فصلنامه زمین شناسی اقتصادی
سال یازدهم شماره 4 (پیاپی 23، زمستان 1398)

The Qoyjeh Yeylaq Pb-Zn (Ag) deposit located 120 km southeast of Zanjan, is situated in the Urumieh-Dokhtar magmatic arc.apart from Prior to this research no work has been published on Pb-Zn (Ag) mineralization at the Qoyjeh Yeylaq except for small scale geological maps of the area, i.e. 1:250,000 geological maps of Kabudar Ahang (Bolourchi and Hajian, 1979), 1:100,000 geological maps of Marzban (Majidifard and Shafei, 2006) and a number of unpublished Pb-Zn exploration reports.The present paper provides an overview of the geological framework, mineralization characteristics, and results of geochemistry study of the Qoyjeh Yeylaq deposit with application to ore genesis. Identification of these characteristics can be used as a model for exploration of this type of Pb-Zn (Ag) mineralization in this area and elsewhere.

Detailed field work has been carried out at different scales in the Qoyjeh Yeylaq area. About 26 polished- thin and thin sections from host rocks, mineralized and altered zones were studied by conventional petrographic and mineralogic methods at the University of Zanjan. In addition, a total of 11 samples from fresh and altered host rocks and ore zones at the Qoyjeh Yeylaq deposit were analyzed by ICP-MS for trace elements and REE compositions at Zarazma Co., Tehran, Iran.

The host rocks at the Qoyjeh Yeylaq deposit consist of Oligo-Miocene volcano-sedimentary rocks which are overlain conformably by Oligo-Miocene sedimentary rocks. Volcanic rocks are mostly basaltic andesite and andesite lava flows. Basaltic andesites with porphyritic texture consist of predominantly plagioclase (70 vol%) and clinopyroxene (25 vol%) phenocrysts with accessory Hornblende (<5 vol%) crystals. Andesites consists of plagioclase (75 vol%), hornblende (15 vol%), and clinopyroxene (10 vol%) phenocrysts set in fine-grained groundmass. The Oligo-Miocene sedimentary units consist of alternation of sandstone, red marl, and siltstone as well as medium-bedded to massive limestone with interlayers of tuff and shale. The Miocene sedimentary units consist mostly of alternations of red and green marl and red to grey sandstone.Mineralization at Qoyjeh Yeylaq occurs as quartz-sulfide veins in Oligo-Miocene basaltic andesite and andesite lavas. The ore zone reaches up to 150 m in length and 10 m in width. It has NNW-trending and mostly dips 70-80o to SW. Three stages of mineralization can be distinguished at the Qoyjeh Yeylaq deposit. Stage-1 is the most abundant, widespread, and economically important ore forming stage at Qoyjeh Yeylaq and is represented by quartz and sulfide (galena, sphalerite, and chalcopyrite) veins (up to 5 mm wide) plus breccias cement. Stage-2 is represented by 2 mm wide individual or sets of late calcite veins and veinlets that usually cut stage-1 mineralization. No sulfide minerals are recognized with stage-2. Covellite, cerussite, Fe-oxides and hydroxides are formed during the supergene stage (stage-3). They usually show replacement and vug infill textures.The hydrothermal alteration assemblages at Qoyjeh Yeylaq grade from proximal quartz and calcite to distal sericite, epidote, calcite and chlorite (propylitic alteration). The quartz and calcite alteration types are spatially and temporally closely associated with Pb-Zn (Ag) mineralization. The propylitic alteration marks the outer limit of the hydrothermal system.The ore minerals at Qoyjeh Yeylaq are formed as vein-veinlet and hydrothermal breccia cements, and show vein-veinlet, vug infill, and disseminated textures. Galena, sphalerite, and chalcopyrite are the main ore minerals; covellite, cerussite, and goethite are supergene minerals. Quartz, and calcite are present in the gangue minerals that represent vein-veinlet, breccia, vug--infill, and replacement textures. Comparison of Chondrite normalized (Nakamura, 1974) REE patterns of Oligo-Miocene fresh and altered basaltic andesite, andesite lavas, and the mineralized samples at Qoyjeh Yeylaq indicate that mineralization is probably genetically related with basaltic andesite and andesite lavas. In this case, leaching of some elements from the host basaltic andesite and andesite lavas may have been involved in mineralization.The geological, mineralogical, geochemical, textural and structural characteristics of the Qoyjeh Yeylaq deposit reveals that mineralization at the Qoyjeh Yeylaq deposit is an example of intermediate-sulfidation type of epithermal base metal (Ag) mineralization.

