Base and Precious Metal Ore-Forming System in the Cheshme Hafez and Challu Mining Area, Torud-Chah Shirin Magmatic Arc

The Torud-Chah Shirin volcanic-intrusive arc, in the south of Kavir-e-Chah Jam depression (SW of Damghan), hosted many Pb, Zn, Cu, Ag and Au occurrences and deposits. Cheshmeh Hafez (Pb-Zn±Cu±Ag±Au) and Challu (Cu-Au±Ag) polymetallic vein-type ore deposits are the major one located in the central part. The Tertiary calc-alkaline volcanism and related mineralization occurred along the main Anjillo fault in the north and the Torud fault in the south with NW-SE trend. The exposed rocks in the Torud-Chah Shirin consist of volcaniclastic sequence composed of siltstone, thin bedded sandstone, lapilli tuff and volcano breccias and mostly andesitic and andesitic-basalt flows. Main host rocks at Cheshmeh Hafez are andesite and andesitic-basalt, while in Challu are trachy-andesite and basaltic trachyandesite, hosted polymetal hydrothermal mineralization in the area. Mineralization in the Cheshmeh Hafez occurred in three main stage includes stage 1) vein and disseminated pyrite and chalcopyrite hosted in quartz with homogenization temperature of 188 to 238°C and salinity of 6 to 14 wt.% NaCl equiv, stage 2) main sulfide mineralization with vein, disseminated and brecciate texture hosted in quartz with homogenization temperature of 243 to 276°C and salinity of 11 to 18 wt.% NaCl equiv and stage 3) replacement mineralization and vein-type (quartz and barren calcite) with homogenization temperature of 148 to 185°C and salinity of 4 to 11 wt.% NaCl equiv. Mineralization in the Challu district with low expanse and simple mineralogy occurred at two stage composed of stage 1) vein and veinlet pre-mineralization stage includes specularite, magnetite, chalcopyrite and pyrite (I) hosted in quartz with homogenization temperature of 332 to 356°C and salinity of 7 to 11 wt.% NaCl equiv and stage 2) brecciate and stock-work post-mineralization stage includes pyrite (II), bornite, tetrahedrite, vein-type calcite and chlorite with homogenization temperature of 290 to 322°C and salinity of 3 to 7 wt.% NaCl equiv. According to the recent studies, it can be inferred that with distance increasing from Challu district to Chesmeh Hafez mining area, homogenization temperatures (Th), salinity and depth of mineralization decreases gradually and mineralization at Challu and Cheshmeh Hafez districts have characteristics of an individual mineralization system that caused by mixing of hydrothermal fluid with meteoric water.