Chemical Variation of Tourmaline and Source of Hydrothermal Solutions in Nezam Abad W-(Sn) Ore Deposit, Sanandaj-Sirjan Zone, West-Central Iran

Tourmalinization characterizes the most pervasive alteration type in the Nezam Abad ore deposit, west-central Iran. It delineates high-temperature centers of mineralization and together with quartz and cassiterite form inner parts of the alteration halo. The composition of tourmalines plots mostly along and between the proton and alkali-deficient end members. Tourmaline in quartzdioritic host is chemically and optically homogenous, with a general tendency toward more schorlitic compositions and is marked by Al deficiency in R3. Tourmaline in hydrothermal veins shows fine-scale chemical and optical zonation, tendency to more dravitic compositions and is characterized by lower F content and larger Fe/(Fe+Mg) variation with generally lesser values than quartzdioritic counterpart. The Rb-Sr and Sm-Nd isotope analyses of quartzdioritic units of the Boroujerd complex and separated hydrothermal tourmalines (?Nd -6.43 to -3.24) imply derivation from enriched sources with a lower Sm/Nd ratio than Chondritic Uniform Reservoir. The ?18O values (11.9 to 13.8‰) of quartz of hydrothermal veins suggest magmatic mineralizing fluids whose ?18O values have been increased through subsequent interaction with metamorphic country rocks. The range of ?11B values determined for hydrothermal tourmalines are relatively wide and falls at the lighter end of the range for typical continental crust.