Discovery of a kimberlite pipe near Budikonda, Dharwar craton, south India: Field approaches, preliminary petrography and mineral chemistry

Abstract

Multi-parametric and systematic exploration for kimberlite search was made in the vicinity of the Kalyandurg area within the Closepet granite, Dharwar craton, south India involving Remote Sensing and Airborne Geophysical Surveys (100 and 200 m spacing; 60 m AGL), Stream Sediment Sampling as well as Electron Probe analysis of heavy indicator minerals. The bipolar aeromagnetic anomaly (pronounced by high-low pair) falls in the positive drainage catchment delineated by stream sediment sampling. Subsequent drilling by a private party over the suspected anomalous zone resulted in the discovery of kimberlite. This is being reported here as the KL-7 kimberlite of the Kalyandurg cluster. Petrographically, the kimberlite shows typical porphyritic texture with macrocrystal olivine grains (~ 500–4500 μm) set in a groundmass composed of abundant phlogopite, perovskite and microcrystal olivine and clinopyroxene. Xenocrystic chromite grains were also observed. Preliminary studies on the mineral chemistry indicates that the olivine grains are foresterite-rich (Fo = 88–92) with an average MgO wt. % of 49.61. Groundmass phlogopites are of kimberlitic affinity with high Mg# (Mg/Mg+Fe²⁺) ranging between 0.88 and 0.91. The Cr-spinel macrocrysts with high Cr₂O₃ (> 62 wt. %) are considered to have formed from a primary garnet-peridotite-derived melt. The ilmenites have 8 to 12 wt % MgO and indicate kimberlitic affinity. Based on the current discovery, a suitable investigation strategy is also being suggested here for future kimberlite exploration in the area within the Closepet granite of the Dharwar craton, South India.