The kimberlites of Guinea, West Africa

Abstract

The most extensive field of kimberlites in West Africa occurs in south-central Guinea, but in spite of their discovery in 1952 by Soguinex and later considerable work by Russian geologists in the 1960's (Vladimirov et al., 1971) little information is available in the scientific literature. About 20 small kimberlite pipes and numerous dikes have been emplaced into Archaean basement rocks consisting mostly of granitic gneisses and quartzitic schists, possibly of Dahomeyan or Birrimian age. Extensive dolerite magmatism occurred about 180 Ma ago and this predates the kimberlitic events. The kimberlite dikes are often oriented almost E-W, but other trends such as 055° and 115° are present.Dikes vary in width from thin stringers or veins (cms), to proper dikes 3 m thick. Dikes may occur "en echelon" or in groups of 3 or more, and extend for 2-3 km. The pipes are relatively small, resembling more the "blows" of South Africa. The largest pipe, Antochka, is roughly 5.2 ha in size.In some instances numerous veins and stringers are localized and form kimberlite stockworks. Clusters of pipes occur, for example at Banankoro, and often it appears that pipes have originated at the inter¬ section of dikes. The absolute age of the kimberlitic magmatism is unknown, but is younger than the 180 Ma age of the dolerites which are often cross-cut by the kimberlite dikes. The kimberlites have undergone erosion since emplacement and probably represent root zone facies.