Ta-Nb-Sn-W-Au mineralization in the Mesoproterozoic metasediments of the Karagwe-Ankole belt (Rwanda, DRC) and its relation to early Neoproterozoic orogeny and magmatism

A recent renewal of interest and research into Nb, Ta, Sn, W, Li and Au deposits of the Central African Mesoproterozoic Karagwe-Ankole belt (KAB) has led to new insights regarding its metallogenesis. This study provides an overview of the geodynamic framework of the KAB, including its magmatism and mineralization. During compressional deformation, barren quartz veins are intensely folded. A second quartz vein generation developed inside the fold hinges. Reverse faults occur in the hinge zone of such folds. After compression, but still during tectonism, Neoproterozoic granite intrusions (G4) are emplaced. Hydrothermal W-rich quartz veins with a mixed magmatic and metamorphic origin formed after folding and cleavage development. Highly fractionated and often metasomatized pegmatites are enriched in Ta-Nb and Sn. Extensional tectonism is evidenced by boudinaged pegmatites, which post-date vein-type W mineralization. Sigmoidal quartz veins and shear zones are an expression of late tectonic shearing. Gold mineralization at Byumba (Rwanda) could be related to this shear phase, but a hydrothermal magmatic source for this deposit cannot be excluded. Sn mineralization is associated with greisenization of pegmatites and with quartz veins. These Sn deposits originate from magmatic fluids, exolved from pegmatitic melt and postdate folding and faulting