[1] School of Geosciences, University of the Witwatersrand, Johannesburg 2050, Private Bag 3, PO WITS
[2] Impact Cratering Research Group, School of Geosciences, University of the Witwatersrand, Johannesburg 2050, Private Bag 3, PO WITS
[3] Tsodilo Resources Ltd., Box 508, Toronto, ON M5J 2SI