Total Rare Earth Elements Content Research Articles

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

Chemical Composition and Genesis Implication of Garnet from the Laoshankou Fe-Cu-Au Deposit, the Northern Margin of East Junggar, NW China

In order to reveal the formation mechanism of different garnets and its implications for the fluid evolution in the Laoshankou Fe-Cu-Au deposit in the northern margin of East Junggar (NW China), three types of garnet have been investigated in detail in this study. (1) Type 1 grossular, formed at Ca-silicate stage (stage I, the pre-mineralization stage), was replaced by Type 2 garnet and magnetite, and displays a compositional range of Grs44–53Adr44–53, which has relatively lower total REE (rare earth elements) contents (8.14–32.8 ppm) and markedly depleted LREE (light rare earth elements) with distinctive positive Eu anomaly (1.36–9.61). (2) Type 2 Al-rich andradite, formed at the early sub-stage of amphibole-epidote-magnetite stage (stage II, the main magnetite mineralization stage), can be divided into two sub-types, i.e., Type 2a and Type 2b. Type 2a garnets exhibit polysynthetic twinning and relatively narrow compositional variations of Adr63–66Grs31–34 with HREE-(heavy rare-earth elements) enrichment and positive Eu anomalies (3.22–3.69). Type 2b garnets own wide compositional variations of Adr55–77Grs21–43 with relatively higher REE contents (49.1–124 ppm), markedly depleted LREE and a distinctive positive Eu anomaly (2.11–4.61). (3) Type 3 andradite (Adr>91) associated with sulfide stage (stage III, the main copper-gold mineralization stage) is different from other types of garnets in Laoshankou, which are characterized by lowest total REE contents (1.66–91.1 ppm), flat HREE patterns, LREE-enrichment and the strongest positive Eu anomalies (3.31–45.48). Incorporation of REE into garnet is largely controlled by external factors, such as fluid chemistry, pH, ƒO2 and water-rock ratios as well as its crystal chemistry. Type 1 and 2 garnets mainly follow the creation of X2+ (e.g., Ca2+) site vacancy, e.g., [X2+]−3VIII[]+1VIII[REE3+]+2VIII. The REE3+ substitution mechanism for Type 3 garnet is the Na+-REE3+ coupled substitutions, e.g., [X2+]−2VIII[X+]+1VIII[REE3+]+1VIII, without the evaluation of the creation of site vacancy. The compositional variations from Type 1 to Type 3 garnet indicate significant differences of fluid compositions and physicochemical conditions, and can be used to trace the fluid–rock interaction and hydrothermal evolution of garnet. Type 1 grossular was formed by magmatic fluid under low water–rock ratios and ƒO2, and neutral pH environment by diffusion metasomatism in a nearly closed system with the preferential incorporation into the grossular of HREE. As the long fluid pore residence and continuing infiltration metasomatism under nearly closed-system conditions, fluids with high water/rock ratios were characterized by increased ƒO2, more active incorporation of Fe3+ and REE, and formed Type 2 Al-rich andradite. In contrast, Type 3 garnet formed by oxidizing magmatic fluid under a mildly acidic environment with highest ƒO2 and water–rock ratios, and was influenced by externally derived high salinity and Ca-rich fluids in an open system. Thus, the geochemical features of different types and generations of garnets in the Laoshankou deposit can provide important information of fluid evolution, revealing a transition from neutral magmatic fluid to oxidizing magmatic fluid with addition of external non-magmatic Ca-rich fluid from the Ca-silicate stage to the sulfide stage. The above proved the fluid evolution process further indicates that the Laoshankou deposit prefers to be an IOCG-like (iron oxide-copper-gold) deposit rather than a typical skarn deposit.

Rare Earth Element in Bivalves' Soft Tissues of French Metropolitan Coasts: Spatial and Temporal Distribution.

Rare earth elements (REE) are becoming an environmental pollutant of emerging concern, linked to their use in various anthropic processes. Because REE bioconcentrate in marine organisms throughout their food webs, a better understanding of biogeochemical processes leading to REE concentrations found in coastal species is necessary. This study was designed to assess REEs concentrations in various common bivalves from the French coastline to identify possible geographic, taxonomic, or temporal variations of concentrations. Based on the French Mussel Watch program, three species of bivalves (oyster Crassostrea gigas and mussels Mytilus edulis and Mytilus galloprovincialis) were collected all along the French metropolitan coast and soft tissues were analyzed forREEconcentrations. Results have shown higher REE concentrations in bivalve soft tissues near estuaries without taxonomic nor national geographic differences. The highest levels have been observed in the Gironde estuary with total REE concentrations (∑REE) in oysters up to 10.94µgg-1 d.w. The REE distribution pattern in both mussel species described a particle-like (inverse V-shape) pattern, whereas C. gigas REE distribution pattern changes from a particle-like to a dissolved-like pattern with a heavy REE (HREE) enrichment. However, no environmental parameter could be linked to these pattern changes. Finally, neither Gd anomalies nor an evolution of REE concentrations over a 30-year period have been detected in bivalves' soft tissues.

