Estimating the relative contributions of bedrock geology, mineralisation and anthropogenic contamination to the chemistry of samples collected at the Earth’s surface is critical in research and application fields as diverse as environmental impact studies and regional mineral exploration programs. The element lead (Pb) is a particularly useful tracer in this context, representing a toxin of environmental concern and associated with many other anthropogenic contaminants (e.g. mine wastes, waters, paints, aerosols), as well as with mineralisation. Although Pb concentration data are frequently collected in geochemical studies, isotopic analysis offers an important advantage, allowing discrimination between different sources of Pb. The Pb isotopic composition of regolith is likely to reflect contributions from underlying rock (including Pb-rich mineralisation), wind-blown dust and possibly anthropogenic sources (industry, transport, agriculture, residential, waste handling). Regolith samples collected at different depths may show distinct compositions; bedrock isotopic signatures are expected to dominate in deeper soils, whilst airborne dust and anthropogenic signatures are more important at the surface. Pb isotope ratios in the continental crust show large variations, which will be transferred to the regolith, providing a potentially unique bedrock signal that is easily measured. This research program examines if soil Pb isotope mapping can identify the underlying geology and metallogenic provinces, if different sampling and analytical approaches produce very different results, and how anthropogenic signals vary across the continent. Here, we present our results for the Northern Territory, where single regolith samples from many (not all) catchments define apparently consistent isotopic domains that can be interpreted in relation to the underlying geology (crystalline basement, basins) and mineral deposits. <b>Citation:</b> Desem, C.U., Maas, R., Woodhead, J., Carr, G. and de Caritat P., 2020. Towards a Pb isotope regolith map of the Australian continent: a Northern Territory perspective. In: Czarnota, K., Roach, I., Abbott, S., Haynes, M., Kositcin, N., Ray, A. and Slatter, E. (eds.) Exploring for the Future: Extended Abstracts, Geoscience Australia, Canberra, 1–4.

<div>Lead isotopic data implies that Th and U were fractionated from one another in Earth's early history, however, the origin of this fractionation is poorly understood. We report new <em>in-situ</em> Pb isotope data from orthoclase in 144 granites, sampled across the Archean Yilgarn Craton to characterize its Pb isotope variability and evolution. Granite Pb isotope compositions reveal three Pb sources, a mantle derived Pb reservoir and two crustal Pb reservoirs, distinguished by their implied source 232Th/238U (κPb). High-κPb granites reflect sources with high 232Th/238U (~4.7) and are largely co-located with Eoarchean–Paleoarchean crust. The Pb isotope compositions of most granites, and those of VHMS and gold ores, define a mixing array between a mantle Pb source and a Th-rich Eoarchean-Paleoarchean source. Pb isotope modelling indicates that the high-κPb source rocks experienced Th/U fractionation at ~3.3 Ga. As Th/U fractionation in the Yilgarn Craton must have occurred before Earth’s atmosphere was oxygenated, subaerial weathering cannot explain the apparent differences in their geochemical behavior. Instead, the high Th/U source reflects Eoarchean–Paleoarchean rocks that experienced prior high-temperature metamorphism, partial melting, and melt loss in the presence of a Th-sequestering mineral like monazite. Archean Pb isotope variability thus has its origins in open-system high-temperature metamorphic processes responsible for the differentiation and stabilization of Earth’s continental crust.</div> <b>Citation:</b> M.I.H. Hartnady, C.L. Kirkand, S.P. Johnson, R.H. Smithies, L.S. Doucet, D.R. Mole; <i>Origin of Archean Pb isotope variability through open-system Paleoarchean crustal anatexis</i>. Geology 2023; doi: https://doi.org/10.1130/G51507.1

