Talc-quartz equilibria and the stability of magnesium chloride complexes in NaCl-MgCl sub 2 solutions at 300, 350, and 400 degree C, 500 bars

Journal Article · Fri Nov 30 23:00:00 EST 1990 · Geochimica et Cosmochimica Acta; (USA)

DOI:https://doi.org/10.1016/0016-7037(90)90285-S· OSTI ID:5982426

Saccocia, P J; Seyfried, Jr, W E ^[1]

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1. Univ. of Minnesota, Minneapolis (USA)

Solubility measurements for the assemblage talc + quartz were investigate the speciation of magnesium in NaCl-MgCl{sub 2} solutions at 300, 350, and 400{degree}C, 500 bars, for total chloride concentrations <1 m. At constant temperature and pressure, measured pH (25{degree}C) systematically decreases upon increasing the Mg/Cl ratio of the solution, consistent with buffering of {alpha}{sub Mg{sup 2+}}/{alpha}{sup 2}{sub H{sup +}} by talc-quartz equilibria. Measured quartz solubilities increase with increasing concentration of total dissolved salts (NaCl + MgCl{sub 2}), suggesting a salting-in behavior for aqueous SiO{sub 2} at these conditions. A thermodynamic analysis of talc-quartz-solution equilibria in the Na{sub 2}O-MgO-SiO{sub 2}-H{sub 2}O-HCl system indicates that ion-pairing between Mg{sup 2+} and Cl{sup {minus}} is necessary to account for our measured talc solubilities. The retrieval of thermodynamic data for Mg minerals from solubility measurements in chloride solutions must, therefore, take into account MgCl{sup +} explicitly. The authors apply results to the stability of caminite, an important constituents of hydrothermal vent deposits on the seafloor. At 300 to 350{degree}C, 500 bars, the stability of caminite is predicted to increase relative to estimates originally computed from solubility measurements in hydrothermal seawater experiments where no provision was made for ion-pairing between magnesium and chloride. The data presented in this study should, therefore, improve the accuracy of mass-transfer calculations designed to predict the fate of seawater-derived Mg in the oceanic crust.

• OSTI ID: 5982426
• Journal Information: Geochimica et Cosmochimica Acta; (USA), Journal Name: Geochimica et Cosmochimica Acta; (USA) Vol. 54:12; ISSN GCACA; ISSN 0016-7037
• Country of Publication: United States
• Language: English

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58 GEOSCIENCES
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ALKALINE EARTH METAL COMPOUNDS
AQUEOUS SOLUTIONS
CHALCOGENIDES
CHLORIDES
CHLORINE COMPLEXES
CHLORINE COMPOUNDS
COMPLEXES
DISPERSIONS
DISSOLUTION
EARTH CRUST
ELECTROLYTES
EQUILIBRIUM
FLUIDS
GEOTHERMAL FLUIDS
GEOTHERMAL SYSTEMS
HALIDES
HALOGEN COMPOUNDS
MAGNESIUM CHLORIDES
MAGNESIUM COMPOUNDS
MAGNESIUM SILICATES
MINERALS
MIXTURES
OCEANIC CRUST
OXIDE MINERALS
OXIDES
OXYGEN COMPOUNDS
PHYSICAL PROPERTIES
PRESSURE EFFECTS
QUARTZ
ROCK-FLUID INTERACTIONS
SILICATE MINERALS
SILICATES
SILICON COMPOUNDS
SILICON OXIDES
SOLUBILITY
SOLUTIONS
TALC
THERMODYNAMIC ACTIVITY
THERMODYNAMIC PROPERTIES