Helium in solubility equilibrium with quartz and porefluids in rocks - a new approach in hydrology

Lehmann, Bernhard; Waber, Niklaus; Tolstikhin, Igor; Kamensky, Igor; Gannibal, Maria; Kalashnikov, Evgenii; Pevzner, Boris (2003). Helium in solubility equilibrium with quartz and porefluids in rocks - a new approach in hydrology. Geophysical Research Letters, 30(3), pp. 1128-1131. American Geophysical Union 10.1029/2002GL016074

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Quartz crystals in sandstones at depths of 1200 m–1400 m below the surface appear to reach a solubility equilibrium with the 4He-concentration in the surrounding pore- or groundwater after some time. A rather high 4Heconcentration of 4.5x10E-3 cc STP 4He/cm3 of water measured in a groundwater sample would for instance maintain a He pressure of 0.47 atm in a related volume. This value is equal within analytical error to the pressure deduced from the measured helium content of the quartz and its internal helium-accessible volume. To determine this volume, quartz crystals of 0.1 to 1 mm were separated from sandstones and exposed to a helium gas pressure of 32 atm at a temperature of 290°C for up to 2 months. By crushing, melting or isothermal heating the helium was then extracted from the helium saturated samples. Avolume on the order of 0.1% of the crystal volume is only accessible to helium atoms but not to argon atoms or water molecules. By monitoring the diffusive loss of He from the crystals at 350°C an effective diffusion constant on the order of 10E-9 cm2/s is estimated. Extrapolation to the temperature of 70°C in the sediments at a depth of 1400 m gives a typical time of about 100 000 years to reach equilibrium between helium in porewaters and the internal He-accessible volume of quartz crystals. In a geologic situation with stagnant pore- or groundwaters in sediments it therefore appears to be possible with this new method to deduce a 4He depth profile for porewaters in impermeable rocks based on their mineral record.

Item Type:

Journal Article (Original Article)

Division/Institute:

08 Faculty of Science > Institute of Geological Sciences

UniBE Contributor:

Lehmann, Bernhard and Waber, Niklaus

Subjects:

500 Science > 550 Earth sciences & geology
500 Science > 530 Physics

ISSN:

0094-8276

Publisher:

American Geophysical Union

Language:

English

Submitter:

Niklaus Waber

Date Deposited:

11 Jul 2016 09:16

Last Modified:

11 Jul 2016 09:16

Publisher DOI:

10.1029/2002GL016074

URI:

https://boris.unibe.ch/id/eprint/84398

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