铁氧化物型铜金矿中磁铁矿微量元素含量对结构参数影响的初步研究

磁铁矿是一种重要的铁氧化物,广泛分布于自然界的三大类岩石和各种不同类型的矿床中.采用激光剥蚀电感耦合等离子质谱仪,分析了澳大利亚Ernest Henry铁氧化物型铜金矿床中磁铁矿的微量元素含量,并用X衍射测定微量元素含量最高和最低时磁铁矿相应的晶胞参数,从而评价微量元素变化对磁铁矿结构参数的影响.结果表明,磁铁矿中存在着阳离子替代关系;微量元素含量高的磁铁矿晶胞参数a0值小于标准磁铁矿的a0值,含微量元素低的磁铁矿晶胞参数a0值则大于标准磁铁矿的a0值;磁铁矿中所含微量元素不同,其对应的晶胞参数a0值亦有明显变化.     

主编絮语

第一行过渡金属元素及痕量贵金属元素高度富集在硫化物矿物中,常形成具有工业意义的矿床,使得硫化物具有重大的经济价值。对天然硫化物矿物中的这些痕量金属元素丰度及其分布的研究,在矿石成因学、经济地质学、环境地球化学等领域具有重要的应用价值。激光剥蚀-电感耦合等离子体质谱(LA-ICP-MS)微区分析技术是一种强大的痕量元素分析工具,非常适合直接分析硫化物矿物中痕量元素的浓度及其空间分布。由于硫化物的激光剥蚀特性与硅酸盐及氧化物不同,分析校准用的标准物质又极度缺乏,严重阻碍了这一技术在硫化物矿物微区分析中的应用。本文评述了硫化物简介、硫化物中痕量金属元素分析的意义、LA-ICP-MS微区分析技术在硫化物矿物痕量元素分析中的优势及近年来的应用进展、硫化物分析中的干扰与校准、包含铂族元素及金的硫化物标准物质的研制进展及合成硫化物标准物质最有应用前景的方法。     

赣中大王山石英脉型钨钼多金属矿床成岩成矿年代学及其地质意义

赣中大王山钨钼多金属矿床位于钦杭结合带西缘大王山—于山W-U-Sn-Au多金属成矿带,为典型的石英脉型矿床,其赋矿岩体具有多阶段特征.通过LA-ICPMS锆石U-Pb测年技术,得到晚阶段细粒花岗岩成岩年龄为145.1±0.89 Ma,与早阶段形成的中粗粒花岗岩形成时间接近(147.8±1.9 Ma);利用辉钼矿Re-Os同位素测年技术,得到成矿年龄为147.6±1.8 Ma,表明该矿床形成于晚侏罗世,与南岭地区及其周边的燕山期石英脉型钨钼多金属矿床的成岩、成矿时代一致.辉钼矿中Re的含量具有指示成矿物质来源的重要参考价值,大王山钨多金属矿床的辉钼矿中Re含量较低,为2215× 10-9~ 10 183× 10-9,与以钨为主、共生或伴生钼的矿床特征相吻合,指示其成矿物质主要来自于壳源或壳幔混合源,即在160~ 110 Ma之间,古太平洋板块与欧亚板块之间的主应力作用方向发生转变,促使我国东部岩浆活动频繁,岩浆期后热液与围岩碱交代明显,大量成矿物质被萃取,并在成矿有利部位富集.     

磁铁矿中微量元素的激光剥蚀-电感耦合等离子体质谱分析方法探讨

微区原位分析提供了固体物质的元素及同位素组成的空间分布信息,有利于解决不同的地质问题、环境问题和工业方面的问题。磁铁矿中微量元素地球化学组成有助于研究成矿时的物理化学条件和示踪新的矿床。本文建立了利用激光剥蚀-电感耦合等离子体质谱(LA-ICP-MS)分析磁铁矿中微量元素的方法,探讨了选择必要的分析元素,选择合适的内标、外标,选择恰当的束斑大小等方法。以LA-ICP-MS分析澳大利亚Ernest Henry IOCG矿床磁铁矿中微量元素的方法为例,采用NIST SRM 610作为外标,Fe作为内标较为合理;正常情况下采用32~60 μm的激光束,但对于个别样品中磁铁矿颗粒较小,可以考虑使用较小的激光束(24 μm或16 μm);为消除质谱干扰,Ti选择测量⁴⁹Ti,Cu选择测量⁶⁵Cu,Sn选择测量¹¹⁸Sn。     

