Search Results (273)

Regional metamorphic graphite deposits in the North China Craton (NCC) are important crystalline graphite resources, but the links among sedimentary protolith, metamorphic evolution, and graphite mineralization remain insufficiently constrained in many ore belts. In the Datong–Xinrong graphite belt of northern Shanxi Province, the studied ore is hosted by graphite-bearing gneiss of the Paleoproterozoic Huangtuyao Formation. The graphite-bearing rocks are interpreted as mudstone-derived paragneiss and contain graphite, plagioclase, quartz, biotite, diopside, garnet, alkali feldspar, pyrrhotite, and minor sillimanite. To clarify the ore-controlling factors and metallogenic evolution of these rocks, we integrated whole-rock geochemistry, Raman spectroscopy of carbonaceous material (CM), and zircon U-Pb geochronology. Geochemical indicators and discrimination diagrams show that the protolith was deposited in a continental-margin setting under dry, brackish-water, and generally oxygen-rich conditions. Raman CM thermometry yields peak metamorphic temperatures of 445.9–534.0 °C, and mineral assemblage constraints indicate pressures of 6.10–7.13 kbar. Zircon U-Pb ages constrain the maximum depositional age of the sedimentary protolith to 2102 ± 42 Ma and the age of mineralization-related metamorphism to 1888 ± 25 Ma. These results support a sedimentary–metamorphic model in which carbon-bearing mudstone was deposited along an early Paleoproterozoic continental margin and was later transformed into graphite-bearing gneiss during late Paleoproterozoic orogenic metamorphism. Full article

Heilongjiang Province, northeastern China, occupies a key metallogenic position between the eastern Central Asian Orogenic Belt and the western Pacific continental margin. This review integrates published geological, geochronological, fluid–inclusion, and H–O–S–Pb isotope data to evaluate tectonic controls on endogenic gold mineralization. Four principal metallogenic episodes are recognized: Caledonian porphyry-related mineralization associated with Paleo–Asian Ocean subduction–accretion; Variscan skarn-forming magmatic–hydrothermal activity; Indosinian post-collisional structurally focused and epithermal hydrothermal activity; and Yanshanian mineralization characterized by Late Jurassic compressional reworking followed by a dominant Cretaceous Paleo–Pacific-related magmatic–hydrothermal pulse. Ore-forming fluids evolved non-monotonically from Paleozoic high-temperature magmatic fluids to more heterogeneous crustal, metamorphic, and meteoric–water–influenced systems. Zhengguang and Laozuoshan provide clear evidence for temporally distinct superimposed mineralization. Later hydrothermal reactivation could either remobilize and reconcentrate Au or leach, disperse, and obscure earlier mineralization. Exploration should therefore prioritize reactivated structural corridors where intrusive centers, reactive wall rocks, volcanic basins, and multi-stage alteration overlap. Full article

The Cretaceous-to-Eocene Julian (JB) and Brkini (BK) flysch basins have recently been studied for their heavy mineral assemblages; however, the rutile component has so far been neglected. To fill this gap, this study explores their detrital rutile trace element contents and U-Pb ages to define their possible provenance(s). In JB, there are very few rutile grains, mainly related to amphibolite–eclogite facies metamorphic units, with about 80% metapelitic grains. Among the few rutile grains from JB, only eight gave robust U-Pb ages. These ages are all Palaeozoic, resembling those of the closure/opening of the Rheic Ocean and the Variscan orogeny. In BK, the number of rutile grains is much higher than in JB, testifying to differences in the supply areas. The rutile grains are mainly in the amphibolite–eclogite facies, but they decrease, moving upward, accompanied by an increase in UHT. The metapelitic rutile component is higher than 74%. When considering the BK rutile grains, there are no Palaeozoic ages at the bottom of the sequence, while they are newly visible upward. In BK, the most abundant rutile grains show Mesozoic ages that can be considered as representatives of the opening/closure of the Vardar Ocean and the ophiolite emplacement in the Dinarides area. Full article

