Search Results (21)

Reliable information on the chemical and physical makeup of mine tailings is critical in meeting environmental and regulatory requirements, as well as identifying whether contained elements, including critical minerals, might be economically recovered in future to meet growing demands. Detailed mineralogical characterization, supported by chemical assays and automated mineralogy (MLA) data on different size fractions, underpins a case study of flotation tailings from the processing plant at the Carrapateena mine, South Australia. The study provides valuable insights into the deportment of minor and critical elements, including rare earth elements (REEs), along with uranium (U). REE-minerals are represented by major phosphates (monazite and florencite) and subordinate REE-fluorocarbonates (bastnäsite and synchysite). More than half the REE-minerals are concentrated in the finest size fraction (−10 μm). REEs in coarser fractions are largely locked in gangue, such that economic recovery is unlikely to be viable. MLA data shows that the main REE-minerals all display specific associations with gangue, which change with particle size. Quartz and hematite are the most common associations, followed by sericite. Synchysite shows a strong affiliation to carbonates. The contents of other critical elements (e.g., tungsten, molybdenum, cobalt) are low and for the most part occur within other common minerals as submicron-sized inclusions or in the lattice, rather than discrete minerals. Nevertheless, analysis of mine tailings from a large mining–processing operation provides an opportunity to observe intergrowth and replacement relationships in a composite sample representing different ore types from across the deposit. U-bearing species are brannerite (associated with rutile and chlorite), coffinite (in quartz), and uraninite (in hematite). Understanding the ore mineralogy of the Carrapateena deposit and how the ore has evolved in response to overprinting events is advanced by observation of ore textures, including between hematite and rutile, rutile and brannerite, zircon and xenotime, and the U-carbonate minerals rutherfordine and wyartite, the latter two replacing pre-existing U-minerals (uraninite, coffinite, and brannerite). The results of this study are fundamental inputs into future studies evaluating the technical and economic viability of potentially recovering value metals at Carrapateena. They can also guide efforts in understanding the distributions of valuable metals in analogous tailings from elsewhere. Lastly, the study demonstrates the utility of geometallurgical data on process materials to assist in geological interpretation. Full article

The Neoproterozoic period in the Jabal Sayid and Dayheen areas is characterized by three distinct magmatic phases: an early magmatic phase of granodiorite–diorite association, a transitional magmatic phase of monzogranites, and a highly evolved magmatic phase of peralkaline granites and associated pegmatites. The presence of various accessory minerals in the peralkaline granites and pegmatites, such as synchysite, bastnaesite, xenotime, monazite, allanite, pyrochlore, samarskite, and zircon, plays an important role as contributors of REEs, Zr, Y, Nb, Th, and U. The geochemical characteristics indicate that the concentration of these elements occurred primarily during the crystallization and differentiation of the parent magma, with no significant contributions from post-magmatic hydrothermal processes. The obtained geochemical data shed light on the changing nature of magmas during the orogenic cycle, transitioning from subduction-related granodiorite–diorite compositions to collision-related monzogranites and post-collisional peralkaline suites. The granodiorite–diorite association is thought to be derived from the partial melting of predominantly metabasaltic sources, whereas the monzogranites are derived from metatonalite and metagraywacke sources. The peralkaline granites and associated pegmatites are thought to originate from the continental crust. It is assumed that these rocks are formed by the partial melting of metapelitic rocks that are enriched with rare metals. The final peralkaline phase of magmatic evolution is characterized by the enrichment of the residual melt with alkalis (such as sodium and potassium), silica, water, and fluorine. The presence of liquid-saturated melt plays a decisive role in the formation of pegmatites. Full article

