Earthquakes may bind veins of quartz to gold

Most of the world's gold nuggets come from quartz veins found in ancient mountain belts. Hot solutions of water and dissolved elements migrated deeply into these areas when they were active, depositing quartz along faults, fractures, and other rock boundaries. From those hydrothermal fluids, pieces of gold also crystallized.

Until now, scientists wonder how gold could be concentrated enough to form such large nuggets (pebble-sized to fist-sized). New research published in the journal Nature Geoscience shows that persistent earthquakes may have seeded and planted them.

Before this work, it was “almost impossible” to explain the concentration of gold found in some parts of the quartz veins, said Damien Gaboury, a retired geologist from the University of Quebec at Chicoutimi in Canada who was not involved in the work.

This image taken with a powerful microscope shows the location of gold deposits on quartz after hammering that simulates earthquake shocks. Credit: Chris Voysey

“Because gold has a low solubility in natural liquids, it would take a large amount of liquid to form a solid mass of gold in a vein,” said Chris Voysey, a geologist at Monash University in Melbourne, Australia, who led the new work. For example, if there is one part per million of gold in the solution, it would take five Olympic swimming pools of that liquid to form a 10-kilogram (22 lb) piece of gold.

This is where earthquakes come into play. Earthquakes send seismic waves that ripple through the Earth, compressing and deforming rocks. Quartz, a mineral made of silica, has a property known as piezoelectricity. When quartz is compressed, it releases electrons and generates an electrical voltage. Stress resulting from tectonic stress, such as that resulting from earthquakes, can play a role in some chemical reactions. Foisy and his colleagues wondered whether the reactions that form gold could also be affected.

Quartz bombardment

Fawazi and his colleagues tested the idea. “What I wanted to do was cause an earthquake in the lab,” Voysey said. Using a tool resembling a motorized hammer, he pounded quartz crystals in a solution containing gold for an hour. When he looked at the crystals under a microscope, he saw tiny pieces of metallic gold stuck to the quartz. “I went crazy,” Voysey said. “I was, like, jumping around the lab, throwing chairs.” A piece of quartz that has not been hammered does not show signs of gold metal.

“She was basically trying to make nuggets.”

The researchers noticed that the gold had collected on the metal plates that formed the gold, forming small particles instead of a uniform layer on the quartz. “She was basically trying to make nuggets,” Voysey said.

When the group knocked over pieces of quartz that naturally contained gold, they saw that gold from the solution was deposited on the gold already in the vein. “That was the exciting thing,” he said. “This was where we could start building large accumulations of gold.”

Since this gold deposition is an electrochemical process, the gold in the solution prefers to agglomerate on metallic gold, an electrically conductive material, rather than on quartz, which is an insulator and tends to trap charges rather than allow current to flow.

“This kind of mechanism is exactly what you need to get gold out of solution,” said Ian Pitcairn, an ore geologist at Stockholm University in Sweden. “You need something to trap the gold in the liquid quickly and in one place, otherwise it scatters away and never forms a gold deposit.”

Although this experiment provides the first evidence of how gold forms coins on environmental quartz electrochemically, the process is reminiscent of industrial processes for gold deposition, Gaboury noted.

Places where the original gold deposits were located had experienced several low-magnitude earthquakes every day for between 10,000 and 1 million years, allowing gold to accumulate almost continuously, he said.

Scientists have known that gold in natural liquids can form ultrafine particles in some ores. Researchers have discovered how the piezoelectricity of quartz can initiate reactions to produce hydrogen. Pitcairn, who was not involved in the study, said it is still unknown how long interconnected gold networks form in quartz. “It's the first time someone has explained this kind of texture.”

“It is perhaps one of the most important contributions from decades of searching for gold deposits.”

The new study brings together what scientists knew about quartz veins and the physical properties of quartz. “This is perhaps one of the most important contributions in decades of research on gold deposits,” Al-Jubouri said.

Voysey said there is much to explore at the intersection of quartz piezoelectricity and geology. The team plans to further investigate seismic deposition and whether it can seed other minerals, such as those containing both gold and antimony.

The quest to understand mountain gold deposits is far from over. Pitcairn said researchers still don't know what makes some veins full of gold and others not.

—Carolyn Wilke (@CarolynMWilke), science writer

Citation: Wilke, C. (2024), Earthquakes may link quartz veins to gold, EOS, 105, https://doi.org/10.1029/2024EO240447. Published October 8, 2024. Text © 2024. The Authors. CC BY-NC-ND 3.0 Unless otherwise noted, images are subject to copyright. Any reuse without express permission of the copyright owner is prohibited.

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