Summary:
RBPlat is located on the Western Limb of the Bushveld Igneous Complex (BIC), the largest known host of PGMs, chromium and vanadium commodities in the world.
The BIC formed approximately 2.04 billion years ago on the stable geological foundation made up of the Kaapvaal and Zimbabwe cratons in Southern Africa, together with other large mafic and ultramafic layered intrusions. The Bushveld Complex has been mined for several decades for its high-value ore and plays a key role in the South African economy.
The BIC consists of three main geological units, namely the Rooiberg Group, Lebowa Granite Suite and the Rustenburg Layered Suite.
The Rustenburg Layered Suite is host to a variety of sub-suites (upper, main, upper critical, lower critical, lower and marginal zones), which comprises igneous intrusive layering, known as stratigraphy, with each layer having distinct mineralogical and geochemical characteristics.
The western extremity of the Maseve ore body subcrops 160mbs. The northern boundary is the operational Wesizwe Platinum’s mining right area, and the remainder of the ore body borders RBPlat’s operations.
Proximity of the basement (and possibly its palaeotopography) to the Merensky and UG2 reefs influenced the geometry and succession of the local stratigraphy, which primarily resulted from local basement upliftment. Upliftment caused the folded or rolling nature of the stratigraphic geometries which are preserved as anticlines and synclines. The frequency of the rolling towards the west becomes narrower with steeper dips resulting in some of the stratigraphic units not fully developed or not present. Ductile deformation due to basement upliftment was interpreted to be the major cause of vertical displacement within the ore body.
Prominent geological structures within the Maseve ore body are iron-rich ultramafic pegmatoid (IRUP) intrusions (which mainly affect the Merensky reef), the east-west trending Chaneng dyke, and the North and South UG2 faults.
The Transition Zone has been delineated between the Central reef facies and Normal reef facies, where the reef and surrounding lithologies settle between the two facies types and are characterised by a thickening of the footwall, anorthosite, from approximately 1.5m to 5m. This thickening is not consistent or gradual and is characteristic of frequent undulations of the Merensky reef.
PGE mineralisation occurs within the Upper Critical Zone along two specific layers, the Merensky reef and the Upper Group 2 reef (UG2 reef). RBPlat’s operations mine the Merensky and UG2 reef layers.
Two well understood geological structures are present within the RBPlat mining rights, namely the Elands River graben, situated north of Styldrift, just south of the Caldera fault, and the Boundary fault, situated to the east of Styldrift I shaft:
- The Elands River graben is a series of faults with sinistral deformation, striking ENE-WSW, resulting in a graben structure.
- The Boundary fault is a dextral strike slip fault, striking NNW-SSE with horizontal displacement of 100m.
Both structures are accounted for in the known geological losses which are used in the Mineral Resources and Reserves evaluation.
Regional variations in the geological characteristics of the Merensky and UG2 reefs are fundamental to understanding the nature, origin and economical extraction of the reef. The Rustenburg layered suite is divided into two regional facies, namely the Rustenburg facies to the south and the Swartklip facies to the north of the Pilanesberg Alkaline Complex. The transition of the Rustenburg facies to the Swartklip facies occurs on the Styldrift 90 JQ farm.
This distinction was made on several grounds, including the greatly reduced stratigraphic sequence between the UG2 reef and the Merensky reef, the mineralised envelope, mainly for the Merensky reef, across these two regional facies and the presence of olivine-bearing layers in the Swartklip facies. RBPlat’s mining rights fall within these two regional facies, which are then further subdivided per reef type into localised facies based on specific geological features and attributes such as lithology, thickness, mineralisation profile and bottom reef contact.
The Merensky reef at RBPlat operations encompasses six localised geological facies types. Named from west to east: Abutment, Terrace, Central, Normal, Normal Thick and Main reef facies. Specific facies can be further subdivided, i.e. Abutment has shallow Abutment, deep Abutment and transition Abutment. The understanding of the local facies delineation plays a fundamental role in planning the optimised mining method.
The UG2 reef has three distinct facies types, with emphasis of character based on position of the leading chromitite bands in the hangingwall in relation to the UG2 main chromitite band. Named from south to north along apparent dip: Central High, Leader and General facies types predominant facies types are the Leader and General facies, which account for 85% of the total UG2 reef ore body.