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Seismoelectric responses from sulphide orebodies

University of British Columbia

In the early 1980's a group of Russian researchers reported finding a new seismoelectric phenomenon associated with sulphide minerals. They asserted that strong bursts of broadband electromagnetic emissions appeared when a seismic wave passed through a sulphide orebody. This discovery has aroused considerable commercial interest because of the economic importance of mining sulphide minerals for zinc, copper, lead, gold, and other metals. However, there have been no reported follow-up studies of their findings, and no evaluation of the exploration potential of this phenomenon. This thesis reports a number of field experiments designed to examine the Russian claims and explore the properties of the phenomenon. These field trials have confirmed the existence of this relatively unknown seismoelectric phenomenaon and have substantially increased our knowledge of its charcteristics. In the tests 0.2-0.5 kg explosive charges were detonated to provide a strong source of seismic energy. When the seismic disturbance passed through a zone of sulphide mineralization, high frequency electromagnetic emissions were produced. The electromagnetic emissions appear in the form of brief pulses, 2 to 5 microseconds in duration. Typical peak amplitudes, measured 80 to 120 m from the zones of sulphide mineralization, are 10 mV/m and 2 nT. The spectrum of the electromag netic pulses spans a very wide range of frequencies, from 1 kHz to 3 MHz. Fourier analysis of the digital records from one of our sites shows a peak in the emission spectrum, at 1.1-1.4 MHz. This spectral peak was consistently reproduced from various portions of the sulphide orebody. New measurement and interpretion techniques were developed to study the electromagnetic signals. These techniques were applied to data from each field trial to demonstrate the potential of seismoelectric techniques for exploration. The results show that the high frequency seismoelectric phenomenon can be used to locate massive sulphides in underground mines. A physical framework to describe the field measurements has been developed. It is proposed that the seismic wave induces electrification via crack formation in the orebody. The electrified surfaces of the crack recombine rapidly in a gas discharge to produce the observed range of electromagnetic frequencies.

Thesis/Dissertation

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2009-02-19

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http://hdl.handle.net/2429/4817

Geophysics

University of British Columbia

UBCV

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