扬-泰-靖地区地下水系统水力联系与硫酸盐污染特征

本文对长江三角洲扬-泰-靖地区第四系松散层地下水中环境同位素(D、18O、34S)的分布特征进行了分析,旨在揭示大气降水、长江水、潜水及承压水之间的水力联系,辨别地下水中硫酸盐的来源及其污染状况。研究结果表明潜水含水层接受大气降水及长江水的补给,硫酸盐主要为农业污染来源或与海源硫酸盐的混合。承压含水层主要接受大气降水的补给,与潜水含水层及长江之间的水力联系较差,硫酸盐来源不同。在研究区顶部和沿江地段的浅层孔隙承压水中,硫酸盐来源于硫化物的氧化;在东部的深层孔隙承压水中,硫酸盐主要来源于硫酸盐岩的溶解或海源硫酸盐的滞留,基本未受到潜水或地表水中硫酸盐的污染。     

贵州乌江水系枯水期河水硫同位素组成研究

对枯水期乌江及其主要支流河水的硫同位素组成进行了研究。河水SO42-的δ34S值在-15.7‰～18.9‰之间,干流δ34S值介于-3.7‰～0.0‰之间。主要支流河水的SO42-浓度和δ34S值具有明显的区域性差异:上游碳酸盐岩地区支流河水SO42-浓度较高而δ34S值较低,河水中的SO24-来源于煤中还原态硫的氧化、矿床硫化物氧化和大气降水;下游碳酸盐岩夹碎屑岩地区支流河水则相反,具有较低SO24-浓度和较高δ34S值,河水中的SO24-来源于硫酸盐蒸发岩溶解、大气降水以及煤中还原态硫的氧化。干流的硫同位素组成显示枯水期河水中的硫酸盐主要来源于碳酸盐岩地区。     

喀什平原区地下水硫同位素分布特征及其硫酸盐来源研究

喀什平原区是沙漠与戈壁交界的绿洲平原,属于典型的水质型缺水地区,地下水的化学特征主要表现为高硫酸盐、高硬度、高矿化度。本文针对喀什平原区300 m以浅钻孔中完成的地下水样品硫同位素进行测试,结果显示,地下水中δ34S值均为正值,δ34S值范围为2.1‰~13.6‰之间。采用统计、对比分析的方法 ,研究了喀什平原区地下水中硫同位素分布特征及其硫酸盐来源,表明研究区地下水中的硫酸盐主要来自于不同沉积相蒸发岩的溶解以及大气降水的补给。从区域分布看,南部盖孜河地下水流亚系统的地下水中硫酸盐浓度相对较低,北部克孜勒河地下水流亚系统的地下水硫酸盐浓度较高,沿水流方向,SO42-的浓度逐渐增加,而δ34S值变化不大,是蒸发浓缩和沿程累积共同作用的结果。研究结果为喀什平原区水质典型缺水地区的地下水资源开发、利用与保护提供科学依据。     

扬子地台灯影组碳酸盐岩中的硫和碳同位素记录

扬子地区灯影组的海相碳酸盐岩地层不仅记录了当时海水的碳同位素变化，也保存了海水的硫同位素记录，能够通过测定所提取的微量硫酸盐的硫同位素组成来获得。灯影组碳酸盐岩中微量硫酸盐的δ^34S值大部分在 20.0‰～ 38．7‰之间变化，碳酸盐岩的δ^13C值变化在 0．5‰～ 5．0‰之间。除灯影组顶、底界线处外，δ^34S和δ^13C值总体上变化幅度较小，大体上呈逐渐降低的变化趋势。灯影组碳酸盐岩中连续的硫、碳同位素记录分别反映了同期海水中溶解硫酸盐和碳酸盐的硫、碳同位素的变化特征。灯影组微量硫酸盐和碳酸盐岩的同位素特征，意味着灯影期海洋中具有高的生物产率和有机碳埋藏速率；除了顶底界线处，具有相对稳定的古气候条件和古海洋环境。灯影期海水的δ^34S值和δ^13C值同时呈逐渐降低的变化趋势，可能是由海洋深部水体逐渐氧化所致。     

