The movement of gold from deep within Earth’s mantle to its surface relies heavily on sulfur bubbling beneath active volcanoes. This process, driven by intense geological activity, enables gold to bond with sulfur molecules, allowing it to ascend rather than remain trapped in the mantle.
Recent research sheds light on the role of sulfur in this phenomenon but leaves room for debate. Two new studies offer different perspectives on which sulfur compound plays the most critical role in gold transport.
Deng-Yang He and his team at the China University of Geosciences suggest trisulfur is the key player. Meanwhile, Stefan Farsang and Zoltán Zajacz from the University of Geneva argue that bisulfide is the crucial agent. Despite their differences, both studies contribute valuable insights that could help us better understand gold deposits and optimize the use of this precious resource.
Golden ore deposits often form near volcanic regions along tectonic plate boundaries, especially in subduction zones. These zones occur where one tectonic plate slides beneath another, generating intense geological activity, including earthquakes and volcanic eruptions. The Pacific Ring of Fire is a prime example of such a region, hosting numerous volcanoes and associated gold deposits.
How Volcanic Activity and Sulfur Drive Gold’s Journey to the Surface
Golden ore originates deep within Earth’s mantle, where it would typically remain due to its density. However, volcanic activity incorporates gold into rising magma, which carries the metal to the surface and deposits it in the crust. Sulfur plays a pivotal role in this process by forming strong bonds with heavy metals like gold. The specific form of sulfur that facilitates gold transport, however, remains a topic of scientific debate.
Deng-Yang He’s team developed a thermodynamic model to simulate the conditions necessary for gold transport. Their experiments revealed that under specific pressures and temperatures, gold bonds with trisulfur to form a soluble complex with the formula Au(HS)S3–. This compound efficiently transports gold, enabling concentrations several thousand times higher than the average abundance of gold in the mantle to migrate to the crust.
“This thermodynamic model is the first to demonstrate the existence of the gold-trisulfur complex under these conditions,” explains Adam Simon, a geologist from the University of Michigan. “It provides a compelling explanation for the high concentrations of gold in some subduction zone mineral systems.”
Geneva Team’s Findings: Bisulfide’s Role in Gold Transport at Magmatic Temperatures
However, the Geneva team challenges this interpretation. Farsang and Zajacz conducted experiments under magmatic conditions, tweaking the oxidation state of sulfur at pressures and temperatures around 875°C (1607°F). They observed that bisulfide, hydrogen sulfide, and sulfur dioxide also play significant roles in transporting gold. Contrary to previous beliefs, their findings demonstrate that bisulfide can exist at magmatic temperatures.
Using advanced laser techniques, Farsang’s team corrected earlier measurements, showing that trisulfur’s role might have been overestimated. “We proved that the results of the heavily cited 2011 study were based on a measurement artifact, settling this long-standing debate,” Farsang asserts.
The debate between trisulfur and bisulfide continues to energize the scientific community. As researchers refine their methods and conduct further experiments, these competing theories may converge, offering a more comprehensive understanding of the processes that transport gold from Earth’s mantle to its surface. For now, the field is poised for the next breakthrough—your move, trisulfur!
Read Original Article: Science Alert
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