The MTPy Python library is open source software that aims to facilitate processing, analysis, modelling, and inversion of magnetotelluric (MT) data. Until recently, MTpy has contained bugs and gaps in both functionality and documentation, which have limited its use to date. We are developing MTPy to rectify these problems and expand functionality. Key improvements include adding new functions and classes to the modules that handle ModEM inputs and outputs, improving data and model visualization tools, refactoring the code to improve maintainability, quality, and consistency, and developing documentation.

As global metal demands are increasing whilst new discoveries are declining, the magnetotelluric (MT) technique has shown promise as an effective technique to aid mineral systems mapping. Several case studies have shown a spatial correlation between mineral deposits and conductors, with some showing that resistivity models derived from MT are capable of mapping mineral systems from the lithosphere to deposit scale. However, until now, the statistical significance of such correlations has not been demonstrated and therefore hindered robust utilization of MT data in mineral potential assessments. Here we quantitatively analyze resistivity models from Australia, the United States of America (USA), South America and China and demonstrate that there is a statistically-significant correlation between upper mantle conductors and porphyry copper deposits, and between mid-crustal conductors and orogenic gold deposits. Volcanic hosted massive sulfide deposits show significant correlation with upper mantle conductors in Australia. Differences in the correlation pattern between these deposit types likely relate to differences in the chemistry, redox state and location of source mineralizing fluids and magmas, and indicate signatures of mineral system processes can be preserved in the crust and mantle lithosphere for hundreds of millions of years. Appeared in Scientific Reports volume 12, Article number: 8190 (2022), 17 May 2022

The Coompana Project is a collaborative project between Geoscience Australia (GA) and the Geological Survey of South Australia (GSSA), which aims to provide new precompetitive geological, geophysical and geochemical data in the under-explored Coompana Province in South Australia. The pre-drilling geophysics program was undertaken to assist the drilling process by reducing the uncertainty associated with intersecting the targeted stratigraphy. Firstly, the magnetotellurics (MT) technique was tested at six sites where previous drill holes were located to benchmark the application of MT method with respect to estimating cover thickness in the region. Comparison with drill-hole details indicates that the method is capable of identifying major stratigraphic structures and providing cover thickness estimates with a reasonable accuracy (within 10%). Subsequently, MT data were acquired at eight proposed drilling sites in February 2017. 1D and 2D data modelling were undertaken using different algorithms to improve confidence level. Finally, estimates of the cover thickness with specified uncertainty at proposed drilling sites are produced. This report presents MT data acquisition and processing, data inversion and preliminary interpretation of model results. Limitations and uncertainty associated with the MT technique is discussed.

Several narrow, linear, highly electrically conductive zones in the crust have been detected across Australia by geomagnetic deep sounding and magnetotelluric measurements made during the previous 50 years. Three major such conductivity anomalies collectively span Australia from north to south; the Carpentaria anomaly in Queensland and the Flinders and Eyre Peninsula anomalies in South Australia. They do not appear to be electrically connected at present; whether they are related in origin is a subject of further research. Recently, new magnetotelluric data have been acquired across or near to all three zones along deep seismic reflection transects which were designed to investigate crustal architecture and mineral and energy potential. Results from the seismic and MT surveys across the Carpentaria Anomaly suggest that the data are imaging a west-dipping suture forming the eastern margin of the Mount Isa province. The suture is interpreted to be the consequence of subduction and accretion prior to 1850 Ma. The Flinders Anomaly extends in an arcuate belt to the east of Lake Frome in the Curnamona Province to transect the Willyama Supergroup and the southern Flinders Ranges in a south-westerly direction, following structural trends. New magnetotelluric data acquired along two seismic transects has further refined the position and depth of the conductive zone.

