Sulfur Isotope Measurements Research Articles

A productivity collapse to end Earth’s Great Oxidation

It has been hypothesized that the overall size of-or efficiency of carbon export from-the biosphere decreased at the end of the Great Oxidation Event (GOE) (ca. 2,400 to 2,050 Ma). However, the timing, tempo, and trigger for this decrease remain poorly constrained. Here we test this hypothesis by studying the isotope geochemistry of sulfate minerals from the Belcher Group, in subarctic Canada. Using insights from sulfur and barium isotope measurements, combined with radiometric ages from bracketing strata, we infer that the sulfate minerals studied here record ambient sulfate in the immediate aftermath of the GOE (ca. 2,018 Ma). These sulfate minerals captured negative triple-oxygen isotope anomalies as low as ∼ -0.8‰. Such negative values occurring shortly after the GOE require a rapid reduction in primary productivity of >80%, although even larger reductions are plausible. Given that these data imply a collapse in primary productivity rather than export efficiency, the trigger for this shift in the Earth system must reflect a change in the availability of nutrients, such as phosphorus. Cumulatively, these data highlight that Earth's GOE is a tale of feast and famine: A geologically unprecedented reduction in the size of the biosphere occurred across the end-GOE transition.

Sulfur isotopes ratio of atmospheric carbonyl sulfide constrains its sources

Carbonyl sulfide (COS) is the major long-lived sulfur bearing gas in the atmosphere, and is used to estimate the rates of regional and global (both past and current) photosynthesis. Sulfur isotope measurements (34S/32S ratio, δ34S) of COS may offer a way for improved determinations of atmospheric COS sources. However, measuring the COS δ34S at the atmospheric concentrations of ~0.5 ppb is challenging. Here we present high-accuracy δ34S measurements of atmospheric COS done by gas chromatograph (GC) connected to a multicollector inductively coupled plasma mass spectrometer (MC-ICPMS), after pre-concentrating from 2-liters of air. We showed that the precision of COS δ34S measurement for gas standards is ≤0.2‰, and that N2 and CO2 in the gas standard mixture had no effect on the measured δ34S. Natural air samples were collected in Israel and in the Canary Islands. The COS δ34S values in both locations were found to be 13.2 ± 0.6‰, and are believed to represent the background tropospheric value. This δ34S value is markedly different from the previously reported value of 4.9‰. We estimate the expected isotopic signature of COS sources and sinks, and use the δ34S value of atmospheric COS we measured to estimate that ~48% of it originates from the ocean.

Sulfur cycle in the Valles Caldera volcanic complex, New Mexico – Letter 1: Sulfate sources in aqueous system, and implications for S isotope record in Gale Crater on Mars

Initial in situ sulfur (S) isotope measurements of the Martian bedrock in Gale Crater have revealed an unexpectedly wide range of δ34S values (−47 to +28‰). Generally, it is unclear what processes could have contributed to these large isotope fractionations. Therefore, we studied S sources and aqueous SO42− cycling in the Valles Caldera volcanic complex, New Mexico to better understand S isotope fractionations related to S degassing, hydrothermal activity, and low-temperature processes in aqueous environment. Overall, our study demonstrates that volcanic systems show large spatial heterogeneity in δ34S. Magmatic S sources are obvious in steam-dominated H2S degassing and precipitation of secondary minerals from hydrothermal fluids with low δ34S values of +0.9 ± 3‰. Locally, however, hydrothermal processes have resulted in more negative δ34S values in sulfide minerals (−18 to −4‰) and more positive δ34S values in sulfate minerals (−1 to +3‰). Major aqueous SO42− sources are oxidation of H2S from modern hydrothermal gas emission, and oxidation and dissolution of sulfide and sulfate minerals present in the hydrothermally altered bedrock and crater-lake sediments. The δ34S of aqueous SO42− in surface water and groundwater varies widely (−8 to +5‰) and is similar to major S endmembers that undergo oxidation and/or dissolution by active hydrological system. Minor SO42− contributions with more positive δ34S values (+9 to +14‰) come from deeply circulating geothermal fluids and negligible amounts from atmospheric deposition (+5 to +7‰ in snow). Elevated SO42− contents are mainly associated with modern and past H2S emissions and oxidations near the surface. On regional scale, however, most of the intracaldera bedrock is S-depleted, thus the SO42− contents are usually low in the surface aquatic system and younger sedimentary lake deposits formed at times of negligible near surface hydrothermal activity. In general, magmatic-hydrothermal processes apparently cause the largest δ34S variation in S-bearing minerals on volcanic terrains. Therefore, we infer that the measured wide range of δ34S values in the Gale sediments by the Curiosity rover on Mars can be explained by S isotope composition of magmatic-hydrothermal sulfide and sulfate minerals that were present in the initial igneous/volcanic rocks prior to crater formation. Later aqueous processes involved oxidation and dissolution of S minerals initially present in these rocks and led to subsequent formation of diagenetic fluids and alteration products enriched in SO42− with relatively large δ34S variation. Additionally, physical erosion, transport and deposition of detrital hydrothermal S minerals from igneous/volcanic rocks might be in part responsible for the measured wide range of δ34S in Gale Crater. These unique S isotope results, measured in situ on another planet for the first time, imply the importance of magmatic-hydrothermal fluids in S transport on early Mars and their subsequent alteration in low-temperature aqueous environments.

