A Review of Origins and Occurrences of 3Ts Mineralisation in Rwanda

Rwanda is geologically situated in the Karagwe Ankole Belt, center east Africa. Karagwe Ankole Belt (KAB) is separated from Kibaran Belt (KIB) by a Paleoproterozoic Rusizian terrane and they both form mesoproterozoic orogenic belts of Central Africa. The part of the KAB located in Rwanda contains the bulk of cassiterite, columbite-tantalite, and wolframite. These ore minerals have been termed 3Ts and occur in Nb-Ta-Sn pegmatites, W-Sn hydrothermal quartz vein deposits and Sn greisens, which are components of one composite metallogenic system related to the granite generation (G4-granite or fertile granite) that occurred at 986±10Ma. The composition of hydrothermal fluid is H2O–CO2–CH4–N2–NaCl, and this fluid is characterized by the low to moderate salinity (2.7-14.2 eq. wt.%NaCl), high pressure (~100MPa), and the mesothermal temperature (~300°C). The isotopic composition of the fluids indicated that the mineralised quartz veins are much more likely to be formed from the fluid mainly subjected to metamorphic processes. The book owes the brief on the current status of views about the mineralisation of 3Ts minerals in Rwanda.