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.

<p>The footprint of a mineral system is potentially detectable at a variety of scales, from the ore deposit to the Earth’s crust and lithosphere. In order to map these systems, Geoscience Australia has undertaken a series of integrated studies to identify key regions of mineral potential using new data from the Exploring for the Future program together with legacy datasets. <p>The recently acquired long-period magnetotellurics (MT) data under the national-scale AusLAMP project mapped a lithospheric scale electrical conductivity anomaly to the east of Tennant Creek. This deep anomaly may represent a potential source region for mineral systems in the crust. In order to refine the geometry of this anomaly, high-resolution broadband and audio MT data were acquired at 131 stations in the East Tennant region and were released in Dec 2019 (http://dx.doi.org/10.26186/5df80d8615367). We have used these high-resolution MT data to produce a new 3D conductivity model to investigate crustal architecture and to link to mineral potential. The model revealed two prominent conductors in the resistive host, whose combined responses link to the deeper lithospheric-scale conductivity anomaly mapped in the broader AusLAMP model. The resistivity contrasts coincide with the major faults that have been interpreted from seismic reflection and potential field data. Most importantly, the conductive structures extend from the lower crust to near-surface, strongly suggesting that the major faults are deep penetrating structures that potentially act as pathways for transporting metalliferous fluids to the upper crust where they can form mineral deposits. Given the geological setting, these results suggest that the mineral prospectivity for iron oxide copper-gold deposits is enhanced in the vicinity of the major faults in the region. <p>This release package includes the 3D conductivity model produced using ModEM code in sGrid format and Geo-referenced depth slices in .tif format.

Geoscience Australia in partnership with State and Territory Geological Surveys has applied the magnetotelluric (MT) technique to image Australia’s resistivity structure over the last decade. As part of the Mount Isa Geophysics Initiative program, MT data were collected at 138 sites along a 690 km transect in the South-Eastern Mount Isa. Geoscience Australia undertook data analysis and data inversion to create the most plausible resistivity model. 2D and 3D data modelling were undertaken using well-verified algorithms. The 2D and 3D resistivity models derived from the MT data show some consistent features that are likely to be the real subsurface geology. The near-surface conductive layer resolved by the MT models represents the Carpentaria and Eromanga sedimentary basins reasonably well, in terms of resistivity and thickness. The MT models reveal a predominant crustal-scale conductor, which is interpreted to be part of the Carpentaria Conductivity Anomaly. A number of localised zones of enhanced conductivity are also detected within the crust. These conductors correspond to known major faults identified by seismic and geological data. One of the faults, i.e. the Cork Fault, marks the tectonic boundary between the Mount Isa terrane and the Thomson Orogen. The geometries of these conductive bodies suggest that the enhanced conductivity may be caused by deformation or mineralisation associated with faulting. Some of these faults linking into the middle and lower crust are considered as the primary factors in the partitioning of mineralisation in the region. Results from the magnetotelluric data provide new insights into the understanding of the complex crustal structure where little geological history is known.

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.

The Australian Lithospheric Architecture Magnetotelluric Project (AusLAMP) aims to collect long period magnetotelluric data on a half degree grid across the Australian continent. Data were collected in northern Australia under Geoscience Australia’s Exploring for the Future (EFTF) program from 2016 to 2019. This survey covers the area in south parts of Northern Territory and north western region of Queensland. The project aims to improve understanding of the lithospheric structure in northern Australia. It also provide pre-competitive data and knowledge for selecting mineral prospective areas in the under-explored and covered regions. This data package contains the preferred resistivity model and associated information for the project. The report provides details for data acquisition, data process and data inversion. The results provide new insights on the lithospheric architecture and mineral potential in the region.

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.

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.

Magnetotelluric (MT) measures the natural variations of the Earth's magnetic and electrical (telluric) fields. The Audio-Magnetotelluric method (AMT) samples signals in the frequency range of 10k Hz down to ~1Hz and provides information to the upper few kilometres of the crust. AMT data were collected at ten sites in the southern Thomson Orogen using Phoenix Geophysics equipment (MTU-5A, MTC-150L and PE5 electrodes). Instrument deployment periods were 7/Oct -29/Oct 2015 and 03/Aug-10/Aug 2016. Time series data were processed into frequency domain using remote reference and Robust Processing scheme. After quality assurance, processed data were exported to industry-standard EDI files. Time series data are available on request.

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.

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.