Low δ34S Values Research Articles

Multi-stage growth and fluid evolution of a hydrothermal sulphide chimney in the East Pacific Ridge 1–2° S hydrothermal field: constraints from in situ sulphur isotopes

AbstractSulphur isotopes can be used as a powerful tool to trace fluid evolution and explore the formation of chimneys. To clarify the in situ S isotopic variations of sulphides at the micro-scale, we analyzed a sulphide chimney collected from the hydrothermal field in the East Pacific Rise 1–2° S using a sensitive high-mass-resolution ion micro-probe for stable isotopes (SHRIMP SI). Three mineral zones can be identified in the chimney: an external outer wall of porous anhydrite and colloform pyrite, an internal middle zone of sub-euhedral pyrite and massive chalcopyrite, and an inner zone of massive pyrite. The δ34SV-CDT values of the sulphides fall within the range 1.83–7.51 ‰ (avg. 4.05 ‰, n = 16), and S isotopic values increase from the core (3.09 ‰, n = 3) to the middle (3.78 ‰, n = 11) to the edge (6.99 ‰, n = 2). These results illustrate mineral crystallization processes and the mixing between seawater-derived S and magmatic–hydrothermal fluids during the growth of the chimney. The zones from the edge to the core are characterized by crystal morphologies of colloform/anhedral pyrite to massive pyrite with decreasing δ34S values, revealing multi-stage mineral deposition and sulphur isotopic fractionation. In contrast to the increase in δ34S values from the core to the edge in one profile (profile A), anomalously low δ34S values in fine-grained pyrite relative to chalcopyrite in another profile (profile B) in the middle zone result from S isotopic exchange between seawater SO42− and fluid H2S due to different fluid–seawater mixing, possibly caused by variations in permeability and porosity across the chimney.

Environmental controls on sulfur isotopic compositions of sulfide minerals in seep carbonates from the South China Sea

Authigenic carbonates and pyrite associated with sulfate-driven anaerobic oxidation of methane (AOM) at methane seeps provide archives to explore the biogeochemical processes involved and seepage dynamics over time. The wide range and extremely high δ34S values of pyrite (δ34Spy) have been used to trace the AOM-related processes. However, the detailed mechanism for this phenomenon is not well understood. We propose that the characteristics of δ34Spy were mainly controlled by the competition between sulfate reduction and sulfate supply, as well as the redox condition. To test this hypothesis, we investigated Sr/Ca and Mg/Ca ratios, trace element compositions, pyrite contents and sulfur isotopic compositions in seep carbonates from Site F and Haima in the northern South China Sea. Calcite and aragonite contents were distinguished through the Sr/Ca and Mg/Ca ratios. The data show that aragonites are always associated with relatively low δ34Spy values compared to calcites. The Mo contents show a good correlation with pyrite contents in calcites and aragonites, and the slope in aragonites is larger than that in calcites. This relationship indicates that the aragonite precipitated in a relatively open system with higher Mo availability. Thus, we conclude that sulfides with low δ34S values formed at high supply of sulfate under the relatively open system with respect to diffusive replenishment of sulfate, where the carbonate precipitation occurred close to the seafloor due to a strong methane flux. Under vigorous methane flux simultaneously, the high potential of less anoxic conditions, which could limit the additional pyrite accumulation and/or favor the microbial disproportionation, could also be the cause of the low δ34Spy, as supported by samples from the Haima sites. Evidence for this assumption is based on the occurrence of bivalve shells and less enrichment in As and Sb. Conversely, the positive δ34Spy values result from near to complete exhaustion of dissolve sulfate via AOM within a deeper sulfate-methane transition zone, where Mo is less available. The combination of a detailed elemental study of authigenic carbonates with sulfur isotopic composition of sulfide minerals in carbonates is a promising tool for reconstructing the dynamics of seep intensities at modern and, potentially, geological seep sites.

Does carbonate-associated sulphate record nutrition in lucinid and thyasirid bivalve shells from modern hydrocarbon seeps?

We test whether chemosymbiotic bivalves with sulphide-oxidizing bacteria record their nutritional strategy in the sulphur isotope composition of the carbonate-associated sulphate (CAS) in their shells, as a possible indicator of thiotrophic chemosymbiosis in the fossil record. The hypothesis rests on the possible incorporation of ³⁴S-depleted sulphate resulting from sulphide oxidation in sufficient quantity to affect the intrashell sulphate-sulphur isotope mass balance and hence the isotopic composition of sulphate, which is incorporated into carbonate with little or no fractionation. We analysed shell material of lucinid (Lucinoma asapheus) and thyasirid (Thyasira vulcolutre) bivalves from active mud volcanoes in the Gulf of Cadiz. Our results show that the CAS-δ³⁴S values of the bivalve shells do not reflect the variety of sulphur sources present at hydrocarbon seeps, but instead only record seawater sulphate values. Low δ³⁴S values were, however, measured in the animals’ soft tissues and shell organic matter (SOM), both displaying a strong influence of the depleted sulphide used as nutrition by the chemosynthethic bacteria. Given its potential for long-term preservation, SOM may therefore represent a more promising record of chemosymbiosis in the fossil record, while CAS from seep bivalves can be used to reconstruct local seawater sulphate.

