Implanted ^3He, ^4He, and Xe in further studies of diamonds from Western Australia
Abstract
In measurements of the noble gases in additional samples of diamonds from the Argyle and Ellendale lamproites in Western Australia we have failed to encounter any neon-rich stones such as showed solar-like isotopic compositions in earlier work. No neon was detected above the relatively high blank levels in our glass apparatus. White and brown diamonds showed no differences in noble gas content, nor did samples segregated by the color of long-wave UF fluorescence. The rare gas patterns in the 1.2 Ga Argyle pipe are largely consistent with implanted ^3He, ^4He, and fissiogenic Xe from U/Th in the matrix rock in which the diamonds have been stored for so long. These implanted species are absent in diamonds from the much younger (approximately 20 Ma) Ellendale pipe. We give implantation formulae for several models of inhomogeneously distributed U/Th. Differences in ^3He content between pipe and alluvial Argyle samples are consistent with expected cosmogenic production in the latter. An expanded data base for helium and carbon isotopic data on the same samples supports a negative [^4He]-δ^(13)C correlation seen earlier in work from our group, but if the Argyle samples, which contain light carbon, are corrected for implanted ^4He-δ^(13)C, the correlation is considerably weakened. We no longer see an earlier ^3He/^4He-δ^(13)C correlation.
Additional Information
© 1991 Pergamon Press. Received June 25, 1990; accepted in revised form April 18, 1991. The work at Berkeley was supported in part by NASA under grant NAG 9-34 and bears code number 155. The participation of one of us (JHR) was supported in part by the US Department of Energy. The isotopic analyses of carbon made at Pasadena were supported in part by the National Science Foundation under grant EAR 8404096. We thank Dr. C. B. Smith and others at CRA Exploration Pty. Ltd., Western Australia, for supplying the Australian samples for this paper and for responding to numerous queries about them and the host lamproites. We are indebted to Dr. J. B. Hawthorne at De Beers Consolidated Mines, Ltd., for supplying the Finsch samples for which we present the data in Table 4 labeled UP90. Others we thank for responses are Dr. Al L. Jaques of the Australian Bureau of Mineral Resources, Camberra, and Dr. M. Honda at the Australian National University. Reviews of the paper by Prof. Lal at UC, San Diego, and Prof. Ozima at Tokyo have led to substantial improvements, and we thank them for their efforts. We thank Dr. I. McDougall at ANU and Dr. R. Burgess at the National Engineering Laboratory, Department of Trade and Industry, Glasgow, for much needed assistance in communications between the authors at a time when one of us (PM) was traveling. We appreciate the help we received in data reduction and calibration runs from Ms. Teressa Rae Ho while she was a volunteer student assistant from the Berkeley Physics Department. Editorial handling: K. MartiAdditional details
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- CaltechAUTHORS:20131113-121654668
- NAG 9-34
- NASA
- Department of Energy (DOE)
- EAR 8404096
- NSF
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