海相石膏的硫同位素

海水硫酸盐参与许多发生在海洋水中和海相沉积物中的氧化还原作用,并且是多种沉积物和矿床中硫的来源。海水硫酸盐的硫同位素组成与海相环境中各种含硫化合物的硫同位素组成有着直接或间接的成因联系。在很大程度上,海水硫酸盐的硫同位素组成提供了海相环境中硫同位素演变的起点。找到这一起点才能正确阐明同时代海相沉积物中硫同位素之间的关系,进而探寻其演变规律。目前,对确定古海洋硫同位素组成最方便的研究对象是海相石膏。     

陆相咸化湖泊沉积硫酸盐岩硫同位素组成及其地质意义

现代海洋中的硫酸盐矿物和海水硫酸盐本身常有相似的硫同位素组成,因而可根据现代蒸发岩的硫酸盐同位素来判断古环境。据李任伟［１］引用Ｈｏｌｓｅｒ和Ｋａｐｌａｎ及格里年科的资料报道,海相蒸发岩及其所反映的古海洋硫酸盐的硫同位素组成只在较狭窄的范围内变化,现...     

四川盆地三叠纪海水的硫同位素分布特点及其地质意义

四川盆地海相三叠系地层发育齐全。通过盆地海相三叠系各层段众多的硫酸盐（ 石膏、硬石膏） 和盐卤水硫同位素分析样的系统整理和研究,可见同一层段的硫同位素（δ３４Ｓ）组成稳定,而沿剖面由下而上δ３４Ｓ呈阶梯状递减轻化趋势,与已知全球海相三叠硫酸盐δ３４Ｓ的研究的结果有明显差异,这对全球海相三叠系硫酸盐δ３４Ｓ的研究是一个重要的补充和贡献。对地层划分对比、盐卤水产层和成因、蒸发岩形成环境、咸化发展方向及成钾预测等方面的研究,也有重要意义。     

云南会泽铅锌矿田硫同位素研究

为探讨会泽铅锌矿田成矿流体总硫同位素组成、成矿温度、硫源及还原硫的形成机制,在分析前人的硫同位素数据基础上对麒麟厂矿床上部原生矿体硫化物(黄铁矿、闪锌矿和方铅矿)及麒麟厂和矿山厂矿床外围新发现的硫酸盐矿物(重晶石)进行了硫同位素研究。结果显示,原生矿体中的硫化物的δ34S变化为8.0‰~17.68‰,成矿流体中硫同位素已达分馏平衡;矿床外围的硫酸盐δ34S变化为17.95‰~24.30‰。利用共生矿物对Pinckney法,估算获得成矿流体的δ34SΣS为14.44‰,与海相硫酸盐的δ34S相近;通过同位素地质温度计,估算获得成矿温度为134~388℃;包裹体测温发现,重晶石为热液成因,暗示成矿流体中的硫可能来自矿区及矿区外围各个地层的海相硫酸盐或是矿区发现的热液重晶石。硫酸盐的还原机制应为热化学还原作用(TSR)。     

TSR成因H2S的硫同位素分馏特征与机制

热化学硫酸盐还原反应(TSR)是深层碳酸盐岩油气藏中硫化氢的主要成因机制,目前已在全球发现了50多个TSR成因的大中型含硫化氢天然气田。通过对中国四川盆地含硫化氢气田硫化物的采集与同位素分析,结合全球含硫化氢天然气田硫同位素分析数据,研究了TSR过程中硫同位素的地球化学行为和分馏特征。研究发现,TSR成因的高含硫化氢天然气中,硫化氢与硫酸盐的硫同位素分馏值小于15‰,主要分布范围为2.5‰~13.82‰,平均在10‰。四川盆地海相层系膏岩的硫同位素值分布较宽,并呈现阶梯状变化,而硫化氢的硫同位素则呈现出相似的分布规律,表明各主要含硫化氢气田硫化氢中的硫来自于本层系的硫酸盐,TSR主要发生在各自的储集层中。四川盆地各气田TSR发生的温度条件相似,硫同位素分馏比较接近。TSR过程中硫同位素的分馏过程与硫酸盐本身硫同位素值的高低无关,而与TSR反应程度有关。TSR反应程度越高,硫化氢的硫同位素值与地层硫酸盐的硫同位素越相近。通过系统分析整理全球含硫化氢气田的硫化物硫同位素数据,并结合四川盆地地质条件和油气演化过程,揭示了TSR过程中硫同位素的分馏特征,并绘制出四川盆地和全球各时代硫化氢和石膏的硫同位素分布曲线图,为研究含油气盆地蒸发岩沉积演化和硫化氢成因提供了参考。     

