The smectite to chlorite transition in the Chipilapa geothermal system, El Salvador

Abstract

Clay mineralogical X-ray diffraction and electron microprobe studies have been carried out on separated <2 m fractions from cutting and core material from three wells in the Chipilapa geothermal system in El Salvador. The data indicate that the smectite to chlorite transition is prevalent, but a secondary smectite to illite transition is also present. At depths approximately <750 m, smectite with very minor chlorite mixed-layers (approximately <15%) is dominant, and has a composition midway between a di-and tri-smectite. At ~750 m there is a very clear distinction and sharp transition into discrete chlorite with very minor smectite mixed-layers (approximately <10%). Corrensite is recorded only as a rare and minor phase.