Abstract
Five ilmenite megacrysts from the Premier kimberlite pipe have been analysed by Mossbauer spectroscopic and electron microprobe techniques for their Fe3+/Fe2+ ratio; and by nuclear bombardment techniques for their N2 content. Comparison of the Fe3+/Fe2+ ratio determined from electron microprobe analysis for total Fe assuming stoichiometry with the direct determination of this ratio by Mossbauer techniques is sufficiently good that the former method which is very widely used may be considered reliable. The N2 content of the ilmenite samples ranges from 0.5 to 2.0%, considerably in excess of that for most minerals. Heating experiments suggest that the N2 is not located in liquid inclusions. Isotopic analysis of ilmenite is not available and so its origin is uncertain, but these results suggest that ilmenite could be a major reservoir for N2 in the earth's mantle.
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