Potential applications in baseline geochemical data for Geoscience Australia - a report of findings from a pilot study

Australia's geochemical environment affects our well-being. It directly affects public health, agriculture and mining activities, yet nation-wide geochemical surveys such as conducted in the United Kingdom, Wales and China are yet to be established in Australia. To obtain the most information from geochemical data, appropriate methodologies to analyse the data are essential. This report investigates the use of various methodologies for the assessment and integration of whole-rock geochemical data at regional and local scales. A broad-scale regional study conducted over southeastern Australia, mainly focused on NSW and Victoria, whilst the other was a more specific study conducted over the Bathurst 1:250,000 map sheet area.
Regional scale studies have low sample densities and the possibility of sampling bias being incorporated and intensified during data analysis across large areas are high. However, regional scale mapping is a low cost, time efficient way of identifying broad trends and smaller target areas. Accordingly, the methods used on regional data are quick and easy with relatively little data preparation. Mineral occurrence densities were created and concentrations of uranium, lead, zinc, gold and arsenic were overlaid to identify anomalous values. Hot spots for these elements often corresponded to mining districts. However, the analysis highlighted that some anomalous samples related to local mineralisation and should have been removed from the analysis. The Bathurst study area had a higher sample density so more comprehensive analysis was possible. Statistical analysis was conducted which identified spurious data that were then removed from the dataset. The geochemical points were validated to ensure that they were in the correct geological polygon and hence there was a higher confidence in the data than in the regional scale study. The geochemical values were averaged across like geological polygons and trends of elemental concentrations in rock types became apparent. This was important as it allowed the geochemistry to be viewed in its geological context.
Both studies indicated that existing whole-rock geochemical data is inappropriate for baseline geochemical surveying due to sample biases associated with the data. It does, however, identify methods that can be applied to the more appropriate data. The studies identified the need for conducting a nation-wide baseline geochemical survey. Benefits of such a survey would include a raised awareness of public health, agricultural, environmental and land use issues, as well as helping to identify mineral resource targets. It is recognised that determining high concentrations of elements is not in itself sufficient as high background concentrations may not lead to the formation of an ore deposit, nor be detrimental to human and animal health. An assessment of bioavailability is critical because elements may occur in stable compounds within the environment hence will not pose a health risk, no matter how high their concentrations. As a follow-on from this study, assessment of element bioavailability is an important step.