Thermodynamic model determines how gold reaches the earth’s surface

A research team including scientists from the University of Michigan has discovered a new gold-sulfur complex that can help researchers understand how gold deposits form.

Gold in deposits associated with volcanoes around the Pacific Ring of Fire originates from the Earth’s mantle and is transported to the surface by magma. But how that money comes to the surface is a subject of debate. Now, the researchers have used numerical modeling to uncover the specific conditions that lead to the enrichment of gold in magma that rises from the Earth’s mantle to the surface.

Specifically, the model reveals the importance of the gold-trisulfur complex, the existence of which has been hotly debated, said Adam Simon, professor of earth and environmental sciences and co-author of the study. He states:

The presence of this gold-trisulfur complex in the mantle 30 to 50 miles beneath an active volcano under very specific pressures and temperatures allows the gold to move from the mantle into the magma and eventually to the surface. I will. The team’s results will be published in the Proceedings of the National Academy of Sciences.

“This thermodynamic model that we present now reveals for the first time the existence of a gold-trisulfur complex that we previously didn’t know existed under these conditions,” Simon said. . “This provides a plausible explanation for the very high concentrations of gold in some mineral systems in subduction zone environments.”

Volcano-related gold deposits form in so-called subduction zones. A subduction zone is an area where a continental plate (the Pacific plate below the Pacific Ocean) slides beneath the continental plate that surrounds it. At these seams, where continental plates meet each other, magma from the Earth’s mantle has an opportunity to rise to the surface.

“Every continent around the Pacific Ocean, from New Zealand to Indonesia, the Philippines, Japan, Russia, Alaska, the western United States, Canada and Chile, has many active volcanoes,” Simon said. . “All of these active volcanoes form on or within a subduction zone environment. The same type of processes that cause volcanic eruptions are the ones that form gold deposits.”

Gold lives happily in the Earth’s mantle above a subducting oceanic plate. However, if the conditions are right, where a fluid containing trisulfur ions is added to the mantle from a subducting plate, gold strongly prefers to combine with trisulfur to form gold-trisulfur complexes. This complex is highly mobile in magma.

Scientists have long known that gold forms complexes with various sulfur ions, but this study, involving scientists from China, Switzerland, Australia and France, reveals the existence and significance of gold-trisulfur complexes. This is the first to present a robust thermodynamic model for the

To identify this new complex, the researchers developed a thermodynamic model based on laboratory experiments in which they controlled the pressure and temperature of the experiment and measured the results of the experiment. The researchers then developed a thermodynamic model to predict the outcome of the experiment. This thermodynamic model can be applied to real-world conditions.

“These results provide a very robust understanding of what causes highly gold-rich deposits in certain subduction zones,” Simon said. “Combining the results of this study with existing research could ultimately improve our understanding of how gold deposits form and positively impact exploration.”