Rare Earth Element Exploration Research Articles

Detecting rare earth elements using EnMAP hyperspectral satellite data: a case study from Mountain Pass, California

Rare earth elements (REEs) exhibit diagnostic absorption features in the visible-near infrared region, enabling their detection and identification via spectroscopic methods. Satellite-based remote sensing mapping of REEs, however, has not been attainable so far due to the necessity for high-quality hyperspectral data to resolve their narrow absorption features. This research leverages EnMAP hyperspectral satellite data to map REEs in Mountain Pass, California—a mining area known to host bastnaesite-Ce ore in sövite and beforsite carbonatites. By employing a polynomial fitting technique to characterize the diagnostic absorption features of Neodymium (Nd) at ∼740 and ∼800 nm, the surface occurrence of Nd was successfully mapped at a 30m pixel resolution. The relative abundance of Nd was represented using the continuum-removed area of the 800 nm feature. The resulting map, highlighting hundreds of anomalous pixels, was validated through laboratory spectroscopy, surface geology, and high-resolution satellite imagery. This study marks a major advancement in REE exploration, demonstrating for the first time, the possibility of directly detecting Nd in geologic environments using the EnMAP hyperspectral satellite data. This capability can offer a fast and cost-effective method for screening Earth’s surfaces for REE signature, complementing the existing exploration portfolio and facilitating the discovery of new resources.

Controls on rapid rare earth element enrichment in sediments deposited by a continental-scale river system

Clay-hosted rare earth element (REE) deposits, generally considered products of extended subtropical weathering of REE-rich igneous protoliths, are a critical source of REEs globally.The Koppamurra deposit of southeast South Australia, in contrast, is developed in Pleistocene lacustrine clays overlying a REE-poor marine limestone. Here we examine the REE + Y (REY) sources and enrichment mechanisms of this unusual setting. We find that the greatest REY enrichment (up to 5000 ppm) occurs in lacustrine clays at the base of a ∼1–2 m thick contact zone with the underlying limestone. This zone features an increased proportion of leachable REYs (>50 %), increased smectite abundance and a sharp increase in pH from ∼5.0 to ∼8.3. Co-variation of HREEs with a suite of clay-specific elements demonstrates that HREEs are hosted mainly by Fe-rich smectite, with separate sorbed vs structurally bound HREE pools that are of similar magnitude. LREEs are mainly hosted in secondary LREE carbonates, these are preferentially intergrown with smectite but are only rarely present in kaolinite domains. Cerium occurs mainly as cerianite. The narrow range and overlapping εNd of samples within and above the REY enriched zone suggests that enrichment is related to internal redistribution within the clay unit. The clays are isotopically incompatible with local igneous or metasedimentary rocks, but 87Sr/86Sr and εNd isotopic fingerprinting shows that they were deposited by the Murray River, Australia’s largest river system. Murray sediments are enriched in REY due to the presence of material eroded from the Lachlan Orogen granites of southeast Australia. Deposition of these sediments occurred in a coastal lacustrine setting analogous to the modern-day Coorong, with tectonic uplift and shoreline progradation allowing the onset of subaerial weathering ∼1–2 Mya. We propose that vertical and lateral solute transport allowed for the concentration of REEs in local depressions in the karst-weathering surface which separates the limestone and overlying clay, facilitated by water table oscillation and pore water redox cycling driven by seasonally contrasted rainfall. Poor soil drainage, evaporative concentration of soil waters and alkaline pH adjacent to the limestone immobilized REEs in secondary carbonates and Fe-rich smectite. Our findings illustrate that REE mobilization and enrichment in clay deposits can occur more rapidly, over a larger area and in a broader range of host phases and geologic settings than is currently appreciated, with important implications not only for REE exploration but also for the use of REEs as tracers in the Earth Sciences.

Trust in numbers: Serious numbers and speculative fictions in rare earth elements exploration.

In the early 2010s, a spectacular fall in prices for a class of mineral commodities called the rare earth elements (REEs) and the collapse of hundreds of new exploration companies made clear the fragility of the high-risk markets around these companies and the strategies of legitimation that supported them. New regulatory processes built around technical disclosures generated vast stores of geotechnical data. Rather than generating trust among market actors, however, these processes dramatically altered the temporalities of global extraction and energized unruly narrative spaces. In their efforts to keep mineral claims active and companies afloat, REE-focused exploration experts have struggled to navigate different arenas of discussion while holding their respective logics in tension. Drawing on ethnographic fieldwork with exploration geologists and promoters, this article examines how experts federate flows of 'serious' and 'speculative' information in both carefully regulated reports and rumor-filled online forums. Such spaces are organized by aesthetic conventions and social criteria for establishing persuasiveness-forms that STS scholars have long analyzed as literary technologies. Rather than helping to secure experts' authority, however, I argue that the diverse literary technologies that now dominate exploration promotion and finance work have radically redistributed interpretive roles. In their struggles to mediate senses of 'crisis' endemic within venture markets, exploration experts must enact the ideals undergirding new regulatory requirements even as they learn to defer to the speculative musings of others.

