Nighthawk Gold Corp. May 22 said preliminary metallurgical testing on material from the Colomac gold project on its Indin Lake property in Northwest Territories returned favorable recoveries for all process options.

"Although at the early stages of metallurgical test-work, the results to-date describe Colomac rock as exceptional in terms of grind characteristics, gold recoveries, purity, and responsiveness to all standard gold recovery technologies," said Nighthawk President and CEO Michael Byron.

The best results were from a combination of gravity and cyanide leach recovery processes, which recovered 96.5 percent of the gold from the lower-grade material tested and up to 98 percent on the higher-grade rock. This is a substantial increase in recovery over the 88.1 percent recoveries achieved during the 1990s.

Two initial bottle roll leach tests were carried out to assess the feasibility of recovering the Colomac gold using heap leach. Minus-1.27-centimeter material registered up to 81.8 percent recoveries on lower-grade rock averaging 1.81 grams per metric ton gold but only 57.5 percent on the higher-grade material averaging 4.99 g/t gold. One column leach test has been completed to date on higher-grade mineralization posting a recovery of 34.3 percent. Nighthawk said such recovery variability is not uncommon as significant fluctuations have also been documented in recent metallurgical studies on other notable northern deposits and is largely a function of the particle size that interacts with the leachate.

Despite the variability, Nighthawk said it is encouraged that the Colomac results convey a positive indication of the deposit's heap leach potential, falling within the expected performance range for crushed ore.

"Although initial heap leach gold recoveries show significant variability, other northern deposits including the Fort Knox mine in Alaska, and Yukon's Coffee Gold deposit, Eagle Gold Project, and the Brewery Creek Mine all note variability in their recoveries," said Byron. "To address this, metallurgical testing is planned for 2018, that will cover some of the other mineralized zones, and will include additional bottle roll and column leach test-work as we continue to evaluate the potential heap leach option for the project."

The metallurgical work has revealed a relatively uniform hardness for all Colomac material tested to-date.

Nighthawk said additional metallurgical work is required to arrive at a statistically relevant population of results for all deposit types, mineralized zones and corresponding grade variations. As in the previous sampling programs, future metallurgical work will be carried out on Colomac drill core from recent drilling.

–SHANE LASLEY