<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.

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.

The Australian Lithospheric Architecture Magnetotelluric Project (AusLAMP): New South Wales (NSW) magnetotelluric survey is a collaborative project between the Geological Survey of New South Wales (GSNSW) and Geoscience Australia. Long period magnetotelluric data are being acquired at around 305 sites on a half degree grid spacing across the state of NSW. <u>Phase one</u> This record outlines the field acquisition, data QA/QC, and data processing methodologies relating to the 224 sites released in phase one. The data are released in EDI format containing impedance estimates and transfer functions for each processed site. <u>Phase two</u> A further 73 EDI format data are released as part of phase two. These data were collected and processed using the same methodology as described in the GA record released as part of phase one.

<p>The East Tennant Magnetotelluric (MT) Survey is funded under Geoscience Australia’s (GA) Exploring for the Future program. The survey is aimed to assist in regional stratigraphic drilling program to understand basement architecture and mineral potential in the east of Tennant Creek, Northern Territory, Australia. The survey covers an area of approximate 90 km x 100 km. Geoscience Australia contracted Zonge Engineering and Research Organisation (Australia) to undertake the survey from 22nd July to 19th Aug 2019. Broadband Magnetotelluric and Audio Magnetotelluric data were acquired at 131 stations with site spacing of ~2 km to ~15 km. <p>This data package includes MT data originally processed by the contractor and edited MT data by GA for modelling purpose. All the data were industry-standard EDI files. <p>Time series data are available on request from clientservices@ga.gov.au

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.

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.

The geology and mineral prospectivity of the southern Thomson Orogen is poorly understood because the vast majority of its extent is buried beneath younger regolith and/or sedimentary rocks. To address this issue a collaborative program to drill 16 stratigraphic boreholes was proposed to collect samples of the basement geology that can be comprehensively analysed to improve the understanding of the geological evolution of this region. To reduce the uncertainty associated with intersecting the target stratigraphy at each of the borehole sites, estimates of the cover thickness were obtained by applying the geophysical techniques of refraction seismic, audio-magnetotellurics (AMT) and targeted magnetic inversion modelling (TMIM) prior to drilling. Refraction seismic was acquired at all 16 proposed borehole sites using a system with 48 single-component geophones and a propelled weight drop primary-wave source. At 14 of the sites clear basement refractors were observed in the data. At the two other sites, Nantilla 1 and Barrygowan 1, loss of signal due to seismic attenuation at far offsets meant that a clear basement refractor was not observed. With the exception of these two sites, three distinct refractors are generally observed in the data. Those with velocities ranging from 0.4 km/s to 1.5 km/s are interpreted as regolith, those ranging from 1.8 km/s to 2.4 km/s are interpreted as Eromanga Basin sediments, and those ranging from 3.9 km/s to 5.7 km/s are interpreted as metamorphic/igneous basement. Two-dimensional velocity models of the subsurface geology were then generated using the time-term inversion method, which allowed for the thickness of each layer to be estimated. Cover thickness estimates using refraction data vary widely from site to site, with the shallowest estimate being Overshot 1 (49 m - 55 m) and the deepest Adventure Way 1 (295 m - 317 m). These variations in cover thickness estimates from site to site are indicative of basement topography variations and are not error margins. Audio-magnetotelluric data was collected at ten sites by simultaneously deploying four porous pot electrodes, to collect the two orthogonal components of telluric data (Ex and Ey), and three magnetic induction coils, to collect the three components of magnetic data (Hx, Hy and Hz). For each dataset, a one-dimensional inversion model was produced, from which resistivity contrasts were identified and used to describe electrical conductivity discontinuities in the subsurface geology. In general, the models show a near-surface conductive layer with resistivity values ≤10 Ω·m overlying layers with continuously increasing resistivities with depth (up to 102-103 Ω·m). Those layers which were >10 Ω·m were interpreted as metamorphic/igneous basement rocks and were observed to occur at depths of ~100 m to ~300 m across the survey sites, except at Overshot 1 (38 m ±10%) and Barrygowan 1 (480 m ±10%). Targeted magnetic inversion modelling (TMIM) was applied to freely available, good quality, regional airborne magnetic survey data. Depth to magnetic source estimates were generated for 53 targets, with confidence ratings, using a dipping tabular source body to model targeted magnetic anomalies in the vicinity of the borehole sites. A combined depth estimate was generated using a distance and confidence weighted average from multiple depth estimates at all but two borehole sites. Only a single depth estimate was available at Adventure Way 1 while no depth estimates were generated at Eulo 1. These combined depth estimates provide cover thickness estimates at the sites as they are likely sourced from, or near, the top of basement. Of the ten proposed borehole sites with coincident AMT and refraction seismic data, five sites have overlapping cover thickness estimates. Cover thickness estimates from the TMIM overlap both the AMT and refraction data at four sites and at two sites where only the refraction depth estimates were available. 2 Estimating Cover Thickness in the Southern Thomson Orogen The cover thickness estimates presented in this report lower the risks associated with the proposed southern Thomson Orogen stratigraphic drilling program by reducing the uncertainty in intersecting the target stratigraphy at each of the borehole sites as well as allowing for better project and program planning. Successful completion of the stratigraphic drilling program in the southern Thomson Orogen will allow for each of these geophysical methods for estimating cover thickness to be benchmarked using actual cover thicknesses measured in the boreholes.

Broadband and audio magnetotelluric (BBMT and AMT) data at 476 sites on a 2 Km grid were acquired in the Cloncurry region between July and November 2016. The survey covered an area of appriximatly 40 km x 60 km on the eastern margin of the Mount Isa Province. The Cloncurry magnetotelluric (MT) project was funded by the Geological Survey of Queensland and is a collaborative project between the Geological Survey of Queensland and Geoscience Australia. Geoscience Australia managed the project and peformed data QA/QC, data analysis, and produced two-dimensional (2D) and three dimensional (3D) inverse models for both the BBMT and AMT data. This report details the field acquisition program and the methodologies used for processing, analysing, modelling and inverting the data.

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.

Long-period magnetotelluric (MT) data allow geoscientists to investigate the link between mineralisation and lithospheric-scale features and processes. In particular, the highly conductive structures imaged by MT data appear to map the pathways of large-scale palaeo-fluid migration, the identification of which is an important element of several mineral system models. Given the importance of these data, governments and academia have united under the Australian Lithospheric Architecture Magnetotelluric Project (AusLAMP) to collect long-period MT data across the continent on a ~55 km-spaced grid. Here, we use AusLAMP data to demonstrate the MT method as a regional-scale tool to identify and select prospective areas for mineral exploration undercover. We focus on the region between Tennant Creek in the Northern Territory and east of Mount Isa in Queensland. Our results image major conductive structures up to 150 km deep in the lithosphere, such as the Carpentaria Conductivity Anomaly east of Mount Isa. This anomaly is a significant lithospheric-scale conductivity structure that shows spatial correlations with a major suture zone and known iron oxide–copper–gold deposits. Our results also identify similar features in several under-explored areas that are now considered to be prospective for mineral discovery. These observations provide a powerful means of selecting frontier regions for mineral exploration undercover.. <b>Citation:</b> Duan, J., Kyi, D., Jiang, W. and Costelloe, M., 2020. AusLAMP: imaging the Australian lithosphere for resource potential, an example from northern Australia. In: Czarnota, K., Roach, I., Abbott, S., Haynes, M., Kositcin, N., Ray, A. and Slatter, E. (eds.) Exploring for the Future: Extended Abstracts, Geoscience Australia, Canberra, 1–4.