Concentrations Of Light Rare Earth Elements Research Articles

Geochemistry and origin of the Late Carboniferous ultramafic, mafic, and felsic plutonic rocks (NW Iran)

The Late Carboniferous Gharabagh-Mamkan-Mingol plutonic complex (GMMP) consists of a variety of ultramafic, mafic, felsic intrusive rocks, including the 325–315 Ma Gharabagh gabbroic, granitic, and monzonitic rocks and Mamkan-Mingol 320–315 Ma massive appinites (hornblende-rich gabbros) and 300–295 Ma layered mafic-ultramafic (gabbro, appinitic gabbro, and appinite) rocks in the northwestern Sanandaj-Sirjan zone, Iran. The relationships between various rock types in the plutonic complex are unknown. To address these issues, we conducted a detailed petrologic and geochemical study of the complex, and its country rocks.The abundance of major and trace elements and isotopic ratios of 87/86Sr (0.70379–0.70428) and 143/144Nd (0.51228–0.51245) systems showed that the Gharabagh gabbros formed from a metasomatized amphibole-bearing spinel lherzolite from an ancient subduction-modified mantle source with OIB characteristics including high contents of light rare earth elements (LREEs), Ti, Nb, Ta, and Ba, as well as low concentrations of Sr, Hf, and Zr. The geochemical data show that monzonites had high concentrations of LREEs, Ba, U, K, Hand Zr, and the low contents of Th, Nb, Ta, Sr, P, and HREEs and Eu-positive anomalies and originated from the melting of the continental crustal base in the subducted mantle wedge. The granites are similar to monzonites, with their difference being in the high concentrations of Th and Eu-negative anomalies. Combining petrographic, petrological, geochemical, and isotopic data suggests that Gharabagh plutonic rocks were formed as a result of Paleo-Tethys slab break-off, and slab sinking, during trans-tensional collision between the Central Iranian microplate and Gondwanaland during the Late Carboniferous. As a result of this event, decompression melting began in the upwelling mantle, coeval with the formation of the pull-apart basin, during major strike-slip faulting, leading to a hydrous mafic melt with about 10–12% partial melting.The Mamkan-Mingol massive and layered masses have a tholeiitic affinity. The Mamkan-Mingol rocks are characterized by different trace element patterns, especially in the concentrations of REEs and high field strength elements (HFSEs) such as Nb, Ta, Hf, Zr, and P and large-ion lithophile elements (LILEs) such as Th, U, Sr, K, Rb, and Ba. The massive and layered rocks mostly show a variably developed negative anomaly in HFSEs, and widely varying ratios of (La/Yb)n (1.0–5.2). Massive appinites and layered gabbros of GMMP originated due to different partial melting in the upwelling zone of metasomatized OIB-like amphibole-bearing spinel lherzolite and a less hydrous- to dry upwelling mantle zone, respectively, in an environment associated with the initiation of rifting, where the remnants of the Paleo-Tethys subducted slab plunges deep into the mantle. Contrasting Nd isotopic ranges are present between the massive appinites (ɛNd = +0.39) and different types of mafic-ultramafic rocks in layered outcrops (ɛNd = +1.12 to +2.07) of the complex. Based on the geochemical and isotopic (ratios of Sr, Nd, and Pb) data, we suggest that variations in of contribution of slab-derived fluids or crustal components in the primary melt caused the generation of massive appinites and different types of layered gabbros.

Dissolved rare earth elements in the North Pacific Subtropical Gyre: Lithogenic sources and water mass mixing control

