δ34S Data Research Articles

A Machine-Learning Approach to Biosignature Exploration on Early Earth and Mars Using Sulfur Isotope and Trace Element Data in Pyrite.

We propose a novel approach to identify the origin of pyrite grains and distinguish biologically influenced sedimentary pyrite using combined in situ sulfur isotope (δ34S) and trace element (TE) analyses. To classify and predict the origin of individual pyrite grains, we applied multiple machine-learning algorithms to coupled δ34S and TE data from pyrite grains formed from diverse sedimentary, hydrothermal, and metasomatic processes across geologic time. Our unsupervised classification algorithm, K-means++ cluster analysis, yielded six classes based on the formation environment of the pyrite: sedimentary, low temperature hydrothermal, medium temperature, polymetallic hydrothermal, high temperature, and large euhedral. We tested three supervised models (random forest [RF], Naïve Bayes, k-nearest neighbors), and RF outperformed the others in predicting pyrite formation type, achieving a precision (area under the ROC curve) of 0.979 ± 0.005 and an overall average class accuracy of 0.878 ± 0.005. Moreover, we found that coupling TE and δ34S data significantly improved the performance of the RF model compared with using either TE or δ34S data alone. Our data provide a novel framework for exploring sedimentary rocks that have undergone multiple hydrothermal, magmatic, and metamorphic alterations. Most significant, however, is the demonstrated potential for distinguishing between biogenic and abiotic pyrite in samples from early Earth. This approach could also be applied to the search for potential biosignatures in samples returned from Mars.

Orogenic Gold Deposits of Northern Transbaikalia, Russia: Geology, Age, Sources, and Genesis

The paper presents newly obtained and summarizes preexisting data of long-term geochronological and isotope studies of orogenic mesothermal gold deposits in the world’s largest Lena metallogenic province and reviews interpretations of their genesis. Geochronologic data indicate that the gold mineralization was formed during three ore-forming Paleozoic events. The early Late Ordovician–Early Silurian (450–430 Ma) event produced the abundant veinlet—disseminated gold–sulfide mineralization in Neoproterozoic carbonaceous terrigenous–carbonate rocks of the Baikal–Patom foldbelt (BPB). The mineralization was formed simultaneously with regional metamorphic processes. The rejuvenation of hydrothermal activity in the BPB resulted in gold-bearing quartz veins, which was produced in the Middle Carboniferous (340–330 Ma) in relation to postcollisional granitoid magmatism. The latest ore-forming event occurred in the Early Permian (290–280 Ma) and affected exclusively in Precambrian structures of the Baikal-Muya foldbelt (BMB). It was synchronous with the development of intraplate alkaline and subalkaline magmatism in the region. Newly obtained and preexisting isotopic-geochemical (87Sr/86Sr, 143Nd/144Nd, Pb–Pb, and δ34S) data indicate that the mesothermal ore-forming systems of northern Transbaikalia were heterogeneous in their isotopic characteristics, which distinguishes them from the ore–magmatic (intrusion-related type) systems. Comparison of the Sr, Nd, and Pb isotopic composition of the ores and rocks, including magmatic rocks coeval with the gold mineralization, indicates that the Precambrian continental crust was the dominant source of mineral-forming components for the hydrothermal systems of the gold deposits. The contribution of the magmatic source to the genesis of the orogenic gold mineralization was limited and is identifiable only for the Early Permian ore-forming systems of the BMB, for which the input of metals from alkaline mafic melts was suggested.

Trace Element and Sulfur Isotope Signatures of Volcanogenic Massive Sulfide (VMS) Mineralization: A Case Study from the Sunnhordland Area in SW Norway

