Eastern Transbaikal Region Research Articles

Development of fluvial‐lacustrine systems in the rift basins fostered Jehol Biota origin: Palaeobiogeographic insights on Dabeigou‐type ostracod fauna

The Lower Cretaceous Dabeigou Formation (135–130 Ma) in the Luanping Basin, associated with its contemporary strata in northeastern China, contains the earliest documented fossils of the Jehol Biota. This includes the Luanpingella—Eoparacypris—Ocrocypris ostracod assemblage, referred to in this study as the Dabeigou‐type ostracod fauna (DOF). Ostracods, which are small (0.5–2 mm) aquatic crustaceans, are abundant and easily preserved as fossils. Outlining a clear palaeobiogeographic range of the DOF can help expand the distribution range of the early Jehol Biota, providing valuable information on its origin. Results show that the DOF is mainly distributed in a series of rift basins along the Yanliao area of China to the eastern Transbaikal region of Russia, with a roughly narrow north‐south distribution. Rift basin development in the eastern part of the North China Craton, combined with humid climatic conditions, provided a suitable environment (e.g., fluvial‐lacustrine systems) for the emergence of the Jehol Biota.

Improving the quality of zeolite-containing rocks of the Eastern Transbaikal region on the basis of the application of directed energy impacts

Improving the quality of zeolite-containing rocks of the Eastern Transbaikal region on the basis of the application of directed energy impacts

Gold in Natural and Synthetic Pyrite: a Case of the Darasun Gold District, Eastern Transbaikal Region, Russia

Gold in Natural and Synthetic Pyrite: a Case of the Darasun Gold District, Eastern Transbaikal Region, Russia

Anna Nikolaevna Bek is the First Pediatrician in Eastern Transbaikal Region

The article is devoted to the history of pediatrics in Transbaikal Region and Anna Nikolaevna Bek role in children healthcare development. The topicality of Anna Nikolaevna and Evgeniy Vladimirovich Bek works in studying of Urov disease is discussed. The little-known facts about the first kindergartens implementation in Chita are presented.

Geochemical heterogeneity of polychronous relict zircons from restitogenic ultramafic rocks of the Shaman massif (Eastern Transbaikal region)

Research subject. The distribution patterns of rare earth elements (REE), as well as Y and Th, in the grains of polychromous zircons from the restitogenic ultramafic rocks of the Shaman massif (Eastern Transbaikalia). This massif is a steeply inclined protrusion that is part of the eastern branch of the Baikal-Muya ophiolite belt.Materials and methods. 31 zircon grains 100–150 μm in size were isolated from a composite sample of harzburgites and dunites with a total weight of 4 kg for their subsequent U-Pb isotope dating. These analyzes were performed by the LA-ICP-MS method by scanning along straight profiles on the plane of sections of representative zircon grains.Results. All zircon grains from the general collection are characterized by a rounded shape, a rough surface, microfracturing, a weak cathodoluminescent glow to a complete absence, and an irregular oscillatory zoning. In some grains, microinclusions of epigenetic minerals, such as quartz, mica, etc. were found. It was previously determined that, within the entire collection of zircon grains, the values of their age, as well as U and Th contents, vary across rather wide intervals (3049–502 Ma), the reasons for which are the subject of discussions. The LA-ICP-MS scanning over the profiles of representative zircon grains from the general collection showed that REE, Th, and Y are distributed highly unevenly, occasionally showing signs of zoning. It is assumed that the zircons found in the ultramafic rocks of this massif are a relict phase and appeared as a result of the transformation of very ancient (more than 3 billion years old) juvenile crystals of this mineral, which had been originally located in the upper mantle protolith.Conclusions. Transformations of juvenile zircons and their transformation into a relict phase occurred in the process of partial melting of the protolith, during which they underwent thermal action (annealing), chemical resorption, as well as disturbances in their U-Pb systems, which caused uneven “rejuvenation” of their isotopic age. It is also assumed that the revealed geochemical heterogeneity of relict zircons was mainly due to the later redistribution of trace elements with the simultaneous formation of microinclusions of epigenetic minerals in the process of infiltration along microcracks into ultramafic rocks, precipitated by acidic melts.