In the North Pacific Subtropical Gyre, which is one of the largest oligotrophic regions, there is a lack of information regarding the sources and transport of trace metals through water mass mixing. Rare earth elements (REEs) are essential for tracing lithogenic sources and water mass transport. In this study, we present dissolved REE concentrations and the factors controlling their distributions in the northwest Pacific during a GEOTRACES cruise (GP09). In the surface water along 11°N, we observed input signals from the Philippine and the Hawaiian Islands, characterized by positive Eu anomalies and slightly elevated REE concentrations. By incorporating our data and published REE data from the northwest Pacific to the southeast Pacific (40°N–40°S), we demonstrated that the REE concentrations and Yb/Nd ratios can distinguish North Pacific Intermediate Water (NPIW), Antarctic Intermediate Water (AAIW), and modified AAIW. By estimating the ratio of water mass mixing, we suggest that heavy REEs are predominantly contributed by water mass mixing (e.g., 93 % ± 4% for Yb) and can be used as semi-conservative tracers to quantify the mixing of NPIW and modified AAIW at the potential density of 27.2 kg/m3. At ∼800 m depth at stations K12, K13, and K14, weak negative Ce anomalies (>0.1) were observed, indicating the lateral transport of water masses imprinted with sediment signals from the Philippine Islands. In the deep waters (>1500 m) at the Luzon Strait (station K1), we propose that the weak Ce negative anomalies (>0.08) and low Yb/Nd ratios (<5), combined with the low beam transmission, are the result of particle resuspension and release. In deep water (>2000 m), combining high-resolution REE measurements with water mass analysis, our research reveals that dissolved REEs (except Ce) are dominantly controlled by water mass mixing (e.g., 80 %∼100 % for Yb and 70 %∼100 % for Nd). For the non-conservative behavior, which is not explained by water mass mixing, the residual fraction of heavy REEs (<20 % for Yb) originates from release of sinking particles (organic matter and siliceous particles), while the remaining concentrations of light REEs (<30 % for Nd) may be influenced by a combination of particle release and scavenging processes. These findings highlight valuable information about lithogenic sources and the proportions of REE distributions that are controlled by physical and biogeochemical processes. Moreover, it emphasizes the applicability of heavy REEs as effective tracers for understanding basin-scale water mass mixing in the northwest Pacific.

Light rare earth elements stabilize G-quadruplex structure in variants of human telomeric sequences

Recently, light rare earth elements (LREEs) are gaining importance in modern-day technologies. Thus, the entry of LREEs into biochemical pathways cannot be ignored, which might affect the conformation of biomacromolecules. Herein, for the first time, we discover the G-quadruplex formation in the human telomeric variants in presence of micromolar concentrations of LREEs. Thermal melting show that the LREE-induced unimolecular G-quadruplex structure. Isothermal titration calorimetry, UV–vis, and CD spectroscopy results suggest the binding stoichiometry of lanthanide ions to telomeric variants is 2:1. The data confirms that the LREE ions coordinate between adjacent G-quartets. The excess LREE ions are most likely binding to quadruplex loops. The CD spectra revealed that the LREE-induced quadruplex in human telomere and its variant have antiparallel orientation. The binding equilibria of LREEs have been studied both in the presence and absence of competing metal cations. Addition of LREEs to the Na+ or K+-induced G-quadruplexes led to conformational change, which may be ascribed to the displacement of K+ or Na+ ions by LREE ions and formation of a more compact LREE-induced G-quadruplex structure in human telomeric variant. Moreover, the thymine in the central loop of the human telomeric sequence stabilizes LREE induced G-quadruplex.

Harnessing the composition of dissolved organic matter in lagoon sediment in association with rare earth elements using fluorescence and UV–visible absorption spectroscopy

Dissolved Organic Matter (DOM) plays a pivotal role in influencing metal binding and mobility within lagoon sediments. However, there exists a gap in understanding the compositional alterations of DOM concerning Rare Earth Elements (REEs) across varying pollution gradients. This study aimed to characterize DOM and examine its relationship with REEs in sediment cores from different pollution levels in Yundang Lagoon, China using excitation-emission matrix-parallel factor analysis (EEM-PARAFAC). The results raveled four distinct fluorescent components. Among these, two correspond to humic-like substances, while the remaining two are attributed to protein-like substances. Remarkably, the prevalence of protein-like compounds was observed to exceed 58% of the total fluorescence intensity across all the investigated sites. Furthermore, a substantial discrepancy in total fluorescence intensity was detected between the Songbai Lake and the Inner and Outer Lagoon, indicating a variance in DOM content. In terms of REEs, the average concentration of total REEs was notably elevated within the Songbai Lake sediments (318.36 mg/kg) as compared to the Inner and Outer Lagoon sediments (296.36 and 278.05 mg/kg, respectively). Of significance is the enrichment of Light Rare Earth Elements (LREEs), particularly Ce, La, Pr, and Nd, over Heavy REEs (HREEs) across all surveyed locations. Intriguingly, a coherent trend emerged wherein the fluorescence intensity and LREE concentrations exhibited a synchronized increase from Outer to Inner to Songbai Lake core sediments. This observation substantiates a strong correlation between DOM content and pollution levels (p < 0.05). By shedding light on the intricate interplay between DOM and REEs within urban aquatic sediments, this study imparts novel insights which enrich our comprehension of urban environmental dynamics.

