CARBONATITE OCCURRENCES IN RAJASTHAN, INDIA

The carbonatite occurrences in the State of Rajasthan, Western India, comprise two age groups: the Newania Complex relates to the Aravalli o rogeny (Proterozoic), while the remaining three: Mundwara, Sarnu-Danda li-Kamathi, and Bhamni, represent the pre-Deccan Flood Basalt carbonat ite-alkalic activity at ca 68.5 Ma. Geochemical, Sr isotope (varying f rom 0.7021 to 0.7034), and C and O isotopic data (between -5 and +8 pa rts per thousand respectively), for the Newania carbonatite indicate t hat it is a mantle-derived primary melt that has preserved its initial composition. Low Sr isotopic composition and negative epsilon(Nd) val ue indicate that the Newania rauhaugite is derived from an old, LREE-e nriched lithospheric mantle source. The younger carbonatite occurrence s are closely associated with nephelinites and phonolites into which t hey penetrate as dikes. The significant feature of the Newania carbona tites is their varied mineral assemblages from cumulate apatite, magne tite, pyrochlore, Nb-silicate in rauhaugite to pyrite, chalcopyrite, m alachite, monazite in the late-phase ankeritic carbonatite. Pyrochlore is exceptionally rich in UO2, varying between 18.68 to 22.92%. There are mainly two types of pyrochlores; one rich in BaO (2.41% to 9.68%) and the other very poor in BaO (0.20 to 0.31%), Chalcopyrite does not show much variation (S = 35.07%, Fe = 30.18% and Cu = 35.09%), while m alachite shows small variation in Cu content (average CuO = 72%). The alvikite dikes in Kamathi are highly enriched in REE (total REE at tim es exceeds 15%), while in the Bhamni area carbonatite contains appreci able amounts of fluorite and lead-zinc ore (PbO = 22.12%, ZnO = 32.50% , Fe2O3 = 16.02%, CdO = 0.25%, Sb2O3 = 0.03%, SiO2 = 9.05%, Zr = 814 p pm, Cu = 160 ppm, Cr = 70 ppm, Co = 23 ppm, and Ni = 23 ppm).