- Geology and Mineralization
- Mining and Processing
Purchased in 1994, preproduction development at the Eagle River Underground Mine commenced in 1995 and the first gold bar was poured on October 17, 1995. Commercial production was declared January 1, 1996, and to December 31, 2019, a total of 4.2 million tonnes of ore averaging 9.6 g/t Au from the Eagle River Mine totalling approximately 1.3 million oz Au. Gold mineralization at Eagle River occurs within quartz veins that are hosted primarily by subvertical east-west striking shear zones within an elliptical diorite stock. Mineable portions of the individual zones form ore shoots that plunge steeply to the east. The bulk of the historic production has come from the 6 and 8 Zones, which are entirely within the intrusive diorite.
The recent discovery of at least two new significant parallel zones in the west portion of the mine (the 300 and 7 Zones) have helped increase Mineral Reserves and Mineral Resources and have stimulated an increased pace of exploration drilling. The mine is currently operating approximately 500 tonnes per day. To date, they have only been identified in the west end of the mine, at depth. Surface and underground drilling currently underway will provide a first pass evaluation of 1.8 kilometres of previously untested potential adjacent existing mine workings.
Unless stated otherwise, the information in this section is based upon the NI 43-101 technical report (the “Eagle River Complex Technical Report”) entitled “Technical Report for the Eagle River Mining Complex Including the Eagle River Gold Mine and the Mishi Gold Mine and Related Infrastructure” dated March 17, 2016, prepared by George Mannard, P. Geo, former Vice President of Exploration for the Company, and Philip Ng, P. Eng, former Chief Operating Officer of the Company.
The Eagle River mine occurs within the Mishibishu greenstone belt that is a broad arcuate syncline 55 km long east-west and 16 km wide north-south. This belt is part of the Wawa Subprovince of the Archean age Superior Province. Supracrustal rocks in the belt are dominated by greenschist facies mafic to intermediate volcanic rocks with lesser sedimentary rocks including iron formation and intermediate to felsic volcanic rocks. The belt is surrounded by Archean granitic rocks and includes two internal granitic batholiths occupying the central portion of the belt.
The northern limb of the belt, where the Mishi Mine is located, is dominated by an assemblage of clastic sedimentary rocks, felsic tuffs and mafic flows. The southern limb, where the Eagle River Mine is located, is dominated by tholeitic basalts and calc-alkaline andesites with minor interflow clastic sedimentary rocks and lean chert-magnetite iron formation.
Gold in the Mishibishu Lake greenstone belt occurs primarily in quartz vein deposits located within regional zones of deformation. The Mishibishu Deformation Zone follows a volcanic-sedimentary contact in the north limb of the belt hosting the Magnacon and Mishi deposits while the Eagle River Deformation Zone hosts the Eagle River deposit along the south limb of the belt. Late northeast striking and lesser northwest striking faults and fractures offset the greenstone stratigraphy and deformation zones.
Essentially all of the gold mineralization at the Eagle River mine occurs within a series of thick, white laminated quartz vein lenses. 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 2.4 km east-west and 0.5 km 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.
In general, the ore shoots mined to date occur at a spacing of 400 m along a 2.4 km strike length. They appear to be spatially related to an array of oblique 110º striking mafic dykes that are interpreted to post-date conjugate structures. 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. The veins vary in thickness from one metre to three metres, averaging about 2.5 metres. 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.
Recently, two new significant parallel zones have been discovered in the western portion of the mine diorite, namely the 300 and 7 Zones, located 200 and 400 metres north respectively of the main 8 Zone structure. Exploration is continuing to find the lateral extent of these parallel zones.
In addition, the most recent discovery of the 303 high grade lens is having a significant positive impact on the Eagle River mine production and mineral reserves, which is considerably higher grade and wider compared to previously mined ore. Locally the 303 lens is folded back on itself forming tight S-folds or “ballrooms” which form plunging, pipe-like bodies 12 to 15 metres in diameter often grading over 1 oz/t Au or 30 g/t Au. The 303 Lens has now been extended an additional 300 m down plunge to the 1,300 m-level, while continuing to illustrate above average widths and grades.
Eagle River Parallel Gold Zones Remain Open
In 2018, surface drilling in the volcanics to the west of the mine diorite encountered two sub-parallel structures that broadly follow the stratigraphy within the mafic/felsic volcanic rocks. These could be extensions of the 300 and 7 zone structures which lie approximately 200 m to the east within the mine diorite. Both structures exhibit broad zones of deformed rock (3-20 m wide shear zones) affiliated with strong silicification over 20-50 m width. The two new mineralized zones identified by surface drilling define an area termed the Falcon Zones. The Falcon Zones occur near the contact between tholeiitic mafic volcanic and calc-alkaline felsic to intermediate volcanics, which are commonly sheared with biotite-sericite altered and laminated quartz veins with visible gold. Surface drilling has continued to expand the zone of mineralization to a depth of 4400 m elevation (i.e. 600 vertical m below surface) and over a strike of 200 m.
