Contributions of Ground Geophysical Data from the AfricaArray Geophysics Field School to the Proposed Airborne Geophysical Test Site at the Vredefort Impact Structure, South Africa

South Africa is currently embarking on an ambitious project to upgrade its geological and geophysical mapping. This activity coincides with a recent gas discovery off shore South Africa and sustained interest in resource exploration in the southern African region. Efforts by the South African Geophysical Association and the Council for Geoscience to establish an airborne geophysical test site at the Vredefort Impact structure located near Parys, South Africa include the compilation of legacy data and plans to collect new airborne data. Both Australia, at Kauring, and Canada, at Reid Mahaffy, host airborne geophysical test sites which were initially used to establish basic performance criteria of airborne geophysical systems. These sites also enable new airborne geophysical systems to be bench marked against existing airborne and ground geophysical data. Establishing a geophysical test site at Vredefort will ensure that airborne geophysical contractors in Africa have a suitable site to test and calibrate systems.

The Vredefort Dome is the eroded remnant of a 2023 Ma impact into the Witwatersrand Basin that produced extensive uplift and deformation. The lowermost Witwatersrand shales and BIFs are overturned at the contact with the Archean granites that extend to the center of the Dome. The wide variety of lithologies, extensive faulting and enigmatic, extensively shocked, deep crustal lithologies provide a wide variety of geophysical targets at various scales and depths.

The AfricaArray geophysics field school has been collecting ground geophysical data for five years in the area of the proposed airborne test site. These ground geophysical studies are being used to delineate anomalies suitable for magnetic, gravity and EM investigations at various scales. These anomalies include archaeological sites that would be suitable for investigation using drones to the large scale variations in crustal structure associated with deep exhumation of the mid to lower crust. These ground data will be archived and available to the geophysical community and will be linked to physical property measurements being acquired on borehole cores from the area.