Search

The fluxes of metal cations and isotopes released by weathering of silicate rocks are crucial and a prerequisite for constraining geochemical fluxes to rivers and oceans. This study presents mineral and elemental compositions along with 87Sr/86Sr and δ88Sr data from a basaltic weathering regolith on Hainan Island, South China to elucidate Sr isotope fractionation and weathering fluxes. The 87Sr/86Sr ratios vary from 0.703936 to 0.706338 as a result of differential weathering of the minerals. δ88Sr values in the weathering regolith range from −0.29 to 0.37‰, with the majority of the weathering regolith having lower δ88Sr values than the parent rock. Sr is leached into the soil solution during plagioclase decomposition, while 86Sr is preferentially adsorbed on the surface of secondary minerals. As weathering progresses, smectite decomposes and kaolinite desorbs under weakly acidic conditions, releasing the previously adsorbed 86Sr into the soil solution. The differential weathering of kaolinite and smectite controls the δ88Sr values of the weathering regolith, with pH being an important determinant of isotope fractionation. Furthermore, Sr elemental fluxes (SrFlux) and Sr isotopic fluxes (δ88SrFlux) of this weathering regolith were calculated using a mass balance model, yielding mean values of 0.20 (mg cm−3 Myr−1) and 0.052 (‰ (mg cm−3 Myr−1)), respectively. The δ88SrFlux exhibits a nonlinear positive correlation with the Chemical Index of Alteration (CIA), indicating that enhanced weathering leads to significant stable Sr isotope fractionation at CIA values below 95%. Our research promotes the understanding of Sr recycling and the fractionation behavior of stable Sr isotopes during consecutive weathering. Plain Language Summary: The stable Sr isotopic composition is sensitive to continental weathering processes and offers insights into weathering mechanisms. However, the fractionation mechanism of stable Sr isotopes remains elusive. Significant stable Sr isotope fractionation was observed in a basaltic weathering regolith on Hainan Island, South China. Plagioclase decomposition releases Sr, with isotopically light Sr adsorbed onto the surfaces of secondary minerals during incipient weathering. Smectite decomposition and kaolinite desorption control the stable Sr isotopic composition of the weathering regolith during advanced weathering. The variable pH of the regolith is an important external control factor. We focus on modeling Sr isotopic fluxes and Sr elemental fluxes from weathering regolith. Our results show that within a certain range, an increase in weathering intensity leads to a nonlinear increase in weathering fluxes. The δ88Sr values of the loss component are consistent with those in silicate–dominated river catchments, suggesting that metal cations from the weathering of silicate rocks have a significant influence on the hydrochemical and isotopic composition of river waters in these catchments. Stable Sr isotope fractionation thus provides quantitative constraints on continental weathering fluxes. Key Points: Significant fractionation of stable Sr isotopes occurs with increasing weathering intensity at CIA values of less than 95%Secondary clay minerals control the variation in δ88Sr values in the weathering regolith, with 86Sr being preferentially adsorbed by kaoliniteThe model has been developed to simulate both Sr isotopic fluxes and Sr elemental fluxes from the weathering regolith [ABSTRACT FROM AUTHOR]

Hydrothermal alteration is crucial in the formation of many ore deposits, with potassium (K) mobilization and cycling being prevalent. Potassic metasomatism of wall rocks generally forms K-bearing minerals, such as hydrothermal feldspar and mica. However, determining the source and redistribution of K (and other elements transported by the same fluid) in hydrothermal systems is challenging. K isotopes offer a potential solution to this problem. This study presents new K isotope data from two K-rich alteration assemblages — K-feldspar and sericite-quartz-pyrite — in the Jiaodong gold province of China. The data covers a compositional range from unaltered granites to syn -magmatic potassic alteration (formation of K-feldspar) and post-magmatic syn -mineralization phyllic alteration (formation of sericite). Potassic alteration in granite correlates with significant K addition, whereas phyllic alteration of earlier phases of magmatic and hydrothermal K-feldspar resulted in K loss. K-feldspar altered granites display similar δ41K values (–0.55 to –0.42 ‰ for whole-rocks and –0.56 to –0.48 ‰ for K-feldspar separates) as unaltered granite (–0.52 to –0.47 ‰). The narrow δ41K range suggests that magmatic fluid exsolution and magmatic-hydrothermal alteration have a minor effect on δ41K of the altered rock. Phyllic alteration of K-feldspar altered precursor rock leads to K loss and elevated δ41K values ranging from –0.36 to –0.19 ‰ for whole-rocks and –0.34 to –0.17 ‰ for sericite mineral separates. As sericite preferentially incorporates 41K, sericite will have higher δ41K values than the precursor K-feldspar, whereas the fluids will have lower δ41K values. Our study demonstrates that hydrothermal alteration may affect the K isotope composition of altered rocks in several ways, contingent on the nature of the involved phases, making K isotopes a promising tool for studying hydrothermal alteration and associated mineralization. [ABSTRACT FROM AUTHOR]

The genesis of peralkaline granites has fundamental implications for understanding their source characters and tectonic settings, yet it remains highly controversial after decades of research. Two major challenges in studies of peralkaline granites are how the peralkaline magmas evolve and how to trace their magmatic evolution. Here we use K isotopes in granites from Zhoushan archipelago of southeast China to explore these two issues. The Zhoushan archipelago hosts two groups of Cretaceous high-silica granites, which are the peralkaline rocks (PAG) and the calc-alkaline rocks (CAG). The CAG rocks exhibit a small variation (δ41K = −0.54 ± 0.06 ‰ to −0.36 ± 0.06 ‰) in K isotopic compositions, in contrast to the larger variation for the PAG rocks (δ41K = −0.67 ± 0.07 ‰ to −0.27 ± 0.05 ‰). The PAG rocks show strong correlations between δ41K values and various whole-rock major elements (i.e., Al 2 O 3 , Na 2 O, and K 2 O contents), but these correlations are absent for the CAG rocks. We propose that the separation of Na-rich alkali-feldspar, rather than low-Na alkali-feldspar and/or plagioclase, controlled the K isotope variability in PAG. The alkali-feldspar in PAG is enriched in Na, among which the alkali-feldspar with Or (orthoclase; mol. %) <15 is characterized by high δ41K ranging from −0.34 ‰ to 0.36 ‰. Geochemical modeling demonstrates that 23–33 % fractional crystallization of such Na-rich alkali-feldspar is required to generate the geochemical trends observed in PAG. Those findings suggest that crystallization of Na-rich alkali-feldspars dominates the magma evolution for peralkaline magmatism, supporting strong fractional crystallization in high-silica peralkaline magma. K isotopes show promise to trace detailed magmatic processes and provide constraints on the generation of peralkaline granites. [ABSTRACT FROM AUTHOR]

The Xihuashan and Yaogangxian granitic plutons in South China comprise highly evolved multiphase Li‐rich granites and host quartz‐vein‐type tungsten deposits. The δ7Li values of Phase A (early stage), B (middle stage), and C (late stage) from the Xihuashan pluton are 1.0–1.2‰, 1.1–3.0‰, and 2.4–2.8‰ respectively, increasing through chemical evolution. The granites from the Yaogangxian pluton also display gradually enriched in heavy Li isotopes in a later stage, although systematically lighter than those of the Xihuashan pluton. In both plutons, the δ7Li shows good correlations with SiO2 and Li concentrations as well as Rb/Sr, Nb/Ta, and Zr/Hf ratios, indicating Li isotopic fractionation most likely caused by magmatic differentiation. In situ analyses show that the minerals of Xihuashan pluton record a continuous elemental spectrum, reflecting the results of progressive magmatic differentiation. The δ7Li values of quartz, feldspar, mica, and zircon all correlate well with the chemical evolutions of granitic magma, systematically elevated in Phases B and C relative to Phase A. The Li isotope data of the mineral separates further document that the enrichment of 7Li in the residual melt was most likely due to the equilibrium fractionation between the mineral and melts. The data are interpreted to reflect that intense magmatic differentiation was responsible for Li isotopic variations coupled with the enrichment in the Li, F, P, and rare metals in the late‐phase granites of the Xihuashan pluton. The lithium isotope behavior documented in this study provides new insights into magmatic differentiation and associated rare‐metal mineralization. Plain Language Summary: In the past, magmatic differentiation was thought not to produce resolvable Li isotopic fractionation based on studies of basaltic rocks. Overall, only sparse studies on Li isotopes of highly evolved granites have been reported, and thus possible isotope fractionation of Li isotopes during differentiation of felsic magma could have been neglected. In this study, we present evidence of Li isotope fractionation during the differentiation of granitic magma. The most evolved (late‐stage) rare‐metal‐rich granites are systematically enriched in heavier Li isotopes. The chemical and isotopic compositions of both bulk rocks and mineral separates (e.g., zircon and mica) indicate that equilibrium fractionation during fractional crystallization governs Li isotopic behavior and enriches heavier Li isotopes in the residual melts. Our quantitative modeling also supports the equilibrium fractionation between minerals and magma as the primary mechanism for the observed Li isotopic variations. Key Points: Large Li isotopic fractionations are observed in rare‐metal‐rich peraluminous granitesFractional crystallization governs Li isotopic behavior and enriches heavier Li isotopes in the highly evolved granitesLithium isotopes provide new insights into the granitic magmatic differentiation process and rare‐metal mineralization [ABSTRACT FROM AUTHOR]

