Geophysical interpretation and tectonic synthesis of the Proterozoic southern McArthur Basin, northern Australia

Abstract

The southern McArthur Basin is highly prospective for sediment-hosted Zn-Pb-Ag mineralisation, and hosts the McArthur River and Teena deposits within the Batten Fault Zone. The basin formed in response to widespread extension and thermal subsidence, and was subsequently deformed during crustal shortening events that affected the North Australian Craton during the Proterozoic. Mineralisation is hosted in structurally controlled sub-basins that formed during deposition of the middle McArthur Group. Recognition of structures controlling these sub-basins has traditionally been challenging because overprinting relationships from several extension and crustal shortening events created a complex fault and depositional architecture. In this work, we interpret and model newly acquired and existing gravity, magnetic and seismic data to better understand the regional structural architecture and evolution of the southern McArthur Basin. Important for base metal exploration, results from this study suggest that the prospective lower Barney Creek Formation was deposited during intermittent, and broadly north–south-directed extension at ca. 1645–1640 Ma. This caused strike-slip movement along major north-northwest-trending faults, and normal movement along east–west to east-northeast-trending faults. Faulting resulted in significant sub-basin deepening in some areas, and uplift and erosion in others. These sub-basins developed in transtensional segments of strike-slip faults, and adjacent to normal faults. Geophysical modelling also identified an anomalously thick pile of mafic volcanics within the early basin fill represented by the Tawallah Group. This is significant because mafic volcanics have previously been interpreted as the source of base metals within the region, and the thick volcanic pile we identified occurs in close proximity to the McArthur River and Teena deposits. Sub-basin bounding faults that were active during mineralization tap into this anomalously thick pile of volcanics, suggesting that they likely represented fluid pathways for ascending metalliferous brines.