Las Pailas geothermal area Rincon de la Veija volcano, Costa Rica

Abstract

The Rincón de la Vieja is a composite strato-volcano in the northwestern part of Costa Rica, 240 km from the capital (San José). The volcano is a part of the Guanacaste volcanic mountain belt. The most significant hydrothermal manifestations in the country occur on the southwestern flank of the volcano. The Pacific side of Rincón de la Vieja has been studied from aerial photos. The apparent geological features on these photos have been correlated with rock formations, making use of previous work. Age-dating and rock composition show a magmatic evolution from basaltic-andesitic through andesite to more acidic rocks with decreasing age. This evolution extends from west to east and then to the northeast. The present study focuses on an area 30 km2 in size, here referred to as the Las Pailas geothermal area. Las Pailas hydrothermal manifestations are on the northeastern side of this area, and the Hornillas hydrothermal manifestations are close to its northern margin. The study includes the lithology, clay mineralogy and thermal distribution in thermal gradient wells. A magmatic evolutionary model is presented as well as two competing hydrothermal models, A and B. Model A assumes a geothermal reservoir within an assumed San Vicente caldera, younger than 1 m.y. old. Model B assumes the hydrothermal reservoir is linked to the presently active Rincón de la Vieja volcanoic complex, younger than 500,000 m.y. Model A is favoured for exploitation outside the Rincón de la Vieja national park and needs to be tested accordingly.