Tourmaline as a Recorder of the Magmatic–Hydrothermal Evolution From the Boroujerd Pegmatites, Sanandaj–Sirjan Zone, Western Iran

ABSTRACT The morphologies and compositional zoning of tourmaline‐group minerals can provide insight into the evolution of pegmatite‐forming melts. We present a dataset of major element compositions of the pegmatite‐hosted tourmalines from six localities in the Boroujerd region, Lorestan (western Iran), to document the origin of tourmaline and its genetic implications. All tourmalines from the Boroujerd pegmatites belong to the alkali group and the schorl (NaFe 2+ 3 Al 6 (Si 6 O 18 )(BO 3 ) 3 (OH) 3 (OH))‐foitite(◻(Fe 2+ 2 Al)Al 6 (Si 6 O 18 )(BO 3 ) 3 (OH) 3 (OH)) solid‐solution series. The compositional variations of these tourmalines can thus be expressed by the substitution ❑Al(NaMg) −1 , AlFe −1 and MgFe −1 . The data presented here suggest that the distinct major‐element zoning observed in tourmaline from pegmatites can best be explained in terms of processes occurring during tourmaline growth and evolution of pegmatite‐forming melts. Morphological and geochemical characteristics indicate that two different types of tourmalines have been recognised in the Boroujerd pegmatites, including primary (magmatic) and intermediate (magmatic–hydrothermal). This study, and others like it, demonstrate that tourmaline composition can serve as a useful proxy for deciphering the petrogenesis of granitic pegmatites and trace the magmatic–hydrothermal transition.