Association between light rare earth elements in maternal plasma and the risk of spontaneous preterm birth: a nested case-control study from the Beijing birth cohort study

BackgroundParental exposure to rare earth elements (REEs) could increase the risk of premature rupture of membranes, a major cause of spontaneous preterm birth (SPB). In addition, different subtypes of SPB, such as spontaneous preterm labor (SPL) and preterm premature rupture of membranes (PPROM), may have different susceptibility to environmental exposure. Therefore, we investigated the potential associations between REE exposure in different trimesters and SPB and its subtypes.MethodsA nested case-control study was performed. We included 244 women with SPB as cases and 244 women with full-term delivery as controls. The plasma concentrations of light REEs were measured in the first and third trimesters. Logistic regression was used to analyze the associations between single REE levels and SPB, and Bayesian kernel machine regression (BKMR) was used to analyze the mixed-exposure effect.ResultsExposure to light REEs was associated with SPB and its subtypes only in the third trimester. Specifically, the intermediate- and highest-tertile concentration groups of La and the highest-tertile concentration group of Sm were associated with an increased risk of SPL, with adjusted odds ratios (AORs) of 2.00 (95% CIs: 1.07–3.75), 1.87 (95% CIs: 1.01–3.44), and 1.82 (95% CIs: 1.00–3.30), respectively. The highest-tertile concentration group of Pr was associated with an increased risk of PPROM, with an AOR of 1.69 (95% CIs: 1.00–2.85). Similar results were also found in BKMR models.ConclusionsLa and Sm levels in plasma may be associated with the risk of SPL, and Pr levels in plasma may be associated with the risk of PPROM.

Zirconium/hafnium fractionation and rare earth element systematics in sub-cratonic garnet pyroxenites, Norway

Ten previously studied garnet pyroxenites and one eclogite from orogenic peridotites in the Western Gneiss Region of Norway were analysed for whole-rock major and trace and mineral trace elements to characterise the evolutionary stages of the East Greenland sub-cratonic mantle. A continuous range of whole-rock MgO contents (17–30 wt.%) correlates inversely with hbox {Na}_2hbox {O}, hbox {Al}_2hbox {O}_3, and CaO contents. In contrast, rare earth element (REE) compositions allow the samples to be devided into two types. Type I samples have relatively flat primitive mantle (PM) normalised REE patterns (0.4-6.8 times PM values) with minor fractionation of middle–heavy REEs. Type II samples are simlar to type I samples but have higher light REE contents (6.1–57 times PM values) that reflect metasomatic enrichment. Whole-rock Zr contents (1–27,upmu hbox {g},hbox {g}^{-1}) and Zr/Hf ratios (17–39) are positively correlated. Type I samples have low Zr/Hf ratios that mostly differ from type II samples, indicating that metasomatism modified the initially sub-chondritic Zr/Hf ratios. Garnet Zr–Zr/Hf–Y–Ti systematics suggest that metasomatic enrichment transformed the type I samples into type II samples, consistent with processes observed in other cratonic areas (e.g., the northern East European Platform and the Kaapvaal Craton). The formation of type I pyroxenite in dunite from a melt at sim 100,text {km} depth implies the sub-chondritic Zr/Hf ratios were inherited from that melt. Such melts are thought to form by melting of garnet-bearing, melt-depleted mantle, which is consistent with models for recycling of Archaean palaeo-oceanic crust throughout the mantle prior to the formation of the sub-cratonic lithosphere beneath East Greenland.

DEFICIENCY OF RARE-EARTH ELEMENTS IN NATURAL LANDSCAPE COMPONENTS AS A CAUSE OF GEOPHYGY AMONG UNGULATES ON OLKHON ISLAND

The actuality of the work lies in the systematic study of the causes of geophagy from the viewpoint of the rare earth hypothesis. From the original results of complex geological-hydrobiogeochemical studies carried out on Olkhon Island (Lake Baikal). ), it follows that the phenomenon of geophagy among wild and domestic ungulates on the island is due to a deficiency of light rare earth elements (LREE) in plant foods and natural waters. The deficit is associated with a low concentration of LREE in the composition of the most common metamorphic terrigenous-carbonate rocks, deluvium and soils on the island. The similar geochemical specificity of landscapes can be the cause of LREE imbalance in the hormonal system of the body. Hormonal stress causes animals to regularly and periodically consume kaolinite clays of weathering rocks enriched with the necessary elements.