High-sensitivity sulfur isotopic measurements for Antarctic ice core analyses.

Sulfur is widely distributed in nature, and sulfur isotopic measurements have been applied to elucidate the origin and transport of sulfuric compounds in the lithosphere, biosphere, and atmosphere. Analyses of samples containing small amounts of sulfur, such as the Antarctic ice core samples analyzed herein, require a high-sensitivity analytical method. We developed a high-sensitivity sulfur isotopic ratio (δ34 S value) analytical system equipped with an elemental analyzer, a cryo-flow device, and an isotope ratio mass spectrometer, and established a measurement and calibration procedure. Using this system, we precisely measured the δ34 S values of samples containing 5-40 nmol sulfate. Test runs were performed on samples from the Antarctic shallow ice core DF01, and the data obtained were consistent with those obtained by previous studies that reported δ34 S values for Antarctic snow and ice samples of more than 200 g (containing more than 150 nmol sulfate). Among the analyzed samples, one showed a peak sulfate concentration in its depth profile that is considered to have resulted from a large volcanic eruption. The δ34 S value obtained at that depth in the sample was distinct from values at other depths and consistent with reported values for volcanic sulfates. The analytical system developed herein is a powerful tool for trace sulfur isotopic analyses. The results obtained from the DF01 ice core samples are the first step towards elucidating high-time-resolution (less than 1 year) paleo-environmental changes by sulfur isotopic analyses.

Off‐Mount Calibration and One New Potential Pyrrhotite Reference Material for Sulfur Isotope Measurement by Secondary Ion Mass Spectrometry

Sulfur isotope measurements in three sulfide (two pyrite and one pyrrhotite) samples on two epoxy mounts showed that the mount‐to‐mount variation of raw δ34S values was negligible when secondary ion mass spectrometry (SIMS) analytical settings remained stable. In consequence, an off‐mount calibration procedure for SIMS sulfur isotope analysis was applied in this study. YP136 is a pyrrhotite sample collected from northern Finland. Examination of thin sections with a polarising microscope, backscattered electron image analyses and wavelength dispersive spectrometry mapping showed that the sample grains display no internal growth or other zoning. A total of 318 sulfur isotope (spot) measurements conducted on more than 100 randomly selected grains yielded highly consistent sulfur isotope ratios. The repeatability of all the analytical results of 34S/32S was 0.3‰ (2s, n = 318), which is the same as that of the well‐characterised pyrite reference materials PPP‐1 and UWPy‐1. Its δ34S value determined by gas mass spectrometry was 1.5 ± 0.1‰ (2s, n = 11), which agrees with the SIMS data (1.5 ± 0.3‰, 2s) calibrated by pyrrhotite reference material Po‐10. Therefore, YP136 pyrrhotite is considered a candidate reference material for in situ sulfur isotope determination.

