Evidences of the manto type copper mineralization in the Asmanou area (Shahrood North East), on the basis of mineralogy, alteration and fluid inclusion characteristics

The Asmanou deposit is located in 85 km east of Shahrood, in the Sabzevar zone and Toroud- Abbas Abad district. The host rocks of mineralization are pyroxene andesite, basalt, basaltic trachyandesite and trachybasalt which display shoshonitic affinity and characteristic of continental arc setting. The country rocks in the Asmanou variably altered and two type of alterations, regional and local, could be distinguished; zeolite- carbonate regional alteration is widespread in the area and local alteration associated to the mineralization are chloritic and hematitic. Mineralization occurs as vein and stratiform and the common textures are disseminated, vein- veinlet, stock work and open space filling. Chalcosite is the main ore mineral accompanied by subordinate magnetite, hematite, bornite, chalcopyrite, pyrite and secondary minerals including covelite, malachite, coprite and goethite. Nonmetallic minerals are calcite, quartz, chlorite and zeolite. Fluid inclusion studies from the calcite and quartz from the main hypogene stage yielded the homogenization temperature between 79 to 350 °C for calcite, and 160 to 250 °C for quartz. Salinities for calcite is between 2.3 to 22 wt% NaCl eq. and for quartz between 6.1 to11.3 wt% NaCl eq. The results of this studies show the mixing and boiling are two important factors in the mineralization. Geophysical studies using resistivity (Rs) and induction polarization (IP) show the high values of IP-Rs in 5 to 40 m depth. Mineralogy, ore texture and structure, and fluid inclusion characteristics in the Asmanou deposit are similar to those manto type copper deposits.