Modern Mining August 2016

GOLD

research by DRDGOLD revealed that pyrite particles, containing some 40 % of the gold entering the Brakpan facility, were not respond- ing as well as expected to the CIL process used at the plant. “We decided that the best way to improve the recovery would be to introduce fine grinding to liberate the gold within the pyrite particles. But you can’t fine grind 1,8 Mt of material a month, as the energy costs would be prohibitive. So we’ve also reintroduced flotation – a process used by Anglo American when it originally commissioned the Brakpan plant but which was subsequently discontinued – to separate out the sulphides contained in the incoming feed. The new flotation and milling sections, together with a small dedicated leaching plant, constitute the FFG circuit.” Schoeman added that while a 0,03 g/t increase in gold recovery might seem small, the huge volumes processed at Brakpan meant that this marginal improvement translated into sig- nificant additional gold production of around 50 kg or 1 700 ounces a month. Although the FFG or high-grade circuit came on line in January 2014, it operated for less than three months before DRDGOLD decided to suspend operations as it was not delivering the outcomes expected and, in addition, was having a negative impact on the low-grade CIL circuit. At the time, Pretorius described the decision to take the FFG offline as the biggest and most difficult decision he had had to take during his tenure as CEO of DRDGOLD. By September 2014, DRDGOLD had com- pleted an analysis of the problems and optimised the circuits and was confident enough to reintroduce one stream of the three- stream FFG circuit, with generally positive results. It followed up in January 2015 by restarting the other two circuits. The result was

Above: One of the vertical mills in the fine grind section of the FFG circuit (photo: Arthur Tassell).

Right: Another view of hydraulic mining by

DRDGOLD. The hydraulic mining method is the main ‘mining’ method used by DRDGOLD although front- end loaders are used to reclaim a small proportion of the company’s tailings resource – specifically, the sand dumps which resulted from the early ‘stamp milling’ process.

30  MODERN MINING  August 2016