Constrained potential field inversions in areas under cover: examples from Gawler Craton IOCG prospects

Abstract

The future of greenfields mineral exploration will be driven towards covered terranes with little or no outcrop. Consequently, the inherent risk and costs of such exploration will rise. The exploration focus will be pushed towards inexpensive methods and more importantly obtaining the most value from them. Potential field geophysics provide a solution to this impending issue with regional datasets often available in the public domain and higher resolution data being relatively inexpensive to acquire. Constrained potential field inversion represents a method for adding or maximising the value from the associated datasets. Many greenfields environments have an apparent absence of a priori data to constrain the first pass inversion. This paper suggests that although this absence may exist, meaningful ?soft? constraints will still be present which when included in the model objective function, improve and add value to the inversion process. Additionally the same constraints can be used to test whether a proposed geological hypothesis is a viable model. Using gravity data over covered IOCG prospects within the Gawler Craton, this paper demonstrates how ?soft? constraints can be employed to enhance the inversion process. Simplified layered geological models representing cover and basement have been discretised, using realistic petrophysical bounds that when incorporated into the model objective function yield more accurate results. Furthermore, the potential of a prospect to host IOCG mineralisation can be simply tested in a similar fashion. When inversion results describe bodies that are geologically unrealistic, the target can be downgraded saving a potentially expensive drillhole.