Work advances on Twickenham decline shafts and infrastructure

16th December 2011 By: Sinette Goosen

Work on the Twickenham platinum mine project is reportedly progressing well and is expected to gain momentum after being delayed by three years.

The Twickenham project, which is fully owned by the world’s largest primary producer of platinum-group metals, Anglo American Platinum (Amplats), has been put on hold several times owing to economic uncertainties, the dwindling platinum price and decline in demand for the metal during the recession.

However, Amplats has now recommitted itself to the project and has given contractors the go-ahead to continue with work on the decline shaft and infrastructure. Engineering project house TWP, which is a subsidiary of Basil Read, was appointed engineering, procurement and construction management (EPCM) consultant in 2008.

A feasibility study indicated that through the develop- ment of mining infrastructure and decline shaft complexes, the operation could deliver 250 000 t/m of ore from the Twickenham and Hackney decline shaft complexes once a steady state is achieved.

The project scope includes surface infrastructure to support the mining methodology for each shaft and a central services area, which includes a concentrator plant with the capacity to treat 250 000 t/m of run-of-mine ore. This greenfield project is about 35 km north-west of Burgersfort, in Limpopo.

It will exploit the Twickenham and Hackney areas by initially mining the upper-group-two reef. Earlier this year, Amplats reported that incremental production was expected to be 180 000 oz/y of refined platinum. A full production rate of three-million tons a year should be reached in 2019.

Amplats approved R7.1-billion to develop the project. Progress Update Mining Weekly understands that construction of the Twickenham and Hackney decline shaft systems is under way. The declines will be extended to 650 m below surface; at this depth, refrigeration will be implemented. Each shaft reportedly consists of three barrels located in the footwall.

The barrels comprise a trackless access, a conveyor belt for ore removal and a chairlift to transport personnel. The mining methodology is based on a conventional track-bound haulage system with footwall drive and a scattered breast mining method.

Another key feature of the project scope includes the approved life-of-mine footprint, which extends down to Level 7, with 11.6 km on strike. The footwall infrastructure and on-reef excavations are being developed to open 250 000 t/m of stoping reserves on ten operating half-levels.

Efforts are being made to ensure that enough stoping reserves are available to be mined for 18 months, if development on the reserves should be halted. Further, the required surface- and underground-engineering infrastructure to support a production rate of 250 000 t/m from the two declines will be established. Steady state production is planned from five levels.

Stoping of the reef will use the well- proven methods of breast mining with face scraping as currently used by Bokoni platinum mine.

Further, battery-powered locomotives and hoppers will collect the broken ore on each level and deliver it to the station tips, from where it will be transferred by a series of decline conveyors to surface silos. From the silos, 33 t on-highway trucks and trailers will be used to transport ore to the concentrator.

Meanwhile, surface- and underground-engineering infrastructure will be required to facilitate a nonpneumatic mining strategy with hydraulic-powered drilling and loading equipment used for primary off-reef development. Drilling for drop raising is also performed by hydraulic- powered rigs.

The central area comprises the bulk infrastructure for potable water, raw water and sewerage. State-owned power utility Eskom’s electricity supply centre will be based at the central area, as will the electricity reticulation, buildings for protection services and the medical facility for the Twickenham business unit.

About 5 000 people will be employed once the Twickenham platinum mine is in full production.