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1.
Pyrite is rapidly accumulating at the contact between the Cretaceous limestones of the Florida Platform and the hemipelagic sediments of the abyssal Gulf of Mexico. Sediments sampled with the submersible “Alvin” in 3266 m of water are associated with a dense community of organisms that depend on chemosynthetic primary production as a food source. Analysis of the chemistry, mineralogy, and textural composition of these sediments indicate that iron sulfide mineralization is occurring at the seafloor within an anoxic micro-habitat sustained by the advection of hydrogen sulfide-charged saline brines from the adjacent platform. The chemosynthetic bacteria that directly overlie the sediments oxidize hydrogen sulfide for energy and provide elemental sulfur that reacts with iron monosulfide to form some of the pyrite. The sediments are mixtures of pyrite ( 30 wt.%), BaSr sulfates ( 4 wt.%), clays, and locally derived biogenic carbonates and are progressively being cemented by iron sulfides. Oxidation of hydrogen sulfide produces locally acidic conditions that corrode the adjacent limestones. Potential sources of S, H2S, Fe, Ba, and Sr are discussed.  相似文献   

2.
Hg contents ranging from 0.026 to 0.19 and 0.1 to 344 ppm were measured by activation analysis in a number of pyrite and sphalerite samples, respectively. The release of Hg based on stepwise heating shows a correlation with metamorphic grade of the pyrite samples and with Fe content of the sphalerite samples. Experiments were undertaken to study the equilibration of Hg at different temperatures in Hg-doped laboratory prepared ZnS and FeS2. On subsequent volatilization, trends in the Hg release were observed which paralleled those in the sulfide minerals.  相似文献   

3.
To ascertain the influence of hydrological boundary conditions on acidity fluxes in lakes influenced by acid mine drainage, acidity budgets were developed for two sediments in areas of differential groundwater inflow (approx. 1 L m?2 d?1 and 10 L m?2 d?1). In both sediments iron was deposited as schwertmannite leading to iron(III) enriched sediments (3.9…6.2 mmol g?1, referred to dry weight). Compared to the surface water, the inflowing groundwater had higher pH (4.5 vs. 3), ferrous iron (6…20 mmol L?1 vs. 0.8…2.0 mmol L?1), and sulfate (5…60 mmol L?1 vs. 8…13 mmol L?1) concentrations. The inflow changed the sediment pore water chemistry and triggered a further increase in pH to above 5.5. In both sediments acidity generation in the surface water (10…30 mol m?2 a?1) strongly prevailed over acidity consumption in the sediments (> ?0.6 mol m?2 a?1). With advective groundwater inflow, however, more acidity was consumed due to TRIS formation (?0.12 mol m?2 a?1 vs. ?0.017 mol m?2 a?1), iron carbonate burial (upper estimate: ?0.14 mol m?2 a?1 vs. ?0.022 mol m?2 a?1), and unspecific ferrous iron retention (?0.39 mol m?2 a?1 vs. ?0.08 mol m?2 a?1). Also, less acidity was generated due to schwertmannite transformation (?2.4 mol m?2 a?1 vs. ?0.11 mol m?2 a?1). The acidity balance of internal processes in the sediment with groundwater inflow was negative, whereas it was positive in the other sediment. The study demonstrates that in acidic and iron rich lakes the hydrological boundary conditions strongly affect geochemical processes as subsumed in acidity fluxes.  相似文献   

