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Although molybdenum (Mo) isotopic compositions of carbonatites, phosphorites and siliceous rocks can be used as proxies to reconstruct conditions of marine chemistry throughout geological time, only a few studies have, so far, analysed these low-Mo (ng g−1) geological samples because of analytical limitations. In this study, a low blank, high yield two-column Mo purification procedure was developed for various low-Mo geological samples. The sample-standard bracketing (SSB) and double-spike (DS) methods for mass fractionation correction were used to compare the accuracy of Mo isotope ratio measurements. Six Mo reference materials, NIST SRM 3134 Mo, JMC Mo, SC+1 and SC−1 (eluted fractions of Sigma-Aldrich Mo), CRM GSR-6 limestone and USGS BCR-2 basalt, were used as quality controls. The results showed that the Mo delta values of reference materials and geological samples corrected by the SSB and DS methods were, within error, consistent with each other and the DS method was the method of choice for samples with ＜0.5 μg g−1 Mo. The average instrument long-term (over 1 year) external reproducibility of NIST SRM 3134 Mo was better than ±0.03‰ amu−1 (2SD, n = 288) and the analytical precision of low-Mo (101 to 103 ng g−1) geological samples was better than ±0.04‰ amu−1. This method can facilitate Mo isotope ratio measurements in geological samples with a low Mo content, offering a possibility to study a wider range of Mo reservoirs in geological processes. [ABSTRACT FROM AUTHOR]

Lithium is of great importance for green energy technology, and most industrial Li is sourced from brine lakes and pegmatites. Recently, strong Li enrichment has been reported in the late Palaeozoic Jiujialu Formation (C 1 jj) in Guizhou, South China; however, the source and the sedimentary processes that formed the Jiujialu Formation remain unclear. We present the U–Pb ages and trace element compositions of detrital zircon grains from the Jiujialu Formation and underlying dolomite of the Loushanguan Group (Cam 2–3 ls), which indicate the grains in the Jiujialu Formation on the margin of the Central Guizhou Uplift and in a depression in southeast Guizhou have three primary age peaks (1000–900, ∼760, and ∼530 Ma). These ages are similar to those of Ordovician strata, indicating a contribution from the Ordovician strata to the Jiujialu Formation in these areas. Detrital zircon grains from the Jiujialu Formation in the core of the Central Guizhou Uplift and the Loushanguan Group have two primary age peaks at ∼760 and ∼530 Ma, which suggests that the underlying Loushanguan Group supplied most of the material to the Jiujialu Formation in this area. The age distribution of detrital zircon grains indicates that sediment erosion from the sedimentary stratal transport was limited, and deposition occurred near the direct source. In addition, the trace element compositions of the detrital zircon grains indicate that their original source was magmatic rocks of the South China Block. An early Palaeozoic intracontinental orogeny in South China uplifted subduction-related magmatic rocks (1000–900 Ma) in the northeast of the South China Block, exposing them to weathering and providing material for the Ordovician strata. This suggests that the weathering of sedimentary strata can form clay-type Li deposits in areas with carbonate bedrock, and that the provenance of Cambrian–Ordovician sedimentary strata in the Yangtze Block was controlled by an early Palaeozoic intracontinental orogeny. [Display omitted] • Detrital zircons from the Loushanguan Group dolomites were studied. • Magmatic rocks around the South China Block are original material source. • Cambrian and Ordovician strata are the provenances of the Jiujialu Formation. • Early Palaeozoic intracontinental orogeny effect on sedimentary strata in Yangtze Block [ABSTRACT FROM AUTHOR]

[Display omitted] • The first time of systematically S-Pb isotopic data for different types of lead–zinc deposits in the southeast margin of Yangtze Block was presented. • Different types of lead–zinc deposits in the southeast margin of Yangtze Block have entirely diverse metal and sulfur sources. • The Nanhua rifting lead to the syngenetic Zn-Pb mineralization. • The Guangxi Orogeny resulted in magmatic-hydrothermal vein mineralization at depth and in MVT mineralization at the shallow crustal levels. Three types of zinc-lead deposits, including polymetallic vein-type, sedimentary-exhalative (SEDEX), and Mississippi valley-type (MVT) Zn–Pb deposits, have been discovered along the southeast margin of the Yangtze Block. A systematically comparative study on the sulphur and metal sources for these deposits, is absent, which significantly limits the understanding of the metallogenic model and geological exploration. Thus, in order to reveal the S and Pb sources of Pb–Zn deposits, an investigation of trace elements of sphalerite and of S–Pb isotopic compositions of sulphides in these three types of Zn–Pb deposits was conducted in this study. We found that, in the vein-type, SEDEX, and MVT Zn–Pb deposits, (1) the sulphur was derived respectively from granitic magmatism related to the Guangxi Orogeny, early Cambrian stratified seawater and connate water; (2) the lead isotope variation indicates that the ore-forming metals were mainly derived from the granitic hydrothermal fluids for vein-type deposits, from basement rocks for SEDEX deposits, and mainly from early Cambrian sedimentary rocks for MVT mineralization. The Nanhua rifting lead to the syngenetic Zn-Pb mineralization, while the Guangxi Orogeny resulted in magmatic-hydrothermal vein mineralization at depth and in MVT mineralization at the shallow crustal levels. [ABSTRACT FROM AUTHOR]

Cadmium (Cd) isotopes in seawater have been proven as an important geochemical tool for tracing ocean Cd circulation in the modern ocean. In this study, we evaluated a new method to separate Cd (~ 60 ng) from seawater using Chelex resin (1.0 g) coupled with AG-MP-1M resin. The results show that the Chelex resin is sufficient to remove Cd from Na and Mg matrix with Cd recoveries at 98.3 ± 3.5 % (2SD, N = 6); while AG-MP-1M resin could separate Cd from the residual Na, Mg, and isobaric inferences. The total Cd recoveries of the method are 96.3 ± 1.5 % (2SD; N = 4) and the salinity of the samples has no significant impacts on Cd recovery. Cd isotope ratios were measured using a Nu Plasma III MC-ICP-MS and 111Cd–110Cd double spike technique. By comparing the δ114/110Cd values (0.00 ± 0.06‰) of synthetic seawaters doped with Cd isotope standard (NIST-3108; treated by Chelex + AG-MP-1M resin) and the reference value (~ 0.00 ‰), no variations were observed. We also analyzed the Cd isotope compositions of three deep seawaters from a column at the Southwest Indian Ocean Ridges (SWIR). The δ114/110Cd values of the column are decreased from 1.05 ± 0.05 ‰ at 3200 m to 0.36 ± 0.05 ‰ at 2800 m, differing from reported δ114/110Cd values of deep seawater in other oceans. Considering the spatial distance between the column and active hydrothermal vents in SWIR (~ 13 km), we propose that such positive δ114/110Cd values of deep seawater were likely contaminated by vent fluids, which could provide heavy Cd isotope to deep seawaters. This study demonstrates that Cd isotope is more sufficient to distinguish the impact of plumes on deep seawater. [ABSTRACT FROM AUTHOR]

[Display omitted] • Cd isotope compositions of the largest hydrothermal system from the SYG. • Light Cd isotopes preferentially enriched in galena rather than sphalerite. • Cd was derived from the mixing between the Emeishan basalts and sedimentary rocks. • Cd isotope as a powerful geochemical tracer for hydrothermal systems. The Sichuan–Yunnan–Guizhou (SYG) Zn–Pb metallogenic zone in SW China contains >400 carbonate-hosted hydrothermal Zn–Pb deposits. Some of these, such as the Huize, Tianbaoshan, and Daliangzi deposits, are super-large deposits with significant reserves of Cd, Ge, and Ag. However, the sources of these metals remain controversial. This study investigated the Cd isotopic geochemistry of the Huize deposit, the largest Zn–Pb deposit in the SYG area. Sphalerites formed at three stages in the deposit have different colors: black or dark brown (Stage I), red (Stage II), and light-yellow (Stage III). The δ 114/110Cd values of the sphalerites are in the order Stage III < Stage I < Stage II. Kinetic isotopic fractionation is likely the key factor causing the lower δ 114/110Cd values in the early formed Stage I sphalerites than in later-formed Stage II sphalerites, with cooling of ore-forming fluids being responsible for the still lower values of the Stage III sphalerites. In galena, the δ 114/110Cd values are inversely correlated with Cd contents and tend to be higher in high-Zn galena. We speculate that Cd isotopic fractionation was significant during the precipitation of sphalerite and galena, with light Cd isotopes being enriched in galena rather than sphalerite. Comparison of the Cd isotopic signatures and Zn/Cd ratios of different endmembers suggests that the δ 114/110Cd values and Zn/Cd ratios of sphalerite from the Huize deposit, as well as other large-scale deposits from the SYG area, are lie in those range of Emeishan basalts and sedimentary rocks and the mean δ 114/110Cd values of these deposits show good negative correlation with 1/Cd, suggesting that the ore-forming materials of these deposits were derived from the mixing of Emeishan basalts and sedimentary rocks. This study demonstrates that Cd isotopes can be useful proxies in elucidating ore genesis in large Zn–Pb deposits. [ABSTRACT FROM AUTHOR]

