Gold and uranium deposits in the De Bron Merriespruit (DBM) Project are hosted by quartz-pebble conglomerates developed on laterally continuous unconformity surfaces. These reefs are generally characterised by shallow dips of between 10° to 25° and thicknesses of 0.6 m to 2.1 m that make them suitable for exploitation by means of typical narrow stoping techniques. However, central to the establishment of any mining operation within the Wits Gold project areas is the delineation of sufficiently large areas of laterally continuous bodies of economically mineralised conglomerates.

The DBM Project is situated on the eastern up-throw side of the De Bron Fault, to the immediate south of Harmony Gold Mine where a triangular block of the Central Rand Group is preserved. Four prospective reefs, namely the Beatrix, Kalkoenkrans, B and Leader Reefs, are developed within a 20 m to 40 m stratigraphic interval occurring at depths of 500 m to 1,200 m below surface. Within the project boundaries, the reefs extend by up to 8 km in a north-easterly direction and as much as 4 km in a north-westerly direction.

Conglomerate Reefs
Three primary reef horizons containing gold and uranium are developed on well-defined regional unconformities in this area. These include the Beatrix, Kalkoenkrans and Leader Reefs, all of which have been mined extensively in the SOFS region. The B Reef is considered a secondary reef horizon.

Beatrix/VS5 Reef
The erosion and re ........

A number of high-level trade-off mining methods were investigated during the first phase of the PFS. Finally two main options were selected for the more detailed final stage of the PFS. The first option (“Option 1”) is based on standard conventional breast mining practiced in the Witwatersrand Basin, while the second option (“Option 2”) investigates a semi-mechanised variation to the down- dip mining methodology currently practiced in the platinum mining industry of the Bushveld Complex.

For both options it is envisaged that a twin shaft system will be sunk to 660 m with a top production level commencing on 560 m, from where a twin decline system will provide access to the deeper parts of the orebody. For both options the off-reef infrastructure has been developed using trackless mechanised equipment to facilitate a rapid production build up with conventional on-reef development in order to minimize dilution. A system of off-reef trackless footwall haulages are developed on strike below the orebody.

For Option 1, cross-cuts to reef are spaced at 180 metres with on-reef raises and conventional breast stoping completing the layout. Option 2 differs from Option 1 in that the on-reef development and mining is done on dip as opposed to on strike.

The mining method for Option 2 involves closely spaced on-reef raises (spaced 30 m apart). Pre- development of these raises will improve orebody understanding and also allows for selective mining and im ........

- subscription is required.

Ore is withdrawn from the mill silos with vibrating feeders and fed to the ROM mills. The mill discharge is pumped to the cyclones where classification by particle size takes place. The cyclone underflow containing the coarse particles is returned to the mill for regrinding while the cyclone overflow containing the fine particles passes to the thickener. A linear screen on the thickener feed removes woodchips and any tramp material such as plastic particles. These particles, if not removed, will blind the carbon screens in the CIL circuit.

If gravity concentration is included in the flowsheet, a portion of the cyclone underflow will be fed into the gravity concentrator. The tailings from the gravity concentrator will be returned to the mill, while the gravity concentrate will pass to the smelthouse for further upgrading and smelting.

Lime and flocculant are added to the thickener feed to aid settling of the finer particles. The lime addition is controlled to prov ........