Don Chipley

Geographic Variation of Strontium and Hydrogen Isotopes in Avian Tissue: Implications for Tracking Migration and Dispersal

Background Isotopes can provide unique solutions to fundamental problems related to the ecology and evolution of migration and dispersal because prior movements of individuals can theoretically be tracked from tissues collected from a single capture. However, there is still remarkably little information available about how and why isotopes vary in wild animal tissues, especially over large spatial scales. Methodology/Principal Findings Here, we describe variation in both stable-hydrogen (δDF) and strontium (87Sr/86SrF) isotopic compositions in the feathers of a migratory songbird, the Tree Swallow (Tachycineta bicolor), across 18 sampling sites in North America and then examine potential mechanisms driving this variation. We found that δDF was correlated with latitude of the sampling site, whereas 87Sr/86SrF was correlated with longitude. δDF was related to δD of meteoric waters where molting occurred and 87Sr/86SrF was influenced primarily by the geology in the area where feathers were grown. Using simulation models, we then assessed the utility of combining both markers to estimate the origin of individuals. Using 13 geographic regions, we found that the number of individuals correctly assigned to their site of origin increased from less than 40% using either δD or 87Sr/86Sr alone to 74% using both isotopes. Conclusions/Significance Our results suggest that these isotopes have the potential to provide predictable and complementary markers for estimating long-distance animal movements. Combining isotopes influenced by different global-scale processes may allow researchers to link the population dynamics of animals across large geographic ranges.

Mobile Pb-isotopes in Proterozoic sedimentary basins as guides for exploration of uranium deposits

Lead isotope ratios and associated trace element concentrations (U, Th and Pb) extracted by partial-leaching with 2% nitric acid from Proterozoic sandstones and basement rocks reveal much about the fluid evolution of sedimentary basins hosting unconformity-type uranium deposits. In addition, these techniques have great potential as a guide for exploration of uranium and other types of deposits in basins of any age. Isotope ratios of Pb in Proterozoic sandstones from basins known to contain high-grade uranium deposits are radiogenic at key geological localities and settings distal to known mineralization and particularly in altered zones proximal to mineralization. Sandstones completely cemented by quartz overgrowths typically have non-radiogenic Pb isotope ratios, indicating early closure of porosity and isolation of these rocks from later fluid events. Alternatively, the unconformity served as both a source of uranium and radiogenic Pb as well as an avenue for late-stage (<250–900 Ma) fluid flow. The mafic volcanic units, which are relatively reducing lithologies and therefore have removed uranium from basinal brines, have uranium-supported radiogenic Pb isotope ratios. Comparison of 238U/206Pb and 206Pb/204Pb ratios is useful in determining the timing and nature of U and Pb migration before, during and after mineralization in these basins. This comparison can be used to delineate the presence of radiogenic Pb isotope ratios that are not internally supported by uranium and thorium in rocks, eventually providing the explorationist with geochemical vectors that point toward sites of high potential for economic uranium mineralization.

Direct determination of trace levels of Os, Ir, Ru, Pt and Re in kimberlite and other geological materials using HR-ICP-MS

A fast and simple method for the direct determination of low concentrations of Os, Ir, Ru, Pt and Re from the same sample aliquot has been developed. It exploits the superior mass resolution capabilities of a double focussing sector field mass spectrometer (Finnigan MAT Element), in combination with a highly sensitive, high TDS tolerant teflon® Microflow nebulizer. Samples are spiked with an Os isotopic tracer, and digested in inverse aqua regia in sealed Carius tubes for 24 hours at 240 °C. Osmium is subsequently separated from the matrix (which contains the other PGEs) in a previously developed solvent extraction step, and measured in low resolution mode. The remaining sample solution is dried, redissolved in 2% HCl and analyzed directly for Ir, Ru, Pt and Re using the method of standard addition, in high resolution mode. Procedural blanks are <0.009 ppb for all PGEs except Pt (∼0.046 ppb) and Rh (∼0.0143 ppb). Instrumental detection limits based on the 3σ criterion for background are 0.0009 ppb for Re, 0.0048 ppb for Os, 0.002 ppb for Ru, and 0.003 and 0.01 ppb for Ir and Pt, respectively. The accuracy of the analytical method has been verified by comparing the results obtained in this study for three PGE reference materials (komatiite WITS1, komatiite KAL1, and peridotite GP13) with those reported in the literature.