The Sunnhordland area in SW Norway hosts more than 100 known mineral occurrences, mostly of volcanogenic massive sulfide (VMS) and orogeny Au types. The VMS mineralization is hosted by plutonic, volcanic and sedimentary lithologies of the Lower Ordovician ophiolitic complexes. This study presents new trace element and δ34S data from VMS deposits hosted by gabbro and basalt of the Lykling Ophiolite Complex and organic-rich sediments of the Langevåg Group. The Alsvågen gabbro-hosted VMS mineralization exhibits a significant Cu content (1.2 to >10 wt.%), with chalcopyrite and cubanite being the main Cu-bearing minerals. The enrichment of pyrite in Co, Se, and Te and the high Se/As and Se/Tl ratios indicate elevated formation temperatures, while the high Se/S ratio indicates a contribution of magmatic volatiles. The δ34S values of the sulfide phases also support a substantial influx of magmatic sulfur. Chalcopyrite from the Alsvågen VMS mineralization shows significant enrichment in Se, Ag, Zn, Cd and In, while pyrrhotite concentrates Ni and Co. The Lindøya basalt-hosted VMS mineralization consists mainly of pyrite and pyrrhotite. Pyrite is enriched in As, Mn, Pb, Sb, V, and Tl. The δ34S values of sulfides and the Se/S ratio in pyrite suggest that sulfur was predominantly sourced from the host basalt. The Litlabø sediment-hosted VMS mineralization is also dominated by pyrite and pyrrhotite. Pyrite is enriched in As, Mn, Pb, Sb, V and Tl. The δ34S values, which range from −19.7 to −15.7 ‰ VCDT, point to the bacterial reduction of marine sulfate as the main source of sulfur. Trace element characteristics of pyrite, especially the Tl, Sb, Se, As, Co and Ni concentrations, together with their mutual ratios, provide a solid basis for distinguishing gabbro-hosted VMS mineralization from basalt- and sediment-hosted types of VMS mineralization in the study area. The distinctive trace element features of pyrite, in conjunction with its sulfur isotope signature, have been identified as a robust tool for the discrimination of gabbro-, basalt- and sediment-hosted VMS mineralization.

Mineral and S-Isotope Compositions of Cu-Sulfide Deposits in Southern Siberia (Kodar–Udokan Region), Russia

The Kodaro–Udokan region is a huge Cu metallogenic province in Southern Siberia, one of the largest on Earth. It contains world-class copper sandstone-hosted Udokan (Cu reserves of 26.7 Mt) and PGE-Ni-Cu Chineysky deposits related to gabbro–anorthosite pluton (Cu—10 Mt; Fe-Ti-V, 30 Gt of ore). Furthermore, there are many small deposits of sulfide ores in sedimentary and igneous rocks in this region as well. For many decades, their genesis has been hotly debated. We studied the mineral composition and the sulfur isotopes in several deposits located at different levels of the stratigraphic sequence and in gabbro intruded in sandstones of the Udokan complex. The differences in ore compositions were found. The Burpala and Skvoznoy deposits consisting of the chalcocite–bornite association are characterized only by negative δ34S. The δ34S values for the Udokan deposits are mostly <0 (up to −28‰). The positive δ34S data characterize the ores of the Chineysky and Luktursky intrusions. Two Cu sandstone-hosted deposits are characterized by complex ore composition, i.e., the Krasny deposit, comprising chalcopyrite–pyrrhotite ores, is enriched in Co, Ni, Bi, Sb, Mo, Pb, Zn, Se, Te, and U and has a wide range of δ34S = −8.1–+13.5‰, and the Pravoingamakitsky deposit (Basaltovy section), consisting of quartz–chalcopyrite veins, has high PGE contents in ores with δ34S = +2.9–+4.0‰. These deposits are located near the gabbro massifs, and it is supposed that their ore compositions were influenced by magmatic fluids. The general regularities of the localization of the deposits in rift zones, and the proximity of mineral and isotopic composition allow us to conclude that the main source of copper could be rocks of basic composition because only they contain high Cu contents. Fluids from deep zones could penetrate to the surface and form Cu sandstone-hosted deposits.

Carbon and sulfur cycling across the Silurian-Devonian boundary in the Qujing Basin, South China

During the late Silurian – Early Devonian there were significant changes in the biosphere and environment. However, there are few integrated studies of carbon and sulfur cycling in the Qujing Basin, in South China, which has extremely well-preserved sarcopterygian fossils. Here we report C-isotopic data of organic carbon (δ13Corg) and multiple S-isotopes of pyrite (δ34S and Δ33S) from two sections in the Qujing Basin. Our δ13Corg data show an increase of ~4‰ near the Silurian-Devonian boundary which can be correlated globally. We suggest that this rise in δ13Corg near the Silurian-Devonian boundary may have resulted from the weathering of the 13C-enriched carbonate platform, rather than from oceanic anoxia. This interpretation may explain why there is little evidence of a mass extinction near the Silurian-Devonian boundary in the Qujing Basin. Our S-isotopic data show positive δ34S values with either positive or negative Δ33S values, and most of the δ34S and Δ33S data can be explained by microbial sulfate reduction and Rayleigh distillation processes. The S-isotopic data from both sections suggest that seawater sulfate concentrations were very low in the Qujing Basin during the late Silurian – Early Devonian.

