Geochemical microanalysis of patina layers on rock artefacts from the Central Karoo and Southern Free State, South Africa

In this study, patina layers on artefacts composed of different rock types were examined, with all specimens originating from arid and semi-arid environments of South Africa. Microscopic observations showed a continuous mineralogical change from the unaltered core to the rim, suggesting that the patina layer is the result of weathering and/or chemical leaching of the rock surface. Elemental mapping by micro-PIXE and SEM showed depletion in leachable elements such as Mg, K, Ca, Fe and to a lesser extent Al, Si and Mn towards the surface for all artefacts analysed. This kind of distribution suggests the possibility that a leaching and exudation process through fluid activity might be responsible for the gradual, and in some cases extensive removal of the elements towards the patina surface.