Tourmaline compositions from the Salikvan porphyry Cu-Mo deposit and vicinity, northeastern Turkey

Tourmaline-bearing rocks occur in the Pontide volcanic island arc of NE Turkey which hosts numerous small Cu-Pb-Zn and Cu-Mo deposits. Three main environments of tourmaline formation are: 1) quartz-tourmaline veins, 2) tonalite porphyry and, to a lesser extent, coarse granodiorite, and 3) tourmaline-rich rocks at the contacts of coarse granodiorite and basic volcanic rocks. EPMA results show that the tourmaline is relatively rich in Fe (super 2+) and Ca, with a general trend from dravite to uvite; the Salikvan tourmaline formed by reaction of Fe-rich hydrothermal fluids with Ca-rich amphibole and plagioclase in tonalite porphyry and granodiorite. The dominant variability appears to be controlled by the exchange vector CaMgO[] (sub -1) Al (sub -1) (OH) (sub -1) . Tourmaline in quartz-tourmaline veins has moderate Fe/(Fe + Mg) values of 0.37-0.51, whereas that in tonalite porphyry is more iron-rich with Fe/(Fe + Mg) 0.45-0.53, and tourmaline in tourmaline-rich rocks is magnesian with Fe/(Fe + Mg) 0.30-0.46. The contents of trace elements and REE are discussed. Boron isotope analyses of tourmaline from quartz-tourmaline veins and from tourmaline-rich rocks have delta (super 11) B values of -9.4 and -9.0%, respectively, consistent with late-magmatic hydrothermal fluids.