The Stillwater Complex is a large layered igneous complex resulting from magma intrusion through regional transverse faults into highly deformed Archaean sedimentary rocks. However, the flat-lying part of the Stillwater Complex occurs at significant depth below surface, which makes the exploitation of the J-M Reef in this part of the complex uneconomic.

The magma intrusion and emplacement relating to the Stillwater Complex were accompanied by fractionation and accumulation of magmatic crystals that gave rise to the conspicuous magmatic layering observed in the complex. The magmatic layering is reflected by the changes in mineralogy, mode, grain size and texture across the stratigraphic profile of the complex. However, the overall texture of the lithological units in the Stillwater Complex is typified by subhedral to euhedral cumulate grains in a framework of post- cumulus interstitial material including oikocrysts. The mineralogical, modal, grain size and textural variations formed the basis for subdividing the Stillwater Complex into five major series (from bottom upwards) as follows: the Basal Series, Ultramafic Series, Lower Banded Series, Middle Banded Series and Upper Banded Series. The Ultramafic Series (UMS) is further subdivided into the Bronzitite Zone and Peridotite Zone. The Lower Banded Series hosts the J-M Reef targeted at Stillwater and East Boulder Mines.

The steep dipping nature of the lithological layers in the exposed part of the Stillw ........

The J-M Reef outcrops over a 28-mile strike length on the Sibanye-Stillwater Mining Claims but the topography, altitude and thickness of the reef preclude economic exploitation of the reef through open pit mining methods. Accordingly, waste stripping which would be applicable to an open pit mining is not required. The J-M Reef at East Boulder Mine dips 35° to 55° (averaging 50°) to the north. The shallowest dip (35°) is observed in the far west area accessed by the 6500 Level Footwall Lateral.

Both Stillwater and East Boulder Mines employ the following underground mining methods, whic suited for the variable steep dips and narrow widths of the J-M Reef:
- Captive Cut and Fill stoping, utilising either conventional, AlimakTM or raise boring to create accesses, and the resulting stopes are also known as captive stopes - this method is being phased out;
- Ramp and Fill using overhand or underhand approaches; and
- Sub-level extraction by long hole open stoping with subsequent backfill. Longitudinal and transverse stoping methods are variations of the long hole stoping method in use at the mines.

The mining method mix is adjustable and largely driven by mineralisation grade, ground conditions encountered and the requirement to minimise dilution. The percentage distribution (frequency of use) of the three mining methods within each of the mines since FY2016 indicating the predominance of the mechanised Ramp and Fill method. Ramp and Fill stopi ........

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