The mining operations at Barplats are situated on the western limb of the BIC (Bushveld Igneous Complex). The BIC is a 2.05 billion year old layered igneous intrusion underlying an area of approximately 65,000 km2.

The mafic rocks of the BIC display a maximum vertical thickness of approximately 8 km with some individual layers being traced for over 150 km along strike. The BIC constitutes the most voluminous preserved mafic intrusion with the world’s largest ore reserves of PGEs (Platinum Group Elements), Cr2O3 (Chromium Oxide) and V (Vanadium) being exploited at numerous operations.

The BIC (as well as the suite of rocks encompassed by the Bushveld event) can be categorised into three subdivisions, namely, into the mafic rocks of the Rustenburg Layered Suite (RLS), the Lebowa Granite Suite (LGS) and the Rashoop Granophyre Suite.

The units contained within the RLS comprise of dunite and pyroxenite through norite, gabbro, anorthosite to magnetite and apatite rich diorites. A subdivision has been proposed by using traditional zonal stratigraphy which comprises of a noritic Marginal Zone, and ultramafic Lower Zone (LZ), and ultramafic to mafic Critical Zone (CZ), a gabbronoritic Main Zone (MZ) and a ferrogabbroic Upper Zone (UZ).

Barplats is underlain by the CZ stratigraphy. The CZ is noted for carrying massive deposits of chromite within the Lower (LG), Middle (MG) and Upper (UG) Group chromitite layers and the worlds largest platinum bearing ore bodies the Merensky Reef (MR) and UG2.

The Lower Critical Zone (LCZ) is an 800 m thick pyroxenitic cumulate with up to seven chromitite layers (LG1-LG7). Nearly all of the LG layers contain minor disseminated chromite.

The Upper Critical Zone (UCZ) of the RLS strikes east-west and contains both the MR and UG2 which outcrop on the area. The MR intercepted in this part of the western limb comprises a thick feldspathic pyroxenite unit of up to 14 m thick and is considered to be relatively uneconomic. The UG2, which typically consists of a single chromitite layer, has an average vertical thickness of 1.4 m. It is composed of two sub-units called the C1 and C2 units, which are separated by a 1 cm to 8 cm wide pyroxenite parting. The higher grade mineralisation occurs at the base of the C1 and the C2 units, however over the bulk of the lease area at Barplats only the C1 unit is present.

Barplats mines the UG2 as it outcrops at surface, continuing down to depths in excess of 2,000 m with an average dip of 17°. The host rocks that bound the UG2 are the overlying feldspathic pyroxenite and the underlying pegmatoidal feldspathic pyroxenite with the norite below it. In Barplats’ Maroelabult section the UG2 varies in thickness from 1.4 m to 1.5 m, whereas in the Zandfontein section, it is thinner and varies from 1.3 m to 1.4 m thick.

Mineralisation.
Common features of the UG2 are the undulating nature of the Bottom Reef Contact (BRC), the presence of mafic/ultramafic pegmatites and potholes. The chromatitic leader hangingwall layers are generally absent or have coalesced with the main band to form a virtually homogenous chromitite. A very thin chromitite stringer (approximately 1 mm thick) is seen to occur at varying heights above the top of the chromitite in the immediate hanging wall.

The footwall is typically a Pegmatoidal Feldspathic Pyroxenite (PFP) but where the BRC transgresses through the PFP the footwall is a norite. The Top Reef Contact (TRC) is generally sharp and stable. The UG2 is predominantly impure chromitite with interstitial silicate, comprising of pyroxene (bronzite) and feldspar (anorthosite).

The UG2 is bottom and middle loaded with PGMs and the associated disseminated sulphides are concentrated in the lower part of the reef.

The 3E PGEs and Au concentration of the UG2 at Barplats varies from 2.5 g/t to 6.6 g/t. The major PGMs are Laurite (Ru(Os,Ir)S2) and Platinum (Pt), Palladium (Pd) Sulphide (Cooperite (Pt,Pd)S and Braggite (Pt,Pd,Ni)S). At Barplats, Pt makes up 62.6% of the 3E PGEs and Pd 26.2%, Rhodium (Rh) 10.4% and Au 0.8%. The Pt to Pd ratio of the UG2 at Barplats is 2.38.

