Distribution of alteration, mineralization and fluid inclusion features in porphyry – high sulfidation epithermal systems: The Chodarchay example, NW Iran

Abstract

The Chodarchay Cu-Au deposit in northwestern Iran represents an example of the transition from the deep porphyry mineralization stage overprinted by the shallow high-sulfidation epithermal stage in porphyry – high sulfidation epithermal systems. The mineralization at Chodarchay mostly occurred within the Eocene volcanic and volcaniclastic units; some parts are hosted within an Oligocene quartz monzonite intrusion. The porphyry mineralization is mainly associated with a potassic zone in the deepest part of the stock. The potassic alteration is followed by late alteration types of phyllic, argillic and propylitic. The advanced argillic alteration near the surface postdates other alteration types. Based on the phase contents, six types of fluid inclusions are recognized. At depth, the early generation of halite-bearing inclusions that in some places contain opaque daughter minerals indicates a high-density, high-salinity mineralizing fluid. Usual trails of only vapor-rich inclusions in the shallow parts, suggest intense boiling at (or below) this level. Coexisting vapor-rich and halite-bearing inclusions, as well as vapor-rich and type II fluid inclusion assemblages, indicate fluid immiscibility. The distribution of alteration, mineralization, and fluid inclusion features at Chodarchay provides an example for systematic variations from depth to surface in porphyry–epithermal systems.