New research from the Adelaide University is offering a fresh geological lens for locating rare earth elements.
Research from the Adelaide University suggests the key to unlocking rare earth element (REE) deposits lies not in recent surface geology, but in tectonic processes that occurred billions of years ago.
Published in Science Advances, the study identifies a strong global link between ancient subduction zones and the formation of REE deposits, challenging long-standing assumptions about their origin.
Led by School of Physics, Chemistry and Earth Sciences professor Carl Spandler, the research team reconstructed Earth’s tectonic evolution over the past two billion years using advanced plate modelling. Their findings suggest the conditions required for REE deposits were established deep in Earth’s past, long before the minerals themselves became economically relevant.
Rare earth elements are essential to technologies such as electric vehicles, wind turbines, smartphones, and defence systems. However, identifying viable deposits remains a major challenge for the resources sector.
The Adelaide researchers propose a two-stage formation model. The first stage occurs during subduction, when one tectonic plate is forced beneath another. This process releases fluids and elements into the overlying mantle.
The second stage can occur hundreds of millions, or even billions, of years later, when geological conditions trigger melting. This produces carbonatite magmas, which can host high concentrations of REEs and eventually form mineable deposits.
Professor Spandler said the research highlights just how long these processes can take to translate into accessible resources.
“This research shows that the ingredients for these critical mineral deposits were put in place many million to even billions of years ago,” he said.
“This time lag is one of the most surprising aspects of our findings.
“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 study found that fertilised mantle regions are associated with approximately 67 per cent of carbonatites and 72 per cent of REE deposits formed over the past 1.8 billion years. For older deposits, that figure rises to more than 90 per cent.
These regions now underlie around 35 per cent of Earth’s continental crust, with the highest concentrations of REEs found where multiple subduction events have overlapped.
Professor Spandler said this provides a more precise framework for exploration.
“By identifying where these ancient processes occurred, we can significantly narrow down the search areas for future discoveries,” he said.
Implications for quarrying
The findings challenge previous theories that linked REE deposits primarily to mantle plumes, instead positioning subduction as the dominant control on their formation.
Exploration strategies can be refined by focusing on ancient tectonic boundaries, improving efficiency and reducing the cost of discovery.
Co-author Andrew Merdith noted that targeting these zones could help governments and companies better respond to rising global demand for critical minerals.
“By focusing on these ancient tectonic zones, exploration companies and governments can take a more targeted and efficient approach to finding new deposits,” Merdith said.
“This is especially important as demand for rare earth elements continues to grow.”
Beyond resource exploration, the research provides new insights into Earth’s geological evolution. It demonstrates how the mantle can preserve chemically enriched regions over immense timescales, influencing not only mineral formation but also broader processes such as carbon and water storage. •
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