Geochemical characteristics and petrogenesis of basic rocks in the Ako’ozam–Njabilobe area, Southwestern Cameroon: implications for Au genesis

Abstract

Greenstone belts are known to host important gold mineralization across the globe. Greenstone rocks outcrop within the gneissic basement of the Ako’ozam–Njabilobe area, in the Paleoproterozoic Nyong unit, Southwestern Cameroon, known to host significant placer gold mineralization. Major, trace and rare-earth elements of amphibolites and metadolerites in the Ako’ozam–Njabilobe area were examined to ascertain their petrogenesis and their role in gold mineralization. The rocks are of tholeiitic affinity, enriched in LILE and base metals notably Cu and Zn. The basic rocks were sourced from basalts and emplaced in continental settings. The low Rb/Sr ratio (0.08 to 0.13), high Ba/Rb and Nb/Ta ratios (8.04 to 10.0 and 7.27 to 11.557 respectively), suggest that the basaltic magma was sourced from the lithospheric mantle. The mineral inclusion chemistry (Fe-rich biotite, Fe-oxide, and rutile) of placer gold in the Ako’ozam–Njabilobe area suggests that the mineralizing fluids interacted with the mafic rocks in the area. It is suggested that a gold-bearing magmatic rock was metamorphosed into amphibolite and metadolerite with the subsequent partitioning of Fe-oxide, rutile and Fe-rich biotite in the gold grains during mobilization of gold from the basic rocks by hydrothermal fluids.