Mineralogical and geochemical evidence of late epithermal alteration in the Kisladag porphyry gold deposit, Usak, Western Turkey

The Kisladag porphyry gold deposit is related to Miocene intrusive and sub-volcanic rocks that resulted from an extensional tectonic regime in western Anatolia. The main lithologies of the deposit are quartz-trachytes to quartz-latites and volcanoclastic rocks intruded by sub-volcanic porphyritic rocks. Three different intrusive phases which have been identified from their age, alteration grade and mineralization (IN-1: the oldest intrusion, intense potassic alteration, IN-212A: intense clay-quartz alteration, IN-3: the youngest intrusion, weak alteration). IN-1 contains quartz, illite and kaolinite, IN-2A has quartz, adularia, illite, kaolinite and smectite. Alunite, jarosite and tourmaline increase in IN-1 and IN-2A; whereas biotite and illite increase in IN-1 and IN-2A, respectively. The volcanoclastic rocks are composed of quartz, alunite and kaolinite/halloysite indicating advanced argillic alteration. Although the microscopic data confirms potassic and phyllic alterations in IN-1 and IN-2A, mineralogical (well crystallized 1M and poorly crystallized 1 M-d illite, kaolinite/halloysite, alunite, jarosite) and geochemical (K/Ar age data for different grain-sized illite indicating late overprinting at least 5 Ma) data indicate that the early stage alteration phases were overprinted by the late stage epithermal alteration.