We have performed a case study on the use of magnetic amplitude inversion in imaging volcanic rocks that are buried in a sedimentary basin and have strong remanent magnetization. The application arises in exploration for natural gas hosted in volcanic rocks in basin environments. The weak anomaly associated with the volcanic units and the presence of remanent magnetization therein pose major challenges in the magnetic interpretation. We first use a Wiener filter based on an ensemble analysis to examine the depth characteristics of the anomalies, and then we use an inversion-based signal separation to extract the anomaly for final interpretation. We apply an amplitude inversion method to recover the distribution of effective susceptibility in the absence of the knowledge about the total magnetization direction. The result effectively identifies the volcanic rock units at large depths and the imaged distribution of these units is consistent with information from drillholes and local geology.