جستجوی مقالات مرتبط با کلیدواژه "sanandaj- sirjan zone" در نشریات گروه "زمین شناسی"

The Khabr iron ore is located in about 55 km southwest of Baft and 15 km northeast of Khabr in the southeastern part of the Sanandaj-Sirjan zone. This zone hosts a large number of iron deposits of Iran such as Golegohar in Sirjan. The Khabr iron ore is a small and unknown deposit, mainly composed of supergene iron hydroxides outcrops. The Khabr iron ore is a hydrothermal mineralization that has occurred in marble during primary and secondary stages as oxide and sulfide (Dehghani Soltani, 2012). There is rare information about mineralogy, paragenesis and genesis of the study deposit This paper aims to study the mineralogy of hypogene and supergene ores and the chemistry of sulfide minerals.

Following field study and sampling from the rock units, alteration zones, iron ore and sulfide veins, 45 thin sections and 12 polished sections were prepared and studied by transmission and reflective light microscopes at the University of Sistan and Baluchestan and X-ray diffractometry (XRD) at the Yamagata University. The sulfide minerals are analyzed by the Electron Probe Micro Analyze (EPMA) model of JEOL. JXA-8600 with an accelerator voltage of 15kv and current of 2×10-8 A in Yamagata University. 

Geology:

The oldest rocks in the Sanandaj-Sirjan zone are metamorphic rocks of the late Precambrian-Cambrian period (Ghorbani, 2008), In this zone, Paleozoic and Mesozoic rocks such as carbonate, quartzite, and volcanic rocks with layers of shale and sandstone are covered by Hamedan phyllites (Ghorbani, 2008). The Cretaceous rocks in this zone are mainly carbonated rocks and ophiolitic complex. The Tertiary outcrops in the Sanandaj-Sirjan zone are relatively small. Several intrusive bodies in the Sanandaj-Sirjan zone were formed in the Middle and Late Triassic, Late Jurassic, Late Cretaceous and Paleocene periods. They are mainly intermediate to acidic in composition (Ghorbani, 2008). Most pre-Mesozoic rocks in the Sanandaj-Sirjan zone were metamorphosed. The metamorphic complexes in the study area are Golegohar, Rutchun and Khabr (Figure 1B). The Khabr Iron mineralization is located in the Rutchun complex, which is on top of the Golegohar complex (lower Cambrian) and below the Khabr complex (Devonian) (Figure 1B). The host rock units in this area are an alternation of carbonate rocks, phyllite, greenschist, mica schist and quartz-schist ranging in age from Upper Cambrian to Ordovician. The dominant minerals in these rock units are calcite, quartz, biotite and muscovite including sericite, paragonite, chlorite and clay minerals.

