It is widely considered that porphyry Cu deposits formed via oceanic slab subduction are closely associated with hydrous and oxidized arc magmas. Of note, two suites of neighboring (similar to 40 km apart) Carboniferous arc volcanic rocks in Northwest China show different extents of mineralization: volcanic rocks from the Dananhu arc (DNHA) host one of the most important porphyry Cu deposit belts in China, whereas those from the Yamansu arc (YMSA), adjacent to DNHA, are ore-barren. These arc volcanic rocks, thus, provide a precious opportunity to explore the main factor that controls the genetic links between coeval arc lavas and porphyry Cu mineralization. Here we report whole rock major and trace element compositions and Mg-Sr-Nd-Pb isotopic data, generating a comprehensive geochemical comparison for these two suites of volcanic rocks from basalt to dacite. The whole-rock geochemical analyses suggest that at a given SiO2 content, the YMSA basalts show lower MgO, CaO, Fe2O3T , and TiO2 contents than the DNHA basalts. The DNHA volcanic rocks have higher Sr/Y and (La/Yb)N ratios, which are positively correlated, indicating that these two suites of rocks were derived from different magma sources. The DNHA rocks are characterized by radiogenic Pb isotopic compositions with 206Pb/204Pb up to 19.457, clearly distinct from the YMSA volcanic rocks with less radiogenic Pb isotopic compositions (206Pb/204Pb = 18.146-18.487), suggesting variable assimilation of crust-derived components during magma evolution. The d26Mg values of the DNHA rocks (-0.35%0 to +0.06%0) are largely similar to those of the YMSA rocks (-0.24%0 to +0.04%0), and both sets of isotopic ratio ranges have tendency toward heavy Mg isotopes, which could be attributed to serpentinite-derived high-d26Mg fluids in their mantle sources. Both suites of arc lavas have constant Cu contents and Cu/Sc ratios, indicating inconspicuous pre-enrichment of Cu contents. Geochemical comparisons indicate that the DNHA rocks were derived from partial melting of peridotite at the depth around the spinel-garnet transitional stability field, whereas the YMSA rocks were derived from partial melting of spinel peridotite, and the DNHA magmas had a thicker overlying plate than that of the YMSA magmas. The thickened arc lithosphere facilitates water-rich magmas accumulation and garnet fractionation, driving the magmas to become more oxidized, thereby preventing sulfide segregation and releasing sulfide-bound Cu. Thus, magmas differentiation in the thickened arc lithosphere is a key factor influencing porphyry Cu ore potential. (c) 2025 China University of Geosciences (Beijing) and Peking University. Published by Elsevier B.V. on behalf of China University of Geosciences (Beijing). This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Understanding continental crustal architecture and its control on mineral systems is fundamental to the earth sciences. Here we integrate zircon U-Pb geochronology, whole-rock Nd-Hf isotopes, lithogeochemical data, and regional metallogenic records from Cambrian to Triassic magmatic rocks across the Solonker-Alxa region of Inner Mongolia to define crustal domains and their metallogenic significance. Two contrasting isotopic provinces are identified: (1) an enriched domain [epsilon(Nd)(t) < -4, epsilon(Hf)(t) < 0] encompassing the North China Craton-Alxa Block and (2) a depleted domain [epsilon(Nd)(t) > -4, epsilon(Hf)(t) > 0] typifies the Central Asian orogenic belt (CAOB). These domains are separated by the Chifeng-Bayan Obo fault, the area north of Chaganhua, and the Quagan Qulu-Tebai fault. Crustal thickness patterns show a belt of thinned crust (<40 km) along the Mandula, Solonker, Ganqimandu, Yingba, and northern Enger Us fault zones, marking the boundary between the Mongolia collage and the Tarim-North China collage. Variations in crustal thickness suggest that the Alxa Block is a distinct Precambrian terrane, separate from the North China Craton. The protracted subduction-accretion and slab rollback of the Paleo-Asian Ocean have driven significant crustal growth in the Solonker-Alxa region, with juvenile crust contributions estimated at 37% in the southern CAOB. Crustal maturation and felsic differentiation resulted from polyphase melting events involving mafic lower crust, oceanic crust, and the middle to upper crust. A systematic correlation exists between isotopic domains, crustal architecture, and metallogenic distribution. Depleted domains with thin crust (<50 km) preferentially host porphyry Cu (+/- Au), epithermal Pb-Zn-Cu, and volcanic massive sulphide-type Cu deposits, whereas enriched isotopic domains and their peripheries contain porphyry Mo, skarn Cu-Fe, vein-type Au deposits, and magmatic Cu-Ni sulfide deposits, indicating genetic links to ancient crustal recycling and metasomatized lithospheric mantle. This synthesis provides a coherent tectono-metallogenic framework for the Solonker-Alxa segment of the southern CAOB and offers guidance for mineral exploration.

