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Trace element composition and cathodoluminescence properties of southern African kimberlitic zircons

Published online by Cambridge University Press:  05 July 2018

E. A. Belousova ,
W. L. Griffin  and
N. J. Pearson
E. A. Belousova
Affiliation:
National Key Centre for Geochemical Evolution and Metallogeny of Continents, School of Earth Sciences, Macquarie University, Sydney, NSW 2109, Australia
W. L. Griffin
Affiliation:
National Key Centre for Geochemical Evolution and Metallogeny of Continents, School of Earth Sciences, Macquarie University, Sydney, NSW 2109, Australia CSIRO Exploration and Mining, P.O. Box 136, North Ryde, NSW 2113, Australia
N. J. Pearson
Affiliation:
National Key Centre for Geochemical Evolution and Metallogeny of Continents, School of Earth Sciences, Macquarie University, Sydney, NSW 2109, Australia
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Abstract

Zircon frequently occurs as a minor mineral in kimberlites, and is recognised as a member of a suite of mantle-derived megacryst minerals. Cathodoluminescence (CL) microscopy and laser ablation ICPMS analysis were used to study the internal structure and chemical composition of zircon crystals from southern African kimberlites. Zoning revealed by CL ranges from fine oscillatory to broad homogeneous cores and overgrowths. The ICPMS data show that kimberlite zircons have distinctive trace element contents, with well defined ranges for REE, Y, U, Th, P and some other trace elements. Both low REE contents (ΣREE < 50 ppm), and distinctive chondrite-normalised REE patterns with low and flat HREE are characteristic of kimberlite zircons. Samples or zones with yellow CL have higher Th, U, Y, and REE than those with blue-violet CL. Variations in the concentrations of a range of trace elements lead to different amounts of lattice defects, creating the possibility for different levels of direct excitation of luminescence centres, and therefore different CL colours. The distinctive CL and compositional features described here can rapidly identify kimberlite zircons in prospecting samples taken during exploration for kimberlite bodies.

Keywords

zirconkimberlitecathodoluminescencetrace elementssouthern Africa
Type
Research Article
Information
Mineralogical Magazine , Volume 62 , Issue 3 , June 1998 , pp. 355 - 366
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1998

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