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25 pages, 7201 KiB  
Article
The REE-Zr-U-Th Minerals of the Maronia Monzodiorite, N. Greece: Implications on the Saturation and Segregation Mechanisms of Critical Metals in Intermediate–Mafic Compositions
by Charalampos Vasilatos and Angeliki Papoutsa
Minerals 2023, 13(10), 1256; https://doi.org/10.3390/min13101256 - 26 Sep 2023
Cited by 1 | Viewed by 1977
Abstract
This work delves into the presence of REE-Ti-Zr-U-Th minerals, in the mafic–intermediate rocks of the Maronia pluton, Greece, an Oligocene intrusion formed through arc-magmatism during subduction. In Maronia monzodiorite, critical metals are contained in three principal mineral groups, namely, the REE-Ti-Zr, REE-Ca-P, and [...] Read more.
This work delves into the presence of REE-Ti-Zr-U-Th minerals, in the mafic–intermediate rocks of the Maronia pluton, Greece, an Oligocene intrusion formed through arc-magmatism during subduction. In Maronia monzodiorite, critical metals are contained in three principal mineral groups, namely, the REE-Ti-Zr, REE-Ca-P, and U-Th assemblages. The REE-Ti-Zr group includes REE-ilmenite, chevkinite-like phases, zirconolite, and baddeleyite. The REE-Ca-P assemblage is represented by allanite-(Ce), monazite-(Ce), and huttonitic monazite-(Ce). The U-Th assemblage comprises thorite–coffinite and uraninite–thorianite solid solutions. The paragenetic sequencing of these minerals offers insights into their formation conditions and correlation with the pluton’s magmatic evolution. In the REE-Ti-Zr group, mineral formation progresses from REE-ilmenite to baddeleyite through chevkinite-like phases and zirconolite under oxidizing conditions. The REE-Ca-P sequence involves allanite-(Ce), followed by monazite-(Ce), late allanite-(Ce), and huttonitic monazite-(Ce). In the U-Th group, earlier thorite–coffinite phases are succeeded by uraninite–thorianite solid solutions, indicating Si-undersaturation at late magmatic stages. Fluctuations in Ca-activity induce alternating formations of allanite-(Ce) and monazite-(Ce). These mineral variations are attributed to early-stage interactions between high-K calc-alkaline and shoshonitic gabbroic melts, influencing critical metal enrichment and mineral speciation. The study’s insights into paragenesis and geological processes offer implications for mineral exploration in analogous geological settings. Full article
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32 pages, 8845 KiB  
Article
Petrology of Granites of the Tommot Rare-Earth Ore Field (Verkhoyansk–Kolyma Orogenic Belt)
by Vera A. Trunilina and Andrei V. Prokopiev
Minerals 2022, 12(11), 1347; https://doi.org/10.3390/min12111347 - 24 Oct 2022
Cited by 3 | Viewed by 2153
Abstract
The article presents the results of studying the aegirine–arfvedsonite granites of the Somnitelnyi massif within the Tommot ore field located in the Verkhoyansk–Kolyma orogenic belt (NE Asia). Along with the crustal signatures, the rocks display features of mantle contamination at their origin. Their [...] Read more.
The article presents the results of studying the aegirine–arfvedsonite granites of the Somnitelnyi massif within the Tommot ore field located in the Verkhoyansk–Kolyma orogenic belt (NE Asia). Along with the crustal signatures, the rocks display features of mantle contamination at their origin. Their affinity for A-type granites characteristic of continental rifts and hot spots is shown. The associated Tommot REE deposit is the only one discovered in NE Russia. New data are presented for the previously studied Tommot massif within the same ore field, with a wide compositional range from alkaline-ultrabasic rocks to alkaline syenites. It is established that despite a common geochemical enrichment of both massifs’ rocks with REEs, the Somnitelnyi massif granites cannot be interpreted as the final phase of the Tommot massif emplacement. Specific REE mineralization and high crystallization temperatures (up to 1045 °C) of the Somnitelnyi granites may be explained by the existence within the study area of an undepleted mantle source (“hot spot”), whose maximum activity occurred during the granitic melt generation. The ore bodies of the Tommot deposit consist of fenitized albitites, granite gneisses, and, more rarely, the cross-cutting pegmatite veins. They are confined mostly to exocontacts of the Somnitelnyi massif, are less often in its endocontacts, and are not found in the host rocks and in the inner part of the massif away from the contacts. Principal ore minerals are chevkinite, yttrialite, gadolinite, and fergusonite. Based on the data obtained, the deposit is classified as a metasomatic complex Ce–Y–Nb–Zr deposit associated with the alkaline granites. Full article
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18 pages, 3333 KiB  
Article
Extreme Alteration of Chevkinite-(Ce) by Pb-CO2-Rich Fluids: Evidence from the White Tundra Pegmatite, Keivy Massif, Kola Peninsula
by Ray Macdonald, Bogusław Bagiński, Marcin Stachowicz, Dmitry Zozulya, Jakub Kotowski and Petras Jokubauskas
Minerals 2022, 12(8), 989; https://doi.org/10.3390/min12080989 - 3 Aug 2022
Viewed by 2062
Abstract
An unusual hydrothermal alteration scheme was presented for chevkinite-(Ce) from the White Tundra pegmatite (2656 ± 5 Ma), Keivy massif, Kola Peninsula. Pb-CO2-rich fluids initially removed REE and Y from the chevkinite-(Ce), with enrichment in Pb and U. PbO abundances reaching [...] Read more.
