Status update on AusLAMP deployment
Acquisition of the South Australian component of the national magnetotelluric AusLAMP dataset continues to provide valuable precompetitive data on the state’s mineral prospectivity.
The Australian Lithospheric Architecture Magnetotelluric Project (AusLAMP) aims to provide a 3D image of the electrical resistivity distribution of the crust and mantle beneath the Australian continent. Zones of low resistivity are now widely established to be areas of mechanically weak lithosphere, which have undergone extensive shearing and faulting and have provided pathways for fluid and magmatic flux. This insight has wide-ranging implications for our understanding of the evolution of the Australian continent and helps to map out fertile zones in the crust that have witnessed large fluid movement at some stage in the tectonic history. As a result, it will inform about the prospectivity of the state.
Figure 1 South Australian AusLAMP deployment, status at 4 July 2017.
The Geological Survey of South Australia (GSSA) has been an early supporter of this national initiative and has been aggressively pushing its roll-out in South Australia since 2014. This large-scale deployment of long-period magnetotelluric (MT) stations collected every ~55 km has acquired 317 stations to date, covering roughly 80% of the state (Fig. 1). It is the largest number of MT stations in any jurisdiction for this type of continent-wide MT deployment. Data acquisition was largely funded by PACE initiatives with additional funding by Geoscience Australia, National Collaborative Research Infrastructure Strategy and the University of Adelaide. The southern two-thirds of the state have been deployed and the current $650,000 PACE Copper funded acquisition stage is focusing on the Far North East, across the Cooper Basin and Simpson Desert. This area is largely unexplored for minerals and there exist large uncertainties in our understanding of its tectonic evolution. The AusLAMP PACE Copper project will complete acquisition in August 2017 before moving to the final stage in the Anangu Pitjantjatjara Yankunytjatjara Lands, land access permitting.
Data acquisition is undertaken in collaboration with the University of Adelaide and their dedicated AusLAMP acquisition team of Philippa Mawby, Bruce Goleby and Geoff Axford, who have established lasting relationships with native title holders, pastoralists and national park agencies to roll out the environmentally low impact AusLAMP program across the state. Processing and modelling is done within the GSSA and at the University of Adelaide. Highlights of the 3D resistivity models have been:
- The unveiling of a remarkable connection between deep-crustal low resistivity zones beneath the prospective eastern Gawler Craton Olympic Domain and the abundance of mineral occurrences in this iron oxide – copper–gold (IOCG) belt.
- The 3D MT model across the Ikara-Flinders Ranges and the Curnamona Province which has established compelling conductivity anomalies along the Nackara Arc and Curnamona Province (Robertson, Heinson and Thiel 2016, 2017), strongly renewing interest in the Broken Hill Domain.
- Delineation of the western margin of the Gawler Craton and, in joint analysis with closer-spaced profile MT data, identification of large-scale lithospheric boundaries.
This new groundbreaking statewide dataset will add another geoscientific layer of information for stakeholders. Together with other statewide geophysical data and widespread geochemical isotope data, this vital dataset will assist the GSSA’s new Lithospheric Architecture team to enhance our understanding of the tectonic history of the state and reduce risk in mineral exploration.
The revelation that conductive crustal anomalies act as possible fertility corridors across the state has led to new follow-up initiatives using closer spaced and higher frequency MT surveys. Examples are the PACE Copper funded Olympic Domain MT survey across the Stuart Shelf including numerous IOCG prospects; and the planned deployment of two broadband MT profiles across the Broken Hill Domain led by the University of Adelaide with collaboration and funding from the GSSA. The aim of both surveys is to focus in on the conductivity corridors and how they are resolved into the upper crust. This work also follows on from previous highly informative insights from the Olympic Dam MT profile (University of Adelaide), and high-density MT profile across the Beverley uranium mine (Thiel et al. 2016).
Robertson K, Heinson G and Thiel S 2016. Lithospheric reworking at the Proterozoic-Phanerozoic transition of Australia imaged using AusLAMP magnetotelluric data. Earth and Planetary Science Letters 452:27–35.
Robertson K, Heinson G and Thiel S 2017. Mapping lithospheric alteration using AusLAMP MT data in the Ikara-Flinders Ranges and Curnamona Province. MESA Journal 83:4–7. Department of the Premier and Cabinet, Adelaide.
Thiel S, Soeffky P, Krieger L, Regenauer-Lieb K, Peacock J and Heinson G 2016. Conductivity response to intraplate deformation: evidence for metamorphic devolatilization and crustal-scale fluid focusing. Geophysical Research Letters 43:11,236–11,244.
– Stephan Thiel and Kate Robertson