Magnetotellurics (MT) is a passive geophysical method which uses natural time variations of the Earth's magnetic and electric fields to measure the electrical resistivity of the sub-surface. Electrical resistivity is a bulk property of a volume of Earth material and is associated with factors such as rock composition, porosity and permeability as well as temperature and pressure. The Magnetotelurics (MT) Data Collection includes datasets from The Australian Lithospheric Architecture Magnetotelluric Project (AusLAMP) and regional-scale MT surveys across the Australian continent. These data were collected by Geoscience Australia in collaboration with the State and Territory Geological Surveys and other partners. <b>Value: </b>Magnetotelluric data to expand the geoscientific understanding of the earth's lithospheric structure and provide new insights into Australia's onshore energy and mineral potential. <b>Scope: </b>AusLAMP is being conducted over multiple years to create a national MT dataset and map lithospheric structure of the Australian continent. MT data have also been acquired for mapping crustal structure and resource potential at regional scale. These data provide valuable information for multi-disciplinary interpretations. To view the magnetotellurics data via the Geoscience Australia internet page click on the following URL: <a href="https://www.ga.gov.au/about/projects/resources/regional-mt-program">https://www.ga.gov.au/about/projects/resources/regional-mt-program</a> For further information about the Australian Lithospheric Architecture Magnetotelluric Project (AusLAMP) click on the following URL: <a href="https://www.ga.gov.au/about/projects/resources/auslamp">https://www.ga.gov.au/about/projects/resources/auslamp</a>

Magnetotelluric survey data acquired in association with the L184 Isa-Georgetown Deep Crustal Seismic Survey and L185 Charters Towers Deep Crustal Seismic Survey. These surveys were funded through the Geoscience Australia's Onshore Energy Security Program and the Queensland Governments Smart Mining - Future Prosperity Program. Quantec Geoscience were contracted to acquire and process these data. The aim of the surveys was to produce a two-dimensional image of electrical conductivity structure of the crust and upper mantle over the Isa and Georgetown blocks. This information is complementary to the reflection seismic and gravity data acquired along lines 07GA-IG1, 07GA-IG2 and 07GA-GC1. Data are supplied as EDI files with support information and models.

Magnetotelluric survey data acquired in association with the L189 Gawler-Curnamona-Arrowie Deep Crustal Seismic Survey over the Gawler Craton. This survey was a collaborative project with the University of Adelaide and was funded through the Onshore Energy Security Program. The aim of the survey was to produce a two-dimensional image of electrical conductivity structure of the crust and upper mantle over the Gawler Craton. This information is complementary to the reflection seismic and gravity data acquired along the 08GA-G1 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 data have recently been collected in New South Wales under a National Collaborative Framework agreement between Geoscience Australia and the Geological Survey of New South Wales. This data release contains a preferred resistivity model and associated inversion files for southeast Australia using data from AusLAMP Victoria (Duan & Kyi, 2018), far west NSW (Robertson et al. 2016) and from the rest of New South Wales up to August 2019 (Kyi et al 2020). The original work behind this model can be cited through the following paper which contains discussion on model development and its significance for tectonic evolution and metallogenic potential: Kirkby, A., Musgrave, R.J., Czarnota, K., Doublier, M.P., Duan, J., Cayley, R.A., Kyi, D., 2020. Lithospheric architecture of a Phanerozoic orogen from magnetotellurics: AusLAMP in the Tasmanides, southeast Australia. Tectonophysics, v. 793, 228560.

Magnetotelluric survey data acquired in association with the L190 Gawler-Officer-Musgrave-Amadeus Deep Crustal Seismic Survey. This survey was co-funded through AuScope, Primary Industry and Resources South Australia and Geoscience Australia's Onshore Energy Security Program. Data was acquired, processed and modelled 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. This information is complementary to the reflection seismic and gravity data acquired along the 08GA-OM1 traverse. Data are supplied as EDI files with support information.

