A low dilution fusion technique for the determination of major, minor and trace elements in Lamproite and Kimberlite samples by X-ray fluorescence spectrometry

Master Thesis


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University of Cape Town

A low dilution fusion technique using a 2:1 flux:sample ratio has been developed for the accurate determination of major, minor and trace elements by x-ray fluorescence spectrometry (XRFS). This method has been used to analyze geological samples of widely varying and unusual composition such as lamproites and kimberlites. The results are shown to be of comparable if not better accuracy than other methods of sample preparation for XRFS. Analytical conditions, including corrections for spectral line interferences are reported for all the elements determined. For major element analysis three methods of calculating appropriate alpha coefficients were investigated, namely (1) multiple regression analysis, (2) Norrish and Hutton method and (3) a computer program, NBSGSC, involving fundamental parameters and the COLA equation. Methods (1) and (2) gave poor results for rock types of widely varying composition. The third method requires that the variation of alpha coefficients with varying weight fraction of the analyte element be taken into account when calculating alpha coefficients if accurate values for major and minor elements are to be obtained on low dilution fusion discs. For trace element analysis the average relative error was less than 5% and there was a decrease in sensitivity by about a factor of 2 compared with XRFS determinations on powder pellets. The elimination of particle size effects in the homogeneous glass fusion discs is a major advantage over the use of powder pellets, especially for the determination of elements such as Ba, Cr and the REEs. A loss on fusion technique has been employed to ensure complete loss of volatiles from the rock samples. Data presented highlight the problems encountered in the determination of the volatile content in geological samples. The oxidation and retention of sulphur in the discs was also investigated.

Bibliography: pages 200-204.