<div>Throughout geological history, marine organic-rich shales show variable but appreciable enrichment in uranium (U), < 5 to > 500 ppm. Here we report the results of high-energy resolution fluorescence detection (HERFD) x-ray absorption spectroscopy at U L3 and M4 edges to characterize U speciation in marine sediments.</div><div><br></div><div>We characterised U oxidation state in samples from the Cretaceous Toolebuc Formation of the Eromanga Basin, Australia. Nine samples were carbonaceous shales with high total organic carbon (TOC) content of 5.9 to 13.4 wt&nbsp;% and with low maturity organic matter. Two samples of coquinite were selected for comparison (TOC 0.3 and 2.4 wt %).</div><div><br></div><div>Our results suggest that a significant proportion of U in marine black shales (~20 to 30%) exists as U(VI) (Figures 1-2), despite the extremely reducing (anoxic to euxinic) conditions during sediment precipitation and diagenesis. Within individual samples, spot analyses indicate variation in the estimated oxidation state within a range of ~20% of U(VI). Uranium is unevenly distributed at mm to nanoscale. Nanoscale secondary ion mass spectrometry (NanoSIMS) reveals different associations that often coexist in single samples; nano-particulate uranium is associated with organic matter matrix or sulphide minerals, whereas phosphate minerals display diffuse uranium enrichment. The coquinite has a higher proportion of U(VI), consistent with the dysoxic depositional environment (Boreham and Powell, 1987).</div><div><br></div><div>The unexpectedly enhanced proportion of U(VI) relative to U(IV) within marine organic-rich shales implies that U might not be immediately fixed by reduction processes during sedimentation, but adsorbed by accumulating organic matter, at least in part as U(VI). This is consistent with the behaviour of uranium reported within the water column of the anoxic Black Sea (Anderson, 1989), experiments on U(VI) sorption by organic matter (e.g., Bhat et al., 2008), and previously documented redox state of U from continental organic-rich Eocene (56-34 Ma) sediments of paleochannel and lacustrine origin (Cumberland et al., 2018).</div><div><br></div><div>The results are significant for improving hydrocarbon exploration in known fields (covering the gap to a carbon-free economy without development of new greenfield oil provinces); economic geology (uranium, base-metal, and critical-metal deposits); and environmental management (evaluating potential mobilization of U by groundwaters).</div><div><br></div>This Abstract was submitted and presented to the 2023 Goldschmidt Conference Lyon, France (https://conf.goldschmidt.info/goldschmidt/2023/meetingapp.cgi)

A comprehensive geochemical program was carried out on rock samples collected in the NDI Carrara 1 drill hole, the first stratigraphic test of the newly discovered Carrara Sub-basin located in the South Nicholson region of northern Australia. The drill hole recovered continuous core from 284 m to total depth at 1750 m and intersected approximately 1120 m of Proterozoic sedimentary rocks, unconformably overlain by 630 m of Cambrian Georgina Basin carbonate-rich rocks. Total organic carbon (TOC) contents from Rock-Eval pyrolysis highlight the potential for several thick black shales to be a source of petroleum for conventional and unconventional plays. Cambrian rocks contain an organic-rich section with TOC contents of up to 4.7 wt.% and excellent oil-generating potential. The Proterozoic section is overmature for oil generation but mature for gas generation, with potential for generating gas in carbonaceous mudstones showing TOC contents up to 5.5 wt.% between 680 and 725 m depth. A sustained release of methane (up to 2%) recorded during drilling from 1150 to 1500 m suggests potential for an unconventional gas system in the Proterozoic rocks from 950 to 1415 m depth, which exhibit favourable organic richness and thermal maturity. The Proterozoic rocks, which are comparable in age to the sediment-hosted deposits of the Century Mine, contain local occurrences of lead, zinc and copper sulfide minerals providing hints of mineralisation. The combined geochemical results offer the promise of a potential new resource province in northern Australia. <b>Citation:</b> E. Grosjean, A.J.M. Jarrett, C.J. Boreham, L. Wang, L. Johnson, J.M. Hope, P. Ranasinghe, J.J. Brocks, A.H.E. Bailey, G.A. Butcher, C.J. Carson, Resource potential of the Proterozoic–Paleozoic Carrara depocentre, South Nicholson region, Australia: Insights from stratigraphic drilling, <i>Organic Geochemistry</i>, Volume 186, 2023, 104688, ISSN 0146-6380, DOI: https://doi.org/10.1016/j.orggeochem.2023.104688.

The Roebuck Basin on Australia’s offshore north-western margin is the focus of a regional hydrocarbon prospectivity assessment being undertaken by the Offshore Energy Systems Section. This offshore program is designed to produce pre-competitive information to assist with the evaluation of the hydrocarbon resource potential of the central North West Shelf and attract exploration investment to Australia. As part of this program, molecular and isotopic analyses were undertaken by Geoscience Australia on gas samples from the well Dorado 1 and the raw data from these analyses are released in this report.

