Guangzhou Institute of Geochemistry
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Zircon S513-A New Gem-Quality Reference Material for <i>In Situ</i> Microbeam U-Th-Pb, (U-Th)/He Geochronology and Hf-O Isotope Measurement
No full textA new gem-quality zircon reference material, S513, was developed for in situ microbeam U-Th-Pb, (U-Th)/He geochronology and Hf-O isotope measurement. The well-cut gem-quality zircon weighed 51.3 carats. Its U, Th, Pb and Hf mass fractions were 924 +/- 64.6 mu g g-1 (2s), 89.6 +/- 3.92 mu g g(-1 )(2s), 119 +/- 5.20 mu g g(-1) (2s) and 8259 +/- 244 mu g g(-1) (2s), respectively. Imaging results from LA-ICP-ToF-MS analysis showed homogeneous distribution of elements in S513. The Th-corrected weighted mean Pb-206/U-238, Pb-207/U-235 and 207Pb/206Pb ratios of S513 zircon from eight ID-TIMS analyses are 0.090955 +/- 0.000019 (2s, MSWD = 0.22, n = 8), 0.73873 +/- 0.00023 (2s, MSWD = 0.19, n = 8) and 0.058934 +/- 0.000008 (2s, MSWD = 0.35, n = 8), respectively. The Th-corrected weighted mean Pb-206/U-238 age obtained from chemical abrasion-isotope dilution-thermal ionisation mass spectrometry is 561.18 +/- 0.63 Ma (n = 8, 95% conf., MSWD = 0.9), which is recommended as the best age estimate of S513. The weighted mean Pb-206/U-238 ages obtained from in situ microbeam analysis (i.e., LA-ICP-MS and SIMS) were 560.8 +/- 5.8/10.2 Ma (2s, n = 260) and 562.4 +/- 7.2/13.4 Ma (2s, n = 198). The measured weighted mean Pb-208/Th-232 age of S513 from LA analyses was 561.3 +/- 3.3/11.7 Ma (2s, n = 86). The U-Pb and Th-Pb ages of S513 obtained with in situ methods showed good agreement with the CA-ID-TIMS results, respectively. The obtained (U-Th)/He age of S513 from thirty-seven aliquots analysed with U-Th isotope dilution method was 420.3 +/- 7.6 Ma (2s, MSWD = 0.72). The recommended reference value of Hf isotope ratio was 0.281606 +/- 0.000010 (2s, MSWD = 1.4, n = 12) according to the mean 176Hf/177Hf ratio acquired with solution MC-ICP-MS analysis. All the LA analyses yielded a mean Hf-176/Hf-177 ratio of 0.281605 +/- 0.000008 (2s, MSWD = 0.53, n = 310), which was consistent with the reference value. Laser fluorination analyses yielded mean delta O-18 values of S513 were 11.71 +/- 0.11 parts per thousand (2s, MSWD = 0.25, n = 5). The results obtained with multiple analytical methods show that zircon S513 is homogeneous to 8% (1s) or better for contents of Y, Nb, Ce, Gd, heavy REE, Ta, U, Th, Pb and Hf. Additionally, the homogeneity is observed at 0.12 parts per thousand (2s) for U-Pb ages, 1.8% (2s) for (U-Th)/He ages, 0.0036% (2s) for Hf isotopes, and 0.11 parts per thousand (2s) for O isotope ratios. Zircon S513 is proposed as a new potential primary calibration or quality control reference material for microbeam U-Th-Pb geochronology and Hf-O isotope measurement
Microbial-mediated bastnaesite dissolution as a viable source of clay-adsorbed rare earth elements in the regolith-hosted deposits
No full textUnderstanding the weathering processes of minerals containing rare earth elements (REE) is crucial for unraveling the genesis of regolith-hosted REE deposits. However, the weathering mechanisms of bastnaesite, a primary REE carrier in parent rocks, remain uncertain. Discrepancies between field observations and thermodynamic calculations regarding its weatherability during mineral-groundwater interactions have raised questions about the factors controlling the natural weathering of bastnaesite. Here, we propose that microbial activities significantly contribute to the dissolution of bastnaesite. To test this hypothesis, we conducted bio-weathering experiments using natural bastnaesite and a wild strain, Bacillus thuringiensis (Bt) isolated from regolith-hosted REE deposits. The results indicate that, consistent with thermodynamic predictions, bastnaesite exhibited resistance to dissolution under simulated groundwater pH conditions (similar to 6). However, the presence of Bt significantly enhanced bastnaesite dissolution. Bt exuded various types of organic acids, acidifying the solution during bio-weathering. Comparative biotic and abiotic experiments demonstrated that Bt could induce bastnaesite dissolution through acidolysis and ligand complexation. These effects were further strengthened by direct cell attachment to the mineral surfaces. Existing field studies suggest the rapid dissolution of bastnaesite during the very early rock weathering period, adding uncertainty about the contribution of bastnaesite to the enrichment of clay-adsorbed REE. Our results indicate that the dissolution of bastnaesite is largely pH-dependent, with bio-dissolution rates (R-Ce = 10(-13) - 10(-12) molm(-2)s(-1)) close to or slightly lower than the lab-determined dissolution rates of feldspars and micas at weakly acidic to neutral pH levels. Since the weathering of these aluminosilicate minerals provides the dominant source of clay minerals, we infer that some REE released from bastnaesite can be retained by clay minerals in the weathering profile. These findings may provide new insights into the natural weathering of bastnaesite and advance our understanding of the REE biogeochemical cycling during the formation of regolith-hosted REE deposits
