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Location: 36 km SW from Burgersfort, South Africa
ARM house 29 Impala Road Chislehurston SandtonJohannesburgSouth Africa2196
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The Two Rivers Platinum Mine (TRP) comprises of both the Merensky and the underlying Upper Group 2 Reefs (UG2). The UG2 outcrops in the Klein Dwarsrivier valley over a north-south strike length of 7.5km and dips to the west at approximately 7 to 10 degrees. TRP is exploiting platinum group metals (PGMs) and associated by-products comprising chromite and base metals (Cu, Ni and Co) which are hosted in the UG2 and Merensky reefs of the Bushveld Complex. The Bushveld Complex is the largest layered igneous complex in the world, hosting approximately 85% of known global platinum group metals resources. The area’s geological structure is dominated by the regional north-northeast to southsouthwest trending Kalkfontein Fault, which has an apparent vertical displacement of 1 200m down thrown to the west. A series of sub-parallel faults occur to the southeast adjacent to the Kalkfontein Fault, which affect both the Merensky and UG2 Reefs. These faults exhibit variable apparent vertical displacements of between 20m and 110m. The Merensky and UG2 Reefs are separated by a sequence of primarily anorthositic and noritic layered units of some 140m to 160m in combined thickness. Both the Merensky and UG2 Reefs are present — however, no Merensky Reef is present on Tweefontein 360 KT, and the UG2 Reef only occurs on a small portion of this farm. The UG2 Reef outcrops in the Klein Dwarsrivier valley over a north-south strike of 7.5km and dips to the west at 7° to 10°. Due to the extreme topography, the Merensky Reef outcrops further up the mountain slope. Steelpoortpark granite, which is unique to this area, occurs in the southwest part of the project. Three distinct reef types have been defined for the UG2 Reef, namely the ‘normal’ reef with a thick main chromitite layer; a ‘split’ reef characterised by an internal pyroxenite/norite lens within the main chromitite layer; and a ‘multiple-split’ reef with numerous pyroxenite/norite lenses occurring within the main chromitite layer. The multiple-split reef predominates in the southern portion of the mining area. The Merensky Reef is a pyroxenite layer with a chromitite stringer close to the hangingwall contact and at the basal contact. Mineralisation is primarily associated with the upper and lower chromitite stringers. The schematic section for Two Rivers demonstrates the approximate 8km north-south striking Merensky and the UG2 orebodies dipping 7° to 10° towards the west, relative to the extreme mountain topography of the Main Zone sequence. Surface exploration drilling and geological fieldwork were challenged by the mountainous terrain that overlays the two economic orebodies. A flatter area on the mountain’s eastern side is used for the mine’s general infrastructure and can be accessed from the tar road that connects with the R555 and R540. The mining area is bounded by the St George’s Fault on the eastern side, where it cuts through a portion of the UG2 Reef that can be accessed and mined by Anglo American Platinum’s Mototolo operation, where a royalty agreement is in place. The middling between the Merensky Reef and the UG2 Reef is approximately 140 metres to 160 metres. There is a notable increase in the middling between the UG2 and Merensky reef horizons from north to south across the mine. The UG2 Reef is a chromitite hosted PGM orebody with poorly mineralised pyroxenite partings. High PGM concentrations are closely associated with the chromitite layers while the pyroxenite layers within and between the chromites contain low to no concentrations of PGMs. The UG2 Reef outcrops along the Klein Dwarsrivier valley on Dwarsrivier 372 KT farm, with a north-south strike length of 7.5 kilometres, dipping to the west at between 7º to 10º. Elevated topography in the lease area results in the UG2 occurring at a depth of approximately 935 metres on the western extent of Dwarsrivier 372 KT farm. Elevated concentrations of PGMs in the UG2 Reef generally occur in the basal and uppermost 10 centimetre portions of the main chromitite layer with basal contact having higher PGM grades. The following three reef facies have been defined for the UG2 at Two Rivers Platinum Mine: • UG2 Normal Reef facies which is characterised by an 80 to 120 centimetre-thick main chromitite layer overlain by up to three chromitite “leader layers” collectively termed the UG2A chromitites. • UG2 Split Reef facies, characterised by a chromitite seam that is separated by a broadly persistent, 50 centimetres to 400 centimetres single layer of fine to medium-grained pyroxenite unit in the southern, west-central and north-eastern parts of the mine • The UG2 Multiple Split Reef facies which is represented by multiple splitting of the UG2 main chromitite by internal pyroxenite layers of variable thicknesses. It occurs mainly in the southern section of the mine on the Dwarsrivier 372 KT farm as well as the east-central section of Buffelshoek 368 KT farm. The Merensky Reef is a pyroxenite unit consisting of orthopyroxene with lesser amounts of plagioclase and clinopyroxene. Thin chromitite stringers (usually 1 to 4 millimetres thick) occur near the upper and lower contacts of the reef. The upper chromitite stringer occurs approximately 20 centimetres to 30 centimetres below the top contact of the Merensky pyroxenite unit. It is associated with highest concentrations of PGMs. The bottom chromitite stringer occurs at the base of the pyroxenite unit, above the anorthosite footwall. It is associated with a pronounced PGM bottom mineralisation peak. The Merensky Reef has variable thicknesses across the mine. There is a general decrease in thickness from east to west from Dwarsrivier 372 KT farm (4 metres to 2 metres thick), through Kalkfontein 367 KT up to Buffelshoek 368 KT farm where the reef reduces to 20 centimetres in thickness. Prominent northeast to southwest trending, upthrow faults with displacements ranging from 5 metres to 60 metres are common on the northern portion of the mine. There is regional north-northeast to south southwest trending Kalkfontein fault, with a vertical displacement of greater than 1 000 metres down thrown to the west. This fault marks the limit of the eastern structural domain for both the UG2 and Merensky reefs. The ground to the western side of the Kalkfontein fault is declared as an exploration target because the reef occurs at depths greater than 1 000 metres from surface and there is insufficient exploration drilling information.
