电感耦合等离子体发射光谱法测定西藏日多温泉地热水中11种主次量元素

西藏地热水的矿化度普遍较高,矿物质种类丰富,本文建立了采用电感耦合等离子体发射光谱(ICP-OES)同时测定西藏日多温泉地热水中11种主次量元素(钾钠钙镁硅硼锂锶砷铁和硫酸根)的分析方法。使用双向观测模式可确保不同浓度元素的同时检出,且地热水采用1%硝酸介质保存,在5周时间内11种元素含量的测定值基本稳定。方法检出限为0.0006~0.0162 mg/L,加标回收率为95.5%~105.8%,精密度(RSD,n=10)均小于6%,实际水样的测试结果与传统方法基本吻合。本方法为西藏温泉的水文地球化学研究提供了大量可靠的数据。     

电感耦合等离子体发射光谱法测定地表水和地下水中的硫酸根

建立了盐酸直接酸化地表水和地下水,电感耦合等离子体发射光谱法测定硫酸根含量的方法。方法检出限为0.031 mg/L。在硫波长182.0 nm处测定的线性范围为0.03~100 mg/L,182.6 nm处的线性范围为100~700 mg/L。对实际水样进行连续12次测定,方法精密度(RSD)为0.76%。经国家水标准物质验证,结果与标准值相符。方法快速、准确。     

氧化性岩浆与斑岩铜金成矿

<正>我们研究发现,高氧逸度和洋壳部分熔融是控制斑岩铜(金)矿床形成的两个关键。作为亲硫元素,铜(金)的性质受还原态的硫(S2-)的控制,而硫的性质受氧逸度的控制:硫酸盐在岩浆中的溶解度是硫化物的十倍。岩浆形成过程中,在ΔFMQ+2以上时,硫主要以硫酸盐形式存在。有利于源区硫化物被破坏,大幅度提高初始岩浆铜金含量高;与此同时,岩浆中硫化物保持不饱和状态,有利于铜金通过岩浆演化进一步富集。在磁铁矿结晶等过程中,岩浆体系的氧逸度降低,硫酸根被还原,还原态的硫(S2-)将岩浆中的     

大陆环境与Cu(Au)成矿有关的岩浆氧逸度特征及形成机制:以金沙江—红河富碱岩为例

岩浆氧逸度是制约Cu、Au成矿的重要因素之一,Cu、Au为亲硫元素,岩浆结晶分异过程中如果S2-大量存在就会导致Cu、Au硫化物过饱和而过早沉淀,不利于残余岩浆中Cu、Au的富集和晚阶段含Cu、Au岩浆流体的形成,因而不利于Cu、Au矿床的形成。高氧逸度条件下,岩浆中的硫绝大多数以SO42-和SO2形式溶解在硅酸盐熔体中,能形成硫化物的S2-含量很低,硫化物     

地热水中竞争巯基化影响下的砷、锑形态分布：以西藏阿里典型水热区为例

砷、锑是地热水中的典型有害组分,受地热水独特水化学条件影响,常呈现与其他类型天然水体相异的形态分布特征。本文以西藏阿里的朗久、曲色涌巴、门士、莫落江等地热区为研究区,分析了含硫化物地热水中砷、锑在竞争巯基化过程影响下的形态分布特征。受富砷、锑岩浆流体输入或高温条件下热储围岩加强淋滤的影响,上述地热区排泄的地热水中砷、锑浓度范围分别可达5 833～20 750μg/L和579～2 129μg/L。地热水中砷以亚砷酸盐和砷酸盐为主要存在形态,但同时存在占总砷百分比在0.1%～55.1%之间的硫代砷酸盐;与砷的情况不同,地热水中锑检测出的形态均为亚锑酸盐和/或锑酸盐,所有样品中均未检出硫代锑酸盐。考虑到相当一部分地热水样品的S/Sb摩尔比在理论上满足硫代锑酸盐的形成条件,且所有样品中砷的富集程度均不同程度高于锑,我们认为地热水中锑的含氧络阴离子的巯基化过程受到了共存砷的强烈抑制。在硫化物相对于砷、锑总量并不充分盈余的情况下,砷的竞争巯基化是控制地热水中硫代锑酸盐形成的最重要因素。本工作及其研究结果有助于深入理解西藏地热水环境中砷、锑的环境地球化学行为。     

