Rare Earth Minerals Research Articles

Gravity-based pre-concentration strategies for complex rare earth ore containing niobium and zirconium

The Balzhe rare earth mine, renowned for its rich reservoirs of niobium, zirconium, and rare earth elements, poses a unique challenge due to its diverse and interbedded mineral composition. Despite the abundance of these elements, their valuable grade remains notably low, falling short of economic thresholds. To this end, pre-concentration of valuable minerals to discard gangue minerals before flotation would be an economical option. In response, this study delves into the feasibility of gravity-induced pre-concentration, aiming to segregate valuable minerals from gangue for subsequent flotation processes. Conducting float-and-sink tests on varied particle sizes (-2+0.5 mm, -0.5+0.074 mm, and -0.074+0.02 mm) within heavy liquids of specific gravities (ranging from 2.55 to 2.85), the study reveals the effectiveness of gravity separation. Notably, particles sized -2+0.5 mm and -0.074+0.02 mm demonstrated superior separation performance over the -0.5+0.074 mm fraction. Comparative analysis of diverse gravity separation equipment unveiled compelling results. The dense medium cyclone separator showcased impressive recovery rates and high-grade concentrates of Nb<sub>2</sub>O<sub>5</sub>, ZrO<sub>2</sub>, and total rare earth oxides (TREO) at 0.34%, 8.20%, and 0.41%, respectively, surpassing the sand table's performance for -2+0.5 mm particles. Conversely, for -0.5+0.074 mm particles, the shaking table exhibited optimal separation efficiency, yielding grades of Nb<sub>2</sub>O<sub>5</sub>, ZrO<sub>2</sub>, and TREO at 0.37%, 4.08%, and 0.44%, with substantial recovery values. Ultimately, the Knelson centrifugal separator proved most effective for -0.074+0.02 mm particles, yielding notable grades and recoveries of Nb<sub>2</sub>O<sub>5</sub>, ZrO<sub>2</sub>, and TREO. This study underscores the promising potential of gravity-induced pre-concentration techniques for enhancing the recovery of valuable elements from the complex Balzhe rare earth ore, offering critical insights into optimizing mineral extraction processes.

Physical property characterization of rocks in the Bayan Obo REE-Nb-Fe deposit, China

Bayan Obo ore deposit is the world’s largest rare-earth element (REE) resource, the second largest niobium (Nb) resource, and also a significant iron (Fe) resource in China. Evaluating resource potential for the deposit has become a focus of global interest. Rock-physical properties bridge geophysical exploration and geologic modeling; variation in these parameters is necessary for successful geophysical application. REE, Nb, iron, and potassium are mainly hosted in dolomite and slate of the Bayan Obo Group, and REE mineralization is genetically associated with carbonatite. Three physical properties (resistivity, polarizability, and magnetic susceptibility [MS]) of iron ore, slate, dolomite, and carbonatite dike outcrop samples at Bayan Obo are measured and statistically analyzed using 3D reconstruction, 1D/2D/3D kernel density estimation, scatterplot matrix, 3D histogram, and Pearson- and maximum information coefficient-based correlation analysis. It is evident that iron ore, iron-mineralized fine-grained dolomite, and iron-mineralized slate are mainly of low resistivity, and iron ore and iron-mineralized fine-grained dolomite have high MS. MS favorably distinguishes iron ore from slate; MS and resistivity distinguish between iron-mineralized fine-grained dolomite and carbonatite dikes. The physical properties and whole-rock geochemistry (major and trace elements) jointly demonstrate that MS of iron ore, slate, and dolomite is positively correlated with TFe2O3 content, polarizability is correlated with TFe2O3, SiO2 content is correlated with K2O, and resistivity is correlated with MS and polarizability, respectively. Resistivity of iron ore and dolomite is negatively correlated with TFe2O3 content. Resistivity of iron ore is negatively correlated with TFe2O3, total REE ([Formula: see text]), and Nb, respectively, and correlated with thorium. The methods used have intuitive visual expression and reflect the characteristics of the physical properties and their correlation with the mineralogical composition. The results will be beneficial for determining the geometry of ore-hosting rock masses and providing crucial evidence for the resource evaluation.

