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The uranium content of garnet lherzolite xenoliths from kimberlites

Published online by Cambridge University Press:  05 July 2018

D. A. Carswell
Affiliation:
Department of Geology, University of Sheffield, Mappin Street, Sheffield S1 3JD
C. M. Rice
Affiliation:
Department of Geology and Mineralogy, University of Aberdeen, Marischal College, Aberdeen, AB9 1AS

Summary

Uranium contents ranging from 0.03–1.18 ppm have been determined by delayed neutron activation analysis in a suite of 19 ultrabasic xenoliths (mostly of the common garnet lherzolite type) from the kimberlites of southern Africa. Consideration of these and previous data lead us to conclude that the U content of uncontaminated garnet lherzolite in the uppermost mantle is on average roughly 0.04–0.05 ppm, levels which are sufficient to account for the observed U contents of fresh basalts. Higher U contents in mantle-derived ultrabasic xenoliths are the result of secondary alteration processes, most probably related to infiltration metasomatism stemming from contact with kimberlitic or carbonatitic magma fractions. This introduced U is concentrated along the boundaries of the primary mineral grains and is mostly readily removed by acid leaching. A partial analysis is given for a secondary uraniferous calcium phosphate phase observed in kelyphitic rims around garnets.

Type
Research Article
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1980

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