A new look at the olivine-lamproitic rocks of the Maddur-Narayanpet area, Mahbubnagar district, Andhra Pradesh, India

Abstract

The olivine-lamproitic/kimberlitic rocks occuring in parts of the Mahbubnagar district of Andhra Pradesh are re-examined in the light of new petrological and geochemical data. The titanium poor (<3 TiO2 wt%) phlogopites, presence of primary calcite and composition of perovskites in these rocks are akin to those found in kimberlites. Calcium-rich iron silicate-kirschsteinite is being reported for the first time from Indian kimberlites in this work. The geochemical signatures of these rocks like potassic (K2O <3 wt% character, magnesian rich nature (>30 wt% MgO), high Mg numbers (73-82) and incompatible element enrichment levels further characterise them to be kimberlites. The abundances and the chondrite normalized distribution patterns of their REE are remarkably different from the olivine lamproites of Western Australia. It is put forward here that all these occurrences are true kimberlites and not olivine-lamproites resembling those of Western Australia, as suggested by some workers elsewhere. It is further argued that all the kimberlites of Mahbubnagar district;Ire genetically related and are different in this aspect from at least one kimberlite from the Anantapur district - Chigicherla pipe-2, the latest pipe find in the Anantapur district, suggesting that the Mahbubnagar kimberlitic activity could be unrelated to the southern Anantapur.