Similar to garnet or olivine, pyroxene commonly occurs in diverse igneous and metamorphic rocks such as peridotites, eclogites, skarns and meteorites. Its oxygen isotope compositions can be analysed in situ using secondary ion mass spectrometry (SIMS) or an ion microprobe to help constrain the formation of rocks. However, unlike garnet and olivine, calibration of matrix-induced oxygen isotope (18O/16O) discrimination in pyroxene is not fully established, limiting its wide application in Earth and planetary sciences. This study provides preliminary matrix bias calibrations using 51 reference materials and/or samples of pyroxene, either low-Ca or high-Ca, including omphacite and jadeite, some (18) of which have also been analysed here by laser fluorination isotope ratio mass spectrometry. Both conventional offline (bias delta 18O vs. mole fractions of ferrosilite or jadeite endmembers: XFs or XJd) and online (bias delta 18O vs.56Fe16O/16O) calibration methods can be applicable, including the first matrix bias estimation for jadeitic clinopyroxene or omphacite as well as Mn-rich pyroxene. Investigation is needed for intermediate-Ca, particularly Ti-rich pyroxene.

Emergent continental crust is important for the evolution of Earth's surface system and the development of habitability, and it is apparent that early Archean cratons were locally emerged. However, it remains unresolved if the North China Craton, which preserves ancient (4.1-4.0 Ga) crustal remnants, had emergent continental crust during the early Archean. Here, we report geochronological and geochemical data on Paleo-Mesoarchean potassic granites in Eastern Hebei, within the North China Craton, to determine whether or not there was any early Archean exposed landmass in this craton. We constrain that the studied potassic granites formed at ca. 3.2 Ga, and their bulk-rock and zircon Hf isotopic geochemistry reveals that they were produced by anatexis of Paleoarchean tonalite-trondhjemite-granodiorite (TTG) crust. Their low zircon delta 18O values should have been inherited from their Paleoarchean TTG source, and 18O-depletion of this Paleoarchean TTG source was achieved through high-temperature hydrothermal alteration with the infiltration of isotopically light meteoric water into the shallow crust, prior to the ca. 3.2 Ga anatexis. The identification of Paleoarchean TTG crust altered by meteoric water in Eastern Hebei indicates the emergence of continental crust in the North China Craton during 3.6-3.2 Ga, and this Paleoarchean continental emergence could have been associated with magmatic underplating during mantle plume activities, which is also evidenced by the Paleoarchean enriched plume remnants in Eastern Hebei.

Variable isotope signatures of granite plutons have differently been ascribed to the generation and delivery of magmas from source to emplacement. Migmatite terranes are the key subject for tracing the genesis of granite plutons. Here, we present an integrated study of in situ U-Pb and Hf/Nd-O isotopes of zircon, apatite and titanite, along with whole-rock Hf-Nd isotope compositions, for migmatites from the North Dabie terrane. Anatectic zircons and/or titanites record two episodes of partial melting at ca. 140 and 125 Ma, respectively, probably registering the ages of fluid-present and biotite dehydration melting. The variable Hf-O isotope compositions of anatectic zircons in the mesosomes are suggested to mainly inherited from the diversity of the protolith zircons with a minor effect of external melt. There are also large Nd isotope variations in whole-rock samples and in apatite and titanite grains within the mesosomes. All these observations suggest that Hf-O-Nd isotope disequilibrium occurs within a single sample and even within individual grains during partial melting. In two leucosome samples, variable epsilon Hf(t) values of zircon and consistent epsilon Nd(t) values of apatite and/or titanite imply that the Hf isotope compositions in zircon are more sensitive to melt hybridization than the Nd isotope compositions of apatite and titanite. Magmatic zircons in two granitic dyke samples have a larger range of epsilon Hf(t) values than but a smaller range of delta 18O values compared to those in the nearby leucosomes. The decoupling of Hf-O isotope features implies that the inherited zircons play a decisive role in Hf isotopes, while the rock forming minerals involved in the melting reaction control the O isotopes. The apatite and/or titanite crystals in the granitic dykes have more variable epsilon Nd(t) values than those in the nearby leucosomes. It is inferred that the confluence of melts drained into the granitic dykes would have produced hybridized isotope compositions at a sub-grain scale. All the results suggest that the isotope heterogeneities of granites might be inherited mainly from their sources and have then been enhanced by the disequilibrium melting and hybridization of individual batches of magma during melt extraction and ascent. Our study highlights the value of combined study of zircon and LREE accessory minerals in migmatite terranes to track the processes from partial melting to pluton construction.

