Both the Eagle River and Mishi deposits are mesothermal lode gold deposits hosted by Archean Greenstone Belts.

The Eagle River deposit has been described as a vein type deposit along a regional deformation zone with discrete brittle-ductile shears localized along lithological contacts (Heather 1986 and 1991).

Gold bearing quartz veins at Eagle River are hosted primarily by subvertical to steeply north dipping east-west striking shear zones within an elliptical quartz diorite stock with dimensions of 2.0 kilometres east-west and 0.5 kilometres north- south.

The quartz diorite stock intrudes a steeply dipping north-facing sequence of thin mafic to intermediate volcanic flows, flow breccias and interflow volcaniclastic rocks.

A number of different ore zones have been distinguished that constitute different segments of the overall shear zone corridor and each has its own gold grade characteristic. Mineable portions of the individual zones form ore shoots that plunge steeply to the east. The bulk of the historic production has come from Zone 8 and Zone 6, which are entirely within the intrusive quartz diorite, while Zone 2 mineralization is hosted in sheared mafic volcanic rocks just east of the stock.

In general, the ore shoots mined to date occur at a spacing of 400 metres along a 2.4 kilometre strikelength. They appear to be spatially related to an array of oblique 110º striking mafic dykes, which pre-date mineralization ........

The ERM was initially mined using a shrinkage mining method before converting to its current mining method of captive sub-level open stoping with access to the sub-level provided by Alimak raises, a variant of longhole mining. The site is currently transitioning to mechanized sub-level open stoping with access to the sub-levels being provided by ramp access.

Currently, ERM utilizes a mix of captive and mechanized access to the sub-levels depending on how close the ramps are. Mechanized access is more productive, but also requires more lateral development with some areas being unable to support mechanized access. Minimum mining widths are 1.5 with 1 m of external dilution expected. The ore body strikes eastwest with strike length varying between 50 and 80 m depending on mining zone. Generally, 19% of the mill feed comes from sill development and 81% comes from stope production.

The main access to the ERM is via a portal, which connects to the mines through three primary ramp systems (East, West, and Central ramps). The majority of materials entering the mine and personnel access is through these ramps. Development waste rock is also handled via the ramp systems, generally being hauled to a stope requiring backfill, although some waste must be hoisted to surface.

The East or Main Ramp is the primary ramp for the mining zones. This ramp extends from surface to the deepest levels of the mine and provides access to the majority of the active mining ........

Stockpiles and Crushing Circuit
There are three stockpile floors that can feed the mill with a front-end loader (FEL). The crushing circuit is a standard two stage process (2CB). From the stockpile a FEL deposits the ore into the jaw crusher. Coarse ore is transported by conveyor to be classified on a double deck vibrating screen. Oversize material goes to the secondary crushing and is reclassified after size reduction (cone crusher is in closed circuit with the vibrating screen). Undersize material is directed to the fine ore bin. The fine ore is transported from the fine ore bin by two conveyors to the primary ball mill (the second conveyor is fitted with a weightometer).

Grinding Circuit
The grinding circuit consists of a primary ball mill followed by a secondary ball mill in closed circuit with hydrocyclones (cyclones). The primary ball mill discharges into the cyclone pumpbox, and the slurry is then pumped to cyclones for classification. Process water (mill solutions) is added to the primary ball mill and cyclone feed pumpbox to obtain the required cyclone feed density. Lime slurry is added to the cyclone pumpbox to target the pH for cyanide leaching and downstream Merrill Crowe circuit.

Cyclone undersize material reports to the secondary ball mill, which also discharges into the cyclone pumpbox. The cyclone overflow is sent to the vibrating trash screen and via gravity, the slurry enters the thickener pumpbox to be pumped to the thickener feedbox. The trash screen oversize is collected in drums and periodically removed.

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