فصلنامه زمین شناسی اقتصادی
سال یازدهم شماره 2 (پیاپی 21، تابستان 1398)

The pseudo-section method, first proposed by Hensen (1971), is used today by scientists to determine the thermodynamic conditions of mineral crystallization and modeling in metamorphic lithology (Hoschek, 2004; Omrani et al., 2013). The principle of this method is based on the fact that in order to have a complete chemistry of a rock sample with certain minerals in equilibrium, only one equilibrium pressure and temperature can be considered. However, the whole rock chemistry is fixed, mineral changes show some changes in temperature and pressure and new thermodynamic conditions. The superiority of using the pseudo-section method of temperature and pressure calculation is knowing the composition of minerals (microprobe data). By knowing the whole chemistry of the rock and the type of minerals found in the rock, the range of temperature and the pressure of rock formation can be determined. However, possession of mineral chemistry data and microprobe data can help us in more advanced computing and modeling. Accessing the whole rock's chemistry data is easier and calculating the temperature and pressure by pseudo-section methods has high capabilities (Moazzen et al., 2015). This paper investigates the results of this method for calcsilicate hornfelses of the Cheshne area of Hamedan. In this study, the theriak-domino program and the thermodynamic data database of minerals (Powell and Holland, 1988) have been used. In this research study, we tried to determine the temperature and the pressure for the studied rocks by using the two software: Thermocalc and Theriak-domino. Furthermore, the zoning of garnet and clinopyroxene have been studied by the pseudo-section method. After a careful examination of the area, a number of samples were taken. Sampling was done based on the collection of the best samples that represent the whole of the studied rocks. After the preparation of thin sections of suitable samples, according to the objective of the study, three samples of calc-silicate hornfels of Hamedan area were selected for chemical decomposition of the main elements. During the sampling, samples were taken from fresh and non-rough sections of the rock and were selected such as to represent the actual changes in their chemical composition and mineralogy. These samples were sent to Kanpajoh for analysis. The main elements were analyzed by the X-ray fluorescence (XRF) method. In addition, it should be noted that the data from chemical minerals, which was presented in the article by Ghorbani et al. (2016)+, was used in this study (Ghorbani et al., 2016). The major oxidative disintegrations in three samples of calc-silicate hornfelses show that the most abundant oxide in these samples is SiO2, which averages about 45.04. Decreasing calcium in the Grossular garnets can indicate a decrease in pressure. In fact, by describing the garnet in calcsilicate rocks in the Hamedan area, a prograde metamorphism has been created that has reduced the amount of this element after decreasing the temperature and pressure due to the retrograde metamorphism and the uplift and removal of pressure of the upper floors and the influence of the fluids. The combined variations of the garnets are in the Grossular range. The Garnets are the ultimate members of the Pyrope, the Almandine and the Spessartine poor (Ghorbani et al., 2016). The combination of clinopyroxenes in the En-WoFs graph shows that most of the analyzed points are located within the diopside (Ghorbani et al., 2016). We supposed that all solid solution minerals were pure final members, and unit activity for solid solution phases (such as diopside and garnet) and pure phases (such as quartz). Then, the equilibrium reactions at 3.3 kb pressure were calculated by the Thermocalc software and plotted on P-T charts. The calculated temperature for the garnet and clinopyroxene minerals was calculated to be about 550 ° C and the calculated pressure was 2.5 to 3.5 kb. In this paper, using the whole rock chemistry and minerals chemistry, the method of calculating the temperature and pressure was applied to the pseudo-section method. For this purpose, the percentage of the main oxides was calculated as the molar percentage of the elements, then molar percentage of the elements was used as input for the Theriakdomino program. The pressure and temperature calculated by the Theriak-domino software package are from 2.5 to 3.5 kb and 500 to 550 degrees C, respectively.
References.