The origin of lunar water-whether inherited during its formation (endogenous) or delivered later (exogenous)-remains a fundamental question in planetary science. Previous studies relying on hydrous minerals or melt inclusions are often compromised by post-magmatic processes. Zircon, with robust physico-chemical stability, serves as a superior archive for preserving primary magmatic composition. Here, we report the first SIMS measurements of water content and hydrogen isotopes in a ca.similar to 4.38 Ga zircon from lunar meteorite NWA 10049. The zircon exhibits a distinct core-rim structure with anomalous H2O-delta D compositions: while the core maintains relatively homogeneous water content (735 to 1164 mu g/g) with elevated delta D (+1320 to +1882 parts per thousand), the rim displays variable and inversely correlated water content (879 to 4268 mu g/g) and delta D (+1879 to +250 parts per thousand). Such H2O-delta D systematics-combined with geochemical and petrological signatures-precludes magmatic degassing or post-magmatic alteration. Instead, we attribute these variations to magma mixing and the subsequent assimilation of heterogeneous exogenous hydrous materials within a massive impact melt sheet. Our findings provide key evidence for the accretion of meteoritic material into the lunar interior before 4.38 Ga, which delivered substantial amounts of water and likely played a critical role in shaping the composition and spatial distribution of volatiles in the early Moon.

Tungsten-bearing garnet is an important reservoir of W in oxidized W skarns. However, the degree to which W is remobilized from garnet into scheelite is unknown. In addition, differences between W skarns and Cu and Pb-Zn skarn fluids are poorly characterized. This study focuses on these issues and presents new backscattered electron (BSE) imaging, in situ major element, trace element concentration, and O isotope data for four types of garnets with different spatial locations and textures from the oxidized Fujiashan W skarn deposit. The Fujiashan garnets have Al-depleted cores and Al-enriched rims, reflecting temporal changes in fluid chemistry. In addition, garnet from proximal skarn areas is depleted in grossular (Grs = 2) and F (up to 0.10 wt%) in comparison to distal skarn garnet, which is enriched in grossular (Grs = 69) and F (up to 1.41 wt%). These spatial variations imply that F may have played a role in transporting Al to the distal parts of the skarns. Fujiashan andradite (Adr = 95) contains variable W (7.4-1780 ppm), indicating that the incorporation of W into garnet is controlled not just by Fe3+ abundance but also the availability of W in ore-forming fluids, dynamic external factors, and the concentration of Ti in garnet. Fujiashan garnet also contains relatively high W concentrations (up to 2221 ppm) and lacks evidence of re-equilibration during retrograde alteration. These relationships suggest that W-rich garnet is not the source for scheelite, potentially explaining the typical low W grades of oxidized W skarn deposits. In situ O isotopic values for Fujiashan garnet range from 4.2 to 7.4 parts per thousand, indicating that the garnet formed from a mixture of magmatic and metamorphic fluids, with a limited contribution from meteoric fluids. These fluid characteristics contrast with the significant meteoric water contribution recorded by garnet in Cu and Pb-Zn skarn systems, suggesting significant differences between these skarn systems and the processes involved in the generation of W skarn mineralization.

Lode gold deposits are among the most important types of gold ore deposits and are typically characterized by medium to low-temperature CO2-rich hydrothermal fluids. Consequently, they are commonly accompanied by the precipitation of abundant carbonates. However, the key role of CO2 in the transport and precipitation of gold remains unclear. Here, we discuss the genetic relationships between carbonate and gold associated with the Rongdu deposit, which is the largest gold deposit in the Wuhe mining district along the southern margin of the North China Craton (NCC). The C-O isotopic compositions of carbonates from different generations suggest that the CO2-rich hydrothermal fluids of the gold deposit were derived from magma. The precipitation of carbonates preceded the formation of high-grade gold ores, possibly as a result of large-scale fluid boiling. After the formation of ankerite (Ank1), the deposit underwent repeated magmatic hydrothermal fluid replenishment; however, external fluids were not introduced during this process. Moreover, the fluctuating anomalous Fe content in the carbonates suggests a competitive relationship for the incorporation of iron between sulfides and carbonates. The formation of carbonates hindered gold precipitation to some extent, but as an indicator of fluid boiling, it can serve as a prospecting indicator for gold in the area.

