میرعلی اصغر مختاری

Kourcheshmeh Pb-Zn-Cu deposit is located 40 km southwest of Takestan (Qazvin province) and west of the Mardabad-Bouinzahra volcanic belt. The mineralization occurred as Pb-Zn-Cu-bearing quartz veins hosted by early-middle Eocene tuff and lava strata and show a close spatial relationship with the middle Eocene pyroxene quartz monzodiorite body. The main ore vein ranges from 70 to 200 meters long, and 0.5 to 2 meters thick. Pyrite, chalcopyrite, galena, sphalerite, and tennantite-tetrahedrite, accompanied by minor pyrolusite and psilomelane, are the main ore minerals; quartz, calcite, siderite, barite, and sericite-illite are gangue minerals. Goethite, cerussite, smithsonite, malachite, and covellite are formed by supergene processes. The ore minerals formed as disseminated, vein-veinlets, brecciated, comb, crustiform, colloform, plumose, and vug infill textures. Six stages of mineralization can be distinguished at Kourcheshmeh, where Pb-Zn-Cu mineralization occurred as quartz-pyrite-chalcopyrite-galena-sphalerite ± tennantite-tetrahedrite veins and breccias in the second stage. Wall-rock alteration comprises silicification, intermediate argillic, carbonate, and propylitic alteration. Chondrite–normalized trace elements and REE patterns of ore samples, pyroxene quartz monzodiorite body, and fresh host acidic crystal tuff are comparable. This specifies that alteration and leaching of elements from the host volcanic rocks are involved in mineralization. Features of the Kourcheshmeh Pb-Zn-Cu deposit are similar to the intermediate-sulfidation type of epithermal deposits.

Qaraie sub-volcanic dome in the west of Zanjan is part of the Urumieh-Dokhtar magmatic arc in the Central Iran zone. Qaraie dome with columnar joints was intruded into the Upper Red Formation sequence and Kahrizbeik granitoid intrusion with Upper Proterozoic age. Based on petrographical studies, this dome is composed of dacite-rhyodacite and consists of plagioclase, biotite, quartz, as well as occasionally hornblende and sanidine phenocrysts within the fine-grained groundmass. These rocks have a porphyritic texture and present vesicular plus flow textures. On the petrological diagrams, rock units of the Qaraie dome have dacite, rhyodacite, and trachy-dacite composition and indicate high-K calc-alkaline to shoshonitic nature. Based on primitive mantle normalized spider diagrams, samples of the Qaraie dome indicate positive anomalies of LILEs (Rb, Ba, Th, U, K, and Cs) along with negative anomalies of HFSEs (Nb, P, and Ti) together with distinctive positive anomaly of Pb. Chondrite-normalized REE patterns demonstrate LREE enrichment and a high ratio of LREE/HREE. Samples from the Qaraie dome demonstrate geochemical similarity with adakites and are classified as high-silica adakites. These rocks resulted from 25% partial melting of the Lower continental crust with garnet-amphibolite composition in a post-collisional setting.

Tozlou Pb-Zn mineralization, ~250-300m long, and ~50m thick, is hosted by limestone units of the Qom Formation. The main mineralization zone occurred as vein-veinlets and vug infill textures, where mineralization is observed as Pb-Zn-bearing barite veins or supergene minerals (cerussite and smithsonite). Mineralization at Tozlou can be divided into five stages. Stage 1 is the decarbonatization of the limestone host rock, which is characterized by the increased porosity and permeability of the host rock. Stage 2 is categorized with dolomitization processes along with minor pyrite. Stage 3 occurred as Pb-Zn-bearing barite and calcite (calcite II) veins. Stage 4 includes late-stage calcite (calcite III) veins. Stage 5 is related to supergene processes. Hydrothermal alterations include decarbonatization, carbonatization ± silicification, and late carbonatization. Ore minerals include galena and pyrite along with minor sphalerite. Calcite, barite, and quartz are gangue minerals. Smithsonite, cerussite, and goethite are formed by supergene processes. The ore minerals show vein-veinlets, brecciated, disseminated, vug infill, colloform, cockade, replacement, and residual textures. The Chondrite-normalized rare earth elements pattern of ore samples, fresh and altered limestones is similar, which can indicate the major role of host rocks in the concentration of ore-forming elements. This pattern is almost similar for different ore samples, which can indicate that they have been formed by the same mineralization system. Characteristics of Tozlou occurrence are comparable with intermediate-sulfidation type of epithermal deposits.

Epithermal deposits are a group of base/precious-metal deposits that are formed by hydrothermal fluids in shallow environments under pressure/temperature changes and fluid-rock interactions (Hedenquist et al., 2000). Based on the host rock, epithermal deposits are divided into volcanic-hosted deposits and sedimentary-hosted deposits. According to the tectonic setting and magma type, they are divided into calc-alkaline magmas (including three subcategories of high-, intermediate-, and low-sulfidation) and alkaline magmas (White and Hedenquist, 1990; Cooke and Simmons, 2000; Hedenquist et al., 2000; Simmons et al., 2005). These types of deposits include a continuous range of deposits formed by magmatic/meteoric fluids and show different geometry, but have the same formation mechanism, especially the hydrothermal fluids circulation (Sillitoe and Hedenquist, 2003; Simmons et al., 2005).
Sedimentary rock-hosted deposits are divided into two groups: Carlin-type and sediment-hosted disseminated deposits. Carlin-type deposits are often formed as strata-bound or replacements at the boundary of rock units and are controlled by faults. They are distinguished by invisible Au in As-rich pyrite and arsenopyrite and do not show compatible spatial relationships to magmatic centers (Kuehn and Rose, 1992). Sediment-hosted disseminated deposits occurred as disseminated ore in sedimentary rocks (Hofstra and Cline, 2000). These deposits are physically and chemically comparable to Carlin-type deposits, but spatially and temporally are related to sub-volcanic porphyry intrusions (Theodore et al., 2000; Hofstra and Cline, 2000).
Tozlou Pb-Zn occurrence is 50km south of Qeydar in Zanjan province. This occurrence was first discovered/explored in 2017. Although general geological characteristics of Tozlou occurrence have been determined (Majidifard and Shafei, 2006), the mineralogy and origin of Tozlou occurrence have not been studied in detail. Here, detailed geology, mineralogy, alteration styles, and geochemistry of Tozlou occurrence are investigated to constrain the genetic model and type of its mineralization system. These results may have implications for future exploration of base-metal mineralization in this region and nearby areas. 

Comprehensive field and laboratory works have been carried out on Tozlou area. During the fieldwork, a detailed stratigraphic section of limestone units of Qom Formation was measured, sampled, and described. Fifty samples were collected from ore zones and limestone host rocks for laboratory analysis. Then, 34 thin and 15 polished-thin sections were prepared for mineralogical studies in the laboratory at the University of Zanjan, Iran. Fourteen typical samples from the ore zones and fresh/altered host limestone were analyzed for geochemical analysis using ICP–MS in Zarazma Analytical Laboratories, Tehran, Iran.

The main rock units exposed in Tozlou occurrence belong to Eocene sequence, Lower Red Formation, Qom Formation, and Quaternary units. Small outcrops of gabbro-gabbro diorite (gb) can also be seen in this region. Eocene strata include brown thin-bedded sandstone (Unit Es), alternating tuff and shale (Unit Etsh), and thin- to medium-bedded tuffs (Unit Et). Lower Red Formation includes a polygenetic conglomerate (Unit Ollrc) of Oligocene age. Qom Formation consists of massive- to medium-bedded cream-to-grey limestones (Unit OMql) and alternating marl and thin-bedded grey limestone (Unit OMqml). Quaternary units include terrigenous sediments.
Pb-Zn mineralization at Tozlou has ~250-300 m leng and ~50 m thick and is hosted by limestone units of Qom Formation. The main mineralization zone occurred as vein-veinlets and vug infill textures, where mineralization is observed as Pb-Zn-bearing barite veins or supergene minerals (cerussite and smithsonite). Decarbonatization, carbonatization±silicic, dolomitization, and late carbonatization are hydrothermal alterations in Tozlou area. Mineralization processes at Tozlou can be divided into five stages. Stage 1 comprises the decarbonatization of the limestone host rock, which is characterized by the increased porosity and permeability of the host rock. Stage 2 is represented by the dolomitization of the limestone host rock, which is accompanied by minor pyrite. Stage 3 occurs as Pb-Zn-bearing barite and calcite (calcite II) veins. Stage 4 is characterized by late-stage calcite (calcite III) veins. Stage 5 is related to supergene processes.
Ore minerals include galena and pyrite along with minor sphalerite. Calcite, barite, and quartz are gangue minerals. Smithsonite, cerussite, and goethite are formed by supergene processes. The ore minerals show vein-veinlets, brecciated, disseminated, vug infill, colloform, cockade, replacement, and residual textures. The Chondrite-normalized rare earth elements patterns of ore samples, fresh and altered limestones, are similar, which can indicate the major role of host rocks in the concentration of ore-forming elements. This pattern is almost similar for different ore samples, which can indicate that they have been formed by the same mineralization system. Despite carbonate host rock, we think that mineralization at Tozlou is similar to the intermediate-sulfidation style of epithermal base metal deposits.

