Rare Earth Elements And Yttrium Research Articles

Surface water oxygenation and low bioproductivity during deposition of iron formation of the Jacadigo Group (Brazil): Insights from combined cadmium – Chromium isotopes

The Banda Alta Formation (Urucum district, Mato Grosso do Sul, Brazil) comprises ∼600 Ma Fe and Mn deposits, which are among the world's youngest and largest Neoproterozoic sedimentary Fe and Mn formations (IF; MnF). These have been deposited in a redox-stratified, marine sub-basin (Jacadigo Basin), which was strongly influenced by glacial advance/retraction cycles with temporary influx of continental freshwater and upwelling of metal-enriched deep anoxic seawater. Cr and Cd isotopes measured on meticulously separated hematite mesobands from drill core samples are relatively homogenous throughout the ca. 325 m thick sequence sampled in the Banda Alta Fm., with average authigenic δ53Cr values of +0.93 ± 0.24 ‰ (2σ; n = 23) and δ114Cd values of −0.14 ± 0.14 ‰ (2σ; n = 15). The significant enrichment of Cr, in parallel with the strong enrichments of other redox sensitive elements (U, Mo), attests for effective and efficient reduction removal processes in the surface waters during cycles where upwelling Fe2+-rich waters reached the oxygenated surface layer exposed to the atmosphere during episodic glacier retreat stages. Assuming a similar quantitative and efficient removal pathway of dissolved Cd by iron oxyhydroxides, the so-inferred average δ114Cd signature of −0.14 ± 0.14 ‰ in the Jacadigo Basin surface water is significantly lower than signatures of modern ocean surface waters with a range of δ114Cd of ca. ∼0.4 to ∼1 ‰ and even lower than the signature of modern ocean deep waters with δ114Cd of ∼0.3 ‰. It possibly attests to reduced primary production levels and lower nutrient utilization rates during deposition of the Late Neoproterozoic Jacadigo Group, compared to today. This despite the inferred oxidized surface water layer that must have prevailed during this time, as implied by the strongly positively fractionated Cr isotope signatures and pronouncedly negative Ce-anomalies recorded in the seawater-like, shale-normalized Rare Earth Element and Yttrium (REY) patterns exhibited by the hematite mesobands. Data presented herein speak for: (1) a stable, isotopically heavy Cr input to the Jacadigo Basin at the time of deposition, implying high atmospheric O2 levels in the Late Neoproterozoic (2) likely quantitative, reductive incorporation / adsorption processes of dissolved Cr and Cd, respectively, into/onto precipitating iron oxyhydroxides, and (3) the prevalence of low nutrient concentrations and utilization rates in the Jacadigo Basin during glacier retreat cycles. Banded iron formations are considered suitable archives for reconstructing redox and bioproductivity levels in past marine depositional basin, including those prevalent in Neoproterozoic glacial conditions, via employing the CrCd isotope double tracer to iron-rich mesobands.

Study on the material source and enrichment mechanism of REE-rich phosphorite in Zhijin, Guizhou

Rare earth element (REE)-rich phosphorite in the Guizhou region mainly exists in the Doushantuo Formation and Gezhongwu Formation in early Cambrian strata, which are some of the important strata containing phosphorite resources in China. The early Cambrian Zhijin phosphorite in Guizhou Province, China, has high rare earth element and yttrium (REY) contents of up to 2500 ppm, with heavy REY (HREY) contents accounting for ~ 30% of the total REY contents. However, the specific controlling source and environment of phosphorite (especially the REEs in Zhijin phosphorite) are still unsolved. Through field geological investigations; mineralogical, geochemical, Sr–Nd isotope analyses; and tectonic characteristics, the material source, sedimentary environment and seawater dynamics of REEs in phosphorite are studied. It is considered that the REEs enriched in the Zhijin phosphorite are mainly affected by precipitation from hydrothermal fluid. Moreover, from the late Ediacaran to the early Cambrian, the depositional environment from the bottom to the top of the water tended to be hypoxic, and the activity of hot water fluid tended to be strong. The change in redox conditions is closely related to the rise and fall of sea level. Combined with the tectonic background, these results show that the weakly oxidized environment may be an important factor controlling the enrichment of REEs. The enrichment of REEs may be closely related to volcanic hydrothermal activity, later diagenesis and seawater dynamics.

