Petrography, Sedimentology and Geochemistry of Rocks and Sediments from Three Key Localities from the South-East Region of the Yaoundé Group (Centre Region, Cameroon): Implications for Rutile Exploration

Abstract

The Otele, Matomb and Nguibassal localities correspond to the SW part of the Yaounde Group. Field observations, rocks and stream sediments of the study area were examined using rock tin sections, granulometric, morphoscopic and X-ray fluorescence analysis to identify their distribution, the nature of the basement, provenance useful minerals and some weathering process that affect them to show the exploration significance of these outcomes. From these it appears that, three rocks types occur in the areas: gneisses, micaschists and amphibolite, respectively with the following minerals assemblage: (Fks + Bt + Qz + Ky + Pl + Msc + Grt + Op), (Bt + Qz + Msc + Fks + Op + Ky + Grt) and (Amp + Bt + Pl + Kfs + Qz + Px + Grt + Op). Sedimentological analyses reveal the dominance of unworn grains of rutile quartz and kyanite that suggest a short transport; while less abundant minor shiny dulls and sub-rounded grains suggest a long transport. Sediments collected are homometric, well sorted, well classified, with immature rutile due to their angular shapes. Silica is the most important major element ranging in concentration between 47.56 wt% SiO2 in amphibolite to 61.21 wt% SiO2 in gneiss. Stream sediments chemistry equally showed that silica and alumina are the remarkable elements with values of 53.92 wt% and 13.33 wt% respectively with important increase of TiO2 ranging between 51.77 and 95.03 wt%. The TiO2 percentage met in minerals of the global fraction and rutile concentrate come from the same minerals in the rock, and percentage increases when linked to heavy minerals observation suggested the Ti percentage to mainly come from rutile. Impurities present in the rutile lattice include: V, Nb, Ta, Cr and CaO. Rutile was found to come from the same area but with several source rocks (Felsic and mafic). High Nb contents (277 - 768.33 ppm) as compared to Cr (394 - 444.33 ppm) associated to the elevated ratio of LREE/HREE coupled to the negative Eu anomalies in rocks and sediments of the study area are indicative of felsic source material. Moreover, enrichment in Cr as compared to Nb at Nguibassal suggested rutile to originate from mafic rocks.