A new fused quartz glass reference material, NWU-Qtz, has been developed for in situ Si isotope measurement by femtosecond laser ablation multi-collector inductively coupled plasma-mass spectrometry (fsLA-MC-ICP-MS). Major element characterization suggests that the NWU-Qtz glass has no growth rim or zoning, and extensive measurements performed by fsLA-MC-ICP-MS demonstrate its homogeneity in Si isotopes. Traditional bulk Si isotope analyses of NWU-Qtz glass by solution nebuliser (SN)-MC-ICP-MS and gas source-isotope ratio mass spectrometry (GS-IRMS) yielded a mean delta 30SiNBS-28 value of 0.12 +/- 0.12 parts per thousand (2s, n = 6). Randomly selected chips of NWU-Qtz analyzed by fsLA-MC-ICP-MS gave a mean delta 30SiNBS-28 value of 0.12 +/- 0.17 parts per thousand (2s, n = 373). The intermediate measurement precision across five analytical sessions was better than 0.21 parts per thousand (2s), suggesting that NWU-Qtz glass is suitable as a microanalysis reference material for Si isotope measurements. Six well-characterized reference materials analyzed using fsLA-MC-ICP-MS and calibrated against NWU-Qtz yield delta 30SiNBS-28 values in agreement with previously published data, further validating the feasibility of NWU-Qtz glass as a proposed reference material. The recommended mean delta 30SiNBS-28 value for NWU-Qtz glass is 0.12 +/- 0.12 parts per thousand (2s, n = 6), as determined by bulk SN-MC-ICP-MS and GS-IRMS analyses.

This study investigated matrix effects during in situ Sn isotope analysis using a femtosecond (fs) laser ablation system coupled to a multi-collector ICP-MS. Contrary to the common perception of "matrix-free" analysis, matrix effects are evident during in situ analysis. The measured delta Sn-124/Sn-120 ratios of cassiterite and bronze deviated from the true values by up to 0.7 parts per thousand and 0.5 parts per thousand, respectively, when using a pure tin metal as the bracketing standard. Introducing water vapour into the carrier gas substantially reduced these matrix effects, though minor deviations, from -0.24 parts per thousand to -0.33 parts per thousand, persisted for cassiterite and bronze when tin metal was used as a non-matrix-matched calibration under wet plasma conditions, indicating that ablation-related processes also contribute to matrix effects. Therefore, matrix-matched reference materials are required for high-precision and accurate Sn isotope analyses of cassiterite and bronze samples. We evaluated four candidate samples, NWU-CAS (a natural cassiterite), NWU-Sn (tin metal plate), GBW02140 and GBW02137 (two certified bronze reference materials from the National Research Center for Certified Reference Material of China). Repeated analyses of the two candidates by fsLA-MC-ICP-MS yielded a good external reproducibility of < 0.10% (2SD) for delta Sn-124/Sn-120, validating their suitability as matrix-matched reference materials for in situ Sn isotope analysis of cassiterite and bronze.

Microanalysis of silver isotopes in gold (Au) by laser ablation multi-collector inductively coupled plasma mass spectrometry (LA-MC-ICP-MS) has been an important tool to reveal the source and enrichment processes of Au. However, preparing an Au-matrix reference material with homogeneous Ag isotope compositions at a micron scale remains a major challenge. This study presents a novel method to synthesize a homogeneous gold reference material, named NWU-Au, via flux-free fusion. Moreover, a natural gold reference material, DD440, is prepared for in situ Ag isotope measurement by LA-MC-ICP-MS. Elemental mapping obtained by electron probe microanalysis indicates that both gold reference materials have homogeneous Au and Ag contents, while LA-MC-ICP-MS measurements further demonstrate their homogeneous distribution of Ag isotopes. The intermediate precision of delta 109Ag was better than 0.06 parts per thousand (2s) for NWU-Au and DD440, which were suitable to serve as matrix-matched calibration materials. Silver isotopic compositions of six gold samples were also determined using LA-MC-ICP-MS with matrix-matched calibration, and the delta 109AgNIST978a values were consistent with those obtained by SN-MC-ICP-MS, suggesting that LA-MC-ICP-MS can accurately determine Ag isotopic ratios in gold samples. Thus, this synthesis method, along with an analytical approach, enables potential determination of spatially resolved Ag isotope compositions at the mineral scale to reveal the source and enrichment processes of Au in the Au deposit.

