The Rb-Sr isotopic system is widely used for the geochronology of rocks and minerals. However, conventional measurement techniques are plagued by the isobaric interference of ⁸⁷Rb on ⁸⁷Sr during mass spectrometry. This necessitates tedious chemical separation of Rb and Sr, leading to a time-consuming analytical process with high consumption of chemical reagents. Moreover, the conventional Rb-Sr dating approach makes it challenging to distinguish minerals formed during different geological events or growth stages. Recent advancements in laser ablation inductively coupled plasma tandem mass spectrometry (LA-ICP-MS/MS) have made in-situ Rb-Sr dating a feasible alternative. By introducing reactive gases (e.g., N₂O or SF₆) into the collision/reaction cell, LA-ICP-MS/MS converts Sr⁺ to SrO⁺ and SrF⁺, thereby achieving online separation of ⁸⁷Rb and ⁸⁷Sr. This capability enables in-situ Rb-Sr dating, which offers significant advantages such as high efficiency, low cost, and high spatial resolution. This article introduces the principles of in-situ Rb-Sr dating and discusses challenges such as element fractionation and matrix effects associated with this technique. Its further reviews recent research progress in the application of LA-ICP-MS/MS Rb-Sr geochronology, with a focus on applications including the direct determination of stratigraphic ages in sedimentary rocks, precise dating of basic magmatic rocks and pegmatites, identification of multiple metamorphic events, constraining the timing of fault activities, and determining the age of gold mineralization. In-situ Rb-Sr dating also demonstrates considerable potential for analyzing lunar samples. The development and application of LA-ICP-MS/MS Rb-Sr dating provide new avenues for deciphering the evolutionary history of geological bodies, holding significant promise for future geochronological research and outlining its promising prospects in Earth sciences.

Eucryptite is one of the main lithium aluminosilicates in lithium-rich granitic pegmatites, yet its origin remains unclear. This study investigates the formation of eucryptite in granitic pegmatites through in situ high-temperature and high-pressure experiments using a hydrothermal diamond-anvil cell and Raman spectroscopy. The experimental results show that under quartz-saturated conditions, eucryptite becomes unstable and reacts with quartz to form spodumene at 250-300 ℃ and 244-343 MPa. In contrast, under quartz-undersaturated conditions, eucryptite can crystallize and remain stable at temperatures and pressures up to 695 ℃ and 954 MPa. Furthermore, the experimental results reveal that hydrothermal alteration of spodumene to eucryptite requires fluids with high lithium activities and that alkaline pH conditions accelerate the reaction. We propose that eucryptite can be classified as a silica-undersaturated mineral, which explains its rarity in granitic pegmatites. The eucryptite+quartz assemblage forms under low-temperature and low-pressure conditions, resulting from retrograde decomposition of lithium aluminosilicates, e.g., spodumene. In contrast, “eucryptite vein”, “eucryptite+albite” assemblage, and “eucryptite nodule” can form under relatively high-temperature and high-pressure conditions. In local silica-undersaturated environments, e.g., mineral fractures, eucryptite crystallizes directly from lithium-rich fluids or from hydrothermal alteration of primary minerals, e.g., spodumene. Our study demonstrates that eucryptite can form under a wide range of temperature and pressure conditions. Therefore, caution is required when using its occurrence for thermobarometric estimates of Li-rich pegmatite p-T-x evolution; its specific mode of occurrence must be taken into account.

Visible to shortwave-infrared (VSWIR, 350-2500 nm) reflectance spectroscopy is a key technique for rapid exploration of rare earth element (REE) resources, as it can quickly derive characteristic absorption parameters of target materials. Regolith-hosted REE deposits represent a major global source of heavy rare earth elements (HREE). To advance the application of reflectance spectroscopy in exploring these deposits, this study focuses on a granite regolith profile from the Jiaping area of Guangxi. This profile is characterized by an enrichment of light rare earth elements (LREE) in the upper section and HREE in the lower section. We investigated the response of visible to shortwave-infrared reflectance spectroscopy to both weathering intensity and REE content within the profile. Our results demonstrate that the ratios of absorption depths related to clay minerals (d₁₃₉₆/d₁₉₁₀ and d₁₃₉₆/d₂₁₇₀) show a strong positive correlation with the chemical index of alteration (CIA), which measures weathering intensity. These spectral ratios thus provide a reliable and accurate means to characterize the profile’s weathering intensity. Furthermore, second-derivative spectral parameters effectively indicate REE contents. Specifically, the peak value of the second derivative around 794 nm serves as a robust indicator for Nd content and the total LREE content (ΣLREE), whereas the peak value around 484 nm effectively indicates Er content and the total HREE content (ΣHREE). This study offers useful information for using reflectance spectroscopy to explore regolith-hosted REE deposits, particularly those rich in HREE.

Apatite, as an important associated mineral in granite-pegmatite system, records magma differentiation and fluid evolution during the diagenetic and mineralization process. The Himalaya orogenic belt is a significant rare-metal potential region in China, where apatite is widely distributed in the leucogranite-pegmatite system. This study investigates apatite from three spodumene-bearing pegmatite dykes (No.1, No.2 and No.3) and the wall-rock muscovite granite in the Kuqu intrusion, eastern Himalaya. The internal structures, major and trace element compositions of apatite were analyzed. Cathodoluminescence and backscattered electron imaging reveal homogeneous, core-rim (growth or alteration rim), and patchy patterns in spodumene-bearing pegmatites, and homogeneous and oscillatory zoning patterns in muscovite granite. Apatite contains 0.06%-1.69% MnO and 2.59%-3.28% F, with molar proportions of X(Fap), X(Cap), and X(Hap) being 0.689-0.885, <0.002, and 0.115-0.311, respectively. Trace element contents (e.g., Li, Ga, Ge, Sr, Y, Pb, Th, U) vary considerably, while Zn, Cd, and Sn are extremely low. The REE distribution patterns exhibit strong tetrad effects and negative Eu anomalies. Compared to those in the muscovite granite, apatite grains from the spodumene-bearing pegmatite dykes are depleted in Sr and enriched in Mn, Pb, REE, Li, Ga, and Ge, have low Sr/Y ratios (0.002-0.104), and display strong REE tetrad effects (TE_1,3=1.26-1.64), high Y/Ho values (30.7-65.0), extremely low Eu/Eu^* values (0.002-0.016), and high Ce/Ce^* values (1.08-1.23). These chemical characteristics indicate that the lithium-rich pegmatite magmas were highly fractionated and experienced extensive fluid exsolution. The trace element composition of apatite correlates with changes in the physiochemical conditions of the crystallizing medium caused by magma fractionation and evolution. The trace element contents (Mn, Sr, Y, REE, Pb, etc.) and element pair ratios of apatites, such as Sr/Y and (La/Yb)_N, in three spodumene-bearing pegmatite dykes are compared. Within the No.1 pegmatite dyke, the physicochemical conditions of the crystallizing medium varied significantly and the pegmatite with more spodumene crystals is highly fractionated and evolved. Compared to the No.1 pegmatite dyke, the No.2 and No.3 pegmatite dykes exhibit a higher degree of magma differentiation, with the No.3 pegmatite dyke having experienced more extensive plagioclase crystallization and fluid exsolution. The chemical differences between the core and the alteration rim/patch of apatite in the spodumene-bearing pegmatite dykes indicate element mobilities with various degrees during fluid-assisted replacement, reflecting variations in fluid properties. The fluids involved in the evolution of different spodumene-bearing pegmatite dykes were compositionally distinct, indicating complex fluid activities within the lithium-rich pegmatite system. A comparison with apatites from the Qiongjiagang and Gabo lithium deposits in the central and eastern Himalaya, respectively, suggests that the lithium-rich magmas and their formation and evolution processes may differ between the eastern and central Himalaya regions.

