Zn-rich type of chimney, which is more porous than the Cu-rich chimney, the inner
part will become partially clogged. In the Cu-rich chimneys, the inner part consists
essentially of coarse-grained chalcopyrite. In the Cu–Zn chimneys, the inner walls
will be the sites of Zn-sulfide precipitation before the crystallization of chalcopyrite. The actual construction of a hydrothermal chimney was monitored and is
discussed in Chap. 7 in a section about the Chain Site on the East Pacific Rise.
Some chimneys are more than 30 m tall. Commonly the average height of a
hydrothermal edifice is about 3–7 m as seen at 20°N, 10–13°N, and 17–21°S on
the East Pacific Rise. Sometimes it is difficult to assign a definite geometry to these
edifices, and several edifices could be erected on top of piles of fragmented and recemented sulfides. Other edifices may have the aspect of a tree with several
branching chimneys on top of a bulbous shaped porous sulfide deposit. At their
base, sulfide chimneys can be found sitting on an irregular surface and may even
cover sheet flows and fissures. However, chimneys do not extend along the entire
length of a fissure, and instead are always localized.
Phases Forming Hydrothermal Deposits
Hydrothermal activity will probably take place over several steps within a
restricted area of the sea floor surface and this will contribute to the construction of
sizable metalliferous deposits. Different events in the formation of an extensive
deposit have been observed in various locations on the sea floor. The formation of
a metalliferous deposit can be divided into five stages (Fig. 6.5a–e) as follows:
(1) The first phase involves the discharge of low (\150 °C) temperature fluid
through pillow lavas and/or sheet flows discharging iron-silicates and some
sulfides (Fig. 6.5a, b). This type of low temperature discharge is accompanied
by a gathering of the benthic animal community such as tube worms, clams,
etc.
(2) High temperature ([350 °C) exiting fluids are found during the next stage of
activity, resulting in the construction of chimneys to channel this fluid and
provoking the precipitation of iron-copper sulfides and anhydrite (CaSO 4 )
(Fig. 6.5c).
(3) A coalescence of several chimneys leads to the formation of a porous edifice
or mound, through which more seawater can enter the lithosphere, and where
hydrothermal fluids can more easily percolate, with the precipitation of ironcopper-zinc sulfides. At the same time, the circulation of hot fluids will
enhance the alteration of the country rock and the precipitation of metalliferous compounds forming stockwork.
(4) At the declining stage of hot hydrothermal activity, cooler fluid ([200 °C) will
be discharged forming mineral compounds that will eventually fill the pores or
fissures of the hydrothermal mounds (Fig. 6.5d). This event will give rise to a
zonal distribution where copper rich precipitates are more plentiful at the
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6 Hydrothermal Activity and Metalliferous Deposits
part will become partially clogged. In the Cu-rich chimneys, the inner part consists
essentially of coarse-grained chalcopyrite. In the Cu–Zn chimneys, the inner walls
will be the sites of Zn-sulfide precipitation before the crystallization of chalcopyrite. The actual construction of a hydrothermal chimney was monitored and is
discussed in Chap. 7 in a section about the Chain Site on the East Pacific Rise.
Some chimneys are more than 30 m tall. Commonly the average height of a
hydrothermal edifice is about 3–7 m as seen at 20°N, 10–13°N, and 17–21°S on
the East Pacific Rise. Sometimes it is difficult to assign a definite geometry to these
edifices, and several edifices could be erected on top of piles of fragmented and recemented sulfides. Other edifices may have the aspect of a tree with several
branching chimneys on top of a bulbous shaped porous sulfide deposit. At their
base, sulfide chimneys can be found sitting on an irregular surface and may even
cover sheet flows and fissures. However, chimneys do not extend along the entire
length of a fissure, and instead are always localized.
Phases Forming Hydrothermal Deposits
Hydrothermal activity will probably take place over several steps within a
restricted area of the sea floor surface and this will contribute to the construction of
sizable metalliferous deposits. Different events in the formation of an extensive
deposit have been observed in various locations on the sea floor. The formation of
a metalliferous deposit can be divided into five stages (Fig. 6.5a–e) as follows:
(1) The first phase involves the discharge of low (\150 °C) temperature fluid
through pillow lavas and/or sheet flows discharging iron-silicates and some
sulfides (Fig. 6.5a, b). This type of low temperature discharge is accompanied
by a gathering of the benthic animal community such as tube worms, clams,
etc.
(2) High temperature ([350 °C) exiting fluids are found during the next stage of
activity, resulting in the construction of chimneys to channel this fluid and
provoking the precipitation of iron-copper sulfides and anhydrite (CaSO 4 )
(Fig. 6.5c).
(3) A coalescence of several chimneys leads to the formation of a porous edifice
or mound, through which more seawater can enter the lithosphere, and where
hydrothermal fluids can more easily percolate, with the precipitation of ironcopper-zinc sulfides. At the same time, the circulation of hot fluids will
enhance the alteration of the country rock and the precipitation of metalliferous compounds forming stockwork.
(4) At the declining stage of hot hydrothermal activity, cooler fluid ([200 °C) will
be discharged forming mineral compounds that will eventually fill the pores or
fissures of the hydrothermal mounds (Fig. 6.5d). This event will give rise to a
zonal distribution where copper rich precipitates are more plentiful at the
160
6 Hydrothermal Activity and Metalliferous Deposits