The main geothermal reservoir of Acqui Terme-Visone hosts Na-Cl waters,
which are in chemical equilibrium at 120-130 degrees C with typical
hydrothermal minerals including quartz, albite, K-feldspar, illite,
chlorite (or smectite), anhydrite, calcite and an unspecified
Ca-Al-silicate. In the Acqui Terme-Visone area, these geothermal waters
ascend along zones of high vertical permeability and discharge at the
surface almost undiluted or mixed with cold, shallow waters. To the SW
of Acqui Terme, other ascending geothermal waters, either undiluted or
mixed with low-salinity waters, enter relatively shallow secondary
reservoirs, where they reequilibrate at 65-70 degrees C.
Both chemical and isotopic data indicate that bacterial SO4 reduction
affects all these waters, especially those discharged by the secondary
reservoirs. Therefore, geothermal waters must get in contact with oil,
acquiring the relatively oxidized organic substances needed by
SO4-reducing bacteria. This oil-water interaction process deserves
further investigations, for potential economic implications. (C) 2000
Elsevier Science Ltd. All rights reserved.