Modern Mining July 2020

waste rock and tailings treatment

He says tailings retreatment is a high-volume business: “DRDGOLD, for example, has a very large resource and reserve – 9,8 and 5,8 Moz respec- tively. It’s a substantially mechanised business, characterised by a small, highly skilled workforce and high-tech, fit-for-purpose plants.” Loots mentions as an additional key benefit the deposing of the retreated and detoxified material into modern tailings facilities with smaller footprints and better dust suppression. “This frees up the footprint of the older dams for alternate and more sustainable land uses such as agriculture and property development. This also reduces our environmental liabilities and allows us to leave a sustainable legacy for the surrounding communities.” Technological trends Loots counts modern extraction processes as tech- nological innovations enabling rock dump and tailing extraction. These, he says, do not require regrind mills and thickeners, use lower reagent consump- tion, have the benefits of cyanide detoxification, and also recycle process water, which implies a lower impact on the environment. To Pretorius, dump reclamation methodologies involving front-end loading and trucking, and high- pressure water jetting are well-established. He says where water jetting is applied, the reclaimed material is pumped as a slurry via pipelines from reclamation sites to metallurgical plants for gold recovery. “In years gone by, water jets were operated

processing and tailings facilities make the option of retreating surface tailings ever more appealing. “In the current economic environment,” he says, “the capital cost of constructing a new underground mine and related infrastructure, the high labour intensity in underground mines, health and safety considerations and long lead times to production all contribute to this fact. “Given the sustained increase in the price of gold, both in US dollar and rand per kg, and the compara- tively lower cost of tailings retreatment, the impact on profit margins will be extremely positive – if done properly.” “Of course,” says DRDGOLD’s Pretorius, “there are mining companies that remain committed to underground gold mining, and they are up to the challenges posed by increasing depth and declining grade. For us, surface retreatment is the preferred option.” He says that, while there is “much oppor- tunity” in gold surface retreatment, the company’s thoughts have already turned to how it can leverage its gold surface retreatment expertise with other min- erals such as platinum group metals (PGMs). Benefits Pretorius says tailings and sand dumps are also eas- ier to access, which contributes to the lower safety risk. “While sand dumps are generally older and there- fore higher in grade and more in demand, they are now scarcer, while slimes dumps, although lower in grade, are in relatively plentiful supply.”

Far West Gold Recoveries is one of DRDGOLD’s flagship operations.

July 2020  MODERN MINING  21