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Kalateh Pialeh prospect area is located in the Kopeh Dagh zone, approximately 15 km northeastern of Esfarayen city. The area is composed of sedimentary rocks deposited during the Jurassic, Cretaceous, and Tertiary periods, which include microconglomerate, dolomitic limestone, sandy limestone, limestone, conglomerate, and marl. Mineralization occurs as epigenetic deposits hosted by dolomitic limestone and limestone. Two mineralization stages were identified. The first stage consists of a pyrite-galena-sphalerite assemblage with replacement and breccia textures, and the second stage comprising a galena-sphalerite assemblage with vein-veinlet, open space filling, and replacement textures. Dolomite and calcite are the most abundant gangue minerals associated with lesser amount of quartz and barite. Main alterations consist of calcitization and dolomitization. Galena mineral exhibits maximum geochemical anomalies of 1843 ppm for zinc, 7 ppm for arsenic, and 11 ppm for copper. Microthermometric studies on primary fluid inclusions (LV) reveal homogenization temperatures ranging from 180°C to 265°C for stage 1, and from 167°C to 214°C for stage 2. Salinities for these stages were found to be between 7.8 wt.% to 14.5 wt.% NaCl equiv., and 11.7 wt.% to 12.2 wt.% NaCl equiv., respectively. Based on evidence such as structurally controlled mineralization, the type of alterations and their linear expansion, simple mineralogy of ore, geochemistry, and fluid inclusion data, Kalateh Pialeh prospect area is similar to lead-zinc epithermal deposits. Introduction Sediment-hosted Pb–Zn deposits are typically found in clastic-carbonate (Sedex type deposits) and carbonate (Irish type and Mississippi Valley-type (MVT) deposits) rocks (e.g., Goodfellow & Lydon, 2007). In Iran, the wide distribution of clastic and carbonate rocks has led to the formation of various types of sedimentary-hosted lead and zinc deposits.These deposits occur in Cretaceous carbonate units, including Malayer-Esfahan, Tabas- Poshte-Badam, Yazd-Anarak, and Central Alborz metallogenic belts (Rajabi et al., 2012). Kalateh Pialeh prospect area, located in Kopeh Dagh zone, about 15 km northeastern of Esfarayen city, is the first report of lead and zinc mineralization in this zone. Kopeh Dagh zone is characterized by the absence of magmatic activity, the presence of limestone formations, and abundant hydrocarbon reserves (such as Khangiran Gas Field). This study summarizes the alteration, mineralogy, geochemistry, and fluid inclusion studies, and then discuss the ore genesis of Kalateh Pialeh prospect area. Material and methods Following field work, thin sections and polished slabs from the host rocks, veins and veinlets were studied using optical microscope. Red alizarin was also used to differentiate between calcite and dolomite. Galena minerals were seperated from host rock by using standard techniques involving crushing and handpicking under a binocular microscope at Ferdowsi University of Mashhad. Minor and rare element metal concentrations from galena were analyzed using ICP-OES techniques on five samples at Zarazma laboratory in Iran, while XRD analysis of the samples was done at the same laboratory. Microthermometric analysis of fluid inclusions was carried out on seven samples using a Linkam THM 600 heating-freezing stage combined with an Olympus TH4–200 microscope stage at Ferdowsi University of Mashhad, Mashhad, Iran. Results and Discussion The area comprises sedimentary units of microconglomerate, dolomitic limestone, sandy limestone, limestone, conglomerate, and marl. Vein-type epigenetic mineralization occurs along fault zones with trending NW–SE/vertical dip in dolomitic limestone and limestone. Mineralization can be divided into two stages: Pyrite-galena-sphalerite assemblage (with replacement and breccia textures), and galena-sphalerite assemblage (with vein-veinlet, open space filling, and replacement textures). The main alterations consist of calcitization and dolomitization. The oxidation and weathering processes have resulted in the formation of hemimorphite, smithsonite, cerussite, goethite, and hematite in the ore zones. Gangue minerals consist of calcite and dolomite with lesser amounts of barite and quartz. Geochemical analyses of the galena mineral reveal maximum anomalies for zinc (1843 ppm), arsenic (7 ppm), and copper (11 ppm). Microthermometric studies on primary fluid inclusions (LV) show homogenization temperatures ranging from 180 to 265°C and from 167 to 214°C for stages 1 and 2, respectively. The fluid salinities for these stages range from 7.8 to 14.5 wt.% NaCl and from 11.7 to 12.2 wt.% NaCl, indicating a wide range of salinities.The temperature of ore-forming fluids in MVT deposits varies from 50 to 250°C, with the majority falling within the 70 to 170°C range , and their salinity is between 10 and 30 wt. % NaCl (Leach et al., 2010). In Kalateh Pialeh sam ples, primary fluid inclusions hosted in quartz crystals homogenize to the liquid phase at temperatures ranging from 167°C to 265°C, (mostly in the range of 80 to 200°C) and the average salinity of 11 wt. % NaCl. The salinity of the hydrothermal fluids at studied area varies from 7.8 to 14.5 wt. % NaCl. This wide range can be attributed to the mixing of two fluids with different salinities. These salinities can be divided into two groups with low salinity (7.8 to 10 wt. % NaCl) and high salinity (13.9 to 14.5 wt. % NaCl). The presence of two types of primary inclusions with different salinity but similar homogenization temperature is a sign of isothermal mixing of two fluids. |