 The iron mineralization occurs at the contact of carbonate rocks and phyllite and schists. The mineralization develops in a northeast-southwest orientation as hill-like and isolated outcrops including hypogene oxide and sulfide mineralization and supergene iron oxide mineralization. The hypogene iron mineralization is characterized by magnetite euhedral crystals, formed as replacements in carbonate rocks by hydrothermal solutions. The hypogene sulfide mineralization forms following the oxide mineralization as silica veins, cavities and open space filling. Sulfides are associated with quartz and composed of pyrite, arsenopyrite, chalcopyrite, bornite and covellite. The chemistry of arsenopyrite, pyrite and chalcopyrite contain low volumes of gold, silver, bismuth, Pb, Zn, Te and mercury. Some pyrite grains contain Au (maximum 700 ppm) (Table 2). The iron ore outcrops are mainly supergene-type formed as open space filling in fractures or around gangue grains boundary. The supergene iron mineralization is due to the weathering of hypogene minerals such as magnetite and sulfide minerals. The margin of the outcrops of the sulfide veins are partially altered to iron hydroxides in brown, red and yellow. The supergene ore minerals are mainly goethite, hematite and limonite. Calcite, dolomite, quartz and phyllosilicates are the predominant gangue minerals. There exist many secondary structures in iron ore like grape-like, colloidal, box-like, cavity-like, rhythmic, replacement and vein-like and open space filling all are indication of weathering and supergene processes. Some textures of the host rocks are similar to clastic rocks like the magnetite-rich sandstone. The magnetite texture reveals that, the Khabr hypogene iron mineralization is mainly formed as a replacement in carbonated rocks by hydrothermal solutions. High temperature acidic hydrothermal solutions containing chloride complexes, dissolve the carbonate rocks upon reaction with them (Robb, 2005). By dissolving carbonate rocks and increasing the pH, chloride complexes became unstable and magnetite replaced limestone. The Khabr sulfides mineralization in the quartz veins is more characteristic of hydrothermal solutions. The hydrothermal solutions containing metal-sulfide complexes had migrated along faults and permeable zones and then with a decrease in the temperature and pressure, the sulfides had been formed. The fluids responsible for the Khabr sulfide stage have the same salinity and temperature as of the those of epithermal deposits (Dehghani Soltani, 2012).The formation mechanism of supergene mineralization is well-known (Guibert and Park, 1986). The Khabr supergene iron ores are the result of magnetite and sulfide oxidation to goethite, hematite and limonite. The magnetites replaced in limestone and marble and magnetites in clastic sandstone have been weathered and altered by oxygen- and carbon dioxide-rich surface waters. The mineralization zone is severely faulted, crushed and permeable. As a result, the circulation of the oxygen-rich waters toward depths or decomposition of magnetite and sulfides had been possible.

The Khabr Fe mineralization can be divided into hypogene and supergene stages. The hypogene stage can be divided into sub-stages of oxide and sulfide mineralization. The hypogene oxide stage is characterized by magnetite, formed as a replacement in limestone by hydrothermal solution or as clastic grains in sandstone. The remarkable features of the hypogene sulfide stage are the presence of arsenopyrite, pyrite and chalcopyrite in quartz veinlets precipitated from hydrothermal solutions like those of epithermal type. The supergene mineralization is characterized by iron oxides and hydroxides as hematite, goethite and limonite precipitated from surface waters.

The granitic gneisses of Abadchi village is located in the north of Zayandeh-Rud dam, and the area is a part of Sanandaj-Sirjan Zone. The mineralogical composition of these rocks are composed of quartz, plagioclase, K-feldspar, biotite, amphibole, muscovite, zircon, titanite and allanite. Quartz crystals, as the most abundant mineral constituents of these rocks, display the different conditions of deformation dynamic on the studied rocks according to their texture. Moreover, quartz crystals show evidences of bulging recrystallization (BLG), sub grain rotation (SGR), and grain boundary migration (GBM). Deformation of quartz crystals depends on the temperature and strain-rate and can be determine using T/strain- rate diagram. Therefore, the fractal dimension at quartz grain boundary sutures is between 1.23 and 1.11 and temperatures between 250-400 °C and 500 -750 °C in the granitic gneisses. Using the fractal dimension and calculation of temperature, the strain rates are measured 10-11.6 to 10-6.6for the four domain of granitic gneiss sample. The results obtained from the diagram are consistent with the deformation evidence of quartz crystals (GBM, SGR, BLG).

The South-Gharezagh intrusive exposed in northwest of the Sorsat metamorphic complex, which is structurally a part of the Sanandaj-Sirjan zone. Intrusive of South-Gharezagh is located in the shear zone and are mylonitized. Morphologically, the crystallization of zircon in the intrusive and mylonitic mass of South-Gharezagh includes {110} prisms and {211} pyramids, which indicates their crystallization from S-type magmas. The crystallization temperature is calculated to be 698 to 770 ◦C, based on the morphology of zircon, in the massive and mylonitic parts of the South-Gharezagh massif, zircon saturation thermometry and geochemistry of the whole rock. In addition, the thermobarometric chemistry of biotite mineral has been calculated at a temperature of 677 ◦C and a pressure of 0.8 kbar. The petrofabric evidence shows that chemical and petrofabric changes have been gradually occurred along with the deformation progress in mylonites. As a result of petrofabric, the recrystallized quartz grains and the migration of the grain boundary in the recrystallization is clear, which indicates a change in the facies of the green schist metamorphism.