蒸发岩中硫同位素的地球化学特征及其沉积学意义——以思茅盆地MZK- 3井为例

思茅盆地目前是中国唯一的含古代固体钾盐矿床的沉积盆地,其钾盐形成时代、物源特征、海侵方向等多年来一直存在争议。本文依据海相硬石膏的形成条件、存在形式、同位素分馏机理,重点分析了盆地内MZK-3井蒸发岩硫同位素的地球化学特征。结果表明:①岩盐中的硬石膏在蒸发盆地析岩盐阶段即可形成,单独成层的硬石膏是由原始沉积的石膏经历了沉积埋藏升温进而脱水而成;②岩盐中硬石膏的硫同位素值具有"双峰"特征,分别为14‰～16‰和8‰～10‰或6‰～8‰,这体现了硫酸盐的双重来源——原始海水中的硫酸盐和陆源淡水输入的硫酸盐或火山活动提供的硫源;③硬石膏层的硫同位素在区域上具有对比性,结合~(87)Sr/~(86)Sr值的特征,认为其代表了海相的沉积环境;④硬石膏层的硫同位素值平面上由南向北降低,可能反映了在此方向陆源淡水或火山活动对蒸发岩盆地的影响逐渐增强,进而说明这可能也是海侵的方向。可见对硬石膏硫同位素的研究,不仅在沉积学上能揭示物源、沉积环境、海侵方向等信息,更能对研究区钾盐矿床勘查提供有益的参考。     

思茅盆地下白垩统蒸发岩硫同位素地球化学特征及其钾盐成矿意义

关于思茅盆地下白垩统勐野井组蒸发岩主要物源为海水的认识争议很少,但是关于其成矿时代和成矿模式的认识还有争议,关于陆源淡水对蒸发岩物质成分的影响还缺乏探讨。本文主要通过分析盆地内L2井27件蒸发岩样品的化学成分和硫同位素地球化学特征,结合邻区已发表的硫同位素数据,探讨了蒸发岩的物质来源、陆源淡水对蒸发岩物质成分的影响、成盐时代以及可能的钾盐成矿模式。结果表明:(1)思茅盆地蒸发岩受陆源淡水和火山热液补给,其中陆源淡水补给使蒸发岩硫同位素明显低于同一地质时期的其他海相样品;(2)海水可能自现今盆地北西方向补给,一级周期上海水补给存在两次,二级周期上海水补给至少存在七次;(3)物源海水的时代为中侏罗世,沉积析盐的时代为早白垩世晚期,可能的钾盐成矿模式为中侏罗世海水侧向迁移成矿。这些结果对解释思茅盆地及邻区海相蒸发岩异常低的硫同位素值、高硫同位素值与中侏罗世海水相当以及钾盐成矿缺失"碳酸盐岩相和硫酸盐岩相"有重要的意义。     

由BaSO4直接热分解制备用于同位素分析的SO2

硫同位素地质研究工作中,经常遇到的研究对象是硫酸盐矿物。如何把这些硫酸盐矿物转化为适于质谱测定硫同位素组成的SO₂气体,是我国硫同位素地质研究中急待建立的实验手段之一。 经典的方法中,可溶于水的硫酸盐,通常是先把它沉淀为BaSO₄,然后通过一系列的化学反应转化为SO₂。 七十年代初期,B.D.Holt等人提出直接加热分解BaSO₄制备SO₂的方法。     

