34S Enrichment Research Articles

Mineralogic and sulfur isotopic effects accompanying oxidation of pyrite in millimolar solutions of hydrogen peroxide at temperatures from 4 to 150 °C

Oxidation of pyrite by hydrogen peroxide (H 2O 2) at millimolar levels has been studied from 4 to 150 °C in order to evaluate isotopic effects potentially associated with radiolytic oxidation of pyrite. Gaseous, aqueous, and solid phases were collected and measured following sealed-tube experiments that lasted from 1 to 14 days. The dominant gaseous product was molecular oxygen. No volatile sulfur species were recovered from any experiment. Sulfate was the only aqueous sulfur species detected in solution, with sulfite and thiosulfate below the detection limits. X-ray diffraction patterns and images from scanning electron microscopy reveal solid residues composed primarily of hydrated ferric iron sulfates and sporadic ferric–ferrous iron sulfates. Hematite was detected only in solid residue produced during high temperature experiments. Elemental sulfur and/or polysulfides are inferred to be form on reacting pyrite surface based on extraction with organic solvents. Pyrite oxidation by H 2O 2 increases in rate with increasing H 2O 2concentration, pyrite surface area, and temperature. Rates measured in sealed-tube experiments at 25°C, for H 2O 2 concentration of 2 × 10 −3 M are 8.8 × 10 −9 M/m 2/sec, which are higher than previous estimates. A combination of reactive oxygen species from H 2O 2 decomposition products and reactive iron species from pyrite dissolution is inferred to aggressively oxidize the receding pyrite surface. Competing oxidants with temperature-dependent oxidation efficiencies results in multiple reaction mechanisms for different temperatures and surface conditions. Sulfur isotope values of remaining pyrite were unchanged during the experiments, but showed distinct enrichment of 34S in produced sulfate and depletion in elemental sulfur. The Δ sulfate–pyrite and Δ elemental sulfur–pyrite was +0.5 to +1.5‰ and was −0.2 to −1‰, respectively. Isotope data from high-temperature experiments indicate an additional 34S-depleted sulfur fraction, with up to 4‰ depletion of 34S, in the hematite. Sulfur isotope trends were not influenced by H 2O 2 concentration, temperature, or reaction time. Results of this study indicate that radiolytically produced oxidants, such as hydrogen peroxide and hydroxyl radicals, could efficiently oxidize pyrite in an otherwise oxygen-limited environment. Although H 2O 2 is generally regarded as being of minor geochemical significance on Earth, the H 2O 2 molecule plays a pivotal role in Martian atmospheric and soil chemistry. Additional experimental and field studies are needed to characterize sulfur and oxygen isotope systematics during radiolytical oxidation of metallic sulfides and elemental sulfur.

Sulfur isotopic zonation in the Cadia district, southeastern Australia: exploration significance and implications for the genesis of alkalic porphyry gold–copper deposits

The alkalic porphyry gold–copper deposits of the Cadia district occur in the eastern Lachlan Fold Belt of New South Wales, Australia. The district comprises four porphyry deposits (Ridgeway, Cadia Quarry, Cadia Hill, and Cadia East) and two iron–copper–gold skarn deposits (Big Cadia and Little Cadia). Almost 1,000 tonnes of contained gold and more than four million tonnes of copper have been discovered in these systems, making Cadia the world’s largest known alkalic porphyry district, in terms of contained gold. Porphyry gold–copper ore at Cadia is associated with quartz monzonite intrusive complexes, and is hosted by central stockwork and sheeted quartz–sulfide–(carbonate) vein systems. The Cadia porphyry deposits are characterized by cores of potassic and/or calc–potassic alteration assemblages, and peripheral halos of propylitic alteration, with late-stage phyllic alteration mostly restricted to fault zones. Hematite dusting is an important component of the propylitic alteration assemblage, and has produced a distinctive reddening of feldspar minerals in the volcanic wall rocks around the mineralized centers. Sulfide mineralization is strongly zoned at Ridgeway and Cadia East, with bornite-rich cores surrounded by chalcopyrite-rich halos and peripheral zones of pyrite mineralization. The Cadia Hill and Cadia Quarry deposits have chalcopyrite-rich cores and pyrite-rich halos, and Cadia Hill contains a high-level bornite-rich zone. Distinctive sulfur isotopic zonation patterns have been identified at Ridgeway, Cadia Hill, and Cadia East. The deposit cores are characterized by low δ34Ssulfide values (−10 to −4‰), consistent with sulfide precipitation from an oxidized (sulfate-predominant) magmatic fluid at 450 to 400°C. Pyrite grains that occur in the propylitic alteration halos typically have δ34Ssulfide values near 0‰. There is a gradual increase in δ34Ssulfide values outwards from the deposit cores through the propylitic halos. Water–rock interaction during propylitic alteration caused magmatic sulfate reduction and concomitant oxidation of ferrous iron-bearing minerals, resulting in enrichment of 34S in pyrite and also producing the distinctive reddened, hematite-rich alteration halos to the Cadia deposits. These results show that sulfur isotope analyses have potential applications in the exploration of alkalic porphyry-style deposits, with zones of depleted δ34Ssulfide values most prospective for high-grade mineralization.

