Rare Earth Element Enrichment Research Articles

Molybdenum isotopes demonstrate that multistage upgrading is required to generate heavy rare earth element–enriched carbonatites

Carbonatites with heavy rare earth element (HREE) enrichment are a rare and intriguing prospect for economic geology research, due to the growing global demand for HREEs in various industries. However, debate persists over the mechanism responsible for HREE enrichment in carbonatites, with the mantle source, magmatic-hydrothermal evolution, or a combination of these factors proposed to be responsible. This study examines three adjacent Late Triassic carbonatites (from the Huanglongpu, Huayangchuan, and Jialu carbonatite dike systems) in the Lesser Qinling of Central China and uses Mo isotope systematics to provide unique insights into the HREE enrichment process of these magmas. All three carbonatites exhibit elevated total REE (ΣREE) concentrations (up to 4600 ppm), along with significant HREE enrichment (ΣHREE/ΣREE = 0.1−0.4). Notably, Jialu carbonatite stands out for having the highest total HREE concentrations (≥360 ppm) and ΣHREE/ΣREE ratios (0.2−0.4). Regardless of their variable degrees of HREE enrichment, the three carbonatites display similar Sr-Nd-Pb isotope signatures, which indicates a shared enriched mantle source. The Huanglongpu and Huayangchuan carbonatites mostly display significantly lighter δ98/95Mo (−1.71‰ to −0.15‰) values than the depleted mantle, which indicates an origin from an enriched mantle influenced by recycled pelagic clays and Fe-Mn nodules. Both types of marine sediments are enriched in REEs and would have undergone initial HREE enrichment during slab dehydration and metamorphism, resulting in an HREE-enriched mantle source region. In contrast, Jialu carbonatite possesses significantly heavier δ98/95Mo (0.13‰−1.89‰), which is indicative of the subsequent influence of hydrothermal processes. Additional evidence of this hydrothermal influence at Jialu is preserved in calcite crystal fluid inclusions, elevated δ18O (8.71‰−10.72‰), non-charge-and-radius−controlled (CHARAC) Y/Ho ratios (36−41), and low Sr concentrations (<4800 ppm). Secondary upgrading of HREEs at Jialu occurred due to preferential complexation and transportation during hydrothermal exsolution. This study demonstrates that maximum HREE enrichment in carbonatites is achieved through a two-stage process that involves both a refertilized mantle source and late-stage hydrothermal exsolution.

Occurrence and enrichment of critical metals in ferromanganese deposits in the western Pacific

Co-rich ferromanganese nodules and crusts are economically valuable deep-sea ferromanganese deposits widely distributed in the western Pacific Ocean and are rich in critical metals such as Co, Ni, Cu and rare earth elements (REEs). However, the lack of fine delineation and systematic comparisons of the distributions of these critical metals in these ferromanganese deposits limits the understanding of the occurrence states of Co, Ni, Cu and REEs and the metallogenesis of ferromanganese deposits. Therefore, the authors selected one nodule and one crust from the western Pacific Ocean, and utilized high-resolution methods such as micro-area X-ray fluorescence spectrometry (μ-XRF), laser-ablation inductively-coupled plasma time-of-flight mass spectrometry (LA-ICP-TOF-MS), and laser-ablation inductively-coupled plasma mass spectrometry (LA-ICP-MS) to depict elemental distribution and elemental profile.The results show that the ferromanganese deposits are predominantly composed of Fe-vernadite with low Mn/Fe ratios. Co, Ni and Cu exist primarily in the manganate octahedral layer of Fe-vernadite. REEs mostly exist in feroxyhite of Fe-vernadite, and manganate octahedral layer of Fe-vernadite also have high Ce content. Co, Ni and Cu contents of ferromanganese deposits are closely correlated with Mn/Fe ratios: Co, Ni and Cu contents increase with Mn/Fe ratios until the Mn/Fe ratios rises up to 4, and remain stable when Mn/Fe ratios > 6. The enrichment of Co, Ni and Cu in ferromanganese deposits is controlled by the redox conditions of seawater during accretion, whereas REEs enrichment is related to Mn and Fe fluxes in seawater during accretion. The coupling relationships between elemental distributions help to reveal the elemental occurrence state, and the geochemistry of ferromanganese deposits are analyzed to identify element enrichment mechanism.

