Northern Australia Geochemical Survey

Map showing the distribution of copper in the Northern Australia Geochemical Survey (NAGS) samples over the Tennant Creek — Mt Isa study area. This is from the results of the MMI™ extraction (the sediment 0-2 mm fraction).

The Northern Australia Geochemical Survey (NAGS) project is a low-impact, low-density geochemical survey, designed to determine the regional distribution of chemical elements within soils. Such knowledge provides a basis for informed decision making about regional land use, agriculture, mineral and energy resource potential. NAGS aimed to advance methods and approaches originally developed by the National Geochemical Survey of Australia (NGSA; Caritat and Cooper, 2011) to systematically characterise the chemical nature of Australian soils and the processes that control their composition. This includes interpretation of the results of low-density geochemical surveys as a potential technique to locate "blind" mineral deposits buried under younger rocks. The resulting data also provide an excellent environment baseline dataset, which can be used to assess the impact of any future development in the area. Besides mineral exploration and environmental applications, NAGS results can be used for mapping soil quality for agricultural purposes, mapping distribution of chemical elements that are regarded as essential nutrients for plant and animal growth (e.g. Ca, Cu, Fe, K, Mg, Mn, P and Zn).

Aerial view of the Barkly Tablelands, an area of the Northern Australia Geochemical Survey.

The NAGS project targeted transported soil samples, collected on the floodplains of large water catchments.

The project focused on the Tennant Creek—Mt Isa region in the Northern Territory and Queensland, with one sample representing approximately 500 km2. The sample collection followed a cut-down version of the NGSA routine (only the top 0-10 cm depth of the soil profile is sampled).

To extract the maximum amount of geochemical information, the samples have been analysed for more than 60 elements using state-of-the-art analytical techniques.

Results

In 2017 soil samples from 780 sites were acquired in the Tennant Creek—Mt Isa region in the Northern Territory and Queensland. To access sampling sites in the harsh remote areas, two helicopters were used to transport field crews to these locations. The samples were processed for chemical analyses in a purposefully set up laboratory at the Centre for Appropriate Technology facility in Alice Springs. Two size fractions – (<75 um) and < 2 mm) were produced for each sample. Both size fractions were analysed for their elemental composition (>50 chemical elements) by several different analytical methods. Analyses were performed by GA laboratories in Canberra (X-Ray Fluorescence (XRF) and Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) for total digestion), SGS Australia mineral services in Perth (Mobile Metal Ion™, MMI) and ALS laboratories in Perth (aqua regia, AR, and fire assay, FA).

Outputs

Locations of the Northern Australia Geochemical Survey sites in the Tennant Creek—Mount Isa region in Northern Territory and Queensland.

  • Publicly available datasets of quality-controlled data and associated metadata. Two data releases from the project are now available: data release I and data release II. These datasets include:
    • Information on the sampling sites (catchments and sample locations);
    • Analytical data obtained from the samples by Geoscience Australia and external laboratories:
      • Bulk sample properties (Munsell colour, pH and EC);
      • Results of XRF analyses and ICP-MS analyses for the coarse (< 2 mm) and fine (<75 mm) fraction of the samples;
      • Results of ICP-MS analyses of the MMI™ extractions (0-2 mm);
      • Results of ICP-MS analyses of the Aqua Regia digestion of coarse and fine fraction samples;
      • Results of Fire Assay analyses for platinum group elements of coarse and fine fraction samples
  • Digital map images for (1) individual chemical elements that passed quality control and assurance requirements and for (2) principal components for the element datasets compiled in this study. The complete datasets can be downloaded from Geoscience Australia Data and Publications database: data release I and data release II.
  • In-depth interpretation of the current data will be reported in forthcoming publications.
  • Recommendations on using low-density (1 site per >500 km2) soil geochemistry in Australia as a tool to aid mineral exploration in areas covered by rocks younger than mineralisation.

Collaborations

The project has been undertaken in collaboration with the Geological Surveys of the Northern Territory and Queensland. Further collaboration with industry, academia (University of Melbourne and Monash University) and other government and research organisations (NTGS, CSIRO) will enhance the quality and breadth of analytical work and data interpretation. NAGS researchers collaborate with Australian Microbiome, CSIRO, University of Canberra, University of Adelaide and Flinders University on defining the soil microbiome of Australia from local to regional to continental scales.

Sample processing for the first stage of the project has been completed in collaboration with the Alice Springs Aboriginal and Torres Strait Islander not-for-profit company, the Centre for Appropriate Technology (CAT). Partnering with CAT has given Geoscience Australia the opportunity to access a local workforce, providing employment and training for Indigenous workers.