The ore-forming fluids in the West Qinling orogenic gold deposit were predominantly derived from dehydration reactions of hydrous minerals during prograde metamorphism of regional strata. Although conventional methods such as X-ray diffraction, Fourier transform infrared spectroscopy, and Raman spectroscopy have been widely used for identifying hydrous minerals, they still exhibit significant limitations in precisely identifying hydrous mineral types and quantitatively analyzing rock water content due to their low sensitivity to hydrogen, significant interference from water-related signals, and fluorescence effects. As a non-destructive spectroscopic technique, terahertz time-domain spectroscopy (THz-TDS) is highly sensitive to the collective vibrational modes of water molecules and the occurrence states of water within mineral lattices, providing a novel technical approach for the effective identification and characterization of hydrous minerals in rocks. This study focuses on the Triassic strata in the Gannan region of the West Qinling orogenic belt. Integrating petrographic observations with THz-TDS analysis, we identified hydrous minerals and analyzed the state of water, thereby constraining the potential of different lithologies to undergo dehydration reactions during prograde metamorphism. The results indicate that hydrous minerals such as sericite, biotite, chlorite, and limonite in the Triassic strata exhibit distinct terahertz absorption features, with limonite (containing molecular water) showing the most prominent absorption peak. Sandstones rich in chlorite as the primary hydrous mineral display higher terahertz absorption coefficients and refractive indices, reflecting their higher water content. This suggests that such rocks can provide significant ore-forming fluids through dehydration reactions during prograde metamorphism. This study confirms the efficacy of THz-TDS in characterizing the aqueous properties and hydrous minerals of sedimentary rocks, offering a new technical method for tracing the source of ore-forming fluids in orogenic gold deposits.

The Danchi fold-and-thrust belt is one of the most important tin polymetallic regions in South China. Tin polymetallic mineralization is closely linked to the Late Cretaceous biotite granite (the Longxianggai pluton) in the Dachang district, middle of the Danchi fold-and-thrust belt. However, the chemical compositions of melts and ore-forming fluids, volatiles, and oxygen fugacity ( f_{O_2}) during the evolution of magmatic-hydrothermal process remain unclear. Fortunately, euhedral coarse-grained hydrothermal apatite associated with tin mineralization was identified in the No.22-1 orebody of the Dafulou Sn-Zn deposit, eastern segment of the Dachang district. Combined with previous geochemical data of unaltered magmatic apatite, hydrothermally altered apatite in biotite granite and granite porphyry dike. These materials provide an opportunity to investigate the geochemical properties of melts and ore-forming fluids, as well as their constraint on tin mineralization and ore genesis. At the same time, we attempt to establish a new comprehensive diagram to distinguish tin deposits from other deposit types, providing guidance for exploration. Herein, detailed mineralogical studies, laser ablation-inductively coupled plasma-mass (LA-ICP-MS) U-Pb dating, X-ray photoelectron spectroscopy (XPS) analyses, and electronic probe analyses (EPMA) were conducted on hydrothermal apatite of the Dafulou deposit. The mineralogical features of apatite from oxide stage show that euhedral coarse-grained apatite (50-200 μm) is intergrowth with Fe-oxides, cassiterite, ilmenite, and quartz. The apatite does not show any zoning in the electron backscatter images (BSE). Calcium, P, and F elements show the relative homogeneous distributions in apatite grains by X-ray mapping. EPMA suggest apatite is significantly enriched in F (3.63%-4.47%), but depleted in Cl (<0.036%). In situ U-Pb dating implies apatite formed at (96.2±5.7) Ma. The high F characteristics of unaltered magmatic apatite indicate the initial magma of the Longxianggai pluton is relatively F-rich, which effectively reduces the magmatic solidus temperature and viscosity, prolongs the process of magmatic evolution, and facilitates Sn enrichment in residual melts. The low As contents (1.15-7.18 ppm) of magmatic apatite, as well as the occurrence of CH₄ in fluid inclusions of the Dafulou deposit, indicate that the oxygen fugacity ( f_{O_2}) were relatively low during the evolution of magma and the hydrothermal mineralization stage of the Dafulou deposit. Combined with previous fluid inclusion composition analysis and microthermometric results, we conclude that fluid cooling is the main trigger for cassiterite deposition and the redox buffering between cassiterite and arsenopyrite also plays an important role in cassiterite precipitation of the cassiterite-sulfides stage in the Dafulou Sn-Zn deposit. The results of principal component analysis (PCA) and kernel density estimation (KDE) of trace elements in apatite from typical tin deposits in South China and other deposit types show that the apatite associated with tin mineralizations is relatively enriched in La, Ce, Pr, Sm, Gd, Dy, Yb, and Y elements, which can be used to distinguish tin deposits from other deposit types.

The Gongjiaping is a recently defined, middle-sized gold deposit in the North Qinling terrane. Ore bodies occur primarily as quartz veins within the NW- to NWW-trending brittle-ductile faults. The ores are characterized by an Au-Ag-Te-(Bi) mineral assemblage; however, the textures of this assemblage, the ore-forming physicochemical conditions, and the mechanisms of gold enrichment remain poorly constrained. Integrated micro-mineralogical observations and electron microprobe analysis reveal that tellurides are predominately petzite, hessite, stützite, altaite, tellurobismuthite, tetradymite, and joseite-B. Gold occurs mainly in gold-bearing tellurides and as native gold, with a fineness of 835-889 (mean of 855). The physicochemical conditions of the metallogenic fluids at different stages were reconstructed based on mineral equilibria diagrams and fluid inclusion analysis. Three primary types of fluid inclusions were identified in main-ore stage quartz: H₂O-NaCl inclusions (type W), CO₂-H₂O-NaCl inclusions (type C), and pure CO₂ inclusions (type PC). The ore-forming fluids are characterized by medium temperature (180-320 ℃), low salinity (0.7%-8.7%), medium-to-low pH, low oxygen fugacity, high tellurium fugacity, relatively low sulfur fugacity, and belonged to a reduced CO₂-H₂O-NaCl±CH₄ system. The metallogenic fluid of stage Ⅱ has pH, logfO₂, logfTe₂, and logfS₂ values ranging from 4.1 to 6.2, -42.0 to -36.5, -13.2 to -10.5, and -14.4 to -11.1, respectively, with typical Bi-Te-(S) mineral assemblages of tellurobismuthite+tetradymite+joseite-B. Nevertheless, plenty of Au-Ag-(Pb)-Bi minerals (native gold+petzite+hessite+stützite+altaite) are present in the stage Ⅲ veins, which formed at the conditions of pH=4.1-5.7, logfO₂=-42.0--36.5, logfTe₂=-10.5--9.5, and logfS₂=-14.4--11.9. Our results suggest that the scavenging of Au from hydrothermal fluids by Au-Ag-Te-rich melts was a key mechanism for gold enrichment and precipitation in the Gongjiaping gold deposit.

