فصلنامه زمین شناسی اقتصادی
سال یازدهم شماره 3 (پیاپی 22، پاییز 1398)

According to Hitzman et al. (2005) and Hayes et al. (2015), the sediment-hosted copper deposits (SHC) are stratiform disseminated to veinlet copper mineralization within the reduced black shale, sandstone, and carbonate rocks. These deposits have formed during the middle-late Paleoproterozoic (e.g., Udokan, Russia: Volodin et al. 1994, Yinmin, South China: Zhao et al. 2013) to Tertiary (e.g., Corocoro, Bolivia: Flint 1989). The SHC deposits, frequently labeled as “stratiform” or “stratabound” and/or “diagenetic” deposits have been subdivided into three types (Cox 1986, Cox et al. 2003, Hitzman et al. 2005): 1- reduced-facies (RF), 2- Redbed (RB) and 3- Revett (RV). There are several SHC deposits in the Zanjan region hosted by the Upper Red Formation. The Chehrabad, Cherlangoush, Ghezeljeh, Halab, Ortasou and Sarikand deposits are the most important ones and are well-developed in this district. These deposits consist predominantly of bedding-parallel replacement and disseminated Cu-Pb-Zn sulfides, roughly concordant with stratification. The average Cu and Pb values of these deposits are ~3 and 2 wt.%, respectively. These deposits are small but they are actively mined at present. The aim of this work is to expand knowledge on the geological framework, mineralization features, geochemistry and genesis of the Ortasu Pb-Zn deposit. The study of the Ortasu deposit can be used as an exploration model for similar deposits in the Zanjan district and other places.

Detailed field studies have been done at different scales in the Ortasou area. Polished thin and thin sections from mineralized zones and host rocks were studied by conventional petrographic and mineralogic methods at the University of Zanjan. Furthermore, a total of six samples from mineralized host rocks were analyzed by ICP-MS for major and trace elements and Rare Earth Elements (REE) at Lab West Co., Australia.

The Ortasu Pb-Zn deposit is located in the northwest of Zanjan and Central Iran zone. The outcrop formations in this region involve Lower Red, Qom and Upper Red Formations from which the Upper Red Formation hosts the mineralized zones. In this region, the Upper Red Formation consists of alternation of red to brown and grey to greenish marl associated with interbedded sandstone sequences. Based on petrographic studies, composition of the mineralized host rocks are litharenite which consist of sedimentary, metamorphic and igneous fragments, quartz and feldspar. In the Ortasu Pb-Zn deposit, mineralization has occurred within two horizons of reduced-grey sandstone with about five to six m thickness and about 100 m length. These horizons contain both red oxidized zone and bleached zone with a mineralized reduced subzone which is located within the bleached zone. The red oxidized zone consists of red marl and sandstone layers containing iron oxides which is located adjacent to the reduced horizons. The red color of this zone is caused by the presence of iron oxides around the grains. The oxidized pyrite crystals are the main important minerals in this zone. The bleached zone is part of sandstone sequences whose color has changed by the alteration processes. Grey and green colors in the bleached zone have occurred due to the presence of organic materials and diagenetic pyrites. The mineralization subzone has occurred within the organic materials-bearing bleached zones. Plant debris, plant fossils, diagenetic pyrites and permeability of host rock have the main important role for Pb-Zn mineralization. Galena, sphalerite, pyrite and chalcopyrite are the main important minerals in the Ortasu Pb-Zn deposit in some parts. They have been replaced by secondary minerals such as cerussite, chalcocite, covellite and iron oxides due to the supergene and weathering processes. The most important textures in this deposit are disseminated and cemented textures. It should be mentioned that the laminated-like, framboidal pyrite, replacement and relict textures are also observed in this deposit. The presence of fining-upward sequences is due to the sediment cycles of channels, layered structures, abundant organic materials in paleochannels and debris of plant fossil all of which indicate that the Ortasu Pb-Zn deposit is formed in a continental to tidal environment. Geochemical studies show that the sandstones were deposited in an active continental margin. These sandstones originated from felsic magmatic rock and were deposited in an arid climate condition. According to host rock, geometry, structure and texture, and mineralogy it can be concluded that the Ortasu Pb-Zn deposit has more similarity with the distal parts of Redbed type of sediment-hosted copper deposits