Three fundamental goals will be followed in the study of metamorphic terrains including: 1- study of fabric in metamorphic rocks in order to recognize the relationship between metamorphism and deformation, 2- the identification of thermodynamic conditions of metamorphism for evaluating the geothermal gradient, and 3- study of protolites of metamorphic rocks and the recognition of Paleo-tectonomagmatic setting of igneous rocks. Takab-Takht-e-Soleyman-Angouran metallogenic –metamorphic zone located parallel to the Zagros suture zone within the Alpine–Himalayan orogenic belt. Halab metamorphic sequence is located in the Eastern part of this zone. This metamorphic sequence is composed of pelitic, mafic and felsic schists intercalated with marble, mylonitic rhyolite and quartzite which are metamorphosed in amphibolite and green schist facieses. Takab-Takht-e-Soleyman-Angouran metallogenic –metamorphic zone is one of the most important metallogenic zones in Iran. The Zarshouran As–Au deposit, Aghdareh Sb–Au deposit and Angouran Zn–Pb deposit along with some Fe, Pb–Zn, Au, Cu and Mn mineralization were formed within this zone. Most of this mineralization was studied during the past years and valuable information is present about their geological and mineralization characteristics. However, geochemistry and tectonomagmatic settings of metamorphosed volcanic rocks (felsic and mafic schists) were not studied. This research can be divided into two parts including field and laboratory studies. Field studies include the recognition of different metamorphic rocks along with sampling from metamorphic rocks for laboratory studies. In this base, 40 samples were chosen for petrographic and analytical studies. Twenty thin sections were used for petrographic studies and recognition of metamorphic fabrics. For geochemical studies, thirteen samples from felsic and mafic schists were analyzed by XRF and ICP–MS methods in GSI and Zarazma laboratories. Mafic schists are one of the most important metamorphic rocks in the Halab area. Compositionally, these rocks include actinolite schist, hornblende schist and amphibole schist. Felsic schists are the other important rocks in the Halab metamorphic sequence. These rocks include albite-quartz schist, biotite-quartz schist, amphibole-biotite-quartz schist and mylonitic rhyolite. Geochemically, mafic schists show a similar composition to basalt, trachy-basalt, basaltic andesite and basaltic trachy-andesite while felsic schist show rhyolitic composition. All of these rocks have calc-alkaline to high-K calc-alkaline affinity.  Trace elements normalized by primitive mantle (McDonough and Sun, 1995) and NMORB (Gale et. al., 2013) for felsic schists indicate LILE enrichment along with negative HFSE anomaly and distinctive positive Pb anomaly. A similar pattern is observed for most of the mafic schists. Amphibole schists do not show LILE enrichment, as well as positive Pb and negative HFSE anomalies. Chondrite-normalized (McDonough and Sun, 1995) REE patterns for felsic schists demonstrate LREE enrichment along with negative Eu anomaly and flat HREE patterns. Most of the mafic schists have similar patterns without negative Eu anomaly. Amphibole schists indicate a flat REE pattern with less LREE enrichment and relative enrichment in HREE compared with other mafic schists. Comparison of Chondrite-normalized REE patterns of mafic schists with NMORB and EMORB patterns and island arc basalts (Gale et al., 2013) indicate that basic schists of Halab area have similar patterns to EMORB. Based on Ta/Yb vs. Th/Yb and Yb vs. Th/Ta discrimination diagrams, protolites of mafic schists were formed in within plate volcanic zone and active continental margin while protolites of felsic schists were formed within active continental margin. On the Nb/Yb vs. Th/Yb diagram, mafic schists belongs to subduction-unrelated setting and originated from mantle similar to OIB source.  Takab-Takht-e-Soleyman-Angouran metallogenic –metamorphic zone is considered as a micro-continent with similar features to Gondwana (Hajialioghli et al., 2007). The oldest outcrops of metamorphic rocks in this zone are the result of metamorphism of magmatic arc rocks with Neo-Protrozoic–Early Cambrian age (Saki, 2010). As it was mentioned before, mafic and felsic schists of the Halab area demonstrate calc-alkaline to high-K calc-alkaline affinity. High-K calc-alkaline rocks are usually formed in magmatic arcs and post collision setting and are less seen within plate setting (Bonin, 2004). Enrichment in LILE and LREE along with Nb and Ti negative anomalies in spider diagrams are indicators of subduction related magmas which are originated from enriched mantle by metasomatic fluids released from subducted slab (Wang and Chung, 2004). Geochemical characteristics of mafic and felsic schists of the Halab area indicate that the protolites of mafic schists originated from partial melting of metasomatized mantle by past subduction in an extensional setting within a magmatic arc. Felsic schists are the result of crustal partial melting by mentioned basaltic magma.

