Genetic model and type of Sarcheleshk Pb–Zn (F–Ba) deposit, Savadkouh area, Mazandaran province

Abstract

Introduction There 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 methods Detailed 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 conclusion The 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.

Keywords

• pb–zn (f–ba) mineralization
• elika formation
• sarcheleshk
• savadkouh
• mazandaran