A novel extraction process for efficient recovery of rare earth elements from the leaching liquor of ion-adsorption type rare earth ore using unsaponified N, N-di(2-ethylhexyl)-diglycolamic acid

There are still challenges in the recovery of rare earth elements (REEs) from leaching liquor of ion-adsorption type rare earth ore. In this paper, unsaponified N, N-di(2-ethylhexyl)-diglycolamic acid (HDEHDGA) was used to develop a green extraction process for efficient separation and enrichment of REEs. The cation exchange mechanism of RE(III) extraction was proposed by slope analysis and FT-IR spectra. HDEHDGA exhibited excellent extraction performances, such as short equilibrium time, high selectivity towards RE(III) and easy stripping by 0.5 mol/L HCl solution. REEs was enriched from 287.5 mg/L to 63.30 g/L by five-stage counter-current extraction and three-stage counter-current stripping using unsaponified HDEHDGA. The enrichment factor reached 220, and the proportion of REEs was increased from 80.76 wt% to 98.82 %. The loss of REEs was controlled below 2.14 wt%. This extraction strategy helps to improve the REEs recovery and avoid ammonia–nitrogen wastewater, which demonstrates its application potential in the ion-adsorption type rare earth ore.

Interpretation of vertical migration and enrichment processes of rare earth elements (REEs) in ion-adsorption-type mineralization in Japan based on REE speciation analyses

Typical vertical profiles of ion-adsorption-type rare earth element (REE) deposits discovered in southwest Japan were studied by conducting speciation analyses, including X-ray absorption fine structure and laser-induced fluorescence spectroscopy combined with transmission electron microscopy and adsorption/desorption experiments. The results revealed that REE speciation, migration, and enrichment in weathered granite is largely controlled by soil pH, which in turn controls the variable charges of kaolinite, the REE host phase. Both the distribution coefficient Kd and the soil pH increase with depth. As a result, (i) REE dissolution and migration occur in the near-surface acidic environment of the upper layers, where hydroxyls of kaolinite basal surfaces and edges are deprotonated to a lesser degree, and (ii) REEs accumulate in the relatively high-pH environment below the surface, where hydroxyls of kaolinite basal surfaces and edges are deprotonated to a larger degree, producing REE adsorption sites with variable charges. An increase of soil pH to greater than 6 in deeper layers promotes inner-sphere complexation of REEs. Although inner-sphere complexation inhibits the ion-exchange extraction of REEs, the inner-sphere complexes can be still extracted by lowering the pH of the extraction solution. This fact, which indicates that the adsorption of both inner- and outer-sphere complexes is reversible, is important in terms of both (i) understanding vertical REE profiles in which the pH varies and (ii) the efficient recovery of REEs from REE-enriched layers at all depths in weathered granite.

The mechanism of dolomitization in a stromatolite mound in the late Cambrian Chaomidian Formation, Shandong Province, China

Clarifying the mechanism of dolomitization is of pivotal importance and represents a burning issue among geologists. A comprehensive model to define the genesis of dolomitization in the Cambrian Chaomidian Formation carbonates is still lacking. In the highly focused study, the advanced integration of X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), clumped isotope and carbon/oxygen isotope analyses was used to reveal complex interactions between the genesis and dolomitization of a stromatolite mound in the late Cambrian Chaomidian Formation of China. The results show that the dolomite content increases from bottom to top, along with a shift in lithology from limestone to dolostone. Additionally, as we moved from the base to the summit of the stromatolite mound, the Fe, Mn, and Na contents increase with increasing Mg levels, whereas the δ13C and δ18O values became more positive. Conversely, the levels of Sr and total rare earth elements (REEs) gradually decreased. The dolomite grains in the stromatolite mound are micritic and euhedral to subhedral, with foggy cores and bright edges and low cation ordering. The stromatolite limestone, dolostone, and underlying lime mudstone samples exhibit similar REE patterns: light REE enrichment, heavy REE loss, negative δEu anomalies, and weak negative δCe anomalies. The δ13C and δ18O values fall within the late Cambrian seawater range, suggesting that dolomitizing fluids originated mainly from concentrated seawater and migrated from top to bottom. The δ18O values indicate lower dolomite formation temperatures than calcite formation temperatures, supporting dolomitization during the penecontemporaneous diagenetic stage. Petrographic evidence reveals the presence of pyrite, indicating sulfate-reducing bacterial activity during diagenesis. XPS analysis revealed similar organic functional groups in both the stromatolite limestone and the dolostone, including C-(C = O)-O, C–C/C-(C–H), C-O and C-N. However, the dolostone spectrum exhibited a larger C-OH/C-O peak area, suggesting significant microbial organic matter involvement in dolomite formation. While a kinetic obstacle is recognized as a primary cause of dolomite formation, this study also suggested that microbial activity weakened this obstacle during diagenesis. Thus, microbial metabolism or cyanobacterial decomposition facilitates dolomite formation during the penecontemporaneous diagenetic stage.

