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Two approaches may be utilized to determine and quantify non-conservative behavior of the elements of interest. The first involves preparing artificial laboratory solutions that contain known quantities of the elements of interest, and then simply treating these artificial solutions as if they were unknown samples by subjecting them to a full sample decomposition and ICPMS analysis. This characterization of analytical recovery is discussed here, while the second approach, which involves determining elemental concentrations in a CRM and comparing these data with the reference values, is discussed below in the section regarding analytical accuracy. Analytical recoveries of multi-element spikes (10 μg/kg) for the carbonate and HF-HClO 4 decomposition methods are presented in Figure 10. Recoveries for most elements are excellent, particularly for the carbonate decomposition, in which 27 of 32 elements have measured concentrations between 97-103% of the expected values. However, measured Ni in the carbonate digestion spike solution is ~30% too high, whereas Ta and W exhibit quite low recoveries of ~24% and ~80%, respectively. The anomalously high Ni recovery is attributed to contamination, as method blanks for the carbonate decomposition typically contain 2-5 μg/kg Ni. The significant loss observed for Ta and W is likely due to the filtration procedure performed for the carbonate decomposition. During the filtration step, the sample solution (10 ml of 5 M HNO 3 ) is passed over a 0.2 μm cellulose acetate filter (Fig. 1), which is subsequently rinsed with ~20 ml of 0.5 M HNO 3 . Whereas this rinse step appears sufficient for most elements, Ta and W (and to a lesser extent Nb) are apparently retained, and may only be quantitatively rinsed from the filter by adding trace amounts of HF (0.05 M) to the rinsing solution (K. Schmidt, personal communication). The addition of HF to the rinsing solution should only be utilized if information regarding W is critical, as HF can form unstable complexes with other trace metals, particularly the rare earths, potentially limiting quantitative recovery of these elements. With regard to Nb and Ta, the use of HF during the filter rinse step is not particularly informative , as these are immobile elements expected to be hosted in refractory aluminosilicate phases, which are resistant to dissolution by the carbonate decomposition method. For the HF-HClO 4 decomposition, analytical recovery for the 32 elements in the spike solution is more variable than that observed for the carbonate decomposition. Low mass elements tend to have slightly low recoveries around 95%, 25
1.35 1.30 1.25 1.20 1.15 HNO 3 carbonate decomp. HF-HClO 4 decomp. HF-HClO 4 decomp. pre- June 2006 1.35 1.30 1.25 1.20 1.15 fraction recovered 1.10 1.05 1.00 0.95 0.90 0.85 0.80 0.75 0.30 0.20 0.10 1.10 1.05 1.00 0.95 0.90 0.85 0.80 0.75 0.30 0.20 0.10 Sc Ti Co Ni Rb Sr Y Zr NbMoCs Ba La Ce Pr NdSmEu Gd Tb Dy Ho Er TmYb Lu Hf Ta W Pb Th U Figure 10. Multi-element analytical recoveries for the carbonate and HF-HClO 4 decomposition methods, expressed as a ratio of the measured element concentration divided by the spike concentration. Note break in the y-axis between 0.35-0.75. Spike solutions contained 10 μg/kg of the standard 32 elements analyzed, except for the pre-June 2006 HF-HClO 4 decomposition, which contained 1 μg/kg of the 24 elements routinely measured prior to June, 2006. Recoveries for most elements are between 95- 105%, particularly for the carbonate and pre-June 2006 decompositions. Notable exceptions are Ni, Ta, and W for the carbonate digestion, which suggests contamination/interferences (Ni) and loss (Ta and W) during the decomposition, perhaps as a result of the filtering step. The large spread and general increase as a function of mass, in the fraction recovered for the 32 element HF-HClO 4 decomposition is attributed to effects arising from the utilization of the internal standards 101 Ru and 187 Re (see text for details). and analytical recovery generally increases with increasing mass, though Ta does not follow this trend (Fig. 10). However, a test of analytical recovery performed prior to June 2006, conducted with the 24 elements originally analyzed by ICPMS within the JUB Geochemistry Lab, resulted in recovery percentages significantly better for many elements, particularly for elements with atomic masses below 138 (Ba). The exact reason for the more variable recovery observed for the full 32 element analysis currently conducted is not clear, though it is likely related to the internal standard correction. The generally constant analytical recovery of ~95% for elements with masses below 100, followed by the monotonic increase in recovery between masses 133 (Cs) and 183 (W), is mirrored by the IS correction factor for this analysis, which was 0.95 for all masses below 133 Cs, before linearly increasing to 0.98 for 183 W, and then decreasing to 0.96 for Pb, Th, and U. 26
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Iron sedimentation and the neodymiu
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The process(es) by which IFs were d
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This thesis represents original and
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viii
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goal of the research is to discern
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Figure 1. Map of southern Africa sh
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appropriate to briefly discuss: 1)
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100 10 MORB 1 0.1 raw data (mg/kg)
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10 -2 hydrothermal fluid 10 -3 10 -
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seawater and returned to the sedime
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100 MCO + 3 + M(CO 3 )- 2 rare eart
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net effect of carbonate complexatio
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feature was not recognized in early
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Page 42 and 43: Haley B.A., Klinkhammer G.P. (2003)
Page 44 and 45: Lee J.H. and Byrne R.H. (1993) Comp
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Page 48 and 49: Tosiani T., Loubet M., Viers J., Va
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Page 52 and 53: Abstract The benefits of inductivel
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Page 82 and 83: For the more recent, full 32 elemen
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Page 92 and 93: 1 IF-G/shale 0.1 0.01 La Ce Pr Nd P
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Page 112 and 113: Govindaraju K. (1995) 1995 working
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Page 118 and 119: Appendix 1 continued. Data in mg/kg
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Nd isotopes in 2.9 Ga Archean surfa
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Table 2 Trace element concentration
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Author's personal copy B.W. Alexand
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and preservation of oxide-facies IF
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TOP relative stratigraphic position
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The mechanism by which the alkali m
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6. Widdel, F. et al. Ferrous iron o
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82 PRESERVATION OF PRIMARY REE PATT
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ulk, open ocean seawater tended to
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