Critical raw materials associated with the lateritic bauxite and red mud in West Kalimantan, Indonesia

The Western Indonesia Bauxite Province in Kalimantan is a lateritic bauxite region with a complex history and poorly known sustainable metal contents within the bauxite residue. Bauxite residue produced using the Bayer process contains, notably, scandium. We present new geochemical, mineralogical and geological data from the lateritic bauxite and red mud from the active mine and deposit, which allow us to investigate the behaviour of critical elements during weathering. The geochemical analysis and translated isocon results have shown that the content of scandium in red mud is higher than the average concentration of crustal rocks and is concentrated in the ferrite layer and bauxite residue. A positive correlation between the existence of iron oxyhydroxide mineral in the residual iron-rich layer and red muds with the rare earth elements (REEs) and scandium concentrations may be interpreted as a scavenging effect of mobile REEs. The weathering and leaching processes in bauxite allows the adsorption of the trivalent scandium cation (Sc 3+ ) on goethite and are followed by ionic substitution with other trivalent cations in crystals of hematite. The study illustrates the importance of understanding processes during weathering and laterization for geochemical processes and REE exploration in tropical areas. Supplementary material: Material A, (A) Mineralogical profile of the bauxite, ferrite, and tonalite in Tayan and Mempawah, (B) Ternary diagram of bauxite and their parent rocks, (C) Trace element ratios in bauxite; Material B, Spearman's correlation rank of bauxite and associated rocks from Tayan mine ( n = 35); Material C, (A) XRD patterns of representative samples from the Tayan mine and Mempawah deposit, West Kalimantan, (B) Typical normal (left) and continuum (right) removed reflectance spectral curves of samples are available at https://doi.org/10.6084/m9.figshare.c.6689139 Thematic collection: This article is part of the Geochemical processes related to mined, milled, or natural metal deposits collection available at: https://www.lyellcollection.org/topic/collections/geochemical-processes-related-to-mined-milled-or-natural-metal-deposits

GEOCHEMICAL AND MAGNETIC CHARACTERISTICS OF PLACER GOLD DEPOSITS FROM CENTRAL KALIMANTAN, INDONESIA

Massive tailings have resulted from the extensive use of placer deposits in Central Kalimantan, Indonesia, by artisanal and small-scale gold mining (ASGM) activities. Recently, the placer deposits and their tailings have been exploited for heavy minerals. In this study, geochemical and magnetic analyses were carried out on these deposits to identify the prospect of REE (rare earth element) exploration in the materials already collected by ASGM activities. Samples were collected from ten different locations. For each location, two different fractions were prepared for analyses, i.e. the heavy mineral (HM) fraction and the panned (M60) fraction. All HM and M60 samples were subjected to magnetic susceptibility measurements, but only representative samples were subjected to x-ray fluorescence (XRF) measurements (for Si, Ti, Fe, Zr, and Al) and to inductively coupled plasma-emission spectroscopy (ICP-OES) measurements (for Eu, Tb, Dy, and Sc). The results showed that the concentrations of major elements (Ti, Fe, Zr, and Al) vary significantly from deposits along one river to another, while the concentration of Si is rather similar. Compared to M60 samples, the HM samples have higher concentrations of Ti, Fe, Zr, Al, and Sc, implying that the sluice-box separation enhances the concentration of valuable minerals. Magnetic susceptibility is found to be correlated with Fe and Sc concentrations, confirming the potential use of magnetic measurements as a complementary tool for Fe and Sc exploitation in placer deposits. It is believed that both the source rocks and the sedimentary settings of these deposits determine whether certain elements (Sc, Fe, and Zr) are present or absent in Central Kalimantan placer deposits. The prospect of exploring and exploiting Sc in these placer deposits might augment the ASGM activities in Central Kalimantan.

