APPLICATION OF SEISMIC METHODS TO MINERAL EXPLORATION

Plots of compressional (Vp) and shear (Vs) wave velocity vs. density for rocks at elevated confining pressures show that velocities tend to increase with density along the well known Nafe-Drake curves for silicate rocks. Because of their high densities, however, many ores fall far to the right of the Nafe-Drake curves and display higher impedances than their common hosts, suggesting that it should be possible to detect and prospect for ores using high-resolution reflection techniques if the deposits meet the size, thickness, and presentation constraints required for reflection or diffraction. Experiments conducted by the Geological Survey of Canada, universities, and industry in hardrock mining camps across Canada over the past decade show that 2-D surveys are well suited to the determination of structure and the detection of orebodies, while 3-D surveys may be used for detection and delineation, and vertical seismic profiling (VSP) for delineation. Due to the small size of most deposits, the structural complexity of hard rock terranes and their low signal-to-noise ratios, the best results are obtained from carefully designed surveys using high frequency sources and customized processing sequences designed to identify both reflections and diffractors. 2-D and 3-D surveys have successfully detected and imaged large massive sulphide deposits such as the magmatic and volcanic massive sulphide (VMS) deposits in Sudbury and Bathurst and should also be useful for the detection of massive sedimentary exhalitive (SEDEX) and iron oxide copper gold (IOCG) deposits. Other types of deposits are more likely to be detected indirectly: lode gold and porphyry deposits by reflections from alteration haloes, unconformity Uranium deposits by haloes and basement offsets, and Mississippi Valley-type (MVT) deposits by white spots in otherwise reflective carbonates. Similarly, the high impedances between kimberlites and their hosts allow pipes to be delineated using VSP techniques.