The Andean Central Volcanic Zone, which runs parallel the Central Andean Cordillera
crossing from North to South the Tarapacà and Antofagasta regions of northern Chile,
consists of several volcanoes that have shown historical and present activity (e.g.
Tacora, Guallatiri, Isluga, Ollague, Putana, Lascar, Lastarria). Such an intense
volcanism is produced by the subduction process thrusting the oceanic Nazca Plate
beneath the South America Plate. The anomalous geothermal gradient related to the
geodynamic assessment of this extended area gives also rise to intense geothermal
activity not necessarily associated with the volcanic structures. Preliminary
investigations on fluids discharging from some of these hydrothermal systems (e.g. El
Tatio, Puchuldiza and Apacheta) have already been performed (Cusicanqui et al., 1975;
Giggenbach, 1978; Urzua et al., 2002; Tassi et al., 2005), in response to the
increasing Chilean energy demand from alternative sources. Nevertheless, the
geochemical features of the majority of the thermal fluid discharges widespread all
over this area are still almost unknown and, at the present, a correct evaluation of
the geothermal potential of northern Chile remains a challenge. In this work the
chemical and isotopic compositions of gas and water discharges collected, from
November 2002 to October 2006, at several different thermal emission sites (e.g. El
Tatio, Apacheta, Surire, Puchuldiza-Tuya, Puritama, Salar de Tara, Hecar) are
presented and discussed in order to propose conceptual models aimed to describe the
main mechanisms regulating the underground fluid circulation for geothermal purposes.

References
Cusicanqui, H., Mahon, W.A., Ellis, A.J., 1975. The geochemistry of the El Tatio
geothermal field, Northern Chile. In: 2nd UN Symposium Development and Utilization of
Geothermal Resources, San Francisco, 703–711.
Giggenbach, W.F., 1978. The isotopic composition of waters from the El Tatio
geothermal field, Northern Chile. Geochim. Cosmochim. Acta 42, 979–988.
Tassi, F., Martinez, C, Vaselli, O., Capaccioni, B., Viramonte, J., 2005. Light
hydrocarbons as redox and temperature indicators in the geothermal field of El Tatio
(northern Chile). Appl. Geochem., 20, 2049-2062.
Urzua, L., Powell, T., Cumming, W.B., Dobson, P., 2002. Apacheta, a new geothermal
prospect in northern Chile.
Geothermal Resource Council, Reno, NV (US), 24 May, 1–10.

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