The Youjiang basin, located at the southwest margin of the Yangtze craton, is an important component of the large-scale low-temperature metallogenic domain in South China. It hosts numerous hydrothermal deposits (Au, As, Sb, Hg), which are classified as typical Carlin-type gold deposits. In many of these deposits, late-stage Au-Sb-Hg mineralization is widely developed, representing a significant overprinting event within the Carlin-type hydrothermal system. However, the processes controlling this late-stage mineralization remain poorly understood, hindering a comprehensive understanding of the regional metallogeny. The Linwang and Lannigou gold deposits are typical fault-controlled gold deposits in this region. They share similar characteristics in terms of host rocks, structures, and alteration types, as well as late-stage Au-Sb-Hg mineralization. Petrographic studies reveal that the early-ore stage is characterized by disseminated mineralization consisting of fine-grained pyrite (Py1), Fe-dolomite, quartz, and illite. The late-ore stage is marked by vein-type mineralization comprising coarse-grained pyrite (Py2), stibnite, quartz, calcite, and bitumen. LA-ICP-MS trace element analyses of pyrite (Py1 and Py2) indicate that the late-stage, coarse-grained Py2 is gold-bearing and may have inherited its characteristics from early-stage pyrite through a multi-stage dissolution-reprecipitation process. Element mapping reveals a negative correlation between Au and As in Py2, with gold concentrations higher in the core than in the rim, suggesting that hydrocarbon-bearing fluids did not significantly contribute to gold mineralization during the late stage. fs-LA-MC-ICP-MS sulfur isotope analyses of sulfides (pyrite, stibnite, and cinnabar) demonstrate that both mineralization stages share a common sulfur source, likely derived from Triassic sedimentary rocks. We conclude that the late-stage vein-type mineralization overprinted the early disseminated mineralization, with both stages likely being part of a unified ore-forming system. This process may have caused the remobilization and further enrichment of gold through fluid-rock interaction.

The mechanisms enabling the transport and anomalous enrichment of gold at the nanoscale remain a research hotspot in economic geology. The microstructure of gold-hosting pyrite is key to understanding the occurrence of gold and constraining the processes leading to its extreme enrichment. The Xincheng gold deposit in Jiaodong is a typical altered rock-type deposit characterized by high-grade ores and significant gold enrichment within pyrite. Petrographic and mineralogical studies identified four types of ore-stage pyrite. To investigate their nanostructures, we employed a combination of focused ion beam-scanning electron microscopy (FIB-SEM), spherical aberration-corrected transmission electron microscopy (Cs-TEM), and atom probe tomography (APT). The results show that: (1) Pyrite hosts numerous plastic deformation features, including discontinuous dislocation lines, tangles, and deformation twins. (2) Electron diffraction patterns from the [$\bar{2} $01] zone axis of gold-bearing pyrite indicate interplanar spacings ranging from 0.219 nm to 0.545 nm. (3) Atom probe tomography (APT) indicates a non-stoichiometric pyrite composition approaching FeS_1.73. Gold is homogeneously distributed at the atomic scale, with a concentration of ~2 ppm and a detection sensitivity of 4.25 ppb, while silver forms discrete clusters. In summary, the nanoscale crystal defects (e.g., dislocations) generated by deformation in pyrite exert a primary control on the distribution and enrichment of gold, from the atomic scale to the cluster scale.

The Hushan gold deposit is a newly discovered, large gold deposit in the Qixia area of Jiaodong, with gold resources exceeding 30 tons. The ore bodies are hosted in the Neoarchean Zhujiakuang Formation biotite granulite and TTG gneiss, controlled by the NNE-trending Xilin-Douya Fault. The Hushan gold deposit exhibits unique two-stage gold mineralization: an early stage characterized by sericitization and pyritization, and a late stage characterized by quartz-pyrite-polymetallic sulfide-barite mineralization. During the early mineralization stage, hydrothermal monazite is observed coexisting with quartz-pyrite veins. SHRIMP U-Pb dating of this hydrothermal monazite yields an age of (119.5±3.3) Ma, representing the early mineralization age of the deposit. This mineralization age belongs to the Early Cretaceous, consistent with the peak of large-scale gold mineralization events in the Jiaodong Peninsula. The trace element composition of pyrite suggests that the ore-forming fluids were primarily derived from magmatic hydrothermal sources. In situ sulfur isotope analysis reveals that the δ³⁴S values of late-stage pyrite (average 6.75‰) are generally lower than those of early-stage pyrite (average 7.26‰). This suggests an increase in the oxygen fugacity of the ore-forming system during the mineralization process. During the Early Cretaceous (around 120 Ma), the regional tectonic regime in the Jiaodong Peninsula transitioned from compression to extension, which triggered large-scale magmatic activity and associated hydrothermal mineralization. The extensional tectonics provided favorable conditions for the decompression of ore-forming fluids and the precipitation of gold. H-O isotope studies indicate that meteoric water mixed into the ore-forming fluids during the late mineralization stage, leading to a decrease in the δ¹⁸O and δD values of the fluids. Integrated with recent research findings, we conclude that the subduction of the Paleo-Pacific Plate beneath the Eurasian Plate and the consequent transition of the tectonic regime from compression to extension played a critical role in the formation of the Hushan gold deposit.

The Changdian deposit is a quartz-vein type gold deposit (>1t@2.90×10^-6), located on the Yalujiang Gold Metallogenic Belt, Liaodong Peninsula. The gold orebody occurred as vein within the gneissic biotite granite. Some previous work largely focused on basic geological surveys there has not been a systematic study on the Changdian gold deposit, which greatly restricts the understanding of source of ore-forming materials and fluids, as well as the genetic type of the Changdian gold deposit. In this study, we first conducted a field basic geological survey, and reported Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) trace elements and Laser Ablation Multi-Collector Inductively Coupled Plasma Mass Spectrometry (LA-MC-ICP-MS) S-Pb isotopic analyses on pyrite that closely related to gold mineralization. In-situ S isotopic analyses show that pyrite yielded δ³⁴S value of 6.6‰-8.2‰, which is slightly higher than that of mantle/magmatic sulfur, but overlaps with the δ³⁴S value range of the Gaixian Formation, revealing that the sulfur mainly derived from magma, with a small amount of sulfur sources mixed from the Gaixian Formation. In-situ Pb isotopic analyses indicate that pyrite yielded ²⁰⁸Pb/²⁰⁴Pb, ²⁰⁷Pb/²⁰⁴Pb, and ²⁰⁶Pb/²⁰⁴Pb ratios of 38.190-39.576, 15.528-15.928, and 17.374-17.803, respectively, suggesting that lead primarily derived from the lower crust, with some input from the Gaixian Formation. In-situ trace elements analyses show that pyrite yielded high Co/Ni (0.32-2.57) and Te/Au (>10) ratios, is evidently enriched in Co, Ni, As, Ag, Te, W, Bi, and Pb, implying that the fluid was initially of magmatic-hydrothermal origin. The Gaixian Formation brought a large amount of ore-forming elements into gold mineralization by intensive water-rock interaction. Combining previous research, we propose that the Changdian deposit is a magmatic-hydrothermal gold deposit, which is closely related to the Early Cretaceous magmatic activity.

