Analysis of Trace Elements in Basalts by Shipboard X-Ray Fluorescence Spectrometry: A Discussion of Niobium

Abstract

X-ray fluorescence spectrometry was used on board the Glomar Challenger during Leg 82 for analysis of "hygromagmaphile" trace elements that are useful to identify so-called "depleted" or "enriched" basalts; the results were used in choosing the new sites to be drilled on the basis of the "enriched" or "depleted" character of previous sites. This chapter describes a hitherto unpublished method for deducing concentrations from intensity measurements; the method yielded the precision (better than 1 ppm for Nb) necessary for purposes of the cruise.The procedure for the matrix-effect correction is described. The case of Nb is discussed in detail because Nb concentrations in basalts are the lowest among the elements investigated (Nb, Zr, Ti, Y, V) and because it is the key element for deducing the enriched or depleted character of the different basalt units. Ta neutron-activation measurements made on shore after the cruise demonstrate, on the basis of the well-known constant Nb/Ta ratio in basalts, that the accuracy of the shipboard measurements of Nb concentrations in basalt units is about 0.5 ppm.

Precise Quantitative Determination of Niobium at Low Level Concentrations in Geological Samples by WD‐XRF

“…Hall and Pelchat (1990), Garbe-Schönberg (1993) and Münker (1998) reported 99 µg g -1 , 116 µg g -1 and 108 µg g -1 Nb respectively, in BE-N by ICP-MS. The reference material BE-N has come to replace BR for which we found 114 µg g -1 and 115 µg g -1 Nb in a previous paper (Etoubleau et al 1985). Such differences cannot be explained by inhomogeneities in batches distributed to laboratories.…”

“…The detection limit depends on counting time, and sensitivity varies with the element to be measured: the long wavelengths of low atomic number elements and the weak responses of L spectra lines yield the least sensitive results. However, the non-destructive character of this technique and high stability of modern equipment make long counting times possible, reducing the detection limit to 0.1 µg g -1 for some trace elements in rocks, as demonstrated by Chappell et al (1969), Galson et al (1983), Etoubleau et al (1985) and more recently by Jochum et al (1990) and Chappell (1991).…”