1. Department of Geology, University of Johannesburg, P.O. Box 524, Auckland Park 2006, Johannesburg, South Africa
2. Department of Earth Sciences, Stellenbosch University, Private Bag X1, 7602 Matieland, South Africa
3. Department of Geology, Lund University, Sölvegatan 12, SE-223 62, Lund, Sweden Institute of Geophysics, Polish Academy of Sciences, 01-452, Warsaw, Poland
4. Department of Geological Sciences, University of Cape Town, Rondebosch, 7701, South Africa