Over half of the world´s presently exploited metal deposits were formed in a submarine environment, the majority by processes related to rifting of arc crust. Such rifting is observed today in the NE Lau Basin, where a complex microplate mosaic offers a unique opportunity to study crustal growth and mineral endowment of emerging continental crust. Using an integrated approach of high-resolution 2D seismics, electromagnetics and sampling, ARCHIMEDES I will image the deep structure of the Fonualei Rift, where rifting of arc crust and widespread hydrothermal activity occur at the edge of the Niuafo’ou microplate. The role of the arc basement and the transition to adjacent back-arc basin crust in this region has never been investigated in detail. Our study will use high-quality MCS and refraction profiles to address a major unsolved question of submarine arcs: at what stage in the structural and thermal evolution of arc rifting does magmatic and hydrothermal activity set in and mineral deposits begin to form.