Synsedimentary versus metamorphic control of S, O and Sr isotopic compositions in gypsum evaporites from the Cameros Basin, Spain

Sulfate δ 34S and δ 18O and Sr isotope compositions are presented for Berriasian (Upper Jurassic) gypsum evaporites from the Cameros Basin, a continental basin in the Iberian ranges of northern Spain. Solute sources to the ephemeral lakes in which the evaporites formed are dominated by weathering of sediments containing older Keuper marine evaporites and granitic/metamorphic Variscan basement. Strontium isotopic ratios of the continental evaporites ( 87Sr/ 86Sr = 0.707882 to 0.707933) are elevated compared to the Keuper source ( 87Sr/ 86Sr = 0.707605 to 0.707799), most likely reflecting a radiogenic component from basement lithologies. Sulfate δ 34S in the continental evaporites (at around 18.2 ‰ V-CDT) is higher than any possible mixture of solutes to the basin. The degree of 34S enrichment is small (≈ 3.7‰) and is most likely the result of partial bacterial reduction of lake-water sulfate. The same process would also enrich sulfate in 18O, but by only ≈ 1‰. Evaporite sulfate δ 18O (at around 21.7‰ V-SMOW) is, in fact, enriched by ≈ 10‰ relative to sulfate sources to the basin. This large effect is most likely the result of re-equilibration of oxygen isotopes during low grade metamorphism of the basinal sequence. Sulfur and strontium isotopes in the evaporites remained internally buffered and thus unchanged during metamorphism while oxygen isotopes were open to exchange with aqueous fluid and/or interbedded carbonates that constituted a large exchangeable oxygen reservoir. The potential of sulfate oxygen to undergo isotopic exchange at elevated temperatures must be taken into account when interpreting the significance of evaporite sulfate oxygen data from units that have undergone deep burial or low grade metamorphism.

Calculation of sulfur isotope fractionation in sulfides

The increment method has been successfully applied to calculate thermodynamic isotope fractionation factors of oxygen in silicates, oxides, carbonates, and sulfates. In this paper, we modified the increment method to calculate thermodynamic isotope fractionation factors of sulfur in sulfides, based on chemical features of sulfur–metal bonds and crystal features of sulfide minerals. To approximate the bond strength of sulfides, a new constant, known as the Madelung constant, was introduced. The increment method was then extended to calculate the reduced partition function ratios of sphalerite, chalcopyrite, galena, pyrrhotite, greenockite, bornite, cubanite, sulvanite, and violarite, as well as the isotope fractionation factors between them over the temperature range from 0 to 1000 °C. The order of 34S enrichment in these nine minerals is pyrrhotite > greenockite > sphalerite > chalcopyrite > cubanite > sulvanite > bornite > violarite > galena. Our improved method constitutes another model for calculating the thermodynamic isotope fractionation factors of sulfur in sulfides of geochemical interest.

The Paleoproterozoic carbonate-hosted Pering Zn–Pb deposit, South Africa. II: fluid inclusion, fluid chemistry and stable isotope constraints

The Pering deposit is the prime example of Zn–Pb mineralisation hosted by stromatolitic dolostones of the Neoarchean to Paleoproterozoic Transvaal Supergroup. The hydrothermal deposit centers on subvertical breccia pipes that crosscut stromatolitic dolostones of the Reivilo Formation, the lowermost portion of the Campbellrand Subgroup. Four distinct stages of hydrothermal mineralisation are recognised. Early pyritic rock matrix brecciation is followed by collomorphous sphalerite mineralisation with replacive character, which, in turn, is succeeded by coarse grained open-space-infill of sphalerite, galena, sparry dolomite, and quartz. Together, the latter two stages account for ore-grade Zn–Pb mineralisation. The fourth and final paragenetic stage is characterised by open-space-infill by coarse sparry calcite. The present study documents the results of a detailed geochemical study of the Pering deposit, including fluid inclusion microthermometry, fluid chemistry and stable isotope geochemistry of sulphides (δ34S) and carbonate gangue (δ13C and δ18O). Microthermometric fluid inclusion studies carried out on a series of coarsely grained crystalline quartz and sphalerite samples of the latter, open-space-infill stage of the main mineralisation event reveal the presence of three major fluid types: (1) a halite–saturated aqueous fluid H2O–NaCl–CaCl2 (>33 wt% NaCl equivalent) brine, (2) low-salinity meteoric fluid (<7 wt% NaCl) and (3) a carbonic CH4–CO2–HS− fluid that may be derived from organic material present within the host dolostone. Mixing of these fluids have given rise to variable mixtures (H2O–CaCl2–NaCl ±(CH4–CO2–HS−), 2 to 25 wt% NaCl+CaCl2). Heterogeneous trapping of the aqueous and carbonic fluids occurred under conditions of immiscibility. Fluid temperature and pressure conditions during mineralisation are determined to be 200–210°C and 1.1–1.4 kbar, corresponding to a depth of mineralisation of 4.1–5.2 km. Chemical analyses of the brine inclusions show them to be dominated by Na and Cl with lesser amounts of Ca, K and SO4. Fluid ratios of Cl/Br indicate that they originated as halite saturated seawater brines that mixed with lower salinity fluids. Analyses of individual brine inclusions document high concentrations of Zn and Pb (∼1,500 and ∼200 ppm respectively) and identify the brine as responsible for the introduction of base metals. Stable isotope data were acquired for host rock and hydrothermal carbonates (dolomite, calcite) and sulphides (pyrite, sphalerite, galena and chalcopyrite). The ore-forming sulphides show a trend to 34S enrichment from pyrite nodules in the pyritic rock matrix breccia (δ34S = −9.9 to +3.7‰) to paragenetically late chalcopyrite of the main mineralisation event (δ34S = +30.0‰). The observed trend is attributed to Rayleigh fractionation during the complete reduction of sulphate in a restricted reservoir by thermochemical sulphate reduction, and incremental precipitation of the generated sulphide. The initial sulphate reservoir is expected to have had an isotopic signature around 0‰, and may well represent magmatic sulphur, oxidised and leached by the metal-bearing brine. The δ18O values of successive generations of dolomite, from host dolostone to paragenetically late saddle dolomite follow a consistent trend that yields convincing evidence for extensive water rock interaction at variable fluid–rock ratios. Values of δ13C remain virtually unchanged and similar to the host dolostone, thus suggesting insignificant influx of CO2 during the early and main stages of mineralisation. On the other hand, δ13C and δ18O of post-ore calcite define two distinct clusters that may be attributed to changes in the relative abundance in CH4 and CO2 during waning stages of hydrothermal fluid flow.