Analysis of the data in Jingwen Mao's paper on the stable isotopes (δDH2O, δ18OH2O, δ 34S) of the gold deposits in Jiaodong Peninsula, China

In 2008, Jingwen Mao published a paper on the stable isotopes of gold deposits in the Jiaodong Peninsula. The paper has a series of problems in obtaining δDH2O and δ18OH2O of ore-forming fluids and interpreting δ34S data. ① In order to obtain δDH2O and δ18OH2O data of ore-forming fluids, Jingwen Mao selected sericite (a total of 25 samples) as the target mineral. Sericite is not an independent mineral and has no fixed molecular formula. New research has shown that it is a fine-grained aggregate composed of muscovite, illite, and sodium mica (at least muscovite and sodium mica). The water content in sericite is very complicated, including structural water, interlayer water, fissure water, primary and secondary inclusion water. Jingwen Mao extracted water from sericite by crushing, and this mixed water cannot represent the ore-forming fluids. It is unreliable to determine the source of ore-forming fluids using δDH2O measured by this kind of mixed water. ② So far, no oxygen isotope fractionation coefficient relationship between sericite and water has been obtained, whether through theoretical calculation or experimental research. In order to calculate the δ18OH2O of ore-forming fluids by measuring the δ18O of sericite, Jingwen Mao used the oxygen isotope fractionation coefficient relationship between muscovite and water for calculation, which is completely wrong. ③ The data of δ18OH2O and δDH2O of ore-forming fluids obtained by Jingwen Mao using sericite are very different from the relevant data obtained by previous researchers using quartz as the target mineral (131 samples). Based on those unreliable data, Jingwen Mao believed that the ore-forming fluids came from the mixed source of crust and mantle, while the relevant data of previous researchers proved that the ore-forming fluids came from the products of atmospheric precipitation exchanging with Jiaodong Group metamorphic rocks under different temperatures and different W/R ratios. ④ For the relationship between the high or low δ 34S value of sulfide minerals and the large or small logfO2 value, Jingwen Mao's explanation is completely opposite to the research results of Ohmoto and Wang. Ohmoto believed that the two were negatively correlated, while Jingwen Mao believed that they were positively correlated. This is a common sense mistake.

Textural, trace element, and sulfur isotope analyses of pyrite from the Yindongpo deposit, East Qinling Orogen: Implications for gold mineralization

The Yindongpo deposit is a large-scale gold deposit with complicate mineralization types in East Qinling Orogen, triggering the debate on its ore genesis. Here we conduct textural, in situ trace elements and sulfur isotope analyses of pyrite to elucidate the genesis of gold mineralization in the Yindongpo deposit. Three types of pyrite were identified according to their occurrences in different hydrothermal veins. Py-Ⅰ mainly formed in the host rock, parallel to the foliation of the schist, occurring as crystal nodules with blurred boundary. Py-Ⅱ principally occur in the quartz-pyrite veins crosscutting the stratum. It is characterized by the pervasive occurrence of sulfide and silicate inclusions, which suggest phase separation (fluid boiling) took place during its formation. Py-Ⅲ commonly precipitate within quartz-dolomite-pyrite veins crosscutting or overprinting former quartz-pyrite veins, commonly associated with coarse-grained sulfides and native gold/electrum. All pyrite types exhibit a superimposed history. The Co, Ni, As characteristics and δ34S data show that from Py-Ⅰ, through Py-Ⅱ, to Py-Ⅲ, the portion of magmatic-hydrothermal fluid is increasing. Gold is tightly associated with base metal sulfides (galena, sphalerite, chalcopyrite), filling the voids, cracks, or margins of Py-Ⅰ, Py-Ⅱ, and Py-Ⅲ. The trace element bounded in the lattice of base metal sulfides include: (1) Cd for sphalerite, (2) Ag, Sb for galena, (3) Ag for tetrahedrite. Combined with previous studies, we conclude that the magmatic-hydrothermal activities at Early Cretaceous formed the major gold mineralization in the Yindongpo deposit.

Spatially heterogenous seawater δ34S and global cessation of Ca-sulfate burial during the Toarcian oceanic anoxic event