Tin (Sn) isotopes in cassiterite (Cas) are important tracers of fluid evolution and Sn sources, but high-precision μm-scale in situ Sn isotope analysis remains constrained by the limited availability of suitable reference materials (RMs). Here, we report the development of a synthetic Cas-matrix RM to serve as a bracketing standard for laser ablation coupled with multicollector inductively coupled plasma mass spectrometry (LA-MC-ICP-MS) analysis. Ultrafine cassiterite powder was compressed, sealed in silver tubes, and sintered at 600 °C and 1.0 GPa, producing homogeneous pellets with yields up to 7 g per batch. Two independent laboratories, Northwest University (Xi'an, China) and Leibniz University Hannover (Germany), evaluated the isotopic uniformity (δ124/120Sn) of the pellets using femtosecond laser ablation (fs-LA)-MC-ICP-MS, yielding consistent δ124/120Sn values within analytical uncertainty. Solution nebulization (SN)-MC-ICP-MS analysis of the starting powder and pellet subsamples yielded a recommended δ124/120SnNIST SRM 3161a value of 0.63‰, with an expanded uncertainty (URM) of ∼ 0.07‰ (k = 2) and a precision of ±0.02‰ (2SD, n = 14). The agreement between in situ and solution measurements of natural cassiterite further validates the RM. A total of 28 g of synthetic cassiterite RM was prepared in four batches for distribution to the global geochemical community. This RM will advance Sn isotope analysis in cassiterite by providing a reliable standard for precise in situ measurements and interlaboratory comparison.

Stable isotope systems of iron, copper, and zinc have emerged as powerful tracers in understanding metal sources, migration, and deposit formation processes. Accurate and precise determination of Fe, Cu, and Zn isotopic compositions in sulfide minerals, especially in simple-matrix minerals characterized by their relatively pure composition, with low content of impurity elements and few interfering components, requires matrix-matched reference materials to validate analytical methods, particularly for direct analysis protocols without column chromatography. This study introduces a suite of novel secondary reference materials (NWU-Fe, NWU-Cu, and NWU-Zn sulfide powders) developed to address the critical gap in calibration standards for direct isotopic analysis without column chemistry of simple-matrix minerals. These sulfide powders exhibit excellent homogeneity and stability, fulfilling the requirements for high-precision determination of Fe, Cu, and Zn isotope ratios using MC-ICP-MS without column chemistry. Reference values were derived from interlaboratory comparisons across three independent laboratories. The isotopic compositions (6 values), reported in per mil notation relative to international standards (IRMM-014 for Fe, NIST SRM-976 for Cu, and JMC-Lyon for Zn), are as follows: 656Fe =-0.38 +/- 0.03%o (2s), 665Cu = 0.44 +/- 0.04%o (2s), 666Zn =-0.04 +/- 0.02%o (2s). This study provides a robust calibration framework for Fe-Cu-Zn isotopic studies in geochemistry and environmental science.

The subcontinental lithospheric mantle (SCLM) represents a significant carbon reservoir, releasing CO2 through continental rift systems and impacting climate. However, the processes of carbonate recycling in the SCLM remain uncertain. Here we present Zn-Sr-Nd isotopes and bulk elemental compositions for the Late Cretaceous Gejiu alkaline complex, Southwest China. The monzogabbros exhibit low SiO2 and high CaO, MgO, Ba, and Sr contents, together with enriched Sr-Nd isotopes [initial 87Sr/86Sr = 0.7100-0.7110; epsilon Nd(t) = -6.8 to-6.5], indicating derivation from a metasomatized SCLM. Although their mid-oceanic-ridge basalt-like delta 66Zn (0.25 +/- 0.02%0) values are consistent with an unmodified mantle source, the high Zr and Hf contents, elevated Th/Nb (0.48-0.83) and Ba/Th (87.3-250) ratios, and low Ti/Eu ratios collectively suggest mantle metasomatism by "ghost-like," carbonate-bearing sediment-derived fluids. The monzonites display geochemical and isotopic affinities similar to those of the monzogabbros (delta 66Zn = 0.25%0 +/- 0.03%0), supporting a cogenetic origin. The nepheline syenite exhibits extremely high K2O, Na2O, and light rare earth element contents, elevated La/ Yb and Sm/Yb ratios, and enriched Sr-Nd isotopes [initial 87Sr/86Sr = 0.7097-0.7101; epsilon Nd(t) = -7.5 to-6.7], consistent with derivation from a metasomatized SCLM source. However, their heavy and variable delta 66Zn values (0.25%0-0.39%0), together with high Th/Ta (29.0-69.4) ratios and positive Gd anomalies, are attributed to the injection of similar to 5%-10% carbonated silicate melt. These results record a considerable carbonate signature in the petrogenesis of the Gejiu alkaline complex. Combined with the regional geology, these carbonate-bearing sediments could have been introduced into the SCLM during Paleo-Tethys subduction, after which the heterogeneous carbonated SCLM was remobilized during Late Cretaceous intracontinental extension. This study demonstrates that intraplate alkaline magmatism can effectively remobilize ancient, subduction-introduced carbonate in the SCLM, highlighting its critical role in carbon recycling over long-term geodynamic processes.

