Temperatures geothermal systems

Arnorsson, S., Bjornsson, S., Johannesson, H. Gunnlaugsson, E. 1992. The Production Characteristics of the Reykjavik District Heating Service low-Temperature Geothermal Systems. Arbok Verkfrcedingafelags Islands 1991/1992. Reykjavik, 344-366. (In Icelandic.)... 

Brown, K. Simmons, S. 2003. Precious metals in high temperature geothermal systems. Geother-mics, 32, 619-625. 

Figure 1.142 shows the dependence of solubility of Si02 minerals (quartz, cristobalite) on temperature. As described already, cristobalite occurs in peripheral and shallower part of hydrothermal alteration zone. Quartz is present in zones occurring in deeper and closer to the gold-quartz veins. Such zoning from quartz to cristobalite is also common in main active geothermal systems (Hayashi, 1973 Takeno et al., 2000). 

Temperature of each reservoir was estimated from the assemblage of hydrothermal alteration minerals and temperature of alteration zone in active geothermal system (e.g., Hayashi, 1973 Takeno et al., 2000). 

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 generalized sequence of alteration minerals from shallower to deeper portions and/or from lower to higher temperatures in active geothermal systems, which is constructed mainly based on the work by Henley and Ellis (1983), is given in Fig. 2.25. It is shown in Fig. 2.25 that the change in alteration and gangue minerals largely depends on temperature as well as on the other physicochemical parameters such as /s2, /o2> /c02> and pH. 

It has been pointed out by Giggenbach (1981) on the basis of thermochemical calculations that epidote occurs at higher temperatures of at least more than 240°C, and K-feldspar occurs at restricted temperatures, i.e. below ca. 250°C, in active geothermal systems. These theoretical results seem to be consistent with those observed in epithermal vein-type deposits in Japan. 

Fig. 2.26. Range of carbon dioxide fugacity (fco ) and temperature for the propylitic alteration (epidote zone) in the Seigoshi area and same active geothermal systems. Seigoshi = propylitic alteration of the Seigoshi district. The curves A-B and A -B are equilibria for epidote (Xpis = 0.30) - K-mica (oK-mica = 0-9) -K-feldspar (aK-feidspar = 0.95) - calcite assemblages at saturated water vapor pressure condition (Shikazono, 1985a).

Grant, M.K. (1982) On the lack of a unique relation between CO2 partial pressure and temperature in geothermal systems. Comment on Geothermal mineral equilibria by Giggenbach, W.F. Geochim. Cosmochim. Acta, 46, 2677-2680. 

One of the main applications of hydrogen and oxygen isotope thermometry in geochemistry is the estimation of the reservoir temperatures of active geothermal systems or the evaluation of the ruling T conditions during deposition or alter-... 

Truesdell AH (1974) Oxygen isotope activities and concentrations in aqueous salt solution at elevated temperatures consequences for isotope geochemistry. Earth Planet Sci Lett 23 387-396 Truesdell AH, Hulston JR (1980) Isotopic evidence on environments of geothermal systems. In Eritz P, Pontes J (eds) Handbook of environmental isotope geochemistry, vol 1. Elsevier, New York, Amsterdam, pp 179-226... 

Convective geothermal systems have been classified as volcanic (also termed high-temperature or high-enthalpy) and non-volcanic (low-temperature or low-enthalpy). By definition, high-71 systems have temperatures of >180 CC... 

Arnorsson, S. 1985. The use of mixing models and chemical geothermometers for estimating underground temperatures in geothermal systems. Journal of Volcanological and Geothermal Research, 23, 299-335. 

This paper presents two aspects of the research project, namely the geophysical and the minera-logical evolution of the geothermal system as a direct consequence of fluid injection. It is a geological, mineralogical, petrophysical, and geochemical study of water-rock interactions at temperatures of up to, and higher than, 200 °C... 

Flash Steam Generation The most common type of hydroelectric power generation technique. Flash steam describes a system where a high temperature geothermal steam source can be used to directly drive a turbine. Also see Binary Cycle Generation. ... 

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