22 May 2018
Nighthawk Gold Corp. is pleased to provide a summary of results from its ongoing preliminary metallurgical testwork on the Colomac Gold Project. Findings reveal: a relatively uniform hardness for material tested to-date; that the rock is amenable to all standard gold recovery technologies; and using a combination of gravity and cyanide leach recovery processes, testing showed that gold recoveries range from 96.5% on the lower-grade material and up to 98.0% on the higher-grade rock, representing a significant increase in recovery over historic production results of 88.1% (1994 to 1997).
Two initial bottle roll leach tests were carried out to assess cyanide heap leach feasibility. Minus 12,700 micron (1.27 centimetre) material registered up to 81.8% recoveries on lower-grade rock (1.81 grams per tonne gold "gpt Au",head grade) and 57.50% on the higher-grade material (4.99 gpt Au). One column leach test has been completed to date on higher-grade mineralization posting a recovery of 34.30%. Such noted 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.
Higher-Grade Testwork Highlights:
•Minimal variation in rock hardness of all test samples indicates relatively homogeneous host rock;
•Favourable recoveries were achieved for all process options, including, flotation, gravity separation, and heap leaching;
•Gold extraction by flotation ranged from 90.7% - 94.6% with maximum tested recoveries achieved at a feed size F80 of 75 microns (optimum grade-recovery performance was not examined);
•Cyanidation of ground rock after gravity concentration increased gold recoveries significantly up to 98.0%;
•Cyanide heap leach results show considerable variability between testing methods and grade of material processed but fall within expected performance range for crushed ore (recoveries between 34.30% up to 81.8%).