Mineralogical and textural variation of silica minerals in hydrothermal flow-through experiments: Implications for quartz vein formation

Okamoto, Atsushi; Saishu, Hanae; Hirano, Nobuo; Tsuchiya, Noriyoshi

doi:10.1016/j.gca.2010.03.031

Cited by 55 publications

(46 citation statements)

References 40 publications

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“…In the case of low salinity, the activities of water and dissolved silica equal unity, and we can approximate

a_{H_{4} {SiO}_{4}}

C_{H_{4} {SiO}_{4}}

, the molar concentration of orthosilicic acid, and K sp by

C_{H_{4} {SiO}_{4}}^{eq}

, the equilibrium concentration determined for our experimental conditions (98 ppm, Okamoto et al . ). The driving force is the deviation of the saturation index S = Q / K sp from unity.…”

Section: Phase‐field Modelmentioning

confidence: 97%

“…From the solution made by dissolution of granite sand, silica precipitation occurred mainly as epitaxial overgrowth of existing grains (Okamoto et al . ; Okamoto & Sekine ) and was attributed to impurity concentrations of Na, K, and Al in the range of several ppm in the solution.…”

Section: Hydrothermal Experiments For Quartz Vein Formationmentioning

confidence: 99%

“…Dissolution–precipitation series in the temperature and pressure range of our experimental setup were carried out in (Okamoto et al . ), from which the rate coefficient was determined as log( k – ) = −0.0886–2638/ T s −1 ( T in K ) and the surface‐to‐mass ratio A s / M = 33.6 kg m −2 for T = 390°C.…”

Section: Phase‐field Modelmentioning

confidence: 99%

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Phase‐field modeling of epitaxial growth of polycrystalline quartz veins in hydrothermal experiments

2015

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Mineral precipitation in an open fracture plays a crucial role in the evolution of fracture permeability in rocks, and the microstructural development and precipitation rates are closely linked to fluid composition, the kind of host rock as well as temperature and pressure. In this study, we develop a continuum thermodynamic model to understand polycrystalline growth of quartz aggregates from the rock surface. The adapted multiphase‐field model takes into consideration both the absolute growth rate as a function of the driving force of the reaction (free energy differences between solid and liquid phases), and the equilibrium crystal shape (Wulff shape). In addition, we realize the anisotropic shape of the quartz crystal by introducing relative growth rates of the facets. The missing parameters of the model, including surface energy and relative growth rates, are determined by detailed analysis of the crystal shapes and crystallographic orientation of polycrystalline quartz aggregates in veins synthesized in previous hydrothermal experiments. The growth simulations were carried out for a single crystal and for grain aggregates from a rock surface. The single crystal simulation reveals the importance of crystal facetting on the growth rate; for example, growth velocity in the c‐axis direction drops by a factor of ~9 when the faceting is complete. The textures produced by the polycrystal simulations are similar to those observed in the hydrothermal experiments, including the number of surviving grains and crystallographic preferred orientations as a function of the distance from the rock wall. Our model and the methods to define its parameters provide a basis for further investigation of fracture sealing under varying conditions.

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“…In the case of low salinity, the activities of water and dissolved silica equal unity, and we can approximate

a_{H_{4} {SiO}_{4}}

C_{H_{4} {SiO}_{4}}

, the molar concentration of orthosilicic acid, and K sp by

C_{H_{4} {SiO}_{4}}^{eq}

, the equilibrium concentration determined for our experimental conditions (98 ppm, Okamoto et al . ). The driving force is the deviation of the saturation index S = Q / K sp from unity.…”

Section: Phase‐field Modelmentioning

confidence: 97%

Section: Hydrothermal Experiments For Quartz Vein Formationmentioning

confidence: 99%

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Phase‐field modeling of epitaxial growth of polycrystalline quartz veins in hydrothermal experiments

2015

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“…There is an extensive literature describing and analyzing natural vein microstructures ( Hilgers and Urai [], van Noten et al [], and many more). Experimental simulation of crystal growth in veins [ Hilgers and Urai , ; Hilgers and Tenthorey , ; Hilgers and Urai , ; Nollet et al , ; Okamoto et al , ; Okamoto and Sekine , ; Hilgers and Urai , ; Hilgers et al , ] has provided a basis for comparison with natural veins in addition to the numerical simulations.…”

Section: Introductionmentioning

confidence: 99%

Microstructural evolution in bitaxial crack‐seal veins: A phase‐field study

2015

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Bitaxial crack sealing by epitaxial crystal growth is the most common vein‐forming process in Earth's crust, but the details of the microstructural processes in these are not well understood. Here we model the evolution of bitaxial crack‐seal quartz veins in two and three dimensions, using the phase‐field method. Our numerical simulations show the influence of different parameters, such as the obliquity of crack opening and crack location, grain size, and orientations on the evolving vein microstructure. We examine the underlying growth competition observed during epitaxial growth of quartz. Results show many similarities with natural microstructures such as stretched crystals and compare well with the previous numerical findings. As the ratio of crack aperture and matrix grain size for the present studies is chosen to be sufficiently large for growth competition to occur before complete sealing, it leads to the formation of crystal fragments along the crack‐opening trajectory. We explain how such fragment trails act as potential indicators of the opening of crack‐seal veins, if they are confirmed to be common in natural microstructures. Finally, we highlight the importance of accounting for the third dimension in the numerical simulations by analyzing the evolution of fluid connectivity in 2‐D and 3‐D during the sealing process.

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“…As described above, the high-temperature deposition of precursor silica hydrate is a product of SiO 2 -supersaturation from a one-phase magmatic vapor, during adiabatic expansion through fracture arrays in the crust (Fournier, 1985;Okamoto et al, 2010;Henley and Berger, 2011). The rapid decompression triggered by vein dilation results in very high SiO 2 -supersaturation and consequent exsolution of a SiO 2 -rich fluid, caused by simultaneous decrease in quartz solubility (e.g.…”

Section: Why Does Silica Hydrate Form?mentioning

confidence: 99%

Silica hydrate preserved with δ18O-rich quartz in high-temperature hydrothermal quartz in the high sulfidation copper-gold deposit at El Indio, Chile

et al. 2015

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Mineralogical and textural variation of silica minerals in hydrothermal flow-through experiments: Implications for quartz vein formation

Cited by 55 publications

References 40 publications

Phase‐field modeling of epitaxial growth of polycrystalline quartz veins in hydrothermal experiments

Phase‐field modeling of epitaxial growth of polycrystalline quartz veins in hydrothermal experiments

Microstructural evolution in bitaxial crack‐seal veins: A phase‐field study

Silica hydrate preserved with δ18O-rich quartz in high-temperature hydrothermal quartz in the high sulfidation copper-gold deposit at El Indio, Chile

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