The plane-wave quasi-static magnetic susceptibility sounding method can acquire magnetic susceptibility information at different frequencies, achieving physical magnetic susceptibility–frequency sounding, which is advantageous for extracting deep magnetic information. Therefore, an applied study was conducted using the Pingyao manganese carbonate deposit in Tiandeng County, Guangxi, as a case study. First, the principle and formula derivation of the plane-wave quasi-static magnetic susceptibility sounding method are described. Then, forward modeling was carried out based on the geological and geophysical characteristics as well as the manganese mineralization model of the study area to calculate the magnetic susceptibility responses at different frequencies for an inclined plate-shaped manganese ore body. Subsequently, synchronous field observations of horizontal magnetic fields were performed at base stations and survey points, and the magnetic susceptibility at different frequencies was calculated. Using Quasi Static Magnetic susceptibility processing software, magnetic susceptibility information at various depths underground was inverted. Combined with geological data, comprehensive profile analysis was conducted to delineate the manganese carbonate ore body. Finally, by analyzing the correspondence between geological information revealed by verification drilling and geophysical anomalies, the effectiveness of the method was demonstrated. The results indicate that the quasi-static magnetic susceptibility sounding method can effectively distinguish manganese-bearing rock series from surrounding rocks, delineate the spatial distribution pattern of manganese ore, and achieve refined detection of manganese carbonate deposits. This provides new prospecting ideas and technical approaches for the exploration of similar metallic and non-metallic mineral deposits with magnetic indicators.