Lift off! CO2 bubbles carry vital metals, Leicester team discovers

Carbon dioxide, so often the villain of the piece for the environment, plays a crucial role in making metals used in green technologies accessible for mining, a team led by researchers from the University of Leicester have discovered.

In a paper published today in Nature Communications, lead author Daryl Blanks of the University of Leicester reveals that nickel, copper, cobalt and platinum-group elements, normally inaccessible hundreds of miles underground in the Earth’s mantle, can be carried by CO₂ ‘bubbles’ through magma away from the mantle and into the upper crust, where they have the potential to form large ore deposits.

These metals are vital for resourcing green technologies such as electric vehicle batteries, catalytic converters, as well as smart phones, but deposits are rare, given their usually inaccessible location. The discovery may assist in the search for new deposits, allowing exploration to broaden out to viable locations that may not have previously been considered.

Using a number of natural geological laboratories from around the world, PhD researcher Daryl Blanks and Associate Professor Dr David Holwell from the Centre for Sustainable Resource Extraction at the University of Leicester led an international team to identify that certain types of magma produce a supercritical CO₂ fluid in the mantle, which has a strong attraction to sulphide liquid droplets.

Critically, this CO₂ fluid is less dense than the magma itself and so rises, carrying the dense metal-rich sulphides with it. As the CO₂ and sulphide get closer to the surface, they then part ways, leaving no evidence of CO₂ in the upper crust. The team’s evidence of carbonate and sulphide in the lower crustal rocks provide a vital snapshot of this deep process in action, before it is eradicated in the upper crust.

Lead author Daryl Blanks said: “CO₂ has been viewed in recent times as having a negative role in science, considered the villain in causing climate change, but we show that it is actually a hidden hero in bringing us the metals essential for the future of clean energy. The idea here is that CO₂ plays a critical role in the transfer of metals from the mantle and has major implications in the formation of metal-rich magmatic deposits which are used for technologies like electric vehicle batteries.

“The process of transporting metals by CO₂ is like the initial fuel boosters on a rocket launch to space. The fuel boosters (CO₂) are essential in getting the rocket (magma) and its precious cargo (metal-rich sulfides) off the ground, but once spent, the fuel tanks separate, and the evidence they were there by the time the rocket reaches space is gone!”

The team led by University of Leicester included: Marco Fiorentini (Centre for Exploration Targeting, University of Western Australia); Marilena Moroni (University of Milan, Italy); Andrea Giuliani (ETH Zurich, Switzerland); Santiago Tassara (Yale University, USA); Jose-Maria Gonzalez-Jimenez (Universidad de Granada, Spain); Adrian Boyce (Scottish Universities Environmental Research Centre); and Elena Ferrari (University of Milan, Italy).

• Fluxing of mantle carbon as a physical agent for metallogenic fertilization of the crust