Highlights

• A University of Adelaide study published in Science Advances shows that 72% of known rare earth deposits lie above ancient subduction zones where tectonic plates collided up to 2 billion years ago, suggesting a predictable geological pattern rather than random distribution.
• The research identifies a two-stage formation process: subduction first “fertilizes” the mantle with enriched elements, then a separate trigger millions to billions of years later causes melting that concentrates rare earths into mineable deposits.
• The findings enable more targeted mineral exploration by focusing searches on ancient tectonic belts near stable cratons, potentially reducing exploration costs and uncertainty for the critical minerals supply chain.

A new global study led by Carl Spandler of the University of Adelaide, alongside Andrew S. Merdith and Amber Griffin, offers a striking reframing of where rare earth elements (REEs) come from—and where to find them. Published in Science Advances, the research shows that most REE deposits are not random, but sit above ancient zones where tectonic plates once collided and sank deep into the Earth. These long-buried “fertilized” mantle regions now underlie roughly 72% of known rare earth ore deposits and 67% of carbonatite systems, the key host rocks for REEs. The implication is profound: today’s critical mineral supply chains may be rooted in geological processes that began up to 2 billion years ago, long before the deposits themselves formed.

Study Methods: Reconstructing Deep Time

The team used advanced plate tectonic modeling (via GPlates) to reconstruct Earth’s continental movements over the past 2 billion years. They identified long-lived subduction zones—where one plate dives beneath another—and mapped “fertilized mantle lithosphere” regions extending up to 900 km inland. These zones were then compared against a global dataset of 304 carbonatites and 108 REE deposits to test for spatial overlap.

Key Findings: A Two-Stage Geological Process

The results point to a two-stage formation model. First, subduction injects fluids and elements into the mantle, enriching it chemically—what researchers call a “primer.” Then, often millions to billions of years later, a separate “trigger” (such as tectonic stretching or heat flow) causes melting, concentrating rare earths into mineable deposits.

Notably, the study finds no direct timing link between these stages—explaining why deposits can appear far from active plate boundaries today.

Limitations and Open Questions

The model captures only long-lived subduction systems and excludes other processes like mantle plumes or short-lived tectonic events. It also cannot fully account for deposits formed before 2 billion years ago or those altered by erosion and crustal movement. Correlation is strong—but not absolute.

Implications: Narrowing the Search

For industry, the takeaway is clear: exploration can be more targeted. Instead of scanning entire continents, companies can focus on ancient tectonic belts—especially near stable cratons—reducing cost and uncertainty.

What Comes Next?

Future work will refine tectonic reconstructions and integrate additional formation mechanisms. For investors and policymakers, the message is simple: the next generation of rare earth discoveries may depend less on new technology—and more on better understanding Earth’s deep past.

Source: Spandler et al., Science Advances (2026) — https://www.science.org/doi/10.1126/sciadv.aeb2942 (opens in a new tab)