大同盆地地下水中碳硫同位素组成特征及其对碘迁移富集的指示

为深入探究地下水系统中影响碘迁移转化的主控水文生物地球化学过程,对大同盆地典型高碘地下水区完成样品采集,分析地下水样品基础理化性质及碳硫同位素组成特征.结果表明,大同盆地地下水碘含量变化范围为14.40~1 030.00 μg/L,高碘地下水（I>100 μg/L）主要分布在盆地中心排泄区.地下水中溶解性无机碳的δ13C_DIC值变化范围为-12.11‰~-9.79‰,硫酸盐δ34S_SO4值介于4.04‰~16.63‰.δ13C_DIC和DOC之间存在较明显的正相关关系,表明有机质的微生物降解过程是区域地下水无机碳的重要来源之一.同时,δ13C_DIC与δ34S_SO4一定的负相关关系表明硫酸盐是有机质微生物降解过程中潜在电子受体之一,且地下水水环境以偏还原环境为主.高碘地下水表现出低δ13C_DIC、高δ34S_SO4的同位素特征,表明有机质的微生物降解过程是控制地下水中碘迁移释放的主要过程之一,与该过程相伴而生的碘形态转化进一步促使碘以碘离子的形式在偏还原的地下水环境中发生富集.      

招远金矿区水体中硫同位素特征及其对污染来源的指示

稳定同位素因其指纹效应已成为分析矿区污染来源的重要技术手段。文章以招远金矿区为例，应用硫同位素联合水化学分析、聚类分析及氢氧同位素分析招远金矿区水污染特征和成因。通过分析可知，矿区内地表水和地下水主要接受大气降水补给，水力联系密切。水化学类型以SO₄—Ca和SO₄—Na型为主，阴离子以SO₄2-为主，地表水和地下水的NO₃-和Cl-在空间上变异性较大。地表水硫酸盐含量普遍偏高，硫酸盐污染较为严重，高值区出现在玲珑金矿、金翅岭金矿和张星镇附近；而地下水高值区都出现在玲珑金矿附近，且SO₄2-浓度沿着径流方向逐渐降低。地表水中硫酸盐δ34S值介于1.8‰~9.8‰，地下水中硫酸盐δ34S值介于2.7‰~9.6‰，地表水和地下水硫酸盐含量受玲珑金矿硫化、玲珑花岗岩和胶东岩群影响明显。在地下水径流途中，有地表水入渗污染地下水的现象。另外，工业废水的排放也是硫酸盐含量升高的主要原因。研究表明:硫同位素在金矿区硫酸盐污染的来源和特征方面有很好的指示作用，是评价矿山开采对地下水污染的有效工具。     

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)。     

黔东北西溪堡锰矿的沉淀形式与含锰层位中黄铁矿异常高δ34S值的成因

笔者等对黔东北松桃县的西溪堡锰矿床中锰矿石进行了元素含量分析,对含锰层位中黄铁矿进行了S同位素和微量元素分析.锰矿石稀土元素和微量元素特征表明,Mn是以氧化物或氢氧化物的形式沉淀,锰碳酸岩是在成岩过程中转化而成.黄铁矿形态学、微量元素和稀土元素特征指示黄铁矿形成于强还原、偏碱性的成岩环境.黄铁矿异常高的δ34S值反映了新元古代间冰期海洋深部低硫酸盐浓度和高的硫酸盐细菌还原速率,表明南华纪(成冰纪)大塘坡早期阶段深部海洋并没有被完全氧化.含锰层位中黄铁矿异常高的δ34S值存在两种可能的形成机制:①在极低SO42-浓度下,通过BSR即可产生δ34SCDT高达58.7‰的黄铁矿;②海洋深部硫酸盐虽然具有很高的δ34S值,但却并没有高达58.7‰,δ34 SCDT高达58.7‰的黄铁矿的形成是BSR和H2S与Mn02之间发生厌氧歧化氧化反应两个过程综合作用的结果,即在水体中SO42-浓度极低的情况下,硫酸盐和还原产物H2S之间硫同位素分馏达到最小,H2S的δ34S值接近母体硫酸盐,BSR产生的H2S被活性铁矿物固定形成的FeS与Mn02之间发生歧化氧化反应所产生的同位素动力学分馏效应使FeS相对硫酸盐富集34S.     

