Abstract
| Originalsprog | Engelsk |
|---|---|
| Tidsskrift | Chemical Geology |
| Vol/bind | 244 |
| Sider (fra-til) | 330–343 |
| ISSN | 0009-2541 |
| Status | Udgivet - 2007 |
Emneord
- Det Natur- og Biovidenskabelige Fakultet
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I: Chemical Geology, Bind 244, 2007, s. 330–343.
Publikation: Bidrag til tidsskrift › Tidsskriftartikel › Forskning › peer review
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TY - JOUR
T1 - Fe-oxide fracture fillings as a palæo-redox indicator
T2 - structure, crystal form and Fe isotope composition
AU - Dideriksen, Knud
AU - Christiansen, Bo C.
AU - Baker, J.A.
AU - Frandsen, C.
AU - Balic Zunic, Tonci
AU - Tullborg, E.
AU - Mørup, S.
AU - Stipp, Susan Louise Svane
PY - 2007
Y1 - 2007
N2 - Penetration of oxygenated waters to the deeper sub-surface may occur in association with deglaciation events and significantlychange the geochemical processes acting at depth. Such a scenario may compromise long-term storage of radioactive waste in underground repositories where copper canisters would corrode in the presence of oxygen. In this study, Fe-oxides from fractures in granite drill-cores and from drilling debris were investigated and a method developed to trace the low-temperature, oxidising conditions whichmay have been caused by prior deglaciations.X-ray diffraction andMössbauer spectroscopy showed that all the examined fracture fillings contained Fe-oxides. Based on their structure and form, three genetic types of Fe-oxides were identified: (I) coarse-grained (~ 100 nm) hydrothermal hematite; (II) very fine-grained (~ 10 nm) amorphous Fe-oxides that precipitated during drilling; (III) Intermediate grain-size crystalline Fe-oxides, that are interpreted to have formed naturally at low-temperatures (~ 10 °C). Fe isotope composition of the Fe-oxides was determined by multiple-collector inductively coupled plasma mass spectrometry using a 58Fe-54Fe double-spike. d56Fe of the Fe-oxides ranges from -0.8 to +0.8‰ (relative to the IRMM-14 standard). Hydrothermal samples have intermediate d56Fe (-0.3 to 0.0‰), whereas natural low-temperature samples may be isotopically lighter (-0.8 to 0.0‰), and samples precipitated from drilling activity are isotopically heavier (-0.2 to 0.8‰). Within the three genetic suites, d56Fe correlates with the relative proportion of Fe(III). For the hydrothermal samples, Fe isotope composition likely reflects input of partially dissolved chlorite. The Fe isotope composition and Fe redox state of the low-temperature and drillinduced samples is consistent with a conceptual model where Fe isotope fractionation occurs during dissolution and oxidation. In our study, the deepest sample showing evidence of natural low-temperature oxidation, putatively as a result of penetration of oxidising surface waters during deglaciation, is from a depth of ~ 100 m.
AB - Penetration of oxygenated waters to the deeper sub-surface may occur in association with deglaciation events and significantlychange the geochemical processes acting at depth. Such a scenario may compromise long-term storage of radioactive waste in underground repositories where copper canisters would corrode in the presence of oxygen. In this study, Fe-oxides from fractures in granite drill-cores and from drilling debris were investigated and a method developed to trace the low-temperature, oxidising conditions whichmay have been caused by prior deglaciations.X-ray diffraction andMössbauer spectroscopy showed that all the examined fracture fillings contained Fe-oxides. Based on their structure and form, three genetic types of Fe-oxides were identified: (I) coarse-grained (~ 100 nm) hydrothermal hematite; (II) very fine-grained (~ 10 nm) amorphous Fe-oxides that precipitated during drilling; (III) Intermediate grain-size crystalline Fe-oxides, that are interpreted to have formed naturally at low-temperatures (~ 10 °C). Fe isotope composition of the Fe-oxides was determined by multiple-collector inductively coupled plasma mass spectrometry using a 58Fe-54Fe double-spike. d56Fe of the Fe-oxides ranges from -0.8 to +0.8‰ (relative to the IRMM-14 standard). Hydrothermal samples have intermediate d56Fe (-0.3 to 0.0‰), whereas natural low-temperature samples may be isotopically lighter (-0.8 to 0.0‰), and samples precipitated from drilling activity are isotopically heavier (-0.2 to 0.8‰). Within the three genetic suites, d56Fe correlates with the relative proportion of Fe(III). For the hydrothermal samples, Fe isotope composition likely reflects input of partially dissolved chlorite. The Fe isotope composition and Fe redox state of the low-temperature and drillinduced samples is consistent with a conceptual model where Fe isotope fractionation occurs during dissolution and oxidation. In our study, the deepest sample showing evidence of natural low-temperature oxidation, putatively as a result of penetration of oxidising surface waters during deglaciation, is from a depth of ~ 100 m.
KW - Faculty of Science
KW - Radioactive waste repository
KW - Fe isotope
KW - Granite
KW - Fractures
KW - Fe-oxide
KW - Oxidation
M3 - Journal article
SN - 0009-2541
VL - 244
SP - 330
EP - 343
JO - Chemical Geology
JF - Chemical Geology
ER -