JOURNAL OF ECONOMIC GEOLOGY
Year:2023 | Volume:15 | Issue:2|Papers Count:6

Macroscopic, microscopic and geochemical studies carried out on albite-bearing metasomatites and metasomatic rhyolites hosting the magnetite-apatite deposit of Chogharat indicate the presence of three generations of albite with different concentrations of REE-Y-Ti-Th, in response to T-P reduction and chemical changes of the fluids and the ratio of fluid to rock. The geochemical analysis of the low Ca/Na fluids shows a deficiency in REE-Th mineralization in the white albites, while in the fluids with medium Ca/Na, the REE mineralization (REE>Th) has occurred in the pinkish albites. In contrast, fluids with high Ca/Na indicate Th mineralization (Th>REE) in the red albites. The stable isotopes of C-O on the paragenetic calcites show REE-Y-Ti-Th mineralization of albites due to High-T hydrothermal fluids. Otherwise, the stable O-C isotopes of the Ghoghart apatites and stable isotopes of S in the ore deposits of the BMD verify the role of evaporitic brines and fluid-rock interaction on the mineralization. The presence of calcite and titanite, associated with the calcic-amphiboles and clinopyroxenes, Ca-inclusions in the thorite structure and Ca-content of the thorites, indicate thorite mineralization from the Co32- and Ca2+ fluids due to low activity of the chlorine. According to this study, the source of metasomatism is mainly evaporitic brines with a minor amount of magmatic and related hydrothermal fluids. Mineralization is the result of interaction of the magmatic and hydrothermal fluids of the Late Ediacaran- Early Cambrian plutonic/ subvolcanic intrusions with the evaporitic brines, derived from the synchronous evaporitic sequence. IntroductionMetasomatism often causes the extensive mineralogic and chemical changes of rocks (Enjvik et al., 2018). Alkaline metasomatism, as one of the most important mineralization processes, could be classified to the high-temperature and medium- to low-temperature types (Zhao, 2005). High-T and medium- to low-T alkaline metasomatism are associated with the Nb-Ta-Li-Br and U-REE mineralization, respectively. The mean array of U, Th, and REE of the associated ore deposits of alkali-metasomatism is not high, but because of their relatively high tonnage are considered important prospecting goals that usually form in the faulted area and in relation to the deep regional structures (Zhao, 2005; Cuney and Kyser, 2008). Until now different sources of metasomatic processes are suggested for the Ghoghart magnetite-apatite in the BMD (e.g. Khoshnoodi et al., 2017; Aftabi and Mohseni, 2020; Bonyadi and Sadeghi, 2020; Aftabi et al., 2021; Majidi et al., 2021). In addition, association of Ti with this type of ore deposits is less reported and associated with U(Th), REE, Ti is considered a rare phenomena in the ore deposits of this district, not reported yet. In this research, the nature of REE-Y-Ti-Th mineralizing fluids in the Ghoghart deposit would be studied. Research methodAfter field studies, 44 samples of the Ghoghart host metasomatic rhyolites are selected for petrographic microscopy out of 63 collected samples. For complementary mineralogical studies, 24 samples of the 3-generation albite-bearing metasmatites are studied by the Scanning Electron microscopy, model LEO-1400 with 17-19kV, ray dim. 12 and 20 nA and 12 samples of different-generation albites are analyzed XRD by the Philips Xpert pro in the Iranian mineral processing center and 9 samples are analyzed by the Raman spectrometer of Senterra 2009 model of the Germany Brucker Co. with penetration depth of 2µm, spectral width of 200-3500 cm-1, wavelength of 785 nm, CCD detector and resolution> 3 cm-1 in the nano-electronic Lab of the Tehran University. Furthermore 22 samples of metasomatites with different generations of albites are analyzed ICP-MS at the Zarazma Lab, Iran. To constrain the source of mineralizing fluids, O-H isotopic analysis of 4 apatite samples are performed at the Hangaria Lab, Hungry. After petrography of fluid inclusion on the 1-generation calcite of albite-bearing metasomatites, 8 selected samples of calcite are analyzed in the Ottawa University Lab., Canada. ResultsThe macroscopic, microscopic, and geochemical studies on the host albite-bearing metasomatites and metasomatic rhyolites of the Ghoghart magnetite-apatite deposit show extensive and intense effect of alkali-metasomatic and hydrothermal processes, associated with the sodic, sodic-calcic, potassic, and late carbonate± quartz alterations. The REE-Y-Ti-Th mineralization is related to the sodic-calcic alteration, which is shown as the 2- and the 3-generation albites. Intimate association of this mineralization with the related albites reveal their common genesis and follow the spatial pattern of the sodic, and sodic-calcic alterations. The REE and incompatible REE patterns show a common pattern of the LREE enrichment to the HREE, which is the characteristic of subduction zone magmas, in all samples. The stable O-H isotopes of the paragenetic calcite with the albites show albitization and REE-Y-Ti-Th mineralization due to the HT-hydrothermal fluids. The stable O-H isotopic study on the 1-generation apatites of the Ghoghart magnetite ore rocks display the role of evaporitic brines and rock-fluid interaction on the ore formation. Mixing of magmatic and HT-hydrothermal fluids with these evaporitic brines caused mineralization and associated alteration in the Ghoghard deposit. Moreover, stable sulfur isotopes show evaporitic brines as the main source of mineralizing fluids with minor effect of magmatic fluids. Infiltration of the hot oxide brines enriched in the REE-Y-Ti-Th, P, and Ca ± Fe, caused the weak sodic alteration (> 170 ºC) and sodic-calcic alteration (> 280ºC) of the host rocks, which was associated with extensive deposition of the magnetite-albite, low-grade magnetite-scapolite, and high-grade magnetite-actinolite. In the late stage of