A drill hole into the modelled upper sequence of mineralisation at Boundary West returned 4.22% zinc, 0.34% lead and 25.6 g/t silver over 76.5m, including 6.46% Zn, 0.77% Pb and 47.5 g/t Ag over 24.1m, from a depth of 90m.
Assays from other holes are pending, including one Fireweed said had also intersected the lower mineralised sequence.
Boundary Zone West mineralisation lies about 360m west of the Boundary Zone area.
Fireweed said results pointed to similarities with known deposits at Macmillan Pass. It had intersected massive sulphides, Boundary Zone-style vein-hosted and replacement-style mineralisation, and bedded laminate mineralisation similar to that seen at Tom and Jason.
Subsequent on-section drilling intersected a second, lower sequence of zinc-lead mineralisation and vein-hosted zinc.
Fireweed estimates the massive sulphide intersection to have an actual thickness of about 15m, but cautions the veins' stockwork nature means they pinch and swell on a centimetre to metre-scale.
Fireweed has not yet published an initial resource estimate for Boundary Zone, but says the deposit should be amenable to openpit mining with a low strip ratio.
Recent drilling at Boundary Zone returned further significant, broad intersections of mineralisation, including 4.42% Zn over 212.7m containing 25.58% Zn over 5.81m.
"The massive pyrite-sphalerite-galena present in this upper interval demonstrate not just healthy zinc grades, but intriguing silver levels," Fireweed CEO Brandon Macdonald said.
Tom-Jason hosts indicated resources of 1.6 billion pounds grading 9.61% zinc-equivalent, with another 4.91Blb inferred at 10% Zn-eq. Fireweed's 2018 PEA - sans the new discoveries and better metal prices - calculated an after-tax IRR of 24% and an NPV of C$448 million. Capex was put at $404 million.
Resource Capital Funds and Teck Resources are among the company's cornerstone investors.
Fireweed shares (TSXV:FWZ) gained more than 16% in Toronto to C$1.07 during the morning session before closing up 5.4% at 97c, giving the company a market value of $54 million.