Aurum Resources says it has obtained outstanding gold leach results exceeding 93 per cent recovery in recent metallurgical testwork on 50 samples from its Boundiali BDT1 target in Côte D’Ivoire, West Africa.
The company says samples selected for 24-hour cyanide bottle-roll leach tests were drawn from diamond core at various stages of oxidation and across a range of gold grades expected to be encountered in routine open pit mining. It considers the sample suite to be representative of the BDT1 prospect in an area measuring 500m north-to-south, 300m east-to-west and to a vertical depth maximum of 326m below surface, but averaging 106m below surface.
The metallurgical work was undertaken at Intertek’s laboratories in Ghana. Samples were pulverized to 85 per cent passing 75-micron (0.075mm) and then subjected to a bottle-roll cyanide leach for 24 hours using Intertek’s cyanide technique.
Analysis of the leach liquor was undertaken to measure its gold grade. The residue was then filtered and analysed by 50g fire assay to provide a grade for the remaining tails.
The two final analyses are combined to provide a calculated head grade for the original sample and the gold recovery percentage is then derived by dividing the leach grade by the total head grade. The company describes the results from the test work as encouraging, with calculated recoveries for oxidised samples ranging between 91 per cent and 99 per cent and averaging 97.5 per cent.
Aurum Resources managing director Caigen Wang said: “Preliminary gold recoveries meet our expectations and confirm gold at BDT1 is highly-amenable to standard cyanide leaching. While further work is needed, these are very encouraging results.”
Samples with head grades higher than 0.25 grams per tonne gold reported average recoveries of 93 per cent, while fresh rock samples of all rock types – ranging from sandstone, sericite schist, shale and volcanic rocks – reported an average recovery of 90.3 per cent.
Management says it has noted a direct correlation between sample head grade and recovery, with head grades higher than 0.25g/t gold typically correlating with recoveries above 93 per cent, as has been observed in similar “free-milling” gold deposits.
Sometimes better recoveries can be obtained from lower-grade rocks in such cases, but usually require a finer grind size, for which the returns from the additional energy input required may not always be worth the greater expense in horsepower and other milling and reagent costs – and perhaps even an increase in leach residence time.
Management says the company is well-funded following a recent $17 million capital raise, with more to come if shareholders approve a second placement tranche slated for next month.
Aurum is charging ahead with a rapidly-expanding drilling program at Boundiali and expects to have six of its own diamond rigs running from the end of August. It will enable the company to drill more than 45,000m this year to meet its goal of delivering an initial Boundiali JORC resource by the end of 2024.
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By Doug Bright
