Petrographic characterization and genetic implications of pegmatites from São José da Safira (MG), Eastern Brazilian Pegmatite Province

Abstract

The São José da Safira Pegmatite District, part of the Eastern Brazilian Pegmatite Province, hosts pegmatitic intrusions of economic and scientific relevance, containing tourmaline and beryl of high gemological quality, in addition to significant concentrations of B–Cs–Li–Ba–P–Ta. This study presents a petrographic investigation of the internal zoning of these pegmatites, based on the identification of their mineral assemblages, textural features, and genetic implications supported by the most widely used classification systems for pegmatites, aiming to understand the petrogenetic models and the probable sources of their forming magmas. The mineralogical-textural variations indicate that these are complex pegmatites, with internal zoning formed by primary zones (border–intermediate–core) and secondary albitization zones. They exhibit granitic composition, rare-element minerals (beryl–spodumene–lepidolite–tourmaline–xenotime), and miarolitic cavities. They are classified as Muscovite–Rare Element (emplaced into country units of 3–7 kbar and 520–650 °C metamorphic conditions), LCT Family (lithium–cesium–tantalum), Group 1 (spodumene-dominant), and Types DPA (direct product of anatexis) or RMG (residual melts of granitic magmatism). The genetic implications of these classifications, associated with the adjacent (Rio Doce Group and G4 supersuite) and country unities (Ribeirão da Folha and Salinas formations), support two petrogenetic hypotheses: i) formation of these pegmatites by anatexis of supracrustal metasedimentary rocks of the Rio Doce Group and/or the Ribeirão da Folha and Salinas formations; or (ii) magmatic fractionation of syenogranites of the G4 supersuite.