Marshoun area located 120Km Southeast of Zanjan, is a part of the Tarom-Hashtjin metallogenic-magmatic subzone within the Alborz-Azarbaijan zone. Similar to most parts of the Alborz-Azarbaijan zone, the Eocene-Oligocene volcanic and the intrusive rocks of this subzone were formed as a result of the Alpine orogenic phase, which has a close spatial and temporal relationship with metallic mineralization (Kouhestani et al., 2019). Several studies have been conducted on metallic mineralizations in different parts of the Tarom-Hashtjin subzone. The petrological studies carried out in this subzone are mainly focused on intrusive rocks (e.g., Seyed Qaraeini et al., 2020) and volcanic rocks' geochemical and petrological characteristics have been less considered. Marshoun area is composed of volcanic-sedimentary sequences which are hosts for Pb-Zn-Cu mineralization (Kouhestani et al., 2019). A detailed scientific study has not been done on the lithological sequence and their geochemical and petrological characteristics in the Marshoun area so far. In the present study, the lithological and geochemical characteristics including Sr, Nd, and Pb isotopic data, as well as the tectonomagmatic environment of the volcanic rocks of the area have been investigated.

During fieldwork, a 1:25000 geological map prepared from different lithological units of the area and over 30 samples were taken. Also, 17 thin sections for petrographical studies, 10 samples for chemical and 4 samples (2 andesites and 2 dacites) for iaoopic analyses. Chemical analyses (XRF and ICP–MS methods) were carried out at Zarazma Laboratory, Tehran, Iran., and isotopic studies (i.e. Nd, Sr, and Pb isotope studies at Institute of Geology and Geophysics, Chinese Academy of Geosciences, Beijing, China.

The predominant rock units in the Marshoun area are Eocene acidic tuffs, dacitic-rhyodacitic lava, and occasionally ignimbrite at the base and alternation of intermediate tuff with minor andesite and basaltic andesite intercalation in the top, along with some intrusive rocks with (Zajkan intrusion), and some gabbroic dykes.Zajkan intrusion including pyroxene quartz monzodiorite, quartz monzodiorite, and granodiorite composition intruded acidic volcano-sedimentary rocks with a total thickness of 930 meters can be divided into 9 parts.Volcanic rocks of the Marshoun area are classified as rhyolite, rhyodacite, dacite, andesite, basaltic andesite, and trachy-andesite with high-K calc-alkaline affinity. Dacitic-rhyodacitic rocks have porphyritic, flow, and spherolitic textures, composed of plagioclase, quartz, alkali feldspar, and mafic minerals (amphibole and biotite) set in a quartz-felspathic groundmass whereas, andesitic rocks show porphyritic, glomeroporphyritic, and amygdaloidal textures, composed of plagioclase and mafic minerals (amphibole and some pyroxene) set in a fine-grained and occasionally microlithic groundmass.All samples under study on primitive mantle normalized spider diagrams, have similar patterns indicative of their genetic relations. LILEs and HFSEs.negative anomalies are remarkable features of these rocks. Chondrite-normalized REE patterns demonstrate a relatively steep to low slope pattern with LREE enrichment and a high ratio of LREE/HREE, (La/Yb)N, and (La/Sm)N ratio between 3.8-30.1 and 1.2-8.25, respectively. On tectonomagmatic setting discrimination diagrams, volcanic rocks of the Marshoun area have been formed in an active continental margin tectonic setting. Isotopic data of Sr (0.70485-0.70622), Nd (0.512695-0.712733), and Pb (206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb between 18.743-18.803, 15.5938-15.6112 and 38.8138-18.0721, respectively) point to dominant role of mantle in the formation of the investigated rocks. According to the Pb isotopes, the area's acidic rocks originated either from a more enriched mantle or were contaminated by crustal materials during ascending magma.

As the geochemical data indicate the primary magma of Marshoun volcanic rocks is generated by the partial melting of subcontinental metasomatized mantle lithosphere as a result of the subduction process within the continental margin environment. According to data obtained from the present study as well as the previous research, it can be concluded that the result of the subduction of the active continental margin and the shortening of the crust in Alborz during the Eocene gave rise to the thickening of continental crust and further led to the separation and subsidence of the lower part of the subcontinental lithospheric mantle (delamination).As a result of this event, the ascending of asthenosphere currents has led to an increase in the thermal gradient and partial melting of the subcontinental lithosphere and generation of basic magma which during ascending contaminated by crustal materials. Finally, the differentiation process led to the formation of intermediate and acidic rocks.

Antimony mineralization at Moghanlou occurs as 2-3 meters siliceous-sulfide zone consisting of up to 10 centimeters wide quartz-stibnite breccia veins. The ore zone is hosted by amphibolite enclaves within feldspathic gr2 granite, and has N50E-trending that generally dips to the southeast at 75o. The hydrothermal alteration includes feldspathic, silicification, carbonatization and propylitic. The feldspar, quartz and carbonate alteration types are spatially associated with ore zone, whereas propylitic alteration affected amphibolite host rocks. Three stages of mineralization are distinguished at Moghanlou. Stage 1 is represented by silicification and carbonatization of host rocks along with minor disseminated pyrite. This stage is a pre-ore stage and it is usually crosscut by later stages. Breccia clasts of this stage have been recognized in the hydrothermal cements of stage 2 breccias. Stage 2 is the main ore-stage at the Moghanlou deposit. It is characterized by 2 to 10 cm wide quartz (calcite)-stibnite veins and breccias that usually cut stage 1 and, in turn, crosscut by stage 3 calcite veins. Stage 3 is a barren post-ore stage marked by calcite as vug infill and 1 cm wide veins. The ore minerals at Moghanlou are stibnite and minor pyrite. Stibiconite and goethite are the supergene assemblages, and the gangue minerals include quartz, calcite, actinolite, chlorite and talc. Ore minerals display disseminated, vein-veinlet, brecciated, comb, crustiform, cockade, plumose, vug infill and replacement textures.

Precious and base metal mineralization in the Qebchaq deposit occurred as brecciated quartz-sulfide veins within the Eocene tuff and lava strata, and the Oligocene quartz diorite-gabbro intrusion. Pyrite, chalcopyrite, galena, sphalerite, and gold along with minor realgar, psilomelane, and pyrolusite, are ore minerals; quartz, sericite, chlorite and calcite are gangue minerals. The ore minerals show disseminated, vein-veinlet, brecciated, comb, cockade, colloform, crustiform, plumose, and vug infill textures. Five stages of mineralization can be distinguished at Qebchaq. Stage 1 is represented by silicification of host rocks along with minor disseminated pyrite. Stage 2 is characterized by quartz veins and breccias that contain variable amounts of disseminated pyrite, chalcopyrite, galena, sphalerite ± native gold ± realgar. Stage 3 is marked by quartz-manganese oxides-hydroxides (psilomelane, pyrolusite, braunite) veins and hydrothermal breccia cements. Stage 4 is represented by quartz (calcite-chlorite) vein-veinlets, and stage 5 is characterized by calcite as veinlets and vug infill texture. Wall-rock alterations include silicification, intermediate argillic, carbonate, chlorite and propylitic alteration. Chondrite–normalized trace elements and REE patterns of the mineralized samples and the host rocks are similar and indicate that host rocks are probably involved in mineralization. Characteristics of Qebchaq deposit are comparable with intermediate-sulfidation type of epithermal deposits. 