陕西柞水银洞子银铅矿床硫同位素地质研究

在银洞子银铅矿床中,硫同位素组成变化很大,围岩地层中硫化物的δ~(34)S/‰值为-3.2—+6.5,13号矿体的硫同位素以富集重硫为特征,硫化物和硫酸盐的δ~(34)S/‰值为+4—+28.48,而小铅矿体群的硫同位素以相对富集轻硫为特征,硫化物的δ~(34)S/‰为-3.5—+4.67,其顶板岩石为接近零的负值.研究表明,矿体和围岩中的硫主要来自封闭盆地中海水硫酸盐的还原,沉积环境经历了对H_2S的封闭—开放—封闭的过程,矿体是在海底热卤水中沉积形成的,硫化物的δ~(34)值受沉积环境和热卤水的物理化学条件所制约.     

腾冲热海地热田高温热泉中的硫代砷化物及其地球化学成因

以我国大陆范围内典型的岩浆热源型水热系统——云南腾冲热海为研究区,在国内首次对热泉中硫代砷化物含量及其地球化学成因进行了分析.研究采用的在野外对富硫化物水样进行快速冷冻处理、而后在实验室进行砷的形态分离和测试的方法明显优于当前通用的水样砷含量及其形态分析的预处理和测试方法.主要原因为后者在采样现场对水样的酸化处理可使样品中三硫代砷酸盐以非定形态硫砷化合物的形式沉淀,且用常规阴离子交换柱在野外无法实现硫代砷酸盐的完全回收及其与砷酸盐的分离.受岩浆流体输入和热储内高温条件下强烈流体-岩石相互作用的控制,热海水热系统排泄的中性-偏碱性热泉中富集硫化物和砷,为热泉中硫代砷化物的形成提供了必要条件.热海热泉中检出的硫代砷化物包括一硫代砷酸盐、二硫代砷酸盐和三硫代砷酸盐,在总砷中所占比例最高分别可达26.7%、43.3%和33.7%.热海地热田的2个子区(硫磺塘和澡塘河) 的热泉沿不同断裂带出露,地热水升流过程中经历的冷却方式也不同,使硫磺塘热泉具有相对较高的总硫化物含量和总砷含量,并导致其中各类硫代砷酸盐具有更高的含量范围.      

答读者问

孙素芬同志:伏尔科夫法测定铀的几个问题的解答之四——干扰元素的影响1.含有大量的硫酸根离子,对四价铀磷酸盐的沉淀起着不良的影响,此时磷酸盐沉淀凝结很慢,并生成细小的沉淀。如溶液含有10毫克硫酸铵时,会引起沉淀不完全,会引起结果偏低。此干扰可用氢氧化铵使铀成为重铀酸铵沉淀以与硫酸根离子分离的方法消除之。2.含有大量铅时,如二硫四氧酸钠生成白色的二硫四氧酸铅沉淀,而在用33％硫酸溶解时生成亚硫酸,这样会使结果偏高。在这种情况下,沉淀后须加热到60-80℃使它能转变为黑色的硫化物,这样就不妨碍铀的测定。当溶液中含有铜、铋、钼、砷、     

贵州东南部地热水地球化学特征及成因

为探讨贵州东南部地热水的地球化学特征、控制因素及补给来源和补给年龄,采集了7组地热水样进行离子特征、~(87)Sr/~(86)Sr、~3H和~(14)C,δD与δ~(18)O稳定同位素分析。结果表明,贵州东南部地热水温度为23.5～50℃,溶解性总固体(TDS)为192.38～1 103.21 mg/L,~(87)Sr/~(86)Sr值为0.717 9～0.731 6,δD和δ~(18)O分别为-69.8‰～-54.3‰与-10.49‰～-8.19‰。区内水化学类型均为HCO_3-Na型,并含有一定量的F、H_2SiO_3。~(87)Sr/~(86)Sr值表明硅酸盐矿物的溶解是控制区内水化学组分的主要因素,富含CO_2的大气降水与钠长石的溶解为Na~+和HCO~-_3的主要来源,F主要来源于萤石的溶解,石英的溶解为H_2SiO_3的主要来源。H、O同位素组成指示地热水的补给来源为大气降水,H2、H3有明显的氧漂移,主要是水-岩作用程度较低与高程效应的影响。~3H和~(14)C测年结果表明,区内地热水为1952年前入渗补给的"古水",校正的~(14)C年龄为10 975～33 263 a,表明地热水经过长时间、远距离的径流。     

