Metallurgical testwork conducted for The Broken Hill Proprietary Company Limited on Coronation Hill ore.

Abstract

The objectives of the testwork were to obtain data required for plant design and process engineering at Coronation Hill. The testwork was to determine the conditions of optimum gold recovery, while monitoring the recovery of Pd and Pt. There were nine specific aims of the testwork: 1. To determine the effect of gravity concentration on precious metals 2. To optimise grind size with respect to gold recovery 3. To assess the effect of leach additives on metal recoveries 4. To perform carbon selection testwork and adsorption modelling 5. To study pulp rheology as it would affect agitator design 6. To study the effect of aging ore prior to leach 7. To determine the Bond work index of ore 8. To determine the abrasion index of ore 9. To generate a tailings sample for tailings dam engineering. 200kg of -3mm ore from Coronation Hill was supplied for recovery testwork. This was determined to have an average grade of 3.66g/t Au, 0.20g/t Pt, and 0.648g/t Pd. A gravity circuit is recommended to recover gold as soon as possible, because 25% of gold could be recovered in 0.5% of the total mass. It is possible that at grinds finer than 80% passing 150micron, some gold goes to slimes which are then not recoverable by gravity and do not leach well unless the ore is further ground to finer than 80% passing 53 micron. An optimum grind size of 80% passing 75 micron is recommended. With gravity concentration and 48hours leaching, this would give gold recoveries of >98%, Pd recoveries of 67%, and Pt recoveries of 17%. Reagent additions would be of the order of 1.2kg NaCN/ t of ore, and 2.4kg Ca(OH)2/t ore. No other leach additives are recommended. Pt levels were too low to study, but Pd was found not to load well onto any activated carbon, and was readily displaced by gold. If activated carbon is to be used, Norit RO 3515 (extruded type carbon) is recommended. However, tests on resin showed this was superior to carbon with respect to both gold and palladium. There is nothing unusual about the rheology of the slurry with regard to design of agitators, and the ore did not age over one week after grinding to fine size and exposure to the atmosphere. The Bond Work Indices of the ore types were: QFP: 17.5kWhr/T; QTZ 20.5kWhr/T; and GTS 20.3kWhr/T. The abrasion index was determined at 0.1043.