<div>Alluvial sediments have long been used in geochemical surveys as their compositions are assumed to be representative of areas upstream. Overbank and floodplain sediments, in particular, are increasingly used for regional to continental-scale geochemical mapping. However, during downstream transport, sediments from heterogeneous source regions are carried away from their source regions and mixed. Consequently, using alluvial sedimentary geochemical data to generate continuous geochemical maps remains challenging. In this study we demonstrate a technique that numerically unmixes alluvial sediments to make a geochemical map of their upstream catchments. The unmixing approach uses a model that predicts the concentration of elements in downstream sediments, given a map of the drainage network and element concentrations in the source region. To unmix sedimentary chemistry, we seek the upstream geochemical map that, when mixed downstream, best fits geochemical observations downstream. To prevent overfitting we penalise the roughness of the geochemical model. To demonstrate our approach we apply it to alluvial samples gathered as part of the Northern Australia Geochemical Survey. This survey gathered samples collected over a ∼ 500,000 km2 area in northern Australia. We first validate our approach for this sample distribution with synthetic tests, which indicate that we can resolve geochemical variability at scales greater than 0.5 – 1◦ in size. We proceed to invert real geochemical data from the total digestion of fine-grained fraction of alluvial sediments. The resulting geochemical maps for two elements of potential economic interest, Cu and Nd, are evaluated in detail. We find that in both cases, our predicted downstream concentrations match well against a held-out, unseen subset of the data, as well as against data from an independent geochemical survey. By performing principal component analysis on maps generated for all 46 available elements we produce a synthesis map showing the significant geochemical domains of this part of northern Australia. This map shows strong spatial similarities to the underlying lithological map of the area. Finally, we compare the results from our approach to a geochemical map produced by kriging. We find that, unlike the method presented here, kriging generates geochemical maps that are both dampened relative to expected magnitude, as well as being spatially distorted. We argue that the unmixing approach is the most appropriate method for generating geochemical maps from regional-scale alluvial surveys.&nbsp;</div> <b>Citation:</b> Alex G. Lipp, Patrice de Caritat, Gareth G. Roberts, Geochemical mapping by unmixing alluvial sediments: An example from northern Australia, <i>Journal of Geochemical Exploration,</i> Volume 248, <b>2023</b>, 107174, ISSN 0375-6742, https://doi.org/10.1016/j.gexplo.2023.107174. (https://www.sciencedirect.com/science/article/pii/S0375674223000213)

<div>Geochemical and mineralogical analysis of surficial materials (streams, soils, catchment samples, etc) can provide valuable information about the potential for mineral systems, and the background mineralogical and geochemical variation for a region. However, collecting new samples can be time consuming and expensive, particularly for regional-scale studies. Fortunately, Geoscience Australia has a large holding of archived samples from regional- to continental-scale geochemical studies conducted over the last 50 years, the majority collected at high sampling densities that would be cost-prohibitive today. Although all these samples have already been analysed, their vintage can mean that analyses were obtained by a variety of analytical methods, are of variable quality, and often only available for a small number of elements. As part of the Australian government’s Exploring for the Future program, funding was dedicated to re-analyse ~9,000 samples from these legacy surveys. They were re-analysed for 63 elements (total content) at a single laboratory producing a seamless, internally consistent, high-quality dataset, providing valuable new insights.</div><div><br></div><div>A large number (7,700) of these legacy samples were collected from north Queensland, predominantly in the Cape York – Georgetown area (5,472) — an area with both a wide-range of existing deposit types and known potential for many critical minerals. The sample densities of these studies, up to 1 sample per ~2.5 km2 for Georgetown, makes them directly applicable for determining local- and regional-scale areas of interest for mineral potential. Early interpretation of the Cape York – Georgetown data has identified several locations with stream sediments enriched in both heavy and light rare earth elements (maximum 4000 and 31,800 ppm, respectively), demonstrating the potential of this dataset, particularly for critical minerals. The greater sampling density means that these samples can also provide much more granular geochemical background information and contribute to our understanding of the lower density data commonly used in regional- and national-scale geochemical background studies.</div><div><br></div><div>In addition to the geochemical re-analysis of legacy surface samples, Geoscience Australia has also been undertaking mineral analysis of legacy continental-scale geochemical samples. The National Geochemical Survey of Australia (NGSA) sample archive has been utilised to provide a valuable new dataset. By separating and identifying heavy minerals (i.e., those with a specific gravity >2.9 g/cm3) new information about the mineral potential and provenance of samples can be gained. The Heavy Mineral Map of Australia (HMMA) project, undertaken in collaboration with Curtin University, has analysed the NGSA sample archive, with~81% coverage of the continent. The project has identified over 145 million individual mineral grains belonging to 163 unique mineral species. Preliminary analysis of the data has indicated that zinc minerals and native elements may be useful for mineral prospectivity. Due to the large amount of data generated as part of this HMMA project, a mineral network analysis tool has been developed to help visualise the relationship between minerals and aid in the interpretation of the data. Abstract presented to the Australian Institute of Geoscientists – ALS Friday Seminar Series: Geophysical and Geochemical Signatures of Queensland Mineral Deposits October 2023 (https://www.aig.org.au/events/aig-als-friday-seminar-series-geophysical-and-geochemical-signatures-of-qld-mineral-deposits/)

