| 1. |
- Fehr, Manuela A., et al.
(författare)
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Iron isotope variations in Holocene sediments of the Gotland Deep, Baltic Sea
- 2008
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Ingår i: Geochimica et Cosmochimica Acta. - : Elsevier BV. - 0016-7037 .- 1872-9533. ; 72:3, s. 807-826
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Forskningsöversikt (refereegranskat)abstract
- Holocene sediments from the Gotland Deep basin in the Baltic Sea were investigated for their Fe isotopic composition in order to assess the impact of changes in redox conditions and a transition from freshwater to brackish water on the isotope signature of iron. The sediments display variations in delta Fe-56 (differences in the Fe-56/Fe-54 ratio relative to the IRMM-14 standard) from -0.27 +/- 0.09 parts per thousand to +0.21 +/- 0.08 parts per thousand. Samples deposited in a mainly limnic environment with oxygenated bottom water have a mean delta Fe-56 of +0.08 +/- 0.13 parts per thousand, which is identical to the mean Fe isotopic composition of igneous rocks and oxic marine sediments. In contrast, sediments that formed in brackish water under periodically euxinic conditions display significantly lighter Fe isotope signatures with a mean delta Fe-56 of -0.14 +/- 0.19 parts per thousand. Negative correlations of the delta Fe-56 values with the Fe/Al ratio and S content of the samples suggest that the isotopically light Fe in the periodically euxinic samples is associated with reactive Fe enrichments and sulfides. This is supported by analyses of pyrite separates from this unit that have a mean Fe isotopic composition of -1.06 +/- 0.20 parts per thousand for delta Fe-56. The supply of additional Fe with a light Fe isotopic signature can be explained with the shelf to basin Fe shuttle model. According to the Fe shuttle model, oxides and benthic ferrous Fe that is derived from dissimilatory iron reduction from shelves is transported and accumulated in euxinic basins. The data furthermore suggest that the euxinic water has a negative dissolved delta Fe-56 value of about -1.4 parts per thousand to -0.9 parts per thousand. If negative Fe isotopic signatures are characteristic for euxinic sediment formation, widespread euxinia in the past might have shifted the Fe isotopic composition of dissolved Fe in the ocean towards more positive delta Fe-56 values.
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| 2. |
- Vuorinen, Jaana Hode, et al.
(författare)
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Nb-, Zr- and LREE-rich titanite from the ALnö alkaline complex: Crystal chemistry and its importance as a petrogenetic indicator
- 2005
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Ingår i: Lithos. - : Elsevier B.V.. - 0024-4937 .- 1872-6143. ; 83:1-2, s. 128-142
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Tidskriftsartikel (refereegranskat)abstract
- Titanite occurs as an accessory phase in melteigite, ijolite and nepheline syenite from the Alnö alkaline intrusion and is typically associated with Ti-andradite and calcite±perovskite. Titanite from 7 samples was investigated using microanalytical techniques including EMPA, 57Fe Mössbauer spectroscopy, powder X-ray diffractometry and FTIR-spectroscopy. A common feature of the analysed titanite is high amounts of Nb2O5 (up to 7.3 wt.%), ZrO2 (up to 2.8 wt.%) and LREE2O3 (up to 3.9 wt.%), and significant amounts of Al2O3+Fe2O3 (up to 4.3 wt.%). Important substitutions are consequently (i) 2[7]Ca→[7]Na++[7]LREE3+, (ii) [7]Ca2++[6]Ti4+→[7]LREE3++[6](Al, Fe3+), (iii) 2[6]Ti4+→[6]M5++[6](Al, Fe3+). Zr is most likely accommodated into the structure through simple direct isovalent octahedral substitution for Ti, contrasting with other proposed, more complex models for Zr-incorporation in titanite. Stoichiometric calculations indicate all iron to be present as Fe3+ but 57Fe Mössbauer analyses show a small fraction (10%) of ferrous iron to be present as well. FTIR-spectroscopy indicate 0.14–0.26 wt.% H2O in the investigated titanites and X-ray diffraction data yield cell parameters close to the ideal synthetic end-member values. Chondrite normalised LREE patterns for the analysed titanites show (Ce+Pr)N>LaN similar to patterns reported from other occurrences and enrichment factors are typically in the order of 103–104. Comparison of whole rock Nb-, Zr- and LREE-contents with variations in modal amounts of trace element enriched titanite shows a significant effect which needs to be addressed when modeling magma evolution. The use of the prv–ttn assemblage for estimating silica-activity during crystallization of silica undersaturated alkaline rocks is discussed.
