| 1. |
- Drake, Henrik, 1979, et al.
(författare)
-
Fracture zone-scale variation of trace elements and stable isotopes in calcite in a crystalline rock setting
- 2014
-
Ingår i: Applied Geochemistry. - : Elsevier BV. - 0883-2927 .- 1872-9134. ; 40, s. 11-24
-
Tidskriftsartikel (refereegranskat)abstract
- With an aim to increase the understanding about the isotopic and chemical heterogeneity of calcites in water-conducting fracture zones with different crystalline wall rock compositions at different depths, we present trace element chemistry, isotopic composition (delta O-18, delta C-13, Sr-87/Sr-86) and biomarkers of euhedral low-temperature fracture-coating calcite. Paleohydrogeological fluctuations and wall rock influence on the hydrochemistry in the deep groundwater are explored. Samples are from several fracture zone sub-fractures (at -360 to -740 m), retrieved during an extensive core drilling campaign in Sweden. Calcite generally showed fracture zone specific values of delta C-13,delta O-18 and Sr-87/Sr-86, which indicates precipitation from relatively homogeneous fluid (similar to the modern groundwater at the site) at the same event in each fracture zone. delta O-18 and delta C-13 in the different fracture zones were consistent with precipitation from waters of different salinity and decreasing organic input with depth, respectively. The latter is also supported by biomarkers showing clear indications of SRB-related organic compounds (e. g. iso- and anteiso-C-17:0-branched fatty acids), except in the deepest zone. In contrast to the isotopes, variation in trace elements within the fracture zones was generally up to several orders of magnitude. Manganese and REE, as oppose to the other metals, were higher in the shallow fracture zones (112-1130 and 44-97 ppm, respectively) than in the deeper (28-272 and 5-11 ppm, respectively), in agreement with the groundwater composition. Although the rock types varied between and within the different fracture zones, this had insignificant influence on the trace element chemistry of the calcites. Co-variation was generally relatively large for many trace elements, with isometric logratio correlation generally better than 0.75, which indicates that their variation in the calcites is due to variation of Ca in the fracture water, but other local factors, especially uptake in co-precipitating minerals (clay minerals, barite, pyrite and zeolites), but also microbial activity and metal speciation may have influenced the metal incorporation into calcite. These detailed studies of fracture calcite are of importance for the understanding of variation in fluid chemistry and trace metal uptake in fracture zones, adding together with hydrochemical studies detailed information optimal for site characterisation. (c) 2013 Elsevier Ltd. All rights reserved.
|
|
| 2. |
- Drake, Henrik, 1979-, et al.
(författare)
-
Trace metal distribution and isotope variations in low-temperature calcite and groundwaters in granitoid fractures down to 1 km depth
- 2012
-
Ingår i: Geochimica et Cosmochimica Acta. - : Elsevier. - 0016-7037 .- 1872-9533. ; 84, s. 217-238
-
Tidskriftsartikel (refereegranskat)abstract
- Studies of low-temperature fracture calcite in Proterozoic or Archaean crystalline rocks are very limited, mainly becausethis calcite usually is, first, not very abundant and second, very fine-grained or forms rims on older (and much more abundant)hydrothermal calcite and is thus difficult to distinguish. Knowledge of chemical characteristics and the correlation withgroundwater chemistry is thus scarce for low-temperature calcite in these settings, and consequently, knowledge of the recentpalaeohydrogeological history is limited. Boreholes drilled with triple-tube technique in the upper 1 km of the Palaeoproterozoiccrystalline crust at Laxemar, SE Sweden, have enabled preservation of fragile and potentially recently formed fractureminerals. Earlier investigations of these boreholes have resulted in an extensive set of groundwater chemistry data from variousdepths, and in detailed knowledge of the fracture mineral assemblages (ranging from 1.8 Ga to present). This has made itpossible to identify and sample low-temperature, potentially recently formed, calcite from water-flowing fractures for whichrepresentative groundwater chemical data exists. This, in turn, provides an opportunity to detailed comparisons of fracturecalcite (age span in the order of million years, with possibility of post-glacial contributes) and groundwater (age in the order ofdecades to more than a million year depending on depth) in terms of both isotopic and geochemical properties, giving input tothe understanding of groundwater history, partition coefficients derived in laboratory experiment, and reliability of calcitegeochemistry in terms of representing the actual source fluid composition. In this study, the focus is on trace elements (Fe,Mg, Mn and Sr), stable isotopes and Sr isotopes and, for the groundwater data set, also aquatic speciation with Visual MINTEQ.An optimised step-by-step sample specific analytical procedure was used for the collection of calcite coatings. The methodsused depended on the crystal homogeneity (one or several calcite generations), discerned by detailed SEM-investigations(back-scatter and cathodo-luminescence). 87Sr/86Sr ratios as well as d18O signatures in calcite are in the range expected for theprecipitates from present-day groundwater, or older groundwater with similar composition (except in sections with a considerableportion of glacial water, where calcite definitely is older than the latest glaciation). Stable carbon isotopes in calcitegenerally show values typically associated with HCO3 originating from soil organic matter but at intermediate depth frequentlywith HCO3 originating from in situ microbial anaerobic oxidation of methane (highly depleted d13C). For one ofthe studied metals – manganese – there was a strong correlation between the sampled calcite coatings and hypothetical calcitepredicted by applying laboratory-based partition coefficients (literature data) on groundwater chemistry for sections correspondingto those where the calcites were sampled. This points to temporal and spatial stability in groundwater Mn/Ca ratiosover millions of years, or even more, and show that it is possible to assess, based on laboratory-derived data on Mn partitioning,past groundwater Mn-composition from fracture calcites. For other metals – Fe, Sr, and Mg – which are expected to interact with co-precipitating minerals to a higher degree than Mn, the correlations between measured and predicted calcitewere weaker for various reasons.
|
|
| 3. |
- Drake, Henrik, 1979-, et al.
