The mineral assets are historical gold plant tailings material from the mining of auriferous and uraniferous ore from the goldbearing, late Archaean (2.7Ga to 3.2Ga), Witwatersrand Basin in the West Rand Goldfield. The typical composition is quartz (70 – 80%), mica (10%), chlorite and chloritoid (9% – 18%) and pyrite (1% – 2%). Gold, uranium oxide, zirconium and chromium are minor constituents.

The composition of a TSF depends on the geochemical make-up of the material being mined and the chemicals used in the mining and extraction process. Further, the internal structure of the TSF reflects the mining strategy and depositional methodologies employed for each operation. The bulk density of tailings material and the lateral and vertical variation in moisture content is a critical factor in the accurate estimation of tonnages. In addition, secondary processes such as metal re-mobilisation, erosion, weathering, leaching and acid mine drainage can affect the geochemical characteristics of a TSF. Gold can undergo mobilisation within the TSF over time, and hence, may exhibit areas of re-concentration, and even be present in the sub-structure (footprint) soil. These factors can result in a considerable variation in gold content and distribution throughout the TSF and such variation has an impact on final recoveries and projected revenues for the operation.

Hydraulic mining (hydro-mining) using high-pressure water cannons to hydraulically excavate tailings material. A second mining method employed by Ergo is the use of front-end loaders (FEL) to load slimes/sand. The FEL loads directly into a truck which then transports the ore to the processing plant.

Ergo’s assets include multiple TSFs, a 50km pipeline, and tailings deposition facilities including the significant Brakpan/Withok TSF. Sandy material is reclaimed using mechanical front-end loaders, re-pulped with water and pumped to the plant. Tailings are reclaimed hydraulically using high pressure water monitoring guns. The re-pulped slime is pumped to the plant and the reclaimed material is treated using screens, cyclones, ball mills, and Carbon-in-Leach (“CIL”) technology to extract the gold.

At the Ergo plant, material is delivered via two feeder lines from the Elsburg tailings complex, Van Dyk and the 4L30 reclamation sites. A further 0.5Mtpm is delivered from the City Deep area (including 4L2, 3L42 and externally sourced material). Material treated at the Knight plant is deposited onto the Brakpan/Withok TSF shared with the Ergo plant.

At FWGR, the upgraded Driefontein No. 2 Plant currently treats around 0.5Mtpm of material from Driefontein 5 TSF. Tailings ........