Water key in bringing volcanic copper to the surface and creating ore deposits

Copper. It’s in our mobile phones, the wiring and plumbing in our house and it’s an increasingly important material in green technologies such as electric vehicles (EVs) and wind turbines. Our daily lives depend on this critical metal and, as we transition to a sustainable future, demand is set to skyrocket.

Almost all copper comes from porphyry copper deposits that form around arc volcanoes, which occur along the subducting edge of tectonic plates. But only a subset of volcanic arcs host copper ore deposits, and scientists have been trying to understand why.

In a recent study, researchers from Cambridge Earth Sciences analysed information about global arc volcanoes to establish which magmatic conditions maximize the likelihood for copper ore formation at the surface.

Just add water

Copper porphyry deposits form when hot hydrothermal fluids from cooling magma concentrate metals and deposit them within fractures in rocks.

“The question we wanted to ask was how these fluids become enriched in copper,” said Marie Edmonds, co-author of the study from Cambridge Earth Sciences.

It’s a puzzle, she explained, because copper is normally scavenged by sulfide minerals as they crystallise from magma. These early‑formed sulfides soak up copper and sink deeper into the crust, locking the metal away. So how does this deep‑seated copper make it back to the surface to be deposited as ore?

To investigate, study author Olivia Hogg – formerly a PhD student at Cambridge Earth Sciences and now Lead Volcanologist at Ascension Earth Resources – built a model containing detailed information about the magmatic systems of global arc volcanoes.

Within this framework, Olivia varied factors such as water content, magma composition, salinity and oxygen availability to see which conditions could mobilize copper from buried sulfide minerals.

The model showed that water was the most likely vehicle for raising copper from the deep crust. Olivia found that when hot, water-rich magma is injected at depth, it percolates through the sulfide minerals – dissolving them to release the copper. As this now copper-boosted fluid moves upward it eventually reaches lower pressures where the fluids cool to form copper ore.

The authors think this scenario is most likely when the crust is particularly thick and mature. In this setting, magmas tend to be more water rich, and the higher pressures in the deep crust make sulfide minerals less stable – allowing them to dissolve more easily and release their copper back into the magma.

Marie said the results match global observations of copper deposits, which are concentrated in areas where the crust is thickened and mature.

The research forms part of a broader investigation by Marie and her group into the lifecycle of volcanic metals — from their enrichment in magmas to their transfer into hydrothermal fluids, mineral phases, and volcanic gases.

Olivia’s findings also help explain why volcanic gases in copper‑mining regions have chemical fingerprints almost identical to those of sulfide minerals. “That suggests the sulfides are breaking down, and those copper‑enriched fluids are also feeding the gases,” explained Marie.

Reference

Hogg, O. R., Edmonds, M., Wieser, P. E., Gleeson, M., Jenner, F. E., & Blundy, J. (2026). Copper-rich fluids arising from sulfide resorption by hydrous arc melts. Scientific Reports.

Feature image: Soufrière Hills, Montserrat, captured mid-eruption by Marie Edmonds.