Abstract

Over 99.5 percent of ore grading 0.5 percent copper is waste and almost all of this ends up in tailings. Reducing the proportion sent to tailings reduces processing costs by at least US$10 for each tonne of coarse ore rejected prior to milling. Significant savings occur when large operations reject 5-20% of their planned plant feed through sensing and rejection while incurring only minor metal losses. A ten million tonnes per year operation could save US$5-20 million per year in unnecessary waste processing while increasing feed grade by 10-15 percent and generating 10-15 percent more metal in concentrate for the same plant throughput due to the higher feed grade and more consistent feed quality.

These results are being achieved when high specification, representative, sensing techniques are applied to conveyed flows after primary crushing. Prompt Gamma Neutron Activation Analysis (PGNAA) systems provide measurements with 0.02 percent copper precision on flows up to 6,000 tonnes per hour and allow increments of 30 seconds (up to 50 tonnes) to be diverted as needed. The use of high precision measurement systems reduces the misallocation of ore as waste or waste as ore by more than 50 percent compared with less representative, surface sensing techniques such as XRF, LIBS, hyperspectral scanning, etc.

The significant improvements in ore and waste allocation increases GHG savings by ensuring the automation of grade control and more effective separation of waste from ore prior to further comminution and processing. Furthermore, the waste can be categorised as clean or acid generating depending on sulphide or clay content so that clean waste can be used for construction purposes.