The early Toarcian of the Early Jurassic saw a long-term positive carbon-isotope excursion (CIE) abruptly interrupted by a significant negative excursion (nCIE), associated with rapid global warming and an oceanic anoxic event (T-OAE, ∼183 Ma). However, the detailed processes and mechanisms behind widespread ocean deoxygenation are unclear. Here, we present high-resolution carbonate-associated sulfate sulfur-isotope (δ34SCAS) records spanning the late Pliensbachian–Toarcian (Pl–To) interval from the Tibetan Himalaya. We observe a large positive sulfur-isotope excursion (SIE) from ∼20‰ (around the Pl–To boundary) to ∼40‰ (around the end of the T-OAE nCIE), attributed to large-scale burial of reduced sulfur (pyrite and sulfurized organic matter) under widespread anoxic/euxinic conditions. Importantly, high δ34SCAS values were maintained into the mid–late Toarcian, even when global anoxic conditions diminished. The δ34S data confirm significant spatial heterogeneity in seawater δ34S compositions during the whole of the Toarcian, and provide strong evidence for a two-phase pattern of ocean deoxygenation. Upwelling of 34S-enriched equatorial deep water, affected by significant reduced-sulfur burial, likely caused the greatly amplified SIE in the formerly adjacent Tibetan area. By contrast, the dampened magnitude of the Toarcian SIE in Europe is attributed to a smaller, local reduced-sulfur sink. Box-modeling results indicate that the persistent post-T-OAE positive δ34S values were likely maintained because of a global reduction in Ca-sulfate (gypsum and anhydrite) burial driven by declining and continuously low seawater sulfate concentrations during and after the T-OAE. This geochemical pattern, albeit markedly reducing the total amount of global pyrite sequestration, increased the proportion of reduced to oxidized sulfur burial needed to generate the observed positive δ34S values.

Peri‐urban systems alter trophic niche size and overlap in sympatric coastal bird species

AbstractUrban habitats can create empty trophic niche space by providing abundant alternative dietary resources, allowing some generalist species to either shift or expand their trophic niches. Resulting changes to trophic niche size may consequently affect interspecific interactions and competition, although trophic impacts are less clear in peri‐urban systems, where both natural and urban resources are readily accessible to highly mobile species. We combined stable isotope (δ13C, δ15N, δ34S) data with GPS tracking of two sympatric coastal bird species (Larus argentatus, L. marinus) across four study sites on the east coast of the United States, ranging from a study site in New York City (the most populous city in the United States) to less‐urban sites off Massachusetts. We quantified the trophic niche size and trophic niche overlap in three‐dimensional isotopic space and assessed spatial overlap in foraging habitat between species at both peri‐urban and less‐urban study sites. We found that for both species, birds at peri‐urban study sites had significantly larger trophic niches than birds from the less‐urban sites. Furthermore, for study sites where both species occurred, we found that overlap in trophic niche space and foraging habitats between species was lower at the peri‐urban study site than at the less‐urban site. These results suggest that peri‐urban environments may facilitate trophic niche expansion and decrease niche overlap in mobile generalist species, contrasting with previous studies showing increased trophic niche overlap in more isolated urban populations. Following further analysis, we found that trophic niche expansion was facilitated by both within‐ and between‐individual differences in foraging strategies. We posit that peri‐urban environments, particularly along coastal areas, can reduce interspecific competition between sympatric species by providing access to a variety of natural and anthropogenic diet items, especially for highly mobile generalist consumers that can access both natural and urban foraging areas. Research assessing how and at what scale peri‐urban systems influence wildlife is key to understanding how further global urbanization will shape ecosystem structures.

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.

Mitogenomic diversity and stable isotopes provide insights into the maternal genetic history, mobility patterns, and diet of early medieval individuals from the Eastern Italian Alps

The Eastern Italian Alps (South Tyrol) is a connection area between continental Italy and the northern Alps. Various local factors, such as the heterogeneous environment, complex historical events, and different mobility patterns, may have influenced the genetic makeup of early medieval alpine groups. However, no ancient genetic data from these groups are currently available. This study provides a first picture of the ancient mitochondrial DNA (mtDNA) diversity of alpine groups from four locations in South Tyrol (Adige, Isarco, Venosta, and Merano). In total, 94 ancient mitogenomes of individuals (dated from 400 to 1100AD) were reconstructed by shotgun sequencing and a mtDNA capture approach. Moreover, stable isotope ratios (δ13C, δ15N, δ34S) were analyzed in a subset of 32 individuals. The results indicate different mtDNA haplogroup distributions among the alpine locations and the presence of rare lineages besides a possible maternal relatedness between individuals buried in the same and in diverse archaeological contexts. The study also shows differences in the genetic and mobility patterns (δ34S) between individuals from the central and north-eastern parts (Adige, Merano, Isarco) and those from the north-western part of South Tyrol (Venosta). These results suggest genetic exchanges with allochthonous people in the first group probably linked to high mobility and to geomorphological, historical, and socio-cultural factors. Comparisons extended to present-day alpine populations also suggested maternal genetic continuity in this alpine area. Finally, stable isotope (δ13C, δ15N, δ34S) data provided further support for regional differences in the diet of past alpine groups possibly linked to altitude and/or social status.

