M Boveiri Konari; E Rastad; M Rastad; A Nakini; M Haghdoost
Abstract
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, ...
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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.
A Nakini; M Mohajjel; A Yarmohammadi
Abstract
Anjireh-Vejin Mines of Tiran are located 60 km west of Isfahan. Exposed rocks in these mines are Early Cretaceous (Early Baremian-Albian) in age. These rock units are exposed in NW-SE trending anticlines plunging shallowly to SE in three Vejin Paein, Vejin Bala and Anjireh-Chekab Mines. Folding in all ...
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Anjireh-Vejin Mines of Tiran are located 60 km west of Isfahan. Exposed rocks in these mines are Early Cretaceous (Early Baremian-Albian) in age. These rock units are exposed in NW-SE trending anticlines plunging shallowly to SE in three Vejin Paein, Vejin Bala and Anjireh-Chekab Mines. Folding in all three mines exhibits same style, indicating that the mines are closely structurally related. At the SW side of all the mines, anticlines formed above the hangingwall of a major reverse fault are breached and expose older Cretaceous units. In the trenches of Anjireh-Chekab mines, which cut the steeply-dipping and overturned limb of the anticlines, older rock units are observed. In the trench cutting the Vejin Bala mine, layers in the SW limb are of steeply-dipping to locally overturned attitudes. Structural evidence from these mines clearly indicated that all the three mines are situated in a unique anticline with overturned SW limb and a folding style that consistently characterize “break-thrust fold” model. This anticline plunges gently by 15º to N150º. In btreak-thrust model, as folding progressively advances, a major reverse fault is being generated along the overturned limb of the anticline, which is well observed along the SW part of the mines in the study area. The mines are separated by E-W trending faults producing the present geometry. In addition to presenting a fold style model, we explored the relation between faults and fractures in all the mines using field observations and satellite images. Fractures are dominantly oriented along NW-SE direction sub-parallel with the strike of the axial plane of the anticlines. Structural analysis revealed three types of ore concentrations: 1) parallel to the original stratigraphic layering, 2) along the reverse fault in the overturned limb of the anticline, and 3) in the fracture systems.
