Earthquakes may have a slow Midas touch according to a new study.
Pressure changes in the Earth’s crust cause precious metal to deposit each time the crust moves. Over hundreds of thousands of years, these mineral deposits build up to be substantial amounts worth the time of a gold mining operation according to the study published in the journal Nature Geoscience. Dion Weatherley, a geophysicist at the University of Queensland in Australia and lead author of the study.
Earthquakes with magnitude 4.5+ in the last 30 days. Screenshot from USGS Earthquake Hazards Program.
A brief summary of the science from OurAmazingPlanet:
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 6 miles (10 kilometers) 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. It’s like pulling the lid off a pressure cooker: The water inside the void instantly vaporizes, flashing to steam and forcing silica, which forms the mineral quartz, and gold out of the fluids and onto nearby surfaces, suggest Weatherley and co-author Richard Henley, of the Australian National University in Canberra.
While scientists have long suspected that sudden pressure drops could account for the link between giant gold deposits and ancient faults, the study takes this idea to the extreme, said Jamie Wilkinson, a geochemist at Imperial College London in the United Kingdom, who was not involved in the study.
It is the work of the smaller-magnitude earthquakes that cause minimal damage driving the formation of gold deposits in the earth’s faults. “You [can] have thousands to hundreds of thousands of small earthquakes per year in a single fault system,” Weatherley says. “Over the course of hundreds of thousands of years, you have the potential to precipitate very large quantities of gold. Small bits add up.”
The formation of quartz in this process sheds light on the famous deposits such as the placer gold of the 19th-century California gold rush. Placer gold is an alluvial deposit where gold particles, flakes, and nuggets are mixed in with the sediment of riverbeds. Such deposits, often overlooked by industrial operations, are the target of small-scale mining operations due to the low cost of extraction. Placer gold is what has turned Peru’s Madre de Dios region, a low-governance area, into a hotspot for illicit and unregulated gold mining activity.
In the quest for gold, humans have removed over 188,000 tons (171,000 metric tons) of the metal from the ground, exhausting easily accessed sources, according to the World Gold Council. Just in Peru, illicit miners loot 18 tons, over $190 million, or gold every year contributing to a modern day gold rush destroying important Amazonian habitat.