Entity alignment (EA) algorithms have been developed to identify and use links between entities in knowledge graphs (KGs), which are essential for data integration and information sharing. Given their significance, it is important to thoroughly evaluate EA algorithms to measure their performance on KGs. However, testing methods are still in the early stages, and few studies assess EA algorithms. To address this issue, this article uses the metamorphic testing methodology to automate the testing of EA algorithms. We first design eight metamorphic relations (MRs), grouped into four main groups in the context of EA, which EA algorithms are expected to satisfy. We argue that these eight relations define the necessary or expected properties of EA algorithms. To assess the performance of our proposed MRs, we tested five popular EA algorithms on three widely used datasets using a comprehensive set of metrics. The results show the following: (a) The four MRs influence EA algorithm outputs, with inference-related MR being the most challenging due to advanced reasoning needed. (b) Varying MRs affect EA effectiveness; simpler algorithms like MTransE and SEA perform better on easier datasets when evaluated with MRs. EA algorithms have violated metamorphic relations in some cases, indicating that they still lack certain necessary properties that require further improvement. Full article

Located 30 km south–southeast of Kabul in Logar province, Aynak is the largest and best-known copper orebody in Afghanistan. The deposit is hosted by the Loy Khwar Formation, a Neoproterozoic–Cambrian metasedimentary sequence of dolomite marble, carbonaceous quartz schist and quartz–biotite–dolomite schist. The primary ore minerals are chalcopyrite and bornite, with less abundant pyrite and minor cobaltite, chalcocite, pyrrhotite, sphalerite and molybdenite. Sulphides occur as bedded laminae and disseminations, in metamorphic segregations, and in syn- to post-metamorphic cross-cutting veins. Building on the mineralogical, lithogeochemical and sulphur isotope framework established by Waizy et al. (2020), ICP-MS analyses of sulphide-rich separates from Central and Western Aynak (n = 31) were undertaken to characterise trace-element distributions, evaluate possible metal sources, and further constrain the genetic model of the deposit. Co and As enrichment in chalcopyrite-dominant samples is consistent with cobaltite, whereas Co enrichment in the absence of arsenic suggests the possible presence of carrollite. Fluid inclusion analyses of secondary quartz-hosted inclusions indicate interaction between the Aynak deposits and saline aqueous fluids (32 to 47 equivalent wt% NaCl) at minimum P-T conditions of ~100–200 MPa and 300 °C. It is uncertain whether these fluid parameters relate to primary copper transport and deposition, or to remobilisation during metamorphism. Nevertheless, comparison with analogous sediment-hosted copper deposits suggests that highly saline basinal brines played an important role in the formation and evolution of the deposit. Occurrences of scapolite provide additional evidence for a model of brine-related mineralisation. Together with previously published mineralogical, lithogeochemical and sulphur isotope evidence, these findings support a sedimentary–diagenetic origin for the Aynak copper deposit that is broadly comparable with sediment-hosted stratiform copper systems of the Central African Copperbelt. Full article

The basement lithology in the northern South China Sea remains poorly constrained because of the lack of drilling data, which creates major challenges for predicting bedrock buried-hill reservoirs. This study is based on 2D and 3D seismic data, together with gravity and magnetic data, and is constrained by previous studies on the regional tectonic framework and lithologic distribution of the northern South China Sea. We investigated the basement lithologic composition of the XS area, established an integrated gravity–magnetic–seismic interpretation framework for basement lithology, and discussed the possible geological controls on basement lithologic distribution. The results show the following: (1) The basement in the study area is mainly composed of granite intrusive bodies, metamorphic rocks, and volcanic rocks. Granite bodies are characterized by irregular to intrusive seismic geometries, strong double-peak reflections at the upper boundary, and weak-amplitude, medium- to low-frequency internal reflections, reflecting their intrusive characteristics. Metamorphic rocks show diverse external seismic geometries, single-peak or weak reflections at the upper boundary, and medium- to strong-amplitude parallel internal reflections that intersect the upper boundary at high angles. Their gravity and magnetic responses show considerable overlap with those of granitic rocks. Volcanic rocks commonly show mound-shaped or lenticular seismic geometries and medium- to strong-amplitude, moderately continuous internal reflections. Intermediate–mafic volcanic rocks are associated with relatively stronger gravity and magnetic anomaly responses, whereas felsic volcanic rocks generally exhibit weak to moderate gravity and magnetic responses. These characteristics provide an integrated seismic–gravity–magnetic constraint framework for basement lithology interpretation in the South China Sea. (2) Integrated gravity–magnetic–seismic interpretation indicates that, near the present top of the pre-Cenozoic basement in the XS area, granite intrusive bodies are the dominant lithology. Metamorphic rocks mainly occur as discontinuous basement remnants in local structural lows or erosional windows, whereas volcanic rocks are mainly distributed near fault intersections or occur as bead-like bodies along fault zones. (3) The distribution of granite intrusive bodies and metamorphic basement is interpreted to be related to Indosinian–Yanshanian magmatic activity, tectonic deformation, and subsequent denudation. Faults formed during Early Yanshanian compression were later reactivated during the Himalayan period and may have acted as magma conduits, promoting the development of volcanic edifices along fault zones. Full article

