Chronostratigraphic basin framework for Palaeoproterozoic rocks (1730–1575 Ma) in northern Australia and implications for base‐metal mineralisation

Abstract

Sequence‐stratigraphic interpretations of outcrop, drillcore, wireline and seismic datasets are integrated with SHRIMP zircon and palaeomagnetic determinations to provide a detailed chrono‐stratigraphic basin framework for the base‐metal‐rich Palaeoproterozoic rocks of the southern McArthur, Lawn Hill and Mt Isa regions. The analysis forms a basis for future correlations across northern Australia. Nine second‐order unconformity‐bounded supersequences are identified. Supersequences have a duration of 10–20 million years; some hitherto‐unrecognised unconformity surfaces record up to 25 million years of missing rock record. The second‐order supersequences contain a series of nested third‐, fourth‐ and fifth‐order sequences many of which can be correlated across the Mt Isa, Lawn Hill and southern McArthur regions. The analysis relates accommodation history to major intraplate tectonic events evident on the apparent polar wander path for northern Australia. Major tectonic events at approximately 1735 Ma, 1700 Ma, 1670 Ma, 1650 Ma, 1640 Ma, 1615 Ma, 1600 Ma and 1575 Ma impacted on accommodation rates and basin shape in northern Australia. Sub‐basin depocentres, the hosts for major sulfide mineralisation, are attributed to reactivated faults that controlled local subsidence. Pb/Pb model ages of 1653 Ma, 1640 Ma and 1575 Ma for the Mt Isa, McArthur River and Century Pb–Zn–Ag deposits, suggest that changes to intraplate stresses at tectonic events of like age resulted in the migration of metal‐bearing fluids into the sub‐basins. A Pb/Pb model age of 1675 for the Broken Hill deposit suggests that intraplate stresses manifest in northern Australia also affected rocks of similar age further south. Magmatic events close to 1700 Ma (Weberra Granite) and 1675 Ma (Sybella Granite) coincide with times of regional incision and the formation of supersequence‐bounding unconformity surfaces.