Diamonds from the Behradih Kimberlite Pipe, Bastar Craton, India: A Reconnaissance Study

Abstract

The Behradih kimberlite is a diamondiferous, diatreme facies kimberlite intrusion with surface dimension of ~300 m × 160 m and is the largest among six intrusions known in the end-Cretaceous Mainpur Kimberlite Field of the Bastar Craton in east-central India. From drillcore material, 34 macrodiamonds with sizes in the range 0.6–2.2 mm and 86 microdiamonds of <0.6 mm size were recovered. The majority of the Behradih diamonds are colourless, while a small population consists of light brown and pale yellow diamonds. The microdiamonds have experienced significant resorption after crystallisation as evidenced by the development of dodecahedral faces in 50 % of the studied population. The macrodiamonds are mostly broken fragments, but several grains exhibit identifiable octahedral or dodecahedral faces. Sixteen macrodiamonds from the Behradih kimberlite were analysed for structurally bound nitrogen aggregation using infrared absorption spectroscopy. All grains belong to the IaAB diamond Type with a predominance of A-centre over B-centre. Their total nitrogen content (Ntotal) falls in the range of 358–950 at.ppm. The proportion of aggregated nitrogen [%NB = 100NB/(NA + NB)] in the studied diamonds varies from 22 to 45 %. Based on this parameter, the Behradih diamonds are interpreted to have formed at c. 1100–1125 °C, assuming a diamond age of c. 3 Ga. Based on Ntotal and %NB, the Behradih diamonds are similar to those from major primary diamond deposits worldwide.