Scientists at the Earth Sciences department of the University of Oxford demonstrate how to directly extract valuable metals from hot salty fluids (brines) trapped in porous rocks at roughly 2km below dormant volcanoes. They propose that this green-mining approach will sustainably provide essential metals for a net-zero future.
Magma underneath volcanoes releases metal-rich gasses that ascend toward the surface. These gases separate into brine and steam as the pressure drops. Most of the dissolved metals in the original magmatic gas become concentrated in the dense brine, which gets trapped in porous rock. The less-dense and metal-depleted steam continues to rise to the surface, where it forms fumaroles, the gases, and steam seen at the many active volcanoes around the world.
In a paper published on June 30, 2021, in the journal Royal Society Open Science, scientists reveal how this trapped, underground brine is a potential ‘liquid ore’ containing valuable metals, including copper, gold, zinc, silver, and lithium. These metals could be exploited by extracting the salty fluids to the surface via deep wells.
The Oxford team’s models indicate that the brines potentially contain several million tons of copper, a critical metal for making the transition to net-zero due to its importance in electric vehicles, electricity generation, and transmission.
Prof. Jon Blundy, from the Department of Earth Sciences and the study’s lead author, 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 also shows how geothermal energy will be a significant by-product of the green-mining approach, meaning operations at the well-head will be carbon-neutral.
Conventional mining involves extracting metals, like copper, from underground mines or deep pits in the form of solid ores that need to be ground and processed. Among several downfalls, such mines are environmentally impactful, energy-demanding, and CO2-producing, very expensive to construct and decommission, and produce massive amounts of waste rock. In the case of copper mining, more than 99% of the crushed stone is waste.
Extracting metals in solution form via wells reduces the cost of mining and ore processing, and as a bonus, it also exploits geothermal power to drive operations. This drastically reduces the environmental impact of metal production.
Prof. Blundy, who is funded by a research professorship from the Royal Society to investigate green mining and volcanoes, explained:
Active volcanoes around the world discharge to the atmosphere prodigious quantities of valuable metals. Some of this metal endowment does not reach the surface but becomes trapped as fluids in hot rocks at around 2 km depth. Green mining represents a novel way to extract both metal-bearing fluids and geothermal power, in a way that dramatically reduces the environmental impact of conventional mining.
The study is part of an international effort (between Russia and the UK) that uses hydrodynamic modeling, volcanology, geophysics, geochemistry, and high-temperature experiments.
The Oxford team has worked on drill core from several deep geothermal systems worldwide, including in Italy, Mexico, Japan, Indonesia, and Montserrat, to confirm their estimates of metal-rich brines. In addition, while analyzing the geophysical surveys of volcanoes, the scientists found that almost every dormant and active volcano hosts a potentially exploitable ‘lens’ of metal-rich brine.
Prof. Blundy added:
Green mining is a scientific and engineering challenge that we hope that scientists and governments alike will embrace in the drive to net zero.
The Oxford scientists need to overcome some technological risks, such as preventing scale formation and well-bore corrosion. But, according to the Oxford team, many of these challenges are being addressed via deep, hot geothermal drilling projects and developments in materials science to create resistive coatings.
Another risk that’s small but must be assessed is triggering volcanic eruptions. To avoid this, they plan to drill into the hot rocks above the magma chamber rather than the magma itself. In addition, Oxford scientists have patented an idea for fluid extraction that ensures the fluids continue to flow into the well once drilled.
Over the past five years, the scientists have ‘de-risked the concept and are now ready to drill an experimental well at a dormant volcano. This will illuminate many of the risks and challenges described and will advance our knowledge of volcanoes and their vast abundance of energy and metals. “Continuing the de-risking work, which we are pursuing on many fronts through international collaboration, is important. Likewise, we need to identify the best test-case volcano to drill an exploration well,” explained Prof. Blundy.
The Oxford team predicts that a working ‘brine mine’ could be five to fifteen years away, depending on how well these challenges can be addressed.