Magnetotelluric survey data acquired in association with the L192 Georgina-Arunta Deep Crustal Seismic Survey. This survey was funded through the Onshore Energy Security Program using the Auscope equipment from the ANSIR pool. The aim of the survey was to produce a two-dimensional image of electrical conductivity structure of the crust and upper mantle over the western Georgina Basin and the Arunta region of the Northern Territory. This information is complementary to the reflection seismic and gravity data acquired along the 09GA-GA1 traverse. Data are supplied as EDI files with support information.

The magnetotelluric (MT) data were acquired along a total of 690 km of the Youanmi deep seismic reflection traverses 10GA-YU1, 10GA-YU2 and 10GA-YU3-in Western Australia. This was a collaborative project between Geoscience Australia (GA) and the Geological Survey of Western Australia (GSWA), which provided the funding. The aim of the MT survey was to produce information of the electrical conductivity structure of the crust and upper mantle. This information is complementary to that obtained from deep seismic reflection, gravity, magnetic and geological data, which together provide new knowledge of the crustal architecture, rock properties and geodynamics of the region, important for helping to determine the potential for both mineral and energy resources. Data are supplied as EDI files with support information.

Geoscience Australia (GA) and the Geological Survey of Queensland (GSQ) conducted the Cloncurry Magnetotelluric (MT) survey. MT data (0.001 s to 1000 s in period) at 476 sites with a grid spacing of 2km were acquired over an approximate 40km x 60km area in the Cloncurry region from July to November 2016. The survey area covers the eastern margin of the Mount Isa Block situated to the west of the Eromanga Basin. The MT data can image the thickness of cover, the basement architecture and the crustal architecture in this area that has high resource exploration potential. Data QA/QC were performed during the data acquisition stage of the survey. This release includes processed MT data and a data acquisiton report written by the contractor. Details on the data processing, data analysis, and modelling/inversion of the data will be released as a comprehensive report at a later date.

Geoscience Australia (GA) and the Geological Surveys of Queensland (GSQ) and NSW (GSNSW) are undertaking a multi-year, multi-disciplinary collaborative project with the aim of characterising the largely unexplored southern Thomson Oregon region (Figure 1). As part of this, a number of precompetitive geophysical datasets have been acquired or are planned to be acquired within the southern Thomson region. These datasets will support an improved understanding of the: - thickness and nature of cover; - geology obscured by recent sedimentary cover or regolith; and, - mineral systems potential of the region. Magnetotellurics is a passive geophysical technique which records the earth's natural time-varying electrical and magnetic fields to provide a measure of the subsurface conductivity/resistivity (these two physical properties are related as resistivity is the inverse of conductivity). The frequencies of magnetic and electrical sources recorded provide different depth information - audiomagnetotellurics (AMT) which records higher frequency data and images shallower electrical structure, while broadband MT (BBMT) records lower frequencies that image relatively deeper electrical structure. Although the depth of investigation of the technique varies according to the local resistivity structure, in general AMT images the shallowest upper crust only (14 km depth) and BBMT images the crust (~60 km depth). For the southern Thomson region, BBMT was acquired along 2 long and one shorter transect to provide pictures of the entire crust of the region, while AMT was acquired along shorter and higher-resolution lines to provide knowledge of the cover of the region. Within this document we detail the acquisition, processing and analysis of the MT data, and present preliminary resistivity models. These data, their analyses and models are released as underpinning datasets to support future geophysical analyses and geological interpretation. Accordingly, this report focuses primarily on the core geophysical aspects from acquisition through to preliminary modelling.

The AusLAMP-Victoria magnetotelluric survey was a collaborative project between the Geological Survey of Victoria and Geoscience Australia. Long period magnetotelluric data were acquired at 100 sites on a half degree grid spacing across Victoria in the south-east of Australia between December 2013 and September 2014. Some repeated sites were acquired in December 2017. Geoscience Australia managed the project and performed data acquisition, data processing, and data QA/QC. In this record, the field acquisition, data QA/QC, and data processing methodologies are discussed. A separate report will provide information on data analysis, data modelling/inversion, and data interpretation.