MINERALIZAÇÕES EM METAIS RAROS RELACIONADAS A TURMALINA GRANITOS NEOPROTEROZOICOS, DA ZONA DE INTERFERÊNCIA DAS FAIXAS RIBEIRA E BRASÍLIA, MINAS GERAIS, BRASIL

Abstract

Tin and tantalum mineralizations related to two S-type granites are located in southern Minas Gerais State, Brazil. The granitic bodies, named Capivara and Itanhandu granites, are slightly foliated tourmaline granites cropping out in the interference zone of the Brasilia and Ribeira belts, developed during the Neoproterozoic Brasiliano Orogeny. They are hosted by a migmatitic leucogneiss derived from the Andrelândia Megasequence. Geochemical and geological data point to calcalkaline, peraluminous (Stype), syn-tectonic and parautochthonous characteristics. The geochemical features and the 207 Pb/ 206 Pb zircon ages of the Capivara (605 ± 11 Ma) and Itanhandu (649 ± 6 Ma) granites probably relate these bodies to the metamorphism of the Ribeira and Brasilia belts, respectively. Three distinct groups of pegmatites showing heterogeneous (PG-1 and PG-2) and homogeneous (PG-3) textures linked to the Capivara granite are concentrated around the body. From SEM-EDS studies two distinct kinds of Nb/Ta-bearing minerals and cassiterite were identified in the Itanhandu and Itamonte (Monte Belo-Capivara) areas. The Monte Belo-Capivara columbite-tantalite consists of a zoned oxide, with a tantaliferous core and a niobiferous rim. Its inclusions are cassiterite, plumbotantalite, tantalite, microlite, zircon and uraninite. The Itanhandu columbite-tantalite is a homogeneous, non zoned Sc and Ti-rich oxide, that may also be ixiolite. Its inclusions are ilmenorutile, columbite-tantalite, tantaliferous rutile, pyrochlore, uraninite and cassiterite. Two generations of cassiterite were identified in the Itanhandu and Itamonte (Monte Belo-Capivara) areas. The Monte Belo-Capivara cassiterite is Ta-enriched (1.8 % Ta 2 O 5 ), compared to the Itanhandu one (0.7% Ta 2 O 5 ). The inclusions in the Itanhandu cassiterite are ilmenorutile and Ti-Sc columbite-tantalite (possibly ixiolite) and in the Monte Belo-Capivara cassiterite they are pyrite, zircon, plumbotantalite, pyrochlore and small zoned crystals of columbite-tantalite with niobiferous core and a tantaliferous rim.