Affiliation: | University of Botswana, Department of Physics, Private Bag UB00704,;Gaborone, Botswana. E-mail: University of Botswana, Department of Geology, Private Bag UB00704,;Gaborone, Botswana Geological Survey of Botswana, Private Bag 14,;Lobatse, Botswana Council for Geosciences, Bag X112,;Pretoria 0001, South Africa *Now at: Atekwana-Department of Geology and Geophysics, University of Missouri-Rolla, Rolla, MO 65409, USA. |