Off-Mount Calibration and One New Potential Pyrrhotite Reference Material for Sulfur Isotope Measurement by Secondary Ion Mass Spectrometry

Sulfur isotope measurements in three sulfide (two pyrite and one pyrrhotite) samples on two epoxy mounts showed that the mount-to-mount variation of raw delta S-34 values was negligible when secondary ion mass spectrometry (SIMS) analytical settings remained stable. In consequence, an off-mount calibration procedure for SIMS sulfur isotope analysis was applied in this study. YP136 is a pyrrhotite sample collected from northern Finland. Examination of thin sections with a polarising microscope, backscattered electron image analyses and wavelength dispersive spectrometry mapping showed that the sample grains display no internal growth or other zoning. A total of 318 sulfur isotope (spot) measurements conducted on more than 100 randomly selected grains yielded highly consistent sulfur isotope ratios. The repeatability of all the analytical results of S-34/S-32 was 0.3 parts per thousand (2s, n = 318), which is the same as that of the well-characterised pyrite reference materials PPP-1 and UWPy-1. Its delta S-34 value determined by gas mass spectrometry was 1.5 +/- 0.1 parts per thousand (2s, n = 11), which agrees with the SIMS data (1.5 +/- 0.3 parts per thousand, 2s) calibrated by pyrrhotite reference material Po-10. Therefore, YP136 pyrrhotite is considered a candidate reference material for in situ sulfur isotope determination.