Understanding the migration of hydrothermal fluids represents a continuous 
task for successful exploration of geothermal resources. Contributions to better 
constrain the hydrological models in geothermal areas can derive from field and 
laboratory studies on fossil geothermal systems, evidenced by the 
concentration of ore deposits in wide areas. In this presentation we show data 
from fluid inclusions and structural studies dealing with the path of the 
hydrothermal fluid-flow in the mineralised Boccheggiano-Montieri area. Here a 
deep seated granite (3Ma) was recently reached by boreholes at about 3km 
depth. In this area, the widespread mineralization is located within tectonic 
breccias belonging to the Miocene and Pliocene normal faults and to the 
Oligocene thrusts. Independently from the structural level, fluid inclusions 
investigation indicate that a fluid flow, mainly consisting of meteoric water, 
occurred through the damage zones of the Pliocene normal faults and within 
the cataclasites of the older detachment surfaces. Then, since temperatures 
indicated by fluid inclusions are higher in the Pliocene faults, it is suggested 
that such faults might act as an infiltration path-way of the meteoric fluids 
down to the granite, and as the up-flow conduit for the fluid heated by the 
intrusion. In the Larderello geothermal field extensional North-East dipping 
crustal shear zones have been recognised as possible conduits controlling the 
present hydrothermal circulation. If it is the case, the Boccheggiano-Montieri 
geothermal system would represent a possible analogue of the Larderello 
geothermal system.

Campus SIAF, SP del Monte Volterrano
Localita' Il Cipresso
Volterra, Italy