Petrography and stratigraphic Os isotopic ages of ferromanganese nodules from the Northwest Pacific east of Minamitorishima Island

The area offshore of Minamitorishima Island, Northwestern Pacific Ocean, contains large amounts of seafloor mineral resources such as ferromanganese (Fe–Mn) nodules, Fe–Mn crusts, and rare-earth element and yttrium (REY)-rich muds. In this study, we applied stratigraphic Os isotopic dating to a Fe–Mn nodule for the first time to date its formation/depositional age, and mineralogical and texturally characterized a complementary nodule. Based on macroscopic and microscopic observations, the studied Fe–Mn nodules can be divided into three layers: Layers L2, L1, and L0 from core to rim. Under the microscope, the Fe–Mn nodules are dominated by vernadite and Fe-oxyhydroxide. In particular, Layer L1 is dominated by banded-columnar vernadite and contains lower amounts of clay minerals derived from the detrital component than Layers L2 and L0. The bulk major and trace element geochemical compositions of sampled layers in the Fe–Mn nodules all plotted in the hydrogenous field in several discrimination diagrams. The Os isotopic ages determined by fitting to the paleo-seawater 187Os/188Os curve can be divided into three clusters (35.7–31.0, 19.0–9.0, and 4.0–1.0 Ma, corresponding to Layers L2, L1, and L0, respectively). These Os isotopic ages indicate that two periods of very slow growth or growth hiatuses occurred during the formation of the Fe–Mn nodule; these age gaps are related to the intermittent (discontinuous) timings of the beginning of Fe–Mn nodule formation offshore Minamitorishima Island.

Geological features of the Zn-Pb prospect in the Bou-Izourane district (Morocco)

The Zn-Pb mineralization in the Bou-Izourane district, located in the High Atlas Mountains of Morocco, contains estimated reserves of 40 200 tons of ore with an average grade of 20% Zn and 3.5% Pb. It is developed on N–S to NNW–SSE-trending faults that cut Liassic carbonate marl deposits. The paragenetic mineral sequence consists of galena, sphalerite and late-stage calcite. Oxidation phases of galena into cerussite and sphalerite into smithsonite are common in the Bou-Izourane ore, linked to the infiltration of meteoric waters and the oxidation of these sulphides. The Zn-Pb mineralization runs parallel to the fluorite veins associated with the igneous rocks of Tamazeght, but no petrographic or field relationship has been demonstrated between these two mineralizations (i.e., Zn-Pb and fluorite). The distribution of rare earth elements and yttrium (REY) in the Zn-Pb mineralization of Bou-Izourane shows a notable similarity with the Mississippi Valley Type (MVT) mineralization of the Central High Atlas of Morocco, although the concentrations more closely resemble those of REY in fluorite linked to the magmatic-hydrothermal activity of Tamazeght. However, the analysis of their distribution in post-fluorite calcite and post-Zn-Pb calcite reveals a strong concordance, suggesting that these two calcites are associated with the same phase and have a common origin. The classification of the Zn-Pb prospect in Bou-Izourane remains controversial, fluctuating between an MVT-type mineralization, similar to most Zn-Pb mineralizations in the Central High Atlas of Morocco, and a mineralization linked to the magmatic-hydrothermal activity of Tamazeght, which could provide heat and metallogenic material. Characterizing the Zn-Pb ore of Bou-Izourane is crucial for the future exploration of zinc and lead deposits in the High Atlas of Morocco and could advance the development of Zn-Pb mining in the region, from artisanal exploitation to professional mining

Enrichment of Smectite in the REY‐Rich Mud of the Clarion‐Clipperton Fracture Zone in the Eastern Pacific and Its Geological Significance

AbstractREY‐rich mud, consisting of deep‐sea sediments with high concentrations of rare‐earth elements and yttrium (REY), holds significant economic potential. Many studies have been conducted on biogenic apatite, ferromanganese micronodule, and phillipsite within these deposits to ascertain the REY enrichment mechanisms. However, the knowledge of clay minerals in REY‐rich mud, which is the predominant component of pelagic sediments, is still limited. In this study, two adjacent gravity cores (core GC02: REY‐rich mud; core GC03: typical sediments of equatorial Pacific) were collected from the Clarion‐Clipperton Fracture Zone (CCFZ) of the Eastern Pacific to study the role of different clay minerals in REY enrichment. The clay minerals in core GC03 and core GC02 are primarily illite (averaging 60%) and smectite (averaging 63%), respectively, and the smectite in core GC02 was mainly Fe‐rich, which was probably formed via the reaction between opal and FeOOH. Moreover, multiple studies have reported similar smectite enrichment in REY‐rich mud, suggesting that it is a common characteristic. The presumed hydrothermal or volcanic origination of smectite in REY‐rich layers of core GC02 indicates the essential role of hydrothermal and volcanic activities in REY‐rich mud formation during the Oligocene in the western CCFZ.

