Cambridge geoscientists are developing an atlas that could lead to a more complete understanding of how viable rare earth element deposits form and help locate more secure sources, by mapping the global distribution of critical metals deposits within unusual igneous rocks.
Rare earth elements are vital components in many everyday and high-tech devices, from smartphones and lightbulbs to clean energy solutions like wind turbines and electric vehicles.
With the global shift towards low-carbon energy sources, the demand for rare earths is soaring. While there are rare earth deposits around the world, China dominates the global supply chain, accounting for 70% of rare earth ore extraction and 90% of rare earth ore processing. The UK and EU currently have no domestic source or refining capabilities, leading to concerns over the security of supplies.
“These are critical raw materials; critical both because we need them in almost every gadget and technology, but also because the supply chain is so precarious,” said Professor Sally Gibson from Cambridge’s Department of Earth Sciences.
US President Donald Trump’s recent statements about accessing rare earth deposits in Greenland and Ukraine have once again highlighted how fragile the supply chain is for these vital minerals.
“We really need to identify rare earth deposits which have a security of supply,” said Gibson, who currently holds a £1-million project to investigate how rare earth element deposits form, research that could help guide efforts to pinpoint new, economically viable sources.
Rare earth deposits are typically associated with a type of igneous rock called carbonatite. Packed full of calcium, these rocks are unlike other magmas because their chemistry is rich in CO2 and rare earth elements.
The volcano Ol Doinyo Lengai, in Tanzania, is known for its unique, low tempeature carbonatite lava. Credit: Sally Gibson.
Gibson has been studying carbonatites for around 30 years. “Carbonatites have long been seen as geological curiosities, things that no one was that interested in in terms of big-picture science,” she said.
But that outlook has changed in recent years, she added, as the need for rare earths has come to the fore. “How these rocks form is becoming an increasingly important question.”
It’s a question that many geoscientists are asking, but what makes Gibson’s project unique is that, rather than focusing on how individual localities or ‘provinces’ of rare earth deposits form, she is zooming out and examining their global distribution.
Gibson and her colleagues are also looking deeper into Earth’s interior for clues that might explain the surface expression of carbonatites. Project co-lead, Professor Sergei Lebedev, also from Cambridge Earth Sciences, is a geophysicist who uses earthquake waves to ‘see’ into the Earth’s interior, similar to how sonar pings can pick out features on the seabed.
“By combining the geophysical and geochemical evidence, we are learning more about both the deep dynamics and evolution of the Earth’s continents, and the generation of carbonatites and the associated mineral resources,” Lebedev said.
The REE-LITH project was inspired by Gibson and Lebedev’s hunch that differences in the properties of Earth’s lithosphere – the outermost layers of our planet’s structure – might play a guiding role in where carbonatites form, and perhaps their level of rare earth element enrichment.
“We know that lithospheric thickness matters for other special igneous rocks that host diamonds,” said Gibson. “Typically, diamond-hosting ‘kimberlite’ rocks only occur in areas where the lithosphere is particularly thick. I thought it was time we tested if there was a similar relationship for carbonatites.”
Mapping Rare Earths
Over the last year, the team, which includes postdoctoral researchers Siyuan Sui and Emilie Bowman from Cambridge, have been building their new map, drawing on a bank of data on carbonatites and related rare earth deposits and combining this with information about the lithosphere.
As part of this mission, Sui has been using new seismic data extracted from earthquakes to create computer-generated images of the lithosphere, its thickness and other properties. Alongside this, Bowman has been running statistical analyses of geochemical data on magmas to test their relationship to associated rare earth deposits.
When the researchers started to plot occurrences of carbonatites on a map of lithosphere thickness, they quickly saw a pattern.
“We can already tell that carbonatites occur in specific areas, limited to the steep margins that border Earth’s thickest and oldest lithosphere,” said Gibson. “These regions are typically found in the cores of our planet’s major continents.”
Gibson said that while the resolution of their map is increasing, and they can narrow down the regions where carbonatites should occur, they now need to establish why only certain carbonatites generate economically important rare earths. “Having some kind of model that could predict the most likely locations for rare earth deposits is really the ultimate goal for many geologists,” she said.
Collaboration will be key to unlocking that mystery, Gibson said. Her project brings together researchers from across Cambridge Earth Sciences, drawing on the extensive bank of seismic data collected by geophysicists at the Bullard Laboratory and the Department’s expertise in igneous petrology and geochemistry. The team also includes collaborators at the Universities of St Andrews and Exeter.
“Without that multidisciplinary approach, we wouldn’t have been able to pick out these global-scaled patterns in carbonatite occurrence,” she said.
Listen to Sally speak about her project on the Naked Scientists podcast.