Qebchaq base and precious metal deposit, 15 km northwest of Qarachaman, is located in the Western Alborz–Azerbaijan zone, northwestern Iran. Several types of deposits are present in this zone including porphyry and skarn Cu-Mo (Au) porphyry deposits, Cu-Mo and Fe skarn deposits, Cu-Mo-Au vein deposits, and epithermal Au deposits (Jamali et al., 2010; Kouhestani et al., 2018). The most important deposit discovered to date within the Western Alborz–Azerbaijan zone is the Sungun porphyry Cu-Mo deposit, which has a defined reserve of 796 Mt at 0.6% Cu (Hezarkhani and Williams-Jones, 1998; Aghazadeh et al., 2015; Simmonds et al., 2017). Other important deposits or occurrences include Haft-Cheshmeh, Sonajil, Ali Javad, Mirkuh-e-Ali Mirza, Astergan, Avan, Anjerd, Mazraeh, Astamal, Pahnavar, Masjed Daghi, Sharafabad, Mivehroud, Nabijan, Zaglig, Aniq, Zaily Darreh, Qara Darreh and Qarachilar (Ebrahimi et al., 2011; Jamali et al., 2010; Mokhtari, 2012; Maghsoudi et al., 2014; Mokhtari et al., 2014; Adeli et al., 2015; Baghban et al., 2015; Baghban et al., 2016; Simmonds and Moazzen, 2015; Kouhestani et al., 2018).
Although geological general characteristics of the location of the Qebchaq deposit have been determined (Asadian et al., 1993), no detailed studies have been conducted on the mineralogy, geochemistry, and genesis of the Qebchaq deposit. In this paper, detailed geology, mineralogy, geochemistry, and alteration styles of the Qebchaq deposit to constrain its ore genesis are investigated. These results may have implications for the regional exploration of epithermal base and precious metal deposits in the Western Alborz–Azerbaijan zone.

Detailed fieldwork has been carried out at different scales in the Qebchaq area. A total of 50 samples were collected from various parts of ore veins and breccias, host volcanic rocks, and intrusions. The samples were prepared for thin (n=8) and polished-thin (n=32) sections in the laboratory at the University of Zanjan, Zanjan, Iran. Thirty nine representative samples from the mineralized veins and breccias, 1 sample from host dacitic rocks, and 1 sample from altered quartz diorite-gabbro intrusion were analyzed for REE, Au, Ag, Cu, Pb, Zn, and other rare elements using Fire Assay and ICP–MS in the Zarazma Analytical Laboratories, Tehran, Iran.

The geological units hosting the Qebchaq deposit are mainly Eocene volcanic and volcaniclastic rocks that have been intruded by Oligocene intrusions. The Eocene sequence includes tuff, andesite, and andesitic basalt, rhyolite, rhyodacite-dacite, and ignimbrite. The intrusive rocks in the Qebchaq area include Oligocene quartz diorite-gabbro and granite-alkali granite. They show porphyritic, microgranular, and granular textures. Mineralization at Qebchaq occurs as the epithermal base and precious metal quartz-sulfide brecciated vein that occupies NE-trending faults in the Eocene volcanic rocks and Oligocene intrusions.  The ore veins are 50 to 1000 m long, from 0.5 to 4 m wide, and generally, dip steeply (65–85°) to the southeast and northwest. Wall-rock alterations developed at the Qebchaq deposit include silicification, intermediate argillic, carbonate, chlorite, and propylitic alteration. The first four types are closely related to mineralization. Five stages of mineralization can be distinguished at Qebchaq. Stage 1 is represented by silicification of host rocks along with minor disseminated pyrite. This stage is usually crosscut by stage 2. Stage 2 (the main ore-stage) is characterized by millimeters to several centimeters wide quartz veins and breccias that contain variable amounts of disseminated pyrite, chalcopyrite, galena, sphalerite ± native gold ± realgar. Clasts of this stage and associated wall-rock alteration have been recognized in the hydrothermal cement of stage 3 breccias. Stage 3 is marked by quartz- manganese oxides-hydroxides (psilomelane, pyrolusite, braunite) veins and breccia cement. It is usually crosscut stage 2 and is cut by stage 4 veinlets. Stage 4 is represented by < 1 mm wide quartz (calcite-chlorite) vein-veinlets. This stage usually crosscuts previous ore stages. No sulfide minerals are recognized in stage 4. Stage 5 is characterized by up to 2 mm wide veinlets or vug infill texture of calcite. Stage 5 calcite veinlets usually crosscut previous ore stages. The ore minerals at Qebchaq have been formed as vein-veinlet and hydrothermal breccia cement, and show disseminated, vein-veinlet, brecciated, comb, cockade, colloform, crustiform, plumose, and vug infill textures. Pyrite, chalcopyrite, galena, sphalerite, native gold, realgar, psilomelane, and pyrolusite are the main ore minerals. Malachite, azurite, smithsonite, cerussite, goethite, secondary pyrolusite, and braunite are supergene minerals. Quartz, sericite, chlorite, and calcite are present in the gangue minerals. 
Comparison of Chondrite–normalized rare elements and REE patterns of host dacitic lavas, fresh and altered quartz diorite-gabbro intrusion, and the mineralized samples at Qebchaq indicate that leaching of some elements from the host rock units may have been involved in mineralization. The data in this study suggest that Qebchaq is an example of intermediate-sulfidation type of epithermal base and precious metal mineralization.

The geological units exposed in the Qaradash area are Paleozoic metamorphic rocks. Microscopic studies reveal that the skarnoid aureole in Qaradash is composed of garnet hornfels, garnet-pyroxene hornfels, pyroxene hornfels, epidote-garnet-pyroxene hornfels, epidote hornfels and marble subzones. Pb–Zn mineralization at Qaradash occurred as quartz-sulfide vein-veinlets within skarnoid aureole.The ore zone can be traced 200 m along strike and up to 15 m in width. The hydrothermal alteration includes of decarbonatization, actinolization-epidotization, carbonatization, and silicification. The ore minerals at Qaradash are pyrite, chalcopyrite, galena, sphalerite, and hematite. The gangue minerals include garnet, clinopyroxene, calcite, quartz, epidote, chlorite, and actinolite. Ore minerals display disseminated, vein-veinlet, brecciated, replacement, and relict textures. Similar Chondrite–normalized rare elements and REE patterns (McDonough and Sun, 1995) of ore and skarnoid aureole sub-zones samples indicate that they are genetically related. Based on mineralogical and textural studies, skarnification processes in the Qaradash occurrence can be divided into 2 stages including: (1) prograde metasomatic stage and (2) retrograde metasomatic stage. Pb–Zn mineralization occurred during retrograde metasomatic stage. Based on mineralogical and textural evidence, prograde metasomatic stage was formed simultaneously in 430–550 °C and ƒO2 was equal to 10-23 to 10-26 (e.g., Einaudi, 1982). According to mineralogical complex of the early retrograde stage, it seems that metasomatic fluids had ƒS2 ≈ 10-6.5 (e.g., Einaudi, 1982). Based on field evidences as well as ore geology, skarnoid aureole sub-zones, marble host rock, structure and texture and paragenetic sequences, we conclude that the Qaradash occurrence is a calcic Pb–Zn skarn mineralization.

The Arabshah Fe mineralization is the only known magnetite-apatite mineralization at the Takab–Takht-e-Soleyman–Angouran subzone in southeast of Takab. The oldest rock units in the mineralization area include sedimentary succession of the Qom Formation that was intruded by the Pliocene Ayoub Ansar volcanic dome. Magnetite- apatite mineralization at the Arabshah occurs as vein-veinlets with E-W stright within the Ayoub Ansar dacitic dome. Brecciated zones containing narrow magnetite vein- veinlets occur at footwall and hanging wall of the main vein. Hydrothermal alterations include sodic-calcic, silicification and argillic. Magnetite is the only ore mineral in this mineralization which is accompanied with apatite, clinopyroxene, albite and quartz as gangue minerals. Mineralization textures in the Arabshah deposit include vein-veinlet, brecciated, disseminated, and replacement. REEs concentration within apatite crystals are more than 1%, and demonstrate LREE enrichment with high LREE/HREE ratio and distinctive negative Eu anomalies which is indicative for Kiruna- type iron ores. The result of fluid inclusion studies indicates the presence of two-phase and poly-phase inclusions include LV, VL, LVH, LVS and LVHS fluid inclusions with homogenization between 230-550 °C. The salinity of halite bearing poly-phase fluid vary between 35-60 wt.% NaCl equiv. Fluid inclusion data indicates that Arabshah magnetite-apatite mineralization originated from magmatic fluids. Evidences like mineral assemblages, hydrothermal alteration, ore structure and textures, geochemical characteristics and fluid inclusion data, indicate that the Arabshah magnetite-apatite mineralization can be classified as Kiruna-type iron ores.

