Tracing rare earth elements distribution and enrichment mechanism in phosphorites of the Paleoproterozoic Bijawar Group in Mardeora Mine, Chattarpur district, Madhya Pradesh (M.P.), India

Hydrothermal enrichment of rare earth elements in the Lower Permian Lijiatian bauxite deposit, southern China

Rare earth element enrichment in sedimentary phosphorites formed during the Precambrian–Cambrian transition, Southwest China

Climatic and morphological control of rare earth element distribution in weathering mantles on alkaline rocks

A window in the course of alkaline magma differentiation conducive to immiscible REE-rich carbonatites

Lavas and included xenoliths from the Comores Archipelago have been analysed for the rare earth elements (REE) La-Lu. Among basaltic lava types fractionation of REE rock/chondrite distribution patterns is more extreme with greater SiO2 undersaturation and contents of incompatible elements. Enrichment and slight fractionation of REE in the rock series basanite-phonolite is considered compatible with a model of fractional crystallisation at low pressures involving mainly olivine and clinopyroxene, and to a much lesser extent, plagioclase. Apatite is probably effective in curtailing further enrichment of REE. High level fractional crystallisation and eclogite fractionation at depth appear unlikely causes for the relative enrichment of light REE (La-Eu) in the undersaturated basalts. This effect is more probably due to mineralogical control during partial melting in the upper mantle. Lherzolite xenoliths are poor in REE, exhibiting a slight relative depletion in the light REE. These patterns are interpreted as those of possible mantle material subjected to small degrees of partial melting, although not necessarily related to those melts erupted as lava flows at the surface.

Radiogenic Pb reservoir contributes to the rare earth element (REE) enrichment in South Qinling carbonatites

Rare earth element (REE) concentrations and patterns in granites control the generation of regolith-hosted REE deposits; however, REE occurrence and enrichment mechanisms in granites with few primary REE-rich minerals, such as allanite and titanite, are not well studied. In this contribution, we conducted detailed whole-rock and in situ mineral geochemical studies on the Xunwu biotite monzogranite and muscovite syenogranite in the southern part of Jiangxi Province, South China, where some monzogranite samples yield total REE contents higher than 1000 ppm. The monzogranite and syenogranite were generated in the Late Cretaceous with similar zircon U-Pb ages (95.3 ± 0.3 Ma and 96.4 ± 0.3 Ma, respectively). REE-phosphates and Ti-Fe oxides (magnetite and ilmenite) are the dominating REE-bearing minerals in the monzogranite and syenogranite. The REE-phosphates are distributed radially in fractures of feldspar or occur around and replace the primary apatite, indicating generation due to interaction between primary apatite and REE-rich fluid. The Ti-Fe oxides generally show high REE contents, which are also caused by interaction with the REE-rich fluid. The higher P and Fe contents in the monzogranite make it more effective at fixing REEs during fluid-rock interaction and thus display higher REE contents than those of the syenogranite. The occurrence of negative Ce anomalies in altered minerals from both the monzogranite and syenogranite indicates that the fluids had high oxygen fugacity with high REEs but low Ce abundance. This kind of fluid is consistent with the circulating meteoric water carrying REE ions from the weathering crust. This study highlights the progressive enrichment process of REEs between their parent granites and weathering crust as follows: (1) Granites intrude and their upper parts are weathered to generate REE-bearing weathered crust; (2) circulating REE-bearing meteoric fluids replace apatite with REE phosphates and enrich Ti-Fe oxides in granite with REEs; followed by (3) continued upgrading of REE enrichment lower in the developing weathered granite profile over time by downward circulating meteoric fluids, which leach REEs from previously formed phosphate and oxide minerals and likely their weathered equivalents in the upper parts of the granite regolith. These processes favor the generation of regolith-hosted REE deposits in the weathering profile for granites where primary REE-rich minerals are absent.

Rare earth element components in atmospheric particulates in the Bayan Obo mine region

Rare earth elements (REE) are important raw materials for electronic products and green-energy technology and deep-sea sediment as an important potential source of REE mineral. It is of great scientific significance to understand the influence of REE in deep-sea sediments. In this paper, thirty sediments samples and eleven sediments samples were collected at the site SH3 and SH1 of Shenhu area, respectively. The trace elements, major elements, and different Fe-Mn minerals were analyzed to investigate the role of anaerobic oxidation of methane (AOM) in the enrichment of rare earth elements in the marine sediments. The result showed that the content of ∑REE/Ti increased at the top of sulfate and methane transition zone (SMTZ) at site SH1 and SH3. Combined with the analysis of different forms of ferromanganese minerals and the REE patterns, it is inferred that there is little influence of terrigenous input to the REE content. In contrary, the REE-rich carbonate phase and REE-rich Fe-Mn oxides (hydroxides) phase have important contribution of REE enrichment at the top of SMTZ. Meanwhile, the calculations of the quantitative relationship between the REE-rich carbonate phase and REE-rich Fe-Mn oxides (hydroxides) phase also confirm this conclusion. And the AOM caused the decrease of the REE-rich Fe-Mn oxides (hydroxides) phase and increase of the REE-rich carbonate phase. This is the potential explanation of ∑REE/Ti enrichment at the top of SMTZ. This study is of great scientific significance for the study of REE enrichment mechanism in the methane seeps and provided a new sight of REE enrichment mechanism in deep-sea sediments.

