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Russian Geology and Geophysics

2016 year, number 8

LITHIUM-CONTAINING Na-Fe-AMPHIBOLE FROM CRYOLITE ROCKS OF THE KATUGIN RARE-METAL DEPOSIT (Transbaikalia, Russia): CHEMICAL FEATURES AND CRYSTAL STRUCTURE

V.V. Sharygin1,2, N.V. Zubkova3, I.V. Pekov3, V.S. Rusakov4, D.A. Ksenofontov3, E.N. Nigmatulina1, N.V. Vladykin5, D.Yu. Pushcharovsky3
1V.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences, pr. Akademika Koptyuga 3, Novosibirsk, 630090, Russia
2Novosibirsk State University, ul. Pirogova 2, Novosibirsk, 630090, Russia
3Faculty of Geology, M.V. Lomonosov Moscow State University, Leninskiye Gory 1, Moscow, 119991, Russia
4Faculty of Physics, M.V. Lomonosov Moscow State University, Leninskiye Gory 1-2, Moscow, 119991, Russia
5A.V. Vinogradov Institute of Geochemistry, Siberian Branch of the Russian Academy of Sciences, ul. Favorskogo 1a, Irkutsk, 664033, Russia
Keywords: Na-amphibole subgroup, ferro-ferri-fluoro-leakeite, ferro-ferri-fluoro-nybшite, fluoro-riebeckite, fluoro-arfvedsonite, cryolite, alkali granites, Katugin deposit, Transbaikalia

Abstract

Detailed chemical and structural studies were carried out for Li-Na-Fe-amphibole from cryolite rocks of the Katugin deposit, Transbaikalia. The rocks contain 30-70 vol.% cryolite, mafic minerals as Fe-silicates (Li-Na-Fe-amphibole, Li-containing fluorannite, and bafertisite), oxides (magnetite, ilmenite, pyrochlore, cassiterite, and others), and sulfides (sphalerite, pyrite, and chalcopyrite). Quartz, K-feldspar, polylithionite, REE-fluorides, and albite occur as minor or accessory phases. The chemical composition of amphibole (wt.%) varies as follows: SiO2, 48.5-48.9; TiO2, 0.4-0.8; Al2O3, 1.6-2.2; Fe2O3, 15.9-17.1; FeO, 17.6-18.4; MnO, 0.8-0.9; ZnO, 0.3-1.1; MgO, 0.2-0.3; CaO, <0.1; Na2O, 8.4-8.7; K2O, 1.4-1.5; Li2O, 0.6-0.8; H2O, 0.7-0.8; and F, 2.2-2.5. The amphibole has a specific composition intermediate among the F-Fe members of the Na-amphibole subgroup: 40-45 mol.% ferro-ferri-fluoro-nybøite, 40-45 mol.% ferro-ferri-fluoro-leakeite, and 10-20 mol.% fluoro-riebeckite ± fluoro-arfvedsonite. The mineral is monoclinic, space group C 2/ m , a = 9.7978(2), b = 17.9993(3), c = 5.33232(13) Å, b = 103.748(2)º, V = 913.43(3) Å3, and Z = 2. The structural formula of Li-Na-Fe-amphibole is (Na0.46K0.240.30)Na2.00(Fe2+0.95Mg0.05)2(Fe3+0.95Ti0.025Mg0.025)2(Li0.37Fe2+0.48Mn0.10Zn0.05)[(Si0.91Al0.09)4Si4O22](F0.58(OH)0.42)2. Raman and Mössbauer spectroscopy data are given for this amphibole.