Laser Ablation Multi-collector ICP-MS Research Articles

Uranium age dating measurements by laser ablation multi-collector ICP-MS in uranium materials

The aim of the present work was to develop a direct method for age dating (production date measurement) of uranium samples by laser ablation multi-collector inductively coupled plasma mass spectrometry (LA-MC-ICP-MS) by the measurement of the 230Th/234U ratio. The major instrumental conditions and sample characteristics affecting the accuracy and precision were investigated in this systematic study. By comparing the obtained LA-MC-ICP-MS results with those obtained after chemical separation measurements, it shows that the LA-MC-ICP-MS method is capable to produce accurate results for pure highly enriched uranium. Natural and low-enriched uranium, however, needs a higher mass resolution to remove the identified interferences, which can lead to erroneous results.

Spatially-resolved uranium isotopic analysis of contaminated scrap metal using laser ablation multi-collector ICP-MS.

Laser ablation multi-collector inductively coupled plasma mass spectrometry (LA-MC-ICP-MS) was applied to the detailed investigation of the uranium (U) isotopic composition (234U, 235U, 236U, and 238U) of five contaminated scrap metal samples found within the European Union. Pressed pellets of the two certified U isotopic reference materials CRM U-020 and CRM U-030 were included in the measurement protocol for mass bias correction, calculation of the ion counter gains and for quality assurance. Since the investigated samples had low U content (0.15–14.3 wt%) compared to typically analysed pure U compounds (>60 wt%), the applied experimental parameters had to be adjusted. Spatially-resolved U isotopic information was obtained by line scan analysis of each sample. While other analytical techniques used typically in nuclear forensic investigations, such as γ-spectrometry and thermal ionisation mass spectrometry (TIMS) yielded average U isotopic compositions of the entire sample, LA-MC-ICP-MS provided substantial added value, highlighting the inhomogeneous distribution of U isotopes within various scrap metal samples. Analysis of individual particles via secondary ion mass spectrometry (SIMS) confirmed the large range of 235U enrichment levels in heterogeneous scrap metal samples. Four out of five scrap metal samples contained 236U (∼0.05–∼0.11 wt%), indicating the presence of reprocessed U. Taken together, LA-MC-ICP-MS analysis provided fast and accurate spatially-resolved U isotopic information without consuming or altering the scrap metal samples, a key feature for nuclear forensics investigations.

Analytical considerations in the determination of uranium isotope ratios in solid uranium materials using laser ablation multi-collector ICP-MS

Validated analytical measurement protocols for the fast and accurate determination of the uranium (U) isotopic composition (234U, 235U, 236U, 238U) of solid nuclear materials were developed employing ns-laser ablation (LA) coupled to multi-collector ICP-MS. The accuracy of the analytical procedure was assured by frequent (n = 65) analysis of a pressed pellet of certified isotopic reference material CRM U-030 (∼3 wt% 235U). The expanded uncertainty (k = 2) for the n(235U)/n(238U) ratio was as low as 0.05%, rising to 0.62% and 1.09% for n(234U)/n(238U) and n(236U)/n(238U) ratios, respectively. LA-MC-ICP-MS measurements of a pressed pellet of certified isotopic reference material CRM U-020 (∼2 wt% 235U) before analysis of each sample allowed calculation of the ion counter gains and mass bias correction. Both individual spot analysis and line scan analysis were used to measure n(234U)/n(238U), n(235U)/n(238U), and n(236U)/n(238U) ratios in two low-enriched UO2 pellets from the fourth Collaborative Materials Exercise (CMX-4), four seized low-enriched UO2 pellets intercepted from illicit trafficking and one metal sample consisting of depleted U. LA-MC-ICP-MS results of all investigated samples matched well with U isotope ratios obtained by thermal ionisation mass spectrometry (TIMS). This independent confirmation of the LA-MC-ICP-MS results by TIMS underpinned the high quality of generated analytical data. Acquisition of several thousand data points within a couple of minutes during line scan analysis yielded detailed information on the spatial distribution of the U isotopic composition of selected UO2 pellets, revealing straightforwardly their (in˗)homogeneity on the μm-scale. Calculating skewness and half width of the frequency distributions of the n(235U)/n(238U) amount ratio allowed the quantitative assessment of the (in-)homogeneity of the investigated samples. This information allows drawing conclusions on the starting materials used for the production of the pellets. From a nuclear forensics perspective, LA-MC-ICP-MS provides quick, accurate results on the spatial distribution of major and minor U isotopes while preserving the sample i.e. piece of evidence, essentially intact.

Accurate and precise microscale measurements of boron isotope ratios in calcium carbonates using laser ablation multicollector-ICPMS

The boron isotope compositions (δ11B) of biogenic carbonates have proven to be an invaluable tool for investigating changes in ocean carbonate chemistry, especially the impacts of declining seawater pH due to rising levels of atmospheric CO2.

