共查询到20条相似文献，搜索用时 375 毫秒
1.
非质量硫同位素分馏效应是目前国际上最前沿的稳定同位素地球化学研究领域之一。在简要介绍非质量分馏理论的基础上,对近几年非质量硫同位素分馏效应的最新研究成果进行总结和分析。关于非质量硫同位素分馏的微观来源机制存在较多争议,有待于进一步探索;采用SF6为工作气体是现有硫同位素高精度测定的主要制样技术;非质量硫同位素分馏效应研究为火星大气演化及火星生命痕迹探询、古代大气氧化条件、地球早期硫循环、火山活动对气候的影响等重大地质科学问题的解释开辟了一条独特的新途径。最后对非质量硫同位素分馏领域研究趋势进行了探讨。 相似文献
2.
3.
贵州天柱大河边重晶石矿床硫同位素研究 总被引：4，自引：0，他引：4
对贵州天柱大河边重晶石矿床硫同位素组成进行了系统研究,该矿床重晶石的硫同位素组成为36.7‰-41．6‰,具有比同期海水硫酸盐高得多的硫同位素组成特征,且在834S分布直方图上呈塔式,表明形成该矿床的硫来源单一,主要来自于海水中硫酸盐并经历了较强的生物细菌分馏作用,且矿床形成环境为半封闭一封闭的台地泻湖环境。 相似文献
4.
硫同位素研究在喀拉通克岩体的地壳物质混染过程中有重要意义。通过对块状和浸染状矿石、斑点状和脉状矿石以及围岩中硫化物进行硫同位素测试,分析了黄铜矿、黄铁矿、磁黄铁矿的硫同位素在硫化物中的富集状态,探讨了喀拉通克铜镍矿床硫同位素组成特征及其地质意义。结果表明：块状矿石的同位素测定值与标准值之间的千分偏差δ（34S）为（-1.30～1.84）×10-3,浸染状矿石的δ（34S）为（-2.50～0.85）×10-3,脉状矿石的δ（34S）为（-1.54～3.00）×10-3,围岩中黄铁矿的δ（34S）为（-7.8～-3.3）×10-3;硫同位素在硫化物中的富集从大到小依次为黄铁矿、磁黄铁矿、黄铜矿,说明硫化物之间基本达到了硫同位素平衡;喀拉通克铜镍矿床的硫主要来自于地幔,只在岩浆熔离作用形成的浸染状矿石和岩浆后期热液阶段形成的脉状矿石以及晚期黄铁矿中有少量或局部地壳硫混染的痕迹;地壳硫的加入没有在岩浆源区发生,可能发生在岩浆上升并发生硫化物就地熔离的局部过程中,几乎不对硫饱和及硫化物的熔离产生影响;岩浆在地壳深部发生的橄榄石、铬铁矿等矿物的分离结晶作用,有可能是促使硫饱和与硫化物熔离的主要因素。 相似文献
5.
【研究目的】草莓状黄铁矿广泛存在于现代沉积物和沉积岩中,其成因机制总体上分为有机成因和无机成因两种,尽管两种机制均有理论与实验的支撑,但尚未建立一种具有普遍意义的形成机制。【研究方法】本文对目前草莓状黄铁矿的形成机理、氧化还原环境的应用及后期环境变化的影响进行了系统的综合研究。【研究结果】不同氧化-还原环境下形成的草莓状黄铁矿在粒径、形态以及硫同位素之间均存在较大的差异,可做为反演古氧化-还原环境的指标。草莓状黄铁矿的微晶尽管与粒径具有一定的正相关性,但是两者在形态演化序列、生长模式、聚集因素等方面与古氧化-还原环境的关系尚不清楚。仅凭草莓状黄铁矿粒径与铬还原法测定的硫同位素反演古氧化-还原环境存在一定的局限性,需要其他指标综合判定,尚需进一步开展草莓状黄铁矿原位硫同位素值与粒径对古氧化-还原环境反演的研究。后期氧化可使草莓状黄铁矿表面化学成分发生变化,但粒径分布依然具有古氧化-还原环境的指示意义。【结论】草莓状黄铁矿的实验模拟、理论体系和多学科交叉的研究中仍存在一些问题,尚需进一步研究。 相似文献
6.