(författare)
-
Unprecedented S-34-enrichment of pyrite formed following microbial sulfate reduction in fractured crystalline rocks
- 2018
-
Ingår i: Geobiology. - : Wiley. - 1472-4677 .- 1472-4669. ; 16:5, s. 556-574
-
Tidskriftsartikel (refereegranskat)abstract
- In the deep biosphere, microbial sulfate reduction (MSR) is exploited for energy. Here, we show that, in fractured continental crystalline bedrock in three areas in Sweden, this process produced sulfide that reacted with iron to form pyrite extremely enriched in S-34 relative to S-32. As documented by secondary ion mass spectrometry (SIMS) microanalyses, the S-34(pyrite) values are up to +132 parts per thousand V-CDT and with a total range of 186 parts per thousand. The lightest S-34(pyrite) values (-54 parts per thousand) suggest very large fractionation during MSR from an initial sulfate with S-34 values (S-34(sulfate,0)) of +14 to +28 parts per thousand. Fractionation of this magnitude requires a slow MSR rate, a feature we attribute to nutrient and electron donor shortage as well as initial sulfate abundance. The superheavy S-34(pyrite) values were produced by Rayleigh fractionation effects in a diminishing sulfate pool. Large volumes of pyrite with superheavy values (+120 +/- 15 parts per thousand) within single fracture intercepts in the boreholes, associated heavy average values up to +75 parts per thousand and heavy minimum S-34(pyrite) values, suggest isolation of significant amounts of isotopically light sulfide in other parts of the fracture system. Large fracture-specific S-34(pyrite) variability and overall average S-34(pyrite) values (+11 to +16 parts per thousand) lower than the anticipated S-34(sulfate,0) support this hypothesis. The superheavy pyrite found locally in the borehole intercepts thus represents a late stage in a much larger fracture system undergoing Rayleigh fractionation. Microscale Rb-Sr dating and U/Th-He dating of cogenetic minerals reveal that most pyrite formed in the early Paleozoic era, but crystal overgrowths may be significantly younger. The C-13 values in cogenetic calcite suggest that the superheavy S-34(pyrite) values are related to organotrophic MSR, in contrast to findings from marine sediments where superheavy pyrite has been proposed to be linked to anaerobic oxidation of methane. The findings provide new insights into MSR-related S-isotope systematics, particularly regarding formation of large fractions of S-34-rich pyrite.
|
|
| 4. |
- Maskenskaya, Olga M., et al.
(författare)
-
Source and character of syntaxial hydrothermal calcite veins in Paleoproterozoic crystalline rocks revealed by fine-scale investigations
- 2014
-
Ingår i: Geofluids. - : Wiley. - 1468-8115 .- 1468-8123. ; 14:4, s. 495-511
-
Tidskriftsartikel (refereegranskat)abstract
- Calcite veins in Paleoproterozoic granitoids on the Baltic Shield are the focus of this study. These veins are distinguished by their monomineralic character, unusual thickness and closeness to Neoproterozoic dolerite dykes and therefore have drawn attention. The aim of this study was to define the source of these veins and to unravel their isotopic and chemical nature by carrying out fine-scale studies. Seven calcite veins covering a depth interval of 50-420m below the ground surface and composed of breccias or crack-sealed fillings typically expressing syntaxial growth were sampled and analysed for a variety of physicochemical variables: homogenization temperature (T-h) and salinity of fluid inclusions, and stable isotopes (Sr-87/Sr-86, C-13/C-12, O-18/O-16), trace-element concentrations (Fe, Mn, Mg, Sr, rare earth elements) and cathodoluminescence (CL) of the solid phase. The fluid-inclusion data show that the calcites were precipitated mainly from relatively low-temperature (T-h=73-106 degrees C) brines (13.4-24.5wt.% CaCl2), and the Sr-87/Sr-86 is more radiogenic than expected for Rb-poor minerals precipitated from Neoproterozoic fluids. These features, together with the distribution of C-13 and O-18 values, provide evidence that the calcite veins are not genetic with the nearby Neoproterozoic dolerite dykes, but are of Paleozoic age and were precipitated from warm brines expressing a rather large variability in salinity. Whereas the isotopic and chemical variables express rather constant average values among the individual veins, they vary considerably on fine-scale across individual veins. This has implications for understanding processes causing calcite-rich veins to form and capture trace metals in crystalline bedrock settings.
|
|
| 5. |
- Sallstedt, Therese, et al.
(författare)
-
Instant Attraction : Clay Authigenesis in Fossil Fungal Biofilms
- 2019
-
Ingår i: Geosciences. - Basel : MDPI. - 2076-3263. ; 9:9, s. 1-21
-
Forskningsöversikt (refereegranskat)abstract
- Clay authigenesis associated with the activity of microorganisms is an important process for biofilm preservation and may provide clues to the formation of biominerals on the ancient Earth. Fossilization of fungal biofilms attached to vesicles or cracks in igneous rock, is characterized by fungal-induced clay mineralization and can be tracked in deep rock and deep time, from late Paleoproterozoic (2.4 Ga), to the present. Here we briefly review the current data on clay mineralization by fossil fungal biofilms from oceanic and continental subsurface igneous rock. The aim of this study was to compare the nature of subsurface fungal clays from different igneous settings to evaluate the importance of host rock and ambient redox conditions for clay speciation related to fossil microorganisms. Our study suggests that the most common type of authigenic clay associated with pristine fossil fungal biofilms in both oxic (basaltic) and anoxic (granitic) settings are montmorillonite-like smectites and confirms a significant role of fungal biofilms in the cycling of elements between host rock, ocean and secondary precipitates. The presence of life in the deep subsurface may thus prove more significant than host rock geochemistry in directing the precipitation of authigenic clays in the igneous crust, the extent of which remains to be fully understood.
|
|
| 6. |
- Tillberg, Mikael, et al.
