Textures and chemical compositions of the Narm iron oxide-apatite deposit in Kuh-e-Sarhangi District (Central Iran): Insights into the magmatic-hydrothermal mineralization

The Narm deposit is located in the Kuh-e-Sarhangi district which is a main part of the most significant Iranian iron mineralization belt, the Kashmar-Kerman Tectonic Zone (KKTZ) in Central Iran. The Narm deposit comprises an estimated total of similar to 135000 tons of iron ore with an average grade of similar to 55% Fe and is hosted in Early Cambrian volcano sedimentary rocks of the Rizu formation. Ore occurrences in this deposit consist of lens-shaped magnetite ore bodies, magnetite-apatite-actinolite veins and locally rare brecciated dolomite with magnetite clasts. Magnetite, pyrite, chalcopyrite and specularite associated with apatite, actinolite, biotite and carbonate minerals form the primary main mineral assemblage which is accompanied by hematite and goethite as the secondary minerals. Magnetite as the most current mineral of Narm deposit reveal the magmatic to hydrothermal evolution of mineralization. Magmatic magnetite minerals (Mag I) are dark-gray inclusion-rich magnetite spatially correlated with high temperature Ca-Fe alteration. The brighter inclusion-free hydrothermal magnetite groups (Mag II and Mag III) form during the temperature decreasing of the mineralizing fluid. According to the magnetite chemistry examination, most magnetite fall into the field for magnetite from iron-oxide apatite (IOA) deposits. Apatite minerals with F/Cl > 2, belong geochemically to the fluorapatite type. In addition to the primary dolomite, there are some hydrothermal Fe-rich dolomites and Mn bearing ones, indicating the hydrothermal fluid playing the important role for Fe-rich mineralization. In respect to fluid evolution, fluid inclusion analysis of calcite and apatite minerals form the magnetite paragenesis assemblage represent homogenization temperature range for fluid between 325 and 557 degrees C. The salinity of fluid varied from 7.7 to 11.6 wt% NaCl equivalent and a cooling trend with the dominant chlorine complex as an agent for deposition of the Fe-rich ores. The geochemical characteristics of the delta O-18(fluid) values of magnetite (from + 6.1 to + 10.4%) and delta O-18(fluid) values of actinolite (from + 7.7 to + 12.5%) represent the magmatic-hydrothermal (delta O-18(fluid) > + 0.9 %) formation process. The iron rich Al-clinochlore composition from the alteration zone indicates a temperature range between 250 and 330. which points to a temperature reduction of hydrothermal fluids in this mineralizing zone. The integrated geochemical data from this investigation, including mineral chemistry, microthermometry of fluid inclusions and oxygen isotope data all reveal a magmatic-hydrothermal genesis for this deposit.