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. This package contains data generated in the field as part of stratigraphic drilling operations in the Delamerian region of the western New South Wales during 2023 funded through the Exploring for the Future program. A range of geological, geophysical and geochemical data are included, as well as associated borehole information such as core photographs. The data can be viewed and downloaded via the Geoscience Australia Portal - https://portal.ga.gov.au/. The data that is available is from several databases which are associated to this record. <i>These data are published with the permission of the CEO, Geoscience Australia. </i>

<div>A novel method of estimating the silica (SiO2) and loss-on-ignition (LOI) concentrations for the North American Soil Geochemical Landscapes (NASGL) project datasets is proposed. Combining the precision of the geochemical determinations with the completeness of the mineralogical NASGL data, we suggest a ‘reverse normative’ or inversion approach to calculate first the minimum SiO2, water (H2O) and carbon dioxide (CO2) concentrations in weight percent (wt%) in these samples. These can be used in a first step to compute minimum and maximum estimates for SiO2. In a recursive step, a ‘consensus’ SiO2 is then established as the average between the two aforementioned estimates, trimmed as necessary to yield a total composition (major oxides converted from reported Al, Ca, Fe, K, Mg, Mn, Na, P, S, and Ti elemental concentrations + ‘consensus’ SiO2 + reported trace element concentrations converted to wt% + ‘normative’ H2O + ‘normative’ CO2) of no more than 100 wt%. Any remaining compositional gap between 100 wt% and this sum is considered ‘other’ LOI and likely includes H2O and CO2 from the reported ‘amorphous’ phase (of unknown geochemical or mineralogical composition) as well as other volatile components present in soil. We validate the technique against a separate dataset from Australia where geochemical (including all major oxides) and mineralogical data exist on the same samples. The correlation between predicted and observed SiO2 is linear, strong (R2 = 0.91) and homoscedastic. We also compare the estimated NASGL SiO2 concentrations with another publicly available continental-scale survey over the conterminous USA, the ‘Shacklette and Boerngen’ dataset. This comparison shows the new data to be a reasonable representation of SiO2 values measured on the ground over the same study area. We recommend the approach of combining geochemical and mineralogical information to estimate missing SiO2 and LOI by the recursive inversion approach in datasets elsewhere, with the caveat to validate results.</div><div><br></div><div>The major oxide concentrations, including those for the estimated SiO2 and LOI, for the NASGL A and C horizons are available for download, as CSV files. A worked example for five selected NASGL C horizon samples is also available for download, as an XLSX file.</div> <b>Citation:</b> P. de Caritat, E. Grunsky, D.B. Smith; Estimating the silica content and loss-on-ignition in the North American Soil Geochemical Landscapes datasets: a recursive inversion approach. <i>Geochemistry: Exploration, Environment, Analysis</i> 2023; 23 (3): 2023-039 doi: https://doi.org/10.1144/geochem2023-039 This article appears in multiple journals (Lyell Collection & GeoScienceWorld)

