Positive Ce Research Articles

Geochemical Characteristics of Nephrite from Chuncheon, South Korea: Implications for Geographic Origin Determination of Nephrite from Dolomite-Related Deposits

The Chuncheon nephrite deposit in South Korea is one of the major nephrite deposits in the world, but its origin has been rarely studied. This study explores the mineralogical and geochemical characteristics of the Chuncheon nephrite using a polarizing microscope, an electron microprobe, laser ablation, inductively coupled plasma mass spectrometry, and hydrogen–oxygen isotope analyses and compares them with dolomite-related nephrite worldwide. The main mineral of Chuncheon nephrite is tremolite, which has a felted blastic texture, secondary filling texture, and metasomatic pseudomorphic texture that nephrites from other regions do not have. Chuncheon nephrite is dolomite-related; the total content of rare earth elements is generally low, with highly variable positive and negative Eu anomalies and weak positive Ce anomalies; and the light rare earth elements are enriched. The Chuncheon nephrite formed in an anaerobic alkaline environment with a low degree of mineralization, and the hydrothermal fluids are predominantly meteoric water. Nephrite from different regions has different geochemical characteristics as well as different abundances of rare earth element contents. According to the content and range of elements, such as δCe, δEu, ΣREE, (La/Sm)N, and other rare earth elements, dolomite-type nephrite from different origins can be roughly distinguished.

Evidence of a distal axis inactive high-temperature hydrothermal field on the ultraslow spreading Southwest Indian Ridge: Insights from mineralogy and geochemistry studies

The development of hydrothermal activities on mid-ocean ridges is primarily influenced by magmatic and tectonic activities close to the ridge axis. On slow and ultraslow spreading ridges featured by limited magma supply, prolonged hydrothermal activity can also occur in non-transform offsets (NTO), where sustained ultramafic-related hydrothermal circulation happens due to prolonged hydrothermal processes associated with the expose of ultramafic rocks. In contrast, basalt-hosted hydrothermal fields are barely developed in NTOs, especially in off-axis area, due to insufficient magma supply. In this study, we reported the occurrence of a distal axis (∼9.5 km) basalt-hosted hydrothermal field (50.63°E) on the NTO of segment 27 of the ultraslow spreading Southwest Indian ridge. The hydrothermal products are characterized by layered crusts mainly composed of oxides, such as limonite and goethite, rich in Fe and depleted in Si. These crusts contain high contents of trace elements derived from seawater, such as P, As, Mo, U, and Sb and show REE pattens with negative Eu and mostly positive Ce anomalies. However, the high Cu content (1.82 ± 0.89 wt%, N = 27), low absorption ratio of Cu (18.39 ± 12.71%, N = 9), and residual chalcopyrite altered by goethite suggest prior high-temperature hydrothermal activity. Lead isotopic composition with basaltic rocks signatures that distinct from those of low-temperature crusts of seawater origin also support this conclusion. The Fe-rich crusts appears to be the result of high-temperature sulfides altered by late-stage low-temperature diffuse flow. This field is currently the furthest known distal axis basalt-hosted hydrothermal field located in NTOs of ultraslow spreading ridges. The hydrothermal circulation is likely due to a combination of off-axis normal fault and gabbro diking. Our results emphasize the occurrence of distal axis basalt-hosted high-temperature hydrothermal activities on NTOs of ultraslow spreading ridges, and may lead to an increased estimation of hydrothermal heat and chemical influx to the ocean.

REE + Y uptake in bioapatite revisited: Facies-controlled variability in coeval conodonts

REE + Y concentrations in bioapatite have been repeatedly shown to be ambiguous carriers of information for paleo-seawater reconstructions. The uptake of REE + Y begins rapidly after deposition, and bioapatite can, therefore, potentially record the pore water conditions during early diagenesis. In this study, we examined the REE + Y composition of conodonts belonging to a single species from three coeval facies across the Ordovician Baltic Paleobasin carbonate shelf. We show that the REE + Y concentrations, as well as Ce/Ce*, bell-shape index (BSI), Y/Ho and LaN/SmN ratios, vary systematically in conodonts from facies with different host rock compositions. Dissimilarly, REE + Y patterns and ratios of conodont dental elements from the same facies are uniform, indicating that the local depositional environment imposes principal control on the REE + Y uptake by bioapatite. Furthermore, our results show that even though REE + Y concentrations in different histological tissues of the same conodont vary significantly, no REE-specific fractionation occurs, resulting in similar REE + Y ratios in all tissue types. Our results illustrate that conodonts can record modified seawater-like characteristics of REE compositions if the input of FeMn oxyhydroxides and particulate organic carbon (POC) is low. In contrast, under elevated POC and FeMn oxyhydroxide loading, the conodonts show increasingly positive Ce anomalies and MREE enrichment. Collectively, these results suggest that, although primary seawater signatures are not captured in bioapatite, the conodont REE + Y patterns are controlled by local depositional environments and can record early diagenetic pore water conditions.

