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Niobium and rare earth minerals from the Virulundo carbonatite, Namibe, Angola

Published online by Cambridge University Press:  05 July 2018

L. Torró ,
C. Villanova ,
M. Castillo ,
M. Campeny ,
A. O. Gonçalves  and
J. C. Melgarejo
L. Torró
Affiliation:
Departament de Cristal·lografia, Mineralogía i Dipósits Minerals, Universitat de Barcelona, c/Martí i Franqués s/n, 08028 Barcelona, Catalonia, Spain
C. Villanova
Affiliation:
Departament de Cristal·lografia, Mineralogía i Dipósits Minerals, Universitat de Barcelona, c/Martí i Franqués s/n, 08028 Barcelona, Catalonia, Spain
M. Castillo
Affiliation:
Departament de Cristal·lografia, Mineralogía i Dipósits Minerals, Universitat de Barcelona, c/Martí i Franqués s/n, 08028 Barcelona, Catalonia, Spain
M. Campeny
Affiliation:
Departament de Cristal·lografia, Mineralogía i Dipósits Minerals, Universitat de Barcelona, c/Martí i Franqués s/n, 08028 Barcelona, Catalonia, Spain
A. O. Gonçalves
Affiliation:
Departamento de Geologia, Faculdade de Ciências, Universidade Agostinho Neto, Av. 4 de Fevereiro 7, 815 Luanda, Angola
J. C. Melgarejo*
Affiliation:
Departament de Cristal·lografia, Mineralogía i Dipósits Minerals, Universitat de Barcelona, c/Martí i Franqués s/n, 08028 Barcelona, Catalonia, Spain
*
*E-mail: [email protected]
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Abstract

The Virulundo carbonatite in Angola is one of the largest in the world and contains pyrochlore as an accessory mineral in all of the carbonatite units (calciocarbonatites, ferrocarbonatites, carbonatite breccias and trachytoids). The primary magmatic pyrochlore is fluorine dominant and typically contains about equal molar quantities of Ca and Na at the A site. High-temperature hydrothermal processes have resulted in the pseudomorphic replacement of the primary pyrochlore by a second generation of pyrochlore with less F and Na. Low-temperature hydrothermal replacement of the first and second generation pyrochlore, associated with quartz-carbonate-fluorite vein formation in the carbonatite, has produced a third generation of pyrochlore, with a high Sr content. The Sr appears to have been released by low-temperature hydrothermal replacement of the primary magmatic carbonates. Finally, supergene alteration processes have produced late-stage carbonates, goethite, hollandite and rare earth element (REE) minerals (mainly synchysite-(Ce), britholite-(Ce), britholite-(La), cerite-(Ce)). Cerium separated from the other REE s in oxidizing conditions and Ce4+ was incorporated into a late generation of supergene pyrochlore, which is strongly enriched in Ba and strongly depleted in Ca and Na.

Keywords

angolacarbonatitepyrochloreREEmagmatichydrothermalweatheringVirulundo
Type
Research Article
Information
Mineralogical Magazine , Volume 76 , Issue 2 , April 2012 , pp. 393 - 409
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 2012

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