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arsenic and gold

Scanning electron microscopy photomicrograph showing gold microparticles (bright color) deposited with pyrite crystals from a hydrothermal solution in a laboratory experiment. Image: Maria Kokh and Gleb Pokrovski

French scientists have dived deeper than ever before into gold and arsenic’s relationship, improving the understanding of gold concentration and how it can be recovered more effectively.

Using intense X-ray machines from the European Synchotron in France, the researchers probed the chemical bonds between gold and minerals containing iron and arsenic, such as pyrite and arsenopyrite.

They found the minerals behave like a sponge, concentrating gold to a million times more than anywhere else in nature.

Gold was able to enter the mineral structural sites, binding to the arsenic and forming chemical bonds Au(2+) and As(1-).

The findings should allow mining-related enterprises to optimise their exploration practices, with better understanding and control of the chemical reactions involved with gold processing.

While arsenic has caused health issues for gold miners for centuries, this research at an atomic level may allow further studies to find ways of preventing or mitigating the risks.

The study added to an influx of similar studies which aimed to understand the nature of gold formation in 2021.

One such study out of Canada’s McGill University found the cause of ultra high-grade gold formations, describing the nature of the deposits as “much like milk.”

“As the concentration of gold in hot water is very low, very large volumes of fluid need to flow through the cracks in the Earth’s crust to deposit mineable concentrations of gold,” the Canadian team explained.

“This process would require millions of years to fill a single centimetre-wide crack with gold, whereas these (bonanza deposit) cracks typically seal in days, months or years.”

More recent research released in June by a Curtin University research team in Western Australia found “invisible gold” trapped in pyrite.

Such atomic behaviours had never been observed in gold until the Curtin team used a special technique called atom probe tomography.

The process observe nanoscale defects in the pyrite called dislocations – one hundred thousand times smaller than the width of a human hair.