Geological, fluid inclusion microthermometry and geochemical constraints on the ankeritic-sideritic iron deposits in the Delijan mining district, Malayer-Esfahan metallogenic belt, Iran

Abstract

The Kahak, Raveh, and Khoreh stratabound sideritic-ankeritic iron deposits are located in the Malayer-Esfahan metallogenic belt (MEMB), Iran. Geological, geochemical, fluid inclusion and S isotope studies have been carried out on the Kahak, Raveh, and Khoreh deposits which are hosted by different types of Lower Cretaceous dolomite, sandstone, and tuff in the Delijan mining district (DMD). Ankerite and siderite ores display a strong lithological control and form stratabound stacked ore lenses hosted in different horizons by Kc2, Kcv, Kc3, and Km units. Economic orebodies are restricted to the hanging wall of the syn-sedimentary normal faults. Three ore types can be distinguished based on the petrographic studies: stringer zone ore facies, bedded ore facies, and massive-replacement ore facies. Ore minerals are predominantly ankerite, siderite, barite, chalcopyrite, sphalerite, galena, and pyrite. Ore mineralization in the Kahak, Raveh, and Khoreh deposits has emplaced in two stages. The fine-grained ore bands (stage 1) which are intricately interlayered with host rock beds, exhibit sedimentary textures such as lamina and bedding and indicate a syn-sedimentary origin. The coarser-grained stage 2 ores show massive and vein-veinlet textures that are considered to form by replacement during sub-seafloor fluid flow. Hydrothermal alteration minerals developed in the wall rock include dolomite, quartz, and calcite. A microthermometric study of fluid inclusions from the barite samples indicates homogenization temperatures between 162 and 210 °C. Salinities of ore-forming fluids range from 7.8 to 16.8 wt% NaCl eq. Fluid inclusion studies suggest that the ore-forming fluids were derived from basinal or formational brines. Fluid mixing (basinal brine and seawater) may have played an important role during Fe mineralization. Calculated δ34S values for the ore fluid vary between + 10.69 and + 31.98‰. Sulfur isotopic compositions suggest that the source of sulfur for barite was derived from seawater. These data show that the Kahak, Raveh, and Khoreh ankeritic-sideritic iron deposits are comparable with those of sub-seafloor carbonate-replacement SEDEX-type deposits.