The abrupt appearance of abundant small shelly fossils (SSFs) near the base of the Cambrian System signals a key event in the evolutionary history of the Kingdom Metazoa. Among the probable cnidarian taxa, the SSF family Hexangulaconulariidae (Terreneuvian Series) is characterized by a fan-shaped, biradially symmetrical periderm having distinct apical and abapical portions, the latter of which bears multiple faces. Documented herein are three new hexangulaconulariid specimens from Cambrian Stage 2 on the Yangtze Platform (South China). The new specimens exhibit nine or 11 faces on each of the two sides of the abapical portion. Results of a Bayesian analysis of the phylogenetic relationships among hexangulaconulariids, carinachitids, conulariids, olivooids, and extant cnidarian genera indicate that hexangulaconulariids constitute a well-defined clade within a polytomic, stem-group Medusozoa that also includes carinachitids, conulariids and olivooids. The evolution of hexangulaconulariids featured multiple instances of increase in the total number of faces, modification of the morphology of the interfacial boundaries, and increase in the total size of the periderm. Increase in the number of faces appears to have been achieved in part by the transformation of a single ancestral face into three faces, through the development of a longitudinal furrow or ridge along each of the two adapically converging loci of inflection points (angular bends) of the prominent transverse ribs of the ancestral face. [ABSTRACT FROM AUTHOR]

Gallium isotope is a potential geochemical tool for understanding planetary processes, environmental pollution, and ore deposit formation. The reported Ga isotope compositions (δ71GaNIST994 values) of some international geological standards, such as BCR-2 and BHVO-2 basalts, exhibit inconsistencies between different laboratories. During mass spectrometry analysis, we found that δ71GaNIST994 values of geological standards with or without the correction of the interference of 138Ba2+ (mass/charge ratio = 69) on 69Ga show significant isotope offsets, and thus efficient separation of Ba and correcting the interference of 138Ba2+ are both crucial to obtain accurate δ71Ga values. By comparing δ71GaNIST994 values (relative to NIST SRM 994 Ga) of the same geostandards from different laboratories, we suggest that the isotopic heterogeneity from NIST SRM 994 Ga is one of the key reasons for the inconsistencies in δ71GaNIST994 values of BCR-2 and BHVO-2. To facilitate inter-laboratory comparisons, we measured the Ga isotopic compositions of 11 geological reference materials (including Pb-Zn ore, bauxite, igneous rocks, and loess) and two Ga solution standards (NIST SRM 3119a and Alfa Aesar). The δ71GaNIST994 and δ71GaIPGP values of these reference materials vary from 1.12 ‰ to 2.63 ‰ and − 0.13 ‰ to 1.38 ‰, respectively, and can be used to evaluate the precision and accuracy of Ga isotope data from different laboratories. [ABSTRACT FROM AUTHOR]

The end-Permian mass extinction was the most severe biotic crisis of the Phanerozoic. Oceanic anoxia has long been considered one of the main drivers of the biotic crisis. We examined the molybdenum isotope compositions of bulk carbonate samples from two Permian–Triassic boundary sections in southern China: the Meishan Global Stratotype Section and Point and the Dajiang section (an isolated carbonate platform). We also measured the Mo contents of the carbonate phases, oxides, and sulfides of the carbonate samples via sequential extraction to investigate the samples' Mo-bearing minerals. In the Meishan section, from Bed 23 to the middle of Bed 24, the δ98/95Mo corr.Al values decrease slowly from +0.89‰ to +0.35‰, while from the middle of Bed 24 to Bed 25, the δ98/95Mo corr.Al values abruptly increase from +0.35‰ to +1.78‰. In the Dajiang section, samples below the mass extinction boundary have relatively low δ98/95Mo corr.Al values with a narrow variation range (−0.05‰ to +0.46‰; average + 0.19‰); the δ98/95Mo corr.Al values of the five samples directly above the extinction boundary increase abruptly (vary from +1.38‰ to +1.63‰; average of +1.53‰), and the δ98/95Mo corr.Al values of other samples above the mass extinction boundary fluctuate slightly before returning to pre-extinction values. The results of the sequential extraction procedure indicate that carbonate-phase Mo accounts for a small portion of the total Mo (average of 13.6 and 18.4 wt% for the Meishan and Dajiang sections, respectively), oxidized and sulfided Mo are the dominant forms in the carbonate samples. Moreover, the carbonate samples with high δ98/95Mo values tend to have high contents of sulfided Mo. We suggest that marine carbonate sediments record paleo-ocean Mo isotopic signals by a mechanism similar to that of other open-ocean sediments (e.g., shales): higher δ98/95Mo values in the sediments indicate a more reducing sedimentary environment. Based on this assumption, the δ98/95Mo values of the studied sections indicate that during the Permian–Triassic transition, oceanic anoxia coincided with or slightly predated the mass extinction, and the ocean anoxic event lasted for a relatively short time, likely less than 0.061 Myr. [Display omitted] • Mo isotope variations from the Meishan GSSP and Dajiang section were investigated. • Paleo-ocean Mo isotopic signals recorded in marine carbonate. • During the P-T transition, oceanic anoxia coincided with or slightly preceded mass extinction. • For the oceanic anoxic event a duration <0.061 Ma has been estimated. [ABSTRACT FROM AUTHOR]

This study examines the Ga isotopic compositions of sulfides in the Yuhuang and Duanqiao hydrothermal fields on the Southwest Indian Ridge, mid-ocean ridge basalts (MORB), and calcareous sediments around the hydrothermal fields. The δ 71/69Ga NIST-994 values of the MORB samples vary little (+1.20‰ to +1.23‰, with an average of +1.22‰) and are consistent with the δ 71/69Ga NIST-994 values of two standard basalt samples (BCR-2 and BHVO-2), indicating that Ga isotopes may either not fractionate or fractionate only slightly under high-temperature geological processes; therefore, the δ 71/69Ga NIST-994 value of oceanic crust may be +1.22‰. The sediments (+1.28‰ to +1.47‰, with an average of +1.38‰) are rich in heavier Ga isotopes than the basalts, and the Ga present in the sediments may have originated from soluble Ga present in the seawater that was adsorbed by (Mn, Fe) oxides/hydroxides. The Ga contribution of basaltic debris to the sediments was almost negligible. Thus, we speculate that the δ 71/69Ga NIST-994 value of seawater in the study area fell within a range from +1.92‰ to +2.36‰. The δ 71/69Ga NIST-994 values of the sulfides in the Yuhuang hydrothermal field range from +0.99‰ to +1.57‰, with an average of +1.25‰, and the δ 71/69Ga NIST-994 values of the sulfides in the Duanqiao hydrothermal field range from +0.93‰ to +1.55‰, with an average of +1.19‰. The δ 71/69Ga NIST-994 ranges of the sulfides in the Yuhuang and Duanqiao hydrothermal fields are similar, with the Ga isotopic fractionation reaching 0.58‰ and 0.62‰, respectively. The average δ 71/69Ga NIST-994 values in the sulfides are close to those in the MORBs. This suggests that Ga within the sulfides in the Yuhuang and Duanqiao hydrothermal fields mainly originated from MORBs, with seawater and sediments making only small contributions. The Ga isotopic fractionation in the sulfides may be related to processes associated with the formation of sulfides, such as rapid precipitation or the admixture of different stages of sulfide. This study is of great significance for understanding the global distribution of Ga isotopes and the Ga cycle in submarine hydrothermal systems. [Display omitted] • δ 71Ga of sulfides, MORBs and sediments from the Southwest Indian Ridge are obtained. • Ga isotopic compositions of the basalts are homogeneous (+1.20‰ to +1.23‰). • δ 71Ga ranges of the sulfides in the Yuhuang and Duanqiao hydrothermal fields are similar. • Ga in the sulfides from both hydrothermal fields is mainly from MORBs. • Ga in the sediments is mainly from seawater by adsorption of Fe oxides/hydroxides. [ABSTRACT FROM AUTHOR]

