Bravo Martin Mbang Bonda^1,, Akumbom Vishiti¹, Mbai Simon Joel¹, Bayiga Elie Constantin², Ngon Ngon Gilbert François², Etamé Jacques^{1, 2}

The Sanaga magnetite bearing iron ore deposit is hosted in the eburnean Nyong complex which constitutes the northwestern edge of the Congo Craton. It is compose predominantly of magnetite bearing quartzite and magnetite-biotite gneisses related to charnockites and amphibole orthogneisses. In this study we use the composition of the magnetite bearing ore to determine their origin and ore formation process. A deposit model is also proposed for a better understanding of the emplacement of the iron ore. EMPA analysis on magnetite reveal variable amount of V, Ti, Al, and Mn. Most of the samples present Ti contents > 0.1%, this indicates a hydrothermal overprint. Although the texture and chemical composition of the magnetite bearing rocks neither represents typical skarn nor BIFs, on Ca + Al + Mn vs Ti + V and Ni + Cr vs Ti + V discrimination diagrams the magnetite reveals a double affinity for skarn and BIF. Elevated contents of Al, Mn and Mg in the magnetite signify crustal contamination while BIF signatures are related to hydrothermal activities. The variable content of V and Ti/V ratio suggests a mixture of reducing and oxidizing environments. On the Al + Mn vs Ti + V binary diagram the magnetite bearing ore reveal hydrothermal temperatures that vary between 200-300°C and 300-500°C. This suggests their precipitation from hydrothermal fluid with medium to high temperature and slight enrichment in Al and Ti. Integrating the data obtained from studies such as regional geology, ore geology and mineral microchemistry, we suggest that the Sanaga magnetite bearing iron ore deposit is similar to the Lake Superior iron ore type and was formed from transgression-regression in back arc basin or continental margin.

magnetite, trace element, hydrothermal alteration, Sanaga prospect, Cameroon