Distribution Of Rare Earth Elements Research Articles

Experimental constraints on the role of temperature and pyrogenic mineral assemblage in wildfire-induced major and trace element mobilisation

Wildfires impact a large and increasing proportion of the Earth’s surface. With documented soil surface temperatures of up to ∼850 °C, wildfires may fundamentally alter the mineralogy and geochemistry of soils and regolith, more conventionally thought to be dominated by low temperature weathering processes. Here we use an experimental approach to test the effect of temperature on the formation of pyrogenic minerals, and on the distribution and mobility of major, trace and rare earth elements following post-fire chemical weathering. We focus on ferruginous nodules, common Fe-oxide cemented components of soils, which transform from non-magnetic to maghemite-bearing, magnetic nodules under wildfire conditions. These transformations provide a valuable record of fire impacts and facilitate the study of thermal processes and element mobility. Our results show heating produces a typical pyrogenic mineral assemblage of hematite, maghemite, metakaolin and transition alumina. At 900 °C the high temperature Fe2O3 polymorph luogufengite forms, which has never been reported in natural fire-affected substrates and therefore places an upper boundary on palaeowildfire temperatures at the soil-fire interface. Chemical leaching, employed to simulate the impacts of post-fire weathering, demonstrates that formation and subsequent breakdown of these pyrogenic minerals results in increased mobility of several elements including Li, Si, Sc, Cr, Co, Cu, Zn, Rb, Cs, La, Pb and U. Further, we propose that incongruent dissolution of pyrogenic metakaolin may be responsible for the formation of fusic material, an aluminous cement commonly found in soils. We conclude by discussing the significance of these results for the release of potentially toxic metals following a fire, identify trace elements that have the greatest potential to be used as palaeowildfire geochemical proxies (decreased alkali metal concentrations, decreased U/Th ratios, and decreased La compared to other rare earth elements), and the potential impact of wildfire on global geochemical cycles.

Effect of rare earth element Y on the crack propagation behavior of Mg alloys: A molecular dynamics simulation

The effect of the distribution and concentration of rare earth (RE) element Y, crack orientation, temperature, and strain rate on the crack propagation behavior of the Mg alloys is investigated by molecular dynamics/Monte Carlo simulations. The results show that the RE element Y tends to form locally short-range order structures in the Mg alloys, and the introduction of the RE element Y can enhance the fracture toughness of the Mg alloys. The results indicate that with the increase of Y concentration, the crack propagation mode of the Mg alloys shifts from a mode, dominated by the dislocation emissions at the crack tip and the crack cleavage propagation to a mode dominated by the solid-state amorphization and the slip of amorphous bands. In addition, the results show that the faster the strain rate, the slower the crack propagation speed, and the crack propagation resistance increases with increasing temperature.

Refinement of eutectic structure and precipitates of Cu–20Ag alloy due to Y microalloying

Copper-silver alloy rod with high mechanical properties and stable conductivity are the key materials for the preparation of microfilaments used in endoscopy and other medical fields. In this paper, the microstructure of Cu–20Ag rod was regulated by adding trace rare earth Y in order to improve the comprehensive performance of copper-silver alloy further. and studies the distribution and existence of rare earth Y as well as the influence on the performance of copper-silver alloy rod billet. The results of research show that: rare earth Y mainly exists in the branching nodes of the eutectic organization, so that the alloy in the solidification of constitutional supercooling increases, thus refining the eutectic structure, and make it uniformly distributed. After addition of 0.01 wt%Y, Cu4Y was precipitated in the eutectic structure of the rod. After adding 0.03 wt%Y, the precipitates types increased to trace intermetallic compound AgY and nanoparticles Cu4Y. The increase of the interface between eutectic structure and Cu matrix decreases the electron scattering probability. This is the main factor to lead to the decrease of electrical conductivity. The precipitation hardening of precipitated phase and the increase of interface between eutectic structure and Cu matrix are the main factors for the increase of tensile strength of bar billet. The main factor of the decrease in the conductivity of rod billet is the increase of Ag phase dissolved in eutectic structure and the interface between eutectic structure and Cu matrix.

