Chah-Mesi polymetallic epithermal vein deposit, NE Shahr-e-Babak: The source of ore fluids and the relation between fracture patterns and the emplacement of mineralized veins

In this study, geology, source of ore fluids, and the mode of emplacement of mineralized quartz veins at Chah-Mesi polymetallic deposit, NE Shahr-e-Babak, have been investigated by field and laboratories studies including EMPA and stable oxygen isotopic. The results of these investigations showed that Chah-Mesi vein deposit evolved as an epithermal system within the Eocene host volcano-sedimentary rocks with the shear fractures being the major structural control of mineralization. The mineralization at Chah-Mesi comprises pyrite, chalcopyrite, sphalerite, galena, and, in much smaller amounts, sulfosalt minerals. These ore minerals contain the base metals, Cu, Pb, Zn, and to lesser amounts, precious metals, like Au and Ag, at Chah-Mesi; the EMPA investigations showed the sulfosalt minerals are the main carriers of Au and Ag at Chah-Mesi deposit. The stable O isotopic composition of quartz associated with the mineralization indicates that both magmatic and meteoric fluids contributed to the ore fluids, and thus were responsible for the formation of ore-bearing quartz veins, at Chah-Mesi. The general attitude of veins at Chah-Mesi is N-S, NE-SW, and NW-SE which correlate well with the trends of fractures in the area. The structural analysis of mineralized veins at Chah-Mesi indicate the significant role of a shear system, i.e. shear fractures (types R, R', T), in the emplacement of mineralized veins. The N-S trending veins occurred in the tension fractures. These veins emplaced as tension-gash veins in mode-I shear fractures. In contrast, the NE-SW- and NW-SE-trending veins include the pennant veins in the region which have been emplaced in Riedel and anti-Riedel mode-II shear fractures.