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The isotopic composition of silver and lead in two iron meteorites: Cape York and Grant

Chen, J. H. and Wasserburg, G. J. (1983) The isotopic composition of silver and lead in two iron meteorites: Cape York and Grant. Geochimica et Cosmochimica Acta, 47 (10). pp. 1725-1737. ISSN 0016-7037. doi:10.1016/0016-7037(83)90022-4.

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Silver in the metal phases of Cape York (IIIA) and Grant (IIIB) has been determined after an extensive surface cleaning process. The ^(107)Ag/^(109)Ag was found to be enriched over that found in terrestrial Ag by ~7%. to 19%., demonstrating the presence of excess ^(107)Ag (^(107)Ag^∗) in this class of meteorites. An effort was made to find schreibersite with a distinctive ^(108)Pd/^(109)Ag ratio in order to establish a three-point isochron, but the results are not markedly different from those obtained for the bulk metal. The Ag isotopic ratio of sulfides from the same meteorites were nearly normal in composition. These results demonstrate correlations of ^(107)Ag/^(109)Ag with ^(108)Pd/^(109)Ag between coexisting phases of two iron meteorites that are associated with planetary differentiation processes. The ratios ^(107)Ag^*/^(109)Pd were found to be 1.7 × 10^(−5) and 1.2 × 10^(−5) for Cape York and Grant, respectively. These observations are in support of the widespread presence of ^(107)Pd in the early solar system. The difference in isotopic composition between metal and sulfide phases demonstrates that silver diffusion was small (over 6.5 × 10^6 y) indicating a cooling rate much greater than 150°C/my for meteorites which have been attributed to small planetary cores. Uranium determinations were carried out on the metal phases and concentrations of ~ 1 × 10 ^(12) g U/g and 2 × 10^(−10)g U/g were found for Cape York and Grant, respectively. The Pb in these meteorites was determined using the improved cleaning procedures and chemical separations with low blank levels. The results confirm the presence of variable proportions of radiogenic Pb in both the metal and sulfide phases of iron meteorites. No simple explanation for the presence of radiogenic lead is apparent; while terrestrial contamination may appear to be the obvious explanation, it is possible that this effect could result from relatively recent metamorphism in the meteorite parent body.

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Wasserburg, G. J.0000-0002-7957-8029
Additional Information:© 1983 Pergamon Press Ltd. Received March 10, 1983; accepted in revised form June 28, 1983. We wish to thank Vagn F. Buchwald for his generosity and courtesy in providing us with prime samples of metal and troilite from his favorite meteorite. The sample of Grant was obtained from the United States National Museum through the aid and courtesy of Roy Clarke. The authors wish to thank W. R. Kelly. D. M. Unruh and John T. Wasson for thorough reviews and valuable constructive and critical comments. L. E. Nyquist served not only as associate editor but also as a helpful "volunteer" reviewer. This paper was supported by the National Aeronautics and Space Association Grant No. NGL 05-002-188 and the National Science Foundation Grant No. PHY79-23638A2. Contribution Number 3755 (412) of the Division of Geological and Planetary Sciences.
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NASANGL 05-002-188
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Caltech Division of Geological and Planetary Sciences3755
Lunatic Asylum Lab412
Issue or Number:10
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Official Citation:J.H. Chen, G.J. Wasserburg, The isotopic composition of silver and lead in two iron meteorites: Cape York and Grant, Geochimica et Cosmochimica Acta, Volume 47, Issue 10, October 1983, Pages 1725-1737, ISSN 0016-7037, (
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ID Code:42109
Deposited On:29 Oct 2013 18:37
Last Modified:10 Nov 2021 16:17

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