<div>Soil is a complex and spatially variable material that has a demonstrated potential to be a useful evidence class in forensic casework and intelligence operations. Here, the capability to spatially constrain searches and prioritise resources by triaging areas as low and high interest is advantageous. Conducted between 2017 and 2021, a forensically relevant topsoil survey (0-5 cm depth; 1 sample per 1 km2) has been carried out over Canberra, Australia, with the aims of documenting the distribution of chemical elements in an urban/suburban environment, and of acting as a testbed for investigating various aspects of forensic soil provenancing. Geochemical data from X-Ray Fluorescence (XRF; for total major oxides) and Inductively Coupled Plasma-Mass Spectrometry (ICP-MS; for trace elements) following a total digestion (HF + HNO3) were obtained from the survey’s 685 topsoil samples (plus 138 additional quality control samples and six “Blind” simulated evidentiary samples). Using those “Blind” samples, we document a likelihood ratio approach where for each grid cell the analytical similarity between the grid cell and evidentiary sample is attributed from a measure of overlap between both Cauchy distributions, including appropriate uncertainties. Unlike existing methods that base inclusion/exclusion on an arbitrary threshold (e.g., ± three standard deviations), our approach is free from strict binary or Boolean thresholds, providing an unconstrained gradual transition dictated by the analytical similarity. Using this provenancing model, we present and evaluate a new method for upscaling from a fine (25 m x 25 m) interpolated grid to a more appropriate coarser (500 m x 500 m) grid, in addition to an objective method using Random Match Probabilities for ranking individual variables to be used for provenancing prior to receiving evidentiary material. Our results show this collective procedure generates more consistent and robust provenance maps between two different interpolation algorithms (e.g., inverse distance weighting, and natural neighbour), grid placements (e.g., grid shifts to the north or east) and theoretical users (e.g., different computer systems, or forensic geoscientists).</div> <b>Citation:</b> Michael G. Aberle, Patrice de Caritat, James Robertson, Jurian A. Hoogewerff, A robust interpolation-based method for forensic soil provenancing: A Bayesian likelihood ratio approach,<i> Forensic Science International</i>, Volume 353, 2023, 111883, ISSN 0379-0738. https://doi.org/10.1016/j.forsciint.2023.111883.

<div>With a higher demand for lithium (Li), a better understanding of its concentration and spatial distribution is important to delineate potential anomalous areas. This study uses a digital soil mapping framework to combine data from recent geochemical surveys and environmental covariates to predict and map Li content across the 7.6 million km2 area of Australia. Soil samples were collected by the National Geochemical Survey of Australia at a total of 1315 sites, with both top (0–10 cm depth) and bottom (on average 60–80 cm depth) catchment outlet sediments sampled. We developed 50 bootstrap models using a Cubist regression tree algorithm for both depths. The spatial prediction models were validated on an independent Northern Australia Geochemical Survey dataset, showing a good prediction with an RMSE of 3.82 mg kg-1 for the top depth. The model for the bottom depth has yet to be validated. The variables of importance for the models indicated that the first three Landsat bands and gamma radiometric dose have a strong impact on Li prediction. The bootstrapped models were then used to generate digital soil Li prediction maps for both depths, which could select and delineate areas with anomalously high Li concentrations in the regolith. The map shows high Li concentration around existing mines and other potentially anomalous Li areas. The same mapping principles can potentially be applied to other elements.&nbsp;</div> <b>Citation:</b> Ng, W., Minasny, B., McBratney, A., de Caritat, P., and Wilford, J.: Digital soil mapping of lithium in Australia, <i>Earth Syst. Sci. Data</i>, 15, 2465–2482, https://doi.org/10.5194/essd-15-2465-2023, <b>2023</b>.

<div>The Darling-Curnamona-Delamerian (DCD) project focused on the covered portion of the Delamerian orogen, situated in the south-eastern mainland states of Australia.&nbsp;The aims of the project were to develop a greater understanding of the geodynamic history of the Delamerian Orogen, characterise known magmatic-hydrothermal mineral systems, and assess mineral potential for a suite of minerals including copper (Cu), gold (Au), and nickel (Ni), and critical minerals like platinum-group elements (PGEs) and rare-earth elements (REEs). </div><div>Here, we collate whole rock geochemistry data from new and legacy samples of mafic to intermediate magmatic rocks of the Loch Lilly-Kars Belt in order to determine the likely source of these magmas and constrain the prevailing tectonic setting during their emplacement. We apply multi-elemental diagrams and various elemental discrimination diagrams to characterise various groups of magmatic rocks in these belts, taking into account their geographic affinity and new geochronological data (e.g. Mole et al., 2023; Mole et al., 2024). The geochemical characteristics of these groups and the implications for the tectonic setting into which they were emplaced are discussed. Comparisons are made with potentially similar magmatic rocks of the&nbsp;Koonenberry Belt and Grampians-Stavely Zone. Results from this study have significant implications for the tectonic setting in which the Loch Lilly-Kars Belt developed, and hence also the mineral potential of the Belt. </div><div> </div>