元素分析仪-气体同位素质谱法分析硫酸钙样品的硫同位素组成 总被引：2，自引：1，他引：1
硫酸盐硫同位素的常规分析方法是将硫酸盐转化为硫酸钡后搭配双路进样SO2法,该法易于操作、数据稳定,但样品用量大、费时费力,需要繁杂的前处理,无法满足微量分析发展方向的需求。本文以石膏为例,以元素分析仪-气体同位素质谱法(EA-IRMS)直接测定硫酸钙样品硫同位素比值,对同一样品分别采用:①硫酸钙与V2O5混合后包裹于锡杯中密封,直接进行元素分析仪-气体同位素质谱分析;②硫酸钙充分溶于去离子水中,向溶有硫酸钙样品的液体中加入沉淀试剂BaCl2,将生成的硫酸钡沉淀滤出后,用去离子水清洗2~3遍,烘干后与V2O5混合包裹于锡杯中密封再进行质谱测定。实验选取了13件δ34S值变化范围介于-20‰^+30‰之间的天然石膏样品,将获得的硫同位素比值进行对比,二者δ34SV-CDT绝对差值在0.00‰~0.24‰,表明同一样品的硫同位素比值结果在误差范围内基本一致。与常规分析方法相比,本文建立的直接在线分析时无需任何化学前处理,只需直接加入适量的V2O5,V2O5和氧气中的外部氧在瞬间燃烧的过程中替代了硫酸钙本身的氧,生成的SO2气体的氧是均一的,其硫同位素比值能代表样品的硫同位素组成,无需进行氧同位素的校正。经过验证表明,硫酸钙样品的直接在线分析是完全可行的。 相似文献
7.
硫的来源对于了解铁氧化物铜金矿床的形成过程和成因具有重要的意义。文中统计了拉拉铁氧化物铜金矿硫化物的 硫同位素数据,并结合地质特征和矿相学研究,分析和讨论了硫的同位素组成特征和硫的来源。结果表明,拉拉铜金矿硫 同位素组成变化较大(不考虑一个异常样品,δ34S 值极差达到 14.9‰),表明成矿硫来源的多样性;其中,黄铁矿 δ34S 值范 围为 -1.4‰ ~4.9‰(平均 1.8‰),黄铜矿的 δ34S 值范围为 -5.9‰ ~9‰(平均 1.5‰)。结合硫化物的生成机制分析,并与其 他典型矿床硫同位素数据对比,表明海水沉淀的蒸发岩是黄铁矿和黄铜矿的重要硫来源,但也不能排除岩浆硫的贡献。目 前没有证据支持变质作用减少拉拉矿区硫化物的硫同位素组成差异。 相似文献
8.
地球化学异常成因研究是评价其成矿前景、矿化类型的基础资料。本文借鉴稳定同位素示踪成矿物质来源的原理和方法,将硫同位素引入到地球化学异常成因研究中,通过对乌奴格吐山和垦山试验区Cu矿化体、Cu异常地段硫同位素组成特征的研究,发现在乌奴格吐山试验区Cu矿化及Cu异常地段硫的来源是一致的,表明应用硫同位素组成特征判断地球化学异常成因是可行的;对比发现,垦山试验区Cu异常地段硫同位素值较乌奴格吐山试验区偏高,推断该Cu异常是由后期热液作用形成的,由此针对该异常的地质找矿及工作部署应该围绕热液矿床进行。 相似文献
9.
This study investigates the sulfur and oxygen isotope fractionations of dissimilatory sulfate reduction and works to reconcile the relationships between the oxygen and sulfur isotopic and elemental systems. We report results of experiments with natural populations of sulfate-reducing bacteria using sediment and seawater from a marine lagoon at Fællestrand on the northern shore of the island of Fyn, Denmark. The experiments yielded relatively large magnitude sulfur isotope fractionations for dissimilatory sulfate reduction (up to approximately 45‰ for 34S/32S) with higher δ18O accompanying higher δ34S, similar to that observed in previous studies. The seawater used in the experiments was spiked by addition of 17O-labeled water and the 17O content of residual sulfate was found to depend on the fraction of sulfate reduced in the experiments. The 17O data provides evidence for recycling of sulfur from metabolic intermediates and for an 18O/16O fractionation of ∼25-30‰ for dissimilatory sulfate reduction. The close correlation between the 17O data and the sulfur isotope data suggests that isotopic exchange between cell water and external water (reactor water) was rapid under experimental conditions. The molar ratio of oxygen exchange to sulfate reduction was found to be about 2.5. This value is slightly lower than observed in studies of natural ecosystems [e.g., Wortmann U. G., Chernyavsky B., Bernasconi S. M., Brunner B., Böttcher M. E. and Swart P. K. (2007) Oxygen isotope biogeochemistry of pore water sulfate in the deep biosphere: dominance of isotope exchange reactions with ambient water during microbial sulfate reduction (ODP Site 1130). Geochim. Cosmochim. Acta71, 4221-4232]. Using recent models of sulfur isotope fractionations we find that our combined sulfur and oxygen isotopic data places constraints on the proportion of sulfate recycled to the medium (78-96%), the proportion of sulfur intermediate sulfite that was recycled by way of APS to sulfate and released back to the external sulfate pool (∼70%), and also that a fraction of the sulfur intermediates between sulfite and sulfide were recycled to sulfate. These parameters can be constrained because of the independent information provided by δ18O, δ34S, δ17O labels, and Δ33S. 相似文献
10.