Application of GIS and Earth Remote Sensing Data for the Evaluation of the Spatiotemporal Spread of Rabies in Eastern Trans-Baikal Region

The aim of the study was to improve monitoring of natural foci of rabies based on the use of modern technologies of cartographic analysis.Materials and methods. A retrospective study was carried out on the data of official registration of rabies in the Trans-Baikal Territory (Eastern Trans-Baikal Region) for 1950–2020. The spatial spread of rabies among animals was compared for two time periods: 1972–1978 (n=157 cases) and 2014–2020 (n=61 cases). Software packages QGIS 3.16.0, ArcMap 10.8.1, ArcScene 10.8.1 and electronic landscape-geographical maps of the world “Natural Earth”, “OpenStreetMap” were used for the mapping. Analyzed territorial units (ATUs) tied to a degree grid (0,5º × 0,5º) were marked on the cartograms. The interdependence between the localization of rabies cases and landscape elements was assessed statistically, comparing between the rabies free and the rabies affected ATUs.Results and discussion. Differences in the landscape confinedness of rabies epizootics in Eastern Trans-Baikal Region at different periods of time have been established. Until 1983, dog rabies prevailed, and epizootics spread beyond the forest-steppe zone. In 1984–2013 rabies among animals was not recorded. In 2014–2020 red foxes (Vulpes vulpes) were the main source of the rabies virus. The area of the epizootic has more than halved in comparison with 1972–1978. The main manifestations of rabies were observed at the junction of lowland and mountainous, steppe and forest areas. The rabies affected ATUs were characterized by more pronounced landscape variables. Possible routes of cross-border spread of the rabies virus have been identified. The connection between the features of the spatiotemporal spread of rabies and genetic variants of the virus, climate change, animal migrations and anthropogenic factors in Eastern Trans-Baikal Region in 1950–2020 is discussed. The results of the study are proposed to be used to adjust the programs for barrier oral vaccination of the foxes.

Evidences of Wooden Materials Utilization in Construction of Medieval Mongolian Towns in Eastern Trans-Baikal Region (13th – 14th CC.)

Findings of structures remains discovered during excavations on Medieval Mongolian Sites in Eastern Trans-Baikal Region were summarized in the article. They were excavated during exploration of Alestui Mansion, at Khirkhira fortress, as well as at Konduy town site. The similar findings at Sutai Mansion in Buryatia, at Den-Terek fortress in Tuva, Karakorum, Shangdu, at Avraga fortress in Mongolia can be drawn on for comparison. In addition to traditional archaeological methods of the material investigation, an anatomical study of wood has been accomplished at Federal Scientific Center of the East Asia Terrestrial Biodiversity FEBRAS (Vladivostok). The study results evidence that some of samples collected belongs to Pinaceae, and one of them is the wood of Larix gmelinii or Dahurian Larch, vegetated in this region. Despite of rarity and fragmentariness of this kind of sources on Medieval sites of Central Asia and Far East, it was found out that the wood of local origin was utilized by the Mongols for monumental objects construction. This research is only a part of work on construction materials investigation of Medieval Mongolian Archaeological Culture.

Types, structure and location of fractured gold pockets

Fractured gold ore pockets of various types are classified and their structure is described in detail. This will allow explorationists to confirm high-grade gold ores, which is especially important in underground deposit mining. Gold pockets were mapped and analyzed by the author at deposits in Uzbekistan (Muruntau, Daugyz, Charmitan, Kokpatas), eastern Trans-Baikal region (Darasun, Balei, etc.) and Kochkarskoye (South Urals). Also, the paper describes the material collected by the author at gold pockets in Natalkinskoye, Nezhdaninskoye, Pavlik and Kyuchus deposits in Yakutia, Berikul in Western Siberia, Bakyrchik in Kazakhstan as well as deposits from Australia (Kalgoorlie, Northman, etc.), USA (Comstock, etc.), Canada (Porcupine), among others.