Sr and Nd isotopic compositions of individual olivine-hosted melt inclusions from Hawai'i and Samoa: Implications for the origin of isotopic heterogeneity in melt inclusions from OIB lavas

Geochemical investigations of mantle heterogeneity as sampled by ocean island basalts (OIB) have long relied on isotopic analyses of whole rock lavas. However recent work has shown that significant isotopic disequilibrium can exist between the phases (groundmass and phenocrysts) of a single OIB lava. In this study, we target individual olivine-hosted melt inclusions from two samples—one Samoan and one Hawai'ian—with melt inclusion 87Sr/86Sr heterogeneity previously measured using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). We report 87Sr/86Sr and 143Nd/144Nd in individual melt inclusions analyzed by thermal ionization mass spectrometry (TIMS). In melt inclusions from Samoan sample AVON3-71-2, we find highly heterogeneous (935 ppm) 87Sr/86Sr (0.705193–0.705853, N = 6), consistent with previously identified 87Sr/86Sr heterogeneity (~2030 ppm) by laser ablation multi-collector ICP-MS (0.70459–0.70602, N = 12). In contrast, we find comparatively little (251 ppm) 87Sr/86Sr heterogeneity (0.703761–0.703938, N = 9) in olivine-hosted melt inclusions contained in a Hawaiian scoria clast from the Pu'u Wahi eruption (Mauna Loa). This result contrasts with a previous measurements by single-collector LA-ICP-MS that found highly heterogeneous (~8500 ppm) 87Sr/86Sr in olivine-hosted melt inclusions from the same eruption (0.7021–0.7081, N = 137). In both the AVON3-71-2 and Pu'u Wahi melt inclusions, 143Nd/144Nd is indistinguishable from their respective whole rock 143Nd/144Nd values. The isotopic measurements on the melt inclusions are paired with major and trace element concentrations to investigate the mechanisms generating 87Sr/86Sr variability in melt inclusions. The lack of significant 87Sr/86Sr variability in the Hawai'ian melt inclusions (only 251 ppm) from Pu'u Wahi suggests a relatively simple magmatic history. In contrast, for the Samoan melt inclusions, we present evidence that supports the mixing of isotopically-heterogeneous mantle-derived melts as the mechanism generating the observed 87Sr/86Sr and trace element variability in the melt inclusions from AVON3-71-2. However, brine interaction appears to have increased the Cl concentrations of some of the Samoan inclusions without significantly modifying the 87Sr/86Sr or the other elemental budgets examined in this study.

Spatial distribution of uranium isotopes in solid nuclear materials using laser ablation multi-collector ICP-MS

Employing laser ablation multi-collector ICP-MS (LA-MC-ICP-MS), its potential for evaluating the homogeneity of solid uranium (U) bearing materials was investigated. To this end, the n(235U)/n(238U) ratio of two low-enriched U certified reference materials (CRMs), i.e. powdered standard reference material U-010 (~1wt% 235U) and a UO2 pellet of CRM 125-A (~4wt% 235U) was determined using line scan analysis. Four spots of 5μm diameter each were ablated per second with the LA system moved at a speed of 20μms−1 for several minutes. Experimental and certified U isotope ratios matched perfectly, unequivocally validating the accuracy of the applied analytical methodology. In addition, the narrow and symmetric frequency distribution of the n(235U)/n(238U) ratio of both CRMs confirmed their homogeneity with respect to the U isotopic composition. Utilizing LA-MC-ICP-MS line scan analysis of two similar UO2 pellets (~1wt% 235U) from the 5th Collaborative Materials Exercise (CMX-5) revealed diverse inhomogeneity regarding their n(235U)/n(238U) ratio. Although both UO2 pellets used for the CMX-5 exercise were prepared from identical source materials, their different production routes yielded largely contrasting frequency distributions of the n(235U)/n(238U) ratio. While 235U isotope abundance ranged from 0.75%–1.6% for the first pellet, this value fluctuated between 0.45% and 3.0% for the second pellet. This specific information sheds additional light on the production process of these materials and is helpful in nuclear forensics investigations when determining the origin of unknown nuclear material. The depleted nature (~0.4wt% 235U) of two seized U metal samples was established through LA-MC-ICP-MS analysis of the n(235U)/n(238U) ratio. As black and yellow regions within both U bearing samples had identical U isotopic composition, the observed colour differences might arise from different degrees of U oxidation and are not associated with U isotopic inhomogeneity within the material. The significantly different 235U abundance of the two samples (0.3670±0.0015 wt.% and 0.4146±0.0013 wt.%), however, clearly indicates they were prepared from different source materials and/or from diverse amounts of them.