四川布托县乌依铅矿床是川滇黔相邻区赋存于奥陶系大箐组地层中的典型密西西比河谷型矿床之一,其成矿物质来源仍不清楚。本文开展了方铅矿和石膏硫同位素及方铅矿稀土元素地球化学研究,获得方铅矿硫同位素δ~(34)S平均值为-4.04‰(n=31),石膏δ~(34)S平均值为29‰(n=15)。方铅矿稀土元素地球化学表明,轻稀土富集,重稀土明显亏损,稀土配分模式曲线大致向右倾,Eu正异常和Ce负异常。结合前人的硫、铅同位素数据,认为乌依铅矿床硫来源于细菌还原地层中硫酸盐所产生的硫,矿石铅来自上地壳,成矿物质来源为奥陶系大箐组,与峨眉山玄武岩无关。 相似文献
11.
Alexandra V. Turchyn Volker Brüchert Gregory S. Engel Daniel P. Schrag 《Geochimica et cosmochimica acta》2010,74(7):2011-6698
Kinetic isotope effects related to the breaking of chemical bonds drive sulfur isotope fractionation during dissimilatory sulfate reduction (DSR), whereas oxygen isotope fractionation during DSR is dominated by exchange between intercellular sulfur intermediates and water. We use a simplified biochemical model for DSR to explore how a kinetic oxygen isotope effect may be expressed. We then explore these relationships in light of evolving sulfur and oxygen isotope compositions (δ34SSO4 and δ18OSO4) during batch culture growth of twelve strains of sulfate-reducing bacteria. Cultured under conditions to optimize growth and with identical δ18OH2O and initial δ18OSO4, all strains show 34S enrichment, whereas only six strains show significant 18O enrichment. The remaining six show no (or minimal) change in δ18OSO4 over the growth of the bacteria. We use these experimental and theoretical results to address three questions: (i) which sulfur intermediates exchange oxygen isotopes with water, (ii) what is the kinetic oxygen isotope effect related to the reduction of adenosine phosphosulfate (APS) to sulfite (SO32−), (iii) does a kinetic oxygen isotope effect impact the apparent oxygen isotope equilibrium values? We conclude that oxygen isotope exchange between water and a sulfur intermediate likely occurs downstream of APS and that our data constrain the kinetic oxygen isotope fractionation for the reduction of APS to sulfite to be smaller than 4‰. This small oxygen isotope effect impacts the apparent oxygen isotope equilibrium as controlled by the extent to which APS reduction is rate-limiting. 相似文献
12.
Investigating pathways of diagenetic organic matter sulfurization using compound-specific sulfur isotope analysis 总被引：1，自引：0，他引：1
Josef P. Werne Timothy W. Lyons Stefan Schouten Jaap S. Sinninghe Damsté 《Geochimica et cosmochimica acta》2008,72(14):3489-3502
We present the results of compound-specific sulfur isotope analyses performed on organic sulfur compounds (OSCs) isolated from sediments deposited in the euxinic Cariaco Basin, Venezuela. Individual OSCs (sulfurized highly branched isoprenoids and malabaricatriene) have sulfur isotope compositions of ca. −15‰, which is 34S enriched by 5-15‰ relative to coeval bulk organic and inorganic sulfur pools. These observed differences in the sulfur isotope composition of bulk organic sulfur in the kerogen and bitumen pools and individual OSCs demonstrate that there are multiple pathways of organic sulfur formation operating simultaneously in marine sediments. Comparison of our measured compound-specific sulfur isotope data with values predicted using simple isotopic mass balance assumptions suggests that the sulfurization process likely involves multiple sources of inorganic sulfur. Further, the isotopic composition of these various precursor inorganic sulfur species and the specific pathway of sulfur incorporation into organic matter (OM) impart distinct isotopic compositions to the resulting organic sulfur compounds. These data represent the first compound-specific sulfur isotope measurements made in marine sediments, and demonstrate the utility of compound-specific sulfur isotope analysis in identification of inorganic sulfur sources for OM sulfurization and tracking pathways of sulfur incorporation, which will lead to a more complete understanding of diagenetic sulfurization of OM. 相似文献
13.
