## 1 Introduction  
The constant increase in raw materials demand to supply the global industry necessitates the investigation of increasingly complex mineral deposits at greater depths. This type of project represents a challenge, in which the development of investigation tools is a fundamental pillar. In this context, geophysical investigation techniques are presented as a fundamental tool for the investigation and analysis of these new mineral deposits.  
In the North of Spain there is an industry based on the extraction of potassium salts. The exploitation of these salts is carried out by dissolution processes through drilling and subsequent evaporation and processing of the extracted brine in ponds. These salts are found within the Barbastro Formation, which is located in an outcropping anticline structure (Barbastro-Balaguer Anticline). The progressive depletion of the currently exploited areas, located in the outcropping part of the formation and nearby areas, makes necessary the investigation and delimitation of the saline materials at greater depths, given its affectation by the regional anticline structure.  
The application of geophysical tools in the resolution of geological and structural problems has experienced an important evolution in recent times, due to the improvement in the equipment power, resolution and penetration capacity. In this case, one of the most used geophysical investigation systems due to its high resolution and penetration capacity is the time domain electromagnetic method (TDEM).  
TDEM surveys have been widely applied to investigate and solve problems in geology, hydrogeology, environmental studies, mining and geothermics, providing subsurface resistivity models at relatively shallow depths (up to 1000 m) [1; 2; 3; 4; 5; 6; 7; 8]. There are few publications about the use of the TDEM system (Monex Geoscope LTD.; The Basin, VIC, Australia) to analyze great depths, mainly due to the technical limitations of the equipment; however, depths greater than 2000 m have been reached in hydrogeological studies [9; 10; 11; 12; 13; 14], and also in oil and gas exploration, in which TEM data allows a resources estimation and well optimization [10]. The equipment used in this study, TerraTEM with TerraX-50 transmitter (Monex Geoscope LTD.; The Basin, VIC, Australia) and the acquisition parameters and configuration (coincident-loop 600 m \(\times\) 600 m square configuration, 96 volts output voltage and 40 ampere transmitter current, and late delay times (over 1 s)) allowed us to reach larger depth ranges than usual in the industry, reaching up to 3000 m depth.  
In this study, TDEM was applied to obtain a novel approach to the structure of the saline-evaporitic Barbastro formation in the southern flank of the Barbastro-Balaguer anticline in an area southwest of Graus (Huesca, Spain), where the development of new mining projects related to the exploitation of potassium salts is expected. Different inverted models were confronted with one parametric layered constrained model based on a lithological drilling log (borehole Monzon-1). The parametric constrained model was then used in the rest of the TDEM survey points as a starting model. Data, 1D models, and formation surfaces arising from a new electromagnetic survey are presented. The applied methodology allows for an improved detailed geological and structural view of the saline-evaporitic Barbastro Formation.  
The new survey suggests that the general structure of the saline-evaporitic Barbastro Formation, and, therefore, of the materials affected by the regional anticlinal structure, presents a ramp hanging wall and close to flat footwall structure dipping to the SW, in concordance with the previous accepted geological structural model. This structure involves a thickness loss to the SW due to the defined structure, ranging in the survey area from 1103 m to 601 m. Hence, our study contributes to improving the geological structure and position of the saline materials, allowing design and drilling optimization in future mining exploitations.