GEOCHEMICAL MICROANALYSIS OF PATINA LAYERS ON ROCK ARTIFACTS FROM THECENTRAL KAROO AND SOUTHERN FREE STATE, SOUTH-AFRICA

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