Carbonates and REE bearing barite from Carbonatite complex of Tiruppattur, Tamil Nadu, India

A barite sample collected from 200 m SE of Onnakarai village located in the ultramafic alkaline carbonatite complex of Tiruppattur is studied under polarizing microscope, scanning electron microscope and carried out X-ray diffraction analyses and Energy Dispersive X-ray micro Analyses (EDAX). Conventional wet gravimetric analyses are also made. EDAX analyses show presence of significant quantity of normative alkali-carbonates and niobium bearing rutile minerals. The carbonatitic barite is composed of significant proportion of (SrSO4 )2.88-18.26% replacing barite molecules. Though barite incorporates significant amount of TiO2 , no rutile needles are found within barite crystals, indicating that it is crystallized above eutectic temperature of~1200oC BaO-TiO2 system under atmospheric conditions. Petrographic studies of fluids inclusions presence primary and secondary fluid inclusions carrying H2O, liquid CO2 and CO2 phases with maximum peak of decrepitating pulses at 280oC indicate that the mineral is consolidated relatively at very high pressure condition much above atmospheric pressure. It is also enriched with incompatible elements like Ti, Nb, Zr, Hf, Y, Sc and REE constituents. The analyses show that the structural formula of the barite on the basis of 4 (O) ions is Ba0.95-0.32Sr0.10-0.03P0.00-0.04Ti0.35-0.28 Si0.17-0.01 Al0.02-0.00Fe0.01-0.00Mg0.02-0.00Ca0.04-0.01Na0.08-0.00K0.03-01CO20.35-0.03S O40.97-0.66. The EDAX analyses show that barite has enriched with significant amount of CO2 and SO3 . In the field it occurs in the form of small vein lets (< 3 x 0.3m) and lenses in ultramafic rock at the contact ultrapotassic garnetiferous syenites. It is closely associated with benstonite-riebeckite carbonatite, ferro-carbonatites, monazite-riebeckite bearing albitite and ilmenorutile-apatite veins.