Origin and Tectonic Framework of the Ngovayang Iron Massifs, South Cameroon

摘要

The Ngovayang massifs belong to the Paleoproterozoic Nyong unit complex located in the north western edge of the Congo Craton of southern Cameroon. It consists of granitoids and a banded series. The banded series presents the petrographic and geochemical characteristics of greenstone belts similar to those of Sao Francisco Craton in Brazil. Pervious works in this area involved geochemical (% Fe), mineralogical (hematite/magnetite) and geophysical characterization of the formation ores. The sedimentary and tectonic events related to the ore emplacement are poorly understood and has an effect on the exploitation of these ores in Cameroon. The objective of this work is to generate new petrographic and geochemical data of the Ngovayang massifs, and to determine the origin and emplacement process that favored the accumulation of these ironbearing ferruginous quartzites in the study area. Polished thin sections were produced and observed using a scanning electron microscope at the Centre for Microscopy and Microanalysis, University of Western Australia CMM-UWA. Geochemical analysis of major and trace elements were carried out using XRF and ICP/MS in OMAC laboratory of Ireland. The results showed that the iron formation of the Ngovayang area composed of ferruginous and banded ferruginous quartzites series. Quartz, hematite and aluminosilicates occur as the main minerals associated with the ferruginous quartzite series. Geochemically, these ferruginous facies are very rich in Fe and Si but poor in other elements. Platy and massive type of mineralization were common with the hematites and are indicative of either metasomatic (or hydrothermal) origin and lateritic through meteoric water circulation. Three phase mineralization were identified from microscopic study: early Syn-sedimentary phase linked to the sedimentation of BIFs, a secondary tectonics phase and a tertiary phase related to weathering. The Ngovayang iron formations are characteristic of the lake superior-type.