sodic-calcic alteration, magnetite-apatite (280-245ºC) has formed. The potassic alteration after the former aforementioned mineralization phases (> 280ºC, ~ 200ºC) and then the sericite, chlorite, and epidote assemblage is formed by the LT-hydrothermal fluids (180-250ºC) as the last stage of mineralization (Bonyadi and Sadeghi, 2020). Microtheremore data of the fluid inclusions of the calcites, related to the albite-bering metasomatites, and 1-generation apatites confirm the recorded alteration temperatures.Association of the calcite, titanite with the calcic-amphiboles and clino-pyroxene (actinolite and augite), Ca-inclusions in the thorite structure and Ca content of the thorites (CaO ~ 2.3%) indicate deposition of the thorites from the Ca2+ and Co32- bearing carbonate fluids due to the low-activity of Cl in the REE-Y-Ti-Th mineralization zones. According to this study, fluids with low-content of Ca/Na, did not cause or were associated with minor REE and Th mineralization (white 1-generation albites). The fluids with medium amount of Ca/Na caused the REE mineralization (REE>Th, 2-generation pale pink albitities) whereas the high Ca/Na content fluids was associated with the Th mineralization (Th>REE, 3-generation dark pink albites). The Th deposition occurred under the Eh and ph changes and also the fluid/rock ratio, revealed by the exsolution evidences; In fact, the increase of ph has occurred due to the expelling of CO2 from the mineralizing fluids along the fractures.This phenomena had a considerable effect on deposition of the Th-bearing carbonate complexes. The ph increase of the mineralizing fluid was associated with silica content of the fluid as the silicic acid that caused deposition of the Th-silicates. Discussion and conclusionSubduction of the Prototethys under the central Iranian crustal blocks during the late Neoproterozoic-Early Cambrian caused an extensive granitoid magmatism that was accompanied by deposition of the equivalent evaporitic-volcaniclastic deposition (Esfordi Formation) in the extensional back-arc basins (Ramezani and Tucker, 2003). The edicaran-lower Cambrian Fe-P mineralization in the BMD shows a genetic relation with these granitoids, related volcanic rocks, and associated synchronous evaporitic-volcaniclastic deposits. In fact, the intrusive and subvolcanic intrusions, as a thermal, engine caused heating of the evaporitic brines of the synchronous adjacent basins. The most important characteristic of these brines is their high Na/K and Cl/S content.  These hot alkali-enriched, sulfur- oxide brines leached their passing host rocks and transferred the REE-Y-Ti-Th elements. The result was sodic and sodic-calcic metasomatism with REE-Y-Ti-Th mineralization. The results of this research constrain the mainly evaporitic brines with a minor amount of magmatic and related hydrothermal fluids as the source of metasomatism. In fact, mineralization is the result of magmatic and hydrothermal fluids of the Late Ediacaran- Early Cambrian plutonic/ subvolcanic interaction with the evaporitic brines, derived from the evaporitic sequence (Esfordi Formation). AcknowledgementsThe authors appreciate the Iranian Central Iron Ore Company manager and staff for their assistance during this research.

The Zanjan-Takab complex is a metamorphic belt with NW-SE trend that includes gneiss, amphibolite and gneissic amphibolite, old metagranites, pelitic schists with migmatites and metaophiolites. Takab mafic migmatites, based on field evidence and partial melting degree, are divided into two main groups of metatexites with patchy, ophthalmitic, diktyonitic, agmatic, stromatic structures and diatexites with schollen, ptygmatic, folded, stictolithic, phlebetic, schliren, nebulitic structures. These migmatites consist of mesosome part with textures of porphyroblastic, xinoblastic, granoblastic and nematoblastic and main minerals plagioclase, hornblende, biotite, melanosome part with nematoblastic, xinoblastic, granoblastic and oriented textures and main minerals hornblende and plagioclase. The leucosome part is composed of granular, sympletic and myrmekitic textures and the main minerals are plagioclase, quartz, k-feldspare, titanite, hornblende and biotite. Investigating the shape of the crystal size scatter diagrams (CSD) shows the physical conditions and petrological processes are effective in the studied rocks. In order to investigate these processes, plagioclase crystals in 4 leucosome samples were quantitatively analyzed with the help of Jmicro vision and CSD Corrections software, and then the results obtained from the analysis of different leucosome samples were compared. The crystal size scatter diagrams of plagioclase crystals show two stages of growth with different speeds in the studied samples, so that the larger crystals (the end part of the curved diagram on the right) belong to a melt that is at greater depths or it cooled in a calmer environment. Nevertheless, the initial part of the diagram on the left side crystallized in more superficial areas and at a higher speed.Introduction The crystallization history of a rock is recorded in the size and distribution of its minerals (Muller et al., 2009). The most common method of quantitative measurement of textures is investigation of crystal size dispersion (CSD) (Higgins, 1998). Crystal size dispersion (CSD) deals with the quantitative measurement of crystals of a specific mineral with a unit volume in size intervals (Cashman, 1993; O'Driscoll et al., 2007). Many researchers, including Cashman and Marsh (1988), Cashman (1993), Zieg and Marsh (2002), Higgins and Roberge (2003), Higgins and Roberge (2007), Kaneko et al., (2005), Cashman and Ferry (1988), Higgins (1996) and O'Driscoll et al., (2007) in their studies of CSD diagrams to determine kinetic indices of crystallization of magmatic systems, cooling history, temperature, magmatic mixing, texture maturity, dominant size of crystals, density Crystals and partial volume