Behavior Of Rare Earth Elements Research Articles

Rare Earth Elements and Fractionation of Zr-Hf and Y-Ho: Implication to Petrogenesis of Idanre Granite, Nigeria

Idanre area which is situated within the Nigerian shield is affected by orogenic activities accompanied by emplacement of Pan-African granitoids. This paper presents a new information on geochemical behaviour of Rare Earth Elements (REEs) and High Field Strength Elements (HFSEs) Zr-Hf and Y-Ho that can explain post magmatic processes relating to the origin and evolution of the Idanre granite. Zr-Hf, Hf-(Zr/Hf) and Y-Ho, (Y/Ho)-Ho variation diagrams depicted similar mobility and migration patterns for Zr, Hf, Y and Ho. Binary plots of Log Zr/Hf vs Log Hf, Log Y/Ho vs Log Ho; high LREE/HREE and negative Eu anomaly shows extensive plagioclase and calcic amphibole fractionation. High Ce/Yb values 113.49, 134.97, and 123.6 reflects low partial melting in the source rocks. Similar Zr/Hf ratios 39.16; 39.3 and 43.26 for members of the granite suite suggest a common source for the minimally differentiated magmatic fluid. Y/Ho ratios of 27.15, 27.12 and 25.91 indicate that the rock units are comagmatic. Mean Zr/Hf (41.69) and Y/Ho (27.18) ratios indicate the host migmatite may be the source rock for the Idanre granite complex.

Geochemical and mineralogical correlations between the bog iron ores and roasted iron ores of the Podravina region, Croatia

Throughout the Podravina region, NE Croatia, over one hundred locations with signs of iron production, dating to the late Antique period and the Middle Ages, have been discovered in the last 30 years. Recently, signs of various bog iron ore types and formations were discovered throughout the area. This study investigates the mineralogical and geochemical characteristics of local bog iron and roasted iron ores. Furthermore, statistical clustering of different geochemical components in the ores is presented, while the abundance and distribution of macro-, micro- and rare earth elements (REE) and how they correlate within the bog iron ores and roasted iron ores is considered. A total of 15 samples acquired from geological investigations and 13 samples found during archaeological excavations were analysed using geochemical and mineralogical methods. In bog iron ores, X-ray diffraction (XRD) confirmed goethite and quartz as the primary mineral phases, while roasted iron ores contained several Fe minerals and had variable quartz and clay mineral contents. Chemical analyses confirmed high Fe contents in both bog iron ores (up to 70.89 mass. %) and roasted iron ores (up to 84.97 mass. %), with a distinct differentiation of Fe and Si between the different bog iron ore types. Scanning electron microscopy with attached EDS detector (SEM-EDS) showed features of laminar Fe and Mn mineralization, confirming the theory that bog iron ore forms as seasonal precipitation from groundwater. Using the hierarchical clustering analysis, a geochemical correlation of the iron component in bog iron ores and roasted iron ores was compared to other major oxides, micro- and REEs. It was established that the iron component has very little influence on REE and microelements behaviour. Therefore, microelements and REEs were used as a tracer for establishing a geographical connection between the bog iron ores and roasted iron ores in the Podravina region.

Rare earth elements (REE) in soils and plants of a uranium-REE mine site and exploration target in Central Queensland, Australia

Investigations on the biogeochemical behaviour of rare earth elements (REEs) in natural systems broaden our understanding on their occurrence and fate in ecosystems. The aim of this study was to assess the prevailing REE concentration patterns in soils and plants in a uranium REE-rich area in Central Queensland, Australia. We collected and analysed matching soil and plant material samples from both undisturbed and mine-affected areas enriched in REEs near the now abandoned Mary Kathleen Mine. We found that in the soil, Ce had the highest concentrations (1550 μg g−1), followed by La (645 μg g−1), whereas that of Gd (25 μg g−1) and Lu (1.5 μg g−1) were comparatively low. Soil REE patterns had a slight HREE enrichment relative to LREE, with a positive Ce anomaly, suggesting oxidizing conditions. The REE patterns of the DTPA-extracts had LREE enrichment relative to HREE. Soil pH was negatively correlated with DTPA-REE (−0.68 ≤ R ≤ -0.40; p < 0.001). In the plants, we found interspecies variation in REE accumulation, with REE concentrations higher in the dicots than in the monocots. The plant REE patterns displayed HREE enrichment relative to LREEs, and foliar REE concentrations were correlated with Mn, Fe, Mg, Al and Ca in some species (0.57 ≤ R ≤ 0.96; p < 0.05). Our findings suggest that Mn-Fe-oxyhydroxides and soil pH influenced REE accumulation patterns, while within the plant, foliar REE accumulation could be attributed to a mechanism which is common for macronutrients and certain trace metals.

