Dormant volcanoes could hold key to green mining

After 10,000 years of ‘magma degassing’, kilometres below Earth’s surface, the biproducts of volcanic magma become steam and a dense brine.

Once trapped between porous volcanic rocks, the brine can be found to contain a range of precious and base metals.

Additionally, as geothermal power can be harnessed as a biproduct of the mining process, this approach could be considered carbon neutral.

Lead author on the paper, Jon Blundy, said finding environmentally friendly mining techniques has become increasingly important.

“Green mining represents a novel way to extract both the metal-bearing fluids and geothermal power, in a way that dramatically reduces the environmental impact of conventional mining,” Blundy said.

“Getting to net zero will place unprecedented demand on natural metal resources, demand that recycling alone cannot meet.

“We need to be thinking of low-energy, sustainable ways to extract metals from the ground. Volcanoes are an obvious and ubiquitous target.”

The research speculated that copper concentrations in sub-volcanic contexts could be as high as 7000 parts per million, for over one million tonnes of dissolved copper.

The biggest obstacles to this method involved the extreme depths at which the brine must be extracted – around two to four kilometres deep – and the extreme heat experienced at such depths – above 400 degrees Celsius.

The research paper explained the intricacies of extraction.

“In order to become potential economic metal resources, hot, metal-rich brines would need to be extracted efficiently without significant reservoir clogging or well-bore scaling,” the paper stated.

“The extent to which such a resource could be exploited depends on the technological challenges and costs of drilling into hot reservoir rocks and recovering hypersaline liquid.”

Positively, there are unexplored ways to improve the extraction process, and obvious benefits to doing so.

“If copper can be extracted in solution form, copper processing costs may be greatly reduced. Similarly, the co-production of geothermal energy to power fluid extraction and processing would confer additional economic and environmental benefit,” the paper stated.