The Lysan alkaline–ultramafic complex is located in the Sisim shear zone at the contact of the two largest tectonic structures of the accretion–collisional belt in the southwestern frame of the Siberian craton. Intrusions of the complex consist of ore-bearing olivinites, kaersutite clinopyroxenites, and banded kaersutite gabbro, which have been «cut» by albitite dykes and veins. The veins and veinlets of the carbonate rocks are mainly associated with the albitites. The present paper represents the first detailed mineralogical study of carbonate rocks and albitites in the Podlysansky Massif of the Neoproterozoic Lysan alkaline–ultramafic complex. The mineral composition was determined in situ in a polished section by scanning electron microscopy, energy dispersive spectrometry, and electron probe microanalysis. The carbonate rocks of the Podlysan Massif have been found to contain minerals that are typical of siderite–carbonatites (senso stricto), including calcite, siderite, phengitic muscovite, apatite, monazite, REE fluorocarbonates, pyrite, and sphalerite. These rocks are enriched in light rare earth elements due to the presence of monazite-(Ce), bastnäsite-(Ce), parisite-(Ce), and synchysite-(Ce). The albitites were formed as a result of the fenitization of leucocratic gabbro by alkali-rich carbo-hydrothermal fluids in zones of intense development of tectonic fractures. Infiltration was the dominant mechanism of fenitization. The obtained data significantly enhance the current understanding of the geochemical and ore specialization of rocks in the Lysan Complex. Full article

Rare earth element (REE) fluorocarbonate mineralization occurs in lacustrine shales in the Lower Devonian Rhynie chert, Aberdeenshire, UK, preserved by hot spring silicification. Mineralization follows a combination of first-cycle erosion of granite to yield detrital monazite grains, bioweathering of the monazite to liberate REEs, and interaction with fluorine-rich hot spring fluids in an alkaline sedimentary environment. The mineral composition of most of the fluorocarbonates is referable to synchysite. Mineralization occurs at the surface, and the host shales subsequently experience maximum temperatures of about 110 ℃. Most fluorocarbonate mineralization originates at much higher temperatures, but the Rhynie occurrence emphasizes that low-temperature deposits are possible when both fluorine and REEs are available from granite into the sedimentary environment. Full article

In Mongolia, rare earth element (REE) mineralization of economic significance is related either to the Mesozoic carbonatites or to the Paleozoic peralkaline granitoid rocks. Carbonatites occur as part of alkaline silicate-carbonatite complexes, which are composed mainly of nepheline syenites and equivalent volcanic rocks. The complexes were emplaced in the Gobi-Tien Shan rift zone in southern Mongolia where carbonatites usually form dikes, plugs or intruded into brecciated rocks. In mineralized carbonatites, REE occur mainly as fluorocarbonates (bastnäsite, synchysite, parisite) and apatite. Apatite is also present in the carbonatite-hosted apatite-magnetite (mostly altered to hematite) bodies. Alkaline silicate rocks and carbonatites show common geochemical features such as enrichment of light REE but relative depletion of Ti, Zr, Nb, Ta and Hf and similar Sr and Nd isotopic characteristics suggesting the involvement of the heterogeneous lithospheric mantle in the formation of both carbonatites and associated silicate rocks. Hydrothermal fluids of magmatic origin played an important role in the genesis of the carbonatite-hosted REE deposits. The REE mineralization associated with peralkaline felsic rocks (peralkaline granites, syenites and pegmatites) mainly occurs in Mongolian Altai in northwestern Mongolia. The mineralization is largely hosted in accessory minerals (mainly elpidite, monazite, xenotime, fluorocarbonates), which can reach percentage levels in mineralized zones. These rocks are the results of protracted fractional crystallization of the magma that led to an enrichment of REE, especially in the late stages of magma evolution. The primary magmatic mineralization was overprinted (remobilized and enriched) by late magmatic to hydrothermal fluids. The mineralization associated with peralkaline granitic rocks also contains significant concentrations of Zr, Nb, Th and U. There are promising occurrences of both types of rare earth mineralization in Mongolia and at present, three of them have already established significant economic potential. They are mineralization related to Mesozoic Mushgai Khudag and Khotgor carbonatites in southern Mongolia and to the Devonian Khalzan Buregtei peralkaline granites in northwestern Mongolia. Full article

