Gold stored in gum leaves: a ‘Eureka moment’

By Joanna Egan 24 October 2013
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Eucalyptus trees can absorb gold and store it in their leaves, a world-first study has revealed.

EUCALYPTUS TREES ARE ABLE to absorb gold from beneath the ground and store it in their leaves, scientists have discovered.

Microscopic particles were detected in the leaves, twigs and bark of gum trees at gold prospecting sites in the Kalgoorlie region of Western Australia, and researchers say the finding may lead to non-invasive methods of prospecting.

“We were surprised and delighted by our findings,” says Dr Melvyn Lintern, a geochemist at the CSIRO and leader of the study. “It was a Eureka moment to discover gold contained within the leaves.”

Eucalyptus trees can store gold

Invisible to the human eye, the fine gold particles measure about 8 micrometres in width – less than one-fifth the diameter of a human hair.

The research team used x-ray imaging to identify the gold particles in the trees. The team compared tree samples collected at gold prospecting sites with samples collected about 1500km away. They also conducted a series of controlled experiments in greenhouses, where they grew eucalypts in gold-dosed soil, as well as in normal potting soil.

The findings, published this week in Nature Communications, suggest that when gold is present in the soil, minute particles are absorbed by the trees’ roots and transported to their leaves and branches.

The average concentration of gold found in the sample leaves was only about 46 parts per billion. This means it would take more than 500 trees growing above a gold deposit to yield enough of the precious metal for a wedding band.

“We found that some trees are able to bring up gold from 35m depth – that is the equivalent of a 10-storey building,” says Melvyn. “We also found that some gold falls to the ground from the leaf surfaces.”

Gum trees hold clues for gold mining

“This research may change the way we go about mineral exploration,” says Melvyn. The findings could also lead to the development of new technologies that allow mineral exploration without invasive drilling or excavation.

“Ground that was too difficult or too expensive to explore because of the deep barren sediments might [now] reveal gold deposits relatively inexpensively,” says Melvyn, adding that companies may now be able to explore in an environmentally friendly way.

Until this study, scientists had debated whether the traces of gold found on plant surfaces and in topsoil were blown there by the wind.

“This represents the first conclusive evidence that elevated gold concentrations measured in trees are not a surface contamination,” says Professor Cliff Stanley, a geologist at Acadia University in Canada.

Rather, the gold has made its way into trees in solution via the roots, and has subsequently been transported and precipitated as native gold in the leaves of the tree.”

Dr Nigel Radford, a geochemist based in Perth, says the implications for the gold mining industry are significant. “These findings will open the way for exploration companies to collect samples of leaves and soil from surface and deduce with some real confidence what the distribution of gold deeper in the ground is likely to be,” he says.

Nigel says sampling on surface is much quicker and cheaper than drilling closely spaced drill holes. Surface sampling also has a far lower environmental impact than current sampling methods.


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