Giant gold nuggets formed in quartz veins could be the result of earthquakes and electricity, say researchers at Australia’s Monash University.
How exactly gold nuggets form has had scientists scratching their heads for many years.
Often found nestled within quartz veins, gold flakes will sometimes clump together to form very large nuggets. Indeed, the 78kg ‘Welcome Stranger’, found in Australia in 1869, is often considered the biggest gold nugget ever found.
However, how these nuggets form has remained a mystery – a mystery that new research led by Chris Voisey from Australia’s Monash University School of Earth Atmosphere and Environment has helped solve.
“The standard explanation is that gold precipitates from hot, water-rich fluids as they flow through cracks in the Earth’s crust,” said Voisey. “As these fluids cool or undergo chemical changes, gold separates out and becomes trapped in quartz veins.
“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.”
For the study, Voisey and his team tested a property within quartz called piezoelectricity, which is able to generate an electric charge when subjected to stress.
The researchers wondered what impact the stress from an earthquake would have on quartz lying within the Earth.
To replicate this stress, the researchers submerged quartz crystals in a gold-rich fluid and then used a motor to simulate the shaking of an earthquake.
“The stressed quartz not only electrochemically deposited gold onto its surface, but it also formed and accumulated gold nanoparticles,” said study co-author Professor Andy Tomkins.
“Remarkably, the gold had a tendency to deposit on existing gold grains rather than forming new ones,” he added.
The reason it does this is because quartz is an electrical insulator, while gold is a conductor.
Once some gold is deposited, it becomes a focal point for further growth, effectively “plating” the gold grains with more gold.
The researchers explained that as the quartz is repeatedly stressed by earthquakes, it generates piezoelectric voltages that can reduce dissolved gold from the surrounding fluid, causing it to deposit.
Over time, this process could lead to the formation of significant gold accumulations, ultimately producing nuggets as big as the ‘Welcome Stranger’.
“In essence, the quartz acts like a natural battery, with gold as the electrode, slowly accumulating more gold with each seismic event,” said Voisey.
This process could explain why large gold nuggets are so often associated with quartz veins formed in earthquake-related deposits.
Source: E&T
