Formation of Gold Nuggets by Earthquakes: How Seismic Activity Shapes Valuable Deposits

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Much of the world’s gold is mined from networks of branching mineral layers — or veins — made mostly of quartz, called orogenic gold deposits. These deposits are constructed piecemeal by earthquakes, usually around six to 12 kilometers underground. The temblors open fractures, which are then infiltrated by subterranean fluids that deposit quartz and gold, forming veins. Subsequent quakes create more fractures and reopen existing veins, incrementally swelling and ramifying the deposit over time.

Gold Nugget Formation

Geologists have shown how this process can form small and diffuse quantities of gold, but not how the metal becomes concentrated in large nuggets. The fluids involved contain meager amounts of gold, and quartz is an unreactive medium.

Voisey and colleagues hypothesized that the key was quartz’s piezoelectricity, or its ability to develop electrical charge when strained. They plunged quartz slabs into solutions containing dissolved gold or gold nanoparticles and used actuators to strike some of the submerged slabs at a frequency of 20 hertz, mimicking small quakes. This experimental method shed light on the process of gold concentration through the interaction of quartz and gold-fluids.

Quartz’s Role in Gold Deposition

The striking generated voltages up to 1.4 volts, causing gold grains to aggregate on the slab surfaces. No gold deposited on slabs that weren’t struck. When the experiment was repeated with a chunk of a gold-quartz vein, gold deposition became concentrated on the already existing gold. The existing gold adopts the voltage of the charged and less conductive quartz, attracting more gold to itself and concentrating the mineralization. This finding highlights how quartz plays a crucial role in the concentration of gold deposits.