Multi Scales Exploration Strategy - Example of Research For Hydrothermal Mineralization in the French EEZ of Wallis and Futuna

Abstract

Abstract As part of a Public Private consortium, explorations to locate sulfide mineralization in the French EEZ of Wallis and Futuna allowed to discover new hydrothermal fields. Three cruises organized between 2010 and 2012 have explored this area. The first phase focused on a regional mapping to find areas of recent volcanism using multibeam echosounders and acoustic imaging. Hydrothermal plumes produced by high temperature hydrothermal activity were located using chemical and physical anomalies in the water column. Using a CTD/rosette we collected water samples and measured physical parameters. Onboard methane and manganese concentrations and physical parameters studies helped to locate active fields with a precision of about 5 km. Physical anomalies caused by the hydrothermal plumes were also recorded by analyzing the multibeam backscattered signals of the water column. In a second phase, an AUV, operated at 70m above the seafloor, helped to establish high-resolution (1 m) bathymetric maps on targets identified during Phase 1. Near seafloor, magnetic anomalies were recorded using a deep magnetometer on the AUV. Analysis of AUV acoustic signals in the water column allowed to find the vertical part of the hydrothermal plumes and to pinpoint areas of fluids discharge with a precision of a few meters. During the third phase, manned submersible dives were conducted on the hydrothermal fields to study the hydrothermal fluids, the different types of mineralization and associated ecosystems. This multi-scale strategy allows gaining considerable time in exploration, and led to the discovery of several hundred of active and inactive fields and associated sulfides mineralization on an area not previously mapped. The AUV high-resolution mapping and detection of vertical plumes and inactive chimneys can thus be considered as a missing link of the exploration strategy to locate hydrothermal deposits.