Dr Jeremie Eugene Cyril Giraud1,2, Dr Mark Lindsay1,2, Dr Mark Jessell1,2
1Centre For Exploration Targeting, School of Earth Sciences, University Of Western Australia, Crawley, Australia, 2Mineral Exploration Cooperative Research Centre, School of Earth Sciences, University of Western Australia, Crawley, Australia
We present a geophysical inversion technique designed for the recovery of the geometry of rock units in 3D. It relies on the iterative adjustment of the location of interfaces between homogenous rock units implicitly defined by the signed-distance to each contact. We formulate the inverse problem using a generalized level-set method capable of dealing with any number of rock units. Our implementation uses a deterministic least-squares inversion framework. It is flexible and allows the incorporation of prior geological information such as the location, shape and aspect ratio of rock units in the regularisation function and to adjust the thickness of the interface between them. While the utilisation of this algorithm focuses on adjusting pre-existing geological models to honour geophysical data it also supports topological changes during the inversion. We first explore the capabilities of the proposed inversion approach using noisy synthetic gravity data and perform the proof-of-concept. We then model field gravity data from the North-eastern part of the Yerrida Basin (Western Australia) to model the geometry of a prospective greenstone belt that previous studies highlighted as requiring further investigation.
The synthetic example demonstrates the capability of the proposed method to improve the recovery of the geological bodies’ geometry and to change the initial geological model’s topology to honour the geophysical measurements. The application to real world data allows suggests revision of the accepted tectonic setting and structure is required. In particular, results suggest that the undercover mafic greenstone belt may be shallower and thinner than predicted by surface geology alone, perhaps influenced by previously unidentified deeppenetrating structure.
We acknowledge the support of the MinEx CRC and the Loop: Enabling Stochastic 3D Geological Modelling (LP170100985) consortia. The work has been supported by the Mineral Exploration Cooperative Research Centre whose activities are funded by the Australian Government’s Cooperative Research Centre Programme. This is MinEx CRC Document 2020/xx.
Jeremie Giraud is a research fellow at the Centre for Exploration Targeting. His research efforts focus on the integration of geophysics and geology and on multi-physics integration.