Sulfur Isotopic Composition Research Articles

Oxidation of pyrite during barite extraction

Marine barite is widely considered a reliable recorder of sulfur and oxygen isotope compositions of seawater sulfate. The traditional barite extraction method involves multiple oxidative cleaning steps to sequentially remove other minerals from sediments and additional purification steps to remove residual insoluble O-bearing minerals like rutile. During these processes pyrite is likely oxidized, thereby introducing sulfur from pyrite and oxygen from water and/or air to sulfate. We systematically investigate the effects of pyrite oxidation during barite extraction using two sets of synthetic marine sediments spiked with varying amounts of pyrite. One is subjected to acid-based leaching and Na2CO3-based purification, while the other is only treated with Na2CO3. Our results show a negative correlation between the pyrite-to-barite mass ratio and the apparent S- and O-isotope values of extracted barite. The difference in S-isotope ratios between two sample sets suggests that acid leaching with subsequent Na2CO3 purification results in the conversion of approximately 9% of the added pyrite to barite, whereas purification alone converts about 4.8% of the added pyrite. Based on these findings, we estimate that for marine sediments with a pyrite-to-barite ratio lower than 3 wt% and an S-isotope difference smaller than 50‰ between marine barite and sedimentary pyrite, the S-isotope offset imparted by pyrite oxidation during sequential leaching is within a 0.3‰ error.

Genesis of the Xinfang magmatic-hydrothermal gold deposit, Liaodong Peninsula, China: Constraints from pyrite Re-Os isotopes, C, O, S, Pb, Si, He and Ar isotopes

The Xinfang gold deposit (>20 t@ 2.85 g/t) is situated in the southwest of the Liaodong Peninsula. Ore bodies are hosted by the Archean gneiss in the footwall and Neoproterozoic metasandstone in the hangingwall of the Xinfang Metamorphic Core Complex. Here, we conduct pyrite Re-Os dating, C, O, Si, He-Ar, S, and Pb isotopes in order to constrain the ore-forming age and genesis of the deposit. Field observations show that three ore-forming processes are recognized: (1) quartz- coarse-grained pyrite stage (stage Ⅰ), (2) quartz-polymetallic sulfide-gold stage (stage Ⅱ), and (3) quartz – calcite ± pyrite stage (stage III). Pyrite from the quartz-polymetallic sulfide-gold vein yielded Re-Os isochron age of 121.1 ± 1.2 Ma (Initial 187Os/188Os = 1.49 ± 0.01, MSWD = 1.2), which is interpreted to be the ore-formation age.Theδ13CV-PDB and 18Ov-SMO W values of calcite from stage III range from −5.1‰ to −4.9‰ and from 9.7‰ to 10.1‰, and the δ30Si values of quartz from stage Ⅰto stage III range from −0.5‰ to −0.4‰, −0.1‰ to −0.3‰, and −0.2‰ to −0.1‰, respectively, indicating that ore-forming fluids were derived from a magmatic-hydrothermal source. Sulfur isotopic compositions of sulfides between −1.9 ‰ and 4.4 ‰ (mean = 2.4 ‰), are consistent with that of magmatic sulfur. The galena yielded a wide range of lead isotopic composition (206Pb/204Pb = 16.995–17.252, 207Pb/204Pb = 15.335–16.343, 208Pb/204Pb = 37.461–37.580) suggesting an external lead source. The He and Ar isotope compositions of pyrite and galena (3He/4He = 0.14Ra-0.62Ra), indicate a crustal source with minor mantle contributions. Combining all available data results, we propose that a magmatic -hydrothermal source for the Xinfang gold deposit and the ore formation was related to the subduction of the Paleo-Pacific Plate beneath Eurasia.

Sulfur Isotope and Trace Element Systematics in Arc Magmas: Seeing through the Degassing via a Melt Inclusion Study of Kyushu Island Volcanoes, Japan

