نشریه پترولوژی
پیاپی 54 (تابستان 1402)

The Zorrati granitoid (ZG) pluton exposed on the eastern edge of the Lut block trending north-south. The Lut block surrounded in the north by the Darone fault, in the south by the Jazmurian fault and in the east and  the  west by Nahbandan and Naiband faults respectively (Naderi Miqan and Akrami, 2006). A number of  investigations have been carried out  by various researchers regarding  how and when the magmatism and volcanism of the Lut Block was initiated among which Eftekharnezhad (1980) can be notable, who predicted the subduction of the oceanic crust towards the west and under the Lut Block based on the volume and time distribution. Saccani et al. (2010) suggested that the subduction of the oceanic crust took place towards the east and under the Afghan block. The closest intrusive bodies to the Zorrati granitoid are the Shah Kouh granitoid, the Deh Salam granitoid, the Chahar Farsakh granitoid, and the Sefidkoh granitoid.

Regional Geology:

This dominant rocks of the pluton under study are  biotite tonalite and syenogranite-alkali feldspar granite together with biotite and tourmaline porphyritic granodiorite, and granite. The ZG consisting of igneous and metasediment enclaves as well as felsic veins and dykes. According to several studies including field observations, petrology, and geochemical studies the rock units make up the studied pluton have possibly different origins.

For lithological and geochemical investigations of the Zorrati granitoid pluton and its tonalitic enclaves, after microscopic studies, 11 fresh samples were selected and sent to the Institute of Geology and Geophysics of the Chinese Academy of Sciences for XRF and ICP-MS analyses.

Petrography:

The constituent minerals of the granitoid rocks are quartz, plagioclase, microcline, orthoclase, biotite, muscovite and tourmaline.

Whole Rock Chemistry:

The Zorrati granitoid (ZG) is a high potassium calc-alkaline, peraluminous, and S-type granitoid. Trace element plots show at least two trends, which probably point to  different origins for the rock units forming this pluton. The studied rocks are Rb, Th, U, K, and Pb enrichment and depleted in Nb, Sr, P, Ti, and Zr, indicative of the crustal origin of the relevant magmas in a collision zone. Tourmaline porphyritic granodiorite and syenogranite-alkali feldspar granite were formed by melting a clay-rich metapelitic protolith with upper crust origin due to muscovite dehydration without the intervention of the mantle in a continental collision zone. Porphyritic biotite granodiorite along with granite, biotite tonalite, and igneous enclaves were formed by melting of a metagreywacke-poor clay protolith with upper crustal origin due to biotite dehydration without the intervention of the mantle in a collision and a post-collision settings, respectively. Water pressure of ≥5 kbar and temperature of 650 to 700 °C were estimated for the tourmaline-biotite porphyritic granodiorites and the syenogranite-alkali feldspar granite. Likewise, temperature of ~775 °C was determined for the granite, biotite tonalite and igneous enclaves.

Biotite tonalite and syenogranite to alkali feldspar granite units are the two main and large granitoid units  covering most of the area. The other units including granite, biotite, and tourmaline porphyritic granodiorite along with dikes and aplitic and pegmatite veins show high potassium and peraluminous calc-alkaline series related to S-type granites. The remarkable features of these rocks are  of the Rb, Th, U, K, Pb enrichment and the Nb, Sr, P, Ti, and Zr depletion as well as having  different origins and different tectonic environment. For example, the tourmaline-bearing porphyritic granodiorite and syenogranite to alkali feldspar granite were originated by melting of a metapelitic clay-rich source in the upper crust without mantle intervention, in a collisional tectonic environment while  muscovite dehydration plays a significant role. Biotite-bearing porphyritic granodiorite along with granite, biotite-bearing tonalite, and its enclaves formed by melting of a plagioclase-rich metagreywacke in the upper crust without mantle interference, in a collisional and post-collisional tectonic environment, respectively, while dehydration of biotite was involved in their formation. According to their lithological, geochemical, tectonic characteristics and different origin, like the other granitoids in this part of the Lut block (Moradi Noghondar et al., 2012), two different ages of the Middle Jurassic (biotite-bearing tonalite) and the Eocene - Oligocene (syenogranite - alkali feldspar granite) can be suggested for the Zorrati granitoid (ZG) pluton.