Первое антракологическое исследование древесных углей в Восточной Сибири: по материалам мастерской им. А.П. Окладникова

Archaeological wood is a rich source of information about people and paleoenvironment. Wood usually survives from the Paleolithic in the form of charcoal. That is why anthracological analysis or identification of timber species is the best way to study the remains of Paleolithic wood. Charcoal fragments found during the excavations in 1961 by V.E. Larichev and A.P. Okladnikov at the “A.P. Okladnikov Workshop” site located on Titovskaya Sopka (near the city of Chita) in the Eastern Transbaikal region, have been studied. Unique terrain, favorable location near a river valley, and presence of rich deposits of isotropic raw materials attracted humans to that area in the ancient times. Anthracological methods were employed for answering the questions about the strategies of using wood both for household needs and ritual purposes. The analysis of macroscopic features of anatomical wood structure has revealed that the samples belonged to the species of Rhododendron dauricum L. (Ericaceae). This species is widespread in the Eastern Transbaikal region and grows next to the archaeological site. For reconstructing the vegetation cover, the sources need to be expanded. The problem of the main type of fuel at that time remains open, since the Daurian rhododendron is a small shrub. Another curious question is how it was preserved after thermal exposure out of the variety of wood species. It might have been used for fumigation or for ritual purposes. Anthracological research is just beginning to be introduced into archeology, and therefore, testing the methodology on Siberian evidence is of crucial importance.

Изменчивость признаков вегетативных органов лиственницы Гмелина в Забайкальском крае

Изменчивость признаков вегетативных органов лиственницы Гмелина в Забайкальском крае

Уненкер – палеолитическое местонахождение культуры хэнгэрэктэ-сухотино в Забайкалье

Recent research has shown that the stone industries of the Barun-Alan-1 site (lower level of layer 6, level 6/7, and layer 7) in the Western Transbaikal region and Sukhotino-4 site in the Eastern Transbaikal region belong to the same Khengerekte-Sukhotino culture. The earliest layers containing the evidence of this culture at the Barun-Alan-1 site are associated with the Final Early Upper Palaeolithic, while the latest layer were dated to the Final Upper Palaeolithic. It was believed that the area of this archaeological culture had the western boundary in Barun-Alan-1 and eastern boundary in Sukhotino-4 253 km to the east. Works in the archives of the Transbaikal State University in Chita have made it possible to identify similar features in the industries of Sukhotino-4 and Unenker located in the lower part of the Ingoda River valley (130 km to the east from Sukhotino-4). Field research at the Unenker site was conducted in 1984. Presently, the evidence of the Paleolithic Unenker site has been analyzed in detail. It has been discovered that stone artifacts from Unenker were identical to artifacts from Sukhotino-4 in terms of morphology and methods of tool production. The fact that the Unenker site belongs to the Khengerekte-Sukhotino culture makes it possible to expand the boundaries of the area where this culture was spread 130 km to the east. Judging by the geographical position of the Unenker and Sukhotino-4 sites, the Ingoda River valley should be considered as the most promising area in search for new sites of the Khengerekte-Sukhotino culture. Since the study of this culture is still at the early stage, the research problems to be addressed include the origin of this culture, directions of its expansion, specific regional features, etc.

Oscillatory Zoning in Tennantite-(Fe) at the Darasun Gold Deposit (Eastern Transbaikal Region, Russia)

