Aspects of magmatic–hydrothermal evolution of Kahang porphyry copper deposit, Central Iran

Kahang porphyry copper deposit in Isfahan Province, Iran, is located in the middle of Urmia-Dokhtar Magmatic Arc. Petrographic studies revealed that igneous rocks in the eastern part of the deposit are divided into three types: host rocks, mineralizing stocks, and post-mineralization barren dikes. Host rocks are mainly Paleocene-Eocene aged, ranging in composition from andesite through quartz-andesite to trachyte-andesite and tuff. Oligo-Miocene quartz-diorite–granodiorite and late dacite have intruded into these volcanic rocks, and are cut by barren andesitic and dacitic dikes. Quartz-diorite has composed more than 70 % of the main mineralizing stock, followed by dacite and less commonly by granodiorite. Geochemistry of plutonic and volcanic rocks confirms that these rocks were crystallized from a single calk-alkaline magma through the differentiation process. Intensive hydrothermal alteration in the deposit is characterized by outward zoning from potassic (biotitic), overprinted by phyllic, quartz-sericitic, to propylitic (chloritic-calcitic), and argillic (jarositic) alteration. Potassic alteration in depths less than 730 m is mainly biotitic, and has no K-feldspar. But, in deeper depths, K-feldspar, quartz, and biotite form the typical potassic alteration zone. The most extensive alteration type in the deposit is phyllic that has mainly affected mineralizing dacitic rocks. Six main groups of veins and breccias were identified related to alteration processes. These groups, from oldest to youngest types, are: Bt-M-, A-, B-, P-, D-T-, and L-type veins and breccias. Fluid inclusion studies on mineralized quartz veins in potassic zone show that mineralization has occurred in a minimum temperature, pressure, and depth of 415 °C, 340 bars, and 1.3 km, respectively.