The BCGS is excited to kick off the fall season with its first technical talk at this month. Hope to see you there.
SPEAKER: Dr. Ron Clowes
TITLE: High-Resolution Seismic Reflection Imaging of a Thin, Diamondiferous Kimberlite Dyke – A unique experiment
DATE: Tuesday, September 25th 2012
TIME: 4:30pm
LOCATION: Room 451, 409 Granville (UK Building at Granville and Hastings)
ABSTRACT: Seismic reflection techniques, for the first time, have imaged a thin, diamondiferous, kimberlite dyke. Standard exploration techniques for vertical kimberlite pipes fail to reveal subhorizontal or shallow-dipping intrusions whereas seismic reflection may be a suitable tool. A feasibility study and subsequent seismic survey were undertaken on the diamondiferous Snap Lake dyke (Northwest Territories, Canada). A drilling program mapped the dyke as a gently dipping sheet about 2–3 m thick. The feasibility study involved lab measurements of Vp and ρ on core samples and computer modeling to determine necessary acquisition parameters. Two 2-D lines that provide comparative datasets for different sources (explosive and vibroseis) and ground types (land and lake ice) were acquired. The explosive-source profile recorded on land yielded a superb image of the dyke from depths of 60 m to more than 1500 m over a lateral distance of 5700 m, an image that correlates well with adjacent drillhole data. On land the vibroseis source also imaged the dyke, but on ice no image was obtained due to reverberation and attenuation effects. The frequency response and unusually strong reflection amplitudes from the dyke indicate the importance of tuning effects and multiples. Finite-difference modeling confirms the variability observed on the seismic section. Apparent correlations between reflection amplitudes and dyke structure (e.g., thickness, feathering, 3-D geometry) suggest that seismic reflection data may be valuable for guiding drilling programs. Results demonstrate that high-resolution seismic methods have potential for use in kimberlite exploration, subsurface mapping and detailed imaging for mine development purposes.