(författare)
-
Fractionation of Rare Earth Elements in Greisen and Hydrothermal Veins Related to A-Type Magmatism
- 2019
-
Ingår i: Geofluids. - : Hindawi Limited. - 1468-8115 .- 1468-8123. ; 2019
-
Tidskriftsartikel (refereegranskat)abstract
- This study focuses on concentrations and fractionation of rare earth elements (REE) in a variety of minerals and bulk materials of hydrothermal greisen and vein mineralization in Paleoproterozoic monzodiorite to granodiorite related to the intrusion of Mesoproterozoic alkali- and fluorine-rich granite. The greisen consists of coarse-grained quartz, muscovite, and fluorite, whereas the veins mainly contain quartz, calcite, epidote, chlorite, and fluorite in order of abundance. A temporal and thus genetic link between the granite and the greisen/veins is established via high spatial resolution in situ Rb-Sr dating, supported by several other isotopic signatures (delta S-34, Sr-87/Sr-86, delta O-18, and delta C-13). Fluid-inclusion microthermometry reveals that multiple pulses of moderately to highly saline aqueous to carbonic solutions caused greisenization and vein formation at temperatures above 200-250 degrees C and up to 430 degrees C at the early hydrothermal stage in the veins. Low calculated Sigma REE concentration for bulk vein (15ppm) compared to greisen (75ppm), country rocks (173-224ppm), and the intruding granite (320ppm) points to overall low REE levels in the hydrothermal fluids emanating from the granite. This is explained by efficient REE retention in the granite via incorporation in accessory phosphates, zircon, and fluorite and unfavorable conditions for REE partitioning in fluids at the magmatic and early hydrothermal stages. A noteworthy feature is substantial heavy REE (HREE) enrichment of calcite in the vein system, in contrast to the relatively flat patterns of greisen calcite. The REE fractionation of the vein calcite is explained mainly by fractional crystallization, where the initially precipitated epidote in the veins preferentially incorporates most of the light REE (LREE) pool, leaving a residual fluid enriched in the HREE from which calcite precipitated. Fluorite occurs throughout the system and displays decreasing REE concentrations from granite towards greisen and veins and different fractionation patterns among all these three materials. Taken together, these features confirm efficient REE retention in the early stages of the system and minor control of the REE uptake by mineral-specific partitioning. REE-fractionation patterns and fluid-inclusion data suggest that chloride complexation dominated REE transport during greisenization, whereas carbonate complexation contributed to the HREE enrichment in vein calcite.
|
|
| 7. |
- Tillberg, Mikael, 1990, et al.
(författare)
-
In situ Rb-Sr dating of fine-grained vein mineralizations using LAICP-MS
- 2017
-
Ingår i: Procedia Earth and Planetary Science. 15th Water-Rock Interaction International Symposium (WRI), 16-21 Oct 2017, Evora, Portugal.. - Amsterdam : Elsevier. - 1878-5220. ; , s. 464-467
-
Konferensbidrag (refereegranskat)abstract
- Direct mineral dating is critical for thorough understanding of the genesis of hydrothermal mineralizations, ore forming processes and events of fracturing and related fluid-rock interaction. Since minerals of suitable type and sample volume for conventional techniques can be rare, development of high-precision in situ Rb-Sr dating of common rock-forming minerals such as micas, feldspars and calcite offers possibilities to gain temporal constraints of a wide variety of geological features with detailed spatial and depth resolution. This technique separates Sr-87 from Rb-87 by introducing a reaction gas between two quadropoles in a LAICP- MS system. In this study, in situ Rb-Sr geochronology distinguishes the timing of several different fracture-controlled hydrothermal events: 1 and 2) greisen mineralizations and associated far-field hydrothermal veins adjacent to a granite intrusion, 3) reactivation events within a mylonite shear zone and 4) low-temperature precipitation from saline organic-rich brines in thin veinlets. We demonstrate that in situ Rb-Sr dating is feasible for a broad range of mineral assemblages, textures, temperatures and ages, emphasizing the impending use of this new method in ore deposit exploration and many other research fields.
|
|
| 8. |
- Tillberg, Mikael, 1990, et al.
(författare)
-
Reconstructing craton-scale tectonic events via in situ Rb-Sr geochronology of poly-phased vein mineralization
- 2021
-
Ingår i: Terra Nova. - : Wiley. - 0954-4879 .- 1365-3121. ; 33:5, s. 502-510
-
Tidskriftsartikel (refereegranskat)abstract
- Fault- and fracture-hosted multi-stage mineral assemblages that formed by fracture reactivation and fluid migration, constitute archives of the tectonic evolution of Precambrian cratons. Complex intergrowth patterns of these mineral records often hinder absolute dating of mineralization events for geological models. We apply LA-ICP-MS/MS in situ Rb-Sr dating of single crystal growth zones in sub-mm-wide vein mineralization assemblages including illite, K-feldspar, albite, calcite, mica, zeolites, fluorite and/or epidote at three Palaeoproterozoic crystalline bedrock sites over 300 km apart in the Fennoscandian Shield. The dating campaign reveals multiple age clusters between ca. 1757 +/- 15 and 355 +/- 12 Ma correlating with fluid flow and fracture reactivation events initiated by far-field orogens and their foreland basin evolution. This new approach for reconstructing geological histories of Precambrian cratons connects micro-scale age determinations of different mineral growth zones in fractures with regional-scale crustal dynamic responses to tectonic events.
|
|
| 9. |
- Yu, Changxun, 1983-, et al.
