Tracking an Archean orogenic gold deposit evolution through multiple sulfur isotopes

The ability to detect mass-independent fractionation of sulfur (MIF-S) with reliable precision at the micro-scale has opened a new dimension in tracking changes of hydrothermal fluid conditions and sulfur reservoirs. Orogenic hydrothermal fluids often transport gold associated with sulfur complexes. However, the origin of sulfur in these fluids remains elusive. Furthermore, the mechanism for gold precipitation is yet to be fully understood. Interpretation of widespread delta S-34 values in the past indicate a severe limitation in distinguishing between changes in P-T-pH-fO(2) conditions versus a change in sulfur reservoirs. To address these knowledge gaps, we apply multiple sulfur isotope analysis to rocks in the structurally controlled Kanowna Belle deposit, Kalgoorlie Terrane of Western Australia, where five temporally-distinct vein sets intrude different Archean lithologies. Results yield a consistent positive MIF-S (Delta S-33 = +0.05 parts per thousand to +0.39 parts per thousand) with highly variable delta S-34 values (-10.46 parts per thousand to +12.47 parts per thousand) across different vein sets. These results are consistent with previous sulfur isotope results in other orogenic gold systems across the Yilgarn Craton and are compiling to show that the hydrothermal fluids source sulfur away from the precipitation site. Gold is later released from hydrothermal fluids through thermodynamic changes as preserved by the delta S-34 spread in mineralised vein sets.