Abstract Sulfur is a minor element in magmas but one of the major volatile elements released in volcanic systems, from the magma to the fluid phase upon ascent. Not only are sulfur gasses potentially toxic for humans and plants, they are also involved in causing drastic climate changes after major volcanic eruptions. Therefore, studies are carried out by the geoscience community to assess the magmatic sulfur flux by looking at the sulfur content and isotopes in erupted products, with the ultimate aim of improving understanding of the sulfur cycle in subduction zones. Kyushu Island in Japan hosts 25 volcanoes, among which 11 are active and represent a natural hazard for the local population. It is perhaps the most suitable site for the study of the sulfur cycle for its availability of recent volcanic deposits and its many highly monitored volcanoes. We investigated sulfur and sulfur isotope compositions of the magma source of Kyushu Island arc using olivine-hosted melt inclusions in mafic tephras and lavas, from eight volcanoes (nine Holocene samples) going from Northern Kyushu with Oninomi, Yufu, Kuju, and Aso, to Southern Kyushu volcanoes such as Kirishima-Ohachidake, Kirishima-Shinmoedake, Sumiyoshi-ike, and Kaimondake, and one back arc volcano, Fukue-Onidake. We measured major, trace and volatile elements and S isotopes (δ34S) in melt inclusions. Magma composition recorded in the inclusions ranges from basalt to andesite (SiO2 ranging from 40.3 to 60.7 wt%). For each edifice, we identified the least degassed and least differentiated compositions based on volatile and trace element systematics and selected the melt inclusions closest to their primitive melts. Comparing these primitive magmas, Sr/Y underlines a compositional dichotomy between volcanoes from northern (Sr/Y > 20) and southern Kyushu (Sr/Y < 20), separated by a non-volcanic area corresponding to the subduction of the Kyushu-Palau ridge. The δ34S in melt inclusions range from −0.32 ± 0.79‰ to +9.43 ± 0.47‰ (2σ) and trace the source of the magma from the different volcanoes, rather than degassing or crustal fractionation processes. δ34S is not fractionated by the nature of the fluid (aqueous or melt) metasomatizing the mantle wedge, therefore it is not the first-order factor controlling the sulfur isotope variations. Instead, this study illustrates the need for a heavy δ34S component, likely sulfate from seawater, contained in the agent that metasomatized the mantle beneath the arc. If such an observation is confirmed in other subduction zones, sulfur isotopes in melt inclusions may be an effective way to trace seawater input into the mantle beneath

Enhanced Oxidation of SO2 by H2O2 During Haze Events: Constraints From Sulfur Isotopes

AbstractSulfate aerosols play a critical role in atmospheric chemistry and climate change. However, the mechanism of sulfate formation during haze events remains highly uncertain. In this study, sulfur isotopic compositions of SO2 and sulfate in PM2.5 samples collected in Tianjin, China as well as a Rayleigh distillation model are used to constrain SO2 oxidation pathways. The sulfur isotopic fractionation (ε) between SO2 and sulfate displays a seasonal change with low values in summer (−0.1 ± 1.0‰, n = 16) and high values in winter (2.1 ± 1.2‰, n = 16). Although an influence of temperature effect to this seasonal trend cannot be ignored, the relation between ε values and SO2 oxidation ratios indicates that the seasonality is mainly attributed to the changes in relative contributions of oxidation pathways. In addition, an elevated ε value has been observed during the first stage of haze event, suggesting that the relative contribution of H2O2 pathway to sulfate formation is higher in haze days than that in normal days. Our results highlight the important role of SO2 oxidation by H2O2 in the first stage of haze event.

Multi-stage evolution of the Lost City hydrothermal vent fluids

Serpentinization-influenced hydrothermal systems, such as the Lost City Hydrothermal Field (LCHF), are considered as potential sites for the origin of life. Despite an abundance of reducing power in this system (H2 and CH4), microbial habitability may be limited by high pH, elevated temperatures, and/or low concentrations of bioavailable carbon. At the LCHF, the relative contribution of biotic and abiotic processes to the vent fluid composition, especially in the lower temperature vents, remain poorly constrained. We present fluid chemistry and isotope data that suggest that all LCHF fluids are derived from a single endmember produced in the hotter, deeper subsurface essentially in the absence of microbial activity. The strontium isotope composition (87Sr/86Sr) of this fluid records the influence of underlying mantle and/or gabbroic rocks, whereas sulfur isotope composition indicates closed-system thermochemical sulfate reduction. Conductive cooling and transport is accompanied by continued sulfate reduction, likely microbial, and mixing with unaltered seawater, which produce second-order vents characterized by higher δ34Ssulfide and lower δ34Ssulfate values. Third-order vent fluids are produced by varying degrees of subsurface mixing between the first- and second-order fluids and a seawater-dominated fluid. Additional biotic and abiotic processes along different flow paths are needed to explain the spatial variability among the vents. Relationships between sulfur geochemistry and hydrogen concentrations dominantly reflect variations in temperature and/or distance from the primary outflow path. Methane concentrations are constant across the field which point to an origin independent of flow path and venting temperature. At Lost City, not all vent fluids appear to have zero Mg concentrations. Thus, we propose an extrapolation to a Sr isotope-endmember composition as an alternative method to estimate endmember fluid compositions at least in similar systems where a two-component mixing with respect to Sr isotopes between seawater and endmember fluids can be established.

