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 Mesoproterozoic South Nicholson Basin, straddling the NT and QLD border, sits between, and partly overlies, the Paleoproterozoic components of the Mount Isa Province to the east and the southern McArthur Basin to the northwest. While the McArthur Basin and Mount Isa Province are comparatively well studied and considered highly prospective for both mineral and energy resources, rocks of the South Nicholson region are mostly undercover and, as such, there is incomplete understanding of their geological evolution and resource potential. Geoscience Australia (in collaboration with the Northern Territory Geological Survey and the Geological Survey of Queensland, and co-funded by AuScope) undertook the South Nicholson Basin deep crustal seismic reflection survey (e.g. Carr et al., 2019). This survey was conducted under the federally funded Exploring for the Future (EFTF) initiative, a $100.4 million, four year program to evaluate the resource potential across all of northern Australia.

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.

<p>This Record presents the results of 26 new zircon U-Pb isotopic analyses, conducted on Geoscience Australia’s Sensitive High Resolution Ion Micro Probe (SHRIMP2e), under the Commonwealth Government’s Exploring for the Future (EFTF) program, a $100.5 million, four year, initiative to better understand the mineral, energy and groundwater potential across northern Australia. <p>These new data, determined on sedimentary and volcanic rocks, were collected from across the South Nicholson region, located in the north-eastern Northern Territory. The South Nicholson region is geographically located between two highly prospective geological provinces, the greater McArthur Basin in the Northern Territory and the Mount Isa Province in Queensland, regions noted for their hydrocarbon potential and world-class base-metal endowment. <p>The South Nicholson region has been sparsely investigated by modern geological investigations, and, as such, these new SHRIMP U-Pb data, in concert with other complementary EFTF geochronological, geochemical and geophysical datasets from the region (e.g. Anderson et al., 2019; Carr et al., 2019; Ley-Cooper and Brodie, 2019; Jarrett et al., 2019) will place important geological constraints on the geological evolution, the timing of deposition, sedimentary processes, basin architecture and evolution of the South Nicholson region and, arguably most significantly, provide new improved lithostratigraphic and chronostratigraphic correlations with the adjacent highly prospective Proterozoic Basins. <p>Such geological correlations are critical for reducing exploration risk, improve resource prospectivity and enabling targeted ‘greenfield’ resource exploration activities, a tangible key objective under the Exploring for the Future initiative.

The energy component of Geoscience Australia’s Exploring for the Future (EFTF) program aimed to improve our understanding of the petroleum resource potential of northern Australia. The sediments of the Mesoproterozoic South Nicholson Basin and the Paleoproterozoic Isa Superbasin on the northern Lawn Hill Platfrom (nLHP) are primary targets of the EFTF program, as they are known to contain highly prospective organic-rich units with the potential to host unconventional gas plays. A defining feature of shale gas plays is that they require technological intervention to increase bulk rock permeability and achieve commercial flow rates. The Egilabria prospect, intersecting nLHP sediments in northwest Queensland, flowed gas to surface from a fracture-stimulated lateral well, demonstrating a technical success. Elsewhere in the region, shale gas prospectivity is limited by a lack of well data. Shale rock brittleness in the nLHP part of the Isa Superbasin was analysed in two studies under the EFTF program. These studies showed that shale brittleness ranges from ductile to brittle; zones of brittle shales were present in all supersequences. Shale brittleness is controlled by increasing quartz and decreasing clay content, with carbonate content proving insignificant. Organic-rich target zones in the Lawn and River supersequences are demonstrated to be brittle and favourable for fracture stimulation. <b>Citation:</b> Bailey, A.H.E., Jarrett, A.J.M., Wang, L., Champion, D.C., Hall, L.S. and Henson, P., 2020. Shale brittleness in the Isa Superbasin on the northern Lawn Hill Platform. 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.

NDI Carrara 1 is a deep stratigraphic drill hole completed in 2020 as part of the MinEx CRC National Drilling Initiative (NDI) in collaboration with Geoscience Australia and the Northern Territory Geological Survey. It is the first test of the Carrara Sub-Basin, a depocentre newly discovered in the South Nicholson region based on interpretation from seismic surveys (L210 in 2017 and L212 in 2019) recently acquired as part of the Exploring for the Future program. The drill hole intersected approximately 1120 m of Proterozoic sedimentary rocks unconformably overlain by 630 m of Cambrian Georgina Basin carbonates. Continuous cores recovered from 283 m to a total depth of 1750 m provide samples of the highest quality for a comprehensive geochemical program designed to inform on the energy and mineral prospectivity of the Carrara Sub-basin. Total Organic Carbon (TOC) contents from Rock-Eval pyrolysis of the Cambrian and Proterozoic sections demonstrate the potential for several thick black shales as source rocks and unconventional plays. Evidence for retained hydrocarbons included bituminous oil stains in centimetre-scale vugs within the Cambrian Georgina Basin and several oil bleeds within the Proterozoic section. The latter also contains surface gas with up to 2% methane concentrations measured within carbonaceous mudstones. Geochemical analyses of hydrocarbon shows highlight the occurrence of several petroleum systems operating in this frontier region. The results at NDI Carrara 1 offer the promise of a new exciting resource province in northern Australia.