The trace element chemistry of quartz in carbonatite-related REE deposits: Implication for REE exploration

Quartz is a common gangue mineral in many magmatic-hydrothermal ore deposits (e.g., porphyry, epithermal and skarn deposits) and its trace element composition was widely used to constrain ore genesis. Quartz is also a common phase in carbonatite-related rare earth element (REE) deposits, but its geochemical characteristics and significance for ore genesis have not previously been documented in this environment. In this contribution, we report in-situ LA-ICP-MS trace element compositions of quartz from seven carbonatite-related REE deposits, namely the Maoniuping, Lizhuang and Dalucao deposits in the Mianning-Dechang REE metallogenic belt, SW China and the Miaoya, Taipingzhen, Huangshuian and Huanglongpu deposits in the Qinling REE metallogenic belt, Central China. Rare earth element mineralization in these deposits is associated with well-developed hydrothermal systems in which the dominant REE minerals, bastnäsite, parisite, and monazite, are intergrown with aegirine-augite, arfvedsonite, calcite, fluorite, barite, and quartz. The results show that quartz grains from the carbonatite-related REE deposits are characterized by low budgets of trace elements, of which Al is generally less than 50 ppm whereas others are generally less than 10 ppm. In general, the trace element concentrations in quartz from different deposits are similar (the total concentration is commonly <50 ppm), and are distinguishable from those of quartz in other magmatic-hydrothermal systems. The low concentration of trace elements in carbonatite-related REE deposits is controlled by the unusual nature of carbonatitic magmas and their derived fluids, and thus can be used for defining the affinity of hydrothermal REE systems that are of unknown origin. Significantly, the trace element chemistry of quartz samples collected from a cross-section in the open pit of the Maoniuping REE deposit displays a systematic spatial variation such that the concentrations of Al, Ti, Na, and K decrease with increasing distance of the samples from carbonatites. This spatial variation correlates well with the variation of physio-chemical conditions during the evolution of ore-forming fluids. This implies that the geochemistry of quartz can be used as a vector detecting the concealed carbonatite intrusions in carbonatite-related REE deposits.

Targeting REE deposits associated with carbonatite and alkaline complexes in northeast India

Rare earth elements (REEs) are considered critical metals globally. About 62% of the global resources of REEs occur associated with carbonatites and alkaline complexes. However, the entire production of REEs in India currently comes from monazite-bearing beach sands, although a variety of REE enriched source rocks, particularly carbonatites and alkaline complexes occur in different parts of the country. There is, therefore, a significant potential in the county for new REE deposit discoveries associated with carbonatites and alkaline complexes. This paper describes a generalised carbonatite-alkaline complex related REE mineral systems model and applies a knowledge-driven model to demarcate REE exploration targets in the Karbi-Meghalaya plateau, NE India. The main components of the mineral systems are (1) pockets of metasomatised subcontinental lithospheric mantle (SCLM) which form fertile source regions for REE-bearing fluids; (2) extensional geodynamics; (3) permeable lithosphere architecture for tapping REE-enriched fluids from SCLM and focusing them to near-surface levels, and (4) a post-emplacement tectonic regime that preserves the deposits. Spatial proxies representing each of these components are mapped and integrated using fuzzy inference system (FIS) to identify prospective targets. Systemic and stochastic uncertainties associated with the model were quantified to aid target selection and further work.Main recommendations of this exercise are the following: (1) project-scale ground exploration for the Sung valley and Jasra complexes; (2) further regional-scale data collection for the Mikir Hills in the areas surrounding Samchampi and Barpung Complexes and around the swarms of dykes in the Garo Hills around Swangkre; (3) follow-up exploration in the areas north of Silchar and south of Nongstoin and (4) detailed geochemical sampling and surface or air-borne radiometric surveys for the Mawpyut Ultramafic Complex.The REE-mineral-systems model and the workflow demonstrated in this article could be used for targeting REE deposits in geologically similar terrains worldwide.

Distinct Depositional Environments Of Two Internal Reference Materials With Marine Sediment Matrix From Nearby Bangka Island

Internal reference materials are generated by laboratories to overcome the high cost and limited matrix of certified reference materials (CRM). Rare earth elements (REE) are strategic metals which is used in modern technology and explored within different matrices. Rare earth elements exploration surely needs appropriate reference materials for accurate interpretation. The current study aims to explain internal standard reference materials generation of marine sediment matrices from nearby the tin Bangka Island, especially the rare earth elements character, to overcome the CRM dependency. The first sample was taken with a dredger while the second one using a suction vessel. Repeated samples measurements were done by applying inductively coupled plasma - mass spectrometry (ICP-MS) from the Center for Geological Survey Indonesia for repeatability tests. The samples were analyzed in another certified laboratory in Indonesia using the same device for reproducibility assessment. The two candidates should be deposited in different environments with different influx material due to their distinct rare earth elements characters. Most of the analytes’ contents are suitable to be set as internal reference material values according to acceptable repeatability and reproducibility evaluations. The internal reference materials are ready for studying suitable matrices in the future.

