Abstract: The Coriolis Troughs located in the Vanuatu backarc of the southwestern Pacific consist of the Vate Trough to the north, the Erromango Basin in the middle and the Futuna Trough to the south. Major hydrothermal activity responsible for the formation of Sulfides- and barite-bearing Fe-Si oxyhydroxide deposits as well as biological communities of living galatheid crabs and gastropods occurs at the caldera rim of a submarine volcano in the northern Vate Trough. The deposits consist of major nontronite and amorphous Fe-Si oxyhydroxides, minor sulfides and barite, and are associated with traces of Mn. Galena, chalcopyrite, pyrite, sphalerite, marcasite and covellite are the principle sulfide minerals. The deposits occur sporadically on pillow lavas and breccias as small chimneys, mounds, flat slabs and infillings in water depths between 1100 and 1400 m. The deposits are more than several tens of meters wide and extend about 1 km in one direction at the northwestern and eastern caldera rims. The appearance of shimmering water was observed in the holes between the pillow lavas and tubes, and was associated with a positive temperature anomaly by 0.2 °C relative to the ambient seawater. Dark back-scattered acoustic images obtained by side-scan sonar revealed the occurrence of mounds. This suggests the presence of several hydrothermal deposits on the eastern rim of the caldera. In the Futuna Trough, sulfide-bearing Fe-Si oxyhydroxide deposits are present as flat slabs and infillings of brownish fragments and reddish brown sediments and Mn precipitation on volcanic rocks near the summit of a submarine volcano on the northwestern flank in water depths between 940 to 980 m. The deposits are characterized by the presence of bacterial filaments, high concentrations of Fe (max. 42 wt%) and As (max. 2.7 wt%), major goethite and amorphous Fe-Si oxyhydroxides, birnessite, and sulfides. The hydrothermal nontronite deposits of the Vate Trough were formed under more reduced conditions than the goethite of the Futuna Trough. Sulfides and barite from the Vate deposits were formed as a result of the precipitation from hydrothermal fluids in the deposits whereas sulfides of the Futuna deposits were deposited from hydrothermal vents further away. The presence of sulfides in the Vate Fe-Si oxyhydroxide deposits suggests that extensive sulfide deposits may exist in the volcanic pile of the caldera. The Coriolis Troughs are still active, especially in the Vate Trough. There are a number of areas with the potential for hydrothermal precipitation of sulfide-bearing Fe-Si oxyhydroxide deposits in both the Vate and Futuna Troughs.

EXPLOR_STEP=$WICRI_ROOT/Wicri/Terre/explor/NissirosV1/Data/Main/Exploration

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{{Explor lien
   |wiki=    Wicri/Terre
   |area=    NissirosV1
   |flux=    Main
   |étape=   Exploration
   |type=    RBID
   |clé=     ISTEX:DDFEB959D3E6FCCF22118D6A64CB7B42374F3CD3
   |texte=   Hydrothermal sulfide-bearing Fe-Si oxyhydroxide deposits from the Coriolis Troughs, Vanuatu backarc, southwestern Pacific
}}