Geochemical characteristics of rare earth elements (REEs) in soils developed on different parent materials, in the Baoshan area, Yunnan Province, SW China

The geochemistry of rare earth elements (REEs) was studied in rock samples from host formations, ore samples from two mineral deposits (the Hetaoping Cu-Pb-Zn mine: HTP and the Heiyanao Fe-Cu-Pb-Zn mine: HYA) and the overlying or nearby soils to better understand REE concentrations, distributions and behaviour during weathering from different parent materials at the regional scale, Baoshan area, Yunnan Province, SW China. The mudstone and sandstone formations have the highest total REE (ΣREE) contents. Chondrite-normalized diagrams for rocks and ores show significant light REEs (LREEs) enrichments and Eu depletion (except for ores in HYA). Cerium displays an obvious negative anomaly in carbonate rocks (Є-3-R, C-R, D-R, T-1-R and T-2-R). Soils overlying carbonate rock formations (T-1-S, C-S and Є-3-S) have the highest ΣREE contents, while soils overlying basalts have the lowest ΣREE contents. Soils show enrichments in LREEs with negative Eu anomalies and slight Ce anomalies in the studied soils. Soils with high ∑LREE/∑heavy REE (HREE) values may result from the preferential absorption of LREEs by organic matter. Negative Eu anomalies in soils occur for parent materials in the study area lacking feldspar, especially soils developed from carbonates. Compared to the parent materials, most soils show REE enrichment because alkali metals are removed and REEs are concentrated by low mobility in surficial processes and positive Ce anomalies because of weathering dissolution of other trivalent REEs with ionic radii similar to that of Ca 2+ . Supplementary material: Additional data (Tables S1 and S2) and sample locations (Fig. S1) are available at https://doi.org/10.6084/m9.figshare.c.5303140

Rare-Earth Incorporated Alloy Catalysts: Synthesis, Properties, and Applications.

To improve the performance of metallic catalysts, alloying provides an efficient methodology to design state-of-the-art materials. As emerging functional materials, rare-earth metal compounds can integrate the unique orbital structure and catalytic behavior of rare earth elements into metallic materials. Such rare-earth containing alloy catalysts proffer an opportunity to tailor electronic properties, tune charged carrier transport, and synergize surface reactivity, which are expected to significantly improve the performance and stability of catalysis. Despite its significance, there are only few reviews on rare earth containing alloys or related topics. This review summarizes the composition, synthesis, and applications of rare earth containing alloys in the field of catalysis. Subsequent to comprehensively summarizing and constructively discussing the existing work, the challenges and possibilities of future research on rare-earth metal compound materials are evaluated.

Leaching Behaviour and Kinetic of Light and Heavy Rare Earth Elements (REE) from Zircon Tailings in Indonesia

Zircon tailings containing rare earth metals are one of the alternative raw materials from secondary sources in Indonesia. The objective is to determine the effects of several operating conditions in the leaching process. Under specified leaching conditions including 2 M hydrochloric acid concentration, 10 g/100 mL solid-liquid ratio, and a temperature of 80°C, the optimum rare earth metal leaching recovery was obtained. Under these conditions, as much as 60%, 74%, and 65% for cerium, lanthanum, and neodymium can be leached, respectively. With the same conditions, HREE was leached as much as 71%, 61%, and 60% for erbium, gadolinium, and samarium. The leaching process was described using the kinetic model known as the Zhuravlev–Leshokin–Templeman model. Activation energy values for light and heavy rare earth element leaching were found to be 25.31 kJ/mol and 7.05 kJ/mol, respectively.