Rare earth elements in alkaline Lake Neusiedl, Austria, and the use of gadolinium microcontamination as water source tracer

The rare earth elements are increasingly used in high-tech enabling technologies and have become emerging (micro)contaminants. Their environmental impact is poorly known and regulated. Here we focus on the rare earths and yttrium (REY) systematics in Lake Neusiedl at the border between Austria and Hungary. Lake Neusiedl is the largest alkaline steppe lake in Europe and is characterised by unique and dynamic geobiological conditions. Steppe lakes, in general, are very susceptible to anthropogenic influence, as contaminants can easily accumulate under an endorheic setting. We report the first REY data for water samples from Lake Neusiedl and surrounding lakes. Lake Neusiedl shows the REY signature typical of alkaline lakes, i.e. a positive Ce anomaly and enrichment of heavy relative to light REY. More importantly, we identified prominent anthropogenic positive Gd anomalies that can be used as a water source tracer in Lake Neusiedl. The anthropogenic Gd can be tracked back to the Wulka River, one of its tributaries, and originates from medical contrast agents. As these cannot be removed from sewage during wastewater treatment, they are released into the river with the effluents from wastewater treatment plants. Additional REY data from the surrounding smaller lakes suggest that smaller amounts of anthropogenic Gd may also be present in local groundwater. We demonstrate that the anthropogenic Gd can be utilised to quantify the riverine component in Lake Neusiedl waters. However, as it reveals the presence of wastewater-derived substances in the National Park waters in general, it also hints to the potential presence of other contaminants that may have higher (eco)toxicities than the contrast agents.

REE + Y distribution in Tremadocian shelly phosphorites (Toolse, Estonia): Multi-stages enrichment in shallow marine sediments during early diagenesis

Sedimentary phosphorites in Cambrian-Ordovician boundary beds in Estonia are among Europe's most extensive phosphate rock reserves, with a tonnage of approximately three billion tonnes. In addition, they are potential sources of rare earth elements and yttrium (REE + Y). The ore consists of sandstone rich in phosphatic brachiopod fragments deposited in a shallow marine peritidal environment of the Baltic Paleobasin. A detailed geochemical and mineralogical investigation was conducted on the northern part of the Toolse deposit based on three drill core cross-sections. The REE sequestration model was developed based on the correlation of the sedimentary facies of the members of the Kallavere formation. Analyses were conducted on 140 whole-rock samples and 14 discrete black shale samples. Inductively coupled plasma mass spectrometry (ICP-MS), X-ray fluorescence (XRF) and X-ray diffraction (XRD) measurements were performed for each sample. Textural analyses were conducted with field-emission scanning electron microscopy (FE-SEM), and quantitative wavelength dispersive spectrometer (WDS) analysis of major and trace elements was performed with an emission electron probe microanalyser (EPMA).The PAAS normalised REE + Y patterns were relatively homogeneous throughout the deposit except for the cerium and yttrium contents. The REE + Y contents of the phosphorites indicate a distinctive ‘bell-shaped’ pattern enriched with middle-REE (MREE) enriched. In the lower part of the deposit, the ∑REE + Y concentration is enriched up to 12-fold, compared to the average shale, reaching up to 1234 ppm. LREE enrichment is observed in these horizons, with a 9-fold peak at neodymium. In terms of absolute values, the most prevalent REEs are, in order, Ce, Y, Nd, and La, which respectively reach maximum mean values of 296 ppm, 248 ppm, 164 ppm and 135 ppm.The profiles indicate multistage uptake during transport, deposition, and early diagenesis of brachiopod detritus. The sedimentation was associated with a steep redox gradient in the porewater in a coastal environment during the beginning of marine transgression. The near-shore upwelling of oxygen-poor deeper water rich in dissolved nutrients and Mn, combined with the input of lithogenic Fe, helped create favourable conditions for REE sequestration. Positive Y anomalies indicate an initial uptake of REE + Y by hydroxyapatite through Ca substitution in an oxic environment near the sediment–water interface. The sediment burial induced the formation of carbonate fluorapatite (CAF) and a shift to the REE adsorption uptake mechanism, reinforced by the significant intercrystalline porosity of the shells. The transition to a suboxic environment below the surface layers resulted in the reductive dissolution of Mn-(oxyhydr)oxides and the release of LREE in the porewater system, resulting in an overprint of the original REE pattern to the point of inducing positive Ce anomalies. A late enrichment in MREE occurred during early diagenesis as a result of desorption of REE from the Fe-(oxyhydr)oxides and organic-rich particles under relatively anoxic conditions.

