Evolution of Fluid System at the Chahfirouzeh Porphyry Cu Deposit, Kerman Cenozoic Magmatic arc, Iran

Abstract

The Chahfirouzeh porphyry copper deposit is situated within the Kerman Cenozoic magmatic arc and forms part of the Urumieh–Dokhtar magmatic belt in southern Iran. Copper mineralization in the deposit is associated to a Miocene diorite/granodiorite stock. The ore–forming process can be categorized into early, main, and late stages. Based on the microthermometry results, the salinities of the fluid system evolved from 5.86 to 16.15 wt% NaCl equivalent in the early stage, through bimodal ranges of 2.4–12.2 and 30.39–42.56 wt% NaCl equivalent in the main stage, and to 8.14–23 wt% NaCl equivalent in the late stage, strongly suggesting that fluid boiling and CO₂ escape occurred during the main stage of the Chahfirouzeh porphyry system. Furthermore, the total homogenization temperatures of fluid inclusions decrease from 327 to 492 °C during the early, to 313–458 °C during the main, and finally to 250–377 °C during the late events. Laser Raman results also show the presence of CO₂ and CH₄ in the main stage fluid inclusion, which may be due to an equilibrium between them linked to the transition from potassic to phyllic alteration. We propose that the phase separation and release of CO₂ could be crucial for enhancing the activities of NaCl and S²⁻ in the fluids, reducing the oxidation of the fluids, and leading to the deposition of metal sulfides and the entrapment of halite–bearing inclusions in the Chahfirouzeh hydrothermal system.