Редкие и редкоземельные элементы в Cu-Ni рудах Норильского района

The deposits of the Norilsk region are confined to the marginal northwestern part of the Siberian platform and are associated with the manifestation of the Early Mesozoic trap volcanism. Sulfide mineralization is concentrated in the intrusive facies of the volcano-intrusive complex. Four main types of Cu-Ni ores are distinguished according to textural features: massive, vein-disseminated, brecciated, and disseminated. The main types of Cu-Ni ores differ significantly from each other in the chemical composition and content of rock- and ore-forming components. The enrichment ratios of ore trace elements in the Oktyabrskaya and Talnakhskaya vein-disseminated ore mainly reach hundreds (S, Pt, Au, Se,Te, Pb, As, Sn, Mo) and thousands (Ni, Cu, Ag, Pd) times. A rather high enrichment of all types of Bi, Re and Cd ores has been revealed, which are potentially industrially significant as high-tech metals, and can be promising for associated mining. The amount of rare-earth elements (REE) in ores is several times less than in the upper crust and more than in the primitive mantle. The concentration of rare earths in the main types of ores, with the exception of massive ones, exceeds the level of the chondrite standard, and REE fractionation is weak. The distribution spectra of chondrite-normalized REEs have a slight negative slope: the total content of light REEs is higher than that of heavy ones. The similarity of the geometry of the REE spectra of massive, vein-disseminated, brecciated and disseminated types of ores containing a significant admixture of host rocks indicates the inheritance of the REE composition in ores from the host rocks. In the disseminated ores of common taxite gabbro-dolerites, the Eu anomaly is present in the Kharaelakhsky (Oktyabrskoye Deposit) and Talnakhsky (Talnakhskoye Deposit) intrusions, it is positive, and in the Norilsk I Intrusive (in the same rocks), it is negative. Higher concentrations of REEs and significant fractionation of light and heavy rare elements are typical for host contact-metamorphic and metasomatic rocks with vein-disseminated (exocontact) ores. For olivine-free hornfels and skarns in brecciated ores, as well as for vein-disseminated ores, significant fractionation of light REEs with relatively heavy ones and a pronounced Eu minimum are characteristic. In massive ores, the distribution of REEs is determined by the composition of xenoliths.

Occurrence and Contamination of Rare Earth Elements in Urban Mangroves of Shenzhen, South China

Mangroves acted as sinks of terrestrial pollutants, but the occurrence and contamination of rare earth elements (REEs) in urban mangroves lacked systematic evaluation. In rapidly developing Shenzhen, China, four typical urban mangroves were selected to determine the REEs in urban mangroves, including Baguang mangrove (BGM) and Futian mangrove (FTM) featured with ecological preserve and central business district, respectively; Xixiang mangrove (XXM) and Shajing mangrove (SJM) both featured with industry district. The mean concentrations of total REEs (TREEs) in sediment (0–25 cm depth, μg g−1) were SJM (465.28) > FTM (411.25) > XXM (342.76) > BGM (118.63), with Ce to be the dominant REEs element. The depositions of REEs in urban mangroves were significantly affected by sediment sulfur accumulation and fine sediment, including silt and clay fractions. The main fractionation pattern of REEs in urban mangroves was the enrichment of light REEs (LREEs) and loss of heavy REEs (HREEs). Geo−accumulation index, modified degree of contamination, pollution load index, and potential ecological risk index showed the moderately contaminated level of REEs in FTM, followed by SJM, and XXM, with uncontaminated level in BGM. This study provided important information on REEs in urban mangroves for pollution prevention and remediation in the future.

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.

