Researchers said Tuesday they had found a surprising marker for deep-buried gold: miniscule traces in the leaves of Eucalyptus trees growing over veins of the yellow metal.
The unusual finding may prove a boon for prospectors in a time of dwindling gold reserves and skyrocketing prices, with new discoveries down 45 percent in the past decade, according to a study in the journal Nature Communications.
"This link between... vegetation growth and buried gold deposits could prove instrumental in developing new technologies for mineral exploration," said a press summary.
Eucalyptus trees can send their roots deep into the ground in search of water in dry areas, even breaking into gold-rich zones where they absorb microscopic metal particles as they drink.
A team of scientists from Australia said they have now shown that gold can be absorbed by the roots and travel through the tree, all the way to its leaves, though in negligible concentrations.
According to the World Gold Council, more than 174,000 tonnes of gold have been extracted from Earth since the beginning of civilisation.
In 2011, the US Geological Survey estimated there were 51,000 tonnes of gold left in reserve in the world.
The price of the precious metal skyrocketed 482 percent between December 2000 and March this year. Sixty percent becomes jewellery, but gold is also a crucial component in electronics and is used in medical technology, including for cancer treatment.
For the study, the team investigated Eucalyptus trees growing at two gold prospecting sites in south and west Australia, using X-ray imaging to check for gold in the leaves, twigs, bark, litter and soil.
Eucalyptus trees, some of which can grow taller than 10 metres (33 feet) have an unusually deep and extensive root system -- some have been documented at a depth of 40 metres.
The concentrations were weak -- several hundredths to thousandths of a gram per tonne, but highest in the leaves, the researchers found.
"Gold is probably toxic to plants and is moved to its extremities (such as leaves)," they said.
Minute traces of gold have sometimes been found on plants, but it had never been clear whether these had been absorbed or blown there by the wind.
The new finding "promotes confidence in an emerging technique that may lead to future exploration success and maintain continuity of supply" of gold, wrote the study authors.