More than 300 sediment-hosted Zn–Pb deposits and occurrences have been recognized in Iran (Rajabi et al., 2013). Most of these deposits are concentrated in the Central Alborz, Tabas-Posht-e-Badam, Malayer-Esfahan and Yazd-Anarak metallogenic belts (Rajabi et al., 2012). Several Pb–Zn deposits and occurrences such as Tarz, Tappeh-Sorkh, Deh-Askar, Abheydar, Gicherkuh, Ahmadabad (BonehAnar), Gujer, Karvangah, Tajkuh, Magasou and Gavar (Javar) occur in Kuhbanan-Bahabad area in the Central Iran zone. The Tarz deposit is situated about 15 km east of the Kuhbanan city in the Tabas-Posht e Badam metallogenic belt. The aims of this study are to investigate ore and host rock petrography, geochemical investigations of ore samples, fluid inclusions in coexisting transparent gangue minerals (calcite) and Microthermometric analysis of fluid inclusions in the various paragenetic stages present in the Tarz deposit. These studies have led to a genetic model of the Tarz deposit.

Ore samples were collected from both mining tunnels and surface outcrops of mineralization. Detailed petrographic studies were conducted on hand specimens, thin and polish sections using reflected and transmitted light microscope. Representative samples were analyzed by using inductively coupled plasma emission spectrometry (ICP-ES) for major and minor elements at the Zar Azma Company in Tehran, following acid digestion. Calcite samples of different mineralization stages were collected from all major orebodies and were prepared as doubly polished sections. Microthermometric measurements were carried out on a Linkam THMSG600 Heating–Freezing stage in Fluid Inclusion, with a German Zeiss microscope.

The primary Zn–Pb sulfide mineralization in the Tarz mine occurs as vein-type and open-space filling, consisting mainly of sphalerite and galena with minor amounts of pyrite and trace chalcopyrite. Wall-rock alteration in the Tarz deposit is also simple and consists of dolomitization and minor silicification. Within the sulfide ore zones, structures consist of massive and vein types and textures consist of anhedral to euhedral granular and open space fillings. Pyrite has cubic form. Calcite occurs as patches in width. In vein ores, sphalerite is also fine-to coarse-grained with anhedral to euhedral. Galena fills vein and fracture. Calcite crystal is an important host mineral among the two hypogene stages. Microthermometric measurements from the Tarz deposit show that ore minerals were deposited at low-temperature (85-196°C), with moderate salinities (18–22.5 wt.% NaCl). The Tarz Zn–Pb deposit has many similarities with the most important characteristics of the Mississippi Valley-type (MVT) deposits (characteristics such as tectonic setting, faults and fractures, the epigenetic nature of mineralization, ore structureand texture, the host rocks, wall-rock alteration and homogenization temperature of fluid inclusions).

The Tarz Zn–Pb deposit is a stratabound, epigenetic hosted in Upper Permian-Lower Triassic (Rajabi et al., 2013) thick sequence of carbonate rocks (dolomitic limestone). Ore mineralogy of the Tarz deposit is relatively simple. The principal economic ore minerals are galena and sphalerite. Other minor minerals include pyrite with trace chalcopyrite. The gangue minerals are mainly dolomite, calcite and minor quartz. Textural evidence shows that the ore minerals have been mostly replaced by carbonate host rocks. Smithsonite and hydrozincite, malachite, hematite, goethite and covellite are secondary minerals that have developed from the primary hypogene Zn–(Fe–Pb) sulfides through weathering. Gossan coexists with Pb–Zn sulfide ores and is usually located in the upper levels of the sulfide ores. This ore body is strata-bound and occurs along the fault. Based on crosscutting, overgrowth and replacement relationships, the paragenetic sequence of the Tarz deposit is shown. Calcite and dolomite constitute the carbonate matrix of the ore. Microthermometric measurements were performed on the primary two-phase (L-V) (the ratio of gas to liquid is 2–20%) inclusions larger than 5 μm in diameter that are interpreted as representing the fluids present at the time of hydrothermal mineral growth. The type of inclusions in Calcite is two-phase, liquid-rich that homogenize into a liquid state upon heating. Fluid inclusion shapes are elliptical, rod-shaped, round, or irregular. Homogenization temperatures (Th) values range from 85 to 196°C. The final ice melting temperatures (Tmice) values range from -14.2 to -20.2°C. Salinities of aqueous inclusions were calculated using Bodnar’s (1993) for the NaCl–H2O system and yielded 18–22.5 wt.%NaCl.