ІДЕНТИФІКАЦІЯ ТА АНАЛІЗ СТРУКТУРНО-ТЕКТОНІЧНИХ ОСОБЛИВОСТЕЙ ТЕРИТОРІЇ НА ОСНОВІ ЛІНЕАМЕНТНОГО АНАЛІЗУ: ПРИКЛАДИ ГЕОМОДЕЛЮВАННЯ ДЛЯ ТЕРИТОРІЇ КАНАДСЬКОГО ТА УКРАЇНСЬКОГО ЩИТІВ

Nowadays, rare earth elements (REEs), which belong to the group of rare metals, are considered worldwide to be strategic critical raw materials and are extremely important for the economic development of any country. Various methods and approaches are used for prospecting and exploration of deposits of these critical metals; among which the methods of 3D geological modeling are currently prioritized, which allow a comprehensive analysis of the structural features of potentially promising areas as well as individual deposits. One of the methods used for REE exploration is structural mapping combined with geological terrain analysis, including structural lineament analysis. The latter is considered an important geological tool for identifying the primary and secondary structural and tectonic features of our study areas of investigation. The objectives of the present research work are: 1) to identify structural lineaments within two studied areas – the Alces Lake area (Northern Saskatchewan, Canadian Shield) and the Western Azov region (Azov block of the Ukrainian Shield) using automated and manual approaches, 2) to compare the results obtained for both areas, and 3) to discuss interpretation/conclusions over the overall suitability of the method for the exploration purposes. In the current research, we conducted the extraction and geospatial analysis of linear features and their tectonic interpretation. During the modeling process, remote sensing and geostatistical methods were used to analyze topographic, geological and geophysical data. As a result, the main structural lineament trends for the two studied areas were identified and structural-tectonic criteria for the formation and localization of deposits of rare earth elements were determined/proposed.

Petrogenesis of Pre-Tertiary A-Type Granitoid in Jambi Area and its Implications of Rare Earth Element Potential on Main Range Sumatra Belt

Granitoid rocks are one of the main sources of rare earth elements (REE). This makes granitoid characterization become important in the early stages of REE exploration. Almost all granitoids in Indonesia have been mapped. However, more detailed granitoid studies in Indonesia are still focused on Bangka and Belitung granites (tin belt granite). In contrast to Bangka and Belitung granites, studies related to petrogenesis and granite characteristics on the mainland of Sumatra Island (Sumatra Main Range) are rarely done, such as granitoid in Jambi area. The aim of this study is to determine the characteristics of the Pre-Tertiary granitoids located in the Tigapuluh and Duabelas Mountains, Jambi. The Tanjungjabung Barat granitoid represent the Tigapuluh Mountains area while the Sarolangun granitoid represent the Duabelas Mountains area. These two granitoids interpreted to be Triassic to Jurassic in age. Granitoid characteristics include petrological and geochemical characters. This study also focuses on the petrogenesis of Pre-Tertiary granitoid and its implications for the abundance of REEs. Megascopic observation, petrographic, and geochemical analysis are done in this study. Geochemical analysis was done at the Center of Geological Survey Laboratory, Bandung using the ICP-MS Thermo Icap-Q and XRF ADVANT XP Thermo ARL9900 instruments. Based on megascopic and petrographic observations, both of the granitoids are classified as granite. Geochemically, these two granitoids show the character of A-type granite which is formed in the post-collision environment, and derived from the crustal melting with ferrous alkalic to alkali-calcic peraluminous affinities. This crustal melting happened due to the collision of the Sibumasu Block with Indochina resulting in crustal thickening and crustal melting. The magma then contaminated effectively in the rift environment due to the subduction roll-back of Meso-Tethys in the Late Triassic. Subduction in the West Sumatra also play roles in the genesis and it is shown by the geochemical character of the Sarolangun granitoid. Effective contamination derives the characteristics of A-type granite so that the REE content in both granites are abundant. The abundance of REE is indicated by the presence of the allanite, monazite, apatite, zircon, and titanite. The REE concentration of the Sarolangun granitoid reaches 330 ppm, while the Tanjungjabung Barat granitoid reaches 261 ppm. The REE concentrations of A-type granitoid in Jambi then compared with A-type granitoids from the world and showed relatively the same REE concentrations. The REE concentrations of these granitoids are also higher than the other type granitoids in Indonesia. However, the REE concentrations of Jambi granitoids are similar to the fractionated S-type granite in Bangka. With a recent study showing the presence of A-type granitoid in Sarudik (North Sumatra) and Bukit Batu (South Sumatra), the A-type granitoid in this study indicates the existence of A-type granitoid belt in the Sumatra Main Range. This belt will have a high abundance of REE concentrations and potentially become the source for REE deposits. The author hopes that this study could improve the understanding of tectonic in Sumatra and suggestion for REE exploration in the area.

