The paper is devoted to kinetic studies of thermal decomposition of organic matter in organic-rich rocks. Kinetic studies are the consisting part of geochemical investigations of source rocks and petroleum systems. The results are required for petroleum generation prediction and assessment of reservoir hydrocarbons quantity and quality using basin modelling. Kinetic data is also applied for simulation of in-situ kerogen conversion and hydrocarbons generation, which are the main processes of thermal methods of enhanced oil recovery (thermal EOR).

The paper summarizes fundamental concepts and experimental approaches for kinetic studies of organic matter thermal transformation, it provides an overview of modern methods, equipment and experimental procedures for obtaining bulk and compositional activation energy distributions (spectra) in open and closed systems, and discusses the benefits, limitations, and possible applications of the different methods.

The paper presents the scope of experimental procedures, which have been elaborated at Skoltech, and the obtained results: (i) bulk kinetic spectra, which are aimed at express prediction of the total yield of mobile hydrocarbons during kerogen transformation; (ii) compositional kinetic spectra, which considers the amount and composition of hydrocarbon products; (iii) kinetic model of organic matter transformation in a closed system, which considers primary kerogen decomposition and secondary reactions of the hydrocarbons. The kinetic spectra were obtained for various organic-rich rocks collected within the Russian Federation.

This work studies the geochemical features of the composition of kerogens from Jurassic deposits in the north of Western Siberia. The patterns of changes in the pyrolytic and isotopic characteristics of organic matter were established, information was obtained on its genetic type, maturity and residual oil and gas generation potential of organic matter. In the Jurassic deposits, the main oil-producing complexes were identified (Bazhenov horizon), as well as horizons capable of producing predominantly gaseous hydrocarbons due to their high maturity (Malyshevsky, Leontievsky, to a lesser extent Levinsky, Kiterbyutsky).

The studied Upper Jurassic and Lower Cretaceous bituminous shales of the Kashpirskoe field contain organic matter (OM) terrestrial in carbon isotopic composition (δ¹³C > –24‰) and marine in pyrolytic characteristics (HI > 500 mg HC/g TOC). Shales contain autochthonous bitumens that are marine (Pr/Ph ≤ 0.5, Ph/nC₁₈> 1, distribution of biosteranes with C₂₉/C₂₇ ≤ 1.5, presence of long-chain alkyl naphthalenes – indicator of marine algae Gloeocapsomorpha prisca, “V-shaped” distribution of methyldibenzothiophenes). At the same time, a number of parameters correspond to the terrestrial OM (in n-alkanes nC₂₇/nC₁₇ >>1, P_wax (0.6–0.7) > P_aq(0.4–0.5), the indicator of coniferous plants reten is marked in the aromatic fraction), which indicates the proximity of land. Isorenieratene derivatives, biomarkers of specific Chlorobiaceae bacteria, were found in the samples; therefore, despite the probable proximity of land, anoxia occurred in the photic layer of the sedimentation basin. The presence of diasterenes indicates diagenetic transformations also under conditions of anoxic sediment. According to the results of pyrolysis, the OM is catagenetically weakly mature (very low T_max), which is confirmed by the composition of the bitumen (CPI ≥ 1.7 in n-alkanes, high Pr/nC₁₇ and Ph/nC₁₈ ratios, absence of isoand diasteranes, presence of biosteranes and sterenes, low concentrations or absence of typical terpanes, presence of biohopanes and hopenes, low the ratio of homohopanes C₃₁22S/(22S+22R) << 0.5, low ratios of MDR (0.5–1.0) and MPI-1 (0.4–0.8), mostly absent (not yet formed) monoand triaromatic steroids).

The Lower Cretaceous shales from the boundary interval between the Volgian and Ryazan stages, not characterized by fauna, are more enriched in terrestrial components compared to the Upper Jurassic oil shales from the Dorsoplanites panderi ammonite zone. The peculiarities in the characteristics of the studied shales are associated with the genetic specificity of the OM, with anoxia in water and sediment with the accumulation of OM, and with its weak catagenetic maturity at fairly high concentrations.

