Sulfur Isotope Geochemistry Research Articles

Sulfur Isotope Geochemistry of Sn–Polymetallic Depositsin Dafulou District of Guangxi Province, China

The Dachang tin-polymetallic ore deposit is one of the largest Sn ore deposit in the world. For a long time, the Danchi mineralization belt was studied from different perspective, i.e., the mineralization age, the ore source, the deposit model, etc. In fact, the contradistinction of the three mineralization belts has an important macroscopic significance for deepen the genetic mechanism of the Danchi mineralization belt. In the Changpo ore deposit of the west mineralization belt, besides three δ34S values (+4.794, +2.31, +2.6), the δ34S values belong to negative value, yet in the Lamo ore deposit of the middle mineralization belt, most of the δ34S values show positive besides two sulfur isotope sample (δ34S=－0.36, －1.6). But in the Dafulou ore deposit of the east mineralization belt, the δ34S values range from negative value to positive value. So there are only same ore resource partly for the Lamo ore deposit and the Changpo ore deposit. Overall, the ore source of the Dafulou ore deposit is more extensive than other ore deposit, and shares the same ore source with the other ore deposit.

Sulfur Isotope Geochemistry of Sn–Polymetallic Depositsin Dafulou District of Guangxi Province, China

The Dachang tin-polymetallic ore deposit is one of the largest Sn ore deposit in the world. For a long time, the Danchi mineralization belt was studied from different perspective, i.e., the mineralization age, the ore source, the deposit model, etc. In fact, the contradistinction of the three mineralization belts has an important macroscopic significance for deepen the genetic mechanism of the Danchi mineralization belt. In the Changpo ore deposit of the west mineralization belt, besides three δ34S values (+4.794, +2.31, +2.6), the δ34S values belong to negative value, yet in the Lamo ore deposit of the middle mineralization belt, most of the δ34S values show positive besides two sulfur isotope sample (δ34S=－0.36, －1.6). But in the Dafulou ore deposit of the east mineralization belt, the δ34S values range from negative value to positive value. So there are only same ore resource partly for the Lamo ore deposit and the Changpo ore deposit. Overall, the ore source of the Dafulou ore deposit is more extensive than other ore deposit, and shares the same ore source with the other ore deposit.

Sulfur Isotopes in Magmatic-Hydrothermal Systems, Melts, and Magmas

The first studies on sulfur isotope geochemistry were performed approximately sixty years ago (e.g., Thode et al. 1949; Trofimov 1949). Since these early measurements on terrestrial and extra-terrestrial materials, S isotopes have been used to highlight and investigate several processes, such as the evolution of the solar system; the oxidation of the Earth’s atmosphere and hydrosphere; the genesis of ore deposits and fossil fuels (coal, oil, and gases); the origin and provenance of S species in different natural fluids, including groundwater, rainwater, as well as present-day and ancient marine waters (as recorded by evaporite deposits); the S isotope fractionation in bacterially-mediated processes; the impact of anthropogenic activities, for instance mining and related acid drainage; and others. The sulfur isotopic compositions of volcanic rocks, magmatic gases, and closely related hydrothermal fluids were the subject of numerous investigations. Among these, a considerable contribution was provided by Sakai and coworkers, who elucidated the importance of degassing and sulfide separation and the different effects of these processes, depending on the redox state of the melt and, in the case of degassing, of the separated magmatic gases as well. All of these applications were made possible due to the experimental and theoretical works devoted to the determination of the fractionation factors between different S-bearing species and compounds and their temperature dependence. This review is devoted to the magmatic-hydrothermal environment as a whole, focusing on active systems and their past analogues, which are represented by different types of ore deposits. Special emphasis is given to the use of S isotopes to investigate the effects of degassing and separation of sulfide and sulfate minerals from silicate melts. For the sake of clarity, we recall the meaning of the following terms:

The petrogenesis of Sarıçimen (Çaldıran-Van) quartz monzodiorite: Implication for initiation of magmatism (Late Medial Miocene) in the east Anatolian collision zone, Turkey

