云南个旧锡矿床铅、硫同位素研究

对个旧锡矿床的铅、硫同位素进行了研究,研究结果表明,矿石中的铅、硫同位素主要来自基性岩,少量来自花岗岩,矿床的形成经历了印支期的基性火山成矿作用(铅模式年龄200-280Ma)和燕山期花岗岩的叠加改造成矿作用(铅模式年龄80-160Ma).进一步表明,个旧锡矿床为一个多成因多物质来源的矿床.     

扬子地块南缘锑矿床中矿石铅的组成及其地质意义

锑是我国的特色矿产,扬子地同缘锑带是世界上最大的锑成矿带。铅同位素研究表明,该 锑矿床中矿石铅的组成变化较大,在铅同位素组成图解中,线性分布明显,但它不具有等时意义,而是于低放射性成因铅和高放射成因铅两个端元混合所致,矿石铅属壳、幔混合铅。成矿作用应发生于开放体系之中,深部幔源物质可能参与了锑的成矿作用。     

广东圆珠顶斑岩型铜钼矿床成矿物质、成矿流体来源和成矿机理研究

圆珠顶斑岩型铜钼矿床位于钦杭成矿带西南端,是该成矿带近年来发现的又一大型铜钼矿床。文中通过对圆珠顶矿床地质特征的详细剖析并结合H、O、S、Pb等同位素地球化学的研究,对圆珠顶斑岩型铜钼矿床的成矿流体和成矿物质来源进行了初步的讨论。研究结果表明：矿石金属硫化物δ34S 值分布于-4.3‰~3.9‰,硫主要来源于岩浆岩;矿石铅同位素组成稳定,为正常普通铅;不同成矿阶段H、O同位素组成变化及流体包裹体研究指示大气降水与含矿岩浆热液混合是金属矿物从成矿流体中沉淀的重要因素。结合成矿动力学背景研究,认为圆珠顶矿床成矿作用与岩浆活动密切相关,矿床成因是由于板块俯冲作用引起的地壳与地幔物质混合。     

兰坪白秧坪铜银多金属矿床成矿物质来源的铅和硫同位素示踪

白秧坪铜银多金属矿床主要产于白垩系下统景星组石英砂岩、粉砂岩中，矿石铅同位素组成特征与景星组砂岩的铅同位素组成比较接近，表明壳源物质参与了成矿作用。作ZartMan图解和△γ—△β图解表明，矿石铅属于壳幔混合来源。矿石铅μ值介于9．43—9．65之间，Th/U比值介于3．72—3．87之间，表明矿石铅为壳幔混合铅。该矿床硫同位素组成表明，硫来源于深部地幔硫遭受地壳硫的混入。该矿床的成矿作用发生于开放体系之中，成矿物质来源为深部幔源物质混合了壳源物质。     

西藏山南地区成矿带S、Pb同位素地球化学研究

西藏山南地区位于冈底斯东段南缘的火山-岩浆构造带,是一条资源潜力巨大的成矿带。本文通过对该成矿带的典型矿床矿石硫化物S、Pb同位素进行系统性分析,并结合区域构造演化,从成矿系统中"源"的角度对其来源特征和成矿规律进行探讨。研究结果显示,各个矿床的岩石铅和矿石铅的206Pb/204Pb、207Pb/204Pb、208Pb/204Pb比值范围分别为18.34～19.03、15.54～15.86、38.31～39.66和18.38～19.58、15.54～15.86、38.25～39.66,均富含放射成因铅,且在Pb同位素构造演化图中表现出良好的相关性,反映了物质来源上的同一性。结合Pb构造图和Δγ-Δβ成因分类图,矿石铅样品均投影于冈底斯岩基区域,表明成矿物质发生壳幔相互作用,显示造山带铅的特征。在时空上矿石铅也显示明显的变化规律,矿床成矿物质从雅鲁藏布江北侧到南侧,地壳来源物质逐渐增多,同时成矿物质由早期偏向于地幔铅向晚期地壳铅演化,指示晚期成矿物质主要为地壳来源,而早期成矿物质来源可能混有较多的幔源物质。S同位素组成具有一致的深源岩浆硫特征,克鲁、双步结热矿床矿石的硫同位素的δ34S平均值明显小于努日、程巴、明则、冲木达等矿床,也表明晚期成矿物质来源中参与了较多的地壳物质。     

