The Samchampi Carbonatites in Karbianglon district of Central Assam constitute one of the prominent alkaline-carbonatite body, falling within the alkaline ultramafic belt of NE India, stretching from Meghalaya to Assam in a NW-SE direction. Petrographic and chemical data show that the carbonatites are predominantly sovitic with rerrolian calcite. Trace element contents reveal pronounced preference of Sr, Ba, Ce, La, Nd, P and Nb over other elements. EMPA studies show average of 60.19% Nb2O5, 62.60% RE2O3 and 41.68% P2O5 in the mineral species pyrochlore, monazite and apatite in the carbonatites. Oxygen and carbon isotope values suggest a primary igneous origin for these carbonaties. The chemical, mineralogical and isotopic data reveal that the Samchampi carbonatites are magmatic, fractionated and may have originated from a mantle derived carbonated alkali ultramafic magma.
Alkaline carbonatite complex, liquid immisibility, Kalyani lineament
