The investigation of chemical composition of tourmalines in ‎biotite- muscovite granite of Mashhad

Tourmaline occurs in the biotite-muscovite granite of Mashhad as nodule, euhedral tourmalines in pegmatite and aplite, quartz-tourmaline veins, tourmaline-rich veins and radial tourmalines. Compositionally, they all are between schorl and dravite end- members and alkali group tourmalines. The euhedral tourmalines in pegmatite and aplite are Fe - enriched schorl whereas the nodule, quartz-tourmalines, the radial and the vein tourmalines are Mg- rich schorl. The higher Mg concentration in these tourmalines relative to those of the pegmatite and aplite are probably related to the crystallization of Fe -rich minerals including biotite, garnet, and the pegmatite and aplite tourmalines during the evolution of granitic magma. The LA ICP (MS) results indicate that all types of studied tourmalines are characterized by low trace element abundances and have more concentration of Sr, Ga, Li, Be, Sn, Pb as well as some transitional elements. The tourmalines studied show similar REE patterns, LREE enrichment and positive Eu anomalies. The low Ba, Rb, W, Sn، Y, Nb and HREE concentrations can be due to crystallization of some minerals such as garnet, biotite, muscovite and feldspar prior to the tourmalines. The correlation between major and trace elements of the tourmalines is the effects of atomic sites and thermodynamic in the crystal chemistry and the behavior of trace elements in the tourmalines.