Sulfur Isotope Variations Research Articles

Improved Standard Addition Method for Measuring Stable Isotopic Compositions and Its Application to Sulfur Isotope Composition.

The standard addition method (SAM) is widely used to measure the isotopic compositions of natural samples, particularly those with a complex matrix. However, traditional SAM has limitations for isotope systems with significant variations in isotope composition due to its reliance on approximation in calculation and the requirement for a priori estimates of analyte isotopic compositions and accurate concentrations. To overcome the issues, our work proposes an improved SAM that explicitly calculates isotope ratio R (i.e., XE/YE, 34S/32S for example) instead of approximating R* (mass number of isotope X divided by total mass number of all isotopes of an element) with R in SAM. Additionally, the sample fraction within standard-sample mixture in improved SAM is determined using the isotope compositions of standards, sample-standard mixtures, and the mixtures of both standards, rather than relying on sample concentrations and volumes. Both improvements not only overcome the shortcomings of traditional SAM but also empowered the approach's ability to accurately determine sample concentrations. To validate its effectiveness, we applied the improved SAM to natural samples with substantial sulfur (S) isotope variation (1.94 to 27.19‰) and low S concentration (0.81 to 3.47 μg g-1). The calculated δ34S values and concentrations of these samples are consistent with direct measurements within the error ranges while reducing sample sizes to 20% of those required for direct measurement. Moreover, our method achieves higher accuracy in δ34S values compared with traditional SAM. Both comparisons affirm the reliability and superiority of improved SAM.

Sulfur isotopic variations in the products of the 1895 CE eruption at Zao volcano (NE Japan): Implications for connecting eruption source and syn-eruptive magmatic-hydrothermal processes

Sulfur isotopic ratio in sulfate and sulfide in subvolcanic hydrothermal systems is a valuable tracer to study the magmatic-hydrothermal processes from the magma source through to volcanic eruptions. Zao volcano is among the most active volcanoes in NE Japan, with historical explosive eruptions occurring during the last thousand years and unrest episodes since 2013. This necessitates a detailed assessment of the potential risk of future volcanic hazards. We investigated the magmatic-hydrothermal processes that occurred during the 1895 CE eruption sequence at Zao volcano by conducting mineralogical and sulfur isotope analyses in the exposed well: (i) six volcanic units (Layers 1–6) of the 1895 CE eruption products (clayish ash deposits with andesitic bombs, lapilli of scoria, and minor altered lithic fragments) deposited on the rim of Okama crater lake; and (ii) clay-altered and silicified rocks from the Nigorikawa alteration zone (NGA) surrounding the Goshikidake cone. Mineralogical data show that the samples mainly consist of alunite, pyrite, and gypsum. Alunite and pyrite occur as fine crystal mixtures associated with mineral assemblages of both advanced argillic alteration (i.e., those of cristobalite and kaolinite) and silicification (i.e., those of cristobalite, tridymite and native sulfur). Gypsum typically appears as isolated euhedral crystals of several millimeters in size. Samples of the 1895 CE eruption products have a narrow range of δ34S values from +3 ‰ to +5 ‰ for gypsum, from +9 ‰ to +13 ‰ for alunite, and approximately −10 ‰ for pyrite. For the NGA samples, the δ34Sgypsum, δ34Snative sulfur, and δ34Spyrite values range from −12 ‰ to −9 ‰, whereas for alunite, these range from +8 ‰ to +18 ‰. This indicates that alunite and pyrite in the 1895 CE eruption products were derived from the advanced argillic alteration and silicification zones that developed under Okama crater, which is exposed as the NGA. Estimated alteration temperatures based on the sulfur isotopic equilibrium between alunite and pyrite pairs are 200 °C–300 °C. By contrast, δ34Sgypsum values in the 1895 CE products are significantly higher than those in the NGA (which are derived from oxidation of pyrite or H2S, or both), ranging between an estimated parental fluid of δ34Sbulk-initial = ca. +1 ‰ and the Quaternary volcanic rocks of the Japan arc. This suggests that gypsum in the 1895 CE eruption products derived from magmatic vapor condensate (anhydrite) formed in the volcanic conduit during the eruption, thus becoming replacement of anhydrite by gypsum after or during the tephra deposition on the Zao summit surface. Our results on sulfur-bearing minerals provide new clues for better understanding (and monitoring) the syn-eruptive processes of volcanic eruptions focused on subvolcanic hydrothermal systems.

