Vol 43, No 2 (2020)
Geology, Prospecting and Exploration of Mineral Deposits
Fluorite-bastnaesite rocks of the Ulan-Ude rare earth occurrence as a new type of carbonatites: Western Transbaikalia, Russia
Abstract
The aim of the study is to show evidence confirm the magmatic nature of the bastnaesite-fluorite rocks of the Ulan-Ude occurrence that represent a specific type of carbonatites. The minerals have been studied using electron microscopy, thermometry, and analysis of stable isotopes. In many cases, the content of both fluorite and bastnaesite in the studied rocks reaches 50%. The rocks formation time (134.2 ± 2.6 Ma) is close to that of the carbonatites in the Western Transbaikalia province. The temperature of bastnaesite and fluorite formation in the rocks exceeds 500 C. The studied rocks contain phenocrysts of fluorite, bastnaesite, and tetraferriflogopite. Their crystallization began in the intermediate focus. The fine-grain fluorite matrix with small bastnaesite scales was formed in near-to-the-surface conditions and fixed by the hardening of the rocks. The carbonatites feature melt “dryness”, which determines an extremely low occurrence of the hydrothermal processes, changes in the xenoliths and previously formed minerals. The low fluid saturation level is confirmed by the absence of phlogopite water in position A, filled with fluorine only. The carbonatites are characterized by a higher content of sulfates represented by tenardite, glauberite, plumbojarosite, and corkite that are present in the composition of the salt melts released at the later stage of the melt crystallization.
Earth sciences and subsoil use. 2020;43(2):145-159
145-159
Mineralogical and petrographic characteristics of the Ugahan deposit
Abstract
The article considers the mineralogical-petrographic and geochemical characteristics of the Ugahan gold ore deposit with the aim of creating a scheme of the mineralogical associations’ formation that is inscribed in the general geodynamic evolution of the Bodaibo region. The study has been carried out on the copyright material obtained in the research area during the fieldwork. The mineralogical-petrographic and analytical work has been carried out at the Research Sharing Center “Isotope-geochemical studies” of Vinogradov Institute of Geochemistry, the Siberian Branch of the Russian Academy of Sciences. The mineralogical and petrographic research has identified three generations of carbonate minerals, formed at different times and associated with different stages of the field formation. Within the deposit, the development of the regenerative quartz aggregates is widely observed. The phenomenon is especially widespread in the upper members of the Buzhuikhta formation that are composed of quartz sandstones. The development of the mineral associations in the deposit took place in the following order. At the early low-temperature stage, the framboid and small idiomorphic pyrite were formed (I and II). Later, the high-temperature minerals association developed, that included arsenopyrite, pyrrhotite, pyrite-III, native gold, galena, sphalerite, and gray copper ores. At the post-ore stage, the pyrite-IV crystallization in a quartz-carbonate rim occurred. A similar sequence of mineral association formation is observed at the Krasny and Sukhoy Log deposits, which suggests that the formation of ore mineralization of the Sukhoy Log type deposits is a result of similar ore-forming processes. The confinement of the Ugahan deposit to the Buzhuikhta formation allows us to consider this stratigraphic unit as promising in terms of further exploration for gold deposits. The content of arsenic (as the main gold-accompanying element in the Bodaibo region) in the deposits of the Buzhuikhta formation is an order of magnitude lower, which suggests that it should be excluded from the search characteristics within the boundaries of this stratigraphic level.
