Hydrous multi-stage mantle melting controls gold enrichment in mafic Kermadec arc magmas

Many exceptionally Au-rich deposits are associated with subduction zones and Au-rich magmas. However, the origin of Au enrichment in arc magmas remains controversial. Here, we present a new high-precision geochemical dataset on 66 submarine glasses from the length of the oceanic Kermadec arc and Havre Trough back-arc system. The combined systematics of Au with other chalcophile elements (Ag, Cu, Se, Pt) shows that hydrous melting in the Kermadec subarc mantle occurs predominantely at relatively high temperatures above the sulfide liquidus and produces magmas with mantle-like Ag/Cu values. The highest Au (up to 6 ng/g) and Au/Cu (up to 0.06 × 10 ^-3 ) exceeds that in fertile mantle and primitive MORB by far, requiring remelting of previously depleted mantle. We demonstrate that high-degree multiple-stage melting of hydrous and oxidized subarc mantle are major drivers of Au enrichment of parental magmas in intra-oceanic island arcs, such as the Kermadec arc.