Gold nugget formation from earthquake-induced piezoelectricity in quartz

Gold nuggets occur predominantly in quartz veins, and the current paradigm posits that gold precipitates from dilute (<1 mg kg−1 gold), hot, water ± carbon dioxide-rich fluids owing to changes in temperature, pressure and/or fluid chemistry. However, the widespread occurrence of large gold nuggets is at odds with the dilute nature of these fluids and the chemical inertness of quartz. Quartz is the only abundant piezoelectric mineral on Earth, and the cyclical nature of earthquake activity that drives orogenic gold deposit formation means that quartz crystals in veins will experience thousands of episodes of deviatoric stress. Here we use quartz deformation experiments and piezoelectric modelling to investigate whether piezoelectric discharge from quartz can explain the ubiquitous gold–quartz association and the formation of gold nuggets. We find that stress on quartz crystals can generate enough voltage to electrochemically deposit aqueous gold from solution as well as accumulate gold nanoparticles. Nucleation of gold via piezo-driven reactions is rate-limiting because quartz is an insulator; however, since gold is a conductor, our results show that existing gold grains are the focus of ongoing growth. We suggest this mechanism can help explain the creation of large nuggets and the commonly observed highly interconnected gold networks within quartz vein fractures. Quartz emits a piezoelectric charge during deformation that may promote the formation of gold nuggets within veins in orogenic settings that experience earthquakes, according to a study using quartz deformation experiments and piezoelectric modelling.