A continental-scale geochemical atlas for resource exploration and environmental management: the National Geochemical Survey of Australia
The National Geochemical Survey of Australia (NGSA) was carried out to bridge a vast knowledge gap about the concentration and distribution of chemical elements at the Earth’s surface in Australia and consequent poor understanding of processes controlling their distribution here. The aim of the project was to contribute to improving exploration for energy and mineral resources through the pre-competitive delivery of a new spatial layer of compositional data and information.
Surface (0–10 cm depth) and shallow (c. 60–80 cm) samples of catchment outlet sediments were collected from 1315 sites located near the outlet of 1186 catchments (c. 10% of which were sampled in duplicate) from across Australia. The total area covered by the survey was 6.174 million km2, or c. 81% of Australia, at an average sampling density of 1 site per c. 5200 km2. A number of field parameters (e.g. soil colour, pH), bulk parameters (e.g. electrical conductivity, particle size distribution) and geochemical parameters (i.e. multi-element composition of dry sieved <2 mm and <75 μm grain-size fractions) were determined. The grain-size fractions were analysed to determine (1) total, (2) aqua regia soluble, and (3) Mobile Metal Ion (MMI®) extractable element contents.
These data were collated into a spreadsheet and graphically represented as a series of 529 geochemical maps (http://www.ga.gov.au/ngsa). These constitute the first continental-scale series of geochemical maps for Australia based on internally consistent, state-of-the-art data pertaining to the same sampling medium collected, prepared and analysed in a uniform and thoroughly documented manner and over a short time period. They are being used to better understand the accumulation, mobility and significance of chemical elements in the near-surface environment. Applications to date and ongoing and future directions are discussed.