4.
Previous studies on multiple sulfur isotopes (32S, 33S, and 34S) in sedimentary pyrite at the end-Permian suggested a shoaling of anoxic/sulfidic deep-water contributing to the extinction. This scenario is based on an assumption that the sedimentary sulfur cycle was largely controlled by benthos activity, though a stratigraphic correlation between the sulfur records and ichnofabrics of the sediments at the end-Permian has not yet been examined. We report the multiple sulfur isotopic composition of pyrite in the Permian–Triassic boundary interval at Chaotian, South China. Our data can be generally explained by a mixing of sulfur in sulfide from two different sources: one produced via sulfate reduction in an open system with respect to sulfate and the other produced in a closed system. In particular, the former with the substantially low δ34S (<−40 ‰) and high ∆33S (up to +0.100 ‰) values was likely produced via water-mass sulfate reduction or via sulfate reduction in oxic sediments with common burrows. The frequent occurrence of small pyrite framboids (mostly <5 μm in diameter) in the Lopingian (Late Permian) Dalong Formation of deep-water facies supports the enhanced water-mass sulfate reduction in an anoxic deep-water mass. The negative ∆33S values are observed only in the oxic limestones, and no substantial ∆33S change is observed across the extinction horizon despite of the disappearance of bioturbation. Our results are apparently inconsistent with the previous shoaling model. We expand the model and infer that, when the deep-water was sulfidic and its shoaling rate was high, a substantial amount of hydrogen sulfide (H2S) was supplied onto the shelf via the shoaling; that resulted in the positive ∆33S value of the bulk sediments. The observed ∆33S variation on a global scale suggests a substantial variation in H2S concentration and/or in upwelling rate of shoaling deep-waters during the Permian–Triassic transition.  相似文献   

5.
Biogreigites are formed inside sulfate reducing bacteria through crystallization of a 3D nanocrystal of Fe3S4 surrounded by a liposome. Two different types of clusters of twinned ferrimagnetic structures can be found, magnetotactic and framboidal biogreigites. Biogreigites are only stable under anoxic conditions. Under oxic conditions, ferrimagnetic biogreigites (Fe3S4) react to non-magnetic pyrite (FeS2) and FeOOH. We investigated gravity cores of the Black and the Marmara Sea as well as sediments of the Cretaceous/Paleogene (K/T) fallout from the meteorite impact (??66 million years ago) at Chicxulub (Yucatan, Mexico) regarding their greigite content. The samples were analyzed by X-ray diffractometry, ore microscopy, transmission, and scanning electron microscopy. Four applications of cluster analyses of twinned nanocrystalline greigites in sediments are presented: Proof of the evidence of sulfuric acid rain, investigation of climatic cycles in the Black Sea, analysis of the evolution of water and sediment flow in a sublacustrine river valley, and determination of the velocity and the amount of the water transport through the Bosporus.  相似文献   

6.
A detailed geochemical-petrological examination of layer 2 basalts recovered during Leg 37 of the DSDP has revealed that the original distribution, form and abundance of igneous sulfide have been profoundly altered during low-grade oxidative diagenesis. The net result appears to have been a rather pervasive remobilization of igneous sulfide to form secondary pyrite accompanied by a bulk loss of sulfur equivalent to about 50–60% of the original igneous value, assuming initial saturation. It is suggested that during infiltration of seawater into the massive crystal-line rock, igneous sulfide has experienced pervasive oxidation, under conditions of limited oxidation potential, to form a series of unstable, soluble sulfur species, primarily in the form of SO32? and S2O32?. Spontaneous decomposition of these intermediate compounds through disproportionation has resulted in partial reconstitution of the sulfur as secondary pyrite and the generation of SO42? ion, which, due to its kinetic stability, has been lost from the basalt system and ultimately transferred to the ocean. This model not only satisfies the geochemical and petrological observations but also provides a suitable explanation for the highly variable δ34S values which characterize secondary sulfides in deep ocean floor basalts.  相似文献   

7.
Implementation of aquifer storage recovery (ASR) for water resource management in Florida is impeded by arsenic mobilization. Arsenic, released by pyrite oxidation during the recharge phase, sometimes results in groundwater concentrations that exceed the 10 µg/L criterion defined in the Safe Drinking Water Act. ASR was proposed as a major storage component for the Comprehensive Everglades Restoration Plan (CERP), in which excess surface water is stored during the wet season, and then distributed during the dry season for ecosystem restoration. To evaluate ASR system performance for CERP goals, three cycle tests were conducted, with extensive water‐quality monitoring in the Upper Floridan Aquifer (UFA) at the Kissimmee River ASR (KRASR) pilot system. During each cycle test, redox evolution from sub‐oxic to sulfate‐reducing conditions occurs in the UFA storage zone, as indicated by decreasing Fe2+/H2S mass ratios. Arsenic, released by pyrite oxidation during recharge, is sequestered during storage and recovery by co‐precipitation with iron sulfide. Mineral saturation indices indicate that amorphous iron oxide (a sorption surface for arsenic) is stable only during oxic and sub‐oxic conditions of the recharge phase, but iron sulfide (which co‐precipitates arsenic) is stable during the sulfate‐reducing conditions of the storage and recovery phases. Resultant arsenic concentrations in recovered water are below the 10 µg/L regulatory criterion during cycle tests 2 and 3. The arsenic sequestration process is appropriate for other ASR systems that recharge treated surface water into a sulfate‐reducing aquifer.  相似文献   

