Three South African silcrete sources can be identified regardless of heat treatment using solution ICP-MS and LA-ICP-MS

Abstract

Silcrete is widely used for stone tool manufacture throughout various parts of the world and is sometimes heat-treated to improve flaking quality. Properly sourcing this raw material can provide insight into exchange networks and mobility patterns of early human populations, however, we only have a minor understanding of how heat treatment impacts the geochemistry of silcrete and how this varies between and within sources. This is particularly important in South Africa where heat-treated silcrete artifacts are common during the later Middle Stone Age. Here, we examine how heat treatment affects the geochemical composition of silcrete from three sources near the Pinnacle Point site complex in South Africa. We selected five unheated and five experimentally heat-treated silcrete samples from each source (n = 30) for solution ICP-MS analysis. We also test whether laser ablation ICP-MS is a viable method for sourcing silcrete since sample preparation for solution analyses can be challenging (i.e., use of harsh chemicals, issues digesting the sample). Our results suggest that all sources can be distinguished regardless of the treatment state and for both analytical approaches. The results of this study will help inform future provenience studies of silcrete artifacts to better understand how early humans living near Pinnacle Point interacted with the landscape.