Magnetotelluric data were acquired for Geoscience Australia by contract along the north-south 08GA-C1-Curnamona seismic traverse to the east of Lake Frome from November 2008 to January 2009 as part of the Australian Government's energy security initiative. 25 sites were spaced an average of 10 km apart, and five-component broadband data were recorded with a frequency bandwidth of 0.001 Hz to 250 Hz and dipole lengths of 100 m. Apparent resistivity and phase plots are presented, along with dimensional analyses of the data based on rotational invariants, the representation of the data by the phase tensor, and Parkinson arrows. These analyses provide insight into the complexity of the Earth conductivity giving rise to the MT responses and are a useful precursor to modelling.

Magnetotelluric (MT) data have been acquired in 2008 and 2009 at 40 broadband (0:01 s to 500 s) and 12 long-period (10 s to 10 000 s) sites along the east-west deep seismic reflection transect of northern Eyre Peninsula, South Australia. The MT survey is a joint project between the University of Adelaide and Geoscience Australia and is funded by the Australian Government as part of the Onshore Energy Security Program. Long-period sites are spaced 20 km apart and broadband sites infill this spacing to 10 km with also some 5 km spacing. This ensures sufficient coverage to map the upper crustal to upper mantle structures beneath northern Eyre Peninsula.

As part of the Australian Government's Onshore Energy Security Program and the Queensland Government's Smart Mining and Smart Exploration initiatives, deep seismic reflection surveys (~2300 line km) were conducted in North Queensland to establish the architecture and geodynamic framework of this area in 2006 (Mt Isa Survey; also involving OZ Minerals and pmd*CRC) and 2007 (Cloncurry-Georgetown-Charters Towers Survey; also involving AuScope). The purpose here is to use new geodynamic insights inferred from the seismic and other data to provide comments on the large-scale geodynamic controls on energy and other mineral potential in North Queensland.

This article presents the results of studies in North Queensland associated with the 2007 Mt Isa-Georgetown-Charters Towers seismic survey. Results include seismic interpretation, geophysical studies and 3D maps, tectonic and metallogenic syntheses and energy potential assessment.

In 2007, three seismic lines were collected by Geoscience Australia and the Geological Survey of Queensland from Cloncurry to south of Charters Towers via Croydon and Georgetown, and a fourth line by AuScope to the northeast of Mt Surprise. Signals were recorded to ~20 seconds two-way travel time (TWT), which equates to about 60 kilometres in depth. The recent lines are among the latest in a series of deep seismic profiles conducted across Queensland since 1980.

The Natural Fields EM Forum was held in Brisbane, Queensland, Australia, on February 26, 2012, in conjunction with the ASEG 22nd International Geophysical Conference & Exhibition 2012. The forum was organised to review the current state of development of natural field EM methods (NFEM), being those methods that utilise the ambient electromagnetic field rather than deploying an additional active source as an element of a survey. NFEM methods are used to acquire data from which various parameters can be obtained to help interpret the electrical characteristics of the subsurface.

Magnetotelluric (MT) techniques measure natural time variations of the Earth's magnetic and electric fields to infer subsurface electrical conductivity structure. Data are collected over a range of frequencies, providing insights into how this structure varies with depth. Depending on the Earth conductivity and frequencies used, information can be obtained from the near surface to depths of hundreds of kilometres. MT surveying has been used in a wide variety of geological scenarios, from investigations of continental-scale structures to mineral and geothermal exploration, and even in the search for ground-water, and many such surveys have now been undertaken in South Australia. Recently, surveys have been conducted by Geoscience Australia (GA) under the Australian Government's Onshore Energy Security Program (OESP) along deep crustal seismic reflection transects, in part in collaboration with the University of Adelaide (UA), the Geological Survey of South Australia, Primary Industry and Resources South Australia (GSSA, PIRSA) and the Australian National Seismic Imaging Resource (ANSIR) across the Gawler Craton and Curnamona Province. Given the wide range of applications for MT data, it is proposed to deliver these data online as industry-standard electrical data interchange (EDI) files, starting with the most modern datasets. This paper presents an overview of the MT data and reports presently available for South Australia. All MT data are available for download online from the South Australian Resources Information Geoserver (SARIG), and both seismic and MT data acquired by GA and collaborators under the OESP are available for download from the GA web site.

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.

2009 Georgina-Arunta Seismic and MT Surveys - Acquisition and Processing

Geoscience Australia has been acquiring deep crustal reflection seismic transects throughout Australia since the 1960s. The results of these surveys have motivated major interpretations of important geological regions, contributed to the development of continental-scale geodynamic models and improved understanding about large-scale controls on mineral systems. Under the Onshore Energy Security Program, Geoscience Australia has acquired, processed and interpreted over 5000 km of new seismic reflection data. These transects are targeted over geological terrains in all mainland states which have potential for hydrocarbons, uranium and geothermal energy systems. The first project was undertaken in the Mt Isa and Georgetown regions of North Queensland. Interpretations of these results have identified several features of interest to mineral and energy explorers: a previously unknown basin with possible hydrocarbon and geothermal potential; a favourable setting for iron oxide uranium-copper-gold deposits; and, a favourable structural setting for orogenic gold deposits under basin cover. Other geophysical data were used to map these features in 3D, particularly into areas under cover. Seismic imaging of the full thickness of the crust provides essential, fundamental data to economic geologists about why major deposits occur where they do and reduces risk for companies considering expensive exploration programs under cover.