In situ simultaneous measurement of Rb–Sr/Sm–Nd or Sm–Nd/Lu–Hf isotopes in natural minerals using laser ablation multi-collector ICP-MS

This study presents a combined methodology of simultaneously measuring Rb–Sr/Sm–Nd or Sm–Nd/Lu–Hf isotopes in natural minerals by a means of two multiple collector inductively coupled plasma mass spectrometers connected to a 193 nm excimer laser ablation system.

Measurement of in Situ Sulfur Isotopes by Laser Ablation Multi-Collector ICPMS: Opening Pandora's Box

Laser ablation multi-collector ICPMS is a modern tool for in situ measurement of S isotopes. Advantages of the technique are speed of analysis and relatively minor matrix effects combined with spatial resolution sufficient for many applications. The main disadvantage is a more destructive sampling mechanism relative to the ion microprobe technique. Recent advances in instrumentation allow precise measurement with spatial resolutions down to 25 microns. We describe specific examples from economic geology where increased spatial resolution has greatly expanded insights into the sources and evolution of fluids that cause mineralization and illuminated genetic relations between individual deposits in single mineral districts.

Strontium isotope analysis of curved tooth enamel surfaces by laser-ablation multi-collector ICP-MS

Laser ablation multi-collector ICP-MS (LA-MC-ICP-MS) is increasingly applied to measure the strontium isotope composition (87Sr/86Sr) of fossil or modern tooth samples in order to address questions about mobility. Recently, concerns have been raised that an analytical bias due to instrumental isotopic mass fractionation might be introduced when this method is used to sample across naturally curved tooth enamel surfaces.We address this concern by reanalyzing data that were originally produced using 750μm linear LA-MC-ICP-MS scans on the external, slightly curved surfaces of fossil hominin teeth (Australopithecus and Paranthropus) from South Africa. By re-integrating the first and last 1/3 of the data along the original 750μm linear scans, we compared 87Sr/86Sr results produced by sections of each scan with varying degrees of laser focus. The results show no evidence of any analytical scatter between strontium isotope values for the different sections of the curved tooth surfaces and results for the different sections of each linear scan agree well within the precision of the method (external 2σ ± 0.0004). Furthermore, each analytical session was bracketed by analysis of a curved rodent (Otomys sp.) tooth in-house standard with up to ±100μm vertical change along the 750μm linear scan. Long-term, average LA-MC-ICP-MS 87Sr/86Sr results for one such Otomys tooth standard (0.72989±0.00029, n=71) agree well with the solution MC-ICP-MS analysis of the same tooth (0.72976±0.00002). New LA-MC-ICP-MS 87Sr/86Sr ratios, using both a 213nm and solid-state 193nm laser ablation system, for sets of consecutive 750μm linear scans along the curved, outer tooth enamel surface on another single Otomys tooth in-house standard agree within ±0.0004 regardless of progressively more extreme vertical change during analysis (±10μm to ±900μm).These results are similar to LA-MC-ICP-MS Sr isotope analyses, using the same instrumentation and methodology, of an in-house, polished, flat clinopyroxene mineral standard (LA: 0.70482±0.00029, n=155; solution: 0.70495±0.00003).We conclude that, provided the stable 86Sr/88Sr ratio is used in conjunction with the exponential law to constantly correct for instrumental isotopic mass fractionation during acquisition, curved tooth enamel surfaces represent no impediment to accurate LA-MC-ICP-MS strontium isotope analyses.

Sources of cratonic metasomatic fluids: In situ LA-MC-ICPMS analysis of Sr, Nd, Hf and Pb isotopes in Lima from the Jagersfontein Kimberlite

LIMA phases (LIndsleyite-MAthiasite: K-Ba-Zr-Cr titanates of the crichtonite series) in the Jagersfontein kimberlite (95 ± 5 Ma) are xenocrysts, related to the Phlogopite-K richterite-Peridotite (PKP) style of metasomatism that has affected the lithospheric mantle beneath the Kaapvaal Craton. The LIMA grains contain high levels of Sr, Hf, Nd, Pb and U, allowing a multi-isotope approach to the timing of metasomatism and the sources of metasomatic material. We provide a detailed discussion of the interference-correction and mass-bias issues involved in the in-situ isotopic analysis of these elements. Multiple in situ isotopic analyses of 11 grains by laser-ablation multi-collector ICPMS (and 2 by solution techniques) show significant within-grain and inter-grain variability in Sr and Pb isotopic composition, less variation in Nd-isotope composition, and very little variation in Hf-isotope composition. U-Pb dating, limited by high levels of initial Pb, gives a poorly constrained age of 162 ± 46 Ma, which may reflect an episode of PKP metasomatism. Back-calculation of the Pb-isotope data using measured 238U/204Pb values, and comparison with mantle evolution models, indicate a maximum age for the PKP metasomatism of 180 Ma, suggesting a link with the plume-related Karoo volcanism (179-183 Ma). The relationships between Pb, Sr, Hf and Nd isotopic compositions in LIMA, and published data on PKP–series xenoliths, suggest mixing between two components. One had high 87Sr/86Sr but low 206Pb/204Pb and 143Nd/144Nd, similar to the EM1 “reservoir.” This component probably represents lithospheric mantle that was enriched in Rb/Sr before the metasomatic episode that produced the LIMA phases. The other has isotopic characteristics similar to the “HIMU” reservoir, and may correspond to a plume-related fluid or melt responsible for at least the initiation of the metasomatism.