Rare-Earth Mineralization in Terrigenous Rocks of the Shatak Complex (Southern Urals): Species Diversity and Features of Chemical Composition

Rare-Earth Mineralization in Terrigenous Rocks of the Shatak Complex (Southern Urals): Species Diversity and Features of Chemical Composition

The primary geology of the Paleoproterozoic Mt Weld Carbonatite Complex, Western Australia

Abstract The paleoregolith overlying the c. 2.06 Ga Mt Weld carbonatite (eastern Yilgarn Craton, Western Australia) hosts one of the largest Rare Earth Element (REE) deposits globally. Historic exploration and research has focussed on this weathered material, with a lack of unweathered samples preventing a thorough investigation into the nature of the underlying carbonatite. Recent deep drilling has allowed this first in-depth study into the primary geology, mineralogy and geochemistry of the carbonatite complex. Mt Weld shares a similar lithological architecture to other global carbonatite complexes, such as Ngualla (Tanzania, Bonga (Angola), Chilwa Island (Malawi) and Mirima Hill (Malawi), displaying a central (~600 m diameter) unit of magnesio- to ferrocarbonatite is surrounded by a broad (~1.2 km) annulus of calciocarbonatite, itself surrounded by a fenitic halo. Primary REE mineralisation occurs within the central magnesio- to ferrocarbonatites (~2% Total Rare Earth Oxides in bulk rock) and is dominated by fine-grained monazite hosted within fractures and voids, as well as late magmatic synchysite/bastnäsite. Both high and low phosphourous ferrocarbonatites occur within this central magnesio- to ferrocarbonatite unit that display (respectively) monazite or synchysite/bastnäsite mineralisation with textural evidence for these REE-bearing carbonates occasionally forming as polycrystalline pseudomorphs of earlier burbankite group minerals. Magnesio- to ferrocarbonatite dykes with zhonghuacerite/olekminskite/ancylite assemblages occur throughout the otherwise REE-poor calciocarbonatites (~0.2% Total Rare Earth Oxides in bulk rock). Late hydrothermal events strongly influenced the modern-day mineral assemblages with much of the existing ore mineral textures interpreted as hydrothermal reworkings of pre-existing REE-bearing minerals. A comparison of the fresh carbonatite and the paleoregolith geochemistry suggests minimal horizontal migration of ore elements during paleoregolith formation, with the overlying paleoregolith material broadly reflecting the underlying carbonatite trace and minor element signatures. This allows the inference of an approximately 5× upgrade in REE (and Nb) concentrations from the primary carbonatite to the overlying paleoregolith. Mt Weld shows distinct geological, mineralogical and isotopic differences to other currently mined carbonatite-associated REE deposits, such as Bayan Obo (China), Mountain Pass (USA) and the Mianning-Dechang belt (China), which suggests that fundamentally different carbonatite mantle sources and evolutionary paths can form world-class REE ore bodies.

Synthesis and characterization of hydroxamic acid N,3-dihydroxy-2-naphthamide and its copper (II) complex per keto/enol forms and rare earth flotation

Flotation is the most common beneficiation process used for separating minerals, but for rare earth minerals (REMs), performance can suffer due to the dilute nature of the rare earth elements. Furthermore, the REMs tend to possess smaller grain sizes, making the use of traditional flotation cells difficult if total liberation is needed. Consequently, improved efficiencies are needed for extracting REMs from various sources. For these systems, hydroxamic acids are commonly used as flotation collectors. Two such hydroxamic collectors were studied in this work: salicylhydroxamic acid (SHA) and N,3-dihydroxy-2-naphthamide (H2O5). Because there is no documented synthesis route for H2O5, several synthesis approaches were examined. Furthermore, because there is no information on H2O5, important structural and characteristic data was gathered regarding its (1) preferred structural isomer as a Cu2+ complex and (2) electrostatic potential values of the possible dentate groups in different tautomeric forms, thereby allowing H2O5 to be compared to SHA, particularly regarding flotation behavior. Hydrogen nuclear magnetic resonance (H-NMR), Laser Raman Spectroscopy (LRS), and predominantly Fourier-Transform Infrared (FT-IR) spectroscopy showed that both SHA and H2O5 preferred to be keto tautomers when uncomplexed; however, once chelated to Cu2+ ions, the collectors adopted enol forms. Molecular modeling using Spartan software showed an increase in the electrostatic potential of the possible dentate groups in both molecules for the enol form. H2O5 also resulted in an increased recovery by flotation of REMs of about 23% compared to SHA at similar reagent dosages.

