Mineral chemistry and genesis determination of tourmalines from the granite-gneiss pluton in the northeast of Jan mine (Lorestan province(

The outcrop of mylonitic granite-gneiss in the northwest of Azna city and the northeast of the Jan building stone mine is a part of Sanandaj-Sirjan zone. The tourmalines from these rocks are black and patchy or fine association. Based on EPMA data the tourmalines studied are shorl-dravite in composition with more tendency towards shorl. They belong to granitic environment and precipitated during hydrothermal condition. The chemical composition of the host granite is a major factor in distribution of elements in the studied tourmaline structural framework during the process of differentiation, as well as, faulting and uplifting of granitoid body. Some of the dominant substitution mechanisms in the structure of the investigated tourmalines are as follow: □X Al (Na R2+)-1, 21 xNa-1 zAl-1+xCa1 YR (OH)-1, Fe2+ Fe3+) (Mg Al)-1.