Trace sulfate in mid-Proterozoic carbonates and the sulfur isotope record of biospheric evolution

Concentrations of oceanic and atmospheric oxygen have varied over geologic time as a function of sulfur and carbon cycling at or near the Earth’s surface. This balance is expressed in the sulfur isotope composition of seawater sulfate. Given the near absence of gypsum in pre-Phanerozoic sediments, trace amounts of carbonate-associated sulfate (CAS) within limestones or dolostones provide the best available constraints on the isotopic composition of sulfate in Precambrian seawater. Although absolute CAS concentrations, which range from those below detection to ∼120 ppm sulfate in this study, may be compromised by diagenesis, the sulfur isotope compositions can be buffered sufficiently to retain primary values. Stratigraphically controlled δ 34S measurements for CAS from three mid-Proterozoic carbonate successions (∼1.2 Ga Mescal Limestone, Apache Group, Arizona, USA; ∼1.45–1.47 Ga Helena and Newland formations, Belt Supergroup, Montana, USA; and ∼1.65 Ga Paradise Creek Formation, McNamara Group, NW Queensland, Australia) show large isotopic variability (+9.1‰ to +18.9‰, −1.1‰ to +27.3‰, and +14.1‰ to +37.3‰, respectively) over stratigraphic intervals of ∼50 to 450 m. This rapid variability, ranging from scattered to highly systematic, and overall low CAS abundances can be linked to sulfate concentrations in the mid-Proterozoic ocean that were substantially lower than those of the Phanerozoic but higher than values inferred for the Archean. Results from the Belt Supergroup specifically corroborate previous arguments for seawater contributions to the basin. Limited sulfate availability that tracks the oxygenation history of the early atmosphere is also consistent with the possibility of extensive deep-ocean sulfate reduction, the scarcity of bedded gypsum, and the stratigraphic δ 34S trends and 34S enrichments commonly observed for iron sulfides of mid-Proterozoic age.

Sulfur Speciation and Stable Isotope Trends of Water-Soluble Sulfates in Mine Tailings Profiles

Sulfur speciation and the sources of water-soluble sulfate in three oxidizing sulfidic mine tailings impoundments were investigated by selective dissolution and stable isotopes. The studied tailings impoundments--Piuquenes, Cauquenes, and Salvador No. 1--formed from the exploitation of the Rio Blanco/La Andina, El Teniente, and El Salvador Chilean porphyry copper deposits, which are located in Alpine, Mediterranean, and hyperarid climates, respectively. The water-soluble sulfate may originate from dissolution of primary ore sulfates (e.g., gypsum, anhydrite, jarosite) or from oxidation of sulfide minerals exposed to aerobic conditions during mining activity. With increasing aridity and decreasing pyrite content of the tailings, the sulfur speciation in the unsaturated oxidation zones showed a trend from dominantly Fe(III) oxyhydroxide fixed sulfate (e.g., jarosite and schwertmannite) in Piuquenes toward increasing presence of water-soluble sulfate at Cauquenes and Salvador No. 1. In the saturated primary zones, sulfate is predominantly present in water-soluble form (mainly as anhydrite and/or gypsum). In the unsaturated zone at Piuquenes and Cauquenes, the delta34S(SO4)values ranged from +0.5 per thousand to +2.0 per thousand and from -0.4 per thousand to +1.4 per thousand Vienna Canyon Diablo Troilite (V-CDT), respectively, indicating a major sulfate source from pyrite oxidation (delta34S(pyrite) = -1.1 per thousand and -0.9 per thousand). In the saturated zone at Piuquenes and Cauquenes, the values ranged from -0.8 per thousand to +0.3 per thousand and from +2.2 per thousand to +3.9 per thousand, respectively. At Cauquenes the 34S enrichment in the saturated zone toward depth indicates the increasing contribution of isotopically heavy dissolved sulfate from primary anhydrite (approximately +10.9 per thousand). At El Salvador No. 1, the delta34S(SO4) average value is -0.9 per thousand, suggesting dissolution of supergene sulfate minerals (jarosite, alunite, gypsum) with a delta34S approximately -0.7 per thousand as the most probable sulfate source. The gradual decrease of delta18O(SO4) values from the surface to the oxidation front in the tailings impoundments at Piuquenes (from -4.5 per thousand to -8.6 per thousand Vienna Standard Mean Ocean Water, V-SMOW) and at Cauquenes (from -1.3 per thousand to -3.5 per thousand) indicates the increasing importance of ferric iron as the main electron acceptor in the oxidation of pyrite. The different delta18O(SO4) values between the tailings impoundments studied here reflect the local climates.

