Previously, it was thought that both the known and undiscovered gold reserves across all of Earth’s gold mines may not have formed on our planet. Nonetheless, researchers have never uncovered enough gold within any single asteroid to back up the idea that, similar to how much of Earth’s water came from asteroids, gold also made this journey. It has been established by scientists that the gold found in the Earth’s crust actually originates from the mantle.
A global team of scientists has managed to decode the intricate connection between gold and sulfur. This breakthrough offers a more precise comprehension of how gold moved from the Earth’s mantle to its exterior. Furthermore, they've verified that all the gold in the cosmos originates solely from the intense circumstances occurring when two neutron stars collide.
The enigma of gold within the Earth’s mantle
All the gold that exists on our planet came from space billions of years ago and eventually made its way into the mantle following numerous geological events. Nevertheless, how it managed to rise up to the Earth's crust was still an enigma. Despite extensive research, scientists could not provide a conclusive explanation for this occurrence until recently.
The gold deposits found in the Pacific Ring of Fire emerged from deep inside the Earth’s mantle, ascending to the surface via magma. To gain insights into this exact mechanism, researchers carried out a recent investigation detailed in the Proceedings of the National Academy of Sciences.
Through numerical modeling, scientists identified the circumstances enabling the rise of gold-rich magma. This model underscored the importance of the "gold trisulphide complex," bolstering a theory that was once controversial. The research offers fresh support for the credibility of this idea.
Rise of Gold: From Depths to Digs
In its natural form, gold typically stays buried deep inside the Earth’s mantle. However, its strong attraction to sulfur is key to its movement towards the surface.
When gold encounters sulphur, a chemical reaction occurs, transforming the precious metal into a “gold trisulphide complex”. This complex is inherently unstable within the mantle’s environment. When geological conditions align – such as during periods of volcanic activity – the unstable gold trisulphide complex, carried within rising magma, begins its ascent from the depths.
Conditions to reach the surface
However, gold cannot rise from everywhere. The ideal location for this is a subduction zone, an area where one tectonic plate is forced under another. This “gold trisulphide complex” needs specific pressure and temperature conditions, found 50 to 80 kilometres below an active volcano. In such conditions, the temperature must reach 875 degrees Celsius, typically the temperature of magma. Consequently, gold ascends from the mantle to the surface along with the magma.
Gold readily bonds with trisulphide, forming a flexible substance that moves easily within the magma. Researchers claim this is the first time the role of the “gold trisulphide complex” has been explained in this process, a phenomenon previously unknown to them. This discovery also explains why gold is abundant near certain minerals within the subduction zone environment.
