Search Results (148)

The Bailingshan submarine volcanic-hosted iron deposit in the Eastern Tianshan provides an opportunity to investigate skarn hydrothermal evolution and high-grade Fe mineralization. This study integrates garnet petrography, in situ major- and trace-element analyses, garnet U–Pb geochronology, and amphibole ⁴⁰Ar/³⁹Ar geochronology. Four generations of grossular–andradite garnet (Grt1–Grt4) exhibit systematic textural and compositional variations reflecting the combined effects of crystal-chemical controls, hydrothermal fluid composition, and fluid–rock interaction. U–Pb dating of Grt2 yields 331.8 ± 8.9 Ma, linking the principal skarn formation and Fe mineralization stage to Early Carboniferous volcanism. Amphibole ⁴⁰Ar/³⁹Ar dating yields 302.6 ± 2.4 Ma, constraining a younger, localized hydrothermal overprint with limited Fe addition. Integrated evidence indicates that the Bailingshan deposit formed through a multistage, episodic hydrothermal evolution involving initial skarn formation, the principal Grt2–magnetite stage, subsequent shifts in hydrothermal conditions recorded by Grt3 and Grt4, and a localized late-stage hydrothermal overprint. These results not only constrain the timing of mineralization and subsequent overprinting but also offer valuable exploration implications for high-grade Fe mineralization in the Eastern Tianshan and comparable submarine volcanic-hosted iron districts. Full article

The nanoscale structural heterogeneity of carbons plays a crucial role in regulating the surface activity, catalytic performance, and wettability of substances. Herein, we quantitatively investigate the nanostructural evolution of a coal-derived carbon during high-temperature treatment, using high-resolution transmission electron microscopy (HRTEM). To elucidate the intrinsic nanoscale structural heterogeneity of carbonaceous materials during thermal treatment, a particle-edge preferential graphitization is hypothesized in this study. Based on quantitative HRTEM analysis of coal-derived carbon heat-treated up to 3000 °C, this study demonstrates that particle boundaries act as intrinsic geometric templates and stress concentrators, governing the carbon nanostructural evolution. The length enhancement of the aromatic structural transformation occurs at 300 °C, 1000 °C, and 2550 °C, respectively, with substantially decreased small-size lattice fringes and substantially increased medium- and large-size lattice fringes. The average curvature displays a non-monotonic decrease and a transient increase during the second carbonization and pregraphitization processes, driven by the formation of concentric and twisted nanostructures. During graphitization, lattice fringe curvature becomes geometrically constrained by particle edges, resulting in an unexpected positive correlation with fringe length. Lattice fringes at particle edges develop highly ordered, boundary-parallel orientations, whereas interior regions experience delayed ordering with randomly oriented graphitic domains. Edge-preferential graphitization explains the non-uniform evolution of carbon structures, providing a crucial theoretical basis for the comprehensive utilization of complex amorphous carbon precursors, including coal and biomass-derived fuels. Full article

This study systematically investigates the microstructure, physical properties, and sealing capacity of mudstone under thermal action using scanning electron microscopy (SEM), high-pressure mercury intrusion, breakthrough pressure testing, and diffusion coefficient analysis. Pore-throat structure, porosity, permeability, breakthrough pressure, and diffusion coefficient were measured at 25, 300, 600, 900, and 1200 °C, while additional SEM observations were conducted at 100, 200, 400, and 500 °C. Based on the integration of these discrete measurements and supplementary SEM observations, the evolution of mudstone sealing capability was interpreted as follows. (1) At 25–200 °C, mineral dehydration exposes primary pores, with porosity and permeability increasing gradually while strong sealing capacity is maintained. (2) At 200–400 °C, clay mineral dehydration, thermal expansion, and secondary fracture development increase pore connectivity, resulting in a sharp decline in sealing capability. (3) At 400–1200 °C, mineral structure collapse, pore-fracture connection, and mineral melting further increase porosity and permeability, leading to progressive sealing failure. (4) The threshold temperature for mudstone sealing failure is inferred to be approximately 400 °C. (5) Mudstone affected by temperatures below 200 °C is recommended as an effective caprock for underground coal gasification chambers. This study provides theoretical guidance for caprock selection and safe operation in underground coal gasification engineering. Full article

