Veins of Gold

28 Jan 2019

At ... earthquakes make veins of gold in an instant. Pressure changes can cause precious metals to form when the crust moves. Geologists have long known veins of gold are formed by mineral deposition from hot fluids flowing through cracks deep below the surfacve. A study in Nature Geoscience has found the process can occur virtually in an instant - even within a fraction of a second. The process takes place along 'fault jogs' - sideways zigzag cracks that connect main fault lines in rock, according to Dion Weatherley, a seismologist at the University of Queensland. When an earthquake strikes the side of the main fault line it slips along the fault. The two sides rub against each other. However, the fault jogs, on the other hand, open out. Weatherley and Henley (a geochemist) wondered what happened to fluid availability through the fault jogs at the time of an earthquake. What they discovered was a rapid depressurisation (high pressure conditions deep in the crust dropping to pressures closer to those at the surface). A magnitude 4 earthquake (relatively puny) is capable of a 1000 fold reduction in pressure - which is quite dramatic. When mineral laden water is involved the minerals in the water will crystalise almost instantly (which is known as flash vapourisation or flash deposition) - and hey presto. It is theorised that a single earthquake can generate a gold vein - albeit very thin and spidery (but gold none the less). Bigger earthquakes or earth movements have yet to be tested.