The Sarıçimen porphyry is exposed as a sub-volcanic pluton within the Upper Cretaceous ophiolitic rocks in East Anatolian Accretionary Complex. The pluton is quartz monzodioritic in composition consisting of feldspar, hornblende, and biotite phenocrysts set in a fine-grained matrix. Major element geochemistry indicates the pluton is of high-K, calc-alkaline, metaluminous character, with a low (0.81–0.90) Aluminum Saturation Index (ASI). Trace element and sulfur isotope geochemistry suggests that the Sarıçimen porphyry was mantle-derived and contaminated by crustal materials during ascent. Tectonically, this and related volcanic and plutonic rocks in eastern Turkey and Iran are subduction-related and comprise the earliest documented neotectonic igneous activity associated with the final closure of the neo-Tethys between the Arabian and Eurasia plates at ~ 14–13 Ma.

Helium, lead and sulfur isotope geochemistry of the Gejiu Sn-polymetallic ore deposit and the sources of ore-forming materials

Studies on the helium, lead and sulfur isotopic composition were performed of the Gejiu super-large Sn-polymetallic ore deposit. The results indicated that the ore-forming materials came from different sources and the deposit is a product of superimposed mineralization. The deposit is characterized by multi-source and multi-period mineralization, which experienced submarine hydrothermal deposition and Late Yanshanian magmatic hydrothermal mineralization. It is held that the Gejiu super-large Sn-polymetallic ore deposit is a multi-genesis deposit.

Sulfur and carbon isotope geochemistry of coal and derived coal-combustion by-products: An example from an Eastern Kentucky mine and power plant

The isotopic compositions of S ( δ 34S) and C ( δ 13C) were determined for the coal utilized by a power plant and for the fly ash produced as a by-product of the coal combustion in a 220-MW utility boiler. The coal samples analyzed represent different lithologies within a single mine, the coal supplied to the power plant, the pulverized feed coal, and the coal rejected by the pulverizer. The ash was collected at various stages of the ash-collection system in the plant. There is a notable enrichment in 34S from the base to the top of the coal seam in the mine, with much of the variation due to an upwards enrichment in the δ 34S values of the pyrite. Variations in δ 34S and in the amount of pyritic S in the coal delivered to the plant show that there was a change of source of coal supplied to the plant, between week one and week two of monitoring, supporting a previous study based on metal and sulfide geochemistry for the same plant. The fly ash has a more enriched δ 34S than the pulverized coal and, in general, the δ 34S is more enriched in fly ashes collected at cooler points in the ash-collection system. This pattern of δ 34S suggests an increased isotopic fractionation due to temperature, with the fly ash becoming progressively depleted in 34S and the flue gas S-containing components becoming progressively enriched in 34S with increasing temperatures. Substantially less variation is seen in the C isotopes compared to S isotopes. There is little vertical variation in δ 13C in the coal bed, with δ 13C becoming slightly heavier towards the top of the coal seam. An 83–93% loss of solid phase C occurs during coal combustion in the transition from coal to ash owing to loss of CO 2. Despite the significant difference in total C content only a small enrichment of 0.44–0.67‰ in 13C in the ash relative to the coal is observed, demonstrating that redistribution of C isotopes in the boiler and convective passes prior to the arrival of the fly ash in the ash-collections system is minor.

Oxygen and sulfur isotope geochemistry revealing a significant crustal signature in the genesis of the post-collisional granitoids in central Anatolia, Turkey

