Material from those stockpiles is being fed through a crusher ahead of being sent to the plant. Silver processing is due to start at the end of the first quarter of 2022 and run through to the end of October.

Manuka has completed all the major capital upgrades at the Wonawinta plant and wet commissioning on silver-bearing stockpiles is underway.

In February Manuka bought Oceana Gold's Reefton processing plant for $400,000 for Wonawinta.

The plant upgrade was mainly to gain an improvement in efficiencies, silver recoveries and performance.

There were also improvements in plant operational safety specific to silver production.

Metallurgical test work conducted over the past 12 months has helped develop improved material handling and processing procedures for the Wonawinta silver oxide stockpiles.

Manuka also made use of the specific expertise of Australian Minmet Metallurgical Laboratories, Australian Laboratory Services, CSIRO and Como Engineers.

AMML helped verify earlier findings from testwork by Como and ALS.

Thanks to QEMSCAN - quantitative evaluation of minerals by scanning electron microscopy - data from ALS and spectral core analysis by CSIRO, geometallurgical insights were gained in terms of silver distribution and leachability.

Laboratory findings indicate ultrafine clay particles reduce silver adsorption into carbon particles, resulting in suboptimal silver recoveries. This occurs as the ultrafine particles tend to clog the internal porous structure of the carbon and cap maximum adsorption rates.

Further analysis showed desliming upgraded silver recoveries and enhanced dissolution and carbon recovery.

Simply put, by screening out the clays Manuka expects to increase average grade through the plant to more than 85 grams per tonne silver while reducing ore through the plant by about 30%. That will significantly improve profitability and the overall robustness of the project.

The knowledge gleaned from those trials has led the company to what it believes to be the optimal means of processing the stockpiles.

It will also be relevant to the future mining of the oxide resource at Wonawinta. That resource stands at 50.9 million ounces of silver. It does not include the silver in the stockpiles.

The Wonawinta plant has a nameplate capacity of 850,000 tonnes per annum.