The blue color of sapphire is associated with Fe and Ti impurities that replace Al³⁺ in the corundum structure. Typically, sapphire color depends on its geological origin, such as basaltic or metamorphic localities, and the blue hue can change after heating in an oxidizing environment. Nonetheless, previous studies on the blue color mechanism have left some questions unanswered. Therefore, this research examines how the oxidation states of Fe and Ti influence sapphire color and explores the mechanism of blue coloration before and after heating in oxidizing and reducing atmospheres. This study involved collecting sapphire samples from various gem localities, including basalt-related sapphires from Kanchanaburi, Thailand, and metamorphic-related sapphires from Sri Lanka. The samples were heated in an oxidizing environment at 1100 °C, then at either 1300 °C or 1500 °C in both oxidizing and reducing environments. As a result, after heating under an oxidizing environment at either 1300 °C or 1500 °C, the basalt-related sapphires turned from light blue to pale blue, and the metamorphic-related ones turned colorless. The Fe³⁺-Ti⁴⁺ mixed acceptor states decreased because an electron from the valence band recombined with a hole in the color center during heating. On the other hand, the blue color observed in sapphire samples after heating in a reducing environment at 1300 °C could be explained by electrons being depleted from the hole color center associated with Fe³⁺-Ti⁴⁺ mixed acceptor states within the energy band gap, thereby making them ready to receive electrons from the valence band upon optical excitation. Therefore, it can be concluded that the blue color mechanism in sapphires before and after heating under different atmospheric environments can be explained by an energy-band model involving the presence or absence of Fe³⁺-Ti⁴⁺ mixed acceptor states, as well as a hole color center within the energy band gap. Furthermore, after heating at 1300 °C and 1500 °C in a reducing environment, the oxidation state of Fe gradually decreases from 3+ to 2+. The samples turn black upon heating to 1500 °C, indicating that Fe²⁺-Ti⁴⁺ is responsible for the black color rather than the blue observed in sapphires. Full article

The Casas Novas gold deposit is located in the Escoural Gold District of the Ossa Morena Zone (OMZ, SW Iberia) and consists of an orogenic gold system characterized by structurally controlled mesothermal lodes, which are related to a major shear zone. The mineralization shows evidence of two distinct metallogenic phases during regional metamorphism: (i) an early higher-temperature stage marked by Co-Ni-rich loellingite hosting Au-(Ag) alloys accompanied by pyrrhotite, and (ii) a later low-temperature stage with arsenopyrite, gold, maldonite and Bi-Te sulfosalts. Detailed textural analysis documents the evolution from initial Au-Ag alloys enclosed in Co-Ni-rich loellingite to subsequent Au-Bi-Te phases and newly formed arsenopyrite. The results show the thermal and chemical changes in the system, demonstrating the importance of fluid–rock interactions in the redox conditions, which became more oxidized, controlling the gold deposition. The comprehensive overview of the processes that led to the concentration of gold in the Casas Novas deposit provides a valuable contribution to the ongoing studies into the auriferous region of the Escoural Gold District. Full article

