Turning over a gold leaf

Underexplored and highly prospective, South Australia’s Gawler Craton has long drawn interest from those interested in tapping its mineral potential.

It’s unlikely, however, that many have turned to the sprawling mulga trees which span the area as an indicator of what lies beneath; until now.

Gold explorer Marmota recently embarked on an innovative exploration campaign to sample the leaves of the mulga and senna trees on its Aurora Tank prospect in the Woomera Prohibited Area, with promising results.

When processed and tested, the tree leaves had absorbed and contained higher levels of gold over better mineralised areas, and low gold content over poorly mineralised zones.

It’s a process which has been around for some time abroad, but not one that’s particularly well-known or used, according to Marmota Executive Director of Exploration Kevin Wills.

“We decided we wanted to try something new because there’s a chance that, because the anomalies in the leaves are generated by tree roots which sink quite deep, they may be able to see mineralisation deeper than we would see by conventional sampling,” he said.

“The idea is to try and collect leaf samples over the area and look for anomalies, and we’re actually about to begin a program to test some of those anomalies we’ve found.

“That’s going to be interesting.”

A form of biogeochemical exploration, Dr Wills said testing leaves was a low-impact exploration method, requiring just two people on foot or quad bike and allowed for the collection of 60-90 samples per day.

Originally out of Soviet Russia, the technique is one which has been popular in Canadian exploration for a number of years but is yet to really penetrate the Australian exploration market, according to CSIRO Senior Geochemist Nathan Reid.

“Because Australia has a greater species diversity than in the northern hemisphere, there’s been a lot of scepticism around how you use plants to search for mineral deposits,” he said.

“There’s been a lot of research by CSIRO that’s also been part of some larger AMIRA projects which Ravi Anand has run. Collaboration with universities and Geoscience Australia has looked at different plants and environments where this might work, what sort of elements you look for and how you target different styles of mineralisation – not just gold, but all sorts of things like volcanogenic massive sulfide, copper and lead.”

Science is golden

Explorers are typically focused on the ground, so the idea that gold could make its way into the leaves of local trees is one which may seem counter-intuitive.

The key to this is in the plant roots, which often stretch further beneath the surface than auger drilling or soil sampling are likely to reach.

“If you have gold in an accessible part of the subsurface where roots are sitting, and the plants can access it, they’ll inadvertently take up the gold,” Dr Reid said.

“They don’t actually need gold to grow; what they do need is copper. In their absorption of copper, gold being of a similar size and charge will inadvertently pass up the same uptake channels and plant roots, and if there is a larger concentration in that zone you’ll see it transferred into the plant material.

“If you’ve got a gold system you’ll quite often look for arsenic in the plant as well, because a lot of the gold systems have arsenic pyrite in the system. Things like tungsten can be around, and silver sometimes – single elements are good but it’s better if you’ve got a multi-element halo.”

To test consistency, explorers are encouraged to sample at consistent heights and multiple trees within an area.

Dr Reid said uptake of the technology had been mixed in recent years, but the potential was there for further use in the mining space.

“The benefit really is that we’re moving into areas where pretty much everything that’s sticking out of the ground has been found,” he said.

“There’s not much scope left there, so you start looking at areas of transported cover, and the minute that cover gets any more than a metre depth then a lot of the usual techniques don’t work anymore – you either spend a lot of money to send out a drill rig or you use a different technique.

“A lot of people use soil sampling or other ways of testing, but in many cases soil sampling doesn’t work either. If you’ve got too much erosion and nothing’s building up on surface then soil sampling won’t work – but something with a little extra depth could.”

Back in South Australia, Dr Wills believes the exploration technique will bloom the moment someone makes a significant discovery with it.

“It needs more successful usage,” he said.

“As with any new technique, as soon as you find something everyone jumps on the bandwagon. We didn’t originate this technique, it’s not widely used. It is well known amongst the exploration community, but it hasn’t been able to be shown to be successful at finding things as yet.

“If we do find something with it it’ll certainly get a kick- along in terms of future use I think.”

The secrets of the Woomera mulga trees may soon be unlocked.

Image: Taking tree samples at Aurora Tank.

latest news

Sandfire chases $94.5m tie-up with MOD Resources

Sandfire Resources has approached fellow ASX-listed metals miner MOD Resources about a potential takeover.

Read more

WA Gov chasing BHP for unpaid royalties

The State Government is reportedly looking to recover hundreds of millions of dollars in iron ore royalties owed to it by mining giant BHP.

Read more

Union at loggerheads with FMG on rail car asbestos

Fortescue Metals Group’s removal of asbestos from about 3400 Chinese rail cars is being done without sufficient safety precautions, according to the union that represents rail maintenance workers.

Read more

BHP ignore Bill Shorten’s scathing attack

BHP has refused to be drawn into a growing political stoush over its scrapping of an historic domestic shipping contract as Opposition Leader Bill Shorten extended his attack on the mining giant.

Read more

South32 flags C-suite shuffle as cash builds

South32 shareholders may be about to reap more cash returns from the diversified miner as it continues to enjoy healthy prices for its commodities and benefits from strong operating results.

Read more

Tianqi fires up $700m lithium game changer

Tianqi Lithium’s landmark first-stage $400 million plant at Kwinana is all-but finished and into a long commissioning phase that should lead to Asian customers taking high-value lithium hydroxide from WA in the second half of the year.

Read more

 

industry insight

From high vis to health monitoring?

The impact of recent technological advancement on mining processes and efficiencies is well

...
Products & Technology

Automation to suit the operator

When it comes to better drilling efficiencies, it’s all about going the extra mile; something Cat’s latest rotary blasthole drills have taken to heart.

People & Projects

Optimism returning as industry picks up pace

It has been a big 12 months for the Western Australian mining sector.

Occupational Health and Safety

The new benchmark in safety

When it comes to building trust and transparency, identifying and implanting safety standards is paramount to any mining business.

interview

A greenfield renaissance?

Ongoing and sophisticated greenfield mineral exploration is vital to the longevity of the mining industry, yet nationally Australia’s mining sector is experiencing a chronic shortage in greenfield...

Read more