A strontium isoscape of southwestern Australia and progress toward a national strontium isoscape

Abstract. Strontium isotopes (87Sr/86Sr) are widely used tracers in the geosciences. Here we exploit an opportunity to determine 87Sr/86Sr ratios on archived fluvial sediment samples from the low-density National Geochemical Survey of Australia. The present study targeted the Yilgarn Craton in southwestern Australia. One hundred and seven new samples were taken from a depth of ~ 60–80 cm in floodplain deposits at or near the outlet of large catchments (drainage basins). A coarse ( 100 km) patterns that appear to be broadly consistent with surface geology, regolith/soil type, and/or nearby outcropping bedrock. The most radiogenic sediment values in the Yilgarn region (87Sr/86Sr > 0.8) all come from sites underlain by Archaean bedrock (2500–4000 Ma) and almost exclusively felsic intrusive lithologies. Conversely, almost all sites underlain by younger and non-granitic bedrock have outlet sediments of a less radiogenic character (87Sr/86Sr 0.8), whilst over half of the registered mineral resources come from an intermediate, yet still elevated, catchment sediment 87Sr/86Sr range (87Sr/86Sr = 0.728–0.767). Avenues for future work are proposed, including a national-scale Sr isoscape for Australia. Such isoscape could be useful in future geological, forensic, archaeological, paleontological and ecological studies. The new spatial Sr isotope dataset for the southwestern Australia region is publicly available (de Caritat et al., 2024; https://dx.doi.org/10.26186/149755).