Geo-Electrical Resistivity Investigation of Mineral Bearing Rocks in Rongo Gold Mining Area in Migori County

Abstract

Rongo Gold field forms part of the Lake Victoria greenstone belt and is a highly prospective area. However, it has to date been underexplored due to overburden which obscure the mineralized zones beneath. An electrical resistivity survey was used to detect gold bearing rocks and dense bodies of rocks within host formation in Kamwango area of Rongo district, Migori County. To achieve this, a terrameter (ABEM SAS 1000) was used to determine apparent resistivities using Wenner and Schlumberger configurations. For good vertical resolution, Wenner array was employed to map horizontal structures where a total of 30 stations were done with a probe depth of 45m. Values from Wenner array were used to plot a contour map using Surfer 10 software. The eastern central part of the study area (40km2) is a region of low resistivity as seen from the contour map. Sounding was done on this region of low resistivity along transects using Schlumberger array where a total of 8 stations were sounded as identified from the contour map. IP2WIN software was used to process and model the apparent resistivity values to get true resistivity values. Soundings done on this region gave an average basement depth of 21.86m and a steady rise depth of 32.68m which indicate the depth at which the country rock was hit. High resistivity values indicate the compact volcanic Nyanzian system rocks that are porphyritic, andesites and dacites. The values go up to 1000 Ωm in some parts of the study and the depth is in the range between 40m and 130m. Depths with low resistivity are composed of the highly fractured volcanics with resistivity as low as 13Ωm. The subsurface and the weathered section also have low values due to presence of groundwater. The conductive zones give resistivity values that correspond to mineral ores that bear gold and related minerals.