The National Geochemical Survey of Australia (NGSA) project was established under the Australian Government's Onshore Energy Security Initiative which was announced in August 2006 and is part of the initiative'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 is no complete geochemical coverage available for Australia and because such a data layer is fundamental to successful exploration for energy-related and other commodities.
The current distribution of geochemical data available through the national repository (OZCHEM database) is shown in Figure 1. The map shows that there are vast areas of the country (>60%) which lack any geochemical information. Also, where geochemical data are available, they are often not comparable as a result of:
Figure 1. Distribution of whole rock geochemical data in Australia extracted from the OZCHEM national database as at June 2006, overlain on bedrock and regolith coverage.
Similarly, the current airborne gamma-ray spectrometric (radiometric) survey coverage available at a resolution deemed appropriate for exploration does not provide a complete national picture of the distribution of radiogenic elements potassium (K), uranium (U) or thorium (Th) (Figure 2). This situation is being remedied by the new project AWAGS2 which, together with NGSA, will result in a significantly improved understanding of the distribution of K, U and Th in Australia.
Figure 2. National coverage of airborne gamma-ray data acquired by Geoscience Australia and the State and the Northern Territory geoscience agencies as at June 2006. Red colour indicates appropriate density (quality) of data (500 metre line spacing or better), blue colours indicate sub-standard data (1,600 metre line spacing or worse), purple colour indicates planned surveys, and beige colour indicates no survey available to date.
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.
The objectives of the NGSA project are to:
A sampling method has been adapted to Australian landscape 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/1,000 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 a 10 centimetre interval at a depth of between around 60 and 90 centimetres).
Sampling sites: 1,390 catchments covering 91% (or about seven million square kilometres) of Australia across all States and Territories have been targeted for sampling (Figure 3). Most catchments will be sampled near their outlet, while those exhibiting internal or poorly defined drainage will be sampled at, or as close as possible to, their lowest point. Catchments smaller than 1,000 square kilometres (mostly coastal) and small islands are 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/5,500 square kilometres.
Figure 3. Distribution of catchments for the National Geochemical Survey of Australia.
Figure 4. Distribution of target sampling sites for the National Geochemical Survey of Australia.
Sample collection: A detailed Field Manual has been compiled and all sampling equipment and consumables have been centrally purchased. Sample collection is 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, and dry and moist soil Munsell® colours are recorded and several photographs are taken. All information is recorded digitally to facilitate subsequent uploading into databases.
Sample preparation: Samples will be dried, rotary split and sieved to <2 millimetre and <75 micrometer fractions. The <2 millimetre fractions will be mechanically ground for some analyses, while the finer fraction will not. A split of each sample will be archived for future investigations.
Sample analysis: Sample analysis is planned for 60+ elements using mainly XRF and collision cell ICP-MS at Geoscience Australia. The ICP-MS analyses will be carried out either on a total digest (HF+HNO3) of fragments of the XRF beads, or on the beads themselves using laser ablation (LA-ICP-MS), depending on results of upcoming tests. Other parameters to be recorded routinely at Geoscience Australia are pH 1:5, EC 1:5, and laser particle size distribution. Analyses for selected elements not available at Geoscience Australia (e.g. gold (Au), fluorine (F), selenium (Se), and possibly platinum group elements (PGEs) will take place externally. Additional digests/analyses (e.g. after aqua regia digestion, MMI® will be considered in the light of budgetary and time constraints. Individuals or organisations interested in undertaking additional analyses should contact the Project Leader, Dr Patrice de Caritat.
Quality assessment/quality control: Sample numbers have been 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 will be introduced at regular intervals in the analytical streams.
Data analysis: Graphical and statistical data analysis will be carried out at various scales (regional, States/Northern Territory, and National). Non-parametric univariate and multi-variate analysis along with the production of geochemical maps will be carried out.
Timeline: Following planning in the first half of 2007, fieldwork, including initial training, began in mid 2007 and is expected to continue until late 2008 (wet season prohibiting field work in northern Australia for six months each year). Figure 5 shows the catchments sampled to date. Sample preparation started in late 2007 and will continue until early 2009. Sample analysis is planned to occur in a single batch, most probably in 2009. Data analysis and reporting are planned to take place in 2010 and early 2011. The project concludes on 30 June 2011.
Figure 5. Distribution of catchments sampled for the National Geochemical Survey of Australia, as at 30 September 2008 (1032 catchments, or 74%, completed).
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 is taking place during 2007 and may extend into the early part of 2008. The knowledge transfer mechanisms comprise a detailed Field Manual, a training presentation [PDF 1MB] and several days of in-field sample collection under the guidance of NGSA staff.
|
A promotional poster for the NGSA project is available for download in two formats.
The high resolution PDf is suitable for printing up to A0, while the low resolution PDF is more suitable for printing on A3 or A4. |
National Geochemical Survey of Australia email: ngsa@ga.gov.au