Petrology of weathering materials developed on granites in Biou area, North-Cameroon: implication for rare-earth elements (REE) exploration in semi-arid regions

Due to the increasing demand resulting from the use of REE in many fields of human life, a weathering profile developed on granites in the semi-arid region of Biou area (North-Cameroon) has been characterized for rare-earth elements (REE) exploration. The mineralogical compositions of weathered materials were revealed by X-ray diffraction (XRD). X-ray Fluorescence (XRF) and Inductively Coupled Plasmas-Mass Spectrometry (ICP-MS) have been used to determine the geochemical composition of granites and the overlying weathered materials. The S-type and peraluminous granites are constituted by quartz, orthoclase, microcline, plagioclase, biotite, muscovite, pyroxene and opaque minerals. Accessory minerals are probably responsible for the interesting contents in REE + Y and some trace elements (e.g., Zr, Zn, Ba, Rb). The weathering profile show from the bottom to the top: (i) saprolitic horizons; (ii) lower loose clayey horizon; (iii) iron duricrust horizon; (iv) upper loose clayey horizon; (v) and organo-mineral horizon. Some weathered rock fragments remain in the loose clayey and organo-mineral horizons. The mineralogical composition of the weathering materials is dominated by illite, muscovite and feldspar. The low weathering degree of the materials is justified by the climatic and reducing conditions. The large ion lithophiles and ferromagnesian elements (Mg, Fe, V, Cu, Co, Cs Cr, Ni, Sc and Li) which are supposed to be mobile are so much accumulated in the weathering materials. REE show very low degree of fractionation in weathering profile due probably to the lack of good drainage. The whole weathering materials shows high REE + Y contents as its parent rock. Geochemical mass balance and enrichment factor reveal that REE, especially light REE, are so much enriched in the iron duricrust horizon (ion-adsorption REE deposit type). Some heavy REE are also enriched in the lower loose clayey horizon. This first survey has revealed that the weathering materials developed on granites in Biou area are favorable for further REE exploration.

Detecting REE-rich areas in heterogeneous drill cores from Storkwitz using LIBS and a combination of k-means clustering and spatial raster analysis

This paper presents a novel approach to calculate matrix-matched intensity limits for the spatially resolved detection of rare earth element (REE) enrichments in highly heterogeneous geological material from the Storkwitz carbonatite based on scanning Laser Induced Breakdown Spectroscopy (LIBS). A drill core from the Storkwitz carbonatite was mapped in detail with a LIBS drill core scanner. For reference purposes, μ-EDXRF was applied for qualitative REE detection, and a microprobe was used for quantitative REE analysis.Microprobe analysis of thin sections verified the existence of rare earth elements and revealed an accumulation of REEs around mineral rims. Microprobe measurements also revealed that the main carrier of rare earth elements in the analysed drill core are REE-carbonates with contents as high as 24.4 wt% for Ce, 15.4 wt% for La, and 9.2 wt% for Nd. Apatite and pyrochlore are carrier for rare earth elements as well, however, with significantly lower concentrations of Ce (1.0 wt%), La (0.3 wt%), and Nd (0.3 wt%).K-means clustering was applied on the LIBS mapping to separate classes that show similarities in chemical composition. The classes represent carbonates, silicates, and rock matrix, respectively. According to the microprobe results, most REE-carbonates were found to be related to elevated porosity or microfractures in the rock matrix, forming very thin rims of idiomorphic and hypidiomorphic minute crystals and rarely dense aggregates around exposed minerals and fractured rock fragments. Therefore, a buffer zone calculation was performed on the distinct mineral classes to extract pixel belonging to mineral rims only. Rims without any enrichment in rare earth elements were then used to calculate matrix-matched intensity limits for REE enrichments. Based on the observed similarity in chemical composition for rim pixel and rock matrix pixel, this intensity limit could be transferred to all pixels belonging to the rock matrix.Based on the calculated intensity limits for La, 1.4 area % of the sample was found to be enriched in REE-carbonates. This result was validated qualitatively by comparing it to a μ-EDXRF mapping of the same sample. Optical comparison showed good agreement and pixel counting confirmed similar zones of enrichment. The results reveal that La enrichments in REE-carbonates are reliably detected with LIBS. A mass balance calculation has shown that about 88% of the REE enrichments in the investigated drill core seem to occur as pure REE-carbonates. The fast detection of drill core areas that are enriched in REEs makes LIBS a viable addition to the currently used methods in REE exploration.

