Barite hydrothermal

Authigenic barium sulfate or barite [13462-86-7] is found in relatively high concentrations in sediments covering active diverging oceanic plate boundaries. It occurs as rounded masses containing up to 75% BaSO or as a dispersed constituent of the sediment. Its origins are uncertain, but it is likely that it is associated with hydrothermal actions. 

Kaolin minerals (kaolinite, dickite, nacrite), pyrophyllite and mica-rich mica/smec-tite mixed layer mineral occur as envelopes around barite-sulfide ore bodies in the footwall alteration zones of the Minamishiraoi and Inarizawa deposits, northern part of Japan (south Hokkaido) (Marumo, 1989). Marumo (1989) considered from the phase relation in Al203-Si02-H20 system that the hydrothermal alteration minerals in these deposits formed at relatively lower temperature and farther from the heat source than larger sulfide-sulfate deposits in the Hokuroku district. 

Positive Eu anomaly is observed for barite, Kuroko ores, ferruginous chert (tet-susekiei), and hydrothermally altered basaltic and dacitic rocks overlying the Kuroko ores. 

Figure 1.46. REE patterns of the altered volcanogenic rocks and Kuroko ores. Data sources Shikazono (1999a). (A) Hydrothermally altered dacite and anhydrite underlying the Kuroko ores. (B) Barite, Kuroko ore and ferruginous chert. (C) Hydrothermally altered basalt overlying the Kuroko ores (Shikazono, 1999a).

Heavy Rare Earth Element). Therefore, it is considered that negative Ce and positive Eu anomalies in hydrothermally altered volcanic rocks, Kuroko ores, and ferruginous chert and LREE enrichment in the Kuroko ores have been caused by hydrothermal alteration and precipitations of minerals from hydrothermal solution responsible for sulfides-sulfate (barite) mineralization. 

Positive Eu anomaly is observed for hydrothermal solution issuing from the hydrothermal vent on the seawater at East Pacific Rise (Bence, 1983 Michard et al., 1983 Michard and AlbarMe, 1986). Guichard et al. (1979) have shown that the continental hydrothermal barites have a positive Eu anomaly, indicating a relatively reduced environment. Graf (1977) has shown that massive sulfide deposits and associated rocks from the Bathurst-Newcastle district. New Brunswick have positive Eu anomalies. These data are compatible with positive Eu anomaly of altered basaltic rocks, ferruginous chert and Kuroko ores in Kuroko mine area having positive Eu anomaly and strongly support that Eu is present as divalent state in hydrothermal solution responsible for the hydrothermal alteration and Kuroko mineralization. 

Precipitation of barite and quartz. Barite and quartz are the most common gangue minerals in the submarine hydrothermal ore deposits such as Kuroko deposits and back-arc basin deposits (e.g., Okinawa, Mariana deposits) (Halbach et al., 1989 Shikazono, 1994 Shikazono and Kusakabe, 1999). These minerals are also common in midoceanic ridge deposits. 

The behavior of silica and barite precipitation from the hydrothermal solution which mixes with cold seawater above and below the seafloor based on the thermochemical equilibrium model and coupled fluid flow-precipitation kinetics model is described below. 

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. 

Barite is abundant in back-arc basin hydrothermal system such as Okinawa, Manus and Mariana (Shikazono and Kusakabe, 1999). 

Solubilities of quartz and amorphous silica in aqueous solutions increase with increasing of temperature (Holland and Malinin, 1979). Solubility of barite depends on salinity and temperature (Blount, 1977). The solubility of barite in hydrothermal solution having more than 1 molal NaCl concentration increases with increasing temperature, while a solubility maximum exists in the solution with NaCl concentration less than ca. 0.2 molal (Blount, 1977). 

However, as already noted, the barite content in Kuroko ore inversely correlates to the quartz content and the occurrences of barite and quartz in the submarine hydrothermal ore deposits are different. The discrepancy between the results of thermochemical equilibrium calculations based on the mixing model and the mode of occurrences of barite and quartz in the submarine hydrothermal ore deposits clearly indicate that barite and quartz precipitated from supersaturated solutions under non-equilibrium conditions. Thus, it is considered that the flow rate and precipitation kinetics affect the precipitations of barite and quartz. 

A comparison of the calculated results (Figs. 1.53 and 1.54) with the mode of occurrences of quartz and barite in the submarine hydrothermal ore deposits indicates... 