贵州小屯乡萤石-锑矿床硫同位素地球化学特征及其地质意义

贵州省贞丰县小屯乡萤石矿床地处黔西南州中部，其深部发育锑矿体，是近年来新发现的锑资源。为查明锑矿体中硫的来源与演化，通过岩相学观察、全矿物消融法及原位激光剥蚀法，对锑矿体的矿物组合和辉锑矿的硫同位素组成进行了分析。结果表明，含硫矿物主要为辉锑矿，极少量为黄铁矿，脉石矿物主要有石英和萤石。辉锑矿亏损重硫同位素(δ³⁴S为-28.40‰～-25.07‰,n=9,全矿物消融法；δ³⁴S为-26.74‰～-22.44‰,n=12,原位激光剥蚀法),其硫同位素组成明显不同于华南锑矿带上大部分锑矿床的硫同位素组成，暗示二者硫的来源或还原硫形成机制不同。在开放体系中，细菌硫酸盐还原作用(BSR)可以产生大量显著亏损重硫同位素的还原硫，小屯乡矿床的赋矿围岩中有草莓状沉积黄铁矿和海相硫酸盐矿物发育，暗示有BSR存在。因此，本文推测该矿床的硫主要来自地层(沉积黄铁矿和海相硫酸盐),是BSR过程的产物。另外，萤石的流体包裹体测温结果(100～176℃)显示成矿温度超出细菌存活温度，故推测BSR发生在锑成矿之前。小屯乡矿床的辉锑矿与沉积黄铁矿均亏损重硫同位素，表明富...     

华南震旦、寒武系海相沉积成因重晶石的硫同位素组成及其在地质学上的意义

华南震旦、寒武系海相沉积成因重晶石的硫同位素组成,其δS~(34)值为 35— 47‰。究其原因,沉积环境对沉积物的稳定同位素组成的影响是最重要的。这一发现对各时代海相硫酸盐的同位素演化的研究,提供了新的资料。     

浙江长兴二叠系和三叠系界限地层的碳同位素

研究海相碳酸盐岩的碳和氧同位素已有三十多年,积累了数千个数据,其目的在于研究古海洋碳和氧同位素的演变。在此期间,一部分研究者认为,海相碳酸盐岩的δ¹³C值在0±2范围内变化,未表现出与地质时代相关的变化趋势(Clayton和Degens,1959;Degens和Epstein,1962;Keith和Weber,1964;Galimov,1965;Becker和Clayton,1972;Schidlowski等,1975)。但是,另一些学者,如Jeffery等(1955),Baertschi(1975),Compston(1960),Weber(1967),Garrels和Parry(1974)却认为,海相碳酸盐岩的δ¹³C值随地质时代而有规律地变化。     

城门山及武山铜矿床的硫同位素研究

地质概况江西城门山矿床和武山矿床是长江中下游铁铜成矿带大冶-九江成矿亚带东南部位的两个与斑岩有成因关系的铜矿床。在地质构造上,前者处于九江-瑞昌东西向拗陷带中的长山-城门湖背斜倾伏端的北翼,后者处在横立山-黄桥向斜东端的北翼。两矿区的地层分布相似,主要是志留系至三叠系地层。其中,泥盆系上统五通组砂岩及石炭系中统黄龙组灰岩与矿床关系密切。     

Discovery of an abnormally high-δ34S barite deposit and a new understanding of global sulfur isotope variation during geological history

The evolution of the global sulfur isotope curve was plotted based on the δ34S values of evaporates resultant from oceanic evaporation. In the long period of geological history the δ34S values showed obvious peaks for three times during the process of ancient oceans’ sulfur isotope evolution, namely the Early Cambrian (+30‰), the Late Devonian (+25‰) and the Permian-Triassic transition interval (+17‰), but the causes of the abnormal rise of sulfur isotopic values during the geological period are still in question. In this paper, 18 samples collected from a large Devonian barite deposit from Zhenning County were analyzed to determine their δ34S values, revealing that the 18 samples have very high δ34S values (δ34S=41.88‰-+68.39‰), with an average close to 56.30‰, which are higher than the isotopic values of contemporary sulfates (+17‰- +25‰). A comparative analysis was conducted of the emerging of high δ34S barite deposits (from Cambrian and Devonian) and the δ34S variation curves of the ancient oceans. The results indicate that the time when the obvious peaks of δ34S values appeared and the time of massive sedimentation of high δ34S barite deposits are very close to each other, which, in our opinion, is not a coincidence. There may exist some correlations between the sulfur isotope evolution of ancient oceans during the diverse periods of geological history and the massive sedimentation of high δ34S barite deposits. Therefore, it is inferred that perhaps it was the massive sedimentation of high δ34S barites that caused the sharp rise of δ34S values in a short period of time.     