Synchysite was identified in the Rožná uranium deposit in a quartz–carbonate–sulfide vein, which is a part of the late (post-uranium and, post-Variscan) stage of the development of the hydrothermal system. The synchysite forms needles or lamellae, which are almost exclusively bound to the quartz filling of the veins. The structure of the quartz vein-filling, i.e., the preserved tubular syneresis crack pattern, Liesegang bands formed by hematite, chaotic grain size distribution of quartz grains, and ribbons of fibrous SiO₂ grains, indicate that the synchysite crystallized in a silica gel. Its formation may be explained by the reaction of hydrothermal acid fluids rich in Fe²⁺ and rare earth elements (REEs) with alkaline Ca²⁺ HCO₃⁻ and F-rich fluids expelled from the gel during syneresis, or by its ageing. The subsequent recrystallization of the gel to form euhedral quartz grains was accompanied by the deformation of previously formed Liesegang rings, and the development of quartz rosettes. The study of fluid inclusions indicated that the silica gel originated at a very low temperature. The temperatures of the homogenization of two-phase inclusions in carbonate and quartz vein-filling varied between 38 and 74 °C, and the salinity ranged between 4 and 10 wt.% NaCl equiv. The δ¹³C carbonate values (from −4.65 to −5.21‰, PDB) indicate the deep-seated source of CO₂, and δ¹⁸O values (from 14.76 to 18.22‰, SMOW) show that the source of the hydrothermal fluids was mainly surface water, with a possible admixture of fossil saline brines. The main sources of REEs are thought to have predominantly been uranium minerals (coffinitized uraninite and coffinite) that form a part of the breccia fragments embedded in the vein filling. The results illustrate the significant mobility of REEs in the late, low-temperature hydrothermal system, and they indicate the multiple remobilizations of REEs in the uranium deposits in general. Full article

Rare earth elements (REEs) are considered critical elements in modern society due to their irreplaceable role in new innovative and energy technologies. The giant carbonatite-related Bayan Obo deposit contributes most REE resources in the world’s market, while its origin is still unclear because of the complicated and diverse REE ore mineralogy and texture. Thescanning electron mircroscopy SEM)-based automated mineralogy allows for the numeric assessment of rocks and ores’ compositional and textural properties. Here, we use TIMA (TESCAN Integrated Mineral Analyzer) to quantitatively characterize REE ore mineralogy from the deep drill core within the H8 unit (“dolomite marble”) to better understand the deposit. The mineral composition, occurrence, and Ce elemental deportment of the borehole ores at different depths (i.e., 1107 m, 1246 m, 1406 m, 1546 m, and 1682 m) were obtained. The results show that the main types of ores in the investigated samples can be divided into banded REE-Fe ores, banded REE ores, disseminated REE-Fe ores, and veined REE ores. REE and gangue minerals vary significantly in abundance and occurrence. Monazite-(Ce) and bastnäsite-(Ce) are the primary REE host minerals, and both contribute the most to the REE budget. Other REE minerals, such as parisite-(Ce)/synchysite-(Ce), cerite-(Ce), huanghoite-(Ce)/cebaite-(Ce), and aeschynite-(Ce), are significant contributors. The gangue minerals generally include fluorite, barite, magnetite, pyrite, quartz, magnesio-arfvedsonite, and minerals of the biotite and apatite groups, among others. Combined with the newly published mineral-scale chronological and isotopic geochemical analyses, it is reasonable to conclude that the later hydrothermal fluids remobilized and redistributed the original Mesoproterozoic carbonatitic REE minerals and formed a high variable ore mineral assemblage. Furthermore, it is demonstrated that the mineralogical study using TIMA can provide accurate and reliable mineralogy data for the comprehensive interpretation of the complex REE ores, and extend our understanding of the deposit. Full article

The present research represents an approach toward the recycling of extractive waste inspired by circular economy and sustainability that is developed in accordance with Goal 12 of the United Nations 2030 Agenda for Sustainable Development Goals. A new procedure for the recovery of REEs from fluorite–barite–galena ores with calcite gangue from the Silius mine (Sardinia, Italy) is presented. The considered samples are waste materials of Silius mineralization, collected in the old processing plant of Assemini (near Cagliari). In this orebody, REE minerals consist of prevailing synchysite (a REE-bearing fluorocarbonate) and subordinate xenotime-Y (a Y-bearing phosphate). REE fluorocarbonates are extracted using 50% K₂CO₃ as the leaching solution, at 100 °C. Using a solution (mL)/sample (g) ratio of 25, about 10% of the total REE content of the considered sample is extracted within 1 h. At the laboratory scale, such alkaline leaching of REE from the waste materials allows the recovery of the CO₂ produced as K₂CO₃ from concentrated KOH, in accordance with a circular flow. Further work is ongoing to scale up the process into a pilot plant, to prove that the method developed within this research can be economically feasible, socially suitable, and environmentally respectful. Full article

