Economic Geology
Hossein Ali Tajeddin; Ebrahim Rastad; Abdolmajid Yaghoubpour; Mohammad Mohajjel
Abstract
The Mirgenaghshineh gold deposit is located 43 km northwest of Saqqez in the northwestern part of the Sanandaj–Sirjan zone. The rocks in the deposit area predominantly consist of Precambrian volcanosedimentary sequences of schist, metasandstone, slate and metaandesite which are intruded by granitoid ...
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The Mirgenaghshineh gold deposit is located 43 km northwest of Saqqez in the northwestern part of the Sanandaj–Sirjan zone. The rocks in the deposit area predominantly consist of Precambrian volcanosedimentary sequences of schist, metasandstone, slate and metaandesite which are intruded by granitoid bodies. The Gold mineralization in the Mirgenaghshineh deposit is hosted mostly in Northwest-Southeast shear zone. The high grade gold ores occure in highly deformed mylonitic and ultramylonitic rocks that are associated with quartz, sericite-muscovite and sulfide alteration minerals. Ore mineral assemblages of the deposit are simple and consist of pyrite, arsenopyrite, sphalerite, chalcopyrite, galena and electrum. The electrum grains range in size from less than 5 µm to 140 µm and occur in quartz and also in the form of inclusion and veinlet in pyrites. According of geochemical data, gold-bearing ores carry up to 64.3 ppm Au, 9.9 ppm Ag, 2096 ppm As, 506 ppm Pb, 354 ppm Zn, and 244 ppm Cu. Fluid inclusion studies on gold-bearing quartz indicate homogenization temperatures between 158 and 215°C and salinity between 3.3 to 14.5 wt% NaCl eq. for the ore fluid. The study indicates that main characteristics of the geology and mineralization of the Mirgenaghshineh are similar to those of the epizonal orogenic gold deposits.
Tectonics
Masoud Biralvand; Mohammad Mohajjel; Mohammad Reza Ghassemi
Abstract
In Takht-e-Suleiman region, travertine deposits are widespread in the footwall of the Chahartagh fault. Three factors played roles in forming travertine in this area: magmatism and high geothermal gradient, existence of carbonates between thermal source at depth and travertine springs on the ground, ...
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In Takht-e-Suleiman region, travertine deposits are widespread in the footwall of the Chahartagh fault. Three factors played roles in forming travertine in this area: magmatism and high geothermal gradient, existence of carbonates between thermal source at depth and travertine springs on the ground, so that the hydrothermal solution can provide the necessary ingredients for the formation of travertine. The third factor is extensional faults and fractures to conduct water containing dissolved calcium carbonate up to the surface. Absence of travertine on the top of the metamorphic basement, even in the footwall of the Chahartagh fault, highlights the essential role of second factor in formation of the travertine. Sources of travertines in this area are carbonates from the Jangoutaran and Qom formations, with the more emphasis on the latter based on our data. Right-lateral kinematics on the Chahartagh fault led to an NNW extension in the southeastern termination of the fault, paving the way for emergence of the travertine. However, there is evidence for a regional NE extension responsible for NW-SE normal faults in the area. Such an extension may be associated with slab rollback and slab breakoff of the Neotethian oceanic lithosphere, lithosphere delamination deformation or basement-involved thick-skinned deformation in this area.
Economic Geology
H Tajeddin; Ebrahim Rastad; Abdolmajid Yaghoubpour; Mohammad Mohajjel; Richard Goldfarb
Abstract
Barika gold (and silver)-rich volcanogenic massive sulfide deposit is located 18 km east of Sardasht city in the northwestern of Sanandaj–Sirjan metamorphic Zone. The rocks in the vicinity of the Barika deposit predominantly consist of Cretaceous volcanosedimentary sequences of phyllite, slate, ...