of crystals and thermodynamic and kinetic models were used. In addition, researchers such as Kaneko et al., (2005), Cashman and Ferry (1988), Moazzen and Modjarrad (2005) and Muller et al., (2009) studied the crystal size distribution in metamorphic rocks. In this research, an attempt has been made to investigate the plagioclase crystals in the leucosome section in the migmatites of North-Eastern Takab using the crystal size dispersion (CSD) technique, and by examining the resulting diagrams, the petrological processes and the nucleation rate of the crystals plagioclase should be expressed during melting and finally the formation of leucosomal parts. Materials and methodsIn the study of Ghareh naz migmatites, after taking digital photos of the leucosomal part, they were put together with Adobe Illustrator software for better coverage, and then all the plagioclase crystals were drawn and measured separately. Then the images were transferred to JMicroVision v1.2.7 software and the necessary measurements for all 4 locosome samples (7n, 6p, 6m, mh) including length, width, area, angle, location of the center of crystals (coordinates of X and Y points) in the environment of this software was done. It should be mentioned that considering that the studies are done on thin section images, so to eliminate the errors caused by this problem, all the software settings were entered based on the Higgins (1998) method. Then the obtained data were transferred to CSD Corrections 1.40 software and according to the information obtained from the frequency and size of plagioclase crystals, a natural semi-logarithmic diagram based on the method provided by Higgins (1998) for 4 leucosome samples of migmatite Ghareh naz was drawn separately. In these diagrams, the population density axis, Ln(n)(mm-4) is plotted against the size axis of the largest crystal dimension, (mm) equal to L. The unit of measurement for bulk density is mm-4 (Marsh, 1988; Higgins, 2006; Bindeman, 2003; Higgins ana Roberge, 2003, Higgins ana Roberge, 2007; Gulda, 2006; Higgins and Chandrasekharam, 2007; Brugger and Hammer, 2010) and for crystal size is mm. ResultStudies show that downward concavity in the direction of small crystal sizes indicates coarsening (Higgins ana Roberge, 2007; Vanderzwan et al., 2013) or, in other words, indicates the cessation of nucleation along with successive crystal growth (Lentz and Mcsween, 2000; Higgins ana Roberge, 2007; Vanderzwan et al., 2013). The amount of low concavity in some samples can be considered as an almost linear trend. The almost linear trend on the right side of some graphs indicates the successive growth and nucleation of crystals, the process of subtraction (crystal separation during subtractive crystallization) and crystal accumulation (Higgins, 2009). As can be seen in the diagrams, the very small break created in the crystal size scatter diagram indicates the accumulation or increase of large grains, or in other words, the sedimentation and separation of crystals (Lentz and Mcsween, 2000). In other words, the coarsening process in the studied migmatite locosome occurs when small grains in multiphase mixtures have a higher surface free energy per unit volume than large grains and for this reason, they are less stable (Higgins, 1998, Higgins, 1999). DiscussionThe scatter diagrams of the crystal size in the studied leucosomal samples show that the larger crystals (the end part of the curved diagram on the right) belong to a melt that cooled at greater depths or in a calmer environment. Nevertheless, the initial part of the diagram in the left side crystallized in more superficial areas and at a higher speed. Based on the studies conducted on the plagioclase crystals in the migmatite locosome, it was observed that the plagioclase crystals have a non-linear CSD trend, which indicates two stages of growth with different speeds for these crystals. In the initial stages of crystallization, plagioclase is in the form of coarse crystals with low number of spores, high gradient and high growth rate, and in the next stage, smaller plagioclase with high nucleation rate, low gradient and low growth rate are developed. Plagioclase crystals with their large number and relatively large size indicate their slow cooling and low nucleation.

Producing mineral potential model using GIS software has been increased over the past years. In this study, predictive map consisted of argillic alteration, philic alteration, iron oxide alteration, reduction to pole of aeromagnetic data, lineaments, cu geochemistry anomaly, and principal component analysis (component 3) were prepared from Shahre Babak area. For training model, 37 mineralized points were used. Point pattern analysis was used as well for making non-deposit points and for training model, percepteron artificial neural network with two layers was applied. The training model was used to prepare the final mineral potential model. Based on the mentioned model, the main promising areas were identified to be in the northwest and eastern part of the studied area. Moreover, two areas in the northern and southwestern parts of this area were identified for additional studies. For evaluating the model, ROC curve was used. ROC curve shows high precision of the produced model. For more evaluating, sensitivity, specificity, positive predict value, negative predict value, accuracy, and kappa were computed. The coefficients confirm the high accuracy of the mineral potential model. IntroductionMineral prospectivity mapping (MPM) is a multicriteria decision-making task that aims to outline and prioritize prospective areas for exploring undiscovered mineral deposits of the type sought (Carranza and Laborte, 2015; Yousefi and Carranza, 2015; Sun et al., 2019). In the early stages of exploration, if there are enough known indices in an area, data-driven modeling is proper for mineral potential prospectivity. In this method, at first, all the characteristics of the