Ambient Noise Rayleigh and Love Wave Tomography beneath the Sally Palladium Copper Deposit (Ontario, Canada)

Summary Passive seismic imaging is a low-impact, low-cost technique used for exploration of ore deposits. Autonomous seismometers (“nodes”) allow for continuous recording of seismic data for weeks. In addition to improving field operations for traditional active-source surveys, nodes increase the flexibility of seismic survey design and permit low-cost collection of passive seismic data with minimal impact on the local environment. The technique uses ambient seismic noise from natural and anthropogenic sources for subsurface imaging. A seismic velocity model built from analysis of surface wave is used to establish the structure and physical characteristics of materials in the sub-surface. The Sally platinum-group metal (PGM) Deposit is located at the North margin of the Coldwell Complex. The goal of the seismic survey was to determine the structure and geometry of the Eastern Gabbros, a series of high-density, seismically-fast gabbros and pyroxenites that host the mineralization. The resulting surface wave velocity model traced the lower margin of the Eastern Gabbros and also identified a strong velocity anomaly in Archean footwall granodiorite to below the main intrusion (1.5 km in depth). The anomaly seems to coincide with a magnetic anomaly and is interpreted as a pyroxenite intrusion of the type that hosts the PGM mineralisation.