Sanandaj-Sirjan Metamorphic Belt Research Articles

Oligocene–late Miocene basin evolution in the Yengejeh syncline in the Central Iranian Basin in response to the Arabia–Eurasia orogeny

Abstract The Central Iranian Basin has developed during a multi-episodic collision between the Arabian and Eurasian continents since the late Eocene–early Oligocene, following the subduction of the Neo-Tethys Ocean. Herein, we present detailed sedimentological and provenance data of the Oligocene–upper Miocene synorogenic strata, including the unconformity-bounded Lower Red, Qom, and Upper Red formations, in the Yengejeh syncline in the NW termination of Central Iran, to analyze stratigraphy, depositional environments, and provenance. Our results indicate that the sedimentary system has evolved in five stages coeval with regional deformational and volcanic events: a) deposition of the Lower Red Formation in an alluvial fan containing the first appearance of Sanandaj–Sirjan metamorphic clasts sourced from the proximal southwestern Takab Complex, exhumed by the onset of Arabian–Eurasian soft collision in late Eocene–early Oligocene; b) Burdigalian transgression of the Qom Sea and shallow-water carbonate sedimentation influenced by continuous pyroclastic inputs and lava flows from an active volcanic center; c) deposition of the M1 unit of the Upper Red Formation in a continental sabkha in arid climate conditions during Burdigalian–Langhian and the first appearance of internal clasts derived from the folded Qom Formation layers due to the Arabian–Eurasian hard collision; d) fluvial deposition of the M2 unit during the Langhian–Tortonian with sediments derived from the Qom Formation and Takab Complex; and e) deposition of the uppermost siliciclastics of the M2 unit at the edge of an alluvial fan during the late Miocene, after a period of pyroclastic fallout in the Tortonian. In general, the source-to-sink relationship is controlled by the development of tectono-topographic relief in the crystalline core of the Zagros Mountains that configured the source areas in the Sanandaj–Sirjan metamorphic belt supplying the NW termination of Central Iran through a well-developed drainage system towards the Caspian Sea. Coeval with the deformational events, magmatic phases supplied a large volume of volcaniclastic inputs both before the Neo-Tethys slab break-off and after the hard continental collision. The depositional environments and provenance of the studied sedimentary record provide an analog for the development of synorogenic hinterland basins worldwide along with the well-known Altiplano Basin of the Andes and Hoh Xil Basin of Tibet.

Strain pattern and vorticity analysis in the transpressional Kamandan area within the Sanandaj-Sirjan Metamorphic Belt, Iran

New structural data on radiolarite and quartz mylonite rocks from the well-exposed Kamandan area are presented with the aim to shed light on the quantitative finite strain and vorticity analyses and strain partitioning along the Zagros transpression zone. Duplex structures, imbricate fans, thrust sheets and shear zones are well developed in the Kamandan region, located in the Sanandaj-Sirjan Metamorphic Belt, western Iran. Kinematic shear sense indicators associated with Kamandan shear zone show top-to-the-NE sense of ductile shearing deformation. Integrated quantitative finite strain and kinematic vorticity analyses of deformed rocks indicate deformation pattern and geometry. The strain parameter measurements vis. strain ratios and strain ellipsoid shape (k) show that radiolarite and quartz mylonite rocks have deformed in the constrictional to approximately plane-strain conditions. The quartz mylonite rocks highlight general-shear (sub-simple shear) deformation (Wm = 0.68–0.81) associated with the spatial increase in simple-shear component (47%–60%) from NE to SW. Our results of structural, strain, and vorticity analyses confirm a dextral transpression with strain partitioning into the pure-shear and simple-shear components in the Kamandan shear zone. Estimated Wm-values display the θ angle between the transpressional boundary and the maximum instantaneous strain axis (ISA) is the range from 63 to 69°. Accordingly, the oblique convergence angle (α) between the flow apophyses was estimated at about 35–48° that causes a horizontal shortening of ∼32–42% perpendicular to the boundaries of the Kmandan shear zone.

