Regional Geology:
The Kaapvaal and Zimbabwe cartons in Southern Africa are characterised by the presence of large mafic to ultramafic layered complexes. By far the most important and economically viable of these is the Bushveld complex (BC) which was intruded 2.06bn years ago into the rocks of the Transvaal Supergroup along the unconformity between the Magalieburg quartzites and overlying Rooiberg felsites. The total estimated area of the BC is 66 000km squared (about 55% of which is covered by younger formations. The mafic rocks of the BC can be divided into a number of units according to their representative gravity anomalies. These include the northwestern and southwestern lobes, separated by the Pilanesburg Alkaline complex; and the north eastern and south eastern lobes that are separated by the Steelpoort fault.
The mafic rocks (collectively known as the Rustenburg layered suit - RLS) can be divided into five zones known (from the top downwards) as the Upper Zone (UZ), Main Zone (MZ), Critical Zone (CZ) and the Marginal Zone. At the base, the marginal zone consists of generally finer grained rocks than those of the interior of the complex and contains an abundance of xenoliths.
It is highly variable in thickness, may be completely absent in some areas and contains no economic mineralization. The chromite layers are confined to the critical zone and are subdivided into the lower, middle and upper groups. All the layers of the lower group (LG) occur within pyroxenites of the lower critical zone. The middle group (MG) of layers occur at the transition from the lower to the upper critical zone, at a level where plagioclase first becomes persistently cumulus within the whole BC sequence. The Mg chromite layers are either hosted by pyroxenites or by plagioclase-rich norites and anorthosites. The UG of layers occurs within the upper critical zone below the Merensky Reef. The western BIC contains seven LG, four MG and two UG layers.
The most productive layers for chromite have been the LG6, MG4 and MG2 horizons.
Local Geology:
The project area comprises of two distinct chromite mineralisation areas, namely, a southeastern portion and a western graben in which the LG and MG chromites are exposed respectively. The majority of the project area's eastern side is covered by the pyroxenites of the critical zone with the northern parts being covered by quartzites, diabase rocks and shales of the Waterberg Supergroup.
The western block has the entire chromite sequence of the LG6, MG1, MG2, MG3, and MG4 seams. A major fault that lies in the South western portion of the farm displaces the chrome reefs by 1.7km's to the south east. This has resulted in the displacement of the MG chromites present in the south western corner of the project out of the Langpan farm boundary in the south east.
The chrome reefs, as intersected in the trenches, have a northeasterly/southwesterly strike and dip at 20-22 to the southeast. The LG is, on average, 0.83m thick and the thickness of the MG chromites ranges from 0.39 - 1.58m.