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Title:
Thorium mineralization in hyperalkaline pegmatites and hydrothermalites of the Lovozero pluton, Kola Peninsula
Authors:
Ermolaeva, V. N.; Pekov, I. V.; Chukanov, N. V.; Zadov, A. E.
Affiliation:
AA(Laboratory of Geochemistry of Igneous Rocks, Institute of Geochemistry and Analytical Chemistry, Russian Academy of Sciences), AB(Faculty of Geology, Moscow State University), AC(Institute of Problems of Chemical Physics, Russian Academy of Sciences), AD(NPO Regenerator)
Publication:
Geology of Ore Deposits, Volume 49, Issue 8, pp.758-775
Publication Date:
12/2007
Origin:
SPRINGER
Abstract Copyright:
(c) 2007: Pleiades Publishing, Ltd.
DOI:
10.1134/S1075701507080107
Bibliographic Code:
2007GeoOD..49..758E

Abstract

The Lovozero pluton (Kola Peninsula, Russia) is an unique object from the standpoint of the abundance, diversity, and originality of Th mineralization. In contrast to other igneous rocks and to such chemical elements as Ca, REE, U, and Na, Th in the hyperalkaline pegmatites and hydrothermalites of the Lovozero pluton commonly occurs as its own mineral phases. Umbozerite Na3Sr4Th(Mn,Zn,Fe,Mg)[Si8O24](OH) (7 samples), Ti-Th silicate Na0 7Sr0 1ThTi1 2Si8O22 23(OH) · nH2O (8 samples), Na-Th silicate (Na,K)4Th3[Si8(O,OH)24] · nH2O (6 samples), thorite (2 samples), steenstrupine-(Ce)-thorosteenstrupine series minerals (5 samples), and Th phosphate (Th,Na,K,Ca,Mg,U,Sr,Ba)[(P,Si, Al)1O4] · nH2O (1 sample) were investigated in this study. Ti-Th silicates and Th phosphate have been described for the first time. All of the above-mentioned minerals have been examined with electron microprobe, IR spectroscopy, powder diffraction, thermogravimetric and optical methods. High-Th minerals such as steenstrupine, umbozerite, Th phosphate, and Na-Th silicates crystallized mainly during the ussingite stage of the pegmatite-forming process. At the early hydrothermal high-alkaline stage, steenstrupine was replaced with REE and Th aggregates (belovite, vitusite, seidite, Na-Th silicates, Ti-Th silicates, etc.). Thorite, Ti-Th silicates, and minerals of the rhabdophane and monazite groups were formed at the late hydrothermal low-alkaline stage. Despite the metamict features of almost all samples, stoichiometric ratios of cations in umbozerites and Ti-Th silicates remain stable. Clear relationships have been revealed between umbozerites and Ti-Th silicates, on the one hand, and seidite-(Ce), a Ti-silicate that has a zeolite-like structure, on the other. This implies that, under certain conditions, these minerals may be regarded as potential suppliers of Th to the environment due to the leaching of Th from zeolite channels.
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