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Open AccessFeature PaperArticle

Occurrence and Composition of Columbite-(Fe) In the Reduced A-Type Desemborque Pluton, Graciosa Province (S-SE Brazil)

Institute of Geosciences, Department of Mineralogy and Geotectonics, University of São Paulo, 05508-060 São Paulo, Brazil
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Minerals 2020, 10(5), 411; https://doi.org/10.3390/min10050411
Received: 30 March 2020 / Revised: 26 April 2020 / Accepted: 30 April 2020 / Published: 4 May 2020
(This article belongs to the Special Issue Granite-Related Mineralization Systems )
Columbite-(Fe) is a post-magmatic accessory mineral occurring within syenogranites and greisens from the Desemborque Pluton. The petrographic (SEM) and geochemical (EPMA and LA-ICPMS) examination of this mineral shows two distinct textural types within both the rocks, named columbite-1 and columbite-2. The columbite-1 type is characterized by zoned crystals with two stages of crystallization: i) An early Nb-rich cores with low Ta/(Ta + Nb) and Mn/(Mn + Fe) ratios (0.02–0.08 and 0.17 to 0.21 apfu, respectively), and ii) a later Ta-rich rims with higher Ta/(Ta + Nb) ratios (0.11–0.26) and similar Mn/(Mn + Fe) ratios (from 0.14 to 0.22) relative to the former cores. On the other hand, the columbite-2 type is defined by irregular crystals with patchy textures and very low Ta/(Ta + Nb) ratios (0.008–0.038) and moderate Mn/(Mn + Fe) ratios between 0.20 and 0.38. Trace element compositions of all columbite-(Fe) crystals are relatively enriched in HREEs and HFSEs; however, the columbite-2 presents higher abundances of REEs, Y, Th, U, Pb, Sc, and Sn relative to the columbite-1. This study highlights a unique hydrothermal origin for both the columbite types, but the textural relations of the columbite-2 crystals indicated that its formation is related to fluid-induced alterations of post-magmatic fluorite and/or cassiterite crystals at the final stage of the post-magmatic evolution. View Full-Text
Keywords: columbite-(Fe); A-type granites; greisens; hydrothermal processes; EPMA; LA-ICPMS columbite-(Fe); A-type granites; greisens; hydrothermal processes; EPMA; LA-ICPMS
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Siachoque, A.; Garcia, R.; Vlach, S.R. Occurrence and Composition of Columbite-(Fe) In the Reduced A-Type Desemborque Pluton, Graciosa Province (S-SE Brazil). Minerals 2020, 10, 411.

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