Rare earth elements in fucus algae Barents Sea

Patterns of distribution of rare earth elements (REE) in natural objects are important geochemical indicators of the state of the environment. For the first time, data on REE contents in fucus algae from various horizons of the littoral of the Barents Sea are presented. The behavior of REE in natural processes is controlled by the solubility of their compounds, the ability to complex, and the tetrad effect of fractionation. Natural factors determining REE migration in the sediment–water–macrophytes system are discussed.

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.

Genesis of the Ulaan silver-lead–zinc deposit in Northeast Mongolia: Constraints from S and Pb isotopes, together with U-Pb and Rb-Sr geochronology

The Ulaan silver-lead–zinc deposit (hereinafter referred to as the Ulaan deposit) is identified as the largest silver-lead–zinc polymetallic deposit in Mongolia, with proved reserves including 2,240 tons of silver (Ag; average grade: 49 g/t), 440,000 tons of lead (Pb; average grade: 1.13 %), and 810,000 tons of zinc (Zn; average grade: 2.07 %). However, the genesis of this deposit remains unclear. The Ag-Pb-Zn ore bodies in the deposit, occurring as cylinders in shape within the Middle-Late Jurassic rhyolites, are governed by a concealed breccia pipe. The ore minerals include galena, sphalerite, and pyrite, followed by chalcopyrite, hematite, stibnite, and siderite. The primary alterations of the surrounding rocks include silicification, chloritization, kaolinization, argillization, carbonatization, and skarnization. The Rb-Sr dating of sulfide minerals and associated vein minerals in the ores yielded isochron ages varying in a range of 146 ± 3 Ma (n = 6, MSWD=1.3), suggesting mineralization during the Late Jurassic. The δ34S values of sulfide minerals in the ores range from 1.6 ‰ to 4.3 ‰, suggesting that the sulfur originated primarily from magmas or deep sources. The isotopic compositions of coexisting sphalerite-galena minerals in the deposit revealed mineralization temperature estimates ranging between 331 °C and 449 °C, indicating a medium- to high-temperature ore-forming conditions. The sulfide minerals exhibit 208Pb/204Pb ratios ranging from 38.138 to 38.301, 207Pb/204Pb ratios from 15.543 to 15.594, and 206Pb/204Pb ratios from 18.318 to 18.354, suggesting that ore-forming metals, represented by Pb, also originated primarily from mantle source. The zircon U-Pb dating of rhyolites in the ore-hosting strata and ore-controlling breccia pipes yielded ages of 160.6 ± 1.7 Ma (n = 24, MSWD=0.68) and 161.6 ± 1.6 Ma (n = 30, MSWD=0.89), respectively, indicating volcanic eruptions during the early Late Jurassic. These ore-hosting rhyolites exhibit characteristics of A-type rhyolites, suggesting that they were formed in an intracontinental extensional environment. These rhyolites share similar rare earth element (REE) distribution patterns with fluorite formed in the main mineralization stage, suggesting a genetic link between the mineralization and magmatic processes. This study proposes that the Ulaan deposit was a hydrothermal deposit formed in an extensional environment following the closure of the Mongol-Okhotsk Ocean, with ore-forming metals and hydrothermal fluids associated with volcanic rocks or magmatic-hydrothermal processes.

Late Triassic extension of thickened lithosphere of the East Kunlun orogenic Belt, northern Tibetan Plateau: Evidence from the geochemistry and geochronology of mafic magmatism

The East Kunlun Orogenic Belt (E-KOB) evolved into an extensional tectonic setting with plenty of mafic magmatism after the closure of the Paleo-Tethys Ocean. However, the deep tectonic system and geodynamic processes in this context still need further clarification. The detailed field geological, petrological, geochronological and geochemical works carried out on the Yeniugou gabbros in this study could provide key evidence for clarifying this issue. The gabbros are predominantly composed of clinopyroxene, orthopyroxene, plagioclase, olivine and ilmenite. Zircon U–Pb dating results suggest that their formation at ca. 209–207 Ma. Characterized by a relatively low SiO2 content and a moderate total alkaline content, these rocks are classified as alkalic to subalkaline series. High values of Mg# (42.2–59.4) and high concentrations of compatible elements (V, Cr, Co, Ni) suggest that their parent magma was generated through high partial melting of a lithospheric mantle source. The left-leaning rare earth element distribution patterns, combined with the characteristic spikes of Nb-Ta, indicate that they were originated from the lithospheric mantle metasomatized by subducting components. The positive zircon εHf(t) values (0.1–5.7), along with elevated Nb/La ratios (0.45–0.67), further confirm a small amount of asthenosphere mantle contribution. Elevated Zr/Y ratios, plus a slightly positive correlation between Alz and TiO2 in clinopyroxene, imply that they formed within an extensional setting, where the upwelling of the asthenospheric mantle provided heat for partial melting of the metasomatic lithospheric mantle. Combined with previous data, we suggest that E-KOB underwent delamination of thickened lithosphere in the late Triassic, following the closure of the Paleo-Tethys Ocean.