8.
The transport of reactive iron (i.e. colloidal and dissolved) by a glacier‐fed stream system draining a high relief periglacial landscape in the high Arctic archipelago of Svalbard is described. A negative, non‐linear relationship between discharge and iron concentration is found, indicative of increased iron acquisition along baseflow pathways. Because the glaciers are cold‐based and there are no intra‐ or sub‐permafrost groundwater springs, baseflow is principally supplied by the active layer and the colluvial and alluvial sediments in the lower valley. Collectively, these environments increase the flux of iron in the stream by 40% over a floodplain length of just 8 km, resulting in 6 kg Fe km?2a?1 of reactive iron export for a 20% glacierized watershed. We show that pyrite oxidation in shallow‐groundwater flowpaths of the floodplain is the most important source of reactive iron, although it is far less influential in the upper parts of the catchment where other sources are significant (including ironstone and secondary oxide coatings). Microbial catalysis of the pyrite oxidation occurs in the floodplain, enabling rapid, hyporheic water exchange to enhance the iron fluxes at high discharge and cause the non‐linear relationship between discharge and reactive iron concentrations. Furthermore, because the pyrite oxidation is tightly coupled to carbonate and silicate mineral weathering, other nutrients such as base cations and silica are also released to the stream system. Our work therefore shows that high Arctic floodplains should be regarded as critically important regulators of terrestrial nutrient fluxes to coastal ecosystems from glacial and periglacial sources. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

9.
Elemental sulfur in northern South China Sea sediments and its significance   总被引：2，自引：0，他引：2  
Elemental sulfur(ES) is one of the intermediates in the inorganic sulfur cycle and thus plays a key role in the fractionation of stable sulfur isotopes in different reservoirs and the marine environment. In this study, solid ES is discovered in sediments near the Jiulong Methane Reef in the northern South China Sea by scanning electron microscopy and Raman spectroscopy. Combining the morphology and distribution of ES, pyrite concentrations, and sulfur isotopes, we conclude that:(1) solid ES coexists with pyrite microcrystals and sulfide(oxyhydr)oxides as well as clay minerals, and they are mainly distributed on the surface of mineral aggregates;(2) ES mainly occurs within and near the sulfate-methane transition zone(SMTZ) despite little morphological diversity;(3) ES formation might be related to hydrogen sulfide oxidation and is therefore linked with fluctuations in the SMTZ. Within the SMTZ, hydrogen sulfide is produced and pyrite precipitates because of enhanced anaerobic oxidation of methane coupled with dissimilatory sulfate reduction. This enhances the efficiency of the inorganic sulfur cycle and provides favorable conditions for ES formation. The discovery of solid ES in sediments near the Jiulong Methane Reef suggests an important relationship with SMTZ fluctuations that could have implications for the evolution of methane hydrate in the South China Sea.  相似文献   

10.
Stable isotope ratios of S, O and Sr have been measured for active vent materials which were first found and sampled in April 1987 from the Mariana backarc spreading axis at 18°N. Chimneys consisted mostly of barite with a lesser proportion of sulfide minerals such as sphalerite, galena, chalcopyrite and pyrite. Theδ34S values of sphalerite and galena taken from several chimneys and various parts of a chimney showed a narrow range from 2.1 to 3.1‰, suggesting uniform conditions of fluid chemistry during chimney growth. The sulfur isotopic results imply a contribution of hydrogen sulfide reduced from seawater sulfate in the deep hydrothermal reaction zone, considering that fresh glasses of the Mariana Trough basalts haveδ34S= −0.6 ± 0.3‰. Sulfur isotopic compositions of hydrogen sulfide in the high temperature vent fluids (δ34S= 3.6–4.8‰) which are higher than those of the sulfide minerals suggest the secondary addition of hydrogen sulfide partially reduced from entrained seawater SO42− at a basal part of the chimneys. This interpretation is consistent with theδ34S values of barite (21–22‰) that are higher than those of seawater sulfate. The residence time of the entrained SO42− was an order of an hour on a basis of oxygen isotopic disequilibrium of barite. Strontium isotopic variations of barite and vent waters indicated that Sr in barite was mostly derived from the Mariana Trough basalts with a slight contribution from Sr in circulating sea-water, and that 10–20% mixing of seawater with ascending hydrothermal fluids induced precipitation of barite at the sea-floor.  相似文献   

