δ34S Variations Research Articles

Sulfur isotopic composition of sulfides and sulphates from rocks of carbonatite complexes of the devonian Kola alkaline province

This study presents the sulfur isotopic characteristics in baryte from carbonatites of the Sallanlatva massif and sulfides (mainly pyrite and pyrrhotite) from carbonatites, phoscorites and products of their contact interaction with the host silicate rocks of most carbonatite-bearing complexes of the Devonian Kola Alkaline Province (KAP). For some complexes (Ozernaya Varaka, Kontozero), these characteristics are reported for the first time. The determined range of δ34S variations of sulfides in one complex does not exceed 4‰, but reaches 20‰ for the entire Kola Alkaline Province. This may be related to the evolution style of carbonatites and associated rocks. It is shown that the δ34S value in sulfides decreases from (1) the least evolved volcanic carbonatites of the Kontozero complex (δ34Savg. = –1.3‰) through (2) carbonatites and phoscorites of the Kovdor, Ozernaya Varaka, Sokli, and Salmagora massifs towards (3) the rocks of Seblyavr, Vuoriyarvi, and, finally, the carbonatites of Sallanlatva (δ34Savg. = –14.7‰) massifs, where sulfides differ from those of other KAP carbonatites in their exceptionally low δ34S values. The carbonatite volcanics of Kontozero are almost barren of REE mineralization; carbonatites of the second group contain accessory amounts of REE minerals; the third group is peculiar in the abundance of late carbonatites, where REE carbonates are frequently major minerals. Thus, the greater the volume of REE minerals in carbonatites of the complex, the lower the δ34S value in sulfides from its carbonatites and associated rocks. For the first time in the KAP, the sulfur isotopic composition of associated baryte–pyrite pairs was studied in the Sallanlatva carbonatites. The sulfur isotopic characteristics are shown to correspond to the final low-temperature (250–350°C) stage of carbonatite evolution in oxidized conditions, which satisfies the parameters of baryte crystallization. Since the studied samples of the Sallanlatva carbonatites are explosive breccias, the oxidized composition of fluids may indicate their phreatomagmatic nature, i.e., formation due to the interaction of intruded hot matter (melt/fluid) with meteoric waters.

Microscale δ34S and δ18O variations of barite as an archive for fluid mixing and microbial sulphur metabolisms in igneous rock aquifers

ABSTRACT The stable isotope compositions of sulphur (δ34S) and oxygen (δ18O) in barite are frequently used as proxies for microbial sulphate reduction (MSR) in diverse environments, such as in relation to anaerobic oxidation of methane in marine cold seeps. There, isotopically heavy barite is used as a marker for MSR from a sulphate pool that has undergone semi-closed system conditions. Closed-system MSR is also a commonly observed feature in igneous rock hosted fracture aquifers, as shown by extremely 34S-enriched pyrite. What is less well-constrained is whether δ34S in barite can be used as a proxy for MSR in such systems. Here we explore the microscale heterogeneity of δ34S and δ18O via secondary ion mass spectrometry and the trace element Sr via LA-ICP-MS maps in barite precipitated in granite-hosted boreholes during a 17-year experiment, at Äspö, Sweden. We compare it with δ18Osulfate, δ34Ssulfate, and δ34Ssulfide of the fracture fluids and with paragenetic pyrite with δ34S values reflecting closed system MSR. The δ18O values in barite (+9.4 to +16.9 ‰) represent two generations of barite, one with low values and one with high values. The latter are likely impacted by sulphur disproportionating or -oxidizing bacteria. The barite reflects a much smaller span in δ34S (+14.5 to +28.6 ‰) than the pyrite (−47.2 to +53.3 ‰). This lack of extremely high δ34Sbarite values is proposed to be due to that barite saturation only occurred in the early parts of the Rayleigh cycle. Additionally, fluid migration has affected the δ34S values to lower values, accompanied by higher Sr concentrations. Taken together, barite δ34S values cannot be regarded as a reliable independent proxy for MSR in deep sulphate-poor igneous rock hosted aquifers. However, the relation between the δ34S values of coeval barite and pyrite is regarded as a useful proxy for MSR-related fractionation during early stages of MSR.

Occurrence and enrichment of cobalt and nickel in the Yindongshan ultramafic–mafic intrusion-hosted iron deposit, western Hubei Province, China