Falcon Zones Highlights:
- Hole ERM-2019-22: 18.5 g/t over 5.8 m core length (11.5 g/t Au cut, 3.3 m true width)
- Hole ERM-2019-36: 3,389.0 g/t Au over 0.3 m core length (60.0 g/t Au cut, 0.21 m width)
- Hole ERM-2019-15: 73.5 g/t Au over 1.3 m core length (34.7 g/t Au cut, 1.1 m true width)
- Hole ERM-2019-35: 51.1 g/t Au over 0.6 m core length (32.1 g/t Au cut, 0.4m true width)
Assays capped at 60 g/t Au. True widths are estimated
The Eagle River Mine has been in continuous commercial production since January 1, 1996. In its early years, the deposit was mined using shrinkage methods before converting to its current mining method of longhole stoping with a typical sub-level interval of 15 m between levels.
Presently, about 30% to 50% of gold production comes from silling/development ore with the balance from longhole stoping. Minimum mining width is 1.5 m with sublevels being typically 15 m apart vertically. Fan double cable bolt holes are grouted in both the hanging wall and footwall to reduce overbreak and control dilution. Dilution is included in the conversion from resource tonnage and grade to reserve tonnage and grade. Cavity monitoring surveys are routinely carried out and indicate 1.0 m of wall overbreak between the hanging wall and footwall is typical.
Mining recovery is a measure of the resource ounces that is extracted, with losses resulting from planned (e.g., pillars) or unplanned (e.g., failure to break to designed stope limits) events. Mining recovery is included in the conversion from resource tonnage to reserve tonnage but does not affect grade as the grade of losses is assumed to equal the resource average. The mining recovery for bulk methods is typically 90 percent.
There are currently three primary ramp systems at Eagle River Mine: the West Ramp, East Ramp, and the Shaft Ramp. The West Ramp starts at 325 m level and continues to the 590 m-level. The ramp is currently inactive with respect to production activity. Services are available along this ramp and pumping is ongoing.
The East Ramp is the primary ramp for the mining zones in Eagle River Mine. It accesses the primary stoping areas at various take off points: 2 Zone @ the 220 m level, 3 Zone @ 750 m-level, 6 Zone, 7 Zone, 807/808/809/810/811/817 zones at various levels. This ramp currently goes from surface to the deepest level of the mine, which now extends pass the 1062 m level.
The Shaft Ramp starts at approx. 650 m level and continues down to the 779 m level. The Eagle River Mine has four shaft stations below the 70 m: 220 m, 460 m, 520 m, and 580 m levels. General ramp design is based on the maximum size equipment used in the mine. The cross section is required to be 4 m height by 5 m width. Ramp grades vary from between +15% and -15%. The main ramp reached the 1102 level at the end of 2019.
The underground mobile mining fleet at Eagle River Mine includes jumbos, scoops, haulage trucks, scissor lifts and multiple utility vehicles. The access to the mine is via two portals.
Besides ramp access to underground workings, the Eagle River Mine has a three-compartment shaft and currently operates with a Canadian Ingersoll-Rand 2.4 m (8-foot) diameter double drum, double clutch hoist driven by two DC motors through a single reduction open gear and pinions. Each motor is rated at 400HP at 400rpm with a maximum hoisting speed of 1194 fpm and a payload of 8800 pounds. Based on 20 operating hours per day, the hoisting capacity is approximately 3,100 tonnes per day from a hoisting depth of 420 m.
Mine ventilation in the western portion of the mine is supplied by a 700 HP fresh air fan that brings a total of 275,000 cubic feet per minute (“CFM”) underground. Two 200-HP fans, located in the east supply 140K CFM. The Company is working to maximize underground ventilation flow in order to maintain the amount of fresh air adequate at depth.
The Company intends to test the alimak mining method in one specific area of the mine in 2020. The alimak mining method utilizes access the ore body via an alimak raise and to subsequently drill and install deep support in the hanging wall of the stope and then drill and blast ore material from bottom-up. The alimak mining method has been proven to accelerate the stope cycle and to reduce mine dilution.
The contents of this page have been verified and approved by the Company’s VP Exploration, Michael Michaud, P. Geo. a “Qualified Person” for the purpose of National Instrument 43-101 Standards of Disclosure for Mineral Projects. Please refer to Company AIF available on the Company’s website and sedar.com