The principal gold-bearing ore body at the Tshepong and Phakisa sections is the stratiform and stratabound Basal Reef (known as the Basal Reef Zone or BRZ). This unit comprises a thin conglomerate at the base of the BRZ, overlain by clean ‘placer’ quartzites. The BRZ is underlain by a thick series of siliceous and argillaceous quartzites comprising the Welkom Formation and is overlain by shales and quartzites of the Harmony Formation, both of the Johannesburg sub-Group of the Central Rand Group. Although not apparent within the Mines Lease, the BRZ sits unconformably on the Welkom Formation.

At the Phakisa section, the reef dips towards the east at 25° in the north and up to 45° in the south. The Lower Cycle Black Chert facies predominates in the north with a north-west south-east value trend. The reef consists of an oligomictic small pebble matrix-supported conglomerate lag with fly-speck carbon contact. The rest of the reef package constitutes barren siliceous fine-grained reef quartzite. The entire reef package reaches up to 160cm thick and is overlain by 1cm – 30cm of lower Khaki Shale. This in turn is overlain by the approximately 3-4m thick Waxy Brown Leader Quartzite, above which lies the 3-4m thick Upper Khaki shale.

The Upper Cycle Black Chert facies Basal Reef prevails in the south of the lease area, and consists of a slightly polymictic (yellow shale specks present), matrix-supported medium pebble conglomerate with a more gradational contact absent of carbon where mineralisation is associated with fine disseminated and buck-shot pyrite. The conglomerate is slightly thicker compared to the Lower Cycle, but is also overlain by barren reef quartzite, the entire package reaching characteristically up to only 40cm thick. The lower Khaki Shale is up to 1m thicker.

The Central Rand Group itself is overlain in turn by lavas and sediments of the Ventersdorp System and the more recent sediments of the Karoo Group.

The B Reef occurs approximately 150 metres stratigraphically above the Basal Reef (or approximately two production working levels). Consequently, the B Reef is not normally intersected in either Basal Reef development or routine diamond drilling.

The lowest unit is a basal lag (Zone A), sitting on the underlying Doornkop Quartzite Formation. Where this unit is developed (or preserved), it may be highly mineralised oligomictic or polymictic conglomerate, with visible gold, buckshot pyrite and carbon mineralisation. This unit may carry gold values of many thousands of cmg/t and represents a potentially rewarding exploration target.

The unit overlying the Zone A may be either Zone B, which is comprised of a mildly erosive pebbly quartzite formation, and/or the stratigraphically younger Zone C, which is a polymictic conglomerate with low values which is also erosional into the underlying A and B zones.

Nature of the operation
The Tshepong section is a mature underground operation mining at moderate depths of between 1 600m and 2 400m below surface. The bulk of mining currently takes place in the decline (Sub 66) and northeastern portions of the lease area.

The Phakisa section is a moderate- to deep-level conventional underground operation, which together with the Tshepong section makes up the Tshepong Operations. Currently, mining activity takes place largely in the north and south of the mine lease area. However, over the next three years the focus will shift solely to the south of the lease area.

Mining method and mine planning
At the Tshepong section, the reef horizon is accessed via conventional grid development. The shaft’s primary economic reef horizon, Basal Reef, is extracted by undercut mining, leaving a quartzite beam in the hangingwall to ensure the stability of the overlaying shale. Minor amounts of B Reef that do not exceed 18% of the on-reef area mined annually are extracted via open stoping mining. The B Reef is located approximately 140m stratigraphically above the Basal Reef, necessitating separate infrastructure (footwall development) from that for the Basal Reef. The presence of khaki shale approximately 6m thick above the Basal Reef strains the footwall development rates of the B Reef, requiring the installation of ring sets for the first 25m of development. The Tshepong section has significant Ore Reserves to maintain a longterm mine life, however, extraction of ore from pillars will become more important as the life of mine progresses, but volumetrically these reserves are not significant.

At the Phakisa section, the Basal Reef is mined conventionally from a single shaft barrel reaching a depth of 2 600m below collar. The reef horizon is accessed by means of conventional grid development and is extracted as an open mining operation to the south of the 69 raise line, but undercut mining has begun as mining progressed north. Phakisa reached full production in October 2016. Pillar mining crews are also planned as the life of mine progresses to ensure depletion of the pillar reserves within the life-of-mine time frame.

Infrastructure
The surface and underground infrastructure for Tshepong section as well as the power and water supplies available exceed planned peak production requirements. Broken rock handling above 66 level is track-bound, with the rock transferred to several inter-level sub-vertical transfer systems that are gravity fed to the main silos on 68 level. Broken rock handling below 66 level is track-bound, transferred to a decline belt system that feeds to the silos on 66 level from where the rock is transferred by track to the main inter-level sub-vertical transfer system on 66 level. The rock is hoisted to surface through the main shaft. From the shaft, the rock is transported to the processing plant by train.

At the Phakisa section, surface and underground infrastructure as well as the power and water services available exceed planned peak life of mine production requirements. Broken rock handling on all levels is track-bound. Several inter-level sub-vertical transfer systems feed the main silos on 77 level from where the rock is hoisted to 55 level. A rail-veyor system transports the rock from Phakisa to the Nyala shaft and from here the rock is hoisted to surface by means of the koepe winder, and then transported to the processing plant by train.

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.

Harmony One Gold Plant is located near Bambanani shaft, on the southern edge of the City of Welkom in the Free State Province of South Africa. The plant was built in 1986, and the milling, leaching and carbon-in-pulp technology reflects the technology which was current at the time. Plant design capacity is 390,000 tpm (tonnes per month), steady state. The operations at the Harmony One Plant consist of the following.

Stoping ore and development rock from the Tshepong section are hoisted and processed separately above 66 level. Below 66 level, stoping and development rock is hoisted and processed as one product currently.

At the Phakisa section, stoping ore and development rock are hoisted and processed separately. The reef, stoping ore, is milled and processed at Harmony one plant with gold recovered by means of cyanide leaching.

Tshepong operations shares the Harmony One plant with three other Harmony operations and four Harmony waste rock dumps. The ........