The authors are grateful to the University of Zanjan Grant Commission for research funding. The Journal of Economic Geology reviewers and editor are also thanked for their constructive suggestions on modifications of the manuscript.

This research study is based on  knowledge-driven approach to synthesize the different parameters which rule on the formation of carbonate hosted zinc and lead deposits. The analysis of available data sets of the north Irankuh district demonstrates the complexity of decision making due to the different anomalous prospects introduced by geophysical, geochemical and surface evidences.Five known deposit/active mines, namely Gushfil, Zone 1 Gushfil, Blind, Tapeh Sorkh and Zone 5 Romarmar with total geological resources quoted as 13.4 million tons at 5.53% combined lead and zinc (Fig. 10) were selected to be examined in order to asset a knowledge-driven approach to the exploration of carbonate hosted zinc and lead deposits. The diversity of geometry, mineralogy and host rock of the deposits is tightly confined by the parameters surrounding the genesis of MVT deposits such as genetics of solutions, temperature of deposit formation, tectonic channel ways, different episodes of deposition of sphalerite and galena, hydrologic system of area, solution direction, wall rock reactions (Leach et al., 2010), depth of solution penetration, solution response to the Magnesian regime and metal bearing.

The present study consists of detailed  underground and surface mapping, reinterpretation of district geology, detailed logging of about 100000 meters’ diamond drilling, ore geology, tectonic settings, deposits geometry, geochemical and geophysical survey within 7 square kilometers of north Irankuh district between the Gushfil and Tapeh Sorkh deposits.

Five known deposits in the north Irankuh district occur in the area of an intense detachment faulting (Fig. 1 and Fig. 5). The Gushfil, Zone 1 Gushfil and Blind deposits occur in north Irankuh reverse fault and Tapeh Sorkh and Zone 5 Romarmar in the trust fault. The deposits are confined to a certain stratigraphic unit locally called K3D (Figs. 2 and 3). Widespread regional selective dolomitization shows an extensive lateral movement from NW to SE and the depth of dolomitization in certain units drastically decreases. Two main regimes of solutions initially started with sphalerite and they were subsequently followed by galena the later of which is found in the secondary porosity. Mineralogy of the deposits is simple but the pyrite amount of the deposits varies from 2% to 20% which reflects the higher temperature of the solutions responsible for sulphide precipitation (Marie et al., 2001), geometry of the deposits and their distance to the current topography effect on chargeability values (Fig. 20).Sparry dolomite is found in three types as barren, with pyrite and light color sphalerite that occur in country rocks of all deposits except for the blind deposits. They can be used as a guide, addressing potential deposits.EPMA analysis revealed a considerable amount of Cadmium, Silver, Antimony, Arsenic and Copper within Sphalerite and Galena minerals (Fig. 12). Because of the semiarid climate in the area the decomposition of sphalerite, galena (Hitzman et al., 2003) and carbonate host rock has caused widespread distribution of Zn, Pb, Ag, Cd, Sb, As, Cu, Mn, Mg, Fe and Ca in the secondary halo of the area. The soil samples have been studied based on the static and machine learning methods (Figs. 13–A and B) by different researchers (Zekri et al., 2019). The anomalous areas based on geochemical studies have been tested by core drilling and the results are considered to be negative even in the area called Zone 3 which coincides with both geochemical and geophysical anomallies. In a different approach to understand the structure of geochemical elements the distribution of Zn, Pb, Ag, Cd, Sb, As, Cu, Mn, Ba together with elements such as Mg, Fe and Ca has been compared (Figs. 14, 15 and 16).The soils are heavily polluted due to widespread mineralization and no background value (Reimann and De Caritat, 2012) can be recognized.The comparative analysis of element concentrations in 5 selected populations in the studied area (Fig. 15) did not show any signs that could help  recognize important anomalies from the false anomaly. However,  it seems that the sudden decrease of Mg content (Fig. 17–C) in the area of Zone 3  (Zekri et al., 2019) is meaningful. Two geochemical profiles of soil samples crossing along this population and the next one crossing an active mine (Zone 5 Romarmar) (Fig. 18) provide us with a better understanding of the important anomalies versus the false anomaly since in the false anomaly the increase of Zn, Pb, Ag, Cd, Sb, As, Cu coincides with a sudden drop of concentration of Mg, Fe and Ca (Figs. 18–A and B). Recognition of ore containing strata (Sangster, 1995) is very important (Figs. 2 and 3) in locating successful drill holes in the exploration of carbonate hosted zinc and lead deposits. Eventually the use of data driven methods even opting advanced machine learning methods is not properly sufficient  to recognize  productive areas and we recommended the knowledge -driven approach.