known indices, of the type of mineralization sought, are collected and the relationship of these characteristics with evidence and spatial patterns is quantified. Then, points with similar characteristics are searched in those areas.Shahre Babak as the studied area is a part of Urumieh-Dokhtar zone. Urumieh-Dokhtar zone is proper for porphyry copper deposits.In this study, at the first stage, conceptual model was defined for porphyry copper modelling. Then, based on the model, some predictive layers were made ready and the data were imported to the trained model of artificial neural network in MATLAB 2021. At the next stage, final model was presented. Material and methodsFor constructing mineral potential model, a conceptual model was defined. Based on this model, some predictive layers consisted of argillic alteration, iron oxide alteration, phillic alteration, reduction to pole of airborne magnetic map, cu geochemistry anomaly, principal component geochemistry anomaly, intrusive units, lineaments structures, and digital elevation models were made in ARCGIS in raster formats. The pixel size of the raster files is 100m*100m. After fuzzification of raster files, these features were extracted to ASCII formats. Geology data (Intrusive body, faults, and dykes)Shahre Babak geology map in 1:250000 scale was used for extracting geological information. The intrusive bodies, faults, and dykes were extracted from Shahre Babak geology map. After extracting geological information, based on the Euclidean distance, the distance maps were made in ARCGIS. Then these maps became fuzzy.Airborne magnetic dataThe airborne magnetic data were surveyed by Atomic Energy Organization of Iran (AEOI) during 1977 and 1978. The flight lines distance and the sensor altitude were about 500 and 120 m, respectively. The reduction to pole filter was applied on total magnetic intensity map. Geochemistry dataGeochemistry data in 1:250000 scale was used for geochemical interpretations. The cu geochemistry anomaly was drawn from the data. Principal component analysis method was applied on geochemical data. Component 3 was extracted from the data. Aster dataBand ratio method was used for extracting the alterations. Iron oxide alteration, philic alteration, and argillic alteration were drawn in ENVI software in raster format. The iron oxide, argillic, and philic alteration files were imported to ARCGIS software and transformed to shapefile format. The distance maps were drawn based on the Euclidean distance. Then these maps became fuzzy. Digital Elevation ModelDigital Elevation Model (DEM) was extracted from Aster data. The data became fuzzy. Training dataset For training model, 37 deposit points were selected. Point pattern analysis was used for non-deposit points. Based on this method, 37 non-deposit points were extracted of the Shahre Babak (the studied area). Each of the labels was located in a unique pixel. The features of these points were extracted from the predictive maps. Then these points were imported to artificial neural network (perceptron neural network with two layers). 70% of data were used for training model and 30% were used for testing model. Then the trained model was applied on the ASCII format. The resulting model was drawn using ARCGIS. Artificial neural networkANN is a modelling approach that simulates human brain system inspired by biological neural networks (Celik and Basarir, 2017). ANN can be effectively applied for pattern recognition in a wide variety of geoscience investigations. In this network, the neurons of different layers are interconnected to exchange information in a unidirectional way starting from the input layer through hidden layers to the output layer (Rodriguez-Galiano et al., 2015; Celik and Basarir, 2017). The flow of information is performed by assigning weights to the connections of different neurons (Rodriguez-Galiano et al., 2015).The back-propagation algorithm is employed to ensure the learning capability of ANN. This algorithm computes the error between the outputted value and real target value, then feeds back it to ANN in order to adjust the weights and biases (Celik and Basarir, 2017).ResultsMineral potential map of studied area was produced by artificial neural network. Based on resulting model, the first-class promising areas were detected in north western and eastern parts of the studied area. Moreover, two areas in north and south western parts of studied area were identified. For evaluating the model, ROC curve was used. This curve shows model accuracy with high precision. For further evaluation, sensitivity, specificity, positive predictive value, negative predictive value, accuracy, and kappa were calculated with 94.7%, 91.8%, 92.3%, 94.4%, 93.3%, and 89%, respectively. These coefficients also confirm the high accuracy of the mineral potential model.

Ruchun-Mazar region is located in southern Sanandaj-Sirjan Zone, southwest of Baft city in Kerman province, Iran. Seh Chah, Chah Sorbi, Chah Nar, Zardbazi Dar, and Chah Sorbi Arjmand Pb-Zn deposits located in this region were investigated. The most outcrops of the geological units in the area include the Paleozoic metamorphic complexes of Gol Ghohar (amphibolite, gneiss and micaschist), Ruchun (schist, marble, calcschist, black chert, slate and phyllite), and Khabar (marble, calcschist). Microdioritic, monzodioritic and diabasic dykes have intruded into the metamorphic units. Dolomitic and calcitic marble of Ruchun complex is the host rock for Pb-Zn mineralization. Primary mineralization in Seh Chah, Chah Sorbi, and Chah Nar deposits includes galena, sphalerite, and pyrite ± chalcopyrite along with quartz, calcite, and dolomite ± barite. Vein-veinlet, open space filling, brecciated ± disseminated ± laminate structures and textures can be seen in these deposits. The most important alterations in these deposits are silicification and carbonitization (calcitic and dolomitic alterations). Primary sulfide ore in Zardbazi