As part of Geoscience Australia’s Exploring for the Future Program, Broadband and Audio Magnetotelluric (MT) data were acquired at 131 stations in the East Tennant region, Northern Territory, in 2019. This survey aimed to characterise major crustal structures, to map cover thickness to assist in stratigraphic drill targeting, and to help understand mineral potential in the region. The data package was released in December 2019 (http://dx.doi.org/10.26186/5df80d8615367) and the 3D resistivity model was released in March 2020 (https://pid.geoscience.gov.au/dataset/ga/135011). We applied a probabilistic approach to inverting high-frequency MT data for cover thickness estimation using the 1D Rj-McMCMT code, newly developed in Geoscience Australia. The inversion employs multiple Markov chains in parallel to generate an ensemble of millions of resistivity models that adequately fit the data given the assigned noise levels. The algorithm uses trans-dimensional Markov chain Monte Carlo techniques to solve for a probabilistic resistivity-depth model. Once the ensemble of models is generated, its statistics are analysed to assess the posterior probability distribution of the resistivity at any particular depth, as well as the number of layers and the depths of the interfaces. This stochastic approach gives a thorough exploration of the model space and a more robust estimation of uncertainty than deterministic methods allow. This release package includes the results of probabilistic inversion of Audio Magnetotelluric data at the 131 stations. They can be used to estimate cover thickness for drill site planning, and to map the base of geological basins in the region. Model data files are large, but can be made available on request to clientservices@ga.gov.au.

Magnetotelluric (MT) measures the natural variations of the Earth' magnetic and electrical (telluric) fields. The Audio-Magnetotelluric method (AMT) samples signal frequencies in the range of 20k Hz down to ~1Hz and provides data pertaining to the upper few kilometres of the Earth' crust. Broadband MT (BBMT) measures frequencies ranging from ~400 Hz down to periods of ~5000 s, providing measures of the conductivity of the crust. AMT and BBMT data were acquired at 138 stations with an interval of 2.5-5.0 km along a 690 km transect extending from Four Ways to Longreach in the South-eastern Mount Isa region. Full-waveform time series data were acquired and processed into frequency-domain transfer functions. Remote reference was applied to eliminate uncorrelated noise. After quality assurance, processed data were exported to industry-standard EDI files containing site info, impedance tensor, apparent resistivity, phase and vertical transfer function.

Magnetotelluric (MT) measures the natural variations of the Earth’ magnetic and electrical (telluric) fields. In 2018, MT data including broadband and audio-magnetotelluric data were collected across the Olympic Domain in South Australia. MT data at 327 sites with spacings from ~1.5km to ~10km were collected by contractor Zonge Engineering and Research Organisation Australia, on behalf of Geological Survey of South Australia and Geoscience Australia. The survey was funded by the Geological Survey of South Australia's PaceCopper Initiative. Six extra MT stations (MASLIN1-6) were collected and funded by Investigator Resources Ltd. They were provided by Geological Survey of South Australia. This data package contains 333 processed edi files across the Olympic Domain in South Australia.

This OGC compliant service provides access to magnetotelluric data and associated products, which have been produced by Geoscience Australia’s Magnetotelluric Program. This program includes regional magnetotelluric projects and the Australian Lithospheric Architecture Magnetotelluric Project (AusLAMP), a collaborative project between Geoscience Australia, the State and Northern Territory geological surveys, universities, and other research organisations. The data provided in this service comprise resistivity model depth sections and the locations of sites used in these studies.

Magnetotelluric survey data acquired in association with the L189 Gawler-Curnamona-Arrowie Deep Crustal Seismic Survey over the Curnamona Province. This survey was funded through the Onshore Energy Security Program. Data was acquired by Quantec Geoscience. Analysis and modelling was undertaken by Geoscience Australia . The aim of the survey was to produce a two-dimensional image of electrical conductivity structure of the crust and upper mantle over the Curnamona Province. This information is complementary to the reflection seismic and gravity data acquired along the 08GA-C1 traverse. Data are supplied as EDI files with support information.

The Australian Lithospheric Architecture Magnetotelluric Project (AusLAMP) aims to collect long period magnetotelluric data on a half degree (~55 km) grid across the Australian continent. New datasets have been collected in Northern Australia, as part of Geoscience Australia’s Exploring for the Future (EFTF) program with in-kind contributions from the Northern Territory Geological Survey and the Geological Survey of Queensland. This web service depicts the location of the 155 sites which were used in this study.