Summary:
The Bushveld stratigraphic sequence at Zondereinde is typical of the northern portion of the western limb. The Critical Zone stratigraphy is compressed and dominated by mafic lithologies, with the vertical separation between the Merensky and UG2 Reefs ranging between 20 m and 40 m. Both reefs dip at 20° towards the south-east and extend from a depth of 1 100 m to 3 000 m below surface.
While there is lateral continuity of both reefs across the mine property, the Merensky Reef displays a variety of reef sub-types. The distribution of these is determined from a combination of surface exploration boreholes, ongoing prospect drilling from underground development and on-reef mapping in mine excavations.
Merensky Reef
The Merensky Reef is a zone of mineralisation that straddles the base of the Merensky cyclic unit. In the area of Zondereinde mine, the Merensky Reef consists of two sub-facies of the Zwartklip facies, namely the Normal and Regional Pothole sub-facies. The latter may be further subdivided into three sub- types, each of which occurs at a specific stratigraphic level below that of the Normal subfacies. Sub- types include NP2 and P2, which constitute the main sources of ore, and FWP2 which, whilst not historically considered a primary mining target due to its undulating morphology in the central portions of the mine, is now successfully exploited in the western portion of the current mining area where it displays lesser disruption. This trend is expected to continue throughout the Western extension section.
The Mineral Resource channel is the planned mining cut on the Merensky Reef and is dependent upon the reef sub-type mined and the geozone in which it is located. In all mining cuts, the Merensky chromitite is exposed with a minimum of 10 cm of the overlying mineralised Merensky pyroxenite as hangingwall.
UG2 Reef
The UG2 Reef at Zondereinde mine is remarkably conformable when compared with the Merensky Reef. Disruption, in the form of potholes and reef rolls, is extremely limited and localised. The reef consists of three chromitite seams separated by narrow pyroxenite partings. The lower seam, termed the Main member, is generally in the order of 85 cm thick, and is overlain by two Leader seams, each in the order of 15 cm thick. The Mineral Resource channel, comprising these seams, inclusive of a 10 cm portion of mineralised reef footwall, which is the planned mining cut, is in the order of 140 cm to 160 cm thickness. There is no basis for subdividing the UG2 Reef into sub-types.
Historically, UG2 mining was limited to de-stressed areas underlying previously mined Merensky Reef. A full reef mining cut enhances metal output, hangingwall stability and safe working practices. UG2 operations are migrating to areas where there has been no previous Merensky mining. In these areas, support regimes and layouts similar to those employed on the Merensky Reef are adopted.