The Yindongshan iron deposit in western Hubei Province of China is hosted within Ordovician ultramafic–mafic intrusions. Recent field geological surveys have detected cobalt (Co) and nickel (Ni) enrichment within the Yindongshan clinopyroxenite, suggesting good potential for subeconomic Co-Ni mineralization. This study investigated the occurrence modes and enrichment processes of Co and Ni in the Yindongshan deposit through field geology and in situ analysis of the rock texture, geochronology, and geochemistry of sulfides, Fe-Ti oxides, and silicate minerals. The Yindongshan clinopyroxenites were emplaced at 440.2 ± 7.2 Ma via titanite LA-ICP-MS U-Pb dating, and underwent extensive post-magmatic metamorphism at 401.2 ± 8.6 Ma via apatite U-Pb dating. This metamorphism led to the widespread formation of amphibole via the replacement of clinopyroxene. Subsequently, hydrothermal epidote-albite veins, calcite-pyrite veins, and later actinolite veins developed. Pyrites from both clinopyroxenites and calcite veins show limited δ34S variations from −5.4 ‰ to −1.2 ‰, suggesting a magmatic sulfur source. Late-vein actinolites display geochemical characteristics distinct from those of amphiboles, indicating possible involvement of external fluids. LA–ICP–MS trace element results reveal a general increase in Co and Ni contents from silicate minerals and Fe-Ti oxides to pyrite and from earlier-crystallized coarse-grained clinopyroxenite to later medium- to fine-grained clinopyroxenite. The highest Co and Ni contents observed in pyrite from coarse-grained clinopyroxenite suggest their preferential incorporation into early sulfide minerals and then progressively depleted through magmatic evolution such as fractional crystallization. The positive correlation between Co and Ni with Fe in pyrite, along with the consistent parallel time-resolved LA–ICP–MS depth profiles among different mineral phases, indicates that isomorphic substitution occurred in pyrite. In silicate minerals, the Co and Ni contents increase from pyroxene, amphibole, to actinolite, with almost no Co or Ni present in epidote. The elevated Co and Ni contents in metamorphic amphiboles are attributed to their remobilization from magmatic pyrite to newly formed amphiboles. During the late hydrothermal phase, external fluids might transport additional Co and Ni, contributing to higher concentrations in late actinolite veins. In general, Co and Ni in the Yindongshan iron deposit are primarily hosted in sulfide minerals and can be remobilized during regional metamorphism and metasomatism. Thus, magmatic iron or iron–titanium oxide deposits hosted by mafic–ultramafic intrusions with sulfide mineralization may serve as promising targets for further Co-Ni exploration.

Improved organic and pesticide-free rice (Oryza sativa L.) authentication based on multiple stable isotope ratio analysis and rice milling state

This study looked at the application of multiple bulk stable isotope ratio analysis to accurately authenticate organic rice and counteract organic fraud within the expanding global organic market. Variations of δ13C, δ15N, δ18O, and δ34S in organic, pesticide-free, and conventional rice were assessed across different milling states (brown, milled, and bran). Individual stable isotope ratio alone such as δ15N demonstrated limited capacity to correctly differentiate organic, pesticide-free, and conventional rice. A support vector machine model—incorporating δ13C, δ15N, δ18O, and δ34S in milled rice—yielded overall predictability (95%) in distinguishing organic, pesticide-free, and conventional rice, where δ18O emerged as the pivotal variable based on the feature weights in the SVM model. These findings suggest the potential of multi-isotope and advanced statistical approaches in combating organic fraud and ensuring authenticity in the food supply chain.

Geographic distribution of feather δ34S in Europe

AbstractGeographic distribution models of environmentally stable isotopes (the so‐called “isoscapes”) are widely employed in animal ecology, and wildlife forensics and conservation. However, the application of isoscapes is limited to elements and regions for which the spatial patterns have been estimated. Here, we focused on the ubiquitous yet less commonly used stable sulfur isotopes (δ34S). To predict the European δ34S isoscape, we used 242 feather samples from Eurasian Reed Warbler (Acrocephalus scirpaceus) formed at 69 European wetland sites. We quantified the relationships between sample δ34S and environmental covariates using a random forest regression model and applied the model to predict the geographic distribution of δ34S. We also quantified within‐site variation in δ34S and complementarity with other isotopes on both individual and isoscape levels. The predicted feather δ34S isoscape shows only slight differences between the central and southern parts of Europe while the coastal regions were most enriched in 34S. The most important covariates of δ34S were distance to coastline, surface elevation, and atmospheric concentrations of SO2 gases. The absence of a systematic spatial pattern impedes the application of the δ34S isoscape, but high complementarity with other isoscapes advocates the combination of multiple isoscapes to increase the precision of animal tracing. Feather δ34S compositions showed considerable within‐site variation with highest values in inland parts of Europe, likely attributed to wetland anaerobic conditions and redox sensitivity of sulfur. The complex European geography and topography as well as using δ34S samples from wetlands may contribute to the absence of a systematic spatial gradient of δ34S values in Europe. We thus encourage future studies to focus on the geographic distribution of δ34S using tissues from diverse taxa collected in various habitats over large land masses in the world (i.e., Africa, South America, or East Asia).

