Exploration of buried travertine layers by combining geoelectric and geological data in Mahallat area

Geoelectric studies by electrical resistivity method and by determining and evaluating the characteristics of subsurface travertine layer such as tailings depth, thickness of travertine layer and depth of its floor rock are the objectives of this article. In addition to reviewing the geological data, the resistivity of the electrical conduction sections in one and two dimensions were also analyzed with RES2DINV software after conversion from apparent resistance to real resistance. This study showed that travertine layers with an average thickness of 15 meters are located at depths of 5 to 80 meters and its specific resistivity varies from 120 to 3500 ohm meters due to breakage and crushing. Combining geoelectric data with surface geology by drilling 9 boreholes and drawing maps of both thickness and depth of travertine showed that the tailings (soil and alluvium) buried on travertine had a depth of 2 to 80 meters and travertine is variable. Base rock of travertine is made of red conglomerate and dark shale and sandstone. By interpreting the apparent resistivity data along different profiles and matching them with the geological information of the region, it was shown that the high resistivity is the conglomerate layers, the low resistivity is the alluvium and clay sandstones and the medium resistivity is travertine layers. Examination of the accuracy of resistance data with drilling logs showed that the accuracy in separating the tail depth, thickness and depth of the travertine layer was 27%, 1% and 63%, respectively. Electrical resistance data by predicting the depth of travertine base rock has been a good guide to determine the position and depth of drilling in travertine buried in the area.