Abstract

Field trials of a Soviet inspired seismoelectric method at an underground zinc mine in British Columbia, Canada, have demonstrated its effectiveness and confirmed some of the claims by the inventors of the method. The deposit investigated is a massive sulphide orebody principally made up of sphalerite, grading about 15% Zn in the area investigated. This deposit is a difficult target for standard geophysical techniques as it is virtually indistinguishable from the andesite/rhyolite host rock. However, we were able to demonstrate that the massive sulphide ore produces high frequency electromagnetic emissions when a strong seismic wave passes through the orebody. An explosive seismic source (less than 1 kg) and wide bandwidth, 1?5000 kHz, EM sensors connected to a computer data acquisition system were used to produce and collect the seismoelectric signals. Our experiments show that there was a substantial increase in high frequency EM activity when seismic waves passed through the orebody. Thus, EM signal arrival time and shot point location could be used to locate the source of the EM signals. To demonstrate this capability shotpoints were placed around a known portion of the orebody in order to image the extent of the ore zones. A two dimensional image of the zones creating the EM signals was constructed from data gathered at 14 shot positions. The location and extent of a large anomaly in the image corresponds well with the drill-inferred position of the orebody. Another smaller anomaly appears to be coincident with the known location of a pillar of ore left behind by previous mining.