BUSHVELD IGNEOUS COMPLEX
The Bushveld Igneous Complex (BIC) is a large, layered igneous intrusion, which encircles the Transvaal geological basin in South Africa. Formed around 2 billion years ago, the BIC contains some of the richest metal ore deposits on Earth.
South Africa is estimated to hold 82% of the world’s chrome ore resources, the vast majority being located within the BIC. The BIC also contains around 90% of the world’s reserves of platinum group metals (PGMs), and vast quantities of iron, tin, titanium and vanadium. The mineral resources of the BIC have been mined continuously for nearly 120 years, having been first discovered by the Dutch geologist Gustaaf Molengraaff in 1897. Despite this, there are enough mineral resources remaining within the BIC for mining activity to be able to continue for hundreds more years at current rates of extraction.
The BIC is bounded by Pretoria to the south and Pietersburg to the north. From east to west it measures about 350km. The BIC divides into two main sections – one on the east and one on the west. There is also a smaller section to the north.
The BIC is made up of many layered seams, which each have different geological characteristics. At the top is the Merensky Reef, which contains the largest part of the PGM resources in the BIC. Below the Merensky Reef are the Upper Group seams, the higher of which (UG2) also contains substantial PGM resources. Traditionally, chrome ore has generally been mined from the deeper layers of the BIC, from the middle and lower group seams. Resource depletion has, however, led to the need to mine chrome ore within these seams at deeper and deeper depths, leading to rising production costs and more challenging mining operations.
The UG2 seam was traditionally mined solely for its PGM content, however it also has a chromium content ranging from 10% to 25% Cr2O3. This can be upgraded to 40% to 42% Cr2O3 after processing. Over the past decade, the proportion of South Africa’s chrome ore production deriving from the UG2 seam has increased from zero to around 25%, with chrome ore now providing an important by-product credit for all the major PGM producers in the BIC.
As of 2013, South Africa produced just over 45% of the world’s chrome ore, yet held 82% of the world’s chrome ore resources. It is clear from these statistics that, as resources elsewhere in the world gradually deplete, South Africa will be relied upon more and more to satisfy the growth in global demand for chrome ore in the coming decades.