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Open AccessArticle

Pyrochlore-Group Minerals in the Granite-Hosted Katugin Rare-Metal Deposit, Transbaikalia, Russia

1
V.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences, 3 Akad. Koptyug av., 630090 Novosibirsk, Russia
2
Department of Geology and Geophysics, Novosibirsk State University, 2 Pirogov st., 630090 Novosibirsk, Russia
3
Institute of the Earth’s Crust, Siberian Branch of the Russian Academy of Sciences, 128 Lermontova st., 664033 Irkutsk, Russia
4
School of Engineering, Far East Federal University, 8 Sukhanov st., 690091 Vladivostok, Russia
5
Geological Institute, Siberian Branch of the Russian Academy of Sciences, 6a, Sakhjanova st., 670047 Ulan-Ude, Russia
*
Author to whom correspondence should be addressed.
Minerals 2019, 9(8), 490; https://doi.org/10.3390/min9080490
Received: 8 May 2019 / Revised: 4 August 2019 / Accepted: 13 August 2019 / Published: 15 August 2019
(This article belongs to the Special Issue Accessory Minerals in Silicic Igneous Rocks)
Pyrochlore group minerals are the main raw phases in granitic rocks of the Katugin complex-ore deposit that stores Nb, Ta, Y, REE, U, Th, Zr, and cryolite. There are three main types: Primary magmatic, early postmagmatic (secondary-I), and late hydrothermal (secondary-II) pyrochlores. The primary magmatic phase is fluornatropyrochlore, which has high concentrations of Na2O (to 10.5 wt.%), F (to 5.4 wt.%), and REE2O3 (to 17.3 wt.%) but also low CaO (0.6–4.3 wt.%), UO2 (to 2.6 wt.%), ThO2 (to 1.8 wt.%), and PbO (to 1.4 wt.%). Pyrochlore of this type is very rare in nature and is limited to a few occurrences: Rare-metal deposits of Nechalacho in syenite and nepheline syenite (Canada) and Mariupol in nepheline syenite (Ukraine). It may have crystallized synchronously with or slightly later than melanocratic minerals (aegirine, biotite, and arfvedsonite) at the late magmatic stage when Fe from the melt became bound, which hindered the crystallization of columbite. Secondary-I pyrochlore follows cracks or replaces primary pyrochlore in grain rims and is compositionally similar to the early phase, except for lower Na2O concentrations (2.8 wt.%), relatively low F (4 wt.%), and less complete A- and Y-sites occupancy. Secondary-II pyrochlore is a product of late hydrothermal alteration, which postdated the formation of the Katugin deposit. It differs in large ranges of elements and contains minor K, Ba, Pb, Fe, and significant Si concentrations but also low Na and F. Its composition mostly falls within the field of hydro- and keno-pyrochlore. View Full-Text
Keywords: pyrochlore-group minerals; fluornatropyrochlore; alkaline granites; Katugin rare-metal deposit; East Transbaikalia pyrochlore-group minerals; fluornatropyrochlore; alkaline granites; Katugin rare-metal deposit; East Transbaikalia
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Starikova, A.E.; Bazarova, E.P.; Savel’eva, V.B.; Sklyarov, E.V.; Khromova, E.A.; Kanakin, S.V. Pyrochlore-Group Minerals in the Granite-Hosted Katugin Rare-Metal Deposit, Transbaikalia, Russia. Minerals 2019, 9, 490.

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