Earthquakes make gold nuggets in quartz

For decades, researchers have known that earthquakes, quartz, and gold were linked—nearly 75% of gold circulating today came from nuggets originally embedded in quartz deposits near faults. But in places with no clear evidence for geochemical reactions, geologist Chris Voisey says, “the conundrum is, how did we make gold in the middle of the quartz vein?”

Quartz deposits in fault zones might experience thousands of earthquakes, Voisey says. The shaking ground puts strain on the deposits, generating piezoelectricity, and creates cracks where gold-bearing water can percolate. Then, he posits, it’s a straightforward redox reaction: the excess electrons from the quartz transfer to aqueous gold ions, reducing them and precipitating solid gold.

Once some gold is deposited, “it’ll basically become the lightning rod for more reactions,” Voisey says. “This could explain large gold nugget formation.”

Voisey built an apparatus that mechanically strains quartz crystals submerged in a gold-containing solution. After months of trial and error, Voisey was elated to find gold deposits on the crystals, using scanning electron microscopy.

This new work is a fresh perspective on the association “between faults, earthquakes, and gold deposition,” says Randy Williams, an earthquake geologist at the University of Wisconsin–Madison who refereed the paper. “I think it is the kind of thing that can potentially change the field.”