ALKALINE BERYL (VOROBYEVITE) FROM THE SHUK-BYUL DEPOSIT, SANGILEN HIGHLANDS, TUVA
Yu. D. Gritsenko1,2, M. F. Vigasina1, L. P. Ogorodova1, S. V. Vyatkin1, S. V. Sukonkin3, A. K. Gavrilchik4,5, S. G. Skublov5,4, D.A. Ksenofontov1, L.V. Melchakova1
1Lomonosov Moscow State University, faculty of Geology, Moscow, Russia
2Fersman mineralogical museum of the Russian Academy of Sciences, Moscow, Russia
3Lomonosov Moscow State University, faculty of Chemistry, Moscow, Russia
4Empress Catherine II Saint Petersburg Mining University, St. Petersburg, Russia
5Institute of Precambrian Geology and Geochronology, Russian Academy of Sciences, St. Petersburg, Russia
Keywords: beryl, vorobyevite, Shuk-Bul, electron probe, ion probe, IR spectroscopy, Raman spectroscopy, EPR spectroscopy, paramagnetic centers H0, Calvet microcalorimetry, enthalpy, entropy, Gibbs energy
Abstract
A detailed study of an alkali beryl sample (vorobyevite) from the Shuk-Bul rare-metal lithium pegmatite (Sangilen Highlands, Tuva) was conducted using electron microprobe and ion probe(SIMS) analysis, X-ray diffraction, EPR spectroscopy, infrared absorption spectroscopy, Raman spectroscopy. The empirical formula of beryl studied was calculated: (Na 0.2Cs 0.1) ∑0.3(Be 2.7Li 0.3) ∑3.0Al 2Si 6O 18·0.7H 2O. The ratio of water types I and II in beryl channels is estimated. Beryl from the Shuk-Bul deposit shows significant similarity in trace element composition with beryl from another lithium pegmatite deposit of the Sangilen Highlands (Kara-Adyr). Together, they differ from beryl from LCT-pegmatites of Afghanistan and the Kola Peninsula (the Shongui deposit) in their increased content of alkali metals - Cs and Rb, as well as F, and reduced – Fe and Mg. The content of Na and Li in beryl from Tuva deposits is comparable to the Shongui deposit and exceeds the values for beryl from LCT-pegmatites of Afghanistan. The presence of paramagnetic centers H 0 in beryl, formed from water molecules under the influence of radioactive irradiation, has been established. Using a Calvet microcalorimeter, the enthalpy of formation of the studied beryl was determined (−9245 ±11 kJ/mol) by dissolving it in a 2PbO∙B 2O 3 melt at T=973 K, the standard entropy was estimated (390.7J/(mol∙K)), and the Gibbs energy of formation was calculated (−8696 ±11 kJ/mol).
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