The Mashhad- Virani complex has been sandwiched between the collided Lut block and Turan plate. This complex is composed of the following four units: 1) ultramafic-mafic rocks, 2) metamorphosed sedimentary rocks, 3) pyroclastic rocks and 4) Mashhad’s granitoids including quartz-diorite, tonalite, granodiorite and monzogranite (interpreted as granitoids formed in an arc regime during the subduction of the Paleo-Tethys Ocean under the Turan Plate by Karimpour et. al., 2011). The association rocks in the Mashhad-Virani complex have experienced varying degrees of hydrothermal alteration and regional metamorphism. These rocks are typically metamorphosed in lower to upper green-schist facies, but rarely to pyroxene hornfels facies along the contacts with the Mashhad granitoids. Researchers have challenging ideas on the nature of these rocks. Firstly, Majidi (1981) reported the komatiitic nature of these rocks. However, most of the geologists believed that these rocks are a part of an ideal ophiolitic sequence (Alavi, 1979; Fazel-Valipour, 2002). However, some geological studies have provided strong evidence that contradicts the ophiolite nature of these ultramafic- mafic rocks. Detailed studies of this research show that according to the petrological issues, field relationships, textures and internal stratigraphy, these rocks are not only an ophiolitic sequence but are also an ultramafic- mafic volcanics precisely named komatiite. In this complex, although the contact of the ultramafic rocks with the adjacent sediments is not visible in the majority of cases due to the coverage of Quaternary sediments and tectonic processes. However, this contact is partly preserved in the Khurshid Park and Zuh peak where there is some evidence of ultramafic lava eruption on the sediments. In these places, sediments in the border with komatiitic rocks has been clearly baked. They also have very interesting skeletal, microspinifex, and harrisite textures. These observations suggest that the ultramafic rocks in the Mashhad-Virani complex are ultramafic volcanic flows. Field studies have been carried out in more than twenty cross sections in the southwest-northwest of Mashhad. More than 400 thin and polished sections were made from rock samples and studied in the petrography laboratory of the Faculty of Earth Sciences at the Shahrood University of Technology. Moreover, after detailed petrography studies, five samples with the least alteration were selected for preparing polished thin sections. Major element analyses on selected minerals (amphibole, plagioclase, pyroxene and olivine) were performed on a JEOL EPMA JXA-8900R electron microprobe at the Institute of Earth Sciences, Academia Sinica, Taiwan. Analytical conditions included an accelerating voltage of 15 kV, a beam current with 2μm diameter of 12nA and counting times of 10s on peaks and 5s on the background. For calibration of all elements, a set of mineral and synthetic standards has been used. The Mashhad-Virani complex includes an assemblage of ultramafic-mafic rocks with approximate length of 32km along the western side of the city of Mashhad. This complex consists of dunite, ortho- meso and crescumulate (harrisite) wherlite, clinopyroxenite, cumulative and noncumulative amphibole gabbro and differentiated- undifferentiated komatiitic flows. These komatiites have been shown with a wide range of textures such as random acicular pyroxene, hopper and chevron olivine, hopper pyroxene, skeletal olivine, skeletal pyroxene, micrographic intergrowth of plagioclase and clinopyroxene, dendritic pyroxene, olivine harrisitic, olivine orthocumulate, olivine mesocumulate, and olivine adcumulate textures. The rate of cooling and thermal gradient in the volcanic rocks along with super-saturation, exsolution of volatiles and magma mixing in the sub-volcanic rocks are the most important controlling factors in creation of these disequilibrium textures. Amphibole gabbro sills are one of the main magmatic units of the upper parts of the lower horizons in the Mashhad-Virani complex. After detailed petrographical studies, five samples were analyzed for mineral chemistry measurements. In this study, only the composition of clinopyroxenes has been used for thermobarometry studies. Based on the obtained results, the clinopyroxenes are in the range of Ca-Mg-Fe sub-types in the Q-J diagram and in the diopside to augite fields on the Wo-En-Fs ternary diagram (Morimoto et. al., 1988). The results of the thermo-barometeric calculations by single clinopyroxene method indicate mean temperature of 1222°C and pressure of 2.4 kb that are in concord with the dyke and sill forms of gabbroic outcrops and also are very close to the crystallization temperatures of these magma types. Skeletal, spinifex and harrisite textures are the first unequivocal evidences reported from komatiitic sills and lava flows in the Mashhad-Virani Complex. These rocks are a part of the upper Paleozoic volcano-sedimentary sequence with approximately 32km length with NW-SE trend in the South and Southwest of Mashhad. This complex consists of dunite, ortho- meso and crescumulate (harrisite) wherlite, clinopyroxenite, cumulative and noncumulative amphibole gabbro and differentiated- undifferentiated komatiite flows. Application of the thermobarometry calculations on the single clinopyroxene from the amphibole gabbros (average pressure of 2.4 kb and average temperature of 1222 °C) are highly acceptable and consistent with the field and petrographic evidences.