Formation of the Qixiashan Pb–Zn deposit in Middle-Lower Yangtze River Valley, eastern China: Insights from fluid inclusions and in situ LA-ICP-MS sulfur isotope data

The Qixiashan Pb–Zn deposit, Jiangsu Province (1212011220678), is hosted in Huanglong Formation limestones and is one of the largest Pb–Zn deposits in the Lower Yangtze region, China, which is an important Cu–Pb–Zn metallogenic belt. Here we report in situ sulfur isotopic analyses of sulfides using LA-ICP-MS method, together with fluid inclusion data. Three types of pyrite mineralization were identified in the host rocks and ores, corresponding to three genetic stages: (1) fine-grained framboidal or colloform pyrite hosted in limestone (Py1); (2) fine-grained euhedral–subhedral pyrite (Py2) associated with brown sphalerite (Sph1), occurring as massive sulfide ores; and (3) coarse-grained euhedral–subhedral pyrite (Py3) associated with yellow–brown sphalerite (Sph2) in breccia-type or massive ores. Stages 2 and 3 constitute the main Pb–Zn-forming event. Depending on the stage in which they were formed, the sulfides exhibit different sulfur isotope values, implying different ore-forming processes. The Stage 1 Py1 was formed by bacterial sulfate reduction and yields extremely low δ34S values, in the range −14.39‰ to −3.08‰. Stage 2 Py2 and Sph1 have δ34S values ranging from 6.5‰ to 9.4‰ and from 5.0‰ to 8.3‰, respectively. Stage 3 Py3 and Sph2 have δ34S values of 1.3‰ to 3.2‰ and −0.05‰ to 2.5‰, respectively. The δ34S value of pyrite is greater than that of sphalerite for each coexisting pyrite–sphalerite pair, indicating that sulfur isotope equilibrium was reached between these minerals. The total δ34S values and formation temperatures of the ore fluids in Stages 2 and 3 were 9.4‰ and 173 °C–279 °C, and 2.3‰ and 195 °C–328 °C, respectively. The high total δ34S in Stage 2 ore fluids was a result of the interaction of magmatic fluids with marine sulfur, whereas the low total δ34S in Stage 3 ore fluids reveal that these fluids were derived from magmatic water only. Two-phase liquid-rich aqueous inclusions in Stage 2 sphalerite (Sph1) yield homogenization temperatures and salinities of 182 °C–284 °C and 0.9–8.8 wt% NaCl equivalent, respectively. Such inclusions in Stage 3 sphalerite (Sph2) yielded higher homogenization temperatures (207 °C–306 °C) and higher salinities (0.4–12.3 wt% NaCl equivalent), suggesting an increase in magmatic–hydrothermal activity from Stage 2 to 3. Such high-salinity fluids may be produced by magmatic water exsolving from a concealed intrusion beneath the Qixiashan ore district. On the basis of ore fluid temperatures and total δ34S values, sulfides in Stage 2 (δ34S = 9.4‰, T = ~250 °C) are inferred to have precipitated under conditions of pH 2–6 and log fO2 −38 to −33, and sulfides in Stage 3 (δ34S = 2.3‰, T = ~350 °C) are inferred to have precipitated under conditions of pH 2–6 and log fO2 −31 to −27. The textural, fluid inclusion, and sulfur isotopic evidence indicate that the Qixiashan Pb–Zn orebody is a hybrid deposit (rather than a SEDEX or magmatic–hydrothermal deposit) that formed by syngenetic sedimentary deposition and hydrothermal overprinting.

Regional variations of sulfur isotope compositions for metallic deposits in the Taebaeksan Mineralized District, South Korea

Metallic ore deposits of various genetic types are distributed in the Taebaeksan mineralized district in South Korea. The different basements or host rocks for these deposits vary across the northern and southern regions of the district with the Baegunsan Syncline as its center. Previous and newly analyzed sulfur isotope data of 374 sulfide minerals collected from 45 ore deposits were reviewed to compare the genetic characteristics of the two regions. Metallic deposits in the study area were classified into skarn, hydrothermal replacement, and hydrothermal vein based on genetic types and W-Mo, Fe-Cu(-Mo-Pb-Zn), Pb-Zn(-Cu-Au- Ag), and Au-Ag(-Cu-Pb-Zn) deposits with regard to ore species. For each genetic type, average sulfur isotope values were found to be 6.8‰, 7.7‰, and 6.3‰ in the northern region, and 2.3‰, 3.6‰, and 3.5‰ in the southern region, respectively. Average sulfur isotope values for each of the ore species were 11.3‰, 2.6‰, 6.6‰, and 6.9‰ in the northern region, and 1.3‰,–0.2‰, 4.2‰, and 3.3‰ in the southern region, respectively. The results indicate that sulfur isotope compositions for both genetic types and ore species are distinctly higher in the northern region than in the southern region. These differences could be ascribed to different sulfur isotope compositions of basement and host rocks that provided sulfur to ore minerals during the evolution of hydrothermal fluids, though the mineralizing fluids were originated from magmatic source. In the northern region, higher δ34S values of ore sulfurs could be attributed to high δ34S values of sulfate and sulfide in carbonate rocks formed in seawater. On the contrary, lower δ34S values of sulfide minerals in the southern region seem to be attributed to metasedimentary rocks that have lower δ34S values as a result of bacterial sulfate reduction.

