Tento přispěvek přinasi informace o geneticky kompletni radě
ložisek prvků ze skupiny vzacných zemin (REE) v Mongolsku;
konkretně vazaných na karbonatity (ložiska Mushgai Khudag,
Bayan Khushu, Khotgor, Cogt Obo, Ulugei Khid, Lugiin Gol, Omnot
Olgii, Khurimt Khad Tolgod) a peralkalicke granity se Zr-Nb-REE
mineralizaci (Khaldzan Buregtei a Khan Bogd) a metasomatity s
nejasnou genezi (Bomin Khara, Gzarta Hudag).
Abstract The effects of ultrasonic milling, dry and wet ball milling, and vibro‐milling on the particulate properties, crystalline characteristics, morphology, and surface area of clinoptilolite (Cpt) have been investigated. Laser beam scattering technique, X‐ray diffraction (XRD), scanning electron microscopy (SEM), and nitrogen adsorption/desorption at 77 K are used to characterize the initial and ground Cpt powders. Results show that Cpt particle size is significantly reduced by all carried out milling methods in which vibro‐milling could produce particles with diameter less than 100 nm. The size distribution of Cpt is remarkably narrowed by using vibro‐ and wet ball milling. The crystallinity of Cpt noticeably decreases for the samples obtained by ball milling while vibro‐ and ultrasonic millings show a negligible effect on crystallinity. The specific surface area of Cpt is enhanced by all four milling methods.
Abstract Carbonatite intrusions host the world’s most important light rare earth element (LREE) deposits, and their formation generally requires extraordinary fertile sources, magmatic evolution, and hydrothermal events. However, carbonatitic magma evolution, particularly the role of fractional crystallization and contamination from silicate rocks in REE enrichment, remains enigmatic. The Maoniuping world-class REE deposit in southwestern China, is an ideal target to decipher magmatic evolution and related REE enrichment as it shows continuous textual evolution from medium- to coarse-grained calcite carbonatite (carbonatite I) at depth, to progressively pegmatoidal calcite carbonatite (carbonatite II) at shallow levels. In both types of calcite carbonatites, four generations of calcite can be classified according to petrographic and geochemical characteristics. Early-crystalizing calcite (Cal-I and Cal-II) are found in carbonatite I and exhibit equigranular and a polygonal mosaic textures, while late calcites (Cal-III and Cal-IV) in carbonatite II are large-size oikocrysts (>0.5 mm in length) with strain-induced undulatory extinction and bent twinning lamellae. All these generations of calcite yield similar, near-chondritic, Y/Ho ratios (26.6–28.1) and are inferred to be of magmatic origin. Remarkably, gradual enrichment of MgO, FeO and MnO from Cal-I to Cal-IV is coupled with a significant increase in REE contents (~800 to 2000 ppm), with LREE-rich and gentle-to-steep chondrite-normalized REE patterns ((La/Yb)N = 3.1–26.8 and (La/Sm)N = 0.9–3.9, respectively). Such significant REE enrichment is ascribed to protracted magma fractional crystallization with initial low degree of fractional crystallization (fraction of melt remining (F) = ~0.95) evolving to late stage (F = 0.5–0.6) by formation of abundant calcite cumulates. Differential LREE and HREE behavior during magma evolution largely depend on separation of phlogopite, amphibole, and clinopyroxene from the carbonatitic melt, which is indicated by progressively elevated (La/Yb)N ratios ranging from 3.1 to 26.8. The four generations of calcite have significantly different C and Sr isotopic compositions with δ13CV-PDB decreasing from −3.28 to −9.97‰ and 87Sr/86Sr increasing from 0.70613 to 0.70670. According to spatial relations and petrographic observations, the relative enrichment of δ13C and depletion in 87Sr/86Sr ratios of Cal-I and Cal-II show primary isotopic characteristics inherited from initial carbonatitic magma. By contrast, the variable Sr and C isotopic compositions of Cal-III and Cal-IV are interpreted as the results of contamination by components derived from silicate wall rocks and loss of CO2 by decarbonation reactions. To model such contamination processes, Raleigh volatilization and Monte Carlo simulation have been invoked and the model results reveal that carbonatitic melt-wall rock interaction requires 40% radiogenic Sr contamination from silicate rocks and 35% CO2 degassing from carbonatitic melt. Moreover, positive correlations between decreasing δ13C values and increasing REE contents, together with bastnäsite-(Ce) precipitation, indicate further REE accumulation during the contamination processes. In summary, alongside REE-rich magma sources, the extent of fractional crystallization and contamination during carbonatitic magma evolution are inferred to be important mechanisms in terms of REE enrichment and mineralization in carbonatite-related REE deposits worldwide.
Ložiska REE (rare earth elements) nabohacených jilů byla
objevena v 60. letech minuleho stoleti v jižni Cině. Tento
ložiskový typ vznikal předevsim lateritovým zvětravanim živci
bohatých hornin s akcesorickým obsahem mineralů REE. Přispěvek
byl zaměřen na studium REE v mineralech z dane oblasti.
The relative criticality of mineral commodities is evaluated using a wide range of parameters and in different contexts (e.g., from the standpoint of their importance to national security, or to a specific industrial application), which explains the multiplicity of classification schemes and variations in terminology applied to these commodities in the literature, media and government reports. The core group of critical metals, listed alphabetically, includes: antimony, beryllium, chromium, cobalt, gallium, germanium, indium, lithium, niobium, platinoids, rare-earth elements (REE, including yttrium), tantalum and tungsten. The present retrospect briefly describes the emergence of critical metals as a distinct resource type and the evolution of society's perception of these commodities over the past 100 years.
Abstract Carbonatites, usually occurring within intra-continental rift-related settings, have strong light rare earth element (LREE) enrichment; they rarely contain economic heavy REE (HREE). Here, we report the identification of Late Triassic HREE-Mo-rich carbonatites in the northernmost Qinling orogen. The rocks contain abundant primary HREE minerals and molybdenite. Calcite-hosted fluid inclusions, inferred to represent a magmatic-derived aqueous fluid phase, contain significant concentrations of Mo (~17 ppm), reinforcing the inference that these carbonatitic magmas had high Mo concentrations. By contrast, Late Triassic carbonatites in southernmost Qinling have economic LREE concentrations, but are depleted in HREE and Mo. Both of these carbonatite types have low δ 26 Mg values (−1.89 to −1.07‰), similar to sedimentary carbonates, suggesting a recycled sediment contribution for REE enrichment in their mantle sources. We propose that the carbonatites in the Qinling orogen were formed, at least in part, by the melting of a subducted carbonate-bearing slab, and that 10 Ma younger carbonatite magmas in the northernmost Qinling metasomatized the thickened eclogitic lower crust to produce high levels of HREE and Mo.
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