Carbon, nitrogen, and sulfur elemental and isotopic variations in mouse hair and bone collagen during short-term graded calorie restriction

This study characterized the effect of calorie restriction (CR) on elemental content and stable isotope ratio measurements of bone "collagen" and hair keratin. Adult mice on graded CR (10-40%; 84days) showed decreased hair δ 15N, δ 13C, and δ 34S values (significantly for δ 15N) with increasing CR, alongside a significant increase in bone "collagen" δ 15N values and a decrease in "collagen" δ 13C values. We propose this was likely due to the intensified mobilization of endogenous proteins, as well as lipids in newly synthesized "collagen". Elemental analysis of bone "collagen" revealed decreased carbon, nitrogen, and sulfur%content with increasing CR which is attributed to a change in the invivo bone "collagen" structure with extent of CR. This complexity challenges the use of elemental indicators in the assessment of collagen quality in archaeological studies where nutritional stress may be a factor.

Carbon-Sulfur isotope and major and trace element variations across the Permian–Triassic boundary on a shallow platform setting (Xiejiacao, South China)

We examined microbialites deposited near the Permian–Triassic boundary (PTB) at the Xiejiacao section of South China, including the size and morphology of pyrite framboids, carbonate carbon isotopes (δ13Ccarb), carbonate associated sulfur isotope (δ34SCAS), major and trace elements, and total organic carbon (TOC) concentrations. The microbialite unit is much thicker than the PTB beds in deeper water sections, providing more detailed geochemical records from that time. A prominent negative δ13Ccarb excursion was recognized in association with the second phase of the Permian–Triassic mass extinction (PTME), comparable with that of several other shallow platform facies sections worldwide. δ34SCAS stratigraphic profiles also show a negative excursion, with minimum values occurring slightly later than those of δ13Ccarb. The minimum peak can be calibrated to the middle part of the conodont Isarcicella staeschei Zone, corresponding to the second phase of PTME. Over all, the carbon and sulfur isotopes demonstrate a coupled long-term relationship with large negative excursions during the Permian–Triassic transition followed by gradual recovery in the lowest Triassic, represented an extremely low concentration of sulfate in the ocean during this period. In contrast, the CS isotopes are strongly decoupled within the microbialite unit, which could be linked with the oxygen-poor conditions and microbial sulfate reduction (MSR: Sulfate reducing microorganisms facilitated the precipitation of sulfide and carbonate, such as SO42− + 2CH2O → H2S + 2HCO3−). The second phase of PTME was calibrated to the top of the microbialite unit, which was marked by the second δ13Ccarb-δ34SCAS negative excursions. The distinct marine oxygen deficiency was indicated by the small pyrite framboids, relatively high values of UEF (>1) and Ce/Ce* (>0.8). Combined with the previous biostratigraphic work, we propose that continuous volcanic activity induced intensified marine anoxia, leading to biotic mortality in the second phase of the PTME. Overall, our isotopic and geochemical data, integrated with results of previous studies, provided a new explanation for the carbon and sulfur isotope variations and additional evidences into the concurrent environmental changes during the Permian–Triassic transition.

Origin and evolution of a porphyry-skarn-stratabound system: constraints from geology, magmatic-hydrothermal zircon U–Pb and molybdenite Re–Os geochronology, and in situ S isotopes of the Dongguashan Cu(–Au) deposit, eastern China

Intrusion-related stratabound deposits within Late Carboniferous carbonate units are an abundant and highly economically significant ore type in eastern China. In such deposits, stratabound mineralization commonly coexists with porphyry and/or skarn mineralization, and the vast majority of reserves (>90 %) are derived from extensive stratabound orebodies, which are easy to exploit and of great interest to geologists. However, it is unclear whether these deposits were formed via the Late Carboniferous seafloor sedimentary exhalation formation or the Early Cretaceous magmatic-hydrothermal processes. Moreover, the fluid and sulfur isotope variations within porphyry-skarn-stratabound systems have not been adequately constrained. We investigated the Dongguashan deposit, one of the largest and most representative stratabound Cu(–Au) deposits in eastern China. Three mineralization types were recognized based on field and petrologic studies: porphyry, skarn, and stratabound. In the stratabound mineralization zone, magmatic and hydrothermal zircons from laminated ores yielded concordant U–Pb ages of 137.3 ± 1.1 and 135.7 ± 1.4 Ma, respectively, while molybdenite samples from vein-like ores yielded Re–Os model ages of 137.8–133.1 Ma (isochron age, 135.9 ± 1.4 Ma). These ages were consistent with the zircon U–Pb age of quartz monzodiorite (137.8 ± 1.7 Ma). A total of 146 in situ S isotope analyses yielded δ34S values (1.9–7.4 ‰) indicating that the sulfur was derived from a magmatic source. Therefore, the Dongguashan deposit resulted from Early Cretaceous magmatism rather than submarine exhalative sedimentary processes. The fluctuations in S isotopes of sulfides across the three mineralization types are attributable to different factors (pH, temperature, and oxygen fugacity) during the evolution of hydrothermal ore-forming fluids. This study demonstrates the importance of geochronology of mineralization and in situ sulfur isotope analysis under robust geological and petrographic frameworks, which can yield information about the ore-forming processes and ore genesis.

