African Mining Brief

Expansion at Bafokeng Rasimone Platinum Mine

The Bafokeng Rasimone Platinum Mine (BRPM) is located on the Western Limb of the Bushveld Complex, approximately 30km north west of the town of Rustenburg in South Africa’s North West Province. Jointly owned by Anglo Platinum (the world’s largest platinum producer) and Royal Bafokeng Holdings, the eleven-year-old mine was established to exploit platinum-group metals (PGMs) in the Merensky and UG2 reefs near Rustenburg. The BRPM complex comprises the Boschkoppie and Styldrift mining right areas (owned respectively by Anglo Platinum and Royal Bafokeng Nation), along with a portion of the Frischgewaagd prospecting right area (owned by Anglo Platinum).

The current expansion project, a Joint Venture between Royal Bafokeng Resources (RBR) and Anglo Platinum (AP), will exploit the Merensky ore body underlying a portion of the Styldrift and Frischgewaagd farms situated to the north and north-west of BRPM. Known as the Styldrift Merensky Phase 1 Project, the new facility will have an extraction capacity of 230 000 tonnes per month (2.76 million tonnes per annum) by the time it reaches steady state in 2017. The total budget is R11.8 billion ($1.55 billion) (nominal).

Geology and mineralisation
Used as communal farmland, the gently undulating surface of the project area is bisected by the Elands River flowing in a northeasterly direction across the Styldrift project area. The project area overlies the western limb of the layered Bushveld Complex – a rich source of platinum, palladium and other PGMs, chrome and vanadium. Rocks of the Transvaal Supergroup constitute the floor to the layered rocks of the Bushveld Complex. In this portion, the Upper Critical Zone of the Complex, the most pronounced PGM mineralisation is associated with the Merensky Reef. The UG2 chromitite layer is the second most important platiniferous unit.

The structural geology of the Styldrift Project area is well delineated and is supported by hundreds of surface diamond drilled boreholes; complete coverage of high-resolution 3D Seismics; advanced geotechnical investigations; and several remote sensing techniques which have been applied to map the orebody.

The Merensky Reef underlying the Styldrift Project area comprises four facies types. From west to east, these facies include the Edge, Central-Mid, Central-Upper and Thick Reef Facies. Continuous drilling programmes have been used to refine the facies’ delineation. 3D Seismics and remote sensing techniques demarcate the shallow dipping 4-6º Merensky Reef as well as all the major structural intersections. The orientation and wide PGE mineralisation of the reef define an orebody that can be suitably extracted with conventional and mechanised mining techniques.

The mineral resources of the Merensky Reef underlying the project area are estimated at 72.62 million tonnes at a 4E PGE grade of 5.47g/t. At the shaft location, in the centre of gravity, the Merensky Reef and UG2 chromitite elevations intersect at 597m and 646m respectively below surface.

Project scope
Following a feasibility study from early 2006 to May 2008, the Styldrift Project Investment Proposal was given the go-ahead by Anglo American and Royal Bafokeng in July and September 2008 respectively. In the Investment Proposal, cost estimates were provided for all the surface and underground infrastructure and equipment required for the new 230 000 tpm mine. The R 11.8 billion (nominal) project estimate includes:

All preparatory civil and earthworks necessary for the commencement of shaft sinking.
Sinking of the twin vertical shafts and associated underground shaft system infrastructure.
Development of all planned capital cost underground haulages and arteries necessary for production ramp-up.
Procurement of all capital or other equipment necessary for the construction and permanent condition of the mine (underground and surface).
The construction of a concentrator plant adjacent to the current BRPM concentrator, for the processing of the 230 000 tpm of ore from the Styldrift Merensky Phase 1 project.

Twin vertical shaft system
Access to the underground workings will be via a twin, concrete-lined vertical shaft system comprising a 10.5m-diameter Main shaft and a 6.5m-diameter Services shaft, blind sunk to a depth of 740m and 725m respectively. Footwall infrastructure, mainly for the transporting of ore to the shaft, will be developed approximately 25m below the Merensky reef horizon. Two 22-tonne rock skips will be used to hoist the ore to the surface via the Main shaft. A second footwall network will be developed at 690m, at the base of the UG2 horizon, for future exploitation of the UG2 reef.

