THE ROLE OF PETROGRAPHY AND LITHOGEOCHEMISTRY IN EXPLORATION FOR DIAMONDIFEROUS ROCKS

Rock samples obtained during an exploration program may be identified and assessed as to their diamond potential by a combination of transmitted light petrography, back scattered electron imagery and energy dispersive X-ray spectrometry. Fresh and slightly altered potentially-diamondiferous rocks such as kimberlite, orangeite and lamproite may be distinguished from petrographically superficially similar un-economic lamprophyres using mineralogical genetic classifications of the former. Highly altered rocks or diatreme and crater facies rocks may be identified from relict textures and oxide minerals or volcanogenic clasts respectively, by similar methods. Whole rock major and trace element compositions are of little use in distinguishing between various groups of diamondiferous rocks but are useful in distinguishing these from highly altered un-economic rocks. Mineralogical criteria for the identification of diverse alkaline ultramafic rocks are presented.