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.

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

Metal-rich organic matter and hot continental passive margin: drivers for Devonian copper-cobalt-germanium mineralization in dolomitized reef-bearing carbonate platform

The abundance and types of reef-bearing carbonate platforms reflect the evolution of Devonian climate, with conspicuous microbial-algal reefs in the warm Early and Late Devonian and sponge-coral reefs in the cooler Middle Devonian. A dolomitized Wenlock-Lower Devonian microbial-algal reef-bearing carbonate platform hosts epigenetic copper-cobalt-germanium (Cu-Co-Ge) sulfide mineralization at Ruby Creek-Bornite in the Brooks Range, Alaska. Here, we present rhenium-osmium (Re-Os) radiometric ages and molybdenum and sulfur (δ98/95Mo = +2.04 to +5.48‰ and δ34S = −28.5 to −1.8‰) isotope variations for individual Cu-Co-Fe sulfide phases along the paragenetic sequence carrollite-bornite-pyrite. In the context of a hot, extensional passive margin, greenhouse conditions in the Early Devonian favored restriction of platform-top seawater circulation and episodic reflux of oxidized brines during growth of the carbonaceous carbonate platform. Molybdenum and sulfur isotope data signal the stepwise reduction of hot brines carrying Cu during latent reflux and geothermal circulation for at least ca. 15 million years from the Early Devonian until Cu-Co sulfide mineralization ca. 379–378 million years ago (Ma) in the Frasnian, Late Devonian (weighted mean of Re-Os model ages of carrollite at 379 ± 15 Ma [n = 4]; Re-Os isochron age of bornite at 378 ± 15 Ma [n = 6]). On the basis of petrographic relationships between sulfides and solid bitumen, and the Mo and S isotope data for sulfides, we imply that the endowment in critical metals (e.g., Co, Ge, Re) in the Ruby Creek-Bornite deposit is linked to the activity of primary producers that removed trace metals from the warm Early Devonian seawater and concentrated Co, Ge, and Re in algal-bacterial organic matter in carbonate sediments.

A Comparative Study of Sulfur Isotope Variations within the Flatreef and Merensky Reef of the Bushveld Complex, South Africa

ABSTRACT The Flatreef, a down-dip, sub-horizontal extension of the Platreef, which underlies the Turfspruit and Macalacaskop farms, represents the future of platinum mining in South Africa. The stratigraphic connection between the Platreef, located at the base of the northern limb of the Bushveld Complex, and the Merensky Reef in the western and eastern limbs of the complex, was disputed for many years due to the heterogeneous nature of the Platreef along strike. However, the discovery of the Flatreef led to a new perspective on the Platreef as the former allowed for the study of a magmatic stratigraphy less affected by footwall interaction. Here, we report whole-rock S isotope (δ34S) compositions across the stratigraphic units of the Flatreef and its footwall and hanging wall as intersected by boreholes UMT-276 and UMT-393, as well as stratigraphic units of the Merensky Reef at Two Rivers Platinum mine in the eastern limb. The units of the Flatreef containing platinum group element mineralization, namely the Main Reef and Upper Reef, have δ34S values that overlap with the range recorded for the Merensky Reef in the western and eastern limbs. In UMT-393, Main Reef δ34S values range between 0.2 and 1.5‰ (with the exception of three outliers, 9.7‰, 11.1‰, and 7.9‰), and 0.52‰ and 11.2‰ for two Upper Reef samples. However, in UMT-276, Main Reef δ34S values range between –0.96 and 2.24‰ and 3.19‰ was recorded for an Upper Reef sample. The S isotope compositions recorded for the Merensky Reef pyroxenite at Two Rivers Platinum mine are relatively higher with δ34S values ranging between 1.24 and 4.83‰. The top unit of the Flatreef, which is a transition zone below the Main Zone, as well as the Footwall Cyclic Unit have heavier S isotope compositions with δ34S values ranging between 6 and 17‰ for the former and 0.7 and 18.6‰ for the latter. At Two Rivers Platinum mine, the hanging-wall anorthosite has a δ34S value of 2.9‰ in contrast to the 5.7‰ measured for the footwall anorthosite and 3.27‰ for the footwall feldspathic pyroxenite. The consistent near-mantle S isotope signature and accompanying metal enrichment in the Main Reef of the Flatreef may be explained by extensive interaction of sulfide minerals in a Lower Zone conduit/pre-Platreef staging chamber with large volumes of uncontaminated magma. The δ34S values of the Merensky Reef at Two Rivers Platinum mine are slightly higher compared to that of the Main Reef at Turfspruit and Macalacaskop possibly due to interaction with underlying carbonate rocks.

