Contrôle structural du partage de Rb entre fluide et micas potassiques dans les pegmatites du Brésil |
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Authors: | Joël Quéméneur Marcel Volfinger Luciana Azevedo |
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Institution: | 1. CPMTC, IGC, UFMG, Belo Horizonte, Brésil;2. ISTO, CNRS, université d''Orléans, 1A, rue de la Férollerie, 45071 Orléans, France;3. IGC, UFMG, Belo Horizonte, Brésil |
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Abstract: | A geochemical study of pegmatitic micas from Minas Gerais State in Brazil was performed with an electron microprobe, in order to examine the variations of Rb, K, Al and F contents. It is observed a linear decreasing relationship between the Rb/K] ratio of the micas and their contents in AlVI. The interpretation is based on the hypothesis that the partition coefficient CRb/Kmica/fl between fluid and mineral does not vary significantly as a function of temperature and pressure in the narrow conditions of crystallization of pegmatites. It is suggested that the relation: CRb/Kmica/fl=0.55×(5?AlVI]) is of crystallochemical order. Micas with low contents in Al take higher contents in Rb because the potassic sites where Rb enters are larger. This relation gives another way of calculating the values Rb/K] of the fluids knowing Rb, K, Al and Si in the micas. This crystallochemistry also allows us to foresee a direct correlation between Rb and F in the pegmatitic micas. To cite this article: J. Quéméneur et al., C. R. Geoscience 336 (2004). |
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Keywords: | rubidium coefficient de partage mica cristallochimie pegmatites rubidium partition coefficient mica crystallochemistry pegmatites |
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