Chromite operations at the Dwarsrivier Mine form part of the Chrome Ores & Alloys of Assmang Limited. The mine is situated on the farm Dwarsrivier (372KT), approximately 30 kilometres from Steelpoort and 60 kilometres from Lydenburg, in the Mpumalanga province in South Africa. Located at longitude 30°05’00”E/latitude 24°59’00”S, Assmang purchased the farm from Gold Fields Limited, together with all surface and mineral rights in October 1998.
Neighbouring properties to the north and south of Dwarsrivier had existing chrome mining operations at the time of purchase. The feasibility study of the plant, tailings dam and designs for the open-cast and underground mines then commenced. After the completion of the feasibility study, approval to proceed with the final design and construction work was given in July 1999.
All the chromite production from Dwarsrivier Mine is sourced from underground. Chromite used to be obtained from the open-cast mining areas at a rate of approximately 0.9 million tons per year; however these reserves were exhausted in 2005. Underground mining commenced in 2005 at a rate of 1.2 million tons Run of Mine (ROM) per year. Current underground design capacity is 120,000 tons per month ROM. The Dwarsrivier Mine is specifically geared to deliver high quality metallurgical grade chromite to the Machadodorp Works. In addition the plant has been designed to produce chemical grade products. The mine has ISO9001/2008 and ISO14001/2004 certification.
The Dwarsrivier Mine is situated in the eastern limb of the Bushveld Complex, which comprises persistent layers of mafic and ultramafic rocks, containing the world’s largest known resources of platinum group metals, chromium and vanadium. The mafic rocks termed the Rustenburg Layered Suite, are approximately 8 kilometres thick in the Eastern Lobe, and are divided formally into five zones.
The rocks of the Marginal Zone at the base of the succession consist mainly of pyroxenites with some dunites and harzburgites. Above the Marginal Zone, the Lower Zone comprises mainly pyroxenites, harzburgites and dunite, and is present only in the northern part of the Eastern Lobe, and only as far south as Steelpoort. The appearance of chromitite layers marks the start of the Critical Zone, economically the most important zone. The layers are grouped into three sets termed the Lower, Middle and Upper groups. The sixth chromitite seam in the Lower Group (LG6), is an important source of chromite ore and is the orebody being mined at the Dwarsrivier Mine. In the Eastern Lobe, in the vicinity of Dwarsrivier, the strike is nearly north-south, with a dip of approximately 10 degrees towards the west. Average thickness of the LG6 seam is about 1,86 metres in the Dwarsrivier area. Pipe-like dunite intrusions are evident in the area, as well as dolerite dykes that on average strike northeast-southwest. No significant grade variation is evident, especially not vertically in the ore seam. Small, insignificant regional variations do, however, exist.
|Lumpy/Chip||Metallurgical Fines||Chemical Fines|
|Cr2O3 38% min||Cr2O3 44% min||Cr2O3 46% min|
|SiO2 9% max||SiO2 4% max||SiO2 0.9% max|
Dwarsrivier Mine currently operates with a complement of 1,165 employees. In addition, certain functions such as tailings dam operations, as well as security services, health services, garden services and office cleaning services are outsourced.
The mine is currently developing a North shaft which, when complete, will add a further 80,000 tons of ROM material per month to the current capacity. The beneficiation plant will be expanded to cater for the additional feed.