Investigation of mineral chemistry and causes of tourmaline formation in biotite amphibolits of Gol-e-Gohar mining and industrial area (Sirjan), Kerman province

The Gol-e-Gohar metamorphic complex is located in the southeast of Sanandaj-Sirjan Zone, in Sirjan city (Kerman Province). According to EPMA data of the tourmaline in the biotite-amphibolite of the studied area, these tourmalines are high Mg tourmalines and dravite ones and belong to the alkaline series. The positive correlation between Mg and Fe contents, high contents of Mg in the studied tourmalines, as well as the negative correlation between Al and Fe/(Fe+Mg) and Ca vs. Na, are all indicative of the substitution of []AlNa-1Mg-1, which indicating that these minerals are not magmatic tourmalines, instead metamorphic minerals. It appears that the reason for the formation of this mineral can be related to the high presence of biotite in the studied rocks and boron-rich fluids that concentrated in interstitial fluids. The boron-rich fluids reacted with biotite and formed the studied tourmalines.