The Pipe-15 kimberlite: A new addition to the Wajrakarur cluster of the Wajrakarur kimberlite field, Eastern Dharwar craton, Southern India

This paper serves to report, for the first time, on the chemical composition of primary groundmass minerals occurring in a newly discovered kimberlite located 150m NE of the well known Pipe 2 kimberlite in the Wajrakarur cluster of the Wajrakarur kimberlite field, Eastern Dharwar craton, Southern India. These mineral compositions are also compared with newly acquired analyses of groundmass minerals in the Pipe 2 kimberlite. The kimberlite in this newly discovered intrusion (here referred to as Pipe 15) is characterized by a magmatic, microcrystic rock texture, consisting of microcrysts of serpentinised olivine in a finer groundmass rich in phlogopite, clinopyroxene, spinel, perovskite and apatite (in a base of serpentine). The rock is intensely altered. Phlogopite in the Pipe 15 kimberlite has comparatively low Al and higher Fe than phlogopite in Pipe 2 and (on this basis) is markedly different to phlogopite from Pipe 2. Spinels in Pipe 15 are also compositionally markedly different to that in Pipe 2 in that lower Ti/(Ti+Cr+Al) and Fe/ (Fe+Mg) are seen in spinels from Pipe 15, when compared to spinels from Pipe 2. Furthermore, Fe-poor, primary (groundmass) clinopyroxenes are abundant in Pipe 15, while it is almost totally absent in Pipe 2. In view of these compositional differences, it is here considered likely that Pipe 15 represents a new, separate intrusion and that it is not simply a satellite of Pipe 2, in the Wajrakarur kimberlite cluster. The compositions of the phlogopites, spinels and clinopyroxenes from the Pipe 15 kimberlite, as analyzed in the present study, are strikingly similar to that of the groundmass phases (phlogopite, spinel and clinopyroxene) in Group 2 kimberlites (orangeites) from the Bastar craton in Central India, as well as for typical orangeites from the Kaapvaal craton in South Africa. A genetic relationship to Group 2 kimberlites (orangeites) can therefore be inferred in view of modern mineralogical genetic classification. The recent discovery of Late-Cretaceous orangeite in the nearby Timmasamudram kimberlite cluster is also indicative of Group 2 kimberlite (orangeite) magmatism in this region of kimberlite intrusions, and serves to support the classification proposed here for Pipe 15.