Tourmaline is a borosilicate mineral with general formula of XY3Z6[T6O18](BO3)3V3W. Experimental studies demonstrate a wide range of stability for tourmaline-supergroup minerals to record different geological processes. They occur in metamorphic, granitic pegmatites, and clastic sedimentary rocks and are associated with hydrothermal activities (Dutrow and Henry, 2011; Slack and Trumbull, 2011). Textural and compositional features of tourmaline can be used as an indicator of environment in which it crystallized. Tourmaline from porphyry deposits generally show a. frequently crystal zoning, b. development from Fe-rich to Mg-rich, and c. total Mg content is ~2 apfu in copper deposits and 1-2 apfu in Au deposits (Baksheev et al., 2012). It is believed that the world-class Dashkasan gold deposit records the transformation of porphyry to low-sulfide epithermal (Richards et al., 2006). The Dashkasan gold deposit located in the Kurdistan Province can be a significant region for better understanding the origin and the evolution of ore-forming fluids using chemistry of tourmaline. For the present study, we also tried to apply fluid inclusions data on quartz-tourmaline-pyrite veins from the Dashkasan deposit.

Polished-thin sections of various tourmalines of the Dashkasan deposit were examined using a Cameca SX100 Electron Probe Micro Analysis (EPMA) at the Iran Mineral Processing Research Center, Karaj. Fluid inclusion studies were performed on quartz crystals of quartz-tourmaline-pyrite veins. The microthermometric parametes of fluid inclsions were measured by Linkam-THMS-600 stage at the University of Isfahan.

The Dashkasan gold deposit with 52 Mt of oxidized ore and average grades of 1.77 g/t Au is hosted by the Middle-Miocene porphyritic dacite/rhyodacite and dacitic breccia rocks. The main minerals are quartz, K-feldspar, hornblende and biotite mainly altered.. This deposit is characterized by the transition from the porphyry to the epidermal system with the presence of tourmaline minerals in phyllic and silicification alteration associated with gold veins. As petrographic examination shows tourmaline occurs as disseminated, vein/veinlet, and breccia textures in three types: Tur-1 occurred as needle shape in dacitic rocks associated with phyllic alteration; Tur-2 crystallized as radial shape mainly coexisting with silicification; and Tur-3 with elongated shape is present in dacitic breccia with phyllic alteration.

Mineral Chemistry:

The geochemical composition of three types tourmalines points to the nature and the evolution of ore-forming fluids. Electron microprobe analyses of the studied tourmalines indicate that the Tur-1 and Tur-3 are dravite, and the Tur-2 is dravite to schorl in composition and they belong to alkaline group. The third type, unlike the other two, is characterized by poor zoning and higher values of Na, K, Fe, Mg and lower values of Ca. On Fetot-Ca-Mg ternary diagram, they plotted in the Ca-poor metapelites, metapsammites, and quartz-tourmaline rocks host. Magmatic genesis inferred from the higher Fe/(Fe+Mg) ratio for Tur-1 and Tur-2, while this ratio in the Tur-3 is different and shifted towards hydrothermal source.

Microthermometric Study:

Richards et al. (2006) present the fluid inclusion assemblages from quartz-tourmaline veins in sericitized wall rocks in the Dashkasan deposit consisting of hypersaline and rare vapor-rich inclusion. They have homogenization temperatures of 246° to 360 ℃, yielding salinities of 34.4 to 46.1 wt% NaCl equiv. (Richards et al., 2006). Fluids inclusions studies on quartz-tourmaline-pyrite veins related to transition between stage-1 and stage-2 of mineralization in the Dashkasan shows a salinity values from 15.9 to 16.8 wt% NaCl equiv. and homogenization temperature values between 185° to 254 °C.

On the basis of optical and scanning electron microscopy, three tourmaline types(Turs -1,-2 and -3) in the Dashkasan deposit, can be distinguished. Despite the lack of zoning in Tur-1 and Tur-2, the third type displays the poor zoning. The first-and the third-types of tourmalines are dravite (Mg-rich), whereas the second-type is dravite to schorl in composition. Magmatic genesis is reflected by higher Ʃ(Fe+Mg) and FeO/(MgO+FeO) ratios for the first two types. While these ratios in the Tur-3 is different and shifted toward hydrothermal source. To sum up, the occurrence of quartz-tourmaline-pyrite veins in the Dashkasan deposit is due to the existence of a fault system under the physicochemical performance of the ore-mineralized fluid by a sudden depressurization and probably gradual mixing with shallow water.

