March 19, 2013 3:50 pm
When a fault slips and the Earth grinds against itself—an earthquake—veins of gold can suddenly appear in the cracks that form between slabs of rock, says new research by Australian scientists Dion Weatherley and Richard Henley.
In the Earth’s crust, gold makes up about two out of every billion atoms, a rare metal in a sea of sand and salt and rock. Normally, deep underground, the weight of the earth above and the strain of two tectonic plates locked against one another makes the pressure along a fault really, really high—thousands of times that it is on the surface. But when an earthquake strikes and parts of the fault open up, a sudden drop of pressure causes liquid that is flowing around in the fault to rapidly vaporize, says Nature, dumping the gold out of solution in small but highly purified deposits.
The idea of an earthquake-driven drop in pressure drawing gold and other materials out of the crustal mix is a new one, say the scientists, and could help explain why “the rocks in gold-bearing quartz deposits are often marbled with a spider web of tiny gold veins.”
“Isolated slips do not, of course, generate economically viable gold deposits,” the scientists write in the study. But, over time,“multiple earthquakes [can] progressively build economic-grade gold deposits.”
The earthquake-induced pressure drop and consequent “flash deposition” of minerals, say the scientists, could account for “the formation of more than 80% of the world’s gold deposits; a simple repetitive process related to the everyday occurrence of earthquakes.” They say that this process, repeating over and over in a highly active area like the Southern Alps or New Zealand could produce an 110-ton gold deposit in around 100,000 years.
As massively destructive surges in the very body of the Earth, earthquakes may seem like incredibly rare events. Though large earthquakes are indeed quite rare, their smaller brethren (more that strong enough to cause this process) are not: the USGS has counted 180 in the past week.
The knowledge of this new process, say the scientists, could help in finding new gold deposits worldwide. It could also help seismologists better understand the earthquakes themselves, says Nature.
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