Structure, contents and setting of Pb-Zn mineralisation in the McArthur Basin, northern Australia

Quantitative regional geophysical analysis of the McArthur Basin in northern Australia has shown that it includes sequences with a total thickness in excess of 20 km. Little of the deeper section, which includes thick volcanic and rift sequences, is exposed but the implied stratigraphy is consistent, and may be grossly correlated, with the adjacent western sequence of the Mt Isa Basin. Thick basal felsic and covering flood basalts can be inferred within the primary rift structures. Thinner cover sequences, including the predominantly siliciclastic Tawallah and dolomitic McArthur Groups, are developed in subsidiary basins controlled by underlying rift elements while the overlying Roper Group is much thicker and more widespread. Major erosive events are recognisable across the basin. Most tectonic activity has been focused in the zone known as the Batten Trough although this name is not appropriate because the region has been largely uplifted throughout its history. Other uplifted zones such as the Murphy Tectonic Zone tend to be oriented east-southeast to east-northeast across an original crustal grain which may have been oriented northwest-southeast and north-northeast-south-southwest. The basin may have evolved from a series of aligned convective cells which produced a disjointed rift pattern along strike. Older basin elements were not simply connected but were overtopped and the covering sequences have interlinked. No clearly defined ultimate limits have been recognised for the basin which appears to be an extension of the Mt Isa Basin to the southeast. Significant Pb-Zn mineralisation within the basin appears to be related to regions where rift margins have been persistently uplifted. Known mineralised sites lie on the rim horsts in zones where crustal fracturing is focused, and where young granitoids, which may have influenced basin circulation, are nearby.