Investigation on the genesis of metals and ore bearing fluids in Irankuh Pb-Zn deposit

The Cretaceous limestone and Jurassic shale are the main country rocks of Zn-Pb Irankuh mine. Jurassic units in this region are composed of dark and olive shale and sandstone that are unconformably covered by Cretaceous carbonate rocks. Mineralization has mainly occurred in carbonate rocks, but because of the high concentration of heavy metals in shales, they are selected for the investigation of their role as a probable source of metals in mineralization. For this purpose, field, geochemical and mineralogical studies were carried on the samples selected from shale unit. Also, due to the importance of the fluid inclusions in study of the origin of deposits, some samples were selected and prepared for this purpose.Atomic absorption geochemical analysis results for Zn, Pb, Ag, Ni elements has revealed a wide range of changes in their concentration in faulted rocks, unaffected rocks from the ore bearing fluids and mineralized regions. Microthermometric studies of the samples show a homogenization temperature range of 100-160C and a salinity range of 17-22 eq. wt% NaCl which is well confined to that range of Mississippi valley-type Pb-Zn ore deposits. Based on the results of this research, it seems that ore bearing fluids in this area have many similarities with the basinal brines and it seems that ore elements were leached from the shale units and upwelled along the fault and fractures which has at last mixed with ground waters and mineralization has occurred in the carbonate rocks.