19 Oct 2023
 | 19 Oct 2023
Status: this preprint is currently under review for the journal ESSD.

A regolith lead isoscape of Australia

Candan Desem, Patrice de Caritat, Jon Woodhead, Roland Maas, and Graham Carr

Abstract. We present the first national-scale lead (Pb) isotope maps of Australia based on surface regolith for five isotope ratios, 206Pb/204Pb, 207Pb/204Pb, 208Pb/204Pb, 207Pb/206Pb, and 208Pb/206Pb, determined by single collector Sector Field-Inductively Coupled Plasma-Mass Spectrometry after an Ammonium Acetate leach followed by Aqua Regia digestion. The dataset is underpinned principally by the National Geochemical Survey of Australia (NGSA) archived floodplain sediment samples. We analysed 1219 ‘top coarse’ (0–10 cm depth, <2 mm grain size) samples, collected near the outlet of 1119 large catchments covering 5.647 million km2 (~75 % of Australia). The samples consist of mixtures of the dominant soils and rocks weathering in their respective catchments (and possibly those upstream) and are therefore assumed to form a reasonable representation of the average isotopic signature of those catchments. This assumption was tested in one of the NGSA catchments, within which 12 similar ‘top coarse’ samples were also taken; results show that the Pb isotope ratios of the NGSA catchment outlet sediment sample are close to the average of the 12 sub-catchment, upstream samples. National minimum, median and maximum values reported for 206Pb/204Pb were 15.558, 18.844, 30.635; for 207Pb/204Pb 14.358, 15.687, 18.012; for 208Pb/204Pb 33.558, 38.989, 48.873; for 207Pb/206Pb 0.5880, 0.8318, 0.9847; and for 208Pb/206Pb 1.4149, 2.0665, 2.3002, respectively. The new dataset was compared with published bedrock and ore Pb isotope data, and was found to dependably represent crustal elements of various ages from Archean to Phanerozoic. This suggests that floodplain sediment samples are a suitable proxy for basement and basin geology at this scale, despite various degrees of transport, mixing, and weathering experienced in the regolith environment, locally over protracted periods of time. An example of atmospheric Pb contamination around Port Pirie, South Australia, where a Pb smelter has operated since the 1890s, is shown to illustrate potential environmental applications of this new dataset. Other applications may include elucidating detail of Australian crustal evolution and mineralisation-related investigations. The new regolith Pb isotope dataset for Australia is publicly available (Desem et al., 2023;

Candan Desem et al.

Status: open (until 12 Jan 2024)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on essd-2023-357', Brian Gulson, 05 Nov 2023 reply

Candan Desem et al.

Data sets

National Geochemical Survey of Australia: Lead Isotopes Dataset C. U. Desem, P. de Caritat, J. D. Woodhead, R. Maas, and G. Carr

Candan Desem et al.


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Short summary
Lead (Pb) isotopes form a potent tracer in studies of provenance, mineral exploration and environmental remediation. Previously, however, Pb-isotope analysis has rarely been deployed at a continental scale. Here we present a new regolith Pb-isotope dataset for Australia, which includes 1119 large catchments encompassing 5.6 million km2, or close to ~75 % of the continent. Isoscape maps have been produced for use in diverse fields of study.