Use of azimuthal resistivity survey in mapping subsurface fractures and assessing their hydraulic properties in crystalline rocks in Ghana.

Azimuthal resistivity surveys (ARS) using the square array configuration were conducted at selected farmland sites in Nsawam District, Ghana with the objective of predicting the orientation of subsurface fractures which may serve as conduits for fluid flow and contaminant transport. Information about the orientations, apertures and lengths of fractures in the study area were obtained from geological mapping of few exposed outcrops. For areas with no outcrops, electrical resistivity surveys were performed to estimate the fracture parameters. The results of the fracture mapping using geophysical resistivity study correlated well with that of the geological mapping. This integrated geological and geophysical study indicates that there are two dominant fracture directions in the study area with other minor orientations which may control groundwater flow in the area. One fracture system is dominantly oriented in NW-SE direction (Kitase and Amanfrom) and another is in the NE-SW direction (Nsakye). It is thus shown that in the absence of rock exposure, ARS could be a viable complement in mapping subsurface fractures. Other fracture characteristics, fracture porosity, specific surface area which could give potential information on the hydraulic properties were also assessed.