Rare Earth Element Exploration Research Articles

The Saint-Honoré Carbonatite REE Zone, Québec, Canada: Combined Magmatic and Hydrothermal Processes

The Saint-Honoré carbonatite complex hosts a rare earth element (REE) deposit traditionally interpreted as being produced by late-stage hydrothermal fluids that leached REE from apatite or dolomite found in the early units and concentrated the REE in the late-stage units. New evidence from deeper units suggest that the Fe-carbonatite was mineralized by a combination of both magmatic and hydrothermal crystallization of rare earth minerals. The upper Fe-carbonatite has characteristics typical of hydrothermal mineralization—polycrystalline clusters hosting bastnäsite-(Ce), which crystallized radially from carbonate or barite crystals, as well as the presence of halite and silicification within strongly brecciated units. However, bastnäsite-(Ce) inclusions in primary magmatic barite crystals have also been identified deeper in the Fe-carbonatite (below 1000 m), suggesting that primary crystallization of rare earth minerals occurred prior to hydrothermal leaching. Based on the intensity of hydrothermal brecciation, Cl depletion at depth and greater abundance of secondary fluid inclusions in carbonates in the upper levels, it is interpreted that hydrothermal activity was weaker in this deepest portion, thereby preserving the original magmatic textures. This early magmatic crystallization of rare earth minerals could be a significant factor in generating high-volume REE deposits. Crystallization of primary barite could be an important guide for REE exploration.

A hyperspectral study (V-NIR-SWIR) of the Nechalacho REE-Nb-Zr deposit, Canada

This paper reports the results of a visible, near-infrared and short wave infrared (V-NIR-SWIR) spectroscopic study of the Nechalacho rare earth element (REE)-Nb-Zr deposit (Canada), associated rare metal pegmatites and select samples from other REE deposits. The zoning of minerals produced by hydrothermal alteration is traced using V-NIR-SWIR spectroscopic measurements in combination with geological, geochemical and mineralogical data. The minerals detected using V-NIR-SWIR spectroscopy (analcime, ankerite, biotite, chlorite, illite, REE-fluorocarbonates) display complex spatial distributions that were strongly controlled by the pathways and composition of multiple stages of hydrothermal fluids as well as the precursor lithology. Magmatic-hydrothermal analcime ± amphibole alteration was overprinted by regional biotite + magnetite + illite + ankerite + chlorite + REE-fluorocarbonate replacement. A qualitative mass change analysis indicates that the latter alteration (main-stage) was associated with significant gains in Mg and losses of Na at temperatures of ~300 °C, as indicated by the presence of phengitic to muscovitic illite. Low-temperature ankerite ± chlorite alteration was mainly fluid-controlled and associated with the formation of hydrothermal REE-fluorocarbonate minerals that crystallized as a result of the interaction of aqueous-carbonic hydrothermal fluids with eudialyte syenite protoliths, locally leading to leaching and re-deposition of light REE. The ankerite ± chlorite alteration also affected pegmatites peripheral to the Nechalacho intrusion and surrounding hydrothermally altered zones. Analysis of a variety of REE-mineral specimens and geochemically characterized bulk rock samples showed that the relative depths of the 741 and 864 nm NIR absorption features of Nd can be used as qualitative and quantitative proxies for the detection of the REE. In combination with fast measurement and processing capabilities, this allows field-based V-NIR-SWIR spectroscopy to be deployed as a powerful tool for regional and deposit-scale REE exploration, deposit characterization and mine production grade control.

Towards the challenging REE exploration in Indonesia

Rare earth elements (REE) are the seventeen elements, including fifteen from 57La to 71Lu, in addition to 21Sc and 39Y. In rock-forming minerals, rare earth elements typically occur in compounds as trivalent cations in carbonates, oxides, phosphates, and silicates. The REE occur in a wide range of rock types: igneous, sedimentary and metamorphic rocks. REE are one of the critical metals in the world. Their occurrences are important to supply the world needs on high technology materials. Indonesia has a lot of potential sources of REE that are mainly from residual tin mining processes in Bangka islands, which are associated with radioactive minerals e.g. monazite and xenotime. However, the REE from monazite and xenotime are difficult to extract and contain high radioactivity. Granitoids are widely distributed in Sumatra, Sulawesi, Kalimantan and Papua. They also have a very thick weathering crusts. Important REE-bearing minerals are allanite and titanite. Their low susceptibilities during weathering result an economically potential REE concentration. I-/A- type granitoids and their weathered crusts are important REE sources in Indonesia. Unfortunately, their distribution and genesis have not been deeply studied. Future REE explorations challenge are mainly of the granitoids their weathered crusts. Geochemical and mineralogical characterization of type of granitoids and their weathered crusts, the hydrothermally altered rocks, and clear REE regulation will help discover REE deposits in Indonesia.

