Geophysical investigations of photolineaments in southeast Zimbabwe

Abstract

The paper presents preliminary results of continuing studies in SE Zimbabwe aimed at understanding the role of fracturing in hard rock aquifers. This is a semi-arid region in which a high proportion of boreholes drilled for water supply are dry or provide minimal yields for hand-pump usage. Remote sensing, using satellite images and aerial photographs, provides a rapid means of identifying potential fracture systems but field evidence of the nature and precise location of such fractures is limited. Ground geophysical techniques such as resistivity, electromagnetic and magnetic surveying have been extensively tested over a few selected sites in an attempt to characterize their response where photolineaments occur. These data reveal the presence of anomalies, predominantly of shallow origin, some of which correspond with the lineaments. Initial results suggest that the lineaments studied do not represent major, open groundwater conduits. Drilling and borehole logging information confirms the view that fracturing is poorly developed in general. An interpretation of pump test data collected as part of hydraulic fracturing tests suggests that drilling itself results in the preferential opening of vertical fissures near the borehole but that background transmissivity is very low. The work is continuing with a programme of core drilling and cross-hole seismic tomography, the results of which will be incorporated in further modelling of the geophysical data.

Aeromagnetic and Landsat TM structural interpretation for identifying regional groundwater exploration targets, south-central Zimbabwe Craton

“…Furthermore, the coincidence of AM/TM lineaments is important: AM data have been used to map buried magnetic dykes under weathered zones and also deep fractures likely to be open groundwater conduits. TM lineaments, although not necessarily open (e.g., Carruthers et al, 1991;Greenbaum, 1992a,b;Owen et al, 2002), have outlined fracture (Table 2; Ranganai, 1995). 0.00-0.60 -density/intensity which reflects recharge capacity.…”

GIS-based model of groundwater occurrence using geological and hydrogeological data in Precambrian Oban Massif southeastern Nigeria

“…6 and Table 1). The deep-weathered localized areas have a better hydrogeologic prospect in basement complex terrains (Faniran and Omorinbola 1980;Agbede 1996;Ajayi and Hassan 1990;Greenbaum 1992;Carruthers et al 1991). In addition, optimum borehole yields are achieved when the borehole penetrates both the lower saprolite and the overlying fractured basement (Davies and Robins 2007).…”

Hard-rock hydrotectonics using geographic information systems in the central highlands of Eritrea: Implications for groundwater exploration

“…Tension zones are generally considered to have a high porosity at shallow crustal levels (e.g., Larsson, 1984), although all fractures at >500-100 m are in the state of tension due to gravitational unloading, temperature changes and lateral expansion during uplift and erosion (e.g. Greenbaum, 1992a) promoting groundwater movement (Carruthers et al, 1991). In the case of unequal horizontal stresses acting on a population of faults, Set 2 shear fractures might have also been changed to tensile fractures at depth and might have enhanced permeability of the rocks.…”