Spatial association between talc-rich mineralization and sulfide-bearing deposits in a newly discovered inactive and weakly actie fields (Mid-Atlantic Ridge)

Abstract

Since 1977 and the discovery of the first high temperature (HT) hydrothermal vent, more than 300 sites are known (about 600 including inferred ones). Among these hydrothermal sites, the talc-rich deposit is the most recent class of hydrothermal system discovered on the seafloor [1]. Only three talc-rich deposits have been described so far: (i) the active Von Damm Vent Field (VDVF), (ii) the inactive St Paul’s and (iii) Conrad fracture zones deposits [2]. These hydrothermal sites are associated with lower crustal rocks and/or serpentinized peridotites and might be widespread at slow or ultraslow spreading ridge. However, no clear spatial or temporal relationship of this new class of hydrothermal system and the “black smoker”-like system has been highlighted. During the HERMINE (March-April 2017) and HERMINE2 (July-August 2022) cruises [3], [4], two hydrothermal areas with talc-rich deposits have been discovered during Nautile HOV dives. The first one (23°N) is an inactive hydrothermal area located 28km northwest of the Snake Pit vent field (25km west of the axial rift). At least two deposits have been observed: (i) a talc-silica deposit and (ii) a fully oxidized SMS-type deposit characterized by copper concentrations up to 3.3wt.%. The second hydrothermal area (26°N) is composed of one large and weakly-active deposit composed of silica-sulfides rocks and at least two small talc-silica deposits. To our knowledge, this is the first time that such a spatial relationship has been described between these two classes of deposits. The preliminary results on these newly discovered hydrothermal field will be presented here. [1] Hodgkinson et al. (2015) Nat.. Commun 6:10150doi: 10.1038/ncomms10150 .[2] D’Orazio et al. (2004) Eur. J. Mineral. 16, 73-83[3] Fouquet and Pelleter (2017), https://doi.org/10.17600/17000200[4] Pelleter and Cathalot (2022),https://doi.org/10.17600/1800185