The results of calculations are in agreement with the occurrences of barite and silica and chemical features of discharging fluids in the submarine hydrothermal ore deposits namely, quartz is inferred to precipitate in subseafloor environment and barite in seabottom environment. 

The above-mentioned consideration indicates that important factors controlling the precipitations of barite and silica are surface area/water mass ratio (A/M), temperature, precipitation rate constant (k) and flow rate (u), and the coupled fluid flow-precipitation models are applicable to understanding the distributions of minerals in submarine hydrothermal ore deposits. 

Barite precipitation highly depends on SO and Ba " concentrations in the fluids. That means that the mixing ratio of hydrothermal solution and seawater is also an important factor for the precipitation of barite, together with the factors mentioned above. 

Isotopic compositions of minerals and fluid inclusions can be used to estimate those of Kuroko ore fluids. Estimated isotopic compositions of Kuroko ore fluids are given in Table 1.10. All these data indicate that the isotopic compositions lie between seawater value and igneous value. For instance, Sr/ Sr of ore fluids responsible for barite and anhydrite precipitations is 0.7069-0.7087, and 0.7082-0.7087, respectively which are between present-day. seawater value (0.7091) and igneous value (0.704-0.705). From these data, Shikazono et al. (1983), Farrell and Holland (1983) and Kusakabe and Chiba (1983) thought that barite and anhydrite precipitated by the mixing of hydrothermal solution with low Sr/ Sr and seawater with high Sr/ Sr. 

Yoneda, T. and Shirahata, H. (1995) Acid alteration associated with Kuroko-type mineralization and Sr isotope study of hydrothermal alteration at the Minamishiraoi barite deposit, southwestern Hokkaido, Japan. Resource Geology Special Issue, 18, 203-210. 

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. 

Sulfates (barite and anhydrite) precipitate due to the mixing of discharging hydrothermal solution with cold seawater above the seafloor at an early stage of hydrothermal activity. Ca and Ba in hydrothermal solution react with SO in cold seawater, leading to the precipitations of anhydrite and barite. It is observed that anhydrite precipitated earlier than barite. This may depend on the initial Ca and Ba concentrations of end member hydrothermal solutions, temperature and degree of mixing of hydrothermal solutions and... 

The 8 S data on barites from the Yanahara and Hitachi (Yamamoto et al., 1984b Kase and Yamamoto, 1985) are -f-12%o to - -15%o which is similar to those of Late Paleozoic seawater sulfate, indicating that barite formed by the mixing of seawater and hydrothermal solution as same as Kuroko barite (Kusakabe and Chiba, 1983). 

Barite and sphalerite tend to precipitate at lower temperature from the hydrothermal solution mixed with a large amount of cold seawater (but mixing ratio (seawater/hydrothermal solution) may be less than 0.2). These minerals precipitate on the seafloor and/or at very shallow subsurface environment. However, chalcopyrite tends to precipitate from high temperature solutions in ore bodies and/or at the sub-seafloor sediments. Usually shale which is relatively impermeable overlies the Besshi-type ore bodies. This suggests that hydrothermal solution could not issue from the seafloor and... 

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). 

Fig. 22.3. Mineralogical results (top) of mixing cold seawater into one kg of hot hydrothermal fluid from the NGS field. Minerals present in volumes less than 0.01 cm3 are not shown. These minerals, in order of decreasing abundance, are sphalerite, barite, potassium mor-denite, calcium clinoptilolite, and covellite. Also shown (bottom) is the temperature of the fluid during mixing.

DRIFT spectra, acquiring, 24 111. See also Diffuse reflectance infrared Fourier transform spectroscopy (DRIFT) Drilling, of hydrothermal wells, 12 525-527 Drilling fluid (drilling mud) companies, 9 2 Drilling fluid materials, 9 2, 9-25. See also Drilling fluids Drilling muds alkalinity control in, 9 19 barite, 9 9-10 calcite, 9 10... 

Turner, R.J.W. 1990. Jason stratiform Zn-Pb-barite deposit, Selwyn Basin, Canada (NTS 105/01). Geological setting hydrothermal facies and genesis. In Abbott, J.G Turner, R.J.W. (eds.), Mineral Deposits of the Northern Canadian Cordillera International Association on the Genesis of Ore Deposits. Field Trip 14, Guidebook, 137-175. 

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