The main structures at Joel are associated with the Platberg Extension. These faults are north-south striking, steeply dipping and typically have downthrows to the east of 10m to 100m. These downthrows form a graben against the De Bron Fault, which has a 450m upthrow to the east. East of the De Bron Fault, the reef has been either truncated or eroded against the Karoo Supergroup.

Minor east-west striking faults are also present. However, displacements on these faults are generally less than 10m, which are believed to be Klipriviersberg in age. Low angle reverse faulting is also present. These structures trend north-south, have small displacements and dip towards the east. These structures may be related to the central Rand Contractional event.

The Klippan Formation has been preserved as an east-west trending erosional channel that has eroded deeply through the Witwatersrand sediments and has eliminated the Beatrix/VS5 horizon in the eastern portion of the mine and cut out a significant chunk in an east west direction through the middle of the lease area. Regionally the Klippan Formation is preserved in the north-south striking basin, known as the Virginia Basin in the Southern Free State, which parallels the De Bron Fault.

A deep erosional channel of Platberg Group volcano-sedimentary rock, known as the Klippan Channel, truncates the Beatrix Reef some 1.8km to the north of south shaft. This washout feature is wedge-shaped with its apex to the west and widening to the east. The estimated dimension from the apex to the eastern property boundary is approximately 1.8km. The reef has been shown to be continuous to the north of this feature.

Where unaffected by the Klippan Channel, the reef is bound to the east by the De Bron Fault, which strikes north-north-east. The CD Fault, which strikes north-east and is roughly halfway between the two shafts, has a 320m sinistral lateral displacement south of the fault towards the north-east.

The complex nature of the reef has resulted in a highly irregular distribution of gold throughout the mining area. There are broad low- and high-grade zones over hundreds of metres, which are considered likely to be repeated within the reef environment beyond the limits of the current development. However, the detailed grade distribution within these zones remains very unpredictable.

For the purposes of resource estimation, a detailed facies model is used and is based on detailed sedimentological observations.

Joel operates at an intermediate mining depth and the mining method is tailor-made for the variable grades intersected as well as the associated rock-related hazards anticipated at this depth.

Given the variable grades and geological complexity, mining is conducted mainly in terms of a pre-developed scattered mining system. This system allows for unpay and geologically complex areas to be left unmined with some cognisance taken of the overall panel configuration and stability of footwall development. This allows for selective mining, based on the proven ore reserve during the development phase.

In addition, stoping panel stability in an intermediate stress environment may require additional stabilising pillars be left to support the immediate hangingwall. These take the form of inter-panel crush pillars between neighbouring mining panels. The major rock-related risk is the occurrence of unexpected panel collapses.

Minor falls of ground, due to geology, bedding, shale and jointing, do occur but are mostly addressed via a proven in-stope support system. As the largest portion of Joel’s production is currently mined between 129 and 137 levels, production is focused mainly on four raise lines this year but the plan is to increase this to five raise lines before the end of next year.

In addition, as mining has advanced into more complex geological areas, dip- and strike-related structures are more commonly intersected. The change to a higher support resistance system, given the intersection of a more complex geological environment, has been largely successful and the occurrence of large geological “back breaks” and falls of ground are rare. Timber-based packs were installed along gullies and as breaker line support in panels to improve hangingwall stability. From a management perspective, it is of utmost importance that geological structures are reported, mapped and properly supported using high-support resistance pack units to ensure a stable stoping horizon.

With the marginal increase in depth and the more complex geological environment, the incidence of low magnitude (<1.5) seismic events has slowly increased. This activity has manifested mainly in reasonably low stress (45Mpa) strike-orientated dyke intersections with stoping excavations. The installation of a 10-station regional seismic network to highlight potentially unstable areas and structures prone to bursting was completed with the seismic data used to highlight potential problem areas. The seismic network is maintained, and its operational and health status are kept well above the 80% mark

The Joel plant was decommissioned in FY19 and ore mined is processed at the Harmony One plant.
[OPERATIONAL PERFORMANCE 2019. P.19]

The ore is taken up the slow-moving conveyers from underneath the silos and discharged directly into the feed hopper for the six fully autogenous mills. For control purposes the mill feed belts and the mill discharge pumps both have variable speed drives. Each mill is a closed circuit with a 1200mm primary cyclone with mass flow measurement on the feed. The primary cyclone overflow is screened on a 600µm linear screen for the removal of coarse woodchips and tramp steel.

Calcium Oxide (lime) is added to the 6 thickeners (operating in 3 parallel modules) as slaked lime with levels of CaO being controlled at between 0.014 and 0.016% CaO. The lime maintains a protective level of alkalinity in the leach section to prevent the generation of poisonous HCN (cyanide) gas in the process. Thickening is carried out in six 60m diameter, cable ........