Geochemistry of Rare Earth Elements in Pahang River Sediment, Malaysia

Rare earth elements (REE) are a set of 17 chemically similar metallic elements including 15 lanthanides, scandium and yttrium. The current status of REE as a global strategic commodity has encouraged the identification of REE ore deposits. This research is carried out to identify the mining feasibility of fluvial sediment REE and to understand the sediment's physical and chemical characteristics and effects on the geochemical behaviour of REE in the longest river of Peninsular Malaysia namely Pahang River. Surface sediment samples were collected along Pahang River (n=44) in approximately 10 km distance intervals. The sediment samples were analyzed using XRF to determine the major oxide content. Meanwhile, REE content in the sediment samples was extracted using the Total Digestion method and analysed using ICP-MS. The results show the average value of ΣREE at surface sediments of the Pahang River is 42.58 ppm and can be considered too low to be economically mined. Each area shows higher fractionation of light REE than heavy REE with negative europium anomalies, suggesting sediments in this area were derived from felsic rocks. The concentration of REE in Pahang River surface sediments was controlled by the porosity and organic matter as showed by the correlation of ΣREE with porosity (R2=0.65) and organic matter content (R2=0.71). In conclusion, this research's findings are generally useful for further REE mineral exploration and fluvial sediment environmental monitoring.

Rare earth element transport and mineralization linked to fluids from carbonatite systems

Abstract Rare earth elements are critical constituents for modern technologies, and some of their largest natural resource deposits are related to carbonatite systems. However, the mechanisms leading to rare earth element mineralization and the role of magmatic fluids in carbonatite systems remain poorly understood. Here, we present the first in situ characterization of fluids and their trace-element compositions in natural carbonatite systems by studying secondary quartz-hosted fluid inclusions from Oldoinyo Lengai volcano. By comparing our data to other fluids and melts from various carbonatite systems, we constructed a model for fluid-mediated rare earth element transport and mineralization. We show that carbonatite-related fluids are rich in alkali-carbonate + sulfate + chloride and CO2, but poor in H2O, and they can be significant carriers of rare earth elements (>1600 ppm). We argue that fluid CO2 contents are essential to preclude or slow down the interaction with wall rock during migration and that fluid-mediated rare earth element mineralization occurs when partial pressure of CO2 decreases in the fluid (i.e., during degassing).

Selective extraction of rare earth elements and cobalt from iron residue containing rare earth using mechanical activation and reductive leaching method

NdFeB waste is an important rare earth secondary resource, which is usually treated by hydrochloric acid preferential method in traditional industrial process. Herein, leaching residue containing about 0.5–1 % rare earth elements (REEs) and a small amount of cobalt is generated as a by-product in the process. The leaching residue is mainly composed of iron oxide and generally sold to steelmaking plants, resulting in the waste of REEs and cobalt resource. An efficient recycling process is proposed for selectively extracting REEs and cobalt from the iron residue containing rare earth by mechanical activation and reductive leaching method based on mineral liberation analysis (MLA) and thermodynamic analysis. By analyzing the composition of the raw materials, magnetite and limonite are in an encapsulated state with rare earth minerals. REEs and cobalt are mainly present in the rare earth aluminate phase. To achieve deep extraction of REEs and cobalt, the first step is to change the insoluble phase of iron residue by mechanical activation method. During this process, the crystal structures of Fe2O3 and Fe3O4 in the iron residue containing rare earth are disrupted and transformed into amorphous states. During the reductive leaching process, part of the iron is converted into divalent. The iron in the leaching solution can be removed by hematite method and achieved phase reconstruction. Thus, REEs and cobalt can be extracted selectively from leaching residue of NdFeB waste.