Controls on the distribution and fractionation of rare earth elements in recent sediments from the rivers along the west coast of India

Controls on the distribution and fractionation of rare earth elements in recent sediments from the rivers along the west coast of India

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.

Distribution of Rare Earth Elements in Ash from Lignite Combustion in Polish Power Plants.

Rare earth elements are an essential critical raw material in the development of modern technologies and are highly sensitive to both supply chain disruptions and market turbulence. The presented study examines the characteristics of fuel, fly ash, and bottom ash from lignite combustion in power plant units. Also, we attempted to determine the amount of amorphous glass in the ashes and whether and to what extent the glass from the ash samples is bound to REY. The suitability of the ash was assessed as an alternative source of REY. The fuel and ash samples were acquired from power plants in Poland. The tests determined the fuel quality parameters, including the chemical and phase composition, of amorphous glass using ICP-MS and XRD methods, respectively. The study showed that all ash samples dissolved in 4% HF were enriched in REY. The efficiency of REY enrichment varied, and its presence in the residue samples was found to be in similar proportions compared to the raw sample. All ash residue samples were enriched in critical elements. The obtained values of the Coutl prospective coefficient allowed for the classification of some of the analyzed ashes and their residues after dissolution in 4% HF as prospective REY raw materials.

Sediment-Hosted Rare-Earth Elements Mineralization from the Dian-Qian District, Southwest China: Mineralogy and Mode of Occurrence

The Xuanwei Formation’s claystones in the Dian-Qian District of Southwest China are rich in rare-earth elements (REEs), suggesting their potential as a source of medium and heavy rare earths. However, the REE content in these rocks is lower than other types of rare-earth deposits, and the interrelationship among clay minerals is intricate. There is no direct evidence indicating the mineralization of REEs, limiting their beneficiation and extraction. The objective of this study is the characterization of REE distribution in the Dian-Qian District. The sedimentary rocks in this district are mainly composed of kaolinite, boehmite, quartz, rutile, and pyrite. The results of continuous chemical extraction of REE-rich claystone and transmission electron microscope (TEM) observations have confirmed that REEs occurred as florencite in the rocks, and that the ion-absorption state makes only a negligible contribution to the REE content. A close relationship between florencite and kaolinite makes traditional mineral processing operations very difficult. Combined with the properties of kaolinite, roasting-acid leaching was the efficacious approach for rare-earth resources extracted from the rare earth-rich clay rocks of the Xuanwei Formation.

The yengejeh diasporic karst bauxite deposit, NW Iran: Constraints on distribution and fractionation of major and rare earth elements

The Yengejeh diasporic karst bauxite deposit (NW Iran) was developed as discontinuous layers and lenses along the contact of dolomitic limestone of the Ruteh Formation (middle-upper Permian) and dolomite of the Elika Formation (Triassic). This deposit is constituted by two conspicuous subset layers, (1) green bauxite (GB) and (2) red bauxite (RB). The XRD analytic data revealed that diaspore is accompanied by chlorite and anatase in the GB subset and by hematite in the RB subset. Minerals such as pyrophyllite, kaolinite, illite, and rutile are present within the both subsets. The antithetical distributions of Al with Fe and Al with Ti in the deposit are indicative of the controlling role of climatic changes of the depositional environment and the function of post-formation diagenetic processes. The increment in certain geochemical ratios like La/Y, (La/Yb)N, and (LREE/HREE)N from the top toward the bottom of the horizon is designative of pH increase in depositional milieu by buffering of the percolating solutions, and of preferential scavenging of LREE by hematite. The positive Ce anomaly in the GB subset took place as the result of change in the oxidation state of this element from Ce3+ to Ce4+. However, the positive Ce anomalies in the RB subset implicates preferential scavenging of Ce onto hematite. The marked variation range in anomaly values of Eu/Eu* (0.38–1.01) at Yengejeh reveals that this index acted as non-conservative during the evolution of this deposit, and this behavior is related most likely to influences of post-formation diagenetic processes.

