Deposit Types
Two main PGE deposit types occur within the Bushveld Complex:
• Relatively narrow (maximum 1 m wide) stratiform layers (reefs) that occur towards the top of the Upper Critical Zone typically 2 km above the base of the intrusion (Merensky reef-style), mainly found in the Western and Eastern Limbs. These narrow zones have been the principal targets for mining in the past; however, more recently wider zones with more irregular footwall contacts have been mined (termed potholes).
• Contact-style mineralisation at the base of the intrusion (Platreef-type) occurs mainly in the Northern Limb.

In general, within the Northern Limb, the Platreef comprises a variably layered, composite norite–pyroxenite–harzburgite intrusion that lies at the base of the Bushveld Complex, in contact with metasedimentary and granitic floor rocks. McDonald and Holwell (2011) reviewed the major literature on the Platreef and Northern Limb, and have concluded:
• The Platreef remains a complex and enigmatic deposit.
• Stratigraphic relationships with other stratiform deposits such as the Merensky and UG2 reefs have been suggested.
• The extent to which the Northern Limb was connected to the rest of the complex across the Thabazimbi–Murchison Lineament remains to be established.
• The Platreef represents a complex of sills intruded into basement granite-gneiss, Transvaal Supergroup sediments or pre-Platreef Lower Zone intrusions.
• Intrusive relationships of the Main Zone gabbronorites, into solidified and deformed Platreef, removes the Main Zone as a source of metals for the Platreef.
• Mineral chemistry, bulk geochemistry, and Sr, Nd, and Os isotope geochemistry of the Platreef are most consistent with an ultramafic (Critical or Lower zone) component.
• Platreef Nd values and 187Os/188Os initial isotope ratios overlap clearly with the Merensky Reef but not the UCZ.
• Conventional and mass-independent S isotopes suggest a primary mantle source of S that was overprinted by the addition of local crustal S where Platreef intruded pyrite-rich shales. Assimilation of S is viewed as a modifying process, not as the primary trigger for mineralisation.

Mineralisation
The Platreef Project is hosted within the Palaeoproterozoic (2.06 Ga) Bushveld Igneous Complex (BIC), which is the largest of the known layered igneous intrusions, covering an area > 65,000 km². The BIC hosts up to 75% of the world’s platinum resources (Naldrett et al, 2009).

The BIC includes an early bimodal volcanic sequence (the Rooiberg Group) that is followed by an intrusive layered series of ultramafic and mafic units known as the Rustenburg Layered Suite (RLS) and the Lebowa Granite and Rashoop Granophyre Suites. The RLS is 7 to 8 km thick and ranges in composition from dunite to diorite.

Hall (1932) divided the RLS into 5 zones in descending order:
• Upper Zone (UZ) — Gabbroic succession.
• Main Zone (MZ) — A succession of gabbronorites with occasional anorthosite and pyroxenite bands.
• Critical Zone (CZ) — The Lower Critical Zone (LCZ) consists of orthopyroxenitic cumulates, and the Upper Critical Zone (UCZ) comprises packages of chromitite, harzburgite, pyroxenite, norite, and anorthosite. The CZ hosts PGE–Au–Ni–Cu and chromite deposits in several different chromitite layers known as reefs. The most significant are the Merensky Reef and the Upper Group 2 (UG2) Reef of the Eastern and Western Limbs. These range on average from 0.4–1.5 m in thickness and the contained PGE (Pt, Pd, Rh, Au) content typically ranges from 4–10 g/t (Cawthorn, 2005).
• Lower Zone (LZ) — Upper and lower peridotites separated by a central harzburgite.
• Marginal Zone (MZN) — Norites with variable proportions of accessory clinopyroxene, quartz, biotite and hornblende, indicating magma contamination from the underlying metasediments. This unit is not always present.