Hercynite-rich spinel is a typical mineral of both quartz-bearing and quartz-free metapelitic rocks that form under low-pressure high-temperature conditions in the granulite facies (Sengupta et al., 1991) or upper-amphibolite facies of regional and contact metamorphism (Pattison and Tracy, 1991). Temperature-pressure estimation of metamorphic terrains is necessary to understand how large-scale crust evolution has occurred. High-temperature phase equilibrium cannot be properly evaluated solely based on normal cationic couple geothermobarometers, as ferromagnesian cationic exchange undergoes processes related to retrogression during cooling after peak metamorphism. Instead, key mineral parageneses are preserved and standard petrogenetic grids study based on reaction textures and mineral chemistry can be very helpful in better estimating temperature pressure.

Regional Geology:

Dorbeh's contact aureole is formed in West Azerbaijan province, south of Urmia, north of Oshnavieh, and the Sanandaj-Sirjan zone around Dorbeh diorite. 
The intrusion is one of the components of the Urmia Plutonic Complex (UPC) which is spread along with granites and alkali syenites/granites at the northwest end of the Sanandaj-Sirjan zone in the south of Urmia. This diorite intruded sedimentary units of shale and carbonate belonging to Permian to Triassic-Jurassic including the Doroud and Ruteh Formations and have metamorphosed them in contact aureole, causing hornfels and calc-silicate to sometimes scarn deposits in the area (Modjarrad and Mohamed, 2015). This intrusion is covered by Miocene units (Ghalamghash, 2009). The observed parageneses in Dorbeh aureole including Cld + Chl, Ctd + And, Alm + Cld, And+Alm, Hc+Alm, Chl + Hc + And + Sil, Alm + And + Sil, Alm + And + Sil + Hc. The peak metamorphism assemblage is Alm + And + Sil + Hc. The reactions responsible for the parageneses productions were introduced in the previous studies (Modjarrad and Mohamed, 2015).

 50 microscopic thin sections were prepared and petrographically examined. A reagent sample with the highest number of parageneses and experienced peak metamorphism was analyzed by JEOL JXA-8200 microprobes electron device for garnet, chlorite, chloritoid, spinel, iron oxide, aluminosilicate, and apatite at the University of Potsdam, Germany. For whole rock chemistry, several metapelite samples were analyzed by XRF at the ALS-Chemex Laboratory of Canada.

The main purpose of the present paper is to investigate the parageneses, the mineral chemistry, and the temperature-pressure estimation in the metamorphic contact aureole around Dorbeh intrusive. This intrusion consists of amphibole, plagioclase, and clinopyroxene, is a part of the Urmia Intrusive Complex (UPC), and with dioritic composition was intruded the Upper Cretaceous into the Paleozoic pelitic and limestone sedimentary rocks and metamorphosed them. The metapelite section of the aureole has exhibited interesting parageneses due to the exceptional iron-rich composition of the protolith. The hornfels part of the Dorbeh aureole is dominated by chlorite + chloritoid + garnet + aluminosilicates + spinel + opaque minerals and less quartz in the matrix. Mineral chemistry studies showed that Fe-chlorite between Repidolite to Bronswigite, Fe-chloritoid, Almandine garnet, Hercynitic spinel, and ilmenite are the minerals composition which is in agreement with the Fe-rich content of the parent rock. There was no specific zoning pattern in the metapelites garnet grains. It was also found that there is a reverse relationship between Si content and iron, magnesium, titanium, and chromium in chlorite and aluminosilicate structures. The metamorphic conditions for Dorbeh aureole by the multi-equilibria method by THERMOCALC software have been estimated at 570±7°C, at a pressure of 2.8±0.2 kbar.Detailed investigation of phase relationships of metamorphic rocks can be considered a desirable method along with quantitative data-based methods to evaluate the occurrence of progressive metamorphism. This method is based on direct observation of reaction textures and is more objective in estimating metamorphic conditions by the method of the intersection of equilibrium reactions. Most of the time, secondary cationic exchanges penetrate from the mineral boundary to a considerable stratum and question the accuracy of the temperature and pressure calculated on the cationic couple's geothermometers to a large extent. The contact aureole with higher than normal temperatures specific to the margins of dry mafic intrusives is sometimes associated with the formation of special parageneses such as Grt+Sil+And+Hc. This paragenesis has also been reported from high-temperature (granolithic) regional metamorphic terrains, but its production conditions are more limited in contact aureoles and require a high molar fraction of iron/aluminum or mass dryness and/or aureole. Therefore, the composition of all ferromagnesian minerals is very close to the final iron end member and no specific temperature fluctuation in the aureole is understood from the garnet zoning pattern. Although staurolite has not been seen in the studied sections, the evidence suggests that hercynite in the area was caused by staurolite breakdown. With precision in the composition of analyzed chlorites, it was found that there is a direct relationship between Si and alkaline content in chlorite structure, but titano-ferromagnesian content is in contrast with Si content. An almost similar relationship was observed in the aluminosilicate crystals. The inverse relationship between silica and Fe, Ti, and Cr oxides prevails.

