Geothermal fluids isotopic variations

Table 1. Summary of helium isotope variations in arc-related volcanics and geothermal fluids worldwide.

Table 2. Summary of neon isotope variations in arc-related lavas and geothermal fluids.

Chapter 2 covers the partial chemical equilibria as they pertain to water-rock interaction in geothermal areas. This includes oxygen isotope variations, formation of minerals by boiling, due to mixing of fluids and due to mixing hydrothermal solutions with seawater or groundwater. 

Fig. 5. Variation of the Sl80 and 8D values of the fluid delivered from well 131, located 500 m away from the re-injection site, during an injection test conducted in the peripheral area of Serrazzano in the Larderello field (open squares). The figure also shows graphically, and in arbitrary units, the flow rate Q of water re-injected into the well as a function of time, and the position of each sample collected. Theoretical isotopic pattern of the steam produced by re-injected water, assuming continuous steam separation at depth, is also reported. Since the actual evaporation temperature and the fraction of residual water are unknown, calculations were made for three different temperatures (140, 160, and 180 °C) and fractions (/w) of residual liquid water after boiling. Dashed line represents the hypothetical mixing between deep geothermal steam (W) and completely evaporated re-injected water (R).

Kusakabe M., Komoda Y., Takano B., and Abiko T. (2000) Sulfur isotopic effects in the disproportionation reaction of sulfur dioxide in hydrothermal fluids implications for the delta S-34 variations of dissolved bisulfate and elemental sulfur from active crater lakes. J. Volcanol. Geotherm. Res. 97(1-4), 287-307. 

Giggenbach W. F. (1995) Variations in the chemical and isotopic composition of fluids discharged from the Taupo volcanic zone. New Zealand. J. Volcan. Geotherm Res. 68, 89 116. 

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