Rare earth elements in tea garden soils and their bioavailability to tea buds in Taiwan

Tea (Camellia sinensis) is a widespread beverage plant that prefers aluminum-enriched acidic soils. However, rare earth elements (REEs) might be highly phyto-available in these soils. With the increasing demands for REEs in high-technology industries, understanding the dynamics of REEs in the environment is essential. Thus, this study identified the total concentration of REEs in the root-zone soils and corresponding tea buds (n = 35) collected from tea gardens in Taiwan. Additionally, the labile REEs in the soils were extracted with 1 M KCl, 0.1 M HCl, and 0.05 M ethylenediaminetetraacetic acid (EDTA) to elucidate the fractionation tendency of REEs in the soil-plant system and the relationships between REEs and Al in the tea buds. The concentration of light REEs (LREEs) was higher than those of medium REEs (MREEs) and heavy REEs (HREEs) in all soil and tea bud samples. According to the upper continental crust (UCC) normalization, MREEs and HREEs were more abundant than LREEs in the tea buds. Furthermore, REEs remarkably increased with increasing Al in the tea buds, whereas the linear correlations between Al and MREEs and HREEs were stronger than between LREEs. Compared with LREEs, the extractabilities of MREEs and HREEs by all single extractants in the soils were higher, coinciding with their higher UCC-normalization-based enrichments in the tea buds. Moreover, the 0.1 M HCl- and 0.05 M EDTA-extractable REEs were affected by soil properties and significantly correlated with the total REEs in the tea buds. The concentration of REEs in the tea buds was successfully predicted by empirical equations of extractable REEs with 0.1 M HCl and 0.05 M EDTA, as well as general soil properties including pH, organic carbon, dithionite-citrate-bicarbonate-extractable iron, aluminum, and phosphorus. However, this prediction should be further verified using many soil and tea types in the future.

The different responses of trace elements to equilibrium and disequilibrium melting: Implications for crustal differentiation and granite compositions

Equilibrium and disequilibrium meltings are two common mechanisms in the geochemical differentiation of the continental crust. However, responses of trace elements to the two melting processes are still not fully understood in granite petrogenesis. To address this, we conducted trace element modelling of open system melting using phase equilibrium calculations combined with solubility equations for accessory minerals and mineral–melt partition coefficients based on three melt-reintegrated felsic granulite compositions. The results indicate systematic differences between the compositions of disequilibrium (Type I) and equilibrium (Type II) melts involving water-present melting reaction, fluid-absent melting reaction involving biotite, and fluid-absent melting reaction in the absence of biotite. Type I melts generally have higher Rb, Ba, Co, Ni, V, and Cr contents, and Rb/Sr and Nb/Ta ratios, and lower Sr, P, Th, U, and light rare earth element contents than Type II melts. Significantly, disequilibrium melting involving biotite can produce melts with high Nb contents and super-chondritic Nb/Ta ratios, which may be a reservoir for the missing Nb on Earth. Compared with Type II melts, the trace element contents and ratios of Type I melts exhibit a larger range, more complex trends, and are more sensitive to changes in melting reaction types and melt loss. This suggests that, in addition to petrogenetic processes such as crystal entrainment, fractional crystallization and magma mixing, the disequilibrium melting would also contribute to the compositional diversity of granites. The modelling results also show that the trace element signatures of granites that are commonly used to determine their petrogenetic processes and tectonic setting may lead to erroneous conclusions if the granitic melts were produced by disequilibrium melting.

Protracted Thermal Evolution of a Migmatitic Terrane as Revealed by Multiple Geochronometers From the Retro‐Arc of the Early Paleozoic Famatinian Orogen in NW Argentina