Clay mineralogy and geochemistry of surface sediments in the equatorial western Indian Ocean and implications for sediment sources and the Antarctic bottom water inputs

Sediments in the equatorial western Indian Ocean are mixed products from biological, terrigenous, autogenic, volcanic, and hydrothermal materials influenced by various circulation and water masses. The sediments record information of sources and sedimentary environments. To identify the different sources of non-carbonate components in the sediments of the equatorial western Indian Ocean and explore the factors influencing their sedimentary characteristics, surface sediments of the equatorial western Indian Ocean were analysed for clay minerals as well as major and rare earth elements following carbonate removal. Palygorskite, as an indicative mineral of aeolian dust from the North Africa-Arabian Peninsula, is ubiquitous in the sediment of the equatorial western Indian Ocean. These non-carbonate materials are mainly derived from the North Africa-Arabian Peninsula as well as the Indus River and Deccan Traps. The study area can be divided into two sedimentary zones according to the water depth, major element content, and related indexes of rare earth elements (δCe, δEu, LREE/HREE). The sediments of Zone II, being influenced by the Antarctic bottom water, are mainly calcareous clay and characterised by a significant positive Ce anomaly and relative MnO enrichment, with relatively high palygorskite, Al2O3 content, and LREE/HREE ratio (mean values of 24%, 13.95% and 14.00). The sediments of Zone I are mainly clayey calcareous ooze, with a relatively weak positive Ce anomaly and a low palygorskite content (20%). Low Al/(Al+Fe+Mn) values in the sediments of Zone I demonstrate slight signs of hydrothermal input. This study revealed that continental weathering debris is an important source of non-carbonate sediments in the equatorial western Indian Ocean and established that the Antarctic bottom water is an integral factor affecting the sedimentary environment in this region. We present a complete regional sedimentological study of the equatorial western Indian Ocean and provide theoretical support for the reconstruction of the paleo-oceanic environment.

Cadomian Iron ore bodies in the Bafq-Saghand metallogenic province, Iran: genetic constraints from field observations and laser ablation ICP-MS mineral studies

ABSTRACT The volcano-sedimentary unit in the Bafq-Saghand metallogenic province (BSMP) of Central Iran hosts various types of iron ore bodies including Fe-oxides with jaspilite beds, Mn-dominated iron lenses, magnetite-apatite lenses, and massive magnetite-apatite deposits. The Fe-oxides with jaspilite beds and Mn-dominated iron lenses have limited outcrops and show volcano-sedimentary features in the field. The main features are the presence of syngenetic submarine rhyolite-hosted magnetite, lamination and bedding of iron ore body, jaspilite and dropstone. Volcano-sedimentary origin is testified by magnetite composition showing affinity to BIF and positive Eu and negative Ce anomaly. Magnetite-apatite lenses and massive magnetite-apatite deposits that having spatio-temporal correlation form the main economically important deposits. They have magmatic to high-temperature hydrothermal field characteristics (lava flow-like ore bodies, the presence of degassing tubes in ore bodies, occurrence of brecciated texture and developed Na-Ca metasomatism). Mineral composition (enrichment of LREE, magnetite and apatite negative Eu anomaly and Co/Ni < 1 in pyrites) is in agreement with magmatic and high temperature hydrothermal origin. We propose a hydrous and oxidizing mantle derived iron-rich basic magma that formed in an extensional post-collisional setting for origin of Kiruna-type IOA ore bodies of the BSMP. Fe-oxides with jaspilite beds and Mn-dominated iron lenses resulted from degassing or eruption of iron-rich magma during Ediacaran in a submarine environment. However, magnetite-apatite lenses and massive magnetite-apatite deposits formed from an Early Cambrian magmatic-hydrothermal transition system from a magnetite-crystal mush zone.

Diagnostic REE patterns of magmatic and hydrothermal apatite in the Zhuxi tungsten skarn deposit, China