(författare)
-
A cryogenic XPS study of Ce fixation on nanosized manganite and vernadite: Interfacial reactions and effects of fulvic acid complexation
- 2018
-
Ingår i: Chemical Geology. - : Elsevier BV. - 0009-2541 .- 1872-6836. ; 483, s. 304-311
-
Tidskriftsartikel (refereegranskat)abstract
- This study investigated interfacial reactions between aqueous Ce(III) and two synthetic nanosized Mn (hydr-) oxides (manganite: gamma-MnOOH, and vernadite: delta-MnO2) in the absence and presence of Nordic Lake fulvic acid (NLFA) at circumneutral pH by batch experiments and cryogenic X-ray photoelectron spectroscopy (XPS). The surfaces of manganite and vernadite were negatively charged (XPS-derived loadings of (Na+ K)/Cl > 1) and loaded with 0.42-4.33 Ce ions nm(-2). Manganite stabilized Ce-oxidation states almost identical to those for vernadite (approximately 75% Ce(IV) and 25% Ce(III)), providing the first experimental evidence that also a Mn (III) phase (manganite) can act as an important scavenger for Ce(IV) and thus, contribute to the decoupling of Ce from its neighboring rare earth elements and the development of Ce anomaly. In contrast, when exposed to Ce (III)-NLFA complexes, the oxidation of Ce by these two Mn (hydr-) oxides was strongly suppressed, suggesting that the formation of Ce(III) complexes with fulvic acid can stabilize Ce(III) even in the presence of oxidative Mn-oxide surfaces. The experiments also showed that Ce(III) complexed with excess NLFA was nearly completely removed, pointing to a strong preferential sorption of Ce(III)-complexed NLFA over free NLFA. This finding suggests that the Ce(III)-NLFA complexes were most likely sorbed by their cation side, i.e. Ce(III) bridging between oxide groups on the Mn (hydr-) oxides and negatively-charged functional groups in NLFA. Hence, Ce(III) was in direct contact with the oxidative manganite and vernadite but despite that not oxidized. An implication is that in organic-rich environments there may be an absence of Ce(IV) and Ce anomaly despite otherwise favorable conditions for Ce(III) oxidation.
|
|
| 10. |
- Bailey, Lydia R., et al.
(författare)
-
Characteristics and Consequences of Red Bed Bleaching by Hydrocarbon Migration : A Natural Example From the Entrada Sandstone, Southern Utah
- 2022
-
Ingår i: Geochemistry Geophysics Geosystems. - : John Wiley & Sons. - 1525-2027. ; 23:8
-
Tidskriftsartikel (refereegranskat)abstract
- Extensive regions of yellow and white ("bleached") sandstones within the terrestrial Jurassic red bed deposits of the Colorado Plateau reflect widespread interaction with subsurface reduced fluids which resulted in the dissolution of iron-oxide grain coatings. Reduced fluids such as hydrocarbons, CO2, and organic acids have been proposed as bleaching agents. In this study, we characterize an altered section of the Slick Rock member of the Jurassic Entrada Sandstone that exposes bleached sandstone with bitumen-saturated pore spaces. We observe differences in texture, porosity, mineralogy, and geochemistry between red, pink, yellow, and gray facies. In the bleached yellow facies we observe quartz overgrowths, partially dissolved K-feldspar, calcite cement, fine-grained illite, TiO2-minerals, and pyrite concretions. Clay mineral content is highest at the margins of the bleached section. Fe2O3 concentrations are reduced up to 3x from the red to gray facies but enriched up to 50x in iron-oxide concretions. Metals such as Zn, Pb, and rare-earth elements are significantly enriched in the concretions. Supported by a batch geochemical model, we conclude the interaction of red sandstones with reduced hydrocarbon-bearing fluids caused iron-oxide and K-feldspar dissolution, and precipitation of quartz, calcite, clay, and pyrite. Localized redistribution of iron into concretions can account for most of the iron removed during bleaching. Pyrite and carbonate stable isotopic data suggest the hydrocarbons were sourced from the Pennsylvanian Paradox Formation. Bitumen in pore spaces and pyrite precipitation formed a reductant trap required to produce Cu, U, and V enrichment in all altered facies by younger, oxidized saline brines.
|
|
| 11. |
|
|
| 12. |
|
|
| 13. |
- Drake, Henrik, 1979-, et al.
(författare)
-
Activity of sulfur reducing bacteria in deep bedrock fractures revealed by variability of δ34S in pyrite and dissolved sulphate
- 2013
-
Ingår i: Procedia Earth and Planetary Science. - : Elsevier. - 1878-5220. ; 7, s. 228-231
-
Tidskriftsartikel (refereegranskat)abstract
- Euhedral pyrite crystals coating 46 granite fractures at depths down to nearly 1 km at Laxemar, Sweden, were analysed for sulfur isotopes (δ34Spyr) by in situ SIMS (secondary ion mass spectrometry) analysis. Most of these fractures had corresponding chemical and isotopic groundwater data, providing a unique opportunity of pyrite-sulfate comparison within the same fracture network. Comparison of the isotopic ratios (δ18O, δ13C, 87Sr/86Sr) of co-genetic calcite with the groundwater showed that the sampled fractures carried pyrite and calcite that are of low-temperature origin, and with some exceptions, possibly precipitated from the present groundwater, or similar pre-modern fluids.The δ34Spyr showed huge variations across individual crystals (such as -32 to +73‰) and an extreme overall range (-50‰ to +91‰), which can only be explained by the activity of sulfur reducing bacteria (SRB). The most common sub-grain features were an increase in δ34Spyr with crystal growth related to successively higher δ34SSO4 caused by ongoing SRB activity and Rayleigh fractionation in fractures with low flow. The groundwater δ34SSO4 values (+9 to +37‰) are, in particular in the sulfate-poor waters down to -400 m, higher than the anticipated initial values, and this can also be explained by SRB-related Rayleigh distillation. The δ34SSO4 of the groundwater is, however, lower than that required to produce the highest δ34Spyr values, which may be due to the signal of groundwater in low-flow fractures (carrying 34S-rich sulfate and pyrite) being masked in the water data by high-flow parts of the water-flowing structure carrying abundant and less fractionated sulfate.
|
|
| 14. |
- Drake, Henrik, 1979-, et al.
