Proton-microprobe analyses of platinum-group element and gold grains

Abstract Noble metal grains were separated from sediments of a paleoterrace of the Mekong river, northeast Thailand. Preliminary scanning-electron microscopy investigations show that all levels of the sediment are characterized by the coexistence of Au and Pt grains. This coexistence in one geological site is rare. Proton-microprobe analyses were carried out in order to detect trace elements which are indicative of their source region(s) and the physico-chemical conditions during formation. Special attention was given to the trace-element contamination of the used absorbers and to the influence of the response function of our Si(Li)-detector on the data evaluation. Both effects play an important role in judging the reliability of our results.