The Shyngys–Tarbagatai folded system of Kazakhstan, located in the southwestern part of the Central Asian Orogenic Belt, represents a promising yet still insufficiently studied metallogenic region of Kazakhstan. The aim of the present study was to reassess its ore potential based on modern geotectonic concepts and a comprehensive metallogenic analysis. An evaluation of the ore potential of nine structural–formational zones was carried out, and their metallogenic specialization was determined. The dominant role of gold and copper mineralization was established, along with the features of spatial distribution of ore occurrences and the most promising areas for further exploration. It was shown that the most ore-rich stratigraphic levels include the Early Cambrian, Late Ordovician, Early Silurian, Early Devonian, and Late Devonian units. It was demonstrated that the formation of the main ore types is closely related to productive geodynamic settings, including Early Paleozoic oceanic rifts, island-arc complexes, and the Devonian continental-margin volcano-plutonic belt. Based on the obtained results, a map of prospective areas at a scale of 1:1,500,000 was compiled, and these areas were ranked according to their degree of prospectivity. A total of 51 targets were identified as priority sites for follow-up prospecting, evaluation, and detailed exploration work. Full article

Multispectral satellite imagery is a very useful technique to identify altered wall rocks around orogenic gold systems. In this study in the Akzhal–Vasilyevskoye district, Kazakhstan, we show that a geology-based ASTER band-ratio workflow is a useful technique to trace metasomatic footprints of mineralization. In the West Kalba camp, beresite and listvenite both produce usable ASTER SWIR signals, while pyrite and arsenopyrite are largely featureless at multispectral resolution. Five ratios on AST_07XT surface-reflectance data, screened with upper-tail anomaly masks, have enabled identification of sericitic cores, chloritic and carbonate halos, ferric caps, and zones containing mixtures of ferrous phyllosilicates. We show that district-scale Al–OH sericitic anomalies occur within Mg–OH and carbonate shells. At Vasilyevskoye the pattern is due to beresite nuclei within listvenite rims, while at Tokum the sericitic centres remain compact within wider Mg–OH and carbonate halos. Mean polygon spectra differ between the two footprints across Bands B4–B6 and across the SWIR tail (B7–B9). SEM–EDS at Vasilyevskoye links the mapped anomalies to chlorite, sericite, and carbonate gangue assemblages with sulfide-bearing volumes. The data also allow identification of subordinate REE, phosphate, and Ti enrichment within carbonaceous and polymineralic host lithologies. Full article

Geochemical anomaly detection plays a critical role in mineral exploration, yet conventional methods are often limited by compositional effects, sensitivity to outliers, and insufficient consideration of spatial relationships. To address these issues, this study proposes an integrated analytical framework that combines compositional data analysis and spatial statistics for robust geochemical anomaly identification. The framework incorporates isometric log-ratio (ILR) transformation to eliminate the closure effect, robust principal component analysis (RPCA) to extract stable geochemical patterns, local indicators of spatial association (LISAs) to characterize spatial clustering, and compositional balance analysis (CoBA) to enhance anomaly signals. The method is applied to the Barkol Lake area in the Eastern Tianshan, a key metallogenic belt within the Central Asian Orogenic Belt. The results reveal significant geochemical anomalies characterized by Cu-associated element assemblages (e.g., Cu–Ni–Cr), which are spatially correlated with major fault zones and volcanic–intrusive complexes. The identified anomalies show strong consistency with known mineral occurrences and delineate several prospective targets for copper polymetallic mineralization. Compared with conventional approaches, the proposed framework demonstrates improved robustness to outliers, enhanced sensitivity to weak anomalies, and better integration of compositional and spatial constraints. Full article