Titanite is a widespread accessory mineral in magmatic, metamorphic, and hydrothermal systems and can incorporate trace elements that are sensitive to ore-forming processes. Although titanite trace-element chemistry has been widely applied to individual ore systems and deposit comparisons, its potential for supervised machine-learning-based discrimination across multiple ore deposit types remains less systematically explored. In this study, we compiled a literature-based LA-ICP-MS titanite trace-element dataset comprising 1679 analyses from five major ore deposit types: porphyry, skarn, iron oxide–apatite (IOA), iron oxide copper–gold (IOCG), and orogenic Au deposits. A common feature set of 21 trace elements, including REE, Y, Zr, Hf, Nb, Ta, Th, and U, was used to evaluate six supervised machine-learning algorithms: K-nearest neighbors, support vector machine, random forest, XGBoost, TabMap, and TabPFN. Two-dimensional element and element-ratio diagrams showed substantial overlap among deposit types, whereas machine-learning models better captured deposit-type-related multielement patterns in the compiled dataset. TabPFN achieved the highest stratified 5-fold cross-validation performance, with an accuracy of 0.957 ± 0.011 and a macro-F1 score of 0.944 ± 0.012, followed by TabMap and XGBoost. SHAP and TabMap-SHAP interpretations suggest that deposit classification is mainly associated with coupled variations in REE-Y, Eu, HFSE, and Th-U systematics rather than with a single diagnostic element. These results indicate that titanite trace-element compositions may provide a useful quantitative and interpretable approach for deposit-type discrimination within compiled geochemical datasets, while broader application requires expanded standardized datasets and independent validation samples. 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

Geochemical data provide direct constraints on mineralization, and the extraction of mineralization-related geochemical anomalies is essential for mineral resource prediction and assessment. The regional geochemical field reflects the spatial expression of ore-forming environments resulting from the superposition of multiple geological processes, with distinct elemental assemblages corresponding to different processes. The Ailaoshan metallogenic belt, located in the southeastern segment of the India–Eurasia collisional orogen, experienced multiple episodes of opening and closure, extension, amalgamation, and compression, leading to intense deformation. Its complex structural framework, multistage magmatism, and metamorphism have generated abundant mineral resources, particularly Au, Sn, Cu, Pb-Zn, and Ni deposits. Using the 1:200,000–scale national stream sediment geochemical dataset, principal component analysis (PCA) was applied to identify major ore-forming elemental assemblages. Singular value decomposition (SVD) was then used to extract regional and local anomalies for PC2 (Ag-As-Bi-Cu-Mn-Pb-Sn), PC3 (B-Be-Bi-Cu-F-W), PC4 (La-Nb-Th-U-Y-Zr), and PC10 (Au-Hg). Ultimately, six metallogenic prospective areas were consequently delineated. Full article

The protein folding problem has traditionally been defined by two complementary challenges: predicting the three-dimensional structure of a protein from its amino acid sequence and understanding the mechanism by which this structure is attained. While recent advances in artificial intelligence have largely addressed the former, the latter remains unresolved. Early studies showed that many small proteins fold in a cooperative two-state manner, shifting attention toward transition states and energy landscapes. Comparative analyses of protein families further revealed that folding mechanisms are often conserved among proteins sharing the same topology, suggesting a dominant role of structure in shaping folding pathways. However, this framework does not explain when and how a protein commits to a specific topology. Metamorphic proteins, in which highly similar sequences adopt distinct native folds, provide a powerful complementary approach. Studies of these systems show that closely related sequences can follow different folding mechanisms without sharing common intermediates. These findings indicate that folding pathways are determined at very early stages and are encoded within the denatured ensemble through subtle structural and energetic biases. Here, we review the evolution of protein folding studies and propose a unified view in which folding mechanisms are selected early, with the denatured state playing a central role in defining both folding pathways and final topology. Full article

