The Macmillan Pass Project, located in Canada's mining-friendly Yukon Territory, is host to large zinc-lead-silver deposits. The project is accessible via a 3 km road from the North Canol Road off the Robert Campbell Hwy in southeast Yukon. The territorial government is highly supportive of the mining industry and the Yukon is one of Canada's top provinces for new mine developments. Find out more about the latest work being done on the property here.
In 2020, Fireweed significantly expanded the property to 948 km2. The new area includes an along-strike continuation of the highly prospective Fertile Corridor that has never been systematically explored for zinc-lead-silver deposits.
There has been a significant amount of historical exploration on the Tom and Jason properties commencing with the discovery of the Tom West Zone in 1951. This has resulted in the drilling of 128 holes on the Jason property for a total of 37,924 m and 212 holes on the Tom property, for a total of 33,495 m. In addition, an adit with approximately 3,423 m of underground development and a spiral decline were put into the Tom deposit to assist exploration and bulk sampling. Exploration effectively ceased on the properties after 1992. There has been minimal modern exploration on the properties since that time.
HudBay Minerals Inc. commissioned a mineral resource estimate in 2007 that reported 6.43 Mt indicated resources at both Tom and Jason at 6.33% Zn, 5.05% Pb and 56.55g/t Ag, and 24.55 Mt inferred resources at 6.71% Zn, 3.48% Pb and 33.85g/t Ag (Click here to read cautionary statement regarding historic resources). Through a program of relogging and sampling historic core as well as new drilling, Fireweed Zinc plans to update the historical data and work towards publication of a current mineral resource estimate followed by a preliminary economic analysis of the project.
Please click here for the full 2017 technical report
Fireweed Zinc's Macmillan Pass Project is located in the south east of Canada's Yukon Territory, approximately 372 km east of the capital city of, Whitehorse. The deposit is accessible from the North Canol Road off the Robert Campbell Hwy. Access to the Tom, Jason, Boundary Zone & End Zone is via networks of location gravel roads.
The government regional Macmillan Pass Airstrip is located on the property within three kilometers of the Tom camp and deposit and is capable of landing 18 passenger aircraft. Flight time to the capital, Whitehorse, is approximately one hour. Other regional airstrips exist, notably the Ross River Airport located one kilometer south of the town of Ross River.
The regional climate is characterized by annual precipitation of 600-700 mm. Mean annual temperatures range from -5 to -8°C. Winters are characterized by relatively dry, cold conditions with mean temperatures of -20°C in January. Summers extreme temperatures would range from -5 to 30°C in valley floors. The wettest months are in July and August with rainfall amounts of 60-90 mm.
The Tom and Jason zinc-lead-silver deposits are proximal vent SEDEX deposits formed during Devonian rifting activity in the Selwyn Basin. The Selwyn Basin is one of the most productive basins for SEDEX zinc-lead-silver deposits in the world and hosts 12 large deposits including the Tom and Jason deposits. Regional past producers were Faro (aka Anvil), Grum and Vangorda. The Howards Pass deposit (aka Selwyn) is currently one of the world’s largest undeveloped zinc deposits1. SEDEX mineralization of the Selwyn Basin occurs in four main districts of different ages: Anvil/Faro (Cambrian), Howards Pass/Selwyn (Silurian), Gataga/Cirque (Late Devonian) and MacMillan Pass/Tom-Jason (Late Devonian). Synchronous and genetically related Mississippi Valley Type zinc-lead mineralization occurs in the carbonate platforms along the east side of the Selwyn Basin.
Click here for regional geology maps, mineralization models, and Tom and Jason deposit maps and sections
1 Source:https:// https://www.woodmac.com/reports/metals-selwyn-howards-pass-zinc-mine-project-16157559
Zinc- lead- silver- barite mineralization at the Tom deposit varies from well layered to a brecciated stockwork zone adjacent to the Tom fault. The Tom West and Tom East Zones, both of which are exposed at surface, are interpreted to have formed one continuous lens prior to folding of the Tom Sequence. The Southeast Zone is interpreted to have formed in a separate sub-basin to the main structure hosting the Tom West and Tom East Zones. All three zones have been affected by folding.
The Tom West Zone dips 60 degrees to the southwest, has a strike extent of approximately one kilometer and extends up to 400 m down dip. It is about 40 m thick at its widest and breaks into two discrete layers in the centre. The highest grade portion of the Tom West Zone occurs along the southern portion of the zone where Zinc+Lead+Silver grades exceed 10%. The Tom West Zone hosts the bulk of the historical resource at the Tom deposit.
The Tom East Zone occurs near the hinge of the anticline that has folded the originally planar deposit, and which plunges northward in this area. It consists of a series of fault bounded pods of interbedded sphalerite, galena, barite and chert.
