Characterization of the shallow structure of El Tatio geothermal field in the Central Andes, Chile using transient electromagnetics

This study presents the first high resolution geophysical survey conducted in The El Tatio geothermal field, northern of Chile, focused on the detection of shallow subsurface structures and identification of ascending fluid pathways. TEM data was collected along 5 profiles crossing the two main geothermal basins (Upper and Middle Basin) to obtain an electrical resistivity model up to 200 m depth. The models show important structures that allowed us to improve the conceptual model of the field connecting these geophysical observations with the geology and the geochemistry of the area. We found a shallow (<60 m) high conductivity layer in all profiles. This layer was interpreted as a shallow aquifer of thermal water, which is probably the water supplier of surface manifestations. In the Upper Basin a main permeable zone allows the ascent of fluids from deep aquifers to the shallower one, and a structure that probably act as impermeable geological barrier that forces the fluids to ascend has been detected. In the Middle Basin fluid ascent zones are less clear than in the Upper Basin but it is possible to observe areas of lower resistivity that could be associated with higher permeability.