The Shengtieling rare earth element (REE) deposit in central Liaoning Province is hosted within the Paleoproterozoic South Liaohe Group of the Jiao-Liao-Ji tectonic belt; however, the origin of the REE-bearing magnetite leptynite remains poorly constrained. This study employs an integrated approach including petrography, zircon and monazite U-Pb geochronology, trace element analysis, and whole-rock geochemistry to constrain the petrogenesis, tectonic setting, and genetic type of the magnetite leptynite. Integrated petrography, backscatter image, electron probe analysis, and monazite LA-ICP-MS in-situ trace elements reveal that the REE mineralization is primarily hosted in magnetite-plagioclase and magnetite-biotite-plagioclase leptynites of the Lieryu Formation, with monazite, xenotime, and apatite as the main REE-bearing phases. Zircon U-Pb dating yields a maximum depositional age of ~1.95 Ga from detrital grains, whilst monazite and metamorphic zircon records indicate regional metamorphism at 1.90-1.87 Ga. Whole-rock geochemical data (Th-Sc-Zr/10, Th-Co-Zr/10) are consistent with a continental island arc setting. Combined with previously published data for the Liaohe Group, we propose that the protolith was dominated by arc-derived sediments. The metamorphic age of the magnetite leptynite (1.90-1.87 Ga) is synchronous with the regional metamorphism of the Liaohe Group, thereby confirming arc-continent collision during the assembly of the Jiao-Liao-Ji Belt. Based on the occurrence of REEs, the petrogenesis of the host rock, and its tectonic environment, the Shengtieling deposit is classified as a volcano-sedimentary metamorphic type REE deposit. This finding provides a theoretical basis for further exploration and highlights the potential for discovering similar volcanic-sedimentary metamorphic REE deposits in Liaoning Province, with magnetite leptynite of the Lieryu Formation serving as a key prospecting indicator.

Rare earth elements (REEs) are important strategic metal resources, and ion-adsorption type heavy rare earth ores are a distinctive resource in China. The Shitouping heavy REE (HREY: Gd-Lu and Y) deposit, recently discovered in southern Jiangxi Province, is a super-large ion-adsorption type HREY-rich deposit. The ore body exhibits differentiated enrichment characteristics with the coexistence of light REE (LREE: La-Eu) and HREY ores, described as “upper LREE and lower HREY”. However, the genetic mechanism of this deposit has not been well constrained to date. Here, an integrated genetic study was conducted on a typical weathering crust profile from the Shitouping deposit using mineralogy, element geochemistry, REE speciation analysis, and pH measurement via techniques including X-ray Diffraction, Electron Probe Microanalysis, X-ray Fluorescence Spectroscopy, Inductively Coupled Plasma Mass Spectrometry, and Sequential Extraction.The results indicate that the underlying syenogranite bedrock is rich in easily weatherable LREE- and HREY-bearing minerals such as bastnäsite and synchysite. Upon weathering and decomposition, these minerals release abundant LREE and HREY ions into the weathering crust, serving as the primary material source for REE mineralization. The bedrock has a total REE content of 558×10^-6, with both LREE and HREY being fertile, and HREY is more enriched (LREE: 242×10^-6, HREY: 316×10^-6, LREE/HREY ratio=0.77; HREY accounts for 56.6%), classifying it as a HREY-rich ore-forming parent rock. From bottom to top in the weathering profile, rock-forming minerals such as feldspar and mica gradually weather and decompose, eventually being replaced by secondary clay minerals dominated by kaolinite and illite, which become the main hosts for adsorbed REE ions. Due to weathering and leaching, REEs migrate within the weathering crust and concentrate in the lower part of the fully weathered layer to form an ion-adsorption type REE ore body. The upper section of the ore body is primarily enriched in LREE, while the lower section is more strongly enriched in HREY, demonstrating a dual-layer enrichment pattern of “upper LREE and lower HREY”.In the studied profile, REEs are present mainly in the ion-exchangeable (F2: (29.8-330)×10^-6, accounting for 4.5%-59.0%), Fe-Mn (hydr)oxide (F5: (55.9-318)×10^-6, 11.6%-40.8%), and residual (F7: (74.7-197)×10^-6, 22.2%-29.8%) fractions. In contrast, only minor amounts of REEs were found in the humic acid-bound (F4: (5.02-86.3)×10^-6, 1.49%-11.0%), strongly organic-bound (F6: (23.1-182)×10^-6, 9.47%-23.4%), carbonate-bound (F3: (0.11-3.41)×10^-6, 0.01%-1.4%), and water-soluble (F1: (0.11-4.26)×10^-6, 0.02%-0.55%) fractions. The pH of the weathering crust profile transitions from weakly acidic at the top to weakly alkaline at the bottom, with values ranging from 5.4 to 8.8. Based on our findings, we propose that the “upper LREE and lower HREY” enrichment pattern in the Shitouping deposit is primarily controlled by the REE characteristics of the parent rock and the distinct speciation and migration behaviors of LREEs and HREYs during weathering. Firstly, the parent rock provides ample sources for both LREE and HREY mineralization. Secondly, the ion-exchangeable, Fe-Mn (hydr)oxide, and organic-bound fractions are the dominant, potentially minable phases. Notably, the ion-exchangeable fraction is more enriched in LREEs and is concentrated in the upper part of the profile. In contrast, the Fe-Mn (hydr)oxide and organic-bound fractions show a strong preference for HREY and are more enriched in the middle and lower parts. This differential distribution is a key factor leading to the development of the dual-layer ore body. Furthermore, the genesis of the deposit is also influenced by the properties of clay minerals, pH conditions, redox environment, and groundwater mobility within the weathering crust.

The Shuimogo REE deposit in Luanchuan County, Henan Province, is a newly discovered, high-grade deposit on the southern margin of the North China Craton, dominated by light rare earth elements (LREEs). REE ore bodies occur as irregular veins within a NW- to WWN-trending structural zone of the Late Paleoproterozoic Longwangzhuang alkaline granite and are hosted by medium- to coarse-grained sodic-ferro-amphibole syenitic granite, which itself has high REE content. This study investigates the metallogenic age and processes through detailed mineralogy, rare earth element geochemistry, and bastnäsite U-Th-Pb geochronology by LA-ICP-MS. Mineralogical analysis shows that the main REE minerals are bastnäsite, parisite, allanite, and ellestadite. The presence of obvious metasomatic textures indicates that late-stage hydrothermal activity played a critical role in REE enrichment and mineralization. Geochemically, the ore is strongly enriched in LREEs, shows a high degree of LREE-HREE fractionation, and exhibits a right-sloping REE distribution pattern with a moderate negative Eu anomaly. These patterns are generally similar to the geochemical signature of the Longwangzhuang alkaline granites, implying a genetic affinity. Bastnäsite U-Th-Pb dating yielded a weighted average age of (381.4±6.5) Ma, indicating that the main mineralization phase occurred during the early Late Devonian. The REE mineralization process of Shuimogou REE deposit involved three key stages: (1) Initial REEs enrichment occurred during the Late Paleoproterozoic, accompanied by extensive fractional crystallization of the Longwangzhuang alkaline granitic magma. (2) During the Devonian as main mineralization stage, REEs within the alkaline granite were mobilized by tectonic compression, migrated along fault zones, and accumulated to form ore bodies. (3) In the Mesozoic, tectonic-thermal events remobilized some REEs, leading to local modification and further enrichment of pre-existing ore bodies.

The Longbaoshan alkaline complex, located in the southeastern Luxi Terrane of the North China Craton, hosts a newly discovered REE deposit. However, the petrogenesis of the complex and the mechanisms of rare earth element (REE) enrichment remain poorly understood. This study presents a systematic investigation of the whole-rock geochemistry of the syenite porphyry, quartz syenite porphyry, and amphibole-bearing syenite porphyry within the complex, aiming to elucidate its petrogenesis and reveal the REE enrichment mechanisms. The results indicate that the Longbaoshan alkaline complex formed in the Early Cretaceous (130-128 Ma). It is characterized by high SiO₂, Na₂O + K₂O, and Al₂O₃ contents, but low MgO, FeO, and CaO, displaying metaluminous to peralkaline and belongs to the high-K calc-alkaline to shoshonitic series. All samples exhibit enriched Sr-Nd isotopic compositions and are enriched in large-ion lithophile element (LILE) and light rare earth element (LREE), but are depleted in high field strength element (HFSE; e.g., Nb, Ta, Ti) and heavy rare earth element (HREE). They also feature low Ba/Th and high Nb/Y, Th/Yb, and La/Sm ratios. These geochemical characteristics suggest that the mantle source was metasomatized by melts derived from subducted sediments, which provided the initial REE enrichment. During early magmatic evolution, fractional crystallization of hornblende and biotite promoted further enrichment of REE. The albitization results from hydrothermal processes, and late magmatic-hydrothermal metasomatism resulted in ore-forming REE enrichment. Therefore, the Longbaoshan alkaline complex originated from the partial melting of enriched lithospheric mantle. Initial REE enrichment by metasomatic subduction-related melts was crucial for mineralization, while subsequent magmatic-hydrothermal processes were key to further enrichment and ore formation.

