The Raman spectra of five
B-bearing tourmalines of different composition synthesized at 700 °C/4.0 GPa (including first-time synthesis of Na-Li-
B-tourmaline, Ca-Li-
B-tourmaline, and Ca-bearing ◻-
...B-tourmaline) reveal a strong correlation between the tetrahedral boron content and the summed relative intensity of all OH-stretching bands between 3300–3430 cm
. The band shift to low wavenumbers is explained by strong O3-H···O5 hydrogen bridge bonding. Applying the regression equation to natural
B-bearing tourmaline from the Koralpe (Austria) reproduces the EMPA-derived value perfectly EMPA: 0.67(12)
B pfu vs. Raman: 0.66(13)
B pfu. This demonstrates that Raman spectroscopy provides a fast and easy-to-use tool for the quantification of tetrahedral boron in tourmaline. The knowledge of the amount of tetrahedral boron in tourmaline has important implications for the better understanding and modeling of B-isotope fractionation between tourmaline and fluid/melt, widely used as a tracer of mass transfer processes.
Here we report on the oxygen isotope compositions of four proposed apatite reference materials (chlorapatite MGMH#133648 and fluorapatite specimens MGMH#128441A, MZ‐TH and ES‐MM). The samples were ...initially screened for 18O/16O homogeneity using secondary ion mass spectrometry (SIMS) followed by δ18O determinations in six gas source isotope ratio mass spectrometry laboratories (GS‐IRMS) using a variety of analytical protocols for determining either phosphate‐bonded or “bulk” oxygen compositions. We also report preliminary δ17O and Δ’17O data, major and trace element compositions collected using EPMA, as well as CO32− and OH− contents in the apatite structure assessed using thermogravimetric analysis and infrared spectroscopy. The repeatability of our SIMS measurements was better than ± 0.25 ‰ (1s) for all four materials that cover a wide range of 103δ18O values between +5.8 and +21.7. The GS‐IRMS results show, however, a significant offset of 103δ18O values between the “phosphate” and “bulk” analyses that could not be correlated with chemical characteristics of the studied samples. Therefore, we provide two sets of working values specific to these two classes of analytical methodologies as well as current working values for SIMS data calibration.
Key Points
Four potential apatite reference materials have been characterised for oxygen isotopes by SIMS and six GS‐IRMS laboratories.
Determined δ18O values are method‐specific and show a significant offset between the laboratories employing differing analytical protocols.
Non‐systematic variations between the datasets do not correlate with chemical characteristics of the studied samples.
The ability to precisely constrain the physical–chemical conditions of serpentinization, such as temperature and fluid source, is limited by the accuracy of calibrations for oxygen isotope ...fractionation between serpentine and water – i.e., 1000 lnα(serpentine-water) – which disagree by up to 20‰ when extrapolated to T < 200 °C. In this study, we present a new empirical calibration of 1000 lnα(serpentine-water) aiming to improve applications of oxygen isotope geochemistry to very low-T serpentinization (T < 100 °C). We used the high-spatial resolution capabilities of Secondary Ion Mass Spectrometry (SIMS) to analyze oxygen isotope ratios in mineral pairs of calcite + serpentine, quartz + serpentine and talc + serpentine co-crystallized at scales ≤ 50 μm in six serpentinite samples from the Samail ophiolite (Oman). SIMS analysis shows that the mineral pairs are relatively homogenous in oxygen isotope ratios with variability in δ18O values ≤2‰ (2 s). Clumped isotope thermometry and petrological constraints indicate crystallization temperatures from 25 to 100 °C for the investigated samples. These independent constraints on temperature allowed us to derive 1000 lnα(serpentine-water) by combining Δ18O(quartz-serpentine), Δ18O(talc-serpentine) and Δ18O(calcite-serpentine) measured by SIMS in the investigated samples with Δ18O(quartz-water), Δ18O(talc-water) and Δ18O(calcite-water) calibrations available in the literature. Our empirical calibration of 1000 lnα(serpentine-water) = 1.04 ± 0.20 (2SE) × 106/T2 (T in K), from T = 25 to 100 °C, is within uncertainty of former high-temperature empirical calibrations extrapolated to T < 100 °C and matches experimental calibrations when extrapolated to T = 250 °C. The new serpentine-water calibration enables more accurate reconstructions of fluid-rock interactions occurring during low-temperature serpentinization processes in various tectonic settings.
