Tharisa Mine is located in the south-western sector of the Bushveld Complex, 35km east of Rustenburg, South Africa. Owned and operated by Tharisa Minerals, the mine has 17 years of open-pit operations and 40 years of underground mining operations.
The mine, which contains platinum group metals (PGMs) and chrome concentrates, began first production in November 2009.
The Tharisa Mine produced 143,600 ounces (oz) of contained PGMs (5PGE +Au) and 1.3 million tons (Mt) of chrome concentrates including 323,100t of specialty-grade concentrates in 2017.
Tharisa Mine geology
The Tharisa deposit is underlain by two chromitite layers, Middle Group (MG) and Upper Group (UG). The MG chromitite layers strike from north-west to south-east of the property and rest above the UG chromitite layers.
The MG chromitite reef package is divided into six chromitite layers, namely MG0, MG1, MG2, MG3, MG4, and MG4A. The MG0 chromitite layer lies at the bottom, followed by the rest of the layers arranged in the form of tabular deposits. The MG2, MG3 and MG4 reefs hold PGMs.
The intrusive rocks found in the MG chromitite layers are of pyroxenite, anorthosite or norite type. The MG reef package varies from 50m in the west to 74m in the east, including the partings.
The mineral resources of the mine are estimated to be 867.5Mt grading 1.59g/t 6PGE+Au and 20.7% chromium oxide (Cr2O3). The mineral reserves are estimated to be 97Mt grading 1.39g/t 5PGE+Au and 18.9% chromium oxide (Cr2O3).
Mining at Tharisa Mine
The Tharisa Mine currently implements open-pit mining, which is expected to continue until 2034, following which underground operation will be started using bord and pillar mining method.
The underground mining is planned to take place at depths up to 750m.
Processing and production
The Tharisa mine employs two processing plants, namely Genesis plant and Voyager plant to treat the MG chromitite layers.
Commissioned in 2011, the 1.2 million tonnes per annum (Mtpa) Genesis Plant integrates a 100,000 tonnes per month (tpm) run-of-mine (ROM) chrome circuit and a PGM circuit. The plant processes reef layers with higher chromite grades and lower PGM.
The 3.6Mtpa Voyager plant was commissioned December 2012. It processes higher PGMs and lower chrome grades and has the processing capacity of 300,000tpm ROM ore. The chrome processing circuit of the plant was modified in 2016 to expand the product range.
Both the plants use crushing and grinding processes, followed by primary elimination of chrome concentrate from spirals and then PGM flotation from the chrome tails and a second stage spiral recovery of chrome from the PGM tails.
Specialty-grade concentrates are processed by the Challenger plant, which is the feed circuit of the Genesis plant. Commissioned in July 2013, the Challenger plant produces chemical and foundry-grade chrome concentrates.
The mine has a steady mining rate of 5Mtpa with an average stripping ratio of 9.6 on an m3:m3 basis.
Tharisa Mine infrastructure
The mine area has local un-surfaced roads originally built for the local farming community. It is connected to N4 Bakwena Highway by a local bitumen road passing through Buffelspoort and Marikana.
The highway links the mine to Rustenburg and then to Mozambique, Botswana, and Namibia. A 6km-long rail track facilitates transport of the chrome products to the port at Richards Bay.
Power supply for the mine is from Bighorn-Middlekraal and Selene-Middlekraaal substations.
Water for the mine is sourced from the boreholes drilled in the area as well as from the pit dewatering pumps and excess water from nearby mining companies.
MDM Engineering Group signed an engineering, procurement and construction (EPC) contract with Tharisa Minerals for the project in November 2011.
Open-pit mining has been conducted by specialist mining contractors until the mining fleet was acquired by Tharisa Minerals in 2017.
Tharisa Minerals signed an agreement with MCC Contracts to purchase the assets and equipment from MCC. Approximately 900 on-site employees of MCC were transferred to Tharisa Minerals, under the agreement.