Terrane and basement discrimination in northern Britain using sulphur isotopes and mineralogy of ore deposits

Abstract This study of four well characterized and adjacent terranes in Northern Britain outlines the sulphur isotope variations, assesses the overall importance of crustal and mantle sulphur, and presents a model that can be applied to terrane distinction throughout the North Atlantic Caledonides. The characteristics of metal components within the mineralization provide additional information that can be related to the nature of underlying basement and events from the onset of sedimentation to the cessation of mineralization within stratigraphically linked packages of rock. The δ 34 S data show that the dominant crustal units in each terrane, whether upper crustal sediments or cratonic basement, provide the main alternative sulphur source to the mantle and act also as the main contaminant of subcrustal melts. The δ 34 S values of granitoid-related mineralization are either within the subcrustal melt-range of −3‰ to +3‰ or deviate toward the values of major crustal units in the terrane, i.e. toward 34 S depletion in the Southern Uplands and toward 34 S enrichment in the Lakesman and Grampian terranes. More complex mineralization in the Northern Highland terrane is linked to the presence of thick North Atlantic craton beneath upper crustal metasediments. Across the region the vein systems beyond the influence of magmatic components represent homogenized sulphur, metals and fluids from local upper crustal units. The sulphur isotope data and style of mineralization for the British terranes are compared with terranes of similar age along strike in Eastern Canada revealing notable correlations.

Mechanisms of sulfur introduction chemically controlled: δ34S imprint

Organic sulfur in marine sediment is 34S enriched relative to the co-existing pyrite. This phenomenon is still enigmatic. Timing of the sulfur incorporation, immobilization and different sulfur species involved are part of the explanations. The reduced sulfur species incorporation into organic matter (OM) is generally assumed to have negligible δ 34S fractionation. This assumption has never been confirmed by laboratory experimental data. The present study measures the δ 34S changes resulting from reduced sulfur species (sulfides and polysulfide anions) incorporation into organic model compounds in an aquatic and low temperature (25 °C) system that simulates diagenetic marine environment. In addition, we also investigate the δ 34S fractionation and the isotope chemical mixing in the formation of polysulfide anions produced from elemental sulfur and sulfide anions. The results showed total isotope mixing between the two species in the formation of polysulfides. Acidification of the polysulfides solution caused δ 34S fractionation between the released elemental sulfur and H 2S. The incorporation of polysulfides and sulfides into carbonyl groups, caused 34S enrichment relative to the starting polysulfides and sulfide of 4–5‰. The 34S enrichment of the sulfurized carbonyl groups showed a minimal effect by temperature (0–70 °C) and is not affected by salinity, polysulfides composition, reaction time or solubility in water. The incorporation of polysulfides and sulfides into brominated organic compounds was negligibly 34S enriched. The chemical mechanisms controlling the polysulfides incorporation into OM depend mostly on the functional groups and determine the 34S enrichment of the sulfurized OM. The results presented in this study can explain part of the difference between pyrite δ 34S and sulfurized OM δ 34S in natural marine sediments.

Sulfur isotope geochemistry of the Black Sea water column

We studied the isotopic composition of dissolved sulfide in the Black Sea water column during different seasons at a total of 15 stations spanning the entire basin. The isotopic composition of dissolved sulfide averaged over all depths varies between −42.0‰ and −32.6‰, ave. −39.6±1.3‰ (1 σ) (118 data points). Seasonal and spatial (open sea vs. coastal stations) differences in the δ 34S–H 2S values are not observed. Slight 34S enrichments in the sulfide isotope composition are revealed in the uppermost and the lowest parts of the anoxic water column. The upper trend is explained as (i) the effect of mixing with 34S-enriched sulfide produced near the interface by chemical oxidation with MnO 2 or O 2, (ii) small fractionation during biological sulfide oxidation, (iii) a result of a decreased isotope fractionation factor due to higher sulfate reduction rates. The lower trend is likely the result of the mixing with 34S-enriched pore water sulfide. We generated the first isotope data for sulfur intermediates in the lower part of the anoxic zone, which show values close to the isotope composition of dissolved sulfide. We hypothesize that the high isotope depletions of sulfide observed in the entire Black Sea water column are a result of low sulfate reduction rates and superimposed disproportionation reactions within the oxidative part of the sulfur cycle. Different physical and chemical mechanisms facilitating the formation and transport of sulfur intermediates in the anoxic interior are discussed.