Geochemical evidence suggests that arsenic is a crucial factor reinforcing gold mineralization in pyrite. The systematic presence of Au-bearing arsenian pyrite in hydrothermal systems suggests a coupled Au-As geochemical behavior in various physico-chemical conditions. However, there is a lack of understanding of elemental interactions at the atomic scale during gold mineralization, leaving unresolved which specific structural configurations host Au-As interactions and whether other trace elements can exert effects similar to arsenic. In this study, we use ab initio simulations to quantitatively evaluate interactions between elemental impurities in pyrite, specifically focusing on the gold-arsenic relation. We consider a wide range of chemical and structural substitutions, for which we monitor the structural distortions they induce and calculate their formation energies. We show that individual incorporations of impurity atoms are prohibitive. But joint substitutions better accommodate the induced stress, decrease energy barriers, and thereby facilitate gold incorporation. Among various trace elements, arsenic substitution for sulfur is the most favorable for gold incorporation, due to the formation of [AuAsnS6-n] coordination octahedra, with Au substituting Fe. The presence of As effectively alleviates the lattice stress associated with Au substitution, and restricts it within the local coordination polyhedron, thereby facilitating the large-scale, long-term preservation of Au in pyrite. Our study provides a novel insight into co-evolutionary processes in ore deposits, with a focus on pyrite-hosted Au deposits.

Porphyry deposits are the major source of copper and molybdenum of the world. The Great Xing'an Range in northeastern China is widely known for its abundant Mo deposits, some of which have giant sizes (i.e., >0.5 Mt Mo). In total, there are 27 porphyry Mo (-Cu) deposits and 14 porphyry Cu (-Mo) deposits in the region. Whether and how the formation of these deposits was controlled by the regional crust architecture remains unclear. Here, we integrated geologic and geochemical data (including zircon U-Pb dating results and Lu-Hf isotopic compositions) for the Paleozoic-Mesozoic felsic rocks and porphyry Cu (-Mo) and Mo (-Cu) deposits in the Great Xing'an Range, and imaged the crustal architecture by zircon Hf isotopic mapping. The results indicate that most of the study area is of juvenile crustal domains, with a significant mantle contribution in their formation. The northern Erguna Block and the southwestern Songliao Accretionary Terrane are characterized by ancient and reworked crustal domains, respectively. Porphyry Cu (-Mo) deposits are predominantly located in these juvenile crustal domains with high epsilon(Hf)(t) (>+3) values, and their distribution was controlled by the NE-trending tectonic systems. High Sr/Y and high oxygen fugacity arc magmas are associated with the formation of the subduction-related porphyry Cu (-Mo) deposits during the Early-Paleozoic and Triassic. By contrast, fault zones or the intersection of faults are favorable sites for the formation of the Jurassic to Early-Cretaceous Cu (-Mo) deposits. Porphyry Mo (-Cu) deposits in the Great Xing'an Range, however, are located in both juvenile and reworked crustal domains. The Permian to Triassic Mo (-Cu) deposits have different magmatic sources under different tectonic settings. During the Jurassic to Early-Cretaceous, a transition of the tectonic regime from compression to extension is conducive to the large-scale porphyry Mo mineralization event. This study demonstrates the usefulness of Hf isotopic mapping as a tool in characterizing the relationship between crustal architecture and porphyry deposits' locations and types, and provides a better focus for further exploration for porphyry deposits regionally.

The coupled disaster of coal spontaneous combustion (CSC) and gas explosions in the goaf of high-gas mines is a critical focus for disaster prevention. This paper reviewed the current research on these mechanisms and associated risk assessments, aiming to support the development of prevention technologies in China. The review covered three areas: Gas explosion mechanisms, coal spontaneous combustion characteristics and risk assessment, and the coupling laws and risk evaluation of these disasters in goafs. Five key issues for future research are identified: The need for more detailed studies on the explosion mechanisms of multi-component gas mixtures; further exploration of coal spontaneous combustion evolution and risk determination in goafs; systematic improvement of theories on coupled coal combustion and gas explosion disasters; clarification of flame shock wave propagation in gas explosions; and the urgent development of a risk evaluation system for these coupled disasters. Continuous research in this field is of vital importance for enhancing the safety standards of coalmines, promoting the sustainable development of the coal industry, and achieving the goals of carbon peak and carbon neutrality.

The opening of the Meso-Tethyan Ocean in the Early Permian led to the separation of the South Qiangtang and Baoshan blocks from the eastern Gondwana and coincided with the termination of the Late Paleozoic Ice Age (LPIA). The mechanisms linking continental breakup and coeval global deglaciation remain controversial. Here we present new zircon UPb geochronology, whole-rock geochemistry, and SrNd isotopic data that collectively document a long-lived mantle superplume beneath the northern Gondwana between ca. 324 and 280 Ma. We identify an age-progressive OIB-CFB volcanic system comprising (1) 324-316 Ma oceanic island basalts (OIB) preserved in the Changning-Menglian accretionary wedge, (2) 320-280 Ma continental flood basalts (CFB) in the Baoshan block, (3) contemporaneous OIB-CFB suites in the South Qiangtang block, and (4) the ca. 290 Ma Panjal Traps in the northern India. Geochemical indicators of melting depth (TiO2/Yb), along with Nd isotopic systematics, distinguish deep garnet-facies plume melts from shallow, lithosphere-modified basalts, indicating a plume system with at least two spatially separated heads. We propose that plume-induced lithospheric heating and thinning initiated rifting along the northern Gondwana margin, culminating in the opening of the Meso-Tethyan Ocean at similar to 280 Ma. The temporal coincidence of superplume magmatism with an atmospheric CO2 rise at similar to 294 Ma, and the subsequent rapid deglaciation, supports a possible causal link. We argue that prolonged degassing from the plume-related large igneous province supplied the sustained CO2 flux necessary to overwhelm the Late Paleozoic carbon sinks and terminated the LPIA.