硫化物矿物中痕量元素的激光剥蚀-电感耦合等离子体质谱微区分析进展

第一行过渡金属元素及痕量贵金属元素高度富集在硫化物矿物中,常形成具有工业意义的矿床,使得硫化物具有重大的经济价值。对天然硫化物矿物中的这些痕量金属元素丰度及其分布的研究,在矿石成因学、经济地质学、环境地球化学等领域具有重要的应用价值。激光剥蚀-电感耦合等离子体质谱(LA-ICP-MS)微区分析技术是一种强大的痕量元素分析工具,非常适合直接分析硫化物矿物中痕量元素的浓度及其空间分布。由于硫化物的激光剥蚀特性与硅酸盐及氧化物不同,分析校准用的标准物质又极度缺乏,严重阻碍了这一技术在硫化物矿物微区分析中的应用。本文评述了硫化物简介、硫化物中痕量金属元素分析的意义、LA-ICP-MS微区分析技术在硫化物矿物痕量元素分析中的优势及近年来的应用进展、硫化物分析中的干扰与校准、包含铂族元素及金的硫化物标准物质的研制进展及合成硫化物标准物质最有应用前景的方法。     

新疆磁海铁矿床Fe-O-S同位素和元素地球化学示踪

新疆磁海铁矿位于北山构造-成矿带西端,以磁海矿段为主要组成部分,铁矿体主要为透镜状、似层状,围岩以辉绿岩为主,二者接触线截然且平直;另外一种矿体产在基性岩体与地层接触带的石榴子石透辉石矽卡岩岩体内,整个矽卡岩岩体即为铁矿体。通过野外矿床特征与矿相学研究,成矿过程可分为:(1)矿浆期,以磁铁矿+单斜辉石+普通角闪石的近同时产出为特征;(2)矽卡岩期,先期以石榴子石+透辉石+磁铁矿为特征,后期以透闪石/阳起石+石英+磁黄铁矿+黄铜矿+黄铁矿的组合为特征。通过对矿浆期及矽卡岩期典型矿物的地球化学及Fe、S、O同位素结果分析,认为矿浆期铁质具有幔源特征,矽卡岩期成矿流体对矿浆期具有继承性。通过与前人研究结果对比分析,认为磁海成矿可能形成于塔里木地区二叠纪地幔柱背景,含矿母岩浆可能为地幔柱的分支。     

胶东金青顶金矿床成矿流体来源的黄铁矿微量元素及He-Ar同位素证据

金青顶金矿床是目前国内最大的石英单脉型金矿,其金储量超过50 t,规模为大型。对该矿床成矿流体性质和来源的研究十分必要。笔者通过Ⅱ号矿体主要载金矿物黄铁矿微量元素的研究发现,其Co/Ni为2.317～11.734(平均7.17),显示主要为热液成因;高场强元素(HFSE)特征显示,成矿早期以富F流体为主,主成矿期以富Cl流体为主;稀土配分模式显示成矿物质并不是直接来源于围岩昆嵛山二长花岗岩。对黄铁矿流体包裹体He、Ar同位素特征的研究表明,3He/4He、40Ar/36Ar分别为0.1～2.2 Ra(平均值0.60 Ra),462.7～1 507.5(平均值831),显示成矿流体主要源自地壳,并与深部幔源流体发生了不同程度的混合,且上升过程中有少量大气降水加入。     

Determination of trace elemental signatures in placer gold by laser ablation–inductively coupled plasma–mass spectrometry as a potential aid for gold exploration