An unusual hydrothermal alteration scheme was presented for chevkinite-(Ce) from the White Tundra pegmatite (2656 ± 5 Ma), Keivy massif, Kola Peninsula. Pb-CO2-rich fluids initially removed REE and Y from the chevkinite-(Ce), with enrichment in Pb and U. PbO abundances reaching 17.35 wt%. Continued alteration resulted in the altered chevkinite-(Ce) being progressively transformed to a Pb-Ti-Fe-Si phase, which proved, upon EBSD analysis, to be almost totally amorphous. Pb enrichment was accompanied by a loss of LREE, especially La, relative to HREE, and the development of strong positive Ce anomalies. A notably U-rich aeschynite-(Y), with UO2 values ≤7.67 wt%, crystallized along with the chevkinite-(Ce). Aeschynite-(Y) with a lower UO2 value (3.91 wt%) and bastnäsite-(Ce) formed during alteration. The formation of bastnäsite-(Ce) rather than cerussite, which might have been expected in a high Pb-CO2 environment, is ascribed to the fluids being acidic. Full article
(This article belongs to the Special Issue Mineralogy, Petrology and Crystallography of Silicate Minerals)
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13 pages, 7872 KiB  
Article
The Effect of X-ray Energy Overlaps on the Microanalysis of Chevkinite (Ce, La, Ca, Th)4(Fe2+, Mg)2(Ti, Fe3+)3Si4O22 Using SEM EDS-WDS
by Alicja Lacinska, Jeremy Rushton, Simon Burgess, Eimear A. Deady and Gren Turner
Minerals 2021, 11(10), 1063; https://doi.org/10.3390/min11101063 - 28 Sep 2021
Cited by 6 | Viewed by 3059
Abstract
A light REE (LREE)-bearing mineral called chevkinite (Ce, La, Ca, Th)4(Fe2+, Mg)2(Ti, Fe3+)3Si4O22, originating from a heavy metal placer deposit Aksu Diamas in Turkey, previously assessed for potential REE extraction [...] Read more.
A light REE (LREE)-bearing mineral called chevkinite (Ce, La, Ca, Th)4(Fe2+, Mg)2(Ti, Fe3+)3Si4O22, originating from a heavy metal placer deposit Aksu Diamas in Turkey, previously assessed for potential REE extraction as a by-product of magnetite production, was studied using scanning electron microscopy with energy and wavelength-dispersive spectrometers (SEM EDS-WDS). This mineral exhibits analytical challenges associated with severe X-ray energy overlaps between the REE, titanium, and barium. Here, we present an iterative process, showing that SEM EDS-WDS is a viable technique for obtaining good quality quantitative data. SEM EDS-WDS is an in situ, non-destructive, and relatively non-expensive technique, but operator’s experience is essential to obtain good quality data. In cases where the peak fitting remains challenging, in particular, and where the constituents have large differences in abundance, an assessment of the X-ray spectrum to qualitatively assign all peaks is essential prior to quantitative analysis. Full article
(This article belongs to the Special Issue Electron Microbeam and X-ray Techniques: Advances and Applications)
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20 pages, 13910 KiB  
Article
REE Minerals as Geochemical Proxies of Late-Tertiary Alkalic Silicate ± Carbonatite Intrusions Beneath Carpathian Back-Arc Basin
by Vratislav Hurai, Monika Huraiová and Patrik Konečný
Minerals 2021, 11(4), 369; https://doi.org/10.3390/min11040369 - 31 Mar 2021
Cited by 6 | Viewed by 2830
Abstract
The accessory mineral assemblage (AMA) of igneous cumulate xenoliths in volcanoclastic deposits and lava flows in the Carpathian back-arc basin testifies to the composition of intrusive complexes sampled by Upper Miocene-Pliocene basalt volcanoes. The magmatic reservoir beneath Pinciná maar is composed of gabbro, [...] Read more.
