A New Occurrence of Kimberlite Near Kotakonda, Mahboobnagar District, Andhra Pradesh

Abstract A Kimberlite dyke, with the appearance of a conglomerate due to the presence of mega and macro-crysts of olivine resembling pebbles, is located for the first time near Kotakonda, at about 10 km SSE of the known kimberlitic occurrences of Maddur area. Its massive look, lack of country rock xenoliths, local trachytic texture and concentration of megacrysts of olivine and orthopyroxene reflect hypabyssal nature. It consists mainly of rounded and corroded mega and macro-crysts of serpentine pseudomorphs of olivine and subordinate ortho- and clinopyroxene set in a fine-grained matrix containing microphenocrysts of euhedral olivine, monticellite. perovskite, spinel, apatite, calcite, ilmenite, magnetite, chromite and pyrite. The intergranular space is occupied by phlogopite, serpentite and carbonates. The major element chemistry of Kotakonda kimberlite, with low Niggili Si and high K and Mg values and alkali- and alumina-poor and cafemic-rich nature, matches well with that of kimberlite pipes 2,3,4 and 7 of Vajrakarur and kimberlites of Russia and Greenland. Its REE data agrees with that of 'basaltic kimberlites' of south India. The Kotakonda and Maddur kimberlite occurrences, possibly representing thc northern loci of kimberlitic activity of Vajrakarur area, show a rise of + 10 mgl over the background value in the regional gravity picture and fall within the zone of intersection of NE-SW and NNW-SSE lineaments, which could be a manifestation of mantle uplift and crustal thinning, thereby opening a new vista for the search of kimberlites.