Geochemistry of pegmatitic and vein tourmalines and their formation mechanism in the Mashhad leucogranites

The studied area is located in the Binalud Zone and comprises Mashhad leucogranites (g2) that include pegmatites and tourmaline veins. According to studies of the Mashhad leucogranites¡ these granites are peraluminous¡ highly differentiated and resulted from melting metapelites. In these granites¡ tourmaline can be seen in various forms of dendritic¡ nodules¡ vein and pegmatitic forms. For geochemical studies of vein and pegmatitic tourmalines¡ it was used microprobe analysis (EPMA)¡ XRF and ICP- MS. Based on these analyses¡ pegmatitic tourmalines include schorl and vein tourmalines which are magnesium-rich- schorl and both are classified in the range of alkaline tourmalines. They have oscillatory chemical zoning and bluish green to brown pleochroism that is probably due to changes in concentration of Ti¡ Ca¡ and Fe. In the studied tourmalines¡ major substitutions took place including Na(Fe)= X-Vacancy and Na(Fe)OH=Na(O). Both types of tourmalines are resulted from magma differentiation with this difference that pegmatitic tourmalines show magmatic system characteristics but vein tourmalines have magmatic-hydrothermal system characteristics. These properties are related to the pegmatitic development stages and fluids obtained during their evolution.