Although recent research has proposed models for enrichment of gold in some mineral deposits, current hypotheses fail to explain exceptionally high-grade mineralization in reduced intrusion-related gold deposits. This study proposes the mechanisms that enriched gold to unusually high levels in the Ludousou deposit. The ores formed in two stages, a low-grade Stage 1 (< 3 g/t Au) and a high-grade Stage 2 (avg. 30 g/t Au). In Stage 1, pyrite (Py1) and arsenopyrite (Apy1) host sub micro-meter scale Au with median concentrations of 0.01 and 0.1 ppm, respectively, with negative median δ34S values of -4.8 and -5.3 ‰, respectively. Fluid inclusion in quartz (Qz1) indicate phase separation and ores formed at 240 °C and 0.5 kbar, from a fluid with a median salinity of 22.9 wt.

The extent of eastward growth of the Tibetan Plateau and deformation of the Sichuan Basin remain controversial, primarily due to the lack of direct evidence for Cenozoic deformation within the Central Sichuan Basin. This study presents anisotropy of magnetic susceptibility (AMS) data from an-210-km-long transect across the Central Sichuan Basin to unravel penetrative layerparallel shortening (LPS) strain. Our results delineate a distinct structural zonation where an-110-km-wide western incipient deformational belt with NW-SE LPS is separated from an-10-km-wide eastern belt with both NW-SE and NE-SW LPS by an-74-km-wide central undeformed belt. This zonation reveals that late Cenozoic eastward plateau growth has propagated far beyond the frontal Longquan Shan fault, penetrating-110 km into the Central Sichuan Basin as widespread LPS. Conversely, the narrow eastern belt likely records late Mesozoic orogenic events. We attribute this long-distance propagation to enhanced slip along a shallow Triassic d & eacute;collement, driven by substantial topographic and sedimentary loading coupled with a low strain rate in the Longmen Shan. This penetrative strain accommodates an estimated-24 km of previously unrecognized uppercrustal shortening, confirming LPS as a major contributor to Cenozoic basin deformation. The central undeformed belt defines the eastern limit of this upper-crustal shortening, signifying that late Cenozoic rapid exhumation of the Eastern Sichuan Basin likely resulted from tectonic uplift via strain accumulation along a midcrustal d & eacute;collement and enhanced climate-driven erosion. Our findings highlight the crucial roles of uppercrustal penetrative strain, midcrustal strain transfer, and surface processes in shaping the eastern Tibetan Plateau and Sichuan Basin.

Mantle-derived mafic magma recharge is widely recognized as a critical factor in porphyry Cu mineralization; however, the nature of the mantle contribution to fertile magmas in postcollisional settings remains poorly constrained. Here, we present new data on in situ apatite, its host zircon, and other silicate minerals (amphibole and plagioclase) from a suite of Miocene intrusions associated with the giant Zhunuo porphyry Cu deposit in southern Tibet. These results are compared with a compilation of published magmatic apatite and zircon data from other postcollisional porphyry Cu deposits in the Gangdese belt, southern Tibet. Zircons from mantle-derived mafic rocks have consistently high Eu/Eu* ratios (mostly 0.3-0.6) and a restricted range of magmatic oxygen fugacity (fO(2); Delta FMQ = +0.5 to +2.0), indicating that the mantle-derived magmas were hydrous and oxidized. Zircon-hosted apatites in syn-mineralization high-Mg diorite porphyry exhibit large variations in Cl contents (0.10-1.01 wt%) and X-F/X-Cl ratios (4-60), reflecting crystallization from volatile-undersaturated to fluid-saturated magmas. In contrast, apatites in postmineralization ultrapotassic lamprophyre have higher X-F/X-Cl ratios (similar to 20-100) and lower Cl contents (mostly <0.20 wt%) that decrease with increasing X-F/X-Cl ratios, suggesting crystallization from a fluid-saturated magma that experienced early devolatilization during underplating in the lower crust. The estimated Cl and S contents of the high-Mg dioritic magma are slightly higher than those of the ore-forming magmas, identifying it as a potential volatile source for porphyry Cu mineralization. We propose that repeated injections of hydrous, oxidized, mantle-derived mafic magmas released H2O-Cl-S-rich volatiles into the lower and middle-upper crust, thereby fertilizing the porphyry system and facilitating porphyry Cu mineralization in the Gangdese belt and analogous postcollisional settings.