Preservation of Hydrothermal Fluid Copper Isotope Signatures in Chalcopyrite‐Rich Chimneys: A Case Study From the PACMANUS Vent Field, Manus Basin

AbstractCopper isotopes (δ65Cu) in hydrothermal fluids have the potential to provide information on ore‐forming processes occurring below the seafloor, but Cu isotope data from high‐temperature fluids are scarce. Here, we examine the extent to which coexisting sulfide minerals in a hydrothermal chimney can preserve fluid Cu isotope ratios using a fluid‐solid pair of a black smoker (333°C) from the Roman Ruins vent area (PACMANUS) in the Manus Basin. Two ca. 3 cm long transects through the chalcopyrite‐rich chimney wall show an increase in δ65Cu from 0.48 to 2.28‰ from the interior to the exterior, coupled with limited variation in sulfide δ34S (1.52–4.72‰). The Cu isotopic composition of chalcopyrite from the innermost wall closely resembles the δ65Cu value of the paired hydrothermal fluid, indicating that chalcopyrite in the inner ∼5 mm of the chimney records the Cu isotope ratio of the venting fluid. Beyond this, an increase in sulfide δ65Cu toward the exterior correlates with an increase in the relative abundance of secondary Cu sulfides. The appearance of bornite coincides with the presence of small barite crystals, suggesting this represents a redox gradient between reduced hydrothermal fluids and oxidized seawater admixing inwards. Elevated δ65Cu in this zone can be explained by the precipitation of secondary Cu sulfides from 65Cu‐enriched fluids formed during oxidative chalcopyrite dissolution. Our findings indicate that interactions with oxidizing seawater shift chalcopyrite δ65Cu values over small spatial scales, and that caution must be applied if chimney sulfides are used to reconstruct δ65Cu values of high‐temperature hydrothermal fluids.

The Bougrine Zn-Pb deposit, the largest salt diapir-related Mississippi Valley-type deposit in the Eastern Maghreb salt diapir province, Tunisia

The Bougrine Zn-Pb sulfide deposit (5.5 Mt @ 12 % Zn + 2.5 % Pb) in the Eastern Maghreb salt diapir province of Tunisia is located at the northeastern end of the Lorbeus-Bougrine diapir. The several-km large diapir is composed of Triassic evaporite that intruded about 10 km-thick Jurassic and Cretaceous marine sedimentary rocks during the Cretaceous and Tertiary. Mineralization occurs in breccia zones at the contact with the Triassic diapir and in the peridiapiric Cretaceous strata. Most of the ore is stratabound (F2 orebody) with microsphalerite disseminations in organic-rich laminated black limestone of the Cenomanian-Turonian Bahloul Formation, where sphalerite occurs as infill of Globigerina shells, as massive replacement of Globigerina-rich layers, as banded colloform sphalerite and in voids as euhedral, coarse-grained crystals together with skeletal galena and minor marcasite. Abundant degraded oil seepages in the orebodies and their host rocks testify to the existence of a (former) hydrocarbon reservoir.The various sphalerite generations have highly variable Mn and Fe contents; Cd has an average content of 445 ppm; As and Hg contents are in the 200 ppm range; Tl content is about 40 ppm; Ga content is about 10 ppm; and In content is consistently <1 ppm. Fluid inclusions in celestite, coarse-grained late-stage sphalerite and calcite indicate moderate fluid salinities (16 ± 2 wt% NaCl eq.) and moderate temperatures (85 to 146 °C). The empirical trace-element sphalerite geothermometer gives 184 ± 38 °C for the main-stage microsphalerite and the banded colloform sphalerite which have no measurable fluid inclusions.A wide range of δ13C (-13.6 to 5.6 ‰) and δ18O (-19.8 to 33 ‰) values is observed in ore-stage and post-ore calcite. Ore-stage calcite commonly has negative δ13C values reflecting involvement of carbon from organic matter; its δ18O composition with an average of 22.6 ± 2 ‰ (19.7 to 26.0 ‰) may be explained by a moderate-temperature hydrothermal fluid. There is no systematic δ34S variation between and across the different styles of mineralization. The range of δ34S of 6–19 ‰ with a mean of 13 ‰ is close to the δ34S value of local and regional Triassic marine sulfate (δ34S = 16 ‰). Thermochemical reduction of Triassic sulfate, likely mediated by hydrocarbons, is the most probable source for sulfur in the ores. Lead isotope data on galena are within a narrow field of upper crustal signature (206Pb/204Pb = 18.71–18.77; 207Pb/204Pb = 15.66–15.70; 208Pb/206Pb = 38.81–38.97) indicating a homogeneous ore fluid.The major characteristics of the Bougrine ore deposit are typical of Mississippi Valley type Pb-Zn deposits and indicate large-scale fluid circulation likely related to stacking and uplift in the northern Tunisian Nappes Zone during the Miocene. Both the hydraulic load of meteoric water and over-pressured basinal and basement fluids during compressional movements favored southward fluid migration along basement discontinuities and most permeable strata in the Mesozoic-Cenozoic sedimentary pile. Low-pressure domains around salt diapirs in a rifting environment allowed focused upward fluid flow, and the hydrocarbon reservoir of the Bahloul Formation then provided the geochemical trap for efficient base metal deposition.