It is possible that placer gold retains the trace element composition (`signature') of the parent lode. Laser ablation–inductively coupled plasma–mass spectrometry (LA–ICP–MS) offers sensitive detection limits of 59 elements with sub-millimetre sample spot sizes, ideal for signature analysis of placer. Here, the optimum laser parameters, analytical precision and reproducibility of elemental signatures are determined in placer nuggets by infrared LA–ICP–MS. The highest precision was offered by Q-switched ablation at a relatively low energy level, using Au as an internal standard; these parameters gave median precision values of 33–82% RSD for trace elements in nuggets. In addition to major constituents such as Ag, Cu and Hg, placer from several rivers world-wide commonly contained a wide range of trace elements including, in some cases, unusual REE patterns. At least two distinct signatures could be distinguished in placer from most of the rivers examined, while multiple examples of certain signatures were also seen. Tracking these signatures back to their original tributaries may offer a means of identifying the number and approximate location of deposits within a river watershed, thereby significantly aiding exploration.     

保山地块漕涧花岗伟晶岩地球化学、锆石U-Pb年代学及其地质意义

本文对出露于保山地块北部漕涧地区的花岗伟晶岩脉进行了全岩元素地球化学、锆石U-Pb年代学和Hf同位素组成研究,旨于揭示与紧邻的漕涧花岗岩体间的成因关系及其形成环境。伟晶岩样品表现出高硅(Si O2=73.02%~75.35%)、富碱(K2O+Na2O=9.10%~10.79%)、过铝质(A/CNK=1.05~1.13)特征,在Si O2-K2O岩石判别图解上属钾玄岩系列;微量元素原始地幔标准化配分曲线上,花岗伟晶岩显示清晰的Rb、U、Ta和Pb正异常,Ba、Sr、Ti、Th和Nb负异常;稀土元素含量很低,总量3.99×10-6~17.29×10-6,稀土元素球粒陨石标准化配分曲线表现为轻稀土富集型,具有明显的正Eu异常(δEu=2.92~14.7)。锆石形态学与原位稀土元素组成显示:锆石颗粒粗大(颗粒长约150~400μm),阴极发光强度较弱,内部为海绵状结构,边部发育韵律环带;锆石Th/U比值低,主要介于0.004~0.009,重稀土元素富集。通过图解(Sm/La)N-La和Ce/Ce*-(Sm/La)N,判断锆石具有岩浆锆石与热液锆石过渡的特征。2件样品单颗粒锆石U-Pb年龄变化于85~54Ma,测点位于锆石边部韵律环带发育的微区所得出的谐和年龄分别为73.44±1.0Ma(MSWD=1.03)和67.12±1.60Ma(MSWD=4.2);其余测点的谐和年龄为61~57Ma。花岗伟晶岩脉中锆石εHf(t)值分布范围为-10.1~-4.7(集中于-6.7~-5.7),分布较为集中,对应的Hf同位素地壳模式年龄tC DM为1260~1565Ma(集中于1310~1360Ma)。这些地化特征综合表明漕涧花岗伟晶岩脉与花岗岩体有着亲缘关系,共系保山地块先存加厚地壳元古代基底物质的减压熔融的产物,其形成于新特提斯洋俯冲末期至随后发生的印度欧亚大陆碰撞初期的构造背景下。     

The Precision and Sensitivity of Thermal Ionisation Mass Spectrometry (TIMS): An Overview of the Present Status

This paper illustrates that sample size cannot be reduced below a theoretical limit and still achieve the highest precision obtainable on modern mass spectrometers. Reproducibility at the few ppm level is achievable and is related essentially to ion counting statistics. The number of atoms necessary to carry out such measurements is related directly to the sensitivity of the instrumentation. As most of the elements of interest are not major constituents of natural silicates, a lower limit to the size of the starting sample is assessed. Even for a number of elements for which very high ion per atom yields are attained by TIMS, minimum sample mass is an important limiting factor for precious or rare samples and may reduce the scientific output of experiments or place a major constraint on the sampling strategy itself. For rare meteorites or individual Martian samples expected to be returned in amounts at the gramme scale for rocks or at the microgramme scale for dust, the high sensitivity of TIMS is a requirement. Nevertheless, a compromise has to be found between sample consumption and the minimal desirable precision for a useful isotopic measurement.     