The Qarkhotlou bauxite deposit occurs as a semi-continuous horizon situated along the parallel unconformity surfaces between Ruteh and Shemshak Formations. Based on color, facies and textural features, three distinct bauxitic facies are distinguished in the Qarkhotlou deposit, which is, from bottom to top include: (1) lower red-brown pisolitic bauxite, (2) middle red bauxite and (3) upper brick-yellow bauxite. Hematite, goethite, boehmite, diaspore, kaolinite, and pyrophillite are the major mineral components in the Qarkhotlou bauxite ores; muscovite-illite, anatase, rutile, and chlorite are minor minerals. Petrographic observations indicate that panidiomorphic, microgranular, pelitomorphic, pisolitic, and oolitic are the main texture-forming components in the Qarkhotlou ores. These ore textures suggest that the bauxite material has an authigenic origin. However, the existence of clastic assemblages in the pelitomorphic matrix, as well as flow and breccia textures of the ore indicate that the bauxite at Qarkhotlou was locally experienced transportation and re-deposition. Geochemical data indicate that the Qarkhotlou bauxite deposit has bauxite and bauxitic clay compositions, and suggests that trachy andesibasalt lavas are the main component of their parent material. This data reveals that the bauxite horizon at Qarkhotlou formed in pH of 4 to 7 and Eh of 0.4 to 0.6 and experienced a moderate degree of lateritization. The bauxite samples and trachy andesibasalt lava show similar chondrite-normalized REE patterns indicating that they are genetically related. The petrographical, textural and geochemical studies of the Qarkhotlou deposit indicate that this deposit can be classified as Mediterranean karst bauxite.

The Zajkan base (± precious) metal deposit is located in the Tarom-e-Sofla part of the Qazvin province, and is part of the Tarom-Hashtjin metallogenic belt (THMB). The THMB has been documented as one of the most important epithermal metallogenic belts in Iran (Ghorbani, 2013; Kouhestani et al., 2018) that host numerous epithermal precious and base metal deposits (i.e., Rashtabad, Gulojeh, Aqkand, Aliabad–Khanchy, Chodarchay, Khalyfehlou, Chargar, Lubin-Zardeh, Marshoun, Abbasabad, Zehabad, and Shah Ali Beiglou).Mining at Zajkan started around 1970 and continued to the beginning of 1980s. Recent exploration work at the Zajkan deposit started from 2017 by Roy Godaz Company, and the deposit is still under exploration. In this paper, we present detailed geology and mineralization characteristics of the Zajkan deposit along with geochemical and fluid inclusions data to investigate ore genesis of the deposit. These results may have implication for the regional exploration of epithermal deposits in the THMB.

Mineralization in the Marshoun 2 occurrence occurs as quartz-sulfide veins hosted by intermediate tuff units, and is divided into four stages. Stage 1 is represented by silicification of host rocks along with minor disseminated pyrite. Stage 2 is characterized by quartz-sulfide (chalcopyrite, pyrite) veins and breccia cements. Stage 3 is characterized by quartz (calcite)-sphalerite-galena ± chalcopyrite ± pyrite veins and breccia cements. Stage 4 is barren post-ore quartz-calcite vein-veinlets. The hydrothermal alteration includes of silicification, intermediate argillic, carbonate, and propylitic alteration. The ore minerals are pyrite, chalcopyrite, galena, and sphalerite; quartz, sericite, chlorite and calcite are present as gangue minerals. Ore minerals display vein-veinlet, brecciated, comb, crustiform, colloform, cockade, plumose, bladed, skeletal, and vug infill textures. Similar Chondrite–normalized rare elements and REE patterns of mineralized samples indicate that hey may have fomed by same hydrothermal process. Microthermometric data reveal that ore-forming fluids at the Marshoun deposit belong to the moderate-temperature and low-salinity H2O–NaCl system. Fluid boiling and mixing were important processes in the evolution of the ore-forming fluids. Marshoun 2 is an intermediate-sulfidation epithermal deposit.

IntroductionThere are several carbonate-hosted Pb–Zn (F–Ba) deposits in the central Alborz zone hosted by upper part of Elika Formation. From an economic point of view, the most important deposits discovered to date are Sheshroudbar, Pachi Miana, Kamarposht and Era. It makes the central Alborz zone as one of the most important Pb–Zn (F–Ba) districts in Iran. In this district, Elika Formation is restricted by NE–SW-trending reverse faults, and thrusted over the Shemshak Formation. The main orebodies occurred in open spaces which formed due to angles between normal and reverse faults in the carbonate rocks of Elika Formation (Tabasi, 1997). Some of these deposits have been studied, and various models such as syn-diagenesis to epigenetic are presented for ore genesis (Alirezaei, 1989; Gorjizad, 1996; Rastad and Shariatmadar, 2002; Rajabi et al., 2013; Vahabzadeh et al., 2014; Nabiloo et al., 2018).Sarcheleshk is an abandoned mine of Pb–Zn (F–Ba) mineralization in the central Alborz zone. Except for small-scale geological maps of the area, i.e., 1:100,000 geological map of Pol-e-Sefid (Vahdati Daneshmand and Karimi, 2004) and Semnan (Nabavi, 1988), previous studies of Pb–Zn (F–Ba) mineralization at Sarcheleshk was limited and include Mohammadi Lisehroudi (2019). In this contribution, we provide the first detailed geological, mineralogical and geochemical studies in the Sarcheleshk deposit to reveal more details of the type and genetic model of ore formation. Materials and methodsDetailed field work has been carried out at different scales in the Sarcheleshk area. A total of 60 samples were collected from various parts of orebodies, host carbonate and mafic igneous rocks. The samples prepared for thin (n=32) and polished-thin (n=12) sections in the laboratory of University of Zanjan, Zanjan, Iran. Representative 8 samples from the ore zone, 1 sample from barren dolomitic limestone and 3 samples from mafic igneous rocks, were analyzed for major, trace and rare earth elements using XRF and ICP–MS in the Zarazma Analytical Laboratories, Tehran, Iran. Discussion and conclusionThe Sarcheleshk Pb–Zn (F–Ba) deposit is located 20 km southwest of Pol-e-Sefid, Mazandaran province. The most important rock units exposed in this area include early to middle Triassic dolomitic limestone (Elika Fm.), late Triassic gypsum, dolomitic limestone and marl (Paland Fm.), late Triassic mafic igneous rocks, late Triassic to early Jurassic shale, siltstone and sandstone (Shemshak Fm.), middle Jurassic ammonite-bearing marl, calcareous marl and marly limestone (Dalichay Fm.), late Jurassic cherty limestone and dolomitic limestone (Lar Fm.), and early Eocene Alveolina–Nummulitic limestone (Ziarat Fm.).Mineralization at Sarcheleshk occurs as strata-bound orebodies hosted by dolomitic limestone of Elika Formation, and controlled structurally by faults, fractures and dissolution collapse breccias. The ore veins have a varying width from 0.5 to 1.5 m. Detailed field geology and petrographic studies indicate that wall-rock alterations developed at the Sarcheleshk deposit include dolomitization, silicification, and calcitization. The ores at Sarcheleshk are dominated by galena, sphalerite, pyrite, fluorite, and barite, with lesser, chalcopyrite, and tetrahedrite, all of which are hosted by a dolomite, calcite, and quartz gangue assemblage. The ore minerals show vein-veinlets, open space filling, brecciated, rhythmic, disseminated, replacement, and relict textures. The mineralization process at Sarcheleshk can be divided into three stages. Stage 1 is diagenesis stage represented by rhythmic texture of fluorite, galena, sphalerite, and calcite bands. Stage 2 (epigenetic stage), volumetrically most important, is marked by fluorite-sphalerite-galena-pyrite-chalcopyrite, barite-pyrite and barite-calcite, and late stage calcite veins and veinlets. Stage 3 is the supergene mineral assemblages consisting of smithsonite, cerussite, chalcocite, covellite, azurite, and goethite. The ore samples and mafic igneous rocks show different Chondrite-normalized trace and REE patterns, indicating that they are genetically unconnected. It is declined syn-sedimentary and/or hydrothermal igneous origins for the Sarcheleshk deposit, and specify that basinal brines may have played a role in Pb–Zn (F–Ba) mineralization at Sarcheleshk deposit.Our data suggests that Sarcheleshk deposit is a F–Ba-rich MVT deposit and is comparable with other Pb–Zn (F–Ba) deposits of central Alborz zone.