The influence of environmental parameters on spatial variation in zoobenthic density and stable isotopes (δ13C, δ15N, and δ34S) within a large lake

AbstractThe use of baselines in stable isotope studies to interpret food web structure is essential, but baseline isotope values are often assumed to be spatially homogeneous, even in large aquatic ecosystems. To test this assumption in large lakes, we quantified spatial variation in δ13C, δ15N (deposit‐feeding Oligochaeta and filter‐feeding Dreissena spp.), and δ34S (Dreissena spp. only) and density in Lake Erie between 2014 and 2016. Lake Erie's three distinct basins differ in size, bathymetry, and nutrient loading, making it an excellent system for exploring spatial variation in stable isotopes of baseline organisms. Dreissena spp. densities were highest in the western and lowest in the seasonally hypoxic central basin, while Oligochaeta densities were relatively consistent throughout Lake Erie. Values of δ13C, δ15N, and δ34S exhibited distinct spatial trends that were not related to population densities but followed the west to east direction of water flow within the lake. For both taxa, δ13C was lower in the deeper, oligotrophic east basin than the shallow, mesotrophic west basin, and δ15N and δ34S increased from west to east. Spatial patterns of low δ34S in Dreissena spp. in the western and central basins were likely related to hypoxia, whereas patterns of δ15N in both taxa were probably related to the greater influence of agricultural land uses in the western basin. Spatial trends of stable isotopes in large lake zoobenthos are driven by complex interactions of environmental gradients, which could introduce bias in evaluations of trophic structures within aquatic ecosystems that use stable isotopes.

Fe and S isotopes variation of pyrite from hydrothermal mineralization in the Zijinshan region in Fujian Province, SE China

The Zijinshan district, Fujian Province, southeastern China, is a globally renowned CuAu orefield and hosts a wide variety of ore deposits within the Zijinshan granite complex and surrounding volcano-sedimentary rocks. We performed FeS isotope analysis on pyrite separates from the Zijinshan high-sulfidation epithermal deposit, Yueyang intermediate-sulfidation epithermal deposit, Wuziqilong transition-type (from high-sulfidation epithermal to porphyry) deposit, and Jintonghu porphyry CuMo deposit, aiming to understand the formation process of Fe-sulfides and the evolution of ore-forming fluids in different deposits. Pyrites from the Jintonghu porphyry CuMo deposit show variations in δ56Fe and δ34S from −0.15 ‰ to 0. 45 ‰, and from 1.81 ‰ to 2.70 ‰, respectively. In contrast, pyrites from epithermal-type deposits (i.e., Zijinshan, Yueyang, and Wuziqilong) show a negatively shifted Fe isotopic composition from −1.74 ‰ to 0.45 ‰. The combination of Fe isotopic data from the Jintonghu porphyry CuMo deposit with published minerals-fluid fractionation factors and the use of a Rayleigh fractionation model allowed us to determine the δ56Fe range of regional ore-forming fluids (−1.00 ‰ to −0.40 ‰), which is consistent with the previous “light fluid” hypothesis, suggesting that pyrite of porphyry CuMo deposits has isotopic compositions reflecting the isotopic value of the hydrothermal fluids. For the epithermal deposits, pyrite Fe isotopic composition is the result of a complex interaction of Rayleigh fractionation, rapid precipitation and kinetic fractionation, and δ56Fe values of the initial fluids is difficult to estimate. Integrating the Fe and S isotope data for pyrite of different genesis, we found that porphyry CuMo deposits (δ56Fe: −0.9 ‰ to 0.46 ‰; δ34S: −4.06 ‰ to 3.9 ‰) can be distinguished from a non-magmatic/low-temperature region, while the transitional area of which may be a porphyry-related hydrothermal deposit (i.e., epithermal deposit). In general, we suggest that the Fe and S isotopic signatures of pyrite can effectively distinguish porphyry-type deposits from their associated hydrothermal deposits.

The Roles of Various Types of Crustal Contamination in the Genesis of the Jinchuan Magmatic Ni-Cu-PGE Deposit: New Mineralogical and C-S-Sr-Nd Isotope Constraints

