Article
Pressure sensitive “silica geothermometer” determined from quartz solubility experiments at 250 °C

https://doi.org/10.1016/0016-7037(83)90159-XGet rights and content

Abstract

Experimentally reversed quartz solubilities at 250°C and at 250, 500 and 1000 bars yield values of the logarithm of the molality of aqueous silica of −2.126, −2.087 and −2.038, respectively. Extrapolation of quartz solubility to the saturation pressure of water at 250°C results in a log molality of aqueous silica of-2.168. These solubility determinations and analyses of fluid pressures in geothermal systems indicate that pressure is significant when calculating quartz equilibrium temperatures from silica concentrations in waters of deep thermal reservoirs.

The results of this investigation, combined with other reported quartz solubility measurements, yielded a pressure-sensitive “silica geothermometer” for fluids that have undergone adiabatic steam loss of t°C = 874 − 0.156P(log mSi(OH)4 · 2H2O)2 + 411 log mSi(OH4 · 2H2O + 51 (log mSi(OH)4 · 2H2O)2 where P is the fluid pressure in bars and mSi(OH)4 · 2H2O represents the molality of aqueous silica measured in surface samples. The geothermometer is applicable to solutions in equilibrium with quartz from 180°C to 340°C and fluid pressures from H2O saturation to 500 bars.

References (49)

  • E Mazor et al.

    Geochemical tracing in producing geothermal fields: A case study at Cerro Prieto

    Geothermics

    (1979)
  • G.W Morey et al.

    The solubility of quartz in water in the temperature interval from 25° to 300°C

    Geochim. Cosmochim. Acta

    (1962)
  • J.D Rimstidt et al.

    The kinetics of silica-water reactions

    Geochim. Cosmochim. Acta

    (1980)
  • T.M Seward

    Determination of the first ionization constant of silicic acid from quartz solubility in borate buffer solutions to 350°C

    Geochim. Cosmochim. Acta

    (1974)
  • A.H Truesdell et al.

    Downhole measurements and fluid chemistry of a Castle Rock steam well, The Geysers, Lake County, California

    Geothermics

    (1981)
  • J.D Willey

    The effect of pressure on the solubility of amorphous silica in seawater at 0°C

    Mar. Chem.

    (1974)
  • J.D Willey

    Note: Partial molal volume calculations for the dissolutoin of aged amorphous silica in salt water and seawater at 0–2 °C

    Geochim. Cosmochim. Acta

    (1982)
  • G.M Anderson et al.

    The solubility of quartz in super-critical water

    Amer. J. Sci.

    (1965)
  • S Arnórsson et al.

    The chemistry of geothermal waters in Iceland. III Chemical geothermometry in geothermal investigations

    Geochim. Cosmochim. Acta

    (1983)
  • A.J Baltasar

    Interpretations of the water and gas chemistry from three geothermal areas in the Philippines—Manito in Albay, Biliran Island and Tongonan in Leyte

  • G Bödvarsson

    Exploration and exploitation of natural heat in Iceland

    Bull. Volcanol., Ser. 2

    (1980)
  • G Bödvarsson et al.

    Exploration of subsurface temperatures in Iceland

  • G.S Bödvarsson et al.

    Modeling studies of the natural state of the Krafla geothermal field, Iceland

  • C.J Bruton et al.

    Calculation of the chemical and thermodynamic consequences of differences between fluid and geostatic pressure in hydrothermal systems

    Amer. J. Sci.

    (1983)
  • Cited by (36)

    • 7.04 - Geochemical Aspects of Geothermal Utilization

      2012, Comprehensive Renewable Energy
    • Silicate adsorption by goethite at elevated temperatures

      2009, Chemical Geology
      Citation Excerpt :

      Hydrothermal waters, on the other hand, are not only chloride but often also silicate enriched, with concentrations commonly in the range 100–1000 mg L− 1 depending on the source temperature. In fact, estimation of underground source temperatures is commonly based on the silica content of water from hot springs (White et al., 1956; Fournier and Potter, 1982; Ragnarsdóttir and Walther, 1983; Gunnarsson and Arnorsson, 2000). By exposing this brine to the surface, silica may become supersaturated upon flushing (concentration effect) and pond cooling (prograde solubility effect).

    View all citing articles on Scopus
    View full text