THE RARE EARTH ELEMENTS: AN IN-DEPTH EXPLORATION OF INDUSTRIAL UTILIZATION, RECYCLING POTENTIAL AND ENVIRONMENTAL RAMIFICATIONS

This comprehensive study delves into the extensive spectrum of applications attributed to rare earth elements (REEs), their potential for effective recycling, and the intricate environmental considerations entwined with their extraction and utilization. The realm of rare earth elements is undergoing rapid transformations fueled by technological progress and the escalating demand for these essential components. The spectrum of REEs encompasses the lanthanide series elements, namely La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu, as well as Sc and Y. These metals currently hold utmost significance across a multitude of contemporary technologies, spanning from smartphones, televisions, LED light bulbs, to wind turbines. This paper concisely outlines the environmental perils encompassing human health that stem from REE mining practices and the large-scale disposal of electronic waste containing noteworthy concentrations of REEs. Within these pages, we encapsulate novel strategies aimed at ensuring the future availability of REEs, including recent advancements in REE extraction from Coal Field Ash and innovative e-waste recycling methodologies. Additionally, we spotlight recent breakthroughs in the domain of individual REE separation techniques, encompassing both metallurgical and recycling operations.

The vulnerability of shifting towards a greener world: The impact of the EU's green transition on material demand

The green transition from fossil fuels to renewables requires acquisition of rare earth minerals and other materials for construction of renewable energy technologies and may lead to new dependencies through imports potentially causing immense pressure on global supply chains. This study investigates the material vulnerability of sectors and countries in the EU. Vulnerability maps are created for the EU's material demands by combining three analyses: input-output analysis, forward linkage analysis and network analysis. The approach reveals the relative importance of individual sectors and their vulnerability given increasing demand. As such, the analyses help to identify which sectors, based on their current implementation of renewable energy sources, could put a country and the EU at risk of not meeting their mitigation targets by 2050. The analysis concludes that Austria, Germany, the Czech Republic, Denmark and Slovakia will experience particularly large material vulnerabilities in several of the materials investigated. Hence, such findings can provide early warnings to sectors and countries about potential implications in their supply chains along with potential mitigation measures such as secondary sourcing, material substitution and material diplomacy.

Identifying recycled oceanic components and volatiles in the Lizhuang carbonatite-associated REE deposit in southwest China: New constrain from in situ Hf–O isotopes

Carbonatite-associated rare earth element (REE) deposits (CARD) are mainly found at the edges of cratons in the rift or post-collisional settings, but only a minority carbonatite can form large to giant REE deposit. Fluids rich in volatiles (such as F, Cl, S) are critical for the extraordinary enrichment of REE, but the manner in which volatiles and REE concentrate in the mantle source of CARD remains unclear. This study focuses on the Lizhuang syenite from the Mianning–Dechang REE belt, southwest China, to investigate its petrogenesis, source characteristics, and volatiles evolution, through in situ Hf–O isotope analysis, coupled with mineral chemistry, bulk-rock geochemistry, and geochronology. The Lizhuang syenite was generated in a post-collisional setting at about 27 Ma, resulting from partial melting of an enriched lithospheric mantle, followed by fractional crystallization and immiscibility. When contrasted with barren carbonatite-syenite complexes worldwide, the syenite in REE deposit has a relatively higher content of F and S, with no significant difference in Cl content, and there is no clear correlation between magma oxygen fugacity and REE mineralization. The Hf–O isotopic signatures of zircon and apatite, along with bulk-rock Sr–Nd isotopic modeling, reveal that the mantle source of the Mianning–Dechang CARD experienced metasomatic processes related to the melts/fluids derived from both marine sediments and altered oceanic crust during subduction. The cratonic root, enriched in volatiles and REE, is reactivated during the upwelling of asthenosphere, and the released volatiles are able to participate in the formation of CARD.

Geochemical Characteristics of Deep-Sea Sediments in Different Pacific Ocean Regions: Insights from Fractal Modeling