Provenance and sedimentary environment of REY-rich sediments from the Wharton Basin, Indian Ocean

Rare earth elements and yttrium (REY) in deep-sea sediments have emerged as potential strategic resources. In order to investigate the provenance, sedimentary environment, and mechanism of REY enrichment of pelagic sediments in Indian Ocean, we analyzed the grain size, bulk major and trace element concentrations and mineralogy of clay fractions (<2 μm) of sediments in the Wharton Basin, Indian Ocean. Based on the characteristics of biostratigraphic, we speculated that the sediments were deposited during the period from 11 Ma to 2 Ma. Sediments in the upper part (0–100 cm) of the sequence were mainly derived from aeolian material in Australia, whereas sediments in the lower part (100–258 cm) were mainly sourced from volcanic and hydrothermal materials which associated with submarine volcanic activity. The oxygen-rich environment below the calcite compensation depth (CCD) is crucial for the formation of REY-rich sediments. Additionally, there is a strong correlation between ΣREY, clay-grained sediments, Al2O3, and Fe2O3, suggesting that clay fractions contribute significantly to the enrichment of REY in the deep-sea sediments.

Recognition and (semi-)quantitative analysis of REE-bearing minerals in coal using automated scanning electron microscopy

The recognition and quantification of rare earth and yttrium (REY) minerals in coal is extremely important for understanding their geological origin and developing high-efficiency extraction techniques. This study developed an automated image analysis by scanning electron microscopy (AIA-SEM) method for characterizing REY minerals in coal. Carbon and copper were used as grey-scale calibration standard to assure the consistency per experiment and differentiate organic matter and minerals with different brightness. Two critical issues in determining REY including rapid recognition of fine REY-bearing particles and accurate classification and quantification of REY minerals in coal are resolved by (1) establishing grey threshold standard to locate REY-bearing grains and a two-step image scan; (2) developing classification criteria supplemented with spot- and EDS-mapping analysis for questionable particles. By using the established method, a total of 166 REY-bearing mineral grains were identified from 12,930 particles in a medium-volatile bituminous coal (REY concentration: 149.21 ppm; ash yield: 21.25%). It is found that Ca-REE flurocarbonates, monazite, and (Sc, Y)-bearing zircon are the dominant REY species in the studied coal sample. REE-aluminophosphates are also important hosts for REE in coal, with total amounts being >10%. REY minerals are fine in particle size. Over 50% of monazite, xenotime, Ca-REE flurocarbonate, and REE-aluminophosphate have particle size below 5 μm and monazite occurs mostly as submicron particle. Most REY minerals (> 60%) are embedded into coal macerals as included minerals. About 80% of REY-bearing phosphates and zircon are partly or completely encapsulated in clay minerals, whereas more than half of Ca-REY-fluorocarbonates mineral grains is free of other minerals.

Identification of core carcinogenic elements based on the age-standardized mortality rate of lung cancer in Xuanwei Formation coal in China.

