Mapping Deep Electrical Conductivity Structure in the Mount Isa region, Northern Australia: Implications for Mineral Prospectivity

摘要

The Mount Isa Province in northern Australia is one of the world's most strongly endowed regions for base metals and host to major iron-oxide-copper-gold (IOCG) deposits. The Carpentaria conductivity anomaly at the eastern margin of the province is a major electrical conductivity structure of the Australian continent. We use magnetotelluric data to image the crustal architecture in this highly mineralized region. The resistivity models reveal a number of prominent crustal-scale conductors, suggesting that the Carpentaria conductivity anomaly is likely caused by a series of isolated or interconnected bodies. These conductors confirm the position and geometry of the ancient Gidyea Suture zone, the eastern boundary of the Mount Isa Province, interpreted as a west-dipping subduction zone. The Carpentaria conductivity anomaly may record the activity of fluid dehydration involved during a subduction event, with the enhanced conductivity likely being caused by deformation or mineralization of graphitic or sulfidic rocks during orogenesis. The major iron oxide in the Ernest Henry IOCG deposit located in the hanging wall of the Gidyea Suture zone is magnetite, suggesting another possible conductive source. The distribution of known gold and copper deposits shows a close spatial correlation with the suture zone, suggesting that this structure is potentially a fundamental control on IOCG deposits in its vicinity. The implication is that crustal-penetrating structures act as potential pathways for fluid movement to form mineral deposits in the upper crust. The significance of mapping such structures using geophysics is highlighted for mineral exploration.