The global demand for rare earth elements (REEs) is expected to increase significantly because of their importance in renewable energy and clean storage technologies, which are critical for drastic carbon dioxide emission reduction to achieve a carbon-neutral society. REE ore deposits around the world are scarce and those that have been identified but remain unexploited need to be developed to supply future demands. In this study, the Khalzan Buregtei deposit located in western Mongolia was studied with the aim of upgrading low-grade REE ore via magnetic separation techniques. The total REE content in this ore was ~6720 ppm (~3540 ppm light REE (LREE) + ~3180 ppm heavy REE (HREE)) with bastnaesite, pyrochlore, synchysite, and columbite-(Fe) identified as the main REE-bearing minerals. As the particle size fraction decreased from −4.0 + 2.0 mm to −0.5 + 0.1 mm, the recovery by dry high-intensity magnetic separation (DHIMS) increased from 20% to 70% of total rare earth oxide (TREO) while the enrichment ratio reached 2.8 from 1.3. Although effective, gangue minerals such as quartz and aluminosilicates were recovered (~22%) due most likely to insufficient liberation. Meanwhile, the wet high-intensity magnetic separation (WHIMS) could produce a magnetic concentrate with TREO recovery of ~80% and enrichment ratio of 5.5 under the following conditions: particle size fraction, −106 + 75 μm; feed flow rate, 3.2 L/min; magnetic induction, 0.8 T. These results indicate that combining DHIMS and WHIMS to upgrade the low-grade REE ore from the Khalzan Buregtei deposit is an effective approach. Full article

Rippite K₂(Nb,Ti)₂(Si₄O₁₂)(O,F)₂, a new K-Nb-cyclosilicate, has been discovered in calciocarbonatites from the Chuktukon massif (Chadobets upland, SW Siberian Platform, Krasnoyarsk Territory, Russia). It was found in a primary mineral assemblage, which also includes calcite, fluorcalciopyrochlore, tainiolite, fluorapatite, fluorite, Nb-rich rutile, olekminskite, K-feldspar, Fe-Mn–dolomite and quartz. Goethite, francolite (Sr-rich carbonate–fluorapatite) and psilomelane (romanèchite ± hollandite) aggregates as well as barite, monazite-(Ce), parisite-(Ce), synchysite-(Ce) and Sr-Ba-Pb-rich keno-/hydropyrochlore are related to a stage of metasomatic (hydrothermal) alteration of carbonatites. The calcite–dolomite coexistence assumes crystallization temperature near 837 °C for the primary carbonatite paragenesis. Rippite is tetragonal: P4bm, a = 8.73885(16), c = 8.1277(2) Å, V = 620.69(2) ų, Z = 2. It is closely identical in the structure and cell parameters to synthetic K₂Nb₂(Si₄O₁₂)O₂ (or KNbSi₂O₇). Similar to synthetic phase, the mineral has nonlinear properties. Some optical and physical properties for rippite are: colorless; Mohs’ hardness—4–5; cleavage—(001) very perfect, (100) perfect to distinct; density (meas.)—3.17(2) g/cm³; density (calc.)—3.198 g/cm³; optically uniaxial (+); ω = 1.737-1.739; ε = 1.747 (589 nm). The empirical formula of the holotype rippite (mean of 120 analyses) is K₂(Nb_1.90Ti_0.09Zr_0.01)[Si₄O₁₂](O_1.78OH_0.12F_0.10). Majority of rippite prismatic crystals are weakly zoned and show Ti-poor composition K₂(Nb_1.93Ti_0.05Zr_0.02)[Si₄O₁₂](O_1.93F_0.07). Raman and IR spectroscopy, and SIMS data indicate very low H₂O content (0.09–0.23 wt %). Some grains may contain an outermost zone, which is enriched in Ti (+Zr) and F, up to K₂(Nb_1.67Ti_0.32Zr_0.01)[Si₄O₁₂](O_1.67F_0.33). It strongly suggests the incorporation of (Ti,Zr) and F in the structure of rippite via the isomorphism Nb⁵⁺ + O²⁻ → (Ti,Zr)⁴⁺ + F¹⁻. The content of a hypothetical end-member K₂Ti₂[Si₄O₁₂]F₂ may be up to 17 mol. %. Rippite represents a new structural type among [Si₄O₁₂]-cyclosilicates because of specific type of connection of the octahedral chains and [Si₄O₁₂]⁸⁻ rings. In structural and chemical aspects it seems to be in close with the labuntsovite-supergroup minerals, namely with vuoriyarvite-(K), K₂(Nb,Ti)₂(Si₄O₁₂)(O,OH)₂∙4H₂O. Full article

