In the nearly 30 years since the discovery of hydrothermal
venting along open-ocean spreading centers, much has been
learned about the generation of vent fluids and associated deposits.
The hot, reducing, metal-rich, magnesium- and sulfatepoor
hydrothermal fluids that exit “black smoker” and “white
smoker” chimneys are formed through interactions of seawater
with oceanic crust. These interactions (1) modify the composition
of oceanic crust, (2) affect ocean chemistry, (3) form
metal-rich deposits (possible analogs to ore deposits present on
land), and (4) provide energy sources for biological communities
in the deep sea.