Quartzites containing malachite–azurite mineralization identified in the Kırşehir region (Central Anatolia, Türkiye) are located within the Kırşehir Massif. This study aims to comprehensively characterize the mineralogical, petrographic, geochemical, and gemological properties of these quartzites and to evaluate their potential as ornamental and decorative stones. Due to their characteristic green and blue colors, malachite and azurite possess significant aesthetic value. Their occurrence within silica-rich and mechanically resistant quartzites enhances the visual appearance of the host rock while maintaining its structural integrity. Petrographic observations indicate that the quartzites exhibit a granoblastic texture composed of interlocking quartz crystals. Malachite–azurite mineralization is structurally controlled by NW–SE-trending fracture systems and occurs predominantly as fracture-filling and cavity-coating phases, indicating an epigenetic origin related to post-metamorphic fluid circulation. Geochemical analyses reveal that the samples are dominated by SiO₂ (~95.33 wt.%), with CuO (~1.77 wt.%) and elevated Cu contents (3205 ppm) confirming the presence of copper carbonate mineralization. Although the high silica content contributes to overall mechanical strength, the relatively low Mohs hardness (3–4) and chemical sensitivity of malachite and azurite represent important limitations. Quantitative gemological measurements further indicate that quartz-rich domains exhibit high hardness values (up to ~907 HL), whereas malachite–azurite-bearing zones display significantly lower hardness (~735 HL) due to fracture-controlled heterogeneity and the presence of softer carbonate phases. Surface brightness measurements show moderate to high gloss values (~73–80 GU), with noticeable improvement following epoxy impregnation. These results demonstrate that while the material exhibits favorable optical properties, its mechanical performance is strongly influenced by mineralogical contrasts and structural discontinuities. Quartzites bearing malachite–azurite mineralization are therefore suitable primarily for decorative stones, ornamental objects, and small-scale jewelry applications rather than high-quality gemstones. The striking color contrast between azurite, malachite, and quartz enhances their visual appeal, and with appropriate stabilization techniques, their durability and economic value can be partially improved. Full article

Space photovoltaics remains the primary power source for satellites and spacecraft, where high efficiency, radiation resistance, and low mass are essential requirements. While conventional III–V multijunction solar cells currently represent the technological benchmark, recent advances in materials science and device architectures have significantly expanded the design space of space photovoltaic systems. This review provides a comprehensive overview of the fundamental physical principles, material platforms, and device concepts relevant to photovoltaic operation under space conditions, with particular emphasis on the AM0 spectrum, radiation effects, and thermal cycling. Special attention is devoted to advanced architectures, including inverted metamorphic multijunction solar cells, concentrator photovoltaic systems, and emerging tandem concepts such as perovskite/silicon and all-perovskite devices. The review highlights the growing importance of system-level metrics, particularly specific power and integration flexibility, which increasingly complement efficiency as key performance indicators. Although emerging technologies offer unprecedented opportunities for lightweight and high-efficiency photovoltaic systems, challenges related to long-term stability, defect control, and scalability remain critical for their practical implementation. Overall, the future of space photovoltaics lies in the development of application-specific solutions that balance efficiency, durability, mass, and cost, enabling next-generation space missions and energy systems. Full article

The Ailinwudui gold deposit is located in central Jilin Province and represents a newly discovered typical vein-type gold deposit hosted in a Paleozoic metamorphic rock series in recent years. At present, the metallogenic epoch and regional metallogenic tectonic setting of the deposit remain poorly constrained, which seriously restricts the understanding of gold metallogenic regularities and subsequent mineral exploration deployment in central Jilin. Previous studies indicate that the Ailinwudui gold deposit is a structurally controlled vein-type gold deposit. In this study, zircon U-Pb and muscovite ⁴⁰Ar/³⁹Ar geo-chronology were employed to precisely constrain the metallogenic timing of the gold mineralization. Zircon U-Pb dating yields an emplacement age of 174.7 ± 0.85 Ma for the granodiorite and a formation age of 209.5 ± 1.40 Ma for the rhyolite porphyry. Muscovite ⁴⁰Ar/³⁹Ar dating yields a plateau age of 180.39 ± 1.83 Ma, which confines the gold mineralization to the Early–Middle Jurassic. Whole-rock geochemical results reveal that the granitoids in the study area are enriched in large-ion lithophile elements (LILEs) and light rare earth elements (LREEs) and depleted in high-field-strength elements (HFSEs), showing typical arc-related magmatic affinities. The formation of this gold deposit is related to the subduction of the Paleo-Pacific Plate during the Early–Middle Jurassic. The research results can provide important geochronological and geochemical evidence for the study of gold metallogenic mechanisms and mineral exploration in central Jilin Province. Full article