Abstract Laser wavelength largely governs analytical accuracy in laser ablation microanalysis. Most routine laser ablation systems rely on 193 nm excimer lasers, while the considerably shorter 157 nm wavelength has only been applied sparingly to in situ microanalysis. This study presents a 157 nm F2 laser system with an optical path purged and protected by an inert gas (N2) and provides a comprehensive performance evaluation of its integration with LA-(MC-) ICP-MS. The 157 nm laser effectively ablates transparent minerals such as quartz and fluorite, producing flat-bottomed craters free of fracturing. Systematic evaluations of trace elements, zircon U–Pb dating, and in situ Hf–B isotopic analyses consistently demonstrate robust analytical performance of the 157 nm laser across diverse in situ microanalysis applications. These capabilities position the 157 nm laser to enhance spatial resolution in highly transparent minerals, facilitating the acquisition of finer-scale chemical insights for a broad range of Earth science and environmental investigations.

High-quality carbon and oxygen isotope data critically depend on the quality of reference materials used for instrumental calibration and data monitoring during in situ analysis. We present a new natural calcite reference material MNP for in situ carbon and oxygen isotope analysis by LA-MC-ICP-MS and SIMS, respectively. Extensive characterization by IRMS, LA-MC-ICP-MS and SIMS analyses demonstrated that MNP calcite is homogeneous in carbon and oxygen isotopes. Bulk isotope analyses yielded a mean delta 13CVPDB of -6.81 +/- 0.33 parts per thousand (2SD, n = 15) and a mean delta 18OVPDB of -22.38 +/- 0.41 parts per thousand (2SD, n = 15) across two independent laboratories. A total of 469 LA-MC-ICP-MS carbon isotope analyses of randomly selected calcite grains show homogeneous isotopic compositions with an average delta 13CVPDB of -6.82 +/- 0.40 parts per thousand (2SD, n = 469), consistent with the bulk analytical data. Carbon isotopic compositions determined from five LA-MC-ICP-MS sessions agree with those obtained by IRMS analysis, suggesting that MNP calcite is suitable as a matrix-matched calibration reference material. Moreover, a total of 80 SIMS oxygen isotope analyses of randomly selected calcite grains show consistent oxygen isotopic compositions with an average delta 18OVPDB of -22.41 +/- 0.32 parts per thousand (2SD, n = 80), consistent with bulk analyses. These findings suggest that MNP calcite is a homogeneous, matrix-matched reference material suitable for in situ carbon and oxygen isotope determinations.

