Variation Of δ34S Values Research Articles

Sulfur isotope study of vent chimneys from Upper Cretaceous volcanogenic massive sulfide deposits of the eastern Pontide metallogenic belt, NE Turkey

We obtained sulfur isotope analysis results of sulfide samples from hydrothermal vent chimneys of the eastern Pontide volcanogenic massive sulfide (VMS) deposits. The total range of δ34S values for vent chimneys in the eastern Pontide VMS deposits is -2.7 to 6.5 per mil. Sulfide Δ34S values show narrow variation in the Lahanos, Killik, and Kutlular deposits, but wider variation in the Kizilkaya and Cayeli deposits. The δ34S values of sulfides in Cayeli chimney samples gave a slightly higher range than the other Pontide chimney samples. In some samples, a rough isotopic zonation pattern was observed throughout chimney zones. Variations in δ34S values of sulfides within chimney walls were probably caused by chemical reactions of reprecipitation and replacement between vent fluids and earlier sulfide minerals in the chimney. Ranges of Δ34S values of sulfide minerals are similar for different deposits within the same region. Variations in the δ34S values of the Pontide deposits appear to be geographic rather than stratigraphic. The sulfur isotope values of the deposits have a narrow compositional range, indicative of a fairly specific origin. Although deep-seated sulfur may be a potential source in the Pontide district, a significant contribution of seawater sulfate cannot be ruled out. The δ34S values of selected samples from Pontide vent chimneys are within the range of sulfur values obtained from Phanerozoic VMS deposits. The range is similar to, but slightly broader than, the range of values reported for modern vent chimneys and ancient vent chimneys from the Yaman-Kasy deposit.

In-situ Isotopic and Chemical Study of Pyrite from Chu-Sarysu (Kazakhstan) Roll-front Uranium Deposit

Pyrite is common in roll-front type uranium deposit in Chu-sarysu basin, Kazakhstan. Combined in-situ microstructural, isotopic and chemical analysis of pyrite indicates variation in precipitation conditions and in fluid composition. Broad-scale δ34S heterogeneity indicates a complex multi-facet evolution. First generation authigenic framboïdal aggregates are biogenic as demonstrated by the lowest δ34S values of -48‰ to -28‰. The latest generation pyrites are probably hydrothermal with greater δ34S variation (-30‰ to +12‰). This hydrothermal pyrite commonly displays variable enrichment of several trace elements especially As, Co and Ni. Strong variation in δ34S values and variable trace element enrichment is interpreted in terms of continuous variations in fluid composition.

Sources and meteorological factors that control seasonal variation of δ34S values in rainwater

Sulfate concentrations and sulfur isotopic compositions were measured in rainwater in Guiyang city in Southwest China between October 2008 and September 2009 to identify sulfur sources and their impacts on sulfur isotopic composition. The δ34S values of 1235 samples collected during this period ranged from−12.0 to +9.4‰, with a volume-weighted mean of−2.8±9.8‰, suggesting that rainwater sulfate in Guiyang was mainly derived from SO2 produced during coal combustion. The δ34S values of rainwater sulfate increased from 1987 to 2009, with an increment of about +0.16‰ per year, reflecting a gradual reduction in 34S-depleted SO2 emitted during coal combustion. Seasonal variations in δ34S values were pronounced, with higher values in winter than in summer. Long-distance transport of SO2 from coal burned in northern cities (which was higher than the component from southern cities), and more importantly, the aqueous oxidation of SO2 during transport affected the seasonal variation of rainwater δ34S values in Guiyang. Temperature-dependent aqueous oxidation of SO2 suggested that lower rainwater δ34S coincides with higher temperature.

Sulfur isotopic systematics of granitoids from southwestern New Brunswick, Canada: implications for magmatic-hydrothermal processes, redox conditions, and gold mineralization