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| 3. |
- Holtstam, Dan, et al.
(författare)
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Ulfanderssonite-(Ce), a new Cl-bearing REE silicate mineral species from the Malmkärra mine, Norberg, Sweden
- 2017
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Ingår i: European journal of mineralogy. - : Schweizerbart. - 0935-1221 .- 1617-4011. ; 29:6, s. 1015-1026
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Tidskriftsartikel (refereegranskat)abstract
- Ulfanderssonite-(Ce) is a new mineral (IMA 2016-107) from the long-abandoned Malmkärra iron mine, one of the Bastnäs-type Fe-rare earth element (REE) deposits in the Bergslagen ore region, central Sweden. It is named for Ulf B. Andersson, a Swedish geologist and petrologist. In the type specimen, the mineral occurs with västmanlandite-(Ce), bastnäsite-(Ce), phlogopite, talc, magnetite, pyrite, fluorbritholite-(Ce) and scheelite. Ulfanderssonite-(Ce) forms pinkish, translucent subhedral grains, 100-300 mu m, in aggregates up to 2 mm. Fracture is uneven, and there is an indistinct cleavage parallel (001). Mohs' hardness is 5-6, D-calc = 4.97 g cm(-3). Optically, ulfanderssonite-(Ce) is nonpleochroic, biaxial negative, with 2V(meas) = 55 degrees and n(calc) = 1.82. The ideal composition is Ce15CaMg2(SiO4)(10)(SiO3OH)(OH,F)(5)Cl-3. Electron microprobe and LA-ICP-MS chemical analyses yielded (in wt%) La2O3 11.87, Ce2O3 30.98, Pr2O3 3.99, Nd2O3 17.14, Sm2O3 2.81, Eu2O3 0.18, Gd2O3 1.15, Dy2O3 0.30, Tb2O3 0.10, Y2O3 1.11, CaO 2.26, FeO 0.02, MgO 1.97, P2O5 0.08, SiO2 19.13, H2Ocalc 1.07, F 1.09, Cl 2.89, O=(F, Cl) -1.10, sum 97.04. The five strongest powder X-ray diffraction lines are [I(%) d(obs) (angstrom) (hkl)]: 100 2.948 (- 421), 47 2.923 (204), 32 2.660 (- 225), 26 3.524 (40-1), 25 1.7601 (6-23). Ulfanderssonite-(Ce) is monoclinic, Cm, with a = 14.1403(8), b = 10.7430(7), c = 15.498(1) angstrom, b = 106.615(6)degrees and V = 2256.0 (2) angstrom 3 for Z = 2. The crystal structure has been solved by direct methods and refined to R-1 = 2.97% for 5280 observed reflections. It consists of a regular alternation of two layers, designated A and B, along the c-axis: A (ca. 9 angstrom thickness), with composition [(Ce8Ca) MgSi7O22(OH, F) 4](8+), and B (ca. 6.5 angstrom), with composition [Ce7MgSi4O21(OH, F)(2)Cl-3](8); the A layer is topologically and chemically closely related to cerite-(Ce). A FTIR spectrum shows strong absorption in the region 2850-3650 cm(-1), related to the presence of OH stretching bands. Ulfanderssonite-(Ce) is interpreted as a primary mineral at the deposit, along with the more common fluorbritholite-(Ce), formed by a magmatic-hydrothermal fluid with REE, Si, F and Cl ion complexes reacting with dolomite marble. The presence of ulfanderssonite-(Ce) is direct evidence of a Cl-rich mineral-forming aqueous solution, normally not reflected in the composition of skarn minerals in Bastnäs-type deposits.
