Modern Mining January 2019

GOLD

adjustments caused overloads and mill grind- outs, with a consequent loss of production.” To optimise the performance of the SABC circuit, a focused comminution initiative was launched by Asanko Gold. The measures imple- mented have included fragmentation mapping and BWI mapping within the pits along with modifications to the comminution circuit to reduce the size fraction of fresh ore delivered to the SAG mill. In addition, mill feed monitoring equipment has been installed on the SAG mill in the shape of American technology known as the MillSlicer, which was supplied to AGM by the African agent for the system, Pro-Op Industries in South Africa. “The various interventions have worked incredibly well and the plant is now easily meeting – and indeed consistently exceeding – its 5 Mt/a nameplate capacity,” says Bradford. “Current milling rates, in fact, have reached 5,8 Mt/a when annualised. The MillSlicer tech- nology – which adjusts the feed tonnage based on the level in the mill which ensures that we have the right blend of ore at the right tonnages in the mill – has been absolutely key to the success and since its installation it’s almost as though we’re dealing with a new mine.” In essence, the MillSlicer is an instrument that monitors – via a number of vibration

modifications consisted of an additional tail- ings line and pump train to the tailings storage facility; larger inter-tank screens; cyclone over- flow and thickener underflow pipe diameter increases; and a larger pump and delivery line on the thickener underflow. Implementation of P5M was handled by DRA (responsible for designing and building the original Asanko plant) and the upgrades were commissioned by the end of 2017. In December 2017, the plant achieved the targeted throughput for the first time. According to Bradford, the upgrades to the plant were not sufficient in themselves to guarantee the success of P5M. “Despite all the modifications being implemented, from the mill discharge to the tailings line, it ini- tially proved difficult to consistently achieve the required mill feed rate,” he explains. “We determined that this was due to a number of factors, notably a lack of understanding of ore hardness and Bond Work Index (BWI) require- ments for the various ore types, poor mill feed fragmentation due to inadequate crushing capability at the new tonnages and insufficient oxide in the feed blend. “Compounding the problems were ineffec- tive over- or under-predicted interventions made by SCADA operators. Over-zealous

Mining operations in the main Nkran pit.

In December 2017, the plant achieved the targeted throughput for the first time.

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January 2019 _ MODERN MINING _ 63