Deep anomaly localization using surface-borehole TEM and its application in the Wulong Gold deposit

The localization of deep anomalies is a crucial geophysical topic. Surface-borehole transient electromagnetic method (TEM) offers advantages over traditional surface TEM method, including reduced interference from the ground and enhanced resolution capabilities for deep-seated local anomalies. In this study, the localization of deep anomalies was conducted using surface-borehole TEM methods. Based on the equivalence between the pure anomaly field generated by the anomaly body and the electromagnetic field generated by eddy current loops, the calculation of the pure anomaly field was achieved. The extraction of the pure anomaly field was accomplished through fitting the transient electromagnetic response over a large spatial range. By fitting the pure anomaly field with the eddy current loop field, the geometric parameters of the anomaly body were determined, which enabling anomaly localization. The effectiveness of the proposed method was evaluated through synthetic example and demonstrated through its application in the Wulong Gold Mine area. The results showcase the localization of anomalies exceeding a depth of 2800 m using surface-borehole TEM methods, highlighting their superior resolution capabilities compared to the surface TEM methods. Comprehensive well logging and downhole geochemical surveys indicate that the anomaly localized using surface-borehole TEM methods hold multi-metallogenic prospects, including Cu, Pb, Zn, Au, and Ag, presenting significant research value and potential economic benefits.