Zimbabwe
Platinum was discovered in Zimbabwe’s Great Dyke in 1925, but early attempts at mining were generally unsuccessful, and it is only in recent years that platinum production has reached significant levels.
The Great Dyke
The Great Dyke is a geological feature running through the heart of Zimbabwe for about 550 kilometres in a roughly north-south direction. The pgm occur in a layer known as the Main Sulphide Zone, which is typically about 3 metres thick. However, the economic mining width may be as little as one metre, depending on grade, metal prices and the chosen mining method. The pgm content is lower than that of South African ores, with head grades generally below 4 grams per tonne, of which about 55 per cent is platinum. Nickel and copper values are typically higher than those found in South African platinum ores.
Mimosa
Zimbabwe’s oldest platinum mine is the Mimosa operation, located in the southern part of the Great Dyke on the Wedza Geological Complex. Ownership is currently split 50:50 between Impala Platinum and Aquarius Platinum.
Mining at Mimosa has a long history: the deposit was exploited briefly in the 1920s, and trial mining was undertaken by Union Carbide Zimbabwe between 1966 and 1975. Zimasco (a ferrochrome mining and smelting company) took over Mimosa in 1992. The pilot plant was refurbished, and mining recommenced in 1994, gradually building up to a rate of just under 30,000 tonnes of ore per month. Although small, the operation was highly successful, and began to attract the attention of the South African pgm producers. A proposed acquisition by Anglo American collapsed in 2000, but the following year Impala Platinum acquired a 35 per cent stake in the mine. In 2002 Impala took a further 15 per cent, with Aquarius Platinum taking the remaining 50 per cent of the company.
Since 2002, output at Mimosa has gradually been expanded, and the mine – which is among the lowest-cost platinum producers in the world - extracts around 85,000 oz of platinum annually.
Zimplats
During the early 1990s, a second mine, the Hartley Platinum Project, was developed by a joint venture between the Australian companies BHP and Delta Gold. It opened in 1995, but following a string of geological and metallurgical problems, underground operations were suspended in June 1999. BHP’s interest in Hartley Platinum was sold to Zimbabwe Platinum Mines (Zimplats), a spin off of Delta Gold’s platinum assets, which began to develop a new open-cast mine further south, at Ngezi. Operations here began in 2001, following the acquisition of a share of the project by Impala Platinum and the South African bank Absa. Over the next two years, Impala increased its holding in Zimplats, and by June 2006 it held 86.9 per cent of the company.
In 2006, Ngezi produced about 90,000 oz of platinum, from an open pit and from a newly-developed underground section. Impala now plans to increase production to over 150,000 oz of platinum per annum, which will involved the construction of two new underground sections and will cost an estimated US$258 million.
Unki
A third platinum mine, Anglo American’s Unki project, is due to come into production in around 2008, and is expected to process around 120,000 tonnes of ore per month.