Headline: New Study Unveils How Gold Reaches Earth’s Surface, Shedding Light on Giant Deposits
Subhead: Researchers from the University of Michigan and international collaborators discover a gold-sulfur complex that plays a crucial role in gold’s journey from Earth’s mantle to its surface.
Article:
A team of researchers, including scientists from the University of Michigan, has made a groundbreaking discovery that sheds light on how gold reaches the Earth’s surface. Their findings, published in the Proceedings of the National Academy of Sciences, reveal the importance of a gold-trisulfur complex in the formation of gold deposits.
Gold is known to be associated with volcanic activity around the Pacific Ring of Fire, originating from the Earth’s mantle and transported to the surface by magma. However, how gold actually makes its way to the surface has been a topic of debate. The research team, led by Adam Simon, a professor of earth and environmental sciences at UM and one of the study’s authors, has used numerical models to uncover the specific conditions that cause gold enrichment in magma as it rises from the mantle to the surface.
The study highlights the significance of the gold-trisulfur complex, whose existence has been hotly debated. Under a specific range of pressure and temperature conditions, between 30 and 50 miles beneath active volcanoes, the complex causes gold to migrate from the mantle into magma, which eventually makes its way to the Earth’s surface.
"Our published thermodynamic model is the first to confirm the existence of the gold-trisulfur complex under these conditions," said Simon. "This provides the most plausible explanation for the extremely high concentrations of gold found in some mineral systems in subduction zone environments."
Gold deposits associated with volcanoes form in a process known as subduction, where one tectonic plate (like the Pacific Plate) sinks beneath another. In the zones where these plates meet, magma from the mantle can rise to the surface.
"From New Zealand to Indonesia, the Philippines, Japan, Russia, Alaska, the western US, Canada, and Chile, we have many active volcanoes," Simon explained. "All of these active volcanoes form in or near subduction zones, and it’s the same process that generates gold deposits."
Gold happily resides in the mantle above subducting plates. However, when conditions are right for adding sulfur-rich fluid from the subducting plate to the mantle, gold prefers to bond with trisulfur to form the mobile gold-trisulfur complex.
This study, involving scientists from China, Switzerland, Australia, and France, is the first to present a robust thermodynamic model for the existence and importance of the gold-trisulfur complex. The team developed the model based on laboratory experiments where they controlled pressure and temperature and measured the results. They then created a thermodynamic model that predicts the results of these experiments, which can be applied to real-world conditions.
"Our findings provide a strong understanding of what causes certain subduction zones to produce extremely gold-rich ore deposits," said Simon. "Combining these results with existing research will ultimately enhance our understanding of how gold deposits form and could have positive implications for exploration."
More Information:
Deng-Yang He et al, Mantle oxidation by sulfur promotes the formation of giant gold deposits in subduction zones, Proceedings of the National Academy of Sciences (2024). DOI: 10.1073/pnas.2404731121
Image Caption: Gold-sulfur complex formation in magma. Credit: Proceedings of the National Academy of Sciences (2024). DOI: 10.1073/pnas.2404731121