Rare Earth Elements (REEs) in veterinary medicine: practical applications and tissue distribution in terrestrial vertebrate animals.

Rare earth elements (REEs) have shown promising potential in veterinary medicine, particularly as feed additives and diagnostic and therapeutic tools. Moreover, the increasing industrial use of REEs has raised concerns about their potential environmental contamination and bioaccumulation in animal tissues. While numerous studies have focused on the distribution of REEs in marine and freshwater ecosystems, information regarding their presence in terrestrial environments remains fragmented. This narrative review aims to describe the practical applications of REEs in veterinary medicine, with a specific focus on studies evaluating the potential accumulation of these elements in the tissues of terrestrial vertebrate animals. Additionally, the review addresses research on the intentional residual presence of REEs and in-field studies evaluating the contamination burden from REE exposure in domestic and wild animals. In conclusion, this review identifies critical scientific gaps and provides future research directions to advance understanding of the long-term effects, mechanisms of action, and environmental impacts of REEs in veterinary practices.

Spatial distribution of soil rare earth elements in Sicily (Italy)

Rare earth elements (REEs) are becoming increasingly interesting as indicators of soil processes, and modelling their spatial distribution has become a fundamental requirement for this purpose. This study aims to model and quantify the spatial distribution of soil REEs taking into account their compositional nature in their mapping, and to assess the associated spatial uncertainty. In particular, the cerium anomaly (Ce⁎) and the ratio of the sum (Σ) of light to heavy REEs (ΣLREEs/ΣHREEs) were calculated and analysed. The study was carried out in Sicily (Italy), one of the largest (25,832 km2) and most populous island in the Mediterranean Sea. Soil REE data were obtained from the soil database of Sicily region. Soil REEs were transformed into a vector of isometric log-ratio (ilr) coordinates and analysed using a geostatistical approach for predicting their values at unsampled locations and generating 100 REEs realizations using turning bands simulation. Each REE element and Ce⁎ were mapped as well as the ΣLREEs/ΣHREEs ratio. The joint variability of the investigated REEs and the ΣLREEs/ΣHREEs ratio provided insights into their abundance and distribution patterns. From the simulated realizations, standard deviation maps were calculated for the Ce⁎ and the ΣLREEs/ΣHREEs ratio, providing a measure of their spatial uncertainty. Although with some limitations, the study established a first baseline of the Ce⁎ and the ΣLREEs/ΣHREEs ratio. The maps of spatial uncertainty may be a useful tool for planning future soil sampling and optimise the choice of new sampling locations.

Busting the dust: Evaluating local vs distal sources in Quaternary sediments at Thirlmere Lakes

The Quaternary sediments preserved within the Thirlmere Lakes system, Greater Blue Mountains World Heritage Area, Australia, are an important regional environmental record representing at least the last two interglacials. Understanding the source and evolution of these sediments, both temporally and spatially, is an essential component of the site's reconstruction. In this study, we evaluate this question using physical, mineralogical, elemental, and isotopic analytical techniques. Four distinct lake sediment facies all show bi-modal distributions of coarse sand and clay to fine silts, representing various mixtures of catchment Hawkesbury Sandstone and Ashfield Shale. Clays are predominantly kaolinite-dickite, however, the 7 Å dehydrated form of halloysite is prominent in an orange-yellow oxidised lake facies unit. The relative distribution and concentration of rare earth elements, including yttrium (REY), is heterogeneous across all the lake facies, varying between both lakes and with depth. This variability suggests a geochemical signature reflecting a combination of mixed sources and secondary mineral precipitation, driven by catchment geomorphology and specific site conditions. Slightly positive Ce anomalies in the oxidised lake facies, combined with the greater halloysite representation, represents a period of dry conditions and sub-aerial exposure. Evaluation of catchment, regional and continental REY ratios, Eu anomalies and εNd data implies a predominant internal catchment source signature, with any external contributions restricted to the local Bringelly Shale and the immediate south-eastern Australia, including the Murray River Basin. Geochemical and isotopic values for these proposed internal and external sediment sources predicts that an aeolian source from outside the immediate catchment represents a maximum of 30% of the fine-grained sediment fraction.