(författare)
-
Anaerobic consortia of fungi and sulfate reducing bacteria in deep granite fractures
- 2017
-
Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 8:55, s. 1-9
-
Tidskriftsartikel (refereegranskat)abstract
- The deep biosphere is one of the least understood ecosystems on Earth. Although most microbiological studies in this system have focused on prokaryotes and neglected microeukaryotes, recent discoveries have revealed existence of fossil and active fungi in marine sediments and sub-seafloor basalts, with proposed importance for the subsurface energy cycle. However, studies of fungi in deep continental crystalline rocks are surprisingly few. Consequently, the characteristics and processes of fungi and fungus-prokaryote interactions in this vast environment remain enigmatic. Here we report the first findings of partly organically preserved and partly mineralized fungi at great depth in fractured crystalline rock (-740 m). Based on environmental parameters and mineralogy the fungi are interpreted as anaerobic. Synchrotron-based techniques and stable isotope microanalysis confirm a coupling between the fungi and sulfate reducing bacteria. The cryptoendolithic fungi have significantly weathered neighboring zeolite crystals and thus have implications for storage of toxic wastes using zeolite barriers.
|
|
| 15. |
- Drake, Henrik, 1979-, et al.
(författare)
-
Ancient microbial activity in deep hydraulically conductive fracture zones within the Forsmark target area for deep geological nuclear waste disposal, Sweden
- 2018
-
Ingår i: Geosciences. - : MDPI AG. - 2076-3263. ; 8
-
Tidskriftsartikel (refereegranskat)abstract
- Recent studies reveal that organisms from all three domains of life—Archaea, Bacteria, and even Eukarya—can thrive under energy-poor, dark, and anoxic conditions at large depths in the fractured crystalline continental crust. There is a need for an increased understanding of the processes and lifeforms in this vast realm, for example, regarding the spatiotemporal extent and variability of the different processes in the crust. Here, we present a study that set out to detect signs of ancient microbial life in the Forsmark area—the target area for deep geological nuclear waste disposal in Sweden. Stable isotope compositions were determined with high spatial resolution analyses within mineral coatings, and mineralized remains of putative microorganisms were studied in several deep water-conducting fracture zones (down to 663 m depth), from which hydrochemical and gas data exist. Large isotopic variabilities of 13Ccalcite (?36.2 to +20.2‰V-PDB) and 34Spyrite (?11.7 to +37.8‰V-CDT) disclose discrete periods of methanogenesis, and potentially, anaerobic oxidation of methane and related microbial sulfate reduction at several depth intervals. Dominant calcite–water disequilibrium of 18O and 87Sr/86Sr precludes abundant recent precipitation. Instead, the mineral coatings largely reflect an ancient archive of episodic microbial processes in the fracture system, which, according to our microscale Rb–Sr dating of co-genetic adularia and calcite, date back to the mid-Paleozoic. Potential Quaternary precipitation exists mainly at ~400 m depth in one of the boreholes, where mineral–water compositions corresponded.
|
|
| 16. |
- Drake, Henrik, Docent, 1979-, et al.
(författare)
-
Biosignatures of ancient microbial life are present across the igneous crust of the Fennoscandian shield
- 2021
-
Ingår i: Communications Earth & Environment. - : Springer Nature. - 2662-4435. ; 2:1
-
Tidskriftsartikel (refereegranskat)abstract
- Earth’s crust contains a substantial proportion of global biomass, hosting microbial life up to several kilometers depth. Yet, knowledge of the evolution and extent of life in this environment remains elusive and patchy. Here we present isotopic, molecular and morphological signatures for deep ancient life in vein mineral specimens from mines distributed across the Precambrian Fennoscandian shield. Stable carbon isotopic signatures of calcite indicate microbial methanogenesis. In addition, sulfur isotope variability in pyrite, supported by stable carbon isotopic signatures of methyl-branched fatty acids, suggest subsequent bacterial sulfate reduction. Carbonate geochronology constrains the timing of these processes to the Cenozoic. We suggest that signatures of an ancient deep biosphere and long-term microbial activity are present throughout this shield. We suggest that microbes may have been active in the continental igneous crust over geological timescales, and that subsurface investigations may be valuable in the search for extra-terrestrial life.
|
|
| 17. |
- Drake, Henrik, 1979, et al.
(författare)
-
Detecting the near-surface redox front in crystalline bedrock using fracture mineral distribution, geochemistry and U-series disequilibrium
- 2009
-
Ingår i: Applied Geochemistry. ; 24:5, s. 1023-1039
-
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.
|
|
| 18. |
- Drake, Henrik, 1979, et al.
(författare)
-
Detection of the near surface redox front in crystalline bedrock.
- 2008
-
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.
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)
|
|
| 19. |
|
|
| 20. |
- Drake, Henrik, 1979, et al.
(författare)
-
Distinguished multiple events of fracture mineralisation related to far-field orogenic effects in Paleoproterozoic crystalline rocks, Simpevarp area, SE Sweden
- 2009
-
Ingår i: Lithos. - : Elsevier BV. - 0024-4937. ; 110:1-4, s. 37-49
-
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.
|
|
| 21. |
- Drake, Henrik, 1979-, et al.
