Geochemical characterization of surface sediments from Tongo Gandima (Eastern Cameroon): implications for gold exploration

Abstract

This paper deals with the mineralogy and geochemistry of alluvial sediments from the Tongo Gandima (Eastern Cameroon) using XRD, XRF, and ICP-MS instruments. The main aim of this work is to discuss the provenance of sediments and carry out a geochemical exploration in the areas where gold mining is taking place. Granites and monzonites outcrop as large masses of several decameters with granular texture. Petrographic description and SiO2, Al2O3, and TiO2 contents reveal the intermediate igneous rock nature of monzonites and the felsic igneous rock nature of granites. Both rocks fall into the field of peraluminous and S-type granites. The high proportion of feldspars and biotite led to high Al2O3, Fe2O3, CaO, Ba, Sr, Th, Zn, Zr, and REE (rare earth element) contents particularly in monzonites. The presence of accessory minerals results in high trace element contents including REEs. The alluvial sediments are composed of quartz, kaolinite, rutile, smectite, zircon, magnetite, and gibbsite. They are mainly classified as shale, wacke, Fe-shale, and Fe-sand. The chemical index of alteration (CIA) reveals moderate to intense weathering of the source rock highlighted by the depletion of alkaline (Na+, K+, and Ca2+) and the enrichment of Al2O3. The high Th/Sc ratio which is an indicator of chemical differentiation suggests a high degree of sediment recycling. The variable chemical differentiation corroborates with the variable contents in Zr, Hf, TiO2, P2O5, and REEs. The chondrite-normalized REEs show high REE contents and negative Eu-anomalies. The negative Eu-anomalies in sediments indicate reduction conditions or the depletion of europium bearing minerals. The few amounts of Cr, V, Ni, and Sc as well as the abundance of Th and REEs justify the felsic nature of rocks. There is a similarity between REE behavior of host rocks (granites and monzonites) and sediments. These rocks may contribute a lot as the sediment sources. The felsic source is confirmed by light REE-abundance and negative Eu-anomalies. In addition, both lithotypes show high REE contents while alluvial sediments possess attractive contents in Ba, Sr, Au, and REEs. These data suggest that the potential of the surface sediments of Tongo Gandima as gold deposits is low.