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Micas of the muscovite–lepidolite series from Karibib pegmatites, Namibia

Published online by Cambridge University Press:  05 July 2018

E. Roda ,
P. Keller ,
A. Pesquera  and
F. Fontan
E. Roda*
Affiliation:
Departamento de Mineralogía y Petrología, Universidad País Vasco/EHU, Apdo. 644, E-48080 Bilbao, Spain
P. Keller
Affiliation:
Institut für Mineralogie und Kristallchemie, Universitat Stuttgart, Pfaffenwaldring 55, D-70569 Stuttgart, Germany
A. Pesquera
Affiliation:
Departamento de Mineralogía y Petrología, Universidad País Vasco/EHU, Apdo. 644, E-48080 Bilbao, Spain
F. Fontan
Affiliation:
Laboratoire de Cristallographie et Minéralogie, URA-067-Université Paul Sabatier de Toulouse, Allées Jules-Guesde 39, F-31400, Toulouse, France
*
E-mail: [email protected]
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Abstract

Micas of the muscovite–lepidolite series are main constituents of the evolved pegmatites from the Okatjimukuju-Kaliombo portion of the Karibib belt, Namibia. The compositional variations shown by the micas from the intermediate zones are mainly controlled by the Li3Al-1□-2 and SiLi2Al-2□-1 substitution schemes, whereas for the micas from the core margins and the replacement bodies, only the first of these two exchange vectors seems to operate. The chemical composition of the micas not only depends on the degree of pegmatite evolution, but also on the position in the internal zonation of the pegmatite. Micas from the core margins and the replacement units are generally richer in F, Li, Rb, Cs and Zn than those from the intermediate zones. In general, the contents of these elements increase with decreasing K/Rb ratio. However, some data departing from this general trend are also observed, which could be related to subsolidus processes. Some pegmatite bodies show a complete internal evolution, developed from the margins to the core zone, which is reflected in the chemical composition of the micas. The regional distribution of pegmatites does not define a zonation, because an overlapping of pegmatites with different degrees of evolution occurs. This could be due to the high level of evolution attained by most of the rare-element pegmatites, and to their topography with respect to a dome structure of the basement.

Keywords

micasgranitic pegmatitesmineral chemistryKaribibNamibia
Type
Research Article
Information
Mineralogical Magazine , Volume 71 , Issue 1 , February 2007 , pp. 41 - 62
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 2007

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