Earth may have a hidden “gold kitchen” deep beneath the seafloor, according to new research highlighted by ScienceDaily. Scientists have long wondered why island arcs — chains of volcanoes above subduction zones — are often especially rich in gold.
Led by Dr. Christian Timm of GEOMAR Helmholtz Centre for Ocean Research Kiel, the study points to hydrous mantle melting as the main reason gold becomes concentrated in these settings. The team examined 66 volcanic glass samples from the Kermadec island arc and the nearby Havre Trough north of New Zealand.
Volcanic glass preserves the chemistry of magma that cooled rapidly underwater, giving researchers a snapshot of conditions deep below the seafloor. In the most primitive samples, the scientists found gold levels several times higher than those seen in comparable mid-ocean ridge magmas.
According to the researchers, the enrichment is best explained by repeated, high-degree melting of a water-rich, oxidized mantle that had already been depleted by earlier melting. The study found that water mainly helps drive the melting process, while intense melting releases gold that is often bound in sulfide minerals inside the mantle.
Even with the elevated gold levels, the rocks are not rich enough to be mined commercially. Still, the findings help explain how gold-rich magmas and some submarine hydrothermal sulfide deposits may begin forming long before material reaches the surface.
