Petrogenetic characterization of the host rocks of the Sanaga iron ore prospect, southern Cameroon

The Sanaga iron ore prospect is a recent discovery in the Nyong Series with a resource estimated at 82.9 Mt at 32.1% Fe and whose origin remains debatable. The mineralization occurs as NE-SW oriented discontinuous lenticular bodies of magnetite-bearing pyroxene-gneisses (MPG) hosted by ortho-derived gneisses. Rare amphibolites are observed. The MPG mineral assemblage consists of quartz-magnetite-orthopyroxene-garnet-tremolite/actinolite exhibiting a granoblastic texture, which is characteristic of granulite facies metamorphism. The granodioritic gneisses show compositional features of the tonalite-trondhjemite-granodiorite association. Their trace and REE element geochemistry indicate their protolith melt resulted from the partial melting of a subducted oceanic slab, with interaction with the overlying mantle wedge during ascent. The amphibolites show enrichment in LILE with negative Ta-Nb and Zr-Hf indicating arc-related magmas generated by partial melting of a sub-continental lithospheric mantle source with metasomatism by subduction-related fluids. The MPG exhibits oxidation-exsolution features characterized by ilmenite lamellae, with hematite fracture-filling in magnetite, and lacks features characteristic of typical BIF such as LREE depletion relative to HREE, positive Eu, La, and Y anomalies. Based on the results of this study, we interpret the Sanaga MPG as a possible skarn-type mineralization formed by the metamorphism/metasomatism of a possible BIF protolith. The results of this study compare with similar magnetite-rich mineralization in the Sao Francisco craton in northeastern Brazil and enhance the correlation of pre-drift reconstructions of the Sao Francisco-Congo Cratons.