Multitechnique investigation of sulfur phases in the corrosion product layers of iron corroded in long‐term anoxic conditions: From micrometer to nanometer scale

The understanding of anoxic corrosion mechanism is essential to develop predictive models targeting to optimize extraction and conservation operations as well as aging behavior of industrial or cultural heritage ferrous objects. The corrosion product layers issued from carbonated anoxic environment of iron often contain iron sulfides, as pyrite FeS2, greigite Fe3S4, and mackinawite FeS, mixed at the submicron scale, and their presence strongly impacts the corrosion processes. The determination of their spatial arrangement in corrosion product layer directly informs about their origin (bacterial or inorganic) and, so, about the corrosion mechanisms. Previous studies have displayed that sulfur isotopic measurements using nano‐Secondary Ion Mass Spectrometry (SIMS) are particularly relevant to discriminate between biotic or abiotic origin of iron sulfides. But this technique does not enable to correlate this origin to the nature of sulfide compounds. In this work, an innovative approach combining μ‐Raman spectroscopy (structural identification) for sulfide compounds localization at micrometric scale and nano‐Auger spectroscopy (chemical diagnostic) at higher spatial resolution is presented. This multi‐technique methodology is detailed and its capabilities evaluated on an archeological system. Auger spectra of pure iron sulfides phases (pyrite, greigite, and mackinawite) are obtained and, by considering the derivative spectra of Fe‐MVV and of S‐LVV spectral regions, evidence‐specific signatures for each phase, and so, the possibility to differentiate them. This result enables to propose a complete determination of the iron sulfides mix by coupling nano‐SIMS and nano‐Auger to get a complete knowledge of the role of iron sulfides in the anoxic corrosion of ferrous objects.

Five-S-isotope evidence of two distinct mass-independent sulfur isotope effects and implications for the modern and Archean atmospheres

The signature of mass-independent fractionation of quadruple sulfur stable isotopes (S-MIF) in Archean rocks, ice cores, and Martian meteorites provides a unique probe of the oxygen and sulfur cycles in the terrestrial and Martian paleoatmospheres. Its mechanistic origin, however, contains some uncertainties. Even for the modern atmosphere, the primary mechanism responsible for the S-MIF observed in nearly all tropospheric sulfates has not been identified. Here we present high-sensitivity measurements of a fifth sulfur isotope, stratospherically produced radiosulfur, along with all four stable sulfur isotopes in the same sulfate aerosols and a suite of chemical species to define sources and mechanisms on a field observational basis. The five-sulfur-isotope and multiple chemical species analysis approach provides strong evidence that S-MIF signatures in tropospheric sulfates are concomitantly affected by two distinct processes: an altitude-dependent positive 33S anomaly, likely linked to stratospheric SO2 photolysis, and a negative 36S anomaly mainly associated with combustion. Our quadruple stable sulfur isotopic measurements in varying coal samples (formed in the Carboniferous, Permian, and Triassic periods) and in SO2 emitted from combustion display normal 33S and 36S, indicating that the observed negative 36S anomalies originate from a previously unknown S-MIF mechanism during combustion (likely recombination reactions) instead of coal itself. The basic chemical physics of S-MIF in both photolytic and thermal reactions and their interplay, which were not explored together in the past, may be another ingredient for providing deeper understanding of the evolution of Earth's atmosphere and life's origin.

Stable sulfur isotope measurements to trace the fate of SO2 in the Athabasca oil sands region