Oscillatory zoning in tennantite-(Fe) crystals found in carbonate–sulfide aggregates at the Darasun gold deposit has been studied. Similar elements have been distinguished in zoned crystals: core, “identical oscillatory rhythm,” rhythms with crystallographic and wavy oscillatory zoning, and rim with poorly defined fine oscillatory zoning. Oscillatory zoning is due to considerable variations in the contents of semimetals (As and Sb) and formally divalent metals (Fe and Zn). Variations in As and Sb are coupled with changes in Fe and Zn, respectively. Both As and Fe contents increase in zoned crystals from the center to the edge: Sb/(Sb + As) ratio varies from 0.44 to 0.03, while Fe/(Fe + Zn) ratio varies from 0.38 to 0.75. The evolution of the composition of zoned tennantite-(Fe) crystals is similar to that of the fahlore at the deposit and to that in pseudomorphic rhythmically zoned tennantite aggregates. A negative relationship between Sb/(Sb + As) and Fe/(Fe + Zn) ratios has been revealed: it is stronger in the internal rhythms than in the external. The oscillatory zoning formed under conditions close to local equilibrium under the influence of external factors at the early crystal growth stages. The composition of zones reflects (random) fluctuations of the external parameters caused by variations in physicochemical conditions (T, fS2, fO2, and pH) and fluid composition, by fluid boiling or mixing of fluids from different sources. Subsequently, changes in the crystal morphology, irregular fluctuations in crystal compositions, and various trends in the behavior of components were caused by the appearance of a concentration gradient at the mineral–fluid boundary and kinetic phenomena on the mineral growth surface. The zoning developed under the influence of “internal” mechanisms under conditions far from equilibrium due to the interrelation between the growth of zones enriched in one component, resulting from the concentration gradient at the crystal–fluid boundary, and the incorporation of another component, in particular, as a result of the self-organization process uninfluenced by external factors. It has been concluded that the oscillatory zoning in fahlore is caused by the difference in solubility of the end-members of the tennantite–tetrahedrite solid solution due to changes in the metal and semimetal migration conditions with a decrease in temperature and fluid salinity. Hence, the oscillatory zoning in tennantite-(Fe) crystals at the Darasun deposit was related to self-organization processes complicated by random fluctuations (noise) of the external parameters.

The dynamics of biogenic elements in the ecosystem of Lake Arakhley (Eastern Transbaikal Region)

This study presents the interannual dynamics of biogenic elements (nitrogen and phosphorus) in Lake Arakhley and compares functioning values of the water ecosystem within different types of intra-annual (seasonal) dynamics of the content of biogenic elements and organic matter in low water years and high water years. The research shows tendencies of increasing and decreasing contents of nitrogen and phosphorus. In low water years, organic matter is autochtonous, whereas in high water years its origin is allochtonous. The concentrations of biogenic elements do not exceed the values of maximum permissible concentration in fishery waters which means that eutrophication has not started. It was found that the dynamics of the content of nitrogen and phosphorus is determined by change in abiotic conditions and rate of biochemical and biological processes. The findings provide better understanding how mesotrophic lakes function.

Paleovolcanic necks and extrusions: Indicators of large uranium orebelts in the territories joining Russia, Mongolia, and China

The large ore clusters and uranium deposits detected in southeast Russia (eastern Transbaikal Region), eastern Mongolia, and northern China constitutes a large area, specialised in U, with a wide range of geological and mineral ore types. Amongst various types of uranium ore, hydrothermal deposits related to volcanic rocks, infiltration deposits of uranium sandstone and polygenous mineralisation in leucogranites represent main commercial interest. Large uranium clusters are located on the outer, side and peripheral parts of the Great Xing'an volcano-plutonic belt as well as in the framing taphrogenic depressions. The clusters formation timed to late Mesozoic (I-K) geodynamic processes. Deep geodynamics allowed the fluid flows of asthenosphere which were concentrating around the periphery of the slab stagnated in the transition mantle zone to penetrate into the above lithosphere and earth's crust with formation of pockets of magma, and ore-bearing volcano-tectonic depressions eventually. Therefore, the presence of igneous stocks, extrusions, and volcanic necks within the volcano-plutonic belts and depressions can be indicative of mineral potential of the area.

