A groundbreaking thermodynamic model reveals how gold travels from deep within Earth’s mantle to its surface through volcanic activity, solving a longstanding mystery about the formation of major gold deposits around the Pacific Ring of Fire.
Published in Proceedings of the National Academy of Sciences | Estimated reading time: 4 minutes
An international research team has identified a crucial new gold-sulphur complex that helps explain how gold becomes concentrated in rich deposits around volcanically active regions. Their discovery illuminates the specific conditions deep within Earth that allow gold to be transported from the mantle to the surface through magma.
“This thermodynamic model that we’ve now published is the first to reveal the presence of the gold-trisulphur complex that we previously did not know existed at these conditions,” said Adam Simon, professor of earth and environmental sciences at the University of Michigan and co-author of the study. “This offers the most plausible explanation for the very high concentrations of gold in some mineral systems in subduction zone environments.”
The research focuses on subduction zones – regions where oceanic plates dive beneath continental plates around the Pacific Ocean. These geological seams create conditions where magma from Earth’s mantle can rise to the surface, carrying gold with it. The process occurs at depths of 30 to 50 miles beneath active volcanoes, where specific pressures and temperatures allow gold to bond with trisulphur to form a highly mobile complex.
“On all of the continents around the Pacific Ocean, from New Zealand to Indonesia, the Philippines, Japan, Russia, Alaska, the western United States and Canada, all the way down to Chile, we have lots of active volcanoes,” Simon explained. “All of those active volcanoes form over or in a subduction zone environment. The same types of processes that result in volcanic eruptions are processes that form gold deposits.”
The team’s model demonstrates that when fluids containing trisulphur ions from subducting plates interact with the mantle under precise conditions, gold strongly prefers to bond with trisulphur. This new complex can concentrate gold up to 1,000 times more than its average mantle abundance, explaining the formation of rich deposits near volcanic regions.
To develop their model, researchers combined laboratory experiments under controlled pressure and temperature conditions with theoretical predictions. The resulting thermodynamic framework provides real-world insights that could improve gold exploration efforts.
Glossary:
- Subduction Zone: A region where one tectonic plate dives beneath another, creating conditions for volcanic activity
- Mantle: The layer of Earth between the crust and core where magma originates
- Thermodynamic Model: A mathematical framework that predicts how materials behave under different temperatures and pressures
Test Your Knowledge
Where do most gold deposits associated with volcanoes form?
In subduction zones around the Pacific Ring of Fire, where oceanic plates dive beneath continental plates.
How does gold become mobile enough to travel through magma?
Gold bonds with trisulphur to form a gold-trisulphur complex that is highly mobile in magma.
How much can the gold-trisulphur complex concentrate gold compared to normal mantle levels?
The complex can concentrate gold up to 1,000 times more than its average abundance in the mantle.
What were the two key components combined to develop the new thermodynamic model?
The researchers combined laboratory experiments under controlled pressure and temperature conditions with theoretical predictions to create their model.
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