The occurrence of tourmaline in Kuh Zar (Baghoo) Au-Cu mine, south of Semnan province

The Kuh Zar Au- Cu mine is located south of Semnan province within volcano-plutonic belt of Troud-Chah-Shirin with upper Eocene to Mio-Pliocene age. The tourmaline of the study area occurred as concentration or massive forms within altered zone in contact with the granodioritic intrusion and related to the hydrothermal system. In the area, the tourmalinization process is pervasive and in association with mineral assemblage sericite+quartz+tourmaline+pyrite+feldspars as well as Cu ore deposit. The composition of tourmalines is Shorle–dravite series with more tendency towards dravite component. These phases belong to alkaline tourmaline and are associated with quartz- tourmaline, meta-pelites, Ca-depleted meta-psamiteand and meta-pelites associated with Al-phase. The studied tourmalines contain X-Ca=61.07-1.77, X-Mg=0.01-0.1 and Al>6a.p.f.u. Therefore, the replacements of AlO(Mg)(OH), CaMgNa-1Al-1 and Al(Na-Mg) is possible in their structure. High Mg content and chemical zoning of these minerals point to their hydrothermal origin. The FeO/MgO+FeO ratio <0.6 in the studied tourmalines confirms the role of hydrothermal fluids.