Was there a conflict at the Neoproterozoic-Cambrian boundary: Evidence from sulfur isotope composition?

Based on evaporite sequences of the Irkutsk amphitheater, it is shown that sulfur in the Vendian-Lower Cambrian sedimentary sulfates displays a very wide scatter of sulfur isotope ratios and enrichment in heavy sulfur up to average values of δ³⁴S ≈ +(27–30)‰. These features are related to sulfate reduction, which is distinctly expressed like other secondary alterations in the studied sections. Average δ³⁴S values reflect the dynamics of isotopic effects rather than the initial sulfur composition of the oceanic water. The Irkutsk amphitheater can be considered natural model of sulfur isotopic variations in ancient evaporites. Existing concepts of the sulfur isotopic composition of Cambrian oceans need to be revised.     

Micro-scale sulfur isotope and chemical variations in sphalerite from the Bleiberg Pb-Zn deposit,Eastern Alps,Austria

The Bleiberg Pb-Zn deposit in the Drau Range is the type locality of Alpine-type carbonate-hosted Pb-Zn deposits. Its origin has been the subject of on-going controversy with two contrasting genetic models proposed: (1) the SEDEX model, with ore forming contemporaneously with sedimentation of the Triassic host rocks at about 220 Ma vs. (2) the epigenetic MVT model, with ores forming after host rock sedimentation at about 200 Ma or later. Both models assume that, on a deposit or even district scale, a fixed paragenetic sequence of ore minerals can be established. The results of our detailed petrographic, chemical and sulfur isotope study of two key ore-samples from two major ore horizons in the Wetterstein Formation at Bleiberg (EHK02 Erzkalk horizon and Blb17 Maxer Bänke horizon) demonstrate that there is no fixed paragenetic sequence of ore minerals. Small-scale non-systematic variations are recorded in textures, sphalerite chemistry and δ³⁴S. In each sample, texturally different sphalerite types (colloform schalenblende, fine- and coarse-grained crystalline sphalerite) co-occur on a millimeter to centimeter scale. These sphalerites represent multiple mineralization stages/pulses since they differ in their trace element inventory and in their δ³⁴S. Nonetheless, there is some correspondence of sphalerite micro-textures, sulfur isotope and chemical composition between the two samples, with microcrystalline colloform schalenblende being Fe-rich, having high Fe/Cd (15 and 9, respectively) and a light sulfur isotope composition (δ³⁴S −26.0 to −16.2‰). Cadmium-rich and Fe-poor sphalerite in both samples has relatively heavier sulfur isotope composition: in sample EHK02 this sphalerite has Fe/Cd of ∼0.5 and δ³⁴S from −6.6 to −4.6‰; in sample Blb17 Fe/Cd is ∼0.1 and δ³⁴S ranges from −15.0 to −1.5‰. Barite, which is restricted to sample EHK02, has δ³⁴S ≈ 17‰. The large variations in δ³⁴S recorded on the mm to cm-scale is consistent with variable contributions of reduced sulfur from two different sulfur reservoirs. The dominant reservoir with δ³⁴S values <−20‰ likely results from local bacteriogenic sulfate reduction (BSR), whereas the second reservoir, with δ³⁴S about −5‰ suggests a hydrothermal source likely linked with thermochemical sulfate reduction (TSR). Based on this small- to micro-scale study, no simple, deposit-wide paragenetic and sulfur isotope evolution with time can be established. In the Erzkalk ore (sample EHK02) an earlier Pb-Zn-Ba stage, characterized by heavy sulfur isotope values, is succeeded by a light δ³⁴S-dominated Zn-Pb-F stage. In contrast, the several mineralization pulses identified in the stratiform Zn-Pb-F Maxer Bänke ore (sample Blb17) define a broad trend to heavier sulfur isotope values with time. The interaction documented in these samples between two sulfur reservoirs is considered a key mechanism of ore formation.     