Distribution, fractionation and sources of rare earth elements in suspended particulate matter in a tropical agricultural catchment, northeast Thailand

Forty-eight suspended particulate matter (SPM) samples were collected from the Mun River, northeast Thailand and its junction with the Mekong River, to investigate the relationship between the distribution of rare earth elements (REE) in SPM and the soils in the watershed. The total REE contents (∑REE) in SPM in the Mun River ranged from 78.5 to 377.8 mg/kg with the average of 189.3 mg/kg, which was lower than ∑REE of 222.3 mg/kg at the Mekong River (one sample at junction). The Post Archean Australia Shale (PAAS)-normalized ratios of light REE (LREE), middle REE (MREE) and heavy REE (HREE) were averaged to 1.0, 1.3 and 1.0, which showed a clear enrichment in MREE. In short, along the Mun River, the REE contents in SPM were decreasing, and the PAAS-normalized patterns of REE showed gradually flat. The REE content in SPM and soils are highest in the upper catchment, indicating that soil/bedrock is the most important source of REE in SPM. Additionally, the positive Eu anomaly was enhanced by the higher Ca content in SPM (R = 0.45), which may be caused by more feldspars or carbonates with Ca and Eu substituting Ca. The results present the REE behaviors of SPM in the Mun River and relationship between REE in SPM and soil/bedrock, the findings may support the other studies in catchment weathering.

Geochemical Behaviors of Rare Earth Elements (REEs) in Karst Soils under Different Land-Use Types: A Case in Yinjiang Karst Catchment, Southwest China.

The geochemical characteristics of rare earth elements (REEs) can be employed to identify the anthropogenic and natural influence on the distributions of REEs in soils. A total of 47 soil samples from the three soil profiles of the secondary forest land, abandoned cropland, and shrubland in the Yinjiang county of Guizhou province, southwest China, were collected to determine the contents and distribution of REEs in the soil environment. The total REEs (ΣREE) contents in different soil profiles are in the following sequence: secondary forest land (mean: 204.59 mg·kg−1) > abandoned cropland (mean: 186.67 mg·kg−1) > shrubland (mean: 139.50 mg·kg−1). The ratios of (La/Gd)N and (Gd/Yb)N ranged from 0.62 to 1.00 and 1.18 to 2.16, which indicated that the enrichment of the medium rare earth elements (MREEs) was more obvious than that of the light rare earth elements (LREEs) and the heavy rare earth elements (HREEs). The phenomenon could be attributed to the preferential absorption of MREEs by fine particles and the substitution of Ca2+ by MREEs. Most soil samples were characterized by the negative Ce anomalies (anomalies values: 0.30–1.10) and positive Eu anomalies (anomalies values: 0.43–2.90). The contents of REEs in the profiles of secondary forest land and shrubland were mainly regulated by soil pH and Fe contents while clay content and agricultural activities were the main controlling factors in the soil profile of abandoned cropland. This study highlights the role of agricultural activities in affecting the distributions of REEs in karst soils, which could provide some insights for the protection of the soil environment.

Microwave chloride leaching of valuable elements from spent automotive catalysts: Understanding the role of hydrogen peroxide

This study reports on the microwave-assisted leaching behavior of platinum group metals (PGMs) and light rare earth elements (LREEs) from two representative end-of-life automotive ceramic catalyst materials in 6 M HCl at 150 °C with and without the addition of 10 v/v% H2O2 solution. It was shown that the in situ generated headspace gas in the pressure-tight reactor and the elemental speciation in the spent catalysts influence the leachability of PGMs and LREEs. The formation of Cl2 in the headspace provided the 6 M HCl system with a suitable oxidizing environment to leach PGMs as soluble chloro‑complexes. Indeed, spent catalyst containing prevalently oxidized PGM species leached best in 6 M HCl (93.9 ± 0.7% Pd, 98±3% Pt, 70.7 ± 0.4% Rh). Whereas, H2O2 addition moderately decreased the PGM leaching efficiency due to surface passivation by an oxide layer. However, spent catalyst containing other oxidizable substrates (e.g. Ce3+, zerovalent PGMs) that give rise to H2 evolution, compensated partially the oxidation potential of the HCl system. In such case, H2O2 addition slightly improved the PGM leachability (Rh 91.8 ± 0.1% Pd, 96±4% Pt, 89.9 ± 0.2% Rh).Among the studied LREEs, Ce leaching was mainly affected by the passivation of Ce3+ through oxidation, thus in the absence of H2O2 and at lower initial Ce3+ concentration Ce leached best (87–94%). The effect of hydrogen peroxide was negligible for La and Nd, and moderate towards Y leaching. The leaching of these elements was constrained by their association with Al and Zr oxides, respectively.