The composition of minerals in igneous rocks is influenced by the type and nature of their parent magma, and for this reason, minerals can provide valuable information regarding the original magma. Zircon (with the general formula ZrSiO4), due to its widespread distribution in various types of rocks,  is considered a valuable tool in many geological studies. For this study, the composition of trace elements in zircon crystals from Neoproterozoic to Lower Cambrian granitoids in the Kaboodan area Sabzevar is geochemically investigated. As the previous studies have documented the granitoids in this area are classified into two distinct groups, I- and S-type (Mazhari et al., 2020).

Regional Geology:

The study area lies in the northeast of Iran and belongs to the Central Iran Zone on the northern margin of the Lut Block. The granitoids from the southern part of the Sabzevar region were investigated for this research. The main fault of the Taknar separates the northern Sabzevar Zone and the southern Taknar Zone occurrences in this area.A small part of the intrusive complex appearing in the Kaboodan area includes both felsic and mafic rocks with the Cretaceous age. The geochemical and isotopic characteristics of these rocks point to their formation in an active arc setting during the Late Cretaceous (Mazhari et al., 2019). However, the main volume of the rock formations in the Kaboodan area consists of various magmatic rocks related to Cadomian events. The mafic intrusive rocks, with an age of Ma 552-545, consist of a gabbro-diorite composition derived from the partial melting of a mantle source enriched in spinel peridotite at shallow depths (Mazhari et al., 2020a). The granitoid rocks in the area are of two different types, I (Ma 549-547) and S. (Ma 531-528) types (Mazhari et al., 2020a).

Two samples of S-type (Ka18 and Ka39) and two samples of I-type granitoids (Ka6 and Ka33) were selected. The trace element analysis of zircons was carried out using the Agilent 7700x ICP–MS, which was equipped with a Resonetics Resolution M-50 series 193nm excimer laser ablation system. The laser ablation beams had a diameter of approximately 31 μm with a laser energy density of 8.5 J/cm2. All spot analyses were conducted with a repetition rate of 10 Hz. External standards NIST SRM610 and TEMORA 2 (TEM) were utilized for the analysis. The detailed operating conditions for the laser ablation system and the ICP-MS instrument, as well as data reduction procedures, were the same as those described by Liang et al. (2018). Petrography, nature, and formation setting of zircon crystals The separated zircon samples from the two types of granitoids have a similar appearance. They are all transparent and come in various colors ranging from colorless to pale yellow and light brown. The length ofthe zircon crystals is approximately 100 to 300 microns, andthe length-to-width ratio is about 3:1. The zircon grains in the studied granitoids are mostly euhedral to subhedral and often exhibit zoning. The observed zoning in the zircon samples is mostly of the oscillatory or sector type, and some crystals also display banding textures. These textures are prominent features of magmatic zircon crystals. All the analyzed crystals have high Th/U ratios (>0.1), which is consistent with zircons of magmatic origin. Moreover, the Th/U ratio is approximately 1.5-1 in these zircons. All zircon crystals in the studied samples exhibit a rare earth element (REE) pattern similar tomagmatic zircons. The U/Yb ratios in the zircon crystals indicate that the studied zircons fall within the range of continental zircons. Trace element distinction between I- and S- types of granitoids With careful examination of the results of trace element analysis in the zircon crystals from different types of granitoids in the studied region, significant differences are observable. While some elements like Sr, Nb, and Ta show consistent ranges of variation in zircon crystals from different granitoid types, the composition of other trace elements varies significantly. Zircon crystals in S-type granitoids are enriched in elements (i.e. Ti, P, Hf) compared to I-type granitoids, whereas in I type samples, zircons are relatively enriched in elements like Y, Th, U, and REE. These compositional differences in magmatic zircon crystals indicate different sources and distinct evolutionary processes that gave rise to the formation of the primary magmas.Crystallization temperature and oxygen partial pressure (fO2) in zircon crystals The calculation of the Titanium-in-Zircon Thermometry (TZT) documents that zircon crystals in S-type granitoids crystallized at higher temperatures (877-910°C) compared to I-type granitoids(808-860°C). The concentrations of elements (i.e. Nb, Hf, Th, U) in zircon crystals decrease with increasing crystallization temperature in both I- and S-type granitoids. The trend of variation in trace elements with increasing crystallization temperature in zircon crystals indicates systematic changes in the melt composition simultaneous with the cooling of the system. This behavior of trace elements is in line with magmatic differentiation processes such as fractional crystallization.I-type granitoids were formed at higher oxygen partial pressures compared to S-type samples. The average values of ∆FMQ for zircon crystals in S-type granitoids are -18.8, while the zircon crystals in I-type granitoids have an average of -16.3. The relationship between temperature and oxygen partial pressure indicates that all samples were formed under conditions lower than FMQ. The calculation of temperature and fO2 using the trace element composition of zircon crystals in the studied region suggests higher temperatures and lower oxygen partial pressures for S-type granitoids compared to I-type ones.

