Gold hunters need only consult the trees if they want to track down some of that sweet Au. Why? Because when certain trees strike gold with their roots, the chemical element ends up in their leaves. It seems in Australia, gold quite literally grows on trees.
The gold leaves are found on eucalyptus trees that are able to transport microscopic particles of gold from deep deposits thanks to their incredibly long roots. The roots of Eucalyptus marginata can stretch 40 meters (130 feet) into the ground in search of water in an arid landscape, and it seems they pick up a few things along the way.
We’ve known about Australia's gold-leaved trees for a while now thanks to a 2013 paper that explores the use of vegetation sampling as a means of searching for minerals. At one point it was thought that detecting gold in plant samples was to do with surface contamination rather than it having been absorbed from the environment, but their research showed it’s possible for particular Au to ride the eucalyptus root trains all the way to the surface.
Proving that eucalyptus trees could do this meant finding gold country, so they headed for the Freddo Gold Prospect north of Kalgoorlie in Western Australia. On top of its deep-dwelling gold layer are large eucalyptus trees whose leaves, twigs, and bark revealed significantly high Au (the chemical element symbol for gold) content.
The findings were mirrored in a greenhouse experiment that grew seedlings in sand pots dosed with gold. Just like their wild relatives, scanning electron microscopy revealed Au particles in their leaves.
In 2019, a company struck gold in South Australia thanks to a tip-off from trees that it was hiding deep below the surface. The 6-meter (20-foot) vein of Au was packing 3.4 grams of gold per ton, according to New Scientist, at a cumbersome depth of 44 meters (144 feet). It was a remarkable find as the deposit was 450 meters (1,476 feet) away from any other known gold sources.
It might not be the weight-of-a-man nugget that hunters dream of, but finding trees with expensive leaves is a less invasive way to go prospecting. At least, until the digging begins.