X射线荧光光谱法测定富含硫砷钒铁矿石中的主次量元素

以钴(钴玻璃粉形式)作内标元素,准确测定全铁含量;加入保护剂硝酸铵和稳定剂碳酸锂,使硫转化为硫酸盐,有效地防止硫的挥发损失。通过条件实验,确立了样品熔融温度和钴玻璃粉的用量。选择经筛选的仪器测定条件,用X射线荧光光谱法同时测定铁矿石中TFe、SiO2、CaO、MgO、Al2O3、TiO2、P、S、Mn、V2O5、As、K2O、Na2O、Cu、Ni等15种主次量元素。采用干扰曲线法对几乎完全重叠的TiΚβ谱线与VΚα谱线进行谱线重叠校正,用理论α系数法校正基体效应。建立的方法可以准确测定全铁和质量分数高达5.29%的S。采用多种标准物质和人工配制标准物质制作工作曲线,可以测定质量分数为5.00%的V2O5及0.1%的As,测定值与标准值符合较好,除低含量钠外方法精密度(RSD)<3.5%,分析误差符合实验质量要求。本法可以快速、准确地测定含砷的钒钛铁矿及含硫高的铁矿石中的主次量元素,满足了日常生产对铁矿石中硫和钒的测定要求。     

电感耦合等离子体质谱法测定硫时不同形态硫的影响

电感耦合等离子体质谱(ICP-MS)常常被应用于矿石、蛋白质和化石燃料等材料中硫含量的测定。文章综合研究比较了四极杆电感耦合等离子体质谱(Q-ICP-MS)和扇形磁场电感耦合等离子体质谱(SF-ICP-MS)测定硫的灵敏度、检出限及空白干扰。重点考察了两种不同的样品介质(水和2% HNO₃)中不同形态的硫对SF-ICP-MS测定硫信号的影响,并且深入研究了影响的原因。结果表明,硫含量相同但形态不同的含硫阴离子(S^2-、S₂O₃^2-、SO₃^2-、SO₄^2-)在2%的HNO₃介质中的信号比在水介质中的信号稳定,2%的HNO₃更适合于作为ICP-MS测定硫的介质。在2%的HNO₃介质中,S^2-、SO₃^2-中S的ICP-MS测量灵敏度(即标准曲线的斜率)分别为7828 cps/(μg·L^-1)、5528 cps/(μg·L^-1),SO₄^2-和S₂O₃^2-的测量灵敏度分别是为1321 cps/(μg·L^-1)、1299 cps/(μg·L^-1)。S^2-和SO₃^2-的灵敏度分别约为SO₄^2-的6倍和4倍;而S₂O₃^2-的灵敏度与SO₄^2-基本一致。主要原因在于S^2-、SO₃^2-形态的硫在HNO₃介质中形成了气态的H₂S和SO₂,相当于提高了雾化效率,从而使这两种形态硫的灵敏度大幅度提高。     

Stable sulfur isotopes in the water column of the Cariaco Basin

Previous geochemical and microbiological studies in the Cariaco Basin indicate intense elemental cycling and a dynamic microbial loop near the oxic-anoxic interface. We obtained detailed distributions of sulfur isotopes of total dissolved sulfide and sulfate as part of the on-going CARIACO time series project to explore the critical pathways at the level of individual sulfur species. Isotopic patterns of sulfate (δ³⁴S_SO4) and sulfide (δ³⁴S_H2S) were similar to trends observed in the Black Sea water column: δ³⁴S_H2S and δ³⁴S_SO4 were constant in the deep anoxic water (varying within 0.6‰ for sulfide and 0.3‰ for sulfate), with sulfide roughly 54‰ depleted in ³⁴S relative to sulfate. Near the oxic-anoxic interface, however, the δ³⁴S_H2S value was ∼3‰ heavier than that in the deep water, which may reflect sulfide oxidation and/or a change in fractionation during in situ sulfide production through sulfate reduction (SR). δ³⁴S_H2S and Δ³³S_H2S data near the oxic-anoxic interface did not provide unequivocal evidence to support the important role of sulfur-intermediate disproportionation suggested by previous studies. Repeated observation of minimum δ³⁴S_SO4 values near the interface suggests ‘readdition’ of ³⁴S-depleted sulfate during sulfide oxidation. A slight increase in δ³⁴S_SO4 values with depth extended over the water column may indicate a reservoir effect associated with removal of ³⁴S-depleted sulfur during sulfide production through SR. Our δ³⁴S_H2S and Δ³³S_H2S data also do not show a clear role for sulfur-intermediate disproportionation in the deep anoxic water column. We interpret the large difference in δ³⁴S between sulfate and sulfide as reflecting fractionations during SR in the Cariaco deep waters that are larger than those generally observed in culturing studies.     