Kinematic vorticity, finite strain, and deformation thermometry analyses of the exhumed mylonites in the Samen ductile shear zone (Sanandaj-Sirjan Metamorphic Belt, Iran)

Quantitative microstructural investigations involving finite strain and vorticity analyses of quartz-rich mylonites provide significant information regarding the kinematic characteristics of the Samen shear zone (SSZ) within the Sanandaj–Sirjan Metamorphic Belt, Zagros Mountain of Iran. A dominant top-to-the-SE sense shear in the study area is recognized by several kinematic indicators. The results of the finite strain analyses indicate approximately plane strain deformation conditions (Rxz = 2.46–3.53). The mylonitic granitoid rocks record general-shear deformation (Wm = 0.37–0.94) associated with a spatial increase in simple-shear component (23%–78%) from W to E. In the study area, kinematic analyses indicate spatial variations of finite strain, deformation temperature, and the kinematic vorticity numbers resulted in partitioned progressive deformation. These spatial variations reveal an increase of all values towards the Samen thrust sheet. Ductile SSZ developed under greenschist-amphibolite facies metamorphic conditions (464–619 °C), as indicated by the presence of quartz, feldspar, biotite, muscovite, hornblende mineral assemblages, opening angles (OAs) of quartz c-axis fabrics and recrystallization regimes. The dynamic and kinematic characteristics of the study area were generally controlled by ongoing oblique convergence of the Afro-Arabian plate and the Iranian plateau with estimation of a horizontal shortening of ∼20–38% measured perpendicular to the boundaries of the SSZ.

Strain and vorticity analyses using rotated porphyroclasts in the Tanbour metamorphic rocks: Evidence of transpressional deformation along the Sanandaj-Sirjan metamorphic belt, SW Iran

The Tanbour Metamorphic Complex (TMC) is located within the Sanandaj-Sirjan Metamorphic Belt, SW Iran, along the northeastern margin of the Afro-Arabian plate. Detailed kinematic and strain analyses were combined with vorticity estimates on rocks from the TMC to document patterns and geometry of deformation. The strain parameter measurements including strain ratio in the XZ principal plane of strain ellipsoid (RXZ), strain ellipsoid shape (K) and strain intensity (D), highlight the deformed gneissic rocks in the TMC exhibit constrictional to approximately plane-strain shape of the strain ellipsoids. Several kinematic shear sense indicators including S/C fabrics, mantled porphyroclasts, oblique grain shape, micro-shears with bookshelf geometry and mineral fish show top-to-the-SE sense of shear. The quantitative kinematic analyses highlight that Wk varies between 0.64 and 0.78, implying a general shear flow with 44% < simple shear <58% and 42% < pure shear <57%. The exhumation of TMC is attributed to the exhumation-controlled transpressive tectonic process during oblique convergence between the Afro-Arabian continent and the Central-Iranian microcontinent which started since Upper Cretaceous.

Doming along the Zagros transpression zone, SW Iran: insights from microstructural analysis of heterogeneous deformation

Detailed structural and kinematic analyses of deformed structures in the Sanandaj-Sirjan Metamorphic Belt in the Ghouri area revealed the occurrence of three gneissic sub-domes with semi-elliptical shapes with their major axes parallel to the Zagros Transpression Zone boundary (NW-SE direction). These sub-domes are cored by sheared quartzo-feldspathic gneisses which surrounded by sequences consisting of garnet amphibolites, phyllites, phyllonites, muscovite schists, and deformed conglomerates. The Kuh-e-Zard, Chah-Sabz, and Chah-Goni sub-domes resulted from the interaction of the lower to middle continental crust and hot subducting Tethyan oceanic crust during subduction/continental collision. These sub-domes were squeezed between thrusts in the Zagros dextral transpression zone. The variations in the kinematic vorticity and strain estimates revealed that sub-simple shear transpressional deformation is highly heterogeneous in each sub-domes.

