Metallogeny of the northeastern Kibaran belt, Central Africa

Abstract

The evolution of the intracontinental Kibaran beit spans the period from about 1400 to 950 Ma. Its earlier history involved the deposition of a very thick psammitic–pelitic sedimentary pile with some intercalated volcanic rocks, which were folded around 1200 Ma ago. This deformation created essentially upright structures, which were controlled by rigid basement blocks. Metamorphism related to igneous granite intrusions were more intense in anticlinal structures. From about 1000–950 Ma a renewed compressive phase equivalent to the Lomanian orogeny was associated with the emplacement of LIL-element enriched ‘tin’ granites. They formed sheets at basement/sediment and granite/sediment contacts, with cupolas at tectonic highs. Pegmatites and quartz veins with Sn, W, Nb/Ta, Be and Li are derived from the ‘tin’ granites. Generally, this mineralization shows a pronounced structural control with a clear symmetry relation to N–S trending folds and thrusts. Gold-rich quartz veins occurring in districts marginal to the Sn–W mineralization, are a distal and lower temperature phase. Mafic–ultramafic layered intrusions with Ni, Co, Cu, platinum-group metals and Fe/Ti deposits form a belt parallel to the eastern margin of the Kibaran towards the Tanzanian craton. These rocks may be related to the Bukoban/Malagarasian basalts with an age of 1000–850 Ma. Subvolcanic alkaline and carbonatite complexes which were the source for small Ree deposits are clearly post-Kibaran in age. Mineralization.