The Impala platinum mine, located on the western limb of the world-renowned Bushveld Complex in South Africa, has been operational since 1969.
Impala Platinum Holdings (IMPLATS) holds a 96% ownership in the mining operation through its subsidiary Impala Refining Services (IRS) while the remaining 4% is held under an Employee Share Ownership Trust.
The Bushveld Igneous Complex which is considered to hold the world’s biggest platinum group metals (PGMs) resources was discovered by Hans Merensky in 1924. Union Corporation developed the first vertical shaft in 1967 and Impala Platinum Limited was formed as its subsidiary in April 1968.
Commercial production began from the Merensky Reef section of the complex in July 1969 after a mining lease was granted in 1968. Mining on the UG2 chromitite layer started later in 1980 with the development of technology to smelt higher chrome ore.
The impala mine produced a total of 753,800 ounces (oz) of refined platinum in 2019. The remaining mine life of the platinum mine was estimated to be 15 more years as of the same year.
The Impala mine operations were put on hold in March 2020 due to the outbreak of the COVID-19 pandemic while a partial restarting of operations was planned in April 2020. This decision led to criminal charges being filed by the state against Impala Platinum on grounds of violating certain regulations of the Disaster Management Act 57 of 2020. The charges were later dropped in August 2020.
Location and geology
The Impala platinum mine is located in the North West province of South Africa, approximately 25km north-west of Rustenburg and 140km west of Pretoria. The project is a 10-shaft mining complex covering a total area of approximately 250km2.
The Impala platinum mine exploits the Merensky and UG2 Reefs of the Bushveld Igneous Complex.
The Merensky Reef is generally composed of an upper feldspathic pyroxenite, overlying a thin basal chromitite stringer, followed by an anorthosite to norite footwall. The UG2 Reef is defined as the main chromitite layer, followed by a poorly mineralised pegmatoidal pyroxenite footwall.
Platinum reserves at Impala
The mine’s proven and probable mineral reserves in the Merensky and the UG2 ore bodies were estimated to be 51.4Mt and 44.0Mt respectively, as of June 2019.
The mine’s total contained platinum in proven and probable reserves was estimated to be seven million ounces (Moz).
Mining methods at Impala
The Merensky and the UG2 Reefs are mined concurrently though the conventional double-sided breast mining method. The central shaft position is cross-cut in the opposite direction by the haulages. The footwall drives are developed at approximately 18m to 30m below the reef horizon with a 180m and 250m separation between the on-reef connections.
The panel face lengths at Merensky and UG2 vary from 15m to 30m with panels separated by 6m x 3m grid pillars. The stoping widths at Merensky and UG2 reefs are approximately 1.3m and 1.1m respectively with an average stoping width of 1.9m for mechanised panels.
The shafts are divided into three groupings under Old Men (4, 6, 7, 7A, 9 and E/F), the Big 5 (1, 10, 11, 12 and 14) and the Build-up shafts (16 and 20) with approximately 40% of the mineral Reserves located in the Build-up shafts.
The base and precious metal refineries for the Impala platinum mine are located in Springs, east of Johannesburg. The high chromium grade ore from the shafts is allocated to the UG2 Plant while the PGMs ore from the Merensky reef is processed in the Central Concentrator.
The Central Concentrator comprises of 10 primary mills that feed two units of a nine-stage, tank cell flotation banks. The concentrator tailings from both the plants are further processed at the Tailings Scavenging plant to improve the overall recovery rate of precious metals.
The concentrate from the Central Concentrator and the UG2 plants are treated in an onsite smelting facility. The moisture content of the concentrate is reduced to below 0.5% by drying and is then treated in electric arc furnaces to produce a copper, nickel, iron sulphide-rich matte.
A converter circuit then treats the matte to reduce the tonnage by approximately 70% to 80% by reducing the iron content to below 1%. The slag from the arc furnace and converter circuits undergo flotation at the Slag Plant to further enhance the recovery of valuable metals.
The Impala platinum mine receives electricity from Eskom’s 945MVa Ararat Main Transmission sub-station (MTS) via eight 88kV sub-stations which convert the electricity to 33kV and 6.6kV for surface and underground distributions. An alternate source of electricity is also available from the Marang MTS to provide electricity during emergency conditions.
Impala receives water supply from the Vaal River system (Vaal Dam) at a rate of 32 megalitres (Ml) per day. It also receives 3Ml per day of water from the Crocodile River system (Vaalkop Dam) via the Magalies Water system. A potable water supply of 5 Ml per day is received from the Kanana take-off.
The treated effluent water is supplied at a rate of 10Ml per day by the Rustenburg municipal water care works for the two processing plants. Impala also has three on-site water care works that supply approximately 3 Ml to 5 Ml per day of treated effluent water to the mineral processes operations.