It is known that gold is found in quartz veins formed during periods of mountain building as long as three billion years ago and deposited by mineral-rich water flowing through cracks deep in the Earth's crust.
The veins are formed as a result of earthquake-triggered fluctuating pressures. But the magnitude of the pressure changes and their influence on mineral deposition was not known. Using a simple thermo-mechanical piston model, researchers from the Australian National University in Canberra and University of Queensland in Brisbane, Australia, have now found that gold could be deposited almost instantaneously in the Earth's crust during earthquakes.
When an earthquake strikes, it moves along a fracture in the ground called a fault. Faults can have small fractures along their length that are connected by jogs. Water fills in these fractures and jogs. Deep below the surface (under high temperature and pressure), the water carries high concentrations of carbon dioxide, silica and elements like gold, reported OurAmazingPlanet.
During an earthquake, the sides of the main fault line slip along the fault line's direction, thus rubbing against each other. The fault jogs suddenly open up wider, leading to depressurization of high pressure conditions that normally prevail deep within the Earth.
According to researchers, the pressure in the fault jog drops to a pressure that exists on the Earth's surface. This causes the water inside the fault to vapourise and minerals in the water crystallize almost instantly, forcing them out of fluids and onto nearby surfaces. This process is called flash vapourisation or flash deposition.
A single event of an earthquake could deposit only small amounts of gold because the fluids deep in Earth's crust carry at most one part per million of the element. But New Zealand's Alpine Fault (one of the world's fastest earthquake zone) could deposit a minable quantity of gold in 100, 000 years, lead author Dion Weatherley, a geophysicist at the University of Queensland, told OurAmazingPlanet.
While bigger earthquakes produce bigger pressure drops, even small earthquakes can cause flash vapourisation, the study finds.
Weatherley said that the new study might help in future gold exploration efforts. He said that prospectors could use remote sensing techniques to find out gold deposits in deeply buried rocks with lots of jogs. "Fault systems with lots of jogs can be places where gold can be distributed," he explained to Nature News.
The details of the study are published in the journal Nature Geoscience.