| Abstract |
A 20 km2 soil CO2 gas flux and shallow temperature survey was undertaken in and around the San Jacinto-Tizate geothermal power project, Nicaragua. Conditions during the survey were undertaken in the dry season (March-April, 2017), and were dry and hot for the entire survey period. This provided a high-quality CO2 flux dataset with apparently negligible interference from biological gas flux. The survey showed a broad area of low CO2 flux (LFZ), which surrounds the central production area. This may result from a low permeability capping formation; the capping formation blocks CO2 flux from reaching the surface. The LFZ partly encircles a high-flux zone (HFZ), an area of relatively high CO2 flux that occurs to the NNW of the steamfield. The HFZ is closely associated with i) a magnetic high anomaly, previously interpreted to result from unaltered material, ii) MT resistivity high, and iii) watershed catchment boundaries. Together, these observations suggest the area is hydrologically isolated from the central production area, and may lack a reservoir. Comparison with an earlier CO2 flux survey in the same area (2011) is complicated by the much drier soil conditions in 2017. Despite this, results provide additional confirmation of the SJ10 fault, first identified in 2011 CO2 flux survey. Results suggest CO2 gas flux surveys are particularly well suited to arid environments (e.g. Atacama Desert), or in areas with a pronounced dry season (Central America, East Africa). Under these conditions, CO2 flux surveys may be able to identify the clay cap as a zone of relatively low CO2 flux. This is a key objective of well targeting and geothermal exploration. |