Geothermal system and hydrothermal alteration in the Zunil geothermal field, Guatemala.

概要

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The Zunil geothermal field contains the pre-Tertiary granitic basement and various kinds of Quaternary rhyolitic and andesitic rocks. A depression zone and upheaved zones elongating NE to SW have been formed since the late Pleistocene time. The geothermal fluid is derived from deep source at the uplifted zone of west side and discharged at the depression zone during the past time. The water table elevation measured in this geothermal aquifer is 1, 950 meters above sea level, and also elevates to 2, 050 meters with increasing of subsurface temperature from east to west. Alteration produced from alkali chloride hot water/rock interaction is observed below this water table in elevation. The siliceous deposits are found at an elevation higher over 100 meters than the measured water table, of which formation age was dated to be 4, 450 years B.P. by carbon-14 method. It is considered that the hydrothermal alteration were took place during the past time when the water table was higher than the present one, and also when the subsurface temperature might be higher than the present one.
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