SPL1495 Sigatoka Exploration Area

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Summary of previous exploration results
Geology of the area
Seismic survey
Seismic survey area
Seismic survey results
Magnetometer survey
Magnetometer Survey Results
Initial engineering scoping study findings

The Magma exploration area is on the plains at the mouth of the Sigatoka River. Sediment eroded from magnetite-heavy mineral bearing volcanic and intrusive rocks was carried toward the sea by the river. As the river neared the outlet the action of wind, current and waves caused concentrations of heavier minerals to form. Their present distribution and the depositional environment that produced the magnetite-heavy mineral sands led Magma to “peg” the area to the west of the river as well as into the sea – this was based on previous exploration carried out in the 1970′s.


Figure 2 – SPL 1495 iron sand deposit location

Initial testing and estimates indicate that onshore alluvial material may amount to as much as 200,000,000 tonnes of mineralised sand. There is also a considerable quantity of sand offshore within the Magma exploration area. Detailed drilling is now proposed to confirm the magnetite-heavy mineral content of these sand deposits and to provide samples for metallurgical recovery test-work and other mine planning activities.

The Magma deposit is readily accessible and being an alluvial heavy mineral deposit, extraction is a commonly achieved by dredging. The magnetite and heavy minerals are collected as concentrates by gravity separation processes. Once a deposit is proven to be economic to mine, development and production can occur very quickly.

In advance of the planned drilling program, during 2011 Magma commissioned a seismic survey over all of the land-based exploration area to define the depth of the alluvial deposits and also the topography of the basement.

The highly encouraging results from this survey reveal an alluvial deposit that is about 10 metres deeper than first thought.

While the seismic survey was conducted, company geologists covered the area, undertaking a detailed survey of existing features such as water bores to gain an indication of the strata of the alluvial deposit.

The next exploration stage is to bring in the sonic drill machine and to engage appropriate specialists to conduct the drilling program. Results will be assessed leading to a pre-feasibility evaluation studies as soon as possible.

Summary of previous exploration results

The presence of elevated concentrations of magnetite was first observed and studied by NJ Guest in 1949 on behalf of the Geological Survey of Fiji (FGS). More detailed mapping and sampling was completed by JA Hirst for the Geological Survey in 1962 when he estimated that the large, exposed sand dunes represented approximately 60 Mt of sand containing up to 9.1% magnetic material (94% magnetite and 6% titanium dioxide).*

*Note this estimate is not compliant with the JORC code and further testing by Magma is required to confirm these numbers.

The first scout drill testing of the sands off shore to water depths of 30m took place in 1982 by the Fiji Government. Samples collected by drilling were processed by Central Mineralogical Services of Australia and they reported magnetite contents that varied from 4.5% to 17.3%.

Between 1967-70 Crawford Marine Specialists investigated the eastern parts of the area and immediately offshore and determined there was potentially between 1.8 and 2 Mt of magnetite in the deposits. Samples collected offshore contained up to 21% magnetite by volume. This work was followed by Manganex Ltd (1970), FGS –UNDP (1982) and Field Investments Ltd in 1991, all of whom confirmed that high concentrations of magnetite and other heavy minerals were present both onshore and offshore. The FGS-UNDP work also showed that up to 3% chromite and traces of zircon and gold were also present in samples of the sands.

It is notable that this historical work was done at a time when iron ore prices and particularly magnetite prices were much lower than they currently are. Magma is now undertaking the first systematic sampling program of the deposits using a reliable drilling method, which if successful will form the basis for resource-reserve estimates and mine feasibility studies. Presently, there are four potential saleable products that could be produced as a result of successful exploration by concentrating the magnetite:

  • Blast furnace grade concentrate
  • Blast furnace grade pellets
  • Direct reduced iron grade concentrate
  • Direct reduced iron pellets

Geology of the area

The satellite image in figure 5 shows the main geological features of the area. The alluvial sands cover a down-thrown fault block and are most probably underlain by a combination of marls and limestone debris. The Sigatoka river course initially followed a course along the western margin of this alluvial plain and has migrated eastward gradually building up large iron sand deposits with the assistance of the prevailing westerly trade winds and ocean currents.

Large volumes of sand containing visible magnetite (black colouring on figure 5) have accumulated at the western side of the river mouth and in the active river, as is evident on the satellite image below.Sand deposits containing magnetite have also developed off shore westward from the river mouth that have been confirmed by past exploration and these deposits will also be drilled by Magma as the project moves forward.