Sulfur geochemistry of Jurassic high-sulfur coals from Egypt

Jurassic high-sulfur coals from the Maghara area in Egypt were analyzed for the abundance and isotopic composition of different forms of sulfur. Analyses indicated that the sulfur occurs in the form of organic, pyrite, and sulfate forms. Pyrite sulfur represents the major fraction, while sulfate sulfur is minor and could be formed during sample preparation for the analyses.The δ³⁴S CDT values of the organic sulfur are positive ranging between 1.0‰ and 13.5‰ with an average of 9.1‰. Pyrite δ³⁴S values are also positive ranging between 1.5‰ and 15.4‰ with an average of 6.6‰. The high δ³⁴S values of the organic sulfur in the Maghara coals suggest a freshwater origin of the organic components of these coals. The lack of correlation between pyrite and organic sulfur isotopes implies different incorporation mechanisms of sulfur. The high-sulfur contents along with the positive and high δ³⁴S values suggest a marine origin of pyrite sulfur and support the geological interpretation of marine invasion after the peat formation that was responsible for the incorporation of the pyrite sulfur.The occurrence of pyrite as euhedral crystals as well as the high and positive δ³⁴S values of the pyrite sulfur indicates the formation of pyrite during diagenesis as a result of marine water invasion of the preexisting peat in a brackish coastal plain environment.     

Indicator Isotope–Geochemical Characteristics of Sulfides from the Satka Magnesite Ore Field (South Urals Province)

The stable enrichment of pyrite from magnesite ores in δ³⁴S isotope (from 5.4 to 6.9‰) compared with pyrite from the host (sedimentary and igneous) rocks was established in the classical Satka sparry magnesite ore field. Concretionary segregations of fine-grained pyrite in dolomite are depleted in the heavy sulfur isotope (δ³⁴S, from–9.1 to–5.8‰). Pyrite from dolerite is characterized by δ³⁴S values (–1.1 and 1.7‰) close to the meteorite sulfur. The δ³⁴S values in barite from the underlying dolomite horizon vary in the range of 32.3–41.4‰. The high degree of homogeneity of the sulfur isotope composition in pyrite from magnesite is a result of thermochemical sulfate reduction during the syngenetic crystallization of pyrite and magnesite from epigenetic brines, formed during dissolution of evaporite sulfate minerals at the stage of early catagenesis of the Riphean deposits.

     

Sulfur sources of sedimentary “buckshot” pyrite in the Auriferous Conglomerates of the Mesoarchean Witwatersrand and Ventersdorp Supergroups,Kaapvaal Craton,South Africa

