Discrete element modelling applied to mineral prospectivity analysis in the eastern Mount Isa Inlier

Abstract

Numerical modelling using a discrete element technique is employed here to examine the response of a fracture system in the eastern Mount Isa Inlier to an applied stress regime. Model scale, parameters and boundary conditions were varied to test which combinations of geometry and material properties produce the best correspondence between the known mineral-deposit distribution and zones of anomalous model stress. Modelled areas of combined low-minimum principal stress ( σ 3) and low-mean stress ( σ m) show the best correlation with deposits, but these areas do not clearly correspond to specific fault orientations or configurations. Rather, the models produce complex zoning of stress anomalies in response to the partitioning of stress across complex fault blocks, and the interaction between more competent granitoid bodies, less competent meta-sedimentary rocks, and the fault and rock boundary complexities. Adding fluid to the models, and identifying an optimum orientation of the stress field (with σ 1 in an ESE direction), produces the highest degree of visual correspondence with the known mineral-deposit distribution and the previous empirical prospectivity analysis, and also identifies several potentially prospective areas that may not have been previously tested by explorers. The models are consistent with mineralisation occurring (or being remobilised from earlier concentrations) during a major phase of regional fluid flow facilitated by a complex fault array, late during the evolution of the Isan Orogeny and synchronous with the waning stages of the emplacement of the Williams Batholith.