The Tom Southeast Zone is not exposed at surface, and consists of a tabular, stratiform body 0.5m to 6m thick with a strike length of approximately 400 m and a down dip extension of at least 350 m dipping 60-70º to the east. It is located near the nose of the southeast plunging Tom anticline on its eastern limb. Mineralization consists of finely laminated sphalerite, galena, pyrite and black cherty mudstone.
The Jason deposit is hosted by a Devonian sequence disrupted by faulting and folded into a series of “upright tight west-trending, shallowly east-plunging folds". The Jason Main Zone is located on the northern limb of the east-plunging Jason syncline, while the Jason South Zone occurs on the southern limb. The South Zone consists of two separate horizons whereas the Main zone is defined by a single horizon.
Click here for regional geology maps, mineralization models, and Tom and Jason deposit maps and sections.
Click here for NI43-101 disclosure and the Qualified Person information.
The Nidd property covers the western extension of the mineralized “fertile corridor” that is host to all four of the known large zinc mineralized systems in the Macmillan Pass Zinc District – Tom, Jason, End Zone and Boundary Zone (see attached map). This fertile corridor traces critical stratigraphic rock units, structural features and exploration targets from east of the Tom Deposit to west of the Boundary Zone over a length of at least 25 kilometres.
The most significant mineralization found to date on the property is the Boundary Zone where 24 historic core holes were drilled. Known mineralization is spread over an area two kilometres long and 200 to 800 metres wide with drilled mineralization in a central area 300 metres long and a true thickness of up to 285 metres of over 2% Zinc. The zone remains open to depth and along trend for further exploration. The Boundary mineralization consists of sphalerite-siderite-pyrite and minor galena in veins, stockworks, interstitial disseminations, and as replacement of matrix and clasts within diamictites and chert pebble conglomerates.
The Boundary Zone is located adjacent to a major synsedimentary structure and contains large volumes of boulder diamictites indicating that the area underwent active tectonic extension during the formation of the basin, a similar setting to the Tom and Jason areas. The Boundary Zone area is part of a distinct sub-basin that contains significant volumes of strongly siderite altered basaltic pyroclastics and lava flows within the same Earn Group formation that hosts the Tom and Jason deposits. The presence of synsedimentary faulting, a distinct sub-basin, volcanic rocks, abundant zinc mineralization, and strong alteration indicate the area is host to a robust zinc mineralizing system.
Location of Boundary Zone at Macmillan Pass
Boundary Zone is on the Nidd property roughly 15 km northwest of the Jason deposit, and is part of the Macmillan Pass Zn-Pb-Ag project, Yukon, Canada. In 2020, Fireweed made a significant new discovery at Boundary Zone West, including intervals of stratiform and vein-hosted zinc mineralization as well as a massive sulphide cap to the system.
Historic exploration work defined a central 200 x 800 m core of vein-hosted, stockwork, disseminated, and replacement-style zinc mineralization within a broader system over 2 km in strike length. Recent Fireweed drilling has shown the central system extends from surface to at least 285 m and remains open at depth and has made a new discovery, Boundary West, 350 m west of previously known mineralization.
The Boundary Zone area was initially explored by Cominco between the late 1970s and early 1990s. Work included 35 diamond drill holes as well as extensive geochemical sampling and geophysical surveying. Historic drill intersections such as 224.0 m of 2.50% zinc and 0.30% lead, including 4.5 m of 16.40% zinc, demonstrated potential for both bulk tonnage open pit and high-grade underground mineralization.
In 2019, Fireweed drilled two holes into the central part of the known Boundary Zone mineralization. Both holes intersected wide zones of high-grade replacement-style and vein- and breccia-hosted zinc mineralization, including 100.0 m (true width) of 7.94% zinc from surface including 6.4 m of 42.49% zinc within 230.0 m of 4.14% zinc.
2019 drill results (more photos in Core Photos section below)
NB19-001 93.45-97.20 Breccia-hosted and stockwork vein-hosted sph-py in black carbonaceous mudstone (more photos in Core Photos section below)
In 2020, Fireweed focused drilling at Boundary Zone, completing a total of 2,314 m in nine drill holes. Drilling was planned to test along-strike and down-dip continuity of known mineralization as well as the orientation of structures and veins, confirming the presence of a vein stockwork with multiple vein orientations. Based on ground gravity work conducted in 2020, several holes tested a large anomaly west of Boundary Zone, resulting in the discovery of Boundary West.
Boundary Zone mineralization is hosted in Mid-Late Devonian mafic volcaniclastic rocks, conglomerates, diamictites and mudstones of the Earn Group. Recent Boundary West drilling demonstrated that mineralization is also hosted in Late Ordovician-Early Silurian rocks of the Road River Group.
