Types of Hydrothermal Deposits
Deposits of hydrothermal origin exposed on the ocean floor have been classified
according to their structure, their textural appearance and their composition. They
include: massive sulfide edifices, hydrothermal mounds, porous deposits, native
sulfur, Fe–Mn deposits, ochreous deposits, Fe-oxyhydroxides, siliceous deposits
(colloidal form), and silicates (clay-like deposits). Stockwork and veins of mineralization formed within the lithosphere (which are also evidence of hydrothermal
activity) will be treated as a separate classification.
Massive Sulfides
Consisting essentially of Zn, Cu and Fe rich metalliferous deposits, massive sulfides appear blocky, as it they were constructed of concrete blocks of various
shapes and sizes. The variously shaped blocks are generally composed of a core
enriched in chalcopyrite while the outer portion of the blocks is essentially made
up of pyrite. The Cu-rich massive sulfides and the Fe-rich massive sulfides differ
from each other not only in their relative proportion of iron and copper mineral
contents, but also in their degree of porosity because the Fe-rich massive sulfides
appear to have a porosity of 10–15 % while the porosity of the Cu-rich massive
sulfides is less than 10 %. Nevertheless, both types of massive sulfides are definitely less porous than any other sulfide deposit, and their pores are filled with
visible crystalline (idiomorphic) pyrite and/or chalcopyrite as well as with opaline
material.
Snow Balls and Beehives (Porous Sulfide Deposits)
‘‘Snow balls’’ were created by white-colored low-temperature exiting fluids
(Speiss et al. 1980; Haymon and Kastner 1981) and are composed of more than
50 % pore spaces. These extremely porous deposits form relatively small (\2 m in
diameter) structures, which are colonized by tubular worms (pogonophoara and
alvinella) due to the biological activity associated with hydrothermalism. Fossilized worm remains are also often found in the vicinity of ‘‘dead vents’’ where
hydrothermal activity is no longer occurring.
The mineral constituents of snowballs and bee-hives are mainly zinc sulfides
(sphalerite) and a smaller amount of pyrite. The worm tubes observed on these
structures contain concentric, extremely thin layers (lamellae) of shapeless (collomorph texture) zinc sulfides, Fe-sulfides, and amorphous silica. These types of
deposits show a low temperature sequence of mineral crystallization except for the
occurrence of some isolated grains of Cu-rich sulfide phases, which suggest that at
152
6 Hydrothermal Activity and Metalliferous Deposits
Deposits of hydrothermal origin exposed on the ocean floor have been classified
according to their structure, their textural appearance and their composition. They
include: massive sulfide edifices, hydrothermal mounds, porous deposits, native
sulfur, Fe–Mn deposits, ochreous deposits, Fe-oxyhydroxides, siliceous deposits
(colloidal form), and silicates (clay-like deposits). Stockwork and veins of mineralization formed within the lithosphere (which are also evidence of hydrothermal
activity) will be treated as a separate classification.
Massive Sulfides
Consisting essentially of Zn, Cu and Fe rich metalliferous deposits, massive sulfides appear blocky, as it they were constructed of concrete blocks of various
shapes and sizes. The variously shaped blocks are generally composed of a core
enriched in chalcopyrite while the outer portion of the blocks is essentially made
up of pyrite. The Cu-rich massive sulfides and the Fe-rich massive sulfides differ
from each other not only in their relative proportion of iron and copper mineral
contents, but also in their degree of porosity because the Fe-rich massive sulfides
appear to have a porosity of 10–15 % while the porosity of the Cu-rich massive
sulfides is less than 10 %. Nevertheless, both types of massive sulfides are definitely less porous than any other sulfide deposit, and their pores are filled with
visible crystalline (idiomorphic) pyrite and/or chalcopyrite as well as with opaline
material.
Snow Balls and Beehives (Porous Sulfide Deposits)
‘‘Snow balls’’ were created by white-colored low-temperature exiting fluids
(Speiss et al. 1980; Haymon and Kastner 1981) and are composed of more than
50 % pore spaces. These extremely porous deposits form relatively small (\2 m in
diameter) structures, which are colonized by tubular worms (pogonophoara and
alvinella) due to the biological activity associated with hydrothermalism. Fossilized worm remains are also often found in the vicinity of ‘‘dead vents’’ where
hydrothermal activity is no longer occurring.
The mineral constituents of snowballs and bee-hives are mainly zinc sulfides
(sphalerite) and a smaller amount of pyrite. The worm tubes observed on these
structures contain concentric, extremely thin layers (lamellae) of shapeless (collomorph texture) zinc sulfides, Fe-sulfides, and amorphous silica. These types of
deposits show a low temperature sequence of mineral crystallization except for the
occurrence of some isolated grains of Cu-rich sulfide phases, which suggest that at
152
6 Hydrothermal Activity and Metalliferous Deposits