Toryan area is located in the Central Iranian zone, about 120 km northwest of Zanjan. In this area, the exposed rock units belong to the Upper Red Formation (URF). The thickness of the URF at Toryan is 1010 m, and consist of four main parts. These parts, from bottom to top, consist of: 1-alternation of gypsiferous (locally salt) green marls (300 m), 2-alternation of red marls and grey to red sandstones (275 m), 3-alternation of red and green marls intercalated with sandstone (210 m), and 4-green marls with interbedded green siltstones (225 m). Based on microscopic studies, average particle size of sandstones in the Toryan area is about 0.2 mm. These sandstones also display poor orientation, poor to moderate sorting, and mainly are angular to semi-angular. Based on component types and results of point counting, the studied sandstones contains 16% quartz (included mono and poly-crystalline with both straight and wavy extinction), different types of rock fragments (sedimentary, metamorphic and volcanic) and 10% feldspar (mainly ortoz). According to Folk (1980) classification, it can be stated that the studied sandstones are litharenite to feldspathic litharenite with calcite and evaporitic cements. Based on the main components and the results of petrographic, major and minor elements geochemical analyses, the tectonic setting of these sandstones is related to foreland and collision basins. These data represent an intermediate to felsic source rock for these sandstones, which were affected by semi-arid to arid climate.

Varmazyar Pb–Zn (Ag) occurrence, 65 km north of Zanjan, is located in the Tarom–Hashtjin metallogenic belt (THMB). The THMB has been recognized as one of the most important epithermal metallogenic belts in Iran (Kouhestani et al., 2018b) that host numerous small- to medium-sized epithermal deposits (i.e., Gulojeh, Aqkand, Aliabad–Khanchy, Chodarchay, Khalyfehlou, Chargar, Zajkan, Marshoun, Abbasabad, Zehabad, and Shah Ali Beiglou). These epithermal deposits are temporally and spatially related to late Eocene granitoids (Mehrabi et al., 2016; Kouhestani et al., 2018b).Although the general geological characteristics of the region, where the Varmazyar occurrence is located, were determined (Faridi and Anvari, 2000), no detailed studies have been conducted on the mineralogy, geochemistry, and the ore-forming fluids characteristics of the Varmazyar occurrence. In this paper, we investigate the geology, mineralogy, geochemistry, fluid inclusions, and alteration styles of the Varmazyar occurrence to constrain its ore genesis. These results may have implication for the regional exploration of epithermal deposits in the THMB.

Detailed field work has been carried out at different scales in the Varmazyar area. A total of 70 samples were collected from various parts of ore veins and breccias, host tuff units and granitoid intrusion. The samples prepared for thin (n=15) and polished-thin (n=27) sections in the laboratory of University of Zanjan, Zanjan, Iran. Representative 7 samples from the mineralized veins and breccias, 1 sample from host intermediate tuff unit and 1 sample from barren and fresh granite intrusion, were analyzed for rare and rare earth elements using ICP–MS in the Zarazma Analytical Laboratories, Tehran, Iran.Fluid inclusion measurements have been conducted on 4 doubly polished thick (~150 μm) sections including crystalline quartz, and sphalerite from the second, and third stages of ore formation. Microthermometric measurements were performed using a Linkam THMSG-600 heating–freezing stage attached to a ZEISS microscope in the fluid inclusion laboratory of Iranian Mineral Processing Research Center, Tehran, Iran.

The geological units hosting the Varmazyar occurrence are mainly Eocene volcanic and volcaniclastic rocks that were intruded by late Eocene granitoids. The volcaniclastic rocks can be divided into two units as acidic (lithic tuff, lithic crystal tuff and crystal tuff) and intermediate (lithic crystal tuff, crystal tuff, and lithic tuff) units. They are metamorphosed to clinopyroxene hornfels facies near contact intrusions. The granodiorite intrusion is the main rock units in the Varmazyar area. It crops out mainly in the south, southwest and northeast of the Varmazyar occurrence. It ranges in composition from monzogranite to syenogranite and shows porphyritic and granular textures.Mineralization at Varmazyar occurs as epithermal base metal quartz-sulfide brecciated vein that occupy NS-trending faults in the Eocene acidic and intermediate tuff units.  The ore vein extends up to 300 m along, from several cm to 2–3 m wide, and generally dip steeply (65–80°) to the west. Wall-rock alterations developed at the Varmazyar occurrence include silicification, intermediate argillic, carbonate, and propylitic alteration; the first three are closely related to the Pb–Zn (Ag) mineralization. The alteration styles show a systematic zonation pattern, from the silica, via intermediate argillic, to propylitic alteration. Four stages of mineralization can be distinguished at Varmazyar. Stage 1 is represented by silicification of host rocks along with minor disseminated pyrite. This stage is a pre-ore stage and usually crosscut by later stages. Stage 2 is the main ore-stage at the Varmazyar occurrence. It is characterized by up to 5 cm wide quartz veins and breccias that contain variable amounts of disseminated galena, sphalerite, and minor pyrite. Clasts of this stage and associated wall-rock alteration have been recognized in the hydrothermal cements of stage 3 breccias. Stage 3 is marked by quartz-calcite-manganese oxides (psilomelane, pyrolusite, braunite) veins and breccia cements. It is usually crosscut previous mineralization stages and, in turn, is cut by stage 4 calcite veinlets. Stage 4 is a barren post-ore stage represented by < 1 mm wide calcite veinlets. This stage usually crosscuts previous ore stages. No sulfide minerals are recognized with stage 4. The ore minerals at Varmazyar formed as vein-veinlet and hydrothermal breccia cements, and show disseminated, vein-veinlet, brecciated, comb, crustiform, colloform, cockade, bladed, plumose, and vug infill textures. Galena, sphalerite, pyrite, psilomelane, and pyrolusite are the main ore minerals; smithsonite, cerussite, goethite, secondary pyrolusite, and braunite are supergene minerals. Quartz, calcite, and sericite are present in the gangue minerals. Comparison of Chondrite–normalized rare elements and REE patterns of host intermediate tuffs, barren and fresh granite intrusion, and the mineralized samples at Varmazyar indicate that mineralization is probably genetically related with granite intrusions. In this case, leaching of some elements from the host tuff units may have involved in mineralization. Ore-forming fluids associated with the quartz-sulfide veins are represented by two-phase aqueous inclusions and by H2O–NaCl fluids with moderate-temperature (135–249 °C) and low-salinity (0.2–6.4 wt.% NaCl equiv.). Fluid inclusion data indicates that fluid boiling and mixing were important processes in the evolution of the ore-forming fluids at Varmazyar. Our data suggest that Varmazyar is an example of intermediate-sulfidation type of epithermal base metal mineralization.

The Toryan occurrence is located in the Central Iran zone, 120 km northwest of Zanjan. Pb–Zn mineralization at Toryan occurred as laminated and lens-shaped parallel to lamination of grey sandstone units of the Upper Red Formation. Mineralization often formed around and within the fragments of the plant fossils, and shows disseminated, replacement, solution seems, intergranoular cement, framboidal, and vein-veinlet textures. At Toryan, ore horizon has 1 m thickness and approximately 350 m length and contains three zones include the red oxidized zone, the bleached zone and the mineralized reduced zone. Galena, sphalerite, pyrite and arsenopyrite are the main ore minerals at Toryan occurrence. Cerussite and goethite are formed during supergene and wethering processes. Comparison of trace elements and REE patterns of barren red and grey host sandstones and mineralized samples indicate that mineralized samples show lower concentrations of trace elements and REE. Based on tectonic setting, sedimentary environment, host rock, presence of plant fossils, geometry, ore texture and mineralogy and alteration, Toryan occurrence can be classified as sediment-hosted Cu deposits of Redbed type, and is comparable with another Redbed type of Cu and Pb–Zn deposits in the Avaj-Zanjan-Tabriz-Khoy belt.

