The Keno Hill deposits do not readily fit into a recognised mineral deposit model and attempts to classify a “deposit type” for the mineralization are questionable since the source(s) of metals and conditions related to ore-deposition are poorly understood.

Beaudoin and Sangster (1992) classified the Keno Hill as sediment-hosted veins, likened to the silver bearing deposits at Coeur d’Alene, USA and the Kokanee Range, Canada. A genetic relationship between silver-lead-zinc and intrusion related gold mineralization has also been postulated (Mair et al., 2006).

The mineralization has been more recently classified as belonging to the Lithogene genetic group (Greybeal and Vikre, 2010) which invokes a depositional environment of re-mobilized metals, with no magmatic contribution or associated gold.

Current information, however, shows that this latter classification is not correct, as there is some magmatic component, with local felsic intrusives acting at least in part as a heat source for hydrothermal fluid circulation and gold is associated with the mineralization.

Mineralization in the Keno Hill Silver District comprises carbonate vein hosted polymetallic silver-lead-zinc as described by Boyle (1965), Cathro (2006), Murphy (1997) and Roots (1997). It typically exhibits a succession of hydrothermally precipitated minerals deposited in veins or veinlets as a result of 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.

BELLEKENO MINE MINERALIZATION
The Bellekeno vein system consists of ten known veins with variable characteristics. Vein material has been extracted from the Ram, Eureka, Tundra, 48, 49, and 50 veins that generally strike 030° to 040°, with dip directions varying 60° southeast to 80° northwest. Recent mechanized mining has focused on the stronger 48 Vein structure, while conventional historical narrower mining focused on the smaller, higher grade vein structures.

LUCKY QUEEN MINERALIZATION
The Lucky Queen vein-fault structure is essentially a singular structure with an average strike of approximately 043o, that locally varies between 025o to 060o, and has an average dip of approximately 045o to the southeast within a range of 30o to 55o. The main structure has a drill defined strike length of approximately 650 m with vein thicknesses ranging from just a few centimetres to several metres and is open along strike in both directions. Stratigraphic units correlated across the structure show a normal separation of approximately 30 to 35 m across the vein-fault. Mineralized zones are largely composed of brecciated wall rock, siderite (± limonite), vein quartz, with silver sulphosalts, galena,
sphalerite, and native silver with minor arsenopyrite and pyrite.

FLAME & MOTH MINERALIZATION
The Flame Vein is unique because of its uniformly singular form, width, grade and length. It occurs over a one kilometre (“km”) strike length orientated at strike of 025o and dipping approximately 65o southeast and has been traced by drilling over to least 300 m depth extent. Two main styles of mineralized veining commonly with multiple banding, internal brecciation and often rehealed 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 are 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.

ONEK MINERALIZATION
The Onek vein system comprises at least three individual vein-faults occurring within a broad northeast striking, southeast dipping structural zone. The vein-faults occur over a strike length of at least 600 m formed in brittle fractured or milled zones, locally containing massive sulphide vein material in, or associated with, siderite and comprising sphalerite and galena along with minor pyrite, and arsenopyrite. Mineralized breccia zones, consisting of wall rock fragments and siderite- sulphide cement are also present, and are often surrounded by brittle fractured zones cemented by siderite and minor sphalerite stringers.

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 (hangingwall to footwall) as the Bermingham, Bermingham Footwall and Bear veins that can be traced over a north easterly strike distance exceeding 850 meters (“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 surface to a depth of approximately 450 m where veining remains open.

The Keno Hill Silver District (KHSD) project contains four separate deposits: Bellekeno, Bermingham, Flame & Moth, and Lucky Queen. All are characterized by high-grades, narrow vein widths, and challenging ground conditions.

All four deposits will be mined by mechanized underground mining methods of cut and fill (MCF) and longhole stoping (LH) with cemented rock fill and unconsolidated rock fill. The location of all four deposits are shown in Figure 16-1 below, the mill, administration, and shop complexes are located near the Flame & Moth Deposit.

The KHSD Project is composed of four silver / lead / zinc narrow-vein hosted deposits located throughout the district; Bellekeno Deposit (BK); Lucky Queen Deposit (LQ); Flame & Moth Deposit (FM); and Bermingham Deposit (BM). It is noted that the Flame & Moth and Bermingham deposits are comprised of several zones. All deposits will be extracted using overhand cut and fill (C&F) and long hole open stoping (LHOS) underground mining methods with cementitious back fill. A top-down extraction approach is planned.

While production mining at KHSD Project will predominantly use mechanized C&F mining method several zones of the Bermingham and Flame & Moth deposits will be extracted using LHOS. In these areas, all available geotechnical drill hole data proximal to the planned stope hanging wall was used for stability analysis.

The Bellekeno, Lucky Queen, and Bermingham proposed mining zones are located above the valley floor. Consequently, this tends to limit the occurrence and effect of adverse hydrogeological conditions.

A first pass assessment of the rock mass in geotechnical domains was completed by considering the Rock Quality Designation (RQD) (after Deere, 1964). RQD is a fundamental input into several rock mass characterization schemes, and is generally regarded as a reliable, basic indicator of ground conditions. The RQD is calculated as the ratio of the sum of the lengths of all core sticks greater than 4 inches / 10 cm in length, to the total length of the drill core run, expressed as a percentage.