Mg isotopic composition of river water is dominantly controlled by the dissolution of both silicate and carbonate sources and a series of biogeochemical processes. However, the relative importance of source and isotopic fractionation control at basin/global scale is poorly constrained. This study presents the Mg isotopic composition of river water and suspended load in river draining silicate rocks in the southeastern coastal region of China. The fractionation effect of silicate weathering on Mg isotopes is documented in both dissolved and solid phases. Mg isotopic composition of rivers draining silicate rocks exhibit ∼0.3‰ δ26Mg difference, the release of Mg from Mg‐rich minerals and formation of clays are the dominant processes controlling Mg isotopic composition of river water. The variation of Mg isotopic compositions of suspended load is closely related to the species of secondary clays (illite and chlorite); the fractionation direction during illite and chlorite formation contrasts, isotopically heavy Mg preferentially incorporates into illite while light Mg incorporates into chlorite. Furthermore, the negative correlation between 1/Mg and Mg isotopic compositions of river water indicates the Mg re‐distribution and isotope fractionation between weathering solutions and secondary clays during silicate weathering. Such isotope fractionation‐induced Mg isotope variations could be employed to estimate the contribution of Mg from silicate weathering at basin/continental scale. Key Points: The δ26Mg values of Southeast Coastal Rivers draining silicate rocks exhibit ∼0.3% difference due to isotope fractionationThere is a clay control on δ26Mg values of suspended loadThe Mg isotope fractionation is coupled with Mg re‐distribution during silicate weathering [ABSTRACT FROM AUTHOR]

The genesis of the giant Ag-Cu-Pb-Zn polymetallic mineralization in the northern Lanping basin, Southwest China, remains controversial. To address the sources of metals, a systematic study on Hg isotope compositions was conducted for the Cu-dominated deposit at Baiyangping and the Pb-Zn-dominated deposits at Fulongchang and Liziping. The Cu deposit shows positive Δ199Hg signatures (0.14 ± 0.13‰), in contrast to the Δ199Hg of the Pb-Zn deposits (− 0.09 ± 0.06‰). As positive Δ199Hg values are commonly observed in marine sediments and the Lanping Triassic marine sedimentary rocks show exclusively positive Δ199Hg signals (0.03 ± 0.07‰), the Hg in Cu ores was mainly sourced from the Triassic strata. The negative Δ199Hg signals observed in the Pb-Zn deposits, typical of terrestrial Hg, agree roughly with those of the Jurassic to Paleocene terrestrial sedimentary rocks (− 0.05 ± 0.08 ‰), indicating that the terrestrial strata provided the Hg in Pb-Zn ores. Compared to the source rocks, the Cu deposit shows isotopically lighter Hg enrichments (δ202Hg = − 2.30 ± 0.35‰), possibly resulting from fractionations induced by Hg2+ sorption, organic complexation, and precipitation of Hg-bearing sulfides. The Pb-Zn deposits show comparable or slightly heavier δ202Hg (− 0.56 ± 0.48‰); moreover, δ202Hg values of late-stage sulfides are higher than early-stage δ202Hg values, suggesting that the δ202Hg variation was primarily caused by sulfide precipitation. Thus, Hg isotope data indicate that separate hydrothermal events resulted in Cu and Pb-Zn mineralization. More importantly, this study reveals the great potential of Hg isotopes to discriminate sedimentary sources of metals for low-temperature hydrothermal deposits. [ABSTRACT FROM AUTHOR]

Rubidium is an active element on Earth, but whether and how its isotopes fractionate during geological processes are not known yet. In this study, we present data showing large variations in δ87Rb in bulk samples and individual mineral species from a granite weathering profile in South China as well as in surrounding stream water. The bulk samples show that the mobility of Rb (τ R b TiO 2 ) fluctuates dramatically from −42.0% to 259%, and δ87Rb values vary from −0.30 ± 0.13‰ in the unaltered bedrock to 0.04 ± 0.08‰ in the weathered saprolites. Significant isotopic variations exist among individual mineral species. In the parent rock, biotite, chlorite, K-feldspar and plagioclase have the δ87Rb values of −0.42‰, −0.30‰, −0.23‰ and +0.01‰, respectively. In weathered products, major Rb-bearing minerals are K-feldspar, illite and kaolinite. The δ87Rb values of K-feldspar range from −0.23‰ to 0.14‰, which are likely influenced by the secondary clay minerals adhered on the surface. Illite is the intermediate secondary mineral during biotite and K-feldspar decomposition into kaolinite. The δ87Rb values of illite vary from −0.28‰ to −0.10‰. As the final product of chemical weathering in this profile, kaolinite has the heaviest isotopic composition, with calculated δ87Rb values ranging from −0.07‰ to 0.20‰. Chemical weathering drives the δ87Rb values of saprolites to become heavier. Nearby stream water has the average δ87Rb value of −0.22‰, which is slightly heavier than the value of parent rock but lighter than the saprolites at the upper part of the profile. Our results demonstrate significant Rb isotope fractionation at the Earth's surface and that adsorption and desorption of clay minerals play a crucial role in triggering Rb isotope fractionation. [ABSTRACT FROM AUTHOR]

Microbial and hydrothermal venting activities on the seafloor are important for the formation of sediment-hosted stratiform sulfide (SHSS) deposits. Fe isotopic compositions are sensitive to both microbial and hydrothermal activities and may be used to investigate the formation of these deposits. However, to the best of our knowledge, no Fe isotopic studies have been conducted on SHSS deposits. In the Devonian Dajiangping SHSS-type pyrite deposit (389 Ma), South China, laminated pyrite ores were precipitated from exhalative hydrothermal fluids, whereas black shales were deposited during intervals with no exhalation. Pyrite grains from black shales mostly display positive δ56Fe -py (0.01–0.73‰), higher than marine sediments (ca. 0‰), due to pyrite deriving Fe from basinal shuttled Fe(III) (hydr-)oxides and slowly crystallizing in pores of sediments with equilibrium fractionation, except for negative δ56Fe -py (−0.17‰ to −0.24‰) of two samples caused by mixing of Fe from underlain laminated ores. The positive δ34S -py (3.50–24.5‰) of black shales reflect that sulfur of pyrite originated from quantitative reduction of sulfate in closed pores of sediments. In contrast, pyrite grains of laminated ores have negative δ56Fe -py (−0.60‰ to −0.21‰), which were not only inherited from the negative δ56Fe of hydrothermal fluids but also caused by kinetic fractionation during rapid precipitation of a pyrite precursor (FeS) in hydrothermal plumes. These ores have negative δ34S -py (−28.7‰ to −1.82‰), because H 2 S for pyrite mineralization was produced by bacterial sulfate reduction (BSR) in a sulfate-rich seawater column or shallow sediments. The δ56Fe -py values of laminated ores co-vary positively with δ34S -py and δ13C -carbonate along the ore stratigraphy, with δ13C -carbonate values ranging from −12.0‰ to −2.50‰. However, they correlate negatively with aluminum-normalized total organic carbon (TOC/Al 2 O 3). Organic carbon is thus considered to enhance the production of H 2 S by BSR activities, increase pyrite precipitation rates and promote the expression of kinetic fractionation of Fe isotopes. Intriguingly, in the ore units with vigorous hydrothermal venting activities, δ56Fe -py , δ34S -py and δ13C -carbonate values display a consistently increasing trend. Such results suggest that venting hydrothermal fluids significantly inhibited the H 2 S production of BSR, which then reduced the pyrite crystallization rate and decreased the kinetic fractionation of Fe isotopes. Our study reveals that the formation of SHSS deposits relies on H 2 S from microbial activities and metals from hydrothermal exhalation on the seafloor, but that vigorous exhalation can inhibit microbial activities and thus sulfide precipitation rates. The integrated use of Fe, S, and C isotopes can effectively elucidate these dynamic interactions between hydrothermal venting and microbial activities during the formation of SHSS deposits. [ABSTRACT FROM AUTHOR]

