Alkaline Rocks and Carbonatites of the World

Setup during HiTech AlkCarb: an online database of alkaline rock and carbonatite occurrences



Occurrence number: 
Congo (Kinshasa)
Longitude: 28.9, Latitude: -1.77

An elliptical intrusion of 8x3.5 km Numbi is emplaced in Precambrian Burundian schists and quartzites. The principal rock type is a nepheline syenite of microcline, which is generally aligned, albite, abundant nepheline, cancrinite, sodalite, green biotite, melanite, titanite, opaque phases, fluorite and apatite; chevkinite and lavenite are accessories. A variant, which is usually found near the margins of the complex, contains aegirine and aegirine-augite, but is free of biotite; this rock type is particularly rich in chevkinite and fluorite. Chemical analyses are available. A small area of ankaratrite with leucite is described by Denaeyer (1958) from 2 km southeast of the Numbi occurrence. This is undoubtedly younger and related to the Virunga volcanic field (No. 6).

A four point whole-rock regression line on samples of granite and syenite from Numbi, Kirumba and Upper Rivubu (Burundi) yielded 648±17 Ma (Cahen et al., 1979 and 1984), and a Rb-Sr whole rock regression on ten syenites gave 830±51 Ma (Kampunzu et al., 1998a).

CAHEN, L., LEDENT, D. and VILLENEUVE, M. 1979. Existence d'une chaine plissee Proterozoique Superieur au Kivu Oriental (Zaire). Donnees geochronologiques relatives au supergroupe de l'Itombwe. Bulletin de la Societé Belge de Géologie, 88: 71-83.CAHEN, L., SNELLING, N.J., DELHAL, J. and VAIL, J.R. 1984. The geochronology and evolution of Africa. Clarendon Press, Oxford. 512 pp.DENAEYER, M.-E. 1958. Les syénites feldspathoïdiques du Kivu et leur rôle dans la genèse des laves des Virunga. Bulletin de la Société Belge de Géologie de Paléontologie et d'Hydrologie (Bruxelles), 67: 459-87.KAMPUNZU, A.B., KRAMERS, J.D. and MAKUTU, M.N. 1998a. Rb-Sr whole rock ages of the Lueshe, Kirumba and Numbi igneous complexes (Kivu, Democratic Republic of Congo) and the break-up of the Rodinia supercontinent. Journal of African Earth Sciences, 26: 29-36.

Scratchpads developed and conceived by (alphabetical): Ed Baker, Katherine Bouton Alice Heaton Dimitris Koureas, Laurence Livermore, Dave Roberts, Simon Rycroft, Ben Scott, Vince Smith