The Cheshmeh Khuri area is located in the north of the Lut Block volcanic–plutonic belt, in eastern Iran, about 111 Km northwest of the city of Birjand. Extensive Tertiary magmatic activity in the Lut Block, is spatially and temporally associated with several types of mineralization events (Karimpour et. al., 2012). The episode of Middle Eocene to lower Oligocene (42–33 Ma) was very important in terms of magmatism and mineralization (Karimpour et. al., 2012). The North Khur area includes numerous cases of Cu±Pb±Zn vein-type mineralization, such as the Shikasteh Sabz, Mir-e-Khash, Rashidi, Shurk, Ghar-e-Kaftar, Howz-e-Dagh, as well as kaolin deposit (Cheshmeh Khuri area). We present and discuss alteration, ore petrography, geochemistry, fluid inclusion micro thermometry, and sulfur isotope geochemistry, which help clarify the ore genesis of the Cheshmeh Khuri area. The present study involves detailed field work and study of thin and polished sections from the intrusive rocks and ore samples under the optical microscope. Metal concentrations were analyzed at the IMPRC laboratory of Iran using the ICP-OES techniques on fifteen samples. Five samples were analyzed for Fire Assay analysis and four samples for XRD analysis at IMPRC laboratory of Iran. Twelve spot analyses (microanalyses) were performed on an X-ray Analytical Microscope at IMPRC laboratory. Doubly polished wafers (150 μm thick) were prepared from five samples taken from surface and trenches. Micro thermometric measurements were carried out using a Linkam THM 600 heating–freezing stage mounted on an Olympus TH4–200 microscope stage at the Ferdowsi University of Mashhad, Iran. Two pyrite samples from quartz-sulfide veinlet were analyzed for the sulfur isotope compositions after careful hand picking and purification at Iso–Analytical limited, United Kingdom. The main alterations consists of propylitic, argillic, quartz-sericite-pyrite and silicified. The mineralization is mainly observed as vein and is disseminated in quartz-sericite-pyrite, argillic- silicified and propylitic alteration zones and is disseminated in the argillic alteration zone. Pyrite is the only primary sulfide mineral in the area. Due to the great influence of weathering processes on the primary ore, secondary sulphide and oxide mineralization (malachite, azurite, chalcocite, covellite, goethite, and hematite) are widely spread and have finally created lithocap (Sillitoe, 1993; Sillitoe et. al., 1998). The maximum anomalies of copper (654 ppm) and lead (1622 ppm) are associated with quartz-sericite-pyrite alteration. Primary fluid inclusions of quartz in paragenesis with mineralization in quartz-sericite-pyrite zone, argillic-silicified zone and calcite in paragnesis with mineralization in propylitic zone have an average of homogenization temperatures of 321°C, 305 °C and 263 °C, respectively. Based on freezing studies, the average calculated temperature of last melting point of these is equal to 12, 11.6 and 7.9 wt.% NaCl, respectively. Homogenization temperature and salinity of the fluids shows a shifting trend from relatively high in quartz-sericite-pyrite zone to relatively low homogenization temperatures in the propylitic zone, which can be due to physicochemical changes in the fluid such as cooling and mixing with meteoric water (Naden et al. 2005). According to the textural evidence, boiling has also been effective during the evolution of the fluid. The amount of δ34S for pyrite has a range between 2.35 to 2.46 and the amount of δ34 equilibrium with pyrite has a range of 1.25 to 1.36 that show a magmatic origin for sulfur (Ohmoto and Rye, 1979; Lesage, 2011). The expansion of propylitic and argillic alteration zones on the surface, the limited quartz-sericite -pyrite zone, the absence of potassic alteration, the existence of lithocap, geochemical anomalies, the range of temperature and salinity of the fluid inclusion can be indicative of the upper part of a porphyry copper system.

