Neoproterozoic granitoid-hosted quartz-magnetite mega veins at Mayo Binka, western Cameroon: Field disposition and petrochemical characteristics

Abstract

Enigmatic shear zone-related mega quartz-magnetite veins, hosted by Neoproterozoic granitoids of the Central African Fold Belt (CAFB) in Mayo Binka, western Cameroon, are investigated using new field, ore microscopy, bulk-rock geochemistry, and magnetite microchemical datasets to elucidate their origin and deposit type. Magnetite is paragenetically the earliest Fe-oxide phase in the Mayo Binka prospect. Its partial replacement by mechanically twinned specular hematite and martite, along with ilmenite exsolution textures, indicates hydrothermal processes. The magnetite ores are characterized by high Fe₂O₃ (~81 wt%) and low SiO₂ (~15.7 wt%), Al₂O₃ (~0.48 wt%), TiO₂ (~0.01 wt%), and P₂O₅ (~0.03 wt%) contents. The rare earth element (REE) signature, marked by low ΣREE content (~12.62 ppm), enrichment in LREE (La/Yb_CN ~4.16) over HREE (Gd/Yb_CN ~1.48), a slight negative Eu anomaly (~0.97), and a strong negative La anomaly (~0.52), suggests elevated-temperature, igneous origin for the magnetite deposits rather than sedimentary. Magnetite microchemistry reveals high concentrations of Ti (~16 wt%), V (~3881 ppm), Al (~12,031 ppm), Mn (~3058 ppm), and Ga (~39 ppm), indicating magmatic crystallization under low oxygen fugacity (fO₂) in contrast to the hydrothermal signatures shown by petrographic observations. Trace element-based discrimination diagrams classify the Mayo Binka prospect as an Fe–Ti–V magmatic magnetite deposit. Field association with granitoids, fault rocks, and metavocanosedimentary rocks (schist, amphibolite, gneiss, and quartzite), coupled with petrographic, mineralogical, and geochemical datasets, suggests that the Mayo Binka massive ferriferous veins likely formed in a complex geodynamic continental back-arc setting, where magmatic sedimentary and tectonic processes controlled the localization and evolution of the mineralization.