[Display omitted] • Cu++In3+↔Zn2++Fe2+ is the most plausible indium substitution mechanism for ZnS in polymetallic vein along the western Jiangnan Orogen. • Zn and Cd isotopic data suggest ore-forming fluids were derived from magmatic-hydrothermal systems. • Hydrothermal fluids of polymetallic vein deposit mightderive from the fractionation of Zn, Cd, Cu, In and Sn in the Guangxi Orogeny related to granitic magma. Polymetallic veins of Zn-Pb (Cu) deposits containing elevated levels of indium are hosted within the upper part of the Banxi Group in the western Jiangnan Orogen. The indium in the polymetallic vein deposits is hosted within sphalerite and chalcopyrite. Cu++In3+↔Zn2++Fe2+ is the most plausible indium substitution mechanism for ZnS in these deposits. Hydrothermal fluids were enriched in Cu, In, Co, Mn and Fe in the later mineralization stage. Ores, sphalerite and dolomite minerals displayed analogous Ce and Eu anomalies, and Zn/Cd ratios, while being noticeably different from its host rocks, that provided its mineralized metals were not derived from its host rock. Despite the Zn and Cd isotopic variations in sphalerite being relatively narrow (δ66Zn JMC = +0.01‰–+0.28‰; δ114Cd Spex = −0.14‰–+0.11‰), they display increase during mineralization and are negatively correlated to Cd concentrations; the Rayleigh distillation might be the fractionation mechanism. Zn/Cd ratios and Zn-Cd isotopic variations suggest the magmatic-hydrothermal origin of the polymetallic vein-type deposits. These hydrothermal fluids might derive from the fractionation of Zn, Cd, Cu, In and Sn in the granitic magma. This is triggered by crust thickening and the detachment of the lower crust along the Jiangnan Orogen during the intracontinental orogenic events of the Guangxi orogeny. This period of granitic magmatism might be another important indium mineralization episode in South China. [ABSTRACT FROM AUTHOR]

Hydrothermal activity on mid-ocean ridges is an important mechanism for the delivery of Zn from the mantle to the surface environment. Zinc isotopic fractionation during hydrothermal activity is mainly controlled by the precipitation of Zn-bearing sulfide minerals, in which isotopically light Zn is preferentially retained in solid phases rather than in solution during mineral precipitation. Thus, seafloor hydrothermal activity is expected to supply isotopically heavy Zn to the ocean. Here, we studied sulfide-rich samples from the Duanqiao-1 hydrothermal field, located on the Southwest Indian Ridge. We report that, at the hand-specimen scale, late-stage conduit sulfide material has lower δ66Zn values (−0.05 ± 0.15 ‰; n = 19) than early-stage material (+0.13 ± 0.15 ‰; n = 10). These lower values correlate with enrichments in Pb, As, Cd, and Ag, and elevated δ34S values. We attribute the low δ66Zn values to the remobilization of earlier sub-seafloor Zn-rich mineralization. Based on endmember mass balance calculations, and an assumption of a fractionation factor (α ZnS-Sol.) of about 0.9997 between sphalerite and its parent solution, the remobilized Zn was found consist of about 1/3 to 2/3 of the total Zn in the fluid that formed the conduit samples. Our study suggests that late-stage subsurface hydrothermal remobilization may release isotopically-light Zn to the ocean, and that this process may be common along mid-ocean ridges, thus increasing the size of the previously identified isotopically light Zn sink in the ocean. [ABSTRACT FROM AUTHOR]

• A systematic study on "dispersed elements": Ga, Ge, Se, Cd, In, Te, Re and Tl in marine Fe-Mn deposits. • Compared with the Earth's crust and the pelagic clay, the marine Fe–Mn deposits are highly enriched in Te, Tl, Se and Cd. • Se, Cd, Te and Tl concentrations in marine Fe–Mn deposits show some specific variations on global, regional, intra crust/nodule scales and different water depth. • Under conditions of hydrogenetic and hydrogenetic-diagenetic, Cd, Se, Te and Tl are incorporated in marine Fe-Mn deposits mainly by adsorption onto the Mn-oxides or/and Fe oxyhydroxides. • The processes of coupled redox and coprecipitation on Fe-Mn(oxyhydr)oxides could generate Te enrichment. The eight elements Ga, Ge, Se, Cd, In, Te, Re and Tl are usually referred to as "dispersed elements", and they have a lower average abundance in the Earth's crust. Marine Fe–Mn crusts and nodules are potential resources for many of the metals used in emerging high- and green-technology applications. This study examines the concentrations of the dispersed elements in marine Fe–Mn deposits at different locations from the Pacific Ocean, ascertains the genesis and dispersed elements enrichment characteristics of marine Fe-Mn deposits, discusses the variations of the dispersed elements in marine Fe–Mn deposits profiles and variations with the dependency of genesis and water depth, and elucidates their incorporation mechanisms in marine Fe–Mn deposits. Nodules from the Mid-Pacific Mountains (CAD19 and CXD05) and Magellan Seamounts (MID18) formed under hydrogenetic conditions, nodules from the CCZ (WD1101, WT0301 and ET0301) formed under a mixture of hydrogenetic and diagenetic conditions, and the Fe–Mn crust MKD12 from the Magellan Seamounts formed under hydrogenetic condition throughout its growth history. Compared with the Earth's crust and the pelagic clay, the marine Fe–Mn deposits are highly enriched in Te, Tl, Se and Cd, not enriched in Re, Ga, Ge, In. Elemental relationships show that there are distinct differences between the enrichment mechanisms of the dispersed elements in different types of Fe–Mn deposits. Cd, Se, Te and Tl in Fe-Mn nodules and crust profiles show certain regular variations, which mainly related to the changes of the relative contents of Mn minerals and Fe minerals, for the phosphatized crusts, the concentrations of dispersed elements would be influenced by phosphatization. There are obvious differences of Cd, Se, Te and Tl concentrations in different genetic types of Fe–Mn deposits, which probably attributed to the differences of sources, deposition rates and mineral compositions. The concentrations of Se, Cd, Te and Tl in Fe-Mn deposits from the Pacific Ocean mainly distribute in the ranges of 1000 ~ 2500 m and 4000 ~ 6000 m water depth. The water depth dependence of Se, Cd, Te and Tl concentrations in hydrogenetic Fe-Mn nodules and crusts display different variation patterns, which might be controlled by several factors such as the Mn-phase and Fe-phase system, sedimentation rates, biological productivity, diagenesis, as well as the geochemical behaviors of the elements themselves. Under the conditions of hydrogenetic and hydrogenetic-diagenetic, Cd, Se, Te and Tl are incorporated in marine Fe-Mn deposits mainly by adsorption onto the Mn-oxide or/and Fe oxyhydroxide particles. The processes of coupled redox and coprecipitation on Fe-Mn(oxyhydr)oxides could generate Te enrichment. [ABSTRACT FROM AUTHOR]