Geochemical characteristics of organic-rich intervals within the Cryogenian non-glacial Datangpo Formation in southeastern Yangtze Block-implications for paleoenvironment and its control on organic matter accumulation

To understand the mechanism of organic matter enrichment in the organic-rich intervals of the Cryogenian non-glacial strata, we report high-resolution geochemical data of the well-developed non-glacial Datangpo Formation at a section in the southeastern margin of the Yangtze Block, including iron (Fe) speciation, sulfur and organic carbon isotopic compositions and elemental contents. The organic-rich intervals are mainly distributed in the basal manganese (Mn) carbonate and Mn-bearing shales (intervalⅠ), and overlying black shales (intervalⅡ). The paleo-redox reconstruction shows a transition from ferruginous-dominated watermass during deposition of the IntervalⅠto euxinic-dominated watermass during deposition of the IntervalⅡ, which provides good conditions for the preservation of organic matter. A variety of geochemical indicators demonstrate that during deposition of the IntervalⅠ, elevated primary productivity in the surface water driven by hydrothermal activities and improved post-glacial basinal watermass exchange, coupled with some organic carbon influx from the dissolved organic carbon reservoir, collectively promoted the enrichment of organic matter. For the interval Ⅱ, enhanced chemical weathering accompanied by persistently warm climatic conditions exerted a major control on the organic matter enrichment by importing abundant nutrients, resulting in enhanced surface-water primary productivity. In addition, favorable sedimentation rates also made positive contributions to the organic-rich black shales in the intervalⅡ. Based on a combined analysis of paleoclimates, hydrological conditions and hydrothermal activities, this study puts forward organic matter enrichment models for the organic-rich intervals deposited during the Cryogenian non-glacial period.

Sinking particles in the Black Sea waters: Vertical fluxes of elements and pyrite to the bottom, isotopic composition of pyrite sulfur, and hydrogen sulfide production

The Black Sea is the largest anoxic basin with hydrogen sulfide at depths below 100 m. Anoxic condition significantly affects fluxes of particulate matter due to consuming organic material for sulfate reduction and syngenetic pyrite formation. Composition of sinking particles was studied for 6 water depths of the Black Sea (100–1750 m) with deployment period of over one year. As a result, the data on chemical and mineral composition of sinking particles including the contents of reduced sulfur species (acid volatile sulfides and Cr reducible species) and isotopic composition of Cr reducible sulfur species were obtained.Mineral composition of trapped material changes with depth mainly due to dissolution of plankton carbonate shells, which decreases to the bottom to reach 90%, and also due to oxidation of organic carbon (by 59%). While sinking, particulate matter loses Fe, S, U, Co, Mo, Tl, and Ag to the least extent. Framboidal pyrite appears in sinking particles in the upper part of anoxic water column shallower than 180 m. Its quantity increases down to the deeper waters amounting to 0.4 wt% of dry weight. The δ34S values in syngenetic pyrite from depths of 980, 1680, and 1775 m range from −42.2 to −42.6‰ vs. VCDT and were found to be close to those of sulfur isotopic composition in dissolved hydrogen sulfide.Based on a decrease of particulate organic carbon flux, the annual production of hydrogen sulfide in 2015–2016 was calculated to be 5.9 Tg H2S /year, the main part of which (80%) generates above a depth of about 980 m. Our estimate of H2S consumption for pyrite formation in the water column is 0.030 Tg H2S /year (0.5% of annual H2S production) which is believed insignificant for hydrogen sulfide balance in the Black Sea.

The Paleo-Mesoarchaean Gondpipri Mafic-Ultramafic Intrusions, Western Bastar Archaean Craton, Central India: Insights from Bulk-Rock Geochemistry and Sm-Nd and S Isotope Studies on the Formation of Ni-Cu-PGE Mineralization

Abstract Magmatic Ni-Cu-platinum group element (PGE)-Te mineralization in the Gondpipri mafic-ultramafic layered intrusion of ca. 3323 ± 74 Ma age, western Bastar craton, central India, is one of the most prospective exploration targets for magmatic sulfides in India. The Gondpipri layered intrusion is divided into two distinct groups of rocks based on their mineralization potential, which include (1) mineralized layered gabbro and pyroxenite and (2) a barren olivine gabbro intrusion. The host rocks show Cu + Ni concentrations up to 5,000 ppm with a Cu/Ni ratio <1 and all PGE values between 0.1 and 1.1 ppm. Mineralization occurs in two modes: type I mineralization occurring as blebs, specks, and dissemination and type II mineralization occurring as stringers and minor veins. The geochemical data suggest that the parental magma of the host rock was generated at depths between spinel and garnet peridotite mantle source regions and subsequently modified by assimilation fractional crystallization (AFC) of the continental crust. High large ion lithophile elements, Th/Yb ratios of the studied rocks, and Sm-Nd isotope studies are consistent with a depleted mantle source. The geochemical proxies such as Th versus Ba/Th and (Ta/La)PM versus (Hf/Sm)PM and higher Sr/Nd (2.21–82.58) ratios indicate involvement of fluid-related subduction metasomatism and enrichment processes in an island-arc tectonic setting. Mineral assemblages and textural relationships between platinum group minerals (PGMs) and base metal sulfides suggest that sulfide-silicate liquid immiscibility was brought about by the precipitation of magnetite/Cr magnetite resulting in sulfide saturation in the melt by decreasing S solubility. Sulfur isotope compositions (δ34S: 1.61–3.30‰) and Sm-Nd geochemistry suggest that the sulfur was added in the tholeiitic magma by magmatic process. Crustal contamination played a significant role in sulfide saturation and in bringing about PGE and Te, As, Bi, Sb, Se (TABS) mineralization. PGM-NiTeBi developed at relatively low temperatures, whereas moncheite (PtPd)Te2 and merenskyite (PdTe) were formed at 650°C. The identification of Ni-Cu-PGM-Te in the margin of the western Bastar craton boosts deeper subsurface exploration.