Mineralogical, Geochemical, and Raman Spectral Characteristics of Amphibole Mineral Types in Amphibolite from Southern Sanandaj-Sirjan Metamorphic Belt (Iran)

DOI: 10.17014/ijog.8.1.59-72The current study is related to amphiboles in amphibolite rocks in the northwest of Golgohar Iron Mine located in the southern part of Sanandaj-Sirjan metamorphic zone.Petrography observations indicate that the studied rocks are of ortho-amphibolite type, formed from metamorphism of igneous rocks. The analysis of amphibole crystals in amphibolites of the region was done by petrography, electron microprobe, and Raman spectroscopy. Raman spectral pattern of the studied minerals was discussed in comparison to mineral type and chemistry characteristics. Based on mineral chemistry studies, it was discovered that all amphiboles in the studied rocks are calcic with (Ca+Na)B≥1.34 and SiIV between 6.27 and 6.76 atoms per formula unit. Based on their enrichment in the elements Al and Fe3+, their composition varies from tschermakite to magnesio-hornblende. Raman spectral peak pattern for amphiboles and terrestrial tremolite does not have significant discriminable differences. However, Raman peak patterns of tremolite have clearly different features versus tschermakite. According to the general formula of amphiboles [A0-1B2C5T8O22(OH, F, Cl)2], the Raman spectrum variability of the tschermakite and tremolite can be due to the position of A site, Al incorporation into M1 + M2 + M3 sites and into the T site.

Spatial Data and Remote Sensing Techniques Integration to Detection and Slicing of Bavanat Red Bed Copper Deposits (NE Shiraz, Iran)

Bavanat red bed copper deposits (Jolani area) are located in south Sanandaj-Sirjan metamorphic belt and approximately 15 km NW of Bavanat. In terms of lithology, these deposits include purple to red siltstone(PSS) which are also seen among the layers of green sandstone(GS). Copper mineralization such as malachite is observed in the GS unit at the surface. Both PSS and GS units have Jurassic age. The current study, has used Landsat 8 and SPOT 5 images for RS processing. This study indicated that RGB=432 color composite in SPOT 5 image has the best contrast for enhancement and detection of PSS and GS units. Only the Landsat 8 fused image has been able to enhance and detect the GS unit. Also, based on band ratio technique, RGB=(b6/b2), (b5/b3), (b7/b1) color composite for Landsat 8 data, has the best contrast for PSS and GS units. PCA method shows that RGB=PC4, PC2, PC1 for Spot 5 dataand RGB=PC1, PC2, PC3 for Landsat 8 data have the best contrast for enhancement and detection of the Bavanat red bed copper deposits. In this study, different methods of supervised classification such as SAM, SID and SVM were reviewed. Among these methods, SVM technique has the best layout for SPOT 5 image. This important layout as a basic geological map, can be very useful in additional exploration studies on the Bavanat red bed deposits.

Metamorphic Evolution of High-pressure Pelitic Schists from Northwest of Nahavand in the Sanandaj-Sirjan Metamorphic Belt, Iran

Metamorphic Evolution of High-pressure Pelitic Schists from Northwest of Nahavand in the Sanandaj-Sirjan Metamorphic Belt, Iran

Geochemical description and sulfur isotope data for Shahrak intrusive body and related Fe‐mineralization (east Takab), northwest Iran

AbstractThe Shahrak intrusive body (SIB) occurs at the intersection of the Urumieh–Dokhtar Volcanic Belt and the Sanandaj–Sirjan metamorphic belt in northwest Iran. This intrusive body consists of granodiorite, monzonite, monzodiorite, and monzogabbro, that intruded Oligo‐Miocene sedimentary units and Cretaceous and Precambrian metamorphic rocks. Iron mineralization has occurred as magnetite skarn with hematite and pyrite in calcareous units at the contact with the SIB. The Rb–Sr age dating shows that the age of the SIB is about 24.9 Ma (Chattian). Whole rock geochemical studies indicate that the magma has calc‐alkaline to high‐K calc‐alkaline affinities and is metaluminous. The multi‐elements spider diagrams normalized to chondrite and primitive mantle show significant enrichment of light rare earth element against heavy rare earth element and depletion of Ti, P, Ta, and Nb, indicating characteristic features of the volcanic arc rocks in a subduction setting. Furthermore, the various types of tectonomagmatic diagrams show that these rocks are generated in an active continental margin. The parental magma of the rocks probably originated from an enriched mantle on the basis of the geochemistry of the REE elements. The average Sr isotopic composition of the SIB is 87Sr/86Sr(i) = 0.706. Therefore, the parent magma of the SIB may be the result of partial melting of enriched mantle or subducted slab contaminated with the continental crust. The sulfur isotope composition of pyrite grains (ave., +5.29 ‰) in the Korkora‐1 iron deposit indicates that the sulfides are formed from magma or due to in situ dissolution and leaching of igneous sources. Dehydration melting of the subducted part of oceanic crust has likely produced the fluids that are necessary for melting of the mantle wedge to produce mafic‐intermediate melts. The generated melts penetrated into the crust, and during their ascent they underwent a little crustal contamination and eventually were emplaced as intrusive bodies comprising gabbrodiorite to granodiorite.