Exploration of mineral resources in the deep sea has become an international trend. However, deep-sea mineral exploration faces challenges such as complex offshore drilling and the weak and mixed signals of ore deposits. Therefore, studying methods for identifying weak and mixed anomalies and extracting composite information in the deep sea is crucial for innovative prediction and evaluation of deep-sea mineral resources. In this study, the Central Pacific Ocean, Northwestern Pacific Ocean, and Eastern Pacific Ocean were selected as research areas. Drawing upon the fractal self-similarity exhibited by rare earth minerals in the deep-sea sediments within the Pacific Ocean, we conducted an analysis and comparison of the fractal geochemical characteristics in various regions of the Pacific Ocean’s deep-sea sediments. Thereafter, we studied the spatial distribution of rare earth elements (REEs) in deep-sea sediments in these regions to explore the mechanisms responsible for rare earth enrichment in the Pacific Ocean. The results revealed that the geochemical fractal characteristics of deep-sea sediments in the Northwestern Pacific Ocean Basin and the Central Pacific Ocean Basin were similar, whereas there were slight differences in the fractal characteristics observed in the Eastern Pacific Ocean Basin. By calculating the singularity index of CaO/P2O5, it was found that the singularity index in the Central and Northwestern Pacific Ocean basins was lower than that in the Eastern Pacific Ocean Basin, suggesting that the phosphorus content in the Eastern Pacific Ocean Basin was lower than that in the Central and Northwestern Pacific Ocean basins. In the Eastern Pacific Ocean, we found that phosphorus content in deep-sea sediments was the primary controlling factor for REE enrichment. Conversely, in the Central and Northwestern Pacific Ocean, both the phosphorus and calcium content in deep-sea sediments played significant roles in REE enrichment.

Non-negligible N2O emission hotspots: Rivers impacted by ion-adsorption rare earth mining

Rare earth mining causes severe riverine nitrogen pollution, but its effect on nitrous oxide (N2O) emissions and the associated nitrogen transformation processes remain unclear. Here, we characterized N2O fluxes from China's largest ion-adsorption rare earth mining watershed and elucidated the mechanisms that drove N2O production and consumption using advanced isotope mapping and molecular biology techniques. Compared to the undisturbed river, the mining-affected river exhibited higher N2O fluxes (7.96 ± 10.18 mmol m−2d−1 vs. 2.88 ± 8.27 mmol m−2d−1, P = 0.002), confirming that mining-affected rivers are N2O emission hotspots. Flux variations scaled with high nitrogen supply (resulting from mining activities), and were mainly attributed to changes in water chemistry (i.e., pH, and metal concentrations), sediment property (i.e., particle size), and hydrogeomorphic factors (e.g., river order and slope). Coupled nitrification-denitrification and N2O reduction were the dominant processes controlling the N2O dynamics. Of these, the contribution of incomplete denitrification to N2O production was greater than that of nitrification, especially in the heavily mining-affected reaches. Co-occurrence network analysis identified Thiomonas and Rhodanobacter as the key genus closely associated with N2O production, suggesting their potential roles for denitrification. This is the first study to elucidate N2O emission and influential mechanisms in mining-affected rivers using combined isotopic and molecular techniques. The discovery of this study enhances our understanding of the distinctive processes driving N2O production and consumption in highly anthropogenically disturbed aquatic systems, and also provides the foundation for accurate assessment of N2O emissions from mining-affected rivers on regional and global scales.

Mineralogy and element geochemistry of the Bayan Obo (China) carbonatite dykes: Implications for REE mineralization

The Bayan Obo deposit in China is the world's largest rare earth element (REE) deposit. However, its genesis remains highly debated. It is considered to have a close genetic association with carbonatites because of the presence of nearby carbonatite dykes and the geochemical similarities between these dykes and the orebody. However, the evolution of these dykes and associated REE mineralization remain poorly understood, hindering the origin interpretation of the deposit. This study provides new insights into the petrography, mineralogy, and major- and trace-element geochemistry of these carbonatite dykes and rock-forming minerals to reconstruct the magmatic evolution and REE enrichment of the deposit. The dykes evolved from dolomite- to calcite-dominated (i.e., calcite and fenitized calcite) carbonatites, and their REE content remarkably increased, with the latter developing strong REE mineralization. The dolomites and minor calcites within the dolomite carbonatites exhibit a steep negative slope with high light REE (LREE) enrichment and heavy REE (HREE) depletion, similar to the whole rock. In contrast, the calcites from the calcite-dominated carbonatites exhibit flat REE patterns with HREE enrichment. Combined with previous isotopic data and our petrology, mineralogy, and geochemistry study, we propose that these rocks are derived directly from the low-degree melting of the underlying mantle source. REE mineralization may be related to the progressive crystallization of rock-forming calcites of calcite-dominated carbonatites. Monazite, bastnäsite, parisite, and huanghoite are the dominant REE minerals and exhibit intimate associations with barite and alkaline silicate minerals such as aegirine, biotite, K-feldspar, and albite. This assemblage indicates that the REE were primarily transported via REE–sulfate and REE–alkali complexes, with the latter favoring HREE, and the precipitation of alkaline silicate minerals destabilized these REE complexes, facilitating REE mineralization.