The UG2 is Pd and Rh enriched relative to the Merensky Reef. 9% of the PGMs are associated with Chromite; 46% of the PGMs are associated with the silicates and 45% of the PGMs are associated with the base metal sulphides. The base metal sulphides that occur in the UG2 are the following, listed in decreasing order of abundance Pyrrhotite (Fe2S2), Pentlandite (Ni,Fe)S2, Chalcopyrite (Fe,Cu)S2 and Pyrite (FeS2). The Cu content averages about 0.05% and Ni averages about 0.1%. The relative density of the UG2 in the western BIC ranges between 3.50 t/m3 and 3.90 t/m3 ; the average relative density is 3.85 t/m3. Potholes commonly occur in the UG2 (pothole losses commonly vary from 10-20%) and mafic and ultramafic pegmatites are also present.

At Barplats the 3E PGEs and Au content averages 4.29 g/t, at an average thickness of 140 cm; this gives an average of 600 cmg/t.

Barplats’ preference is not to establish a new TSF (Tailing Storage Facility) and so the strategy is for the tailings from the plant to be placed back onto the footprint of the existing TSF while it is being exploited. The TSF has been divided into six areas as part of a strategy to exploit the total volume of tailings material.

Hydraulic mining and Mechanical loading of material on the north-western section will start simultaneously. The associated tailings from the plant following processing will be re- deposited using the cyclone method.

Mechanical loading is necessary in the coarse area of the TSF where material is chemically bonded in layers, which is not able to be hydraulically broken down to the minus 3mm fraction, which is the maximum plant feed size.

Mining Methodology.
Modelling was used to determine the most suitable technique for mining the TSF. The methodology involves continual and simultaneous cleaning, construction, hydraulic mining and deposition activities.

Certain areas need to be excavated using mechanised equipment (i.e. coarser harder material) while other sections of the TSF can be mined hydraulically (i.e. finer softer material).

Mechanised Operations.
Coarse material will be excavated, using a dry mechanised mining method.

The mechanically mined material will be trucked to a scalping screen, which will dry screen the vegetation from the material, after which it will pass through a roller crusher that will ensure that all the material is screened to minus 28 mm.

The material will be pulped and pumped with a jet pump at a planned rate of 203 tph, to the central pumping station with a 3mm wet screen where it will be mixed with the hydraulically mined material.

At the central pumping station, the oversize material (+3 mm), from the test work, indicated to be approximately 50% of the mechanically mined material (100 tph), will pass through a scrubber in closed circuit with the 3mm screen.

The grizzly feeder screen will be set at 40mm and a roller crusher set at 10 mm to protect the booster pump which will transfer the slurry through HDPE pipes to the main slurry pump station.

Hydraulic Operations.
Hydraulic mining involves the material being hydraulically sluiced from the planned sections or blocks of the TSF and transferred in a slurry form to a collection sump via a system of drains or launders. A pump station is then used to pump the slurry to the plant.

The hydraulic sluicing is achieved by using track mounted high pressure water monitor guns (one operating and one on standby) to generate a slurry from the material, which has a specific gravity (SG) of 3.6 t/m3. The resulting slurry density is expected to fluctuate from 1.35 t/m3 to 1.80 t/m3. Water is moved through a series of pumps to increase the pressure of the water to approximately 275 kPa before it is directed through a network of pipes to the high-pressure monitor units on top of the TSF.

The slurry will flow through a launder system to a launder collection sump (on-dam catchment area) and collection barge vertical spindle pump.

A series of 110 kW satellite spindle pumps will be positioned to assist the flow. Static screens (+50 mm) will be used at the satellite pumps to remove debris and vegetation. The 12 m deep catchment area and launder will be created using an excavator. A floating “tripod” barge will be installed in the catchment area to include a vertical spindle pump for onward transfer of the slurry to the main slurry pump station.

Following completion of an upper bench, a second catchment sump will need to be established. Two vertical spindle pumps will be used on a barge system to feed the main transfer slurry pump station. The final cut will follow the same sequence of launder and mining the final footprint from the higher contour levels towards the lower contour levels.

The two satellite pumps will be placed inside the final cut catchment area as a sump and feed the main pump station with slurry. The collection sump, together with the high wall will act to safe guard against flooding of the pump station by collecting runoff water and barricading between the sump and pump station.

The CRP will remain within the existing processing complex. Its design is based on tried and tested technology and comprises the use of spiral concentrators (spirals), which are generally standard throughout the South African chrome industry. Wherever possible, existing equipment will be retained to reduce capital expenditure. The old spirals will, however, all be replaced with modern spirals to improve recovery and yield. The existing spiral structure will be retained with a few structural modifications. Existing sumps, pumps and pipelines will be upgraded and repositioned to cater for the increase in throughput to 240 ktpm.

