In 2010, Peel undertook preliminary metallurgical testwork on two representative samples of Apollo Hill mineralisation to determine potential extraction characteristics.
The key findings of the test were highly encouraging:
- Overall gold extraction was excellent for both samples; 98.68% and 98.76% total gold was extracted for Samples 1 (15m – 16m) and 2 (154m – 155m) respectively.
- Leach kinetics were rapid, with a significant proportion of gold solubilised within the first two hours of cyanide contact.
- Both samples contained a significant amount of gravity recoverable gold, greater than 80%. Reagent consumption levels were low to moderate, with relatively low base metal levels.
- Organic carbon levels were also below detectable limit, indicating very little chance of pre-robbing occurring during cyanidation.
More comprehensive metallurgical testwork in 2012 also returned promising outcomes:
- Assays indicate clean, coarse-grained mineralisation with variable assay repeatability
- SMC testwork indicates hard to very-hard rock strength of larger particle sizes (DWI average of 11.3 kWh/m3)
- Bond Ball Mill Work Index indicates medium hardness of smaller particle sizes (BWI average of 14.3 kWh/t)
- Bond Abrasion Index indicates low abrasiveness of ore (BAI of 0.055 Ai), meaning low steel ball consumption and low wear on pipework and crushing and grinding equipment
- Excellent gravity gold extraction with 88% recovery at 75 µm; 68% recovery at 500 µm.
- Excellent gravity plus cyanide leach gold extraction (48hrs) with 99% recovery at 75 µm; 96% recovery at 500 µm; moderate cyanide consumption, low lime consumption
- Moderate to good cyanide leach gold extraction at coarse grind/fine crush sizes: 86% at 2mm; 72% at 4mm; 73% at 6mm; moderate cyanide consumption, low lime consumption
The latest testwork on ore from Apollo Hill was conducted in 2016, and results continue to highlight the positive metallurgical characteristics of the gold deposit:
- Excellent Au extraction with agitated cyanide leach; 92 – 98% recovery at P80 sizes of 300, 150 and 90 microns
Excellent gravity Au extraction; Gravity Recoverable Gold (GRG) test returned 82.5% recovery
- Moderate to good Au extraction with column leach; heap leach simulation tests at HPGR crush sizes of -4mm and -8mm achieved 76.7% and 69.1% recovery respectively; moderate cyanide consumption