The presence of Ca-Mg-carbonates affects the melting and phase relations of peridotites and eclogites in the mantle, and (partial) melting of carbonates liberates carbon from the mantle to shallower ...depths. The onset and composition of incipient melting of carbonated peridotites and carbonated eclogites are influenced by the pure CaCO3-MgCO3-system making the understanding of the phase relations of Ca-Mg-carbonates fundamental in assessing carbon fluxes in the mantle. By performing high-pressure and high-temperature experiments, this study clarifies the suprasolidus phase relations of the nominally anhydrous CaCO3-MgCO3-system at 6 GPa showing that Ca-Mg-carbonates will (partially) melt for temperatures above ∼1300 °C. A comparison with data from thermodynamic modeling confirms the experimental results. Furthermore, partition coefficients for Li, Na, K, Sr, Ba, Nb, Y, and rare earth elements between calcite and dolomitic melt, Ca-magnesite and dolomitic melt, and magnesite and dolomitic melt are established. Experiments were performed at 6 GPa and between 1350 to 1600 °C utilizing a rotating multi-anvil press. Rotation of the multi-anvil press is indispensable to establish equilibrium between solids and carbonate liquid. Major and trace elements were quantified with EPMA and LA-ICP-MS, respectively. The melting temperature and phase relations of Ca-Mg-carbonates depend on the Mg/Ca-ratio. For instance, Ca-rich carbonates with a molar Mg/(Mg+Ca)-ratio (XMg) of 0.2 will transform into a dolomitic melt (XMg = 0.33-0.31) and calcite crystals (XMg = 0.19-0.14) at 1350-1440 °C. Partial melting of Mg-rich carbonates (XMg = 0.85) will produce a dolomitic melt (XMg = 0.5-0.8) and Ca-bearing magnesite (XMg = 0.89-0.96) at 1400-1600 °C. Trace element distribution into calcite and magnesite seems to follow lattice constraints for divalent cations. For instance, the compatibility of calcite (XMg = 0.14-0.19) for Sr and Ba decreases as the cation radii increases. Ca-Mg-carbonates are incompatible for rare earth elements (REEs), whereby the distribution between carbonates and dolomitic melt depends on the Mg/Ca ratio and temperature. For instance, at 1600 °C, partition coefficients between magnesite (XMg = 0.96) and dolomitic melt (XMg = 0.8) vary by two orders of magnitudes from 0.001 to 0.1 for light-REEs to heavy-REEs. In contrast, partition coefficients of REEs (and Sr, Ba, Nb, and Y) between magnesite (XMg = 0.89) and dolomitic melt (XMg = 0.5) are more uniform scattering marginal between ∼0.1-0.2 at 1400 °C.
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•Textural-chemical evolution of Fe-As-S sulfide minerals can be a pertinent approach to evaluate the sources of the different ore-forming fluids.•Gold precipitation occurs due to ...destabilization of Au-bisulfide complexes during the phase separation.•O-H isotope data suggest involvement of meteoric water during late- to post ore-stages.
