High-resolution seismic reflection imaging of a thin, diamondiferous kimberlite dyke

Seismic reflection techniques are, for the first time, used to image a thin, diamondiferous kimberlite dyke from subcrop to depths greater than 1300 m. Geophysical exploration for kimberlite deposits typically involves airborne potential field surveys that are well suited for detecting vertical outcropping pipes but often fail to reveal thin, subhorizontal dykes and sills. Because seismic techniques are especially well suited for mapping structures that have shallow dips and strong impedance contrasts, a feasibility study and seismic reflection survey were undertaken on the diamondiferous Snap Lake dyke (Northwest Territories, Canada) to evaluate the potential for using seismic techniques on these targets. The dyke (average thickness 2-3 m) provides an excellent test site because a drilling program has defined the gross dyke geometry and provides core samples from the kimberlite and host rocks. ne feasibility study involved measuring P-velocity and density of selected cores. Using these data, reflectivity and finite-difference synthetic seismogram techniques were used to explore the resolution limitations and determine the acquisition parameters for a reflection survey. ne seismic survey included two 2D lines designed to obtain comparative data sets from different sources (explosives and vibroseis) and ground types (land or lake-ice). ne explosive-source land data yielded a superb image of the thin dyke. The vibroseis data, however, detected the dyke only when sources and geophones were on land; the dyke was not imaged beneath the ice due to reverberation and attenuation effects. Correlations are observed between reflection attributes and dyke properties (thickness, structure, and physical properties). The results demonstrate that, in the appropriate situation, seismic methods have great potential for use in kimberlite exploration, subsurface mapping, and detailed imaging for mine development purposes.