THE APPLICATION OF LASER ABLATION–INDUCTIVELY COUPLED PLASMA–MASS SPECTROMETRY (LA–ICP–MS) TO THE ANALYSIS OF SELECTED SULPHIDE MINERALS

Abstract

Laser ablation--inductively coupled plasma--mass spectrometry (LA--ICP--MS) has been assessed for use in the direct quantitative analysis of selected sulphide minerals. This paper details the use of chalcopyrite, galena, stibnite, pyrite, sphalerite and arsenopyrite, to investigate the feasibility of direct analysis of sulphides using LA--ICP--MS and examines the applicability of the method in assessing trace- and ultratrace-element partitioning between coexisting sulphide matrices. Scanning electron microscopy (SEM) with an energy-dispersive X-ray analytical (EDXRA) facility has been used to identify the presence of modified mineral phases in melt products from the ablation process and to confirm selective volatilisation of elements from the bulk matrix. Analytical protocols have been developed to provide qualitative elemental inter-comparability of data for these sulphide minerals. However, direct quantification of the elemental composition of minerals, using a 1064-nm Nd:YAG laser in free-running mode, is still not considered possible. The feasibility of using LA--ICP--MS for the analysis of a borate glass melt, made from the individual sulphide minerals following roasting, has also been investigated. While galena-, sphalerite-, pyrite- and chalcopyrite-based borate glasses retain physical integrity under acceptable laser conditions, stibnite- and arsenopyrite-based borate glasses shatter immediately. Data from all borate glasses analysed are extremely imprecise and of little quantitative value. Experiments using pressed powders did, however, prove successful and quantitative analytical data were obtained from all minerals investigated.