Petrogenesis of 1000 Ma Felsic Tuffs, Chhattisgarh and Indravati Basins, Bastar Craton, India: Geochemical and Hf Isotope Constraints

AbstractThe 1000 Ma felsic tuffs that occur near the top of both the Chhattisgarh and Indravati Basins in peninsular India have been attributed to a “rhyolite flare-up” occasioned by the collision of parts of East Antarctica with India, in what is now the Eastern Ghats Mobile Belt, and the suturing of the North and South Indian cratonic blocks along the Central Indian Tectonic Zone, all during the assembly of Rodinia. In this study we present (1) new U-Pb SHRIMP ages of zircons from the granitic basement; (2) Hf isotopic compositions (laser ablation multicollector ICP-MS) from previously dated zircons from a number of tuff samples and a sample of the Archean basement (Bastar craton); and (3) major, minor, trace, and rare earth element compositions of these and a randomly collected additional set of samples from the Bastar craton basement. We have used these data to infer the petrogenesis of the tuffs. The Hf isotopic data preclude derivation of the parent magmas of the tuffs from simple melting of the bas...

In-situ Pb isotope analysis of Fe–Ni–Cu sulphides by laser ablation multi-collector ICPMS: New insights into ore formation in the Sudbury impact melt sheet

Laser-ablation (LA) multi-collector inductively coupled plasma mass spectrometry (MC-ICPMS) is ideally suited to in situ determination of isotope ratios in sulphide minerals. Using samples of magmatic sulphide ore from the Sudbury impact structure, we test LA-MC-ICPMS analytical protocols that aim to meet a range of analytical challenges in the analysis of Pb isotopes. These include: potential matrix sensitive isotopic fractionation; interferences on Pb isotopes; low melting points of many sulphide minerals; the availability of standards.Magmatic sulphides of wide ranging mineralogy (pyrrhotite, pentlandite, chalcopyrite, pyrite and sphalerite) were analysed for Pb isotopic composition, using the silicate glass NIST SRM 610 as an external standard to correct for instrumental mass-fractionation. Despite matrix sensitive melting and re-deposition around ablation pits, several lines of evidence indicate that all analyses are accurate, within typical analytical uncertainties of 0.003–2% (2σ), and that the defined approach is insensitive to compositional diversity in sample matrix: (a) laser ablation and dissolution based measurements of sulphide powders are in agreement; (b) analyses from each sample define isochron ages within uncertainty of the known crystallization age (1850Ma); (c) the results of sulphide measurements by laser ablation are consistent with age-corrected feldspar analyses from the same samples.The results have important implications for ore formation in Sudbury. The Pb isotope data regressions are consistent with age corrected feldspar analyses from each respective sample, which together with time integrated Th/U ratios that match whole rock values (3.1, 4.0 and 6.1 for the Worthington, Copper Cliff and Parkin Offset Dykes, respectively) indicate chemical equilibrium between the silicate and sulphide systems during ore formation. The sulphides within each respective sample have indistinguishable model initial Pb isotope ratios (207Pb/204Pbm), irrespective of mineralogy or texture, indicating a common origin for ores within each of three different Offset Dykes. Furthermore, variations between Offset Dykes (e.g., 207Pb/204Pbm=15.514±0.012, 15.399±0.009 and 15.275±0.003) show that the ores have differing crustal sources on previously unrecognized scales. Mass balance considerations, particularly for MgO, Ni and Cu, indicate that the spatial distribution of mafic target rocks played a significant role in controlling the mineralization potential in different parts of the melt sheet.

