School of Engineering and Science - Jacobs University

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B.W. Alexander et al. / Earth and Planetary Science Letters 283 (2009) 144–155
147
varying between 5 and 10 cm in length and labelled as IF1 to IF7. The
entire length of sampled drill core is highly magnetic. The IF is finely
laminated on millimeter scales and displays thicker banding on
centimeter scales. The longest individual pieces of drill core were
subdivided two or three times and these samples are identified as
such, e.g., IF6, IF6a, and IF6b are individual samples from the ~10 cm
long IF6 piece of drill core. This resulted in a total of fourteen samples,
each representing relatively homogenous ~1 cm thick bands that
contained varying amounts of Fe. Samples were crushed with a steel
jaw crusher and powdered with an agate ball mill. Major element
concentrations were determined by X-ray fluorescence (XRF) at the
SpectRAU laboratory of the University of Johannesburg, South Africa.
Trace element concentrations were determined at Jacobs University
Bremen using inductively-coupled plasma mass spectrometry
(ICPMS) following the methods described by Dulski (2001). Briefly,
for both trace metal and Sm–Nd isotopic analyses, powdered samples
were digested under pressure at high temperature (TN160 °C) in
Teflon vessels using concentrated ultrapure perchloric (HClO 4 ) and
hydrofluoric (HF) acids. Following HClO 4 –HF evaporation the samples
were re-dissolved in hydrochloric acid prior to ICPMS analysis or REE
separation. Analytical quality for major and trace element determinations
was monitored using the iron-formation standard FeR-2
(Geological Survey of Canada), analysis of which produced good
agreement with reference values (Table 1).
Samples for Sm–Nd isotope determinations were spiked prior
to dissolution with a mixed 147 Sm/ 150 Nd spike, and analyzed at the
Laboratory for Isotope Geology (LIG), Swedish Museum of Natural
History. Samarium and Nd were separated using ion exchange chromatography
techniques described in Andersson et al. (2008). The
isotopic ratios were determined with a Thermo Scientific TritonTIMS
(thermal ionization mass spectrometer) using multicollector static
mode. Samarium and Nd were loaded on double rhenium filaments. The
total Nd blank averaged 43 pg for three separate digestion batches and is
an insignificant contribution to the sample isotopic composition. Measured
isotope ratios were reduced assuming exponential fractionation.
Samarium ratios were normalized to 149 Sm/ 152 Sm = 0.516747. Neodymium
was run in static mode using rotating gain compensation, and
calculated ratios were normalized to 146 Nd/ 144 Nd=0.7219.
The La Jolla standard yielded 143 Nd/ 144 Nd=0.511848 ±0.0000047
(2σ, n=32). No corrections were applied to the measured ratios and
Table 1
Major and trace element data for Pietersburg IF.
Sample IF1 IF1a IF2 IF2a IF2b IF3 IF4 IF5 IF5a IF6 IF6a IF6b IF7 IF7a FeR-2 Ref a
(wt.%)
SiO 2 49.3 33.7 61.3 44.7 38.4 43.5 38.8 28.6 38.4 49.1 44.7 61.8 44.8 nd 50.4 49.21
TiO 2 0.04 0.05 0.02 0.07 0.07 0.09 0.07 0.04 0.01 0.02 0.03 0.02 0.25 nd 0.19 0.18
Al 2 O 3 0.73 0.72 0.32 1.06 0.91 1.50 1.53 0.33 0.13 0.26 0.54 0.30 5.30 nd 5.19 5.16
Fe 2 O 3 45.6 60.5 36.8 43.7 56.4 48.3 52.5 68.7 58.8 48.7 49.8 37.0 42.1 nd 39.67 39.21
MnO 0.20 0.28 0.05 0.13 0.11 0.21 0.53 0.79 0.64 0.08 0.08 0.09 0.12 nd 0.12 0.12
MgO 3.23 0.07 1.65 4.25 3.55 3.90 3.19 2.67 1.42 1.84 2.17 2.22 5.15 nd 2.23 2.10
