Natural Clinopyroxene Reference Materials for In Situ Microanalysis

Two clinopyroxene megacrysts, DMP-2 and DMP-3, were collected from Cenozoic alkali basalts in the Hannuoba region of China. They were characterised for major and trace element compositions for in situ microanalysis. EPMA and LA-ICP-MS analyses indicate homogeneity in the element mass fractions in both clinopyroxene samples. Bulk analyses using various techniques (XRF, ICP-OES and solution ICP-MS) also reveal good consistency in their major and trace element data. They, thus, can be used as potential reference materials for elemental in situ microanalysis. Accordingly, element mass fractions are recommended for thirty-two elements.     

New Reference Materials,Analytical Procedures and Data Reduction Strategies for Sr Isotope Measurements in Geological Materials by LA-MC-ICP-MS

Laser ablation multi-collector mass spectrometry (LA-MC-ICP-MS) has emerged as the technique of choice for in situ measurements of Sr isotopes in geological minerals. However, the method poses analytical challenges and there is no widely adopted standardised approach to collecting these data or correcting the numerous potential isobaric inferences. Here, we outline practical analytical procedures and data reduction strategies to help establish a consistent framework for collecting and correcting Sr isotope measurements in geological materials by LA-MC-ICP-MS. We characterise a new set of plagioclase reference materials, which are available for distribution to the community, and present a new data reduction scheme for the Iolite software package to correct isobaric interferences for different materials and analytical conditions. Our tests show that a combination of Kr-baseline subtraction, Rb-peak-stripping using βRb derived from a bracketing glass reference material, and a CaCa or CaAr correction for plagioclase and CaCa or CaAr + REE²⁺ correction for rock glasses, yields the most accurate and precise ⁸⁷Sr/⁸⁶Sr measurements for these materials. Using the analytical and correction procedures outlined herein, spot analyses using a beam diameter of 100 μm or rastering with a 50–65 μm diameter beam can readily achieve < 100 ppm 2SE repeatability ("internal") precision for ⁸⁷Sr/⁸⁶Sr measurements for materials with < 1000 μg g^-1 Sr.     

Reference Materials for Geochemical Studies: New Analytical Data by ICP-MS and Critical Discussion of Reference Values

Abundances of twenty four trace elements, including Y and fourteen rare earth elements (REE), are reported for eighty six geological reference materials and four proficiency testing samples. Analytical data were obtained by ICP-MS using solution nebulisation after mixed acid digestion (HF-HClO₄) under pressure. Analysed samples cover a wide range of element concentrations and mineralogical compositions, including samples for which there are few previously published data. Precision for elemental determinations in nearly 90% of the samples analysed is better than 5%. Accuracy, estimated by comparison with data from compilations is better than 6% for well characterized reference materials. Results obtained for samples that are low in trace elements are often significantly lower than compiled reference values. A critical discussion of the compiled data sets, especially for Y and the REEs, indicates that some reference values seem to be erroneous.     

A LA-ICP-MS Comparison of Reference Materials Used in Cassiterite U-Pb Geochronology

Laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) is used to compare the suitability of four cassiterite (SnO₂) materials (SPG, Yankee, AY-4 and Jian-1), and three matrix-mismatched reference materials (NIST SRM 612, NIST SRM 614 and 91500 zircon) for normalisation of U-Pb and Pb-Pb isotope ratios in cassiterite. The excess variance of ages determined by LA-ICP-MS is estimated to be ±0.33% for ²⁰⁷Pb/²⁰⁶Pb vs. ²⁰⁸Pb/²⁰⁶Pb isochron ages and ± 1.8% and for U-Pb ages. Incorporation of this excess variance in cassiterite ages is necessary for realistic uncertainties. ²⁰⁷Pb-²⁰⁶Pb ages are advantageous for dating Precambrian cassiterite such as SPG compared with U-Pb ages as matrix effect on instrumental mass fractionation of Pb isotopes are generally considered to be minor. We note minor bias in ²⁰⁷Pb/²⁰⁶Pb vs. ²⁰⁸Pb/²⁰⁶Pb isochron ages (~ 0.6%) when using either the NIST SRM 614 or 91500 zircon reference materials and emphasise the requirement for uncertainty propagation of all sources of error and reference materials with comparable U and Pb mass fraction to the cassiterite. The ²³⁸U/²⁰⁶Pb isotopic ratios from normalisation to matrix-mismatched reference materials show varied results, which emphasises the need to use matrix-matched reference materials for calculating U-Pb ages. When cross-calibrated against each other, LA-ICP-MS U-Pb ages of the ca. 1535 Ma SPG, ca. 245 Ma Yankee and ca. 155 Ma Jian-1 cassiterites are all consistent with their ID-TIMS values.     

