Hydrothermal alteration of monazite-(Ce) from the Santa Maria de Itabira pegmatite district (Minas Gerais, Brazil)

Monazite-(Ce) is found in granitic pegmatites in the Santa Maria de Itabira pegmatite district (Minas Gerais, Brazil). During the magmatic stage, monazite-(Ce) seems to have had higher contents of cheralite and buttonite in the solid solution. The Th content in primary monazite-(Ce) is high and characteristic for each pegmatite body. During the late stage (albitisation), the mean LREE content in the altered zone is slightly higher and Th content is very low. The accessory mineral assemblages changed; buttonite and cheralite crystallize together with Th-poor and La-rich monazite-(Ce) at the border of altered crystals. Nd/Sm and U/Pb ratios also changed during the hydrothermal stage. (authors)