Sulfur Isotope Geochemistry Research Articles

Subaerial sulfate mineral formation related to acid aerosols at the Zhenzhu Spring, Tengchong, China

AbstractThe Zhenzhu Spring, located in the Tengchong volcanic field, Yunnan, China, is an acid hot spring with high SO42−concentrations and intense acid aerosol generation. In order to understand the formation mechanism of sulfate minerals at the Zhenzhu Spring and provide a better insight into the sulfur isotope geochemistry of the associated Rehai hydrothermal system, we investigated the spring water hydrochemistry, mineralogy and major-element geochemistry of sulfate minerals at the Zhenzhu Spring together with the sulfur-oxygen isotope geochemistry of sulfur-containing materials at the Rehai geothermal field and compared the isotope results with those in other steam-heated environments. Subaerial minerals include a wide variety of sulfate minerals (gypsum, alunogen, pickeringite, tamarugite, magnesiovoltaite and a minor Mg–S–O phase) and amorphous SiO2. The δ34S values of the subaerial sulfate minerals at the Zhenzhu Spring varied subtly from –0.33 to 1.88‰ and were almost consistent with the δ34S values of local H2S (–2.6 to 0.6‰) and dissolved SO42−(–0.2 to 5.8‰), while the δ18O values (–8.94 to 20.1‰) were between that of the spring waters (–10.19 to –6.7‰) and atmospheric O2(~23.88‰). The results suggest that most of the sulfate minerals are derived from the oxidation of H2S, similar to many sulfate minerals from modern steam-heated environments. However, the rapid environmental change (different ratio of atmospheric and water oxygen) at the Zhenzhu Spring accounts for the large variation of δ18O. The formation of subaerial sulfate minerals around the Zhenzhu Spring is related to acid aerosols (vapour and acid water droplets). The intense activity of spring water around vents supply the aerosol with H2SO4(H2S oxidation and acid water droplets formed by bubble bursting) and few cations. Deposition of the acid sulfate aerosol forms the acid condensate, which attacks the underlying rocks and releases many cations and anions to form subaerial sulfate minerals at the Zhenzhu Spring.

Source of Mineralization Material of Xiaochigou Gold Deposit in Western Henan: Sulfur and Lead Isotope Geochemistry

Xiaochigou Gold Deposit is located in the middle of Xiongershan metamorphic core complex in Qinling orogenic belt. Based on the analysis of sulfur and lead isotopes in altered rock type ores formed in the main metallogenic stage of the deposit, it is found that the δ34S of sulfur isotope of the deposit is between-3.05% and 10.93%, mostly remaining within the range of meteorite sulfur, indicating that the sulfur mainly comes from the mantle with the addition of crustal sulfur, which reflects the sulfur isotopic composition of mantle sulfur after being mixed with crustal materials. The lead isotope 206Pb/204Pb value is 17.09-17.53, 207Pb/204Pb value is 15.31-15.61, and 208Pb/204Pb value is 37.20-38.10. The variation range is not wide, belonging to normal lead range. Lead isotopic characteristic parameters and related diagrams show that the lead in ores has crust-mantle mixing characteristics. The sulfur and lead isotope compositions show that the ore-forming materials of the deposit are mainly mantle-derived materials, and the deep mantle-derived materials are mixed with crust-derived materials.

Mineralogy, alteration, and sulfur isotope geochemistry of the Zehabad intermediate-sulfidation epithermal deposit, NW Iran

The Zehabad Pb-Zn-Au-Ag (Cu) deposit lies in the Alborz magmatic arc of northwestern Iran. Ore-bearing breccia veins hosted by Eocene tuffs emplaced along the 80?130° trending fault and fracture zone. Mineralization occurs in the contact of the late Eocene igneous bodies and the Eocene volcanic and volcanosedimentary Karaj Formation. Mineralization formed in five stages: 1) disseminated framboidal pyrite and minor chalcopyrite and sphalerite; 2) quartz veins containing chalcopyrite, bornite, pyrite, and sphalerite; 3) deposition of specularite and gold grains hosted in quartz veins that crosscut chalcopyrite; 4) the main stage of mineralization that contains galena, sphalerite, tennantite-tetrahedrite, pyrite, sulfosalts, and gold; 5) barren quartz-calcite veins with sulfide mineral fragments of earlier stages. The hydrothermal alteration from closest to the veins outwards includes: a) silicification; b) phyllic with quartz, pyrite, sericite, and calcite; c) argillic with illite, kaolinite, and montmorillonite; d) propylitic containing epidote, calcite, chlorite, and sericite and; e) carbonatization that crosscuts all previous alteration types. Quartz and calcite are the most important gangue minerals at the deposit and show a close relationship with mineralization. Sulfur isotope compositions (0.8‰ to -10.1‰) suggest that the ore-forming fluids derived from magmatic sources with a temperature range of 276-288 °C. According to the field (macroscopic), microscopic, alteration, and sulfur isotope studies, the Zehabad base and precious metal mineralization is considered an intermediate-sulfidation epithermal deposit.

