The structure of the West Rand goldfield is dominated by the Witpoortjie and Panvlakte Horst blocks, which are superimposed over broadfolding associated with the southeast plunging West Rand syncline.

The Doornkop shaft lease area is bounded by and lies to the southeast of the major northeasterly striking Roodepoort fault, which dips to the south and constitutes the southern edge of the Witpoortjie Horst block or gap. This Horst block comprises the stratigraphically older sediments of the West Rand Group, the overlying Central Rand Group sediments having been removed by erosion. A number of other faults, forming part of and lying southeast of the Roodepoort fault, including the Saxon fault, also constitute conspicuous structural breaks. A second major fault, the Doornkop fault, which trends in an eastwest direction, occurs toward the southern portion of the lease area. This fault dips to the south and has an up throw to the north.

Nearly the entire upper Witwatersrand section is present in the lease area and therefore all the major zones are present, though due to the distance of the area from the primary source of gold, the number of economic bands and their payability is limited. Eight of the well-known reefs are present in the area, but only the South Reef is considered viable at this stage.

The South Reef is between 7.5m and 60m above the Main Reef horizon. The hanging wall to the South Reef consists of siliceous quartzites with non-persistent bands of ‘blue-shot’ grit and thin argillite partings. The footwall to the South Reef is a light coloured and fairly siliceous quartzite. Secondary conglomerate bands and stringers in the hanging wall and footwall of the South Reef may contain sporadic gold values. The general strike of the reef is eastwest, with a flat dip from 5 to 15 degrees. Due to the limited geological information, one of the biggest risks for the operation is the intersection of any geological structures that may have a significant change in the reef elevations which can result in some of the resources ending up below infrastructure, rendering it inaccessible from current levels with a potential to negatively affect the declared reserves. To curb this risk, Doornkop has embarked on extensive exploration drilling from underground platforms.

Doornkop, a single-shaft operation, is located in the Gauteng province of South Africa, approximately 30km west of Johannesburg, on the northern rim of the Witwatersrand Basin. Mining is conducted to a depth of 2219m below surface, with ore hoisted through the main shaft. The operation focuses on narrow-reef conventional mining of the South Reef. Ore from the operation is processed at the Doornkop plant, a carbon-in-pulp plant. [OPERATIONAL PERFORMANCE 2019. P. 17]

The mining method used is longwall mining with stability pillars on major geological structures. The flat dip, which results in the development of long cross cuts, presents challenges in terms of ore handling, especially for the bottom part of the raises, ventilation and in the long lead times between the start of cross cut development to completion of stoping per raise line.

The gold plant consists of a milling section for grinding of ore, thickeners for dewatering (pulp for leach feed), a leach section for dissolution of gold, using liquid sodium cyanide as one of the reagents, Carbon in Pulp for adsorption of dissolved gold and a recovery section which consists of elution, electro-wining and a smelt house. All tailings are pumped to a Tailings Storage Facility, adjacent to the plant on the northern side.

The Doornkop TSF consists of one active compartment which is raised in the upstream direction. The residue is deposited hydraulically by means of ring feed pipeline to open ended pipe deposition points along the day wall, pool wall including the wing walls both sides of the penstock and into the basin. All supernatant and storm water is decanted off the deposits through a gravity penstock that discharges into a canal draining to the return water dam located east of the TSF. From the return water dam, the water is pumped back to the plant for reuse.