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| 4. |
- Altieri, Alessandra, et al.
(författare)
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Dark-coloured Mn-rich overgrowths in an elbaitic tourmaline crystal from the Rosina pegmatite, San Piero in Campo, Elba Island, Italy: witness of late-stage opening of the geochemical system
- 2023
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Ingår i: Mineralogical magazine. - : Mineralogical Society. - 0026-461X .- 1471-8022. ; 87:1, s. 130-142
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Tidskriftsartikel (refereegranskat)abstract
- Multicoloured tourmalines from Elba Island, commonly display dark-coloured terminations due to incorporation of Fe, and also occasionally Mn. The mechanisms which led to the availability of these elements in the late-stage residual fluids are not yet completely understood. For this purpose, we investigated a representative tourmaline crystal found naturally in two fragments within a wide miarolitic cavity in the Rosina pegmatite (San Piero in Campo, Elba Island, Italy), and characterised by late-stage dark-coloured overgrowths. Microstructural and paragenetic observations, together with compositional and spectroscopic data (electron microprobe and optical absorption spectroscopy), provide evidence which shows that the formation of the dark-coloured Mn-rich overgrowths are the result of a pocket rupture. This event caused alteration of the cavity-coating spessartine garnet by highly-reactive late-stage cavity fluids by leaching processes, with the subsequent release of Mn to the residual fluids. We argue that the two fragments were originally a single crystal, which underwent natural breakage followed by the simultaneous growth of Mn-rich dark terminations at both breakage surfaces. This conclusion supports the evidence for a pocket rupture event, responsible for both the shattering of the tourmaline crystal and the compositional variation of the cavity-fluids related to the availability of Mn, which was incorporated by the tourmaline crystals. Additionally, a comparison of the dark overgrowths formed at the analogous and the antilogous poles, provides information on tourmaline crystallisation at the two different poles. The antilogous pole is characterised by a higher affinity for Ca, F and Ti, and a selective uptake of Mn2+, even in the presence of a considerable amount of Mn3+ in the system. This uneven uptake of Mn ions resulted in the yellow–orange colouration of the antilogous overgrowth (Mn2+ dependent) rather than the purple-reddish colour of the analogous overgrowths (Mn3+ dependent).
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| 5. |
- Fehr, Manuela A., et al.
(författare)
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Iron enrichments and Fe isotopic compositions of surface sediments from the Gotland Deep, Baltic Sea
- 2010
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Ingår i: Chemical Geology. - : Elsevier BV. - 0009-2541 .- 1872-6836. ; 277:3-4, s. 310-322
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Tidskriftsartikel (refereegranskat)abstract
- Recent sediments from the Gotland Deep display enrichments in reactive Fe, associated with elevated Fe/Al ratios and light Fe isotopic signatures of the bulk sediments that are indicative of euxinic (anoxic and sulfidic) conditions. These enrichments can be explained by the Fe shuttle model where benthic Fe is transported from the shelf to the euxinic basin and transferred to the sediments by pyrite precipitation in the sulfidic water. The data provide evidence that the Fe shuttle at present results in accumulations of Fe that are larger compared to Fe enrichments during the Litorina Sea stage in the Gotland Deep probably caused by an increase of the benthic Fe flux from the shelf to the basin. The derived Fe enrichments are also larger compared to those in recent Black Sea sediments, which likely reflects the larger shelf to basin ratio of the Gotland Deep compare to the Black Sea. The Fe isotope data show no correlation with the organic C content of the samples indicating that the negative Fe isotope signatures are not associated with organic materials, as was suggested as an alternative explanation for the origin of the isotopically light Fe in sediments from the Litorina Sea stage. Conversely, pyrites carry the negative Fe isotopic signature of the sediments, which supports the Fe shuttle model. Variations in the abundance and Fe isotopic signature of reactive Fe and pyrite with depth suggest that syngenetically formed pyrite in the sulfidic water column has a less negative Fe isotopic composition compared to diagenetically produced pyrite.
