Humanity’s fascination with gold spans thousands of years, with gold mining practices documented in ancient Greek and Roman texts. Gold rushes, particularly in the 19th century, significantly influenced the development of the modern world. This dense, yellow metal is often found within quartz veins due to the simultaneous condensation of both substances from hot fluids underground, influenced by variations in temperature, pressure, and chemical composition.
While geologists have a good understanding of how gold and quartz form together, the occurrence of large gold nuggets has been puzzling. Given that natural fluids contain gold at very low concentrations (around one part per million), it is intriguing how gold forms into sizable nuggets weighing tens or hundreds of kilograms.
According to a recent study published in Nature Geoscience, the formation of these large nuggets may be influenced by the unique electrical properties of quartz, especially under the stress of seismic activity.
Quartz’s piezoelectric properties
Quartz is a piezoelectric material, meaning it generates an electrical charge when mechanical stress, such as compression or stretching, is applied to it. This property is rare among Earth’s minerals, with quartz being the most abundant piezoelectric material.
In laboratory conditions, researchers have observed that when quartz is placed under stress, it can deposit gold onto its surface. Moreover, the gold tends to accumulate into nanoparticles and is more likely to deposit onto existing gold grains than onto quartz itself. This is because quartz is an electrical insulator, while gold is a conductor. The gold grains inherit the electrical potential from the nearby quartz, becoming focal points for further gold deposition, much like the process used in industrial gold-plating.
Formation of gold nuggets in nature
Applying these findings to natural settings, some of the largest gold nuggets have been discovered in quartz veins located within earthquake-prone regions. In these areas, gold-bearing fluids traverse faults in the rock. The seismic stress applied to quartz can generate piezoelectric voltages strong enough to extract gold from these fluids. Once deposited, the gold becomes the center of continued deposition through piezoelectric plating, as the fluid continues to infiltrate. Over millions of years, this repetitive process can result in the formation of substantial gold nuggets.
This research provides significant insight into why large gold nuggets are often found in certain quartz veins, suggesting that piezoelectric properties of quartz under seismic pressure play a crucial role in the natural formation of these valuable deposits.