Abstract. Concentrations and δ34S values for SO2 and size-segregated sulfate aerosols were determined for air monitoring station 13 (AMS 13) at Fort MacKay in the Athabasca oil sands region, northeastern Alberta, Canada as part of the Joint Canada-Alberta Implementation Plan for Oil Sands Monitoring (JOSM) campaign from 13 August to 5 September 2013. Sulfate aerosols and SO2 were collected on filters using a high-volume sampler, with 12 or 24 h time intervals. Sulfur dioxide (SO2) enriched in 34S was exhausted by a chemical ionization mass spectrometer (CIMS) operated at the measurement site and affected isotope samples for a portion of the sampling period. It was realized that this could be a useful tracer and samples collected were divided into two sets. The first set includes periods when the CIMS was not running (CIMS-OFF) and no 34SO2 was emitted. The second set is for periods when the CIMS was running (CIMS-ON) and 34SO2 was expected to affect SO2 and sulfate high-volume filter samples. δ34S values for sulfate aerosols with diameter D>0.49 µm during CIMS-OFF periods (no tracer 34SO2 present) indicate the sulfur isotope characteristics of secondary sulfate in the region. Such aerosols had δ34S values that were isotopically lighter (down to −5.3 ‰) than what was expected according to potential sulfur sources in the Athabasca oil sands region (+3.9 to +11.5 ‰). Lighter δ34S values for larger aerosol size fractions are contrary to expectations for primary unrefined sulfur from untreated oil sands (+6.4 ‰) mixed with secondary sulfate from SO2 oxidation and accompanied by isotope fractionation in gas phase reactions with OH or the aqueous phase by H2O2 or O3. Furthermore, analysis of 34S enhancements of sulfate and SO2 during CIMS-ON periods indicated rapid oxidation of SO2 from this local source at ground level on the surface of aerosols before reaching the high-volume sampler or on the collected aerosols on the filters in the high-volume sampler. Anti-correlations between δ34S values of dominantly secondary sulfate aerosols with D< 0.49 µm and the concentrations of Fe and Mn (r = −0.80 and r = −0.76, respectively) were observed, suggesting that SO2 was oxidized by a transition metal ion (TMI) catalyzed pathway involving O2 and Fe3+ and/or Mn2+, an oxidation pathway known to favor lighter sulfur isotopes. Correlations between SO2 to sulfate conversion ratio (F(s)) and the concentrations of α-pinene (r = 0.85), β-pinene (r = 0.87), and limonene (r = 0.82) during daytime suggests that SO2 oxidation by Criegee biradicals may be a potential oxidation pathway in the study region.

Disentangling Diagenesis From the Rock Record: An Example From the Permo‐Triassic Wordie Creek Formation, East Greenland

AbstractThe measurement of isotope ratios in sedimentary rocks deposited over geological time can provide key insights to past environmental change over important intervals in the past. However, it is important to be aware that secondary alteration can overprint the original isotopic records. We demonstrate this principle using high‐resolution carbon, sulfur, and oxygen isotope measurements in organic carbon, pyrite, and carbonate minerals (δ13Corg, δ34Spyr, δ34SCAS, δ13Ccarb, and δ18Ocarb) and kerogen analyses (HI and OI) from the Wordie Creek Formation, East Greenland. These sediments were initially deposited across the Permo‐Triassic transition, but as we will show, the carbonate record has been altered by interaction with meteoric water significantly after initial deposition. Comparison of the better preserved organic carbon and pyrite records with a proximal Permo‐Triassic sequence reveals significant pyrite‐sulfur isotope variability across the Permo‐Triassic transition. This regional heterogeneity argues against basin‐wide euxinia and instead suggests localized changes in sulfur fractionation in response to variations in organic carbon flux. This hypothesis can be used to explain seemingly inconsistent regional trends in other sulfur isotopes across the Permo‐Triassic transition.

Unraveling multiple phases of sulfur cycling during the alteration of ancient ultramafic oceanic lithosphere

Ultramafic-hosted hydrothermal systems – characterized by ongoing serpentinization reactions – exert an important influence on the global sulfur cycle. Extensive water-rock interaction causes elemental exchange between seawater and the oceanic lithosphere, effectively removing sulfate from seawater through both abiogenic and biogenic processes. Here, we use bulk rock multiple sulfur isotope signatures (32S, 33S, 34S) and in situ sulfide analyses together with petrographic observations to track the sulfur cycling processes and the hydrothermal evolution of ancient peridotite-hosted hydrothermal systems. We investigate serpentinized peridotites from the Northern Apennine ophiolite in Italy and the Santa Elena ophiolite in Costa Rica and compare those with the Iberian Margin (Ocean Drilling Program (ODP) Leg 149 and 173) and the 15°20′N Fracture Zone along the Mid-Atlantic Ridge (ODP Leg 209).In situ measurements of sulfides in the Northern Apennine serpentinites preserve a large range in δ34Ssulfide of −33.8 to +13.3‰ with significant heterogeneities within single sulfide grains and depending on mineralogy. Detailed mineralogical investigation and comparison with bulk rock Δ33Ssulfide and in situ δ34Ssulfide data implies a thermal evolution of the system from high temperatures (∼350 °C) that allowed thermochemical sulfate reduction and input of hydrothermal sulfide to lower temperatures (<120 °C) that permitted microbial activity. The change in temperature regime is locally preserved in individual samples and correlates with the progressive uplift and exposure of mantle rock associated with detachment faulting along a mid-ocean ridge spreading center. The Santa Elena peridotites preserve distinct signatures for fluid circulation at high temperatures with both closed system thermochemical sulfate reduction and input of mafic-derived sulfur. In addition, the peridotites provide strong evidence that low Ca2+ concentrations in peridotite-hosted systems can limit sulfate removal during anhydrite precipitation at temperatures above 150 °C. This may play a central role for the availability of sulfate to microbial communities within these systems. Overall, the combined application of in situ and bulk rock multiple sulfur isotope measurements with petrographic observations allows us to resolve the different episodes of sulfur cycling during alteration of the oceanic lithosphere and the temporal changes between abiogenic and biogenic processes that control the sulfur cycling in these systems.

