Gold explodes out of water during earthquakes: study
TED ALJIBE/AFP/Getty ImagesA new study says that gold veins and gold nuggets can form almost instantly during earthquakes.
Long thought to be a slow process, a new study published in Nature Geoscience says that gold veins are produced in an instant by earthquakes.
Scientists have long known that veins of gold and other precious minerals form around fault lines, but it was generally thought that this process took an extremely long time.
However, the new study shows that quick changes in pressure could cause the gold to form, essentially, instantaneously.
“We find that cavity expansion generates extreme reductions in pressure that cause the fluid that is trapped in the jog to expand to a very low-density vapour,” study authors Dion K. Weatherley and Richard W. Henley write in their journal abstract.
From Scientific American:
For example, a magnitude-4 earthquake at a depth of 11 kilometers would cause the pressure in a suddenly opening fault jog to drop from 290 megapascals (MPa) to 0.2 MPa. (By comparison, air pressure at sea level is 0.1 MPa.) “So you’re looking at a 1,000-fold reduction in pressure,” Weatherley says.
What this means is that there are small bits of gold trapped in underground water flows that are super-heated and under super-high pressure. When the Earth shifts during a quake, the pressure on the water drops a thousandfold nearly instantly. Since the water is super-heated, the pressure was the only thing keeping it in liquid form. When the pressure goes away, it flash vapourizes and the elements within it, such as gold, remain in veins through the rock.
The scientists tracked how quickly this process could occur by recreating the pressure drops in a lab using a “thermo-mechanical piston.”
Weatherley said that the process happens to a small extent even during smaller Earthquakes, including ones as low as -2 magnitude.
“You [can] have thousands to hundreds of thousands of small earthquakes per year in a single fault system,” he told Scientific American. “Over the course of hundreds of thousands of years, you have the potential to precipitate very large quantities of gold. Small bits add up.”
These discoveries aren’t just good for helping prospectors find gold however. Scott Sutherland at the Geekquinox blog points out that these discoveries could also help scientists understand how the earthquakes themselves work.
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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