Decratonic gold mineralization: Evidence from the Shangzhuang gold deposit, eastern North China Craton

The Jiaodong Peninsula in the eastern North China Craton (NCC) hosts some of the world-class gold deposits. Among these, the Shangzhuang gold deposit represents a typical fault-zone hosted disseminated- and stockwork-style gold mineralization. The mineralization is characterized by intense hydrothermal alteration halos in the wallrocks with the mineralized veins intruding into altered wallrocks. Zircon U-Pb isotope dating constrains the timing of emplacement of the Guojialing granodiorite as 130±1Ma. Five molybdenite samples from the main mineralization stage veins yielded a well-fitted isochron age of 126±2Ma (MSWD=1.3), marking the timing of gold mineralization. Four types of fluid inclusions are identified at Shangzhuang, and their petrographic and microthermometric features suggest fluid immiscibility followed by fluid mixing. This inference is also supported by oxygen and hydrogen isotopic data of quartz veins from stage III. The measured δ18O values of quartz are +12.3 to +13.7‰ for stage II and +11.7 to +12.0‰ for stage III, with calculated δ18Ofluid values for stage II ranging from +5.9 to +7.3‰ and for stage III from +3.4 to +3.7‰. δD values for stage II and III quartz range from −65.3 to −75.2‰ and −70.6 to −74.7‰, respectively. The data suggest that the ore-forming fluids were initially derived from magmatic sources, followed by mixing with meteoric water. SIMS in-situ sulfur isotope analyses of two types of pyrite (Py I and Py II) from different mineralization stages show different sulfur isotope features. The δ34S values for Py I (+10.2 to +11.3‰, mean=+10.8‰, n=25) are higher than those of the later mostly gold-related Py II (+4.1 to +6.8‰, mean=+5.4‰, n=27). The higher δ34S values of Py I are correlated to degassing of mantle wedge metasomatized by the slab fluids. The relatively lower δ34S values of Py II might suggest increasing of fO2 through fluid mixing between ore-forming fluids and meteoric water.The temporal, spatial and tectonic relations between the giant gold mineralization and destruction of the NCC suggest a genetic linkage. The gold mineralization between 126 and 117Ma at Jiaodong was probably initiated at the peak of decratonization (ca. 125Ma) of the eastern NCC. Phanerozoic craton margin orogeny also played a critical role in the generation of the early Cretaceous giant gold deposits in the eastern NCC. Integrated geological characteristics, mineralization features, metallogenic age, sources of ore-forming fluids and sulfur, and tectonic settings favor a decratonic gold mineralization model for the Shangzhuang gold deposit. The geodynamic scenario proposed for the early Cretaceous giant gold mineralization event in the eastern NCC includes the paleo-West Pacific plate subduction, asthenospheric upwelling, multiple subduction-collision processes along the margins.

Geochemical behavior of Cu and sulfur isotopes in the tropical mining region of Taxco, Guerrero (southern Mexico)

This study was aimed to identify the main processes involved in the release of metals using sulfur isotopes and those acting on the fractionation of copper isotopes. We determined sulfur and copper isotopic ratios in rocks, tailings, precipitates and soils samples from the historical mining district of Taxco, Southern Mexico. Ratios of sulfur isotopes are reported in notation of δ per mil, and standardization was based on international standards OGS-1 and NBS123. Only copper ratio isotopes were studied in pyrite (Py), sphalerite (Sph) and galena. Results are reported as δ65Cu=((65Cu/63Cusample/65Cu/63CuNIST976standar)−1)∗1000. Error for all the analyzed samples was 0.01‰ and any mass bias was corrected trough bracketing method. The sulfur isotopic value of a sample from the Mexcala shale Formation was −7.7‰. The δ34S values in tailing ponds ranged from −2.6 to 1.2‰, in precipitates from −7.2 to −3.2‰, and in soils from −0.8 to 4.5‰. Isotopic δ34S values in rocks evidenced a magmatic influence of sulfides present in the Mexcala Formation. Oxidation of sulfides contained in tailings and precipitates was observed related with their low δ34S values close to zero, oxidation followed the order: sphalerite>pyrite>pyrite rich in copper>chalcopyrite>galena. In soils, oxidation is not the main process as supported by their positive δ34S values and low sulfate content. Results of δ65Cu values in rocks were −0.09 to 0.54‰; in sulfides values were δ65Cu=0.18‰ (Py) and δ65Cu=−0.20‰ (Sph), concentration of copper in galena was not enough to get a reliable isotopic value. In tailings δ65Cu ranged from −1.19 to 0.91‰ and in precipitates from −0.36 to 0.92‰; in soils values were between 0.26 and 1.72‰. Results in rocks indicate an igneous influence on copper provenance. The δ65Cu values in Py and Sph were within the range of terrestrial primary sulfides (from −1 to 1‰) confirming its igneous provenance. Processes related with fractionation of copper isotopes were oxidation of tailings and reprecipitation of 65Cu in tailings with a high content of Fe oxyhydroxides. Enrichment in 65Cu in precipitates and soils is favored by organic matter presence that retains 63Cu. Erosion of rocks and tailings is the main source of copper being rocks the initial and tailings the end members. The isotopic studies on environmental research provide a useful tool on: 1) The behavior of copper and sulfur isotopes in environments where both, natural and anthropogenic activities, are present. 2) Understanding surficial processes of dispersion of metals and identifying their source in mining areas surrounded by villages and agricultural soils.

Tectonic transition from a compressional to extensional metallogenic environment at ∼120 Ma revealed in the Hushan gold deposit, Jiaodong, North China Craton

