Metallogeny of the northeastern Kibara belt, Central Africa—Recent perspectives

Abstract

The Kibara belt is an intracontinental mobile belt formed between 1400 and 900 Ma within a craton of Lower Proterozoic age. The belt's evolution started by early rifting at about 1400 Ma, and continued by transition into a marine basin filled by clastic sediments > 10 km thick, with minor basic and acidic volcanic rocks. At about 1300 Ma, the pile was deformed by thrusting and folding of the main Kibaran Orogeny and intruded by numerous large syn-orogenic granite bodies. Wide areas of the Kibaran experienced only very low-grade metamorphism, but halos of high-temperature/low-pressure metamorphism surround intrusive bodies. A post-orogenic phase of rifting followed at about 1275 Ma and was accompanied by the intrusion of alkaline granites and layered mafic intrusions with Ni, Cu, Co, Ti, V and possibly also PGM mineralization. Also at about this time, molasse sedimentation set in, both within the belt and in foreland troughs. The western molasse and the whole belt were again orogenically deformed at around 950 Ma by the Lomamian Orogeny; concurrently, small metallogenetically specialized granite bodies were emplaced. Fertile members (“tin granites”) of the latter produced numerous pegmatitic and quartz vein deposits with Sn, W, Nb Ta , Li, Be and Au. Other auriferous and locally Pt-bearing quartz veins and breccias are not spatially related to tin granites, but appear near large fault zones that may be associated with deep structures separating basement blocks. Both the tin granites, and the fluids which formed gold ores not related to granites, are suggested to have been derived from metamorphic devolatilization and partial melting of older (Archean and Lower Proterozoic) basement underneath the Kibaran Orogen.