Comprehensive characterization of secondary sources originating from Turkey in terms of rare earth elements and scandium

REEs are essential materials for modern technology due to their unmatched physical and chemical properties. This paper reviews the potential and types of rare earth elements (REE) in 32 different secondary sources that contain water, wastewater, and slime/solid wastes originating from Turkey. Secondary sources were classified into five different categories as mining wastes (M), combustion residuals (C), sediments and sludges (S), e-waste (E), and wastewater (WW). After pre-processing and acidic digestion of solid samples, elemental concentrations of wastewaters and acidic leachates were measured. The highest total REE (REE total ) concentration was obtained in a combustion residue sample coded as C5 with 379 mg/kg. Besides, the highest critical REE (REE critical ) content was found in an e-waste sample including 346 mg/kg total REE and 76% critical REE. In addition, boron mine wastewater (W5) with a total REE concentration of 110 μg/L was evaluated as a significant important secondary source in terms of yttrium. The association, between scandium and total REE concentrations of category M and S, was evaluated and correlation coefficients of 0.86 and 0.69, respectively were calculated. E-waste and thermal power plant (TPP) ashes were evaluated as the secondary sources with the highest REE potential among the whole type of waste/wastewater. • REE potential of hazardous waste incineration plant ash was demonstrated. • The correlation between total REE and Sc concentrations was exhibited. • REE concentrations were evaluated for their potential to be a secondary source. • E-waste and fly ashes were evaluated as more critical secondary sources.

Rare Earth Elements of Sediments in Rivers and Estuaries of the East Coast of India

The rare earth elements (REE) in the clay fraction of sediments in 15 rivers and their estuaries along the east coast of India were analysed in this study. The total REE content (ΣREE) varied from 130.98 to 289.85 μg/g and from 70.89 to 352.61 μg/g in rivers and estuaries respectively. The ΣREEs of estuarine clays (except the Brahmani and Baitarani) was lower than in rivers. The Post-Archean average Australian Shale-normalized REE patterns in rivers and estuaries were similar and categorized into three types. The REE patterns reflect the composition of dominant geological formations in river basins and extent of sediment mixing from different sources during transport. Hydrodynamic conditions controlled the abundance and fractionation of REE in the estuaries. The Sm/Nd ratios of clays were largely controlled by mineral composition and Y/Ho ratios were affected by sedimentary processes in the estuaries.

Rare earth elements in plastics

Because of their unique properties, rare earth elements (REEs), comprising the lanthanide elements plus Sc and Y, have a variety of integral applications in modern electronic equipment. Consequently, it has been suggested that REEs may act as contaminants of and tracers for recycled electrical and electronic plastics in consumer goods. In this study, REEs have been determined in a range of consumer plastics of different polymeric makeup (n = 31), and purchased new and in societal circulation, by inductively coupled plasma-mass spectrometry following acid digestion. Samples were also screened by X-ray fluorescence spectrometry for Br and Sb as markers of brominated flame retardants and the retardant synergist, Sb2O3, respectively. One or more REE was detected in 24 samples, with four samples returning detectable concentrations of all REEs analysed and with total REE concentrations up to 8 mg kg−1. REEs were most commonly observed in samples containing Br and Sb at levels insufficient to effect flame retardancy and, therefore, likely derived from recycled electronic plastic, but were not detectable in new electrical plastics. Various REEs were also present in plastics with no detectable Br and Sb, however, and where unregulated recycling is prohibited (e.g. food packaging). This observation, and correlations between pairs of REEs for all samples considered, suggests a more generic source of these elements in consumer plastics in addition to the recycling of electrical and electronic waste. REEs reported in the literature for beached marine plastics were characterised by similar concentrations and inter-element correlations, suggesting that REEs are ubiquitous and pervasive contaminants of both contemporary and historical consumer and environmental plastics.

Mineralogy, Geochemistry, and Genesis of Kaolinitic Claystone Deposits in the Datong Coalfield, Northern China

AbstractGray-black kaolinitic claystones of industrial value are abundant in Upper Carboniferous–Lower Permian coal-bearing strata of the Datong Coalfield of northern China. The main types are tonsteins and cryptocrystalline kaolinitic claystones, distinguished by the thinness and greater crystallinity of kaolinite in the former and by the presence of detrital illite and authigenic pyrite in the latter. In order to determine the formation history of these two types of kaolinitic claystone, the petrological, mineralogical, and geochemical characteristics of borehole samples from the Upper Carboniferous Taiyuan Formation which comprises siliciclastics and coal seams deposited in a coastal environment, were analyzed. In addition to kaolinite, the claystones contain subordinate illite, quartz, pyrite, anatase, feldspar, siderite, and calcite. The tonsteins and cryptocrystalline kaolinitic claystones have different sources, as shown by petrographic data, elemental ratios, and chondrite-normalized rare earth element (REE) patterns. The volcanic origin of the tonsteins is revealed by an abundance of volcanic quartz and vitric fragments as well as Al2O3/TiO2, Zr/Hf, and Nb/Ta ratios consistent with a felsic igneous source. Their REE fraction was derived from feldspars or micas of the parent rocks, and the fraction decreased with alteration of these minerals to kaolinite. The sedimentary origin of the cryptocrystalline kaolinitic claystones is revealed by an abundance of detrital quartz and illite grains derived from either granite or sedimentary upper crust, and by the total REE contents (ΣREE) and (La/Yb)N values which are consistent with granitic material. Their depositional environment was in a transitional (coastal) setting (as shown by intermediate Sr/Ba ratios) hosting an open acidic hydrologic system (as shown by high chemical index of alteration (CIA) values indicative of intensive chemical weathering) that was suboxic to anoxic (as shown by high U/Th ratios and trace-metal enrichment factors). The present chemistry of these claystones was thus controlled by a combination of parent rock type and diagenetic alteration.