Calcium Isotopic Fractionation and Compositions of Geochemical Reference Materials

High‐precision calcium isotopic compositions of a set of geological reference materials from the IAG (OU‐6), ANRT (UB‐N), MPI‐DING, USGS and GSJ, relative to NIST SRM 915a, are reported here. Measurements were performed by thermal ionisation mass spectrometry (Triton instrument) using a ⁴²Ca–⁴³Ca double spike. δ^44/40Ca values of selected reference materials, mainly felsic rocks, are reported for the first time. Felsic rock values of δ^44/40Ca ranged from 0.13‰ to 1.17‰, probably implying Ca isotopic fractionation could occur during magma evolution. δ^44/40Ca values of ultramafic rocks, ranging from 0.74‰ to 1.51‰, were positively correlated with MgO and negatively with CaO contents, possibly owing to Ca isotopic fractionation during partial melting. δ^44/40Ca of intermediate‐mafic rocks were around 0.78‰ and displayed limited variation, suggesting Ca isotopic fractionation is insignificant during magma evolution processes. As expected, δ^44/40Ca of sedimentary and metamorphic rocks varied widely due to complex geological processes.     

A Preliminary Appraisal of Seven Natural Zircon Reference Materials for In Situ Hf Isotope Determination

There is a growing need for new zircon reference materials for in situ Hf-isotope analysis by laser ablation-multicollector inductively coupled plasma-mass spectrometry (LA-MC-ICP-MS). In this contribution we document the results of a preliminary investigation of seven natural zircons, conducted in order to test their suitability in this regard. Solution MC-ICP-MS data on separated Lu and Hf fractions provided reference compositional data while the results of ca. 750 in situ LA-MC-ICP-MS analyses allowed assessment of potential micrometre-scale heterogeneity. On the basis of these analyses and additional relevant considerations such as availability, size and (Lu)Yb/Hf ratio, we suggest that, of the currently available zircons, Temora-2 and Mud Tank are most likely to provide robust reference materials for Hf isotope determinations both at the present time and into the future. The former has the advantage of also being well-characterised for U-Th-Pb systematics and suitable for in situ age determination, while the latter is the most readily available and is of very large grain size. Additional materials such as BR266, and 91500, although limited in supply, show more consistent Lu/Hf ratios and are thus of use in monitoring elemental fractionation during ICP-MS analysis.     

Boron Isotopic Composition and Concentration of Ten Geological Reference Materials

We present boron isotope and concentration data from magmatic (komatiitic to rhyolitic) and sedimentary geological silicate and artificial glass reference materials that cover a wide spectrum of boron isotope compositions and boron concentrations. Boron isotope compositions were determined by TIMS (Cs₂BO₂⁺ -graphite and BO₂^- method) and boron concentrations by ICP-AES. Boron concentrations ranged from 7 to 159μ g^-1 and agree within 14% with published values. Based on replicate analyses of individually prepared sample aliquots an overall external reproducibility of better than 10% was determined. The obtained δ¹¹B values ranged from -12.6 to +13.6% and were reproducible within 1.1 % (2 RSD; excluding NTIMS) on the basis of individually prepared sample aliquots. The δ¹¹B values of JA-1 (+5.3%), JB-3 (+5.9%) and JR-2 (+2.9%) overlap the published data within analytical uncertainty. For the first time δ¹¹B values for the TB (-12.6%) and the MPI-DING glasses GOR-128-G (+13.6%), GOR-132-G (+7.1 %) and StHs6/80-G (-4.5%) are reported. The δ¹¹B values obtained by the Cs₂BO₂⁺ -graphite and the BO₂^- method as well as the majority of δ¹¹B values obtained using different sample preparation methods agree within analytical uncertainty. Therefore, we conclude that none of these analytical methods introduce any systematic error on the obtained δ¹¹B values.     

Molybdenum Concentrations Measured in Eleven USGS Geochemical Reference Materials by Isotope Dilution Thermal Ionisation Mass Spectrometry

Molybdenum concentrations in eleven USGS geochemical reference materials AGV-1, BCR-1, BHVO-1, BIR-1, DNC-1, DTS-1, G-2, GSP-1, MAG-1, PCC-1 and W-2 were measured by isotope dilution thermal ionisation mass spectrometry (ID-TIMS). In every case but one, the concentrations determined in this study were significantly lower than the current consensus values. Molybdenum concentrations determined by ID-TIMS are inherently more accurate and precisions may be up to an order of magnitude higher than those measured by other analytical techniques.     