• Magnesium isotopic compositions are reported of magnetite in layered mafic intrusions for the first time. • Large Mg isotopic variation in magnetite is primarily governed by subsolidus processes. • Magnesium isotopic compositions of magnetite are related to mineral proportions in the cumulates. • Primitive Mg isotopic signature of coexisting Fe–Ti oxides indicates early crystallization in origin. To constrain the mechanisms governing the extremely large variations of Mg and Fe isotopes in magmatic Fe–Ti oxides in layered mafic intrusions, we investigate Mg isotopic compositions of magnetite, coupled with its chemical data and whole-rock major element and Sr-Nd isotope compositions from the Baima layered mafic intrusion in the Emeishan large igneous province, SW China. The Baima intrusion is mainly composed of magnetite-wehrlite and magnetite-troctolite (i.e., oxide-rich rocks) in the Lower Zone, and troctolite and gabbro (i.e., oxide-barren rocks) in the Middle and Upper Zones. Magnetite separates display large Mg isotopic variation, with δ26Mg ranging from −0.17 ± 0.06 to +0.58 ± 0.04‰ in the oxide-rich rocks and from −0.18 ± 0.06 to +0.98 ± 0.04‰ in the oxide-barren ones. The lack of correlation of δ26Mg with trace elements in magnetite and whole-rock Sr-Nd isotopic compositions indicates that the large Mg isotopic variation in magnetite was not produced by fractional crystallization, magma mixing, crustal contamination, and/or trapped liquid shift. Instead, equilibrium isotope fractionation induced by Mg–Fe re-equilibration between magnetite and ilmenite at different subsolidus temperatures controlled the Mg isotopic variation in the oxide-rich rocks; and kinetic isotope fractionation driven by Mg–Fe inter-diffusion between magnetite and olivine and/or clinopyroxene dominated the oxide-barren rocks. Both processes were primarily controlled by the assemblage and modal abundance of coexisting minerals to which magnetite adjoins. Overall, fractional crystallization and subsequent subsolidus diffusion played crucial roles in the genesis of the Fe–Ti oxides in the Baima intrusion. Our results also reveal widespread isotope disequilibrium between coexisting minerals in mafic magma chambers and suggest that Mg isotope geochemistry has a great potential to characterize the formation of Fe–Ti oxides in layered mafic intrusions. [ABSTRACT FROM AUTHOR]

Weathering of silicate rocks, particularly granitic rocks, generates the pedosphere that is of crucial importance in functioning terrestrial ecosystems. The pedosphere hosts large amounts of mercury (Hg). The source of Hg in granite weathering products is currently poorly constrained, however. Here we conducted Hg isotopic analyses on two weathering profiles developed on granitic plutons in Central and South China. Soils from both profiles show a downward decrease in Hg concentration but consistently negative ∆199Hg values. Mercury in precipitation, granites, and vegetation display positive, near-zero, and negative ∆199Hg values, respectively. The negative ∆199Hg values in the two weathering profiles are consistent with estimates of vegetation-derived Hg, supporting that Hg in weathering profiles are dominantly sourced from vegetation. Hg in vegetation is transported into surface soil firmly bonded to organic matter and migrates downwards weathering profiles. This study provides insights into the biogeochemical cycle of Hg in the granite-weathering crust and helps to explain the negative ∆199Hg values observed in terrestrial-derived sedimentary rocks. [ABSTRACT FROM AUTHOR]

• Stibnites from a large hydrothermal system reveal a large δ 123Sb range of −0.27 to +0.86‰. • Sulfide separation from the fluid causes significant Sb isotope fractionation, and the best estimated Sb isotope fractionation factor (α fluid-stibnite) is ~0.9994. • Estimated initial Sb isotope composition may constrain potential metal sources. • Sb isotopes can be used to fingerprint hydrothermal fluid flow directionality. In order to characterize antimony (Sb) isotope fractionation in hydrothermal systems, we present Sb isotope compositions of primary stibnite ores from a large Sb deposit in south China. A total number of 39 analyses reveals a large δ 123Sb range of −0.27 to +0.86‰, representing an up to 1.13‰ variation in this hydrothermal system. A gradual increase of Sb isotope ratios from the proximal to the distal parts was observed in stibnite ores. Rayleigh distillation models the systematic variation trend of the Sb isotope values, demonstrating that ore fluids are preferentially enriched in heavier Sb isotopes during the precipitation of isotopically light stibnite. In this way, we consider that separation of stibnite from a Sb-bearing fluid related to reaction kinetics as a cause for Sb isotope fractionation. The modeled data constrain a Sb isotope fractionation factor (α fluid-stibnite) between hydrothermal fluid and stibnite at approximately 0.9994. The model also constrains an initial Sb isotope value of ~0.45‰, which indicates metal sources in the basement rocks of the study area. Given that distal stibnites possess higher Sb isotopic values, Sb isotopes could be used to fingerprint hydrothermal fluid flow and unravel different processes in natural systems. [ABSTRACT FROM AUTHOR]

Isotope technology is widely used in geochemical mechanisms analysis; however, studies on the origin of pit lake water by isotopes in coal concentration areas in grassland are rare. In this study, 20 groups of water samples were collected, which were subjected to chemical analysis to determine the hydrogeochemical characteristics of pit lake water. The mechanisms of pit lake water formation and recharge-evaporation were ascertained through principal component analysis and the Rayleigh fractionation model. The results indicate that the phreatic water is least affected by evaporation, followed by confined water, surface water and pit lake water. The ionic composition of surface water, phreatic water and most of the confined water is mainly affected by leaching, some confined water can be recharged by surface or phreatic water; while the ionic composition of pit lake water is dominantly affected by evaporation (69.4 %) and is less affected by groundwater recharge (17.1 %) and human activities (11.5 %). The pit lake water is recharged by precipitation, phreatic water and the lateral runoff of confined water; however, the proportion of phreatic and confined water recharge is small. The evaporative loss of the pit lake water is 40-61 % of the initial water body.

Nitrate pollution in groundwater has become a global concern. One of the most important issues in controlling the nitrate pollution of groundwater is to identify the pollution source quickly and accurately. In this review, we firstly summarized the isotopic background values of potential sources of nitrate pollution in groundwater in 17 provinces (cities, autonomous regions) and 29 study areas in China, which could provide the fundamental database for subsequent research. Secondly, we reviewed the research progress of nitrate isotopes combined with multiple tracers for tracing nitrate in groundwater, and discussed their applicable conditions, advantages, and disadvantages. We found that halides and microorganisms combined with nitrate isotopes could accurately trace the pollution sources of domestic sewage, excrement and agricultural activities. The combination of Δ 17 O and nitrate isotopes could effectively distinguish the source of atmospheric deposition of nitrate in groundwater. The combination of groundwater age and nitrate isotopes could further determine the time scale of nitrate pollution. In addition, we summarized the application cases and compared the characteristics of mass balance mixing model, IsoSource model, Bayesian isotope mixing model, and EMMTE model for quantitative identification of nitrate pollution in groundwater. For the complexity and concealment of groundwater pollution sources, the coupling of nitrate isotopes with other chemical and biological tracing methods, as well as the application of nitrate isotope quantitative models, are effective tools for reliably identifying groundwater nitrate sources and transformation processes.