Protecting the environment and public health from rare earth mining

AbstractAs increasing demand for green energy and high‐tech devices grows, so does the rising prospecting of rare earth metals required for their production. Protecting the environment and public health from rare earth element (REE) mining as well as emerging pollutants is urgently required to achieve sustainable development. This study mapped Earth's hidden REE deposits to identify potential contamination hotspots with the aim of preventing its deleterious effects on the environment. We worry that there would be widespread tailing facilities concomitant with serious pollutions, such as the Bayan Obo tailings site, and argue that a tradeoff between the underground REE exploration and environment conservation should be reached as soon as possible.

Rare earth element enrichment in Palaeoproterozoic Fengzhen carbonatite from the North China block

ABSTRACTCarbonatites are characterized by the highest concentration of rare earth elements (REEs) of any igneous rock and are therefore good targets for REE exploration. Supergene, hydrothermal, and magmatic REE deposits associated with carbonatites have been widely studied. REE enrichment related to fluorapatite metasomatism in Fengzhen carbonatites in the North China block is reported in this study. REE minerals (monazite, britholite, and Ca-REE-fluorocarbonates) associated with barite and quartz formed as inclusions within the fluorapatite and externally on its surface. Monazite, allanite, barite, and quartz occur as rim grains on the edges of the fluorapatite. Zoned fluorapatite was observed and showed varying chemical composition. Based on back-scattered electron imaging, the dark domains with mineral inclusions contain lower Si (0.3–0.6 wt.% SiO2) and light REE (LREE) [0.36–1.54 wt.% (Y+LREE)2O3] contents than inclusion-poor areas [0.7–1 wt.% SiO2; 2.16–4.51 wt.% (Y + LREE)2O3]. This indicates a dissolution–re-precipitation texture. Different types of monazites were distinguished by their chemical compositions. Monazite inclusions have lower La2O3contents (~13 wt.%) and La/Ndcn (~3) ratios than those (18–26 wt.% and 10–14 for La2O3 and La/Ndcn, respectively) growing externally on the fluorapatite. REE enrichment in the metasomatic fluorapatites is related to different stages of carbonatitic liquids. The early carbonatite-exsolved fluids metasomatized the fluorapatites to form REE mineral inclusions. The late carbonatitic fluids from carbonatite magmas that underwent strong fractional crystallization were enriched in REEs, Al, and Fe and metasomatized the fluorapatites to produce allanite and monazite rim grains.

A geochemical modeling to predict the different concentrations of REE and their hidden patterns using several supervised learning methods: Choghart iron deposit, bafq, Iran

The Bafq mining district hosts some Kiruna-type iron oxide-apatite (IOA) deposits which are commonly formed as a result of the multistage interaction of hydrothermal-magmatic processes within the Early Cambrian volcano-sedimentary sequence. Rare earth elements (REEs) are potentially concentrated under different physicochemical conditions in IOA deposits. Choghart orebody is one of the main magnetite-apatite deposits in the region. A wide range of primary and secondary geological events have affected the Choghart deposit, causing the behavior of REEs to vary in different zones. This study proposes a suitable exploration technique using various classification methods to identify the different concentrations of REE and their hidden patterns. To provide the required data, a systematic lithogeochemical sampling was performed in the north and NE of the Choghart orebody. The REE contents of samples were transformed into discrete values as distinct classes based on the results of clustering analysis. All possible combinations of features, being the geographical location and the major oxide composition of samples, were selected as subsets of predictors in every classification method. For each REE, 455 prediction models were constructed using these predictors. The performances of the classification methods were evaluated by error criteria with regard to all cases. Having the least amount of errors, the decision tree method was selected as the most suitable method. Based on decision tree results, the best subsets of predictors were chosen for each element. The existence of a significant relationship between the distribution patterns of each REE and the related predictors was assessed by its prediction errors. The assessment illustrated that some REE are reasonably predictable, and others are too irregular to be modeled. The extracted classification rules describe the geochemical relationships among the most important factors influencing the different concentrations of REE in the Choghart orebody. These results can be extended to other similar deposits to predetermine some REE-enriched zones based on major elements analysis. Merely by employing such techniques in REE exploration projects, a great savings in time and cost will be affected.

