Time Domain Electromagnetic Sounding In Southern Africa: Recent Case Studies

The Council for Geoscience carried out ground based time domain electromagnetic sounding (TDEM) surveys on prospects in five countries in Southern Africa namely Democratic Republic of Congo (DRC), Mozambique, Rwanda, South Africa and Zimbabwe. The surveys were undertaken on mining, mineral exploration and engineering sites. The TEMFAST-48HPC and TSIKL-5 instruments were used for data acquisition. In addition, the Geonics Protem 47 and Zonge Nano-TEM systems are being used in South Africa for geology and groundwater investigations. The Interpretation of time domain electromagnetic data was performed using different programs namely ERA, TEM-RESEARCHER (TEM-RES-WIN), IRAF and Sτ Inversion. The parameters that were obtained from modelled data for three case studies comprised of resistivity, chargeability and magnetic susceptibility. Modelling of TDEM data collected in most parts of Southern Africa should take into consideration, the super-paramagnetic effect. In South Africa TDEM surveys were used to delineate mined-out and non-mined areas in the eMalahleni coal mining areas. Building materials and aggregates were mapped using the TDEM technique in the Democratic Republic of Congo (DRC). In Rwanda aeromagnetic interpretation targets were investigated using the TDEM method for potential mineralisation. The coal bearing and mined out areas were demarcated on the basis of resistivity contrasts for the South Africa case study. The thickness of building aggregates was estimated from resistivity data for the DRC site. Areas with high chargeability and low resistivity were identified as potential targets for mineral exploration for the Rwanda prospect. The TDEM method has proved to be an important non-invasive tool for carrying out groundwater, mineral and engineering investigations.