Golden fungi could point to future discoveries 

Can nature offer yet more clues at the Earth’s surface to indicate the presence of gold below?

A research collaboration between CSIRO, The University of Western Australia, Murdoch University and Curtin University has offered hope through a multi-disciplinary approach harnessing geology, molecular biology, informatics analysis and astrobiology, resulting in the discovery of gold-coated fungi near Boddington in Western Australia.

Building on previous CSIRO research which found native trees around Kalgoorlie and in South Australia’s Gawler Craton could draw gold particles up into their leaves, this latest breakthrough saw a team of scientists screen, identify and characterise the gold-oxidising fungus, pointing to its potential use in exploration activities.

The findings were published in a report titled Evidence for fungi and gold redox interaction under Earth surface conditions in the journal Nature Communications.

Using a molecular probe called tetramethylbenzidine, the researchers screened microbial colonies cultured on an agar plate spiked with gold particles.

CSIRO Chief Research Scientist Dr Ravi Anand said the work made clear that fungi could oxidatively interact with element gold, which was of significance for gold biogeochemical cycling.

The thread-like fungi lives in soils and attaches balls of gold to its strands through an oxidisation process, dissolving and precipitating particles from its surroundings.

“This cycling process may contribute to how gold and other elements are distributed around the Earth’s surface,” Dr Anand said.

When you consider the importance of gold in Australia’s commodity mix, the potential significance of the discovery is clear.

The Department of Industry, Innovation and Science’s June 2019 Resources and Energy Quarterly report ranked the nation as the second largest producer of gold in the world. In 2018, Australia produced 315 tonnes of the precious metal, or 9.4 per cent of total global production.

But forecasts envisage production will decline in the near-future unless new gold deposits are found.

The report predicted world gold supply would fall at an average annual rate of 1.6 per cent between 2019 and 2021.

“This reflects long-established projects reaching end of life, with few new projects and expansions to take their place,” it said.

“Declining world mine production is expected across most major gold-producing countries, and will be particularly evident in Australia — which is expected to account for the closure of over 51 tonnes of mine capacity between 2019 and 2021.”

Dr Tsing Bohu, CSIRO lead author of the fungi research, said this underscored the need for new, low-impact exploration tools to fuel the next generation of discoveries.

“The deposits of these resources are difficult to find in Australia because much of our continent is covered by a blanket of deeply weathered and altered rocks, soil and sediments called regolith, rendering them incredibly hard to interpret,” he said.

“The industry is actively using innovative exploration sampling techniques such as gum leaves and termite mounds, which can store tiny traces of gold and can be linked to bigger deposits below the surface.

“We want to understand if the fungi we studied, known as fusarium oxsporum, and its functional genes can be used in combination with these exploration tools to help industry to target prospective areas in a way that’s less impactful and more cost-effective than drilling.”

Dr Bohu said the fungi’s ability to interact with gold was surprising given the commodity is one of the most chemically inactive elements on earth.

“Fungi are well-known for playing an essential role in the degradation and recycling of organic material, such as leaves and bark, as well as for the cycling of other metals, including aluminium, iron, manganese and calcium,” he said.

“This interaction is both unusual and surprising – it had to be seen to be believed.”

The gold-coated fungi were found to grow bigger and spread quicker than those that didn’t interact with gold. They also played a central role in a biodiverse soil community.

It could herald the first evidence that fungi may play a role in the cycling of gold around the earth’s surface.

“We are conceiving an array of experiments to verify if the gold coated fungi could be used for gold mine exploration,” Dr Anand said. “During the research, we realised the in-situ abundance of the fungus may not be an indirect indicator of an undercover gold mine.

“If our hypothesis is true, we may add a new tool to the portfolio of mineral exploration. Like other surface exploration proxies, the mycological method can help mining companies narrow down the targeting area, which is of great economic advantage.”

 

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