Geology, stable isotope, and U–Pb geochronology of the Mariquita porphyry copper and Lucy Cu–Mo deposits, Cananea District, Mexico: A contribution to regional exploration

The Mariquita porphyry Cu and Lucy Cu–Mo deposits are located in the western section of the Cananea porphyry copper district in northwestern Mexico. Four hydrothermal stages are found in Mariquita: stage I is composed of quartz–pyrite–biotite–magnetite; stage II corresponds to orthoclase–quartz; stage III consists of unidirectional veinlets of quartz–pyrite–chalcopyrite–magnetite and minor molybdenite; and stage IV consists of alunite veinlets. The Lucy deposit is characterized by only one stage and consists of quartz–molybdenite–chalcopyrite.The temperatures and emplacement depths of the mineralization in Mariquita is 1 to 1.2km and 430 to 380°C, respectively. In contrast, the mineralization in the Lucy deposit shows deeper emplacement depths (~3km) and higher mineralization temperatures (550–500°C). The sulfur isotope range (−4.6 to 3.8‰) indicates that the source of sulfur for both deposits is clearly magmatic. The δ34S values (1 to 2.5‰) from alunites from stage IV in Mariquita are the result of oxidation of sulfides from previous hydrothermal stages. The oxygen and hydrogen isotope compositions of the ore fluids involved during the mineralization of hydrothermal stages I to III in Mariquita indicate a magmatic origin, whereas the stage IV fluid involved mixing between magmatic and meteoric water components. The oxygen isotope data of the ore fluids from the Lucy deposit also suggests a magmatic origin.The new U–Pb zircon analysis, using laser ablation multi-collector ICP-MS, from the granodiorite rock that hosts Lucy deposit gives an age of 63.8±1.1Ma. The new U–Pb ages of zircons reported for two mineralizing quartz feldspathic porphyries in Mariquita yield crystallization ages of 60.4±1.1Ma and 62.7±1.3Ma. The magmatic-mineralizing pulses reported for the western portion of Cananea district increase the potential for the presence of undiscovered mineralized bodies either emplaced within the Cuitaca granodiorite (e.g. Lucy), or within the Laramide volcanic rocks. The geology and geochronology reported here contribute to a better understanding of the western and northwestern sections of the Cananea district.

Mass-dependent and mass-independent sulfur isotope fractionation (δ34S and δ33S) from Brazilian Archean and Proterozoic sulfide deposits by laser ablation multi-collector ICP-MS

Mass-independent sulfur isotope fractionation (MIF) has been observed in rocks of the geological record older than about 2.45Ga, a characteristic which is thought to be related to processes in the Neoarchean atmosphere. Samples recording a MIF effect therefore have to contain sulfur of the exogenic sulfur cycle, while endogenic sulfur should not show this effect. The sulfides analysed from six Brazilian deposits represent either exogenic or endogenic sulfur sources, with supposed ages ranging from about 1.9 to 2.7Ga. Sulfur isotopes were analysed by in‐situ laser ablation MC-ICP-MS. A range of experiments were conducted using international and in-house isotope standards, which were run under various conditions and set-ups. These include the reference materials IAEA-S1, IAEA-S3, NBS123 (sphalerite), NBS127 (barite), and in-house standards BSB-py (pyrite) and BSB-cpy (chalcopyrite). During six days of analysis, an internal precision of sulfide analyses of 0.10–0.15‰ (1s) for δ34S and 0.40–0.60‰ (1s) for δ33S, and an accuracy of ~0.30‰ for δ34S and δ33S was achieved. The standard measurements define a δ33S/δ34S relationship of δ33S=0.513*δ34S+0.149, with R²=0.9997, which is close to the theoretical relationship for mass-dependent fractionation. The by far best analytical errors were obtained for natural pyrite, reaching a within-run precision of about 0.05–0.15‰ for δ34S (1s), and 0.10–0.15‰ (1s) for δ33S determinations. Including all precision and accuracy data, we arrive at the following 1s error limits to which sulfur isotope analyses for MIF studies obtained with this method are reliable: 0.32, 0.34 and 0.46‰ for pyrite (δ34S, δ33S and Δ33S determinations, respectively), 0.34, 0.42 and 0.54‰ for pyrrhotite, and 0.34, 0.50 and 0.58‰ for chalcopyrite.Pyrites and pyrrhotites from 2200Ma old sediments and volcanics associated with the Pilar greenstone belt, Goiás, have δ34S from −15.0 to +2.0‰, and δ33S from −8.0 to +1.0‰, with Δ33S being slightly but not significantly positive. Pyrites from supposed ca. 2060Ma old clastic sediments of the Águas Claras Formation (Carajás, Pará), have δ34S=9.5–12.5‰ and δ33S=5.0–6.5‰ with Δ33S close to zero. Chalcopyrites from the Salobo and Sequerinha sulfide deposits, also Carajás, are genetically related to 2570Ma old A-type alkaline granites with endogenic sources. They have δ34S=1.6–2.9‰ and δ33S=1.0–1.5‰, and δ34S=0.2–0.9‰ and δ33S=0.65‰, respectively, with Δ33S ranging from −0.15 to 0.56. The only Δ33S values of this study which clearly suggest sulfur isotope MIF come from the mineralized banded iron-formations of the Quadrilátero Ferrífero, Minas Gerais. Pyrites from the Mina de Cuiabá deposit (2700Ma) have δ34S=3.8–5.1‰ and δ33S=2.9–4.8‰ with Δ33S=0.9–2.2‰, while pyrites and chalcopyrites from São Bento (2720Ma) have δ34S=1.6–3.2‰ and δ33S=1.5–2.8‰ with Δ33S=0.2–1.5‰. The sulfides represent an epigenetic mineralization, derived from supracrustal rocks making part of an exogenic sulfur cycle. The study shows, that in-situ laser ablation ICP-MS is sufficiently sensitive for detecting MIF effects in Neoarchean rocks. Whether or not such samples show MIF-related Δ33S values depends on the age and provenance of the sulfur.

