A routine high-precision method for Lu-Hf isotope geochemistry and chronology |
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| Authors: | P J Patchett M Tatsumoto |
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| Institution: | (1) US Geological Survey, Denver Federal Center, 80228 Denver, CO, USA;(2) Colorado School of Mines, 80401 Golden, CO, USA |
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| Abstract: | A method for chemical separation of Lu and Hf from rock, meteorite and mineral samples is described, together with a much improved mass spectrometric running technique for Hf. This allows (i) geo- and cosmochronology using the176Lu 176Hf+
– decay scheme, and (ii) geochemical studies of planetary processes in the earth and moon.Chemical yields for the three-stage ion-exchange column procedure average 90% for Hf. Chemical blanks are <0.2 ng for Lu and Hf. From 1  g of Hf, a total ion current of 0.5×10–11 Ampere can be maintained for 3–5 h, yielding 0.01–0.03% precision on the ratio176Hf/177Hf. Normalisation to179Hf/177Hf=0.7325 is used.Extensive results for the Johnson Matthey Hf standard JMC 475 are presented, and this sample is urged as an international mass spectrometric standard; suitable aliquots, prepared from a single batch of JMC 475, are available from Denver.Lu-Hf analyses of the standard rocks BCR-1 and JB-1 are given. The potential of the Lu-Hf method in isotope geochemistry is assessed. |
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