The Xiadian orogenic gold deposit, located within the giant Jiaodong gold province, is remarkable for hosting three orebody groups with distinct structural, alteration, and mineralization characteristics within the footwall of the Zhao-Ping fault zone. The No. 1 orebody group, containing 75% of the gold resources, is situated within the immediate footwall. The No. 2 and No. 3 orebody groups are located progressively farther from the main fault within the footwall, with correspondingly fewer gold resources. This deposit geometry provides a rare opportunity to investigate the critical factors controlling deposit architecture and mineralization processes. Integrated macroscopic geologic mapping and in situ analysis of pyrite textures, trace elements, and sulfur isotope ratios indicate that each orebody group formed under different structural-hydrodynamic regimes from a single fluid source. The No. 1 orebody group represents a fault core, where quasicontinuous fluid flow under low differential stress formed large tonnage and disseminated ores. The No. 2 orebody group, interpreted as a damage zone, experienced episodic pressure fluctuations and fluid immiscibility, leading to discontinuous gold mineralization and stockwork ores. In contrast, the No. 3 orebody group experienced highly localized, intense fluid pulses through extensional-shear fractures, resulting in higher gold grades but limited resources. This study highlights the importance of coupling macroscopic and microscopic parameters to understand the structural and hydrodynamic factors that control the spatial distribution of gold mineralization in and adjacent to fault zones. This research establishes a predictive model for gold exploration in similar structural settings.

The coupling between extension veining and fluid evolution in orogenic Au-Sb deposits remains poorly understood. This study presents an integrated structural, geochronological (sericite Ar-Ar, monazite U-Pb), fluid inclusion, and oxygen isotopic investigation of the Zaorendao Au-Sb deposit (China). The deposit is hosted within an Early Triassic quartz diorite stock that intrudes slate and contains two main ore types: extensional quartz-stibnite-sphalerite veins (Sb) and disseminated sulfide-hosted Au ores in the wall rocks. Structural analysis reveals that competency contrasts between a quartz diorite and slate localized tensile failure. Geochronology constrains this veining and mineralization to 231 Ma during regional NE-SW shortening. Four hydrothermal stages are identified. Stage 1 is characterized by elongated coarse quartz (Qz1) veins and disseminated Au mineralization, with chlorite geothermometry from the alteration halo of 300 ± 33 °C. Extension structure suggests high-pressure fluid under near lithostatic conditions drove continuous extension and fluid discharge into the wall rocks, leading to Au precipitation via fluid-rock interaction. Stages 2 and 3 involve microfracturing and healing of Qz1, forming quartz overgrowth rim (Qz2). Pseudo-secondary fluid inclusion assemblages (FIAs) in healed microfractures within Qz1 contain coexisting liquid-rich and vapor-rich inclusions and yield a mean homogenization temperature of 181 ± 10 °C, reflecting a significant drop in fluid pressure (from near lithostatic to near hydrostatic levels) and temperature (from ∼300 °C to ∼180 °C). Similar δ18O values of Qz1 (20.0‰) and Qz2 (19.4‰) support a colloidal silica model, wherein silica colloids of Qz2 formed during Stage 2 (∼300 °C) under fluid decompression and coagulated onto Qz1 surface during Stage 3 as fluid cooling. In Stage 4, stibnite and sphalerite fill the veins, with FIAs in sphalerite showing temperatures of ∼180 °C, indicating that decompression-induced fluid cooling triggers stibnite precipitation. This study demonstrates a continuous genetic sequence where extension veining dynamics directly governed fluid evolution (pressure release and cooling) and sequential Au-Sb precipitation, providing a fundamental framework for understanding similar orogenic systems.

The role of Archean mantle metasomatism in pre-enriching the lithospheric mantle as driver for subsequent formation of giant ore deposits remains poorly understood, particularly regarding how metasomatic styles and melting pressures control metal endowments. Here we address this issue through an integrated analysis of whole-rock geochemical and zircon U-Pb-Hf isotope data from Archean TTGs and greenstones in the Luxi and Jiaobei terranes of the North China Craton, combined with phase equilibrium modelling. Our data shows TTGs in our study include crust-derived TTGs and mantle-derived sanukitoids. The Jiaobei Terrane records a longer magmatic history (ca. 2.9–2.5 Ga) within a thicker arc crust, whereas the Luxi Terrane documents a shorter magmatic history (ca. 2.7–2.5 Ga) within a thinner arc crust. Greenstones, sanukitoids and TTGs reveal different metasomatic histories beneath the two terranes. The Luxi Terrane records a transition from fluid- to melt-dominated metasomatism, whereas the Jiaobei Terrane records fluid-controlled metasomatism. These contrasting styles, coupled with distinct melting pressures, explain the different metal endowments in these terranes. Low-pressure melting of mantle that had been metasomatized by sediment-derived melts in the Luxi Terrane promoted REE enrichment, whereas high-pressure melting of fluid-metasomatized mantle in the Jiaobei Terrane facilitated enrichment in gold. These Archean processes preconditioned the lithosphere for subsequent Mesozoic mineralization, with the Luxi Terrane hosting REE deposits and the Jiaobei Terrane hosting giant gold provinces. Our findings demonstrate that the integrated use of greenstones, sanukitoids, and TTGs provides a robust framework for tracking mantle metasomatic evolution and its metallogenic consequences in Archean cratons.