贵州东部及邻区南华纪锰矿中黄铁矿硫同位素高异常及地质意义

贵州东部及邻区南华纪锰矿层中的黄铁矿产出形态多样,为了研究它们的成因标志,通过野外和镜下观察发现黄铁矿主要呈浸染状、条带状和结核状产出,并以草莓状和自形-半自形粒状结构为主。硫同位素测试结果显示含锰岩系中黄铁矿具有异常高δ34S值的特征,介于+37.9‰~+62.6‰之间(平均52.7‰),呈塔式分布,峰值在+46‰~+59‰之间,沿同一矿体剖面从下到上逐渐减小,不同矿床间差异大。结果表明沉积盆地的封闭性和冰川事件使海水硫酸盐浓度降低并富集重硫同位素,随后形成的硫酸盐最低带进一步减小了硫同位素的分馏,使黄铁矿的δ34S达到异常高值。随着沉积盆地逐渐变开放,矿层由下而上黄铁矿的δ34S值逐渐减小,而不同矿床黄铁矿的δ34S值差异则是因为沉积盆地封闭性的差异。因此,封闭的局限沉积盆地是锰矿床形成的重要地质背景条件,而渗流热卤水或火山锰源可能是矿床的主要锰质来源。     

贵州红枫湖硫酸盐来源及循环过程的硫同位素地球化学研究

红枫湖是云贵高原上一个中等富营养化的季节性厌氧湖泊。对红枫湖流域湖水及其入湖河流河水一年内四个季节的水体硫酸盐硫同位素组成进行了系统研究,结果表明,红枫湖湖水硫酸盐的δ^34S值介于-8．7‰-4．9‰之间,平均-6．8‰,入湖河流的δ^34S值变化范围为-14．7‰-＋0．8‰。湖水的硫同位素组成主要受煤以及大气降水的控制,硫化物和蒸发岩的贡献较小。全年内湖水的δ^34S值季节性变化明显,表现为夏季〉秋季〉冬季、春季的特征,反映了大气降水对湖水硫酸盐贡献的季节性差异。此外,湖水垂直剖面上呈现出明显的季节性差异,冬季、春季湖水的剖面上下δ^34S值几乎没有变化,而夏季、秋季湖水表层和底层相对较高,呈规律性变化,这与湖水冬季混合、夏季分层的特点有关;夏季湖水分层期间雨水在湖泊表层的滞留,以及湖泊底层的硫酸盐细菌还原等相关生物地球化学过程是水体垂直剖面上δ^34S值规律性变化的主要原因。     

Different isotopic evolutionary trends of δ34S and δ18O compositions of dissolved sulfate in an anaerobic deltaic aquifer system

Concentration and isotope ratios (δ³⁴S_SO4 and δ¹⁸O_SO4) of dissolved sulfate of groundwater were analyzed in a very large anaerobic aquifer system under the Lower Central Plain (LCP) (25,000 km²) in Thailand. Groundwater samples were collected in two different kinds of aquifers; type 1 with a saline water contribution and type 2 lateritic aquifers with no saline water contribution. Two different isotopic compositional trends were observed: in type 1 aquifers sulfate isotope ratios range from low values (+2.2‰ for δ³⁴S_SO4 and +8.0‰ for δ¹⁸O_SO4) to high values (+49.9‰ for δ³⁴S_SO4 and +17.9‰ for δ¹⁸O_SO4); in type 2 aquifers sulfate isotope ratios range from low values (−0.1‰ for δ³⁴S_SO4 and +12.2‰ for δ¹⁸O_SO4) to high δ¹⁸O_SO4 ratios (+18.4‰) but with low δ³⁴S_SO4 ratios (<+12.9‰). Isotopic comparison with possible source materials and theoretical geochemical models suggests that the sulfate isotope variation for type 1 aquifer groundwater can be explained by two main processes. One is the contribution of remnant seawater, which has experienced dissimilatory sulfate reduction in the marine clay, into recharge water of freshwater origin. This process accounts for the high salinity groundwater. The other process, explaining for the modest salinity groundwater, is the bacterial sulfate reduction of the mixture water between high salinity water and fresh groundwater. Isotopic variation of type 2 aquifer groundwater may also be explained by bacterial sulfate reduction, with slower reduction rate than that of the groundwater with saline water effect. The origin of groundwater sulfate with low δ³⁴S_SO4 but high δ¹⁸O_SO4 is recognized as an important topic to be examined in a future investigation.     

