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A nest of little gold-diggers

The dirt-sampling technique only works in cases where the minerals are relatively close to the surface.
The dirt-sampling technique only works in cases where the minerals are relatively close to the surface. PHOTO SUPPLIED

A nest of little gold-diggers

A mining exploration firm working in the remote jungles of northeastern Cambodia is using termites in its search for gold

Deep in the heart of Ratanakkiri province, the earthen mounds that pepper the forest floor provide clues as to the mineral wealth that lies below.

The mounds – some reaching three metres in height – are just the visible tip of a huge underground mining operation carried out by an army of termites, which dig to great depths in search of nourishment and water.

While digging, the industrious insects transport tiny particles of gold and other minerals to the surface to build up their mounds. By analysing the contents of these dirt structures, geologists can learn a lot about the composition of the soil and rock below.

Ravi Anand, chief research scientist at CSIRO Mineral Resources, a division of Australia’s national science agency, said termite mound sampling has a proven track record as a cost-effective way of finding new mineral resources.

“Termites are capable of generating [mineral] anomalies at the surface,” he said, while noting that the under-lying source of the minerals must be relatively close to the surface for this to be possible.

During the dry season, termites burrow 30 metres or more below the surface to reach the water table, digesting whatever material they encounter along the way.

The ingested particles of rock and soil in their guts are excreted upon returning to the surface to construct the mounds that protect their nests.

Anand said the excretion of these soil particles is “a driving force in the redistribution of metals in the surface layer of earth”.

Since first touching down in Cambodia six years ago, Canadian mining firm Angkor Gold has collected samples from more than 110,000 termite mounds on its prospects in Ratanakkiri and Mondulkiri provinces.

The samples have helped the company to identify concentrations of gold and base metals such as copper and molybdenum on its seven tenements, which cover 1,500 square kilometres.

John-Paul Dau, Angkor Gold’s vice president of operations, said the high density of termite mounds in Cambodia – with colonies spaced less than 20 metres apart – lends itself to the technique.

Termite mound testing has already yielded results in Cambodia.
Termite mound testing has already yielded results in Cambodia. PHOTO SUPPLIED

“It works really well here because there is such a high density of termite mounds, so you end up getting a proper sample of [a prospect’s] geochemistry,” he said.

According to Dau, termite mound sampling is about three times more cost-effective than conventional ‘C’ zone augur drilling, requiring less manpower, time and equipment. But it all comes down to a company’s ability to discern the geochemical pointers embedded in the termites’ droppings.

“The termite is not coming up and pooping gold, he is pooping dirt,” said Dau. “But that dirt always has a signature – and maybe occasionally there’s a grain or two of gold.”

Angkor Gold collects two samples from each termite mound, recording the coordinates of the mound in its mapping database. The first sample is dissolved in water and panned for gold-bearing concentrates.

The second is pounded down to a powder and run through a fine sieve, then sent to a laboratory for analysis using an XRF spectrometer – an instrument that measures the trace elements
in the powdered samples.

“With all this repeated several times, you start to paint a picture of what’s happening under the earth’s surface,” Dau said.

However, the results of the sampling must be weighed judiciously, as soils are often transported from elsewhere.

“If it’s an indication of structure, you go back and follow it up, but if you’ve got sporadic gold samples, you really want to be very careful about how you interpret that,” Dau explained.

“With gold, you have to take it like a grain of salt and see how it fits in with the bigger picture, whereas with base metals, it is far more accurate as a tool here in Cambodia.”

He said termite mound sampling is a fast and cost-effective way for Angkor Gold to cover a lot of ground while minimising its environmental footprint. But it is only one tool in the company’s resource-mapping arsenal.

Where the sampling indicates a gold or base metal deposit, further exploration is conducted with traditional techniques such as exploratory drilling, induced polarisation surveys and aerial magnetic mapping.

To date, Angkor Gold is the only mining firm using termite mound sampling extensively in Cambodia. Others have acknowledged the technique’s merit, but say it is of limited use for their projects.

Justin Tremain, managing director of Renaissance Minerals, an Australian mining firm that is exploring gold prospects in Mondulkiri province, said the technique is not suited to the topography of his company’s tenements.

“Some environments get a thin layer of soil at the surface [that is transferred from elsewhere], so surface sampling doesn’t give an effective look at what’s below,” he said. “But in our case, the surface soil should represent the soil at depth, [reflecting] the rocks beneath the soil.”

And even without termites to point the way, test drilling at these prospects has confirmed the presence of gold.


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