Early mining of chromite was on a small-scale and was relatively straightforward from outcrops or to shallow depths followed by hand sorting.
With the increased demand, conventional open-pit mining and mechanical underground mining became necessary. Underground mining of stratiform deposits is most often required but can be particularly difficult due to the narrow seam thickness (less than 1.5m), weathering close to surface and faulting. Open-pit mining is generally applied to the podiform ores at first but this progresses to underground mining as deeper levels of the deposit are reached. Weathering through serpentinisation and faulting are often encountered.
Historically, there was sufficient high-grade metallurgical ore to meet demand but with the rapid growth of the stainless and other alloy steel industries, the much larger reserves of the lower grade, higher iron, ores have had to be exploited.
Reserves and Resources
Reserves are defined as proven in-situ tonnages, while resources are estimated additional tonnages.
- The United States Geological Survey states that world resources of chromite exceed 11 billion tonnes, sufficient to meet world demand for many centuries.
- South Africa and Zimbabwe hold about 90% of the world's chromite reserves and resources, with South Africa having reserves of about 3.1 billion tonnes and a further estimated resource of 5.5 billion tonnes.
- Zimbabwe has reserves of about 140 million tonnes with resources of a further 1 billion tonnes. It is the only country to exploit both stratiform and podiform deposits. The stratiform deposits occur in the Great Dyke, approx. 550 km long and 11 km wide, while the podiform deposits occur in the Selukwe and Belingwe areas.
- Kazakhstan has podiform deposits in the southern Ural Mountain region with reserves of 320 million tonnes and a further 320 million tonnes resource. The ores vary greatly in chromium content and in Cr:Fe ratios.
- India's output is from podiform bodies on the east coast of the state of Orissa. Its reserves are put at 27 million tonnes with a further resource of 67 million tonnes.
- Finland has podiform deposits near Kemi in northern Finland. Although the Cr2O3 content is very low, the ore has been successfully mined, concentrated and smelted to ferrochromium, and then converted to stainless steel on site. Reserves are given as 41 million tonnes and resources as 120 million tonnes.
- In Brazil, production is concentrated in Bahia and Minas Gerais, although chromite deposits have been identified in other states. These are mainly stratiform deposits with reserves of 14 million tonnes and resources of 17 million tonnes.
- China's chromium resources are contained in podiform and stratiform deposits but are largely unknown in terms of possible reserves and resources. There is a chromite mine in Tibet. Russia also has mines in the Ural mountains with further developments above the arctic circle.
- Other countries with smaller chromite deposits include Oman, Iran, Turkey and Albania. Total reserves and resources of these and others are 24 million tonnes and 538 million tonnes respectively.
World Production and Global Development
While demand for chromium alloys has been expanding by some 5% annually over the past decade, the output of chromite ore followed closely with an average growth rate of 4.6% per annum.
However, the market performance showed an unusual pattern:
Between 1994 and 1999, chrome ore production stagnated whereas from the year 2000 onwards, market volumes increased from 15 million tonnes to 24 million tonnes in 2008. This substantial increase can be primarily explained from the rapidly rising global stainless steel demand and production in China, where local ferroalloy plants converted strongly rising imports of chrome ore into chromium alloys.
In the year 2009, world chromite ore production stood at nearly 19 million tonnes with the following breakdown: South Africa accounted for 33% of production, whilst Kazakhstan and India provided 17% and 20% respectively. Brazil, Finland, Oman, Russia, and Turkey together contributed a further 21%, whilst some 12 smaller producer countries brought the balance of 9%. Within the total volume of ore and concentrates produced in 2009, 95% were metallurgical grade, 2% chemical grade and the balance of 3% were refractory and foundry grade.