Development of in situ sulfur four-isotope analysis with multiple Faraday cup detectors by SIMS and application to pyrite grains in a Paleoproterozoic glaciogenic sandstone

An in situ sulfur four-isotope analysis technique with multiple Faraday cup detectors by ion microprobe was developed and applied to detrital pyrite grains in ~ 2.4 Ga glaciogenic sandstone from the Meteorite Bore Member of the Turee Creek Group, Western Australia. Data are standardized with the UWPy-1 pyrite standard (δ 34 S = 16.04 ± 0.18‰, Δ 33 S = − 0.003 ± 0.009‰, and Δ 36 S = − 0.21 ± 0.24‰, 2 SD) whose sulfur four isotopes were newly determined by gas-source mass spectrometry. Typical reproducibility at two standard deviations (2 SD) of spot-to-spot analyses of standard UWPy-1 pyrite with a primary beam size of ~ 20 μm were ± 0.23, ± 0.05, and ± 0.86‰ for δ 34 S, Δ 33 S, and Δ 36 S, respectively. The measured 36 S/ 32 S ratio [1 / (6641 ± 27)] is approximately 19‰ lower than the published ratio for VCDT, and we propose a revision of the 36 S abundance in VCDT. Pyrite grains in ~ 2.4 Ga glaciogenic sandstone have wide ranging sulfur isotope ratios (− 32.7 to 13.5 for δ 34 S, − 3.03 to 11.66 for Δ 33 S, and − 9.7 to 4.6 for Δ 36 S, respectively). Some pyrite grains are zoned in δ 34 S values within a grain. Sulfur isotope ratios of most pyrite grains are distributed along a line with slope = − 0.9 for Δ 33 S vs. Δ 36 S, suggesting that pyrite grains mostly derived from a limited range of source rocks and near-surface sulfur reservoirs. One pyrite aggregate has a distinct texture from other pyrite grains in the same sandstone, and yields a significant mass-independent deficit in 36 S with a small excess in 33 S (Δ 36 S/Δ 33 S ~ − 4‰). This is used to suggest that this grain authigenically formed by biological activity during or after sedimentation. This work demonstrates that the use of multiple Faraday cup detectors provides improved accuracy and precision for in situ sulfur four-isotope analysis with secondary ion mass spectrometry.