Variation in rare earth element (REE), aluminium (Al) and silicon (Si) accumulation among populations of the hyperaccumulator Dicranopteris linearis in southern China

Dicranopteris linearis is a rare earth element (REE), aluminium (Al) and silicon (Si) hyperaccumulator plant which occurs in southern China. To date, there have been no studies on the variation in elemental accumulation among populations of Dicranopteris linearis occurring on REE-enriched and non-REE enriched soils. In total 43 Dicranopteris linearis individuals and the corresponding rhizosphere soils from 7 populations in southern China were sampled and the plant material and soil composition were chemically analysed for REE and other elements. Dicranopteris linearis populations from REE-enriched soils and non-REE enriched soils both have the ability to accumulate high concentrations of REE (> 1000 mg kg− 1), Al (> 1000 mg kg− 1) and Si (> 10 000 mg kg− 1). The ratios of light REEs (LREEs) to heavy REEs (HREEs) in Dicranopteris linearis pinnae are consistently > 1, regardless of their ratios in the corresponding soils. Concentrations of REE in Dicranopteris linearis pinnae vary significantly among populations and have positive correlations with total and extractable soil REE concentrations. The plant Al and Si concentrations in Dicranopteris linearis populations are uncoupled from variations in soil Al and Si concentrations. The plant REE concentrations have no obvious relationships with the prevailing Al concentrations, but are positively correlated with plant Si and Mn, and negatively correlated with soil extractable P concentrations. The hyperaccumulation of REEs (LREE > HREE), Al and Si in non-REE enriched soils is a species-wide trait. The accumulation of REEs is highly variable and associated with soil REE concentrations, nutrients status, and other soil properties.

К вопросу о вхождении редкоземельных элементов в структуру хромпироповых гранатов

Rare earth elements (REE) in garnet are of interest in various fields of modern geology. The geochemistry of REEs in magmatic minerals is widely used in determining the distribution coefficients of crystal/melt and crystal/fluid, modeling the processes of melting and crystallization of magmatic rocks, studying deep mantle processes, age estimates and other issues of petrogenesis. The aim of the present work was a synthesis of a peridotite mineral association including the garnet containing REE at high pressure and high temperature. The initial sample consisted mainly of natural serpentine collected from ophiolites of the Eastern Sayan (Russia). As is known, the extreme stage of the regressive metamorphism of peridotites is serpentinization. It is depleted in calcium, but can recrystallize at high PT conditions into a harzburgite paragenesis, and at the initial stage of the experiment the chemical composition of the sample was a model harzburgite depleted in calcium and chromium, as well as a fluid of predominantly aqueous composition. As a source of chromium, chromite grains of 1–2 mm in size from peridotite xenoliths of the Udachnaya kimberlite pipe (Yakutia) were used. REE were added to the initial charge in the form of water-soluble salts. The experiment at a pressure of 5 GPa and temperature 1300 was performed on a multi-anvil high-pressure apparatus of the “split sphere” type (BARS) designed and developed at the V.S. Sobolev Institute of Geology and Mineralogy SB RAS. A container based on refractory oxide ZrO2 was used as a highpressure medium. The pressure in the cell before sample heating was estimated using the reference substances Bi and PbSe. The temperature was measured by a platinum-platinum-rhodium thermocouple PtRh30-PtRh6. The quenched was performed by switching off the voltage in the heater circuit. The experiment products contain an association of olivine + garnet + orthopyroxene + newly formed spinel. The predominant phase was olivine of a forsterite composition. A low-Fe orthopyroxene (1.49 – 1.68 wt% FeO) was found in elongated grains uniformly distributed throughout the sample. The newly formed spinel shows the faceted grains. The chromium content in the spinel significantly exceeds that of the initially added to the initial charge, 61.63 and 54.04 wt% Cr2O3, respectively. The garnet is characterized by a purple color, and was identified in the sample volume between olivine grains in the form of individual faceted crystals or their clusters. The largest garnets reached 0.5 mm in size. The synthesized garnet was determined as a high-Cr low-Ca pyrope variety. The contents of Cr2O3 and CaO are 10.15-11.21 and 0.06-0.11 wt%, respectively. The total content of REE in the garnet identified by the microprobe analysis is relatively high reaching 5-7 wt%. As a result of the work a mineral association corresponding to the peridotite paragenesis was obtained, including the subcalcic Crrich pyrope containing rare earth elements in significant amounts. It was estimated that their content in garnet mainly depends on the size of the ionic radius and, accordingly, on the atomic weight. This is consistent with the known facts about the preferable position of heavy REEs into the garnet structure compared to the light REEs.