The mineralogical and textural characteristics of rock materials have an important influence on physico-mechanical properties. The effects of some textural characteristics like grain size (Brace, 1961), grain shape (Cox and Budhu, 2008), grain surface (Diepenbroek et al., 1992), grain size distribution (Gurkan Ozgurel and Vipulanandan, 2005), and grains interlocking (Hoek, 1965) on physico-mechanical behavior of rock materials has always been emphasized. On the other hand, it has been found that textural properties are originally controlled by the mineralogy and chemistry of rock materials (Locat et al., 1984). Knowing the textural, mineralogical and chemical properties of rock materials and understanding the governing relationships can help us predict the quantitative and qualitative behavior of rock materials. The aim of this study is to investigate the interrelationships among the various textural properties besides the relationship between the textural characteristics and the mineralogy and chemical composition.

All of the major tectonic zones of Iran, except for the Kopet-Dagh, contain Pan-African crystalline basement. Subduction of the Proto-Tethys at about 630 Ma caused Cadomian arc– and backarc magmatism in the northern margin of Gondwana (Hassanzadeh and Wernicke 2016). Sanandaj-Sirjan Zone with NW-SE trend is the most active zone in Iran that extends to the southeast of Turkey and then to Bitlis Massif. There are many similarities between the Precambrian basement in the zone from Iran with Bitlis and Menderes massifs from Turkey. The study area is a part of a large-scale ductile shear zone, containing a wide range of metamorphic rocks with sedimentary and magmatic origins. Metasedimentary rocks comprise of paragneiss, various schists and meta-carbonates that have cropped out through the shear zone which extends along the Zayandeh-Rood River. Metabasic rocks of the North Shahrekord Metamorphic Complex (NSMC) are composed of amphibolites, garnet amphibolites and eclogites as lenses in metagranitoid bodies and other metamorphic rocks. The work is focused on the origin of the eclogites based on field geology, petrography, geochemistry and Sr-Nd isotopic ratios. The new petrological and geochemical analyses are presented to show a geodynamic model for the protolith of the eclogites and their relations to Proto-Tethys subduction during Late Neoproterozoic.

After microscopic studies, nine fresh samples were selected for whole-rock geochemical analysis (XRF and ICP-MS analysis) for determining the major trace elements, and REE contents. Six samples were analyzed at Nagoya University (Japan) and three samples were analyzed for XRF at Salzburg University (Austria) and ICP-MS, in ACME lab (Vancouver, Canada).

Chondrite normalized REE diagrams display minor enrichment of LREE in comparison with HREE. (La/Yb)cn ratio varies between 1.7 to 2.7 without Eu anomaly. Primary mantle normalized diagram of trace elements show negative anomaly in P, Ti, Nb and Zr. Initial magma had been a basalt to andesite-basalt composition. Tholeiitic magma are revealed by relatively flat REE patterns and geochemical diagrams for their protolith. The geochemical data of the NSMC eclogites shows compositional characteristics of E-MORB which is composed of a mix of lithospheric and asthenospheric mantle, and final melt segregation has occurred at depths between 10 to 30 km. Spinel was aluminum bearing phase in the mantle. Tectonic discrimination diagrams display that magma is formed in a back-arc basin environment. Studying Sr-Nd isotopes specifies a range of 0.707 to 0.711 for 87Sr/86Sr and 0.5129 as an average of 143Nd/144Nd. ɛNdt varies between 3 to 7. Moreover, the initial 87Sr/86Sr ratios of the samples vary from 0.705–0.709 (Malek-Mahmoudi et al., 2017). The isotopic evidences indicate that the initial magmas are formed from the mixture of EMII and MORB reservoir with a 0.4 to 0.8 influence of the subduction component.