A massive magmatic degassing event drove the Late Smithian Thermal Maximum and Smithian–Spathian boundary mass extinction

The role of volcanism as a driver of climate change remains widely debated. Following the end-Permian mass extinction, the protracted Early Triassic recovery interval was characterized by extreme climatic and environmental perturbations (hyperwarming, intense subaerial weathering, and extensive marine euxinia) and large carbon- and sulfur-cycle perturbations. Although a magmatic trigger is widely accepted, details regarding the timing and magnitude of degassing and its relationship to contemporaneous climate changes remain poorly understood. In this study, we present new paired carbonate δ13C and carbonate-associated-sulfate δ34S data from deep-water settings in the Lower Triassic of South China to evaluate these issues. Our dataset reveals large positive shifts of both proxies across the Smithian/Spathian boundary (SSB), recording globally synchronous changes in the C and S cycles linked to co-burial of large quantities of organic matter and pyrite. Biogeochemical modeling of the C-S cycles shows that massive carbon release linked to increased magmatic degassing can account for observations of concurrent positive shifts of δ34S and δ13C, enhanced weathering, expanded marine euxinia, and the Late Smithian Thermal Maximum (LSTM). Measured increases in δ13C (+3.2 ± 1.6‰) and δ34S (+7.3 ± 2.3‰) across the SSB relative to their baseline values are consistent with a major magmatic degassing event during the Early to Middle Smithian, whose magnitude and rate we estimate at ~78,000 ± 13,000 Gt C and 0.26 Gt C yr−1, respectively. Our results provide evidence that Early–Middle Smithian degassing was the primary trigger of the LSTM and concurrent biotic crisis.

Isotopic signature of anthropogenic sources of groundwater contamination with sulfate and its application to groundwater in a heavily urbanized and industrialized area (Upper Silesia, Poland)

Isotopic signatures of anthropogenic sulfate sources within the Upper Silesian urban area (southern Poland) were investigated to increase the reliability of the origin assessment of groundwater contaminants. To analyze δ34S and δ18O in sulfate, 64 samples were collected, representing several sulfate sources: synthetic and organic fertilizers, raw and treated wastewater, mine water, leachate from landfills, mine heaps, and industrial waste dumps. Additionally, 10 surface water samples were taken from contaminated rivers regarded as potential groundwater pollution sources. Results of δ34S and δ18O in sulfate derived from anthropogenic sources were compared with literature data, which indicated significant discrepancies for some contamination sources. The results were applied to assess SO42- origin in groundwater samples from the Gliwice aquifer. Apart from the δ34S and δ18O data, the study included measurements of major ions, inorganic nitrogen forms, trichloroethene and tetrachloroethene in groundwater. Isotopic analyses of river water samples confirmed the impact of urbanized and industrialized areas on surface water pollution and possible influence on groundwater contamination. The values of δ34S and δ18O similar to wastewater were reported for most groundwater samples from the Gliwice carbonate aquifer. Groundwater contamination was also manifested by higher values of electrical conductivity and concentrations of chloride, sodium, trichloroethene and tetrachloroethene. The comparison of recent isotopic data on SO42- sources with literature values clearly shows that it is very important to investigate local potential contamination sources to increase their reliability in determining the source of groundwater or river water pollution.

Genesis of the Gaolong gold deposit in Northwest Guangxi Province, South China: Insights from in situ trace elements and sulfur isotopes of pyrite