Natural Titanite Reference Materials for In Situ U‐Pb and Sm‐Nd Isotopic Measurements by LA‐(MC)‐ICP‐MS

Titanite is a common accessory mineral that preferentially incorporates considerable amounts of U and light rare earth elements in its structure, making it a versatile mineral for in situ U‐Pb dating and Sm‐Nd isotopic measurement. Here, we present in situ U‐Pb ages and Sm‐Nd isotope measurement results for four well‐known titanite reference materials (Khan, BLR‐1, OLT1 and MKED1) and eight titanite crystals that could be considered potential reference material candidates (Ontario, YQ‐82, T3, T4, TLS‐36, NW‐IOA, Pakistan and C253), with ages ranging from ~ 20 Ma to ~ 1840 Ma. Results indicate that BLR‐1, OLT1, Ontario, MKED1 and T3 titanite have relatively homogeneous Sm‐Nd isotopes and low common Pb and thus can serve as primary reference materials for U‐Pb and Sm‐Nd microanalysis. YQ‐82 and T4 titanite can be used as secondary reference materials for in situ U‐Pb analysis because of their low common Pb. However, internal structures and mineral inclusions in YQ‐82 will require careful selection of suitable target domains. Pakistan titanite is almost concordant with an age of 21 Ma and can be used as a reference material when dating Cenozoic titanite samples.     

U-Pb Zircon Geochronology with an Integrated LA-ICP-MS Microanalytical Workstation: Achievements in Precision and Accuracy

Laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) is a microanalytical tool especially suitable for providing fast and precise U-Pb geochronological results on zircon grains. A new 193 nm excimer laser adapted to a micromachining workstation, equipped with a newly designed two-volume ablation cell and coupled with a quadrupole ICP-MS, is presented here. The system was tuned routinely to achieve sensitivities in the range of 3000 cps/μg g⁻¹ for ²³⁸U (< 2% RSD), with a 34 μm spot size, at 5 Hz and ∼ 8 J cm⁻², while ablating the NIST SRM 612 glass reference material. The system was capable of providing fast (< 1.5 minutes each analysis) and precise (generally < 1.5% 1s errors) ²⁰⁶Pb/²³⁸U zircon ages. The ages of widely used reference material zircons (Plesovice, 337 Ma; Temora, 416 Ma; R33, 418 Ma; Sri Lanka, 564 Ma; 91500, 1065 Ma) could be precisely matched, with an accuracy on isotopic ratios that ranged from ∼ 2 to ∼ 6%, depending on the homogeneity of the natural reference materials.     

Mud Tank Zircon: Long‐Term Evaluation of a Reference Material for U‐Pb Dating,Hf‐Isotope Analysis and Trace Element Analysis

Zircon megacrysts from the Mud Tank carbonatite, Australia, are being used in many laboratories as a reference material for LA‐ICP‐MS U‐Pb dating and trace element measurement, and LA‐MC‐ICP‐MS determination of Hf isotopes. We summarise a database of > 10000 analyses of Mud Tank zircon (MTZ), collected from 2000 to 2018 during its use as a secondary reference material for simultaneous U‐Pb and trace element analysis, and for Hf‐isotope analysis. Trace element mass fractions are highest in dark red‐brown stones and lowest in colourless and gem‐quality ones. Individual unzoned grains can be chemically homogeneous, while significant variations in trace element mass fraction are associated with oscillatory zoning. Chondrite‐normalised trace element patterns are essentially parallel over large mass fraction ranges. A Concordia age of 731.0 ± 0.2 Ma (2s, n = 2272) is taken as the age of crystallisation. Some grains show lower concordant to mildly discordant ages, probably reflecting minor Pb loss associated with cooling and the Alice Springs Orogeny (450–300 Ma). Our weighted mean ¹⁷⁶Hf/¹⁷⁷Hf is 0.282523 ± 10 (2s, n = 9350); the uncertainties on this ratio reflect some heterogeneity, mainly between grains. A few analyses suggest that colourless grains have generally lower ¹⁷⁶Hf/¹⁷⁷Hf. MTZ is a useful secondary reference material for U‐Pb and Hf‐isotope analysis, but individual grains need to be carefully selected using CL imaging and tested for homogeneity, and ideally should be standardised by solution analysis.     