Fahlore and Sphalerite from the Darasun Gold Deposit in the Eastern Transbaikal Region, Russia: II. Fe and Zn Partitioning, Fluid Inclusions, and Formation Conditions

The partitioning of Fe and Zn between coexisting fahlore and sphalerite and fluid inclusions in sphalerite from the Darasun gold deposit have been studied. These data were used to estimate the formation temperature of the minerals by the sphalerite–fahlore geothermometer. The calculated crystallization temperature of 175–355°С is close to the homogenization temperature of fluid inclusions in sphalerite of 225–385°С.The estimated pressure for fluid inclusion trapping ranged from 340 to 1420 bar. The sulfur fugacity obtained from the FeS content in sphalerite associated with pyrite and the calculated temperature ranges from 10–5.5 to 10–11 bar.

Slab Melt as a Potential Source of Profiling Elements of Gold and Heavy Metal Deposits

Spatial/genetic control by slab magma products at gold deposits is shown in this paper by the example of granitoids in the Ust’-Kara area of the Eastern Trans-Baikal Region. The investigation performed makes it possible to take a fresh look at the problem of metal sources in the East Trans-Baikal gold deposits and to relate their formation to material flow from the oceanic lithosphere in the subduction zone, material conservation within the subcontinental mantle, and possible remobilization under large tectonic reconstructions.

Fahlore and Sphalerite from the Darasun Gold Deposit in the Eastern Transbaikal Region, Russia: I. Mineral Assemblages and Intergrowths, Chemical Composition, and Its Evolution

The mineral assemblages, mode of occurrence, and chemical compositions of coexisting fahlore and sphalerite from the Darasun gold deposit have been described. Three generations of fahlore and three generations of sphalerite have been recognized. The FeS content in sphalerite coexisting with fahlore ranges from 0.8 to 9.4 mol %. The complete solid solution series Fe-tetrahedrite–Zn-tetrahedrite–Fe-tennantite–Zn-tennantite reflected in Sb/(Sb + As) and Fe/(Fe + Zn) ratios ranging from 0 to 0.97 and from 0.07 to 1.00, respectively, with a predominant negative relationship between these ratios has been identified for the first time at the deposit. Stepped, oscillatory, and combined stepped-oscillatory growth zonings within fahlore grains and heterogeneous aggregates of fahlore have been found. Fahlore is enriched in As with respect to Sb, and Zn-tetrahedrite is followed by Fe- and Zn-tennantite from early to late generation; Zn-tetrahedrite is followed by Fe-tennantite in zoned grains and overgrown rims; sphalerite crystallized at decreased temperature and sulfur fugacity. The evolution of the chemical composition of fahlores was caused by the evolving temperature, fluid salinity, and conditions of metal migration.

Typomorphic Characteristics of Molybdenite from the Bystrinsky Cu–Au Porphyry–Skarn Deposit, Eastern Transbaikal Region, Russia

The paper presents pioneering data on the composition, texture, and crystal structure of molybdenite from various types of molybdenum mineralization at the Bystrinsky Cu–Au–Fe porphyry–skarn deposit in the eastern Transbaikal region, Russia. The data were obtained using electron microprobe analysis (EMPA), laser ablation–inductively coupled plasma mass spectrometry (LA-ICP-MS), and high-resolution transmission electron microscopy (HRTEM). Molybdenite found at the deposit in skarn, sulfide-poor quartz veins, and quartz–feldspar alteration markedly differs in the concentrations of trace elements determined by their species in the mineral, as well as in its structural features. Molybdenite-2H from skarn associated with phyllosilicates occurs as ultrafine crystals with uniform shape and texture; no dislocations or inclusions were found but amorphous silica was. The molybdenite composition is highly contrasting in the content and distribution of both structure-related (Re, W, and Se) and other (Mn, Co, Ni, Cu, Zn, As, Ag, Cd, Sb, Te, Ag, Pd, Au, Hg, Pb, and Bi) metals. In the sulfide-poor quartz veins, highly structurally heterogeneous (2H + 3R) molybdenite microcrystals with abundant defects (dislocations and volumetrically distributed inclusions) are associated with illite, goethite, and barite. Some single crystals are unique three-phase (2H + 3R polytypes + amorphous MoS2). The mineral has a low concentration of all trace elements, which are uniformly distributed. However, individual domains with uniquely high Pd, Te, Ni, Hg, and W concentrations caused by mineral inclusions are found in some grains. Molybdenite from quartz–feldspar alteration is characterized by low concentrations of all trace elements except for Re and Se, which enrich some domains of the grains. Our data indicate that the compositional and structural heterogeneity of molybdenite from the Bystrinsky deposit are its crucial features, which obviously correlate with the types of Mo mineralization.

