| 1. |
- Maskenskaya, Olga M., 1984-
(författare)
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Abundance and fractionation of rare earth elements in calcite and other secondary minerals in fractures in the upper kilometre of crystalline bedrock, SE Sweden
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis focuses on the geochemistry of secondary minerals, mainly calcite but also others such as fluorite and Ca/Al silicates, precipitated throughout the last 1.5 billion years in fractures of crystalline rock, SE Sweden. The work was based on previous reconnaissance studies and has been possible thanks to access to high-quality drill cores and associated mapping data provided by the Swedish Nuclear Fuel and Waste Management Co (SKB). Concentrations of rare earth elements (REEs) and occasionally other metals were determined in a variety of secondary minerals from fractures (mainly open systems) and veins (mainly sealed systems) and in primary minerals from the bedrock. Stable-isotope composition was measured in the secondary minerals. The overall aim was to define the sources, uptake and fractionation of REEs in calcite, and a few other co-genetic minerals, precipitated throughout the geological history under conditions ranging from hydrothermal to low temperatures.Collectively, the findings of the individual studies show that there is no easy and straightforward control of REE abundance and fractionation in calcite and other minerals in fractures and veins in crystalline bedrock settings. For example, the REE features in calcite vary extensively within sub-generations of single vein-precipitating events, on micro scale in transects across individual veins, and unsystematically over the geological history characterised by successively decreasing temperatures of mineral formation. Although the REE content in, and release from, the crystalline bedrock can have an influence on REE distribution in calcite and other minerals, it is of overall minor importance within a given bedrock domain. The main advantage of determining REEs in secondary minerals in fractures and veins in crystalline rock is therefore, as revealed in this work, to assess the character and evolution of the conditions (including features of the paleofluids) during confined mineral-precipitating events.
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| 2. |
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| 3. |
- Maskenskaya, Olga M., et al.
(författare)
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Geochemistry of calcite veins : records of fluid mixing and fluid-rock interaction
- 2013
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Ingår i: PROCEEDINGS OF THE FOURTEENTH INTERNATIONAL SYMPOSIUM ON WATER-ROCK INTERACTION, WRI 14. - : Elsevier. ; , s. 566-569
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Konferensbidrag (refereegranskat)abstract
- Detailed geochemical investigations of calcite veins, genetically related to intrusions and vein-hosting bedrock, have been used to indicate fluid evolution during intrusion-related hydrothermal mineralization, involving fluid mixing and water rock interaction. The area of investigation is located in the southeast of Sweden. The 1.85 Ga granitoid country rocks and the 0.9 Ga dolerite vein-related intrusions differ in chemical, geochemical, and stable isotope composition. The variation in rare earth and stable isotope composition across calcite veins and the presence of two groups of fluid inclusions suggests mixing of two types of fluids. Light rare earth enrichment and increasing Sr-87/Sr-86-ratios suggest water rock interaction of one/both fluids. (C) 2013 The Authors. Published by Elsevier B.V.
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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. |
- Maskenskaya, Olga M., et al.
(författare)
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The role of carbonate complexes and crystal habit on rare earth element uptake in low-temperature calcite in fractured crystalline rock
- 2015
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Ingår i: Chemical Geology. - : Elsevier BV. - 0009-2541 .- 1872-6836. ; 391, s. 100-110
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Tidskriftsartikel (refereegranskat)abstract
- This study focuses on rare earth element (REE) geochemistry of low-temperature calcite coatings occurring on the walls of fractures throughout the upper kilometer of crystalline rocks of the Baltic Shield. Fifty one calcite coatings were sampled from cores drilled with the triple-tube technique which successfully preserved the fragile calcite coatings on the fracture walls. The calcites, which based on geological and isotopic evidence were precipitated over the last 10 million years, had highly variable Sigma REE concentrations (0.61-2276 ppm) that decreased weakly with the depth the calcite was sampled from. When normalized to shale (and host rock), the REE concentrations of habits with c-axis approximate to a-axes and the closely associated c-axis > a-axes, the most abundant crystal morphologies in the system, decreased strongly and smoothly across the series. In contrast, the REEs of habits with c-axis >> a-axes, identified only in fractures in the uppermost 260m of the bedrock, were flatter and occasionally expressed a weak middle REE enrichment. By using calcite-water partition coefficients derived for REEs in previous laboratory experiments, the La/Yb of the paleogroundwater from which the calcites precipitated was back-calculated and found to be overall similar (range 0.15-452) overlap to the corresponding ratio of the present groundwater (range: 2.1-36.4). In terms of REE/Ca, the values for the back-calculated paleogroundwater (La / Ca 9.9 (*) 10(-11)-3.9 (*) 10(-7); Yb / Ca 1.5 (*) 10(-10)-2.2(*)10(-7)) were similar to those of LaCO3+ / Ca (4.5(*)10(-10)-8.5 (*) 10(-7)) and (YbCO3+ + Yb(CO3)(2)(-)) / Ca (5.4 (*) 10(-11)-1.8 (*) 10(-8)), respectively, in the present groundwater. These patterns indicate that the LREE to HREE and REE to Ca ratios in the groundwater at the site are broadly similar to those existing when the calcites precipitated, and that carbonate complexes present in the paleogroundwater played a crucial role in sequestration and fractionation of REEs in calcite. The findings have implications for bedrock storage of high-level radioactivewaste, which contains actinides for which the REEs can be used as natural analogues. (C) 2014 Elsevier B.V. All rights reserved.
