JOHANNESBURG (miningweekly.com) – Extensive metallurgical testwork at Liberian gold exploration and development company Hummingbird Resources’ Tuzon deposit, in Liberia, has achieved increased recovery rates of 90%, up from the 88% recovery rates announced in the preliminary economic assessment (PEA).

The variability tests, which were carried out as part of a of a definitive feasibility study (DFS), yielded recoveries ranging from 86.3% to 93.5%, with average recoveries of 90% for sulphide samples and 92% for oxide samples. 

The oxide portion of the deposit made up less than 10%. 

Further, diagnostic leach tests indicated that the recovery of between 9% and 11% of gold was associated with sulphide minerals, leading to a decision to evaluate lead nitrate as a potential catalyst for gold leaching, which was found to yield a significant reduction in cynanide and lime consumption. 

Notably, cyanide consumption was reduced by 67%, from 0.9 kg/t to 0.3 kg/t, as a result of the addition of lead nitrate.

The testwork also led to the selection of a grind size of 75 micron, with gold recovery showing an increasing trend with fineness of grind from 150 micron to 75 micron.

Hummingbird CEO Dan Betts said on Tuesday that the improved recovery results marked another important step in the company’s optimisation of the project and its progress with regard to completing the DFS. 

“Building on the work done for our PEA, we are very pleased that, following further comprehensive testwork, an increase in recoveries to 90% across the Tuzon deposit has been achieved. The company remains fully funded beyond DFS," he commented.

To further optimise the metallurgy of the Tuzon deposit, ongoing testwork would focus on testing pre-oxidation and carbon-in-leach at elevated oxygen levels to see if this yielded similar results to the lead nitrate addition at a lower cost.

Further studies would also look to improve the efficiency of the lead nitrate addition rate and investigate alternative oxidants and sources of nitrate to reduce costs.

Further work would also be done to determine final thickener sizing.

“The above optimisations will be included in the DFS if they offer superior recoveries or technical or economic benefits over the existing selected process,” said Hummingbird.