This petroleum systems summary report provides a compilation of the current understanding of petroleum systems for the South Nicholson Basin and Isa Superbasin region. The contents of this report are also available via the Geoscience Australia Portal at https://portal.ga.gov.au/, called The Petroleum Systems Summary Assessment Tool (Edwards et al., 2020). Three summaries have been developed as part of the Exploring for the Future (EFTF) program (Czarnota et al., 2020); the McArthur Basin, the Canning Basin, and a combined summary of the South Nicholson Basin and Isa Superbasin region. The petroleum systems summary reports aim to facilitate exploration by summarizing key datasets related to conventional and unconventional hydrocarbon exploration, enabling a quick, high-level assessment the hydrocarbon prospectivity of the region.

The structural evolution of the South Nicholson region is not well understood, hindering full appraisal of the resource potential across the region. Here, we outline new insights from a recent deep-reflection seismic survey, collected as part of the Australian Government’s Exploring for the Future initiative. The new seismic profiles, and new field observations and geochronology, indicate that the South Nicholson region was characterised by episodic development of a series of ENE-trending half grabens. These graben structures experienced two major episodes of extension, at ca. 1725 Ma and ca. 1640 Ma, broadly correlating with extensional events identified from the Lawn Hill Platform and the Mount Isa Province to the east. Southward stratal thickening of both Calvert and Isa Superbasin sequences (Paleoproterozoic Carrara Range and McNamara groups, respectively) into north-dipping bounding faults is consistent with syndepositional extension during half graben formation. Subsequent basin inversion, and reactivation of the half graben bounding faults as south-verging thrusts, appears to have been episodic. The observed geometry and offset are interpreted as the cumulative effect of multiple tectonic events, including the Isan Orogeny, with thrust movement on faults occurring until at least the Paleozoic Alice Springs Orogeny. <b>Citation:</b> Carson, C.J.. Henson, P.A., Doublier, M.P., Williams, B., Simmons, J., Hutton, L. and Close, D., 2020. Structural evolution of the South Nicholson region: insight from the 2017 L210 reflection seismic survey. 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.

The Buddycurrawa Volcanics (BV, Benmara Group) are a sequence of trachyte lavas and interleaved shallow-marine siliciclastic rocks, exposed in the Benmara region, northwestern Mount Drummond 1:250 000 map sheet, Northern Territory. Previous information, including resource potential, on the BV was limited, and stratigraphic correlation with other regional volcanic units was speculative. Our new geochronology data establish the extrusion age of the BV as late Paleoproterozoic, constrained by a maximum age of ca. 1662 Ma (SHRIMP U-Pb zircon) and a minimum age of ca 1631 Ma (in situ laser Rb-Sr on glauconite within vesicles). The BV are, therefore, temporally equivalent to numerous ash fall tuffs reported throughout regional highly prospective late Paleoproterozoic successions. The BV also host vertical siliceous pipes, representing ‘white smokers’—peripheral low-temperature equivalents of black smokers—suggestive of a regional shallow-marine hydrothermal circulatory system and potential for associated base metal mineral systems. The BV are pervasively potassically altered. Laser Rb-Sr dating on matrix secondary microcline returns ages ca. 1612–1323 Ma, reflecting timing of fluid flow responsible for at least some of the potassic alteration. These are broadly consistent with similar estimates of episodes of regional fluid flow and base metal mineralisation and/or remobilisation in the Mount Isa Province. <b>Citation:</b> Carson, C.J., Kositcin, N., Farkas, J., Champion, D.C., Whelan, J., Redaa, A., Gilbert. S., Henson, P.A., Maas, R., Williams, B. and Doublier, M.P., 2020. The late Paleoproterozoic Buddycurrawa Volcanics, South Nicholson region. 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.

Following the publication of Geoscience Australia record 2014/09: Petroleum geology inventory of Australia's offshore frontier basins by Totterdell et. al, (2014), the onshore petroleum section embarked upon a similar project for onshore Australian basins. The purpose of this project is to provide a thorough basis for whole of basin information to advise the Australia Government and other stakeholders, such as the petroleum industry, regarding the exploration status and prospectivity of onshore Australian basins. Eight onshore Australian basins have been selected for this volume and these include: the McArthur, South Nicholson, Georgina, Amadeus, Warburton, Wiso, Galilee and Cooper basins. This record provides a comprehensive whole of basin inventory of the geology, petroleum systems, exploration status and data coverage for these eight onshore Australian basins. It draws on precompetitive work programs by Geoscience Australia as well as publicly available exploration results and geoscience literature. Furthermore, the record provides an assessment of issues and unanswered questions and recommends future work directions to meet these unknowns.