Dar and Chah Sorbi Arjmand deposits has been weathered and mining has been carried out on nonsulfide ore (supergene ore). The nonsulfide ore formed at the expense of sulfides, and mainly consists of smithsonite, hydrozincite, hemimorphite, and cerussite. It seems that these deposits belong to the direct replacement and, to a lesser extent, wall rock replacement nonsulfide zinc deposits. Based on the geological, mineralogical and alteration evidence, the primary mineralization in the region can be divided into two groups of SEDEX type (Chah Sorbi deposit) and vein type (Chah Nar and Seh Chah deposits). It was concluded that under supergene conditions in some deposits, nonsulfide ore was also formed. Moreover, the deposits of this region can be categorized into primary sulfide (hydrothermal) and nonsulfide (supergene). IntroductionIran embraces extensive areas having high potential for carbonate-hosted (CH) Zn-Pb deposits due to the suitable geodynamic conditions and the occurrence of large carbonate platforms (Rajabi et al., 2012). A wide variety of Zn-Pb deposits have been reported along Sanandaj-Sirjan Zone (SSZ) in Iran. The development of SSZ is related to the generation of the Neo-Tethys Ocean during the Permian and its subsequent destruction due to the convergent and continental collision between the Arabian and Iran plates during Cretaceous to Tertiary periods (Mohajjel et al., 2003; Ghasemi and Talbot, 2006). Ruchun-Mazar (Rechan) region is located in the southern Sanandaj-Sirjan zone (Fig. 1). This area is located at 75 km southwest of Baft city in Kerman province, Iran. In this region, the lower paleozoic marble rocks of Ruchun complex host numerous Zn-Pb deposits (Fig. 2). Although sulfide mineralization is dominant in this region (e.g., Seh Chah, Chah Sorbi, and Chah Nar deposits), secondary non-sulfide ores are common (e.g., Zardbazi Dar and Chah Sorbi Arjmand deposits). Based on geology, mineralogy, mineralization and alteration, the similarities and differences among the Pb-Zn deposits of this region were investigated. Material and methodsAt the first step, a 1:50,000 integrated geological map of Ruchun-Mazar region was prepared. Then, a more detailed investigation of the deposits, including field sampling of rock units, ore veins, tunnels and other mining works was done. Field observations were supplemented by petrographic studies and X-ray powder diffraction (XRD) analysis. From the collected samples (224 samples), 95 thin sections, 48 polished thin sections, and 41 polished sections were prepared for petrographic and mineralogical studies. Twenty-eight samples (sulfide and nonsulfide ores and gossan) were analyzed by XRD at the GSI. Nonsulfide ores, which contain Zn, were identified (stained bright red) by Zinc Zap, a solution of 3% potassium ferricyanide K3Fe(CN)6 and 0.5% diethylaniline dissolved in 3% oxalic acid. ResultsRuchun-Mazar mining area is located in the southern part of Sanandaj-Sirjan zone (Fig. 1). Based on stratigraphy of the region, chronological sequences from the oldest to youngest include Paleozoic Gol Gohar, Ruchun and Khabar metamorphic complexes, Permian-Triassic metamorphosed carbonates, Jurassic-Cretaceous meta flysch, Cretaceous marbles (Koh-e-Khabar), Eocene-Oligocene flysch, and Quaternary sediments (Fig. 2). Gol Gohar complex (unit Pz2) contains gneiss, micaschist and amphibolite with a probable Cambrian age which has been intruded by mafic intrusive bodies. The Ruchun complex (unit Pz3) is the host complex for lead, zinc and iron mineralizations in the region. Sequence of stratigraphic layers from bottom to the top contains Gol Gohar complex (Camberian), Ruchun complex (Camberian-Ordovician), and Khabar complex (Middle-Upper Devonian), respectively. Metamorphosed carbonate rocks (dolomitic and calcitic marbles) of Ruchun complex (Pz3d and Pz3m) are seen in brown and light to dark gray colors and often alternate associated with metamorphosed sedimentary and volcanic rocks (Pz3sch unit) (Fig. 3A). The Ruchun complex was intruded by microdiorite, monzodiorite, microgabbro, and diabase dikes (Fig. 3B). Quartz and calcite veins have cut most of the Ruchun complex units (Fig. 3C and 3D). Calcitic and dolomitic marbles with probable Permian-Triassic age (Fig. 3E and F) can be seen on Ruchun complex (units PTm and PTd). Mafic (gabbro) to felsic (granite) intrusive bodies (gabbro to granite) were exposed in the west of DehSard village, next to Permian-Triassic dolomite (Fig. 3F).Pb-Zn mineralization in the Mazar-Ruchun region is formed in the calcitic and dolomitic marble (Pz3d and Pz3m) of the Ruchun complex (Fig. 4A, B, C and D). These metamorphosed carbonates are composed of calcite and dolomite, and minor minerals such as muscovite, quartz, and opaque minerals (Fig. 4E and F). Based on the morphology of calcite blade (Burkhard, 1993), and the presence of calcite (type I and II), the temperature of metamorphism of this marble is between 250 and 350 degrees, which corresponds with the green schist facies. Marbles alternate associate with schist (green schist, mica schist and graphite schist) and phyllite (Fig. 3A, E and G).Primary mineralization in Seh Chah, Chah Sorbi and Chah Nar deposits includes galena, sphalerite, pyrite ± chalcopyrite associated with quartz, calcite, and dolomite ± barite. Vein-veinlet, open space filling, brecciated ± disseminated ± laminated structures and textures can be seen in these deposits. The most important alterations in these deposits are silicification and carbonitization (calcitic and dolomitic alterations). Carbonate host rock and structural control can be considered as the most important factors for controlling primary ore mineralization in the Seh Chah and Chah Nar Pb-Zn deposits. Dolomitic and calcitic marble in the Seh Chah deposit are highly altered (Fig. 4B). A number of basic to intermediate intrusive bodies (often as dykes) can be seen in this area. Chah Nar and Seh Chah deposits were formed