The Borujerd-Kermanshah ophiolite is a part of the ophiolite complex belonging to the Zagros Mountains and is a part of the Alpes-Himalayan belt (Alavi, 1994). The Boroujerd-Kermanshah Ophiolite complex consists of serpentinized peridotite, layered metagabbro, isotropic gabbro, diabase dyke, plagiogranite, pillow lavas and sedimentary rocks (Miocene radiolarite and limestone). In the upper part, the radiolarite layers are covered by jasperoid rocks and pelagic limestone (Mohajjel et al., 2003; Saccani et al., 2013). The Noorabad Delfan manganese deposit is subjected to mineralogical and geochemical studies in order to elucidate its petrogenesis. The Noorabad Delfan manganese deposit is located along the ophiolite belt of the upper Jurassic-lower Cretaceous period. Manganese mineralization occurs as syngenetic to epigenetic with jasperoid and silicified veins in the carbonate and radiolarian chert units. Geochemical studies show that some elements such as Ce, Cu, Ni are enriched in the mineralized zone. Mobile and trace elements (Sr, As, Zn, Ba, Fe, Mn, Si) and the ratio of Mn/Fe, Al/Ti, show similar characteristics with submarine hydrothermal-hydrogenous manganese deposits. In geochemical studies, SEM, XRD and EPMA results show that pyrolusite is the majar mineral in the ore deposit, and nsutite and rhodochrosite are formed as the accessory phase.

During the field work, 53 samples were collected from the mineralization zone and host rocks. A total of 30 polished and thin sections were studied by Zeiss polarized microscope (Axioplan-2), in the Kharazmi University and the Iran Mineral Processing Research Center (IMPRC). Suitable sections were selected for more study by Zeiss 1450vp SEM at the Iranian Mineral Processing Research Center (IMPRC). The SEM-EDS analyses and secondary electron (SEM-SE) images at the IMPRC were acquired on beam currents between 0.05 and 5 nA, and electron acceleration potentials of 5 to 20 kV. The Electron microprobe analysis of selected points by SEM was carried out using a Cameca SX100 at IMPRC in the 20 kV and 20 nA current and 1 to 5 mm beam long. The Cameca PAP correction software was used for data reduction. Backscattered electron images were used in order to select more analytical points. A total of 15 samples were selected for whole rock chemical analysis. Samples were prepared with regular methods and finally they were analyzed for major and rare elements by the XRF and ICP-MS methods in Zarazma and Iran Minerals Processing Research Center Laboratory.

