Compiled laboratory measurements of the densities (p) and compressional (V•) and shear (V s) wave ve-locities of common rocks demonstrate that the velocities of silicate rocks increase with density along the Nafe-Drake curve as the rocks become more mafic and increase in metamorphic grade. Reflection coefficients calculated from impedance contrasts between felsic and mafic rocks and other common lithologies in hardrock terranes often exceed 6%, the estimated minimum value required to give strong reflections. This finding is consistent with observations of deep structure and stratigraphy in high-grade terranes using seismic reflection. Sulfides lie far to the right of the Nafe-Drake curve in a large velocity-density field controlled by mixing lines connecting individual sulfide minerals and their hosts. The elastic properties and acoustic impedances of massive sulfides differ significantly from those of most common host rocks, suggesting that large massive sulfide deposits should be detectable as reflectors or scatterers using high-resolution seismic reflection techniques, a prediction confirmed by recent VSP, 2D and 3D MCS surveys in Canada. Laboratory measurements of acoustic velocities under in-situ conditions provide the basis for the interpretation of seismic refraction and stacking velocities in terms of lithology.

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.

Multioffset, multiazimuth downhole seismic data were acquired at Halfmile lake, New Brunswick, to image known massive sulfide lenses and to investigate the potential existence of a steeply dipping mineralized zone connecting them. The massive sulfide lenses, which have significantly higher elastic impedances than host rocks, produce strong scattering. The downhole seismic data show prominent scattered (P‐P and S‐S) and mode‐converted (P‐S and S‐P) waves originating from the deposit. Such complex scattering from massive sulfide ore was not observed previously in vertical seismic profiling data. Migration of the scattered and mode‐converted waves from several shot points imaged different parts of the deepest lens. The scattered S‐waves and mode‐converted waves provide additional imaging capabilities that should be considered when selecting downhole seismic methods for mining exploration.

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