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Barika gold (and silver)-rich volcanogenic massive sulfide deposit is located 18 km east of Sardasht city in the northwestern of Sanandaj–Sirjan metamorphic Zone. The rocks in the vicinity of the Barika deposit predominantly consist of Cretaceous volcanosedimentary sequences of phyllite, slate, andesite and tuffite, metamorphosed under greenschist facies grade. Barika deposit is composed of stratiform ore and stringer zone that both are hosted in an altered and sheared metaandesite unit. Fluid inclusion studies indicated that quartz (stringer zone) and barite (stratiform ore) samples homogenized between 132° and 283°C. Salinities of the fluids inclusions show a range from 1.4 to 9.6% wt NaCl equivalent that are close to that of normal seawater. The study indicates the colling occurred in the initial ore fluids, as a result of mixing with sea water, is an important process in the formation of Barika deposit. The δ34S values of sulfide minerals (pyrite, sphalerite and galena) from stockwork mineralization in the Barika deposit range from -0.8 to +5.6 per mil and fall within the range of values observed for volcanogenic massive sulfide deposits. The narrow range of measured δ34S values from the sulfide minerals suggests that similar to almost of Kuroko VMS deposits, the ore-forming sulfur derived from the leaching of igneous sulfur from the underlying andesitic rocks. Calculated sulfur isotope temperatures for twelve coexisting galena-sphalerite and galena-pyrite pairs range from 146-293 ْ C that is consistent with temperatures estimated from fluid inclusion studies.
H Haji Hosseinlou; A Solgi; M Mohajjel; M Pourkermani
Abstract
The Khoy shear zone (KSZ) is exposed 130 Km north of Uremia and 650 km west of Tehran. Structural analysis in the Khoy Shear Zone (KSZ) indicated that they consist of NW-SE oriented various metamorphic rocks. They contain NW-SE trending moderate to steeply dipping mylonitic foliation to the NE. Stretching ...
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The Khoy shear zone (KSZ) is exposed 130 Km north of Uremia and 650 km west of Tehran. Structural analysis in the Khoy Shear Zone (KSZ) indicated that they consist of NW-SE oriented various metamorphic rocks. They contain NW-SE trending moderate to steeply dipping mylonitic foliation to the NE. Stretching lineation plunge shallowly to moderately towards NE. Thrust faults are oriented the same as mylonitic foliation. Ductile fabrics are superimposed by brittle structures. Orientation of the structures indicates that the main stress trend is NE-SW. Four deformation stages (D1-D4) identified in KSZ. The first two stages are ductile that superimposed by the two other ductile-brittle stages. Shear sense indicators such as S/C fabrics, shear bands, shear folds, book-shelf structures, fishes and mantled porphyroclasts indicate that the KSZ deformed via dextral transpression tectonic regime. The Khoy area contains both NW-SE striking dextral strike-slip and SW verging NE dipping ductile reverse shear fabrics. Ductile shear fabrics are overprinted by subsequent younger both thrust and strike-slip fault systems. Abundant syn-tectonic granitoids were intruded in the Khoy area during convergent. The shear deformation fabrics are well identified in both deformed intrusive and metamorphic-ophiolite complex. The geometry and kinematics of shear fabrics indicate a deformation partitioning in both ductile and brittle conditions during a progressive transpression tectonic regime. The KSZ deformed during an oblique convergence scenario between the Arabian and West Alborz- Azerbayjan blocks in NW Iran.
K Orang; M Mohajjel; G.R Tajbakhsh
Abstract
The kinematic analysis of the Koushk-e-Nosrat Fault (striking WNW-ESE) at north Saveh city indicates that since a time after early Miocene it has been inverted from dextral strike-slip (and reverse-dextral-oblique slip) to reverse-sinistral (and sinistral strike-slip( displacement. The Kinematic evidences ...
