Uranium and thorium in carbonatitic minerals from the Guli massif, Polar Siberia

This paper reports a geochemical and mineralogical study on carbonatites from the Guli massif, which hosts rare-metal mineralization. The principal carriers of radioactive elements in the carbonatites are pyrochlore-group minerals, zirconolite, and thorianite, which are described here. They are char...

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Bibliographic Details
Published in:Geochemistry international 2013-10, Vol.51 (10), p.767-776
Main Authors: Kogarko, L. N., Sorokhtina, N. V., Kononkova, N. N., Klimovich, I. V.
Format: Article
Language:English
Subjects:
Calcite
Carbonates
Dolomite
Earth and Environmental Science
Earth Sciences
Evolutionary
Fractionation
Geochemistry
Magma
Massifs
Mineralization
Mineralogy
Minerals
Radioisotopes
Raw materials
Tantalum
Thorium
Uranium
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Summary:This paper reports a geochemical and mineralogical study on carbonatites from the Guli massif, which hosts rare-metal mineralization. The principal carriers of radioactive elements in the carbonatites are pyrochlore-group minerals, zirconolite, and thorianite, which are described here. They are characterized by elevated concentrations (wt %) of radioactive elements: up to 17.89 UO 2 and 20.01 ThO 2 in pyrochlore, up to 6.49 UO 2 and 94.29 ThO 2 in thorianite, and up to 6.74 ThO 2 in zirconolite. The pyrochlore-group minerals, zirconolite, and thorianite from the early calcite carbonatites occur in intimate association with Ti-Zr oxides calzirtite, perovskite, and baddeleyite. Significant radioactive element fractionation in early-stage derivatives results in the depletion of the residual magmatic products in these elements. The dolomite carbonatites are reported to contain only trace amounts of pyrochlore-group minerals. It was shown that the distribution of U, Th, Nb, and Ta in the calcite and dolomite carbonatites is correlated with the evolutionary trends of pyrochlore composition. Typical schemes of isomorphic substitution are proposed for pyrochlore-group minerals and zirconolite. The pyrochlore-group minerals show an apparent evolutionary trend from U-rich towards more Th- and Ta-rich varieties, and Ba-Sr cation-deficient varieties originate during the latest stage of the evolution. The pyrochlore-group minerals, zirconolite, and thorianite may also accumulate in placers, together with gold. Because of the relative ease of extraction of the accessory minerals, the carbonatites of the Guli massif can be considered as commercial sources of radioactive raw materials.
ISSN:0016-7029
1556-1968
DOI:10.1134/S0016702913090036