AusAEM

An aircraft fitted with Airborne Electromagnetic System to carry out geophysical surveys. Image courtesy of CGG.

This activity aims to undertake a series of airborne electromagnetic (AEM) surveys of a large region of northern Australia, using a broad line spacing of 20 km. It represents the largest AEM survey of its kind ever undertaken. The AEM technique enables mapping of the subsurface electrical conductivity of rocks, sediments and waters, to depths of up to several hundred metres, depending on factors such as the AEM system used and the electrical conductivity of the sub-surface.

The AusAEM data and derived products will be used to map the thickness and character of sedimentary and regolith cover in regions flanking crystalline basement outcrop. Previous surveys by Geoscience Australia using wide line spacing (e.g. 6 km) have shown the utility of the method in mapping cover thickness and its character. The survey results will also be used by the groundwater community to assess the potential for groundwater resources in Australia's arid zones to support remote communities in the survey areas.

The AusAEM surveys have been divided into blocks approximately based on 1:1 million map sheets, for flying during the northern dry season to maximise survey production rates. The multi-year survey program will be delivered in yearly instalments to ensure that regular scheduled data releases occur throughout the life of the program.

The data will be archived and released only when the data have passed all quality assurance and quality control checks and are thus deemed by Geoscience Australia's geophysicists as fit-for-purpose and use by the geophysical community. This process generally takes several months.

Survey 1: AusAEM Year 1 NT/QLD

Map showing airborne electromagnetic survey (AusAEM) completed and planned flight lines over an area on the border of the Northern Territory and Queensland.

The first survey in the program covers the Newcastle Waters and Alice Springs 1:1 Million Standard map Sheets in the NT and the Normanton and Cloncurry Standard Million Map Sheets in Qld. This survey was conducted by Geoscience Australia in collaboration with the geological surveys of Qld and the NT as part of the Exploring for the Future (EFTF) program.

The newly acquired AEM data will be integrated with other datasets collected as part of the EFTF program (surface geochemistry, groundwater hydrochemistry, seismic, magnetotelluric, potential field, solid geology, isotopic mapping) to assist with stratigraphic drilling to characterise the under-cover geology. The ultimate aim of the programme is to enable government, the exploration industry and the research community to better understand the mineral potential of northern Australia.

Specifications

The table below summarises the specification of the AusAEM Year 1 NT/QLD Airborne Electromagnetic Survey.

Survey Name AusAEM Year 1 NT/QLD TEMPEST® Airborne Electromagnetic Survey
State(s) NT and QLD
Contractor CGG Aviation (Australia) Pty Ltd, Perth WA
Aircraft Cessna 208B (VH-FAY)
AEM System TEMPEST (25 Hz base frequency)
Line Spacing 20 km plus infill areas at tighter spacing
Line Direction N-S (NT) and E-W (QLD)
Total Survey Line Kilometres Approximately 60,000 line km
Survey Area 1,117,000 km2
Nominal Terrain Clearance of the aircraft 120 m above ground level
Acquisition Start Date 6 August 2017
Acquisition Progress to 6 June 2018 79% complete (of the entire survey)
Estimated Completion of Acquisition Date August 2018

Collaborations

Geoscience Australia is partnering with State and Territory government geoscience agencies to deliver the AusAEM program. Industry have subscribed to areas of infill in the first survey area as this approach was successfully used in a previous exploration initiative of the Commonwealth Government — the Onshore Energy Security Program (OESP). Industry benefits include low acquisition and zero mobilisation costs.

The infill line data are confidential for a period of twelve (12) months from the date the final survey data is provided to the subscriber. Upon expiry of this moratorium period the infill data will be released as soon as possible by Geoscience Australia to the public domain for use in the minerals, energy and groundwater sectors.

Progress

Map showing airborne electromagnetic survey (AusAEM) completed flight lines over an area in the Northern Territory.

2017 field season
Over 19,000 line kilometres were acquired in the 2017 field season. The AusAEM survey also includes over 2,200 line kilometres of infill flying at tighter line spacing, which was funded by private exploration companies, in certain infill blocks within the survey area.

2018 field season
To complete the first survey in this program an additional 40,000 line kilometres are being acquired in the current 2018 field season. As of 6 June 2018, progress has seen 79% of the data acquisition completed for the entire survey. Data acquisition is estimated to be completed in August 2018.

Outputs

Tranche 1, Phase 1 data release (13 June 2018)
Public release of the data acquired in the 2017 field season is now available from Geoscience Australia's website free of charge: AusAEM Year 1 NT/QLD data. The package contains the final survey deliverables produced by the contractor CGG, including point located final EM line data and conductivity estimates generated by the EM Flow conductivity depth imaging algorithm, as well as grids and graphical multiplots and section.

Summary of the Tranche 1, Phase 1 data release package:

  • The Tranche 1 survey logistics and processing report
  • Final processed electromagnetic, magnetic and elevation point located line data
  • Final processed electromagnetic, magnetic and elevation grids
  • Conductivity estimates generated by the EM Flow® conductivity depth imaging algorithm
  • Graphical multiplots of line data and EM Flow® conductivity sections
  • Graphical stacked EM Flow® conductivity sections

Future data releases
Future data release packages are expected to contain data flown after October 7 2017 (Tranche 2, etc.) and further inversion and interpretation products generated by Geoscience Australia.