Identifying uranium sources in erosion source areas is crucial for exploring sandstone-type uranium deposits in sedimentary basins. This study focuses on the central and northern Junggar Basin. By analyzing the uranium content, age distribution, and zircon Hf isotope composition of magmatic rocks in the source area, we aim to: (1) characterize their spatial and temporal distribution, (2) evaluate uranium source conditions, and (3) identify the features of magmatic rocks that favor uranium supply. This work provides a basis for predicting sandstone-type uranium mineralization in the region. Our results show that uranium-rich magmatic rocks in the source area were primarily formed during the Ordovician, Late Silurian to Late Devonian, and Early Carboniferous to Late Permian, with a minor phase in the Early Jurassic. Spatially, uranium content and the ability to provide uranium generally decrease from north to south and are higher in the east than in the west. Specifically, the central Altai Orogenic Belt and the Yemaquan Island Arc Belt in the East Junggar exhibit high uranium potential, whereas the West Junggar Orogenic Belt is relatively uranium-poor. Among the different magmatic rock types, acidic intrusive rocks possess the highest inherent uranium content and strongest potential to release uranium, followed by alkaline rocks and acidic extrusive rocks, whereas intermediate-mafic magmatic rocks have the lowest potential. Regarding petrogenesis, S-type granites offer more favorable uranium source conditions than A-type and I-type granites. Additionally, zircon Hf isotopes indicate that crust-derived magmas are more enriched in uranium than those derived from the mantle. Consequently, a combination of these factors controls the formation of favorable uranium sources. Finally, by integrating the distribution of these favorable sources with known mineralization data, we propose that the Kamster area (eastern Junggar), the northwestern margin of the Kupu Basin, the northern Fujin Basin, and the northern Hestoluogai Basin are promising targets for sandstone-type uranium exploration.

Gold resources are critical strategic minerals for China. With increasing challenges in discovering new orebodies at the surface, exploration focus has shifted to deeper regions. Traditional two-dimensional (2D) measurements of structural superimposed halos have yielded satisfactory results in deep exploration. However, they remain limited in (1) quantitatively constructing primary halo assemblages, (2) precisely delineating deep orebody distributions, and (3) elucidating mineralization processes. The rapid development of computer science has emerged as a pivotal approach to addressing this challenge. By applying mathematical statistical analysis methods to quantitatively characterize the elemental associations of front, near, and tail halos, it is possible to establish a three-dimensional (3D) primary halo model for prospecting prediction. This study focuses on the Xinjiazui gold deposit in the Longmenshan tectonic belt to conduct 3D primary halo deep prospecting predictions. Comprehensive field geological investigations were first carried out to systematically delineate the regional tectonic evolution and geological characteristics of the mining area. Analysis of gold grade contour maps revealed that the orebody dips to the northwest and plunges towards the southwest, indicating that ore-forming fluids likely migrated from depth in the southwest to shallower levels in the northeast. Based on the mineralization and alteration characteristics, a systematic sampling campaign was conducted at the Xinjiazui deposit. This included collecting 17 structural superimposed halo samples from the main mineralization stage of the AuⅠ orebody and 626 three-dimensional primary halo samples from the surrounding rocks. Using a concentration-length (C-L) fractal model, the anomaly thresholds for each element in the Cambrian and Silurian strata were determined, and the z-score method was employed to eliminate inter-element background differences. Subsequently, hierarchical cluster analysis categorized 10 elements from the structural superimposed halo into three clusters. By comparing these elemental associations with the ideal primary halo model for hydrothermal gold deposits in China, the following indicator elements for the mining area were identified: As and Sb for the front halo; Au, Ag, and W for the near halo; and Co, Mo, Cu, Zn, and Ni for the tail halo. Principal component analysis was then used to quantitatively characterize the linear relationships among these elements. Using Micromine software, a 3D primary halo deep prospecting model was established for the mining area. Based on deep primary halo indicators and geological understanding, the model predicts that: (1) the AuⅠ orebody extends further to the southwest at depth; (2) a blind orebody likely exists within a 300 m depth range of the AuⅡ orebody; and (3) the AuⅢ orebody extends approximately 300 to 560 m to the southwest. The 3D primary halo prediction results are mutually consistent with and validated by geological and geophysical exploration data, demonstrating high reliability and accuracy in delineating mineralization targets.

Giant deposits are prime targets in mineral exploration, and understanding their formation and localization is a major research frontier in earth sciences. The spatial distribution pattern of ore bodies is crucial for this understanding and for prospecting. The Jiaodong Peninsula, the world’s third-largest gold province, is a hotspot for giant gold deposit studies, hosting multi-hundred-ton deposits like Jiaojia, Sanshandao, and Linglong. The Taishang-Shuiwangzhuang deposit, located in the northern Zhaoping Fault belt, is a recent successful exploration case at depths of 500 to 2 500 m, with proven resources exceeding 700 tons, making it an ideal site for studying ore body distribution and prospecting models. Based on a systematic review of shallow and deep exploration results, this study analyzes the spatial distribution pattern of ore bodies, proposes sectional enrichment characteristics, constructs a deep exploration model, and performs predictive targeting and verification. The results show that: (1) The distribution of the main orebodies is strictly controlled by the Zhaoping Fault. They are hosted in pyrite-sericite-quartz altered rocks beneath the main fault plane and exhibit pinch-and-swell structure and recurrence along strike and dip. (2) Mineralization intensity correlates with variations in the fault’s dip angle. Enrichment zones are primarily found where the fault transitions from steep to gentle dips and in the gently dipping segments with angles between 10° and 35°. (3) The main orebodies generally pitch towards NEE, showing a sectional enrichment pattern along pitch with approximately equally spaced gold-enriched zones. (4) The elevation range of -2 800 to -1 200 m between exploration lines 53 and 149 of No.Ⅰ orebody is highly prospective for deep ore bodies. (5) The potential gold resources from -50 00 to -2 000 m elevation are predicted to be 642-723 tons using the volume -grade method. (6) Verification in the target area confirmed the effectiveness of this predictive methodology, providing robust guidance for deep prospecting.