Felsic igneous rocks record crustal evolutions and provide an important tool for determining the composition and modification of the crust (Zhang et al., 2018). Up to now, several classifications have been proposed for granites and rhyolites. Alphabetic classification is the most common approach used by petrologists. In this approach, granites and rhyolites have been divided into I, S, M, and A-types according to their geochemical, mineralogical composition, and origin characteristics (Loiselle and Wones, 1979; White, 1979). A-type granites and rhyolites include a wide range of felsic rocks. Currently, the formation of A-type suites has been attributed to both with-in-plate (anorogenic) and postcolision (orogenic) settings (Eby, 1990; Bonin, 2007; El Dabe, 2015).In this study, petrological characteristics of Noraldinabad rhyolites have been studied. These rhyolites exposed adjacent to Gushchi granitoids, which petrologically, have been studied before (e.g. Advay et al., 2010; Shafaii Moghadam et al., 2015). These studies exhibit that the Gushchi granitoides are A-type and formed in an extensional rift-related setting. Nevertheless, there is not any comprehensive study on the Noraldinabad rhyolites and the present study would be the first effort to constrain the geochemical characteristics of these rocks. 

Regional Geology:

The area of study, in aspect of lithological characteristics as well as geological structures has attributed to various zones e.g., Khoy-Mahabad zone (Nabavi, 1976), Sanandaj-Sirjan Zone (Alavi, 1991), and junction of the structural zones of Sanandaj-Sirjan and Central Iran (Alavi-Naini, 1972). Nabavi (1976) believes that the lithological characteristics of Central Iran, Sanandaj-Sirjan, and Alborz-Azerbaijan zones are visible in the northwest of Iran. In this case, the observed geologic successions in the northwest Iran are similar to those of the of Central Iran zone (Shafaii Moghadam et al., 2015). The exposure of Kahar Formation (Late Neoproterozoic) is common in the northwest of Iran, Central Iran, Alborz, and Sanandaj-Sirjan zones (Shafaii Moghadam et al., 2015). However, according to Sabzehi and Mohammadiha (2003), the main characteristics of the Sanandaj-Sirjan zone are not visible in this region but could be considered as the northwest termination of the Sanandaj-Sirjan zone.

Following the field observations and collecting several rhyolite samples microscopic studies were performed to determine petrographic features. Also, 10, least altered rhyolite samples, were selected for whole rock analyses, including XRF and ICP-MS, performed at the Zarazma Zanjan laboratories (Zanjan, Iran).

Petrography:

The Noraldinabad rhyolites display porphyritic texture with quartz, alkali feldspar, and subordinate plagioclase phenocrysts. Opaque minerals and zircon are the main accessory minerals. Altered mafic minerals can be seen in some samples. The matrix is composed of medium- to fine-grained quartz and alkali feldspar. Secondary minerals, mostly sericite and chlorite, are ubiquitous in the matrix of some samples. Along with porphyritic texture, flow-alignment (in the matrix of some fine-grained samples), spherulitic (in the matrix of medium-grained samples), embayed, Perthitic, and subordinate granophyric textures are the main visible textures.

