Impala

 

 

Impala
 

Mineral Resources and Mineral Reserves

The Impala mining operation is located just to the north of Rustenburg on the western limb of the Bushveld Complex. Impala together with the joint venture with the RBR holds contiguous mining and prospecting rights over a total area of 33 534ha across 20 farms or portions of farms.

Both the Merensky and UG2 Reefs are exploited. The Merensky Reef is generally composed of an upper feldspathic pyroxenite, overlying a thin basal chromitite stringer, followed by an anorthosite to norite footwall. Locally this is termed a “pyroxenite reef”. Occasionally a pegmatoidal pyroxenite and a second chromitite stringer may be developed between the feldspathic pyroxenite and the footwall units. This is termed a “pegmatoid reef”. As an aid to mining operations the Merensky Reef is further defined as being “A”, “B” or “C” Reef if it rests on specific footwall units, ie locally called Footwall 1, 2 and 3 respectively.

The UG2 Reef is defined as a main chromitite layer, with most of the mineralisation confined to this unit, followed by a poorly mineralised pegmatoidal pyroxenite footwall. The hangingwall to the main chromitite layer is a feldspathic pyroxenite containing up to three thin weakly mineralised chromitite layers.

Both mineralised horizons dip gently away from the sub-outcrop in a north-easterly direction at 10° to 12°. The vertical separation between the Merensky and UG2 Reefs varies from about 125m in the south to 45m in the north of the mining area. The reefs may be disrupted by minor and major faults, lamprophyre and dolerite dykes, late stage ultramafic replacement pegmatoid bodies and potholes. The latter features are generally circular in shape and represent “erosion” or “slumping” into the footwall units. They vary in size from a few metres to tens of metres across and up to tens of metres in depth. All the above mentioned features contribute to dilution of the mineralised channel and are accounted for in the Mineral Resource and Mineral Reserve statements as geological losses.

The Merensky and UG2 Reefs are mined concurrently; the mining method is predominantly conventional breast mining. Mechanised bord and pillar (trackless) mining occurs in selected Merensky Reef areas on two of the shafts (No 12 and No 14 Shafts).

Limited opencast mining takes place at the outcrop positions to a maximum depth of 50m.

Stoping at the operations is carried out through conventional double-sided breast mining in accordance with Impala’s best practice principles. The haulages are developed in opposite directions from a central shaft position, following the two reef horizons on strike in the footwall and are defined as half levels. Footwall drives are developed at approximately 18m to 20m below the reef horizon with on reef raise/winze connections being between 180m and 250m apart.

 

 

Panel face lengths vary from 15m to 30m for both Merensky and UG2 Reefs, with panels being typically separated by 6 x 3m grid pillars with 2m ventilation holings. Stoping widths are approximately 1.2m and 1.0m for conventional Merensky and UG2 Reefs respectively, depending on the width of the economical reef horizon. The average stoping width of mechanised panels is about 1.9m.

Mine design and scheduling of operational shafts is done utilising CadsMine™ software, while the mine design and scheduling for projects are done using Mine 2-4D™ software. Geological models/ore blocks are updated and validated using G-Blocks and boundaries in the MRM information system. Grade block models are developed utilising Isatis™.

The mine design for the first five years is scheduled in much detail – monthly per crew. This is extended on an annual basis for the remaining period of the LoM. Key modifying factors such as overbreak, underbreak, off-reef mining, development dimensions, sweepings and mine call factors are applied to the mining area (centare profile) to generate tonnage and grade profiles.

The 30-year LoM profile for Impala is depicted in the graph that follows. LoM I comprises the profile of 14 operating vertical shafts, five associated with declines and three approved shafts (16, 17 and 20) under construction. The No 20 Shaft UG2 and the Extension of No 20 Shaft Merensky to 26 and 27 Levels constitute LoM II. LoM III is made up of potential future shaft blocks currently in different stages of project studies. This profile is based on current assumptions and may change in future.


 

Impala Mineral Resources and Mineral Reserves (100%)
as at 30 June 2012

 Mineral Resources        as at 30 June 2012        as at 30 June 2011  
 Orebody   Category   Tonnes  
Mt  
Width  
cm  
4E  
grade  
g/t  
6E  
grade  
g/t  
4E  
Moz  
6E  
Moz  
Pt  
Moz  
Tonnes  
Mt  
4E  
grade  
g/t  
6E  
grade  
g/t  
4E  
Moz  
Pt  
Moz  
 Merensky   Measured   153.7   125   5.90   6.59   29.2   32.5   18.5   131.0   6.32   7.05   26.6   16.8  
  Indicated   87.0   107   6.15   6.86   17.2   19.2   10.9   90.4   5.48   6.12   15.9   10.1  
  Inferred   65.2   130   5.46   6.09   11.4   12.8   7.2   75.8   5.37   5.99   13.1   8.3  
 UG2   Measured   135.9   64   7.32   8.80   32.0   38.4   18.6   132.4   7.37   8.86   31.4   18.1  
  Indicated   68.3   63   7.22   8.67   15.9   19.0   9.2   59.9   7.15   8.60   13.8   8.0  
  Inferred   33.3   63   7.40   8.89   7.9   9.5   4.6   43.4   7.00   8.41   9.8   5.6  
  Total   543.4     6.50   7.53   113.6   131.5   68.9   532.9   6.45   7.48   110.5   66.9  
                           