Apatite is increasingly used as a tracer for petrogenetic and hydrothermal processes. We studied the cathodoluminescence (CL) texture and composition of igneous and hydrothermal apatite from the Zhuxi biotite granite and its associated hydrothermal tungsten system in the Late Mesozoic Jiangnan porphyry-skarn tungsten belt in South China. Both magmatic and hydrothermal apatite is anhedral to subhedral, with up to >1 mm grain size. Igneous apatite has relatively constant ΣREE + Y contents in the 2700–6500 ppm range (3970 ± 1003 ppm; n = 52). Hydrothermal apatite in exoskarn has lower ΣREE + Y contents in the range from <1 ppm to ∼1500 ppm, i.e. a strongly heterogeneous REE distribution (101 ± 253 ppm; n = 68). The ΣREE + Y contents correlate positively with CL brightness in both magmatic and hydrothermal apatite.The REE patterns of magmatic apatite display patterns similar to the host rock (Zhuxi biotite granite): generally flat ((La/Yb)N = 1.19–8.06), with moderately negative Eu anomalies (EuN/EuN* = 0.11–0.51), slightly positive Ce anomalies (CeN/CeN* = 1.05–1.12), and chondritic Y/Ho ratios (25–36, average = 30). The hydrothermal apatite is much different: downward-convex (MREE depleted) patterns ((La/Yb)N = 2.48–211), slightly to strongly positive Eu anomalies (EuN/EuN* = 1.11–540), slightly positive to moderately negative Ce anomalies (CeN/CeN* = 0.40–1.16), and non-chondritic Y/Ho ratios (40–152, average = 84). Since the hydrothermal samples are located outside of the pluton, excluding the influence of feldspar on Eu content, the differences of the Ce and Eu anomalies between magmatic and hydrothermal apatite from the retrograde skarn suggest that the retrograde skarn formed in a more oxidized environment than the granite.The low and variable contents of REEs, low Th/U, and non-chondritic Y/Ho ratios can be diagnostically used to distinguish hydrothermal from magmatic apatite, and the MREE-depleted REE pattern may be a common feature of apatite from retrograde tungsten skarn deposits.

Geochemistry of Neoproterozoic Nagod Limestones from the Girgita Mine, Bhander Group, Madhya Pradesh, India

Vindhyan limestone of the Bander Group (Late Neoproterozoic) in the Maihar area, Satna district, is a part of an anticlinal fold and it forms an outlier in the study area. Geochemical analysis reveals that the proportion of Rare Earth Elements (REEs; La-Lu) in limestones varies between 14.8 ppm and 49.5 ppm. The Eu and Ce anomalies (normalized against Post Archean Australian Shale; PAAS) range from ~ 0.53 to 0.69 and ~ 0.57 to 1.07, respectively. The results of this study revealed that the limestones were principally controlled by the admixture of detrital materials, i.e., (i) The low values of REEs (ii) high values of Y/Ho (iii) positive correlation between REEs and Si, Al, Ti, V, Co, Ni, and Nb, and (iv) slightly negative correlation between CaO and REEs. Further, the variations in Ce anomaly may be due to the influx of detrital materials and positive Ce anomaly was attributable to the shallow marine depositional condition. The distribution of REEs (Chondrite normalized values) illustrates different patterns in the Nagod limestone due to the degree of differentiation in terms of LREEs and HREEs and Eu anomaly. The variations in elemental concentrations and the REE patterns revealed the mixing of detrital materials in the Nagod limestones.

Fluid mobilization of rare earth elements, Th, and U during the terrestrial alteration of H chondrites

AbstractThe chemical effects of terrestrial alteration, with a particular focus on lithophile trace elements, were studied for a set of H chondrites displaying various degrees of weathering from fresh falls to altered finds collected from hot deserts. According to their trace element distributions, a considerable fraction of rare earth elements (REEs), Th, and U resides within cracks observed in weathered meteorite specimens. These cracks appear to accumulate unbound REEs locally accompanied by Th and U relative to the major element abundances, especially P and Si. The deposition of Ce is observed in cracks in the case of most of the weathered samples. Trace element maps visually confirm the accumulation of these elements in such cracks, as previously inferred based on chemical leaching experiments. Because the positive Ce anomalies and unbound REE depositions in cracks occur in all weathered samples studied here while none of such features are observed in less altered samples including falls (except for altered fall sample Nuevo Mercurio), these features are interpreted to have been caused by terrestrial weathering following chemical leaching. However, the overall effects on the bulk chemical composition remain limited as the data for all Antarctic meteorites studied in this work (except for heavily weathered sample A 09516, H6) are in good agreement with published data for unaltered meteorites.

Genesis of ferromanganese nodules associated with mud volcanoes in the southeastern Dongsha waters of the northern South China Sea: Implications for regional deep Mesozoic hydrocarbon prospects

