Geothermal composition

Chry sotile is a hydrated magnesium siHcate and its stoicliiometric chemical composition may be given as AIg2Si20 (0H)4 [12001 -29-5]. However, the geothermal processes wliich ield the chry sotile fiber formations usually involve the co-deposition of v arious other minerals. Tliese mineral contaminants comprise brucite [1317-43-7] (AIg(OH)2), magnetite [1309-38-2] (Fe O, calcite [13397-26-7] (CaCO ), dolomite [16389-88-1] (AIg,CaC02),... 

Shikazono (1984) summarized analytical data of the epidote from geothermal areas to consider the relationship between the composition of epidote and that of the original fresh rocks and to inspect the other factors controlling the compositional variations in epidote. The discussion on the epidote composition by Shikazono (1984) is described below. 

Ragnarsdottir, K.V., Walther, J.V. and Amorsson, S. (1984) Description and interpretation of the composition of fluid and alteration mineralogy in the geothermal system, at Svartsengi, Iceland. Geochim. Cosmochim. Acta, 48, 1535-1553. 

Shikazono, N. (1984) Compositional variations in epidote from geothermal areas. Geochem. J., 18, 181-187. 

Shikazono, N. (1989) Oxygen and carbon isotopic compositions of carbonates from the Neogene epithermal vein-type deposits of Japan Implication for evolution of terrestrial geothermal activity. Chem. Geol, 76, 239-247. 

Chemical compositions of geothermal waters controlled by hydrothermal alteration mineral assemblage... 

Previous studies clearly indicated that the chemical compositions of geothermal waters are intimately related both to the hydrothermal alteration mineral assemblages of country rocks and to temperature. Shikazono (1976, 1978a) used a logarithmie cation-Cl concentration diagram to interpret the concentrations of alkali and alkaline earth elements and pH of geothermal waters based on thermochemical equilibrium between hydrothermal solution and alteration minerals. 

The chemical compositions of geothermal water plot in Figs. 23-2.9. All data plot near the equilibrium curves. This indicates that the geothermal waters considered... 

The above discussions are based on the assumption of constant temperature. However, temperature varies widely. The chemical compositions of geothermal waters intimately relate to temperature. For example, the correlation between Na/K ratio in geothermal waters and temperature has been interpreted as indicating that this ratio is controlled by albite and K-feldspar (White, 1965 Ellis, 1969, 1970). 

Summary of fluid compositions of Japanese geothermal systems (Chiba, 1991)... 

These results indicate that the chemical composition of geothermal water at 250°C is largely controlled by such minerals commonly occurring in geothermal area as albite, K-feldspar, sericite, calcite, wairakite and quartz. 

The chemical compositions of geothermal waters are characterized by low total dissolved solid (<300 mg/1), near neutral pH, and Na-Cl domination (Sakai et al., 1986 Ueda et al., 1991). 

Chemical composition of geothermal water associated with base-metal deposits (White, 1967)... 

Rubin KH, Wheller GE, Tanzer MO, MacDougall JD, Vame R, Finkel R (1989) decay series systematics of young lavas from Batur volcano, Sunda arc. J Volcanol Geotherm Res 38 215-226 Rudnick RL, Fountain DM (1995) Nature and composition of the continental cmst a lower cmstal perspective. Rev Geophys 33 267-309... 

Table 23.2. Chemical compositions of water and steam discharged from wet-steam geothermal wells in Iceland (Arnorsson et al., 1983)...

Arnorsson, S., E. Gunnlaugsson and H. Svavarsson, 1983, The chemistry of geothermal waters in Iceland, II. Mineral equilibria and independent variables controlling water compositions. Geochimica et Cosmochimica Acta 47, 547-566. 

Michard, G. and E. Roekens, 1983, Modelling of the chemical composition of alkaline hot waters. Geothermics 12, 161-169. 

Delmelle, P. Bernard, A. 2000. Downstream composition changes of acidic volcanic waters discharged into the Banyupahit stream, Ijen caldera, Indonesia. Journal of Volcanology and Geothermal Research, 97, 55-75. 

Figure 14. Plot of Li isotopic composition vs. concentration of thermal waters from the continents and the oceans (see text for references). Differences between the isotopic range of marine versus non-marine fluids emphasizes the variability in 5 Li of continental rocks compared to oceanic basalt. The dilution of the continental fluids goes along with their lower temperatures vent fluids are the only truly geothermal samples here, with temperatures in excess of 300°C.

Figure 6. Stable-Cl isotopic composition of fumarolic minerals, volcanic gas condensates and geothermal waters. Bracketed numbers correspond to references listed in Figure 3, Figure 4, and, [18] Wahrenberger et al. 1997 [19] Godon et al. 2004 and [20] Kaufmann 1989.

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