(författare)
-
Episodic microbial methanogenesis, methane oxidation and sulfate reduction in deep granite fractures at Forsmark, Sweden
- 2017
-
Ingår i: 15TH WATER-ROCK INTERACTION INTERNATIONAL SYMPOSIUM, WRI-15. - : Elsevier BV. ; , s. 702-705
-
Konferensbidrag (refereegranskat)abstract
- An extensive microanalytical isotope study of calcite and pyrite has been carried out in bedrock fractures at Forsmark, Sweden. The very large delta C-13(calcite)-variation of 103.4% V-PDB in total (-69.2 to +34.2%) evidences significant spatial and temporal variability in processes and carbon sources in the deep fracture system during the period when these minerals were formed (Phanerozoic). The substantial delta C-13(calcite)-span is mainly methane-related, with heavy and very light delta C-13 originating from ubiquitous in situ microbial methanogenesis and anaerobic oxidation of methane (AOM), respectively. Co-genetic cubic and framboidal pyrite showed substantial sulfate reducing bacteria (SRB)-related delta S-34 variation of 95% V-CDT overall (-29 to +66%), indicating closed system isotope distillation and point to similar genetic SRB methane-oxidizer relationships as in marine sediments. The depth distribution of the methanogenesis-, SRB- and AOM-signatures are from just below the ground surface down to about 800 m, which marks the deepest occurrence of AOM-related carbonate yet reported from the continental crystalline crust. Biomarkers and fluid inclusions suggest that the microbial activity in the bedrock fractures was closely related to descending surficial fluids and basinal brines rich in organic matter, in at least two pulses (70-80 degrees C and <50-62 degrees C). (C) 2017 Published by Elsevier B.V.
|
|
| 22. |
- Drake, Henrik, Docent, 1979-, et al.
(författare)
-
Fossil svamp i Siljansringens meteoritkrater
- 2021
-
Ingår i: Geologiskt Forum. - Stockholm : Geologiska föreningen. - 1104-4721. ; 110, s. 18-21
-
Tidskriftsartikel (populärvet., debatt m.m.)
|
|
| 23. |
- Drake, Henrik, Docent, 1979-, et al.
(författare)
-
Fossilized anaerobic and possibly methanogenesis-fueling fungi identified deep within the Siljan impact structure, Sweden
- 2021
-
Ingår i: Communications Earth & Environment. - : Springer Science and Business Media LLC. - 2662-4435. ; 2:1, s. 1-11
-
Tidskriftsartikel (refereegranskat)abstract
- Recent discoveries of extant and fossilized communities indicate that eukaryotes, including fungi, inhabit energy-poor and anoxic environments deep within the fractured igneous crust. This subterranean biosphere may constitute the largest fungal habitat on our planet, but knowledge of abyssal fungi and their syntrophic interactions with prokaryotes and their concomitant metabolisms is scarce. Here we report findings of fossilized, chitin-bearing fungal hyphae at ~540 m depth in fractured bedrock of the Siljan impact structure, the largest crater in Europe. Strong 13C-enrichment of calcite precipitated with and on the fungi suggests formation following methanogenesis, and that the anaerobic fungi decomposed dispersed organic matter producing for example H2 that may have fueled autotrophic methanogens. An Eocene age determined for the calcite infers the first timing constraint of fossilized fungi in the continental igneous crust. Fungi may be widespread decomposers of organic matter and overlooked providers of H2 to autotrophs in the vast rock-hosted deep biosphere.
|
|
| 24. |
|
|
| 25. |
|
|
| 26. |
- Drake, Henrik, 1979, et al.
(författare)
-
Fracture Mineralogy
- 2006
-
Ingår i: Preliminary site description. Laxemar subarea - version 1.2, SKB-R-06-10. - Stockholm : SKB. ; , s. 163-167
-
Bokkapitel (övrigt vetenskapligt/konstnärligt)
|
|
| 27. |
- Drake, Henrik, 1979-, et al.
(författare)
-
Geochronology and Stable Isotope Analysis of Fracture-Fill and Karst Mineralization Reveal Sub-Surface Paleo-Fluid Flow and Microbial Activity of the COSC-1 Borehole, Scandinavian Caledonides
- 2020
-
Ingår i: Geosciences. - : MDPI AG. - 2076-3263.
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- The deep biosphere hosted in fractured rocks within the upper continental crust is one of the least understood and studied ecological realms on Earth. Scarce knowledge of ancient life and paleo-fluid flow within this realm is owing to the lack of deep drilling into the crust. Here we apply microscale high spatial-resolution analytical techniques to fine-grained secondary minerals in a deep borehole (COSC-1) drilled into the Silurian-Devonian Scandinavian Caledonide mountain range in central Sweden. The aim is to detect and date signs of ancient microbial activity and low-temperature fluid circulation in micro-karsts (foliation-parallel dissolution cavities in the rock) and fractures at depth in the nappe system. Vein carbonates sampled at 684 to 2210 m show a decreased C isotope variability at depths below 1050 m; likely due to decreased influence of organic-C at great depth. Micro-karsts at 122–178 m depth feature at least two generations of secondary calcite and pyrite growth in the voids as shown by secondary ion mass spectrometry analytical transects within individual grains. The younger of these two precipitation phases shows 34S-depleted δ34Spyrite values (−19.8 ± 1.6‰ vs. Vienna-Canyon Diablo Troilite (V-CDT)) suggesting microbial sulfate reduction in situ. The calcite of this late phase can be distinguished from the older calcite by higher δ18Ocalcite values that correspond to precipitation from ambient meteoric water. The late stage calcite gave two separate laser ablation inductively coupled mass spectrometry-derived U-Pb ages (9.6 ± 1.3 Ma and 2.5 ± 0.2 Ma), marking a minimum age for widespread micro-karst formation within the nappe. Several stages of fluid flow and mineral precipitation followed karst formation; with related bacterial activity as late as the Neogene-Quaternary; in structures presently water conducting. The results show that our combined high spatial-resolution stable isotope and geochronology approach is suitable for characterizing paleo-fluid flow in micro-karst; in this case, of the crystalline crust comprising orogenic nappe units.
|
|
| 28. |
|
|
| 29. |
- Drake, Henrik, Docent, 1979-, et al.
