Alto nails gold leach recoveries to 97 per cent at Sandstone
Metallurgical testing on reverse-circulation (RC) drill samples from Alto Metals’ Indomitable target at Sandstone in Western Australia has achieved 97 per cent gold recovery at a 150 micron grind.
The company says the result has important implications for its Sandstone project, demonstrating that Indomitable and all other deposits within the operation are amenable to conventional cyanide extraction.
The samples comprised selected intervals of sheared ultramafic rocks with quartz veining and sulphides. They included what Alto believes to be primary gold and representative of Indomitable’s mineralisation style.
Gold recovery testwork was undertaken by Independent Metallurgical Operations on composited drill-chip samples from below the oxide zone in six drillholes, with depths ranging between 110m and 224m. It involved a process that not only provides an insight into the relatively simple initial mechanical gravity recovery of the gold component of the sample material, but also reduces the duration and cyanide (or other leach reagent) consumption that would occur if gravity gold was not separated out.
Management says some antimony – a hot commodity currently in world markets – had also been noted in its initial head assay analyses.
Gold recoveries at the grind size of 150 micron were 89.4 per cent within two hours, 94.3 per cent within four hours, 96.1 per cent within eight hours, 97 per cent within 24 hours and 95.8 per cent within 48 hours. Ultimately, the bottle roll recoveries were added to the gravity gold recoveries to produce the final recovered gold results.
The best leach result was for the “Composite 1” coarse (150 micron) fraction that yielded the 97 per cent gold recovery in 24 hours, with a gravity recovered grade of 3.07 grams per tonne for an overall recovery of 95.8 per cent.
Cyanide consumption for the 150 micron (coarse) bottle roll leach was 0.42kg per tonne, which is considered relatively low, and 0.12kg per tonne of lime was added to maintain a 9.5pH.
Management says the fresh rock recoveries were complementary to previous accelerated cyanide leach tests on oxide material using the trademarked Leachwell process that achieved a 93 per cent recovery on material from Indomitable.
This latest metallurgical testwork carried out on samples from our Indomitable deposit demonstrates that primary mineralisation within the fresh rock has excellent overall recoveries including a high gravity gold component. Importantly, the testwork confirms the material can be processed using conventional gravity and cyanide leaching, further de-risking the Indomitable deposit and the Sandstone Gold Project.
The company is also well into its planned 3500m RC drilling program it launched last month at Sandstone in a search for extensional targets beyond the defined mineral resources at its Vanguard, Ladybird and Bull Oak gold deposits.
It follows a review of previous gold-in-lag and drill-collar soil geochemical results that defined solid gold concentrations and significant lower-grade haloes over the Vanguard and Vanguard North deposits, which contain a combined mineral resource totalling 150,000 ounces.
The program also includes initial scout drilling at Alto’s new Lightning prospect that sits within its own mining lease and abuts one of its exploration licences, about 3km west of the Vanguard camp. Management says a 1km-long, open-ended and untested gold-in-soil anomaly with a peak value of 242 parts per billion gold lies in a favourable structural setting in the northern part of the Lightning mining lease and extends into its adjacent exploration licence.
It has been compiling and validating historical data relating to the Lightning lease and expects the information to inform future targeting as it ramps up its exploration of the new area, including the imminent drilling. Alto recently secured the nearby Lightning gold prospect through an option and tenement sale agreement with a private vendor for a $20,000 option fee for the right to acquire 100 per cent of the ground at any time within two years by paying a further $100,000.
In early August, the company revealed an agreement to merge with Brightstar Resources to consolidate the Sandstone gold operations. The Alto board has unanimously recommended the deal.
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