Forget looking for a pot of gold at the end of a rainbow. New research is suggesting fault lines might hold recently produced deposits of the valuable metal.
The study published in Nature Geoscience describes how gold deposits can be derived from seismic activity, like earthquakes.
Gold in granite and quartz. (Photo: Shutterstock.com)
Most of the world's gold stores, the study abstract states, came from quartz veins that opened during mountain building events. For such an event to catalyze the precipitation of gold challenges the previously held thought that its formation was slower. The study's evidence suggests the process of gold precipitation actually happens rather quickly.
“While geochemical and geological evidence has long alluded to a connection between earthquakes and the deposition of gold, there has been much debate through the decades as to whether the precipitation of gold was a slow, equilibrium process or whether, as Professor Henley was proposing, it was a rapid and far from equilibrium process,” study co-author Dr. Dion Weatherley said, according to the University of Queensland in Australia.
Weatherley went on to say that even seismic activity of a small magnitude can generate enough of a pressure reduction in a fault to start "flash precipitation of gold and quartz." The amount of gold deposited by one earthquake is relatively small, but Wealtherley said when you consider the tens or hundreds of thousands of small magnitude earthquakes that occur each year, "over time, large gold deposits may result."
Scientific American explained more in detail about how this process occurs:
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.
When mineral-laden water at around 390 °C is subjected to that kind of pressure drop, Weatherley says, the liquid rapidly vaporizes and the minerals in the now-supersaturated water crystallize almost instantly — a process that engineers call flash vaporization or flash deposition. The effect, he says, “is sufficiently large that quartz and any of its associated minerals and metals will fall out of solution”.
Eventually, more fluid percolates out of the surrounding rocks into the gap, restoring the initial pressure. But that doesn’t occur immediately, and so in the interim a single earthquake can produce an instant (albeit tiny) gold vein.
Weatherley said the research could be used to find new mineable gold deposits.
“Most of the world's ore deposits that are exposed at the earth's surface have either been found or already mined. Our research paper aims to reveal new findings and knowledge about the physical processes that will assist exploration geologists to discover blind ore deposits that are deeper within the earth," he told the university website.
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