Sandstone-type uranium deposits have become a vital component of China’s uranium resources. Breakthroughs have been achieved in uranium exploration technology, mineralization, leaching process innovation, and post-leaching environment remediation. Exploration is no longer limited to the traditional “grey-black” stratigraphic but has innovatively incorporated the concept of “red-black coupling,” significantly broadening the horizons and scope of exploration. At the theoretical level of uranium ore-forming, a series of ore-forming models have been successfully introduced and deeply studied, including hydrothermal superposition mineralization, bio-mineralization, hydrocarbon reduction mineralization, and exudative mineralization. These mechanisms have not only greatly enriched our understanding of the genesis of sandstone-type uranium deposits but also provided a more solid theoretical foundation for ore-finding practices. In in-situ leaching field, the more environmentally friendly, economical, and efficient CO2+O2 leaching has been widely applied. However, the latest environmental assessment results indicate that both H2SO4 and CO2+O2 leaching processes require a long period of natural remediation to meet regulatory requirements. Therefore, implementing scientific and effective environmental remediation measures for decommissioned areas has become a top priority. Interdisciplinary collaboration is the key force driving the sustainable and resilient development of uranium resources in China. Future research directions will focus on four main aspects: (1) Researchers will develop high-precision analytical techniques and create homogeneous U-Pb dating reference materials to accurately determine the minerals’ geochemical composition and mineralization age. (2) Researchers will integrate multi-source data, including uranium leaching processes, post-leaching environmental remediation, and fluid inclusions in ore-forming fluids, with computer numerical simulation techniques. This integration will facilitate the study of uranium’s migration, enrichment, and precipitation mechanisms in ore-forming environments, thereby enhancing the understanding of its geochemical behavior. (3) Researchers will enhance research in process mineralogy, ion kinetics of leaching fluids, and changes in geological structural physical properties. This research will provide new ideas and methods for addressing practical challenges in uranium leaching. (4) Researchers will closely link theoretical research with practical operations. This linkage will help develop scientific management policies, strengthen legal frameworks, and promote industry standards, ensuring the smooth progress of decommissioned mine remediation and achieving the goal of sustainable green mining.

Secondary-ion mass spectrometry (SIMS) and related in situ microanalytical techniques allow precise chemical and isotopic characterization at micron and submicron scales, providing insights into spatially heterogeneous processes. However, the quantitative accuracy of SIMS is limited by matrix effects, which cause instrumental mass fractionation (IMF) between measured and true isotope ratios. Accurate quantification requires matrix-matched reference materials (RMs) with identical physical and chemical properties to the unknown samples. Most existing SIMS RMs are derived from natural minerals, which often exhibit heterogeneity, limiting reproducibility and interlaboratory comparability. Synthetic RMs offer a promising solution, but their development for SIMS has been challenging due to the sensitivity of SIMS to microstructural attributes such as surface smoothness and grain size. This study presents a novel synthesis strategy for producing matrix-matched pyrite (FeS2) RMs. By combining hydrothermal precursor synthesis with low-temperature ultrahigh-pressure (UHP) sintering, we fabricated dense, nanocrystalline pyrite ceramics with controlled stoichiometry and exceptional sulfur-isotope homogeneity. The resulting material exhibited sputtering behavior indistinguishable from that of natural pyrite, demonstrating the strategy as a robust framework for producing synthetic sulfide RMs. This approach facilitates the improvement of analytical accuracy and reproducibility in microanalytical science and can be extended to other mineral systems.

The age homogeneity of GBW04420 has been questioned, and its stock is nearly exhausted, making the development of new reference materials for U-Pb dating an urgent priority. Uraninite from pegmatite-type uranium deposits is a promising candidate due to its high uranium content and excellent crystallinity. As a typical pegmatite-type uranium deposit in China, the Chenjiazhuang deposit provides an ideal case to evaluate the potential of uraninite as a reference material. In this study, we systematically investigated uraninite from the Chenjiazhuang deposit using optical microscopy, electron probe microanalysis (EPMA), and laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS), with focus on its mineralogical, geochemical, and geochronological characteristics. Analytical results show that uraninite grains are relatively coarse (100-200 mu m), dominated by UO2 with minor ThO2 and PbO. Their trace element compositions indicate crystallization under high-temperature reducing conditions, associated with magma-wall rock (biotite-plagioclase gneiss) assimilation and fractional crystallization. Geochronological data reveal that the ore-bearing pegmatite formed at 425 +/- 2.5 Ma (zircon U-Pb age), whereas uraninite crystallized at 401 +/- 5.4 Ma, approximately 24 Ma after pegmatite emplacement. A tectono-thermal event at 380-370 Ma, recorded by late-stage zircon, apatite, and monazite ages (369-380 Ma), caused localized alteration but did not reset the U-Pb system of uraninite. The alteration of uraninite is characterized by UO2 loss, while PbO and ThO2 remained relatively stable. EPMA dating yields a weighted mean age of 404 +/- 10 Ma for uraninite, which is consistent with the LA-ICP-MS result (401 +/- 5.4 Ma) and previous studies (similar to 406 Ma). The absence of significant age differences among uraninite grains of different sizes confirms a single mineralization event. Notably, both unaltered coarse-grained and slightly altered fine-grained uraninite show excellent compositional homogeneity: UO2 yields RSD values of 0.79% and 2.31%, and PbO yields RSD values of 4.62% and 4.12%, respectively, which are significantly better than those of the GBW04420 reference material. These features demonstrate that Chenjiazhuang uraninite has great potential as a high-precision reference material for in situ U-Pb dating, as long as obviously altered domains are avoided.