Bulk δ 34Srock values, sulfur contents, and magnetic susceptibility were determined for 12 gold-related granitoid intrusions in southwestern New Brunswick, the Canadian Appalachians. The sulfur isotope compositions of sulfide minerals in some of the granitoid samples were also analyzed. This new dataset was used to characterize two distinctive groups of granitoids: (1) a Late Devonian granitic series (GS) and (2) a Late Silurian to Early Devonian granodioritic to monzogranitic series (GMS). The GS rocks have a large range in δ 34S values of −7.1‰ to +13‰ with an average of 2.2 ± 5.0‰ (1σ), low bulk-S contents (33 to 7,710 ppm) and low magnetic susceptibility values (<10−4 SI), consistent with reduced ilmenite-series granites. The GMS rocks have a relatively narrower variation in δ 34S values of −4.4‰ to +7.3‰ with an average 1.2 ± 2.9‰ but with larger ranges in bulk-S contents (45 to 11,100 ppm) and high magnetic susceptibility values (>10−3 SI), indicative of oxidized magnetite-series granites. The exceptions for the GMS rocks are the Lake George granodiorite and Tower Hill granite that display reduced characteristics, which may have resulted from interaction of the magmas forming these intrusions with graphite- or organic carbon-bearing sedimentary rocks. The bulk δ 34S values and S contents of the GMS rocks are interpreted in terms of selective assimilation–fractional crystallization (SAFC) processes. Degassing processes may account for the δ 34S values and S contents of some GS rocks. The characteristics of our sulfur isotope and abundance data suggest that mineralizing components S and Au in intrusion-related gold systems are dominantly derived from magmatic sources, although minor contaminants derived from country rocks are evident. In addition, the molar sulfate to sulfide ratio in a granitic rock sample can be calculated from the δ 34Srock value of the whole-rock sample and the δ 34Ssulfide (or δ 34Ssulfate) value of sulfide and/or sulfate mineral in the sample on the basis of S-isotope fractionation and mass balance under the condition of magmatic equilibrium. This may be used to predict the speciation of sulfur in granitic rocks, which can be a potential exploration tool for intrusion-related gold systems.

Influence of structural setting on sulphur isotopes in Archean orogenic gold deposits, Eastern Goldfields Province, Yilgarn, Western Australia

The published mean δ34S values of ore-related pyrites from orogenic gold deposits of the Eastern Goldfields Province, Yilgarn Craton lie between −4‰ and +4‰. As for orogenic gold deposits worldwide, most deposits have positive means and a restricted range of δ34S values, but some have negative means and wider ranges of δ34S values. Wall-rock carbonation and back-mixing of similar-source fluids with different fluid pathways can explain some of the more negative δ34S signatures. However, structural setting appears to be the most important factor controlling ore-fluid oxidation state and hence the distribution of δ34S values in gold-related pyrites. Shear-hosted deposits appear to have experienced fluid-dominated processes such as phase separation, whereas stockwork, vein-hosted or disseminated deposits formed under conditions of greater rock buffering. At Victory-Defiance, in particular, negative δ34S values are more common in gently dipping dilational structures, compared to more compressional steeply dipping structures. It appears most likely that fluid-pressure fluctuations during fault-valve cycles establish different fluid-flow regimes in structures with different orientations. Rapid fluid-pressure fluctuations in dilational structures during seismic activity can cause partitioning of reduced gas phases from the ore fluid during extreme phase separation and hence are an effective method of ore-fluid oxidation, leading to large, local fluctuations in oxidation state. It is thus not necessary to invoke mixing with oxidised magmatic fluids to explain δ34S signatures indicative of oxidation. In any case, available, robust geochronology in the Eastern Goldfields Province does not support the direct involvement of oxidised magmatic fluids from adjacent granitic intrusions in orogenic gold genesis. Thus, negative mean δ34S values and large variations in δ34S values of ore-related pyrites in world-class orogenic gold deposits are interpreted to result from multiple mechanisms of gold precipitation from a single, ubiquitous ore fluid in varying structural settings, rather than from the involvement of oxidised ore fluids from a different source. Such signatures are indicative, but not diagnostic, of anomalously large orogenic gold systems.

Seasonal and event variations in δ34S values of stream sulfate in a Vermont forested catchment: Implications for sulfur sources and cycling

Stable sulfur (S) isotope ratios can be used to identify the sources of sulfate contributing to streamwater. We collected weekly and high-flow stream samples for S isotopic analysis of sulfate through the entire water year 2003 plus the snowmelt period of 2004. The study area was the 41-ha forested W-9 catchment at Sleepers River Research Watershed, Vermont, a site known to produce sulfate from weathering of sulfide minerals in the bedrock. The δ 34S values of streamwater sulfate followed an annual sinusoidal pattern ranging from about 6.5‰ in early spring to about 10‰ in early fall. During high-flow events, δ 34S values typically decreased by 1 to 3‰ from the prevailing seasonal value. The isotopic evidence suggests that stream sulfate concentrations are controlled by: (1) an overall dominance of bedrock-derived sulfate ( δ 34S ~ 6–14‰); (2) contributions of pedogenic sulfate ( δ 34S ~ 5–6‰) during snowmelt and storms with progressively diminishing contributions during base flow recession; and (3) minor effects of dissimilatory bacterial sulfate reduction and subsequent reoxidation of sulfides. Bedrock should not be overlooked as a source of S in catchment sulfate budgets.

