Emily Chan
Interestingly enough, earthquakes have the ability to cause quartz to form large gold nuggets, a fact that has been well-known among scientists for decades. What has managed to elude them for just as long is how exactly earthquakes help gold emerge from quartz. Finally, a new study has solved the mystery.
Quartz is the second-most abundant mineral in Earth’s crust—the first is feldspar. Gold naturally develops in quartz, but the way it forms is unique from other gold deposits. Those found in quartz often crop up as clusters of giant nuggets.
“Gold forms in quartz all the time,” said Chris Voisey, the lead author of the study and a geologist from Monash University in Australia. “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.”
The nuggets float in the middle of “quartz veins,” which are just cracks in rocks rich with quartz. The cracks are periodically pumped with hydrothermal fluids from deep in the crust. The hydrothermal fluids carry gold atoms from down below to the quartz veins.
Theoretically, the gold should spread out evenly rather than build up as nuggets. According to the study, the nuggets are extra valuable and makeup about 75 percent of all the gold that has ever been mined.
Voisey and colleagues came across two separate clues that helped lead them to an explanation behind the gold nuggets. The first was that the largest nuggets occurred in orogenic deposits, which are formed during earthquakes.
Secondly, quartz is a piezoelectric mineral. This means it responds to geologic stress, such as earthquakes, by generating an electric charge.
The researchers discovered that earthquakes fracture rocks and push hydrothermal fluids up into the cracks, filling them with dissolved gold.
The quartz veins respond to the stress of the earthquakes by producing an electric charge that reacts with the gold. As a result, the gold precipitates and solidifies.
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