In this study, the core carcinogenic elements in Xuanwei Formation coal were identified. Thirty-one samples were collected based on the age-standardized mortality rate (ASMR) of lung cancer; Si, V, Cr, Co, Ni, As, Mo, Cd, Sb, Pb, and rare earth elements and yttrium (REYs) were analyzed and compared; multivariate statistical analyses (CA, PCA, and FDA) were performed; and comprehensive identification was carried out by combining multivariate statistical analyses with toxicology and mineralogy. The final results indicated that (1) the high-concentration Si, Ni, V, Cr, Co, and Cd in coal may have some potential carcinogenic risk. (2) The concentrations of Cr, Ni, As, Mo, Cd, and Pb meet the zoning characteristics of the ASMR, while the Si concentration is not completely consistent. (3) The REY distribution pattern in Longtan Formation coal is lower than that in Xuanwei Formation coal, indicating that the materials of these elements in coal are different. (5) The heatmap divides the sampling sites into two clusters and subtypes in accordance with carcinogenic zoning based on the ASMR. (6) PC1, PC2, and PC3 explain 62.629% of the total variance, identifying Co, Ni, As, Cd, Mo, Cr, and V. (7) Fisher discriminant analysis identifies Ni, Si, Cd, As, and Co based on the discriminant function. (8) Comprehensive identification reveals that Ni is the primary carcinogenic element, followed by Co, Cd, and Si in combination with toxicology. (9) The paragenesis of Si (nanoquartz), Ni, Co, and Cd is an interesting finding. In other words, carcinogenic elements Ni, Co, Cd, and Si and their paragenetic properties should receive more attention.

Migration and exchange of rare earth elements between phosphate and iron manganese phase: A case study from fish tooth-bearing nodules

Deep-sea sediments that are widely distributed in the Pacific Ocean could be an important future resource for rare earth element (REE) and yttrium (REY) due to their high concentrations of REY. Bioapatite fossils as well as Fe-Mn (oxyhydr) oxides (e.g., micronodules) are recognized as significant carriers of REY in deep-sea sediments. Notably, bioapatite fossils, account for more than 60% of the total REY content in bulk sediments, underscoring their significance as primary host for REY. However, the mechanisms of REY enrichments, variations in Ce anomalies, and REY substitution in bioapatite fossils remain under explained. In this study, we performed detailed in situ geochemical, isotope geochemical and chemical imaging analyses on fish tooth-bearing nodules.Our results indicate that fish teeth are mainly composed of Ca, P, F and Na, which accounting for over 95 % of the total composition of these teeth. On the one hand, the concentrations of Ca, P and F exhibit strong positive correlations with each other: their contents increase from the inside to the outside of the dentine shell. On the other hand, Na concentration display a different trend that the highest concentration is found in the center part of shark teeth. Despite the theoretical nearly absence of seawater as potential transport media, REYs migrated from the ferromanganese oxides phase to phosphate phase, and their contents decreased from inside layers to outside layers of dentine. During the long-term substitution processes in geological time, a portion of Ce3+ would be oxidized into immobile Ce4+ under oxic conditions, resulting in less incorporation of Ce3+ into the outer layers of dentine compared to other REY3+. As a consequence, stronger negative Ce anomalies were observed in the inside layers than in outside layers of dentine. The laser ablation–inductively coupled plasma–mass spectrometry (LA-ICP-MS) mapping together with the in-situ geochemistry results indicate the negligible participation of Si in REY substitution, whereas Na exhibits a pronounced preference for substituting Ca2+ with REY3+. Therefore, we propose the following substitution scheme for incorporating REY into the crystal lattice of fish teeth: REY3+ + Na+↔ 2Ca2+. Our study clarified the fraction of REY during their migration from the Fe-Mn phase to the phosphate phase, and also contributes to a deeper understanding of the REY enrichment mechanism in pelagic sediments.

Concentration, speciation, and fractionation of rare earth elements in alluvial soils in contiguous karst landform, southwestern China

Karst is a unique landform formed by strong chemical weathering of carbonate rocks. This study investigated the concentration and speciation of rare earth elements and yttrium (REY) in alluvial soils and REY fractionation from carbonate rocks and alluvial soils in the world's largest contiguous karst landform in southwestern China. The results showed that the REY of alluvial soils ranged from 73.77 to 1251.56 μg⋅g−1, with a median value of 230.30 μg⋅g−1, which was higher than that of alluvial soils across China (178 μg⋅g−1) and the upper continental crust (168 μg⋅g−1), revealing a high background of REY in these karst areas. Meanwhile, the average REY in alluvial soils (244.96 μg⋅g−1) was close to 14 times that in carbonate rocks (17.61 μg⋅g−1) in the study area, indicating that REY was significantly enriched in the pedogenesis. Correlation analysis showed that the REY concentration was not significantly related to any single factor (i.e., Fe2O3, MnO, Al2O3, TOC, pH, or CIX). BCR speciation analysis revealed a declining trend in the proportion of REY across the residual (F4, 73.21 %), reducible (F2, 19.40 %), oxidizable (F3, 6.89 %), and weakly acid-extracted (F1, 0.50 %) phases. Additionally, significant REY fractionations from carbonate rocks to alluvial soils were observed. The bedrock-normalized REY pattern revealed an enrichment of light rare-earth elements (LREE) and middle rare-earth elements (MREE), a depletion of heavy rare-earth elements and yttrium (HREY), and positive Ce and Gd anomalies. Secondary mineral phases that formed during weathering—such as clay minerals, oxyhydroxides, phosphates, and organic matter—played an important role in the retention and fractionation of the REY in the soils. Besides these natural factors, anthropogenic inputs also contributed to the REY fractionation, as indicated by the slight positive Gd anomaly in the karst alluvial soils. Furthermore, the differences of δCe and δEu in the soils developed from three types of pedogenic rocks—including carbonate, basalt, and granite—were discussed. The different δEu anomalies could help to identify the parent rocks of alluvial soils.

