f The Green tuff units of Mt. Epomeo, Ischia Island (Italy): evidence of an exhumed fossil geothermal system

The hydrothermally altered Green Tuff units that outcrop on the Western and North-Western<br>flanks of Mt Epomeo on Ischia island offer the rare opportunity to see a section of a<br>hydrothermal system exposed on the surface. The Ischia island fossil hydrothermal system<br>shows numerous common features with the typical active geothermal systems developed on<br>volcanic islands.<br>The mineralogy, the chemistry and the space distribution of the hydrothermal assemblages<br>observed in the Green Tuff units and in hydrothermally altered xenoliths agree with most of<br>geothermal environments (Browne, 1978). Based on (1) the occurrence of temperaturesensitive<br>minerals such as mixed layers I/S (<150°C), illite-phengite-chlorite (>220-240°C)<br>and biotite (>320°C), and (2) chlorite and illite geothermometry, the secondary minerals of<br>Ischia island fossil hydrothermal system indicate ambient paleo-temperatures ranging from<br>120-140°C to about 340°C.