Geochronology, mineral chemistry and genesis of REE mineralization in alkaline rocks from the Kohistan Island Arc, Pakistan

Alkaline igneous-related rare earth element (REE) deposits constitute a major global economic resource of REE. However, our understanding of their geodynamic settings and magmatic-hydrothermal processes remains uncertain. Here, we present an investigation of petrography, geochronology and mineral chemistry of newly discovered REE mineralization in the alkaline syenite and pegmatite from the Kohistan Batholith in the Kohistan Island Arc, Pakistan. The pegmatite contains abundant chevkinite and monazite (up to 10–35% in volume), which formed from crystallization of a REE-oversaturated evolved melt and are the main REE-bearing phases. U-Th-Pb isotopic dating of zircon from the syenite yields the emplacement age of 31.2 ± 0.3 Ma, which closely matches the ages of zircon and monazite from the pegmatite (30.1 ± 0.3 Ma and 30.9 ± 0.3 Ma, respectively). Zircons from the syenite and the pegmatite have similar ɛHf(t) values, ranging from + 0.2 to + 2.5, indicating that the syenite and the pegmatite are co-magmatic in origin. The alkaline magma likely formed by partial melting of the enriched lithospheric mantle induced by the asthenospheric upwelling, which was related to slab break-off at the post-collisional stage following the collision of the Kohistan Island Arc with the Indian Plate. Zircons show the evolutional trend in trace element compositions from the syenite to the pegmatite, marked by increases in REE, Hf, Y, U, volatiles and fo2. These changes reflect prolonged fractional crystallization processes of the alkaline magma, which were responsible for the REE enrichment in the residual pegmatitic melt. Post-collisional alkaline magmatic rocks are widely distributed in many places along the Tethyan orogenic belt. These observations suggest that these post-collisional alkaline rocks may be good targets for REE exploration.

Mineralogical and Geochemical Characteristics of Lithium and Rare Earth Elements in High-Sulfur Coal from the Donggou Mine, Chongqing, Southwestern China

Coal and coal by-products are considered as the potential raw materials for critical elements (e.g., rare earth elements, Li, Ga, Ge, etc.), which have attracted much attention in recent years. The purpose of this study is to investigate the mineralogical and geochemical characteristics, and controlling geological factors of lithium and rare earth elements in the Lopingian (Wujiaping Formation) coal from the Donggou Mine, southeastern Chongqing Coalfield, China. Results indicate that lithium and rare earth elements are significantly enriched in the Donggou coals, which could be new potential alternative sources for critical elements. Concentrations of lithium and rare earth elements in the Donggou coals gradually increase from top to bottom. Lithium is mainly associated with kaolinite, while rhabdophane, florencite, goyazite, and xenotime are the main hosts of rare earth elements. The controlling geological factor is the groundwater leaching of underlying tuff, and to a lesser extent, the terrigenous clastic materials input from the top layer of the Kangdian Upland. This study provides mineralization information for lithium and rare earth elements exploration in coal measures.

Contrasting composition of two biotite generations in the Lizhuang rare‐earth element deposit, Sichuan Province, Southwestern China

Biotite is an important silicate mineral that can be used to decipher the physicochemical attributes of magmatic or hydrothermal systems. The Lizhuang rare‐earth element (REE) deposit in Sichuan Province, Southwestern China, formed from continuous magmatic‐hydrothermal processes is related to a Cenozoic carbonatite–syenite complex. Biotites are abundant in this deposit, which can be divided into two generations: generation I in intergrown with alkaline feldspar and aegirine‐augite and generation II in association with bastnäsite‐(Ce). We investigated chemical composition of the two biotite generations using electron‐microprobe(EMPA) and laser ablation–inductively coupled plasma–mass spectrometer (LA–ICP–MS) analyses to understand the development of REE mineralization. Generation I biotite has relatively high Al2O3 (10.2–12.4 wt%), TiO2 (0.49–1.85 wt%), and FeOtot (12.2–15.9 wt%), but low SiO2 (40.0–42.5 wt%) contents compared to generation II counterpart. These two generations of biotite also differ in some key trace elements. Specifically, generation I biotite has much higher concentrations of Sr (up to 234 ppm) and Ba (up to 20,796 ppm), but lower levels of Li (47.5–126 ppm) with respect to its generation II counterpart. When comparing Lizhuang biotites with those of other barren carbonatite complexes, we identified an unusual compositional trend in the generation II biotites termed as fluorphlogopite trend. This trend is marked by the continuous increase in the Mg content towards mineralization and, therefore, can serve as a diagnostic attribute in the determination of mineralized carbonatite complexes. Fluorine in biotite is an important parameter that can be used as a vector for REE exploration, because the generation II biotite presents much higher fluorine contents (2.20–4.06 wt%) than its generation I counterpart (0.87–1.59 wt%). The compositional data of the two biotite generations indicate a depletion of Fe and a progressive enrichment in Mg and F in the ore‐forming system during its evolutionary process. Physicochemical parameters estimated by biotite composition suggest that there is a trend of strongly decreasing temperature from the crystallization of generation I to generation II biotite. It is therefore concluded that temperature is a major factor favourable for REE mineralization in the Lizhuang deposit, particularly given related experimental studies. Taken together, we propose that biotite composition could serve as a proxy for REE mineralization processes and as a reliable index for REE routine exploration in a carbonatite‐related setting.

