The Mount Isa Copper mine is located adjacent to the township of Mount Isa, northwest Queensland and lies within a series of Paleoproterozoic to Mesoproterozoic Superbasins. The deposit is hosted almost entirely within the Urquhart Shale, a unit of the Mount Isa Group sediments and part of the Isa Superbasin. The copper mineralisation is separated into two distinct orebodies; the X41 mine (1100 and 1900 orebodies) and the Enterprise mine (3000 and 3500 orebodies). The orebodies are situated in the hangingwall of the major controlling structures, the Paroo Fault, which has juxtaposed older basement Eastern Creek Volcanics (ECV’s) against the younger Mount Isa Group sediments cf. 1655 ± 4 Ma. Conjecture remains over the exact timing of this thrust event. However, it is clear that inflections on the Paroo Fault have a close association with the orebodies and are an important structural feature in the mineralisation of the Mount Isa Copper Deposit.
GMEX was requested by Xstrata to assist them to better understand the geomechanical response of the mine sequence during regional deformation events, by employing Finite Element Analysis (FEA) in an attempt to help them delineate targets for their within mine and near mine exploration program. A conceptual 3D model was constructed using available 3D structural data from the mine and exploration team, primarily Minesight® data and available reports and cross sectional information. This conceptual model included all the main lithological units and structures. The conceptual model aimed at testing the effects of deformation on the main lithological and structural components of the system, and attempted to highlight areas of anomalous stress and strain which may indicate a higher likelihood of fluid focussing and mineralisation potential.
Geomechanical modelling results for volumetric strain, fluid flow and shear strain indicate that late stages of the NE-SW (D3) contraction event display the best correlation with the current Enterprise (3000, 3500, W-Block) and X41 (1100) Copper orebodies. As a result, this close correlation was one of the principal determining factors in using the geomechanical modelling data as a primary targeting tool for the MICO team. Several targets were generated from the modelling results and targets close to the 3000 orebody have been drilled and have showed encouraging results. A number of wedges have since been proposed from the parent hole for further testing. The employment of innovative techniques such as 3D geomechanical modelling coupled with good structural geology and geological planning has provided a valuable outcome for both the exploration and resource geology team. Having this critical understanding of how the deformation events relate to both structures and geomechanical response has enabled the MICO team to a) gain a greater understanding of the system, b) prioritise drilling campaigns in a more cost effective manner c) return successful and promising assay results with planned drilling intersections and d) increase the potential for discovery of mineralisation extensions and extend the current life of mine.