The design takes cognisance of the following operating requirements:
- Metal accounting samplers will comply with international best practice;
- All pump boxes, sampler boxes, pipelines, and similar will support a wet, settled slurry density of 5.0 t/m3;
- All process pump boxes will be installed above ground level;
- All slurry sumps will be sized to have a residence time of 90 seconds and minimum valley angles of 45° on the lateral and 60° on the rear;
- There will be adequate, safe access to operating equipment, and spiral nests will be provided for CRP personnel;
- Ergonomically acceptable and corrosion resistant, galvanized walkways with kick plates, hand railings and 2 m of head room will be provided;
- Hard piped, high pressure flushing water facilities and drain points will be provided on all slurry pipelines and pumps, for handling spillage;
- Standard pipelines will be sized to ensure adequate slurry velocities for the full suspension of solids at all times. The minimum slurry velocities will be maintained between 2.7 m/s and 2.9 m/s. The chrome concentrates will be moved at a minimum velocity of 3.2 m/s;
- The pump gland service water supply lines will be automated and fitted with check valves, sight glasses and pressure relief valves;
- The potential for blockages and spillage will be low to minimise maintenance and to maximise overall plant availability;
- The layout makes maximum use of gravity and will seek to ensure that optimum even slurry splits on the distributors are achieved;
- All flow and density measuring equipment installations will allow effective and efficient calibration at regular intervals.

The availability of the CRP (Chrome Recovery Plant) will be dependent of the operational availability of the hydraulic mining equipment on the TSF and "visa versa", and therefore a facility to bypass the recovery circuit is not in the design.

Slurry from the TSF will report to a spiral feed tank (TK100), where process water will be added through a density control circuit to reduce the pulp relative density from an average of 1.35 kg/l to 1.29 kg/l as required for the cluster cyclone feed.

This density may vary between 1.25 kg/l and 1.45 kg/l. The higher figure was used for the dilution water requirement, and the lower figure was used for the maximum pumped volume requirement in the design.

The CRP feed and tailings lines will be equipped with a densitometer and flow meter for mass integration capability to control the feed.

The design of the cluster cyclones will result in a relatively fine underflow (i.e. cutting at approximately 45µm). The underflow from the cluster cyclones will be controlled to a density of 1.70 kg/l gravitated directly to the rougher spiral feed tank (TK300) ahead of the spiral banks. The overflow from the cluster cyclone will gravitate into tank (TK200) and will be pumped to the tailings thickener.

The CRP will consist of twenty five banks of spirals. Spiral clusters will be arranged in a pattern so as to ensure an optimum even feed distribution between the spirals. The rougher and scavenger spirals will be vertically stacked above one another, making use of gravity feed to each section below. All of the spirals will have adjustable cutters that will allow for the production concentrate and a tailings stream on all stages.

There will be an automatic isolation valve on each discharge of the eight-way pressure distributor so that a single nest may be taken off-line at a time without affecting the rest of the CRP. This will include the process water take-off of the ring main manifold for each specific bank in order to facilitate maintenance, or if the average volumetric flow rate is too low.

The rougher spirals comprise three banks of ten spirals with five turns each. They will be fed at a pulp density of 1.7 kg/l.

The scavenger and re-scavenger spirals will be similar to the rougher spirals. The four banks of cleaner spirals with three turns will be fed at a pulp density of 1.6 kg/l.

The re-cleaner and re-re-cleaner spirals will also be of the three turn, double start type, and will consist of one and three quarter turns each. They will be fed at a pulp density of 1.5 kg/l. At each stage, the concentrate will be processed for further cleaning, whilst the tailings will be split off into a central discard pipe reporting to spiral tails sump (TK 400).

Diluting water will be added to the feed of each spiral stage via a ring type manifold and each spiral will have its own manual control valve. Concentrate from the re-re- cleaner spiral bank will gravitate to the final cleaner feed sump (TK 600) and report to the hydrosizer for final cleaning. The tailings stream will gravitate to the cleaner feed tank (TK 500).

The oversize from the hydrosizer will be pumped to a spiral receiving tank. The under flow will report to the distributor from where product will go to its own sump with control water added prior to being pumped to the metallurgical concentrate stockpile de-watering cyclone. Make-up water to the chrome product sumps will be evenly split between manual water addition to the respective product launders, and level control water added directly to the sumps.