Vol 279

This study experimentally investigates the patterns of hydrogenation of olivine crystals by an aqueous fluid in equilibrium with olivine and orthopyroxene at a pressure of 5.5 GPa and temperatures of 850, 940, 1030, and 1100 °C. It is shown that at P-T parameters characteristic of slabs and the portion of the mantle wedge mechanically coupled to slabs under the thermal regimes of warm and hot subduction, the interaction of the aqueous fluid with olivine is largely controlled by the concentration of pre-existing silicon vacancies in olivine crystal structure. As a result, at a temperature of 850 °C, the concentration of OH defects related to Si vacancies increases noticeably relative to the initial value; however, calculated as H₂O, it does not exceed 110 ppm. At 1030 °C, no new Si vacancies are formed, and the water content in olivine remains at the same level as after experiments at lower temperatures. The formation of Si vacancies and their protonation during olivine recrystallization in an aqueous fluid are recorded only at 1100 °C, near the peridotite solidus. In newly formed olivine, the water content reaches 350 ppm. It has been established that an increase in oxygen fugacity from the values of the Ni-NiO (NNO) buffer to those of the Fe₂O₃-Fe₃O₄ (HM) buffer, as well as an increase in NaCl concentration in the fluid from 0 to 9 wt.%, have little or no effect on the solubility of water in olivine. It is concluded that due to the low solubility of water in olivine immediately following the complete dehydration of serpentinized peridotites at depths of ~150-200 km, the efficiency of water transport into the mantle by slabs under the thermal regimes of warm and hot subduction must decrease sharply. Under such conditions, a significant volume of aqueous fluid is released within the slabs, which can participate in the generation of deep magmas and mantle metasomatism.

The paper considers the problem of refining the critical depth of rock burst hazard for the Nyorkpakhk apatite-nepheline ore deposit in the context of transition to underground mining. The relevance of the study results from the discrepancy between the value of 400 m (according to regulatory documentation) and the actual mining and geological conditions, especially considering the significant impact of the existing open pit on the stress-strain state of the rock mass and other natural factors of the region. The aim of the study is the development and testing of a comprehensive methodology for assessing the critical depth of rock burst hazard, including core discing analysis, seismicity monitoring, spatial numerical modeling of the stress-strain state using the CAE Simulia Abaqus software, assessment of the rock burst hazard potential of rocks based on the Kaiser criterion, and comparison with a geomechanically similar analogue Oleniy Ruchey deposit. Core discing analysis revealed only local stress zones associated with tectonic faults, without characteristics pointing to rock burst hazard down to the +100 m level. The results of numerical modeling confirmed the absence of stress concentrations down to the +35 m level both before the start and after the completion of open pit mining. Comparison using the similarity method showed expected manifestation of rock burst hazard below the +50 m level. The studies, according to the described methodology, enabled scientific justification of increasing the critical depth of rock burst hazard relative to the regulatory value, down to the +100 m level. It has also been determined that for the Khibiny deposits there is no direct correlation between the brittleness criterion and the propensity for rock burst hazard. The proposed methodology is recommended for testing at rock burst hazardous deposits with complex mining and geological conditions.

The stress wave generated by rock blasting causes vibrations in the off-contour massif. The rock strength is significantly reduced in those off-contour massif areas where the permissible velocity is exceeded. This can lead to the collapse of nearby ledges. The aims of the study are to develop a methodology for determining the boundary of the off-contour massif seismically hazardous zone, as well as to assess the well delay interval effect on the hazardous zone boundary position. Elastic vibrations of the off-contour rock under the effect of a blast wave are considered. The dependence of the rock mass displacement under the action of stress is a function of time and distance from the blast site. A series of production experiments were conducted at the “Valley” quarry of Amur Minerals JSC to determine the coefficients values that take into account the attenuation of the stress wave in the rock with increasing distance from the blast site. A method to determine the position of the off-contour massif boundary has been developed. Beyond that boundary the rate of rock displacement does not exceed the permissible value. The initial data for the calculation are the rock mass physical and mechanical characteristics and the parameters of the explosives used. In the Simulink environment a simulation model was developed to implement the described method. A methodology for energy assessment of the process of rock displacement under the effect of a stress wave was developed to verify the modeling results. By analy-zing the results obtained, a conclusion was made about the sufficient accuracy of the proposed method for practical calculations. Displacement energy values of the same point of the off-contour massif are compared at different well delay interval. Rock blasting with increased well delay intervals allows to improve the off-contour massif safety, as well as the overlying horizons ledges. The quality of blasted rock loosening is maintained.