Abstract Addition of crustal sulfur to the Jinchuan magma or oxidation of the magma associated with carbonate assimilation has been considered to be the main cause of sulfide saturation in the magma by two opposing groups of researchers. To address this controversy, we have carried out an integrated mineralogical and C-S-Sr-Nd isotope study of the Jinchuan magmatic Ni-Cu-platinum group element (PGE) sulfide ore deposit. Pure marble, olivine marble, serpentine marble, and hybrid rocks occur in the contact zone. The δ13Ccarb values of the Jinchuan sulfide-bearing ultramafic rocks containing calcite xenocrysts are from –4.7 to –2.9‰, which are similar to or slightly lower than those of the marbles and associated hybrid rocks (–3.9 to 0.8‰) but significantly higher than those of the calcite-barren intrusive rocks (–9.3 to –8.0‰). This, together with the calcite xenocrysts and calcium-silicate minerals in hybrid rocks and some intrusive rocks, indicates that carbonate assimilation took place during magma-carbonate interaction. Only less than several hundred ppm of the CO2 gas produced in the reaction zone could be added to the Jinchuan magma. Such a trace amount of additional CO2 was rapidly swamped by the much greater mass of FeO in the magma, resulting in little change in the FeO/Fe2O3 of the magma, and thereby negligible change of magma redox state. This is evident from similar calculated fO2 values for the calcite-bearing (~QFM+0.7) and calcite-barren (~QFM+0.6) intrusive rocks. The new results rule out the possibility that sulfide saturation in the Jinchuan magma resulted from in situ carbonate assimilation. The Sr-Nd isotope data from this study and previous studies are consistent with up to 20% bulk contamination with siliceous crustal materials at depth, followed by minor amounts of in situ carbonate assimilation by the Jinchuan magma. Our new sulfur isotope data expand the range of δ34S for the Jinchuan deposit significantly. The new range is from −7.6 to 3.0‰, with an average of −1.8‰, which is generally lower than the mantle value (0 ± 2‰). The new result supports the premise that crustal sulfur was involved in the genesis of the Jinchuan deposit. Very high, crustal-like S/Se ratios (as high as 8080) for some of the samples from the deposit provide additional support for the interpretation. The country rocks in the vicinity of the Jinchuan deposit analyzed to date have δ34S values varying from −4.0 to 11.3‰, with an average of 2.9‰, which is higher than both the mantle value and the average value of the Jinchuan deposit, suggesting that the Jinchuan magma acquired some crustal sulfur at depth, likely concurrent with the siliceous assimilation. Numerical modeling of δ34S-S/Se of sulfide ores and country rocks further illustrates that the observed variations of δ34S and S/Se ratios are related to the assimilation of S-rich rocks located at depth, followed by progressive dilution of the contaminated δ34S-S/Se signature. Based on the new results, we conclude that contamination with siliceous crustal materials as well as addition of crustal sulfur at depth played a critical role in triggering sulfide saturation in the Jinchuan magma.

Isotope diffusion and re-equilibration of copper and evaporation of mercury during weathering of tetrahedrite in an oxidation zone

To understand the mobility of heavy metals during oxidative weathering of sulfides, we investigated weathering processes of tetrahedrite [(Cu,Fe,Zn,Hg)12(Sb,As)4S13] in an oxidation zone with abundant siderite (FeCO3) and baryte (BaSO4) at Rudňany (Slovakia). The focus of this work lied in the isotopic (δ65Cu, δ202Hg, δ34S) variations of the minerals during weathering and the interpretation of such changes. In the studied oxidation zone, Hg-rich tetrahedrite converts in situ to pockets of powdery cinnabar (HgS) and an X-ray amorphous mixture rich in Sb, Fe, and Cu that slowly re-crystallizes to Cu-rich tripuhyite (FeSbO4). Copper is mobile and precipitates as malachite [Cu2(OH)2(CO3)], azurite [Cu3(OH)2(CO3)2], or less abundant clinoclase [Cu3(AsO4)(OH)3]. The isotopic composition (δ65Cu) of tetrahedrite correlates well with the degree of weathering and varies between 0.0 ‰ and −4.0 ‰. This correlation is caused by isotopic changes during dissolution and subsequent rapid equilibration of δ65Cu values in the tetrahedrite relics. Simple diffusion models showed that equilibration of Cu isotopic values in the tetrahedrite relics proceeds rapidly, on the order of hundreds or thousands of years. Abundant secondary iron oxides draw light Cu isotopes from the aqueous solutions and shift the isotopic composition of malachite and azurite to higher δ65Cu values as the distance to the primary tetrahedrite increases. Clinoclase and tripuhyite have lower δ65Cu values and are spatially restricted near to the weathering tetrahedrite. The Hg and S isotopic composition of tetrahedrite is δ202Hg = −1.27 ‰, δ34S = −1.89 ‰, that of the powdery secondary cinnabar is δ202Hg = +0.07 ‰, δ34S = −5.50 ‰. The Hg isotopic difference can be explained by partial reduction of Hg(II) to Hg(0) by siderite and the following evaporation of Hg(0). The S isotopic changes indicate no involvement of biotic reactions in the oxidation zone, probably because of its hostility owing to high concentrations of toxic elements. This work shows that the Cu isotopic composition of the primary sulfides minerals changes during weathering through self-diffusion of Cu in those minerals. This finding is important for the use of Cu isotopes as tracers of geochemical cycling of metals in the environment. Another important finding is the Hg in the oxidation zones evaporates and contributes to the global cycling of this element through atmospheric emission.

Are Large Sulfur Isotope Variations Biosignatures in an Ancient, Impact-Induced Hydrothermal Mars Analog?

Discrepancies have emerged concerning the application of sulfur stable isotope ratios as a biosignature in impact crater paleolakes. The first in situ δ34S data from Mars at Gale crater display a ∼75‰ range that has been attributed to an abiotic mechanism. Yet biogeochemical studies of ancient environments on Earth generally interpret δ34S fractionations >21‰ as indicative of a biological origin, and studies of δ34S at analog impact crater lakes on Earth have followed the same approach. We performed analyses (including δ34S, total organic carbon wt%, and scanning electron microscope imaging) on multiple lithologies from the Nördlinger Ries impact crater, focusing on hydrothermally altered impact breccias and associated sedimentary lake-fill sequences to determine whether the δ34S properties define a biosignature. The differences in δ34S between the host lithologies may have resulted from thermochemical sulfate reduction, microbial sulfate reduction, hydrothermal equilibrium fractionation, or any combination thereof. Despite abundant samples and instrumental precision currently exclusive to Earth-bound analyses, assertions of biogenicity from δ34S variations >21‰ at the Miocene Ries impact crater are tenuous. This discourages the use of δ34S as a biosignature in similar environments without independent checks that include the full geologic, biogeochemical, and textural context, as well as a comprehensive acknowledgment of alternative hypotheses.