Late Cretaceous granitoid rocks from central Anatolia comprise S-I-A-type plutons derived from the collisional stages of the Neo-Tethyan convergence system in central Turkey. These granitoids intrude the tectonic imbrication zone consisting of blocks of supra-subduction zone-type (SSZ-type) central Anatolian ophiolite and crustal metasediments which are present in the İzmir-Ankara-Erzincan suture zone. The plutons are overlain by Late Palaeocene-Early Eocene or younger detrital sediments. Granitoid formation is thought to be related to magma generation processes occurring in a post-collisional lithospheric detachment-related geodynamic setting that resulted from slab break-off or lithospheric delamination. Whole-rock S and quartz/feldspar O isotope data from these plutons yields a broad range of values, and both parameters indicate a nearly exclusively supracrustal origin for the S-type granites, as well as a significant crustal contribution in the genesis of the hybrid I-type and A-type granitoids. The more mafic I-type and A-type granitoid rocks of any given suite have lower S and O values, indicative of their larger degree of mantle component. The combined stable isotope geochemical compositions, when coupled with major, trace and REE geochemistry and regional geology, provide evidence that the significant crustal contribution originated from a metasomatized mantle layer which was affected by earlier SSZ-derived fluids, and then accreted into the subcontinental lithosphere as collision occurred. The partial melting of such a metasomatized mantle layer in a post-collisional extensional geodynamic setting, supplied either by the slab break-off or lithospheric delamination mechanisms, provided the significant crustal signature in the hybrid magmas of the Late Cretaceous I-type and A-type granitoids in central Anatolia, Turkey.

Isotope geochemistry of the Huize Zn-Pb ore field, Yunnan Province, Southwestern China: Implication for the sources of ore fluid and metals

The Huize ore field, which is the most famous high-grade Zn-Pb ore field in China, comprises the Kuangshanchang and Qilinchang deposits. The Zn and Pb reserves of these two deposits are more than 5 Mt with ore grades ranging from 25% to 35% in weight. Lead, sulfur, carbon, oxygen, hydrogen and strontium isotope geochemistry is reported to help understand the sources of the ore fluid and metals. The 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb values of the ores range from 18.251–18.530, 15.663–15.855 and 38.487–39.433, respectively. These values are similar to those of the wall rocks. The pyrites disseminated in the wall rocks have indistinguishable Pb isotope composition with the ores. These data indicate that the wall rocks provided metals to the ore fluid. Most δ34S values of the ores range from 13 to 17 per mil. The sulfur of the ores originated by in situ reduction of sulfate. Three kinds of gangue calcite from the ores have similar isotope compositions, which have δ13C values in the range of −2.1 to −3.5 per mil with respect to PDB and δ18O values in the range of 16.8 to 18.6 per mil with respect to SMOW. The δDFI values of fluid inclusions in the three kinds of gangue calcites have a narrow range of −50 to −60 per mil and the δ18OH2O values calculated from δ18O values of calcite range from 7.0 to 8.8 per mil at 200°C. These data suggest that the ore fluid was a basinal brine that passed through shale, clastic rocks and mudstone underlying the host rock. Initial 87Sr/86Sr values of the pyrite, sphalerite and calcite from the ores range from 0.714 to 0.717. The initial 87Sr/86Sr values of unaltered host rock (0.7083–0.7093) are lower than that of the altered host rock (0.7106). It suggests that the ore fluids have higher initial 87Sr/86Sr values than the wall rocks. These high initial 87Sr/86Sr values may be due to the reaction between the ore fluid and the shale, clastic rocks and mudstone underlying the host rock or the fluid might have originated from these rocks.

Sulfur Isotope Geochemistry of the Supergiant Xikuangshan Sb Deposit, Central Hunan, China: Constraints on Sources of Ore Constituents

. The supergiant Xikuangshan Sb deposit is located in the Middle to Upper Devonian limestone of central Hunan, China. Primary ores are composed of early-stage stibnite and calcite with rare pyrite, early main-stage stibnite and quartz, and late main-stage stibnite and calcite. New sulfur isotope data reveal the clustering of δ34S values (+5 ∼ +8 %) for both early and late main-stage stibnite; a single early-stage stibnite exhibits δ34S value (+7.5 %) identical to its main ore-stage counterparts and the coexisting calcite has almost unmodified carbon isotope composition (-4.4 %). The data suggest a probable common source of sulfur for stibnite that was deposited at different paragenetic stages. A much wider variation in δ34S values for early main-stage stibnite (+3.5 to +16.3 %, av. +7.5 %) compared to that for late main-stage stibnite (+5.3 to +8.1 %, av. +6.2 %) can be interpreted to be due to local interaction of earlier ore fluid with Devonian host rocks. The previous studies show that the Precambrian basement contains elevated Sb concentrations, and two distinctive sulfur reservoirs with δ34Spyrite values at ca. +11 ∼ +24 % and -7.0 ∼-11 %. The homogenizing effect for sulfur hydrothermally leached from the two reservoirs might have provided ore constituents for the Xikuangshan fluids.