Iranian basement rocks that were affected by the Cadomian orogeny are reported from different zones of Iran with an age range between 630 to 514 Ma (Hassanzadeh and Wernicke 2016). Neoproterozoic rocks of the Gondwana supercontinent, which were formed in a back-arc basin setting, have been reported from some zones of Iran, such as Alborz, Central Iran and Zagros Hormoz complex (e.g. Etemad Saeed et al., 2015; Faramarzi et al., 2015; Hosseini et al., 2015( and also from Turkey (e.g. Gürsu and Göncüoglu, 2005). Ages of the back-arc successions range from 570 to 530 Ma (e.g., Abbo et al., 2015; Shafaii Moghadam et al., 2016). Our geochemical evidences indicate the formation of a continental back-arc basin in Sanandaj-Sirjan Zone during Late Neoproterozoic. The association of eclogites with meta-sedimentary rocks including paragneiss, schist, quartzite, metadolomite and metasandstone, display a shallow marine sedimentary environment. The combination of field observations and chemical composition of the eclogites shows that the protolith of the rocks are formed at a rifted back-arc basin at the Gondwana during late Neoproterozoic to early Cambrian. Then, high-pressure metamorphic phase was affected on the rocks during Early Jurassic (Davoudian et al., 2016).

Located in the NE Iran, the early Tertiary volcanic sequences host a vast stratabound Cu mineralization (manto type), which is likely to be significant economically (Samani, 2002). The Pirmardan copper deposit is located 130 km southwest of Shahrood and is classified as a manto type mineralization, hosted by altered andesite to trachyandesite, volcanic breccia and tuff. The host rock suffers from two kinds of local and regional hydrothermal alterations of sericite- carbonate, and propylitic, respectively. Sulfide minerals occur as disseminated vein and veinlet forms in the host rock. Manto mineralization type in the northeast and central Iran could be a new prospective for the copper deposits subsequence of the Cu porphyry deposits in Iran (Samani, 2002).Our studies focus on the mineralogy, geology, fluid inclusion and ore formation in an attempt to understand the characteristics of ore fluids and mechanisms of ore formation, and to develop exploration criteria for Pirmardan and similar occurrences in the northeast of Iran. 

Various rock types and alteration assemblages, and mineral paragenesis, were characterized by transmitted and reflected light microscopy, X-ray diffraction (XRD) and X-ray Fluorescence (XRF) analysis. Representative samples from drill holes were selected for fluid inclusion studies. Microthermometric measurements were carried out by the linkam stage for heating and freezing system at the Geological Survey of Iran (GSI).

Several mineralized zones with the width of 0.5-20 m and length of 5-300 m have been found in the Pirmardan area.  Mineralization occurs in the shape of vein and veinlet, breccia, stockwork and open space filling. The copper mineralization in the area occurs as strata bound and sulfide minerals are disseminated in the andesitic rock in a depth of 30 m up to 20 m thickness. The ore grade is about 2% and ore minerals include chalcocite, malachite, azurite, hematite, pyrite and chalcopyrite. Based on microscopic and macroscopic studies, the mineralization at the Pirmardan area is divided into two stages: hypogene stage, which is further subdivided into early and main stages; and supergene stage, which includes sulfidation and oxidation stages. Given the results of the geological and geophysical investigations carried out in the study area, six exploration bore-holes were suggested to be drilled to a depth ranging from 34 to 45 m. The results of drilling confirmed a level of mineralization containing amounts of copper. Mineralization in the depth of (0 to 28 m) occurs in the forms of vein and veinlet with a disseminated texture. Fluid inclusions in the veinlet of calcite from the main hypogene stage occur typically as isolated bodies. Homogenization temperatures are between 117 and 400 ºC. The final melting temperatures are between -0.8 and -9.2 ºC, giving apparent fluid salinities of 1.3 to 13.0 % weight NaCl equivalent.

