Redefining copper exploration at Oak Dam IOCG deposit through high-end hardrock seismic processing

The application of seismic methods to mineral exploration has started to gain traction in recent years, as miners are increasingly looking to enhance understanding of deep deposits in order to optimize drilling campaigns and meet growing demands. However, widespread adoption is still limited due to the inherent challenges faced by hard rock seismic exploration. This includes low impedance contrast, lack of coherent sub-horizontal reflectors, and fast subsurface velocities. Recently, Schijns et al. (2023) successfully applied high-end processing, including Time-Lag Full-Waveform Inversion (TLFWI) and 3D Kirchhoff Pre-stack Depth Migration (KirPSDM), to sparse 3D surface seismic data acquired at Olympic Dam, a flagship iron-oxide copper gold (IOCG) deposit. Building on this experience, sparse 3D surface seismic and distributed acoustic sensing (DAS) vertical seismic profiling (VSP) data were acquired at the nearby Oak Dam IOCG deposit. State-of-the-art processing technologies including 30Hz Dynamic Resolution TLFWI (DRTLFWI) with free-surface topography, iterative Least-Squares KirPSDM (LSKirPSDM), and 80Hz Reverse Time Migration (RTM) were employed to obtain a high-quality structural image and P-wave velocity model. The resulting image shows clear delineation of the Hardy Hill Fault, which bounds the mineralisation target. The fault position agrees well with the velocity contrast in the FWI model, further validating the inversion. In the shallow section, velocity inversion at the Tregolana shale layer in the FWI model agrees well with core sample lab measurements. At target depth (~1 km), the identified Hematite breccia complex appears clearly as a low velocity zone in the FWI model with position and size corroborating well with drilling data. The seismic results have allowed, within a relatively short timeframe, a complete and independent revision of the geological model obtained from > 60 km of drilling data. Additionally, velocity lows in the 30Hz FWI model open up new exploration targets with the potential for Hematite breccia-hosted high-grade copper mineralisation.