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According to scientists, when gold encounters sulphur, it leads to a chemical reaction. This transforms the precious metal into a “gold trisulphide complex”
Gold, in its natural state, tends to remain deep within the Earth’s mantle. (Representative/Shutterstock)
It was previously believed that gold discovered and yet to be discovered in all of Earth’s gold mines might not have originated on Earth. However, scientists have never found sufficient gold in any asteroid to support the theory that, just as much of Earth’s water arrived via asteroids, so did gold. Scientists knew that gold present in the Earth’s crust originated in the mantle.
An international team of researchers has successfully unravelled the complex relationship between gold and sulphur. This discovery has provided a clearer understanding of how gold travelled from the Earth’s mantle to its surface. Additionally, they have confirmed that gold in the universe is formed only under the extreme conditions present during the collision of two neutron stars.
The mystery of gold in the Earth’s mantle
All the gold present on Earth arrived billions of years ago and, after going through various processes, settled in the mantle. However, the mechanism by which it ascended to the Earth’s surface remained a mystery. Scientists had long investigated this phenomenon but were unable to reach a definitive answer.
The gold ore deposited in the Pacific Ring of Fire originated deep within the Earth’s mantle, rising to the surface through magma. To understand the precise process, scientists conducted a new study published in the Proceedings of the National Academy of Sciences.
Using numerical modelling, researchers determined the conditions facilitating the ascent of gold-rich magma. This model highlighted the role of the “gold trisulphide complex”, supporting a previously debated theory. The study provides new evidence for the validity of this concept.
Gold’s Ascent: From Mantle to Mine
Gold, in its natural state, tends to remain deep within the Earth’s mantle. Its affinity for the element sulphur, however, plays a crucial role in its journey to 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.
