The magmatic layering in the RLS is laterally persistent and can be correlated throughout most of the complex. Layering is generally shallow dipping towards the centre of the complex. The RLS stratigraphy is sub-divided into five zones, which are, from lowest to highest, the marginal zone, the lower zone, the critical zone (which is further subdivided into a lower and upper unit), the main zone and the upper zone.

Historically, PGM production was concentrated on the western limb but, in recent years, the eastern limb has been the focus of new mine development.

The two wholly-owned Northam properties, the Zondereinde and Booysendal mines, contain resources of both the UG2 and Merensky reefs.

Zondereinde mine is situated in the northern portion of the western limb of the Bushveld Complex, approximately 30km south of the town of Thabazimbi in the Limpopo province of South Africa. The mining concession covers some 7 625ha underlain by both the Merensky and UG2 orebodies, which dip at approximately 20° and extend from a depth of 1 100m to 2 900m below surface.

The company exploits both the Merensky and UG2 reefs of the upper critical zone of the Bushveld Complex. While there is lateral continuity of both reefs across the mine property, the Merensky reef displays a variety of reef types. The distribution of these is determined by a combination of surface exploration boreholes, ongoing prospect drilling from underground development and reef mapping in development and stoping. In contrast to the Merensky reef, the UG2 displays little variation in reef attributes.

The Bushveld sequence at Zondereinde is typical of the northern portion of the western limb. The critical zone stratigraphy is telescoped and dominated by mafic lithologies. Vertical separation between the UG2 and Merensky reefs is in the range of 20m to 40m

Underground mining focuses on the exploitation of PGM ores by means of traditional narrow tabular reef drill and blast mining methods. A standard breast mining layout is used at Northam. The vertical interval (distance) between levels is 63m. With the orebody dipping at 20°, this provides a raise length of 180m allowing for six panels of 30m each per raise connection.

Surface metallurgical infrastructure includes a UG2 concentrator and a dense media separation plant. Concentrate is sold to Zondereinde and all material is smelted and further processed at Zondereinde.

Concentrating: Merensky and UG2 plants
• In the crushing/screening circuit the ore is crushed to reduce its size before it reports into the mill.
• Merensky ore feeds into a fully autogenous (FAG) mill. In the UG2 plant, the ore feeds into a high pressure grinding roll crusher and then into a primary ball mill.
• The flotation circuit includes rougher cells, scavenger cells and cleaner columns. External sparger column cells act as a cleaner and this helps to produce a final UG2 concentrate with significantly lower chrome content while maintaining PGM recoveries.

The existing smelter at the Zondereinde metallurgical complex has a 15MW capacity. Key processes include drying and smelting the concentrate and converting the furnace matte. Concentrate brought in is blended and dried concentrate is pulverised and then stored in silos. Concentrate and flue dust is mixed with lime and then fed through to the day bin and into the furnace where electrodes provide heat via resistance to the current through the material in the bath. The lighter oxides float to the top as slag and the more dense sulphides, which contain the PGMs, sink to the hearth as furnace matte.

Final precious metal concentrate is transported from the Zondereinde metallurgical complex for refining to the Heraeus facilities in Hanau, Germany and Port Elizabeth. Heraeus is a registered member of the London Platinum and Palladium Market (LPPM) and has London-Zurich ‘Good Delivery’ status for metal production. The refinery in Hanau is subject to strict European Union and materials handling protocols. Product transportation is also strictly defined by international aviation regulations.