Mimosa platinum mine is an underground platinum group metals (PGM) mine located on the Great Dyke in Zimbabwe. Owned by Mimosa Mining Company, a joint venture between Sibanye-Stillwater and Impala Platinum, Mimosa is the oldest platinum mine in Zimbabwe.
The mine is accessed through the Wedza and Mtshingwe shafts, of which Wedza has been extensively mined. The Mtshingwe shaft is currently in development stage, which is expected to take the life of mine beyond the currently estimated 2032.
Mimosa platinum mine background
Mining operations at Mimosa platinum mine began in 1926 and two vertical shafts were sunk with trial mining starting in 1966 when 40,000t of platinum was processed. The operations were suspended in 1971 and Blore Shaft was established, from which 90,000t of ore was processed in 1975. The mining operations were further suspended in 1978.
Sibanye purchased 50% in the mine by acquiring Aquarius in 2016, with Impala Platinum owning the remaining 50% in the project.
Mimosa platinum mine location, geology. and mineralisation
The Mimosa mine is situated in the Wedza subchamber of the Great Dyke of Zimbabwe. It is located 32km from the town of Zvishavane and approximately 340km from Harare, the capital of Zimbabwe.
The Great Dyke, which is 11km-wide and 550km-long, consists of four geological complexes, which include the Wedza Complex, Selukwe Complex, Musengezi Complex, and Hartley Geological Complex. The Wedza subchamber, located southernmost in the Great Dyke, is home to the economic sulphide zone and consists of PGM and base metal deposits.
The mineralisation of the Mimosa platinum mine is made up of ultramafic and an overlying mafic sequence. The ultramafic sequence contains the P1 pyroxenite, which is home to the main sulphide zone (MSZ) containing PGM.
The mine has a well-balanced profile containing nickel, platinum and palladium at the top, middle, and base, respectively.
Mimosa platinum mine reserves
The proven and probable ore reserves at the Mimosa platinum mine as of December 2018 were 152.7Mt with 6E PGM graded at 4.2g/t. Contained resources are estimated to be 20.8Moz of 6E PGM.
Mining and processing at Mimosa platinum mine
The mining method used at the Mimosa platinum mine is the bord-and-pillar mining method, with an average stoping width of 2m. The ore body at Mimosa mine is superficial and is accessed through the Wedza and Mtshingwe shafts.
The Wedza subchamber hosts the economic main sulphide zone, which comprises the economic PGM and base metals. The mining bords proceed along the strike and the mining process entails mechanised support drilling and installation, mechanised face drilling, charging, and blasting.
The mined ore will be sent to an underground bunker through a conveyor network by using mechanised lashing. The project has a steady-state platinum production capacity of 115,000oz a year.
The ore is processed in the on-site concentrator at a rate of 227,000t per month. The resultant concentrates are sent to South Africa through trucks to Impala Platinum facilities, where they are smelted and refined before being packed and sent to customers.
The mine produced 25,000oz of concentrate at a grade of 3.85g/t platinum.