Quakes turn water into gold: Study

Midas touch! Earthquakes cause water in faults to vaporise, depositing gold in the earth's crust, according to a new study.

The study, published in the journal Nature Geoscience, provides a quantitative mechanism for the link between the precious metal and quartz seen in many of the world's gold deposits, said Dion Weatherley, a geophysicist at the University of Queensland in Australia and lead author of the study.

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.
About 10 kilometres below the surface, under incredible temperatures and pressures, the water carries high concentrations of carbon dioxide, silica and economically attractive elements like gold.

During an earthquake, the fault jog suddenly opens wider. The water inside the void instantly vaporises, flashing to steam and forcing silica, which forms the mineral quartz, and gold out of the fluids and onto nearby surfaces, suggested Weatherley and co-author Richard Henley, of the Australian National University in Canberra.

Previously, scientists suspected fluids would effervesce, bubbling like an opened soda bottle, during earthquakes or other pressure changes. This would line underground pockets with gold. Others suggested minerals would simply accumulate slowly over time.
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.

The quartz doesn't even have time to crystallise, the study indicated. 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 crystallise over time.

Even earthquakes smaller than magnitude 4.0 can trigger flash vaporisation.
"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," he said.