The Gold–Palladium Ozernoe Occurrence (Polar Urals, Russia): Mineralogy, Conditions of Formation, Sources of Ore Matter and Fluid

We studied the mineralization and sulfur isotopic composition of sulfides of gold–palladium ores in olivine clinopyroxenites from the Dzelyatyshor massif made up of a continuous layered series of rocks: olivine-free clinopyroxenite–olivine clinopyroxenite–wehrlite. The primary igneous layering of rocks, manifested as different quantitative ratios of clinopyroxene and olivine in them, controls the local trends of variability in the chemistry of mineral-forming medium and the concentrations of ore components, including noble metals, and sulfur in each separate layer during its cooling. The replacement of primary rock-forming minerals by secondary minerals, when the temperature decreases, is a characteristic trend for pyroxenites: (a) olivine → serpentine, secondary magnetite, and (b) clinopyroxene → amphibole, secondary magnetite → chlorite. The deposition of native gold in parageneses with PGM and sulfides at the Ozernoe occurrence took place during the replacement of earlier rock-forming minerals by chlorite. This process completed mineral formation at the deposit and took place at temperatures 150–250 °C and at the high activity of S, Te, Sb, and As of fluid. The variability of mineral formation conditions during chloritization is reflected in the change of native-sulfide forms of Pd by arsenide-antimonide forms and the sulfur isotopic composition of sulfides. The Pd content in native gold increases in the series—Au-Ag solid solution (<1.5 wt.% Pd)—Au-Cu intermetallides (to 6 wt.% Pd)—Cu-Au-Pd solid solutions (16.2–16.9 wt.% Pd). The sulfur isotopic composition of pyrite, chalcopyrite, and bornite varies from −2.1 to −2.9‰. It is assumed that a deep-seated magmatic basic melt was the source of fluid, ore components, and sulfur.

Monitoring the evolution of sulfur isotope and metal concentrations across gold-bearing pyrite of Carlin-type gold deposits in the Youjiang Basin, SW China

The Youjiang Basin in Southwest China is the world’s second largest Carlin-type gold (Au)-producing region. However, the source of reduced sulfur that accounts for Au transport in ore-forming fluids remains controversial. Finely characterizing the sulfur isotopic compositions (δ34S values) in micron-scale zonation of Au-bearing pyrite is the key to clearly identify sulfur source. Here, we used high-resolution nanoscale secondary ion mass spectrometry (Nano-SIMS) to characterize the temporal variation in δ34S values and its relationship with metal contents across Au-bearing pyrite from the Linwang and Badu deposits in the Youjiang Basin, with the aim of monitoring the source and evolution of reduced sulfur in auriferous fluids. The Au-bearing pyrite rims in the Linwang deposit contain three growth stages that record episodic injections of Au- and As-rich fluids. Within these rims, the δ34S values vary inversely with Au concentrations. The inner rims with the high Au contents have δ34S values of −1.7‰ to +3.3‰ that are comparable to those of magmatic sulfur. The outer rims with decreasing Au contents have δ34S values of +1.3‰ to +15.7‰ that gradually approach those of pre-ore pyrite in the host rock. Such a variation indicates that the reduced sulfur in the initial Au-bearing ore-forming fluids was primarily originated from deep magmatic-hydrothermal systems while the host rock-derived 34S-enriched sulfur increasingly dominated through fluid-rock interactions during mineralization. In contrast, Au-bearing pyrite from the Badu deposit has positive δ34S values ranging from +9.0‰ to +25.8‰, which overlap those of diagenetic pyrite in the Devonian sedimentary rocks. Combining the intimate spatial association between Au mineralization and the Devonian strata, we propose that the initial ore-forming fluids have leached substantial sulfur from the Devonian strata. Significant contaminations of sedimentary sulfur erased the primary sulfur isotopic signals of the initial auriferous fluids. Our interpretations of these two deposits may also apply to other Carlin-type Au deposits in the Youjiang Basin, where δ34S values of Au-bearing pyrite show host rock-dependent variations. This study demonstrates that high-resolution Nano-SIMS sulfur isotope and elemental analysis of Au-bearing pyrite is a potent tool for tracing the source and evolution of reduced sulfur in ore-forming fluids for sedimentary-host Au deposits worldwide.