Improved analytical techniques of sulfur isotopic composition in nanomole quantities by MC-ICP-MS

We propose an improved method for precise sulfur isotopic measurements by multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS) in conjunction with a membrane desolvation nebulization system. The problems of sulfur loss through the membrane desolvation apparatus are carefully quantified and resolved. The method overcomes low intrinsic sulfur transmission through the instrument, which was initially 1% when operating at a desolvation temperature of 160 °C. Sulfur loss through the membrane desolvation apparatus was resolved by doping with sodium. A Na/S ratio of 2 mol mol−1 produced sulfur transmissions with 98% recovery. Samples of 3 nmol (100 ng) sulfur achieved an external precision of ±0.18‰ (2 SD) for δ34S and ±0.10‰ (2 SD) for Δ33S (uppercase delta expresses the extent of mass-independent isotopic fractionation). Measurements made on certified reference materials and in-house standards demonstrate analytical accuracy and reproducibility. We applied the method to examine microbial-induced sulfur transformation in marine sediment pore waters from the sulfate-methane transition zone. The technique is quite versatile, and can be applied to a range of materials, including natural waters and minerals.

Preparation of standards for in situ sulfur isotope measurement in sulfides using femtosecond laser ablation MC-ICP-MS

We show the way to synthesize chalcopyrite glass for in situ sulfur isotope measurements using fsLA-MC-ICP-MS.

How sulfate-driven anaerobic oxidation of methane affects the sulfur isotopic composition of pyrite: A SIMS study from the South China Sea

Sulfate-driven anaerobic oxidation of methane (SO4-AOM) in marine sediments commonly leads to the precipitation of pyrite. It is, however, frequently challenging to unequivocally unravel the entire history of pyritization, because of the common coexistence of SO4-AOM derived pyrite with pyrite resulting from organiclastic sulfate reduction (OSR). To better understand how SO4-AOM affects pyritization in methane-bearing sediments and how this can be identified, we applied secondary ion mass spectroscopy (SIMS) to analyze the sulfur isotope composition (δ34S) of authigenic pyrite in addition to sulfur isotope measurements of bulk sulfide and hand-picked pyrite aggregates from the two seafloor sites, HS148 and HS217, in the Shenhu seepage area, South China Sea. Authigenic, mostly tubular pyrite aggregates from these sites consist of three types of pyrite: framboids, zoned aggregates with radial overgrowths surrounding a framboidal core, and euhedral pyrite crystals. Framboids with low SIMS δ34S values (as low as −41.6‰ at HS148, and −38.8‰ at HS217) are dispersed throughout the cores, but are especially abundant in the shallow part of the sedimentary column (i.e. above 483cmbsf in HS148; above 670cmbsf in HS217). These patterns are interpreted to reflect the dominance of OSR during early diagenetic processes in the shallow sediments. With increasing depth, both δ34S values of bulk sulfide minerals and hand-picked pyrite aggregates increase sharply at 483cmbsf in core HS148, and at 700cmbsf in core HS217, respectively. Radial pyrite overgrowths and euhedral crystals become abundant at depth typified by high δ34S values for hand-picked pyrite. Moreover, SIMS analysis reveals an extreme variability of δ34S values for the three pyrite types on a small scale in these zones. Besides some moderately 34S enriched framboids, most of the overgrowths and euhedral crystals display extremely high SIMS δ34S values (as high as +114.8‰ at HS148, and +74.3‰ at HS217), representing the heaviest stable sulfur isotope composition of pyrite ever reported to the best of our knowledge. Such an abrupt and extreme increase in δ34Spyrite values with depth is best explained by an enrichment of 34S in the pool of dissolved sulfide caused by SO4-AOM in the sulfate methane transition zone (SMTZ). The increase in δ34S values from framboidal cores to overgrowth layers and euhedral crystals indicates continuous, and finally near to complete exhaustion of dissolved sulfate at the SMTZ following a Rayleigh distillation process. SO4-AOM allowed for subsequent growth of later stage pyrite over the initial framboids, part of which formed earlier and at shallower depth by OSR. The combination of a detailed petrographic study of authigenic pyrite with SIMS analysis of stable sulfur isotopes in organic-rich strata proves to be a powerful tool for reconstructing the dynamics of sulfur cycling in modern and, potentially, ancient sedimentary sequences.

