During the National Geochemical Survey of Australia over 1300 top (0-10cm depth) and bottom (~60-80cm depth) sediment samples (including ~10% field duplicates) were collected from the outlet of 1186 catchments covering 81% of the continent at an average sample density of 1 site/5200km2. The <2mm fraction of these samples was analysed for 59 elements by ICP-MS following an aqua regia digestion. Results are used here to establish the geochemical background variation of these elements, including potentially toxic elements (PTEs), in Australian surface soil. Different methods of obtaining geochemical threshold values, which differentiate between background and those samples with unusually high element concentrations and requiring attention, are presented and compared to Western Australia's 'ecological investigation levels' (EILs) established for 14 PTEs. For Mn and V these EILs are so low that an unrealistically large proportion (~24%) of the sampled sites would need investigation in Australia. For the 12 remaining elements (As, Ba, Cd, Co, Cr, Cu, Hg, Mo, Ni, Pb, Sn and Zn) few sample sites require investigation and as most of these are located far from human activity centres, they potentially suggest either minor local contamination or mineral exploration potential rather than pollution. No major diffuse source of contamination by PTEs affects Australian soil at the continental scale. Of the statistical methods used to establish geochemical threshold values, the most pertinent results come from identifying breaks in cumulative probability distributions, the Tukey inner fence and the 98th percentile. Geochemical threshold values for 59 elements, including emerging 'high-tech' critical elements such as lanthanides, Be, Ga or Ge, for which no EILs currently exist, are presented.
RESULTS The results indicate that groundwater composition is affected by a number of processes: evaporation; evapo-transpiration; mixing; ion exchange; precipitation/dissolution; adsorption/desorption; and, oxidation/reduction. The impact of each of these major processes is teased out using 'conservative' tracers (Cl, Br), isotopes and geochemical modelling. Figure 1: Location of the Curnamona Province.
It is a great honour that the Association of Applied Geochemists (A AG) has bestowed upon me to serve as its President for 2022-2023.I thank Dennis Arne for leading the A AG strongly over the past two years, which were made difficult by the Covid-19 pandemic.So difficult were those two years that the AAG was unable to celebrate its 50 th anniversary at the 29 th International Applied Geochemistry Symposium (IAGS), which was scheduled originally for November 2020 in Viña del Mar, Chile.I also thank Brian Townley, chair of the local organizing committee, for persevering in the organization of the 29 th IAGS in those two difficult years.We are now hopeful, even though Covid-19 has not yet fully gone away, that we will be able to finally hold the 29 th IAGS in the same Chilean city on October 16-22, 2022.
We describe the information content of soil visible–near infrared (vis–NIR) reflectance spectra and map their spatial distribution across Australia. The spectra of 4030 surface soil samples from across the country were measured with a vis–NIR spectrometer in the range 350 to 2500 nm. The spectra were compressed by a principal component analysis (PCA) and the resulting scores were mapped by ordinary point kriging. The largely dominant and common feature in the maps was the difference between the more expansive, older and more weathered landscapes in the centre and west of Australia and the generally younger, more complex landscapes in the east. A surface soil class map derived from the clustering of the principal components was similar to an existing soil classification map. We show that vis–NIR reflectance spectra (i) provide a rapid and efficient integrative measure of the composition of the soil, (ii) can replace the use of traditional soil properties to describe the soil and make pedological interpretations of its spatial distribution and (iii) can be used to classify soil objectively.
The National Geochemical Survey of Australia (NGSA) provides an internally consistent, state-of-the-art, continental-scale geochemical dataset that can be used to assess areas of Australia more elevated in commodity metals and/or pathfinder elements than others. But do regions elevated in such elements correspond to known mineralized provinces, and what is the best method for detecting and thus potentially predicting those? Here, using base metal associations as an example, I compare a trivariate rank-based index and a multivariate-based Principal Component Analysis method. The analysis suggests that the simpler rank-based index better discriminates catchments endowed with known base metal mineralization from barren ones and could be used as a first-pass prospectivity tool.
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