X射线荧光光谱法直接测定地质样品中多种痕量元素

采用低压聚乙烯镶边垫底的粉末压饼法制样,Ｘ射线荧光光谱法直接测定了地质样品中痕量元素Ａｓ、Ｇａ、Ｓｃ、Ｌａ、Ｙ、Ｃｅ、Ｗ、Ｍｏ、Ｓｎ、Ｃｏ和Ｐｂ。讨论了背景校正、谱线重叠校正、基体效应校正和仪器漂移校正等问题。利用理论α系数代替经验系数,使方法具有较高的准确度和较低的检出限。所测１１个元素的检出限在（０．３０～２．０２）×１０－６水平,精度（ＲＳＤ,ｎ＝１１）在０．９５％～１３．０％。方法经国家一级标准物质分析验证,结果与标准值相符。     

地质标准物质均匀性检验方法评介与探讨

评介了目前中国地质标准物质研制中样品均匀性检验与评价所用方法,包括:检测方法,统计判别模式,结果的定性、定量表达和最小取样量确定等。对照国家相关技术规范、国际标准化组织导则和国际地质分析者协会的地质标准物质定值协议,探讨了我国地质标准物质均匀性检验与评价中的难点及现存问题。     

Study and Application of Geochemical Reference Materials in the Institute of Geophysical and Geochemical Exploration (IGGE), China

In order to meet the needs of geochemical mapping and geochemical exploration, 125 geochemical reference materials have been successively prepared by the Institute of Geophysical and Geochemical Exploration (IGGE) since 1978. They include certified reference materials of stream sediments (GSD1-14), soils (GSS1-16; ASA 1–6, for analysis of available elements), various rocks (GSR1-6, GSR13-15), biological material (GSV1-4 and GSB 1–10), synthetic silicates (GSES I 1–11) and limestones (GSES II 1–9 for spectral analysis). They also include geochemical reference materials for ore analysis: Cu-Pb-Zn ores (GSO1-4), Cu-Pb-Zn concentrates (GSO5-7), platinum-group element (PGE) ores (GPt5-6 and GPt9-10), silver ores (GAg1-6) and geochemical reference materials for Au (GAu8-14) and PGE determination (GPt1-4, and GPt7-8). A multi-laboratory collaborative analysis scheme was adopted in the certification procedure of the IGGE. Dozens of competent laboratories with hundreds of senior analysts in China participated in the certification analysis. These samples have been supplied to more than thirty countries and more than 4000 customers from national industrial, agricultural, environmental, scientific and educational fields. Most of the geochemical reference materials are used for the calibration of measuring apparatus, evaluation of analytical methods, certification studies, quality control and laboratory accreditation programmes.     

Rutile R632 – A New Natural Reference Material for U‐Pb and Zr Determination

A new natural rutile reference material is presented, suitable for U‐Pb dating and Zr‐in‐rutile thermometry by microbeam methods. U‐Pb dating of rutile R632 using laser ablation ICP‐MS with both magnetic sector field and quadrupole instruments as well as isotope dilution‐thermal ionisation mass spectrometry yielded a concordia age of 496 ± 2 Ma. The high U content (> 300 μg g^?1) enabled measurement of high‐precision U‐Pb ages despite its young age. The sample was found to have a Zr content of 4294 ± 196 μg g^?1, which makes it an excellent complementary reference material for Zr‐in‐rutile thermometry. Individual rutile grains have homogeneous compositions of a number of other trace elements including V, Cr, Fe, Nb, Mo, Sn, Sb, Hf, Ta and W. This newly characterised material significantly expands the range of available rutile reference materials relevant for age and temperature determinations.     

Determination of Selenium in Fifty Two Geochemical Reference Materials by Hydride Generation Atomic Absorption Spectrometry

The selenium content of fifty two geochemical reference samples, issued by several reference material producers (ANRT, GIT-IWG, USGS, NIST and GSJ) has been determined by continuous hydride generation and atomic absorption spectrometry. Selenium(VI) in the digested solutions was pre-reduced to selenium(IV) by heating in 6 mol l⁻¹ HCl solution. The limit of detection was 3 ng g⁻¹ selenium in common geological samples. Some samples which contain a large amount of heavy metals were analysed by the standard addition technique. The agreement between the reported results and published data is satisfactory.     