The Bohemian magmatic complex belongs to granitoid plutons of the Central European Variscides. Hydrothermal uranium mineralization evolved in the small uranium deposits Nahošín and Mečichov is associated with N–S shear zones occurring on the SW margin of the Central Bohemian plutonic complex formed by amphibole-bearing biotite granodiorites of the Blatná suite. The purpose of presented study is description of uranium mineralization bounded on brittle shear zones, which is coupled with intense low-temperature hydrothermal alteration of granitic rocks. Uranium mineralization, formed predominantly of coffinite, rare uraninite, and thorite, is accompanied by intense hematitization, albitization, chloritization, and carbonatization of original granitic rocks that could be described as aceites. These alterations are accompanied by the enrichment in U, Ti, Mg, Ca, Na, K, Y, and Zr and depletion in Si, Ba, and Sr. The analyzed coffinite is enriched in Y (up to 3.1 wt % Y₂O₃). Uraninite is enriched in Th (up to 9.8 wt % ThO₂) and thorite is enriched in Zr (up to 5.7 wt % ZrO₂). The REE-elements are concentrated in the REE-fluorcarbonate synchysite-(Ce). Full article

The mineral composition and melt inclusions of ultramafic lamprophyres of the Terina complex were investigated. The rocks identified were aillikites, mela-aillikites, and damtjernites, and they were originally composed of olivine macrocrysts and phenocrysts, as well as phlogopite phenocrysts in carbonate groundmass, containing phlogopite, clinopyroxene and feldspars. Minor and accessory minerals were fluorapatite, ilmenite, rutile, titanite, and sulphides. Secondary minerals identified were quartz, calcite, dolomite, serpentine, chlorite, rutile, barite, synchysite-(Ce), and monazite-(Ce). Phlogopite, calcite, clinopyroxene, Ca-amphibole, fluorapatite, magnetite, and ilmenite occurred as daughter-phases in melt inclusions. The melt inclusions also contained Fe–Ni sulphides, synchysite-(Ce) and, probably, anhydrite. The olivine macrocrysts included orthopyroxene and ilmenite, and the olivine phenocrysts included Cr-spinel and Ti-magnetite inclusions. Crystal-fluid inclusions in fluorapatite from damtjernites contain calcite, clinopyroxene, dolomite, and barite. The data that were obtained confirm that the ultramafic lamprophyres of the Terina complex crystallized from peridotite mantle-derived carbonated melts and they have not undergone significant fractional crystallization. The investigated rocks are considered to be representative of melts that are derived from carbonate-rich mantle beneath the Siberian craton. Full article

The Vuoriyarvi Devonian alkaline–ultramafic complex (northwest Russia) contains magnesiocarbonatites with rare earth mineralization localized in the Petyayan-Vara area. High concentrations of rare earth elements are found in two types of these rocks: (a) ancylite-dominant magnesiocarbonatites with ancylite–baryte–strontianite–calcite–quartz (±late Ca–Fe–Mg carbonates) ore assemblage, i.e., “ancylite ores”; (b) breccias of magnesiocarbonatites with a quartz–bastnäsite matrix (±late Ca–Fe–Mg carbonates), i.e., “bastnäsite ores.” We studied fluid inclusions in quartz and late-stage Ca–Fe–Mg carbonates from these ore assemblages. Fluid inclusion data show that ore-related mineralization was formed in several stages. We propose the following TX evolution scheme for ore-related processes: (1) the formation of ancylite ores began under the influence of highly concentrated (>50 wt.%) sulphate fluids (with thenardite and anhydrite predominant in the daughter phases of inclusions) at a temperature above300–350 °C; (2) the completion of the formation of ancylite ores and their auto-metasomatic alteration occurred under the influence of concentrated (40–45 wt.%) carbonate fluids (shortite and synchysite–Ce in fluid inclusions) at a temperature above 250–275 °C; (3) bastnäsite ores deposited from low-concentrated (20–30 wt.%) hydrocarbonate–chloride fluids (halite, nahcolite, and/or gaylussite in fluid inclusions) at a temperature of 190–250 °C or higher. Later hydrothermal mineralization was related to the low-concentration hydrocarbonate–chloride fluids (<15 wt.% NaCl-equ.) at 150–200 °C. The presented data show the specific features of the mineral and fluid evolution of ore-related late-stage hydrothermal rare earth element (REE) mineralization of the Vuoriyarvi alkaline–ultramafic complex. Full article