Geology and market-dependent significance of rare earth element resources

China started to produce rare earth elements (REEs) in the 1980s, and since the mid-1990s, it has become the dominant producer. Rare earth element export quotas first introduced by the Chinese government in the early 2000s were severely reduced in 2010 and 2011. This led to strong government-created disparity between prices within China and the rest of the world. Industrialized countries identified several REEs as strategic metals. Because of rapid price increases of REE outside of China, we have witnessed a world-scale REE exploration rush. The REE resources are concentrated in carbonatite-related deposits, peralkaline igneous rocks, pegmatites, monazite ± apatite veins, ion adsorption clays, placers, and some deep ocean sediments. REE could also be derived as a by-product of phosphate fertilizer production, U processing, mining of Ti-Zr-bearing placers, and exploitation of Olympic Dam subtype iron oxide copper gold (IOCG) deposits. Currently, REEs are produced mostly from carbonatite-related deposits, but ion adsorption clay deposits are an important source of heavy REE (HREE). Small quantities of REE are derived from placer deposits and one peralkaline intrusion-related deposit. The ideal REE development targets would be located in a politically stable jurisdiction with a pro-mining disposition such as Canada and Australia. REE grade, HREE/light REE (LREE) ratio of the mineralization, tonnage, mineralogy, and permissive metallurgy are some of the key technical factors that could be used to screen potential development projects. As REEs are considered strategic metals from economic, national security, and environmental points of view, technical and economic parameters alone are unlikely to be used in REE project development decision-making. Recycling of REE is in its infancy and unless legislated, in the short term, it is not expected to contribute significantly to the supply of REE.

Biogeochemical multi-element signatures in common juniper at Mäkärärova, Finnish Lapland: Implications for Au and REE exploration

Biogeochemical exploration methods involve chemical analyses of soil organic matter and plant species with a minimal environmental influence. Common juniper (Juniperus communis L.) was assessed as a medium for gold and rare earth element exploration in a shear zone of the Tanaelv Complex, northern Finland. Highest gold concentrations in the juniper twigs spatially coincide with weathered Au-rich hematite–quartz veins in the bedrock. Although gold concentrations were generally low (≤5ppb), the results suggest that the chemical analysis of common juniper is a feasible biogeochemical exploration tool for gold. Concentrations of rare earth elements (REEs) were high in the area where juniper growth was restricted as evidenced by low tissue nutrient concentrations. The restricted growth of REE-rich twigs indicates that they comprised more years of growth compared to other same-sized twig samples. The results indicate that the twigs of common juniper accumulate REEs over time and therefore, in biogeochemical sampling, the twig age should be taken into account. Furthermore, the results suggest that exceptionally dense coverages of Solidago virgaurea L. and Trientalis europaea L. can potentially be used for focusing REE exploration on suitable areas.

Biogeochemical expression of rare earth element and zirconium mineralization at Norra Kärr, Southern Sweden

Biogeochemical samples were collected from the Norra Kärr Alkaline Complex, a rare earth element (REE) and zirconium enriched deposit in Southern Sweden, to determine which sample medium is the most effective grassroots exploration tool for delineating concealed REE mineralization. The fern species Dryopteris filix-mas and Athyrium filix-femina were found to be widespread in the study area and surrounding countryside, and particularly efficient at concentrating high levels of REEs in their leaf tissue.There was distinct elemental fractionation in all three fern species. Each species showed enrichment in the LREEs (light rare earth elements), especially A. filix-femina. D. filix-mas showed the most enrichment in HREEs (heavy rare earth elements); Pteridium aquilinum had lower levels of REEs than the other two species.The best contrast was observed in D. filix-mas samples from areas over mineralization compared to samples taken over barren Växjö granites, which suggests that D. filix-mas is the preferred biogeochemical sample medium for REE exploration in this environment.