Annual fluctuations in sulfur isotope fractionation in the water column of a euxinic marine basin

The sulfur cycle of Mariager Fjord was studied by following the pool of sulfide in the anoxic water and its isotopic composition during a period of 3 yr. Though most of the sulfide accumulating in the fjord was formed in the sediment, the isotopic composition of sulfide in the water was different from the isotopic composition of sulfide diffusing into the water from the sediment. The mean isotopic composition of the water column sulfide (δ³⁴S) varied during the year between −13‰ and −21‰ with the most negative values reached during winter/early spring, while the sulfide diffusing into the water from the sediment had a mean isotope composition of −11.3‰. This annual pattern suggested that processes in the oxidative part of the sulfur cycle were responsible for the excess fractionation, and mass-balance considerations indicated that the excess fractionation of the sulfur isotopes could be accounted for by disproportionation of S⁰ or S₂O₃²⁻ in the water column, but not by water column sulfate reduction or sulfide oxidation alone. MPN counts demonstrated that a population of more than 3 × 10⁴ cells mL⁻¹ capable of growing by disproportionation of these two substrates was present in all depths of the fjord. The results presented in this communication demonstrate that the isotopic depletion of sulfide in anoxic systems may vary between periods of net sulfate reduction versus periods of net sulfide oxidation and indicate that disproportionation of sulfur compounds may be an important step in the sulfur cycle of euxinic basins.     

膏盐层在Ni-Cu-PGE硫化物矿床成矿中的作用 ——以俄罗斯诺里尔斯克矿床为例

与基性-超基性侵入体有关的Ni-Cu-PGE硫化物矿床是镍-铜-铂族元素矿床的最重要类型。传统观点认为,Ni-Cu-PGE硫化物矿床是由成矿岩浆分异演化、熔离形成的,与围岩性质关系不大。实际上,大部分基性-超基性岩浆是硫化物不饱和的,在岩浆自身演化过程中难以聚集大量硫化物而形成有经济价值的大型高品位NiCu-PGE硫化物矿床。因此,壳源硫的加入是基性-超基性岩浆中硫化物浓度达到过饱和,熔离形成Ni-Cu-PGE硫化物矿床的关键。膏盐层是富含石膏等硫酸盐(SO24-)的蒸发沉积建造,除SO24-外,还富含Cl-、CO23-、Na+、K+等盐类物质,在自然界分布广、面积大,是地壳中重要的硫源层和氧化障。但膏盐层在Ni-Cu-PGE硫化物矿床中的作用长期被忽视,制约了Ni-Cu-PGE硫化物矿床成矿找矿理论的发展。文章以世界最大的俄罗斯诺里尔斯克Ni-CuPGE硫化物矿床为例,介绍了膏盐层与矿床分布的空间关系、石膏等硫酸盐矿物在矿床和蚀变围岩中的分布、成矿元素和硫同位素组成特征及变化规律,阐明了膏盐层在成矿中的作用和控矿机理。膏盐(SO24-)的加入,可以大幅度提高成矿系统的氧逸度,将成矿岩浆中Fe2+氧化成Fe3+,形成铁氧化物,SO24-自身被还原,向成矿系统提供还原硫S2-,与Cu2+、Ni2+等结合,形成铜镍硫化物等,使基性-超基性成矿岩浆由硫化物不饱和变为过饱和,形成硫化物小液滴,在岩浆房经聚集-熔离-富集,形成岩浆型Ni-Cu-PGE硫化物矿床。除膏盐层外,富含硫化物的地层也是形成Ni-Cu-PGE硫化物矿床的重要硫源层。     

Equilibria in a sulfide rich water from Enghien-les-Bains,France

A complete analysis of a sulfide rich water from a sedimentary area has been achieved. The formation of metastable sulfur species (polysulfide ions, colloidal sulfur and thiosulfate) is very important. The relative concentrations of the sulfur species is controlled by bacterial processes (Desulfovibrio and Thiobacteriaceae). Electrochemical measurements and results of the analyses are in agreement. A possible repartition of polysulfide ions is S^2?₆ ≈- S^2?₅ >S^2?₄. This repartition, although out of equilibrium, is characteristic of the processes leading to the formation of the metastable sulfur species.The water is in equilibrium with amorphous FeS formation. When sulfide, polysulfide and thiosulfate complexing of trace metals Cu, Cd and Pb is taken into account, an agreement is reached between their concentrations in water and their concentrations in the FeS precipitate.     

