The study of monazite beach deposits and the underlying basement along the Brazilian continental margin indicates that monazite is first concentrated in pegmatite and augengneiss which have crystallized from a water-rich mobilizate phase during partial melting events within a migmatite-charnockite Archean terrain. Erosion of such rocks has reconcentrated the monazite in the late Precambrian quartzites of the Sepetiba group, now metamorphosed in the granulite facies. Recrystallization of monazite took place during progressive metamorphism simultaneously with the muscovite-sillimanite reaction. The monazite deposits of Guanabara were derived directly from the Sepetiba quartzites whereas those of Rio de Janeiro, Espirito Santo, and Bahia have the Tertiary clayish sediments of the Barreiras formation as an additional host.

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