Stable isotopic and trace element evidence for restricted fluid migration in 2 GPa eclogites

Mineral stable isotopic and trace element studies in 2 GPa banded eclogites of the Tauern Window, eastern Alps, record mm- to cm-scale heterogeneities that reflect compositional variations in the accompanying metamorphic fluids. A close correlation between dolomite mode and dolomite δ¹⁸O is consistent with equilibrium partitioning among coexisting minerals and fluids. Small variations in dolomite δ¹³C values correspond with δ¹⁸O variations, but an overall decrease in dolomite δ¹³C by c. 1%o across a 12-cm sample is a relict feature that pre-dates eclogite equilibration. Garnet, omphacite, and clinozoisite rims show little systematic mineral-mineral partitioning behaviour for Ti, V, Cr, Y, Sr, or Zr; major elements, however, are well equilibrated among these same minerals. Despite the apparent lack of mineral-mineral trace element equilibration, most of the trace elements vary systematically with water activity calculated in each layer. Trace element behaviour during the eclogite metamorphism thus appears to have been controlled largely by mineral-fluid interactions along grain boundaries. Shallow structural levels in other subduction complexes (c. 10-45 km) typically exhibit fracture-controlled permeability and extensive metasomatism, but there is no field or geochemical evidence for extensive fluid advection during high-pressure metamorphism in the Tauern eclogites. Because most dewatering and devolatilization during tectonic burial occurs prior to eclogite conditions, the volumetric fluid/rock ratio in eclogites should generally be low. Low fluid/rock ratios, coupled with the possible non-wetting nature of the fluids, permits the production and preservation of fine-scale chemical heterogeneities in deeply subducted eclogites and associated fluids. However, the eventual breakdown at greater depth of volatile-bearing dolomite, phengite, clinozoisite, zoisite, or amphibole could lead to renewed fracture-controlled fluid release from the subducted rocks to regions appropriate for arc magma generation.     

西南天山前寒武纪基底时代和特征：锆石U—Pb年龄和Nd—Sr同位素组成

采用锆石U-Pb定年方法,精确测定了西南天山木扎尔特群花岗片麻岩的结晶锆石年龄为（707±13）Ma(MSWD=0.33)。元素地球化学特征和低的ε     

云南个旧西凹蚀变花岗岩型铜-锡多金属矿床萤石地球化学特征及其地质意义

关键金属锡作为全球高科技产业的重要战略性资源,其成矿作用及找矿勘查均是目前国际矿床学领域研究的热点.位于滇东南有色金属成矿带西端的个旧具有全球规模最大的锡矿储量,因其具有独特的成矿条件而备受关注.近年来,在个旧老厂矿田西部凹陷带花岗岩体内部发现中型-大型铜-锡多金属矿体,但对其尚缺乏系统的研究.文章对个旧老厂矿田重点坑道和钻孔开展构造-岩相蚀变特征解析,观察到锡铜矿化主要以石英-电气石-萤石-硫化物-锡石脉的形式产于似斑状蚀变花岗岩中,少量以萤石硫化物形式产于花岗岩与碳酸盐接触带的矽卡岩中.文章对与2种成矿作用相关的萤石开展LA-ICP-MS及ICP-MS微量元素和Sr-Nd同位素分析.结果显示:蚀变花岗岩型脉状萤石∑REE为(7～749)×10-6(LA-ICP-MS)、(45.5～77.4)×10-6(ICP-MS),具有强烈的Eu负异常(δEu=0.01～0.08)和弱Ce负异常(δCe=0.56～0.92),(87Sr/86Sr)i变化于0.70953～0.71147;矽卡岩型萤石∑REE为(27.2～1277.0)×10-6(LA-ICP-MS)、(29.8～161.0)×10-6(ICP-MS),具有显著的Eu负异常(δEu=0.01～0.19)和弱的Ce负异常(δCe=0.44～1.05),(87Sr/86Sr)i变化于0.70870～0.71553.通过综合分析这2类萤石的地球化学特征,认为蚀变花岗岩型脉状萤石与矽卡岩型萤石均形成于氧化向还原过渡的环境,且均为岩浆热液活动的产物.2类萤石为近同期形成,其中矽卡岩型萤石中Ca来源于老卡等粒花岗岩和碳酸盐岩地层,蚀变花岗岩型萤石中Ca主要来源于老卡等粒花岗岩.综上,个旧老厂矿田西部凹陷带的似斑状花岗岩为老卡等粒花岗岩体边部的早阶段岩体,其未提供成矿物质,但提供了流体运移通道和就位空间,晚阶段流体上升侵位在老厂西部凹陷带似斑状花岗岩体内部形成岩浆热液脉型铜-锡多金属矿体.该研究可以为个旧锡矿深部及外围增储和滇东南锡矿带下一步找矿方向提供重要的理论指导.     