Rare earth element (REE) enrichment of the late Ediacaran Kalyus Beds (East European Platform) through diagenetic uptake

The Kalyus Beds of the late Ediacaran Nagoryany Formation occurring in the northeastern part of the Republic of Moldova are dominated by black argillites with phosphorites and calcareous concretions. Four lithological groups were examined with respect to their rare earth element (REE), major and trace element geochemistry: phosphorites, enriched argillites, pure argillites and carbonates. Phosphorites and enriched argillites exhibit a pronounced middle-REE bulge suggesting a strong diagenetic uptake of REEs. Y/Ho ratios are mostly <35, values that are consistent with derivation of >90% of REEs from lithogenous sources. Pure argillites show a flat REE distribution similar to that of average upper continental crust (UCC), indicating that REEs are likely related to detrital siliciclastics derived from felsic to mafic source rocks of the adjacent regions of Baltica, which was isolated within paleo-oceans during the late Ediacaran. Carbonates show a light-REE depleted pattern with relatively high Y/Ho ratios (up to 53) that suggests the preservation of a predominantly hydrogenous (seawater-derived) REE signal. Ce/Ce* ratios of ∼0.80–1.02 reflect suboxic to anoxic seawater conditions. This is a locally and temporally constrained anoxic event, since widespread oxic conditions were specific for the continental margins of Baltica. The phosphorites and enriched argillites groups of the Kalyus Beds show high middle-REE enrichment comparable to those of other known world phosphorite deposits. Their total REE contents are high (793–1735 ppm) and are of potential economic interest. These results provide insights for expanding global REE exploration targets and may have implications for a better understanding of the depositional environments during the late Ediacaran.

Bands of Zircon, Allanite and Magnetite in Paleozoic Alkali Granite in the Chungju Unit, South Korea, and Origin of REE Mineralizations

High-grade Zr–Nb–Y–rare earth element (REE) mineralization occurs as zircon–allanite–magnetite bands in layered Paleozoic alkali rocks which intruded the Gyemyeongsan Formation of the Chungju unit, South Korea. The mineralization period and genesis have been controversial. We investigated the petrological and mineralogical properties of the newly discovered zircon–allanite–magnetite bands and the geochronological properties of zircon within the bands in the alkali granite. We analyzed the zircon with laser ablation multi-collector inductively coupled plasma mass spectrometry (LA-MC-ICP-MS). The repeated quartz–feldspar-rich layers in the alkali granite show grain-sized grading textures and equilibrium igneous textures. Magnetite and allanite grains in these layers varied in size and exhibited isolated, aggregated, and coalesced textures. In addition, the settling texture of zircon grains onto the other minerals was observed. These observations could reasonably be explained by the process of gravitational accumulation during the solidification of magma. The 206Pb/238U ages obtained from zircon from the zircon–allanite–magnetite-rich layer and the alkali aplite were 331.1 ± 1.5 Ma and 334.5 ± 8.9 Ma, respectively. Therefore, we suggest that the Zr–Y–Nb–REE mineralization developed in the alkali rocks and the Gyemyeongsan Formation in the Chungju unit were formed by fractional crystallization of alkali magma and hydrothermal fluids which evolved from alkali magma fractional crystallization, respectively. The correlation between alkaline granite and REE mineralization found in this study could be used as a tool for REE exploration in other regions where the permeable geological unit is intruded by the alkali granite.

Fast 2D Laser-Induced Fluorescence Spectroscopy Mapping of Rare Earth Elements in Rock Samples.

Due to the rapidly increasing use of energy-efficient technologies, the need for complex materials containing rare earth elements (REEs) is steadily growing. The high demand for REEs requires the exploration of new mineral deposits of these valuable elements, as recovery by recycling is still very low. Easy-to-deploy sensor technologies featuring high sensitivity to REEs are required to overcome limitations by traditional techniques, such as X-ray fluorescence. We demonstrate the ability of laser-induced fluorescence (LIF) to detect REEs rapidly in relevant geological samples. We introduce two-dimensional LIF mapping to scan rock samples from two Namibian REE deposits and cross-validate the obtained results by employing mineral liberation analysis (MLA) and hyperspectral imaging (HSI). Technique-specific parameters, such as acquisition speed, spatial resolution, and detection limits, are discussed and compared to established analysis methods. We also focus on the attribution of REE occurrences to mineralogical features, which may be helpful for the further geological interpretation of a deposit. This study sets the basis for the development of a combined mapping sensor for HSI and 2D LIF measurements, which could be used for drill-core logging in REE exploration, as well as in recovery plants.

