Hillgrove Resources (HGO) commenced open pit mining of the Kanmantoo mine, South Australia in 2011 implementing an industry standard grade control method using blast hole sampling and ordinary kriged estimation methods. Reconciliation against mine and mill shows the process resulted in significant mis-classification of ore and waste. At the International Mining Geology conference in 2017, the results of introducing a more appropriate grade control process for the style of geology was presented. Since the implementation of the new process in March 2016 the mine to mill reconciliation has averaged +3 per cent Cu metal. With confidence in the grade control practices and the elimination of fighting mine vs mill 'spot-fires', focus has been able to turn to continuous improvements in ore assaying and in acid rock characterisation.In mid-2017 the concept of utilising portable x-ray fluorescence (pXRF) for blast hole sample assaying was investigated. Despite a clear benefit to costs, the accuracy and reliability of the pXRF assaying method on blast hole cuttings is often a concern for grade control purposes. However, after ensuring the correct calibration of the pXRF process for the Kanmantoo mineralisation through various trials, the Company successfully implemented a pXRF grade control process and reduced costs by over $1 million dollars per annum. The operation has since experienced continued excellent mine to mill reconciliation. In early 2018 the Company investigated the causes of the empirical observation that historical sulphide waste dumps were not generating any acid mine drainage (AMD). Test-work showed that pyrrhotite and almandine, common minerals in Kanmantoo waste rock, had beneficial impacts on acid generation capacity and neutralisation capacity respectively, and it was found that common AMD testing methods undervalued the effect of these minerals. Rigorous test work resulted in non-acid forming (NAF) waste rock at the Kanmantoo mine being re-classified as <0.6 per cent sulphur, compared to the previous <0.3 per cent S. This is a significant result allowing a substantial increase in NAF rock volumes for greater encapsulation of high sulphur bearing waste rock.This paper provides summaries of the continuous improvement investigations implemented as a result of having a reliable grade control process.
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