1 Rock Art Research Institute, School of Geography, Archaeology and Environmental Studies, University of the Witwatersrand, Johannesburg, South Africa. david.pearce@wits.ac.za.
2 Rock Art Research Institute, School of Geography, Archaeology and Environmental Studies, University of the Witwatersrand, Johannesburg, South Africa.
3 Archaeology Laboratories, Archaeometry Research Group and CELAT, Laval University, Quebec City, Quebec, Canada.