| 1. |
- Drake, Henrik, 1979, et al.
(författare)
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Fracture zone-scale variation of trace elements and stable isotopes in calcite in a crystalline rock setting
- 2014
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Ingår i: Applied Geochemistry. - : Elsevier BV. - 0883-2927 .- 1872-9134. ; 40, s. 11-24
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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.
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| 2. |
- Drake, Henrik, 1979-, et al.
(författare)
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Trace metal distribution and isotope variations in low-temperature calcite and groundwaters in granitoid fractures down to 1 km depth
- 2012
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Ingår i: Geochimica et Cosmochimica Acta. - : Elsevier. - 0016-7037 .- 1872-9533. ; 84, s. 217-238
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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.
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| 3. |
- 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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| 4. |
- Maskenskaya, Olga M., et al.
(författare)
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Source and character of syntaxial hydrothermal calcite veins in Paleoproterozoic crystalline rocks revealed by fine-scale investigations
- 2014
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Ingår i: Geofluids. - : Wiley. - 1468-8115 .- 1468-8123. ; 14:4, s. 495-511
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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.
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| 5. |
- 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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| 6. |
- 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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| 7. |
- 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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| 8. |
- Tillberg, Mikael, 1990, et al.
(författare)
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Reconstructing craton-scale tectonic events via in situ Rb-Sr geochronology of poly-phased vein mineralization
- 2021
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Ingår i: Terra Nova. - : Wiley. - 0954-4879 .- 1365-3121. ; 33:5, s. 502-510
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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.
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| 9. |
- 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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| 10. |
- Bailey, Lydia R., et al.
(författare)
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Characteristics and Consequences of Red Bed Bleaching by Hydrocarbon Migration : A Natural Example From the Entrada Sandstone, Southern Utah
- 2022
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Ingår i: Geochemistry Geophysics Geosystems. - : John Wiley & Sons. - 1525-2027. ; 23:8
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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.
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