The Bastielieke W-polymetallic deposit, located in the Xinjiang Altay metallogenic belt, records a complex hydrothermal history critical to understanding multi-stage metallogenic processes in the southern Altay. This study integrates in situ U-Pb dating of hydrothermal titanite and zircon with textural and compositional analyses of titanite to reconstruct this history. Three types of hydrothermal titanite, identified from pyroxene skarn (TtnI), epidote skarn (TtnII), and quartz–sulfide ore (TtnIII), display dissolution–reprecipitation textures and systematic compositional variations, indicating distinct fluid compositions and origins. TtnI, TtnII, and TtnIII yield U-Pb ages of 244.7 ± 7.8 Ma, 252.4 ± 5.5 Ma, and 250.6 ± 3.0 Ma, respectively, and hydrothermal zircon from pyroxene skarn yields an age of 249.9 ± 2.1 Ma, constraining the hydrothermal event to the latest Permian to Early Triassic. These ages are interpreted to record the timing of U-Pb system resetting during regional shear–thrust movements. Compositional variations among the three titanite types reveal a two-stage hydrothermal history. The earlier stage involved W–Cu mineralization and protolith titanite precipitation related to magmatic–hydrothermal fluids exsolved from Permian granites. The later stage was driven by regional shear–thrust movements and metamorphic–hydrothermal processes, which reset the titanite U-Pb systems, partially altered TtnI and TtnII, precipitated TtnIII, and remobilized metals. This model links the Bastielieke deposit to multi-stage hydrothermal processes and provides insights into similar metallogenic events along the southern margin of Xinjiang Altay. Full article

Multisource remote sensing and Earth observation (EO) products provide scalable covariates for regional mineral prospectivity mapping, but their integration with incomplete and preferentially sampled occurrence records can produce biased prediction maps. We present a bias-aware machine learning workflow for porphyry copper prospectivity mapping that integrates satellite-derived alteration proxies, topographic variables, regional geology, structural context, and accessibility-related EO layers on a harmonized 1 km grid. The workflow separates remote sensing/geological predictors from survey-effort proxies and combines this decomposition with positive-unlabeled learning, stacked ensembling, rank-optimized blending, fold-wise calibration, and spatial block cross-validation. The case study covers the eastern Central Asian Orogenic Belt (CAOB) and uses porphyry Cu occurrences together with covariates derived from ASTER short-wave infrared information, Landsat 8 reflectance, SRTM topography, VIIRS night-time lights, GHSL population data, geological units, and active fault information. Across held-out spatial folds, the final RO-BAB ensemble provides a modest but exploration-relevant improvement in ranking relative to the all-covariate XGBoost baseline, increasing PR-AUC from 0.0297 to 0.0364 and recovering 26.75% of known deposits within the top 5% of ranked cells. The resulting maps delineate coherent remote sensing-supported prospective corridors while exposing regions where predictions may be influenced by historical accessibility and recording effort. The study demonstrates how machine learning that accounts for sampling bias can improve the reliability and interpretability of remote sensing mineral prospectivity products in the presence of only reference data. Full article

Volcanic rocks of the Qi’eshan Group, which are widely distributed in the Dananhu arc of the Eastern Tianshan, NW China, have long been debated in terms of their formation age and tectonic setting. In this study, we conducted an integrated study of U-Pb apatite geochronology, whole-rock major and trace element geochemistry, in situ major element analyses of clinopyroxene, and “Rhyolite-MELTS” thermodynamic modeling on the basalts from the Qi’eshan Group. Geochronological data show that the weighted mean of ²⁰⁶Pb/²³⁸U ages of apatite is 329 ± 10 Ma. The basalts belong to the tholeiitic series and are characterized by enrichment in large ion lithophile elements (LILEs), depletion in high field strength elements (HFSEs), and enrichment of light rare earth elements (LREEs) relative to heavy rare earth elements (HREEs) with weak negative Eu anomalies. They were derived by partial melting of garnet-spinel lherzolite in a depleted mantle source metasomatized by subduction-related fluids, followed by fractional crystallization of spinel, olivine, and clinopyroxene. Clinopyroxene is dominated by augite, characterized by high Mg and Ca contents and low Al and Na contents. Machine-learning-based thermobarometry indicates that clinopyroxene crystallized at temperatures of 1027–1033 °C and pressures of 1.1–1.6 kbar. “Rhyolite-MELTS” isobaric crystallization simulations suggest that mantle-derived magma, with an initial water content of 4 wt.% and oxygen fugacity of FMQ, can generate melts compositionally similar to the volcanic rocks of the Qi’eshan Group through fractional crystallization at a pressure of 1.5 kbar. Combined with previous studies, we propose that the Qi’eshan Group basalts formed in an extensional arc setting related to southward rollback of the northward-subducting Kanguer oceanic slab, which caused asthenosphere upwelling and lithospheric extension, thereby promoting partial melting of the subduction-metasomatized mantle. Our data provide new insights into the Carboniferous rollback of the Kanguer oceanic slab in the northern part of the Eastern Tianshan. Full article

