Sulfate-sulfide chimneys

Shikazono, N. and Kusakabe, M. (1999) Mineralogical characteristics and formation mechanism of sulfate-sulfide chimneys from Kuroko area, Mariana trough and midocean ridges. Resource Geology Special Issue, 20, 1-12. 

Model for the formation of sulfate-sulfide chimneys and massive deposits on the seafloor... 

The above summarized mineralogical and geochemical studies on Kuroko and Mariana chimneys (Shikazono and Kusakabe, 1999), and previous studies on midoceanic ridge chimneys, combined with the studies of mineral particle behaviors in the plumbing system, are used to develop the following plausible model for the growth history of sulfate-sulfide chimneys on the seafloor (Shikazono and Kusakabe, 1999). 

Central Manus Basin Vienna Woods (3° ID S, 150°17 E) 2500 2-km-wide axial rift graben of the northeast spreading center. Mostly massive pillow lava floor. Sulfide chimneys up to 20 m high are venting clear, milky and black fluids. Sulfate smokers are also present. Sphalerite, wurtzite, pyrite, marcasite, chalcopyrite, galena, amorphous silica, barite. Sulfate chimney anhydrite, silica, barite. 

Fig. 2.45. Hypothetical mineral paragenesis for a sulfide-sulfate-silica chimney. Approximate temperature ranges for different minerals are based on direct measurements of vent fluid temperatures and analyses of fluid inclusions in real chimneys (Hannington et al., 1995).

ZnS or CdS precipitates from vent waters and any sulfur-bearing phases from the solid samples are analyzed for 5 a using an automated elemental analyzer interfaced to an isotope ratio mass spectrometer. Laser probe microanalysis has been used to study zonation in sulfide chimney walls (Crowe and Valley 1992 Shanks et al. 1998). 5 " S error is estimated to be 0.2%o. analysis of silicates, sulfates, and whole rock samples were carried out using the BrFs method of Clayton and... 

Mariana Trough is a back-arc spreading center that occurs between a remnant arc and the currently active Mariana arc. On the flanks of axial volcanoes in the central Mariana Trough are several vent fields with measured temperatures up to 287°C and sulfide-sulfate chimneys comprised of sphalerite, galena, and barite, due to metal sources from the underlying andesitic crust. An unusual occurrence in the northeast portion of the Mariana Arc is a serpentinite mud volcano called Conical Seamount. Carbonate (calcite, aragonite) and silicate (Mg silicate) chimneys occur near the mud volcano summit. Associated fluids are cold, sulfate-sulfide-carbonate-silica-rich, and have pHs as high as... 

Manus Basin is a back-arc basin located north of the New Britain island arc that consists of NE-SW trending ridge segments offset by transform faults. On the Manus Spreading Center in central Manus Basin the Vienna Woods hydrothermal field consists of a 300 m-diameter sulfide mound with an extensive foresf of active and inactive sphalerite-barite-rich, sulfide-sulfate-oxide chimneys up to 15 m-long atop it. Vent fluids from one of the active chimneys reach temperatures as high as 302°C. In the eastern Manus Basin, two important hydrothermal fields are known. The PACMANUS field includes discontinuous sulfide occurrences over a 3 by 0.8 km area and active venting of unknown nature. Volcanic rocks are andesitic to rhyodacitic. 

Koski, R.A., Jonasson, I.R., Kadko, D.C., Smith, V.K. and Wong, E.L., 1994. Compositions, growth mechanisms, and temporal relations of hydrothermal sulfide-sulfate-silica chimneys at the northern Cleft segment, Juan de Euca Ridge. Journal of Geophysical Research, 99 4813-4832. 

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 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 ... 

Graham, V.M., Bluth, G.J. and Ohmoto, H. (1988) Sulfide-sulfate chimneys on the East Pacific Rise 11° and 13°N latitudes. Part I mineralogy and paragenesis. Can. Mineral, 26, 487-504. 

Hydrothermal solution issues from mid-oceanic ridges and back arc basins. Sulfates and sulfides precipitate from hydrothermal solution, resulting to the formation of chimney (Fig. 3.14). Mineral assemblages vary from outer to inner parts of the... 

Chimney (Fig. 4.2) is mainly composed of sulfides, sulfates and silica which precipitated by the mixing of hydrothermal solutirai and cold ambient seawater. Formation mechanism of chimney has been explained in terms of several models. Partial equilibrium model was applied to the precipitatirais of minerals during the mixing of hydrothermal solution and cold seawater (Ohmoto et al. 1983). However, this model cannot explain the following features of chimney and submarine hydro-thermal ore deposits. 

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