3D diffraction and mode-converted scattering signatures of base metal deposits, Bathurst Mining Camp, Canada

The localized and isolated nature of base-metal deposits can generate a complex scattered wavefield that may include P-P, P-S, S-P, and S-S events. Multi-component VSP data have previously confirmed the presence of several wave types scattered by a deep-seated base metal deposit at Halfmile Lake, Bathurst Mining Camp, Canada. However, mode-converted waves scattered from a massive sulphide deposit have not previously been recognized on surface seismic data. In this study, we used 3D surface seismic data acquired with an explosive source and vertical geophones to investigate the possible presence of P-P, P-S, S-P, and S-S events scattered at a base metal, lens-shaped body at about 1.2 km depth. We show that this body produces a diagnostic P-P diffraction and use finite-difference modelling to show it could produce mode-converted scattered signals. Results from a target-oriented azimuthal scattering analysis based on 3D prestack migration reveal amplitude anomalies at the location of the base metal lens for S-P waves and possibly P-S waves. The identification of these events confirms that mode-converted waves scattered from the deep sulphide lens were recorded on the 3D data. However, the real potential of these complementary wave modes for mineral exploration will only be realistically evaluated using P- and S-wave sources and multi-component receivers.