Influence of spatial and temporal variation on establishing stable isotope baselines of δ15N, δ13C, and δ34S in a large freshwater lake

Abstract It is essential to establish a baseline in studies using stable isotopes to interpret trophic relationships across ecosystems and through time. Studies in freshwater ecosystems struggle to quantify baseline stable isotopes due to difficulties collecting representative samples, particularly from pelagic habitats. We assessed temporal and spatial variation in δ13C, δ15N, and δ34S in a commonly used pelagic baseline, seston (n = 156), in Lake Erie to understand mechanisms that correlate with baseline stable isotope dynamics in large lakes. Seston contains a wide range of material which can confound stable isotope interpretation, and we examined the utility of element content and ratios to account for variation in sample source. Seston was collected in each of the three basins of Lake Erie from May to October in 2017–2019 at nearshore (&lt;10 m depth) and offshore (&gt;10 m depth) sites. General linear models were conducted on each stable isotope (δ15N, δ13C, and δ34S) and sample composition (variables: %N, %C, %S, C:N, C:S, and N:S) to assess how basin, month, and collection year influenced seston stable isotopes and composition. Sample composition (variables: %N, %C, %S, C:N, C:S, and N:S), which is rarely reported for organisms in stable isotope studies, was constant throughout the sample period with no temporal or spatial trends except for small variations in %C, C:N, C:S, and N:S. This indicated that the temporal and spatial trends observed within the stable isotopes were related to seasonal changes in system processes and plankton community dynamics, with few or minimal changes in the amount of detrital and inorganic material within seston. Values and trends of δ15N, δ13C, and δ34S in seston were comparable to those measured previously in Lake Erie and other Laurentian Great Lakes. All three isotopes increased from May to October of each sample year and varied spatially, δ15N was higher, δ34S was lower, and δ13C was the same in the west basin compared to the central and eastern basins of Lake Erie, which did not differ. These trends probably reflect seasonal changes in plankton community composition and nutrient cycling throughout the lake and are potentially linked to the presence of Microcystis blooms in the western basin during the late summer and autumn. Seston turns over quickly, as shown by the rapid changes in stable isotope values throughout the study, which confounds the investigation of stable isotopes in upper trophic levels, and especially in organisms that have slower tissue turnover and move throughout the lake seasonally. Additionally, the variable composition of seston (e.g., % C, % N, % S, C:N, C:S, N:S) necessitates analysing sample composition to determine the degree of abiotic (e.g., detritus, sediment, particulate organic matter) and biotic (e.g., phytoplankton, zooplankton) content in it.

Freshwater wetland–driven variation in sulfur isotope compositions: Implications for human paleodiet and ecological research

Sulfur isotope (δ34S) analyses are an important archaeological and ecological tool for understanding human and animal migration and diet, but δ34S can be difficult to interpret, particularly in archaeological human-mobility studies, when measured isotope compositions are strongly 34S-depleted relative to regional baselines. Sulfides, which accumulate under anoxic conditions and have distinctively low δ34S, are potentially key for understanding this but are often overlooked in studies of vertebrate δ34S. We analyze an ecologically wide range of archaeological taxa to build an interpretive framework for understanding the impact of sulfide-influenced δ34S on vertebrate consumers. Results provide the first demonstration that δ34S of higher-level consumers can be heavily impacted by freshwater wetland resource use. This source of δ34S variation is significant because it is linked to a globally distributed habitat and occurs at the bottom of the δ34S spectrum, which, for archaeologists, is primarily used for assessing human mobility. Our findings have significant implications for rethinking traditional interpretive frameworks of human mobility and diet, and for exploring the historical ecology of past freshwater wetland ecosystems. Given the tremendous importance of wetlands’ ecosystem services today, such insights on the structure and human dynamics of past wetlands could be valuable for guiding restoration work.

In-situ trace element and S isotope systematics in pyrite from three porphyry-epithermal prospects, Limnos Island, Greece

