| 1. |
- Drake, Henrik, 1979-, et al.
(författare)
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Unprecedented S-34-enrichment of pyrite formed following microbial sulfate reduction in fractured crystalline rocks
- 2018
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Ingår i: Geobiology. - : Wiley. - 1472-4677 .- 1472-4669. ; 16:5, s. 556-574
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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.
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| 2. |
- Sallstedt, Therese, et al.
(författare)
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Instant Attraction : Clay Authigenesis in Fossil Fungal Biofilms
- 2019
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Ingår i: Geosciences. - Basel : MDPI. - 2076-3263. ; 9:9, s. 1-21
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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.
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| 3. |
- Tillberg, Mikael, et al.
(författare)
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Fractionation of Rare Earth Elements in Greisen and Hydrothermal Veins Related to A-Type Magmatism
- 2019
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Ingår i: Geofluids. - : Hindawi Limited. - 1468-8115 .- 1468-8123. ; 2019
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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.
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| 4. |
- Tillberg, Mikael, 1990, et al.
(författare)
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In situ Rb-Sr dating of fine-grained vein mineralizations using LAICP-MS
- 2017
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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
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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.
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| 5. |
- Yu, Changxun, 1983-, et al.
(författare)
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A cryogenic XPS study of Ce fixation on nanosized manganite and vernadite: Interfacial reactions and effects of fulvic acid complexation
- 2018
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Ingår i: Chemical Geology. - : Elsevier BV. - 0009-2541 .- 1872-6836. ; 483, s. 304-311
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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.
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| 6. |
- Drake, Henrik, 1979-, et al.
(författare)
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Anaerobic consortia of fungi and sulfate reducing bacteria in deep granite fractures
- 2017
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Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 8:55, s. 1-9
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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.
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| 7. |
- Drake, Henrik, 1979-, et al.
(författare)
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Ancient microbial activity in deep hydraulically conductive fracture zones within the Forsmark target area for deep geological nuclear waste disposal, Sweden
- 2018
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Ingår i: Geosciences. - : MDPI AG. - 2076-3263. ; 8
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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.
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| 8. |
- Drake, Henrik, 1979-, et al.
(författare)
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Episodic microbial methanogenesis, methane oxidation and sulfate reduction in deep granite fractures at Forsmark, Sweden
- 2017
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Ingår i: 15TH WATER-ROCK INTERACTION INTERNATIONAL SYMPOSIUM, WRI-15. - : Elsevier BV. ; , s. 702-705
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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.
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| 9. |
- Drake, Henrik, 1979-, et al.
(författare)
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Incorporation of Metals into Calcite in a Deep Anoxic Granite Aquifer
- 2018
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Ingår i: Environmental Science & Technology. - : American Chemical Society (ACS). - 0013-936X .- 1520-5851 .- 1086-931X .- 1520-6912. ; 52:2, s. 493-502
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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.
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| 10. |
- Drake, Henrik, 1979-, et al.
(författare)
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Incorporation of trace elements into calcite precipitated from deep anoxic groundwater in fractured granitoid rocks
- 2017
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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
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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.
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