Linkage of the late Cambrian microbe-metazoan transition (MMT) to shallow-marine oxygenation during the SPICE event

Microbe-metazoan transitions (MMTs), representing a switch from microbe-mediated to metazoan-mediated carbonate production, have been linked to major changes in Earth-surface conditions. The ‘late Cambrian MMT’ (nomen novum), during which microbial reefs were replaced by maceriate and lithistid sponge reefs, coincided with a sharp rise in atmospheric O2 levels attributed to the Steptoean Positive Carbon Isotope Excursion (SPICE) at ~497–494 Ma. However, relationships between atmospheric oxygenation, marine redox conditions, and the MMT have not been thoroughly investigated to date. Here, we conducted paired analyses of carbonate carbon isotopes (δ13Ccarb), sulfur isotopes of carbonate-associated sulfate (δ34SCAS) and pyrite (δ34SPy), pyrite morphologies, and fossil assemblages of two upper Cambrian shallow-marine sections on the North China Platform (Tangwangzhai and Huangyangshan). The sulfur isotopic composition of framboidal pyrite (δ34SFrPy) was calculated from that of total pyrite (δ34STPy) assuming a varied fractionation with euhedral pyrite based on pyrite morphological analyses. Modelling of S-isotope fractionations (Δ34SCAS-FrPy) indicates that contemporaneous seawater had low sulfate concentrations (i.e., [SO42––]sw ~4–6 mM) with locally high spatial heterogeneity during the Rising SPICE (early to middle Paibian), which were the product of massive burial of pyrite (together with organic matter) linked to extensive oceanic anoxia. Immediately following the SPICE, a reduced pyrite burial rate and an increased flux of terrestrially sourced, 34S-depleted sulfate to shallow-marine environments resulted in lower δ34SCAS values. [SO42–]sw rose to a maximum of ~9–16 mM and became more uniform during the Post-SPICE (middle to late Jiangshanian), suggesting a more oxidized condition of seawater and the atmosphere. Rising O2 levels in both the atmosphere and marine environments triggered the late Cambrian MMT and set the stage for the subsequent Great Ordovician Biodiversity Event.

The mineralization of Daxiao carbonate-hosted Pb-Zn deposit, northeast Yunnan province, SW China: Constraints from Rb-Sr isotopic dating and H[sbnd]O[sbnd]S-Pb isotopes

The Sichuan-Yunnan-Guizhou (SYG) Pb-Zn metallogenic province located in western Yangtze Block contains more than 400 carbonate-hosted Pb-Zn deposits. Uncertain mineralization age and ore-forming material source causing debates on the genesis of these carbonate-hosted Pb-Zn deposits. To address this issue, the Daxiao Pb-Zn deposit was chosen as a case study. The orebodies of Daxiao deposit are hosted in Mesoproterozoic Heishan formation argillaceous dolomite interbedded with slate. Three main mineralization stages have been identified, including syn-sedimentary stage, hydrothermal stage and supergene stage. The ore minerals consist of galena, sphalerite, chalcopyrite, argentite, smithsonite, anglesite and cerussite in the deposit. The early hydrothermal stage sphalerite yielded a Rb-Sr isochron age of 223.5 ± 2.9 Ma, consistent with the spike of Pb-Zn mineralization in SYG metallogenic province. Quartz in hydrothermal stage yields δDSMOW values of −69.6 to −65.8 ‰ and calculated δ18OFluid values of + 3.4 – +5.6 ‰, showing an affinity of metamorphic water. While the quartz in supergene stage yields δDSMOW values of −68.3 to −65.8 ‰ and calculated δ18OFluid values of −4.1 to −1.7 ‰, indicating abundant basinal brine or meteoric water had mixed into ore-forming fluid during its evolution from hydrothermal stage to supergene stage. Sulfur isotopic composition (δ34S = +6.3 – +19.1 ‰) of different stage sulfides reveal that the ore-forming sulfur originated from sulfates within the wall rocks, and mainly reduced by Thermal-chemical reduction (TSR). Moreover, the 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb ratios of early hydrothermal stage sphalerite are 18.282 – 18.312, 15.603 – 15.681and 38.287 – 38.311, respectively. Those of late hydrothermal stage galena are 18.315 – 18.491, 15.676 – 15.721 and 38.314 – 38.326, respectively. All of them plot in the overlapping area of Emeishan flood basalts, Kunyang and Huili groups and Sinian to Triassic strata, indicating that these wall rocks jointly contributed the ore-forming metals for these Pb-Zn deposits in SYG metallogenic province. Hence, a metallogenic model for Daxiao and other carbonate-hosted Pb-Zn deposit in SYG metallogenic province was proposed: In the thrustfold systems caused by the subduction of Paleo-Pacific and the closure of Jinshajiang-Ailaoshan Paleo-Tethys ocean in Late Triassic to Early Jurassic. The fluids originated from metamorphic water migrated along deep faults and extracted ore-forming materials from wall rocks (including Proterozoic basement rocks, Sinian to Triassic sedimentary wall rocks and Permian Emeishan flood basalts), and then precipitated ores in the secondary thrust faults or interlayered fractures within these thrustfold systems.

