New Potential Sphalerite, Chalcopyrite, Galena and Pyrite Reference Materials for Sulfur Isotope Determination by Laser Ablation-MC-ICP-MS

The sulfur isotope system is important in tracing a variety of geochemical processes. However, the availability of matrix-matched reference materials for in situ sulfur isotope ratio measurement is limited. This study analysed four sulfide specimens to investigate their potential as reference materials for in situ sulfur isotope determination, including three natural sulfide minerals (sphalerite SPH-1, chalcopyrite GC-1 and galena NWU-GN), and one resin preserved pyrite powder (RPPY). These four sulfides were analysed independently in four laboratories using both bulk and microbeam analysis techniques, all of which gave equivalent results within uncertainty with comparable accuracy and precision. The sulfur isotopes of these four sulfides are homogeneous based on a large number of isotope determinations by solution nebulisation multi-collector inductively coupled plasma-mass spectrometry (MC-ICP-MS) and laser ablation (LA) MC-ICP-MS. The mean delta S-34 values for SPH-1, RPPY, GC-1 and NWU-GN determined by gas source isotope ratio mass spectrometry (GS-IRMS) and solution nebulisation MC-ICP-MS are -7.13 +/- 0.41 parts per thousand (2s), 3.66 +/- 0.24 parts per thousand (2s), -0.65 +/- 0.28 parts per thousand (2s), 28.21 +/- 0.17 parts per thousand (2s) relative to the Vienna-Canyon Diablo troilite (V-CDT) reference value, respectively, and which are proposed as potential preferred values. Over 400 spot analyses performed on randomly selected fragments of each sulfide by LA-MC-ICP-MS yielded highly consistent delta S-34 values with the preferred values. Thus, SPH-1, GC-1, NWU-GN and RPPY are considered a set of candidate matrix-matched sulfide reference materials for in situ sulfur isotope determination.