Cassiterite and columbo-tantalite (Coltan) mineralisation in the Proterozoic rocks of the northern part of the Kibara orogen (Central Africa): preliminary results

The Central African Kibara orogen extends from the southeastern part of Uganda to the southern part of the Democratic Republic of Congo (DRC). It forms a met- allogenic province that hosts different types of granite-related mineralization: cassiterite, columbite-tantalite, wolframite, gold, monazite, amblygonite, beryl, etc. These minerals are present in different types of mineralization. The minerals occur as primary mineraliza- tion in quartz veins and pegmatites, but also as secondary mineralization in alluvial or elu- vial deposits. In this study, we focus on the metallogeny of the primary tin and columbite- tantalite mineralization in the northern part of the Kibara orogen (Rwanda, Burundi, Uganda, Tanzania, Maniema and Kivu in the DRC). Based on a systematic overview of mining data in the archives of the RMCA, field work, petrography, geochemical, miner- alogical and microthermometric investigations of ore and gangue minerals and based on a comparison with recent ore-forming models of granite-related ore deposits, a preliminary metallogenic model is proposed. The main granite generation G1-3 intruded at 1380 +/- 10 Ma in the Palaeo- and Mesoproterozoic rocks of the Kibara orogen. At ~986 Ma, the youngest G4 granite gener- ation formed. Although historically called tin -granite, this granite generation is not min- eralized. After consolidation of the G4-granite, pegmatites were emplaced (~ 960 Ma). Some of these pegmatites are mineralized in columbite-tantalite. At ~940 Ma, cassiterite- mineralized quartz veins formed. In the pegmatite area, this hydrothermal phase resulted in an intense alteration of the pegmatitic bodies.