Rock Bodies Research Articles

Apatite of alkaline rocks of the Vishnevogorsky complex, South Urals

Apatite Ca5(PO4)3(F,Cl,OH) is a widespread accessory mineral of alkaline rocks of the Vishnevye Mountains in the Urals. There are small bodies of carbonatites and micaceous rocks, where apatite is a rock-forming mineral. The rocks mostly contain fuorapatite and, locally, apatite-(CaOH). The Cl-bearing apatite is rare. Apatite is enriched in Na2O (up to 1.77 wt. %), REE2O3 (up to 6.98 wt. %) and SrO (up to 3.63 wt. %), locally, P substitutes by S (up to 2.38 wt. % SO3).

Petrel2ANSYS: Accessible software for simulation of crustal stress fields using constraints provided by multiple 3D models employing different types of grids

Crustal stresses play an important role in both exploration and development in the oil and gas industry. However, it is difficult to simulate crustal stress distributions accurately, because of the incompatibilities that exist among different software. Here, a series of algorithms is developed and integrated in the Petrel2ANSYS to carry out two-way conversions between the 3D attribute models that employ corner-point grids used in Petrel and the 3D finite-element grids used in ANSYS. Furthermore, a modified method of simulating stress characteristics and analyzing stress fields using the finite-element method and multiple finely resolved 3D models is proposed. Compared to the traditional finite-element simulation-based approach, which involves describing the heterogeneous within a rock body or sedimentary facies in detail and simulating the stress distribution, the single grid cell-based approach focuses on a greater degree on combining the rock mechanics described by 3D corner-point grid models with the finely resolved material characteristics of 3D finite-element models. Different models that use structured and unstructured grids are verified in Petrel2ANSYS to assess the feasibility. In addition, with minor modifications, platforms based on the present algorithms can be extended to other models to convert corner-point grids to the finite-element grids constructed by other software.

Late stages in the evolution of the late Mesozoic East Mongolian volcanic areal: rock age and composition

The Mandakh-Madal-Gobi (MMG) zone of alkali basalt magmatism has been delineated in the Late Mesozoic East Mongolian volcanic areal. It comprises clusters of igneous rock bodies and isolated stocks, domes, sills, laccoliths, dikes, and limited fragments of lava flows composed of tephrite, phono-tephrite, and trachybasalt. Two pulses of magmatism in the MMG zone have occurred in the Late Cretaceous (about 85 Ma) and Early Cenozoic (about 50 Ma). Recognition of this zone and deciphering of its formation history demonstrated that the development of the entire East Mongolian volcanic areal had the same regularities as those identified in other major regions of the Late Mesozoic Central Asia magmatic province. This indicates that the areal undoubtedly belongs to the latter. These facts support the conclusion that the correlation observed through the zone’s evolution between reduction in the volume of igneous products and the change in their composition towards the OIB was apparently determined by a decrease in the effect of thermal sublithospheric mantle melts upon a metasomatically enriched lithospheric mantle, leading to its gradual elimination from the magma sources.

Episyenites\u2014Characteristics, Genetic Constraints, and Mineral Potential

Episyenites are sub-solidus, quartz-depleted alkali-feldspar-rich rocks. They form veins and lenticular bodies in granitoid rocks and migmatites in a late- to post-orogenic or anorogenic setting. Leaching of quartz is usually a response to a flux of weakly saline hydrothermal solution in circulation cells above cooling intrusions, where sufficient fluid-rock ratios and thermal gradients are achieved. Fluid Si-undersaturation is achieved by rapid cooling within the field of retrograde Si solubility or by temperature and pressure increase outside retrograde conditions. Some quartz may also be consumed in metasomatic reactions and in response to pressure fluctuation in sealed episyenite bodies. The small size and overall rarity of episyenites imply that conditions for episyenite formation are not commonly encountered in the crust. In addition to quartz depletion, episyenites record complex histories of metasomatic alteration and hydrothermal mineral growth. Nearly all episyenites have undergone Na-metasomatism, which may have led to the formation of nearly monomineralic albitite, and which is occasionally followed by late K-metasomatism, phyllic alteration, and argillization. Depending on the effectiveness of later compaction, recrystallization and vug-filling episyenites may preserve the macroscopic porosity formed by quartz dissolution and brittle deformation. Vuggy episyenites can act as significant sinks for metals carried by crustal fluids and host many significant U, Sn, and Au deposits worldwide. Rare earth-critical syenitic fenites around alkaline intrusions share mineralogical and genetic traits with episyenites.