Coarse-grained uraninite in the Haita area (Miyi County, Sichuan Province, China) is characterized by exceptionally large crystal sizes and euhedral forms. However, uraninite in this district has experienced substantial post-ore alteration. This study therefore focuses on well-preserved remnant titanite domains for in-situ analysis to minimize screening costs and ensure data reliability. Titanite U–Pb analysis yields a concordant age of 765.5 ± 8.6 Ma, representing the crystallization age of uraninite and indicating a Neoproterozoic mineralization event. Titanite geochemical analysis indicates that the ore-forming fluids were enriched in F–H2O and other mineralizing agents, with REE patterns comparable to those of coarse-grained uraninite and high-temperature magmatic uraninite deposits. Thermobarometric estimates reveal that titanite crystallized at 650–770 °C and 160–260 MPa. The uraninite–titanite–apatite–albite mineral assemblage and Ce–Eu anomalies collectively indicate that the ore-forming fluids were Ti4+-P5+-F−-Na+-rich and reducing. Uranium migrated as U4+–F− complexes in the fluids and precipitated as coarse-grained uraninite upon slow cooling and complex decomposition. Following crystallization, the U–Pb system remained open, yielding a discordant age cluster at 400–200 Ma that may record a thermal event, though further verification is required. In conclusion, remnant titanite can constrain the formation processes and crystallization age of coarse-grained uraninite.

Paleozoic igneous rocks exposed in the northern Yili Block are thought to have resulted from the subduction of the North Tianshan oceanic crust. However, the exact timing of the transition of the northern margin of the Yili Block from a passive to an active continental margin remains unknown. In this paper, the petrological and geochemical features, zircon U-Pb chronology, Lu-Hf isotopes, and Sr-Nd isotopes of volcanic rocks in the Nailenggeledaban area on the northern margin of the Yili Block were studied. Zircon U-Pb dating results show that the crystallization ages of the volcanic rocks in the Nailenggeledaban area on the northern margin of the Yili Block are 491 ± 2 Ma and 500 ± 2 Ma, suggesting they were formed during the Late Cambrian. Geochemical features show that the volcanic rocks are alkaline basalts with rare earth and trace element distribution patterns similar to OIB, although they exhibit some degree of Zr and Hf depletion. The εHf(t) values of alkaline basalts in the Nailenggeledaban area at the northern Yili Block range from −3.48 to −1.00, with a TDM1 age of 1152 to 1263 Ma. The εNd(t) values range from −3.53 to −0.96, with a TDM1 age of 1471 to 2162 Ma. Combined with geochemical data, the alkaline basalt magma in the Nailenggeledaban area on the northern margin of the Yili Block may be derived from the Mesoproterozoic enriched lithospheric mantle. The composition of the mantle source area is potentially garnet lherzolite, and the magma appears to have been either unaffected or only minimally contaminated by crustal materials during the ascending process. On the basis of the research results of the Early Paleozoic tectonic evolution in the northern margin of the Yili Block, this paper proposes that the volcanic rocks in the Nailenggeledaban area, located on the northern margin of the Yili Block, were formed in a back-arc extensional environment resulting from the subduction of the North Tianshan Ocean (or Junggar Ocean) beneath the northern margin of the Yili Block during the Late Cambrian.

