Resource World Magazine

54 www.resourceworld.com F E B R U A R Y / M A R C H 2 0 1 4 MININGWORLD Vancouver, British Columbia-based Precision GeoSurveys Inc. recently brought on board some updated geophysical surveying tech- nology that provides their clients with the ability to 'see' deep into the earth. The company has been offering helicopter- borne geophysical surveys on a worldwide scale, specializing in mountainous terrain that includes hi-resolution magnetic, radio - metric and electromagnetic surveys (EM). Harmen Keyser, P.Geol., President of Precision GeoSurveys, told Resource World that "we worked with an Australian com- pany called GeoSolutions to develop time domain electromagnetic technology. The original technology had been around for over a decade; however, it has been evolving and we have adapted it for use in mountainous terrain." "Our new, third generation 1TEM technol - ogy is light weight, has very good low drag aerodynamic properties when towed below the helicopter and has a low resistance to turning that makes it good for tight line spacings. This allows us to provide superior data over difficult terrain," said Keyser. The 1TEM system is used to map conductivity and resistivity. The transmitted 1TEM field induces a series of currents in the earth at increasing depths over time. These currents, in turn, create magnetic fields that can be measured to map subsurface conductive properties. Because measurements are made while the transmitter current is turned off, the more sensitive measurement of the magnetic field generated by the subsurface enhances the resolution of the conductive features at great depth. Jenny Poon, a geophysicist with Precision GeoSurveys, explained that the newly acquired technology is different from the geophysical technologies the company has been using. "It can be used to explore for various minerals, oil and gas, as well as hydrology and environmental studies. Its ramp-off time of 35 microseconds is the best in the business. The faster that we can turn off the primary field that is generated from the transmitter, the better resolution we have to detect the eddy current from the sub-sur - face conductor," said Poon. "Depending on the size of the target, the topography and the client's budget, we fly a grid pattern with lines spaced between 50 and 200 metres apart," said Keyser. "We have pilots that specialize in flying over mountain - ous terrain, so we are able to maintain a very high level of accuracy both left and right as well as up and down; the lower the flight, the better the data. We try to stay at the same distance from the ground over any kind of terrain." Keyser said that airborne EM systems map conductors, or conductive sources. "Not all metals and minerals are conductive, so not all mineral deposits are suitable for airborne EM survey methods," noted Keyser. "The ideal targets for airborne EM technology would be massive sulphides, graphite, diamonds (kimberlite bodies), gold, silver copper, uranium and groundwater. We try to use the right technology for the target that our clients are looking for. For porphyries, we look for structures that relate to where the deposits are located. While there are complex geophysical factors involved, under ideal conditions, using our new 1TEM geophysics technology, we can look down to about 300 metres into the earth. Results are available within hours." Precision GeoSurveys has three helicopters in the Vancouver area along with a research and development facility. For most jobs in North America, the company uses its own aircraft flown by specialty survey pilots. "We recently did a survey near Revelstoke, southeastern British Columbia, in extremely difficult terrain up to 10,000 feet in altitude," said Keyser. "We were able to identify a con - ductive bedrock source in ground where the client thought there was an interesting target. The client followed up with ground EM geophysics and was able to confirm the presence of a significant conductive source of massive sulphide copper." For work in Asia, Africa and Europe, the company uses local helicopters, sometimes with its own pilots and sometimes with local pilots experienced in airborne geophysics. "For foreign work, we ship our geophysi - cal technology equipment overseas and have partnered with companies in New Zealand, Papua New Guinea, Kenya, Uganda, Finland and Alaska," explained Keyser. n A Precision GeoSurveys helicopter at work in mountainous terrain. Photo courtesy Precision GeoSurveys Inc. Precision GeoSurveys offers deep electromagnetic geophysics By Ellsworth Dickson

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