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Minerals 2018, 8(6), 260; https://doi.org/10.3390/min8060260

Three-D Mineralogical Mapping of the Kovdor Phoscorite–Carbonatite Complex, NW Russia: I. Forsterite

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
*
Author to whom correspondence should be addressed.
Received: 30 May 2018 / Revised: 14 June 2018 / Accepted: 16 June 2018 / Published: 20 June 2018
(This article belongs to the Special Issue Arctic Mineral Resources: Science and Technology)
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Abstract

The Kovdor alkaline-ultrabasic massif (NW Russia) is formed by three consequent intrusions: peridotite, foidolite–melilitolite and phoscorite–carbonatite. Forsterite is the earliest mineral of both peridotite and phoscorite–carbonatite, and its crystallization governed evolution of magmatic systems. Crystallization of forsterite from Ca-Fe-rich peridotite melt produced Si-Al-Na-K-rich residual melt-I corresponding to foidolite–melilitolite. In turn, consolidation of foidolite and melilitolite resulted in Fe-Ca-C-P-F-rich residual melt-II that emplaced in silicate rocks as a phoscorite–carbonatite pipe. Crystallization of phoscorite began from forsterite, which launched destruction of silicate-carbonate-ferri-phosphate subnetworks of melt-II, and further precipitation of apatite and magnetite from the pipe wall to its axis with formation of carbonatite melt-III in the pipe axial zone. This petrogenetic model is based on petrography, mineral chemistry, crystal size distribution and crystallochemistry of forsterite. Marginal forsterite-rich phoscorite consists of Fe2+-Mn-Ni-Ti-rich forsterite similar to olivine from peridotite, intermediate low-carbonate magnetite-rich phoscorite includes Mg-Fe3+-rich forsterite, and axial carbonate-rich phoscorite and carbonatites contain Fe2+-Mn-rich forsterite. Incorporation of trivalent iron in the octahedral M1 and M2 sites reduced volume of these polyhedra; while volume of tetrahedral set has not changed. Thus, trivalent iron incorporates into forsterite by schema (3Fe2+)oct → (2Fe3+ + □)oct that reflects redox conditions of the rock formation resulting in good agreement between compositions of apatite, magnetite, calcite and forsterite. View Full-Text
Keywords: forsterite; typochemistry; crystal structure; Kovdor phoscorite–carbonatite complex forsterite; 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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Mikhailova, J.A.; Ivanyuk, G.Y.; Kalashnikov, A.O.; Pakhomovsky, Y.A.; Bazai, A.V.; Panikorovskii, T.L.; Yakovenchuk, V.N.; Konopleva, N.G.; Goryainov, P.M. Three-D Mineralogical Mapping of the Kovdor Phoscorite–Carbonatite Complex, NW Russia: I. Forsterite. Minerals 2018, 8, 260.

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