Discovery of Permian crustal carbonatite in the northwestern margin of Tarim Basin and its geological significance

碳酸岩是自然界较为特殊的一类火成岩，由于其在上侵过程中不易受到地壳物质的混染，可以很好地保留源区原始特征，因而在揭示岩浆源区属性和地球深部碳循环等方面具有重要的研究价值。塔里木盆地西北缘阿克苏-乌什南部地区发育多条侵位到新元古界南华系中的火成碳酸岩岩墙或岩脉。这些岩脉的锆石U-Pb测年结果显示出多个年龄峰值，其中最年轻一组（3颗）岩浆锆石的谐和加权年龄为272±4Ma，另外还有400Ma、450Ma、790Ma、850Ma等年龄峰，而这些锆石可能均为碳酸岩岩浆捕获成因。结合区域上发育大量早二叠世辉绿岩岩床及岩墙等侵入事件，推测这些碳酸岩很可能形成于早二叠世（~270Ma）。碳酸岩主要由方解石（90%以上）构成，并含少量的白云石、重晶石、天青石、赤铁矿等其它矿物，可见方解石与白云石之间明显的出溶结构以及野外宏观上碳酸岩包裹围岩等现象。元素地球化学分析显示，碳酸岩CaO含量高（44.40%~50.40%），SiO₂含量低（1.83%~7.97%）；稀土元素总量很低（ΣREE=21.67×10^-6~91.32×10^-6），轻重稀土分异明显（LREE/HREE=3.90~8.40），具有中等负铕异常（δEu=0.61~0.68）和中等至弱负铈异常（δCe=0.59~0.98）；大离子亲石元素Sr、Rb、Ba等相对富集，Nb、Ta、Ti等高场强元素相对亏损；稳定同位素δ¹³C_V-PDB值高（-2.69‰~-2.93‰）、δ¹⁸O_V-SMOW值高（17.33‰~17.86‰）。这些特征与壳源碳酸岩特征相似，而与幔源碳酸岩差别较大。Sr-Nd同位素结果显示高的（⁸⁷Sr/⁸⁶Sr）_i值（0.710106~0.710558），低的ε_Nd（t）值（-8.46~-12.80），也进一步证实碳酸岩为地壳来源。综合分析认为这些碳酸岩很可能是塔里木二叠纪大火成岩省晚期岩浆事件的组成部分，系由塔里木西北缘地幔柱减压熔融后形成高温的基性岩浆向上侵位运移时，导致下地壳的碳酸盐储库部分熔融形成碳酸岩岩浆，并沿着断裂快速向上侵位形成。本文研究不仅丰富了塔里木大火成岩省的岩石组成认识，而且有助于增进对二叠纪深部复杂壳幔作用过程的理解。;Igneous carbonatites is a kind of special igneous rock in nature. Because they are not easily contaminated by crustal materials in the process of upwelling, they can well retain the original characteristics of the magma source. Therefore, they have important research value in revealing the properties of the magma source and the carbon cycle of the deep earth. Several carbonatite dikes or dykes are found intruded into the Neoproterozoic Nanhua System in the southern Aksu-Wushi area, the northwestern margin of Tarim Basin. Zircon U-Pb geochronology dating of these carbonatites yield multiple peak ages, including a youngest one at 272±4Ma obtained by three zircons, and other ones at 400Ma, 450Ma, 790Ma, 850Ma, respectively. However, all these zircons were probably captured by carbonate magma. Considering the intrusive events of massive Early Permian diabase sills and dikes in the region, we speculate that these carbonatite dikes were probably formed in the Early Permian (~270Ma). The carbonatites are mainly composed of calcite (over 90%) and a small amount of dolomite, barite, celestite, hematite and other minerals. In addition, the carbonatites have obvious exsolution structures between calcite and dolomite, and the country rock breccias are found wrapped by the carbonatites in the field. The element geochemistry analysis results show that carbonatites have high CaO content (44.40%~50.40%), low SiO₂ content (1.83%~7.97%), extremely low total rare earth elements content (21.67×10^-6~91.32×10^-6) with obvious differentiation of LREE and HREE (LREE/HREE=3.90~8.40) and weak negative Eu and Ce anomalies (δEu=0.61~0.68; δCe=0.59~0.98). And the large ion lithophile elements like Sr, Rb, Ba are relatively enriched, and high field-strength elements such as Nb, Ta, Ti are relatively depleted. The stable isotope of δ¹³C_V-PDB and δ¹⁸O_V-SMOW are high (-2.69~-2.93‰ and 17.33~17.86‰, respectively). All these characteristics are similar to the crustal carbonatite, but quite different from the mantle carbonatite. The Sr-Nd isotopic results of high (⁸⁷Sr/⁸⁶Sr)_i values (0.710106~0.710558) and low ε_Nd(t) values (-8.46~-12.80) also confirm that the Aksu carbonatites are derived from the crust. After comprehensive analysis, we propose that these carbonatites are probably the components of the late magmatic event in the Permian Tarim Large Igneous Province. When the mantle plume in the northwestern margin of Tarim was decompressed, it would form high-temperature basic magma and emplaced upward. These basic magma would heated the carbonate reservoir in the lower crust and partially melted it to form carbonatites magma, which was rapidly emplaced upward along the extension fault. This study not only enriched the petrological compositions of the Permian Tarim Large Igneous Province, but also promoted the understanding of the complex crust-mantle interaction processes in the deep area of Permian Tarim Basin.