Sulfur Isotope Geochemistry of Sulfide Minerals

Research Article| January 01, 2006 Sulfur Isotope Geochemistry of Sulfide Minerals Robert R. Seal, II Robert R. Seal, II U.S. Geological Survey 954 National Center Reston, Virginia, 20192, U.S.A., e-mail: rseal@usgs.gov Search for other works by this author on: GSW Google Scholar Reviews in Mineralogy and Geochemistry (2006) 61 (1): 633–677. https://doi.org/10.2138/rmg.2006.61.12 Article history first online: 13 Jul 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Robert R. Seal; Sulfur Isotope Geochemistry of Sulfide Minerals. Reviews in Mineralogy and Geochemistry 2006;; 61 (1): 633–677. doi: https://doi.org/10.2138/rmg.2006.61.12 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyReviews in Mineralogy and Geochemistry Search Advanced Search Sulfur, the 10th most abundant element in the universe and the 14th most abundant element in the Earth’s crust, is the defining element of sulfide minerals and provides insights into the origins of these minerals through its stable isotopes. The insights come from variations in the isotopic composition of sulfide minerals and related compounds such as sulfate minerals or aqueous sulfur species, caused by preferential partitioning of isotopes among sulfur-bearing phases, known as fractionation. These variations arise from differences in temperature, or more importantly, oxidation and reduction reactions acting upon the sulfur. The oxidation and reduction reactions can... You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Fe isotope fractionation on FeS formation in ambient aqueous solution

Iron sulfide phases are the ultimate repository of iron and reduced sulfur in sediments. The sulfur isotope geochemistry of pyrite has had much to tell us about modern and ancient Earth environments and it is likely that Fe isotopes will too, once fractionations for key processes are known. We report the results of an experimental study of Fe isotope fractionation on precipitation of FeS, synthetic mackinawite, from excess aqueous Fe(II) solutions by addition of sodium sulfide solution at 2–40 °C. The results show a significant kinetic isotope effect in the absence of a redox process. No detectable effect of temperature on the fractionation factor was observed. The Fe isotope fractionation for zero-age FeS is Δ Fe(II)–FeS = 0.85 ± 0.30‰ across the temperature range studied, giving a kinetic isotope fractionation factor of α Fe(II)–FeS = 1.0009 ± 0.0003. On ageing, the FeS in contact with aqueous Fe(II) becomes progressively isotopically heavier, indicating that the initial fractionations are kinetic rather than equilibrium. From published reaction mechanisms, the opportunity for Fe isotope fractionation appears to occur during inner sphere ligand exchange between hexaqua Fe(II) and aqueous sulfide complexes. Fe isotope fractionation on mackinawite formation is expected to be most significant under early diagenetic situations where a readily available reactive Fe source is available. Since FeS (aq) is a key reactive component in natural pyrite formation, kinetic Fe isotope fractionations will contribute to the Fe isotope signatures sequestered by pyrite, subject to the relative rate of FeS 2 formation versus FeS–Fe(II) (aq) isotopic equilibration.