Ion-adsorption rare earth element (REE) deposits represent strategic critical resources in China, which were traditionally considered to be predominantly hosted in granite weathering crusts. However, the recent discovery of new deposit types within the weathering crusts of shallow metamorphic rocks in South China has opened up novel exploration frontiers, while research on their metallogenic mechanisms remains insufficient. To elucidate the REE enrichment mechanisms in shallow metamorphic rock weathering crusts, this study focuses on the Getengzui ion-adsorption REE deposit in southern Jiangxi Province. Twenty-four samples were collected from the weathering crust profiles of the Qingbaikouan Shenshan and Kuli Formations. Multiple analytical approaches were employed, including major and trace element analysis, Chemical Index of Alteration (CIA), Base Leaching Index (BA), and quantitative evaluation of element mass transfer coefficients (τ). Trace element spider diagrams, REE distribution patterns, and A-CN-K diagram analysis were also utilized. The results reveal that the weathering crusts have progressed to the middle–late stage of chemical weathering. The average CIA value is 83 for the middle-upper part of the completely weathered horizon in the Kuli Formation. In contrast, for the completely weathered horizon in the Shenshan Formation, the value is 86. Intense chemical weathering has resulted in the near-complete decomposition of primary silicate minerals and extensive leaching of base cations. This progress has created an acidic pore water environment, which is critical for REE mobilization. REEs exhibit characteristics of in situ secondary enrichment, with significant enrichment of ΣREE in the middle-upper part of the completely weathered horizon. The peak τ(ΣREE) values reach 0.78 and 2.43 for the Kuli and Shenshan Formations, respectively. Apatite dissolution is identified as the primary source of REE ions. Differences exist in the geochemical mobility sequences of elements between the two formations. REE enrichment is controlled by multi-stage geochemical barriers, including an oxidation barrier and a clay adsorption barrier. The oxidation barrier preferentially fixes Ce4+, whereas the clay adsorption barrier serves as the dominant mechanism for large-scale REE enrichment. Parent rock lithology is the primary factor governing the efficiency, scale, and fractionation characteristics of REE enrichment. The Kuli Formation is favorable for forming the thick, large-scale orebodies enriched in light rare earth elements (LREEs). In the contrast, the Shenshan Formation tends to host higher-grade orebodies, characterized by a relatively balanced ratio of LREEs and heavy rare earth elements (HREEs). This study clarifies the main controlling factors for ion-adsorption REE mineralization in two shallow metamorphic rocks. It thereby provides a theoretical basis for future exploration. This framework is applicable to analogous REE resources within shallow metamorphic rock distributions across South China and nationwide.

Weathered crust elution-deposited rare earth ores (WCE-REOs) are the primary global source of medium and heavy rare earth elements (M/HREEs). The recent discovery of high-altitude (1500–2500 m) WCE-REOs in southern Yunnan Province, China, presents new opportunities for the development of M/HREE resources. This study investigates the enrichment and fractionation mechanisms of rare earth elements (REEs) in these deposits through a systematic analysis of three representative weathering profiles associated with the Lincang granite batholith. The analytical results indicate that the profiles consist mainly of clay minerals (kaolinite, halloysite, illite, minor montmorillonite) and iron oxides, with high SiO2 (64.10–74.40 wt.%) and Al2O3 (15.50–20.20 wt.%) and low CaO/MgO—typical of weathered REE deposits. The total REE contents (238.12–1545.53 ppm) show distinct fractionation: LREE-enriched upper layers and HREE-enriched deeper zones. Sequential extraction revealed that the REEs in the Lincang granite weathering profiles predominantly occur in ion-exchangeable, residual, and iron-manganese oxide-bound states (>95% total REEs). Ion-exchangeable REEs showed depth-dependent enrichment (peaking at 819.96 ppm), while iron-manganese oxides exhibited a strong REE affinity (up to 47% total REEs), with amorphous phases that were preferentially enriched in Ce (partitioning >80%). Fissure systems exerted critical control over the redistribution of elements, particularly REEs.