Radial distribution of lead and lead isotopes in stem wood of Norway spruce: A reliable archive of pollution trends in Central Europe

Annual growth rings of a common hardwood species, Picea abies L., were investigated as a potential archive of past atmospheric Pb pollution. Wide distribution of trees in terrestrial settings and straightforward chronology are two advantages of this potential geochemical archive, but several processes described in the literature may obscure the trends in past Pb deposition. These confounding factors include, e.g., radial post-depositional mobility of Pb in xylem, and ecosystem acidification leading to higher bioavailability of Pb. One- to five-year annual wood increments were analyzed for Pb concentrations and 206Pb/ 207Pb ratios at Jezeri (JEZ), Uhlirska (UHL) and Na Lizu (LIZ), three sites in the Czech Republic, differing in atmospheric Pb loads. Three to four trees per site were included in the study. Distinct Pb concentration maxima between 1960 and 1990 at the two heavily polluted sites (JEZ and UHL) coincided with historical Pb emissions known from inventories of industrial production. No Pb concentration maxima were found at one site, LIZ, situated in a national park 150 km from major pollution sources. Spruce tree rings from JEZ, located just 5 km from coal-burning power stations, contained a large proportion of coal-derived Pb (a high- 206Pb/ 207Pb ratio of 1.19). A coal-related maximum in 206Pb/ 207Pb in JEZ tree rings was found using two different analytical techniques, laser-ablation multi-collector ICP MS, and single-collector sector-field ICP MS. In a three-isotope graph ( 206Pb/ 207Pb vs. 208Pb/ 207Pb), tree-ring data plotted into the field of ombrotrophic (i.e., rain-fed) peat bogs, suggesting negligible contribution of bedrock-derived Pb in the xylem. We concluded that none of the potential confounding factors played a major role at our sites. Annual growth rings of P. abies in Central Europe faithfully recorded historical changes in atmospheric Pb depositions.

Lithium isotope analysis of natural and synthetic glass by laser ablation MC-ICP-MS

This contribution presents the first laser ablation multicollector ICP-MS (LA-MC-ICP-MS) technique for the measurement of Li isotopes. A Nu Instruments NuPlasma HR operating at 6 kV and fitted with a non-standard “low-mass, high abundance” skimmer cone is used, coupled to a NewWave UP213 213 nm laser ablation unit operating under a He atmosphere. Asymmetric tuning of the quad lenses on the NuPlasma allows the simultaneous measurement of 7Li and 6Li on a Faraday-ion counter configuration. Use of the standard-bracketing technique for analysis of unknowns obviates any cross calibration between Faraday cup and ion counter. Use of a natural glass as bracketing standard (e.g. BCR-2G) yields accurate Li isotope data with external, measured 2σ δ7Li precision of <1‰ at Li concentrations of 3–35 ppm.

Determination of Sr isotopes in calcium phosphates using laser ablation inductively coupled plasma mass spectrometry and their application to archaeological tooth enamel