11.
The sediment of Lagoa dos Patos‐MS, Brazil, was investigated to verify the influence of metal sulfides and oxyhydroxides of Mn and Fe on the heavy metal availability. The spectrophotometric method of methylene blue was used, with 8 interlinked tubes containing the samples with SnCl2, where N2 was introduced to release the H2S extracted with 6.0 mol L–1 HCl, and trapped in 0.05 M NaOH solution. The influence of SO42–, Mn(IV) and Fe(III) oxyhydroxides was investigated with samples constituted by a mixture of MnO2; Na2SO4; FeCl3, and sediments. The presence of SnCl2 was very important to avoid the interferences of iron and manganese oxyhydroxides. The method of standard addition was applied and the efficiency was (100.8 ± 9.4)%. The ratio among the quantities of metals potentially available and the acid volatile sulfide (AVS) indicate that the system presents small metals availability to the benthic community, by the existence of sulfide capable to immobilize the metal as insoluble sulfide.  相似文献   

12.
Depth profiles of solute chemistry and sulfate isotopic compositions are presented for groundwater and pore water in a sequence of Quaternary glacial outwash sediments. Sand units show evidence for hydraulic connection to the surface and thus modern sources of solutes. Finer‐grained sediments show a general pattern of increasing solute concentrations with depth, with sulfate derived from ancient rainwater and pyrite oxidation in the soil/drift. In these sediments sulfate has undergone bacterial sulfate reduction (BSR) to produce biogenic sulfide. In clay sediments, with d10 ≤ 1·6 µm, high concentrations of sulfate and acetate now co‐exist, implying that BSR is inhibited. The correlation with smaller sediment grain size indicates that this is due to pore size exclusion of the sulfate reducing bacteria. Mechanical restriction of microbial function thus provides a fundamental limitation on microbial respiration in buried clay‐rich sediments, which acts as a control on the chemical evolution of their pore waters. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

13.
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14.
Pyrite (FeS2) oxidation in modern sedimentary environments is neither a purely chemical nor purely microbial process, but it is significantly enhanced by the activity of microorganisms that use reduced forms of iron and sulphur in their metabolisms. On the early Earth, where oxygen levels were thought to be < 10?5 of the present atmospheric level and chemical oxidants scarce, such biological mediation may have been critical in the redox cycles of iron and sulphur. Here, we show that detrital sedimentary pyrite grains in a ~ 3.4 billion-year-old sandstone were colonised by microbial communities. The detrital pyrite comes from the basal quartz arenite member of the 3.43–3.35 Ga Strelley Pool Formation (SPF) in the East Strelley greenstone belt of the Pilbara Craton, Western Australia. Rock chips and petrographic thin sections of black sandstones occurring on two ridges close to the SPF type locality of Strelley Pool were investigated using optical microscopy, SEM, TEM, laser Raman and NanoSIMS. The detrital pyrite grains exhibit laminated carbonaceous coatings of early Archean age, with localised enrichments of nitrogen that are interpreted as the in situ remains of biofilms growing on these nutrient-rich minerals. Pyrite surfaces contain spherical pits, chains of pits and channels that are morphologically distinct from abiotic alteration features. The pits and channels are widespread, have a clustered distribution typical of microbial colonisation, and are closely comparable to biologically mediated microstructures in the younger rock record and those created by extant Fe- and S-oxidising microbes in the laboratory. They are thus interpreted as trace fossils formed by the attachment of bacteria to the pyrite surfaces. A nano-layer and discreet nano-grains of secondary mineral precipitates, namely Fe-oxides belonging to the magnetite-maghaemite group, attest to pyrite oxidation. These are intimately associated with the biofilms and trace fossils, and are interpreted to represent the fossilised mineral products of biologically mediated pyrite oxidation. These data extend the geological range of microbes capable of metabolising reduced Fe and/or S compounds back to the early Archean and indicate that pyrite-rich sedimentary rocks provide promising targets in the search for extraterrestrial life.  相似文献   

