Science reveals how to bring gold to the surface from Earth's mantle

Gold is more abundant in Earth’s bulk composition than lead. Its presence on the surface, however, has long been a puzzle because gold atoms prefer to stay buried far below.

On December 29, 2024, a team of international researchers announced results that might solve this longstanding mystery.

They introduced a model that highlights how molten rock, or magma, can carry gold from the Earth’s mantle to higher levels.

The team included Adam Simon, a scientist from the University of Michigan, who collaborated with experts from China, Switzerland, Australia, and France.

Why deeper stores matter

The Earth’s mantle, located many miles below our feet, is a site of intense pressure and heat. Gold atoms mostly remain locked there, yet people have mined gold at the surface for centuries.

Scientists have been curious about what mechanism can nudge gold atoms upward. Researchers have looked at processes like partial melting and volatile fluids, but the exact reason for gold’s movement remained unclear until now.

Geology textbooks often point out that gold does not easily form chemical bonds with other elements. That is still true in typical conditions, but something special happens in certain high-temperature areas below active volcanoes.

The sulfur secret

A key finding involves sulfur in a specific chemical state. A freshly discovered gold-trisulfur complex appears to be good at holding and transporting gold.

This complex arises when sulfur-rich fluid interacts with mantle rock under pressures found about 30 to 50 miles underground. It helps gold stay dissolved rather than clinging to the solid mantle.

Once the complex is formed, gold becomes more mobile in the molten sections of Earth’s interior. Fluid and melt can then carry it upward, where it may eventually end up closer to the surface.

The subduction zone link

A subduction zone forms when one tectonic plate slides beneath another. In these regions, water and sulfur get released from the descending plate, contributing to chemical reactions below.

Molten rock under volcanoes in subduction zones contains more of these dissolved components. The new model suggests that this environment is perfect for building the gold-trisulfur complex.

“All of those active volcanoes form over or in a subduction zone environment,” said Adam Simon. Researchers have linked these same geologic settings to the largest gold deposits on the planet.

Lab-based breakthroughs

In controlled laboratory experiments, scientists replicated conditions found below active volcanoes. They artificially produced magma to track how gold interacts with sulfur.

Data from these experiments fed into a thermodynamic model, which predicts gold’s behavior at various temperatures and pressures.

The model points to a stable gold-trisulfur complex that travels more easily than other forms of gold.

These findings confirm that sulfur changes the chemical state of gold just enough to pull it from deeper zones. As magma rises, gold-enriched fluids bubble out, leaving behind the valuable metal in veins.

A broader view on gold exploration

Results from this study could benefit mineral exploration, especially near subduction zones circling the Pacific. The focus may shift to areas where sulfur-laden fluids circulate, signaling a higher chance of finding gold.

Experts note that these sulfur-driven chemical reactions also involve other metals, hinting at broader implications for mining.

Knowing where and how these fluids move provides new clues about which volcanic arcs might hold more riches.

Better understanding of gold’s path could also offer a clearer picture of the planet’s internal processes.

Researchers continue to refine their models, exploring how each component (heat, fluid, pressure, and chemistry) converges to shape ore deposits.

The future of gold research

Geologists look to apply this knowledge in targeted field studies of regions with active volcanoes. Each volcanic zone has subtle differences in composition and fluid pathways, providing a chance to test predictions from the lab.

Many of these volcanoes sit around the well-known Pacific “Ring of Fire,” but similar processes can occur wherever plates converge. Future fieldwork may explore lesser-known arcs that share these geologic traits.

Understanding how gold ascends through molten rock not only solves a longstanding riddle but also broadens our approach to resource discovery.

By merging laboratory data with field observations, scientists hope to piece together the puzzle of gold’s remarkable migration over geologic timescales.

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