Distant off-fault damage and gold mineralization: The impact of rock heterogeneity

- Mechanical heterogeneity exerts first-order control on fracture/fault evolution.
- Off-fault damage can develop at large distances from principal slip surfaces.
- Damage continues to evolve even after linkage on adjacent stepovers.

Field observations have established that fault-related damage can occur at locations, far from the principal slip surface, which are well outside the fractured region currently predicted by models of fault damage. We use a finite element model to simulate fracture initiation due to fault linkage and show how variations in rock properties allow off-fault damage to develop at surprisingly large distances away from the main fault. Off-fault damage continues to grow even after two adjacent, closely spaced fault segments have interacted and linked. We demonstrate that this process was important for the formation of fracture-hosted gold deposits in the Mount Pleasant goldfield, Western Australia. The strength of lithological contacts also has a significant impact on off-fault damage location and intensity. Our approach may go some way to explaining the non-intuitive distribution of mineralization in certain mineral systems, as well as being applicable to predict subsurface fracturing and fluid flow in hydrothermal/geothermal reservoirs.