On the origin and morphology of Z-shaped splitting of coal deposits (on the example of Eastern Donbass)

Статья посвящена выявлению морфологии и происхождения распространенных во многих угольных регионах мира уникальных углепородных структур – Z-образных расщеплений угольных залежей, впервые обнаруженных автором в Восточном Донбассе. Актуальность работыопределяется необходимостью разработки научных основ угленакопления для определения промышленной ценности и минерагенических перспектив территорий. Цель работы. Совершенствование теории угленакопления и первичного структурообразования в осадочных формациях в целом. Методы работы. Вещественно-структурный анализ пересекающихся геологических разрезов угленосной территории западной части Восточного Донбасса известными литолого-структурными методами, сопоставление выявленного Z-объекта с аналогичными структурами других угольных регионов и гипотез о формировании Z-расщеплений. Результаты работы. Обнаружено и исследовано первое в Восточном Донбассе Z-образное расщепление угольной залежи. Залежь k2н каменской свиты С25 каменноугольной системы у г. Красный Сулин асимметрична в разрезе и плане. Высота Z-объекта составляет первые десятки метров, площадь – многие десятки км2, протяженность с севера на юг превышает 20 км. Объект имеет угольные основание и свод в плане, сопряжение их угольным соединением. Z-образность объекта проявляется в субмеридиональных сечениях. Уникальны односторонняя – с запада – замкнутость соединения, наличие угольных пачек-перемычек, неразвившихся до соединения. Выявлена этапность формирования объекта. На конкретном примере определены условия развития Z-объектов: попеременное фронтальное поступление крупных сбалансированных порций в основном растительного или растительно-минерального материала на смежные участки территории с разных сторон с частичным заходом языка минеральных осадков на покрытый углематеринской массой один из них. Нарушение условий приводит к отклонению облика структуры от типовой либо прекращению ее образования. Механизм поступления материала – разливы рукавов палеодельты. Односторонняя замкнутость соединения в плане вызвана поступлением локальных потоков минерального материала. Ниша седиментации создана процессами тектонического относительного опускания смежных участков территории. Исследованная структура возникла в условиях сочетания тектонических и седиментационных предпосылок, главный вклад в ее формирование принадлежит деятельности палеорусел. В этой связи структура отнесена к аккумулятивному типу. Приведены примеры других Z-объектов. Z-структуры развиты на различных масштабных уровнях. Результаты исследований имеют значение для различных регионов угленакопления и решения общих вопросов седиментации. The article is dedicated to the identification of the morphology and origin of unique coal-bearing structures common in many coal regions of the world - Z-shaped splitting of coal deposits, first discovered by the author in the Eastern Donbass. The relevance of the work is determined by the need to develop the scientific foundations of coal accumulation to determine the industrial value and mineragenic prospects of the territories. Aim. Improvement of the theory of coal accumulation and primary structure formation in sedimentary formations in general. Methods. Material-structural analysis of intersecting geological sections of the coal-bearing territory of the western part of the Eastern Donbass using well-known lithological-structural methods, comparison of the identified Z-object with similar structures of other coal regions and hypotheses about the formation of Z-splits. Results. The first Z-shaped splitting of a coal deposit in the Eastern Donbas was discovered and investigated. The k2n deposit of the Kamenskaya suite C25 of the Carboniferous system near the town of Krasny Sulin is asymmetric in section and plan. The height of the Z-object is the first tens of meters, the area is many tens of km2, and the length from north to south is 20 km wide. The object has a coal base and a vault in plan, their conjugation with a carbon connection. The Z-shape of the object appears in submeridional sections. Unique is the one-sided - from the west - closed connection, the presence of coal bundles-bridges that did not develop before the connection. The stages in the formation of the object are revealed. On a specific example of the conditions for the development of Z-objects: the transverse frontal supply of large balanced portions of mainly plant or plant-mineral material in different parts of the territory from different mineral sediments with a partial entry of the tongue onto one of them covered with a source coal mass. Violation of the conditions leads to a deviation of the structure from the typical one or to the termination of its formation. The mechanism of material receipt is the spill of the paleodelta arms. One-sided closedness of the connection is in terms of providing local flows of mineral material. The sedimentation niche was created by the processes of tectonic relative subsidence of additional areas of the territory. The investigated structure arose under the conditions of a combination of tectonic and sedimentation prerequisites; the main contribution to its formation was the activity of the paleochannels. In this regard, the structure is classified as an accumulative type. Examples of other Z - objects are given. Z-structures are developed at various levels. Research results are of significance for different regions of coal accumulation and solution of general sedimentation issues.

