Summary:
Mineralization in the Keno Hill (KH) comprises carbonate vein-hosted polymetallic silver-lead-zinc as described by Boyle (1965), Cathro (2006), Murphy (1997), and Roots (1997). Mineralized zones typically exhibit a succession of hydrothermally precipitated minerals deposited in veins or veinlets resulting from multiple pulses of hydrothermal fluid boiling events, probably related to repeated depressurization due to movement along the host fault structures. As a result, a progressive series of differing mineral depositional stages, assemblages, and textures can be identified. To a minor extent, supergene alteration may have further changed the nature of the mineralogy in the veins, although this may have been largely removed due to glacial erosion.
In general, common gangue minerals include (manganiferous) siderite and, to a lesser extent, quartz, and calcite. Silver occurs predominantly in argentiferous galena and argentiferous tetrahedrite (freibergite) with associated native silver, and the silver-bearing sulfosalts polybasite, stephanite, and pyrargyrite are other important silver-bearing minerals. Lead occurs in galena and zinc in sphalerite, which can be either an iron-rich or iron-poor variety. Other sulfides include pyrite, pyrrhotite, arsenopyrite, and chalcopyrite.
Historically, it was believed that economic mineralization in the Keno Hill mining camp was restricted to a shallow zone of approximately 120 m thickness. However, the 370 m depth of production from the Hector-Calumet mine and drill indicated mineralization to over 350 m depth at Flame and Moth and Bermingham demonstrate that silver-rich veins do exist over greater vertical intervals and suggest that other known veins may exhibit exploration potential at depth. It has been suggested (Cathro, 2006) that the mineralization may exhibit a vertical zonation with a typical mineralized shoot displaying a high silver and lead-rich top down to a low silver-zinc-rich base; however, this has not been verified.
Across the District, favorable environments for mineralization are considered to occur where:
• Competent quartzite or greenstone host rock is present on one wall of the vein fault as it can be observed that veins pinch down significantly in schist-bound structures.
• The vein-fault splits to form a more northerly striking orientation.
• The vein-fault changes to a steeper dip.
Wide veining with the development of high-grade silver mineralization is spatially associated with veinfault domains exhibiting steeper dips and/or more northerly strikes.
Flame And Moth Mineralization
The Flame Vein is unique because of its uniformly singular form, width, grade, and length. It occurs over a strike length of one kilometer (km) orientated at a strike of 025° and dipping approximately 65° southeast and has been traced by drilling to over 300 m depth extent. Two main styles of mineralized veining commonly with multiple banding, internal brecciation, and often re-healed textures are observed. The early phase comprises dominantly quartz gangue with abundant but irregular amounts of pyrite, pyrrhotite, sphalerite and arsenopyrite, while a later phase comprises predominantly siderite containing abundant sphalerite, pyrite, galena, with minor chalcopyrite and trace amounts of tetrahedrite, pyrargyrite, jamesonite, boulangerite and cassiterite as identified in thin section samples.
The vein is divided into two parts by an approximate 90 m right lateral offset on the post-mineral Mill Fault that is referred to as the Lightning Zone in the southeast and the Christal Zone in the northwest.
The associated Moth Vein, the subject of historic prospecting, is considered to represent a footwall splay of the Flame Vein, although the relationship is not fully understood.
Bermingham Mineralization
The Bermingham zone comprises a closely spaced series of subparallel steeply southeast dipping vein sets related to the master Bermingham vein-fault system. These are identified (hanging wall to footwall) as the Bermingham, Bermingham Footwall and Bear veins that can be traced over a northeasterly strike distance exceeding 850 m. In addition, a small resource is contained in a conjugate set of related West Dipping veins. In places less extensive, north-northeast striking vein geometries are observed within the mineralized system. Recent detailed underground and surface drilling work has focused on the Arctic and Bear Zones where the vein sets are connected either laterally or vertically within the wider Bermingham vein-fault structural corridor. Mineralization extends from between 90 m to 160 m below the surface to a depth of approximately 450 m where veining remains open.
The mineralized veins are displaced by several post-mineral faults that subdivide the system into several zones used for Mineral Resource estimation purposes, with the sequence from the southwest being Etta, Arctic, Bear, and Northeast Zones separated by the Mastiff, Arctic, and Ruby B faults, respectively.
The early Aho Vein comprises predominantly quartz that occurs over several meters’ width within a wide halo of structurally damaged rocks. Minor sulfides are present with arsenopyrite and pyrite being the most abundant, with accessory galena and sphalerite.
The Bermingham Vein has a strike between 029° and 042° and dips between 40° and 64° to the southeast and the structure accommodates approximately 65 m of the total Bermingham displacement. In the Etta Zone, and within the hanging wall of the post-mineralization Mastiff fault, the Bermingham vein at its most southwestern extent is observed to converge with the Aho Vein structure; while to the northeast, it converges with the Bermingham Footwall vein.
The Bermingham Footwall Vein has a strike of between 040° and 060°, and dips between 67° and 73° to the southeast, and the structure accommodates approximately 70 m of the total Bermingham displacement. In the Etta Zone, the Bermingham Footwall Vein terminates against the Bermingham Vein up-dip and this intersection plunges moderately steeply to the northeast into the Arctic Zone in the footwall of the post-mineral Mastiff fault. At depth, the Bermingham Footwall Vein terminates against the Aho Vein along a steep plunging north-easterly trajectory. The
Bermingham and Bermingham Footwall veins typically exist within a 5 m to 10 m wide structurally damaged zone containing numerous stringers, veinlets, breccias, and gouge and generally form a discrete silver mineralized vein 0.5 m to 2.5 m wide within this zone. It consists predominantly of carbonate (dolomite, ankerite, siderite, and calcite), and quartz gangue, with the sulfides galena, sphalerite, pyrite, and arsenopyrite, and accessory, chalcopyrite, argentiferous tetrahedrite (freibergite), jamesonite, pyrargyrite and native silver.
The Bear Vein strikes between 010°and 050° and dips between 65°and 80° to the southeast and accommodates approximately 30 m of the total Bermingham displacement. It occupies a position in the footwall of the system beneath a major flexure in the Bermingham Vein, with which it joins up-dip. At depth and to the southwest, the Bear Vein junctions with the Bermingham Footwall Vein. Early phase mineralization is absent, and the Bear structure is considered a late response to the slip-impeding flexure in the Bermingham Vein noted above, with the high-grade silver mineralization located on the more northerly striking and steeper dipping areas.
The West Dipping Vein is located between the Bear and Bermingham veins and it strikes 020° and dips 50° to the west.
Lucky Queen Mineralization
The Lucky Queen vein-fault structure is essentially a singular structure with an average strike of approximately 043°, that locally varies between 025° to 060°, and has an average dip of approximately 045° to the southeast with a range of 30° to 55°. The main structure has a drill-defined length of approximately 650 m and 230 m.