Comparison of the pegmatite-type Nb-Ta-Sn and vein-type Sn-W deposits in Rwanda: metallogenetic implications.

The aim of this research is to compare the pegmatite-type Nb-Ta-Sn with the vein-type Sn-W deposits of the Mesoproterozoic Karagwe-Ankole Belt (KAB) in Rwanda. Both types of ore deposits are spatially and temporally related to the same granite generation (i.e. G4-granites of 986 ± 10 Ma; Tack et al., 2010; Dewaele et al., 2011), but one coherent and combined metallogenic model that links both types of deposits is absent. Research will be carried out on the type and physico-chemical conditions and the geochemical evolution of the mineralising fluids form the Nb-Ta-mineralisation (pegmatites) to the Sn- (pegmatites, hydrothermal quartz veins) and W-mineralisation (hydrothermal quartz veins). Both types of mineralisation will be described and modelled in terms of magmatic and hydrothermal geochemical processes around granite intrusions (G4-granites). During this research the origin and the evolution of the mineralising fluids will be determined. Different techniques will be used to study the mineralisation: minor and trace element geochemistry, stable isotope geochemistry, Laser Raman spectrometry, fluid/melt inclusion microthermometry and [laser ablation] inductively coupled plasma mass spectrometry ([LA-]ICP-MS). All results will be synthesised and combined with existing data (e.g. Dewaele et al., 2011; De Clercq, 2012) to reconstruct a metallogenic model for granite-related mineralisation in the KAB.