The world-class giant gold province (>4000t) in the Jiaodong Peninsula has attracted global attention and extensive studies for decades. However, most of the works have been focused on the western Zhaoyuan-Laizhou and eastern Muping-Rushan gold metallogenic belt, leaving the middle Penglai-Qixia belt largely unexplored. The Hushan gold deposit in the Penglai-Qixia belt shows a unique two-stage gold mineralization, i.e., an early-stage pyrite-sericite-quartz altered-rock type mineralization and a late-stage pyrite-pyrrhotite vein type mineralization. Hydrothermal monazite coexisting with Au-bearing pyrite is observed in the early-stage mineralization. The widespread “circular zoned” metasomatic relict structures indicate that monazite was formed by the strong interaction between (Ca, P, REE)-rich fluids and feldspars (plagioclase and K-feldspar). Therefore obtained in-situ U-Pb age of 120.0±3.1Ma for the “pure” monazite without mineral inclusions (such as feldspars) can represent the timing of the early-stage gold mineralization. The in-situ monazite εNd (t) (t=120Ma) values vary from −20.6 to −18.4, well corresponding to Nd isotopes of the late Jurassic Linglong granite. It is inferred that the REE-rich components in the ore-forming fluids were extracted during the process of primary mineralizing fluids passing through the lower Linglong granite body, and that the Nd isotopic compositions were altered due to the strong fluid-rock interaction. In this regard, Linglong granite contributes some ore-forming materials to the mineralizing fluids during fluid-rock interaction.The early-stage altered-rock type gold mineralization indicates a compressional (closed) ore-forming system, whereas the late-stage pyrite-pyrrhotite vein type mineralization and the occurrences of fracture, geode and hole in the ore samples reflect an extensional (open) ore-forming system. The presence of barite and magnetite in the late-stage mineralization also suggests an increase of oxidation state during the process. Furthermore, pyrites in the late stage generally have lower δ34S values (5.69–6.98‰, av.=6.47‰) than pyrites in the early stage (δ34S values=7.06–7.85‰, av.=7.42‰), which can also be well explained by the increase of oxidation state. Therefore, the Hushan gold deposit uniquely records a metallogenic environmental transition from compressional, reduced to extensional, oxidized at ∼120Ma. In addition, the mineralizing fluids with higher oxidation state in the late-stage is supposed to superimpose on the early-stage mineralization, dissolve and rework previously crystalized pyrite to form the high-grade gold mineralization. Unlike the gold deposits in the western and eastern belts, the Hushan gold deposit temporally preserves two types of mineralization in one single deposit, as a response to regional stress field transition.

Origin of sulfur and crustal recycling of copper in polymetallic (Cu-Au-Co-Bi-U ± Ag) iron-oxide-dominated systems of the Great Bear Magmatic Zone, NWT, Canada

The Great Bear Magmatic Zone, in northwest Canada, contains numerous polymetallic mineral occurrences, prospects, and deposits of the iron oxide copper-gold deposit (IOCG) family. The mineralization is hosted by the Treasure Lake Group and igneous rocks of the Great Bear arc and was deposited concomitantly with the arc magmatism (ca. 1.88 to 1.87 Ga). In situ δ 34S (n = 48) and δ 65Cu (n = 79) analyses were carried out on ore-related sulfides from a number of these systems. The δ 34S values mainly vary between 0 and +5‰, consistent with derivation of sulfur from the mantle. Lower δ 34S values (−7.7 to +1.4‰) from the Sue-Dianne breccia may indicate SO2 disproportionation of a magmatic hydrothermal fluid. The δ 65Cu values vary between −1.2 and −0.3‰, and are lower than the igneous δ 65Cu range of values (0.0 ± 0.27‰). The S and Cu isotopic data are decoupled, which suggests that Cu (and possibly some S) was dissolved and remobilized from supracrustal rocks during early stages of alteration (e.g., sodic alteration) and then precipitated by lower temperature, more oxidizing fluids (e.g., Ca-Fe-K alteration). A limited fluid inclusion dataset and δ 13C and δ 18O values are also presented. The δ 18Ofluid values are consistent with a magmatic origin or a host-rock equilibrated meteoric water source, whereas the δ 13Cfluid values support a marine carbonate source. Combined, the S and Cu isotopic data indicate that while the emplacement of the Great Bear magmatic bodies may have driven fluid convection and may be the source of fluids and sulfur, metals such as Cu could have been recycled from crustal sources.

Orebody geometry, fluid and metal sources of the Omitiomire Cu deposit in the Ekuja Dome of the Damara Belt in Namibia

The Omitiomire Cu deposit (resource of 137 Mt at 0.54% Cu) in the Ekuja Dome of the Damara Belt in Namibia is hosted by an anastomosing, low-angle Pan-African (ca. 520 Ma) shear zone system developed around an older (ca. 1100–1060 Ma), late Mesoproterozoic intrusive breccia between a suite of mafic rocks (originally lava flows) and later tonalitic gneisses. High-grade ore shoots preferentially formed along contacts between tectonically interleaved biotite-epidote-quartz-chalcocite schists and felsic gneisses, and are directly related to an increase in the number and cumulative thickness of thin, contact-parallel mineralized shear zones. Alteration and mineralization are associated with elevated concentrations of K2O, Cr, Rb, S, and Cu and a loss of Na2O, CaO, and MgO. Oxygen isotope fractionation for quartz-biotite, quartz-feldspar, and quartz-amphibole mineral pairs support equilibrium temperatures of between 500 and 650 °C during the fluid/rock interaction. Mineral separates from amphibole-biotite gneisses and mineralized schists have similar ranges in δ18O values of about 1.2 to 2 ‰ relative to VSMOW. Coexisting minerals are arranged in an order of increasing δ18O values from biotite, to epidote, amphibole, and quartz, suggesting that the Omitiomire Shear Zone was a rock-dominated system. Similarly, H-isotope results for mineral separates from biotite-epidote schists and amphibole gneisses do not show any reversals for D/H fractionations, with δD values of between −48 and −82 ‰, typical of metamorphic-magmatic rocks. The homogeneous and low δ34S values (−6.1 to −4.7 ‰ CDT) are compatible with a local redistribution of sulfur from magmatic rocks and interaction with sulfur derived from metamorphic fluids of metasedimentary origin. The relatively low fluid/rock ratios and elevated Cu values (>1500 ppm) from unaltered amphibolite point to a local redistribution of an earlier (late Mesoproterozoic) Keweenaw-type Cu mineralization into later Pan-African shear zones during the exhumation of the Ekuja Dome. The timing, polyphase evolution, and tectonic setting of the Omitiomire deposit show remarkable similarities with the large Cu deposits of the Domes Region in the adjoining Lufilian Arc of northern Zambia. This suggests the presence of a much larger, regionally significant Cu province extending from central Namibia, through northern Botswana, and into Zambia.