Cenozoic acidic volcanic rocks at the south of Qezel Ozan River are located within the Western Alborz-Azarbaijan magmatic zone and northern part of the Iranian-Turkish Plateau. The Oligocene acidic lavas in north part of Zanjan show rhyolitic to dacitic composition.  Hyaloporphyritic to hyalomicrolithic porphyritic textures are the main texture in these rocks. They were erupted along the main faults in this area. Feldspars, biotites and hornblendes are the major phenocrysts which are embedded in a glass matrix or micro phenocrysts of felsic and mafic minerals. By Geochemical studies it is indicated that these rocks have high-K calc-alkaline to shoshonitic nature and classified as meta-aluminous and I-type acidic rocks. In the chondrite normalized rare earth elements diagram, these rocks demonstrate LREE enrichment and high LREE/HREE ratio. Enrichment in LREE and depletion in HREE is characteristic of the calc-alkaline rocks in active continental margins. Furthermore, these rocks show enrichment in LILEs and negative anomalies of HFSEs (Ti, Nb and Ta) which is the feature of magmatic rocks associated with Post-COLG subduction zones. The geochemical evidences suggest that the parental acidic magma is resulted from partial melting of lower crust as a result of pressure reduction during the local tension mechanism.

Fe skarn deposits are the largest skarn deposits which are exploited for Fe as well as by-products of Cu, Co, Ni and Au (Meinert et al., 2005). They are one of the most important Fe deposits in the Zanjan province which have been exploited in recent years. The Alamkandi Fe deposit is one of these Fe skarn deposits which is located at 35 km west of the Mahneshan within the Takab-Takht-e-Soleyman subzone, northern Sanandaj- Sirjan zone. In this area, alternation of amphibolite, amphibole schist and biotite schist with intercalations of marble belonging to Paleozoic and intruded by late Oligocene alamkandi granitoid exist. This intrusion has caused contact metamorphism and formation of Fe mineralization. Some of the Fe skarn deposits in the Zanjan province were studied during the past years (i.e., Nabatian et al., 2017; Mokhtari et al., 2019) and valuable information is present about their geological and mineralization characteristics. However, the Alamkandi granitoid and Fe deposit have not been studied until the present. In this research study, geochemistry and petrogenesis of the Alamhandi granitoid along with mineralogy, textures and geochemistry of Fe deposit and thermodynamic conditions for formation of contact metamorphic rocks have been studied.

This research can be divided into two parts including field and laboratory studies. Field studies include recognition of different parts of granitoid intrusion and skarn aureole along with sampling for laboratory studies. During field work, 65 samples were selected for petrographic and analytical studies. 19 thin sections and 13 polished thin sections were used for petrographical and mineralogical studies. For geochemical studies, 15 samples from granitoid and ore skarn sub-zone were analyzed by XRF and ICP-MS methods at the Zarazma laboratory, Tehran, Iran. 
  

Based on petrographic studies, the Alamkandi granitoid is composed of granodiorite, quartz diorite and porphyritic diorite. Granodiorites with hetrogranular texture are composed of plagioclase, quartz, K-feldspar, hornblende and biotite. Quartz diorites indicate porphyroid to seriate and hetrogranular textures and are composed of plagioclase, clinopyroxene, hornblende and quartz. Porphyritic diorites have porphyritic texture with plagioclase and amphiboles phenocrysts. The Alamkandi granitoids demonstrate calc-alkaline to high-K calc-alkaline affinity and can be classified as metaluminous I-type granitoids. Primitive mantle-normalized (McDonough and Sun, 1995) trace elements patterns for the Alamkandi granitoids indicate LILE and LREE enrichment along with negative HFSE anomalies and positive Pb anomaly. Chondrite-normalized (McDonough and Sun, 1995) REE patterns for these rocks demonstrate LREE enrichment (high LREE/HREE ratio). Based on tectonic setting discrimination diagrams, the Alamkandi granitoids were formed in the active continental margin.Fe mineralization in the Alamkandi area crops out in discrete places as massive and lens-shaped bodies. The Northern outcrop body has 150m length and up to 50m width, while the southern outcrop body has 100m length and up to 20m width.  Microscopic studies reveal that the skarn zone at the Alamkandi granitoid is composed of garnet skarn, pyroxene skarn, epidote pyroxene skarn, serpentine skarn, and ore skarn sub-zones. Magnetite is the main ore mineral along with some pyrite and chalcopyrite. Garnet, clinopyroxene, olivine, serpentine, epidote, actinolite, calcite and quartz are present as gangue minerals. Based on the field and microscopic studies, the Alamkandi Fe deposit has massive, banded, disseminated, brecciated, vein-veinlets, replacement and relict textures. Based on mineralogical and textural studies, the skarnization processes in the Alamkandi deposit can be divided into 3 stages including: (1) isochemical metamorphic stage, (2) prograde metasomatic stage and (3) retrograde metasomatic stage.

Based on skarn mineralogy, the XCO2 vs. T and T vs. logƒO2 diagrams were used to determine the possible physio-chemical conditions. According to these diagrams and considering mineralogical and textural evidence, maximum temperature for formation of olivine in XCO2≈0.1 and P=1kb was about 450-600°C. Furthermore, garnet and clinopyroxene were formed simultaneously at 430-550°C and ƒO2 equal 10-18 to 10-22. In temperatures less than 450°C, olivine was replaced by serpentine while in temperatures less than 430°C and increasing ƒO2, garnet and clinopyroxene were replaced by epidote + quartz + calcite and actinolite + quartz + calcite, respectively. In temperatures less than 430°C, fluids in equilibrium with granitic intrusion and with relatively high sulfidation (ƒS2>10-6), were not in equilibrium with andradite. Therefore, andradite was replaced with quartz + calcite + pyrite. With reducing ƒS2 (<10-6), andradite was replaced by quartz + calcite + magnetite. During the early retrograde stage, magnetite and pyrite were formed along with quartz and calcite. Mineralogical studies indicate that pyrite was formed after magnetite. In this regard, it seems that metasomatic fluids probably had ƒS2≈10-6.5 and less than 430°C temperature in the beginning of the retrograde stage. Presence of hematite lamella within the magnetite demonstrates that ƒO2 was probably about 10-22 in the beginning of retrograde stage.

North Chargar Cu-Au mineralization located within the Tarom-Hashtjin sub-zone. This area composed of andesite and quartz-andesite lavas alternated with tuffaceouce rocks. The volcanic rocks have calc-alkaline nature and were formed in an active continental margin. Mineralization present as ore-bearing quartz vein-veinlets within a silicified zone. Based on mineralogical studies, chalcopyrite and pyrite are the main ore minerals, and malachite, covellite, chalcocite and goethite were formed by supergene processes. Quartz, barite and chlorite present as gangue minerals. Hydrothermal alterations include silicification, chloritization, sericitization and argillic. Ore and gangue minerals show disseminated, vein-veinlet, brecciated, cockade, comb, replacement, relict and open space filling textures. Based on field and microscopic studies, Cu-Au mineralization in the north Chargar can be divided into four stages: 1- the first stage is silicification of volcano-sedimentary host rock along with disseminated pyrite mineralization, 2- the second stage present as chalcopyrite and pyrite-bearing quartz vein-veinlets and hydrothermal breccia cement, 3- the third stage includes barite vein-veinlets crosscutting the previous stages of mineralization, 4- the last stage is related to supergene processes. Geological features, mineralogy and ore structure-textures in the north Chargar Cu-Au occurrence indicate most similarity with base metal epithermal (intermediate sulfidation) deposit type.

The studied chromite mineralization in the Gharanaz-Alamkandi area is located in the west of Zanjan province and Sanandaj-Sirjan zone. The outcrops rock units consist of amphibolite, granitic gneiss, marble, amphibol schist, garnet mica schist and also ultrabasic sequences. Chromite mineralization occurred as lenzoid, veinlets and disseminated within the peridotite rocks such as serpentinized dunite, serpentinized harzburgite and serpentinit. Olivine, orthopyroxene, clinopyroxene, serpentine, asbestos, chromite and magnetite are the main minerals at these rock units. Mineral chemistry of olivines indicate that the olivines in the peridotites are rich in magnesium and show forsterite composition. Clinopyroxene in the peridotites of the study area are iron- magnesium-calcium rich with mainly are augite in composition. Orthopyroxene minerlas show mainly brunzite composition with minor amounts of hypersthene composition. The mineral chemistry of chromspinels indicate that the chromite mineralization in the study area is podiform type which enriched in Cr and Mg and depleted in Ti. In addition, the mineral chemistry studies in this area show that the host rocks of chromite mineralization and dunite- lherzolite sufferd at least 20% and 40% partial melting, rspectively. On the other hands, it can be state that both of partial melting and depleted mantle melthad important role in the formation of peridotite in the study area. According to this study, it can be note that the chromite mineralization in the study area is ophiolite type mineralization and formed from a boninitic magma in the supra subduction zone during the subduxtion of Proto-Tethys ocean beneath the Iranian block Precambrian-Cambrian time.

