Rewards of high risk strategies
Rewards of high risk strategies In 2014, the Moti Group constructed the first semi mobile processing plant of its subsidiary, African Chrome Mines ACF in the Zimbabwean Midlands, when former president Robert Mugabe was still firmly in control of the country. Although many people frowned upon the timing of the investment, ACF stuck it out and remained in Zimbabwe during what can only be described as a sombre period in the country’s history. But the high risk strategy has paid off, and four years later, the company is reaping the rewards of believing in its great potential. In doing so, ACF has created significant job opportunities in an area starved for investment. Operations Rewards of high risk strategies A chrome operation in the Zimbabwean Midlands has created significant job opportunities in an area starved for investment, writes Leon Louw. Wash Plant 5 in full tilt. Operations In 2014, the Moti Group constructed the first semi mobile processing plant of its subsidiary, African Chrome Mines ACF , when former president Robert Mugabe was still firmly in control of Zimbabwe. Although many people frowned upon the timing of the investment, ACF stuck it out and remained in Zimbabwe during what can only be described as a sombre period in the country’s history. But the high risk strategy has paid off, and four years later, the company is reaping the rewards of believing in its great potential. ‘The chrome deposit, located in the platinum rich Great Dyke of Zimbabwe, occurs on surface and therefore, strip mining is the most appropriate method to use. The area has been subject to extensive exploration work in the past, and Anglo American developed a pilot plant in the 1990s, which is still in operation today. Since commissioning its first plant Plant 1 in 2014, ACF has built five more, and Plant 7 is in the pipeline. Plant 6 was commissioned towards the end of April 2018. The chrome deposits are found in several valleys spread over a large area, which resulted in management’s decision not to use a central plant. Instead, each of the processing plants is the central unit around which mining takes place in a radius of three to five kilometres. ‘This also allows for easier relocation to new mining centroids, as each plant is dismantled after three to five years and moved to another chromite rich deposit identified during the exploration programme. According to Leon Richardson, chief operation officer at ACF, some of the chromite will be processed into low and ultra low carbon ferrochrome in the aluminothermic facility, currently under construction, to be used in the alloy and stainless steel industries. The company’s main chrome processing facility is located at a site near Chinyika in the Lalapanzi Black Rhino Conservation area, located north of the Sebakwe Dam, south of the Munyati River. In a country where the unemployment levels are estimated to be between 90% and 95% depending on the source , ACF’s project has been a saviour for many families in the region. Ashruf Kaka, CEO of the Moti Group, says the mine employs more than 1 100 local Zimbabweans and about 36 expatriates, and with skills transfer programmes in place, Zimbabweans are set to reap more benefits in the future. “Our recruitment programme specifically targets local employees from the Midlands area and only specialised skills are sought outside the Midlands Province,” says Kaka. Operations Stripping the chrome The big advantage of strip mining is of course that there is no drilling and blasting involved, so the impact on the environment is minimal. Moreover, it reduces the operating cost significantly. The mine is really a large earthmoving project and as a result, it requires substantial infrastructure development and maintenance. ACF has constructed about 87km of gravel roads in the past four years to access the mining units. Negotiating harsh road conditions impacts heavily on equipment and haul trucks and requires a stringent maintenance regime, but that cost is offset by the straightforward mining and processing methods and the fact that the strip ratio is zero, although the grade is not the best in the world. Methods to extract the chrome are continuously being improved.The installation of thickeners will reduce water usage as well as increase efficiencies and the percentage of solids present in the slurry. ACF’s chrome is so close to surface that it can be detected without digging. “It is an alluvial deposit, and we do strip mining in the enriched valleys based on extensive geological prospecting. We define the resource in terms of a split that means in two components, namely a ‘washable’ portion and a ‘non washable’ portion. The ‘non washable’ portion does not have economic value,” says Richardson. The vegetation in the area is normally a good indicator of the quality of the specific deposit. According to Barry Jones, group geologist, tall grasses are a sign of better splits: “Big trees indicate a very poor split; in other words, most of the material in that Operations area is bigger than lmm. In most cases though, the deposit is heterogenous, where the split can be anything from 20% ‘washable’ and 80% ‘non washable’, to 85% ‘washable’ and 15% ‘non washable’.”The chrome content is defined at a minimum of 7% chrome in some places, and more than 20% in others. Basic mining methods According to Richardson, the mining cycle is reasonably straightforward: “It starts with the definition of the resource, a description of the vegetation type, and then we do a complete evaluation. After mine planning, we start with bush clearing, primary extraction, pre screening, transportation to the washing plant, return of the discard to the mining site, and then the rehabilitation,” says Richardson. Haul trucks load the stripped material, it is processed in the washing plants, and the slurry is then stored in a dam and left to dry, after which it is returned to the mining site, where it is used again to fill the mined out area. This entire process takes about 18 months. “However,” says Richardson, “the long time lag is one of the reasons why we introduced new thickeners. We aim to improve the process with each new plant we build, and through good engineering and innovation, Plant 6 is kitted out with the most advanced technology, including the Magra thickeners. The thickeners will accelerate the process tremendously,” says Richardson. According to Marike Barnard, process manager at ACF, the new thickeners are being installed to improve water recovery and efficiency. “With the new thickeners, we are recovering about 80% of our water, which reduces the environmental impact, and we don’t source as much water from the boreholes as we used to. The slurry that is pumped out now dries out faster and we are able to return it to the rehabilitation areas a lot quicker. Not only does it reduce our environmental footprint, but it also ensures better water quality and better production and efficiencies in the plant, and eventually, a better quality product,” says Barnard. ACF has purchased thickeners for all the plants, but they are still to be installed at all the plants. A second thickener will be commissioned at Plant 6 soon, and after that Plant 5, Plant 1, and Plant 4 will be boosted by new thickeners. All of these thickeners are manufactured and installed by South Africa based Magra. At the moment, the tailings in ACF’s slurry dams contain about 17% solids, while the thickeners will increase that figure to approximately more than 65%. This will reduce the drying time of the slurry dramatically and as a result, the material will be ready for rehabilitation sooner. Where the split is poor, the mine uses scalping screens. However, where a large percentage of the material is ‘washable’, the mined material is sent to the plant directly. The processing plants consist of a configuration of scrubbers, screens, spirals, and magnetic separators to liberate and extract the chromite from the 1mm fraction. tY AUGUST 2018 AFRICAN MINING 31 Six washing plants are currently proc F, with a seventh in the pipeline.