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Study reveals secrets of gold in gold deposits

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A recent study aimed to unravel the mysteries of the concentration of gold in gold deposits. The question was how gold deposits could form in the earth’s crust. The results of this work also point to new possibilities for the location and exploitation of other deposits.

Gold “hidden” in minerals

Typically, less than one milligram of gold is found per tonne of rock. However, the concentration of this precious metal is a thousand times greater in gold deposits. Gold is poorly soluble in fluids and magmas, so that this level of concentration can only be explained by hydrothermalism. This is the phase separation process that occurs when the fluid is subjected to high temperatures and pressures. On the other hand, you should know that a good part of the gold in the deposits is found in a form hidden in minerals such as pyrite (Fe (S, As) 2) and arsenopyrite (FeAsS). However, the metal is then not usable via conventional methods detection and extraction.

A study published on April 20, 2021 in the journal Geochemical Perspective Letters explains the nature of this invisible gold. Researchers from the CNRS and the University Paul Sabatier Toulouse III also evoke the phenomenon responsible for the concentration of gold in the deposits. Enough to answer questions that have preoccupied geologists, miners and other metallurgists since the industrial era.

A study for new possibilities

The study authors used the X-ray absorption spectroscopy high resolution synchrotron. This allowed them to analyze naturally occurring auriferous pyrite and arsenopyrite minerals, as well as synthetic equivalents obtained in the laboratory. These data were then interpreted using thermodynamic and molecular models. However, this technique made it possible to identify chemical and structural state hidden gold.

Credits: CNRS

According to the results, gold is only incorporated into minerals when it binds to arsenic. The meeting between the fluid and the mineral forms atomic clusters [AuAsnS6-n] after an oxidation-reduction reaction. In other words, arsenic minerals work like “gold pumps”. Indeed, these minerals ensure a massive extraction from fluids which have for their part only a low capacity of concentration in gold.

According to scientists, this work may help to locate new gold resources (and other precious metals). This will also improve the processing of minerals. Researchers have also mentioned the case of the Super Pit open-cast gold mine (Australia) where a large part of the gold is invisible in arseniferous pyrite and arsenopyrite.


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