A model of the Bazhenov formation hydrocarbon system was calculated of an area of about 13,000 km² including the territory of Priobskoye, Prirazlomnoye and a number of other oil fields discovered in the Frolovskaya megadepression and the Salym megaval in the West Siberian basin. Temperature history was simulated in two programs: TemisFlow and GST using heat flow maps and maps of modern temperatures of the Bazhenov formation. The amount of hydrocarbons generated by the Bazhenov formation was estimated using the organic matter transformation ratio map and the residual generation potential map. Hydrocarbon capacity of the Bazhenov formation was calculated in two ways: by using S₁ pyrolytic parameter and based on the results of basin modeling. The initial total geological oil resources of the Bazhenov formation were estimated and compared between each other using three approaches: basin modeling, quantitative geological regularities and volumetric methods. All three estimates fall within the range of 74–90 mln t.

Analyses of the three predominant types of sedimentation – siliciclastic, carbonate and black shale – revealed their discontinuity/continuity across various facies environments within the Middle and Late Devonian of the central part of the Volga-Urals petroleum province. These environments include condensed and non-condensed depressions, slopes of depressions and shallow water settings located on tectonic arches or local biohermal uplifts.

The regional zonation of conodonts, correlated with the International chronostratigraphic chart, confirms the general stratigraphic completeness of the Middle-Upper Devonian geological record in this area. Meanwhile, sedimentation exhibited a discontinuous pattern, which enables to speak about the socalled “discontinuous continuity”. In particular, the sedimentation of organic-rich black shales, traditionally considered as oil-source rocks, lasted more than 29 million years, from the Late Eifelian up to the Devoniancarboniferous boundary. The longest hiatus (ca. 2.5 Ma) in the accumulation of black shales (as well as carbonates) took place at the end of the Givetian. Notably, this interval contains the most productive siliciclastic reservoirs.

During the Early Eifelian to Early Frasnian (ca. 17 Ma), siliciclastic sediments demonstrate the highest accumulation rates and the maximum discontinuity caused by short marine transgressive episodes. Simultaneously, the most complete sequences were deposited in the depressions where carbonate and black shale sediments accumulated. During the Famennian (ca. 12 Ma), siliciclastic sedimentation completely ceased, leading to the stable accumulation of carbonate sediments on the slopes of depressions and in shallow waters; the deposition of organic-rich black shales continued in the deep axial settings of the troughs. Our results highlight the complexity of the spatial relationship between various coexisting sedimentation types and the incompleteness of the geological record in different environments.

In 2023, comprehensive studies of shallow-water methane gas emissions were conducted during expeditionary work in the coastal area of Laspi Bay (southwestern coast of Crimea). The research included determining the component and isotopic composition of bubble gas, measuring methane concentration in the gas emission area, estimating bubble flux rates, and measuring hydrophysical parameters above the seep site. The obtained results of the carbon isotopic composition of methane and ethane in the studied samples corresponded to (δ¹³C_mean = –36.0 ± 0.8‰, δ¹³C_mean = –37.5 ± 0.2‰, respectively) and indicate the presence of thermocatalytic methane migration along fault systems. It was found that the methane seeps of the Crimean coast are relatively low-flow, with a specific flux ranging from 5 to 10 m³ year-1 from an individual seep. The presented temporal dynamics of dissolved СН₄ concentration above the seep and changes in the isotopic ratio of δ¹³C-СН₄ in bubble gas indicate the constancy of the process over time and the absence of connection with external hydrological changes in the water area. The obtained ratios of the carbon isotopic composition of methane and ethane demonstrate that the gas mixture was most likely generated from source organic matter of marine origin, and one of the main sources of hydrocarbon fluids is the Upper Eocene and Oligocene deposits in the Western Black Sea basin.

