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The challenge

Finding new, cost-effective ways to find precious metals

[Music plays and text appears: CSIRO discovers gold grows on trees]

[Image changes to Dr Mel Lintern, CSIRO geochemist]

Dr Lintern:  We’ve actually discovered something really interesting about Australian eucalypt trees. We’ve discovered that gold grains are growing within the leaves of the eucalypt trees. Now this actually tells us something about the environment in which the trees are growing. In the case of the gold growing in the leaves it tells us that there’s a gold deposit beneath where we’re standing and in some of the research we’ve done the gold deposit was down 30 metres below the surface which is an incredible ten storeys high.

[Image changes to show a computer generated tree and it’s roots system with yellow dots moving up the tree, which represent the nutrients and gold being taken from the ground]

The tree acts like a hydraulic pump. Water’s being brought up with nutrients and a little bit of gold right up to the foliage and in so doing the gold is being deposited in the leaves and being shed by the tree.

[Once the yellow dots reach the leaves, the leaves drop to the ground]

The reason why the tree is shedding this gold is because the tree sees the gold, even though there’s small amounts of it, as being quite toxic and so it’s trying to get rid of that gold from its system.

[Image changes to show Dr Lintern holding a eucalypt leaf in his hands]

Of course the amount of gold that’s in the leaf is very, very tiny and you can’t see it with the naked eye. And that is when we need the powers of the Australian Synchrotron to help us see this gold. Now the Australian Synchrotron is a fantastic piece of equipment. It’s able to analyse elements such as gold in three dimensions within the leaf and this has enabled us to see that the gold is actually contained within the leaf and not on the surface as dust which is very important.

[Image changes to show an aerial view of trees]

By sampling leaves and vegetation and the soil and even termite mounds what we’re actually doing is driving the exploration dollar a bit further. Drilling can be expensive, it’s very useful but it can be expensive so by analysing the vegetation at the surface we can cut down costs so that the money for exploration can be used for other things. The other point of course as well is that sampling vegetation is a very environmentally benign way of exploring.

[Image has changed back to Dr Lintern]

We've only really scratched the surface with this research. We’ve found that some trees will take up gold, others don’t and so we need to do some more research to find out why this is happening, to make it into a robust exploration technique.

[Music plays, CSIRO logo appears with the text: Big ideas start here]

Dr Mel Lintern explains how he's using eucalypt trees to find gold deposits.

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Pinpointing mineable ore deposits through covered terrain is often expensive and technologically intensive.

The search for ores containing metals such as gold is often based on finding geological indicator minerals such as calcrete. Using indicator minerals or materials from near the surface helps companies to better target where they focus their exploration effort.

However there are some limitations with traditional surface based sampling methods.

That's why, we're developing new, cost effective and environmentally-friendly geochemical-based exploration approaches that can be used in conjunction with traditional methods to enable exploration success at lower cost.

Our response

Tree or leaf sampling

Through industry-sponsored projects, we explored whether vegetation or other surface-based indicators could be used for exploration.

Sampling gum leaves from trees in a suspected gold-rich region.

Examining eucalyptus tree samples from the Kalgoorlie region of Western Australia using the Maia detector for x-ray elemental imaging at the Australian Synchrotron, revealed traces of gold in the leaves.

Eucalypt roots extend tens of metres into the ground and act like a hydraulic pump, drawing up water and other minerals, including traces of metals, from the soil.

Gold is likely to be toxic to the plant and so is moved to the leaves and branches where it can be released or shed to the ground.

Our advanced x-ray imaging enabled researchers to examine the leaves and produce clear images of the traces of gold and other metals, nestled within their structure for the first time.

The results

Trees can be used to pinpoint gold deposits below the surface

The technique provides a golden opportunity for mineral exploration, as the leaves or soil underneath the trees could indicate gold ore deposits buried up to tens of metres underground and under sediments that are up to 60 million years old.

Microscopic close up of a gum leaf showing red, blue and green areas depicting presence of gold, copper and strontium, respectively.

By sampling and analysing vegetation for traces of minerals using highly advanced x-ray imaging, companies may get an idea of what's happening below the surface without the need to drill. It's a more targeted way of searching for minerals, and in combination with other tools, may provide a more cost effective and environmentally friendly exploration technique

Since making the discovery, tree or leaf sampling is being successfully used by gold exploration and mining companies in Australia.

For example, Marmota Limited, a gold mining company working out of South Australia, reported in 2019 that they had identified new gold targets using biogeochemical sampling at their Aurora Tank prospect.

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