Sedibelo Platinum Mines Limited (“SPM”) and its subsidiaries (together “the Group”) is a natural resources group of companies engaged in the acquisition, exploration, development and operation of Platinum Group Metals mineral deposits in South Africa. Through its 100% owned subsidiary, Pilanesberg Platinum Mines Proprietary Limited, the Group has established the Pilanesberg Platinum Mines (“PPM”) on the Western Limb of the Bushveld Complex.
The Gemfields Group holds a 6.54% equity interest in SPM.
- subscription is required.
Summary:
Pilanesberg (PPM) is situated in the Western Limb of the Bushveld Igneous Complex (BIC), a layered igneous complex where platinum group elements (PGE) are currently mined as a primary product (Metago, 2007).
The Bushveld Complex (BC) of South Africa is the world’s largest and hence the most important repository of the PGMs in the world with an exposed surface area of some 67 000 km2 . The BC consists of a massive ultramafic-mafic layered intrusion and a suite of associated granitoid rocks intrusive into the early Proterozoic Transvaal Basin within the north central Kaapvaal Craton. The ultramafic-mafic layered rocks collectively referred to as the Rustenburg Layered Suite (RLS) are in five so-called lobes, namely the Western, Far Western, Eastern, Northern and Southern (Bethal) lobes. The magmatic layering of the RLS is remarkably consistent and can be correlated throughout most of the BC.
The RLS is divided into five major stratigraphic units, as follows:
• The lowermost Marginal Zone ranges in thickness from several metres to several hundred metres and comprises a heterogeneous succession of generally unlayered basic rocks dominated by norites;
• Ultramafic rocks dominate the Lower Zone. These vary in thickness with the thinnest units developed over structural highs in the basin floor;
• The Critical Zone contains the economic PGM resources of the BC: the Lower Critical Zone, Upper Critical Zone and the chromitite layers which occur in three distinct groupings i.e., the Lower Group (LG), the Middle Group (MG) and the Upper Group (UG);
• The Main Zone is the thickest unit within the RLS and comprises approximately half the RLS stratigraphic interval. It consists of gabbro-norites with some anorthosite and pyroxenite layering. Banding or layering is not as well developed as in the Critical and Lower Zones; and
• The Upper Zone is dominated by gabbros with some banded anorthosite and magnetite. There is no chilled contact with the overlying rhyolite and granophyres of the Lebowa Granite Suite.
The two most economically significant PGM mineralized layers of the BC, namely the Merensky Reef and the UG2, are continuous over hundreds of kilometres. The PGMs include varying proportions of Pt, Pd, Rh, Ru, Ir and Os, as well as elevated concentrations of Ni, Cu and Co as base metal sulfides.
The Western Limb of the BC is subdivided into two sectors separated by the younger Pilanesberg alkaline intrusive complex: the northern ‘Swartklip’ sector and the southern ‘Rustenburg’ sector. In the Swartklip sector where the PPM-Sedibelo-Magazynskraal Project is located, the Upper Critical Zone stratigraphy between the UG2 and Merensky Reef is significantly telescoped, ranging in thickness between 12 and 25 m, compared with a thickness of 120 m or more in other parts of the BC. In addition, the interval between the UG2 and the Merensky Reef contains the PGM bearing Pseudo Reef Package, which is not encountered elsewhere in the BC.
The Merensky Reef Layer
The MR has been traced over 150 km along strike in the eastern BC and over 110 km strike in the southern sector of the western Limb. There is also extensive mining on the western sector from Pilanesberg to Thabazimbi giving a total strike length of approximately 250 km. Within the Northern Limb the geological succession is unique with only the Upper Critical Zone present and the Platreef, developed near the floor of the complex, is the local equivalent to the MR. Generally, two types of MR exist; the normal and potholed reefs. Where fully developed within the P-S-M Project footprint, the MR consists of an orthopyroxenitic or harzburgitic pegmatoid, between 1 cm and 1 m thick, bounded top and bottom by thin (1 cm or less) chromitite stringers. The MR, where fully developed, is more olivine rich than in other parts of the BC.
Within the MR, the PGMs occur as small (<20 µm) grains, most commonly at the contact between the base metal sulfides and silicate minerals. Their composition varies considerably, from sulfides through tellurides to Pt-Fe alloys. Grade varies considerably over short distances in the MR. Where the pegmatoidal pyroxenite of the MR is greater than 50 cm, grade is concentrated at or near the upper chromitite with a smaller peak on the lower chromitite. Platinum Group Element (PGE) mineralization is generally low grade in the body of the pegmatoid itself.
The Pseudo Reef Layer
Pseudo Reef consists of two distinct portions; the Lower Pseudo Reef (LPR), a coarse-grained pegmatoidal feldspathic harzburgite, and the Upper Pseudo Reef (UPR), a finer grained feldspathic harzburgite. The Pseudo Reef may contain significant concentrations of PGMs. The lateral continuity of the Pseudo Reef is not as extensive in comparison to the MR and UG2 reefs.
The UG2 Chromitite Layer
The UG2 is hosted within pyroxenites and typically consists of a main chromitite band, typically 50 to 120 cm wide, often accompanied by a series of smaller chromitite stringers in the immediate hanging wall. These stringers range from 0.5 cm to several tens of cm in width. Additionally, pyroxenite stringers may be developed within the main chromitite layer. The footwall to the UG2 consists of a coarse-grained feldspathic, pegmatoidal pyroxenite or harzburgite unit of variable thickness. Discontinuous chromitite stringers and blebs are present within the pegmatoid footwall. Pyroxenite is developed beneath the pegmatoidal pyroxenite zone. The common signature of the UG2 reef within this ultramafic layer is the massive 1 m thick chromitite found within the package of alternating thin chromite seams. Overlying the UG2 is mostly norite or pyroxenite; the only exception is in the northern part of the Western Limb where the UG2 is overlain by harzburgite.
The PGM mineralogy of the UG2 is simpler than that of the MR, being dominated by PGE sulfides, although the grain size is smaller (<10 µm) than in the MR. The 4E grade tends to peak at the bottom and top contact of the main UG2 chromitite seam.
The UG2 is the most consistently developed mineralized horizon within the P-S-M Project footprint.