The work studied the lithological and geochemical characteristics of oil and gas source rocks of the central part of the Volga-Ural oil and gas bearing province. The purpose of the work was to reconstruct their formation conditions, study the generation potential and maturity of organic matter, and examine prospects for industrial development. The rocks were studied macroscopically, as well as X-ray analysis, pyrolysis using the Rock-Eval method, SARA analysis, and gas chromatography-mass spectrometry. The formation of the Domanik deposits, Bobrikovsky and Pashiysky horizon mudstones, and Upper Kazan substage clays have all been proven to have occurred in a maritime environment. The content of organic matter in the rocks varies from 0.35 to 11.16%. Minute amounts of organic matter that are difficult to accurately in terms of their geochemical properties can be found in the clayey deposits of the Vereisky and Timan horizons. The Upper Kazan substage clays contain type II/ III kerogen. Mudstones of the Bobrikovsky and Pashiysky horizons, as well as Domanik deposits, contain organic matter represented by type II kerogen. The data obtained may indicate common mechanisms for the accumulation of sapropelic organic matter on the territory of the Volga-Ural basin from Pashian (Frasnian stage) to Bobrikovian (Visean stage) times. It was revealed that the studied deposits are at the stage of catagenesis (PC-MK1). At the same time, Domanik deposits have very good and excellent generation potential, which is characterized by the greatest maturity. Mudstones of the Bobrikovsky horizon have similar generation potential.

The Neoproterozoic Katav Formation, which is a part of the Ural stratotype section, was considered to be remagnetized in the Late Paleozoic for many years. If the primary magnetization of the rocks is proven, the magnetostratigraphic record found in the Katav Formation may become a good paleomagnetic benchmark in the Neoproterozoic history of the Earth and serve as a source of information about deep processes in the Earth and their evolution. In this work, the arguments in favor of the primacy of the high-temperature characteristic component of magnetization of the Neoproterozoic Katav Formation rocks, previously put forward by V.E. Pavlov and I. Galle, were verified and confirmed on more extensive and detailed material. New paleomagnetic data have been obtained for two sections of the Katav Formation in the Southern Urals near the town of Yuryuzan and the village of Galiakberovo, as well as the overlying Inzer Formation near the village of Galiakberovo. A detailed magnetostratigraphic section of the Katav Formation for the Yuryuzan section is presented. The analysis of the upper part of the section shows 39 polarity intervals within the 74.6 m thick strata. The new data confirmed the existence of a trend of displacement of paleomagnetic directions from bottom to top along the studied sections of the Katav Formation, directed towards the paleomagnetic direction of the overlying Inzer Formation. The total value of the displacement in the Katav Formation is consistent in sections located at a distance from each other, located in areas with slightly different geological history. A significant difference in the direction of the characteristic component of magnetization in the Katav Formation from the corresponding directions in the Inzer Formation was confirmed. Generalization of new and previously obtained data gives grounds to consider the primary characteristic component of magnetization of the Katav Formation deposits, previously considered to be remagnetized. The frequency estimates of the geomagnetic reversals revealed by the new data in the upper part of the Yuryuzan section using the results of our previously performed cyclostratigraphic analysis are 11–12 reversals per million years. Thus, the existence of another interval of geomagnetic field hyperactivity in the Neoproterozoic is confirmed.

The Dagestan offshore of the Caspian Sea, surrounded on all sides by oil and gas bearing areas, represents an exceptional interest for the exploration of hydrocarbon fields.

The applied sequence stratigraphic analysis allows to stratify the Cenozoic section for the resource’s estimation of the Karagan-Chokrak deposits in new prospective offshore areas. The analysis used well data from the onshore and Dagestan offshore, as well as 2D seismic data.

Five sequences were identified in the Cenozoic sediments according to the seismic and well data, from bottom to the top: Maikop SQ1, Chokrak SQ2, Sarmatian SQ3, Akchagyl SQ4, and Apsheron SQ5, in each of them regressive and transgressive tracts have been identified. The boundaries of regressive and transgressive tracts in wells were distinguished on the basis of a mathematical model proposed by the authors for the automated geological interpretation of gamma-ray logging. For evaluation the petrophysical properties of the reservoir rocks the volumetric mineralogical model has been created.

