Classic Minerals (ASX:CLZ) reports assay results received from a recent pilot Gekko plant test work has returned an average head grade of 6.06g/t Au at the Kat Gap prospect, located in Western Australia.
The company says the mining of the bulk sample combined with the lab studies of September 2020 and processing ore through the Gekko pilot plant give a ‘large’ degree of confidence to the company.
The original JORC resource was calculated to be 1Mt @ 3g/t Au for 93,000oz, and the actual grade calculated from the pilot plant run of 6.06g/t Au is ‘much higher’ than the average inferred resource grade calculated in April 2020.
The ore material put through the Gekko pilot plant test run was sourced from the last material mined from the base of the bulk sample pit.
This material, from flitch and bench 376m to 374m RL had an average resource block model grade of 5.12g/t Au.
The result from the Gekko plant pilot is 16% higher than the predicted block model grade. The gravity gold recovery is in line with the company’s expectations, with a recovery of 73.2% into a mass pull of 4.6% of the feed.
The company says this compares ‘very well’ against previous bench scale metallurgical test work of 65% to 75% gravity gold recovery in approximately 5% mass pull.
These results demonstrate that the Gekko plant is suited to Kat Gap-style ore capable of extracting ‘high-levels’ of gravity gold at a low cost.
The company says the concentrate produced at a low cost with no chemical reagents provides confidence of the viability of the milling process.
The concentrate contained crushed material with a top size of 2.5mm, which was predominantly quartz with minor fractions of iron oxide and other base metal minerals.
Classic Minerals notes that gold was present as both freely liberated gold (38% of the concentrate gold) and as binary gold and gangue particles.
Examination of the concentrate with a loupe evidenced gold particles partially liberated within quartz particles, as well as fully liberated gold particles (base metal scans currently underway to determine minerals and metals present in the concentrate).
The pilot run demonstrates the Gekko flowsheet effectively concentrates the gold ore to produce a ‘high-grade’ concentrate, whilst discarding a proportion of the gold into a ‘low-grade’; tailing stream.
In this instance, the concentrate assayed approximately 90g/t Au, with a tailings grade of 1.62g/t Au, giving an overall head grade of 6.06g/t Au.
By controlling the mass pull into an optimal value, the project financials may be maximised based on the gold price, and ore feed grade, and 3 configurations may be entertained with the current plant flowsheet.
Configuration A is a ‘low-grade’ feed upgraded to an economic grade to an economic grade at a high throughput rate.
Configuration B is upgrading ‘high grade’ ore to discard most of the mill feed as a ‘low grade’ tail which may be economical to process at a later date when there are sufficient tonnes.
Configuration C is ‘high grade’ ores processed through the Gekko plant to produce a gravity concentrate at low cost and reagent usage, with gravity tail leached.
The Gekko plant offers a ‘versatile’ gold processing plant that will allow Classic to optimise recovery at the Kat Gap plant, depending on market conditions, ore competency, ore grade and gold price.
The Gekko plant, followed by a grinding and leaching circuit has been shown to demonstrate 98% gold recovery in metallurgical testwork.
The ore type is a typical free milling non-refractory ore type that is common in the eastern goldfields, with recoveries ranging from 95% and higher for most of these ore types when milled with ‘reasonable diligence’.
Classic says these early results are very encouraging and bode well for the future of open pit mining.
Classic Minerals CEO Dean Goodwin said the grades returned from the Gekko pilot run do not come as a surprise.
“The higher grades returned from the Gekko pilot run are not surprising to me given most of the open pits I’ve worked on in the Forrestania area returned positive reconciliations meaning we got more gold out of them that we originally thought we would get.
“Seeing these higher than expected results from Kat Gap, albeit exciting, are not surprising”
Seeing these higher than expected results from Kat Gap, albeit exciting, are not surprising.
Let’s look at Lady Ada for instance… it’s pre mining block model resource was 154,374t @ 4.57g/t for contained 22,536oz, but when Sons of Gwalia mined it back in 2003, they ended up mining 95,865t @ 8.81g/t Au for 27,154oz, substantially higher grade and more ounces than predicted.
There is no geological reason why Kat Gap won’t perform in a similar manner, maybe a few less tonnes but at a higher grade and more ounces.”
Classic Minerals Chairman John Lester said the company is ‘ecstatic’ about the ‘high grades’ coming from the metallurgical reports.
“We were aware that there was a high degree of gravity recovery from the Kat Gap ore, but the 73.2% is admirable.
Furthermore, the metallurgical test results showing a 98% recovery of gold from Kat Gap ore will mean that this extent of recovery can be repeated during ant toll milling that may be undertaken while we are waiting for all our processing licences.
I believe that the Kat Gap plant will be in the lower cost quartile due to the benefaction of the ore prior to gold recovery. All this bodes extremely well for the future revenue generation for Classic.”.
Classic Minerals is a Western Australia-based minerals explorer that holds approximately 578km-square of tenements across two major regional exploration areas in Western Australia.
The company’s flagship Kat Gap Gold Project has been the focus of the majority of its recent exploration effort and is located 170km south of Southern Cross, and is 50km from Classic’s Forrestania Gold Project.
Classic has a global Mineral Resource of 8.24Mt @ 1.52g/t for 403,906oz Au.