The seismic signature of the Elura orebody

A limited, experimental seismic refraction survey over the Elura massive lead-zinc sulphide orebody obtained travel time data and time-distance plots with distinctive features. These can be regarded as a seismic signature of a zone of low seismic velocity, limited in dimensions by the higher velocity weathered host rock, and the much higher velocity fresh host rock and ore at depth. At Elura, these are produced by the low velocity plug of gossan which extends down through the weathered bedrock to the level of the fresh host rock and ore at a depth of about 90m. The signature shows low seismic apparent velocities across the area of limited surface gossan. These apparent velocities are only slightly greater than the velocity of the surface material. In addition, there occur marked negative apparent velocity segments on the travel time-distance plots. These only occur on the further edge of the low velocity (gossan) zone to that of the location of the shotpoints.

It is considered that these features or seismic signatures are produced by diffraction effects around the low velocity zone.