Seismic imaging of massive sulfide deposits .3. Borehole seismic imaging of near-vertical structures

Surface seismic profiling is well suited for geologic provinces characterized by low to moderate dip, but it is less effective where dips exceed 65 degrees due to inherent limitations of the recording geometry and processing algorithms. Vertical seismic profiling (VSP), a method used mainly for hydrocarbon exploration in sedimentary basins, overcomes this limitation by utilizing deep boreholes as an alternative acquisition datum. Here, we evaluate the effectiveness of this method for imaging massive sulfide deposits associated with folded and steeply dipping volcanic units near the Kidd Creek orebody in Ontario, Canada. Small (150-225 g) explosive charges placed in a water-filled pit provided a consistent energy source, with sufficient band width and signal penetration to image the target zone to a depth of at least 1.0 km. After preliminary processing, the vertical seismic profile record sections were mapped into cross sectional format using a transformation based on ray tracing. This transformation facilitates the extrapolation of subsurface contacts updip from borehole intersections, and the resulting images delineate several stratigraphic contacts in addition to a prominent seismic reflection from a massive sulfide body.