This study compared boron (B) isotopic compositions of six chemically diverse tourmalines (including schorl, dravite, and elbaite types) using 257 nm femtosecond (fs) and 193 nm nanosecond (ns) laser ablation coupled with multi-collector inductively coupled plasma mass spectrometry (LA-MC-ICP-MS). Significant matrix effects were observed when non-matrix-matched standards were used, leading to delta 11B deviations of -0.70 parts per thousand to -0.41 parts per thousand for fs-LA and -0.63 parts per thousand to -0.57 parts per thousand for ns-LA when using dravite GIGT as a bracketing standard for schorl (TOUR1 and TOUR4) and elbaite (TOUR6). In contrast, using GIGT as the matrix-matched bracketing standard in the B analysis of dravites (TOUR2, TOUR3, and TOUR5) yielded significantly lower deviations of -0.22 parts per thousand to -0.18 parts per thousand for fs-LA and -0.44 parts per thousand to 0.12 parts per thousand for ns-LA. These findings necessitate matrix-matched standards for precise and accurate in situ measurements of B isotopes. We characterized four natural tourmaline reference materials (TOUR1, TOUR4, TOUR5, and TOUR6) for in situ B isotope analysis using LA-MC-ICP-MS and confirmed their isotopic homogeneity. The measured mean delta 11B values were -11.14 +/- 0.40 parts per thousand (2SD, n = 597), -13.42 +/- 0.57 parts per thousand (2SD, n = 509), -9.09 +/- 0.60 parts per thousand (2SD, n = 486), and -8.57 +/- 0.17 parts per thousand (2SD, n = 164), respectively, agreeing well with those obtained by solution nebulizer (SN)-MC-ICP-MS. Thus, schorl (TOUR1 and TOUR4), dravite (TOUR5), and elbaite (TOUR6) are recommended as candidate matrix-matched tourmaline reference materials for in situ B isotope determination.

Two new reference materials, NWU-GN and PY-FHP, have been developed and characterised for the calibration of in situ Pb analyses of sulfide minerals by LA-MC-ICP-MS.

Based on the verification of the suitability of the pitchblende certified reference material (GBW04420) for uranium mineral dating, this study conducted in-situ micro-area U-Pb dating on sandstone-hosted uranium deposits in the northern Ordos Basin by integrating femtosecond laser ablation inductively coupled plasma mass spectrometry (fs-LA-ICP-MS) and secondary ion mass spectrometry (SIMS). The fs-LA-ICP-MS method enables age determination for uranium minerals larger than 20 μm, while SIMS complements the analysis for micro-minerals ranging from 5 to 20 μm. Thus, this combined approach delivers highly precise and comprehensive age results. The overall dating results reveal four distinct mineralization periods: Late Cretaceous, Eocene-Oligocene, Miocene, and Pliocene. The uranium mineralization demonstrates clear multi-phase characteristics, showing strong correlation with later geological events such as basin reworking. This coherence further validates the reliability of the obtained age data.

The factors leading to the coexistence of tin (Sn) and copper (Cu) mineralization within a single mineral system are ill-constrained. Sn and Cu isotopes can shed new light on metal sources and ore-forming processes, in turn allowing an unravelling of the mechanisms involved in Sn-Cu ore formation. This study utilizes Sn- and Cu-isotope data from the Dulong Sn-Cu-Zn-In deposit, South China, combined with quantitative geochemical modeling, to understand the processes by which Sn-Cu mineralization formed. Results show that the δ124Sn values of cassiterite (relative to National Institute of Standards and Technology Standard Reference Material 3161a) gradually decrease from the skarn and massive sulfide Sn ore with minor Cu to vein Cu-Sn ore (+1.59‰ to −1.95‰), suggesting that Sn-isotope fractionation is redox-controlled during progressive cassiterite precipitation. The δ65Cu values of chalcopyrite decrease from the skarn and massive sulfide ore and are attributed to fluid-rock interaction. The variable and lower Sn-isotope compositions (−1.95‰ to +0.34‰) of cassiterite and elevated δ65Cu values (+0.73‰ to +1.03‰) of chalcopyrite from vein ore are indicative of an additional pulse of magmatic (Cu-rich) fluids. These observations collectively indicate that progressive fluid-rock interaction, involving the leaching of Cu from the country rocks, accounts for the small-scale Cu mineralization found alongside Sn mineralization. In contrast, the addition of a pulse of Cu-rich fluids sourced from oxidized mafic magmas into coeval reduced felsic magmas led to the coexistence of large-scale Cu mineralization and large-scale Sn mineralization (e.g., San Rafael and Gejiu). The two distinct mineralizing episodes could further explain the different scale of Sn-Cu ore formation worldwide.

