A comparative copper isotope study of porphyry copper deposits in Iran

Copper isotope ratios and Cu concentrations have been measured in oxide and sulphide minerals from leached cap (hematite-goethite-jarosite-malachite), supergene (chalcocite-pyrite-hematite) and hypogene (pyrite-chalcopyrite) zones in the Chahfiroozeh, Darrehzar, Iju and Parkam porphyry Cu deposits from the Kerman porphyry Cu belt of Iran. In general, S Cu values show distinctive values of 0.23‰ to 0.79‰ in hypogene, 2.52‰ to 4.82‰ in supergene and -1.00‰ to -6.16‰ in leached cap minerals. Leach cap minerals contain less Cu than supergene and hypogene minerals. This study supports previous distinct Cu isotopic patterns for leached cap, supergene and hypogene zones reported from other porphyry Cu deposits. Weathering and oxidative dissolution of Cu sulphide minerals normally generate isotopically heavier fluids and lighter residual minerals. Upon encountering reducing conditions at greater depths, the oxidative solutions precipitate secondary Cu-sulphides in the enriched zone and the new minerals possess heavier Cu isotopic compositions. The degree of isotopic separation and difference in concentrations among the three reservoirs is most likely related to the weathering processes and the isotopic signatures present in the leach cap may have exploration potential.