Trace element geochemistry of sphalerite in contrasting hydrothermal fluid systems of the Freiberg district, Germany: insights from LA-ICP-MS analysis, near-infrared light microthermometry of sphalerite-hosted fluid inclusions, and sulfur isotope geochemistry

The historic silver mining district of Freiberg (Germany) comprises hydrothermal vein-style mineralization of Permian and Cretaceous age. We compare sphalerite compositions with associated ore-forming fluids and constrain the behavior of critical metals such as In, Ge, and Ga in contrasting hydrothermal environments. Fluid inclusion studies reveal that the Permian veins formed due to boiling and cooling of a low-salinity (0 to 6% eq. w[NaCl]) magmatic-hydrothermal fluid at 350 to 230 °C. In contrast, Cretaceous veins formed by mixing of highly saline (17 to 24% eq. w[NaCl + CaCl2] and variable Na/(Na + Ca) ratios) brines at low temperatures (~ 120 °C). Sulfides of the Permian ore stage have a narrow range of δ34SVCDT from − 2.3 to + 0.9‰, while the sulfides of the Cretaceous stage have a large scatter and significantly more negative δ34SVCDT values (− 30.9 to − 5.5‰), supporting the different nature of the hydrothermal systems. Contrasting fluid systems and ore-forming mechanisms correspond to markedly different trace element systematics in sphalerite. Permian sphalerite is significantly enriched in In (up to 2500 μg/g In) relative to two sphalerite generations of Cretaceous veins. The latter have higher Ge (up to 2700 μg/g Ge) and Ga (up to 1000 μg/g Ga) concentrations. The observed trace element systematics of different sphalerite generations imply that In is enriched in high-temperature, low- to intermediate-salinity fluids with a significant magmatic-hydrothermal fluid component, while Ge and Ga are more concentrated in low-temperature, high-salinity crustal fluids with no obvious magmatic-hydrothermal affiliation.

Tectonic and metallogenic evolution of the Curaçá Valley Copper Province, Bahia, Brazil: A review based on new SHRIMP zircon U-Pb dating and sulfur isotope geochemistry

