Hydrous mantle melting controls gold enrichment in Kermadec arc magmas

Abstract

Many economic gold deposits on Earth are associated with volcanic arcs. However, little is known about the factors that control the gold endowment of the parental arc magmas. Here, we present new high-precision geochemical data from submarine glasses recovered from the length of the Kermadec arc. We show that the combined systematics of Au, Ag and Cu helps to decipher sources and processes responsible for Au enrichment in arc magmas. These data show that hydrous melting in the Kermadec subarc mantle occurs predominantely at high temperatures in the presence of sulfide liquid. The highest Au (>8 ppb at MgO> 5 wt.%), Au/Cu (up to 6*10^-6) and mantle-like Ag/Cu values correspond to high-temperature second-stage melting. Elevated temperatures in a hydrous subarc mantle enables enhanced and multiple-stage melting of highly depleted mantle and thus is a prerequisite of Au enrichment in parental arc magmas.