Measurement of U-Pb ages of uraninite and davidite by laser ablation-HR-ICP-MS

Abstract Laser-ablation high-resolution inductively coupled plasma mass spectrometry (LA-HR-ICP-MS) is a rapid, accurate, and inexpensive technique for making in situ U-Pb isotopic measurements of uraninite and davidite. The advantages of this method include: (1) mineral separation and chemical digestion are not required; (2) measurements on complex samples are feasible because significant isobaric interferences can be resolved; and (3) accurate U-Pb and 207Pb/206Pb dates on 10-25 μm spots can be obtained rapidly. The LA-HR-ICP-MS method is applied to U oxide minerals from four deposits and prospects from northern Australia, and the new dates are compared to previously published conventional thermal ionization mass spectroscopy (TIMS) dates, and to known ages of geologically important events. These comparisons permit us to assess elemental fractionation of U and Pb for uraninite and davidite of the new method, relative to zircon, as well as its geochronological accuracy and precision. U-Pb apparent ages measured previously agree well with our measurements for El Sherena, Palette, and Mt. Isa. Additionally, the upper-intercept 207Pb/206Pb dates for Adelaide River (701 ± 190 Ma, 1σ) and Palette (841 ± 94 Ma, 1σ) uraninite, measured here, are similar to those previously obtained for Palette (730 Ma), Nabarlek (920 Ma), and Koongarra (870 Ma), and the upper-intercept date for El Sherena uraninite (1573 ± 160 Ma) is within error of that previously determined for Ranger (1550 ± 15 and 1472 ± 40 Ma). Such apparent-age agreement for uraninite (and similarly for davidite) indicates that U and Pb fractionations are within error of that for zircon, whereas the inherent imprecision of our dates and their associated MSWD values greater than 2.5 probably indicate that multiple resetting events affected our samples. Analytically, these results demonstrate that the LA-HR-ICP-MS technique provides excellent spatial resolution while also removing argide, phosphide, sulfide, and halide interferences that can otherwise lead to erroneous data when using quadrupole-ICP-MS. Geologically, the individual 207Pb/206Pb and upper-intercept U-Pb dates of uraninite from Adelaide River and Palette are ca. 800 Ma, possibly reflecting recrystallization of uraninite during the break-up of Rodinia.

Experimental evidence shows no fractionation of strontium isotopes (87Sr/86Sr) among soil, plants, and herbivores: implications for tracking wildlife and forensic science

Strontium isotopes (87Sr/86Sr) can be useful biological markers for a wide range of forensic science applications, including wildlife tracking. However, one of the main advantages of using 87Sr/86Sr values, that there is no fractionation from geological bedrock sources through the food web, also happens to be a critical assumption that has never been tested experimentally. We test this assumption by measuring 87Sr/86Sr values across three trophic levels in a controlled greenhouse experiment. Adult monarch butterflies were raised on obligate larval host milkweed plants that were, in turn, grown on seven different soil types collected across Canada. We found no significant differences between 87Sr/86Sr values in leachable Sr from soil minerals, organic soil, milkweed leaves, and monarch butterfly wings. Our results suggest that strontium isoscapes developed from 87Sr/86Sr values in bedrock or soil may serve as a reliable biological marker in forensic science for a range of taxa and across large geographic areas.

Fabrication of solid calibration standards by a sol–gel process and use in laser ablation ICPMS

A method for the fabrication of solid multi-element calibration standards by a sol–gel process, suitable for laser ablation ICPMS, is described. The addition of an analyte (Se) and an internal standard (S) to a normal sol–gel method does not impair the production of the glass-like discs (xerogels). Heterogeneity of Se and S concentrations in the xerogels is less than that of NIST SRM 610 and 612 glass standards. Small differences in slopes of calibrations based on sulfide standards and those based on xerogel standards reflect differential matrix effects. The calculated S contents in the NIST SRM 610 (634 ± 151 µg g−1) and 612 (133 ± 17 µg g−1), using the xerogels as standards, are comparable to available S concentration data. Multiple element standards of Se, S and transition metals are hampered by the formation of inclusions resulting in visible heterogeneity, limiting the concentrations of transition metals with Se and S in the xerogels. The xerogels are potential standards for a variety of elements in glasses, minerals and other materials