More than three hundred mafic-ultramafic bodies of different sizes, containing copper sulfide mineralization, are present in the Curaçá River Valley Copper Province, northeastern São Francisco Craton, Bahia State, Brazil, covering an area of about 1700 km2. The basement, supracrustal sequence, and mafic-ultramafic intrusive rocks underwent granulite facies metamorphism and were reworked during the evolution of the Itabuna-Salvador-Curaçá Orogeny, resulting in retrograde metamorphism to the amphibolite facies, partial migmatization, and intrusion of granitic and syenitic rocks. During the slow and progressive rise of the terrain, hydrothermal reactions mainly along shear zones retrogressed part of these rocks to assemblages characteristic of the greenschist metamorphic facies. The main orebodies with copper sulfide minerals are associated with pyroxenite, mica-rich (glimmerite) and noritoid rocks. The present investigation focuses on the major Caraíba, Sussuarana, Surubim, and Vermelhos deposits. Chalcopyrite and bornite compose the ore, in a ratio of 70–30%, with copper grade varying between 0.69% and 1.4%, and associated gold and silver. The sulfide minerals are invariably accompanied by magnetite. Two mineralization styles are distinguished: (i) disseminated in non-altered mafic-ultramafic rocks; and (ii) tectonic controlled related to hydrothermal alteration zones. New geochronological data show that quartz-microcline metasomatites of the Caraíba Mine contain Neoarchean inherited zircons (upper intercept at 2723 ± 51 Ma), related to the early stages of magmatism, whereas Orosirian ages (2047 ± 12 and 2042 ± 15 Ma) are related to the main hydrothermal mineralization activity. Norite from the Surubim Mine has a Paleoproterozoic age (2047 ± 11 Ma), and the dated gabbro shows Pb loss in the Neoproterozoic, probably related to the Brasiliano Orogeny (670–490 Ma). Previous studies have demonstrated that the main hydrothermal event is Paleoproterozoic. Phlogopite Ar-Ar dating from the Caraíba Mine yields plateau-ages around 2000–2100 Ma. A cluster of δ34S values approaching zero is related to interstitial sulfide minerals in the least-altered ultramafic rocks, while values above and below zero are related to remobilized sulfides. These data support the hypothesis of the existence of a primary (magmatic) mineralizing event, alleged to have precipitated disseminated, interstitial sulfide minerals, and a second (hydrothermal) event, responsible for the economically more important mineralization, which is structurally controlled and related to significant potassic alteration. The sulfide minerals are associated with different generations of magmatic and hydrothermal magnetite, as well as distal plagioclase and microcline alteration halos. The combination of these features reaffirms the concept that the Curaçá Valley deposits may be part of the same alteration system, as described in IOCG deposits, with the deepest deposits being located further south. Based on the data obtained during the present study, it is possible to establish a tectono-metallogenic evolutionary model to explain the genesis of the copper mineralization in the Curaçá Valley. The mafic-ultramafic bodies were emplaced as multiple intrusions in Neoarchean arc-related gneisses and chemical sediments, along with bornite and chalcopyrite mineralization. The sulfide minerals that preserve the characteristics of this stage are chalcopyrite or bornite, both with δ34S values around 0‰V-CDT.A continental collision affected the Caraíba arc and the related sequences between 2100 and 2080 Ma. During this Rhyacian-Orosirian orogeny, deformation and amphibolite-granulite facies metamorphism, the rocks underwent partial melting, and sapphirine formation developed. Between 2050 and 2020 Ma, the main mineralization stage took place at Caraíba, Vermelhos, and Surubim, which corresponds to an earlier stage in the Sussuarana deposits. The southern deposits were formed deeper than those to the north, resulting in less extensive potassic alteration and related hydrothermal mineralization. The sulfide minerals of the deeper deposits have negative δ34S (between 0‰ and −6.81‰), to slightly positive values, where the igneous protoliths are best preserved. This alteration took place near the brittle-ductile boundary, mainly associated with ductile structures.The latest stage of mineralization took place between 1950 and 1920 Ma, in the Caraíba, Vermelhos and Surubim deposits, along with major sulfide remobilization in Sussuarana. This stage was characterized by the participation of oxidizing fluids, possibly meteoric waters, which raised the δ34S values up to +11.77‰.

Sulfur isotope and fluid inclusion geochemistry of metamorphic Cu–Au vein deposits, central Cobar area, NSW, Australia

ABSTRACTVein-type, structurally controlled Cu–Au mineralisation hosted by turbidites of late Silurian to earliest Devonian age, forms an important resource close to the eastern margin of the Cobar Basin. Here we report 103 new sulfur isotope analyses, together with homogenisation temperatures and salinity data for 545 primary two-phase fluid inclusions for the mineralised zones from the central area of the Cobar mining district. A range in δ34S values from 3.8 to 11.2‰ (average 7.9‰) is present. Sulfur is likely to have been derived from rock sulfur/sulfide in basin and basement rocks, but there may be an additional connate-derived component. Homogenisation temperatures (Th) for inclusion fluids trapped in quartz and minor calcite veins range from near 150°C to 397°C. Fluid inclusions are characterised by a low CO2 content and low, but variable salinities (2.1–9.1 wt% NaCl equivalent). Generations of inclusion fluids correspond to six paragenetic stages of vein quartz deposition and recrystallisation at the Chesney mine. Primary fluid inclusions in the first two stages were subjected to re-equilibration resulting from increased confining pressure. Their Th range (151–317°C) is considered a minimum for the temperature of these fluids. Sulfide and gold deposition at Chesney appears to be related to fluids of moderately high Th (range 270–397°C) associated with the final paragenetic stage. Th for the ore-related fluids may be close to the solvus of the H2O–NaCl–CO2 system and hence near trapping temperatures. Late-stage entry of a hot, moderately saline ore-forming fluid is implicated as the origin of the Cu–Au mineralisation. However, comparison with geochemical data for the vein-style Zn–Pb–Ag deposits at Cobar demonstrates that differences in metal content for individual zones cannot be attributed to major differences in fluid temperature or salinity. Rather, these differences are probably due to variations in source-rock reservoirs and structural pathways along which the ore-forming fluids moved.