Garnet, commonly found in eclogites, granulites and skarns, is a geological "archival mineral". In situ microanalysis of garnet provides insights into rock formation, mineralisation, tectonic environments and the Earth's evolution. It has long been recognised that, due to the complex mineralogical chemistry of garnet, significant instrumental mass (or isotope) fractionation can occur when measuring its oxygen isotope ratio using secondary ion mass spectrometry (SIMS). However, calibration for matrix effects (or matrix-induced isotopic mass fractionation) has not been documented for certain endmembers, such as Ca-Ti garnet (CTG). This study, for the first time, measured 44 garnet reference materials and/or samples using SIMS and/or laser fluorination isotope ratio mass spectrometry to determine the matrix bias calibration for Ti-bearing garnets in addition to grossular, spessartine and andradite. Matrix biases as large as 5.7 parts per thousand were observed for garnets with XCTG = 0.4. Therefore, caution is required when performing SIMS oxygen isotope analysis of Ti-bearing garnets along with grossular, spessartine and andradite.

The succession from adakitic granite to peralkaline ultrapotassic rocks within collisional orogens provides valuable insights into the regional tectonic evolution. This study presents detailed petrography, zircon U-Pb ages, whole-rock geochemical data, and isotopic data from newly discovered adakitic granite and peralkaline ultrapotassic syenite rocks from the Kohistan Batholith in the Kohistan Island Arc (KIA), northern Pakistan. Zircon U-Pb dating indicates that the adakitic granite was emplaced at similar to 33.6 Ma, slightly earlier than the syenite at similar to 31.2 Ma. The adakitic granite is characterized by high contents of SiO2, K2O, Na2O, Al2O3, Sr, and Sr/Y ratios, as well as low MgO, Ni, and Cr, which likely reflects partial melting of water-fluxed mafic rocks in the thickened lower crust. The positive epsilon(Hf)(t) (avg. +3.6) and mantle-like delta O-18(zir) (avg. +5.3 parts per thousand) values of the adakitic granite suggest that the magma was derived from a thickened lower crustal mafic source, with no significant contribution from subducted sediments or upper crustal materials. The syenite is potassic to ultrapotassic/shoshonitic, characterized by high K2O contents (8.7-10.3 wt%) and K2O/Na2O ratios (2.2-3.2), and exhibits enrichment in LILE and LREE while being depleted in HFSE. Geochemical and Sr-Nd-Hf-O isotopic data indicate that the syenite likely derived from partial melting of the metasomatized lithospheric mantle beneath the thickened lower crust. The low Ba/La (avg. 7.4) and Hf/Sm (avg. 0.06) ratios, combined with isotopic modeling, reveal a 10-20 % contribution of subducted pelagic marine sediments to the mantle source of ultrapotassic peralkaline rocks in the KIA, which is linked to subduction of the earlier Tethyan Ocean crust. These geochemical results provide evidence that slab break-off occurred in the western Himalaya similar to 10 Ma after the India-KIA collision at similar to 45 Ma, and resulted in the emplacement of the adakitic and ultrapotassic rocks, similar to post-collisional alkaline magmatism observed elsewhere in the Tethys Orogenic Belt. These coeval but petrogenetically distinct magmas highlight the interplay of crustal and mantle heterogeneity during post-collisional evolution across the Tethyan Orogen. In addition, this study refines our understanding of the post-collisional alkaline magmatism in the KIA and provides a broader geodynamic model applicable to other similar convergent orogenic belts worldwide.