(författare)
-
In Situ Rb/Sr Geochronology and Stable Isotope Geochemistry Evidence for Neoproterozoic and Paleozoic Fracture-Hosted Fluid Flow and Microbial Activity in Paleoproterozoic Basement, SW Sweden
- 2023
-
Ingår i: Geochemistry Geophysics Geosystems. - : American Geophysical Union (AGU). - 1525-2027. ; 24:5
-
Tidskriftsartikel (refereegranskat)abstract
- Recent studies have shown that biosignatures of ancient microbial life exist in mineral coatings in deep bedrock fractures of Precambrian cratons, but such surveys have been few and far between. Here, we report results from southwestern Sweden in an area of 1.6-1.5 Ga Paleoproterozoic rocks heavily reworked by the 1.14-0.96 Ga Sveconorwegian orogeny, a terrane previously scarcely explored for ancient microbial biosignatures. Calcite-pyrite-adularia-illite-coated fractures were analyzed for stable isotopes via Secondary Ion Mass Spectrometry (delta C-13, delta O-18, delta S-34) and in situ Rb/Sr geochronology via Laser-ablation inductively coupled plasma mass spectrometry. The Rb/Sr ages for calcite-adularia and calcite-illite show that several fluid flow events can be discerned (797 +/- 18-769 +/- 7, 391 +/- 5-387 +/- 6, 356 +/- 5-347 +/- 4, and 301 +/- 7 Ma). The delta C-13, delta O-18 and Sr-87/Sr-86 values of different calcite growth zones further confirmed episodic fluid flow. Pyrite delta S-34 values down to -49.9% V-CDT, together with systematically increased delta S-34 from crystal core to rim, suggest formation following microbial sulfate reduction under semi-closed conditions. Assemblages involving MSR-related pyrite generally have Devonian to Permian Rb/Sr ages, indicating an association to extension-related fracturing and fluid mixing during foreland-basin formation linked to Caledonian orogeny in the northwest. An assemblage with an age of 301 +/- 7 Ma is potentially related to Oslo Rift extension, whereas the Neo-Proterozoic ages relate to post-Sveconorwegian extensional tectonics. Remnants of short-chained fatty acids in the youngest calcite coatings further indicate a biogenic origin, while the absence of organic molecules in older calcite is in line with thermal degradation, potentially related to heating during Caledonian foreland basin burial. Plain Language Summary This study investigates mineral coatings in Proterozoic basement fractures of Southwestern Sweden, within the Precambrian Fennoscandian shield, to gain insights into ancient microbial life and paleo-fluid flow. Isotopic signatures of these mineral coatings suggest that microbial sulfate reducers have been present in the system as also indicated by preserved organic molecules. Microanalytical geochronology determinations reveal that the fracture system has been activated several times in the Neoproterozoic, Devonian-Early Carboniferous, and Late Carboniferous/Early Permian. These activations are associated with extension events following the Sveconorwegian and Caledonian orogenies as well as formation of the Oslo Rift. The signs of microbial activity are related to the youngest of these events, post-dating burial in the Caledonian foreland basin, when bedrock temperatures became habitable.
|
|
| 30. |
- Drake, Henrik, 1979-, et al.
(författare)
-
Incorporation of Metals into Calcite in a Deep Anoxic Granite Aquifer
- 2018
-
Ingår i: Environmental Science & Technology. - : American Chemical Society (ACS). - 0013-936X .- 1520-5851 .- 1086-931X .- 1520-6912. ; 52:2, s. 493-502
-
Tidskriftsartikel (refereegranskat)abstract
- Understanding metal scavenging by calcite in deep aquifers in granite is of importance for deciphering and modeling hydrochemical fluctuations and water rock interaction in the upper crust and for retention mechanisms associated With underground, repositories for toxic wastes. Metal scavenging into calcite has generally been established in the laboratory or in natural environments that cannot be unreservedly applied to conditions in deep crystalline rocks, an environment of broad interest, for nuclear waste repositories. Here, we report a microanalytical study: of calcite precipitated over a period of 17 years from anoxic, low-temperature (14 degrees C), neutral (pH: 7.4-7.7), and brackish (Cl: 1700-7100 mg/L) groundwater flowing in fractures at >400 m depth in granite rock. This enabled assessment of the trace metal uptake by calcite under these deep-seated conditions. Aquatic speciation modeling was carried out to assess influence of metal complexation on the partitioning into calcite. The resulting environment-specific partition coefficients were for several divalent ions in line with values obtained in controlled laboratory experiments, whereas for several other ions they differed substantially. High absolute uptake of rare earth elements and U(IV) suggests that coprecipitation into calcite can be an important sink for these metals and analogousactinides in the vicinity of geological repositories.
|
|
| 31. |
- Drake, Henrik, 1979-, et al.
(författare)
-
Incorporation of trace elements into calcite precipitated from deep anoxic groundwater in fractured granitoid rocks
- 2017
-
Ingår i: Procedia Earth and Planetary Science. 15th Water-Rock Interaction International Symposium (WRI). Evora, Portugal, OCT 16-21, 2016.. - : Elsevier BV. - 1878-5220. ; , s. 841-844
-
Konferensbidrag (refereegranskat)abstract
- An extensive microanalytical study of calcite precipitated from groundwater flowing into boreholes at >400 m depth in the Aspo Hard Rock Laboratory, Sweden, has been carried out. Hydrochemical variations in packed-off sections, isolating water-conducting fractures intersected by two boreholes, were documented over a period of 17 years. The extraction of the borehole equipment revealed calcite precipitation on the equipment. This mineral material enabled unique assessment of uptake of different trace elements by calcite during precipitation from granitoid fracture groundwater, at anoxic, low-temperature (c.a 14 degrees C), and neutral (pH: 7.4-7.7) conditions, under variable salinity (Cl: 2500-7000 mg/L) prevailing at these depths. Temporal hydrochemical variations could be traced by detailed micro-analytical transects in the calcites and the influence of metal speciation and complexation on partitioning into calcite could be assessed (e.g. explaining unexpectedly low incorporation of REEs). The resulting environment-specific partition coefficients for a large number of metals are relevant in models of radionuclide retention around proposed deep nuclear waste repositories in this kind of environment, particularly because 1) elements such as REEs act as natural analogues to actinides, and 2) existing coefficients established in laboratory or in other natural environments cannot be unreservedly applied to conditions in deep crystalline rocks.
|
|
| 32. |
- Drake, Henrik, 1979-, et al.