The Dongsha waters of the South China Sea are the location of thick Mesozoic deposits and many mud volcanoes that suggest hydrocarbon accumulation. Knowledge of the mechanism, fluid source and evolution of these mud volcanoes, however, remains inadequate. Ferromanganese nodules have been sampled from several deep-water mud volcanoes in waters around Southeast Dongsha island and provide a unique opportunity to study the fluid origin and evolution of the mud volcanoes in the area. In this contribution, the petrology, geochemistry and C–O isotopes of fluid inclusions in the nodules have been analyzed. The ferromanganese nodules are composed of distinct black Fe–Mn crust layers and light-yellow nucleus that contain quartz that hosts fluid inclusions. The outermost layers mainly consist of iron manganese minerals with high Mn/Fe ratios (0.9∼1.57), whereas the nucleus are dominated by siliceous debris. Positive Ce anomalies (δCe: 1.45∼2.13) and negative Y anomalies in growth layers indicate an anoxic environment, which is conducive to hydromanganite precipitation. In contrast, negative Ce anomalies (δCe: 0.27∼0.96) and positive Y anomalies in the nucleus suggest oxidized conditions. The absence of obvious Eu anomalies may be related to low-temperature hydrothermal conditions. The nucleus is enriched in δ13C (−2.59∼1.09‰) and weakly depleted in δ18O (−4.94∼0.89‰), whereas the growth layers are strongly depleted both in δ13C (−16.94∼–12.57‰) and δ18O (−23.05∼–17.48‰). These values indicate that carbon in the nucleus is mainly inorganic carbon from volcanism, whereas the carbon in the growth layers is related to the leakage of deep old hydrocarbon. The fluid inclusions in the quartz from the nucleus show records of at least two periods of CO2-rich hydrothermal activity and an origin from deep Mesozoic strata before release by mud volcanism. Given the widespread mud volcanism, the quartz from the nucleus may come from debris carried by mud volcano eruptions; the quartz also experienced diagenesis related with micro-organisms. The growth layers are considered to be hydrogenic and affected by the leakage of mature thermogenic hydrocarbons from deep old strata. These findings provide insights into deep mature hydrocarbon sources and thermogenic activity and improve understanding of mud volcanism and deep oil and gas resources in the southeastern Dongsha waters.

Geochemistry, U-Pb zircon geochronology, and Fe isotopes of the Shanzhuang banded iron formation in the North China Craton: Implications for genesis and depositional environment

The Shanzhuang banded iron formation (BIF) occurs in the Shancaoyu Formation, Taishan Group, in the western Shandong Province (WSP), eastern North China Craton (NCC). We constrained the Shanzhuang BIF depositional age of ∼2.50 Ga based on the zircon U-Pb dating of the leptynite interlayers and the cross-cutting metagranitoid. After deposition, the Shanzhuang BIF was subsequently metamorphosed into amphibolite facies at 2.50–2.45 Ga. According to different mineral assemblages, the Fe ores can be divided into three types: magnetite + quartz ± hornblende (type-1 ore), magnetite + quartz + hornblende + garnet ± hematite (type-2 ore), and quartz + hematite ± magnetite ± hornblende (type-3 ore). In the Post-Archean Australian Shale (PAAS)-normalized rare earth element and yttrium (REY) patterns, the three ore types show consistent flat REY curves. All ore types have moderate ƩREY concentrations (27.24–143 ppm), (La/Yb)N values of 0.29–2.31, significant positive Eu anomalies (1.05–3.47), slightly negative or positive Ce anomalies (0.87–1.26), slightly positive Y anomalies (1.16–1.48), and no apparent fractionation between light REEs (LREEs) and heavy REEs (HREEs), indicating mixing of hydrothermal fluid and seawater. The similar REY patterns and heavy Fe isotopes (0.47–1.02‰) of the three ore types suggest a certain amount of continental detritus was incorporated during the precipitation of the Fe phases in the Neoarchean-Paleoproterozoic oceans. The post-depositional metamorphism did not significantly affect the original REY geochemical signature of the BIF. The Shanzhuang BIF ores are not highly pure chemical sediments, but the type-1 ore is relatively pure and more representative of the original sedimentary composition. By contrast, the type-3 ore tends to have higher δ56Fe ratios (0.74–1.02‰) but lower δEu (1.27–1.97‰), implying substantial post-depositional hydrothermal alteration. The Shanzhuang Fe deposit is an Algoma-type BIF, and the surrounding rock consists of pyroclastic materials. Our model indicates that the Shanzhuang BIF was probably deposited in a redox stratified paleo-ocean environment.

Synchronous formation of the ‘forearc’ Bay of Islands ophiolite and its basal high-temperature metamorphic sole constrained by U–Pb zircon ages