Podiform chromite deposits are small magmatic chromite bodies formed in the lower section of an ophiolite complex. Podiform chromite mines have produced 57.4 percent of the world’s total chromite production. Most ore bodies are irregularly dispersed and relatively small, between 0.0004 and 1 Mt, averaging 0.011 Mt (United States Geological Survey, 2012), and reserves greater than 1Mt are most uncommon (Evans, 1998).The Khoy ophiolite covers an extensive area in the northwest of Iran along the Iran-Turkey border. This ophiolite zone comprises one of the most promising areas for prospecting of chromite deposits as a result of extensive outcrops of ultramafic rocks. The Kochuk area is located in the western domain of the Khoy ophiolite (Fig. 1). Some geological and geochemical investigations have been carried out for recognition of chromite deposits in this area by the authors during the last 15 years. The geological criteria of prospecting for chromite deposits from the Khoy ophiolite are discussed in this study. In this research, geological methods were used to identify chromite deposits in the Khoy ophiolite. Geological surveys at scale of 1:20000 were implemented in an area of about 70 km2. Lithogeochemical sampling (eighty five samples), petrography (five samples), ore microscopy (eighteen samples) and sampling for determination of specific gravity of ore (eleven samples) were performed in these study. Testing of bedrock mineralization was performed in a relatively straightforward manner by sampling of outcrops in areas where chromite orebodies cropped out or were underlain below a thin soil cover. In contrast, chromite mineralization prospecting in locations with thick cover were carried out by pitting and trenching. Chemical analysis of the samples was carried out by the XRF method in the Kansaran Binaloud laboratory. In this study, geological mapping allows discrimination of ophiolite lithologies (ultramafic rocks, chromitite, basaltic pillow lava, gabbro-diorite, ophiolite mélange, listwaenite and other associated rocks). Ultramafic rocks are important in prospecting for chromite mineralization. Geological prospecting led to the identification of a chromite ore field with a remarkable potential since more than 20 chromite orebodies were recognized. Five mineralized zones called A, B, C, D, E and 13 chromite indices were recognized in the Kochuk chromite field. The A zone is located almost in the central part of the study area. Four ore bodies have been recognized in this zone. The A1 orebody extended by 68 meters in length and 6-9 m in thickness. This subzone is characterized by a lenticular shape with an east-west-trending strike (N115S) and a 60o dipping toward THE south. The B zone is located at ~2.9 km west of the A zone. The B1 orebody consists of the largest known chromite orebody in this area which comprises N120S-trending and 50 NW dipping lenticular geometry extended by 118 meters in length. The thickness of the B1 orebody varies between 6 and 12 meters averaging around seven meters. There are three chromite orebodies recognized as C1, C2, and C3 subzones in the C zone. The C1 orebody is composed of 74 meter-long lens with variable thickness between 3.5 and 9 meters. It has a N40E-trending strike, which dips 45-50 degrees to the west. In the D zone, three small chromite orebodies have been identified. The D1 orebody consists of a 20 meter-long lens ranging from 1 to 5 (avg. 3.5) meters in thickness. This orebody is oriented by a N160S in strike and a 50 NE in dip. The chromitite occurrences have lenticular, tubular and vein-like shapes host by hurzburgite. Rocks of the upper mantle-lower crust transition zone and probably the associated chromite deposits have not been recognized yet in this area (Imamalipour, 2011). The typical ore textures consist of disseminated, nodular, massive, banded and cataclastic. Exploration of podiform chromite deposits has been a challenge due to their unpredictable occurrence, the small size of most orebodies and the intensive tectonic dislocations (United States Geological Survey, 2012). Moreover, the absence of primary geochemical halos and associated alteration are matters that have led to difficulties in prospecting for podiform chromites. Chromite as an accessory mineral is associated with harzburgite host rocks. This mineral is released during the weathering process and is accumulated within the stream sediment heavy minerals. Therefore, application of the stream sediment geochemistry method may not necessarily result in useful information for determining the location of chromite outcrops. In this study, geological methods were used for podiform chromites prospecting which culminated valuable results. The Kochuk chromite-bearing area was recognized as a chromite ore field in the western city of Khoy. The most important geological criteria of prospecting for chromite deposits from