Key Highlights

  • All three test composites recovered more than 95 per cent of their gold after 24 hours of leaching.
  • Final recoveries ranged from about 96.7 to 98.6 per cent at a finer 125 micron grind.
  • The testwork replicated the process at the Lefroy plant operated by St Ives Gold Mining.
  • Hustler has a resource of 826,000 tonnes at 1.4 g/t gold for 36,200 ounces.

Lunnon Metals (ASX:LM8) reported on 5 November that metallurgical testwork on its Hustler gold deposit at Kambalda in Western Australia returned high gold recoveries, with all three test composites recovering more than 95 per cent of their gold after 24 hours of leaching. The results add technical information to a small deposit the company is evaluating as a possible follow-on to its completed Lady Herial open pit.

The testing was carried out by ALS Metallurgy on three composites made from diamond core drilled during the June quarter. The flowsheet used gravity concentration followed by conventional cyanide leaching, and was designed to replicate the process at the Lefroy plant operated by St Ives Gold Mining, a Gold Fields subsidiary. Matching the regime to a specific nearby mill is meant to give a more realistic indication of how Hustler ore might perform if it were treated there.

The recovery figures

At a grind size of 150 microns, recoveries reached 93.9 per cent after 12 hours, 96.4 per cent after 24 hours and 97.4 per cent after 48 hours, with final results across the composites ranging from 96.8 to 98.5 per cent. At a finer 125 micron grind, recoveries were 95.6 per cent at 12 hours, 97.3 per cent at 24 hours and 97.6 per cent at 48 hours, with a final range of 96.7 to 98.6 per cent.

Gravity recovery, the share of gold captured before leaching, averaged about 32.2 per cent at 150 microns and 31.2 per cent at 125 microns. The company reported no adverse metallurgical effects, although using St Ives process water increased lime consumption, a reagent cost that would need to be considered in any processing arrangement.

How Hustler compares with Lady Herial

The figures compare with testwork on Lady Herial, which returned 91.4 per cent at 12 hours and 94.6 per cent at 24 hours at a 150 micron grind. The ore purchase agreement under which Lady Herial was mined used a 91 per cent recovery assumption. Lunnon mined more than 300,000 tonnes at 1.68 g/t gold from Lady Herial, with Mining completed in August.

Hustler lies about 400 metres south-east of the Lady Herial pit. It has a mineral resource of 826,000 tonnes at 1.4 g/t gold for 36,200 ounces, classified as Indicated and Inferred. There is no ore reserve. Across the wider Foster-Baker project area, after depleting Lady Herial for completed mining, the company reports a combined resource of 1,415,600 tonnes at 1.6 g/t for 73,200 ounces.

Limitations and next steps

Laboratory recoveries from three composites indicate how the ore responds under controlled conditions, but plant performance can differ, and recovery is only one input to economics. Hustler is small, its grade is modest, and any development would depend on mining costs, haulage, gold prices and the terms of a toll treatment or ore sale agreement, none of which has been announced for this deposit.

Lunnon plans to update the mineral resource estimates for Hustler and Lady Herial, with the results to feed into a scoping study. Geotechnical work will continue, and the company will decide whether further infill drilling is warranted. Managing director Edmund Ainscough said Lunnon would "still never take anything for granted", signalling a cautious approach despite the encouraging metallurgy.

The scoping study will be the next substantive indicator of whether Hustler can follow Lady Herial into production. Until then, the recovery results reduce one technical uncertainty but leave the commercial questions open. A further consideration is that the more encouraging Hustler recoveries, if confirmed at larger scale, would compare favourably with the 91 per cent assumption used for Lady Herial, which could become relevant to the company when negotiating terms for any future ore sale arrangement.