LOW-TEMPERATURE FLUID-FLOW THROUGH SULFIDIC SEDIMENTS FROM TAG - MODIFICATION OF FLUID CHEMISTRY AND ALTERATION OF MINERAL-DEPOSITS

Low-temperature fluid flow has been identified as an important compone nt of the heat, mass and chemical flux at sites of active venting. One way to study the movement of water through hydrothermal deposits is t o analyse the pore-fluids extracted from sulfidic sediments. The compo sition of diffuse flow fluids in one sediment core from the south of t he active TAG mound reflects the dilution of high-temperature, black s moker fluids, with modification inside the mound during ongoing circul ation. Fluid modification includes conductive cooling, removal of Si f rom solution and entrainment and removal of U from seawater which can represent significant sinks of these elements. Precipitation of clay m inerals and Fe-oxides is currently occurring within this sediment core generating ochreous type material subsurface. Extensive low-temperatu re alteration of basaltic material at the core-top is apparent in conj unction with supergene enrichment of Cu and Mn.