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

Autor(es)

Siachoque, Astrid ^[1] ; Garcia, Rodolfo ^[1] ; Vlach, Silvio R. F. ^[1]

Afiliação do(s) autor(es)

^[1] Univ Sao Paulo, Inst Geosci, Dept Mineral & Geotecton, BR-05508060 Sao Paulo - Brazil

• Tipo de documento: Artigo Científico
• Fonte: MINERALS; v. 10, n. 5 MAY 2020.
• Citações Web of Science: 0

Resumo

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. (AU)

• Processo FAPESP: 08/00562-0 - Interação manto-crosta e a geração e evolução do magmatismo pós-colisional de tipo-A: registros geoquímicos e isotópicos da Província Graciosa, S-SE do Brasil
• Beneficiário: Silvio Roberto Farias Vlach
• Modalidade de apoio: Auxílio à Pesquisa - Regular
• Processo FAPESP: 19/17343-4 - Propriedades geoquímicas e texturais de minerais acessórios como indicadoras petrológicas e geocronológicas em rochas graníticas e greisens associados
• Beneficiário: Silvio Roberto Farias Vlach
• Modalidade de apoio: Auxílio à Pesquisa - Regular