Genesis of the sediment-hosted Haerdaban Zn-Pb deposit, Western Tianshan, NW China: Constraints from textural, compositional and sulfur isotope variations of sulfides

The sediment-hosted Haerdaban Zn-Pb deposit is a newly discovered Zn-Pb deposit in the Sailimu terrane, Western Tianshan (NW China), containing ca. 0.64 Mt of ore at 6.19 wt% Zn and 1.09 wt% Pb. The mineralization consists mainly of veins, breccias and semi-massive sulfide ores within the dolomitic limestone and calcareous slate. Using LA-ICP-MS, this study investigates trace element and sulfur isotope composition of sulfide to constrain the genesis of the deposit. Four pyrite types were identified by variations in texture and composition. Porous pyrite (Py1) shows a significant enrichment in Mn, Ag, Sb, Tl, Ba, Pb, Cu, and Zn, whereas the pyrite overgrowth (Py2) and euhedral pyrite (Py3) are enriched in Co and As, but depleted in all other trace elements. This compositional trend is attributed to the release of trace elements from pyrite during recrystallization from a porous to massive texture. Pyrite (Py4) associated with sphalerite is inclusion-rich, but exhibits a depletion in most trace elements, except Ni and Sb. The underlying carbonaceous sediments are interpreted as a source of Ni, Sb and other metals for the ore-forming fluids. Sphalerite displays a wide variety of colors from dark brown to pale yellow, primarily related to variations in Fe contents. The overall Fe contents (0.25 to 6.12 wt%), Cd contents (524 to 1875 ppm) and Zn/Cd ratios (320 to 1258) in sphalerite are compatible with those of SEDEX Zn-Pb deposit. The contents of other elements in sphalerite are generally low. Calculated temperatures using trace element contents in sphalerite (GGIMFis geothermometer) range from 163 °C to 309 °C, indicating progressive cooling of ore-forming fluid. Pyrite, sphalerite and galena display a wide range of δ34S values from +3.9 to +18.3‰. The association of lower positive δ34S values (+3.9 to +8.8‰) and epithermal suite elements (Ni, As, Sb, and Tl) enrichment in porous pyrite indicate that sulfur in early sulfides was derived from thermochemical sulfate reduction (TSR) with a possible magmatic input. The dominant population of heavier δ34S values (+13.8 to +18.3‰) of massive sulfide support TSR as the main source of sulfur. The intermediate δ34S values (+7.0 to +13.0‰) of vein sulfide are likely a mixing of TSR-derived sulfur with light sulfur leached from diagenetic pyrite. The current data support the classification of Haerdaban as a metamorphosed SEDEX Zn-Pb deposit, where the main mineralization was the product of remobilization and upgrading of early exhalative ores during hydrothermal events.

Phanerozoic variation in dolomite abundance linked to oceanic anoxia: REPLY

The abundance of dolomitic strata in the geological record contrasts with the general rarity of locations where dolomite forms today, a discrepancy that has long posed a problem for their interpretation. Recent culture experiments show that dolomite can precipitate at room temperature, raising the possibility that many ancient dolomites may be of syngenetic origin. We compiled a large geodata set of secular variations in dolomite abundance in the Phanerozoic, coupled with compilations of genus richness of marine benthic invertebrates and sulfur-isotope variations in marine carbonates. These data show that dolomite abundance is negatively correlated to genus diversity, with four dolomite peaks occurring during mass extinctions. Dolomite peaks also correspond to the rapid increase in sulfur-isotope composition (δ³⁴S), an indicator of enhanced sulfate reduction, in anoxic oceans. These results confirm that variations in dolomite abundance during the Phanerozoic were closely linked with changes in marine benthic diversity, with both in turn related to oceanic redox conditions.