A geological and geophysical model of the structure of the earth’s crust and upper mantle along the Middle Ural transect is presented (as a vertical section of a three-dimensional seismic density model). The methodology for constructing a 3D density model of the earth’s crust and upper mantle for the Middle Urals is outlined. The model was created based on the results of interpretation of gravity anomalies in the Bouguer reduction and deep seismic sounding data. Creating a volumetric one consists of several stages. At the first stage, gradient velocity sections were constructed in the format of grid functions (2D models of seismic velocity distribution) to a depth of 80 km, which were converted into density ones using refined formulas. Next, a threedimensional zero-approximation density model is constructed (using interpolation methods) and the difference between the observed gravitational field and the field of this model is calculated. For the difference field, the inverse problem is solved the density values at the nodes of the computational grid are determined, which need to be added to the zeroapproximation model in order to satisfy the observed field. A comparison is made of the gradient density section obtained by a vertical section of the author’s volumetric density model of the earth’s crust and upper mantle of the Middle Urals along the line of the Middle Ural transect, with a density model created on the basis of a two-dimensional interpretation along this transect (according to the EUROPROBE program). The cross-section of the volumetric density model reflects the main features of the deep structure of the study area, presented in the two-dimensional model, and supplements them with new data on the distribution of physical parameters in the earth’s crust and mantle. This illustrates the fact that a three-dimensional density model, the construction of which takes into account geophysical data specified over the entire study area, carries more information about the structure of the earth’s crust than two-dimensional models.

The article considers the results of applying a multi-layer approach to the quantitative interpretation of electrical and induction logging data in vertical wells for formation evaluation of the Achimov formation in the central part of Western Siberia. Interpretation of electrical logging data by conventional methods often leads to errors in estimating the oil saturation of thin reservoirs due to the complex apparent resistivity logs, which are significantly influenced by the high-contrast invaded zones and shoulder beds. The approach proposed at Institute of Petroleum Geology and Geophysics of the Siberian Branch of the Russian Academy of Sciences is based on joint multilayer 2D inversion of signals from a complex of galvanic and induction probes. The signals are calculated using a verified finite element algorithm. This naturally takes into account changes in the well diameter and drilling mud resistivity, radial and vertical distribution of electrical properties in the section, different sensitivity of the signals to various elements of the environment around the logging tool, as well as design parameters of the most common Russian electrical logging tools. The approach has been tested on logging data provided under an agreement with SNIIGGiMS. Geoelectric models of Lower Cretaceous deposits were built for several dozen wells, typical examples of which are given in the article.

The target formation of a brown oilfield in Western Siberia is composed of a shallowing-up succession represented by siltstones in its base gradually replaced by sandstones toward its top. Due to the absence of detailed rockand electrotyping, the siltstones, having much lower resistivity and permeability, were assigned to a water-bearing section. However, the following up well tests detected considerable oil inflow from them as well. This motivated current research aimed at developing a new methodology of rockand electrotyping of low-resistive, low-permeable clastic reservoirs. The methodology comprises detailed workflow for laboratory tests, rock typing by means of the alternative flow zone indicator (FZI), and, finally, transfer of core-derived rock types to well log electrotypes. The proposed application of the dimensionless FZI parameter, incorporating porosity and irreducible water saturation, appeared to be very effective for electrotyping of the formation, including low-resistive and low-permeable intervals.

Since the intervals are characterized by a low correlation between permeability and porosity, applying the latter log for computing permeability results in unreliable calculation of the parameter and further incorrect electrotyping. In order to resolve this issue, the study suggests an effective alternative technique for calculating permeability as a multivariate parameter from other logs.

Further, the research proposes a well log interpretation workflow that enables conversion of the defined rock types to electrotypes, maintaining the same classification principles for both core and well logs data. This ensures compatibility of the core and well log-derived classes.

The petrophysical interpretation workflow is enhanced with machine learning algorithms for reconstructing lacking logs as well as extending the defined electrotypes to uninterpreted wells. The proposed approaches to rockand electrotyping allows detection of previously missed productive intervals and thus enables extend the lifetime of the brownfield.