<div><strong>Output type: </strong>Exploring for the Future Extended Abstract</div><div><br></div><div><strong>Short abstract: </strong>Australian sediment-hosted mineral systems play a crucial role in providing base metals and critical minerals essential for the global low-carbon economy. The Georgina Basin has the key components for forming and preserving a sediment-hosted Zn-Pb mineral system, but historically has been considered ‘cover’ to deeper, more prospective Proterozoic basement rocks. Thus, the basin has remained relatively under-explored, with many questions yet to be resolved on its sediment-hosted Zn-Pb mineral system and prospectivity for Zn-Pb. Utilising new whole-rock and isotope geochemistry of the Georgina Basin from recently drilled holes in the Northern Territory, we demonstrate the sensitivity of local redox boundaries to detect regional mineralisation. Two geochemically enriched zones have been identified and interpreted as redox interfaces which have trapped and concentrated metals from the surrounding basin, a ‘supergene zone’ and a ‘water intercept zone’. The ‘supergene zone’ is a paleo water table horizon, while the ‘water intercept zone’ is an active redox front at the uppermost part of the Cambrian Limestone Aquifer. The enrichment of these redox zones is consistent across multiple drill holes, reaching up to 395 ppm Pb and 1550 ppm Zn. Additionally, the Pb isotopes of high-Pb and sulfidic intervals have a highly radiogenic character (206Pb/204Pb ~22.0–23.0) that is diagnostic of Georgina Basin’s Mississippi Valley-type Zn-Pb mineralisation. Taken together, these results suggest there may be buried mineralisation in this part of the Georgina Basin, as well as highlight the potential of these redox interfaces as a regional reconnaissance target for exploration.</div><div><br></div><div><strong>Citation: </strong>Schroder I.F., Huston D. & de Caritat P., 2024. The geochemistry of redox interfaces for insights into Zn-Pb prospectivity in the Georgina Basin. In: Czarnota, K. (ed.) Exploring for the Future: Extended Abstracts, Geoscience Australia, Canberra, https://doi.org/10.26186/149116 </div>

<div>This report contains new whole-rock and isotope (Pb and Sr) geochemical data, associated sample metadata, an assessment of the data’s quality assurance, for 76 samples collected from the Georgina Basin of the East Tennant National Drilling Initiative (NDI) in 2021. The data can be downloaded via the Geoscience Australia EFTF portal (https://portal.ga.gov.au/persona/eftf) or in the files attached with this record (http://pid.geoscience.gov.au/dataset/ga/148954).</div><div><br></div><div>This new geochemistry data release builds on the success of the East Tennant NDI, addressing the data-gap in earlier geochemical sampling of these holes, by providing whole-rock geochemistry (and Pb+Sr isotopes) for the Georgina Basin cover sequence. Improved geochemical characterisation of Georgina Basin geology is valuable from both a hydrogeological and mineral systems perspective. The Georgina Basin extends across much of the Northern Territory and into western Queensland, comprised of Cryogenian to Devonian sediment packages.</div><div><br></div><div>Geoscience Australia’s Exploring for the Future program provides precompetitive information to inform decision-making by government, community and industry on the sustainable development of Australia's mineral, energy and groundwater resources. By gathering, analysing and interpreting new and existing precompetitive geoscience data and knowledge, we are building a national picture of Australia’s geology and resource potential. This leads to a strong economy, resilient society and sustainable environment for the benefit of all Australians. This includes supporting Australia’s transition to net zero emissions, strong, sustainable resources and agriculture sectors, and economic opportunities and social benefits for Australia’s regional and remote communities. The Exploring for the Future program, which commenced in 2016, is an eight year, $225m investment by the Australian Government.</div><div><br></div>

A dataset of global zinc-bearing mineral deposits has been developed that complements previous such datasets (Franklin et al., 2005; Meinert et al., 2005; Mosier et al., 2009a,b; Taylor et al. 2009). The new dataset provides information on name, location, type, metal endowment, host rocks, associated igneous rocks, regional and proximal alteration assemblages (including, where possible, spatial and temporal zonation), Fe-S-O mineralogy, the presence of sulfate minerals, and sulfur and lead isotope data. In particular, unlike previous datasets, the age information provides the uncertainties of age determinations along with information on the assumptions and analytical methods used to determine the age. The dataset is meant to be used in conjunction with previous datasets and will be updated. Analysis of trends and relationships within the datasets are ongoing and will be published separately.