Manganese deposits with hydrothermal origin are usually related to silica gels. These deposits are associated with submarine volcanic eruptions and hydrothermal-hydrogenous activity and they are rich in metal elements. This kind of deposits, is basically emplaced with interlayer marine sediments (Roy, 1992). Titanium in the hydrothermal fluids is an immobile element and can be used as an indicator for measuring the amount of continental crest sediment. The relatively high TiO2 levels in the manganese deposits indicate the composition of the material during sedimentation (Sugisaki, 1984). Therefore, in the hydrothermal deposits, the TiO2 ratio is lower than other kinds of manganese ore mineralization types. Nicholson (Nicholson, 1992a) believes that hydrothermal manganese deposits are known by enrichment of As, Ba, Cu, Pb, Sb, Sr, Li, Cd, Mo, V, Zn, Co, Cu, Ni and sedimentary deposits are distinguished by K, Na, Ca, Mg, Sr (Nicholson, 1992b). According to this statement, the manganese mineralization of the Noorabad Delfan deposit may be classified as hydrothermal to hydrogenous ore deposits related to oceanic crust ophiolitics.

The Noorabad Delfan deposit with 5 km long is formed in radiolarite sequences in the west of Iran. Based on field observation, mineralogy and geochemistry and the major/trace and rare elements ratio, Noorabad Delfan mineralization is classified as a hydrothermal-hydrogenous deposit. In the study area, the manganese mineralization is formed with interlayer of radiolarite as syngenetic to epigenetic mineralized zones.The hydrothermal systems are generated by submarine volcanic activity and seawater. Due to the rotation of submarine volcanic activity related fluids, the hot oceanic water carries metalliferous phases. The metalliferous phase has been deposited during cooling, pressure reductions and Eh-pH changes. The hydrothermal to hydrogenous activity is the main factor in manganese mineralization in the Noorabad Delphan deposit. Mineralogical and geochemical evidences support a primary hydrothermal source for Mn-mineralization.

The Aliabad area is located in the northwest of Nain. Volcanic rocks of the Aliabad area have andesitic to rhyolitic composition.On the basis of petrographic investigations, porphyritic texture is the main texture of these rocks. Thus, they have experienced two crystallization stages. In these rocks, phenocrysts have been crystallized in the first stage, and in the second stage the cooling processes were fast, resulting in a groundmass of glass and fine crystals.The second stage of crystallization in these rocks took place at (near) the earth surface. The composition of phenocrysts such as amphibole, biotite and pyroxene provide valuable data about magmatic series, pressure, and temperature history of the primary magma during crystallization. In this study, the clinopyroxene of these rocks was analyzed in order to estimate the physicochemical conditions of the parent magma.

Field work in the Aliabad area was carried out to identify volcanic units and their relationships. About 65 samples were collected. Thin sections were prepared for petrographic studies to select suitable samples of the volcanic rocks for more detailed mineralogical and geochemical studies. The chemical composition of minerals was determined using a wavelength dispersive EPMA (Cameca-SX 100) at Iran Minerals Research and Processing Center. Analytical conditions for the minerals were accelerating voltage of and a beam current of 15 nA. 15 kV.  Also, the Minpet software package was used for processing the relevant data and calculating the structural formula of clinopyroxene minerals based on 6 oxygen atoms.

The chemical compositions of clinopyroxenes were used to estimate the chemical evolution and P-T conditions of the magmas during crystallization. Microprobe analyses show that clinopyroxenes in the andesitic rocks are augite (En43-45Wo 38-42 Fs14-18).According to the clinopyroxene thrmobarometry calculations done by several methods, it was inferred that the clinopyroxenes are crystallized at temperatures of 1009-1200 °C and pressures of 2.5-7 kbar.By noting the distribution of aluminum in clinopyroxenes, these phenocrysts were formed in a range of low to medium pressure that shows the crystallization of those during the ascending of magma in different depths of 9 to 18 km. According to the Helz diagram (1973), the amount of water is about 10 percent. Clinopyroxene composition along petrographic investigations in the studied rocks confirm that ƒO2 is high.