Kiruna-type or IOA deposits are characterized by magnetite-apatite-actinolite associations and may contain considerable amounts of rare earth elements (REEs) that can be exploited as by-products. REEs in the Kiruna-type deposit, heterogeneously distributed, are mainly hosted in phosphates (e.g. apatite). Published data of apatite, together with other evidence, can be used to decipher the source, enrichment mechanism, and post-ore modification of REEs in the Kiruna-type deposits. Sr isotopes and melt inclusions compositions of apatite, together with other evidence, support a mantle + evaporite affinity for the ore-forming materials of many IOA deposits. Ore-forming materials of different IOA deposits may originate from primitive, depleted, or enriched mantle sources respectively. This suggests that magmatic-hydrothermal evolutions, rather than REE-enriched mantle source, are probably more important for REE enrichment in Kiruna-type deposits. Increasing evidence supports an ortho-magmatic origin of IOA deposits, yet detailed forming model is still in debate. From the perspective of models forming Fe-P-rich melts, we tentatively test the REE enrichment mechanism of IOA deposit. Sulphate-rich, Fe-P-bearing melts have been observed in the Iron Springs, Buena Vista, and El Laco IOA deposits. These melts may extract REEs from silicate magmas and thus contribute to REE enrichment. Compiled experimental data show that Fe-P melts would incorporate more REEs than the silicate-rich melts during magma Fe-Si immiscibility. As a result, magma Fe-Si immiscibility potentially occurring in IOA deposits may also assist in the enrichment of REEs. Hydrothermal events in the Kiruna-type deposits could result in formation of monazite and xenotime, which is beneficial for industrial recovery of REE. Finally, the existence of various magmatic-hydrothermal Fe-REE assemblages (e.g. IOA deposit, Bayan Obo deposit) implies that co-enrichment of iron and REEs can occur during various magmatic-hydrothermal processes.

The eastern part of the northern margin of the North China Craton is a key metal metallogenic province in China, hosting many important rare metal and rare earth element (REE) deposits and having great resource potential. This study investigated the Saima deposit, a niobium (Nb) and tantalum (Ta) deposit and the Baerzhe deposit hosting zirconium (Zr), Nb and REEs. Based on previous LA-ICP-MS zircon U–Pb dating results obtained by the authors’ team, this study compared the whole-rock geochemistry and whole-rock Sr–Nd–Pb isotopes of an orebody with its surrounding rocks. The geochemical characteristics of both deposits are used to systematically review the evolution of the alkaline magma and the differences in the physical and chemical conditions for enrichment and mineralisation of late-stage rare elements and REEs such as Nb, Ta and Zr. Comparing the mineralisation of the Saima and Baerzhe deposits, the alkaline magmatic evolution plays a crucial role in the enrichment of rare-earth elements, which are generally formed in the late stage of alkaline magmatic evolution.

Coal waste is a potential source of rare-earth elements (REEs) and some economically critical elements recovery. The present study reports the abundance and enrichment of REEs and critical elements in the Hancheng Permo-Carboniferous (Weibei coalfield) and Binxian Jurassic coals (Huanglong coalfield) of Shaanxi, China. The Binxian coal is distinctly enriched in all REEs. The Hancheng coal is enriched in Y, Ce, Sc, La, Yb, Nd, Pr, Gd, Er, Sm and Dy and depleted in Lu, Eu, Ho, Tb and Tm, compared with that of the average earth’s crust abundance (ECA), world coal and the US coal. In the Binxian raw coal, the REEs contents, namely Sc 13.8, Y 13.1, La 27.8, Ce 48.49, Sm 4.1, Nd 22, Eu 0.8, Gd 3.8, Pr 5.43, Dy 2.5, Er 1.4 and Yb 1.3 in mg kg−1. The contents (mg kg−1) of REEs in the Hancheng raw coal were Sc 8.8, Y 18.6, La 34.8, Ce 60.2, Nd 26, Yb 1.8, Eu 01, Pr 6.71, Sm 5.3, Dy 3.4, Tb 0.66, Er 1.9 and Gd 5.16. The contents (mg kg−1) of critical elements in the Binxian raw coal were Cr 30.8, Pb 41.5, Ni 49.7, Cu 35.7, Ba 257.9, V 51.7, Zn 63.1, Li 135, Ga 20.6, U 2.9, Th 10.2 As 12.7, Al 98,887, Fe 23,916 and Ti 4289. The contents (mg kg−1) of critical elements in the Hancheng coal were Cr 384, Pb 56.1, Ni 93.9, Cu 49.5, Ba 371, V 90.7, Zn 7653, Li 183, Ga 35.9, U 4.9, Th 17.7, As 10.1, Al 108,344, Fe 20,433 and Ti 2873. The contents of REEs in the Binxian and Hancheng coals were not in a promising range, whereas some of the critical elements were highly abundant. The Al2O3/TiO2 ratio indicated that the Ordos Basin sediment was derived from intermediate-felsic rocks with a slight variation (r = 0.98). The Eu and Gd show positive anomalies with negative Ce anomalies almost in all the samples. The positive anomalies of Gd represent the intrusion of hydrothermal fluid with possibly Ba interference in the Binxian coal. The high volatile matter in the Binxian coal reflects bituminous to anthracite coal, whereas the low volatility of the Hancheng coal reflects peat to lignite coal. The recovery of the REEs and critical elements as a by-product from these coals may not only increase the revenue but will also lead to an improvement in the environmental quality.

Enrichment of rare earth elements in the early Cambrian Zhijin phosphorite deposit, SW China: Evidence from francolite micro-petrography and geochemistry