Hydrothermal alteration and mineralization of porphyry-skarn deposits in the Geunteut area, Nanggroe Aceh Darussalam, Indonesia

The Geunteut area is located 55 km south of Banda Aceh. The research was conducted to characterize the hydrothermal alteration and mineralization of the porphyry-skarn deposits. The alterations and mineralizations were described according to their association and zonation of the hydrothermal minerals, alteration intensity, texture and ore mineral paragenesis. The porphyry-skarn deposits in the Geunteut area are related to the magmatic activity in Middle Miocene by granodiorite and diorite intrusions (Intrusion Rock Units) that resulted in the hydrothermal alteration and mineralization. Hydrothermal alteration can be grouped into five zones: biotite-orthoclase-actinolite, epidote-chlorite-actinolite, garnet- clinopyroxene-tremolite, quartz-sericite and chlorite-calcite-clinoptilolite. The forming temperature of the hydrothermal alteration is between 120 - 360°C with the intensity ranging from very weak to totally altered. The porphyry-skarn deposits exhibit two episodes of mineralization. The early episode was related to the hypogene mineralization, as evidenced by the formation of magnetite, ilmenite, chalcopyrite and pyrite. The late episode was related to the supergene enrichment that allowed the formation of chalcocite, covellite, iron oxide and malachite.