Matachewan, Ontario, Canada
Young-Davidson is a prospective gold mine located nearly 60km west of Kirkland Lake in Matachewan, Ontario, US. Acquired by Northgate Minerals in 2005, the property includes contiguous mineral leases and is spread over 11,000 acres. A recently completed feasibility study proved the economic viability of the project. The mine is expected to produce an average of 180,000oz of gold a year and 2.5Moz of gold during its estimated life of 15 years.
The estimated cost of the project is $339m. Construction commenced in September 2010. Commissioning is scheduled to take place in late 2011 while full production has been targeted for 2012.
The open pit deposit contains an estimated 4.9Mt of probable reserves graded at 1.66g/t. The proven and probable reserves, both open pit and underground, total 3.4Mt and 22.74Mt graded at 3.22g/t and 2.92g/t, respectively. The underground indicated reserves have been estimated at 132,000t graded at 3.08g/t. The inferred reserves, open pit and underground, stood at 5.9Mt as of 14 July 2009.
The deposit lies within the south-western section of the Abitibi Greenstone Belt. The belt is characterised by a diverse and complex spectrum of volcanic, sedimentary and plutonic rocks that have been metamorphosed to greenschist facies grade. Regionally, the rocks maintain the amphibolite facies grade.
The volcanic rocks, ranging between rhyolitic and komatiitic, exist as mafic to felsic volcanic cycles. Sedimentary rocks are hosted as intravolcanic sequences and as a sequence that overlies the intravolcanic sequence.
A broad spectrum of pre-tectonic, syntectonic and post-tectonic intrusive rocks occur as mafic to felsic. All lithologies are cut by diabase dikes belonging to the late Proterozoic age and trending mostly north-east.
Within the Abitibi Greenstone belt, a series of complex deformation events have taken place including fabricless folding and faulting, faulting and ductile shearing. Faulting and ductile shearing resulted in the formation of large, crustal-scale structures, generally east-west trending. The structures took the form of a lozenge-like pattern.
The Larder Lake-Cadillac Fault Zone cuts through the project area. Characterised by chlorite-talc-carbonate schist, the zone dips sub-vertically and has an east-west strike.
The three key Archean sedimentary rock groups found within the district are the Pontiac Group, the Porcupine Group and the Timiskaming Group. The Pontiac Group is the oldest and exists as thick assemblages within the Québec bedrock. The Porcupine Group consists of turbiditic siltstones and greywackes found interbedded within the Larder Lake Group volcanic rocks. The Timiskiming Group along with turbidite and iron formations overlie the Porcupine Group.
Throughout the district, the Archean intrusive rocks are hosted as plugs, small stocks and dikes of augite syenite, syenite and feldspar porphyry that are associated with the spread of the Timiskiming group sediments. The syenite mass that hosts most of the property’s gold mineralisation extends 900m east west and 300m north-south.
The southern limit of the Abitibi belt is defined by overlapping Huronian Proterozoic sedimentary rocks that are co-related to the Gowganda Formation tillite. The Huronian unconformity in the project zone is categorised by post-Archean dike rocks including the Matachewan diabase and the Nipissing Diabase.
Within the belt, the open pit and underground gold resources are hosted largely within syenite rocks. Syenite-hosted gold mineralisation includes a stockwork of quartz veinlets and fine quartz veins found within a wider halo of largely spread pyrite.
The narrower quartz veinlets are glass textured making the contained gold highly visible. The mineralisation zones are easily distinguishable as they are characterised by brick red to pink K-feldspar rich syenite.
Open pit mining will be carried out using traditional methods including 5m benches, 8m³ front-end loaders, 45t haul trucks, drills and support equipment. Initially, an open stope at the eastern end of the pit will be filled with waste rock to reduce dilution and loss during mining. The waste rock backfill will be excavated during bench mining activities.
The mill will be fed at a rate of 2.16Mt/yr. In the initial two years, low-grade stockpile will be used to result in higher head grade. After the pit is exhausted, the base of the open pit will be connected to the underground deposit located between 210m and 1,500m below surface. A 6.5m-diameter shaft will be declined at a depth of 1,500m towards the east of the deposit. Access to the underground mine will be through a ramp that will be sunk 460m from the current exploration ramp to the bottom of the mine.
Sublevels at 60m vertical intervals will access the shrinkage mining method. The sublevels will access other methods at intervals of 30m. Scooptrams will load stope production and transfer it to the ore pass system. Hoisting will be carried out via 18mt skips.
The select processing method includes single stage autogenous grinding with a gravity circuit followed by flotation. A carbon-in-leach circuit will leach the flotation tailings. After the gold has been recovered from the carbon it will be poured into dore bars. A 92.5% gold recovery rate has been indicated for the average grade samples.
The engineering, procurement and construction (EPC) contract for the project was awarded to AMEC in August 2010.
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