Hydrochemistry, mineralogy and sulfur isotope geochemistry of acid mine drainage at the Mt. Morgan mine environment, Queensland, Australia

Mineralogical, hydrochemical and S isotope data were used to constrain hydrogeochemical processes that produce acid mine drainage from sulfidic waste at the historic Mount Morgan Au–Cu mine, and the factors controlling the concentration of SO 4 and environmentally hazardous metals in the nearby Dee River in Queensland, Australia. Some highly contaminated acid waters, with metal contents up to hundreds of orders of magnitude greater than the Australia–New Zealand environmental standards, by-pass the water management system at the site and drain into the adjacent Dee River. Mine drainage precipitates at Mt. Morgan were classified into 4 major groups and were identified as hydrous sulfates and hydroxides of Fe and Al with various contents of other metals. These minerals contain adsorbed or mineralogically bound metals that are released into the water system after rainfall events. Sulfate in open pit water and collection sumps generally has a narrow range of S isotope compositions ( δ 34S = 1.8–3.7‰) that is comparable to the orebody sulfides and makes S isotopes useful for tracing SO 4 back to its source. The higher δ 34S values for No. 2 Mill Diesel sump may be attributed to a difference in the source. Dissolved SO 4 in the river above the mine influence and 20 km downstream show distinctive heavier isotope compositions ( δ 34S = 5.4–6.8‰). The Dee River downstream of the mine is enriched in 34S ( δ 34S = 2.8–5.4‰) compared with mine drainage possibly as a result of bacterial SO 4 reduction in the weir pools, and in the water bodies within the river channel. The SO 4 and metals attenuate downstream by a combination of dilution with the receiving waters, SO 4 reduction, and the precipitation of Fe and Al sulfates and hydroxides. It is suggested here that in subtropical Queensland, with distinct wet and dry seasons, temporary reducing environments in the river play an important role in S isotope systematics.

Sulfur and strontium isotope geochemistry of tributary rivers of Lake Biwa: implications for human impact on the decadal change of lake water quality

To study the deterioration of the water quality in Lake Biwa, Japan, over the last 40 years, we measured the concentrations and isotopic ratios of sulfur and strontium of water in 41 inflowing rivers and one discharging river. The concentrations of SO 4 and Sr of inflowing rivers at downstream sites were generally high in the southern urban area and in the eastern area, where a large agricultural plain is situated, but low in the northern and western areas, whose watersheds are mountainous and with low population density. SO 4 and Sr concentrations are also lower at upstream sites, which are closer to mountainous areas. Thus, the inflowing river receives large amounts of SO 4 and Sr as it flows across the plain, where human activity levels are high. The δ 34S or 87Sr/ 86Sr values of most eastern rivers at downstream sites are lower than those of water in Lake Biwa, and values become more uniform as the proportion of the plain area in the watershed increases. River water in other areas has higher values of δ 34S or 87Sr/ 86Sr than the lake water. This result indicates that the decadal decrease of δ 34S and 87Sr/ 86Sr in the lake water has been caused mainly by the increased flux of SO 4 and Sr from rivers in the eastern plain. We assume that in the plain, sulfur, nitrogen, and organic compounds induced by human activities generate sulfuric, nitric, and organic acids in the water, which accelerate the extraction of Sr from bedrocks, leading to the generation of Sr in the river water in the area.

Geological setting, nature of ore fluids and sulphur isotope geochemistry of the Fu Ning Carlin‐type gold deposits, Yunnan Province, China

