The National Geochemical Survey of Australia (NGSA) project was established under the Australian Government's Onshore Energy Security Program, which was announced in August 2006 and is part of the program's five year work plan.
The primary aim of the national geochemical survey is to provide pre-competitive data and knowledge to support exploration for energy resources in Australia. In particular, it will improve the existing knowledge of the concentrations and distributions of energy-related elements such as uranium (U) and thorium (Th) at the national scale.
The project is underpinned by a series of pilot geochemical surveys carried out in recent years by Geoscience Australia and the Cooperative Research Centre for Landscape Environments and Mineral Exploration (CRCLEME) to test robust and cost-effective protocols for sample collection, preparation and analysis. Examples of these are the Riverina and the Thomson pilot geochemical surveys.
The current national project is being conducted in collaboration with the State and the Northern Territory geoscience agencies.
The national geochemical survey was initiated because of the realisation that there was no complete geochemical coverage available for Australia and because such a data layer is fundamental to successful exploration for energy-related and other commodities.
Figure 1
Distribution of whole rock
geochemical
data in
Australia (2006)
© Geoscience Australia
The distribution of geochemical data available through the national repository (OZCHEM database) before the NGSA project started is shown in Figure 1. The map shows that a large proportion of the country (>60 per cent) lacks any geochemical information. Also, where geochemical data are available, they are often not comparable as a result of:
Similarly, the airborne gamma-ray spectrometric (radiometric) survey coverage available at a resolution deemed appropriate for exploration before the NGSA project started did not provide a complete national picture of the distribution of radiogenic elements potassium (K), uranium (U) or thorium (Th) (Figure 2). This situation has been remedied by the Australia Wide Geophysical Survey (AWAGS) project which, together with NGSA, will result in a significantly improved understanding of the distribution of K, U and Th in Australia.
Some recent regional geochemical surveys have been carried out in parts of Australia, but no national coverage exists. Since the inception of the concept of regional geochemical surveys in the 1960s, they have proven to be a reliable tool for mineral exploration.
Figure 2
National coverage of airborne
gamma-ray
data acquired by
States and Northern Territory
geological surveys and
Geoscience Australia (2006)
© Geoscience Australia
The objectives of the NGSA project are to:
A sampling method has been adapted to Australian landscapes and climate conditions. It has been field-tested in the Riverina, Gawler and Thomson pilot projects. The cost of a national survey is kept reasonably low by applying an ultra low sampling density approach (1 site/1000 square kilometres to 1 site/10 000 square kilometres).
The strategy adopted for the national geochemical survey is described below.
Sampling media: Catchment outlet sediments (similar to floodplain sediments in most cases), sampled at two depths (0-10 centimetres below the surface as well as between around 60 and 80 centimetres depth).
Figure 3
Distribution of drainage
catchments for the NGSA
© Geoscience Australia
Sampling sites: 11390 catchments covering 91 per cent (or about seven million square kilometres) of Australia across all States and Territories were targeted for sampling (Figure 3). Most catchments were sampled near their outlet, while those exhibiting internal or poorly defined drainage were sampled at, or as close as possible to, their lowest point. Catchments smaller than 1000 square kilometres (mostly coastal) and small islands were not included in the survey. The resulting distribution of catchment outlet sites targeted for sampling is shown in Figure 4 and translates to an average sampling density of around 1 site/5500 square kilometres.
Sample collection: A detailed National Geochemical Survey of Australia: Field Manual was compiled and all sampling equipment and consumables were centrally purchased. Sample collection was carried out by the State and the Northern Territory geoscience agencies after exhaustive training by the NGSA team. At each locality a detailed site description, field pH (Figure 5), and dry and moist soil Munsell®colours were recorded and several photographs were taken. All information was recorded digitally to facilitate subsequent uploading into databases.
Sample preparation: Samples were dried, riffle split and sieved to <2 millimetre and <75 micrometre fractions. The <2 millimetre fraction was mechanically ground for some analyses, while the finer fraction was not. A split of each bulk sample was archived for future investigations. More details can be found in the National Geochemical Survey of Australia: Sample Preparation Manual.
Figure 4
Distribution of target
sampling sites for the NGSA
© Geoscience Australia
Sample analysis: Sample analysis is ongoing for 60+ elements using mainly XRF and collision cell ICP-MS at Geoscience Australia. The ICP-MS analyses are carried out on a total digest (HF+HNO3) of fragments of the XRF beads. Other parameters routinely recorded at Geoscience Australia are pH 1:5 (soil:water slurry), EC 1:5, and laser particle size analysis. Selected elements for which analysis is not available at Geoscience Australia (gold (Au), fluorine (F), selenium (Se), and platinum group elements (PGEs) are analysed externally. Other digests/analyses (for example after aqua regia digestion, MMI® extraction) have been added to the analytical protocols. Individuals or organisations interested in undertaking additional analyses should contact the Project Leader, by emailing ngsa@ga.gov.au.
Quality assessment/quality control: Sample numbers were randomised to minimise regional bias, help separate false from true anomalies and obtain meaningful estimates of the variance of duplicates. Field duplicates, analytical duplicates, in-house standards and certified reference materials were introduced at regular intervals in the analytical streams.
Data analysis: The production of national-scale geochemical maps will be carried out prior to their release as a web-based atlas on our website. Reports providing preliminary interpretations and graphical and statistical analysis also will be released on the web site.
Figure 5
Preliminary soil pH map of
Australia (BOS samples)
© Geoscience Australia
Timeline: Following planning in the first half of 2007, fieldwork, including initial training, began in mid 2007 and ran until late 2009. Figure 6 shows the final distribution of sampled catchments. Of the 1390 targeted catchments, 1187 could be accessed in time, yielding approximately 80 per cent coverage of the nation. Sample preparation started in late 2007 and concluded at the end of 2009. Sample analysis began in late 2008 and will conclude in mid 2010. Data analysis and reporting are planned to take place during the 2010-11 financial year. The project will conclude on 30 June 2011.
Figure 6
Distribution of catchments
sampled for the NGSA
© Geoscience Australia
Publications
The following CRCLEME open file reports are available from the CRCLEME Open File Report INDEX:
Presentations
Plans for the National Geochemical Survey of Australia were presented to the geoscience agencies of all States and the Northern Territory in early 2007. The presentation entitled National Geochemical Survey of Australia: outline of a new proposal was given to:
Field training with the geoscience agencies of all States and the Northern Territory took place during 2007 and early 2008. The knowledge transfer mechanisms comprise a detailed National Geochemical Survey of Australia: Field Manual, a training presentation and several days of in-field sample collection under the guidance of NGSA staff.
National Geochemical Survey of Australia email: ngsa@ga.gov.au