近年来,在相山铀矿田的西部牛头山地区深部发现了铅锌矿化体,其成因机制不明.为探讨牛头山铅锌矿化体物质来源,开展了硫化物原位硫同位素分析研究.根据硫化物矿物之间的充填和包裹关系判断,铅锌矿化体金属硫化物形成的先后顺序是:黄铁矿形成最早,方铅矿和闪锌矿次之,细脉状黄铜矿形成最晚.利用LA-MC-ICP-MS技术对矿化体中几种金属硫化物分别进行了系统的原位硫同位素分析.结果显示:黄铁矿、闪锌矿、方铅矿、细脉状黄铜矿的δ34S值介于-4.8‰~+5.4‰之间,各硫化物矿物之间硫同位素未达到完全平衡分馏,利用黄铁矿δ34S值得到的矿化流体δ34SΣS值（总硫同位素组成）近似为+3.7‰,与共生矿物对（闪锌矿-方铅矿）图解法得到的闪锌矿和方铅矿沉淀时矿化流体的δ34SΣS值（+3.2‰）相近,表明形成牛头山铅锌矿化体的矿化流体δ34SΣS值大约为+3.7‰,为岩浆硫.结合前人的岩浆岩年龄数据,我们判断该铅锌矿化体金属硫化物的硫可能主要来自次火山岩相花岗斑岩岩浆热液.同一薄片中闪锌矿δ34S值高于共生的方铅矿,表明两者硫同位素基本平衡,利用共生矿物对（闪锌矿-方铅矿）硫同位素温度计计算得出平衡温度为197~476℃,与前人通过脉石矿物流体包裹体得到的铅锌矿化流体温度基本一致.相山火山盆地与相邻的北武夷黄岗山、梨子坑等产铅锌矿的火山盆地具有相似的成矿条件及成矿物质来源,使相山火山盆地具有良好的铅锌多金属找矿前景. 相似文献
14.
G. S. Ripp I. A. Izbrodin E. I. Lastochkin A. G. Doroshkevich M. O. Rampilov V. F. Posokhov 《Geochemistry International》2016,54(9):748-764
Isotope-geochemical study of the Ermakovskoe fluorine–beryllium deposit was carried out to estimate the ore sources and role of host carbonate rocks in its formation. We analyzed oxygen and carbon isotope compositions in marbles, skarn carbonates, ore and post-ore parageneses; oxygen isotope compositions in oxides, silicates, apatite; and sulfur isotope composition in sulfides and sulfates. Sources of fluids participating in the rock and ore formation were determined using hydrogen and oxygen isotope compositions in hydroxyl-bearing minerals: phlogopite from marbles, vesuvian from skarns, eudidymite and bertrandite from ore parageneses, and bavenite of the post-ore stage. Isotopic studies suggest crustal source of sulfur, oxygen, and carbon dioxide, while oxygen and hydrogen isotope compositions in the hydroxyl-bearing minerals points to the contribution of meteoric waters in the formation of the fluorine-beryllium ores. 相似文献
15.
