The Nepean Test site is located around the Nepean Nickel Mine (Figure 1a). It is conveniently located 24km by road from Coolgardie and 52km from the airport at Kalgoorlie (Figure 1b). 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 Focus Minerals Ltd (www.focusminerals.com.au), 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.

Figure 1a. Nepean Location
Figure 1a. Nepean Location
Figure 1b. Aerial Map of Nepean Location
Figure 1b. Aerial Map of Nepean Location

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 & Comparative Plots

Figure 2. Nepean Airborne Magnetic Survey
Figure 2. Nepean Airborne Magnetic Survey
Figure 3. Nepean Ground EM
Figure 3. Nepean Ground EM
Table 1. Geophysical Datasets
Table 1. Geophysical Datasets
Figure 4. Nepean Airborne EM
Figure 4. Nepean Airborne EM
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