The determination of accurate Sr isotope ratios in calcium phosphate matrices by laser ablation multi-collector ICP-MS is demonstrated as possible even with low Sr concentration archaeological material. Multiple on-line interference correction routines for doubly-charged REE, Ca dimers and Rb with additional calibration against TIMS-characterised materials are required to achieve this. The calibration strategy proposed uses both inorganic and biogenic apatite matrices to monitor and correct for a 40Ca– 31P– 16O polyatomic present at levels of 0.3–1% of the non-oxide peak, which interferes on 87Sr causing inaccuracies of 0.03–0.4% in the 87Sr/ 86Sr isotope ratio. The possibility also exists for synthetic materials to be used in this calibration. After correction for interferences total combined uncertainties of 0.04–0.15% (2SD) are achieved for analyses of 13–24 μg of archaeological tooth enamel with Sr concentrations of ca. 100–500 ppm using MC-ICP-MS. In particular, for samples containing >300 ppm Sr, total uncertainties of ∼0.05% are possible utilising 7–12 ng Sr. Data quality is monitored by determination of 84Sr/ 86Sr ratios. When applied to an archaeological cattle tooth this approach shows Sr-isotope variations along the length of the tooth in agreement with independent TIMS data. The 40Ca– 31P– 16O polyatomic interference is the root cause of the bias at mass 87 during laser ablation ICP-MS analysis of inorganic and biogenic calcium phosphate (apatite) matrices. This results in inaccurate 87Sr/ 86Sr ratios even after correction of Ca dimers and doubly charged rare earth elements. This interference is essentially constant at specific ablation conditions and therefore the effect on 87Sr/ 86Sr data varies in proportion to changes in the Sr concentration of the ablated material. Complete elimination of this interference is unlikely through normal analytical mechanisms and therefore represents a limitation on the achievable accuracy of LA-(MC-)ICP-MS 87Sr/ 86Sr data without rigorous calibration to known reference materials.

Concurrent Pb–Hf isotope analysis of zircon by laser ablation multi-collector ICP-MS, with implications for the crustal evolution of Greenland and the Himalayas

The in situ Lu–Hf isotope analysis of zircon by laser ablation has emerged as a high-calibre tool for tackling magmatic and crustal evolution. The strength of the approach lies with the ability to target specific zircon growth domains identified by imaging, and thus to unravel polyphase crystallisation histories. However, due to the volume of material being sampled during analysis there remains the possibility of ablation-induced mixing between Hf from domains of different age. Inaccurate Hf isotope ratios and spurious geological interpretations could result. One approach to this problem involves dating the same volume of material analysed for Hf isotopes by concurrently measuring 207Pb/ 206Pb ratios during ablation [Woodhead, J.D., Hergt, J.M., Shelley, M., Eggins, S., Kemp, R. 2004. Zircon Hf-isotope analysis with an excimer laser, depth profiling, ablation of complex geometries, and concomitant age estimation. Chemical Geology 209, 121–135.]. This paper explores the viability of this dual analysis by investigating complex zircons from three different geological contexts, detrital zircons in sedimentary rocks, inherited zircons in granites, and zircons in metamorphosed Eo-Archaean TTG gneisses from Greenland. The implications of the Greenland data for Archaean crustal evolution are discussed in the light of published solution zircon Hf isotope datasets from these gneisses. A case study of detrital zircons from modern river sands in the Himalayas highlights the potential of the technique for providing a rapid, cost-effective picture of crustal evolution that should complement regional bulk rock studies.

Lead Isotope Homogeneity of NIST SRM 610 and 612 Glass Reference Materials: Constraints from Laser Ablation Multicollector ICP‐MS (LA‐MC‐ICP‐MS) Analysis

This contribution presents data for laser ablation multicollector ICP‐MS (LA‐MC‐ICP‐MS) analyses of NIST SRM 610 and 612 glasses with the express purpose of examining the Pb isotope homogeneity of these glasses at the ∼ 100 μm spatial scale, relevant to in situ analysis. Investigation of homogeneity at these scales is important as these glasses are widely used as calibrators for in situ measurements of Pb isotope composition. Results showed that at the levels of analytical uncertainty obtained, there was no discernable heterogeneity in Pb isotope composition of NIST SRM 610 and also most probably for NIST SRM 612. Traverses across the ∼ 1.5 mm glass wafers supplied by NIST, consisting of between 75 and 133 individual measurements, showed no compositional outliers at the two standard deviation level beyond those expected from population statistics. Overall, the measured Pb isotope ratios from individual traverses across NIST SRM 610 and 612 wafers closely approximate single normally‐distributed populations, with standard deviations similar to the average internal uncertainty for individual measurement blocks. Further, Pb isotope ratios do not correlate with Tl/Pb ratios measured during the analysis, suggesting that regions of volatile element depletion (marked by low Tl/Pb) in these glasses are not associated with changes in Pb isotope composition. For NIST SRM 610 there also appeared to be no variation in Pb isotope composition related to incomplete mixing of glass base and trace element spike during manufacture. For NIST SRM 612 there was some dispersion of measured ratios, including some in a direction parallel to the expected mixing line for base‐spike mixing. However, there was no significant correlation parallel to the mixing line. At this time this cannot be unequivocally demonstrated to result from glass heterogeneity, but it is suggested that NIST SRM 610 be preferred for standardising in situ Pb isotope measurements. Data from this study also showed significantly better accuracy and somewhat better precision for ratios corrected for mass bias by external normalisation to Pb isotope ratios measured in bracketing calibrators compared to mass bias corrected via internal normalisation to measured 205Tl/203Tl, although the Tl isotopic composition of both glasses appears to be homogeneous.