Sedimentary Environments and Coal Accumulation of the Middle Xishanyao Formation, Jurassic, in the Western Dananhu Coalfield, Turpan-Hami Basin

The Dananhu coalfield, at the southern margin of Turpan-Hami Basin, Xinjiang, has good coal-forming geological conditions. Due to the low research level on the depositional environment and coal accumulation, the comprehensive coal mining is restricted. Based on drilling and sectioning outcrop data, the depositional characteristics, lithofacies, paleogeography, and coal accumulation of the coal-bearing formations in western Dananhu coalfield are analyzed. The middle member of the Xishanyao Formation is the major coal-bearing strata of the Dananhu coalfield, composed of conglomerate, sandstone, siltstone, mudstone, and combustible organic rock, which can be further subdivided into 14 lithofacies according to substance composition, sediment texture, and structure. During the early Middle Jurassic coal-accumulating period, alluvial fan, fluvial plain, fluvial delta, and shallow lacustrine deposits were developed from northeast to southwest in the western Dananhu mining area. Coal accumulation was most developed in the center regions of the study area extending from northeast to southwest, which were primarily concentrated in margin fans, floodplains, interdeltaic bays, and lakeshore environments, especially the transitional zone between the fluvial plain and the delta plain in the west of No. 1 mining area. This coal accumulation was mainly controlled by synsedimentary tectonic subsidence and clastic sediments supply or sedimentary environment, where tectonic subsidence was the primary controlling factor and the source supply was the secondary controlling factor for coal accumulation, which provided theoretical support for the coal prediction and geological exploration in western Dananhu coalfield.

Study of rare earth elements in the coals of the Shubarkol deposit

The work studies mineralogical and geochemical features of the Jurassic coals of the Shubarkol deposit. The samples were examined using the method of scanning electron microscopy (SEM-EDX) Hitachi S-3400N, which was carried out at the Uranium Geology Research and Development Center at the Department of Geoecology and Geochemistry of TPU. Coal geochemistry was studied by instrumental neutron activation analysis (INAA) at the nuclear geochemical laboratory of the Department of Geoecology and Geochemistry of National Research Tomsk Polytechnic University (TPU). The choice of this object of study was determined by the tasks of research including the study of the patterns of accumulation of abnormal concentrations of REE, the effect of various factors of the geological environment on the levels of their accumulation in coals, as well as the conditions of its concentration and forms of occurrence in coals to expand the mineral resource base of Kazakhstan for rare earth elements. According to the results of scanning microscopic analysis, aluminosilicates, sulfides and sulfates with inclusions of microparticles of rare and rare earth elements were found in the composition of the Shubarkol deposit coals. According to the INNA results, abnormal concentrations of Sc, Ta, Nb, Hf, Zr, Ba, Sr, Ce and REE were found. Weathering processes led mainly to the loss and redistribution of REE in the coal seams of the Shubarkol deposit, which in turn led to increasing the content of rare earth elements from the bottom up the section. As a result of the action of multiple processes, increased concentrations of rare earth metals, mainly of the yttrium group, were formed. The absence of negative europium anomaly was determined, which confirms the original rocks composition peculiarity. The maximum contents of rare-earth metals are confined to weathered coals; for the medium-heavy group (Nd, PM, Sm, Eu), they are almost a hundredfold higher than the clarke in the upper continental crust. The tenfold excess of the clarke for elements from Gd to Lu was found in clayey sandstones and siltstones; for the rest of the rocks of the deposit the excess over the clarke is significantly lower. It was found that the coals of the deposit belong to the H-type and L-type of REE distribution. During the formation of oxidized H-type coals, clayey matter of terrigenous ash predominated as a carrier of REE, while unoxidized L-type coals were formed with the introduction of REE into the coal accumulation basin mainly in the composition of clay minerals and LREE-phosphates. Here the main source of REE was apparently the weathering crust over acidic rocks.

