Observations of extensive mineral replacement at Von Damm vent field

The Von Damm vent field, on the Mt. Dent oceanic core complex of the Mid Cayman Rise, is unique among known modern hydrothermal systems as talc is the dominant hydrothermal precipitate. This is despite the fact that talc appears abundantly as a primary and secondary mineral at other hydrothermal locations. Analysis of collected in 2020 and analyzed using XRD, Raman imaging microscopy, and SEM/EDS reveals that in addition to talc, carbonate minerals are a major class of mineral at Von Damm. The carbonate minerals that are present at Von Damm include aragonite, calcite, magnesium rich calcite, and dolomite. We demonstrate that the composition of these major minerals varies based on the subregion of the vent field in which the samples were collected, and that in most of the samples, the carbonate assemblage is being replaced by talc. In addition, , we found that a diverse range of metal sulfide minerals and metal sulfide weathering products are well represented in Von Damm samples, and occur within both the carbonate and talc minerals. These micro- and nano- particulate rare minerals occur throughout the assemblage and show evidence of highly reducing conditions, as well as processes of metal remobilization. The observed mineral sequence is characteristic of serpentinization and resembles systems associated with subduction, including modern systems in the Mariana forearc. We use this new data to consider processes of mineral replacement, including element transport, and suggest that at the seafloor surface, hydrothermal-oceanic interfaces similar to those occurring at the Von Damm vent field, many elements occurring in mineralized hydrothermal systems may be highly transitory over geologic time scales.