The Northern Australia Hydrogeochemical Survey (NAHS), part of the Exploring for the Future Programme, has been investigating geochemical pathfinders for mapping components of mineral and energy systems within northern Australia.
A groundwater sampling program has been conducted thus far across the Lake Woods (35 locations), Tennant Creek (46 locations) and McArthur River (60 locations) regions. Analysis for a comprehensive suite of major and trace elements, stable isotopes and dissolved gases and organic species has been undertaken. The sampling sites were selected to ensure a regional coverage, utilising existing domestic and pastoral pump infrastructure; where applicable, higher priority was given to bores proximal to basement geology. Results presented here reflect initial findings from the survey. Interpretation is focused on understanding water-rock interaction along the groundwater flow-paths to evaluate the presence or absence of critical mineral system components. In particular, indicators are sought identify enriched or depleted source rocks for metals, evidence for significant vertical fluid pathways providing a transport mechanism for metals; and the presence of evaporites, brines or dolomitic shales that act as traps for migrating fluids.
The major element chemistry across these surveys largely matches spatial trends in existing Northern Territory (NT) hydrochemistry datasets, and broadly reflects changes in solid geology and regolith across the NT [1]. Clear divisions can be seen in the water chemistry, such as sulfur and metal and REE concentrations, for instance between younger Georgina Basin sediments overlying Paleoproterozoic basement in Tennant Creek and the Meso- to Paleo-Proterozoic McArthur Group in McArthur River. We will expand on our understanding of key regional and local scale water-rock interactions in two ways: by understanding the mineral saturation indices and how these vary spatially; and by exploring the Pb-isotope signatures in relation to 87Sr/86Sr and δ34S isotope systems and the trace element chemistry.
This regional approach of utilising hydrogeochemistry as a tool for understanding mineral system components will be further expanded as later NAHS groundwater surveys are incorporated. The NAHS is ongoing with additional sampling and analysis in the southwest McArthur Basin and South Nicholson Basin; to be released in 2020.
References
[1] Wallace, L., Schroder, I., de Caritat, P., English, P., Boreham, C., Sohn, J., Palatty, P. and Czarnota, K. 2018. Northern Australia Hydrogeochemical Survey: Data release, Preliminary Interpretation and Atlas – Tennant Creek, McArthur River and Lake Woods regions. Record 2018/48. Geoscience Australia, Canberra.