Magmatic and post-magmatic evolution of the Newania carbonatite complex, Rajasthan, north-western India

This work describes the mineralogy of dolomite carbonatite occurring at the Newania carbonatite complex, Rajasthan, north-western India. The mineralogy records the textural and compositional features of magmatic and post-magmatic stages of carbonatite evolution. Ferroan dolomite is the principal constituent and displays variable degrees of deformation, ranging from brittle-to-ductile deformation regimes. Apatite exhibits textural and compositional evolutionary trends from early-to-late stages of carbonatite evolution. Two varieties of amphibole are reported for the first time from this complex, ferri-winchite and cummingtonite; the former is magmatic and the latter is metamorphic in origin. The columbite-tantalite-series minerals are columbite-(Fe), and their paragenesis evolves from composite grains with pyrochlore to individual crystals. Pyrochlore is magmatic with U-Ta-Ti-rich compositions and shows evolution from calciopyrochlore to kenopyrochlore, followed by alteration during late-stages of carbonatite evolution. Monazite and baryte constitute the post-magmatic mineral assemblage; the former is hydrothermal and crystallised after precursor apatite, whereas the latter is associated exclusively with columbite-pyrochlore composites. On the basis of the mineralogy of the carbonatite, it is concluded that the parent magma was generated by low-degree partial melting of magnesite-phlogopite-bearing peridotite.