Secondary Enrichment of Ferriferous Pre-Cambrian Quartzites by Meteorical Weathering in South Cameroon

Abstract

The meteoric weathering of Precambrian ferriferous quartzites from Meyomessi in southern Cameroon has led, in a humid tropical climate, to the formation of secondary oxidized ores. The weathering profile of the ferriferous quartzites shows from the base to the summit: the bedrock, the saprolites, the gravel horizon and a surface sandy clayey aggregate, ferriferous quartzite is a finely banded rock showing alternating quartz beds and iron oxide beds. The main features of the Meyomessi quartzite geochemistry show that the ferruginous facies are remarkably poor in any element other than Fe and Si. The alteration of the materials shows high Fe, Si, Al, Cr, Zr, Ba, Ga, Nb and Th. Rare earth elements levels are generally low compared to Ce, La and Nd, which are concentrated in upper gravel and sandy-clay levels. The rare earth elements spectrum indicates a positive anomaly in Ce and a negative anomaly in Eu. The results obtained from the calculated balances show a very high enrichment in Al, Ti and K in all the altered materials, low in Si and P in the higher levels and weak in iron in the weathered fragments and in the sandy clay loam level. The losses are total and moderate for all the trace elements, while the rare earths elements are enriched in the soft materials of the whole profile. The iron content in the bedrock (64.9%) versus 68% in the weathered rock fragments (ore), shows that the climatic alteration improves the quality of the ore in the ferruginous fragments by dissolution of the silica and relative concentration iron.