Joel is located in the Free State Province on the southern edge of the Witwatersrand Basin.

The basin, situated on the Kaapvaal Craton, has been filled by a 6km thick succession of sedimentary rocks, which extends laterally for hundreds of kilometres.

The Free State goldfield is divided into two sections, cut by the northsouth striking De Bron fault. This major structure has a downward vertical displacement to the west of about 1 500m in the region of Bambanani, as well as a dextral shift of 4km. This lateral shift can allow a reconstruction of the ore bodies of Unisel to the west of the De Bron and Masimong to the east. A number of other major faults (Stuirmanspan, Dagbreek, Arrarat and Eureka) lie parallel to the De Bron fault.

To the west of the De Bron fault, current operating mines are Target, Tshepong, Phakisa, Unisel, Bambanani and Joel. Dips of the reef are mostly towards the east, averaging 30 degrees but become steeper approaching the De Bron fault. To the east of the fault lies Masimong mine. These reefs mostly dip towards the west at 20 degrees, although Masimong is structurally complex and dips of up to 40 degrees have been measured. Between these two blocks lie the uplifted Horst block of West Rand Group sediments with no reef preserved.

Most of the mineral resource tends to be concentrated in reef bands located on one or two distinct unconformities. A minority of the mineral resource is located on other unconformities. Mining that has taken place is mostly deep-level underground mining, exploiting the narrow, generally shallow dipping tabular reefs.

The Basal Reef is the most common reef horizon and is mined at all shafts except Target 1 and Joel. It varies from a single pebble lag to channels of more than 2m thick. It is commonly overlain by shale, which thickens northwards. Tshepong has resorted to undercutting in its mining panels to reduce the effect of shale dilution.

The second major reef is the Leader Reef, 15m to 20m above the Basal Reef.

The B Reef is a highly channelised ore body located 140m stratigraphically above the Basal Reef.

Joel mine, 30km south of Welkom, is the only Harmony Free State operation to mine the Beatrix Reef. This reef varies from a single pebble lag to a multiple conglomerate, often showing mixing of the reef with some of the overlying lower-grade VS5 (mixed pebble conglomerate) material. None of the other reefs are present this far south, having sub-cropped against the Beatrix Reef.

The mine comprises two shafts: North and South. The primary economic reef horizon is a narrow tabular Beatrix Reef deposit, which is accessed via conventional grid development. Mining is currently being conducted to a depth of 1 379m below collar.

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

Due to variable grades as well as geological complexity, the mining is conducted mainly in terms of a pre-developed scattered mining system. This system allows for un-pay 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 mining to be selective based on the proven ore reserve during the development phase.

In addition, the stability of stoping panels in an intermediate stress environment, may require additional stabilising pillars be left to support the immediate hangingwall. These take the form of interpanel crush pillars left between neighbouring mining panels. The major rock-related risk is 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 production currently being mined between 121 and 129 levels, production is relatively concentrated to four or five raise lines.

Mining also has progressed to more complex geological areas and dip and strike related structures are more commonly intersected. The changes to higher support resistance systems due to the intersection of more complex geological environment has been largely successful and the occurrence of large geological driven “back breaks” and falls of ground are rare. Timber-based packs were introduced along gullies and as breaker line support in panels to improve hangingwall stability in these areas. 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.

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 ........