The Guangxi-Yunnan-Guizhou district, also named Dian-Qian-Gui “Golden Triangle”, in Southwest China has a large amount of Carlin-type Au deposits. Gaolong is one source of Carlin-type Au deposit in the northwestern Guangxi Province. Pyrites are the major Au-bearing sulfides. Majority of Au are structurally bound Au+, with a few nanoparticles (Au0) occurring in the sulfides. In this study, in situ chemical and S isotopes of pyrites in the Gaolong Au deposit were analyzed by laser ablation inductively-coupled plasma mass spectrometry and laser ablation multi-collector inductively-coupled plasma mass spectrometry, respectively. Backscattered electron (BSE) images and chemical composition analysis showed that the pyrites were divided into four main types: (1) As-poor Py1 (pre-ore sedimentary or diagenetic stage, with prominent spotted and aggregate structures. These are fine-grained pyrite aggregates with rough surfaces and low brightness under the BSE, with edges often eroded by hydrothermal fluid); (2) As-weak Py2 (early ore stage, the core of the rim pyrite, with good crystallization and characteristic corrosion spots in the particle, and with the edge dissolved to show irregular structure); (3) As-rich Py3 (main ore stage, the narrow pyrite rims overgrowing Py1 and Py2, irregularly-shaped and less than 50 μm in width); and (4) As-rich Py4 (fine-grained pyrite, with good crystallization, high brightness, and symbiotic with Py3 and Py1, or an isolated distribution). Py1 contains higher concentrations of S, Fe, and W, and lower Co/Ni ratios (average of 0.91), suggesting a pre-ore origin. The ore-stage pyrites Py2, Py3, and Py4, have elevated mineralization elements—Au of 0.25–72 ppm, As of 2214–40613 ppm, Tl of 0.95–109 ppm, Sb of 31.16–1851 ppm, Cu of 49.09–910 ppm, with average Co/Ni ratios of 0.43. Au was positively correlated with As, Tl, Cu, and Ni in these pyrites. Electron micro probe analyzer (EMPA) elemental mappings show that: 1) Py1 has a low Au content, while Py2, Py3, and Py4 have high Au, As, Cu, Ti, and Mg contents; 2) Au occurs in As-rich pyrite in the form of invisible gold; 3) Rim pyrite contains high concentrations of Cu, which has a good positive correlation with As, while As and Au are decoupled on a smaller scale. The Au contents and Au/As ratios show that the Au-carrying fluids are unsaturated with Au. In situ S isotopes show that the δ34S values range from 10.19‰ to 13.79‰ with a mean value of 12.07‰ for Py1, 8.60‰ to 10.78‰ with a mean value of 9.77‰ for Py2, 1.42‰ to 8.29‰ with a mean value of 6.81‰ for Py3, and − 0.49‰ to 4.42‰ with a mean value of 1.67‰ for Py4. The δ34S data decreased from Py1 to Py4, whereas the As content increased significantly. This indicates that Au and As are enriched in ore-forming fluids, and the ore-forming fluids have low S isotope values. Based on a comprehensive study of geological and geochemical data, we believe that the magmatic hydrothermal genetic model can explain the genesis of the Gaolong gold deposit. We conclude that the S isotope of pyrites resulted from the mixing of magmatic S and sedimentary S, and the Au-bearing fluid came from deep-concealed granite, establishing a magma genesis of the Gaolong Au deposit.

Mineralogical and Geochemical Characteristics of Lead-zinc Ore Deposits, and Potential Accompanying Components in the Cho Don - Cho Dien Area, Bac Kan Province, Vietnam

The Pb-Zn mineralization in the Cho Don - Cho Dien ore districts often occurs in 2 types: (1)oxidized ore near to the surface and (2) sulfide ore at deeper section. Based on microscopic observations,sulfide ores can be divided into sphalerite-galena-pyrite and/or galena-sphalerite mineralization types. Toexamine the geochemical features of the Pb-Zn ores, SEM-EDX and ICP-MS analytical methods wereperformed in this study. Previous δ34S data of Pb-Zn concentrates, and sulfide minerals from variousdeposits suggest that the Pb-Zn ore-forming fluids might be related to the felsic-granitic magmaticactivities rather than a genesis of stratiform type. Geochemical data show that the major, minor, and traceelement compositions of lead-zinc ores have wide ranges of variation even in each deposit. The sulfideores are generally higher in economic components than those in the oxidized ores. The positivecorrelations between Pb-Ag can be found in the entire dataset, whereas excellent Zn-Cd correlation canonly be observed from Cho Don ore samples. Apart from the principal components (Pb and Zn), the oresalso contain other accompanying elements that supply high-technological manufacturing industries. Ofwhich As, Cu, Ag, Sb, and Cd could be potential by-products and can be extracted during smelting Pb/Znconcentrate processes, and need more detailed studies for every deposit.

Anhydrite replacement reaction in nodular pyrite breccia and its geochemical controls on the δ34S signature of pyrite in the TAG hydrothermal mound, 26° N Mid Atlantic Ridge