AbstractCarlin‐type gold deposits in southern China are present in Palaeozoic to Mesozoic siliciclastic and carbonate rocks. The border region of Yunnan, Guizhou and Guangxi Provinces contains gold deposits on the south‐western margin of the Pre‐Cambrian South China Craton in south‐eastern Yunnan Province. The Fu Ning gold deposits host epigenetic, micron‐sized disseminated gold in: (i) Middle Devonian (D1p) black carbonaceous mudstone at the Kuzhubao gold deposit and (ii) fault breccia zones at the contact between Triassic gabbro (β\mathrm{\mu} ^{1}_{5}) and the Devonian mudstone (D1p) at the Bashishan gold deposit. The deposits are associated with zones of intense deformation with enhanced permeability and porosity that focused hydrothermal fluid flow, especially where low‐angle N‐S striking thrust faults are cut by NW striking strike‐slip and/or NE striking normal faults. Major sulphide ore minerals in the Fu Ning gold deposits are pyrite, arsenopyrite, arsenic‐rich pyrite, stibnite and minor iron‐poor sphalerite. Gangue minerals are quartz, sericite, calcite, ankerite and chlorite. Hypogene ore grades range from 1 to 7 g t−1 Au and up to 18 g t−1 Au at the Kuzhubao gold deposit and are generally less than 3 g t−1 Au at the Bashishan gold deposit. Sub‐microscopic gold mineralization is associated with finely disseminated arsenic‐rich pyrite in the Stage III mineral assemblage. Two types of primary fluid inclusions have been recorded: Type I liquid–vapour inclusions with moderate‐to‐high liquid/vapour ratios, and Type II inclusions containing moderate liquid/vapour ratios with CO2 as determined from laser Raman analysis. Temperature of homogenization (Th) data collected from these primary fluid inclusions in gold‐ore Stage III quartz ranged from 180 to 275°C at the Kuzhubao gold deposit and 210 to 330°C at the Bashishan gold deposit. Salinity results indicate that there were possibly two fluids present during gold deposition, including: (i) an early fluid with 0.8–6.5 wt.% NaCl equivalent, similar to salinity in shear‐zone‐hosted gold deposits with metamorphic derived fluids; and (ii) a late fluid with 11.8–13.4 wt.% NaCl equivalent, indicating possible derivation from connate waters and/or brine sources. CO2 and trace CH4 were only detected by laser Raman spectrometry in gold‐ore‐stage primary fluid inclusions. Results of sulphur isotope studies showed that δ34S values for pyrite and arsenopyrite associated with gold‐ore mineralization during Stage III at the Kuzhubao and Bashishan gold deposits are isotopically similar and moderately heavy with a range from +9 to +15 per mil, and also fall into the range of δ34S values reported for Carlin‐type gold deposits. Sulphur isotopes suggest that the Fu Ning gold deposits were formed from connate waters and/or basinal brines. Fluid geochemistry data from the Fu Ning gold deposits suggest a Carlin‐type genetic model, involving fluid mixing between: (i) deep CO2‐rich metamorphic fluids, (ii) moderately saline, reduced connate waters and/or basinal brines; and (iii) evolved meteoric waters.

Sulfur isotope geochemistry of the submarine hydrothermalcoastal vents of Punta Mita, Mexico

Coastal hydrothermal submarine vents occur near Punta Mita (Mexico) through a seafloor fissure hosted by basaltic rocks and partially covered by recent sediments. Hydrothermal venting produces calcareous tufa mounds, with minor sulfides, barite and apatite. Pyrite is the most abundant sulfide mineral that precipitates around the submarine hot springs. It occurs as framboids, euhedral crystals, thin botryoidal coatings interbedded with calcite, and as replacement of detrital magnetite grains. Vent fluids have temperature below 100 °C, and methane is abundant. Sulfur isotopic composition of pyrite predominantly has δ 34S values from − 10.7 to +4.9 suggesting that the source of sulfur is microbially reduced sulfate seawater.

Sulphur isotope geochemistry of black shale-hosted antimony mineralization, Arnsberg, northern Rhenish Massif, Germany: implications for late-stage fluid flow during the Variscan orogeny