Radon migration in the area around the coal mine during closing process

The Upper Silesian Coal Basin (USCB) in Poland is an excellent example of an area affected by an increased migration of radon and by radon penetration into buildings. This occurs due to changes in the geological environment caused by the exploitation of mineral resources. Studies conducted in the past showed that the levels of radon emission, depend to a large extent on the geological structure of the subsurface layers. Mining-induced changes of the rock body are one of the main factors influencing the radon's ability to migrate. Some investigations were made near shafts which were closed many years before, and it was found that physical changes and disintegration of the rock body caused by mining activity (e.g. subsidence) could still influence the environment. Enhanced radon emission was observed even in the case of shafts closed for >50 years.The “Anna” coal mine - our study area – was opened in 1832, and hard coal was extracted until 2017. In this paper, we present the results of radon emission monitoring within a mine closure context. Measurements started in 2016, when the underground coal mine was still under operation; observations continued during the liquidation process, and more measurements will be taken in the post-closure period.The importance of the hazards related to radon emission has been reported by many organisations. According to the World Health Organization (WHO), a statistically significant increase in the risk of lung cancer occurs as a result of prolonged exposure to radon when the concentration is at 100 Bq/m3, and increases by 16% per each 100 Bq/m3 increase. Moreover, the United States Environmental Protection Agency (EPA) stated that radon exposure is the second leading cause of lung cancer after smoking. For these reasons, the Council Directive 2013/59/EURATOM of 5 December 2013 established basic safety standards for protection against the hazards related to ionizing radiation in 2013, paying particular attention to issues related to radon exposure. The goal of our work was to collect data on radon migration in an area influenced by mining activity around the “Anna” coal mine, and to assess the corresponding radon hazard.

Sulfide ore prospecting in carbon-containing stratum using comprehensive time-domain induced polarization and controlled-source audio-frequency magnetotellurics

Carbon-bearing stratum normally features low resistance and high polarization. If the lithostratigraphy of the exploration area contains large amounts of carbon, the induced polarization anomaly caused by metal sulfide ore bodies will be inundated by the high polarization of carbon-containing wall rock. In this work, we adopted time-domain induced polarization (TDIP) and controlled-source audio-frequency magnetotellurics (CSAMT) on deep prospecting of the carbon-bearing stratum of the Ar Horqin Banner, Inner Mongolia. The underground medium is divided into target geologic bodies according to the geological information within the known exploration line borehole, and the physical properties of various target geologic bodies are calculated using weighted averages to build a geologic-geophysical model that can fit the observation data. Consequently, we can determine the range and morphological characteristics of the electrical properties of the ore-bearing geologic bodies in the inversion results in the study area. Then we can use the characteristics summarized from the known exploration line to interpret unknown exploration line. Results indicated that, when the difference in physical properties between the ore body and interference wall rock is not clear, the geologic body can be classifi ed via the paragenetic (associated) assemblage relations of the underground medium. Geological interpretation is guided by the comprehensive physical properties of ore-bearing geologic bodies to avoid interferences.

