AEM is a geophysical survey technology that uses airborne transmitters and receivers to create a 3D picture of the conductivity of the subsurface. It provides rich information on the likely type of rock units, including highly conductive massive sulfide minerals.

The new systems are more powerful and penetrate deeper, with high resolution, 3D images of subsurface conductivity now commonly reaching depths of 500m.

There’s also a bigger choice of systems designed for regional surveys, where the economy of fixed wing systems allows wide coverage at lower cost.

AEM is a top-shelf exploration tool, costing about 20 times the amount spent on an airborne magnetic survey per line kilometre.

The high cost means the AEM revolution has taken place largely within the walls of exploration houses with big budgets, including Anglo American and BHP Billiton.

But it’s trickling down to an increasing number of junior explorers, including Emmerson Resources, Traka Resources and Pepinnini Minerals.

These companies are eager to boost their appeal to investors by publicising what AEM can offer in terms of potential exploration breakthroughs. Their efforts are also giving a higher profile to the use of AEM systems in mineral exploration.

AEM is also receiving a massive boost from Geoscience Australia, which has added it to the menu of pre-competitive regional data offered to the private sector.

Resources Minister Martin Ferguson last week launched a Geoscience Australia report on a 32,000 line kilometre AEM survey in the Lake Frome district of north eastern South Australia. The survey covered almost one tenth of the state and is the largest conducted in Australia.

It targeted uranium deposits in palaeochannels but also provides clues in the search for copper, gold, silver, lead, zinc, iron ore, coal and groundwater.

State government water departments are also making greater use of AEM to map groundwater resources.

AEM is not new on the Australian exploration scene. Fugro has been flying its Tempest system since 1999 and is the most active AEM provider in the Australian market. Geotech’s VTEM has also been cropping up in the quarterly and annual reports of explorers for years.

But recently some new names have come to prominence. These include Fugro’s Helitem, Anglo’s Spectrem2000 and more recently SkyTEM, developed by a Danish company.

AEM systems are divided into two categories — fixed-wing and helicopter. Fixed-wing set-ups cover large areas at lower cost. Helicopter-towed systems are suited to prospect-scale surveys, where higher resolution at depth is a priority.

Anglo was a pioneer in developing fixed-wing AEM, mounting a system on a DC3 back in the 1980s. It was rudimentary by today’s standards, but the Anglo technology quickly proved its worth by uncovering major sulfide deposits at Hudson Bay in Canada.

Anglo commercialised the technology in the 1990s by establishing a wholly owned subsidiary, Spectrem Air, to provide contract AEM surveys to other explorers.

The company’s South Africa-based fixed wing aircraft was first used in Australia in late 2010. It is currently in Kalgoorlie, which has been the base for a series of sweeps over the eastern Yilgarn province for Anglo.

Other work in Australia has been done in the Musgrave district for Traka Resources, which was the first to use Spectrem in Australia.

Traka holds most of exploration rights over the Musgraves in Western Australia, including ground surrounding BHP Billiton’s giant but low grade Nebo/Babel nickel deposit. BHP Billiton has also used Spectrem in the Musgraves, as well as Fugro’s fixed-wing systems, Tempest and Geotem.

Tempest, jointly developed with CSIRO, is a fully calibrated system, meaning it produces consistent, repeatable data suitable for accurate 3D models. It was used by Geoscience Australia for the Lake Frome survey and other large pre-competitive data gathering studies at Pine Creek NT, and Paterson North, WA.

Geotem is a higher power, deeper penetrating system with a long history, having successfully flown more than 2 million line kilometres of survey worldwide.



The major helicopter-borne systems used in Australia are Fugro’s Helitem, Geotech’s VTEM and the more newly arrived SkyTem.

Fugro sales and marketing manager Craig Annison told MiningNewsPremium that heli-borne AEM systems had become significantly more powerful in recent years.

“These are being used for more focused and deeper surveys than previously possible. Helitem is achieving some great results for clients,” he said.

“Emmerson Resources in Tennant Creek is a good example, where we have found targets at depths of more than 330m that no one knew existed, despite years of exploration, drilling and high detailed magnetic and gravity surveys.

“We have also had successes for clients in Cloncurry, Cobar and other districts across Australia. These are not so public, but the more powerful systems are clearly proving their worth.”

He said AEM was the only airborne geophysical tool that could provide a detailed 3D picture of the subsurface, but uptake was subdued in the current market.

“Heli-borne AEM is a great tool for small base metal targets but metal prices are down compared to a few years ago and this type of activity is subdued at the moment.”

Traka managing director Patrick Verbeek said Spectrem had been a “very good” tool in the company’s greenefields exploration program over large areas of the Musgrave Ranges.

“It can find orebodies very easily if they are massive sulfides located away from anything else,” he said.

“Of course, that situation is rare, but Spectrem is a very good screening tool. It adds another layer of information about potential targets, and it also provides a lot of information about the local terrain, such as the location of palaeochannels and regolith features.”

Verbeek said one of the most attractive features of Spectrem was its ability to cover very large areas at significantly lower cost than helicopter systems.

“You don’t get the same power into the ground as a helicopter system. But the loss of resolution is subtle,” he said.

Pepinnini Minerals is another greenfields explorer in the Musgrave Ranges using AEM to come to grips with a huge field of potential prospects. The Adelaide-based company is using a more powerful version of SkyTEM to help explore tenements on the South Australian side of the ranges. It is the first Australian outing for the new SkyTEM technology.

Pepinnini last week released the results of a 1300 line kilometre survey, conducted with the help of a PACE exploration grant from the SA government.

The survey identified 14 strongly electromagnetic targets. The company believes these are within highly conductive bedrock and are potential markers of massive sulfides of nickel and copper. These will be ranked for testing by drilling as soon as the company received statutory approvals and heritage clearances.

Results with the drill bit will be watched closely by other explorers, eager to know whether AEM can provide a shortcut to the potentially massive rewards of greenfields exploration.