New research from Adelaide University has revealed that geological processes dating back billions of years are critical to locating the rare earth elements needed for modern technologies and the global clean energy transition.

Rare earth elements are essential components in technologies such as electric vehicles, wind turbines, smartphones, and defence systems. However, locating economically viable deposits remains a major global challenge.

Led by Professor Carl Spandler from the School of Physics, Chemistry and Earth Sciences, the research team reconstructed Earth’s geological history over the past two billion years using advanced plate tectonic modelling.

They identified regions of the Earth’s mantle that had been fertilised by subduction processes, where material from one tectonic plate is forced beneath another, releasing fluids and elements into the overlying mantle.

The Adelaide University researchers found that these fertilised mantle regions now underlie approximately 67% of carbonatites and 72% of REE deposits formed over the past 1.8 billion years. For older deposits, that figure rises to 92%.

Prof Spandler said the findings provide compelling evidence that ancient subduction zones play a fundamental role in creating the conditions needed for rare earth deposits to form.

“This research shows that the ingredients for these critical mineral deposits were put in place many million to even billions of years ago,” Prof Spandler said. “By identifying where these ancient processes occurred, we can significantly narrow down the search areas for future discoveries.”

The study also challenges previous theories that linked these deposits primarily to mantle plumes –columns of hot material rising from deep within the Earth.

Instead, the research highlights a two-stage process: an initial fertilisation of the mantle during subduction, followed – sometimes hundreds of millions or even billions of years later – by a separate event that triggers melting and magma formation.

“This time lag is one of the most surprising aspects of our findings,” Prof Spandler said. “It shows that the Earth’s mantle can store these enriched zones for incredibly long periods before the right conditions arise to form mineral deposits.”

The research team mapped these regions across the globe, finding they cover around 35% of the Earth’s continental crust. Importantly, areas where multiple subduction events overlapped were found to host particularly high concentrations of REE deposits.

Co-author Dr Andrew Merdith said the work has significant implications for mineral exploration.

“By focusing on these ancient tectonic zones, exploration companies and governments can take a more targeted and efficient approach to finding new deposits,” Dr Merdith said. “This is especially important as demand for rare earth elements continues to grow.”

The findings also provide new insights into Earth’s geological evolution, including how continents have been shaped over billions of years and how deep Earth processes influence surface resources.

Beyond resource exploration, the study highlights the long-term storage of carbon and water in the Earth’s mantle, with implications for understanding past climate and volcanic activity.

The research was conducted in collaboration with the ARC Centre in Critical Resources for the Future.

‘Linking carbonatites, rare earth ores, and subduction-fertilized mantle lithosphere’ is published in Science Advances. DOI: 10.1126/sciadv.aeb2942