Earthquakes can trigger quartz into forming giant gold nuggets, study finds

Scientists have discovered exactly how earthquakes trigger quartz into forming large gold nuggets — finally solving a mystery that's puzzled researchers for decades.

Gold naturally forms in quartz — the second-most abundant mineral in Earth's crust after feldspar. But unlike other types of gold deposits, those found in quartz often cluster into giant nuggets. These nuggets float in the middle of what geologists call quartz veins, which are cracks in quartz-rich rocks that periodically get pumped full of hydrothermal fluids from deep within the crust.

"Gold forms in quartz all the time," said Chris Voisey, a geologist at Monash University in Australia and the lead author of a new study published Monday (Sept. 2) in the journal Nature GeoScience. "The thing that's weird is really, really large gold nugget formation. We didn't know how that worked — how you get a large volume of gold to mineralize in one discreet little place," Voisey told Live Science.

Hydrothermal fluids carry gold atoms up from the deep and flush them through quartz veins, meaning gold should theoretically become evenly spread in the cracks rather than concentrated into nuggets, Voisey said. These nuggets are exceptionally valuable and represent up to 75% of all the gold ever mined, according to the study.

Two separate clues helped Voisey and his colleagues solve the gold nugget mystery, he said. The first was that the largest nuggets occur in orogenic gold deposits, which are deposits that form during earthquakes. The second was that quartz is a piezoelectric mineral, meaning it creates its own electric charge in response to geologic stress, such as the stress generated by earthquakes.

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"When you actually put it together, it almost works out a bit too neat," Voisey said. The researchers found that earthquakes fracture rocks and force hydrothermal fluids up into the quartz veins, filling them with dissolved gold. In response to the stress of the earthquake, quartz veins simultaneously generate an electric charge that reacts with the gold, causing it to precipitate and solidify.