Green remediation of REEs-contaminated soil by biodegradable chelators with optimization and risk assessment
No full textThe omnipresence of rare earth elements (REEs) in the environment, driven by their extensive industrial applications and common occurrence in some weathered crusts, has raised significant concerns as emerging pollutants. Soil washing has been recognized as an effective approach to remediate REEs-contaminated soils. However, traditional washing agents frequently lead to soil acidification and salinization, adversely affecting soil microbial communities and plant growth. This study explored the use of biodegradable chelators (BCs)-specifically N,N-bis(carboxymethyl)-L-glutamic acid (GLDA), iminodisuccinic acid (ISA), and polyaspartic acid (PASP)-as alternatives for removing REEs from contaminated agricultural soils. Our findings demonstrated that the removal efficiency of REEs positively correlates with BCs concentration, liquid-to-solid ratio, and washing time, while showing a negative correlation with solution pH. Through response surface analysis, we determined the optimal parameters for the washing process, revealing that GLDA, ISA, and PASP achieved total REEs removal efficiencies of 50.8%, 40.5%, and 23.2%, respectively. Statistical analysis confirmed that the concentration of BCs was the primary factor influencing washing effectiveness. Moreover, washing with BCs significantly removed reducible REEs-those bound to iron/manganese oxides-thereby decreasing the mobility and bioavailability of REEs in soil. The reduction in bioavailable REEs significantly lowered the environmental risk associated with contaminated soil. Notably, the activity of soil enzymes improved post-washing with BCs, indicating a positive impact on soil health. This study provides valuable insights into the remediation of REEscontaminated soils using BCs, with GLDA emerging as a particularly effective agent
Molybdenum isotopes demonstrate that multistage upgrading is required to generate heavy rare earth element-enriched carbonatites
No full textCarbonatites with heavy rare earth element (HREE) enrichment are a rare and intriguing prospect for economic geology research, due to the growing global demand for HREEs in various industries. However, debate persists over the mechanism responsible for HREE enrichment in carbonatites, with the mantle source, magmatic-hydrothermal evolution, or a combination of these factors proposed to be responsible. This study examines three adjacent Late Triassic carbonatites (from the Huanglongpu, Huayangchuan, and Jialu carbonatite dike systems) in the Lesser Qinling of Central China and uses Mo isotope systematics to provide unique insights into the HREE enrichment process of these magmas. All three carbonatites exhibit elevated total REE (Sigma REE) concentrations (up to 4600 ppm), along with significant HREE enrichment (Sigma HREE/Sigma REE = 0.1-0.4). Notably, Jialu carbonatite stands out for having the highest total HREE concentrations (>= 360 ppm) and Sigma HREE/Sigma REE ratios (0.2-0.4). Regardless of their variable degrees of HREE enrichment, the three carbonatites display similar Sr-Nd-Pb isotope signatures, which indicates a shared enriched mantle source. The Huanglongpu and Huayangchuan carbonatites mostly display significantly lighter delta Mo-98/95 (-1.71 parts per thousand to -0.15 parts per thousand) values than the depleted mantle, which indicates an origin from an enriched mantle influenced by recycled pelagic clays and Fe-Mn nodules. Both types of marine sediments are enriched in REEs and would have undergone initial HREE enrichment during slab dehydration and metamorphism, resulting in an HREE-enriched mantle source region. In contrast, Jialu carbonatite possesses significantly heavier delta Mo-98/95 (0.13 parts per thousand-1.89 parts per thousand), which is indicative of the subsequent influence of hydrothermal processes. Additional evidence of this hydrothermal influence at Jialu is preserved in calcite crystal fluid inclusions, elevated delta O-18 (8.71 parts per thousand-10.72 parts per thousand), non-charge-and-radius-controlled (CHARAC) Y/Ho ratios (36-41), and low Sr concentrations (<4800 ppm). Secondary upgrading of HREEs at Jialu occurred due to preferential complexation and transportation during hydrothermal exsolution. This study demonstrates that maximum HREE enrichment in carbonatites is achieved through a two-stage process that involves both a refertilized mantle source and late-stage hydrothermal exsolution
Effects of fine terrain complexity on cloud and precipitation changes over the Tibetan Plateau: a modeling study