The welded metamorphic sole at the base of the Bay of Islands Ophiolite Complex (BOIC) in the Northern Appalachians of Newfoundland shows a typical inverted pressure-temperature (P-T) metamorphic gradient from HT-MP granulite to LT-LP greenschist facies. It incorporates mafic volcanic/plutonic protoliths mixed with pelagic, hemi-pelagic and coarser epiclastic sedimentary protoliths. New LA-ICP-MS U–Pb concordia ages, trace elements, and Ti-in-zircon geothermometry for ∼250 zircon analyses from three metabasites of the upper HT sole amphibolites with N-MORB-like protoliths are reported. Two samples collected within meters of the ophiolite peridotite-sole contact of the Blow Me Down Mountain and North Arm Mountain massifs yielded the oldest comparable concordia ages of 487.7±2.6 Ma and 489.1±3.1 Ma, respectively, that are both within error of the igneous age of 488.3±1.5 Ma of the directly overlying BOIC ophiolite, which formed at a supra-subduction zone (SSZ) forearc spreading center. A third slightly younger age of 484.2±2.4 Ma was obtained for an upper HT amphibolite sample with similar phase assemblages but collected ∼30 m below the peridotite contact of the Table Mountain massif. Zircon crystals analyzed have similar size and morphologies, subparallel rare earth element (REE) variation patterns, and steep heavy REE-enrichments ((Lu/Gd)cn >20), significant positive Ce anomalies (dominantly >5) and slight positive to dominantly negative Eu anomalies (1.2 – 0.4). Zircon shows Th/U mean values of 0.37 – 0.48 with little to no rim to core variation. Minimum Ti-in-zircon mean crystallization temperatures range from ∼764 – 787 °C. These neocrystallized zircon crystals appear to be derived from thin leucosomes within the three amphibolites. Two other samples also from the upper HT sole show evidence of inherited detrital zircon with core dates spanning the Cambrian Notre Dame Arc through older Laurentian-like basement and rift age ranges.Subcretion of the sole took place below a hot forearc asthenospheric wedge, that is, a consequence of the newly-formed BOIC forearc spreading center extending from the back arc to a triple junction along the westward- (or paleo-northward) verging trench of the Notre Dame arc. The early HT sole formation age at ca. 489–488 Ma is long prior to initiation of obduction at ca. 470 Ma and long after initiation of subduction beneath the paleo-northward verging Notre Dame peri-Laurentian arc at ca. 514 Ma. This indicates Newfoundland sole ages of the BOIC and St. Anthony Complex are correlated with the age of SSZ spreading, but not necessarily subduction initiation because previously existing and self-sustaining subduction was ongoing. Sole ages are then not correlated with the younger age of obduction-related orogenic events (e.g., proposed Taconic I and II) in the Newfoundland Appalachians.

Pollution and health risk assessment of rare earth elements in Citrus sinensis growing soil in mining area of southern China.

Analyzing the pollution and health risk of rare earth elements (REEs) in crop-growing soils around rare earth deposits can facilitate the improvement of REE mining-influenced area. In this study, pollution status, fraction and anomaly, plant accumulation characteristics, and potential risks of REEs (including heavy and light rare earth elements, HREEs and LREEs) in C. sinensis planting soil near ion-adsorption deposits in southern Ganzhou were analyzed. The influence of the soil environment on REEs in soil and fruit of C. sinensis was also explored. The geo-accumulation index (Igeo) and ecological risk index(RI) were used to analyze the pollution potential and ecological risks of REEs in soils, respectively. Health risk index and translocation factor (TF) were applied to analyze the accumulation and health risks of REEs in fruit of C. sinensis. The influence of soil factors on REEs in soil and fruit of C. sinensis were determined via correlation and redundancy analysis. Comparison with background values and assessment of Igeo and RI indicated that the soil was polluted by REEs, albeit at varying degrees. Fractionation between LREEs and HREEs occurred, along with significant positive Ce anomaly and negative Eu anomaly. With TF values < 1, our results suggest that C. sinensis has a weak ability to accumulate REEs in its fruit. The concentrations of REEs in fruit differed between LREEs and HREEs, with content of HREE in fruit ordered as Jiading > Anxi > Wuyang and of LREE in fruit higher in Wuyang. Correlation and redundancy analysis indicated that K2O, Fe2O3 and TOC are important soil factors influencing REE accumulation by C. sinensis, with K2O positively related and Fe2O3 and TOC negatively related to the accumulation process.

Co-existing two distinct formation mechanisms of micro-scale ooid-like manganese carbonates hosted in Cryogenian organic-rich black shales in South China

Manganese-rich deposits in the lower member of the Datangpo Formation (DTP) (ca. 663–654 Ma) in South China formed in the aftermath of the Cryogenian Sturtian glaciation. The Mn in the DTP occurs dominantly as rhodochrosite and Ca-rhodochrosite. A hydrothermal origin of the Mn2+ is shown by the rare earth element distribution and significantly high Mn/Fe ratios (3–19, average = 10.1). Previous studies suggested a microbially-mediated process for controlling the DTP black-shale hosted Mn carbonate deposits. However, detailed reports on the formation mechanisms of micro-scale (<2–5 μm) ooid-like Mn carbonates in the DTP have rarely been published. Systematic petrography and geochemical analyses in this study demonstrate the coexistence of two types of micro-scale ooidal-like Mn carbonates formed through two distinct mechanisms, either dominated by microbially-mediated or physiochemically-forced pathways. The Type I Mn carbonate has relatively larger grain size of 2–5 μm and exhibits a radial-concentric microfabric that shows signs of growth banding in the form of alternating light and dark laminae, which mainly express variation in Ca and Mn concentrations. The initial precipitation phase of the Type I Mn carbonate is interpreted to be Mn oxide/hydroxide, based on positive Ce anomalies and selective enrichments of particular trace elements. Novel evidence indicates that the capture of Mn as a carbonate phase directly from the water column by primarily precipitated calcite, which is referred to as the Type II Mn carbonate, has also contributed to the DTP Mn-rich deposits. Multiple roles of organic matter in Mn carbonate formation have been established: (1) catalysed Mn-redox cycling; (2) trapping and transportation of initial mineral precipitates to sediments; (3) serving as a carbon source; (4) regulating the morphology of the Mn carbonate. As a key link for understanding Cryogenian carbon and Mn cycling, specific formation pathways for the DTP Mn-carbonates are likely to have been controlled by given atmospheric-oceanic compositions (including oxygen level, pCO2, and redox conditions) in response to major geological and biological events during the interglacial period. In turn, massive storage of inorganic carbon and phosphorous in Mn carbonate phases would have had a substantial influence on biogeochemical carbon cycling during the Cryogenian.