Sulfur Isotope Geochemistry of the Supergiant Xikuangshan Sb Deposit, Central Hunan, China: Constraints on Sources of Ore Constituents

. The supergiant Xikuangshan Sb deposit is located in the Middle to Upper Devonian limestone of central Hunan, China. Primary ores are composed of early-stage stibnite and calcite with rare pyrite, early main-stage stibnite and quartz, and late main-stage stibnite and calcite. New sulfur isotope data reveal the clustering of δ34S values (+5 ∼ +8 %) for both early and late main-stage stibnite; a single early-stage stibnite exhibits δ34S value (+7.5 %) identical to its main ore-stage counterparts and the coexisting calcite has almost unmodified carbon isotope composition (-4.4 %). The data suggest a probable common source of sulfur for stibnite that was deposited at different paragenetic stages. A much wider variation in δ34S values for early main-stage stibnite (+3.5 to +16.3 %, av. +7.5 %) compared to that for late main-stage stibnite (+5.3 to +8.1 %, av. +6.2 %) can be interpreted to be due to local interaction of earlier ore fluid with Devonian host rocks. The previous studies show that the Precambrian basement contains elevated Sb concentrations, and two distinctive sulfur reservoirs with δ34Spyrite values at ca. +11 ∼ +24 % and -7.0 ∼-11 %. The homogenizing effect for sulfur hydrothermally leached from the two reservoirs might have provided ore constituents for the Xikuangshan fluids.

Sulfur Isotope Study on Hg and Sb Deposits in Japan

Abstract. Sulfur isotope ratios of cinnabar from Hg deposits and stibnite, jamesonite and berthierite from Sb deposits in Japan are examined in order to understand metallogeneses of Hg and Sb deposits in Japanese island arcs. The studied Hg and Sb deposits include the Hg deposit at Yamato‐suigin (Honshu) and the Sb deposit at Ichinokawa (Shikoku) in the Southwest Japan arc. In addition, Hg deposits including Itomuka and Ryushoden in central Hokkaido and Hg and Sb mineralizations in Northeast Japan arc are examined.The δ34S values of cinnabar from the Hidaka‐Kitami district, central Hokkaido, including the Itomuka and Ryushoden deposits range widely, from ‐10 to +16 %o, the highest values encountered at the Samani deposit. The δ34S values of cinnabar from other areas in Japan range from ‐12 to +5 %o, having δ34S values higher than +2 %o from southwestern Hokkaido (Meiji deposit), Shikoku (Suii deposit) and Kyushu (Hasami and Yamagano deposits). On the other hand, the δ34S values of stibnite from all areas in Japan range from ‐14 to +5 %o, having positive δ34S values higher than +2 %o up to +5 %o from southwestern Hokkaido (Yakumo, Toyotomi and Teine deposits) and eastern‐central Honshu (Hachiman and Daikoku deposits).The variation in δ34S values of Hg and Sb deposits may reflect the variation in δ34S values of country rocks or variation in mixing ratio of sulfur extracted from the country rocks, sulfur derived from seawater sulfate, and sulfur derived from magmatic emanations. The relatively high δ34S values of cinnabar and stibnite higher than +2 %o from southwestern Hokkaido, eastern‐central Honshu and Kyushu are probably caused by contribution of volcanic emanation from arc magmas having positive σδ34S values, whereas the positive δ34S values of cinnabar higher than +2 %o from Suii deposit in Shikoku may be attributed to structurally substituted sulfate in limestone country rocks and/or sulfur derived from seawater sulfate. However, the wide range of the δ34S values of cinnabar from the Hidaka‐Kitami district, central Hokkaido, is difficult to explain at this moment. Other relatively low, negative δ34S values of cinnabar and stibnite, berthierite from other areas in Japan may be attributed to 1) incorporation of isotopically light sedimentary sulfur or sulfur derived from ilmenite‐series silicic magma, or 2) less contribution of volcanic emanation from arc magmas having positive σδ34S values.

