From 1 - 10 / 26
  • 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.

  • 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.

  • 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 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.

  • 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.

  • 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.

  • <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

  • 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.

  • 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.

  • 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.