The rare earth elements of sequentially leached phases in the loess-paleosol sequence at Weinan on the southeastern Chinese Loess Plateau

The rare earth elements (REEs) in loess sediments may preserve key information of paleoenvironmental changes in East Asia but remain poorly explored. Here we present the REE compositions of sequentially leached phases of loess sediments from a 16 m long loess-paleosol sequence collected from Weinan at the southern margin of the Chinese Loess Plateau (CLP). The REEs associated with carbonates, easily reducible oxides, reducible oxides, clay minerals, and the residual silicate minerals were sequentially leached with Na-acetate, hydroxylamine-HCl, Na-dithionite/Na-citrate, 12 mol L−1 HCl and concentrated HF-HNO3 solutions. The results show that the REE concentrations of different phases vary in the loess-paleosol layers and are most enriched in the easily reducible phase (except for the residual phase), which is likely explained by the association of REEs with Mn-oxides. Significant Eu anomalies can only be found in the carbonate and easily reducible phases, with the carbonate phase being characterized by appreciable positive Eu anomalies and the easily reducible phase being characterized by negative Eu anomalies, indicating the incorporation of Eu2+ into secondary carbonates that leaves the authigenic Mn-oxides with depleted Eu relative to other REEs. The carbonate phase shows significant negative Ce anomalies, which is likely due to the preferential removal of Ce4+ by Mn oxides before the formation of secondary carbonates. Nevertheless, appreciable positive Ce anomalies for the easily reducible phase can only be found at the bottom of the paleosol S1 while significant negative Ce anomalies were found within the paleosol S1, indicating the downward leaching of Ce4+ that shows stronger complexation with the organic matters than REE3+ in the soil solution. This may partly account for the negative Ce anomalies previously found in the paleosols. Overall, our results suggest a two-stage evolution of Eu and Ce anomalies of the carbonate phase, with the first stage controlled by the formation of both Mn-oxides and secondary carbonates and the second stage dominated by the precipitation of secondary carbonates. The comparison of carbonate Eu and Ce anomalies with other paleoclimatic proxies indicates that the combination of Eu and Ce anomalies of the carbonate fraction of loess may be applied as novel proxy records of climate change in East Asia.

Rare earth elements in soil around coal mining and utilization: Contamination, characteristics, and effect of soil physicochemical properties

REEs are emerging contaminants, and soils nearby coal and coal ash with high REEs composition are vulnerable to REEs contamination. Besides, coal industry can alter surrounding soil characteristics. However, there is information paucity about REEs contamination and geochemical behaviors along with soil characteristics around coal industrial areas, which are essential for understanding their toxicity and mobilization. The study was conducted in soils surrounding Kriel coal-fired power plant (KCM) and Greenside coal mining in Witbank (GSCM), South Africa. Multivariate statistical analysis, pollution and fractionation indices, and BCR sequential extraction were applied. The ∑REEs in the soils were compared to ∑REEs abundance in the upper earth's crust (UEC), and slightly higher ∑REEs was found in KCM but slightly lower in GSCM. Generally, LREEs are abundant. The soil REEs were normalized using the Post-Archean Australian Shale (PAAS) and Eu and Gd in KCM and Gd in GSCM were >1. Contamination assessment revealed that the soils are slightly to moderately contaminated by REEs. ∑REEs in KCM was significantly correlated with soil particle sizes of 2.00–50.00 μm, Al2O3, Fe2O3, and MnO, while with 2.00–3.00 μm and Al2O3 in GSCM. Fractionation characteristics showed a positive Ce anomaly, with positive linear regressions with Fe2O3 and MnO. In contrast, a negative Eu anomaly was found with positive linear regressions with Al, Ca, and Mg-oxides. Oxidizable fractioned REEs accounted for 32.33% of the ∑REEs in GSCM and 35.85% in KCM, and their high EF suggests enrichment that could be due to coal mining and utilization. Most soil physicochemical properties appear to be negatively correlated with the exchangeable REEs. Overall, the soils are contaminated by REEs and the REEs characteristics are considerably influenced by major elements oxide, U, and Th contents. Therefore, more attention should be paid to REEs contamination and impacts around coal mining and utilization.

