Singular mineral assemblages and paragenesis of the pegmatites of the Galiléia (Minas Gerais) region.

Abstract

The Galiléia region is famous worldwide due to the periodic discovery of rare minerals and/or mineral for collectors. Such minerals are related to pegmatitic bodies that have been originated from granitic intrusions of Brasiliano age (550-500 My). Regional rocks in which these granites intrude are micaschists and gneisses of uncertain age. Three geographic areas were recognized, where the mineralized pegmatites occur: Sapucaia do Norte, Fazenda Boa Vista e Serra do Urucum. In these areas, the main deposits are studied emphasizing their mineral assemblages and paragenesis. Thus, pegmatites are classified into five different types, related to the phosphatic mineral phases, that are: (1) Li-rich pegmatites, with primary montebrasite, (2) Li-rich pegmatites, with primary triphylite, (3) pegmatites with primary and secondary apatite, (4) pegmatites without primary phosphates, with paragenesis from the montebrasite alteration, and (5) pegmatites without primary phosphates, with paragenesis from the triphylite alteration. Based on such mineral assemblages, some non-phosphatic rare and very rare minerals (eg., stokesite, helvite, lindbergite, coutinhoite, etc.) that occur in this region are also characterized.