Sulfur isotopic variations in soft tissues of five benthic animals from the reductive, tidal-flat sediments in northern Kyushu, Japan

The sulfur nutrition of five benthic animals living in or on reductive, tidal-flat sediments has been studied by using the sulfur isotopic signatures of their soft tissues. The mean δ34S values (+6.1‰ to +13.8‰, relative to the Canyon Diablo troilite reference) of these animals' tissues are lower than those of many common marine animals, which have values close to those of seawater sulfate-sulfur (+21‰). This indicates that these animals use a 34S-depleted sulfur source, which may be derived from bacterial sulfide in the sediments (less than –20‰). The animals that inhabit such sediments are adapted to an anoxic environment, where toxic hydrogen sulfide prevails. Due to the sulfide-rich habitat, benthic animals are expected to assimilate hydrogen sulfide directly during detoxification, or to prefer a diet which has a low δ34S signature. Variations in δ34S values of the sampled molluscs were fairly small, whereas migratory shrimp and fish tended to have larger variations, implying that migratory animals feed on diverse prey, while the molluscs feed on a common food, or their assimilative capacity for sulfide-sulfur does not vary among individuals. A gastropod inhabiting the surface of the reductive sediment showed a distinctively low δ34S value (+5.8‰ to +6.4‰), indicating that the animal fed on detritus from reeds and halophytes with low δ34S values (–19.1‰ to –2.1‰). This study suggests that some benthic animals incorporate sulfide-sulfur for their nutrition and that sulfur isotope composition can be a useful indicator in the analysis of the food habitat of animals.

Palaeoenvironmental significance of rounded pyrite in siliciclastic sequences of the Late Archaean Witwatersrand Basin: oxygen‐deficient atmosphere or hydrothermal alteration?

AbstractPetrographic and sulphur isotope studies support the long‐held contention that rounded grains of pyrite in siliciclastic sequences of the Late Archaean Witwatersrand Supergroup originated as placer grains. The grains are concentrated at sites where detrital heavy minerals are abundant within quartz‐pebble conglomerates and quartzose sandstones. Depositional sites with abundant pyrite are: (1) within the matrix of bar‐type, clast‐supported conglomerates; (2) on scoured or winnowed surfaces; and (3) on stratification planes. The grains are internally compact or porous, with truncation of internal structure at outer margins indicating fragmentation and rounding of pyritic source‐rocks during erosion and sediment transport. A large range in textures reflects source‐rock lithologies, with known varieties linked to sedimentary‐hosted diagenetic pyrite, volcanic‐hosted massive sulphide deposits and hydrothermal pyrite. Laser ablation sulphur isotope analysis of pyrite reveals a broader range in δ34S values (− 5·3 to + 6·7‰) than that of previously reported conventional bulk‐grain analyses (− 1 to + 4‰). Rounded pyrite from the Steyn Reef has significant variation in δ34S values (− 4·7 to + 6·7‰) that establishes heterogeneous sulphur compositions, with even adjacent grains having diverse isotopic signatures. The heterogeneity supports a placer origin for rounded pyrite. Euhedral pyrite and pyrite overgrowths which are undoubtedly authigenic have restricted δ34S values (− 0·5 to + 2·5‰), are chemically distinct from rounded pyrite and are probably the products of metamorphism or hydrothermal alteration. The placer origin of rounded pyrite indicates that pyrite was a stable heavy mineral during erosion and transport in the early atmosphere. Its distribution in three sequences (Witwatersrand Supergroup, Ventersdorp Contact Reef and Black Reef), and in other sequences not linked to Witwatersrand‐type Au‐U ore deposits, implies deposition of redox‐sensitive detrital heavy minerals during the Late Archaean. Consequently, rounded grains of detrital pyrite are strong indicators of an oxygen‐poor atmosphere. While not confirming a placer origin for gold in Witwatersrand Au‐U ore deposits, the palaeoenvironmental significance of rounded pyrite negates its link to hydrothermal mineralization.

Sulfur and strontium isotope composition of the Llobregat river (NE Spain): Tracers of natural and anthropogenic chemicals in stream waters

The use of sulfur and strontium isotopes as tracers forthe source/s of water contaminants have been applied to thewater of the Llobregat River system (NE Spain). Surfacewater samples from June 1997 were collected from theLlobregat River and its main tributaries and creeks. Thechemistry of most stream waters are controlled mainly bythe weathering of Tertiary chemical sediments within thedrainage basin. The largest variation in δ34Svalues were found in the small creeks with values rangingfrom –9.9 to 15‰, whilst in the main river channels valuesranged from 6.3 to 12.4‰. The 87Sr/86Sr ratio fordissolved strontium ranged from 0.70795 for a non-pollutedsite to 0.70882 for a polluted one. Most of the waters withhigh NO3 and low Ca/Na ratio converge to the same87Sr/86Sr value, pointing to dominant pollutantend member contribution or a mixing of pollutants with anisotopic composition around 0.7083–0.7085. Although theconcentration of the natural inputs in the river forsulfate and strontium are high, as a result of the sulfateoutcrops within the geology of the basin, their isotopiccharacteristics suggest that they can be used as adiscriminating device in water pollution problems. Howeverto establish the detailed characteristics of the isotopesas geochemical tools, specific high-resolution case studiesare necessary in small areas, where the inputs are well known.

