Home – Home – Jornals – Russian Geology and Geophysics 2024 number 8

The methods of Infrared (IR) and Raman spectroscopy, as well as gas chromatography, were used to assess the distribution, content and composition of water-containing defects in variously deformed milky-white vein quartz of the Larino deposit. Weakly deformed quartz and quartz with intensive polygonization and recrystallization, in which water is present in molecular form, in fractures, channels, intergranular space, as well as in the composition of fluid inclusions, are analyzed. The content of water-containing defects, according to IR spectroscopy and gas chromatography, decreases in a series from weakly deformed primary granular coarse-grained quartz to blocked and recrystallized. The obtained results indicate the release of water during recrystallization, along the newly formed grain boundaries by diffusion and further homogenization to achieve an equilibrium state. Gas content also depends on the degree of deformation changes in samples and decreases from large coarse-grained differences to intensely deformed quartz with a high content of recrystallized grains.

In this work, based on structural and phase analysis data, we consider the behavior of Au nanoparticles (NP) during the formation of interphase boundaries between quartz and copper and iron selenides upon annealing at 450 °C and different selenium activities: lg f _Se2 = -2.4 with a melted selenium buffer and lg f _Se2 = -3.15 according to the indications of the indicator mineral mixture γ-Fe_{1- x} Se and δ-Fe_{1- x} Se. In two series of experiments, contrasting textural features (nano- and microstates) of the initial metal phases were used, which made it possible to construct 2D and 3D models of interphase boundaries. In the first case, thin layers of gold NPs (~30 nm thick), iron (~50 nm thick), and copper (~50 nm thick) were deposited onto quartz crystals less than 40 μm in size by magnetron sputtering, i.e., all metals were in a nanosized state. In the second case, iron, copper, and selenium (in eskebornite stoichiometry - CuFeSe₂) were introduced into the system in the form of micron-sized powder materials (1-10 microns). Gold still remained in the form of NPs on the quartz surface. The thermal annealing products were studied by X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses, and X-ray photoelectron spectroscopy (XPS). The study showed that, regardless of the activity of selenium, annealing of Au NPs leads to partial enlargement of particles (up to submicron sizes) based on the self-assembly mechanism (the size distribution of Au particles corresponds to a lognormal law with a maximum shifted towards smaller sizes), and gold remains in the metallic state. The 2D model of the interphase boundary is a mineral mixture of copper selenides (Cu₂Se), iron (γ-Fe_{1- x} Se) and islands of submicron gold particles formed on the surface of quartz. The 3D model of the interphase boundary is characterized by the fact that Au particles are concentrated mainly in eskebornite, and not on the quartz surface. Moreover, NPs are localized in the pores of mesoporous eskebornite, and submicron particles with a size of ~ 200 nm or more are displaced to the surface of eskebornite particles. Based on the data obtained, typomorphic features of the presence of Au NPs in the ore-forming processes of the formation and development of gold ore deposits are formulated.

Data from the Chuktukon, Tomtor (Russia), and Morro dos Seis Lagos (Brazil) mineral deposits demonstrate that the mineral potential of laterite produced by weathering of carbonatites can be extended with Fe, Mn, Ti, and V, which are commonly beyond the conventional ore production. Several previously unknown factors have been revealed, which control the mineral potential of laterite: reduction of weathering products, composition and ore contents of carbonatite, lateral and vertical migration of elements, as well as liquid fractionation of colloids in upper zones of weathering profiles. The reported study provides additional arguments for the idea that laterite derived from carbonatites stores unique multicomponent mineralization of heavy lanthanides, Y, Sc, Fe, Mn, Ti, V, Sr, Ba, Al, and Ga, besides the common target commodities of Nb, La, Ce, and P.

The search for oil and gas in folded zones and in the foredeep of the cis-Uralian region for many decades was reduced to drilling quite easily identified anticlinal structures and reefs located at shallow depths. Many important discoveries were made as a result, but the overall effectiveness of the work remained relatively low. On the one hand, this was due to the insufficient information content of the data for reliable preparation of structures in regions of complex structure. On the other hand, the peculiarities of the development of oil and gas systems in these regions were ignored during the assessment of prospecting sites. In comparison with traditional producing centers in the platform regions of the Volga-Ural and Timan-Pechora basins, this distinguishing feature was caused by a thicker sedimentary cover, the variability of its composition and structure, and multiple phases of structural development. Many failures were due to the formation of traps after the passage of the primary migration flow of oil and gas, low capacity of reservoirs, and their breaching by faults. As shown by interpretation of new geodata using modern knowledge about the oil and gas potential of regions of similar structure, the cis-Uralian region contains poorly studied oil and gas accumulation zones that can contain large deposits. These include blind thrust regions, subsalt traps in zones of dislocated diapirs, and also stratigraphic and combined traps associated with unconformities and facies changes. The utmost attention is paid to new prospecting objects in the Timan-Pechora basin in which the thickness of the Paleozoic cover has increased. The delineation of new promising objects in these zones has become possible due to new knowledge and better geophysical data.

