Exploring for the future presentation- The structure and stratigraphy of the South Nicholson region – implications for resource prospectivity; Insight from the EFTF geochronology and deep reflection seismic programs

The Exploring for the Future Program (EFTF) is a $100.5 million four year, federally funded initiative to better characterise the mineral, energy and groundwater potential of northern Australia. As part of this initiative, this record presents new whole-rock geochemistry data from 967 samples of sedimentary rocks sampled from 26 wells in the South Nicholson region, including the Proterozoic South Nicholson Basin and Lawn Hill Platform, the Neoproterozoic to Devonian Georgina Basin and the Jurassic to Cretaceous Carpenteria Basin. This work complements other components of the EFTF program, including the South Nicholson Basin seismic survey, a comprehensive geochronology program and hydrocarbon prospectivity studies to better understand the geological evolution and basin architecture of the region, and facilitate identification of areas of unrecognised resource potential and prospectivity. The South Nicholson region, straddling north-eastern Northern Territory and north-western Queensland, arguably represents one of the least geologically understood regions of Proterozoic northern Australia. The South Nicholson region is situated between two highly prospective provinces, the greater McArthur Basin in the Northern Territory, the Lawn Hill Platform and the Mount Isa Province in Queensland, both with demonstrated hydrocarbon and base metal potential. These new geochemical data provide baseline understanding of regional resource prospectivity of sedimentary rocks in the South Nicholson region. During 2017 and 2018, 967 drill core and cuttings were sampled from 26 legacy boreholes that intersected the South Nicholson region housed in Northern Territory Geological Survey’s core repository in Darwin, the Geological Survey of Queensland’s core repository in Brisbane and Geoscience Australia’s core repository in Canberra. This data release contains the results of elemental analyses on these samples, which include X-Ray Fluorescence (XRF), Loss-On-Ignition (LOI), Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) for all samples, in addition to ron titration (FeO) for selected samples. The data was generated in the Inorganic Geochemistry laboratory at Geoscience Australia between 2017 and 2019 as part of the EFTF program. All data was quality controlled based on Certified Reference Material standards (CRMs) and duplicate samples analysed with each batch of samples.

The ca. 1.4 billion years (Ga) old Roper Group of the McArthur Basin, northern Australia, is one of the most extensive Proterozoic hydrocarbon-bearing basins deposited in a large epeiric sea known as the Roper Seaway. Black shales from the Velkerri Formation were deposited in a deep water shoaling sequence and are well preserved in the Altree 2 drillcore in the Beetaloo Sub-basin. These shales were analysed to determine their organic geochemical (biomarker) signatures which were used to interpret the microbial diversity and palaeoenvironment of the Roper Seaway. The results were integrated with published inorganic geochemistry and microfossil distributions. The indigenous hydrocarbon biomarker assemblages describe a water column dominated by bacteria with large scale heterotrophic reworking of the organic matter in the water column or bottom sediment. Evidence for microbial reworking includes a large unresolved complex mixture (UCM) and high ratios of monomethyl alkanes relative to n-alkanes—features characteristic of indigenous Proterozoic bitumen. Steranes, biomarkers for single-celled and multicellular eukaryotes, were below detection limits in all extracts analysed, despite eukaryotic microfossils having been previously identified in the Roper Group. These data suggest that eukaryotes, while present in the Roper Seaway, were ecologically restricted and contributed little to the net biomass. The combination of increased dibenzothiophene in the middle Velkerri Formation and low concentrations of 2,3,6-trimethyl aryl isoprenoids throughout the Velkerri Formation suggest that the water column at the time of deposition was transiently euxinic. As a comparison we reanalysed extracts from the 1.64 Ga Barney Creek Formation of the McArthur Basin. The biomarker assemblages differ between the Velkerri and Barney Creek Formations between is a biomarkers and water column chemistry, demonstrating that the microbial environments and water column geochemistry were variable in the Proterozoic.

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. The Paleo to Mesoproterozoic Birrindudu Basin is an underexplored frontier basin located in northwestern Northern Territory and northeastern Western Australia. The Birrindudu Basin is a region of focus for the second phase of the EFTF program (2020–2024) as it contains strata of similar age to the prospective McArthur Basin, South Nicholson region and Mount Isa Province, but remains comparatively poorly understood. Geoscience Australia have undertaken (via the service provider, FIT, Schlumberger) stratigraphic reconstructions of bulk volatile chemistry from fluid inclusions from an mineral exploration drillhole LBD2, Birrindudu Basin, located in the northwest Northern Territory This ecat record releases the final report and raw data files (*.LAS) by FIT Schlumberger. Company reference number FI230005a.

Zircon and xenotime U–Pb SHRIMP geochronology was conducted on samples from the South Nicholson Basin, and western Mount Isa Orogen. These samples were collected from outcrop and core from the Northern Territory and Queensland. The age data indicate the South Nicholson Basin was deposited after ca 1483 Ma but deposition most likely had ceased by ca 1266 Ma; the latter age likely represents post-diagenetic fluid flow in the area, based on U–Pb xenotime data. Geochronology presented here provides the first direct age data confirming the South Nicholson Group is broadly contemporaneous with the Roper Group of the McArthur Basin, which has identified facies with high hydrocarbon prospectivity. In addition, geochronology on the Paleoproterozoic McNamara Group provides new age constraints that have implications for the regional stratigraphy. The data obtained in this geochronological study allow for a comprehensive revision of the existing stratigraphic framework, new correlations and enhances commodity prospectivity in central northern Australia.

The Proterozoic alkaline and related igneous rocks of Australia web map service depicts the spatial representation of the alkaline and related rocks of Proterozoic age.

The Exploring for the Future program is an initiative by the Australian Government dedicated to boosting investment in resource exploration in Australia. As part of the Exploring for the Future program, this study aims to improve our understanding of the petroleum resource potential of northern Australia. This data release presents the bulk kerogen kinetics of 21 potential source rocks from the McArthur Basin and the Lawn Hill Platform to understand the rate of hydrocarbon conversion. Kerogen was isolated from bulk rock, and analysed by a Rock-Eval 6 (Vinci Technologies, France) using four different temperature ramps. All sample preparation and analyses were carried out in Geoscience Australia’s in-house laboratories. The results of this study can be used to improve our understanding of the hydrocarbon generative potential of Proterozoic aged source rocks in northern Australia.

The Proterozoic alkaline and related igneous rocks of Australia web map service depicts the spatial representation of the alkaline and related rocks of Proterozoic age.

The Proterozoic alkaline and related igneous rocks of Australia web map service depicts the spatial representation of the alkaline and related rocks of Proterozoic age.

<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.</div><div><br></div><div>The Paleo to Mesoproterozoic Birrindudu Basin is an underexplored frontier basin located in northwestern Northern Territory and northeastern Western Australia. The Birrindudu Basin is a region of focus for the second phase of the EFTF program (2020–2024) as it contains strata of similar age to the prospective McArthur Basin, South Nicholson region and Mount Isa Province, but remains comparatively poorly understood.</div><div><br></div><div>Geoscience Australia have undertaken (via the service provider, FIT, Schlumberger) Fluid Inclusion Petrography and Microthermometry analysis of samples for the drillhole 99VRNTGSDD1, Birrindudu Basin, located in the northwest Northern Territory (Company reference number MT#F1230005c).</div><div><br></div><div>This eCat Record accompanies the report containing the results of fluid inclusion stratigraphy on this drillhole (eCat record 148973).</div>