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.

The Booysendal mining concession is located in the southern compartment of the eastern limb of the Bushveld Complex, approximately 35km west of the town of Mashishing (formerly Lydenburg), straddling the border of Limpopo and Mpumalanga provinces in South Africa.

The Bushveld sequence at Booysendal is similar to that found across the southern compartment of the eastern limb. The critical zone stratigraphy is fully developed, and middling between the UG2 and Merensky reefs is in the order of 175m in the northern and central portions of Booysendal. The sequence is, however, subject to thinning in the far southern portion, which is linked to the Bushveld rocks abutting basement highs. The impact of this ‘abutment’ is further manifested in localised zones of disruption to surface morphology and internal structure of the two reefs. This has led to the characterisation of three geozones within the Booysendal concession, these being the normal, slump and abutment geozones. Despite this progressive disruption to the south, the continuity of the reef surfaces is robust across the property.

The UG2 reef consists of an upper leader chromitite and a lower main chromitite with a combined thickness of some 140cm. These seams are generally juxtaposed or merged, but can display variable internal silicate partings.

The Merensky reef is the upper mineralised portion of the Merensky pyroxenite, generally extending over 110cm. The Merensky reef is immediately overlain by a sequence of competent norites.

The UG2 sections of Booysendal North and South mines are underground, mechanised bord and pillar mines, accessed from surface via ramp decline systems. The North mine decline system comprises three declines on the plane of reef and one decline situated 20m into the footwall of the reef, containing a belt for ore handling. Decline systems for the South UG2 mines comprise four declines on the plane of reef.

Mining sections extend over a dip length of 144m, equating to a vertical interval of 25m. Strike drives are inclined at 5° above the line of strike. Strike belts within the drives transport ore to the central decline dip belt system for transport to a UG2 concentrator plant on surface. Mechanised boom rigs and LHDs are employed in mining and development.

The Booysendal North UG2 mine is a shallow, mechanised room and pillar underground operation. The North shaft complex comprises four declines, three on reef and one in the reef footwall, which are accessed by a reverse decline system.

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.

The Booysendal concentrator plant is a typical MF2 circuit type plant and is designed to receive 187 500 ROM ore from the underground workings via the reverse decline conveying systems. A DMS plant is installed to remove 37 500 tonnes of waste from the ROM material and to improve the head grade feed to the primary mill and reduce milling requirements.

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.