Quick Search:    advanced search

GSW Home   GeoRef Home   My GSW Alerts   Contact GSW   About GSW   Journals List   Help

This Article Figures Only Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in ISI Web of Science Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Roda, E. Articles by Fontan, F. Search for Related Content GeoRef GeoRef Citation

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

¹ Departamento de Mineralogía y Petrología, Universidad País Vasco/EHU, Apdo. 644, E-48080 Bilbao, Spain
² Institut für Mineralogie und Kristallchemie, Universitat Stuttgart, Pfaffenwaldring 55, D-70569 Stuttgart, Germany
³ Laboratoire de Cristallographie et Minéralogie, URA-067-Université Paul Sabatier de Toulouse, Allées Jules-Guesde 39, F-31400, Toulouse, France

^* E-mail: encar.roda{at}ehu.es

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: micas, granitic pegmatites, mineral chemistry, Karibib, Namibia