Whole rock chemistry:

The Noraldinabad rhyolites have high SiO2 values, consistent with “high silica rhyolitic systems” (SiO2 > 70 wt%) (Gualda and Ghiorso, 2013; Arakawa et al., 2019). The Al2O3 content of the studied rhyolites is lower than of \ this oxide in calc-alkaline rhyolites (> 14 wt%) (Philpotts, 1990). Based on alkali elements content, the rhyolites under study can be divided into two groups: Na2O- and K2O-rich, in concordance with petrographic studies. The K2O-rich samples are dominated by the presence of K-feldspar whereas the Na2O-rich samples are characterized by high numbers of anorthoclase. Except for alkali elements, the contents of other major elements in these two groups are not significantly different. Except for one sample (0.54), the FeOt/(FeOt+MgO) ratio is high and varies between 0.73 to 0.94. All analyzed samples have high A/CNK ratios, indicating their peraluminous characteristics. The studied rocks show shoshonitic magmatic series affinity and are characterized by LREEs enrichment and HREEs depletion with obvious negative Eu anomaly in the chondrite-normalized diagrams. In the NMORB-normalized trace element spider diagram, the samples display enrichment in LILEs, Ba, Nb, Ta, Sr, Zr, Hf, Eu, and Ti negative anomalies, weakly Rb and Pb positive anomalies. The Eu, Sr, Ba, and Ti depletion indicates plagioclase and titano-magnetite fractionation, respectively (Shafaii Moghadam et al., 2015).

The remarkable geochemical features of the Noraldinabad rhyolites are high amounts of SiO2, Na2O+K2O, Fe2O3t and low abundances of CaO, MgO, and P2O5. Furthermore, the concentration of REEs (except for Eu) and LILEs are high, and the contents of Sr and Rb, and compatible elements (i.e., Co, Sc, Cr, and Ni) are low. These geochemical features disclose the A-type nature for the studied rhyolites (Loiselle and Wones, 1979; Eby, 1990; Bonin, 2007). Genetically, considering the high ratios of Y/Nb, Rb/Sr, Rb/Nb, and relatively low amounts of Nb, the investigated rocks can be attributed to the A2-subtype of the A-type rhyolites.The low Sr concentration, negative Eu anomaly and HREEs flat- pattern indicate a garnet-absent and plagioclase-bearing, as a residue of partial melting, origin for studied rhyolites which confirmed these rocks formed by partial melting under shallow depth and low-pressure conditions (Norman et al., 1992; Petford and Atherton, 1996; Jia et al., 2019). The Y/Nb ratio is helpful to determine the characteristics of parent magma (Eby, 1990). Granitoids derived from mantle have Y/Nb<1.2, while crustal granitoids have Y/Nb > 1.2. The Y/Nb ratio in the Noraldinabad rhyolites varies from 1.30 to 4.72 compatible with crustal origin. Additionally, the trace element ratios (i.e., Th/U, Nb/U, Y/Nb) are similar to those of the continental crust composition.Considering tectonic setting discriminant diagrams, the studied rhyolites are anorogenic and formed in within-plate related to rift-related extensional environment. The presence of bimodal magmatism in the studied region, along with the exposure of coeval A-type granites and rhyolites in northwest Iran, can confirm the formation of the studied rhyolites in a continental rift (possibly Neotethys rift) setting.

The main aim of this paper is to identify the formation environment and the physicochemical conditions of chlorite minerals in Dalayon area by their mineralogical and geochemical features (Ciesielczuk, 2002). The geochemical characteristics, mineralogical and formation mechanism of granitic rocks can be investigated using the biotite hydrothermal alteration to chlorite (Morad et al., 2011). The temperature data obtained from chlorite geo-thermometry can be compared with the data obtained through fluid inclusion (Cathelineau and Nieva, 1985; Kordi and Shahrokhi, 2021; Shahrokhi, 2021).

Regional Geology:

Dalayoun area is located in the east of Drood city and is a small part of Sanandaj-Sirjan metamorphosed zone. Lithologically, the oldest units belonging to the Upper Triassic-Jurassic and are including a relatively uniform sequence of slate, schists with siliceous veins and veinlets, and cordierite and sillimanite mica schists along with black hornfelses and metamorphosed sandstones. (Shahrokhi, 2002).