湘东南铜山岭铅锌多金属矿床成矿时代与成矿物质来源——Sm-Nd等时线年龄和Pb同位素证据

铜山岭铅锌多金属矿床位于扬子地块湘南-桂东北坳陷与华夏地块粤北坳陷的拼贴部位,是中国南岭多金属成矿区代表性矿床之一。为确定矿床成矿时代,挑选铜山岭铅锌多金属矿床中含矿矽卡岩的石榴子石进行Sm-Nd同位素定年,获得的等时线年龄为173±3Ma,指示成矿作用发生于燕山早期。对金属硫化物矿物进行了Pb同位素分析,其~(206)Pb/~(204)Pb、~(207)Pb/~(204)Pb、~(208)Pb/~(204)Pb平均值分别为18.602、15.701、38.729,表明成矿物质来源于相对富集铀铅、略微亏损钍铅的上地壳源区。从(~(207)Pb/~(204)Pb)i-(~(206)Pb/~(204)Pb)i铅同位素演化模式图可知,寄主花岗闪长岩是铜山岭铅锌多金属矿床的重要物质来源,且成矿物质中可能含有寄存在花岗闪长岩中的地幔组分。     

四川省拉拉铜矿床同位素地球化学特征及成矿意义

拉拉铜矿床位于康滇地轴西南缘,赋矿围岩是古元古界变质火山岩。通过矿床硫同位素、氢氧同位素、K-Ar同位素、铅同位素、Rb-Sr同位素及辉钼矿中Re-Os同位素的组成特点讨论了成矿时代、物质来源、成矿介质性质及矿床成因等问题。新元古代晋宁期发生的区域变质作用是促使矿床形成的主要成矿作用,古元古代形成的火山岩提供了大部分的成矿物质来源,成矿介质以变质水为主后期有大量地下水的加入。矿床为火山沉积-变质成因的层控型铜矿床。     

华南地区泥盆系MVT铅锌矿床S、Pb同位素特征

华南泥盆系密西西比河谷型(MVT)铅锌矿床,受控于泥盆系海进序列的台地碳酸盐岩,大体可分为以凡口为代表的中低温热液型和以泗顶、北山为代表的低温热液型。在矿床学研究基础上,对研究区内不同类型的铅锌矿、硫铁矿开展系统的硫、铅同位素分析,收集和测定493件S和64件Pb同位素数据,总结硫、铅的来源和硫同位素分馏机制,并初步探讨了成矿机制。硫同位素研究显示,矿石硫有多种来源,主要来自于还原性卤水,部分来自氧化性卤水中ΣSO_4~(2-)的还原,少量硫来自于矿区含矿地层。不同矿床在成矿作用过程中硫同位素的分馏机制不同。在以凡口为代表的中低温热液矿床中,矿石δ~(34)S值高且相对集中,以热力学分馏为主,生物分馏作用较微弱;在以泗顶、北山为代表的低温热液矿床中,矿石δ~(34)S值低且分散,以生物分馏作用为主,仅部分中粗粒铅锌矿石以热力学分馏为主。成矿作用过程中硫同位素分馏远未达到平衡状态。不同矿床的矿石铅同位素组成呈线性分布,反映出不同来源铅的混合。古老铅来自遭剥蚀的古陆,年轻铅代表泥盆系沉积物的普通铅。二者的比例与岩石中陆源物质(Pb)的含量相对应。成矿时的铅直接来自于氧化性卤水,间接来自于卤水对流经的泥盆系含矿层(尤其是底部碎屑岩)的淋滤,更间接地来自古陆剥蚀区以及海相沉积物。金属物质的迅速沉淀成矿作用与两类流体的混合有关,氧化性卤水来自蒸发盐红层盆地,沿泥盆系底部紫色砂岩经区域性迁移,其中富含大量金属成矿元素,并含有少量呈ΣSO_4~(2-)的硫;而还原性流体中富含ΣH2S的硫。流体的混合作用局限于矿区范围内,并不存在区域性的简单大规模流体混合过程。     

