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3-D Joint Inversion of Magnetotelluric and Airborne Tipper Data: A case study from the Morrison porphyry Cu-Au-Mo deposit, British Columbia, Canada

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  • Z-axis tipper electromagnetic (ZTEM) and broadband magnetotelluric (MT) data were used to determine three-dimensional (3-D) electrical resistivity models of the Morrison porphyry Cu-Au-Mo deposit in British Columbia. ZTEM data are collected with a helicopter, thus allowing rapid surveys with uniform spatial sampling. Ground-based MT surveys can achieve a greater exploration depth than ZTEM, but data collection is slower and can be limited by difficult terrain. The airborne ZTEM tipper data and the ground MT tipper data show good agreement at the Morrison deposit despite differences in the data collection method, spatial sampling and collection date. Resistivity models derived from individual inversions of the ZTEM tipper data and MT impedance data contain some similar features, but the ZTEM model appears to lack resolution below a depth of 1 km and the MT model suffers from non-uniform and relatively sparse spatial sampling. The joint ZTEM-MT inversion solves these issues by combining the dense spatial sampling of the airborne ZTEM technique and the deeper penetration of the lower frequency MT data. The resulting joint resistivity model correlates well with the known geology and distribution of alteration at the Morrison deposit. Higher resistivity is associated with the potassic alteration zone and volcanic country rocks, whereas areas of lower resistivity agree with known faults and sedimentary units. The pyrite halo and ≥0.3 % Cu zone have the moderate resistivity that is expected of disseminated sulfides. The joint ZTEM-MT inversion provides an improved resistivity model by enhancing the lateral and depth resolution of resistivity features compared to the individual ZTEM and MT inversions. This case study shows that a joint ZTEM-MT approach effectively images the interpreted mineralized zone at the Morrison deposit and could be beneficial in exploration for disseminated sulfides at other porphyry deposits.

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    standard copyright agreement (Green Open Access)