In order to study the mineralogical and geochemical composition of chlorites in the area of study, 10 thin-polish sections were studied. In addition to, chemical analyses of 10 samples by XRD method and 20 points by EPMA of chlorite mineral as well as the study of the fluid inclusion on 3 quartz mineral samples were carried out. The structural formula was calculated based on 14 oxygens for chlorite.Petrography, Mineral chemistry, Whole rocks chemistryThe intrusive bodies in the studied area have infiltrated volcanic and metamorphic rocks (Shahrokhi, 2020). Based on field Geology and microscopic studies, the mineralogy of these rocks includes quartz, plagioclase, orthoclase, microcline and chlorite as the main minerals and biotite, muscovite, apatite, garnet, rutile, leucoxene, titanium minerals, sphene and zircon as the secondary minerals. Chlorite can be seen in the form of coarse crystals, needles and very narrow in the background of the rocks, and they have been replaced in the remains of crystalline molds of the primary biotite type. Based on this, it can be said that the transformation of biotite to chlorite is associated with the depletion of K2O and the reduction of SiO2 which gave rise to the formation of potassium feldspar (Czamanske et al., 1988). Completely rutile and sphene crystalline can be seen in the process of chlorite cleavage. The presence of a small amount of garnet in the form of crystalline and cubic indicates low pressure or poor magnesium in the primary rock (Yardley, 1989). Also, the study of polished sections shows the presence of minerals such as pyrite, hematite, corundum and Au. The amount of pyrite and gold increases when approaching granodiorites, which can indicate the effect of intrusive bodies and post-magmatic fluids in mineralization in these rocks. X-ray diffraction (XRD) mineralogical study shows that the most important variation in chlorite is in Dalayon area. The main minerals in the host rock include chlorite, quartz, muscovite, illite, microcline, and secondary minerals are rutile and biotite. It can be concluded that biotite has been transformed into chlorite in the presence of hot fluids containing Fe and Mg. With the help of Fe2+/ (Fe2++Mg2+) versus 2*Si diagram (Pflumio, 1991) and also the Si content of Dalayon chlorites is of ripidolite-pychnochlorite type and show the presence of iron-bearing chlorites. The amount of Si indicates the purity of chlorites, and the very small amounts of calcium and also the amount of Xc points to the absence of smectite and the high purity of chlorites (Lori et al., 1988). The very low Ti content of chlorites and the presence of rutile, sphene, and leucoxene indicate that the Ti content of primary biotite is formed secondarily in the form of Ti-bearing minerals and in the form of thin blades parallel to the chlorite cleavage and orthogonal to it (Czamanske, 1988; Parry and Downey, 1982). Considering that the sum of octahedral cations in the samples is very close to 6, which indicates that all octahedral sites are occupied by divalent cations and are of triple octahedral type (Xie et al., 1997). Although the existence of a vacancy cannot be proven with certainty (Jiang et al., 1994), but with the help of the structural formula of ideal chlorite, the vacancy is calculated as 0.26-0.66 apfu (Xie et al., 1997).

The formation conditions of chlorite reflect its structure and chemical composition and can be used as a geothermometer (Jiang et al., 1994). The crystallization temperature of chlorites with the help of T-Al (IV) diagram (Cathelineau, 1988) is in the range of 379⁰C -305⁰C, with an average of 353⁰C and does not show much change. As the available data, display it can be said that by moving away from the granitoid intrusive bodies, the formation temperature of chlorites decreases. Therefore, the points located in the far area and in the metamorphic rocks with ore have a lower formation temperature. The existence of an inverse correlation between the crystallization temperature of chlorites and their silica content can be due to the substitution of silica instead of aluminum. The fluid inclusion studies on the quartz mineral co-growing with the chlorites of the Dalayon area shows the thermal range of homogenization between 305 and 384 ⁰C with an average of 345.6⁰C, which is consistent with the temperature of formation obtained through thermometric chlorites and indicates the effectiveness of the thermometer by chlorites. The fluid inclusions studies and chlorite thermometry show the influence of mesothermal or orogenic hydrothermal fluids in the formation of chlorite and placement within the skarn range, which confirms each other and is consistent with mineralogical studies and field observations. Overall., the formation of chlorite under study at a temperature equivalent to the high temperature of the hydrothermal stage of granites demonstrates the influence of hot fluids derived from the granitic magma and the metamorphic function in the formation of chlorite.