Multiple sulfur isotope geochemistry of Dharwar Supergroup, Southern India: Late Archean record of changing atmospheric chemistry

Earth's tectonic and climatic systems may have changed fundamentally before the Great Oxidation Event (GOE) at about 2.3 Ga. Sulfur Mass Independent Fractionation (S-MIF) has demonstrated that Earth's atmosphere was virtually oxygen-free before the GOE. During 3.0 to 2.4 Ga, the change in Δ33S and Δ36S signals may reflect the perturbation of atmospheric chemistry, though the mechanisms of the change are uncertain. Here, we reported multiple sulfur isotopic studies of Archean volcano-sedimentary sequences of the Dharwar Supergroup, distributed in the Chitradurga Schist Belt (CSB), Southern India. New field mapping and zircon U–Pb dating allows us to reconstruct detailed lithostratigraphy of the Dharwar Supergroup. The lower unit consists of post-3.0 Ga conglomerate, stromatolitic carbonate, siliciclastics with diamictite, chert/BIF and pillowed basalt in ascending order, all of which are older than the 2676 Ma dacite dyke that had intruded into the lower unit. The upper unit unconformably overlies the pillow basalts at the top of the lower unit, and consists of conglomerate/sandstone with ∼2600 Ma detrital zircons, komatiitic basalt, BIF and siliciclastic sequence with mafic volcanics. Sulfur isotope analysis of extracted sulfides shows MIF signals (ΔS33>+1‰) with clear ΔS33–ΔS36 correlations. The lower group of the Dharwar Supergroup shows a ΔS36/ΔS33 slope of −1.48, the middle group shows −1.16 and −1.07, and the upper group shows −0.94. Reassessment of all the Archean S-MIF records from sedimentary rocks indicates that the ΔS36/ΔS33 slope systematically changed during the Archean period. The observed trend in the Indian section is similar to those of its Pilbara–Kaapvaal equivalents, thus it could reflect a global atmospheric signature. Moreover, the isotopic trend seems to correlate with mid-Archean glaciation. Thus, the ΔS36/ΔS33 slope could be a useful tracer for atmospheric chemistry and its link with climate change before the GOE.

Sulfur Isotope Geochemistry Indicating the Source of Dissolved Sulfate in Gonghe Geothermal Waters, Northwestern China

The Gonghe region is characterized by the most active geothermal manifestation in Qinghai Province, northwestern China. The geothermal waters from three hydrothermal areas (Qiabuqia, Guide and Xinghai) of Gonghe have different hydrochemical and isotopic compositions. Nevertheless, most geothermal water samples fall into the area of evaporitic gypsum defined by the range of its δ34S-sulfate values and a few samples plot right on the border dividing the gypsum area and the atmospheric precipitation area, indicating that the formation of sulfate in Gonghe geothermal waters is commonly attributed to the dissolution of gypsum and/or anhydrite in host rocks, with a possible minor contribution of atmospheric precipitation. Moreover, the sulfate in Guide geothermal waters may originate partly from the oxidation of H2S at near-surface oxidizing environment. Sulfur isotopes are proved to be good indicators for identifying the geochemical genesis of geothermal water.

Mineralogy and sulfur isotope compositions of the uraniferous black slates in the Ogcheon Metamorphic Belt, South Korea

