Ore Sorting of Low-Grade Gold Sulphide Deposits

"The mining industry continues to remain challenged. Lower commodity prices, increasing labor costs and more importantly diminishing reserves are amongst some of the primary factors contributing to the difficulties faced. Ore sorting technologies have demonstrated their potential to improve the downstream beneficiation performance. The general processing route sees all primary crushed material milled for liberation and then processed in accordance with characteristics of the gold therein, i.e.: refractory golds would require direct leaching or oxidation whilst free gold would follow the conventional cyanidation process, after gravity concentration. Ore dilution increases the associated operating costs within each stage of this process. The opportunity to process the same throughput at a higher grade can only be achieved through pre-concentration. Sensor based sorting has been examined on numerous occasions by various gold producers. Test work carried out on different bulk low grade gold ores has shown the successful applicability of ore sorting to remove waste, whilst maintaining high recovery rates of gold. The results of a combined XRT/Laser sensor sorter have shown grade improvements of over 300% from feed grades of 0,25g/t to 1,15g/t at gold recoveries of 66% and waste ejection rates of 85%. This paper presents some of the results from the work undertaken by STEINERT with respect to gold sulphide ore sorting and presents a modelled financial scenario, which can enable a company to target and reclaim low grade ores.INTRODUCTION The mining and minerals processing industry presents with many different challenges including, volatile commodity prices, increasing labor costs and more importantly diminishing reserves. Conventional processing routes will continue to play a crucial role in the beneficiation process, however innovative methods of reducing operating costs and optimizing on the overall circuit performance is where technologies such as sensor based sorting come into the fore. Sensor based sorting as a dry mechanical process not only reduces water consumption by eliminating unnecessary waste but also reduces the requirements for reagents in the downstream processes. Sensor based sorting under dry conditions presents a highly efficient alternative to wet pre-concentration methods such as dense medium separation (DMS)."