Fractionation and fixation of rare earth elements in soils: Effect of spiking with lanthanum, cerium, and neodymium chlorides

Industrial and agricultural activities lead to the release of rare earth elements (REEs) in wastewater and aquatic ecosystems, and their accumulation in soils. However, the behavior of REEs in soils remains somewhat unclear. In the present work the fractionation and fixation of REEs in soddy-podzolic and chernozem soils spiked with La, Ce, and Nd chlorides were studied using dynamic (continuous flow) extraction, which allows natural conditions to be mimicked and artefacts to be minimised. The eluents applied are aimed to dissolve exchangeable, specifically sorbed, bound to Mn oxides, bound to metal–organic complexes, and bound to amorphous and poorly ordered Fe/Al oxides fractions extractable by 0.05 mol/L Ca(NO3)2, 0.43 mol/L CH3COOH, 0.1 mol/L NH2OH·HCl, 0.1 mol/L K4P2O7 at pH 11, and 0.1 mol/L (NH4)2C2O4 at pH 3.2, respectively. It is found that the fixations of added La, Ce, and Nd in the form of metal–organic complexes is predominant for both types of soils: 35%–38% in soddy-podzolic soil and 50%–79% in chernozem. The fixation of added elements in the first three fractions (exchangeable, specifically sorbed, and bound to Mn oxides) is significant for soddy-podzolic soil (5%–25%). For chernozem, the relative contents of added Ce and Nd in these fractions are nearly negligible. Only the content of exchangeable La is notable, about 5%. Adding any of three elements (La, Ce, or Nd) at the level of 100 mg/kg to an initial sample results in changing the fractionation and bioaccessibility of other REEs present in soil. Their contents increase in the first three fractions and decrease in fifth (oxalate extractable) fraction for both soddy-podzolic soil and chernozem. The main difference is the behavior of REEs in pyrophosphate extractable fraction. For soddy-podzolic soil, adding La, Ce, or Nd results in decreasing the contents of other REEs associated with organic matter. For chernozem, on the contrary, the contents of REEs in the form of metal–organic complexes slightly increase. These processes may be attributed to competitive binding of elements and soil properties; they must be taken into account when assessing the environmental risks of soil pollution with REEs.

Particulate rare earth element behavior in the North Atlantic (GEOVIDE cruise)

Abstract. Particulate concentrations of the 14 Rare Earth Elements (PREE), yttrium, and 232-thorium were measured in 200 samples collected in the epipelagic (ca. 0–200 m) and mesopelagic (ca. 200–1500 m) zones of the North Atlantic during the GEOVIDE cruise (May/June 2014, R/V Pourquoi Pas?, GEOTRACES GA01), providing the most detailed snapshot of the PREE distribution in the North Atlantic so far. Concentrations of particulate cerium (PCe) varied between 0.2 and 16 pmol L−1, while particulate neodymium (PNd) concentrations ranged between 0.1 and 6.1 pmol L−1. Particulate ytterbium (PYb) concentrations ranged between 0.01 and 0.50 pmol L−1. In addition, this study showed that PREE distributions were also controlled by the biological production in the upper sunlit ocean and by remineralization processes in the mesopelagic area. Low surface concentrations combined with normalized PREE patterns displaying a negative Ce anomaly and HREE enrichments pointed to freshly formed biogenic particles imprinting the seawater signature. A significant relationship between biogenic silica (BSi) and PHREE was also observed in the Labrador and Irminger seas, due to the occurrence of strong diatom blooms at the sampling time. In order to identify dissolved-particulate processes independent of the ionic radius, we used PHo∕PY ratios and showed that absorption processes were predominant in the upper ocean, while adsorption processes dominated at deeper depths. This study highlighted different lithogenic fractions of PREE and dispersion depending on the shelf: off the Iberian margin, up to 100 % of the PREE were determined to have a lithogenic origin. This lithogenic input spread westward along an intermediate nepheloid layer (INL), following isopycnals up to 1700 km away from the margin. In contrast, along the Greenland and Newfoundland margins, the circulation maintained lithogenic inputs of PREE along the coasts.