Sequence stratigraphy and coal accumulation model of the Taiyuan Formation in the Tashan Mine, Datong Basin, China

Datong Basin is a platform uplift formed in the Cenozoic era and has a significant coal-bearing geological unit in China. Tashan Mine is located in the middle-eastern part of the Datong Basin, the coal resources of the Taiyuan Formation are abundant, and the research value is enormous. Of the coal resources, coal seams 3–5 and 8 are the main. The lack of research in sequence stratigraphy, coal-forming environment, coal-accumulating model limits the layout efficiency of working face and the exploration and development efficiency of coal measures associated resources. This study used sedimentary and sequence stratigraphy and calculated and measured field drilling data to investigate the sequence stratigraphic characteristics, paleogeographic pattern, and coal accumulation model of the Taiyuan Formation. The sequence boundary and system tract boundary were identified, and the Taiyuan Formation was divided into four third-order sequences. The paleogeographic pattern was reconstructed with the third-order sequence as a unit by applying the single-factor analysis and multifactor comprehensive mapping. Additionally, the distribution characteristics of the main coal seams were clarified, and the corresponding coal accumulation model was reconstructed. The results exhibit that the sedimentary facies transformed from carbonate platform–tidal flat–lagoon–shallow water delta facies to shallow water delta facies from SQ1 to SQ2, coal seam 8 formed in interdistributary bay microfacies and peat swamp microfacies in SQ1. Transgression further expanded in SQ3, and the sedimentary facies were still dominated by the shallow water delta facies. Coal seams 3–5 are formed in distributary channel microfacies, which consist of interdistributary bay microfacies and peat swamp microfacies. The paleogeographic pattern was still dominated by shallow water delta in SQ4, in which interdistributary depressions and peat swamp microfacies widely developed. The thickness of coal seams 3–5 is in the range of 2.40–25.90 m, in which the northwestern study area is characterized by moderate water depth and sufficient fine sediment, and the widely developed distributary bay and peat swamp deposited a thick coal seam. The thickness of coal seam 8 is in the range of 0.5–10.5 m, and the thickness is stable (mostly thicker than 6 m) controlled by the widely developed lagoon, mud flat, and peat swamp microfacies and reduction water environment.

FORMS OF ORE COMPONENT OCCURRENCE AND CONDITIONS OF THEIR TRANSPORT INTO BROWN COALS WITHIN THE ZONES OF CONTRAST JUNCTION BETWEEN SEDIMENTARY BASINS AND OROGENS USING THE ZEYA-BUREYA BASIN AND TURAN MASSIF AS AN EXAMPLE (FAR EAST, RUSSIA)

The conditions for the formation of Paleogene-Neogene metalliferous coals in a setting of tectonic movement intensification in the zone of junction between the Turan massif and Zeya-Bureya basin have been studied. The massif with the Selemdzha-Tomsk and Arkhara grabens separated by the Bureya horst and bounded by the systems of northeastern strike-slip faults was found to have a keyboard structure. The research showed that the most favorable conditions for the ore microcomponent accumulation in coals through the erosion of the Late Cretaceous ore-bearing chemical residue were within the submerged blocks of the massif. The paleodrainage system carrying microcomponents drained the grabens and the associated sedimentary sub-basins of the Zeya-Bureya basin eastern margin. Ore components were transported mainly in solution and as solid clasts to the areas of coal accumulation as evidenced by the resemblance of the elementary composition of coals in the Zeya-Bureya basin and geochemical anomalies of the Turan massif.