The accessory mineral assemblage (AMA) of igneous cumulate xenoliths in volcanoclastic deposits and lava flows in the Carpathian back-arc basin testifies to the composition of intrusive complexes sampled by Upper Miocene-Pliocene basalt volcanoes. The magmatic reservoir beneath Pinciná maar is composed of gabbro, moderately alkalic to alkali-calcic syenite, and calcic orthopyroxene granite (pincinite). The intrusive complex beneath the wider area around Fiľakovo and Hajnáčka maars contains mafic cumulates, alkalic syenite, carbonatite, and calc-alkalic granite. Both reservoirs originated during the basaltic magma underplating, differentiation, and interaction with the surrounding mantle and crust. The AMA of syenites is characterized by yttrialite-Y, britholite-Y, britholite-Ce, chevkinite-Ce, monazite-Ce, and rhabdophane(?). Baddeleyite and REE-zirconolite are typical of alkalic syenite associated with carbonatite. Pyrochlore, columbite-Mn, and Ca-niobates occur in calc-alkalic granites with strong peralkalic affinity. Nb-rutile, niobian ilmenite, and fergusonite-Y are crystallized from mildly alkalic syenite and calc-alkalic granite. Zircons with increased Hf/Zr and Th/U ratios occur in all felsic-to-intermediate rock-types. If rock fragments are absent in the volcanic ejecta, the composition of the sub-volcanic reservoir can be reconstructed from the specific AMA and zircon xenocrysts–xenolith relics disintegrated during the basaltic magma fragmentation and explosion. Full article
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31 pages, 7721 KiB  
Article
Volcanic-Derived Placers as a Potential Resource of Rare Earth Elements: The Aksu Diamas Case Study, Turkey
by Eimear Deady, Alicja Lacinska, Kathryn M. Goodenough, Richard A. Shaw and Nick M. W. Roberts
Minerals 2019, 9(4), 208; https://doi.org/10.3390/min9040208 - 30 Mar 2019
Cited by 17 | Viewed by 9352
Abstract
Rare earth elements (REE) are essential raw materials used in modern technology. Current production of REE is dominated by hard-rock mining, particularly in China, which typically requires high energy input. In order to expand the resource base of the REE, it is important [...] Read more.
Rare earth elements (REE) are essential raw materials used in modern technology. Current production of REE is dominated by hard-rock mining, particularly in China, which typically requires high energy input. In order to expand the resource base of the REE, it is important to determine what alternative sources exist. REE placers have been known for many years, and require less energy than mining of hard rock, but the REE ore minerals are typically derived from eroded granitic rocks and are commonly radioactive. Other types of REE placers, such as those derived from volcanic activity, are rare. The Aksu Diamas heavy mineral placer in Turkey has been assessed for potential REE extraction as a by-product of magnetite production, but its genesis was not previously well understood. REE at Aksu Diamas are hosted in an array of mineral phases, including apatite, chevkinite group minerals (CGM), monazite, allanite and britholite, which are concentrated in lenses and channels in unconsolidated Quaternary sands. Fingerprinting of pyroxene, CGM, magnetite and zircon have identified the source of the placer as the nearby Gölcük alkaline volcanic complex, which has a history of eruption throughout the Plio-Quaternary. Heavy minerals were eroded from tephra and reworked into basinal sediments. This type of deposit may represent a potential resource of REE in other areas of alkaline volcanism. Full article
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14 pages, 19168 KiB  
Article
Nöggerathite-(Ce), (Ce,Ca)2Zr2(Nb,Ti)(Ti,Nb)2Fe2+O14, a New Zirconolite-Related Mineral from the Eifel Volcanic Region, Germany
by Nikita V. Chukanov, Natalia V. Zubkova, Sergey N. Britvin, Igor V. Pekov, Marina F. Vigasina, Christof Schäfer, Bernd Ternes, Willi Schüller, Yury S. Polekhovsky, Vera N. Ermolaeva and Dmitry Yu. Pushcharovsky
Minerals 2018, 8(10), 449; https://doi.org/10.3390/min8100449 - 12 Oct 2018
Cited by 18 | Viewed by 4451
Abstract
The new mineral nöggerathite-(Ce) was discovered in a sanidinite volcanic ejectum from the Laach Lake (Laacher See) paleovolcano in the Eifel region, Rhineland-Palatinate, Germany. Associated minerals are sanidine, dark mica, magnetite, baddeleyite, nosean, and a chevkinite-group mineral. Nöggerathite-(Ce) has a color that ranges [...] Read more.
