Airborne time-domain electromagnetic investigation of the Granisle polymetallic deposit: qualitative interpretation and rapid conductivity-depth imaging

Airborne time-domain electromagnetic (ATEM) surveys have emerged as one of the most effective tools for detecting conductive structures and concealed mineral targets, achieving remarkable accuracy and efficiency in recent years. In this study, airborne electromagnetic data from the QUEST-West project were utilized to reconstruct the three-dimensional geometry of alteration and mineralization zones within the Granisle porphyry Cu–Au deposit in the Babine district of British Columbia. Qualitative analysis of off-time channels and the Late Time Decay Constant (τ) map revealed three prominent conductive zones with a northeast–southwest trend. In addition, conductivity-depth imaging (CDI), implemented via a fast approximate transform, was applied to generate independent depth sections for each flight line, which were subsequently merged through multidimensional interpolation into a quasi–three-dimensional conductivity model. The CDI results indicate the presence of a focused conductive body with a shallow top (on the order of tens of meters below surface) and a significant vertical extent, spatially coincident with the historic open pit at the Granisle deposit—a geometry consistent with the known distribution of mineralized zones and vein networks at Granisle. By circumventing computationally intensive inversion procedures, this approach provides a stable and geologically coherent first-order image of subsurface conductivity and can serve as a reference model for quantitative inversion, drill targeting, and exploration decision-making in the historically mined Granisle porphyry deposit.

کلیدواژه ها:

Airborne time-domain electromagnetics ، conductivity-depth imaging ، Porphyry Mineralization ، Granisle deposit ، Pseudo-۳D conductivity model