海洋天然气水合物氢氧同位素分馏初探

天然气水合物的形成会造成氢、氧同位素的分馏.在实验室合成研究中,利用天然海水 [(含 0.03%十二烷基硫酸钠 (SDS)]与甲烷气体反应,通过对水合物生成前后溶液中的 Cl-的质量浓度和氢、氧同位素组成的测定,研究了天然气水合物生成过程中氢、氧同位素的分馏情况.实验证明氢、氧的重同位素易于富集在水合物中,其在天然海水-甲烷体系中的分馏系数分别为 1.018～ 1.036和 1.003 4～ 1.006 3,这一分馏系数稍大于前人在纯水和 NaCl溶液中所测得的分馏系数.     

Multicollector ICPMS as tool for isotopic fingerprinting in environmental, biomedical and geochemical studies

Stable isotopes, such as C, N, O and S, are successfully used as classical environmental tracers. During the last few years, heavy stable isotopes are getting more and more attention as tracers and proxies in biogeochemical and environmental studies. Multicollector Inductively Coupled Plasma Mass Spectrometry （MC-ICPMS） has enabled scientists to obtain high precise isotopic analyses of heavy elements such as Cl, Ca, Fe, Cu, Zn, Hg and Pb. These isotopic systems can be used as important tracers in studying metal contaminants, biomedical processes and pollution of aquatic environments. MC-ICPMS is a powerful technique for the isotopic analysis of most elements, with the exception of light elements such as H, C, N and O and noble gases. The advantage of the ICP source is that it can ionize all elements with very high sensitivity. Various inlet systems can be used to introduce samples into the mass spectrometer, for instance gas chromatography （GC）, liquid chromatography （LC）, laser ablation, or conventional liquid nebulization. The aerosol is transported by an Ar and/or He gas flow into the ICP source where it is effectively ionized and introduced into the mass analyzer through a differential pumping system. The variable multicollector detector array allows the user to adjust the detector positions along the focal plane of the mass spectrometer so that all isotopes of interest can be measured simultaneously. Molecular interferences as carbides, nitrides, oxides, argides or doubly-charged species can show up in the mass spectrum and interfere with the elemental isotope peaks. High mass resolution is needed to effectively discriminate against these interferences. The ion optics of the Finnigan NEPTUNE is specially designed to meet this requirement and expand the power of isotope ratio measurements even to elements where previously isobaric interferences were the limit.     

Quantification and isotopic analysis of nitrogen in rocks at the ppm level using sealed tube combustion technique: A prelude to the study of altered oceanic crust

The present paper reports recent improvements in sealed tube combustion technique used for the determination of N isotopic composition in various rocks characterized by low N contents (i.e. few ppm). Nitrogen is extracted from samples by combustion in quartz tubes sealed under vacuum. The nitrogen gas purified using Cu, CuO and CaO, is quantified as dinitrogen N₂ by capacitance manometry in ultra-high vacuum line. Nitrogen isotopic analysis is performed on a triple-collector static vacuum mass spectrometer, allowing measurement of nanomole quantity of N₂. Nitrogen amount and isotopic composition of the analytical blanks are low and describe Gaussian distribution with mean values of 0.65 ± 0.30 nmol N and − 3.7‰ ± 2.7‰, respectively (2σ). Systematic analyses of international and internal standards demonstrate that this technique provides accurate and precise results. The precision on N content and isotopic composition are better than ± 8% and ± 0.5‰ respectively, even for samples containing less than 2 ppm N. The sealed tube combustion technique is shown to apply successfully to rocks of various lithologies such as metagabbros, metaperidotites and altered basalts. It is thus suitable for studying oceanic crust in a perspective to better constrain N exchanges between Earth mantle and surface reservoirs. The investigation can also be extended to analysis of small size samples, particularly when little sample exists and when high spatial resolution is required.     