The Zarshuran gold deposit (155 t Au, average grade: 2.63 g/t), NW Iran, provides a new paradigm for understanding the multicomponent ore-forming processes and metallogeny of gold during the evolution of hydrothermal fluids. It is characterized by auriferous quartz veins and gold coexisting with disseminated Fe-As-S sulfide minerals that are hosted in a sequence of Early Cambrian metasedimentary rocks. A complex paragenesis is defined by five sulfide stages: pre-ore stage pyrite (Py0), early ore-stage pyrite (Py1 and Py2), middle ore-stage pyrite (Py3a, Py3b, and Py3c), late ore-stage pyrite (Py4), and post ore-stage pyrite (Py5). Py0 with framboidal texture is characterized by relatively low concentrations of As, Au, Cu, and Sb, and has a broad range of negative δ34S values from −28.2 to −3.7 ‰, indicating microbial reduction of marine sulfate. Py1 and Py2 show porous texture with As-rich bright bands also having high Au (mean: 18.4 ppm). Similarly, narrow ranges in δ34S from −3.6 to +3.2 ‰ likely suggest a deep-seated magmatic sulfur source. In the middle ore-stage, Py3a cryptocrystalline cores have a range of positive δ34S (+5.4 to +26.7 ‰) values and high concentration of As(-Au), whereas later well-crystallized outer rim Py3c is Co(-Ni) rich, has a much more restricted δ34S range (−2.9 to +1.4 ‰), indicating an evolution of fluid composition from As-rich to Co-rich. Most of the gold (mean: 20.2 ppm) and trace elements (Hg, Ag, Sb, and Tl) were deposited in Py4, whose δ34S values (+5.4 to +26.7 ‰) show that ore fluid sulfur in this stage was mainly sourced from a mixture of magmatic sulfur with minor input of reduced sedimentary rocks. Low gold and trace element content with slightly negative δ34S values (–8.5 to –4.2 ‰) of Py5 show that they were likely formed from a metal-poor oxidizing fluid.
The mineralizing fluid system can be described as carbonic-aqueous with low to moderate salinity (3.2–15.1 wt% NaCl equiv.) and medium temperature of 285 to 317 °C (early ore-stage) and 255 to 290 °C (late ore-stage), which suggests that phase separation was responsible for gold precipitation during late ore-stage As-Hg-Sb sulfide veins. The δ18Ofluid ranges from −7.8 to +4.2 ‰, and the δD values for fluid inclusions in mineral range from −105 to −65 ‰, suggesting involvement of meteoric water during late- to post ore-stages. Our results indicate that the Zarshuran is a distal disseminated gold deposit formed during southward subduction of the Proto-Tethys oceanic lithosphere beneath the northern margin of Gondwanan terranes through the early Cambrian.
Secondary ion mass spectrometry was used to test the δ18O and δ34S nanogram‐scale homogeneity of a suite of candidate sulfate minerals, ultimately selecting three barite, two anhydrite, and two ...gypsum samples from the Royal Ontario Museum that have repeatabilities for their SIMS measurements of better than ±0.39‰ and ±0.37‰ (1s) for oxygen and sulfur isotope ratios, respectively. Metrological splits of each of the seven materials were sent to multiple gas source isotope ratio mass spectrometry laboratories in order to establish their absolute 18O/16O and 34S/32S ratios. The inter‐laboratory results of GS‐IRMS analyses yielded reasonably narrow ranges in δ18OVSMOW, whereas larger variations in δ34SVCDT values were found between the results from the gas source laboratories. All samples have good reproducibility within laboratories of GS‐IRMS 103δ18O values of between ±0.24‰ and ±0.44‰ (1s). The reproducibility within laboratories of GS‐IRMS 103δ34S values range from ±0.07‰ to ±0.99‰ (1s). Here we also discuss some of the current analytical limitations affecting these isotope‐mineral systems. A total of 256 metrological splits have been prepared from each of these seven materials; these aliquots will be made available to the global geochemical community.
Key points
Three barite, two anhydrite and two gypsum reference materials for in situ SIMS oxygen and sulfur isotope ratio measurements.
All seven materials have good measurement repeatability by SIMS ‐ better than ±0.39‰ and ±0.37‰ (1s) for oxygen and sulfur isotope ratios, respectively.
Good reproducibility of GS‐IRMS 103δ18O values between ±0.24‰ and ±0.44‰ (1s), whereas an acceptable reproducibility of GS‐IRMS 103δ34S values ranges from ±0.07‰ to ±0.99‰ (1s).