Contrasting Depositional Environment of Iron Formation at Endengue Area, NW Congo Craton, Southern Cameroon: New Insights from Trace and Rare Earth Elements Geochemistry

The Endengue Banded Iron Formation (BIF) is located in the northwestern edge of the Congo craton in Cameroon. Here, we report geochemical data of trace and rare earth elements (REE) of the Endengue BIF samples from the Archean Ntem complex and investigate their environmental setting. Two types of BIF occur at Endengue area, both containing minimal contamination from terrestrial material. Total REE (ΣREE) contents in the Type 1 BIF are extremely low, ranging from 0.34 to 1.83 ppm, similarly to pure chemical sediments while Type 2 BIF displays ΣREE contents ranging from 2.98 to 24.26 ppm. The PAAS-normalized REE + Y patterns of the two BIF types display LREE enrichment relative to HREE and weak positive Eu anomaly, most likely suggesting that the source of iron and siliceous of the Endengue BIFs is mainly from the contribution of low-temperature hydrothermal alteration of the crust. Type 1 BIF shows very low Nd content (* and positive Ce anomalies which suggests suboxic or anoxic seawater similar to the depositional environment of Elom BIF in Archean Ntem complex. In contrast, Type 2 BIF displays low to moderate Nd contents (1 and 100 ppm with the exception of sample LBR65) with negative correlation between Nd and Ce/Ce* and negative Ce anomalies. These features indicate precipatation of Type 2 BIF from oxic iron-rich solution that changed to oxidized surface by rapid precipitation of the hydrothermal Fe. The Endengue BIFs were deposited in the continental margin ocean in presence of low-temperature hydrothermal fluids mixed with seawater, similar to Paleoproterozoic Kpwa-Atog Boga BIFs within the Nyong group and other Paleoproterozoic Superior-type BIFs worldwide.

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.

Occurrence forms of rare earth elements in coal and coal gangue and their combustion products

Distribution of rare earth elements (REEs) in six speciations extracted from coal and coal gangue and their combustion products (slag and fly ash) generated by three different power plants in China were determined by sequential extraction procedure combined with inductively coupled plasma mass spectrometry method. The results show that the REEs mainly occurred as acid soluble and silicate & aluminosilicate fraction, e.g., approximately 42.54% and 45.62% in coal gangue, 32.85% and 57.13% in lignite, and 18.10% and 75.46% in bituminous coal, respectively. However, REEs in the combustion products were mainly presented in silicate & aluminosilicate fraction regardless of coal or coal gangue, reaching up to approximately 80% of the total REEs content. During combustion, around 36%, 23%, and 5% from the other five fractions (water soluble, ion-exchangeable, acid soluble, organic, and sulfide) were transformed to silicate & aluminosilicate fraction from coal gangue, lignite, and bituminous coal, respectively. In the case of coal or coal gangue, the amount of each REEs in the same extracted fraction was different, but the distribution trend of REEs from La to Lu in each fraction was followed in the same rule. In the case of slag and fly ash generated from coal or coal gangue, distribution of REEs from La to Lu in each fraction showed the different trend between fly ash and slag. This was due to the fly ash exposed in flue gas system was much longer than the time for slag formation.