How the intraplate deformation of the East Asian continent was coupled with ocean-continent subduction during the Early Cretaceous has been hotly debated over the past few decades. In this study, magnetic fabric analysis of 26 Early Cretaceous mantle-sourced intermediate-mafic dikes (376 samples) in the Jiaodong Peninsula of eastern China was conducted to constrain the paleostress fields during dike emplacement. The results indicate that the asymmetric arrangement of magnetic foliations about the dike symmetry plane resulted from syn-emplacement tectonic stresses. Based primarily on the magnetic fabric results of the dikes, we demonstrate that the Jiaodong Peninsula experienced five stages of Early Cretaceous tectonic deformation, i.e., WNW-ESE extension (135-124 Ma), NW-SE compression (123-122 Ma), NW-SE (121-117 Ma) and NNW-SSE (116-112 Ma) extensions, and NNW-SSE compression (111-107 Ma). It is inferred that the cyclic intraplate extension and compression were controlled predominantly by plate margin dynamics. The Early Cretaceous subduction direction of the Paleo-Pacific Plate beneath the Eurasian Plate changed from west-northwest (135-124 Ma), through northwest (123-117 Ma), to northnorthwest (116-107 Ma). Therefore, acting as a tectonic bridge, these dikes provide critical evidence linking intraplate deformation to subduction processes along the plate margin.

Gold,a strategic and critical mineral resource,poses substantial challenges in deep exploration.This study systematically reviews and analyzes the geochemical behavior of gold mineralization,the mechanisms of gold mineralization,and the technical systems for deep exploration.Gold concentrations in crust-mantle layers remain at low levels(10-9).Through diverse fluid mineralization processes,gold achieves enrichment over a thousand-fold to form industrial-scale ore bodies.The geological characteristics,genetic models,and spatiotemporal distribution of various mineralization types-including orogenic,Jiaodong-type,porphyry-skarn,epithermal,intrusion-related gold deposits(IRGD),Carlin-type,iron oxide copper-gold(IOCG),and volcanogenic massive sulfide(VMS)deposits-indicate extensive gold mineralization processes involving the transportation and enrichment of gold by mantle-derived fluids,magmatic hydrothermal fluids,meteoric water,and other media.A tectono-dynamic model for gold mineralization is established to show diverse deposits demonstrate genetic relationships with convergent plate margin dynamics,implying their temporal distribution has correlation with supercontinent cycles.Gold mineralization in China occurs primarily in four tectonic settings:accretionary orogenesis,cratonic destruction,continental collision,and intracontinental reactivation.Research on orogenic gold deposits has advanced beyond traditional models emphasizing purely crustal metamorphic fluids in compressional settings.Current understanding recognizes that these deposits frequently form in transextensional tectonic regimes with significant contributions from mantle-derived fluids.Gold-rich porphyry deposit is considered to be formed in the middle crust thickness.Ore-forming fluid release has evolved from a model of shallow,near-ore magma exsolution to one involving exsolution from deeper magma chambers.Concurrently,the conceptual framework for magmatic evolution has shifted from the traditional"magma chamber"paradigm toward the modern"crystal mush"model.Mineralization exhibits hierarchical structural control spanning lithospheric-scale deep faults and mantle upwelling zones down to ore-field-scale features such as fault bends,fold hinges,and intrusive contacts.These multi-scale structures collectively provide essential conduits and depositional sites for fluid focusing and gold precipitation.Based on the analysis of the mineralization system,the exploration of magma and hydrothermal channels at different scales and depths,as well as the occurrence space of ore bodies,through multi-scale and multi-depth geophysical methods is a crucial approach in gold exploration.Geophysical methods,including magnetotellurics and dense nodal array,delineate deep geological structures,while wide-field electromagnetic method,spectral induced polarization,and surface-borehole transient electromagnetic method identify ore-related anomalies.Deep-penetrating geochemistry(nanoparticle tracing)is employed to detect the vertical migration patterns of elements within concealed ore bodies.Mineral spectroscopy incorporating short-wave and thermal infrared analysis enables precise targeting of hydrothermal centers and mineralized zones.Designing tailored exploration methods based on the metallogenic factors of different gold deposits,and utilize three-dimensional modeling and artificial intelligence further support multi-source data integration and intelligent prospect analysis.The establishment of genetic models,the combination of diverse prospecting techniques,and a tripartite"knowledge-data-simulation"driven prediction approach represents a critical direction for future exploration of concealed gold deposits.

