Hydrothermal chimney

Because the concentration difference between MORB and hydrothermal chimney materials for both Ba and Ra is greater than lO , incorporation of small amounts of barite from hydrothermal systems could create the high ( Ra)/( °Th) observed in MORB. However, if Ra excess results from this process, then Ba concentrations (and Ba/Th) should be equally raised by such contamination. However, Ba/Th in highly depleted glasses from the Siquieros Transform that have ( Ra)/( °Th) greater than 3 are typical for MORB and do not have anomalously high Ba contents (Lundstrom et al. 1999). 

Hydrothermal chimney formation. Source-. After Edmond, J. M. (1984). Oceanus 27, 15-19. 

Chevaldonne, P. and Godfroy, A. (1997) Enumeration of microorganisms from deep-sea hydrothermal chimney samples. FEMS Microbiology, 146, 211-216. 

Both, R.A., Crook, K., Taylor, B., Brogan, S., Chapell, B., Frankel, E., Liu, L., Sinton, J. and Tiffin, D., 1986. Hydrothermal chimneys and associated fauna in the Manus back - arc basin, Papua New Guinea. American Geophysical Union Translations, 67 489-490. 

Deposits which are forming are frequentiy characterized by venting streams of hot (300°C) mineralized fluid known as smokers. These result in the local formation of metalliferous mud, rock chimneys, or mounds rich in sulfides. In the upper fractured zone or deep in the rock mass beneath the vents, vein or massive sulfide deposits may be formed by the ckculating fluids and preserved as the cmstal plates move across the oceans. These off-axis deposits are potentially the most significant resources of hydrothermal deposits, even though none has yet been located. 

The above lines of evidence suggest that the precipitation of minerals in. submarine hydrothermal ore deposits on the seafloor is taking place from the fluids with high flow rate at the orifices of the chimney (ca. 1-10 m/s) and with high degree of supersaturation under the non-equilibrium conditions. 

Amorphous silica and barite precipitate simultaneously from white smoker in midoceanic ridge hydrothermal system (Edmond et al., 1979). It is inferred that amorphous silica precipitates in the chimney at a later stage than sulfides and sulfates (anhydrite and barite) which constitute chimneys from which black smoker is emerging. 

It is thought that the precipitation of amorphous silica is caused by conductive cooling from the hydrothermal solution which flows laterally in the chimney (Herzig et al., 1988). 

Herzig, RM., Becker, K.P., Stofeers, R, Backer, H. and Bulum, N. (1988) Hydrothermal silica chimney fields in the Galapagos spreading center. Earth Planet. Sci. Lett., 89, 261-272. 

Farrell and Holland (1983) cited ba,sed on Sr isotope study on anhydrite and barite in Kuroko deposits that the most appealing model for the formation of Kuroko strata-bound ores would seem to entail precipitation of the minerals from a hydrothermal solution within the discharge vent or in the interior of a hydrothermal plume formed immediately below above the vent exit in the overlying seawater (Eldridge et al., 1983). The study on the chimney ores from Kuroko deposits support this model which is discussed below. 

Recently, chimney-like ores have been described from Kuroko deposits (Matsuku-ma, 1989 Shimazaki and Horikoshi, 1990 Shikazono and Kusakabe, 1999). The formation mechanism of chimney from the hydrothermal ore deposits at midoceanic ridges was clarified. Thus, these studies constrain the formation mechanism of Kuroko ore deposits. 

It is worth elucidating mineral particle behavior in hydrothermal plumes in order to consider the formation mechanism of chimney and massive ores on the seafloor. Using the grain size data on sulfides and sulfates, the density of the fluids and of the minerals, the relationship between vertical settling rate and grain size of sulfides and sulfates can be derived based on the following Stokes equation ... 

Haymon, R.M. (1983) The growth history of hydrothermal black smoker chimneys. Nature, 301, 695-698. 

Janecky, D.R. and Shanks, W.C. Ill (1988) Computational modeling of chemical and sulfur isotopic reaction processes in seafloor hydrothermal systems, chimney, massive sulfides, and subjacent alteration zones. Can. Mineral, 26, 805—826. 

Woodruff, L.G. and Shanks, W.C. Ill (1988) Sulfur isotope. study of chimney minerals and vent fluids from 21°N East Pacific Rise Hydrothermal sulfur sources and disequilibrium sulfate reduction. J. Geophys. Res., 93, 4562-4572,... 

Mid-depth maxima are produced by mid-depth sources of metals. Some of these maxima are created by remineralization of detrital biogenic particles, such as seen in Figure 11.4f for cadmium. Others are caused by lateral transport of metals mobilized from coastal sediments as illustrated in Figure 11.17(a) for manganese. Mid-depth maxima can also result from hydrothermal emissions as shown in Figure 11.19 for Mn (aq) and He(g) at a site in the Eastern North Pacific Ocean. Hydrothermal fluids are emitted into the ocean from chimneys located atop the East Pacific Rise at water depths of about 2500 m. After entering the ocean, the Mn and He are entrained in subsurfece currents and... 

Some of the hydrothermal emissions occur as focused and very hot discharges emitted through the annular orifices of rock chimneys that are tens of meters in height. The... 

The ridge crest is a dynamic setting in which volcanic activity creates new vents while old ones die. On fast-spreading centers, hydrothermal circulation supports focused discharges through chimneys that have an average life span of a few decades. 

In locations where hydrothermal fluid exits directly into the bottom ocean with little subsurfece dilution, large chimneys are deposited by the rapid precipitation of anhydrite... 

The formation of these anhydrite walls prevents the hydrothermal fluids flowing through the chimney from mixing with seawater and provides a framework to enable precipitation of sulfide minerals. In some cases, the discharge of fluids is so rapid that the sulfide precipitates are emitted as clouds of black particles moving at a speed of... 

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