Biosignatures of ancient microbial life are present across the igneous crust of the Fennoscandian shield

Earth’s crust contains a substantial proportion of global biomass, hosting microbial life up to several kilometers depth. Yet, knowledge of the evolution and extent of life in this environment remains elusive and patchy. Here we present isotopic, molecular and morphological signatures for deep ancient life in vein mineral specimens from mines distributed across the Precambrian Fennoscandian shield. Stable carbon isotopic signatures of calcite indicate microbial methanogenesis. In addition, sulfur isotope variability in pyrite, supported by stable carbon isotopic signatures of methyl-branched fatty acids, suggest subsequent bacterial sulfate reduction. Carbonate geochronology constrains the timing of these processes to the Cenozoic. We suggest that signatures of an ancient deep biosphere and long-term microbial activity are present throughout this shield. We suggest that microbes may have been active in the continental igneous crust over geological timescales, and that subsurface investigations may be valuable in the search for extra-terrestrial life.

Triple sulfur-oxygen-strontium isotopes probabilistic geographic assignment of archaeological remains using a novel sulfur isoscape of western Europe.

Sulfur isotope composition of organic tissues is a commonly used tool for gathering information about provenance and diet in archaeology and paleoecology. However, the lack of maps predicting sulfur isotope variations on the landscape limits the possibility to use this isotopic system in quantitative geographic assignments. We compiled a database of 2,680 sulfur isotope analyses in the collagen of archaeological human and animal teeth from 221 individual locations across Western Europe. We used this isotopic compilation and remote sensing data to apply a multivariate machine-learning regression, and to predict sulfur isotope variations across Western Europe. The resulting model shows that sulfur isotope patterns are highly predictable, with 65% of sulfur isotope variations explained using only 4 variables representing marine sulfate deposition and local geological conditions. We used this novel sulfur isoscape and existing strontium and oxygen isoscapes of Western Europe to apply triple isotopes continuous-surface probabilistic geographic assignments to assess the origin of a series of teeth from local animals and humans from Brittany. We accurately and precisely constrained the origin of these individuals to limited regions of Brittany. This approach is broadly transferable to studies in archaeology and paleoecology as illustrated in a companion paper (Colleter et al. 2021).

Regional variations of sulfur isotope compositions for metallic deposits in South Korea

AbstractSouthern Korean peninsula comprises five major geotectonic provinces, throughout which various metallic deposits are distributed. We reviewed sulfur isotope data (n = 1,574) of sulfide minerals collected from previous works for 177 metallic deposits in the provinces to interpret the sulfur isotope characteristics of each province, comprising different wall rocks and geologic settings. The averaged δ34S values of each metallic deposit associated with Precambrian metamorphic rocks and Jurassic granitoids in the Gyeonggi massif and Yeongnam massif range from −7.1 to +10.3‰ (av. +4.5‰) and from −3.6 to +7.8‰ (av. +3.5‰), respectively. The Taebaeksan basin produced the highest δ34S value among the five, −0.4 to +13.2‰ (av. +6.1‰). This was influenced by sulfate sulfur derived from marine carbonate host rock. The Okcheon metamorphic belt, comprising metasedimentary and metavolcanics rocks, shows an isotope range from +1.9 to +8.3‰ (av. +5.7‰). The sulfur isotope distribution of the Gyeongsang basin with a range from −1.2 to +11.7‰ (av. +5.2‰) can be divided into two zones: higher δ34S values from the inner zone related to the volcanic rocks and magnetite‐series Cretaceous granitoids, and lower δ34S values from the outer zone related to the organic‐rich sedimentary rocks. Sulfur isotope variations of metallic deposits in each geotectonic province were mainly influenced by igneous sulfur and inherent wall rock sulfur sources, 32S‐enriched sedimentary sulfur (e.g., Precambrian metasedimentary rocks and biogenic sulfur‐rich sedimentary rocks), and 34S‐enriched seawater sulfur (e.g., carbonates and acid to intermediate volcanic rocks). These wall rocks also contributed to the changes in δ34S values for granitoid rocks and metallic deposits by time, ore genetic type, and ore species in South Korea.

