Pre‐stack depth imaging techniques for the delineation of the Carosue Dam gold deposit, Western Australia

Abstract

In this study, we explore the latest generation of seismic imaging algorithms (migration) that have been successful in the oil and gas exploration industry and apply them in the more challenging hard rock environment. Seismic migration is a crucial processing step required to build an accurate image of the Earth's subsurface. The seismic method applied in a hard rock environment has a specific set of challenges: complex geological settings often comprised of steeply dipping interfaces and heterogeneities (faults, fracture zones, thrusts, etc.); spatially variable zones of alteration, low intrinsic signal‐to‐noise ratio; complex near‐surface conditions (the weathered overburden has a very high contrast in seismic properties with base formations). Here, we present how a dense source–receiver 3D grid in combination with the latest pre‐stack depth imaging techniques can image the geology with a remarkable level of detail and to depths as shallow as the top of fresh rock. We also propose a comprehensive velocity model building strategy applied specifically to the Carosue Dam deposit, Western Australia, which is mainly characterized by volcaniclastic and volcanic rocks within the Carosue Basin disrupted by a complex system of gold‐bearing faults. To arrive at an optimized velocity model for pre‐stack depth imaging, we combine drillhole data with tomographic refinement. Excellent correlation between resultant seismic images and refraction tomography, vertical seismic profiling and drillholes can be attributed to the integrated velocity model building workflow used for depth migration.