Sulfide chemistry and sulfur isotope characteristics of the Cenozoic volcanic-hosted Kuh-Pang copper deposit, Saveh county, northwestern central Iran

The several-hundred-m-thick Eocene-Oligocene volcanic units in the Urmia-Dokhtar magmatic arc in northwestern Central Iran host stratabound and fault-controlled copper mineralization. The Kuh-Pang deposit (2.8Mt at 1.65wt% Cu, 0.52g/t Au, 34g/t Ag) has vein-style copper mineralization, with primary Cu-sulfides of chalcopyrite, bornite, chalcocite and digenite, and supergene Cu-sulfides of chalcocite, covellite, malachite and azurite, in a tectonic–hydrothermal breccia zone within rhyodacite and andesite flows. The mineralization is accompanied by a variety of alterations including silicic, carbonate, argillic and advanced argillic within a broad-scale propylitic halo. The main ore formation is related to hydrothermal breccias, and has a close association with silicic and argillic alterations. Sulfides formed during hydrothermal alteration, as indicated by: 1) the occurrence of disseminated sulfides in the groundmass of hydrothermally altered rocks, 2) the co-precipitation of sulfides and alteration minerals (e.g., kaolinite, alunite) in the cement of hydrothermal breccias, and 3) the occurrence of sulfides filling fissures and voids of hydrothermally altered rocks (vuggy quartz). The main mineralization stages include: (i) pre-ore stage with pyrite and arsenopyrite, (ii) main ore-stage with chalcopyrite, bornite, chalcocite I and digenite, and (iii) late-ore and supergene enrichment stage with chalcocite II and covellite. Electron microprobe analyses of pyrite show that As, Cu and Co are the most abundant minor elements. Back-scatter electron imaging of pyrite shows zoning features that closely reflect variations in the As/S ratio. High Cu concentration in pyrite is probably related to the presence of sub-micrometer particles and aggregates of chalcopyrite or other Cu-bearing sulfide minerals. Silver is preferentially enriched in supergene chalcocite and covellite. The mineral assemblage indicates a trend from intermediate to high sulfidation state, and arsenopyrite geothermometry defines temperatures for the pre-ore sulfides ranging from 250 to 370°C. The sulfur isotope composition of pre-ore pyrite and arsenopyrite shows a δ34S range of −1 to 3‰, indicating a magmatic sulfur-source. The copper sulfides have lower δ34S values (−9 to −3‰), indicating that the ore-forming fluids gradually became SO42−-enriched and relatively oxidized during Cu mineralization. The tectono-magmatic setting, mineral assemblage and hydrothermal alteration, including advanced argillic and silicic zones, suggest that the Kuh-Pang copper deposit is a high sulfidation epithermal deposit in a volcanic arc terrain.

How sulfate-driven anaerobic oxidation of methane affects the sulfur isotopic composition of pyrite: A SIMS study from the South China Sea

Sulfate-driven anaerobic oxidation of methane (SO4-AOM) in marine sediments commonly leads to the precipitation of pyrite. It is, however, frequently challenging to unequivocally unravel the entire history of pyritization, because of the common coexistence of SO4-AOM derived pyrite with pyrite resulting from organiclastic sulfate reduction (OSR). To better understand how SO4-AOM affects pyritization in methane-bearing sediments and how this can be identified, we applied secondary ion mass spectroscopy (SIMS) to analyze the sulfur isotope composition (δ34S) of authigenic pyrite in addition to sulfur isotope measurements of bulk sulfide and hand-picked pyrite aggregates from the two seafloor sites, HS148 and HS217, in the Shenhu seepage area, South China Sea. Authigenic, mostly tubular pyrite aggregates from these sites consist of three types of pyrite: framboids, zoned aggregates with radial overgrowths surrounding a framboidal core, and euhedral pyrite crystals. Framboids with low SIMS δ34S values (as low as −41.6‰ at HS148, and −38.8‰ at HS217) are dispersed throughout the cores, but are especially abundant in the shallow part of the sedimentary column (i.e. above 483cmbsf in HS148; above 670cmbsf in HS217). These patterns are interpreted to reflect the dominance of OSR during early diagenetic processes in the shallow sediments. With increasing depth, both δ34S values of bulk sulfide minerals and hand-picked pyrite aggregates increase sharply at 483cmbsf in core HS148, and at 700cmbsf in core HS217, respectively. Radial pyrite overgrowths and euhedral crystals become abundant at depth typified by high δ34S values for hand-picked pyrite. Moreover, SIMS analysis reveals an extreme variability of δ34S values for the three pyrite types on a small scale in these zones. Besides some moderately 34S enriched framboids, most of the overgrowths and euhedral crystals display extremely high SIMS δ34S values (as high as +114.8‰ at HS148, and +74.3‰ at HS217), representing the heaviest stable sulfur isotope composition of pyrite ever reported to the best of our knowledge. Such an abrupt and extreme increase in δ34Spyrite values with depth is best explained by an enrichment of 34S in the pool of dissolved sulfide caused by SO4-AOM in the sulfate methane transition zone (SMTZ). The increase in δ34S values from framboidal cores to overgrowth layers and euhedral crystals indicates continuous, and finally near to complete exhaustion of dissolved sulfate at the SMTZ following a Rayleigh distillation process. SO4-AOM allowed for subsequent growth of later stage pyrite over the initial framboids, part of which formed earlier and at shallower depth by OSR. The combination of a detailed petrographic study of authigenic pyrite with SIMS analysis of stable sulfur isotopes in organic-rich strata proves to be a powerful tool for reconstructing the dynamics of sulfur cycling in modern and, potentially, ancient sedimentary sequences.