Continuous leach inductively coupled plasma mass spectrometry : applications for exploration and environmental geochemistry

Continuous leach inductively coupled plasma mass spectrometry (CL-ICP-MS) is a new analytical technique developed to address some of the shortcomings of bulk leach techniques while overcoming the uncertainties associated with interpreting selective extraction data. It provides information on the specific geochemical sites and mineral phases from which elements are being released using real-time data generated by continually analysing progressively reactive solutions from water to 30% nitric acid as they are pumped through a sample directly into a high resolution ICP mass spectrometer. Mineral breakdown reactions can be monitored from the major elements released, thereby eliminating uncertainties related to host phase/trace element associations. By comparing major and minor element release patterns, trace elements can be reliably assigned to host phases. Results from single mineral phases, mixtures of mineral phases, and natural ore samples indicate that the release of elements from specific minerals is not obscured in more complex samples and that reprecipitation and back reactions are not a concern with this method. Scanning electron micrograph (SEM) examination of the reaction products has been used to verify which phases react and to support the CL-ICP-MS data interpretation. Results for natural soil samples indicate that ‘false’ mobile element anomalies can be identified using CL-ICP-MS and underscore the importance of understanding where trace elements reside in samples used for environmental studies or mineral exploration.

Selenium measurement in sulphides by hydride generation high-resolution inductively coupled plasma mass spectrometry

ABSTRACT Selenium concentrations of transition metal sulphides, albeit low, may be an important tool in exploration for economic ore deposits. These low concentrations necessitate the use of hydride generation for sample introduction, a very sensitive means of pre-concentration that results in low interference. However, transition metals interfere with the production of selenium hydride so that their removal from solutions made from dissolution of transition metal sulphides is necessary for hydride generation of selenium to be effective. We have devised a two-step process for the determination of Se concentrations in small samples (c. 50 mg) of sulphide minerals wherein dissolved transition metals are removed by precipitation as metal hydroxides under alkaline conditions (pH c. 12) to prevent sorption of Se, followed by further metal removal by chelating resin. Determinations made by hydride generation inductively coupled plasma mass spectrometry on the CCU-1c certified reference material (copper concentrate) and concentration standards showed quantitative recoveries (100 ± 5%) of Se. Using this technique we find that sulphide minerals from the Horne volcanic-hosted massive sulphide deposit give high Se concentrations ranging from 250 to 750 μg g−1. Average precision, expressed as relative standard deviation, is 10% and the detection limit is 4 μg g−1 of Se in a sulphide mineral. The procedure offers a method for Se determination of sulphides that is operationally simpler than many other methods.

Measurement of Pb isotope ratios by continuous leach–inductively coupled plasma–mass spectrometry: quantification of precision and accuracy

Precision and accuracy have been quantified for the determination of lead isotope ratios using continuous leach–inductively coupled plasma–mass spectrometry (CL-ICP-MS) by optimizing acquisition parameters and minimizing the number of elements in the method. By analysing for only 204Pb, 206Pb, 207Pb, 208Pb, 200Hg, and 202Hg, counting times can be increased allowing improvements in isotope ratio precision over normal CL-ICP-MS determinations, which measure these elements as part of a much larger suite. At total Pb concentrations of 1 ppb in solution, results show that precisions of 6.7% to 8.3% and 7.8% to 21% can be achieved for 207Pb/206Pb and 207Pb/204Pb, respectively, over the 0% to 30% HNO3 concentrations used in CL-ICP-MS. Accuracy, as measured against the certified values for NIST 981, ranges from 0.5% to 1.4% and 1.4% to 21% for 207Pb/206Pb and 207Pb/204Pb, respectively. The improvement in precision and accuracy afforded by this technique allows greater differentiation of isotopically distinct reservoirs of Pb within natural samples collected for exploration and environmental geochemistry.