Porphyry-epithermal systems associated with high-K calc-alkaline to alkaline igneous host rocks may be prospective for the recovery of Te among related elements like Cu, Ag, and Au. Limnos Island, as part of the Tethyan magmatic belt, is such an example, where (telescoped) porphyry-epithermal mineralization is accompanied by different alteration-styles reflecting various hydrothermal processes. Here, we present in-situ S isotope and trace element data of pyrite, which records the fluid evolution from the early porphyry to the late epithermal stage in three distinct prospects (Fakos, Kaspakas, Sardes) on Limnos Island. Pyrite in the sericitic alteration of Fakos mainly formed from single-phase magma-derived fluids lacking evidence for phase separation, as reflected by relatively constant δ34S (about −4‰) and Co/Ni (0.1-1) values. By contrast, in the sericitic alteration of Kaspakas and the following epithermal stages, an influence of boiling is implied by negative δ34S values to −15‰, significant intergrain δ34S variations (&amp;gt;3‰), highly variable Co/Ni (100-0.01) and As/Co (10-0.001) in pyrite. Higher δ34S values (above −4‰) in porphyry pyrite from Sardes and partly in the other two hydrothermal systems are related to mixing between magmatic S, and S which was transported through deeply circulated seawater and/or meteoric water. We propose that fluid-rock interaction buffered the pH to higher values, which enhanced the solubility of Au and Te. Subsequent boiling processes caused the Au deposition, whereas Te partitioned into the vapor and finally precipitated upon condensation into meteoric water. This process is accompanied by continuous cooling during fluid ascent from 780°C to &amp;lt;300°C, as indicated by increasing Sb, Tl, and Pb in pyrite from the porphyry to the epithermal stage. Consequently, the in situ δ34S and trace element analysis allows to constrain the depositional environment of economic metals like Au and Te in porphyry-epithermal prospects.

New constraints for crustal sulfur contamination of gold source: Evidence from complex δ34S of pyrite in the northwestern Jiaodong gold province, China

The formation processes of the complex δ34S variations for the Jiaodong-type gold deposits are still equivocal, which cannot give a robust identification for the sulfur sources, by inference, Au sources. The δ34S and trace elements of ore-related pyrite collected from the northwestern Jiaodong gold province (Jiaojia and Sanshandao-Xinli goldfields) are analyzed by in-situ methods, to reveal more clues for understanding the complex δ34S variations and ore material sources. Gold deposits in the northwestern Jiaodong contain quartz-Au-pyrite (Py-a) stage (III) and quartz-Au-pyrite (Py-b)-polymetallic stage (IV). In the Jiaojia goldfield, Py-a has a δ34S range of 9.9–24.4‰, whereas Py-b has a δ34S range of 7.3–9.3‰. In the Sanshandao-Xinli goldfield, Py-a has a δ34S range of 6.9–34.7‰, and δ34S of Py-b ranges in 0.2–19.2‰. Single-point and mapping analyses show that As-Au-Co-Ni contents have considerable variations in Py-a and Py-b. The δ34S and As-Au-Co-Ni contents in Py-a and Py-b show diverse correlations. Equilibrium and Rayleigh (or sulfidation) fractionations cannot account for the large δ34S variation due to the pyrite-chalcopyrite-pyrrhotite buffer. The rapid decompression with oxidization of ore-forming fluids by immiscibility can only result in the δ34S decrease, rather than increase to 14.0–34.7‰ from the concentrated δ34S range of 9.6–13.4‰ in Py-a and Py-b. Therefore, the analyzed δ34S values in the ore-related pyrites should represent those of ore-forming fluids. Considering the simple physicochemical processes cannot reconcile the complex matches between large δ34S variations and As-Au-Co-Ni contents, it is suggested the As-rich and Au-As-rich ore-forming fluids with large δ34S range and variable Co-Ni concentrations should flow into mineralization sites during stages III and IV in the Sanshandao-Xinli goldfield. The sulfur with large δ34S range and Au-As-Co-Ni elements with variable contents in the ore-related pyrites of the Jiaojia and Sanshandao-Xinli goldfields were most likely inherited from the sedimentary sulfides that were reduced from seawater sulfates, by comparisons with those in the typical sedimentary, metamorphic hydrothermal and magmatic hydrothermal pyrites. Combining with previous researches for the ore-forming materials sources of the Jiaodong-type gold deposits, the metamorphic Precambrian rocks, especially those metasedimentary rocks containing sulfides reduced from seawater sulfates, can be considered as the feasible ore-forming materials sources for the large δ34S range and variable trace elements in the Jiaojia and Sanshandao-Xinli goldfields. Through the δ34S comparison for the Jiaodong-type gold deposits, we propose an important process that the single-sourced ore-forming fluids, which were initially derived from the metasomatized lithospheric mantle, have extracted the ore materials (including sulfur-Au-As elements) from the metamorphic Precambrian rocks (possible Precambrian metamorphic basement in the Jiaodong gold province or the subducted Late Neoproterozoic rocks of the YC), and mixed heterogeneously to precipitate pyrites with complex δ34S and trace elements throughout the Jiaodong-type gold deposits.

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.