The Dinapigui Au (Cu) deposit is in the Sierra Madre Mountain Range of northeastern Luzon Island. As one of the few deposits in this region, its state of gold occurrence and precipitation mechanisms remain unclear. This study systematically examines alteration mineral assemblages, sulfur isotopes, and in-situ trace elements data for the Dinapigui deposit, in order to determine its deposit type, reveal the distribution and precipitation of gold, and provide valuable insights into the ore-forming processes. The Dinapigui deposit exhibits significant alunitization, kaolinitization, and silicification, indicative of a high-sulfidation epithermal deposit. Based on pyrite's zoning and morphological characteristics, it is classified into three types (Py1a, Py1b, Py2). In-situ elemental analysis of pyrite reveals that invisible gold in Py1b and Py2 primarily exists probably as lattice-bound Au+ and inclusions. The different types of pyrite samples exhibit variable Co/Ni (Py1a > Py1b approximate to Py2), Se/Tl (Py1a > Py1b approximate to Py2), and Se/Ni (Py1a > Py1b > Py2) ratios, varying As contents (Py1a < Py1b approximate to Py2), higher Cu contents, lower Tl/Pb (<0.02) and Sb/Pb (<0.4) ratios, and relatively consistent sulfur isotope compositions (5.2 parts per thousand to 10.6 parts per thousand).Precipitation and enrichment of gold in the Dinapigui deposit result from trace element fractionation during boiling, triggered by mixing meteoric water with ascending higher-temperature magmatic-hydrothermal fluids. By comparison with typical porphyry-epithermal systems in northwestern Luzon Island, this study offers clues for exploring deep-seated porphyry Cu-Au mineral resources in northeastern Luzon Island.

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.

Denudation histories are of great significance for constraining landscape evolution and underlying tectonic and climatic drivers. Rock exhumation toward the Earth's surface by denudation results in cooling of rocks, as recorded by mineral thermochronometers. Decades of global thermochronologic studies have produced a large database of rock temperature history models, which have been used as indices for denudation. However, quantitative conversion of the data set into denudation histories remains lacking. This study presents a new method for inverting rock cooling paths to produce denudation histories. The method solves the 1‐D thermal advection‐conduction equation and uses a Bayesian method for searching the denudation rate and geothermal parameter space. In addition to thermochronometric data used by other methods, inputs also include geothermal and geological constraints. We applied the method to explore the post‐orogenic denudation history of the Paleozoic–early Mesozoic Dabie orogen using a compilation of published and new rock cooling histories ( n = 158). The results show episodic differential Cretaceous (145‐110 Ma) and regional Late Cenozoic (10‐0 Ma) phases of denudation. Relatively high rates of Cretaceous denudation, which locally continued to the early Cenozoic, occurred along major normal faults in response to the retreat of westward subduction of the Paleo‐Pacific plate. Enhanced regional late Cenozoic denudation coincides with coeval intensification of the East Asian monsoon. The method demonstrated here will be useful for utilizing the big global thermochronologic data for quantifying spatiotemporal changes in denudation, to advance our understanding of the interactions among tectonics, climate, landscape evolution and preservation of ore deposits.

Luohe magnetite apatite deposit is the largest iron deposit in the Luzong volcanic basin in eastern China. Its early hydrothermal stage developed a diopside + magnetite + anhydrite assemblage, and developed a large amounts of anhydrite + pyrite in late stage. This provides a good research opportunity for the evolution process of hydrothermal fluid in sulfate rich IOA deposit (Fe-P-SO4 system). SHRIMP in situ oxygen isotope analysis showed the early fluid 518O is 9.73 %o - 10.76 %o, higher than that of magmatic water, indicating that the ore-forming hydrothermal fluid had equilibrated with Triassic marine carbonate and evaporite strata. Luohe has five alteration/mineralization stages; at the end of stage II 518Ofluid decreased (5.04 %o average), then increased in stage III (10.66 %o average), and decreased again from the end of stage III (-4.23 %o - 2.52 %o). Combining fluid inclusion study results, the high temperature, high salinity, and high 518O fluid deposited diopside, epidote, chlorite, magnetite, and apatite. The low temperature, low salinity, low 518O fluid is interpreted as meteoric water, and corresponds to the formation of anhydrite + pyrite. The addition of meteoric water led to a decrease in fluid temperature and Sigma SO42-/Sigma H2S ratio, resulting in the change from magnetite to pyrite stability. Pyrite and anhydrite sulfur isotopes show that SO42- was not reduced at stage II, and that 1/3 of the sulfur in the stage IV pyrite is derived from the reduction of SO42-. The precipitation of large amounts of anhydrite indicates that a significant portion of SO42- did not participate in the oxidation of Fe2+. Combining with the related research on other IOA deposits in the region, we have established an evaporite contamination model of the IOA system, propose that the incorporation of a large amount of evaporite during the magmatic stage or the initial fluid exsolution stage can facilitate the complete oxidation of Fe2+, leading to the formation of high-grade IOA-type ore deposits.