The study area is located in the Pirmardan district along with other manto type Cu deposits in the northeast of Iran that occur mostly in the felsic-intermediate volcanic and pyroclastic rocks of Tertiary range. The geological studies in this area indicate the two main hydrothermal events of copper mineralization and alterations resulting from circulating heated waters (e.g. Oyarzun et al., 1998). It is likely that both of the hydrothermal events have contributed to extensive mineralization in shallow and deeper parts of the subsurface area. Mineralization in the shallow depths is controlled by local faults and fractures. These fractures are mineralized by chalcosite, malachite, pyrite, chalcopyrite and Fe-oxides minerals associated with veinlets of calcite and quartz. Microthermometric data indicate that the ore formation was mainly related to the low to moderate temperatures (117-400 °C) and salinities (1.3 to 13 wt.% NaCl).  The widespread salinity in the Pirmardan area could be explained by the processes of boiling. Mixing and boiling are two important processes during the ore formation in the hydrothermal systems (Oyarzun et al., 1998). The occurrence of hydrothermal breccias and coexistence of fluid-rich and vapor-rich inclusions (Oyarzun et al., 1998) in calcite indicate that boiling is one of the main ore-forming processes, especially during the main hypogene stage in the Pirmardan district. Overall, the host rocks, alteration, ore mineralogy, ore structure and texture and fluid inclusions characteristics in the Pirmardan district are similar to those deposits belonging to the Cenozoic manto type deposits in the South America (Kojima et al., 2003; Wilson and Zentilli, 2006).

The Khunik gold prospecting area is located 106 km south of Birjand, in the Khorasan Jonoubi province. The Khunik area is located in a strategic part of the Lut Block that includes many instances of mineralization such as the Qaleh Zari IOCG deposit (Karimpour et al., 2005; Richards et al., 2012), the Maherabad porphyry-type Cu-Au (Malekzadeh Shafaroudi et al., 2010, 2015), the Cu porphyry type of Dehsalm (Arjmandzadeh, 2011), the  Kooh-Shah (Abdi et al., 2010) and the Hired intrusion-related (reduced type granitoid) gold deposit (Karimpour et al., 2007). According to geology, alteration, geochemistry and mineralization evidence the Khunik area is a hydrothermal breccia gold system. The important styles of mineralization are: hydrothermal breccia, veinlet and disseminated. The maximum gold concentration occurs along the hydrothermal breccia zone. The aim of this study is surface and deep investigation of alteration, mineralization and geochemical characteristics of hydrothermal breccia as the most important part of mineralization in the Khunik area.

Two hundred samples were collected from both surface and drill holes. Mineralization and paragnesis of the system were studied based on 150 polish and thin polish sections. Doubly polished thin sections were prepared for twelve samples containing quartz and calcite. Based on detailed petrography study of the fluid inclusion, representative fluid inclusions were selected for the measurement. Using a Linkam TH600 heating- freezing stage attached to a Zeiss transmitted light microscope at the Ferdowsi University of Mashhad, Iran. six pyrite samples prepared for conventional isotopic analysis were sent to the Isoanalythical laboratory in England.