Precise and accurate 186Os/ 188Os and 187Os/ 188Os measurements by Multi-collector Plasma Ionisation Mass Spectrometry, part II: Laser ablation and its application to single-grain Pt–Os and Re–Os geochronology

The abundance of platinum group alloy (PGA) grains available from some alluvial deposits combined with their great chemical resistance to conventional acid attack generates the need for an alternative method of obtaining routine, rapid yet precise Os isotopic data. Laser ablation multi-collector ICP-MS (LA-MC-ICP-MS) is ideally suited for this purpose and has been applied, in a relatively limited extent, to Os-rich samples by previous workers (e.g., Hirata, T., Michinari Hattori, M., and Tsuyoshi Tanaka, T., 1998. In-situ osmium isotope ratio analyses of iridosmines by laser ablation-multiple collector-inductively coupled plasma mass spectrometry. Chem Geol., 144, 269–280.; Malitch, K.N., 2004. Osmium isotope constraints on contrasting sources and prolonged melting in the Proterozoic upper mantle: evidence from ophiolitic Ru–Os sulfides and Ru–Os–Ir alloys. Chem Geol. 208. 157–173.; Walker, R.J., Brandon, A.D., Bird, J.M., Piccolia, P.M., McDonougha, W.F., R.D., Asha, R.D., 2005. 187Os– 186Os systematics of Os–Ir–Ru alloy grains from southwestern Oregon. Earth Planet. Sci. Lett. 230, 211–226.). The wide variety of PGA minerals yield a broad spectrum of Pt, Re and Os contents which translate into a wide spread in parent–daughter ratios that is an attractive proposition for geochronology using the Re–Os and Pt–Os decay schemes. Here we show that single PGA grains, can contain sufficient internal Re, Pt and Os elemental variability and coupled variations in parent/daughter and daughter isotope compositions that they present an opportunity to obtain ‘isochron’ ages from two different isotope decay systems. We present a rapid (40 s acquisition time), precise and accurate LA-MC-ICP-MS methodology suitable for applying Pt–Os and Re–Os geochronology approaches to single PGA grains, for use in dating chromitite deposits and identifying and dating multiple sources in alluvial PGA deposits. Because of isobaric interferences from Pt, PGA analyses by LA-MC-ICP-MS are best corrected for instrumental mass fractionation using the 189Os/ 188Os ratio. We demonstrate that, within our analytical uncertainties, mass bias effects for Os isotope ratios during LA-MC-ICP-MS are similar in nature and magnitude to mass bias variations observed during normal solution-mode analysis. While robust elemental interference corrections can be applied for Re and W on the Os mass spectrum during solution analyses (Nowell, G.M., Luguet, A., Pearson, D.A., Horstwood, M.S.A., 2008-this volume. Precise and accurate 186Os/ 188Os and 187Os/ 188Os measurements by Multi-Collector Plasma Ionisation Mass Spectrometry (MC-ICP-MS) part I: solution analyses. Chem Geol.) we show that the accurate correction for the Re interference on Os during laser ablation is problematic at 187Re/ 188Os ratios > ∼ 0.5 which means that Re-corrected 187Os/ 188Os ratios for some PGAs and high Re/Os sulfides must be regarded as problematic. Our interfering element correction approach can also be used for the correction for Os on 190Pt for obtaining 190Pt/ 188Os ratios, removing the need for an independent Pt monitor isotope. Accurate and precise geochronology by LA-MC-ICP-MS can be further limited by poorly quantified fractionation of the parent/daughter elemental ratio during ablation. Although additional work is required to understand the nature and exact extent of inter-element fractionation of the Pt/Os and Re/Os ratios during laser ablation analysis of Pt- and Re-rich PGA grains, our best estimate is that fractionation of the Pt/Os during laser ablation is around 5% or less. We present multi-grain isochrons and single-grain internal ‘isochrons’ for the Re–Os and Pt–Os isotope systems in PGA grains from Lapland. In all cases, the Pt–Os isotope system gives significantly more precise ‘isochrons’ than the Re–Os system. We interpret this discordance between the two systems as being most likely due to problems inherent with Re interference corrections at elevated Re/Os ratios. We show that a suite of Pt-rich PGA grains from the Central Lapland greenstone belt yields a spectrum of internal Pt–Os isochron ages that coincides well with pulses of formation of chromitite-bearing ophiolitic material within this magmatic terrane and we take this to indicate the record of chromitite formation in different magmatic units. The single-grain Pt–Os and Re–Os geochronology technique shows great promise in the dating of chromitite deposits in ophiolites and in the discrimination of multiple source regions within alluvial PGA deposits.