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The kinematic analysis of the Koushk-e-Nosrat Fault (striking WNW-ESE) at north Saveh city indicates that since a time after early Miocene it has been inverted from dextral strike-slip (and reverse-dextral-oblique slip) to reverse-sinistral (and sinistral strike-slip( displacement. The Kinematic evidences of right-lateral strike-slip displacement are: 1) Generation of the Koushk-e-Nosrat pull-apart basin along the bended segment of the fault in north Saveh city where a thin sequence of the Qom Formation (late- Oligocene to early Miocene) has been deposited in this narrow basin. 2) Shear bands and other kinematic indicators of right-lateral strike-slip and reverse-dextral-oblique slip displacements exist in the fault zone. 3) Synthetic right-lateral and antithetic left-lateral strike-slip faults are observed in wall damage zones around the main fault zone. The evidences of left-lateral strike-slip displacements after slip sense inversion are: sinistral- reverse faults, pure reverse faults, sinistral strike-slip faults and folds are generated in the Koushk-e-Nosrat Fault zone. The younger left-lateral reverse kinematic of the Koushk-e-Nosrat Fault is another significant evidence for the main role of the left-lateral reverse faults in deformation of the Qom-Saveh district in NW part of the Central Iran Block that has been tested before by structural and morphological kinematics of other major faults in the area like the Ipak (south Boin-zahrah) and Alborz (north Qom) Faults and seismological evidence of earthquake in the Boin-zahra areas.
M Mohajjel; S Niroomand
Abstract
Structural analysis of folds in the Kharapeh area clears tow co-axial folding stages in the Cretaceous metamorphic rocks, in this part of the Sanandaj-Sirjan zone. First stage folds are tight to isoclinal recumbent folds that were co-axially refolded by second stage upright open to close folds. Normal ...
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Structural analysis of folds in the Kharapeh area clears tow co-axial folding stages in the Cretaceous metamorphic rocks, in this part of the Sanandaj-Sirjan zone. First stage folds are tight to isoclinal recumbent folds that were co-axially refolded by second stage upright open to close folds. Normal faults, mafic dykes and abundant quartz veins oriented sub-parallel to the axial surface of the kharapeh antiform implying that the extensions were synchronous with folding perpendicular to the fold axis, during second stage folding process in the area. This is well concordant with tangential longitudinal strain folding mechanism for the second stage folding. By this folding mechanism, tension was produced at the outer arc of the Kharapeh anticline and quarts veins were generated by compression in the core area and filled in the tension fractures that were mostly produced in the fold hinge area during the folding process. In fractures where it was accompanied with shearing, some clasts from wall rocks were engaged in the fault zone breccias. The field observations reveal that the fractures were produced synchronous with the second folding stage in the Kharapeh anticline and filled by the gold bearing quartz veins.
S Khodaparast; M Mohajjel; S Haj-Amini
Abstract
The marine facies of the Qom Formation was deposited between two detritus continental facies of the Lower and Upper Red Formations. The type section of the Qom Formation was observed in Qom city, but its most thickness has been reported from the Dokhan area in west Saveh. Stratigraphic studies revealed ...
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The marine facies of the Qom Formation was deposited between two detritus continental facies of the Lower and Upper Red Formations. The type section of the Qom Formation was observed in Qom city, but its most thickness has been reported from the Dokhan area in west Saveh. Stratigraphic studies revealed that its thickness has sudden changes in the Dokhan area through short distances. Geometry of the structures was strongly influenced by change of thickness in different rocks of the Qom Formation. The main question that has been answered in this study is what caused change of thickness in short distances. The geometry and kinematic observations of the major faults in the Dokhan area showed that their displacement style during sedimentation influenced on change of the thickness and folding style during deformation of the Qom Formation. This study showed that the Dokhan area is located in the extension termination of the NW-SE trending major strike-slip faults such as the Tafresh, Talkhab and Indus faults.
L Izadi kian; M Mohajjel; S.A Alavi
Abstract
Hamedan area is in the NW of the Sanandaj-Sirjan Zone. Different types of plutonic rocks are outcropped in this area which in turn, surrounded by the various metamorphic rocks (regional and contact metamorphism). Four ductile deformation stages were recognized. Each of them is accompanied with formation ...