Large rounded pyrite grains (>1 mm), commonly referred to as “buckshot” pyrite grains, are a characteristic feature of the auriferous conglomerates (reefs) in the Witwatersrand and Ventersdorp supergroups, Kaapvaal Craton, South Africa. Detailed petrographic analyses of the reefs indicated that the vast majority of the buckshot pyrite grains are of reworked sedimentary origin, i.e., that the pyrite grains originally formed in the sedimentary environment during sedimentation and diagenesis. Forty-one of these reworked sedimentary pyrite grains from the Main, Vaal, Basal, Kalkoenkrans, Beatrix, and Ventersdorp Contact reefs were analyzed for their multiple sulfur isotope compositions (δ³⁴S, Δ³³S, and Δ³⁶S) to determine the source of the pyrite sulfur. In addition, five epigenetic pyrite samples (pyrite formed after sedimentation and lithification) from the Middelvlei and the Ventersdorp Contact reefs were measured for comparison. The δ³⁴S, Δ³³S, and Δ³⁶S values of all 41 reworked sedimentary pyrite grains indicate clear signatures of mass-dependent and mass-independent fractionation and range from ?6.8 to +13.8?‰, ?1.7 to +1.7?‰, and ?3.9 to +0.9?‰, respectively. In contrast, the five epigenetic pyrite samples display a very limited range of δ³⁴S, Δ³³S, and Δ³⁶S values (+0.7 to +4.0?‰, ?0.3 to +0.0?‰. and ?0.3 to +0.1?‰, respectively). Despite the clear signatures of mass-independent sulfur isotope fractionation, very few data points plot along the primary Archean photochemical array suggesting a weak photolytic control over the data set. Instead, other factors command a greater degree of influence such as pyrite paragenesis, the prevailing depositional environment, and non-photolytic sulfur sources. In relation to pyrite paragenesis, reworked syngenetic sedimentary pyrite grains (pyrite originally precipitated along the sediment-water interface) are characterized by negative δ³⁴S and Δ³³S values, suggesting open system conditions with respect to sulfate supply and the presence of microbial sulfate reducers. On the contrary, most reworked diagenetic sedimentary pyrite grains (pyrite originally precipitated below the sediment-water interface) show positive δ³⁴S and negative Δ³³S values, suggesting closed system conditions. Negligible Δ³³S anomalies from epigenetic pyrite suggest that the sulfur was sourced from a mass-dependent or isotopically homogenous metamorphic/hydrothermal fluid. Contrasting sulfur isotope compositions were also observed from different depositional environments, namely fluvial conglomerates and marine-modified fluvial conglomerates. The bulk of the pyrite grains from fluvial conglomerates are characterized by a wide range of δ³⁴S values (?6.2 to +4.8?‰) and small Δ³³S values (±0.3?‰). This signature likely represents a crustal sulfate reservoir derived from either volcanic degassing or from weathering of sulfide minerals in the hinterland. Reworked sedimentary pyrite grains from marine-modified fluvial conglomerates share similar isotope compositions, but also produce a positive Δ³³S/δ³⁴S array that overlaps with the composition of Archean barite, suggesting the introduction of marine sulfur. These results demonstrate the presence of multiple sources of sulfur, which include atmospheric, crustal, and marine reservoirs. The prevalence of the mass-dependent crustal sulfur isotope signature in fluvial conglomerates suggests that sulfate concentrations were probably much higher in terrestrial settings in comparison to marine environments, which were sulfate-deficient. However, the optimum conditions for forming terrestrial sedimentary pyrite were probably not during fluvial progradation but rather during the early phases of flooding of low angle unconformities, i.e., during retrogradational fluvial deposition, coupled in some cases with marine transgressions, immediately following inflection points of maximum rate of relative sea level fall.     

Traces of brine and hydrocarbon migration in carbon,oxygen, and sulfur isotopic compositions of reservoir rocks in the Talakan petroleum field,Southwestern Yakutia

Dolomites from the productive Osa horizon (upper subformation of the Lower Cambrian Bilir Formation) in the Talakan petroleum field show a prominent 1–2‰ decrease in δ¹⁸O (from 23–24 to 21–22‰), which presumably marks a zone of relatively high water/rock ratios. Productive boreholes are characterized by moderate δ³⁴S values (from 25.1 to 30.6‰) and negative correlation between δ³⁴S in anhydrite and δ¹⁸O in associated dolomite, which points to a partial sulfate reduction during catagenesis. In nonproductive borehole, δ³⁴S values increase significantly (from 31.4 to 35.6‰) and show positive correlation with δ¹⁸O in dolomite. Rocks recovered by nonproductive borehole possibly recrystallized during early diagenesis, and, correspondingly lost their permeability and capacity to form pores. Limestones and dolomites of the Osa horizon have a carbon isotopic composition within the range of normal marine carbonates (δ¹³C = 0 ± 1 ‰), which does not indicate a significant role of organic matter in postsedimentary recrystallization of carbonate sediments. A positive δ¹³C excursion up to 4.5‰ recorded in the lower subformation of the Bilir Formation presumably occurred at the sedimentation stage under conditions of high rates of bioproductivity and organic matter burial in sediments.