15.
Abiotic degradation of chlorinated solvents by reactive iron minerals such as iron sulfides, magnetite, green rust, and other Fe(II)‐containing minerals has been observed in both laboratory and field studies. These reactive iron minerals form under iron‐ and sulfate‐reducing conditions which are commonly found in permeable reactive barriers (PRBs), enhanced reductive dechlorination (ERD) treatment locations, landfills, and aquifers that are chemically reducing. The objective of this review is to synthesize current understanding of abiotic degradation of chlorinated solvents by reactive iron minerals, with special focus on how abiotic processes relate to groundwater remediation. Degradation of chlorinated solvents by reactive minerals can proceed through reductive elimination, hydrogenolysis, dehydrohalogenation, and hydrolysis reactions. Degradation products of abiotic reactions depend on degradation pathways and parent compounds. Some degradation products (e.g., acetylene) have the potential to serve as a signature product for demonstrating abiotic reactions. Laboratory and field studies show that various minerals have a range of reactivity toward chlorinated solvents. A general trend of mineral reactivity for degradation of chlorinated solvents can be approximated as follows: disordered FeS > FeS > Fe(0) > FeS2 > sorbed Fe2+ > green rust = magnetite > biotite = vermiculite. Reaction kinetics are also influenced by factors such as pH, natural organic matter (NOM), coexisting metal ions, and sulfide concentration in the system. In practice, abiotic reactions can be engineered to stimulate reactive mineral formation for groundwater remediation. Under appropriate site geochemical conditions, abiotic reactions can occur naturally, and can be incorporated into remedial strategies such as monitored natural attenuation.  相似文献   

16.
A critical evaluation of literature values for the solubility products, K sp NBS = [Fe2+][HS–] Fe2+ HS– (H NBS + )–1, of various iron sulphide phases results in consensus values for the pKs of 2.95 ± 0.1 for amorphous ferrous sulphide, 3.6 ± 0.2 for mackinawite, 4.4 ± 0.1 for greigite, 5.1 ± 0.1 for pyrrhotite, 5.25 ± 0.2 for troilite and 16.4 ± 1.2 for pyrite.Where the analogous ion activity products have been measured in anoxic freshwaters in which there is evidence for the presence of solid phase FeS, the values lie within the range of 2.6–3.22, indicating that amorphous iron sulphide is the controlling phase. The single value for a groundwater of 2.65 (2.98 considering carbonate complexation) agrees. In seawater four values range between 3.85 to 4.2, indicating that mackinawite or greigite may be the controlling phase. The single low value of 2.94 is in a situation where particularly high fluxes of Fe (II) and S (–II) may result in the preferential precipitation of amorphous iron sulphide. Formation of framboidal pyrite in these sulphidic environments may occur in micro-niches and does not appear to influence bulk concentrations. Calculations show that the formation of Fe2S2 species probably accounts for very little of the iron or sulphide in most natural waters. Previously reported stability constants for the formation of Fe (HS)2 and (Fe (HS)3)– are shown to be suspect, and these species are also thought to be negligible in natural waters. In completely anoxic pore waters polysulphides also have a negligible effect on speciation, but in tidal sediments they may reach appreciable concentrations and lead to the direct formation of pyrite. Concentrations of iron and sulphide in pore waters can be controlled by the more soluble iron sulphide phase. The change in the IAP with depth within the sediment may reflect ageing of the solid phase or a greater flux of Fe (II) and S (–II) nearer the sediment surface. This possible kinetic influence on the value of IAPs has implications for their use in geochemical studies involving phase formation.  相似文献   

