Geology and geochemistry of the sediment-hosted Cheshmeh-Konan redbed-type copper deposit,NW Iran |
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| Institution: | 1. Research Center for Ore Deposits of Eastern Iran, Ferdowsi University of Mashhad, Iran;2. Department of Geological Sciences, University of Colorado, CB-399, Boulder, CO 80309-399, USA;1. Department of Geology, Faculty of Natural Sciences, University of Tabriz, Tabriz, Iran;2. Department of Geology, Faculty of Basic Sciences, Tarbiat Modares University, Tehran, Iran;3. Chrono-Environnement, Université de Franche-Comté/CNRS, 25030 Besançon Cedex, France;1. Antofagasta Minerals S.A., Apoquindo 4001, piso 18, Las Condes, Santiago, Chile;2. 27 West Hill Park, Highgate Village, London N6 6ND, England, United Kingdom;3. Orsu Metals Corporation, Berkeley Square House, Berkeley Square, London W1J 6BD, England, United Kingdom;4. School of the Environment, Washington State University, Pullman, WA 99164-2812, USA;1. KU Leuven, Department of Earth and Environmental Sciences, Celestijnenlaan 200E, 3001 Leuven, Belgium;2. University of Johannesburg, Department of Geology, Auckland Park 2006, Johannesburg, South Africa;3. Ghent University, Department of Analytical Chemistry, Krijgslaan 281-S12, 9000 Ghent, Belgium;1. Department of Earth Sciences, Royal Holloway, Egham, Surrey TW20 0EX, UK;2. Department of Earth Sciences, University of Durham, DH1 3LE, UK;3. Faculty of Geology, Geophysics and Environmental Protection, University of Science and Technology (AGH), Ave Mickiewicza 30, 30-059 Krakow, Poland |
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| Abstract: | The several-hundred-m-thick Miocene Upper Red Formation in northwestern Iran hosts stratiform and fault-controlled copper mineralization. Copper enrichment in the percent range occurs in dm-thick carbonaceous sandstone and shale units within the clastic redbed sequence and consists of fine-grained disseminated copper sulfides (chalcopyrite, bornite, chalcocite) and supergene alteration minerals (covellite, malachite and azurite). The copper mineralization formed after calcite cementation of the primary rock permeability. Copper sulfides occur mainly as replacement of diagenetic pyrite, which, in turn, replaced organic matter. Electron microprobe analysis on bornite, chalcocite and covellite identifies elevated silver contents in these minerals (up to 0.12, 0.72 and 1.21 wt%, respectively), whereas chalcopyrite and pyrite have only trace amounts of silver (<0.26 and 0.06 wt%, respectively). Microthermometric data on fluid inclusions in authigenic quartz and calcite indicate that the Cu mineralization is related to a diagenetic fluid of moderate-to low temperature (Th = 96–160 °C) but high salinity (25–38 wt% CaCl2 equiv.). The range of δ34S in pyrite is ?41.9 to ?16.4‰ (average ?31.4‰), where framboidal pyrite shows the most negative values between ?41.9 and ?31.8‰, and fine-grained pyrite has relatively heavier δ34S values (?29.2 to ?16.4‰), consistent with a bacteriogenic derivation of the sulfur. The Cu-sulfides (chalcopyrite, bornite and chalcocite) show slightly heavier values from ?14.6 to ?9.0‰, and their sulfur sources may be both the precursor pyrite-S and the bacterial reduction of sulfate-bearing basinal brines. Carbonates related to the ore stage show isotopically light values of δ13CV-PDB from ?8.2 to ?5.1‰ and δ18OV-PDB from ?10.3 to ?7.2‰, indicating a mixed source of oxidation of organic carbon (ca. ?20‰) and HCO3? from seawater/porewater (ca. 0‰). The copper mineralization is mainly controlled by organic matter content and paleopermeability (intragranular space to large fracture patterns), enhanced by feldspar and calcite dissolution. The Cheshmeh-Konan deposit can be classified as a redbed-type sediment-hosted stratiform copper (SSC) deposit. |
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| Keywords: | Cheshmeh-Konan Diagenesis Organic matter Redbed-type copper deposit NW Iran |
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