A brief description of the geological structure of the sedimentary cover within the Kempendyai depression is given, in which two intervals of formation of unstable layers in the Cambrian and Devonian are distinguished, and their salt saturation is estimated. A generalized geo-density model of the sedimentary cover has been compiled, and approximate scales and duration of interruptions in the Phanerozoic sedimentation history are given. Numerical modeling of salt tectogenesis is performed by solving the problem of calculating the creeping flow of a Newtonian fluid with variable density and constant viscosity. The leading role of the surfacing of Devonian salts, the most active phase of which occurred in the Jurassic period, in the formation of local sedimentary cover structures with the subordinate nature of the dynamics of Cambrian salts is shown. It is proposed to identify subcortical zones composed of Devonian diapir salts as the most promising areas in terms of oil and gas content, and possibly in terms of lithium-bearing brines.

Well productivity index is one of the most important indicators for the development of carbonate reservoirs of oil fields, control and maintenance of high values of which determines the levels of hydrocarbon production. Determination of the complex influence of geological and technological factors on production capabilities of wells remains an actual direction of research in the field of oil producing. The present paper is devoted to improving the efficiency of production wells in a carbonate reservoir oil deposit based on the results of evaluation and consideration of the relationship between the productivity index and geological and field parameters such as reservoir pressure, bottomhole pressure, skin-factor, gas-oil ratio, water cut, using statistical methods of analysis. At the stage of preparation of initial data the materials of hydrodynamic and production-geophysical studies performed on the wells during the whole period of development of oil reservoir of one of the fields of Perm region were involved. The analysis of the obtained data sample with the use of statistical methods allowed us to study the relationships between the specific well productivity index and the considered geological and production parameters. Multivariate statistical models were developed using stepby-step regression analysis, collectively demonstrating the predominant influence of bottomhole pressure, reservoir pressure and water cut on the specific well productivity index based on the frequencies of occurrence of parameters and the order of their inclusion in the model. The study of the dynamics of changes in the accumulated multiple correlation coefficient during the development of statistical models allowed us to identify the ranges (areas) of change in the values of the specific well productivity index, which are characterized by individual correlations with geological and production parameters described by the corresponding mathematical dependencies. The developed models are characterized by high quality, which is confirmed by their statistical evaluations when comparing forecast and factual values of specific well productivity index. The criteria of applicability of models for conditions of carbonate reservoirs of oil fields are formed. The results of the study can be used for justification and regulation of technological modes of well operation, planning programs of optimization measures.

This article reviews the evolution of hydraulic fracturing (HF) technologies for the carbonate sediments of the kashirsky and podolsky horizons of the Arlanskoe oilfield (the Republic of Bashkortostan and the Udmurt Republic) by the influence of changes in current development conditions, reserve depletion, clarification of the geological structure, and scientific and technical advancements. It presents an overview of the main technologies of primary hydraulic fracturing and re-fracturing actively used today and/or are being introduced on the industrial scale. For horizontal wells, hydraulic fracturing with hydraulic jet perforation (HJP) is employed. This technology enables the development of previously untapped or underperforming sections of the wellbore by allowing selective acid and proppant injection into specific intervals, offering high controllability and predictability. Both HJP and HF stages are completed in a single tripping operation without the need for a coiled tubing fleet. For directional wells, high-tonnage hydraulic fracturing with increased proppant mass up to 40–50 tons is a promising technological solution. This approach enhances to increase starting oil flow rates by improving coverage ratio due to involving poorly drained and previously undeveloped overlying and underlying layers. The article consolidates practical experience with hydraulic fracturing technologies, analyzes their effectiveness, identifies the features of hydraulic fracturing in directional and horizontal wells, and develops an algorithm for the selection of hydraulic fracturing technology for the conditions of a carbonate reservoir.

A finite-element scheme has been developed, including a section of reservoir rock, cement stone, casing and perforation channels. It is noted that in order to exclude the occurrence of stress concentrators at the casing – cement stone and cement stone – rock contacts, contact elements are specified in the numerical model, due to this, structural elements «slip», but at the same time, a reliable redistribution of stresses is carried out. Numerical simulation of the stress state of the near-wellbore zone using the developed model with varying depression on terrigenous reservoir for the conditions of one of the Perm Region oil field is carried out. It is shown that the safety factor of the casing is about 3–4 units, with the exception of small areas near the upper and lower areas of the perforations, where this indicator is close to one. For cement stone, the safety factor was 2-3 units and however, areas with its lowest value (1.35), also concentrated near the perforation channels, were note. To analyze the change in permeability, the dependence of this characteristic on effective stresses was used and it was found that zones of reduced stresses and an increase in permeability up to 20% of the initial value are detected in the upper and lower parts of the perforations. With an increase in depression on the reservoir, permeability decreases, especially in the lateral sections of the holes, where this parameter can decrease by 25% of the initial value. Using the Coulomb-Mohr criterion, areas of rock destruction from stretching and compression were identified. It is noted that with increasing depression, the areas of destruction under tensile stresses disappear and the areas of destruction under compression increase. An analysis of the change in the productivity coefficient depending on the depression showed that when creating a maximum depression on the 12 MPa formation, the productivity coefficient of the well can decrease by 15% due to compaction of the reservoir rock caused by an increase in effective stresses.

