Osisko Metals Incorporated announced preliminary metallurgical and grindability testwork results from the Gaspé Copper Project located near Murdochville in the Gaspé peninsula in Québec. Testwork was performed on eighteen composite samples of mineralized drill core from selected intersections of the 2023 drill program at Copper Mountain, and employed a conventional copper-molybdenum flotation flowsheet and reagents. A bench-scale metallurgical test work program was undertaken at Base Metallurgical Laboratories located in Kamloops British Columbia.

The testwork program included: Sample Characterization; Grindability; Conventional flotation flowsheet and reagent schemes; Batch and locked-cycle Cu-Mo bulk flotation tests to produce copper (Cu) and molybdenum (Mo) concentrates; Composite Cu-Mo bulk flotation followed by Cu-Mo separation tests; Head grades tested ranged from 0.21% to 0.90% copper, 44 to 1347 g/t molybdenum and 0.9 to 5.0 g/t silver. Eighteen composite samples, totaling of 1100 kg, produced from drill core providing a suitable range of copper grades were selected for metallurgical testing. Head assays for the eighteen composite samples ranged from 0.21% to 0.90% copper, 44 to 1347 g/t molybdenum, 0.9 to 5.0 g/t silver and 0.01 to 0.07 g/t gold.

Composites were created based on the selected drill core intervals (Table 2). Once created each composite was stage crushed to nominal 1.5 inch (3.8 cm), representative mass was split out for SMC testing at the -31.5 mm and +26.5 mm range. Once SMC testing was completed the products were returned and the composites were again stage crushed to -½ inch (-1.3 cm) where 15 kg was removed for Rod Mill Work Index testing.

The remaining mass was stage-crushed to -6 mesh. The crushed material was blended and split into 24 kg sub-lots, each sub-lot was rotary split into 2 kg charges. A single test charge was riffle split to remove 250 g for head assay.

The head cuts were pulverized to 80% passing 75 µm. Metallurgical samples comprising drill core were crushed, split and sub-sampled for comminution testwork and head assays. Samples were wet-grinded in a closed batch mill at 65% solids targeting the required grind size. Ground samples were discharged into a flotation cell and pulp-level adjusted to the appropriate volume and density for flotation testing.

The pulp was conditioned with reagents before beginning flotation. A series of open-circuit batch rougher and cleaner flotation tests were undertaken to optimize flotation conditions prior to operating locked-cycle flotation tests. The combined rougher concentrate was dewatered ahead of regrinding while retaining the process water for the cleaner stage.

The rougher concentrate was reground to a target size with the regrind discharge size confirmed by laser particle sizing. The reground product was cleaned in successive dilution stages. The final concentrate and intermediate tails were filtered and dried separately in a low temperature oven before assaying.

The general approach to locked cycle testing was conducted as per the batch tests. Each cycle test was completed with 5 cycles, the rougher and 1st cleaner were completed open circuit, the intermediate cleaner tailings were recirculated to the feed of each subsequent stage for the following cycle; that is the 3rd cleaner tailing of cycle A was recirculated to the 2nd cleaner Feed of cycle B, the 2nd cleaner tail A was recirculated to the feed of the 1st cleaner Feed B. This process continued for cycles C, D and E. All final products and final intermediate streams were filtered, dried, and assayed for metallurgical balancing. Locked cycle testing provides a methodology to best estimate steady-state metallurgical projections for a full-scale operation.

Reagents used for bulk Cu-Mo flotation included lime, potassium amyl xanthate (PAX), 3418A, and methyl isobutyl carbinol (MIBC). Nitrogen sparging, fuel oil, sodium hydrosulfide (NaHS) and MIBC were used for Cu-Mo separation. Analysis was completed on pulverized sample splits using wet digestion methods for copper, molybdenum and silver.

In each case, the samples were digested by a strong oxidization using a combination of Aqua-Regia, potassium chlorate and bromine. Copper was analyzed using atomic adsorption (AA) spectroscopy, and molybdenum and silver by inductively coupled plasma ? optical emission spectroscopy (ICP-OES).

Metallurgical tests assay quality is evaluated by producing material balances of all products reconciled head which is compared to the direct head for all elements in consideration. Grindability tests were performed on each of the metallurgical samples. The average SMC Axb value was 46.6, average Bond Ball Mill Work index (BWi) was 10.49 kWh/t, average Rod Mill Work Index (RWi) was 13.89 kWh/t and average Abrasion index (Ai) was 0.384.

A composite sample was initially tested with average copper grade to determine the optimal grind size for further flotation tests. Four (4) grind sizes ranging from 80% passing (P80) of 66 microns to 125 microns were tested. P80 of 75 microns was selected as the primary grind size for further testing.

Cu-Mo locked cycle tests (LCT) were performed at a grind size of 75 microns for the rougher stage with regrind to a target of 30 microns for the cleaner stages. Copper concentrate grades ranged from 17.1% to 30.9% with recoveries ranging from 86.1% to 95.7%. Molybdenum grades ranged from 0.08% to 2.74% with recoveries ranging from 75.7% to 92.3%.

To produce molybdenum concentrates, due to the low feed concentrations, metallurgical samples were combined to produce three larger composite samples (low-, medium- and high-grade copper samples) for batch bulk flotation tests and subsequent Cu-Mo separation testing. Copper head grades ranged from 0.26% to 0.55%, molybdenum grades ranged from 135 to 234 g/t and silver head were consistently 2.2 g/t. Multiple large batch flotation tests were performed for each composite sample to produce bulk Cu-Mo concentrates followed by Cu-Mo separation tests. Three Cu-Mo separation locked-cycle tests were performed at a grind size of 30 microns for the rougher stage with regrind to a target of 15 microns for the cleaner stages.

Table 4 shows final copper concentrate grades and recoveries for the locked-cycle tests. Copper grade ranged from 22.2% to 30.9% with recoveries ranging from 92.3% to 96.6%.