硫同位素技术在北方岩溶水资源调查中的应用实例

从地球化学背景方面看,在以奥陶系碳酸盐岩为含水介质的中国北方多数岩溶地下水浅循环系统中,岩溶水的硫酸根有三个主要来源,分别是水对中奥陶统中石膏的溶解、岩溶含水层上覆煤系地层中黄铁矿氧化溶解并补给岩溶水以及与土层密切相关的地表水中硫酸根的加入。上述三类水的δ34S同位素值的差别很大,中奥陶统中石膏硫同位素最重,δ34S值一般在20‰～32‰;煤系地层中黄铁矿的硫同位素最轻,一般在－10‰～10‰,多数低于4‰;而地表水的硫同位素介于上述二者之间,δ34S值较稳定分布在7‰～12‰之间。利用这一具有示踪意义的特点,我们对一些泉域系统的岩溶地下水补、排关系以及一些水化学成分的来源进行了成功的解释,为进一步认识岩溶水文地质条件提供了有力的佐证。      

黔东松桃地区南华系大塘坡组锰矿中黄铁矿硫同位素特征及其地质意义

黔东松桃地区是我国重要的锰矿富集区,其中大塘坡组中黄铁矿δ34S存在比较大的差异.通过CF-IRSM法对松桃李家湾、道坨、西溪堡矿区菱锰矿样品中黄铁矿硫同位素组成开展研究,结果显示出两个明显的特征:(1) 样品中黄铁矿普遍具有极高的δ34S值,为47.69‰~66.76‰;(2) 在同一成锰盆地中,水深相对较浅的李家湾矿区黄铁矿δ34S值(47.69‰~59.15‰)明显低于水深相对较深的道坨矿区的δ34S值(53.85‰~62.86‰),且中心相δ34S的值(53.85‰~66.76‰)明显高于过渡相δ34S的值(47.69‰~59.15‰),黄铁矿硫同位素组成表现出明显的深度梯度效应.大塘坡组含锰层位黄铁矿异常高的δ34S值及其明显的深度梯度特征表明,在新元古代Sturtian冰期刚刚结束的间冰期初期,海水硫酸盐浓度极低,海洋呈现显著的分层现象,这一时期深部海洋可能并没有完全氧化.      

Hydrogeochemistry and possible sulfate sources in karst groundwater in Chongqing, China