Rare earth elements and Yttrium (REYs) are critical to the emerging high-tech and green-energy industries, generating tremendous REY demand in recent decades. Recently, many sedimentary phosphorites have been reported to have extraordinary REY enrichment (> 1000 ppm) and may become new REY resources. However, the controls of REY enrichment in phosphorites have not been well constrained. To better understand the discrepant REY enrichment in phosphorites, the early Cambrian high-REY Zhijin (ZJ) phosphorites (∼500–2000 ppm) and the relatively low-REY Meishucun (MSC, ∼200–400 ppm) and Xia'an (X'A, mostly < 200 ppm) phosphorites on the Yangtze Block of South China were investigated with mineralogy, bulk-rock elements, total organic carbon, in-situ elements, and Zn-Fe isotopes. The mineral characteristics, REY indexes, and in-situ REY mapping indicate that the X'A phosphorites may represent pristine phosphorites, whereas the ZJ and MSC phosphorites may have experienced intensive diagenetic alteration. Diagenetic alteration can only explain the REY enrichment in the MSC phosphorites compared to the pristine X'A phosphorites, but it does not sufficiently explain the extraordinary REY enrichment in the ZJ phosphorites. Additionally, the lower δ66Zn values of the ZJ and X'A phosphorites (δ66Zn average = 0.16‰ and 0.14‰, respectively) than those of the MSC phosphorites (δ66Zn average = 0.75‰) indicate higher productivity levels in the ZJ and X'A areas. However, the high-productivity X'A phosphorites yielded very low REY concentrations, indicating that the extraordinary REY enrichment in the ZJ phosphorites cannot be ascribed to high productivity levels. Notably, the ZJ phosphorites may have experienced more intensive Fe redox cycling under fluctuating oxic–suboxic deposition conditions (∼0.0‰–0.45‰ δ56Fe values in near-pure phosphorites) than the MSC and X'A phosphorites with completely oxic deposition conditions (∼0.0‰ δ56Fe values). Frequent Fe redox cycling can greatly enrich REYs in porewater, which can be subsequently transferred into francolites during its formation and early diagenesis. Therefore, frequent Fe redox cycling driven by fluctuating oxic–suboxic seawater conditions may be responsible for the extraordinary REY enrichment in the ZJ phosphorites. If this is the case, we propose that phosphorites deposited near the oxic–suboxic redox chemocline are favorable for extraordinary REY enrichment, such as the coeval near-slope phosphate concretions on the Yangtze Block and other phosphorites or phosphatic rocks formed in different basins at different geological times. [ABSTRACT FROM AUTHOR]

The ion-adsorption-type rare earth element (iREE) deposits dominantly supply global resources of the heavy rare earth elements (HREEs), which have a critical role in a variety of advanced technological applications. The initial enrichment of REEs in the parent granites controls the formation of iREE deposits. Many Mesozoic and Cenozoic granites are associated with iREE mineralization in the Tengchong block, Southwest China. However, it is unclear how vital the mineralogical and geochemical characteristics of these granites are to the formation of iREE mineralization. We conducted geochronology, geochemistry, and Hf isotope analyses of the Yingpanshan–Damanbie granitoids associated with the iREE deposit in the Tengchong block with the aims to discuss their petrogenesis and illustrate the process of the initial REE enrichment in the granites. The results showed that the Yingpanshan–Damanbie pluton consists of syenogranite and monzogranite, containing REE-bearing accessory minerals such as monazite, xenotime, apatite, zircon, allanite, and titanite, with a high REE concentration (210–626 ppm, mean value is 402 ppm). The parent granites have Zr + Nb + Ce + Y (333–747 ppm) contents and a high FeOT/MgO ratio (5.89–11.4), and are enriched in Th (mean value of 43.6 ppm), U (mean value of 4.57 ppm), Zr (mean value of 305 ppm), Hf (mean value of 7.94 ppm), Rb (mean value of 198 ppm), K (mean value of 48,902 ppm), and have depletions of Sr (mean value of 188 ppm), Ba (mean value of 699 ppm), P (mean value of 586 ppm), Ti (mean value of 2757 ppm). The granites plot in the A-type area in FeOT/MgO vs. Zr + Nb + Ce + Y and Zr vs. 10,000 Ga/Al diagrams, suggesting that they are A2-type granites. These granites are believed to have formed through the partial melting of amphibolites at a post-collisional extension setting when the Tethys Ocean closed. REE-bearing minerals (e.g., apatite, titanite, allanite, and fluorite) and rock-forming minerals (e.g., potassium feldspar, plagioclase, biotite, muscovite) supply rare earth elements in weathering regolith for the Yingpanshan–Damanbie iREE deposit. [ABSTRACT FROM AUTHOR]

The article discusses the late mesozoic mafic dyke swarms located in Fujian Province, Southeast China and its geochemistry. The article also includes the geodynamic information containing geologic terrain in the region and their lithospheric extension derived mainly from the asthenospheric mantle and discusses the ancient continental block breakup and paleotectonic stress state there.

The basal unit of the Early Cambrian black shale sequence of South China hosts sulfide-rich polymetallic units, non-sulfidic vanadium-rich black shales, sapropelic alginite (combustible shale), barite, and phosphorite. This rock spectrum occurs in a paleoceanographic similar, and stratigraphically correlated, transgressive upwelling setting on the passive continental margin of the Neoproterozoic Yangtze Platform. Several centimeter-thick polymetallic sulfidic units (3–13 wt% Mo+Ni, 100–600 ppm U) have relatively light Mo (δ98/95Mo = 1.1 ± 0.2‰) and relatively heavy U isotope composition (δ238/235U = 0.2 ± 0.1‰). Several meter-thick V-rich shales with multiple ore-grade layers (0.1–0.8 wt% V, < 100 ppm U, Mo and Ni ~ 100 ppm) have isotopically lighter Mo (δ98/95Mo = 0.3 ± 0.4‰) and heavier U composition (δ238/235U = 0.4 ± 0.2‰ and up to 0.7‰). The inverse Mo versus U isotope correlation suggests that both metals were enriched by removal from anoxic to strongly euxinic bottom water in restricted basins along the rifted continental margin. Metal replenishment probably occurred via the cycling of Fe–Mn-oxyhydroxide particles across the redox boundary, with sorption/desorption of Mo (and likely Ni) in a stratified water column. In contrast, V enrichment with much lower Mo, Ni, and U contents, but more fractionated Mo and U isotope composition, reflects non-sulfidic anoxic depositional conditions in a partly open system with higher bottom water renewal rates. While Mo isotope fractionation likely occurred in the water column, U isotope fractionation may dominantly have occurred at the water-sediment interface, perhaps in a benthic organic flocculent layer. These findings indicate that local hydrodynamic control and stratified water column redox conditions may explain the observed variation of metal enrichment (Mo–Ni versus V) in the black shales. Furthermore, the high δ98/95Mo values up to 2.6‰ of the black shales studied and the correlated U and Mo isotope data suggest that Early Cambrian seawater was at least episodically broadly similar to modern seawater. [ABSTRACT FROM AUTHOR]

The Cambrian explosion is a critical evolutionary milestone in life history, but the mechanistic relationship between the Cambrian explosion, rising atmospheric and oceanic oxygen levels, and the primary productivity remains controversial. Here, we present new mercury (Hg) isotope data from Cambrian marine sediments of the ∼521–514 Ma Yu'anshan and Shuijingtuo Formations (Nanhua Basin, South China), which preserve the famous ∼518 Ma Chengjiang and Qingjiang Cambrian Biotas, respectively. We find evidence that, prior to Cambrian animal diversification, local terrestrial and/or atmospheric inputs are important drivers of Hg enrichment in the shallow shelf Yu'anshan and Shuijintuo Formations. Elevated Hg and total organic carbon (TOC) concentrations of coeval deeper shelf and slope sections of the Niutitang Formation are mainly attributed to upwelling of Hg associated with dissolved organic carbon (Hg-DOC) from pelagic seawater, unrelated to locally high primary productivity. During the deposition of fossiliferous strata, negative shifts of Δ199Hg and δ202Hg values in the shallow water shelf shales from the Shuijingtuo Formation, combined with similar Hg isotope characteristics in the deeper shelf and slope shales, demonstrate a significant shallow and deep-water oxygenation event took place in the Nanhua Basin. A comparable negative shift of Δ199Hg values occurs in coeval Indian Craton sediments, suggesting this oxygenation event could be regional, or possibly even global, in scale. Our newly-collected Hg isotope data provide strong evidence that rising molecular oxygen levels in both surface and deep seawater are associated with enhanced marine primary productivity and could be a critical driver of the Cambrian explosion. Finally, we also argue that Hg isotopes are an emerging and promising redox proxy for studies of Precambrian seawater, but the chemical response of Hg to atmospheric and ocean oxygenation requires further calibration. [ABSTRACT FROM AUTHOR]