Application of lanthanides tetrad effect as a geochemical indicator to identify fluorite generations: A case study from the Laal-Kan fluorite deposit, NW Iran

The Laal-Kan fluorite deposit situated in north margin of the Sanandaj-Sirjan metamorphic belt and Urmia-Dokhtar magmatic arc, NW Iran. The fluorite mineralization in the form of open-space filling, veins and veinlets have been deposited in the contact zone between highly metamorphosed schist, gneiss, amphibolite of the Paleozoic age and the Jangutaran limestone of the Precambrian age. The occurrence of convex tetrad effect and the calculated tetrad values indicate that early and late stage fluorite mineralization display various geochemical behavior, which are supported by the bivariate diagrams including T1, T3 and T4 versus each other and some geochemical parameters such as La/Ho, Y/Ho and Zr/Hf ratios. It can, therefore, deduced that fluorite have been probably formed during two stages from hydrothermal fluids with a relatively constant composition. The fluid-rock interaction during deposition of fluorite and REE-F complex were likely the main mechanisms for the occurrence of tetrad effect.

Strain pattern and vorticity analysis of deformed conglomerates in the Heneshk area within the Sanandaj–Sirjan Metamorphic Belt, Zagros Mountains, Iran

Strain measurements have been carried out, using the Rf/ϕ method on a Jurassic deformed conglomerate, in the Sanandaj–Sirjan Metamorphic Belt, Zagros Mountain of Iran. Estimated finite strain ellipsoids range from general flattening to near plane strain (Flinn parameter K = 0.6–0.9) with strain ratios in the X/Z plane with Rxz = 5.4. Quantitative kinematic analyses were performed on the conglomerates using the rigid clast method. Estimated kinematic vorticity numbers (Wk) varied between 0.43 and 0.63, implying a general shear flow (30% < simple shear < 42% and 58% < pure shear < 70%, i.e., pure shear-dominated non-coaxial flow). Combining strain and vorticity data, we estimated a horizontal shortening of ~ 42–55% measured normal to the walls of the deformation zone. We discuss this pure shear-dominated deformation in terms of convergence between the Afro-Arabian continent and the Central-Iranian microcontinents.

Mineralization, Mineralogy and Geochemistry of Saheb Fe-Cu Deposit of Saqqez (Kurdestan), NW Iran

The Saheb Fe-Cu skarn deposit is located in the Sanandaj-Sirjan metamorphic belt, SE Saqqez, western Iran and has been formed along the contact between the Oligo-Miocene aged Saheb granitoid and the Permian aged impure calcareous rocks and includes endoskarn and exoskarn. Exoskarn is widely developed and includes garnet and epidote skarn zones. The majority of mineralized zones are concentrated in garnet skarn. The relatively oxidizing mineralogical assemblage of the Saheb skarn includes garnet (andradite-grossular), pyroxene (diopside-hedenbergite), magnetite and hematite. Magnetite is the main and abundant ore mineral throughout the ore deposit. Based on field evidences and microscopic studies of skarn zone samples, two stages of prograde and retrograde alteration are distinguishable. According to the results of sample analysis of Saheb skarn intrusive body by XRF and ICP-MS techniques, the combination of this body is chiefly granite to granodiorite-diorite and belongs to the I-type granitoids, metaluminous and K-rich calc-alkaline series. The Saheb granitoid is related to the VAG (Volcanic Arc Granite) tectonic setting.

