The Sudbury Structure on the southern margin of the Superior craton was created by a catastrophic explosion in 1.85 Ga and hosts one of the world's largest Ni‐Cu reserves. As a unique terrestrial geological feature, its genesis has been vigorously debated for more than a century. In an effort to optimize the image from seismic reflection data acquired across the center of the Sudbury Structure, we have developed a straight‐line common midpoint binning strategy and employed cross‐dip corrections. These pseudo‐three‐dimensional seismic processing techniques, coupled with standard processing methods, have overcome limitations associated with conventional two‐dimensional seismic data processing and have substantially enhanced the seismic image, warranting a more detailed and reliable structural interpretation. The new image has revealed a major, previously unrecognized, zone of imbricated NW thrusts. Interpretation of these thrusts provides critical timing constraints relating the Sudbury tectonic deformation to deposition of the Sudbury Basin sediments. The Onwatin argillites are penetrated by blind thrust faults, whereas the overlying Chelmsford turbidites are undeformed and most likely postdate the thrusting. Thus the uniform paleocurrent trends observed in the Chelmsford reflect subsequent deformation history and may be dismissed as evidence against an impact origin. Based on our interpretation of the seismic image, the original volume of the Sudbury Igneous Complex, likely an impact melt sheet, is ∼1 × 104 km3, supporting the claim that the Sudbury Structure represents the eroded and tectonized remanent of one of the largest known impact structure (∼200 km) on Earth.

Following extensive petrophysical studies and presite surveys, the Trill area of the Sudbury basin was selected for conducting the first 3-D seismic survey for mineral exploration in North America. The 3-D seismic experiment confirms that in a geological setting such as the Sudbury Igneous Complex, massive sulfide bodies cause a characteristic seismic scattering response. This provides an excellent basis for the direct detection of massive sulfides by seismic methods. The feasibility study suggests that high‐resolution seismic methods offer a large detection radius in the order of hundreds to thousands of meters, together with accurate depth estimates.

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Laboratory studies show that the acoustic impedances of massive sulfides can be predicted from the physical properties (V p , density) and modal abundances of common sulfide minerals using simple mixing relations. Most sulfides have significantly higher impedances than silicate rocks, implying that seismic reflection techniques can be used directly for base metals exploration, provided the deposits meet the geometric constraints required for detection. To test this concept, a series of 1-, 2-, and 3-D seismic experiments were conducted to image known ore bodies in central and eastern Canada. In one recent test, conducted at the Halfmile Lake coppernickel deposit in the Bathurst camp, laboratory measurements on representative samples of ore and country rock demonstrated that the ores should make strong reflectors at the site, while velocity and density logging confirmed that these reflectors should persist at formation scales. These predictions have been confirmed by the detection of strong reflections from the deposit using vertical seismic profiling and 2-D multichannel seismic imaging techniques.

Reflection seismic and borehole geophysical data place important constraints on the subsurface geometry of the Sudbury Structure, which is the site of the world's largest Ni‐Cu camp. Seismic reflections can be traced from outcrop within the Sudbury North Range to about 4.5 km depth beneath the center of the Sudbury Basin, where the layer thickens abruptly from 1 to 3 km. Further south the North Range norite can be followed to about 10 km depth beneath the South Range. Borehole studies show systematic variations of p‐ and s‐wave velocity, Poisson's ratio and density within the Igneous Complex. Quartz‐rich granophyre is distinguished from the norite and footwall rocks by relatively low Poisson's ratios (0.20–0.23 versus 0.23–0.25). These changes in physical rock properties define an important subdivision of the Igneous Complex, compatible with a simple model involving differentiation of melted crustal rock into dominantly felsic and mafic components. This study documents the importance of interlayering to the seismic reflection response of the crystalline crust.