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| 6. |
- Mathurin, Frédéric A., et al.
(författare)
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REE and Y in groundwater in the upper 1.2 km of Proterozoic granitoids (Eastern Sweden) - Assessing the role of composition and origin of groundwaters, geochemistry of fractures, and organic/inorganic aqueous complexation
- 2014
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Ingår i: Geochimica et Cosmochimica Acta. - : Elsevier BV. - 0016-7037 .- 1872-9533. ; 144, s. 342-378
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Tidskriftsartikel (refereegranskat)abstract
- Yttrium and rare earth elements (YREEs) are studied in groundwater in the shallow regolith aquifer and the fracture networks of the upper 1.2 km of Paleoproterozoic granitoids in boreal Europe (Laxemar and Forsmark areas, Sweden). The study includes groundwater sampled via a total of 34 shallow boreholes reaching the bottom of the regolith aquifer, and 72 deep boreholes with equipment designed for retrieval of representative groundwater at controlled depths in the fractured bedrock. The groundwater composition differs substantially between regolith and fracture groundwater and between areas, which affects the dissolved YREE features, including concentrations and NASC normalized patterns. In the fresh groundwater in the regolith aquifers, highest YREE concentrations occur (10th and 90th percentile; Laxemar: 4.4-82 mu g L-1; Forsmark: 1.9-19 mu g L-1), especially in the slightly acidic groundwater (pH: 6.3-7.2 - Laxemar), where the normalized YREE patterns are slightly enriched in light REEs (La-NASC/Y-NASC: 1.1-2.4). In the recharge areas, where redox potentials of the regolith groundwater is more moderate, negative Ce anomaly (Laxemar: 0.37-0.45; Forsmark: 0.15-0.92) and positive Y anomaly (mainly in Forsmark: 1.0-1.7) are systematically more pronounced than in discharge areas. The significant correlations between the YREE features and dissolved organic carbon, minor elements, and somewhat pH suggest a strong control of humic substances (HSs) together with Al rich colloids and redox sensitive Fe-Mn hydrous precipitates on the dissolved YREE pools. In the bedrock fractures, the groundwater is circumneutral to slightly basic and displays YREE concentrations that are at least one order of magnitude lower than the regolith groundwater, and commonly below detection limit in the deep brackish and saline groundwater, with some exceptions such as La and Y. At intermediate depth (>50 m), where groundwater of meteoric origin percolates, the La-NASC/Y-NASC values moderately to substantially decrease (Laxemar: 0.24-2.65; Forsmark: 0.02-0.06) and Y and Ce anomalies are negligible as compared to the regolith groundwater. Aqueous speciation modeling predicts substantial binding of dissolved Y and La, respectively, to HSs. This, in turn, suggests that the features of the YREE pool in the meteoric fracture groundwater are dominantly controlled by the capacity of fracture minerals to sorb HS ligands inherited from the overlying terrestrial regolith. In the deep bedrock fractures (>100/200 m), the YREE features vary substantially with the groundwater paleo-origin. In Laxemar, where groundwater with pronounced glacial origin percolates, the YREE concentrations decrease with increasing mixing fraction of glacial melt water. There, the dissolved YREEs are mostly bound to HSs, and inherited their fractionation features (La-NASC/Y-NASC: 0.15-2.1) from water-rock interaction in the intermediate bedrock fractures. In Forsmark, the YREE and heavy REE enrichment (La-NASC/Y-NASC: 0.007-0.23) are more systematic in the groundwater with pronounced marine origin, due to water-mineral interactions in the sea sediment and in the fractures while infiltrating and percolating. YREE features significantly change in the deep saline groundwater with a long residence time, which displays La-NASC/Y-NASC similar to those of the local bedrock. The findings of this study are relevant in terms of safety assessment for nuclear waste disposal in crystalline rock carrying groundwater influenced by various paleo-climatic recharges. (C) 2014 Elsevier Ltd. All rights reserved.
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| 7. |
- 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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