 Mineral Reserves        as at 30 June 2012        as at 30 June 2011  
 Orebody   Category   Tonnes  
Mt  
Width  
cm  
4E  
grade  
g/t  
6E  
grade  
g/t  
4E  
Moz  
6E  
Moz  
Pt  
Moz  
Tonnes  
Mt  
4E  
grade  
g/t  
6E  
grade  
g/t  
4E  
Moz  
Pt  
Moz  
 Merensky   Proved   10.9   129   4.10   4.57   1.4   1.6   0.9   11.5   4.03   4.50   1.5   0.9  
  Probable   113.2   131   4.25   4.74   15.5   17.2   9.8   119.1   4.14   4.62   15.9   10.0  
 UG2   Proved   15.9   98   4.07   4.89   2.1   2.5   1.2   14.3   3.97   4.77   1.8   1.1  
  Probable   123.2   99   3.87   4.65   15.3   18.4   8.9   130.9   3.92   4.72   16.5   9.6  
  Total   263.3     4.05   4.70   34.3   39.8   20.8   275.8   4.02   4.67   35.7   21.6  
                           
 Mineral Resources        as at 30 June 2012        as at 30 June 2011  
 Orebody   Category   Tonnes  
Mt  
  Pt  
grade  
g/t  
      Pt  
Moz  
Tonnes  
Mt  
  Pt  
grade  
g/t  
  Pt  
Moz  
 1 & 2
 Tailings  
 Complex  
Indicated   48.1     0.42         0.6   48.1     0.42     0.6  

Impala/RBR joint venture

 Mineral Resources        as at 30 June 2012        as at 30 June 2011  
 Orebody   Category   Tonnes  
Mt  
Width  
cm  
4E  
grade  
g/t  
6E  
grade  
g/t  
4E  
Moz  
6E  
Moz  
Pt  
Moz  
Tonnes  
Mt  
4E  
grade  
g/t  
6E  
grade  
g/t  
4E  
Moz  
Pt  
Moz  
 Merensky   Measured   5.3   152   6.52   7.28   1.1   1.2   0.7   2.7   7.40   8.26   0.6   0.4  
  Indicated   7.0   150   6.84   7.64   1.5   1.7   1.0   5.8   7.22   8.06   1.3   0.9  
  Inferred   23.4   122   6.51   7.27   4.9   5.5   3.1   23.0   6.02   6.72   4.5   2.8  
 UG2   Measured   2.3   53   7.49   9.00   0.6   0.7   0.3   2.0   7.59   9.13   0.5   0.3  
  Indicated   1.8   54   7.86   9.44   0.5   0.5   0.3   2.0   7.66   9.21   0.5   0.3  
  Inferred   8.6   57   7.43   8.93   2.1   2.5   1.2   10.8   7.45   8.96   2.6   1.5  
  Total   48.5     6.82   7.78   10.6   12.1   6.6   46.3   6.73   7.71   10.0   6.1  

 

Notes

  • Mineral Resources are quoted inclusive of Mineral Reserves
  • Mineral Resource estimates allow for estimated geological losses but not for anticipated pillar losses during eventual mining
  • The modifying factors used to convert a Mineral Resource to a Mineral Reserve are derived from historical performance using an in-house ore accounting system. This system is able to provide dilution factors that are applied to in situ estimates to project the final product delivered to the mill
  • Mineral Reserves quoted reflect the grade delivered to the mill rather than an in situ channel grade quoted in respect of Mineral Resources
  • The increase in the Merensky Reef Mineral Reserve estimate is mostly due to the increase in the estimated width. This was offset by the reassessment of certain areas and to some extent by changes in some dilution factors
  • The year-on-year reduction in Proved Merensky Mineral Reserves illustrates that main development remains a focus area
  • Mineral Resources and Mineral Reserve grades are shown as both 4E and 6E grade. The 4E grade was recalculated from 6E to represent the summation of individual Pt, Pd, Rh and Au grades. This is different from the previous year and the 2011 4E grades were restated for ease of comparison
  • Rounding of numbers may result in minor computational discrepancies.

 

 

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