In order to investigate Ca isotope fractionation during crustal melting and magma differentiation, we report high-precision Ca isotopic data of 17 well-characterized granitoids from the Dabie orogen, China, and 22 mineral separates from two representative granitoids and nine local eclogites and garnet peridotites. Hornblende and plagioclase pairs have nearly constant Δ44/42Ca hbl–plg , ranging from +0.09 ± 0.04 (in 2SE if not specified) to +0.12 ± 0.03, which likely reflects equilibrium inter-mineral isotope fractionation at 660–760 °C according to the plagioclase–hornblende geothermometry. Δ44/42Ca grt–cpx of eclogites and garnet peridotites range from +0.06 ± 0.03 to +0.38 ± 0.04, consistent with a stronger Ca O bond in garnet than clinopyroxene. A grt–cpx (A grt - c p x = Δ 44 / 42 Ca grt - c p x × T 2 / 10 6 , T in Kelvin), representative of inter-mineral isotope fractionation corrected for temperature effect, decreases with increasing jadeite proportion in clinopyroxene, indicating a compositional control on equilibrium inter-mineral isotope fractionation. Eight I-type non-adakitic granitoids with CaO contents ranging from 1.59 wt.% to 6.96 wt.% have homogeneous Ca isotopic compositions with an average δ44/42Ca of +0.37 ± 0.03 (2SD, N = 8), identical to the mean value of the local basement (+0.36 ± 0.06, 2SD), indicating insignificant Ca isotope fractionation during crustal melting and magma differentiation at low pressures (e.g., without a role of garnet). According to the negligible isotope fractionation between hornblende and plagioclase ( Δ 44 / 42 Ca hbl - p l g = (+ 0.10 ± 0.02) × 10 6 / T 2) at the liquidus temperatures, the Ca isotope fractionations between melt and hornblende, plagioclase are very small. Nine low-Mg adakitic granitoids have δ44/42Ca ranging from +0.24 ± 0.02 to +0.38 ± 0.02. Given their low chemical index of alteration (<51), limited CaO variation (1.86–3.07 wt.%), and mineral assemblage similar to that of non-adakitic granitoids, δ44/42Ca variation in low-Mg adakitic samples cannot be explained by either weathering or fractional crystallization. δ44/42Ca is negatively correlated with (Dy/Yb) N , which most likely reflects the role of residual jadeite-rich clinopyroxene and garnet. Model calculation suggests that the lowest δ44/42Ca adakitic sample requires 30% garnet and 70% clinopyroxene (with 28% jadeite) in its residue, consistent with a local crust thickness greater than 50 km. Our results indicate that Ca isotopes can be used as a potential tool to constrain the magma generation depth, because garnet and jadeite-rich clinopyroxene tend to be rich in heavier Ca isotopes. Combined with literature data, the upper continent crust δ44/42Ca is estimated to be +0.35 ± 0.05 (2SE, 95% c.i.). [ABSTRACT FROM AUTHOR]

Iron (Fe) isotope fractionation could occur during crustal melting, which may contribute to the isotopic variations of granites. Our current knowledge on Fe isotope fractionation during crustal melting remains rare. Thirteen leucosomes, 9 melanosomes and 1 amphibolitic schollen in 11 migmatites from the Dabie orogen, Central China were measured to investigate Fe isotope fractionation during crustal anatexis. The melanosomes and amphibolitic schollen yield δ 56 Fe values from 0.018 ± 0.031‰ to 0.152 ± 0.027‰ with an average of 0.106‰. The leucosomes have δ 56 Fe values from 0.107 ± 0.035‰ to 0.512 ± 0.028‰, variably higher than their coexisting melanosomes by 0.00 ~ 0.36‰. The δ 56 Fe of leucosomes and melanosomes, as well as apparent isotope fractionation (Δ 56 Fe L-M ) between them, do not correlate with the abundance of crystalline carbonate, loss on ignition, and Th/U, indicating the insignificant effect of fluid components. High δ 56 Fe values of three leucosomes (≥ 0.34‰), giving large Δ 56 Fe L-M from 0.22 to 0.36‰, were likely produced by feldspar accumulation, evidenced by their high Eu*, low FeOt/Al 2 O 3 and high plagioclase abundance up to 50 vol%. Capture of peritectic amphiboles in another leucosome may explain its low Δ 56 Fe L-M ~ 0‰. After screening out these samples, 7 leucosome – melanosome pairs yield identical Δ 56 Fe L-M averaging 0.093 ± 0.056‰ (2SD, N = 7) within analytical uncertainties. No correlation between Δ 56 Fe L-M and Mg#, FeOt/Al 2 O 3 or TiO 2 /FeOt rules out the possibility that the fractionation observed here is produced by fractional crystallization and/or sub-solidus isotope re-equilibrium between leucosomes and melanosomes. Therefore, we suggest these consistent Δ 56 Fe L-M should record equilibrium Fe isotope fractionation during crustal anatexis producing these migmatites. The leucosomes and melanosomes have comparable Fe 3 + /ΣFe ~ 0.40, and Δ 56 Fe L-M approximates 0.07‰ at Fe 3 + / ΣFe leucosome Fe 3 + / ΣFe menalosome = 1. Fe isotope fractionation during crustal anatexis revealed here thus is not dominantly controlled by distribution of Fe 3 + and Fe 2 + , but by the difference in coordination number of iron between granitic melts and residual mafic minerals. The observation here argues that Fe isotope fractionation during crustal partial melting should also contribute to the previously revealed δ 56 Fe variation in high silica granitic rocks. [ABSTRACT FROM AUTHOR]

Because nitrogen isotopes (δ15N) of emitted nitric oxide (e-NO) from combustion-related sources (mainly fossil fuels and biomasses) remain unknown, the δ15N values of emitted N oxides (e-NO x , the sum of emitted N dioxide (e-NO 2) and e-NO) have long been employed in the isotopic tracing of nitrate (NO 3 −) in the atmosphere, causing substantial uncertainties in the isotope differentiation of source contributions. Here we measured concentrations and δ15N values of e-NO x and NO 3 − from the burning of four biomass materials (corn, wheat, poplar, and pine) in northern China, based on which we calculated concentrations and δ15N values of the corresponding e-NO, e-NO 2 , initially produced NO (i-NO) and NO 2 (i-NO 2) before emissions and oxidizations. We found that 58 ± 12% of i-NO emitted as e-NO and 42 ± 10% was oxidized to i-NO 2 , 77 ± 7% of i-NO 2 emitted as e-NO 2 and 23 ± 3% was oxidized to NO 3 −, and the mean δ15N e-NO (−10.2 ± 6.0‰) was distinctly lower than the δ15N e-NOx (−2.3 ± 3.9‰) and δ15N e-NO2 (11.8 ± 3.6‰). Based on the δ15N i – NO (−0.2 ± 3.2‰) and δ15N i – NO2 (13.5 ± 3.8‰), we obtained the theoretical N isotope fractionations for the transformations from i-NO to i-NO 2 (23.8 ± 14.3‰) and from i-NO 2 to NO 3 − (8.0 ± 11.3‰) during biomass burning. These results filled the long-standing knowledge gap of species-specific δ15N signatures of NO x produced by biomass burning, expanded the understanding of N isotope fractionations of N oxidization under burning processes, and provided critical parameters for isotope source apportionment of NO x and NO 3 − in the atmosphere. [Display omitted] • δ15N of nitrate and NO x from biomass burning were measured in northern China. • δ15N of nitrate and NO x averaged 19.5 ± 4.1‰ and −2.3 ± 3.9‰, respectively. • δ15N of NO and NO 2 were first calculated as −10.2 ± 6.0‰ and 11.8 ± 3.6‰, respectively. • N isotope fractionations of the NO oxidation to NO 2 averaged 23.8 ± 14.3‰. • N isotope fractionations of the NO 2 oxidation to nitrate averaged 8.0 ± 11.3‰. [ABSTRACT FROM AUTHOR]

The Taihu (Tai lake) region is one of the most economically prospering areas of China. Due to its location within this district of high anthropogenic activities, Taihu represents a drastic example of water pollution with nutrients (nitrogen, phosphate), organic contaminants and heavy metals. High nutrient levels combined with very shallow water create large eutrophication problems, threatening the drinking water supply of the surrounding cities. Within the international research project SIGN (SinoGerman Water Supply Network, ), funded by the German Federal Ministry of Education and Research (BMBF), a powerful consortium of fifteen German partners is working on the overall aim of assuring good water quality from the source to the tap by taking the whole water cycle into account: The diverse research topics range from future proof strategies for urban catchment, innovative monitoring and early warning approaches for lake and drinking water, control and use of biological degradation processes, efficient water treatment technologies, adapted water distribution up to promoting sector policy by good governance. The implementation in China is warranted, since the leading Chinese research institutes as well as the most important local stakeholders, e.g. water suppliers, are involved. [ABSTRACT FROM AUTHOR]