Vein-type and bedding-concordant mesothermal (180–410 °C) stibnite–sulphosalt mineralization at Arnsberg, NE Rhenish Massif, Germany, is hosted by Carboniferous pyrite-rich black shales and siliceous limestones. A detailed sulphur isotope study of the stibnite–sulphosalt mineralization and pyrite from a variety of regional host-rock lithologies has been carried out using an in situ laser combustion technique. The δ 34 S values of stibnite of various textural types are distinctly negative and lie in a narrow range between −23.9‰ and −17.1‰ (mean −20.1‰). In contrast, regional sedimentary–diagenetic pyrites display a large variation of their δ 34 S values between −45.4‰ and +9.3‰. There is little evidence for significant modification of the hydrothermal fluid during deposition and the S isotope signatures suggest that the sulphur of the stibnite mineralization was not locally derived. The δ 34 S values of pyrite in Givetian shales display a significantly narrower range of −28.2‰ to −7.5‰ and their mean composition (−17.1‰) is close to the δ 34 S values of the Arnsberg stibnite deposits. Considering the temperature-dependent isotopic fractionation between stibnite and reduced sulfur species, the δ 34 S values of the mineralizing fluid (−16.8‰; 200 °C) and the Givetian rock source are essentially identical. Therefore, we propose a model of leaching and isotopic homogenization of sulphur from the Middle Devonian shales and a subsequent northward migration of these fluids. The fluids were trapped in permeability-controlled positions within anticlinal zones, where fluid cooling induced deposition of stibnite and sulphosalts.

Sulphur isotope geochemistry of pyrite from the Upper Cretaceous Marshybank Formation, Western Interior Basin

Variations in the texture and sulphur isotopic composition of pyrite in the Upper Cretaceous Marshybank Formation are linked to depositional environment. Abundant, framboidal (and lesser euhedral) pyrite precipitated in offshore marine rocks. Moderate quantities of pyrite also crystallized in brackish, coastal plain rocks. However, in contrast to marine pyrite, coastal plain pyrite is dominantly euhedral in texture, reflecting direct precipitation from a porewater with a relatively low dissolved sulphide concentration. In the marine rocks, pyrite δ 34S values range from −35.7‰ to +27.4‰ (avg. −4.8‰ Canyon Diablo Troilite, CDT). Pyrite within carbonate concretions hosted in these marine rocks has a similar isotopic composition (−49.8‰ to +10.6‰ CDT). However, isotopic values are often highly variable within individual concretions as a result of the heterogeneous nature of sulphate reduction and pyrite formation within marine sediments. Pyrite in coastal plain rocks is characterized by relatively high δ 34S values (−4.2‰ to +35.5‰, avg. +13.2‰ CDT), while the overlying sideritized conglomerates have the lowest δ 34S values reported for Cretaceous rocks from the Western Interior Basin of North America (−49.8‰ to −41.7‰ CDT). Very low δ 34S values, which are only observed in the marine rocks, are indicative of microbial sulphate reduction and pyrite formation in a sulphate-replete (i.e., open) system. Higher δ 34S values (up to +18‰), which were obtained for both the marine and coastal plain rocks, are indicative of progressive pyrite crystallization in a sulphate-limited (i.e., closed) system. Such conditions are expected in marine sediments as burial occurs, and in brackish (i.e., low sulphate) sediments. Pyrite with very high δ 34S values (>+18‰) is common in the coastal plain rocks. These high values are the result of influx of 34S-enriched, residual sulphide derived from overlying marine units. A minor amount of 34S-enriched pyrite is also present within, and proximal to marine sedimentary Unit H, which was deposited at the same time as the coastal plain rocks. We hypothesize that porewater containing 34S-enriched, residual sulphide flowed from the coastal plain and along Unit H, into the marine sediments, thus producing anomalously high δ 34S pyrite.

Celestite formation, bacterial sulphate reduction and carbonate cementation of Eocene reefs and basinal sediments (Igualada, NE Spain)

