GEOPHYSICAL INTERPRETATION AND MODELLING OF THE SOUTHERN MCARTHUR BASIN, NORTHERN AUSTRALIA: IMPLICATIONS FOR SUB-BASIN DEVELOPMENT AND BASE METALS MINERALISATION (Invited Presentation)

The Palaeo- to Mesoproterozoic McArthur Basin located in the north-east of the Northern Territory (Australia) is highly prospective for sediment hosted Zn-Pb-Ag mineralisation. Mineralisation is hosted within structurally controlled sub-basins, and several world-class deposits (e.g., McArthur River and Teena) have been discovered in the 50-80 km wide structural corridor known as the Batten Fault Zone. The Batten Fault Zone preserves a complex stratigraphic and fault architecture that developed during multiple episodes of extension and mild crustal shortening. The complex architecture and poor exposure of the basin has made recognition of sub-basins challenging.

To better understand the regional structural architecture and sub-basin development, this study integrated geophysical interpretation and modelling with detailed sedimentology and sequence stratigraphy. Interpretation of gravity, magnetic, radiometric and AEM data helped to delineate the spatial distribution of sedimentary rocks and determine the extent and overprinting relationship of faults. Seven forward models of the gravity and magnetic data constrained by available seismic data were produced to understand the geometry of major faults and broad scale variations in the preserved thickness of stratigraphy. Integration of these results with a newly developed stratigraphic framework allowed observations of depositional cycles and shifting depocentres to be placed in context of the structural framework of the basin.

Results from this integrated geophysical and geological analysis suggest two styles of sub-basins developed within the Batten Fault Zone under broadly north-south directed extension. These include transtensional sub-basins, which developed between segments of the north–northwest-trending Emu Fault Zone, and east–west-trending sub-basins developed adjacent to east–west-trending normal and north–northwest-trending transfer faults. Forward modelling of the gravity data also suggests the presence of a thick mafic volcanic pile located within basal sequences of the McArthur Basin. These volcanics are located proximal to known Pb-Zn-Ag deposits in the region and may have been an important source for base metals.