Mid-to late Neoproterozoic rifting-related magmatism along the northern margin of the South China Block provides key constraints on its paleogeographic position and geodynamic evolution within Rodinia and Gondwana reconstructions. New zircon U-Pb ages for volcanic and plutonic rocks from this region span ca. 740-640 Ma. The ca. 740 Ma Neixiang basalts exhibit intraplate-like geochemical features, with moderate positive epsilon Nd(t) (+0.9 to +3.2) and highly positive epsilon Hf(t) (+7.2 to +10.6), suggesting derivation from the melting of a depleted mantle source. Associated felsic volcanics and plutonic rocks from the Tuwushan region show A-type granite affinities, characterized by high 10,000 x Ga/Al and Fe/Mg ratios, high Zr-saturation temperatures (802-981 degrees C), negative epsilon Nd(t) (-2.1 to-1.9), moderately positive epsilon Hf(t) (+1.0 to +1.8), and low zircon delta 18O signatures (0.1%0-6.2%0). These features suggest an origin from the remelting of high-temperature, hydrothermally altered infracrustal materials in a low-pressure, high-temperature, extensional environment. The ca. 717-709 Ma Banbanshan-Zhenggou granitoids exhibit relatively high Na2O/ K2O ratios (1.02-1.56), moderate zircon saturation temperatures (760-780 degrees C), negative epsilon Nd(t) (-2.7 to-0.9), and slightly positive epsilon Hf(t) (+2.1 to +3.6). These characteristics are comparable to those of the Neixiang and Tuwushan A-type granitoids, suggesting derivation from a similar crustal source with a greater melting depth. The ca. 720 Ma Banbanshan and ca. 640 Ma Nianpangou mafic intrusions show enriched mid-oceanic-ridge basalt and oceanic-island basalt-like geochemical characteristics, which were likely derived from heterogeneous mantle sources in an extensional setting. The integrated geochemical and geochronological data for Neoproterozoic magmatic rocks suggests that variations in basaltic melt extraction depths coincide with the periodic changes in crustal thickness along the northern margin of the South China Block. These episodes of rifting magmatism and extension were likely induced by the periodic retreat of subduction along the north margin of the South China Block and ultimately initiated the breakup of Rodinia.

Porphyry copper (-gold) deposits in both arc and non-arc settings are hosted by oxidized magmatic rocks, but the exact mechanism by which the source magmas of these non-arc deposits become oxidized remains obscure. Through whole-rock geochemistry, mineral chemistry, and zircon isotopic analyses, here we show that the Neoproterozoic root of the Cretaceous Shaxi porphyry copper-gold deposit in the Jiangnan orogen is reduced and copper-sulfide rich, whereas the Cretaceous ore-forming magmas are oxidized. An oxidized mafic melt flushed the Neoproterozoic root zone, extracted copper and gold, and transported them to the upper crust where the Cretaceous Shaxi deposit formed. Evidence is recorded in growth zones of clinopyroxene, zircon, spinel, and plagioclase. Our results indicate that the relatively reduced, sulfide-enriched sub-continental lithospheric mantle or lower crust is essential but not sufficient for the formation of fertile non-arc porphyry magmas. Addition of a newer oxidized magma is crucial for the formation of this mineralization style.