CaO 1.75 1.74 0.89 3.45 1.28 2.13 2.77 1.18 1.43 1.07 1.64 2.79 1.33 nd 2.13 2.17
Na 2 O bd bd bd bd bd bd bd bd bd bd bd bd bd nd 0.39 0.51
K 2 O bd 0.02 bd 0.04 0.03 0.02 0.01 bd 0.01 bd 0.01 0.01 0.09 nd 1.34 1.33
P 2 O 5 0.19 0.23 0.11 0.20 0.24 0.30 0.22 0.21 0.10 0.14 0.21 0.16 0.16 nd 0.27 0.27
S bd bd 0.56 0.24 0.12 0.03 0.11 bd bd 0.57 0.17 0.22 0.54 nd 0.33 0.17
Total 101.04 97.31 101.70 98.84 101.11 99.98 99.73 102.52 100.94 101.78 99.35 104.61 99.84 nd 102.27
mg/kg
Sc 1.81 2.06 b1.30 2.86 3.03 2.83 2.85 b1.30 b1.30 b1.30 b1.30 b1.30 7.20 b1.0 4.94 6
Ti 195 306 101 438 488 384 352 172 47.4 80.7 161 91.9 1284 151 1045 1079
Co 4.11 6.00 1.94 7.73 6.94 6.02 6.24 2.61 1.20 1.58 2.31 1.67 14.3 2.29 6.50 7
Ni 26.2 22.3 12.3 57.6 47.2 33.3 31.0 13.9 5.38 8.94 15.1 11.2 128 15.2 22.0 21
Rb 1.17 1.13 0.703 2.46 2.05 2.00 2.07 1.17 0.368 0.52 0.657 0.498 5.60 0.837 62.6 66
Sr 29.5 28.5 11.0 51.2 15.8 33.8 41.0 24.2 29.8 14.8 25.0 38.4 17.9 21.7 60.8 58
Y 10.3 12.6 4.98 10.5 8.96 15.0 18.3 10.8 5.91 6.01 9.68 7.54 12.7 8.74 12.4 15
Zr 9.88 10.0 4.81 14.4 11.7 16.6 15.6 8.20 1.67 3.87 5.15 2.90 61.4 4.90 36.4 39
Cs 0.366 0.417 0.160 0.633 0.60 0.681 0.661 0.467 0.166 0.144 0.265 0.155 1.45 0.273 4.55 5
Ba 2.13 4.26 1.41 6.13 4.33 3.83 3.03 5.77 1.62 2.07 1.31 1.07 6.26 1.39 223 240
La 4.62 4.96 1.96 4.45 5.28 7.69 9.06 4.47 1.43 2.22 3.42 2.44 8.49 2.60 11.8 14
Ce 8.43 9.14 3.53 8.34 9.56 14.0 18.0 7.87 1.88 3.79 5.56 3.87 17.1 4.38 24.1 25
Pr 1.01 1.12 0.425 1.02 1.11 1.65 2.12 0.942 0.204 0.439 0.633 0.454 2.01 0.505 2.83 3
Nd 4.24 4.89 1.80 4.38 4.68 6.84 8.84 3.91 0.894 1.90 2.76 1.95 8.01 2.20 11.5 12
Sm 0.983 1.16 0.393 0.990 1.08 1.55 2.02 0.890 0.183 0.410 0.592 0.431 1.68 0.504 2.44 2.6
Eu 0.418 0.561 0.190 0.473 0.461 0.688 0.973 0.544 0.121 0.241 0.306 0.276 0.601 0.266 1.20 1.25
Gd 1.27 1.55 0.539 1.31 1.39 1.96 2.55 1.24 0.326 0.594 0.879 0.676 1.87 0.743 2.25 2
Tb 0.192 0.236 0.079 0.211 0.201 0.308 0.417 0.191 0.048 0.090 0.140 0.101 0.294 0.118 0.332 0.32
Dy 1.30 1.59 0.560 1.36 1.25 2.07 2.82 1.31 0.344 0.644 0.960 0.708 1.91 0.809 2.10 2
Ho 0.298 0.357 0.128 0.304 0.272 0.463 0.621 0.300 0.093 0.153 0.237 0.180 0.412 0.195 0.436 0.6
Er 0.910 1.12 0.406 0.957 0.840 1.43 1.92 0.945 0.304 0.489 0.751 0.550 1.30 0.618 1.31 1.5
Tm 0.132 0.158 0.061 0.135 0.118 0.199 0.271 0.136 0.045 0.070 0.107 0.081 0.193 0.089 0.187 0.2
Yb 0.870 1.01 0.368 0.881 0.755 1.26 1.73 0.884 0.276 0.462 0.686 0.515 1.27 0.583 1.23 1.3
Lu 0.137 0.166 0.062 0.143 0.123 0.203 0.268 0.141 0.047 0.076 0.114 0.084 0.200 0.096 0.191 0.2
Hf 0.248 0.258 0.118 0.370 0.291 0.438 0.373 0.220 0.037 0.102 0.135 0.073 1.68 0.114 0.955 1
Ta 0.040 0.044 0.017 0.052 0.046 0.074 0.064 0.036 0.007 0.015 0.022 0.013 0.264 0.020 0.147 0.2
W 50.9 140 21.1 43.4 27.9 61.5 134 31.3 59.9 52.2 74.1 39.2 55.9 86.7 2.36
Pb 1.80 2.09 1.29 2.94 1.94 2.25 2.71 2.34 1.41 1.41 1.37 1.69 2.21 1.27 8.43 11
Th 0.330 0.380 0.155 0.473 0.430 0.523 0.506 0.280 0.066 0.174 0.208 0.124 1.46 0.174 2.44 3
U 0.083 0.102 0.041 0.113 0.108 0.146 0.146 0.079 0.020 0.036 0.053 0.031 0.500 0.050 1.33 1.2
bd=below determination limit.
nd=not determined.
a Ref =values for FeR-2 iron-formation standard as provided by issuing agency (Canada Centre for Mineral and Energy Technology-Mining and Mineral Sciences Laboratories, Abbey
et al., 1983), except for italicized data which are obtained from the GeoReM database (Jochum et al., 2005).