Petrographic and geochemical studies of an Upper Eocene reef and associated basinal sediments from the mixed carbonate–siliciclastic fill of the south‐eastern Pyrenean foreland basin near Igualada (NE Spain) provide new insights into the evolution of subsurface hydrology during the restriction of a marine basin. The reef deposits are located on delta‐lobe sandstones and prodelta marls, which are overlain by hypersaline carbonates and Upper Eocene evaporites. Authigenic celestite (SrSO4) is an important component in the observed diagenetic sequences. Celestite is a significant palaeohydrological indicator because its low solubility constrains transportation of Sr2+ and SO42− in the same diagenetic fluid. Stable isotopic analyses of carbonates in the reef indicate that meteoric recharge was responsible for aragonite stabilization and calcite cementation. Sulphur and oxygen isotope geochemistry of the celestite demonstrates that it formed from residual sulphate after bacterial sulphate reduction, but also requires that there was a prior episode of sulphate recycling. Meteoric water reaching the reef and basinal areas was most probably charged with SO42− from the dissolution of younger Upper Eocene marine evaporites. This sulphate, combined with organic matter present in the sediments, fuelled bacterial sulphate reduction in the meteoric palaeoaquifer. Strontium for celestite precipitation was partly derived in situ from dissolution of aragonite corals in the reef and basinal counterparts. However, 87Sr/86Sr data also suggest that Sr2+ was partly derived from dissolution of overlying evaporites. Mixing of these two fluids promoted celestite formation. The carbonate stable isotopic data suggest that the local meteoric water was enriched in 18O compared with that responsible for stabilization of other reefs along the basin margin. Furthermore, meteoric recharge at Igualada post‐dated evaporite deposition in the basin, whereas other parts of the same reef complex were stabilized before evaporite formation. This discrepancy resulted from the spatial distribution of continental siliciclastic units that acted as groundwater conduits.

Sources of natural and anthropogenic sulphur around the Teruel power station, NE Spain. Inferences from sulphur isotope geochemistry

Stable sulphur isotopic ratios were used for the identification of sources of atmospheric sulphur compounds, and the assessment of their contribution to the atmospheric sulphur deposition load around a coal-fired power plant in NE Spain. The study consists of a number of stages: identification of the sources, clarification of the chemical pathways of the sulphur from these sources, assessment of their contribution to the overall load, and determination of the emission impact on the natural sulphur cycle in the area. Sulphur isotope analyses were carried out on bedrock and sediment samples, surface and groundwater, wet-only and total deposition, total suspended particles and SO 2 emissions from the power plant. The results are useful in indicating the sources of sulphate in the atmosphere, allow us to exclude some other potential sources, and demonstrate that: (a) the total load of sulphate is largely unaccounted for by Cl and is, therefore, of non-sea spray origin; (b) this excess sulphate does not originate from bedrock and sediments in the area; (c) there is a significant contribution of sulphur from remote sources such as the Atlantic–north European areas; (d) the multitude of local and remote sources involved and the rapid change in their relative contribution do not facilitate the quantification of the deposition derived from the emissions of the power station. However, given the low conversion efficiency and the relative constancy of the δ 34S of the emitted SO 2 it is suggested that sulphate deposits with δ 34S of around 2.5‰ originate from the Teruel power station.

Mineralogy, sulphur isotope geochemistry and the development of sulphide structures at the Broken Spur hydrothermal vent site, 29°10’N, Mid-Atlantic Ridge

A large collection of hydrothermal sulphides from the Broken Spur hydrothermal vent site, including representative samples of mound sulphide materials, has been characterized using optical mineralogy and sulphur isotope analysis. Young mound sulphides from Broken Spur have a pyrrhotite-dominated mineralogy unusual for bare ridge vent systems. However, pyrrhotite is metastable and is ultimately converted to iron disulphides. Mature sulphides are indurated, recrystallized and contain abundant quartz. Sulphide mound materials are developed by three major processes: (i) coalescing of chimney structures; (ii) accumulation of talus from mass wasting and (iii) precipitation and growth in response to hydrothermal flow. Progressive maturation of mound materials is by modification of primary textures, development of mineralogical zoning and replacement of metastable phases. Sulphur isotope analysis of 35 mineral separates returned δ 34 S values of – 0.5 to +3.2‰. These values are similar to those previously measured for Broken Spur and Snakepit, but are distinctly 32 S enriched compared to the TAG active mound and some Pacific sites. Seawater entrainment and sulphate reduction within the subsurface feeder zone below Broken Spur mounds do not appear to be important processes at Broken Spur, in contrast to the TAG active mound.