Mineralogy and fluid inclusion investigations in the Reagan Porphyry System, Iran, the path to an uneconomic porphyry copper deposit

The Reagan Porphyry System in southeastern Iran (Kerman Province) is associated with diorite/granodiorite to quartz-monzonitic rocks of Miocene age. Three stages of hydrothermal alteration and associated mineralization have produced new minerals, created new textural relationships and in many cases obliterated the primary character of the rocks. Potassic, phyllic and propylitic are the main hydrothermal alteration types within the intrusive stock. The early hydrothermal alteration produced a potassic assemblage in the central part of the stock; propylitic alteration occurred contemporaneously with potassic alteration, but in the peripheral parts, phyllic alteration which contains the main copper mineralization, occurred later, overprinting the earlier alteration. Phyllic is also the major alteration in the Reagan system. The early hydrothermal fluids are represented by high temperature (487–598 °C), high salinity (up to 61.1 wt% NaCl equiv.) liquid-rich fluid inclusions, and high temperature (397–401 °C), low-salinity, vapor-rich inclusions, which are interpreted to originate from very hot orthomagmatic fluids. The brines are interpreted to have caused potassic alteration, producing first generation chalcopyrite. Propylitic alteration is attributed to a lower temperature, liquid- and Ca-rich, evolved meteoric fluid. Influx of meteoric water into the system, and mixing with magmatic fluid produced deep albitization, and shallow phyllic alteration. This influx also caused dissolution of early formed copper sulfides and remobilization of Cu into the phyllic zone. The following data indicate that the mineralizing fluid temperature was too high to produce an economic porphyry copper deposit at the studied area. Supergene alteration was restricted to a very thin blanket with uneconomic levels of Cu in the form of Cu-sulfides and oxides.