The process of bringing gold to the surface from deep within the Earth’s mantle relies on sulfur bubbling beneath active volcanoes.
Two new papers agree that some forms of sulfur form molecular bonds with gold, allowing the valuable element that would otherwise remain isolated within the mantle to rise. did.
What they don’t completely agree on is which form of sulfur is most important.
Numerical modeling and experiments conducted by a team of geologists led by Deng-Yang He of the China University of Geosciences show that trisulfur is the key. But experiments conducted by Stéphane Farsang and Zoltan Zajac at the University of Geneva show that disulfides play a key role.
Both results are interesting and worth tracking. Because understanding how gold deposits form can help you make the most of this beautiful and valuable gold deposit. useful resource.
The gold deposit is often associated with It involves volcanic activity where tectonic plates meet. There, the edge of one tectonic plate can slide beneath an adjacent plate, forming a so-called subduction zone. The interaction between the two plates forms regions riddled with earthquakes and volcanoes, including a long chain of volcanoes known as . Pacific Ring of Fire.
The gold in these deposits occurs deep beneath the Earth’s surface, within the mantle. If left alone, the dense metal will remain there. However, as a result of volcanic activity, it is absorbed into magma that rises to the surface, where it is deposited.
Scientists believe that the key to its transport is sulfur. Sulfur binds strongly heavy metalinclude gold. But how that sulfur transports gold through Earth’s subduction zones is a matter of debate among Earth scientists.
Deng-Yang He and colleagues experimented with different pressures and temperatures to develop a thermodynamic model that could predict the real-world conditions that cause gold transport. They found that at a very specific set of temperatures and pressures where water is heated and oxidized as the Earth’s crust sinks, gold and trisulfides combine to form a soluble complex with the formula Au(HS)S. I discovered that.3–.
Their calculations showed that the complex could transport gold concentrations of several grams per cubic meter of fluid. This is more than three orders of magnitude higher than the average abundance of gold in Earth’s mantle. This is a very efficient means of swallowing gold from the mantle and releasing it into the crust.
“The thermodynamic model we present now reveals for the first time the existence of a gold-trisulfur complex that we did not previously know existed under these conditions.” geologist Adam Simon says of the University of Michigan.
“This provides a plausible explanation for the very high concentrations of gold in some mineral systems in subduction zone environments.”
But it may not be your only means of transportation. In an experiment conducted at the University of Geneva, Farsang and Zajac oxidation state In their experiments, they added sulfur to pressure conditions and temperatures of 875 degrees Celsius (1607 degrees Fahrenheit), matching the temperature of natural magma.
Previous experiments, including: Highly Cited 2011 Papersindicating that trisulfur is involved in transport. The new results showed that disulfide, hydrogen sulfide and sulfur dioxide are all strongly present at magma temperatures.
This is interesting because disulfides play a role in metal transport in low-temperature hydrothermal fluids. It was thought that disulfides could not exist at magma temperatures. But Farsang and Zajacz’s research shows that it is possible.
“By carefully choosing the laser wavelength,” Farsang says“We also show that previous studies had significantly overestimated the amount of sulfur radicals in geological fluids, and that the 2011 study results were actually based on measurement artifacts, putting an end to this debate.” Ta.”
These are the words they used to fight. Your movement, three sulphurs.
The two papers were published in the following journals: Proceedings of the National Academy of Sciencesand natural earth sciencerespectively.
