A regolith lead isoscape of Australia

We present the first national-scale lead (Pb) isotope maps of Australia based on surface regolith for five isotope ratios, 206 Pb / 204 Pb , 207 Pb / 204 Pb , 208 Pb / 204 Pb , 207 Pb / 206 Pb , and 208 Pb / 206 Pb , 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 samples (0-10 cm depth, < 2 mm grain size), collected near the outlet of 1119 large catchments covering 5.647 x 10 6 km 2 ( similar to 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 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 upstream sub-catchment samples. National minimum, median, and maximum values were 15.56, 18.84, and 30.64 for 206 Pb / 204 Pb ; 14.36, 15.69, and 18.01 for 207 Pb / 204 Pb ; 33.56, 38.99, and 48.87 for 208 Pb / 204 Pb ; 0.5880, 0.8318, and 0.9847 for 207 Pb / 206 Pb ; and 1.4149, 2.0665, and 2.3002 for 208 Pb / 206 Pb , respectively. The new dataset was compared with published bedrock and ore Pb isotope data, and it was found to dependably represent crustal elements of various ages from Archaean 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 details of Australian crustal evolution and mineralisation-related investigations. The new regolith Pb isotope dataset for Australia is publicly available (Desem et al., 2023; 10.26186/5ea8f6fd3de64).