In recent decades, researchers have identified an important and in some cases leading role of biological processes, primarily microbiota activity, in the formation of weathering crusts. The study of new features associated with crust formation is of both theoretical and practical interest. The aim of this work is to clarify the role of microbiota in the formation of the Mesozoic kaolinite-type weathering crust (exemplified by the Turgoyakskoye kaolin deposit) using microprobe analysis and electron microscopy. The research showed active involvement of diverse microbial communities in the formation of kaolin clays: scientists found various fossilized bacterial structures, including mineralized biofilms, pseudomorphs after coccoid and rod‑shaped bacteria, glycocalyx remnants, and filamentous microfossils. This microbiota is morphologically similar to bacterial forms described in laterites, but the biominerals composing them are fundamentally different. In kaolins, they consist of silicates and aluminosilicates, while in laterites they consist of Fe, Al, and Mn oxides and hydroxides, which indicates a different species composition of microbiota involved in the formation of lateritic and kaolinitic weathering crusts. These findings likely show that during weathering, climate controls not only chemical but also bacterial mineral formation. Unlike laterites, the distribution of microorganisms in kaolin clays is uneven – ranging from isolated remnants to mass accumulations. During kaolin formation, microbiota biomechanically destroys the matrix of the parent rock and simultaneously synthesizes new minerals, forming biomorphs from them. Among the latter, biomorphs after “titanium” bacteria are of particular interest. Their discovery confirms Academician V.I.Vernadskii’s view on the predominantly biogenic nature of titanium in rocks of mature weathering crusts.

The Spitsbergen archipelago is at the junction of the northern segment of the Norwegian-Greenland Basin and the western part of the Arctic Ocean, which makes it a key area for deciphering the formation history and geological structure of the region. Crystalline basement rocks and sedimentary cover units outcrop here, including those that constitute the petroleum-bearing complexes of the shelf. There is a clear need to substantiate the presence of evidence for the Baikalian (Timanian) tectono-magmatic activation within the Earth’s crust of the Spitsbergen archipelago, as well as to determine the conditions of its manifestation. To address this objective, a comprehensive description of the Trollheimen volcanogenic formation – whose rocks are known within Oscar II Land – is provided for the first time, based on the authors’ own data. We examine geotectonic features, material composition, age, and geodynamic interpretations of the formation settings. The authors identified that the sedimentary-volcanogenic complex described in the mountainous glacial part of Oscar II Land was formed during the Vendian (574-558 Ma) as a result of tectono-magmatic activation of the epi-Grenvillian paraplatform. They provide the petrographic and petro‑geochemical profile of the identified metabasalts, metaandesites, and metatuffs. The results of studying the petrochemical features of the Trollheimen volcanogenic formation indicate magma generation at great depths; the rift-related nature of these formations is determined. The authors carry out a correlation with the previously identified sedimentary-volcanogenic complex of the Chamberlaindalen Series in the northern part of Wedel Jarlsberg Land. The presented data confirm the previously proposed arguments for the Vendian-Baikalian, Timanian intraplate activation in the archipelago, as well as the widespread development of these complexes within the cover of the epi-Grenvillian paraplatform of Spitsbergen.

One of the pressing scientific challenges in the field of hydrocarbon production enhancement from hard-to-recover reserves using hydraulic fracturing is the insufficient understanding of how the elastic properties of hydraulic fracturing fluids affect proppant retention efficiency during fracture initiation in the near-wellbore zone. Earlier domestic and foreign studies on proppant transport capacity assert that fluid viscosity plays a key role in proppant retention; however, recent data indicate a significant influence of the elastic properties of polymer systems, particularly when using low-viscosity synthetic hydraulic fracturing fluids based on polyacrylamide (PAM). This study aims to provide a fundamental substantiation of the effect of viscoelastic properties of hydraulic fracturing fluids on proppant transport efficiency. The article presents the methodology and results of laboratory tests evaluating the viscoelastic and proppant transport properties of PAM-based and guar polymer-based hydraulic fracturing fluids. The findings demonstrate that PAM-based hydraulic fracturing fluids, despite their low effective system viscosity, exhibit more pronounced elastic properties compared to linear guar gels: the relaxation time and the first normal stress difference for the synthetic hydraulic fracturing fluid are 1.99 and 4 times greater than the corresponding values for the linear guar gel. The test results confirmed that the proppant settling rate in the PAM-based hydraulic fracturing fluid under static conditions was 28 times lower than that in the linear guar gel at equivalent active substance concentrations. The elastic properties of hydraulic fracturing fluids have a substantial effect on proppant transport capacity, supporting the potential of using low-viscosity synthetic PAM-based hydraulic fracturing fluids to enhance hydrocarbon production from reservoirs with permeability less than 1 mD.