The mechanism of damage in gas-bearing coal–rock combination bodies and gas seepage in coals

ABSTRACT With the gradually exhausted shallow coal resources, many coal mines have been carried forward to the deep mining stage. Meanwhile, the outburst-rockburst coupling dynamic disaster is becoming more and more serious, which is becoming a major threat to national energy security. This kind of disaster is essentially induced by the coupling instability of damage in gas-bearing coal–rock combination body and gas seepage in coal. First, based on the study of force analysis and failure criterion of gas-bearing coal–rock combination body, the mechanical failure mechanism of gas-bearing coal–rock combination body is obtained and verified. It is found that the existence of additional stress generated at the interfaces of the coal body and rock body is the fundamental reason for the extremely complex damage and failure of combination body. In the actual mining process, due to the larger strength of roof than coal, the major stress state during the instability and failure of combination body is as follows: with the increase of axial stress, the strength of rock body at contact surface decreases but still greater than that of coal body far from the contact surface. Meanwhile, the strength of coal body at the contact surface increases but still less than that of rock body far from the contact surface. The theoretical failure mode of gas-bearing coal–rock combination body is mainly the failure of coal part, which only in some cases will lead to the failure of local rock part. Then, based on the permeability model of single coal in the full stress–strain process, the permeability model of coal under the influence of coal–rock combination body is established and verified. Finally, the gas–solid coupling instability mechanism of gas-bearing coal–rock combination body is discussed.

GEOLOGY OF BUKIT PANAU, TANAH MERAH, KELANTAN

A unique isolated hill of Bukit Panau around a flatland deposits comprise of Jurassic-Cretaceous sedimentary sequence overlying the Triassic granite rock body underneath it. Previous researchers claim that the contact between those two rock units is a nonconformity, but the evidences are insufficient to validate those claims. Therefore, this research studies the type of contact between the rock two rock units and verifies the geological age of the Panau Formation. Several fieldworks were conducted to the study area and petrographic and geochemical studies were performed on selected rock samples retrieved from the fieldwork. As a result, it is believed that Bukit Panau could possibly have two types of unconformities and that the Panau Formation is not the only formation there.
 Keywords: formation, unconformities, angular unconformity, nonconformity, granite intrusion, boundary range granite.

Transversely Anisotropic Damage Characteristics of Loaded Rock under Freeze-thaw Cycles

Flake metamorphic rocks and sedimentary rocks tend to show obvious transversely isotropic mechanical properties in deformation and strength because of the existence of weak structural surface or soft-hard interlayer structure. The rock in cold area is affected by load and freeze-thaw cycles, and the prevention and control of freeze-thaw disaster has become an urgent problem to be solved in the construction of cold area. Based on the strength of Rock Micro Element subjecting to Weibull random distribution and the macroscopic statistical damage model of rock, this paper used the transversely isotropic elastomer model to describe the damage evolution equation of freeze-thaw rocks in the whole process of the load deformation, and established the corresponding damage constitutive model. The results showed that this model more accurately describes the effect of freeze-thaw cycles on rock mechanical behavior, and had positive theoretical and practical significance for solving engineering problems in complex rock body.

Late Stages in the Evolution of the Late Mesozoic East Mongolian Volcanic Areal: Rock Age and Composition

The Mandakh-Madal-Gobi (MMG) zone of alkali basalt magmatism has been delineated in the Late Mesozoic East Mongolian volcanic areal. It comprises clusters of igneous rock bodies and isolated stocks, domes, sills, laccoliths, dikes, and limited fragments of lava flows composed of tephrite, phono-tephrite, and trachybasalt. Two pulses of magmatism in the MMG zone have occurred in the Late Cretaceous (about 85 Ma) and Early Cenozoic (about 50 Ma). Recognition of this zone and deciphering of its formation history demonstrated that the development of the entire East Mongolian volcanic areal had the same regularities as those identified in other major regions of the Late Mesozoic Central Asia magmatic province. This indicates that the areal undoubtedly belongs to the latter. These facts support the conclusion that the correlation observed through the zone’s evolution between reduction in the volume of igneous products and the change in their composition towards the OIB was apparently determined by a decrease in the effect of thermal sublithospheric mantle melts upon a metasomatically enriched lithospheric mantle, leading to its gradual elimination from the magma sources.