The late Triassic metabasites in the southeast of Borujerd area in the middle part of Sanandaj Sirjan zone (SaSZ) are associated with marble and locally intersected by mafic dykes. Metabasites rocks are metamorphosed in the lower green schist facies and are mainly composed of plagioclase and amphibole. However, they locally preserve ophitic and porphyritic igneous textures. The electronmicroprope analysis showed that feldspars are albite, oligoclase and anorthoclase. Also, according to this analysis, type of amphiboles is calcic and includes actinolite, actinolite-hornblend, magnesiohornblend and tschermakit-hornblend to tschermakit. According to geochemical studies, these rocks have alkaline magmas characteristics. The chondrite normalized REE patterns show enrichment in LREE and the Primitive-Mantle normalized multi-element patterns show uniformly enriched LREE, Th, Nb, Ta. These characteristics are similar to those of basalts derived from OIB-like mantle sources. Trace-element ratios, including Ce/Nb (1.22– 2.20), Hf/Nb (0.08–0.2), Zr/Nb (3.63–6) and high TiO2/Yb and Nb/Yb ratios, indicate that these magmas were derived from a deep OIB reservoir, i.e. an enriched asthenospheric mantle source. These rocks underwent slight crustal contamination. These geochemical characteristics of these late Triassic metabasites suggests that they formed in an intra-continental rifting regime.

In the northwestern part of the Sanandaj-Sirjan zone, mafic intrusive bodies are aligned with the trend of the Zagros orogenic belt. In this part of the Iranian lithosphere, magmatic activity occurred during three main periods: Cretaceous, Eocene, and Miocene-Quaternary. In the first of two stages, the magmatic activity was associated with subduction-related magmatism at the active continental margin, whereas the last phase was characterized by calc-alkaline magmatism related to post-collision regime. The intrusive mafic bodies of Qobadlo, Chupankareh, and Qaraqoshun at the southern margin of Lake Urmia in the northern part of the Sanandaj-Sirjan zone intruded within the complex of Cretaceous shale, shale-sandstone, and siltstone. U-Pb dating on zircon performed on these bodies indicates an age of 99 Ma. The SiO2 content of these bodies ranges from 46.17 to 53.35%, Al2O3 13.1 to 18.49 % Fe2O3 3.11 to 5.8%, and their TiO2 content ranges from 1.9 to 4.0%. Positive anomalies of large ion lithophile elements and LREE compared with negative anomalies of elements such as Nb, P, Zr, and Ta (HFSE), the La/Nb, Ba/Nb ratios, and the REE pattern show a good correlation with the magmatic rocks of subduction zones.

Intrusive rocks are exposed in southwest of Naqdeh in the Sanandaj-Sirjan zone, northwest Iran. There are mafic-intermediate appinitic rocks with calc-alkaline affinity. The accompanying granite is strongly evolved with the affinity of calc-alkaline and rich in potassium. The geochemical analysis of appinite and granitic rocks display LREE enrichment relative to HREE, enrichment of LILE elements, and negative Th and Nb anomalies. According to discrimination diagrams, appinite and granite rocks formed in the continental arc tectonic setting. The appinitic rocks have a lithospheric mantle with subducting slab fluids source. The granitic rocks have an asthenospheric-lithospheric mantle with metagreywaky continental crust contamination. We suggest that appinitic magma formed by roll-back of subducted Neo-Tethys oceanic lithosphere and granitic magma formed by breck-off the subducted Neo-Tethyan oceanic slab. The asthenospheric upwelling would also have provided enough heat for the partial melting of continental crust. It is possible that magma formed at a great depth and underwent a long period of fractional crystallization. Finally, evolved granitic rocks have been placed at a shallow depth of the crust.

