Earthquakes Prove to Produce “Economic-Grade” Gold Deposits
Apparently, there's a silver lining in the occurrence of earthquakes—and it comes in the form of gold. Australian scientists recently confirmed the link between the formation of gold deposits as a result of earth's naturally occurring 20,000 annual earthquakes.
Researchers from the University of Queensland and Australian National University released the study detailing the process to Nature Geoscience—the first time the hypothesis has ever been mathematically demonstrated. According to their findings, mineral rich fluids in the earth's crust undergo intense pressure reduction during an earthquake, instantly vaporizing while the minerals inside the solution crystalize almost instantly (within just a few tenths of a second). This process of flash vaporization along 'fault jogs,' the cracks connecting the main fault lines in the earth's crust, forces silica and gold out of the fluids and onto nearby surfaces.
Although scientists have long suspected a link between gold deposits and ancient faults, the study takes the idea to a new extreme.
"To me, it seems pretty plausible. It's something that people would probably want to model either experimentally or numerically in a bit more detail to see if it would actually work," Jamie Wilkinson, a geochemist at Imperial College London in the United Kingdom, told OurAmazingPlanet.
A single event would produce just a tiny gold vein, but the process occurs in even small earthquakes. In a single fault system, thousands to hundreds of thousands of small earthquakes could occur per year, which could lead to a sizable buildup of gold reserves.
“Over the course of hundreds of thousands of years, you have the potential to precipitate very large quantities of gold,” University of Queensland seismologist Dion Weatherley told Mining Australia. “Small bits add up.”
Repeated earthquakes could even lead to “economic-grade gold deposits,” he says, helping future prospectors find new regions where fault jogs are common.
The study also points to the reason why rocks in gold-bearing quartz deposits are marbled with small gold veins, using the mathematical model to calculate the impact earthquakes have on fluids in certain fault zones.
"They expected for any given vein, depending on its size, it may be years to tens of years for the fracture to fill up with quartz and the associated metals such as gold,” Weatherley told Australia's ABC News.
"The most surprising aspect of the mathematical modeling was that we thought there was a good chance that very large magnitude earthquakes might be able to achieve this, but what we actually found is that even very small magnitude earthquakes [do so].
"It was a bit hard to imagine that very small earthquakes - in the order of magnitude two to magnitude four - would do much work on the fluid.
"But when we did the calculations we found that, in fact, a magnitude four earthquake was far and away large enough to produce a massive pressure differential of the order of about 1,000 times.
"While the amount of gold that would be deposited in any one earthquake is quite small, when you consider that tens or hundreds of magnitude four quakes and thousands of smaller magnitude quakes may occur each year within an earthquake fault system, the possibility exists that over time, large gold deposits may result."
Although most of the world's ore deposits exposed at the surface have been mined, the study could help prospectors tap significant deposits at new depths. The earth experiences roughly 50 earthquakes per day, or 20,000 earthquakes per year, according to the National Earthquake Information Center.
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," said Weatherley.
