Tourmaline along with quartz is the main mineral in the quartz-tourmaline veins, which cut the granitic massif and the clastic rocks of Shemshak Formation in the northern part of the Shah-Kuh area, Eastern Iran. This mineral is also present in the greisens and some leochocratic microgranities as accessory mineral. A total of 27 point analysis of tourmalines from these rocks have been carried out by the electron microprobe. Accordingly, the tourmalines fall in the Schorl field of the Fe50 Al50-Al-Mg50 diagram. Some of the major elements in the tourmalines, including Fe, Mg, Ca, Al and B, in the northern part of the pluton, could be driven from the sedimentary rocks of Shemshak Formation.
The chemical composition of the tourmalines has been compared with tourmalines associated with granite related to Sn and Sn-W hydrothermal mineralization in South Africa, Namibia and NewZeland. The FeO*/(FeO*+MgO) ratio of tourmalines from the veins reduces toward the pluton center. This indicates the proximity of the element-rich fluids, thus, the origin of these elements could be ascribed to the Shemshak Formation.
According to the electron microprobe analysis Sn is an important trace element in the tourmaline of the veins. The image analysis shows that Sn is present in this mineral as disseminated or as fine inclusions of cassiterite. Compositions plotting below the Schorl- Dravite line, on the ternary cations plot of Fe50 Al50-Al-Mg50 and Al50 point to substitution of some Al by Fe+3, hence, to relatively more oxidizing conditions. These conditions induce the formation of cassiterite