Fluid inclusion and stable isotope geochemistry of the orogenic–type Zinvinjian Cu–Pb–Zn–Au deposit in the Sanandaj–Sirjan metamorphic belt, Northwest Iran

The Zinvinjian polymetallic deposit occurs as veins controlled by a NW–SE trending–structure within the Cretaceous metamorphosed limestone and dolomite, schist, and metavolcanic rocks, northwest of Iran. The retrograde greenschist facies metamorphism was accompanied by large–scale transpressional faulting, crack–seal veins, infiltration of large volumes of hydrous fluid with high XCO2, and is largely overlapped by the main hydrothermal events. The metamorphism has resulted in two stages of mineralization in the Zinvinjian deposit. These are early–stage polymetallic sulfides–quartz and late–stage pyrite–quartz veins. The early–stage veins filled fractures and are undeformed, suggesting a tensional shear setting. The late–stage veins are also mainly open–space fissure–fillings that cut or replace earlier veins. Three types of fluid inclusions (FIs), including aqueous (type–I), mixed carbonic–aqueous (type–II), and carbonic (type–III), were identified in ore–related quartz veins. The early–stage quartz contained all three types of primary FIs homogenized at temperatures of range 197–300°C and salinities of 2.5–15.2wt% NaCl equivalent. In contrast, the late–stage quartz veins contained only type–I FIs with homogenization temperatures ranging between 192 and 210°C, and salinities of 0.2–2.7wt% NaCl equivalent. This indicates that the metallogenic system evolved from a carbonic–rich, metamorphic fluid to a carbonic–poor, one through input of meteoric fluids. All three types of FIs in the early–stage minerals displayed evidence of vein formation during an episode of fluid immiscibility. Quartz δ18O (+15.3 to +19.0‰) and sulfide δ34S (−9.4 to +11.6‰) indicate isotopic equilibrium with host metasediments (rock buffering) and a metasedimentary source of sulfur during early–stage. It is believed that ore mineralization is the result of a decrease in base–metal solubility during an episode of the fluid immiscibility. This study suggests that mineralization at the Zinvinjian deposit is metamorphogenic in style, probably related to a deep–seated orogenic system.

Investigation on mineralogy, geochemistry and fluid inclusions of the Goushti hydrothermal magnetite deposit, Fars Province, SW Iran: A comparison with IOCGs

The Goushti iron deposit from Dehbid area located in the Sanandaj-Sirjan metamorphic Belt (SSB), SW Iran is hosted by the Early Mesozoic silicified dolomite. Mineralized zones are lithostructurally controlled and oriented NW-SE parallel to the Zagros Orogenic Belt (ZOB). Magnetite, the major ore mineral, occurs as open space fillings and is accompanied by the secondary mineral phases hematite, goethite and martite. Gangue minerals mainly include quartz, dolomite and K-feldspar are associated with minor hydrosilicates. Calc-silicates such as wollastonite and diopside, minerals typical of skarns, are virtually absent from the ore zones. Fe2O3 content in the mineralized zones varies in the range of 38–75wt%. The concentrations of Au, Cu, P, Ti, Cr and V as well as Co/Ni, Cr/V, (LREE)/(HREE), Eu/Sm and La/Lu values and Eu-Ce anomalies of the studied ores indicate that the Goushti deposit is a hydrothermal magnetite type. The subvolcanic rhyolite and basalt in this area are regarded as the source of iron and heat in the mineralizing system. The fluid inclusion data showed that magnetite deposited from the ore-bearing fluid with salinities 1–7wt% NaCl equivalent at temperatures of 130–200°C. A decrease in temperature and pressure, supplemented by fluid mixing, is the major controlling factor in iron oxide precipitation. The field relationships and mineralogical–geochemical characteristics of iron ores indicate that the Goushti hydrothermal deposit could not be classified as a member of the IOCG (Iron Oxide-Copper-Gold) deposits.

Tectonic evolution of the Zagros Orogen in the realm of the Neotethys between the Central Iran and Arabian Plates: An ophiolite perspective

The Zagros Orogenic Belt includes the Fold and Thrust Belt, the High Zagros Belt, the Outer Zagros Ophiolitic Belt, the Sanandaj–Sirjan Metamorphic Belt, the Inner Zagros Ophiolitic Belt, and the Urumieh–Dokhtar Magmatic Belt. We divide the High Zagros evolutionary history into five stages: (1) triple junction formation, (2) continental lithosphere rifting, (3) generation, spreading, and maturation of the Neotethys Ocean, (4) subduction of the oceanic lithosphere, and (5) collision. The Neotethys triple junction, located at the southeastern corner of the Arabian Plate, formed during the Late Silurian–Early Carboniferous. Subsequently, this triple junction became a rift basin due to normal faulting and basalt eruption. The rifting stage occurred during the Late Carboniferous–Early Permian. Thereafter, extension of the basin continued, leading to spreading and maturation of the Neotethys oceanic basin during the Late Permian–Late Triassic. Probably at the end of the Late Triassic, closure of the Paleotethys...