Massive sulfide deposits are the major global sources of Cu, Zn, Au, Ag, and other metals. Gold-rich massive sulfide deposits are defined by their anomalously high gold content. The Huangtan Au-Cu deposit, located in the southeastern part of the Kalatag district in the Eastern Tianshan, is hosted within marine volcanic rocks of the Middle Ordovician Daliugou Formation and primarily contains gold. Its formation involved a VMS mineralization event, subdivided into a pyrite stage and a subsequent chalcopyrite-sphalerite stage, followed by a hydrothermal mineralization event comprising quartz-sulfide and quartz-calcite stages. Gold was primarily deposited during the hydrothermal event. Fluid inclusions in the Huangtan deposit are predominantly aqueous, including liquid-rich, two-phase inclusions (W-L type), vapor-rich, two-phase inclusions (W-V type), and single-phase aqueous inclusions (L type). During the VMS stage, fluid inclusions exhibited homogenization temperatures of 275-346 ℃ and salinities of 5.7%-10.7% NaCl equivalent. The vapor phase in these inclusions was primarily composed of H₂O, with trace amounts of CO₂. In contrast, during the hydrothermal stage, homogenization temperatures ranged from 110 to 190 ℃, with salinities of 1.1%-6.8% NaCl equivalent, and the vapor phase was predominantly H₂O. These findings indicate that the gold-bearing fluid was a H₂O-NaCl-dominated system with low temperature and salinity. Fluid mapping using the Kriging interpolation method reveals that higher fluid temperatures and salinities are concentrated at elevations of 250, 350, and 450 meters along the 5100 exploration line. Gold mineralization is particularly pronounced at the 250 m and 350 m levels, where high Au grades show a close spatial relationship with the heat source center of the ore-forming fluid. The Au grade decreases outward from this center, suggesting that locating the heat source center can serve as a valuable guide for gold exploration.

The Chepaizi Uplift, a key new area in the Junggar Basin, has witnessed significant breakthroughs in sandstone-type uranium exploration in recent years, with mineralization identified in multiple drill holes. This has established it as one of the most promising exploration targets in the basin. The primary uranium-hosting sequences are the lower member of the Miocene Shawan Formation and the overlying Taxihe Formation. In this study, we present detrital zircon U-Pb geochronological and Hf isotopic data for sandstones from these two sequences across different parts of the uplift. Integrated with heavy mineral assemblage analysis, these data were used to delineate sediment provenance areas and to discuss the basin-mountain synergistic evolution processes during the Miocene. Our findings reveal that the Miocene Shawan Formation was fed by a north-south bidirectional provenance system, primarily derived from the northern Zhayier Mountain and the southern Middle Tianshan Mountains. The northern part of the uplift was dominated by sediments from the Zhayier Mountains, while the central and southern parts received substantial input from the Middle Tianshan Mountains. In contrast, the overlying Taxihe Formation sediments were predominantly sourced from the northern Zhayier Mountain, with only a minor contribution from the Tianshan Mountains. This indicates that during the early Miocene, the Middle Tianshan Mountains on the southern margin of the Junggar Basin experienced stronger uplift than the Northern Tianshan Mountains and served as a significant sediment source for the basin. By the mid-Miocene, the distal stress propagation from the India-Eurasia collision caused rapid uplift of the northern Tianshan Mountains. This tectonic activity led to tilting of the Neogene strata in the Chepaizi Uplift, a southward shift of the sedimentary center, and ultimately cut off the sediment supply from the southern Tianshan Mountains. Consequently, the northern Zhayier Mountains became the sole provenance for the Chepaizi Uplift. The stable distribution and high connectivity of the sand bodies formed at the confluence of these dual provenances constitute favorable targets for uranium mineralization.

Pyrite formed in depositional versus hydrothermal systems reflects fundamentally different conditions, making its genetic identification key to reconstructing hydrocarbon accumulation. In the Gaoquan area of the Sikeshu Sag, where conventional fluid inclusion evidence is limited, this study uses pyrite from the Cretaceous Qingshuihe Formation sandstone to clarify the reservoir’s complex accumulation history through integrated analyses including optical microscopy, Scanning Electron Microscopy(SEM), Raman spectroscopy, Laser Ablation Multi-Collector Inductively Coupled Plasma Mass Spectrometry (LA-MC-ICP-MS), and U-Pb dating of calcite. Two pyrite generations are recognized: (1) Early-stage Massive Pyrite (~122 Ma) with subhedral morphology, low Co/Ni (<1), and highly negative δ³⁴S (-36.42‰ to -30.08‰), indicating a depositional origin via low-temperature bacterial sulfate reduction; (2) Late-stage Anhedral Pyrite (~10.7 Ma) with high Co/Ni (>2), less negative δ³⁴S (-28.62‰ to -18.02‰), and association with calcite and bitumen, indicating a hydrothermal origin linked to thermochemical sulfate reduction and sulfur from hydrocarbon cracking. (3) The late-stage pyrite constrains the main hydrocarbon charge to ~11 Ma and records TSR-related reservoir alteration, demonstrating that pyrite is a powerful indicator of hydrocarbon charge timing, fluid properties, and post-accumulation processes in clastic reservoirs.

The Luang Prabang (Laos)-Loei (Thailand) metallogenic belt hosts orogenic-type deposits in its northern section, porphyry-skarn deposits in the middle, and epithermal gold deposits in the south. The recently discovered Sangthong vein-type gold deposit in the middle section of this belt provides key insights into regional metallogeny and has important implications for gold exploration. Based on detailed mineralogy and petrology, combined with fluid inclusion microthermometry and H-O isotope analysis, we determined the characteristics and evolution of the ore-forming fluids. Our results indicate a magmatic-dominant source for the fluids. The initial ore-forming fluid belongs to a medium-temperature, low-salinity H₂O-NaCl system. During its evolution, this fluid mixed with a medium-low temperature, high-salinity, CO₂-rich fluid, with significant meteoric water input occurring in the late hydrothermal stage. The Sangthong deposit is classified as a low-sulfidation epithermal gold deposit, formed at depths of 1.1-1.8 km. While it shares geological characteristics with the large-scale Chatree epithermal deposit in the southern part of the belt, Sangthong exhibits a relatively deeper mineralization depth and less meteoric water involvement in its fluid system. We therefore propose that the intermediate-acidic volcanic rock areas adjacent to extensional faults in the middle section of the Luang Prabang-Loei metallogenic belt are highly prospective for new epithermal gold discoveries. Furthermore, the epithermal gold occurrences in the middle section of the belt show significant potential for gold discovery at greater depths.

The co-enrichment of Au with Ag-Pb-Zn in structurally controlled lode deposits is interpreted through differing models, including overprinting by multiple fluid events or evolution from a common fluid source. To address this, we focus on the Beishan region in the central segment of the southern Central Asian Orogenic Belt. The Sangejing deposit, a typical co-enriched Au-Ag-Pb-Zn system, is examined to elucidate the characteristics and genetic mechanisms of this mineralization style. Our results show that the ore-forming fluids at Sangejing represent a metamorphic-derived, moderate- to low-temperature (375-304 ℃), moderate- to low-salinity (1.7%-13.5% NaCl_eqv) H₂O-CO₂-NaCl system. Mineral precipitation during the sericitic-pyritic alteration stage (S1) resulted primarily from water-rock interaction, whereas the quartz-siderite-polymetallic sulfide stage (S2) was driven mainly by fluid boiling. Mineral dissolution-reprecipitation was pervasive during S2, facilitating variable redistribution of ore-forming elements. The early substage (S2-1) featured Au mineralization, and the late substage (S2-2) was characterized by Ag-Pb-Zn mineralization. The findings demonstrate that the Au and Ag-Pb-Zn co-enrichment at Sangejing did not originate from the simple overprinting of two distinct fluids but from the sequential precipitation from a single evolving fluid system in response to physicochemical changes.