There are several outcrops of granitoid subvolcanic intrusions as dykes and stocks in the area which intruded volcanic rocks. The subvolcanic bodies consist mainly of diorite, monzonite and monzodiorite. In addition, they include hydrothermal breccia outcrops in the area. Alteration in the Khunik area is related to some intrusives. Exposed alterations at the surface are: propylitic, argillic, hydrothermal breccia and carbonate. Alteration zones at depth are: quartz-sericite-pyrite, quartz- tourmaline, carbonatization and less argillic. Mineralization is related to subvolcanic units with an age of 38.4 Ma. Mineralization outcrops in the central portion of the area are as disseminated, veinlet, and hydrothermal breccia. Hydrothermal breccia is the most important part of the mineralization in the central part of the Khunik area. This zone is about 730×750 meter. The hydrothermal breccia is mostly mosaic to rubble monomictic breccia with hydrothermal cement. Detailed systematic mapping leads us to the recognition of two distinct breccia bases on cement: carbonate- quartz cement breccia and carbonate cement breccia. Mineralization occurs in both clast and cement of hydrothermal breccia and in the truncated veinlet. Metallic minerals are dominantly pyrite, and they contain chalcopyrite and tetrahedrite only in trace amounts. Based on the lithogeochemical data, the concentration of elements are as follows: Au: 2-4600 ppb, Ag: 40-980 ppb, Sb: 6.9-133.5 ppm, As: 0.5-158 ppm, Hg: 0.2-4.95 ppm, Cu: 21-601 ppm, Pb: 4-1485 ppm, Zn: 18-1095 ppm. Geochemical data in the drill cores indicated different anomalies in gold concentration. These anomalies are related to altered subvolcanic units to quartz-sericite-pyrite and hydrothermal breccia. Thermometric analysis was performed on L+V fluid inclusions. The result of Th vs. frequency and salinity vs. frequency plots indicate that quartz and calcite- hosted in the cement of hydrothermal breccia mineralization may have taken place between 300 to 430ºC from a moderately saline hydrothermal fluid (2-12 wt.% NaCl equiv.). The presence of hydrothermal breccia is consistent with boiling. The average calculated δ34S H2S values for clast and cement of hydrothermal breccia are respectively -2.4‰ and 0.9‰ for pyrite that are consistent with a magmatic source for sulfur (Andrew et al., 2008). Gold deposition at hydrothermal breccia is inferred to have been largely by boiling, although mixing with meteoric waters may have also accured.

The Dohneh copper deposit is located northeast of Zanjan within the Tarom subzone and the western Alborz-Azarbayjan magmatic belt. There are several reports of copper mineralization in the Tarom region such as the Aliabad Mousavi-Khanchay Cu deposit (Saeedi, 2015),the Lolan Cu-Au deposit (Zamanian et al., 2016), the Mari Cu deposit (Hosseinzadeh et al., 2016) and the Gheshlagh Cu deposit (Abbaspour, 2017) which make this subzone an important metallogenic zone in Iran. Prior to the present research, there was no detailed study done on the Dohneh Cu deposit. Thus, the aim of this research is to present detailed characteristics of geology, mineralogy and geochemistry of the host rock as well as the origin of Cu mineralization in the Dohneh area. The results of this study can be considered as an exploratory pattern in the Tarom-Hashtjin metallogenic belt in terms of time and space.

Petrographic and mineralogical features of the Dohneh Cu mineralization and host volcanic rocks were determined by studying 52 thin and thin-polished sections. Major and trace element compositions of six volcanic samples (the host of mineralization) were determined by the Iran Mineral Processing Research Center and Zarazma Company using XRF and ICP-MS methods, respectively. Furthermore, four samples were selected for electron microprobe and scanning electron microscope (SEM) analysis in the Iran Mineral Processing Research Center, Karaj.