Pegmatite dikes are important prospecting indicators for rare-metal deposits, whereas traditional methods for pegmatite dike identification are constrained by the limited capability of human visual interpretation to capture information from remote sensing imagery, resulting in low identification accuracy and efficiency. In recent years, global research on semantic segmentation of different surface features and remote sensing-based mineral exploration using deep learning methods and high-resolution remote sensing imagery has made significant progress; however, studies on surface-exposed geological bodies such as pegmatite dikes remain highly insufficient. To address the key problem of efficiently identifying pegmatite dikes in remote sensing imagery, this study proposes an improved model based on UNet++, termed GAD-UNet++. In the field of remote sensing geology, this study constructed a pegmatite dike semantic segmentation dataset based on high-resolution RGB imagery by using 0.66 m RGB imagery for visual delineation and ZY1F hyperspectral data for spectral constraint and label refinement; on this basis, semantic segmentation of surface pegmatite dikes in the Yilanlike area of the South Tianshan Mountains, Xinjiang, was conducted using RGB remote sensing image patches as model input. Specifically, because pegmatite dikes are small targets characterized by slender structures, indistinct boundaries, and sparse regional distribution, this study introduced a lightweight feature extraction structure (GhostNetV2) and a long-range dependency attention module (DFC) at the encoder stage, and further incorporated the Coordinate Attention module (CA) to enhance spatial localization and boundary representation of the targets. Finally, focal cross-entropy loss and a deep supervision strategy were adopted to improve the accuracy of semantic information extraction for pegmatite dikes, as well as the training stability and segmentation accuracy under class-imbalance conditions. The results show that the proposed model achieved an mIoU of 93.11% and an F1-score of 94.95% on the test set. Compared with existing semantic segmentation models, the proposed model achieved superior performance in both identification accuracy and computational efficiency for pegmatite dikes. In addition, this study delineated 18 potential pegmatite dike enrichment zones in the Yilanlike area, providing technical support for remote sensing-based rare-metal prospecting and geological interpretation in the study area. Full article

The South Tianshan Orogenic Belt, as the southernmost part of the Central Asian Orogenic Belt (CAOB), records the final closure of the Paleo-Asian Ocean and the subsequent collision between the Tarim Craton and the Central Tianshan–Yili Block. However, the timing of this collision and the subduction polarity of the South Tianshan Ocean remain controversial. In this study, we present integrated detrital zircon U-Pb geochronology, Lu-Hf isotopes, and rare earth element (REE) geochemistry for Carboniferous to Permian sedimentary rocks from the northern Tarim Craton and the South Tianshan Orogenic Belt. Our results show that the detrital zircon age spectra are dominated by peaks at ~290 Ma, ~420 Ma, ~640–620 Ma, ~840–830 Ma, and ~1900–1800 Ma, with a notable scarcity of 380–310 Ma zircons. The ε_Hf(t) values of Paleozoic zircons are predominantly negative, consistent with the magmatic records of the Tarim Craton but distinct from those of the Central Tianshan–Yili Block. These provenance signatures indicate that most of the Carboniferous–Permian sedimentary rocks were derived from the Tarim Craton, with only a minor mixed-source component (e.g., the Balikelike Formation silty limestone) involving the Central Tianshan–Yili Block. The absence of significant 380–310 Ma detrital zircons in the foreland strata, together with the passive margin affinity of the northern Tarim, supports northward subduction of the South Tianshan Ocean. A sharp decrease in detrital zircon r_Dz values and crystallization temperatures at ~310 Ma signals a tectonic transition from convergence to collision, constraining the final closure to the Late Carboniferous (~310 Ma). Furthermore, crustal thickness estimates based on zircon Eu anomalies remain stable at ~60 km across the subduction and collision stages, suggesting limited tectonic shortening and thus a soft collision. Full article