Deformation Field Evolution and Failure Mechanisms of Coal–Rock Combination Based on the Digital Speckle Correlation Method

The stability of a deep composite roof is a powerful guarantee for the safe and efficient production of a coal mine. The coal–rock combination, the single rock or coal bodies have different bearing capacity; thus, we can accurately obtain the deformation field evolution and failure mechanisms of the combination, which is useful in the deformation control of a composite roof. In this study, based on the digital speckle correlation method (DSCM), a uniaxial compression test was applied to coal–rock combinations with different height ratios. The results revealed that the compressive strength, elastic modulus, and secant modulus of the combination gradually decreased, while the decreasing amplitude weakened with the increase of coal height. Additionally, the strain field map of the combination had different characteristics in different stages. As the height of the coal body continuously increased, the gradient of the strain cloud and the area of local strain increase moved upwards. Moreover, the cracks caused by the failure of the coal body in the combination triggered the failure of the rock body. According to the test results, two principles are proposed for the deformation control of the composite roof, and are expected to be useful in applications for the similar geological conditions.

The caspian sea basin: tectonic events and sedimentation at the turn of the early–middle carboniferrous and the formation of oil and gas reservoirs

A structural-facies map of the Bashkir stage of the Caspian basin, the southeastern part of the East European platform and the Turan plate is compiled on the basis of drilling data generalization. The sequence of tectonic events and sedimentation processes in the early‒ late Bashkir century of the middle Carboniferous was reconstructed. It is shown that cessation of reef formation, appearance of erosion surfaces and partial destruction of the side ledges of Caspian depression occurred under the influence of Varis orogenesis and the global fall of the World Ocean level due to the glaciation of the Paleogondvana at the turn of early‒middle Carboniferous. It is assumed that oil and gas reservoirs in the rocks of Vise‒Bashkir age are confined to large bodies of carbonate-clastic rocks with clinoform structure that arose on the slopes of the depression due to destruction of its side ledges.

A geostatistical methodology to simulate the transmissivity in a highly heterogeneous rock body based on borehole data and pumping tests

A geostatistical methodology is developed with the aim of simulating three-dimensional grids of transmissivity. The case study is a highly heterogeneous massif rock body, mainly composed of granites and schists with distinct weathering and fracture conditions, that surrounds and is part of a former uranium mine in central Portugal. Contrasting hydraulic behaviour is given by fractured rock and a pervasively weathered rock matrix composed mainly by clay minerals. Lithology, weathering, and fracture were the geological attributes selected for simulation. Data and information were analysed in detail for their respective integration into a sequential geostatistical modelling approach. The simulation process was conditioned to local data histograms. Simulation images of transmissivity show high degrees of heterogeneity both laterally and vertically. Potential areas for high-flow propagation are restricted in number and interconnectivity is not particularly evident. Small channels, the main structures responsible for groundwater flow propagation, can be identified within the rock body.

Characterization of a Proposed Quarry Site using Multi-Electrode Electrical Resistivity Tomography

This research focuses on the delineation of subsurface basement granitic structures suitable for engineering construction materials for the sitting of quarry industry in the area. The key objective of the study was to locate and delineate the depths of burial to the subsurface granite rock bodies and the regolith thickness overlain the bedrock unit. 14 resistivity profile lines with a surveyed length of 200 m and electrode spacing of 5 m, were carried out with the application of electrical resistivity tomography software, to image the subsurface structural units around this area, utilizing pole-dipole electrode configurations method towards assisting the Engineers in obtaining information on the subsurface geological features in this part of the Peninsula Malaysia. The focus is on characterizing engineering construction materials suitable for sitting the quarry industry, determination of the longitudinal conductance and coefficient of anisotropy of subsurface lithological units that determines the competency of the bedrock underneath the area from the geoelectric parameters obtained through the interpretations of the RES2DINV ERT images. The depth of bedrock unit as delineated from the results ranged from about 5 m to 100 m while the resistivity values recorded was greater than 6000 Ω-m in most of the profiles. Groundwater bearing channels that would serve the factory needs was delineated alongside the granitic rock unit. These results make the subsurface granitic bedrock unit to be adjudged competent and suitable enough as quarry construction materials for sitting the factory in the area.