Constraining exhumation and tectonic processes along an orogenic plateau's boundary provides important insights into the mechanisms leading to plateau expansion and crustal evolution. The Longshou Shan thrust belt (LSSTB) is located in the foreland of the northern Qilian Shan thrust belt, which is commonly regarded as the northeastern margin of the Tibetan Plateau. The LSSTB is thus ideal for decoding the recent expansion of the Tibetan Plateau by tracking deformational pattern at its northeastern margin. In this study, the spatiotemporal characteristics of exhumation and deformation along the LSSTB are investigated by detailed analysis and numerical modeling of published and new thermochronological data. Five Proterozoic basement and intrusion samples yielded Cretaceous apatite fission-track central ages (126–74 Ma, with mean track lengths of 12.6–13.3 μm), and Late Cretaceous to Eocene apatite (U Th)/He mean ages (84–51 Ma). Inverse thermal history modeling reveals multi-stage exhumation of the LSSTB in the Permo-Triassic, late Mesozoic, Paleogene, and post-middle Miocene. Permo–Triassic exhumation hints at a > 250 Ma-old peneplain surface that may have formed in response to the closure of the Paleo-Tethys and Paleo-Asian oceans. Late Mesozoic exhumation likely resulted from intracontinental extensional deformation associated with tectonic processes at the Eurasian continental margin. Exhumation during the Paleogene was likely triggered by the India-Asia collision. Post-middle Miocene periods of uplifts along the reactivated Longshou Shan thrusts (no later than 10 Ma and 5 Ma on the southern and northern Longshou Shan Thrust, respectively) were driven by the northeastward expansion of the Tibetan Plateau. Our results support the LSSTB as a long-lived block boundary since the Permo-Triassic and an emerging plateau boundary that has lately been reactivated by the Tibetan Plateau expansion. • Permotriassic exhumation driven by closure of Paleo-Tethys and Paleo Asian Oceans. • Late Mesozoic episodic exhumations responding to far-field tectonic processes. • Eocene exhumation as an immediate response to the initial India-Asia collision. • Post-middle Miocene exhumation due to expansion of the Tibetan Plateau. • Longshou Shan thrust belt marks an newly-emerged NE boundary of Tibetan Plateau. [ABSTRACT FROM AUTHOR]

[Display omitted] • Multiple fluid sources are identified by variation range of Cl isotopes and Cl/Br ratios from. • Vein-type Zn-Pb mineralization is triggered by mixing of evaporated seawater and magmatic hydrothermal fluids. • Quantitative model shows that the mixing volume ratios of both sources are between 1:9 and 4:6. Numerous hydrothermal vein-type Zn–Pb deposits worldwide are characterized by low-temperature metallogeny, no spatial relationship with plutons, and strong water-rock interaction, which result in the difficulty of constraining the fluid origin and the process of ore formation by traditional geochemistry. In this study, we employ chemical and chlorine isotopic composition of bulk fluid inclusions from ore-bearing and ore-barren quartz veins to constrain the possible sources of ore-forming fluids and the process of metal precipitation in the hydrothermal systems of the economic vein-type mineralization in eastern Guizhou Province, SW China. Our new geochemical data are indicative of two end-members in the systems, one identified in the ore-bearing veins with high K/Na, Li/Na, Cl/Br ratios, and δ37Cl values representing magmatic hydrothermal fluids, another distinguished in the ore-barren veins with low Cl/Br ratios and δ37Cl values representing evaporated seawater. We conclude there is a systematic variation of these geochemical data as the results of the mixing between the former and the latter end-member. In the meantime, the mixing is quantitively assessed to study the mixing volume ratios of both end-members. Based on our data and our own previous study, a genetic fluid mixing model involving the magmatic hydrothermal fluids related to deep magma activity and the evaporated seawater is established for the formation of the vein-type Zn–Pb deposits. This study provides a novel geochemical approach for recognizing hydrothermal mineralizing systems. [ABSTRACT FROM AUTHOR]

Many instrumental quantifications for heavy metals require the establishment of the calibration curve between calibrator's signals and mass concentrations based on linear regression model. However, linear fitting based on the ordinary least squares regression model faces the challenges from the instruments, such as homoscedasticity of signals, which may result in the poor performance for the measurement of low mass concentration. In comparison, the linear weighted regression model in many studies has been proven to better address the problem of heteroscedasticity in inductively coupled plasma emission spectrometer (ICP-OES). This study developed a computational software incorporating the linear weighted regression model for the bottom-up evaluation of the measurement uncertainty from a few replicate signals of calibrators and sample. It includes a model of signal precision variation in calibration interval based on the adjustment factor from the previously detailed and daily calibration. In addition, normal distribution for signal repeatability in ICP-OES was confirmed by using the Jarque-Bera test. The Monte Carlo method (MCM) employed here is designed for simplicity and intuitiveness, thus minimizing complex mathematical maneuvers, although it does presuppose a basic proficiency in computer programming. The method was successfully applied to assess the mass concentration of heavy metals (Cu, Zn, Fe, and Mn) in acid mine drainage by ICP-OES after necessary sample dilution. The robustness of developed measurement uncertainty method, which will not be limited by this assumption of the quality of calibrators preparation, was validated through the analysis of control standards with known mass concentration and sample with several spiking levels. The metrological compatibility of mass concentration and respective uncertainty was given to show the feasibility, practicality and reliability of the MCM simulations. A user-friendly software for the MCM is provided in the supplementary material. Overall, this study makes a contribution to the objectivity of the evaluation of environmental sample analysis. [Display omitted] • Development of a user-friendly tool of instrumental quantification uncertainty. • Monte Carlo simulation for evaluations of measurement uncertainty. • Application of the precise model based on detailed and daily calibration. • Linear weighted regression model for processing approximately heteroscedastic data. • The tool was successfully used for the measurement of heavy metals in acid mine drainage by ICP-OES. [ABSTRACT FROM AUTHOR]

Rare earth elements and yttrium (REY) composition of paleo-seawater and redox conditions of localized water masses during deposition are documented by the REY preserved in modern pristine chemical sedimentary phosphorites. However, contrary to modern phosphorites, some older ones (e.g., Cambrian and Proterozoic phosphorites) display anomalous REY patterns that deviate from modern seawater, and limit the use of their parameters (e.g., Ce anomalies) as a reliable proxy for redox conditions in this case. In this work, elements of bulk-rocks and apatite grains, Sr Nd isotopes, and phosphate oxygen isotopes (δ18O P) from Jingxiang (JX), Yichang (YC), and Xingshen (XS) phosphorites of the Ediacaran Doushantuo Formation in South China were investigated to address this quandary. The REY indexes and patterns of bulk-rocks and apatite, as well as Nd isotopes of bulk-rocks, suggest that the phosphorites deposited in the lower, middle, and upper members of the Ediacaran Doushantuo Formation record the sources of REY as being of terrigenous, mixed, and seawater origins, respectively. During the deposition of the Ediacaran Doushantuo Formation, high δ18O P values (18.61 ± 1.04) of all bulk-rocks, close to contemporary marine authigenic apatite, indicate that phosphorus has been involved in strong marine bio-cycling, assuming a final terrestrial source. However, REY composition of the seawater column recorded by authigenic apatite in the lower member of Doushantuo Formation exhibited a right-leaning REY pattern, representing a terrestrial REY end-member. The 87Sr/86Sr ratios of bulk-rocks (0.71031 ± 0.00719) and apatite grains (0.71098 ± 0.00099) also remained consistent throughout the Ediacaran Doushantuo Formation, except for the high 87Sr/86Sr values found in bulk-rocks (0.72200 ± 0.00085) and apatite (0.72271 ± 0.00064) in the lower member of JX, which are presumed to result from source rocks with high radioactive Sr. Combined with REY indexes (Ce anomalies, Y/Ho ratios, and the differentiation of REY) and constant 87Sr/86Sr values of apatite, varying REY patterns from the lower to upper members of the Doushantuo Formation indicate that the scavenging rate of terrestrial REY inputs to the ocean by suspended particles (e.g., Fe Mn oxyhydroxides) in the water column is controlled by the degree of seawater oxidation. Our study highlights that REY inputs to seawater could undergo seawater cycling (i.e., the removal of REY by particulates of seawater under oxygen-containing conditions), and only REY that undergo sufficient seawater cycling can reflect the true redox conditions of the water column. Therefore, the sources and cycling of REY in seawater should be carefully identified when applying Ce anomalies and Y/Ho ratios of phosphorites to trace the redox conditions of ancient seawater. [Display omitted] • REY are not always the same source as phosphorus in the Neoproterozoic phosphorite. • Authigenic apatite in hypoxic condition commonly preserve the terrestrial REY pattern. • REY experienced sufficient oceanic cycling can record paleo-seawater redox conditions. [ABSTRACT FROM AUTHOR]