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Hamedan area is in the NW of the Sanandaj-Sirjan Zone. Different types of plutonic rocks are outcropped in this area which in turn, surrounded by the various metamorphic rocks (regional and contact metamorphism). Four ductile deformation stages were recognized. Each of them is accompanied with formation of fold, foliation and lineation. The first generation foliation (S1) and folds (F1) formed at the first stage of deformation (D1). The second deformation defined by refolding of the first axial surface and forming of the second foliation (S2) and folds (F2). This stage is the strongest deformation and formed main foliation in this area. Axis of these folds changes from horizontal to vertical. The direction of this fold axis follows the Alvand pluton form. The second foliation shows wide dispersal in orientation and their trends follows the Alvand pluton form. The third deformation (D3) defined by close to open, mostly upright with curved hinges folds (F3) and the axial-plane foliation (S3). This foliation (S3) is predominant in areas east of the Alvand pluton and is crenulation cleavage to fracture foliation. The most axis of F3 show N165 plunging. Because of the interference pattern between the first, second and third folding at the regional and contact metamorphic rocks, these stages of deformation are coaxial deformation. D4 is characterized by a crenulation cleavage (S4) and a mineral lineation (L4(. L4 have a NE-SW plunging. This lineation does not exist at the contact metamorphic rocks. The rotation of axis of F2 and the second foliation is obvious around the Alvand pluton. This rotation shows that the final strain field is followed the pluton forms and probably the main granitic Alvand pluton intruded during the second deformation in this area.
E Moosavi; M Mohajjel
Abstract
The North Esfajerd ductile shear zone is exposed in NE Golpaygan in the Sanandaj-Sirjan zone. The shear sense indicators are observed in the both outcrop and microscopic scales in this shear zone. These indicators are representing a NW striking dextral shear. The dynamic analysis and outcrop- scale indicators ...
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The North Esfajerd ductile shear zone is exposed in NE Golpaygan in the Sanandaj-Sirjan zone. The shear sense indicators are observed in the both outcrop and microscopic scales in this shear zone. These indicators are representing a NW striking dextral shear. The dynamic analysis and outcrop- scale indicators of extension direction exhibit a NW extension sub-parallel to the dextral shear and a compression perpendicular to it. The relative simultaneity and parallelism between North Esfajerd ductile shear zone and North Varzaneh thrust shear zone propose the partitioning of strain components in a transpressional deformation. Regarding the geochronologic data and the angular unconformity between the middle Cretaceous and Eocene rock units, the transpressional deformation and its related mylonitization occurred during the Laramide orogeny in late Cretaceous-Paleocene. The gently dipping mylonitic foliations with dextral shear imply an incompatibility between geometry and kinematics in the North Esfajerd ductile shear zone. However, the kinematic and dynamic characteristics of the North Esfajerd ductile shear zone are accommodated with lateral extrusion of material in a dextral domain.
Parallelism between the trends of dominant stretching lineations and the second generation large scale fold axes document that the major mylonitization in the North Esfajerd shear zone occurred during the second generation deformation. These mylonitic fabrics were folded due to the third generation deformation. Two generations of crenulation cleavages, respectively in relation to two refolding events, can be recognized in this shear zone. One of the refolding events with type III interference patterns (coaxial refolding) occurred during the second stage deformation in the late Cretaceous- Paleocene interval, caused the formation of the North Esfajerd shear zone, and can be observed in an outcrop scale. The other has emerged during the third stage of deformation, probably in the post Paleocene-pre Miocene interval, folded the North Esfajerd shear zone and formed the type II (boomerang shape) interference pattern in a map scale.
K. Orang; Mohammad Mohajjel; F. Mousivand; E. Rastad
Abstract
The Chah Gaz Zn-Pb-Cu volcanogenic massive sulfide (VMS) deposit is a polydeformed, polymetamorphosed ore body in southern part of the Sanandaj-Sirjan zone. The ore bodies are comprised predominantly of stratiform, tabular and lenticular massive sulfide lenses and are elongated in 0600-0700 orientation. ...