The main rock units in the Dohneh area include Eocene tuffs and basalts which are related to the Kordkand member of the Karaj Formation. The tuff unit displays basic composition and is comprised of plagioclase, pyroxene, minor olivine and opaque minerals. There are also some basaltic fragments within the tuff unit. The Dohneh volcanic lavas can be divided into two lava flows varying in texture and mineralogy. The amygdaloidal basalt shows porphyritic and amygdaloidal textures and contains plagioclase, clinopyroxene, orthopyroxene, olivine and opaque minerals. The secondary minerals are carbonate, serpentine, epidote, chlorite, zeolite (filling the cavities), sericite and iron oxide. The second lava flow in the Dohneh area is the porphyritic basalt which shows specified porphyry texture which consists of pyroxene phenocrysts enveloped within the fine-grained matrix including plagioclase, olivine and pyroxene. The geochemical features of the Dohneh basaltic lavas show calc-alkaline nature with enrichment in LILE and LREE and depletion in HFSE and HREE. The Dohneh samples show negative anomaly of Nb, Ta and Ti in primitive mantle normalized spider diagrams. This geochemical evidence together with trace element data suggest that the Dohneh lavas have formed through partial melting of metasomatized lithospheric mantle. The status of the Dohneh samples in the tectonic discrimination diagrams shows subduction related magmatism analogous to those reported from the Tarom and Qazvin areas (Nabatian et al. 2014; Asiabanha and Foden, 2012). The Cu mineralization occurred in both amygdaloidal and porphyritic basalt lavas. According to e mineralography studies, the Dohneh deposit includes native copper, native silver, cuprite, malachite and azurite minerals. The minerals occur in the forms of vein-veinlet, open space filling, replacement and residual. The major alteration minerals in the Dohneh deposit include carbonate, chlorite, zeolite, and serpentinite and minor epidote, which have formed as replacement, vein-veinlet and open space filling in the host rocks. The field and microscopic observations, whole rock chemistry and mineral chemistry data from the Dohneh deposit suggest that the mineralization fluids and hot saline aqueous fluids have been generated during the late diagenesis and burial metamorphism in the volcanic sequence. During the ascending of fluids through the fractures and faults, the copper metal leached out of silicate minerals and turned into an elemental Cu2+ which is soluble in the fluid. Then, through the injection of mineralized fluids into the fractures and empty spaces of host rocks which was associated with decreasing pressure, copper and native silver minerals associated with zeolite formed at the end of the diagenetic stage, and in particular in the burial metamorphic phase. Moreover, during the circulation of fluids in the host rock, secondary minerals have formed. Consequently, mineralization of zeolite and part of copper mineralization occurred during burial metamorphism. In the final stages of mineralization and during the supergene and meteoric waters affected the minerals and caused formation of secondary minerals. In the final stages of mineralization and during the supergene and weathering activities secondary minerals have been generated. According to this study and comparing the characteristics of the Dohneh deposit to Michigan copper type deposits, it can be stated that the characteristics of the Dohneh copper deposit is the most similar to those of the Michigan copper deposits.

The majority of recent works accept that agates are formed at temperatures <100˚C (Moxon and Reed, 2006) and consist of a variety of silica minerals. The Reza Abad agates are located 150 km from SE Shahrood in the northern parts of Central Iran structural zone with geographic coordinates of 56˚ 25′ 22.52″ to 56˚ 47′ 2.50″E longitudes and 35˚ 55′ 32.68″ to 36˚ 07′ 5.54″N latitudes. The area is a part of the magmatic belt of northern Central Iran, containing a main period of magmatic activities from Eocene to late Miocene in a subduction related volcanic arc setting (Ghasemi and Rezaei-Kahkhaei, 2015). Analyses of the distribution of trace elements and stable isotopes should provide important information concerning the geochemistry of agate and genetic aspects of agate formation. Therefore, in this study, we tried to study the geochemical characteristics of Reza Abad agates, the origin and formation temperature based on the oxygen stable isotope data.

In this research more than 300 samples of agates were collected and six samples of them and three samples of their host rocks were selected for analysis by ICP-AES and ICP-MS methods. The samples were powdered and sent to ALS Chemex Company in Loughrea, Ireland. The oxygen stable isotope studies have been conducted on six samples in black, green, white, gray, red, and yellow agates. Oxygen isotope analyses were carried out on powdered agate using the conventional fluorination method at the Stable Isotope Laboratory in the Department of Geological Sciences, the University of Cape Town, South Africa.

Geochemistry of the agates The studied agates have 97.1 to 99.6 wt.% SiO2 with minor amounts of Al2O3 (0.01-0.13 wt.%), Fe2O3 (0.01-0.59 wt.%), Na2O (0.01-0.06 wt.%), and CaO (0.05-1.08 wt.%). The amount of aluminum is reduced by increasing the percentage of silica in most agates (except black agates) as illustrated in Figure 6. The amount of sodium oxide in brown, red, yellow and white agates is also reduced by increasing the silica content. The trace element analyses of Reza Abad agates and associated volcanic parent were carried out to obtain more information about the geochemistry of agates and their mineral-forming fluids. For this purpose, trace elements and rare earth element values are normalized to chondrite values. The general REE trend is characterized by a negative slope from La to Nd with enriched light REE contents (e.g., La, Ce). Most of the agate samples show a positive Eu anomaly except for white agates (Figure 7). The Reza Abad agates host rocks show an LREE-enriched pattern on the chondrite normalized REE diagram. The similarities in the shape and slope of the rare earth element patterns of the agates and the host volcanic rocks show that the elements forming the agates may have originated from fluids circulating in the host volcanic rock.