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| 6. |
- Grew, Edward S., et al.
(författare)
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Fluor-elbaite, lepidolite and Ta–Nb oxides from a pegmatite of the 3000Ma Sinceni Pluton, Swaziland: evidence for lithium–cesium–tantalum (LCT) pegmatites in the Mesoarchean
- 2018
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Ingår i: European journal of mineralogy. - : Schweizerbart. - 0935-1221 .- 1617-4011. ; 30:2, s. 205-218
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Tidskriftsartikel (refereegranskat)abstract
- Mineral evolution is concerned with the timing of mineral occurrences, such as the earliest reported occurrences in the geologic record. Minerals containing essential Li have not been reported from rocks older than ca. 3000 Ma, thus the lithian tourmaline (fluor-elbaite) and mica (lepidolite) assemblage from a pegmatite near Zishineni associated with the ca. 3000Ma Sinceni Pluton presents unusual interest. Fluor-elbaite (0.75–0.98 F per formula unit) forms green crystals up to 50mm long. Spindle stage measurements give ω = 1.652(1), ε = 1.627(1) (589.3 nm). Optical absorption spectroscopy shows Fe and Mn are divalent; infra-red spectroscopy demonstrates the presence of Li and indicates the presence of (OH) at both the (OH) sites. Electron microprobe analysis of 330 points on several prisms, the largest of which is zoned in Fe and Ca, gives the following average and standard deviations in wt%: SiO2 37.29 (0.26), TiO2 0.05 (0.05), Al2O3 38.14 (0.35), Cr2O3 0 (0.02), MgO 0.02 (0.01), MnO 3.57 (0.25), FeO 2.48 (0.60), Na2O 2.48 (0.09), K2O 0.03 (0.12), CaO 0.77 (0.21), F 1.80 (0.11), Cl 0 (0.01) wt%. Nuclear reaction analyses gave Li2O 0.91 (0.04) and B2O3 10.55 (0.45). The empirical formula of fluor-elbaite was determined by integrating crystal-chemical data from electron microprobe analysis, nuclear reaction analysis, crystal structure refinement using X-ray diffraction, infra-red and optical absorption spectroscopy:X(□0.09Na0.77K0.01Ca0.13)Σ1.00 Y(□0.35Li0.59Mn2+0.49Fe2+0.33Al1.23Ti0.01)Σ3.00Al6(Si6O18)(BO3)3O3(OH)3O1[F0.92(OH)0.08]Σ1.00. The crystal structure of fluor-elbaite was refined to statistical indices R1 for 1454 reflections ∼2% using MoKa X-ray intensity data. Structural data confirm the presence of significant vacancies at the Y site. Micas include lepidolite in flakes several millimeters across that are veined and overgrown by fine-grainedmuscovite. Silica and (FeO+MnO) increase, and Al decreases with F, all giving tight linear fits for both micas taken together, suggesting bothmicas can be regarded as interstratified muscovite and lithium mica consisting of 35.2 wt% masutomilite containing nearly equal amounts of Mn and Fe, 52.8 wt% polylithionite and 11.9 wt% trilithionite. Muscovite and lepidolite contain <0.2 wt% and 0.7–2.25 wt% Cs2O and 1.0–1.1 wt% and 1.4–1.5wt% Rb2O, respectively. Other minerals include spessartine (e.g., Sps93Alm4Grs3) in scattered grains up to 0.5mm across and monazite.Oxides occur sparsely in muscovite, rarely in lepidolite, as grains up to 11 mm long, including fluorcalciomicrolite, columbite-(Mn) withNb>Ta, hübnerite(?) and a possible Pb-bearing microlite (Ta>Nb). The oxides, together with the muscovite, are interpreted to be related to later hydrothermal reworking of the primary lepidolite–fluorelbaite assemblage. Given the 2990 ± 43MaRb–Sr isochron and 3074 ± 4Ma evaporation Pb–Pb ages reported for the Sinceni Pluton and Rb/Sr mineral ages ranging from 2906 ± 31Ma to 3072 ± 33Ma reported for the pegmatites, the fluor-elbaite–cesian lepidolite–fluorcalciomicrolite-bearing pegmatite is the first reported occurrence of a lithian tourmaline and lepidolite in the geologic record, as well as one of the two earliest known examples of the lithium–cesium–tantalum (LCT) family of pegmatites. The Sinceni magma is most plausibly derived from a metasedimentary source by intrusion of hot mantle melts into the crust from below, thereby indicating that a “mature” continental crust existed in the Kaapvaal craton at ca. 3000 Ma.