As the graphic below shows, the shaft system will be linked to the up-dip and down-dip on-reef roadway clusters on both the reef horizon and the footwall level. A network of on-strike haulages will underlie all sections for the transportation of ore to the Main shaft.

Merensky Footwall Infrastructure
Situated 25m below the Merensky reef horizon in the Room & Pillar (R&P) and Breast Mining sections, the Merensky footwall is the main artery of the proposed mine. Apart from travelling ways, all footwall infrastructure will be mechanically developed. This infrastructure includes tipping points on the reef horizon, from which ore will be sent via boxholes to the trucking haulage points 25m below. Fifty-tonne diesel-powered trucks will then transport the ore to ore passes feeding an underlying conveyor belt system 18m below. The conveyor system will include the main conveyor belt decline and an adjacent auxiliary decline.

Stoping
In line with the dominant mining approach in the area, a combination of mechanised Room & Pillar (R&P) and conventional breast stoping will be used. The former will be applied in the Thick and Central Upper Merensky Reefs, while the Central Mid and Edge Merensky Reef facies will be exploited via conventional, scattered breast mining, using handheld equipment and truck hauling.

The project ramp-up phase will be mainly characterised by mechanised, trackless mining, with the rooms providing the primary source of reef in each section. Thirteen metres wide, the rooms will vary in height between 1.9m and 3.3m (reef width plus over-break). Regional pillars of 17m in width will form a boundary along the length of each mining section. Forty per cent of these pillars will be extracted in the secondary extraction phase. Conventional mining will follow trackless mining after ten years.

Stoping width in the R&P section is expected to range from 1.9m to 3.3m, and from 0.88m to 1.6m in the scattered breast mining sections. In the R&P section, LHDs will be used to convey ore directly to the boxholes (76m apart), or to “fish” belts connected to the boxholes. In the conventional breast stope section, there will be two boxholes per stope, plus stope-face winches, advance strike gullies and centre gullies which will be used for stope cleaning. The conventional sections will be supported using of a combination of 200mm diameter elongates, bolting and netting. Bolting will be used in the hanging wall of the R&P sections.

Bulk Infrastructure
During the construction phase, the electrical supply will be provided by the mine’s existing network, using 11kV lines linked to the national electrical utility’s substation at Boschkoppie. Two 88kV overhead lines will be installed to provide a Life of Mine link to the Boschkoppie substation, and a substation will be constructed at the mine site. Three 2.8MW generators will provide an emergency electrical supply.

Water will be supplied to the mine via a new pipeline connected to the existing mine pipeline. To reduce dependency on the existing Magalies water supply, all excess water produced by mining operations at Styldrift will be pumped to the BRPM concentrator complex and reused for ore processing.

A 1.2km gravel road will provide a link between the project site and the existing access road during the construction phase, and will be upgraded to a permanent tarred road before heavy equipment arrives on site. A second gravel road will form a service link along the conveyor service corridor and connect the BRPM complex to the Styldrift mine.

Shaft Infrastructure
The configuration of the Main shaft allows for (1) a single deck, personnel and material cage compartment (capable of transporting 185 persons); (2) a cage counterweight compartment; (3) two Merensky reef skip compartments, each designed to accommodate a 22-tonne skip; and (4) two future UG2 skip compartments (each to accommodate a 13-tonne skip). The Services shaft will comprise a personnel and equipment cage compartment (40 persons), plus a cage counterweight compartment.

Four winders will be used during the project construction phase and three during the production phase. The height of the Main shaft headgear will be 58.6m, and the Service shaft 41.3m.

Project schedule
The development of site infrastructure commenced in March 2009, and the civil works for the headgear foundations and winder houses commenced in February 2010. Installation of the overhead power lines between the BRPM mine and the project site began in March 2010. The shaft sinking contractor is expected to start on site at the end of 2010.

Production ramp-up will begin in 2015, with the planned commencement of stoping in February of that year. Steady state should be reached in 2017. The Merensky reef (phase 1 project area) ore body should be depleted in year 2044, giving the mine a lifespan of approximately 30 years.

The project is currently ahead of schedule (10% complete) and well under budget. All bulk earthworks on the project site have been completed and bulk civil works necessary for the start of shaft sinking are currently under way and are due for completion by the fourth quarter of 2010.

Project Team