Prevalence of rare earth elements in natural waters of Khanty-Mansiysk

Relevance. New data on the content of lanthanides in the water–rock system are important for understanding the behavior of rare-earth elements in the environment, open up the possibility of using them as indicators of geochemical processes and anthropogenic factor, taking into account the specialities of their migration and fractionation. Aim. Assessment of the quantitative content and distribution of rare-earth elements (La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu) in the surface and underground waters of Khanty-Mansiysk to identify the main patterns of their behavior. Objects. Surface and underground waters of the natural reserve Samarovsky Chugas, as well as ground deposits and products of secondary mineral formation. Methods. The bulk analysis of water is performed by a standard set of spectral and electrochemical methods. The rare-earth content was determined by inductively coupled plasma mass spectrometry. Chemical composition of ground deposits and secondary mineral formation products – by neutron activation analysis. Results. The paper demonstrates rare-earth elements behavior in aqueous medium, ground deposits and products of secondary mineral formation. Different approaches to rare-earth elements rationing in waters and solid sediments showed comparability of lanthanide distribution spectra to each other and made it possible to identify some features of the rare-earth elements distribution pattern in different environments. In the waters, there are positive anomalies of europium and gadolinium and negative anomaly of cesium. Gadolinium anomalies were detected in ground deposits, and europium in secondary mineral formation products. The high migration activity of the entire considered series of rare-earth elements in the solution coming from the holding deposits was established. During following geochemical processes, mainly middle lanthanides (Sm, Eu, Gd, and Tb) fall out of the solution in the form of secondary mineral formation products.

Rare Earth Elements Distribution and Bacteriome to Assess and Characterize the Soil Landscapes of Old Olive Orchards

The presence of the olive tree in Tuscany, Italy, in its forms that have survived to the present day as an essential component of the landscape dates back many centuries. Global change is now threatening it. Therefore, it is important to find markers to enhance the olive tree environment in terms of its resilience. The aim of the research was to investigate the composition of soil bacteriomes in contrasting geochemical environments using a geochemistry approach based on the behavior of the REEs, inherited from parent rock material. Bacteriome assemblages and REE content were analyzed in 48 topsoils developed in six geochemical Tuscan environments. Combined geochemical, geoinformatic, and bioinformatic techniques highlighted the existence of four bacteriome assemblages depending on Light-REEs. Further results showed that the soil bioavailable fraction of REEs was related to parent rock materials, pH, and bacteriome composition. The most abundant bacteria were Microlunatus in graded fluvio-lacustrine soils, Gaiella in graded arenaceous soils, Bradyrizhobium in pyroclastic soils, and Rubrobacter in soils on gentle slopes of calcareous and carbonatic lithologies. This research represents a starting point to define new indicators able to assess the resilience of the olive trees in the Mediterranean landscape and characterize the territory of extra virgin olive oils.

Mineralogy and rare earth elements spatial distribution in the carboniferous rocks of the eastern El Galala El Bahariya, Egypt