Grain Size Analyses and Mineral Compositions of Core Sediments in the Western North Pacific Ocean: Implications for the Rare Earth Element and Yttrium Enrichment and Deposition Environment

Rare earth element and Yttrium (REY)-rich deep-sea sediments have been identified as significant potential resources. Although grain size analysis is important for the study of deposition environment and the future exploration of REY, related research is limited. Here, we have investigated the grain size and mineral composition of bulk pelagic sediments from Western North Pacific to indicate the evolutions of deposition environment. Grain size analysis results reveal that silt contents are dominant, and the grain size ranges between 20 and 40 μm and can be an additional grain characteristic indicator for REY-rich sediments. Furthermore, the better sorting coefficient of REY-rich sediments reflects the scouring action of bottom currents, which allows the preservation of coarse-grained bioapatite and the removal of clay fraction particles. ΣREY is negatively correlated with clay fractions but positively correlated with sand and silt fractions for the REY-rich sediments, and this is consistent with the dominant distribution of silt-sized biogenic apatite. In addition, grain size distribution (GSD) varies significantly after HCl treatment in the REY-rich sediment. Therefore, for deep-sea sediments collected below the carbonate compensation depth (CCD), an additional presence of a grain size peak at ~20–40 μm and distinct differences in GSD after HCl treatment can serve as important indicators for REY enrichment sediments.

Rare earth element and yttrium (REY) geochemistry of 3.46–2.45 Ga greenalite-bearing banded iron formations: New insights into iron deposition and ancient ocean chemistry

Finely laminated cherts enclosing nanoparticles of greenalite and apatite are ubiquitous in Archean-Paleoproterozoic (3.46–2.45 Ga) ferruginous cherts, jaspilites and Banded Iron Formations (BIFs) and the greenalite and apatite are considered to be primary deposits. The cherts and BIFs are chemical sedimentary rocks interpreted to have been precipitated in marine settings prior to the first permanent rise in atmospheric oxygen at the Great Oxidation Event (GOE) ca. 2.45–2.32 M.y. ago. As chemical sediments, they are potential archives of the solutions from which they precipitated, incorporating signals from hydrothermal fluids and ambient seawater. Previous studies of rare earth elements and Y (REY) in pre-GOE BIFs have mostly found an “Archean seawater signature” with positive Eu anomalies, attributed to the influence of high-temperature hydrothermal processes, and positive anomalies for La, Gd and Y, ascribed to seawater. REY abundances determined by in situ LA-ICP-MS are presented for well-preserved, laminated greenalite-bearing cherts from ten formations of pre-GOE ferruginous cherts and BIFs from Western Australia. The samples come from a wide range of depositional environments, e.g., submarine proximal volcanic environments, basin floor, slope and deep marine shelf, and are between 3.46 Ga to 2.45 Ga in age. Five groups with different REY patterns are identified, namely (i) mafic-volcanic-influenced vent-proximal chert from the Marble Bar Chert Member of the Duffer Formation of the Warrawoona Group; (ii) felsic volcanic- and sediment-associated chert from the Kangaroo Caves Formation of the Sulphur Springs Group and the Wilgie Mia Formation of the Murchison Supergroup, (iii) ferruginous cherts in shelf sediments from the Bee Gorge Member of the Wittenoom Formation of the Hamersley Group, (iv) BIFs from the Nammuldi Member of the Marra Mamba Iron Formation and Joffre Member of the Brockman Iron Formation, Hamersley Group, and (v) BIFs from the Dales Gorge Member of the Brockman Iron Formation. Of these, only the Dales Gorge Member BIF has a typical Archean seawater signature while the others have REY patterns likely reflecting differing source fluids and environments of deposition but not necessarily global ocean chemistry. Analyses of chert containing sub-micron-sized particles of greenalite and apatite indicate that the likely hosts of the REEs are apatite, siderite and possibly greenalite. The REY patterns of the greenalite-bearing cherts may differ from those of bulk samples of the same formations, perhaps reflecting a diagenetic overprint in the bulk samples, whereas the greenalite-bearing cherts likely preserve their depositional compositions, locked in by early silicification.