大兴安岭中北段二道河铅锌银多金属矿床地质特征与成矿物质来源

二道河矿床是近年来大兴安岭中北段新发现的一处大型矽卡岩型铅锌银多金属矿床.矿床成矿作用经历了早矽卡岩阶段、晚矽卡岩阶段、磁黄铁矿-黄铁矿-石英阶段、石英多金属硫化物阶段和石英-碳酸盐等5个阶段的演化.为探讨矿床成矿物质来源,本文对矿床主要金属硫化物、与成矿关系密切的花岗斑岩、闪长岩、中生代火山岩开展了S、Pb同位素分析.结果表明,矿床主要金属矿物 δ34S分布范围为5.8‰～8.9‰,呈"塔式分布",与典型矽卡岩型铅锌矿床及区域典型铅锌矿床硫同位素组成相近,与花岗质岩石较相似,表明该矿床硫主要来自于深部岩浆热液体系,热液演化过程中与奥陶系海相地层进行了硫同位素交换.矿床硫同位素组成表现为δ34Spy＞δ34SSp＞δ34SCcp＞δ34SGn,暗示主成矿阶段硫同位素分馏达到了平衡,计算得到各共存矿物对的平衡温度范围为227～382℃.该矿床矿石矿物具有高放射性壳源铅的特征,而花岗斑岩及闪长岩、中生代火山岩铅同位素则具低放射性铅特征,铅同位素数据均落入造山带演化线附近,构造图解中具有明显线性分布特征,表明其具有相同铅源及铅同位素演化特征,在Aγ-Δβ图解中均落入与岩浆作用有关的上地壳与地幔混合俯冲带铅源区.综上表明,矿床成矿物质具有多元组分的贡献,而矿石矿物与花岗斑岩及闪长岩铅同位素组成、μ值和Th/U比值都较为接近,综合矿床铅锌矿体主要产出于花岗斑岩、闪长岩与碳酸盐岩接触带的空间关系,反映其主要物质来源为燕山期中酸性侵入岩.     

陆相火山岩中银矿床的地质特征与成矿作用

本文概述了陆相火山岩的特点,论述了陆相火山岩中银矿床的共同特征,并从岩石化学成分,硫、铅同位素,成矿温度及碳、氧同位素等方面推论其成矿作用。     

New constraints on the sources and behavior of neodymium and hafnium in seawater from Pacific Ocean ferromanganese crusts

The behavior of dissolved Hf in the marine environment is not well understood due to the lack of direct seawater measurements of Hf isotopes and the limited number of Hf isotope time-series obtained from ferromanganese crusts. In order to place better constraints on input sources and develop further applications, a combined Nd-Hf isotope time-series study of five Pacific ferromanganese crusts was carried out. The samples cover the past 38 Myr and their locations range from sites at the margin of the ocean to remote areas, sites from previously unstudied North and South Pacific areas, and water depths corresponding to deep and bottom waters.For most of the samples a broad coupling of Nd and Hf isotopes is observed. In the Equatorial Pacific ε_Nd and ε_Hf both decrease with water depth. Similarly, ε_Nd and ε_Hf both increase from the South to the North Pacific. These data indicate that the Hf isotopic composition is, in general terms, a suitable tracer for ocean circulation, since inflow and progressive admixture of bottom water is clearly identifiable.The time-series data indicate that inputs and outputs have been balanced throughout much of the late Cenozoic. A simple box model can constrain the relative importance of potential input sources to the North Pacific. Assuming steady state, the model implies significant contributions of radiogenic Nd and Hf from young circum-Pacific arcs and a subordinate role of dust inputs from the Asian continent for the dissolved Nd and Hf budget of the North Pacific.Some changes in ocean circulation that are clearly recognizable in Nd isotopes do not appear to be reflected by Hf isotopic compositions. At two locations within the Pacific Ocean a decoupling of Nd and Hf isotopes is found, indicating limited potential for Hf isotopes as a stand-alone oceanographic tracer and providing evidence of additional local processes that govern the Hf isotopic composition of deep water masses. In the case of the Southwest Pacific there is evidence that decoupling may have been the result of changes in weathering style related to the buildup of Antarctic glaciation.     

Lithium Isotopic Geochemistry in Subduction Zones: Retrospects and Prospects

Subduction zones involve many complex geological processes, including the release of slab-derived fluids, fluid/rock interactions, partial melting, isotopic fractionations, elemental transporting, and crust/mantle interactions. Lithium (Li) isotopes (6Li and 7Li) have relative mass difference up to 16%, being the largest among metal elements. Thus, Li isotopes have advantage to interprete trace various geological processes. Most importantly, during crust/mantle interactions in deep subduction zones, surface materials and mantle rocks usually have distinct Li isotopic compositions. Li isotopes can be potential tracer for subduction processes, from the onset of subduction to the release of Li from subducted slabs and interaction with mantle wedge, as well as the fate of Li in slab-derived fluids and residual slabs. Moreover, the Li isotopic composition of subducting output materials can provide useful information for understanding global Li circulation. With developments in measurement and expansion of Li isotopic database, Li isotopic geochemistry will provide more inference and be a powerful tracer for understanding subduction-related processes. This work retrospected the application of Li isotopes in tracing successive subduction processes, and made some prospects for further studies of Li isotopes.     

