Section 3 Rare-metal pegmatites and their mineralization
This chapter consists of two papers, both reviews, concerning pegmatites in Africa. The first paper by von Knorring and Concliffe discuss potential rare-element pegmatites which are widespread on the African continent, especially south of the equator, along the Kibaran orogenic belt extending from Uganda, through Rwanda and Kivu, and Maniema and Shaba provinces of Zaire. They are also prominent within the Mozambiquian fold belt of Pan-African age in East Africa, Mozambique, Madagascar, and within the Damaran fold belt in Namibia. Other areas include the Namaqualand metamorphic complex along the Orange River belt, and the basement rocks in Zimbabwe. In their paper, von Knorring and Concliffe concentrate on the mineralogy and geochemistry of the pegmatite deposits in Africa, paying particular attention to the occurrences of tin and tantalum mineralization.
There are two distinctive periods of pegmatite formation in Africa developed at end-orogeny times during the closing stages of the Kibaran and the Pan-African orogeny. These periods correspond to approximately 900 Ma and 500 Ma. According to Matheis the pegmatites in Nigeria, like those in other parts of Africa, are also Pan-African in age. Indeed most of Africa's rare-metal pegmatite potential is linked to the closing stages of the Pan-African orogeny. In his paper Matheis concentrates on the Nigerian tin province in terms of its economic rare-metal mineralization paying particular attention to occurrences of mineralized pegmatites in the Nigerian Precambrian basement. Matheis concludes that reactivation of old tectonic lineaments during the Pan-African orogeny provided excess fluid and heat to form late Proterozoic and early Palaeozoic rare-metal pegmatites by partial melting and selective leaching. Later plate tectonic movements and anorogenic activity caused partial resetting of the isotopic ages of the pegmatitic minerals.