Figure 5 – Satellite image with outlines of the principal iron sand deposits. Although not outlined in this image sand deposits of potential economic importance are also present in the river itself and offshore from the river mouth toward the west.

Seismic survey

Magma commissioned Logantek Mongolia LLC to conduct a seismic survey of the Sigatoka area in September 2010. Seismic involves measurement of the speed of shock waves as they pass from surface through various materials. In this case the speed of travel of the shock wave through surficial deposits and unconsolidated sandy sediments is much slower than through underlying bedrock and by plotting these differences the thickness of each of these layers is determined and mapped. This information is then used to calculate the volume of the unconsolidated sediments.

Seismic survey area

  • The seismic survey lines are shown in figure 6 with the blue lines being east-west and orange lines north-south
  • The line layout is based on the local grid
  • The yellow-dashed outline is the mapped surface limit of alluvial sands – the potential deposit
  • North of this line are laminated marls, forming the hills and ridges with some raised coral reef near the coastal areas
  • The western lobe of the sand dune is part of the potential deposit

Figure 6 – Satellite image showing locations of the seismic survey lines

Seismic survey results


Figure 7 – Three dimensional representations of main seismic layers detected during the survey

  • Figure 7 is a three-dimensional model of seismic surfaces that shows the three units defined in the survey. There is about 10 times the vertical to horizontal exaggeration to highlight variations in the target iron sand deposits
  • The lower grey surface represents the shape of the interpreted basement rocks
  • In the western area the basement forms a north-trending ridge with the alluvial sand following the basement contours
  • The main alluvial plain in the centre and east has various depressions, but no obvious ancient river channels
  • The overlying alluvial layer shows subdued topography that has smoothed out the underlying basement topography.

Based on calculations of the volume of alluvial deposits identified by the seismic survey there is between 258 and 579 million cubic metres of sand present. Sonic drilling will now be used to establish the magnetite and heavy mineral content of this deposit.

Magnetometer survey

Commencing late October 2011, Magma Mines Limited engaged Alpha Geoscience Pty Ltd (Alpha) to undertake a detailed ground geophysical survey of the Sigatoka sand deposits as defined during the seismic survey.

The magnetometer survey was conducted using a G-858 Magnetometer and accurate station and line positions were established using a differential GPS (see figure 8).


Figure 8 – Photograph showing magnetometer survey method. Note the grey colour is typical of magnetite bearing sands

The survey lines were completed at 50m spacing where possible and total field measurements were recorded at intervals of approximately 1m along the lines.

The processed data was plotted on a colour coded contour map and the magnetic responses sub-divided into six Zones detonated A, B, C, D, E, F and G (see figure 9).

Magnetometer Survey Results


Figure 9 – Plot showing the colour coded smoothed first order residual magnetic data

  • Zone A represents data collected on and behind the dune/beach and shows highly variable wave length features and some strong negative (purple) components
  • Zone B represents data collected on an island on the eastern side of the survey area bordered on the east by the active Sigatoka river channel and shows some of the highest brood scale magnetic response in the surveyed area
  • Zone C represents data collected on the large alluvial plain where cultural noise has caused higher magnetic responses within an area of generally strong response
  • Zone D represents data collected on the large alluvial plain away from cultural noise that has a consistent high response
  • Zone E consists of data collected on the large dunes to the west and shows the weakest magnetic response of the area surveyed and may represent an older sand deposit when the magnetic field was reversed at the time of deposition
  • Zone F represents data collected south of Zone E that has magnetic response similar to Zone D

In conclusion, the detailed ground magnetometer survey confirmed that the area is underlain by sands that have a high magnetic character. These sand deposits continue beyond the surveyed area.

Initial engineering scoping study findings

Magma has commissioned initial conceptual engineering studies to compare possible sand extraction and mineral processing options and to calculate the normative industry capital and operating costs of these options. The study cannot be complete until detailed drilling and analytical results as well as an understanding of the three dimensional geography of the sand deposits and the magnetite/heavy mineral distribution within them along with metallurgical testwork to confirm concentrate recovery methodologies are known.

The initial studies do indicate that at low magnetite concentrations of 6% and applying typical sand mining equipment capital and operating costs, mineral recovery in line with known iron sand operations and production of a saleable magnetite concentrate at current market prices, that the Sigatoka deposits could have very robust economic potential.