Growth of Black Smokers and Massive Sulfide Mounds

3 Growth of Black Smokers and Massive Sulfide Mounds 

Black smoker activity begins when the hydro-thermal flnids contain enongh metals and snlfur to canse precipitation of snlfide particles dnring mixing at the vent orifice. In order to cany these metals in solntion, flnids arriving at the seafloor are nsnally hotter than 300°C. At many black smoker chimneys measnrements of vent tempe-ratnres in the range of 350°-400°C are common. 

Most chimneys have growth rates that are rapid in comparison to the half-life of Pb (22.3 years), and radioisotope ages of several days or less for precipitates of some active vents are consistent with growth rates observed from submer-sibles (5-10 cm per day Hekinian et al. 1983 Johnson and Tunnicliffe 1985). Larger vent complexes commonly have measured ages on the order of decades (Koski et al. 1994), but the data for entire vent fields may span several thousands of years (Lalou et al. 1993). 

At typical black smoker vents, a very large proportion (at least 90%) of the metals and sulfur carried in solution are lost to a hydrothermal plume in the overlying water column rather than deposited as chimneys. The metals are precipitated as sulfide particles in the plume above the black smokers and are rapidly oxidized and dispersed over distances of several kilometers from the vent (Feely et al. 1987, 1994a,b Mottl and McConachy 1990). Due to oxidation and dissolu- 

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