Abiotic legacies mediate plant–soil feedback during early vegetation succession on rare earth element mine tailings

Abstract An increasing number of studies have shown how feedback interactions between plants and soil can influence primary and secondary succession. However, very little is known about the patterns and mechanisms of such plant–soil feedbacks on stressed mine tailings ecosystem, which can be severely contaminated by a range of toxic elements. In a two‐phase plant–soil feedback experiment based on the rare earth element (REE) mine tailing soil, we investigated biotic (changes in bacterial and fungal communities) and abiotic (changes in chemical properties) legacies of three pioneer grass species, and examined feedback effects of three grasses, two legumes and two woody plants with different root traits. Positive plant–soil feedbacks were found in Miscanthus sinensis, Paspalum thunbergii and Tephrosia candida, and neutral feedbacks were observed in the other four plants. These effects corresponded with an increase in nutrients and total organic carbon, as well as a decrease in acidity and extractable aluminium and REEs. There were less signs of biotic changes in the conditioned tailings. The correlation analysis suggested a relationship between plants' responses to soil legacies and root traits, as well as root economics spectrum. On the mine tailings, acquisitive species with higher specific root length appeared to have greater potential for positive feedback. Synthesis and application. Our study shows that early succession on contaminated rare earth element mine tailings may lead to more positive plant–soil feedback than predicted based on results of non‐contaminated soils, mainly due to the alleviation of abiotic stress in tailings. Therefore, the improvement of specific abiotic soil stress and the trait‐based selection of acquisitive plants should be preferentially considered to promote the primary restoration of degraded land.

Concentration and distribution patterns of rare earth elements (REEs) in stream sediments of Pakistan

Currently, the metals of Rare Earth Elements (REEs) have become very critical to various modern technologies ranging from cell phones and televisions to LED light bulbs and wind turbines. This work was carried out as the Pakistani contribution to the National-scale Geochemical Survey of South and Central Asia (NGSSCA) project. The objective of this study was to document and study the amounts and distribution of REEs in stream sediment of Pakistan, where such national-scale geochemical mapping was launched for the first time. A total of 4277 regular and 168 duplicate samples were collected, encompassing approximately 360,000 km2 of Pakistani outcrop regions. The findings from the geochemical analysis of stream sediment in Pakistan revealed a spectrum in the total Rare Earth Elements (ΣREE) concentration, spanning from 10.22 mg/kg to 1403.1 mg/kg, averaging at 132.5 mg/kg. LREEs are relatively enriched compared to HREEs with an average of LREEs/HREEs of 3.08. The distribution patterns of REEs in stream sediment are demonstrated. It's has been concluded that high concentrations of REEs are mainly distributed in the Himalayan fold and thrust belt, the Karakoram terrane and the Kohistan island arc in the northern part of Pakistan. The bedrock mineralogy and lithology significantly affect the distribution patterns of REEs in stream sediments. The national geochemical mapping of Pakistan provides a useful method for locating alkaline igneous rocks and identifying potential REE mineralization.

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.

Impacts of Ion Adsorption Type Rare Earth Mining Techniques on Topsoil in Mining Area

Impacts of Ion Adsorption Type Rare Earth Mining Techniques on Topsoil in Mining Area

МИНЕРАЛЫ РЕДКОЗЕМЕЛЬНЫХ ЭЛЕМЕНТОВ В УЛЬТРАБАЗИТАХ МАССИВА ИЛЬДЕУС (СТАНОВОЙ КРАТОННЫЙ СУПЕРТЕРРЕЙН): ВЛИЯНИЕ ПОСТКОЛЛИЗИОННЫХ ПРОЦЕССОВ НА ГЛУБИННЫЕ РУДНО-МАГМАТИЧЕСКИЕ СИСТЕМЫ КОНВЕРГЕНТНЫХ ГРАНИЦ ПЛИТ