Accumulation of rare earth elements in human gallstones: a perspective from dietary and human health

BackgroundGallstone disease poses a global threat to human health and is strongly linked to environmental factors. However, there is currently no data on the presence of rare earth elements (REEs) in human gallstones. This paper investigates the concentration and distribution of REEs in gallstones for the first time, aiming to explore the environmental implications on human health.MethodsA total of 25 gallstone samples were collected in Shanghai and the content of REEs was measured by Inductively coupled plasma-Mass Spectrometry (ICP-MS) to explore the distribution of REEs in gallstones.ResultsThe concentration of REEs in gallstones ranged from 4.89 to 190.8 ng/g (mean 39.21). In most of the gallstone analyses, REEs have been detected and generally attributed to environmental exposure or food contamination. The Y/Ho ratio of gallstones was lower than that of continental rocks, similar to that in the blood, indicating limited fractionation during fluid transport processes in the gallbladder.ConclusionsThe upper continental crust (UCC)-normalized REEs pattern in gallstones showed depletion of light REEs, while most showed enrichment of heavy REEs. Positive Gd anomalies were found in most samples, while few samples suggested anthropogenic influence. Whether exogenous inputs or in vivo biofractionation lead to changes in REEs fractionated patterns require further analyses.

Scalable and facile fabrication of sulfonic-acid-functionalized porous hypercrosslinked polymers for efficient recovery of rare earth elements from tailing wastewater

The separation and enrichment of rare earth elements (REEs) from tailing wastewater is of great significance for the sustainable supply of REEs and environmental remediation. As Al3+ exhibits extreme similar properties with REE3+, selective recovery of REE3+ from the sulphate tailing wastewater remains a considerable challenge. Based on the difference in the binding stability of REE3+ and Al3+ with sulfate ions, the utilization of sulfonic acid groups may provide a promising method for enhancing the selectivity of REE3+/Al3+ in the sulphate aqueous solution. Herein, a series of sulfonic-acid-functionalized hyper-crosslinked polymers (SHCP-Ps) were successfully synthesized through a facile, scalable and one-step method catalyzed by chlorosulfonic acid, which has the advantages of high sulfonic acid density (3.27 mmol/g), specific surface area (1044.6 m2/g), abundant micropores and superhydrophilicity. These properties result in SHCP-P exhibiting fast adsorption kinetics (30 min) and high adsorption capacities (106.78 mg/g (La), 111.99 mg/g (Eu) and 126.27 mg/g (Lu)). Additionally, it exhibits extremely high REE3+/Al3+ selectivity (SF(La/Al) = 6929, SF(Eu/Al) = 4810, SF(Lu/Al) = 3003) in sulfate medium, surpassing that of most existing REEs adsorbents. Upon application of SHCP-P to actual wastewater, the recovery rate of total REE3+ was observed to reach 87 %, while the adsorption rate of Al3+ was found to be 0. Simultaneously, SHCP-P exhibits both high reusability and magnification synthesis capabilities. The results indicate that SHCP-P has significant potential for industrial applications in the selective recovery of REEs from tailing wastewater.

Mesoproterozoic depleted spinel peridotites metasomatized by high-K hydrous melt in the Patagonian back-arc

Here we report the first investigation of spinel-bearing mantle xenoliths from Los Gemelos volcano, Canquel Plateau, Patagonia. They are highly-depleted Mesoproterozoic (ReOs model ages of 1.3–0.9 Ga) harzburgites and clinopyroxene-poor lherzolites characterized by typical indicators of partial melt extraction, such as low whole-rock Al2O3 and CaO contents (<1.5 wt%), high Mg# of silicate phases (90–95), and Cr-rich spinel (Cr# 0.20–0.42). Depletion of incompatible highly siderophile elements (Re, Ru, Pd) relative to the primitive upper mantle supports high degrees of melt extraction. The occurrence of phlogopite and K-rich alkaline glass veins with high- and low-SiO2 compositions is clear evidence of modal metasomatism. The light rare earth element (LREE) enrichment in clinopyroxene, as well as the whole-rock U-shaped REE pattern, confirms cryptic metasomatism. This melt-rock interaction is corroborated by major (i.e., Mg# vs. basaltic elements) and trace (i.e., La/YbN vs. Sr/Y and Ti/Eu; and Sr vs. Ti/Eu) element contents of pyroxenes. The calculated compositions of melts in equilibrium with clinopyroxene coexisting with phlogopite suggest interaction with slab-derived materials. This metasomatism has been generated by a chromatographic fractionation-reaction process, from deep to shallow mantle domains. The percolation of a high-K hydrous magma probably is associated with the upwelling of asthenospheric material through a slab-window, which caused partial melting of oceanic crust and overlying sediments during the Paleocene. The varying intensities of metasomatic imprints recorded by mantle xenoliths from Los Gemelos provide valuable insights into the interaction of slab-derived materials near the lithosphere-asthenosphere boundary, at a distance of ∼600 km from the Andean volcanic arc.

