02609nas a2200253   4500000000100000008004100001653001700042653002700059653001100086653001400097653003000111653000800141100002100149700002100170700002100191700001800212700002100230700001900251245010300270856007300373300001800446490000700464520188400471       2023                            d10ageochemistry10ahydrothermal sediments10ametals10aporewater10aseafloor massive sulfides10aTAG1 aAdeline Dutrieux1 aAnna Lichtschlag1 aFernando Barriga1 aSofia Martins1 aJelena Milinovic1 aBramley Murton00aMetal Preservation and Mobilization in Sediments at the TAG Hydrothermal Field, Mid-Atlantic Ridge  uhttps://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2023GC010879  ae2023GC0108790 v243 a<p>Abstract At the Trans-Atlantic Geotraverse hydrothermal field, metalliferous sediments cover extinct hydrothermal mounds and the surrounding seafloor. Here, we report the morphological, mineralogical and geochemical processes that deposit these sediments, remobilize their metals, and affect their preservation. We found that the initial sediment metal tenor is controlled by physical transport of hydrothermal material from its source, followed by diagenetic redistribution and potentially diffuse fluid flow after high-temperature hydrothermal activity has ceased. We distinguished three different environments: (a) proximal metalliferous sediments on top of extinct mounds are mainly derived from oxidative weathering of primary sulfide structures and are predominantly composed of Fe oxyhydroxides with low contents of Cu, Co, and Zn; metal enrichments in specific layers are likely related to upward flow of low-temperature hydrothermal fluids; (b) medial distant metalliferous sediments found at the base of the mounds, deposited by mass transport, contain cm-thick layers of unsorted sulfide sands with high base metal contents (e.g., up to 28\% Cu); these buried sulfides continue to undergo dissolution, resulting in metal release into porewaters; (c) distal metalliferous sediments, found in depositional basins a few hundreds of meters from the extinct mounds, include fining-upwards sequences of thin sulfide sand layers with Fe oxyhydroxides and were deposited by recurrent turbiditic flows. Dissolved metals (e.g., Cu2+ and Mn2+) diffuse upwards under reducing conditions and precipitate within the sediment. Hence, when using hydrothermal sediments to construct reliable geochronological records of hydrothermal activity, distance from source, local seafloor morphology, mass-transport and depositional, and diagenetic modification should all be considered.</p>