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Tooba Jafari, Department of Geology (Islamic Republic of Iran)
Majid Ghaderi, Department of Geology (Islamic Republic of Iran)
Nematollah Rashidnejad-Omran, Department of Geology (Islamic Republic of Iran)
Ebrahim Rastad, Department of Geology (Islamic Republic of Iran)
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There are several barite mines of Cambrian to Eocene age in Alborz structural zone, northern Iran, one of which is Amirnan barite (Pb-Cu) deposit located in Central Alborz. The host rocks of the deposit comprise a Lower Cretaceous volcano-sedimentary sequence including carbonates, as well as calcareous and bimodal tuffs. Mineralogy consists of barite together with minor galena, pyrite, chalcopyrite, anglesite, cerussite, covellite, malachite, siderite as well as Fe-oxides and hydroxides. Facies analysis of the ore-bearing horizons indicates that ore minerals are related to certain sedimentary facies. The horizon-I is in calcareous mudstone, wackestone and biopackestone facies only consisting barite. Horizon-II in calcareous tuff facies mostly consists of Ba and Pb minerals. Horizon-III is in bimodal tuff facies and includes barite, galena, pyrite, and chalcopyrite. Depositional environment of all the facies is tidal flat. The ore geometry, textures and structures indicate that the ore minerals are formed in three stages: 1- Early diagenetic barite: includes bladed and lenticular barite; 2- Late diagenetic barite: includes baritized orbitulina, laminated, open space filling, and veinlets 3- Epigenetic barite: includes breccias, vein barite in crack fractures, and replacement structures. Sedimentological, textural, and mineralogical studies of the Amirnan deposit indicate that barite (Pb-Cu) was deposited through sedimentary-exhalative processes. Therefore, Amirnan can be regarded as a sedimentary-exhalative Ba (Pb-Cu) deposit in Central Alborz.
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