Uraniferous black slates, extending for over 100km in the Ogcheon Metamorphic Belt, South Korea, have been explored for their uranium mineralization. Coaly slates interbedded in the black slates, forming a layer about 20–40m thick showing brecciated and flow texture with random-oriented minerals, are more carbonaceous and uraniferous than the surrounding rocks. Uranium minerals include uraninite, uranothorite, brannerite, ekanite, thorutite, and coffinite. Of these, uraninite is the most abundant phase in the coaly slates, while uranothorite is the most abundant in the black slates. Chlorites in the black slates have Fe/(Fe+Mg) ratios of 0.42–0.66, while those in the coaly slates have lower values, 0.10–0.20. Chlorite geothermometry indicates temperature ranges of 259–309°C, and 200–287°C in the coaly and black slates, respectively. Muscovites in the coaly slates have higher concentrations of 0.85–1.55wt.% BaO and 0.22–0.28wt.% V2O3 than those in the black slates. This can be ascribed to hydrothermal venting of Ba-V-rich fluids into the marine basin. Most uranothorites in the black slates have lower U and higher Th contents than those in the coaly slates due to their solubility differences. In contrast to the comparatively low and wide-ranging δ34S values of pyrite from −5.9 to 6.6‰ in the black slates, the coaly slates have relatively high and uniform values from 11.0 to 12.7‰, implying an influx of isotopically heavy sulfur derived from the inorganic reduction of seawater sulfate under a high temperature hydrothermal system. The differences of rock texture, mineralogy, and sulfur isotope geochemistry in relation to uranium mineralization between the black slates and the coaly slates would reflect the influence of submarine hydrothermal process before they suffered regional metamorphism.

Styles, Textural Evolution, and Sulfur Isotope Systematics of Cu-Rich Sulfides from the Cambrian Whalesback Volcanogenic Massive Sulfide Deposit, Central Newfoundland, Canada

The Whalesback Cu-rich volcanogenic massive sulfide deposit in the Newfoundland Appalachians is a highly deformed deposit found on a steep limb of a closed and boudinaged overturned fold. The deposit was intensely deformed at low temperature but medium pressure (>175 MPa) during the accretion of the composite Lushs Bight oceanic tract-Dashwoods terrane onto the Humber margin at ca. 480 Ma. The ore mineralogy consists of chalcopyrite, pyrrhotite, and pyrite with lesser sphalerite and trace Ag, Bi, and Hg tellurides. Four styles of sulfide mineralization are present: (1) disseminated (5%); (2) vein (50%); (3) breccia (25%); and (4) semimassive to massive (20%). Independent of mineralization style, massive pyrite and pyrrhotite (and some chalcopyrite) are commonly parallel to main S 2 schistosity in the deposit, whereas late chalcopyrite piercement veins occur at a high angle to S 2 . The progressive increase in pressure and temperature produced a remobilization sequence wherein sphalerite was the first sulfide phase to cross the brittle-ductile boundary, followed by pyrrhotite and, finally, chalcopyrite. Maximum temperature was not high enough for the pyrite to cross the brittle-ductile boundary. Instead, pyrite grains were incorporated and transported by pyrrhotite and chalcopyrite during the ductile remobilization events, rounding and fracturing them. Remobilization of the sulfides occurred mainly by plastic flow, but some solution transport and reprecipitation is locally observed. In situ secondary ion mass spectrometry sulfur isotope geochemistry of sulfides yielded values of δ 34 S ranging from 2.7‰ to 4.7‰ for pyrite, 2.1‰ to 4.0‰ for pyrrhotite, and 1.3‰ to 4.7‰ for chalcopyrite. Sulfur isotope modeling suggests that at least 60% of the sulfur was derived from leaching of igneous rocks (i.e., basalts), with the remainder derived from thermochemical sulfate reduction of seawater sulfate during alteration of the basalts by seawater. At the deposit scale, sulfur isotopes retained their original signature and did not reequilibrate during the secondary deformation and remobilization events.

Petrochemistry, hydrothermal alteration, mineralogy, and sulfur isotope geochemistry of the Turgeon Cu–Zn volcanogenic massive sulfide deposit, northern New Brunswick, Canada

