Toward a Mineral System Understanding of the Palaeoproterozoic Zinc Belt of northern Australia: Determining Basement Configuration, Basin Shape and Sediment Architecture at 1640 and 1575 Ma.

Abstract

Airborne magnetics, ground gravity, seismic and wireline log geophysical datasets are integrated with outcrop and drill core stratigraphic, structural, geochronology and palaeomagnetic information to derive three forward model profiles for the Palaeo-Mesoproterozoic rocks of the central and northern Lawn Hill Platform of northern Australia. Each profile depicts current basin geometries and sedimentary architecture. Two of the profiles are subsequently reconstructed to depict sediment architecture at 1640 Ma. and 1575Ma., the times of fluid migration at the Grevillea and Walford Creek Prospects and the Century zinc deposit. Surfaces of chronostratigraphic significance are used to constrain the depositional architecture and bound time-equivalent facies packages. This enables basin scale aquitard and aquifer lithologies to be represented, relationships between these shallow- to deep-burial diagenetic packages and basin scale faults to be depicted and fluid migration scenarios to be tested through numerical mechanical and convective modelling simulations. The two north-south profiles depict an early (1800-1740 Ma.) Leichhardt Superbasin phase of basin-geometries related to E-W extension. This template controlled subsequent extension during the 1740-1680 Ma. Calvert Superbasin. Rocks of the overlying Isa Superbasin can be split into an upper (1640-1575Ma.) and a lower (1680-1640Ma.) basin phase. Rocks of the lower basin phase include the Gun and Loretta Supersequences characterised by facies relationships that show deeper water facies to the south east and east. Rocks of the overlying River-Doom Supersequences define a southward thickening megawedge whose geometry is controlled by growth on the E-W oriented Little Range Fault.