KArMars: A Breadboard Model for In Situ Absolute Geochronology Based on the K–Ar Method Using UV‐Laser‐Induced Breakdown Spectroscopy and Quadrupole Mass Spectrometry

We present a breadboard prototype to perform in situ dating applicable to planetary exploration. Based on the K–Ar dating method and using instruments inspired by flight‐proven analytical components, ‘KArMars’ ablated a geological sample under high vacuum with a quadrupled ultraviolet (UV at 266 nm) Nd:YAG laser. During ablation, the K content of the target material was given by laser‐induced breakdown spectroscopy and the released ⁴⁰Ar was measured with a quadrupole mass spectrometer. Because K was measured as a concentration and ⁴⁰Ar as a count of atoms, these values were converted using the ablated mass given by the product of the density and the ablated volume. The uncertainties of the age measurement were < 15%. The quality of the K–Ar measurements was enhanced by the advantages of UV laser ablation such as the minimisation of thermal effects on argon diffusion. This work demonstrates that a specialised instrument inspired by this set‐up could provide in situ absolute geochronology with sufficient precision for scientific investigations, particularly where the crater density counting provides higher uncertainties on Mars.     

激光探针等离子体质谱同时测定锆石微区铀—铅年龄及微量元素

建立了一种利用激光探针等离子体质谱技术同时原位测定锆石Ｐｂ－Ｐｂ及Ｐｂ－Ｕ年龄和２５个微量元素的快速分析方法。Ｐ的检出限为１４μｇ／ｇ,Ｓｃ的检出限为３μｇ／ｇ,Ｒｂ、Ｎｂ、Ｂａ稀土元素Ｎｄ、Ｇｄ、Ｄｙ、Ｅｒ及Ｙｂ的检出限为０．１￣０．３μｇ／ｇ,Ｐｂ的检出限０．５μｇ／ｇ,其它稀土元素及Ｓｒ、ｙ、Ｈｆ、Ｔａ、Ｔｈ和Ｕ的检出限为１０￣９０ｎｇ／ｇ。方法对绝大多数微量元素的相对标准偏差为５￣１５％;     

西藏青草山斑岩铜金矿含矿斑岩锆石U-Pb年代学、微量元素地球化学及地质意义

西藏青草山斑岩铜金矿是班公湖-怒江缝合带北侧、羌塘地块南缘新发现的具有超大型远景的斑岩型铜金矿床。本文首次对青草山含矿花岗岩闪长斑岩的锆石进行了 LA-ICPMS U-Pb年代学和微量元素地球化学研究,通过对含矿斑岩中锆石的13个点的U-Pb定年,得出锆石²⁰⁶Pb/²³⁸U加权平均年龄为114.60±1.20Ma (MSWD=1.07),此年龄与同样分布于该带上的多不杂斑岩铜矿含矿斑岩成岩年龄、波龙斑岩铜矿成矿年龄基本一致。应用锆石Ti温度计,计算出含矿斑岩中绝大部分锆石的结晶温度小于700℃,如此低的结晶温度指示含矿斑岩岩浆来源于水近饱和条件下发生的部分熔融。通过对锆石微量元素的详细研究,得出青草山含矿斑岩形成于活动大陆边缘的陆缘弧环境,这与前人研究得出的多不杂斑岩铜矿的形成构造背景一致。相近的成岩成矿年龄和一致的形成构造背景揭示以多不杂、青草山、波龙斑岩铜(金)矿床为主要组成的班公湖-怒江斑岩铜矿带的客观存在。依据青草山斑岩铜金矿和多不杂斑岩铜矿的含矿斑岩和同期火山岩的地球化学特征,并结合已有弧环境斑岩铜矿的经典成矿模型,本文提出班公湖-怒江斑岩铜矿带形成的动力学机制,即在早白垩世,班公湖-怒江洋壳向北俯冲,大洋板片向下俯冲到一定深度时,发生大规模脱水作用,释放的流体交代上覆地幔楔,诱发其部分熔融,产生的富含成矿物质的岩浆向上运移,在浅部地壳发育成与成矿相关的岩浆房,部分岩浆上升直接喷出地表,形成下白垩统美日切错组火山岩,部分浅成-超浅成侵位成斑岩体及斑岩型矿床,随着岩浆的多点多期次侵位,最终形成班公湖-怒江斑岩铜矿带。     

地质标准物质中痕量元素量值溯源性探讨

标准物质的特性量值应该具备溯源性。然而地质标准物质溯源性的建立往往是很困难的。对痕量元素量值溯源的若干难点进行了讨论;提出了建立标准物质研制的质量体系的建议并就相关问题进行了阐述;应重视量值的信息反馈,提高定值的质量。