Controls of Tellurium enrichment in the rare earth elements and yttrium (REY) rich deep-sea sediments from the Central Indian Ocean Basin (CIOB)

As a potential Te reservoir for the global budget, the occurrence, material sources, migration and enrichment mechanism of Te in deep-sea sediments remain unclear. Based on the major and trace elements measurements of bulk sediments, this study proposed a procedure to quantify the contribution of Te by main host minerals, combining with TIMA and LA-ICP-MS in two cores (GC04 and GC11) from the Central Indian Ocean Basin (CIOB) and a core from east of the 90°E Ridge (GC03). Te shows the highest enrichment coefficient of 650 referred to UCC (Upper Continental Crust) in the REY (Rare Earth Elements and Yittrium) rich sediments in GC04, GC11 and GC02 (a core at the south of GC04 and GC11). Clinoptilolite-K and osumilite are indicated as the main host minerals, which correlates Te sources with volcanogenic materials and weathering products of terrigenous rocks. The inter elements correlation, cluster analysis and factors analysis further indicate distinct hydrothermal genetic Te. So, we put forward a hypothesis that Te is mainly sourced from the submarine volcanogenic hydrothermal activities, which are closely associated with local intraplate volcanism episodes from late Miocene with spatial and temporal differences. This study is the first attempt to quantify Te from different minerals and to reveal its geochemical behavior in the deep sea sediments, which will be benefit to the understanding of Te reservoir and cycle in deep sea and the comprehensive utilization of REY-rich deep-sea sediments. However, for the abundant presence of undetectable nanoscale minerals in these sediments, the contribution of Fe-Mn (oxyhydr) oxides and clay minerals of Te need more investigation.

Geochronology, Mineralogy, and Geochemistry of the Tonsteins from the Permo–Carboniferous Benxi Formation, Ordos Basin, North China Craton

AbstractTonstein layers are found worldwide in the Permo–Carboniferous coal‐bearing strata. This study investigates the geochronology, mineralogy, and geochemistry of four tonstein samples from the Permo–Carboniferous Benxi Formation, Ordos Basin, North China Craton (NCC). The typical features of the studied tonsteins include thin beds, lateral continuity, angular quartz grains, and euhedral zircons with similar U‐Pb ages, indicating a significant pyroclastic origin. In addition, the tonstein samples have low TiO2/Al2O3 ratios (&lt;0.02) and rare earth elements and yttrium (REY) concentrations with obvious negative Eu anomalies, indicating that the tonsteins have a felsic magma origin. Moreover, compared with the mean composition of clay shale, the studied tonsteins are characterized by high concentrations of the elements Nb and Ta, which may affect the concentration of the corresponding elements in surrounding coal seams. The zircon U‐Pb ages of the tonsteins (293.9–298.8 Ma) provide a precise chronological framework on the Benxi Formation in the Ordos Basin, constraining the Gzhelian–Aselian stages. The tonsteins were probably sourced from arc volcanism along the western margin of the NCC during the early Permian, implying that the Alxa Terrane had not amalgamated with the NCC at that time.

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.