Mobility and fractionation of rare earth elements during black shale weathering: Implications from acid rock drainage and sequential extraction study

Black shale is a type of sedimentary rocks that are enriched in rare earth elements (REEs). It is of both economic importance and environmental significance to understand REE mobility during black shale weathering. The present study approaches to this by analysing REEs in acid rock drainage (ARD) from black shale weathering system, fresh and weathered black shales, soils derived from black shales, and sequential extractants from black shales at Dongping town in Hunan province (China). Results showed that REEs had variable high concentrations in ARD as shown by total REE + Y (∑REY) concentrations from 162 to 4074 (μg/L). REEs in ARD displayed hat-shape NASC-normalized patterns with significant enrichments of middle REEs (MREE) relative to light REEs (LREE) and heavy REEs (HREE), and had significant negative Ce (Ce/Ce⁎ = 0.6) and positive Y (Y/Y⁎ = 1.5) anomalies. MREE enrichment in ARD could be evaluated using MREE/MREE⁎ values, which varied from 1.43 to 1.81 with a mean of 1.65, distinctly higher than those of whole rocks (around 1.0). 1 M HCl extraction results suggested that REEs were integratedly mobilized during shale weathering, while six-step extraction studies identified that REEs in ARD resulted from exchangeable and Fe-oxide fractions with MREE and HREE enrichment in shales respectively. MREE in exchangeable and HREE in Fe-oxide fractions were preferentially released during weathering, as illustrated by plots of MREE/MREE⁎ against HREE/LREE ratios of ARD and six-step extractants. Therefore, geochemical processes for REE mobility during black shale weathering included integrated mobilization and preferential release. Integrated REE mobilization resulted from the dissolution of REE-bearing minerals and oxidation of sulfides. Preferential REE release resulted from acid fluids produced by sulfide oxidation during weathering. Thus, a new model was proposed for interpreting geochemical processes of REE mobility during black shale weathering, and for understanding REE distribution in ARD from natural and anthropogenic systems.

Enhanced enrichment of rare earth elements during pedogenesis under subtropical climate

Rare earth elements (REE) are crucial strategic resources, and weathering-crust rare earth deposits are one of the primary sources. To systematically understand the geochemical behavior (e.g., enrichment and leaching) of REE in soils (or weathering crusts) formed from diverse parent rocks under varying climatic conditions, 171 soil profiles (weathering crusts) developed from three main types of parent rocks (granite, basalt, and carbonate rock) worldwide were studied. Granite shows the highest concentration of rare earth elements at 264 (interquartile range (IQR): 278) ppm, 171 (IQR: 151) ppm and 11.9 (IQR: 36.4) ppm in basalt and carbonate rock, respectively (median test: p &lt; 0.05). The median REE values within the soil profiles were significantly different (median test: p &lt; 0.05), with the concentration of 318 (IQR: 441) ppm, 267 (IQR: 217) ppm and 207 (IQR: 417) ppm in soils derived from granite, carbonate rock, and basalt, respectively. Principal component analysis (PCA) and Linear mixed-effects models (LME) revealed that soils developed from granite and basalt inherit the mineral characteristics of their parent rocks, with REE concentrations primarily influenced by the REE content of the parent rock and climate. In contrast, the REE concentrations in soils developed from carbonate rocks are predominantly controlled by climate. LME and correlation analysis indicates that the enrichment of REE (Q REE ) shows a trend of initially increasing and then decreasing with rising temperature and precipitation, due to variations host clay minerals. The greatest enrichment occurs in the subtropical region (mean annual temperature (MAT) = 15 ̶ 23 °C; mean annual precipitation (MAP) = 1000 ̶ 2000 mm); weathering-crust type REE deposits are primarily found in the subtropics.

Enhanced deep-water circulation facilitated rare earth elements enrichment in pelagic sediments from the northwestern Pacific Ocean

The lack of knowledge about the enrichment mechanism of rare earth elements and yttrium (REY) in deep-sea sediments is impeding the development of theories and exploration strategies for pelagic REY-rich sediments. Ocean circulation variability seems to be crucial in enriching REY in pelagic sediments, which, however, has not been extensively studied. Here, we examined the Pb-Nd isotopic signals of bottom water recorded by the authigenic ferromanganese oxyhydroxide fractions, as well as the Mn/Al and Mn/Ti ratios of bulk samples from a well-dated sediment core in the northwestern Pacific Ocean. These proxies consistently indicate that enhanced deep-water circulation occurred in the study area at ∼11.5–9.5 Ma, which was most likely to be caused by changes in the flow path of bottom currents. The age of this distinct event consists with the forming age of highly REY-rich sediments. We propose that enhanced deep-water circulation in seamount areas could increase the flux of micronodules and fish debris into the pelagic sediments, facilitating the scavenging of REY from seawater. Our findings establish a connection between enhanced deep-water circulation and the enrichment of REY in pelagic sediments.

