ANALYSIS OF SILICATE ROCKS USING FIELD-PORTABLE X-RAY-FLUORESCENCE INSTRUMENTATION INCORPORATING A MERCURY(II) IODIDE DETECTOR - A PRELIMINARY ASSESSMENT OF ANALYTICAL PERFORMANCE

An assessment is reported of the performance of a field-portable energy dispersive X-ray fluorescence analysis system using Fe-55, Cd-109 and Am-241 excitation sources and a high resolution mercury(II) iodide detector, Seventy international reference materials, mainly of silicate composition, were analysed as compressed powder pellets. Results from spectra recorded for live times of 200 s (per source) showed that the major elements K, Ca, Ti, Mn and Fe and the trace elements Ba, Nb, Rb, Sr, Y and Zr could be determined routinely in 'normal' silicate rocks and in addition Co, Cr, Cu, Ga, La, Nd, Ni, V and Zn at higher concentrations or in mineralized samples, Detection limits for the most sensitively measured trace elements (Rb, Sr, Y, Zr, Nb) were found to be in the range 6-14 mu g g(-1) and for Ba (K-line), 21 mu g g(-1) Precision in the determination of the major elements was generally in the range 0.45-2% (relative standard deviation) and a high degree of accuracy was achieved when judged from a self-consistent comparison of analysed values with the expected compositions of the 70 reference materials, Having characterized performance in the laboratory with 'ideal' control over sample presentation, work is now in progress to evaluate additional discrepancies that will be encountered in the analysis of geological and archaeological samples in the field.