Yushui is a high-grade stratiform base metal deposit (291 Mt at 3.5% Cu, 4.3% Pb, 2.9% Zn, 112 g/t Ag) located at a sedimentary unconformity between Lower Carboniferous red sandstone and Upper Carboniferous dolostone and limestone in South China. The genesis of the Yushui deposit is much debated, with several models put forward, including Carboniferous (ca. 308 Ma) seafl oor hydrothermal formation, Triassic (ca. 223 Ma) epigenetic sediment-hosted stratiform Cu (SSC) mineralization, or Middle-Late Jurassic magmatic-hydrothermal genesis. The Yushui deposit is mainly composed of massive Cu mineralization, which is divided into a lower chalcopyrite-rich part and an upper galena-rich part, with vein-style orebodies cutting through the massive ore. We combine in situ sulfide S-Pb-Cu isotope and trace-element analysis with apatite in situ Nd isotope and trace-element analysis to unravel the ore genesis and metal sources of the Yushui deposit. The lower chalcopyrite-rich massive orebody contains variable amounts of heavy rare earth element (HREE) minerals and uraninite. The sulfides have a radiogenic Pb isotopic signature (208Pb/204Pb: 37.368-39.902; 207Pb/204Pb: 15.324-15.991; 206Pb/204Pb: 17.926-23.642), variable 634S values (-16.8%0 to-6.8%0), and a wide range of 665Cu values (-1.02%0 to +1.98%0). Radiometric data on uraninite and HREE minerals coexisting with chalcopyrite indicate a Triassic (ca. 223 Ma) SSC-style basinal brine origin. In contrast, the upper galena-rich part of the massive orebody and the vein-style orebody display a linear array of Pb isotopic ratios (208Pb/204Pb: 37.217-39.910; 207Pb/204Pb: 15.239-15.965; 206Pb/204Pb: 17.535-18.736), magmatic sulfur signatures, and markedly lower 665Cu values (down to-1.70%0). These isotopic characteristics are consistent with those of Middle-Late Jurassic Cu deposits and associated magmatic rocks in southeastern China, and coupled with the mineralization age of vein-style orebodies (ca. 163 Ma), thus indicate a magmatic-hydrothermal origin. Moreover, apatite Nd isotope and traceelement data indicate that the mineral system is genetically related to both Triassic basinal brines and Middle-Late Jurassic magmatichydrothermal fluids. Collectively, the data suggest that the ore-forming metals at Yushui were derived from Triassic oxidized basinal brines that leached the footwall sandstone and from Middle-Late Jurassic magmatichydrothermal fluids. There is no evidence for Carboniferous seafloor hydrothermal activity contributing Cu. Cu isotope mass-balance calculations suggest that magmatic-hydrothermal fluids likely contributed similar to 40% to 70% of the Cu in samples that exhibit mixed S-Cu isotope characteristics. Therefore, the Triassic SSC mineralization was enriched and overprinted by Middle-Late Jurassic magmatic-hydrothermal fluids. Our results indicate multiple metal sources were involved in generating the high-grade mineralization and that these findings might be applied to analogous deposits worldwide. The study highlights the advantages of coupling in situ Cu isotopes with traditional isotope and trace-element geochemistry for identifying metal sources in complex mineral systems.

Here we combine in-situ Sn and O isotope analysis of cassiterite from the multiphase granites of the Cretaceous Mikengshan Sn district, South China, to better constrain the key factors for tin ore genesis. Petrological imaging and trace-element compositions of distinct cassiterite types indicate that they crystallized from distinct pulses of exsolved magmatic fluids. Cassiterite oxygen isotope compositions imply that these fluids had variable contributions of meteoric water, up to 50 %. Corresponding Sn isotopes define a trend in which delta Sn-124 decreases from early to late cassiterite, indicating a redox-controlled mechanism for cassiterite formation. Furthermore, the variable but relatively elevated delta Sn-124 values in cassiterite are explained through a combination of vapor- and redoxcontrolled isotope fractionation. These findings suggest that post-magmatic meteoric-water incursion during progressive cooling of shallow granitic intrusions leads to oxidation. This process plays a key role in the redistribution of Sn and formation of large-scale deposits, indicating the timing of meteoric-water incursion as a key control on the scale of Sn mineralization.