Mineralogy and sulfur isotope compositions of the uraniferous black slates in the Ogcheon Metamorphic Belt, South Korea

Uraniferous black slates, extending for over 100km in the Ogcheon Metamorphic Belt, South Korea, have been explored for their uranium mineralization. Coaly slates interbedded in the black slates, forming a layer about 20–40m thick showing brecciated and flow texture with random-oriented minerals, are more carbonaceous and uraniferous than the surrounding rocks. Uranium minerals include uraninite, uranothorite, brannerite, ekanite, thorutite, and coffinite. Of these, uraninite is the most abundant phase in the coaly slates, while uranothorite is the most abundant in the black slates. Chlorites in the black slates have Fe/(Fe+Mg) ratios of 0.42–0.66, while those in the coaly slates have lower values, 0.10–0.20. Chlorite geothermometry indicates temperature ranges of 259–309°C, and 200–287°C in the coaly and black slates, respectively. Muscovites in the coaly slates have higher concentrations of 0.85–1.55wt.% BaO and 0.22–0.28wt.% V2O3 than those in the black slates. This can be ascribed to hydrothermal venting of Ba-V-rich fluids into the marine basin. Most uranothorites in the black slates have lower U and higher Th contents than those in the coaly slates due to their solubility differences. In contrast to the comparatively low and wide-ranging δ34S values of pyrite from −5.9 to 6.6‰ in the black slates, the coaly slates have relatively high and uniform values from 11.0 to 12.7‰, implying an influx of isotopically heavy sulfur derived from the inorganic reduction of seawater sulfate under a high temperature hydrothermal system. The differences of rock texture, mineralogy, and sulfur isotope geochemistry in relation to uranium mineralization between the black slates and the coaly slates would reflect the influence of submarine hydrothermal process before they suffered regional metamorphism.

Sulfur isotope geochemistry and mineralogy of Balcilar vein type barite-sulphide mineralization, Biga peninsula, NW Turkey

The Balcilar (Canakkale) barite-galena mineralization is a typical example of the vein type barite-lead-zinc deposits in the Biga Peninsula. The lithologic units in the study area are Akcaalan andesite, Eocene, Adadagi pyroclastics, Oligocene, Dededag dacite, Miocene, Karaomerler basalt, Plio-Quaternary and alluvium Quaternary. Barite-galena veins occurred along the faults developed within the andesites. Barite, quartz and galena are main minerals and are accompanied by minor amounts of sphalerite, pyrite, chalcopyrite, covellite and marcasite. The earliest barite (barite I) occurs as coarse-grained subhedral-euhedral crystals and the later (barite II) as small tabular crystals in between the earlier coarse crystals. Quartz occurs as fine-grained crystals with the later small barite crystals. Galena, sphalerite, chalcopyrite, pyrite, marcasite and covellite occur open spaces within the earlier barite (barite I) crystals. Sulfur isotopes indicate that in galena the reduced sulfur from bacterially or inorganically reduced sulphate, or from an isotopically light reduced S-source. The δ34SH2S values calculated from the barite-H2S and galena-H2S fractionation factors, in the same samples, indicate a temperature of between 200 and 300 °C. Relatively lower δ34S values of barites than dissolved sulphate in modern oceans or Eocene sea waters have been evaluated as the ore forming hydrothermal fluids were derived from interacting throughout the magmatic host-rocks.

Sulfur isotope homogeneity of lunar mare basalts

We present a new set of high precision measurements of relative 33S/32S, 34S/32S, and 36S/32S values in lunar mare basalts. The measurements are referenced to the Vienna-Canyon Diablo Troilite (V-CDT) scale, on which the international reference material, IAEA-S-1, is characterized by δ33S=−0.061‰, δ34S≡−0.3‰ and δ36S=−1.27‰. The present dataset confirms that lunar mare basalts are characterized by a remarkable degree of sulfur isotopic homogeneity, with most new and published SF6-based sulfur isotope measurements consistent with a single mass-dependent mean isotopic composition of δ34S=0.58±0.05‰, Δ33S=0.008±0.006‰, and Δ36S=0.2±0.2‰, relative to V-CDT, where the uncertainties are quoted as 99% confidence intervals on the mean. This homogeneity allows identification of a single sample (12022, 281) with an apparent 33S enrichment, possibly reflecting cosmic-ray-induced spallation reactions. It also reveals that some mare basalts have slightly lower δ34S values than the population mean, which is consistent with sulfur loss from a reduced basaltic melt prior to eruption at the lunar surface. Both the sulfur isotope homogeneity of the lunar mare basalts and the predicted sensitivity of sulfur isotopes to vaporization-driven fractionation suggest that less than ≈1–10% of lunar sulfur was lost after a potential moon-forming impact event.