Tracing the paleo-methane seepage activity over the past 20,000 years in the sediments of Qiongdongnan Basin, northwestern South China Sea

The seepage activity of paleo-methane has been proven to exist in geological history and play an important role in the evolution of the Earth's environment. This study reports grain size, major/trace elements, total nitrogen (TN), total carbon (TC), total organic carbon (TOC), total sulfur (TS), magnetic susceptibility and AMS-14C measurements for sediment samples in a drill core (~282 cm long; Site Q6 at ~1400 m water depth) from the ‘Haima seep’ sedimentary area in the Qiongdongnan Basin, along the northern slope of the South China Sea (SCS). The alternative index system for paleo-methane seepage identification was established through testing and analysis, and three methane release events (MREs) were successfully identified: 254–282 cm (MRE1: 19.3–17.8 ka), 144–162 cm (MRE2: 11. 9–10.8 ka) and 90–124 cm (MRE3: 10.0–8.5 ka). When methane seepage occurred, the enrichment of authigenic carbonate minerals (high Mg-calcite or aragonite) led to the increase in the content of CaO and ‘dilution’ in the total rare earth element content (∑REE). However, the occurrence of authigenic pyrite resulted in a significant increase in TS and the total sulfur/total organic carbon ratio (S/C) in the sediments, and a synchronous decrease in the magnetic susceptibility. Meanwhile, the change of redox environment also induced the enrichment of Mo, U, and the positive anomaly of δCe. Based on the records of methane release events, the control mechanisms for the different time scales and different periods, such as sea level change, sea floor temperature change, and turbidity current activity were preliminarily discussed. Finally, the history of methane seepage activity was reconstructed, and conceptual diagrams were drawn of the study area encompassing the last 20 ka.

Dissolved rare earth elements estimation of ion-absorption rare earth ores using reflectance spectroscopy in south Jiangxi province, China

Ion-absorption rare earth ores are an important mineral resource in China. Nowadays, the unauthorized mining has become a serious problem, resulting in severe water pollution and the wastage of rare earth elements (REEs). Being able to estimate the concentration of dissolved REEs in water bodies near mines is essential for tackling this environmental problem. Conventionally, quantitative analyses of the contents of dissolved REEs are performed using laboratory-based techniques, which can be time consuming and costly. Spectral reflectance is a rapid and cost-effective means of characterizing the chemical compositions of light-absorbing materials. In this study, reflectance spectroscopy was performed on dissolved REEs, and the correlation between their reflectance characteristics and REE content was determined. A total of 50 aqueous media samples collected in south Jiangxi Province and 25 laboratory-produced aqueous media samples were tested, and their reflectance spectra and REE contents were measured using reflectance spectroscopy and inductively coupled plasma mass spectrometry, respectively. Next, the reflectance, differential reflectance, and absorption depth were analysed based on the REE content. Six diagnostic absorption features related to REEs are recognised in the visible and near-infrared wavelength regions, along with several smaller peaks. It indicates that the results of the absorption depth analysis are in accordance with the absorption spectra characteristics of the REEs, with the R2 value being higher than 0.97. The intensity of each of the six absorption bands exhibits a linear correlation to the total REE content. Therefore, linear regression models can be derived for estimating the total concentration of REEs in aqueous media samples. What's more, the detection limit for REEs is determined to be about 30 μg/L. Thus, it can be concluded that reflectance spectroscopy is a suitable technique for estimating the concentration of dissolved REEs.