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The Chah Gaz Zn-Pb-Cu volcanogenic massive sulfide (VMS) deposit is a polydeformed, polymetamorphosed ore body in southern part of the Sanandaj-Sirjan zone. The ore bodies are comprised predominantly of stratiform, tabular and lenticular massive sulfide lenses and are elongated in 0600-0700 orientation. The host rocks and massive sulfides have been complexly deformed during three deformation stages (D1, D2, D3) and two associated episodes of green schist facies metamorphism (M1, M2) that all events occurred after middle Jurassic. The earliest structural elements in the mine area are bedding and continuous foliation (S1) that are preserved in the host rocks; include phyllites, slates and schists. F1 folds have not been identified in the ore bodies, Although they do recognized as shallowly to moderately plunging to NW and isoclinal folds within the Chah Gaz area. Geometry of ore bodies was mainly controlled by D2 structures (include folds and foliations). F2 plunge shallowly to NE or SW. F2 are close to open and their axial planes dip steeply to S and N. Ore bodies are commonly transposed from S0-S1 and show rearrangement parallel to axial planar foliation (AS2) and composite foliation (ST2). ST2 is vertical and strikes NE-SW. Sulfide minerals in the ore bodies have undergone extensive deformation, remobilization and dynamic recrystallisation during D2 tectono-thermal stage. D3 structures are locally controller of ore bodies and include folds and shear zones.
Mohammad Mohajjel; Z. Rahami; F. Shabani
Abstract
Lower-red, Qom and Upper-red Formations with Pliocene conglomerates were all folded in Shurab syncline containing northwest-southeast axial trace in southeast Qom city. In the southeastern part of the northern limb of the Shurab syncline, gypsum and marl elastic units of the Qom Formation have played ...
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Lower-red, Qom and Upper-red Formations with Pliocene conglomerates were all folded in Shurab syncline containing northwest-southeast axial trace in southeast Qom city. In the southeastern part of the northern limb of the Shurab syncline, gypsum and marl elastic units of the Qom Formation have played a detachment surface role against the most competent layers of the Upper-red Formation due to high competency contrast. Rock units of the Qom Formation were thickened and locally folded with about north-northeast orientation in the southeastern part of the northern limb of the Shurab syncline. The thickening and folding in this part of the Shurab syncline is interpreted as the shearing process which has been produced in a shear zone initiated between the detachment surface and the Qom fault segment in the northern part of the Shurab syncline that was activated by right-lateral strike-slip displacement of the Qom fault in post Miocene.
A. H. Sadr; Mohammad Mohajjel; A. Yasaghi
Abstract
The style of deformation changes from the hinterland (Sanandaj-Sirjan zone) to the foreland (Zagros) through the Zagros Orogen containing thick-skinned and thin-skinned deformation respectively. NW-SE trending thrust faults dipping to northeast have carried the older rock sequences to the surface. The ...
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The style of deformation changes from the hinterland (Sanandaj-Sirjan zone) to the foreland (Zagros) through the Zagros Orogen containing thick-skinned and thin-skinned deformation respectively. NW-SE trending thrust faults dipping to northeast have carried the older rock sequences to the surface. The Zagros collision zone could be divided into two distinct parts based on deformation mode that is separated by the Main Zagros Thrust. The southwestern part contains imbricate thrust sheets instead, to the northeastern part large amount of shortening is documented by basement deformation with duplex structures. Abundant crystalline deep origin thrust sheets have transported (2 up to 20 km) the metamorphic rock units upon the Zagros suture zone by gravity or tectonic forces. Despite the collision thrust faults, both NW oriented (Main Recent Fault) and NE oriented (named here Azna Fault) basement wrench faults have also activated and caused different style and amount of deformation in the collision zone.