Reduced forms of carbon in pegmatitesтезисы доклада Тезисы

Дата последнего поиска статьи во внешних источниках: 24 октября 2018 г.

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[1] Ermolaeva V. N., Chukanov N. V., Pekov I. V. Reduced forms of carbon in pegmatites // 24th Int. Meeting on Organic Geochemistry, Bremen, Germany 6th – 11th September 2009. — Bremen, Germany, 2009. — P. 524–524. Organic compounds are known in pegmatites of different types. In alkaline pegmatites, especially on the hydrothermal stage, the content of carbon in the form of bituminous compounds greatly increases as compared with earlier magmatic-stage rocks [1]. Analogical tendency is typical for a number of rare non-coherent elements (Th, U, REE, Zr, Hf, Nb, Ta, W, Sn, Ti), both in alkaline and granitoid formations. In particular, thucholite (carboniferous substance, containing U and/or Th) from granitic pegmatites of Canada, where it was described for the first time, is associated with uraninite, zircon (zirtolite), titanite, allanite, samarskite [2]. In this work, a comparative study of carboniferous substances from the following objects was performed: a) rare-metal pegmatites (Viitaniemi, Finland) containing spherical inclusions of thucholite up to 1 cm in diameter included in albite in close association with zirkone, tantalite and pyrochlore; b) alkaline-granitic amazonite pegmatites (Ploskaya mountain, West Keyvy, Kola Peninsula) where dispersed organic compounds were discovered by IR-spectroscopy method in thorite from late-pegmatitic albitite; c) granitic pegmatite of mica type (Lopatovaya Guba locality, North Karelia) in which carbon substance forms pseudomorphs after cubic crystals of uraninite and is accompanied by rare-metal mineralization (monazite-(Ce), xenotime-(Y), zircone); d) hydrothermally processed core of peralkaline pegmatite (Koashva mountain, Khibiny massif) with macroscopic spherical segregations of bituminous substance included in aegirine-natrolite aggregates, in association with late Ti- and Zr-silicates. All studied samples are inhomogeneous being thin intergrowths of carboniferous substance and mineral microphases, including phases with Th, REE, Nb, Ti (Fig. 1). In thucholite from sugar-like albite zone in Viitaniemi pegmatite, uranium is distributed between carboniferous phase and spherical inclusions of autunite or metaautunite aggregates (Ca0.89Fe0.25Sr0.11Sb0.07Zr0.04Pb0.02)1.39[U2.08Ox][PO4]2, whereas thorium is present only in a mineral phase, namely in brockite-grayite (Сa0.48Th0.39Al0.19Pb0.16Fe0.06U0.04Sr0.03Y0.03Ti0.01Zr0.01 La0.01Ce0.01)1.42[PO4]S0.03. Carburan from Lopatovaya Guba deposit is bearing obvious features of the replacement of a mineral phase (uraninite) by a carboniferous substance. Among mineral phases in carburan exist uranium phosphosilicate (U0.69Pb0.15Th0.14Dy0.03)1.01[Si0.61P0.35As0.05]1.01Ox·nH2O. Bitumen from peralkaline pegmatites of Khibiny-Lovozero complex are characterized by high contents of both aliphatic hydro-carbone groups and show С-Н-stretching IR-bands (in the range 2800-3000 cm-1) and unsaturated organic compounds (the range 1200-1680 cm-1). IR spectrum of Viitaniemi thucholite shows lowercontents of aliphatic hydrocarbon groups, but higher contents of aromatic compounds. The above data and our early data [4] demonstrated the general tendency to the co-existence of carboniferous substances with minerals concentrating specific uncoherent rare bitumophilic elements (Th, U, REE, Zr, Hf, Nb, Ta, W, Sn, Ti) in pegmatites of different genetic types. It is remarkable, that this group unites almost the same elements as the group of carbophilic elements, discovered on the basis of very large and representative statistical material for solid kaustobiolithes, generalized in the last monographs [5].

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