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Striking gold: Quakes deposit precious metal

AFP-JIJI

Solid gold can be deposited in the Earth’s crust “almost instantaneously” during earthquakes, a study published in the journal Nature Geoscience reported Sunday.

The gold is formed when a tremor splits open a fluid-filled cavity in the crust, causing a sudden drop in pressure, according to a team of Australian researchers.

This causes the fluid to expand rapidly and evaporate, and any gold particles that had been dissolved in it to “precipitate almost immediately,” said a press release. “Repeated earthquakes could therefore lead to the buildup of economic-grade gold deposits.”

The researchers said much of the world’s known gold was derived from quartz veins that were formed during geological periods of mountain building as much as 3 billion years ago.

The veins formed during earthquakes, but the magnitude of pressure fluctuations or how they drove gold mineralization were not known.

For this study, researchers used a numerical model to simulate the drop in pressure in a fluid-filled fault cavity during an earthquake.

In so doing, they answered a long-standing question about the world’s gold resources — how the metal becomes so concentrated from a highly dissolved state to a solid, mineable one.

The study said single tremors would not generate economically viable gold deposits, which were built up one thin coating at a time.

Forming a 100-ton gold vein deposit would take less than 100,000 years, the team wrote.