Removal of the feldspar-derived luminescence component from polymineral fine silt samples for optical dating applications: evaluation of chemical treatment protocols and quality control procedures

Abstract

In optical dating of fine silt samples, the use of the quartz fraction only is often preferred. This approach requires the elimination of contaminating luminescence signals from feldspars. We compare here the effectiveness of different chemical treatments using diluted and concentrated hydrofluoric (HF) acid, and describe different tests to monitor the extent of feldspar contamination. The results suggest that the use of concentrated acid for a short time is the most suitable option. Satisfactory results were achieved with diluted HF for several tens of minutes only if the impurity component was small. Four “feldspar contamination tests” were examined in this study. Three of these were based on infrared (IR)-stimulation response and one was based on thermoluminescence (TL) signals. All tests show similar trends of decreasing feldspar contamination with increasing etching time or increasing acid strength, but seem to provide different detection limits. None of the tests proved to be an unambiguous stand-alone test. Consequently, a combination of IR- and TL-based tests is recommended.