Hydrothermal calcite

Figure 5. Plot of and 5 C values for the Tierra Blanca Limestone and hydrothermal calcites. Symbols represent distance from the skam/marble contact. Curves A-B and A-C show depletion resulting from Batch and Rayleigh decarbonation, respectively. Curves A-D, A-E represent progressive depletion in limestone resulting from isotope exchange with meteoric water in eqnilibrinm with the Hanover-Fierro pluton at 315°C and water-rock ratios of 0.01-0.001. Cnrve A-E (dotted line) is calculated at 400°C using the fractionation factor of Chiba et al. (1989), assuming X(C02) = 0.02. Curve A-F (dashed line) defines progressive depletion resulting from water/rock interaction at 400°C using the fractionation factor of O Neil et al. (1969) (from Turner and Bowman 1993).

Faure G, Kallstrom ML, Mensing TM (1984) Classification and age of terrestrial boulders in the Elephant and Reckling moraines. Antarctic J US 19(5) 28-29 Faure G, Taylor KS, Jones LM (1986) Hydrothermal calcite in the Elephant Moraine. Antarctic J US 21(5) 21 Faure G, Strobel ML, Hagen EH, Buchanan D (1987) Glacial geology of the Reckling Moraine on the East Antarctic ice sheet. Antarctic J US 22(5) 61-63... 

Magnesite, dolomite and calcite occur in hydrothermally altered rocks near Kuroko orebody. The following equations are used to constrain /coa values of hydrothermal solutions (Shikazono et al., 1998) (Fig. 1.39). 

Supergroup rocks in the Hishikari district suffered hydrothermal alteration. Chlorite, quartz and sericite occur abundantly near the veins. The other constituents are pyrite, albite, calcite and organic matter. 

Imai, A. and Uto, T. (2001) Association of electrum and calcite and its significance to the genesis of the Hishikari low-sulfidation epithermal gold deposits, southern Kyushu, Japan. Proc. International Symposium on Gold and Hydrothermal Systems, pp. 83-88. 

Shikazono, N. (1988a) Oxygen and carbon isotopic ratios of calcite and evolution of hydrothermal activities in the Seigoshi gold-silver mining district, Japan. Mining Geology Special Issue, 12, 1-16. 

The Okuaizu geothermal system is characterized by high temperatures (maximum 340°C), high salinity (about 2 wt% total dissolved solids (TDS)) and large amounts of non-condensable gases (1 wt% CO2 and 200 ppm H2S). The pH of the hydrothermal solution measured at 25°C is 6.44 (Table 2.6). However, the pH of the original fluid in the reservoir is computed to be 4.05. This pH as well as alkali and alkali earth element concentrations are plotted near the equilibrium curve of albite, K-mica, anhydrite and calcite (Fig. 2.19) (Seki, 1991). 

The H2S concentration of hydrothermal solution is plotted in Fig. 2.33. Based on these data, we can estimate the temperature of hydrothermal solution buffered by alteration mineral assemblages such as anhydrite-pyrite-calcite-magnetite and pyrite-pyrrhotite-magnetite for Okinawa fluids. 

For example, assuming anhydrite-magnetite-calcite-pyrite-pyrrhotite buffers redox in sub-seafloor reaction zones and a pressure of 500 bars, dissolved H2Saq concentrations of 21 °N EPR fluid indicate a temperature of 370-385°C. However, the estimated temperatures are higher than those of the measurement. This difference could be explained by adiabatic ascension and probably conductive heat loss during ascension of hydrothermal solution from deeper parts where chemical compositions of hydrothermal solutions are buffered by these assemblages. 

The vesicle volume of the Kuroko basalt is large (average 20%) and vesicles are filled with hydrothermal minerals (epidote, calcite, chlorite, pyrite, quartz) which formed... 