Chromatographic behavior of six lanthanides on a centrifugal mixer-settler extractor cascade

This work furthers the development of counter-current chromatography as an industrial separation process method. It was demonstrated that the industrial counter-current chromatography methods, in particular, for the separation groups of rare earth metals, can be implemented in a modified cascade of centrifugal mixer-settler extractors. The retention behavior of rare earth elements (samarium, europium, gadolinium, terbium, dysprosium and yttrium) on the pilot chromatographic unit consisting of 70 serially connected centrifugal mixer-settler extractors was experimentally studied under isocratic elution conditions using the mixture of 30 vol.% CyanexⓇ572 + 10 vol.% tributylphosphate in a hydrocarbon diluent as the stationary phase and aqueous nitric acid as the mobile phase. Theoretical analysis of experimental studies showed an acceptable agreement between the assumptions of the theory and experimental results.

Rare earth element distributions in rivers and sediments from the Erdenet Cu–Mo mining area, Mongolia

River water and sediments collected from the Erdenet, Gavil, and Khangal Rivers, near the Erdenet Cu–Mo mine were analyzed for their rare earth elements (REE) and yttrium (YREE) contents. Surface water samples were also collected from the tailing pond and ash pond of the mine, as well as in the seepage from the ash pond, where a part of the effluent flows into the Khangal river. The major chemical compositions of river and surface waters were found to vary slightly with water flow. The river water is Ca–HCO3-dominated in the upstream of the Erdenet and Gavil Rivers and ash pond; Ca–SO4-dominated in the tailing pond and seepage from the ash pond; and Ca–HCO3–SO4-dominated downstream of the Erdenet and Khangal Rivers. Both river and surface water exhibited a significant diatom content and the dissolved organic matter mainly comprise of fulvic acid-like materials, protein-like materials and microbial materials.The concentrations of YREE in river and surface waters ranged from 4.6 to 14.9 ng/L, whereas those of the sediments and rocks were 10–43 mg/kg and 25–34 mg/kg, respectively. Shale-normalized YREE patterns of river and surface waters, irrespective of water type, were characterized by enrichments in the middle REE (MREE) and heavy REE (HREE) relative to the light REE (LREE), exceptionally positive La anomalies, and super-chondritic Y/Ho ratios. The predominant REE species were REE(CO3)2−, REECO3+, and REESO4+ in the Ca–SO4-rich water. The HREE enrichment in both river and surface waters resulted in stronger complexation with carbonate ions and fulvic-acid like materials with increasing atomic number and preferential sorption of LREE onto sediments in neutral to slightly alkaline pH water. The YREE patterns of sediments showed MREE enrichment. Total YREE contents in the river sediments were correlated with Fe2O3, P2O5 and loss on ignition (LOI), suggesting the MREE enrichment fractionated by precipitation of authigenic MREE-enriched minerals such as phosphate, Fe (oxy)hydroxides and organic matter. With the exception of La, there were significant correlations among neighboring YREE concentrations, indicating that most YREEs were fractionated by the same geochemical processes, such as aqueous complexation and sorption onto the sediment surfaces. The concentrations of La did not correlate with those of the other YREE, suggesting that the La anomaly was probably induced by a biogenic activity such as diatom blooming and/or anthropogenic processes. Our results provide better understanding of REE behavior because of (bio)geochemical and anthropogenic contamination in terrestrial water systems.

Carbonatite-Related REE Deposits: An Overview

The rare earth elements (REEs) have unique and diverse properties that make them function as an “industrial vitamin” and thus, many countries consider them as strategically important resources. China, responsible for more than 60% of the world’s REE production, is one of the REE-rich countries in the world. Most REE (especially light rare earth elements (LREE)) deposits are closely related to carbonatite in China. Such a type of deposit may also contain appreciable amounts of industrially critical metals, such as Nb, Th and Sc. According to the genesis, the carbonatite-related REE deposits can be divided into three types: primary magmatic type, hydrothermal type and carbonatite weathering-crust type. This paper provides an overview of the carbonatite-related endogenetic REE deposits, i.e., primary magmatic type and hydrothermal type. The carbonatite-related endogenetic REE deposits are mainly distributed in continental margin depression or rift belts, e.g., Bayan Obo REE-Nb-Fe deposit, and orogenic belts on the margin of craton such as the Miaoya Nb-REE deposit. The genesis of carbonatite-related endogenetic REE deposits is still debated. It is generally believed that the carbonatite magma is originated from the low-degree partial melting of the mantle. During the evolution process, the carbonatite rocks or dykes rich in REE were formed through the immiscibility of carbonate-silicate magma and fractional crystallization of carbonate minerals from carbonatite magma. The ore-forming elements are mainly sourced from primitive mantle, with possible contribution of crustal materials that carry a large amount of REE. In the magmatic-hydrothermal system, REEs migrate in the form of complexes, and precipitate corresponding to changes of temperature, pressure, pH and composition of the fluids. A simple magmatic evolution process cannot ensure massive enrichment of REE to economic values. Fractional crystallization of carbonate minerals and immiscibility of melts and hydrothermal fluids in the hydrothermal evolution stage play an important role in upgrading the REE mineralization. Future work of experimental petrology will be fundamental to understand the partitioning behaviors of REE in magmatic-hydrothermal system through simulation of the metallogenic geological environment. Applying “comparative metallogeny” methods to investigate both REE fertile and barren carbonatites will enhance the understanding of factors controlling the fertility.

