THE URUBU PEGMATITE, ARACUAI, MINAS-GERAI S (BRAZIL), AN EXAMPLE OF COMPLEX PETALITE-SUBTYPE PEGMATITE - MINERALOGICAL ZONATION AND GEOCHEMISTRY OF MICAS AND TOURMALINES

The Urubu pegmatite of Cambrian age, situated in the Eastern pegmatiti c province of Minas Gerais, is a Li, Cs, B and Sn pegmatite which exhi bits a complex mineralogical zonation with lepidolite, petalite and po llucite at the centre. The pegmatite is surrounded by a contact metamo rphic aureole containing zinnwaldite rich in Fe, Mg, Rb and Cs and Fe- Mg-lich tourmaline. Micas and tourmalines in the pegmatite are richer in Fe and Mg at the rim and in Li, Cs and F at the centre following th e classical model of fractional crystallization. The contact aureole i s considered to have been formed during the intrusion of the magma.