The new mineral nöggerathite-(Ce) was discovered in a sanidinite volcanic ejectum from the Laach Lake (Laacher See) paleovolcano in the Eifel region, Rhineland-Palatinate, Germany. Associated minerals are sanidine, dark mica, magnetite, baddeleyite, nosean, and a chevkinite-group mineral. Nöggerathite-(Ce) has a color that ranges from brown to deep brownish red, with adamantine luster; the streak is brownish red. It occurs in cavities of sanidinite and forms long prismatic crystals measuring up to 0.02 × 0.03 × 1.0 mm, with twins and random intergrowths. Its density calculated using the empirical formula is 5.332 g/cm3. The Vickers hardness number (VHN) is 615 kgf/mm2, which corresponds to a Mohs’ hardness of 5½. The mean refractive index calculated using the Gladstone–Dale equation is 2.267. The Raman spectrum shows the absence of hydrogen-bearing groups. The chemical composition (electron microprobe holotype/cotype in wt %) is as follows: CaO 5.45/5.29, MnO 4.19/4.16, FeO 7.63/6.62, Al2O3 0.27/0.59, Y2O3 0.00/0.90, La2O3 3.17/3.64, Ce2O3 11.48/11.22, Pr2O3 1.04/0.92, Nd2O3 2.18/2.46, ThO2 2.32/1.98, TiO2 17.78/18.69, ZrO2 27.01/27.69, Nb2O5 17.04/15.77, total 99.59/99.82, respectively. The empirical formulae based on 14 O atoms per formula unit (apfu) are: (Ce0.59La0.165Nd0.11Pr0.05)Σ0.915Ca0.82Th0.07Mn0.50Fe0.90Al0.045Zr1.86Ti1.88Nb1.07O14 (holotype), and (Ce0.57La0.19Nd0.12Pr0.05Y0.06)Σ0.99Ca0.79Th0.06Mn0.49Fe0.77Al0.10Zr1.89Ti1.96Nb1.00O14 (cotype). The simplified formula is (Ce,Ca)2Zr2(Nb,Ti)(Ti,Nb)2Fe2+O14. Nöggerathite-(Ce) is orthorhombic, of the space group Cmca. The unit cell parameters are: a = 7.2985(3), b = 14.1454(4), c = 10.1607(4) Å, and V = 1048.99(7) Å3. The crystal structure was solved using single-crystal X-ray diffraction data. Nöggerathite-(Ce) is an analogue of zirconolite-3O, ideally CaZrTi2O7, with Nb dominant over Ti in one of two octahedral sites and REE dominant over Ca in the eight-fold coordinated site. The strongest lines of the powder X-ray diffraction pattern (d, Å (I, %) (hkl)) are: 2.963 (91) (202), 2.903 (100) (042), 2.540 (39) (004), 1.823 (15) (400), 1.796 (51) (244), 1.543 (20) (442), and 1.519 (16) (282), respectively. The type material is deposited in the collections of the Fersman Mineralogical Museum of the Russian Academy of Sciences, Moscow, Russia (registration number 5123/1). Full article
(This article belongs to the Special Issue New Mineral Species and Their Crystal Structures)
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39 pages, 37544 KiB  
Article
Geology and Mineralogy of Rare Earth Elements Deposits and Occurrences in Finland
by Thair Al-Ani, Ferenc Molnár, Panu Lintinen and Seppo Leinonen
Minerals 2018, 8(8), 356; https://doi.org/10.3390/min8080356 - 18 Aug 2018
Cited by 18 | Viewed by 15816
Abstract
Rare earth elements (REE) have critical importance in the manufacturing of many electronic products in the high-tech and green-tech industries. Currently, mining and processing of REE is strongly concentrated in China. A substantial growth in global exploration for REE deposits has taken place [...] Read more.