Prestack elastic RTM for VTI media using vector wavefield decomposition and vector imaging conditions

ABSTRACTTo date, studies of elastic reverse time migration (RTM) have undergone much improvement, but mainly focus on isotropic media. Because anisotropic media is widespread, it is necessary to explore the application of elastic RTM in anisotropic media. We extend the wavefield decomposition method, which is based on decoupled propagation, and three vector imaging conditions to transversely isotropic media with vertical symmetry isotropy (VTI). Two of the imaging conditions are based on the excitation amplitude (EA) and the third is based on source-normalized cross-correlation. First, the wavefield decomposition method is extended to VTI media. This is then tested in a two-layer model. The results show that this extension cannot decompose P- and S-waves perfectly in VTI media; some weak residuals remain. However, the results of a simple model test show that no obvious crosstalk is generated by these weak residuals. Finally, a Hess VTI model is adopted to test the adaptive use of this method in complex media. Many subsurface structures can be clearly recognized in the migrated result, for example, the high-velocity rock body, a fault and two low-velocity interlayers. Compared with PP images, converted PS images have many merits, such as clearer imaging of the anisotropic body, higher resolution and a wider migration aperture. We conclude that the vector decomposition method and three vector imaging conditions can be applied to prestack elastic RTM for VTI media and satisfactory results obtained.

The Caspian Sea Basin: Tectonic Events and Sedimentation at the Turn of the Early‒Middle Carboniferrous and the Formation of Oil and Gas Reservoirs

A structural-facies map of the Bashkir stage of the Caspian basin, the southeastern part of the East European platform and the Turan plate is compiled on the basis of drilling data generalization. The sequence of tectonic events and sedimentation processes in the early‒ late Bashkir century of the middle Carboniferous was reconstructed. It is shown that cessation of reef formation, appearance of erosion surfaces and partial destruction of the side ledges of Caspian depression occurred under the influence of Varis orogenesis and the global fall of the World Ocean level due to the glaciation of the Paleogondvana at the turn of early‒middle Carboniferous. It is assumed that oil and gas reservoirs in the rocks of Vise‒Bashkir age are confined to large bodies of carbonate-clastic rocks with clinoform structure that arose on the slopes of the depression due to destruction of its side ledges.

Paleobasins – a new concept of modeling the history of geological development and oil and gas bearing of regions

“Paleobasin” is an area of long-term and steady subsidence of the Earth’s crust at a certain stage of geological development in the past, during which a body of sedimentary rocks of a mega-regional scale is formed, subsequently subjected to the influence of various kinds of geological processes leading to a reduction in its size, as well as changes in geometry and structure. Paleobasin is not a new concept. However, for petroleum, historical analysis was used only for those sedimentary strata that were not metamorphosed or collapsed into folds. As a result, the side zones of the basins and deep horizons were excluded from the basin modeling. The proposed approach to the analysis of paleobasins, regardless of the degree of their subsequent transformation, makes it possible to assess the petroleum potential of past eras, both primary and residual, especially in those zones and horizons that were previously derived from a general consideration of the prospects for finding oil and gas. The article shows the need for an integrated historical approach to the analysis of the oil and gas potential of the territory, both at the basin level and at the local level, including sedimentary strata and strata, which are often referred to as the “acoustic foundation”. Unfortunately, very often when modeling a promising object and assessing its resources or reserves, some of these attributes are taken for the type of work already done and do not adapt to a single model of oil and gas deposits, which reduces the reliability of the final result.

