The bottle roll acid leach test of the Green Hill oxide sample showed very favorable extraction of copper, recovering a total of 90.4% of the copper and 30.7% of the cobalt with fast extraction rates (leach kinetics) achieving 75% extraction after less than 20 hours and 90.4% after 7 days. The high copper extraction rate and fast leach kinetics displayed in the bottle roll test were likely enhanced due to the presence of ferric iron (as goethite) in the Green Hill mineralisation, which can increase the solubilisation of copper sulphide minerals like chalcocite that typically achieve lower solubility under heap leach conditions. This phenomenon will take place in an operating heap leach pad as well.

These test results indicate that the Green Hills oxide mineralization is very amenable to standard low-cost heap leach recovery of copper. While the dissolution of cobalt for the sample was relatively good, the low overall concentration in the Green Hill mineralization suggests that the recovery of cobalt to a mixed hydroxide product may not be economical. Next Steps for Dianne Metallurgy: The metallurgical recoveries will be incorporated into the initial Dianne MRE, which is well advanced and planned for delivery in fourth quarter/2022.

Further metallurgical test work would focus on a process path of bulk flotation of the primary MS to recover copper and zinc into one rougher concentrate. Followed by ultra-fine grinding of the concentrate before flotation into separate copper and zinc concentrates. This approach is anticipated to improve overall recovery and give better separation of the copper and zinc into a higher-grade zinc and a separate higher grade copper concentrate.

Further metallurgical test work for the Green Hill mineralization would progress to column leach test work that would more accurately predict copper recovery under heap leach conditions.