In the summer of 1983, G. A. Sobolev and V. M. Demin of the U.S.S.R. came to Canada to demonstrate techniques using piezoelectrical and other mechanoelectrical effects for in-mine geophysical surveys. We performed field trials using Soviet and Canadian equipment in the Giant Yellowknife Mine, N. W. T., and the Sullivan Mine, Kimberley, B.C., Canada.The principle of the technique involves detonating an explosive charge and subsequently measuring the strength and delay time of electromagnetic fields generated by excited minerals.Ore grade gold zones at the Giant Yellowknife Mine occur within large quartz lenses in a shear zone in Archean volcanics. Our tests there produced strong signals in the 8 kHz range, which were very similar to piezoelectrical signals produced by quartz samples, in the laboratory at the University of British Columbia.The Sullivan orebody is a 160 million ton iron-lead-zinc sulfide deposit lying comformably in Proterozoic rock. Our tests there yielded some very strong electromagnetic signals with frequencies as high as 350 kHz. The short delay times of these signals preclude any possibility that the signals were simple seismic phenomena generated at the antenna sites. Sobolev et al., (1982a, b) suggest that such high-frequency signals are produced by a highly nonlinear discharge phenomenon occurring at the grain boundaries of naturally occurring semiconductors such as galena, sphalerite, and pyrrhotite.