<p>Microscopic image of a gum leaf showing gold, copper and strontium.</p>
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Microscopic image of a gum leaf showing gold, copper and strontium.

Gold leaf, au naturel

The Australian national science agency has published its discovery that eucalyptus trees absorb gold through their deep roots and excrete it through their leaves and bark.

Australian researchers have found traces of gold in the country’s eucalyptus trees, but don’t expect a modern-day gold rush. First of all, the tree needs to sit atop a gold deposit. In addition, the amount of gold found in the leaves is minuscule – “nuggets” one-fifth the thickness of a human hair. This means it would take gold from 500 large eucalyptus trees growing directly over a gold deposit to produce enough gold for a wedding ring. A special detector, such as the high-tech Maia system used by Australia’s Commonwealth Scientific and Industrial Research Organisation (CSIRO), is also required to spot the gold. After all that, the exploration samples can be routinely measured in most analytical laboratories.

CSIRO at a glance

The Commonwealth Scientific and Industrial Research Organisation (CSIRO) is Australia’s national science agency. It has 11 research divisions, including earth science and resource engineering. Founded in 1926, it now has more than 50 sites and 6,600 employees across Australia and overseas.

This study focused on eucalyptus and acacia trees in the mining-rich Kalgoorlie region of Western Australia and in sand dunes in the southern part of the country. CSIRO’s findings were published in the journal Nature Communications.

The research was partly sponsored by the Australian Mineral Institute Research Association.

Even though miners won’t get rich by tapping into these trees, the discovery could offer companies an alternative exploration method to drilling, since eucalyptus trees are so common across Australia.

“Analyzing the mineral content of leaves and bark could prove a more cost-effective and environmentally friendly way of locating and assessing mineral deposits, particularly for smaller mining companies with less capital and equipment,” says Dr. Mel Lintern, who headed the research team.

Since the 1980s, CSIRO has been researching how trees – in particular, eucalyptus and acacia trees – absorb metals and minerals. Using samples from the leaves of eucalyptus trees can indicate the levels of gold ore in the ground beneath. It is a useful technique in areas with deep river sediments, sand dunes and weathered rock, where it is often difficult to see the minerals through the cover.

Some mining companies have already incorporated tree sampling into their exploration activities, Lintern says. Tree sampling is being used in thick forests in Canada and Russia, as well as in South America where bringing in drill rigs can be difficult.

“The next step for us now is to merge our results into a robust technique that exploration companies can use, including for other metals like zinc and copper,” he says.