Ce, Y, W, Bi) mineralization in the Severny pluton.

The most industrially developed methods of enhanced oil recovery of the production of high-viscosity oils and natural bitumen are thermal methods of influencing the reservoir: steam cyclic stimulation of production wells, steam assisted gravity drainage, and areal steam injection. The thermal methods also include the thermomine method, which involves the construction of underground mine working with galleries of producing wells and a thermally enhanced oil recovery. An example of using the thermomine method – the Yarega area of the Yarega field. The technology of the thermomine method are continuously being improved during the development of Yarega area. The most common the underground-surface method: the steam is injected from the surface through vertical steam injection wells, and oil is extracted in the underground mine through gently sloping production wells. The practice of areal steam injection and the results of geophysical studies of steam injection wells have shown that when using the underground-surface method of production the Yarega area, the steam mainly enters the upper part of the reservoir, which implies uneven production of reserves in thickness. There is a need to increase the pressure of steam injection in order to involve reserves of extra-viscous oil in the process of the heat carrier treatment. However, an increase in the injection pressure of the steam is problematic in some cases due to the presence of heterogeneities in the formation (disjunctive seismic faults every 20-25 m, as well as numerous microfractures with fissure opening). The paper presents the results of an experimental study of the use of sedimentation compounds during steam injection under different thermobaric conditions. The scientific novelty is to evaluate the effectiveness of the use of sedimentation compounds when injecting steam into zonally heterogeneous sand packed tubes. Solutions of iron sulfate, sodium carbonate, and calcium chloride were selected as sedimentation compounds. The average permeability of the heterogeneous sand packed tube was reduced by 55 % when steam was injected with a temperature of more than 170 °C as a result of performing three treatments with sedimentation compounds. The effective pore volume during steam injection has been increased by 70.6 %, which, during well tests affects an increase in the surface efficiency of steam treatment, and as a result, an increase in oil recovery.