Hydrothermal alteration minerals from midoceanic basalt are analcite, stilbite, heulandite, natrolite-mesolite-scolecite series, chlorite and smectite for zeolite facies, prehnite, chlorite, calcite and epidote for prehnite-pumpellyite facies, albite, actinolite, chlorite, epidote, quartz, sphene, hornblende, tremolite, talc, magnetite, and nontronite for green schist facies, hornblende, plagioclase, actinolite, leucoxene, quartz, chlorite, apatite, biotite, epidote, magnetite and sphene for amphibolite facies (Humphris and Thompson, 1978). 

It is likely that the minerals controlling /CO2 of hydrothermal solution at back-arc basins are dolomite, siderite, calcite, hematite, magnetite, graphite, K-mica and kaolinite. Most of these minerals are not found in altered ridge basalt. 

Berndt et al. (1989) have indicated that aQ +/a + and aNa+/r H+ of midoceanic ridge hydrothermal fluids is controlled by clinozoisite, Ca-feldspar, and Na-feldspar. In addition to these assemblages, calcite is in equilibrium with fluids. Therefore, we can derive the /CO2 temperature relationship from the following equilibrium relations. 

If the above argument is correct and the /CO2 of hydrothermal solutions from back-arc basins is in equilibrium with alteration mineral assemblage including dolomite and calcite, t[ g2+ lmQ + of fluids can be estimated to be 0.03-0.055 from dolomite-calcite-... 

Shikazono (1978) theoretically derived that the concentrations of alkali and alkali earth elements in chloride-rich hydrothermal solution are nearly in equilibrium with hydrothermal alteration minerals such as albite, K-feldspar, K-mica, quartz, calcite, wairakite, and Mg-chlorite. If we use 500 mmol/kg H2O as the average Cl concentration of hydrothermal solution from the back-arc basin, which is in equilibrium with... 

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... 

Trace elements are useful tracers of geochemical processes mostly because they are dilute their behavior depends primarily on the trace element-matrix interaction (e.g., Rb-host feldspar, Sr-calcite) and very little on the trace-trace interaction (e.g., Rb-Rb, Sr-Sr). Consequently, the distribution of trace elements among natural phases largely obeys the linear Henry s law. The modeling of trace elements in various geological environments (magmas, hydrothermal fluids, seawater,...) relies on three different aspects... 

Hydrothermal alteration is laterally extensive and manifest as Fe-carbonate, Fe-oxide (supergene ), sericite, calcite and minor chlorite. Clay alteration is so pervasive that much of the core disintegrates via clay hydration processes after very short exposure to the atmospheric conditions. Although limited XRD work has not shown the presence of swelling clays sericite which is abundant does have the capacity to swell (Eberl et al. 1987). Additional intense clay alteration is controlled by faulting and is spatially related to sulfide emplacement. 

Advantages of the carbonate-exchange technique are (1) experiments up to 1,400°C, (2) no problems associated with mineral solubility and (3) ease of mineral separation (reaction of carbonate with acid). Mineral fractionations derived from hydrothermal and carbonate exchange techniques are generally in good agreement except for fractionations involving quartz and calcite. A possible explanation is a salt effect in the quartz-water system, but no salt effect has been observed in the calcite-water system (Hu and Clayton 2003). 

Figure 3.12 presents 5 C and 5 0-values of hydrothermal carbonates from the Pb-Zn deposits of Bad Grund and Lautenthal, Germany. The positive correlation between and 0/ 0-ratios can be explained either by calcite precipitation... 

Figure A4-1 Comparison of oxygen diffusivity in various minerals under hydrothermal conditions- Mineral names (from high to low diffusivity) An, anorthite Ah, albite Bt, biotite Ms, muscovite Phi, phlogopite Cc, calcite Qz, quartz Ap, apatite Mt, magnetite Hb, hornblende Tr, tremolitel Tt, titanite Di, diopside Rut, rutile Aim, almandine.

Chai B.H.T. (1974) Mass transfer of calcite during hydrothermal recrystallization. In Geochemical Transport and Kinetics, Vol. 634 (ed. A.W. Hofmann, B.J. Giletti, H.S. Yoder, and R.A. Yund), pp. 205-218. Garnegie Institution of Washington Publ. 

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