Carson, Chris1, Henson, Paul1, Lidena, Carr1, Southby, Chris1 and Anderson, Jade1.
1Geoscience Australia, Canberra, Australia
Proterozoic rocks of the South Nicholson region, which straddle the NT and QLD border, are juxtaposed between the Proterozoic Mount Isa Province to the east and the southern McArthur Basin to the northwest. The McArthur Basin and Mount Isa Province are comparatively well-studied and prospective for energy and mineral resources. In contrast, rocks of the South Nicholson region are mostly undercover and, as such, there is incomplete understanding of their geological evolution, relationship with adjacent geological provinces and resource potential. To address this gap, two deep crustal seismic reflection surveys, the South Nicholson and Barkly surveys (completed in 2017 and 2019, respectively), were conducted across the South Nicholson region by Geoscience Australia, under the federally funded Exploring for the Future (EFTF) initiative, in collaboration with the Northern Territory Geological Survey, the Geological Survey of Queensland and AuScope (e.g. Carr et al., 2019, 2020). While the Barkly seismic data are still being interpreted, these seismic datasets, together with other complementary regional studies, provides an improved understanding of the geological evolution and resource potential across this poorly understood region.
Both seismic surveys targeted both suspected undercover sedimentary basins and known crustal structures to resolve regional subsurface fault geometry. A key finding from the South Nicholson seismic survey is the discovery of a large concealed sedimentary sag basin that is up to 8 km deep, around 120 km wide and 190 km from north to south, called the Carrara Sub-basin (e.g. Carr et al., 2019). The sub-basin is interpreted to contain Mesoproterozoic to late Paleoproterozoic rocks equivalent to those outcropping in the Lawn Hill Platform and Mount Isa Province. The eastern end of the one of the lines (17GA-SN1), connects with a legacy seismic line that intersects the world class Pb-Zn Century deposit on the Lawn Hill Platform, the late Paleoproterozoic host rocks of which can be traced into the Carrara Sub-basin.
The South Nicholson profiles also reveal a series of ENE–trending, north-dipping half grabens which evolved during two episodes of crustal extension, at ca. 1725 Ma and ca. 1640 Ma, broadly coinciding with structural and basin forming events identified from the Lawn Hill Platform and the Mount Isa Province. Inversion of the half-graben bounding faults, resulting in south–verging thrusts, probably commenced during N-S crustal contraction characteristic of the early Isan Orogeny at ca. 1600-1580 Ma to at least the Paleozoic Alice Springs Orogeny (ca. 400-300 Ma).
Furthermore, our comprehensive regional geochronology program proposes extensive revision of regional stratigraphic relationships. Some successions, previously mapped as Mesoproterozoic South Nicholson Group may instead represent late Paleoproterozoic successions, that form part of the highly prospective Isa Superbasin (and the broadly stratigraphic equivalent McArthur Group in the McArthur Basin), which hosts numerous viable base metal deposits and is prospective for energy commodities (e.g. Jarrett et al., 2020; MacFarlane et al., 2020). Our findings significantly expand the extent of highly prospective late Paleoproterozoic stratigraphy across the South Nicholson region, which, possibly, extends an as yet unknown distance west beneath the Georgina and Carpentaria basins.
Carr, L.K., et al., 2019. Exploring for the Future: South Nicholson Basin Geological summary and seismic data interpretation. Record 2019/21. Geoscience Australia, Canberra. http://dx.doi.org/10.11636/Record.2019.021
Carr, L.K., et al., 2020. South Nicholson seismic interpretation. In: Czarnota, K., et al., (eds.) Exploring for the Future Extended Abstracts, Geoscience Australia, http://dx.doi.org/10.11636/132029
Jarrett A.J.M., et al., 2020. A multidisciplinary approach to improving energy prospectivity in the South Nicholson region. In: Czarnota, K., et al., (eds.) Exploring for the Future Extended Abstracts, Geoscience Australia, http://dx.doi.org/10.11636/134164
MacFarlane, S. et al., 2020. A regional perspective of the Paleo- and Mesoproterozoic petroleum systems of northern Australia In: Czarnota, K., et al., (eds.) Exploring for the Future Extended Abstracts, Geoscience Australia, http://dx.doi.org/10.11636/133716
Chris has worked in Antarctica, Canadian Arctic, Alaska, New Caledonia and northern and central Australia, specialising in metamorphic petrology, geochronology and structural geology. Joining Geoscience Australia in 2006 he dabbled in SHRIMP geochronology and, in 2017, joined the Onshore Energy program, working in the South Nicholson region of the NT.