Four major sediment-hosted lead-zinc-copper-silver deposits: Broken Hill, Swartberg, Big Syncline and Gamsberg, occur in the Aggeneys area.

The Deep ore body?s western extremity is approximately 390 m east of, and 240 m below, the current deepest level of the mine (800 m below surface). It has a known down plunge extent of 1 100 m and is open at depth. The deepest position of the ore body is 1 680 m below surface. The Deep ore body is sub-divided into five geologically distinct zones each comprising of iron formation and massive sulphide. Lead -zinc copper-silver mineralisation occurs as fine to coarse disseminations or interbanded in the iron formations. Mineralisation in the massive sulphide is fine-grained and often brecciated. Economic ore occurs in all of the five ore body zones and is predominantly situated at or close to the footwall of each zone. The Deep ore body is contained in a synformal structure with a steep (63°-70°) and extensive southern limb.

The dip is to the north at 55° (fifty-five degrees) near surface and varies from almost sub horizontal to 40° in the lower western portion of the ore bodies. The contacts of the massive sulphide ore with the host rock are sharp. The ore bodies extend over a strike length of 1,600m from a surface outcrop in the west to about 800m in the east. The stratigraphy consists primarily of footwall schists, which contain little or no water. An unconsolidated weak zone 3m thick, consisting of graphite and mica rich ground, occurs in the footwall. The ore bodies and the hanging wall quartzite?s contain water which is associated with fissures and cracks.

The ore body is exploited by means of a surface vertical shaft having a 7.4m diameter, sunk to a depth of 1,752m below collar, and by the extension of the main decline of the Broken Hill mine. The decline from Broken Hill mine have dimensions of 5.5m x 4.7m ramps down at an inclination of –15% (8.5° or 1:6.7). The stoping method is Ramp-in Stope (RIS) cut and fill. The RIS method was developed from the sub level cut and fill method; the only difference being the position of the access ramp, which in RIS is also in ore. RIS cut and fill has the important advantage of reducing the amount of secondary waste development required for access to the stopes.

The concentrator at Black Mountain Mine (BMM) treats ore from the Broken Hill Deeps ore body. Ore can also be supplied from the Broken Hill, Swartberg and Gamsberg ore bodies.

The blasted material is taken for crushing. A crushing section is where the ore is crushed by primary, secondary and tertiary crushers to a final product size of –12mm with an 80% passing. Dust generated in this section is suppressed by a dust suppression system to clean the dust-laden air prior to it being discharged to atmosphere (see crushing circuit below).

Following the crushing section there is a wet grinding section consisting of a rod mill and ball mill, which does not produce dust, where the crushed ore is further reduced in size to facilitate flotation of the various minerals. The rod mill discharge is fed to the first stage cyclones (6 cyclones – 4 in use, 2 stand-by), the overflow is gravity fed to the aeration circuit and the underflow goes into the second stage cyclone feed sump.

The cyclone overflow feeds the aeration circuit. From the aeration cells it is pumped to the first conditioner tank of the copper flotation circuit.

Flotation is an extraction process in which the mineral particles are fed in the form of pulp into a bank of flotation cells in which the pulp is agitated by impellers and air is bubbled through. By suitable chemical conditioning the desired mineral can be made to adhere to an air bubble so that a mineral-rich froth is removed and cleaned in further flotation stages, where after it is thickened and filtered to obtain the mineral concentrate.