Mineralogy and BCR sequential leaching of ion-adsorption type REE: A novelty study at Johor, Malaysia

Since year 2010, advance research in resource investigation, mineralogy and geochemistry, environmental impact as well as processing technique of ion-adsorption type rare earth elements (REE) deposit particularly in mining industry has been conducted worldwide. Ion-adsorption type REEs are formed by weathering process of igneous rocks (typically granites) that contain certain REE-bearing minerals. Effect of the rapidly weathering, REE minerals are decomposed, and ionized REEs are absorbed on clay minerals such as kaolinite and halloysite. A research study has been made in discovery the ion-adsorption type REE prospecting in Johor, Southern Peninsular Malaysia with three vertical weathering profiles (up to 11 m) sampled on Besar island, Tengah island and Hujung island. Parent granite is A-type consist of quartz, K-feldspar, plagioclase, biotite and 0.6–1.4 wt% accessory minerals (zircon, apatite, monazite-(Ce) and chlorite). The main REE-bearing minerals are monazite-(Ce), apatite, zircon, titanite, allanite-(Ce) and bastnaesite-(Ce). Total REE concentrations in raw saprolite (potential REE horizon in weathering profiles) is ranging between 1167 and 2339 ppm. The laboratory leach ability of the REE in different parts of the A-type granite weathering profiles was determined by carrying out a three step BCR sequential extraction procedures. The evidence from the three-step BCR-701 (certified freshwater sediment standard) sequential extraction procedure for ion-adsorption was consistent with a near instant process (≤1 h) with 70–80% recovery rate. This is due to the re-precipitation of REE3+ ions in solution and due to hydrolysis of ions on the clay surface. The ion-adsorption (leached) fraction was enriched in light rare earth elements (LREE) compared with the raw sample compositions of the saprolites and saprocks (Ce/Ce* ratio range largely from 0.17 to 0.82). The LREE accounted for 80–90% of the total REE content in the investigated saprolite and saprock; allowed in agreement with the trend that was observed in Thailand and South China ores.

Major, trace and rare earth element (REE) geochemistry of the Oligocene stratiform manganese oxide-hydroxide deposits in the Nikopol, Ukraine

The Nikopol manganese deposit is situated in the west and north of Nikopol, Ukraine and one of the world's largest deposits among the sedimentary manganese deposits. The Nikopol Oligocene basin consists of two structural stages, Precambrian crystalline basement rocks and sedimentary cover rocks (Cretaceous to Quaternary). Nikopol Ore horizon is traced in a thickness varying from several cm to 4.5 m and a single stratum from the west to the eastwards to about 250 km. Nikopol manganese ore horizon was separated to three different units; carbonate ore, mixed carbonate-oxide ore, and oxide ore. The main minerals of supergene oxidation zone in Nikopol manganese deposits are: manganite, pyrolusite, todorokite, cryptomelane, birnessite, rancieite. The manganese oxide-hydroxide ores were analyzed for major oxides using ICP-AES and, trace and rare earth elements (REE) using ICP-MS. The mean major oxide contents of the manganese ores are 40.7 wt% MnO, 4.1 wt% Fe2O3, 15.6 wt% SiO2, 4.17 wt% for Al2O3, and 7.1 wt% for CaO. The average Mn/Fe, Co/Ni, Co/Zn, and Zr/Hf ratios in the Nikopol manganese deposit are 25, 0.54, 1.15, and57, respectively. The total REE contents are between 60 and 197 ppm, with a mean of 108 ppm. The PAAS-normalized REE patterns of the Nikopol manganese oxide ores have similar trends and show MREE (middle rare earth element) and HREEs (heavy rare earth element) enrichments. The Ce/Ce* values of manganese oxide-hydroxide ores collected from the study area vary from 0.88 to 1.43, with the mean of 1.16. Most of manganese samples have positive Ce anomalies except for a few samples, indicating that ore-forming rocks were primarily marine chemical or biogenic deposit. The Eu/ Eu* anomalies of the manganese oxide-hydroxide ores are close to 1 with a range of 0.68 to 1.12 (mean: 0.96). The Y concentrations vary from 9.1 to 47.1 ppm, with an average of 18.2 ppm and show negative Y anomalies, except for three samples. The Pb isotope ratios are 19.0 for 206Pb/204Pb, 15.7 for 207Pb/204Pb and 39.4 for 208Pb/204Pb isotopes. All these data indicate that the Nikopol manganese oxide-hydroxide ores formed rapidly within oxic/suboxic seawater as reflected by Ce anomalies close to 1 in compared to similar environments, low-oxygen fugacity in source of the hydrothermal fluids, volcanogenic input or hydrothermal contributions to seawater, and high Co, Ni, Cu, Sr, Ba and As and low V, Rb, Nb, Hf, U, Th, Pb and Zn values. Also, our results point out that the metals were transported from both a hydrothermal source in deeper water (chemical discrimination diagrams) and terrestrial sources (Pb isotopic data). The metals formed to the Mn-oxide ores syngenetically likely came from water depths deeper than the area where the carbonate-ore deposits formed.