Probing on the move

To dig a little deeper and find undiscovered treasures is the dream of every explorer, and one that could become reality for a number of mining companies through Gap Geophysics and its SAMSON Deep Exploration technology.

SAMSON is a powerful geophysical surveying technology designed for deep penetration mineral exploration surveys. Using an electromagnetic technique, it is great for the detection of high-conducting ore bodies such as nickel or copper sulphides.

The technology is capable of surveying down to 1km below the surface of the Earth, a depth that Gap Geophysics CEO Dr Malcolm Cattach believes is crucial for exploration. Prior to this technology, the deepest point that could be seen in surveys was about 300m below the surface.

“If you assume that only the top 300 metres has been explored with traditional electromagnetic technologies, then everything between 300m and 1km is effectively unexplored and obviously has very high potential still,” Dr Cattach said.

Origins

The idea for the SAMSON technology initially came about from a need to speed up geophysics surveying techniques. Dr Malcolm Cattach devised the idea for the technology in the 1980s when he was completing his Masters degree as well as working as a research scientist for the Geophysical Research Institute of the University of New England.

The SAMSON technology comprises two major components; the first is the high-powered transmitter and the second is the extremely high-precision receiver.

“We call the receiver a total field magnetometer,” Dr Cattach said. “It is based on the core technology called Sub Audio Magnetics (SAM), which I developed in the 1990s as part of my PhD project.

“Back when I started doing geophysics, if you wanted to do a magnetic survey you had to walk to a point, take one measurement, and then you might walk 50m to take another measurement; it was very slow and tedious.

“My initial research was to develop equipment capable of rapidly acquiring data for magnetic fields. This was a continuous acquisition using a total field magnetometer so we were able to take measurements ten times a second while continuously moving.”

Conventional electromagnetic receivers measure the changes in secondary electromagnetic fields, typically made up of three components. In order to measure these components they have to be precisely oriented and levelled. They also have to be kept extremely still in order to take a measurement, because any movement in the actual sensor introduces noise that could distort the results.

The SAMSON receiver is different; it is capable of reading very minute changes in the electromagnetic field. It is a total field sensor, which means it measures the changes in the direction of the earth’s magnetic field.

“The SAMSON receiver does not have to be levelled or oriented, which means it is much quicker to set up; and because you don’t have to orient it to get these three components, it can acquire data while you’re still moving,” Dr Cattach said.

“The thing for us is, because of this aspect, we’re able to take it airborne. We can string it underneath the helicopter in a mode called HeliSAM, and we also have an Unmanned Aerial Vehicle (UAV) mode in development too. These sorts of developments wouldn’t be possible with a conventional approach.”

HeliSAM/airborne surveys

One of the main advantages of using airborne techniques for surveying is the ability to cover a greater area in a shorter amount of time. This does mean that the precision of the results is lessened, but Dr Cattach believes the depth at which this technology is able to survey counteracts this.

The other key point to note is that the deeper you explore into the ground, the larger the survey scale needs to be to cover the response and actually recognise it.

“I think the deeper that we’re exploring, the less pertinent our near-surface geology is going to be,” Dr Cattach said.

“I think that in the future, statistics are going to be a lot more important.

“The more ground you can cover, the more chance you’ve actually got of detecting these anomalies at depth. Consequently, the better chance you’ve got of actually finding something of value, but as I say, statistics are going to come into it; the more ground you can cover for the exploration budget you’ve got, the better off you’re going to be.”

Typically, it is only possible to take a stationary measurement every 50m on survey lines that are about 200-400m apart. This is mainly because measuring survey points that are closer together would take too much time and expense.

Comparatively, HeliSAM technology makes it possible to take measurements every 5-10m on lines 50m apart in a third or half the time it takes to do the stationary measurements.
“If you can cover a bigger area in greater detail then you’ve got more of an idea of what the response is doing. I think if you’re restricted by the number of measurements you can take because of the cost, then you’ll never get as good an image of the response,” Dr Cattach said.

“With stationary measurements you take repetitive readings continuously. You might take them for five minutes, but you have to average all of your readings before you are happy with the quality of the data.

“That is why the other approach to take less precise measurements, but to take many of them, is so pertinent. Statistically you can still define the shape of the anomalies from a much greater density of data than having very few measurements that are very precise.”

Dr Cattach said the main aim of the HeliSAM technology was to be able to define the same results, but to do it as cost-effectively as possible.

Another great advantage of the HeliSAM technology is the ability to survey over remote sites. Gap Geophysics has partnered with a Canadian geophysical survey company called Discovery International Geophysics, based in Saskatoon, to help it survey in remote areas.

Discovery International Geophysics has developed a Heliwinder system that allows it to lay out the wire for loops in remote areas that it would be very hard to access on foot.

“Their loops might be 2km by 2km, so to lay it out by hand would be extremely tedious. They would need to cut through the forests to lay the wire and they wouldn’t be able to use the heavy wire because the guys have to physically carry it,” Dr Cattach said.

The combination of their Heliwinder system and our HeliSAM means they can lay the loops in a matter of a day or two and fly the survey in a day. It’s like doing a month’s work in two days.”

As well as using the Helisam technology, Gap Geophysics has also run a number of surveys using its UAV. There are some great advantages to using the UAV, but Dr Cattach doesn’t want to rely too heavily on it.

“I don’t think UAVs are going to be the answer to everything,” he said. “For our biggest surveys I’d much rather use a helicopter, but for the right sized surveys the UAV is going to have a lot of application.”

The main advantage of using the UAV over HeliSAM is the speed at which the UAV is able to fly at. In Australia there is a very conductive overburden, meaning the transmit frequencies have to be quite low to be able to see things at depth.

Due to the fact that a helicopter is manned, it needs to retain a certain forward speed in order to safely pull out of any engine failures.

“This means the lowest transmit frequency we can use when we’re flying the helicopter is about four or five hertz, but with the UAV we can fly much slower due to there being no person on board,” Dr Cattach said. “This means we should be able to transmit sub-1 hertz transmission frequencies, which produces high-quality data.”

Looking deep into the future

The future for the SAMSON technology appears to be a fairly bright one due to the impact is has already had on the mining industry.

It has been trialled in some fairly high-profile exploration success stories, such as the Nova Bollinger project by Sirius Resources. Though Gap Geophysics did not discover the ore body, it was asked to come in and see how clearly it could define the shape and size of Bollinger.

“We could see Bollinger very clearly with the SAMSON technology; it’s at a depth of 500m, so it couldn’t be seen with conventional technology, but we could see it easily,” Dr Cattach said.

Other high-profile studies have seen Gap Geophysics working with St George Mining.

“We’ve just completed a deep-penetration electromagnetic project for them at the Cathedral Belt. I think their officers are very happy with the results so far,” Dr Cattach said.

As this technology has been a concept for development since the late 1980s, there has been a lot of development work that has gone into it. One of the main reasons it has taken so long for the technology to really establish itself is the concept was a bit ahead of what the surrounding technology was capable of doing.

“It wasn’t until the end of the 90s/early 2000s, when the required electronics, high-capacity memory and GPS became available, that we were really able to commercialise properly. It probably wasn’t until 2004 when we built the current SAM receiver prototype that we really had a commercially capable instrument,” Dr Cattach said.

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