Simpson, J.M.1, Brown, D.D.1, Duan, J.2 and Kyi, D.2.
1 Geological Survey of Queensland, Brisbane, Australia, 2 Geoscience Australia, Canberra, Australia
The electrical structure of Queensland is dominated by the Carpentaria Conductivity Anomaly (CCA). It stretches hundreds of kilometres from the Gulf of Carpentaria in the north, possibly extending as far south as Birdsville. It is present in the crust and extends down into the mantle. The CCA is of great interest as it underlies significant mineral deposits in the Eastern Succession of Mount Isa such as Ernest Henry. Modelling of existing broadband and long period MT data has been used to suggest the CCA may be associated with collisional tectonics along the Gidyea Suture during the Proterozoic.
A new MT survey in the Cloncurry region offers insight into the crustal portion of this anomaly. The survey offers over 500 new MT sites at 2 km station spacing and was collected in 2020. Conductive anomalies are imaged by the new data which are associated with both the Mount Margaret and the Quamby/Fountain Rage Faults. The conductive response occurs from approximately 2 km depth and extends into the deep crust. These are both major structures that have accommodated significant crustal movements throughout the complex history of Mount Isa. Mount Margaret Fault is related to the Gidyea Suture, while different interpretations of deep crustal seismic data in the area suggests that the Quamby/Fountain Range Fault extends either into the mid-crust or is full crustal thickness structure.
The presence of conductive anomalies along such major structures suggests that they could be functioning as more localised fluid pathways from the deeper part of the conductive anomaly. The presence of conductive anomalies along both these structures, rather than just along the Gidyea Suture associated Mount Margaret Fault suggests that the CCA is not simply a suture related feature.
Janelle is a senior geophysicist with the Geological Survey of Queensland. She is passionate about the integration of geology and geophysics to produce more meaningful interpretations.