Annually Resolved Profiles of δ34S and Sulfate in Shallow Ice Core DF01 (Dome Fuji, Antarctica) Spanning the Nineteenth Century and Their Geochemical Implications

AbstractWe report the results of a high‐sensitivity sulfur‐isotope (δ34S) analysis of samples from shallow ice core DF01 from Dome Fuji, East Antarctica, and present chronological profiles of the data with an annual resolution covering the entire nineteenth century. In the δ34S and non‐sea‐salt (nss)‐sulfate ([SO42−]nss) profiles, the signals of five well‐known nineteenth century volcanic eruptions were confirmed: Krakatau 1883 (and Tarawera 1886), Makian 1861, Cosiguina 1835, Tambora 1815, and Unknown 1809. Due to large influence of sulfate caused by volcanic eruptions in the first half of the nineteenth century, the averages of nss‐sulfur‐isotope composition (δ34Snss) and [SO42−]nss for the second half (+14.6‰ and 67.6 μg/L), calculated after excluding these prominent signals, were found to differ from those of the first half century (+9.1‰ and 84.1 μg/L). We also examined anomalous variations other than the five major volcanic signals in the δ34S and [SO42−]nss profiles based on not only variations in δ34S and [SO42−]nss but also variations in the concentrations of other ions. We then identified the presence of three additional volcanic signals: Babuyan 1831, Galunggung 1822, and an unknown volcanic eruption around 1807. The latter two signals confirmed for the first time in Antarctic ice cores. Other δ34S and [SO42−]nss anomalies may be related to an influx of coastal air masses, a nonstratospheric volcanic eruption near Antarctica or an increase in the relative contribution of a stratospheric component to the precipitation in inland Antarctica. These demonstrate the importance of obtaining the annually resolved, continuous δ34S profile over a certain period.

Subseafloor mineralization related to the shallow seawater-hydrothermal circulation system in the Longqi hydrothermal field, Southwest Indian Ridge (49.6°E): Evidence from in situ trace element and sulfur isotope compositions of pyrite varieties

The shallow seawater-hydrothermal circulation system plays a crucial role in the subseafloor mineralization of the hydrothermal field. However, its key fluid processes and impacts on the metal mobilization and sulfur cycles in the stockwork mineralization are still poorly understood. We first present the systemic variations in micro-scale trace element and sulfur isotope compositions of pyrite varieties in a stockwork-like sulfide assemblage from the Longqi hydrothermal field to constrain the transport and deposition of metals and the origins and cycles of sulfur in the shallow seawater-hydrothermal circulation system. Pyrites considered as the dominant sulfides can be clarified into disseminated fine-grained (Py-I), euhedral (Py-II), and subhedral-euhedral (Py-III) varieties based on the textures. The wall-rock-derived elements Ti, Cu, and Ni and seawater-derived elements V, U, Mo, Mg, and Mn are concentrated in Py-I in the breccias, which is related to the fluid-rock interaction and fluid-seawater mixing in the shallow seawater-hydrothermal circulation system. Short-lived shallow seawater-hydrothermal circulation results in fluid fluctuation and oscillatory-zoned Py-II with depletion of Co, Ni, Cu, As, and Se in the mantles relative to those in the rims and cores. As the later hydrothermal activity was active, Py-III was overgrown from Py-II rich in hydrothermally inherited metals Se, Te, and Co, possibly implying the hydrothermal field is coming into the main mineralization. The sulfur isotope compositions of pyrites range from 4.30 to 9.98‰ (n = 37), with distinct δ34S variations in the individual Py-I crystals (>1.5 ‰ within a 20 × 20 µm2 region). This variation is attributed to changes in the relative proportion of sulfur sourced from (i) the shallow-origin reduced seawater via reduction by ferrous iron released from basalt, and (ii) the reduction of pre-existing anhydrite by later hydrothermal overprinting in the shallow subseafloor. These findings provide evidence for a model to better understand the effect of the shallow seawater-hydrothermal circulation system on the subseafloor stockwork mineralization of hydrothermal fields.

We are what we eat, plus some per mill: Using stable isotopes to estimate diet composition in Gyps vultures over space and time.

Dietary studies in birds of prey involve direct observation and examination of food remains at resting and nesting sites. Although these methods accurately identify diet in raptors, they are time‐consuming, resource‐intensive, and associated with biases from the feeding ecology of raptors like Gyps vultures. Our study set out to estimate diet composition in Gyps vultures informed by stable isotopes that provide a good representation of assimilated diet from local systems.We hypothesized that differences in Gyps vulture diet composition is a function of sampling location and that these vultures move between Serengeti National Park and Selous Game Reserve to forage. We also theorized that grazing ungulates are the principal items in Gyps vulture diet.Through combined linear and Bayesian modeling, diet derived from δ13C in Gyps vultures consisted of grazing herbivores across sites, with those in Serengeti National Park consuming higher proportions of grazing herbivores (>87%). δ13C differences in vulture feather subsets did not indicate shifts in vulture diet and combined with blood δ13C, vultures fed largely on grazers for ~159 days before they were sampled. Similarly, δ15N values indicated Gyps vultures fed largely on herbivores. δ34S ratios separated where vultures fed when the two sites were compared. δ34S variation in vultures across sites resulted from baseline differences in plant δ34S values, though it is not possible to match δ34S to specific locations.Our findings highlight the relevance of repeated sampling that considers tissues with varying isotopic turnover and emerging Bayesian techniques for dietary studies using stable isotopes. Findings also suggested limited vulture movement between the two local systems. However, more sampling coupled with environmental data is required to fully comprehend this observation and its implications to Gyps vulture ecology and conservation.