Metamorphic rocks in the Faryab complex are part of the Bajgan metamorphic complex with Upper Cretaceous age that crops out in the southeast of Sanandaj-Sirjan zone, south Iran. The metamorphic rocks of Faryab Complex have been metamorphosed in greenschist and amphibolite facies include garnet mica schist, epidote schist, epidote amphibole schist, amphibole schist, epidote amphibolite, amphibolite and garnet amphibolite. Minerals composing amphibolites are garnet, amphibole, epidote, plagioclase, quartz, chlorite and sphene as well as titanite and magnetite as secondary minerals. The composition of amphiboles in amphibolite and epidote amphibolite are made of calcic types and their chemistry varies from magnesio-hornblende through ferro-tschermakite-hornblende, ferro paragasite-hornblende, ferro edenite-hornblende to ferroedenite. The composition of plagioclas ranges from albite to oligoclase. The protolith of most amphibolites and epidote amphibolites in the Faryab complex are defined by the occurrence of key minerals in metabasites and are considered as basalt and gabbro. Several thermobarometeric calculation methods indicate that the highest temperature and pressure for the amphibolites, which were appeared adjacent to peridotites and located in the northern part of the complex, are about 700 °C and 9.7 kbar. By moving away from the peridotites into the lower structural units in the southern part of the Faryab complex, the temperature and pressure range in the amphibolite and epidote amphibolite and decrease to 510°C and 4.34 kbar on average, which is beginning of amphibolite and middle amphibolite facies. Investigation of the P-T pathes in conjunction with close associations of isograde lines show that geothermal gradients were high even at the beginning of metamorphism. Mineral chemistry and thermobarometric calculations along with consideration of the structural position of the Faryab complex indicate that the tectonic position of the Faryab complex in the Sanandaj-Sirjan zone may remined us an accretion-subduction complex. This complex was constructed in the north-dipping Neo-Tethyan subduction zone during the Late Cretaceous time, which caused the higher degree metamorphic rocks were thrusted onto the shallower ones.

Garnet amphibolite and garnet micaschists of the Faryab complex, located in the southeast of the Sanandaj-Sirjan zone, are exposed immediately under the peridotites and sometimes a few meters away from the peridotites of this region with fault boundaries. Some garnet amphibolites mainly include poikiloblasts of garnet and amphibole, plagioclase, quartz, secondary minerals of epidote, biotite, chlorite, as well as oxide minerals of, magnetite, ilmenite, titanite and apatite mineral. Garnet micaschists include the main minerals garnet, amphibole, muscovite, epidote, plagioclase, quartz, and secondary minerals biotite, chlorite, rutile, apatite, titanite, and ilmenite. Considering the chemistry of garnet poikiloblasts and the chemistry of amphiboles, temperatures of 505 to 708°C and average pressures of 6.7 to 8.6 kbar (upper amphibolite facies) for garnet amphibolites and temperatures 450 to 650°C and average pressures of 6.7 to 7.2 kbar (lower amphibolite facies) have been determined for garnet micaschists. Accordingly, garnet amphibolites show the highest metamorphic degree, while garnet micaschists show a lower metamorphic degree. Such a situation indicates a type of geothermal gradient. Geochemically, garnet amphibolites can be classified in two groups. Group I, which together with garnet micaschists have the geochemical characteristics of sedimentary rocks, while garnet amphibolites of group II show the typical characteristics of basalts. The Faryab metamorphic complex next to the ophiolitic remnants of the region may indicate the evolution of this ophiolitic complex in a Neotethys accretion-subduction position during the Upper Cretaceous.

