1. Department of Geosciences, University of Oslo, P.O. Box 1047 Blindern, N-0316 Oslo, Norway
2. Department of Geology, University of Johannesburg, P.O. Box 524, Auckland Park, 2006, Johannesburg, South Africa e-mail: tom.andersen@geo.uio.no
3. Council for Geoscience, P.O. Box 900, Pietermaritzburg, 3200, South Africa. e-mail: gabotha@geoscience.org.za
4. Department of Geology, University of Johannesburg, P.O. Box 524, Auckland Park, 2006, Johannesburg, South Africa e-mail: marlinae@uj.ac.za