Recycling of terrigenous sediments recorded in late Permian-early Triassic Fe-rich intrusions from Yunkai Massif, South China

The origin of Fe-rich intrusion remains debatable regarding the respective role of magmatic evolution and Fe enrichment in the source. Here, we report detailed mineral and bulk-rock geochemistry of Permian-Triassic (251–250 Ma) mafic intrusions from the Tengxian area in Yunkai Massif, South China. These rocks consist of hornblende norites, show Fe-rich affinities with high FeO*(FeO* = FeOt / (FeOt + MgO) in weight ratio, >0.8, based on total iron oxide in the rock), and exhibit significant enrichment in large ion lithophile elements (LILEs) and light rare earth elements (LREEs) but depletion in Sr and high field strength elements (HFSEs), resembling subduction-related magmas. In addition, they show remarkable features that include very high δ18O values in zircon (δ18O = 8.8–10.6 ‰) and apatite (δ18O = 8.7–10.8 ‰), and extremely enriched SrPb [e.g. 87Sr/86Sr(i) = 0.7181–0.7196, 207Pb/204Pb(i) = 15.77–15.78, 208Pb/204Pb(i) = 38.95–39.05] and nonradiogenic NdHf isotopic compositions [e.g. εNd(t) = −11.1 ~ − 10.1, εHf(t) = −8.8 ~ −7.3] in bulk rocks. These characteristics distinguish the Tengxian norites from modern arc basalts and subduction-related magmas in the Paleo-Pacific Tectonic Domain. Instead, they are isotopically similar to Cenozoic Tibetan and Mediterranean potassic to ultrapotassic rocks in the Tethys Tectonic Domain. Regardless of variable influence by orthopyroxene and plagioclase accumulation, the intrinsically low SiO2 and high FeOt and Fe/Mn ratios in these rocks were likely attributed to significant contribution of a Fe-rich mantle component such as Si-poor pyroxenite, which might have formed through crystal accumulation of mafic magmas at mantle conditions. The highly evolved Sr-Nd-Pb-Hf isotopic signatures and very high δ18O values in zircon and apatite required substantial (10–20 %) involvement of recycled crust in the mantle source. The combined mineral and bulk-rock geochemical data suggest that the parental magmas for the Tengxian norites originated from a metasomatized mantle wedge through addition of terrigenous sediment-derived melt following the subduction of Paleo-Tethys Ocean beneath the Yunkai Massif.

Surface complexation of rare earth elements on goethite in sea-floor hydrothermal environment: Insight from first principles simulations

Deep-sea mud shows tremendous resource potential for rare earth elements (REEs) and its formation is closely associated with sea-floor hydrothermal activities. Iron (oxyhydr)oxides link the sources and sinks of REEs in sea-floor hydrothermal systems. However, the complexation mechanisms of REEs on iron (oxyhydr)oxides have not been well understood yet. In this study, by using the first principles molecular dynamics technique, we first calculated the pKa’s of surface groups on goethite (110) surface at elevated temperatures relevant to sea-floor hydrothermal systems and then evaluated the complexation structures and free energies of REEs on goethite (110) and (010) surfaces using the method of constraint by taking Sc3+, Y3+, and La3+ as model REE cations. The results show that REE complexation occurs in mildly acidic to neutral conditions. The most thermodynamically stable complexes of REEs are bidentate complexes on two neighboring FeOH sites on goethite (110) surface and tridentate complexes on two neighboring FeOH sites plus one Fe2OH site on goethite (010) surface. Sc3+ complexes match the goethite lattice and can be incorporated into the lattice. The stabilities of REE complexes increase with the distance from hydrothermal vents. Complexation of Y3+ is less favored on goethite compared to other REEs whereas Sc3+ prefers complexation on goethite (010) surface and La3+ exhibits similar stabilities on both (010) and (110) surfaces. The derived atomic level complexation mechanisms would be helpful for the interpretation of experimental data and the prediction of REEs’ behavior in the sea-floor. The findings presented here provide valuable insights into REEs fractionation and enrichment in deep-sea muds.

