Regional trends in mineral assemblages of Swedish Proterozoic granitic pegmatites and their geological significance

Abstract

Abstract In the Svecokarelian rocks of Sweden the pegmatites can be divided into two main types, both of late orogenic affiliation: (1) The tourmaline ± Li-mineral type occurring in lower medium- to medium-grade metasediments. Typical minerals are tourmaline, garnet, beryl, columbite-tantalite, triphylite, primary Ca-Fe-Mn-phosphates, Li-aluminosilicates. (2) The Y-REE-mineral type comprising three subgroups: a) those in migmatitic environment, b) those with beryl and garnet in areas dominated by mainly felsic metavolcanics in lower medium- to medium-metamorphic grade, and c) those associated with granites of the Transscandinavian Granite-Porphyry Belt. In the Svecononvegian rocks of SW Sweden the rare-mineral bearing pegmatites, contemporaneous with the late- to postoro-genic Bohus granite, show similar trends with schorl, columbite and beryl in lower-grade rocks and Y-REE-minerals in higher-grade rocks. The trends in this region are not obvious because of the polymetamorphic environment. Li-minerals and primary Ca-Fe-Mn-phosphates are absent or very rare. The differences in mineralogy of the late erogenic pegmatites can be related to the dominant type of surrounding and underlying regional lithologies, which significantly affected the compositions of the parent granitic melts.