The Garmkhani-Meyham region is located in SE-Qorveh city, in the northwestern part of the Sanandaj-Sirjan zone. This area includes a variety of regional and contact metamorphic rocks. Microprobe data of mineral chemistry show that amphiboles, magnesium-hornblende type; plagioclases, andesine to albite type; biotite crystals, siderophyllite type; white mica, muscovite type and epidotes, clino-zoisite type are in composition.  Based on the mineral chemistry of amphibole, the magmatic series of its constituent magma is the subalkaline and its tectonic environment is supra-subduction. Geothermometric estimates on the amphibole and plagioclase minerals in amphibole- schists, a temperature ranges from 464 to 570 °C and pressure between 3 to 5.6 kbar illustrate passing from greenschist facies to amphibolite facies.

The Balestan iron deposit is located about 55 km southeast of Urmia city. The main host rock is the quartz sericite schist unit of the Early Precambrian age. Major mineralization occurred along the schistocytes of the host rock. However, open space filling structure is also abundantly observed in the fault zones. Based on field evidence and microscopic studies, the dominant iron mineralization is in the form of magnetite, which is observed along with pyrite and chalcopyrite. Geochemical investigations revealed that the distribution patterns of trace elements and major oxides are very similar to other hydrothermal iron deposits. The microthermometric studies of fluid inclusions shows an average homogenization temperature and salinity of about 276°C and 7.3 wt% NaCl equivalent, respectively.The variation trends in salinity and Th of fluid inclusions can be explained by a cooling and pressurization of ore-bearing fluids. Also, these data show that the Balestan iron ore deposit is located within the field of mesothermal ore deposits.

Ruchun-Mazar region is located in southern Sanandaj-Sirjan Zone, southwest of Baft city in Kerman province, Iran. Seh Chah, Chah Sorbi, Chah Nar, Zardbazi Dar, and Chah Sorbi Arjmand Pb-Zn deposits located in this region were investigated. The most outcrops of the geological units in the area include the Paleozoic metamorphic complexes of Gol Ghohar (amphibolite, gneiss and micaschist), Ruchun (schist, marble, calcschist, black chert, slate and phyllite), and Khabar (marble, calcschist). Microdioritic, monzodioritic and diabasic dykes have intruded into the metamorphic units. Dolomitic and calcitic marble of Ruchun complex is the host rock for Pb-Zn mineralization. Primary mineralization in Seh Chah, Chah Sorbi, and Chah Nar deposits includes galena, sphalerite, and pyrite ± chalcopyrite along with quartz, calcite, and dolomite ± barite. Vein-veinlet, open space filling, brecciated ± disseminated ± laminate structures and textures can be seen in these deposits. The most important alterations in these deposits are silicification and carbonitization (calcitic and dolomitic alterations). Primary sulfide ore in Zardbazi Dar and Chah Sorbi Arjmand deposits has been weathered and mining has been carried out on nonsulfide ore (supergene ore). The nonsulfide ore formed at the expense of sulfides, and mainly consists of smithsonite, hydrozincite, hemimorphite, and cerussite. It seems that these deposits belong to the direct replacement and, to a lesser extent, wall rock replacement nonsulfide zinc deposits. Based on the geological, mineralogical and alteration evidence, the primary mineralization in the region can be divided into two groups of SEDEX type (Chah Sorbi deposit) and vein type (Chah Nar and Seh Chah deposits). It was concluded that under supergene conditions in some deposits, nonsulfide ore was also formed. Moreover, the deposits of this region can be categorized into primary sulfide (hydrothermal) and nonsulfide (supergene).