The shift in Sr stable isotope ratios (88Sr/86Sr, reported as δ88/86Sr values) in weathering systems provides insights into the transformation of the binding form of Sr between the dissolved and solid phases. However, the mechanism behind the fractionation of Sr stable isotopes during chemical weathering remains poorly constrained. We present mineral and elemental compositions along with the radiogenic Sr isotope ratios (87Sr/86Sr) and δ88/86Sr values from a ∼ 1 m deep horizontal spheroidal weathering profile of granodiorite in southeast China. Strontium was markedly lost during granodiorite weathering and a large amount of plagioclase and hornblende was decomposed in saprolite relative to the parent rock. The 87Sr/86Sr ratios substantially increased from 0.708704 to 0.712532 and δ88/86Sr values sharply decreased from 0.29‰ to −0.12‰ in the corestone-near saprolite as the weathering intensity increased. However, these values were rather constant in the corestone-distant saprolite, albeit with a large increase in the abundance of kaolinite. The Sr in the different chemical fractions indicates that the silicate components dominate the Sr isotopic composition in bulk rock and saprolite samples. Differential weathering of minerals is mainly responsible for the Sr stable isotopic composition of the corestone-near saprolite, while the lower δ88/86Sr values of the corestone-distant saprolite point to the possibility of preferential incorporation of lighter Sr isotopes into the structural sites of secondary clay minerals. In contrast, δ88/86Sr values of the exchangeable and reducible fractions (0.11‰–0.48‰) were more positive than those of the corresponding bulk samples because they were able to inherit the isotopic signatures of the weathered minerals. Further, an acid leaching experiment on the granodioritic parent rock reveals that mineral weathering reactions dominated the Sr isotope composition of the dissolved phase. The substantially higher δ88/86Sr values in the leachates relative to those in the residual solids (Δ88/86Sr leachate-residue = 0.14‰–0.42‰) are consistent with the fact that isotopically heavier Sr in the dissolved load of rivers is mostly set by differential weathering of minerals (such as biotite and plagioclase). Combined with classic indices of chemical weathering (such as the chemical depletion fraction (CDF) and chemical index of alteration (CIA)), we suggest that Sr stable isotopes offer a promising proxy of the intensity of silicate weathering in saprolite studies in which isotope fractionation caused by biological cycling is negligible. • Silicate component dominates the bulk radiogenic and Sr stable isotope behaviors. • Decomposing primary minerals controls δ88/86Sr value in early weathering stages. • Structural incorporation of 86Sr in clays is most influential during advanced stages. • δ88/86Sr value is a promising indicator of silicate weathering intensity. [ABSTRACT FROM AUTHOR]

Cadmium (Cd) isotope fractionation patterns within soil profiles and the underlying mechanisms remain unclear and poorly documented. Here, Cd concentrations and isotope compositions of metal ore, surface soils and soil profile samples around a lead-zinc mine in southwest China were determined, and the relationships between soil properties and Cd isotope fractionation within the soil profiles were investigated. Cadmium concentrations of eleven surface soil samples were 0.49–66.1 mg kg−1 and the samples with high Cd concentrations had Cd isotope compositions similar to the metal ore (δ114/110Cd = 0.02‰), indicating that mining activity was the main Cd source at the study areas. Within three soil profiles with different Cd pollution levels the δ114/110Cd values gradually increased with increasing depth from 0 to 40 cm (Δ114/110Cd = 0.08–0.18‰), reaching a maximum at 30–40 cm depth, and then remained fairly constant or decreased with increasing soil depth below 40 cm. Soil δ114/110Cd values were negatively correlated with free iron and manganese oxides contents, which decreased at 0–40 cm depth then increased below 40 cm. This indicates that light Cd isotopes within 0–40 cm depth preferentially migrated downward with free iron and manganese oxides, leaving the soils at a depth of 0–40 cm enriched in heavy Cd isotopes. At 40–90 cm depth the preferential retention of heavy Cd isotopes by hydroxides may be responsible for the gradual decrease in δ114/110Cd values with increasing soil depth. These observations demonstrate that the vertical migration of Cd can induce detectable isotope fractionation within soil profiles and alter the δ114/110Cd values including those of the surface soils. Our study highlights the need to consider Cd mobilization and transport in soil profiles when tracing metal sources using isotope techniques. [Display omitted] • Cd became isotopically heavier at 0–40 cm depth along the agricultural soil profiles. • The δ114/110Cd value was significantly negatively correlated with Fe and Mn oxides. • Cd migration should be considered when using Cd isotopes to trace metal sources. [ABSTRACT FROM AUTHOR]

[Display omitted] • The shale gas resource potential of the Longmaxi Formation was evaluated by using mud gas isotope logging technology. • The reservoir properties of shale were evaluated based on gas isotope fractionation effects. • The shale gas in the Changning area belongs to late kerogen cracking gas. • The lower part of the Longmaxi Formation has a better shale gas exploration potential. The Longmaxi Formation in the Sichuan Basin is one of the most important shale gas producing formations in China. Previous studies of shale gas were mostly carried out on based on laboratory analyses and did not provide effective guidelines for shale gas exploration. In this paper, we present a large amount of carbon isotopic data from mud gas isotope logging and rock-cutting headspace gas in wellsites. The δ13C 1 values showed a significant decrease at the bottom of the Longmaxi Formation. The δ13C 1 and δ13C 2 values in the Changning area were observed to be heavier than those in the Weiyuan and Jiaoshiba areas. The second half of the N216H27-3 horizontal well had obvious outgassing and carbon isotope fractionation effects. This indicates that the bottom of the Longmaxi Formation has better shale gas exploration potential. The shale gas of the Longmaxi Formation in the Changning area belongs to late kerogen cracking gas, where exploration prospects are poorer than those in the Weiyuan and Jiaoshiba areas. There were more oil cracking gas resources and better reservoir conditions at the end of the N216H27-3 horizontal well; therefore, drilling should be continued at this site. [ABSTRACT FROM AUTHOR]

• F. tikoua had significant differences in δ13C and δ15N among different sites • Environmental played an essential role in the population variations inδ13C and δ15N of F. tikoua • A strong stable isotope coupling between F. tikoua and its pollinators The interactions between figs and their pollinators are among the most specialized examples of mutualism between plants and insects. Based on their life-histories and obligate mutualism, it is reasonable to expect an environmentally-dependent trophic cascade exists between figs and their pollinators. Understanding the mechanisms involved in soil-plant-pollinator trophic cascade relationships will advance our knowledge of how obligate mutualist systems respond to environmental change. We sampled rhizosphere soil, leaves, syconia, and fig wasps (Ceratosolen) of a dioecious prostrate shrub, Ficus tikoua from southwestern China, and measured their carbon (δ 13C) and nitrogen (δ 15N) stable isotope ratios. The mean leaves δ 13C values of F. tikoua were -28.86 ± 1.24%, which suggests it is a typical C 3 plant. We detected a significant difference for δ 13C and δ 15N values of F. tikoua among different populations related to environmental factors such as longitude, altitude, and annual average temperature. The δ 13C values showed a significantly positive correlation between fig wasps and host. The δ 15N in fig wasps were 3.4% higher than those in F. tikoua , and were positively correlated with δ 15N in leaves. These results indicated that fig wasps were feeding on F. tikoua. Moreover, the δ 15N values among soil, leaves, and syconia showed significantly positive correlations, indicating the trophic linkage among soil-plant-pollinators. In summary, we noted that environmental factors shaped population variations in stable isotopic patterns of F. tikoua , and such variations drove stable isotopic signatures of its specific pollinators by trophic cascade. Future environmental changes could potentially impact the maintenance and stability of this highly specific pollination system of figs and fig wasps. [ABSTRACT FROM AUTHOR]

It was previously believed that ammonia (NH 3 ) has a short residence time in the atmosphere and cannot be transported far from its sources. In late March, however, this study observed a severe NH 3 episode in urban Beijing when fertilizer was intensively applied on the North China Plain, with the highest hourly concentrations of 66.9 μg m -3 throughout the year. The stable nitrogen isotopic composition of NH 3 (δ 15 N-NH 3 ) during this episode (-37.0 to -20.0‰) fell in the range of endmembers of fertilizer and livestock, suggesting the long-range transport of NH 3 from agricultural to urban regions. Based on a Bayesian isotope mixing model, the contribution of agriculture (fertilization) to urban NH 3 concentrations was apportioned as 43.5% (26.0%) on polluted days. However, these contributions were reduced to 29.1% (12.8%) when nitrogen isotope fractionation between NH 3 and ammonium was considered. In contrast to the limited contribution of agricultural sources, we found that nonagricultural emissions, particularly vehicles, dominate the source of NH 3 in urban Beijing, even during the fertilization period. This finding indicated that nonagricultural sources should be considered when designing a control strategy for NH 3 to reduce haze pollution in the urban atmosphere., Competing Interests: Declaration of competing interest The authors declare no competing financial interest., (Copyright © 2022 Elsevier B.V. All rights reserved.)