No full textInaccurate characterization of complex topography leads to the wet bias in climate models, particularly affecting terrain effects in regions like the Tibetan Plateau (TP). This study utilizes the Weather Research and Forecasting (WRF) model with multiple terrain datasets and introduces the terrain complexity index (TCI) to quantify the degree of terrain changes, aiming to evaluate how terrain complexity affects the cloud and precipitation processes over the TP. The results indicate that fine terrain complexity primarily causes earlier cloud formation and precipitation, resulting in more heavy precipitation on the southern slope of the TP (SSTP) and more light precipitation on the TP platform. The structure of moisture transport and microphysical processes further reveals that this promotes the formation of more medium and high clouds, increasing the proportion of solid precipitation over the SSTP. Over the TP platform, the restriction of medium and high cloud development with enhancing the proportion of low clouds for more liquid precipitation. These findings deepen the understanding of the TP's complex terrain effect on cloud and precipitation changes in the Asian water cycle
Attribute Reduction in a Hybrid Decision Information System Based on Fuzzy Conditional Information Entropy Using Iterative Model and Matrix Operation
No full textAttribute reduction of hybrid decision information systems (HDISs) is a significant research area within the field of machine learning. Due to the presence of nominal attributes, it is difficult to accurately measure the distance between objects in HDISs, which often results in poor attribute reduction for these systems. Rough set theory (RST) is a crucial tool for attribute reduction, but it requires computation of upper and lower approximations, which often leads to computational difficulties. In response to the aforementioned issues, this paper proposes a fast attribute reduction algorithm for HDISs based on fuzzy conditional information entropy that utilizes an iterative model and matrix operations. Firstly, a novel measurement of the distance between nominal attribute values is defined using decision attributes. Subsequently, fuzzy conditional information entropy is calculated from the perspective of "the attribute values is fed back to the attribute set" and its properties are provided. Additionally, an iterative attribute reduction model and difference matrix are established, and two new matrix operations are introduced. Finally, an iterative attribute reduction algorithm is provided. The results of experiments and statistical tests on fifteen UCI datasets, including three large datasets, demonstrate that the proposed algorithm is more effective and efficient than nine state-of-the-art algorithms. This paper not only addresses the issue of difficulty in measuring the distance between nominal attribute values but also significantly improves the computational efficiency of attribute reduction algorithms based on RST, making it possible for them to be applied to large datasets
Magnetotelluric Evidence for Lithospheric Hydration and Thinning Beneath the Youjiang Basin in Southwestern China
No full textDetermining the water content in the lithospheric mantle is crucial for understanding its dynamic evolution. Because the electrical conductivity of mantle minerals is particularly sensitive to water, the magnetotelluric (MT) method becomes a vital tool to determine the water content in the lithospheric mantle. Here we used broadband and long-period MT data collected along a 600-km-long, NS-trending profile to obtain the electrical resistivity structure of the lithosphere across the southwestern South China Block. By combining the results of laboratory electrical conductivity measurements of mantle minerals, xenolith-derived composition, and geotherm information, we further estimated the water content of the lithospheric mantle. The results show that the Youjiang Basin has a relatively thin lithosphere segmented by zones of low-resistivity that spatially coincide with major faults. The relatively conductive mantle lithosphere could be explained by the combined effects of water in nominally anhydrous minerals, sulfide and phlogopite. Combined with regional tectonic context, we proposed that H2O-rich fluids derived from the previously subducted slabs and related metasomatic processes lead to lithospheric hydration and thinning within the Youjiang Basin. Additionally, such processes, together with magmatic-hydrothermal activities, likely contribute to the formation of gold deposits within the basin. By contrast, the lithosphere beneath the Yangtze Craton is characterized by high resistivity extending to a depth of similar to 200 km, representing a typical cratonic lithosphere that has not undergone significant tectonic modification and contains no or very little water
Stable Nd isotopic fractionation in REY-rich deep-sea sediments