AbstractU‐Pb dates of zircon, monazite, and titanite combined with trace element composition, allows characterization of the thermal evolution of the migmatitic Agua del Sapo complex. This complex comprises Al‐rich and Ca‐rich metasedimentary rocks with a detrital zircon maximum depositional age of 550 Ma. The rocks record two consecutive early Paleozoic orogenies. During subduction associated with the 550–510 Ma Pampean orogeny, the complex was in the fore‐arc region and was intruded by 550–520 Ma granites indicative of anomalous heating possibly related to ridge subduction. During the subsequent 500–440 Ma Famatinian orogeny, the arc migrated trenchwards and the region became part of a retro‐arc that underwent melting at upper‐amphibolite facies. This event was recorded differently by each of the accessory phases. Detrital zircon cores were overgrown by rare Famatinian rims that range from 500 to 420 Ma, while monazite records only Famatinian dates with a growth peak at ∼457 Ma that extends to 410 Ma, possibly due to coupled dissolution‐precipitation. Published titanite dates define a 120 Myr thermal history, starting at ∼500 Ma with temperatures of ∼750°C ± 25°C, ending at 380 Ma and ∼700°C ± 25°C. Cooling was accompanied by a decrease in titanite light rare earth element contents in response to increased abundance of allanite/epidote. Thus, the complementary time‐compositional record of the accessory phases reveals continued high heat flow, associated with deformation, to 380 Ma. This prolonged event blurs the boundary between the Famatinian and the subsequent Achalian/Chanic orogenies and extends the Silurian Rinconada tectonic phase of the Famatinian orogeny to the east into the Eastern Sierras Pampeanas.

High light REE enrichments in weathering crust in the Huangmeijian alkaline pluton in Luzong Volcanic Basin: A potential exploration target for ion-adsorption rare earth element deposit

The high light rare earth elements contents (up to 412 ppm) in the weathering crust over the REE industrial grade were observed in the Huangmeijian alkaline pluton of the Luzong Volcanic Basin, firstly revealing the mineralization potential of ion-adsorption rare earth elements deposit in central Anhui Province.

Ultra-depleted melt product preserved in the Ladong ophiolitic peridotites of the North Qilian Orogenic Belt, Northern Tibet

In Earths upper mantle, the compositions of both migrating magmas and solid residues are basically controlled by source materials and melting behavior which are related to tectonic dynamics. Thus, infrequent geochemical signatures recorded by ophiolitic lithologies may reflect a unique source or specific melting history. Here, we report whole-rock and mineral compositions of the harzburgite, wehrlite, and olivine websterite in the Ladong ophiolite complex of the North Qilian Orogen Belt (northern Tibet). The dominant spinel harzburgite has high spinel Cr# values of 65–70 and light rare earth element (LREE) depleted patterns (LaN/YbN = 0.04–0.12), resembling the residua after 20% or more of melt extraction. Wehrlite lenses within the harzburgite display extremely depleted LREE patterns (whole-rock LaN/YbN = 0.04–0.05) and low Na and Ti contents in clinopyroxene. They are interpreted as products of reaction between the host harzburgite and an ultra-depleted melt produced by asthenospheric decompression melting. Outcrops of olivine websterite have well-equilibrated triple junction textures between pyroxene grains and high-Mg olivine (Fo = 85–86; bulk rock Mg# = 93), consistent with a cumulate origin. In the olivine websterite, the depleted LREE concentrations (LaN/YbN = 0.05–0.18) in clinopyroxene suggest a less depleted nature than the wehrlite-forming melt. Thus, the Ladong ophiolite records two episodes of melt activity that produced depleted to ultra-depleted magmas, which may have been generated during subduction initiation in eastern Proto-Tethyan belt.

Mineralogical, Geochronological, and Geochemical Characteristics of Early Cretaceous Granite in South China: Implications for Tectonic Evolution and REE Mineralization

One of the most important geological features of South China are the widespread Mesozoic igneous rocks that play a key role in revealing the tectonic evolution of South China. Due to the thick covering of vegetation and Quaternary sediments, the early Cretaceous magmatism in southwestern South China is still not well constrained. In this paper, we report newly identified early Cretaceous granites in Guangxi, South China. Zircon U–Pb dating results showed that representative fine-grained and coarse-grained granites in northeastern Guangxi indicate the early Cretaceous ages of 141 ± 3 Ma and 141 ± 4 Ma, respectively. Geochemically, both fine-grained and coarse-grained granites had high 10,000 × Ga/Al ratios and belonged to A-type granite. They had undergone high degrees of magma differentiation, as evidenced by extremely negative Sr, Ba, and Eu anomalies. They had high REE (rare earth elements) contents (&gt;451 ppm). The fine-grained granites were characterized by higher HREE (heavy rare earth elements) contents, lower LREE (light rare earth elements) contents, and lower LREE/HREE ratios than the coarse-grained granites. Integrated with regional geological data, the early Cretaceous granites were likely formed in a back-arc extensional environment in response to the increased subduction angle of the Paleo-Pacific plate. Different REE contents in the fine- and coarse-grained granites may be a result of fractional crystallization. Magma differentiation and hydrothermal alteration might have played an important role in REE mineralization of the early Cretaceous granites in Guangxi.