Sulfur diffusion in rhyolite melts

 Diffusion rates for sulfur in rhyolite melt have been measured at temperatures of 800–1100° C, water contents of 0–7.3 wt%, and oxygen fugacities from the quartz-fayalite-magnetite buffer to air. Experiments involved dissolution of anhydrite or pyrrhotite into rhyolite melt over time scales of hours to days. Electron microprobe analysis was used to measure sulfur concentration profiles in the quenched glasses. Regression of the diffusion data in dry rhyolite melt gives D_sulfur=0.05·exp{−221±80RT}, which is one to two orders of magnitude slower than diffusion of other common magmatic volatiles such as H₂O, CO₂ and Cl^-. Diffusion of sulfur in melt with 7 wt% dissolved water is 1.5 to 2 orders of magnitude faster than diffusion in the anhydrous melt, depending on temperature. Sulfur is known to dissolve in silicate melts as at least two different species, S²⁻ and S⁶⁺, the proportions of which vary with oxygen fugacity; despite this, oxygen fugacity does not appear to affect sulfur diffusivity except under extremely oxidizing conditions. This result suggests that diffusion of sulfur is controlled by one species over a large range in oxygen fugacity. The most likely candidate for the diffusing species is the sulfide ion, S²⁻. Re-equilibration between S²⁻ and S⁶⁺ in oxidized melts must generally be slow compared to S²⁻ diffusion in order to explain the observed results. In a silicic melt undergoing degassing, sulfur will tend to be fractionated from other volatile species which diffuse more rapidly. This is consistent with analyses of tephra from the 1991 eruption of Mount Pinatubo, Philippines, and from other high-silica volcanic eruptions. Received: 26 April 1995 / Accepted: 1 November 1995     

Speciation of Polysulfides and Zerovalent Sulfur in Sulfide-rich Water Wells in Southern and Central Israel

Zerovalent sulfur and inorganic polysulfides were determined in nine sulfide-rich water wells in central and southern Israel. Although the two locations belong to the same aquifer, they are characterized by different pH and hydrogen sulfide levels. Hydrogen sulfide in the central Israel wells ranged between 19 and 32 μM, and the pH was 7.26 ± 0.07. The southern basin is characterized by lower water circulation, lower pH (around 6.8), and higher hydrogen sulfide levels (>470 μM). Polysulfides were determined by a rapid single-phase methylation using methyl trifluoromethanesulfonate (methyl triflate) reagent. The summary polysulfide concentration for S₄²⁻–S₇²⁻ species was found to be around 0.14–0.75 μM in the central region of Israel and substantially higher, 2.3–4.6 μM in the southern region. The sum of polysulfide zerovalent sulfur and colloidal sulfur was quantitatively detected by cyanide derivatization and compared to polysulfide sulfur determined by methyl triflate derivatization and to the chloroform extraction of zerovalent sulfur. A method for the determination of sulfur undersaturation level—the ratio between dissolved elemental sulfur and its equilibrium concentration in the presence of solid sulfur—based on the observed levels of the major polysulfide species is described. The observed polysulfide speciation was compared with the predicted speciation under sulfur saturation conditions taking into account the water temperature, its ionic strength, and pH. Criteria for sulfur saturation versus unsaturated conditions were established based on (1) the chain length dependence of the ratio between the observed polysulfide concentrations and their predicted value under sulfur saturated conditions, and (2) the difference between the concentration of zerovalent sulfur, as determined by cyanolysis, and the total polysulfide sulfur. According to this dual criterion five of the water wells were classified as being undersaturated with respect to sulfur, though for all the examined water wells the majority of the zerovalent sulfur was in the form of polysulfide sulfur.     