A stable sulfur and oxygen isotopic investigation of sulfur cycling in an anoxic marine basin, Framvaren Fjord, Norway

In 1993 we measured the δ 34S values of total dissolved sulfide ( δ 34S ∑H 2S ) and sulfate ( δ 34S SO 4 − ) and the δ 18O of sulfate ( δ 18O SO 4 − ) from water samples collected across the oxic–anoxic interface and in the deep permanently anoxic waters of the stratified Framvaren fjord in southern Norway. Near the chemocline, variations in the δ 34S SO 4 − and δ 18O SO 4 − values were generally less than 1‰ from ambient seawater values. However, a minimum δ 34S SO 4 − value of +19.7‰ was detected at 20 m depth, which coincided with the depth that sulfide first appeared and may reflect sulfide oxidation. Small increases in δ 34S SO 4 − and δ 18O SO 4 − values 3 m below this depth are consistent with a zone of sulfur disproportionation. The δ 34S ∑H 2S value near the interface at 22 m was −19.8‰, which is 41.2‰ depleted in 34S relative to the sulfate collected at that depth. In close agreement with earlier measurements made at Framvaren in 1982, the δ 34S SO 4 − values collected from the deeper anoxic waters showed a marked 34S enrichment with depth, which corresponded with a decrease in the sulfate concentration. These results are interpreted to be the result of active dissimilatory sulfate reduction. A Rayleigh plot for the sulfate data measured in 1993 provides estimates for the sulfur and oxygen isotope enrichment factors ( ε s and ε o, respectively) for sulfate reduction of −41.5‰ and −9.8‰, respectively, with the former value matching closely the observed difference in δ 34S between the dissolved sulfide and sulfate near the interface. Our results from 1993, however, contrast with δ 34S SO 4 − and δ 34S ∑H 2S data in the water column made in 1983 by Anderson et al. [Mar. Chem. 23 (1988) 283). We conclude that the results of 1983 may be anomalous, and as a result this may offer additional interpretations than what was previously provided for the origin of reduced inorganic sulfur in the sediments of Framvaren based on their measured δ 34S values. We hypothesize that the lower δ 34S trs values in the sediments relative to δ 34S ∑H 2S values in the water column could also result from different rates of sulfate reduction, or in shallower sediments just beneath the chemocline, also from disproportionation of S∘, S 2O 3 −, or SO 3 −. We hypothesize that the observed ratio of 4.4:1 for the measured changes in δ 34S SO 4 − versus δ 18O SO 4 − within the anoxic waters approximates the 4:1 atom ratio of oxygen to sulfur in the residual sulfate as a result of dissimilatory sulfate reduction and reflects little oxygen isotope exchange between intermediates of sulfur metabolism and water either during bacterial sulfate reduction or from sulfide reoxidation processes. Based on comparisons with other studies, we further propose that this lack of isotopic exchange with water, and the subsequent ∼4:1 ratio of δ 34S SO 4 − versus δ 18O SO 4 − , occurs under conditions that promote a unidirectional biochemical reaction for sulfate reduction during which kinetic isotope effects are fully expressed and are consequently reflected in the δ 34S SO 4 − and δ 18O SO 4 − values.

Global Neoproterozoic (Sturtian) post-glacial sulfide-sulfur isotope anomaly recognised in Namibia

The Neoproterozoic Earth experienced at least two, probably global, glaciations. Each glaciation was superceded by deposition of a layer of carbonate (‘cap-carbonate’) that has a distinctive lithology and depletion in 13C ( δ 13C carbonate ∼ −5‰). The ∼700 Ma Sturtian glaciation is followed by deposition of a cap-carbonate and post-glacial succession which contain bacterially produced sulfides extremely enriched in 34S (average δ 34S sulfide ∼ +30‰) with maximum values up to +60‰. This level of 34S enrichment in sulfides is unique to the Sturtian post-glacial succession and recognised in Australia, Canada, and China. In the Neoproterozoic of the Nama Basin, Namibia, the Gobabis Member is the basal unit of the Court Formation, which overlies the glacial Blaubeker Formation. δ 13C carbonate analyses from the Gobabis Member range from −5.2 to −2.2‰ (average = −3.7‰; n = 10). δ 34S sulfide ranges from +16.1 to +61.1‰ (average = +37.6‰; n = 8). These results are consistent with a Sturtian age for the Blaubeker Formation and overlying Gobabis Member, which have previously been interpreted as Sturtian. The sulfur isotopic results are comparable with δ 34S sulfide in Sturtian post-glacial units of Australia, Canada and China. This adds to the evidence for correlation of the Blaubeker Formation with Sturtian glaciations on other continents. The cause of such elevated δ 34S sulfide is enigmatic. Geochemical evidence suggests the sulfide was not formed from low sulfate waters nor in euxinic conditions, which discounts any known modern analogue. 34S enrichment in sulfides is therefore postulated to be caused by enrichment of 34S in contemporaneous seawater ( δ 34S sulfate up to +60‰?). The rise in seawater δ 34S sulfate is considered to be the result of intense bacterial sulfate reduction in an anoxic ocean during the Sturtian glaciation.

