Structure, Texture, Mineralogy and Genesis of Sulphide Ore Facies In Tappehsorkh Detrital-Carbonate-Hosted Zn-Pb-(Ag) Deposit, South of Esfahan

Tappehsorkh Zn-Pb- (Ag) deposit، hosted by Lower Cretaceous siltstone، tuff and dolomite، is located in the northern part of the Irankuh mountain range، south of Esfahan. Sulphides in this ore have a relatively simple mineralogy including sphalerite، galena، tetrahedrite، pyrite and to a lesser extent، chalcopyrite، marcasite and bornite. Gangue minerals are predominantly dolomite، quartz and barite. Based on zoning in the sulphide mineralization، texture and structure and location of ore facies relative to syn-sedimentary normal faults، theses ore facies are classified as vein-veinlet، laminated and massive. Dolomitic-silicic alteration is among the major processes concomitant with sulphide mineralization. The greatest degrees of alteration and related ore mineralization occur at the vicinity of the normal faults and decrease away from it. Geochemical studies indicate that the ore-bearing fluids were of oxidized composition، which were reduced once reaching favorable host rocks and consequently deposited sulphide minerals. Minor and trace element studies in the various sulfide ore facies demonstrate that the ore-bearing fluid in all the ore facies has a similar composition. Textures such as framboidal pyrite، contemporaneous folding of organic matter along with sulphide lamination in the laminated ore facies، and diagenetic structures such as load casts in the host siltstone indicate that sulphide mineralization has occurred in the sedimentary-diagenetic stage. However، sulphide mineralization in the regional dolomite is considered to have occurred in a shallow diagenetic environment because of replacement of regional dolomite by hydrothermal dolomite. Based on features of ore mineralization such as the extensional tectonic setting، siltstone and carbonate host rocks، and occurrence of various sulphide facies such as vein-veinlet، laminated and massive، the Tappehsorkh deposit is very similar to Sedex-type deposits.