The Prominent Hill deposit is a world-class iron oxide copper–gold (IOCG) deposit in South Australia, characterized by a high Cu/S ratio of the dominant Cu-(Fe) sulfides hosted by hematite breccias. It contains a total resource of 278 Mt of ore at 0.98% Cu and 0.75 g/t Au. Prominent Hill is one of several IOCG deposits and numerous prospects in the Olympic IOCG province that are temporally associated with the 1603–1575 Ma Gawler Range Volcanics, a large igneous province including co-magmatic granitoid intrusions of the Hiltaba Suite. Globally, IOCG deposits share many similar features in terms of their geological environment and mineral association. However, it is not yet clear whether sulfur and copper originate from the same source rocks and which hydrothermal redox processes created the characteristic iron oxide enrichment. Highly variable sulfur isotope compositions of sulfides and sulfates in IOCG deposits have previously been interpreted in terms of diverse sulfur sources that may include contributions from magmatic, sedimentary, seawater or evaporitic sulfur. In order to test these alternatives, we performed a detailed sulfur isotope study of Cu-(Fe) sulfides from Prominent Hill and IOCG prospects nearby. The Prominent Hill deposit shows a wide range in δ34SV-CDT between − 33.5‰ and 29.9‰ for Cu-(Fe) sulfides, and a narrower range of 4.3‰ to 15.8‰ for barite. Iron sulfides (pyrite, pyrrhotite) show a narrow range in sulfur isotope composition, whereas Cu-bearing sulfides show a much wider range, and more negative δ34SV-CDT values on average. We propose a two-stage sulfide mineralization model for the IOCG system in the Prominent Hill area, in which all hydrothermal sulfur is ultimately derived from a magmatic source that had a composition of 4.4 ± 2‰. The diversity in sulfur isotope composition can be produced by different fluid evolution pathways along reducing or oxidizing trajectories. A reduced sulfur evolution pathway is responsible for stage I mineralization, when intrusion-derived magmatic-hydrothermal fluids produced early pyrite and minor chalcopyrite at Prominent Hill, and iron ± copper sulfides in regional magnetite skarns and in some pervasively altered volcanic rocks of the Gawler Range Volcanics. Shallow-venting magmatic-hydrothermal fluids and subaerial volcanic gases that became completely oxidized by reaction with atmospheric oxygen produced sulfate and sulfuric acid with a sulfur isotope composition equal to their magmatic source. This highly oxidized ore fluid probably consisted dominantly of water from the hydrosphere, but contained magmatic solute components, notably sulfate, acidity and Cu. Sulfate reduction produced hydrothermal Cu sulfides with a wide range in sulfur isotope compositions from very negative to moderately positive values. Partial reaction of the Cu-rich stage II fluid with earlier stage I sulfides resulted in mixing of sulfur derived from sulfate reduction and from sulfides deposited during stage I. Modeling of the sulfur isotope fractionation processes in response to reducing and oxidizing pathways demonstrates that the entire spectrum of sulfur isotope data from stage I and stage II mineralization can be explained with a single, ultimately magmatic sulfur source. Such a magmatic sulfur source is also adequate to explain the complete spectrum of sulfur isotope data of other IOCG prospects and deposits in the Olympic province, including Olympic Dam. The results of our study challenge the conventional model that suggests the requirement of multiple and compositionally diverse sulfur sources in hematite-breccia hosted IOCG style mineralization. 相似文献
16.
G. C. Amstutz 《Mineralogy and Petrology》1959,7(1-2):130-133
Four new sulfur isotope ratios of native volcanic sulfur are given and it is shown that isotope distributions are best presented with histograms.Possible causes governing the isotope compositions of native volcanic sulfur are briefly discussed.With 1 Figure 相似文献
17.
Sulfur isotope effects produced by microbial dissimilatory sulfate reduction are used to reconstruct the coupled cycling of carbon and sulfur through geologic time, to constrain the evolution of sulfur-based metabolisms, and to track the oxygenation of Earth’s surface. In this study, we investigate how the coupling of carbon and sulfur metabolisms in batch and continuous cultures of a recently isolated marine sulfate reducing bacterium DMSS-1, a Desulfovibrio sp., influences the fractionation of sulfur isotopes.DMSS-1 grown in batch culture on seven different electron donors (ethanol, glycerol, fructose, glucose, lactate, malate and pyruvate) fractionates 34S/32S ratio from 6‰ to 44‰, demonstrating that the fractionations by an actively growing culture of a single incomplete oxidizing sulfate reducing microbe can span almost the entire range of previously reported values in defined cultures. The magnitude of isotope effect correlates well with cell specific sulfate reduction rates (from 0.7 to 26.1 fmol/cell/day). DMSS-1 grown on lactate in continuous culture produces a larger isotope effect (21-37‰) than the lactate-grown batch culture (6‰), indicating that the isotope effect also depends on the supply rate of the electron donor and microbial growth rate. The largest isotope effect in continuous culture is accompanied by measurable changes in cell length and cellular yield that suggest starvation. The use of multiple sulfur isotopes in the model of metabolic fluxes of sulfur shows that the loss of sulfate from the cell and the intracellular reoxidation of reduced sulfur species contribute to the increase in isotope effects in a correlated manner. Isotope fractionations produced during sulfate reduction in the pure culture of DMSS-1 expand the previously reported range of triple sulfur isotope effects (32S, 33S, and 34S) by marine sulfate reducing bacteria, implying that microbial sulfur disproportionation may have a smaller 33S isotopic fingerprint than previously thought. 相似文献
18.
