Drilling into rock and extracting a core sample is a bit pricey, so it’s good to know where you have a better-than-average chance of finding what you’re looking for. That’s where the brainy experts and high-tech equipment of geophysical surveying come in.
The experts include geophysicists who process data, aircraft pilots and equipment operators who collect the data, and engineers who develop the data-collection technology. Sometimes their work is followed up by the likes of Condor Consulting, a Colorado-based firm that processes and interprets data.
“We take it to the next step after data collection,” explains Condor President Ken Witherly, himself a geophysicist with decades of experience in the mining sector. “We do a kind of forensics, the sleuthing part of geophysical surveying.”
The equipment includes aircraft, navigation systems and data acquisition systems. The technology is often very impressive and mind-boggling to those not schooled in the sciences. Toronto-headquartered Terraquest Ltd. has, for example, a proprietary XDS VLF-EM (Very Low Frequency-Electromagnetic) system that maps electrical conductivity from above. It is, as company President Howard Barrie says, “a very advanced electromagnetic sensor.”
As a field of work, geophysical surveying is ever-changing and brimming with innovation and new ideas. Here’s a look at just some of its exciting developments of recent times.
FROM THE SKY
Exploration companies turn to geophysical survey firms such as Terraquest and Oracle Geoscience to collect data via high-tech devices suspended from airplanes and helicopters. The data may fall under the parameters of magnetics, electromagnetics, radiometrics and gravity.
Magnetics refers to the the measurement of magnetic response to detect, for example, possible kimberlite pipe which might contain diamonds. Electromagnetics involves the measurement of conductivity of what is below the surface. Radiometric data indicate radioactivity, which is useful information if you’re looking for uranium.
What about gravity? Isn’t that the same everywhere? Not exactly. There are fine – very, very fine, in fact – differences depending on the mass and density of minerals directly below, and that’s what is measured.
Pico Envirotec makes airborne surveying easier with equipment such as IMPAC – Integrated Multi-Parameter Airborne Console, a new real-time data acquisition device that combines a number of components into a single unit. “It’s quicker to install, it’s easier to install, and it requires far less effort on the part of the user,” Pico Chief Operating Officer Keith Hall says from company headquarters in Concord, Ontario.
“When you’re paying $1,500 a day to lease a helicopter while you install your equipment in it, being able to install in a couple of hours as opposed to a couple of days is a serious consideration,” he adds.
Pico’s recent innovations don’t begin and end with IMPAC. The company has also developed P-THEM, a versatile time-domain electromagnetic system for use in helicopter-borne surveying. It weighs less than 300 kilograms but has a powerful transmitter, a state-of-the-art receiver and advanced signal-processing software. “And it’s actually for sale, as opposed to having to go to a company that will lease you their services rather than sell you the equipment,” Hall points out.
The airborne survey specialists at Sander Geophysics measure magnetics, gravity, electromagnetics and radiometrics (gamma-ray spectrometry). “Concurrent with these methods, we can record scanning LiDAR (light detection and ranging) data to provide extremely accurate digital elevation models of the topography in the survey area,” adds Malcolm Argyle, Marketing Manager, from his office in Ottawa. The company has a fleet of 14 airplanes and one helicopter.
Sander has designed and developed its own AIRGrav system for gravity surveys. “It’s been used worldwide for petroleum exploration and regional geophysical mapping for over 10 years, but we have recently flown several mineral exploration surveys where higher resolution is required,” Argyle says. “All our AIRGrav surveys record magnetic data concurrently with the gravity, providing our clients with two complementary potential field data sets.”
Goldak Airborne Surveys, out of Saskatoon, was the first company in North America to offer a three-axis AEM (airborne electromagnetic) gradiometer system. Measuring the three axes is important, says Chief Geophysicist Marc Pelletier, because it means you’re “measuring all of the components accurately.” Thus, you get a better idea of what’s below ground.
Pelletier says Goldak has in the last couple of years “been mostly busy with radiometric surveys.” That type of survey is useful for not just uranium exploration, but for detecting a broad range minerals. “In fact,” he adds, “most of what we’ve done recently has been in government geological surveys.” The company’s 20 or so field staff and five office staff have been involved in surveys for the Saskatchewan, Quebec and federal governments and flown over lands from B.C. to Quebec to the Arctic coastline.
