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Geological mystery: Study unearths how copper deposits formed

An international study has revealed how continental collisions may have supercharged the Earth's richest deposits of copper, a metal critical for clean energy technologies and global infrastructure.

Dr. Yongjun Lu, from The University of Western Australia's School of Earth and Oceans and a principal geoscientist at RSC, was co-author of the study published in .

Researchers analyzed magmatic rocks from the Gangdese belt in southern Tibet—one of the world's richest porphyry copper provinces.

Porphyry copper deposits are the largest copper source globally and form when hot hydrothermal fluids travel through fractured rocks and precipitate copper minerals.

"The deposits are typically associated with magmas formed above active subduction zones, where oxidized fluids from descending oceanic plates enrich the overlying mantle," Dr. Lu said.

"Yet, some of the largest copper deposits—like those in southern Tibet—formed millions of years after subduction had ceased, which has been puzzling scientists for decades."

Researchers found sediments from the Indian plate—rich in oxidized components such as carbonates and sulfates—were recycled deep into the mantle during continental collision. These materials helped generate oxidized magmas ideal for concentrating copper.

Using mercury and magnesium isotope analyses alongside geochemical fingerprinting, the team identified evidence of oxidized sedimentary material contributing to post-collisional magmas.

"This finding challenges the notion that only oceanic subduction introduces such oxidants into the mantle," Dr. Lu said.

"Think of it as a second wind for copper-forming magmas—even after the oceanic plate is gone, recycled crustal sediments can continue to fuel metal-rich systems for millions of years."

The results will help to expand the search for future resources into tectonic regions previously overlooked.

"It changes the way we think about where and how to look for giant copper deposits and highlights the potential of post-subduction settings—particularly those involving continent-continent collision—as important frontiers for exploration," Dr. Lu said.

"The discovery is timely, as the global demand for copper has increased with the transition to renewable energy and electrified economies."

The research was conducted in collaboration with partners from institutions in China and Europe.