Rare earth elements (REE) have critical importance in the manufacturing of many electronic products in the high-tech and green-tech industries. Currently, mining and processing of REE is strongly concentrated in China. A substantial growth in global exploration for REE deposits has taken place in the recent years and has resulted in considerable advances in defining new resources. This study provides an overview of the mineralogical and petrological peculiarities of the most important REE prospects and metallogeny of REE in Finland. There is a particularly good potential for future discoveries of carbonatite hosted REE deposits in the Paleozoic Sokli carbonatite complex, as well as in the Paleoproterozoic Korsnäs and Kortejärvi Laivajoki areas. This review also provides information about the highest known REE concentration in the alkaline intrusions of Finland in the Tana Belt and other alkaline rock hosted occurrences (e.g., Otanmäki and Katajakangas). Significant REE enrichments in hydrothermal alteration zones are also known in the Kuusamo Belt (Uuniniemi and Honkilehto), and occurrences of REE-rich mineralisation are also present in granite pegmatite bodies and greisens in central and southern Finland (Kovela monazite granite and the Rapakivi Granite batholith at Vyborg, respectively). REE minerals in all of the localities listed above were identified and analyzed by scanning electron microscopy (SEM) and electron microprobes (EMPs). In localities of northern and central Finland, both primary rock forming and epigenetic-hydrothermal REE minerals were found, namely phosphates (monazite-Ce, xenotime-Y), fluorcarbonates (bastnäsite-Ce, synchysite), and hydrated carbonates (ancylite-Ce), hydrated aluminium silicates (allanite-Ce, Fe-allanite, cerite, chevkinite), oxides (fergusonite, euxenite) and U-Pb rich minerals. The chondrite normalized REE concentrations, the La/Nd ratios and the REE vs. major element contents in several types of REE bearing minerals from prospects in Finland can be used to identify and define variable REE fractionation processes (carbonatites), as well as to discriminate deposits of different origins. Full article
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28 pages, 4395 KiB  
Article
Sources of Extraterrestrial Rare Earth Elements: To the Moon and Beyond
by Claire L. McLeod and Mark. P. S. Krekeler
Resources 2017, 6(3), 40; https://doi.org/10.3390/resources6030040 - 23 Aug 2017
Cited by 42 | Viewed by 23301
Abstract
The resource budget of Earth is limited. Rare-earth elements (REEs) are used across the world by society on a daily basis yet several of these elements have <2500 years of reserves left, based on current demand, mining operations, and technologies. With an increasing [...] Read more.
The resource budget of Earth is limited. Rare-earth elements (REEs) are used across the world by society on a daily basis yet several of these elements have <2500 years of reserves left, based on current demand, mining operations, and technologies. With an increasing population, exploration of potential extraterrestrial REE resources is inevitable, with the Earth’s Moon being a logical first target. Following lunar differentiation at ~4.50–4.45 Ga, a late-stage (after ~99% solidification) residual liquid enriched in Potassium (K), Rare-earth elements (REE), and Phosphorus (P), (or “KREEP”) formed. Today, the KREEP-rich region underlies the Oceanus Procellarum and Imbrium Basin region on the lunar near-side (the Procellarum KREEP Terrain, PKT) and has been tentatively estimated at preserving 2.2 × 108 km3 of KREEP-rich lithologies. The majority of lunar samples (Apollo, Luna, or meteoritic samples) contain REE-bearing minerals as trace phases, e.g., apatite and/or merrillite, with merrillite potentially contributing up to 3% of the PKT. Other lunar REE-bearing lunar phases include monazite, yittrobetafite (up to 94,500 ppm yttrium), and tranquillityite (up to 4.6 wt % yttrium, up to 0.25 wt % neodymium), however, lunar sample REE abundances are low compared to terrestrial ores. At present, there is no geological, mineralogical, or chemical evidence to support REEs being present on the Moon in concentrations that would permit their classification as ores. However, the PKT region has not yet been mapped at high resolution, and certainly has the potential to yield higher REE concentrations at local scales (<10s of kms). Future lunar exploration and mapping efforts may therefore reveal new REE deposits. Beyond the Moon, Mars and other extraterrestrial materials are host to REEs in apatite, chevkinite-perrierite, merrillite, whitlockite, and xenotime. These phases are relatively minor components of the meteorites studied to date, constituting <0.6% of the total sample. Nonetheless, they dominate a samples REE budget with their abundances typically 1–2 orders of magnitude enriched relative to their host rock. As with the Moon, though phases which host REEs have been identified, no extraterrestrial REE resource, or ore, has been identified yet. At present extraterrestrial materials are therefore not suitable REE-mining targets. However, they are host to other resources that will likely be fundamental to the future of space exploration and support the development of in situ resource utilization, for example: metals (Fe, Al, Mg, PGEs) and water. Full article
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