Fine particulate matter (PM 2.5 ) significantly impacts global air quality and human health due to its smaller particle size and larger specific surface area. Nitrogen and carbon aerosols, as the main components of PM 2.5 , play key roles in air pollution. This study identified the sources and seasonal variation of nitrogen and carbon aerosols in PM 2.5 in typical cities of Zhejiang. The annual average PM 2.5 concentrations of Hangzhou (HZ), Ningbo (NB), and Huzhou (HUZ) were 39.8 ± 19.1 μg m -‍3 , 40.0 ± 21.5 μg m -3 , and 50.1 ± 22.6 μg m -3 , respectively, which exceeded the Chinese air quality limit of 35.0 μg m -3 . The results showed that the concentrations of nitrogen aerosols (NO 3 - and NH 4 + ) in water-soluble inorganic ions were higher at 9.6 ± 4.6 μg m -3 , 9.0 ± 4.5 μg m -3 and 11.5 ± 5.4 μg m -3 in HZ, NB and HUZ, respectively, especially in winter, accounting for over 60% of the total. The annual average δ 15 N values of PM 2.5 were 6.2 ± 1.9‰, 6.4 ± 2.2‰ and 6.7 ± 1.9‰ in HZ, NB and HZ, respectively; the δ 15 N values in winter were relatively low. A Bayesian isotopic mixing model was employed to analyse the sources of nitrogen aerosols in winter; the results showed that nitrogen concentration was mainly affected by NH 3 and NO X emitted by motor vehicle exhaust, coal combustion, biomass combustion, biogenic soil emissions, animal wastes and ocean evaporation (NB). In addition, the carbon component analysis of PM 2.5 showed that the annual average mass concentration of TC accounted for 18.7%, 16.4% and 20.1% of PM 2.5 in HZ, HUZ and NB, respectively. The same isotope model was used to analyse the sources of carbon aerosols; the results showed that carbon aerosols were mainly affected by the sources of motor vehicle exhaust, coal combustion, biomass combustion and dust. In the PM 2.5 in Zhejiang, the most contributory sources of nitrogenous aerosols and carbon aerosols were motor vehicle exhaust sources., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

Abstract: Fe isotope compositions of mineral separates and bulk samples from Xinqiao Cu–S–Fe–Au skarn type deposit were investigated. An overall variation in δ57Fe values from −1.22‰ to +0.73‰ has been observed, which shows some regularity. The δ57Fe values of endoskarn and the earliest formed Fe-mineral phase magnetite are ca.1.2‰ and ca. 0.3‰ lower, respectively, relative to the quartz–monzodiorite stock, indicating that fluid exsolved from the stock is enriched in light Fe isotopes. Moreover, spatial and temporal variations in δ57Fe values are observed, which suggest iron isotope fractionation during fluid evolution. Precipitation of Fe-bearing minerals results in the Fe isotope composition of residual fluids evolving with time. Precipitation of Fe (III) minerals incorporating heavy iron isotopes preferentially leaves the remaining fluid enriched in light isotopes, while precipitation of Fe (II) minerals preferentially taking-up light iron isotopes, and makes the Fe isotopic composition of the fluid progressively heavier. The regularity of Fe isotope variations occurred during fluid exsolution and evolution indicates that the dominant Fe source of Xinqiao deposit is magmatic. Overall, this study demonstrates that Fe isotope composition has great potential in unraveling ore-forming processes, as well as constraining the metal sources of ore deposits. [Copyright &y& Elsevier]

• Accurate GIP content was obtained based on the pressure-holding coring technique. • The accuracy of traditional methods and the CIF model were compared and verified. • The CIF model can provide the most accurate estimation results of GIP content. • Carbon isotope fractionation during complete degassing was observed and characterized. • △ δ 13C 1 (fractionation amplitude) was demonstrated to indicate gas-adsorbed ratio. Gas-in-place (GIP) and gas-adsorbed ratio are crucial parameters for resource potential assessment and production strategy optimization. Although various methods have been proposed to evaluate these two parameters, none have been widely recognized due to a lack of convincing comparison and validation. In this study, we established a GIP content calculation method by summing five gas components in the pressure-holding coring (PHC) technique: lost gas during retrieving, extracted gas during depressurization, lost gas during surface exposure, degassed gas, and residual gas. The GIP content of the four pressure-holding shale cores retrieved from the Longmaxi Formation of Lu-2 well, Sichuan Basin, China, ranges from 6.46 cm3/g to 10.58 cm3/g, which is used for comparing and verifying theoretical methods. The comparison results show that traditional methods, including the USBM, polynomial fit, ACF, and MCF methods, failed to accurately evaluate GIP content due to their defects in the theoretical foundation and boundary conditions settings. The carbon isotope fractionation (CIF) model derived on a rigorous theoretical basis and equipped with variable boundary conditions achieves the highest accuracy when evaluating the GIP content. Furthermore, the CIF model can determine the gas-adsorbed ratio, another critical parameter that traditional methods cannot obtain; the calculated gas-adsorbed ratio of five shale samples from the Lu-2 well is between 11.15% and 24.56%, with an average of 17.10%. With the help of the CIF model, we confirmed the general pattern of isotope fractionation during shale gas degassing and discussed the limitation and potential of two empirical parameters, δ 13C 1 of the first sample and △ δ 13C 1 (the difference in δ 13C 1 value between the last and first sample), in indicating the adsorbed gas content. [ABSTRACT FROM AUTHOR]

Abstract: Samples from Archean high-grade metamorphic terranes in China and granulite-facies xenoliths from Australia (Chudleigh and McBride suites) and China (Hannuoba suite) have been analyzed to assess the Li concentrations and isotopic compositions of the middle and lower continental crust, respectively. Thirty composite samples from metamorphic terranes, including tonalite–trondjhemite–granodiorite (TTG) gneisses, amphibolites and felsic to mafic granulites, show a large variation in Li concentrations (5–33 ppm) but a relatively narrow range in δ 7Li values, from +1.7 to +7.5 with a mean of +4.0±1.4 (1σ). These results suggest that the middle continental crust is relatively homogenous in Li isotopic composition and indistinguishable from the upper mantle. This may be a primary feature or may reflect homogenization of Li isotopes during exhumation of the metamorphic terranes. In contrast, Li isotopic compositions of granulite xenoliths from the lower crust vary significantly, with δ 7Li ranging from −17.9 to +15.7. δ 7Li of minerals also shows a very large spread from −17.6 to +16.7 for plagioclases and −14.6 to +12.7 for pyroxenes. Large Li isotopic variations exist between plagioclase and pyroxene, with pyroxenes (13 out of 14) isotopically equal to or lighter than coexisting plagioclases. Lithium concentrations of granulite xenoliths also vary widely (0.5 to 21 ppm) and are, on average, lower than those of terranes (5±4 vs. 13±6 ppm respectively, 1σ), consistent with a higher proportion of mafic lithologies and a higher metamorphic grade for the xenoliths. Pyroxene separates from granulite xenoliths have equal or significantly greater Li than coexisting plagioclase. These large Li isotopic variations between minerals and in whole-rock granulite xenoliths mostly reflect diffusion-driven kinetic isotopic fractionation during the interactions of xenoliths with host magma. Only those xenoliths that reach inter-mineral isotopic equilibria are likely to preserve the initial Li isotopic signatures of the lower crust. Eight such equilibrated samples have δ 7Li from −14 to +14.3, with a concentration weighted average of +2.5, which is our best estimate of the average δ 7Li of the lower continental crust. The substantial isotopic heterogeneity of the lower crust may reflect the combined effects of isotopic fractionation during granulite-facies metamorphism, diffusion-driven isotopic fractionation during igneous intrusion and variable protolith compositions. Consistent with previous B elemental and O isotopic studies, the Li isotopic heterogeneity in the lower crust indicates that pervasive fluid migration and equilibration have not occurred. Using all data for granulite xenoliths, the Li concentration of the lower crust is estimated to be ∼8 ppm. Together with previous estimates of Li concentration in the upper and middle crust, the average Li concentration of the bulk continental crust is estimated to be 18 ppm, which is similar to previous estimates. The average Li isotopic composition of the continental crust is estimated to be +1.2, which is isotopically lighter than upper mantle and may reflect the loss of isotopically heavy Li from the continents during weathering and metamorphic dehydration. [Copyright &y& Elsevier]

