Pilot testing of Classic’s Gekko processing plant has returned encouraging results with the first bulk sample from the Kat Gap project producing a concentrate grading 90g/t gold.

Along with the discarded tailings grading 1.62 grams per tonne (g/t) gold, this works out to a head grade of 6.06g/t gold, which is more than twice the average Inferred resource grade of 1Mt at 3g/t gold calculated in April 2020.

Importantly for Classic Minerals (ASX:CLZ), the higher than expected head grade is an indication that its resource estimate might be a tad conservative.

Some evidence for this can be seen in recent infill drilling, which has returned further high-grade results.

It also proves that the plant is perfectly suited to extracting high levels of gravity gold at a relatively low cost and no chemical reagents from Kat Gap-style ore.

Performance of the plant is also in line with expectations, with a recovery of 73.2% into a mass pull of 4.6% of the feed compared with the bench scale metallurgical test work of between 65% and 75% in about 5% mass pull.

This consistency is encouraging given that the Gekko plant followed by grinding and leaching circuit has been shown to demonstrate 98% gold recovery in metallurgical testwork.

“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 than we originally thought we would get,” chief executive officer Dean Goodwin said.

Taking the Lady Ada deposit as an example, he noted that while it’s pre mining block model resource was 154,374t at 4.57 g/t for 22,536oz of contained gold Sons of Gwalia actually mined 95,865t at 8.81g/t for 27,154oz of contained gold, which is a substantially higher grade and gold 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,” he added.

Likewise chairman John Lester flagged that the results indicated that Kat Gap would be in the lower cost quartile due to the beneficiation of ore prior to gold recovery and that recovery would likely be repeated during any toll milling that might be undertaken prior to securing all processing licences.

“All this bodes extremely well for the future revenue generation for Classic,” he concluded.

Classic Minerals asx clz
Gold concentrate produced by the Kat Gap Gekko plant. Pic: Supplied

Gekko plant results

The Gekko plant produced a concentrate containing crushed material which was mostly quartz with minor fractions of iron oxide and other base metal minerals.

Gold was present as both freely liberated gold (38% of the concentrate gold) and as binary gold/gangue particles.

A base metal scan is also underway to determine what other metals or minerals are present in the concentrate.

Classic noted that by controlling the mass pull to an optimal value, the project financials may be maximised based on the gold price, and ore feed grade.

This allows the company to consider three possible configurations using the current plant flowsheet:

  • Low grade feed upgraded to an economic grade at a high throughput rate;
  • Upgrade high grade ore to discard most of the mill feed as a ‘low grade’ tail which may be economic to process at a later date when there are sufficient tonnes; and
  • Process high grade ore through the Gekko Plant to produce a gravity concentrate at low cost and reagent usage with gravity tail leached.




This article was developed in collaboration with Classic Minerals, a Stockhead advertiser at the time of publishing.


This article does not constitute financial product advice. You should consider obtaining independent advice before making any financial decisions.