Seawater can advectively circulate through young (< 10 Ma), permeable oceanic crust to depths between 1 and 4 km. Associated with such hydrothermal circulation is heating of seawater (to temperatures upto 400 degC), rapid reaction with the surrounding host volcanics and the formation of high-temperature, reducing hydrothermal fluids. These fluids attain hydrostatic buoyancy at depth in the crust and rise rapidly to the seafloor. Hydrothermal activity is manifest most spectacularly at the seafloor in the form of "black smokers". Black smokers are not smokers in the literal sense; rather they are fine-grained black precipitates that form when (initially clear) hydrothermal fluid reacts with seawater and forms sulfide-rich particles that disperse in the overlying water column.
The formation and concentration of these sulfide precipitates at or near the seafloor, as sulfide-sulfate-silica chimneys and basal mounds, is an important mechanisms for producing metal-rich volcanogenic massive sulfide deposits that humans exploit on land for mineral resources. This chimney, from the Mariner vent field, Lau Basin, is venting hydrothermal fluids up to 360 degC, from a massive chimney structure more than 25 m in height and 5 m in diameter.
My thesis focuses on the geochemical conditions that are conducive to the formation of such vent deposits and to the concentration of precious metals (such as Ag, Au, Bi, Cd, Pb) within these deposits. (Copyright 2005 Paul R. Craddock)