Bauxite deposits are an important source of Al and also host a variety of critical metals, including rare earth elements (REEs). However, the parent rocks of bauxite deposits generally have low REE contents, leading to uncertainty over the REE sources and enrichment mechanisms. In this study, we report high REE (2095 ppm; Ce = 1340 ppm) contents in the Lijiatian bauxite deposit in Luxi County, western Hunan Province, South China. The Lijiatian bauxite deposit is the largest deposit in Hunan Province, with a total Al resources exceeding 7 × 106 tons. The ore-bearing strata in the lower Permian Liangshan Formation (ca. 275 Ma) are comprised a 3–5-m-thick bauxite layer (bauxite ore/clay) and an underlying 4–8-m-thick Fe layer (Fe ore/Fe-rich clay). The high REE contents in the bauxites can be attributed to the widespread presence of bastnäsite. The bastnäsite commonly coexists with authigenic chlorite, which formed at temperatures of 221–285 °C, indicative of a hydrothermal origin. Uranium–Pb dating of the bastnäsite yielded an age of 141.4 ± 7.0 Ma, indicating a hydrothermal overprint occurred during the Early Cretaceous, which resulted in the enrichment of REEs in the bauxites. The high contents of REEs, Ba, and P in the Cambrian Niutitang Formation black shales indicate it was a potential source of these elements for bastnäsite and coexisting barite and apatite. The deep-seated hydrothermal fluids (enriched in HF, CO 2 , and H 2 S) associated with the late Yanshanian extensional tectonic event in South China (155–123 Ma) ascended along fractures. The ascending fluids interacted with the black shales, extracting REEs, Ba, and P. When the fluids reached a certain depth, they mixed with the infiltrating basinal waters to form a mineralising fluid. The fluid then migrated towards the bauxite layers, underwent cooling and depressurisation, and precipitated bastnäsite, barite, apatite, and chlorite. We propose that a hydrothermal event led to the enrichment of REEs in the bauxites in Hunan Province. Considering the scarcity of REEs in the parent rocks of bauxites worldwide, hydrothermal activity likely has a key role in REE enrichment in bauxites. [Display omitted] • The main mineral hosting REE (Ce) in Permian bauxite from southern China is Bastnäsite. • The bastnäsite formed during the Cretaceous period due to hydrothermal fluid activity. • The REEs are source from the basement black shale. [ABSTRACT FROM AUTHOR]

During the interglacial period of the Cryogenian glaciation, the extensive "Datangpo-type" manganese ores were deposited in the Nanhua Basin. However, there has been significant controversy over the precipitation mechanism of manganese for decades. Based on iron and nitrogen isotope data from the manganese ores of the Datangpo Formation in Chongqing (South China), combined with previous research, we propose that the manganese ores of the Datangpo Formation precipitated directly in an anoxic bottom-water environment in the form of rhodochrosite. The δ56Fe values in the Bijiashan manganese ore (δ56Fe = −0.19 ± 0.13 ‰) are close to those of modern marine hydrothermal iron, and there is a strong positive correlation between the δ56Fe value and iron concentration (R2 = 0.81), indicating that the precipitation of manganese ore could be mainly affected by hydrothermal input. After comprehensively comparing the δ56Fe values of the whole rock and pyrite in the manganese ore of the Datangpo Formation, we believe that iron from hydrothermal sources directly and quantitatively combined with sulfides to form pyrite. Additionally, the bottom seawater of the basin was mainly anoxic. The nitrogen isotope composition indicates the presence of a stable nitrate reservoir in the ocean at that time, and manganese ore deposition may have been influenced by the input of high-salinity water from the open ocean. Due to the supply of NO 3 - from the open ocean to the graben basin, the δ15N in manganese ore is significantly higher than that in black shale. The input from the open ocean led to an increase in alkalinity in the bottom water of the basin, which favored the precipitation of rhodochrosite. Considering that the oxidation potential required for manganese oxidation precipitation is higher than that required for iron oxidation precipitation, it is most reasonable to conclude that under alkaline anoxic conditions in the bottom water layer, Mn2+ directly precipitated in the form of rhodochrosite. • The iron isotopes in Mn ores indicate extensive hydrothermal activity. • Fe2+ aq was directly precipitated as sulfide during the precipitation of Mn ores. • Nitrogen isotopes prove that Mn ores precipitate with open ocean water input. • The "Datangpo-type" manganese ore may be directly precipitated as rhodochrosite. [ABSTRACT FROM AUTHOR]

Clay-type lithium resources have been developed as an important natural lithium source secondary to hard rock sources and brine sources. In this study, a green and effective lithium extraction process employing ferric salt solutions to leach lithium-rich clay was proposed. Upon calcination treatment, 73.6% of lithium could be leached over a period of 180 min using a 15% ferric sulfate solution at 90 °C. The most suitable calcination temperature, leaching temperature, ferric sulfate concentration, and reaction time were determined to be 600 °C, 90 °C, 15% ferric sulfate, and 180 min, respectively. Ferric chloride and ferric nitrate had similar lithium leaching efficiencies under the same conditions. In addition, ferrous, sodium and calcium salts were introduced and compared in terms of their lithium extraction abilities. The results indicated that ferric ions had good selectivity for lithium leaching. The leaching process was considered to involve ion exchange between ferric ions and lithium ions. [Display omitted] • Ferric salts were efficiently used for lithium leaching from Li-rich clay. • Reagent concentration and leaching temperature/time was respectively studied. • Leaching residues are green and weakly-acidic compared to acid leaching process. • Ferrous, sodium, and calcium ions demonstrated lithium leaching by ion-exchange. [ABSTRACT FROM AUTHOR]

[Display omitted] • Ga isotope compositions of bauxite, claystone and dolostone (bedrock) from the Xiaoshanba bauxite deposit are obtained. • During the supergene weathering process, Ga and Al tend to be enriched in the residual phase, however, a small proportion of Ga and Al migrated with the leachate. • Light Ga isotopes preferred to enrich in residual rather than solutions during weathering. • Ga isotope could provide new insights on tracing the origin of bauxite. We studied the gallium (Ga) isotopic composition of the Xiaoshanba bauxite deposit in central Guizhou Province, southwest China. Claystone with kaolinite as the main mineral has δ71Ga IPGP values of − 0.22‰ to + 0.19‰ (−0.04‰ on average), whereas bauxite with diaspore as the main mineral has δ71Ga IPGP values of − 0.60‰ to − 0.15‰ (−0.35‰ on average). Other samples with diaspore and kaolinite as the main minerals have δ71Ga IPGP values between those of the claystone and bauxite (−0.20‰ on average). Dolostone from the Loushanguan Group has δ71Ga IPGP values of − 0.28‰ to − 0.18‰ (−0.24‰ on average). Samples with kaolinite as the main mineral have higher δ71Ga IPGP values than samples with diaspore as the main mineral. However, δ71Ga IPGP values in the dolostone are lower than those of the claystone. Based on vertical variations in δ71Ga IPGP values and Ga/Al ratios, we speculate that weathered dolostone from the Loushanguan Group may have higher δ71Ga IPGP values than unweathered dolostone. In addition, for both of the Jiujialu and Wulongsi ore bodies, samples from the upper part of the profile are relatively enriched in heavier Ga isotopes than samples in the lower part. During the process of bauxite ore formation, supergene weathering and Ga re-precipitation could have led to enrichment in lighter Ga isotopes. This mechanism of isotopic enrichment has the potential to record the material source of the bauxite. The results of leaching experiments show that, during supergene weathering, Ga is more available to the leaching liquid than Al under neutral to weakly alkaline conditions, whereas Al is more soluble than Ga under weakly acidic conditions. In natural deposits, samples with a high degree of weathering show an obvious decoupling between Ga and Al; consequently, in a given sedimentary environment, samples with kaolinite as the main mineral have higher Ga concentrations than samples with diaspore as the main mineral. Clay minerals such as kaolinite can be important resources of Ga. [ABSTRACT FROM AUTHOR]

