Zondereinde mine is underlain by both the Merensky and UG2 ore bodies, which dip at approximately 20º and extend from a depth of 1 200 metres below surface (mbc) to 2 900 mbc and the company exploits both reefs of the upper critical zone of the Bushveld Igneous Complex.
While there is lateral continuity of both reefs across the mine property, the Merensky reef displays a variety of reef types. The distribution of these is determined from a combination of ongoing prospect drilling from underground development, supplemented by reef mapping in development and stoping. In contrast to the Merensky reef, the UG2 reef displays little variation in reef attributes.
The Bushveld sequence at Zondereinde is typical of the northern portion of the western limb. The critical zone stratigraphy is telescoped and dominated by mafic lithologies. The average separation between the UG2 and Merensky reefs range from 20m to 40m.
The Merensky reef is a zone of mineralisation which straddles the base of the Merensky Cyclic Unit. In the area of Zondereinde mine the Merensky reef consists of two sub-facies of the Zwartklip facies of the RLS, namely the normal and regional pothole sub-facies. The latter may be further subdivided into three reef types, each of which occurs at a specific stratigraphic level below that of the normal reef sub-facies, the NP2 and P2, which constitute the main sources of ore, and FWP2 which, whilst not considered a primary mining target owing to the undulating nature of this reef type, is successfully exploited in the south western quadrant of the current mining area where it displays lesser disruption.
The stoping cut on the Merensky reef is dependent upon the reef type mined, and the geozone in which it is located. In all stoping cuts, the Merensky chromitite is exposed with a minimum of 10cm of the overlying, mineralised Merensky pyroxenite as hanging wall.
The measured resource is an estimate of the in situ tonnage, grade and PGM ounces that have been exposed through development, and is immediately available for mining. The Merensky measured resource has marginally increased from 2.04Mt (547 000oz) in June 2009 to 2.21Mt (581 000oz) in June 2010. This is the result of an increase to the exposed Merensky resource, combined with the application of a lower resource grade in the western portions of the resource block.
The UG2 reef at Zondereinde mine is remarkably conformable when compared with the Merensky reef. Reef disruption, in the form of potholes and reef rolls is extremely limited and localised. The reef consists of three chromitite seams separated by narrow pyroxenite partings. The lower seam, termed the main member, is generally in the order of 75cm thick, and is overlain by two leader seams, each in the order of 15cm thick. Total reef thickness, inclusive of a portion of mineralised reef footwall, is in the order of 140cm to 150cm. There is no basis for subdividing the UG2 reef into facies types
Historically, UG2 mining has been limited to de-stressed areas underlying previously mined Merensky reef. Furthermore, a full reef cut is mined, which enhances metal output, hanging wall stability and safe working practices.
For more in depth information please refer to the Geology section of the Zondereinde technical report (857KB).