Occurrence and geochemistry of bastnäsite in carbonatite-related REE deposits, Mianning–Dechang REE belt, Sichuan Province, SW China

Bastnäsite is the main ore mineral in many carbonatite-related rare earth element (REE) deposits, which account for ∼51% of rare-earth oxide reserves worldwide. However, the occurrence, geochemistry, and genetic significance of bastnäsite has not been methodically investigated. The Cenozoic Mianning–Dechang (MD) REE belt in Sichuan Province, SW China, contains the Maoniuping, Dalucao, Lizhuang, and Muluozhai deposits as well as numerous smaller REE occurrences. Individual deposits within the belt contain different types of bastnäsite-bearing ore, which provides a unique opportunity to explore in detail the common mechanisms controlling the formation of bastnäsite-rich REE deposits.Here, we present detailed results from field observations and petrographic, geochemical, and fluid inclusion studies of bastnäsite from the main MD deposits. Calcite, fluorite, and barite form stable mineral assemblages that are commonly overprinted by bastnäsite. Homogenization temperatures of fluid inclusions in bastnäsite of ∼150–270 °C (Dalucao and Lizhuang deposits) and 155–210 °C (Maoniuping deposit) are systematically lower than those of fluid inclusions in gangue minerals. Therefore, the petrographic studies and homogenization temperatures both show that large-scale crystallization of bastnäsite took place during the later stage of the hydrothermal system. The bastnäsite, relatively geochemically homogeneous within all of the MD deposits, is enriched in Ba (293–8425 ppm), Th (16.4–2527 ppm), and U (4.19–92.7 ppm), and relatively depleted in high field strength elements such as Nb (0.15–17.4 ppm), Ta (0.06–6.48 ppm), Zr (0.71–31.1 ppm), Hf (0.62–5.65 ppm), and Ti (<60 ppm), the same to carbonatite, and ore veins. In comparison, the samples from the study area show an increase in average REE contents from syenites to carbonatites to ore veins (i.e., bastnäsite-bearing ores) and finally to bastnäsite. Lanthanum and Ce were commonly substituted by Th, U, Sc, Ba, and Sr supplied by more evolved hydrothermal fluids.Combining the present results with existing data, we present a three-stage model for the formation of carbonatite-related REE deposits. First, partial melting of metasomatized sub-continental lithospheric mantle, fluxed by REE- and CO2-rich fluids, forms the parental carbonatite–syenite magma. Second, Sr, Ba, and REEs are strongly partitioned into carbonatite melts during liquid immiscibility in the carbonatite–syenite magmatic system. Third, hydrothermal fluids exsolved from the crystalizing syenite and carbonatite magmas form ore veins with early gangue minerals and later bastnäsite overgrowths. Consequently, barite, calcite, and fluorite assemblages are a valuable guide in REE exploration.

Rare Earth Elements in Planetary Crusts: Insights from Chemically Evolved Igneous Suites on Earth and the Moon

The abundance of the rare earth elements (REEs) in Earth’s crust has become the intense focus of study in recent years due to the increasing societal demand for REEs, their increasing utilization in modern-day technology, and the geopolitics associated with their global distribution. Within the context of chemically evolved igneous suites, 122 REE deposits have been identified as being associated with intrusive dike, granitic pegmatites, carbonatites, and alkaline igneous rocks, including A-type granites and undersaturated rocks. These REE resource minerals are not unlimited and with a 5–10% growth in global demand for REEs per annum, consideration of other potential REE sources and their geological and chemical associations is warranted. The Earth’s moon is a planetary object that underwent silicate-metal differentiation early during its history. Following ~99% solidification of a primordial lunar magma ocean, residual liquids were enriched in potassium, REE, and phosphorus (KREEP). While this reservoir has not been directly sampled, its chemical signature has been identified in several lunar lithologies and the Procellarum KREEP Terrane (PKT) on the lunar nearside has an estimated volume of KREEP-rich lithologies at depth of 2.2 × 108 km3. This reservoir therefore offers a prospective location for future lunar REE exploration. Within the context of chemically evolved lithologies, lunar granites are rare with only 22 samples currently classified as granitic. However, these extraterrestrial granites exhibit chemical affinities to terrestrial A-type granites. On Earth, these anorogenic magmatic systems are hosts to U-Th-REE-ore deposits and while to date only U-Th regions of enrichment on the lunar surface have been identified, future exploration of the lunar surface and interior may yet reveal U-Th-REE regions associated with the distribution of these chemically distinct, evolved lithologies.