Earth sciences and subsoil use. 2020;43(2):160-176
160-176
Altered kimberlites of the Vakunaika river: new data and prospects
Abstract
Prospecting for diamonds and their sources started in the Irkutsk region in 1947. After the large diamond deposits were discovered in Yakutia, the high-scale diamond prospecting in the Irkutsk region was nearly abandoned for a number of reasons though there were numerous diamond crystals found in the alluvium of the major watercourses in the north and south of the region. The general search for diamonds in the platform part of the region was conducted by geological survey and dedicated research projects. However, the half-century prospecting failed to identify primary diamond sources in the platform part of the Irkutsk region. The described territory belongs to the Lower-Tunguska (Nepa-Chona) diamond province. Its diamond content is attributable to the magmatic, lithologic-stratigraphic, tectonic, mineralogical, and geomorphological factors. The diamond-bearing prospects of the area were determined by the many-year exploration conducted by the Irkutsk Geology Directorate (“PGO Irkutskgeologia”), the Amakinskaya survey party (“PGO Yakutskgeologia”), and by the dedicated projects of the research-and-production organizations of the USSR and Russian Federation. The heavy mineral sampling identified pyropes and chromespinelides, the minerals that are paragenetically associated with diamonds, in most of the watercourses of the area. LLC Angarsk Investment Company has been prospecting for diamonds in the Irkutsk region including the Katangsky district, since 2006. The aim of the exploration is to identify primary diamond sources, the research object being Verkhnechonskaya license area (hereinafter, Irkutsk area). The research methods include reconnaissance traverse, heavy mineral sampling in small volumes and from depth, ground-based magnetometry, prospecting and core drilling to verify the geophysical and mineralogical anomalies identified by the previous diamond prospecting operations, analytical and laboratory studies, and processing of the obtained data. One of the most significant research results is the discovery of the rocks of kimberlite nature. For the first time, the search in the Siberian platform area has identified formations that resemble kimberlites by their mineralogical, geochemical and petrochemical data. The formations have been provisionally named altered kimberlites. The rocks had been subjected to the intensive superimposed processes that nearly completely altered their original appearance and composition. They form a diatreme of complex morphology, the structure of which shows the signs of repeated tectonic shifts. The structural and tectonic conditions of the diatreme are in many respects similar to those of the kimberlite pipes in the Yakutia diamond-bearing province. The main conclusion is that the discovery of the ultrabasic rocks of the kimberlite group allows us to consider the primary diamond potential of the northern areas in the Irkutsk region to be very high.
Earth sciences and subsoil use. 2020;43(2):177-193
177-193
Azimuthal anisotropy of the Sayan-Baikal fold region by the receiving functions of distant earthquakes
Abstract
The purpose of the work is the determination of a detailed velocity structure of the earth's interior of the seismically active Sayan-Baikal fold region, including the identification of the azimuths and depths in the vicinity of the observation points with anisotropic properties. The source data for the study is the long-term observations by five broadband seismic stations in the Sayano-Baikal fold region. The proposed methodology for identifying the depths and directions of the earth's interior with anisotropic properties is based on the longitudinal receiving function method. The receiving functions for all possible directions of each observation point have been selected from the tele-seismic records. The azimuthal boundaries are identified in relation to the observing station where the receiving functions change significantly, which means a change in the velocity structure when crossing these conditional boundaries. Within the azimuth ranges (BAZ) with homogeneous receiving functions, velocity models (VS) have been calculated by inverting the functions. The models take into account the relationship between the depth of medium sounding (h) and the corresponding distance from the seismic station (d). Based on the one-dimensional velocity sections for different azimuths, circular models VS(h,BAZ,d) have been constructed with the account of the seismic drift. The models visualize the velocity structure in relation to all observation points at the depths up to 70 km and 270 km. As a result of the study, a set of models reflecting the detailed deep-seated velocity structure of the Sayano-Baikal folded region has been obtained. The velocities of the seismic waves VS ( h ) have been determined within the earth's crust with an average depth step of 1 km, and within the mantle, with a step of 5-10 km. The circular models VS(h,BAZ,d) clearly demonstrate the velocity heterogeneity in various directions from the observation point and allow one to identify the anisotropy of the medium. The latter is manifested as the presence of a symmetry axis in the circular models, which on average has a northwest-southeast orientation, but varies with the depth.
Earth sciences and subsoil use. 2020;43(2):194-208
194-208
Exploration and Development of Mineral Deposits
Oil-and-gas potential of the reef deposits in the Vilyuy syneclise south
Abstract
The article discusses the results of the study of the buried Cambrian organogenic reef structures in the Siberian platform east, their reservoir properties assessment, and the nature of their distribution. The basis for the study was the seismic, electrical and geochemical investigations conducted on the territory. Also involved were the results of the paleogeographic reconstructions. The study has defined the resistance levels for the Cambrian-Vendian deposits that correspond to the development of the reservoirs promising for oil. The authors have constructed geoelectric sections that reflect the development of the organogenic structures in the joint area of the Vilyui syneclise and Aldan anteclise. The geoelectric characteristics of the West Yakut barrier reef and the demolition zone of the destroyed buildings have been described. The issues of hydrocarbon migration and accumulation within the region have been considered. Promising zones for drilling prospecting wells have been identified. The buried reef structures and the zone of the organogenic material demolition can serve as foci of hydrocarbon generation. The absence of the extensive high-resistance covers on the site makes it possible to predict the development of fractured-cavernous collectors formed by the leaching processes prevailing against the background of the water saturation of the Perm deposits in the Vilyui syneclise, and the transgression-regression stages. The Domanicoid type Kuonama deposits of the Yudomo-Oleneksky basin bordering the barrier reef can be considered hydrocarbon sources.