<div>Exploring for the Future (EFTF) is a program dedicated to exploring Australia’s resource potential and boosting investment. This program is designed to produce pre-competitive information to assist with the evaluation of the hydrocarbon resource potential of onshore basins and attract exploration investment to Australia. This record presents geochemical analyses of natural gases sampled from Nangwarry 1, located in the onshore Otway Basin, undertaken in partnership with the Department for Energy and Mining – Energy Resources, Government of South Australia, as part of the EFTF program Natural Hydrogen module. The Nangwarry Joint Venture drilled Nangwarry 1 to investigate the potential for the development of food grade, carbon dioxide production from this well. The results of the molecular and stable carbon and hydrogen isotopic analyses undertaken by Geoscience Australia are released in this report. The molecular data show that the gas composition in this well has an average of 96 mol% CO2 with an isotopic signature indicative of a magmatic origin, being comparable with previously produced gases from onshore Otway Basin wells (e.g. Boggy Creek 1, Caroline 1) for use by the food industry. The carbon and hydrogen isotopic composition of the C1–C5 hydrocarbon gases from Nangwarry 1 are suggestive of a source from within the Crayfish Supersequence.</div>

The Australian Government’s $225 million Exploring for the Future (EFTF) program is committed to supporting a strong economy, resilient society and sustainable environment for the benefit of Australians (https://www.ga.gov.au/eftf). At its heart, the program is about stimulating industry now to ensure a sustainable, long-term future for Australia through an improved understanding of the nation’s minerals, energy and groundwater resource potential. By gathering and analysing geological and geophysical data and making the results publicly available, the program supports regional development and informed decision making across Australia, resulting in jobs and growth. The Energy component of this program is designed to produce pre-competitive information to assist with the evaluation of the hydrocarbon resource potential of onshore basins and attract exploration investment to Australia. As part of the EFTF Natural Hydrogen module, molecular and isotopic analyses were undertaken by Geoscience Australia on natural gas samples from the wells Canunda 2 and Ralgnal 1 from the southwestern margin of the Patchawarra Trough in the Cooper Basin, with the raw data from these analyses being released in this report. Some data from these wells were included in the nationwide studies of helium and hydrogen, as published by Boreham et al. (2018; 2021), and build on previous studies that document the composition of Australian natural gases (Boreham et al., 2001). These data are available through the Geoscience Australia portal at https://portal.ga.gov.au/

<b>IMPORTANT NOTICE: </b>This web service has been deprecated. The Australian Onshore and Offshore Boreholes OGC service at https://services.ga.gov.au/gis/boreholes/ows should now be used for accessing Geoscience Australia borehole data. This is an Open Geospatial Consortium (OGC) web service providing access to a subset of Australian geoscience samples data held by Geoscience Australia. The subset currently relates specifically to Australian Boreholes.

<b>IMPORTANT NOTICE:</b> This web service has been deprecated. The Australian Onshore and Offshore Boreholes OGC service at https://services.ga.gov.au/gis/boreholes/ows should now be used for accessing Geoscience Australia borehole data. This is an Open Geospatial Consortium (OGC) web service providing access to a subset of Australian geoscience samples data held by Geoscience Australia. The subset currently relates specifically to Australian Boreholes.

The Roebuck Basin on Australia’s offshore north-western margin is the focus of a regional hydrocarbon prospectivity assessment being undertaken by the Offshore Energy Studies section. This offshore program is designed to produce pre-competitive information to assist with the evaluation of the hydrocarbon resource potential of the central North West Shelf and facilitate exploration investment in Australia. The recent oil and gas discoveries at Phoenix South 1 (2014), Roc 1 (2015-16), Roc 2 (2016), Phoenix South 2 (2016), Phoenix South 3 (2018), Dorado 1 (2018), Dorado 2 (2019) and Dorado 3 (2019) wells in the Bedout Sub-basin demonstrate the presence of a petroleum system in Lower Triassic strata (Thompson, 2020; Thompson et al., 2015 and 2018). The current study aims to better understand this new petroleum system and establish its extent. As part of this program, a range of organic geochemical analyses were acquired on source rocks from the Roc 2 well with these data released in this report.

<b>IMPORTANT NOTICE:</b> This web service has been deprecated. The Hydrochemistry Service OGC service at https://services.ga.gov.au/gis/hydrogeochemistry/ows should now be used for accessing Geoscience Australia hydrochemistry analyses data. This is an Open Geospatial Consortium (OGC) web service providing access to hydrochemistry data (groundwater analyses) obtained from water samples collected from Australian water bores.

<b>Legacy service Retired 29/11/2022 IMPORTANT NOTICE: </b>This web service has been deprecated. The Australian Onshore and Offshore Boreholes OGC service at https://services.ga.gov.au/gis/boreholes/ows should now be used for accessing Geoscience Australia borehole data. This is an Open Geospatial Consortium (OGC) web service providing access to Australian onshore and offshore borehole data. This web service is intended to complement the borehole GeoSciML-Portrayal v4.0 web service, providing access to the data in a simple, non-standardised structure. The borehole data includes Mineral Drillholes, Petroleum Wells and Water Bores along with a variety of others types. The dataset has been restricted to onshore and offshore Australian boreholes, and bores that have the potential to support geological investigations and assessment of a variety of resources.