Geologists solve the mystery of gold nuggets during earthquakes

Geologists have known that gold is formed in quartz by earthquakes. But thanks to a new study, they have finally figured out exactly how circumstances and seismic waves combine to form large nuggets.

Gold is known to naturally form in quartz, the second most abundant mineral in the Earth's crust after feldspar. But unlike other types of gold deposits, those in quartz often cluster into giant nuggets, LiveScience writes.

"Gold is constantly formed in quartz. However, the formation of large gold nuggets is surprising. We didn't know how it works – how you can get a large volume of gold to mineralize in one inconspicuous little place," said Chris Voysey, a geologist at Monash University in Australia and lead author of the new study.

According to the scientists, hydrothermal fluids carry gold atoms up from the depths and flush them through quartz veins. This means that the gold should theoretically be evenly distributed in the fractures, rather than concentrated into nuggets. According to the study, these nuggets are extremely valuable and account for up to 75% of all gold ever mined.

Chris Voysey admitted that two separate clues helped him and his colleagues solve the mystery of the gold nugget. The first was that the largest nuggets are found in orogenic gold deposits, which are formed during earthquakes. Secondly, quartz is a piezoelectric mineral, meaning it creates its electrical charge in response to geological loading, such as that caused by earthquakes.

Researchers have found that earthquakes fracture rocks and cause hydrothermal fluids to rise into quartz veins, filling them with dissolved gold. In response to the stress of the earthquake, the quartz veins simultaneously generate an electrical charge that reacts with the gold, causing it to precipitate and harden.

Gold is concentrated in certain places because, according to Voysey, this metal is diluted in solution, preferentially settling on the gold grains already present." "Gold essentially acts as an electrode for further reactions by accepting the voltage generated by neighboring quartz crystals," the geologist explained.

"This means that in quartz veins, gold hardens into clusters that grow larger with each earthquake. The largest orogenic gold nuggets found to date weigh about 60 kilograms.

To test this idea, the researchers simulated the effects of an earthquake on quartz crystals in the lab. They immersed the crystals in a liquid containing gold and reproduced seismic waves to create a piezoelectric charge. The experiment confirmed that under conditions of geologic activity, quartz can produce a large enough voltage to precipitate gold from the solution.

The modeling also confirmed that gold preferentially solidifies on top of existing gold deposits in quartz veins, which helps explain the formation of large gold nuggets.

Now scientists can make large gold nuggets in the laboratory. "But this is not alchemy. You have to have gold in solution, and then just transfer it from a liquid state to something else," the scientist said.

However, the results don't give geologists and exploration companies any new clues as to where to mine for gold nuggets. The best science can offer at this time is a device that detects piezoelectric signals from quartz at depth. "It can tell you where the quartz veins are, but it can't tell you if there is gold in those quartz veins," Chris Voysey emphasized.

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