The Yu'erya gold deposit is located in eastern Hebei along the northern margin of the North China Craton, which is one of the typical gold deposits associated with Mesozoic granitic intrusions in the region. A systematic characterization on the gold occurrence and sulfide geochemistry are critical for understanding the mineralization process and guiding recovery strategy. However, such information is still lacking for Yu'erya. In this study, the automated mineralogy mapping using TESCAN Integrated Mineral Analyzer (TIMA) and sulfide compositional determination using laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) have been conducted to investigate the gold occurrence and the coupled substitution behavior of Au with other trace elements in pyrite. The results indicate that embedded features of visible gold can be classified as fracture-hosted gold, included gold, and intergranular gold, with fracture-hosted gold being the dominant type, accounting for 57.32 % of the total. Based on the spatial distribution, visible gold is further classified into free gold (spatially independent) and intergrown gold (associated with other minerals), with free gold being the predominant type (67.78 %). In terms of grain size, visible gold can be further divided into four categories: micro-grained gold (1-5 mu m), fine-grained gold (5-10 mu m), medium-grained gold (10-20 mu m), and coarse-grained gold (20-50 mu m). Their proportions in terms of area are 8.10 %, 36.45 %, 37.21 %, and 18.24 %, respectively, and by quantity, the corresponding proportions are 38.91 %, 43.52 %, 15.06 %, and 2.51 %. The invisible gold primarily occurs as solid solutions or mineral inclusions, with its content varying among different sulfide minerals. The average concentrations are 0.92 ppm in pyrite, 1.11 ppm in chalcopyrite, and 0.49 ppm in sphalerite. Notably, tetrahedrite exhibits the highest average value (4.17 ppm), occurring exclusively as solid solutions. The Au content shows strong positive correlations with chalcophile elements (Ag, Bi, Cu, Pb, Sb, and Te) in pyrite, strongly indicating that Au-Cu-Sb-Ag-Bi complexes are incorporated into the pyrite lattice through coupled substitution of Fe2+ ions or as micro-mineral inclusions. These findings provide key insights into gold mineralization mechanisms and offer essential mineralogical constraints for ore beneficiation and metallurgical processing.

Bauxite overlying the paleokarstic surface is rich in rare earth elements (REE), but its occurrence is debatable, which has severely hampered its extraction and utilization. More than 5 billion tons of karstic bauxite were deposited in the North China Craton (NCC) in the Late Carboniferous. This study thoroughly analyzed REE concentrations and occurrences in the major minerals of karstic bauxite in the northern NCC, with the aim of elucidating their migration and enrichment. Bauxite occurs in the Carboniferous Benxi Formation and consists of three layers from bottom to top: Fe-bearing claystone, bauxite, and claystone. The lower Fe-bearing claystone contains primarily illite, kaolinite, diaspore, hematite, goethite, and anatase; the middle bauxite is dominated by diaspore, kaolinite, hematite, goethite, illite, and anatase; and the upper claystone consists primarily of kaolinite, illite, goethite, hematite, diaspore, and anatase. Total REE (Sigma REE) increases from top to bottom along the profile, mainly due to the decrease in pH and leaching. REE are released in the acidic conditions of surface weathering, migrate downward, and accumulate in the alkaline environment of the bottom Fe-bearing claystone (up to 961 ppm). In situ elemental analysis revealed anomalously high REE diaspores (up to 11 666 ppm), suggesting that the diaspore is the main host mineral for REE. The similar geochemical behavior of Al, Ti, and REE in single and different diaspores, as well as the significant negative correlation between Sigma REE and Al (r = -0.36), coupled with the slightly larger diaspore cells of this study compared to the standard diaspore cells, confirms that numerous larger REE3+ enter the diaspore lattice and replace Al3+ during supergene precipitation. The differences in the concentration and occurrence of REE in minerals formed at different stages (e.g., diaspore, anatase, kaolinite, hematite, and goethite) indicate that the occurrence of REE is closely related to the crystal structure and formation process of these minerals. The diaspore and anatase formed during the metallogenic stage are controlled by the rapid nucleation and crystallization process of minerals, resulting in the incorporation of REE into the mineral lattice mainly by isomorphic substitution. Oolitic hematite is also formed by rapid crystallization, but, due to its dense crystal structure and large surface area, REE are adsorbed on the mineral surface primarily via inner-sphere complexation. In minerals formed during the early metallogenic stage (e.g., kaolinite, hematite, and goethite), prolonged weathering processes lead to the predominant incorporation of REE into the mineral lattice via isomorphic substitution. Clarification of the distribution and occurrence of REE in the NCC karstic bauxite provides insight into the enrichment and occurrence of REE in global karstic bauxite deposits.

The lithology of the deep lithosphere is crucial to providing an understanding of its evolution and related dynamic processes. However, the physical properties of rocks that make up these lithologies depend on various factors, such as mineral and chemical composition, confining pressure, temperature, and pore fluid pressure. Uncertainties in rock composition and pressure-temperature conditions at their depth of formation lead to non-uniqueness in geophysical exploration data. This study employs machine learning methods to accurately predict the lithological composition of the lithosphere using experimental data including P-wave velocity (VP), S-wave velocity (VS), density (q), and derivative parameters from 36 rock types. This achieves quantitative evaluation of resulting classifications and improves precision and reproducibility. Taking the South China Block as an example, this study shows that, although the Sichuan Basin preserves a thick cratonic lithosphere, its mantle lithosphere exhibits significant re-fertilization related to the plume activity in the Emeishan Large Igneous Province. More importantly, in the central and eastern South China Block, geological evidence combined with existing geodynamic models allows the reconstruction of post-Mesozoic lithosphere evolution to be divided into four major stages. These are: (1) subduction stage, (2) dehydration and eclogitization of crust in subducting lithosphere, (3) slab rollback and lithosphere delamination stage, and (4) extension stage and mantle-derived magmatic underplating. This study identifies a series of key geological parameters and provides new insights into methodology to understand the architecture and evolution of cratonic lithosphere systems globally provided the terranes have sufficient high-resolution geophysical data. (c) 2026 China University of Geosciences (Beijing) and Peking University. Published by Elsevier B.V. on behalf of China University of Geosciences (Beijing). Thi s is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