Qoyjeh Yeylaq volcanic rocks is located approximately in the 120 km southwest of Zanjan, within the Central Iranian zone. The rock units in this area belong to the Cenozoic which consist of mainly Oligo-Miocene volcanic (basaltic- andesitic lavas) and sedimentary rocks. Based on geochemical classification, the mentioned volcanic rocks are basalt, basaltic andesite and andesite in composition, and have calc- alkaline to high-K calc-alkaline affinity. In the primitive mantle normalized spider diagrams, all of the volcanic rocks show similar patterns with enrichment in LILE (Ba, Th, K, Pb) and negative anomalies of HFSE (Nb, Ti). These rocks show LREE enrichment relative to HREE and high ratio of LREE/HREE. Based on tectonomagmatic discrimination diagrams these volcanic rocks were formed in a continental arc setting. Based on geochemical data, it seems that volcanic rocks of the Qoyjeh Yeylaq area were formed from 5-20 % partial melting of a garnet- spinel lherzolite enriched mantle by subduction of Neo-Tethys under the central Iran, within the Orumieh- Dokhtar magmatic arc.

The Halab Zn–Pb (Ag) deposit, 125-km southwest of Zanjan, is located in the Takab–Takht-e-Soleyman–Angouran metallogenic district (TTAMD), Sanandaj-Sirjan zone. Several types of deposits are present in the TTAMD, including nonsulfide Zn–Pb deposits, sediment-hosted epithermal gold deposits, epithermal precious and base metal deposits, skarn and volcano-sedimentary iron deposits, and massive sulfide Pb-Zn (Ag) deposits. The most important deposits discovered to date within the TTAMD are the Angouran nonsulfide Zn–Pb deposit (Gilg et al., 2006; Boni et al., 2007; Daliran et al., 2013), Zarshuran sediment-hosted epithermal gold deposit (Mehrabi et al., 1999; Asadi et al., 2000; Daliran et al., 2002), and Agdar’reh epithermal gold deposit (Daliran, 2008). Other important deposits or occurrences include Touzlar, Ay Qalasi, Arabshah, Qozlou, Shahrak, Goorgoor, Mianaj, and Halab (Heidari et al., 2015; Mohammadi Niaei et al., 2015; Najafzadeh et al., 2017; Nafisi et al., 2019).To date, no detailed study has been reported to understand the characteristics of Zn–Pb (Ag) mineralization at the Halab deposit. This paper presents the geologic framework, mineralization characteristics, and lithogeochemical signatures of the Halab deposit with emphasis on ore genesis. Identification of these characteristics can serve as a model for exploration of Zn–Pb (Ag) mineralization in the Halab area and other parts of the TTAMD.

Detailed field work was carried out in the Halab deposit. Sixteen polished-thin and thin sections from host rocks and ore horizon were studied by conventional petrographic and mineralogic methods at the University of Zanjan. In addition, a total of 10 samples from barren host rocks and ore horizon at the Halab deposit were analyzed by ICP–MS for trace elements and REE compositions at Zarazma Co., Tehran, Iran.

The host rocks in the Halab area consist of Precambrian deformed metamorphic rocks (equal to the Kahar Formation) that are unconformably overlain by dolomitic marble of the Jangoutaran unit. The metamorphic sequence is composed of pelitic (garnet mica schist, biotite muscovite schist, calcite biotite schist), mafic (biotite amphibole schist and actinolite schist), and felsic (quartz schist) schists intercalated with marble, and quartzite. These rocks are metamorphosed in green schist to amphibolite facies.Mineralization in the Halab deposit occurs as NE-trending foliation-parallel Zn‒Pb (Ag) stratiform horizon hosted by quartz schist units. The ore horizon reaches up to 300 m in length and 3 to 5 m in width, and it is generally 75° SE dipping. Chloritization and silicification of the host rocks are close to the ore horizon, while the sericitic alteration is envelope of the chloritization and silicification. Sphalerite, galena, pyrite and chalcopyrite are the main sulfide minerals in the Halab deposit based on mineralography. Smithsonite, cerussite, chalcocite, covellite and goethite have formed as supergene minerals. Quartz, calcite, chlorite and epidote also present as gangue minerals. The ore minerals show laminated, disseminated, massive, brecciated, replacement and vein-veinlet textures. Chondrite-nonmineralized REE pattern of barren quartz schist host rocks and mineralized samples indicate that mineralized samples are enriched in REE.The main characteristics of the Halab deposit reveal that Zn‒Pb (Ag) mineralization at Halab is comparable with laminated and disseminated parts of Bathurst types of massive sulfide deposits.

In this reaserch for the first time, the sandstones of the middle parts of the Upper Red Formation in the Hamzelou region, 70 Km NW of Zanjan, has been studied based on sedimentology and elemental geochemistary. The studied section is 945 m thick and is divided into four parts. These parts from button to top of the formation consist of  alteration of evaporite beds; green-marl with interbedded of the gypsum (300 m); alternation of red-marl with the layers of red and grey-sandstone and micro-conglomerate (with less frequency) (355 m); the alternation of red and green-marl with interbedded of the grey and red-sandstone (150 m); the alternation of green-grey marls with interbedded of the layers of gypsum (140 m). Based on petrographic studies, these sandstones manily contain different types of the rock fragmensts such as sedimentary, metamorphic and minor amount of volcanic, monocrystalline quartz with straight extinction and finally feldspar manily orthoclase types with a less frequency. Carbonate cements and matrix are also visible between the grains. These sandstones represent manily a feldspathic-litharenite and litharenite (mainly chertarenite) composition with submature to mature in terms of textural maturity. The micro-conglomerate layers are similar in composition to sandstones and classified as an extra-formational conglomerate, ortho-conglomerate (less than 15% matrix) and polymictic conglomerate. Based on the main components of the studied sandstone and results of chemical analysis of the trace elements, the tectonic setting of these sandstones is related to collision and recycled orogenic. Also, according to the obtained data in this research, the source rocks of these sandstones are intermediate to felsic igneous rocks, which were influenced by semi-arid climates in the source area.

Malek Ghasemi and Karimzadeh Somarin (2005) reported that Chromite deposits in Iran occur in Paleozoic and Mesozoic ophiolite complexes in association with serpentinite and serpentinized peridotites and dunites (Ghazi et al., 2004; Shafaii Moghadam and Stern, 2014). There are more than 74 chromite deposits that have been explored in these complexes and they are mainly of alpine-type (Ghorbani, 2013). These ophiolite complexes are part of the Tethyan belts which link to other Asian ophiolite belts such as Pakistan and Tibet in the east as well as ophiolites in the Mediterranean region such as Turkey, Troodos, Greek, and east Europe in the west (Yaghoubpur and Hassannejhad, 2006; Hassanipak and Ghazi, 2000).New data in the current research study are used to infer the geology, mineralization, mineralogy, mineral chemistry and origin of the Qaranaz-Alamkandi chromite.

After preparing 72 samples from the study area, microscopic studies were carried out on 18 thin sections and 23 polished-thin sections for recognition of the microscopic features of the host rock as well as the mineralogy and texture of the ore body. Then, two chromite samples were analyzed at the Iran Mineral Processing Research Center, Karaj, Iran using electron microprobe and scanning electron microscope (SEM) methods.