How to utilize sulfur isotope for many domestic and foreign researchers to trace the sulfur source of metallic sulfide deposit has been explored for many years. Fruitful results have been gained now. Based on summing up the characteristics of sulfur isotopic composition of hydrothermal mineral from metallic sulfide deposits, this paper illuminated the total sulfur isotopic composition of ore-forming fluids is the key factor in estimating the sulfur source. This paper also summarized three approaches about how to obtain the total sulfur isotopic composition (δ34S∑S) of ore-forming fluids. They are physical-chemical equilibrium analysis, mineral paragenetic association analysis and Pinckey-Rafter, respectively. We gave some applied examples and made a brief comment of them as well. There are three points worth noting. Firstly, choosing appropriate approach is a critical factor to acquire the δ34S∑S successfully according to the characteristics of different types of metallic sulfide deposit. Secondly, currently, these above mentioned approaches and applications are effective after the establishment of equilibrium state of sulfur isotope. As to the sulfur isotopic disequilibrium condition in metallic sulfide deposits probably resulted from lower temperature or rapid emplacement, there are quite some problems in theory and technique. Therefore, an in-depth study should also be continued. Thirdly, it is a new development trend to study isotope composition of different forms of sulfur and to discuss their source, forming environment and process respectively, which is probably more effective and significant for tracing sulfur sources of metallic sulfide deposits. 相似文献
19.
黄铁矿特征研究可为页岩沉积环境恢复与页岩气富集保存规律预测提供依据。以贵州岑巩地区岑页1井牛蹄塘组为研究对象,基于岩心、薄片、扫描电镜及微量元素、硫同位素地球化学,确定牛蹄塘组页岩沉积环境及页岩气富集地质条件。研究表明,牛蹄塘组页岩黄铁矿发育为草莓状、自形-半自形及他形(主要为胶状他形)三种形态,不同形态的黄铁矿形成于不同沉积环境,草莓状黄铁矿形成于缺氧还原环境,自形-半自形黄铁矿形成于贫氧环境,胶状他形黄铁矿指示沉积过程有热液活动的参与。测试井牛蹄塘组整体处于较开放的沉积水体,上段为含氧-贫氧环境,硫同位素整体变轻且发生负漂;中段为较缺氧环境,硫同位素跨度大且发生正漂;下段为还原性更强的沉积环境,硫同位素小幅度负漂。黄铁矿含量与有机质富集密切相关,与黄铁矿有关的孔隙为页岩气吸附、保存及运移提供载体,且草莓状黄铁矿指示的缺氧硫化环境更利于有机质保存。研究工作系统梳理了黄铁矿对牛蹄塘组页岩沉积环境及储层页岩气富集的指示作用,为页岩气勘探提供指示。 相似文献
20.
The biogeochemistry of sedimentary sulfur was investigated on the continental shelf off central Chile at water depths between 24 and 88 m under partial influence of an oxygen minimum zone. Dissolved and solid iron and sulfur species, including the sulfur intermediates sulfite, thiosulfate, and elemental sulfur, were analyzed at high resolution in the top 20 cm. All stations were characterized by high rates of sulfate reduction, but only the sediments within the Bay of Concepción contained dissolved sulfide. Due to advection and/or in-situ reoxidation of sulfide, dissolved sulfate was close to bottom water values. Whereas the concentrations of sulfite and thiosulfate were mostly in the submicromolar range, elemental sulfur was by far the dominant sulfur intermediate. Although the large nitrate- and sulfur-storing bacteria Thioploca were abundant, the major part of S0 was located extracellularly. The distribution of sulfur species and dissolved iron suggests the reaction of sulfide with FeOOH as an important pathway for sulfide oxidation and sulfur intermediate formation. This is in agreement with the sulfur isotope composition of co-existing elemental sulfur and iron monosulfides. In the Bay of Concepción, sulfur isotope data suggest that pyrite formation proceeds via the reaction of FeS with polysulfides or H2S. At the shelf stations, on the other hand, pyrite was significantly depleted in 34S relative to its potential precursors FeS and S0. Isotope mass balance considerations suggest further that pyritization at depth includes light sulfide, potentially originating from bacterial sulfur disproportionation. The δ34S-values of pyrite down to −38‰ vs. V-CDT are among the lightest found in organic-rich marine sediments. Seasonal variations in the sulfur isotope composition of dissolved sulfate indicated a dynamic non-steady-state sulfur cycle in the surface sediments. The 18O content of porewater sulfate increased with depth at all sites compared to the bottom water composition due to intracellular isotope exchange reactions during microbial sulfur transformations. 相似文献