榴辉岩相高压-超高压变质岩的He同位素地球化学研究现状与问题

He同位素是区分地壳、地幔物质,研究壳-幔相互作用最灵敏的示踪剂之一,但其在高压-超高压变质作用过程中的地球化学行为目前仍不清楚,因而制约其在榴辉岩研究中的应用。中国作为高压-超高压榴辉岩带分布的重要地区,榴辉岩产出得天独厚,大洋、大陆两种俯冲成因榴辉岩均有分布。本文在归纳榴辉岩相高压-超高压变质岩研究进展的基础上,分析了He同位素示踪在榴辉岩研究中的应用现状。     

“Henry's law” behaviour of Sm in a natural plagioclase/melt system: Importance of experimental procedure

We report an experimental study of the partitioning of Sm in a natural plagioclase/melt system as a function of concentration of Sm at constant pressure, temperature and bulk composition. Both radioactive ¹⁵¹Sm and non-radioactive Sm₂O₃ were used. In experiments in which the sample was initially held at a temperature above the liquidus for only one hour, we find that the plagioclase/ melt partition coefficient for Sm increases with decreasing concentration of Sm. There is also evidence for isotopic heterogeneity in the initially molten charge. In experiments in which the sample was initially held at the same temperature above the liquidus for 24 hours, the partition coefficient was constant as a function of concentration and no evidence for isotopic heterogeneity was observed. These experiments indicate that partition coefficients obtained from experiments involving tracer isotopes are very sensitive to experimental procedure. Our experiments also indicate that the partition coefficient for Sm between plagioclase and melt is constant over the range 3 to 50,000 ppm Sm in the melt. That range encompasses most concentrations in natural systems.     

High-precision osmium isotopes in enstatite and Rumuruti chondrites

Isotopic heterogeneity within the solar nebula has been a long-standing issue. Studies on primitive chondrites and chondrite components for Ba, Sm, Nd, Mo, Ru, Hf, Ti, and Os yielded conflicting results, with some studies suggesting large-scale heterogeneity. Low-grade enstatite and Rumuruti chondrites represent the most extreme ends of the chondrite meteorites in terms of oxidation state, and might thus also present extremes if there is significant isotopic heterogeneity across the region of chondrite formation. Osmium is an ideal tracer because of its multiple isotopes generated by a combination of p-, r-, and s-process and, as a refractory element; it records the earliest stages of condensation.Some grade 3-4 enstatite and Rumuruti chondrites show similar deficits of s-process components as revealed by high-precision Os isotope studies in some low-grade carbonaceous and ordinary chondrites. Enstatite chondrites of grades 5-6 have Os isotopic composition identical within error to terrestrial and solar composition. This supports the view of digestion-resistant presolar grains, most likely SiC, as the major carrier of these anomalies. Destruction of presolar grains during parent body processing, which all high-grade enstatite chondrites, but also some low-grade chondrites seemingly underwent, makes the isotopically anomalous Os accessible for analysis. The magnitude of the anomalies is consistent with the presence of a few ppm of presolar SiC with a highly unusual isotopic composition, produced in a different stellar environment like asymptotic giant branch stars (AGB) and injected into the solar nebula. The presence of similar Os isotopic anomalies throughout all major chondrite groups implies that carriers of Os isotopic anomalies were homogeneously distributed in the solar nebula, at least across the formation region of chondrites.     

