Inverting airborne geophysical data for mega-cell and giga-cell 3D Earth models

Abstract

Today's mineral exploration is driven by the simple fact that discovery rates have not kept pace with the depletion of existing reserves. To improve discovery rates, there is an industry-wide consensus on the need to increase the “discovery space” by exploring under cover and to greater depths. This attracts increased risks which may be mitigated by improved targeting. To do this, mining geophysics needs to shift toward 3D geological models founded upon improved petrophysical understanding and geophysical inversion. Regardless of the inversion methodology used, all geological constraints manifest themselves in the user's prejudice of an a priori model, upper and lower bounds, and choice of regularization. However, the practice of geologically constrained inversion is not the major problem needing to be addressed. It is known (and accepted) that geology is inherently 3D, and is a result of complex, overlapping processes related to genesis, metamorphism, deformation, alteration and/or weathering. Yet, the mining geophysics community to date has not fully accepted that geophysics should also be 3D, and most often relies on qualitative analysis, 1D inversion, and deposit-scale 2D or 3D inversion. There are many reasons for this unfortunate deficiency, not the least of which has been the lack of capacity of existing 3D inversion algorithms. To date, these have not been able to invert entire surveys with sufficient resolution in sufficient time to practically affect exploration decisions.