Behavior of major, trace, and rare earth elements in an atypical lateritic profile overlying micaceous quartzites, Centre Cameroon: imprint of the parent rock structure

An atypical lateritic weathering profile overlying micaceous quartzites in central Cameroon was studied to understand its morphology and the behavior of major and trace elements (including rare earth elements; REE). Mineralogical analyses were performed by X-ray powder diffraction (XRPD). Major and trace element geochemistry were determined using X-ray fluorescence (XRF) and inductively coupled plasma-mass spectrometry (ICP-MS), respectively. The studied micaceous quartzites consist of 1 to 2 cm thick quartzitic platelets separated by millimeter to multi-millimeter beds of ferromagnesian minerals (biotite, hornblende, garnet and, epidote), muscovite, graphite, and magnetite. According to chemical index of alteration, mafic index of alteration, index of lateritization, the A – Fe – Mg – Ca – Na – K diagrams, and the Weathering index of granite, the intense hydrolysis of ferromagnesian beds resulted in the genesis of soil unit consisting of quartz, muscovite, illite, kaolinite, anatase, and hematite which occur within rotten quartzites or coarse saprolites (CS). Thus, the weathering profile presents the following macromorphological organization: micaceous quartzite/CS-soil/CS-soil/CS-soil/CS-soil/ CS-soil/nodular materials/loose stony clayey soil. The pH-Eh diagrams indicate that formation of these soils within the saprolitic zone is the result of differential weathering that occurred under acidic-reductant conditions, which enhanced the rapid weathering of ferromagnesian mineral beds. The main pedogenetic processes along the weathering profile are translocation of REE, the transformation of primary minerals into neoformed-clays and Fe-oxide-hydroxides formation (associated mainly with light REE losses), and the addition of organic matter in surface horizons (associated with an accumulation of transition metals, high field strength elements, and heavy REE).

Electrochemical Removal of Rare Earth Element in LiCl-KCl Molten Salt

This study was carried out to examine the removal of rare earth (RE) elements by electrodeposition for the purification and reuse of LiCl-KCl salt after electrorefining and electrowinning. The electrochemical behavior of RE elements (Dy and Gd) in LiCl-KCl-DyCl3-GdCl3 at 500°C was investigated using the cyclic voltammetry (CV) technique using Mo and Mg electrodes. It was observed that the reduction potential of the RE elements shifted at the Mg electrode owing to the alloy formation with Mg (RE-Mg alloy). Subsequently, a series of potentiostatic electrolysis tests were conducted to remove the RE elements in the salt and check the formation of deposits at the Mg and Mo electrodes. The scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM/EDS) technique was used to confirm that the reduced RE metals were deposited on the surface of the Mg electrode. However, no significant deposit on the Mo electrode was observed, and a mud-like deposit was found on the bottom of the electrochemical cell. The salt analysis performed by employing the inductively coupled plasma-optical emission spectrometry (ICP-OES) indicated that the removal efficiency of Dy3+ and Gd3+ through electrodeposition was 83.5∼95.2 and 91.6∼95.2%, respectively.