Stable isotope systematics of two cenotes from the northern Yucatan Peninsula, Mexico

Deep water‐filled sinkholes, cenotes, are common in the northern Yucatan Peninsula. At least five of these cenotes are deep enough to extend through a freshwater lens of meteoric origin in which δ18O and δD follow the trend δD = 8.11 × δ18O + 10.4. Below this freshwater lies saline water that originated as seawater and has retained its seawater isotopic identity. Deep cenotes, characterized by input of variable amounts of organic debris from tropical vegetation and by poor circulation below the fresh‐/saltwater interface, provide excellent water columns in which to study sulfur redox phenomena. Measurements include O, H, and S isotope composition, conductivity, sulfur speciation, and pH from two cenotes (Ucil, 98 m deep, and Xcolac, 125 m deep). Strong 34S enrichment of sulfate and 34S depletion of sulfide indicate anaerobic bacterial reduction of sulfate. A shift in the isotopic composition of sulfur in Xcolac from a seawater value of +21.0‰ (CDT) to +41.8‰ indicates conversion of sulfate to isotopically light sulfide. Mass balance calculations indicate that escape of isotopically light sulfur from the system is a slow process. At 80 m in Xcolac, a difference in sulfur isotope composition between sulfate and sulfide (△34S) of 63.2‰ is observed and could be the result of multiple sulfate reduction reactions. Higher in the water column, sulfide oxidation occurs, probably the result of bacterially mediated sulfide oxidation processes. A deep observation well (lacking organic matter input) shows only a slight deviation in sulfur isotope composition of sulfate from seawater values.

Stable isotope study of the igneous, metamorphic and mineralized rocks of the Edough complex, Annaba, Northeast Algeria

The petrogenesis of igneous, metamorphic and mineralized rocks in the Edough massif, NE Algeria, indicates an interplay between crustal and magmatic sources, and magmatic and surface fluids, as determined by sulphur and oxygen isotopic analyses. The Tertiary igneous rocks (microgranites and rhyolites) show a tendency towards I-type granitoids with δ 34S values of +5.4±2.2 ‰ (1 σ) and δ 18O between +5.6 ‰ and +6.9 ‰, with the most hydrothermally altered rocks having the lowest δ 18O values. This is indicative of seawater being a major component of the hydrothermal fluids. Seawater interaction with the granitoids produced enrichment in 34S of sulphide-sulphur in both the microgranites and associated skarn mineralization. However, in the Beleleita W–Sn–(Au) deposit, magmatic fluids dominated the mineralization, reflected by δ 34S values of +1.7 ‰ and +1.8 ‰. The basement amphibolites of Kef Lakhal indicate derivation from a basaltic magma with δ 18O ranging from +4.9 ‰ to +8.6 ‰. Locally altered amphibolite has the lowest δ 18O values suggestive of meteoric water interaction, whereas the highest δ 18O indicate the incorporation of crustal material during the genesis of the amphibolites. Crustal contamination is also reflected in their δ 34S of −18 ‰ to +2.1 ‰, with the most contaminated rocks having the lowest δ 34S. Host Palaeozoic mica schists with δ 18O of +12.7 ‰ and δ 34S of −13.2 ‰ and associated marbles ( δ 34S −9.9 ‰ to −17.4 ‰) are thought to be the most likely contaminants. At the Ain Barbar Fe–Cu–Pb–Zn deposit, δ 34S values range between −9.6 ‰ and −10.8 ‰, indicating that the sulphide-sulphur and base-metals were likely leached from the host Cretaceous flysch and/or the underlying mica schists, with local Tertiary magmatic rocks providing the heat for local convection cells. At Boumaiza Fe-deposit, δ 34S values of the sulphide-sulphur extend from −1.2 ‰ to −8.1 ‰ indicative of magmatic sulphur with the incorporation of substantial amounts of sulphur derived from the host mica schists.

Isotopic fractionation of carbonyl sulfide in the atmosphere: Implications for the source of background stratospheric sulfate aerosol

In order to assess the contribution of carbonyl sulfide to stratospheric sulfate aerosol (SSA), we examined the stratospheric OC34S and OC32S concentration profiles in the infrared limb‐transmittance spectra acquired by the JPL MkIV instrument. We found that OC34S is preferentially depleted by solar photolysis. The derived 34S enrichment factor: ε = +73.8 ± 8.6‰, in conjunction with literature values of δ34S ∼ +11‰ for tropospheric OCS, and a ∼ 10% net processing of the OCS transported upwardly into the stratosphere, suggests that aerosol sulfate proceeding from OCS should be highly enriched in δ34S ∼ 80‰, comparing our prediction with previous reports of δ34S ∼ +2.6‰ for background SSA, we infer either that OCS is a minor contributor to SSA or that current views about its 34S‐abundance and atmospheric circulation are seriously flawed.