Ages and geochemistry of garnet reveal multi-types of iron-copper mineralization in the Eastern Tianshan, NW China

The Aqishan-Yamansu Fe-Cu-Au metallogenic belt in the Eastern Tianshan, NW China, hosts numerous Fe and Fe-Cu deposits that may have different genetic models, such as volcanic-hosted and skarn/IOCG types. These variations in genetic models are attributed to whether the mineralization is associated with hydrothermal activity related to volcanic or intrusive rocks. This study primarily focuses on garnets formed during the early skarn alteration in the Shuanglong Fe-Cu and Shaquanzi Fe deposits within this belt. Garnets from the Shuanglong deposit can be divided into two types and exhibit general homogeneity, with SL-Grt1 being Fe-rich and subsequently replaced by the Fe-poor SL-Grt2. Garnets from the Shaquanzi deposit display complex zonation patterns, SQZ-Grt1 show core–oscillatory zoned rim and SQZ-Grt2 show core–mantle–oscillatory zoned rim. Laser-ablation inductively coupled plasma-mass spectrometry (LA-ICP-MS) dating of SL-Grt1 and SL-Grt2 produced lower intercept 206Pb/238U ages ranging from 318.0 ± 6.4 Ma to 303.7 ± 16.4 Ma, coinciding with the multi-stage granite occurrence. In contrast, SQZ-Grt1 and SQZ-Grt2 yielded ages between 328.0 ± 2.6 Ma and 320.4 ± 1.7 Ma, corresponding to the timing of the hosted rhyolite. SL-Grt1 show light rare earth element (LREE) enrichment, and low concentrations of high field strength elements (HFSE), such as V and Zr, and appears to have formed rapidly within an open system. Conversely, SL-Grt2 is characterized by heavy rare earth element (HREE) enrichment and elevated HFSE contents, which could be formed slowly in a closed system. The variable composition in the SQZ-Grt1 and SQZ-Grt2 record cyclical changes in fluid kinetics (vigorous fluid flow vs. fluid stagnation). The cyclical zones in SQZ-Grt2 with HREE and HFSE concentrations below the detection limit indicate multiple inputs of external seawater. The distinct characteristics between Shuanglong and Shaquanzi garnets may reflect the difference between the single magma intrusion and complex volcanic activity. Combining previously published chronological data, this study elucidates a transition from the Middle Carboniferous volcanic-hosted Fe deposits (335–320 Ma) to the Late Carboniferous intrusion-related skarn or IOCG type Fe-Cu deposits (310–300 Ma) in the Aqishan-Yamansu belt.

Synchronous felsic volcanism and carbonate sedimentation as a setting for VMS deposits localization at the Salair terrane, NE Central Asian Orogenic Belt

The Salair terrane located in the northern part of the Central Asian Orogenic Belt (CAOB) contains many epithermal deposits including volcanogenic massive sulphide (VMS) deposits. The host rocks mainly consist of felsic volcanic rocks such as lavas, volcanic breccias and tuffs that associated with thick strata of carbonates. In this study, we present zircon U–Pb ages, whole rock geochemistry, and Nd isotope data from the volcanic rocks, and results of geochemical and isotope (Sr, C, O) studies of carbonates to constrain their age and petrogenesis, and to characterize the tectonic setting. Zircon U–Pb dating reveals that the ore-bearing felsic lavas have age of 519.3 ± 1.9 Ma, while the felsic tuffs have age of 516.0 ± 0.9 Ma. These volcanic rocks are characterized by high SiO2 and Na2O contents, enrichment in light rare-earth elements, remarkable negative Eu anomalies, and pronounced depletion in Nb, Ta, P, and Ti. They have depleted ɛNd(t) values ranging from +4.9 to +6.3, and young two-stage Nd model ages (from 0.82 to 0.64 Ga). The felsic volcanic rocks from the Salair terrane are interpreted as highly evolved I-type magmatic rocks that might be produced by high degree partial melting of juvenile lower crust without a significant contribution of ancient crust and without crustal reworking.Felsic volcanism was accompanied by the formation of thick strata of carbonates. These carbonates are marine limestones with Mg/Ca ratios less than 0.007, δ18O(SMOW) values from 17.1 to 23.8 ‰ and δ13C(PDB) values between –0.9 and +0.9. Their Sr isotope composition varies in a narrow range within 0.70844–0.70859 that interpreted as representing proxy for coeval seawater. These values are consistent with depositional ages of 520–510 Ma and confirms the synchronicity of the formation of carbonates and felsic volcanism. Based on the regional geology and geochemistry, the ore-host rocks of the Salair terrane were formed in the back-arc setting where the marine transgression occurred as a result of graben subsidence. It is important for better understanding epithermal deposits in the northern CAOB and might provide new insights about prospecting the VMS deposits in similar tectonic settings.

