Lateritic Landform-Regolith Mapping of Southwestern Burkina Faso (West Africa): Implications for Long-term Landscape Evolution Processes and Mineral Exploration

Abstract:

Surface remobilization of mineral resources in cratons and shields may essentially be investigated through the study of regolith production and mobility at various scales in the landscape. This provides tools for exploration but also constrains the sediment routing system at the source of many passive margins. Here we develop a regolith mapping protocol at the scale of Southwestern Burkina Faso, which exposes mineralized Paleoproterozoic granite-greenstone terrains and their Neoproterozoic sandstone cover. Mapping is based on a combination of field survey and the interpretation of radiometric data, satellite images and digital topography. The best preserved lateritic regolith unit with clear-cut and unambiguous characteristics are ferricrete capping plateau relicts of a pediment surface called the High glacis, which developed throughout West Africa between ca. 24 and 11 my ago. Topographic reconstruction at 11 Ma based on the distribution of High glacis relicts was used to quantify landscape evolution. Results show that the modern drainage was mostly established at 11 Ma. The initial geometry and dissection of the High glacis slopes were then influenced by their position with respect to watersheds and lithology, impacting the different scales of redistribution in the area. By subtracting the current DEM to the High glacis topography, post-11 Ma denudation is calibrated between 0 and 8 m/my with a very low average (2 m/my). Such regime corresponds to a cratonic background ‘noise’ that is weathering-limited. Results also suggest a minimum timescale in the order of 20 my for resurfacing the landscape, providing new constraints for modelling both the sediment routing system and the surface remobilization of mineralizations. Finally, using our findings, we identify two type-configurations where exploration strategies might be refined: one where High glacis relicts potentially mask mineralized units and one where surface index may originate from lateral remobilization.