A first glance at a geological map of Australia and the untrained eye will conclude that the country’s position as the world’s top uranium producer is all but assured. The stuff is absolutely everywhere.
Delve a little deeper though, and it soon becomes clear that the ‘lie of the land’ presents serious challenges for mining companies trying to get uranium out of the ground.
With no less than 14 different geological classifications for low-grade uranium deposits, Australia’s uranium stocks are extremely diluted (average concentrations are between 0.25 and 0.1%).
According to Deloitte Australia analyst Keith Jones, uranium is only a very small part of Australia’s underlying assets, and to extract it would require the mining of ‘massive amounts of ore’.
But in 2007 uranium spot prices flew off the charts and so too did investment in Australian exploration. Spending is currently around $100m, ten times more than in 2003. That said, the true value of this investment will depend on the industry’s ability to develop and deploy innovative new technologies across the key areas of exploration, mining and processing.
Digging for uranium gold
Australia’s CSIRO, ANSTO and Geosciences Australia (GA) recently announced an alliance aimed at tackling some of the challenges facing Australia’s uranium industry. High on the agenda are exploration and mining. Also of concern are waste management and site remediation, as well as the issue of nuclear energy itself.
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The CSIRO says that efficient mining techniques are essential to ensuring Australia’s international competitiveness in uranium. A recent report states that: “finding buried uranium deposits will require technologies that are able to image or otherwise assess prospective deposits within and beneath the extensive transported sedimentary cover and deeply weathered zones that affect much of the continent.
The CSIRO has highlighted the need to develop seamless data exchange tools that allow efficient integration and 3D interpretation of large exploration datasets. New generation hyperspectral mapping at large and small scales will provide better information on telltale ore signatures in the future. Investment in cheaper, more reliable drilling continues with a view to providing real-time downhole geological, geophysical and geochemical information.
Chemistry is also a major area of concern, with current focus on geochemistry, hydrochemistry and biochemistry tools that would allow detection of subtle ore body haloes.
Measuring gamma radiation is now a popular technique for detecting uranium deposits. Uranium has about the same half life as the earth.
The problem, however, is that this technique is only useful where ore bodies have been present for a long time. “Otherwise it won’t have decay product,” explains Ian Hore-Lacey from the Australian Uranium Association. “You need smarter ways of looking for it that actually detect the uranium.”
If the uranium has only been in its location for two million years or fewer, it may not even produce a reading. If the uranium has been leached within that period of time then gamma logging tools are not useful.
Enter the prompt fission neutron (PFN) tool. The PFN essentially shoots neutrons down a hole, causing fission when they collide with uranium particles. They are especially useful when measuring paleo-channel deposits, which are buried under river beds. Much of the uranium in South and Western Australia is this kind of deposit. However, these gadgets are not cheap, costing around $1m each and there are only three in Australia at the moment.
Tracking uranium deposits
Rio Tinto has flagged two major technology initiatives during 2007. Its laterite treatment plant at Ranger is expected to extract an additional 400t of uranium a year from stockpiled clay material, following completion in 2007. Trials of a radiometric sorting plant are expected to lead to applications for treating other low-grade materials for Rio Tinto. Paladin is also hopeful of achieving results with radiometric sorting.
“You don’t need to sample or have diamond core drilling for everything – you can do reverse circulation,” says Paladin chairman Rick Crabb.
One area of interest is unconformity-type deposits, currently the world’s main source of uranium. They were first discovered in Northern Australia and Saskatchewan in the late 1960s and early 1970s and therefore present a relatively greenfields and exciting opportunity for uranium exploration.
Unconformity deposits form at or near the contact between overlying sandstone and underlying metamorphic rocks, often metamorphosed shales. The orebodies have lens-like or pod-like shapes, and most often occur along fractures in sandstone or in basement rocks. The host rocks often have disseminated uranium minerals and show hydrothermal alterations, which may indicate that the deposits formed after the rocks.
GA is currently looking into whether certain levels of graphite may be associated with unconformity uranium deposits, and if so the possible role of airborne electromagnetics (AEM ) in seeking them out.
“We have seen unconformity deposits in Canada associated with graphite,” says Ian Lambert, GA’s group leader of the onshore energy and minerals division. “We’re looking to see whether graphite is important or not.”
He says that AEM has been deployed with considerable success at unconformity deposits in Canada, where it has been proved to help refine geophysical features to get an appreciation of how deep any uranium mineralisation might be.
However, he adds, that this doesn’t guarantee results in Australia. While deposits may carry the same geological classifications as those overseas, subtle differences between them can preclude or favour the same technologies for exploration.
In-situ leaching in Australia
One model which has gained popularity over the last few years suggests that fluids with dissolved uranium and other metals, moving through the sandstone, encountered the basement rocks, where chemical conditions were ideal to cause the metals to precipitate from solution.
On the actual mining side there are currently three types of uranium mining in practise; underground, open cut and in situ leaching (ISL).
The first two techniques involve removing rock from the ground, breaking it up and treating it to remove the required minerals. ISL, also known as solution mining, or in situ recovery (ISR) in the US, involves leaving the ore where it is in the ground, and using oxygenated water pumped through it to recover the minerals out of the ore.
There are two operating regimes for ISL, determined by the geology and groundwater. If there is significant level of calcium in the orebody (as in limestone or gypsum), alkaline (carbonate) leaching must be used. Otherwise, acid (sulphate) leaching is generally better.
ISL is also seen as an environmentally friendly technique for mining uranium. As stated in a report on the Australian Uranium Association website: “Techniques for ISL have evolved to make it a controllable, safe and environmentally benign method of mining, which can operate under strict environmental controls and often has cost advantages”.
ISL mines tend to be quite small, yet they contribute around a fifth of the world’s uranium. All of the uranium recovered in Kazakhstan and Uzbekistan and most of that found in the US arrives via ISL.
The Beverley mine in South Australia is an ISL mine; however, opinions differ as to the long-term importance generally of ISL for uranium mining in Australia.
While technology for uranium mining and exploration is always evolving, it would seem that the current levels of investment and overall enthusiasm for uranium will see this sector edge ahead in the innovation stakes over the next few years.
Much of what is currently known about uranium is information that has either derived from or can be applied to the exploration for gold, nickel and other elements. Increasingly though, uranium is becoming its own and soon-to-be lucrative speciality.
As Paladin’s Rick Crabb puts it: “You’ve got to be a uranium specialist these days – you can’t just walk out of gold and apply [your knowledge] immediately to uranium.”