Geochemical Constraints on the Origin of Banded Iron Formation-Hosted Iron Ore from the Archaean Ntem Complex (Congo Craton) in the Meyomessi Area, Southern Cameroon

Banded iron formations (BIFs) are the most significant source of iron in the world. In this study, we report petrographic and geochemical data of the BIF from the Meyomessi area in the Ntem Complex, southern Cameroon, and discuss their genesis and the iron enrichment process. Field investigations and petrography have revealed that the studied BIF samples are hard; compact; weakly weathered; and composed of magnetite, subordinate quartz, and geothite. The geochemical composition of the whole rock reveals that iron and silica represent more than 98wt% of the average composition, whereas Al2O3, TiO2, and high-field strength elements (HFSE) contents are very low, similar to detritus-free marine chemical precipitates. The total iron (TFe) contents range from 48.71 to 65.32wt % (average of 53.29wt %) and, together with the low concentrations of deleterious elements (0.19wt % P on average), are consistent with medium-grade iron ores by global standards. This interpretation is confirmed by the SiO2/Fe2O3total versus (MgO+CaO+MnO)/Fe2O3total discrimination plot in which most of the Meyomessi BIF samples fall in the field of medium-grade siliceous ore. Only one sample (MGT94) plots in the high-grade magnetite-geothite ore domain. The high Fe/Ti (376.36), Fe/Al (99.90), and Si/Al (29.26) ratios of the sample are consistent with significant hydrothermal components. The rare earth elements (REE) contents of the studied BIF samples are very low (Sigma REE: 0.81-1.47ppm), and the Post-Archaean Australian Shale (PAAS)-normalized patterns display weak positive Eu anomalies (Eu/Eu*: 1.15-1.33), suggesting a syngenetic low-temperature hydrothermal solutions, similar to other BIF worldwide. However, the Meyomessi BIFs show high Fe contents when compared to the other BIFs. This indicates an epigenetic mineralization process affected the Meyomessi BIF. From the above results and based on the field and analytical data, we propose that the genetic model of iron ores at the Meyomessi area involves two stages of the enrichment process, hypogene enrichment of BIF protore by metamorphic and magmatic fluids followed by supergene alteration as indicated by the presence of goethite in the rocks.