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British Geological Survey, Keyworth, Nottingham, NG12 5GG, UK
The Zimbabwe Craton is a heterogeneous assemblage of crystalline basement rocks in which the groundwater reservoirs are structurally controlled or confined to the weathered overburden. Lineaments, interpreted from Landsat imagery and aerial photographs, represent faults, joints and dykes of several ages. Such fissured rocks are more susceptible to deep weathering and are a main target for borehole siting. An analysis of borehole yields indicates that, although failure rates can be high, fractures of all trends are capable of providing an adequate hand-pump yield (0.25 l/s). Thus, despite their origin as compressional shears, many fractures now appear to provide open conduits for groundwater. It is concluded that within the near-surface zone of most importance to basement rock aquifers (40 to 80 m) fractures of all origins are in a state of tension probably as a result of recent uplift and erosional unloading.
