Low-cost producer of both PGM and chrome concentrate
Tharisa Mine is a shallow and large-scale open pit PGM and chrome mine that has an estimated open pit life of approximately 17 years and an estimated further 40 years underground and has been in production since November 2009.
Significant resource of 867.5 million tonnes located in the Bushveld Complex
The Tharisa Mine is located on the south-western limb of the Bushveld Complex. It is located approximately 95 kilometres north-west of Johannesburg and 35 kilometres east of Rustenburg, and is supported by well-developed infrastructure.
The Tharisa Mine is underlain by the Middle Group (MG) and Upper Group (UG) Chromitite Layers. The MG Chromitite Layers outcrop on the property striking roughly east to west with a gentle change in strike to NW-SE in the far west. The layers dip at between 9° and 15° to the north. Towards the western extent of the outcrop, the dip is steeper. The stratigraphy typically narrows to the west and the dip steepens. The dip typically shallows out at depth across the extent of the mine area. The MG Chromitite Layer package consists of five groups of chromitite layers, being the MG0 Chromitite Layer at the bottom, followed by the MG1 Chromitite Layer, the MG2 Chromitite Layer (sub-divided into C, B and A chromitite layers), the MG3 Chromitite Layer and the MG4 Chromitite Layer (sub-divided into 4(0), 4 and 4A chromitite layers). The layers between the chromitite layers frequently include stringers or disseminations of chromite. The MG Chromitite Layers at the Tharisa Mine are a typical stack of tabular deposits.
The life of mine plan was designed to extract the MG Chromitite Layers, firstly from open pit mining to a maximum depth of 200 m and subsequently from underground extraction (MG2 and MG4 Chromitite Layers) by means of a bord and pillar mining method.
Based on a maximum 200 m highwall, the life of pit and a 400 ktpm production profile, it is expected that open pit mining operations will continue until 2034 before a transition to underground mining. The open pit design and schedule has been completed and a mining method selection study was undertaken to evaluate various methods for the future underground mining operations. The bord-and-pillar method was selected on the basis of its faster development, greater flexibility, enhanced safety and efficiency. Underground mining operations are planned to increase in line with the reduction in open pit production and to take place to depths of up to 750 m.
Large scale open pit mining has traditionally been conducted by specialist mining contractors but in FY2017 Tharisa Minerals announced its plans to transition from contractor to an owner mining model. During that year, the Company acquired the mining fleet from the previous mining contractor and also acquired a drilling sub-contractor’s business to start in-sourcing the drilling operations and, as an owner operator, focus on improving ROM grades and fragmentation. In October 2017, approximately 900 former contract employees were transferred onto the mine.
In April 2017, Tharisa announced its plans to transition from contractor to an owner mining model. Tharisa is in the process of acquiring the mining fleet and transferring employees from the existing mining contractor. The transition in operating model is expected to be completed with-in FY2017.
Tharisa Minerals’ two independent processing plants are designed specifically to treat the MG Chromitite Layers of the Bushveld Complex.
The smaller 1.2 Mtpa Genesis Plant came on stream first, with the 100 ktpm chrome circuit being commissioned in August 2011 and the PGM circuit being commissioned in December 2011 and the larger 3.6 Mtpa Voyager Plant was commissioned in December 2012. The plants have a similar process flow that includes crushing and grinding, primary removal of chrome concentrate from spirals, followed by PGM flotation from the chrome tails and a second spiral recovery of chrome from the PGM tails.
Operating in parallel, the independent plants provide processing flexibility and production stability by allowing one plant to be shut down without hampering the production of the other.
Using off-the-shelf technology, the processing circuits are uniquely engineered to deliver both PGM and chrome production. This innovative approach to production has made Tharisa a world-class PGM and chrome co-producer.
During the year, the Group produced PGM concentrates containing 143.6 koz of contained PGMs (5PGE +Au) and chrome concentrates of 1.3 Mt. Of the chrome concentrates produced, 323.1 kt was specialty grade concentrates. Specialty chrome recovery circuits are integrated into the feed circuit of the Genesis Plant, known as the Challenger Plant. The Challenger Plant, which is owned by subsidiary Arxo Metals, was commissioned in July 2013 and produces chemical and foundry grade chrome concentrates.
The Voyager Plant chrome processing circuit was modified in FY2016 to increase chemical grade chrome production to diversify the product range from metallurgical grade with its Chinese and Asia-centric market to global markets, particularly taking the price differential between the products into account.
Production of specialty grade concentrates accounted for 24.3% of total chrome production in FY2017. Production of specialty grades will be maintained at current levels to ensure that it maintains a strategic market share.
The Group’s initial development plan for the construction and ramp up of its processing facilities comprised three phases: