Electric effect grows gold
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Australian scientists have uncovered new details about the formation of gold in the Earth’s crust.
Gold nuggets are objects of ancient fascination, prized for their beauty and other qualities. However, mystery has surrounded their formation.
Recent research led by geologists at Monash University suggests that the process behind these formations may involve a surprising element - electricity generated by earthquakes.
Traditionally, the formation of gold within quartz veins has been attributed to the cooling of hot, water-rich fluids that flow through cracks in the Earth's crust.
As these fluids cool, gold is believed to precipitate out, becoming trapped within the quartz.
But this conventional explanation does not fully account for the occurrence of large gold nuggets, particularly given the extremely low concentration of gold in these fluids.
“The standard explanation is that gold precipitates from hot, water-rich fluids as they flow through cracks in the Earth’s crust,” says Dr Chris Voisey, lead author of a new study published in Nature Geoscience.
“While this theory is widely accepted, it doesn't fully explain the formation of large gold nuggets, especially considering that the concentration of gold in these fluids is extremely low.”
To explore an alternative explanation, the research team investigated the role of piezoelectricity - a property of quartz that generates an electric charge when subjected to stress.
Quartz, a common host of gold deposits, exhibits this property, which is already harnessed in everyday items such as quartz watches and BBQ lighters, where mechanical force generates a significant voltage.
The team hypothesised that the stress from earthquakes could similarly generate electrical charges within the Earth, potentially influencing gold deposition.
The researchers tested this hypothesis by simulating earthquake conditions in the laboratory.
They submerged quartz crystals in a fluid containing dissolved gold and applied stress using a motor to replicate the shaking caused by seismic activity.
Upon examining the quartz samples under a microscope after the experiment, they found that gold had indeed been deposited on the quartz surfaces.
“The results were stunning,” said Professor Andy Tomkins, a co-author of the study from Monash University’s School of Earth, Atmosphere and Environment.
He explained that the stressed quartz not only facilitated the electrochemical deposition of gold but also led to the formation of gold nanoparticles.
“Remarkably, the gold had a tendency to deposit on existing gold grains rather than forming new ones,” he said, highlighting a crucial aspect of the process.
This accumulation occurs because, while quartz is an electrical insulator, gold is a conductor.
Once a small amount of gold is deposited, it attracts additional gold from the surrounding fluid, effectively ‘plating’ the gold grains over time.
The experts say that when quartz is repeatedly stressed by earthquakes, it generates piezoelectric voltages, which in turn reduce dissolved gold from the surrounding fluid, causing it to deposit.
Over time, this process could result in the formation of significant gold accumulations, eventually leading to the creation of the massive nuggets that have intrigued prospectors and scientists for generations.
“In essence, the quartz acts like a natural battery, with gold as the electrode, slowly accumulating more gold with each seismic event,” Dr Voisey said.