The Aliabad area is located in the Urumieh- Dokhtar volcanoplutonic belt, Northwest of Nain- Iran. In the Aliabad area, the exposed Cenozoic volcanic rocks are compositionally from andesite to rhyolite. These rocks show porphyritic, trachytic, and amygdaloidal textures under the microscope and they consist of plagioclase, clinopyroxene, sanidine, quartz, opaque and apatite.The andesitic rocks of the Aliabad area are composed mainly of plagioclase and clinopyroxene phenocrysts in a groundmass of plagioclase microlites and fine crystals of pyroxene and opaque minerals along with glass. According to the ternary diagram of Wo-En-Fs (Morimoto, 1989), the studied clinopyroxenes are augite in composition. The physical (pressure and temperature) conditions of a magma during crystallization is recorded in the chemical composition of the clinopyroxene phenocrysts. Therefore, clinopyroxenes are representative of magma composition and usually are used for identifying the chemical condition i.e. magmatic series and physical conditions, temperature and pressure of a magma at the time when clinopyroxene was crystallized. Several methods that are applied for this purpose are as follows:1- The Soesoo (1997) method Based on this approach, the pressure and temperature formation of the Aliabad clinopyroxenes are about 3.5-6 kbar and 1150-1200 °C, respectively.2- The Sayari and Sharifi (2014) method According to this method, the pressure and temperature formation of the studied samples are about 2.48-4.8 kbar and 1074-1094 °C, respectively. 3- The Nimis and Taylor (2000) method Using this method, the temperature formation of clinopyroxenes in the Aliabad area is about 1009-1083 °C.

The authors of the manuscript would like to thank the respectable reviewers for valuable suggestions and also Dr. Sayari for his help in using the SCG software.

In the southern margin of the Mashhad plain in Northeastern Iran, there are strips with tens of kilometers length consisting of metamorphic rocks and ophiolite complexes with the NE-SW trend. Ophiolites are fragments of ancient Oceanic crust (Ghaseminejad and Torabi, 2015; Khanchuk et al., 2016; Shirdashtzadeh et al, 2017) most of which consists of ultramafic rocks. Ophiolites are formed during tectonic displacement in the southern part of the Mashhad plain (Alavi, 1991; Karimpour et al., 2010; Sheikholeslami and Kouhpeyma, 2012; Zanchetta et al., 2013; Shafaii Moghadam and Stern, 2014). These undergoing metamorphosed regions ultimately lead to the formation of serpentines complex due to factors of pressure and temperature. Subsequently, tectonic variations create different levels of serpentinization in the region. Different degrees of serpentines have different geotechnical properties that are discussed in this study.

To conduct the lithological studies, 313 samples were collected from surface and trenches in the studied area. Following the preparation of the microscopic cross-section of all specimens, the mineralogical characteristics, texture changes, color changes, degradation and microcrack development were studied. Then, the samples were classified based on the general classification of ultramafic rocks (Streckeisen, 1974). According to this classification, the ultramafics extracted from the studied area were classified in the metaperidotite and metapyroxenite groups. After separating various metaperidotites and metapyroxenites the percentage of serpentinization in all specimens were determined and 60 samples with different serpentinite percentages were selected. Also, the stone blocks were provided for preparing the core samples. Physical tests (such as dry and saturated unit weights, porosity, and water absorption percentage), and mechanical tests (such as uniaxial compressive strength, point load strength, and Brazilian tensile strength) were performed based on the Brown (1981) method in the laboratory of the Ferdowsi University of Mashhad.

The results show that there is a good relationship between the percentage of serpentinization of samples and uniaxial compressive strength (the most important geotechnical parameter in rocks). The ultramafic rocks are divided into three groups based on uniaxial strength and 25 to 40% of serpentine are very strong, 40 to 60% of serpentine are strong and 60 to 75% serpentine are of medium strength. Also, the ultramafics with 75% to 95% of serpentine, are named as serpentinite rocks with weak uniaxial compressive strength.

