Quick Search:    advanced search

GSW Home   GeoRef Home   My GSW Alerts   Contact GSW   About GSW   Journals List   Help

This Article Figures Only Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Web of Science (18) Citing Articles via Google Scholar Google Scholar Articles by Bottomley, D. J. Articles by Clark, I. D. Search for Related Content GeoRef GeoRef Citation

Iodine-129 constraints on residence times of deep marine brines in the Canadian Shield

¹ Canadian Nuclear Safety Commission, 280 Slater Street, Ottawa, Ontario K1P 5S9, Canada
² Department of Earth Sciences, Ottawa-Carleton Geoscience Center, University of Ottawa, Ottawa, Ontario K1N 6N5, Canada
³ Atomic Energy of Canada Ltd., Chalk River Laboratories, Chalk River, Ontario K0J 1J0, Canada
⁴ Department of Earth Sciences, Ottawa-Carleton Geoscience Center, University of Ottawa, Ottawa, Ontario K1N 6N5, Canada

Canadian Shield brines are characterized by high concentrations of both stable iodine and ¹²⁹I, the former reflecting its concentrated but diagenetically modified seawater origin, and the latter its long subsurface residence time within its host shield rocks. Stable iodine concentrations in the Yellowknife brine are as high as 18 mg/L, requiring the contribution of iodine from an external marine reservoir. This reservoir likely comprised organic-rich marine sediments in the basin where the brine was produced. Diagenesis of these sediments released iodine to the brine during its infiltration into the subsurface. ¹²⁹I concentrations in the Yellowknife brine are as high as 3.4 x 10⁸ atom/L and are due to the fission of ²³⁸U in the rock matrix and subsequent diffusion of the radiogenic ¹²⁹I into the fracture fluids. This concentration is close to the predicted secular equilibrium concentration for a fluid in basaltic rock with a uranium concentration of 1 mg/kg after the residence time of 80 m.y. required for secular equilibrium has been attained. This time period is interpreted as the minimum residence time of the Yellowknife brine in the shield, but it may be much greater, possibly dating back to Middle Devonian time when most of the present-day shield was covered by seawater. Similarly high stable iodine and ¹²⁹I concentrations measured in the Sudbury brine support a generic, ancient marine hypothesis for the origin of shield brines. Stable iodine and ¹²⁹I concentrations in the shallower mine waters are the result of mixing between the brine and low-iodine modern meteoric recharge that is enriched in ¹²⁹I due to global fallout from nuclear fuel waste reprocessing activities.

Key Words: shield brines • marine • iodine • iodine-129 • residence time

This article has been cited by other articles:

				A. Katz and A. Starinsky Iodine-129 constraints on residence times of deep marine brines in the Canadian Shield: Comment and Reply: COMMENT Geology, January 1, 2003; 31(1): 93 - 94. [Full Text] [PDF]