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| 7. |
- Hålenius, Ulf, et al.
(författare)
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Mangani-pargasite, NaCa2(Mg4Mn3+)(Si6Al2)O22(OH)2, a new mineral species of the amphibole supergroup
- 2020
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Ingår i: Periodico di Mineralogia. - : EDIZIONI NUOVA CULTURA. - 0369-8963 .- 2239-1002. ; 89:2, s. 125-131
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Tidskriftsartikel (refereegranskat)abstract
- Mangani-pargasite, ideally NaCa2(Mg4Mn3+)(Si6Al2)O-22(OH)(2), is a new mineral species of the calcium amphibole subgroup of the amphibole supergroup. The type specimen was found on the mine dump of the Langban Fe-Mn-(Ba-As-Pb-Sb) deposit in Varmland, Sweden. Crystal chemical analyses resulted in the empirical chemical formula: (A)(Na0.90Pb0.07K0.03)(Sigma 1.00)(B)(Ca1.93Mn0.072+)(Sigma 2.00)(C)(Mg4.25Mn0.393+Al0.26Fe0.103+)Sigma(T)(5.00)(Si6.35Al1.65)Sigma 8.00O22W(OH)(2). In order to complete the description of this newly approved (IMA 2018-151) mineral we report here additional data to those published in papers by Jonsson and Halenius (2010) and Halenius and Bosi (2012). Mangani-pargasite is biaxial positive, with alpha=1.635(5), beta=1.645(5), gamma=1.660(5) and the measured optic angle 2V is 85(5)degrees. The dispersion is weak (r>v), and the optic orientation is: Y parallel to b; Z<^>c=25(3)degrees. Mangani-pargasite is red to brownish red with weak pleochroism; X=pale reddish brown, Y=pale reddish brown and Z=pale brownish red; X approximate to Y>Z. The unit-cell parameters are a=9.9448(5), b=18.0171(9), c=5.2829(3) angstrom, beta=105.445(3)degrees, V=912.39(9) angstrom(3), Z=2, space group C2/m. The ten strongest reflections in the X-ray powder diffraction pattern [d-values in angstrom, I, (h k l)] are: 8.420, 29, (110); 3.368, 17, (131), 3.279, 49, (240); 3.141, 100, (310); 2.817, 44, (33 0); 2.698, 21, (151); 2.389, 18, (350); 1.904, 29, (510); 1.650, 22, (461) and 1.448, 46, (661).
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| 8. |
- Nilsson, Charlotta, et al.
(författare)
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A nuclear geochemical analysis system for boron quantification using a focused ion beam
- 2017
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Ingår i: Journal of Radioanalytical and Nuclear Chemistry. - : Springer Science and Business Media LLC. - 0236-5731 .- 1588-2780. ; 311:1, s. 355-364
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Tidskriftsartikel (refereegranskat)abstract
- Ion beam analysis has for decades been used as a tool for geochemical analysis of trace elements using both X-rays (particle induced X-ray emission) and nuclear reaction analysis. With the geoanalytical setup at the Lund Ion Beam Analysis Facility, the boron content in geological samples with a spatial resolution of 1 µm is determined through nuclear reaction analysis. In the newly upgraded setup, a single detector has been replaced by a double sided silicon strip detector with 2048 segments. After optimization, boron content in geological samples as low as 1 µg g−1 can be measured.
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| 9. |
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| 10. |
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