Evaluating the contribution of hydrothermal fluids and clay minerals to the enrichment of rare earth elements and yttrium (REY) in deep-sea sediments

Deep-sea REY-rich sediments have attracted considerable attention in recent studies because of their extremely high REY resource potential. Previous studies highlighted that hydrothermal precipitates (e.g., Fe-Mn (oxyhydr)oxides) have played an important role in REY enrichment in deep-sea sediments by scavenging REY from seawater. However, the exact extent of the contribution of hydrothermal scavenging to the REY accumulation has not yet been evaluated. In addition, REY enrichment generally occurred in the pelagic clays, and whether the clays have played a role in the REY accumulation is poorly constrained. We studied bulk-sediment geochemistry and mineral fractions of sediments from two sites in the Eastern South Pacific Ocean. The results show that both cores contain REY-rich sediments layers possessing average ΣREY contents of 989 ppm and 1563 ppm, respectively. The calculated REY resource amounts in the 1 km × 1 km × optimal recovery depth (m) of the two sites are summed to 4690 t-REO. Carbonate compensation depth is one of the factors controlling the REY contents in the sediments in our study area. The shale-normalized REY patterns and calculated simulation results suggest that direct input of REY from the hydrothermal sources to the sediments was not significant. The evaluation of the contributions of REY scavenged by hydrothermal Fe-Mn (oxyhydr)oxides suggests that for the metalliferous sediments in which Fe-Mn (oxyhydr)oxides are hydrothermal-dominated, the Fe2O3 and ΣREY contents show a pronounced positive correlation for all cores, implying hydrothermal scavenging of REY significantly contributed to the accumulation of REY. However, with the continuous addition of hydrothermal Fe-Mn (oxyhydr)oxides in the pelagic clay sediments, the ΣREY contents in the REY-rich sediments firstly exhibited an increase, and then when the total Fe2O3 components achieved a certain value (∼25 wt% in this study) they started to decline. This finding suggests the appropriate input of hydrothermal Fe-Mn (oxyhydr)oxides into the sediments certainly increases the ΣREY contents through a scavenging mechanism, but that excessive addition of them would, in turn, decrease the ΣREY contents of the sediments. Additionally, the amount of clay minerals exhibited a significant positive correlation with ΣREY contents, therefore, we inferred that clay minerals probably played an important role in REY accumulation in the sediments.

Phillipsite in pelagic REY-rich sediments and ferromanganese nodules from the Western Pacific: Geochemical characteristics and implications for REY enrichments

Recent studies have shown that the rare earth elements and yttrium (REY)-rich deep-sea sediments often contain abundant phillipsite, which is considered as an indicator mineral for REY-rich sediments. However, the phillipsite contains very low REY content, and the coexistence of abundant phillipsite and REY enrichment is generally explained by the low sedimentation rate in deep sea environment. Whether the phillipsite has the capacity to enrich REY and why it is REY-poor is still unclear. Phillipsite is also present in ferromanganese nodules in the surface of the deep-sea sediments, yet whether there is any compositional/genetic difference between the sediment-hosted and nodule-hosted phillipsite is unclear. Here, we study the phillipsite in pelagic REY-rich sediments and ferromanganese nodules from the Western Pacific Marcus‐Wake seamount chain. Mineralogical, morphologic, and geochemical analyses of the sediment-/nodule-hosted phillipsite were carried out. Our results show that the XRD patterns and Si/Al ratios of the sediment-/nodule-hosted phillipsite are the same, and they are both K-phillipsite. However, the consistent Fe/Ti, Zr/Hf and Nb/Ta ratios as well as similar Zr/Nb and Zr/Ta ratios of sediment-hosted phillipsite indicate that the sediment-hosted phillipsite has a homogeneous parent rock and has undergone the same degree of low-temperature alteration. In contrast, the nodule-hosted phillipsite may have inhomogeneous parent rock and have undergone different degree alteration because of the varying Fe/Ti, Zr/Hf and Nb/Ta ratios, as well as the wide range of Zr/Nb and Zr/Ta ratios in the nodule-hosted phillipsite. Both sediment-/nodule-hosted phillipsite have similar REY patterns to those of the pore water and have low total REY contents, indicating that they do obtain REYs from the pore water. In deep-sea REY-rich sediments, the phillipsite does not enrich REY, although the REY can enter the phillipsite lattice. This may be caused by the low cation exchange selectivity for REYs in phillipsite, which can be attributed to high hydration energy. Our study indicates that phillipsite does not participate in REY-enrichment. The implication of phillipsite for REY enrichment may be attributed to the consistency of the environmental conditions between the phillipsite formation and REY enrichment.