the Khoy ophiolite are: 1) chromite bodies are surrounded by dunite envelopes with variable thickness; 2) the recognized chromite-rich zones are mainly located near gabbroic intrusions; 3) most chromite lenses are oriented along an east–west trend; 4) the existence of chromite fragments on stream beds can be considered to be a suitable sign to define the entry of these anomalous rocks to the stream sediment; 5) morphologically, chromite outcrops often occur protruding from the host rock because of their higher resistance to erosion. This can facilitate the recognition of their outcrops; 6) chromite bearing zones usually do not have or exhibit thin vegetation cover despite the high rate of annual rainfall; 7) outcrops of disseminated ores can indicate the presence of high grade chromite ore in the sub surface parts; 8) the main oxide contents of chromite ores vary from an individual ore body to another one.

Clinopyroxene is one of the most common of the rock forming minerals. Its long formation period (from the earliest crystallization of magma in the core of phenocrysts to the final microcrystalline crystallization in the rock background) can show the history of the host magma crystallization. The composition of clinopyroxene, especially those phenocrysts, in volcanic rocks could well establish the magmatic nature of the host lava.The clinopyroxene composition can point out the magmatic series, the tectonic environment and the source rock (Kushiro, 1960; Nisbet and Pearce, 1977, Leterrier et al., 1982). In addition, it is possible to estimate the temperature and pressure of rock formation by studying the chemistry of clinopyroxenes (Nimis and Taylor, 2000; Putirka, 2008).The study area is located in the middle part of the Urumieh- Dokhtar magmatic belt. It exactly lies in the area between Tarq and Mazdeh, its longitude is 51° 43' to 52° 00' E and its latitude is 33° 15' to 33° 30' N. The Eocene magmatic rocks vary from rather basic to acidic in composition, but they are mainly intermediate and they are rather basic rocks (Ghadirpour, 2017). Previously, various studies on using the chemical composition of the major elements of clinopyroxene were conducted to discover the conditions for the formation of igneous rocks in different parts of Iran (Sayari and Sharifi, 2016; Falahaty et. al., 2016; and Mohammadi et. al., 2017).So far, in all of these studies that have been conducted on volcanic rocks, the mineral chemistry of clinopyroxene has not been used to evaluate the magma's features such as temperature, pressure, and oxygen fugacity. In this article, we are going to study the mentioned features of magma by using chinopyroxene chemistry. To determine the geotectonic setting and the physicochemical conditions of volcanic rocks, thirty thin sections have been prepared. Their minerals and texture have been studied by using polarizing binocular microscope (Olympus BH-2). After detailed mineralogy and selection of suitable samples, microprobe analysis is done by EPMA (JEOL- JXA) in the Naruto University, Japan. The mineral analysis is performed at 15 nA intensity of current and accelerate voltage of 15 Kev. The study area is situated in the South of Natanz, between Tarq and Mazdeh villages. The volcanic rocks vary from acidic to rather basic (basaltic andesite to andesite and rarely rhyolite). Microlitic porphyric, glomeroporphyric and vesicular are some textures which are observed in the volcanics. Plagioclase and euhedral clinopyroxene occasionally with simple twinning are characteristic minerals of rocks.According to Wo-En-Fs diagram (Morimoto, 1989), clinopyroxene shows mainly the composition of augite.It is concluded that the magmatic series of rocks is calc-alkaline which is in relation to the subduction of the Neotethys oceanic crust under the central Iranian plate.There are several diagrams that are used for this purpose which are as follows.The Al2O3-Ti2O diagram (Le Bas, 1962): In this diagram, the studied clinopyroxene shows the nature of calc-alkaline. One of the diagrams used to determine the tectonic setting according to clinopyroxene composition is the F1- F2 diagram (Nisbet and Pearce, 1977). Based on this diagram, the Tarq- Mazdeh volcanic rocks belong to the magmatic arc environment.The Clinopyroxene temperatures are calculated by using a variety of methods which indicate that most of clinopyroxene in temperature range of 1150 to 1200°C has been crystallized (Soesoo, 1997). The temperature indicates changes in crystallization of clinopyroxene. The calculated temperatures of clinopyroxenes by using various methods show that they are crystalized in the temperature range of 1150 to 1200˚c. It mainly means that there is a change in temperature during clinopyroxene crystallization. By considering the barometric diagram, the pressure of clinopyroxene formation has been determined below 10 kb, in the depth range of 2 to 5 km.

