Seismic properties of the Voisey's Bay massive sulfide deposit: Insights into approaches to seismic imaging

Seismic methods offer significant potential advantages for minerals exploration over more traditional geophysical techniques because of the comparatively high resolution of seismic imaging. This is particularly true as minerals exploration is required to explore deeper to find resources. However, adaptation of seismic imaging techniques to the complex crystalline targets common in the mining environment requires a thorough understanding of the physical properties of the specific combination of ore and host rocks under consideration to choose an appropriate imaging technique. Analysis of the sulfide ores and associated host rocks from the Voisey's Bay nickel-copper-cobalt deposit indicates that in the pyrrohotite-pentlandite-rich but pyrite-poor assemblage at Voisey's Bay, seismic velocities are significantly lower (mean similar to 4500 m/s) than either the felsic or mafic host rocks (mean similar to 5900 m/s and similar to 6400 m/s). This observation is in contrast with pyrite-rich massive sulfide ores that have velocities that are significantly higher than typical host rocks. The large velocity contrast between the Voisey's Bay ores and their host rocks makes them good targets for tomographic imaging. However, due to the trade-off between the low velocities and high densities of the Voisey's Bay sulfides, acoustic impedance contrasts can be quite modest making them less attractive for seismic reflection imaging. Detailed analysis of two different mineralized zones at Voisey's Bay further demonstrated that, depending on the limiting signal-to-noise ratio, the choice of an effective seismic imaging technique is not universal across a mineral deposit and may be affected by subtle variations in sulfide mineralogy and by the structural/magmatic setting. Our analysis clearly indicated that knowledge of physical properties and geologic setting is critical to the choice of which seismic technique to apply in a given exploration setting.