epigenetically with vein-veinlet, open space filling and brecciated structures and textures (Fig. 5B and C). Graphite schist in Chah Sorbi deposit is sometimes seen alternating with marble in the Ruchun complex sequence. In this deposit, in addition to vein-veinlet, open space filling and brecciated textures (which were also observed in the Seh Chah and Chah Nar deposits), part of the ore has a laminated and disseminated textures. It seems that the type of sulfide mineralization in Chah Sorbi deposit is different from the other two deposits (Fig. 6A to C). In Chah Sorbi deposit, galena, sphalerite, pyrite and chalcopyrite associated with quartz, calcite, organic matter, dolomite and barite were deposited in the hydrothermal mineralization stage (Fig. 6D and Table 1). The effects of metamorphism and deformation in this deposit can be traced by such evidence as microscopic and mesoscopic folds and faults in the ore and host rock (Fig. 6E and F). In contrast, Chah Nar and Seh Chah deposits were formed after the last metamorphic event (probably post Late Cretaceous) and no evidence of metamorphism can be seen in them.Primary sulfide ores in Zardbazi Dar and Chah Sorbi Arjmand deposits have been weathered and mining has been carried out on nonsulfide ore (supergene ore). The nonsulfide ore formed at the expense of sulfides, and mainly consists of smithsonite, hydrozincite, hemimorphite, and cerussite (Fig. 8A and G, and Table 1). Discussion and conclusionSediment-hosted Pb-Zn deposits represent the world’s largest accumulations of base metals (Goodfellow and Lydon, 2007; Wilkinson, 2014). Table 2 shows a comparison of the general characteristics of these deposits with Pb-Zn deposits in Ruchun-Mazar area. The host rock of the studied deposits (calcitic and dolomitic marble) is different from the SEDEX type deposits (shale as the dominant host rock). Chah Nar and Seh Chah, deposits were formed epigenetically (within fracture and fault and as replacements) and deposited after the last metamorphic event (probably post Late Cretaceous). These deposits are classified as a group of epigenetic deposits and show a significant similarity to MVT deposits, although they also display fundamental differences with this category of ore deposit (especially host rock alteration).The presence of laminated and disseminated textures (before the metamorphism event) in Chah Sorbi deposit classified it as a syngenetic to early diagenetic Pb-Zn deposit (e.g., Irish type or SEDEX). Chah Sorbi deposit shows notable similarity to Howard’s Pass district, Selwyn Basin, of sedimentary exhalative (SEDEX) Zn-Pb deposits (Gadd et al., 2017). Mineralization in Howard’s Pass district (Late Ordovician to Early Silurian) was hosted by carbonaceous, calcareous and, to a lesser extent, siliceous mudstones.Mining works in Zardbazi Dar and Chah Sorbi Arjmand deposits was carried out on nonsulfide ore (supergene ore). The supergene nonsulfide deposits are unmetamorphosed and undeformed. They consist of low-temperature and low-pressure assemblages that precipitated from meteoric fluids, replacing sulfides and carbonate groundmass to form encrustations and fill pore spaces, veins, and fractures.Some of the key controls on the formation of carbonate-hosted nonsulfide Zn-Pb deposits are the nature and availability of near-surface sulfide protore, lithology, sub-aerial exposure, tectonic uplift, climate and favorable hydrology (Hitzman et al., 2003). Hitzman et al. (2003) described two specific forms of nonsulfide ore from various nonsulfide deposits around the world: red ore and white ore. Red ore is gossanous, usually found immediately above the sulfide protore, and typically contains >20% Zn, 7% Fe and Pb, and minor silver (Simandl and Paradis, 2008). Typical red ore nonsulfide minerals include iron-oxyhydroxides, goethite, hematite, hemimorphite, smithsonite, and/or hydrozincite and cerussite (Reichert and Borg, 2008). White ore contains up to 40% Zn but less than 7% Fe and Pb. Smithsonite and hydrozincite are common minerals in white ore with only small amounts of Fe-oxyhydroxides and cerussite (Reichert and Borg, 2008). Zinc and Pb nonsulfides can be used as indirect indicator minerals in exploration for MVT, SEDEX, Irish-type, carbonate replacement, and vein-type Zn-Pb deposits.It seems that Zardbazi Dar and Chah Sorbi Arjmand deposits belong to the direct replacement and lesser extent wall rock replacement nonsulfide zinc deposits.  AcknowledgmentsThis study was done supported by a grant of Ferdowsi University of Mashhad. The study is part of the Project number 41179 and also part of the first author’s doctoral thesis. We gratefully thank Dr. Mohammad Salehi Tinoni, Mohsen Jorjandipour, Ali Rashidi, Dr. Ali Amiri and Dr. Ahmad Rashidi Bosharabadi who helped us in different field works. We are grateful to the respected reviewers who played a significant role in the scientific improvement of the article.

Shotorsang iron skarn is located in 60 km northwest of Neyshabour (Khorasan Razavi, Iran) in Quchan-Sabzevar magmatic belt. Subvolcanic intrusion rocks have intruded into Cretaceous limestones and created skarnization. These rocks are divided into syenite porphyry and granodiorite porphyry based on their geochemical characteristics. They are I type oxidizing, metaluminous, and tectonic. Setting of the subvolcanic rocks are the subduction zone of the continental margin (VAG). Comparing the mineralization potential of the subvolcanic rocks of this area based on the use of the graph of SiO2 against K2O, MgO, Na2O+K2O, and Ni-V shows that they are fertile in terms of the formation of Fe and Cu skarn. Syenite porphyry is the origin of this mineralization, and magnesium in skarn is taken from hydrothermal fluid. The diagram of Eu/Eu*, Ce/Ce*, (Pr/Yb)n ratios also confirms the presence of meteoric water in the formation of the skarn zone. The primary fluid, which has a positive anomaly of Ce/Ce* and Eu/Eu* had acidic and oxidant conditions