Sulfur Content and Isotopic Ratio of Cambro‐Ordovician Carbonate Rocks from South Korea: A Possible Source for Mesozoic Magmatic‐hydrothermal Ore Sulfur

Abstract: Carbonate rocks of Cambrian (18 samples) and lower‐middle Ordovician (11 samples) ages from South Korea were analyzed for sulfur contents of structurally substituted sulfate (SSS) and sulfides and their δ34S values. The δ34S values of SSS ranging from +25.9 to +45.2 permil, are averaged as +33.6 and +33.5 permil for the Cambrian and Ordovician rocks, respectively, which indicate high δ34S values of the Cambro‐Ordovician seawater. The SSS contents in the carbonate rocks are low being 2.9 to 17.3 ppm S (averaged as 7.0 ppm S). Sulfide sulfur, on the contrary, is much abundant containing 3 to 1,880 ppm S and the δ34S values range widely between –17.6 and +31.1 permil. Sulfide sulfur of the studied rocks excluding impure carbonates has an average content of 187 ppm S and δ34S value of +12.8 permil (n=24). The estimated δ34S (sulfate–sulfide) values, which range from 13.8 to 25.4 permil in general with a few exceptions from 36.5 up to 52.3 permil for some impure carbonates, may provide evidence for the persistent oceanic anoxia with its temporary recovery during the Cambro‐Ordovician time.The SSS and sulfide sulfurs have often higher δ34S values than the Mesozoic‐Cenozoic ore sulfur (Ishihara et al., 2000). Since carbonate rocks are very reactive with circulating hydrothermal ore solution, high δ34S values of the Korean ore deposits might be caused to some extent by 34S enrichment from the host carbonates, resulting in the low SSS contents observed.

S- and O-isotopic character of dissolved sulphate in the cover rock aquifers of a Zechstein salt dome

Sulfur and O isotope analyses of dissolved SO 4 were used to constrain a hydrogeological model for the area overlying the Gorleben–Rambow Salt Structure, Northern Germany. Samples were collected from 80 wells screened at different depth-intervals. The study area consists of a set of two vertically stacked aquifer systems. Generally, the isotope data show a good spatial correlation, outlining well-defined groundwater zones containing SO 4 of characteristic isotopic composition. Highly saline waters from deeper parts of the lower aquifer system are characterized by rather constant SO 4 isotopic compositions, which are typical of Permian Zechstein evaporites (δ 34 S=9.6–11.9‰; δ 18 O=9.5–12.1‰). Above this is a transition zone containing ground waters of intermediate salinity and slightly higher isotopic values (average δ 34 S=16.6‰; δ 18 O=15.3‰). The confined groundwater horizon on the top of the lower aquifer system below the low permeable Hamburg Clays is low in total dissolved solids and is characterized by an extreme 34S enrichment (average δ 34 S=39.1‰; δ 18 O=18.4‰), suggesting that bacterially mediated SO 4 reduction is a dominant geochemical process in this zone. Two areas of distinct isotopic composition can be identified in the shallow ground water horizons of the upper hydrogeological system. Sulfate in groundwaters adjacent to the river Elbe and Löcknitz has a typical meteoric isotopic signature (δ 34 S=5.2‰; δ 18 O=8.2‰), whereas the central part of the area is characterized by more elevated isotopic ratios (δ 34 S=12.7‰; δ 18 O=15.6‰). The two major SO 4 pools in the area are represented by Permian seawater SO 4 and a SO 4 of meteoric origin that has been mixed with SO 4 resulting from the oxidation of pyrite. It is suggested that the S-isotope compositions observed reflect the nature of the SO 4 source that have been modified to various extent by bacterial SO 4 reduction. Groundwaters with transitional salinity have resulted from mixing between brines and low-mineralized waters affected by bacterial SO 4 reduction.

Sulfur and chalcophile elements in subduction zones: constraints from a laser ablation ICP-MS study of melt inclusions from Galunggung Volcano, Indonesia

Mafic melt inclusions hosted in olivine phenocrysts (Fo89–78) in high-Mg basalts of Galunggung volcano (Java, Indonesia) were analyzed in situ by laser ablation ICP-MS to determine concentrations of chalcophile and associated trace elements. Our results indicate that sulfur in the mantle beneath Galunggung is significantly enriched relative to MORB source mantle, suggesting large-scale fluxing of sulfur into the mantle wedge during slab dehydration.Melt-inclusion compositions range from strongly undersaturated to transitional basaltic and are characterized by a wide range of sulfur contents (350–2900 ppm). Chalcophile element concentrations are not affected by exsolution of immiscible sulfide liquids and generally fall within the range of whole-rock samples from other arcs. We infer that primary Galunggung melts contain approximately 290 ppm Ni, 60 ppm Co, 190 ppm Cu, and 3 ppm Pb.Patterns of refractory trace elements point to ∼15% melting of a MORB-source mantle below Galunggung, which was enriched in LILE and LREE by slab-derived fluids before melting. Based on this value, we use melting model calculations to investigate whether slab-derived contributions to a MORB-source mantle are required to balance the budgets of sulfur and associated chalcophile elements, assuming that all Cu and S originally resided in sulfides and adopting a Cu concentration of 28 ppm in the presubduction mantle, similar to that in MORB-type mantle.Modeling results predict at least 256 to 465 ppm S in the magma source of Galunggung, which is up to twice the amount commonly assumed for MORB sources. A slab-derived origin of the excess sulfur is consistent with 34S enrichments that commonly characterize arc magmas and gases. Although modeling suggests that elevated copper concentrations relative to MORB can be the consequence of the higher solubility of sulfur in Galunggung melts, the results do not rule out that the subarc mantle was enriched by slab-derived Cu. Lead must have been added, which is readily explained by slab-derived fluids. Other chalcophile elements (Co, Ni) are largely controlled by the nature of the presubduction mantle.

