some point the hydrothermal fluid could have reached the critical temperature of
[300 °C, enabling the formation of chalcopyrite.
The beehive type deposits are comparable to the snow balls, however they are
gray colored and have a conical shape. They differ from hydrothermal chimneys
by the absence of a central conduit, and instead they are made up of of highly
porous material enabling hydrothermal fluids to be diffused throughout all the
pores exposed on their conical surfaces. The presence of the small pores on these
two types of edifices implies a more cloudy, fluid mixing between the exiting
hydrothermal fluid and seawater than that encountered in the normal conduits
found on hydrothermal chimneys.
Hydrothermal Mounds
Mounds are formed by the degradation of previously formed chimneys that have
been subsequently re-cemented together. They are found in association with a
single large or several smaller circular chimneys of sulfides erected on the porous
sulfide mounds. A continued discharge of low temperature hydrothermal fluid
seals the chimney orifices and results in a more massive and larger appearance for
the mound deposits.
Columnar Edifices: Hydrothermal Chimneys
Large vertical tubes varying in size between 30 and 50 cm up to 3 m in diameter
and from 1 to 45 m tall have been reported on several rifted segments of the EPR
axis. When active, they are often surmounted by smaller columns (\30 cm tall)
from which hot hydrothermal fluid is discharged. The main body of the columnar
edifices is formed during the growth of sulfide chimneys around a centrally located
discharge zone.
Barite Chimneys
Barite chimneys are white, as opposed to the reddish-brown sulfide chimneys.
Barium occurs as barite minerals in rocks and precipitates after leaching during the
mixing of hydrothermal fluid with sea water following the equation:
Ba
2+ (fluid) ? SO 4
2+ (sea water) = BaSO 4 (solid)
Types of Hydrothermal Deposits
153
[300 °C, enabling the formation of chalcopyrite.
The beehive type deposits are comparable to the snow balls, however they are
gray colored and have a conical shape. They differ from hydrothermal chimneys
by the absence of a central conduit, and instead they are made up of of highly
porous material enabling hydrothermal fluids to be diffused throughout all the
pores exposed on their conical surfaces. The presence of the small pores on these
two types of edifices implies a more cloudy, fluid mixing between the exiting
hydrothermal fluid and seawater than that encountered in the normal conduits
found on hydrothermal chimneys.
Hydrothermal Mounds
Mounds are formed by the degradation of previously formed chimneys that have
been subsequently re-cemented together. They are found in association with a
single large or several smaller circular chimneys of sulfides erected on the porous
sulfide mounds. A continued discharge of low temperature hydrothermal fluid
seals the chimney orifices and results in a more massive and larger appearance for
the mound deposits.
Columnar Edifices: Hydrothermal Chimneys
Large vertical tubes varying in size between 30 and 50 cm up to 3 m in diameter
and from 1 to 45 m tall have been reported on several rifted segments of the EPR
axis. When active, they are often surmounted by smaller columns (\30 cm tall)
from which hot hydrothermal fluid is discharged. The main body of the columnar
edifices is formed during the growth of sulfide chimneys around a centrally located
discharge zone.
Barite Chimneys
Barite chimneys are white, as opposed to the reddish-brown sulfide chimneys.
Barium occurs as barite minerals in rocks and precipitates after leaching during the
mixing of hydrothermal fluid with sea water following the equation:
Ba
2+ (fluid) ? SO 4
2+ (sea water) = BaSO 4 (solid)
Types of Hydrothermal Deposits
153