PRODUCTION OF A MATRIX-MATCHED STANDARD FOR QUANTITATIVE ANALYSIS OF IRON SULPHIDES BY LASER ABLATION INDUCTIVELY COUPLED PLASMA-MASS SPECTROMETRY BY WELDING: A PILOT STUDY

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Abstract

ABSTRACT. Over the recent years, several laboratories have tried to solve the matrix-match problem for quantitative analysis of sulphides with Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA ICP-MS) by developing artificial standards. This paper investigates the feasibility of a modified welding technique for the production of artificial sulphide crystals as a matrix-matched external standard for quantitative analysis of the trace element content of natural samples with LA ICP-MS. During this research, focus was on pyrite, since this mineral phase is an ubiquitous mineral in several ore deposits and sedimentary/diagenetic successions. The matrix-matched standard has been produced by resistance heating of a µm-size mixture of pyrite and pure elements in graphite electrodes with a procedure modified after Ødegard (1999). During the loss of S during the welding, the formed bead consists of pyrrhotite. Pyrrhotite, however, exhibits similar ablation behaviour as pyrite. For several elements of interest (i.e. Co, Ni, Cu and Ga), the matrix-matched standard shows a homogeneity ≤ 15 % RSD, which is sufficient for a (semi-)quantitative calibration. Some elements (i.e. Zn, Se and Pb) show a rather poor homogeneity (RSD  15 %), which only allows a qualitative analysis. The concentration of Ge and As is below the detection limit in the produced standards, which can be due to vaporisation during welding or during ablation of the beads. The obtained homogeneity is comparable to most of matrix-matched LA ICP-MS sulphide standards described in the literature. The use of the matrix-matched standard has been illustrated on hydrothermal pyrite from a mesozonal orogenic mineralisation (Marcq area, Belgium), which has been analysed as well with the electron microprobe. Owing to the higher sensitivity many more trace elements can be measured with LA ICP-MS. The LA ICP-MS analyses clearly demonstrate a variation of trace element content and enrichment of the elements (Cu, Pb, Zn, Se) towards the rim of the pyrite crystal.

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Acerca de: Stijn DEWAELE

Acerca de: Philippe MUCHEZ

Acerca de: Jan HERTOGEN