The Mining Methods selected for this study are Overhand Cut and Fill and longhole stoping. In the wider areas of the orebody, a Drift and Fill method with cemented rock fill (CRF) will be used. Longhole Open Stoping will be either standard longitudinal retreat with CRF or uphole stoping with no CRF. Longhole stoping will be used where the ground conditions and ore body dip allow or to recover sill pillars between Cut and Fill levels. These mining methods were chosen due to the narrow steeply dipping nature of the orebody and to maximize safety and productivity.

Cut and Fill will be the primary mining method for the Flame & Moth, Bermingham, and Lucky Queen deposits. In Cut and Fill method, an attack ramp is developed from the main ramp at a gradient of -15%. Upon reaching the orebody, an intersection is developed and a lift is developed in both directions along strike, following the geological contact of the orebody. At the end of the lens, the void is backfilled using either unconsolidated rock fill or cemented rockfill (CRF) with a Load Haul Dump (LHD) machine. The LHD utilizes a rammer-jammer plate (a dozer plate modified to be attached to a scoop to push waste tight to the back) to ensure that the backfill is placed tight to the back of the drift.

Longhole Open Stoping will be the preferred mining method when the ground conditions and the lens geometry allow. In Longhole Open Stoping, two drifts are developed along the strike of the orebody at a vertical spacing of 17.5m. After development is complete, rings of holes are drilled in parallel from the top level to the bottom level. These holes are planned to be 64 mm in diameter with a ring of blastholes spaced every 1.0 m. These drill holes will be immediately cased with 50 mm ID plastic pipe to prevent the drill holes from collapsing or plugging.

A modified version of Longhole stoping will be used at the top of a cut and fill level to extract the sill pillar between one cut and fill level and the level above, or in areas where there is no access for a top drift. In Uphole Stoping, a series of parallel rings are drilled from the bottom drift into the back, to the limit of the lens. An inverse raise is drilled on the extremity of the stope and then blasted in one shot. The longhole rings are then blasted into the void and mucked using a remote-operated LHD. No backfill is necessary in this method.

CRUSHING
The crushing system will be operated for 8 h/d at a process rate of 50 t/h (up to 10 h/d at a process rate of 55 t/h). The ROM ore will be crushed in a two-stage crushing circuit closed with a vibrating screen. The final crushed product size P80 will be minus 10 mm. ROM ore will be dumped by 30 t haulage trucks into either a ROM ore stockpile of directly into the jaw crusher feed hopper with a 47 t capacity. The hopper is equipped with a stationary grizzly with a 450 mm aperture opening to prevent oversize ore entering the downstream jaw crusher.

The feed to the primary crusher, the jaw crusher, is controlled by using a vibrating grizzly feeder. The 508 mm by 914 mm jaw crusher with a 75 kW motor will crush the ROM ore from minus 450 mm to a P80 size of 50 mm with the crusher closed side setting of 70 mm. The primary crushing products, joined by the secondary crushing discharge, will feed the sizing screen to produce the final crushed product. The oversize product from the sizing screen will feed the secondary cone crusher.

The crushed material will be conveyed to a fine ore stockpile with 550 t live capacity. Crushed ore reclaim will be achieved via a draw down pockets located beneath the fine ore stockpile.

GRINDING
Crushed ore will be reclaimed from the stockpile onto the ball mill feed conveyor belt at a nominal rate of 18.1 t per operating hour (25 tpd). The primary grinding circuit is a two-stage ball milling process producing a ground material with a P80 size of 100 to 120 µm. The spillage sump and pump are located near the No.1 mill discharge pumpbox. Spillage will be returned to the ball mill feed hopper.

Ore from the ball mill feed conveyor will discharge into the feed chute of the primary No.1 ball grinding mill which will be a heavy-duty tyre driven type grinding mill 1,800 mm in diameter and 3,600 mm long, with an installed power of 150 kW. The primary mill slurry will discharge into a pumpbox and will then be pumped to join the secondary No.2 ball mill discharge. The combined streams will be pumped to the classifying cyclones. The cyclone underflow will
return as feed to the secondary ball mill, while the cyclone overflow will report to flotation circuit. The secondary No.2 ball mill has the same size and motor as the primary ball mill.

Grinding media as steel balls will be added as required via the ball mill feed conveyor. This conveyor will discharge the grinding media into the ball mill feed hopper. The ball mill feed conveyor belt will be sampled every shift to provide a head assay of the feed to the plant.
The reagents 3418A and zinc sulphate will be added to the ball mill feed to suppress zinc minerals during the lead mineral flotation stage.

The primary and secondary ball mill discharges will be combined in a common pumpbox and will then feed a hydrocyclone pack. Two cyclones will be installed each with a diameter of 250 mm. Operating in a mode of one running and one standby, the cyclone undersize material will return to the secondary grind ball mill by gravity, while the cyclone overflow with a P80 size between 100 and 120 µm will gravity flow to the flotation circuit.

The Keno Hill District Mill is based on a conventional sequential flotation process producing lead and zinc concentrates. The lead concentrates are high in silver which typically account for approximately 90 to 95 percent of the mill feed silver values since silver is strongly associated with lead minerals. Overall, silver represents 70 to 80 percent of the value of the ores in the district.

The mill complex consists of the following process sections and unit operations:

• primary and secondary crushing circuits with a radial stacker belt conveyor to transport the crushed ore to the covered fine ore stockpile;

• draw down pocket reclaiming the crushed ore from the covered fine ore stockpile;

• two-stage grinding in a closed circuit with hydro-cyclones to produce a grinding product P80 size of 120 µm;

• a grinding classification circuit to produce a cyclone overflow to feed the lead rougher and rougher scavenger flotation circuit t ........