Diamond prospectivity of Mesoproterozoic lamproites from the Krishna valley, eastern Dharwar craton, southern India: insights from whole-rock geochemistry

Abstract

Diamond prospectivity of Mesoproterozoic lamproites in the Krishna valley at the northern and north-eastern margin of the Cuddapah Basin, southern India, is a matter of significance since several historically world-famous alluvial diamonds were recovered from their near vicinity. As the Krishna lamproites presently expose their root zones the possibility of diamond occurrence in their now-eroded uppermost portions remains an open question and renders assessment of their diamond prospectivity a challenging task. Based on newly developed models from a global data base, that predict diamond potential of hypabyssal facies lamproite/kimberlite from whole-rock geochemistry, we infer the Krishna lamproites to be non-diamondiferous. The non-prospective nature of Krishna lamproites is also additionally corroborated by the (i) non-recovery of macro diamond from bulk processing of samples to date, (ii) relatively larger degree melting of their source regions compared to those of diamondiferous kimberlites from Wajrakarur kimberlite field (Dharwar craton) and also the poorly diamondiferous lamproites from Chelima and Zangamarajupalle (Cuddapah basin) and (iii) their relatively highly fractionated nature. If our proposal is correct, then the primary source(s) for the historically renowned diamonds recovered from the Krishna valley may lie elsewhere or be from host rocks yet to be discovered.