The formation mechanism and timing of the Tibetan Plateau, a globally prominent topographic feature, have long been a focus of intensive research in the geoscientific community. To decipher the uplift dynamics and denudation processes of the plateau margin, this study conducted low-temperature thermochronological analyses on granites from the Numa Township area, southern margin of the Gangdese Belt, Xizang. Seven sets of apatite fission track (AFT) data were acquired, with fission track ages ranging from 30 to 22 Ma. These ages are all younger than the emplacement ages of the Cretaceous-Eocene granite intrusions, thereby faithfully recording the Late Oligocene-Early Miocene uplift and cooling history of the southern Gangdese margin. The average apatite fission track length varies from (13.2±1.8) μm to (14.3±1.8) μm, which is notably shorter than the initial length of ~(16±1) μm, indicating significant thermal annealing of the apatite grains. Thermal history modeling based on the AFT data reveals that the Numa area experienced a continuous uplift-driven cooling process during the Cenozoic, with a total uplift amplitude of 6603-7443 m and an average uplift rate of 0.27-0.31 mm/a. This uplift-cooling process can be subdivided into three distinct phases: 40-20 Ma, 20-10 Ma, and 10 Ma to the present. These phases are genetically linked to three key tectonic events, namely the subduction-collision of the Indian and Eurasian plates, large-scale retrograde overturning tectonism within the Gangdese Belt, and the onset of north-south extensional movement in the Tibetan Plateau, respectively. This study enriches the understanding of the Oligocene uplift mechanism and evolutionary model of the Tibetan Plateau, and provides critical constraints on the preservation potential of pre-Cenozoic mineral deposits in the region.

Analysis of the regional geothermal field is a crucial component of geothermal geological research. Elucidating the influence of various factors on its spatial distribution is a prerequisite for understanding its genetic mechanisms, which in turn provides support for subsequent studies on the regional lithospheric thermal state and the development and utilization of geothermal resources. In this study, the regional geothermal field distribution characteristics were investigated by systematically organizing temperature measurement data from 7 representative boreholes in the Huainan-Huaibei area, rock thermo-physical parameters from different geological age, 264 geothermal gradient values, and 191 terrestrial heat flow values. The study analyzed the primary heat transfer modes in the formation and the spatial distribution characteristics of terrestrial heat flow. Furthermore, integrated with typical regional geological sections and constrained by geothermal and hydrogeological conditions, hydrothermal coupled numerical simulations were performed. The analysis focused on the influence of typical regional thrust nappe structures on geothermal distribution, briefly examined the impact of topographic altitude, and analyzed the differences in the influence of water-conducting faults of varying thicknesses. The results indicate that thrust nappe structures are the primary reason for the relatively low regional geothermal field. This is mainly due to the high thermal conductivity, porosity, and permeability of the carbonate rocks within the nappe, which facilitate the infiltration of cold water. Although topographic altitude in the study area is inversely correlated with heat flow distribution, it is not the primary cause of low heat flow in high-altitude blocks; instead, this is more likely caused by the infiltration of groundwater recharge, such as atmospheric precipitation, into the carbonate rock. Within the scope of this study, the influence of water-conducting faults on geothermal distribution or heat flow increases with their thickness. The results of this study enrich the findings regarding the influencing factors of regional geothermal fields and provide a valuable case reference.

The Luofengpo chromite deposit, located in the Luliangshan ophiolitic belt on the northern margin of the Qaidam Block, is a typical podiform chromite deposit. However, its metallogenic age and tectonic setting have long been debated. This study integrates petrology, zircon U-Pb geochronology, whole-rock geochemistry, Sr-Nd-Hf isotopes, and chromite mineralogy to elucidate the deposit’s genesis and its link to the evolution of the Proto-Tethys Ocean. The plagiogranite is sodic, K-poor, weakly peraluminous, and shows slight enrichment in light rare earth elements with a weak negative Eu anomaly. It is enriched in Th and U but depleted in Nb and Ti. Zircon U-Pb dating yields an age of (504±2.6) Ma. The rocks have ε_Hf(t) values of +12.5 to +16.9 and whole-rock ε_Nd(t) values of +4.54 to +4.68. These isotopic signatures indicate that the plagiogranite originated not from fractional crystallization of basaltic magma but from partial melting of the lower oceanic crust. It is classified as oceanic (M-type) plagiogranite, interpreted to represent either Proto-Tethyan oceanic crust or early subduction-related magmatism, thereby constraining the timing of early subduction. Consistently, the chromite exhibits high Cr^# (79.8-83.8) and very low TiO₂ contents (<0.06 wt%), characteristic of a supra-subduction zone mantle setting. We therefore conclude that the Luofengpo chromite deposit and its host ophiolite formed in a forearc setting during the initial subduction of the Proto-Tethys Ocean, with the metallogenic epoch broadly constrained between approximately 535 and 504 Ma.

An innovative caprock model, which integrates regional lake-flooding mudstone with local calcareous sandstone deposited during transgressive systems tracts, has been proposed for the sand-rich Enping Formation in the Panyu 4 Subsag, Pearl River Mouth Basin. This model successfully guided the discovery of the first large-medium oil field (Panyu 10-6) in the deep strata. Given the critical sealing role of the calcareous sandstone, elucidating its genetic mechanism and distribution model within the Zhuhai-Enping formations is essential for supporting future reserve growth and production enhancement. Using the Zhuhai-Enping Formation in the Panyu 4 Subsag as a case study, this research investigates the petrological characteristics, genetic mechanism, and development model of the calcareous sandstone. The methodology integrates thin-section and scanning electron microscopy observations, trace element and carbon-oxygen isotope analyses, well-log data, and stratigraphic correlation within a transgressive framework, considering both sedimentary environment and material sources. The main findings are as follows: (1) The calcareous sandstone cements are predominantly anhydrite, dolomite, and ferroan dolomite. Anhydrite fills large pores as poikilitic cement enclosing detrital grains. Dolomite occurs as micritic, euhedral to subhedral silt- to fine-crystalline, and anhedral coarse-crystalline varieties. (2) Carbon-oxygen isotopes indicate a freshwater depositional environment. The carbon is primarily derived from CO₂ generated via diagenesis and organic acid decarboxylation. Dolomite oxygen isotope geothermometry suggests the three dolomite types correspond to three distinct diagenetic stages. (3) Lake flooding provided a low sedimentation rate and ions (e.g., Ca²⁺, Mg²⁺), while local transgression induced fluctuations between supersaturation and undersaturation of dolomite, promoting its precipitation. In an evaporative setting, gypsum/anhydrite precipitated from {\mathrm{SO}}_4^{2-} and Ca²⁺ supersaturation, while early calcite/dolomite formed from Ca²⁺ and Mg²⁺ supersaturation. During deeper burial, sulfate reduction and thermal decarboxylation supplied carbon for carbonate cementation. As organic acids were depleted, the diagenetic environment shifted from acidic to alkaline. The smectite-to-illite transformation released Fe²⁺ and Mg²⁺, leading to calcitization and ferroan dolomitization. (4) The reservoir-caprock assemblage (sandstone and calcareous sandstone) exhibits a displacement pressure contrast of 0.738 MPa. The calcareous sandstone caprock has a permeability below 0.3 mD and seals an average hydrocarbon column of 295.2 m. (5) The distribution of calcareous sandstone layers in the upper Enping Formation is primarily controlled by sedimentary facies and paleoenvironments, displaying a ring-shaped pattern in the southeastern part of the southern sub-sag within the Panyu 4 Subsag. In summary, the innovative recognition of calcareous sandstone as an effective caprock is of significant importance for guiding Paleogene oil and gas exploration in the Panyu 4 Subsag.