Apatite as an indicator mineral for mineral exploration: trace-element compositions and their relationship to host rock type

Over 700 apatite grains from a range of rock types have been analysed by laser-ablation microprobe ICPMS for 28 trace elements, to investigate the potential usefulness of apatite as an indicator mineral in mineral exploration. Apatites derived from different rock types have distinctive absolute and relative abundances of many trace elements (including rare-earth elements (REE), Sr, Y, Mn, Th), and chondrite-normalised trace-element patterns. The slope of chondrite-normalised REE patterns varies systematically from ultramafic through mafic/intermediate to highly fractionated granitoid rock types. (Ce/Yb)_cn is very high in apatites from carbonatites and mantle-derived lherzolites (over 100 and over 200, respectively), while (Ce/Yb)_cn values in apatites from granitic pegmatites are generally less than 1, reflecting both HREE enrichment and LREE depletion. Within a large suite of apatites from granitoid rocks, chemical composition is closely related to both the degree of fractionation and the oxidation state of the magma, two important parameters in determining the mineral potential of the magmatic system. Apatite can accept high levels of transition and chalcophile elements and As, making it feasible to recognise apatite associated with specific types of mineralisation. Multivariate statistical analysis has provided a user-friendly scheme to distinguish apatites from different rock types, based on contents of Sr, Y, Mn and total REE, the degree of LREE enrichment and the size of the Eu anomaly. The scheme can be used for the recognition of apatites from specific rock types or styles of mineralisation, so that the provenance of apatite grains in heavy mineral concentrates can be determined and used in geochemical exploration.     

四川省阿坝地区地表水地球化学特征

阿坝州位于四川西北部,与青海、甘肃交界,处于高海拔地区;该地区地表水资源丰富,长江与黄河上游水系均流经该区域。通过系统性采集区内河水(76件)、井水(7件)、溪水(8件)等样品,测试水体中D与18 O的丰度与微量元素含量。结果表明:①受大气降水与流经地层的影响,阿坝地区河水中D与18 O的丰度均显著高于溪水、井水与自来水等介质,线性相关性表明,河水中18 O的富集与硫酸盐矿物的溶解密切相关;②阿坝地区井水、自来水、溪水之间存在明显的水力联系;③对于阿坝地区而言,黄河上游河流中δD与δ18 O值均高于长江上游水系河流,但两者之间差别较小,这由于同一地区水系具有相同的大气降水来源;④河水、井水、溪水等表水中微量元素呈高Ba、Zn、Cr,低As、Pb、Cd的特点,与该地区岩石样品中微量元素特征基本一致,表明该地区表水中微量元素含量主要受地质背景因素控制。     

Multi-Element Isotope Dilution Sector Field ICP-MS: A Precise Technique for the Analysis of Geological Materials and its Application to Geological Reference Materials

We present a multi-element technique for the simultaneous determination of twelve trace elements in geological materials by combined isotope dilution (ID) sector field inductively coupled plasma-mass spectrometry (SF-ICP-MS) following simple sample digestion. In addition, the concentrations of fourteen other trace elements have been obtained using the ID determined elements as internal standards. This method combines the advantages of ID (high precision and accuracy) with those of SF-ICP-MS (multi-element capability, fast sample processing without element separation) and overcomes the most prevailing drawbacks of ICP-MS (matrix effects and drift in sensitivity). Trace element concentration data for BHVO-1 (n = 5) reproduced to within 1–3% RSD with an accuracy of 1–2% relative to respective literature values for ID values and 2–3% for all other values. We have applied this technique to the analysis of seventeen geological reference materials from the USGS, GSJ and IAG. The sample set also included the new USGS reference glasses BCR-2G, BHVO-2G and BIR-1G, as well as the MPI-DING reference glasses KL2-G and ML3B-G, and NIST SRM 612. Most data agreed within 3–4% with respective literature data. The concentration data for the USGS reference glasses agreed in most cases with respective data of the original rock powder within the combined standard uncertainty of the method (2–3%), except the U concentration of BIR-1G, which showed a three times higher concentration compared to BIR-1.