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 energ y dispersive X-ray fluorescence analysis system using Fe-55, Cd-109 an d Am-241 excitation sources and a high resolution mercury(II) iodide d etector, 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 rock s and in addition Co, Cr, Cu, Ga, La, Nd, Ni, V and Zn at higher conce ntrations or in mineralized samples, Detection limits for the most sen sitively 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) Precis ion in the determination of the major elements was generally in the ra nge 0.45-2% (relative standard deviation) and a high degree of accurac y was achieved when judged from a self-consistent comparison of analys ed values with the expected compositions of the 70 reference materials , Having characterized performance in the laboratory with 'ideal' cont rol over sample presentation, work is now in progress to evaluate addi tional discrepancies that will be encountered in the analysis of geolo gical and archaeological samples in the field.