The Turgeon deposit is a mafic-type, Cu–Zn volcanogenic massive sulfide (VMS) deposit. It is hosted by Middle Ordovician pillow basalts of the Devereaux Formation of the Fournier Group within the Elmtree-Belledune inlier, near the Bathurst Mining Camp (BMC) in northern New Brunswick, Canada. The Turgeon deposit consists of two Cu–Zn massive sulfide lenses (“100m Zn”, “48-49”) composed of pyrite, chalcopyrite, pyrrhotite, and sphalerite, which are underlain by chalcopyrite–pyrite stockwork veins. Pyrite is overprinted and replaced by chalcopyrite in the stockwork and vent complex sulfide facies, where both minerals are enriched in Se and Co relative to pyrite and chalcopyrite in the massive pyrite and breccia sulfide facies. In, Se, and Co display a positive covariation with Cu, whereas Zn displays a positive covariation with Cd. Trace element geochemistry indicates that the host rocks are primarily tholeiitic basalts and andesites that have signatures between that of mid-ocean ridge basalt and island-arc tholeiite. The hanging wall rhyolite plots as an ocean ridge rhyolite and is geochemically similar to VMS-bearing FIIIa-type rhyolites. Hydrothermal alteration mineral assemblages in the footwall basalts proximal to mineralization are dominantly chlorite ± quartz in the stockwork zone, which is characterized by compositional gains in Fe and Mg and losses in Na and Ca. The chlorite-altered basalts and andesites have undergone up to 35% mass loss. Stockwork chlorite is an Fe-rich chamosite, whereas chlorite in the massive sulfides is a Mg-rich clinochlore. Chlorite geothermometry yields temperatures of 329–361 °C for chamosite and 246–286 °C for clinochlore. Sulfides at Turgeon have an average δ34SCDT of +6.9‰ (range: +5.8‰ to +10‰), indicating that sulfur was mostly derived from thermochemical reduction of Ordovician seawater sulfate. The Turgeon VMS deposit differs from those of the BMC, which is a reflection of their different tectonic settings; but it is similar to other mafic-type VMS deposits, such as the Betts Cove, Tilt Cove, and Rambler VMS deposits in Newfoundland, Canada.

Two-Generation of Sphalerite from Pb-Zn Mineralization of Riasi Inlier, Jammu and Kashmir, India: Evidences from Sulphur Isotopes

Precambrian carbonate sequence of Riasi Inlier hosts epigenetic lead-zinc mineralization in the form of pockets, lenses and veins. The mineralization is having variable Pb:Zn ratio and shows lithological preferences. The sphalerite rich pockets are concentrated within the dolostone of older Trikuta Formation while galena rich mineralization occurs in form of veins, lenses and pockets hosted within siliceous varieties of dolostone and quartzite belonging to younger Khairikot Formation. Sulphur isotope geochemistry is reported in the present paper for the sphalerire and galena from the area for first time. Overall δ34S of sulphides varies from (+9.67‰ to +34.42‰). Sphalerite ores hosted within older Trikuta Formation and younger Khairikot Formation, however, show different δ34S values. It ranged from +9.67‰ to +10.59‰ for the sphalarite hosted in Trikuta Formation and from +18.38‰ to +34.42‰ for sphalerite hosted within Khairikot Formation. Sulphur isotopic data and ore petrographic data suggest that there is two-generation of sphalerite present in the area.

Sulfur and Lead Isotope Geochemistry Characters of the Hadamengou Gold Deposit in Inner Mongolia

Sulfur and Lead Isotope Geochemistry Characters of the Hadamengou Gold Deposit in Inner Mongolia

Sulfur and Lead Isotope Geochemistry Characters of the Jinchanggouliang Gold Deposit in Inner Mongolia

Sulfur and Lead Isotope Geochemistry Characters of the Jinchanggouliang Gold Deposit in Inner Mongolia

Sulfur Isotope Geochemistry of the Xincheng Gold Deposit, Jiaodong: Constraints on the Material Source and Ore‐forming Environment

Sulfur Isotope Geochemistry of the Xincheng Gold Deposit, Jiaodong: Constraints on the Material Source and Ore‐forming Environment

Sulphur isotope composition of dissolved sulphate in the Cambrian–Vendian aquifer system in the northern part of the Baltic Artesian Basin

The groundwater in the Cambrian–Vendian aquifer system with its δ18Owater values of about −22‰ (VSMOW) and a low radiocarbon concentration is of glacial origin from the Last Ice Age. Earlier surveys have highlighted a negative co-variance of sulphate and bicarbonate content in the groundwater of the Cambrian–Vendian aquifer system, whereas the most depleted dissolved inorganic carbon δ13C values have been measured mainly in groundwater samples with the lowest sulphate concentrations. In this paper we studied the origin of sulphate and the factors controlling the sulphur and carbon isotope geochemistry in the aquifer system. Direct sources of sulphate were not found, but relying upon δ18OSO4 measurements we suggest that the sulphate originates from oxidation of sulphide minerals whereas the δ34S of the dissolved SO42− in the groundwater is more enriched than the δ34S of the surrounding rocks. We show that bacterial activity may have caused the enrichment of δ34S of sulphate.

