U-Pb columbite age of Neoproterozoic Ta-Nb mineralization in Burundi

Lulea University, Department of Applied Geology, Lulea, Sweden
Technical University Clausthal, Federal Republic of Germany

Tin granites and associated Ta-Nb pegmatites in the Kibaran belt of central Africa have been dated earlier only by highly scattered Rb-Sr data that were interpreted to reflect events at 1000 to 900 and 650 to 550 Ma. New U-Pb dating of columbite from the Kivuvu and Ruhembe pegmatites in Burundi precisely determines the age of the mineralization and indirectly also the age of the associated granite magmatism. Columbites from the Kivuvu and Ruhembe pegmatites have variably discordant U-Pb data that define emplacement ages at 962 + or - 2 Ma (2sigma ) and 968 (super +33) (sub -29) Ma, respectively. The lower intercept ages at 628 + or - 110 Ma and 622 + or - 56 Ma are interpreted to reflect the Pan-African brittle reworking of the pegmatite system when Au and Bi were redistributed on fractures and secondary sericite formed. The U-Pb age data from columbite thus confirm earlier interpretations of Rb-Sr data.

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