[Display omitted] • Detrital Zircons in the Shifang phosphorite show three main age peaks. • Zircons in the Shifang phosphorite may directly originate from the underlying strata. • Cambrian phosphorite may provide an important phosphorus source. Phosphorites (P 2 O 5 content > 18 wt%) are widespread in the world; however, high-quality phosphorite (P 2 O 5 content > 30 wt%) is exceptionally rare. In South China, the Devonian Shifang phosphorite deposit represents not only a high-quality phosphorus ore resource but also hosts abundant rare earth elements (up to 3677.6 ppm). Despite its significance, the provenance of this unique phosphorite deposit has remained unclear. In this study, we conducted U-Pb dating, Hf isotope, and trace element concentrations analysis of detrital zircon from the phosphorite in the Shifang phosphorite deposit to well constrain the specific provenance and potential material source of the phosphorite. Cathodoluminescence (CL) images and trace elements analysis of zircons suggested that the majority of zircons have a magmatic origin. The U-Pb dating age of these zircons revealed three main age peaks at ∼ 560–520 Ma, ∼850–750 Ma and ∼ 1050–950 Ma. A comparison of the εHf values of zircons for the same age group worldwide revealed the following: (1) The 1050 ∼ 950 Ma detrital zircon in the Shifang phosphorite deposit could be derived from North India; (2) The 850–750 Ma zircons originated from Tonian granites in the western South China Block; (3) The 560–520 Ma zircons had two sources, one could be the Kuungan orogeny in the east-Gondwana, and another could be the Arabian-Nubian Shield in the northern-west-Gondwana. In addition, our new age histograms of detrital zircon U-Pb ages are well consistent with underlying strata, such as Silurian and early-middle Devonian. Combining these findings with the geological activities in the study area, we conclude that zircons in the Shifang phosphorite deposit may directly originate from the underlying strata in the study area and the Cambrian Qingping phosphorite deposit may have served as an essential phosphorus source for the Shifang phosphorite deposit. [ABSTRACT FROM AUTHOR]

The occurrence of the polymetallic Nb layer in the upper Permian Xuanwei Formation in southwest China has been documented extensively. The origin of Nb, as well as other metals like Zr and rare earth elements (REEs), has received much research attention; however, the source of these elements remains enigmatic. In recent studies, an uncommon Nb-rich titanite (CaTiSiO 5) has been discovered in the Emeishan basalts beneath the Xuanwei Formation in the eastern Yunnan–western Guizhou region. However, its origins and genetic relationship to the polymetallic Nb layer remain unclear. In this study, we used in situ microanalytical and U Pb dating techniques to investigate the titanite in these Emeishan basalts. Our objectives were to determine the origins of the titanite and its relationship to the polymetallic Nb layer in the lowermost Xuanwei Formation. The basalts consist of approximately 70%–90% phenocrysts and 10%–30% matrix. The phenocrysts are mainly coarse-grained (>30 μm) plagioclase, clinopyroxene, and Fe-Ti oxides (ilmenite and magnetite), whereas the matrix comprises mainly fine-grained (<30 μm) titanite and glass. The titanite is hypautomorphic or xenomorphic and occurs as small, disseminated grains within the matrix. The titanite U-Pb dating of basalt sample reveals a Tera–Wasserburg lower intercept age of ca. 259.6 ± 4.3 Ma, which corresponds to the age of the eruption timing of Emeishan large igneous province (ELIP; 260.9–257.4 Ma). This implies that the formation of titanite within the matrix can be attributed to rapid cooling of residual melt subsequent to fractional crystallization of a substantial quantity of phenocrysts. The LA-ICP-MS analysis reveals that the trace element composition of titanites in the Emeishan basalts exhibits similarities to weathering-type titanite, as evidenced by elevated La N /Yb N ratios and low concentrations of Y, ΣREE, Th, and U, as well as reduced Lu/Hf and Th/U ratios. Thus we propose that these titanites crystallised during the late-stage magmatic evolution, resulting from magmatic fractional crystallization and subsequent weathering alteration. The materials required for titanite crystallization in the basalt matrix primarily sourced from the residual melt, while weathering dissolution of plagioclase and clinopyroxene in the phenocrysts may have provided additional Ca and Eu for titanite formation. As weathering progressed, the Nb-rich titanite underwent a transformation into Nb-rich anatase and gradually became enriched in the regolith. This material was subsequently transported to nearby basins and deposited in terrestrial environments, resulting in formation of the polymetallic Nb layer in the lowermost Xuanwei Formation. Our findings provide insights into the origins and evolution of titanite in the Emeishan basalts, as well as formation of the polymetallic Nb layer in the lowermost Xuanwei Formation in the eastern Yunnan–western Guizhou region, southwest China. [Display omitted] • Nb-rich titanite is widely present in the Emeishan basalts in the southwest China. • The titanite originated from fractional crystallization and weathering alteration. • The Nb-rich anatase in the Xuanwei Formation was derived from ELIP basalts. [ABSTRACT FROM AUTHOR]

[Display omitted] • The source and evolution of ore-forming fluids are characterized using lithium and chlorine isotopes. • Magmatic source of ore-forming fluids plays a critical role in the mineralizing systems of the Luziyuan Zn-Pb-Fe-(Cu) deposit. • The increase of δ 7 Li values in the ore-forming fluids during retrograde skarn alteration is the results of Rayleigh fractionation in a closed system. The sources and temporal evolution of fluids related to distal skarn mineralization strongly influence the minerals that form, but remain poorly understood. In this study, we use the lithium and chlorine isotopic compositions of fluid-inclusion leachates (FIL) to elucidate the nature and evolution of fluids that formed the Luziyuan distal skarn Zn–Pb–Fe–(Cu) deposit, China. The δ7Li values of prograde skarn stage rhodonite FIL (+5.37‰–+7.31‰) are similar to those of typical magmatic fluid. The δ7Li values (+11.69‰–+12.54‰) of actinolite FIL are higher than those of rhodonite FIL; this is attributed to Rayleigh fractionation within a closed magmatic–hydrothermal system. It is inferred that up to 70% of fluid-borne Li is sequestered by hydrous minerals during retrograde skarn alteration, consistent with conclusions drawn from previous studies of fluid-inclusions. The δ7Li values of galena FIL (+9.78‰–+13.19‰), black sphalerite FIL (+11.62‰), and reddish-brown sphalerite (+10.44‰–+11.66‰) overlap with those of actinolite FIL, indicating that phase separation occurred during Zn–Pb mineralization at the Luziyuan deposit. The low δ7Li values of light-yellow sphalerite FIL (+6.75‰) and calcite FIL (+3.95‰–+6.49‰) record external fluid input, probably meteoric water. The positive δ37Cl values of rhodonite FIL (+1.82‰–+1.83‰) are consistent with those of magmatic fluids. However, the δ37Cl values of actinolite FIL (+0.49‰) are lower than those of rhodonite FIL, indicating that FIL within hydrous minerals might not record fluid sources reliably. [ABSTRACT FROM AUTHOR]

