EXPLORING HPGR TECHNOLOGY FOR HEAP LEACHING OF FRESH ROCK GOLD ORES

This paper discusses the concept of applying HPGR technology to the preparation of low grade gold ores for heap leaching. Examples of recent testwork results from four Western Australian projects are discussed with key issues for the flowsheet development team identified. Understanding the leach extraction and therefore the lowest cut-off grade that can be fed to a HPGR heap leach circuit is obviously important. Establishment of the upper and lower boundary and variability of the gold grade and recovery window defines the feed limitations. Across a resource, both measures are crucial to project economics. Characteristics that promote the application of HPGR prepared Heap Leach processing for large tonnage projects are presented in the paper. Of note is the potential dual use of the crushing circuit for both the main CIL/P plant and the heap leach. HPGR has been shown to influence the extraction and kinetics of leaching low grade gold ores. A very significant increase in gold extraction is typically returned for HPGR prepared -2 mm feed, compared to cone crushed material in amenable ores. Directly comparing leach extraction performance from machines that inherently produce differing PSDs can however be misleading. Both the increased fines production from the HPGR and the influence of micro-fracturing contribute to the improved leach extraction. Indications suggest a 10 to 11% additional gold leach extraction due to the HPGR micro-fracturing effect, together with gains from increased amounts of fines in an HPGR prepared feed of the same topsize. The HPGR pressing force has been found to be a sensitive operational variable with respect to leach extraction and operational costs. Benefits include better liberation and costs include the need for agglomeration with cement to facilitate percolation through the heap. Scale-up issues are also discussed. The accuracy of testwork sampling and analysis for process design is as critical as that used in the resource estimation.