Multi-scale magnetotelluric surveys - mapping from the lithosphere to the near surface for mineral systems

Geoscience Australia has undertaken a series of integrated studies to map the footprint of mineral systems at multiple scales. We have used long-period data from the Australian Lithospheric Architecture Magnetotelluric Project (AusLAMP) to resolve large-scale lithospheric architecture in northern Australia. A 3D resistivity model reveals a broad conductivity anomaly in the lower crust and upper mantle that extends from the Tennant Region to the Murphy Province. This anomaly represents a potential fertile source region for mineral systems. We then undertook a higher-resolution infill magnetotelluric survey to refine the geometry of major structures and to investigate if the deep conductive structure is connected to the near surface. Resistivity models reveal two prominent conductors in the resistive host whose combined responses represent the lithospheric-scale conductivity anomaly mapped in the AusLAMP model. The resistivity contrasts coincide with major structures interpreted from seismic reflection and potential field data. Most importantly, conductive structures coinciding with major faults in this region extend from the lower crust to the near surface. This observation strongly suggests that the 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 prospectivity for major mineral deposits in the vicinity of these major faults. In addition, we used high-frequency data to estimate cover thickness to assist with stratigraphic drill targeting which, in turn, will validate 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.