Another Saskatoon company, Leaf and Stone Resonance Services, surveys from much further above ground than any plane or chopper goes. Leaf and Stone uses resonance coupling technology to look specifically for whatever mineral you seek.
“Molecular Resonance Coupling is a spectrum change that occurs when two atomic structurally identical substances match each other,” the company website explains. “We have applied this technology and have developed a proprietary method of measuring this response so that given a sample of oil or other mineral, we can locate the same substance that is underground and not yet discovered.”
CEO Robert Fisher says the technique’s very accurate, and has testimonials to back up his assertion. “We commercialized it in October of 2007, and we have not been wrong in our 21 months of tests and since we commercialzed it,” he declares. You can learn more about the firm’s intriguing work at www.leafandstone.ca.
AT GROUND LEVEL
Ground surveying can collect magnetic, electromagnetic, gravity and radiometric data, plus other parameters such as seismic data.
EMpulse Geophysics - principally physicist David Goldak and mathematician Shawn Goldak – applies natural-source electromagnetics to help exploration companies find underground resources. The Saskatchewan firm uses the electromagnetic energy from thunderstorms (which can occur thousands of kilometres away) to map resistivity (how a material resists the flow of electrical current). From that information, inferences can be made about where particular minerals might be found in significant volumes.
EMpulse’s most promising innovations of late are probably in its use of 3D inversion software, post-surveying, to map resistivity distribution in the subsurface. “To make use of all the data we collect, you really have to do a 3D inversion,” David Goldak explains. “In the past, people have been limited to two-dimensional inversions, but when you do a 2D inversion you end up throwing out about half of the data you collect. If you’re able to do a 3D inversion, you’re using all of the data that you collected. You’re making use of all your information.”
Precision borehole surveying technologies are the specialty of Icefield Tools Corporation, which has been designing, manufacturing and selling such products since 1990 (first as Icefield Instruments, then under its present name as a spin-off to that company). Its star product these days is the GyroShot, which has sold well in the mining and petroleum sectors since coming on the market a few years ago. It uses nano-technology to deliver accurate borehole surveys yet it’s also “very rugged,” says President Erik Blake.
Dan Patrie Exploration, operating out of Massey, Ontario, owns claims in Ontario and offers magnetic and electromagnetic survey services to other companies. Owner and CEO Dan Patrie has worked in mining and exploration since 1968, and in geophysical surveying since 1986. He says induced polarization surveying, in which surveyors transmit electrical current to find polarizable targets, has developed a lot in recent years thanks to “more powerful systems” being used in the industry.
Indeed, a recent article in Ontario Mineral Exploration Review detailed how Abitibi Geophysics worked with the National Research Council and several gold mining companies “to commercialize a concept that increases the detection radius [of polarization surveys] by hundreds of metres.” That concept is hole-to-hole induced polarization, an improvement on the classical borehole induced polarization survey.
“The idea is to explore in between the boreholes that they already drilled, looking for pockets of mineralization that they might have missed,” geophysicist Roman Wasylechko, who co-authored the article with Abitibi President Pierre Berube, says from Ottawa. “What we do is, we transmit electrical current to polarize any mineralization that is underground, and we measure the responses cross-hole in the various boreholes.”
The responses give Abitibi staff such as Wasylechko indications as to where there might be the kinds of mineralization that exploration companies are looking for between or below boreholes. By taking measurements between holes, he explains, “our radius of coverage increases, because we’re now measuring a signal from one hole to the other hole.”
Hole-to-hole induced polarization had been tried before, Wasylechko continues. “The problem was what to do with the data – to figure out the mathematics, to develop the model of the electric field. We invested a fair bit of money in terms of research into understanding what happens when you are taking measurements between holes rather than along one single hole at a time.
“Instead of providing people with a simple profile of the response in the hole, we invert the data to produce a 3D image of all the readings that are taken amongst all the holes,” he says.
In laymen’s terms, Wasylechko is saying the bright minds at Abitibi turn the data from hole-to-hole induced polarization surveying into three-dimensional pictures indicating the size, shape and location of the polarizable clumps below ground that seem to have significant mineralization. These are areas for further exploration since, of course, the only way to find out the exact kind of mineralization in those places is to drill a hole and extract a sample.
What Abitibi and the other innovators do is complex stuff requiring advanced scientific knowledge and a lot of hard work to make it happen. For that knowledge and work, exploration and mining companies are surely grateful.
