Wholly-owned and managed projects in study phase include Bloemhoek, De Bron Merriespruit and Beisa. Bloemhoek and De Bron Merriespruit are both gold projects, which form part of the Southern Free State (SOFS) exploration project area.
Sibanye-Stillwater’s subsidiary, WitsGold (Pty) Ltd. (WitsGold), was granted a mining right under DMRE Ref No FS30/5/1/2/2/10005 MR to extract gold, silver and uranium from a 170.22km²area. The right was granted on 25 February 2014, executed on 14 June 2017 and is valid to 13 June 2040.
Summary:
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 reworking of underlying reefs is believed to play a strong role in controlling the gold and uranium mineralisation in the Beatrix Reef. The Leader, B and Kalkoenkrans Reefs all subcrop against the Beatrix/VS5 unconformity. All the unconformities are channelized to some degree, so subcrop patterns are complex. Consequently, gold mineralisation increases south of the respective subcrops, as the Beatrix Reef becomes more oligomictic and is characterised by large durable clasts and heavy minerals, including gold mineralisation due to re-working of the underlying material.
To the north of the project area, limited erosion of the Aandenk Formation has taken place and the Beatrix Reef is developed as an oligomictic conglomerate with large but angular clasts and characterised by lower gold grades. To the south the upper conglomerate bands in the Kalkoenkrans Reef are eroded and incorporated into the Beatrix Reef, with a resultant increase in gold grade.
Kalkoenkrans Reef
Historically, the identification and lateral continuity of conglomerate reefs in the Aandenk Formation were poorly understood due to their irregular preservation below the Eldorado unconformity. These correlation problems resulted in the recognition of up to five different reefs in the Aandenk Formation, all of which were considered to be laterally discontinuous bodies. A re- evaluation of all of the available surface drillholes as well as using published information from underground exposures at Beatrix 4# has resulted in a simplified geological model that has correlated all of the lower Aandenk conglomerates with the Kalkoenkrans Reef. The lateral variability in the characteristics of the Kalkoenkrans Reef can now be related to channel development at the base of the reef, a situation that has been recognised in the adjacent mining operation at Beatrix 4#.
The recognition of the lateral continuity of the Kalkoenkrans Reef, albeit with some internal variation due to channeling, has significantly elevated the importance of this reef as a regional exploration target. Within the DBM Project, the Kalkoenkrans Reef subcrops below the Beatrix Reef in the extreme southern portions but is virtually conformable with the Beatrix Reef over much of the project area. Variations in middling between the two reefs are attributed to channel development at the base of the Kalkoenkrans Reef.
In the DBM Project, northwest-southeast trending zones of higher gold values occur through the central and southern portions. Vertically within the reef zone the highest gold grades invariably occur in the basal conglomerate, where flyspeck carbon may be present.
B Reef
These polymictic conglomerates overlie an unconformity at the base of the Spes Bona Formation. The B Reef is one of the most unpredictable reefs in the Free State Goldfield, due to its variable geological characteristics as well as gold content. Over short distances it may vary from a barren pebble lag to a thick (up to 3 m) coarse conglomerate with spectacular gold values. Generally, high gold values are associated with the presence of large rounded pyrite grains and carbon. The variability of this reef is generally attributed to narrow, often deeply incised, channels that can only be delineated by dense drilling or with underground on-reef development. Although conglomeratic B Reef is consistently intersected in the DBM Project, it represents a secondary exploration target and would be unlikely to be considered a primary reef in a mining plan.
Leader Reef
The Leader Reef is a tabular body at the base of the Dagbreek unconformity. The lower portion of the Dagbreek Formation is generally characterised by interbedded lithic protoquartzites, conglomerates, pebbly quartzites and scattered pebble zones that may be several metres thick. These conglomerates are typically oligomictic with medium to small quartz and chert pebbles.
The Leader Reef has been mined extensively at Merriespruit Gold Mine, although there is a regional south-westerly decrease in gold content to between 2.5 g/t and 5.0 g/t. This trend is reversed south of the Intermediate Reef subcrop, where reworking of the Intermediate Reef and the development of up to three carbon seams within the Leader Reef leads to elevated gold and uranium grades. The Leader Reef is typically bottom loaded with respect to both gold and uranium mineralisation. Elevated gold grades above 5 g/t are generally associated with cumulative conglomerate thicknesses of greater than 50 cm which contain flyspeck or seam carbon.