The rare earth elements (REEs) are classified into light (La, Ce, Pr, Nd, and Sm), medium (Eu, Gd, Tb, Dy, and Y), and heavy (Ho, Er, Tm, Yb, and Lu) groups (Seredin and Dai, 2012). Goldschmidt (1933) was the first to study the REEs in coal in some detail. In recent years, REEs in coal have received much more attention owing to their stable geochemical characteristics and potential economic value (Seredin, 1996; Seredin and Dai, 2012; Rantitsch et al., 2003; Fu et. al., 2010). Coal deposits have since become an important alternative source for REEs (Seredin and Dai, 2012; Hower et al., 2016), However, unusual REE anomalies in coal basins have not attracted special attention, because it seems that there are sufficient resources of these metals in conventional deposits (e.g., carbonatites, alkaline granites, and weathering crusts) ( Seredin and Dai, 2012). The aim of this study is to assess REE content in the South Kouchek -Ali coal mine, located in the Central Iran Coal Basin, about 65 km southwest of the city of Tabas.   Samples were collected from the South Kouchek-Ali coal mine that includes 3 coal samples, five coaly shales. The samples were analyzed by X-ray fluorescence spectrometry (XRF) for major elements. REEs were analyzed by inductively coupled plasma mass spectrometry (ICP-MS). The concentration of rare earth elements of the South Kouchek-Ali coal mine may have resulted in background rare earth elements in the primary mineral matter. The concentration of rare earth elements of south kouchek -Ali coal mine has been determined, and the range of these elements in representive studied samples is compared with the worldwide, Chinese and USA coals. Rare earth elements show positive correlation with major elements, indicating that these elements are mainly associated with clay mineral. Positive correlations of ∑REEs with Al2O3, SiO2, and TiO2 suggest that the REEs are mainly derived from detrital sources and occur dominantly in kaolinite and illite. The concentrations of ∑REEs in representative samples range from 69.54 to 113.06 ppm with an average value of 127.94 ppm, higher than the average ∑REE content of the USA (53.59 ppm) (Finkelman, 1993) and worldwide coals (68ppm) (Yudovich and Ketris, 2006), but lower than that of average Chinese coals (162.51 ppm) (Dai et. al., 2008). The abundance of light rare earth elements is higher relative to heavy rare earth elements. Light rare earth elements may have resulted in high background LREEs in primary mineral matter. The South Kouchek-Ali coal mine occurs in the Middle Jurassic Hojedk Formation, and is located in the western part of the Tabas coalfield. The Hojedk Formation mainly consists of shale, sandstone and carbonate rocks. The concentration of rare earth elements of the South Kouchek-Ali coal mine has been determined, and the range of these elements in coal samples studied is compared with the worldwide types of coal. The Ozbak-Kuh granites have been identified at the north of the Tabas Coal Basin, and Narigan, Zarigan, Chadormalou, and Saghand granites have been identified in the west of the Tabas Basin. During the accumulation of coal-bearing formations, the supply of terrigenous materials originated from here (Pazand, 2015).

