High-precision analysis of multiple sulfur isotopes using NanoSIMS

We report here data of multiple sulfur isotopes (S-32, S-33, and S-34) measured by NanoSIMS 50L ion microprobe in Fe-Ni-Cu standards, and pyrite grains recovered from the Neoarchean Abitibi Supracrustal Terrain, Canada. Careful attention to instrument tuning, sample preparation and sample stage positioning results in highly precise and accurate data for S-32-S-33-S-34 similar to that of larger radius SIMS instruments. Our results using a multi-Faraday collection system demonstrate that the NanoSIMS 50L instrument is capable of high-precision measurements of multiple isotopes of sulfur capable of resolving mass-independent variations in S-33 (Delta S-33) on the order of 0.4 parts per thousand (2 sigma) with improvements possible with higher S count rates. Pyrite grains from the Abitibi Supracrustal terrane have a large range of delta S-34 values between -9.6 and +6.3 parts per thousand, and corresponding Delta S-33 values between -0.8 and +1.5 parts per thousand, consistent with other datasets from Neoarchean sedimentary rocks. The new data indicate the incorporation of atmospheric sulfur affected by mass-independent fractionation (MIF) of S-33 into the Neoarchean marine sulfur cycle and point to subsequent sulfate reducing microorganisms at that time. (C) 2015 Elsevier B.V. All rights reserved.