Formation of monazite-(Ce, La) by fluid-apatite interaction: the Floresta Azul Alkaline Complex, Bahia, Brazil

Jailson Júnior Alves Santos, Herbet Conceição, Marcel Vinícius Santos Leandro, Maria de Lourdes da Silva Rosa
2018 Brazilian Journal of Geology  
Monazite is a common accessory mineral in the Floresta Azul Alkaline Complex, occurring in three different rock types, which form this batholith: nepheline syenite, granite and fenite. Two compositional types of monazite can be found: monazite-(Ce) and monazite-(La), the latter being found only in syenites. Monazite occurs in close association with apatite as anhedral crystals ranging in size from 0.1-100 μm, and textures indicate different genetic processes. In nepheline syenite, monazite is
more » ... osely related to ancylite and apatite, as a late crystallizing phase. Monazite occurs in granites as pore fillings in apatite and was formed by the remobilization of rare earth elements (REE) from apatite by late CO 2 -rich fluids. In fenite, monazite appears as acicular crystals, parallel to apatite's crystallographic c-axis formed by exsolution from apatite by metamorphism. The data show that the monazite genesis was closely related to the activity of fluids associated either with the final stages of crystallization of nepheline syenite and granite or with fenitization of country rock.
doi:10.1590/2317-4889201820180069 fatcat:ncy4fc4hgfhblfbkpvnqjvsyzm