The formation of tectonic–magmatic–sedimentary processes during the Permian in the Beishan region represents a highly debated research topic along the southern margin of the Central Asian Orogenic Belt and even globally: does it mark the final subduction and amalgamation of the Paleo-Asian Ocean, or does it instead represent rifting superimposed upon an earlier orogen? New field observations combined with geochemical analyses reveal that the Liuyuan area is dominated by Early Permian basalts, associated with a rifting sedimentary sequence. During the Mid–Late Permian, gabbro–rhyolite associations were emplaced, accompanied by minor lacustrine sedimentation. The late stage was characterized by minor granitic intrusions or dikes with adakitic affinities, culminating in the emplacement of lamprophyre dikes. The basalts and gabbros in the Liuyuan area display mantle-derived geochemical signatures, with compositions intermediate between MORB and OIB. The exposed Permian basalt–rhyolite bimodal magmatic suite represents a genetically integrated rift-related rock series. Geochemical data from the Ordovician granites and schists within the belt reveal adakitic characteristics, implying that the Permian granitic rocks largely represent remelting products of these early granitic and schistose protoliths. Collectively, the lithological characteristics and magmatic associations clearly demonstrate that the tectonic setting during the Early Permian corresponded to a post-collisional extensional environment superimposed upon the early Paleozoic orogenic belt (Caledonian Huitongshan ophiolite–arc accretionary orogen), which subsequently underwent tectonic inversion to form the present-day orogenic structure. This paper proposes a theoretical model wherein the bimodal magmatic suite was generated by the upwelling of enriched asthenospheric mantle material, providing the driving mechanism for rifting. It formed within a post-collisional extensional environment developed over a complex pre-existing orogenic belt and was subsequently inverted, forming the current tectonic belt—a typical intracontinental Pyrenees-type orogeny. Full article

The Mesozoic dykes in the Xingcheng area of western Liaoning Province in China were investigated through an integrated study involving zircon U–Pb geochronology, whole-rock geochemistry, and zircon Hf isotopic compositions to elucidate their emplacement phases, petrogenesis, and tectonic setting. The dykes are classified into two groups: felsic (granite porphyry, granite aplite) and mafic (diabase, lamprophyre). Emplacement occurred in four discrete phases: Late Triassic (229–212 Ma), Early Jurassic (ca. 179 Ma), Late Jurassic (162–152 Ma), and Early Cretaceous (133–102 Ma). The felsic dykes are characterized by high SiO₂ and alkali contents, low TFeO and MgO abundances, and belong to the high-K calc-alkaline I-type granite series. The mafic dykes exhibit low SiO₂, elevated MgO, and high Na₂O contents, displaying both alkaline and calc-alkaline affinities. Both dyke suites are consistently enriched in light rare earth elements (LREEs) and large-ion lithophile elements (LILEs), and depleted in heavy rare earth elements (HREEs) and high field-strength elements (HFSEs). Zircon ε_Hf(t) values for the felsic dykes range from −22.3 to −7.4, corresponding to two-stage model ages (T_DM2) of 2613–1729 Ma, indicating derivation from partial melting of Neoarchean to Paleoproterozoic crustal material. Late Jurassic mafic dykes yield ε_Hf(t) values between −27.8 and −20.2, consistent with an origin from partial melting of enriched lithospheric mantle. In contrast, Early Cretaceous mafic dykes display a bimodal ε_Hf(t) distribution (−12.9 to −9.5 and +4.3 to +8.4), suggesting a predominant enriched mantle source with variable inputs from depleted mantle components. Integrated with regional tectonic reconstructions, the data indicate that the Xingcheng area evolved within a post-collisional extensional regime following the amalgamation of the North China Craton and the Central Asian Orogenic Belt during the Late Triassic. The Jurassic magmatic pulses are attributed to an active continental margin setting associated with subduction of the Paleo-Pacific Plate, whereas the Early Cretaceous phase reflects regional extension triggered by rollback of the subducting Paleo-Pacific slab. Full article