Fluid Evolution and Scheelite Precipitation Mechanism of the Large-Scale Shangfang Quartz-Vein-Type Tungsten Deposit, South China: Constraints from Rare Earth Element (REE) Behaviour during Fluid/Rock Interaction

Unlike classic skarn-type scheelite deposits directly acquiring sufficient Ca2+ from surrounding limestones, all of the scheelite orebodies of the Shangfang tungsten (W) deposit occur mainly in amphibolite, and this provides a new perspective on the mineralization mechanism of W deposits. The ability of hydrothermal scheelite (CaWO4) to bind REE3+ in their Ca2+ crystal lattices makes it a useful mineral for tracing fluid-rock interactions in hydrothermal mineralization systems. In this study, the REE compositions of scheelite and some silicate minerals were measured systematically in-situ by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) to assess the extent of fluid-rock interactions for the Late Mesozoic quartz-vein-type Shangfang W deposits. According to the variations in CaO and REE among scheelite and silicate minerals, the amphibole and actinolite in amphibolite may be able to release large amounts of Ca2+ and REE3+ into the ore-forming fluids during chlorite alteration, which is critical for scheelite precipitation. Furthermore, an improved batch crystallization model was adopted for simulating the process of scheelite precipitation and fluid evolution. The results of both the in-situ measurements and model calculations demonstrate that the precipitation of early-stage scheelite with medium rare-earth elements (MREE)-rich and [Eu/Eu*]N 1. Even though the partition coefficient of REE is constant, the later-stage scheelite will also inherit a certain degree of MREE-depletion and [Eu/Eu*]N future from the residual fluids. As a common mineral, sheelite forms in various types of hydrothermal ore deposits (e.g., tungsten and gold deposits). Hence, the improved batch crystallization model is also possible for obtaining detailed information regarding fluid evolution for other types of hydrothermal deposits. The results from model calculations also illustrate that the Eu anomalies of scheelite are not an effective index correlated to oxygen fugacity of fluids but rather are dominantly controlled by the continuous precipitation of scheelite.

Geochemical and mineralogical features of karst bauxite deposits from the Alborz zone (Northern Iran): Implications for conditions of formation, behavior of trace and rare earth elements and parental affinity

The present study focuses on three outcrops of Upper Permian to Lower Jurassic karst bauxite deposits in the Alborz zone, north of Iran. The deposits occur as sharp semi-continuous lenses within the Upper Permian Ruteh Formation (Gheshlagh) and the Upper Triassic Elika Formation (Siahrudbar and Separdeh) carbonate rocks. Textural characteristics such as pelitomorphic matrix, local ooidic-pisoidic, fluidal, and clastic textures indicate authigenic-allothigenic origins. Mineralogically, kaolinite, boehmite, goethite, and hematite in the Gheshlagh, diaspore, hematite, and kaolinite in the Siahrudbar, and kaolinite, hematite, goethite, diaspore, siderite, and chamosite in the Separdeh deposits are the main phases. The distribution patterns of major elements normalized to the upper continental crust (UCC) depict enrichments of Al, Fe, and Ti in all three deposits. The three deposits are variably enriched in transition trace elements (Cr, Ni, Co, V), U, Th, and high field strength elements (Ga, Hf, Zr, Nb, Y) relative to UCC. The studied bauxites have average concentrations of rare earth elements (ΣREE, La-Lu) between 305.97 and 373.69 ppm. Geochemical data reveal progressive enrichment of REE and an intense (LREE/HREE)N fractionation toward the lower parts of the profile in the Separdeh deposit due to the alkaline conditions of the carbonate bedrock, and irregular distribution patterns at the Gheshlagh and Siahrudbar deposits due to water level and pH fluctuations. The positive Ce anomalies at Separdeh and Siahrudbar suggest oxidizing conditions in the upper parts of the profiles. At Gheshlagh, the negative to nil Ce anomalies reflect low intensity of oxidation. Based on previous geochemical analysis data, the Upper Permian basalts in the Gheshlagh, and the Upper Triassic basalts in the Separdeh and Siahrudbar areas were the most likely source materials. The local uplift of the Permian-Upper Triassic series led to the formation of karstic topography filled with materials derived from weathering of the basaltic rocks under humid tropical paleoclimate. The initial weathering converted the source rocks to kaolinitic soils characterized by the enrichment of Al, Fe, and Ti. Then, they were transferred to the karstic depressions and sinkholes and underwent in situ leaching and desilicification bringing about a relatively higher ore grade. The overall field and petrographic evidence demonstrate that these deposits were formed in shallow and swampy environments. In the eastern part of the Alborz zone (at Siahrudbar and Gheshlagh), better drainage conditions have enhanced the quality of ores.