Heterogeneity of mineral chemistry and sulfur isotopic composition of alunite in the Mankayan lithocap, northern Luzon, Philippines

The lithocap at Mankayan is a contiguous zone of alunite + quartz + pyrite that occur as pervasive alteration of the metavolcanic basement and dacitic pyroclastic rocks. Alunite + quartz + pyrite assemblage also occurs within hydrothermal gold-bearing veins and breccias. Several high-sulfidation epithermal gold orebodies have been previously delineated in the Lepanto Main Enargite orebody, and in the Northwest, Carmen, Florence West and Florence East quartz-pyrite-gold (QPG) veins. This study presents new data of mineral composition and sulfur isotopic ratios of alunites from different zones of the lithocap at Mankayan. Elemental composition maps and point analysis of alunites indicate compositional heterogeneity within a single alunite crystal. Common substituents to the K+ site are Na+ and H3O+, with few Ca2+ substitution in some sites. Limited occurrences of PO43- substitution to SO42- were also documented. Sulfur isotopic ratios (δ34SCDT) of alunite range from + 13 ‰ to + 24 ‰, which are typical of hypogene alunite. Sulfur isotopic ratios of coexisting pyrite are mostly negative, ranging from −5.4 to −1.0 ‰. Few samples of alunite from the Northwest and Florence West quartz-pyrite-gold veins have sulfur isotopic ratios similar to the values of its coexisting pyrite. The estimated temperature of formation using sulfur isotope geothermometry of alunite-pyrite pairs ranges from 197 °C to 364 °C, with most of the samples varying within 220 to 270 °C. The calculated bulk δ34S of the hydrothermal fluid was found to be + 5 to + 6 ‰ for the different mineralization events in Mankayan.The alunite crystals are heterogeneous even in the microscopic scale. Compositional maps show that K and Na concentration vary within single crystals, as well as among different crystals of a sample. The variations of K and Na content mostly follow the crystal growth structure, however, some alunite crystals with irregular variations are also present. Some samples contain aluminum-phosphate-sulfate (APS) minerals intergrown with alunite. Electron probe microanalysis of the alunite crystals showed a generally wide range of composition between the alunite – natroalunite solid solution.Using thermodynamic functions, a relationship between temperature and K+/Na+ of the hydrothermal fluids was determined across the range of alunite-natroalunite solid solution system. The model curves suggest that at temperatures less than ∼ 250 °C a slight change in fluid composition and/or temperature can vary the number of Na atoms per formula unit by 0.3 units. At higher temperatures, a more significant change in the physicochemical conditions is required for a substitution to occur. This explains the wide range of Na content in the alunites from the different parts of the lithocap.The characteristics compiled in this study reflect the fluctuations in temperature and fluid compositions that occurred during the multiple hydrothermal events in the Mankayan District.

Stable sulfur and oxygen isotopes of sulfate as tracers of antimony and arsenic pollution sources related to antimony mine activities in an impacted river

Source identification of antimony (Sb) and arsenic (As) pollution associated with mine activities is crucial for pollution prevention and control, but is still challenging. A typical river at the Xikuangshan antimony mine affected by known mine activities along the runoff, including mining, beneficiation and smelting, may allow to test the possibility and reliability of stable isotopes of sulfate (δ34SSO4 and δ18OSO4) as tracers to identify Sb and As sources associated with mine activities. The river water and mine wastewater samples were chemically and isotopically characterized in the dry and rainy season respectively. As expected, the concentrations of Sb, As and SO42− in the river increased and varied with the seasons. The spatial and seasonal variations of Sb, As and SO42− concentrations in the river were consistent with the mixing of the mine wastewater discharged into the river. Moreover, the impact of mine activities resulted in the correlations of Sb, As and SO42− of the river water high in the rainy season but low in the dry season. The sulfur and oxygen isotopic compositions of SO42− of the river fell within the range composed of upstream river and its received mine wastewater. The estimated proportional contributions of multiple mine activities to the river by a Bayesian isotope mixing model suggested that the total contribution of the mine activities ranged from 37 ± 10% to 96 ± 4% in the dry season and from 28 ± 8% to 88 ± 8% in the rainy season. The leachate of waste rocks and smelting slag dumps was the predominant contributor in the upper section, with the proportions greater in the dry season (37 ± 9%∼76 ± 12%) than in the rainy season (28 ± 8%∼56 ± 9%). The mining drainage became the primary source (69 ± 8%∼80 ± 8%) in the lower section in the dry season, whereas all sources contributed approximately equally in the rainy season. Leakage from the tailings pond (19 ± 13%) is another important source in the rainy season. This study demonstrated that sulfur and oxygen isotopes can be effective for source identification and qualification of multiple mine activities on Sb and As pollution in the river, which provides new insights into source apportionment of metal(loid)s pollution related to complex mine activities.

