Piezoelectricity from earthquakes plays key role in formation of large gold nuggets: study

Gold nuggets are found primarily in quartz veins, and the current model assumes that gold precipitates from hot water and carbon dioxide-rich fluids due to changes in temperature, pressure and/or fluid chemistry. However, the widespread presence of large gold nuggets contradicts the dilute nature of these fluids and the chemical inertness of quartz. Quartz is the only abundant piezoelectric mineral on Earth, and the cyclic nature of earthquake activity that drives the formation of gold deposits means that quartz crystals in veins will be subjected to thousands of stress episodes. New research by scientists from Monash University, CSIRO Minerals Resources and the Australian Centre for Neutron Scattering suggests that stress on quartz crystals can generate sufficient voltage to electrochemically precipitate gold from solution in addition to accumulating gold nanoparticles.

Energy dispersion spectral map of the sample studied by Voysey et al. Image credit: Chris Voysey.

“Gold nuggets, renowned for their rarity and beauty, have been at the heart of gold rushes for centuries,” said Monash University geologist Chris Voysey.

“The standard explanation is that gold precipitates from hot, water-rich fluids as they flow through cracks in the Earth's crust.”

“When these fluids cool or undergo chemical changes, the gold separates and becomes trapped in the quartz veins.”

“While this theory is widely accepted, it does not fully explain the formation of large gold masses, especially given that the concentration of gold in these fluids is very low.”

Dr. Voisy and his colleagues tested a new concept – piezoelectricity.

Quartz, the mineral that commonly hosts gold deposits, has a unique property called piezoelectricity — it generates an electrical charge when subjected to pressure.

This phenomenon is already familiar to us in everyday objects such as quartz watches and barbecue lighters, where a small mechanical force creates a large electrical voltage.

What if the pressure from earthquakes could do something similar inside the Earth?

To test this hypothesis, the researchers conducted an experiment that simulated the conditions that quartz might experience during an earthquake.

They immersed quartz crystals in a gold-rich liquid and applied pressure with an engine to simulate the vibration of an earthquake.

After the experiment, the quartz samples were examined under a microscope to see if any gold had been deposited.

“The results were amazing,” said Professor Andy Tomkins of Monash University.

“The strained quartz not only electrochemically deposited gold on its surface, but also formed and aggregated gold nanoparticles.”

“Surprisingly, the gold tended to precipitate onto existing gold grains rather than forming new ones.”

“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 coating the gold grains with more gold.”

“Our discovery provides a plausible explanation for the formation of large gold nuggets in quartz veins,” said Dr. Voisy.

As quartz is repeatedly stressed by earthquakes, it generates a piezoelectric voltage that can reduce the gold dissolved in the surrounding fluid, causing it to precipitate.

Over time, this process can lead to the formation of large accumulations of gold, eventually producing massive gold nuggets that have attracted the interest of treasure hunters and geologists alike.

“Basically, quartz acts like a natural battery, with gold as an electrode, and the gold slowly accumulates with each seismic event,” Dr. Voisy said.

“This process may explain why large pieces of gold are often associated with quartz veins formed in sediments associated with earthquakes.”

“This new understanding of gold mass formation not only sheds light on a long-standing geological mystery, but also highlights the interrelationship between Earth’s physical and chemical processes.”

A research paper describing the findings was published today in the journal Nature Geoscience.

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CR Voisey et al. Gold nugget formation from Zazzle-induced piezoelectricity in quartz. Nat. Geosci, published September 2, 2024; doi: 10.1038/s41561-024-01514-1

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