HYDROTHERMAL FLUID EVOLUTION IN THE DALLI PORPHYRY CU-AU DEPOSIT: FLUID INCLUSION MICRO THERMOMETRY STUDIES

Introduction A wide variety of world-class porphyry Cu deposits occur in the Urumieh-Dohktar magmatic arc (UDMA) of Iran.The arc is composed of calcalkaline granitoid rocks, and the ore-hosting porphyry intrusions are dominantly granodiorite to quartz-monzonite (Zarasvandi et al., 2015). It is believed that faults played an important role in the emplacement of intrusions and subsequentporphyry-copper type mineralization (Shahabpour, 1999). Three main centers host the porphyry copper mineralization in the UDMA: (1) Ardestan-SarCheshmeh-Kharestan zone, (2) Saveh-Ardestan district; in the central parts of the UDMA, hosting the Dalli porphyry Cu-Au deposit, and (3) Takab-Mianeh-QharahdaghSabalan zone. Mineralized porphyry coppersystems in the UDMA are restricted to Oligocene to Mioceneintrusions and show potassic, sericitic, argillic, propylitic and locally skarn alteration (Zarasvandi et al., 2005; Zarasvandi et al., 2015). In the Dalli porphyry deposit, four hydrothermal alteration zones, includingpotassic, sericitic, propylitic, and argillic types have been described in the two discrete mineralized areas, namely, northern and southern stocks. Hypogenemineralization includes chalcopyrite, pyrite, and magnetite, with minor occurrences of bornite.Supergene activity has produced gossan, oxidized minerals and enrichment zones. The supergene enrichment zone contains chalcocite and covellite with a 1020 m thickness. Mineralization in the northern stock is mainly composed of pyrite and chalcopyrite. The aim of this study is the investigation and classification of hydrothermal veins and the constraining of physicochemical compositions of ore-forming fluids using systematic investigation of fluid inclusions.