Earthquakes produce instant gold veins

For instant gold vein, just add earthquake and water.

That's what a new study published in the journal Nature Geoscience is saying.

Scientists figured out, a long time ago, that gold veins (and in fact veins of all the precious metals we mine) are deposited as hot, metal- and mineral-laden water flows through cracks in the Earth. However, although it seems as though this process might take a long time, two Australian scientists — seismologist Dion Weatherley, from the University of Queensland in Brisbane, and geochemist Richard Henley, at the Australian National University in Canberra — have found that these veins can actually be laid down in a instant, due to earthquakes.

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Earthquakes mainly occur along faults — fractures in the Earth's crust where the different tectonic plates rub up against or slam into one another. As the rock on either side of these faults moves, it creates zigzag cracks along the boundary, known as 'fault jogs'. When an earthquake happens, the two sides of the fault slip past each other violently, opening up these jogs and releasing tremendous amounts of pressure.

Curious about what happens to water flowing around in these fault jogs when that pressure is released, Weatherley and Henley designed a model to test this out, using measurements of fault jogs taken from gold deposits around the world. Their model showed that, during a magnitude 4.0 earthquake, pressures along the fault can instantly drop from 290 Megapascals (MPa) to just 0.2 MPa.

"So you’re looking at a 1,000-fold reduction in pressure," said Weatherley.

When Weatherley and Henley subjected mineral-laden water at nearly 400°C to that magnitude of pressure drop, the water flash vapourized, depositing the minerals it contained.

When this happens in rock, more water eventually trickles down to fill the jog, the pressure builds again, and more gold and minerals will deposit out during the next earthquake.

"You [can] have thousands to hundreds of thousands of small earthquakes per year in a single fault system," said Weatherley. "Over the course of hundreds of thousands of years, you have the potential to precipitate very large quantities of gold. Small bits add up."

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Weatherley believes that this finding may help future gold exploration efforts. However, other scientists, such as UC Berkeley seismologist Taka’aki Taira, believe that the study's data on how fluid pressure levels rebuild after an earthquake could help improve our ability to predict earthquake aftershocks.

"As far as I know, we do not yet incorporate fluid-pressure variations into estimates of aftershock probabilities," Taira says. "Integrating this could improve earthquake forecasting."

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