Multi-element geochemical analyses on ultrafine soils in Western Australia – towards establishing abundance ranges in mineral exploration settings

Abstract

In this study, we present summary statistics for multi-element soil geochemistry across Western Australia based on over 74 000 soil samples using the UltraFine+ ® method that extracts and analyses the clay (<2 μ m) fraction of a soil sample. This method is a critical advancement for the detection of mobile element signatures for soil geochemical mineral exploration surveys in cover. However, existing estimates of background metal abundances acquired with other methods and on different sample media do not readily provide context for these analyses, as recovery from the fine fraction differs to that of whole-sample analysis. We therefore present herein the geochemical results for 52 elements, including precious, base and critical metals, as well as commonly associated pathfinder elements for Western Australian samples analysed during several research projects by the Commonwealth Scientific and Industrial Research Organisation (CSIRO). This dataset is separated by tectonic unit into the Eastern Goldfields Superterrane and the Youanmi Terrane in the Yilgarn Craton, the Pilbara Craton and Sylvania Inlier, the Gascoyne, Lamboo and Aileron Provinces, and the Bryah and Earaheedy Basins to provide exploration-relevant context in these areas. We discuss some of the general trends observed for 12 of these elements, as well as some considerations for the use of these data in comparison to other geochemical soil surveys and with regards to mineral exploration settings. The samples presented in this study are not evenly distributed across Western Australia and limited information is available to correlate whether lithology at depth is mineralized or barren. However, in the absence of other systematic datasets using the <2 μ m-size fraction, these data present a suitable first-pass resource of element abundance ranges in areas of mineral exploration interest using the UltraFine+ ® method in some of the mineral-endowed areas of Western Australia. Supplementary material: Supplementary data A, UltraFine+ ® Soil Sampling Guide; B, UltraFine+ ® analyses results for available samples in Western Australia; C, Summary statistics of UltraFine+ ® analyses by simplified tectonic units; Supplementary Figure 1, Comparison of elemental mean values and uncertainties for ultrafine reference materials QC 320 and QC 422; Supplementary Figure 2, Violin plots of Ni, Cd, Mg and Au by simplified tectonic unit; Supplementary Figure 3, Location of soil samples in the Eastern Goldfields Superterrane analysed via UltraFine+ ® , and those collected as part of the NGSA and GSWA regolith programme; Supplementary Figure 4, Comparison of W, Al, Mg and Ca results from UltraFine+ ® , NGSA and GSWA analyses in the Eastern Goldfields Superterrane are available at https://doi.org/10.6084/m9.figshare.c.6919933