Iron isotope fractionation in reduced hydrothermal gold deposits: A case study of the Wulong gold deposit, Liaodong Peninsula, East China

Abstract Iron isotope fractionation in hydrothermal systems is a useful diagnostic tool for tracing ore-forming processes. Here, we report on the Fe isotopic compositions of a suite of hydrothermal minerals from ores (pyrite, pyrrhotite, and quartz) from the Wulong gold deposit, Liaodong Peninsula, East China. Pyrites from quartz sulfide ores show a δ56Fe (56Fe/54Fe in the sample relative to IRMM-14) range from +0.11 ± 0.03‰ to +0.78 ± 0.03‰ (2SD), and pyrrhotites from the same vein are isotopically lighter than the pyrites, varying between −0.85 ± 0.01‰ and −0.07 ± 0.00‰. This result is consistent with theoretical predictions of equilibrium fractionation and published mineral compositions. For the first time, to our knowledge, we report the Fe isotopes of hydrothermal quartz that records the isotopic compositions of the ore-forming fluids. Two quartz separates in the quartz-sulfide vein yield δ56Fe values of −0.02 ± 0.02‰ and +0.07 ± 0.07‰. Our Fe isotope fractionation calculations show that pyrrhotite with light Fe isotopes crystallized first from the ore-forming fluids, which indicates a relatively reduced condition for the initial ore-forming fluids. Then the remaining fluids with heavy Fe isotopes precipitated pyrites with positive δ56Fe values, and their mineral crystallization sequence records an increase of oxygen fugacity during mineralization. Gold deposits in Wulong and Jiaodong share many similar geological characteristics. The pyrites from the Wulong deposit have higher δ34S values (+0.5 to +4.1‰) than the pyrrhotites (–1.2 to +1.2‰). Pyrites from the Jiaodong gold deposits show a wide range of both positive and negative δ56Fe values as well as high δ34S values, whereas those from the Wulong deposit have a relatively narrow range of positive δ56Fe values and near-zero δ34S values. The differences in Fe isotopes may be due to early precipitation of pyrrhotite with light Fe isotopes under a relatively low oxygen fugacity environment in the Wulong deposit, resulting in pyrite precipitated from the remaining fluids with heavy isotopes. The sulfur isotope variations between Wulong and Jiaodong gold deposits reflect differences in their source regions rather than oxygen fugacities. In addition, we have compiled Fe isotopic compositions of pyrites and pyrrhotites from different types of ore deposits to investigate their Fe isotopic behavior in magmatic-hydrothermal systems. Pyrite grains show a wide range of δ56Fe values. Positive pyrite δ 56Fe values reflect an equilibrium isotope effect, whereas negative pyrite δ56Fe values may be due to kinetic isotope effects or to a mixture of sedimentary host rocks. Pyrrhotite grains show similar negative δ56Fe values, and they have a strong influence on the Fe isotope systematics in magmatic and hydrothermal systems. Our data show that Fe isotopes can be used to trace precipitation orders of pyrite and pyrrhotite and oxygen fugacity evolution in relatively reduced hydrothermal deposits.

Large sulfur isotope fractionation in lunar volcanic glasses reveals the magmatic differentiation and degassing of the Moon.

Sulfur isotope variations in mantle-derived lavas provide important constraints on the evolution of planetary bodies. Here, we report the first in situ measurements of sulfur isotope ratios dissolved in primitive volcanic glasses and olivine-hosted melt inclusions recovered from the Moon by the Apollo 15 and 17 missions. The new data reveal large variations in 34S/32S ratios, which positively correlates with sulfur and titanium contents within and between the distinct compositional groups of volcanic glasses analyzed. Our results uncover several magmatic events that fractionated the primordial sulfur isotope composition of the Moon: the segregation of the lunar core and the crystallization of the lunar magma ocean, which led to the formation of the heterogeneous sources of the lunar magmatism, followed by magma degassing during generation, transport, and eruption of the lunar lavas. Whether the Earth's and Moon's interiors share a common 34S/32S ratio remains a matter of debate.

