The redistribution of thorium, uranium, potassium by magmatic and hydrothermal processes versus surface processes in the Saraya Batholith (Eastern Senegal): Insights from airborne radiometrics data and topographic roughness

Potassium (K), thorium (Th), and uranium (U) are incompatible elements, with various degrees of mobility with respect to hydrothermal alteration or weathering and are taken as tracers for magmatic, fluid-rock interactions and mineralization. These elements may be mapped from airborne radiometric surveys revealing their spatial distribution at the surface. Magmatic processes (partial melting, migration and crystallization of silicate melts), hydrothermal alteration, and superficial processes (in situ weathering, erosion and transport) are responsible for the distribution of these elements in the rock, regolith and soil. However, these processes do not operate at the same scales, and we postulate that they produce distinct spatial distributions of K, Th and U concentrations. In this study, we combined geostatistical approaches, such as analyses of frequency distributions and variograms with roughness and topographic mapping to decipher the respective role of magmatic and hydrothermal processes versus surface processes on the spatial distribution of K, Th and U concentrations at the surface of the Saraya Batholith (Eastern Senegal). We found that the distributions of K and Th are anisotropic and correlate to the different magmatic sub-units of the Batholith in the northern part of the Saraya Batholith, which is currently incised by a network of riverbeds, as revealed by the roughness map. In contrast, the surface of the southern part of the Saraya Batholith is dominated by chemical weathering and is characterized by depletion and reduced anisotropy of K and enrichment in Th with respect to the northern part. The K, Th and U concentrations in the southern part are therefore controlled by surface processes masking the primary (magmatic) signatures. These results motivate similar analyses of spatial patterns of K, Th and U concentrations in other contexts in support for geological mapping and mineral exploration.