As at 30 September 2024, Tharisa holds a 76.51% interest in Karo Mining Holdings Limited, which in turn holds a 100% interest in Karo Zimbabwe Holdings (Pvt) Ltd, under which Karo Platinum is an 85% subsidiary. The mineral tenure for the Project is held under Karo Platinum. The balance of 15% shareholding in Karo Platinum is held by Generation Minerals (Pvt) Ltd, the representation of the Zimbabwe Ministry of Finance.
The Tharisa attributable beneficial interest in Karo Platinum as at 30 September 2024 is 64.79%.
- subscription is required.
Summary:
The project area is located on both the eastern and western flanks of the Great Dyke. There is no outcrop as the mafic and ultramafic rocks weather easily to a black cotton soil. The area is underlain by both the mafic and ultramafic sequences dipping at 20-32° to the east on the western side of the Great Dyke and 15-33° to the west on the eastern side of the Great Dyke. The MSZ is estimated to be up to 700 m deep in the southern end of the tenement and 800 m deep in the northern end of the tenement. Based on the drilling, a number of faults have been interpolated. These are assumed to be vertical and trend east-west.
Mineralisation
The PGE and chromite mineralisation of the Great Dyke has been known since 1925 when PGEs were first discovered in what is now known as the MSZ. While chromite mineralisation occurs throughout most of the pyroxenite units of the Ultramafic Sequence, PGE mineralisation only occurs near the top of the uppermost P1 pyroxenite. The host to the PGE (+ Cu, Ni, and Co) mineralisation is the uppermost S1 sulphide layer. The portion of this layer that hosts PGE and associated metals is known as the MSZ.
The MSZ at Hartley Mine (Zimplats) is a persistent mineralised zone with no magnetic signature. The host lithology is typically a medium-grained poikiolitic feldspathic orthopyroxenite consisting of 85% cumulus orthopyroxene (En83-84) and 15% postcumulus plagioclase and augite oikocrysts. In addition, the rock contains intercumulus base metal sulphides (pyrrhotite, chalcopyrite, pentlandite, and pyrite), minor phlogopite, quartz, apatite, zircon, rutile, and micrographic intergrowths of K feldspar and quartz. The base metals sulphides are generally anhedral in shape, 0.2-0.3 mm in size and are intercumulus to the pyroxenites. They may be finely disseminated grains or net textured concentrations around oikocrysts. Where the pyroxene grains and base metal sulphides are in contact, the pyroxenes are commonly altered, and the base metals sulphides may be distributed along the pyroxene cleavage planes.
The vertical distribution of the economically important metals at Karo was expected to be similar to that found elsewhere on the Great Dyke. The PGEs are typically enriched just above the base of the main sulphide zone (BMSZ) and into the immediate footwall. The base metals (Cu, Ni) are typically enriched above the BMSZ with little metal concentration in the footwall (FW). The similarity was demonstrated from the work undertaken at the Karo Project.
The P1 pyroxenite is host to three sulphide zones known as S1, S2, and S3, respectively. The uppermost of these, the S1 zone, is host to the MSZ. The MSZ reef itself consists of the lowermost sulphide concentration of the 2 m to 3 m wide S1 zone and appears as a variably visible interstitial sulphide-rich layer of between 10 cm and 30 cm in width, hosted by the uppermost portion of the ~200 m wide P1 plagioclase pyroxenite. While an immediate upper contact of this lower sulphide concentration may not be obvious due to overlying sulphides that constitute the remainder of the S1, its lower contact is usually discernible and is used as a zero datum for sampling and mining. Somewhat unlike the PGE reefs of the Bushveld Complex, the MSZ reef is remarkably similar stratigraphically, petrologically, and geochemically throughout the entire Great Dyke. Also, unlike the Merensky Reef and UG2 Chromitite Layer of the Bushveld Complex, which are highly visible and easily distinguishable from their adjacent stratigraphy, the MSZ reef consists only of a relatively thin, variably visible intercumulus sulphide layer within plagioclase pyroxenite that is both overlain and underlain by relatively sulphide-poor plagioclase pyroxenite. Commonly, a second sulphide layer, virtually identical in appearance, occurs at approximately 1.2 m above the MSZ reef. This layer is effectively PGE-barren. Unlike the Merensky Reef and UG2 Chromitite Layer, potholes do not occur in the MSZ.
The genesis of the MSZ has been explained by the sequential removal of PGE and Au in order of their partitioning ability into sulphide. Detailed computer simulation failed to reproduce the complex and persistent trends observed and, therefore, factors other than just metal-sulphide partitioning should be considered. Sulphide partitioning is proposed as the controlling influence, but that formation was a multistage event of emplacement of similar but heterogeneous magmas which had slightly different compositions and different ways of carrying the PGE. Olivine is considered important which may have critically increased the sulphur solubility and therefore reduced its formation as a primary precipitate scavenging PGE.
Post-mineralisation intrusions of various types and scales which disrupt the mineralisation are known from the operating mines. Areas where the geochemical signature is disrupted and washouts are evident have been located in the MSZ at some operating mines. Potholes such as those found on the Bushveld Complex have not been found on the Great Dyke.