Phanerozoic variation in dolomite abundance linked to oceanic anoxia

Abstract The abundance of dolomitic strata in the geological record contrasts with the general rarity of locations where dolomite forms today, a discrepancy that has long posed a problem for their interpretation. Recent culture experiments show that dolomite can precipitate at room temperature, raising the possibility that many ancient dolomites may be of syngenetic origin. We compiled a large geodata set of secular variations in dolomite abundance in the Phanerozoic, coupled with compilations of genus richness of marine benthic invertebrates and sulfur-isotope variations in marine carbonates. These data show that dolomite abundance is negatively correlated to genus diversity, with four dolomite peaks occurring during mass extinctions. Dolomite peaks also correspond to the rapid increase in sulfur-isotope composition (δ34S), an indicator of enhanced sulfate reduction, in anoxic oceans. These results confirm that variations in dolomite abundance during the Phanerozoic were closely linked with changes in marine benthic diversity, with both in turn related to oceanic redox conditions.

Carbon and sulfur isotope variations through the Upper Ordovician and Lower Silurian of South China linked to volcanism

Pronounced excursions of carbon and sulfur isotopes (δ13C and δ34S) spanning the Ordovician–Silurian (O–S) transition have been recognized globally, yet the causes of these isotope events and their causal relationships to environmental changes, especially during Early Silurian time, remain the topics of debate. In this study, we present organic carbon and pyrite sulfur isotope (δ13Corg and δ34Spyr) records and elemental concentrations from a drill core spanning from the Upper Ordovician (Katian) to Lower Silurian (Aeronian) succession of the Yangtze Platform, China. The newly presented δ13Corg profile records previously recognized positive excursions, including the Hirnantian isotopic carbon excursion (HICE), the middle Rhuddanian excursion, and the early Aeronian positive carbon isotope excursion (EACIE). In addition, two negative δ13Corg excursions are recognized during the Katian to early Hirnantian and late Hirnantian to middle Rhuddanian stages. The δ34Spyr profile exhibits a great amount of variation (−17.8‰ to +19.6‰) but mimics the δ13Corg record. Coupled positive δ13Corg and δ34Spyr excursions during the middle Hirnantian and late Rhuddanian to Aeronian are associated with decreased total organic carbon (TOC) content and less reducing water column conditions, whereas the negative δ13Corg and δ34Spyr excursions during the Katian to early Hirnantian and late Hirnantian to middle Rhuddanian are associated with enhanced TOC values and the establishment of more strongly anoxic to euxinic conditions. The δ13C and δ34S excursions during the O–S transition, then, cannot be explained by changes in redox conditions or the burial of organic carbon and pyrite. The heavier and less variable middle Hirnantian and late Rhuddanian to Aeronian δ34Spyr values probably reflect low marine sulfate concentration. In contrast, negative Katian to early Hirnantian and late Hirnantian to middle Rhuddanian δ34Spyr excursions may reflect increased sulfate concentration. The two negative δ13Corg and δ34Spyr excursions associated with the Katian to early Hirnantian and late Hirnantian to middle Rhuddanian correspond with episodes of volcanism. We therefore propose that volcanism was the main driver of coupled negative δ13Corg and δ34Spyr excursions. As volcanism diminished during the middle Hirnantian and late Rhuddanian to Aeronian, both δ13Corg and δ34Spyr returned to more positive values. Our results indicate that volcanism played a crucial role in triggering carbon and sulfur isotope perturbations and environmental changes during the Late Ordovician and Early Silurian.

Sulfur isotope behavior during metamorphism and anatexis of Archean sedimentary rocks: A case study from the Ghost Lake batholith, Ontario, Canada

