Remote sensing, geological, and geophysical investigation in the area of Ndlambe Municipality, Eastern Cape Province, South Africa: Implications for groundwater potential

Abstract

Potentiality for groundwater in the Ndlambe Municipality, comprising of rocks of the Witteberg Group, Cape Supergroup, was investigated using a combination of different approaches. Distribution of lineaments extracted from a satellite image is hardly homogenous; their density varies with different localities. Areas around the western and southwestern parts of the study area have relatively high-density values (≥39) while the northern, eastern and northeastern parts of the area of study are dominated by low-density values (0-39). Boreholes located in the northeastern part appear to be away from the zones of dense lineaments, have dried up, and were found not to be productive. In the northwest parts of the study area, there are several locations displaying intersections of lineaments, these zones of high lineament intersection can be targeted for groundwater exploration. Most of the lineaments in the study area trend in a northeast-southwest direction; this trend would be identical to the orientation of the preferential flow path. Quartz veins and normal faults seen in the field are good indicators for groundwater potential as they are a structural expression of extensional environmentsThe same applies to quartz grains affected by extensional micro-fractures, which resulted from brittle deformation as seen under the microscope. Subsurface geology investigation from borehole logging has depicted fractures in quartzitic sandstones; thus, micro-fractures in quartz grains and quartzitic sandstones enhance secondary porosity and groundwater flow. Low resistivities from the geophysical investigation in the study area were inferred to be weathered moist sandstone. The low resistivities at depth also indicate an overlying zone of fractured sandstone and quartzite, hence possibility of hosting some groundwater. Low resistivity zones between two large bodies suggest that the massive rock bodies are being weathered and fractured, and fractures act as conduits for groundwater.