Document Type : Original Research Paper
Authors
1 Department of Geology, Payame Noor University, Tehran, Iran
2 Department of Mineral Exploration, Faculty of Mining Engineering, Petroleum and Geophysics, Shahrood University of Technology, Shahrood, Iran
Abstract
Astmal deposit is located in the northwest of Iran and is structurally located in the Arasbaran Magmatic zone. Skarn mineralization related to the Eocene-Oligocene granodiorite rocks which have been permeated to the Upper Cretaceous rocks. Mineralization has formed in the exoskarn zone, and the metasomatic process has started immediately after the penetration of the granodiorite into the limestone. Significant amounts of Si, Mg, and Fe elements lead to the development of anhydrous calc-silicate minerals with medium to coarse grains, and also significant amounts of Cu, Fe elements along with volatile substances such as CO2, H2S are added to the skarn system. As a result, hydrated calcsilicates (epidote, tremolite, and actinolite), sulfides (pyrite and chalcopyrite), oxides (magnetite and hematite) and carbonates (calcite) have been replaced anhydrous calcsilicates. The results of δ34S isotope analysis on pyrite and chalcopyrite ores are in the range of -1.8 to +6.1 ‰, which indicates the magmatic source of sulfide. Also, the results of δ18O and δD isotope data on magnetite, sericite and epidote minerals, which are in the range of -56 to -73 ‰ for hydrogen and -0.5 to +6.8 ‰ for oxygen, indicate a mixture of magmatic fluids associated to the small amounts of meteoric fluids.
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