Should inactive seafloor massive sulfide deposits from the TAG hydrothermal field be protected?

With the world’s growing demand for metals, Seafloor Massive Sulfides (SMS) deposits are now seen as a possible mineral resource that could contributes to secure metal supply for human needs. Although inactive or extinct SMS deposits are likely to be the main target for potential exploitation, only few studies have been devoted to them so far. Relict SMS deposits in Trans-Atlantic Geotraverse (TAG) hydrothermal field are known since the mid-1980s but these so-called inactive sites have only been recently further investigated [1,2,3]. High-resolution acoustic surveys and extensive human occupied vehicle (HOV) dive operations performed during four different expeditions led to the discovery of thirteen new SMS deposits including six large (i.e > 5000 m2) deposits making the TAG hydrothermal field the largest accumulation of SMS deposits (i.e. 21.1 Mt) known on the seafloor. However, copper and zinc grades of the largest SMS deposits remain low (i.e. < 1.4 wt.%) even compared to on-land volcanogenic massive sulfides. Additionally, eight areas of diffuse hydrothermal fluid flow were identified challenging the presumed inactivity of these SMS deposits and, for the first time, emphasizing the importance of low temperature (LT) hydrothermal activity in the whole TAG field.Some authors [4] classified the TAG field as hydrothermally active. This recommendation is relevant, particularly now knowing that all hydrothermal zones in the TAG field exhibit temperature anomalies. Other inactive sulfide deposits might be discovered further east. However, considering knowledge gaps (e.g. patterns of hydrothermal circulation) and based on a precautionary approach, all to-be-discovered deposits belonging to TAG area should be grouped within a single area classified as active and thus protected from exploitation.References:[1]. Murton, B.J., et al., 2019. Geological fate of seafloor massive sulphides at the TAG hydrothermal field (Mid-Atlantic Ridge). Ore Geology Reviews 107, 903–925. https://doi.org/10.1016/j.oregeorev.2019.03.005[2]. Graber, S., et al., 2020. Structural Control, Evolution, and Accumulation Rates of Massive Sulfides in the TAG Hydrothermal Field. Geochemistry, Geophysics, Geosystems 21, e2020GC009185. https://doi.org/10.1029/2020GC009185[3].      Pelleter E., et al., 2024. Diversity, spatial distribution and evolution of inactive and weakly active hydrothermal deposits in the TAG hydrothermal field . Frontiers In Earth Science , 12, 1304993 (25p.) . Publisher's official version : https://doi.org/10.3389/feart.2024.1304993[4]. Jamieson, J.W., Gartman, A., 2020. Defining active, inactive, and extinct seafloor massive sulfide deposits. Marine Policy 117, 103926. https://doi.org/10.1016/j.marpol.2020.10392