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. Mining is conducted to a depth of 1 978m. The operation focuses on narrow-reef conventional mining of the South Reef. The South Reef is a narrow reef, exploited by means of conventional stoping.

Mining of the Kimberley Reef was suspended during FY14 so as to focus on the build-up of mining of the South Reef and to prevent losses resulting from the lower gold price. Mining of the Kimberley Reef may be resumed should economic circumstances improve sufficiently.

The mining method used is longwall mining with stability pillars being left 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 the long lead times between the start of cross cut development to completion of stoping per raise line.

The ore mined at Doornkop is processed at Doornkop’s carbon-in-pulp plant, situated directly next to Doornkop shaft.

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.