The Merensky and UG2 Reefs are separated by a sequence of mostly anorthositic and noritic layered units from 45m in the northern part of the lease area and thickens to 125m in the southern part of the lease area. Both the Merensky and UG2 Reefs are exploited at Impala. 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’, ‘C’ or ‘H’ Reef where it rests on specific footwall units – locally called Footwall 1, 2 and 3, respectively.

The UG2 Reef is defined as a main chromitite layer, with most of the PGM and base metal 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 four thin, poorly mineralised chromitite layers. The vertical grade distribution is depicted in the accompanying graphs, notably showing peak values at reef contacts in association with chromitite. The average 6E metal ratios show the distinct differences between the Merensky and UG2 Reefs, in particular the higher Pt:Pd ratio associated with the Merensky Reef and the relative high proportion of rhodium in the UG2 Reef, as shown below.

Both mineralised horizons dip gently away from the sub-outcrop in a north-easterly direction at 10° to 12°. The reefs may be disrupted by minor and major faults, lamprophyre, syenite and dolerite dykes, late stage ultramafi c 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 of these features are accounted for in the Mineral Resource and Mineral Reserve estimates as geological losses and they contribute to dilution or absence of the mineralised horizons.

The Merensky and UG2 Reefs are mined concurrently at Impala. Stoping at the operations is carried out through conventional double-sided breast mining in accordance with Impala’s best practice principles. The access haulages are developed in opposite directions from cross-cuts connected to a central shaft position, following the two reef horizons on strike in the footwall of the reefs and are defi ned as half levels. Footwall drives are developed at approximately 18m to 30m below the reef horizon with on-reef raise/winze connections being between 180m and 250m apart. Panel face lengths vary from 15m to 28m for both Merensky and UG2 Reefs, with panels being typically separated by 6m x 3m grid pillars with 2m ventilation holes. Stoping widths are approximately 1.4m and 1.1m for conventional Merensky and UG2 Reefs, respectively, depending on the width of the economical reef horizon. Mechanised (trackless) bord and pillar mining occurs in selected Merensky Reef areas at 14 Shaft. The average stoping width of the mechanised panels is about 1.9m.

Processing receives ore from the shafts which is allocated to either the UG2 Plant, for the higher chromium grade material, or the Central Concentrator for Merensky ore. Between 89% and 91% of the PGMs from the Merensky ore are recovered at mass pulls ranging from 5% to 7% utilising 10 primary mills, feeding two, nine stage, tank cell fl otation banks. Tailings from this section are milled for further liberation and fl oated in conventional cells to achieve the aforementioned recovery.

Approximately 79% to 81% of the PGMs are recovered from the UG2 ore at a mass pull of 2% to 3%. The PGM recovery from UG2 ore is performed utilising a more complex circuit confi guration in order to reduce the amount of chromium reporting to the concentrate stream. The MF2 plant, also situated at the Central Concentrator, utilises three primary mills that can accommodate any Merensky ore spill over, as well as UG2 ore. This allows for fl exibility in the ore split received from the mining ope ........