In the East and West Limbs of the BIC, the RLS was intruded into the Magaliesberg Formation of the Proterozoic Transvaal Supergroup. In the North Limb, the RLS intrudes progressively older country rocks northward (Magaliesberg Formation, Malmani Subgroup and Duitschland Formation). In the East and West Limbs of the BIC, the CZ includes the Merensky Reef and UG2 chromitite that are exploited for PGE mineralisation. In the North Limb of the BIC, the mineralised horizons have been referred to as the Platreef. The North Limb hosts the Platreef Project.

Structure
Structurally, the Northern Limb is separated from the rest of the Bushveld Complex by the Thabazimbi-Murchison Lineament (TML). The TML is a pre-Bushveld, major, compressional tectonic boundary (suture zone) that formed as a result of the collision of the Pietersburg terrane and Kaapvaal shield around 2.97 Ga during the Murchison Orogeny (Friese, 2003, 2004). The Ysterberg-Planknek and Zebediela Faults play a significant role in the regional geology of the Northern Limb.

The tectono-thermal evolution can broadly be subdivided into pre- and syn-emplacement folding and multiple faulting events. Folding in the Northern Limb has been controlled by two principal transpressional events caused by movements along the TML in the south and the Palala Shear Zone.

According to Nex, (2005), this led to the formation of two main open-fold geometries within the Transvaal sediments. The first and most dominant folding event was caused by NE-SW sinistral transpression. This resulted in regional NNW trending low amplitude, sub horizontal open folding. These F1 folds developed within Archaean basement and Transvaal Supergroup and represent the earliest developed structures which formed contemporaneously as a result of mild ENE-WSW compression during the Limpopo-Murchison Orogeny at 2.78–2.64 Ga. Subsequent NW-SW transpressive inversion refolded the earlier F1 fold axis resulting in basin and dome fold interference patterns (Friese, 2012).

Significant brittle faults and ductile shear zones are known throughout the Northern Limb, and the major, widely-spaced, ENE-trending shear zones dominate the regional map pattern. These combine to form large strike-slip duplex systems, which host a complex array of riedel shears, normal faults, thrusts and dilational tension fractures that have been invaded in part by igneous dykes and quartz-feldspar veins. These faults are reactivated during a major E-W crustal extension event associated with major brittle fracturing.

Mine planning
Lateral Development:
- Maximum grade will be 15%.
- Ramps will level off at sublevels to reduce risk of rollovers.
- Ore passes will be spaced 400 m apart on the levels.
- Electrical bays will be spaced 400 m apart.
- Level development will be inclined slightly to have water drain to the sumps (actual incline to be designed during detail design).
• Vertical Development:
- All raises except Shaft 1 and Shaft 2 will be raisebored.
- Maximum raisebore diameter is 6 m.
• Longhole Stoping:
- Bottom-up Longhole Stoping will be used.
- Minimum inclination of stopes on the footwall side will be 55°.
- The unfilled stope length for the 20 m high Longhole Stopes should not exceed 60 m.
- As much as possible, stopes should be aligned to minimise the risk of failure.
- A primary-secondary stoping sequence is recommended.
- Adjacent secondary stopes are not mined simultaneously.
- Secondary stope development can be carried out at any stage, regardless of whether nearby stopes have been backfilled.
- Over break thickness for top sides, hanging wall, footwall, end sides, and secondary stope sides is 0.5 m.
- Over break thickness for the floor is 0.3 m.
• Drift-and-Fill:
- Overhand Drift-and-Fill will be used.
- Each horizontal slice is mined completely before mining of the slice above begins.
- Drifts will be driven with flat backs for recovery purposes.
- Mining widths should be limited to 5.5 m to reduce the length of ground support in the back and walls to 2.4 m. If mining widths exceed 5.5 m, additional support will be required.
- Assuming a mining width of no more than 5.5 m, the mining sequence should be primary-secondary-tertiary to ensure that slender backfill ribs are not formed. For this method a 5.0 m width was utilised.
- An average of 0.15 m of over break will be used to estimate the overall dilution from each paste fill rib.