Sulfur, Carbon, Hydrogen, and Oxygen Isotope Geochemistry of the Idaho Cobalt Belt

Cobalt-copper ± gold deposits of the Idaho cobalt belt, including the deposits of the Blackbird district, have been analyzed for their sulfur, carbon, hydrogen, and oxygen isotope compositions to improve the understanding of ore formation. Previous genetic hypotheses have ranged widely, linking the ores to the sedimentary or diagenetic history of the host Mesoproterozoic sedimentary rocks, to Mesoproterozoic or Cretaceous magmatism, or to metamorphic shearing. The δ 34 S values are nearly uniform throughout the Blackbird district, with a mean value for cobaltite (CoAsS, the main cobalt mineral) of 8.0 ± 0.4‰ ( n = 19). The data suggest that (1) sulfur was derived at least partly from sedimentary sources, (2) redox reactions involving sulfur were probably unimportant for ore deposition, and (3) the sulfur was probably transported to sites of ore formation as H 2 S. Hydrogen and oxygen isotope compositions of the ore-forming fluid, which are calculated from analyses of biotite-rich wall rocks and tourmaline, do not uniquely identify the source of the fluid; plausible sources include formation waters, metamorphic waters, and mixtures of magmatic and isotopically heavy meteoric waters. The calculated compositions are a poor match for the modified seawaters that form volcanogenic massive sulfide (VMS) deposits. Carbon and oxygen isotope compositions of siderite, a mineral that is widespread, although sparse, at Blackbird, suggest formation from mixtures of sedimentary organic carbon and magmatic-metamorphic carbon. The isotopic compositions of calcite in alkaline dike rocks of uncertain age are consistent with a magmatic origin. Several lines of evidence suggest that siderite postdated the emplacement of cobalt and copper, so its significance for the ore-forming event is uncertain. From the stable isotope perspective, the mineral deposits of the Idaho cobalt belt contrast with typical VMS and sedimentary exhalative deposits. They show characteristics of deposit types that form in deeper environments and could be related to metamorphic processes or magmatic processes, although the isotopic evidence for magmatic components is relatively weak.

Sulfur geochemistry of peridotite-hosted hydrothermal systems: Comparing the Ligurian ophiolites with oceanic serpentinites

Serpentinization processes at slow- and ultraslow-spreading ridges control the exchange of various elements between seawater and the oceanic lithosphere and play a major role in marine geochemical cycles. We use opaque mineral assemblages and sulfur isotope geochemistry to reconstruct variations in fluid fluxes, redox conditions and microbial activity prevailing during serpentinization and carbonate precipitation of serpentinites and ophicalcites from an ophiolite sequence in the Northern Apennines (Italy). We then compare our results with calcite-veined serpentinites from the Iberian Margin formed during the opening of the North Atlantic, and with serpentinites sampled at the active peridotite-hosted Lost City hydrothermal field on the Atlantis Massif near the Mid-Atlantic Ridge. The sulfide and oxide mineral assemblage of the serpentinites from the Northern Apennines is dominated by pyrite, pentlandite, millerite, siegenite, magnetite, and hematite, reflecting relatively oxidizing conditions, while the sulfur geochemistry reveals a dominance of sulfide sulfur over sulfate sulfur. δ34S values of sulfide and sulfate indicate that microbial sulfate reduction, leaching, and oxidation are the main processes that affected the sulfur isotope signature of these serpentinites. The opaque mineralogy in the serpentinites from the Northern Apennines is similar to that of the Iberian Margin and the southern wall of the Atlantis Massif, and generally represents the late stages of serpentinization, where intense fluid circulation leads to fairly oxidizing conditions and alkaline fluids lead to carbonate precipitation. However, the mineral assemblages also indicate strong fluctuations in oxygen fugacity, likely caused by volume expansion during serpentinization and tectonic activity along a mid-ocean ridge. Additionally, local enrichment in 34S in sulfides suggests that fluids interacted at depth with gabbros and subsequently circulated along shear zones, similar to observations along detachment fault surfaces at the Atlantis Massif. Our results, therefore, give further evidence that the ophicalcites and serpentinites from the Northern Apennines formed in a tectonic setting similar to the Atlantis Massif. We estimate a global annual uptake of seawater sulfate of 5.6 to 12×1011g S by serpentinization of ultramafic rocks exposed to seawater on the ocean floor. We suggest that the thermal structure of the exposed mantle rocks and, in turn, the efficiency of microbes to reduce seawater sulfate to sulfide is a major factor controlling the storage of sulfur in serpentinites. Thus, cycling of sulfur in peridotite-hosted hydrothermal systems during the Jurassic was probably very similar to the processes observed today in systems along the Mid-Atlantic Ridge.

