Understanding regional structural controls on mineralization at the century deposit: A numerical modelling approach

The Century zinc deposit on the Lawn Hill Platform of Northwestern Queensland, Australia, is a world-class sediment-hosted Zn deposit. Despite extensive studies, its genesis is still in debate, as a syngenetic or an epigenetic replacement model. Detailed structural geological work and a recent fluid inclusion study suggest that the formation of the Century deposit is more likely the product of fault-controlled fluid flow and epigenetic replacement processes. However, the mechanism for focusing mineralizing fluids into the intrinsically low permeability ore-hosting shale/siltstone rock unit is still unclear. This numerical modelling study expands on previous investigations by exploring the interaction between deformation and fluid flow in a generic 3D architecture for the Century district. The aims of this study are to explore: 1) how did faults control fluid flow patterns in the district; 2) what were the processes that led to permeability creation and fluid focusing in the low permeability host rocks to the ore bodies; and 3) what were the stratigraphic controls on these processes? Our results suggest factors that facilitated rock tensile failure/dilation and fluid focusing at the Pmh4 level within the siltstone–shale sequences of the Lawn Hill Formation were fault burial depth (“blind” fault versus exposed fault), pore fluid pressure and a relatively-low permeability and high strength of the overlying Widdallion Sandstone.