Study: Sulfur helps gold reach Earth’s surface
Gold deposits are often found in places with intense volcanic activity, and scientists have long known that the sparkly substance gets there with the help of magma, the molten rock that fuels volcanoes. But gold is a dense metal that originates in Earth’s mantle, far beneath the surface. So how does it manage to rise up to form gold deposits on the surface?That question has long vexed scientists, but a recently published analysis in PNAS offers an explanation. The study, conducted by an international team of researchers, developed a thermodynamic model that predicts why gold gushes upward with volcanic activity.The action occurs in deep-sea subduction zones where tectonic plates collide. As one plate slips beneath its neighbor, volcanic activity can move magma from Earth’s mantle — the geologic layer that sits between Earth’s hot core and its crust — upward.Usually, gold is locked within Earth’s mantle. But scientists have long suspected that sulfur, which forms strong chemical bonds with gold, allows it to be transported in magma up to the surface.The new thermodynamic model quantitatively predicts what happens in these subduction zones. The researchers discovered that sulfur in the mantle can combine with gold, creating a stable complex that can transport large amounts of gold upward from Earth’s mantle to its crust through magma.The complex, known as a gold-trisulfur complex, “acts as an extremely effective agent to transport and concentrate” gold, the researchers write, extracting up to 100 times more gold from the mantle than areas without the fluid.“The same types of processes that result in volcanic eruptions are processes that form gold deposits,” Adam Simon, a University of Michigan professor of Earth and environmental sciences and a co-author of the study, said in a news release. “This thermodynamic model that we’ve now published is the first to reveal the presence of the gold-trisulfur complex that we previously did not know existed at these conditions,” Simon said.It’s the “most plausible explanation” for high gold concentrations in places like the gold-rich Ring of Fire region of the Pacific Ocean, which has abundant active volcanoes, he adds.
Scientists have long suspected that sulfur, which forms strong chemical bonds with gold, allows it to be transported up to the surface.
Gold deposits are often found in places with intense volcanic activity, and scientists have long known that the sparkly substance gets there with the help of magma, the molten rock that fuels volcanoes. But gold is a dense metal that originates in Earth’s mantle, far beneath the surface. So how does it manage to rise up to form gold deposits on the surface?
That question has long vexed scientists, but a recently published analysis in PNAS offers an explanation. The study, conducted by an international team of researchers, developed a thermodynamic model that predicts why gold gushes upward with volcanic activity.
The action occurs in deep-sea subduction zones where tectonic plates collide. As one plate slips beneath its neighbor, volcanic activity can move magma from Earth’s mantle — the geologic layer that sits between Earth’s hot core and its crust — upward.
Usually, gold is locked within Earth’s mantle. But scientists have long suspected that sulfur, which forms strong chemical bonds with gold, allows it to be transported in magma up to the surface.
The new thermodynamic model quantitatively predicts what happens in these subduction zones. The researchers discovered that sulfur in the mantle can combine with gold, creating a stable complex that can transport large amounts of gold upward from Earth’s mantle to its crust through magma.
The complex, known as a gold-trisulfur complex, “acts as an extremely effective agent to transport and concentrate” gold, the researchers write, extracting up to 100 times more gold from the mantle than areas without the fluid.
“The same types of processes that result in volcanic eruptions are processes that form gold deposits,” Adam Simon, a University of Michigan professor of Earth and environmental sciences and a co-author of the study, said in a news release. “This thermodynamic model that we’ve now published is the first to reveal the presence of the gold-trisulfur complex that we previously did not know existed at these conditions,” Simon said.
It’s the “most plausible explanation” for high gold concentrations in places like the gold-rich Ring of Fire region of the Pacific Ocean, which has abundant active volcanoes, he adds.