서태평양 지판소멸대의 해저열수분출구에서 관찰되는 황동위원소 조성변화: 열수 생성의 다양성과 마그마의 역할

해저열수시스템은 중앙해령이나 후열도확장대와 같은 해저화산대를 따라 생성된다. 해저열수시스템은 지각-맨틀과 해양의 에너지와 물질이 교환되는 장으로 이를 통해 지각과 해수의 조성이 변화하며, 해저면에 열수분출구를 침전시켜 열수생태계를 형성하고 금속광상이 만들어진다. 상대적으로 단순한 중앙해령과 달리 지판소멸지역의 해저열수시스템은 섭입되는 물질의 재순환과정에서 다양한 특성이 나타난다. 황동위원소 조성은 이러한 열수시스템의 다양성을 평가하는데 유용하다. 이 논문에서는 서태평양의 지판소멸대에서 발견된 열수분출 지역에서 채취된 열수분출구 시료의 황동위원소 조성변화를 살펴보고 이들 환경에서 열수생성의 다양성을 일으키는 요인을 고찰하였다. 지판소멸대의 열수분출구는 황화광물과 황산염광물 모두 낮은 황동위원소 조성을 갖는 것이 특징이며, 이는 마그마로부터 공급된 <TEX>$SO_2$</TEX> 기체의 유입으로 해석된다. 황동위원소 조성 변화를 포함한 열수시스템의 다양성은 열수시스템 생성과정에서 마그마의 적극적인 역할을 지시한다. Seafloor hydrothermal system occurs along the volcanic mid-ocean ridge, back-arc spreading center, and other submarine volcanic regions. The hydrothermal system is one of the fundamental processes controlling the transfer of energy and matter between crust/mantle and ocean; it forms hydrothermal vents where various deepsea biological communities are inhabited and precipitates metal sulfide deposits. Hydrothermal systems at convergence plate boundaries show diverse geochemical properties due to recycle of subducted material compared to simple systems at mid-ocean ridges. Sulfur isotopes can be used to evaluate such diversity in generation and evolution of hydrothermal system. In this paper, we review the sulfur isotope composition and geochemistry of hydrothermal precipitates sampled from several hydrothermal vents in the divergent plate boundaries in the western Pacific region. Both sulfide and sulfate minerals of the hydrothermal vents in the arc and backarc tectonic settings commonly show low sulfur isotope compositions, which can be attributed to input of magmatic <TEX>$SO_2$</TEX> gas. Diversity in geochemistry of hydrothermal system suggests an active role of magma in the formation of seafloor hydrothermal system.

Carbon- and sulfur-isotope geochemistry of the Hirnantian (Late Ordovician) Wangjiawan (Riverside) section, South China: Global correlation and environmental event interpretation

Detailed geochemical analyses (δ13Ccarb, δ13Corg, δ34Ssulfide, and abundance of sulfide, carbonate and organic carbon) were performed on samples from the Wangjiawan (Riverside) section, close to the GSSP (Global Stratotype Section and Point) for the Hirnantian stage of the Ordovician. New data show two increases in carbonate content coincident with two glacial pulses that reduced detrital input. The new δ34Ssulfide data show distinct changes in this section, with relatively high values in the Kuanyinchiao Formation, a pattern observed throughout the Yangtze Platform. However, there is no consensus on the cause of these changes. The new δ13Ccarb data show a sharp rise and peak in the extraordinarius zone, below the previously published δ13Corg peak in the persculptus zone. A compilation of the new results with other sections indicates the Hirnantian carbon-isotope excursion starts near the pacificus–extraordinarius boundary and elevated values remain until the end of the excursion in the persculptus zone for both δ13Corg and δ13Ccarb. The controversy over correlating Hirnantian graptolite zones with chitinozoan zones can also be addressed. The new δ13Ccarb data also allow direct comparison with Hirnantian δ13Ccarb data from Anticosti Island and the Baltic region, which are zoned by chitinozoan fossils. This comparison favors a correlation of the taugourdeaui and scabra chitinozoan zones with the extraordinarius graptolite zone.