| Abstract |
The geoscientific studies indicate a possible shallow magma chamber beneath the Paxmux lavas and a magma pocket beneath Zunil Volcano which are believed to be the major heat sources for the geothermal activity in Zunil-II. This and Zunil-I area lie at opposite sides of Samala River, east and west sides respectively. In the whole geothermal area of Zunil NE-SW and E-W trending faults are considered to be the major structural features for the transport of fluids. The Geochemical studies indicated a Cl-rich hot water reservoir located around the confluence of the Samala and Pachamiya rivers and another around Azufrales, Fuentes Georginas and Aguas Amargas (hereafter Azufrales-Fuentes Georginas). From the geothermometry of the neutral chloride type hot springs, the temperature of subsurface fluids near the confluence of Samala and Pachamiya rivers was estimated in 210oC but the gasgeothermometry of Fumarola Negra rendered a temperature above 300oC. On the other hand, the gas geothermometry applied to fumarolic gases sampled at Azufrales and Fuentes Georginas revealed temperatures in the range of 230o to 290oC. Emanometry of Hg and Rn are also conclusive in the presence of fracture zones for the migration of geothermal fluids. Gravimetry and CSAMT resistivity studies detected structural feature agreeing to interpretations of surface geology. 2.5-D gravity modeling interpreted a dense basement shallower in Zunil-II than that in the Zunil-I. The interpreted gravity basement east of Samala River shows features such as horst and grabens that consolidated to the interpreted resistivity values indicate structural features appropriate to host a geothermal reservoir. The Zunil-II area is divided into two systems, one around the Paxmux area and other around the AzufralesñFuentes Georginas area. Three slim holes were drilled. All three tapped a steam reservoir located in the fractured zones of Quaternary lava flows and in the granitic basement. The steam reservoir is considered overlying a hot water reservoir of neutral Cl waters. The geothermal potential resulted in 25 MW for the Paxmux system and from 16 to 23 MW for the Azufrales-Fuentes Georginas system. |