Although most of the ultramafic rocks have good strength as the foundation for building, the construction of a structure on these rocks has numerous problems due to the formation of minerals such as serpentine and talc with one-directional cleavage. With increasing the degree of serpentinization, some phenomena such as slope instability, sliding, excavation collapse will occur. The results of the present research indicated the priority of serpentinization degree of ultramafic rocks compared to their strength. As it is seen, although in a high degree of serpentinization, the metapyroxenites have higher strength and lower water absorption compared to metaperidotites. Therefore, the mentioned issues demonstrated the importance of the degree of serpentinization compared to strength in ultramafic rocks. 

The authors would like to thank Professor Mohammad Hassan Karimpour for his helpful and effective guidance on the petrography of ultramafics rocks in this paper.

Thermobarometric models based on the chemical equilibrium among coexisting mineral-mineral or mineral-melts pairs are useful tools widely used to estimate the P-T path and chemical evolution during igneous processes. The high sensitivity of amphibole to physicochemical changes makes it a good tracer for thermobarometric models. Majerad Igneous-Metamorphic Complex with NE-SW trend, 40 kilometer length, and 10 kilometer width is located in the southeast of Shahrood in the northern margin of the Central Iran structural zone. Late Neoproterozoic sequence of Majerad metamorphic complex includes a wide range of metamorphic rocks with extensive compositional variety of metacarbonate, metapsammite, metapelite, metabasite and metarhyolite. Metabasites of the Majerad metamorphic complex consist of a greenschist to garnet amphibolite. Late Iranian Neoproterozoic complexes have been studied by  numerous researchers, and a lot of papers have been published related to them (Rahmati Ilkhchi et al., 2011; Balaghi Einalou et al., 2014; Faramarzi et al., 2015; Hosseini et al., 2015; Malekpour-Alamdari et al., 2017). These complexes have cropped out in the different parts of Iran, except the Kopeh Dagh, Makran and the East Iran Flysch structural zones.

The whole-rock major element compositions were determined by X-ray fluorescence using fused glass disks at the Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, China. Trace elements were determined by ICP-MS (Agilent 7500a) at IGGCAS after more than 5-day acid digestion of samples in Teflon bombs. Compositional mineral analyses were performed at the State Key Laboratory of Continental Dynamics, Northwest University, Xian China, using a Cameca JXA-8230 instrument at an acceleration voltage of 15 KV, and beam current of 10 nA.

In the metamorphic environment, aluminous hornblende-bearing assemblages are stable over a wide P-T field that extends from amphibolite to granulite, and high-T eclogite-facies conditions. At lower temperatures, the hornblendic amphibole is replaced by sodic-calcic amphibole at relatively high-P and by actinolite at lower-pressure greenschist-facies conditions (Spear, 1993; Ernst and Liu, 1998; Molina et al., 2015). Amphibole formulas were calculated with the Amp-Excels spreadsheet using the 13 cations method (Leake et al., 1997). Amphiboles of metabasites are calcic, and Amphiboles of actinolite-schists are in the range of actinolite to magnesio-hornblende, and in amphibolites, they are plotted in the range of magnesio-hornblende to tschermakite. Plagioclase are usually oligoclase to bytownite. Temperatures range of metamorphism events of amphibolites of the Majerad complex have been estimated by using the hornblende-plagioclase thermometer. This thermometer is based on the Ca and Na equilibrium exchange between plagioclase and amphibole (Holland and Blundy, 1994). The hornblende-plagioclase pair thermobarometer estimates temperatures of 450 to 690ºC and pressures of 4 to 11 Kb for the formation of the Majerad amphibolites. These temperature-pressure ranges correlate with P-T conditions of the greenschist and amphibolite facies in the typical Barrovian type metamorphism.