Sulfur and carbon isotope analyses of the 2.7Ga Jeerinah Formation, Fortescue Group, Australia.

Sulfur and carbon isotope ratios have been determined on carbonaceous shales of the 2.7 Ga Jeerinah Formation, Hamersley Group, Australia. The analyses were performed using the Nd-YAG laser microprobe method. The δ13C(PDB) values of organic matter range from -38.3‰ to -35.1‰ with an average of -37.0‰ (44 analyses). These carbon isotope compositions support the previously proposed hypothesis that methanogens and methanotrophs were involved in the carbon cycles in the 2.7 Ga Hamersley ocean. Sulfur isotope compositions are ranging from +0.4‰ to +10.2‰ with an average of +4.6‰ (90 analyses). A notable feature is variable δ34S values within a micro-scale area; approximately 6 to 7‰ variations of δ34S values were detected within 5 × 5 mm areas. Such δ34S variations clearly indicate that pyrites in the Jeerinah shales were formed as a result of the sulfate reduction. This suggests that the 2.7 Ga Hamersley ocean contained appreciable amount of dissolved sulfate, opposing to the previously popular H2S-rich ocean model. Because of no evidence for the hydrothermal alterration on the examined samples, pyrites in the 2.7 Ga Jeerinah shales were most likely formed by the biological sulfate reduction in sediments.

Sulfur isotope evidence for penetration of MVT fluids into igneous basement rocks, southeast Missouri, USA

Previous studies of galena and sphalerite from Paleozoic MVT deposits in the Viburnum Trend, southeast Missouri documented large variations in δ34S values throughout the ore-forming event. The present study of Cu-Fe-sulfides reveals a similar δ34S variation that reflects two end-member sulfur reservoirs whose relative importance varied both temporally and spatially. More 34S-enriched sulfides (δ34S approaching 25‰) indicate introduction of sulfur from basinal sedimentary sources, whereas more 32S-enriched sulfides (δ34S 600 m vertically through underlying Precambrian igneous rocks. Such basement involvement has been suggested for other carbonate-hosted base-metal districts (e.g. Irish base metal deposits) and should be considered an integral part of the ore-forming process in southeast Missouri.

Cyclic variations of sulfur isotopes in Cambrian stratabound Ni-Mo-(PGE-Au) ores of southern China

Cyclic variations of δ34S values over a range of at least 48‰ in pyrite nodules from stratabound Ni-Mo-PGE(Au) ores of southern China are attributed to biogenic reduction of seawater sulfate in an anoxic, phosphogenic, and metallogenic basin. Cyclic introduction and mixing of normal seawater into typically stagnant basin waters led to extreme variations in δ34S values of aqueous sulfide species present at different times. Intermittent venting of metal-laden hydrothermal fluids into such a bacteriogenic sulfide-rich environment resulted in precipitation of metal sulfides as pseudomorphous replacements of organic debris and as sulfide sediments that record large δ34SCDT variations from −26 to +22‰. Apatite and silica dominated the replacement of the organic debris when metals were not being introduced into the basin. The combination of abundant organic debris, localized topographic basins for accumulation of the debris, bacterial production of sulfide species, and introduction of metal-bearing hydrothermal fluids provided the environment necessary to form these unusually rich Ni-Mo ores.

MINERALOGY, TEXTURES, AND FORMATION CONDITIONS OF MODERN SULFIDE ORES, MANUS BASIN RIFT ZONE

The mineralogy of active chimneys of the Vienna Woods ore field described in the preceding paper has been studied in detail. Predominant minerals are zinc sulfides (sphalerite and wurtzite), iron disulfude (pyrite and marcasite), amorphous silica, and barite, with lesser amounts of chalcopyrite and galena. The sulfide ores are enriched in silver and antimony, apparently occurring in the form of micrometer-size sulfosalts. Two mineral assemblages have been recognized: the earlier one consists of pyrite, sphalerite (or wurtzite) and chalcopyrite, and the later one includes marcasite, pyrite, sphalerite, galena and sulfosalts. The sulfide minerals display considerable variations in δ34S values, from −4.7 to +6.0‰. The ores were formed below 270° C at pH 4-5 as higher-temperature fluids mixed with seawater.