1.38 Ga magmatism and the extension tectonics in East Kunlun, northern Tibetan Plateau

Numerous Paleo- to Mesoproterozoic magmatic rocks were emplaced during the assembly, accretion and break-up of the Columbia supercontinent, and are keys to illustrating the supercontinent circle. The geological, petrological, geochronological and geochemical data of the newly discovered meta-felsic and meta-mafic magmatic rocks from the Wulonggou area are presented in this study to shed light on the Mesoproterozoic geodynamic setting of the Central Kunlun Belt and the Qaidam Block. Zircon U-Pb geochronological results indicate that the crystallization ages of the meta-felsic samples are 1385–1376 Ma, and the meta-mafic is 1379 ± 25 Ma (MSWD=0.17). Samples from the meta-felsic unit have SiO2 contents of 68.37–73.03 wt% and belong to the high-K calc-alkaline series. They exhibit similar REE distribution patterns and display enrichment in light rare earth elements (LREES) and negative Eu anomalies. Enrichments in Rb, Ba, Th, U and K, depletion in Nb, Ta, Sr, P and Ti are seen in the primitive mantle-normalized trace element pattern diagram. Magmatic zircons from different meta-felsic samples yield variable εHf(t) values of −8.14 to + 9.37 corresponding to ca. 1.7–2.0 Ga two-stage Hf model ages. Samples from the meta-mafic unit have low SiO2 concentrations of 49.87–50.43 wt%, high contents of Fe2O3T, MgO, CaO and TiO2, and Mg# values of 52–58. They show low total REE concentrations of 19.8–30.4 µg/g, and depletion in LREES, flat HREES distribution patterns with (La/Yb)N of 0.27–0.53 and insignificant Eu anomalies. Flat distribution pattern of high field strength elements (HFSEs) is observed in the primitive mantle-normalized trace element pattern diagram. They display similar immobile elements’ concentrations and distribution patterns, low Ti/Y, Nb/Y, La/Yb, and high Nb/La ratios, comparable with the present-day normal middle ocean ridge basalt. Zircons from the meta-mafic sample have mostly positive εHf(t) values ranging from −0.10 to + 4.10 with a single stage Hf model ages of ca. 1.7–2.0 Ga. The geochemical result implies that the meta-felsic unit was generated by partial melting of the Paleoproterozoic juvenile mafic lower-crustal material with mantle attributions, and the meta-mafic unit was probably from partial melting of the lithospheric mantle. Synthesizing the above evidences, Wulonggou Mesoproterozoic meta-magmatic rocks are a bimodal suite formed in a continental extensional tectonic setting which is probably related to the break-up of the Columbia supercontinent.

Mineralogical Characterization and Geochemical Signatures of Supergene Kaolinitic Clay Deposits: Insight of Ropp Complex Kaolins, Northcentral Nigeria

This study presents the chemical and mineralogical composition of clay deposits and associated rock types within the Ropp Complex in order to assess the influence of parent lithology on the kaolinization, genesis, and utility of the deposit. Representative kaolin samples from E horizons of the weathering profiles and their bedrocks were collected from six sites in the Ropp Complex. Clay mineralogy was determined via the XRD technique, while a geochemical analysis was conducted using XRF, SEM coupled with EDS, and ICP-MS. The results showed that all kaolins dominantly contain kaolinite with a content of 77%–98% except for the AS1 kaolin with only minor kaolinite (20%) but mainly illite (65%). The notably lower crystallinity of kaolinite (HI value of 0.53–1.1) as well as its markedly small grain size is consistent with the formation of kaolinite from intensive chemical weathering of igneous rocks. The AS1 kaolin was probably formed from hydrothermal alteration in the burial stage due to the heating of groundwater by the late volcanism. Mobile trace elements (Sr, Ba, and Eu) exhibited a depletion trend, while immobile elements (Hf, Ta, Th) showed enrichment. The relatively more zirconium in kaolins implies the formation of low-temperature kaolinization. The notably high kaolinite content, accompanied by reasonable levels of Fe2O3 and TiO2, signifies a medium-grade quality. Furthermore, chondrite-normalized rare earth element (REE) patterns exhibit congruent trends in rocks and kaolin samples, indicating a relative enrichment in light rare earth elements (LREEs) alongside a discernible negative Eu anomaly. The abundant kaolinite and silicon–aluminum composition make the kaolins suitable for refractories, pharmaceutics, cosmetics, and supplementary cementitious material (SCM).

The Characteristics and Enrichment Process of Dabu Ion-Adsorption Heavy Rare-Earth Element (HREE) Deposits in Jiangxi Province, South China

Ion-adsorption rare-earth deposits supply over 90% of the global market’s heavy rare-earth elements (HREEs). The genesis of these deposits, particularly HREE deposits, has garnered significant attention. To elucidate the metallogenic mechanisms of HREE deposits, a comprehensive study of the weathering profile of granite was conducted in Jiangxi Province, South China. This study focuses on the following two aspects: the petrogeochemistry of HREE-rich granite and the enrichment and fractionation of rare-earth elements (REEs) during the weathering process. The results suggest that the Dabu granites are a typical peraluminous, high-K, calc-alkaline granite series with high silica content (SiO2: 74.5%–76.4%), relatively low phosphorus content (P2O5: &lt;0.05%), and high HREE content (ΣLREE/ΣHREE: 0.16–0.66). Weathering advances the decomposition of minerals and the release of elements. REEs are mainly fixed in the regolith by scavengers, mainly clays, Fe–Mn oxides, and carbonates, and ΣREE can reach 799 ppm in the B horizon. However, HREEs tend to migrate further and preferentially combine with Fe–Mn oxides and carbonates as compared to LREEs, leading to a significant fractionation of REEs in the regolith (ΣLREE/ΣHREE = 0.2–1.1). Additionally, the differential weathering of REE-bearing minerals and the precipitation of secondary REE-bearing minerals are also vital for REE fractionation.