Pulses of atmosphere oxygenation during the Cambrian radiation of animals

Oxygenation of the oceans and atmosphere has been invoked to be the prerequisite for the early Cambrian radiation of animals. However, the temporal and causal relationships between oxygenation and metazoan proliferation have not been fully explored. Here we report sulfur and oxygen isotope compositions (δ34Sanhy and δ18Oanhy) of marine anhydrite deposited around 516 to 506 million years ago (Ma) from the Tarim Basin, NW China. Using a biogeochemical model, we propose that a paired negative δ18Oanhy (∼4.5‰) and δ34Sanhy (∼8‰) excursion between 515 and 510 Ma can best be explained by decreased isotope fractionation factors during sulfate reduction related to a 45% to 100% increase in atmospheric oxygen level (pO2). Significantly, evidence from this interval infers an oxygenation event in the backdrop of the most rapid radiation stage (ca. 520 to 510 Ma) during the Cambrian explosion, confirming that oxygen availability was a crucial factor in accelerating the radiation of marine animals.

Gas Hydrate Dissociation Events During LGM and Their Potential Trigger of Submarine Landslides: Foraminifera and Geochemical Records From Two Cores in the Northern South China Sea

Although submarine slope failures and occurrence of gas hydrates are well known in the Dongsha area of the South China Sea the potential relationship between the aforementioned phenomena has not been clearly understood yet. Herein, we present carbon and oxygen isotope compositions of benthic foraminifera and sulfur isotopic composition of chromium reducible sulfur (CRS; δ34SCRS) from two cores from the Dongsha slope, aiming at identifying gas hydrate dissociation events in geological history. The geochemical data indicated that a large amount of gas hydrate dissociated at the beginning of the Last Glacial Maximum (LGM). Meanwhile, disturbances in the sedimentary strata revealed that a submarine landslide occurred at the end of the Last Glacial Maximum. Moreover, the associated abrupt increase of benthic foraminifera abundance implies that the submarine landslide was probably caused by an intense methane releasing from gas hydrate dissociation. A smaller scale submarine landslide related to gas hydrate dissociation was also recorded in core 973-5, retrieved from the flat area at the base of the slope.

Sulfate Sources Required for Thermochemical Sulfate Reduction in Dolostone Reservoirs in the Upper Permian Changxing Formation, Yuanba Gas Field, Sichuan Basin, China: Insights from the Origin of Celestite

Thermochemical sulfate reduction (TSR) commonly occurred in the dolostone reservoirs of the Upper Permian Changxing Formation (P3c) in the Yuanba (YB) gas field, Sichuan Basin, yet controversy remains regarding the source of sulfate required for TSR. To trace the source of the sulfate, sulfur and strontium isotopic compositions were measured for three diagenetic celestite (SrSO4) samples found in the P3c dolostone reservoirs in the YB gas field. In addition, the sulfur isotopic compositions of Carbonate-associated sulfates (CAS) from the P3c carbonates and spheroidal pyrites in dolomicrites from the P/T boundary (PTB) in the YB gas field were measured for comparative studies. The results show that the sulfur isotopic compositions of celestites are significantly heavier than those of the contemporaneous seawater, and these celestites have strontium isotopic values consistent with those of the host dolostones and contemporaneous seawater. The −33.68‰ fractionation in average δ34S values between pyrites and celestites indicated that their formation was likely to be related to bacterial sulfate reduction (BSR). During the P/T extinction event that accompanied the end-Permian regression, the reflux of brine directly precipitated 34S-rich celestites in the fractures and vugs of the dolostone reservoirs due to the BSR and the evaporation of seawater. These 34S-rich celesites and associated pore fluids provide a new explanation for the source of sulfate required for the late TSR.

Linking Selective Alteration, Mineral Compositional Zonation and Sulfide Melt Emplacement in Orogenic-Type Magmatic Ni–Cu Sulfide Deposits

