Petrology, geochemistry and Ni-Co mineralization of Elig-Mfomo mafic-ultramafic rocks and laterites in Yaounde Group, Cameroon

Nickel (Ni) and cobalt (Co) laterites are supergene deposits formed under subtropical to tropical climatic conditions, through the weathering of olivine-bearing mafic to ultramafic rocks. The objective of this study was to evaluate the economic potential of Ni-Co in the Elig-Mfomo area of the Yaoundé Group. Three rock types were sampled; schist, amphibolite and pyroxenite, and bulk sampling of nine laterites was done from six trenches and these two sets of samples were analyzed for their petrography, mineralogy and geochemical properties. The representative samples were analyzed for major oxides by Inductively Coupled Plasma-Atomic Emission (ICP-AES) and trace and rare earth element using Inductively Coupled Plasma Mass Spectrometry (ICP-MS). The petrographic results show a mineral paragenesis made up of Opx + Cpx+Hbl + Pl+Qz + Zrn±Ox, indicating that the rocks in the Elig-Mfomo area were affected by amphibolite-granulite facies metamorphism typical of the Yaounde group. XRD analysis of two laterite sample indicate that the mineral content of the soil associated with the Ni-Co mineralization is composed of quartz, zeolite, goethite and clay, with goethite being the most dominant mineral. Ni and Co concentrations were higher in the laterites than in the analyzed rock samples, indicating supergene enrichment. Highest concentrations were obtained in samples NS7A and NS7B. High goethite concentrations in both samples indicate an oxidizing environment as further demonstrated by negative Eu and positive Ce anomalies. Samples NS7A had Ni 0.5% and Co 0.9% concentrations and NS7B had Ni 0.7% and Co > 1%. This shows that the Elig-Mfomo area, particularly in areas of samples NS7A and NS7B could be potential in Ni and Co mineralization.