Ground-water in the Orange Free State Gold-Field

Abstract

The difficulties experienced in the control and disposal of large flows of saline water in to the mine workings in the Orange Free State Gold-field provided the impetus for a detailed study of the geohydrological conditions prevailing in the vicinity of the mines. Ground-water occurring at shallow depths was studied by examining borehole results, fissures and water-bearing layers exposed in shafts and the chemical analysis of water obtained from such sources. Information regarding the mode of occurrence of water encountered at depth in the mine workings was obtained from a careful examination of numerous ground-water intersections, records of rates of inflow, water levels in bore-holes and in disused shafts. Records of rates of pumping and mine plans showing the geology and the location and orientation of water-bearing fissures were also available for study. Of considerable value were chemical analyses of samples of water obtained from all the operating mines. A specially designed experiment conducted at the flooded Merriespruit Mine provided valuable information regarding the lowering of the surface of pressure-relief due to a known rate of water removal from the deep-seated aquifer. The available data led the writer to conclude that the saline water and gas contained in fissures in the rocks of the Witwatersrand and Ventersdorp Systems flowed into the fissures during a marine inundation shortly after the deposition of the Dwyka tillite. Saline water intersected in a number of bore-holes drilled for exploration purposes flowed out at the surface.