The Catalao I niobium deposit, central Brazil: Resources, geology and pyrochlore chemistry

作者：de Oliveira Cordeiro Pedro Filipe; Brod Jose Affonso; Palmieri Matheus; de Oliveira Claudinei Gouveia; Rocha Barbosa Elisa Soares; Santos Roberto Ventura; Gaspar Jose Carlos; Assis Luis Carlos

来源：Ore Geology Reviews, 2011, 41(1): 112-121.

DOI：10.1016/j.oregeorev.2011.06.013

• Catalao I
• Carbonatite
• Phoscorite
• Nelsonite
• Pyrochlore

The Catalao 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.% Nb(2)O(5) (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 delta(18)O(SMOW) than expected for carbonates crystallizing from mantle-derived magmas. We interpret both the delta(18)O(SMOW) 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 Catalao 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.

• 出版日期2011-10