Saccharide-mediated transformation of Ce during the formation of manganese (hydr)oxide

Ce anomaly is an important indicator for many geochemical processes. Although the role of strong ligand such as siderophore desferrioxamine B (DFOB) in facilitating negative Ce anomaly formation on Mn (hydr)oxide has been well studied, the effect of ubiquitous weak ligands such as polysaccharides on the mobility of Ce have not been considered. Here, we investigated the effects of polysaccharides with different molecular weights on Mn (hydr)oxide formation as well as the distribution coefficients of rare-earth elements (REEs) at the solid–liquid interface. In coprecipitation experiments, REEs distribution coefficients between Mn (hydr)oxide and the solution showed a negative Ce anomaly during coprecipitation of Mn in the presence of dextran with molecular weight of 5000 Dalton (Dextran 5 k). The molecular size of the saccharides affected the crystal growth of Mn (hydr)oxide. Mn (hydr)oxide was deposited on a matrix of polysaccharide molecules to form a metal–organic framework in the presence of dextran. The crystal size decreased with an increase in the length of the saccharide molecular chain. As a control test, when well crystallized δ-MnO2 was used as an adsorbent, the distribution coefficients of the REEs showed a positive Ce anomaly in the presence of dextran 5 k. Based on the results, we suggest that the mechanism by which saccharides affect the sorption behavior of REEs on Mn (hydr)oxide is different from the reported mechanisms of strong metal-binding ligands such as DFOB. Saccharide-mediated electron transfer may occur between Mn (hydr)oxides and Ce(III), resulting in the formation of an organic-Ce(IV) complex in solution. Our results imply that ubiquitous weak ligands such as polysaccharides may significantly affect the mobility of Ce largely due to the association with Mn oxides, which are widespread natural electron acceptors.

Hydrothermal calcite-fluid REE partitioning experiments at 200 °C and saturated water vapor pressure

Calcite is a common vein mineral associated to ore deposits and alteration zones geothermal systems. The concentration of rare earth elements (REE) in calcite can potentially be used to fingerprint the changing physicochemical conditions during mineralization from hydrothermal fluids. Previous calcite-fluid partitioning experiments have been carried out at ambient temperature but models aiming at predicting the behavior of REE at elevated temperature have not yet been developed. This study aims at determining the controls on REE incorporation into calcite mineralized from hydrothermal aqueous fluids above 100 °C. Here, we present a series of hydrothermal batch-type REE partitioning experiments at 200 °C and saturated water vapor pressure (15.5 bar). The experiments were designed to synthesize REE-doped calcite from fluid mixing with varying initial REE concentrations (250 ppb to 1000 ppb) and permit in situ sampling of the aqueous fluids. Calcite-fluid partition coefficients (KD) were observed to depend on the ionic radius of the REE and vary as a function of initial REE concentrations: logKD of 0.86–1.67 at 250 ppb REE; logKD of 1.05–1.70 at 500 ppb REE; logKD of 0.47–1.07 at 1000 ppb REE. These data fit a parabola according to the lattice strain model from which calculated Young’s modulus (ES) values range between 21.6 and 63.2 GPa. The fits indicate that the partitioning of the light REE is controlled by the strain-induced Ca2+ substitution in the calcite structure, whereas the heavy REE deviate from these trends. The development of a binary REE(OH)3 - CaCO3 solid solution model based on the dual-thermodynamic (DualTh) approach suggests that the REE partitioning is controlled by the following possible coupled substitutions at pH of 6:Eu3++3OH-⇔Ca2++CO32-Eu3++O2-+OH-⇔Ca2++CO32-The lattice strain fits are useful to interpret deviations of the experimental data from the solid solution model and possible non-ideal mixing behavior. Application of this model to natural systems yields some limitations because of the variability of experimental mineral-fluid KD values with REE concentrations in the aqueous fluids. The DualTh approach considers the aqueous speciation and activity-concentration relationships of the aqueous fluids, and therefore, provides an efficient method to evaluate the partitioning of REE between mineral and aqueous fluids. This research is a first step in building an experimental database of calcite-fluid partitioning data at hydrothermal conditions and aims at developing more accurate models for predicting the behavior of the REE in natural mineral-fluid systems.