Identifikasi Penyebaran Zona Mineralisasi Endapan Timah Menggunakan Metode Induksi Polarisasi Konfigurasi Dipole - Dipole Di Bukit Sambunggiri Kecamatan Merawang Kabupaten Bangka

Tin is one of the many mining products found in the Bangka Belitung Islands region. Geophysical exploration was carried out in the Bukit Sambunggiri area, Merawang District, Bangka Regency using the dipole-dipole configuration polarization to detect polarizationel ectricity on surface of metal material and induction method to identify the distribution of tin deposit mineralization. The parameters is measuring area of ​​21 Ha with 6 tracks, length A, B, C is 640 meters, D, E, F is 840 meters, spacing between tracks 50 meters, spacing between electrodes 10 meters and equipment used is Multy Channel RS / IP Supersting. Processing measurement data using Res2dinv software to create 2D cross sections and Montaj Oasis for 3D cross sections. The results of resistivity and chargeability data processing of a total of six trajectories have 3 trajectories which have a clear mineralization area, that is, A trajectory is assumed to be at a distance of 250 - 350 meters and depths from 0 - 50 meters which are characterized by medium-high chargeability - 30) msec and low resistivity (<700) Ohm.m. On track D, it is estimated that there are three parts at a distance of 100 - 220 meters in depth of 50-50 meters, distance of 335 - 440 meters in depth of 50-130 meters and distance of 590 - 680 meters in depth of 50-130 meters. 430 meters at a depth of 0 - 150 meters. The results of interpretation of track A to track C are suspected to have zones of tin mineralization with secondary deposits and it is known that the mineralized zone is thought to be located below the bog iron zone with secondary tin deposits. This is due to the fact that the bog iron is hard rock like granite which is oxidized, so minerals that have a high level of resistance to weathering such as cassiterite and quartz will be released from the rock body and deposited in the lower layer. While path D to trajectory F is suspected to be the continuation of the zone of tin mineralization with primary deposits. This is presumably because the location of the mineralization area spreads between intrusion of granite rocks which have a high chargeability and resistivity value.

Tectonic, diapiric and sedimentary chaotic rocks of the Rakhine coast, western Myanmar

The western margin of Myanmar is the northern extension the active Sunda (India-Eurasia) subduction zone. Coastal regions and offshore islands have remarkable exposures of chaotic rock terranes along wave-cut terraces that allow characteristics of tectonic, sedimentary and diapiric mélanges to be recognized. Tectonic shear zones (tectonic mélanges) contain fragments of Cretaceous ophiolites (chrome-spinel-bearing peridotites and radiolarian cherts) that are in contact with thrust packets of Eocene turbidite units (broken formations). The turbidites contain shale-rich beds that have been sheared during soft-sediment deformation (sedimentary broken formations) and are sandwiched between undeformed thick sandy beds. These are mass transport deposits (MTDs) that most likely formed during deposition of the initial detritus of the Himalayan orogenic zone, probably trench slope basins on the accretionary prism. The ophiolitic and turbiditic thrust slices have been exhumed and are currently being intruded by active mud volcanoes that bring fragments of units up from depth to the surface, forming diapiric mélanges. These diapiric mélange bodies contain only small fragments (<50 cm) that are randomly oriented and do not exhibit shear fabrics. Because the region lacks superimposed deformation characteristic of most orogenic belts, the origins of all three rock bodies can easily be distinguished.

Determination of the nonlinear displacement distribution of the semi-infinite strip – Application to deformable rocking bodies

In the present work, the problem of the semi-infinite strip with traction-free lateral sides is revisited, in order to examine the displacement profile across the semi-infinite strip under an arbitrary normal load distribution on its end. Although the solution of this problem is important even for practical applications (e.g. the prediction of the rocking motion of deformable bodies), only numerical solutions exist until now, which are cumbersome to implement for such cases. In this paper, the displacement profile of the semi-infinite strip under a concentrated normal load is approximated with analytical functions, which must exhibit specific properties. These results are then extended to arbitrary normal load distributions and characteristic cases are presented. Finally, the problem of the determination of the stress distribution across the interface between a deformable rocking body and its base is solved based on the previous derivations.