Li同位素在斜顽辉石、镁铝榴石及镁铝尖晶石晶格内扩散与分馏的理论计算研究

斜顽辉石、镁铝榴石和镁铝尖晶石作为辉石族、石榴石族以及尖晶石族中的重要端元,是地球上地幔主要组成矿物。Li同位素是重要的地幔地球化学示踪剂,其在橄榄石、辉石和石榴石等地幔矿物中的扩散分馏的性质对理解Li同位素作为地幔地球化学示踪剂非常重要。我们通过经典力场经验势方法,从原子尺度上计算研究了不同温压条件下Li同位素在斜顽辉石、镁铝榴石和镁铝尖晶石晶格中分别通过不同的填隙机制和取代空位机制迁移的活化能和其在不同晶格位上的分馏效应。我们发现Li同位素是通过取代空位机制在斜顽辉石、镁铝榴石和镁铝尖晶石中进行迁移扩散。Li同位素在不同晶格位上的分馏作用计算表明,在三种矿物中重同位素7Li会更多地进入晶格填隙位中,而6Li则相对更多进入Mg位。温度是影响这种分馏作用的一个关键因素,相应的结果可用来解释地幔Li同位素组成特征及冷却条件下的同位素分馏等科学问题。     

锂同位素分馏机制讨论

作为一种新兴的稳定同位素示踪工具, 锂同位素地球化学的研究近年来受到了国际地学界日益广泛的关注.其应用领域涵盖了从地表到地幔的流体与矿物之间的相互作用.在地表风化作用过程中, 轻锂同位素(6Li) 优先进入固体相, 而7Li则进入流体相, 因而地表风化作用淋滤出了岩石中的重锂, 致使河水具有重的锂同位素组成, 河水又将重锂同位素组分补给海洋, 洋壳的低温蚀变作用使得海水的锂同位素组成进一步变重.在俯冲带, 由于俯冲板片释放的流体具有重锂同位素组成的特征, 它们上升并交代上覆的地幔楔和相邻的地幔, 使得地幔楔的锂同位素组成变重.同时, 深俯冲的板片由于脱水而具有较轻的锂同位素组成, 它们在地幔中可能形成一个局部轻锂的地幔储源.影响地幔橄榄岩锂同位素分馏的因素主要有3个方面: 温度、扩散机制以及外来熔体的反应.由于高温下地幔矿物之间的锂同位素分馏很小, 而单纯的扩散分馏机制不能够很好的解释我国华北汉诺坝地区地幔橄榄岩中矿物之间的锂同位素分馏.因此, 具有轻锂同位素组成的熔体与橄榄岩之间的反应是上述现象的一个合理解释.需要指出的是, 在橄榄岩-熔体反应的过程中, 锂同位素的扩散作用也对地幔矿物之间的同位素分馏有一定的贡献.      

环境同位素示踪技术在矿井水防治中的应用

环境同位素示踪技术是近几年新发展起来的一项新技术。采用环境同位素作为天然示踪剂可以标识矿井水分布、运移和补给规律,为矿井水害的防治提供直接依据,实例表明,采用该技术具有快捷、准确以及易于推广应用等特点。     

热电离飞行时间质谱法用于铀矿勘查的铅同位素示踪

在自行研制的低成本热电离飞行时间质谱仪(TI-TOF-MS)基础上,开展了应用TI-TOFMS法测定铀矿钻孔样品中铅同位素示踪铀矿勘查的研究。文中介绍了样品的前处理,铅的分离和富集步骤,仪器测量及数据处理等。TI-TOF-MS法测量铅同位素比值~(204)Pb/~(206)Pb、~(207)Pb/~(206)Pb和~(208)Pb/~(206)Pb的精密度分别为0.94%、0.37%和0.14%,可满足铀矿同位素示踪的要求。通过对北方某铀矿钻孔岩心取样的测量结果表明,TI-TOF-MS测量铅同位素的方法能够用于示踪铀矿。     

Conservative mixing of stable isotopes across estuarine salinity gradients: A conceptual framework for monitoring watershed influences on downstream fisheries production

Strong changes in stable isotope tracers commonly occur across estuarine salinity gradients from freshwater to the sea. The tracer gradients reflect the different geochemistries and mixing of freshwater and seawater, and these bottom-up geochemical influences are recorded in estuarine food webs in the isotopic compositions of animals. Conservative mixing calculations suggest that watershed-level inputs of freshwater and nutrients should exert strong influences on isotopic values of estuarine consumers, especially consumers such as bivalves that largely depend on phytoplankton production. Deviations from conservative isotope mixing also occur, and the magnitude of these deviations measures the strength of within-estuary organic matter cycling for estuarine food webs, especially inputs of non-phytoplankton foods such as macrophyte detritus and benthic algae. Measuring consumer isotopes across salinity gradients should be a relatively simple way to monitor effects of watershed nutrient loading and hydrologic flushing in supporting estuarine fisheries production.