The crystal chemistry of tourmaline, XY
3
Z
6
(T
6
O
18
)(BO
3
)
3
V
3
W, has a strong influence on the structure and physical properties. Since tourmalines occur in a wide range of geological ...settings and have large temperature and pressure stability fields, the understanding of the relation between the tourmaline chemistry and thermal expansion allows for better thermodynamic modeling of geological processes. Here, we report dynamic and static thermal expansions as well as mode Grüneisen parameters studied by Raman spectroscopy and single-crystal X-ray diffraction data on several tourmaline species. In addition, oxidation processes in fluor-schorl and Fe
2+
-bearing elbaite were followed by Raman spectroscopy. Our results emphasize the role of Y-/Z-site occupancy disorder to reduce the local strains and demonstrate that small-size octahedrally coordinated cations perturb the topology of the SiO
4
rings, which in turn seems to enhance the anisotropic thermal-expansion response. In addition, it is shown that the temperature-dependent behavior of the
V
OH modes primarily depends on the occupancy of the Y site, whereas that of the
W
OH modes depends on the occupancy of the X site. High-temperature Raman experiments in air allowed to follow the oxidation of Fe
2+
to Fe
3+
in fluor-schorl by analyzing both the framework and OH-stretching phonon modes. It is further demonstrated that under the same conditions, no oxidation of iron is observed for Fe
2+
-bearing elbaite, which implies that at high oxygen fugacity, iron is only oxidized in tourmaline species with prevalent divalent cations at the Y site.
Knowledge of the composition of dissolved organic compounds as well as the main controls on their mobilization from natural organic matter is prerequisite for a comprehensive understanding of the ...fluid–rock interactions taking place in shale environments and coal seams over both geological and human timescales. In this study, black shales and coals from five different geological settings and covering the maturity range Ro=0.3–2.6% were extracted with deionized water. The dissolved organic carbon (DOC) yields were found to decrease rapidly with increasing diagenesis and remain low throughout catagenesis. Four different fractions of DOC have been qualitatively and quantitatively characterized in the study using size exclusion chromatography (SEC). Acetate is the dominant low molecular weight organic acid (LMWOA) in all extracts of shales and coals of bituminous rank. The concentrations of individual LMWOA also decrease with increasing maturity of the samples except for acetate extracted from the overmature Posidonia shale from the Haddessen well, which was influenced by hydrothermal brines. The positive correlation between the Oxygen Index (OI) and respective LMWOA yield indicates that OI is a significant factor influencing the extraction of organic acids from shales. The yields of both DOC and individual organic acids normalized to TOC are in the same order of magnitude for coals and shales with the same maturity. However, the extracts of coals tend to contain more aromatic compounds and the molecular masses of most constituents included in macromolecular fractions are higher than for shale extracts. These results suggested that different kerogen types show comparable amounts of DOC being extracted, but different DOC composition. Thus, both the origin of organic matter and thermal maturation progress during deposition has significant influence on water extract composition.
•Maturity of samples affects the concentration of DOC in water extracts.•Composition of dissolved organic matter is influenced by the kerogen types.•Acetate is the dominant LMWOAs in the water extracts of shale samples.•The concentration of LMWOAs in extracts is constrained by OI of shales and coals.•Hydrothermal processes might enhance the generation of acetate.
Patients with bariatric surgery often show poor long-term compliance to recommendations for prevention of nutrient deficiency but it is unclear which factors contribute. We investigated the ...associations of age, sex, and socioeconomic status (SES) with adherence to guideline recommendations on protein intake and micronutrient supplementation.
In a monocentric cross-sectional study we prospectively recruited patients with sleeve gastrectomy (SG) or Roux-en-Y gastric bypass (RYGB) and a minimum postoperative period of 6 months. Clinical and demographic data were obtained from the patients' medical files and by questionnaire. Patients reported on supplement usage, recorded their dietary intake for seven days and underwent physical examinations including blood testing.
We included 35 patients (SG: n = 25, RYGB: n = 10) with a mean (+SD) postoperative period of 20.2 (±10.4) months. Distributions of age, sex and SES were comparable between the SG and RYGB groups. Non-adherence to recommended protein intake was associated with age ≥ 50 years (p = 0.041) but not sex or SES. Protein intake inversely correlated with markers of obesity. There were no significant associations of age or sex with micronutrient supplementation. Only for vitamins A (p = 0.049) and B1 (p = 0.047) higher SES was associated with greater compliance. The only manifest deficiency associated with non-adherence to micronutrient supplementation was that for folic acid (p = 0.044).
In patients after bariatric surgery, those of older age and of lower SES might have a greater risk of unfavorable outcome and may require greater attention to micronutrient and protein supplementation.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
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