We have studied two groups of overprinted (altered) carbonatites at Amba Dongar, India: weakly overprinted and strongly overprinted. The mineral association of quartz, florencite-(Ce), strontianite, barite and sparse bastnäsite -parisite -synchysite typical of weakly overprinted carbonatites shows evidence of a high activity of OH -, (SO 4 ) 2-, Al and Si in the fluid. Later, the fluid was characterized by an increased activity of F -, (SO 4 ) On the basis of field observations, two phases of alvikite dikes have been recognized. Phase I is coeval with the main intrusion of sövite, and cross-cuts the sandstone, carbonatite breccia and pre-carbonatite basalt, whereas phase-II dikes were emplaced later. Ankeritic carbonatite, which is younger than the calciocarbonatite, invades sövite at several outcrops in the form of dikes and plugs of varying size. The ankeritic carbonatite occurs in three distinct phases. The first phase consists of thin dikes intruding sövite and fenite; the second phase forms large plugs within the sövite ring-dike, whereas the last phase is characterized by high radioactivity owing to the high abundances of cerite, monazite-(Ce), and thorite (Viladkar 1996). Veins of sideritic carbonatite, which are found in ankeritic carbonatites, also contain cerite, monazite and thorite. Locally, the total REE content is well above 15 wt.% (Viladkar 1996). The carbonatite activity appears to have ended with fluorite mineralization.

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