Geochemical Evaluation of Enrichment of Rare-Earth and Critical Elements in Coal Wastes from Jurassic and Permo-Carboniferous Coals in Ordos Basin, China

Laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) was used to determine rare earth element (REE) content of 76 fossil bones collected from the Upper Cretaceous (Campanian) Two Medicine (TMF) and Judith River (JRF) Formations of Montana. REE content is distinctive at the formation scale, with TMF samples exhibiting generally higher overall REE content and greater variability in REE enrichment than JRF samples. Moreover, JRF bones exhibit relative enrichment in heavy REE, whereas TMF bones span heavy and light enrichment fields in roughly equal proportions. TMF bones are also characterized by more negative Ce anomalies and greater U enrichment than JRF bones, which is consistent with more oxidizing diagenetic conditions in the TMF. Bonebeds in both formations show general consistency in REE content, with no indication of spatial or temporal mixing within sites. Previous studies, however, suggest that the bonebeds in question are attritional assemblages that accumulated over considerable time spans. The absence of geochemical evidence for mixing is consistent with diagenesis transpiring in settings that remained chemically and hydrologically stable during recrystallization. Lithology-related patterns in REE content were also compared, and TMF bones recovered from fluvial sandstones show relative enrichment in heavy REE when compared with bones recovered from fine-grained floodplain deposits. In contrast, JRF bones, regardless of lithologic context (sandstone versus mudstone), exhibit similar patterns of REE uptake. This result is consistent with previous reconstructions that suggest that channel-hosted microfossil bonebeds of the JRF developed via the reworking of preexisting concentrations embedded in the interfluve. Geochemical data further indicate that reworked elements were potentially delivered to channels in a recrystallized condition, which is consistent with rapid adsorption of REE postmortem.

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

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

ABSTRACTThe study area is located 4 km east of Haymana, Ankara, Turkey. Major and rare earth element (REE) contents in samples collected from siltstone, carbonaceous claystone, and marl of the Haymana formation in the studied region and their distribution with respect to lithology and correlation relations yield important data on the evaluation of forming conditions of basin. Regarding the abundance of elements in various lithologies, the first and second group elements (SiO2, Al2O3, Na2O, TiO2, P2O5 and Fe2O3, K2O, REE) are more abundant in carbonaceous claystone and siltstone than that in marl, indicating that they are of detrital origin and controlled by clays. The abundance of CaO and TOT/C is lesser in siltstone than that in carbonaceous claystone and marl, implying that they are in marine origin. This is also supported by the correlation of elements. Based on REE abundances, lithologies are ranked in the order of claystone > siltstone > marl, which indicates that clays play an important role in REE enrichment. Correlation of REEs with major elements is indicative of detrital source and association with clay minerals. All the samples are represented by slightly negative Ce anomaly and positive Eu anomaly. Negative Ce and positive Eu anomalies are mostly typically of high oxygenated environments. Since negative Ce anomaly restricts oxygen enrichment to some extent, deposition environment might reflect oxic-anoxic conditions.

Rare earth element behavior in soils and salt pan sediments of a semi-arid granitic terrain in the Western Cape, South Africa

Progress in green and efficient enrichment of rare earth from leaching liquor of ion adsorption type rare earth ores

Rare earth elements (REEs) are crucial strategic resources, and weathering-crust rare earth deposits are one of the primary sources. To systematically understand the geochemical behaviour (e.g. enrichment and leaching) of REEs 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 REEs at 264 [interquartile range (IQR): 278] ppm with 171 (IQR: 151) ppm and 11.9 (IQR: 36.4) ppm in basalt and carbonate rock, respectively (median test: p < 0.05). The median REE values within the soil profiles were significantly different (median test: p < 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 and linear mixed-effects models 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. Linear mixed-effects models and correlation analysis indicate that the enrichment of REEs ( Q REE ) shows a trend of initially increasing and then decreasing with rising temperature and precipitation, due to variations in the host clay minerals. The greatest enrichment occurs in the subtropical region (mean annual temperature = 15–23°C; mean annual precipitation = 1000–2000 mm); weathering-crust type REE deposits are primarily found in the subtropics.

Enrichment of rare earth and radioactive elements concentration in accessory phases from alkaline granite, South Sinai- Egypt

Composition of rare earth elements in settling particles collected in the highly productive North Pacific Ocean and Bering Sea: Implications for siliceous-matter dissolution kinetics and formation of two REE-enriched phases

The Wulu area has an abundance of laterite nickel mineral resources, and based on fluctuations in the chemical value of saprolite limonite zonation, it is evident that further research is required, particularly regarding the presence of REE (Rare Earth Elements) and Scandium in limonite. This study aims to examine the chemical changes of ultramafic rocks under fresh conditions in relation to the enrichment process of laterite elements and their connection to REE, especially scandium. To achieve these objectives, the research was conducted using ED-XRF and ICP-MS methods on several samples representing bedrock and laterite zoning at four locations: Block KBB_1, Block KBB_2, Block KBB_3, and Block KBB_4, to study and investigate the distribution of REE and Sc in nickel laterite. The results indicated that the wehrlite-type ultramafic source found in Block KBB_1 has the highest REE concentration at 0.91 ppm compared to lherzolite and harzburgite rocks. The increase in REE and scandium concentrations occurred significantly during the laterization of wehrlite rocks. REE and scandium concentrations were higher in the limonite zone, with concentrations increasing to 42 ppm for REE and reaching 10.63 ppm for scandium. The presence of bedrock composed of olivine and clinopyroxene minerals of wehrlite composition results in higher REE and scandium contents in the weathering products. This indicates that REE and scandium belong to the lithophile group associated with the presence of iron oxides in laterization. The difference in REE concentration of the ultramafic type is due to an imbalance in the level of laterization, such that the distribution of REE enrichment is inversely proportional; thus, high REE ultramafic types will affect the REE concentration of the laterization results. REE and scandium enrichment are directly proportional to the increase in NiO content, suggesting that REE and scandium can be by-products of nickel laterite and may be utilized in the future.

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.

Economic rare earth element (REE) bearing-heavy mineral accommodation in alluvial deposits (stream sediments) is a well-known process caused by varying rates of weathering and transportation of heavy minerals and sediments, which is significant in geochemical exploration. In the present work, stream sediment samples from Wadi Lethi, Sharm El-Sheikh, were systematically collected. The collected stream sediments were investigated mineralogically and geochemically using collaborative techniques. The separated heavy fractions have been analyzed for trace elements and REE. Identified important heavy minerals are monazite, sphene, apatite, garnet, xenotime, magnetite, ilmenite, hematite, with subordinate riebeckite, epidote, and chlorite. Geochemical analyses of the separated heavy minerals revealed an abnormal concentration of total REE that was more than eleven times higher than in the studied area's granitic rocks. The REE trends of these minerals depicts the enrichment of light rare earth elements (LREE) and the depletion of heavy rare earth elements (HREE), as well as the typical negative Eu anomaly found in granitic magma.

Distribution and potential contamination assessment of rare earth elements (REE) in Indonesian volcanic soil

Behaviour of rare earth and high field strength elements during hydrothermal alteration of meta-turbidites associated with mesothermal gold mineralization in central Victoria, Australia

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