Early Cretaceous monsoonal upwelling along the northern margin of the Gondwana continent: Evidence from radiolarian cherts

Radiolarian-bearing cherts are widely exposed in the volcanic-sedimentary sequences associated with the Purang ophiolitic mélange in the western segment of the Yarlung Tsangpo suture zone. Highly diverse and well preserved Lower Cretaceous (Valanginian–Hauterivian) radiolarian assemblages that correlate to the Cecrops septemporatus Zone occur in bedded cherts in the Peiersanggangmu section of the southern Purang ophiolitic mélange. Fifty-five species belonging to 38 genera, including characteristic species: Archaeodictyomitra apiarium (Rüst), Cecrops septemporatus (Parona), Hemicryptocapsa capita Tan, Pseudodictyomitra carpatica (Lozyniak), and Svinitzium pseudopuga Dumitrica, have been recognized.Geochemistry of the cherts reveals high SiO2 contents (average: 92.23 wt%), Al/(Al + Fe + Mn) ratios, and low LaN/CeN ratios. Post Archean Australian Shale (PAAS) normalized rare earth element (REE) abundance patterns exhibit moderately positive Ce anomalies (mean Ce/Ce* =1.35) with relative enrichment in light rare earth elements (LREEs). These features are indicative of deposition in an oceanic basin close to a continental margin environment. Lithological characteristics and geochemical results suggest that the paleogeographical location for these radiolarian-bearing bedded cherts closely matches northern regions of the Indian continent, where existed enhanced upwelling activity and surface mixing resulting from monsoon activities.

Chronology and critical metals enrichment mechanism of ferromanganese nodules from the Parece Vela Basin, Philippine Sea

Ferromanganese nodules are potential economic metal resources enriched with Mn, Co, Ni, Cu, Ti, and rare earth elements plus yttrium (REY). The mineralogy, magnetic scanning, and geochemistry of ferromanganese nodules from the Parece Vela Basin in the Philippine Sea were documented to verify critical metals variations during nodule growth. Based on in situ magnetic scanning, the nodules from the basin were found to initially form during the late Pliocene. At ∼1.6 Myr, the growth structure of the nodules changed remarkably from lamellar to columnar. The inner part has a dense lamellar structure with unstable buserite I, whereas the outer layers are columnar with stable todorokite (or buserite II). The growth rate of the nodule decreased from 4.39 to 2.82 mm/Myr, which may have been related to the persistently weakening of deep-sea sedimentary dynamics in the Philippine Sea since ∼1.6 Myr. The slower growth rate facilitates the enrichment of Ce, resulting in a higher REY content and strong positive Ce anomalies in the columnar structure. The mineralogical compositions and Mn/Fe ratios indicate that the nodules were primarily hydrogenetic with low diagenetic influences. The contents of Ni and Cu increase rapidly, but the trends of Co and REY display an inflection point from the hydrogenetic to diagenetic. REY was primarily enriched in Mn mineral phases, and hydrogenesis dominated the enrichment of REY. Hydrogenesis is beneficial for the enrichment of Ti, Ge, Se, Nb, and Sn. However, diagenesis facilitated the enrichment of Ga, Cd, Li, Tl, Zn, Mo, and W in the nodules of the Parece Vela Basin.

Expression of the Toarcian Oceanic Anoxic Event in the mixed siliciclastic–carbonate system of the Arabian Plate: Insights from rare-earth element geochemistry and statistical analysis

Rare earth elements and yttrium (REEY) are considered powerful indicators of paleo-redox conditions. However, to date, the utilization of REEY remains limited to either pure carbonates or deep marine shales, with little evidence of attempts to test their ability to depict marine anoxia within mixed carbonate–siliciclastic systems. Across the Tethys Ocean, the Toarcian Oceanic Anoxic Event (T-OAE) is widely recorded by black marine shales with strong negative carbon isotopic excursion. Yet, the occurrence and expression of T-OAE across the mixed siliciclastic and carbonate system of the Arabian Plate has not been recorded or even explored. This provides a unique opportunity to test the robustness and viability of REEY, supported by statistical analysis, in revealing marine anoxia in a mixed system. Our results demonstrate a positive Ce anomaly within the middle Marrat, coupled with a positive Eu anomaly and aluminum-normalized Mn enrichment in the underlying lower Marrat carbonates. This could be hypothetically related to volcanic pulses, which triggered the T-OAE. Overall, the REEY geochemical record and detailed statistical analysis of this study indicate, for the first time, the possibility that T-OAE might have extended to the Arabian Plate for brief periods of time during the deposition of the middle Marrat shallow marine red beds.