Utilizing DAS VSP for orebody imaging at Oak Dam IOCG

Seismic methods have emerged in recent years as a potentially lower-cost alternative to core logging for mineral deposits mapping. However, in many places like Australia, land access can be restrictive posing many challenges to seismic data acquisition. To circumvent this, Distributed Acoustic Sensing (DAS) Vertical Seismic Profiling (VSP) can be employed to achieve minimal environmental footprint. DAS has grown in popularity for subsurface imaging especially in hydrocarbon exploration due to its many benefits including low cost, ease of deployment, and the potential for near continuous sampling in both space and time. However, application of DAS for hard rock seismic has not seen much success. Part of the problem is the inherent challenges with hard rock seismic including low impedance contrast and lack of coherent reflectors. In addition, DAS data suffers from lower S/N compared to its geophone counterpart. In this work, we showcase a successful application of DAS VSP for Oak Dam iron-oxide copper gold (IOCG) deposit where sufficient surface seismic data could not be acquired due to land access restriction. Illumination study confirms that seismic signal from the west flank of the ore body is better recorded by DAS data. This makes DAS a key component to velocity model building and imaging of the ore body. A combination of high-end processing techniques including joint DAS and surface seismic 30Hz Dynamic Resolution Time Lag Full Waveform Inversion (DR-TLFWI) and Least-Squares 3D Kirchhoff Pre-stack Depth Migration (LSKirPSDM) were employed to obtain a good P-velocity model and reduce the migration swings and noise that were pervasive in this data. The final DAS VSP image complements the surface seismic image and agrees well with the ore body model obtained independently from drill holes.