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).
The word “KUKISVUMCHORR”, written across the cover, reads like a magic spell. I know I would want to pull this book off a stand and peek inside at least to learn the story behind the title. Actually, this thirteen-letter loan from Lapp translates roughly as “Long Wooded Range”, and the book
Abstract Loparite-(Ce) is a ubiquitous accessory mineral in modally diverse albite-rich metasomatic rocks of the Burpala alkaline complex, Siberia. Compositionally, the mineral approaches the ideal formula Na REE Ti 2 O 6 ( REE = Ce > La > Nd > Pr > Sm), and contains minor CaTiO 3 (<4.8 mol.%), SrTiO 3 (<4.7 mol.%) and NaNbO 3 (<6.4 mol.%), The mineral is pseudocubic [ a p = 3.8815(3) Å], and produces an XRD pattern similar to that of synthetic NaCeTi 2 O 6 [ Pnma , a = 5.4517(4), b = 7.7058(9), c = 5.4333(6) Å]. The atomic coordinates and isotropic thermal parameters of synthetic NaCeTi 2 O 6 refined from an XRD powder pattern using the Rietveld method, are given. At Burpala, loparite precipitated from an alkaline REE -rich fluid during the metasomatic alteration of earlier-formed intrusive rocks. In some parageneses, loparite was replaced by ‘metaloparite’ during the final stages of metasomatism. ‘Metaloparite’ has the empirical formula REE Ti 2 O 6- x (OH,F) x ·nH 2 O, and shows minor enrichment in Ca and depletion in Sr, compared to co-existing loparite. The formation of ‘metaloparite’ involved cation leaching, hydration and ion-exchange between loparite and a fluid. ‘Metaloparite’ is metamict at room temperature, but some samples regain the perovskite-type structure upon heating.
A study of nioboloparite samples from the Khibina massif, Kola Peninsula, Russia, demonstrates that the majority is merely calcian niobian loparite-(Ce), niobian calcian loparite-(Ce) or niobian loparite-(Ce). The minerals do not differ in structure or significantly, with respect to their composition, from common loparite-(Ce) that occurs as a primary mineral throughout the Khibina complex. They differ from common loparite-(Ce) in that they are zoned from a Nb-enriched core to a margin enriched in rare-earth elements and depleted in Nb. This zonation trend is the opposite of that developed during crystallization of primary loparite and is considered to reflect reaction of primary relatively Nb-rich loparite with late-stage REE-enriched fluids. One sample of nioboloparite from a pegmatite vein in ijolite-urtite is a lanthanian lueshite characterized by enrichment of La over Ce. The term nioboloparite does not correspond to a distinct mineral species and must be discredited.
Abstract Cerianite-(Ce), ideally CeO 2 , occurs as rounded grains up to 5 μm across in a block of highly altered calcite carbonatite lava from the Kerimasi volcano, and as euhedral crystals up to 200 μm across in carbonatite-derived eluvial deposits in the Kisete and Loluni explosion craters in the Gregory Rift, northern Tanzania. X-ray powder diffraction data (a = 5.434(5) Å) and Raman spectroscopy (minor vibration modes at 184 and 571 cm —1 in addition to a strong signal at 449 cm —1 ) suggest the presence of essential amounts of large cations and oxygen vacancies in the Kisete material. Microprobe analyses reveal that the mineral contains both light and heavy trivalent rare earth elements (REE) (7.9-15.5 wt.% LREE 2 O 3 and 4.9-9.7 wt.% HREE 2 O 3 ), and that it is enriched in yttrium (7.1 — 14.5 wt.% Y 2 O 3 ) and fluorine (2.2—3.5 wt.%). Single-crystal structure refinement of the mineral confirms a fluorite-type structure with a cation—anion distance of 2.3471(6) Å. The cerianite-(Ce) is considered to be a late-stage secondary mineral in the carbonatitic rocks.
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