Earthquakes Deposit Gold In Fault Zones

sciencehabit writes "Gold deposits may be created in a flash—literally. Along fault zones deep within Earth's crust, small cavities filled with fluids rich in dissolved substances such as gold and silicate minerals can expand suddenly to as much as 130,000 times their former size during a major earthquake, a new analysis suggests. In such circumstances, pressure drops accordingly, driving a process the scientists call flash evaporation. And when the pressure in the cavity suddenly drops, so does the solubility of minerals in the water there. Along with substantial quantities of quartz, large earthquakes could deposit as much as 0.1 milligrams of gold along each square meter of a fault zone's surface in just a fraction of a second Typical rates of seismicity along a fault, such as the San Andreas fault zone shown in the main image, could generate a 100-metric-ton deposit of gold in less than 100,000 years."

Miners Know

[A10Mechanic]

When I was younger, we'd explore the old 1800's silver mines at Alta, Utah. When the old miners hit a fault line (underground), they'd span out and mine that fault for all it was worth. It was pretty neat for us finding a rock face perfectly smooth and straight (the fault), that had been stoped out a hundred years ago, miles underground. It was like going back in time. In hindsight, it was probably dangerous... Ah, youth.

Something for the goldbugs...

[Anonymous Coward]

The oceans contain about 20 million tons [noaa.gov] of gold, dissolved in the seawater and on the seabed, eclipsing the worlds current stock of mined gold by more than 100 times.

Ironically, those promoting a gold standard for financial stability, would ensure that hyperinflation occurs in the future; as soon as innovations in nanotechnology, make the cost of extracting gold from seawater affordable/cheap, the value of gold itself will then plummet as its availability increases, causing inflation and eventually hyperinflation.

This is what they discovered

[Diamonddavej]

Weatherley and Henley investigated a mesothermal gold deposit, the Revenge Mine in Australia (also known as orogenic gold deposits). These gold deposits form deep underground during mountain building events, generally 3 to 20 km deep, where greater hydrostatic pressures normally prevent fluids from boiling. Previously, geologists speculated that mesothermal gold ore was deposited when fluids cooled or interacted with other fluids with a different chemistry, not so it seems. Weatherley and Henley claim that, even at great depths and pressures, fluid pressure in a fault zone can momentarily approach zero during an earthquake, this is a great surprise. Also, the (normal) temperature and pressures during the formation of the Revenge Mine deposit was 1675 to 2075 bars and 425 to 525 C, this suggests the water was a Supercritical Fluid. I wonder if a phase change from supercritical fluid to a gas facilitated the precipitation of gold.

Also, it should be pointed out that role of Earthquakes in the formation of gold and other mineral deposits has been acknowledged for decades (in particular the near surface epithermal fault hosted gold-silver veins). Epithermal deposits are formed near the surface (generally less than 1 km), the frequent occurrence of breccias, broken rock fragments and voids in the faults attests to vigorous fluid boiling. One famous example of earthquake provoked mineralisation is the San Andreas fault, where hot springs issuing from the fault zone emit more arsenic and mercury after an earthquake, gold is presumably deposited at depth as well e.g.

Sibson, R.H. 1987. Earthquake rupturing as a mineralizing agent in hydrothermal systems. Geology 15(8), 701-704.