Sulfur isotope systematics of basaltic lavas from Indonesia: implications for the sulfur cycle in subduction zones

We report sulfur isotope compositions of basaltic and basaltic andesite lavas from selected volcanoes in the Indonesian arc system covering the spectrum from low-K tholeiitic to high-K calc–alkaline compositions. The results of 25 samples from seven volcanoes, which are associated with different subduction regimes, show a range in δ34S values of +2.0–+7.8‰ (VCDT) with an average of +4.7±1.4‰ (1σ). Averages and within-suite variations of two larger sets of samples from Batur and Soputan volcanoes (+4.2±1.3‰ with n=9 and +5.7±1.4‰ with n=7, respectively) are comparable to those of the entire sample set. Sulfur concentrations are low (mostly between 2 and 74 ppm, average=19 ppm) and do not show correlations with sulfur isotope composition and whole-rock chemistry, or systematic changes with time in any of the lava suites. From model calculations we infer that basaltic magmas will undergo sulfur isotope fractionation during degassing, most commonly towards lower δ34S values, but that the extent is limited at P–T conditions and oxidation states of interest. Hence, δ34S signatures of basaltic lavas will generally be within a few permil from primary magmatic values, even in cases of extensive sulfur loss. Consequently, magmas in the Indonesian arc system originate from mantle sources that are enriched in 34S relative to MORB and OIB sources and are likely to have δ34S values of about +5–+7‰. The enrichment in 34S is considered to reflect addition of slab-derived material, presumably from sediments rather than altered oceanic crust, with fluids being the most likely transport medium. Absence of correlation between δ34S values of Indonesian basalts and chemical proxies for source components or processes at the slab–wedge interface suggests that sulfur isotopes are relatively insensitive to variations in subduction setting and dynamics. This is supported by the modest range in δ34S of the Indonesian volcanoes studied despite significant variations in the nature and amount of subducted material, and by the similarity with average 34S enrichments in other oceanic arc systems.

Mineral Paragenesis, Fluid Inclusions and Sulfur Isotope Systematics of the Lepanto Far Southeast Porphyry Cu‐Au Deposit, Mankayan, Philippines

Abstract: The Lepanto Far Southeast porphyry Cu‐Au deposit is located beneath and to the southeast of the Lepanto enargite‐luzonite Cu–Au deposit in Mankayan, Benguet Province, Philippines.The principal orebody consists of potassic alteration subjected to partial retrograde chlorite alteration that rims stock‐work of quartz‐anhydrite veinlets. Fluid inclusions found in stockwork quartz and anhydrite in the biotitized orebody center are dominated by polyphase inclusions that homogenize at temperatures of &gt;500C. Sulfur isotopic thermometry applied to the sulfides‐anhydrite pairs suggests around 500C. The principal ore minerals associated with quartz‐anhydrite stockworks are chalcopyrite and pyrite with minor bornite and Bi–Te–bearing tennantite, with trace of native gold. Rounded pyrite grains appear fractured and corroded and are interpreted as remnants of primary intermediate solid solution + pyrite assemblage.A breccia pipe truncates the deposit. Mineralization in the breccia pipe is brought by quartz‐anhydrite veinlets and infilling in the interstices between clasts. Chalcopyrite‐Au mineralization associated with molybdenite is recognized in the deeper zone in the breccia pipe. Fluid inclusion microthermometry on polyphase inclusions in veinlet quartz as well as sulfur isotope thermometry applied for the pair of anhydrite and sulfides suggests &gt;450C.Fluid inclusions in veinlet quartz and anhydrite in the fringe advanced argillic alteration are chiefly composed of coexisting liquid‐rich inclusions and gas‐rich inclusions, in addition to coexisting polyphase inclusions and gas‐rich inclusions. These inclusions exhibit a wide range of homogenization temperatures, suggesting heterogeneous entrapping in the two‐fluid unmixing region.Sulfur isotopes of aqueous sulfide and sulfate exhibit a general trend from the smallest fractionation pairs (about 11%) in the biotitized orebody center to the largest fractionation (about 25%) pairs in the fringe advanced argillic alteration, suggesting a simple evolution of hydrothermal system. The slopes of arbitrary regression lines in δ34S versus 34S[SO4 = –H2S] diagram suggest that the abundance ratio of aqueous sulfate to sulfide in the hydrothermal fluid has been broadly constant at about 1:3 through temperature decrease. The intersection of these two regression lines at the δ34S axis indicates that the bulk δ34S is about +6%. Thus, the Lepanto FSE deposit is a further example which confirms enrichment in 34S in the hydrous intermediate to silicic magmas and associated magmatic hydrothermal deposits in the western Luzon arc.