The Foping dome in the South Qinling Belt is a typical gneiss dome that records a multi-stage tectonic evolution from syn-collisional orogenesis to post-orogenic extension. We conducted a detailed petrological and geochronological investigation to constrain the genesis of the dome and its tectonic implications. Field occurrence, mineral assemblage, and metamorphic grade were used to divide the rocks of the Foping dome into three tectonic units. Conventional thermobarometry and pseudosection modelling were used to estimate the P-T conditions of the three units, yielding 640-680 degrees C and 3.4-5.0 kbar for the upper unit, 690-740 degrees C and 4.8-7.8 kbar for the middle unit, and 770-800 degrees C and 5.1-6.8 kbar for the lower unit, corresponding to amphibolite to granulite facies metamorphism under a geothermal gradient of similar to 35 degrees C/km. The metamorphic patterns of three units reveal a metamorphic zonation characterized by decreasing metamorphic temperature from the centre to the periphery of the dome. Monazite SHRIMP U-Pb dating of metapelites yielded two major age clusters at 214-210 Ma and 207-197 Ma. The former cluster represents the timing of early regional progressive metamorphism induced by crustal thickening in a compressional setting, and the latter represents the timing of subsequent thermal metamorphism induced by magmatic diapirism in an extensional setting. The metamorphic zonation characteristics and ages of the Foping dome match with the pattern, nature, and ages of magmatism in this area, suggesting that the dome was formed by magmatic diapirism in a post-collisional extensional setting that was superimposed on the preceding progressive metamorphism associated with crustal thickening.

Debate continues over whether Cr-spinel in mantle peridotites is formed by partial melting or metasomatism. This first systematic report of SIMS oxygen isotope data for the constituent minerals, particularly Cr-spinel, in chromitites, dunites and harzburgites from the mantle sequence of the Lycian ophiolite (SW T & uuml;rkiye) provides compelling evidence for the latter. The delta 18OVSMOW values of Cr-spinel are relatively low across the three rock types, ranging from 2.00 parts per thousand to 4.81 parts per thousand in chromitites, 1.04 parts per thousand to 3.73 parts per thousand in dunites, and 1.89 parts per thousand to 4.87 parts per thousand in harzburgites. The delta 18O values of olivine are relatively higher and more uniform, decreasing from chromitites (5.25-6.68 parts per thousand) to dunites (4.99-5.65 parts per thousand) and harzburgites (4.90-5.44 parts per thousand). The delta 18O values of orthopyroxene and clinopyroxene in the harzburgites are comparable, ranging from 5.18 parts per thousand to 6.63 parts per thousand and 5.14 parts per thousand to 6.56 parts per thousand, respectively. Oxygen isotopic compositions of minerals exclude any influence from low-temperature alteration. Cr-spinel in the chromitites shows decreasing delta 18O with increasing Cr# and lower delta 18O when amphibole is present, suggesting that magma differentiation significantly influences Cr-spinel composition, while the presence of water can significantly lower the Cr-spinel delta 18O. The delta 18O values of olivine in chromitites increase with increasing Fo contents, indicating re-equilibration between olivine and Cr-spinel. In harzburgites, Cr-spinel shows a negative correlation between delta 18O and Cr#, similar to the characteristics of Cr-spinel in chromitites. The negative correlation between delta 18O values and Cr2O3 contents in clinopyroxene excludes the possibility of a partial melting origin. Petrographically, the Cr-spinel in harzburgites is commonly associated with clinopyroxene and contains various mineral inclusions, supporting the notion that Cr-spinel forms via metasomatism. The occurrence of olivine veins in orthopyroxene and the polymineralic (silicates + Cr-spinel) pseudomorphs of orthopyroxene are evidence for significant modifications. Therefore, mineral compositions of harzburgites in ophiolites should be attributed to metasomatism, while their refractory characteristics differ from those produced by refertilization. Notably, Cr-spinel oxygen isotopic compositions exhibit greater sensitivity to such metasomatism, contradicting beliefs of their high resistance to post-formation modification. Our study highlights the utility of oxygen isotopes in deciphering the complex petrogenetic history of mantle rocks, particularly in identifying metasomatic Cr-spinel and associated silicate minerals in peridotites.

Extremely positive S13C is found in calcite veins for the first time in the Huangqiao CO2-gas reservoir, eastern China, with 13C-enriched values as high as +16.9 %o. The calcite cannot be explained as a product of isotopic evaporation fractionation and/or microbial methanogenesis, given the high formation temperatures of 100-160 degrees C. Consequently, we propose a new model that attributes the extremely S13C enrichment to subsurface vapor-liquid CO2 phase separation. In the model, deep CO2 was initially dissolved in the pore water, and then phase-separation occurred when CO2 underwent supersaturation. Light 12CO2 preferentially escaped, leading to the enrichment of heavier 13CO2 in the pore water. During tectonic movements, the 13C-enriched pore water was injected into the gas reservoir strata and the high-S13C calcite veins were precipitated along fractures. Numerical simulation supports this hypothesis, suggesting that phase separation can induce considerable C isotope fractionation. At temperatures below 140 degrees C, S13C in fluid systems can rise to 17 %o through the phase separation of approximately 4.53 x 1011 m3 CO2, aligning with that of the current CO2 reserves in the Huangqiao CO2 gas field. Simultaneously, the S13C values of the escaped CO2 remain relatively stable and fall within the S13C range of the current-day CO2. Our results provide important insights into the isotopic fractionation in subsurface fluid systems.

