1. Department of Geology, University of Johannesburg, P.O. Box 524, Auckland Park, Johannesburg 2006, South Africa. e-mail: hermansvn@uj.ac.za; marlinae@uj.ac.za
2. Department of Geology, University of Johannesburg, P.O. Box 524, Auckland Park, Johannesburg 2006, South Africa. Department of Geosciences, University of Oslo, P.O. Box 1047 Blindern, N-0316 Oslo, Norway. e-mail: tom.andersen@geo.uio.no; tomandersen47@gmail.com
3. Research School of Earth Sciences, The Australian National University, Canberra, ACT 0200, Australia. e-mail: richard.armstrong@anu.edu.au