The Trans-Atlantic Geotraverse (TAG) active mound is a seafloor hydrothermal deposit that has been sampled by drilling to the base of its alteration zone, providing a rare opportunity for in situ investigation of the effects of water-rock interactions. The δ34S signature of sulfide minerals in seafloor hydrothermal settings is commonly explained by invoking isotopic mixing and fractionation based endmember models. Here, we present textural evidence of the replacement reactions that underlie the fractionation model endmember, found in core samples recovered from the TAG active mound during ODP expedition 158. The samples were obtained at the TAG-1 area, at the transition between shallower pyrite-silica (± anhydrite) breccias and deeper pyrite-silica breccias. The shallower breccias show porous domains associated with anhydrite, quartz and pyrite. Similar textures were also observed in the deeper samples, in which anhydrite is absent. Our results suggest that at stockwork depths, anhydrite is removed during its interaction with hydrothermal fluids, leaving behind pores lined by quartz crystals and partially filled by pyrite. The textural evolution suggests that pyrite grows at the expense of anhydrite, leading to δ34S values in pyrite controlled by the isotopic fractionation factor between SO42− and H2S. Our petrographic observations are supported by geochemical modelling at in situ temperatures, estimated from analysis of fluid inclusions in quartz. Our interpretation is in agreement with previously published δ34S data from the TAG active mound. Both the highest δ34S signatures in disseminated pyrite and the lowest δ34S signatures in vein-related mineralization, as well as the progressive 34S-enrichment with depth recorded by the isotopic stratification at the TAG active mound can be explained based on the temperature at which water-rock interactions occurred. This research provides direct evidence of the mineral replacement processes occurring within the active TAG sulfide mound and their link to established models of isotopic fractionation. The textural evidence for these processes is characterized in detail and can aid the interpretation of the evolution of other seafloor hydrothermal deposits.

Erratum to: Crustal Source of Pb and S at the Yubileynoe Porphyry Gold Deposit (Southern Urals, Kazakhstan): High Precision Pb–Pb and δ34S Data

The Yubileinoe large gold deposit, located at the southern end of the Magnitogorsk megazone, is the only known representative of the Au–porphyry systems in the Southern Urals. It is genetically related to granitoids formed in a suprasubduction setting under mature oceanic island arc environment/setting. The obtained isotope (Pb–Pb and δ34S) data indicate the input of mineral-forming components into the Au–porphyry system of the deposit, mainly from granitoid melts, confirming a common source of ore material and ore-bearing granitoids. The geochemical and isotopic characteristics of granitoids indicate the leading role in their genesis of the crustal source, which is considered Late Precambrian continental crust.

The role of porphyry-related skarns in the Chating porphyry copper and gold deposit, eastern China

The Chating deposit is a porphyry copper deposit in the Middle Lower Yangtze River Valley Metallogenic Belt, with skarns found in both the carbonate wall rock and in carbonate xenoliths in the intrusions. Detailed drill hole logging identified endoskarn and exoskarn in Chating, mainly distributed inside the ore–bearing quartz diorite porphyry instead of at the contact with the country rock. The skarns at Chating are unmineralized unless overprinted by porphyry related copper mineralization. Garnet in the Chating skarns can be divided into several types based on their occurrence and whether they were overprinted by porphyry mineralization. The garnets from the ore–bearing (G1a), barren endoskarn (G1b) and proximal ore–bearing exoskarn (G2a) are LREE-enriched, HREE–depleted with positive Eu anomalies whereas garnets from the barren massive exoskarn (G2b) are LREE-enriched with flat HREE and negative Eu anomalies. The G3 garnets are from marbleized skarn distal to the ore-bearing quartz diorite porphyry and consist of Al-rich and Fe-rich andradite; the Al–rich G3 garnets are LREE-depleted and HREE-enriched whereas the Fe-rich G3 garnets are LREE-enriched and HREE-depleted, both have negative Eu anomalies. The physicochemical conditions and composition of skarn-forming fluids controlled the REE, Eu, U and Y distribution in the garnets. The similarities of the REE patterns to those of magmatic–derived fluids suggests a dominantly magmatic fluid formed the endoskarn and proximal exoskarn. Fluid–rock interaction and addition of external fluids diluted the fluid that formed the exoskarn, decreasing the Cl and metal contents, resulting in lower REE contents and negative Eu anomalies in G2b and G3 garnets. The δ34S data for anhydrite from potassic alteration, sericite alteration, endoskarn and exoskarn range from 3.51‰ to 10.92‰, consistent with a dominantly magmatic fluid source. The δ34S for the anhydrite from the skarns ranges from 3.51‰ to 8.74‰, which combined with the absence of coeval sulfides, suggests a very high oxygen fugacity for the skarn-forming fluids. The small-scale skarns in Chating contain more anhydrite than garnet and consequently did not act as ground preparation as they do in typical skarn deposits. We propose that the anhydrite-rich exoskarn and the small scale of the endoskarn, combined with the high oxygen fugacity and low Cl content in the skarn-forming fluids resulted in the barren skarns of the Chating deposit.