and high temperature, and formed pyroxene skarn. A part of magnetite mineralization is formed in this zone, and in this condition, the highest amount of REE entered the pyroxene skarn zone and diluted the fluid in terms of REE. This issue has led to a sharp decrease in the amount of REE in the mineralization zone. Negative Ce/Ce* and Eu/Eu* anomalies indicate alkaline conditions with less concentrated REE content, consistent with chlorite skarn. The highest amount of Fe mineralization is formed in this zone. IntroductionShotorsang iron skarn is located in 60 km northwest of Neyshabour (Khorasan Razavi, Iran) in Quchan-Sabzevar magmatic belt. Subvolcanic intrusion rocks have intruded into Cretaceous limestones and created skarnization (Amini and Khannazer, 2000(. This study found that at least four subvolcanic intrusion rocks are present in this region: Granodiorite porphyry, biotite syenite porphyry, quartz syenite porphyry, and quartz diorite to monzodiorite porphyry. These are divided into syenite porphyry and granodiorite porphyry based on the geochemical characteristics. Material and methodsAbout 90 samples were collected for laboratory investigations of petrogenesis studies. Moreover, 25 samples were selected to be analyzed using the XRF and ICP-MS methods. Laboratory studies were carried out in Ferdowsi University of Mashhad and samples were analyzed in Acme and Zarazma laboratories. ResultsSubvolcanic rocks are I-type oxidizing, metaluminous, and tectonic. Setting of the subvolcanic rocks are the subduction zone of the continental margin (VAG). Moreover, some samples have been placed at the border of syn-collision due to high Rb, which is the result of high potassium. Enrichment of LILE elements such as K, Cs, Ba, Rb and incompatible elements that behave similar to them like Th compared to HFSE elements is observed in all samples compared to the primitive mantle. Enrichment of LILE relative to HFSE indicates magma related to subduction zones. The Sr element shows opposite behavior compared to the LILE elements. This issue can be justified by the high amount of CaO in magnetite ore (from 0.3% to more than 3.5%), because the two elements are similar in terms of chemical properties. Comparing the mineralization potential of the subvolcanic rocks of this area using the graph of SiO2 against K2O, MgO, Na2O+K2O, and Ni-V shows that they are fertile in terms of the formation of Fe and Cu skarn Meinert, 1995(. For igneous rocks, it was confirmed that the amount of Rb increases during the fractionation and crystallization processes (Meinert, 1995 (. Granitoids with potential for iron skarn have lower Rb (39 ppm). This amount is 103 ppm for copper skarn and 69 ppm for gold skarn. The amount of Rb content for all granitoids of Shotorsang area is 80 ppm. Considering the connection of these granitoids with iron skarn in this area, the high Rb content can be justified by crustal contamination of these rocks (Martin-Izard et al., 2000). Moreover, it can be mixing of a mafic magma with a felsic magma at a shallow depth. The amounts of V and Ni in iron skarn deposits are the highest; that is, 152 and 35 ppm, respectively. Ni and V for Shotorsang syenite porphyry group are 16 and 82, respectively and for Shotorsang granodiorite porphyry are 20 and 48, respectively. These values are lower than the global average of iron skarn. In general, the high amount of Rb and the low amount of Ni and V confirm the hypothesis that the magma has been fractionated and contaminated with crust. If the amount of Rb as well as the amount of Ni and V increase, the mixing of a magma derived from the mantle or a mafic magma with a highly fractionated magma would seem to be a more acceptable hypothesis (Meinert, 1995). Therefore, according to what was stated about the tectonic setting and the cases mentioned above, as well as the process of changes in the spider diagram of the rare earth elements of the studied area, it can be expected that the fluid forming the iron skarn of this region has undergone magmatic fractionation and been contaminated with crust. (La/Yb)n, (La/Sm)n and (Gd/Yb)n ratios were used to evaluate the separation degree between REEs. (La/Yb)n determines the degree of separation between LREE and HREE (Aubert et al., 2001; Yusoff et al., 2013), while the other two ratios are used to determine the degree of separation between LREE and MREE, and between MREE and HREE, respectively (Yusoff et al., 2013). These ratios vary for (La/Yb)n from 1.12 to 1.69, for (La/Sm)n from 6.7 to 40.72, and for (Gd/Yb)n from 0.89 to 4.22. As it is known, during the skarnization process, the highest degree of separation has occurred between LREE and HREE (up to about 70 times) and the lowest degree of separation has also occurred between MREE and HREE. The highest value of these ratios is in the mineralization zone, which indicates that the highest amount of separation of REE elements has taken place in this zone. Syenite porphyry is the origin of this mineralization, and magnesium in skarn is taken from hydrothermal fluid. DiscussionThe diagram of Eu/Eu*, Ce/Ce*, (Pr/Yb)n ratios confirms the presence of meteoric water in the formation of the skarn zone (Kato, 1999). The primary fluid, which has a positive anomaly of Ce/Ce* and Eu/Eu*, had acidic and oxidant conditions and high temperature and formed pyroxene skarn. A part of magnetite mineralization is formed in this zone, and in this condition, the highest amount of REE entered in pyroxene skarn zone and diluted the fluid in terms of REE. This issue has led to a sharp decrease in the amount of REE in the mineralization zone. Negative Ce/Ce* and Eu/Eu* anomalies indicate alkaline conditions (Meinert, 1995) with less concentrated REE content, consistent with chlorite skarn. The highest amount of Fe mineralization is formed in this zone. AcknowledgementsThe authors are grateful for the cooperation of the employees of the Shotorsang iron ore mine, especially Mr. Qotbi.