Fertility of Rare-Metal Peraluminous Granites and Formation Conditions of Tungsten Deposits

The tungsten distribution in rocks of the Kukulbei Complex in eastern Transbaikal region results in a high potential of rare-metal peraluminous granites (RPG) for W mineralization and displays a different behavior of W in Li–F and “standard” RPG. These subtypes differ in the behavior of W in melt, spatial localization of mineralization, and the timing of wolframite crystallization relative to the age of the parental granitic rocks. The significant of W concentration is assumed to be due to fractionation of the Li–F melt; however, wolframite mineralization in Li–F enriched granite is not typical in nature. The results of experiments and our calculations of W solubility in granitic melt show that wolframite hardly ever crystallizes directly from melt; it likely migrates in the fluid phase and is then removes from the magma chamber to the host rocks, where secondary concentration takes place in exocontact greisens and quartz–cassiterite–wolframite veins. At the same time, the isotopic age of accessory wolframite (139.5 ± 2.1 Ma) within the Orlovka massif of Li–F granite is close to the formation age of the massif (140.6 ± 2.9 Ma). A different W behavior is recorded in the RPG subtype with a low lithium and fluorine concentration, exemplified by the Spokoininsky massif. There is no significant W gain in the melt. All varieties of wolframite mineralization in the Spokoininsky massif are derived from greisens, veins, and pegmatoids yielding the same crystallization ages (139.5 ± 1.1 Ma), which are 0.9–1.8 Ma later (taking into account the mean-square weighted deviation) than the Spokoininsky granite formation (144.5 ± 1.4 Ma). Perhaps this period corresponds to the time of transition from the magmatic stage to hydrothermal alteration. Comparison of the isotope characteristics (Rb–Sr and Sm–Nd isotope systems) of rocks and the associated ore minerals (wolframite, cassiterite) from all examined deposits shows a depletion in eNd values for ore minerals relative to the rock and the opposite behavior for the intial Sr isotope ratios. This may indicate the specific nature of ore matter, where the effect of the juvenile component is definitely expressed. Our geochronological results show that tantalum and tungsten mineralization took place within a narrow age interval, almost synchronously with the crystallization of associated granites. The coeval development of peraluminous magmatism enriched in lithophile rare elements and volatiles with ore complexes located in different structural settings and separated by a considerable distance from each other (up to 500 km) suggests a regional and deep-seated magma source. Rifting and increased thermal flux from the mantle, manifestations of which have been recorded during this period in the territory, may be a deep-seated process.

Mineralogy and Formation Conditions of Novoshirokinsky Base Metal–Gold Deposit, Eastern Transbaikal Region, Russia

This article presents the new mineralogical, fluid inclusion, and isotopic data for ores of the Novoshirokinsky base metal–gold deposit. Mineralogical sequence is supplemented and specified. The mineral assemblages containing native gold are studied. Morphology, grain size and chemical composition of native gold are described. Major parameters and composition of mineralizing fluids of the main ore stages at the deposit are estimated: main base metal (mid-temperature conditions, fluid salinity 3.1–13.1 wt % equiv NaCl) and carbonate–base metal (low-temperature conditions, fluid salinity 1.0–12.9 wt % equiv. NaCl). Sulfur isotopic composition of sulfides from commercial mineral assemblages has been studied. The δ34S value (+10.5 ± 1‰) of mineralizing fluid has been calculated. The Novoshirokinsky deposit is similar to epithermal deposits and is spatially related to the Late Jurassic porphyry system. Evidence is provided on carbonate rocks of basement involved in the ore-forming process.