The Northern Australia Hydrogeochemistry Survey

Map showing the coverage of groundwater samples collected as part of the Northern Australia Hydrogeochemistry Survey.

The Northern Australia Hydrogeochemical Survey (NAHS) is the culmination of a multi-year, regional groundwater sampling program between Tennant Creek and Mt Isa in the Northern Territory (Figure 1). It uses groundwater chemistry at a regional scale (sampling density ~1 bore/15-25 km2) from existing pastoral water bores to provide insights into the region’s mineral, groundwater and energy resources.

From a mineral resource perspective, this work was conducted to identify the most suitable chemical indicators that apply to various mineral systems. Initially targeting areas of shallow cover near known mineral deposits as well as in barren areas, the project then extended into regions of deeper cover to develop and test these diagnostic tools. The NAHS also sampled above the Beetaloo Basin and South Nicholson Basin which are prospective for energy resources. In these regions the NAHS can provide input into understanding environmental baselines of water composition prior to the potential onset of new industrial developments.

Scientist out in the field taking hydrogeochemistry measurements in the Northern Territory.

In addition to standard measurements including bulk parameters (e.g., temperature, pH, electrical conductivity), major anions, major cations and trace elements, selected groundwater samples were analysed for a comprehensive suite of isotopes (e.g. oxygen, hydrogen, carbon, sulfur, chlorine, strontium, lead, helium), organic compounds, hydrocarbons and dissolved gases. High-quality data are required to make meaningful interpretations from small variations in metal composition in the water, thus careful attention has been given to robust sampling, reproducible analyses and contamination avoidance.

The NAHS is a world-first for the analytical detail collected at each bore and the breadth and geological complexity of the sampled region. Ongoing work will utilise these data to investigate chemical indicators that can be applied as an exploration tool in Australia, with the capability of identifying and targeting parts of mineral systems under cover. The hydrogeochemical data provide insights for improving our understanding of regional aquifers and hydrogeological processes, and feed into broad-scale groundwater baselines for a diverse range of stakeholders.

Progress

The NAHS has been released and is available for download here as of mid-July 2020. It comprises hydrogeochemical data for 238 groundwater bores, with up to 156 analytes per site. In addition the NAHS product includes a summary of the sampling and analysis methodology, a review of the data quality, and an atlas of hydrogeochemical maps. Supplementary data will be added to this release product as new data are collected.

Outputs

  • The first tranche of hydrogeochemical data and a report with initial interpretations of the Lake Woods, Tennant Creek, and McArthur River regions has been released publicly is available for download here. While the data have been superseded the report presents valuable insights e.g., into the relationship between copper in the regolith and groundwater.
  • An updated comprehensive dataset and map product has been released publically in July 2020. This includes updated hydrogeochemistry from the first tranche, as well as new data collected as part of a second tranche in the Beetaloo, East Tennant Creek and South Nicholson regions.
  • An extended abstract demonstrating the application of hydrogeochemistry for understanding and distinguishing the carbonate aquifer systems, and identifying water-rock interactions with mafic volcanics buried under cover can be downloaded here.

Collaborations

We have collaborated with the Northern Territory Geological Survey (NTGS), Northern Territory Department of Environment and Natural Resources (Water Resources) and the Geological Survey of Queensland (GSQ); further collaboration with industry, academia and other government and research organisations (e.g., CSIRO) has greatly enhanced the type of data collected and the quality and breadth of analysis and data interpretation.

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