The positive NI 43-101 PEA determined the project to have an 18-year mine life with its estimated 32.7 million tonnes of ore with a diluted grade of 9.07% zinc-equivalent to be mined and processed at an average 4,900t per day.
A start-up mining rate of about 5,000tpd will be achieved with conventional truck and shovel surface mining from the Tom and Jason deposits, with production the shifting underground in the third year.
The study showed 1.54Mt of zinc, 880,000t of lead and 37 million ounces of silver in concentrate could be shipped, while the average contained-metal production was forecast at 85,000t zinc, 48,000t lead and 2Moz silver.
Looking at the economics, the project was said to have a post-tax net present value (8%) of C$448 million (US$347.3 million) and internal rate of return of 24% using a US$1.21 per pound ($2,668 per tonne) zinc price, 98c lead price and $16.80 per ounce silver price.
The pre-production capital expenditure is expected to be manageable at C$404 million, with a rapid payback possible in four years.
The PEA also showed there were a number of opportunities for Macmillan Pass to see a significant economic improvement, with known zones open for expansion, including high-grade areas, and a large, highly prospective land package untested with modern exploration methods.
Fireweed CEO Brandon Macdonald said the PEA was a significant step towards production at Macmillan Pass, with the economics demonstrating that the project was viable at the zinc, lead and silver prices levels used in the study, as well as "highly robust".
"With consideration of the exploration upside not just at the known zones, but also within the broader land package, the project is steadily shaping up to be a premiere district-scale zinc mining camp in the mining-friendly Yukon Territory," he said.