Gold is more plentiful in the Earth’s makeup than lead. Yet, finding it on the surface has always been a bit of a mystery. Gold atoms usually hide deep underground, far from sight.
On December 29, 2024, a team of researchers from around the world shared findings that may finally explain this puzzle.
They presented a model showing how molten rock, known as magma, can transport gold from the Earth’s mantle to closer depths.
Among the team was Adam Simon from the University of Michigan. He collaborated with experts from China, Switzerland, Australia, and France.
The Earth’s mantle lies deep below us, where heat and pressure are intense. Gold atoms typically remain trapped down there, but people have been mining gold for centuries at the surface. This raises an interesting question: What moves these gold atoms upward?
Scientists have considered several possibilities, like partial melting and volatile fluids, but the exact mechanism was not clear until now. Textbooks often state that gold doesn’t easily bond with other elements. While that is true under normal conditions, unique reactions under high-temperature areas near active volcanoes change this scenario.
A recent discovery points to sulfur in a special state as crucial to moving gold. Researchers found a gold-trisulfur complex that effectively holds and transports gold.
This complex forms when sulfur-rich fluids interact with mantle rocks about 30 to 50 miles underground. In these conditions, gold can remain dissolved in fluid rather than sticking to solid rock.
With the complex in place, gold can move more freely in molten areas of the Earth, allowing it to travel upward until it reaches the surface.
A subduction zone occurs where one tectonic plate slides beneath another. Here, descending plates release water and sulfur, sparking chemical reactions below.
The magma from these subduction zones has higher concentrations of dissolved components, making them ideal for forming the gold-trisulfur complex. “All these active volcanoes are linked to subduction zones,” noted Adam Simon. These areas are also associated with the largest gold deposits globally.
In lab experiments, scientists recreated conditions found beneath active volcanoes to observe how gold behaves in the presence of sulfur.
Their findings contributed to a thermodynamic model predicting how gold behaves under various temperatures and pressures. The results show that the gold-trisulfur complex is more stable and travels better than other forms of gold.
This research could have significant implications for mineral exploration, especially near subduction zones around the Pacific. It’s likely to steer attention to areas with sulfur-rich fluids, which may indicate potential gold deposits.
Moreover, understanding how these fluids move can provide insights into where volcanic arcs might contain more riches. This knowledge could also reveal details about the planet’s internal processes and help researchers uncover how elements like heat, fluid, pressure, and chemistry come together to form ore deposits.
Looking ahead, geologists aim to apply this knowledge in specific field studies of volcanic regions. Each volcano has different compositions and fluid paths, offering opportunities to test lab predictions. While many volcanoes are found along the Pacific “Ring of Fire,” similar processes may happen wherever tectonic plates meet.
This understanding of how gold travels from deep Earth to the surface not only answers a long-standing mystery but also helps refine our exploration techniques for discovering valuable resources. By combining laboratory data and field observations, scientists hope to piece together the impressive journey gold takes over geological timescales.