Earth sciences and subsoil use. 2020;43(2):209-219
209-219
Division of the Parfenovsky horizon reservoirs in the Kovykta field into lithotypes using the well survey data
Abstract
The purpose of the work is to study the heterogeneity of the composition, structure, and filtration-capacity properties of the sandstones in the Parfenovsky horizon of the Chora formation, the Kovykta gas condensate field. An analysis of the behavior of the well geophysical survey curves and differential distributions of the geophysical parameters (double difference parameters of the gamma-ray logging and neutron logging) in the Parfenovsky horizon interval has been conducted. The differential distributions of the geophysical parameters before and after dividing the reservoirs of the Parfenovsky horizon into lithotypes have been compared. The analysis of the logging data and the geophysical parameters obtained based on the above has made it possible to identify three lithotypes of the sandstone reservoirs in the Parfenovsky horizon section. Based on the well survey data, quantitative criteria for dividing the sandstone reservoirs of the Parfenovsky horizon into lithotypes have been substantiated. Directions for the further studies of the structure of the reservoirs in the Parfenovsky horizon have been determined. The study has concluded that there are reservoirs with improved and degraded filtration-capacity properties in the Parfenovsky horizon. The presence of reservoirs with different properties and composition in the deposits of the Parfenovsky horizon shows that it is necessary to revise the petrophysical model and methodological support for the complex interpretation of the well geophysical survey data used in the recalculation of the hydrocarbon reserves of the Kovykta gas condensate field in 2013.
Earth sciences and subsoil use. 2020;43(2):220-229
220-229
Influence of flocculant reagents on the parameters of clay suspensions
Abstract
The purpose of the work is to evaluate the effect of flocculant reagents on the rheological and structural-mechanical properties of clay suspensions, and to select their optimal concentration in the drilling mud. Currently, the industry produces a huge number of drilling mud flocculants that differ in their properties and composition. Most flocculants are water-soluble polymers with a large molecular weight, both of natural and artificial origin. The main purpose of such reagents is to separate the solid and liquid phases of the drilling mud during its dewatering and disposal. However, in clay suspensions, the same reagents are used as thickeners. As drilling fluids are complex systems that differ in their component composition, it is not possible to recommend a universal flocculant. During the study, the analysis of the flocculating and thickening capacity of the reagents was performed in two stages. The study defined an optimal concentration of the polymer at which maximum values of the dynamic shear stress were reached. The clay suspensions containing polymer reagents were been experimentally compared. The values of the rheological, structural-mechanical and filtration parameters of the solution were used as the evaluation criteria. The study has established the following. The reagents BEN-EX, BENTOPLUS and DRB-9 can be used to increase the viscosity of the clay solution, provided that the concentration of the additives BENTOPLUS and DRB-9 does not exceed 0.2 kg/m3. The SPECFLOC A 7950-20 reagent can be used to increase the viscosity of the clay solution in concentrations up to 0.1 kg/m3, while in concentrations of 0.2 and 0.3 kg/m3, the additive mainly effects the drilling mud as a flocculant, reducing the static shear stress of the solution and increasing the filtrate output. If the dynamic sheer stress is the only diagnostic variable when drilling with the SPECFLOC № 6919 additive, the latter can be recommended for use. In all other cases, additional research is required. The conducted laboratory studies allow us to obtain drilling fluids with a set of technological parameters that ensure high quality of the prepared drilling fluids.
Earth sciences and subsoil use. 2020;43(2):230-241
230-241
Geoecology
Modern requirements for occupational risk assessment at gold mining sites
Abstract
Russia is currently in the process of modernizing its legislation, primarily in the areas of occupational safety and health, industrial safety and emergency safety, which concerns the management system for occupational and industrial safety on a state level. The aim of the modernization is to make a transition from the previous inefficient system to the modern one. The old system focuses on health compensation, medical and social assistance to the employees suffering work injuries and occupational risks, while the new system is based on a preventive approach that presupposes continuous improvement of the working conditions, industrial safety enhancement, development of a safe working behavior culture, and creation of a risk-management system. The purpose of the article is to analyze the occupational safety and health management innovations encouraging the employers to implement risk assessment and risk management, and to evaluate the occupational risks in gold mining processes. The authors have examined the modern procedures of risk assessment, evaluated the occupational risks for the gold mines of the Bodaibo district, Irkutsk region, analyzed the risks by two methods and identified high-risk professions. Possible reasons for the incompliance of the physical factors of the gold miners’ working environment with the claimed requirements have been analyzed. The investigated professions are classified as high- and middle-risk ones. The detailed study of the drilling-and-blasting site has concluded that the mechanical hazards caused by the rock fragmentation, dust, or noise are unacceptable. Thus, the priority measures on improving the working conditions should focus on eliminating these adverse factors.
