Abstract: The Bijiashan antimony deposit represents a medium- to low-temperature hydrothermal deposit. Based on the geological characteristics and electrical properties of the deposit, and employing the audio-frequency magnetotelluric (AMT) method, this study detected and analyzed the deep geological structures along the periphery of the deposit, thus effectively identifying the electrical and structural characteristics of the deposit in the subsurface space. Specifically, an AMT-based theoretical model of mineralization (prospecting) was constructed for the deposit. An AMT-based prospecting criterion was determined for the deposit: the anticlinal axis and the transition zones of anticlinal flanks (i.e., interlayer fracture zones) are located on the middle- to high-resistivity contact zone, which exhibits a saddle-shaped distribution on the section. Accordingly, the distribution of the anticlinal core, characterized by steep western and gentle eastern portions, was identified. The anticlinal axis and interlayer fracture zones were accurately localized. Their locations were presumed to be favorable areas for mineralization. The drilling verification of geophysical anomalies reveals the concealed antimony mineralized bodies, marking a breakthrough in deep mineral prospecting and proving the feasibility of the AMT method. Overall, the results of this study demonstrate that the AMT method is an effective geophysical technique in exploring the Bijiashan antimony deposit and other similar deposits.