The sources and processes linking metasomatized mantle lithosphere to potassic magmatism and spatio-temporally associated K-rich orogenic gold deposits remain unclear. This issue is addressed through study of the Badi potassic complex and the adjacent Danba gold deposit in the post‑collisional Tethyan belt, SW China, which share similar phlogopite-biotite-sulfide assemblages. Potassic rocks from the complex exhibit high CaO and MgO contents, arc‑like trace element patterns, and mildly enriched Sr–Nd–Hf isotopes, pointing to a metasomatized mantle source rather than crustal contamination during magma ascent. Zircon U‑Pb dating reveals two magmatic episodes. The second episode (190–186 Ma), slightly postdating early gold ores but coeval with late ores, comprises high-fO2, volatile-rich potassic mafic magmas. Phlogopite, olivine, and clinopyroxene from these rocks exhibit δ41K = –0.57‰ to +0.03‰ and δ26Mg = –0.38‰ to +0.07‰. Rayleigh modeling demonstrates minimal K isotope fractionation (<0.2‰) via fractional crystallization. These data indicate a mantle source metasomatized by altered oceanic crust (AOC)‑dominated slab fluids with relatively minor carbonate‑rich sediment input. After excluding wall‑rock contamination, hydrothermal biotite in early gold ores yields δ41K = –0.50‰ to + 0.07‰ and δ26Mg = –0.51‰ to + 0.04‰, consistent with derivation from the AOC‑metasomatized mantle lithosphere. In contrast, biotite in late gold ores exhibits lower values (δ41K = –0.77‰ to –0.25‰; δ26Mg = –1.21‰ to –0.39‰), indicative of a mantle source metasomatized by carbonate‑rich sediment‑derived fluids. Therefore, the two gold mineralization periods share a common, albeit heterogeneous, mantle lithosphere source with the second‑episode potassic mafic magmas. However, temporal, spatial, and K–Mg isotope contrasts indicate that the gold ores and potassic rocks represent independent products of mantle devolatilization and melting, respectively, suggesting they are coeval companions rather than causally linked. A higher sediment proportion in the metasomatized mantle source appears to favor generating auriferous fluids for orogenic gold mineralization, as supported by modeling of Au content in high‑temperature fluids from mantle devolatilization.

