Unisel mines gold-bearing reefs from the Witwatersrand Super Group, which is situated on the Kaapvaal Craton. The mine lies in the Free State goldfields on the south-western edge of the basin. The Basal and Leader reefs are the main economic horizons in the Unisel area. The Basal Reef occurs at the base of the Harmony Formation and overlies the footwall beds (Welkom Formation) with a marked unconformity. This erosional unconformity cuts progressively deeper into the footwall when traced from north to south. The Leader Reef lies at the base of the Dagbreek Formation. The separation between the Basal and the Leader reefs varies from subcrop of the Basal against the Leader Reef in the west to 17m in the eastern areas of the lease. The subcrop is beyond the mine lease area, within the lease area between the two major gold-bearing reefs, which varies from 13m in the west to 17m in the east. The Middle Reef is a channelised deposit forming a discreet channel running from west to east. This channel lies to the north of the shaft. Stratigraphically, it lies between the Basal and Leader reefs.

Structurally, the sedimentary package, within which Unisel mines, strikes north south and dips to the east with dips ranging between 25 and 40 degrees. Faulting consists predominantly of north-south trending normal faults dipping to the west with a right lateral displacement. The most significant is the Stuirmanspan fault of about 800m and the Unisel fault of 110m. West-east trending thrust faults cut through the property.

Igneous intrusions, in the form of dykes and sills, are present with the sill lying sub parallel to the Basal and Leader reefs with an effect on mining operations with the reef horizon split by the sill.

Unisel is a mature, underground, single-shaft mining operation, operating at depths from 1 100m to 2 200m below surface. Mining operations are scattered and, due to the age of the shaft and the extent of mining, lie 2-4km from the shaft.

Mining operations take place from 2 level down to 13 level, by means mainly of breast panel mining. Limited down-dip panels and wide raises are undertaken periodically. Footwall development comprises haulages and crosscuts with service ways and ore passes developed to access the reef horizons. Face length cannot exceed 30m and strike pillars are left as support between the panels. Planning to extract higher-grade portions of the shaft pillar has begun. This ground will be extracted by means of breast panel mining, as described above.

Unisel does not have its own mineral processing plant. The ore mined is transported by rail for 8km to the Harmony One plant for processing.