The study area is located in 180 kilometers at the South of the city of Birjand and at 4 kilometers North of the Qhaleh-Zari mine, within the Central Lut Block. According to Stocklin and Nabavi (1973), the Lut Block (Eastern Iran) extends over 900 km in a north-south trend and is 200 km wide in an East-West direction. It is confined by the Nayband fault and the Tabas Block on the west, Nehbandan Fault in the east, Doruneh Fault in the north, and the Jaz- Morian Basin in the south. The sixty- five percent of the exposed rocks within the Lut Block consist of volcanic and plutonic rocks (Karimpour et al., 2011). The extensive magmatism of the area has resulted from the west-dipping subduction of the Lut Block zone (Karimpour et. al., 2005). The Koodakan area is located in the north of the Qhaleh-Zari mine, and in fact, it is comprised of the continuation of Qhaleh-Zari mineralization type. In the study area, rock units include Tertiary volcanic, intrusive, subvolcanic, and pyroclastic rocks. The samples were collected from the study area focusing on the vein mineralization for preparing geology, mineralization and geochemistry maps. In addition, the dip and direction of the faults were measured for preparing structural map. Ten samples were analyzed for thirty six elements using Inductively- Coupled Plasma-Mass spectrometry (ICP-MS) in the Zar- Azma Laboratory, Mashhad, Iran. Petrographically, the rocks in the area consist of granodiorite, dioritic dikes, andesite and andesite- basalt. The volcanic rocks have extended throughout the study area and are mainly affected by various intensities of propylitic and/or carbonate alterations. The volcanic rocks are mainly andesitic in composition. Based on field observations and microscopic evidence, volcanic rocks can be subdivided into andesite, hornblende andesite, andesite- basalt and pyroxene andesite. Diorite porphyrtic dikes swarms are the youngest units in the area, and are not related to mineralization. Propylitic alteration comprises dominant alteration in the Koodakan 2 area and is characterized by epidote, chlorite and calcite mineral assemblages. Argillic alteration is locally present within the surface outcrops. Silicification is mainly cropped out in both adjacent to mineralized veins, and to a lesser amount, as pervasive silica. Mineralization is mainly controlled by a system of faults and joints. Three trends of faults are identified in the area including the a) NW-SE. b) NE-SW. c) E-W. The NE-SW trending mineralized veins represent a northeast dip ranging from 60- 70, and a width between 5 cm to 3 meters. In most cases, mineralization is hosted by pyroclastic units (especially agglomerate) or in the contact between agglomerate and andesitic rocks. At least three styles of veins were identified in the area. These are 1) quartz+ specularite+ chalcopyrite ± galena ± pyrite veins. The thickness of these veins varies from 2 cm to >1 m. The type 1 displays a dominant NW-SE strike. Quartz comprises of the most common mineral assemblage within the three types of veins forming uhedral to subhedral crystals with 1-10 cm long. Sulfide mineral dominantly includes chalcopyrite which is weathered to chalcocite at margins- together with galena, and pyrite. 2) quartz+ Fe oxides (limonite) veins range in thickness between 20 cm-1 m, and their ore mineral contents are not as important as types. 3) The NW-SE trending late carbonate veins mainly occurred in northern parts of the study area. These veins do not contain any ore minerals. Based on lithogeochemical studies, the concentration of Cu in mineralized veins ranges from 75-9928 ppm. The highest grade of Cu is related to quartz + malachite ± Fe oxide veins, and the lowest grade is related to silicified- Fe oxide veins. The geochemical abundances of Pb are similar to that of Cu and mainly vary from 7ppm to >3%.Highest concentrations of Zn are consistent with type 1 veins, and range from 25- 109285 ppm. Arsenic represents a widespread distribution of halos in the studied veins and its content varies between 5 and 424 ppm. Based on geology, mineralization, and geochemistry data, mineralization of the Koodakan 2 area is comparable with the veins in the Qaleh- Zari deposit and can be classified as IOCG deposit type. Detailed studies including the fluid inclusion, electron microprobe, and stable isotopic investigations can be further applied to examine the type of mineralization in the Koodakan 2 area.