Recycling of surface-derived sulfur into the deep earth can impart distinct sulfur isotope signatures to magmas. The details of sulfur transfer from sedimentary rocks to magmas (and ultimately igneous rocks) through metamorphism and devolatilization and/or partial melting, however, is difficult to trace. To understand this process in detail we studied multiple-sulfur isotope compositions of sulfides in the Archean (c. 2685 Ma) Ghost Lake batholith (GLB) and its surrounding host metasedimentary rocks of the Superior Craton (Ontario, Canada) by high spatial resolution secondary ion mass spectrometry, complemented by high-precision gas source isotope ratio mass spectrometry measurements. The GLB comprises strongly peraluminous biotite+cordierite, biotite+muscovite, and muscovite+garnet+tourmaline granites to leucogranites, which are thought to represent the partial melts of surrounding metagreywackes and metapelites. The metasedimentary rocks display a range of metamorphic grades increasing from biotite-chlorite (280-380°C) at ∼5 km away from the GLB to sillimanite-K-feldspar grade (∼660°C) immediately adjacent to the batholith, thus providing a natural experiment to understand sulfur isotope variations from low- to high-grade Archean sedimentary rocks, as well as granites representative of their partial melts.We find that metasedimentary sulfide δ34S values increase with progressive metamorphism at most 2-3‰ (from −1‰ up to +1 to +2‰). An increase in δ34S values in pyrrhotite during prograde metamorphism can be explained through Rayleigh fractionation during pyrite desulfidation reactions. Pyrite from all but one of the granite samples preserve δ34S values similar to that of the high-grade metasedimentary rocks, indicating that partial melting did not result in significant fractionation of δ34S. The exception to this is one granite sample from a part of the batholith characterized by abundant metasedimentary inclusions. This sample contains pyrite with heterogeneous and low δ34S values (down to −16‰) which likely resulted from incomplete homogenization of sulfur between the granitic melt and metasedimentary inclusions. Small (several tenths of a permil), mostly positive Δ33S are observed in both the metasedimentary rocks and granites.Our results suggest that Archean strongly peraluminous granites could be a high-fidelity archive to quantify the bulk sulfur isotope composition of the Archean siliciclastic sediments. Further, our findings indicate that subduction of reduced sulfur-bearing sediments in the Archean with δ34S at or near 0‰ should result in release of sulfur-bearing fluids in the mantle wedge with similar values (within a few permil). S-MIF (if initially present in Archean surface material) may be preserved during this process. However, the absence of S-MIF in igneous rocks does not preclude assimilation of Archean sedimentary material as either S-MIF may not be originally present in the Archean sedimentary sulfur and/or homogenization or dilution could obscure any S-MIF originally present in assimilated Archean sediments.

Fluid evolution and gold precipitation in the Muping gold deposit (Jiaodong, China): Insights from in-situ trace elements and sulfur isotope of sulfides

The Early Cretaceous Muping gold deposit is hosted in the Late Jurassic monzogranite. Crosscutting relations of ore veins implied a presence of multiple fluid pulses, and the mineralization process comprises four mineralization stages. Three generations/types of pyrite (Py1, Py2, and Py3) have been discriminated. Coarse-grained and euhedral Py1 pertains to pyrite-quartz veins. Coarse-fine grained and subhedral Py2 comes from quartz-pyrite veins. Fine-grained and anhedral Py3 is from quartz-polymetallic sulfides veins. Py3 further can be divided into three sub-types (Py3a, Py3b, and Py3c), in which Py3a did not have a core-rim texture, Py3b is the core and Py3c is the rim of pyrite with core-rim texture.Py1 and Py2 contain relatively higher Co (738 and 29 ppm on median) and Ni (30 and 7.6 ppm on median), but lower As (754 and 15 ppm on median) and Au (median < 0.1 ppm) content. However, Py3 has extremely low Co and Ni (medians below detection), but elevated As (from 16,290 to 206 ppm on median) and Au (from 36 to 0.4 ppm on median) content. Co and Ni contents of pyrite gradually decreased but As content increased from Py1 to Py3, implied that the temperature of ore-forming fluids progressively decreases. Extremely higher As content and high δ34S of Py3c could be associated with an incursion of As-rich and heavy δ34S meteoric water which has flowed through meta-sedimentary rocks. Sulfur isotopes revealed a gradual decrease from Py1 (+11.6‰) to Py3b (+7.5‰). As for the pyrite with core-rim texture, the sulfur isotope progressively increased from the core (Py3b, +6.0‰) and the rim (Py3c, +11.8‰). The high δ34S could be derived from the metasomatic and fertile lithospheric mantle, and the difference between Py1 and Py2 attributed to suffering from degassing processes with different condition. Rayleigh fractionation process caused a “reservoir effect” can explain the inside variations of Py2, while the increase of fO2 caused by phase separation is the main factor leading to δ34S decrease for Py3. It is the fluid mixture that resulted in the inter-crystalline sulfur isotope variation of pyrite with core-rim texture. Gold and As contents for all types of pyrite plot well below the solubility limit for gold in arsenian pyrite, indicating that invisible gold occurs as Au1+ in the pyrite lattice. The extent of invisible gold was incorporated into pyrite depending on the arsenic content, but visible gold mineralization mainly was controlled by vapor phase escape and fO2 increase which attributed to phase separation.