Gold mineralization in the Mesoproterozoic Karagwe-Ankole belt (Byumba, Rwanda) : new insights from petrography and trace element mapping

Abstract

A recent increase of interest in the various mineral deposits of the Central African Karagwe-Ankole belt (KAB) has led to many new discoveries and exciting research. Gold deposits in the KAB still have many unanswered questions concerning their formation conditions. The aims of this research are to determine the controlling factors on gold distribution at the Byumba deposit (Rwanda) and to resolve the relationship between the different vein generations and the tectonic evolution of the area. To achieve this, drill cores from the Byumba deposit were logged and sampled for further petrographic research and major and trace element mapping. Micro X-ray fluorescence (mu XRF) is used for the identification and distribution of gold and of different types of alteration/mineralization. Five main phases of quartz veining are identified which can be linked to the different phases of deformation that are recognized in the KAB. Important phases of folding and shearing are distinctly present at Byumba and associated with sericitization and chloritization. Sulfides are predominantly present in the form of pyrite, with minor associations of arsenopyrite, chalcopyrite, pyrrhotite and covellite. Primary gold mineralization seems to be correlated to chlorite-rich shear veins. Gold occurs within an early quartz phase and not associated with pyrite