(författare)
-
Isotopic evidence for microbial production and consumption of methane in the upper continental crust throughout the Phanerozoic eon
- 2017
-
Ingår i: Earth and Planetary Science Letters. - : Elsevier BV. - 0012-821X .- 1385-013X. ; 470, s. 108-118
-
Tidskriftsartikel (refereegranskat)abstract
- Microorganisms produce and consume methane in terrestrial surface environments, sea sediments and, as indicated by recent discoveries, in fractured crystalline bedrock. These processes in the crystalline bedrock remain, however, unexplored both in terms of mechanisms and spatiotemporal distribution. Here we have studied these processes via a multi-method approach including microscale analysis of the stable isotope compositions of calcite and pyrite precipitated in bedrock fractures in the upper crust (down to 1.7 km) at three sites on the Baltic Shield. Microbial processes have caused an intriguing variability of the carbon isotopes in the calcites at all sites, with delta C-13 spanning as much as -93.1 parts per thousand (related to anaerobic oxidation of methane) to +36.5 parts per thousand (related to methanogenesis). Spatiotemporal coupling between the stable isotope measurements and radiometric age determinations (micro-scale dating using new high spatial methods: LA-ICP-MS U-Pb for calcite and Rb-Sr for calcite and co-genetic adularia) enabled unprecedented direct timing constraints of the microbial processes to several periods throughout the Phanerozoic eon, dating back to Devonian times. These events have featured variable fluid salinities and temperatures as shown by fluid inclusions in the calcite; dominantly 70-85 degrees C brines in the Paleozoic and lower temperatures (<50-62 degrees C) and salinities in the Mesozoic. Preserved organic compounds, including plant signatures, within the calcite crystals mark the influence of organic matter in descending surficial fluids on the microbial processes in the fracture system, thus linking processes in the deep and surficial biosphere. These findings substantially extend the recognized temporal and spatial range for production and consumption of methane within the upper continental crust. (C) 2017 Elsevier B.V. All rights reserved.
|
|
| 33. |
|
|
| 34. |
|
|
| 35. |
|
|
| 36. |
|
|
| 37. |
|
|
| 38. |
|
|
| 39. |
|
|
| 40. |
|
|
| 41. |
|
|
| 42. |
|
|
| 43. |
|
|
| 44. |
|
|
| 45. |
|
|
| 46. |
- Drake, Henrik, 1979, et al.
(författare)
-
Paleohydrogeological evidences from stable isotopes, fluid inclusions and trace elements in fracture minerals in crystalline rock, Simpevarp area, south-eastern Sweden
- 2008
-
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..
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)
|
|
| 47. |
|
|
| 48. |
|
|
| 49. |
- Drake, Henrik, 1979
(författare)
-
Proterozoic to Quaternary Events of Fracture Mineralisation and Oxidation in SE Sweden
- 2008
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Fracture minerals and altered wall rock have been analysed to reveal the low-temperature evolution, especially regarding redox conditions, of the Simpevarp area, SE Sweden. This area is one of the two areas in Sweden investigated by the Swedish Nuclear fuel and Waste Management Co. (SKB) in order to find a potential geological repository for spent nuclear fuel. The 1.8 Ga granitic to dioritic rocks in the area are generally un-metamorphosed and structurally well-preserved, although low-grade ductile shear zones and repeatedly reactivated fractures exist. Investigations of cross-cutting fractures along with a wide variety of fracture mineral analyses, such as stable isotopes and 40Ar/39Ar geochronology, have been used to distinguish a sequence of fracture filling generations. The characteristics of these generations indicate the low-temperature evolution of the area, including information of e.g. fluid origin, formation temperature, paleo stresses and relation to known geological events. Knowledge of the fracture mineral evolution is important for the conceptual geological and hydrogeochemical understanding of the site and supports predictions of future scenarios in the safety assessment. The fracture mineral generations identified have been formed at widely varying conditions starting in the Proterozoic with formation from inorganic hydrothermal fluids, continuing in the Paleozoic with formation from lower temperature brine type fluids with organic influence, and ranging into minerals formed from waters of varying salinity and with significant organic influence at conditions similar to the present conditions. However, the amount of potentially recent precipitates is very small compared to Proterozoic and Paleozoic precipitates. The fracture mineral parageneses have been associated, with varying confidence, to far-field effects of at least four different orogenies; the Svecokarelian orogeny (>1.75 Ga), the Danapolonian orogeny (~1.47-1.44 Ga), the Sveconorwegian orogeny (~1.1-0.9 Ga) and the Caledonian orogeny (~0.5-0.4 Ga). The fracture minerals related to the Danapolonian orogeny were mainly formed in relation to the intrusion of two granites nearby. Periods of extension and influence from overlying sedimentary successions have also been indicated in the fracture mineral record. Demonstration of long term preservation of stable reducing conditions at repository depth is an important task in the safety assessment of a nuclear waste repository. This is because oxygen may harm the copper canisters and may cause increased mobility of some radionuclides in case of canister leakage. It is therefore important to demonstrate the extent of past oxygen intrusion in the bedrock, i.e. the position of the redox front, at which originally present oxygen have been reduced along the fractures. It is also important to obtain information on the available reducing capacity (mainly Fe2+) of the wall rock, especially regarding the widespread hydrothermally altered, red-stained and supposedly oxidised wall rock. The results from two comprehensive studies on these tasks are satisfying and robust and can be summarised as: 1) The recent redox front is indicated to be located in the uppermost twenty meters of the bedrock, as shown by the depth distribution of redox sensitive minerals pyrite and goethite, Ce-anomalies and U-series nuclides, and 2) red-stained wall rock still has a high reducing capacity, which is largely similar to that of the unaltered rock.
|
|
| 50. |
|
|