Elemental Geochemistry and Pb Isotopic Compositions of the Thick No. 7 Coal Seam in the Datun Mining Area, China

Thick coal seams recorded abundant petrological, geochemical, and mineralogical information regarding their formation, which in turn can reflect the characteristics of the coal-forming environments, provenance attributes, paleoclimate, and so on. In order to explore the geochemical and lead isotope characteristics of thick coal seams, the No. 7 coal seam in the Datun mining area, Jiangsu Province of China, was selected as the research object. In this work, 29 samples (including coal, roof, and floor rock samples) were collected from three coal mines in the Datun mining area. Through an analysis of the mineral composition and element geochemical characteristics in the coal samples, the enrichment degree of trace elements and modes of rare earth elements were determined. The genetic mechanism of abnormal enrichment of enriched elements is discussed, especially the modes of occurrence and isotope characteristics of Pb. The results showed the following: (1) The main minerals in the coal samples include quartz, potassium feldspar, plagioclase, calcite, dolomite, pyrite, gypsum, and clay minerals, with clay minerals, calcite, quartz, and dolomite being the most common. (2) The major element oxides in coal mainly include SiO2, Al2O3, Fe2O3, MgO, CaO, Na2O, K2O, TiO2, P2O5, and FeO. In the vertical direction, the variation of SiO2, Al2O3, Fe2O3, MgO, K2O, and FeO in coal samples from the three coal mines is consistent. The average value of Al2O3/TiO2 in the samples of Kongzhuang, Longdong, and Yaoqiao coal mines is 28.09–50.52, which basically locates the samples in the felsic source area, such that the sediment source is considered to be felsic source rock. (3) Elements U, La, Pb, and other elements are more enriched in Kongzhuang coal mine samples; elements Th, U, La, Pb, and other elements are more enriched in the Longdong coal mine samples; and elements Th, U, La, Pb, and other elements are more enriched in the Yaoqiao coal mine samples. Furthermore, W is enriched in Yaoqiao mine samples and is highly enriched in Longdong mine samples. The mining area is generally rich in the elements U, La, and Pb. The distribution curves of rare earth elements in the three mines are inclined to the right, with negative Eu anomalies. The enrichment is of the light rare earth enrichment type. (4) Pb isotope data show that the samples from the three mines are mainly distributed in the orogenic belt and the subduction zone lead source areas, where the upper crust and the mantle are mixed, with individual sample points distributed in the mantle and upper crust lead source areas.

Audio magnetotelluric view of the giant carbonatite-hosted Bayan Obo REE deposit, Inner Mongolia, northern China

As critical minerals in low-carbon economies, rare-earth elements (REEs) are crucial for modern industry, technology, and medicine. The largest known REE resource in the world is the Bayan Obo (BO) deposit in northern China. However, BO features as complicated mineral compositions and has experienced several geological events. As a reuslt, controversy remains about the BO REE genesis and enrichment mechanism, and debates are also ongoing about the controlling structure of this giant deposit. We carried out an multiscale electromagnetism study on BO mineral deposits. The multiscale study consists a microscale on samples, a small scale targeting mineral deposits and a mid scale concerning the mine field. The small and mid scale study were conducted using audio-magnetotelluric (AMT). This study revealed the controlling structure using geoelectrical characteristics. AMT data were acquired from more than 590 stations, and the petro-electromagnetism of several samples was analyzed to understand the geoelectrical features of the ore deposits and their surrounding rocks. The data were interpreted using Bostick transformation and generalized least-squares inversions. We obtained the geoelectrical structure of the BO complex down to a maximum depth of 3500 m, and we present two-dimensional imaging based on the AMT conversion results. The results show that the BO deposit developed at the transition of the high- and low-resistivity geoelectrical structure from south to north. Our AMT results indicate that the tectonic setting of the BO deposit is the transition zone between the rift edge and craton margin slope. The ore geology is presently controlled by the complex slope and the rift remnant, the ore-bearing dolostone in the profiles is Y-shaped. It goes downward from south to north and potentially features a great mineral prospect deep in the BO deposit.