The early Cambrian ocean was marked by significant redox changes, but the detailed redox evolution of seawater and its relationship to biological expansion are not fully understood. Widespread chert successions are present in lower Cambrian deposits on the Yangtze Block, South China, which have great potential to record oceanic chemistry. Here, we analyze rare earth elements (REE) and Si and Fe isotopes along three regional chert sections to constrain the origin of lower Cambrian cherts and the redox conditions of the early Cambrian ocean. The REE patterns and Si isotopes illustrate that lower Cambrian cherts at the Muyang (MY; Yanjiahe Formation) and Zunyi (ZY; Niutitang Formation) locales originated from the replacement of precursor carbonates and black shales, respectively, whereas cherts at Chuanyanping (CYP; Liuchapo Formation) locale originated from direct chemical precipitation from seawater and/or hydrothermal fluids. All cherts, except for several lower CYP cherts with hydrothermal contributions, primarily preserved seawater chemical signals. The Ce/Ce* and Y/Ho ratios indicate that these cherts were deposited near a suboxic/anoxic interface, where seawater may have been ferruginous overall, while more subtle redox changes, namely, ferruginous (less reducing) and ferruginous (more reducing), were identified by Fe isotopes. Based on new data and previous results, we propose that the early Cambrian ocean on the Yangtze Block was characterized by a stratified redox framework. Before ~535 Ma in the Cambrian, oxic seawater occurred only along the inner shelf (MSC section), below which seawater was primarily ferruginous (less reducing). During ~535–526 Ma, oxic seawater gradually expanded to the outer shelf (MY section) and a metastable ferruginous (more reducing) zone dynamically existed at shelf–slope locations. Temporal and spatial comparisons revealed that the water column on the Yangtze Block may have experienced a progressive deepening of the redoxcline during the early Cambrian (~535–526 Ma). The metastable redox zone may have been an analogue of the modern oxygen minimal zone (OMZ), which is associated with biological activity and high productivity. The occurrence and spatial fluctuation of the metastable ferruginous (more reducing) zone may have been associated with the evolution of small shelly fossils from assemblage 1 (SSF1) to assemblage 3 (SSF3) and their spatial expansion from shelf to slope. Therefore, accompanied by oceanic oxygenation, the occurrence and spatial fluctuation of an OMZ-like metastable zone may have regulated the biological diversification and distribution during the early Cambrian (~535–526 Ma). • Three origins of lower Cambrian cherts were recognized on the Yangtze Block. • An OMZ-like zone dynamically occurred at shelf–slope locations during ~535–526 Ma. • Spatial change of an OMZ-like zone regulated biological distribution and evolution. [ABSTRACT FROM AUTHOR]

• Three major mineralization stages of sulfide ores are identified. • Alternating precipitation of Mo and Ni-Zn sulfides represents a SEDEX deposition. • Sulfur sourced from both hydrothermal emissions and microbial sulfate reduction. • Presence of euxinic water column limited colonization of deep-water habitats. Widespread Ni-Mo sulfide mineralization in South China during the early Cambrian may have affected the seawater chemistry and biodiversity of this region, but its underlying causes are not well-understood. To better understand the formation of sulfide ores in early Cambrian marine systems, this study evaluated the paragenesis and sulfur isotopic composition (δ34S) of sediment-hosted Ni-Mo sulfide ores in the lower Cambrian Niutitang Formation of the Nanhua Basin of South China. Petrographic analysis revealed three types of sulfide aggregates: (1) ubiquitous framboidal and euhedral pyrite (Py-1), (2) a MoSC phase (i.e., Mo mineralization) that was cogenetic with larger pyrite cubes or nodules (Py-2), and (3) intergrown millerite (NiS), sphalerite (ZnS) and veined pyrite (Py-3) (i.e., Ni-Zn mineralization) characterized by laminated and veined textures. Alternating precipitation of Mo and Ni-Zn sulfides was caused by intermittent emission of Mo-Fe or Ni-Zn-rich hydrothermal fluids into euxinic mid-depth waters of the Nanhua Basin, representing a sedimentary exhalative (SEDEX) process. The different sedimentary ore textures are each associated with a characteristic δ34S distribution. At all study sites, the syngenetic Py-1 phase yields δ34S of −15.7 to + 1.9‰, consistent with a seawater sulfate source that was variably fractionated through microbial sulfate reduction (MSR). In the Nayong and Zunyi areas, δ34S values of −11.8 to +4.4‰ are associated with the MoSC phase, and −20.6 to −6.8‰ with the Py-2 phase. In the Zhangjiajie area, Py-2 yields similar values (−25.1 to −10.8‰) but MoSC higher and less variable values (+8.6 to +18.7‰). These phases are thought to contain a mixture of sulfur sourced from seawater sulfate (via MSR) and hydrothermal fluids in varying proportions. A mode of Ni-Zn sulfides δ34S values between −9.1 and +8.0‰ is likely to represent the isotopic composition of hydrothermal sulfur inputs to the Ni-Zn mineralization. As a consequence, both hydrothermal emissions and biogenic production of H 2 S had a significant influence on seawater chemistry, with consequences for contemporaneous evolution of early marine animal life (e.g., the small shelly fauna and Chengjiang Biota) in the early Cambrian Nanhua Basin. [ABSTRACT FROM AUTHOR]

• First report of Hg records at the deep-sea facies of the Cryogenian Datangpo Fm. • The near zero Δ199Hg value in the Mn-ore layer suggest a volcanic origin. • The thick Hg-rich layer with positive Δ199Hg in the suggests a DOC reservoir existed. • The Hg-rich layer was formed by Hg-DOC release in anoxic conditions. An interglacial period existed between the Sturtian (ca. 720 ∼ 660 Ma) and the Marinoan glacial period (ca. 650 ∼ 635 Ma) in the Cryogenian. It is manifested as the Mn-bearing black rock series of the Datangpo Formation in the Nanhua rift basin, South China. In the Datangpo Formation in the Xiangtan area, a continuous mercury-rich stratum nearly 60 m thick was found, while in a previous study of the Wuhe section of the shallow sea shelf area and the Daotuo section of the semi-deep water slope area, no such thick mercury-rich stratum was reported. To explain this problem, comprehensive analyses were performed mainly focused on mercury and its isotopes, combined with total organic carbon (TOC), total sulfur (TS), and major and trace elements. The results show that the Hg content of all samples of the Datangpo Formation in the Xiangtan section is highly correlated with TOC and TS. Among them, the sandstone and Mn-ore units (Interval I) at the bottom are low in mercury content (19.78 ∼ 297.38 ppb), TOC and TS content, with the mercury isotope of Δ199Hg close to 0 ‰ (0.02 ∼ 0.19‰, with 0.07‰ on average), which is relatively lower in the whole section. The black shale in the middle (Interval II) and upper parts (Interval III) of the section has high mercury contents (121.00 ∼ 721.58 ppb) and high TOC and TS contents, with positive Δ199Hg values (0.20‰ on average). This reveals that a large dissolved organic carbon (DOC) reservoir existed in the deep-water area during the Datangpo period. The release of organic carbon and Hg is mainly controlled by the redox environment and is not affected by paleoproductivity. The persistent high Hg value and positive Δ199Hg values can trace the existence of this DOC reservoir. Additionally, the sandstone-black shale-siltstone sequence of the Datangpo Formation from bottom to top shows a complete interglacial climate pattern characterized by initial warming followed by cooling, as well as a rise and subsequent fall in sea level. This study will help us to establish a more complete Hg cycle and redox process for the Datangpo period in the Nanhua basin. [ABSTRACT FROM AUTHOR]

Rare earth elements (REE including Y—REY) in phosphorites have been used widely as a proxy for seawater chemistry at the time of their formation. However, it is unclear whether metamorphism can lead to REE remobilization and alteration of primary seawater signatures recorded in phosphorites. In this study, we examine similarly aged metamorphosed phosphorite ore deposits from the northeastern margin of the Yangtze Block (Jinping and Xinpu ore sections), with contemporaneously deposited unmetamorphosed equivalents in the southwestern margin of the Yangtze Block (Weng'an ore section). New insights have been provided into the migration of rare earth elements and the redistribution of Zn and O isotopes in metamorphosed phosphorite, which suggests that the varying degrees of metamorphic fluid–rock reaction during the metamorphism process significantly reduced the δ18O value of phosphate (13.7‰ ± 2.2‰ of Jinping phosphate and 7.3‰ ± 1.8‰ of Xinpu phosphate) and added light Zn isotope. These metamorphic fluids were likely generated by the metamorphic dehydration of upper slab uplift during the plate subduction in the Triassic. The negative correlation between the O (and Zn) isotope compositions and REY contents in P-rich rocks suggests that REY were likely re-enriched during the recrystallization process of apatite. Preferential migration of LREE led to significant LREE and MREE enrichment in Haizhou metamorphosed P-rich rocks compared to Weng'an unmetamorphosed phosphorites. [Display omitted] [ABSTRACT FROM AUTHOR]