A REAPPRAISAL OF AN ARCHEAN CARBONATITE OF NELLORE SCHIST BELT, SOUTH-INDIA

Field observations, trace element and isotopic results are reported for rocks classified as carbonatites from Vinjamur area in the Nellore schist belt. These carbonate rock-s occur either inter-bedded with metasedimentary quartzites and pelites or in association with calc-alkaline rather than alkaline volcanic rocks. No fenitised contacts are seen. Their Nb and REE contents are too low for carbonatites. Samples free from baryte veins have less than 150 ppm of Sr with an isotopic ratio greater than 07100. delta-C-13(PDB) range from -1.58 to -0.56 parts per thousand and delta-O-18(SMOW) from +14.00 to +16 parts per thousand. All these features, individually and collectively, show that the carbonate rocks of Vinjamur are most probably sedimentary and not igneous in origin.