Modes of occurrence of critical metals (Nb-Ta-Zr-Hf-REY-Ga) in altered volcanic ashes in the Xuanwei Formation, eastern Yunnan Province, SW China: A quantitative evaluation based on sequential chemical extraction

Altered volcanic ash with highly-elevated concentrations of Nb(Ta), Zr(Hf), Ga, and rare earth elements and yttrium (REY) is an untraditional type of critical metal deposit that has been discovered in Yunnan Province, southwest China. Previous studies have briefly described the modes of occurrence of Nb(Ta)-Zr(Hf)-REY-Ga in the ore deposit, showing that Zr and Hf are mostly hosted in zircon; light rare earth elements (LREE) mainly occur in REY-bearing carbonates and phosphates; Nb and Ta are primarily hosted in the former Fe-Ti oxide phases and zircon; and Ga is predominantly associated with clay minerals. However, previous studies of the modes of occurrence of critical metal elements (Nb-Ta-Zr-Hf-REY-Ga) have been limited to qualitative or semi-quantitative studies of individual mineral grains, and quantitative research of the modes of occurrence of these elements in whole rocks is absent. This paper quantifies the modes of occurrence of critical elements (Nb-Ta-Zr-Hf-REY-Ga) using a sequential chemical extraction method. The results show that about 65.3–86.7% Nb is associated with hydrofluoric acid (HF)-soluble aluminosilicates (clays) and 13.3–34.7% in the insoluble phases such as Nb-rutile. Approximately 87.6–90.2% Zr is the primary hosted in zircon and 9.5–12.0% Zr appears to be associated with HF-soluble aluminosilicates in the altered volcanic ash. In felsic altered volcanic ashes (Al2O3/TiO2 ratio between 21 and 70), the REY are predominantly in the authigenic minerals such as REY-bearing aluminum phosphates and sulfates of the alunite supergroup (APS minerals), carbonates or fluorocarbonates. About 74.0–89.4% LREE, 26.5–34.2% middle rare earth elements (MREY), and 22.1–24.8% heavy rare earth elements (HREE) occur in HF-soluble aluminosilicates. In intermediate altered volcanic ash samples (Al2O3/TiO2 ratio between 8 and 21), 93.0% LREE are associated with insoluble phases such as monazite and zircon. Gallium is predominantly associated with HF-soluble aluminosilicates (73.3–80.5%) in all altered volcanic ash samples.

Biomonitoring of rare earth elements in Southern Norway: Distribution, fractionation, and accumulation patterns in the marine bivalves Mytilus spp. and Tapes spp.

Growing extraction and usage of rare earth elements and yttrium (REY) for medical and industrial applications has resulted in increased discharges into the marine environment. Using Mytilus spp. Mussels and Tapes spp. clams as bioindicator organisms, we analyzed 15 REY in soft tissues of specimens collected at two potentially polluted sites in Southern Norway: in the vicinity of an industry producing gadolinium-based MRI contrast agents (GBCAs) (Lindesnes) and in an industrially-affected fjord (Porsgrunn). The spatial distribution of REY and shale-normalized fractionation patterns were determined to assess the potential anthropogenic contribution of REY at the sites. At both sites, the REY fractionation pattern in soft tissue was characterized by enrichment of light rare earth elements (LREE) over heavy rare earth elements (HREE), while also displaying negative cerium and small positive gadolinium (Gd) anomalies. LREEs contributed to over 80% of the total REY concentrations, with increasing relative enrichment following higher total REY. Gd anomalies remained conserved in most sites despite significant differences in total REY; however, a high Gd anomaly (Gd/Gd* = 4.4) was found downstream of the GBCA industry spillwater outlet, indicating biotic uptake of excess anthropogenic Gd at this site. Total REY concentrations in clams in Porsgrunn were one order of magnitude higher than in mussels in Lindesnes. This may be attributable to freshwater influences in Porsgrunn, where clams collected closer to the river mouth had significantly higher total REY concentrations. This study constitutes the first assessment of REY concentrations in marine bivalves in Norway and can provide useful information for future biomonitoring studies on REY contamination.

Mineralogical variations and geochemical distribution of rare earths and Yttrium (REY) in coal and overburden rocks of some Indian coal mines of Gondwana coalfield

Mineralogical variations and geochemical distribution of rare earths and Yttrium (REY) in coal and overburden rocks of some Indian coal mines of Gondwana coalfield