The Catalão I niobium deposit, central Brazil: Resources, geology and pyrochlore chemistry |
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| Authors: | Pedro Filipe de Oliveira Cordeiro José Affonso Brod Matheus Palmieri Claudinei Gouveia de Oliveira Elisa Soares Rocha Barbosa Roberto Ventura Santos José Carlos Gaspar Luis Carlos Assis |
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| Institution: | aUniversidade de Brasília, Campus Darcy Ribeiro ICC Central, Instituto de Geociências, Brasília-DF, 70910-900 Brazil;bUniversidade Federal de Goiás, Campus Samambaia, Instituto de Estudos Sócio-Ambientais, Universidade Federal de Goiás, Goiânia-GO, 74001-970 Brazil;cAnglo American Brazil LTDA, Avenida Interlândia 502, Setor Santa Genoveva, Goiânia-GO, 74672-360 Brazil |
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| Abstract: | The Catalão I alkaline–carbonatite–phoscorite complex contains both fresh rock and residual (weathering-related) niobium mineralization. The fresh rock niobium deposit consists of two plug-shaped orebodies named Mine II and East Area, respectively emplaced in carbonatite and phlogopitite. Together, these orebodies contain 29 Mt at 1.22 wt.% Nb2O5 (measured and indicated). In closer detail, the orebodies consist of dike swarms of pyrochlore-bearing, olivine-free phoscorite-series rocks (nelsonite) that can be either apatite-rich (P2 unit) or magnetite-rich (P3 unit). Dolomite carbonatite (DC) is intimately related with nelsonite. Natropyrochlore and calciopyrochlore are the most abundant niobium phases in the fresh rock deposit. Pyrochlore supergroup chemistry shows a compositional trend from Ca–Na dominant pyrochlores toward Ba-enriched kenopyrochlore in fresh rock and the dominance of Ba-rich kenopyrochlore in the residual deposit. Carbonates associated with Ba-, Sr-enriched pyrochlore show higher δ18OSMOW than expected for carbonates crystallizing from mantle-derived magmas. We interpret both the δ18OSMOW and pyrochlore chemistry variations from the original composition as evidence of interaction with low-temperature fluids which, albeit not responsible for the mineralization, modified its magmatic isotopic features. The origin of the Catalão I niobium deposit is related to carbonatite magmatism but the process that generated such niobium-rich rocks is still undetermined and might be related to crystal accumulation and/or emplacement of a phosphate–iron-oxide magma. |
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| Keywords: | Catalã o I Carbonatite Phoscorite Nelsonite Pyrochlore |
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