DOI: 10.4225/25/5497711797856
title: Southern Thomson Orogen VTEM Airborne Electromagnetic Survey - Inversion Products

description: The Southern Thomson Orogen VTEMplus� Airborne Electromagnetic Survey was conducted by Geoscience Australia as part of a collaborative project with its partners the Geological Survey of New South Wales and the Geological Survey of Queensland.  The Survey contributes to the Australian Academy of Science�s UNCOVER Initiative and Geoscience Australia�s response to this as part of the National Mineral Exploration Strategy.
Geoscience Australia contracted Geotech Airborne Ltd to acquire VTEMplus� airborne electromagnetic (AEM) data over part of the Southern Thomson Orogen in Queensland and New South Wales in April and May 2014.  The data were also processed by Geotech Airborne Ltd using its FullWaveForm� processing techniques.

The survey is designed to assess the under-cover geology and prospectivity of the Southern Thomson Orogen around Hungerford and Eulo and straddles the New South Wales-Queensland border.  The survey comprises two parts:
1.	A regular regional survey on 5000 m spaced east-west flight lines totalling 3352 line km and covering an area of 16 261 km2.
2.	Two regional traverses adjacent to roads totalling 915 line km.

The Southern Thomson Orogen is a priority area for mineral systems research.  Much of the area lies underneath cover of sedimentary basins and is a poorly-understood element of Australia�s geology. The Orogen contains Cambro-Ordovician rocks that have potential for Iron Oxide Copper-Gold (IOCG) resources, porphyry copper-gold and Volcanic-Hosted Massive Sulphide (VHMS) deposits.  Survey data will add to knowledge of cover thickness and character and will inform future geological mapping in the region.


Previously Released Data (Phase 1)

In August 2014 the processed data from the Southern Thomson Orogen VTEMplus� AEM Survey were released in the Phase 1 data release package that is available free of charge from Geoscience Australia�s web site (see http://www.ga.gov.au/metadata-gateway/metadata/record/gcat_81852). The Phase 1 package includes the final processed electromagnetic data, waveform files, multiplots, conductivity estimates from the EM Flow� conductivity depth imaging algorithm, and an operations and processing report, all produced by the contractor Geotech Airborne Ltd.


Current Release (Phase 2)

This Phase 2 data release package contains results from the electromagnetic inversion of the data in the Phase 1 release.  The inversion results were generated using two different types of algorithm, a deterministic regularized gradient based algorithm, which we call GALEISBS (Roach, 2010), and a reversible-jump Markov chain Monte Carlo algorithm, which we call GArjMcMC (Brodie and Sambridge, 2012; Brodie and Reid, 2013).  Both algorithms assume a layered earth or 1D conductivity structure. Each airborne electromagnetic sounding is inverted independently and the results are then stitched into combined sections.

The deterministic GALEISBS inversion products are available for download in four logical parts based on the type of derived product.  These are zipped into the following four files:
1.	galeisbs_point_located_data.zip
2.	galeisbs_sections.zip
3.	galeisbs_georeferenced_sections.zip
4.	galeisbs_gocad_sgrids.zip

The stochastic GArjMcMC inversion products are available for download in five logical parts based on the type of derived product.  These are zipped into the following five files;
1.	rjmcmc_point_located_data.zip
2.	rjmcmc_sections.zip
3.	rjmcmc_georeferenced_sections.zip
4.	rjmcmc_gocad_sgrids.zip
5.	rjmcmc_probability_map_plots.zip