Geochronologic (Re[sbnd]Os) and fluid-chemical constraints on the formation of the Mesoproterozoic-hosted Nanisivik Zn[sbnd]Pb deposit, Nunavut, Canada: Evidence for early diagenetic, low-temperature conditions of formation

The age and origin of the past-producing Nanisivik carbonate-hosted ZnPb deposit in Nunavut, Canada, have been controversial for decades. Various direct and indirect dating methods have produced results ranging from Mesoproterozoic to Ordovician in age, and previous studies of the mineralising fluids have suggested that the fluids were anomalously hot (>150°C). This study combines ReOs (pyrite) geochronology, in-situ sulphur isotope analysis, and fluid inclusion analysis to refine both the timing of mineralisation and the nature of mineralising fluids. ReOs pyrite analysis shows that the Nanisivik deposit formed ca. 1.1Ga, broadly similar to the depositional age of the host rock and with the Grenville orogeny, making it one of few known Precambrian carbonate-hosted ZnPb deposits. In-situ sulphur isotope measurements from Nanisivik show a narrow δ34S range of 27.54±0.72, very similar to what has been reported before in bulk sample analyses. New fluid inclusion data show that the mineralising fluids were ~100°C, which is not anomalous in the context of carbonate-hosted base-metal deposits. The fluids exhibit no significant spatial variation in homogenisation temperature in the 2-km-long ‘upper lens’ of the ore deposit, but recrystallisation and modification of fluid inclusions took place in the immediate vicinity of the cross-cutting ~720Ma “mine dyke”. The deposit is broadly inferred to have formed during late Mesoproterozoic assembly of supercontinent Rodinia, when regional hydrostatic head developed under the influence of far-field stresses originating in the developing Grenville orogen. The Nanisivik deposit remains anomalous only in its age; most other aspects of this ore deposit are now shown to be quite typical for carbonate-hosted ore deposits.

Matrix effects of calcium on high-precision sulfur isotope measurement by multiple-collector inductively coupled plasma mass spectrometry

Multiple-collector inductively coupled plasma mass spectrometry (MC-ICP-MS) has been successfully applied in the rapid and high-precision measurement for sulfur isotope ratios in recent years. During the measurement, the presence of matrix elements would affect the instrumental mass bias for sulfur and these matrix-induced effects have aroused a lot of researchers’ interest. However, these studies have placed more weight on highlighting the necessity for their proposed correction protocols (e.g., chemical purification and matrix-matching) while less attention on the key property of the matrix element gives rise to the matrix effects. In this study, four groups of sulfate solutions, which have different concentrations of sulfur (0.05–0.60mM) but a constant sequence of atomic calcium/sulfur ratios (0.1–50), are investigated under wet (solution) and dry (desolvation) plasma conditions to make a detailed evaluation on the matrix effects from calcium on sulfur isotope measurement. Based on a series of comparative analyses, we indicated that, the matrix effects of calcium on both measured sulfur isotope ratios and detected 32S signal intensities are dependent mainly on the absolute calcium concentration rather than its relative concentration ratio to sulfur (i.e., atomic calcium/sulfur ratio). Also, for the same group of samples, the matrix effects of calcium under dry plasma condition are much more significant than that of wet plasma. This research affords the opportunity to realize direct and relatively precise sulfur isotope measurement for evaporite gypsum, and further provides some suggestions with regard to sulfur isotope analytical protocols for sedimentary pore water.

