Numerical Modelling of Fluid Flow During Structural Closure of the Isa Superbasin in the Lawn Hill Platform, Northern Australia

Abstract

Proterozoic rocks of the Isa Superbasin in northern Australia host globally-significant Pb-Zn-Ag deposits as well as a series of Cu, Cu-Au and U deposits. This numerical modelling study explores fluid flow patterns during the shortening deformation event associated with the initial stages of the structural inversion of the Isa Superbasin at ca. 1575 Ma. We have simulated the following scenarios of coupled deformation and fluid flow processes: 1) fundamental basin fluid flow in a basin-inversion environment subject to shortening; 2) syn-tectonic dehydration-related fluid production; 3) the incorporation of hydrofracturing and permeability creation; 4) aquifer permeability changes with depth; 5) the effect on fluid flow of a buried fault versus an open fault. In a scenario only considering the interaction of deformation and fluid flow during basin inversion, intense upward flow along basin-scale faults and strong lateral flow along the well-connected segments of major aquifer horizons dominate the fluid flow field. The combinations of deformation features, aquifer geometry and fault distribution result in different fluid flow patterns across the simulated section, suggesting some fluid compartmentalization, and mineralisation variations in the region. The incorporation of dehydration fluid production and permeability creation both significantly facilitates fluid flow, expressed as greater fluid fluxes and volumes along faults and aquifer units.