Mineralization at Macmillan Pass occurs along the Fertile Corridor, a trend that follows the Hess fault system across the property. The fault system was initiated during the Late Proterozoic-Early Paleozoic and has been reactivated multiple times since then. Hess fault splays at Boundary Zone provided a deep crustal plumbing system and are an important control on mineralization.
Boundary Zone mineralization formed in multiple episodes and occurs as sphalerite-siderite-pyrite+/-galena in veins, stockworks, disseminations, and replacement of matrix and clasts within coarse clastic rocks. The presence of older stratiform mineralization at Boundary West overprinted by veins is further evidence of a long-lived system that resulted in several styles of mineralization.
Examples of mineralization styles at Boundary Zone
In 2020, Boundary West drilling targeted a large ground gravity anomaly detected in August of the same year. In addition to replacement-style and vein-hosted zinc mineralization, two horizons of stratiform mineralization were also discovered. Their presence has significant implications for exploration work at Boundary Zone and across the Macmillan Pass property.
Boundary Zone 2020 drilling and preliminary gravity data. Cross-section location through Boundary West marked
Geology of Boundary Zone and Boundary West. Left: Cross-section through Boundary West shows two sequences of stratiform mineralization have been discovered. Right: Updated conceptual geology of Boundary Zone with main feeder fault. Upper part had been inferred based on historic and 2019 drilling; lower part including lower sequence stratiform mineralization developed following 2020 drilling
Two distinct sequences were drilled at the new discovery at Boundary West: an upper sequence and a lower sequence of stratiform zinc mineralization. The upper sequence is hosted in Mid-Late Devonian rocks, similar to the stratiform massive and laminar mineralization seen at the Tom deposit, and also contains a massive sulphide cap to the system. The lower sequence is hosted by Late Ordovician-Early Silurian rocks the same age as the host rocks to the large tonnage Howards Pass deposits 90 km to the southeast. The age of the host rocks has been accurately constrained based on dating of graptolite fossils in the host mudstones.
Multiple episodes of sphalerite and pyrite veins overprint the two early stratiform sequences indicating that multiple phases of mineralization have exploited the same fault structure. This points to the long-lived nature of the hydrothermal system and indicates strong potential for significant additional mineralization.
Boundary West stratiform mineralization. Left: Examples of Tom-style mineralization in Devonian mudstone: massive and laminar pyrite+sphalerite and barite replacement. Right: Examples of Howards Pass-style laminar grey sphalerite and quartz vein-hosted tan sphalerite in Late Ordovician-Early Silurian mudstones
Boundary West vein-hosted mineralization. Wide zones of vein-hosted pyrite+sphalerite+/-galena mineralization overprint older stratiform sequences. Multiple pulses of sphalerite mineralization are represented by presence of pink (older) and tan (younger) sphalerite
The discovery of Boundary West was originally announced in Fireweed news release dated 24th September 2020. Assays are pending and will be released when received.
The results of an ore sorting study conducted prior to 2019 drilling demonstrated the potential to upgrade feed grade from 2.5% to 5% Zn with recovery of 80-85% zinc at low cost using X-Ray Fluorescence (XRF) sorting.
XRF sorting uses an XRF sensor to analyse surface metal abundances on rock fragments moving along a conveyor belt. At the end of the conveyor belt, focussed high pressure air jets or mechanical levers separate the designated higher grade rock pieces for processing and reject low-grade and waste pieces, reducing the amount of material and increasing the overall grade of material that is processed further. The amenability to ore sorting depends on the material characteristics of a deposit. Boundary Zone samples responded positively to XRF testing, with surface zinc values of individual rock pieces correlating closely with overall zinc assays of those rocks.
No Mineral Resource has been estimated for Boundary Zone yet and the zone is not included in the current Macmillan Pass 2018 mineral resource. With mineralization occurring from surface, Boundary Zone has potential to be mined in an open pit with a low strip ratio. It may also be amenable to upgrading through low cost, pre-concentration ore sorting processes.
The discovery in 2020 of Boundary West highlights the potential presence of additional zinc mineralization in the area, not only in Late Devonian stratigraphy, but also Ordovician-Silurian rocks that have not previously been considered prospective at Macmillan Pass, considerably widening the search space for zinc. Several targets, including Volcanic Zone to the northeast, Zinc Moss to the north and Eleven at the western edge of the Nidd property have been identified as areas for follow up exploration. The acquisition of the Sol and Oro claims in late 2020 open up potential for further discoveries to the northwest also the Fertile Corridor, including the Imperial zinc and lead soil anomaly.
Technical information in this Boundary Zone write-up has been approved by Gilles Dessureau, P.Geo, Vice President Exploration and a Qualified Person as defined under Canadian National Instrument 43-101.
Corporate Presentation Corporate Factsheet 43-101 Resource Report 43-101 Preliminary Economic Assessment Yukon Geoscience 2020 Presentation Online Townhall 2020 Presentation