The Carboniferous rocks in the eastern part of El Galala El Bahariya were investigated using integrated field and laboratory techniques to determine their mineralogy, rare earth elements (REEs) distribution, and structural lineament density. The succession is mainly composed of argillaceous and minor arenaceous rocks, exhibiting variations in lithology across the study area. The essential minerals of these rocks are quartz, kaolinite, and illite. The accessory minerals include microcline, gypsum, anhydrite, halite, barite, hematite, pyrite, anatase and gibbsite, in addition to, the radioactive and REEs-bearing minerals such as uranophane, xenotime, monazite, and zircon. These minerals are reported in the rocks of the study area for the first time. The types, forms, habits, and modes of occurrence of the recorded minerals indicate multiple origins: allogenic–authigenic, and primary-secondary. REEs in the rocks exhibit enriched patterns with a negative Eu anomaly, likely due to low plagioclase content or and/or Eu removal by alteration processes. The distribution of REEs is influenced by textural attributes, with finer sediments in the southern part showing higher REEs content, ascribed to the high clay content and presence of gibbsite. The preferential mobility of LREEs is evident, explaining elevated LREEs/HREEs ratios in the rocks. Utilizing remote sensing techniques, lithological units and alteration zones were determined using decorrelation stretch and band ratio methods. The structural features, identified by Laplacian filter and edge enhancement, revealed the presence of NW–SE, N–S, and NE–SW faults that structurally regulate alteration zones and REEs distribution. These alteration zones are associated with clay minerals, REEs concentrations, and high lineament structure density. Spatial distribution maps highlight higher REEs concentrations in the southern part of the study area. These findings were validated using various analytical methods, including mineralogical and geochemical investigations, main component analysis, minimum noise fraction, decorrelation stretch, and spectral reflectance studies. They provide new insights into the REEs potential of the Carboniferous rocks and heighten our understanding of REEs genesis and distribution in the region.

Features of Distribution of Rare-Earth Elements in Coals of the Far East

For the first time, the distribution of rare earth elements (REE) has been studied in detail for a number of coal facilities (30 deposits, 650 samples of coal and 210 samples of carbonaceous rocks). The ubiquitous presence of elevated concentrations of REE in coals has been noted. The REE mineral cluster in coals includes the association: ash content of coals – SiO2 – K2O – Al2o3 – TiO2 – Sc – Y – Dy – Ho – Er – Tm – Yb – Lu, and the association La – Ce – Pr – Nd – Sm – Eu – Gd – Tb. The presence of these elements of the mineral part of the coals is preferably in the composition of phosphate minerals – monazite and apatite (according to electron microscopy with microanalysis, the correlation of REE with P2o5). The content of individual REE in humic acids isolated from coals and fractions of coals of different densities has been studied. The specific role of organic matter(s) in the concentration of REE, their presence in the humus component of S and in low-ash coals is shown. Selective accumulation (fractionation) of heavy REE by organic matter has been experimentally established for the first time. Two genetic types of REE mineralization have been identified in coals: mainly terrigenous (hydrogenic) and tufogenic. The increased concentrations of REE in coals are due to the influence of the petrofund. The deposits were ranked according to the degree of prospects for REE based on an assessment of the resource potential of associated REE in the coals of the studied brown coal deposits. REE raw materials (lanthanides in coal ash) differ significantly from traditional types of rare earths ores by an incomparably large relative amount of heavy REE (on average 3–4 times), sometimes reaching 46% of the total REE content. Thus, coal ash is a unique non–traditional source of heavy lanthanides – more rare, valuable and expensive. The coals of the studied deposits should be considered as associated raw materials for rare earths.

Cryolite as a Reference Mineral of Rare Metal Mineralization: An Experimental Study

Abstract Phase relations and the distributions of rare earth elements (REE), Sc, Y, and Li between aluminofluoride and aluminosilicate melts in the model granite system Si–Al–Na–K–Li–F–O–H were experimentally studied at 700°C, 1 and 2 kbar, and water contents of 3 to 50 wt %. Our original and available literature experimental data on phase relations in the granite system saturated with water and fluorine and containing trace elements are compared with the mineral assemblages of rare-metal cryolite-bearing granites from the Zashikhinsky, Katugin, and Ulug-Tanzek deposits in eastern Siberia. Liquid immiscibility between granite and salt aluminofluoride melts, which occurs at high contents of fluorine and lithium in the system, is proved to facilitate the accumulation of rare elements in salt cryolite-like melts. At a temperature of 700°C and pressures of 1 and 2 kbar, aluminofluoride melt in the granite system crystallizes and forms cryolite. Fluorine-bearing minerals of trace and rare earth elements, such as pyrochlore and gagarinite, occur at these deposits in association with cryolite and lithium micas. Comparison of experimental data and natural observations provides arguments in support of the hypothesis that liquid immiscibility should play an important role in the formation of cryolite. Cryolite is thought to be able to serve as a reference mineral for rare metal-rare earth mineralization in granites with high lithium and fluorine content.