Differentiation of continent crust by cumulate remelting during continental slab tearing: Evidence from Miocene high-silica potassic rocks in southern Tibet

The role played by felsic igneous magmatism in crustal differentiation is of importance for the evolution and habitability of Earth system. However, the petrogenesis of felsic rocks and their genetic links to mafic magmas remain controversial, hindering our understanding of crustal differentiation processes. Cenozoic post-collisional felsic potassic rocks occur widely in the well-known Himalaya-Tibet orogen and are intimately associated, in space and time, with mantle-derived ultrapotassic rocks, which thus provide a clear case study to investigate the genesis of felsic rocks and their genetic relationship with mafic rocks. Here we report zircon UPb ages and HfO isotopes, mineral major elements, and whole-rock elemental and Sr-Nd-Pb isotopic compositions for the TangraYumco high-silica potassic rocks (trachytes) in central Lhasa block of southern Tibet. The results, combined with literature data of the TangraYumco ultrapotassic rocks, can help better illuminate their genesis and the role of ultrapotassic rocks in their generation. The trachytes erupted in the Miocene (~13 Ma), coeval with ultrapotassic lavas in this area. They have very enriched Sr-Nd-Pb-Hf-O isotope compositions similar to those of ultrapotassic rocks. However, they display more fractionated LREEs (light rare earth elements) than ultrapotassic rocks. The trachytes also show nearly constant Y and Yb contents with increasing SiO2. This indicates that they were not derived by fractional crystallization from ultrapotassic magmas or by mixing between ultrapotassic and ancient crust-derived felsic magmas. Instead, given their lower LREE contents than ultrapotassic rocks and occurrence of clinopyroxene antecrysts, we suggest that the TangraYumco trachytes were likely produced by remelting of newly-formed, Sr-Nd-Pb isotopically enriched, and K-rich cumulates that crystallized from ultrapotassic magmas. Moreover, taking into account regional magmatism and tectonics, we propose that the TangraYumco-Xuruco post-collisional coeval magmatism and rift system represent a response to tearing of subducted Indian continental slab. Finally, in combination with the nature of post-collisional magmatism in the Lhasa block, we suggest that in addition to reworking of juvenile and ancient crust, underplating of post-collisional mafic magmas and remelting of their cumulates could be an important way to differentiate continental crust in collisional orogeny zones.

Abundance, spatial variation, and sources of rare earth elements in soils around ion-adsorbed rare earth mining areas

Rare earth elements (REEs) concentrated in soils have attracted increasing attention about their impact on soil health as emerging contaminants. However, the sources of REEs enriched in soils are diverse and need to be further investigated. Here, surface soil samples were collected from southern Jiangxi Province, China. REEs contents and soil physicochemical properties were determined, and cerium (Ce) and europium (Eu) anomalies were calculated. Moreover, we established a model to further identify the main sources of REEs accumulation in the studied soils. Results show that the abundance of soil REEs reveals larger spatial variation, suggesting spatially heterogeneous distribution of REEs. The median content of light REEs in soils (154.5 mg kg−1) of the study area was higher than that of heavy REEs and yttrium (35.8 mg kg−1). In addition, most of the soil samples present negative Ce anomalies and all the soil samples present negative Eu anomalies implying the combined effect of weathering and potential exogenous inputs on soil REEs. Positive matrix factorization modeling reveals that soil REEs content is primarily influenced by soil parent materials. Potential anthropogenic sources include mining-related leachate, traffic exhaust, and industrial dust. These results demonstrate that the identification of sources of soil REEs is an important starting point for targeted REEs sources management and regulation of excessive and potentially harmful REEs levels in the soil.

Petrographic and geochemical characteristics of nodular carbonate-bearing fluorapatite in the lacustrine shale of the Shahejie Formation, Dongying Depression, Bohai Bay Basin