Gas-in-place (GIP) content and gas-adsorbed ratio are crucial parameters for resource potential assessment, sweet spot prediction, and production strategy optimization. Various methods have been proposed from different perspectives to evaluate these parameters; however, none have been widely accepted. The carbon isotope fractionation (CIF) model provides a powerful tool for clarifying the mechanism of isotopic fractionation during natural gas transport and evaluating key parameters of unconventional gas resources. In this study, five shale samples from the Longmaxi Formation in the Jiaoshiba area, Sichuan Basin, China, were subjected to canister degassing experiments to investigate degassing behaviors and their variations in the isotopic compositions of methane (δ 13C 1), ethane (δ 13C 2), and carbon dioxide (δ 13C CO2). The results showed that the degassing volume (rate) and isotopic fractionation amplitude (slope) of methane positively correlate with the TOC content after controlling the lost time. The released ethane was more enriched in 12C than methane and did not fractionate during degassing, resulting in an increased isotope reversal. The δ 13C CO2 exhibited complex fractionation features corresponding to later stages (stages III and IV) in the general pattern. Furthermore, we evaluated the GIP content, gas-adsorbed ratio, and in-situ Langmuir parameters (V L and P L) using the CIF model. The calculated GIP content ranges from 3.48 cm3/g to 7.29 cm3/g with an average of 5.32 cm3/g, and the gas-adsorbed ratio is between 13.87% ~ 43.75% (average 30.79%). The optimized V L and P L show an excellent correlation with TOC content, demonstrating the great advantage of the CIF model in evaluating Langmuir parameters. Compared with the CIF model, the traditional USBM method underestimated shale gas resources in the Jiaoshiba area by 2% ~ 22%, with an average of 11.5%. • Degassing volume and fractionation amplitude/slope are controlled by TOC content. • CIF model is a powerful tool for evaluating GIP content and gas-adsorbed ratio. • V L and P L calculated by the CIF model positively correlated with TOC content. • The contribution ratio of adsorbed/free gas dominates the apparent fractionation. • USBM method underestimates the shale gas resource potential in the Jiaoshiba area. [ABSTRACT FROM AUTHOR]

We describe and thoroughly evaluate a method for 13 C analysis in different fractions of carbonaceous aerosols, especially elemental carbon (EC). This method combines a Sunset thermal-optical analyzer and an isotope ratio mass spectrometer (IRMS) via a custom-built automated separation, purification, and injection system. Organic carbon (OC), EC, and other specific fractions from aerosol filter samples can be separated and analyzed automatically for 13 C based on thermal-optical protocols (EUSAAR&#95;2 in this study) at sub-μgC levels. The main challenges in isolating EC for 13 C analysis are the possible artifacts during OC/EC separation, including the premature loss of EC and the formation of pyrolyzed OC (pOC) that is difficult to separate from EC. Since those artifacts can be accompanied with isotope fractionation, their influence on the stable isotopic composition of EC was comprehensively investigated with various test compounds. The results show that the thermal-optical method is relatively successful in OC/EC separation for 13 C analysis. The method was further tested on real aerosols samples. For biomass-burning source samples, (partial) inclusion of pOC into EC has negligible influence on the 13 C signature of EC. However, for ambient samples, the influence of pOC on the 13 C signature of EC can be significant, if it is not well separated from EC, which is true for many current methods for measuring 13 C on EC. A case study in Xi'an, China, where pOC is enriched in 13 C compared to EC, shows that this can lead to an overestimate of coal and an underestimate of traffic emissions in isotope-based source apportionment., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2021 Elsevier B.V. All rights reserved.)

Residential coal combustion (RCC) is a major source of atmospheric mercury (Hg) in rural areas of China, but little is known about the isotope signatures of Hg from this source. In the present study, the isotope compositions of speciated Hg (Hg0, Hg2+, and Hgp) in flue gas emitted from RCC were investigated in two important coal-producing areas (Xingren (XR) and Jinsha (JS)) of Guizhou Province, Southwest China. The total Hg concentration in discharged flue gas is in the range of 1.80–9.65 μg/m3 at the two sites, and the emission ratio reaches 99.87%. Isotope signatures of total Hg in flue gas are similar to those of Hg in feed coal, with near-zero Δ199Hg and negative δ202Hg (−1.47‰ for XR and −3.00‰ for JS) in discharged flue gas. Such isotope signatures are very different from those of Hg emissions from modern coal-fired power plants with much higher δ202Hg signals. Negative shifts from Hg0 to Hg2+ in flue gas for δ202Hg (−0.94‰) and Δ199Hg (−0.51‰) were observed, suggesting that both mass-dependent fractionation and mass-independent fractionation occurred during RCC. The nuclear volume effect produced by chlorine oxidation of Hg0 to Hg2+ may play an important role in the observed mass-independent fractionation in Hg2+. Without any air pollution control devices, RCC potentially increases the atmospheric Hg levels and has a negative-shifting impact on the δ202Hg of atmospheric Hg. Image 1 • Isotope signature of total Hg is consistent between flue gas and feed coal • Obvious MDF occurred among different Hg species in the flue gas • Significant MIF is observed for Hg2+ due to the oxidation of Hg0 • RCC is an important Hg source and potentially impacts atmospheric Hg isotope composition [ABSTRACT FROM AUTHOR]

Coals containing ammonium-bearing aluminosilicates usually have highly-elevated concentrations of critical elements, including Ga, Al, U, V, Re, Se, and rare earth elements. Coals from the Moxinpo and Yishan coalfields of southern China and the Daqingshan Coalfield of northern China are unusual in containing abundant ammonium-bearing minerals (buddingtonite and ammonian illite). Understanding the source of N in the ammonium-bearing minerals could provide useful information, not only for the enrichment of the critical elements, but also for the formation of these unusual minerals. A geochemical and nitrogen isotope study was undertaken in order to investigate the origin and behavior of nitrogen in the minerals and associated coals. The N contents decrease as rank increases from low volatile bituminous to semi-anthracite, indicating that substantial N was thermally lost during coalification. The isotopic composition of organic nitrogen (δ 15N org) ranges from 3.7 to 7.7‰ and increases with coal rank in the studied samples. However, this does not indicate that the isotope fractionation of organic N was due to the coal rank advance; rather, it is largely caused by the depositional environments of peat accumulation and coal-precursor plant assemblages. δ 15N values of inorganic N (δ 15N ino) in NH 4 +-minerals generally have a wider range (5.1 to 12.4‰) than those of organic matter (3.7 to 7.5‰) in coal and are commonly higher than those of δ 15N org in the same coal sample. The N in the ammonium-bearing aluminosilicates was derived from the decomposition of the organic matter of the coals that were subjected to increased geothermal gradient (and fluid flow) as a consequence of igneous intrusion or infiltration of high-temperature hydrothermal fluids. The N released from organic matter was transported by high-T fluids, from which 14N was preferentially converted into volatile matter and 15N readily remained in the fluids. Subsequently NH 4 + in the high-T fluids substituted for K+ in pre-existing minerals or NH 4 + − bearing high-T fluids reacted with pre-existing kaolinite in the coals, leading to more positive δ 15N values for the NH 4 +-bearing minerals than those of the organic matter in these coals. Therefore, the δ 15N ino values in coal, in a wider context, could be potentially used to estimate the degree of high-T heating on coal metamorphism, to trace the pathway of hydrothermal fluids circulating within the coal basin, and to provide useful information on the sources of critical elements that are enriched in coals. [ABSTRACT FROM AUTHOR]