More than 60 gold deposits have been discovered within the Jiaojia fault belt, its footwall-derived subsidiary faults and fractures, and the interlayer-sliding zones formed by interference between basement folds in the hanging wall. These deposits contain proven gold resources exceeding 1,700 tons, constituting four gold mineralization sub-systems: (1) The Jiaojia main belt gold mineralization sub-system, which includes orebody Group I, II and III. (2) The Wang'ershan fault gold mineralization sub-system, and (3) the Lingbei fault gold mineralization sub-system, each comprising orebody Group I, IV and V. (4) The basement fold interference gold mineralization sub-system, whose known orebody groups occur within isolated structural basins. The first three sub-systems are controlled by a rhombic fault network developed in the footwall of the Jiaojia fault, whereas the fourth is located in its hanging wall. The Jiaojia main belt sub-system hosts 23 gold deposits with proven resources of 1,385. 15 tons. Among them, the orebody group I, the major mineralization zone controlled by the main fault, is characterized by fine vein-disseminated gold mineralization of pyrite-sericite-quartz type; the orebody group II, the secondary mineralization zone controlled by the main fault, subsidiary footwall faults, and dense joint systems. It contains both sericite-quartz-pyrite type and quartz vein type gold mineralization in the form of thin veins and stockworks; the orebody group III, the smallest one, is controlled by steeply dipping subsidiary faults and sparse joints in the footwall, showing dominantly steeply dipping quartz-vein and stockwork-type gold mineralization. The Wang'ershan fault sub-system contains seven gold deposits with 132.41 tons of proven resources. The orebody group I, hosted in the core of the Wang'ershan fault, represents the main orebody and is characterized by fine disseminated and massive gold mineralization. The orebody group IV, controlled by steeply dipping subsidiary faults and a series of left-stepping en echelon joints in the footwall, exhibits both pyrite-sericite-quartz and quartz-vein fine disseminated and vein-type mineralization. The orebody group V, controlled by steeply dipping subsidiary faults and joints in the hanging wall, is dominated by quartz (+/- sulfide) vein and stockwork-type mineralization. The Lingbei fault sub-system includes 28 gold deposits with 191.7 tons of proven resources. Its characteristics are similar to those of the Wang'ershan fault sub-system, but individual deposits (or orebodies) are smaller in scale and dip in the opposite direction, forming a near mirror-symmetric relationship between the two. The basement fold interference sub-system hosts four gold deposits with 12. 32 tons of proven resources. These deposits are controlled by interlayer-sliding zones formed during interference of regional Precambrian basement folds. Mineralization occurs within early nearly upright, groove-like tight folds trending NW (similar to 300 degrees) and later oblique broad folds trending NNE (similar to 15 degrees), filled respectively by milky quartz-coarse pyrite veins and smoky quartz-fine pyrite, quartz-polymetallic sulfide, or quartz-carbonate veins. Major ore-forming elements across all sub-systems include Au, Ag, Cu, Pb and Zn. Within the Wang'ershan fault sub-system, Au grades are generally similar among the orebodies, while Ag contents increase progressively from orebody I to V. The Cu, Ag and Pb contents of Jiaojia orebody II and Wang'ershan orebody I, as well as Jiaojia orebody III and Wang'ershan orebody VI, are comparable. The 8S values of pyrite from all four sub-systems show overall similarity and narrow variation, indicating a single sulfur source and the absence of significant external fluid mixing or compositional change during mineralization. The three subsystems in the rhombic lattice fault system all contain pyrite with similar Pb isotopic signatures, suggesting a common origin from the lower crust that was modified by mantle-derived materials. The geological and geochemical evidence collectively indicates that the Jiaojia fault belt gold metallogenic system resulted from long-term tectonic-fluid coupling, with sub-systems that are genetically related yet individually distinct: (1) the basement fold interference sub-system formed under a compressional tectonic regime, with gold mineralization occurring during crustal shortening. Sulfidation reactions and fluid immiscibility during early folding formed thick orebodies, while late-stage flashing of overpressured fluids within interlayer-sliding zones generated ore shoots; (2) the rhombic fault network sub-systems formed under a transcurrent tectonic regime, with gold mineralization occurring during the transition from ductile-brittle to brittle deformation and from compressional-shear to extensional-shear regimes. Intense early water-rock interaction and fluid phase separation produced the fine vein-disseminated and stockwork mineralization that established the overall framework of orebody groups I and II. Moderate late-stage water-rock reaction and pronounced fluid immiscibility controlled the formation of orebody groups III, IV and V (particularly quartz-vein orebodies) and superimposed nearly vertical high-grade ore columns upon the earlier orebodies I and II. Gold orebodies delineated so far are concentrated within a 10km section between Xincheng and Sizhuang along the Jiaojia fault, whereas the northern and southern segments remain poorly explored. Three-dimensional analysis of ore-controlling structures and quantitative modeling of orebody geometry reveal southward extension of these structures and mineralization enrichment patterns, defining 13 exploration targets. Preliminary drilling verification has intersected gold mineralization in 89 boreholes within the main belt subsystem and identified a new orebody (9.5m thick, grading 1.65 similar to 5.79g/t Au) in the Wang'ershan fault sub-system, confirming the validity and applicability of the metallogenic model and exploration predictions, and providing a clear direction for future prospecting.

The West Qinling Orogenic Belt formed during the Late Triassic continental collision between the North China and South China blocks, with regional metamorphism under greenschist-facies conditions releasing fluids during this process, Identifying regionally metamorphosed rocks provides key insights into the evolution of orogenic belts. In this study, terahertz time-domain spectroscopy (THz-TDS) was applied to analyze slate, feldspathic sandstone, quartz sandstone, and diorite porphyrite from the Badu Formation in the West Qinling Orogen, aiming to identify the characteristic terahertz spectral responses of rocks with varying metamorphic grades and to interpret their metamorphic mineral assemblages. The results show that except for quartz sandstone, most samples exhibit distinct chlorite-related absorption peaks in the 1.0 1. 2THz range. Among them, diorite porphyrite and slate display relatively high absorption coefficients and refractive indices, reflecting strong absorption associated with amphibole and greenschist-facies metamorphic minerals. Further terahertz spectral analysis reveals differences in alteration and metamorphic processes among protoliths. Diorite porphyrite, rich in hydrous ferromagnesian minerals such as amphibole and biotite, facilitates the formation of chlorite and sericite during alteration. Slate, as a product of regional greenschist-facies metamorphism, also widely develops hydrous mineral assemblages such as chlorite and sericite, contributing significantly to regional metamorphic fluids. In contrast, feldspathic sandstone and quartz sandstone, with low ferromagnesian mineral content, contain only minor hydrous minerals such as sericite and thus released limited fluids during regional metamorphism. This study not only provides new evidence for understanding the metamorphic-fluid evolution and the origin of metallogenic fluids in the West Qinling Orogenic Belt, but also demonstrates that terahertz time-domain spectroscopy is an effective tool for identifying greenschist-facies metamorphic rocks and assessing alteration intensity, showing great potential for tracing metamorphic-fluid processes.