Sedimentology and isotope geochemistry of transitional evaporitic environments within arid continental settings: From erg to saline lakes

AbstractArid continental basins typically contain a spectrum of coeval environments that coexist and interact from proximal to distal. Within the distal portion, aeolian ergs often border playa, or perennial, desert lakes, fed by fluvial incursions or elevated groundwaters. Evaporites are common features in these dryland, siliciclastic dominant settings. However, sedimentary controls upon evaporite deposition are not widely understood, especially within transitional zones between coeval clastic environments that are dominantly controlled by larger scale allocyclic processes, such as climate. The sulphur (δ34S) and oxygen (δ18O, Δ17O) isotope systematics of evaporites can reveal cryptic aspects of sedimentary cycling and sulphate sources in dryland settings. However, due to the lack of sedimentological understanding of evaporitic systems, isotopic data can be easily misinterpreted. This work presents detailed sedimentological and petrographic observations, coupled with δ34S, δ18O and Δ17O data, for the early Permian Cedar Mesa Sandstone Formation (western USA). Depositional models for mixed evaporitic/clastic sedimentation, which occurs either in erg‐marginal or lacustrine‐marginal settings, are presented to detail the sedimentary interactions present in terms of climate variations that control them. Sedimentological and petrographical analysis of the evaporites within the Cedar Mesa Sandstone Formation reveal a continental depositional environment and two end member depositional models have been developed: erg‐margin and lake‐margin. The δ34S values of gypsum deposits within the Cedar Mesa Sandstone Formation are consistent with late Carboniferous to early Permian marine settings. However, a marine interpretation is inconsistent with sedimentological and petrographic evidence. Consequently, δ34S, δ18O and Δ17O values are probably recycled and do not reflect ocean‐atmosphere values at the time of evaporite precipitation. They are most likely derived from the weathering of older marine evaporites in the hinterland. Thus, the results demonstrate the need for a combination of both sedimentological and geochemical analysis of evaporitic systems to better understand their depositional setting and conditions.

Stable C, O, and S Isotope Record of Magmatic-Hydrothermal Interactions Between the Falémé Fe Skarn and the Loulo Au Systems in Western Mali

Abstract The Gara, Yalea, and Gounkoto Au deposits of the >17 Moz Loulo mining district, largely hosted by the Kofi series metasediments, are located several kilometers to the east of the 650-Mt Fe skarn deposits in the adjacent Falémé batholith. The Au deposits are interpreted to have formed through phase separation of an aqueous-carbonic fluid, which locally mixed with a hypersaline brine of metaevaporite origin. Recognition of an intrusive relationship between the Falémé batholith and Kofi series opens the possibility that the Fe skarns and Au deposits are part of the same mineral system. In this paper, we combine new δ13C, δ18O, and δ34S data from the Karakaene Ndi skarn, Au occurrences along the western margin of the Kofi series, and zircons within plutonic rocks of the Falémé batholith. We combine these with existing data from the Loulo Au deposits to model the contribution of magmatic volatiles to Au mineralization. C and O isotope compositions of auriferous carbonate-quartz-sulfide veins from the Loulo Au deposits have wide ranges (δ13C: –21.7 to –4.5‰ and δ18O: 11.8 to 23.2‰), whereas values from carbonate veins in Kofi series Au prospects close to the Falémé batholith and the Karakaene Ndi Fe skarn deposit have more restricted ranges (δ13C: –16.8 to –3.7‰, δ18O: 11.4 to 17.2‰, and δ13C: –3.0 ± 1‰, δ18O: 12.6 ± 1‰, respectively). Kofi series dolostones have generally higher isotopic values (δ13C: –3.1 to 1.3‰ and δ18O: 19.1 to 23.3‰). Pyrite from Kofi series Au prospects adjacent to the Falémé batholith have a wide range of δ34S values (–4.6 to 14.2‰), similar to pyrite from the Karakaene Ndi skarn (2.8 to 11.9‰), whereas δ34S values of pyrite and arsenopyrite from the Loulo deposits are consistently >6‰. Comparison of the C and O isotope data with water-rock reaction models indicates the Loulo Au deposits formed primarily through unmixing of an aqueous carbonic fluid derived from the devolatilization of sedimentary rocks with an organic carbon component. Isotopic data are permissive of the hypersaline brine that enhanced this phase separation including components derived from both Kofi series evaporite horizons interlayered with the dolostones and a magmatic-hydrothermal brine. This magmatic-hydrothermal component is particularly apparent in O, C, and S isotope data from the Gara deposit and Au prospects immediately adjacent to the Falémé batholith.