Geochemical assessment of supergene manganese ores occurrence from weathering crust of the Lower Dja Series, East Cameroon

Abstract

The Lower Dja Series hosts manganese ore minerals. XRD and whole-rock geochemistry were used to assess the geochemical characteristics of Mn ores. Supergene manganese ores develop in situ though weathering processes. Mn-rich rocks consist of massive coalescent blocks in laterite and free blocks of massive manganese oxide. Laterites are classified as ferruginized sediments, vermiform, and pisolitic suggesting different modes of evolution of laterites. Mn-rich rocks are composed of pyrolusite and hollandite, and classified as high- and low-grade Mn ore. High-grade Mn ores are enriched in manganese minerals and have high contents of Mn/Fe, MnO, Ba, Co, Pb, V, and are depleted in MgO, K 2 O, P 2 O 5 , and Rb compared to low-grade Mn ores. Both high- and low-grade Mn ores show enrichment in high field strength elements, transitional metals, and rare earth elements (REEs). REE profiles reveal REE fractionation (La N /Yb N : 0.34–1.19 for high-grade Mn ore, 0.76–2.75 for low-grade), positive Eu (Eu/Eu*: 1.06–1.54) and Ce (Ce/Ce*: 1.27–2.24) anomalies, consistent with modern Fe-Mn nodules. This implies that the primary sedimentary Mn ore is generated by hydrogenetic activity and has undergone weathering process to form supergene Mn ore minerals in the Cenozoic era. The Supergene Mn occurrence of Bateka is similar to globally recorded deposits in Gabon, South Africa, Côte d’Ivoire, Ghana, Burkina Faso, Australia, Brazil, Ukraine, India, and China. The outcomes of the study not only shed light on the occurrence of manganese occurs, but also serve as a valuable roadmap for pinpointing host rocks and driving future exploration.