Instrumentation and analytical technique for the analysis of regional geochemical samples used at the South African Council for Geoscience. An overview

Abstract

Regional geochemical stream sediment samples are analysed on a 26 fixed and 2 scanner channel simultaneous X-ray fluorescence spectrometer at the South African Council for Geoscience. Twenty-four elements are analysed simultaneously per sample: Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Rb, Sr, Y, Zr, Nb, Mo, Sn, Sb, Ba, W, Pb, Th and U. Rapid quantitative analyses and a high daily sample throughput of 400 samples in a 20 h shift are obtained. The calibration of the instrument involves background determinations, inter-element interference and matrix corrections in order to obtain a good correlation between the X-ray net peak intensity (in kcounts s–1) and the international reference material concentration value (in % or ppm). A wide range of international geological rock and soil reference materials are used for the calibration. Excellent geochemical data are obtained with respect to precision accuracy and determination limits. Precision of the data is of concern because decisions made in exploration geochemistry involve the interpretation of the relative difference in element concentrations and these may be masked by excessive noise. Systematic changes in the analytical system are of concern as they present a source of false geochemical patterns. Of the 24 chemical elements calibrated on the X-ray fluorescence spectrometer, 20 have determination limits significantly below that of the crustal abundance. This facilitates the demarcation of background geochemical trends. An example illustrating how the stream sediment geochemical data of the element Rb reflects the underlying host rocks on a regional scale is presented.