Numerous Mesozoic porphyry-skarn Cu-Au deposits occur in the Middle-Lower Yangtze River metallogenic belt (MLYRB), but their genetically related intermediate-sulfidation (IS) epithermal deposits are rarely reported. The recently discovered Paodaoling deposit (> 35 t Au averaging 1.73 g/t) offers an opportunity to address this gap. The IS epithermal mineralization, structurally controlled by NE-trending faults, is hosted in late Mesozoic granodiorite-quartz diorite porphyries and Silurian sedimentary rocks. There are four vein stages: Stage I quartz-carbonate-polymetallic sulfide veins with minor sulfosalts of Cu-rich phases; Stage II quartz-sphalerite-galena-pyrite ± barite veins featuring various Cu-poor Pb-sulfosalts; Stage III fine-grained pyrite-marcasite-quartz-barite ± realgar ± orpiment veins; and Stage IV barren carbonate-barite ± quartz veins. Gold is invisible in arsenian pyrite and arsenopyrite. Prevalent illite-quartz-pyrite ± carbonate alteration is closely associated with mineralization. The trend in illite crystallinity (0.8–3.5) predicts a hot center at depth around the Paodaoling South Zone. The δ18Ofluid values equilibrated with quartz indicate a predominantly magmatic fluid source for early stages (I-II: 4.5 to 12.7‰, V-SMOW) and gradual meteoric water involvement in late stages (III-IV: 0.5 to 6.1‰). In-situ Rb-Sr dating of hydrothermal white mica coexisting with auriferous pyrite yields ages of 134–132 Ma, later than the host intrusions (148–141 Ma; zircon U-Pb) and main porphyry-skarn mineralization (150–135 Ma) in the MLYRB. The aforementioned lines of evidence support that mineralizing fluids were from a younger hidden intrusion. The preservation of Paodaoling implies potential to find other IS veins within or beneath the extensive early Cretaceous volcanic-sedimentary sequences in the MLYRB.

The western Yunnan tin belts in SW China and the southern Myanmar tin belt in SE Asia are traditionally thought to be part of the SE Asian tin metallogenic province. However, the tectonic setting of the Youjiang tin belt in SW China and its genetic relationship to the other tin belts are poorly documented. In this belt, the giant Gejiu and Dulong tin deposits are typical of skarn-type deposits and both contain contact and distal skarn orebodies. Tin ores of distal orebodies in these two deposits are composed of cassiterite, sulfide and calcite. In both deposits, most cassiterite grains from these ores are rich in Fe and W and depleted in Nb and Ta. They have 238U/206Pb ages between 81.4 and 84.1 Ma, similar to hosting granitic plutons. Two generations of cassiterite with distinctly different microtextures and trace elemental compositions can be recognized. The first generation (Cst-I) is compositionally and texturally homogeneous, but the second generation (Cst-II) displays distinctly oscillatory zoning. Cst-II contains Nb, W, and U lower, and Fe, Ta, Zr and chalcophile elements (Ga, Ge, In, and Sb) higher than Cst-I. These textural and compositional variations reflect the potential involvement of meteoric water in the magmatic-hydrothermal system. In this system, ore-forming fluids were evolved to more alkaline and oxidized to facilitate the precipitation of cassiterite. Our study indicates that these two deposits in the Youjiang tin belt have mineralization styles similar to those in the adjacent western Yunnan and southern Myanmar tin belts and all these tin belts belong to the SE Asian metallogenic provinces. A westward-younging trend of tin mineralization in these three belts can be explained by the rollback of the subducted Neo-Tethyan oceanic slab. This setting is different from the one related to the subduction of the Paleo-Pacific plate.