Synchysite-(Ce) at Cinquevalli occurs as fine needles intergrown with quartz in quartz-dikes and in association with altered K-feldspar and oxidized chalcopyrite as major constituents. Synchysite-(Ce) [Ca_1.00(Ce_0.43La_0.26Nd_0.17Y_0.07Pr_0.04Sm_0.02Gd_0.01)_Σ=1.00(CO₃)₂(F_0.58(OH)_0.42)], shows an overgrowth rim of bastnäsite-(Ce) [(Ce_0.34La_0.25Nd_0.17Pb_0.07C a_0.06Y_0.06Pr_0.04S m_0.02Gd_0.01)_Σ=1.00C O₃(F_0.75(OH)_0.25)]. Unit cell refinement of synchysite (C2/c) and bastnäsite (P62c) led to a = 12.272(4), b = 7.100(2), c = 18.640(5) Å, β = 102.71(5)°, and a = 7.085(1), c = 9.746(2) Å, respectively. Polysomatic faults are sporadic, but polytypic disorder is widespread. High resolution transmission electron microscopy images taken along [100] or ⟨130⟩ show an apparent order and the related diffraction patterns are streak-free. Conversely, along [010] or ⟨110⟩, a high density of stacking faults is observed and the related diffraction patterns show hhl rows with h ≠ 3n affected by streaks. No ordered domain larger than a few unit cells was detected. The stacking sequence of (Ca,REE)-fluorcarbonates can be compared with subfamily-B mica polytypes (2M₂, 2O and 6H), which are characterized by n·60° (n = odd) rotations. Subfamily-A polytypes (1M, 2M₁ and 3T), characterized by n·60° (n = even) rotations, should not be possible. Synchysite, characterized by ±60° rotations, can be likened to the 2M₂ polytype. Full article

The Vuoriyarvi Devonian carbonatite–ijolite–pyroxenite–olivinite complex comprises several carbonatite fields: Neske Vara, Tukhta-Vara, and Petyayan-Vara. The most common carbonatites in the Tukhta-Vara and Neske-Vara fields are calciocarbonatites, which host several P, Fe, Nb, and Ta deposits. This paper focuses on the Petyayan-Vara field, in which the primary magmatic carbonatites are magnesian. The least altered magnesiocarbonatites are composed of dolomite with burbankite and are rich in REE (up to 2.0 wt. %), Sr (up to 1.2 wt. %), and Ba (up to 0.8 wt. %). These carbonatites underwent several stages of metasomatism. Each metasomatic event produced a new rock type with specific mineralization. The introduction of K, Si, Al, Fe, Ti, and Nb by a F-rich fluid (or fluid-saturated melt) resulted in the formation of high-Ti magnesiocarbonatites and silicocarbonatites, composed of dolomite, microcline, Ti-rich phlogopite, and Fe–Ti oxides. Alteration by a phosphate–fluoride fluid caused the crystallization of apatite in the carbonatites. A sulfate-rich Ba–Sr–rare-earth elements (REE) fluid (probably brine-melt) promoted the massive precipitation of ancylite and baryte and, to a lesser extent, strontianite, bastnäsite, and synchysite. Varieties of carbonatite that contain the highest concentrations of REE are ancylite-dominant. The influence of sulfate-rich Ba-Sr-REE fluid on the apatite-bearing rocks resulted in the dissolution and reprecipitation of apatite in situ. The newly formed apatite generation is rich in HREE, Sr, and S. During late-stage transformations, breccias of magnesiocarbonatites with quartz-bastnäsite matrixes were formed. Simultaneously, strontianite, quartz, calcite, monazite, HREE-rich thorite, and Fe-hydroxides were deposited. Breccias with quartz-bastnäsite matrix are poorer in REE (up to 4.5 wt. % total REE) than the ancylite-dominant rocks (up to 11 wt. % total REE). Full article