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Minerals 2018, 8(7), 277; https://doi.org/10.3390/min8070277

Three-D Mineralogical Mapping of the Kovdor Phoscorite-Carbonatite Complex, NW Russia: III. Pyrochlore Supergroup Minerals

1
Nanomaterials Research Centre of Kola Science Centre, Russian Academy of Sciences, 14 Fersman Street, Apatity 184209, Russia
2
Geological Institute of Kola Science Centre, Russian Academy of Sciences, 14 Fersman Street, Apatity 184209, Russia
3
Geo Environmental Centre “Geomodel”, St. Petersburg State University, 1 Ul’yanovskaya Street, St. Petersburg 198504, Russia
*
Author to whom correspondence should be addressed.
Received: 30 May 2018 / Revised: 19 June 2018 / Accepted: 26 June 2018 / Published: 28 June 2018
(This article belongs to the Special Issue Arctic Mineral Resources: Science and Technology)
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Abstract

The pyrochlore supergroup minerals (PSM) are typical secondary phases that replace (with zirconolite–laachite) earlier Sc-Nb-rich baddeleyite under the influence of F-bearing hydrothermal solutions, and form individual well-shaped crystals in surrounding carbonatites. Like primary Sc-Nb-rich baddeleyite, the PSM are concentrated in the axial carbonate-rich zone of the phoscorite-carbonatite complex, so their content, grain size and chemical diversity increase from the pipe margins to axis. There are 12 members of the PSM in the phoscorite-carbonatite complex. Fluorine- and oxygen-dominant phases are spread in host silicate rocks and marginal carbonate-poor phoscorite, while hydroxide-dominant PSM occur mainly in the axial carbonate-rich zone of the ore-pipe. Ti-rich PSM (up to oxycalciobetafite) occur in host silicate rocks and calcite carbonatite veins, and Ta-rich phases (up to microlites) are spread in intermediate and axial magnetite-rich phoscorite. In marginal (apatite)-forsterite phoscorite, there are only Ca-dominant PSM, and the rest of the rocks include Ca-, Na- and vacancy-dominant phases. The crystal structures of oxycalciopyrochlore and hydroxynatropyrochlore were refined in the Fd3¯m space group with R1 values of 0.032 and 0.054 respectively. The total difference in scattering parameters of B sites are in agreement with substitution scheme BTi4+ + YOH = BNb5+ + YO2‒. The perspective process flow diagram for rare-metal “anomalous ore” processing includes sulfur-acidic cleaning of baddeleyite concentrate from PSM and zirconolite–laachite impurities followed by deep metal recovery from baddeleyite concentrate and Nb-Ta-Zr-U-Th-rich sulfatic product from its cleaning. View Full-Text
Keywords: pyrochlore supergroup minerals; typochemistry; crystal structure; Kovdor phoscorite-carbonatite complex pyrochlore supergroup minerals; typochemistry; crystal structure; Kovdor phoscorite-carbonatite complex
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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Ivanyuk, G.Y.; Konopleva, N.G.; Yakovenchuk, V.N.; Pakhomovsky, Y.A.; Panikorovskii, T.L.; Kalashnikov, A.O.; Bocharov, V.N.; Bazai, A.A.; Mikhailova, J.A.; Goryainov, P.M. Three-D Mineralogical Mapping of the Kovdor Phoscorite-Carbonatite Complex, NW Russia: III. Pyrochlore Supergroup Minerals. Minerals 2018, 8, 277.

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