The Haenam volcanic field was formed in the southern part of the Korean peninsula by the climactic igneous activity of the Late Cretaceous. The volcanic field hosts more than nine hydrothermal clay deposits and two epithermal Au-Ag deposits. This study focuses on the relationship between hydrothermal clay alteration and epithermal Au-Ag mineralization based on the geology, alteration mineralogy, geochronology, and mineralization characteristics.These clay and epithermal Au-Ag deposits are interpreted to have formed by the same hydrothermal event which produced two distinct types of mineral systems: 1) Au-dominant epithermal Au-Ag deposit and 2) clay-dominant hydrothermal clay deposit. The two types of mineral systems show a close genetic relationship as suggested by their temporal and spatial relationships. The Seongsan hydrothermal system progressively evolved from a low-intermediate sulfidation epithermal system with Au-Ag mineralization and phyllic alteration to an acid-sulfate high-sulfidation system with Au-Ag mineralization and/or barren advanced argillic/argillic alteration. The Seongsan system evolved during post volcanic hydrothermal activity for at least 10. Ma in the Campanian stage of the late Cretaceous.The Seongsan hydrothermal system shows the rare and unique occurrence of superimposed high to low (intermediate) sulfidation episodes, which persisted for about 10. Ma. © 2014.