BADANIA IZOTOPÓW SIARKI W MINERAŁACH SIARCZKOWYCH ZE ZŁÓŻ RUD POLIMETALICZNYCH W SUDETACH ZA POMOCĄ MIKROSONDY JONOWEJ SHRIMP IIE/MC

SULPHUR ISOTOPE MEASUREMENTS OF SULPHIDE MINERALS FROM THE POLYMETALLIC ORE DEPOSITS IN THE SUDETES, usin g THE SHRIMP IIE/MC ION MICROPROBE Abstract. Results of sulphur isotope analyses in sulphides by use of modern ion microprobe equipment – SHRIMP IIe/MC – are described in the paper. Measurements with an application of the SIMS method indicate high precision, fast procedure as well as high repeatability of results. Considering the sulphur isotopic ratio measured by the IRMS (the conventional method of gas spectrometry), advantage of the SIMS method is clearly visible. It allows for observation of the analysed surface at the micron-scale and for very precise selection of the area of analysis (about 20 μm in diameter), including the avoiding of other mineral microinclusions or microfractures in sulphide crystals, which are common features. In the case of the IRMS sulphur isotope analyses sample homogenization strongly influenced obtained results. The SIMS ion microprobe technique provides high spatial resolution which enables more reliable results. In the case of pyrites analysed from the abandoned Au–Cu–As Radzimowice deposit results of isotopic sulphur are close to δ34S = 0‰ (weighted average of δ34S for sample 10B is +0.84 ±0.24‰, n = 60, for sample M20 +0.37 ±0.13‰, n = 35, and for sample M21 –0.03 ±0.32‰, n = 26), which indicates the source of sulphur from processes related to magmas probably of mantle or lower crust origins. On the other hand pyrites from the old mining prospect in Leszczyniec have negative δ34S values below –1‰ (ranging from –3.24 ±0.08‰ to –1.19 ±0.09‰), which suggest a contamination process and possible minor input of sedimentary protolith during the magma generation.

Sulfur isotope homogeneity of lunar mare basalts

We present a new set of high precision measurements of relative 33S/32S, 34S/32S, and 36S/32S values in lunar mare basalts. The measurements are referenced to the Vienna-Canyon Diablo Troilite (V-CDT) scale, on which the international reference material, IAEA-S-1, is characterized by δ33S=−0.061‰, δ34S≡−0.3‰ and δ36S=−1.27‰. The present dataset confirms that lunar mare basalts are characterized by a remarkable degree of sulfur isotopic homogeneity, with most new and published SF6-based sulfur isotope measurements consistent with a single mass-dependent mean isotopic composition of δ34S=0.58±0.05‰, Δ33S=0.008±0.006‰, and Δ36S=0.2±0.2‰, relative to V-CDT, where the uncertainties are quoted as 99% confidence intervals on the mean. This homogeneity allows identification of a single sample (12022, 281) with an apparent 33S enrichment, possibly reflecting cosmic-ray-induced spallation reactions. It also reveals that some mare basalts have slightly lower δ34S values than the population mean, which is consistent with sulfur loss from a reduced basaltic melt prior to eruption at the lunar surface. Both the sulfur isotope homogeneity of the lunar mare basalts and the predicted sensitivity of sulfur isotopes to vaporization-driven fractionation suggest that less than ≈1–10% of lunar sulfur was lost after a potential moon-forming impact event.

Sulfate and sulfide sulfur isotopes (δ34S and δ33S) measured by solution and laser ablation MC-ICP-MS: An enhanced approach using external correction

