Multiple-scale magnetotelluric surveys – mapping the lithosphere to the near surface for mineral systems

Magnetotellurics is one of few techniques those can provide multiple-scale datasets to understand the larger mineral system. We have used long-period data from the Australian Lithospheric Architecture Magnetotelluric Project (AusLAMP) as first-order reconnaissance survey to resolve large-scale lithospheric architectures for mapping areas of mineral potential in northern Australia. The 3D resistivity model reveals a broad conductivity anomaly extending from the Tennant Region to the Murphy Province, representing a potential fertile source region for mineral systems. We then undertook a higher-resolution infill magnetotellurics survey to refine the geometry of major structures, and to investigate if the deep structure is connected to the near surface by crustal-scale fluid pathways. The resistivity models reveal two prominent conductors in the resistive host whose combined responses result in the lithospheric-scale conductivity anomaly mapped in the AusLAMP model. The resistivity contrasts coincide with major structures preliminarily interpreted from seismic reflection and potential field data. Most importantly, the conductive structures extend from the lower crust to the near surface at where the major faults are located. This observation strongly suggests that these major faults are deep-penetrating structures that potentially acted as pathways for transporting metalliferous fluids to the upper crust where they could form mineral deposits. This result indicates high mineral prospectivity for iron oxide copper–gold deposits in the vicinity of these major faults. We then used high-frequency data to estimate cover thickness to assist with drill targeting for the stratigraphic drilling program which, in turn, will test the models and improve our understanding of basement geology, cover sequences and mineral potential. This study demonstrates that integration of geophysical data from multiscale surveys is an effective approach to scale reduction during mineral exploration in covered terranes. This Abstract was submitted/presented to the 2021 Australasian Exploration Geoscience Conference 13 - 17 September https://2021.aegc.com.au/.