Gammacerane, a C₃₀ triterpenoid biomarker traditionally interpreted as an indicator of water column stratification and salinity, remains enigmatic due to its frequent absence in high-salinity sedimentary environments—a contradiction to conventional models. This multidisciplinary study of Miocene lacustrine shales from the Nördlinger Ries (southern Germany) integrates mineralogy with organic geochemical proxies—including total organic carbon (TOC), total sulfur (TS), biomarkers, kerogen elemental composition, and pyrolysis parameters—to elucidate how water chemistry controls gammacerane preservation through microbial ecology. Our data reveal that the paleolake evolved sequentially through mesosaline, hypersaline, mesosaline, and freshwater phases. Gammacerane abundance shows contrasting correlations with salinity: (1) a positive correlation at lower salinities (e.g., <40‰) in suboxic to weakly reducing conditions, and (2) a negative correlation in hypersaline, intensely anoxic settings. In the latter, extreme salinity and anoxia triggered a collapse of the microbial food web (reflected in diminished prokaryotic biomass). This suppressed the metabolic activity of ciliates (the primary producers of gammacerane), which in turn reduced both gammacerane biosynthesis and denitrification efficiency. The decline of Gammaproteobacteria further limited the proliferation of sulfate-reducing bacteria, as evidenced by coupled shifts in organic sulfur and pyrolysis T_max, thereby curtailing organosulfur compound formation. This study demonstrates that gammacerane preservation is controlled not simply by stratification but rather by ecological feedbacks within the microbial community. It provides a revised framework for interpreting gammacerane records in hypersaline lacustrine systems.

The Dabancheng Sub-sag, located on the southern margin of the Junggar Basin, is largely devoid of Cretaceous strata due to erosion associated with the Yanshanian movement. The sedimentation-erosion process in this area remains poorly constrained, limiting our understanding of its tectonic evolution and hydrocarbon accumulation patterns. Traditional methods for estimating erosion are ill-suited to address the dynamic evolution of sedimentation and erosion. In contrast, basin fluctuation theory provides a novel analytical framework for this problem. In this study, we decomposed periodic fluctuations from the time series of residual stratigraphic sedimentation rates and established a fluctuation equation to reconstruct the sedimentation-erosion history of the Dabancheng Sub-sag since the Permian. The results indicate that the basin’s fluctuation evolution is governed by multi-order periodic fluctuations of 220 Ma, 100 Ma, and 33 Ma, which govern the dramatic shifts in sedimentation or erosion rates across different periods. During the Cretaceous, approximately 430 meters of sedimentary strata accumulated in this area. However, subsequent uplift induced by the Yanshanian movement caused near-total erosion of the Cretaceous system, with partial erosion extending into the underlying Jurassic, resulting in a total erosion thickness of 650 meters. The Dabancheng Sub-sag has undergone four distinct evolutionary stages: a strike-slip extensional basin in the Early-Middle Permian, a compressional basin from the Late Permian to Triassic, a weak extensional rift basin during the Jurassic, and an intracontinental depression to regenerated foreland basin from the Cretaceous to Paleogene. The observed 220 Ma periodic fluctuation in the Junggar Basin is closely correlated with the regional plate tectonic background, reflecting a coupling mechanism between basin fluctuation and plate motion. The sedimentary basin fluctuation analysis method proves effective in identifying sedimentary hiatuses and quantitatively characterizing the development of unconformities, thereby offering a scientific basis for reconstructing palaeo-structural and sedimentary evolution and guiding hydrocarbon exploration in continental basins.

Fluctuations in atmospheric CO₂ concentration throughout geological history have been a pivotal driver of Earth’s surface temperature variations, serving as a key parameter for elucidating transitions between icehouse and greenhouse climates. Modern marine studies confirm that the carbon isotope composition (δ¹³C) of marine phytoplankton, their derived particulate organic carbon, and sedimentary organic matter is primarily controlled by the concentration (or partial pressure) of dissolved CO₂ in seawater ([CO₂(aq)]). Previous work has established that the carbon isotope difference (Δ=δ¹³ C_{C{O}_2}-δ¹³C_org) between seawater [CO₂(aq)] and marine organic matter exhibits a quantifiable relationship with the inverse of [CO₂(aq)]. By incorporating an equation linking sea-surface atmospheric pCO₂ to global average sea surface temperature (GAT), it is possible to estimate past atmospheric pCO₂, mean sea surface temperature, and seawater pH. This study applies this approach to a continuous sedimentary succession spanning the Upper Ordovician Wufeng Formation, the Hirnantian Guanyinqiao Formation, and the Lower Silurian Longmaxi Formation. The Guanyinqiao Formation corresponds to the Hirnantian glaciation. This interval benefits from precise biostratigraphic age control, consists predominantly of organic-rich black shales, and was deposited prior to the emergence of terrestrial plants. Consequently, the δ¹³C of its marine organic matter provides optimal material for reconstructing paleoatmospheric CO₂. Our results indicate that during the deposition of the Guanyinqiao Formation, the average atmospheric pCO₂ was approximately 625 μatm, and the global average sea surface temperature was about 18.46 ℃. This climatic state represents an icehouse condition comparable to that during the Oligocene, following the establishment of the Antarctic Ice Sheet in the Cenozoic era.

The groundwater regime in the piedmont plain of western Baoding City has been significantly altered by combined human activities and climate change, drawing attention to the resurgence of Yimu Spring. Understanding the groundwater circulation patterns and the formation mechanism of Yimu Spring under these changing conditions is crucial for scientific groundwater management and spring protection. This study investigates these issues by employing a combination of hydrochemical and isotopic analyses, groundwater level monitoring, and borehole data. The results reveal: (1) The concealed fractured-karst groundwater is in close hydraulic connection with the overlying porous groundwater in the unconsolidated plain sediments. (2) Under extreme precipitation, both the fractured-karst and shallow porous groundwater in the piedmont plain are highly sensitive to lateral recharge from the mountainous areas, which is the dominant controlling mechanism for water-level fluctuations. The response of the fractured-karst groundwater is more pronounced, indicating its primary role in transmitting recharge. (3) Yimu Spring is primarily sourced from the groundwater in the shallow (Groups I and II) aquifers and shows no direct hydraulic connection to the deeper carbonate fractured-karst water. The spring formation is attributed to a combination of factors: a sharp pinch-out of Aquifer Groups I and II east of the spring, which impedes lateral flow and results in a localized increase in confined hydraulic head; low-lying topography; and the presence of relatively coarse-grained, permeable lithology in the shallow strata. These conditions collectively promote groundwater discharge, leading to the emergence of Yimu Spring.

Extended exposure to uranium-contaminated groundwater can pose health risks. While the hydrogeochemical processes leading to elevated uranium (U) concentrations in groundwater are well-documented, the mechanisms controlling U enrichment in groundwater remain poorly understood. This study investigated in the Hetao Basin, U forms and contents in aquifer sediments obtained from both the piedmont and plain zones. The results showed that the U contents in piedmont aquifer sediments were significantly higher than those in the plain, and U mainly existed in the form of Fe-Mn oxide binding (F3-U) and matrix state (F5-U) in piedmont and plain aquifer sediments, respectively. The U contents in the aquifer sediments increased as sediment grain size decreased. Both Fe and Mn in the aquifer sediments played a crucial role in U enrichment since positive correlations were observed between U and these elements. In the piedmont zone, U enrichment in groundwater primarily occurs through desorption and oxidative dissolution of U-bearing minerals. In contrast, in the plain zone, U released from Fe and Mn oxides reductive dissolution is reduced to U(IV) and immobilized within the aquifer sediments, which leads to high Fe(II) and low U groundwater. This study establishes critical links between the aquifer sediment geochemistry and the U enrichment in groundwater, providing valuable insights into the processes controlling U mobilization.