Iron mineralization has occurred in Larak Island, located 30 km south of Bandar Abbas, within the Persian Gulf, in the Zagros structural zone. Stratigraphically, Larak Island dominantly consists of the Late Proterozoic Hormuz volcanic-sedimentary series, including rhyolitic lava and tuff, shale, and evaporative sediments. Iron mineralization has occurred in a specific stratigraphic horizon within the volcanic-sedimentary sequence. The orebodies involve four ore facies from bottom to top: vein-veinlets, brecciated, massive, and banded. The ore minerals are dominated by magnetite, oligiste, and hematite with gangue minerals including pyrite, apatite and secondary goethite and limonite, associated calcite, quartz, and anhydrite. Wall rock alterations in this area include silicic-sericitic, carbonatic, chloritic, and secondary argillic. The samples obtained from iron ores in the geochemical diagrams including the Fe/Ti versus Al/(Al+Fe+Mn+Na+K+Ca) diagram and Mg versus V/Ti diagram, were plotted in the range of Banded Iron Formation (BIF) deposits. Due to the volcanic-sedimentary nature of the host sequence, lack of observation of glacial sediments, ore facies, ore textures, structures and mineralogy, alteration and geochemical features, the iron mineralization in Larak Island shows the most similarities with the Algoma-type BIF deposits. IntroductionThe study area is located in Hormozgan province and southeast of Qeshm Island, on Larak Island. Based on structural-geological divisions of Iran, Larak Island is located in the southeastern part of the Zagros zone (Figure 1). The major rock outcrops of the region are part of the Hormuz Formation (HF), which is a collection of evaporites, volcanic, pyroclastic, and sedimentary units related to the Precambrian. According to Aghanabati (2004), at the southeastern part of the Zagros, especially in the area between Kazeroon and Minab faults, following the extensional phases of Katanga orogeny, evaporitic basins have been formed accompanied by igneous activities related to Katangan orogenic phase. Age measurements done by Ramezani and Tucker (2003) show that the igneous rocks of HF dates back to Early Cambrian. The HF rock units were exhumed as salt domes in southern Iran. The distribution of salt domes in the south of Iran is not uniform. They are gathered in two areas: One is Bandar Abbas-Sarvestan, including 101 domes and diapers, and the other is the southern part of Kazeroon, including only 14 domes and diapers. The total of 115 salt domes host reserves of salt, gypsum, potash, uranium, phosphate and iron (often hematite and in the form of red soil). Larak Island is one of the salt domes in southern Iran that has been less studied in terms of mineralization. The type and manner of formation of Larak Island rocks are very similar to those of Hormuz Island. Acidic magmatic activities in Larak Island and other salt domes in southern Iran are the result of melting of the upper crust by a magma derived from the upper mantle. Based on recent research, the iron mineralization in the Hormuz Formation is introduced as Rapitan-type Banded Iron Formation (Atapour and Aftabi, 2017). Moreover, the origin of iron and copper ores within the Hormuz volcano-sedimentary sequence in the Zendan salt dome located in Bandar Lengeh is inferred to be related to VMS type mineralization (see Biabangard et al., 2018). The Tang-e-Zagh Fe deposit in Bandar Abbas has been introduced as sedimentary-type (Tavakoli et al., 2014), and a sedimentary and magmatic-hydrothermal origin has been proposed for the genesis of iron and iron-apatite ores of Hormuz Island (Fakhri Dodoei and Alipour Asl, 2020). This study tries to introduce the evidence for genesis of iron-apatite mineralization in Larak Island of Persian Gulf. Materials and methods Various sedimentary and igneous units were taken as samples from Larak Island. About 10 thin sections were prepared and petrographic examinations were performed on them. Moreover, 3 polished sections and 10 thin sections were prepared and studied for mineralization, mineral structures and textures, paragenesis sequence of minerals, and distribution of ore minerals by reflecting microscope. Four samples from alteration zones were selected and studied by X-ray diffraction (XRD) method, and 13 samples of ores were analyzed to determine the amount of major and trace elements by ICP-OES/MS methods in the laboratory of Iran's Minerals Procurement and Production Company (IMPASCO). Results and discussionThe Hormuz series is the major host of iron mineralization in Larak Island. The main rock outcrops of the study area belong to the Late Precambrian-Lower Paleozoic Hormuz Formation, involving rhyolite and rhyodacite lavas, rhyolite tuff, tuff shale, sandstone, marl, sandy limestone, and evaporitic layers. The HF rock units are covered by Cenozoic sequences consisting of sandstone, marl, and fossiliferous limestone. From bottom to top the HF sequence involves four major rock units (Faramarzi et al., 2015): H1 includes marl and limestone, H2 includes tuff, rhyolite, trachyte, diabase, anhydrite, and limestone, H3 includes algal black limestone, and H4 includes sandstone and tuff. The stratabound and stratiform iron mineralization occurred within specific stratigraphic horizons in the H2 unit, as lenticular and layered orebodies underlay by vein-veinlet and brecciated ores hosted by tuff and lavas. The major ore facies involve vein-veinlets (stringer), brecciated, massive, and banded. The ore minerals are dominated by oligiste (hematite), magnetite, and secondary goethite, and limonite. The main gangue minerals are calcite, quartz, and clay minerals. Wall rock alterations in this area generally include sericitic, chloritic, carbonatic, and secondary argillic. The geochemical nature of the volcanic rocks of the region varies from calc-alkaline series to high-grade calc-alkaline and shoshonitic. To classify the ores, in addition to geological and mineralogical studies, geochemical behavior of major and trace elements can be used (Dill, 2010). For this purpose, geochemical charts based on the elements of iron, titanium, aluminum, manganese, sodium, potassium, calcium, magnesium, and vanadium were used. The samples obtained from iron ores in the geochemical diagrams including the Fe/Ti versus Al/(Al+Fe+Mn+Na+K+Ca) diagram (Boström, 1975) and Mg versus V/Ti diagram (Nyström and Henríquez, 1994), were plotted in the range of Banded Iron Formation deposits. Various features of the iron mineralization in Larak Island, including tectonic setting, volcanic host and associated rock-types, geometry of orebodies, different ore facies (from bottom to top including vein-veinlets, brecciated, massive and banded-laminated), ore mineralogy, alteration zones and geochemistry of ores showed that the mineralization is very similar to the Algoma-type BIF deposits (e.g., Gross, 1996; Taner and Chemam, 2015). ConclusionThe features of iron mineralization in Larak Island, involving tectonic setting, host and associated rock-types, geometry of orebodies, different ore facies (from bottom to top including vein-veinlets, brecciated, massive, and banded-laminated), ore mineralogy, alteration zones, and geochemistry of ores show that the mineralization is very similar to the Algoma-type Banded Iron Formation deposits, formed due to seafloor exhalations and subsea-floor replacement of the host rocks at Late Proterozoic-Early Paleozoic time. Due to diagenesis, rare amounts of iron oxides were remobilized and deposited within the overlaying young Asmari-Jahrom limestone units.