Sulfur Isotope Variations of Metallic Ore Deposits in the Gyeongsang Basin, South Korea

AbstractMany metallic ore deposits of the Late Cretaceous to Early Tertiary periods are distributed in the Gyeongsang Basin. Previous and newly analyzed sulfur isotope data of 309 sulfide samples from 56 ore deposits were reviewed to discuss the genetic characteristics in relation to granitoid rocks. The metallogenic provinces of the Gyeongsang Basin are divided into the Au–Ag(–Cu–Pb–Zn) province in the western basin where the sedimentary rocks of the Shindong and Hayang groups are distributed, Pb–Zn(–Au–Ag–Cu), Cu–Pb–Zn(–Au–Ag), and Fe–W(–Mo) province in the central basin where the volcanic rocks of the Yucheon Group are dominant, and Cu(–Mo–W–Fe) province in the southeastern basin where both sedimentary rocks of the Hayang Group and Tertiary volcanic rocks are present. Average sulfur isotope compositions of the ore deposits show high tendencies ranging from 2.2 to 11.7‰ (average 5.4‰) in the Pb–Zn(–Au–Ag–Cu) province, −0.7 to 11.5‰ (average 4.6‰) in the Cu–Pb–Zn(–Au–Ag) province, and 3.7 to 11.4‰ (average 7.5‰) in the Fe–W(–Mo) province in relation to magnetite‐series granitoids, whereas they are low in the Au–Ag(–Cu–Pb–Zn) province in relation to ilmenite‐series granitoids, ranging from −2.9 to 5.7‰ (average 1.7‰). In the Cu(–Mo–W–Fe) province δ34S values are intermediate ranging from 0.3 to 7.7‰ (average 3.6‰) and locally high δ34S values are likely attributable to sulfur derived from the Tertiary volcanic rocks during hydrothermal alteration through faults commonly developed in this region. Magma originated by the partial melting of the 34S‐enriched oceanic plate intruded into the volcanic rocks and formed magnetite‐series granitoids in the central basin, which contributed to high δ34S values of the metallic deposits. Conversely, ilmenite‐series granitoids were formed by assimilation of sedimentary rocks rich in organic sulfur that influenced the low δ34S values of the deposits in the western and southeastern provinces.

Extreme variation of sulfur isotopic compositions in pyrite from the Qiuling sediment-hosted gold deposit, West Qinling orogen, central China: an in situ SIMS study with implications for the source of sulfur

High spatial resolution textural (scanning electron microscope (SEM)), chemical (electron microprobe (EMP)) and laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS)), and sulfur isotopic (secondary ion mass spectrometry (SIMS)) analyses of pyrite from the Qiuling sediment-hosted gold deposit (232 ± 4 Ma) in the West Qinling orogen, central China were conducted to distinguish pyrite types and gain insights into the source and evolution of sulfur in hydrothermal fluids. The results reveal an enormous variation (−27.1 to +69.6 ‰) in sulfur isotopic composition of pyrite deposited during three paragenetic stages. Pre-ore framboidal pyrite, which is characterized by low concentrations of As, Au, Cu, Co, and Ni, has negative δ34S values of −27.1 to −7.6 ‰ that are interpreted in terms of bacterial reduction of marine sulfate during sedimentation and diagenesis of the Paleozoic carbonate and clastic sequences, the predominant lithologies in the deposit area, and the most important hosts of many sediment-hosted gold deposits throughout the West Qinling orogen. The ore-stage hydrothermal pyrite contains high concentrations of Au, As, Cu, Sb, Tl, and Bi and has a relatively narrow range of positive δ34S values ranging from +8.1 to +15.2 ‰. The sulfur isotope data are comparable to those of ore pyrite from many Triassic orogenic gold deposits and Paleozoic sedimentary exhalative (SEDEX) Pb-Zn deposits in the West Qinling orogen, both being hosted mainly in the Devonian sequence. This similarity indicates that sulfur, responsible for the auriferous pyrite at Qiuling, was largely derived from the metamorphic devolatization of Paleozoic marine sedimentary rocks. Post-ore-stage pyrite, which is significantly enriched in Co and Ni but depleted in Au and As, has unusually high δ34S values ranging from +37.4 to +69.6 ‰, that are interpreted to result from thermochemical reduction of evaporite sulfates in underlying Cambrian sedimentary rocks with very high δ34S values. The variations in Au content and sulfur isotopic compositions across a single ore-stage pyrite grain may reflect displacement of indigenous groundwater with low δ34S values by auriferous metamorphic fluids with high δ34S values. The very low-grade metamorphism of the host rocks and the metamorphic derivation of sulfur for the ore pyrite indicate that the Qiuling sediment-hosted gold deposit is an epizonal manifestation of an orogenic gold system in the West Qinling orogen.

Isotope (S–Sr–Nd–Pb) constraints on the genesis of the ca. 850 Ma Tumen Mo–F deposit in the Qinling Orogen, China

The Tumen Mo–F deposit is located on the southern margin of the North China Craton in central China. The deposit represents a fluorite-vein system hosted by carbonate rocks in the Neoproterozoic Luanchuan Group. Previous studies identify four hydrothermal stages at the deposit characterized by: Stage 1 veins of white fluorite, Stage 2 purple fluorite–molybdenite–pyrite (–galena), Stage 3 calcite–galena–pyrite–sphalerite (–chalcopyrite), and Stage 4 carbonate assemblages.The δ34S values for sulfides from the Tumen deposit range between −7.1 and 5.0‰, with a bimodal distribution. The Stage 2 sulfides have δ34S values of −2.7 to 5.0‰ that are similar to that of granitic rocks, but different from andesite in the Xiong’er Group, amphibolitic gneiss in the Taihua Supergroup and the carbonaceous shale and chert in the Luanchuan Group. The near-zero δ34S values indicate a possible magmatic source for the Stage 2 fluids. However, the δ34S values for the Stage 3 sulfides have negative mean and a restricted range from −7.1 to −4.6‰, which is different from that of the Xiong’er Group and Taihua Supergroup. The 34S-depleted fluid for the Stage 3 sulfides was inherited from the host rocks in the Luanchuan Group with low δ34S values of −12.4 to 7.2‰.New Sr–Nd–Pb isotope data obtained from fluorite at Tumen indicate that the fluorite has higher Pb-isotope ratios, higher ɛNd(t) and lower ISr(t) values than the host rocks. The results suggests that the ore-forming fluids had ɛNd(t)>−4.8, ISr(t)<0.7068, (206Pb/204Pb)i>17.998, (207Pb/204Pb)i<15.576 and (208Pb/204Pb)i<38.201, which overlap the values of (ɛNd(t)=−3.8 to −1.3, ISr(t)=0.7006–0.7061 for Neoproterozoic syenite in Qinling Orogen. This suggests that the deposit is related to a magmatic hydrothermal vein system associated with Neoproterozoic syenitic magmatism.