Abstract The chemical characteristics of magmatic Ni–Cu sulfide deposits in orogenic settings differ from those in cratons as they are characterized by extensive alteration, presence of hydrous minerals and typical normal mantle sulfur isotopes. How these characteristics are related to the mode of formation of the Ni–Cu sulfide deposits is still unknown. Here, we present petrological and mineralogical investigations of the Hongqiling Ni–Cu sulfide deposit, a typical representative of such numerous deposits in the Central Asian Orogenic Belt. Observations at various scales of field outcrops, hand specimens, thin sections and microscopes reveal that alterations are selectively exposed in silicate minerals, particularly olivine and pyroxenes that are close to ore bodies and sulfides. Such selective alteration is also related to sulfide type and abundance, and ore texture in the rocks/ores. It is worth noting that alteration of olivine and pyroxenes becomes weak when hydrous minerals (hornblende and phlogopite) are present. Profile analyses demonstrate that the olivine grains enclosed in or in contact with sulfides have compositional zonation with Fe, Mn, Sc and Zn concentrations higher when closer to the contacts with sulfides relative to the cores and contacts with other silicates, while those grains in sulfide-barren rocks show relatively homogeneous compositions. Similarly, the hornblende grains in contact with sulfide show distinct compositional variations. Sulfides in the rocks and ores are all free of alteration and have mantle-like sulfur isotopic compositions (pyrrhotite δ34S = −1.53 to 0.38‰; pentlandite δ34S = −1.28 to 0.25‰; chalcopyrite δ34S = −1.77 to 0.24‰). These features suggest that the selective alterations occurring in early crystallized phases were induced by sulfide melt intrusion and crystallization, instead of late-stage processes as previously thought. The sulfide melts segregated at the early stage of the magma evolution were presumably hydrous and buoyant in the silicate magma and therefore were transported upward and penetrated into silicate grains. The hydrous fluids were independent of the subducted material and metamorphic origin, and contained no significant crustal component in the late Triassic. Finally, when the sulfides crystallized, fluids would be released from the sulfide melts to hydrate surrounding mineral phases and rocks, because sulfides theoretically don’t accommodate hydrous components. The fluids also enhanced compositional exchanges between sulfides and silicates and accounted for the crystallization of hydrous minerals. From this perspective, fluids play a critical role in sulfide melt transportation and silicate compositional alteration, and selective alteration can be considered as a significant indicator of mineralization and exploration in mafic-ultramafic intrusions.

Paleogene Lithostratigraphy and Recognition of the Marine Incursion of the Proto-Paratethys Sea in the Fergana Basin, Uzbekistan

Lithostratigraphy and isotopes of Paleogene sequences consisting mainly of terrestrial clastics and limestone were examined in the northern Fergana Basin of Uzbekistan. The studied sections consisted of two facies: the lower sequence coarse-grained terrestrial clastics and the upper sequence limestone clastics characterized by limestone beds. The sulfur isotopic composition of the bivalve obtained from the lower sequence was relatively low, namely, 14.94–16.82‰, which is equivalent to the Early Cretaceous; however, it is possible that the isotopic composition differed from that obtained in open seawater due to the presence of terrestrial clastics and the freshwater effect. In contrast, the sulfur isotopic composition of limestone from the upper sequence was relatively high, namely, 19.37–21.19‰, thereby indicating that they were likely to originate from the Early to Middle Eocene. Furthermore, the strontium isotopic compositions of the lower and upper sequences were 0.707772–0.707875‰ and 0.707812–0.708063‰, respectively. These values are more similar to those of the Paleogene than the Cretaceous. Finally, lithostratigraphy and age determination allowed us to correlate the upper sequence with representative limestone from the fourth transgression of the proto-Paratethys Sea, whilst the limestone beds were deduced to be remnants of the Eocene marine incursion of the proto-Paratethys Sea.

Fingerprinting the metal source and cycling of the world’s largest antimony deposit in Xikuangshan, China

AbstractThe Xikuangshan antimony (Sb) deposit is the largest Sb deposit in the world; however, the metal source and cycling and a holistic understanding of the deposit genesis remain equivocal. Sulfur isotope signatures offer a means of fingerprinting different sources in a hydrothermal deposit, although one must be careful to rule out subsequent isotope fractionation during fluid ascent, mixing, and ore precipitation. Here, we investigated the sulfur isotope composition of stibnite occurring at depth in the Xikuangshan deposit to distinguish the isotopic signals from the source and the superimposed imprint from near-surface–derived sulfur mixing or isotopic fractionation. All stibnites from the deep orebodies displayed limited δ34S variation from +6.8‰ to +8.4‰, despite their widely varying depths. These results provide direct evidence that δ34S values measured in deep orebodies are representative of the isotopic composition of initial fluids. The most likely factor controlling the variation of the sulfur isotopes in shallow stibnites (+3.5‰ to +16.3‰) is a series of hydrothermal processes, including Rayleigh fractionation during ore precipitation, fluid boiling induced by pressure release, and/or local input of pyrite from wall rocks via fluid-rock interaction. Accordingly, we conclude that the Neoproterozoic basement served as the metal source. We propose a holistic genetic model wherein we envisage that Sb and S were leached from the basement rocks, and the ore-bearing fluids ascended along a deep fault and eventually precipitated beneath the Devonian shale cap. Thus, sulfur isotopic systematics represent a powerful repository for interrogating the metal source and cycling in the hydrothermal ore system.