17.
Intermittent anoxia in the Saanich Inlet water column provides an easily accessible marine O2/H2S interface to study the response of metals to both a steep redox gradient and the availability of reactive reduced sulfur species. Our study indicates a strong anoxic zone sink for copper and cadmium and the characteristically enhanced solubility of manganese and iron. Thiosulfate and sulfite are below detection limits (1 μM and 0.1 μM, respectively) and thus not important in metal complexation. Elemental sulfur concentrations are high at the oxic/anoxic interface and throughout the anoxic zone, indicating the potential for metal complexation by polysulfides. A thermodynamic approach employing metal sulfide formation and class specific sulfidic ligand complexation to generate equilibrium profiles adequately describes the solubility of iron, copper, and cadmium. The extension of this scheme to other transition and class B metals in other marine environments with redox fronts is suggested.  相似文献   

18.
In the Youngcheon Diversion Tunnel area, South Korea, 46 samples of tunnel seepage water (TSW) and borehole groundwater were collected from areas with sedimentary rocks (mainly sandstone and shale) and were examined for hydrogeochemical characteristics. The measured SO4 concentrations range widely from 7·7 to 942·0 mg/l, and exceed the Korean Drinking Water Standard (200 mg/l) in about half the samples. The TDS (total dissolved solid) content generally is high (171–1461 mg/l) from more shale‐rich formations and also reflects varying degrees of water–rock interaction. The water is classified into three groups: Ca? SO4 type (61% of the samples collected), Ca? SO4? HCO3 type (15%) and Ca? HCO3 type (24%). The Ca? HCO3 type water (mean concentrations=369 mg/l Ca, 148 mg/l HCO3 and 23 mg/l SO4) reflected the simple reaction between CO2‐recharged water and calcite, whereas the more SO4‐rich nature of Ca? SO4 type water (mean concentrations=153 mg/l Ca, 66 mg/l HCO3 and 416 mg/l SO4) reflected the oxidation of pyrite in sedimentary rocks and fracture zones. Pyrite oxidation resulted in precipitation of amorphous iron hydroxide locally within the tunnel as well as in high concentrations of Ca (mean 153 mg/l) and Na (mean 49 mg/l) for TSW, and is associated with calcite dissolution resulting in pH buffering. The pyrite oxidation required for the formation of Ca? SO4 type water was enhanced by the diffusion of oxygenated air through the fractures related to the tunnel's construction. The subsequent outgassing of CO2 into the tunnel resulted in precipitation of iron‐bearing carbonate. Copyright © 2001 John Wiley & Sons, Ltd.  相似文献   

19.
The results of biogeochemical and microbiological studies of three small lakes in southwestern Arkhangelsk province are presented. The lakes differ in their morphometric characteristics, thermal and oxygen regimes, and the extent of anthropogenic impact they experience. In the periods of summer and winter stratification, anaerobic water layers with higher phosphates, ammonium, and sulfide sulfur (hydrogen sulfide) are found to form in the bottom horizon of deep-water zones of the lakes. The highest concentrations of sulfide sulfur (150–210 μg dm−3) were recorded in the shallow Beloe Lake during winter low-water period, while in summer, sulfide concentration did not differ from those obtained in other lakes (∼10 μg dm−3). The abundance of sulfate-reducing bacteria in lake bottom sediments varied from 10 to 100000 cell cm−3, and the rate of sulfate reduction process varied from 29 to 3746 μg S dm−3 day−1. Seasonal variations were revealed in hydrogen sulfide distribution over the water column and in the rate of sulfate reduction process in the upper horizons of bottom sediments in the examined lakes.  相似文献   

20.
Chemical data presented in this paper indicate a good correlation between P2O5 and Fe2O3 in some iron-rich volcanogenic sediments from the East Pacific Rise. In addition, adsorption experiments and chemical analyses of deuterically altered and unaltered samples of submarine basalts strongly suggest that this association is due to the reaction of phosphate in sea water with poorly crystallized hydrous ferric oxides. East Pacific Rise sediments adsorb far greater amounts of phosphate from sea water than either carbonate or non-carbonate sediments from other areas of the ocean. From geochemical flux calculations it is concluded that an appreciable proportion of dissolved phosphate delivered to the oceans by rivers is removed by ridge crest volcanogenic iron oxides either as absorbed surface coatings or as discrete, but highly disordered, ferric phosphate phases. This process should be taken into consideration when considering oceanic phosphate budgets, both in the present and past oceans.  相似文献   

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