Water chemistry of San Marcos area, Guatemala

Two well-equilibrated Na-C1 geothermal liquids are recognizable in the San Marcos area. Both have the same C1 concentration (540 mg/kg) and the same isotopic composition (6D of -66.5%o and 6180 of -9%o) under reservoir conditions, but they come from two distinct aquifers with different temperatures, i.e. 240°C below La Cimarrona and 185°C below La Castalia. The numerous thermal Na-CI to Na-CI-HCO3 springs located in the San Marcos area originate through dilution and boiling of these two geothermal liquids and different degrees of re-equilibration at lower temperatures. Silica and K contents are useful in discriminating between dilution, boiling and re-equilibration phenomena. Thermal Na-HCO3 waters, generated through conductive heat transfer or input of geothermal vapor or gases from below, delineate the extent of the geothermal reservoir(s) at depth. © 1998 CNR. Published by Elsevier Science Ltd.