Mining Method
Sublevel Blasthole (Longhole) Stoping with cemented paste fill / rock fill, supplemented with development waste rock, where possible, to fill open stopes in the thicker ore zones. This method will minimise mining costs and achieve the highest productivity. The remainder of production may come from thinner high-grade zones. Drift-and-Fill methods will be used in these zones.

Two longhole mining scenarios were studied and evaluated for the Platreef 2022 FS:
• Transverse Longhole Stoping
• Longitudinal Longhole Stoping.

Longitudinal Longhole Stoping was considered specifically where deposit thickness could not support stope lengths of 15 m or more, normal to the strike, where Transverse Longhole Stoping would not be a suitable option. From the Vertical Miner software results, three major areas (Zone 1 north section, Zone 4, and Zone 2 central locations), were identified as the ideal candidate for this mining method. Stope shapes were created accordingly. After reviewing the longitudinal stope shapes created by MSO, the entire methodology had to be dismissed due to geotechnical considerations, such as hydraulic radius and mining direction. The ribs of the stope were parallel to the fault planes and the hydraulic radius provided would not support such stope shapes with meaningful sizes.

For the thinner and high-grade areas, two mining methods were evaluated:
• Cut-and-Fill
• Drift-and-Fill.
After reviewing the mining shapes (pancakes), it was concluded that Drift-and-Fill mining would be possible and is the most suitable solution due to higher productivities and performance rate.

ROM is crushed underground to a top size (F100) of 270 mm. The pre-production ROM material is conveyed by a ROM handling system and can be routed to either one of the two 5,200 t ROM silos or the ROM stockpile.

Upon commencement of the concentrator plant operations, this stockpiled material will be reclaimed via a ROM reclaim system consisting of a static grizzly, surge bin, vibrating screen and reclaim conveyor fitted with a magnet for tramp metal removal. The reclaim conveyor feeds the secondary screens.

Once the concentrator plant is in production, ROM ore is conveyed from Shaft 2 headgear, at a peak flow rate of 1,350 dry tph and a top size of 270 mm, into either one of the two 5,200 t ROM silos. Each ROM silo is equipped with apron feeders for extraction onto the ROM Screen Feed Conveyor that feeds the secondary screens in the crushing circuit. Tramp metal is removed prior to crushing by means of a tramp metal magnet situated on the conveyor.

Crushing and Screening
The crushing, and screening circuit consists of a modular crushing and screening plant which includes primary, secondary and tertiary crushing. The secondary and tertiary crushers are operated in closed circuit with a crusher circuit screen.

A Front-End Loader (FEL) feeds material from the RoM stockpile into a RoM Bin, which is fitted with a static grizzly to remove any +500 mm ahead of the primary Jaw Crusher.

The Jaw Crusher is fed by a vibrating grizzly feeder. Grizzly feeder oversize is fed to the primary crusher and the combined product (grizzly feeder undersize and crusher product) is conveyed to the Crusher Circuit Screen by means of the Jaw Crusher Discharge Conveyor. Screen top deck oversize (+36 mm) is conveyed to the secondary cone crusher which has a dedicated feed bin and vibratory feeder. Screen bottom deck oversize (+13 mm) is conveyed to the tertiary cone crusher which has a dedicated feed bin and vibratory feeder.

The secondary and tertiary crusher products are combined with the primary crusher product as feed to the Crusher Circuit Screen. The primary crusher product conveyor is fitted with a magnet for removal of tramp metal.

The Circuit Screen Undersize Product Conveyor transfers the final crusher circuit undersize product material (P100 =13 mm) to the overland transfer conveyor which conveys the crusher product to the 1,600 t mill feed silo.

The concentrator crushing and screening circuit consists of secondary and tertiary crushing stages in closed circuit with secondary and tertiary screening stages.

