The hydrogeological regime of the TAG sulfide mound on the Mid-Atlantic Ridge - Insights into metal fluxes from reaction-transport modeling

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Submarine massive sulfides (SMS) are the modern analogues of ancient volcanogenic massive sulfides (VMS) and may represent a future metal resource. They form in response to hydrothermal cooling of the young ocean floor, when hot fluids rising from a magmatic heat source mix with seawater to deposit their metal load. The TAG hydrothermal mound on the Mid-Atlantic Ridge hosts one of the largest submarine sulfide accumulations and is an excellent location for studying the controlling processes. Its internal structure has been probed by ocean drilling (ODP 158) and extensive geological and geophysical data is available. Yet, the detailed hydrogeological regime and the chemical precipitation and dissolution processes that made the mound have never been quantified with reaction-transport models and major knowledge gaps remain – with the consequence that the likely global SMS endowment and also the role of hydrothermal venting in global biogeochemical cycles remain poorly constrained. Here, we will work on narrowing these knowledge gaps using 3-D reaction-transport modeling. Our approach is to couple an existing 3-D hydrothermal flow model, hydrothermalFoam, with the thermodynamic MINES database for fluid rock interactions using the GEMS3K software for Gibbs Free Energy minimization. This will allow us to test scenarios for the formation of the TAG hydrothermal mound and to elucidate the dominant processes that control hydrothermal metal fluxes into, within, and out of hydrothermal mounds.