The Qaranaz-Alamkandi chromite occurrence is located in the west of the Zanjan province and in the northern part of the Sanandaj-Sirjan zone. This area is composed of ultramafic sequences associated with Precambrian metamorphosed rocks such as amphibolite, marble, granitic gneiss and schist.According to petrographic studies rock units in the Qranaz-Alamkandi area consist of serpentinized harzburgite, serpentinized lherzolite, serpentinized dunite, serpentinite, amphibolite, amphibole schist, gneissic granite and mica shcist. This study show that the peridotitic rocks in this region include dunite, harzburgite and lherzolite. Olivine, orthopyroxene and lesser amounts of clinopyroxene associated with secondary minerals (such as serpentine, chlorite and calcite) and opaque minerals (chromite and magnetite) are the main minerals in peridotites.Mineral chemistry of olivines in the peridotites shows magnesium rich olivine with forsterite composition, slightly tending to chrysolite. The composition of olivines falls in the olivine spinel mantle array. Moreover, the olivines of dunites are comparable with those from the oceanic supra-subduction zone peridotites.Clinopyroxenes and orthopyroxenes are Fe-Mg-Ca rich. Furthermore, clinopyroxenes show augite composition and are mainly of the calcium- magnesium type. Orthopyroxenes show mainly bronzite and minor samples showing hypersthene composition. The composition of clinopyroxenes is similar to those of boninites and arc related magmas. This result and the given fact of the low contents of TiO2 and high contents of SiO2 in the structural formula of the pyroxenes suggest that the pyroxenes of the study area are comparable with those from the subduction tectonic settings.Chromite mineralization in the Qaranaz-Alamkandi area has occurred within the ultramafic rocks with serpentinized harzburgite and serpentinite composition. Due to the limited expansion of the peridotitic host rocks, chromite mineralization is also limited and it has occurred as lenses with maximum length up to two meters and one meter width. Chromite mineralization has occurred as massive, disseminated, lenzoid and vein- veinlets form in this area.Mineral chemistry of Chrome spinels from the Qaranaz-Alamkandi area indicate that the chromite samples plot within the ophiolite complexes and high- magnesium chromite field (Leblanc and Nicolas, 1992), which classifies them as podiform chromite deposits in terms of mineralization type (Arai et al., 2004).Chromite mineralization in the Qaranaz-Alamkandi area indicates an Alpine type deposit which is enriched in Cr and Mg and depleted in Ti. The Qaranaz-Alamkandi chromite mineralization has been formed from boninitic magmas which were derived from the subduction process in a supra-subduction zone and fore-arc tectonic settings (Ahrabian, 2018).

Mineralization in the Halab occurrence occurs as Au-bearing silicified-sulfidic zone within Precambrian mafic schist sequence. Ore minerals include arsenopyrite, sphalerite, pyrite, chalcopyrite, pyrrhotite and gold, and quartz, actinolite, clinopyroxene, and chlorite are present as gangue minerals at Halab. The ore minerals show banded, laminated, disseminated, veinlet, brecciated, vug infill, colloform, replacement, and relict textures. Alteration are consist of actinolitization, silicification, and chloritization. Four stages of mineralization can be distinguished at Halab. Gold mineralization is related to hydrothermal stage (stage 3) accompanied with arsenopyrite. Field and analytical results reveal that primary mineralization at Halab occurs as sub-economic stratiform and startabound, laminated and disseminated Zn‒Cu mineralization coeval with the deposition of the volcano-sedimentary units which that overprinted during later metamorphic-deformation process. This primary Zn‒Cu mineralization is comparable with metamorphosed and deformed laminated and disseminated parts of the Besshi type massive sulfide deposits. Gold mineralization is related to late hydrothermal phase which is thought to be result of Miocene magmatism in the Takab–Takht-e-Soleyman–Angouran zone. Investigation of alteration zones within Precambrian metamorphosed units which have spatial relationship with Miocene magmatism, is, therefore, of major importance in exploration of this type of gold mineralization at the Takab–Takht-e-Soleyman–Angouran zone.

Iron oxide-apatite deposits (IOA) are considered to be Kirune-type iron ores which have been formed during Proterozoic to Tertiary eras in different parts of the world. They usually have a connection with calc-alkaline volcanic rocks (Hitzman, 2000). Apatite occurs as a major constituent of these deposits which is accompanied with magnetite and some actinolite. One of the most important features of these deposits (Frietsch and Perdahl, 1995) is higher concentration of REEs.There are some iron oxide-apatite deposits in the Tarom-Hashtjin magmatic-metallogenic belt, northwestern Iran. The Golestan Abad iron oxide-apatite deposit is one of the IOA deposits at the Tarom-Hashtjin belt which is located about 30 km east of Zanjan. The Golestan Abad deposit was studied during the exploration studies, but its geological characteristics, mineralogy, texture, geochemistry and genesis have not been studied yet.

This research study can be divided into two parts that include field and laboratory studies. Field studies include recognition of different lithological units and mineralization zones along with sampling for laboratory studies. During field studies, 60 samples were selected for petrographical, mineralogical and analytical studies. Moreover, 12 thin sections and 15 thin-polished sections were used for petrographical and mineralogical studies. For geochemical studies, 6 samples from intrusive host rocks and 7 samples from mineralized zones were analyzed by XRF and ICP-MS methods at the Zarazma laboratory, Tehran.

The Golestan Abad area is composed of Eocene volcano-sedimentary rocks of the Karaj Formation which have been intruded by quartz monzodiorite, pyroxene quartz monzodiorite and porphyritic quartz diorite intrusions. Based on petrographic studies, the pyroxene quartz monzodiorites have porphyritic and felsophyric textures and are composed of plagioclase, quartz, clinopyroxene, K-feldspar and hornblende phenocrysts set in a quartz-feldspatic groundmass. Quartz monzodiorites show porphyritic and felsophyric textures and composed of plagioclase, hornblende, quartz, K-feldspar and biotite. The quartz monzodiorite and pyroxene quartz monzodiorites have high-K calc-alkaline affinity and may be classified as metaluminous I-type granitoids. Primitive mantle-normalized (McDonough and Sun, 1995) trace elements diagrams for these granitoids indicate LILE enrichment along with negative HFSE and distinctive positive Pb anomalies. Chondrite-normalized (McDonough and Sun, 1995) REE patterns for these granitoids demonstrate LREE enrichment (high LREE/HREE ratio) and weak negative anomalies in Eu. These granitoids were formed in an active continental margin to post collisional tectonic setting.Mineralization at the Golestan Abad occurs as lenses and vein-veinlets of iron oxide-apatite mainly within the quartz monzodiorite- pyroxene quartz monzodiorite intrusions. Stockwork ores occur in the footwall of the main veins. Mineralized lenses and veins have up to 300m length and 20m width. Hydrothermal alterations around the mineralized veins include silicification, calcic (actinolitization), argillic and propylitic. From a mineralogical point of view, this deposit is composed of magnetite, apatite, actinolite, pyrite and chalcopyrite as primary minerals, while hematite, covellite, goethite and gypsum were formed during supergene alteration. Mineralization textures in the Golestan Abad deposit include vein-veinlet, banded, massive, brecciated, disseminated, stockwork, replacement, relict and open space filling. Based on mineralogical and textural studies, 3 stages of apatite formation were distinguished which include: 1- coarse-grained idiomorphic apatite crystals within the magnetite matrix, 2- fine-grained apatite crystals as matrix of brecciated magnetites, and 3- coarse-grained idiomorphic apatite crystals within the actinolite-apatite veins which have been cut in the previous stages. Apatite crystals of the 3 mentioned stages have high concentrations of REE that include 0.98, 0.92 and 0.95%, respectively. Condrite-normalized (McDonough and Sun, 1995) REE patterns for 3 apatite generations demonstrate LREE enrichment with high LREE/HREE ratio and distinctive negative Eu anomalies.

Similar REE patterns of apatite crystals and mineralized samples with host quartz monzodiorite-pyroxene quartz monzodiorite samples demonstrate a genetic link between iron oxide-apatite mineralization and granitoids. Furthermore, REE patterns of the Golestan Abad deposit are similar to other iron oxide-apatite deposits of the Tarom-Hashtjin metallogenic belt (Nabatian and Ghaderi, 2014; Mokhtari et al., 2017), and those of Central Iranian iron ores (Mokhtari et al., 2013). Finally, the REE patterns of the Golestan Abad deposit are similar with the REE patterns of the Kiruna-type iron ores (Frietsch and Perdahle, 1995). Totally, based on mineralogical assemblages, hydrothermal alteration, mineralization textures and geochemical characteristics, the Golestan Abad iron oxide- apatite deposit can be classified as the Kiruna-type iron ores.