A varying abundance of carbonate-bearing fluorapatite (CFA) nodules in Eocene lacustrine shale in the Bohai Bay Basin was observed; however, mineralogical and geochemical awareness is lacking, which limits the specific understanding of CFA formation mechanisms and paleoenvironmental proxies. We specified the petrology, trace elements (TE), rare earth elements and yttrium (REY) of the CFA nodules by using an integrated approach of cathodoluminescence, micro-Fourier transform infrared spectroscopy, electron microprobe analysis and laser ablation–inductively coupled plasma–mass spectrometry. The results suggest that CaO (25.85 to 39.95 wt%), P2O5 (17.19 to 29.35 wt%) and F (0.71 to 2.99 wt%) are the dominant components of the CFA nodules, with low Mn/Fe ratios and few incorporations of CO32−. They show selective concentrations of Sr (avg. 14,963.3 ppm), Ba (avg. 1831.6 ppm), U (avg. 314.2 ppm), Zr (avg. 263.5 ppm), and Th (avg. 185.4 ppm) and apparent negative Y anomalies with low Y/Ho ratios (18.40 to 28.90). These CFA nodules were classified into three types according to REY patterns normalized to the Post-Archean Australian Shale (PAAS). Type A nodules enclosed by micritic calcite laminae are middle rare earth elements (MREE) enriched which yield a typical “bell-shaped” REY pattern, nonanomalies of Ce and a good correlation of ΣREY with Ce/Ce* (R2 = 0.90) and Ba (R2 = 0.95). Type B nodules in the clay and organic-rich laminae were better phosphatized and display more heavy rare earth elements (HREE) depletion, minimal Ce anomalies and a good correlation between CaO and P2O5 (R2 = 0.84) than type A nodules. Type C nodules are rare but show light rare earth elements (LREE) enrichment relative to type A and B nodules. The adsorption of P, TE and REY by Fe-(oxyhydr)oxide and organic matter is significant for CFA formation through the “dissolution-recapture-reprecipitation” process in the ambient pore water of the Fe reduction zone during early diagenesis. The retention of HREE as HREE(CO3)2− in more reducing bottom water is critical to the HREE depletion for type B and C nodules, while the release of LREE from bacterial-mediated degradation of organic matter into ambient pore water enhances the concentration of LREE on type C nodules. Deviation of the REY patterns is probably related to the differential suboxic redoxclines for the deposition of calcite-rich and clay- and organic-rich laminae of shale, which are considered the depositional environment proxies of lacustrine shale.

Identification of potential plant species hyperaccumulating light rare earth elements (LREE) in a mining area in Minas Gerais, Brazil.

Phytoextraction of rare earth elements (REE) from contaminated soils has gained importance during the last few decades. The Poços de Caldas municipality in Brazil is known for its mineral richness, including large reserves of REE. In this study, we report light REE (La, Ce, Sm, Pr, and Nd) in soils and plants collected in an area. Composite soil samples and plant individuals were collected, and total concentrations of LREE in soils were determined by wavelength dispersive X-ray fluorescence (WDXRF). The plant available LREE concentrations in soils were estimated upon the acetic acid method (F1 fractions) of the stepwise sequential extraction procedure, together with plant content that was analysed by inductively coupled plasma mass spectrometry (ICP-MS). The total sum concentrations of tested LREE in soils varied from 5.6 up to 37.9gkg-1, the bioavailable fraction was ca. 1%, and a linear relationship was found between them. The only exception was Sm, whose availability was lesser and did not show a linear relationship. The concentration of LREE in non-accumulator plants varied from 1.3-950mgkg-1 for Ce, La 1.1-99mgkg-1, Sm 0.04-9.31mgkg-1, Pr 0.1-24.1mgkg-1, and Nd 0.55-81mgkg-1. The concentration of LREE among shoots did not show a linear relation either with the available fraction or total content. The screening also revealed Christella dentata (Forssk.) Brownsey & Jermy, Thelypteridaceae family, as a promising hyperaccumulator species. The concentrations of LREE among shoots of six individuals of this species were in the ranges from 115 to 1872mgkg-1 for Ce, La 190-703mgkg-1, Sm 9-48mgkg-1, Pr 32-144mgkg-1, and Nd 105-478mgkg-1.

Rare earth elements associated with pedogenic iron oxides in humid and tropical soils from different parent materials