Reduced sulfur and iron species in anoxic water column of meromictic crater Lake Pavin (Massif Central, France)

The vertical distribution of reduced sulfur species (RSS including H₂S/HS⁻, S⁰, electroactive FeS) and dissolved Fe(II) was studied in the anoxic water column of meromictic Lake Pavin. Sulfide concentrations were determined by two different analytical techniques, i.e. spectophotometry (methylene blue technique) and voltammetry (HMDE electrode). Total sulfide concentrations determined with methylene blue method (∑H₂S_MBRS) were in the range from 0.6 µM to 16.7 µM and were substantially higher than total reduced sulfur species (RSS_V) concentrations determined by voltammetry, which ranged from 0.1 to 5.6 μM. The observed difference in the sulfide concentrations between the two methods can be assigned to the presence of FeS colloidal species.Dissolved Fe was high (> 1000 µM), whereas dissolved Mn was only 25 µM, in the anoxic water column. This indicates that Fe is the dominant metal involved in sulfur redox cycling and precipitation. Consequently, in the anoxic deep layer of Lake Pavin, “free” sulfide, H₂S/HS⁻, was low; and about 80% of total sulfide detected was in the electroactive FeS colloidal form. IAP calculations showed that the Lake Pavin water column is saturated with respect to FeS_am phase. The upper part of monimolimnion layer is characterized by higher concentrations of S(0) (up to 3.4 µM) in comparison to the bottom of the lake. This behavior is probably influenced by sulfide oxidation with Fe(III) oxyhydroxide species.     

Experimental data on the speciation of sulfur as a function of oxygen fugacity in basaltic melts

The speciation of sulfur as a function of oxygen fugacity was calculated in glasses of basaltic composition saturated experimentally with either sulfide or sulfate phases. The experiments were conducted on mixtures of synthetic and natural materials equilibrated at 1300 °C and 1 GPa in a piston-cylinder apparatus. Sulfur speciation was calculated by measuring the peak shift of the sulfur Kα radiation relative to a sulfide standard, whereas oxygen fugacity was calculated from the composition of olivine and spinel present in the assemblages. The results are consistent with sulfur being present as sulfite (S⁴⁺) in addition to sulfate (S⁶⁺) in oxidized melts. Therefore, sulfur speciation derived from SKα peak shifts should be seen as ”sulfate mole fraction equivalents“ (X(S⁶⁺)_eq.). Using the data available, an empiric function:

X(S6+)_eq.=0.86/(1+exp(2.89−2.23ΔFMQ))     

Evaluating the S-isotope fractionation associated with Phanerozoic pyrite burial

This study examines the sulfur isotope record of seawater sulfate proxies using δ³⁴S and Δ³³S to place constraints on the average global fractionation (Δ³⁴S_py) associated with pyrite formation and burial and the exponent λ that relates variations of the ³⁴S/³²S to variations of the ³³S/³²S. The results presented here use an analysis of the sulfur isotope record from seawater sulfate proxies and sedimentary sulfide to extract this quantity as the arithmetic difference between δ³⁴S of seawater sulfate and contemporaneous sulfide. It also uses an independent method that draws on inferences about the Δ³³S evolution of seawater sulfate to evaluate this further. These two methods yield similar results suggesting that Δ³⁴S_py and λ changed over the course of the Phanerozoic from slightly lower values of Δ³⁴S_py (lower values of λ) in the early Phanerozoic (Cambrian-Permian) to higher values of Δ³⁴S_py (higher values of λ) starting in the Triassic. This change of Δ³⁴S_py and the exponent λ is interpreted to reflect a change in the proportion of sulfide that was reoxidized and processed by bacterial disproportionation on a global scale. The revised record of Δ³⁴S_py also yields model pyrite burial curves making them more closely resemble model evolution curves for other element systems and global sea level curves. It is suggested that possible links to sea level may occur via changes in the area of submerged continental shelves which would provide additional loci for pyrite burial.The slightly different constraints used by the two approaches to calculate this fractionation may allow for additional information to be obtained about the sulfur cycle with future studies. For instance, the correspondence of these results suggests that the inferred variation of ³⁴S/³²S of pyrite is real, and that there is no significant missing sink of fractionated sulfur at the resolution of the present study (such as might be associated with organic sulfur). Burial of organic sulfur may, however, have been important at some times in the Phanerozoic and shorter timescale deviations between results provided by these methods may be observed with higher resolution sampling. If observed, this would suggest either that the record for pyrite (or less likely sulfate) is biased, or that another sink (possibly as organic sulfur) was important during these times in the Phanerozoic.