A recent study led by a research team including a University of Michigan scientist has unveiled a new mechanism that helps explain how gold deposits are formed and brought to Earth’s surface, Forbes reports.
Gold, while relatively abundant, is largely locked deep within the Earth’s mantle. On the surface, it is primarily found in volcanic or magmatic rocks, but the process that transports gold from deep within the Earth to the surface has long been a subject of scientific debate.
The new research, which employed numerical modeling, identifies the specific conditions required to enrich gold-bearing magmas. The key factor, according to the study, is a particular form of sulfur that exists under a very specific set of pressures and temperatures found about 50 to 80 kilometers (30 to 50 miles) beneath active volcanoes. This sulfur helps transfer gold from the mantle into magmas, which eventually rise to the surface.
While scientists have known that gold can complex with various sulfur ions, this study presents the first robust thermodynamic model for the gold-trisulfur complex, providing new insights into the process. In its pure form, gold remains inert and tends to stay trapped in the mantle. However, when a fluid containing the trisulfur ion is introduced, gold bonds with the trisulfur to form a mobile gold-trisulfur complex. This complex is highly mobile in the molten magma of the Earth’s mantle, making it possible for gold to migrate upward.
The team developed the thermodynamic model based on laboratory experiments that controlled pressure and temperature to create artificial magma. This model can now be applied to real-world geological conditions, offering a clearer understanding of how gold is transferred from the mantle to magma and eventually to the Earth’s surface.
A particular focus of the research was subduction zones, regions where one tectonic plate dives beneath another. In these zones, magma from the mantle can rise to the surface, and the subducting plate melts, releasing sulfur-rich fluids that help form gold-bearing magmas. These processes, which occur in subduction zones, are believed to play a significant role in the formation of gold deposits.
Adam Simon, a University of Michigan professor of Earth and environmental sciences and a co-author of the study, explains that subduction zones are present in many regions around the Pacific Ocean, including New Zealand, Indonesia, Japan, Russia, Alaska, the western United States, Canada, and Chile. These areas are known for active volcanoes, and the processes that cause volcanic eruptions are also responsible for the formation of gold deposits.
The study’s findings provide a more thorough understanding of why certain subduction zones produce gold-rich ore deposits. By combining these new results with existing research, scientists hope to improve the understanding of gold formation and enhance exploration methods for discovering gold deposits. The study, titled “Mantle Oxidation by Sulfur Drives the Formation of Giant Gold Deposits in Subduction Zones”, was published in the Proceedings of the National Academy of Sciences.