This report contains new whole-rock and isotope geochemical data, associated sample metadata, an assessment of the data’s quality assurance, for 742 samples collected in and around the Curnamona and Delamerian provinces, across numerous drillcore sampling campaigns through 2021-23. 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/148651). Geochemical sampling in the Curnamona region straddles both South Australia and New South Wales. The objective of sampling was to obtain representative coverage (both stratigraphically and spatially) to support developing regional geochemical baselines (in conjunction with existing geochemistry). Thus, this sampling included both the Curnamona Province and the overlying basins (Eromanga Basin, Lake Eyre Basin). Whole-rock geochemistry is reported for 562 samples, with a subset of 13 samples analysed for Pb and Sr isotopes, and another subset of 36 samples analysed by thin section petrography (all presented herein). Geochemical sampling in the Delamerian region has focussed on available legacy drill core in South Australia, New South Wales and Victoria. The objective of sampling was to (systematically) constrain the geochemical character of magmatic rocks across the mainland extent of the Delamerian Orogen, as well as younger volcanics within the Delamerian Orogen and/or overlying cover. This geochemical sampling was conducted in conjunction with geochronology, mineral systems sampling and stratigraphic drilling (all components of the DCD project) to reinterpret the timing, character and fertility of the Delamerian Orogen. Whole-rock geochemistry is reported for 180 samples. Version 2.0 (published 28 November 2023) has added whole rock geochemistry for 22 new samples in the Delamerian region. The data products and report have been updated accordingly.

<div>Diamond exploration over the past decade has led to the discovery of a new province of kimberlitic pipes (the Webb Province) in the Gibson Desert of central Australia. The Webb pipes comprise sparse macrocrystic olivine set in a groundmass of olivine, phlogopite, perovskite, spinel, clinopyroxene, titanian-andradite and carbonate. The pipes resemble ultramafic lamprophyres (notably aillikites) in their mineralogy, major and minor oxide chemistry, and initial 87Sr/ 86Sr and <em>ε</em>Nd-<em>ε</em>Hf isotopic compositions. Ion probe U-Pb geochronology on perovskite (806 ± 22 Ma) indicates the eruption of the pipes was co-eval with plume-related magmatism within central Australia (Willouran-Gairdner Volcanic Event) associated with the opening of the Centralian Superbasin and Rodinia supercontinent break-up. The equilibration pressure and temperature of mantle-derived garnet and chromian (Cr) diopside xenocrysts range between 17 and 40 kbar and 750–1320°C and define a paleo-lithospheric thickness of 140 ± 10 km. Chemical variations of xenocrysts define litho-chemical horizons within the shallow, middle, and deep sub-continental lithospheric mantle (SCLM). The shallow SCLM (50–70 km), which includes garnet-spinel and spinel lherzolite, contains Cr diopside with weakly refertilized rare earth element compositions and unenriched compositions. The mid-lithosphere (70–85 km) has lower modal abundances of Cr diopside. This layer corresponds to a seismic mid-lithosphere discontinuity interpreted as pargasite-bearing lherzolite. The deep SCLM (&gt;90 km) comprises refertilized garnet lherzolite that was metasomatized by a silicate-carbonatite melt.</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><div><strong>Citation:</strong></div><div>Sudholz, Z. J., et al. (2023). Petrology, age, and rift origin of ultramafic lamprophyres (aillikites) at Mount Webb, a new alkaline province in Central Australia. <i>Geochemistry, Geophysics, Geosystems</i>, 24, e2023GC011120.</div><div>https://doi.org/10.1029/2023GC011120</div>

<div>Lithospheric structure and composition have direct relevance for our understanding of mineral prospectivity. Aspects of the lithosphere can be imaged using geophysical inversion or analysed from exhumed samples at the surface of the Earth, but it is a challenge to ensure consistency between competing models and datasets. The LitMod platform provides a probabilistic inversion framework that uses geology as the fabric to unify multiple geophysical techniques and incorporates a priori geochemical information. Here, we present results from the application of LitMod to the Australian continent. The rasters summarise the results and performance of a Markov-chain Monte Carlo sampling from the posterior model space. Release FR23 is developed using primary-mode Rayleigh phase velocity grids adapted from Fishwick & Rawlinson (2012).</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 a low emissions economy, strong 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>