Groundwater from karst subterranean streams is among the world’s most important sources of drinking water supplies, and the hydrochemical characteristics of karst water are affected by both natural environment and people. Therefore, the study of karst groundwater hydrochemistry and its solutes’ sources is very important to ensure the normal function of life support systems. This paper focused on the major ion chemistry and sulfate isotope of karst groundwater in Chongqing for tracing the sulfate sources and related hydrochemical processes. Hydrochemical types of karst groundwater in Chongqing were mainly of the Ca-HCO₃ type or Ca(Mg)-HCO₃ type. However, some hydrochemical types were the K + Na + Ca-SO₄ type (G25 site) or Ca-HCO₃ + SO₄ type (G26 and G14 sites), indicating that the hydrochemistry of these sites may be strongly influenced by anthropogenic activities or unique geological characteristics. The δ³⁴S-SO₄ ^2? of collected karst groundwater sample fell into a range of ?6.8 to 21.5 ‰, with a mean value of 5.6 ‰. In dolomite aquifer, the δ³⁴S-SO₄ ^2? value ranges from ?4.3 to 11.0 ‰, and in limestone aquifer, it ranged from ?6.8 to 21.5 ‰. The groundwater samples from different land use types showed distinctive δ³⁴S-SO₄ ^2? value. The δ³⁴S-SO₄ ^2? value of groundwater samples had range of ?6.8 to 16.7 ‰ (mean 4.0 ‰, n = 11) in cultivated land areas, 1.5–21.5 ‰ (mean 7.2 ‰, n = 20) in forested land areas, and ?4.3 to 0.8 ‰ (mean ?1.7 ‰, n = 2) in coalmine areas. The δ³⁴S-SO₄ ^2? values of groundwater samples collected from factory area and town area were 2.2 and 9.9 ‰, respectively. According to the δ³⁴S information of potential sulfate sources, this paper discussed the possible sulfate sources of collected karst groundwater samples in Chongqing. The variations of both δ³⁴S and 1/SO₄ ^2? values of the groundwater samples indicated that the atmospheric acid deposition (AAD), dissolution of gypsum (GD), oxidation of sulfide mineral (OS) or anthropogenic inputs (SF: sewage or fertilizer) contributed to sulfate in karst groundwater. The influence of oxidation of sulfide mineral, atmospheric acid deposit and anthropogenic inputs to groundwater in Chongqing karst areas was much widespread. For protecting, sustaining, and utilizing the groundwater resources, the sewage possibly originating from urban, mine or industrial area must be controlled and treated, and the use of fertilizer should be limited.     

Using dual isotopic data to track the sources and behaviors of dissolved sulfate in the western North China Plain

This paper investigated the sources and behaviors of sulfate in groundwater of the western North China Plain using sulfur and oxygen isotopic ratios. The groundwaters can be categorized into karst groundwater (KGW), coal mine drainage (CMD) and pore water (subsurface saturated water in interstices of unconsolidated sediment). Pore water in alluvial plain sediments could be further classified into unconfined groundwater (UGW) with depth of less than 30 m and confined groundwater (CGW) with depth of more than 60 m. The isotopic compositions of KGW varied from 9.3‰ to 11.3‰ for δ³⁴S_SO4 with the median value of 10.3‰ (n = 4) and 7.9‰ to 15.6‰ for δ¹⁸O_SO4 with the median value of 14.3‰ (n = 4) respectively, indicating gypsum dissolution in karst aquifers. δ³⁴S_SO4 and δ¹⁸O_SO4 values of sulfate in CMD ranged from 10.8‰ to 12.4‰ and 4.8‰ to 8.7‰ respectively. On the basis of groundwater flow path and geomorphological setting, the pore water samples were divided as three groups: (1) alluvial–proluvial fan (II₁) group with high sulfate concentration (median values of 2.37 mM and 1.95 mM for UGW and CGW, respectively) and positive δ³⁴S_SO4 and δ¹⁸O_SO4 values (median values of 8.8‰ and 6.9‰ for UGW, 12.0‰ and 8.0‰ for CGW); (2) proluvial slope (II₂) group with low sulfate concentration (median values of 1.56 mM and 0.84 mM for UGW and CGW, respectively) and similar δ³⁴S_SO4 and δ¹⁸O_SO4 values (median values of 9.0‰ and 7.4‰ for UGW, 10.2‰ and 7.7‰ for CGW); and (3) low-lying zone (II₃) group with moderate sulfate concentration (median values of 2.13 mM and 1.17 mM for UGW and CGW, respectively) and more positive δ³⁴S_SO4 and δ¹⁸O_SO4 values (median values of 10.7‰ and 7.7‰ for UGW, 20.1‰ and 8.8‰ for CGW). In the present study, three major sources of sulfate could be differentiated as following: sulfate dissolved from Ordovician to Permian rocks (δ³⁴S_SO4 = 10–35‰ and δ¹⁸O_SO4 = 7–20‰), soil sulfate (δ³⁴S_SO4 = 5.9‰ and δ¹⁸O_SO4 = 5.8‰) and sewage water (δ³⁴S_SO4 = 10.0‰ and δ¹⁸O_SO4 = 7.6‰). Kinetic fractionations of sulfur and oxygen isotopes as a result of bacterial sulfate reduction (BSR) were found to be evident in the confined aquifer in stagnant zone (II₃), and enrichment factors of sulfate–sulfur and sulfate–oxygen isotopes calculated by Rayleigh equation were −12.1‰ and −4.7‰ respectively along the flow direction of groundwater at depths of 60–100 m. The results obtained in this study confirm that detailed hydrogeological settings and identification of anthropogenic sources are critical for elucidating evolution of δ³⁴S_SO4 and δ¹⁸O_SO4 values along with groundwater flow path, and this work also provides a useful framework for understanding sulfur cycling in alluvial plain aquifers.     