Integrated seismic, drilling, and other exploration works in the southeastern Anabar-Khatanga petroleum province since the early 1930s led to discoveries of small oil and gas occurrences and one large filed of Central Olgino. However, the petroleum potential of the northwestern part of the province remains poorly investigated and evaluated. The reservoir potential appraisal is attempted in this study using all available seismic, geological, and geochemical data, including evidence from four new wells drilled in the Sopochnoe uplift and the Zhuravliny swell. The obtained data provide constraints on the extent of oil and gas generation, accumulation, and losses from degraded traps in Permian strata that have the highest potential as source rocks. The source rocks of the Upper Kozhevnikovo, Lower Kozhevnikovo, and Tustakh formations have been characterized in terms of thickness, contents of organic carbon and chloroform bitumen, maturity (catagenesis) of organic matter, and density of oil migration and gas generation. The maximum possible estimates of oil and gas resources that can potentially accumulate in structural traps, without migration losses, are obtained for each of the three reservoir formations by basin modeling. Judging by geological and geochemical criteria, the Upper Kozhevnikovo Formation can preserve only a minor portion of initially accumulated hydrocarbons, while the oil and gas accumulations, as well as the petroleum generation potential of organic matter in the Lower Kozhevnikovo and Tustakh formations, were destroyed by late Permian-Early Triassic trap magmatism and Mesozoic-Cenozoic tectonic activity.

The paper presents data on different types of Late Jurassic carbonaceous-siliceous-shale sequences of marine deposits in the western side of the Frolovskoye basin. The diverse sedimentation patterns in the area were presumably controlled by tectonics, sea bottom topography, and currents, with voluminous gas venting through large faults. Recent exploration drilling in the Elizarovo trough and the Vygnlor basin revealed Upper Jurassic sections of a previously unknown type with low-radioactivity lower strata markedly thicker at the account of biogenic radiolarite intercalations affected by postdepositional carbonatization. The lithology of these rocks is described with implications for deposition environments and extent of such sections.

Upper Devonian carbonate reef complexes have been studied on the territory of the Kolyvan-Tom’ Folded Area in sections in the right bank of Tom’ River. Facies analysis of the exposed part of the reef complex indicates the predominance of fore-reef and continental margin depositional environments of a tectonically active margin. The identified conodont associations are represented by cosmopolitan representatives of the genera Ancyrodella , Ancyrolepis , Icriodus , Mehlina , Palmatolepis , Polygnathus and “ Polylophodonta ” suggesting a correlation with the punctata - jamieae , rhenana - linguiformis , triangularis and Lower crepida conodont zones. The largest conodont diversity occurs at the triangularis / crepida boundary. Biofacies analysis of ostracod distribution has led to identification of characteristic associations and their restriction to certain parts of the palaeobasin. Substage boundaries yielded ostracods with both smooth and ornamented shells. In the lower part of the substages, smooth forms predominate, whereas the middle and upper parts of the substages are characterised by forms with tuberculate and reticulated surface. Hollinella valentinae Beds were traced in the Upper Frasnian Solomino Formation, and Acratia granuliformis Beds were traced in the Lower Famennian Kosoy Utyos and lower Mitikha members. Isotope geochemistry of the Upper Devonian sections of the south of Western Siberia reveals Frasnian global events - the Middlesex/ Punctata and the Upper Kellwasser, their stratigraphic position confirmed by palaeontological data, as well by as the globally expressed negative carbon isotope anomaly. These boundaries are marked by changes in depositional regime reflecting sea-level eustatic fluctuations, which are complemented with faunal changes.

To study the geological structure in the search for raw hydrocarbons within the Volga delta and the Caspian Sea, two intersecting profiles of magnetotelluric sounding were performed. The analysis of geoelectric sections based on the one-dimensional inversion of the initial and normalized invariant curves of apparent resistance showed that it is necessary to use methods of three-dimensional mathematical modeling to form reliable geoelectric models. Their initial construction necessary for the three-dimensional interpretation of invariant apparent resistance curves was carried out taking into account their one-dimensional inversion. The resulting model, including the lower structural part, is constructed by the method of interactive matching to the apparent resistance curves of model curves calculated according to the program of three-dimensional mathematical modeling. This approach made it possible to take into account the influence of local galvanic distortions on the apparent resistance curves when evaluating the distribution of electrical conductivity in the lower parts of the subsea deposits. As a result of the integrated interpretation of magnetotelluric data, blocks with increased conductivity have been identified in the subsea deposits of the Northern Caspian Sea, which are most likely associated with high fluid saturation of Cretaceous and Neogene sediments. Their position correlates with the regional discontinuous structures of the region.

Accurate assessment of mineral content and the brittleness index ( BI ) is crucial for designing effective hydraulic fracturing treatments in coal seams, a parameter required in the East Bokaro Coalfield in India. This study combines sidewall-core and well log data, focusing on well A-1, where X-ray diffraction analysis of sidewall cores was conducted to identify mineral content. The obtained mineralogical data were extrapolated to well A-2 through a synthesis of well log parameters, X-ray diffraction analysis, and prior research results. Linear regression equations incorporating known minerals and well log data as input parameters were employed to calculate volumetric mineral content in the formations. The reliability of the model was validated by assessing the minimal difference between predicted and observed log curves. Furthermore, the brittleness index was determined using both geomechanical methods based on compressional wave velocity and mineralogical methods incorporating quartz, feldspar, and dolomite content. Comparative analysis of BI values demonstrated a consistent trend, while variations in the mineralogic BI were observed in relation to mineral content. This study not only establishes a continuous multimineral model for cases with unavailable core data but also contributes to advancing the understanding of mineral content variations. Additionally, the correlation between BI variations and mineral contents enhances our knowledge of the geomechanical properties essential for design of hydraulic fracturing in coal formations. The results presented herein offer valuable insights for optimizing hydraulic fracturing strategies in the East Bokaro Coalfield and provide a foundation for further research in similar geologic settings.