Trial of tunnel radar for cavity and ore detection in the sudbury mining camp, Ontario

The utility of ground penetrating radar (GPR) in metalliferous mines for cavity detection and orebody delineation is under investigation at Ecole Polytechnique. As a first stage in this investigation, fixed offset Pulse Ekko IV radar profiles were read in underground mine drifts at Sudbury in August 1993. At Stobie Mine a 3.7m diameter ventilation shaft was detected unequivocally using unshielded 100MHz antennas, at ranges between 12 and 16m, and an orepass was located at a range of 10m. This demonstrated that GPR is effective in 5m x 5m mine drifts, provided target travel times are greater than about 80ns, corresponding to a range of approximately 5m in Stobie metasediments and greenstones. Reverberation within the drift could obscure reflections from closer targets. Attempts to map massive sulphide ore contacts within 10m of drift walls at Lower Coleman Mine were unsuccessful. This outcome is attributed to sulphide blebs and stringers in the host rock which increase the intensity and longevity of reverberations within the drift (by enhancing the reflectivity of the walls) and which also scatter and attenuate any radar signals propagating to and from the contact. "Geologically minor" sulphide concentrations can thus seriously compromise the effectiveness of radar. Further ore delineation work should be focussed on massive sulphide bodies which make sharp contact with barren host rocks.