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| 2. |
- Drake, Henrik, 1979, et al.
(författare)
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Detecting the near-surface redox front in crystalline bedrock using fracture mineral distribution, geochemistry and U-series disequilibrium
- 2009
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Ingår i: Applied Geochemistry. ; 24:5, s. 1023-1039
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Tidskriftsartikel (refereegranskat)abstract
- Oxidizing conditions normally prevail in surface waters and near-surface groundwaters, but there is usually a change to reducing conditions in groundwater at greater depth. Dissolved O2 originally present is consumed through biogenic and inorganic reactions along the flow paths. Fracture minerals participate in these reactions and the fracture mineralogy and geochemistry can be used to trace the redox front. An important task in the safety assessment of a potential repository for the disposal of nuclear waste in crystalline bedrock, at an approximate depth of 500 m in Sweden, is to demonstrate that reducing conditions can be maintained for a long period of time. Oxygen may damage the Cu canisters that host nuclear waste; additionally, in the event of a canister failure, oxidizing conditions may increase the mobility of some radionuclides. The present study of the near-surface redox front is based on mineralogical (redox-sensitive minerals), geochemical (redox-sensitive elements) and U-series disequilibrium investigations of mineral coatings along open fractures. The fractures have been sampled along drill cores from closely spaced, 100 m deep boreholes, which were drilled during the site investigation work in the Laxemar area, south-eastern Sweden, carried out by the Swedish Nuclear Fuel and Waste Management Co. (SKB). The distribution of the redox-sensitive minerals pyrite and goethite in open fractures shows that the redox front (switch from mainly goethite to mainly pyrite in the fractures) generally occurs at about 15-20 m depth. Calcite leaching by recharging water is indicated in the upper 20-30 m and positive Ce-anomalies suggest oxidation of Ce down to 20 m depth. The U-series radionuclides show disequilibrium in most of the samples, indicating mobility of U during the last 1 Ma. In the upper 20 m, U is mainly removed (due to oxidation) or has experienced complex removal and/or deposition. At depths of 35-55 m, both deposition and removal of U are indicated. Below 55 m, recent deposition of U is generally indicated which suggests removal of U near surface (oxidation) and deposition of U below the redox front. Scattered goethite occurrences below the general redox front (down to ca 80 m) and signs of U removal at 35-55 m mostly correlate with sections of high transmissivity (and/or high fracture frequencies). This shows that highly transmissive fractures are generally required to allow oxygenated groundwaters at depth greater than ca 30 m. Removal of U (oxidation) below 55 m within the last 300 ka is not observed. Although penetration of glacial waters to great depths has been confirmed in the study area, their potential O2 load seems to have been reduced near the surface.
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- Drake, Henrik, 1979, et al.
(författare)
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Detection of the near surface redox front in crystalline bedrock.
- 2008
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Ingår i: Abstract Volume of the 28th Nordic Geological Winter Meeting, Aalborg, Denmark, January 7-10, 2008, Department of Civil Engineering, Aalborg University, Aalborg, Denmark.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)
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| 5. |
- Drake, Henrik, 1979, et al.
(författare)
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Distinguished multiple events of fracture mineralisation related to far-field orogenic effects in Paleoproterozoic crystalline rocks, Simpevarp area, SE Sweden
- 2009
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Ingår i: Lithos. - : Elsevier BV. - 0024-4937. ; 110:1-4, s. 37-49
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Tidskriftsartikel (refereegranskat)abstract
- Detailed investigations of fracture minerals have been carried out in the Simpevarp area, SE Sweden. in order to reveal the low-temperature evolution of the site and to discern different events of deformation, especially in the brittle regime. The study is part of the site characterisation programme for a potential deep-seated repository for spent nuclear fuel. The bedrock in the area is composed of generally un-metamorphosed 1.8 Ga crystalline rocks. Detailed SEM investigations of cross-cutting fracture mineralisations have revealed several generations of fillings formed at gradually lower temperatures during repeated events of fracturing and reactivation from the Paleoproterozoic until the Quaternary. Ar-40/Ar-39 geochronology, and fracture orientation analyses have been used to relate each fracture filling generation to geological events, such as far-field effects from orogenies, as well as more local effects related to intrusions. Fracturing and formation of different fracture mineral parageneses during at least four different orogenies have been indicated: the waning stages of the Svecokarelian orogeny (> 1.75 Ga), the Danopolonian orogeny (similar to 1.47-1.44 Ga), the Sveconorwegian orogeny (similar to 1.1-0.9 Ga) and the Caledonian orogeny (similar to 0.5-0.4 Ga). The fracture minerals and greisen related to the Danopolonian orogeny mainly formed in relation to the intrusion of two indicatively Danopolonian-related granites nearby. Furthermore, periods of extension are indicated in the area by the presence of late-Sveconorwegian dolerites. Fractures filled with lower Cambrian sandstone are plausibly formed in relation to far-field extensional effects of the opening of the Iapetus Ocean. Fracture minerals of Paleozoic age or younger show influence of loading and unloading cycles. The youngest fracture minerals identified indicate precipitation from waters of similar composition as the present groundwater. (C) 2008 Elsevier B.V. All rights reserved.
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| 6. |
- Drake, Henrik, 1979, et al.
(författare)
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Fracture Mineralogy
- 2006
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Ingår i: Preliminary site description. Laxemar subarea - version 1.2, SKB-R-06-10. - Stockholm : SKB. ; , s. 163-167
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Bokkapitel (övrigt vetenskapligt/konstnärligt)
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