Interpretation of resistivity soundings from San Ignacio, Honduras

Abstract

The San Ignacio geothermal field is located in the central part of Honduras. The rocks in the area are primarily of Paleozoic metamorphic origin, overlaid by Tertiary Padre Miguel Group tuffs and alluvial deposits. One-dimensional interpretation of Schlumberger resistivity soundings revealed that the alluvial deposits have a relatively low resistivity and hence obscured possible interesting resistivity structure in the underlaying basement. The geothermal surface manifestations are located where a NE-trending zone of most recent tectonic activity, west of the Arenal-fault, intersects a WNW-trending fault bordering the northern part of the Siria valley. A low-resistivity anomaly is present in the southwest extension of the zone, covering an area of 15 km2. All this together with the presence of the sinter deposits north of La Tembladera might suggest that the geothermal activity is related to this NE-trending fault zone and the low resistivity could be caused by geothermal fluids conducted by these faults and infiltrated into the valley fill.