SOME APPLICATIONS OF GEOPHYSICAL PROSPECTING IN THE UNION OF SOUTH AFRICA

The major application of geophysical prospecting in the Union of South Africa is in determining locations for drilling water wells. Four principal approaches are employed: 1. Permeable contact zones between igneous intrusions and sedimentary rocks are sought by magnetic surveys. 2. Basins of decomposition are sought by the resistivity method. 3. Narrow water‐bearing fissures and fault zones are located by an electromagnetic method. 4. The water‐bearing and water‐yielding properties of rocks are determined from their computed resistivities. The interpretation of resistivity depth probe curves is based on an empirical method which corrects for lateral effects. Another important application of geophysical prospecting in the Union is in gold‐mining. Gravitational and magnetic surveys have been widely used in the search for auriferous reefs in the Wit‐waterstand system which are concealed by a deep cover of younger rocks. Resistivity, electromagnetic, gravitational, and seismic methods have been applied to problems of engineering geology, including the delineation of areas in dolomite where sinkholes may occur.