The X-ray tomography method has several advantages, including its non-destructiveness and the ability to visualize the rock skeleton and pore space in three dimensions. However, one of the main challenges of this method is the limited resolution when studying core samples that are 30 millimeters in diameter, which is typical for petrophysical analysis. In these samples, a significant portion of pores have dimensions smaller than the resolution capabilities of most X-ray tomographic systems, making it impossible to accurately determine the boundary between the pore and skeleton structures in tomograms, nor visualize the entire pore volume.

To verify this hypothesis, tomograms from real oil and gas samples were analyzed. The resulting histograms of X-ray densities revealed that it is not possible to directly measure the threshold value of X-ray density that defines the “skeleton-pore” boundary. In order to solve the problem of estimating boundary values, a technique is proposed in this work that suggests using artificial digital models – phantoms. This approach has been previously used mainly in computer modeling, but it has not been used much in petroleum geology. The main advantage of using phantoms is complete control over the set pore space parameters and X-ray density of the skeleton, which cannot be achieved on real samples.

A computational experiment was conducted in the work, where 124 core phantoms with specific porosity characteristics were generated using numerical modeling. These phantoms were then converted into tomograms, allowing us to determine statistical characteristics of the values for X-ray densities of the samples at the reconstruction stage.

Based on the statistical analysis of the X-ray density distribution in the sample, we determined the boundary values that are most suitable for reliable void space detection. Using regression and correlation methods, we developed a model to estimate the optimal boundary value for X-ray density in void space allocation.

We proposed an algorithm for determining and applying this value in the analysis of core X-ray CT data.This model was tested on real samples that were not used in the development of the forecast model. The use of the proposed model for predicting boundary values on obtained tomograms demonstrated a high degree of consistency with actual data.

The paper presents the results of nuclear magnetic resonance (NMR) study of oil samples taken from production wells from the fields of the Republic of Tatarstan before and after the application of one of the enhanced oil recovery (EOR) methods, namely, flow rejection technology based on injection of microgel compositions into injection wells. A comparative analysis of proton NMR spectra and diffusion attenuation of spin echo in spectrally resolved mode was carried out in order to determine the influence of the used technology on the characteristics of recoverable oil. It is shown that after application of EOR for the majority of wells in the oil composition an increase in the share of hydrocarbon components with large values of molecular weight is registered, and for a number of wells a change in the degree of aromaticity of recoverable hydrocarbons is also recorded. The results obtained are interpreted as a consequence of the inclusion in the development of new reservoir zones, previously not involved in oil production, and demonstrate the potential of NMR method for assessing the efficiency of EOR.

The paper presents results of the experimental study of geochemical processes in the “formation water – CO – rock” system at reservoir conditions for waterand oil-saturated intervals of several typical terrigenous and carbonate formations of Urals-Volga region. Compositions of formation water and dissolved gas are analyzed at each stage of the experiments, as well as mineral composition of core samples before and after the interaction. Based on the experimental results, a summarizing analysis is presented of possible physical and chemical processes occurring in the “formation water – CO₂– rock” system during carbon dioxide injection into waterand oil-bearing formations. The results of the experiments allow us to highlight the significant effects of dissolution and resuspension of carbonates and halite during exposure of carbonized formation water with core material of different lithology and saturation character. In a number of experiments, significant changes in the iron and sulfate anions content were recorded, indicating the interaction of the solution with pyrite and gypsum. There were no significant qualitative and quantitative differences in the results of experiments with core material from water-saturated and oilsaturated intervals of the same lithology.