Rare earth elements, S and Sr isotopes and origin of barite from Bahariya Oasis, Egypt: Implication for the origin of host iron ores

Based on their occurrences and relation to the host iron ores, barites are classified into: (1) fragmented barite occurs as pebble to sand-size white to yellowish white barite along the unconformity between the Bahariya Formation and iron ores, (2) interstitial barite is present as pockets and lenses of large and pure crystals inside the iron ores interstitial barite inside the iron ores, and (3) disseminated barite occurs at the top of the iron ores of relatively large crystals of barite embedded in hematite and goethite matrix. In the current study, these barites have been analyzed for their rare earth elements (REE) as well as strontium and sulfur isotopes to assess their source and origin as well as the origin of host iron ores.Barite samples from the three types are characterized by low ΣREE contents ranging between 12 and 21ppm. Disseminated barite shows relatively lower ΣREE contents (12ppm) compared to the fragmented (19ppm) and interstitial (21ppm) barites. This is probably due to the relatively higher Fe2O3 in the disseminated barite that might dilute its ΣREE content. Chondrite-normalized REE patterns for the three barite mineralizations exhibit enrichment of light rare earth elements (LREE) relative to heavy rare earth elements (HREE) as shown by the high (La/Yb)N ratios that range between 14 and 45 as well as pronounced negative Ce anomalies varying between 0.03 and 0.18. The 87Sr/86Sr ratios in the analyzed samples vary between 0.707422 and 0.712237. These 87Sr/86Sr values are higher than the 87Sr/86Sr ratios of the seawater at the time of barite formation (Middle Eocene with 87Sr/86Sr ratios of 0.70773 to 0.70778) suggesting a contribution of hydrothermal fluid of high Sr isotope ratios. The δ34S values in the analyzed barites range between 14.39‰ and 18.92‰. The lower δ34S ratios in the studied barites compared with those of the seawater at the time of barite formation (Middle Eocene with δ34S ratios of 20–22‰) is attributed to a possible contribution of hydrothermal fluid of low δ34S values that lowered the δ34S values in the studied barites.Rare earth elements distribution and patterns, as well as strontium and sulfur isotopes suggest a mixing of seawater and a hydrothermal fluid as possible sources for barite mineralizations in the Bahariya Oasis. The seawater source is suggested from the low Ce/La ratios, “V” shape of the rare earth patterns and pronounced negative Ce anomalies. On the other hand, the hydrothermal fluid contribution is evident from the low concentrations of rare earth and the deviation in both S and Sr isotopic compositions from those of the seawater during the time of barites formation (Middle Eocene). The relatively heterogeneous Sr and S isotope ratios among the studied barites suggest the Bahariya Formation and Basement Complex as possible sources of the hydrothermal fluids. The similarity in the REE as well as S and Sr isotopic compositions of the three types of barite suggest that they form simultaneously.As the geology and occurrence of the barites suggest a genetic relationship between these barites and the host iron ores, the mixed seawater and hydrothermal sources model of the barites is still applicable for the source of the host iron ores.

Sulfur isotope and chemical composition of the rainwater at the Three Gorges Reservoir

Rainwater samples were collected at the Three Gorges Reservoir (TGR) from June 2009 to July 2010 and the pH, major ion concentrations and δ34S values of sulfate were measured. The results indicated that the rain in this region was seriously acidized, 60% of the rain events' pH were lower than 5.0. SO42− and NO3− were the main anions, and their volume weighted mean (VWM) values were 161.9μeq/L and 65.2μeq/L, respectively, which accounted for 71%–99% of the total measured anions. Ca2+ and NH4+ were the major cations with VWM values of 108.3μeq/L and 88.4μeq/L. Sum of Ca2+ and NH4+ accounted for 25%–94% of the total cations. Analysis of the seasonal variations of the pH showed that the rainwater was more acidized in summer than in the other seasons. Investigations of neutralization factors (NFs) indicated that the acidity of rainwater in winter and spring was neutralized by NH4+ and Ca2+. Studies of the origins of major ions showed that SO42− and NO3− were from coal combustion and fossil fuels, and Na+ and Cl− were from sea sources, while Ca2+, Mg2+ and K+ were from the continental sources.The δ34S values of SO42− in rainwater ranged from −2.1‰ to 6.1‰ (mean value of 2.1‰). The δ34S values of SO42− in winter were much higher than those in other seasons. Analysis of the δ34S values vs. SO42− of rainwater combined with air mass trajectory showed that atmospheric sulfur at TGR was mainly associated with coal combustion and fossil fuels. The lower δ34S values in summer at TGR could be explained by higher contribution of biogenic sulfur.