Distribution of δ~(34)S and δ~(18)O in SO_4~(2-) in Groundwater from the Ordos Cretaceous Groundwater Basin and Geological Implications

<正>The Ordos Cretaceous Groundwater Basin,located in an arid-semiarid area in northwestern China,is a large-style groundwater basin.SO_4~(2-) is one of the major harmful components in groundwater.Dissolved SO_4~(2-) concentrations,andδ~(34)S-SO_4~(2-) andδ~(18)O-SO_4~(2-) in groundwater from 14 boreholes and in gypsum from aquifer were analyzed.Results show that SO_4~(2-) in shallow groundwaters originates from precipitation,sulfide oxidation,and dissolution of stratum sulphate,with a big range ofδ~(34)S values,from-10.7‰to 9.2‰,and addition of SO_4~(2-) in deep groundwater results from dissolution of stratum sulphate,with biggerδ~(34)S values,from 7.8‰to 18.5‰,compared with those in shallow groundwater.This research also indicates that three types of sulphate are present in the strata,and characterized by highδ~(34)S values and highδ~(18)O values-style,highδ~(34)S values and middleδ~(18)O valuesstyle, middleδ~(34)S values and lowδ~(18)O values-style,respectively.Theδ~(34)S-SO_4~(2-) andδ~(18)O-SO_4~(2-) in groundwater have a good perspective for application in distinguishing different groundwater systems and determining groundwater circulation and evolution in this area.     

贵阳地表水—地下水的硫和氯同位素组成特征及其污染物示踪意义

喀斯特地表水和地下水的交换活跃,地下水系统容易受到地表污染物的污染。为了解喀斯特城市地表水—地下水系统污染特征和污染物质来源,对贵阳市地表水、地下水、雨水和城市排污污水的硫同位素和氯同位素组成变化进行了研究。贵阳市不同类型水体的δ³⁷Cl值在-4.07‰～+2.03‰之间变化,δ34SSO4值变化为-20.4‰～+20.9‰。大气输入物质和城市排污污水的δ³⁷Cl、δ³⁴S及Cl^-/SO₄^2-比值与地表水和地下水的不同,稳定硫和氯同位素的结合研究为示踪地下水污染物来源提供了有效研究手段。贵阳市地下水中的Cl^-和SO^₄2-至少有4种来源,人为活动通过城市排污和大气输入向地下水系统大量输入了硫酸盐和氯离子。      

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.

     

Sulphur isotopic investigation of vein lead-zinc mineralization at Tyndrum,Scotland

The Tyndrum Pb+Zn veins, hosted by late Proterozoic quartzites, were probably generated in the Tournaisian (360 Ma). By determination of sulphur isotopic ratios of vein minerals three aspects of the Tyndrum mineralization were addressed, (i) sulphate sulphur sources; (ii) reduced sulphur source; (iii) isotopic equilibrium in the vein system including geothermometry. Twelve galenas have δ³⁴S values ranging from +3.55 ‰ to +6.38 ‰ (this excludes one value of +11.21 ‰ from a large but nearly barren quartz vein). Other sulphides are enriched or depleted in ³⁴S in the sense expected for isotopic equilibrium although there is no evidence for isotopic equilibrium between the vein minerals. The sulphide sulphur source was probably in the Dalradian metasediments where disseminated pyrite averages +6 ‰. Baryte had δ³⁴S values averaging 14 ‰ and was therefore not in isotopic equilibrium with sulphides: a continental groundwater source is most likely.