The Ildeus ore-magmatic basite-ultrabasite system in the central part of the Stanovoy superterrane formed in the Triassic as a result of subduction of the Mongol-Okhotsk basin oceanic lithosphere. In the Jurassic and Early Cretaceous, it underwent hydrothermal-metasomatic alterations during collision and post-collision processes within the southern margin of the Siberian continent. Hydrothermally altered ultrabasites and acid-alkaline albite-quartz-biotite-K-feldspar-apatite (with calcite and barite) metasomatites of Ildeus contain rare earth element (REE) minerals, represented by monazite in association with apatite, xenotime, oxides, REE carbonates, and REE silicates. Native metals and alloys of Ag, Au, Cu, Ni, Zn, Pt and sulfides of Fe, Co, Ni, Cu, Pb, and Zn are associated with REE minerals in rocks of the massif. The total REE content in these rocks varies from 10 to 1938 g/t positively correlating with the concentrations of barium (up to 5876 g/t) and thorium (up to 74.5 g/t). Alkaline-silicate metasomatites with REE minerals are spatially associated with adakite dikes and veins (Sr/Y from 27 to 1716) and were formed in the presence of aqueous-carbonate-sulfate-phosphorus-potassium fluids with hybrid properties characteristic of the fluid phase of mantle alkaline-ultrabasic-carbonatite complexes, on the one hand, and lower crustal adakitic melts, on the other. It is assumed that the enrichment of ultrabasites and metasomatites of Ildeus with rare earth minerals, metals and sulfides is associated with the melting of the sulfidized thickened lower crust under the influence of deep mantle fluids and the intrusion of Early Cretaceous metal-bearing adakites into Triassic supra-subduction igneous complexes.

Enrichment of Rare Earth Elements During the Weathering of Alkaline Igneous Systems: Insights from the Puxiong Regolith-Hosted Rare Earth Element Deposit, SW China

Abstract Regolith-hosted rare earth element (REE) deposits have been the focus of recent studies. Most studies concern deposits formed over granites and felsic volcanic rocks, but little is known about those deposits developed over silica-undersaturated alkaline igneous rocks. The recently discovered Puxiong REE deposit in Southwest China formed through the weathering of nepheline syenite that has REE concentrations ranging from 177 to 9,336 ppm. Hydrothermal processes partially enriched the parent nepheline syenite in REEs. About 60% of the REEs in the bedrock are hosted in britholite-(Ce), tritomite-(Ce), and cerite-(Ce) and ~21% in REE minerals that occur as inclusions in K-feldspar, with the rest in titanite, hiortdahlite, apatite, fluorite, and calcite. These minerals all can be easily decomposed to release REEs into soil solutions during weathering. The released REEs are adsorbed on clay minerals or precipitate as supergene rhabdophane and an Fe-Mn-REE oxyhydroxide phase. Nepheline syenite-derived regolith-hosted REE deposits are enriched in illite and halloysite, which have a higher ion exchange capacity than the parent granites. Illite formed through the weathering of primary alkali minerals in the nepheline syenite. In the strongly eroded midslope and valley, the regolith has the lowest total REE concentration (997 and 1,001 ppm on average, respectively) across the ore-bearing catchment, whereas the regolith in the hilltop and footslope has REE concentrations of up to 1,564 and 1,677 ppm, respectively. Moreover, regolith at the footslope has the highest heavy REE (HREE) concentration of 110 ppm on average. The light REEs (LREEs) tend to be concentrated in the B horizon and laterally across the hilltops, whereas the HREEs are mobilized by groundwater and soil solutions and accumulated in the upper C horizon vertically and the footslope profiles laterally. In conclusion, nepheline syenite was hydrothermally enriched in the REEs, and these elements were released to the weathering solution and then adsorbed onto clay minerals in sufficient concentrations to form economic regolith-hosted REE deposits. This process, which was controlled at Puxiong by the nature of clay minerals, pH, the redox conditions, the mobility of the REEs, and topography, led to maximum enrichment of the LREEs in the lower B horizon at the hilltop, and HREE enrichment in the upper C horizons vertically and in the footslope laterally.