The paper presents new data on the structure and composition of ultramafic rocks in the eastern part of the South Kraka massif. It is shown that the studied area is composed predominantly of spinel peridotites, among which the main role belongs to lherzolites with a low content of clinopyroxene (2–5%) and harzburgites, among which lens-shaped and bandshaped inclusions of monomineral olivine rocks – dunites – are quite often observed. The leading role in the structure of the rocks belongs to high-Mg olivine (Fo_87-94), a secondary role (2016). Nature of the lithospheric mantle beneath the Arabian Shield and genesis of Al-spinel micropods: Evidence from the mantle xenoliths of Harrat is played by high-Mg orthopyroxene (enstatite) and Ca-Mg clinopyroxene diopside. Rare minerals of the mantle stage are amphibole and plagioclase. A typical accessory mineral of ultramafic rocks is spinel, the composition of which varies from high-Al in lherzolites (Cr# = 0.16–0.3), to moderate-Al in harzburgites (Cr# = 0.3–0.55) and to high-Cr in dunites (Cr# = 0.6–0.85). Of the rare accessory minerals in the rocks, the following were identified: native copper, pentlandite, awaruite and PGM (laurite, irarsite, Os-Ir-Ru-alloys). The section of mantle ultramafic rocks of the Sargan Range completed its high-temperature evolution to the levels of the plagioclase peridotite facies, partly in the transition zone from spinel to plagioclase facies. An assessment of oxygen fugacity allows us to speak about more reducing conditions for the formation of rocks of the studied area compared to other similar formations of upper mantle origin and allows us to classify the studied ultramafic rocks as moderately depleted restites of the upper mantle under the riftogenic structure of the Paleo-Ural basin. The geochemical specialization of PGM also indicates a restite origin of ultramafic rocks. At the stage of cooling and tectonic transformations in the crust, ultramafic rocks underwent serpentinization.

The main zeolite deposits in Russia and the other CIS nations are considered, large zeolite provinces are identified, and the most promising territories for expanding the mineral resource base of the Russian Federation are determined. Information on the reserves of deposits, the degree of their exploitation, and production rates is provided. The influence of formation conditions, composition and type of the parent material, on the color and textural-structural features of zeolites is established. The features of geological structure and composition of sedimentary, volcanogenic-sedimentary, and hydrothermal zeolite deposits are considered. A comparative analysis of zeolites from the most important industrial deposits in Russia and the CIS is given, characterizing their mineral and chemical compositions, thermal properties, volume of cation exchange capacity and specific surface area. This work is the result of the authors’ own geological field work on various zeolite deposits in Russia and the CIS, as well as a summary of previously published materials.

The paper provides results of study of platinum group minerals (PGMs) from 18 ore occurrences and deposits of the Kraka massifs, most of these located in ultramafic rocks of the upper mantle section (15), and several occurrences in a crust-mantle transition complex (3). It is shown that chromitites in the upper mantle section have refractory geochemical specialization (Os-Ir-Ru), while chromitites of the transition complex typically contain Pt and Pd minerals. The highest concentrations of the platinum group elements (PGE) are observed in chromitites of the transition complex (up to 2500 ppb of the total PGE). However, minor amounts of chromitites at these sites do not allow us to consider this mineralization type as promising in practical terms. chromitites in the upper mantle section are about an order lower in PGE (50–200 ppb of the total PGE). Analysis of the obtained data suggests the following explanation for various PGM types identified. PGMs occurred in chromitites of the upper mantle section at two stages: 1) disulfides of the laurite-erlichmanite series and, to a lesser extent, Os-Ir-Ru alloys were formed within chromite grains in result of subsolidus processes in the upper mantle restite during solid-phase segregation of PGEs initially incorporated in the crystal lattice of chromite; 2) sulfoarsenides and other PGE compounds with basic metals and antimony were formed by hydrothermal processing of chromitites in crustal conditions. Pt and Pd minerals were produced by differentiation of magmatic melts separated from restite; they were completely or partly transformed under the impact of hydrothermal processes.