Earth sciences and subsoil use. 2020;43(2):242-255
242-255
Results of Field Studies
Conditions of the formation of the main exogenous processes in the southwest part of the Baikal rift system (Russia) and in the eastern part of the south China block (China)
Abstract
The aim of the study is to analyze and compare the causes and conditions for the formation of the exogenous processes in the southwestern part of the Baikal rift system (Russia) and in the eastern part of the South China block (China) with the emphasis on the weathering, gravitational and surface-water processes. The Tunka rift zone is taken as the main site. It is compared with the eastern part of the South China block where the main observation points are associated with the Yangtze River delta and adjacent territories. The main research methods include field routes with visual examination of the observation points and measurement of certain characteristics and parameters, as well as selection and analysis of the published and archive literary sources. The comparison of the geodynamic processes emerging in the study territories has concluded that the dominant processes are weathering and gravitational processes, namely, landslide formation. The intensity of the processes is primarily determined by the sharply broken relief. The differences between the two study regions are determined by the climatic peculiarities including the precipitation level and temperature change, as well as by the seismicity, the presence of the glacier forms, and the landscape features. The combination of the above factors predetermines the wet landslide activity of the Tunka branch of the rift depressions vs. almost none of the kind in the Yangtze River delta. The analysis of the defined factors makes it possible to predict exogenous processes such as landslide and mudslide, and take timely measures on minimizing the negative impact of the above. The lack of the large scale maps showing the danger zones and adequate control of identifying the land areas that are knowingly in need of protection from the geodynamic processes’ impact, are increasingly leading to the extension of the danger zones and associated risk both in the eastern part of China and throughout the Baikal region.
Earth sciences and subsoil use. 2020;43(2):256-270
256-270
Personalia
Man of action: on the 85th anniversary of Professor Zhan Vyacheslavovich Seminsky
Abstract
The work of Zhan Vyacheslavovich Seminsky, Professor of Irkutsk National Research Technical University is multifaceted and highly productive. The article is dedicated to the 85th anniversary of the scientist and aims at familiarizing a wider audience with the achievements in his multi-year research and production work. The article is based on the materials from different editions and personal contacts of the author with Seminsky in the field geological conditions when working on joint research-and-production state budget projects and writing scientific articles together within the frames of preparation of the Ph.D. thesis of the author with Zh.V. Seminsky as the research supervisor. Professor Seminsky has worked for 15 years in the production geological association “Sosnovgeologia” where he defended his candidate thesis on ancient volcanic complexes containing various ore deposits. This experience became later of value for the student’s audience. During his work at Irkutsk National Research Technical University, Professor Seminsky defended his Ph.D. thesis, prepared 20 manuals and a monograph, and became a scientific adviser for 17 postgraduates and Ph.D. students. His studies on the ore field structures, regularities of the ore deposits formation and the metallogeny of Eastern Siberia and Transbaikalia (plate tectonics approach) have made him known as one of the leading specialists in Russia and other countries. Zh.V. Seminsky for 33 years had been chief of the Department of Mineralogy, Petrography and Mineral Resources (later, the Department of Geology and Geochemistry of Mineral Resources). For many years, he has been Chairperson of the Dissertation Council D 212.073.01 of Irkutsk National Research Technical University. Professor Seminsky is full member of the Russian Academy of Natural Sciences, Honored Worker of Science of the Russian Federation, Distinguished Mineral Explorer, Honorary Worker of the Education of Mongolia, Professor Emeritus of Irkutsk National Research Technical University, and Honorary Professor of Mongolia. Of special note is the fact that Seminsky’s many-year work has become the base for this journal: Zh.V. Seminsky for many years had been Editor-in-Chief of the scientific edition “Proceedings of the Siberian Department of the Earth Sciences section of the Russian Academy of Sciences. Geology, prospecting and exploration for mineral deposits” that is on the list of the Higher Attestation Commission.
Earth sciences and subsoil use. 2020;43(2):271-276
271-276