Petrology and mineral chemistry of peraluminous Marziyan granites, Sanandaj-Sirjan metamorphic belt (NW Iran)

AbstractThe Marziyan granites are located in the north of Azna and crop out in the Sanandaj-Sirjan metamorphic belt. These rocks contain minerals such as quartz, K-feldspars, plagioclase, biotite, muscovite, garnet, tourmaline and minor sillimanite. The mineral chemistry of biotite indicates Fe-rich (siderophyllite), low TiO2, high Al2O3, and low MgO nature, suggesting considerable Al concentration in the source magma. These biotites crystallized from peraluminous S-type granite magma belonging to the ilmenite series. The white mica is rich in alumina and has muscovite composition. The peraluminous nature of these rocks is manifested by their remarkably high SiO2, Al2O3and high molar A/CNK (&gt; 1.1) ratio. The latter feature is reflected by the presence of garnet and muscovite. All field observations, petrography, mineral chemistry and petrology evidence indicate a peraluminous, S-type nature of the Marziyan granitic rocks that formed by partial melting of metapelite rocks in the mid to upper crust possibly under vapour-absent conditions. These rocks display geochemical characteristics that span the medium to high-K and calc-alkaline nature and profound chemical features typical of syn-collisional magmatism during collision of the Afro-Arabian continental plate and the Central Iranian microplate.

High-Pressure Marbles from the Nahavand Area in the Sanandaj-Sirjan Metamorphic Belt, Iran

Marbles containing high-pressure mineral assemblage was found from the Sanandaj-Sirjan metamorphic belt in the Nahavand area in western Iran. The high-pressure marbles occur as small bodies or lenses within pelitic schist layers and show compositional banding of carbonate- and silicate- rich bands. Textural analysis revealed two metamorphic stages. The early stage is testified by relicts of the minerals such as rounded jadeite-bearing diopside, epidote (clinozoisite), amphibole 1 (pargasite-edenite) and titanite 1. The second stage (main stage) documented to have phlogopite, chlorite, amphibole 2 (tremolite) and titanite 2. P-T-XCO2 estimates for the early stage of metamorphism give an average pressure, temperature and XCO2 of 13.5 kbar, 670 oC and 0.35, whereas the second stage has been constrained at P=3.8 kbar, T=500 oC and XCO2=0.45. The high-pressure mineral assemblage documented in the Nahavand area, were formed during the subduction stage, while the second metamorphic blastesis were recorded during the exhumation event.

Strain analysis in the Sanandaj–Sirjan HP-LT Metamorphic Belt, SW Iran: Insights from small-scale faults and associated drag folds

This study is aimed at quantifying the kinematics of deformation using a population of drag fold structures associated with small-scale faults in deformed quartzites from Seh-Ghalatoun area within the HP-LT Sanandaj–Sirjan Metamorphic Belt, SW Iran. A total 30 small-scale faults in the quartzite layers were examined to determine the deformation characteristics. Obtained data revealed α0 (initial fault angle) and ω (angle between flow apophyses) are equal to 83° and 32°, respectively. These data yield mean kinematic vorticity number (Wm) equal to 0.79 and mean finite strain (Rs) of 2.32. These results confirm the relative contribution of ∼43% pure shear and ∼57% simple shear components, respectively. The strain partitioning inferred from this quantitative analysis is consistent with a sub-simple or general shear deformation pattern associated with a transpressional flow regime in the study area as a part of the Zagros Orogen. This type of deformation resulted from oblique convergence between the Afro-Arabian and Central-Iranian plates.

