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The peralkaline tin-mineralized madeira cryolite albite-rich granite of Pitinga, Amazonia craton, Brazil : petrography, mineralogy and crystallization processes

Abstract : The 1.818 Ga magmatic, subsolvus, Madeira albite-rich granite of the Pitinga province, exploited at the Pitinga mine, in northern Brazil, crystallized from a F-rich melt, also enriched in Sn, Rb, and HFSE. It is composed of a peralkaline, cryolite-bearing core facies and a peraluminous to metaluminous, oxidized, fluorite-bearing border facies, generated by autometasomatic processes after the crystallization of the core facies. A metaluminous to peralkaline hypersolvus granite is comagmatic with the albite-rich granite. Petrographic studies indicate that quartz was the first phase to crystallize, at ~700°C; the quartz – K-feldspar cotectic was attained at around 650°C, and the ternary feldspar solvus and onset of albite crystallization, down to the solidus, estimated at around 500°C. Massive cryolite and pegmatitic rocks found in the center of the stock were derived from the residual melt. The albite-rich granite probably originated by crystallization of a dense, F-rich, peralkaline phase derived from a peralkaline to metaluminous parental melt by immiscibility.
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Submitted on : Thursday, February 18, 2010 - 3:42:06 PM
Last modification on : Wednesday, September 25, 2019 - 2:56:02 PM

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Hilton Tulio Costi, Roberto Dall'Agnol, Michel Pichavant, Osmo Tapani Ramo. The peralkaline tin-mineralized madeira cryolite albite-rich granite of Pitinga, Amazonia craton, Brazil : petrography, mineralogy and crystallization processes. The Canadian Mineralogist, Mineralogical Association of Canada, 2009, 47, pp.1301-1327. ⟨10.3749/canmin.47.6.1301⟩. ⟨insu-00457865⟩

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