No full textStable Nd isotope ratios are regarded as a potential tracer for marine rare earth elements (REEs) cycling. However, the fractionation behavior of Nd in marine geological processes has not yet been constrained. This study investigates the bulk and leachate compositions (phosphate, Fe-Mn oxides, and aluminosilicates) of a Ndenriched deep-sea sediment core in the western Pacific for both the stable and radiogenic Nd isotopes. The epsilon Nd values of the bulk sediments range from -6.2 to -5.1, indicating a basically consistent source material throughout the core. Compared to the Bulk Silicate Earth (BSE), the core shows enrichment in heavy Nd isotopes, suggesting that marine authigenic components play a key role in controlling the stable Nd isotope behavior. In the phosphate phase, Nd content correlates positively with P2O5 and CaO contents (R2 = 0.97 and R2 = 0.96, respectively), while the stable Nd isotopic compositions exhibit limited variability (0.076 %o +/- 0.055 %o), suggesting that phosphates have the potential to reconstruct the stable Nd isotope composition of paleo-seawater. For Fe-Mn oxide phases, Mn content initially correlates with Nd content and stable Nd isotope composition, and then exhibit a negative relationship, which suggests that Fe-Mn (hydr)oxides initially adsorb heavier 146Nd from seawater and subsequently release it into pore water. The bulk sediment illite abundance and Al2O3 content correlate with bulk Nd content (R2 = 0.55 and R2 = 0.62, respectively) in aluminosilicate phases, but not with stable Nd isotope composition, indicating that illite controls Nd distribution within this phase without causing stable isotope fractionation. These results elucidate the behavior of stable Nd isotope fractionation in REY-rich deep-sea sediments and provide a fundamental understanding of stable Nd isotopes as a tracer for marine REEs cycling
Estimating wastewater emissions and environmental levels of typical organic contaminants based on regionalized modelling
No full textOrganic contaminants (OCs) are released into the environment through effluent discharges from wastewater treatment plants (WWTP), posing risks to environment health. However, emissions from various source, particularly large-scale investigations across different industries, remain poorly understood. Based on both sampling and statistical data, this study estimates the emissions of 10 OCs, including perfluorooctane acid (PFOA), perfluorooctane sulfonate (PFOS), 4-nonylphenol (4-NP), 4-tert-octylphenol (4-t-OP), dibutyl phthalate (DBP), di-iso-butyl phthalate (DIBP), dimethyl phthalate (DMP), butyl benzyl phthalate (BBP), di(2-ethylhexyl) phthalate (DEHP), and bisphenol A (BPA), from the effluents of 160 factories across 8 industries, 541 municipal wastewater treatment plants (MWWTPs), and 8 waste treatment plants (WTPs) in the upper Yangtze River Basin. A level III fugacity multimedia model was used to assess the impacts of these emissions on local watersheds. Among the 8 industries, paper production was the largest contributor, accounting for over 80% of total OC emissions, which amounted to 89.1 kg/yr. The contributions of domestic and industrial sources were 91.5% and 8.5%, respectively, underscoring the predominance of domestic sources in the release of the 10 OCs. PFOA emerged as the most dominant compound, with total emissions amounting to 4464 kg/yr from domestic sources and 170 kg/yr from industrial sources. The predicted concentrations of OCs in the receiving rivers closely aligned with values reported in existing literature, differing by no more than one order of magnitude. To our knowledge, this is the first comprehensive report on emissions from various sources in the upper Yangtze River Basin
Mid-Late Holocene coral calcification dynamics: deciphering climatic and environmental effects
No full textOver the past four decades, a marked decrease in coral calcification has occurred across the world's tropical reefs, closely linked to climate change and the impact of human activity. However, how natural and human-induced factors influence coral calcification remains unclear due to limited understanding of the geological past. This study addresses this gap by investigating the calcification parameters of 82 Porites corals from the northern South China Sea, with growth periods covering distinct climatic epochs during the Mid-Late Holocene, including the Holocene Climate Optimum, 4.2 ka BP event, Medieval Climate Anomaly, Little Ice Age and Current Warm Period. Our findings show a gradual increase in coral skeletal density towards the present, and varied linear extension and calcification rates between warm and cold phases and between pre- and post-industrial periods. This suggests that temperature plays a pivotal role in controlling coral calcification, with contingent influences from volcanic activity and solar radiation. Notably, the linear extension and calcification rates were significantly reduced during the Current Warm Period, suggesting a surpassing impact of contemporary human activities over the natural variability on coral calcification. This raises concerns about the future prospects of coral reefs in the face of ongoing climate change and increasing impact of human activity