Five phases of metallurgical testwork have been completed using samples derived from the Los Candelones deposit. Historical work includes test programs at SGS Lakefield in 2007, ALS in 2012 and SGS Chile in 2014. More recent work includes preliminary testwork on three sulphide and one oxide composite samples at Bureau Veritas Minerals ("BVM"), Vancouver in 2020 and additional ongoing column leach testwork in 2021, also at BVM.
All bottle roll leaching tests using samples of oxide mineralization have shown that conventional agitation leaching would extract between 90% and 95% of the gold.
A 5,000 kg bulk sample of oxide mineralization was collected in Q1of 2021 and shipped to Bureau Veritas in Vancouver for final column testing. A column leach test using agglomerated crushed oxide sample showed fast extraction of gold from the finely crushed Oxide Composite sample. Approximately 90% gold and 40% silver extractions were achieved within 10 days of leaching and the final 30-day leach extractions were 91% and 44% for gold and silver, respectively.
There are no material deleterious elements or compounds associated with the oxide mineralization, although a preliminary geochemical test suggests that the tailings from a leaching process may be acid generating.
Four additional column leach tests were prepared by BVM in 2021 and operated while the PEA was being prepared. Two tests comprised agglomerated oxide composite samples, one crushed to minus ¾ inch or 19 mm (Column 1) and one crushed to minus ½ inch or 12.5 mm (Column 2). The other two columns contained composite samples of minus 12.5 mm agglomerated transition (Column 3) and sulphide mineralization (Column 4).
The two oxide columns were leached for 44 days, and the transition and sulphide columns were leached for 79 days.
These tests show that, even at a crush size of 17 mm the oxide mineralization leached rapidly with 90% gold extraction achieved in 30 days, or a solution to solids ratio of 1.6.
The final transition sample preliminary results showed about 69% gold extraction and the sulphide sample around 32% for the same period. The estimated gold recovery used in the PEA for the three types of mineralization were 80%, 50% and 20% for oxide, transition and sulphide, respectively.
Two large diameter (3.75 m by 0.525 m) metallurgical column tests utilizing Run-of-Mine (“RoM”) oxide material were started after the PEA was released. This test program confirmed that the RoM Oxide mineralization at Candelones is amenable to heap leaching and approximately 95% gold recovery can be expected over 90 days using the reagent concentrations assumed in the PEA. Reducing the reagent concentrations by 40% demonstrated a 91% recovery after 106 days with reagent consumptions 20% lower than the PEA estimate. Leaching was still active when the testing was terminated. These reflect material improvements over the PEA estimates.
The 2021 column leach test results support the PEA estimates even though the final PEA design criteria allowed primary ore breakage only to minus 100 mm to 150 mm using a mineral sizer. Also, it should be noted that there is no sulphide mineralization within the PEA pit design.
Metallurgical testwork in 2019 was completed on three bulk composite samples collected from drill cores completed during Unigold's 2019 drill program. The three composite samples tested were:
- Composite 1 Target A disseminated sulphide mineralization – VMS origin.
- Composite 2 Target A massive to semi-massive sulphide mineralization – epithermal origin.
- Composite 3 Target B polymetallic quartz-barite mineralization – epithermal origin.
Grinding testwork suggests that the sulphide mineralization is of medium hardness with Bond ball mill work indices of around 13 to 15 kilowatt hours per tonne ("kWh/t").
Flotation can recover over 90% of the gold in all types of sulphide mineralization into a sulphide flotation rougher concentrate. Copper concentrates containing >20% Cu and elevated gold and silver credits can be produced from the CE massive sulphide and the Target B mineralization.
Gravity concentration of the B-Zone composite C3 recovered about 50% of the gold into a rougher concentrate grading 29 grams per tonne ("g/t") gold and 16% of the gold into a cleaner concentrate containing 548 g/t gold.
The preliminary leach testwork showed that the epithermal sulphide mineralization at Target B tends to be more amenable to conventional leaching technology, with gold extraction of almost 90% achieved from standard bottle roll tests. The disseminated and semi-massive sulphide flotation concentrates are only [partially amenable to conventional atmospheric cyanide leaching with results between 35 to 60% recovery of the contained gold recovered.
There are no material deleterious elements or compounds associated with the sulphide mineralization, although preliminary Net Acid Generation ("NAG") tests suggest that the tailings from a flotation process will likely be acid generating.
Metallurgical testwork in 2021 was completed on a bulk composite sample collected from Target C drill cores completed during Unigold's 2020 drill program. Once again, this epithermal mineralization behaved in a similar fashion to the Target B mineralization with approximately 90% of gold and silver reporting to a bulk sulphide flotation concentrate.