The Zaghdareh area in the Esfandagheh-Faryab ophiolitic complex, southern Sanandaj-Sirjan belt, embraces extensive outcrops of mafic-intermediate lava flows and a felsic intrusive body. The volcanic rocks are calc-alkaline to tholeiitic, metaluminous, and distinguished by depletions in light rare earth elements and relatively flat patterns for heavy rare earth elements in chondrite-normalized diagram; the (La/Yb)N ratio is lower than unity for most samples. The chemical attributes for the Zaghdareh volcanic rocks are comparable to those developed in suprasubduction zones. The Zaghdareh intrusive body is distinguished by abundant plagioclase and quartz, and subordinate hornblende, phenocrysts in quartz-feldspar rich matrix. Representative samples from the intrusion plot in the trondhjemite-tonalite fields in the normative An-Ab-Or diagram. The intrusion is calc-alkaline to tholeiitic, peraluminous, and marked by enrichments in Na2O and CaO and depletions in K2O, Rb, and most other LILEs, as well as low K2O/ Na2O ratios, very low Rb/Sr ratio, and distinct depletions in light rare earth elements, which are typical of the oceanic plagiogranites. Results from this study and a comparison with other ophiolitic suites in Iran suggest that the occurrence of plagiogranites is a recurring feature associated with the development and evolution of ophiolitic suites in suprasubduction zones.

The magmatic-metamorphic Tutak Complex, as a part of the Bavanat belt, is located in the high pressure-low temperature metamorphic belt of the Sanandaj-Sirjan Zone. The complex contains schists, marbles, granite gneiss, meta-granitoid, meta-aplite granite, amphibolites, and meta-dolerite with different ages and degrees of metamorphism. Based on field evidence, the rocks are not uniformly distributed throughout the complex, thus, the Tutek Complex can be divided into central and marginal sub-zones. In the central sub-zone, most of the metasediments are calcschist, micaschist, garnet-muscovite-schist, and quartz-feldspathic-schist, and types of metabasites include amphibolite and garnet-amphibolite. In the marginal sub-zone, most metasediments are biotite-epidote-schist and meta-basites including of schist-amphibolite and amphibolite. Combining field evidence and microstructures in the metasediments and the metabasites from both sub-zones suggests that the rocks have mainly undergone metamorphism and deformation under the amphibolite to green-schist facies conditions in the central sub-zone and green-schist facies conditions in the marginal sub-zone.

The Granitoid plutons in the Sanandaj-Sirjan zone host numerous pegmatitic dikes. This study is focused on mineral chemistry of zircons in the pegmatite dikes in the Malayer, Boroujerd and Shazand district to evaluate zircon crystallization temperature, oxygen fugacity and Ce4+/Ce3+ ratio and also zircon/rock partition coefficients of REEs and U, Th, Ta, Nb and Y. Trace element discrimination digrams such as Th versus Y and Yb/Sm versus Y and Nb, indicated studied zircons were located in the syenite pegmatite field. Zircon/rock partition coefficients indicate that zircon granis are enriched in the HREE than LREE. Zircon chemistry show that zircon in the Shazand and Malayer pegmatite dikes have more Hf and less REE distribution than zircons in the Boroujerd pegmatite dikes. Consequently, it indicates the role of latter hydrothermal process in the formation of Boroujerd zircons. Crystallization temperature, oxygen fugacity and Ce4+/Ce3+ ratios decrease from Malayer to Shazand and finally Boroujerd pegmatite dikes. Reduced condition of magmatism, Th/U contents below 1 and Y/Ho content higher than 20 indicate that these pegmatities are barren.

Bajgan metamorphic complex is located at the southeastern termination of the Sanandaj-Sirjan zone in north of Makran. The metamorphic rocks, having igneous and sedimentary origins, are in tectonic contact with ophiolite assemblages and colored mélange. The rocks can be divided in four units based on lithological characteristics. These units are covered by Pliocene and Quaternary sediments. Structural study indicates the presence of three syn-metamorphic stages of deformation in ductile condition. The main structures elements are different generation of folds, foliation and lineation, each of them has been generated during a specific stage and superimposed on each other. The structural elements in this complex have emerged during subduction, ophiolite obduction and exhumation, respectively.