Exploring at greater depths

The SAMSON is a stationary technology for generating more precise electromagnetic surveys

As mining companies search deeper underground for mineral deposits, the ability to find major resources more efficiently and cost effectively remains a challenge.

Australian company Gap Geophysics has been developing geophysical technologies for exploration for more than 20 years. One of the innovations is the Sub-Audio Magnetics (SAM) technology for mineral exploration.

Gap Geophysics chief executive officer Malcolm Cattach has been involved in developing SAM, which began as his PhD project during the early 90s.

While traditional exploration surveys conduct magnetic measurements – measuring the changes in the Earth’s magnetic field due to different rock types – Cattach said these technologies have since been refined over the past 25 years.

They are now able to measure both minute changes in Earth’s magnetic fields and detect electromagnetic (EM) responses – measuring the EM response of Earth to a transmitted response (they actually produce and electromagnetic pulse which produces a response from conductors in the ground).

This is where SAM technology fits in, which can measure both magnetic and EM properties in the ground using a fast sampling caesium vapour magnetometer.

“SAM technology, which gives us the ability to do very rapid surveys, (at) very high resolution because we can take measurements without stopping,” Cattach told Australian Mining.

Cattach said it gave users the ability to undertake very rapid and high resolution surveys – able to take measurements without stopping.

“The interesting thing about the Sub-Audio Magnetics technique is that it measures both the magnetic field and the conductivity responses all from one survey,” he said.

For even deeper penetration to deposits further underground, the company developed the SAMSON technology, able to track even more precise measurements.

“The SAMSON technology is much more sensitive to very deep targets, but that does require it to be stationary,” Cattach said.

“It’s the most precise mode of operation for doing electromagnetic surveys.”

Cattach explained that SAMSON takes one long reading, and while doing so, produces an EM pulse that goes through the ground.

“If there are conductors in the ground then what we’re doing is producing an electrical current flow to these conductors underground and we actually elicit a response using the SAMSON technology sitting at the surface,” Cattach said.

“The other thing that we’ve done for deep penetration surveys is we’ve developed very high powered transmitters to the instruments that produce the pulse in the first place.

“[They] have a certain amount of power and the amount of power determines how deep you can actually get a response from it in the ground.”

Cattach added that the signal the high-powered EM transmitters produce is 10 times greater than other conventional transmitters.

“This means that we can see much deeper into the ground than people have been able to survey before,” he said.

This provides a greater opportunity for explorers as they continue to seek deeper ore deposits.

“Over time, a lot of the shallower discoveries have already been made and this is because they’re relatively shallow, relatively simple to detect, so conventional, cheaper, less advanced technology has been able to detect it,” Cattach said.

He emphasised that it caused a greater need for technologies such as SAMSON.

“Given that it’s generally accepted that most of these new surface ore bodies have already been found, the next challenge for the mining industry is to look much deeper than we’ve been able to see with conventional technologies,” Cattach said.

“So our whole objective with the SAMSON technology is to build instruments capable of seeing much deeper and exploring much further in the ground.”

Cattach added that the SAMSON technology has been successful in detecting significant resources and used at BHP and Glencore’s Mt Isa Mines and St George Mining’s Mt Alexander nickel project in Western Australia.

“They’re [St George] still investigating the results of the surveys we just completed for them as well and they’re finding much deeper conductors that what they’d be able to find with conventional technologies so they’re quite excited at the moment,” Cattach said.

Taking SAM to greater heights

Cattach said the company refined the SAM technology even further to achieve deep penetration from airborne platforms.

They developed another technique called HeliSAM, a helicopter-borne magnetic acquisition system, which can detect orebodies several kilometers deep.

The HeliSAM

“We’re doing some final field tests over a known conductor in Western Australia in the next couple of weeks,” Cattach said.

“That could be quite exciting because people have been using a full-sized helicopter and it means they can have lower transmission frequencies and deep penetration.”

The company is also working on an unmanned aerial vehicle (UAV), or drone, for the same use as the HeliSAM.

Cattach explained that as explorers look deeper underground, they were covering bigger areas than they had been expecting.

“Something that is maybe 500m down might produce an anomaly which is 1.5 or 2km wide so the deeper you’re looking, the bigger the scale of the surveys. The bigger the scale of the surveys, the more expensive they become,” he said.

That is, unless the company has a more efficient method of gathering the data.

“So what we’re actually doing with HELISAM and the UAV SAM and even ground SAM for that matter is producing technologies capable of very rapid acquisition of data of these very deep ore bodies,” Cattach said.

“So even if they’re looking much deeper, they can still be quite efficient using the SAM technology.”

What Gap Geophysics is working on now

A key area the company is currently working on is commercialising the HeliSAM technology in Canada.

Cattach said it had a particular application in countries with difficult working environments, like Canada.

“Most of their exploration has to be done in the middle of winter when the lakes are frozen, that’s the only time they can get access to the ground,” he said.

Cattach also highlighted some of Canada’s thick forest terrain where to complete ground surveys, explorers need to cut through the bush and create a clear line before they can begin taking measurements – which is both time consuming and expensive.

“What HeliSAM enables us to do is avoid the need to cut lines through the bush,” he said.

Cattach added that a 100km survey in a deep orebody could be undertaken in two hours with the helicopter technology – this would normally take months to do on the ground, at a greater cost.

“It’s really quite revolutionary-approaching exploration for these high conductance orebodies in very difficult terrain,” he said.

In addition to mineral exploration, Gap also uses its EM technologies for other applications.

Its sub-division, Gap Explosive Ordnance Detection Services (GAP EOD) uses EM technologies to detect unexploded bombs.

“We have instruments operating at the moment in places like Laos, in the Ho Chi Minh trail, finding bombs in mine sites [areas] that were from the Vietnam war,” Cattach said.

He added that the company pioneered this technology, beginning with bomb detection during the 1980s.

“We’re the first people in the world to do digital detection of unexploded ordnance,” he said.

The company also has systems in Germany, finding deeply buried bombs from the Second World War.

With innovation remaining at the heart of several companies, who knows what other applications the company’s electromagnetic technology could be used for next.

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