Using eucalyptus trees to find gold

Researchers had known that eucalyptus leaves contained gold, but they did not know if the gold came from the ground or airborne particles, writes Melvyn Lintern in his research paper published by Nature this month.

“There is no unequivocal evidence that Au is actually absorbed by plants over mineral deposits and that currently measured Au is not merely a result of dust contamination of samples,” writes Lintern, who works for the CSIRO Earth Science and Resource Engineering.

“Thus explorers are reticent to embrace an important emerging technique in which they lack confidence in its applicability, data quality and interpretation of results.”

To test where the gold is coming from, the researchers settled on the Freddo Gold prospect, 40 km north of Kalgoorlie in Western Australia. The Au mineral deposit is under ~30m of clay. There had been exploratory drilling in the area, but importantly no mining. There are also large eucalyptus trees in the area, some greater than 10m in height, a location researchers call “ideal” for their study.

The researchers found that the trees were “. . . highly anomalous in Au exclusively and directly over the buried deposit.”

Gold concentrations in the tree varied from 4 to 80 p.p.b. with leaves showing the highest concentration and bark the lowest.

“This observation conclusively demonstrates active biogeochemical adsorption of Au and provides insight into its behaviour in natural samples,” writes Lintern.

“The confirmation of biogeochemical adsorption of Au, and of a link with abiotic processes, promotes confidence in an emerging technique that may lead to future exploration success and maintain continuity of supply.”