- Geology and Mineralization
- Mining and Processing
The Mishi area has a limited exploration history prior to the discovery of Hemlo in 1981. In the ensuing regional gold rush, exploration work led to the discoveries of the Magnacon deposit by the Northgate Group, the Mishi deposit by Granges Inc. and the Eagle River deposit by Noranda Exploration. The Magnacon property (Patented Claims) was independently brought into production in 1989 by the Muscocho Group and Windarra Minerals and a mill was built. Mining operations were terminated after only 18 months of production and the mill was placed on care and maintenance in October 1990.
The neighbouring Mishi claims were being actively explored by MacMillan Energy Corp in the period 1982-1986. In August 1986, a joint venture agreement was signed with Granges Exploration Ltd. In the fall of 1986 Granges announced encouraging drilling results from a new discovery. Numerous drilling programs and evaluation studies ensued in the period 1986-1990 before the project became largely inactive.
The Mishi Mine is an open pit mining operation that has been intermittently producing since 2002. Production recommenced in 2012 at a rate of 200 tonnes per day and has since expanded to approximately 400 tonnes per day. Recent investments in milling operations have enabled continuous and increasing production since 2013. Reserves are drilled to a depth of 70 metres and Resources to 110 metres. The mineralized system is completely open to the west and at depth.
The Mishi Mine yielded 59,700 oz Au from 831,000 t at a grade of 2.2 g/t Au from 2002-2019. The Company plans to mine out the Mishi Mine pit in 2020. Stockpiled ore at the end of the year will be processed in 2021.
Mineralization is hosted in the Mishibishu Deformation Zone which traverses the property over a 14 km length and is interpreted as a major regional thrust fault which follows a volcanic-sedimentary contact. The northern portion of the property is underlain by mafic volcanic rocks and subvolcanic gabbroic sills. These are overlain to the south by shallow water immature arenaceous/arkosic sediments and polymictic conglomerates, followed by deeper water silts and turbidites progressing southward.
The sequence is overturned dipping moderately north, facing south and striking 90-120º. The deformation zone is 0.5 to 1.0 km wide and characterized by strong ankerite alteration and a schistose fabric dominated by phyllosilicate minerals, sericite and chlorite. Because of the intense deformation, systematic recognition of protoliths and subunits within the deformation zone is problematic.
In the Mishi Mine area mineralization is hosted by a series of at least 8 tabular parallel zones consisting of ankerite-sericite ± chlorite alteration zones containing 2-8% fine disseminated and a system of sub conformable, dislocated, smoky grey quartz veinlets and lenses. Veins generally vary from 5-20% of the bulk volume of the zones with individual quartz lenses commonly 5-15 cm wide. The 8 zones recognized to date are labelled from south (footwall) to north (hanging wall) M2, M4, M6, M8, M10, M12, M14 and M16. Zones M2 and M4 are close together and are merged when modelling into a Main Zone. The zones strike 100°, dip north 40° and plunge northeast. In general, the zones become more felsic, discrete and vein dominated towards the north.
Gold has been intermittently produced from the Mishi Mine since 2002. In 2012, Wesdome began continuous production from the Mishi Mine pit with the highest gold production year in 2015 when approximately 9,500 ounces were produced from the processing 132,000 t of ore.
Mining is undertaken by mining contractors using conventional truck and shovel equipment. Present mining utilizes a surface fleet of equipment consisting of up to four production drills producing 2.5 inch to 3-inch diameter blast holes, up to five 50 tonne haulage trucks, up to three excavators, a dozer and surface utility vehicles on single shifts during the day. The selected truck and an excavator of appropriate size for ore and waste assuming a bench height of 5 m. However, the ramp will be located on the footwall side.
Analysis of mineable blocks on typical benches and cross-sections at the mill cut-off grade indicate the dilution will mainly appear at the ore zone-waste contact, with a minor component along the contact with low grade blocks. Mining recovery is estimated using the assumption that ore loss will mostly occur at the contact between zones and the face angle of broken rock when loading. From cross-sectional evaluation, the dilution was estimated to range between 10-12% pure waste with ore recoveries ranging between 85-90% with good blasting practice as well as good dilution control practices.
The open pit was designed with Whittle Pit software and incorporated a ramp into the pit. The ramp was designed for only single lane traffic on both of the two separate pit bottoms. Based on productivity rate and sensitivity to the stripping ratio, the one-way ramp width has been reduced from 10.85 m to 8.0 m wide to accommodate a 50-tonne-capacity off-road class of rear-dump trucks. The ramp is located on the footwall in case the pit is enlarged or deepened. In order to reduce the volume of waste to be stripped, the last bench on each of the pit bottoms will not have a permanent ramp access. The ramp gradient is 10%, and the ramp exit is on the southwest side of the pit to minimize the haulage distance to the waste dump. The Eagle River Mill is 2 km from the Mishi Mine.