DETERMINING GEOLOGICAL PROVENANCE OF BERYLS USING PORTABLE X-RAY FLUORESCENCE (PXRF) SPECTROMETRY

PXRF spectrometry identifies elements no lighter than Mg and no heavier than U by their distinctive X-Ray emission wavelength or energy. The concentrations of the elements present in the sample are quantified by measuring the intensity of their emissions. The advantages of PXRF are that no sample preparation is required and the method is non-destructive.

The accuracy of PXRF was investigated using 23 standard rock reference materials and 8 elements (Ti, Mn, Fe, Zn, Rb, Sr, Zr, and Mo) that are determined by PXRF. Linear regressions of known concentrations against PXRF analyses yield RSquare values near 1 (0.82 to 0.995), indicating the robustness of PXRF analysis.

This provenance study uses a statistical analysis of PXRF analyses to determine whether a beryl can be traced back to its geological province, district, mine, or its zone within a pegmatite. Preliminary discriminant function analysis has been performed using concentrations of Ti, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Rb, Sr, Ag, Cd, Sn, Ba, Hg, and Pb in 101 beryls from 17 countries (9 US states) and Antarctica. It is significant that Cr, Cu, As, Zr, Mo, Ag, Cd, Hg, and Pb are the most important elements in reducing misclassifications, compared with Ti, Fe, Mn, Co, Ni, Rb, Sr, and Ba. The importance of the chalcophile elements in this discriminant function analysis suggests that pegmatite beryls may be recording major cratonic signatures, as observed in metallogenic provinces. On-going work includes statistical analysis of PXRF analyses of 84 beryls whose locations are known sufficiently well to place them within specific cratons or mobile belts. This database also allows us to examine provenance at the scale of single pegmatites and pegmatite fields.