Ore from the ROM Screen Feed Conveyor, ROM Reclaim Conveyor, and Secondary Crusher Product Conveyor are transferred to the Secondary Screen Feed Bin. Ore from the Secondary Screen Feed Bin is transferred via vibratory feeders to the secondary screening circuit which is comprised of two double-deck screens. The top deck (+30 mm) of both the secondary screens reports to the Secondary Cone Crusher Feed Conveyor which is equipped with a magnet for the removal of tramp metal. The bottom screen deck (+12 mm–30 mm) material of both the screens reports to the Tertiary Cone Crusher Feed Conveyor, which is also equipped with a magnet for the removal of tramp metal. The secondary screen undersize (–12 mm) from both secondary screens reports to the Screen Product Conveyor.

The Secondary Cone Crusher circuit is comprised of two cone crushers operated in parallel. Each cone crusher is fed via a feed bin and vibrating feeder. The secondary crusher product (–35 mm) is removed by the Secondary Cone Crusher Product Conveyor and fed back to the Secondary Screen Feed Bin for re-screening.

The Tertiary Cone Crusher circuit is comprised of two cone crushers operated in parallel. Each cone crusher is fed via a feed bin and belt feeder.

The tertiary crushed material (–10 mm) is removed by the Tertiary Cone Crusher Product Conveyor and fed to the Tertiary Screening Circuit, which is comprised of two single-deck screens (+10 mm). Oversize reports to the tertiary cone crushing area while undersize reports to the Screen Product Conveyor.

The Screen Product Conveyor transfers the final product material (P100 =13 mm) to either of the two 8,000 t mill feed silos. A diverter chute on top of the first silo diverts the material to Mill Silo No.1 or Mill Silo 2 via an additional feed conveyor.

Milling
The mills have been sized to cater for the 85th percentile ore hardness as determined from the comminution variability test data. Each milling circuit is fed with 13 mm tertiary crushed material and will produce a product size of 80% passing 75 µm. The Phase 1 milling circuit is comprised of a single 0.77 Mtpa ball mill and cyclone cluster operated in closed circuit.

The recommended mill size for Phase 1 is an 18’ftØ x 24’ft effective grinding length (EGL) ball mill with a grate discharge liner arrangement and 4.5 MW motor.

The Phase 1 mill motor is fixed speed with modifications to the ball charge allowing for variation in the feed material, required grind size and mill throughput.

For the 4.4 Mtpa concentrator, two separate 2.2 Mtpa milling circuits were selected based on a plant ramp-up and comminution trade-off and concentrator production ramp-up profile. Each milling circuit is comprised of a single 2.2 Mtpa ball mill and cyclone cluster operated in closed circuit.

The recommended ball mill size for each 2.2 Mtpa milling stream is 22½’ft diameter x 34½’ft Effective Grinding Length (EGL) with a grate discharge liner arrangement and 12 MW (2 x 6 MW) variable speed geared pinion drives. The design has been based on a maximum ball charge of 35%. The ball charge, together with the variable speed motor capability, allows feed material variability, required grind size and mill throughput.

The process plant for the Platreef 2022 FS is designed to treat 0.77 Mtpa and 4.4 Mtpa Platreef ore in Phase 1 and 2 respectively. The plants include all processing requirements from the runof-mine (ROM) storage through to final concentrate plant load out and tailings disposal.

The process design for the respective 0.77 Mtpa and 4.4 Mtpa concentrator plants have been developed based on the testwork findings and assessments, various desktop level trade-off studies and relevant DRA design information. The Platreef concentrator flow sheet is based on a conventional three-stage crushing and ball milling circuit followed by flotation. This single-stage milling and flotation process flow sheet is well known in industry, and has historically been proven as a suitable processing route for various platinum ores.

The phased approach to the construction will see the construction of a 0.77 Mtpa concentrator plant in the Phase 1 of the project. This will be followed by the co ........