The Chutuan and Jiashan fluorite deposits are situated in the Donghai–Linshu area within the southwestern segment of the Sulu ultrahigh–pressure metamorphic belt. Both deposits share similar mineralization characteristics, with fluorite veins strictly controlled by fault structures and associated with mineral assemblages comprising fluorite, barite, quartz, and calcite. Two mineralization stages have been identified in both deposits: Stage I (quartz–fluorite–barite stage), representing the main ore–forming event, and Stage II (quartz–barite–calcite stage). This study focuses on integrated geochemical and geochronological analyses of fluorite from Stage I, providing new constraints on the genesis and metallogenic processes of these deposits. Direct Sm–Nd isotopic dating of fluorite yields an isochron age of 104 ± 16 Ma, indicating that mineralization occurred during the late Early Cretaceous. Fluid inclusion and stable isotope studies reveal that the ore–forming fluids constitute a complex hydrothermal system characterized by a wide temperature range (112–324 °C) and variable salinities (0.18–21.87 wt% NaCl eq.). The H–O isotopic compositions exhibit a distinct latitudinal trend, supporting a dominant meteoric water component. However, the presence of high–temperature, high–salinity fluid inclusions, along with a shift in some δD values towards the magmatic water field, suggests episodic mixing between meteoric water and deep–seated magmatic–hydrothermal fluids. Sr–Nd isotopic data (⁸⁷Sr/⁸⁶Sr = 0.711785–0.713424; εNd(t)= −27.7 to −27.5) potentially demonstrate that the ore–forming materials (Ca and REEs) were not derived from coeval magmatic rocks. Instead, they were primarily leached from the Precambrian Donghai Group metamorphic complex through extensive water–rock interaction. Based on these findings, the Chutuan and Jiashan deposits are classified as hydrothermal vein–type systems. Fluorite precipitation was governed by a combination of fluid cooling, water–rock interaction, and fluid mixing. Finally, a metallogenic model is established, offering important insights into the genesis of fluorite mineralization in the Sulu Orogenic Belt and analogous geological settings in eastern China. Full article

With the growing demand for strategic metals and the gradual depletion of traditional metal ore deposits, coal and coal-bearing strata are regarded as potential sources of rare metals; consequently, research into the characteristics of associated elements in coal-bearing strata has become one of the primary avenues of searching for new alternative resources. To investigate the sedimentary environmental characteristics and controlling factors of the coal-bearing strata along the southern margin of the Junggar Basin, coal seams 9–15 of the Xishanyao Formation in Sulphur Gully (Early Middle Jurassic) were selected as the subject of this study. This study employed analytical techniques including industrial analysis, total sulphur analysis, X-ray powder diffraction (XRD), X-ray fluorescence spectroscopy (XRF) and inductively coupled plasma mass spectrometry (ICP-MS) to determine the mineralogical and elemental geochemical characteristics of coal samples from Seylangou mining area, specifically from coal seams 9–15 and their overlying and underlying strata. Based on analyses of elemental ratios such as Al₂O₃/TiO₂, Sr/Ba, Rb/Sr, Ni/Co and V/(Ni + V), the source of material during the deposition of this deposit was identified, and the characteristics of the depositional environment, as indicated by palaeosalinity, palaeoclimate and redox conditions, were revealed. The results indicate that the macroscopic coal-rock types of coal seams 9–15 at the Sulphur Gully Coal Mine on the southern margin of the Junggar Basin are predominantly semi-dull to dull, with small amounts of filamentous coal and lustrous coal. The average proportion of the vitrinite group in the coal is 42.75%, the inertinite group is 51.40%, and the liptinite is 2.25%. The average content of inorganic matter in the coal is 3.60%, and the average maximum reflectance of the vitrinite group is 0.651%. The coal represents a transitional stage from low-rank to medium-rank coal, corresponding to a metamorphic stage of Grade I–II. The coal is classified as a bituminous coal with medium total moisture, very low ash, medium-volatile matter, medium-to-high fixed carbon and very low sulphur. The minerals in the coal seam are predominantly kaolinite, calcite and quartz. The major elements in the ceiling of the coal seam are dominated by SiO₂, followed by Al₂O₃; the coal itself is dominated by CaO, SiO₂ and Al₂O₃; and the base plate of the coal seam is dominated by Al₂O₃. The trace elements Cs and Bi are relatively enriched in the coal seam ceiling; Sr is relatively enriched in the coal; whilst Li, Cr and other elements are highly enriched in the coal seam base plate. The source rocks of the coal and the roof consist of deposits of felsic igneous rock (dacite), whilst the source rocks of the floor consist of deposits of intermediate igneous rock (andesite). The depositional environment ranges from marine brackish water at the base to transitional slightly brackish water and then to terrestrial freshwater at the top; the depositional climate was cold and arid, and the depositional environment was oxidising. This study provides valuable insights for further research into the elemental geochemical characteristics, sediment sources and depositional environments of the Xishanyao Formation coal seams in Liuhuangou, Xinjiang. Full article