Eucalyptus tree roots can delve more than 130 feet (40 meters) deep underground in a thirsty search for water. (See "Koalas Climb a Eucalyptus Tree.")
The Nature Communications journal results, reported by a team led by Melvyn Lintern of Australia's CSIRO Earth Science and Resource Evaluation science agency, settle a long-running dispute. Researchers had disagreed over whether gold particles seen in eucalyptus leaves were merely wind-blown or truly represented ore traces transported by roots.
Why It Matters
With gold costing more than $1,300 an ounce, miners might want to look hard at these eucalyptus tree findings, the team suggests. Gold discoveries have declined roughly 45 percent over the last decade. (Related: "Will Deep-sea Mining Yield an Underwater Gold Rush?")
"Despite the decline in discoveries, falling ore grades and increasing demand for (gold), new exploration technologies for (gold) deposits, incorporating the deep penetrating ability of certain trees, have been seldom reported," the study says.
What They Did
The researchers compared eucalyptus tree leaves at gold prospecting sites in Western Australia with leaves from trees 2,625 feet (800 meters) away. They also grew eucalyptus trees in greenhouses with potting soil dosed with gold particles, as well as in normal potting soil without gold.
What They Found
Leaves preferentially stored microscopic gold particles about eight micrometers wide on average. Study authors speculate the particles came from underground, seemingly taken up by the root system of the trees. About 20 leaves needed to be sampled to statistically reveal the presence of gold underneath the trees.
"Gold is probably toxic to plants and is moved to its extremities (such as leaves) or in preferential zones within cells in order to reduce deleterious biochemical reaction," the authors conclude.
Don't start stuffing eucalyptus leaves in your wallet, however. The average concentration of gold in the leaves was only about 46 parts per billion, less than 0.000005 percent of each leaf by weight.
For would-be gold miners, however, eucalyptus trees might offer cheaper, and better, clues to gold deposits, especially smaller ones that wide-area drilling tests might overlook. "Mineral exploration will benefit by embracing and understanding" how leaves might reveal secrets hidden underground, the study authors conclude. (Related: "Gold 'Mining' Termites Found, May Lead Humans to Riches.")
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