EM Test Ranges

SGC freely maintains and will distribute public datasets for two EM test ranges in Western Australia.

The data may be used for the following applications:

  • Assist companies in the development of new and improved hardware and software.
  • Enable direct performance comparisons of systems.
  • Assist students & researchers with the supply of modern, state-of-the-art datasets.

Data will be supplied on request via Contact Us

SGC supplies dataset for two EM test ranges: Forrestania & Nepean. The targets are different and cover ground typical of the WA Goldfields. The sites have discrete small sulphide orebodies which are particularly useful for systems used in base metal exploration than must detect deep conductors in a conductive earth. They have been surveyed by a different mix of systems.

Forrestania EM Test Range

  • 85km east of Hyden
  • Key targets include a shallow (<100m) and deep (300-400m) sulphide conductors.
  • Known AEM surveys are: VTEM(2007)m, ZTEM(2010), HELITEM (2011), VTEM-max (2011)
  • Known Ground EM surveys are: FLTEM coil and HT squid, MLTEM coil and fluxgate, DHEM (coil),
  • Fixed Loop SAMSON Total Field

The Forrestania EM Test Range is situated approximately 85km by road/track east of Hyden and ~155km by road/track SSE of Southern Cross. The test range is well positioned and provides easy access if traveling from Perth or Kalgoorlie (~4-5hrs).

The Forrestania EM Test Range has been designed to allow testing/trialling of various electromagnetic methods (surface, airborne and downhole techniques) over two, discrete and varying bedrock conductors defined during previous geophysical exploration completed on behalf of Image Resources NL. The two bedrock conductors defined and drilled by Image Resources successfully tested these targets, intersecting barren, semi-massive to massive sulphides (po-rich).

The western conductor (IR2) is of limited areal size (<75x75m), shallow depth <100m, high conductance >7000S and dips northward ~30-40 degrees. This conductor is strongly defined by surface and downhole TEM and makes for an interesting airborne TEM target.

The eastern conductor (IR4) is extensive in strike/plunge extent (~500-600m+) and reasonably well constrained in depth extent (~100-150m). The conductive source is situated at considerable depth ~300-325m (western side) to ~400m+ (eastern side), is highly conductive ~5000-10000S and dips northward ~30-40 degrees. IR4 is a more challenging conductive target for surface TEM methods with smaller transmitter loops.

The local electrical environment is characterised by the presence of a conductive overburden (~10-20S), highly resistive bedrock units and lack of any other bedrock conductors in the immediate area other than the IR2 and IR4.

Work Completed at the EM Test Range

  • FLTEM dB/dt and B-Field HT-SQUID coverage over the IR4 bedrock conductor with large and small transmitter loops. FLTEM dB/dt coverage over the IR2 bedrock conductor with large and small transmitter loops. Figure 1 highlights some of these results. Completed as a standard survey by Outer Rim Exploration Services.
  • MLTEM dB/dt and B-Field fluxgate coverage over the IR4 bedrock conductor (200m transmitter loops, Figure 2 – Courtesy of GEM Geophysical Surveys.
  • DHTEM dB/dt – Crone PEM surveys, holes FRC1 and FRCD3 Figure 3. Completed as a standard survey by Outer Rim Exploration Services.
  • Fixed Loop Total Field (SAMSON) surveying – Figure 4 – courtesy of Khumsup Ltd
  • Helicopter EM surveys – HELITEM (Fugro Airborne Surveys, 2011), VTEM-max (Geotech Airborne Ltd, 2011). An example of the HELITEM and VTEM-max is shown in Figures 5 & Figures 6 respectively. Both datasets are available through the contractors only.
  • ZTEM survey by Geotech Airborne Ltd
  • 200m modern aeromagnetic/radiometric data coverage.

Proposed Work to be Completed at the EM Test Range

  • MLTEM using SQUID
  • DHTEM B-Field surveying of holes FRC1 and FRCD3 (FRCD3 is now blocked).

Nepean EM Test Range

  • 25km south of Coolgardie (60km from Kalgoorlie)
  • Key targets include several shallow (90m) subvertical sulphide conductors
  • Know AEM surveys are: Hoistem(2004),VTEM(2007),Heligeotem(2008), Aerotem (Jan 2009,
    September 2010), XTEM (2009), VTEM (2011)
  • Known Ground EM surveys are: MLTEM (coil & Fluxgate), DHTEM (coil)

The Nepean Test site is located around the Nepean Nickel Mine. It is conveniently located 24km by road from Coolgardie and 52km from the airport at Kalgoorlie. Nepean produced 32,303 tonnes of mined nickel at an average recovered grade of 2.99% Ni over a 17 year period to 1987. The tenements are held by Auroch Minerals and remains an active exploration area.

The current inferred resource based on the mine’s remnant, transitional and fresh mineralisation measures 591,300t @ 2.2% Ni. The nickel mineralisation extended to 500m depth and exploration efforts includes targeting deep sites of satellite mineralisation.

The site is centered on a series of steeply (80 degree) westerly dipping ultramafic flows Variable amphibolites with intercalated metasedimentary rocks separate the ultramafic units (Sheppy & Rowe, 1975). The whole sequence in intruded by sub-horizotal pegmatite units. The regional rocks comprise of granites and metamorphosed felsic and mafic volcaic units.

The EM response from the basement units and regolith in the area is variable and features:

  • Moderately conductive regolith with areas of higher conductivity over ultramafic units
  • Weakly to highly conductive confined basement conductors of shales, and massive sulphides (pyrrhotite, pentlandite,pyrite) at varying depths from 60m

Geophysical Data Sets​

An airborne magnetic and radiometric survey was flown in 1996 (Figure 2). The available geophysical datasets are listed in Table 1.

Ground EM datasets acquired over the Nepean Mine are publicly available. The main survey in the test area was a slingram TDEM survey that provides the most comprehensive information of the conductors in the mine area (Figure 3). A fluxgate magnetometer and coil receiver was used. A single line of inloop data acquired at the same time is also available. DHTEM survey may also be available on request.

In 2004 a Hoistem test survey was flown over the mine with 100m line spacing (Figure 4). The area was reflow in 2007 with the VTEM system at 150m spacing and three exact Hoistem lines were also over flown with the VTEM system to ensure precise spatial repeatability. These data sets started the test range and since then the area has been re-flown by Geotech, GPX, Aeroquest, and Fugro HEM systems.

Nepean Papers and Comparative Plots