Petrographic and Mineral-Chemical Constraints on Porphyry Copper Mineralization: Biotite Chemistry and PIMs in the Potassic Alteration Zone of the Chah-Firozeh Deposit, Kerman Cenozoic Magmatic Arc (Iran).

Abstract

      The Chah-Firozeh porphyry Cu system, situated in the Kerman Cenozoic Magmatic Arc (KCMA), was examined using integrated petrographic observations and quantitative EPMA analyses to elucidate its magmatic–hydrothermal evolution and metallogenic characteristics. The deposit is hosted by Eocene andesitic volcanic rocks intruded by a Miocene quartz-monzodiorite to quartz-diorite porphyritic stock. Hydrothermal alteration is well developed and consists of potassic, phyllic, and propylitic zones, locally overprinted by silicic and late supergene argillic assemblages. Ore mineralization occurs mainly as quartz–sulfide veinlets, stockworks, and disseminations of chalcopyrite, bornite, molybdenite, and pyrite. Biotite, a widespread ferromagnesian phase in both magmatic and hydrothermal domains, was analyzed to constrain physicochemical parameters of fluid evolution. Distinct compositional trends in major elements, halogens, and Fe/Mg ratios delineate multiple magmatic and hydrothermal fluid pulses, reflecting changes in temperature, oxidation state, and halogen fugacity. Halogen contents and calculated fugacity ratios (fCl/fH2O, fF/fH₂O) provide an effective geochemical discriminator between barren and mineralized intrusions across the KCMA. These findings confirm that biotite is a reliable porphyry indicator mineral (PIM) and a sensitive tracer of petrogenetic and metallogenic processes in Andean-type arc settings.

Keywords: Chah-Firozeh, porphyry Cu system, biotite chemistry, EPMA, halogen fugacity, magmatic–hydrothermal evolution, KCMA.