Magmatic fluids and leaching of rocks are regarded as the two sources of magmatic hydrothermal deposits, but their relative contributions to the metals in the deposits are still unclear. In this study, we combine major elements and Fe isotopes in two sets of rocks from the Han-Xing iron skarn deposit in China to constrain the iron sources. The positive correlation between the δ56Fe and ∑Fe2O3/TiO2 of altered diorites (∑Fe2O3 refers to the total iron) demonstrates that heavy Fe isotopes are preferentially leached from diorites during hydrothermal alteration. However, except for the pyrite, all the rocks and minerals formed in the skarn deposit are enriched in the light Fe isotope relative to the fresh/less altered diorites. Therefore, besides the leaching of rocks, the Fe isotopically light magmatic fluid also provides a large quantity of iron for this deposit. Based on the mass balance calculation, we conclude that iron from magmatic fluid is almost 2.6 times as large as that from the leaching of rocks. This is the first study to estimate the relative proportions of iron sources for Fe deposits by using Fe isotopes. Here, we propose that the high δ56Fe of magmatic intrusions combining the positive correlation between their ∑Fe2O3/TiO2 and δ56Fe could be taken as a fingerprint of exsolution or interaction with magmatic fluids, which contributes to the exploration of magmatic hydrothermal ore deposits. [ABSTRACT FROM AUTHOR]

Isotope signatures of mercury (Hg) were determined for Hg fractions in seawater, sediments, porewaters, core sediments and fish from the Yundang Lagoon, Xiamen, China. Sequential extraction was used to extract Hg fractions in sediments and the purge-trap method was used to preconcentrate Hg in seawater. A large variation in mass dependent fractionation (δ 202 Hg: -2.50‰ to -0.36‰) was observed in the lagoon. Seawater and fish samples showed positive mass-independent fractionation (Δ 199 Hg: -0.06‰-0.45‰), while most of sediment and porewater samples displayed insignificant mass-independent fractionation (Δ 199 Hg: -0.10‰-0.07‰). Ancillary parameters (total organic carbon, sulfide, pH, Eh, water content and grain size) were also measured in the sediments to investigate correlations with Hg isotopes. Three sources (domestic sewage, sediments and atmospheric deposition) were identified as the main sources of Hg in the lagoon seawater. Photochemical reaction was the main process causing isotope fractionation in seawater. Through Hg partitioning and deposition, light isotopes were enriched from dissolved Hg to particulate Hg, then to sediments, and then to porewaters. Finally, Hg isotope signatures were used to identify the Hg sources and fractionation processes in core sediments from different depths. Our results demonstrate that Hg isotopes are powerful tools for tracing Hg sources and arriving at a better understanding of Hg biogeochemical cycling in the lagoon after long-term interventions., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

Consumption of rice (Oryza sativa) grain is a major pathway by which humans are exposed to Cd, especially in non-smoking Asian populations. Although the stable isotope signatures of Cd offer a potential tool for tracing its sources, little is known about the isotopic fractionation of Cd across the entire soil-rice-human continuum. Cadmium isotope ratios were determined in field soils, rice grain, and human urine collected from two Cd-contaminated regions in southern China. Additionally, Cd isotopic fractionation in rice plants was investigated using two transgenic plants differing in Cd uptake and accumulation. Analysis of isotope ratios revealed a preferential enrichment of the heavy Cd isotopes from soil to rice grain (δ 114/110 Cd grain-soil  = +0.40‰) and from grain to urine (δ 114/110 Cd urine-grain  = +0.40‰) in both regions. The first increase was mainly caused by partitioning between the soil solid phase and the soil solution, with heavier Cd preferentially enriching in the soil solution. Within the rice plant, we identified multiple processes that alter the isotope ratio, but the net effect throughout the plant was comparatively small. Cd fractionation in humans is presumably due to the preferential enrichment of heavier Cd isotopes by metal transporters DMT1 and ZIP8 (responsible for the absorption of Cd into body from the foods). These findings provide important insights into the Cd isotopic fractionation through the soil-rice-human continuum and are helpful for tracing the sources of Cd., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier B.V. All rights reserved.)

Saltpetre (KNO 3 ; potassium nitrate) is one of the major ingredients of gunpowder. Simplex saltpetre (total 126 samples) together with gunpowder (total 93 samples) commodities which are currently prevailing in local markets as used for wildlife hunting and rocket festivals (local name in Lao: Boun Ban Fai ) were collected from throughout Lao PDR. Dual isotopic composition of nitrates (δ 15 N, δ 18 O) was analyzed by the microbial denitrification method. Binary plotting of the data was conducted to characterize the mode of formation. In Lao PDR, almost all the commodities were imported from neighbouring Thailand, and to a lesser extent from Israel. Binary plotting of δ 15 N vs. δ 18 O of nitrates shows their intrinsic origin manufactured by Haber-Bosch and subsequently Ostwald processes. We observed an inverse correlation (δ 15 N nitrate : up to + 12 ‰; δ 18 O nitrate : down to + 15 ‰), deviating from the reservoir values (free air) of δ 15 N (dinitrogen; up to 0 ‰) and δ 18 O (oxygen; +23.5 ‰), interpreted this as an indication of isotope fractionation during manufacture. The most plausible interpretation for this is the fractionation associated with formation of NO following NO 2 and finally NO 3 products. A nearly comparable inverse relationship is also observed for nitrates in pyrotechnics manufactured in China.

This study aims to clarify the relationship between chemical weathering of rocks and the carbon budget of rivers and better understand the weathering mechanisms of plateau watersheds. We chose to study the Jinsha River, which originates from the Tibetan Plateau and also is in the upper reaches of the Changjiang River. Analysis of hydrochemistry, radiogenic strontium isotope and stable calcium isotopes were conducted of the Jinsha River water samples, which were collected along its mainstream and main tributaries in the summer. The results show that the water chemistry of the mainstream waters is dominated by evaporite weathering, which have low 87Sr/86Sr values (0.7098–0.7108) and wide range of Sr contents (2.70–9.35 μmol/L). In contrast, tributaries of the Jinsha River have higher 87Sr/86Sr (0.7090–0.7157) and lower Sr contents (∼1 μmol/L). Moreover, the Ca isotopic compositions in the mainstream (0.87–1.11‰) are heavier than the tributaries (0.68–0.88‰) and could not be fully explained by the conventional mixing of different sources. We suggest that secondary carbonate precipitation fractionates Ca isotopes in the Jinsha River, and fractionation factors are between 0.99935 and 0.99963. At least 66% of Ca was removed in the mainstream of the Jinsha River through secondary mineral precipitation, and the average value is ∼35% in the tributaries. The results highlight that evaporite weathering results in more carbonate precipitation influencing Ca transportation and cycling in the riverine system constrained by stable Ca isotopic compositions and water chemistry. [ABSTRACT FROM AUTHOR]

• This study is the first report of the microbial effect on C isotope fractionation in the modern speleothems of the Three Gorges Region. • The δ 13C values of the CaCO 3 precipitates induced by bacterial CA exhibit notable C isotope fractionation. • The CaCO 3 formed by CAex is depleted in 13C. Stable oxygen (δ 18O) and carbon (δ 13C) isotopes of speleothems are widely used as important proxies for paleoclimatic and paleoenvironment reconstructions. However, the influence of microbial activity on carbon and oxygen isotope fractionation during speleothem precipitation remains unclear. Bacterial carbonic anhydrase (CA) can promote calcium carbonate precipitation to catalyze the mutual transformation between CO 2 and HCO 3 -. CA-producing bacteria (Lysinibacillus sp. strain LHXY2) were separated in the Xueyu Cave, Chongqing, SW China, and used in laboratory and cave in situ models to investigate their influence on the precipitation amount, mineral components, crystal morphology and carbon and oxygen isotope fractionation of CaCO 3. A CA activity gradient was applied in the laboratory model by considering various CA inhibitor acetazolamide (AZ) concentrations, which showed that the CA activity could substantially enhance precipitation, alter the mineral components and morphology, and reduce the δ 13C and δ 18O values of the CaCO 3 formed. Most importantly, the laboratory and in situ model results revealed approximately -7‰ and -1.4‰ δ 13C shifts, respectively, compared to the bacteria-free model results, which indicated that microbial-driven carbon isotopic fractionation can cause great uncertainties in paleoclimate and paleoenvironment reconstructions. [ABSTRACT FROM AUTHOR]