Isotope ratio measurements using a multi-collector inductively coupled plasma mass spectrometer (MC-ICP-MS) commonly use standard-sample bracketing with a single isotope standard for mass bias correction for elements with narrow-range isotope systems measured by MC-ICP-MS, e.g. Cu, Fe, Zn, and Hg. However, sulfur (S) isotopic composition (δ34S) in nature can range from at least −40 to +40‰, potentially exceeding the ability of standard-sample bracketing using a single sulfur isotope standard to accurately correct for mass bias. Isotopic fractionation via solution and laser ablation introduction was determined during sulfate sulfur (Ssulfate) isotope measurements. An external isotope calibration curve was constructed using in-house and National Institute of Standards and Technology (NIST) Ssulfate isotope reference materials (RM) in an attempt to correct for the difference. The ability of external isotope correction for Ssulfate isotope measurements was evaluated by analyzing NIST and United States Geological Survey (USGS) Ssulfate isotope reference materials as unknowns. Differences in δ34Ssulfate between standard-sample bracketing and standard-sample bracketing with external isotope correction for sulfate samples ranged from 0.72‰ to 2.35‰ over a δ34S range of 1.40‰ to 21.17‰. No isotopic differences were observed when analyzing Ssulfide reference materials over a δ34Ssulfide range of −32.1‰ to 17.3‰ and a δ33S range of −16.5‰ to 8.9‰ via laser ablation (LA)-MC-ICP-MS. Here, we identify a possible plasma induced fractionation for Ssulfate and describe a new method using external isotope calibration corrections using solution and LA-MC-ICP-MS.

Ediacaran sulfur cycle: Insights from sulfur isotope measurements (Δ33S and δ34S) on paired sulfate–pyrite in the Huqf Supergroup of Oman

The Ediacaran Period (635–541Ma) was a time of dramatic environmental and ecological change. Sulfur isotopic records preserved in marine strata provide insights into these changes. Previous work using δ34S in pyrite and carbonate-associated sulfate in the Ediacaran-aged Huqf Supergroup (Sultanate of Oman) suggested increases in marine sulfate concentrations, changing microbial pathways and redox conditions, and a long-term increase in δ34S of sulfate delivery to the ocean. However, δ34S-based analyses on their own were insufficient to uniquely reconstruct these environmental and ecological changes. Here we present new paired δ34S and Δ33S data from carbonate-associated sulfate and pyrite in these strata. The results allow us to provide three new constraints on Ediacaran sulfur cycling. First, a notable increase Δ34SCAS-PY, previously attributed to possible disproportionation, in upper Buah strata is associated with Δ33S-evidence for an increase in sulfide reoxidation, indicating a transition to more oxidizing conditions, possibly associated with the onset of bioturbation. Secondly, Δ33S data indicate that a large positive shift in both sulfate and pyrite δ34S in Ara Group strata is mostly likely due to an increase in delivery of 34S-enriched sulfate to the basin. Finally paired δ34S–Δ33S data constrain possible changes in seawater sulfate concentrations, suggesting an increase in sulfate supply related to enhanced evaporite weathering, consistent with geological and geochemical observations that imply high [SO4] (∼17mM) during deposition of the Ara Group.

Atmospheric record in the Hadean Eon from multiple sulfur isotope measurements in Nuvvuagittuq Greenstone Belt (Nunavik, Quebec)

Mass-independent fractionation of sulfur isotopes (S-MIF) results from photochemical reactions involving short-wavelength UV light. The presence of these anomalies in Archean sediments [(4-2.5 billion years ago, (Ga)] implies that the early atmosphere was free of the appropriate UV absorbers, of which ozone is the most important in the modern atmosphere. Consequently, S-MIF is considered some of the strongest evidence for the lack of free atmospheric oxygen before 2.4 Ga. Although temporal variations in the S-MIF record are thought to depend on changes in the abundances of gas and aerosol species, our limited understanding of photochemical mechanisms complicates interpretation of the S-MIF record in terms of atmospheric composition. Multiple sulfur isotope compositions (δ(33)S, δ(34)S, and δ(36)S) of the >3.8 billion-year-old Nuvvuagittuq Greenstone Belt (Ungava peninsula) have been investigated to track the early origins of S-MIF. Anomalous S-isotope compositions (Δ(33)S up to +2.2‰) confirm a sedimentary origin of sulfide-bearing banded iron and silica-rich formations. Sharp isotopic transitions across sedimentary/igneous lithological boundaries indicate that primary surficial S-isotope compositions have been preserved despite a complicated metamorphic history. Furthermore, Nuvvuagittuq metasediments recorded coupled variations in (33)S/(32)S, (34)S/(32)S, and (36)S/(32)S that are statistically indistinguishable from those identified several times later in the Archean. The recurrence of the same S-isotope pattern at both ends of the Archean Eon is unexpected, given the complex atmospheric, geological, and biological pathways involved in producing and preserving this fractionation. It implies that, within 0.8 billion years of Earth's formation, a common mechanism for S-MIF production was established in the atmosphere.