Dion Weatherley, a geophysicist at the University of Queensland, make a model that would be the target of many people. The model provides a quantitative mechanism for the link between gold and quartz seen in many of the world's gold deposits.
When an earthquake strikes, it moves along a rupture in the ground — a fracture called a fault. Big faults can have many small fractures along their length, connected by jogs that appear as rectangular voids. Water often lubricates faults, filling in fractures and jogs. This study result were published in March 17, 2013 issue of the Nature Geoscience journal.
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| The tyrannosaur of the minerals, this gold nugget in quartz weighs more than 70 ounces (2 Kg). (Picture from: http://www.livescience.com/) |
About 6 miles (10 kilometers) below the surface, under incredible temperatures and pressures, the water carries high concentrations of carbon dioxide, silica and economically attractive elements like gold.
Temperature and pressure causes water to bring the extraordinary high concentrations of carbon dioxide, silica, and other valuable elements, such as gold. During the earthquake, the gap is wide open suddenly.
It's like pulling a pressure cooker lid. The water in the empty space and force evaporates forming silica mineral quartz. While gold will come out together towards the liquid surface.
While scientists have long suspected that sudden pressure drops could account for the link between giant gold deposits and ancient faults, the study takes this idea to the extreme, said Jamie Wilkinson, a geochemist at Imperial College London in the United Kingdom, who was not involved in the study.
Weatherley said the amount of gold left behind after an earthquake is tiny, because underground fluids carry at most only one part per million of the precious element. But an earthquake zone like New Zealand's Alpine Fault, one of the world's fastest, could build a mineable deposit in 100,000 years, he said.
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| Veins of gold may deposit when the high-pressure water in which they were dissolved suddenly vaporizes during an earthquake. (Picture from: http://www.scientificamerican.com/) |
Surprisingly, the quartz doesn't even have time to crystallize, the study indicates. Instead, the mineral comes out of the fluid in the form of nanoparticles, perhaps even making a gel-like substance on the fracture walls. The quartz nanoparticles then crystallize over time.
Even the earthquakes smaller than magnitude 4.0, which may rattle nerves but rarely cause damage, can trigger flash vaporization, the study finds. "Given that small-magnitude earthquakes are exceptionally frequent in fault systems, this process may be the primary driver for the formation of economic gold deposits," Weatherley said.
But earthquakes aren't the only cataclysmic source of gold. Volcanoes and their underground plumbing are just as prolific, if not more so, at producing the precious metal. While Weatherley and Henley suggest that a similar process could take place under volcanoes, Wilkinson, who studies volcano-linked gold, said that's not the case.
"Beneath volcanoes, most of the gold is not precipitated in faults that are active during earthquakes," Wilkinson said. "It's a very different mechanism.". *** [EKA | FROM VARIOUS SOURCES | LIVESCIENCE | ISMI WAHID | KORAN TEMPO 4176]
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