Mineral Chemistry and Geothermometry of Amphibole and Plagioclase in the Metabasites, Located at the Tanbour Metamorphic Complex in Southern Iran

Metabasite refers to metamorphosed basalts and other mafic igneous rocks (rich in iron and magnesium). When a mafic igneous rock is subjected to new pressure and temperature conditions during metamorphism, these chemical components will rearrange themselves to form new minerals. Metabasites can be found in many metamorphic belts including Sanandaj-Sirjan metamorphic belt of Iran. The study area is a Tanbour metamorphic complex in Eastern of Sirjan city, which is geologically located at the Sanandaj-Sirjan metamorphic belt in Southern Iran. Metabasite in this complex consists of greenschist, epidote amphibolite and amphibolite. Amphibole and plagioclase are the main minerals in the greenschist and amphibolite, and the a secondary mineral in some micaschist seen in the study area. The electron microprobe analysis was done on this mineralization in greenschist, epidote amphibolite and amphibolite, which showed that the amphiboles in greenschist was a member of the calcic group and Actinolite type, and the amphiboles in epidote amphibolite was a member of the calcic group and these amphiboles were tschermakite up to Ferro-Tschermakite + Ferro-Hornblende type. The amphibole in amphibolite is a member of the calcic group and this amphibole is Magnesio-Hornblende type. The plagioclases in the greenschist is pure albite (An 3.29 - 3.6), and in the epidote amphibolite is oligoclase (An 19.5 - 24.2), while in the amphibolites is oligoclase (An 16.9 - 26.6). The estimated P–T conditions are in favor of their metamorphism under epidote amphibolite (550°C and 8 kbar) and amphibolite (611°C - 652° Cand 10.5 kbar) facies.

Geochemistry of hydrothermal alteration at the Qolqoleh gold deposit, northern Sanandaj–Sirjan metamorphic belt, northwestern Iran: Vectors to high-grade ore bodies

The Qolqoleh orogenic gold deposit in the northern part of the Sanandaj–Sirjan metamorphic belt in northwestern Iran is hosted by a steeply dipping sequence of greenschist facies Cretaceous volcano–sedimentary rocks, including mafic to intermediate metavolcanic rocks, sericite and chlorite schist, and marble. Geochemical and petrochemical data including the ∑REE, (La/Yb)N and Eu/Eu* ratios were obtained from country rocks, ore-enveloping alteration zones, and mineralized zones to assess the nature of the trace element and rare earth element (REE) interaction between the wall rock and the mineralizing fluid.Quartz–sulfide veins at the deposit are characterized by a pyrite–pyrrhotite–chalcopyrite–sphalerite–arsenopyrite–native gold assemblage. Alteration halos border the mineralized zones and broadly comprise: (1) an outer carbonate–chlorite alteration zone in all rock types, particularly in chlorite schist; (2) a middle sericite–carbonate alteration zone in the sericite schist; and (3) an inner quartz–sulfide alteration zone in sericite schist and mafic to intermediate metavolcanic rocks.The geochemical data indicate that the concentrations of Al2O3, P2O5, TiO2, Y, and Zr are relatively constant, suggesting that these elements were the least mobile during hydrothermal activity. Using Al2O3 as the immobile component, there is evidence for mobility of trace elements, particularly light REE, TiO2, and Zr in the altered wall rocks. The altered rocks show a relatively light REE depletion ((La/Yb)N≅9.41), which clearly correlates with the grades of gold mineralization and intensity of the alteration (3ppm Au). The depletion of light REE is best indicated by a decrease in (La/Yb)N as shown by ratios of 10.5 to 11.8. Wall rock decarbonation reactions during infiltration of the mineralizing fluid resulted in differential mobilization of REE, from a fluid with initially low REE content.The overall trace element geochemistry of the altered wall rock is controlled by the initial composition of the wall rocks and the ore-fluid composition. Hydrothermal ore-forming fluids are recognized as CO2-rich near-neutral reduced fluids with high values of H2S, K, and S content. Observed variability in alteration halos at the Qolqoleh deposit points to major differences in REE and trace element content in original host rocks that have interacted with a relatively similar ore fluid. Therefore, depending on the composition of each host rock lithology, the geochemistry of hydrothermal alteration (e.g., ∑REE content and (La/Yb)N ratios) and alteration mineralogy including the carbonate–sericite–quartz–sulfide assemblages may be used as a primary tool for lithogeochemical exploration for gold deposits in northwestern Iran.