Rare earth elements (REEs) from parent materials are easily trapped by secondary minerals in highly weathered soils that contain high pedogenic iron (Fe) oxide levels. However, few studies have investigated REEs fractionation by Fe oxides during pedogenesis. Therefore, this study examined REEs partitioned in the pedogenic Fe oxides of four pedons developed from schist, andesite, shale, and mafic rocks in Eastern Taiwan; this was achieved by combining the dithionite-citrate-bicarbonate (DCB) extraction for bulk soil samples and microspectroscopic approaches for thin sections. The DCB extraction was applied to pedogenic Fe oxides (Fed). Furthermore, REE concentrations of the Fe extraction were measured to assess the potential mobility of REEs through the dissolution of pedogenic Fe oxides. The spatial distribution of REEs in Fe nodules and surrounding soil matrix was achieved by using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) and electron probe microanalysis (EPMA). The results revealed that total REE content varied with soil depth and among pedons. Total REEs were fractionated during pedogenesis; thus, the ratio of light REEs (LREEs) to heavy REEs (HREEs) varied substantially among all pedons. However, the DCB-extractable REE contents significantly (p < 0.05) increased when the Fed contents increased, indicating the high affinity of pedogenic Fe oxides for REEs. Moreover, the pedogenic Fe oxides exhibited an association preference for HREEs over LREEs even though the DCB-extractable concentrations of LREEs were higher than those of HREEs in the soils. Additionally, the association of REEs with Fe oxides led to HREEs condensation in the Fe nodules identified through LA-ICP-MS and EPMA. Our results elucidated pedogenic Fe oxides as the major carrier of REEs while clarifying the preferential trapping of HREEs by pedogenic Fe oxides.

Petrogenesis of a nepheline syenite from parts of the Chotanagpur Granite Gneissic Complex: implications for Neoproterozoic crustal extension in the East Indian Shield

AbstractThe North Purulia Shear Zone that dissects the granulite basement of the Chotanagpur Granite Gneissic Complex of the East Indian Shield exposes a deformed and metamorphosed nepheline syenite. The studied ‘foid-monzosyenite’ shows high abundances of large ion lithophile elements and high field strength elements with low abundances of compatible elements. Trace-element signatures show negative U, Th, Zr, Ti and Pb and positive Sr, Ba and Eu anomalies with respect to the primitive mantle. The chondrite-normalized diagram shows strongly fractionated rare earth element patterns ((La/Lu)N ∼23–87). Geochemical fingerprints suggest that the basanitic protolith was formed by low-degree partial melting of garnet peridotite in the sub-continental lithospheric mantle. The enriched large ion lithophile, high field strength element and light rare earth element concentrations (relative to primitive mantle) can be explained by a mixed mantle source with components from a previously deformed alkaline rock/carbonatite. Geochemical data do not support any significant crustal contamination and suggest variable fractionation of clinopyroxene, ilmenite, titanite and apatite from the parental melt. Petrological data are consistent with the view that the nepheline syenite magma was emplaced in a rift setting with a minimum temperature of 800–900°C, low fO2 conditions (below the fayalite–magnetite–quartz buffer) at a mid-crustal depth between 950 and 900 Ma. The continental rift zone, however, did not lead to the formation of an open ocean basin. Subsequently, the studied rock and its basement was deformed and metamorphosed in a continent–continent collisional setting at ∼900 Ma. Combining information from the other Indian occurrences with this study, it is demonstrated that the deformed alkaline rocks and carbonatite are potentially valuable for tracing the birth and demise of the palaeo-supercontinents.

Mineral Chemistry and Trace Element Composition of Clinopyroxenes from the Middle Cambrian Ust’-Sema Formation Ankaramites and Diopside Porphyry Basalts and the Related Barangol Complex Intrusions, Gorny Altai, Russia

The origin and geodynamic settings of the Ust’-Sema Formation and the Barangol Complex are some of the most controversial issues in the Early Paleozoic history of the Altai–Sayan Fold Belt. The Ust’-Sema Formation volcanic rocks are enriched in high-Ca clinopyroxene phenocrysts and were classified as ankaramites and diopside porphyry basalts. In this work, we first present LA-ICP-MS analyses of the clinopyroxenes, along with studies of the petrography, mineral composition, and whole-rock chemistry of the Ust’-Sema Formation and related Barangol Complex rocks. An LA-ICP-MS clinopyroxene study showed a slight depletion of light rare-earth elements (La/Yb)N = 0.1–1.0 (on average 0.4); and strong depletion of the high-field-strength elements (Zr, Hf, and Nb) and large-ion lithophile (Rb) elements. An Sr anomaly showed a positive correlation with Mg#. Major- and trace-element composition of the clinopyroxene cores show that these clinopyroxene grains were not captured from the mantle rocks as previously assumed and that the Ust’-Sema Formation and the Barangol Complex rocks were formed from magma with island arc characteristics. The increased titanium and light rare-earth element contents in the phenocryst rims from Biyka volcano suggest an active interaction of the ankaramitic magma with rocks or melts of OIB type.